Peroxisome Proliferator-Activated Receptor Gamma Isoforms Differentially Regulate Preadipocyte Proliferation, Apoptosis, And Differentiation In Chickens

Peroxisome proliferator-activated receptor gamma (PPAR gamma) has 2 protein isoforms (PPAR gamma 1 and PPAR gamma 2) generated by alternative promoter usage and alternative splicing. However, their functional uniqueness and similarity remain unclear. In the study, we investigated the effects of lentivirus-mediated over expression of PPAR gamma 1 and PPAR gamma 2 on proliferation, apoptosis, and differentiation of the immortalized chicken preadipocytes. Cell Counting Kit-8 assay showed PPAR gamma 1 and PPAR gamma 2 overexpression markedly suppressed cell proliferation, and fluorescence activated cell sorting analysis showed that PPAR gamma 1 and PPAR gamma 2 overexpression caused cell cycle arrest at G0/G1 phase. Cell death detection ELISA analysis showed both PPAR gamma 1 and PPAR gamma 2 overexpression induced cell apoptosis. Oil red O staining and gene expression analysis showed both PPAR gamma 1 and PPAR gamma 2 overexpression promoted preadipocyte differentiation. In the presence of PPARy ligand, rosiglitazone, PPAR gamma 2 overexpression was more potent in inducing apoptosis, promoting adipogenesis, and suppressing cell proliferation than PPAR gamma 1 overexpression. We further explored the molecular basis for their functional differences. Reporter gene assay showed that under ligand conditions, PPAR gamma 2 overexpression resulted in 1.68-fold increase in transcription activity compared with PPAR gamma 1. Electrophoretic mobility shift assay showed both PPAR gamma 1 and PPAR gamma 2 could bind to PPAR response element (PPRE) as heterodimer with retinoid X receptor alpha, and by comparison, PPAR gamma 2 had a higher affinity for PPRE than PPAR gamma 1. Reporter gene assay showed expression PPAR gamma 1 and PPAR gamma 2 similarly induced fatty acid synthase and adipocyte fatty acid-binding protein promoter activity but differentially induced lipoprotein lipase and perilipin 1 promoter activities. Coimmunoprecipitation analysis showed that PPAR gamma 1 and PPAR gamma 2 interacted similarly with the coactivators, Tat-interacting protein 60. Taken together, our results demonstrate that PPAR gamma 1 and PPAR gamma 2 differentially regulate preadipocyte proliferation, apoptosis, and differentiation as a result of their distinct and overlapping molecular functions.