Molecular basis of dilated cardiomyopathy Prasad Gunaruwan 21 st June 2011
Dec 17, 2015
Molecular basis of dilated cardiomyopathy
Prasad Gunaruwan
21st June 2011
Introduction
• Didactic, regular questions to the audience
• Pathology of dilated cardiomyopathy
• Myocyte apoptosis, regulators
• Structure of the cardiac myocyte
• Inherited DCM and mechanisms
• Extra-cellular components in DCM
• Therapeutic potential
Classification of DCM
• NEJM pic
N Engl J Med 2011;364:1643-56.
Pathology of DCM
N Engl J Med 2011;364:1643-56.
Pathology of DCM
• LV dilatation
• Systolic dysfunction
• Myocyte death and fibrosis
• Regardless of etiology this is the end result
Pathology of DCM
Systolic dysfunction
LV Dilatation Myocyte death and fibrosis
Cardiac Myocyte Apoptosis
• Myocyte death as a result of necrosis, autophagy (self destruction and recycling of raw material) and apoptosis (programmed cell death)
• Apoptosis mediated via external pathway (death ligands binding to cell surface receptors) and internal pathway (via mitochondria and ER)
• Internal pathway has many stimuli (hypoxia, DNA damage, radiation, loss of trophic factors, toxins…)
• Apoptosis signals kept in check at different levels in the activation cascade
J. Clin. Invest. 115:565–571 (2005).
Question to..last row furthest from the door……(ususally Dr Hayes)
• What is not a pro-apoptotic intra-cellular component?
a)Active caspase 3
b)Active caspase 9
c)Active caspase 12
d)Active caspase 8
e)X linked Inhibitor of Apoptosis (XIAP)
Evidence for increased apoptosis in DCM
• Apoptosis ‘measured’ by caspase activation, mRNA levels of pro-apoptotic components (Bcl-2, Bax, Bcl-xL) and activation of their gene encoding by p-53.
• Control apoptosis rate 0.001-0.002% vs 0.08-0.25% in failing hearts.
• Loss of myocytes is not debated, but the contribution of apoptosis is controversial.
• Causal relationship in mouse models and correlations in human studies
Mouse Model: apoptosis causes DCM
• Transgenic mice, cardiac restricted pro-caspase 8 fusion protein expression.
• The molecule dimerization and activation could be switched on by a drug.
• Within hours of activation death with severe myocyte damage.
These had low levels of caspase and apoptosis (0.023% vs 0.002%).DCM partially arrested with caspase inhibition.
J. Clin. Invest. 111:1497–1504 (2003)
Human Studies: apoptosis in DCM (not causal)
• 4 clinical groups (normal volume status, AR with preserved EF, AR with reduced EF, severe DCM/AR)
• LV biopsies and assay for apoptosis
• Patients were on medications
Caspase levels in DCM
Am J Cardiol 2009;103:1261–1268)
Other Pro-apoptotic markers
Ischaemia and apoptosis
Am J Physiol Heart Circ Physiol280: H2313–H2320, 2001.
Other etiology to apoptosis links • Ang-II
– Gq transduces Ang-II signals– Gαq (over expression of α subunit) predisposes to
transcriptional activation of BH3 like protien Nix/Gp 130/STAT
– Eventually Bcl-xL and apoptosis
• Severe activation of Nix in pregnant mice: fulminant DCM, inhibitors of Nix prevent the DCM.
• Myocardial stretch promotes Titin iso-type switching and p53 activation, which promotes encoding for pro-apoptotic molecules
Question to… Second row furthest from the door.. (usually Prof Fletcher)
• Which of the following DCM etiology is yet to have a identified link to apoptosis?
a)Ischaemic cardiomyopathy
b)Peripartum cardiomyopathy
c)Severe aortic regurgitation
d)Persistantly activated Renin-Ang-Ald system
e)Alcohol induced DCM
Summary so far…
• DCM: LV dilatation, myocyte death/fibrosis, systolic dysfunction.
• Multiple etiologies somehow converge on the above final status.
• Myocyte apoptosis rates higher in severe DCM.• Some data suggest apoptosis causally linked to
DCM.• Some possible pathways to link acquired DCM
etiology to apoptosis.
Inherited DCM
• Genetic defects resulting in structural defects within the sarcomere
• A brief review of normal sarcomeric structure
Sarcomere structure
Lamin A/C DCM
• Lamins are ‘structural’ proteins located within the nuclear side of the nuclear membrane
• How they cause DCM is still being studied
Structure of Lamins
Lamins and the nuclear envelope
Lamins: structural vs functional
• Important molecules to maintain nuclear envelope structure.
• Lamin A has intra-nuclear components that regulates nuclear replication, gene expression and regulates transcription of RNA.
• Mutated Lamin A: mis-localises Emerin to ER, and Lamin C to the nucleoplsm.
• Mis-localisation of Lamin C into the nucleoplsm seems to be key in DCM.
• Mouse models show link to extra-cellular kinase activation
Lamins and Extra-cellular Kinases
• Lamin mutation knock-in mice noted to have increased ERK activity prior to DCM
• Drugs inhibiting ERK activity delayed DCM onset and severity
• ? Lamin mutations may allow RNA transcriptions of these kinases
• ? Normal lamins provide substrate for the kinases
Human Molecular Genetics, 2009, Vol. 18, No. 2 241–247
Question to.. First row furthest from door.. (usually Dr Collins..)
What is incorrect?a) Lamin A/C mutations lead to AutoD and AutoR disorders.
b) Lamins are important structural proteins in the sarcolemma.
c) Lamin mutation may promote extra-cellular kinase activation.
d) Lamins maintain the structure of the nuclear envelope.
e) Mis-localisation of Lamin C is associated with DCM.
Summary so far..
• DCM: LV dilatation, systolic dysfunction, myocyte death and fibrosis.
• Apoptosis may be a key feature in loss of myocytes.
• Links between etiologies and apoptosis.
• Any structural protein abnormality in the sarcolemma can lead to DCM.
• Lamins are not just structural proteins
What about the extra-cellular matrix?
Changes in the ECM with DCM
• Increased collagen turn-over, ratio of C I:III reduced in DCM
• Mast cells and fibroblast activation, increased pro-fibrotic cytokines and growth factors
• Loss of collagen cross-linking, mural re-alignment (‘slippage’)
• Activated Matrix-Metalloproteinases.
Matrix Metallo-Proteinases (MMP)
MMP and TIMP
• TIMPs are Tissue Inhibitors of MMPs
• Ratio between MMP: TIMP in CHF favours persistant activation of MMPs
• MMP inhibitors of benefit in mouse models of MI and LVF
• Led to the trial of MMP inhibitor in Post STEMI LVF: negative result, blamed on inadequate dosing of the MMP inhibitor.
Summary so far..
• DCM: LV dilatation, myocyte death and fibrosis, systolic dysfunction.
• Apoptosis a key in myocyte death, could be causal in DCM
• Any structural protein abnormality can lead to DCM
• Extra cellular matrix changes also contribute to LV dilatation and systolic dysfunction
What about cardiac stem cells?
• Not a lot about what happens to CPC in DCM
• Presume they are also affected by the etiological factors and down-stream cascades
• Anthracycline induced DCM: Injection of CPC harvested prior to exposure reduce effects of DCM
Therapeutic Potential
• Myriad of potential therapeutic targets.
• Apoptosis work > 10 yrs, no clinical trials yet.
• Some trials on ECM have failed.
• ? Kinase inhibitors for lamin DCM
Thank you