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

Abstract

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)g2 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 PPARg2 expression. Next, we investigated the relationship between Stat5A/5B and CCAAT/enhancer binding protein (C/EBP)b/d or PPARg in 3T3-L1 cells. Stat5A/5B stimulated C/EBPb-and C/EBPd-induced adipogenesis with enhancement of PPARg2 expression. In addition, Stat5A/5B enhanced the transcriptional activity of C/EBPb/d in the PPARg gene promoter. Furthermore, Stat5A/5B stimulated PPARg-induced adipogenesis and enhanced the transcriptional activity of PPARg. These results suggest that the GH-Stat5A/5B signaling pathway stimulates adipogenesis in cooperation with C/EBPb/d and PPARg. 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 PPARg 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.

Constitutively active Stat5A and Stat5B promote adipogenesis

“…Thus, it is most likely that the requirement for FBS for efficient adipogenesis correlates with the activity of Stat5. In line with this hypothesis, prolactin and growth hormone, both of which activate Stat5, are shown to promote adipogenesis in the absence/presence of FBS in 3T3-L1 and 3T3-F422A cells, respectively [19][20][21]. In this regard, the weak induction of PPARc and C/EBPa in adipogenesis at both protein and mRNA levels most likely reflects the fact that CS fails to activate Stat5s strongly with the control vector (Fig.…”

Adipogenesis

“…2). Adipocytes are more than inert energy depots, and adipose tissue is a biologically active organ that carries out important (Green et al 1985;Kawai et al 2007) Antiadipogenic in primary rat preadipocytes (Wabitsch et al 1996b) and in human adipocytes (Wabitsch et al 1996a) Insulin/IGF-1 Proadipogenic Proadipogenic in 3T3-L1 cells (Green et al 1985;Smith et al 1988 Inhibitory Antiadipogenic in 3T3-L1 (Kawashima et al 1991), human marrow (Keller et al 1993), and human preadipocyte cells (Meng et al 2001) LTF Controversial No effect on 3T3-L1 adipogenesis (Hogan et al 2005;White et al 2008) Proadipogenic in 3T3-L1 cells (Aubert et al 1998) Antiadipogenic in bone marrow stromal cells (Gimble et al 1994) NP Inhibitory Antiadipogenic in 3T3-L1 cells (White et al 2008) OSM Inhibitory Antiadipogenic in 3T3-L1 cells (Miyaoka et al 2006;White et al 2008), mouse embryonic fibroblasts (Miyaoka et al 2006), and human adipose-derived mesenchymal cells (Song et al 2007) physiological processes including energy homeostasis and whole-body insulin sensitivity. Attenuating adipose tissue expansion can result in pathologies including insulin resistance.…”

“…Of note, STAT5B was unable to display similar proadipogenic properties in these nonprecursor cells (Floyd and Stephens 2003). Studies have shown that the GH-activated STAT5 proteins can induce PPARg expression in 3T3-L1 cells and C3H10T1/2 cells (Kawai et al 2007), suggesting a mechanism by which STAT5 proteins are able to promote adipocyte differentiation. Interestingly, transgenic knockout experiments have shown that disruption in either STA-T5A or STAT5B or both genes resulted in abnormal adipose tissue, and mice lacking both STAT5 proteins had fat pads one-fifth the normal size (Teglund et al 1998).…”

“…Because GH is a potent activator of STAT5, it is not surprising that most studies show that GH promotes adipocyte development. The GH-STAT5 pathway enhances both the expression and the activity of C/EBPb and -d and PPARg (Kawai et al 2007), thus proposing multiple pathways through which GH promotes adipogenesis. Earlier studies showed that GH exerts a dual effect on 3T3-F442A preadipocytes, in which there is an initial direct effect on preadipocytes to initiate the adipogenic program that is followed by an indirect effect of GH to induce insulin-like growth factor-1 (IGF-1) to stimulate growth of the committed cells (Green et al 1985).…”

Construction of suppressor of cytokine signaling 2 (SOCS2) adenoviral overexpression vector and its impact on growth-hormone-induced lipolysis in swine primary adipocytes

“…However, another previous study showed that expression of FAS was not affected with GH treatment at either the mRNA or protein level (Kawai et al, 2007). This difference may be due to different cell types or detection times.…”