CircTUBD1 Regulates Radiation-induced Liver Fibrosis Response via a circTUBD1/micro-203a-3p/Smad3 Positive Feedback Loop.

Background and Aims: Radiation-induced liver fibrosis (RILF), delayed damage to the liver (post-irradiation) remains a major challenge for the radiotherapy of liver malignancies. This study investigated the potential function and mechanism of circTUBD1 in the development of RILF. Methods: By using a dual luciferase assay, RNA pull-down assays, RNA sequencing, chromatin immunoprecipitation (known as ChIP) assays, and a series of gain- or loss-of-function experiments, it was found that circTUBD1 regulated the activation and fibrosis response of LX-2 cells induced by irradiation via a circTUBD1/micro-203a-3p/Smad3 positive feedback loop in a 3D system. Results: Knockdown of circTUBD1 not only reduced the expression of α-SMA, as a marker of LX-2 cell activation, but also significantly decreased the levels of hepatic fibrosis molecules, collagen type I alpha 1 (COL1A1), collagen type III alpha 1 (COL3A1), and connective tissue growth factor (CTGF) in a three-dimensional (3D) culture system and RILF model in vivo. Notably, knockdown of circTUBD1 alleviated early liver fibrosis induced by irradiation in mice models. Conclusions: This study is the first to reveal the mechanism and role of circTUBD1 in RILF via a circTUBD1/micro-203a-3p/Smad3 feedback loop, which provides a novel therapeutic strategy for relieving the progression of RILF.