Insulin acutely regulates the expression of the peroxisome proliferator-activated receptor-gamma in human adipocytes
Peroxisome proliferator-activated receptor (PPAR)-gamma is one of the key actors of adipocyte differentiation. This study demonstrates 1) that PPAR-gamma mRNA expression is not altered in subcutaneous adipose tissue (n = 44) or in skeletal muscle (n = 19) of subjects spanning a wide range of BMIs (20-53 kg/m2) and 2) that insulin acutely increases PPAR-gamma mRNA expression in human adipocytes both in vivo and in vitro. The effect of insulin was investigated in abdominal subcutaneous biopsies obtained before and at the end of a 3-h euglycemic-hyperinsulinemic clamp. Insulin significantly increased PPAR-gamma mRNA levels in lean subjects (88 +/- 17%, n = 6), in type 2 diabetic patients (100 +/- 19%, n = 6), and in nondiabetic obese patients (91 +/- 20%, n = 6). Both PPAR-gamma1 and PPAR-gamma2 mRNA variants were increased (P < 0.05) after insulin infusion. In isolated human adipocytes, insulin induced the two PPAR-gamma mRNAs in a dose-dependent manner, with half-maximal stimulation at a concentration of approximately 1-5 nmol/l. However, PPAR-gamma2 mRNA was rapidly (2 h) and transiently increased, whereas a slow and more progressive induction of PPAR-gamma1 was observed during the 6 h of incubation. In explants of human adipose tissue, PPAR-gamma protein levels were significantly increased (42 +/- 3%, P < 0.05) after 12 h of incubation with insulin. These data demonstrate that PPAR-gamma belongs to the list of the insulin-regulated genes and that obesity and type 2 diabetes are not associated with alteration in the expression of this nuclear receptor in adipose tissue.