Reduced IRS-2 and GLUT4 expression in PPARγ2-induced adipocytes derived from C/ECPβ and C/EBPδ-deficient mouse embroyonic fibroblasts

Abstract

In adipose tissue, the ability of cells to respond to insulin and to express genes such as those encoding fatty-acid-binding protein (422/aP2), lipoprotein lipase (LPL), adipsin and glucose transporter 4 (GLUT4) is acquired during their differentiation into mature adipocytes. It has been recognized that peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding proteins (C/EBPs) play critical roles in adipocyte differentiation. However, it remained uncertain whether PPARγ or which C/EBP is involved in the acquisition of these characteristics. We introduced PPARγ2 into C/EBPβ/δ-double deficient mouse embryonic fibroblasts (MEFs), followed by stimulation with its ligands, in order to define the roles of C/EBPβ and C/EBPδ in phenotypic acquisition during adipocyte differentiation. This procedure resulted in differentiation of these MEFs into mature adipocytes morphologically similar to wild-type MEFs. However, the adipocytes derived from the C/EBPβ/δ-deficient MEFs showed lower expression of GLUT4 and adipsin mRNA than those derived from wild-type MEFs, although aP2 and LPL mRNA levels were similar in both types. The C/EBPβ/δ-deficient adipocytes also expressed lower amounts of insulin receptor substrate 2 (IRS-2) than the adipocytes derived from wild-type MEFs, whereas the amounts of insulin receptor and IRS-1 were similar. Finally, insulin-responsive 2-deoxyglucose uptake was lower in the C/EBPβ/δ-deficient cells. It could thus be demonstrated that C/EBPβ and C/EBPδ are involved in the acquisition of IRS-2 and GLUT4 expression as well as in insulin-sensitive glucose uptake during adipocyte differentiation.