TGF-β Family Inhibitors Blunt Adipogenesis Via Non-Canonical Regulation Of SMAD Pathways

Adipose tissues (AT) expand in response to energy surplus through adipocyte hypertrophy and hyperplasia (i.e., adipogenesis). The latter is a process by which multipotent precursors differentiate into mature adipocytes. This process is directed by growth factors and cytokines, including members of the TGF-β family, which regulate intracellular signaling pathways that control adipogenic transcriptional programs. As ectopic adipogenesis has been linked with metabolic syndrome and other pathological conditions, we undertook to establish how TGF-β family growth factors and their inhibitors regulate this process in a 3T3-L1 adipogenesis model. We found that intracellular SMAD1/5/8 signaling pathways are activated while SMAD2/3 pathways are suppressed in differentiating cells. Addition of SMAD1/5/8 pathway activating ligands promoted cell proliferation, while SMAD2/3 pathway activating ligands suppressed adipocyte formation. We identified several ligand traps that blunted 3T3-L1 adipogenesis. Strikingly, anti-adipogenic traps and ligands exploited the same mechanism of regulation involving a negative feedback loop that links SMAD2/3 activation with SMAD1/5/8 hyper-phosphorylation, cytoplasmic retention, and reduced signaling. The identified anti-adipogenic traps could be used to control hyperplastic AT expansion and its associated pathological conditions.