Cholinergic regulation of macrophage polarization in ulcerative colitis: insights from a DSS-induced mice model

Objective: This study aimed to investigate the regulatory role of the cholinergic pathway on colonic macrophage polarization in ulcerative colitis.Methods: We selected 16 BALB/c mice, randomly divided into Model and Control groups.The Control group mice were fed normally, while the Model group mice were induced to develop colitis by drinking a 3.5% dextran sulfate sodium (DSS) solution for 7 days, followed by a return to normal drinking water for 7 days.During the experiment, we recorded the mice's body weight daily and assessed disease activity index (DAI) scores based on stool consistency, presence of blood in feces, and weight loss.The experiment concluded on day 14, with mice sacrificed to obtain colon samples for analysis.Results: During the DSS treatment period, Model group mice showed significant weight loss and developed soft stools and blood in feces.DAI scores started rising from day 5, peaking on day 8, with subsequent slight weight recovery and reduction in fecal blood.Analysis of colon samples on day 14 indicated that the colon length of mice in the Model group was significantly shorter than that of the Control group, with a markedly higher colon swelling rate (ratio of colon weight to length).Immunohistochemistry results revealed an increase in total macrophage count in the colons of Model group mice, with a higher count of pro-inflammatory M1 macrophages and a reduced count of anti-inflammatory M2 macrophages.Additionally, the expression of barrier proteins Occludin and ZO-1 was reduced in the colons of mice in the Model group.HE staining further demonstrated severe mucosal damage in the colons of the Model group mice.The study also found abnormal spleen enlargement in the Model group mice, associated with the development of colitis.Examination of the cholinergic pathway in the spleen revealed decreased choline acetyltransferase levels and increased acetylcholinesterase levels, indicating reduced acetylcholine levels.Additionally, reduced expression of 7 acetylcholine receptors (7nAChRs) and increased nuclear translocation of nuclear factor B (NF-B) suggested damage to the spleen's cholinergic pathway.Elevated serum levels of pro-inflammatory cytokines were also observed in the Model group mice.Conclusion: Mice drinking 3.5% DSS solution exhibited damage to the spleen's cholinergic pathway, triggering an inflammatory response.Increased pro-inflammatory cytokines and decreased anti-inflammatory cytokines in the serum led to the migration of monocytes to the colon, where they differentiated into pro-inflammatory M1 macrophages, exacerbating inflammation.This excessive inflammatory activity damaged the colonic mucosal epithelium, resulting in soft stools, bloody feces, and weight loss, forming a vicious cycle that ultimately worsened the symptoms of ulcerative colitis.