M-CSF Protects Against Ulcerative Colitis via Aconitate: Mendelian Randomization and Experimental Evidence

BACKGROUND: Although cytokines have been implicated in the development of ulcerative colitis (UC), the potential mediating role of metabolite levels in this association remains unclear. METHODS: Utilizing data from genome-wide association studies (GWAS) encompassing 91 circulating cytokines, 1400 blood metabolites, and 178,689 UC cases, we performed a two-sample Mendelian randomization (MR) analysis to investigate the effect of metabolites mediated cytokines on the development of UC. A two-step MR analysis was conducted to quantitatively evaluate the mediation effect. Additionally, dextran sodium sulfate (DSS)-induced colitis mice were used to further confirm our results. RESULTS: Mendelian randomization (MR) analysis indicated that macrophage colony-stimulating factor (M-CSF) had a causal and positive relationship with aconitate (OR: 1.10, 95% CI: 1.00-1.20, p = 0.043, IVW beta 1 = 0.095). Moreover, MR analysis revealed that high level of aconitate were associated with reduced risk of UC (OR: 0.44, 95% CI: 0.24-0.80, p = 0.008, IVW beta 2 = -0.818). In addition, MR analysis showed M-CSF had an inverse correlation with the disease onset of UC (OR: 0.31, 95% CI: 0.15-0.80, p = 0.002, IVW beta all = -1.16). Furthermore, the mediation effect of aconitate mediated M-CSF on the risk of UC was -0.0777 (95% CI: -0.154 to -0.0018, p = 0.045), accounting for 6.69% of the total effect, and indicating a modest contribution to the protective effect of M-CSF against UC. Subsequently, as an in vivo validation model, DSS-induced colitis was employed to demonstrate that M-CSF treatment significantly ameliorated weight loss, disease activity index (DAI) scores, colon shortening, and histological damage. Additionally, M-CSF treatment also significantly reduced M1 macrophage infiltration, elevated levels of aconitate as well as itaconate, and decreased the levels of pro-inflammatory cytokines in colitis. These results demonstrated that aconitate inhibited the expression of pro-inflammatory cytokines through its enzymatic conversion into the immunometabolite itaconate by aconitate decarboxylase 1 (Acod1), and downregulated the levels of M1 macrophages, thereby ameliorating colitis. CONCLUSION: These findings suggest that M-CSF is an important anti-inflammatory cytokine in UC, which may be a promising therapeutic target in the treatment of UC.