Pioglitazone promotes preadipocyte proliferation by downregulating p16Ink4a

Highlights: → Mechanisms for preadipocyte hyperplasia by pioglitazone, a PPARγ agonist, are shown. → Pioglitazone promotes cell-cycle of 3T3-L1 preadipocytes and increases their number. → Pioglitazone downregulates a cyclin dependent kinase inhibitor, p16Ink4a. → PPARγ transrepresses p16Ink4a gene in preadipocytes, which pioglitazone enhances. -- Abstract: Pioglitazone, a synthetic ligand of peroxisome proliferator-activated receptor (PPAR)γ, causes preadipocyte proliferation through a mechanism which still remains elusive. Here, to address the mechanism, we investigated the effects of PPARγ and pioglitazone on the kinetics of cyclin-dependent kinase inhibitors, especially with p16Ink4a (p16) centered, by employing 3T3-L1 preadipocytes. Pioglitazone promoted preadipocyte proliferation by increasing S and G2/M cell-cycle entry, which was accompanied by decreased p16 mRNA expression. PPARγ overexpression along with the luciferase reporter assay confirmed that PPARγ was crucial for the downregulation of p16 mRNA transcription, and that the action was augmented by pioglitazone. Thus, pioglitazone exerted cell-cycle dependent promoting effect on preadipocyte proliferation, of which mechanisms include p16-downregulation through PPARγ.