Growth hormone stimulates adipogenesis of 3T3-L1 cells through activation of the Stat5A/5B-PPARγ pathway

Growth hormone-deficient (GHD) patients show a decreased number of adipocytes, which is normalized by GH replacement, indicating an adipogenic effect of GH. However, the precise mechanisms underlying this effect remain to be clarified. In this study, we investigated the adipogenic effect of GH. GH stimulated MDI (3-isobutyl-1-methylxanthine, dexamethasone, and insulin)-induced adipogenesis of 3T3-L1 cells with early induction of peroxisome proliferator-activated receptors (PPAR)gamma 2 expression. This adipogenic effect of GH was suppressed by overexpression of Stat5A mutant (Stat5A-Y694F), a transcriptional suppressor for the GH-Stat5A/5B signaling pathway, with the reduction of PPAR gamma 2 expression. Next, we investigated the relationship between Stat5A/5B and CCAAT/enhancer binding protein (C/EBP)beta/delta orPPAR gamma in3T3-L1 cells. Stat5A/5B stimulated C/EBP beta- and C/EBP delta-induced adipogenesis with enhancement of PPAR gamma 2 expression. In addition, Stat5A/5B enhanced the transcriptional activity of C/EBP beta/delta in the PPAR gamma gene promoter. Furthermore, Stat5A/5B stimulated PPAR gamma-induced adipogenesis and enhanced the transcriptional activity of PPAR gamma. These results suggest that the GH-Stat5A/5B signaling pathway stimulates adipogenesis in cooperation with C/EBP beta/delta and PPAR gamma. To completely understand the effect of GH, cDNA microarray analysis was performed to screen genes affected by GH during MDI-induced adipogenesis. Among 4277 genes, 18 and 19 genes were up- and down-regulated respectively. cDNA microarray analysis also indicated the up-regulation of PPAR gamma and the modulation of expression of genes coding for growth factors or growth factor receptors, suggesting that GH stimulates adipogenesis in association with the modulation of cell growth. Thus, the GHStat5A/B signaling pathway stimulates adipogenesis through two distinct steps. In addition, cDNA microarray data provide us the further insights underlying the adipogenic effect of GH.