Mitochondrial-targeted methionine sulfoxide reductase overexpression increases the production of oxidative stress in mitochondria from skeletal muscle

Sulfur Amino Acid Restriction alters mitochondrial function depending on tissue, sex, and Methionine sulfoxide reductase A (MsrA) status

Methionine restriction (MR) has been shown to affect mitochondrial function including altering oxygen consumption, reactive oxygen species (ROS) generation, Complex expression, and oxidative damage. The sulfur-containing amino acid methionine can become oxidized forming methionine sulfoxide which can lead to changes in protein function and signaling. Methionine sulfoxide reductases are endogenous enzymes capable of reducing methionine sulfoxide, with Methionine sulfoxide reductase A (MsrA) being ubiquitously expressed in mammals. Here we investigated if the effects of MR on mitochondrial function required functional MsrA in the liver and kidney which are the major tissues involved in sulfur biochemistry and both highly express MsrA. Moreover, MsrA is endogenously found in the mitochondria thereby providing potential mechanisms linking diet to mitochondrial phenotype. We found sex-specific changes in oxygen consumption of isolated mitochondria and females showed changes with MR in a tissue-dependent manner - increased in liver and decreased in kidney. Loss of MsrA increased or decreased oxygen consumption depending on the tissue and which portion of the electron transport chain was being tested. In general, males had few changes in either tissue regardless of MR or MsrA status. Hydrogen peroxide production was increased in the kidney with MR regardless of sex or MsrA status. However, in the liver, production was increased by MR in females and only slightly higher with loss of MsrA in both sexes. Mitochondrial Complex expression was found to be largely unchanged in either tissue suggesting these effects are driven by regulatory mechanisms and not by changes in expression. Together these results suggest that sex and MsrA status do impact the mitochondrial effects of MR in a tissue-specific manner.

LncRNA TUG1 compromised neuronal mitophagy in cerebral ischemia/reperfusion injury by targeting sirtuin 1

BACKGROUND

Mitophagy protects against cerebral ischemia/reperfusion (CI/R)-induced neuronal apoptosis via mitochondrial clearance. Although taurine-upregulated gene 1 (lncRNA TUG1) has been proposed to be involved in the neuronal apoptosis evoked by CI/R, its specific role in mitophagy during the progression of CI/R injury remains unknown.

METHODS

The CI/R rat model was established using middle cerebral artery occlusion/reperfusion (MCAO/R). Human neuroblastoma cell line SH-SY5Y was subjected to oxygen-glucose deprivation and reoxygenation (OGD/R). Ubiquitination assay, co-immunoprecipitation assay, RNA pull-down, and RNA immunoprecipitation were used to determine the interplay among TUG1, sirtuin 1 (SIRT1), and F-box and WD repeat domain-containing 7 (FBXW7).

RESULTS

The upregulation of the TUG1 level and downregulation of the mitophagy were observed in both MCAO/R-treated rats and OGD/R-treated cells. The administration of si-TUG1 (a siRNA directed against TUG1) potentiated mitophagy and suppressed neuronal apoptosis in OGD/R-treated cells. However, the neuroprotective effect of si-TUG1 was reversed by mitophagy inhibitor or SIRT1 knockdown in vitro. Functionally, TUG1 enhanced FBXW7-mediated SIRT1 ubiquitination by upregulating FBXW7 expression. The overexpression of FBXW7 abrogated the si-TUG1-reinforced mitophagy by decreasing SIRT1 expression, thus aggravating neuronal apoptosis in the OGD/R+si-TUG1-treated cells. In rats with MCAO/R, the interference of TUG1 clearly decreased neuronal apoptosis, lessened the infarct volume, and relieved the neurological deficits.

CONCLUSION

TUG1 knockdown promotes SIRT1-induced mitophagy by suppressing FBXW7-mediated SIRT1 degradation, thus relieving the neuronal apoptosis induced by CI/R injury. LncRNA TUG1 promotes neuronal apoptosis through inhibition of mitophagy. TUG1 decreased SIRT1 expression by promoting FBXW7-mediated SIRT1 ubiquitination. FBXW7/SIRT1 axis mediated the effect of TUG1 on OGD/R-induced neuronal apoptosis by regulating mitophagy.