Sodium chloride exacerbates dextran sulfate sodium-induced colitis by tuning proinflammatory and antiinflammatory lamina propria mononuclear cells through p38/MAPK pathway in mice

Abstract

AIM

To investigate the influence of high salt on dextran sulfate sodium (DSS)-induced colitis in mice and explore the underlying mechanisms of this effect.

METHODS

DSS and NaCl were used to establish the proinflammatory animal model. We evaluated the colitis severity. Flow cytometry was employed for detecting the frequencies of Th1, macrophages and Tregs in spleen, mesenteric lymph node and lamina propria. The important role of macrophages in the promotion of DSS-induced colitis by NaCl was evaluated by depleting macrophages with clodronate liposomes. Activated peritoneal macrophages and lamina propria mononuclear cells (LPMCs) were stimulated with NaCl, and proteins were detected by western blotting. Cytokines and inflammation genes were analyzed by enzyme-linked immunosorbent assay and RT-PCR, respectively.

RESULTS

The study findings indicate that NaCl up-regulates the frequencies of CD11b⁺ macrophages and CD4⁺IFN-γ⁺IL-17⁺ T cells in lamina propria in DSS-treated mice. CD3⁺CD4⁺CD25⁺Foxp3⁺ T cells, which can secrete high levels of IL-10 and TGF-β, increase through feedback in NaCl- and DSS-treated mice. Furthermore, clodronate liposomes pretreatment significantly alleviated DSS-induced colitis, indicating that macrophages play a vital role in NaCl proinflammatory activity. NaCl aggravates peritoneal macrophage inflammation by promoting the expressions of interleukin (IL)-1, IL-6 and mouse inducible nitric oxide synthase. Specifically, high NaCl concentrations promote p38 phosphorylation in lipopolysaccharide- and IFN-γ-activated LPMCs mediated by SGK1.

CONCLUSION

Proinflammatory macrophages may play an essential role in the onset and development of NaCl-promoted inflammation in DSS-induced colitis. The underlining mechanism involves up-regulation of the p38/MAPK axis.

Keywords: Inflammatory bowel disease; Macrophage; NaCl; CD4⁺IFN-γ⁺IL-17⁺ T cell; p38/MAPK

Core tip: NaCl, as an indispensable environmental factor, evokes both innate and adaptive immune proinflammation cell activation in mice affected by dextran sulfate sodium (DSS)-induced colitis. Proinflammatory CD4⁺ cells in DSS- and NaCl-treated mice are mainly double-positive IL-17⁺IFN-γ⁺ T cells. Macrophage depletion significantly alleviates DSS-induced colitis. M1 macrophages play an important role in the proinflammatory effect of NaCl in the mouse gut. NaCl promotes M1 proinflammatory gene expression in lipopolysaccharide-activated peritoneal macrophage. The mechanism by which NaCl promotes DSS-induced colitis involves up-regulation of the p38/MAPK axis.