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ISL1 regulates PPARg activation and early adipogenesis via BMP4-dependent and -independent mechanisms

ABSTRACT: While adipogenesis is controlled by a cascade of transcription factors, the global gene expression profiles in the early phase of adipogenesis are not well defined. Using microarray analysis of gene expression in 3T3-L1 cells we have identified evidence for the activity of 2568 genes during the early phase of adipocyte differentiation. One of these, ISL1, was of interest since its expression was markedly upregulated at 1 h after initiation of differentiation with a subsequent rapid decline. Overexpression of ISL1 at early times during adipocyte differentiation, but not at later times, was found to profoundly inhibit differentiation. This was accompanied by moderate down-regulation of PPARg levels, substantial down-regulation of PPARg downstream genes and down-regulation of BMP4 levels in preadipocytes. Readdition of BMP4 overcame the inhibitory effect of ISL1 on PPARg but not aP2 expression, a downstream gene of PPARg; and BMP4 also partially rescued ISL1 inhibition of adipogenesis, an effect which is additive with rosiglitazone. These results suggest that ISL1 is intimately involved in early regulation of adipogenesis, modulating PPARg expression and activity via BMP4-dependent and -independent mechanisms. Our time course gene expression survey sets the stage for further studies to explore other early and immediate regulators.

ORGANISM(S): Mus musculus

PROVIDER: GSE40565 | GEO | 2012/09/05

SECONDARY ACCESSION(S): PRJNA174313

REPOSITORIES: GEO

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Project description:Visceral fat (VF) and subcutaneous fat (SF) are developmentally different tissues with different gene expression. Islet-1 (ISL1), a LIM-homeobox transcription factor with important developmental and regulatory function in islet, neural, and cardiac tissue, is virtually absent in SF but substantially expressed in the stromovascular [preadipocyte containing] fraction of VF; expression correlates negatively with adiposity in rodents and man. ISL1 expression is transiently increased in 3T3-L1 preadipocytes during early differentiation, suggesting a functional role. To examine the role of ISL1 in adipogenesis, we tested whether retroviral overexpression of ISL1 in 3T3-L1 preadipocytes affected their ability to differentiate into mature adipocytes. Terminal differentiation was assessed by Oil Red O [lipid droplet] staining and by immunoblot detection of adipocyte marker proteins, including aP2 and GLUT4. ISL1 significantly inhibited lipid droplet formation, reduced lipid accumulation (about 80% inhibition, p<0.05), and substantially inhibited aP2 and GLUT4 expression. ISL1 did not inhibit expression of C/EBPb and C/EBPd after induction of differentiation, but reduced PPARg and C/EBPa by >50% at both mRNA and protein level. In addition, the PPARg agonist, rosiglitazone, substantially rescued ISL1 inhibited adipogenesis in the absence of exogenous PPARg, and fully rescued in the presence of exogenous PPARg. In summary, ISL1 overexpression inhibited fat droplet formation, lipid accumulation, and adipocyte-specific gene expression; there was accompanying inhibition of C/EBPa, PPARg and downstream gene expression. We conclude that ISL1 overexpression inhibited adipocyte differentiation by inhibition of PPARg regulated gene expression. As abdominal obesity strongly correlates with insulin resistance, and cardiovascular risk, ISL1 up-regulation may impact abdominal obesity and its concomitant metabolic derangements. Total cellular RNA was isolated from 3T3-L1 cells expressing Flag-ISL1 or not at 48 h following treatment with differentiation cocktail. Individual RNA from biological triplicates was used for microarray analysis.

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ISL1 regulates PPARg activation and early adipogenesis via BMP4-dependent and -independent mechanisms

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