bims-mitpro Biomed News
on Mitochondrial proteostasis
Issue of 2024–11–17
seven papers selected by
Andreas Kohler, Umeå University
  1. Opposing roles for AMPK in regulating distinct mitophagy pathways.
  2. eIF5A controls mitoprotein import by relieving ribosome stalling at TIM50 translocase mRNA.
  3. A PRKN-independent Mechanism Regulating Cardiac Mitochondrial Quality Control.
  4. ATF5-mediated mitochondrial unfolded protein response protects against Pb-induced mitochondria damage in SH-SY5Y cell.
  5. Suppression of PINK1 autophosphorylation attenuates pilocarpine-induced seizures and neuronal injury in rats.
  6. Efficient PHB2 (prohibitin 2) exposure during mitophagy depends on VDAC1 (voltage dependent anion channel 1).
  7. HSF-1 promotes longevity through ubiquilin-1-dependent mitochondrial network remodelling.
  1. Mol Cell. 2024 Nov 05. pii: S1097-2765(24)00865-7. [Epub ahead of print]
    Opposing roles for AMPK in regulating distinct mitophagy pathways.
    Marianna Longo, Aniketh Bishnu, Pierpaolo Risiglione, Lambert Montava-Garriga, Joyceline Cuenco, Kei Sakamoto, Carol MacKintosh, Ian G Ganley.
      Mitophagy degrades damaged mitochondria, but we show here that it can also target functional mitochondria. This latter scenario occurs during programmed mitophagy and involves the mitophagy receptors NIX and BNIP3. Although AMP-activated protein kinase (AMPK), the energy-sensing protein kinase, can influence damaged-induced mitophagy, its role in programmed mitophagy is unclear. We found that AMPK directly inhibits NIX-dependent mitophagy by triggering 14-3-3-mediated sequestration of ULK1, via ULK1 phosphorylation at two sites: Ser556 and an additional identified site, Ser694. By contrast, AMPK activation increases Parkin phosphorylation and enhances the rate of depolarization-induced mitophagy, independently of ULK1. We show that this happens both in cultured cells and tissues in vivo, using the mito-QC mouse model. Our work unveils a mechanism whereby AMPK activation downregulates mitophagy of functional mitochondria but enhances that of dysfunctional/damaged ones.
    Keywords:  14-3-3; AMPK; NIX; Parkin; ULK1; autophagy; liver; mito-QC; mitophagy; skeletal muscle
    DOI:  https://doi.org/10.1016/j.molcel.2024.10.025
  2. J Cell Biol. 2024 Dec 02. pii: e202404094. [Epub ahead of print]223(12):
    eIF5A controls mitoprotein import by relieving ribosome stalling at TIM50 translocase mRNA.
    Marina Barba-Aliaga, Vanessa Bernal, Cynthia Rong, Madeleine E Volfbeyn, Keguang Zhang, Brian M Zid, Paula Alepuz.
      Efficient import of nuclear-encoded proteins into mitochondria is crucial for proper mitochondrial function. The conserved translation factor eIF5A binds ribosomes, alleviating stalling at polyproline-encoding sequences. eIF5A impacts mitochondrial function across species, though the precise molecular mechanism is unclear. We found that eIF5A depletion in yeast reduces the translation and levels of the TCA cycle and oxidative phosphorylation proteins. Loss of eIF5A causes mitoprotein precursors to accumulate in the cytosol and triggers a mitochondrial import stress response. We identify an essential polyproline protein as a direct target of eIF5A: the mitochondrial inner membrane protein and translocase component Tim50. Thus, eIF5A controls mitochondrial protein import by alleviating ribosome stalling along Tim50 mRNA at the mitochondrial surface. Removal of polyprolines from Tim50 partially rescues the mitochondrial import stress response and translation of oxidative phosphorylation genes. Overall, our findings elucidate how eIF5A impacts the mitochondrial function by promoting efficient translation and reducing ribosome stalling of co-translationally imported proteins, thereby positively impacting the mitochondrial import process.
    DOI:  https://doi.org/10.1083/jcb.202404094
  3. Autophagy. 2024 Nov 09.
    A PRKN-independent Mechanism Regulating Cardiac Mitochondrial Quality Control.
    Wenjuan Wang, Jinbao Liu, Jie Li, Huabo Su.
      PRKN-dependent mitophagy plays a crucial role in maintaining mitochondrial health. Yet, PRKN-deficient mice do not exhibit mitochondrial and cardiac phenotypes at baseline, suggesting the existence of other mitochondrial ubiquitin (Ub) ligases. Here, we discuss our recent work identifying RNF7/RBX2 as a novel mitochondrial Ub ligase. Upon mitochondrial depolarization, RNF7 proteins are recruited to the mitochondria, where they directly ubiquitinate mitochondrial proteins and stabilize PINK1 expression, thereby promoting the clearance of damaged mitochondria and regulating mitochondrial turnover in the heart. The actions of RNF7 in mitochondria do not require PRKN. Ablation of Rnf7 in mouse hearts results in severe mitochondrial dysfunction and heart failure. Our findings demonstrate that RNF7 is indispensable for mitochondrial turnover and cardiac homeostasis. These results open new avenues for exploring new PRKN-independent pathways that regulate mitophagy, which could have significant implications for developing therapeutic interventions for cardiac diseases.
    Keywords:  Heart failure; RBX2/SAG; mitophagy; parkin; ubiquitination
    DOI:  https://doi.org/10.1080/15548627.2024.2423329
  4. Neurotoxicology. 2024 Nov 13. pii: S0161-813X(24)00133-5. [Epub ahead of print]
    ATF5-mediated mitochondrial unfolded protein response protects against Pb-induced mitochondria damage in SH-SY5Y cell.
    Yihan Xu, Min Liu, Sikang Gao, Xiaoyi Li, Jun Chen, Fang Ye.
      Mitochondria is the primary target of lead (Pb) in neural cells, and Pb exposure can cause impairment to mitochondrial function and morphology. Recent studies have reported that a conserved cellular stress response, called mitochondrial unfolded protein response (mtUPR), is activated in response to mitochondrial dysfunction and protein misfolding and play protective roles in aging and neurodegeneration, but it's unknown whether mtUPR could protect against Pb-induced neurotoxicity. In this study, we found that sublethal level exposure of PbAc (2.5μM) could cause mitochondria damage and then activate mtUPR by promoting the expression of mitochondrial proteases (LonP1 and ClpP), molecular chaperone (HSPA1A). ATF5 mediated mtUPR activation as knocking out ATF5 significantly inhibited Pb-induced LonP1 and ClpP expression. Moreover, ATF5 deficiency exacerbated Pb-induced mitochondrial morphological and oxidative phosphorylation (OXPHOS) functional damage, resulting in oxidative stress and ultimately promoting cell death. Conversely, overexpression of ATF5 confers protection against Pb-induced oxidative stress and cell death. Collectively, thess results highlight that mtUPR mediated by ATF5 safeguards against mitochondria damage caused by Pb exposure, providing insights into the development of new strategies for mitigating the Pb neurotoxicity.
    Keywords:  ATF5; Lead; Mitochondrial unfolded protein response; Neurotoxicity
    DOI:  https://doi.org/10.1016/j.neuro.2024.11.001
  5. Brain Res Bull. 2024 Nov 08. pii: S0361-9230(24)00251-X. [Epub ahead of print]219 111117
    Suppression of PINK1 autophosphorylation attenuates pilocarpine-induced seizures and neuronal injury in rats.
    Yujie Zhai, Yi Yuan, Yaru Cui, Xiaoqian Wang, Hua Zhou, Qian Teng, Hongjin Wang, Bohan Sun, Hongliu Sun, Jianhua Tang.
      PTEN-induced kinase 1 (PINK1) autophosphorylation triggers the PINK1/Parkin pathway, which is the main mitophagic pathway in the mammalian nervous system. In the present study, we aimed to mechanistically explore the role of PINK1 in pilocarpine-induced status epilepticus (SE) in Sprague-Dawley rats. Evidence from immunohistochemistry, western blotting, biochemical assays, and behavioral testing showed that pilocarpine-induced SE led to increased levels of PINK1 phosphorylation, mitophagy, mitochondrial oxidative stress, neuronal damage and learning and memory deficits. Using shRNA interference to suppress the expression of translocase outer mitochondrial membrane 7, a positive regulator of PINK1 autophosphorylation, lowered the increased levels of phosphorylated PINK1 following pilocarpine administration. It also reduced the levels of mitophagy, mitochondrial oxidative stress and neuronal damage, and attenuated seizure severity and cognitive deficits. In contrast, suppressing the expression of overlapping with the m-AAA protease 1 homolog, a negative regulator of PINK1 autophosphorylation, led to higher levels of phosphorylated PINK1 following pilocarpine administration. It also led to more serious mitophagy, neuronal damage, as well as worsened seizure severity and cognitive deficits. Our results indicate that PINK1 autophosphorylation plays a vital role in epileptic seizures and neuronal injury by mediating mitophagy. Regulating PINK1 autophosphorylation may change the adverse consequences of epilepsy, and may be an effective neuroprotective strategy.
    Keywords:  Mitochondrial oxidative stress; Mitophagy; Neuronal injury; PTEN-induced kinase 1; Status epilepticus
    DOI:  https://doi.org/10.1016/j.brainresbull.2024.111117
  6. Autophagy. 2024 Nov 08.
    Efficient PHB2 (prohibitin 2) exposure during mitophagy depends on VDAC1 (voltage dependent anion channel 1).
    Moumita Roy, Sumangal Nandy, Elena Marchesan, Chayan Banerjee, Rupsha Mondal, Federico Caicci, Elena Ziviani, Joy Chakraborty.
      Exposure of inner mitochondrial membrane resident protein PHB2 (prohibitin 2) during autophagic removal of depolarized mitochondria (mitophagy) depends on the ubiquitin-proteasome system. This uncovering facilitates the PHB2 interaction with phagophore membrane-associated protein MAP1LC3/LC3. It is unclear whether PHB2 is exposed randomly at mitochondrial rupture sites. Prior knowledge and initial screening indicated that VDAC1 (voltage dependent anion channel 1) might play a role in this phenomenon. Through in vitro biochemical assays and imaging, we have found that VDAC1-PHB2 interaction increases during mitochondrial depolarization. Subsequently, this interaction enhances the efficiency of PHB2 exposure and mitophagy. To investigate the relevance in vivo, we utilized porin (equivalent to VDAC1) knockout Drosophila line. Our findings demonstrate that during mitochondrial stress, porin is essential for Phb2 exposure, Phb2-Atg8 interaction and mitophagy. This study highlights that VDAC1 predominantly synchronizes efficient PHB2 exposure through mitochondrial rupture sites during mitophagy. These findings may provide insights to understand progressive neurodegeneration.
    Keywords:  Neurodegeneration; PHB2-LC3 interaction; PINK1-PRKN; parkinson disease; porin; ubiquitin-proteasome system
    DOI:  https://doi.org/10.1080/15548627.2024.2426116
  7. Nat Commun. 2024 Nov 12. 15(1): 9797
    HSF-1 promotes longevity through ubiquilin-1-dependent mitochondrial network remodelling.
    Annmary Paul Erinjeri, Xunyan Wang, Rhianna Williams, Riccardo Zenezini Chiozzi, Konstantinos Thalassinos, Johnathan Labbadia.
      Increased activity of the heat shock factor, HSF-1, suppresses proteotoxicity and enhances longevity. However, the precise mechanisms by which HSF-1 promotes lifespan are unclear. Using an RNAi screen, we identify ubiquilin-1 (ubql-1) as an essential mediator of lifespan extension in worms overexpressing hsf-1. We find that hsf-1 overexpression leads to transcriptional downregulation of all components of the CDC-48-UFD-1-NPL-4 complex, which is central to both endoplasmic reticulum and mitochondria associated protein degradation, and that this is complemented by UBQL-1-dependent turnover of NPL-4.1. As a consequence, mitochondrial network dynamics are altered, leading to increased lifespan. Together, our data establish that HSF-1 mediates lifespan extension through mitochondrial network adaptations that occur in response to down-tuning of components associated with organellar protein degradation pathways.
    DOI:  https://doi.org/10.1038/s41467-024-54136-x
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