Abstract
Objective: This study aimed to investigate the potential causal relationships between 91 circulating inflammatory proteins and colorectal cancer (CRC) using a two-sample bidirectional Mendelian randomization (MR) framework, supplemented by spatial transcriptomic analysis. Methods: Genetic instruments for circulating inflammatory proteins were obtained from genome-wide association studies (GWAS) involving individuals of European ancestry. CRC outcome data were sourced from BioBank Japan. The inverse variance weighted (IVW) method was used as the primary analytical approach, complemented by MR-Egger regression, weighted median, and mode-based estimators. Horizontal pleiotropy and heterogeneity were assessed using the MR-Egger intercept, Mendelian Randomization Pleiotropy RESidual Sum and Outlier (MR-PRESSO) test, and Cochran's Q statistic. The Mendelian randomization Steiger (MR-Steiger) method was employed to verify causal directionality. Spatial transcriptomic profiling of CRC tissue was performed to evaluate the spatial expression patterns and cell-type-specific co-expression profiles of MR-identified candidate genes. Results: Three inflammatory proteins demonstrated significant associations with CRC risk. Tumor necrosis factor receptor superfamily member 9 (TNFRSF9) and interleukin-20 receptor subunit alpha (IL20RA) were positively associated with increased risk, whereas latency-associated peptide transforming growth factor beta 1 (LAP-TGF-β1) showed a protective association. These associations remained robust across all sensitivity analyses. Spatial transcriptomic analysis revealed that TNFRSF9 expression was enriched in immune cell-dense stromal regions, while IL20RA was predominantly expressed in tumor cell-dominated areas, indicating distinct cellular mechanisms. Conclusion: This integrative study provides genetic and spatial evidence supporting the involvement of specific circulating inflammatory proteins in colorectal carcinogenesis. TNFRSF9 and IL20RA may act as pro-tumorigenic mediators, while LAP-TGF-β1 may confer protective effects. These findings offer new insights into inflammation-related CRC pathogenesis and may inform future biomarker or therapeutic targetd evelopment.