Fig. 7

Schematic of epidermal cell autophagy activation by hypoxic hBMSCs: the primary event in this process is HIF-1α expression in hBMSCs in response to hypoxic conditions, which in turn drives TGF-β1 expression and secretion in hypoxic hBMSCs. Then, TGF-β1 from hBMSCs binds to the membrane-associated TGF-β receptors on epidermal cells and subsequently stimulates SMAD2/SMAD3 through direct phosphorylation, which further forms a trimer with SMAD4, and the complex is transferred to the epidermal cell nucleus. Activation of the SMAD pathway, in turn, induces autophagy in HaCaT cells