Glucocorticoid-transforming growth factor-beta crosstalk contributes to the low adipogenic capacity of human visceral adipose stem cells
Pickering, Richard Taylor
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Visceral adipose tissue (AT) mass increases risk for cardiovascular disease and diabetes. Glucocorticoids (GCs) cause preferential expansion of visceral compared to subcutaneous AT through poorly understood mechanisms. GCs are necessary for adipogenesis, the differentiation of adipose stem cells (ASCs) to mature adipocytes. However, this process may be impaired in visceral depots. Insufficient adipogenesis can lead to excessive hypertrophy of existing adipocytes. This hypertrophic expansion increases cell death and inflammation, driving AT dysfunction. To better understand the genes and pathways by which high GCs cause preferential expansion of visceral fat we performed transcriptomic profiling (microarray) on paired samples of visceral (Omental, Om) and abdominal subcutaneous (Abdsc) AT explants cultured with the GC receptor agonist, dexamethasone (Dex), for 7 days. Gene set enrichment analysis showed the transforming growth factor beta (TGFβ) signaling pathway, most notably the secreted anti-adipogenic factors, TGFβ and activin A, was highly enriched in Om and suppressed less by Dex. We hypothesized that Om AT and ASCs secrete factors that inhibit adipogenesis in an autocrine/paracrine manner. Conditioned media (CM) from Om tissue and ASCs suppressed differentiation by 70-80% compared to control; Dex attenuated this anti-adipogenic effect. Both TGFβ and activin A levels were 4-5 fold higher in CM from Om compared to Abdsc ASCs. Both factors signal via cell surface receptors that increase SMAD2 phosphorylation (P-SMAD2), basal levels of which were 3-4 fold higher in Om ASCs. Additionally, CM from Om ASCs increased P-SMAD2. siRNA mediated knockdown of activin A improved differentiation of Om ASCs, but did not reach levels observed in Abdsc. Blocking TGFβ and activin A signaling using SB431542 robustly increased adipogenesis of Om ASCs and prevented the anti-adipogenic effect of CM. GCs decreased production of TGFβ and activin A, but both remained higher in OmCM. Overnight Dex treatment decreased P-SMAD2 and increased the expression of the TGFβ co-receptor, TGFBR3, which decreases TGFβ signaling, in Abdsc ASCs. GCs failed to decrease P-SMAD2 and increased TGFBR3 in Om ASCs only at high concentrations. Taken together, these data implicate GC-TGFβ crosstalk as a determinant of depot differences in adipogenic capacity and hypertrophic vs. healthy hyperplastic expansion of AT.