Mitochondrial Nuclear Retrograde Regulator 1 (MNRR1) rescues the cellular phenotype of MELAS by inducing homeostatic mechanisms

MNRR1 (CHCHD2) is a bi-organellar regulator of mitochondrial function that directly activates cytochrome c oxidase in the mitochondria and functions in the nucleus as a transcriptional activator for hundreds of genes. Since MNRR1 depletion contains features of a mitochondrial disease phenotype, we evaluated the effects of forced expression of MNRR1 on the mitochondrial disease MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes) syndrome. MELAS is a multisystem encephalomyopathy disorder that can result from a heteroplasmic mutation in the mitochondrial DNA (mtDNA; m.3243A > G) at heteroplasmy levels of ∼50 to 90%. Since cybrid cell lines with 73% m.3243A > G heteroplasmy (DW7) display a significant reduction in MNRR1 levels compared to the wild type (0% heteroplasmy) (CL9), we evaluated the effects of MNRR1 levels on mitochondrial functioning. Overexpression of MNRR1 in DW7 cells induces the mitochondrial unfolded protein response (UPRmt), autophagy, and mitochondrial biogenesis, thereby rescuing the mitochondrial phenotype. It does so primarily as a transcription activator, revealing this function to be a potential therapeutic target. The role of MNRR1 in stimulating UPRmt, which is blunted in MELAS cells, was surprising and further investigation uncovered that under conditions of stress the import of MNRR1 into the mitochondria was blocked, allowing the protein to accumulate in the nucleus to enhance its transcription function. In the mammalian system, ATF5, has been identified as a mediator of UPRmt. MNRR1 knockout cells display an ∼40% reduction in the protein levels of ATF5, suggesting that MNRR1 plays an important role upstream of this known mediator of UPRmt.

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Nox4 Mediates RANKL-induced ER-Phagy and Osteoclastogenesis via Activating ROS/PERK/eIF-2α/ATF4 Pathway

10.21203/rs.3.rs-34288/v1 ◽

2020 ◽

Author(s):

Jing Sun ◽

wugui chen ◽

Songtao Li ◽

Sizhen Yang ◽

Ying Zhang ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Bone Resorption ◽

Signaling Pathway ◽

Molecular Mechanisms ◽

Nuclear Factor Κb ◽

Protein Levels ◽

Unfolded Protein ◽

Regulatory Effects ◽

Protein Response

Abstract Background: Receptor activator of nuclear factor-κB ligand (RANKL) has been found to induce osteoclastogenesis and bone resorption. However, the underlying molecular mechanisms remain unclear. Methods: Osteoclastogenesis was evaluated by number of TRAP-positive multinuclear (≥3) osteoclasts, bone resorption pits and expression levels of related genes. Autophagy activity were evaluated by LC3-II/LC3-I ratio, number of autophagic vacuoles and adenovirus-mRFP-GFP-tagged LC3 reporting system; Inhibitor chloroquine (CQ) was used to verified the role of autophagy in RANKL-induced osteoclastogenesis; Via downregulating Nox4 with inhibitor (DPI) and retrovirus-conveyed shRNA, we further explored the importance of Nox4 in RANKL-induced autophagy and osteoclastogenesis, as well as the regulatory effects of Nox4 on nonmitochondrial reactive oxygen species (ROS) and PERK/eIF-2α/ATF4 pathway. Intracellular ROS scavenger (NAC), mitochondrial-targeted antioxidant (MitoTEMPO) and inhibitor of PERK (GSK2606414) were also employed to investigate the role of ROS and PERK/eIF-2α/ATF4 pathway in RANKL-induced autophagy and osteoclastogenesis. Results: RANKL markedly increased autophagy, while CQ treatment caused reduction of RANKL-induced autophagy and osteoclastogenesis. Consistent with the increased autophagy, the protein levels of Nox4 were significantly increased, and Nox4 was selectively localized within the endoplasmic reticulum (ER) after RANKL stimulation. DPI and shRNA efficiently decreased the protein level and (or) activity of Nox4 in the ER and inhibited RANKL-induced autophagy and osteoclastogenesis. Mechanistically, we found that Nox4 regulates RANKL-induced autophagy activation and osteoclastogenesis by stimulating the production of nonmitochondrial ROS. Additionally, Nox4-derived nonmitochondrial ROS dramatically activate PERK/eIF-2α/ATF4, which is a critical unfolded protein response (UPR)-related signaling pathway during ER stress. Blocking the activation of the PERK/eIF-2α/ATF4 signaling pathway either by Nox4 shRNA, ROS antioxidant or PERK inhibitor (GSK2606414) treatment significantly inhibited endoplasmic reticulum autophagy (ER-phagy) during RANKL-induced osteoclastogenesis. Conclusions: Our findings provide new insights into the processes of RANKL-induced osteoclastogenesis and will help the development of new therapeutic strategies for osteoclastogenesis-related diseases.

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Impact of Mitophagy and Mitochondrial Unfolded Protein Response as New Adaptive Mechanisms Underlying Old Pathologies: Sarcopenia and Non-Alcoholic Fatty Liver Disease

International Journal of Molecular Sciences ◽

10.3390/ijms21207704 ◽

2020 ◽

Vol 21 (20) ◽

pp. 7704

Author(s):

Rodrigo Urbina-Varela ◽

Nataly Castillo ◽

Luis A. Videla ◽

Andrea del Campo

Keyword(s):

Liver Disease ◽

Fatty Liver ◽

Fatty Liver Disease ◽

Alcoholic Fatty Liver ◽

Unfolded Protein ◽

Adaptive Mechanisms ◽

Protein Response ◽

Mitochondrial Unfolded Protein Response ◽

Alcoholic Fatty Liver Disease

Mitochondria are the first-line defense of the cell in the presence of stressing processes that can induce mitochondrial dysfunction. Under these conditions, the activation of two axes is accomplished, namely, (i) the mitochondrial unfolded protein response (UPRmt) to promote cell recovery and survival of the mitochondrial network; (ii) the mitophagy process to eliminate altered or dysfunctional mitochondria. For these purposes, the former response induces the expression of chaperones, proteases, antioxidant components and protein import and assembly factors, whereas the latter is signaled through the activation of the PINK1/Parkin and BNIP3/NIX pathways. These adaptive mechanisms may be compromised during aging, leading to the development of several pathologies including sarcopenia, defined as the loss of skeletal muscle mass and performance; and non-alcoholic fatty liver disease (NAFLD). These age-associated diseases are characterized by the progressive loss of organ function due to the accumulation of reactive oxygen species (ROS)-induced damage to biomolecules, since the ability to counteract the continuous and large generation of ROS becomes increasingly inefficient with aging, resulting in mitochondrial dysfunction as a central pathogenic mechanism. Nevertheless, the role of the integrated stress response (ISR) involving UPRmt and mitophagy in the development and progression of these illnesses is still a matter of debate, considering that some studies indicate that the prolonged exposure to low levels of stress may trigger these mechanisms to maintain mitohormesis, whereas others sustain that chronic activation of them could lead to cell death. In this review, we discuss the available research that contributes to unveil the role of the mitochondrial UPR in the development of sarcopenia, in an attempt to describe changes prior to the manifestation of severe symptoms; and in NAFLD, in order to prevent or reverse fat accumulation and its progression by means of suitable protocols to be addressed in future studies.

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Mitochondrial fission facilitates the selective mitophagy of protein aggregates

The Journal of Cell Biology ◽

10.1083/jcb.201612106 ◽

2017 ◽

Vol 216 (10) ◽

pp. 3231-3247 ◽

Cited By ~ 147

Author(s):

Jonathon L. Burman ◽

Sarah Pickles ◽

Chunxin Wang ◽

Shiori Sekine ◽

Jose Norberto S. Vargas ◽

...

Keyword(s):

Protein Aggregation ◽

Matrix Protein ◽

Mitochondrial Fission ◽

Protein Aggregates ◽

Mitochondrial Matrix ◽

Unfolded Protein ◽

Protein Response ◽

Mitochondrial Networks ◽

Mitochondrial Unfolded Protein Response

Within the mitochondrial matrix, protein aggregation activates the mitochondrial unfolded protein response and PINK1–Parkin-mediated mitophagy to mitigate proteotoxicity. We explore how autophagy eliminates protein aggregates from within mitochondria and the role of mitochondrial fission in mitophagy. We show that PINK1 recruits Parkin onto mitochondrial subdomains after actinonin-induced mitochondrial proteotoxicity and that PINK1 recruits Parkin proximal to focal misfolded aggregates of the mitochondrial-localized mutant ornithine transcarbamylase (ΔOTC). Parkin colocalizes on polarized mitochondria harboring misfolded proteins in foci with ubiquitin, optineurin, and LC3. Although inhibiting Drp1-mediated mitochondrial fission suppresses the segregation of mitochondrial subdomains containing ΔOTC, it does not decrease the rate of ΔOTC clearance. Instead, loss of Drp1 enhances the recruitment of Parkin to fused mitochondrial networks and the rate of mitophagy as well as decreases the selectivity for ΔOTC during mitophagy. These results are consistent with a new model that, instead of promoting mitophagy, fission protects healthy mitochondrial domains from elimination by unchecked PINK1–Parkin activity.

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UBL5/Hub1: An Atypical Ubiquitin-Like Protein with a Typical Role as a Stress-Responsive Regulator

International Journal of Molecular Sciences ◽

10.3390/ijms22179384 ◽

2021 ◽

Vol 22 (17) ◽

pp. 9384

Author(s):

Sittinan Chanarat

Keyword(s):

Recent Progress ◽

Stress Protein ◽

Mrna Splicing ◽

Unfolded Protein ◽

Enzyme Cascade ◽

Damage Repair ◽

Carboxy Terminal ◽

Protein Response ◽

Mitochondrial Unfolded Protein Response

Members of the ubiquitin-like protein family are known for their ability to modify substrates by covalent conjugation. The highly conserved ubiquitin relative UBL5/Hub1, however, is atypical because it lacks a carboxy-terminal di-glycine motif required for conjugation, and the whole E1-E2-E3 enzyme cascade is likely absent. Though the conjugation-mediated role of UBL5/Hub1 is controversial, it undoubtedly functions by interacting non-covalently with its partners. Several interactors of UBL5/Hub1 identified to date have suggested broad stress-responsive functions of the protein, for example, stress-induced control of pre-mRNA splicing, Fanconi anemia pathway of DNA damage repair, and mitochondrial unfolded protein response. While having an atypical mode of function, UBL5/Hub1 is still a stress protein that regulates feedback to various stimuli in a similar manner to other ubiquitin-like proteins. In this review, I discuss recent progress in understanding the functions of UBL5/Hub1 and the fundamental questions which remain to be answered.

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Mitochondrial quality control protects photoreceptors against oxidative stress in the H2O2-induced models of retinal degeneration diseases

Cell Death and Disease ◽

10.1038/s41419-021-03660-5 ◽

2021 ◽

Vol 12 (5) ◽

Author(s):

Biting Zhou ◽

Lijun Fang ◽

Yanli Dong ◽

Juhua Yang ◽

Xiaole Chen ◽

...

Keyword(s):

Oxidative Stress ◽

Retinal Degeneration ◽

Mitochondrial Quality Control ◽

Mitochondrial Mass ◽

Nicotinamide Riboside ◽

Unfolded Protein ◽

Protein Response ◽

Retinal Cone ◽

Mitochondrial Unfolded Protein Response

AbstractRetinal degeneration diseases (RDDs) are common and devastating eye diseases characterized by the degeneration of photoreceptors, which are highly associated with oxidative stress. Previous studies reported that mitochondrial dysfunction is associated with various neurodegenerative diseases. However, the role of mitochondrial proteostasis mainly regulated by mitophagy and mitochondrial unfolded protein response (mtUPR) in RDDs is unclear. We hypothesized that the mitochondrial proteostasis is neuroprotective against oxidative injury in RDDs. In this study, the data from our hydrogen peroxide (H2O2)-treated mouse retinal cone cell line (661w) model of RDDs showed that nicotinamide riboside (NR)-activated mitophagy increased the expression of LC3B II and PINK1, and promoted the co-localization of LC3 and mitochondria, as well as PINK1 and Parkin in the H2O2-treated 661w cells. However, the NR-induced mitophagy was remarkably reversed by chloroquine (CQ) and cyclosporine A (CsA), mitophagic inhibitors. In addition, doxycycline (DOX), an inducer of mtUPR, up-regulated the expression of HSP60 and CHOP, the key proteins of mtUPR. Activation of both mitophagy and mtUPR increased the cell viability and reduced the level of apoptosis and oxidative damage in the H2O2-treated 661w cells. Furthermore, both mitophagy and mtUPR played a protective effect on mitochondria by increasing mitochondrial membrane potential and maintaining mitochondrial mass. By contrast, the inhibition of mitophagy by CQ or CsA reversed the beneficial effect of mitophagy in the H2O2-treated 661w cells. Together, our study suggests that the mitophagy and mtUPR pathways may serve as new therapeutic targets to delay the progression of RDDs through enhancing mitochondrial proteostasis.

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Nox4 mediates RANKL-induced ER-phagy and Osteoclastogenesis via activating ROS/PERK/eIF-2α/ATF4 Pathway

10.21203/rs.3.rs-141264/v1 ◽

2021 ◽

Author(s):

Jing Sun ◽

Wugui Cheng ◽

Songtao Li ◽

Sizhen Yang ◽

Ying Zhang ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Signaling Pathway ◽

Molecular Mechanisms ◽

Nuclear Factor Κb ◽

Protein Levels ◽

Unfolded Protein ◽

Ros Scavenger ◽

Regulatory Effects ◽

Protein Response

Abstract Background: Receptor activator of nuclear factor-κB ligand (RANKL) has been found to induce osteoclastogenesis and bone resorption. However, the underlying molecular mechanisms remain unclear. Results: Inhibitor chloroquine (CQ) was used to verified the role of autophagy in RANKL-induced osteoclastogenesis; Via downregulating Nox4 with inhibitor (DPI) and retrovirus-conveyed shRNA, we further explored the importance of Nox4 in RANKL-induced autophagy and osteoclastogenesis, as well as the regulatory effects of Nox4 on nonmitochondrial reactive oxygen species (ROS) and PERK/eIF-2α/ATF4 pathway.Intracellular ROS scavenger (NAC), mitochondrial-targeted antioxidant (Mito-TEMPO) and inhibitor of PERK (GSK2606414) were also employed to investigate the role of ROS and PERK/eIF-2α/ATF4 pathway in RANKL-induced autophagy and osteoclastogenesis. RANKL markedly increased autophagy, while CQ treatment caused reduction of RANKL-induced autophagy and osteoclastogenesis. Consistent with the increased autophagy, the protein levels of Nox4 were significantly increased, and Nox4 was selectively localized within the endoplasmic reticulum (ER) after RANKL stimulation. DPI and shRNA efficiently decreased the protein level and (or) activity of Nox4 in the ER and inhibited RANKL-induced autophagy and osteoclastogenesis. Mechanistically, we found that Nox4 regulates RANKL-induced autophagy activation by stimulating the production of nonmitochondrial ROS. Additionally, Nox4-derived nonmitochondrial ROS dramatically activate PERK/eIF-2α/ATF4, which is a critical unfolded protein response (UPR)-related signaling pathway. Blocking the activation of the PERK/eIF-2α/ATF4 signaling pathway either by Nox4 shRNA, ROS antioxidant or PERK inhibitor (GSK2606414) treatment significantly inhibited endoplasmic reticulum autophagy (ER-phagy) during RANKL-induced osteoclastogenesis. Conclusions: Our findings provide new insights into the processes of RANKL-induced osteoclastogenesis and will help the development of new therapeutic strategies for osteoclastogenesis-related diseases.

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900 MHz Radiofrequency Field Induces Mitochondrial Unfolded Protein Response in Mouse Bone Marrow Stem Cells

Frontiers in Public Health ◽

10.3389/fpubh.2021.724239 ◽

2021 ◽

Vol 9 ◽

Author(s):

Wen Xie ◽

Rui Xu ◽

Caiyun Fan ◽

Chunyu Yang ◽

Haiyan Chen ◽

...

Keyword(s):

Bone Marrow ◽

Unfolded Protein Response ◽

Sham Group ◽

Mouse Bone Marrow ◽

Expression Levels ◽

Protein Levels ◽

Unfolded Protein ◽

Rf Exposure ◽

Protein Response ◽

Mitochondrial Unfolded Protein Response

Objective: To examine whether exposure of mouse bone marrow stromal cells (BMSC) to 900 MHz radiofrequency fields used in mobile communication devices can induce mitochondrial unfolded protein response (UPRmt).Methods: BMSCs were exposed to continuous wave 900 MHz radiofrequency fields (RF) at 120 μW/cm2 power intensity for 4 h/d for 5 consecutive days. Cells in sham group (SH) were cultured in RF exposure system, but without RF radiation. The positive control cells were irradiated with 6 Gy X-ray at a dose rate of 1.103 Gy/min (XR). To inhibit the upstream molecular JNK2 of UPRmt, cells in siRNA + RF, and siRNA + XR group were also pretreated with 100 nM siRNA-JNK2 for 48 h before RF/XR exposure. Thirty minutes, 4 h, and 24 h post-RF/XR exposure, cells were collected, the level of ROS was measured with flow cytometry, the expression levels of UPRmt-related proteins were detected using western blot analysis.Results: Compared with Sham group, the level of ROS in RF and XR group was significantly increased 30 min and 4 h post-RF/XR exposure (P < 0.05), however, the RF/XR-induced increase of ROS level reversed 24 h post-RF/XR exposure. Compared with Sham group, the expression levels of HSP10/HSP60/ClpP proteins in cells of RF and XR group increased significantly 30 min and 4 h post-RF/XR exposure (P < 0.05), however, the RF/XR-induced increase of HSP10/HSP60/ClpP protein levels reversed 24 h post-RF exposure. After interfering with siRNA-JNK2, the RF/XR exposures could not induce the increase of HSP10/HSP60/ClpP protein levels any more.Conclusions: The exposure of 900 MHz RF at 120 μW/cm2 power flux density could increase ROS level and activate a transient UPRmt in BMSC cells. Mitochondrial homeostasis in term of protein folding ability is restored 24 h post-RF exposure. Exposure to RF in our experimental condition did not cause permanent and severe mitochondrial dysfunctions. However, the detailed underlying molecular mechanism of RF-induced UPRmt remains to be further studied.

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Mitochondrial Unfolded Protein Response to Microgravity Stress in Nematode Caenorhabditis elegans

Scientific Reports ◽

10.1038/s41598-019-53004-9 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 25

Author(s):

Peidang Liu ◽

Dan Li ◽

Wenjie Li ◽

Dayong Wang

Keyword(s):

Caenorhabditis Elegans ◽

Unfolded Protein Response ◽

Simulated Microgravity ◽

Biological Effects ◽

Molecular Response ◽

Protective Response ◽

Unfolded Protein ◽

Protein Response ◽

Mitochondrial Unfolded Protein Response

Abstract Caenorhabditis elegans is useful for assessing biological effects of spaceflight and simulated microgravity. The molecular response of organisms to simulated microgravity is still largely unclear. Mitochondrial unfolded protein response (mt UPR) mediates a protective response against toxicity from environmental exposure in nematodes. Using HSP-6 and HSP-60 as markers of mt UPR, we observed a significant activation of mt UPR in simulated microgravity exposed nematodes. The increase in HSP-6 and HSP-60 expression mediated a protective response against toxicity of simulated microgravity. In simulated microgravity treated nematodes, mitochondria-localized ATP-binding cassette protein HAF-1 and homeodomain-containing transcriptional factor DVE-1 regulated the mt UPR activation. In the intestine, a signaling cascade of HAF-1/DVE-1-HSP-6/60 was required for control of toxicity of simulated microgravity. Therefore, our data suggested the important role of mt UPR activation against the toxicity of simulated microgravity in organisms.

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