bims-mikwok 2023-10-08 papers

bims-mikwok

Biomed News

on Mitochondrial quality control

Issue of 2023‒10‒08
eight papers selected by
Gavin McStay, Liverpool John Moores University

The glyoxylate shunt protein ICL-1 protects from mitochondrial superoxide stress through activation of the mitochondrial unfolded protein response.
Syntaxin 17 Protects Against Heart Failure Through Recruitment of CDK1 to Promote DRP1-Dependent Mitophagy.
A conserved, non-canonical insert in FIS1 mediates TBC1D15 and DRP1 recruitment for mitochondrial fission.
Zika virus modulates mitochondrial dynamics, mitophagy, and mitochondria-derived vesicles to facilitate viral replication in trophoblast cells.
Complementary Approaches to Interrogate Mitophagy Flux in Pancreatic β-Cells.
CoCl2 -triggered pseudohypoxic stress induces proteasomal degradation of SIRT4 via polyubiquitination of lysines K78 and K299.
Mitophagy for cardioprotection.
Pgam5-mediated PHB2 dephosphorylation contributes to endotoxemia-induced myocardial dysfunction by inhibiting mitophagy and the mitochondrial unfolded protein response.

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
JACC Basic Transl Sci. 2023 Sep;8(9): 1215-1239

Syntaxin 17 Protects Against Heart Failure Through Recruitment of CDK1 to Promote DRP1-Dependent Mitophagy.

Haixia Xu, Xiang Wang, Wenjun Yu, Shiqun Sun, Ne N Wu, Junbo Ge, Jun Ren, Yingmei Zhang.

  Mitochondrial dysfunction is suggested to be a major contributor for the progression of heart failure (HF). Here we examined the role of syntaxin 17 (STX17) in the progression of HF. Cardiac-specific Stx17 knockout manifested cardiac dysfunction and mitochondrial damage, associated with reduced levels of p(S616)-dynamin-related protein 1 (DRP1) in mitochondria-associated endoplasmic reticulum membranes and dampened mitophagy. Cardiac STX17 overexpression promoted DRP1-dependent mitophagy and attenuated transverse aortic constriction-induced contractile and mitochondrial damage. Furthermore, STX17 recruited cyclin-dependent kinase-1 through its SNARE domain onto mitochondria-associated endoplasmic reticulum membranes, to phosphorylate DRP1 at Ser616 and promote DRP1-mediated mitophagy upon transverse aortic constriction stress. These findings indicate the potential therapeutic benefit of targeting STX17 in the mitigation of HF.

Keywords:  CDK1; DRP1; MAMs; STX17; mitophagy; pressure overload–induced heart failure

DOI:  https://doi.org/10.1016/j.jacbts.2023.04.006
J Biol Chem. 2023 Sep 28. pii: S0021-9258(23)02331-1. [Epub ahead of print] 105303

A conserved, non-canonical insert in FIS1 mediates TBC1D15 and DRP1 recruitment for mitochondrial fission.

Ugochukwu K Ihenacho, Rafael Toro, Rana H Mansour, R Blake Hill.

  Mitochondrial fission protein 1 (FIS1) is conserved in all eukaryotes, yet its function in metazoans is thought divergent from lower eukaryotes like fungi. To address this discrepancy, structure-based sequence alignments revealed a conserved but non-canonical three-residue insert (Ser-X-X) in a turn of FIS1, suggesting a conserved function. In vertebrate FIS1, this insert is serine (S45), lysine (K46), and tyrosine (Y47). To determine the biological role of the "SKY insert" in vertebrates, three variants were evaluated for their fold and tested in HCT116 cells for altered mitochondrial morphology and recruitment of effectors, DRP1 and TBC1D15. Substitution of the SKY insert with three alanine residues (AAA) or deletion of the insert (ΔSKY) did not substantially alter the fold or thermal stability of the protein. Replacing SKY with a canonical turn (ΔSKYD49G) introduced significant conformational heterogeneity by NMR that was removed upon deletion of a known regulatory region, the FIS1 arm. Expression of AAA fragmented mitochondria into perinuclear clumps associated with increased mitochondrial DRP1 similar to the wild-type protein. In contrast, the expression of ΔSKY variants led to elongated mitochondrial networks and reduced mitochondrial DRP1 by colocalization analysis, although DRP1 coimmunoprecipitates were highly enriched with ΔSKY variants. Co-expression of YFP-TBC1D15 with ΔSKY variants rescued mitochondrial morphology, despite a reduced ability to drive YFP-TBC1D15 into punctate structures that is found upon co-expression with wildtype FIS1 or the AAA variant. In support YFP-TBC1D15 coimmunoprecipitates were poorly enriched with ΔSKY variants. Co-expression of YFP-TBC1D15 also revealed a gain of function phenotype with the AAA variant compared to wildtype. Collectively these results show that FIS1 can be modulated by conserved residues, thus supporting a unifying model whereby FIS1 activity is effectively governed by intramolecular interactions between the regulatory FIS1 arm and an S-X-X insert that is conserved across eukaryotes.

Keywords:  Mitochondria; dynamin; fission; mitophagy; nuclear magnetic resonance (NMR); organelle dynamic; peroxisome; protein motif; repeat proteins; tetratricopeptide repeat

DOI:  https://doi.org/10.1016/j.jbc.2023.105303
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
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
FEBS Open Bio. 2023 Oct 06.

CoCl2 -triggered pseudohypoxic stress induces proteasomal degradation of SIRT4 via polyubiquitination of lysines K78 and K299.

Nils Hampel, Jacqueline Georgy, Mehrnaz Mehrabipour, Alexander Lang, Isabell Lehmkuhl, Jürgen Scheller, Mohammad R Ahmadian, Doreen M Floss, Roland P Piekorz.

  SIRT4, together with SIRT3 and SIRT5, comprises the mitochondrially-localized subgroup of sirtuins. SIRT4 regulates mitochondrial bioenergetics, dynamics (mitochondrial fusion), and quality control (mitophagy) via its NAD+ -dependent enzymatic activities. Here, we address the regulation of SIRT4 itself by characterizing its protein stability and degradation upon CoCl2 -induced pseudohypoxic stress that typically triggers mitophagy. Interestingly, we observed that of the mitochondrial sirtuins, only the protein levels of SIRT4 or ectopically expressed SIRT4-eGFP decrease upon CoCl2 treatment of HEK293 cells. Co-treatment with BafA1, an inhibitor of autophagosome-lysosome fusion required for autophagy/mitophagy, or the use of the proteasome inhibitor MG132, prevented CoCl2 -induced SIRT4 downregulation. Consistent with the proteasomal degradation of SIRT4, the lysine mutants SIRT4(K78R) and SIRT4(K299R) showed significantly reduced polyubiquitination upon CoCl2 treatment and were more resistant to pseudohypoxia-induced degradation as compared to SIRT4. Moreover, SIRT4(K78R) and SIRT4(K299R) displayed increased basal protein stability as compared to wild-type SIRT4 when subjected to MG132 treatment or cycloheximide (CHX) chase assays. Thus, our data indicate that stress-induced protein degradation of SIRT4 occurs through two mechanisms: (i) via mitochondrial autophagy/mitophagy, and (ii) as a separate process via proteasomal degradation within the cytoplasm.

Keywords:  SIRT4; Sirtuin; autophagy; proteasome; pseudohypoxia; ubiquitination

DOI:  https://doi.org/10.1002/2211-5463.13715
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
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