Hv1 Upregulation Worsens Spinal, Spleen, and Lung Molecular Pathology and Impairs Locomotion after Spinal Cord Injury in Aged Male Mice

Spinal cord injury (SCI) causes not only intraspinal damage but also systemic organ pathology, with aging as a key determinant of outcomes. The mechanisms by which old age aggravate SCI pathology remain unclear. The voltage-gated proton channel Hv1 plays a key role in regulating immune responses. Hv1 increases with aging and SCI, and Hv1 KO provides neuroprotection in young mice. We hypothesized that age-related Hv1 upregulation worsens spinal cord, spleen, and lung pathology and hinders locomotor recovery after SCI via immune modulation. Using aged Hv1 KO and WT male mice subjected to moderate SCI, we assessed behavioral and molecular outcomes. Transcriptomic analysis revealed that Hv1 mRNA expression was higher in the brains of aged sham mice and further upregulated in injured spinal cord tissues. Spinal cord RNA-seq showed acute innate immune and cytokine activation in both genotypes. Hv1 deletion enhanced chromatin remodeling, epigenetic and Wnt signaling, while suppressing NF-κB-driven inflammation and oxidative stress-induced apoptosis. In the spleen, Hv1 depletion enhanced immune responses while suppressing mitosis. T cell and leukocyte activation increased, whereas lung cytokine signaling decreased. Functional recovery improved with reduced tissue damage. After chronic SCI, Hv1 KO mice showed elevated circadian rhythm and T cell proliferation in the spinal cord, increased mitotic gene expression but reduced adaptive immunity in the spleen, and enhanced immune activation with decreased cilium activity in the lungs. Together, our findings reveal how Hv1 contributes to age-related intraspinal damage and peripheral immune dysfunction after SCI, highlighting a potential therapeutic target for elderly patients.