Stewart, J. B. | bioRxiv Science

bioRxiv2025

An inherited mtDNA mutation remodels inflammatory cytokine responses in macrophages and in vivo

Impaired mitochondrial bioenergetics in macrophages can drive hyperinflammatory cytokine responses1-6, but whether this may also be caused by inherited mtDNA mutations is unknown. Here, we address this question using a multi-omic approach that integrates super-resolution imaging and metabolic analyses to profile macrophages from a mouse model of mitochondrial disease arising from a heteroplasmic mutation (m.5019A>G) in the mitochondrial tRNA for alanine7. These m.5019A>G macrophages exhibit defects in respiratory chain complexes and oxidative phosphorylation (OxPhos) due to decreased intra-mitochondrial translation. To adapt to this metabolic stress, mitochondrial fusion, reductive glutamine metabolism, and aerobic glycolysis are all increased. Upon inflammatory activation, type I interferon (IFN-I) release is enhanced, while the production of pro-inflammatory cytokines and oxylipins are restrained in m.5019A>G macrophages. Finally, an in vivo endotoxemia model using m.5019A>G mice reveal elevated IFN-I levels and sickness behaviour. In conclusion, our study identifies an unexpected imbalance in innate immune signalling in response to a pathogenic mtDNA mutation, with important implications for the progression of pathology in patients with mtDNA diseases8.

immunology↗

bioRxiv2023

Cell division can accelerate the loss of a heteroplasmic mitochondrial DNA mutation in a mouse model of mitochondrial disease

Mitochondrial DNA (mtDNA) mutations accumulate in both mitotic and post-mitotic somatic tissues of normal individuals with age. They clonally expand within individual cells and cause mitochondrial dysfunction. In contrast, in patients with inherited disease-causing mtDNA mutations the mutation load decreases in mitotic tissues over time, whereas the mutations load in post-mitotic tissues remains relatively stable. The mechanisms underlying this decrease in mitotic tissues, and whether mitochondrial function is restored at the tissue level are unknown. Here, using a combination of homogenate tissue and single crypt/muscle fibre pyrosequencing we have shown a decrease in the mutation load of the germline heteroplasmic m.5024C>T mutation in multiple mitotic tissues of a mouse model of inherited mitochondrial disease (C5024T mice). We have then used in silico predictions to model the cellular dynamics of mtDNA mutation load in mitotic and post mitotic tissues. We demonstrate that: (1) the rate of m.5024C>T decrease correlates with the rate of tissue turnover; (2) the mutation load decrease is not associated with changes in overall cellular proliferation and apoptosis within the mitotic colonic epithelium; instead, it could be due to an upper limit of m.5024C>T load in stem cell populations; (3) the m.5024C>T mutation load is maintained in post-mitotic tissues over time with a consistent load amongst individual muscle fibres; (4) in silico modelling supports a scenario where genetic drift is accelerated in mitotic tissues by high levels of mtDNA replication coupled with mtDNA segregation at cell division. This study has advanced our understanding of the dynamics of mtDNA mutations and phenotype development in patients with mtDNA disease. Author SummaryHealthy individuals randomly accumulate pathogenic mtDNA mutations with age in dividing cells, causing mitochondrial dysfunction. Interestingly, patients with mitochondrial disease show a relative decrease in the loads of inherited mtDNA mutations in some dividing cells over time. The mechanisms underlying this decrease are unknown. Here we show a decrease in the load of the germline heteroplasmic m.5024C>T mutation in dividing cells and tissues of a mouse model of mitochondrial disease. In contrast, the mutation load in non-dividing cells and tissue remains stable. Our data are consistent with the hypothesis that a higher frequency of mtDNA replication in dividing cells, coupled with stem cells having an upper tolerance limit for m.5024C>T, causes an overall decrease in m.5024C>T load at the tissue level.

genetics↗