bims-mikwok 2023-07-30 papers

Cell Rep. 2023 Jul 26. pii: S2211-1247(23)00906-3. [Epub ahead of print]42(8): 112895

PGAM5 is an MFN2 phosphatase that plays an essential role in the regulation of mitochondrial dynamics.

Sudeshna Nag, Kaitlin Szederkenyi, Olena Gorbenko, Hannah Tyrrell, Christopher M Yip, G Angus McQuibban.

Mitochondrial morphology is regulated by the post-translational modifications of the dynamin family GTPase proteins including mitofusin 1 (MFN1), MFN2, and dynamin-related protein 1 (DRP1). Mitochondrial phosphatase phosphoglycerate mutase 5 (PGAM5) is emerging as a regulator of these post-translational modifications; however, its precise role in the regulation of mitochondrial morphology is unknown. We show that PGAM5 interacts with MFN2 and DRP1 in a stress-sensitive manner. PGAM5 regulates MFN2 phosphorylation and consequently protects it from ubiquitination and degradation. Further, phosphorylation and dephosphorylation modification of MFN2 regulates its fusion ability. Phosphorylation enhances fission and degradation, whereas dephosphorylation enhances fusion. PGAM5 dephosphorylates MFN2 to promote mitochondrial network formation. Further, using a Drosophila genetic model, we demonstrate that the MFN2 homolog Marf and dPGAM5 are in the same biological pathway. Our results identify MFN2 dephosphorylation as a regulator of mitochondrial fusion and PGAM5 as an MFN2 phosphatase.

Keywords: CP: Molecular biology; DRP1; MFN2; PGAM5; mitochondrial morphology

DOI: https://doi.org/10.1016/j.celrep.2023.112895

EMBO Rep. 2023 Jul 28. e55859

UBQLN2 and HSP70 participate in Parkin-mediated mitophagy by facilitating outer mitochondrial membrane rupture.

Qilian Ma, Jiaqi Xin, Qiang Peng, Ningning Li, Shan Sun, Hongyu Hou, Guoqiang Ma, Nana Wang, Li Zhang, Kin Yip Tam, Heiko Dussmann, Jochen Hm Prehn, Hongfeng Wang, Zheng Ying.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two aging-related neurodegenerative diseases that share common key features, including aggregation of pathogenic proteins, dysfunction of mitochondria, and impairment of autophagy. Mutations in ubiquilin 2 (UBQLN2), a shuttle protein in the ubiquitin-proteasome system (UPS), can cause ALS/FTD, but the mechanism underlying UBQLN2-mediated pathogenesis is still uncertain. Recent studies indicate that mitophagy, a selective form of autophagy which is crucial for mitochondrial quality control, is tightly associated with neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and ALS. In this study, we show that after Parkin-dependent ubiquitination of damaged mitochondria, UBQLN2 is recruited to poly-ubiquitinated mitochondria through the UBA domain. UBQLN2 cooperates with the chaperone HSP70 to promote UPS-driven degradation of outer mitochondrial membrane (OMM) proteins. The resulting rupture of the OMM triggers the autophagosomal recognition of the inner mitochondrial membrane receptor PHB2. UBQLN2 is required for Parkin-mediated mitophagy and neuronal survival upon mitochondrial damage, and the ALS/FTD pathogenic mutations in UBQLN2 impair mitophagy in primary cultured neurons. Taken together, our findings link dysfunctional mitophagy to UBQLN2-mediated neurodegeneration.

Keywords: ALS; Parkin; UBQLN2; mitophagy; ubiquitin

DOI: https://doi.org/10.15252/embr.202255859

bioRxiv. 2023 Jul 11. pii: 2023.07.11.548601. [Epub ahead of print]

Mitochondrial proteostasis mediated by CRL5 Ozz and Alix maintains skeletal muscle function.

Yvan Campos, Ricardo Rodriguez-Enriquez, Gustavo Palacios, Diantha Van de Vlekkert, Xiaohui Qiu, Jayce Weesner, Elida Gomero, Jeroen Demmers, Tulio Bertorini, Joseph T Opferman, Gerard C Grosveld, Alessandra d'Azzo.

High energy-demanding tissues, such as skeletal muscle, require mitochondrial proteostasis to function properly. Two quality-control mechanisms, the ubiquitin proteasome system (UPS) and the release of mitochondria-derived vesicles, safeguard mitochondrial proteostasis. However, whether these processes interact is unknown. Here we show that the E3 ligase CRL5 Ozz , a member of the UPS, and its substrate Alix control the mitochondrial concentration of Slc25A4, a solute carrier that is essential for ATP production. The mitochondria in Ozz -/- or Alix -/- skeletal muscle share overt morphologic alterations (they are supernumerary, swollen, and dysmorphic) and have abnormal metabolomic profiles. We found that CRL5 Ozz ubiquitinates Slc25A4 and promotes its proteasomal degradation, while Alix facilitates SLC25A4 loading into exosomes destined for lysosomal destruction. The loss of Ozz or Alix offsets steady-state levels of Slc25A4, which disturbs mitochondrial metabolism and alters muscle fiber composition. These findings reveal hitherto unknown regulatory functions of Ozz and Alix in mitochondrial proteostasis.

DOI: https://doi.org/10.1101/2023.07.11.548601

J Biol Chem. 2023 Jul 24. pii: S0021-9258(23)02115-4. [Epub ahead of print] 105087

Hyper-ubiquitylation of DNA helicase RECQL4 by E3 ligase MITOL prevents mitochondrial entry and potentiates mitophagy.

Mansoor Hussain, Aftab Mohammed, Shabnam Saifi, Swati Priya, Sagar Sengupta.

Mutations in the DNA helicase RECQL4 lead to Rothmund-Thomson Syndrome (RTS), a disorder characterized by mitochondrial dysfunctions, premature aging, and genomic instability. However, the mechanisms by which these mutations lead to pathology are unclear. Here we report that RECQL4 is ubiquitylated by a mitochondrial E3 ligase, MITOL, at two lysine residues (K1101, K1154) via K6 linkage. This ubiquitylation hampers the interaction of RECQL4 with mitochondrial importer Tom20, thereby restricting its own entry into mitochondria. We show the RECQL4 2K mutant (where both K1101 and K1154 are mutated) has increased entry into mitochondria and demonstrates enhanced mtDNA replication. We observed that the three tested RTS patient mutants were unable to enter the mitochondria and showed decreased mtDNA replication. Furthermore, we found that RECQL4 in RTS patient mutants are hyper-ubiquitylated by MITOL and form insoluble aggregate-like structures on the outer mitochondrial surface. However, depletion of MITOL allows RECQL4 expressed in these RTS mutants to enter mitochondria and rescue mtDNA replication. Finally, we show increased accumulation of hyper-ubiquitylated RECQL4 outside the mitochondria leads to the cells being potentiated to increased mitophagy. Hence, we conclude regulating the turnover of RECQL4 by MITOL may have a therapeutic effect in RTS patients.

Keywords: E3 ligases; RecQ helicases; Rothmund Thomson Syndrome; autophagy; mitochondrial replication

DOI: https://doi.org/10.1016/j.jbc.2023.105087

Front Mol Neurosci. 2023 ;16 1224964

Mechanism of PGC-1α-mediated mitochondrial biogenesis in cerebral ischemia-reperfusion injury.

Ying Yuan, Yuan Tian, Hui Jiang, Luo-Yang Cai, Jie Song, Rui Peng, Xiao-Ming Zhang.

Cerebral ischemia-reperfusion injury (CIRI) is a series of cascade reactions that occur after blood flow recanalization in the ischemic zone in patients with cerebral infarction, causing an imbalance in intracellular homeostasis through multiple pathologies such as increased oxygen free radicals, inflammatory response, calcium overload, and impaired energy metabolism, leading to mitochondrial dysfunction and ultimately apoptosis. Rescue of reversibly damaged neurons in the ischemic hemispheric zone is the key to saving brain infarction and reducing neurological deficits. Complex and active neurological functions are highly dependent on an adequate energy supply from mitochondria. Mitochondrial biogenesis (MB), a process that generates new functional mitochondria and restores normal mitochondrial function by replacing damaged mitochondria, is a major mechanism for maintaining intra-mitochondrial homeostasis and is involved in mitochondrial quality control to ameliorate mitochondrial dysfunction and thus protects against CIRI. The main regulator of MB is peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), which improves mitochondrial function to protect against CIRI by activating its downstream nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A (TFAM) to promote mitochondrial genome replication and transcription. This paper provides a theoretical reference for the treatment of neurological impairment caused by CIRI by discussing the mechanisms of mitochondrial biogenesis during cerebral ischemia-reperfusion injury.

Keywords: PGC-1α; apoptosis; cerebral ischemia–reperfusion injury; mitochondria; mitochondrial biogenesis

DOI: https://doi.org/10.3389/fnmol.2023.1224964