Green Tea Polyphenols Reduced Fat Deposits in High Fat-Fed Rats via erk1/2-PPARγ-Adiponectin Pathway

OBJECTIVE Hypoadiponectinemia contributes to the development of obesity and related disorders such as diabetes, hyperlipidemia, and cardiovascular diseases. In this study we investigated the effects of green tea polyphenols (GTPs) on adiponectin levels and fat deposits in high fat (HF) fed rats, the mechanism of signaling pathway was explored as well. METHODS AND RESULTS Male Wistar rats were fed with high-fat diet. GTPs (0.8, 1.6, 3.2 g/L) were administered via drinking water. Serum adiponectin and insulin were measured by ELISA, mRNA levels of adiponectin and PPARγ in visceral adipose tissue (VAT) were determined by Real-time PCR, protein levels of PPARγ, phospho (p) - PPARγ, extracellular signal regulated kinase (erk) 1/2 and p-erk1/2 in VAT were determined by western blot. GTPs treatment attenuated the VAT accumulation, hypoadiponectinemia and the decreased mRNA level of adiponectin in VAT induced by HF. Decreased expression and increased phosphorylation of PPARγ (the master regulator of adiponectin), and increased activation of erk1/2 were observed in HF group, and these effects could be alleviated by GTPs treatment. To explore the underlying mechanism, VAT was cultured in DMEM with high glucose to mimic the hyperglycemia condition in vitro. Similar to the results of in vivo study, decreased adiponectin levels, decreased expression and increased phosphorylation of PPARγ, and elevated erk1/2 phosphorylation in cultured VAT were observed. These effects could be ameliorated by co-treatment with GTPs or PD98059 (a selective inhibitor of erk1/2). CONCLUSION GTPs reduced fat deposit, ameliorated hypoadiponectinemia in HF-fed rats, and relieved high glucose-induced adiponectin decrease in VAT in vitro. The signaling pathway analysis indicated that PPARγ regulation mediated via erk1/2 pathway was involved.