Leptin Signaling and Obesity: Cardiovascular Consequences

This Review is part of a thematic series on the Pathobiology of Obesity, which includes the following articles:

Adipose-Derived Stem Cells for Regenerative MedicineCardiac Energy Metabolism in Obesity

Leptin Signaling and Obesity: Cardiovascular Consequences

Lipid Disorders and the Metabolic Syndrome

Adiponectin As a Cardiovascular Protectant

Gary Lopaschuk, Guest Editor

Leptin Signaling and ObesityCardiovascular Consequences

Ronghua Yang, Lili A. Barouch

Abstract—Leptin, among the best known hormone markers for obesity, exerts pleiotropic actions on multiple organsystems. In this review, we summarize major leptin signaling pathways, namely Janus-activated kinase/signaltransducers and activators of transcription and mitogen-activated protein kinase, including possible mechanisms ofleptin resistance in obesity. The effects of leptin on the cardiovascular system are discussed in detail, including itscontributions to hypertension, atherosclerosis, depressed myocardial contractile function, fatty acid metabolism,hypertrophic remodeling, and reduction of ischemic/reperfusion injury. The overall goal is to summarize currentunderstanding of how altered leptin signaling in obesity contributes to obesity-related cardiovascular disease. (CircRes. 2007;101:545-559.)

Key Words: leptin � obesity � cardiovascular disease

Over 60% of people in the United States are overweight orobese. Extensive evidence now supports the notion that

maladaptation of the biological system for weight mainte-nance makes it extremely difficult for people to maintainweight loss.1 Several genes have been identified to disclose aphysiological system that maintains body weight within arange of about twenty pounds.2 A key element of this systemis leptin, the 16-kDa hormonal product of the obesity (ob)gene.3 Leptin is primarily secreted by adipocytes and is aclassic member of the more than 50 identified adipocytokinesthat participate in adipose tissue hormonal signaling.4

Since its identification in 1994, leptin has attracted muchattention as one of the most important central and peripheralsignals for the maintenance of energy homeostasis.5–8 Forexample, a 9-year-old girl with extreme obesity was found tolack leptin.9 Leptin treatment reduced her weight to the

normal range for her age, and the same effects were observedin her similarly affected cousin.10 Plasma leptin is generallyproportional to adipose mass.11,12 The primary physiologicalrole of leptin is to communicate to the central nervous system(CNS) the abundance of available energy stores and torestrain food intake and induce energy expenditure. Theabsence of leptin therefore leads to increased appetite andfood intake that result in morbid obesity. Notably, only rarecases of severe early childhood obesity have been associatedwith leptin deficiency.9,13 The remainder of the obese popu-lation typically have elevated leptin levels.14 The failure ofleptin to induce weight loss in these cases is thought to be theresult of leptin resistance.

Hyperleptinemia, nearly universally observed in humanobesity and animal models, is accompanied by a disruption ofthe usual activities of the hormone, possibly at different

Original received May 22, 2007; revision received July 20, 2007; accepted August 6, 2007.From the Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, Md.This manuscript was sent to Richard A. Walsh, Consulting Editor, for review by expert referees, editorial decision, and final disposition.Correspondence to Lili A. Barouch, MD, Johns Hopkins University, 720 Rutland Ave, Ross 1050, Baltimore, MD 21205. E-mail [email protected]© 2007 American Heart Association, Inc.

Circulation Research is available at http://circres.ahajournals.org DOI: 10.1161/CIRCRESAHA.107.156596

545

Review

by guest on April 22, 2016http://circres.ahajournals.org/Downloaded from

http://circres.ahajournals.org/

stages in the circulatory transport and/or in the signalingcascade. Disruption of leptin signaling in the hypothalamusresults in obesity and confirms the central role of thishormone in the maintenance of energy balance.7,15,16 Emerg-ing evidence suggests that leptin resistance in the CNS maybe selective, namely that the effects of leptin on centralmetabolic processes is disrupted, whereas its other effects,such as the sympathetic activation of blood pressure, is stillretained.17 In addition to its actions in the CNS, leptinreceptors (Ob-Rs) are found in multiple peripheral tissuetypes and affect many systemic processes, such as reproduc-tion, immunity, and cardiovascular functions.18–20

Obesity is also a part of the metabolic syndrome, which isdiagnosed by a set of criteria that include abdominal obesity,insulin resistance, dyslipidemia, and hypertension. This pa-tient population faces increased risk for type 2 diabetes andcardiovascular diseases. The widely distributed Ob-Rs makethe hormone an attractive candidate for a molecular link in thepathogenesis of obesity-related diseases. Although disruptionof leptin signaling can lead to altered phenotypic expressionand function of peripheral organs, the relative contributionsof central versus peripheral signal disruption are still contro-versial. Increasing our understanding of how leptin and/orleptin resistance affects the heart and vasculature will beimportant for gaining comprehension of obesity-relatedthreats to cardiovascular health.

Leptin SignalingLeptin and Leptin ReceptorLeptin is primarily secreted by adipocytes and circulates at alevel of 5 to 15 ng/mL in lean subjects.21 Its expression isincreased by overfeeding, insulin, glucocorticoids, endotoxin,and cytokines and is decreased by fasting, testosterone,

thyroid hormone, and exposure to cold temperature.22,23 In theheart, increased leptin expression is seen following reperfu-sion after ischemia,24,25 and leptin concentration in cardio-myocyte culture serum is increased with endothelin (ET)-1and angiotensin (Ang) II treatment,26 suggesting the heart asa site of leptin production.

Six isoforms of the Ob-R (a to f) have been identified in themurine model, and they are closely related to the class Icytokine receptor family. Ob-Ra and Ob-Rb represent thedominant isoforms in the heart, whereas the others areexpressed at low levels27 and are not well conserved amongspecies.28,29 Ob-Re is the secreted form that binds circulatingleptin and regulates the concentration of free leptin.30

Janus-Activated Kinase/Signal Transducers andActivators of TranscriptionOb-Rs have been shown to activate Janus-activated kinase(JAK), signal transducers and activators of transcription(STAT), insulin receptor substrate, and the mitogen-activatedprotein kinase (MAPK) pathways. The best-characterizedpathway in leptin signaling is the JAK/STAT pathway (Fig-ure 1).31 Ligand binding causes Ob-R to undergo homooli-gomerization32,33 and to bind to JAK, primarily JAK2.34 Inthe case of overexpression of JAKs by transient transfection,weak Ob-Rb/JAK1 and Ob-Ra/JAK2 association was ob-served with leptin treatment.35 However, only Ob-Rb con-tains the STAT-binding site.35

Studies in vivo have demonstrated that signaling occursmainly through STAT3.16 Ob-Rb binding to JAK2 leads toJAK2 autophosphorylation and the phosphorylation ofTyr985, Tyr1077, and Tyr1138 on Ob-Rb.32,34,36–38 Phos-phorylation of Tyr1138 recruits STAT proteins to the Ob-Rb/JAK2 complex. Tyrosine phosphorylated STAT3 molecules

Figure 1. Leptin receptor signaling. The binding of leptin to its receptor leads to formation of the Ob-R/JAK2 complex that results incross-phosphorylation. Tyr1138 on Ob-Rb is crucial for STAT3 activation, which stimulates SOCS3 expression that negatively inhibitsleptin signaling via Tyr985 and additional sites on JAK2. Protein tyrosine phosphatase 1B (PTP1B) is also capable of inhibition of leptinsignaling. JAK2 phosphorylation can lead to activation of MAPK and insulin receptor substrate/PI3K signaling pathways. See text.GRB2 indicates growth factor receptor–bound protein 2.

546 Circulation Research September 14, 2007



dimerize and translocate to the nucleus to activate transcrip-tion of target genes, which includes the gene for a member ofthe suppressors of the cytokine signaling family(SOCS3).16,36,39 SOCS3 binding to Tyr985 and other siteswithin the Ob-Rb/JAK2 complex mediates negative feedbackon leptin signaling.40,41 JAK2 phosphorylation of Tyr985 alsoconsequently leads to phosphorylation of the src homology 2(SH2) domain of the tyrosine phosphatase SHP-2 (src homol-ogy 2-containing tyrosine phosphatase), which activates theextracellular signal-regulated kinase (ERK) signaling path-way.36 Overexpression of SHP-2 has been shown to bluntSOCS3-mediated inhibition, likely through competitive bind-ing to Tyr985.40

JAK2 autophosphorylation is independent of tyrosinephosphorylation sites on Ob-Rb and has many subsequenteffects. One of these effects is to phosphorylate insulinreceptor substrate proteins, which recruit the phosphatidyl-inositol 3�-kinase (PI3K) to activate downstream signals.7,42

In the heart, the leptin-associated PI3K pathway, along withERK cascades, seems to be important in cardiomyocyteproliferation and protecting cardiac tissue from ischemia/reperfusion injury.24,43

Mitogen-Activated Protein KinasePhosphorylation of Tyr985 on Ob-Rb leads to SHP-2 andGrb-2 activation of ERK1/2 of the MAPK family.36 ERK1/2activation also occurs via a pathway independent of Tyr985.In this case, JAK2 associates with the SH2 domain-containing SHP-2.36,44 Therefore, both Ob-Ra and Ob-Rb canactivate MAPK.35,36 Shc, another SH-2–containing proteinthat is able to associate with Grb-2, has also been shown tophosphorylate tyrosine after leptin treatment.45 Leptin-induced phosphorylation of STAT3 and ERK1/2 have beenobserved in isolated adult C57BL/6 mouse cardiomyocytes,with maximal activation at 15 minutes after treatment. Four-week leptin treatment also elevated STAT3 and ERK1/2phosphorylation and abundance in cardiac tissue from leptin-deficient ob/ob mice but not from Ob-Rb–deficient db/dbmice.46 Because Ob-Ra is intact in db/db mice and the distalportion of Ob-Rb is not essential for MAPK signaling,35

ERK1/2 phosphorylation would be expected to increase evenif STAT3 phosphorylation were unaltered. Therefore, theresults suggest that either Ob-Rb is the predominant signalingreceptor in the mouse heart or that JAK2-induced ERK1/2phosphorylation does not occurs at a significant level incardiomyocytes. ERK1/2 activation leads to the expression oftarget genes, such as c-fos and egr-1, which participate in cellproliferation and differentiation.

Phosphorylation of p38 MAPK in response to leptin hasalso been demonstrated. The � and � isoforms of p38 MAPKare broadly distributed, including at relatively high levels inthe heart.47 Although the specific mechanism leading toleptin-induced p38 MAPK activation has not been elucidated,it is associated with the onset of hypertrophy and pro-grammed cell death in both rat vascular smooth muscle cells(VSMCs) and cardiomyocytes.24,48,49

As with other cytokines, leptin has the ability to activatethe stress-activated protein kinase c-Jun N-terminal kinase(JNK).50,51 However, we observed that phosphorylation of

JNK was unaltered in cultured adult cardiomyocytes fromC57BL/6, ob/ob, and db/db mouse strains with 15-minuteleptin treatment.46 The effects of long-term leptin treatmenton JNK activity in the heart remain to be investigated.Nuclear factor �B has been proposed as an attractive down-stream target for p38 and JNK MAPK pathways because thistranscription factor is essential in the transcriptional regula-tion of proinflammatory cytokines such as tumor necrosisfactor (TNF)-� and interleukin (IL)-1�.52 Additional leptinsignaling pathways are difficult to consolidate because oftissue specificity. For a comprehensive review of leptinsignaling capabilities, see reviews by Fruhbeck52 orSweeney.53

Leptin Signaling in the CNSHypothalamic Leptin Decreases Food IntakeMost Ob-Rs in the CNS are located in the basomedialhypothalamus.54,55 In neurons that synthesize proopiomelano-cortin and express Ob-Rb, leptin stimulates the synthesis ofproopiomelanocortin, which is processed to produce �-mela-nocyte–stimulating hormone and activate downstreammelanocortin-3 and -4 receptors to decrease appetite.56 Leptinalso inhibits the appetite-stimulating hormone neuropeptideY in the arcuate nucleus, and causes inhibition of agouti-related peptide that restrain melanocortin-3 and -4 receptorsignaling.55,56

Ob-Rb–stimulated JAK2/STAT3 signaling is crucial inleptin control of feeding and energy expenditure. Althoughshort forms of the leptin receptor may be capable of activatingJAK, insulin receptor substrate, and MAPK proteins, onlyOb-Rb is capable of activating STAT3.35,57,58 A homologousreplacement of Ob-Rb by a receptor mutant for Tyr1138established that STAT3 is indispensable for the regulation ofexpression of proopiomelanocortin and neuropeptide Y in thehypothalamus.16

Mechanisms of Central Leptin ResistanceOne theory of leptin resistance involves intracellular signal-ing disruption. STAT3 and protein tyrosine phosphatase 1Bare 2 molecules known to attenuate leptin signaling.40,59–63

Hypothalamic protein tyrosine phosphatase 1B levels are notknown to be altered in obesity, although protein tyrosinephosphatase 1B–null animals develop increased insulin sen-sitivity and have a lean phenotype.64 As previously discussed,leptin can induce its own negative feedback through STAT3-induced SOCS3 accumulation during prolonged Ob-Rb stim-ulation,36,40,61 which can occur via Tyr985 or additional sitesin the Ob-Rb/JAK2 complex.40,41 At low concentrations ofleptin, incremental changes in leptin would be almost fullytranslated into increased Ob-Rb signaling, whereas, at highlevels, accumulated SOCS3 would counter most of theincrease in Ob-Rb signaling.39,65

Another possible mechanism of central leptin resistancestems from the dependency of leptin on saturable transportacross the vascular barrier and, probably to a lesser extent,across the choroid plexus to reach the arcuate nucleus.66 Theactivity of this blood–brain barrier transport system seems todecrease in diet-induced obese (DIO) rodents,67 resulting infailure of circulating leptin to reach its targets in the brain.

Yang and Barouch Leptin Signaling and Obesity 547



Increasing evidence suggests that leptin signaling is prefer-entially reduced in the arcuate nucleus of the hypothalamusbut not in other regions, such as the ventromedial, dorsome-dial, and/or premammillary nucleus of the hypothalamus thatalso express Ob-Rs.68

Leptin Increases Sympathetic OutflowIn addition to reducing appetite and controlling weight gain,leptin centrally activates the sympathetic nervous system. Itsignificantly increases plasma norepinephrine and epineph-rine concentrations via the ventromedial hypothalamus.69

Whereas chronic leptin overstimulation in the hypothalamusdecreases the ability of leptin to regulate appetite, its sympa-thetic excitatory effects are maintained as increased arterialpressure and renal sympathetic nerve activity are presented inobesity (Figure 2).70 This observation suggests that centralleptin resistance is selective.

The concept of selective resistance is suggested by acomparison between ob/ob and Agouti yellow obese mice.Lower arterial pressure is observed in ob/ob mice, which isincreased by leptin reconstitution despite the accompanyingweight loss.71 In contrast, Agouti yellow obese mice developobesity resulting from ubiquitous overexpression of agoutiprotein, which blocks MC4R rather than directly affectingleptin. They have elevated arterial pressure similarly to DIOmice, despite the fact that they have milder obesity than ob/obmice.71,72 This preservation of sympathoactivation effects ofleptin despite disruption of its weight control effects has beenconfirmed in DIO mice, which is considered a more physio-

logic model of human obesity. In C57BL/6J mice fed a10-week high-fat diet, intraperitoneal leptin administrationfailed to decrease appetite and body weight, but increasedrenal sympathetic nerve activity. Sympathetic nerve activityin brown adipose tissue and in hindlimb did not increase onleptin administration, indicating region-specific preservationof leptin sympathoactivation that serves to protect its circu-latory effects.73

The sympathoactivation effect is completely abolished byselective destruction of the arcuate nucleus.74 As the arcuatenucleus is required for both metabolic and sympatheticeffects of leptin, these results seem to suggest that leptinresistance occurs mainly through intracellular signaling dis-ruption. Under resting conditions, it is estimated that only 5%to 25% of Ob-R isoforms are located at the cell surface.75 Theligand–receptor complex internalizes, and studies have shownthat leptin internalization was greater for the Ob-Rb iso-form.75,76 Preferential downregulation of Ob-Rb in responseto prolonged leptin exposure may be important in regulatingdifferent tissue sensitivity to leptin and another cause forselective leptin resistance.

Leptin stimulation of adrenergic overdrive can lead tonumerous adverse effects on the cardiovascular system. Bothin vitro and in vivo studies have demonstrated adrenergicinfluences on the growth of cardiomyocytes.77,78 Patients withthe metabolic syndrome have increased sympathetic activity,hypertension, and higher occurrences of left ventricularhypertrophy (LVH).79,80 Sympathetic influences also modu-lates the elastic properties of large and medium-size arteries

Figure 2. Systemic leptin function. Chronic hyperleptinemia impairs the centrally mediated metabolic actions of the hormone, alyhoughits activation of sympathetic outflow is preserved. Selective central leptin resistance results in obesity and adverse effects on the car-diovascular system including hypertension, atherosclerosis, and LVH. Although leptin can protect against ectopic lipid deposition innonadipose tissue, whether this effect is abolished because of (selective) peripheral leptin resistance requires further examination.




and promote endothelial dysfunction, contributing to thedevelopment of vascular structural alterations and the occur-rence of atherosclerotic lesions.81

Leptin and the Cardiovascular SystemHyperleptinemia is associated with obesity-related hyperten-sion and chronic congestive heart failure (HF) in humans, andvascular endothelial and myocardial dysfunction in animalmodels.82–85 The role of leptin and leptin resistance in thepathogenesis of LVH and HF in obesity remains controver-sial. The Table provides a summary of the leptin signalingpathways involved in the cardiovascular system.

Vascular Effects of Leptin

Development of HypertensionBoth intravenous infusion and intracerebroventricular admin-istration of leptin lead to increased arterial pressure and heartrate in rodents.86,87 Blockade of the adrenergic system inhibitsthe pressor response to leptin.88 In addition to increasedsympathetic activity in hyperleptinemia, other mechanismsmay also contribute to the development of obesity-relatedhypertension. Leptin has been shown to increase the genera-tion of reactive oxygen species (ROS) in endothelial cells50,89

and to stimulate secretion of proinflammatory cytokines suchas TNF-� and IL-6, both of which are promoters of hyper-tension and atherosclerosis.90

While stimulating blood flow via increased sympatheticoutput, leptin has also been shown to have direct vasodilatoryeffects. In both intact rodents and in endothelial cells, leptininduces NO production.83,91 Leptin administration in anesthe-tized rats causes a dose-dependent increase in NO metaboliteconcentrations, and inhibition of NO synthesis increasesarterial pressure.91 In vitro studies have shown that leptinevokes an endothelium-dependent relaxation of arterialrings.92,93 In endothelial cells, leptin activates a PI3K-independent Akt-endothelial NO synthase (eNOS) phosphor-ylation pathway to increase NO production, which can beabolished by erbstatin A, a Ca2�-independent tyrosine kinaseinhibitor.94 However, the vasodilator action of leptin was notfound in conscious rats and the NOS inhibitor NG-nitro-L-

arginine methyl ester did not unmask any pressor effect.95 Ata concentration sufficient to increase sympathetic nerveoutflow, leptin did not change arterial pressure or blood flowin mesenteric, lower aortic, and renal arteries.96 Blockade ofNO synthesis increased heart rate and renal vascular andglomerular response but did not substantially augment thepressor response to leptin,97 indicating a negligible role ofleptin-stimulated NO production on blood pressure in vivo.Leptin has been shown to increases the release of ET-1, avasoconstrictor secreted primarily by endothelial cells butalso by macrophages, fibroblasts, and cardiomyocytes, pos-sibly countering the effects of NO.98

Development of AtherosclerosisThe proatherogenic action of leptin is likely attributable to acombination of its effects on various cell types. In endothelialcells, leptin induces oxidative stress, increases production ofmonocyte chemoattractant protein-1 and ET-1 and potentiatesproliferation.50,89,98,99 In VSMCs, leptin promotes migration,proliferation, and hypertrophy.100–102 Leptin also promotescalcification of cells of the vascular wall and facilitatesthrombosis by increasing platelet aggregation.103,104

Hyperleptinemia has been associated with coronary athero-sclerosis in type 2 diabetes, and this association has beenshown to be independent of insulin resistance.105 In apoli-poprotein E–deficient (apoE�/�) mice that are atherosclerosisprone, recombinant leptin treatment further promoted athero-sclerosis and thrombosis, despite its metabolic benefits.106

This result indicates that elevation of leptin concentration inobesity increases the risk for atherosclerotic damage.

Paradoxically, leptin resistance is also proatherogenic.ApoE�/� mice lacking Ob-Rb (apoE�/� db/db) are character-ized by a 5-fold higher area of spontaneous atheroscleroticlesions in the aorta than apoE�/� with intact Ob-R.107 UnlikeapoE�/� mice, apoE�/� db/db mice are also obese and insulinresistant. Taken together, these data suggest either that asupraphysiological level of exogenous leptin self-inducesresistance that is harmful or that the atherogenic effect seen inapoE�/� db/db is an effect more relevant to lipid profilechange, which is absent in apoE�/� mice.

Summary of Leptin Signaling in the Cardiovascular System

Leptin Action Pathways Involved

Development of hypertension Increased catecholamine release, preserved renalsympathetic nerve activity increase, NO

Development of atherosclerosis Endothelial cell NO and ROS production, VSMCproliferation and hypertrophy, platelet

aggregation, proinflammatory cytokine production

Impaired cardiomyocyte contractility JAK/STAT, NO-cGMP, G protein–coupledreceptor, adenylate cyclase, ET-1, NAPDH, ROS

Liporegulation Increased FA oxidation

Increase in size of cardiomyocyte ET-1, ROS

Deficiency leads to increased rate ofcardiomyocyte apoptosis

p38, caspase-3, DNA damage, Ang II

Enhanced cardiomyocyte mitosis andproliferation

ERK1/2, p38, PI3K, peroxisomeproliferator-activated receptor-�

Protection from ischemia/reperfusion injury PI3K, ERK1/2, NO, ROS




Leptin Attenuates Cardiomyocyte Contractility

Possible Mechanisms Leading to IncreasedNO ProductionSimilar to its effects in endothelial cells, acute leptin infusionin isolated rat ventricular myocytes increases NO activity,which leads to attenuated cardiac contractility (Figure 3).108

Intracellular Ca2� transients were lowered and NO productionwere increased with leptin. These effects were blocked by theNO inhibitor NG-nitro-L-arginine methyl ester108 and by JAK2or p38 MAPK inhibitors AG-490 and SB203580.109

The intermediate steps by which leptin signaling leads toincrease in NO production and the specific NOS isoforms thatmediate the effects of leptin have not been fully elucidated. Inrat VSMCs, leptin inhibits the contractile response inducedby Ang II through increased NO production. The upregula-tion of inducible NO synthase through mechanisms involvingJAK2/STAT3 and PI3K/Akt pathways is responsible for theincrease of NO bioavailability in VSMCs.110

Elucidation of the NOS isoform(s) responsible for theactions of leptin in the heart would lead to a better under-standing of its role in myocardial contractility and hypertro-phy responses. We have shown that spatial confinement ofdifferent constitutive NOS isoforms within separate subcel-lular compartments of the cardiac myocyte allows NO signalsto have independent, and even opposite, effects on cardiacphenotype and contractile response.111 Overexpression of

eNOS inhibits hypertrophy in the remote myocardium andpreserved cardiac function after myocardial infarction, pos-sibly through attenuation of �-adrenergic–stimulated com-pensatory hypertrophy.112 Neuronal NO synthase and eNOSindependently contribute to the development of cardiac hy-pertrophy, leading to marked age-related concentric hyper-trophic remodeling in double-knockout mice lacking bothneuronal NO synthase and eNOS.113,114 Understanding theleptin crosstalk with the �-adrenergic signaling system incardiomyocytes would provide significant insight into theunderstanding of myocardial dysfunction in obesity.

Whereas leptin-induced NO increase directly depressescardiomyocyte contractility, systemic actions such as in-creased sympathetic modulation may indirectly stimulatecontractility. Just as leptin-stimulated NO production inendothelial cells may have a negligible role in blood pressurein vivo, cardiac contractile depression may not manifestunder normal physiologic conditions. However, the depres-sant effect may become important when considered in con-juncture with alterations occurring in obese states.

Leptin Deficiency Leads to Decreased Responsiveness to�-Adrenergic StimulationIn 10 week-old ob/ob isolated myocytes, attenuated sarco-mere shortening and calcium transients and depressed sarco-plasmic reticulum Ca2� stores were seen in response toisoproterenol stimulation of the �-adrenergic receptor or to

Figure 3. Leptin and myocardial contractility. Leptin directly depresses cardiomyocyte contractility. The signaling pathways implicatedin this process include the NO-cGMP pathway and pathways that lead to increased ROS production. Changes that occur in a chronicleptin-deficient state are also illustrated. TG indicates triacylglycerol; iNOS, inducible NO synthase; nNOS, neuronal NO synthase; AC,adenylate cyclase; PKA, protein kinase A; XOR, xanthine oxidoreductase; SR, sarcoplasmic reticulum.




post–receptor level stimulation with forskolin and dibutyryl–cAMP. Leptin replenishment in ob/ob mice restored each ofthese abnormalities toward normal without affecting gross(wall thickness) or microscopic (cell size) measures ofcardiac architecture. Decreased G�s (52 kDa), increasedsarcoplasmic reticulum Ca2�-ATPase, and depressed phos-phorylated phospholamban abundance were detected in ob/obmice. In addition, protein kinase A activity in ob/ob mice wasdepressed at baseline and corrected toward wild-type (WT)level with leptin repletion.46 In the H9c2 cardiac cell line,30-minute leptin treatment increased basal and catechol-amine-stimulated adenylate cyclase activity, whereas 18-hourtreatment was associated with a reduced adenylate cyclaseactivity and a different responsiveness to isoproterenol andnorepinephrine stimulation, likely attributable to differentialactivation of G�s. Adenylate cyclase, G�s (52 kDa), G�i,p21-ras, and phosphorylated ERK1/2 expressions were in-creased with short-term leptin treatment and decreased at 18hours, whereas G�s (45 kDa) continued to increase at 18hours. Receptor level leptin resistance is conceivable inmyocytes, as Ob-R expression is seen to decrease at 18-hourleptin treatment.115 Taken together, leptin deficiency or resis-tance leads to decreased �-adrenergic response, whereasmoderate leptin stimulation can improve the contractileresponse.

Mechanisms Involving ROSMitochondrial formation of ROS is enhanced in obesity.Xanthine oxidoreductase and nicotinamide adenine dinucle-otide phosphate (NADPH) oxidase are 2 main sources ofsuperoxide (O2

.) production in the heart. O2. is capable of

generating a large family of ROS by interacting with othermolecular compounds. In ob/ob hearts, impaired cardiaccontractile function is accompanied by elevated oxidativestress, lipid peroxidation, protein carbonyl formation, redis-tribution of myosin heavy chain isozymes from myosin heavychain-� to -�, and oxidative modification of SERCA2a.116

Neuronal NO synthase constrains xanthine oxidoreductaseactivity.117,118 Reduced neuronal NO synthase expression isobserved in 2- to 6-month-old ob/ob mice, which leads toincreased xanthine oxidoreductase production of O2

. , therebycausing an imbalance between the production of ROS andreactive nitrogen species.119 This nitroso–redox imbalancemay be partially responsible for the myocardial dysfunctionseen in ob/ob mice. Activation of NADPH oxidase is alsoseen in the ob/ob heart.116 Treatment with apocynin, aNADPH oxidase inhibitor, reversed cardiac contractile dys-function in ob/ob myocytes but failed to reserve SERCA2aoxidative modification.116 8-Bromo-cGMP, a membrane-permeable cGMP analog, induced a greater negative effect inob/ob than lean C57BL/6J mice. However, the effect ofadding a NO donor was similar in the obese and lean models,indicating that some cGMP-independent effect of NO pre-vents the enhanced negative cGMP effects in ob/ob cardio-myocytes.120 NAPDH-mediated reduction in NO bioavail-ability could explain the failure of NO donor to elicit furthernegative inotropic response in obese models.121,122 Addition-ally, the interaction between NO and ROS produces per-oxynitrite, which can nitrosylate proteins and exert positive

inotropic effects, thereby offsetting the cGMP-dependentreduction in contractility.120 Peroxynitrite has shown bothnegative and positive inotropy in isolated cardiomyo-cytes,123,124 although it is generally accepted to trigger apo-ptosis in cardiomyocytes in vitro and in vivo, possiblythrough a pathway involving caspase-3 activation and thecleavage of poly(ADP-ribose) polymerase.125

Another recent study proposes that ET-1 is upstream ofNADPH oxidase in leptin-induced myocardial contractileresponse.126 There are at least 2 cardiac ET-1 receptors, ETA

and ETB. Both are known to mediate cardiomyocyte inotropicresponse, and ETA receptors also affect hypertrophy.127 Lep-tin administration to rat neonatal cardiomyocytes inducedintracellular O2

. generation and upregulated protein expres-sion of p67phox and p47phox subunits of NAPDH, the effectof which is attenuated by ETA and ETB receptor antagonistsand apocynin, suggesting that the ET-1 receptors are likelyupstream of NADPH oxidase in leptin-induced cardiac con-tractile response.126

Additional Mechanisms Affecting ContractilityObesity is a lipotoxic disease featuring overtly elevatedceramide levels (see section below, Leptin Shifts MyocardialMetabolism Toward Fatty Acid Utilization). The de novoceramide pathway has been postulated to be key to thelipoapoptosis of pancreatic � cells and cardiomyocytes inobese individuals.128,129 The ability of ceramide to amplifyleptin-induced depression of contractility in adult rat leftventricular myocytes was recently demonstrated.130 Althoughceramide alone did not elicit any effect on cell mechanics andintracellular Ca2� transients, it sensitized leptin-induced ef-fects on myocyte shortening and intracellular Ca2� transients.In vivo obese concentrations of plasma leptin lie in the lownanomolar range, which is seemingly disconnected from thehigh in vitro leptin concentration (�10 nmol/L) needed toaffect cardiac contractile function. The observation thatceramide may augment the cardiac depressive effect of leptinprovides an additional explanation for hyperleptinemia-associated cardiac dysfunction in obesity.

Elevated adipose mass in obesity also increases the secre-tion of other proinflammatory factors, including TNF-�, IL-6,and Ang II. TNF-� and leptin both depress contractility inadult rat ventricular myocytes, although no additive responseby the 2 proinflammatory factors was observed. Inhibitoryeffects were abolished by NG-monomethyl-L-arginine in bothcases and in the case of combined exposure.131 Thus, theinhibitory effect on cardiac contraction by TNF-� and leptinmay mask each other and share a common mechanismdependent on NO.131

It is interesting, however, that hypertension seems toattenuate leptin-induced cardiomyocyte contractile depres-sion. Isolated rat ventricular myocytes from spontaneouslyhypertensive rats (SHR) displayed decreased leptin-induceddepression of myocyte shortening and intracellular Ca2�

transients, as well as blunted leptin-induced NOS activitycompared with the normotensive control mice. Additionally,treatment of SHR myocytes with JAK or p38 inhibitor led tofurther inhibition of myocyte shortening by leptin instead ofabolishing such effects.109 The altered signal transduction of




JAK/STAT and p38 pathways to attenuate leptin-inducedcardiomyocyte dysfunction possibly serves as a compensa-tory mechanism to prevent further impairment of ventricularfunction in sustained hypertension or hyperleptinemia.109

Leptin Shifts Myocardial Metabolism TowardFatty Acid UtilizationAccumulating evidence suggests that leptin regulates energyhomeostasis through direct actions on peripheral lipid andglucose metabolism.132 Fatty acid (FA) oxidation producesthe major source of ATP to sustain contractile function of theheart. AMP-activated protein kinase (AMPK) has a key roleas a fuel gauge in the heart and regulates cardiac FA oxidationby phosphorylation and inhibition of acetyl–coenzyme A(CoA) carboxylase, which then lowers malonyl-CoA levelsand stimulates carnitine palmitoyltransferase-1–induced FAoxidation.133 AMPK activation is also known to reduce FAincorporation into triacylglycerol.134

Examination of leptin effects on cardiac FA oxidationconfirmed that leptin infusion increases FA oxidation andtriacylglycerol lipolysis in isolated working rat hearts, al-though this effect was independent of changes in the AMPK/acetyl-CoA carboxylase/malonyl/CoA axis. Neither did leptinaffect glucose oxidation rates.135 Myocardial oxygen con-sumption was increased, possibly because of increased mito-chondrial uncoupling protein activity.135 In DIO mice, plasmaleptin concentration increase was associated with an induc-tion of uncoupling protein 2 and an increase in phosphoryla-tion of AMPK that led to increased FA oxidation.136 At thisstage, leptin signaling in the heart as assessed by STAT3phosphorylation remained unaltered from WT, suggestingthat the shift to FA oxidation is at least mediated, in part, byleptin. Increased FA oxidation may confer antisteatosis pro-tection to the myocardium during hyperleptinemia in earlystages of obesity. This is consistent with the observation thatDIO rodents exhibit minimal rise in myocardial triacylglyc-erol content, whereas ob/ob, db/db, and fa/fa animals showsignificantly greater accumulation.137 Leptin deficiency per-turbs liporegulation in peripheral organs and results in lipo-toxicity, lipoapoptosis, and generalized steatosis, manifestingin clinical conditions such as nonalcoholic steatohepatitis,type 2 diabetes, and lipotoxic cardiomyopathy.128 Lipotoxiccardiomyopathy has been identified in fa/fa rats and has beentransgenically induced in acyl–CoA synthase transgenicmice.138 Overexpression of acyl–CoA synthase, which activesand esterifies FAs, led to severe cardiomyopathy that wasattenuated by injection of recombinant adenovirus containingthe leptin cDNA.138

Increased de novo lipogenesis and decreased compensatoryoxidation of FAs are two possible mechanisms for intracel-lular accumulation of lipids in nonadipose tissue. Enzymesinvolved in FA oxidation such as acyl-CoA oxidase andcarnitine palmitoyltransferase-1 are observed at attenuatedlevels in fa/fa rats. Hydrolysis of the increased stores oftriacylglycerol to fatty acyl-CoA in fa/fa rats also increasedthe substrate for de novo ceramide synthesis and activated theexpression of inducible NO synthase in the myocardium,which led to acceleration of apoptosis.129 Ceramide alsoactivated protein kinase C isoforms, which can induce gene

transcription through MAPK and nuclear factor �B and areimplicated in the development of cardiomyocyte hypertro-phy.139 It seems paradoxical that enhanced expression of �

oxidation enzymes such as long-chain acyl-CoA dehydroge-nase and carnitine palmitoyltransferase-1 are seen in ob/obmice,140 as leptin-deficient hearts are also characterized byincreased FA utilization.141 This is likely attributable tolong-term adaptation to the changes in the lipid profile inthese animals. Genes for lipoprotein lipase, which generatesfree FAs, and FA transport proteins are seen at an greatlyelevated level in ob/ob myocytes, which causes accumulationof free FAs that promote ceramide, inducible NO synthase,and NO production in the cardiomyocyte.140 When increasedFA delivery and hyperinsulinemia are imposed in ob/obhearts, myocardial function is maintained, albeit with de-creased efficiency, whereas WT hearts are unable to adaptacutely.141

Increased FA uptake accompanied by decreased oxidationleads to lipotoxicity in long-term leptin-treated cardiomyo-cytes. The antisteatotic effects of leptin in early obesity mightbe lost with the progression of leptin resistance occurring inlate stage obesity, leading to lipotoxicity that promotescardiomyocyte contractile dysfunction and apoptosis129 oracts in a maladaptive fashion because of increased ceramidesynthesis.

Leptin Effects on Cardiac Hypertrophyand RemodelingPostmortem clinical studies of obesity-associated hypertro-phy have demonstrated excessive heart weight but lowheart/body weight ratios.142 Fatty infiltration of the myocar-dium, presence of metabolic inclusions, excessive fibrosis, orincreases in extracellular matrix do not appear to play a directrole in augmenting wall thickness in obesity-related hyper-trophy.143 The findings on endomyocardial biopsy in themajority of obese patients with cardiomyopathy appear to beprimarily myocyte hypertrophy.144 Hyperleptinemia is ob-served in patients with LVH.145 Leptin effects on cardiomyo-cyte hypertrophy is not entirely clear. We had previouslyshown leptin repletion to be antihypertrophic in ob/ob hearts.Four- to 6-week leptin infusion reduced weight and reversedLVH, whereas caloric restriction reduced weight but did noteffectively reduce wall thickness and myocyte size.113 Recon-stitution to normal levels may provide the antisteatotic effectof leptin that can reverse lipotoxic effects of FA deposition inthe myocardium. On the other hand, leptin has been shown toinduce hypertrophy in a concentration-dependent manner incultured neonatal rat ventricular myocytes.48,146 Fastingplasma leptin levels are associated with increased myocardialwall thickness in hypertensive humans, although this may berelated to leptin resistance.147 The different types of cardio-myocytes used in experiments could also contribute to theobserved paradoxical effects of leptin on cardiomyocytehypertrophy. Direct effects of leptin on cardiomyocyte hy-pertrophy, apoptosis, proliferation, and extracellular matrixremodeling could all contribute to maladaptive hypertrophyand HF in obesity.




Cardiomyocyte HypertrophyLeptin-induced neonatal cardiomyocyte hypertrophy occursthrough a mechanism involving ET-1 and ROS generation.146

ET-1 has been shown to increase cardiomyocyte surface areawithout increasing cell proliferation.148 In this study, blockingthe ETA receptor with the selective inhibitor ABT-627 par-tially but significantly reduced leptin-induced hypertrophy.146

An interdependence of ET-1 and leptin signaling has beenproposed in the progression of myocardial dysfunction andhypertrophy, suggesting that leptin may cause chronic oxida-tive stress and inflammation in the myocardium, similar toother agents such as TNF-�, norepinephrine, and Ang II, allof which induce hypertrophy via ROS upregulation.149,150

Leptin may indeed have an autocrine role in mediatingET-1 and Ang II–induced cardiomyocyte hypertrophy. Treat-ment of neonatal rat myocytes for 24 hours with leptin, AngII, or ET-1 significantly increased cell area by 37%, 36%, and35%, respectively. In contrast to the study mentioned aboveby Xu et al,146 Rajapurohitam et al26 have shown thatblocking the ETA receptor did not prevent leptin-inducedhypertrophy, neither did blocking the Ang receptor. Leptinblockade attenuated the hypertrophic responses generated byall 3 agents. Ang II and ET-1 significantly increased leptinlevels in the culture medium and increased the gene expres-sion of both Ob-Ra and Ob-Rb. Additionally, Ang II andET-1 increased phosphorylation of ERK1/2, p38, JNK, andnuclear factor �B, but the ability of leptin blockade toattenuate hypertrophic responses was generally dissociatedfrom these effects.26 The discrepancy between the studies byXu et al and Rajapurohitam et al in terms of blockingleptin-induced hypertrophic response with ETA receptorsantagonists (ABT-627 versus BQ123) cautions against theinterpretation of results using pharmacological agents, as theprecise mechanisms of action is unclear in many cases.Another study demonstrates that in 9-week-old mice fed ahigh-fat diet, serum and myocardial ET-1, myocardial leptin,and Ob-R mRNA are all elevated, whereas in ob/ob mice,both serum and myocardial ET-1 levels are not higher thanWT mice, confirming a direct role of leptin in mediatingincreased myocardial ET-1 signaling.151 Simvastatin, a cho-lesterol-lowering drug decreases leptin-induced ROS-mediated hypertrophy in rat neonatal cardiomyocytes.152

ApoptosisOne of the causes of HF is cardiomyocyte apoptosis andnecrosis.153 We recently found that leptin deficiency orresistance results in increased cardiomyocyte apoptosis, asassessed by TUNEL staining and caspase-3 levels.154 Agedob/ob and db/db mice showed increased DNA damagecompared with old WT mice. Leptin reconstitution ob/obanimals reduced the rate of apoptosis, although not to WTlevels.154 This is consistent with earlier work demonstratingincreased apoptosis in islet cells and cardiomyocytes in fa/farats.129,155 These results suggest that leptin signaling isnecessary to maintain normal low levels of cell deathand that leptin provides protection against lipotoxicity-induced apoptosis.

On the other hand, JAK2 has been suggested as a mediatorof the apoptotic response in cardiomyocytes.156 It is promi-

nently involved in the upregulation of the renin–Ang system,and Ang II–treated adult rat cardiomyocytes in culture exhibitincreased apoptosis. The somewhat paradoxical combinationof antiapoptotic roles of leptin and proapoptotic actions ofJAK2 merits further investigation. Leptin acutely increasesphosphorylation of ERK1/2 and p38 MAPK in rat neonatalcardiomyocytes, but leptin-induced p38 activation in ratneonatal cardiomyocytes sustains for a longer period thanERK1/2 activation, suggesting that the downstream transcrip-tion factors of p38 may be involved in the long-termmaladaptive cardiac remodeling in obese HF patients.48

Mitosis and ProliferationLeptin treatment at a level similar to plasma concentration inobese individuals increased proliferation of both HL-1 car-diac muscle cells and human pediatric ventricular myocytes.43

The proliferation was accompanied by increased DNA syn-thesis associated with increased ERK1/2 phosphorylation andincreased association of the p85 regulatory subunit of PI3Kwith phosphotyrosine immunoprecipitates.43 ERK1/2 inhibi-tion significantly attenuated the leptin-induced proliferativeactivity and DNA replication in HL-1 and pediatric humancardiomyocytes43 but failed to decrease [3H]-leucine incorpo-ration in neonatal rat cardiomyocytes treated with leptin.48

Other pathways likely involved in leptin-induced hypertro-phy include the activation of adenylate cyclase,115 peroxi-some proliferator-activated receptor-�,157 and the JAK/STATpathway associated with hsp56 and Ang II.109,158 Leptinsignaling is capable of activating other traditional pathwaysfor the development of hypertrophy, such as PI3K and proteinkinase C.159 Whether these pathways are activated in cardio-myocytes in response to leptin and the specific isoformsinvolved mandate further research.

Extracellular Matrix RemodelingLeptin has been shown to increase the expression of matrixmetalloproteinase-2, and to increase collagen type III and IVmRNA and decrease collagen type I mRNA without affectingtotal collagen synthesis in human pediatric cardiomyo-cytes.160 This suggests that leptin selectively regulates differ-ent forms of collagen although further studies are required tovalidate the regulation of collagen synthesis by leptin and toconfirm these effects on cardiac remodeling in obesity.

Protection in Ischemia/Reperfusion InjuryTimely reperfusion is necessary to salvage myocardium fromacute infarction, but reperfusion usually induces additionalinjury. A recent report shows that exogenous leptin given atearly reperfusion in an isolated mouse heart model reducesinfarct size.24 This cardioprotective action of leptin is asso-ciated with activation of the reperfusion injury salvage kinasepathway that includes PI3K/Akt and ERK1/2, ultimatelyleading to the inhibition of mitochondrial permeability tran-sition pore opening.161 Infarct size in C57BL/6J mouse heartsperfused with leptin was about half that of hearts perfusedwithout leptin. In a rat model, leptin and Ob-Ra expressionswere locally upregulated in scarred tissue following reperfu-sion, whereas Ob-Rb expression was downregulated.24 PI3Kor ERK1/2 inhibition diminished the cardioprotective ef-fect.24 Interestingly, leptin did not increase phosphorylation




of Akt or its downstream targets such as eNOS. Additionally,there was increased phosphorylation of p38 MAPK andreduced abundance and phosphorylation of STAT3 andAMPK.24 Leptin-stimulated ROS production and NO synthe-sis has been shown also to protect against ischemia reperfu-sion injury in the gut and kidney.162,163 Clinically, it isinteresting to note that patients with a higher body mass indexhave better outcomes following an acute coronary syndromeor percutaneous coronary intervention.164,165

Leptin Resistance in theCardiovascular System?

The relative contributions of central and peripheral leptineffects to disease pathogenesis are difficult to decipher.Central leptin resistance disrupts hypothalamic control ofenergy homeostasis, which results in obesity and increasedlipid production. This in turn may lead to ectopic lipiddeposition and lipotoxicity in peripheral organs. The attemptto separate the effects of this pathological process from thephysiological effects of leptin in the cardiovascular systemhas proven to be challenging, complicated by differentisoform signaling capabilities and possible resistance in theperiphery. The question remains whether peripheral leptinresistance occurs in the myocardium itself in obesity. Eventhough chronic leptin stimulation has been seen to decreaseOb-R expression in various studies,75,115 DIO mice showincreased Ob-R mRNA expression.151 On the other hand,Ob-Rb expression in ob/ob left ventricular homogenate islower than WT.126 However, mRNA expression does notnecessarily correlate with receptor density at the membrane;therefore, these results are not conclusive in determiningwhether leptin resistance can occur at the myocyte receptorlevel. One recent study suggests that leptin resistance doesnot occur in the myocardium in a model of early centralresistance. Eight-week DIO C57BL/6 mice showed attenu-ated leptin phosphorylation of STAT3 in hypothalamic tissue,whereas no such attenuation was shown in whole-hearthomogenate.136

Paradoxical results have been reported in almost all leptin-related effects on the myocardium; that is, excessive exoge-nous leptin and leptin deficiency often lead to the same end.Whether these effects occur through entirely different mech-anisms, are mediated through differential regulation of Ob-Risoforms, or are attributable to peripheral resistance requiresfurther investigation. If peripheral myocardial resistance doesoccur, these differences could be resolved if we considerleptin deficiency and leptin resistance both to be states ofdysfunctional downstream signaling.

Interestingly, obesity-induced leptin resistance, althoughnot reported in the myocardium, has been shown to extend toaffect platelets and the vascular wall.166 Obese concentrationsof leptin significantly attenuate coronary vasodilation tointracoronarily administered acetylcholine and significantlyattenuate relaxation in left circumflex coronary rings incontrol dogs. These effects were not seen when the sameconcentrations of leptin were administered to dogs fed ahigh-fat diet, suggesting that leptin resistance does occur inthe vasculature. This resistance is not attributable to altered

coronary dilation, increased endothelium-derived hyperpolar-izing factor, nor changes in coronary Ob-R mRNA levels.166

A recent hypothesis relevant to both central and peripheralleptin resistance involves leptin interaction with circulatingfactors in the blood.167 Five serum leptin–interacting proteinshave been isolated, one of which is C-reactive protein. Itdirectly inhibits the binding of leptin to Ob-Rs and blocks itsability to signal in cultured cells. Infusion of humanC-reactive protein into ob/ob mice blocked leptin treatmenteffects on satiety and weight reduction. Physiological con-centrations of leptin stimulate expression of C-reactive pro-tein in human primary hepatocytes,167 and human C-reactiveprotein has been correlated with increased adiposity andplasma leptin,168 suggesting an systemic self-induced nega-tive feedback that may cause leptin resistance in the obesestate.167

Leptin AntagonistsLeptin antagonists used in animal models have been shown toblock central leptin effects and increase appetite and foodintake.169,170 Three approaches have been employed to antag-onize leptin activity: (1) binding free leptin in the circulation,(2) competitive Ob-R binding by mutants that do not causesignaling activation, and (3) specific anti–Ob-R monoclonalantibodies. An example of the first approach is a recombinanthuman and mouse Ob-R/Fc chimeric glycoprotein.171,172 Onlythe latter 2 approaches have been employed in cardiac-relatedresearch. In neonatal rat ventricular cardiomyocytes, ratL39A/D40A/F41A leptin mutein blocked hypertrophic ef-fects and abolished increases in Ob-R gene expression elic-ited by leptin, Ang II, or ET-1.26 The hypertrophic effects ofleptin are also prevented by antibodies to Ob-Ra and Ob-Rb.26 Cardiac dysfunction did not develop in rats treated withOb-R antibodies after coronary artery ligation compared withsham, indicating that blocking Ob-R can improve postinfarc-tion HF in rats.173 The recent proposal of nanobodies (aunique form of antibodies that is characterized by a singleantigen-binding domain and generally does not cross theblood–brain barrier) may lead to an antagonist that couldselectively inhibit peripheral activities of leptin.174 This formof leptin antagonist might be clinically useful, as they cantarget peripheral adverse effect of leptin without inducingcentral weight gain.

SummaryObesity leads to cardiac hypertrophy, ventricular dysfunction,reduced diastolic compliance, and hypertension, as well astype 2 diabetes and hyperlipidemia.175 The high risk ofdeveloping cardiovascular diseases in obesity has drawnmuch effort to study the neurohormone effects of leptin oncardiac function and remodeling. Hyperleptinemia, centralleptin resistance, and leptin deficiency are all associated withimpaired postreceptor leptin signaling and contractile re-sponse. Short-term administration of leptin seems to havebeneficial effects on the myocardium, including antisteatoticactions, protection against ischemia/reperfusion injury, andparticipation in compensatory myocyte hypertrophy. Interac-tion with enhanced ROS production pathways in obesity, onthe other hand, can cause lipotoxicity and deleterious myo-




cardial effects such as cell death and maladaptive hypertro-phy. Perturbations of leptin signaling and other signal trans-duction pathways regulated by leptin in cardiomyocyteslikely underlie the pathology of cardiomyocyte hypertrophyin obesity. In particular, alterations in JAK/STAT, MAPK,NO, and �-adrenergic pathways have been implicated in thenegative inotropic and hypertrophic responses. Additionalstudies investigating the integrated effects of leptin on car-diomyocytes via SOCS3, PI3K/Akt, protein kinase C, andother signaling pathways could provide a more comprehen-sive understanding of leptin action on the cardiovascularsystem.

The unresolved debate about selective preservation ofperipheral leptin signaling in the setting of hyperleptinemiaand central resistance complicates the interpretation of exper-imental results involving the myocardium. Despite suchchallenges, a picture is emerging in which the risk of obesityis not merely attributable to the physical burden of extraweight but is, rather, a complex condition of hormonaldysregulation. Improved understanding of the actions ofleptin within the cardiovascular system will greatly improveour understanding of obesity-associated heart disease.

Sources of FundingThis work was supported in part by the Donald W. ReynoldsFoundation, NIH grant K08-HL076220, the W.W. Smith CharitableTrust, and the Irvin Talles Endowed Fund for CardiomyopathyResearch.

DisclosuresNone.

References1. Friedman JM. A war on obesity, not the obese. Science. 2003;299:

856–858.2. O’Rahilly S, Farooqi IS, Yeo GS, Challis BG. Minireview: Human

obesity-lessons from monogenic disorders. Endocrinology. 2003;144:3757–3764.

3. Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM.Positional cloning of the mouse obese gene and its human homologue.Nature. 1994;372:425–432.

4. Koerner A, Kratzsch J, Kiess W. Adipocytokines: leptin-the classical,resistin-the controversical, adiponectin-the promising, and more tocome. Best Pract Res Clin Endocrinol Metab. 2005;19:525–546.

5. Friedman JM, Halaas JL. Leptin and the regulation of body weight inmammals. Nature. 1998;395:763–770.

6. Elmquist JK, Elias CF, Saper CB. From lesions to leptin: hypothalamiccontrol of food intake and body weight. Neuron. 1999;22:221–232.

7. Bates SH, Myers MG Jr. The role of leptin receptor signaling in feedingand neuroendocrine function. Trends Endocrinol Metab. 2003;14:447–452.

8. Zhang F, Chen Y, Heiman M, Dimarchi R. Leptin: structure, functionand biology. Vitam Horm. 2005;71:345–372.

9. Montague CT, Farooqi IS, Whitehead JP, Soos MA, Rau H, WarehamNJ, Sewter CP, Digby JE, Mohammed SN, Hurst JA, Cheetham CH,Earley AR, Barnett AH, Prins JB, O’Rahilly S. Congenital leptin defi-ciency is associated with severe early-onset obesity in humans. Nature.1997;387:903–908.

10. Farooqi IS, Matarese G, Lord GM, Keogh JM, Lawrence E, Agwu C,Sanna V, Jebb SA, Perna F, Fontana S, Lechler RI, DePaoli AM,O’Rahilly S. Beneficial effects of leptin on obesity, T cell hyporespon-siveness, and neuroendocrine/metabolic dysfunction of human con-genital leptin deficiency. J Clin Invest. 2002;110:1093–1103.

11. Maffei M, Halaas J, Ravussin E, Pratley RE, Lee GH, Zhang Y, Fei H,Kim S, Lallone R, Ranganathan S. Leptin levels in human and rodent:measurement of plasma leptin and ob RNA in obese and weight-reducedsubjects. Nat Med. 1995;1:1155–1161.

12. Considine RV, Sinha MK, Heiman ML, Kriauciunas A, Stephens TW,Nyce MR, Ohannesian JP, Marco CC, McKee LJ, Bauer TL. Serumimmunoreactive-leptin concentrations in normal-weight and obesehumans. N Engl J Med. 1996;334:292–295.

13. Strobel A, Issad T, Camoin L, Ozata M, Strosberg AD. A leptinmissense mutation associated with hypogonadism and morbid obesity.Nat Genet. 1998;18:213–215.

14. Frederich RC, Hamann A, Anderson S, Lollmann B, Lowell BB, FlierJS. Leptin levels reflect body lipid content in mice: evidence for diet-induced resistance to leptin action. Nat Med. 1995;1:1311–1314.

15. Cohen P, Zhao C, Cai X, Montez JM, Rohani SC, Feinstein P, Mom-baerts P, Friedman JM. Selective deletion of leptin receptor in neuronsleads to obesity. J Clin Invest. 2001;108:1113–1121.

16. Bates SH, Myers MG. The role of leptin-�STAT3 signaling in neu-roendocrine function: an integrative perspective. J Mol Med. 2004;82:12–20.

17. Mark AL, Correia ML, Rahmouni K, Haynes WG. Selective leptinresistance: a new concept in leptin physiology with cardiovascularimplications. J Hypertens. 2002;20:1245–1250.

18. Lord GM, Matarese G, Howard JK, Baker RJ, Bloom SR, Lechler RI.Leptin modulates the T-cell immune response and reverses starvation-induced immunosuppression. Nature. 1998;394:897–901.

19. Margetic S, Gazzola C, Pegg GG, Hill RA. Leptin: a review of itsperipheral actions and interactions. Int J Obes Relat Metab Disord.2002;26:1407–1433.

20. Rahmouni K, Haynes WG. Leptin and the cardiovascular system. RecentProg Horm Res. 2004;59:225–244.

21. Sinha MK, Opentanova I, Ohannesian JP, Kolaczynski JW, Heiman ML,Hale J, Becker GW, Bowsher RR, Stephens TW, Caro JF. Evidence offree and bound leptin in human circulation. Studies in lean and obesesubjects and during short-term fasting. J Clin Invest. 1996;98:1277–1282.

22. Coleman RA, Herrmann TS. Nutritional regulation of leptin in humans.Diabetologia. 1999;42:639–646.

23. Fried SK, Ricci MR, Russell CD, Laferrere B. Regulation of leptinproduction in humans. J Nutr. 2000;130:3127S–3131S.

24. Smith CC, Mocanu MM, Davidson SM, Wynne AM, Simpkin JC,Yellon DM. Leptin, the obesity-associated hormone, exhibits directcardioprotective effects. Br J Pharmacol. 2006;149:5–13.

25. Matsui H, Motooka M, Koike H, Inoue M, Iwasaki T, Suzuki T,Kurabayashi M, Yokoyama T. Ischemia/reperfusion in rat heart inducesleptin and leptin receptor gene expression. Life Sci. 2007;80:672–680.

26. Rajapurohitam V, Javadov S, Purdham DM, Kirshenbaum LA,Karmazyn M. An autocrine role for leptin in mediating the cardiomyo-cyte hypertrophic effects of angiotensin II and endothelin-1. J Mol CellCardiol. 2006;41:265–274.

27. Fei H, Okano HJ, Li C, Lee GH, Zhao C, Darnell R, Friedman JM.Anatomic localization of alternatively spliced leptin receptors (ob-R) inmouse brain and other tissues. Proc Natl Acad Sci U S A. 1997;94:7001–7005.

28. Tartaglia LA. The leptin receptor. J Biol Chem. 1997;272:6093–6096.29. Chua SC Jr, Koutras IK, Han L, Liu SM, Kay J, Young SJ, Chung WK,

Leibel RL. Fine structure of the murine leptin receptor gene: splice sitesuppression is required to form two alternatively spliced transcripts.Genomics. 1997;45:264–270.

30. Ge H, Huang L, Pourbahrami T, Li C. Generation of soluble leptinreceptor by ectodomain shedding of membrane-spanning receptors invitro and in vivo. J Biol Chem. 2002;277:45898–45903.

31. Vaisse C, Halaas JL, Horvath CM, Darnell JE Jr, Stoffel M, FriedmanJM. Leptin activation of Stat3 in the hypothalamus of wild-type andob/ob mice but not db/db mice. Nat Genet. 1996;14:95–97.

32. White DW, Kuropatwinski KK, Devos R, Baumann H, Tartaglia LA.Leptin receptor (OB-R) signaling. Cytoplasmic domain mutational anal-ysis and evidence for receptor homo-oligomerization. J Biol Chem.1997;272:4065–4071.

33. Nakashima K, Narazaki M, Taga T. Leptin receptor (OB-R) oli-gomerizes with itself but not with its closely related cytokine signaltransducer gp130. FEBS Lett. 1997;403:79–82.

34. Kloek C, Haq AK, Dunn SL, Lavery HJ, Banks AS, Myers MG Jr.Regulation of jak kinases by intracellular leptin receptor sequences.J Biol Chem. 2002;277:41547–41555.

35. Bjorbaek C, Uotani S, da Silva B, Flier JS. Divergent signalingcapacities of the long and short isoforms of the leptin receptor. J BiolChem. 1997;272:32686–32695.




36. Banks AS, Davis SM, Bates SH, Myers MG Jr. Activation of down-stream signals by the long form of the leptin receptor. J Biol Chem.2000;275:14563–14572.

37. Eyckerman S, Broekaert D, Verhee A, Vandekerckhove J, Tavernier J.Identification of the Y985 and Y1077 motifs as SOCS3 recruitment sitesin the murine leptin receptor. FEBS Lett. 2000;486:33–37.

38. Hekerman P, Zeidler J, Bamberg-Lemper S, Knobelspies H, Lavens D,Tavernier J, Joost HG, Becker W. Pleiotropy of leptin receptor sig-nalling is defined by distinct roles of the intracellular tyrosines. FEBS J.2005;272:109–119.

39. Munzberg H, Bjornholm M, Bates SH, Myers MG Jr. Leptin receptoraction and mechanisms of leptin resistance. Cell Mol Life Sci. 2005;62:642–652.

40. Bjorbaek C, Buchholz RM, Davis SM, Bates SH, Pierroz DD, Gu H,Neel BG, Myers MG Jr, Flier JS. Divergent roles of SHP-2 in ERKactivation by leptin receptors. J Biol Chem. 2001;276:4747–4755.

41. Dunn SL, Bjornholm M, Bates SH, Chen Z, Seifert M, Myers MG Jr.Feedback inhibition of leptin receptor/Jak2 signaling via Tyr1138 of theleptin receptor and suppressor of cytokine signaling 3. Mol Endocrinol.2005;19:925–938.

42. Niswender KD, Gallis B, Blevins JE, Corson MA, Schwartz MW,Baskin DG. Immunocytochemical detection of phosphatidylinositol3-kinase activation by insulin and leptin. J Histochem Cytochem. 2003;51:275–283.

43. Tajmir P, Ceddia RB, Li RK, Coe IR, Sweeney G. Leptin increasescardiomyocyte hyperplasia via extracellular signal-regulated kinase-and phosphatidylinositol 3-kinase-dependent signaling pathways.Endocrinology. 2004;145:1550–1555.

44. Stofega MR, Herrington J, Billestrup N, Carter-Su C. Mutation of theSHP-2 binding site in growth hormone (GH) receptor prolongsGH-promoted tyrosyl phosphorylation of GH receptor, JAK2, andSTAT5B. Mol Endocrinol. 2000;14:1338–1350.

45. Gualillo O, Eiras S, White DW, Dieguez C, Casanueva FF. Leptinpromotes the tyrosine phosphorylation of SHC proteins and SHC asso-ciation with GRB2. Mol Cell Endocrinol. 2002;190:83–89.

46. Raju SV, Zheng M, Schuleri KH, Phan AC, Bedja D, Saraiva RM,Yiginer O, Vandegaer K, Gabrielson KL, O’donnell CP, Berkowitz DE,Barouch LA, Hare JM. Activation of the cardiac ciliary neurotrophicfactor receptor reverses left ventricular hypertrophy in leptin-deficientand leptin-resistant obesity. Proc Natl Acad Sci U S A. 2006;103:4222–4227.

47. Wang Y, Huang S, Sah VP, Ross J Jr, Brown JH, Han J, Chien KR.Cardiac muscle cell hypertrophy and apoptosis induced by distinctmembers of the p38 mitogen-activated protein kinase family. J BiolChem. 1998;273:2161–2168.

48. Rajapurohitam V, Gan XT, Kirshenbaum LA, Karmazyn M. Theobesity-associated peptide leptin induces hypertrophy in neonatal ratventricular myocytes. Circ Res. 2003;93:277–279.

49. Shin HJ, Oh J, Kang SM, Lee JH, Shin MJ, Hwang KC, Jang Y, ChungJH. Leptin induces hypertrophy via p38 mitogen–activated proteinkinase in rat vascular smooth muscle cells. Biochem Biophys ResCommun. 2005;329:18–24.

50. Bouloumie A, Marumo T, Lafontan M, Busse R. Leptin induces oxi-dative stress in human endothelial cells. FASEB J. 1999;13:1231–1238.

51. Shen J, Sakaida I, Uchida K, Terai S, Okita K. Leptin enhancesTNF-alpha production via p38 and JNK MAPK in LPS-stimulatedkupffer cells. Life Sci. 2005;77:1502–1515.

52. Fruhbeck G. Intracellular signalling pathways activated by leptin.Biochem J. 2006;393:7–20.

53. Sweeney G. Leptin signalling. Cell Signal. 2002;14:655–663.54. Elmquist JK, Maratos-Flier E, Saper CB, Flier JS. Unraveling the central

nervous system pathways underlying responses to leptin. Nat Neurosci.1998;1:445–450.

55. Schwartz MW, Woods SC, Porte D Jr, Seeley RJ, Baskin DG. Centralnervous system control of food intake. Nature. 2000;404:661–671.

56. Cowley MA, Smart JL, Rubinstein M, Cerdan MG, Diano S, HorvathTL, Cone RD, Low MJ. Leptin activates anorexigenic POMC neuronsthrough a neural network in the arcuate nucleus. Nature. 2001;411:480–484.

57. Ghilardi N, Ziegler S, Wiestner A, Stoffel R, Heim MH, Skoda RC.Defective STAT signaling by the leptin receptor in diabetic mice. ProcNatl Acad Sci U S A. 1996;93:6231–6235.

58. Baumann H, Morella KK, White DW, Dembski M, Bailon PS, Kim H,Lai CF, Tartaglia LA. The full-length leptin receptor has signaling

capabilities of interleukin 6-type cytokine receptors. Proc Natl Acad SciU S A. 1996;93:8374–8378.

59. Zabolotny JM, Bence-Hanulec KK, Stricker-Krongrad A, Haj F, WangY, Minokoshi Y, Kim YB, Elmquist JK, Tartaglia LA, Kahn BB, NeelBG. PTP1B regulates leptin signal transduction in vivo. Dev Cell.2002;2:489–495.

60. Cheng A, Uetani N, Simoncic PD, Chaubey VP, Lee-Loy A, McGladeCJ, Kennedy BP, Tremblay ML. Attenuation of leptin action and regu-lation of obesity by protein tyrosine phosphatase 1B. Dev Cell. 2002;2:497–503.

61. Bjorbaek C, Elmquist JK, Frantz JD, Shoelson SE, Flier JS. Identifi-cation of SOCS-3 as a potential mediator of central leptin resistance.Mol Cell. 1998;1:619–625.

62. Howard JK, Cave BJ, Oksanen LJ, Tzameli I, Bjorbaek C, Flier JS.Enhanced leptin sensitivity and attenuation of diet-induced obesity inmice with haploinsufficiency of Socs3. Nat Med. 2004;10:734–738.

63. Mori H, Hanada R, Hanada T, Aki D, Mashima R, Nishinakamura H,Torisu T, Chien KR, Yasukawa H, Yoshimura A. Socs3 deficiency inthe brain elevates leptin sensitivity and confers resistance to diet-induced obesity. Nat Med. 2004;10:739–743.

64. Klaman LD, Boss O, Peroni OD, Kim JK, Martino JL, Zabolotny JM,Moghal N, Lubkin M, Kim YB, Sharpe AH, Stricker-Krongrad A,Shulman GI, Neel BG, Kahn BB. Increased energy expenditure,decreased adiposity, and tissue-specific insulin sensitivity in protein-tyrosine phosphatase 1B-deficient mice. Mol Cell Biol. 2000;20:5479–5489.

65. Munzberg H, Myers MG Jr. Molecular and anatomical determinants ofcentral leptin resistance. Nat Neurosci. 2005;8:566–570.

66. Banks WA. Blood-brain barrier and energy balance. Obesity (SilverSpring). 2006;14(suppl 5):234S–237S.

67. Levin BE, Dunn-Meynell AA, Banks WA. Obesity-prone rats havenormal blood-brain barrier transport but defective central leptin sig-naling before obesity onset. Am J Physiol Regul Integr Comp Physiol.2004;286:R143–R150.

68. Munzberg H, Flier JS, Bjorbaek C. Region-specific leptin resistancewithin the hypothalamus of diet-induced obese mice. Endocrinology.2004;145:4880–4889.

69. Satoh N, Ogawa Y, Katsuura G, Numata Y, Tsuji T, Hayase M, EbiharaK, Masuzaki H, Hosoda K, Yoshimasa Y, Nakao K. Sympathetic acti-vation of leptin via the ventromedial hypothalamus: leptin-inducedincrease in catecholamine secretion. Diabetes. 1999;48:1787–1793.

70. Mark AL, Correia ML, Rahmouni K, Haynes WG. Loss of leptin actionsin obesity: two concepts with cardiovascular implications. Clin ExpHypertens. 2004;26:629–636.

71. Mark AL, Shaffer RA, Correia ML, Morgan DA, Sigmund CD, HaynesWG. Contrasting blood pressure effects of obesity in leptin-deficientob/ob mice and agouti yellow obese mice. J Hypertens. 1999;17:1949–1953.

72. Correia ML, Haynes WG, Rahmouni K, Morgan DA, Sivitz WI, MarkAL. The concept of selective leptin resistance: evidence from agoutiyellow obese mice. Diabetes. 2002;51:439–442.

73. Rahmouni K, Morgan DA, Morgan GM, Mark AL, Haynes WG. Role ofselective leptin resistance in diet-induced obesity hypertension.Diabetes. 2005;54:2012–2018.

74. Haynes WG. Interaction between leptin and sympathetic nervous systemin hypertension. Curr Hypertens Rep. 2000;2:311–318.

75. Barr VA, Lane K, Taylor SI. Subcellular localization and internalizationof the four human leptin receptor isoforms. J Biol Chem. 1999;274:21416–21424.

76. Uotani S, Bjorbaek C, Tornoe J, Flier JS. Functional properties of leptinreceptor isoforms: internalization and degradation of leptin and ligand-induced receptor downregulation. Diabetes. 1999;48:279–286.

77. Sen S, Tarazi RC, Khairallah PA, Bumpus FM. Cardiac hypertrophy inspontaneously hypertensive rats. Circ Res. 1974;35:775–781.

78. Patel MB, Stewart JM, Loud AV, Anversa P, Wang J, Fiegel L, HintzeTH. Altered function and structure of the heart in dogs with chronicelevation in plasma norepinephrine. Circulation. 1991;84:2091–2100.

79. Navarro J, Redon J, Cea-Calvo L, Lozano JV, Fernandez-Perez C, BonetA, Gonzalez-Esteban J. Metabolic syndrome, organ damage and cardio-vascular disease in treated hypertensive patients. the ERIC-HTA study.Blood Press. 2007;16:20–27.

80. Cuspidi C, Meani S, Fusi V, Severgnini B, Valerio C, Catini E, LeonettiG, Magrini F, Zanchetti A. Metabolic syndrome and target organdamage in untreated essential hypertensives. J Hypertens. 2004;22:1991–1998.




81. Grassi G, Giannattasio C. Obesity and vascular stiffness: when body fathas an adverse impact on arterial dynamics. J Hypertens. 2005;23:1789–1791.

82. Aizawa-Abe M, Ogawa Y, Masuzaki H, Ebihara K, Satoh N, Iwai H,Matsuoka N, Hayashi T, Hosoda K, Inoue G, Yoshimasa Y, Nakao K.Pathophysiological role of leptin in obesity-related hypertension. J ClinInvest. 2000;105:1243–1252.

83. Winters B, Mo Z, Brooks-Asplund E, Kim S, Shoukas A, Li D, NyhanD, Berkowitz DE. Reduction of obesity, as induced by leptin, reversesendothelial dysfunction in obese (lep(ob)) mice. J Appl Physiol. 2000;89:2382–2390.

84. Leyva F, Godsland IF, Ghatei M, Proudler AJ, Aldis S, Walton C,Bloom S, Stevenson JC. Hyperleptinemia as a component of a metabolicsyndrome of cardiovascular risk. Arterioscler Thromb Vasc Biol. 1998;18:928–933.

85. Morawietz H, Bornstein SR. Leptin, endothelin, NADPH oxidase, andheart failure. Hypertension. 2006;47:e20; author reply e20–e21.

86. Shek EW, Brands MW, Hall JE. Chronic leptin infusion increasesarterial pressure. Hypertension. 1998;31:409–414.

87. Correia ML, Morgan DA, Sivitz WI, Mark AL, Haynes WG. Leptin actsin the central nervous system to produce dose–dependent changes inarterial pressure. Hypertension. 2001;37:936–942.

88. Carlyle M, Jones OB, Kuo JJ, Hall JE. Chronic cardiovascular and renalactions of leptin: role of adrenergic activity. Hypertension. 2002;39:496–501.

89. Yamagishi SI, Edelstein D, Du XL, Kaneda Y, Guzman M, BrownleeM. Leptin induces mitochondrial superoxide production and monocytechemoattractant protein-1 expression in aortic endothelial cells byincreasing fatty acid oxidation via protein kinase A. J Biol Chem.2001;276:25096–25100.

90. Loffreda S, Yang SQ, Lin HZ, Karp CL, Brengman ML, Wang DJ,Klein AS, Bulkley GB, Bao C, Noble PW, Lane MD, Diehl AM. Leptinregulates proinflammatory immune responses. FASEB J. 1998;12:57–65.

91. Fruhbeck G. Pivotal role of nitric oxide in the control of blood pressureafter leptin administration. Diabetes. 1999;48:903–908.

92. Kimura K, Tsuda K, Baba A, Kawabe T, Boh-oka S, Ibata M, MoriwakiC, Hano T, Nishio I. Involvement of nitric oxide in endothelium-dependent arterial relaxation by leptin. Biochem Biophys Res Commun.2000;273:745–749.

93. Lembo G, Vecchione C, Fratta L, Marino G, Trimarco V, d’Amati G,Trimarco B. Leptin induces direct vasodilation through distinct endo-thelial mechanisms. Diabetes. 2000;49:293–297.

94. Vecchione C, Maffei A, Colella S, Aretini A, Poulet R, Frati G, GentileMT, Fratta L, Trimarco V, Trimarco B, Lembo G. Leptin effect onendothelial nitric oxide is mediated through akt-endothelial nitric oxidesynthase phosphorylation pathway. Diabetes. 2002;51:168–173.

95. Gardiner SM, Kemp PA, March JE, Bennett T. Regional haemodynamiceffects of recombinant murine or human leptin in conscious rats. Br JPharmacol. 2000;130:805–810.

96. Mitchell JL, Morgan DA, Correia ML, Mark AL, Sivitz WI, HaynesWG. Does leptin stimulate nitric oxide to oppose the effects of sympa-thetic activation? Hypertension. 2001;38:1081–1086.

97. Kuo JJ, Jones OB, Hall JE. Inhibition of NO synthesis enhances chroniccardiovascular and renal actions of leptin. Hypertension. 2001;37:670–676.

98. Quehenberger P, Exner M, Sunder-Plassmann R, Ruzicka K,Bieglmayer C, Endler G, Muellner C, Speiser W, Wagner O. Leptininduces endothelin-1 in endothelial cells in vitro. Circ Res. 2002;90:711–718.

99. Park HY, Kwon HM, Lim HJ, Hong BK, Lee JY, Park BE, Jang Y, ChoSY, Kim HS. Potential role of leptin in angiogenesis: leptin inducesendothelial cell proliferation and expression of matrix metallopro-teinases in vivo and in vitro. Exp Mol Med. 2001;33:95–102.

100. Kellerer M, Koch M, Metzinger E, Mushack J, Capp E, Haring HU.Leptin activates PI-3 kinase in C2C12 myotubes via janus kinase-2(JAK-2) and insulin receptor substrate-2 (IRS-2) dependent pathways.Diabetologia. 1997;40:1358–1362.

101. Li L, Mamputu JC, Wiernsperger N, Renier G. Signaling pathwaysinvolved in human vascular smooth muscle cell proliferation and matrixmetalloproteinase-2 expression induced by leptin: inhibitory effect ofmetformin. Diabetes. 2005;54:2227–2234.

102. Oda A, Taniguchi T, Yokoyama M. Leptin stimulates rat aortic smoothmuscle cell proliferation and migration. Kobe J Med Sci. 2001;47:141–150.

103. Nakata M, Yada T, Soejima N, Maruyama I. Leptin promotes aggre-gation of human platelets via the long form of its receptor. Diabetes.1999;48:426–429.

104. Maruyama I, Nakata M, Yamaji K. Effect of leptin in platelet andendothelial cells. Obesity and arterial thrombosis. Ann N Y Acad Sci.2000;902:315–319.

105. Reilly MP, Iqbal N, Schutta M, Wolfe ML, Scally M, Localio AR, RaderDJ, Kimmel SE. Plasma leptin levels are associated with coronaryatherosclerosis in type 2 diabetes. J Clin Endocrinol Metab. 2004;89:3872–3878.

106. Bodary PF, Gu S, Shen Y, Hasty AH, Buckler JM, Eitzman DT.Recombinant leptin promotes atherosclerosis and thrombosis in apoli-poprotein E-deficient mice. Arterioscler Thromb Vasc Biol. 2005;25:e119–e122.

107. Wu KK, Wu TJ, Chin J, Mitnaul LJ, Hernandez M, Cai TQ, Ren N,Waters MG, Wright SD, Cheng K. Increased hypercholesterolemiaand atherosclerosis in mice lacking both ApoE and leptin receptor.Atherosclerosis. 2005;181:251–259.

108. Nickola MW, Wold LE, Colligan PB, Wang GJ, Samson WK, Ren J.Leptin attenuates cardiac contraction in rat ventricular myocytes. Role ofNO. Hypertension. 2000;36:501–505.

109. Wold LE, Relling DP, Duan J, Norby FL, Ren J. Abrogated leptin-induced cardiac contractile response in ventricular myocytes underspontaneous hypertension: role of Jak/STAT pathway. Hypertension.2002;39:69–74.

110. Rodriguez A, Fruhbeck G, Gomez-Ambrosi J, Catalan V, Sainz N, DiezJ, Zalba G, Fortuno A. The inhibitory effect of leptin on angiotensinII-induced vasoconstriction is blunted in spontaneously hypertensiverats. J Hypertens. 2006;24:1589–1597.

111. Barouch LA, Harrison RW, Skaf MW, Rosas GO, Cappola TP, KobeissiZA, Hobai IA, Lemmon CA, Burnett AL, O’Rourke B, Rodriguez ER,Huang PL, Lima JA, Berkowitz DE, Hare JM. Nitric oxide regulates theheart by spatial confinement of nitric oxide synthase isoforms. Nature.2002;416:337–339.

112. Bloch KD, Janssens S. Cardiomyocyte-specific overexpression of nitricoxide synthase 3: impact on left ventricular function and myocardialinfarction. Trends Cardiovasc Med. 2005;15:249–253.

113. Barouch LA, Cappola TP, Harrison RW, Crone JK, Rodriguez ER,Burnett AL, Hare JM. Combined loss of neuronal and endothelial nitricoxide synthase causes premature mortality and age-related hypertrophiccardiac remodeling in mice. J Mol Cell Cardiol. 2003;35:637–644.

114. Cappola TP, Cope L, Cernetich A, Barouch LA, Minhas K, Irizarry RA,Parmigiani G, Durrani S, Lavoie T, Hoffman EP, Ye SQ, Garcia JG,Hare JM. Deficiency of different nitric oxide synthase isoforms activatesdivergent transcriptional programs in cardiac hypertrophy. PhysiolGenomics. 2003;14:25–34.

115. Illiano G, Naviglio S, Pagano M, Spina A, Chiosi E, Barbieri M,Paolisso G. Leptin affects adenylate cyclase activity in H9c2 cardiac cellline: effects of short- and long-term exposure. Am J Hypertens. 2002;15:638–643.

116. Li SY, Yang X, Ceylan-Isik AF, Du M, Sreejayan N, Ren J. Cardiaccontractile dysfunction in Lep/Lep obesity is accompanied by NADPHoxidase activation, oxidative modification of sarco(endo)plasmicreticulum Ca2�-ATPase and myosin heavy chain isozyme switch.Diabetologia. 2006;49:1434–1446.

117. Khan SA, Lee K, Minhas KM, Gonzalez DR, Raju SV, Tejani AD, LiD, Berkowitz DE, Hare JM. Neuronal nitric oxide synthase nega-tively regulates xanthine oxidoreductase inhibition of cardiacexcitation-contraction coupling. Proc Natl Acad Sci U S A. 2004;101:15944 –15948.

118. Kinugawa S, Huang H, Wang Z, Kaminski PM, Wolin MS, Hintze TH.A defect of neuronal nitric oxide synthase increases xanthine oxidase-derived superoxide anion and attenuates the control of myocardialoxygen consumption by nitric oxide derived from endothelial nitricoxide synthase. Circ Res. 2005;96:355–362.

119. Saraiva RM, Minhas KM, Zheng M, Pitz E, Treuer A, Gonzalez D,Schuleri KH, Vandegaer KM, Barouch LA, Hare JM. Reduced neuronalnitric oxide synthase expression contributes to cardiac oxidative stressand nitroso-redox imbalance in ob/ob mice. Nitric Oxide. 2007;16:331–338.

120. Su J, Zhang S, Tse J, Scholz PM, Weiss HR. Alterations in nitricoxide-cGMP pathway in ventricular myocytes from obese leptin-deficient mice. Am J Physiol Heart Circ Physiol. 2003;285:H2111–H2117.




121. Furukawa S, Fujita T, Shimabukuro M, Iwaki M, Yamada Y, NakajimaY, Nakayama O, Makishima M, Matsuda M, Shimomura I. Increasedoxidative stress in obesity and its impact on metabolic syndrome. J ClinInvest. 2004;114:1752–1761.

122. Katakam PV, Tulbert CD, Snipes JA, Erdos B, Miller AW, Busija DW.Impaired insulin-induced vasodilation in small coronary arteries ofzucker obese rats is mediated by reactive oxygen species. Am J PhysiolHeart Circ Physiol. 2005;288:H854–H860.

123. Paolocci N, Ekelund UE, Isoda T, Ozaki M, Vandegaer K, Georgako-poulos D, Harrison RW, Kass DA, Hare JM. cGMP-independent ino-tropic effects of nitric oxide and peroxynitrite donors: potential rolefor nitrosylation. Am J Physiol Heart Circ Physiol. 2000;279:H1982–H1988.

124. Katori T, Donzelli S, Tocchetti CG, Miranda KM, Cormaci G, ThomasDD, Ketner EA, Lee MJ, Mancardi D, Wink DA, Kass DA, Paolocci N.Peroxynitrite and myocardial contractility: in vivo versus in vitro effects.Free Radic Biol Med. 2006;41:1606–1618.

125. Levrand S, Vannay-Bouchiche C, Pesse B, Pacher P, Feihl F, Waeber B,Liaudet L. Peroxynitrite is a major trigger of cardiomyocyte apoptosis invitro and in vivo. Free Radic Biol Med. 2006;41:886–895.

126. Dong F, Zhang X, Ren J. Leptin regulates cardiomyocyte contractilefunction through endothelin-1 receptor-NADPH oxidase pathway.Hypertension. 2006;47:222–229.

127. Pieske B, Beyermann B, Breu V, Loffler BM, Schlotthauer K, Maier LS,Schmidt-Schweda S, Just H, Hasenfuss G. Functional effects of endo-thelin and regulation of endothelin receptors in isolated human non-failing and failing myocardium. Circulation. 1999;99:1802–1809.

128. Unger RH, Orci L. Lipoapoptosis: its mechanism and its diseases.Biochim Biophys Acta. 2002;1585:202–212.

129. Zhou YT, Grayburn P, Karim A, Shimabukuro M, Higa M, Baetens D,Orci L, Unger RH. Lipotoxic heart disease in obese rats: implications forhuman obesity. Proc Natl Acad Sci U S A. 2000;97:1784–1789.

130. Ren J, Relling DP. Leptin-induced suppression of cardiomyocyte con-traction is amplified by ceramide. Peptides. 2006;27:1415–1419.

131. Ren J, Relling DP. Interaction between tumor necrosis factor-alpha andleptin-induced inhibition of cardiac contractile function in isolated ven-tricular myocytes. Cytokine. 2005;32:213–218.

132. Hynes GR, Jones PJ. Leptin and its role in lipid metabolism. Curr OpinLipidol. 2001;12:321–327.

133. Kudo N, Barr AJ, Barr RL, Desai S, Lopaschuk GD. High rates of fattyacid oxidation during reperfusion of ischemic hearts are associated witha decrease in malonyl-CoA levels due to an increase in 5�-AMP-acti-vated protein kinase inhibition of acetyl-CoA carboxylase. J Biol Chem.1995;270:17513–17520.

134. Muoio DM, Seefeld K, Witters LA, Coleman RA. AMP-activated kinasereciprocally regulates triacylglycerol synthesis and fatty acid oxidationin liver and muscle: evidence that sn-glycerol-3-phosphate acyltrans-ferase is a novel target. Biochem J. 1999;338(pt 3):783–791.

135. Atkinson LL, Fischer MA, Lopaschuk GD. Leptin activates cardiac fattyacid oxidation independent of changes in the AMP-activated proteinkinase-acetyl-CoA carboxylase-malonyl-CoA axis. J Biol Chem. 2002;277:29424–29430.

136. Somoza B, Guzman R, Cano V, Merino B, Ramos P, Diez-Fernandez C,Fernandez-Alfonso MS, Ruiz-Gayo M. Induction of cardiac uncouplingprotein-2 expression and adenosine 5�-monophosphate-activated proteinkinase phosphorylation during early states of diet-induced obesity inmice. Endocrinology. 2007;148:924–931.

137. Lee Y, Wang MY, Kakuma T, Wang ZW, Babcock E, McCorkle K,Higa M, Zhou YT, Unger RH. Liporegulation in diet-induced obesity.The antisteatotic role of hyperleptinemia. J Biol Chem. 2001;276:5629–5635.

138. Lee Y, Naseem RH, Duplomb L, Park BH, Garry DJ, Richardson JA,Schaffer JE, Unger RH. Hyperleptinemia prevents lipotoxic cardiomy-opathy in acyl CoA synthase transgenic mice. Proc Natl Acad Sci U S A.2004;101:13624–13629.

139. Murphy S, Frishman WH. Protein kinase C in cardiac disease and as apotential therapeutic target. Cardiol Rev. 2005;13:3–12.

140. Christoffersen C, Bollano E, Lindegaard ML, Bartels ED, Goetze JP,Andersen CB, Nielsen LB. Cardiac lipid accumulation associated withdiastolic dysfunction in obese mice. Endocrinology. 2003;144:3483–3490.

141. Mazumder PK, O’Neill BT, Roberts MW, Buchanan J, Yun UJ,Cooksey RC, Boudina S, Abel ED. Impaired cardiac efficiency andincreased fatty acid oxidation in insulin-resistant ob/ob mouse hearts.Diabetes. 2004;53:2366–2374.

142. Warnes CA, Roberts WC. Sudden coronary death: relation of amountand distribution of coronary narrowing at necropsy to previoussymptoms of myocardial ischemia, left ventricular scarring and heartweight. Am J Cardiol. 1984;54:65–73.

143. Alpert MA. Obesity cardiomyopathy: pathophysiology and evolution ofthe clinical syndrome. Am J Med Sci. 2001;321:225–236.

144. Kasper EK, Hruban RH, Baughman KL. Cardiomyopathy of obesity: aclinicopathologic evaluation of 43 obese patients with heart failure. Am JCardiol. 1992;70:921–924.

145. Sader S, Nian M, Liu P. Leptin: a novel link between obesity, diabetes,cardiovascular risk, and ventricular hypertrophy. Circulation. 2003;108:644–646.

146. Xu FP, Chen MS, Wang YZ, Yi Q, Lin SB, Chen AF, Luo JD. Leptininduces hypertrophy via endothelin-1-reactive oxygen species pathwayin cultured neonatal rat cardiomyocytes. Circulation. 2004;110:1269–1275.

147. Paolisso G, Tagliamonte MR, Galderisi M, Zito GA, Petrocelli A,Carella C, de Divitiis O, Varricchio M. Plasma leptin level is associatedwith myocardial wall thickness in hypertensive insulin–resistant men.Hypertension. 1999;34:1047–1052.

148. Yamashita T, Murakami T, Iida M, Kuwajima M, Shima K. Leptinreceptor of zucker fatty rat performs reduced signal transduction.Diabetes. 1997;46:1077–1080.

149. Nakamura K, Fushimi K, Kouchi H, Mihara K, Miyazaki M, Ohe T,Namba M. Inhibitory effects of antioxidants on neonatal rat cardiacmyocyte hypertrophy induced by tumor necrosis factor-alpha and an-giotensin II. Circulation. 1998;98:794–799.

150. Luo JD, Xie F, Zhang WW, Ma XD, Guan JX, Chen X. Simvastatininhibits noradrenaline-induced hypertrophy of cultured neonatal rat car-diomyocytes. Br J Pharmacol. 2001;132:159–164.

151. Adiarto S, Emoto N, Iwasa N, Yokoyama M. Obesity-induced upregu-lation of myocardial endothelin-1 expression is mediated by leptin.Biochem Biophys Res Commun. 2007;353:623–627.

152. Hu TP, Xu FP, Li YJ, Luo JD. Simvastatin inhibits leptin-inducedhypertrophy in cultured neonatal rat cardiomyocytes. Acta PharmacolSin. 2006;27:419–422.

153. Williams SD, Zhu H, Zhang L, Bernstein HS. Adenoviral delivery ofhuman CDC5 promotes G2/M progression and cell division in neonatalventricular cardiomyocytes. Gene Ther. 2006;13:837–843.

154. Barouch LA, Gao D, Chen L, Miller KL, Xu W, Phan AC, KittlesonMM, Minhas KM, Berkowitz DE, Wei C, Hare JM. Cardiac myocyteapoptosis is associated with increased DNA damage and decreasedsurvival in murine models of obesity. Circ Res. 2006;98:119–124.

155. Unger RH, Zhou YT, Orci L. Regulation of fatty acid homeostasis incells: novel role of leptin. Proc Natl Acad Sci U S A. 1999;96:2327–2332.

156. Mascareno E, Beckles DL, Siddiqui MA. Janus kinase-2 signalingmediates apoptosis in rat cardiomyocytes. Vascul Pharmacol. 2005;43:327–335.

157. Finck BN, Lehman JJ, Leone TC, Welch MJ, Bennett MJ, Kovacs A,Han X, Gross RW, Kozak R, Lopaschuk GD, Kelly DP. The cardiacphenotype induced by PPARalpha overexpression mimics that causedby diabetes mellitus. J Clin Invest. 2002;109:121–130.

158. Kodama H, Fukuda K, Pan J, Makino S, Sano M, Takahashi T, Hori S,Ogawa S. Biphasic activation of the JAK/STAT pathway by angiotensinII in rat cardiomyocytes. Circ Res. 1998;82:244–250.

159. Maroni P, Bendinelli P, Piccoletti R. Intracellular signal transductionpathways induced by leptin in C2C12 cells. Cell Biol Int. 2005;29:542–550.

160. Madani S, De Girolamo S, Munoz DM, Li RK, Sweeney G. Directeffects of leptin on size and extracellular matrix components of humanpediatric ventricular myocytes. Cardiovasc Res. 2006;69:716–725.

161. Hausenloy DJ, Tsang A, Yellon DM. The reperfusion injury salvagekinase pathway: a common target for both ischemic preconditioning andpostconditioning. Trends Cardiovasc Med. 2005;15:69–75.

162. Brzozowski T, Konturek PC, Pajdo R, Kwiecien S, Ptak A, SliwowskiZ, Drozdowicz D, Pawlik M, Konturek SJ, Hahn EG. Brain-gut axis ingastroprotection by leptin and cholecystokinin against ischemia-reperfusion induced gastric lesions. J Physiol Pharmacol. 2001;52:583–602.

163. Erkasap S, Erkasap N, Koken T, Kahraman A, Uzuner K, Yazihan N,Ates E. Effect of leptin on renal ischemia-reperfusion damage in rats.J Physiol Biochem. 2004;60:79–84.

164. Kennedy LM, Dickstein K, Anker SD, Kristianson K, Willenheimer R,OPTIMAAL Study Group. The prognostic importance of body mass




index after complicated myocardial infarction. J Am Coll Cardiol. 2005;45:156–158.

165. Nikolsky E, Stone GW, Grines CL, Cox DA, Garcia E, Tcheng JE, GriffinJJ, Guagliumi G, Stuckey T, Turco M, Negoita M, Lansky AJ, Mehran R.Impact of body mass index on outcomes after primary angioplasty in acutemyocardial infarction. Am Heart J. 2006;151:168–175.

166. Knudson JD, Dincer UD, Dick GM, Shibata H, Akahane R, Saito M,Tune JD. Leptin resistance extends to the coronary vasculature inprediabetic dogs and provides a protective adaptation against endo-thelial dysfunction. Am J Physiol Heart Circ Physiol. 2005;289:H1038 –H1046.

167. Chen K, Li F, Li J, Cai H, Strom S, Bisello A, Kelley DE,Friedman-Einat M, Skibinski GA, McCrory MA, Szalai AJ, Zhao AZ.Induction of leptin resistance through direct interaction of C-reactiveprotein with leptin. Nat Med. 2006;12:425–432.

168. Kazumi T, Kawaguchi A, Hirano T, Yoshino G. C-reactive protein inyoung, apparently healthy men: associations with serum leptin, QTcinterval, and high-density lipoprotein-cholesterol. Metabolism. 2003;52:1113–1116.

169. Scarpace PJ, Matheny M, Zhang Y, Cheng KY, Tumer N. Leptinantagonist reveals an uncoupling between leptin receptor signaltransducer and activator of transcription 3 signaling and metabolicresponses with central leptin resistance. J Pharmacol Exp Ther. 2007;320:706–712.

170. Zhang J, Matheny MK, Tumer N, Mitchell MK, Scarpace PJ. Leptinantagonist reveals that the normalization of caloric intake and thethermic effect of food after high-fat feeding are leptin dependent. Am JPhysiol Regul Integr Comp Physiol. 2007;292:R868–R874.

171. Matarese G, Carrieri PB, La Cava A, Perna F, Sanna V, De Rosa V,Aufiero D, Fontana S, Zappacosta S. Leptin increase in multiplesclerosis associates with reduced number of CD4(�)CD25� regulatoryT cells. Proc Natl Acad Sci U S A. 2005;102:5150–5155.

172. De Rosa V, Procaccini C, La Cava A, Chieffi P, Nicoletti GF, FontanaS, Zappacosta S, Matarese G. Leptin neutralization interferes withpathogenic T cell autoreactivity in autoimmune encephalomyelitis.J Clin Invest. 2006;116:447–455.

173. Purdham DM, Rajapurohitam V, Huang C, Karmazyn M. Attenuation ofcardiac hypertrophy and heart failure by leptin receptor blockade.Circulation. 2005;112(suppl II):II-279 Abstract.

174. Gertler A. Development of leptin antagonists and their potential use inexperimental biology and medicine. Trends Endocrinol Metab. 2006;17:372–378.

175. Eckel RH, Barouch WW, Ershow AG. Report of the national heart,lung, and blood institute-national institute of diabetes and digestiveand kidney diseases working group on the pathophysiology ofobesity-associated cardiovascular disease. Circulation. 2002;105:2923–2928.




Ronghua Yang and Lili A. BarouchLeptin Signaling and Obesity: Cardiovascular Consequences

Print ISSN: 0009-7330. Online ISSN: 1524-4571 Copyright © 2007 American Heart Association, Inc. All rights reserved.is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231Circulation Research

doi: 10.1161/CIRCRESAHA.107.1565962007;101:545-559Circ Res.

http://circres.ahajournals.org/content/101/6/545World Wide Web at:

The online version of this article, along with updated information and services, is located on the

http://circres.ahajournals.org//subscriptions/

is online at: Circulation Research Information about subscribing to Subscriptions:

http://www.lww.com/reprints Information about reprints can be found online at: Reprints:

document. Permissions and Rights Question and Answer about this process is available in the

located, click Request Permissions in the middle column of the Web page under Services. Further informationEditorial Office. Once the online version of the published article for which permission is being requested is

can be obtained via RightsLink, a service of the Copyright Clearance Center, not theCirculation Researchin Requests for permissions to reproduce figures, tables, or portions of articles originally publishedPermissions:


http://circres.ahajournals.org/content/101/6/545

http://www.ahajournals.org/site/rights/

http://www.lww.com/reprints

http://circres.ahajournals.org//subscriptions/


Leptin Signaling and Obesity: Cardiovascular Consequences

Documents