TET2 facilitates PPARγ agonist-mediated gene regulation and insulin sensitization in adipocytes

Emerging evidence indicates that epigenetic mechanisms like DNA methylation directly contribute to metabolic regulation. For example, we previously demonstrated that de novo DNA methyl transferase Dnmt3a plays a causal role in the development of adipocyte insulin resistance. Recent studies suggest that DNA demethylation plays an important role in the developmental process of adipocytes. However, little is known about whether DNA demethylase ten-eleven translocation (TET) proteins regulate the metabolic functions of adipocytes. Methods: The expression of Tet genes was assessed in the fractionated adipocytes of chow- and high fat diet-fed C57/1316 mice using qPCR and western blotting. The effect of Tet2 gain- or loss-of-function in fully mature 3T3-L1 adipocytes in the presence/absence of Rosiglitazone (Rosi) and TNF-alpha on insulin sensitivity was using the insulin-stimulated glucose uptake and insulin signaling assays. Gene expression and DNA methylation analyses of PPAR gamma target genes was performed in the same setting. In addition, PPAR gamma reporter assays, co-immunoprecipitation assays, PPAR gamma ChIP-PCR analyses were performed. Results: We found that adipose expression of TET2, alone among its family members, was significantly reduced in diet-induced insulin resistance. TET2 gain-of-function was sufficient to promote insulin sensitivity while loss-of function was necessary to facilitate insulin sensitization in response to the PPAR gamma agonist Rosiglitazone (Rosi) in cultured adipocytes. Consistent with this, TET2 was required for Rosi-dependent gene activation of certain PPAR gamma targets accompanied by changes in DNA demethylation at the promoter regions. Furthermore, TET2 was necessary to sustain PPAR gamma binding to target loci upon activation with Rosi via physical interaction with PPAR gamma. Conclusions: Our data demonstrate that TET2 works as an epigenetic regulator of Rosi-mediated insulin sensitization and transcriptional regulation in adipocytes. (C) 2018 Elsevier Inc. All rights reserved.