Structure and permeability of goblet cell tight junctions in rat small intestine

Abstract

Two major cell types, goblet and absorptive cells, dominate the epithelial lining of small intestinal villi. We used freeze-fracture replicas of rat ileal mucosa to examine the possibility that tight junction structure, known to relate to transepithelial resistance, might vary with cell type. Tight junctions between absorptive cells were uniform in structure while those associated with villus goblet cells displayed structural variability. In 23% of villus goblet cell tight junctions the strand count was less than 4 and in 30% the depth was less than 200 nm. In contrast, only 4% of absorptive cell tight junctions had less than 4 strands and only 9% had depth measurements less than 200 nm. Other structural features commonly associated with villus goblet cell tight junctions but less commonly with absorptive cell tight junctions were: deficient strand cross-linking, free-ending abluminal strands, and highly fragmented strands. Both in vivo ileal segments and everted loops were exposed to ionic lanthanum. Dense lanthanum precipitates in tight junctions and paracellular spaces were restricted to a subpopulation of villus goblet cells and were not found between villus absorptive cells. After exposure of prefixed ileal loops to lanthanum for 1 hour, faint precipitates of lanthanum were found in 14% of tight junctions and paracellular spaces between absorptive cells compared to 42% of tight junctions and paracellular spaces adjacent to villus goblet cells. When tested in Ussing chambers, the methods used for lanthanum exposure did not lower transepithelial resistance. Everted loops exposed to ionic barium and examined by light microscopy showed dense barium precipitates in the junctional zone and region of the paracellular space of villus goblet cells but not in these regions between absorptive cells. However, the macromolecular tracers, microperoxidase, cytochrome c and horseradish peroxidase, were excluded from both villus goblet cell and absorptive cell paracellular spaces in in vivo segments. These findings suggest that a subpopulation of villus goblet cells may serve as focal sites of high ionic permeability and contribute to the relatively low resistance to ionic flow which characterizes the small intestinal epithelium.

PI3-kinase activation is critical for host barrier permissiveness to Listeria monocytogenes

“…Perez et al (2008) proposed that in stable and cohesive epithelia, PI3-K activity is downregulated to allow the maintenance of Ecad interactions at cell-cell junctions, whereas in more dynamic epithelia, actin cytoskeleton remodeling requires PI3-K activity to disrupt adherens junctions and allow the formation of new sites of Ecad homophilic interactions. Our in vivo findings fit with this model: luminal accessibility of Ecad correlates with high PI3-K activity in intestinal GCs, ECs, and EEFs, where adherens junctions are dynamic (Madara et al, 1980;Madara and Trier, 1982;Kölsch et al, 2007;Marchiando et al, 2011). Indeed, and found, as we previously reported , a significant role for InlA and InlB in third term placental villous explant invasion (Fig.…”

Transcytosis ofListeria monocytogenesacross the intestinal barrier upon specific targeting of goblet cell accessible E-cadherin

“…In a similar fashion as extruding cells, mucus-producing GCs undergo extensive shape changes such as stretch and compression during mucus secretion. These shape changes are accompanied with junctional reorganization, notably variations in length and strand cross-linking and discontinuities (Hull and Staehelin, 1976;Madara and Trier, 1982;Porvaznik et al, 1983;Madara, 1990). Accordingly, we demonstrate here that TJs are disorganized between cells on which Ecad is luminally exposed and establish a correlation between mucus secretion and luminal access to Ecad.…”

“…Ecad luminal accessibility on GCs correlates with cell junction reorganization and mucus secretion Cell-cell junctions involving GCs have been described as heterogeneous and relatively weaker than those between classical enterocytes (Madara et al, 1980;Madara and Trier, 1982). Moreover, cell shape changes that GCs undergo during mucus secretion have been associated with the loosening of their TJs (Hull and Staehelin, 1976;Porvaznik et al, 1983).…”

Maintenance of the macromolecular barrier at cell extrusion sites in intestinal epithelium: Physiological rearrangement of tight junctions

“…Fixation and processing protocols for light and electron microscopy and localization of horseradish peroxidase reaction product were carried out using methods previously detailed by us [10]. For routine electron microscopy, one can prescreen, l-txm sections and thus selectively sample specific sites, such as extrusion zones, for ultrastructural analysis even if they occur infrequently.…”