Exposure to Dietary Nitrite Exacerbates Lupus in MRL/lpr Mice by Enhancing Integrin Alpha M

There is a recognized longitudinal association between serum nitrogen oxides levels and disease activity in lupus nephritis. Recently, increased exposure to high levels of nitrite has raised significant concerns, though its impact on lupus pathogenesis has not been fully elucidated. Using the MRL/lpr spontaneous lupus model, we employed integrated immunological and transcriptomic approaches to investigate nitrite's effects. Flow cytometry revealed significant elevations in splenic double negative T (DN T) cells, T follicular helper (Tfh) cells, and plasma cells following nitrite intervention, along with a reduction in splenic regulatory T (Treg) cells. ELISA quantification revealed elevated serum anti-double-stranded DNA antibodies (anti-dsDNA), antinuclear antibodies (ANA), and pro-inflammatory cytokines (IL-12p70, TNF-α), correlating with aggravated renal pathology in nitrite-exposed mice. Transcriptome analysis further revealed significant gene expression changes in both spleen and kidney tissues associated with nitrite exposure. Notably, three KEGG pathways, cell adhesion molecules, osteoclast differentiation, and B cell receptor signaling pathway, were consistently enriched in both the spleen and kidney transcriptomes. Subsequent western blot analysis identified that the Itgam (integrin alpha M)-related cell adhesion molecule pathway potentially mediated the mechanism by which nitrite aggravated lupus in MRL/lpr mice. To explore this mechanism, the integrin antagonist lifitegrast was used to inhibit the expression of Itgam in the nitrite-exposed MRL/lpr mice, resulting in attenuation of nitrite-induced lupus exacerbation. Collectively, these findings suggested that nitrite exposure could aggravate lupus by promoting Itgam expression.