Hepatocytic ASB3 deficiency alleviates MASLD by decreasing ubiquitin-mediated CPT1A.

Background: Excessive lipid accumulation in hepatocytes is a critical cause of metabolic dysfunction-associated steatotic liver disease (MASLD) progression. Ankyrin repeat and SOCS box protein 3 (ASB3) is an E3 ubiquitin ligase that mediates diverse disease processes; however, the direct substrates of ASB3 in lipid metabolism and its role in MASLD remain unexplored.

Methods: We generated ASB3 knockout mice fed a high-fat diet (HFD) to induce MASLD. Oxygen consumption and fatty acid oxidation (FAO) were used to assess lipid metabolism. LC‒MS/MS and IP were used to verify the ASB3 target protein. Correlation analysis was conducted on the cohort of MASLD patients versus the control group.

Results: Loss of the ASB3 E3 ubiquitin ligase in hepatocytes strengthens mitochondrial FAO, thereby influencing energy consumption to decrease triglyceride storage and lipid accumulation. Quantitative lysine ubiquitination proteomics revealed that ASB3 directly mediated the ubiquitin levels at two sites (K180 and K639) in carnitine palmitoyl transferase 1A (CPT1A), a rate-limiting enzyme of FAO, to induce CPT1A degradation. Moreover, both constitutive and hepatocyte-specific ASB3 knockout enhance FAO and delay lipid accumulation, liver steatosis, and MASLD progression in a CPT1A-dependent manner. Hepatic ASB3 deficiency also delays fibrosis in MASLD. Analysis of public databases and liver tissue samples from MASLD patients revealed that ASB3 was highly expressed in MASLD patients and was negatively correlated with CPT1A.

Conclusions: Our study reveals the key roles of ASB3 in the development of MASLD and suggests a novel therapeutic potential for MASLD.