HIF-1α/NREP axis promotes hypertrophic scar fibroblast proliferation and collagen deposition via activation of the TGF-β1/Smad pathway

BACKGROUND: Hypertrophic scar (HS) is a fibroproliferative skin disorder characterized by excessive fibroblast proliferation and collagen overproduction during aberrant wound healing. Although hypoxia is a well-recognized driver of HS formation, the molecular mechanisms linking hypoxic signaling to fibroblast activation remain incompletely understood. METHODS: In this study, the expression of hypoxia-inducible factor 1α (HIF-1α), neuronal regeneration-related protein (NREP), and phosphorylated small mother against decapentaplegic family member 2/3 (p-Smad2/3) was examined in HS and matched normal tissues from patients. Hypertrophic scar fibroblasts (HSFBs) were cultured under hypoxic or normoxic conditions, followed by genetic manipulation of HIF-1α or NREP to assess their effects on fibroblast proliferation and collagen synthesis. The direct transcriptional regulation of NREP by HIF-1α was confirmed using dual-luciferase reporter and ChIP assays. RESULTS: Compared with normal tissues, HS tissues exhibited markedly elevated expression of HIF-1α, NREP, and phosphorylated Smad2/3. Hypoxia significantly increased HIF-1α and NREP levels in HSFBs, promoting fibroblast proliferation and collagen deposition, whereas knockdown of either HIF-1α or NREP abrogated these effects. Mechanistically, HIF-1α directly bound to the NREP promoter to enhance its transcription, and NREP overexpression partially rescued the suppressive effects of HIF-1α knockdown. Furthermore, HIF-1α-induced NREP upregulation activated the TGF-β1/Smad signaling cascade, while inhibition of this cascade counteracted the effect of NREP overexpression on the changes caused by HIF-1α silencing. CONCLUSION: Our findings identify a novel HIF-1α/NREP/TGF-β1-Smad axis that drives fibroblast hyperproliferation and excessive collagen accumulation in HS. Targeting this signaling pathway may offer a promising therapeutic strategy for preventing or treating HS formation.