Flaxseed Alters Gut Microbiota-Mammary Gland MicroRNA Relationships Differently Than its Oil and Lignan Components

Abstract Objectives Consumption of flaxseed (FS) and its oil (FSO) and lignan (secoisolariciresinol diglucoside, SDG) components have been associated with changes during mammary gland (MG) development which then lead to reduced breast cancer risk in adulthood. FS components are metabolized by the gut microbiota and MG microRNA (miRNA) response to FS may be an underlying mechanism. We aimed to determine if there is an association between the cecal microbiota and MG miRNome, if it is affected by FS or its components, and to identify altered pathways. Methods We used MG miRNome (NanoString nCounterâ system) and cecal microbiota (16S rRNA gene sequencing) data from our previous study where 4–5 week old female C57BL/6 mice were randomized to receive one of four isocaloric diets (n = 5–6/group): basal AIN-93G diet (BD), 10% FS, 3.67% FSO, and 0.15% SDG for 3 weeks. Within-group Spearman correlations between paired (by mouse) miRNA and bacterial genera were compared across the 4 conditions by Differential Correlation Analysis (DGCA v1.0.2 R Package). Genes targeted by miRNA in significantly (q < 0.15) altered correlations were identified with miRDB v6.0 and used for pathway analysis (pathDIP 4, Bonferroni adjusted p-value < 0.05). Results 619,541, 811, and 768 significant miRNA-genera correlations were found in the BD, FS, FSO, and SDG groups, respectively. FS reversed 24 of the BD within-group correlations, but FSO or SDG did not. SDG reversed 24 of the FS within-group correlations, but FSO did not. Of correlations reversed by FS when compared to BD, enriched pathways of miRNA gene targets included cadherin and Wnt signalling, processes vital to MG development, tumour formation and metastasis. When comparing SDG correlations to FS, involved pathways were related to MG development, tumour initiation and progression. Conclusions There is a relationship between gut microbial taxa and MG miRNAs, which is modified by FS. This suggests that the microbiota is a mediator of FS miRNA-dependent effects in the MG. SDG, but not FSO, may participate in FS effects but it does not influence microbial genera-miRNA relationships alone. This suggests that whole FS consumption is necessary for benefits in MG development and breast cancer risk via cecal microbiota-MG miRNA mechanisms. Funding Sources Natural Sciences and Engineering Research Council of Canada.