Expression patterns of claudin family of tight junction membrane proteins in developing mouse submandibular gland

Differences in claudin synthesis in primary cultures of acinar cells from rat salivary gland are correlated with the specific three-dimensional organization of the cells

Tight junctions are essential for the maintenance of epithelial cell polarity. We have previously established a system for the primary culture of salivary parotid acinar cells that retain their ability to generate new secretory granules and to secrete proteins in a signal-dependent manner. Because cell polarity and cell-cell adhesion are prerequisites for the formation of epithelial tissues, we have investigated the structure of the tight junctions in these cultures. We have found two types of cellular organization in the culture: monolayers and semi-spherical clusters. Electron microscopy has revealed tight junctions near the apical region of the lateral membranes between cells in the monolayers and cells at the surface of the clusters. The cells in the interior of the clusters also have tight junctions and are organized around a central lumen. These interior cells retain more secretory granules than the surface or monolayer cells, suggesting that they maintain their original character as acinar cells. The synthesis of claudin-4 increases during culture, although it is not detectable in the cells immediately after isolation from the glands. Immunofluorescence microscopy has shown that claudin-4 is synthesized in the monolayers and at the surface of the clusters, but not inside the clusters. Only claudin-3, which is present in the original acinar cells following isolation and in the intact gland, has been detected inside the clusters. These results suggest that differences in claudin expression are related to the three-dimensional structures of the cell cultures and reflect their ability to function as acinar cells.

Claudins 6, 9, and 13 are developmentally expressed renal tight junction proteins

The adult proximal tubule is a low-resistance epithelium where there are high rates of both active transcellular and passive paracellular NaCl transport. We have previously demonstrated that the neonatal rabbit and rat proximal tubule have substantively different passive paracellular transport properties than the adult proximal tubule, which results in a maturational change in the paracellular passive flux of ions. Neonatal proximal tubules have a higher P(Na)/P(Cl) ratio and lower chloride and bicarbonate permeabilities than adult proximal tubules. Claudins are a large family of proteins which are the gate keepers of the paracellular pathway, and claudin isoform expression determines the permeability characteristics of the paracellular pathway. Previous studies have shown that claudins 1, 2, 3, 4, 5, 7, 8, 10, 11, 12, 15, and 16 are expressed in the adult mouse kidney. To determine whether there are developmental claudin isoforms, we compared the claudin isoforms present in the neonatal and adult kidney using RT-PCR to detect mRNA of claudin isoforms. Claudin 6, claudin 9, and claudin 13 were either not expressed or barely detectable in the adult mouse kidney using traditional PCR, but were expressed in the neonatal mouse kidney. Using real-time RT-PCR, we were able to detect a low level of claudin 6 mRNA expression in the adult kidney compared with the neonate, but claudin 9 and claudin 13 were only detected in the neonatal kidney. There was the same maturational decrease in these claudin proteins with Western blot analysis. Immunohistochemistry showed high levels of expression of claudin 6 in neonatal proximal tubules, thick ascending limb, distal convoluted tubules, and collecting ducts in a paracellular distribution but there was no expression of claudin 6 in the adult kidney. Using real-time RT-PCR claudin 6 and 9 mRNA were present in 1-day-old proximal convoluted tubules and were virtually undetectable in proximal convoluted tubules from adults. Claudin 13 was not detectable in neonatal or adult proximal convoluted tubules. In summary, we have identified developmentally expressed claudin isoforms, claudin 6, claudin 9, and claudin 13. These paracellular proteins may play a role in the maturational changes in paracellular permeability.

Effects of low-intensity focused ultrasound on the mouse submandibular gland

Ultrasound is expected to make a considerable contribution to drug delivery systems (DDSs). We tested the hypothesis that low-intensity focused ultrasound (LIFU) increases vessel permeability in the mouse submandibular gland without causing parenchymal damage. In a preliminary study, LIFU at 3 W/cm2 with a 50% duty cycle for 2 minutes did not cause histologic damage. We therefore applied LIFU to mouse submandibular gland at these conditions before and after injecting horseradish peroxidase. Single labeling laser scanning confocal microscopy revealed positive horseradish peroxidase staining around the excretory ducts in the mucous-producing part of the gland, but absence of staining in control glands. Immunostaining for fibrinogen was positive in the same region. Fibrinogen is an intravascular protein that does not pass through intact vessels. These findings suggest that LIFU increases vessel permeability and disruption without destruction. It is anticipated that this process will be useful in establishing a DDS that uses LIFU.

Hedgehog peptide promotes cell polarization and lumen formation in developing mouse submandibular gland

Tube formation of the developing mouse submandibular salivary gland (SMG) begins at embryonic day (E) 14. The SMG of Sonic hedgehog (Shh) null mice was recently shown to fail to progress to stages beyond around E14. Here, we examined the effects of Shh peptide on tube formation of SMG explants. When the SMG rudiments from E14 mice were cultured, terminal buds of glands treated with Shh peptide formed the acini-like structure with a lumen whereas those of control glands remained as cell masses. In the acini-like terminal buds of the treated glands, tight junction proteins of ZO-1 and claudin-3 delineated the lumen and the apical membrane protein aquaporin-5 accumulated at the luminal cell surfaces. Moreover, laminin-5 deposition at the basal lamina region of terminal buds was accelerated in treated glands. It is suggested that hedgehog signaling promotes lumen formation and cell polarization of developing SMG epithelium.