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

Background: Transforming 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. Objective: The present study was designed to investigate the molecular mechanisms contributing to increased radioprotection in the absence of Smad3. Methods: Primary 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. Results: There 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. Conclusion: The absence of Smad3 may decrease radio-responsiveness by increasing activation of DNA damage sensing mechanisms and decreasing induction of pro-fibrotic genes.