bims-mitdyn 2024-03-03 papers

bims-mitdyn

Biomed News

on Mitochondrial dynamics: mechanisms

Issue of 2024–03–03
twelve papers selected by
Edmond Chan, Queen’s University, School of Medicine

PMF-seq: a highly scalable screening strategy for linking genetics to mitochondrial bioenergetics.
Optic atrophy 1 mediates muscle differentiation by promoting a metabolic switch via the supercomplex assembly factor SCAF1.
Tom20 gates PINK1 activity and mediates its tethering of the TOM and TIM23 translocases upon mitochondrial stress.
Triaging of α-helical proteins to the mitochondrial outer membrane by distinct chaperone machinery based on substrate topology.
Chemical inhibition of phosphatidylcholine biogenesis reveals its role in mitochondrial division.
PKM2 diverts glycolytic flux in dependence on mitochondrial one-carbon cycle.
A spatial map of hepatic mitochondria uncovers functional heterogeneity shaped by nutrient-sensing signaling.
FBXL4: safeguarding against mitochondrial depletion through suppression of mitophagy.
Aging STINGs: mitophagy at the crossroads of neuroinflammation.
Mitochondria in disease: changes in shapes and dynamics.
NEMF-mediated Listerin-independent mitochondrial translational surveillance by E3 ligase Pirh2 and mitochondrial protease ClpXP.
Mitochondrial fusion and altered beta-oxidation drive muscle wasting in a Drosophila cachexia model.

Nat Metab. 2024 Feb 27.

PMF-seq: a highly scalable screening strategy for linking genetics to mitochondrial bioenergetics.

Tsz-Leung To, Jason G McCoy, Naomi K Ostriker, Lev S Sandler, Carmen A Mannella, Vamsi K Mootha.

Our current understanding of mitochondrial organelle physiology has benefited from two broad approaches: classically, cuvette-based measurements with suspensions of isolated mitochondria, in which bioenergetic parameters are monitored acutely in response to respiratory chain substrates and inhibitors1-4, and more recently, highly scalable genetic screens for fitness phenotypes associated with coarse-grained properties of the mitochondrial state5-10. Here we introduce permeabilized-cell mitochondrial function sequencing (PMF-seq) to combine strengths of these two approaches to connect genes to detailed bioenergetic phenotypes. In PMF-seq, the plasma membranes within a pool of CRISPR mutagenized cells are gently permeabilized under conditions that preserve mitochondrial physiology, where detailed bioenergetics can be probed in the same way as with isolated organelles. Cells with desired bioenergetic parameters are selected optically using flow cytometry and subjected to next-generation sequencing. Using PMF-seq, we recover genes differentially required for mitochondrial respiratory chain branching and reversibility. We demonstrate that human D-lactate dehydrogenase specifically conveys electrons from D-lactate into cytochrome c to support mitochondrial membrane polarization. Finally, we screen for genetic modifiers of tBID, a pro-apoptotic protein that acts directly and acutely on mitochondria. We find the loss of the complex V assembly factor ATPAF2 acts as a genetic sensitizer of tBID's acute action. We anticipate that PMF-seq will be valuable for defining genes critical to the physiology of mitochondria and other organelles.

DOI: https://doi.org/10.1038/s42255-024-00994-0
iScience. 2024 Mar 15. 27(3): 109164

Optic atrophy 1 mediates muscle differentiation by promoting a metabolic switch via the supercomplex assembly factor SCAF1.

Matthew Triolo, Nicole Baker, Soniya Agarwal, Nikita Larionov, Tina Podinić, Mireille Khacho.

  Myogenic differentiation is integral for the regeneration of skeletal muscle following tissue damage. Though high-energy post-mitotic muscle relies predominantly on mitochondrial respiration, the importance of mitochondrial remodeling in enabling muscle differentiation and the players involved are not fully known. Here we show that the mitochondrial fusion protein OPA1 is essential for muscle differentiation. Our study demonstrates that OPA1 loss or inhibition, through genetic and pharmacological means, abolishes in vivo muscle regeneration and in vitro myotube formation. We show that both the inhibition and genetic deletion of OPA1 prevent the early onset metabolic switch required to drive myoblast differentiation. In addition, we observe an OPA1-dependent upregulation of the supercomplex assembly factor, SCAF1, at the onset of differentiation. Importantly, preventing the upregulation of SCAF1, through OPA1 loss or siRNA-mediated SCAF1 knockdown, impairs metabolic reprogramming and muscle differentiation. These findings reveal the integral role of OPA1 and mitochondrial reprogramming at the onset of myogenic differentiation.

Keywords:  Molecular biology; Physiology

DOI:  https://doi.org/10.1016/j.isci.2024.109164
Proc Natl Acad Sci U S A. 2024 Mar 05. 121(10): e2313540121

Tom20 gates PINK1 activity and mediates its tethering of the TOM and TIM23 translocases upon mitochondrial stress.

Mohamed A Eldeeb, Andrew N Bayne, Armaan Fallahi, Thomas Goiran, Emma J MacDougall, Andrea Soumbasis, Cornelia E Zorca, Jace-Jones Tabah, Rhalena A Thomas, Nathan Karpilovsky, Meghna Mathur, Thomas M Durcan, Jean-François Trempe, Edward A Fon.

  Mutations in PTEN-induced putative kinase 1 (PINK1) cause autosomal recessive early-onset Parkinson's disease (PD). PINK1 is a Ser/Thr kinase that regulates mitochondrial quality control by triggering mitophagy mediated by the ubiquitin (Ub) ligase Parkin. Upon mitochondrial damage, PINK1 accumulates on the outer mitochondrial membrane forming a high-molecular-weight complex with the translocase of the outer membrane (TOM). PINK1 then phosphorylates Ub, which enables recruitment and activation of Parkin followed by autophagic clearance of the damaged mitochondrion. Thus, Parkin-dependent mitophagy hinges on the stable accumulation of PINK1 on the TOM complex. Yet, the mechanism linking mitochondrial stressors to PINK1 accumulation and whether the translocases of the inner membrane (TIMs) are also involved remain unclear. Herein, we demonstrate that mitochondrial stress induces the formation of a PINK1-TOM-TIM23 supercomplex in human cultured cell lines, dopamine neurons, and midbrain organoids. Moreover, we show that PINK1 is required to stably tether the TOM to TIM23 complexes in response to stress such that the supercomplex fails to accumulate in cells lacking PINK1. This tethering is dependent on an interaction between the PINK1 N-terminal-C-terminal extension module and the cytosolic domain of the Tom20 subunit of the TOM complex, the disruption of which, by either designer or PD-associated PINK1 mutations, inhibits downstream mitophagy. Together, the findings provide key insight into how PINK1 interfaces with the mitochondrial import machinery, with important implications for the mechanisms of mitochondrial quality control and PD pathogenesis.

Keywords:  PINK1; mitochondrial import; mitochondrial quality control; mitophagy; proteolysis

DOI:  https://doi.org/10.1073/pnas.2313540121
Mol Cell. 2024 Feb 27. pii: S1097-2765(24)00095-9. [Epub ahead of print]

Triaging of α-helical proteins to the mitochondrial outer membrane by distinct chaperone machinery based on substrate topology.

Gayathri Muthukumar, Taylor A Stevens, Alison J Inglis, Theodore K Esantsi, Reuben A Saunders, Fabian Schulte, Rebecca M Voorhees, Alina Guna, Jonathan S Weissman.

  Mitochondrial outer membrane ⍺-helical proteins play critical roles in mitochondrial-cytoplasmic communication, but the rules governing the targeting and insertion of these biophysically diverse proteins remain unknown. Here, we first defined the complement of required mammalian biogenesis machinery through genome-wide CRISPRi screens using topologically distinct membrane proteins. Systematic analysis of nine identified factors across 21 diverse ⍺-helical substrates reveals that these components are organized into distinct targeting pathways that act on substrates based on their topology. NAC is required for the efficient targeting of polytopic proteins, whereas signal-anchored proteins require TTC1, a cytosolic chaperone that physically engages substrates. Biochemical and mutational studies reveal that TTC1 employs a conserved TPR domain and a hydrophobic groove in its C-terminal domain to support substrate solubilization and insertion into mitochondria. Thus, the targeting of diverse mitochondrial membrane proteins is achieved through topological triaging in the cytosol using principles with similarities to ER membrane protein biogenesis systems.

Keywords:  CRISPR; NAC; TTC1; cell biology; cytosolic targeting; genetic screens; membrane protein insertion; mitochondrial outer membrane; topology

DOI:  https://doi.org/10.1016/j.molcel.2024.01.028
iScience. 2024 Mar 15. 27(3): 109189

Chemical inhibition of phosphatidylcholine biogenesis reveals its role in mitochondrial division.

Hiroya Shiino, Shinya Tashiro, Michiko Hashimoto, Yuki Sakata, Takamitsu Hosoya, Toshiya Endo, Hirotatsu Kojima, Yasushi Tamura.

  Phospholipids are major components of biological membranes and play structural and regulatory roles in various biological processes. To determine the biological significance of phospholipids, the use of chemical inhibitors of phospholipid metabolism offers an effective approach; however, the availability of such compounds is limited. In this study, we performed a chemical-genetic screening using yeast and identified small molecules capable of inhibiting phosphatidylcholine (PC) biogenesis, which we designated PC inhibitors 1, 2, 3, and 4 (PCiB-1, 2, 3, and 4). Biochemical analyses indicated that PCiB-2, 3, and 4 inhibited the phosphatidylethanolamine (PE) methyltransferase activity of Cho2, whereas PCiB-1 may inhibit PE transport from mitochondria to the endoplasmic reticulum (ER). Interestingly, we found that PCiB treatment resulted in mitochondrial fragmentation, which was suppressed by expression of a dominant-negative mutant of the mitochondrial division factor Dnm1. These results provide evidence that normal PC biogenesis is important for the regulation of mitochondrial division.

Keywords:  Biochemistry; Biological sciences; Cell biology

DOI:  https://doi.org/10.1016/j.isci.2024.109189
Cell Rep. 2024 Feb 28. pii: S2211-1247(24)00196-7. [Epub ahead of print]43(3): 113868

PKM2 diverts glycolytic flux in dependence on mitochondrial one-carbon cycle.

Mohaned Benzarti, Laura Neises, Anais Oudin, Christina Krötz, Elodie Viry, Ernesto Gargiulo, Coralie Pulido, Maryse Schmoetten, Vitaly Pozdeev, Nadia I Lorenz, Michael W Ronellenfitsch, David Sumpton, Marc Warmoes, Christian Jaeger, Antoine Lesur, Björn Becker, Etienne Moussay, Jerome Paggetti, Simone P Niclou, Elisabeth Letellier, Johannes Meiser.

  Modeling tumor metabolism in vitro remains challenging. Here, we used galactose as an in vitro tool compound to mimic glycolytic limitation. In contrast to the established idea that high glycolytic flux reduces pyruvate kinase isozyme M2 (PKM2) activity to support anabolic processes, we have discovered that glycolytic limitation also affects PKM2 activity. Surprisingly, despite limited carbon availability and energetic stress, cells induce a near-complete block of PKM2 to divert carbons toward serine metabolism. Simultaneously, TCA cycle flux is sustained, and oxygen consumption is increased, supported by glutamine. Glutamine not only supports TCA cycle flux but also serine synthesis via distinct mechanisms that are directed through PKM2 inhibition. Finally, deleting mitochondrial one-carbon (1C) cycle reversed the PKM2 block, suggesting a potential formate-dependent crosstalk that coordinates mitochondrial 1C flux and cytosolic glycolysis to support cell survival and proliferation during nutrient-scarce conditions.

Keywords:  CP: Cancer; CP: Metabolism

DOI:  https://doi.org/10.1016/j.celrep.2024.113868
Nat Commun. 2024 Feb 28. 15(1): 1799

A spatial map of hepatic mitochondria uncovers functional heterogeneity shaped by nutrient-sensing signaling.

Sun Woo Sophie Kang, Rory P Cunningham, Colin B Miller, Lauryn A Brown, Constance M Cultraro, Adam Harned, Kedar Narayan, Jonathan Hernandez, Lisa M Jenkins, Alexei Lobanov, Maggie Cam, Natalie Porat-Shliom.

In the liver, mitochondria are exposed to different concentrations of nutrients due to their spatial positioning across the periportal and pericentral axis. How the mitochondria sense and integrate these signals to respond and maintain homeostasis is not known. Here, we combine intravital microscopy, spatial proteomics, and functional assessment to investigate mitochondrial heterogeneity in the context of liver zonation. We find that periportal and pericentral mitochondria are morphologically and functionally distinct; beta-oxidation is elevated in periportal regions, while lipid synthesis is predominant in the pericentral mitochondria. In addition, comparative phosphoproteomics reveals spatially distinct patterns of mitochondrial composition and potential regulation via phosphorylation. Acute pharmacological modulation of nutrient sensing through AMPK and mTOR shifts mitochondrial phenotypes in the periportal and pericentral regions, linking nutrient gradients across the lobule and mitochondrial heterogeneity. This study highlights the role of protein phosphorylation in mitochondrial structure, function, and overall homeostasis in hepatic metabolic zonation. These findings have important implications for liver physiology and disease.

DOI: https://doi.org/10.1038/s41467-024-45751-9
Autophagy. 2024 Feb 29. 1-3

FBXL4: safeguarding against mitochondrial depletion through suppression of mitophagy.

Prajakta Kulkarni, Giang Thanh Nguyen-Dien, Keri-Lyn Kozul, Julia K Pagan.

  Mitophagy is a critical mitochondrial quality control process that selectively removes dysfunctional or excess mitochondria through the autophagy-lysosome system. The process is tightly controlled to ensure cellular and physiological homeostasis. Insufficient mitophagy can result in failure to remove damaged mitochondria and consequent cellular degeneration, but it is equally important to appropriately restrain mitophagy to prevent excessive mitochondrial depletion. Here, we discuss our recent discovery that the SKP1-CUL1-F-box (SCF)-FBXL4 (F-box and leucine-rich repeat protein 4) E3 ubiquitin ligase localizes to the mitochondrial outer membrane, where it constitutively mediates the ubiquitination and degradation of BNIP3L/NIX and BNIP3 mitophagy receptors to suppress mitophagy. The post-translational regulation of BNIP3L and BNIP3 is disrupted in mitochondrial DNA depletion syndrome 13 (MTDPS13), a multi-systemic disorder caused by mutations in the FBXL4 gene and characterized by elevated mitophagy and mitochondrial DNA/mtDNA depletion in patient fibroblasts. Our results demonstrate that mitophagy is not solely stimulated in response to specific conditions but is instead also actively suppressed through the continuous degradation of BNIP3L and BNIP3 mediated by the SCF-FBXL4 ubiquitin ligase. Thus, cellular conditions or signaling events that prevent the FBXL4-mediated turnover of BNIP3L and BNIP3 on specific mitochondria are expected to facilitate their selective removal.

Keywords:  BNIP3; BNIP3L/NIX; FBXL4; MTDPS13; mitophagy; ubiquitin ligase

DOI:  https://doi.org/10.1080/15548627.2024.2318077
Autophagy. 2024 Feb 27.

Aging STINGs: mitophagy at the crossroads of neuroinflammation.

Juan Ignacio Jiménez-Loygorri, Patricia Boya.

  Loss of proteostasis and dysregulated mitochondrial function are part of the traditional hallmarks of aging, and in their last revision impaired macroautophagy and chronic inflammation are also included. Mitophagy is at the intersection of all these processes but whether it undergoes age-associated perturbations was not known. In our recent work, we performed a systematic and systemic analysis of mitolysosome levels in mice and found that, despite the already-known decrease in non-selective macroautophagy, mitophagy remains stable or increases upon aging in all tissues analyzed and is mediated by the PINK1-PRKN-dependent pathway. Further analyses revealed a concomitant increase in mtDNA leakage into the cytosol and activation of the CGAS-STING1 inflammation axis. Notably, both phenomena are also observed in primary fibroblasts from aged human donors. We hypothesized that mitophagy might be selectively upregulated during aging to improve mitochondrial fitness and reduce mtDNA-induced inflammation. Treatment with the mitophagy inducer urolithin A alleviates age-associated neurological decline, including improved synaptic connectivity, cognitive memory and visual function. Supporting our initial hypothesis, urolithin A reduces the levels of cytosolic mtDNA, CGAS-STING1 activation and neuroinflammation. Finally, using an in vitro model of mitochondrial membrane permeabilization we validated that PINK1-PRKN-mediated mitophagy is essential to resolve cytosolic mtDNA-triggered inflammation. These findings open up an integrative approach to tackle aging and increase healthspan via mitophagy induction.

Keywords:  Inflammation; PINK1; Parkin; mitochondria; mtDNA; retina

DOI:  https://doi.org/10.1080/15548627.2024.2322421
Trends Biochem Sci. 2024 Feb 23. pii: S0968-0004(24)00031-8. [Epub ahead of print]

Mitochondria in disease: changes in shapes and dynamics.

Brenita C Jenkins, Kit Neikirk, Prasanna Katti, Steven M Claypool, Annet Kirabo, Melanie R McReynolds, Antentor Hinton.

  Mitochondrial structure often determines the function of these highly dynamic, multifunctional, eukaryotic organelles, which are essential for maintaining cellular health. The dynamic nature of mitochondria is apparent in descriptions of different mitochondrial shapes [e.g., donuts, megamitochondria (MGs), and nanotunnels] and crista dynamics. This review explores the significance of dynamic alterations in mitochondrial morphology and regulators of mitochondrial and cristae shape. We focus on studies across tissue types and also describe new microscopy techniques for detecting mitochondrial morphologies both in vivo and in vitro that can improve understanding of mitochondrial structure. We highlight the potential therapeutic benefits of regulating mitochondrial morphology and discuss prospective avenues to restore mitochondrial bioenergetics to manage diseases related to mitochondrial dysfunction.

Keywords:  clinical diagnostics; contact sites; cristae dynamics; microscopy; mitochondrial morphology; mitochondrial shapes

DOI:  https://doi.org/10.1016/j.tibs.2024.01.011
Cell Rep. 2024 Feb 26. pii: S2211-1247(24)00188-8. [Epub ahead of print]43(3): 113860

NEMF-mediated Listerin-independent mitochondrial translational surveillance by E3 ligase Pirh2 and mitochondrial protease ClpXP.

Liang Lv, Jinyou Mo, Yumin Qing, Shuchao Wang, Leijie Chen, Anna Mei, Ru Xu, Hualin Huang, Jieqiong Tan, Yifu Li, Jia Liu.

  The ribosome-associated protein quality control (RQC) pathway acts as a translational surveillance mechanism to maintain proteostasis. In mammalian cells, the cytoplasmic RQC pathway involves nuclear export mediator factor (NEMF)-dependent recruitment of the E3 ligase Listerin to ubiquitinate ribosome-stalled nascent polypeptides on the lysine residue for degradation. However, the quality control of ribosome-stalled nuclear-encoded mitochondrial nascent polypeptides remains elusive, as these peptides can be partially imported into mitochondria through translocons, restricting accessibility to the lysine by Listerin. Here, we identify a Listerin-independent organelle-specific mitochondrial RQC pathway that acts on NEMF-mediated carboxy-terminal poly-alanine modification. In the pathway, mitochondrial proteins carrying C-end poly-Ala tails are recognized by the cytosolic E3 ligase Pirh2 and the ClpXP protease in the mitochondria, which coordinately clear ribosome-stalled mitochondrial nascent polypeptides. Defects in this elimination pathway result in NEMF-mediated aggregates and mitochondrial integrity failure, thus providing a potential molecular mechanism of the RQC pathway in mitochondrial-associated human diseases.

Keywords:  CP: Microbiology; CP: Molecular biology; ClpXP; Listerin; NEMF; Pirh2; mitochondrion

DOI:  https://doi.org/10.1016/j.celrep.2024.113860
EMBO Rep. 2024 Mar 01.

Mitochondrial fusion and altered beta-oxidation drive muscle wasting in a Drosophila cachexia model.

Callum Dark, Nashia Ali, Sofya Golenkina, Vaibhav Dhyani, Ronnie Blazev, Benjamin L Parker, Kate T Murphy, Gordon S Lynch, Tarosi Senapati, S Sean Millard, Sarah M Judge, Andrew R Judge, Lopamudra Giri, Sarah M Russell, Louise Y Cheng.

  Cancer cachexia is a tumour-induced wasting syndrome, characterised by extreme loss of skeletal muscle. Defective mitochondria can contribute to muscle wasting; however, the underlying mechanisms remain unclear. Using a Drosophila larval model of cancer cachexia, we observed enlarged and dysfunctional muscle mitochondria. Morphological changes were accompanied by upregulation of beta-oxidation proteins and depletion of muscle glycogen and lipid stores. Muscle lipid stores were also decreased in Colon-26 adenocarcinoma mouse muscle samples, and expression of the beta-oxidation gene CPT1A was negatively associated with muscle quality in cachectic patients. Mechanistically, mitochondrial defects result from reduced muscle insulin signalling, downstream of tumour-secreted insulin growth factor binding protein (IGFBP) homologue ImpL2. Strikingly, muscle-specific inhibition of Forkhead box O (FOXO), mitochondrial fusion, or beta-oxidation in tumour-bearing animals preserved muscle integrity. Finally, dietary supplementation with nicotinamide or lipids, improved muscle health in tumour-bearing animals. Overall, our work demonstrates that muscle FOXO, mitochondria dynamics/beta-oxidation and lipid utilisation are key regulators of muscle wasting in cancer cachexia.

Keywords:   Drosophila ; Cachexia; Lipid Metabolism; Muscle

DOI:  https://doi.org/10.1038/s44319-024-00102-z