[Effects of Dendrobium huoshanense polysaccharide in inhibiting intestinal fibrosis in ulcerative colitis via macrophage IL-36α pathway].

Abstract

This study investigated the intervention effects and mechanisms of Dendrobium huoshanense polysaccharide(DHP) on intestinal fibrosis in mice with dextran sulfate sodium(DSS)-induced chronic ulcerative colitis(UC). A chronic UC mouse model was established by administering 2% DSS in drinking water for 56 days. Male C57BL/6J mice were randomly divided into a normal group, a model group, a low-dose DHP(50 mg·kg~(-1)) group, and a high-dose DHP(200 mg·kg~(-1)) group. Disease activity index(DAI), colon length, histopathological changes( HE and sirius red staining), hydroxyproline( HYP) content, and serum inflammatory cytokine levels were assessed. In vitro, phorbol myristate acetate(PMA)-induced human monocytic leukemia cells(THP-1) were differentiated into macrophages and co-cultured with transforming growth factor-β1( TGF-β1)-stimulated normal human fibroblasts(CCD-18Co) to analyze the effects of DHP on key molecules in the interleukin( IL)-36α signaling pathway and fibrosis-related markers. The results showed that DHP significantly improved body weight loss(P<0. 05), elevated DAI scores, and colon shortening(P< 0. 01) in UC mice. It markedly reduced colonic epithelial injury, inflammatory cell infiltration, and submucosal collagen deposition, and decreased HYP content(P< 0. 001). DHP also significantly downregulated serum levels of pro-inflammatory cytokines, including tumor necrosis factor-α(TNF-α), IL-6, and IL-36α, as well as colonic phosphorylated p65(p-p65) expression(P<0. 01), while increasing the anti-inflammatory cytokine IL-10 level(P<0. 01). Immunofluorescence and flow cytometry analyses confirmed that DHP inhibited infiltration of colonic lamina propria monocytes(CD11b~+F4~/80~+) and neutrophils(CD11b~+Gr-1~+), reduced IL-36α secretion by macrophages, and decreased α-smooth muscle actin(α-SMA) expression and activated fibroblast numbers. Western blot and immunohistochemistry further revealed that DHP downregulated the expression of α-SMA and type Ⅰ collagen(ColⅠ) in colonic tissue. In vitro, DHP inhibited M1 macrophage polarization and nuclear factor-κB(NF-κB) activation, significantly reduced the secretion of IL-6, IL-1β, and IL-36α(P<0. 01), and suppressed fibroblast activation and the expression of α-SMA and ColⅠ in CCD-18Co cells by downregulating macrophage-derived IL-36α. In conclusion, DHP alleviates intestinal fibrosis in chronic UC by regulating the macrophage NF-κB/IL-36α signaling axis, thereby interrupting the pathological cascade of immune cell infiltration, inflammatory amplification, fibroblast activation, and extracellular matrix deposition. This study provides new experimental evidence and potential therapeutic targets for natural medicine interventions in UC-associated intestinal fibrosis.