Ndufs4<sup>-/-</sup> mice: a testing ground for longevity interventions.

Mice missing the complex I subunit Ndufs4 of the electron transport chain are widely used as a leading animal model of Leigh syndrome, a pediatric neurodegenerative disorder that leads to premature death. More broadly, this animal model has enabled a better understanding of the pathophysiology of mitochondrial disease and mitochondrial dysfunction(definition) in sporadic disorders. Intriguingly, longevity interventions are very effective at treating symptoms of disease in this model. Herein, we introduce the model and its notable features that may help provide insights in longevity research. We performed a retrospective analysis of historical data from our laboratories over the past 10 years regarding the use of this animal model in aging studies, the manifestation and progression of mitochondrial disease, and factors that influence their premature death. We observed a correlation between weight and lifespan in female animals and a sex-independent correlation between the onset of clasping, a typical neurodegenerative symptom, and overall survival. We observed a sexual dimorphism in lifespan with female mice being more resilient despite a similar age of onset of disease symptoms. Lastly, we report increased lifespan and delayed onset of disease symptoms following treatment with 17-alpha-estradiol, a non-feminizing estrogen which can extend lifespan in genetically heterogeneous mice. This analysis serves as a useful guide for researchers utilizing this animal in the discovery of effective interventions for longevity and to prevent the onset of disease. It suggests there may be unprecedented underlying sex-specific differences in patients with Leigh syndrome and further strengthens the connection between normative aging and mitochondrial dysfunction.