Expression patterns of tight junction proteins in porcine major salivary glands: a comparison study with human and murine glands

Tight junction (TJ) proteins play a dynamic role in paracellular fluid transport in salivary gland epithelia. Most TJ studies are carried out in mice and rats. However, the morphology of rodent salivary glands differs from that of human glands. This study aimed to compare the histological features and the expression pattern of TJ proteins in porcine salivary glands with those of human and mouse. The results showed that porcine parotid glands were pure serous glands. Submandibular glands (SMGs) were serous acinar cell‐predominated mixed glands, whereas sublingual glands were mucous acinar cell‐predominated. Human SMGs were mixed glands containing fewer mucous cells than porcine SMGs, whereas the acinar cells of murine SMGs are seromucous. The histological features of the duct system in the porcine and human SMGs were similar and included intercalated, striated and excretory ducts, but the murine SMG contained a specific structure, the granular convoluted tubule. TJ proteins, including claudin‐1 to claudin‐12, occludin and zonula occludin‐1 (ZO‐1), were detected in the porcine major salivary glands and human SMGs by RT‐PCR; however, claudin‐6, claudin‐9 and claudin‐11 were not detected in the murine SMG. As shown by immunofluorescence, claudin‐1, claudin‐3, claudin‐4, occludin and ZO‐1 were distributed in both acinar and ductal cells in the porcine and human SMGs, whereas claudin‐1 and claudin‐3 were mainly present in acinar cells, and claudin‐4 was mainly distributed in ductal cells in the murine SMG. In addition, 3D images showed that the TJ proteins arranged in a honeycomb‐like structure on the luminal surface of the ducts, whereas their arrangements in acini were irregular in porcine SMGs. In summary, the expression pattern of TJ proteins in salivary glands is similar between human and miniature pig, which may be a candidate animal for studies on salivary gland TJ function.     

Activation of transient receptor potential vanilloid subtype 1 increases expression and permeability of tight junction in normal and hyposecretory submandibular gland

Tight junction (TJ) is an important structure that regulates material transport through the paracellular pathway across the epithelium, but its significance in salivary physiology and pathogenesis of salivary dysfunctional diseases is not fully understood. We previously demonstrated that a functional transient receptor potential vanilloid subtype 1 (TRPV1) expresses in submandibular gland (SMG). However, association of TRPV1-induced saliva secretion with TJ remains unknown. Here we explored the effect of TRPV1 activation on expression and function of TJ of rabbit SMG in vitro and in vivo. RT-PCR and western blot analysis revealed that capsaicin upregulated expression of zonula occludin-1 (ZO-1), claudin (Cldn)-3, and -11, but not Cldn-1, -2, -4, -5, and -7 in cultured SMG cells. Capsaicin also increased the entering of 4?kDa FITC-dextran into the acinar lumen, induced redistribution of cytoskeleton F-actin under confocal microscope, and these effects were abolished by preincubation of capsazepine, a TRPV1 antagonist, indicating that activation of TRPV1 increases expression and permeability of TJ in SMG. Additionally, in a hyposecretory model induced by rabbit SMG transplantation, the expression of ZO-1, Cldn-3, and -11 was decreased, whereas other TJs remained unaltered. The structure of TJ was impaired and the width of apical TJs was reduced under transmission electron microscope, concomitant with diminished immunofluorescence of F-actin in peri-apicolateral region, indicating impaired TJ expression and decreased paracellular permeability in the transplanted SMG. Moreover, topical capsaicin cream increased secretion, decreased TJ structural injury, reversed TJ expression levels, and protected F-actin morphology from disarrangement in transplanted SMGs. These data provide the first evidence to demonstrate that TJ components, particularly ZO-1, Cldn-3, and -11 have important roles in secretion of SMG under both physiological and pathophysiological conditions. The injury in TJ integrity was involved in the hypofunctional SMGs, and TRPV1 might be a potential target to improve saliva secretion through modulating expression and function of TJs.     

Tissue-specific expression of the tight junction proteins claudins and occludin in the rat salivary glands

Tight junctions (TJs) are essential features of endothelial barrier membranes and of fluid-secreting epithelial cells, such as in the salivary glands. Novel integral membrane proteins have been identified as components of TJs, namely claudins and occludin. The aim of the present study was to determine the distribution of occludin and claudins in the large salivary glands of the rat. The parotid, submandibular and sublingual salivary glands were harvested from adult Sprague-Dawley rats and cryostat sections were stained using immunoperoxidase and immunofluorescence methods. Claudin-1 was expressed in endothelial cells of microvessels and in short selected segments of the duct system. Claudin-3 was expressed principally in the acinar cells and intercalated ducts, while claudin-4 was principally expressed by the striated and interlobular ducts. Claudin-5 was specific to endothelial cells of microvessels. Occludin was ubiquitously detected in the duct system. Double labelling and confocal microscopy showed some co-localization of claudin-3 with claudin-4, and minimal co-localization of occludin with claudin-4, in the striated ducts. Claudin 2 was not detected in any of the salivary glands. The results indicate specificity of the chemical composition of tight junctions in the rat salivary glands, and may reflect different physiological roles for TJs in the glandular and duct epithelial cells, and in endothelial cells of salivary gland microvessels.     

The Structure of Tight Junctions in Mouse Submandibular Gland

Salivary gland cells are joined by junctional complexes consisting of a tight junction (TJ), zonula adherens and one or more desmosomes. TJs regulate paracellular permeability, maintain separate apical and basolateral membrane domains, and serve as signaling centers. We examined TJs of mouse submandibular glands (SMG) in thin sections and freeze‐fracture replicas. TJs between acinar cells and between intercalated duct cells had 2–6 parallel strands on the protoplasmic fracture face, with occasional branches, interconnections and free ends, and corresponding grooves on the extracellular face. Granular duct cell TJs had 2–30 strands, a depth of ≤0.5 μm, and occasional loops extending further basally. Where 3 or 4 cells met, the TJs extended basally ≤1 μm and consisted of 2 parallel boundary strands into which the apical strands inserted. Quantitative analyses showed significant differences in TJ complexity, measured by fractal geometry, and strand number of acinar compared to granular duct cells, and a greater number of strands in male compared to female granular ducts. Pilocarpine stimulation increased TJ strand number in female acinar cells, and increased complexity of male granular duct cell TJs. As the salivary gland water channel aquaporin 5 (AQP5) has been proposed to functionally interact with TJs to regulate salivary fluid composition, we also studied glands from AQP5 knock‐out mice. In males lacking AQP5, granular duct TJs were more complex than those of wild‐type mice, and exhibited more strands following pilocarpine stimulation. The results demonstrate specific gender, cell type and genetic differences in TJ structure and response to stimulation. Anat Rec, 2010. © 2009 Wiley‐Liss, Inc.     

Claudin 14 knockout mice,a model for autosomal recessive deafness DFNB29, are deaf due to cochlear hair cell degeneration

Tight junctions (TJs) create ion-selective paracellular permeability barriers between extracellular compartments. In the organ of Corti of the inner ear, TJs of the reticular lamina separate K(+)-rich endolymph and Na(+)-rich perilymph. In humans, mutations of the gene encoding claudin 14 TJ protein cause profound deafness but the underlying pathogenesis is unknown. To explore the role of claudin 14 in the inner ear and in other tissues we created a mouse model by a targeted deletion of Cldn14. In the targeted allele a lacZ cassette is expressed under the Cldn14 promoter. In Cldn14-lacZ heterozygous mice beta-galactosidase activity was detected in cochlear inner and outer hair cells and supporting cells, in the collecting ducts of the kidney, and around the lobules of the liver. Cldn14-null mice have a normal endocochlear potential but are deaf due to rapid degeneration of cochlear outer hair cells, followed by slower degeneration of the inner hair cells, during the first 3 weeks of life. Monolayers of MDCK cells expressing claudin 14 show a 6-fold increase in the transepithelial electrical resistance by decreasing paracellular permeability for cations. In wild type mice, claudin 14 was immunolocalized at hair cell and supporting cell TJs. Our data suggest that the TJ complex at the apex of the reticular lamina requires claudin 14 as a cation-restrictive barrier to maintain the proper ionic composition of the fluid surrounding the basolateral surface of outer hair cells.     

Chronology of peroxidase activity in the developing rat parotid gland

The course of development of salivary peroxidase, an enzyme that has an important role in oral defense mechanisms, has been well documented in rat submandibular glands. However, the only report on salivary peroxidase activity in the other major salivary glands of the rat has been a cytochemical study of the adult parotid gland. In the present investigation, the accumulation of salivary peroxidase activity in developing parotid glands of rats was followed both biochemically and cytochemically. Specific activity (units per mg protein) attributable to salivary peroxidase began at 1 day after birth, then rose rapidly but unevenly, with peaks at 21 and 70 days, and no difference between the sexes at any age. Activity per gland increased progressively to 42 days in both sexes and was significantly higher in males at 70 days. The cytochemical observations on peroxidase activity localized to the rough endoplasmic reticulum and secretory granules of the developing acini were well correlated with the biochemical findings. Peroxidase-negative cells occurred in immature acini at 1 and 7 days, but only in the intercalated ducts thereafter. This observation suggests that the acini are a source of some of the ductal cells, at least during early postnatal development. The developmental pattern of specific activity differed from those of other rat parotid secretory enzymes, indicating that control of their synthesis during development is noncoordinate. The patterns of specific activity of the parotid and submandibular glands were complementary, suggesting that their combined secretions may supply biologically significant peroxidase activity to the oral cavities of rats throughout postnatal development. © 1993 Wiley-Liss, Inc.     

A key claudin extracellular loop domain is critical for epithelial barrier integrity

Intercellular tight junctions (TJs) regulate epithelial barrier properties. Claudins are major structural constituents of TJs and belong to a large family of tetra-spanning membrane proteins that have two predicted extracellular loops (ELs). Given that claudin-1 is widely expressed in epithelia, we further defined the role of its EL domains in determining TJ function. The effects of several claudin-1 EL mimetic peptides on epithelial barrier structure and function were examined. Incubation of model human intestinal epithelial cells with a 27-amino acid peptide corresponding to a portion of the first EL domain (Cldn-1(53-80)) reversibly interfered with epithelial barrier function by inducing the rearrangement of key TJ proteins: occludin, claudin-1, junctional adhesion molecule-A, and zonula occludens-1. Cldn-1(53-80) associated with both claudin-1 and occludin, suggesting both the direct interference with the ability of these proteins to assemble into functional TJs and their close interaction under physiological conditions. These effects were specific for Cldn-1(53-80), because peptides corresponding to other claudin-1 EL domains failed to influence TJ function. Furthermore, the oral administration of Cldn-1(53-80) to rats increased paracellular gastric permeability. Thus, the identification of a critical claudin-1 EL motif, Cldn-1(53-80), capable of regulating TJ structure and function, offers a useful adjunct to treatments that require drug delivery across an epithelial barrier.     

Ectodysplasin receptor-mediated signaling is essential for embryonic submandibular salivary gland development

Hypohidrotic (anhidrotic) ectodermal dysplasia (HED), the most common of the approximately 150 described ectodermal dysplasias, is a disorder characterized by abnormal hair, teeth, sweat glands, and salivary glands. Mutations in the EDA (ectodysplasin-A) and EDAR (ectodysplasin-A receptor) genes are responsible for X-linked and autosomal HED, respectively. Abnormal phenotypes similar to HED are seen in Tabby (Eda(Ta)) and downless (Edar(dl)) mutant mice. Although recent studies have focused on the role of Eda/Edar signaling during hair and tooth development, very little is known about its role during embryonic submandibular salivary gland (SMG) development. To this end, we analyzed the SMG phenotypes in Tabby (Ta) and downless (dl) mutant mice and determined that Ta SMGs are hypoplastic, whereas dl SMGs are severely dysplastic. The absence of SMG ducts and acini in dl SMGs suggests that Eda/Edar signaling is essential for lumina formation and glandular histodifferentiation. Our localization of Eda and Edar proteins at sites of lumen and acini formation supports this conclusion. Moreover, the presence of SMGs in both Ta and dl mutant mice, as well as the absence of immunodetectable Eda and Edar protein in Initial Bud and Early Pseudoglandular stage SMGs, indicate that Eda/Edar-mediated signaling is important for branching morphogenesis and histodifferentiation, but not for initial gland formation. To initially delineate the morphoregulatory role of Eda/Edar-mediated signaling during embryonic SMG development, we cultured embryonic day 14 SMGs with enhanced or abrogated Eda/Edar signaling. Eda supplementation induced a significant increase in SMG branching, and enhanced activation of NF-kappaB. Abrogating Eda/Edar signaling by adding the soluble form of Edar to bind endogenous ligand in embryonic SMGs results in a significant dose-dependent decrease in branching morphogenesis. Taken together, our results suggest that the Eda/Edar/NF-kappaB pathway exerts its effect on SMG epithelial cell proliferation, lumina formation, and histodifferentiation.     

Are alterations of tight junctions at molecular and ultrastructural level different in duodenal biopsies of patients with celiac disease and Crohn's disease?

Abnormalities of transmembrane and cytoplasmic proteins of tight junctions (TJ) have been implicated in pathogenesis of both celiac (CeD) and Crohn’s diseases (CD). Since disease pathogenesis in CeD and CD are different, we planned to study if there is any differential expression pattern of TJ marker proteins and ultrastructural changes, respectively, in duodenal villi vs crypts. Endoscopic duodenal biopsies from treatment naïve patients with CeD (n?=?24), active CD (n?=?28), and functional dyspepsia (as controls, n?=?15), both at baseline and 6 months after treatment, were subjected to light microscopic analysis (modified Marsh grading); immune-histochemical staining and Western blot analysis to see the expression of key TJ proteins [trans-membrane proteins (claudin-2, claudin-3, claudin-4, occludin, and JAM) and cytoplasmic protein (ZO-1)]. Transmission electron microscopy and image analysis of the TJs were also performed. There was significant overexpression of claudin-2 (pore-forming) and occludin (protein maintaining cell polarity) with under-expression of claudin-3 and claudin-4 (pore-sealing proteins) in treatment naïve CeD and active CD with simultaneous alteration in ultrastructure of TJs such as loss of penta-laminar structure and TJ dilatation. Normalization of some of these TJ proteins was noted 6 months after treatment. These changes were not disease specific and were not different in duodenal villi and crypts. Overexpression of pore-forming and under-expression of pore-sealing TJ proteins lead to dilatation of TJ. These changes are neither disease specific nor site specific and the end result of mucosal inflammation.     

TAZ inhibits acinar cell differentiation but promotes immature ductal cell proliferation in adult mouse salivary glands

There are currently no treatments for salivary gland diseases, making it vital to understand signaling mechanisms operating in acinar and ductal cells so as to develop regenerative therapies. To date, little work has focused on elucidating the signaling cascades controlling the differentiation of these cell types in adult mammals. To analyze the function of the Hippo-TAZ/YAP1 pathway in adult mouse salivary glands, we generated adMOB1DKO mice in which both MOB1A and MOB1B were TAM-inducibly deleted when the animals were adults. Three weeks after TAM treatment, adMOB1DKO mice exhibited smaller submandibular glands (SMGs) than controls with a decreased number of acinar cells and an increased number of immature dysplastic ductal cells. The mutants suffered from reduced saliva production accompanied by mild inflammatory cell infiltration and fibrosis in SMGs, similar to the Sjogren's syndrome. MOB1-deficient acinar cells showed normal proliferation and apoptosis but decreased differentiation, leading to an increase in acinar/ductal bilineage progenitor cells. These changes were TAZ-dependent but YAP1-independent. Biochemically, MOB1-deficient salivary epithelial cells showed activation of the TAZ/YAP1 and β-catenin in ductal cells, but reduced SOX2 and SOX10 expression in acinar cells. Thus, Hippo-TAZ signaling is critical for proper ductal and acinar cell differentiation and function i n adult mice.     

凋亡细胞在db/db自发性糖尿病小鼠颌下腺的分布

目的:观察凋亡细胞在db/db糖尿病小鼠颌下腺中的分布。方法:选取3、4、6、8、10月龄db/db糖尿病小鼠及相应月龄的dh/m~(?)小鼠颌下腺,应用TUNEL标记方法染色后进行图像分析.统计凋亡细胞在颌下腺组织中分布的细胞阳性率。结果:随着糖尿病的发展,颌下腺组织出现腺体萎缩及颗粒曲管数目减少,实质细胞排列不整齐,呈簇状堆集,纤维及血管增多。凋亡细胞在对照组及糖尿病组颌下腺中均有分布,糖尿病组凋亡细胞阳性率高于对照组。糖尿病组与对照组凋亡细胞阳性率随月龄增大均呈增加趋势。结论:db/db糖尿病可导致颌下腺组织萎缩及实质细胞形态学改变;凋亡细胞阳性率在糖尿病组随疾病发展而增加显著。这与糖尿病腺体萎缩和功能受损相一致。     

Changes in the Submandibular Salivary Gland Epithelial Cell Subpopulations During Progression of Sjögren's Syndrome‐Like Disease in the NOD/ShiLtJ Mouse Model

Sjögren's syndrome (SS), an autoimmune exocrinopathy, is associated with dysfunction of the secretory salivary gland epithelium, leading to xerostomia. The etiology of SS disease progression is poorly understood as it is typically not diagnosed until late stage. Since mouse models allow the study of disease progression, we investigated the NOD/ShiLtJ mouse to explore temporal changes to the salivary epithelium. In the NOD/ShiLtJ model, SS presents secondary to autoimmune diabetes, and SS disease is reportedly fully established by 20 weeks. We compared epithelial morphology in the submandibular salivary glands (SMG) of NOD/ShiLtJ mice with SMGs from the parental strain at 12, 18, and 22 weeks of age and used immunofluorescence to detect epithelial proteins, including the acinar marker, aquaporin 5, ductal cell marker, cytokeratin 7, myoepithelial cell marker, smooth muscle α‐actin, and the basal cell marker, cytokeratin 5, while confirming immune infiltrates with CD45R. We also compared these proteins in the labial salivary glands of human SS patients with control tissues. In the NOD/ShiLtJ SMG, regions of lymphocytic infiltrates were not associated with widespread epithelial tissue degradation; however, there was a decrease in the area of the gland occupied by secretory epithelial cells in favor of ductal epithelial cells. We observed an expansion of cells expressing cytokeratin 5 within the ducts and within the smooth muscle α‐actin⁺ basal myoepithelial population. The altered acinar/ductal ratio within the NOD/ShiLtJ SMG likely contributes to salivary hypofunction, while the expansion of cytokeratin 5 positive‐basal cells may reflect loss of function or indicate a regenerative response. Anat Rec, 298:1622–1634, 2015. © 2015 Wiley Periodicals, Inc.     

Comparative tight junction protein expressions in colonic Crohn’s disease,ulcerative colitis,and tuberculosis: a new perspective

We intended to see the pattern of TJ protein expression along with ultrastructural changes in colonic biopsies from patients with Crohn’s disease (CD), ulcerative colitis (UC), and tuberculosis (cTB). Colonic biopsies from 11 patients with active CD and ten patients each with active UC and untreated cTB were taken along with biopsies from six patients with irritable bowel syndrome as controls. These were evaluated for expression pattern of key TJ proteins which included claudin-2 as TJ pore-forming protein, claudin-4 as pore-sealing protein, ZO-1 as scaffold protein, and occludin as TJ protein related to cell migration and polarity. Claudin-2 expression was upregulated along the whole length of intercellular junction (ICJ) in biopsies from patients with active CD and UC in comparison to the biopsies from cTB patients and controls, where its expression was limited to the uppermost part of ICJ. There was reduced expression of ZO-1 in UC, CD, and cTB. On transmission electron microscopic examination, the pentalaminar structure of TJs was destroyed in patients with CD and UC but no significant change was seen in those with cTB and in controls. The expression of claudin-2 was distinctly different in active CD and UC in comparison to its expression pattern in patients with cTB and in controls. The redistribution of claudin-2 expression was in accordance with the TJ ultrastructural changes in patients with UC, CD, and cTB. Altered claudin-2 expression, along with destroyed TJs, may result in loss of selective permeability in patients with UC and CD.     

Distribution of calcitonin gene-related peptide immunoreactive nerve fibers in the human submandibular gland

The indirect immunofluorescence technique was used to study the distribution of calcitonin gene-related peptide (CGRP) in human submandibular gland. A relatively low number of thin varicose fibers with intense immunofluorescence for CGRP was seen in samples from seven glands. These CGRP-immunoreactive (CGRP-IR) nerve fibers were mainly seen around or in close contact with intra- and interlobular blood vessels. Some CGRP-IR nerve fibers were also found in association with intra- and interlobular salivary ducts and a few around the submandibular acini. By visual estimation there was no difference in the density of CGRP-IR nerve fibers between specimens of recurrent duct obstruction and laryngeal carcinoma. The present results show that the distribution of CGRP-IR nerve fibers in the stroma and in the glandular secretory elements of the human submandibular gland is quite similar to that seen in the rat and the ferret, which have been reported earlier. Furthermore, the regional distribution of CGRP-IR fibers in the human submandibular gland suggests that CGRP has a physiological role in the regulation of salivary gland function in human salivary glands, e.g. blood flow and secretion.     

Differential Expression of the Tight Junction Proteins,Claudin‐1, Claudin‐4, Occludin,ZO‐1, and PAR3, in the Ameloblasts of Rat Upper Incisors

Tight junctions (TJs) create a paracellular permeability barrier to restrict the passage of ions, small solutes, and water. Ameloblasts are enamel‐forming cells that sequentially differentiate into preameloblasts, secretory, transition, and ruffle‐ended and smooth‐ended maturation ameloblasts (RAs and SAs). TJs are located at the proximal and distal ends of ameloblasts. TJs at the distal ends of secretory ameloblasts and RAs are well‐developed zonula occludens, but other TJs are moderately developed but incomplete zonula occludens (ZO) or less‐developed macula occludens. We herein examined the immunofluorescence localization of TJ proteins, 10 claudin isoforms, occludin, ZO‐1, and PAR3, a cell polarity‐related protein, in ameloblasts of rat upper incisors. ZO‐1 and claudin‐1 were detected at both ends of all ameloblasts except for the distal ends of SAs. Claudin‐4 and occludin were detected at both ends of transition and maturation ameloblasts except for the distal ends of SAs. PAR3 was detected at the proximal TJs of all ameloblasts and faintly at the distal TJs of early RAs. These results indicate that functional zonula occludens formed at the distal ends of the secretory ameloblasts and RAs consisted of different TJ proteins. Therefore, the distal TJs of secretory ameloblasts and RAs may differentially regulate the paracellular permeability to create a microenvironment suitable for enamel deposition and enamel maturation, respectively. In addition, PAR3 may be principally involved in the formation and maintenance of the proximal, but not distal, TJs. Anat Rec, 291:577–585, 2008. © 2008 Wiley‐Liss, Inc.