Reversible, Sexually Dimorphic Sympathetic Aging: Distal Axon Withdrawal Shaped by Prepubertal Gonadal Influences.

Peripheral innervation declines with age, but whether this process is sexually dimorphic and whether it reflects neuronal degeneration or deterioration of nerve-target interactions remain unclear. Using mouse skin as a defined neuroeffector system, we show that sympathetic aging is strongly sexually dimorphic, with greater denervation in aged males. Skin-projecting sympathetic neurons remain intact, indicating that denervation reflects distal axon withdrawal rather than neuronal loss. Nerve-target interactions and the arrector pili muscle niche deteriorate with age, predominantly in males. Aged sympathetic neurons retain NGF responsiveness, and restoring NGF within arrector pili muscles promotes sympathetic reinnervation and hair regeneration in aged males. Genetic and endocrine models show that divergent aging trajectories are associated with gonadal rather than chromosomal sex and are attenuated by early gonadectomy. Together, these findings identify sympathetic aging as a reversible, sexually dimorphic distal axonopathy shaped by the target environment and gonadal influences.