bims-mikwok 2022-08-14 papers

bims-mikwok

Biomed News

on Mitochondrial quality control

Issue of 2022–08–14
seven papers selected by
Avinash N. Mukkala, University of Toronto

Rapid and selective generation of H2S within mitochondria protects against cardiac ischemia-reperfusion injury.
Mitofusin 2 Integrates Mitochondrial Network Remodelling, Mitophagy and Renewal of Respiratory Chain Proteins in Neurons after Oxygen and Glucose Deprivation.
Mitochondria and ischemia reperfusion injury.
Ischemia-Selective Cardioprotection by Malonate for Ischemia/Reperfusion Injury.
Balanced mitochondrial and cytosolic translatomes underlie the biogenesis of human respiratory complexes.
Macrophages induce cardiomyocyte ferroptosis via mitochondrial transfer.
The mitochondrial fission protein Drp1 in liver is required to mitigate NASH and prevents the activation of the mitochondrial ISR.

Redox Biol. 2022 Aug 05. pii: S2213-2317(22)00201-4. [Epub ahead of print]55 102429

Rapid and selective generation of H2S within mitochondria protects against cardiac ischemia-reperfusion injury.

Jan Lj Miljkovic, Nils Burger, Justyna M Gawel, John F Mulvey, Abigail A I Norman, Takanori Nishimura, Yoshiyuki Tsujihata, Angela Logan, Olga Sauchanka, Stuart T Caldwell, Jordan L Morris, Tracy A Prime, Stefan Warrington, Julien Prudent, Georgina R Bates, Dunja Aksentijević, Hiran A Prag, Andrew M James, Thomas Krieg, Richard C Hartley, Michael P Murphy.

  Mitochondria-targeted H2S donors are thought to protect against acute ischemia-reperfusion (IR) injury by releasing H2S that decreases oxidative damage. However, the rate of H2S release by current donors is too slow to be effective upon administration following reperfusion. To overcome this limitation here we develop a mitochondria-targeted agent, MitoPerSulf that very rapidly releases H2S within mitochondria. MitoPerSulf is quickly taken up by mitochondria, where it reacts with endogenous thiols to generate a persulfide intermediate that releases H2S. MitoPerSulf is acutely protective against cardiac IR injury in mice, due to the acute generation of H2S that inhibits respiration at cytochrome c oxidase thereby preventing mitochondrial superoxide production by lowering the membrane potential. Mitochondria-targeted agents that rapidly generate H2S are a new class of therapy for the acute treatment of IR injury.

Keywords:  Hydrogen sulfide donors; Ischemia-reperfusion injury; Mitochondria; Mitochondria targeting; Reverse electron transport (RET)

DOI:  https://doi.org/10.1016/j.redox.2022.102429
Mol Neurobiol. 2022 Aug 13.

Mitofusin 2 Integrates Mitochondrial Network Remodelling, Mitophagy and Renewal of Respiratory Chain Proteins in Neurons after Oxygen and Glucose Deprivation.

Piotr Wojtyniak, Anna Boratynska-Jasinska, Karolina Serwach, Joanna Gruszczynska-Biegala, Barbara Zablocka, Jacek Jaworski, Maria Kawalec.

  In attempts to develop effective therapeutic strategies to limit post-ischemic injury, mitochondria emerge as a key element determining neuronal fate. Mitochondrial damage can be alleviated by various mechanisms including mitochondrial network remodelling, mitochondrial elimination and mitochondrial protein biogenesis. However, the mechanisms regulating relationships between these phenomena are poorly understood. We hypothesized that mitofusin 2 (Mfn2), a mitochondrial GTPase involved in mitochondrial fusion, mitochondria trafficking and mitochondria and endoplasmic reticulum (ER) tethering, may act as one of linking and regulatory factors in neurons following ischemic insult. To verify this assumption, we performed temporal oxygen and glucose deprivation (OGD/R) on rat cortical primary culture to determine whether Mfn2 protein reduction affected the onset of mitophagy, subsequent mitochondrial biogenesis and thus neuronal survival. We found that Mfn2 knockdown increased neuronal susceptibility to OGD/R, prevented mitochondrial network remodelling and resulted in prolonged mitophagosomes formation in response to the insult. Next, Mfn2 knockdown was observed to be accompanied by reduced Parkin protein levels and increased Parkin accumulation on mitochondria. As for wild-type neurons, OGD/R insult was followed by an elevated mtDNA content and an increase in respiratory chain proteins. Neither of these phenomena were observed for Mfn2 knockdown neurons. Collectively, our findings showed that Mfn2 in neurons affected their response to mild and transient OGD stress, balancing the extent of defective mitochondria elimination and positively influencing mitochondrial respiratory protein levels. Our study suggests that Mfn2 is one of essential elements for neuronal response to ischemic insult, necessary for neuronal survival.

Keywords:  Brain ischemia; Mitochondria; Mitochondrial DNA; Mitochondrial biogenesis; Mitofusin 2; Mitophagy; Primary neurons

DOI:  https://doi.org/10.1007/s12035-022-02981-6
Curr Opin Organ Transplant. 2022 Aug 04.

Mitochondria and ischemia reperfusion injury.

Rebecca Panconesi, Jeannette Widmer, Mauricio Flores Carvalho, Janina Eden, Daniele Dondossola, Philipp Dutkowski, Andrea Schlegel.

PURPOSE OF REVIEW: This review describes the role of mitochondria in ischemia-reperfusion-injury (IRI).
RECENT FINDINGS: Mitochondria are the power-house of our cells and play a key role for the success of organ transplantation. With their respiratory chain, mitochondria are the main energy producers, to fuel metabolic processes, control cellular signalling and provide electrochemical integrity. The mitochondrial metabolism is however severely disturbed when ischemia occurs. Cellular energy depletes rapidly and various metabolites, including Succinate accumulate. At reperfusion, reactive oxygen species are immediately released from complex-I and initiate the IRI-cascade of inflammation. Prior to the development of novel therapies, the underlying mechanisms should be explored to target the best possible mitochondrial compound. A clinically relevant treatment should recharge energy and reduce Succinate accumulation before organ implantation. While many interventions focus instead on a specific molecule, which may inhibit downstream IRI-inflammation, mitochondrial protection can be directly achieved through hypothermic oxygenated perfusion (HOPE) before transplantation.
SUMMARY: Mitochondria are attractive targets for novel molecules to limit IRI-associated inflammation. Although dynamic preservation techniques could serve as delivery tool for new therapeutic interventions, their own inherent mechanism should not only be studied, but considered as key treatment to reduce mitochondrial injury, as seen with the HOPE-approach.

DOI: https://doi.org/10.1097/MOT.0000000000001015
Circ Res. 2022 Aug 12. 101161CIRCRESAHA121320717

Ischemia-Selective Cardioprotection by Malonate for Ischemia/Reperfusion Injury.

Hiran A Prag, Dunja Aksentijevic, Andreas Dannhorn, Abigail V Giles, John F Mulvey, Olga Sauchanka, Luping Du, Georgina Bates, Johannes Reinhold, Duvaraka Kula-Alwar, Zhelong Xu, Luc Pellerin, Richard J A Goodwin, Michael P Murphy, Thomas Krieg.

   BACKGROUND: Inhibiting SDH (succinate dehydrogenase), with the competitive inhibitor malonate, has shown promise in ameliorating ischemia/reperfusion injury. However, key for translation to the clinic is understanding the mechanism of malonate entry into cells to enable inhibition of SDH, its mitochondrial target, as malonate itself poorly permeates cellular membranes. The possibility of malonate selectively entering the at-risk heart tissue on reperfusion, however, remains unexplored.
METHODS: C57BL/6J mice, C2C12 and H9c2 myoblasts, and HeLa cells were used to elucidate the mechanism of selective malonate uptake into the ischemic heart upon reperfusion. Cells were treated with malonate while varying pH or together with transport inhibitors. Mouse hearts were either perfused ex vivo (Langendorff) or subjected to in vivo left anterior descending coronary artery ligation as models of ischemia/reperfusion injury. Succinate and malonate levels were assessed by LC-MS/MS, in vivo by mass spectrometry imaging, and infarct size by TTC staining.
RESULTS: Malonate was robustly protective against cardiac ischemia/reperfusion injury, but only if administered at reperfusion and not when infused before ischemia. The extent of malonate uptake into the heart was proportional to the duration of ischemia. Malonate entry into cardiomyocytes in vivo and in vitro was dramatically increased at the low pH (≈6.5) associated with ischemia. This increased uptake of malonate was blocked by selective inhibition of MCT1 (monocarboxylate transporter 1). Reperfusion of the ischemic heart region with malonate led to selective SDH inhibition in the at-risk region. Acid-formulation greatly enhances the cardioprotective potency of malonate.
CONCLUSIONS: Cardioprotection by malonate is dependent on its entry into cardiomyocytes. This is facilitated by the local decrease in pH that occurs during ischemia, leading to its selective uptake upon reperfusion into the at-risk tissue, via MCT1. Thus, malonate's preferential uptake in reperfused tissue means it is an at-risk tissue-selective drug that protects against cardiac ischemia/reperfusion injury.

Keywords:  ischemia; mitochondria; myocardial infarction; reactive oxygen species; reperfusion

DOI:  https://doi.org/10.1161/CIRCRESAHA.121.320717
Genome Biol. 2022 Aug 09. 23(1): 170

Balanced mitochondrial and cytosolic translatomes underlie the biogenesis of human respiratory complexes.

Iliana Soto, Mary Couvillion, Katja G Hansen, Erik McShane, J Conor Moran, Antoni Barrientos, L Stirling Churchman.

BACKGROUND: Oxidative phosphorylation (OXPHOS) complexes consist of nuclear and mitochondrial DNA-encoded subunits. Their biogenesis requires cross-compartment gene regulation to mitigate the accumulation of disproportionate subunits. To determine how human cells coordinate mitochondrial and nuclear gene expression processes, we tailored ribosome profiling for the unique features of the human mitoribosome.
RESULTS: We resolve features of mitochondrial translation initiation and identify a small ORF in the 3' UTR of MT-ND5. Analysis of ribosome footprints in five cell types reveals that average mitochondrial synthesis levels correspond precisely to cytosolic levels across OXPHOS complexes, and these average rates reflect the relative abundances of the complexes. Balanced mitochondrial and cytosolic synthesis does not rely on rapid feedback between the two translation systems, and imbalance caused by mitochondrial translation deficiency is associated with the induction of proteotoxicity pathways.
CONCLUSIONS: Based on our findings, we propose that human OXPHOS complexes are synthesized proportionally to each other, with mitonuclear balance relying on the regulation of OXPHOS subunit translation across cellular compartments, which may represent a proteostasis vulnerability.

DOI: https://doi.org/10.1186/s13059-022-02732-9
Free Radic Biol Med. 2022 Aug 03. pii: S0891-5849(22)00498-1. [Epub ahead of print]190 1-14

Macrophages induce cardiomyocyte ferroptosis via mitochondrial transfer.

Jun Chen, Chun-Yan Fu, Gerong Shen, Jingyu Wang, Lintao Xu, Heyangzi Li, Xi Cao, Ming-Zhi Zheng, Yue-Liang Shen, Jinjie Zhong, Ying-Ying Chen, Lin-Lin Wang.

   INTRODUCTION: Mitochondrial transfer is a new cell-to-cell communication manner. Whether the mitochondrial transfer is also involved in the macrophage infiltration-induced cardiac injury is unclear.
OBJECTIVES: This study aimed to determine whether macrophage mitochondria can be transferred to cardiomyocytes, and to investigate its possible role and mechanism.
METHODS: Mitochondrial transfer between macrophages and cardiomyocytes was detected using immunofluorescence staining and flow cytometry. Cellular metabolites were analyzed using LC-MS technique. Differentially expressed mRNAs were identified using RNA-seq technique.
RESULTS: (1) After cardiomyocytes were cultured with macrophage-conditioned medium (COND + group), macrophage-derived mitochondria have been found in cardiomyocytes, which could be blocked by dynasore (an inhibitor of clathrin-mediated endocytosis). (2) Compared with control (CM) group, there were 545 altered metabolites found in COND + group, most of which were lipids and lipid-like molecules. The altered metabolites were mainly enriched in the β-oxidation of fatty acids and glutathione metabolism. And there were 4824 differentially expressed mRNAs, which were highly enriched in processes like lipid metabolism-associated pathway. (3) Both RNA-seq and qRT-PCR results found that ferroptosis-related mRNAs such as Ptgs2 and Acsl4 increased, and Gpx4 mRNA decreased in COND + group (P < 0.05 vs CM group). (4) The levels of cellular free Fe2+ and mitochondrial lipid peroxidation were increased; while GSH/GSSG ratio, mitochondrial aspect ratio, mitochondrial membrane potential, and ATP production were decreased in cardiomyocytes of COND + group (P < 0.05 vs CM group). All the above phenomena could be blocked by a ferroptosis inhibitor ferrostatin-1 (P < 0.05).
CONCLUSION: Macrophages could transfer mitochondria to cardiomyocytes. Macrophage-derived mitochondria were internalized into cardiomyocytes through clathrin- and/or lipid raft-mediated endocytosis. Uptake of exogenous macrophage mitochondria induced cardiomyocyte injury via triggering ferroptosis.

Keywords:  Cardiomyocytes; Ferroptosis; Macrophages; Mitochondrial transfer

DOI:  https://doi.org/10.1016/j.freeradbiomed.2022.07.015
Mol Metab. 2022 Aug 05. pii: S2212-8778(22)00135-1. [Epub ahead of print] 101566

The mitochondrial fission protein Drp1 in liver is required to mitigate NASH and prevents the activation of the mitochondrial ISR.

Janos Steffen, Jennifer Ngo, Sheng-Ping Wang, Kevin Williams, Henning F Kramer, George Ho, Carlos Rodriguez, Krishna Yekkala, Chidozie Amuzie, Russell Bialecki, Lisa Norquay, Andrea R Nawrocki, Mark Erion, Alessandro Pocai, Orian S Shirihai, Marc Liesa.

   OBJECTIVE: The mitochondrial fission protein Drp1 was proposed to promote NAFLD, as inhibition of hepatocyte Drp1 early in life prevents liver steatosis induced by high-fat diet in mice. However, whether Drp1-knockdown in older mice can reverse established NASH is unknown.
METHODS: N-acetylgalactosamine-siRNA conjugates, an FDA approved method to deliver siRNA selectively to hepatocytes, were used to knockdown hepatocyte-Drp1 in mice (NAG-Drp1si). NASH was induced in C57BL/6NTac mice by Gubra-Amylin-NASH diet (D09100310, 40% fat, 22% fructose and 2% cholesterol) and treatment with NAG-Drp1si was started at week 24 of diet. Circulating transaminases, liver histology, gene expression of fibrosis and inflammation markers, and hydroxyproline synthesis determined NASH severity. Liver NEFA and triglycerides were quantified by GC/MS. Mitochondrial function was determined by respirometry. Western blots of OMA1, OPA1, p-eIF2α, as well as transcriptional analyses of Atf4-regulated genes determined ISR engagement.
RESULTS: NAG-Drp1si treatment decreased body weight and induced liver inflammation in adult healthy mice. Increased hepatic Gdf15 production was the major contributor to body-weight loss caused by NAG-Drp1si treatment, as Gdf15 receptor deletion (Gfral KO) prevented the decrease in food intake and mitigated weight loss. NAG-Drp1si activated the Atf4-controlled integrated stress response (ISR) to increase hepatic Gdf15 expression. NAG-Drp1si in healthy mice caused ER stress and activated the mitochondrial protease Oma1, which are the ER and mitochondrial triggers that activate the Atf4-controlled ISR. Remarkably, induction of NASH was not sufficient to activate Oma1 in liver. However, NAG-Drp1si treatment was sufficient to activate Oma1 in adult mice with NASH, as well as exacerbating NASH-induced ER stress. Consequently, NAG-Drp1si treatment in mice with NASH led to higher ISR activation, exacerbated inflammation, fibrosis and necrosis.
CONCLUSION: Drp1 mitigates NASH by decreasing ER stress, preventing Oma1 activation and ISR exacerbation. The elevation in Gdf15 actions induced by NAG-Drp1si might represent an adaptive response decreasing the nutrient load to liver when mitochondria are misfunctional. Our study argues against blocking Drp1 in hepatocytes to combat NASH.

Keywords:  Atf4; Drp1; ISR; NASH; Oma1; mitochondria

DOI:  https://doi.org/10.1016/j.molmet.2022.101566