Isoform-specific functions of PPARg in gene regulation and adipose metabolism

Peroxisome proliferator-activated receptor g (PPARg) is a nuclear receptor that is a vital regulator of adipogenesis, insulin sensitivity, and lipid metabolism. Activation of PPARg by antidiabetic thiazolidinediones (TZD) reverses insulin resistance but also leads to weight gain that limits the use of these drugs. There are two main PPARg isoforms, but the specific functions of each are not established. Here we generated mouse lines in which endogenous PPARg1 and PPARg2 were epitope-tagged to interrogate isoform-specific genomic binding, and mice deficient in either PPARg1 or PPARg2 to assess isoform-specific gene regulation. Strikingly, although PPARg1 and PPARg2 contain identical DNA binding domains, we uncovered isoform-specific genomic binding sites in addition to shared sites. Moreover, PPARg1 and PPARg2 regulated different set of genes in adipose tissue depots, suggesting distinct roles in adipocyte biology. Indeed, mice with selective deficiency of PPARg1 maintained body temperature better than wild type or PPARg2-deficient mice. Most remarkably, although TZD treatment improved glucose toleranceinsulin resistance in mice lacking either PPARg1 or PPARg2, the PPARg1-deficient mice were protected from TZD-induced body weight gain compared to PPARg2-deficient mice. Thus, PPARg isoforms have specific and separable metabolic functions that may be targeted to improve therapy for insulin resistance and diabetes. Adipose tissues were collected from 3HA-PPARg1, HHA-PPARg2, PPARg1 KO, PPARg2 KO and their littermate control mice