Circular RNA Fgfr2 suppresses hepatic fibrosis through the miR-1941-5p/DDAH1 axis and modulates oxidative stress- and autophagy-related signaling.

Hepatic fibrosis is driven by sustained activation of hepatic stellate cells (HSCs), but the post-transcriptional mechanisms that couple pathogen-induced liver injury to HSC activation remain poorly understood. Here, we profiled circular RNAs (circRNAs) in primary HSCs from Schistosoma japonicum-infected mice and identified circFgfr2, a 639-nt circRNA generated from exons 3-6 of Fgfr2, as a fibrosis-associated transcript. CircFgfr2 was reduced in activated HSCs and fibrotic mouse livers. In human liver specimens from mixed non-schistosomal etiologies, reduced circFgfr2 expression was associated with greater fibrosis severity. CircFgfr2 displayed canonical circular features, including a back-splice junction, resistance to RNase R and enhanced transcript stability, and was predominantly cytoplasmic. Mechanistically, the RNA-binding protein Fused in Sarcoma (FUS) promoted circFgfr2 biogenesis by binding the downstream flanking intron of pre-Fgfr2. CircFgfr2 overexpression suppressed HSC activation and proliferation, whereas selective circFgfr2 knockdown increased α-SMA and COL1A1 expression in JS-1 cells. In vivo, early adeno-associated virus serotype 8 (AAV8)-mediated circFgfr2 overexpression attenuated the subsequent development of schistosomiasis-associated hepatic fibrosis. In the murine experimental system, cytoplasmic circFgfr2 acted as a competing endogenous RNA (ceRNA) for mmu-miR-1941-5p, thereby relieving mmu-miR-1941-5p-mediated repression of dimethylarginine dimethylaminohydrolase 1 (DDAH1), reducing intracellular reactive oxygen species (ROS) accumulation, and altering autophagy-related signaling. These findings support an inhibitory role of circFgfr2 in HSC activation and experimental hepatic fibrogenesis and establish a circFgfr2/mmu-miR-1941-5p/DDAH1 regulatory pathway in the murine experimental system. However, the efficacy of circFgfr2 against established fibrosis and conservation of the murine miRNA-mediated mechanism in humans remain to be determined.