Causal links between diabetes, gut microbiota, and colon cancer: insights from Mendelian randomization

INTRODUCTION: Colon cancer (CC) remains a major global health burden and ranks among the most common malignant tumors. In recentyears, its growing occurrence in younger age groups has presented a substantial challenge to public health systems worldwide. Type 2diabetes (T2D) and gut microbiota may influence its pathogenesis, but the causal relationship remains unexplored. This study aims to examine the causal association between T2D and CC and explore the possible mediating effects of gut microbiota inthis relationship. MATERIAL AND METHODS: A two-sample Mendelian randomization (MR) design was employed to assess causality, with T2D and gut microbiotaas exposures and CC as the outcome variable. Mediation analysis was conducted through the two-step Mendelian randomizationmethod. Additionally, scRNA-seq data were analyzed to characterize the expression patterns of T2D drug target genes in CC. RESULTS: The study revealed a markedly positive causal effect of T2D on benign colon neoplasm risk (odds ratio = 1.074, 95% confidenceinterval: 1.031-1.119, p = 6.084e-4). Further analysis detected 24 gut microbial taxa related to CC risk, among which Bacteroides sp003545565partially mediated the T2D-benign colon neoplasm relationship, accounting for 8.57% of the total effect. scRNA-seq analysis demonstrateddistinct expression profiles of T2D drug target genes (e.g., PPARG, DPP4, INSR, GPD2, and PRKAB1) in CC compared to normal tissues,with cell type-specific expression changes linked to CC progression. CONCLUSIONS: This study provided genetic evidence confirming a causal role of T2D in CC and highlighted the potential mechanisticinvolvement of gut microbiota. These findings suggested novel intervention strategies for CC prevention and treatment.