Decreased LONP1 expression exacerbates MASH-induced liver fibrosis via elevated orotic acid levels

Abstract

Background & aims: Identifying the metabolic targets driving liver fibrosis in metabolic-dysfunction-associated steatohepatitis (MASH) is essential for developing effective preventive therapies. However, the metabolic pathways dysregulated in MASH and the underlying molecular mechanisms remain poorly understood. Lon peptidase 1 (LONP1), a mitochondrial protease, is known for its pivotal role in maintaining mitochondrial protein quality surveillance and performing highly regulated proteolytic reactions. This study aims to explore the precise mechanisms by which LONP1 links proteolytic surveillance to mitochondrial metabolic rewiring in liver fibrosis.

Methods: We used murine liver fibrosis models, a hepatocyte-specific Lonp1 knockout mouse model, and liver biopsies from patients with MASH. Transcriptomics, proteomics and metabolomics were used to identify the potential metabolites that promote MASH-induced liver fibrosis.

Results: LONP1 expression was reduced in patients and mice with MASH. Hepatocyte-specific LONP1 deficiency results in dihydroorotate dehydrogenase (DHODH) accumulation, elevated orotic acid levels, and aggravated MASH-induced fibrosis. Conversely, the overexpression of LONP1 or the administration of a DHODH inhibitor reduced orotic acid levels and alleviated MASH-induced liver fibrosis in mice. Mechanistically, LONP1 was shown to degrade DHODH selectively in an ATP-dependent manner, thus lowering orotic acid levels and suppressing ATF3 (activating transcription factor 3)-mediated activation of hepatic stellate cells. These findings were validated in patients with MASH, as plasma orotic acid levels correlated negatively with hepatic LONP1 levels and positively with both the expression of fibrotic genes and fibrosis scores.

Conclusion: Our findings demonstrate that the LONP1-DHODH interaction regulates orotic acid metabolism and alleviates MASH-induced liver fibrosis.

Impact and implications: Liver fibrosis is one of the main histological determinants of metabolic dysfunction-associated steatohepatitis (MASH), a disease whose incidence has paralleled the worldwide surge in metabolic syndrome. This study reveals that LONP1 links proteolytic surveillance to mitochondrial metabolic rewiring via orotic acid metabolism, contributing to the progression of MASH-induced liver fibrosis. These findings suggest that targeting orotic acid or hepatocyte LONP1 may represent a promising therapeutic strategy. Further investigation into mitochondrial orotic acid metabolism may yield novel insights into the pathogenesis of liver fibrosis.

Keywords: Dihydroorotate dehydrogenase; Lon peptidase 1; Metabolic dysfunction-associated steatohepatitis; Mitochondrial proteostasis; Orotic acid.