GDF15 (Growth/Differentiation Factor-15) Expression in Human Adipose Tissue and in Adipocyte Cell Lines

Background: GDF15 (growth/differentiation factor-15) is part of the transforming growth factor-beta family and represents a cellular stress-induced gene. It might have a role in metaflammation and adipoflammation. We aimed to investigate the effects of Toll-like receptor (TLR) activation and hypoxia-related pathways together with metabolic factors on GDF15 regulation in adipocytes and adipose tissue (AT). Methods: GDF15 mRNA quantities in the human adipocyte cell line SGBS, in visceral (VAT) and subcutaneous adipose tissue (SAT) (resected from n = 96 obese and characterized patients), and in murine 3T3-L1 adipocytes were measured by real-time RT-PCR. GDF15 protein concentrations in cell supernatants and serum were quantified by ELISA. The following stimuli/pathways were investigated: insulin, glucose, TLR ligands (TLR2/6, TLR3, TLR4, TLR7, TLR9), bile acids, synthetic FXR/TGR5 activators, and HIF1α activators. Results: Basal GDF15 expression is low and only marginally induced in SGBS cells. In contrast, GDF15 is expressed in human SAT and VAT and correlates positively with the corresponding GDF15 protein concentration in peripheral blood serum of obese patients. Among metabolic factors, insulin and bile acids such as ursodeoxycholic acid upregulate GDF15 expression in 3T3-L1 adipocytes, the latter via FXR but not via TGR5. Among innate immune regulators, only TLR7 activation and hypoxic mediators upregulate whereas STAT3 signaling downregulates GDF15. Conclusion: GDF15 expression in human SAT and VAT is correlated to peripheral blood GDF15 concentrations and is regulated by metabolic and innate immune response pathways involved in AT inflammation and metaflammation.