Abstract
BACKGROUND & AIMS: Mitochondrial dysfunction has been implicated in aging and various cancer development. As highly dynamic organelles, mitochondria constantly undergo fission, mediated by dynamin-related protein 1 (DRP1, gene name Dnm1l ), and fusion, regulated by mitofusin 1 (MFN1), MFN2, and optic atrophy 1 (OPA1). However, whether and how dysregulation of mitochondria dynamics would be involved in liver pathogenesis and tumorigenesis is unknown. METHODS: Dnm1l Flox/Flox ( Dnm1l (F/F) ), Mfn1 (F/F) and Mfn2 (F/F) mice were crossed with albumin-Cre mice to generate liver-specific Dnm1l knockout (L- Dnm1l KO), L- Mfn1 KO, L- Mfn2 KO, L- Mfn1, Mfn2 double KO (DKO), and L- Mfn1, Mfn2, Dnm1l triple KO (TKO) mice. These mice were housed for various periods up to 18 months. Some mice also received hydrodynamic tail vein injections of a Sleeping Beauty transposon-transposase plasmid system with c-MYC and YAP . Blood and liver tissues were harvested for biochemical and histological analysis. RESULTS: L- Dnm1l KO mice had elevated serum alanine aminotransferase levels and increased hepatic fibrosis as early as two months of age. By 12 to 18 months, male L- Dnm1l KO mice developed spontaneous liver tumors, primarily hepatocellular adenomas. While female L- Dnm1l KO mice also developed liver tumors, their incidence was much lower. In contrast, neither L- Mfn1 KO nor L- Mfn2 KO mice had notable liver injury or tumorigenesis. However, a small portion of DKO mice developed tumors at 15-18 month-old. Increased DNA damage, senescence and compensatory proliferation were observed in L- Dnm1l KO mice but were less evident in L- Mfn1 KO, L- Mfn2 KO or DKO mice, indicating that mitochondrial fission is more important to maintain hepatocyte homeostasis and prevent liver tumorigenesis. Interestingly, further deletion of Mfn1 and Mfn2 in L- Dnm1l KO mice markedly abolished liver injury, fibrosis, and both spontaneous and oncogene-induced tumorigenesis. RNA sequencing and metabolomics analysis revealed significant activation of the cGAS-STING-interferon pathway and alterations in the tumor microenvironment pathways, alongside increased pyrimidine synthesis and metabolism in the livers of L- Dnm1l KO mice. Notably, the changes in gene expression and pyrimidine metabolism were considerably corrected in the TKO mice. CONCLUSIONS: Mitochondrial dynamics and stability are essential for maintaining hepatic mitochondrial homeostasis and hepatocyte functions. Loss of hepatic DRP1 promotes liver tumorigenesis by increasing pyrimidine metabolism and activating the cGAS-STING-mediated innate immune response.