Plant-oriented microbiome inoculum modulates age-related maturation of gut-mucosal expression of innate immune and barrier function genes in suckling and weaned piglets

Lay Summary After weaning, piglets often show symptoms of gut inflammation and reduced performance. The plant-based diet, lack of sow milk, and the resulting novel gut microbiome and metabolite composition in digesta may be causative. However, the acute response of the gut mucosa when exposed to the novel digesta composition has not been fully elucidated. Here, we used the intestinal loop perfusion assay to characterize the immediate effect of a plant-oriented microbiome inoculum (POM) representing postweaning digesta composition on gene expression related to innate immune pathways and barrier function at the jejunal and colonic mucosa in suckling and weaned piglets. Results showed that the recognition of microbial components and barrier function changed in the jejunal and colonic mucosa from pre- to postweaning, indicating age-related maturation and priming by digesta compounds prior to the intestinal loop perfusion assay. In the jejunum, exposure to POM increased expression of receptors recognizing microbial components. In the colon, POM exposure upregulated the expression of genes for pro-inflammatory cytokines and other components of the first line of defense. Results have implications for the formulation of transition feeds for the immediate time after weaning. Inclusion of bioactive porcine milk components may help maintain mucosal immune tolerance towards the novel digesta composition. By means of the intestinal loop perfusion assay, we investigated the acute mucosal response towards a plant-oriented microbiome by assessing the expression of innate immune genes in the small and large intestines of piglets from pre- to postweaning. In the jejunum, the plant-oriented microbiome perfusion activated the expression of pattern-recognition receptors and secretory defense, whereas in the colon, it decreased the expression of tight- and adherens-junction proteins and optimized absorption of microbial metabolites. In the immediate time after weaning, piglets often show symptoms of gut inflammation. The change to a plant-based diet, lack of sow milk, and the resulting novel gut microbiome and metabolite profile in digesta may be causative factors for the observed inflammation. We used the intestinal loop perfusion assay (ILPA) to investigate jejunal and colonic expression of genes for antimicrobial secretion, oxidative stress, barrier function, and inflammatory signaling in suckling and weaned piglets when exposed to "plant-oriented" microbiome (POM) representing postweaning digesta with gut-site specific microbial and metabolite composition. Two serial ILPA were performed in two replicate batches, with 16 piglets preweaning (days 24 to 27) and 16 piglets postweaning (days 38 to 41). Two jejunal and colonic loops were perfused with Krebs-Henseleit buffer (control) or with the respective POM for 2 h. Afterward, RNA was isolated from the loop tissue to determine the relative gene expression. Age-related effects in jejunum included higher expression of genes for antimicrobial secretions and barrier function as well as reduced expression of pattern-recognition receptors post- compared to preweaning (P < 0.05). Age-related effects in the colon comprised downregulation of the expression of pattern-recognition receptors post- compared to preweaning (P < 0.05). Likewise, age reduced the colonic expression of genes encoding for cytokines, antimicrobial secretions, antioxidant enzymes, and tight-junction proteins post- compared to preweaning. Effect of POM in the jejunum comprised an increased the expression of toll-like receptors compared to the control (P < 0.05), demonstrating a specific response to microbial antigens. Similarly, POM administration upregulated the jejunal expression of antioxidant enzymes (P < 0.05). The POM perfusion strongly upregulated the colonic expression of cytokines and altered the expression of barrier function genes, fatty acid receptors and transporters, and antimicrobial secretions (P < 0.05). In conclusion, results indicated that POM signaled via altering the expression of pattern-recognition receptors in the jejunum, which in turn activated the secretory defense and decreased mucosal permeability. In the colon, POM may have acted pro-inflammatory via upregulated cytokine expression. Results are valuable for the formulation of transition feeds for the immediate time after weaning to maintain mucosal immune tolerance towards the novel digesta composition.