Astilbin Alleviates Radiation-Induced Pulmonary Fibrosis via circPRKCE Targeting the TGF-β/Smad7 Pathway to Inhibit Epithelial-Mesenchymal Transition.

Purpose: This study aimed to clarify the protective effect of astilbin (AST) on radiation-induced pulmonary fibrosis (RIPF) and explore its underlying molecular mechanism, focusing on non-coding RNAs. Methods: Mouse lung epithelial cells (MLE-12 and TC-1) and C57BL/6J mice were used to establish in vitro radiation injury models and in vivo RIPF models, respectively. Cell viability, apoptosis, the epithelial-to-mesenchymal transition (EMT), and fibrosis-related markers were assessed using cell-counting kit-8 assays, Western blotting, immunohistochemistry, and histological staining. High-throughput sequencing identified differentially expressed circRNAs. The mechanistic studies included RNA-FISH, a dual-luciferase reporter assay, an RNA immunoprecipitation (RIP) assay, and loss-of-function experiments. Results: AST significantly alleviated radiation-induced apoptosis and EMT in vitro, as well as RIPF in vivo. AST treatment reduced collagen deposition, fibrosis-related protein expression, and EMT marker changes. High-throughput sequencing revealed that AST upregulated circPRKCE, a non-coding RNA that functions through a ceRNA mechanism by binding to miR-15b-5p, thereby promoting Smad7 expression and suppressing the TGF-β/Smad7 pathway. Knockdown of circPRKCE abolished AST's protective effects, confirming its pivotal role in mediating AST's anti-fibrotic activity. Conclusions: This study demonstrates that Astilbin alleviates radiation-induced pulmonary fibrosis via circPRKCE targeting the TGF-β/Smad7 pathway to inhibit EMT, suggesting AST as a potential therapeutic agent for managing this severe complication of radiotherapy.