PPARβ/δ regulates the human SIRT1 gene transcription via Sp1

Abstract

NAD-dependent deacetylase SIRT1 is known to be activated by caloric restriction and is related to longevity. A natural polyphenolic compound resveratrol is also shown to increases SIRT1 activity and extends lifespan. However, the transcriptional regulation of SIRT1 gene has not completely examined in the context of metabolism. Thus, in this study, we characterized the 5’ -flanking region of human SIRT1 gene. We first found that representative metabolic hormones and related factors (glucocorticoid, glucagon/cAMP, and insulin) did not show significant effect on SIRT1 gene transcription. PPARα and PPARγ1 without/with their specific ligands did not have significant effect as well. In contrast, expression of PPARβ/δ (PPARδ markedly increased the 5’ -promoter activity of SIRT1 gene, which was further amplified by the addition of GW501516, a selective PPARδ agonist. Deletion/mutation mapping analyses failed to identify PPAR binding element but revealed the presence of canonical Sp1 binding site, which was conserved among species. The Sp1 site is functional, because Sp1 overexpresson significantly enhanced SIRT1 promoter activity, and the binding of Sp1 to the element was confirmed by EMSA and ChIP assays. Interestingly, specific Sp1 antagonist mithramycin completely abolished the PPARδ-mediated induction of SIRT1 gene transcription. Altogether, our data suggest the predominant role of PPARδ in the transcriptional regulation of SIRT1 gene. Furthermore, the effects of PPARδ seem to be mediated by Sp1. We assume that, in vivo, starvation increases lipolysis-derived free fatty acid and activates PPARδ and the resultant increase in SIRT1 expression, in addition to the activation by NAD and AMPK, facilitates the deacetylation of a variety of proteins involved in mitochondrial β-oxidation pathway and cell survival.