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 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.