TNF and major depressive disorder: Elevated serum levels of miR-9-5p in individuals with depression stimulate the polarization of M1 microglia, triggering excessive release of pro-inflammatory cytokines such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), thereby exacerbating neurological damage (Xian et al., 2022).