β-Sitosterol improves murine ulcerative colitis by inhibiting the expression of ribosomal proteins and the attempted polarization of type 1 macrophages.

Background: As the inflammatory bowel disease subtype, ulcerative colitis (UC) is the idiopathic chronic inflammatory condition affecting colonic mucosa. Characterized by high incidence and therapeutic challenges, UC imposes significant burdens on global health. β-Sitosterol, a phytosterol abundant in fruit and medicinal plants, has demonstrated potential anti-inflammatory properties.

Methods: Herein, the UC mouse model was created by administering dextran sulfate sodium, followed by β-sitosterol treatment. Histopathology, single-cell RNA-sequencing (scRNA-seq), Kyoto Encyclopedia of Genes and Genomes (KEGG), flow cytometry (FCM), enzyme-linked immunosorbent assays (ELISAs), Western blotting, and quantitative real-time reverse transcription PCR (qRT-PCR) were implemented.

Results: Oral administration of β-sitosterol markedly alleviated intestinal damage and inflammation in UC mice. The scRNA-seq assay revealed that the immune cell subpopulations in the colorectal tissues of mice treated by β-sitosterol gavage apparently decreased compared with them in UC mice, with the most significant difference in the number of macrophages. KEGG analysis predicted significant downregulation of ribosome pathway activity in CD68 + MΦ1 macrophages following β-sitosterol treatment. Both FCM and ELISA analyses showed that β-sitosterol significantly downregulated inflammatory factor generation like interleukin-1β (IL-1β) and inducible nitrous oxide synthase (iNOS) by RAW264.7-derived MΦ1 macrophages. In vitro, as confirmed by qRT-PCR and Western blotting analyses, β-sitosterol dramatically inhibited MΦ1 macrophage expression of ribosome pathway core factors.

Conclusions: The present study confirmed that β-sitosterol inhibits MΦ1 macrophage polarization and inflammatory activity by downregulating the key gene transcriptional activity and expression in ribosome signaling pathway in MΦ1 macrophages, thereby ameliorating UC symptoms in mice.