Insulin Inhibits the Expression of Adiponectin and AdipoR2 mRNA in Cultured Bovine Adipocytes

Y G Sun,L S Gui,D P Yang,H B Wang,H F Guo,L S Zan,X L Zhao

doi:10.5713/ajas.2009.90159

Abstract

Adiponectin is an adipocyte-derived protein that has a regulatory role in energy homeostasis and influences insulin sensitivity. Its effects on glucose utilization and lipid metabolism are mediated by AdipoR1 and AdipoR2. How insulin affects adiponectin gene expression and secretion is still controversial. This study was conducted to determine the expression of adiponectin, AdipRs and PPAR-γ during the differentiation of bovine preadipocytes and the effect of insulin on expression of these genes in bovine adipocytes. The bovine preadipocytes started to accumulate lipids three days after differentiation was induced, with increased expression of adiponectin, AdipoR2 and PPAR-γ mRNAs. Insulin decreased the expression of adiponectin mRNA in a dose- and time-dependent fashion, and the inhibition was detectable at insulin concentrations as low as 10 nM and as early as 2 h after addition of 100 nM insulin. Insulin also inhibited the expression of AdipoR2 mRNA at concentrations from 1 to 1,000 nM or 24 h after addition of 100 nM insulin, but did not affect the expression of AdipoR1 in bovine adipocytes. Inhibition of PI3K with LY294002 reversed the inhibition of adiponectin and AdipoR2 mRNA expression by insulin. These results suggest that insulin suppresses the expression of adiponectin and AdipoR2 at least partially via the PI3K signal pathway.

Highlights

Adiponectin, called Acrp30, GBP28, apM1 or AdipoQ, was identified first by Scherer in 1995 (Scherer et al, 1995) and by three other groups (Hu et al, 1996; Maeda et al, 1996; Nakano et al, 1996)
In order to explore the effect of insulin on the expression of adiponectin and adiponectin receptor genes, bovine preadipocytes were allowed to differentiate for nine days until 95% of the attached cells had visible lipid droplets
The growth medium was replaced with differentiation medium and the preadipocytes were induced to differentiate into mature adipocytes

Summary

INTRODUCTION

Adiponectin, called Acrp, GBP28, apM1 or AdipoQ, was identified first by Scherer in 1995 (Scherer et al, 1995) and by three other groups (Hu et al, 1996; Maeda et al, 1996; Nakano et al, 1996). Adiponectin stimulates fatty acid oxidation, decreases plasma triglycerides, and enhances glucose metabolism by increasing insulin sensitivity (Yamauchi et al, 2002). It is involved in the regulation of energy balance and body weight (Fruebis et al, 2001; Yamauchi et al, 2001). Adiponectin binds to the extracellular C-terminal domains of AdipoRs while the cytoplasmic N-terminal domains interact with an adaptor protein Both AdipoR1 and AdipoR2 can mediate adiponectin function and the expression of these two receptors is regulated by PPAR-γ ligands and PPAR-γ in obese patients (Chinetti et al, 2004). The data obtained so far suggest that adiponectin is an important insulin-sensitizing adipocytokine It appears that various factors might increase or decrease insulin sensitivity at least partly by up- or down-regulating adiponectin. We investigated such expression during differentiation of bovine preadipocytes in vitro using semi-quantitative RTPCR, and examined the effect of insulin on those genes expression in bovine adipocytes

MATERIALS AND METHODS

RESULTS

DISCUSSION