Abstract
Oxidative stress has been implicated as a causal role in atherosclerosis, microvascular complications of diabetes as well as in beta cell failure in type 2 diabetes. PPARgamma agonists not only improve insulin sensitivity but also eliminate oxidative stress. In mouse, catalase, a major antioxidant enzyme, is directly regulated by PPARgamma through two PPARgamma binding elements in its promoter. This study examined the regulatory mechanisms of catalase expression in human. Expression of catalase was significantly upregulated in human primary adipocytes upon treatment with a PPARgamma agonist. However, the mouse PPARgamma response elements are not functionally conserved in human catalase promoter. In luciferase reporter assay containing human catalase promoter, PPARgamma /RXRalpha, in combination of a PPARgamma agonist significantly transactivated 19 kb of promoter and this was mediated via a novel PPARgamma response element (PPRE) at -12 kb from transcription initiation site of human catalase gene. Electrophoretic mobility shift assay showed direct binding of PPARgamma to this PPRE. Together, our results indicate that PPARgamma regulates the expression of catalase gene in human through a PPRE distinct from that of mouse, and could explain, at least in part, the observed inhibitory effects of PPARgamma on oxidative stress in human.
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