bims-mitpro 2023-10-08 papers

bims-mitpro

Biomed News

on Mitochondrial Proteostasis

Issue of 2023–10–08
nine papers selected by
Andreas Kohler, Umeå University

Pgam5-mediated PHB2 dephosphorylation contributes to endotoxemia-induced myocardial dysfunction by inhibiting mitophagy and the mitochondrial unfolded protein response.
Mitophagy for cardioprotection.
A bacterial pathogen induces developmental slowing by high reactive oxygen species and mitochondrial dysfunction in Caenorhabditis elegans.
The glyoxylate shunt protein ICL-1 protects from mitochondrial superoxide stress through activation of the mitochondrial unfolded protein response.
Zika virus modulates mitochondrial dynamics, mitophagy, and mitochondria-derived vesicles to facilitate viral replication in trophoblast cells.
Liquid-liquid phase separation regulates alpha-synuclein aggregate and mitophagy in Parkinson's disease.
Complementary Approaches to Interrogate Mitophagy Flux in Pancreatic β-Cells.
Conformational analysis of membrane-proximal segments of GDAP1 in a lipidic environment using synchrotron radiation suggests a mode of assembly at the mitochondrial outer membrane.
Mutation of the PEBP-like domain of the mitoribosomal MrpL35/mL38 protein results in production of nascent chains with impaired capacity to assemble into OXPHOS complexes.

Int J Biol Sci. 2023 ;19(14): 4657-4671

Pgam5-mediated PHB2 dephosphorylation contributes to endotoxemia-induced myocardial dysfunction by inhibiting mitophagy and the mitochondrial unfolded protein response.

Chen Cai, Ziying Li, Zemao Zheng, Zhongzhou Guo, Qian Li, Shuxian Deng, Nengxian Shi, Qing Ou, Hao Zhou, Zhigang Guo, Zhongqing Chen, Hang Zhu.

  Numerous mitochondrial abnormalities are reported to result from excessive inflammation during endotoxemia. Prohibitin 2 (PHB2) and phosphoglycerate mutase 5 (Pgam5) have been associated with altered mitochondrial homeostasis in several cardiovascular diseases; however, their role in endotoxemia-related myocardial dysfunction has not been explored. Our experiments were aimed to evaluate the potential contribution of Pgam5 and PHB2 to endotoxemia-induced mitochondrial dysfunction in cardiomyocytes, with a focus on two endogenous protective programs that sustain mitochondrial integrity, namely mitophagy and the mitochondrial unfolded protein response (UPRmt). We found that PHB2 transgenic mice are resistant to endotoxemia-mediated myocardial depression and mitochondrial damage. Our assays indicated that PHB2 overexpression activates mitophagy and the UPRmt, which maintains mitochondrial metabolism, prevents oxidative stress injury, and enhances cardiomyocyte viability. Molecular analyses further showed that Pgam5 binds to and dephosphorylates PHB2, resulting in cytosolic translocation of mitochondrial PHB2. Silencing of Pgam5 or transfection of a phosphorylated PHB2 mutant in mouse HL-1 cardiomyocytes prevented the loss of mitochondrially-localized PHB2 and activated mitophagy and UPRmt in the presence of LPS. Notably, cardiomyocyte-specific deletion of Pgam5 in vivo attenuated LPS-mediated myocardial dysfunction and preserved cardiomyocyte viability. These findings suggest that Pgam5/PHB2 signaling and mitophagy/UPRmt are potential targets for the treatment of endotoxemia-related cardiac dysfunction.

Keywords:  PHB2; Pgam5; endotoxemia-related cardiac dysfunction

DOI:  https://doi.org/10.7150/ijbs.85767
Basic Res Cardiol. 2023 Oct 05. 118(1): 42

Mitophagy for cardioprotection.

Allen Sam Titus, Eun-Ah Sung, Daniela Zablocki, Junichi Sadoshima.

  Mitochondrial function is maintained by several strictly coordinated mechanisms, collectively termed mitochondrial quality control mechanisms, including fusion and fission, degradation, and biogenesis. As the primary source of energy in cardiomyocytes, mitochondria are the central organelle for maintaining cardiac function. Since adult cardiomyocytes in humans rarely divide, the number of dysfunctional mitochondria cannot easily be diluted through cell division. Thus, efficient degradation of dysfunctional mitochondria is crucial to maintaining cellular function. Mitophagy, a mitochondria specific form of autophagy, is a major mechanism by which damaged or unnecessary mitochondria are targeted and eliminated. Mitophagy is active in cardiomyocytes at baseline and in response to stress, and plays an essential role in maintaining the quality of mitochondria in cardiomyocytes. Mitophagy is mediated through multiple mechanisms in the heart, and each of these mechanisms can partially compensate for the loss of another mechanism. However, insufficient levels of mitophagy eventually lead to mitochondrial dysfunction and the development of heart failure. In this review, we discuss the molecular mechanisms of mitophagy in the heart and the role of mitophagy in cardiac pathophysiology, with the focus on recent findings in the field.

Keywords:  Alternative mitophagy; Drp1; Mitochondrial quality control; Mitophagy

DOI:  https://doi.org/10.1007/s00395-023-01009-x
Cell Rep. 2023 Oct 04. pii: S2211-1247(23)01201-9. [Epub ahead of print]42(10): 113189

A bacterial pathogen induces developmental slowing by high reactive oxygen species and mitochondrial dysfunction in Caenorhabditis elegans.

Zeynep Mirza, Albertha J M Walhout, Victor Ambros.

  Host-pathogen interactions are complex by nature, and the host developmental stage increases this complexity. By utilizing Caenorhabditis elegans larvae as the host and the bacterium Pseudomonas aeruginosa as the pathogen, we investigated how a developing organism copes with pathogenic stress. By screening 36 P. aeruginosa isolates, we found that the CF18 strain causes a severe but reversible developmental delay via induction of reactive oxygen species (ROS) and mitochondrial dysfunction. While the larvae upregulate mitophagy, antimicrobial, and detoxification genes, mitochondrial unfolded protein response (UPRmt) genes are repressed. Either antioxidant or iron supplementation rescues the phenotypes. We examined the virulence factors of CF18 via transposon mutagenesis and RNA sequencing (RNA-seq). We found that non-phenazine toxins that are regulated by quorum sensing (QS) and the GacA/S system are responsible for developmental slowing. This study highlights the importance of ROS levels and mitochondrial health as determinants of developmental rate and how pathogens can attack these important features.

Keywords:  C. elegans; CP: Metabolism; CP: Microbiology; P. aeruginosa; development; iron; mitochondria; reactive oxygen species; slow-killing assay; transposon mutagenesis

DOI:  https://doi.org/10.1016/j.celrep.2023.113189
Free Radic Biol Med. 2023 Sep 25. pii: S0891-5849(23)00654-8. [Epub ahead of print]208 771-779

The glyoxylate shunt protein ICL-1 protects from mitochondrial superoxide stress through activation of the mitochondrial unfolded protein response.

Guoqiang Wang, Ricardo Laranjeiro, Stephanie LeValley, Jeremy M Van Raamsdonk, Monica Driscoll.

Disrupting mitochondrial superoxide dismutase (SOD) causes neonatal lethality in mice and death of flies within 24 h after eclosion. Deletion of mitochondrial sod genes in C. elegans impairs fertility as well, but surprisingly is not detrimental to survival of progeny generated. The comparison of metabolic pathways among mouse, flies and nematodes reveals that mice and flies lack the glyoxylate shunt, a shortcut that bypasses part of the tricarboxylic acid (TCA) cycle. Here we show that ICL-1, the sole protein that catalyzes the glyoxylate shunt, is critical for protection against embryonic lethality resulting from elevated levels of mitochondrial superoxide. In exploring the mechanism by which ICL-1 protects against ROS-mediated embryonic lethality, we find that ICL-1 is required for the efficient activation of mitochondrial unfolded protein response (UPRmt) and that ATFS-1, a key UPRmt transcription factor and an activator of icl-1 gene expression, is essential to limit embryonic/neonatal lethality in animals lacking mitochondrial SOD. In sum, we identify a biochemical pathway that highlights a molecular strategy for combating toxic mitochondrial superoxide consequences in cells.

DOI: https://doi.org/10.1016/j.freeradbiomed.2023.09.029
Front Immunol. 2023 ;14 1203645

Zika virus modulates mitochondrial dynamics, mitophagy, and mitochondria-derived vesicles to facilitate viral replication in trophoblast cells.

Jae Kyung Lee, Ok Sarah Shin.

  Zika virus (ZIKV) remains a global public health threat with the potential risk of a future outbreak. Since viral infections are known to exploit mitochondria-mediated cellular processes, we investigated the effects of ZIKV infection in trophoblast cells in terms of the different mitochondrial quality control pathways that govern mitochondrial integrity and function. Here we demonstrate that ZIKV (PRVABC59) infection of JEG-3 trophoblast cells manipulates mitochondrial dynamics, mitophagy, and formation of mitochondria-derived vesicles (MDVs). Specifically, ZIKV nonstructural protein 4A (NS4A) translocates to the mitochondria, triggers mitochondrial fission and mitophagy, and suppresses mitochondrial associated antiviral protein (MAVS)-mediated type I interferon (IFN) response. Furthermore, proteomics profiling of small extracellular vesicles (sEVs) revealed an enrichment of mitochondrial proteins in sEVs secreted by ZIKV-infected JEG-3 cells, suggesting that MDV formation may also be another mitochondrial quality control mechanism manipulated during placental ZIKV infection. Altogether, our findings highlight the different mitochondrial quality control mechanisms manipulated by ZIKV during infection of placental cells as host immune evasion mechanisms utilized by ZIKV at the placenta to suppress the host antiviral response and facilitate viral infection.

Keywords:  mitochondria-derived vesicles (MDVs); mitochondrial quality control; mitophagy; nonstructural protein 4A (NS4A); zika virus (ZIKV)

DOI:  https://doi.org/10.3389/fimmu.2023.1203645
Front Neurosci. 2023 ;17 1250532

Liquid-liquid phase separation regulates alpha-synuclein aggregate and mitophagy in Parkinson's disease.

Kaiying Hou, Tingting Liu, Jingwen Li, Meiyan Xian, Lin Sun, Jianshe Wei.

  Parkinson's disease (PD) is the second most common neurodegenerative disease in the world, and alpha-synuclein (α-syn) abnormal aggregate and mitochondrial dysfunction play a crucial role in its pathological development. Recent studies have revealed that proteins can form condensates through liquid-liquid phase separation (LLPS), and LLPS has been found to be widely present in α-syn aberrant aggregate and mitophagy-related protein physiological processes. This review summarizes the occurrence of α-syn LLPS and its influencing factors, introduces the production and transformation of the related protein LLPS during PINK1-Parkin-mediated mitophagy, hoping to provide new ideas and methods for the study of PD pathology.

Keywords:  PINK1-Parkin; Parkinson’s disease; alpha-synuclein; liquid-liquid phase separation; mitophagy

DOI:  https://doi.org/10.3389/fnins.2023.1250532
J Vis Exp. 2023 09 15.

Complementary Approaches to Interrogate Mitophagy Flux in Pancreatic β-Cells.

Elena Levi-D'Ancona, Vaibhav Sidarala, Scott A Soleimanpour.

Mitophagy is a quality control mechanism necessary to maintain optimal mitochondrial function. Dysfunctional β-cell mitophagy results in insufficient insulin release. Advanced quantitative assessments of mitophagy often require the use of genetic reporters. The mt-Keima mouse model, which expresses a mitochondria-targeted pH-sensitive dual-excitation ratiometric probe for quantifying mitophagy via flow cytometry, has been optimized in β-cells. The ratio of acidic-to-neutral mt-Keima wavelength emissions can be used to robustly quantify mitophagy. However, using genetic mitophagy reporters can be challenging when working with complex genetic mouse models or difficult-to-transfect cells, such as primary human islets. This protocol describes a novel complementary dye-based method to quantify β-cell mitophagy in primary islets using MtPhagy. MtPhagy is a pH-sensitive, cell-permeable dye that accumulates in the mitochondria and increases its fluorescence intensity when mitochondria are in low pH environments, such as lysosomes during mitophagy. By combining the MtPhagy dye with Fluozin-3-AM, a Zn2+ indicator that selects for β-cells, and Tetramethylrhodamine, ethyl ester (TMRE) to assess mitochondrial membrane potential, mitophagy flux can be quantified specifically in β-cells via flow cytometry. These two approaches are highly complementary, allowing for flexibility and precision in assessing mitochondrial quality control in numerous β-cell models.

DOI: https://doi.org/10.3791/65789
Biophys Chem. 2023 Sep 25. pii: S0301-4622(23)00164-3. [Epub ahead of print]303 107113

Conformational analysis of membrane-proximal segments of GDAP1 in a lipidic environment using synchrotron radiation suggests a mode of assembly at the mitochondrial outer membrane.

Aleksi Sutinen, Nykola C Jones, Søren Vrønning Hoffmann, Salla Ruskamo, Petri Kursula.

  The mitochondrial outer membrane creates a diffusion barrier between the cytosol and the mitochondrial intermembrane space, allowing the exchange of metabolic products, important for efficient mitochondrial function in neurons. The ganglioside-induced differentiation-associated protein 1 (GDAP1) is a mitochondrial outer membrane protein with a critical role in mitochondrial dynamics and metabolic balance in neurons. Missense mutations in the GDAP1 gene are linked to the most common human peripheral neuropathy, Charcot-Marie-Tooth disease (CMT). GDAP1 is a distant member of the glutathione-S-transferase (GST) superfamily, with unknown enzymatic properties or functions at the molecular level. The structure of the cytosol-facing GST-like domain has been described, but there is no consensus on how the protein interacts with the mitochondrial outer membrane. Here, we describe a model for GDAP1 assembly on the membrane using peptides vicinal to the GDAP1 transmembrane domain. We used oriented circular dichroism spectroscopy (OCD) with synchrotron radiation to study the secondary structure and orientation of GDAP1 segments at the outer and inner surfaces of the outer mitochondrial membrane. These experiments were complemented by small-angle X-ray scattering, providing the first experimental structural models for full-length human GDAP1. The results indicate that GDAP1 is bound into the membrane via a single transmembrane helix, flanked by two peripheral helices interacting with the outer and inner leaflets of the mitochondrial outer membrane in different orientations. Impairment of these interactions could be a mechanism for CMT in the case of missense mutations affecting these segments instead of the GST-like domain.

Keywords:  Charcot-Marie-Tooth disease; GDAP1; Mitochondrial outer membrane; Protein biophysics

DOI:  https://doi.org/10.1016/j.bpc.2023.107113
Mol Biol Cell. 2023 Oct 04. mbcE23040132

Mutation of the PEBP-like domain of the mitoribosomal MrpL35/mL38 protein results in production of nascent chains with impaired capacity to assemble into OXPHOS complexes.

Jodie M Box, Jessica M Anderson, Rosemary A Stuart.

Located in the central protuberance region of the mitoribosome, mitospecific mL38 proteins display homology to PEBP (phosphatidylethanolamine binding protein) proteins, a diverse family of proteins reported to bind anionic substrates/ligands and implicated in cellular signaling and differentiation pathways. In this study, we have performed a mutational analysis of the yeast mitoribosomal protein MrpL35/mL38 and demonstrate that mutation of the PEBP-invariant ligand binding residues Asp(D)232 and Arg(R)288 impacted MrpL35/mL38's ability to support OXPHOS-based growth of the cell. Furthermore, our data indicate these residues exist in a functionally important charged microenvironment, which also includes Asp(D)167 of MrpL35/mL38 and Arg(R)127 of the neighboring Mrp7/bL27m protein. We report that mutation of each of these charged residues resulted in a strong reduction in OXPHOS complex levels that was not attributed to a corresponding inhibition of the mitochondrial translation process. Rather, our findings indicate that a disconnect exists in these mutants between the processes of mitochondrial protein translation and the events required to ensure the competency and/or availability of the newly synthesized proteins to assemble into OXPHOS enzymes. Based on our findings, we postulate that the PEBP-homology domain of MrpL35/mL38, together with its partner Mrp7/bL27m, form a key regulatory region of the mitoribosome.

DOI: https://doi.org/10.1091/mbc.E23-04-0132