Oxidative exposure impairs TGF-β pathway via reduction of type II receptor and SMAD3 in human skin fibroblasts

Exposure to oxidants results in cellular alterations that are implicated in aging and age-associated diseases. Here, we report that brief, low-level oxidative exposure leads to long-term elevation of cellular reactive oxygen species (ROS) levels and oxidative damage in human skin fibroblasts. Elevated ROS impairs the transforming growth factor-beta (TGF-beta) pathway, through reduction of type II TGF-beta receptor (T beta RII) and SMAD3 protein levels. This impairment results in reduced expression of connective tissue growth factor (CTGF/CCN2) and type I collagen, which are regulated by TGF-beta. Restoration of T beta RII and SMAD3 together, but not separately, reinstates TGF-beta signaling and increases CTGF/CCN2 and type I collagen levels. Treatment with the anti-oxidant N-acetylcysteine reduces ROS elevation and normalizes TGF-beta signaling and target gene expression. These data reveal a novel linkage between limited oxidant exposure and altered cellular redox homeostasis that results in impairment of TGF-beta signaling. This linkage provides new insights regarding the mechanism by which aberrant redox homeostasis is coupled to decline of collagen production, a hallmark of human skin aging.