PPAR delta Inhibits Hyperglycemia-Triggered Senescence of Retinal Pigment Epithelial Cells by Upregulating SIRT1

Emerging evidence shows that peroxisome proliferator-activated receptor delta (PPAR delta) plays a pivotal role in cellular aging. However, its function in retinal disease processes such as hyperglycemia-associated diabetic retinopathy is unclear. Here, we demonstrate that PPAR delta inhibits premature senescence of retinal pigment epithelial (RPE) cells induced by high glucose (HG) through SIRT1 upregulation. A specific ligand GW501516-activation of PPAR delta suppressed premature senescence and production of reactive oxygen species induced by HG in ARPE-19 cells, a spontaneously arising human RPE cell line. These effects were accompanied by the regulation of the premature senescence-associated genes p53, p21, and SMP-30. Furthermore, GW501516-activated PPAR delta almost completely abolished the effects of HG treatment on the formation of phosphorylated H2A histone family member X (gamma-H2A.X) foci, a molecular marker of aging. These inhibitory effects of GW501516 were significantly reversed in ARPE-19 cells stably expressing small hairpin RNA targeting PPAR delta. Notably, GW501516 significantly increased the mRNA and protein levels of SIRT1, indicating that GW501516-activated PPAR delta exerted its beneficial effects through SIRT1. In addition, GW501516 restored HG-suppressed SIRT1 expression, corroborating the role of SIRT1 in the anti-senescence function of PPAR delta. The effects of PPAR delta on HG-induced premature senescence and the expression of the senescence-associated genes p53, p21, and SMP-30 were mimicked by the SIRT1 activator resveratrol, but blocked by the SIRT1 inhibitor sirtinol. Collectively, these results indicate that GW501516-activated PPAR delta inhibits HG-triggered premature senescence of RPE cells by modulating SIRT1 signaling.