Mitochondrial Quality Control

Transcription

1 Mitochondrial Quality Control You are here Oleh Khalimonchuk, Ph.D. Graduate Course 2214/BIOC 938 Charleston, May 20, 2015 biology4kids.com

2 Cryo-electron microscopy Fluorescent microscopy Yeast Human Semi-autonomous, dynamic organelles essential for a number of vital processes Composed of 1,000-1,500 proteins, majority of which are synthesized in the cytosol and subsequently imported into the mitochondria A small fraction of proteins (8-13) originates from organelle s own genome microcopyu.com

3 Respiration (ATP generation) Cofactor synthesis Ion homeostasis Lipid homeostasis ROS production/signaling Regulation of apoptosis Mitochondria are involved in a variety of vital cellular processes Sustaining normal mitochondrial function is critical as mitochondria iiiare not produced de novo Adapted from Figge et al., Bioessays (2013)

4 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 Improperly assembled redox cofactors can act as proiiioxidants (inherent ability to generate ROS via Fenton iiireactions ) Mismatches in subunits stoichiometry may lead to iiiaccumulation of unassembled/misfolded polypeptides Khalimonchuk et al., J. Biol. Chem. (2007); Khalimonchuk et al., J. Biol. Chem. (2012); Bohovych et al., Antioxid. Redox Signal. (2015)

5 Mitochondrial dysfunction - the road to ruin Nuclear DNA mutations mtdna mutations Misfolded proteins ROS MRC dysfunction Impaired mitochondrial dynamics Ca 2+ overload Impaired cellular energetics Cellular damage/death Cancers: Gliomas Lymphomas Neurological: Leigh syndrome Leukodystrophy Optic nerve atrophy Ataxias Neurodegenerative: Parkinsonism ALS Cardiovascular: Cardiomyopathies Peripheral artery disease and Aging Vafai and Mootha, Nature (2012)

6 Biogenesis Dynamics: fission/fusion Mitophagy Respiration (ATP generation) Cofactor synthesis Ion homeostasis Lipid homeostasis ROS production/signaling Regulation of apoptosis ROS scavenging Protein quality control repair/refolding/degradation DNA repair Multiple mechanisms are involved in sustaining of normal mitochondrial function Adapted from Figge et al., Bioessays (2013)

7 Mitochondrial quality control (MQC) Two levels of MQC: 1). Organellar 2). Molecular (aka intramitochondrial) Molecular and organellar MQC are interdependent and functionally intertwined Rugarli & Langer, EMBO J. (2012)

8 Organellar MQC fusion Mitochondrial content mixing via fusion helps to dilute the damage Fusion No fusion Youle & van der Bliek, Science (2012) Heiko Bugger (unpublished)

9 Organellar MQC fusion OM fusion IM fusion OM and IM fusion are coordinated but physically separate events Charcot-Marie-Tooth Syndrome Dominant Optic Atrophy Ubiquitination Phosphoylation SUMOylation Thiol oxidation Detmer & Chan, Nat. Rev. Mol. Cell. Biol. (2007); Ishihara et al., Antioxid. Redox Signal. (2013)

10 Organellar MQC fusion SIMH = Stress-induced mitochondrial hyperfusion No stress Stress SIMH relies on thiol oxidation of the conserved cysteine residues in Mfn1/2 Anand et al., BBA (2013); Tondera et al., EMBO J. (2009)

11 Organellar MQC fission Neurodegeneration Myocardial Infarction ER Mito Dnm1/Drp1 rings Otera & Mihara, J. Biochem. (2011) Adapted from Hoppins & Nunnari, Science (2013)

12 Organellar MQC - mitophagy Parkinsonism Youle & van der Bliek, Science (2012); Escobar-Henriques & Langer EMBO Rep. (2014) Damaged mitochondria can be segregated through fission and eliminated by mitophagy

13 Organellar MQC mitochondria-derived vesicles Anand et al., BBA (2013); Soubannier et al., PLoS One (2013); Bohovych et al., Antioxid. Redox Signal. (2015) Mitochondria-derived vesicles recently identified non-mitophagy clearance mechanism

14 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 in outer mitochondrial membrane-associated degradation (OMMAD) Paget s disease ALS Adapted from Anand et al., BBA (2013)

15 Organellar/Molecular MQC playing tag with mitochondria Vms1 is an auxiliary factor that tags damaged mitochondria and helps to recruit UPS machinery Heo et al., Mol. Cell (2010) Iryna Bohovych (unpublished) When neither hyperfusion, nor mitophagy can help cells undergo apoptosis

16 Molecular MQC - Proteases Removal of misfolded, damaged or non-assembled polypeptides Recently discovered roles in: mitochondrial biogenesis mitochondrial dynamics mitochondrial signaling lipid homeostasis apoptosis Bohovych et al., Antioxid. Redox Signal. (2015)

17 Molecular MQC - Proteases Two major classes of IMQC proteases: 1). ATP-dependent (AAA+ proteases) 2). ATP-independent Sauer & Baker, Annu. Rev. Biochem (2011)

18 Molecular MQC - Proteases Obesity Hepatic Steatosis Altered thermogenesis ALS (?) Dominant Optic Atrophy (?) Mental Retardation Hereditary Spastic Paraplegia Spinocerebellar Ataxia type 28 Spastic Ataxia-Neuropathy Syndrome Dominant Optic Atrophy (?) Genetic interactions indicate tight functional coupling between MQC proteases Bohovych et al., J. Biol. Chem (2014)

19 Molecular MQC in the matrix Matrix MQC involves several proteases and molecular chaperones Hsp78, Hsp100/Mcx1 are AAA+ proteins lacking proteolytic domain Bohovych et al., Antioxid. Redox Signal. (2015)

20 Molecular MQC in the IM and IMS Proteolytic processing Regulatory proteolysis Proteolytic removal of damaged proteins Adapted from Anand et al., BBA (2013)

21 Where molecular and organellar MQC intersect -DY ROS Heat stress Hypoxia (?) Stress-triggered cleavage of L-OPA1 by activated OMA1 protease inhibits fusion and stimulates fission m-aaa protease also participates in L-OPA1 processing upon loss of DY Anand et al., BBA (2013); Bohovych et al., J. Biol. Chem (2014); Baker et al., EMBO J. (2014)

22 Where molecular and organellar MQC intersect PINK1 accumulation is a consequence of its attenuated turnover by PARL protease Adapted from Anand et al., BBA (2013)

23 Mitochondrion to nucleus stress communication Retrograde (RTG) pathway Yeast-specific pathway controls nucleus-coded genes for mitochondrial rrnas and metabolic enzymes? (ROS, Ca 2+ ) Mammalian cells have a functional equivalent (controls expression of Ca 2+ homeostasis genes, TGFb, etc.) LON, m-aaa and likely Oma1 proteases participate in modulation of mitochondrial ROS and Ca 2+ levels Adapted from Liu et al., Mol. Cell (2003)

24 Mitochondrion to nucleus stress communication Mitochondrial unfolded protein response (UPRmt) Unfolded proteins in the mitochondrial matrix are degraded by ClpXP protease complex The resulting peptides are extruded and stimulate nuclear translocation of the specific transcription factor Mammals Nematodes The transcription factor activates expression of mitochondrial chaperones and proteases Haynes & Ron J. Cell. Sci. (2010)

25 Mitochondrion to nucleus stress communication in worms AFTS-1 = Activating transcription factor associated with stress (bzip transcription factor) Nematodes Under normal conditions AFTS-1 is sent to mitochondria and degraded by LON protease Upon stress, AFTS-1 localizes to the nucleus and initiates UPRmt-like response Nargund et al., Science (2012)

26 Mitochondrion to nucleus stress communication WT oma1d O 2.- O 2.- Bohovych et al., 2015 (submitted) Destabilization of the respiratory supercomplexes in Oma1-deficient mitochondria creates transient interfering ROS signal that impinges on TORC1-Rim15-Msn2/4 signaling axis

27 Take home messages Sustaining normal mitochondrial function is critical for cellular welfare Several aspects of mitochondrial function may turn into disaster routes and need to be tightly controlled by mitochondrial quality control mechanisms 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 Mitochondria effectively communicate with nucleus and other organelles via several mechanisms which involve MQC proteases Under certain conditions, transient mitochondria-derived ROS can be amplified and act as hormetic-like signals interfering with key cellular signaling pathways