Hypoxia-inducible factor-1a activates transforming growth factor-β1/Smad signaling and increases collagen deposition in dermal fibroblasts

Hypoxia of local tissue occurs during the scar formation; however, the degree of ischemia and hypoxia in the central areas of keloids is more serious than those in normal scars. Hypoxia-induced factor (HIF), is one of the main cellular responses to hypoxia, allowing cells to adapt to low-oxygen conditions. We investigated the correlation among hypoxia, transforming growth factor-beta 1/Smad signaling and collagen deposition. Hypoxia up-regulated TGF-beta 1, Smad2/3, p-Smad2/3, Smad4, and total collagen in both normal and keloid fibroblasts via HIF-1a, which was attenuated by HIF-1a inhibition, but T beta RII levels were not significantly altered. Silencing Smad4 under hypoxia decreased the mRNA and protein levels of HIF-1a, suggesting up-regulated Smad4 may also plays a role in promoting HIF-1a. Finally, we examined the role of the TGF-beta 1/Smad pathway in collagen deposition. When T beta RII was inhibited by ITD-1 under hypoxic conditions, p-Smad2/3 levels and collagen deposition decreased. When inhibited T beta RII by siRNA under normoxia, the levels of p-Smad2/3, Smad4 and collagen deposition also decreased. This result demonstrated that hypoxia promoted TGF-beta 1/Smad signaling via HIF-1a and that both HIF-1a and the TGF-beta 1/Smad signaling promotes collagen deposition in hypoxia, which is an important mechanism of keloid formation.