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Regulation of adipogenesis and key adipogenic gene expression by retinoic acid in 3T3 –L1 preadipocytes
Adipogenesis plays an important role in metabolic homeostasis and nutrient pathways, and is crucial for regulating body fat reserves and body weight of mammals. The transcriptional control of adipogenesis requires a sequential series of gene expression events and activation of a number of key signaling pathways. Retinoic acid is considered as a potent inhibitor of adipogenesis for decades, and understanding the mechanism of retinoic acid regulation of adipogenesis is useful for helping to control body fat and to manipulate meat quality in the beef industry. To investigate the function of retinoic acid in regulation of adipogenesis, adipocyte differentiation and key adipogenic gene expression were studied in 3T3-L1 preadipocytes. Lipid accumulation was measured by Oil Red O staining and expression of key adipogenic genes was quantified using quantitative real-time PCR. Adipogenic responses to different concentrations of retinoic acid were determined on day 2, 4, 6, 8, 10 after stimulation of adipogenesis with the traditional hormonal cocktail (dexamethasone, isobutyl-1-methylxanthine and insulin) in the absence or presence of retinoic acid. In response to high concentrations (10-6, 10-7 M) of retinoic acid, lipid accumulation and the expression of PPARγ, C/EBPα, FABP4 and SCD-1 were inhibited through day 8, but on day 10, lipid accumulation and the expression levels of these genes rebounded to levels comparable to the control. Interestingly, the greatest effects of retinoic acid treatments were upon expression of FABP4. However, expression of SREBP-1c was not affected. The lowest retinoic acid concentration (10-10M) did not affect adipocyte differentiation or expression of adipogenic genes. These results indicate that retinoic acid inhibited adipogenesis via suppressing adipogenic specific genes, especially FABP4. Our data indicate that a deeper understanding of the roles of retinoic acid in regulating adipogenesis will be informed by further study of adipogenic specific gene promoter activity.
Keywords: adipogenesis, transcription factors, retinoic acid