Abstract
Adipocyte differentiation is regulated by at least two major transcription factors, CCAAT/enhancer-binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma). Expression of PPARgamma in fibroblasts converts them to fat-laden cells with an adipocyte-like morphology. Here, we investigate the ability of PPARgamma to confer insulin-sensitive glucose transport to a variety of murine fibroblast cell lines. When cultured in the presence of a PPARgamma ligand, Swiss-3T3 and BALB/c-3T3 cells ectopically expressing PPARgamma accumulate lipid droplets, express C/EBPalpha, aP2, insulin-responsive aminopeptidase, and glucose transporter isoform 4 (GLUT4), and exhibit highly insulin-responsive 2-deoxyglucose uptake. In contrast, PPARgamma-expressing NIH-3T3 cells, despite similar lipid accumulation, adipocyte morphology, and aP2 expression, do not express C/EBPalpha or GLUT4 and fail to acquire insulin sensitivity. In cells ectopically expressing PPARgamma, the development of insulin-responsive glucose uptake correlates with C/EBPalpha expression. Furthermore, ectopic expression of C/EBPalpha in NIH-3T3 cells converts them to the adipocyte phenotype and restores insulin-sensitive glucose uptake. We propose that the pathway(s) leading to fat accumulation and morphological changes are distinct from that leading to insulin-dependent glucose transport. Our results suggest that although PPARgamma is sufficient to trigger the adipogenic program, C/EBPalpha is required for establishment of insulin-sensitive glucose transport.
Highlights
The ability of metabolically active cells to respond to insulin is central to the proper regulation of lipid and glucose metabolism in the body
To understand the mechanisms by which peroxisome proliferator-activated receptors (PPARs)␥ regulates development of the adipocyte phenotype, we introduced PPAR␥ by retroviral infection into three well characterized murine fibroblast cell lines: Swiss-3T3, BALB/c-3T3, and NIH-3T3
We have examined the ability of PPAR␥ to activate the program leading to insulin-dependent glucose transport in various murine fibroblast cell lines
Summary
C/EBP, CCAAT/enhancer-binding protein; PPAR, peroxisome proliferator-activated receptor; IRAP, insulinresponsive aminopeptidase; GLUT, glucose transporter isoform; aP2, adipose protein 2/fatty acid-binding protein; DMEM, Dulbecco’s modified Eagle’s medium; PI3-kinase, phosphatidylinositol 3-kinase
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