Ascorbic acid attenuates immunosenescence and cognitive decline via MYH9-Mediated CD8⁺ T cell differentiation

​​ Immune function decline (immunosenescence) accelerates systemic aging and adversely impacts cognitive function. Antioxidants may mitigate these effects; however, the role of ascorbic acid (AA), a key antioxidant, in counteracting immunosenescence and enhancing cognition remains inadequately explored.

In this study, AA administration (0.1 mg/g, tail vein, every 2 days for 30 days) significantly improved cognitive function in aged (16-month) C57BL/6 mice, without altering anxiety-like behavior (as assessed in the open field test). This was associated with elevated peripheral blood lymphocytes (T cells, B cells) and CD8⁺ T cells, alongside reduced myeloid cells (CD11b⁺). Single-cell RNA sequencing of PBMCs revealed AA reversed immunosenescent signatures-increasing T/B cell populations and decreasing neutrophils/macrophages-mimicking youthful immune profiles. In vitro, AA skewed hematopoietic stem cell (HSC) differentiation toward CD8⁺ T cells (increasing DN2 stage, suppressing myeloid CD11b⁺ cells) and enhanced splenic CD8⁺ T cell generation. Mechanistically, AA bound MYH9, activating cytoskeletal pathways. MYH9 inhibition (blebbistatin) reduced CD8⁺ T cells and increased CD11b⁺ cells-effects rescued by AA. Crucially, CD8⁺ T cell depletion abolished AA's cognitive benefits, confirming their essential role.

In summary, AA mitigates immunosenescence and improves cognitive function by targeting MYH9 to regulate CD8⁺ T cell differentiation and function. These findings establish a mechanistic basis for AA as a potential therapeutic agent against age-related immune and cognitive decline.