Increased SIRT3 Expression and Antioxidant Defense under Hyperglycemic Conditions in HepG2 Cells.

Background: Hyperglycemia exacerbates the production of mitochondrial reactive oxygen species and this contributes to a variety of pathological conditions. Sirtuin 3 (SIRT3) has been shown to play a role in decreasing oxidative stress and improving disease outcomes by regulating antioxidant defense. Our understanding of molecular events during oxidative stress under chronic hyperglycemia in the liver is limited. We postulated that SIRT3 may play a role in antioxidant defense under hyperglycemic conditions in HepG2 cells.

Methods: Cell viability was determined in HepG2 and human embryonic kidney (HEK) 293 cells cultured in the presence of 5.5 mM glucose (control), 19.9 mM mannitol (osmotic control), 10 mM glucose and 30 mM glucose (hyperglycemic), and nicotinamide (NAM) (10 mM) at 24-hr and 72-hr time points. SIRT3, peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), and cyclic adenosoine monophosphate (cAMP) response element binding protein (pCREB) protein expression were measured via western blotting. Mitochondrial antioxidant enzymes glutathione peroxidase 1 (GPx1), superoxide dismutase 2 (SOD2), and uncoupling protein 2 (UCP2) and mitochondrial DNA (mtDNA) repair enzyme 8-oxoguanine glycosylase (OGG1) were evaluated via quantitative PCR (qPCR).

Results: Increased cell viability and protein expression of SIRT3, pCREB, and PGC-1α were observed under hyperglycemic conditions at 24 hr. These were further elevated at the 72-hr time point. We also observed higher fold changes of SIRT3, GPx1, SOD2, UCP2, and OGG1 in the treated groups. Treatment with NAM decreased protein and gene expression of SIRT3, pCREB, PGC-1α, GPx1, SOD2, UCP2, and OGG1 at both time points in the hyperglycemic groups.

Conclusions: Our data may allude to the relationship that has been established between SIRT3 and PGC-1α with regard to increased antioxidant defense during oxidative stress. This suggests that SIRT3 may play a role in increasing antioxidant defense and conferring resistance to oxidative stress-induced damage under hyperglycemic conditions in the human hepatoma cell line.