Genetically engineered bacteria expressing IL-34 alleviate DSS-induced experimental colitis by promoting tight junction protein expression in intestinal mucosal epithelial cells

Abstract

Background

The intestinal mucosa of ulcerative colitis patients expresses high levels of interleukin 34, and mice lacking IL-34 have more severe DSS-induced experimental colitis. There are no studies on the effects of directly upregulating intestinal IL-34 on experimental colitis in mice.

Methods

The bacteria EcN/CSF-1 and EcN/IL-34, which express CSF-1 and IL-34, respectively, were genetically engineered from Escherichia coli Nissle 1917 (EcN). Colitis mice received daily gavage of sterile PBS buffer, empty plasmid E. coli (EcN/WT), EcN/CSF-1, or EcN/IL-34. Each group of mice was assessed for body mass, clinical signs, DAI, intestinal mucosal permeability, pathological, and immunohistological changes. In vitro, NCM460 cells were treated with CSF-1 or IL-34 recombinant proteins in the presence of signaling pathway inhibitors to evaluate tight junction protein expression. Additionally, intestinal mucosal epithelial cells isolated from active UC patients were analyzed for IL-34 and tight junction protein levels.

Results

DSS-induced colitis mice are protected by EcN/IL-34 gavage. Pathological results showed that EcN/IL-34 group colonic histological injury was significantly improved and tight junction protein ZO-1 and Occludin expression increased. In NCM460 cells, IL-34 also increased tight junction protein expression. More importantly, expression of IL-34 was positively correlated with the level of tight junction protein expression in epithelial cells of UC patients.

Conclusion

EcN/IL-34 can directly act on damaged intestinal mucosa, up-regulate IL-34 expression, and promote tight junction protein expression in intestinal mucosal epithelial cells to alleviate experimental colitis in mice. IL-34 may be a potential therapeutic target for ulcerative colitis, and genetically engineered bacteria carrying the cytokine may offer new ideas for treating UC.