Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2015
Publication Date: 2/25/2015
Citation: Walker, M.P., Clover, C.M., Elsasser, T.H., Connor, E.E. 2015. Tight junction gene expression in gastrointestinal tract of dairy calves with coccidiosis and treated with glucagon-like peptide-2. Journal of Dairy Science. 98(5):3432-3437.
Interpretive Summary: Intestinal barrier function protects the body from a hostile environment within the gut, while allowing selective passage of nutrients, ions, and other molecules through a network of ion channels, pumps, and tight junctions. We examined expression of 8 tight junction proteins that regulate ion and macromolecule trafficking in samples obtained from the distal small intestine and cecum of Holstein bull calves. Calves were healthy or infected with coccidiosis, and treated with or without glucagon-like peptide 2 (GLP-2), an intestinal hormone known to improve gut function. This work provides novel information on tight junction regulation by GLP- 2 in normal and diseased bovine intestine. This work is useful to animal scientists, veterinarians, and researchers studying gut health and disease.
Technical Abstract: Selective permeability of the intestinal epithelium and efficient nutrient absorption are important functions for proper growth and development of calves. Damage to the intestinal mucosa can give rise to harmful long-term health effects and reduce productivity of the mature animal. Tight junction proteins are integral factors involved in gut barrier function, and treatment with the intestinotrophic hormone glucagon-like peptide-2 (GLP-2) is known to enhance gut integrity. The purpose of this study was to assess changes in gene expression of 8 proteins associated with tight junctions in samples from the ileum and cecum of newborn dairy calves with coccidiosis and treated with GLP-2. Mucosal epithelium from the jejunum, ileum, and cecum was collected at slaughter from 18 Holstein bull calves assigned to 4 treatment groups: uninfected, buffer-treated (n = 5); uninfected, GLP-2 treated (n = 4); Eimeria bovis-infected, buffer-treated (n = 5); and E. bovis-infected, GLP-2-treated (n = 4). The E. bovis-infected calves were orally dosed with 100,000 to 200,000 sporulated oocysts on Study d 0, and GLP-2 treated calves received 50 µg of GLP-2/kg BW s.c. twice daily for 10 d beginning on d 18. Buffer-treated calves received an equal injection volume of sodium bicarbonate buffer. Calves were sacrificed on d 28. The relative mRNA expression of claudins 1, 2, and 4 (CLDN1, CLDN2, and CLDN4), the coxsackie anedovirus receptor (CXADR), F11 receptor (F11R), junction adhesion molecule 2 (JAM2), tight junction protein 1 (TJP1), and occludin (OCLN) was determined by quantitative real-time PCR. Effects of GLP-2 and E. bovis infection on gene expression in ileum and cecum were determined using a general linearized model. The mRNA and protein expressions of tight junction protein 1 and occludin in jejunum, determined by immunohistochemistry, were compared between GLP-2- and buffer-treated uninfected calves using a Student's t-test. Treatment with GLP-2 increased TJP1 and OCLN mRNA expression in jejunum, but protein levels were not affected. In ileum, no main effects of GLP-2 or infection were observed on tight junction gene expression; however, an interaction was detected between GLP-2 and infection for JAM2, OCLN, and TJP1. In cecum, GLP-2 increased expression of CLDN4, F11R, OCLN, and TJP1. Expression of CXADR, CLDN4, F11R, and OCLN mRNA was decreased by E. bovis infection, and an interaction was detected between GLP-2 and infection for JAM2. These findings demonstrate down regulation of tight junction gene expression in ileocecum by E. bovis infection and the ability of GLP-2 to increase expression of selected tight junction genes in healthy calf jejunum. Results support a role of tight junction proteins in mediating GLP-2 effects on improved intestinal barrier function and potential therapeutic uses of GLP-2 to offset negative effects of coccidiosis in dairy calves.