A Transcriptomic Evaluation of Neuroactive Receptors in the Colon of a Dextran Sodium Sulphate Pig Model of Colitis

Abstract

The enteric nervous system (ENS) interacts bidirectionally with the local immune system, responding to inflammation within the gastrointestinal (GI) tract. In a previous study using the same samples, several gene targets were identified as being differentially expressed in the inflamed colonic tissue of pigs challenged with dextran sodium sulphate (DSS). Additionally, animals in the basal DSS group, exhibited reduced growth and increased fecal and pathology scores, while the relative abundance of beneficial taxa was reduced and harmful bacteria increased. While changes in the innate immune response and barrier function are widely cited regarding inflammatory bowel disease (IBD), the effects of inflammation on the local structures of the enteric nervous system (ENS) are less well understood. Hence, the objectives of this study were to: (1) evaluate the expression of a range of functionally diverse neuroactive receptors, transporters and neurotrophic factors in RNA derived from the colonic tissue from the same pigs; (2) examine associations with these neuroactive components and inflammatory, barrier function and matrix remodeling targets. Mature pigs were split into two experimental groups: (1) basal diet (n = 10); (2) basal diet + DSS (n = 11). The pigs were orally challenged with DSS once daily for four days and sacrificed humanely. Colonic tissue was collected for gene expression analysis. Most of the targets evaluated in this study were present at low levels or in some cases were undetectable by QPCR, including the dopamine receptor DRD5 and the serotonin receptor HTR3A. The dopamine receptors (DRD1, DRD3, DRD4), serotonin receptor (HTR4), and other selected neuroactive receptors (GRM7, GABRA2) were down-regulated in the DSS-challenged animals relative to the basal group (p < 0.05). Most notably, DRD2, was up-regulated four-fold, suggesting an active process involving this receptor (p < 0.05). Relationships with (previously published) gene expression data from the same samples suggest that DRD1 and DRD2 are influenced by different pathways and may also be interlinked with matrix remodeling and, more specifically, genes relevant to the epithelial to mesenchymal transition (CDH1, CDH2, IL6, IL13, IL10, MMP1, MMP2) an important fibrotic process in the pathogenesis of IBD.