Analysis of gene expression during adipogenesis in 3T3‐F442A preadipocytes: Insulin and dexamethasone control

Abstract

In the present study, we have investigated dexamethasone and insulin regulation of the expression of adipose-specific mRNA, namely, glycerophosphate dehydrogenase (G3PDH) and adipsin, at different stages of differentiation. During adipose conversion, insulin promotes an accumulation of G3PDH mRNA which is linked to cell differentiation; in fully differentiated cells, insulin is not required to maintain G3PDH gene expression. Differentiating cells in serum deprived medium already exhibit, at day 1, a maximal amount of mRNA encoding for adipsin, which is tenfold decreased by 10 nM of insulin; insulin also exerts a negative effect on the abundance of adipsin mRNA in mature cells. This result indicates that adipsin appears to be a very early marker of adipose conversion, the gene expression of which is down-regulated by the presence of insulin. Dexamethasone (DEX) decreases the G3PDH message at all stages of adipose conversion, while it promotes the accumulation of adipsin mRNA mainly in differentiating cells. In DEX-treated adipocytes, the transcription efficiency of the G3PDH gene is not altered, and reduction to 50% of the message is due essentially to an approximately twofold decrease in its half-life.

Probing Prometheus: Fat Fueling the Fire?

“…18 In a key experiment, they administered high dose (pharmacological) leptin to mice and successfully suppressed hepatic fat synthesis mediated by the process termed adipogenesis (because the genes involved are activated in the transition of preadipocytes to mature, fat-storing adipocytes). 19,20 Despite the apparently essen-tial need for some leptin to progress liver regeneration, 14 the response here was substantial inhibition of the hepatic regenerative response to PH. In a related experiment, these investigators used a conditional knockout strategy to inhibit glucocorticoid actions in the liver, thereby also reducing hepatic adipogenesis.…”

“…Using microarray-based gene expression, they first showed that several key genes that are more typically induced during the differentiation of adipocytes (adipogenesis genes) are upregulated in mouse liver after a two-thirds PH prior to peak accumulation of lipid -that is, liver cells become more like fat-storage cells and accumulate triglycerides because of increased hepatic fatty acid synthesis. 19,20 This result contrasts with NAFLD and alcoholic liver disease in which the reasons for steatosis are more complex, involving increased hepatic uptake of fatty acids derived from the periphery, decreased "fat burning" (mitochondrial ␤-oxidation) and impaired triglyceride processing into very low density lipoproteins for egress from the hepatocyte. Adipogenic genes, such as adipsin, aP2 and FSP-27, 19,20 peaked at 4 to 6 hours post-PH, while hepatocellular fat accumulation was maximal at 12 to 24 hours.…”

Adipogenesis

“…Both of these lines were derived from disaggregated 17-to 19-day-old Swiss 3T3 mouse embryos (Green and Meuth 1974;Green and Kehinde 1976). However, unlike 3T3-L1 cells, 3T3-F442A preadipocytes do not require glucocorticoid-supplemented differentiation cocktail to induce adipogenesis (Rubin et al 1978;Spiegelman and Ginty 1983;Moustaid et al 1990). It is commonly believed that 3T3-F442A precursors are at a more advanced stage of commitment than 3T3-L1's.…”

Disruption of Hepatic Adipogenesis Is Associated With Impaired Liver Regeneration in Mice

“…Included among the genes induced during the regenerative response were several that have previously been classified as "adipogenic" (Table 4), i.e., genes whose expression is specifically induced in cellular models of adipogenesis. [22][23][24][25][26][27] These include adipsin (complement factor D), aP2 (adipocyte fatty acid binding protein), S3-12, and FSP-27. These microarray-based gene expression analysis results were independently verified using real-time RT-PCR analysis, which confirmed the increased expression of each of these adipogenic genes in regenerating liver (Fig.…”