Mitochondrial Quality Controlgenomics.unl.edu/RBC_2018/COURSE_FILES/wed4.pdfRugarli & Langer, EMBO J. (2012) Mitochondrial quality control (MQC) • Two levels of MQC: 1). Organellar

Oleh Khalimonchuk, Ph.D.

Graduate Course 2214/BIOC 998

Charleston, May 23, 2018

Mitochondrial Quality Control

• Respiration (ATP generation)

• Cofactors & metabolites synthesis

• Ion homeostasis

• Lipid homeostasis

• ROS production/signaling

• Regulation of apoptosis

Wilson et al., Nanoscale (2015)

Hyperfusion Fragmentation Normal network

Untreate

d

Homeostatic challenge

Mitochondrial network in primary

rat astrocytes challenged with

TiO2 nanoparticles

2

Bohovych et al., Antiox. Redox Signal. (2015)

• The inner membrane is

extremely protein-rich and is one

of the major sites of essential

mitochondrial functions

• A small fraction of proteins (8-13)

originates from the organelle’s own

genome

• Composed of 1,000 -1,500 proteins,

majority of which are synthesized in

the cytosol and imported into the

organelle

3

What can go wrong in a mitochondrion?

• Extensive ROS production by mitochondrial respiratory

iiichain (MRC) can damage proteins and mtDNA which

iiiare in the close proximity to the MRC

Khalimonchuk et al., J. Biol. Chem. (2007) Khalimonchuk et al., J. Biol. Chem. (2012) Bohovych et al., Antioxid. Redox Signal. (2015)

• Improperly assembled redox cofactors can act as pro-

iiioxidants (inherent ability to generate ROS via Fenton

iiireactions )

• Mismatches in subunits stoichiometry may lead to

iiiaccumulation of unassembled/misfolded proteins

4

Nuclear

DNA

mutations Misfolded

proteins MRC

dysfunction

ROS mtDNA

mutations

• Impaired mitochondrial dynamics

• Ca2+ overload

• Cellular damage/death

• Impaired cellular energetics

Mitochondrial dysfunction - the road to ruin

Cancers:

Gliomas

Lymphomas

Neurological:

Leigh syndrome

Leukodystrophy

ALS

Neurodegenerative:

Optic nerve atrophy

Parkinsonism

Ataxias

Peripheral artery disease

Cardiovascular:

Cardiomyopathies

…and Aging

Vafai and Mootha, Nature (2012)

Levytskyy et al., J. Neuroimmune Pharm. (2016)

5

http://www.memes.com/koala-cant-believe-it/

We’re doomed!!!

…or are we? 6

• Respiration (ATP generation)

• Cofactor synthesis

• Ion homeostasis

• Lipid homeostasis

• ROS production/signaling

• Regulation of apoptosis

ROS

scavenging

Biogenesis Dynamics:

fission/fusion Mitophagy

DNA repair Protein quality control

repair/refolding/degradation

Adapted from Figge et al., Bioessays (2013)

• Multiple mechanisms are involved in

sustaining of normal mitochondrial function

7

Rugarli & Langer, EMBO J. (2012)

Mitochondrial quality control

(MQC)

• Two levels of MQC:

1). Organellar

2). Molecular (aka intramitochondrial)

• Molecular and organellar MQC

are interdependent and

functionally intertwined

8

Organellar MQC – fusion

Youle & van der Bliek, Science (2012) Tsushima et al., Circ. Res. (2018)

• Mitochondrial content

mixing via fusion helps

to dilute the damage

Fu

sion

N

o fu

sion

9

Charcot-Marie-Tooth Syndrome

Dominant Optic Atrophy

OM

fusion

IM

fusion

• OM and IM fusion are coordinated

but physically separate events

Detmer & Chan, Nat. Rev. Mol. Cell. Biol. (2007) Ishihara et al., Antioxid. Redox Signal. (2013) Wai & Langer, Trends Endocrin. Metab. (2016)

Organellar MQC – fusion

Ubiquitination

Phosphoylation

SUMOylation

Thiol oxidation

GSHylation

10

Anand et al., BBA (2013)

Wai & Langer, Trends Endocrin. Metab. (2016)

SIMH = Stress-induced

mitochondrial hyperfusion

• SIMH relies on thiol oxidation and

likely GSH-ylation of the conserved

cysteine residues in Mfn1/2

Organellar MQC – fusion

11

Neurodegeneration

Myocardial Infarction

Otera & Mihara, J. Biochem. (2011); Hoppins & Nunnari, Science (2013)

Wai & Langer, Trends Endocrin. Metab. (2016)

ER

Mito

Dnm1/Drp1

rings

Organellar MQC – fission

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Mitochondrial dynamics at a glance

Mito1

Mito2

Mito3

MFN1/2

Mito4 Mito5

FIS1

13

Youle & van der Bliek, Science (2012) Escobar-Henriques & Langer EMBO Rep. (2014)

Organellar MQC - mitophagy

• Damaged mitochondria can be

segregated through fission and

eliminated by mitophagy

Parkinsonism

14

Anand et al., BBA (2013)

Soubannier et al., PLoS One (2013)

Bohovych et al., Antioxid. Redox Signal. (2015)

Organellar MQC – mitochondria-derived vesicles

• Mitochondria-derived vesicles – recently identified

non-mitophagy clearance mechanism

15

Anand et al., BBA (2013)

Organellar/Molecular MQC – UPS delivers

• Several other factors

appear to work in parallel

or concomitantly with

PINK1/Parkin system

(MITOL, MULAN, Mdm30,

Vms1, DJ-1, etc.)

• MITOL, MULAN and

Mdm30 are ubiquitin

ligases involved

mitochondria-associated

degradation (MAD)

Paget’s disease

ALS, IBD

When neither hyperfusion, nor mitophagy

can help – cells undergo apoptosis… 16

Molecular MQC - Proteases

• Removal of misfolded, damaged

or non-assembled polypeptides

• Central roles in:

mitochondrial biogenesis

mitochondrial dynamics

mitochondrial signaling

lipid homeostasis

apoptosis

Bohovych et al., Antioxid. Redox Signal. (2015)

Sauer & Baker, Annu. Rev. Biochem (2011) Levytskyy et al., J. Neuroimmune Pharm. (2016) Levytskyy et al., Biochemistry (2017)

Two major classes of IMQC

proteases:

1). ATP-dependent (AAA+ proteases)

2). ATP-independent

Molecular MQC - Proteases

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Hereditary Spastic Paraplegia

Spinocerebellar Ataxia type 28

Spastic Ataxia-Neuropathy Syndrome

HFD-induced obesity

Amyotrophic Lateral Sclerosis

Molecular MQC - Proteases

Genetic interactions indicate

tight functional coupling

between MQC proteases

Bohovych et al., J. Biol. Chem (2014)

Mental Retardation

CORDAS syndrome

Dilated

cardiomyopathy

Parkinsonism

Parkinsonism

Molecular MQC in the matrix

• Matrix MQC involves both soluble and mitochondrial inner membrane

anchored proteases

Levytskyy et al., J. Neuroimmune Pharm. (2016)

• Removal of processed

mitochondrial targeting signal

peptides is yet another critical aspect

of the matrix MQC

Alzheimer’s

disease

20

Adapted from Anand et al., BBA (2013)

Molecular MQC in the IM and IMS

Proteolytic

processing

Regulatory

proteolysis

Proteolytic removal

of damaged proteins

21

Where molecular and organellar MQC intersect

Quiros et al., EMBO J. (2012) Bohovych et al., Sci. Rep. (2015) Wai & Langer, Trends Endocrin. Metab. (2016)

• Stress-triggered cleavage of L-

OPA1 by activated OMA1

protease stimulates fission and

leads to metabolic re-tuning

-DY

ROS

Heat stress

Hypoxia (?)

Control

Oma1 MO

22

Where molecular and organellar MQC intersect

Anand et al., BBA (2013)

• PINK1 accumulation is a consequence of its attenuated turnover by PARL protease

23

Mito-nuclear communication

Retrograde responses

• Various signals are

produced by mitochondria

to communicate their

functional states

• LON, m-AAA and Oma1

proteases participate in

modulation of mitochondrial

ROS and Ca2+ levels

24

ROS, Ca2+,

ATP/ADP, NAD+/NADH

Ac-CoA/Citrate

Succinate/Fumarate

(ATP/ADP) AMPK

(ROS) HIF1a MAPK

Sirtuins (NAD+/NADH; Ac-CoA)

(Succinate/Fumarate) HIF1a

TORC1

NRF2L

Calpains FAK RhoA

GTPases (Ca2+)

Bohovych & Khalimonchuk, Front. Cell Dev. Biol. (2016)

Mitochondrion to nucleus communication - Metabolites

• Certain mitochondrial

metabolites can be

transported outside of the

organelle and impinge on

several signaling pathways or

elicit epigenetic modifications

25

Mitochondrion to nucleus communication - UPRmt

• Upon stress, AFTS-1/ATF5

localizes to the nucleus and

initiates UPRmt-like response

Germany et. al, J. Cell Sci. (under review)

No stress Stress

Phsp-6::GFP

Bohovych & Khalimonchuk, Front. Cell Dev. Biol. (2016) 26

• Destabilization of the respiratory supercomplexes in Oma1-deficient

cells impinges on TORC1-Rim15-Msn2/4 signaling axis

Bohovych et al., Mol. Cell. Biol. (2016)

Mitochondrion to nucleus stress communication - ROS

Bohovych & Khalimonchuk, Front. Cell Dev. Biol. (2016)

27

Perhaps I’ve said too much.

28

Take home messages

• Sustaining normal mitochondrial function is critical for cellular welfare

• Mitochondrial quality control is a multi-faceted and hierarchal set of

interdependent mechanisms at both molecular and organellar levels

• Mitochondrial proteases play key roles in the majority of MQC mechanisms

• Several aspects of mitochondrial function may turn into disaster routes and

need to be tightly controlled by mitochondrial quality control mechanisms

• Under certain conditions, transient mitochondria-derived cues can be

amplified and act as hormetic-like signals interfering with key cellular

signaling pathways

• Mitochondria effectively communicate with nucleus and other organelles via

several mechanisms which involve MQC proteases

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