Absence of Smad3 confers radioprotection through modulation of ERK-MAPK in primary dermal fibroblasts

SummaryBackgroundTransforming growth factor-β1 (TGF-β1), a key biological mediator following ionizing radiation, plays a role in a complex tissue reaction involved in local radiation-induced pathological damage. Knocking out Smad3 (S3KO), a downstream signaling intermediate in the TGF-β pathway, in mice protects their skin from radiation damage as demonstrated by decreased epithelial acanthosis and dermal fibrosis as compared to Smad3 wild-type (S3WT) mice.ObjectiveThe present study was designed to investigate the molecular mechanisms contributing to increased radioprotection in the absence of Smad3.MethodsPrimary dermal fibroblasts derived from S3WT and KO mice were exposed to 5 Gy ionizing radiation in vitro. Western blot analyses, immunocytochemistry, and reporter transfections were used to dissect the radiation-induced events.ResultsThere was increased phosphorylation of ERK-MAPK, p53 and H2A.X in S3KO compared to the S3WT fibroblasts, implicating them in a key signaling cascade in response of these cells to radiation. Pro-fibrotic gene expression was decreased in S3KO fibroblasts post-irradiation.ConclusionThe absence of Smad3 may decrease radio-responsiveness by increasing activation of DNA damage sensing mechanisms and decreasing induction of pro-fibrotic genes.