BTRC aggravates FFA-induced lipid accumulation in MASLD via G3BP1 degradation and subsequent SIRT6 mRNA destabilization.

Background

Metabolic dysfunction associated steatotic liver disease (MASLD) features hepatic steatosis and lipotoxicity, yet its molecular mechanisms remain incompletely understood. How post-transcriptional regulation and protein turnover shape hepatocyte lipid homeostasis in MASLD requires further elucidation.

Methods

For in vivo and in vitro validation, C57BL/6 mice were fed a high-fat diet (HFD) for 12 weeks, while HepG2 cells were exposed to free fatty acids (FFA) to induce steatosis. Lipid accumulation and viability were assessed by Oil Red O/BODIPY staining, triglyceride assays, and CCK-8. Mechanisms were explored using RIP and RNA pulldown to verify G3BP1 binding to SIRT6 mRNA, and actinomycin D to determine mRNA stability. BTRC-mediated ubiquitination and degradation of G3BP1 were validated by Co-IP, CHX, and MG132 assays. The lipid metabolism proteins were assessed by Western blotting.

Results

FFA downregulated G3BP1 and SIRT6 and increased BTRC. G3BP1 overexpression preserved viability, reduced lipid droplets and triglycerides, restored CPT1A and PPARα, and suppressed SREBP-1c and FAS. G3BP1 bound SIRT6 mRNA and stabilized SIRT6. BTRC interacted with G3BP1 and promoted its ubiquitination; Functionally, BTRC silencing alleviated FFA-induced lipid accumulation and metabolic dysregulation while elevating G3BP1 and SIRT6; concomitant SIRT6 knockdown abrogated these benefits. In HFD-fed mice, AAV-mediated BTRC silencing alleviated HFD-induced hepatic steatosis and liver injury.

Conclusion

A BTRC-G3BP1-SIRT6 axis governs hepatocyte lipid homeostasis under lipotoxic stress. BTRC promotes steatosis by degrading G3BP1, thereby destabilizing SIRT6 mRNA and impairing fatty acid oxidation. Targeting BTRC or reinforcing G3BP1/SIRT6 offers a potential therapeutic strategy for MASLD.