Publikationsdatenbank

Regulation of the epithelial barrier in the rumen epithelium of sheep by incubation with single short-chain fatty acid at different pH, with glucagon-like peptide 1, glucagon-like peptide 2, and epidermal growth factor (2021)

Art

Hochschulschrift

Autor

Greco, Gabriele (WE 2)

Quelle

Berlin, 2021 — VIII, 88 Seiten

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/30042

Kontakt

Institut für Veterinär-Physiologie

Oertzenweg 19 b
14163 Berlin
+49 30 838 62600
physiologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

The rumen epithelium (RE) functions as an absorbing layer for short-chain fatty acids (SCFA) and at the same time as a protective interface between the blood circulation and the ruminal environment. These functions are strongly interconnected by the epithelial barrier (EB). A failure of this barrier compromises both absorbing and protective abilities and may lead to sickness of the animal and economic loss for the farmer. One of the main causes of EB failure is nutritional oversupply of easily fermentable carbohydrates, which leads to acute or subacute ruminal acidosis. Under these conditions, several changes occur in the rumen environment. One of these changes is the increase of SCFA, which is associated with a decrease of pH. In a previous study, it was demonstrated that the combination of low pH and high SCFA is necessary for impairing the EB of the RE and low pH alone did not impair the EB. In this study the three main SCFA were tested all together in a mix. The present study investigated whether the effect of individual SCFA at physiological and low pH lead to different changes of the EB of the RE. Rumen epithelia for Ussing chamber experiments were obtained from seven sheep. Epithelia were incubated 7 h with 30 mM of either acetate, propionate, or butyrate on the mucosal side at mucosal pH of 6.1 or at pH 5.1. Some extra epithelia were incubated with 100 mM acetate and tested under both pH conditions. Electrophysiological parameters and fluorescein flux rates were monitored during the incubation. Following incubation, mRNA and protein abundance of the TJ proteins claudin-1, -4, -7, and occludin were investigated, and TJ proteins were visualized using immunofluorescence staining. The results showed that SCFA incubation at physiological mucosal pH did not functionally affect the epithelial barrier. However, the results showed increased mRNA expression of some TJ proteins suggesting some protective effects of SCFA on the EB, but also a reduction of claudin-7 at protein level after incubation with 100 mM acetate and 30 mM butyrate. At pH of 5.1 all individual SCFA impaired to a comparable degree the EB and downregulated the TJ proteins. The group of epithelia incubated with 100 mM acetate caused more intense barrier failure. Epithelia incubated without SCFA at pH 5.1 showed no signs or very little evidence of barrier failure. This data suggests that the RE is extremely resistant to low pH environment. However, the combination of low pH with SCFA impairs the EB. Each SCFA caused a similar detrimental effect on the EB if incubated at the same concentration, while increasing their concentration augmented the harmful effect on the EB. The second study focused on molecules that may potentially strengthen the EB. According to literature, GLP-1, -2, and EGF usually improve the EB of other different epithelia. Therefore, their effects on RE were studied in ex vivo experiments. RE were obtained from six sheep and incubated with two different concentrations of GLP-1, GLP-2, and EGF in Ussing chambers. GLP-1 and GLP-2 were incubated on the serosal side. EGF was tested at a higher concentration on the serosal side and on the mucosal side, while a lower concentration of EGF was also tested on the mucosal side. The results of this second study did not show functional effects on the EB from any of the molecules tested. However, some potentially beneficial effects were seen at the mRNA level after incubation with high concentration of GLP-2 and high concentration of EGF on the serosal side. An interesting result was also the downregulation of claudin-7 at mRNA level in all epithelial treated with GLP-1, -2, and EGF. The result suggests that GLP-1 may have no, or a minor, role in EB regulation of RE, while EGF and GLP-2 may potentially regulate and protect the EB of the RE. Further studies in vivo are needed to confirm these results.