Omega-6 lipid-gene module linked to colorectal cancer pre-metastatic niche

Introduction : We recently reported (Soundararajan et. al ., GUT, 2024) a strong pro-inflammatory lipid mediator bias in colorectal cancer (CRC), possibly related to the omega-6 rich fatty acid preponderance in western-style diets. The current project expands on those findings, linking omega-6 fatty acids to expression of inflammatory genes in human CRC and mouse models. Method : We performed an integrative, multi-omics, weighted gene co-expression network analysis (WGCNA) of 25 quantified arachidonic acid-derived lipid mediators with whole transcriptomes from 293 primary and 77 metastatic human CRCs, to identify a lipid-gene module significantly associated with metastasis. In mice fed omega-6:omega-3 (10:1 w/w) vs. control (1:1 w/w) diets, we analyzed syngeneic CRC subcutaneous tumors using whole transcriptome RNA-sequencing. THP1-derived gene expression signatures for M0, M1 and M2 macrophages were correlated with the lipid-gene module. Results : In the human tumors using an unsupervised analysis, we identified a pro-inflammatory lipid-gene module, linked to the clinical feature of metastasis (P< 1.1e-42), with prominence of “hallmark” genes linked to coagulation, complement, inflammation and EMT/tumor progression and associated with M1 macrophages. Analysis of murine tumors derived from animals fed a diet enriched with omega-6 fatty acids revealed a significant (p < 3.7329E-06), shared enrichment of 18 coagulation and EMT related genes --orthologous to those identified in the pro-inflammatory human lipid-gene module. Among the 18 genes, SerpinA1b , SerpinA1d , SerpinA3k , Ambp and Plg with anti-inflammatory and coagulation- inhibitory properties were downregulated in omega-6 fed mice. Moreover, we observed a dramatic decrease in Serpina1 protein expression in the hepatic sinusoids in omega-6 mice. Conclusion : A human tumor pro-inflammatory lipid-gene module was identified, and its gene expression was shared with tumors derived from mice fed with an omega-6-rich diet. Hallmark gene analysis found inflammation and deranged coagulation prominent. In omega-6 fed mice, decrease in Serpina1 protein expression in liver sinusoidal endothelial cells---the first target of metastasizing cells---suggests localized inflammation with enhanced coagulation. Collectively, these data suggest omega-6 enriched murine and human western diets may foster the development of an inflammatory, coagulopathic pre-metastatic liver niche, with M1 macrophages as the main contributors of CRC inflammation.