Synaptic Mitochondrial Oxidative Stress Contributes to Individual Variability in Age-Related Cognitive Inflexibility...

Aging is associated with impairments in cognitive flexibility, a key executive function supported by the medial prefrontal cortex (mPFC), yet the biological mechanisms underlying individual variability in age-related decline remain poorly understood. Here we investigated behavioral, ultrastructural, and proteomic correlates of cognitive inflexibility in mice across aging. Using a touchscreen-based attentional set-shifting task, we observed substantial individual variability in cognitive inflexibility among aged C57BL/6J mice. Volume electron microscopy of the mPFC revealed age-related reductions in synaptic density, but these structural changes did not correlate with cognitive performance. Instead, the proportion of synapses containing presynaptic mitochondria was inversely associated with cognitive flexibility in aged mice. To identify molecular correlates, we performed proteomic profiling of mPFC whole tissue and synaptosome fractions. Proteins associated with individual variability in cognitive inflexibility were largely distinct from those associated with chronological aging. Notably, synaptosomal proteins negatively correlated with cognitive performance were strongly enriched for mitochondrial pathways, including oxidative phosphorylation, mitochondrial translation, and the tricarboxylic acid cycle. Consistent with these findings, the mitochondria-targeted antioxidant MitoQ improved attentional set-shifting performance in aged mice without affecting initial learning. Proteomic analyses revealed that MitoQ reduced the abundance of synaptosomal mitochondrial proteins, particularly those involved in mitochondrial apoptotic signaling. Together, these results suggest that synaptic mitochondrial oxidative stress in the mPFC contributes to individual vulnerability to cognitive inflexibility. Targeting synaptic mitochondrial oxidative stress may therefore represent a promising strategy to preserve executive function during aging.