bims-mitdyn 2022-10-30 papers

bims-mitdyn

Biomed News

on Mitochondrial dynamics: mechanisms

Issue of 2022‒10‒30
25 papers selected by
Edmond Chan
Queen’s University, School of Medicine

Hypoxia promotes osteogenesis by facilitating acetyl-CoA-mediated mitochondrial-nuclear communication.
Structure and functionality of a multimeric human COQ7:COQ9 complex.
Autosomal recessive progeroid syndrome due to homozygosity for a TOMM7 variant.
Mitochondrial dysfunction reactivates α-fetoprotein expression that drives copper-dependent immunosuppression in mitochondrial disease models.
A SARM1/mitochondrial feedback loop drives neuropathogenesis in a Charcot-Marie-Tooth disease type 2A rat model.
Human mtRF1 terminates COX1 translation and its ablation induces mitochondrial ribosome-associated quality control.
Mitoguardin-2-mediated lipid transfer preserves mitochondrial morphology and lipid droplet formation.
A compendium of co-regulated mitoribosomal proteins in pan-cancer uncovers collateral defective events in tumor malignancy.
Mitochondrial Ca2+ Uniporter haploinsufficiency enhances long-term potentiation at hippocampal mossy fibre synapses.
BCL7A-containing SWI/SNF/BAF complexes modulate mitochondrial bioenergetics during neural progenitor differentiation.
ATP13A1 prevents ERAD of folding-competent mislocalized and misoriented proteins.
A hypomorphic variant in the translocase of the outer mitochondrial membrane complex subunit TOMM7 causes short stature and developmental delay.
Multifaceted mitochondrial quality control in brown adipose tissue.
OPA1 drives macrophage metabolism and functional commitment via p65 signaling.
SIAH proteins regulate the degradation and intra-mitochondrial aggregation of PINK1: Implications for mitochondrial pathology in Parkinson's disease.
Structural studies of human fission protein FIS1 reveal a dynamic region important for GTPase DRP1 recruitment and mitochondrial fission.
The oncoprotein MUC1 facilitates breast cancer progression by promoting Pink1-dependent mitophagy via ATAD3A destabilization.
The absence of Parkin does not promote dopamine or mitochondrial dysfunction in PolgAD257A/D257A mitochondrial mutator mice.
TRPV4 interacts with MFN2 and facilitates endoplasmic reticulum-mitochondrial contact points for Ca2+-buffering.
Molecular determinants of mitochondrial shape and function and their role in glaucoma.
Cytoplasmic and mitochondrial aminoacyl-tRNA synthetases differentially regulate lifespan in Caenorhabditis elegans.
Mitophagy in the aging nervous system.
Basal Gp78-dependent mitophagy promotes mitochondrial health and limits mitochondrial ROS.
PINK1-PRKN mediated mitophagy: differences between in vitro and in vivo models.
The Dep1 protein: A new regulator of mitophagy in yeast.

EMBO J. 2022 Oct 24. e111239

Hypoxia promotes osteogenesis by facilitating acetyl-CoA-mediated mitochondrial-nuclear communication.

Andromachi Pouikli, Monika Maleszewska, Swati Parekh, Ming Yang, Chrysa Nikopoulou, Juan Jose Bonfiglio, Constantine Mylonas, Tonantzi Sandoval, Anna-Lena Schumacher, Yvonne Hinze, Ivan Matic, Christian Frezza, Peter Tessarz.

  Bone-derived mesenchymal stem cells (MSCs) reside in a hypoxic niche that maintains their differentiation potential. While hypoxia (low oxygen concentration) was reported to critically support stem cell function and osteogenesis, the molecular events triggering changes in stem cell fate decisions in response to normoxia (high oxygen concentration) remain elusive. Here, we study the impact of normoxia on mitochondrial-nuclear communication during stem cell differentiation. We show that normoxia-cultured murine MSCs undergo profound transcriptional alterations which cause irreversible osteogenesis defects. Mechanistically, high oxygen promotes chromatin compaction and histone hypo-acetylation, particularly on promoters and enhancers of osteogenic genes. Although normoxia induces metabolic rewiring resulting in elevated acetyl-CoA levels, histone hypo-acetylation occurs due to the trapping of acetyl-CoA inside mitochondria owing to decreased citrate carrier (CiC) activity. Restoring the cytosolic acetyl-CoA pool remodels the chromatin landscape and rescues the osteogenic defects. Collectively, our results demonstrate that the metabolism-chromatin-osteogenesis axis is perturbed upon exposure to high oxygen levels and identifies CiC as a novel, oxygen-sensitive regulator of the MSC function.

Keywords:  histone acetylation; hypoxia; mesenchymal stem cells; metabolism; osteogenesis

DOI:  https://doi.org/10.15252/embj.2022111239
Mol Cell. 2022 Oct 21. pii: S1097-2765(22)00960-1. [Epub ahead of print]

Structure and functionality of a multimeric human COQ7:COQ9 complex.

Mateusz Manicki, Halil Aydin, Luciano A Abriata, Katherine A Overmyer, Rachel M Guerra, Joshua J Coon, Matteo Dal Peraro, Adam Frost, David J Pagliarini.

  Coenzyme Q (CoQ) is a redox-active lipid essential for core metabolic pathways and antioxidant defense. CoQ is synthesized upon the mitochondrial inner membrane by an ill-defined "complex Q" metabolon. Here, we present structure-function analyses of a lipid-, substrate-, and NADH-bound complex comprising two complex Q subunits: the hydroxylase COQ7 and the lipid-binding protein COQ9. We reveal that COQ7 adopts a ferritin-like fold with a hydrophobic channel whose substrate-binding capacity is enhanced by COQ9. Using molecular dynamics, we further show that two COQ7:COQ9 heterodimers form a curved tetramer that deforms the membrane, potentially opening a pathway for the CoQ intermediates to translocate from the bilayer to the proteins' lipid-binding sites. Two such tetramers assemble into a soluble octamer with a pseudo-bilayer of lipids captured within. Together, these observations indicate that COQ7 and COQ9 cooperate to access hydrophobic precursors within the membrane and coordinate subsequent synthesis steps toward producing CoQ.

Keywords:  COQ7; COQ9; coenzyme Q; di-iron proteins; mitochondria; protein-lipid complex; protein-membrane interaction; quinone biosynthesis

DOI:  https://doi.org/10.1016/j.molcel.2022.10.003
J Clin Invest. 2022 Oct 25. pii: e156864. [Epub ahead of print]

Autosomal recessive progeroid syndrome due to homozygosity for a TOMM7 variant.

Abhimanyu Garg, Wee-Teik Keng, Zhenkang Chen, Adwait Amod Sathe, Chao Xing, Pavithira Devi Kailasam, Yanqiu Shao, Nicholas P Lesner, Claire B Llamas, Anil K Agarwal, Prashant Mishra.

  Multiple genetic loci have been reported for progeroid syndromes. However, the molecular defects in some extremely rare forms of progeria have yet to be elucidated. Here we report a 21-year-old man of Chinese origin who had a novel autosomal recessive form of progeria, characterized by severe dwarfism, mandibular hypoplasia, hyperopia and partial lipodystrophy. Analyses of exome sequencing data of the entire family revealed only one rare homozygous missense variant, (c.86C>T; p.Pro29Leu), in TOMM7 in the proband, while the parents and two unaffected siblings were heterozygous for the variant. TOMM7, a nuclear gene, encodes a translocase in the outer mitochondrial membrane. The TOMM complex constitutes the outer membrane pore for import of several preproteins into mitochondria. Proteomics analyses of mitochondria from cultured fibroblasts of the proband, as compared to control fibroblasts, revealed increases in several proteins involved in oxidative phosphorylation, but reduced abundance of proteins involved in the phospholipid metabolism. We also observed elevated basal and maximal oxygen consumption rates in the fibroblasts from the proband as compared to control fibroblasts. We conclude that altered mitochondrial protein import due to loss of function bi-allelic variant in TOMM7 can cause severe growth retardation and progeroid features.

Keywords:  Endocrinology; Genetic diseases; Genetics; Mitochondria

DOI:  https://doi.org/10.1172/JCI156864
J Clin Invest. 2022 Oct 27. pii: e154684. [Epub ahead of print]

Mitochondrial dysfunction reactivates α-fetoprotein expression that drives copper-dependent immunosuppression in mitochondrial disease models.

Kimberly A Jett, Zakery N Baker, Amzad Hossain, Aren Boulet, Paul A Cobine, Sagnika Ghosh, Philip Ng, Orhan Yilmaz, Kris Barreto, John DeCoteau, Karen Mochoruk, George N Ioannou, Christopher Savard, Sai Yuan, Osama Hmh Abdalla, Christopher Lowden, Byung-Eun Kim, Hai-Ying Mary Cheng, Brendan J Battersby, Vishal M Gohil, Scot C Leary.

  Signaling circuits crucial to systemic physiology are widespread, yet uncovering their molecular underpinnings remains a barrier to understanding the etiology of many metabolic disorders. Here, we identify a copper-linked signaling circuit activated by disruption of mitochondrial function in the murine liver or heart that results in atrophy of the spleen and thymus and causes a peripheral white blood cell deficiency. We demonstrate that the leukopenia is caused by α-fetoprotein, which requires copper and the cell surface receptor CCR5 to promote white blood cell death. We further show that α-fetoprotein expression is upregulated in several cell types upon inhibition of oxidative phosphorylation, including a muscle cell model of Barth syndrome. Collectively, our data argue that α-fetoprotein secreted by bioenergetically stressed tissue suppresses the immune system, an effect which may explain the recurrent infections that are observed in a subset of mitochondrial diseases or in other disorders with mitochondrial involvement.

Keywords:  Metabolism; Mitochondria

DOI:  https://doi.org/10.1172/JCI154684
J Clin Invest. 2022 Oct 26. pii: e161566. [Epub ahead of print]

A SARM1/mitochondrial feedback loop drives neuropathogenesis in a Charcot-Marie-Tooth disease type 2A rat model.

Yurie Yamada, Amy Strickland, Yo Sasaki, A Joseph Bloom, Aaron DiAntonio, Jeffrey Milbrandt.

  Charcot-Marie-Tooth disease (CMT) type 2A is an axonal neuropathy caused by mutations in the mitofusin 2 (MFN2) gene. MFN2 mutations result in profound mitochondrial abnormalities, but the mechanism underlying axonal pathology is unknown. SARM1, the central executioner of axon degeneration, can induce neuropathy and is activated by dysfunctional mitochondria. We tested the role of SARM1 in a rat model carrying a dominant CMT2A mutation (Mfn2H361Y) that exhibits progressive dying-back axonal degeneration, NMJ abnormalities, muscle atrophy, and mitochondrial abnormalities, all hallmarks of the human disease. We generated Sarm1 knockout and Mfn2H361Y, Sarm1 double mutant rats and find that deletion of Sarm1 rescues axonal, synaptic, muscle, and functional phenotypes, demonstrating that SARM1 is responsible for much of the neuropathology in this model. Despite the presence of mutant MFN2 protein in these double mutant rats, loss of SARM1 also dramatically suppressed many mitochondrial defects, including the number, size, and cristae density defects of synaptic mitochondria. This surprising finding indicates that dysfunctional mitochondria activate SARM1, and activated SARM1 feeds back on mitochondria to exacerbate mitochondrial pathology. As such, this work identifies SARM1 inhibition as an exciting therapeutic candidate for the treatment of CMT2A and other neurodegenerative diseases with prominent mitochondrial pathology.

Keywords:  Neurodegeneration; Neurological disorders; Neuromuscular disease; Neuroscience

DOI:  https://doi.org/10.1172/JCI161566
Nat Commun. 2022 Oct 27. 13(1): 6406

Human mtRF1 terminates COX1 translation and its ablation induces mitochondrial ribosome-associated quality control.

Franziska Nadler, Elena Lavdovskaia, Angelique Krempler, Luis Daniel Cruz-Zaragoza, Sven Dennerlein, Ricarda Richter-Dennerlein.

Translation termination requires release factors that read a STOP codon in the decoding center and subsequently facilitate the hydrolysis of the nascent peptide chain from the peptidyl tRNA within the ribosome. In human mitochondria eleven open reading frames terminate in the standard UAA or UAG STOP codon, which can be recognized by mtRF1a, the proposed major mitochondrial release factor. However, two transcripts encoding for COX1 and ND6 terminate in the non-conventional AGA or AGG codon, respectively. How translation termination is achieved in these two cases is not known. We address this long-standing open question by showing that the non-canonical release factor mtRF1 is a specialized release factor that triggers COX1 translation termination, while mtRF1a terminates the majority of other mitochondrial translation events including the non-canonical ND6. Loss of mtRF1 leads to isolated COX deficiency and activates the mitochondrial ribosome-associated quality control accompanied by the degradation of COX1 mRNA to prevent an overload of the ribosome rescue system. Taken together, these results establish the role of mtRF1 in mitochondrial translation, which had been a mystery for decades, and lead to a comprehensive picture of translation termination in human mitochondria.

DOI: https://doi.org/10.1038/s41467-022-34088-w
J Cell Biol. 2022 Dec 05. pii: e202207022. [Epub ahead of print]221(12):

Mitoguardin-2-mediated lipid transfer preserves mitochondrial morphology and lipid droplet formation.

Zhouping Hong, Jyoti Adlakha, Neng Wan, Emily Guinn, Fabian Giska, Kallol Gupta, Thomas J Melia, Karin M Reinisch.

Lipid transport proteins at membrane contacts, where organelles are closely apposed, are critical in redistributing lipids from the endoplasmic reticulum (ER), where they are made, to other cellular membranes. Such protein-mediated transfer is especially important for maintaining organelles disconnected from secretory pathways, like mitochondria. We identify mitoguardin-2, a mitochondrial protein at contacts with the ER and/or lipid droplets (LDs), as a lipid transporter. An x-ray structure shows that the C-terminal domain of mitoguardin-2 has a hydrophobic cavity that binds lipids. Mass spectrometry analysis reveals that both glycerophospholipids and free-fatty acids co-purify with mitoguardin-2 from cells, and that each mitoguardin-2 can accommodate up to two lipids. Mitoguardin-2 transfers glycerophospholipids between membranes in vitro, and this transport ability is required for roles both in mitochondrial and LD biology. While it is not established that protein-mediated transfer at contacts plays a role in LD metabolism, our findings raise the possibility that mitoguardin-2 functions in transporting fatty acids and glycerophospholipids at mitochondria-LD contacts.

DOI: https://doi.org/10.1083/jcb.202207022
iScience. 2022 Oct 21. 25(10): 105244

A compendium of co-regulated mitoribosomal proteins in pan-cancer uncovers collateral defective events in tumor malignancy.

Ching-Wen Chang, Zhuang Wei, Stewart R Durell, Lichun Ma, Marshonna Forgues, Xin Wei Wang.

  Mitochondria are major organelles responsible for cellular energy and metabolism, and their dysfunction is tightly linked to cancer. The mitochondrial ribosome (mitoribosome) is a protein complex consisting of 82 mitoribosomal proteins (MRPs) encoded by nuclear genes and is essential for mitochondrial protein synthesis. However, their roles in tumorigenesis remain poorly understood. We performed pan-cancer analyses of 18,177 tumors representing 28 cancer types to determine somatic alterations of MRP genes as a genetic basis for tumorigenesis. We identified a set of 20 altered MRPs known to be involved in early assembly of the mitoribosome complex. We found that tumors with affected MRPs were associated with impaired mitochondrial functions and TP53 mutations accompanied by increased genomic instability and intra-tumor heterogeneity. MRP deletions were associated with poor survival. Our results reveal a key role for mitochondrial ribosome biogenesis in tumor malignancy across cancer types.

Keywords:  Bioinformatics; Biological database; Biological sciences; Cancer; Medical informatics

DOI:  https://doi.org/10.1016/j.isci.2022.105244
J Cell Sci. 2022 Oct 24. pii: jcs.259823. [Epub ahead of print]

Mitochondrial Ca2+ Uniporter haploinsufficiency enhances long-term potentiation at hippocampal mossy fibre synapses.

Michael J Devine, Blanka R Szulc, Jack H Howden, Guillermo López-Doménech, Arnaud Ruiz, Josef T Kittler.

  Long-term changes in synaptic strength form the basis of learning and memory. These changes rely upon energy demanding mechanisms which are regulated by local Ca2+ signaling. Mitochondria are optimised for providing energy and buffering Ca2+. However, our understanding of the role of mitochondria in regulating synaptic plasticity is incomplete. Here we have used optical and electrophysiological techniques in cultured hippocampal neurons and ex vivo hippocampal slices from mice with haploinsufficiency of the mitochondrial Ca2+ uniporter (MCU+/-) to address whether reducing mitochondrial Ca2+ uptake alters synaptic transmission and plasticity. We found that cultured MCU+/- hippocampal neurons have impaired Ca2+ clearance, and consequently enhanced synaptic vesicle fusion at presynapses occupied by mitochondria. Furthermore, long-term potentiation (LTP) at mossy fibre (MF) synapses, a process which is dependent on presynaptic Ca2+ accumulation, is enhanced in MCU+/- slices. Our results reveal a previously unrecognized role for mitochondria in regulating presynaptic plasticity of a major excitatory pathway involved in learning and memory.

Keywords:  Calcium; Long-term potentiation; MCU; Mitochondria; Mossy fibre synapse

DOI:  https://doi.org/10.1242/jcs.259823
EMBO J. 2022 Oct 28. e110595

BCL7A-containing SWI/SNF/BAF complexes modulate mitochondrial bioenergetics during neural progenitor differentiation.

Lena Wischhof, Hang-Mao Lee, Janine Tutas, Clemens Overkott, Eileen Tedt, Miriam Stork, Michael Peitz, Oliver Brüstle, Thomas Ulas, Kristian Händler, Joachim L Schultze, Dan Ehninger, Pierluigi Nicotera, Paolo Salomoni, Daniele Bano.

  Mammalian SWI/SNF/BAF chromatin remodeling complexes influence cell lineage determination. While the contribution of these complexes to neural progenitor cell (NPC) proliferation and differentiation has been reported, little is known about the transcriptional profiles that determine neurogenesis or gliogenesis. Here, we report that BCL7A is a modulator of the SWI/SNF/BAF complex that stimulates the genome-wide occupancy of the ATPase subunit BRG1. We demonstrate that BCL7A is dispensable for SWI/SNF/BAF complex integrity, whereas it is essential to regulate Notch/Wnt pathway signaling and mitochondrial bioenergetics in differentiating NPCs. Pharmacological stimulation of Wnt signaling restores mitochondrial respiration and attenuates the defective neurogenic patterns observed in NPCs lacking BCL7A. Consistently, treatment with an enhancer of mitochondrial biogenesis, pioglitazone, partially restores mitochondrial respiration and stimulates neuronal differentiation of BCL7A-deficient NPCs. Using conditional BCL7A knockout mice, we reveal that BCL7A expression in NPCs and postmitotic neurons is required for neuronal plasticity and supports behavioral and cognitive performance. Together, our findings define the specific contribution of BCL7A-containing SWI/SNF/BAF complexes to mitochondria-driven NPC commitment, thereby providing a better understanding of the cell-intrinsic transcriptional processes that connect metabolism, neuronal morphogenesis, and cognitive flexibility.

Keywords:  BCL7A; SWI/SNF/BAF complex; cognitive function; mitochondrial OXPHOS; neural progenitor cells (NPCs)

DOI:  https://doi.org/10.15252/embj.2022110595
Mol Cell. 2022 Oct 15. pii: S1097-2765(22)00956-X. [Epub ahead of print]

ATP13A1 prevents ERAD of folding-competent mislocalized and misoriented proteins.

Michael J McKenna, Benjamin M Adams, Vincent Chu, Joao A Paulo, Sichen Shao.

  The biosynthesis of thousands of proteins requires targeting a signal sequence or transmembrane segment (TM) to the endoplasmic reticulum (ER). These hydrophobic ɑ helices must localize to the appropriate cellular membrane and integrate in the correct topology to maintain a high-fidelity proteome. Here, we show that the P5A-ATPase ATP13A1 prevents the accumulation of mislocalized and misoriented proteins, which are eliminated by different ER-associated degradation (ERAD) pathways in mammalian cells. Without ATP13A1, mitochondrial tail-anchored proteins mislocalize to the ER through the ER membrane protein complex and are cleaved by signal peptide peptidase for ERAD. ATP13A1 also facilitates the topogenesis of a subset of proteins with an N-terminal TM or signal sequence that should insert into the ER membrane with a cytosolic N terminus. Without ATP13A1, such proteins accumulate in the wrong orientation and are targeted for ERAD by distinct ubiquitin ligases. Thus, ATP13A1 prevents ERAD of diverse proteins capable of proper folding.

Keywords:  ER-associated degradation; protein localization; protein topology; quality control; signal sequence; transmembrane proteins

DOI:  https://doi.org/10.1016/j.molcel.2022.09.035
HGG Adv. 2023 Jan 12. 4(1): 100148

A hypomorphic variant in the translocase of the outer mitochondrial membrane complex subunit TOMM7 causes short stature and developmental delay.

Cameron Young, Dominyka Batkovskyte, Miyuki Kitamura, Maria Shvedova, Yutaro Mihara, Jun Akiba, Wen Zhou, Anna Hammarsjö, Gen Nishimura, Shuichi Yatsuga, Giedre Grigelioniene, Tatsuya Kobayashi.

  Mitochondrial diseases are a heterogeneous group of genetic disorders caused by pathogenic variants in genes encoding gene products that regulate mitochondrial function. These genes are located either in the mitochondrial or in the nuclear genome. The TOMM7 gene encodes a regulatory subunit of the translocase of outer mitochondrial membrane (TOM) complex that plays an essential role in translocation of nuclear-encoded mitochondrial proteins into mitochondria. We report an individual with a homozygous variant in TOMM7 (c.73T>C, p.Trp25Arg) that presented with a syndromic short stature, skeletal abnormalities, muscle hypotonia, microvesicular liver steatosis, and developmental delay. Analysis of mouse models strongly suggested that the identified variant is hypomorphic because mice homozygous for this variant showed a milder phenotype than those with homozygous Tomm7 deletion. These Tomm7 mutant mice show pathological changes consistent with mitochondrial dysfunction, including growth defects, severe lipoatrophy, and lipid accumulation in the liver. These mice die prematurely following a rapidly progressive weight loss during the last week of their lives. Tomm7 deficiency causes a unique alteration in mitochondrial function; despite the bioenergetic deficiency, mutant cells show increased oxygen consumption with normal responses to electron transport chain (ETC) inhibitors, suggesting that Tomm7 deficiency leads to an uncoupling between oxidation and ATP synthesis without impairing the function of the tricarboxylic cycle metabolism or ETC. This study presents evidence that a hypomorphic variant in one of the genes encoding a subunit of the TOM complex causes mitochondrial disease.

Keywords:  TOM; TOMM7; developmental delay; fatty liver; growth plate; lipoatrophy; mitochondria; mouse model; skeletal dysplasia; translocase

DOI:  https://doi.org/10.1016/j.xhgg.2022.100148
Trends Cell Biol. 2022 Oct 19. pii: S0962-8924(22)00230-6. [Epub ahead of print]

Multifaceted mitochondrial quality control in brown adipose tissue.

Katia Aquilano, Beiyan Zhou, Jonathan R Brestoff, Daniele Lettieri-Barbato.

  Brown adipose tissue (BAT) controls mammalian core body temperature by non-shivering thermogenesis. BAT is extraordinarily rich in mitochondria, which have the peculiarity of generating heat by uncoupled respiration. Since the mitochondrial activity of BAT is subject to cycles of activation and deactivation in response to environmental temperature changes, an integrated mitochondrial quality control (MQC) system is of fundamental importance to ensure BAT physiology. Here, we provide an overview of the conventional and alternative mechanisms through which thermogenic adipocytes selectively remove damaged parts of mitochondria and how macrophages participate in the MQC system by removing extracellular mitochondrial waste to maintain the thermogenic function of BAT.

Keywords:  adipocytes; extracellular vesicles; immune cells; metabolism; mitochondrial transfer; thermogenesis

DOI:  https://doi.org/10.1016/j.tcb.2022.09.008
Cell Death Differ. 2022 Oct 28.

OPA1 drives macrophage metabolism and functional commitment via p65 signaling.

Ricardo Sánchez-Rodríguez, Caterina Tezze, Andrielly H R Agnellini, Roberta Angioni, Francisca C Venegas, Chiara Cioccarelli, Fabio Munari, Nicole Bertoldi, Marcella Canton, Maria Andrea Desbats, Leonardo Salviati, Rosanna Gissi, Alessandra Castegna, Maria Eugenia Soriano, Marco Sandri, Luca Scorrano, Antonella Viola, Barbara Molon.

Macrophages are essential players for the host response against pathogens, regulation of inflammation and tissue regeneration. The wide range of macrophage functions rely on their heterogeneity and plasticity that enable a dynamic adaptation of their responses according to the surrounding environmental cues. Recent studies suggest that metabolism provides synergistic support for macrophage activation and elicitation of desirable immune responses; however, the metabolic pathways orchestrating macrophage activation are still under scrutiny. Optic atrophy 1 (OPA1) is a mitochondria-shaping protein controlling mitochondrial fusion, cristae biogenesis and respiration; clear evidence shows that the lack or dysfunctional activity of this protein triggers the accumulation of metabolic intermediates of the TCA cycle. In this study, we show that OPA1 has a crucial role in macrophage activation. Selective Opa1 deletion in myeloid cells impairs M1-macrophage commitment. Mechanistically, Opa1 deletion leads to TCA cycle metabolite accumulation and defective NF-κB signaling activation. In an in vivo model of muscle regeneration upon injury, Opa1 knockout macrophages persist within the damaged tissue, leading to excess collagen deposition and impairment in muscle regeneration. Collectively, our data indicate that OPA1 is a key metabolic driver of macrophage functions.

DOI: https://doi.org/10.1038/s41418-022-01076-y
Aging Cell. 2022 Oct 28. e13731

SIAH proteins regulate the degradation and intra-mitochondrial aggregation of PINK1: Implications for mitochondrial pathology in Parkinson's disease.

Fatimah Abd Elghani, Hazem Safory, Haya Hamza, Mor Savyon, Malik Farhoud, Michal Toren-Hershoviz, Zagorka Vitic, Kirsten Ebanks, Vered Shani, Sleman Bisharat, Lihi Shaulov, Claude Brodski, Zhiyin Song, Rina Bandopadhyay, Simone Engelender.

  Parkinson's disease (PD) is characterized by degeneration of neurons, particularly dopaminergic neurons in the substantia nigra. PD brains show accumulation of α-synuclein in Lewy bodies and accumulation of dysfunctional mitochondria. However, the mechanisms leading to mitochondrial pathology in sporadic PD are poorly understood. PINK1 is a key for mitophagy activation and recycling of unfit mitochondria. The activation of mitophagy depends on the accumulation of uncleaved PINK1 at the outer mitochondrial membrane and activation of a cascade of protein ubiquitination at the surface of the organelle. We have now found that SIAH3, a member of the SIAH proteins but lacking ubiquitin-ligase activity, is increased in PD brains and cerebrospinal fluid and in neurons treated with α-synuclein preformed fibrils (α-SynPFF). We also observed that SIAH3 is aggregated together with PINK1 in the mitochondria of PD brains. SIAH3 directly interacts with PINK1, leading to their intra-mitochondrial aggregation in cells and neurons and triggering a cascade of toxicity with PINK1 inactivation along with mitochondrial depolarization and neuronal death. We also found that SIAH1 interacts with PINK1 and promotes ubiquitination and proteasomal degradation of PINK1. Similar to the dimerization of SIAH1/SIAH2, SIAH3 interacts with SIAH1, promoting its translocation to mitochondria and preventing its ubiquitin-ligase activity toward PINK1. Our results support the notion that the increase in SIAH3 and intra-mitochondrial aggregation of SIAH3-PINK1 may mediate α-synuclein pathology by promoting proteotoxicity and preventing the elimination of dysfunctional mitochondria. We consider it possible that PINK1 activity is decreased in sporadic PD, which impedes proper mitochondrial renewal in the disease.

Keywords:  PINK1; Parkinson's disease; SIAH1; SIAH3; intra-mitochondrial protein aggregation; mitochondrial dysfunction; mitophagy; ubiquitin

DOI:  https://doi.org/10.1111/acel.13731
J Biol Chem. 2022 Oct 19. pii: S0021-9258(22)01063-8. [Epub ahead of print] 102620

Structural studies of human fission protein FIS1 reveal a dynamic region important for GTPase DRP1 recruitment and mitochondrial fission.

John M Egner, Kelsey A Nolden, Megan C Harwig, Ryan P Bonate, Jaime De Anda, Maxx H Tessmer, Elizabeth L Noey, Ugochukwu K Ihenacho, Ziwen Liu, Francis C Peterson, Gerard C L Wong, Michael E Widlansky, R Blake Hill.

  Fission protein 1 (FIS1) and dynamin-related protein 1 (DRP1) were initially described as being evolutionarily conserved for mitochondrial fission, yet in humans the role of FIS1 in this process is unclear and disputed by many. In budding yeast where Fis1p helps to recruit the DRP1 ortholog from the cytoplasm to mitochondria for fission, an N-terminal "arm" of Fis1p is required for function. The yeast Fis1p arm interacts intramolecularly with a conserved tetratricopeptide repeat (TPR) core and governs in vitro interactions with yeast DRP1. In human FIS1, NMR and X-ray structures show different arm conformations, but its importance for human DRP1 recruitment is unknown. Here, we use MD simulations and comparisons to experimental NMR chemical shifts to show the human FIS1 arm can adopt an intramolecular conformation akin to that observed with yeast Fis1p. This finding is further supported through intrinsic tryptophan fluorescence and NMR experiments on human FIS1 with and without the arm. Using NMR, we observed the human FIS1 arm is also sensitive to environmental changes. We reveal the importance of these findings in cellular studies where removal of the FIS1 arm reduces DRP1 recruitment and mitochondrial fission similar to the yeast system. Moreover, we determined that expression of mitophagy adaptor TBC1D15 can partially rescue arm-less FIS1 in a manner reminiscent of expression of the adaptor Mdv1p in yeast. These findings point to conserved features of FIS1 important for its activity in mitochondrial morphology. More generally, other TPR-containing proteins are flanked by disordered arms/tails, suggesting possible common regulatory mechanisms.

Keywords:  fission; intrinsic disordered region; mitochondria; molecular dynamics; nuclear magnetic resonance (NMR); protein dynamics; protein structure; tetratricopeptide repeat (TPR)

DOI:  https://doi.org/10.1016/j.jbc.2022.102620
Cell Death Dis. 2022 Oct 26. 13(10): 899

The oncoprotein MUC1 facilitates breast cancer progression by promoting Pink1-dependent mitophagy via ATAD3A destabilization.

Quanfu Li, Yunkai Chu, Shengze Li, Liping Yu, Huayun Deng, Chunhua Liao, Xiaodong Liao, Chihyu Yang, Min Qi, Jinke Cheng, Guoqiang Chen, Lei Huang.

Mitophagy is a vital process that controls mitochondria quality, dysregulation of which can promote cancer. Oncoprotein mucin 1 (MUC1) targets mitochondria to attenuate drug-induced apoptosis. However, little is known about whether and how MUC1 contributes to mitochondrial homeostasis in cancer cells. We identified a novel role of MUC1 in promoting mitophagy. Increased mitophagy is coupled with the translocation of MUC1 to mitochondria, where MUC1 interacts with and induces degradation of ATPase family AAA domain-containing 3A (ATAD3A), resulting in protection of PTEN-induced kinase 1 (Pink1) from ATAD3A-mediated cleavage. Interestingly, MUC1-induced mitophagy is associated with increased oncogenicity of cancer cells. Similarly, inhibition of mitophagy significantly suppresses MUC1-induced cancer cell activity in vitro and in vivo. Consistently, MUC1 and ATAD3A protein levels present an inverse relationship in tumor tissues of breast cancer patients. Our data validate that MUC1/ATAD3A/Pink1 axis-mediated mitophagy constitutes a novel mechanism for maintaining the malignancy of cancer cells, providing a novel therapeutic approach for MUC1-positive cancers.

DOI: https://doi.org/10.1038/s41419-022-05345-z
J Neurosci. 2022 Oct 24. pii: JN-RM-0545-22. [Epub ahead of print]

The absence of Parkin does not promote dopamine or mitochondrial dysfunction in PolgAD257A/D257A mitochondrial mutator mice.

Laura Scott, Senthilkumar S Karuppagounder, Stewart Neifert, Bong Gu Kang, Hu Wang, Valina L Dawson, Ted M Dawson.

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. In this study, we generated a transgenic model by crossing germline Parkin-/- mice with PolgAD257A mice, an established model of premature aging and mitochondrial stress. We hypothesized that loss of Parkin-/- in PolgAD257A/D257A mice would exacerbate mitochondrial dysfunction, leading to loss of dopamine neurons and nigral-striatal specific neurobehavioral motor dysfunction. We found that aged Parkin-/-/PolgAD257A/D257A male and female mice exhibited severe behavioral deficits, nonspecific to the nigral-striatal pathway, with neither dopaminergic neurodegeneration nor reductions in striatal dopamine. We saw no difference in expression levels of nuclear-encoded subunits of mitochondrial markers and mitochondrial complex I and IV activities, though we did observe substantial reductions in mitochondrial-encoded COX41I, indicating mitochondrial dysfunction as a result of PolgAD257A/D257A mtDNA mutations. Expression levels of mitophagy markers LC3I/LC3II remained unchanged between cohorts, suggesting no overt mitophagy defects. Expression levels of the parkin substrates, VDAC, NLRP3, and AIMP2 remained unchanged, suggesting no parkin dysfunction. In summary, we were unable to observe dopaminergic neurodegeneration with corresponding nigral-striatal neurobehavioral deficits, nor Parkin or mitochondrial dysfunction in Parkin-/-/PolgAD257A/D257A mice. These findings support a lack of synergism of Parkin loss on mitochondrial dysfunction in mouse models of mitochondrial deficits.SIGNIFICANCE STATEMENT:Producing a mouse model of PD that is etiologically relevant, recapitulates clinical hallmarks, and exhibits reproducible results is crucial to understanding the underlying pathology and in developing disease-modifying therapies. Here, we show that Parkin-/-/PolgAD257A/D257A mice, a previously reported PD mouse model, fails to reproduce a Parkinsonian phenotype. We show that these mice do not display dopaminergic neurodegeneration nor nigral-striatal-dependent motor deficits. Furthermore, we report that Parkin loss does not synergize with mitochondrial dysfunction. Our results demonstrate that Parkin-/-/PolgAD257A/D257A mice are not a reliable model for PD and adds to a growing body of work demonstrating that Parkin loss does not synergize with mitochondrial dysfunction in mouse models of mitochondrial deficits.

DOI: https://doi.org/10.1523/JNEUROSCI.0545-22.2022
Life Sci. 2022 Oct 22. pii: S0024-3205(22)00812-8. [Epub ahead of print] 121112

TRPV4 interacts with MFN2 and facilitates endoplasmic reticulum-mitochondrial contact points for Ca2+-buffering.

Tusar Kanta Acharya, Ashutosh Kumar, Shamit Kumar, Chandan Goswami.

  AIM: Mitochondrial fission-fusion events, distribution, and Ca2+-buffering abilities are relevant for several diseases, yet are poorly understood events. TRPV4 channels are a group of thermosensitive ion channel which regulate cellular and mitochondrial Ca2+-level. The underlying mechanisms of the change in mitochondrial dynamics upon modulation of TRPV4 channel are ill explored.MAIN METHODS: We have used TRPV4 expressing stable cell line CHO-K1-V4 and compared with CHO-K1-MOCK as a control cell. We have also used mouse bone marrow derived mesenchymal stem cells and purified mitochondria from mouse brain for the interaction study.
KEY FINDINGS: Now we demonstrate that expression and/or pharmacological modulation of TRPV4 regulates mitochondrial morphologies and Ca2+-level. TRPV4 interacts with MFN1/MFN2, the mitochondrial regulatory factors. TRPV4 regulates ER-mito contact points. We used different cellular conditions where cytosolic or ER Ca2+-levels were pharmacologically altered. Analysis of ~55,000 mitochondrial particles, ~125,000 ER-mito contact points from ~900 cells in 10 different cellular conditions suggest that ER-mito contact points are inversely regulated with mitochondrial Ca2+-levels where TRPV4 always elevates mitochondrial Ca2+-levels. These findings link TRPV4 with MFN2-mediated diseases and suggest that different TRPV4-induced channelopathies are likely due to mitochondrial abnormalities.

Keywords:  CMT disease; Ca(2+)-chelation; Channelopathy; Mitochondria-associated ER membrane; Mitochondrial fission-fusion; Thermosensitive ion channel

DOI:  https://doi.org/10.1016/j.lfs.2022.121112
Antioxid Redox Signal. 2022 Oct 27.

Molecular determinants of mitochondrial shape and function and their role in glaucoma.

Oleh Khalimonchuk, Donald Frederick Becker.

SIGNIFICANCE: Cells depend on well-functioning mitochondria for essential processes such as energy production, redox signaling, coordination of metabolic pathways, and cofactor biosynthesis. Mitochondrial dysfunction, metabolic decline and protein stress have been implicated in the etiology of multiple late-onset diseases, including various ataxias, diabetes, sarcopenia, neuromuscular disorders, and neurodegenerative diseases such as parkinsonism, amyotrophic lateral sclerosis and glaucoma.RECENT ADVANCES: New evidence supports increased energy metabolism protects neuron function during aging. Key energy metabolic enzymes, however, are susceptible to oxidative damage making it imperative that the mitochondrial proteome is protected. Over 40 different enzymes have been identified as important factors for guarding mitochondrial health and maintaining a dynamic pool of mitochondria.
CRITICAL ISSUES: Understanding shared mechanisms of age-related disorders of neurodegenerative diseases such as glaucoma, Alzheimer's Disease, and Parkinson's Disease (PD) is important for developing new therapies. Functional mitochondrial shape and dynamics rely on complex interactions between mitochondrial proteases and membrane proteins. Identifying the sequence of molecular events that lead to mitochondrial dysfunction and metabolic stress is a major challenge.
FUTURE DIRECTIONS: A critical need exists for new strategies that reduce mitochondrial protein stress and promote mitochondrial dynamics in age-related neurological disorders. Discovering how mitochondria-associated degradation is related to proteostatic mechanisms in mitochondrial compartments may reveal new opportunities for therapeutic interventions. Also, little is known about how protein and membrane contacts in the inner and outer mitochondrial membrane are regulated, even though they are pivotal for mitochondrial architecture. Future work will need to delineate the molecular details of these processes.

DOI: https://doi.org/10.1089/ars.2022.0124
iScience. 2022 Nov 18. 25(11): 105266

Cytoplasmic and mitochondrial aminoacyl-tRNA synthetases differentially regulate lifespan in Caenorhabditis elegans.

Tianlin Zheng, Qiang Luo, Chengxuan Han, Jiejun Zhou, Jianke Gong, Lei Chun, X Z Shawn Xu, Jianfeng Liu.

  Reducing the rate of translation promotes longevity in multiple organisms, representing a conserved mechanism for lifespan extension. Aminoacyl-tRNA synthetases (ARSs) catalyze the loading of amino acids to their cognate tRNAs, thereby playing an essential role in translation. Mutations in ARS genes are associated with various human diseases. However, little is known about the role of ARSs in aging, particularly whether and how these genes regulate lifespan. Here, using Caenorhabditis elegans as a model, we systematically characterized the role of all three types of ARS genes in lifespan regulation, including mitochondrial, cytoplasmic, and cyto-mito bifunctional ARS genes. We found that, as expected, RNAi knockdown of mitochondrial ARS genes extended lifespan. Surprisingly, knocking down cytoplasmic or cyto-mito bifunctional ARS genes shortened lifespan, though such treatment reduced the rate of translation. These results reveal opposing roles of mitochondrial and cytoplasmic ARSs in lifespan regulation, demonstrating that inhibiting translation may not always extend lifespan.

Keywords:  Cell biology; Molecular biology

DOI:  https://doi.org/10.1016/j.isci.2022.105266
Front Cell Dev Biol. 2022 ;10 978142

Mitophagy in the aging nervous system.

Anna Rappe, Thomas G McWilliams.

  Aging is characterised by the progressive accumulation of cellular dysfunction, stress, and inflammation. A large body of evidence implicates mitochondrial dysfunction as a cause or consequence of age-related diseases including metabolic disorders, neuropathies, various forms of cancer and neurodegenerative diseases. Because neurons have high metabolic demands and cannot divide, they are especially vulnerable to mitochondrial dysfunction which promotes cell dysfunction and cytotoxicity. Mitophagy neutralises mitochondrial dysfunction, providing an adaptive quality control strategy that sustains metabolic homeostasis. Mitophagy has been extensively studied as an inducible stress response in cultured cells and short-lived model organisms. In contrast, our understanding of physiological mitophagy in mammalian aging remains extremely limited, particularly in the nervous system. The recent profiling of mitophagy reporter mice has revealed variegated vistas of steady-state mitochondrial destruction across different tissues. The discovery of patients with congenital autophagy deficiency provokes further intrigue into the mechanisms that underpin neural integrity. These dimensions have considerable implications for targeting mitophagy and other degradative pathways in age-related neurological disease.

Keywords:  aging; autophagy; brain; disease; longevity; mitochondria; mitophagy

DOI:  https://doi.org/10.3389/fcell.2022.978142
Cell Mol Life Sci. 2022 Oct 25. 79(11): 565

Basal Gp78-dependent mitophagy promotes mitochondrial health and limits mitochondrial ROS.

Parsa Alan, Kurt R Vandevoorde, Bharat Joshi, Ben Cardoen, Guang Gao, Yahya Mohammadzadeh, Ghassan Hamarneh, Ivan R Nabi.

  Mitochondria are major sources of cytotoxic reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, that when uncontrolled contribute to cancer progression. Maintaining a finely tuned, healthy mitochondrial population is essential for cellular homeostasis and survival. Mitophagy, the selective elimination of mitochondria by autophagy, monitors and maintains mitochondrial health and integrity, eliminating damaged ROS-producing mitochondria. However, mechanisms underlying mitophagic control of mitochondrial homeostasis under basal conditions remain poorly understood. E3 ubiquitin ligase Gp78 is an endoplasmic reticulum membrane protein that induces mitochondrial fission and mitophagy of depolarized mitochondria. Here, we report that CRISPR/Cas9 knockout of Gp78 in HT-1080 fibrosarcoma cells increased mitochondrial volume, elevated ROS production and rendered cells resistant to carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-induced mitophagy. These effects were phenocopied by knockdown of the essential autophagy protein ATG5 in wild-type HT-1080 cells. Use of the mito-Keima mitophagy probe confirmed that Gp78 promoted both basal and damage-induced mitophagy. Application of a spot detection algorithm (SPECHT) to GFP-mRFP tandem fluorescent-tagged LC3 (tfLC3)-positive autophagosomes reported elevated autophagosomal maturation in wild-type HT-1080 cells relative to Gp78 knockout cells, predominantly in proximity to mitochondria. Mitophagy inhibition by either Gp78 knockout or ATG5 knockdown reduced mitochondrial potential and increased mitochondrial ROS. Live cell analysis of tfLC3 in HT-1080 cells showed the preferential association of autophagosomes with mitochondria of reduced potential. Xenograft tumors of HT-1080 knockout cells show increased labeling for mitochondria and the cell proliferation marker Ki67 and reduced labeling for the TUNEL cell death reporter. Basal Gp78-dependent mitophagic flux is, therefore, selectively associated with reduced potential mitochondria promoting maintenance of a healthy mitochondrial population, limiting ROS production and tumor cell proliferation.

Keywords:  GFP-mRFP tandem fluorescent-tagged LC3; Gp78 ubiquitin ligase; Mitochondria; Mitophagy; Reactive oxygen species; SPECHT; Spot detection

DOI:  https://doi.org/10.1007/s00018-022-04585-8
Autophagy. 2022 Oct 25.

PINK1-PRKN mediated mitophagy: differences between in vitro and in vivo models.

Rui Han, Yanting Liu, Shihua Li, Xiao-Jiang Li, Weili Yang.

  Mitophagy is a key intracellular process that selectively removes damaged mitochondria to prevent their accumulation that can cause neuronal degeneration. During mitophagy, PINK1 (PTEN induced kinase 1), a serine/threonine kinase, works with PRKN/parkin, an E3 ubiquitin ligase, to target damaged mitochondria to the lysosome for degradation. Mutations in the PINK1 and PRKN genes cause early-onset Parkinson disease that is also associated with mitochondrial dysfunction. There are a large number of reports indicating the critical role of PINK1 in mitophagy. However, most of these findings were obtained from in vitro experiments with exogenous PINK1 expression and acute damage of mitochondria by toxins. Recent studies using novel animal models suggest that PINK1-PRKN can also function independent of mitochondria. In this review, we highlight the major differences between in vitro and in vivo models for investigating PINK1 and discuss the potential mechanisms underlying these differences with the aim of understanding how PINK1 functions under different circumstances.

Keywords:  Mitochondria dysfunction; PINK1; PRKN; Parkinson disease; mitophagy

DOI:  https://doi.org/10.1080/15548627.2022.2139080
Biochem Biophys Res Commun. 2022 Oct 19. pii: S0006-291X(22)01454-1. [Epub ahead of print]635 218-226

The Dep1 protein: A new regulator of mitophagy in yeast.

Nadine Camougrand, Pierre Vigié, Jim Dompierre, Aurélie Massoni-Laporte, Jean Paul Lasserre, Ingrid Bhatia-Kiššová.

Mitochondria play a crucial role in most eukaryotic cells. Mitophagy is a process that controls their quality and quantity within the cells. The outer mitochondrial membrane protein, Atg32, serves as the mitophagic receptor. It interacts with the Atg11 protein to initiate mitophagy and with the Atg8 protein to ensure the engulfment of mitochondria into the autophagosomes for elimination. The Atg32 protein is regulated at the transcriptional level but also by posttranslational modifications. In this study, we described a new regulator of mitophagy, the protein Dep1, identified as a part of the Rpd3L histone deacetylase complex. We showed that the Dep1 protein is localized in the nucleus and associated with mitochondria. This protein is needed for mitophagy and to regulate the transcription and expression of the Atg32 protein. The absence of this protein affects the mitophagy process induced by either starvation for nitrogen or the stationary phase of growth.

DOI: https://doi.org/10.1016/j.bbrc.2022.10.052