A read-through circular RNA RCRIN inhibits metabolic dysfunction-associated steatotic liver disease

BACKGROUND & AIMS: The molecular mechanisms underlying metabolic dysfunction-associated steatotic liver disease (MASLD) remain elusive and whether non-coding RNAs can serve as biomarkers and therapeutic targets in MASLD has not been determined. METHODS: Exon capture RNA-sequencing analysis was used to identify read-through circular RNAs (rt-circRNAs) in livers from three patients with MASLD and three controls without MASLD. Hepatocyte-specific deletion or overexpression of rt-circRNA RCRIN were utilized to study MASLD pathogenesis. RESULTS: We identified 1,126 rt-circRNAs in liver tissues from patients with MASLD. RCRIN was highly expressed in normal livers and was downregulated in MASLD livers. Rcrin deletion in hepatocytes caused lipid accumulation and MASLD development, while Rcrin overexpression suppressed MASLD progression. Mechanistically, in normal hepatocytes, highly expressed RCRIN bound to RPL8 protein to recruit RNF2 for its degradation, reducing RPL8-containing ribosome numbers and lipid accumulation. In MASLD livers, low RCRIN expression led to the release of RPL8 protein, increasing RPL8-containing ribosome numbers and lipid synthesis, and leading to greater lipid accumulation and endoplasmic reticulum stress. We synthesized RCRIN and N-acetylgalactosamine (GalNAc)-Rpl8 small-interfering RNAs, which both suppressed the pathogenesis of established MASLD in mice. CONCLUSIONS: Our findings reveal an in vivo function of the rt-circRNA RCRIN, show its inhibitory effects in MASLD pathogenesis, and indicate that RCRIN and RPL8 may be therapeutic targets for candidate nucleic acid drugs to treat MASLD. IMPACT AND IMPLICATIONS: Our finds reveal a novel mechanism connecting a read-through circular RNA RCRIN, ribosome heterogeneity and metabolic dysfunction-associated steatotic liver disease (MASLD) pathogenesis. In normal hepatocytes, RCRIN exerts its role by reducing liver lipid accumulation and endoplasmic reticulum stress through promotion of RPL8 degradation. In patients with MASLD, lower RCRIN levels lead to the release of RPL8 to form RPL8-containing ribosomes, promoting lipid accumulation and endoplasmic reticulum stress. RCRIN overexpression and RPL8 depletion dramatically suppress MASLD development and progression. Our findings indicate that RCRIN and RPL8 might be potential therapeutic targets for the treatment of patients with MASLD.