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Reduced IRS-2 and GLUT4 expression in PPARgamma2-induced adipocytes derived from C/EBPbeta and C/EBPdelta-deficient
Hiroyasu Yamamoto1, Shogo Kurebayashi, Takahisa Hirose
1Department of Molecular Medicine (C-4), Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan.
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 gamma (PPARgamma) and CCAAT/enhancer-binding proteins (C/EBPs) play critical roles in adipocyte differentiation. However, it remained uncertain whether PPARgamma or which C/EBP is involved in the acquisition of these characteristics. We introduced PPARgamma2 into C/EBPbeta/delta-double deficient mouse embryonic fibroblasts (MEFs), followed by stimulation with its ligands, in order to define the roles of C/EBPbeta and C/EBPdelta 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/EBPbeta/delta-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/EBPbeta/delta-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/EBPbeta/delta-deficient cells. It could thus be demonstrated that C/EBPbeta and C/EBPdelta are involved in the acquisition of IRS-2 and GLUT4 expression as well as in insulin-sensitive glucose uptake during adipocyte differentiation.
Insights
CCAAT/enhancer-binding proteins beta and delta (C/EBPbeta/delta) are crucial for adipocyte differentiation, regulating insulin sensitivity and glucose uptake. Their absence impairs expression of key genes like GLUT4 and IRS-2.
Area of Science:
- Cell Biology
- Metabolism
- Molecular Endocrinology
Background:
- Adipocyte differentiation is essential for adipose tissue function, involving the acquisition of insulin responsiveness and specific gene expression.
- Peroxisome proliferator-activated receptor gamma (PPARgamma) and CCAAT/enhancer-binding proteins (C/EBPs) are known regulators of adipocyte differentiation.
- The specific roles of individual C/EBP family members in this process remained unclear.
Purpose of the Study:
- To elucidate the roles of C/EBPbeta and C/EBPdelta in the acquisition of mature adipocyte characteristics.
- To determine their involvement in the expression of key adipocyte genes and insulin sensitivity.
Main Methods:
- Mouse embryonic fibroblasts (MEFs) deficient in C/EBPbeta and C/EBPdelta were generated.
- PPARgamma2 was introduced into these deficient MEFs.
- Cells were stimulated with PPARgamma ligands to induce differentiation.
- Gene expression (aP2, LPL, adipsin, GLUT4, IRS-1, IRS-2) and insulin-stimulated glucose uptake were analyzed.
Main Results:
- C/EBPbeta/delta-deficient MEFs differentiated into morphologically mature adipocytes upon PPARgamma2 introduction and ligand stimulation.
- However, these cells exhibited reduced mRNA expression of GLUT4 and adipsin compared to wild-type controls.
- Insulin receptor substrate 2 (IRS-2) expression and insulin-sensitive 2-deoxyglucose uptake were significantly lower in C/EBPbeta/delta-deficient adipocytes.
Conclusions:
- C/EBPbeta and C/EBPdelta are critical for the full acquisition of adipocyte phenotype during differentiation.
- These transcription factors are specifically required for the expression of IRS-2 and GLUT4.
- C/EBPbeta/delta play a vital role in establishing insulin-sensitive glucose uptake in mature adipocytes.
