Nuclear and mitochondrial genome mutations lead to various mitochondrial diseases, many of which affect the mitochondrial respiratory chain. The proteome of the intermembrane space ( IMS ) of mitochondria consists of several important assembly factors that participate in the biogenesis of mitochondrial respiratory chain complexes. The present study comprehensively analyzed a recently identified IMS protein cytochrome c oxidase assembly factor 7 ( COA 7), or RES piratory chain Assembly 1 ( RESA 1) factor that is associated with a rare form of mitochondrial leukoencephalopathy and complex IV deficiency. We found that COA 7 requires the mitochondrial IMS import and assembly ( MIA ) pathway for efficient accumulation in the IMS . We also found that pathogenic mutant versions of COA 7 are imported slower than the wild‐type protein, and mislocalized proteins are degraded in the cytosol by the proteasome. Interestingly, proteasome inhibition rescued both the mitochondrial localization of COA 7 and complex IV activity in patient‐derived fibroblasts. We propose proteasome inhibition as a novel therapeutic approach for a broad range of mitochondrial pathologies associated with the decreased levels of mitochondrial proteins.

Introduction: Methotrexate, a folate antimetabolite, immunosuppressant and cytotoxic chemotherapeutic agents employed for malignant conditions. Continuous exposure of methotrexate produces adverse side effects especially liver toxicity. Recently, medicinal plants are gaining an importance owing to their phytoconstituents which are responsible for their medicinal value. Capparis decidua is one such medicinal plant widely used in the traditional system of medicine. No study has focused the mechanism of hepatoprotective property of Capparis decidua via Nrf2/HO-1 and PPARγ signaling pathway. Hence the study was mainly focused on its ability to modulate Nrf2 and PPARγ signaling in the methotrexate induced hepatotoxicity in Wistar rats. Materials and Methods: 30 female Wistar albino rats were divided into five groups. Following a single dose of methotrexate (20 mg/kg, intraperitoneally) injection, Wistar rats were orally administered with Capparis decidua at a doses of 250 mg/kg and 500mg/kg for 14 days. AST, ALT and ALP, antioxidants like GST, GPx, GR, were assessed in hepatic tissue. LPO, H 2 O 2 , OH radicals were assessed. mRNA expression of Nrf2, HO-1, PPARү was carried using real-time PCR in hepatic tissue. Nrf2, TNF-α, IL-1β proteins were assessed using western blot. Results: Methotrexate administration significantly increased liver function marker, caused lipid peroxidation and decreased antioxidants levels. Treatment with Capparis decidua caused significant decrease in AST, ALT, ALP, levels and significant increase in GST, GPx, GR. Methotrexate decreased mRNA expression of Nrf2, HO-1, PPARγ. Capparis decidua prevented methotrexate induced liver injury by upregulating Nrf2 and PPARү signaling pathway. Capparis decidua also suppressed inflammatory markers like TNF-α and IL-1β proteins. Conclusion: Capparis decidua has thus attenuated methotrexate induced hepatotoxicity and this could be via up-regulation of Nrf2/HO-1 and PPARγ pathways.

The function of mitochondria depends on the proper organization of mitochondrial membranes. The morphology of the inner membrane is regulated by the recently identified mitochondrial contact site and crista organizing system (MICOS) complex. MICOS mutants exhibit alterations in crista formation, leading to mitochondrial dysfunction. However, the mechanisms that underlie MICOS regulation remain poorly understood. MIC19, a peripheral protein of the inner membrane and component of the MICOS complex, was previously reported to be required for the proper function of MICOS in maintaining the architecture of the inner membrane. Here, we show that human and Saccharomyces cerevisiae MIC19 proteins undergo oxidation in mitochondria and require the mitochondrial intermembrane space assembly (MIA) pathway, which couples the oxidation and import of mitochondrial intermembrane space proteins for mitochondrial localization. Detailed analyses identified yeast Mic19 in two different redox forms. The form that contains an intramolecular disulfide bond is bound to Mic60 of the MICOS complex. Mic19 oxidation is not essential for its integration into the MICOS complex but plays a role in MICOS assembly and the maintenance of the proper inner membrane morphology. These findings suggest that Mic19 is a redox-dependent regulator of MICOS function.

Previous studies demonstrated that cells inhibit protein synthesis as a compensatory mechanism for mitochondrial dysfunction. Protein synthesis can be attenuated by 1) the inhibition of mTOR kinase, which results in a decrease in the phosphorylation of S6K1 and 4E-BP1 proteins, and 2) an increase in the phosphorylation of eIF2α protein. The present study investigated both of these pathways under conditions of short-term acute and long-term mitochondrial stress. Short-term responses were triggered in mammalian cells by treatment with menadione, antimycin A, or CCCP. Long-term mitochondrial stress was induced by prolonged treatment with menadione or rotenone and expression of genetic alterations, such as knocking down the MIA40 oxidoreductase or knocking out NDUFA11 protein. Short-term menadione, antimycin A, or CCCP cell treatment led to the inhibition of protein synthesis, accompanied by a decrease in mTOR kinase activity, an increase in the phosphorylation of eIF2α (Ser51), and an increase in the level of ATF4 transcription factor. Conversely, long-term stress led to a decrease in eIF2α (Ser51) phosphorylation and ATF4 expression and to an increase in S6K1 (Thr389) phosphorylation. Thus, under long-term mitochondrial stress, cells trigger long-lasting adaptive responses for protection against excessive inhibition of protein synthesis.