GS increase mitochondrial function through the SIRT1 pathway in cardiomyocytes subjected to hypoxia and OGD injuries
Generally, ischemia in the heart can cause mitochondrial dysfunction, which consequently reduces energy metabolism to cause further cardiac damage (Kalogeris, Baines, Krenz & Korthuis, 2012). To further explore the protective effect of GS against hypoxia and OGD injuries, cell viability, OCR, ATP production, mitochondrial respiration complexes, and the SIRT1-PGC-1α pathway were investigated in control, injured model, and GS-treated H9c2 cells. As shown in Fig. 6A , hypoxia and OGD led to decreases in H9c2 cell viability, which were slightly recovered by GS. Consistent with current results, we found that hypoxia induced by Cocl2 for 9 h significantly diminished the rate of oxygen consumption and ATP production of H9c2 cells, which were lower during the process of glucose and oxygen deprivation(Fig. 6B-6C) . GS pretreatment for 48 h reversed the decreases of OCR and ATP level induced by hypoxia and OGD in H9c2 cells (Fig. 6B-6C) . Meanwhile, the levels of five mitochondrial respiratory complexes, CV-ATP5A, CIII-UQCRC2, CIV-MTCO1, CII-SDHB, and CI-NDUFB8, were decreased by hypoxia for 9 h, which were obviously recovered by GS at 10 μg/mL ( Fig. 6D-6E) . In addition, Western blot analysis demonstrated that hypoxia and OGD led to decrease in SIRT1 and PGC-1α levels in H9c2 cells and the levels of SIRT1 and PGC-1α in GS-pretreated H9c2 cells were higher than those in the hypoxia- or OGD-induced model group (Fig. 6F-6G) . Taken together, these results clearly demonstrate the protective effect of GS to increase mitochondrial function against the hypoxia- or OGD-induced cardiomyocyte damage through activation of the SIRT1-PGC-1α pathway.