Ileal Tight Junction Gene Expression in Glucagon-like Peptide 2-treated Dairy Bull Calves with and without Coccidiosis

Abstract Text: Intestinal gut permeability is partially regulated by the intestinotrophic hormone glucagon-like peptide 2 (GLP-2). Specifically, disease models in mice and human cell lines have implicated GLP-2 in the regulation of the tight junction milieu within the intestinal tract. Therapeutic administration of GLP-2 ameliorates gastrointestinal lesions and mechanical damage in rodent models of ileitis, porcine models of bowel resection, and humans with small bowel disease. These damages can reduce nutritional absorption and increase bacteria in the blood stream, both of which are  in part attributed to tight junction protein disregulation. The purpose of the present study was to determine whether GLP2 therapy alters tight junction gene expression in ileum of neonatal dairy calves with scours induced by Eimeria bovis infection. Neonatal Holstein bull calves (n =18) were separated into 4 treatment groups; uninfected-buffer (n = 5), uninfected-GLP-2 (n = 4), E. bovis-buffer (n = 5), and E. bovis-GLP-2 (n = 4). On d 0, calves in the E. bovis-buffer and E. bovis-GLP-2 groups were orally dosed with 200,000 sporulated oocysts of E. bovis. For 10 d (d 18 to d 27 of the study), uninfected-GLP-2 and E. bovis-GLP-2 calves were injected every 12 h with 50 µg of GLP-2/kg BW and at d 28 calves were sacrificed for collection of intestinal tissues for RNA extraction. Tight junction genes including CAR, CLDN1, CLDN2, CLDN4, F11R/JAMA, JAM2/JAMB, and TJP1/ZO-1 were evaluated in ileal epithelium by realtime quantitative PCR. Relative mRNA expression normalized to ATP5B and HMBS revealed greater expression of TJP1/ZO-1 in E. bovis-infected calves compared to uninfected calves (P ≤ 0.03) and an E.bovis  infection vs GLP2 treatment interaction (P ≤ 0.004). Expression of all other genes did not differ (P > 0.05) with GLP-2 treatment or E. bovisinfection status. The lack of significant findings among the majority of genes investigated may be explained by large variation among individuals or the timing of sample collection relative to infection status and GLP-2 treatment. Alternatively, tight junctions may not be regulated at the RNA level, whereby analysis at the protein level may be more appropriate. Finally, the cellular localization of tight junction proteins may become altered during infection and with GLP2 treatment due to post-translational modifications or other regulating molecules. A more in-depth histological study could reveal significant findings that analysis of RNA levels alone cannot detect.  

Keywords: dairy cattle, ileum, tight junction