Yuan Zhang,1,2,* Longbin Huang,3,* Ningning Yue,3,* Zhiliang Mai,3,* Chen Kong,3 Chengmei Tian,4 Dao-ru Wei,5 Jun Yao,1 Lisheng Wang,1 Defeng Li1 

1Department of Gastroenterology, Shenzhen People’s Hospital (the Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, Guangdong, People’s Republic of China; 2Department of Medical Administration, Huizhou Institute for Occupational Health, Huizhou, Guangdong, People’s Republic of China; 3Department of Gastroenterology, Shenzhen People’s Hospital (The Second Clinical Medical College, Jinan University), Shenzhen, Guangdong, People’s Republic of China; 4Department of Emergency, Shenzhen People’s Hospital (The Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, Guangdong, People’s Republic of China; 5Department of Rehabilitation, Shenzhen People’s Hospital (The Second Clinical Medical College, Jinan University; the First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, Guangdong, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Lisheng Wang, Department of Gastroenterology, Shenzhen People’s Hospital (The Second Clinical Medical College, Jinan University; the First Affiliated Hospital, Southern University of Science and Technology), No. 1017, Dongmen North Road, Luohu District, Shenzhen, 518020, People’s Republic of China, Tel +86 755 25533018, Email wanglsszrmyy@163.com Defeng Li, Department of Gastroenterology, Shenzhen People’s Hospital (The Second Clinical Medical College, Jinan University; the First Affiliated Hospital, Southern University of Science and Technology), No. 1017, Dongmen North Road, Luohu District, Shenzhen, 518020, People’s Republic of China, Tel +86 755 25533018, Email ldf830712@163.com

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.

Keywords: ulcerative colitis, Mendelian randomization, macrophage colony-stimulating factor, aconitate