Disruption of Mitochondrial Dynamics and Stasis Leads to Liver Injury and Tumorigenesis

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 nameDnm1l), 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

Dnm1lFlox/Flox (Dnm1l^F/F),Mfn1^F/FandMfn2^F/Fmice were crossed with albumin-Cre mice to generate liver-specificDnm1lknockout (L-Dnm1lKO), L-Mfn1KO, L-Mfn2KO, L-Mfn1, Mfn2double KO (DKO), and L-Mfn1, Mfn2, Dnm1ltriple 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 withc-MYCandYAP. Blood and liver tissues were harvested for biochemical and histological analysis.

Results

L-Dnm1lKO 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-Dnm1lKO mice developed spontaneous liver tumors, primarily hepatocellular adenomas. While female L-Dnm1lKO mice also developed liver tumors, their incidence was much lower.

In contrast, neither L-Mfn1KO nor L-Mfn2KO 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-Dnm1lKO mice but were less evident in L-Mfn1KO, L-Mfn2KO or DKO mice, indicating that mitochondrial fission is more important to maintain hepatocyte homeostasis and prevent liver tumorigenesis. Interestingly, further deletion ofMfn1andMfn2in L-Dnm1lKO 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-Dnm1lKO 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.