Publikationsdatenbank

Molecular and functional analysis of the porcine and murine small intestinal tight junction (2018)

Art

Hochschulschrift

Autor

Radloff, Judith (WE 2)

Quelle

Berlin, 2018 — III, 78 Seiten

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/233

Kontakt

Institut für Veterinär-Physiologie

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

Abstract / Zusammenfassung

The tight junction (TJ) surrounds epithelial cells in the upper third of the lateral cellular membrane. It is formed by different proteins that are anchored within the membrane of epithelial cells. The most functional relevance is attributed to the family of claudins. The upper epithelial monolayer in the gastrointestinal tract forms a tight barrier between the ingesta and the mammalian organism. While a sufficient nutrient supply must be guaranteed, a tight barrier against potential pathogens must be maintained. Therefore the TJ regulates the paracellular permeability, giving it a direct control over which substances can selectively enter the body. In this thesis the intestinal TJ was analyzed regarding two different aspects of epithelial barrier function. 1\. Challenging porcine intestinal epithelium by predigested and non-predigested milk. Sufficient energy supply via intestinal absorption is essential within the first weeks of life. While an adequate absorption needs to be maintained, a tight intestinal barrier is required for protection against potentially pathogenous organisms. This raises the questions of if and how the intestinal epithelial barrier is regulated during milk consumption. Employing the Ussing chamber technique, jejunal epithelium of 2 month old piglets was incubated with a 50 % milk-buffer mixture. To simulate possible effects due to digestion processes, predigested and non-predigested milk was used. Even though the transepithelial resistance (TER) was significantly increased after 30 and 150 minutes of incubation, no changes of the paracellular permeability for sodium fluorescein could be detected. Analysis of claudin expression levels revealed no changes for claudin-1, -2, -3 and -4. Relocation to intracellular vesicles and subjunctional compartments could be shown for claudin-3 and -4 via immunohistology. Data obtained in this thesis cannot fully explain which milk component leads to the recorded results. However, it can be conducted that as a generalization, milk strengthens the intestinal barrier. 2\. Functional and molecular characterization of the porcine and murine tight junction within small intestinal Peyer’s patches. Peyer’s Patches are responsible for initiating immune reactions when confronted with potential pathogens. They are specialized areas within the mucosa of the distal small intestine and covered by the follicle-associated epithelium (FAE). An important requirement for the controlled interaction between antigens and the immune system is the maintenance of the epithelial barrier integrity of the FAE. Therefore the second part of this thesis focused on the characterization of the FAE. Porcine and murine PP showed higher TER and lower permeability for paracellular markers fluorescein and FITC Dextran (4, 20 kDa) when compared to villous epithelium. Expression levels of different TJ proteins revealed increased levels of sealing claudins. The paracellular localization of claudins was confirmed via immunohistochemistry, and both studies highlight a major significance for claudin-4 in the FAE of PP in interspecies comparisons. The obtained data supports the assumption that PP are clearly specialized for antigen sampling and representation of antigens to the immune system, while the TJ of the FAE provides a stronger seal of the paracellular pathway.