bims-mitpro Biomed News
on Mitochondrial proteostasis
Issue of 2025–03–09
nine papers selected by
Andreas Kohler, Umeå University
  1. Novel reporter of the PINK1-Parkin mitophagy pathway identifies its damage sensor in the import gate.
  2. Cytoplasmic ribosomes on mitochondria alter the local membrane environment for protein import.
  3. PPTC7 acts as an essential co-factor of the SCFFBXL4 ubiquitin ligase complex to restrict BNIP3/3L-dependent mitophagy.
  4. Mitochondrial proteostasis and cellular health: insights from chaperones and autophagy.
  5. Mitochondrial accumulation and lysosomal dysfunction result in mitochondrial plaques in Alzheimer's disease.
  6. Structural basis for the allosteric activation of Lon by the heat shock protein LarA.
  7. SNX10 functions as a modulator of piecemeal mitophagy and mitochondrial bioenergetics.
  8. Substrate Recognition and Cleavage-Site Preferences of Lon Protease.
  9. Multi-omics-based phenotyping of AFG3L2-mutant lymphoblasts determines key factors of a pathophysiological interplay between mitochondrial vulnerability and neurodegeneration in spastic ataxia type 5.
  1. bioRxiv. 2025 Feb 20. pii: 2025.02.19.639160. [Epub ahead of print]
    Novel reporter of the PINK1-Parkin mitophagy pathway identifies its damage sensor in the import gate.
    Julia A Thayer, Jennifer D Petersen, Xiaoping Huang, James Hawrot, Daniel M Ramos, Shiori Sekine, Yan Li, Michael E Ward, Derek P Narendra.
      Damaged mitochondria can be cleared from the cell by mitophagy, using a pathway formed by the recessive Parkinson's disease genes PINK1 and Parkin. How mitochondrial damage is sensed by the PINK1-Parkin pathway, however, remains uncertain. Here, using a Parkin substrate-based reporter in genome-wide screens, we identified that diverse forms of mitochondrial damage converge on loss of mitochondrial membrane potential (MMP) to activate PINK1. Consistently, the MMP but not the presequence translocase-associated motor (PAM) import motor provided the essential driving force for endogenous PINK1 import through the inner membrane translocase TIM23. In the absence of TIM23, PINK1 arrested in the translocase of the outer membrane (TOM) during import. The energy-state outside of the mitochondria further modulated the pathway by controlling the rate of new PINK1 synthesis. Our results identify separation of PINK1 from TOM by the MMP, as the key damage-sensing switch in the PINK1-Parkin mitophagy pathway.
    Highlights: MFN2-Halo is a quantitative single-cell reporter of PINK1-Parkin activation.Diverse forms of mitochondrial damage, identified in whole-genome screens, activate the PINK1-Parkin pathway by disrupting the mitochondrial membrane potential (MMP).The primary driving force for endogenous PINK1 import through the TIM23 translocase is the MMP with the PAM import motor playing a supporting role.Loss of TIM23 is sufficient to stabilize PINK1 in the TOM complex and activate Parkin.
    DOI:  https://doi.org/10.1101/2025.02.19.639160
  2. J Cell Biol. 2025 Apr 07. pii: e202407110. [Epub ahead of print]224(4):
    Cytoplasmic ribosomes on mitochondria alter the local membrane environment for protein import.
    Ya-Ting Chang, Benjamin A Barad, Juliette Hamid, Hamidreza Rahmani, Brian M Zid, Danielle A Grotjahn.
      Most of the mitochondria proteome is nuclear-encoded, synthesized by cytoplasmic ribosomes, and targeted to the mitochondria posttranslationally. However, a subset of mitochondrial-targeted proteins is imported co-translationally, although the molecular mechanisms governing this process remain unclear. We employ cellular cryo-electron tomography to visualize interactions between cytoplasmic ribosomes and mitochondria in Saccharomyces cerevisiae. We use surface morphometrics tools to identify a subset of ribosomes optimally oriented on mitochondrial membranes for protein import. This allows us to establish the first subtomogram average structure of a cytoplasmic ribosome at the mitochondrial surface in the native cellular context, which showed three distinct connections with the outer mitochondrial membrane surrounding the peptide exit tunnel. Further, this analysis demonstrated that cytoplasmic ribosomes primed for mitochondrial protein import cluster on the outer mitochondrial membrane at sites of local constrictions of the outer and inner mitochondrial membranes. Overall, our study reveals the architecture and the spatial organization of cytoplasmic ribosomes at the mitochondrial surface, providing a native cellular context to define the mechanisms that mediate efficient mitochondrial co-translational protein import.
    DOI:  https://doi.org/10.1083/jcb.202407110
  3. Cell Death Dis. 2025 Mar 01. 16(1): 145
    PPTC7 acts as an essential co-factor of the SCFFBXL4 ubiquitin ligase complex to restrict BNIP3/3L-dependent mitophagy.
    Xiayun Xu, Yingji Chen, Siqi Fei, Xinyue Jiang, Xiaoting Zhou, Yimeng Xue, Yao Li, Shi-Min Zhao, Yan Huang, Chenji Wang.
      Mitophagy is a selective process that targets the damaged, dysfunctional, or superfluous mitochondria for degradation through autophagy. The SCFFBXL4 E3 ubiquitin ligase complex suppresses basal mitophagy by targeting BNIP3 and BNIP3L, two key mitophagy cargo receptors, for ubiquitin-proteasomal degradation. FBXL4 loss-of-function mutations lead to excessive BNIP3/3L-dependent mitophagy, thereby causing a devastating multi-system disorder called mitochondrial DNA depletion syndrome, type 13 (MTDPS13). PPTC7, a mitochondrial matrix phosphatase, is essential for proper mitochondrial function and biogenesis. Here, we show that a proportion of PPTC7 is located on the outer mitochondrial membrane, where it interacts with FBXL4 and BNIP3/3L. PPTC7 decreases BNIP3/3L protein stability in a protein phosphatase activity-independent manner. Using in vitro cell culture and Pptc7 knockout mouse model, we demonstrate that PPTC7 deficiency activates high levels of basal mitophagy in a BNIP3/3L-dependent manner. Mechanistically, PPTC7 facilitates SCFFBXL4-mediated ubiquitin-proteasomal degradation of BNIP3/3L. Overall, these findings establish PPTC7 as an essential co-factor of the SCFFBXL4 complex and a suppressor of BNIP3/3L-dependent mitophagy.
    DOI:  https://doi.org/10.1038/s41419-025-07463-w
  4. J Physiol. 2025 Mar 06.
    Mitochondrial proteostasis and cellular health: insights from chaperones and autophagy.
    Yuvraj Anandrao Jagtap, Akash Choudhary, Sumit Kinger, Prashant Kumar, Sudipta Bhattacharyya, Hem Chandra Jha, Rohan Dhiman, Vivek Sharma, Anil K Suresh, Krishna Mohan Poluri, Amit Mishra.
      Mitochondria are a cell's powerhouse and also have a vital part in cellular processes. The emerging role of mitochondria in several crucial processes highlights their cellular and physiological importance. Mitochondrial homeostasis mechanisms, including proteostasis pathways, are vital for mitochondrial health. Failure of these processes has an important role in establishment of numerous complex disease conditions, such as neurodegeneration and imperfect ageing. However, details of mitochondrial impairments and their contribution to the pathology of neurodegeneration are poorly understood. This review systematically discusses the involvement of mitochondrial homeostasis mechanisms and their role in rejuvenating cellular health and fitness. We also focus on various cellular protein quality control mechanisms essential for mitochondrial proteostasis and how their failure leads to mitochondrial functional disturbances observed in disease conditions. We discuss recent findings based on mitostasis-associated chaperones, mitoproteases, and autophagy responses, which can lead to emergence of new possible therapeutic interventions against complex diseases.
    Keywords:  chaperones; mitochondrial dynamics; mitochondrial homeostasis; mitophagy; mitoproteases; neurodegeneration; proteostasis
    DOI:  https://doi.org/10.1113/JP287635
  5. bioRxiv. 2025 Feb 20. pii: 2025.02.19.639081. [Epub ahead of print]
    Mitochondrial accumulation and lysosomal dysfunction result in mitochondrial plaques in Alzheimer's disease.
    Xiuli Dan, Deborah L Croteau, Wenlong Liu, Xixia Chu, Paul D Robbins, Vilhelm A Bohr.
      Dysfunctional mitophagy is a key component of Alzheimer's disease (AD) pathology, yet direct in vivo evidence and mechanistic insights remain limited. Using a mitophagy reporter in an AD mouse model ( APP / PSEN1 /mt-Keima), we identified mitochondrial plaques (MPs) composed of accumulated mitochondria within or outside lysosomes in AD, but not normal mouse brains. Similar structures were also found in AD human brains, but not in healthy controls. Abnormal mitochondrial accumulation in dystrophic neurites, defective mitophagy, and impaired lysosomal function disrupted proper mitochondrial degradation, resulting in excessive mitochondria accumulation both within and outside autophagic vesicles. The resulting intensive mitochondria-containing neurites coalesce into MPs, which co-develop with amyloid plaques to form mixed plaques. These findings establish MPs as novel pathological entity and a promising therapeutic target in AD.
    DOI:  https://doi.org/10.1101/2025.02.19.639081
  6. Nat Commun. 2025 Mar 05. 16(1): 2212
    Structural basis for the allosteric activation of Lon by the heat shock protein LarA.
    Hsiu-Jung Wang, Yun-Erh Kuan, Meng-Ru Ho, Chung-I Chang.
      Lon is a conserved AAA+ (ATPases associated with diverse cellular activities) proteolytic machine that plays a key regulatory role in cells under proteotoxic stress. Lon-mediated proteolysis can be stimulated by either the unfolded or specific protein substrates accumulated under stress conditions. However, the molecular basis for this substrate-controlled proteolysis remains unclear. Here, we have found that the heat shock protein LarA, a recently discovered Lon substrate and allosteric activator, binds to the N-terminal domain (NTD) of Lon. The crystal structure of the LarA-NTD complex shows that LarA binds to a highly conserved groove in the NTD through the terminal aromatic residue of its C-terminal degron. Crystallographic and biochemical evidence further reveals that this binding exposes the hydrophobic core of LarA, which can bind a leucine residue and promote local protein unfolding. These results define the mechanistic role of the NTD in regulating Lon-mediated proteolysis in response to varying cellular conditions.
    DOI:  https://doi.org/10.1038/s41467-025-57482-6
  7. J Cell Biol. 2025 May 05. pii: e202404009. [Epub ahead of print]224(5):
    SNX10 functions as a modulator of piecemeal mitophagy and mitochondrial bioenergetics.
    Laura Trachsel-Moncho, Chiara Veroni, Benan John Mathai, Ana Lapao, Sakshi Singh, Nagham Theres Asp, Sebastian W Schultz, Serhiy Pankiv, Anne Simonsen.
      We here identify the endosomal protein SNX10 as a negative regulator of piecemeal mitophagy of OXPHOS machinery components. In control conditions, SNX10 localizes to early endocytic compartments in a PtdIns3P-dependent manner and modulates endosomal trafficking but also shows dynamic connections with mitochondria. Upon hypoxia-mimicking conditions, SNX10 localizes to late endosomal structures containing selected mitochondrial proteins, including COX-IV and SAMM50, and the autophagy proteins SQSTM1/p62 and LC3B. The turnover of COX-IV was enhanced in SNX10-depleted cells, with a corresponding reduced mitochondrial respiration and citrate synthase activity. Importantly, zebrafish larvae lacking Snx10 show reduced levels of Cox-IV, as well as elevated ROS levels and ROS-mediated cell death in the brain, demonstrating the in vivo relevance of SNX10-mediated modulation of mitochondrial bioenergetics.
    DOI:  https://doi.org/10.1083/jcb.202404009
  8. J Biol Chem. 2025 Feb 27. pii: S0021-9258(25)00214-5. [Epub ahead of print] 108365
    Substrate Recognition and Cleavage-Site Preferences of Lon Protease.
    Melanie Cragan, Neha Puri, A Wali Karzai.
      The evolutionarily conserved AAA+ Lon protease plays a pivotal role in protein homeostasis by precisely remodeling the proteome and specifically removing unfolded, damaged, and surplus natively folded regulatory proteins. Proteolysis by Lon comprises the three fundamental stages of substrate recognition via specific amino acid sequence motifs (degrons), ATP-fueled substrate unfolding and translocation into a sequestered proteolytic chamber, and cleavage of the translocated polypeptide by the peptidase domain. Although a plethora of Lon substrates have been identified in several bacterial species, broadly applicable rules that govern recognition of numerous substrates, and hence the ability to de novo identify new Lon substrates and regulatory pathways, has lagged behind. Similarly, cleavage-site preferences of Lon proteases, and whether these crucial enzymes from diverse bacterial species share similar preferences, has remained underexplored. In this study, we report the identification and characterization of a class of high-affinity autonomous C-terminal Yersinia Pestis (yp) Lon recognition degrons, variants of which are present in numerous known and new yp-Lon substrates and broadly distributed in diverse bacterial species. Moreover, the identification of this degron group offers the predictive power to discover new Lon substrates in eubacteria. Furthermore, cleavage-site preference analyses of multiple Lon substrates reveal that the Lon peptidase domain preferentially cleaves translocated polypeptides after Phenylalanine residues to generate peptides that range from 7 - 35 residues, with an average length of 11 residues, a general feature conserved amongst Lon proteases from phylogenetically distinct bacterial species.
    Keywords:  ATPases associated with diverse cellular activities (AAA+); Lon protease; Protein homeostasis; Proteolysis; Substrate specificity
    DOI:  https://doi.org/10.1016/j.jbc.2025.108365
  9. Front Mol Neurosci. 2025 ;18 1548255
    Multi-omics-based phenotyping of AFG3L2-mutant lymphoblasts determines key factors of a pathophysiological interplay between mitochondrial vulnerability and neurodegeneration in spastic ataxia type 5.
    Menekse Oeztuerk, Diran Herebian, Kale Dipali, Andreas Hentschel, Nina Rademacher, Florian Kraft, Rita Horvath, Felix Distelmaier, Sven G Meuth, Tobias Ruck, Ulrike Schara-Schmidt, Andreas Roos.
      Mitochondrial integrity is fundamental to cellular function, upheld by a network of proteases that regulate proteostasis and mitochondrial dynamics. Among these proteases, AFG3L2 is critical due to its roles in maintaining mitochondrial homeostasis, regulating mitochondrial protein quality, and facilitating mitochondrial biogenesis. Mutations in AFG3L2 are implicated in a spectrum of diseases, including spinocerebellar ataxia type 28 (SCA28) and spastic ataxia 5 (SPAX5), as well as other systemic conditions. This study employs a multi-omics approach to investigate the biochemical impact of AFG3L2 mutations in immortalized lymphoblastoid cell lines derived from a patient with biallelic variants leading to spastic ataxia (SPAX5). Our proteomic analysis revealed AFG3L2 impairment, with significant dysregulation of proteins critical for mitochondrial function, cytoskeletal integrity, and cellular metabolism. Specifically, disruptions were observed in mitochondrial dynamics and calcium homeostasis, alongside downregulation of key proteins like COX11, a copper chaperone for complex IV assembly, and NFU1, an iron-sulfur cluster protein linked to spastic paraparesis and infection-related worsening. Lipidomic analysis highlighted substantial alterations in lipid composition, with significant decreases in sphingomyelins, phosphatidylethanolamine, and phosphatidylcholine, reflecting disruptions in lipid metabolism and membrane integrity. Metabolomic profiling did not reveal any significant findings. Our comprehensive investigation into loss of functional AFG3L2 elucidates a pathophysiology extending beyond mitochondrial proteostasis, implicating a wide array of cellular processes. The findings reveal substantial cellular disturbances at multiple levels, contributing to neurodegeneration through disrupted mitochondrial respiratory chain, calcium homeostasis, cytoskeletal integrity, and altered lipid homeostasis. This study underscores the complexity of SPAX5 pathophysiology and the importance of multi-omics approaches in developing effective strategies to address the impact of loss of functional AFG3L2. Our data also highlight the value of immortalized lymphoblastoid cells as a tool for pre-clinical testing and research, offering a detailed biochemical fingerprint that enhances our understanding of SPAX5 and identifies potential areas for further investigation.
    Keywords:  AFG3 like matrix AAA peptidase subunit 2; MCU; SPAX5; liquid biopsy; multi-omics lymphoblasts
    DOI:  https://doi.org/10.3389/fnmol.2025.1548255
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