PPAR-γ is a major driver of the accumulation and phenotype of adipose tissue Treg cells

Abstract

Obesity and type-2 diabetes (T2D) have increased dramatically over the past several decades, in parallel. One of the major links between these two disorders is chronic, low-grade inflammation 1. Prolonged nutrient excess promotes the accumulation and activation of leukocytes in visceral adipose tissue (VAT) and ultimately other tissues, which provokes metabolic abnormalities such as insulin resistance, T2D and fatty-liver disease. While invasion of VAT by pro-inflammatory macrophages is considered to be a key event driving adipose-tissue inflammation and insulin resistance, little is known about the roles of other immune-system cell-types in these processes. Recently, a unique population of VAT-resident regulatory T cells (Tregs) was implicated in control of the inflammatory state of adipose tissue and, thereby, insulin sensitivity 2. We have identified peroxisome proliferator-activated receptor gamma (PPARγ), the “master-regulator” of adipocyte differentiation, as a critical molecular orchestrator of VAT Treg accumulation, phenotype and function. Unexpectedly, PPARγ expression by VAT Tregs was necessary for complete restoration of insulin sensitivity in obese mice by the thiazolidinedione (TZD) drug, pioglitazone (Pio). These findings suggest a previously unknown cellular mechanism for this important class of T2D drugs, and provide proof-of-principle that discrete populations of Tregs with unique functions can be precisely targeted to therapeutic ends.