Vav-iCre-Mediated Deletion of TFAM Is Not Recoverable and Is Consistent with Embryonic Lethality.

Genome stability is the cornerstone of cellular health, and imbalances can cause a number of outcomes, including aging, cancer, and other pathologies. DNA damage is a strong driver of both cellular senescence and mitochondrial dysfunction, two other key hallmarks of aging. Both nuclear and mitochondrial genome instability have been shown to drive aging in the hematopoietic system, which then propagates to non-lymphoid tissues, enhancing morbidity and mortality. The loss of TFAM, a key regulator of mitochondrial DNA replication and nucleoid stability, in T cells has been shown to cause mitochondrial dysfunction, leading to premature immune aging and eventual systemic aging. We sought to investigate whether the loss of TFAM in all immune cells would have a comparable or stronger effect on both the immune system and parenchyma. To address this, we attempted to generate Vav-iCre(+/-); Tfam(fl/fl) mice, which are deficient in TFAM in all immune cells. However, this genotype was unrecoverable as no mutant pups were born, suggesting embryonic lethality. Conversely, we generated mice lacking SIRT6, a nuclear DNA repair enzyme that also regulates mitochondrial homeostasis, in all immune cells and found them to be viable and born at expected Mendelian frequencies. Our findings demonstrate the necessity of mitochondrial genome maintenance and homeostasis repair in immunity.