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

Although cytokines have been implicated in the development of ulcerative colitis (UC), the potential mediating role of metabolite levels in this association remains unclear. 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. 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. 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.