Methylsulfonylmethane protects against lethal MRSA infection via binding to PIK3CB to increase macrophage phagocytic function and nitric oxide production.

BACKGROUND: Sepsis is associated with an extremely high global mortality rate, primarily due to the lack of effective therapeutic strategies for clearing bacteria from infected tissues. However, the underlying mechanisms by which methylsulfonylmethane (MSM) protects mice against lethal doses of MRSA infection remain incompletely understood. METHODS: RNA sequencing was used to identify transcriptional differences of peritoneal macrophages (PMs). Immunofluorescence, Western blotting, and RT-qPCR were used to assess target protein and RNA levels. Molecular docking, flow cytometry, and pharmacological inhibitors and agonists were employed to characterize MSM targets, cellular functions, and pathway involvement. RESULTS: MSM significantly enhanced macrophage phagocytic activity without altering cell counts in vivo during MRSA infection. Notably, phagocytic molecule mRNA levels were significantly higher in whole blood from sepsis survivors than non-survivors, linking phagocytic capacity to sepsis outcomes. Transcriptomic analysis revealed MSM upregulated genes involved in phagosomes, JAK-STAT signaling, lysosomes, and GTPase-related functions in macrophages. RT-qPCR confirmed increased phagosome/lysosome marker expression, while immunofluorescence showed MSM induced LAMP1+ late endosome formation. Mechanistically, MSM is predicted to interact with PIK3CB, thereby activating PIP3 signaling and subsequently inducing iNOS expression and nitric oxide (NO) production in CD11b+F4/80+ macrophages. The PI3K/mTOR inhibitor dactolisib blocked MSM-induced PIP3 accumulation and iNOS expression, validating the PI3K-PIP3 pathway's critical role. MSM-stimulated NO production was confirmed to mediate intracellular MRSA killing. CONCLUSIONS: MSM alleviates lethal MRSA infection by enhancing macrophage phagocytosis and promoting NO production to eliminate intracellular bacteria. These findings position MSM as a promising therapeutic agent against drug-resistant bacterial infections, offering a novel strategy for managing sepsis.