CircSETD2 impairs hepatic lipid homeostasis in metabolic dysfunction-associated fatty liver disease by binding CPS1

Dysregulation of hepatic lipid homeostasis constitutes a core pathogenic mechanism in metabolic dysfunction-associated fatty liver disease (MAFLD); however, the regulatory role of circular RNAs (circRNAs) in this process remains unclear. In this study, hepatic circRNAs transcriptomic profiling of MAFLD patients identified circSETD2-generated from exons 16-18 of the SETD2 gene-as a stably expressed and significantly upregulated novel circRNA with a closed circular structure localized in the cytoplasm of MAFLD patient liver tissues. Silencing circSETD2 attenuated free fatty acid - induced lipid accumulation in vitro by reducing lipogenesis and enhancing fatty acid β-oxidation. In high fat diet - fed mice, hepatic circSETD2 silencing mitigated steatosis, improved liver function, and reversed dyslipidemia. Mechanistically, RNA pull-down coupled with LC-MS/MS identified carbamoyl phosphate synthetase 1 (CPS1) as a circSETD2-interacting protein, which was subsequently validated by RNA immunoprecipitation and fluorescence in situ hybridization. Pharmacological modulation of CPS1 enzymatic activity in circSETD2-silenced cells established its mediator role. Specifically, circSETD2 directly bound to CPS1, reducing its enzymatic activity and thereby exacerbating lipid metabolic disturbances and disease progression in MAFLD. In summary, circSETD2 drives MAFLD pathogenesis by impairing CPS1-mediated regulation of lipid homeostasis, positioning it as a promising prognostic biomarker and therapeutic target.