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

The role and mechanism of tight junctions in the regulation of salivary gland secretion

Tight junctions (TJs) are cell-cell interactions that localize at the most apical portion of epithelial/endothelial cells. One of the predominant functions of TJs is to regulate material transport through paracellular pathway, which serves as a selective barrier. In recent years, the expression and function of TJs in salivary glands has attracted great interest. The characteristics of multiple salivary gland TJ proteins have been identified. During salivation, the activation of muscarinic acetylcholine receptor and transient receptor potential vanilloid subtype 1, as well as other stimuli, promote the opening of acinar TJs by inducing internalization of TJs, thereby contributing to increased paracellular permeability. Besides, endothelial TJs are also redistributed with leakage of blood vessels in cholinergic-stimulated submandibular glands. Furthermore, under pathological conditions, such as Sjögren's syndrome, diabetes mellitus, immunoglobulin G4-related sialadenitis, and autotransplantation, the integrity and barrier function of TJ complex are impaired and may contribute to hyposalivation. Moreover, in submandibular glands of Sjögren's syndrome mouse model and patients, the endothelial barrier is disrupted and involved in hyposecretion and lymphocytic infiltration. These findings enrich our understanding of the secretory mechanisms that link the importance of epithelial and endothelial TJ functions to salivation under both physiological and pathophysiological conditions.

CSF1R-dependent macrophages in the salivary gland are essential for epithelial regeneration after radiation-induced injury

The salivary glands often become damaged in individuals receiving radiotherapy for head and neck cancer, resulting in chronic dry mouth. This leads to detrimental effects on their health and quality of life, for which there is no regenerative therapy. Macrophages are the predominant immune cell in the salivary glands and are attractive therapeutic targets due to their unrivaled capacity to drive tissue repair. Yet, the nature and role of macrophages in salivary gland homeostasis and how they may contribute to tissue repair after injury are not well understood. Here, we show that at least two phenotypically and transcriptionally distinct CX3CR1+ macrophage populations are present in the adult salivary gland, which occupy anatomically distinct niches. CD11c+CD206-CD163- macrophages typically associate with gland epithelium, whereas CD11c-CD206+CD163+ macrophages associate with blood vessels and nerves. Using a suite of complementary fate mapping systems, we show that there are highly dynamic changes in the ontogeny and composition of salivary gland macrophages with age. Using an in vivo model of radiation-induced salivary gland injury combined with genetic or antibody-mediated depletion of macrophages, we demonstrate an essential role for macrophages in clearance of cells with DNA damage. Furthermore, we show that epithelial-associated macrophages are indispensable for effective tissue repair and gland function after radiation-induced injury, with their depletion resulting in reduced saliva production. Our data, therefore, provide a strong case for exploring the therapeutic potential of manipulating macrophages to promote tissue repair and thus minimize salivary gland dysfunction after radiotherapy.

Submandibular gland epithelial development and the importance of junctions

Salivary glands consist of highly specialized epithelial cells that secrete the fluid, saliva, and/or transport saliva into the oral cavity. Saliva is essential to lubricate the oral cavity for food consumption and to maintain the hygiene of the oral cavity. In this review, we will focus on the formation of the epithelial cell lineage and the cell junctions that are essential for formation of saliva and maintenance of the epithelial barrier between the ducts that transport saliva and the extracellular environment.

Emerging roles of transmembrane-type tight junction proteins in cancers

Tight junctions (TJs) are the most apical components of the cell-cell adhesion machinery in epithelial and endothelial cells and they play essential roles in homeostasis. Recent studies have revealed that aberrant expression of tight junction proteins (TJPs) is frequently observed in various type of cancers. Here we review cancer-associated aberrant expression of TJPs with focus on transmembrane-type TJPs including claudins, junctional adhesion molecule-A (JAM-A), and occludin. Some transmembrane-type TJPs are upregulated at the early neoplastic stage and their expression persists during dedifferentiation. Aberrant expression of TJPs contributes to proliferation, invasion, and dysregulated signaling of cancer cells. In addition to an increase in their expression level, their localization is altered from a TJ-restricted pattern to distribution throughout the whole cell membrane, making them suitable as therapeutic targets. Extracellular domains of transmembrane-type TJPs can be approached by target drugs not only from the lumen side (apical side) but also from the extracellular matrix side (basal side), including blood vessels. Aberrantly expressed TJPs are potential useful diagnostic markers as well as therapeutic targets for cancers.

Autologous mesenchymal stem cells offer a new paradigm for salivary gland regeneration

Salivary gland (SG) dysfunction, due to radiotherapy, disease, or aging, is a clinical manifestation that has the potential to cause severe oral and/or systemic diseases and compromise quality of life. Currently, the standard-of-care for this condition remains palliative. A variety of approaches have been employed to restore saliva production, but they have largely failed due to damage to both secretory cells and the extracellular matrix (niche). Transplantation of allogeneic cells from healthy donors has been suggested as a potential solution, but no definitive population of SG stem cells, capable of regenerating the gland, has been identified. Alternatively, mesenchymal stem cells (MSCs) are abundant, well characterized, and during SG development/homeostasis engage in signaling crosstalk with the SG epithelium. Further, the trans-differentiation potential of these cells and their ability to regenerate SG tissues have been demonstrated. However, recent findings suggest that the "immuno-privileged" status of allogeneic adult MSCs may not reflect their status post-transplantation. In contrast, autologous MSCs can be recovered from healthy tissues and do not present a challenge to the recipient's immune system. With recent advances in our ability to expand MSCs in vitro on tissue-specific matrices, autologous MSCs may offer a new therapeutic paradigm for restoration of SG function.

Tight junction gene expression in salivary gland tumors

Salivary gland neoplasms comprise a heterogeneous group of lesions with multiple histological subtypes, each with distinct growth patterns, resulting in a spectrum of tumor-specific prognoses; pleomorphic adenoma (PA) and mucoepidermoid carcinoma (MEC) are the most common representatives of these neoplasms. Many studies have associated specific profiles of membrane and adhesion molecules in salivary gland tissues; these profiles appear to be relevant in tumor biology as well as be interpreted as fingerprints for tumor classification, diagnostic prognostic and therapeutic targets. One of these membrane molecule complexes are the tight junctions, composed by various proteins, in which claudins are protagonists. The aim of this study was to evaluate the expressions of genes that encode tight junction proteins (CLDN-1, -3, -4, -5, -7, and -11, occludin [OCLN], zonula occludens [TJP1, TJP2, and TJP3] and junctional adhesion molecule A [F11R]) in MEC and PA using real time RT-PCR. We observed high expression of CLDN-1 and -7 and low expression of CLDN-3, -11 and TJP2 in MEC compared to PA. PA samples demonstrated high OCLN expression when compared to MEC. CRTC1::MAML2 fusion was detected in 12 of 20 (60.0%) MEC samples and was associated with CLDN7 expression, while the absence of fusion was associated with high histological grade. Increased CLDN5 expression was associated with submandibular gland tumors. This study demonstrated differential expressions of genes encoding tight junction constituent proteins and their associations with tumor characteristics, suggesting their potential future role as diagnostic and prognostic markers.

A phase II study assessing the safety and efficacy of ASP1650 in male patients with relapsed refractory germ cell tumors

Claudin6(CLDN6) is a tight junction protein of claudin-tetraspanin family and is of the earliest molecules expressed in embryonic epithelium. CLDN6 is frequently aberrantly expressed in testicular germ-cell tumors(GCT). ASP1650 is a chimeric-mouse/human-IgG1 antibody directed against CLDN6. Two-part, open-label, phase-II trial investigating ASP1650 in patients with relapsed/refractory GCT and no curable options. Part1 was a safety lead-in to establish the recommended-phase-II-dose(RP2D). Part2 was a phase-II study designed to evaluate the antitumor effects of ASP1650. CLDN6 expression was centrally assessed on archival tumor tissue using immunohistochemistry. The primary objectives were to establish the RP2D(safety lead-in) and the antitumor activity(phase-II) of ASP1650. Nineteen male patients were enrolled: 6 patients in 1000 mg/m2 safety lead-in group, and 13 in 1500 mg/m2 group. Median age 37.2 years(range,20-58). Histology was non-seminoma in 17/19 patients. Median number of previous chemotherapy regimens was 3. Thirteen patients had prior high-dose chemotherapy. No dose-limiting toxicity events were reported at any study drug dose. A RP2D of 1500 mg/m2 every 2 weeks was established. No partial or complete responses were observed. The study was stopped at the end of Simon Stage-I due to lack of efficacy. 15/16 subjects with available tissue had CLDN6 positive staining. The mean percent membrane staining was 71.6% and the mean membrane H score was 152.6(SD 76). ASP1650 did not appear to have clinically meaningful single-agent activity in relapsed/refractory GCT. CLDN6 expression seems ubiquitous in all elements of GCT and is worthy of investigation as a diagnostic biomarker and therapeutic target. (Clinical trial information: NCT03760081).

Organ-specific extracellular matrix directs trans-differentiation of mesenchymal stem cells and formation of salivary gland-like organoids in vivo

BACKGROUND

Current treatments for salivary gland (SG) hypofunction are palliative and do not address the underlying cause or progression of the disease. SG-derived stem cells have the potential to treat SG hypofunction, but their isolation is challenging, especially when the tissue has been damaged by disease or irradiation for head and neck cancer. In the current study, we test the hypothesis that multipotent bone marrow-derived mesenchymal stem cells (BM-MSCs) in a rat model are capable of trans-differentiating to the SG epithelial cell lineage when induced by a native SG-specific extracellular matrix (SG-ECM) and thus may be a viable substitute for repairing damaged SGs.

METHODS

Rat BM-MSCs were treated with homogenates of decellularized rat SG-ECM for one hour in cell suspension and then cultured in tissue culture plates for 7 days in growth media. By day 7, the cultures contained cell aggregates and a cell monolayer. The cell aggregates were hand-selected under a dissecting microscope, transferred to a new tissue culture dish, and cultured for an additional 7 days in epithelial cell differentiation media. Cell aggregates and cells isolated from the monolayer were evaluated for expression of SG progenitor and epithelial cell specific markers, cell morphology and ultrastructure, and ability to form SG-like organoids in vivo.

RESULTS

The results showed that this approach was very effective and guided the trans-differentiation of a subpopulation of CD133-positive BM-MSCs to the SG epithelial cell lineage. These cells expressed amylase, tight junction proteins (Cldn 3 and 10), and markers for SG acinar (Aqp5 and Mist 1) and ductal (Krt 14) cells at both the transcript and protein levels, produced intracellular secretory granules which were morphologically identical to those found in submandibular gland, and formed SG-like organoids when implanted in the renal capsule in vivo.

CONCLUSIONS

The results of this study suggest the feasibility of using autologous BM-MSCs as an abundant source of stem cells for treating SG hypofunction and restoring the production of saliva in these patients.

Aberrant expression of claudin-6 contributes to malignant potentials and drug resistance of cervical adenocarcinoma

Recent studies have revealed that aberrant expression of tight junction (TJ) proteins is a hallmark of various solid tumors and it is recognized as a useful therapeutic target. Claudin‐6 (CLDN6), a member of the family of TJ transmembrane proteins, is an ideal therapeutic target because it is not expressed in human adult normal tissues. In this study, we found that CLDN6 is highly expressed in uterine cervical adenocarcinoma (ADC) and that high CLDN6 expression was correlated with lymph node metastasis and lymphovascular infiltration and was an independent prognostic factor. Shotgun proteome analysis revealed that cell‐cell adhesion‐related proteins and drug metabolism‐associated proteins (aldo‐keto reductase [AKR] family proteins) were significantly increased in CLDN6‐overexpressing cells. Furthermore, overexpression of CLDN6 enhanced cell‐cell adhesion properties and attenuated sensitivity to anticancer drugs including doxorubicin, daunorubicin, and cisplatin. Taken together, the results indicate that aberrant expression of CLDN6 enhances malignant potentials and drug resistance of cervical ADC, possibly due to increased cell‐cell adhesion properties and drug metabolism. Our findings provide an insight into a new therapeutic strategy, a CLDN6‐targeting therapy, against cervical ADC.

Tumor necrosis factor-α induces claudin-3 upregulation in kidney tubular epithelial cells through NF-κB and CREB1

Claudins are essential for tight junction formation and paracellular transport, and they affect key cellular events including proliferation and migration. The properties of tight junctions are dynamically modulated by a variety of inputs. We previously showed that the inflammatory cytokine tumor necrosis factor-α (TNFα), a major pathogenic factor in kidney disease, alters epithelial permeability by affecting the expression of claudin-1, -2, and -4 in kidney tubular cells. Here, we explored the effect of TNFα on claudin-3 (Cldn-3), a ubiquitous barrier-forming protein. We found that TNFα elevated Cldn-3 protein expression in tubular epithelial cells (LLC-PK1 and IMCD3) as early as 3 h post treatment. Bafilomycin A and bortezomib, inhibitors of lysosomal and proteasomes, respectively, reduced Cldn-3 degradation. However, TNFα caused a strong upregulation of Cldn-3 in the presence of bafilomycin, suggesting an effect independent from lysosomes. Blocking protein synthesis using cycloheximide prevented Cldn-3 upregulation by TNFα, verifying the contribution of de novo Cldn-3 synthesis. Indeed, TNFα elevated Cldn-3 mRNA levels at early time points. Using pharmacological inhibitors and siRNA-mediated silencing, we determined that the effect of TNFα on Cldn-3 was mediated by extracellular signal regulated kinase (ERK)-dependent activation of NF-κB and PKA-induced activation of CREB1. These two pathways were turned on by TNFα in parallel and both were required for the upregulation of Cldn-3. Because Cldn-3 was suggested to modulate cell migration and epithelial-mesenchymal transition (EMT), and TNFα was shown to affect these processes, Cldn-3 upregulation may modulate regeneration of the tubules following injury.

Sox2 maintains epithelial cell proliferation in the successional dental lamina

OBJECTIVES

The successional dental lamina is the distinctive structure on the lingual side of the vertebrate tooth germ. The aim of this study was to investigate the relationship among Sox2, Claudin10 and laminin5 and the role of Sox2 in successional dental lamina proliferation during vertebrate tooth development.

MATERIALS AND METHODS

To understand the successional dental lamina, two types of successional tooth formation, that in geckos (with multiple rounds of tooth generation) and that in mice (with only one round of tooth generation), were analysed.

RESULTS

Unique coexpression patterns of Sox2 and Claudin10 expression were compared in the successional dental lamina from the cap stage to the late bell stage in the mouse tooth germ and in juvenile gecko teeth to support continuous tooth replacement. Furthermore, Laminin5 expression was shown in the cap stage and decreased after the bell stage. Upon comparing the epithelial cell cycles and cell proliferation in successional dental lamina regions between mouse and gecko molars using BrdU and IdU staining and pulse-chase methods, distinctive patterns of continuous expression were revealed. Moreover, Sox2 overexpression with a lentiviral system resulted in hyperplastic dental epithelium in mouse molars.

CONCLUSIONS

Our findings indicate that the regulation of Sox2 in dental lamina proliferation is fundamental to the successional dental lamina in both species.

Mouse Models of Human Claudin-Associated Disorders: Benefits and Limitations

In higher organisms, epithelia separate compartments in order to guarantee their proper function. Such structures are able to seal but also to allow substances to pass. Within the paracellular pathway, a supramolecular structure, the tight junction transport is largely controlled by the temporospatial regulation of its major protein family called claudins. Besides the fact that the expression of claudins has been identified in different forms of human diseases like cancer, clearly defined mutations in the corresponding claudin genes have been shown to cause distinct human disorders. Such disorders comprise the skin and its adjacent structures, liver, kidney, the inner ear, and the eye. From the phenotype analysis, it has also become clear that different claudins can cause a complex phenotype when expressed in different organs. To gain deeper insights into the physiology and pathophysiology of claudin-associated disorders, several mouse models have been generated. In order to model human disorders in detail, they have been designed either as full knockouts, knock-downs or knock-ins by a variety of techniques. Here, we review human disorders caused by CLDN mutations and their corresponding mouse models that have been generated thus far and assess their usefulness as a model for the corresponding human disorder.

Grhl2 regulation of SPINT1 expression controls salivary gland development

Development of the salivary gland is characterized by extensive branching morphogenesis and lumen formation, the latter of which is closely associated with differentiation into acinar and ductal cells. Although various molecules, including signaling and cell adhesion molecules, have been implicated in salivary gland development, transcription factors (TFs) regulating the expression of those molecules and morphological development of the gland are largely unknown. Here we show that knockdown of the epithelial TF, Grainyhead-like 2 (Grhl2), with siRNA in developing mouse submandibular salivary gland (SMG) cultured ex vivo resulted in retardation of epithelial development. This retardation was concomitant with suppression of gene expression for the cell adhesion molecules, such as E-cadherin and the extracellular protease inhibitor SPINT1, and with the disorganized deposition of the basal lamina protein laminin. ChIP-PCR demonstrated the binding of Grhl2 protein to the Spint1 gene in the SMG. Notably, addition of recombinant SPINT1 protein in cultured SMG overcame the suppressive effects of Grhl2 siRNA on epithelial development and laminin deposition. These findings show that Grhl2 regulation of SPINT1 expression controls salivary gland development.

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.

Morphological and Functional Analyses of the Tight Junction in the Palatal Epithelium of Mouse

Tight junction (TJ) is one of the cell-cell junctions and known to have the barrier and fence functions between adjacent cells in both simple and stratified epithelia. We examined the distribution pattern, constitutive proteins, and permeability of TJ in the stratified squamous epithelium of the palatal mucosa of mice. Ultrastructural observations based on the ultrathin section and freeze-fracture methods revealed that poorly developed TJs are located at the upper layer of the stratum granulosum. The positive immunofluorescence of occludin (OCD), claudin (CLD)-1 and -4 were localized among the upper layer of the stratum granulosum showing a dot-like distribution pattern. And CLD-1 and -4 were localized among the stratum spinosum and the lower part of stratum granulosum additionally showed a positive reaction along the cell profiles. Western blotting of TJ constitutive proteins showed OCD, CLD-1, -2, -4, and -5 bands. The permeability test using biotin as a tracer revealed both the areas where biotin passed through beyond OCD positive points and the areas where biotin stopped at OCD positive points. These results show that poor TJs localize at the upper layer of the stratum granulosum of the palatal epithelium, and the TJs are leaky and include at least CLD-1 and -4.

Multiplex epithelium dysfunction due to CLDN10 mutation: the HELIX syndrome

PurposeWe aimed to identify the genetic cause to a clinical syndrome encompassing hypohidrosis, electrolyte imbalance, lacrimal gland dysfunction, ichthyosis, and xerostomia (HELIX syndrome), and to comprehensively delineate the phenotype.MethodsWe performed homozygosity mapping, whole-genome sequencing, gene sequencing, expression studies, functional tests, protein bioinformatics, and histological characterization in two unrelated families with HELIX syndrome.ResultsWe identified biallelic missense mutations (c.386C>T, p.S131L and c.2T>C, p.M1T) in CLDN10B in six patients from two unrelated families. CLDN10B encodes Claudin-10b, an integral tight junction (TJ) membrane-spanning protein expressed in the kidney, skin, and salivary glands. All patients had hypohidrosis, renal loss of NaCl with secondary hyperaldosteronism and hypokalemia, as well as hypolacrymia, ichthyosis, xerostomia, and severe enamel wear. Functional testing revealed that patients had a decreased NaCl absorption in the thick ascending limb of the loop of Henle and a severely decreased secretion of saliva. Both mutations resulted in reduced or absent Claudin-10 at the plasma membrane of epithelial cells.ConclusionCLDN10 mutations cause a dysfunction in TJs in several tissues and, subsequently, abnormalities in renal ion transport, ectodermal gland homeostasis, and epidermal integrity.

Current trends in salivary gland tight junctions

Tight junctions form a continuous intercellular barrier between epithelial cells that is required to separate tissue spaces and regulate selective movement of solutes across the epithelium. They are composed of strands containing integral membrane proteins (e.g., claudins, occludin and tricellulin, junctional adhesion molecules and the coxsackie adenovirus receptor). These proteins are anchored to the cytoskeleton via scaffolding proteins such as ZO-1 and ZO-2. In salivary glands, tight junctions are involved in polarized saliva secretion and barrier maintenance between the extracellular environment and the glandular lumen. This review seeks to provide an overview of what is currently known, as well as the major questions and future research directions, regarding tight junction expression, organization and function within salivary glands.

Characterization of the first-in-class T-cell-engaging bispecific single-chain antibody for targeted immunotherapy of solid tumors expressing the oncofetal protein claudin 6

The fetal tight junction molecule claudin 6 (CLDN6) is virtually absent from any normal tissue, whereas it is aberrantly and frequently expressed in various cancers of high medical need. We engineered 6PHU3, a T-cell-engaging bispecific single chain molecule (bi-(scFv)₂) with anti-CD3/anti-CLDN6 specificities, and characterized its pharmacodynamic properties. Our data show that upon engagement by 6PHU3, T cells strongly upregulate cytotoxicity and activation markers, proliferate and acquire an effector phenotype. 6PHU3 exerts potent killing of cancer cells in vitro with EC₅₀ values in the pg/mL range. Subcutaneous xenograft tumors in NSG mice engrafted with human PBMCs are eradicated by 6PHU3 treatment and survival of mice is significantly prolonged. Tumors of 6PHU3-treated mice are strongly infiltrated with activated CD4⁺, CD8⁺ T cells and T_EM type cells but not T_regs and display a general activation of a mostly inflammatory phenotype. These effects are only observed upon bispecific but not monospecific engagement of 6PHU3. Together with the exceptionally cancer cell selective expression of the oncofetal tumor marker CLDN6, this provides a safeguard with regard to toxicity. In summary, our data shows that the concept of T-cell redirection combined with that of highly selective targeting of CLDN6-positive solid tumors is effective. Thus, exploring 6PHU3 for clinical therapy is warranted.

ZO-1 and -2 Are Required for TRPV1-Modulated Paracellular Permeability

The tight junction–based paracellular pathway plays an important role in saliva secretion. Zonula occludens (ZO) proteins are submembranous proteins of tight junction complex; however, their function in salivary epithelium is poorly understood. Here, we found that activation of transient receptor potential vanilloid subtype 1 (TRPV1) by capsaicin increased rat saliva secretion both in vivo and ex vivo. Meanwhile, TRPV1 activation enlarged the width of tight junctions between neighboring acinar cells, increased the paracellular flux of 4-kDa fluorescein isothiocyanate (FITC)-dextran in submandibular gland (SMG) tissues, and decreased transepithelial electric resistance (TER) in SMG-C6 cells. ZO-1, -2, and -3 were distributed principally to the apical lateral region of acinar cells in SMG tissues and continuously encircled the peripheries of SMG-C6 cells in the untreated condition. TRPV1 activation obviously diminished ZO-1 and -2 staining, but not ZO-3 or β-catenin, at the cell-cell contacts ex vivo and in vitro. Moreover, in untreated SMG-C6 cells, ZO-1 and -2 single or double knockdown by small interfering RNA (siRNA) increased the paracellular flux of 4-kDa FITC-dextran. In capsaicin-treated cells, ZO-1 and -2 single or double knockdown abolished, whereas their re-expression restored, the capsaicin-induced increase in paracellular permeability. Furthermore, TRPV1 activation increased RhoA activity, and inhibition of either RhoA or Rho kinase (ROCK) abolished the capsaicin-induced TER decrease as well as ZO-1 and -2 redistribution. These results indicate that ZO-1 and -2 play crucial roles in both basal salivary epithelial barrier function and TRPV1-modulated paracellular transport. RhoA-ROCK signaling pathway is responsible for TRPV1-modulated paracellular permeability as well as ZO-1 and -2 redistribution.

Expression patterns of CD66a and CD117 in the mouse submandibular gland

The epithelial tissue of the salivary gland consists of the acinar and ductal parts, the latter of which is further divided into the intercalated, striated and excretory duct segments and is the residential site for salivary stem/progenitor cells. In the present study, the expression patterns of two cell surface molecules, CD66a and CD117, were investigated in the adult mouse submandibular glands (SMG) by immunofluorescence microscopy. Combinations of the two molecules differentially marked several types of SMG epithelial cells, including acinar cells (CD66a-intense, CD117-negative), intercalated duct cells (CD66a-intense, CD117-positive), a subset of the striated and excretory duct cells (CD66a-weak, CD117-positive). Most of the CD117-positive ductal cells were negative for cytokeratin 5 and overlapped with the NKCC1-expressing cells. The CD117- and keratin 5-positive cells resided only in the excretory duct were suggested to correspond to the recently identified salivary stem cells. CD66a and CD117 may be useful markers to isolate several cell types consisting of SMG epithelium and to analyze their molecular and cellular nature. Our data also suggest that CD117-expressing epithelial cells of the gland include at least two distinct populations of the stem/progenitor cells.

Growth Factor Independence-1 (Gfi1) Is Required for Pancreatic Acinar Unit Formation and Centroacinar Cell Differentiation

BACKGROUND & AIMS

The genetic specification of the compartmentalized pancreatic acinar/centroacinar unit is poorly understood. Growth factor independence-1 (Gfi1) is a zinc finger transcriptional repressor that regulates hematopoietic stem cell maintenance, pre-T-cell differentiation, formation of granulocytes, inner ear hair cells, and the development of secretory cell types in the intestine. As GFI1/Gfi1 is expressed in human and rodent pancreas, we characterized the potential function of Gfi1 in mouse pancreatic development.

METHODS

Gfi1 knockout mice were analyzed at histological and molecular levels, including qRT-PCR, in situ hybridization, immunohistochemistry, and electron microscopy.

RESULTS

Loss of Gfi1 impacted formation and structure of the pancreatic acinar/centroacinar unit. Histologic and ultrastructural analysis of Gfi1-null pancreas revealed specific defects at the level of pancreatic acinar cells as well as the centroacinar cells (CACs) in Gfi1^-/- mice when compared with wild-type littermates. Pancreatic endocrine differentiation, islet architecture, and function were unaffected. Organ domain patterning and the formation of ductal cells occurred normally during the murine secondary transition (E13.5-E14.5) in the Gfi1^-/- pancreas. However, at later gestational time points (E18.5), expression of cellular markers for CACs was substantially reduced in Gfi1^-/- mice, corroborated by electron microscopy imaging of the acinar/centroacinar unit. The reduction in CACs was correlated with an exocrine organ defect. Postnatally, Gfi1 deficiency resulted in severe pancreatic acinar dysplasia, including loss of granulation, autolytic vacuolation, and a proliferative and apoptotic response.

CONCLUSIONS

Gfi1 plays an important role in regulating the development of pancreatic CACs and the function of pancreatic acinar cells.

Matriptase deletion initiates a Sjögren's syndrome-like disease in mice

Objective

The objective of this study was to determine the effect of epithelial barrier disruption, caused by deficiency of the membrane-anchored serine protease, matriptase, on salivary gland function and the induction of autoimmunity in an animal model.

Methods

Embryonic and acute ablation of matriptase expression in the salivary glands of mice was induced, leading to decreased epithelial barrier function. Mice were characterized for secretory epithelial function and the induction of autoimmunity including salivary and lacrimal gland dysfunction, lymphocytic infiltration, serum anti-Ro/SSA, anti-La/SSB and antinuclear antibodies. Salivary glands immune activation/regulation, barrier function as well as tight junction proteins expression also were determined. Expression of matriptase in minor salivary gland biopsies was compared among pSS patients and healthy volunteers.

Results

Embryonic ablation of matriptase expression in mice resulted in the loss of secretory epithelial cell function and the induction of autoimmunity similar to that observed in primary Sjögren’s syndrome. Phenotypic changes included exocrine gland dysfunction, lymphocytic infiltrates, production of Sjögren’s syndrome-specific autoantibodies, and overall activation of the immune system. Acute ablation of matriptase expression resulted in significant salivary gland dysfunction in the absence of overt immune activation. Analysis of the salivary glands indicates a loss of electrical potential across the epithelial layer as well as altered distribution of a tight junction protein. Moreover, a significant decrease in matriptase gene expression was detected in the minor salivary glands of pSS patients compared with healthy volunteers.

Conclusions

Our findings demonstrate that local impairment of epithelial barrier function can lead to loss of exocrine gland dysfunction in the absence of inflammation while systemic deletion can induce a primary Sjögren’s syndrome like phenotype with autoimmunity and loss of gland function.

Claudin-6, -10d and -10e contribute to seawater acclimation in the euryhaline puffer fish Tetraodon nigroviridis

Expression profiles of claudin-6, -10d and -10e in the euryhaline teleost fish Tetraodon nigroviridis revealed claudin-6 in brain, eye, gill and skin tissue, while claudin-10d and -10e were found in brain, gill and skin only. In fishes, the gill and skin are important tissue barriers that interface directly with surrounding water, but these organs generally function differently in osmoregulation. Therefore, roles for gill and skin claudin-6, -10d and -10e in the osmoregulatory strategies of T. nigroviridis were investigated. In the gill epithelium, claudin-6, -10d and -10e co-localized with Na(+)-K(+)-ATPase immunoreactive (NKA-ir) ionocytes, and differences in sub-cellular localization could be observed in hypoosmotic (freshwater, FW) versus hyperosmotic (seawater, SW) environments. Claudin-10d and -10e abundance increased in the gills of fish acclimated to SW versus FW, while claudin-6 abundance decreased in the gills of fish acclimated to SW. Taken together with our knowledge of claudin-6 and -10 function in other vertebrates, data support the idea that in SW-acclimated T. nigroviridis, these claudins are abundant in gill ionocytes, where they contribute to the formation of a Na(+) shunt and 'leaky' epithelium, both of which are characteristic of salt-secreting SW fish gills. Skin claudin-10d and -10e abundance also increased in fish acclimated to SW versus those in FW, but so did claudin-6. In skin, claudin-6 was found to co-localize with NKA-ir cells, but claudin-10d and -10e did not. This study provides direct evidence that the gill epithelium contains salinity-responsive tight junction proteins that are abundant primarily in ionocytes. These same proteins also appear to play a role in the osmoregulatory physiology of the epidermis.

Estrogen decreases the expression of claudin-5 in vascular endothelial cells in the murine uterus

Vascular endothelial (VE)-cadherin and claudin-5 are major components of the adherens and tight junctions of vascular endothelial cells, respectively, and decreases in their expression are associated with increases in endothelial paracellular permeability. In the uterus, estrogen induces endometrial edema. However, the in vivo effect of estrogen on endothelial paracellular permeability is unknown. Therefore, we studied the expression of VE-cadherin and claudin-5 in vascular endothelial cells in murine uteri stimulated by estrogen or progesterone. Ovariectomized mature mice were injected with estradiol-17β (1 μg/mouse) or progesterone (1 mg/mouse) at intervals of 24 hours for 6 days. The frozen transverse sections of the uteri of these mice and untreated mice were stained for CD31 (vascular endothelial cell marker) plus VE-cadherin or claudin-5 using a double-immunofluorescence method. Then, the percentages of VE-cadherin- or claudin-5-positive vessels among CD31-positive vessels were examined in the uterine endometria. VE-cadherin and claudin-5 were expressed in most CD31-positive vessels in the endometria of the untreated mice. Progesterone did not affect the expression of both VE-cadherin and claudin-5 and estradiol-17β also did not affect the VE-cadherin expression, but estradiol-17β significantly decreased the claudin-5 expression. This decreasing effect of estradiol-17β was detected from 24 hours later when the water content per a uterus significantly increased. The present study indicates that estrogen, but not progesterone, decreases the expression of claudin-5 in vascular endothelial cells in the murine uterine endometrium from 24 hours later, suggesting that the decrease in the claudin-5 expression contributes to the endometrial edema late after the estrogen stimulation.

Progesterone and heparin-binding epidermal growth factor-like growth factor regulate the expression of tight junction protein Claudin-3 during early pregnancy

OBJECTIVE

To determine Claudin-3 expression and its regulatory factors during embryo implantation.

DESIGN

Experimental mouse models and cell culture.

SETTING

University research laboratory.

ANIMAL(S)

Sexually mature female CD-1 strain mice.

INTERVENTION(S)

Ovariectomy and treatments.

MAIN OUTCOME MEASURE(S)

In situ hybridization and immunohistochemistry for detecting Claudin-3 messenger RNA and protein expression in mouse uterus, respectively; Western blot for detecting protein levels; immunofluorescence for detecting Claudin-3 protein in cultured cells.

RESULT(S)

Claudin-3 is strongly expressed in the uterine luminal epithelium on days 3 and 4 of pregnancy, and diminished at day 5 implantation sites. Then it is expressed at secondary decidual zone on day 8. Pseudopregnant uteri have a similar expression pattern as pregnant uteri from days 1-5. Claudin-3 expression is down-regulated after delayed implantation is activated by estrogen (E) treatment. Meanwhile Claudin-3 expression is stimulated by artificial decidualization. In ovariectomized mice, P induces Claudin-3 expression in the luminal epithelium, which is abrogated by P receptor antagonist RU486. Heparin-binding-epidermal growth factor (HB-EGF) down-regulates Claudin-3 expression, but enhances transcription factor Snail expression. In human endometrial epithelial ECC-1 cells, both E and P could stimulate Claudin-3 expression, whereas HB-EGF decreases Claudin-3 and increases Snail expression.

CONCLUSION(S)

Claudin-3 expression in uterine luminal epithelium is stimulated by P and suppressed by HB-EGF in mice and humans.

Quantitative single cell analysis of cell population dynamics during submandibular salivary gland development and differentiation

Epithelial organ morphogenesis involves reciprocal interactions between epithelial and mesenchymal cell types to balance progenitor cell retention and expansion with cell differentiation for evolution of tissue architecture. Underlying submandibular salivary gland branching morphogenesis is the regulated proliferation and differentiation of perhaps several progenitor cell populations, which have not been characterized throughout development, and yet are critical for understanding organ development, regeneration, and disease. Here we applied a serial multiplexed fluorescent immunohistochemistry technology to map the progressive refinement of the epithelial and mesenchymal cell populations throughout development from embryonic day 14 through postnatal day 20. Using computational single cell analysis methods, we simultaneously mapped the evolving temporal and spatial location of epithelial cells expressing subsets of differentiation and progenitor markers throughout salivary gland development. We mapped epithelial cell differentiation markers, including aquaporin 5, PSP, SABPA, and mucin 10 (acinar cells); cytokeratin 7 (ductal cells); and smooth muscle α-actin (myoepithelial cells) and epithelial progenitor cell markers, cytokeratin 5 and c-kit. We used pairwise correlation and visual mapping of the cells in multiplexed images to quantify the number of single- and double-positive cells expressing these differentiation and progenitor markers at each developmental stage. We identified smooth muscle α-actin as a putative early myoepithelial progenitor marker that is expressed in cytokeratin 5-negative cells. Additionally, our results reveal dynamic expansion and redistributions of c-kit- and K5-positive progenitor cell populations throughout development and in postnatal glands. The data suggest that there are temporally and spatially discreet progenitor populations that contribute to salivary gland development and homeostasis.

Infliximab counteracts tumor necrosis factor-α-enhanced induction of matrix metalloproteinases that degrade claudin and occludin in non-pigmented ciliary epithelium

Infliximab, a monoclonal antibody directed against human tumor necrosis factor-alpha (TNF-α), effectively treats anterior uveitis, which can accompany Behçet's disease. Here, we investigated the underlying mechanism of this action. We examined human, non-pigmented ciliary epithelial cells (HNPCECs), which make up the blood-aqueous barrier (BAB) in the uvea. We measured the expression levels of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs in the presence or absence of TNF-α using quantitative, real-time polymerase chain reaction and enzyme-linked immunosorbent assays. The expression of MMP-1, MMP-3, and MMP-9 increased in the presence of TNF-α, and the addition of infliximab reversed the increase. The TNF-α effects were more attenuated when infliximab was added before than when it was added after TNF-α exposure. Gelatin zymography demonstrated that the protease activity of these MMPs was also increased in the presence of TNF-α and attenuated with infliximab. Immunostaining showed that MMP-1, MMP-3, and MMP-9 degraded claudin-1 and occludin in HNPCECs and in non-pigmented ciliary epithelial cells of the swine ciliary body. In a monolayer of HNPCECs, we found that permeability was significantly increased with MMP treatment. Thus, TNF-α increased levels of MMPs in cells that form the BAB, and MMPs degraded components of the tight junctions in the BAB, which increased permeability through the cellular barrier. Furthermore, infliximab effectively attenuated the TNF-α-induced increases in MMP expression in cells that make up the BAB. These findings might suggest a basis for the clinical prevention of anterior uveitis.

Claudins and the modulation of tight junction permeability

Claudins are tight junction membrane proteins that are expressed in epithelia and endothelia and form paracellular barriers and pores that determine tight junction permeability. This review summarizes our current knowledge of this large protein family and discusses recent advances in our understanding of their structure and physiological functions.

Roles of AQP5/AQP5-G103D in carbamylcholine-induced volume decrease and in reduction of the activation energy for water transport by rat parotid acinar cells

In order to assess the contribution of the water channel aquaporin-5 (AQP5) to water transport by salivary gland acinar cells, we measured the cell volume and activation energy (E (a)) of diffusive water permeability in isolated parotid acinar cells obtained from AQP5-G103D mutant and their wild-type rats. Immunohistochemistry showed that there was no change induced by carbamylcholine (CCh; 1 μM) in the AQP5 detected in the acinar cells in the wild-type rat. Acinar cells from mutant rats, producing low levels of AQP5 in the apical membrane, showed a minimal increase in the AQP5 due to the CCh. In the wild-type rat, CCh caused a transient swelling of the acinus, followed by a rapid agonist-induced cell shrinkage, reaching a plateau at 30 s. In the mutant rat, the acinus did not swell by CCh challenge, and the agonist-induced cell shrinkage was delayed by 8 s, reaching a transient minimum at around 1 min, and recovered spontaneously even though CCh was persistently present. In the unstimulated wild-type acinar cells, E (a) was 3.4 ± 0.6 kcal mol(-1) and showed no detectable change after CCh stimulation. In the unstimulated mutant acinar cells, high E (a) value (5.9 ± 0.1 kcal mol(-1)) was detected and showed a minimal decrease after CCh stimulation (5.0 ± 0.3 kcal mol(-1)). These results suggested that AQP5 was the main pathway for water transport in the acinar cells and that it was responsible for the rapid agonist-induced acinar cell shrinkage and also necessary to keep the acinar cell volume reduced during the steady secretion in the wild-type rat.

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.

Claudin-6 is a nonspecific marker for malignant rhabdoid and other pediatric tumors

Claudins are tight junction proteins with claudin-6 (CLDN6) expression mostly restricted to embryonic and fetal life. Previously reported gene expression microarray analysis showed an increased level of CLDN6 in atypical teratoid rhabdoid tumors (AT/RT) compared with other central nervous system (CNS) tumors and sarcomas. However, there exist conflicting data on expression of CLDN6 as assessed by immunohistochemistry in CNS tumors. We established membranous staining as a specific and reproducible method for evaluating CLDN6 expression based on fetal and adolescent controls. We then evaluated a large group (257) of pediatric tumors using tissue microarrays, including: 47 malignant rhabdoid tumors (MRTs), (31 AT/RTs and 16 non-CNS MRTs); 67 small, round, blue cell tumors (10 Wilms tumors, 10 embryonal rhabdomyosarcomas, 10 neuroblastomas (NBs), 10 synovial sarcomas (SSs), 9 hepatoblastomas (HBs), 9 alveolar rhabdomyosarcomas, and 9 Ewings sarcomas); and 143 CNS tumors (24 medulloblastomas, 21 pilocytic astrocytomas, 14 astrocytomas grade II/III, 13 gangliogliomas, 12 glioblastomas, 12 ependymal tumors, 11 choroid plexus tumors, 10 meningiomas, 8 dysembryoplastic neuroepithelial tumors, 8 oligodendrogliomas, 4 craniopharyngiomas, 2 germinomas, 2 primitive neuroectodermal tumors (PNET), and 2 central neurocytomas). CLDN6 expression was seen in 12 of 31 (39%) AT/RTs, 7 of 16 (44%) non-CNS MRTs, 5 of 10 (50%) Wilms tumors, 1 of 9 (11%) HBs, 2 of 2 (100%) germinomas, 1 of 2 (50%) CNS PNETs, 1 of 24 (4%) medulloblastomas, and 1 of 10 (10%) meningiomas. Ten of 11 (91%) choroid plexus tumors showed apical staining but no concentric membranous staining. Although CLDN6 is expressed in both AT/RTs and MRTs, it is not a specific biomarker as it is expressed in a variety of other pediatric CNS and soft tissue tumors.

Coordination of epithelial branching and salivary gland lumen formation by Wnt and FGF signals

Branching morphogenesis is a molecularly conserved mechanism that is adopted by several organs, such as the lung, kidney, mammary gland and salivary gland, to maximize the surface area of a tissue within a small volume. Branching occurs through repetitive clefting and elongation of spherical epithelial structures, called endbuds, which invade the surrounding mesenchyme. In the salivary gland, lumen formation takes place alongside branching morphogenesis, but in a controlled manner, so that branching is active at the distal ends of epithelial branches while lumen formation initiates at the proximal ends, and spreads distally. We present here data showing that interaction between FGF signaling and the canonical (β-catenin dependent) and non-canonical branches of Wnt signaling coordinates these two processes. Using the Axin2(lacZ) reporter mice, we find Wnt/β-catenin signaling activity first in the mesenchyme and later, at the time of lumen formation, in the ductal epithelium. Gain and loss of function experiments reveal that this pathway exerts an inhibitory effect on salivary gland branching morphogenesis. We have found that endbuds remain devoid of Wnt/β-catenin signaling activity, a hallmark of ductal structures, through FGF-mediated inhibition of this pathway. Our data also show that FGF signaling has a major role in the control of lumen formation by preventing premature hollowing of epithelial endbuds and slowing down the canalization of presumptive ducts. Concomitantly, FGF signaling strongly represses the ductal marker Cp2l1, most likely via repression of Wnt5b and non-canonical Wnt signaling. Inhibition of canonical and non-canonical Wnt signaling in endbuds by FGF signaling occurs at least in part through sFRP1, a secreted inhibitor of Wnt signaling and downstream target of FGF signaling. Altogether, these findings point to a key function of FGF signaling in the maintenance of an undifferentiated state in endbud cells by inhibition of a ductal fate.

Transcriptome-wide identification of preferentially expressed genes in the hypothalamus and pituitary gland

To identify preferentially expressed genes in the central endocrine organs of the hypothalamus and pituitary gland, we generated transcriptome-wide mRNA profiles of the hypothalamus, pituitary gland, and parietal cortex in male mice (12-15 weeks old) using serial analysis of gene expression (SAGE). Total counts of SAGE tags for the hypothalamus, pituitary gland, and parietal cortex were 165824, 126688, and 161045 tags, respectively. This represented 59244, 45151, and 55131 distinct tags, respectively. Comparison of these mRNA profiles revealed that 22 mRNA species, including three potential novel transcripts, were preferentially expressed in the hypothalamus. In addition to well-known hypothalamic transcripts, such as hypocretin, several genes involved in hormone function, intracellular transduction, metabolism, protein transport, steroidogenesis, extracellular matrix, and brain disease were identified as preferentially expressed hypothalamic transcripts. In the pituitary gland, 106 mRNA species, including 60 potential novel transcripts, were preferentially expressed. In addition to well-known pituitary genes, such as growth hormone and thyroid stimulating hormone beta, a number of genes classified to function in transport, amino acid metabolism, intracellular transduction, cell adhesion, disulfide bond formation, stress response, transcription, protein synthesis, and turnover, cell differentiation, the cell cycle, and in the cytoskeleton and extracellular matrix were also preferentially expressed. In conclusion, the current study identified not only well-known hypothalamic and pituitary transcripts but also a number of new candidates likely to be involved in endocrine homeostatic systems regulated by the hypothalamus and pituitary gland.

Analysis of changes in the expression pattern of claudins using salivary acinar cells in primary culture

Primary saliva is produced from blood plasma in the acini of salivary glands and is modified by ion adsorption and secretion as the saliva passes through the ducts. In rodents, acinar cells of salivary glands express claudin-3 but not claudin-4, whereas duct cells express both claudins-3 and -4. The distinct claudin expression patterns may reflect differences in the permeability of tight junctions between acinar and duct cells. To analyze the role of claudins in salivary glands, we established a system for the primary culture of parotid acinar cells, where the expression patterns of claudins are remarkably changed. Real-time RT-PCR and immunoblot analyses reveal that the expression levels of claudins-4 and -6 increased, whereas claudins-3 and -10 decreased. We found that the signal to induce those changes is triggered during cell isolation and is mediated by Src and p38 MAP kinase. Here, we introduce the methods used to determine the signal pathway that induces the change in claudin expression.

Claudins: unlocking the code to tight junction function during embryogenesis and in disease

Claudins are the structural and molecular building blocks of tight junctions. Individual cells express more than one claudin family member, which suggests that a combinatorial claudin code that imparts flexibility and dynamic regulation of tight junction function could exist. Although we have learned much from manipulating claudin expression and function in cell lines, loss-of-function and gain-of-function experiments in animal model systems are essential for understanding how claudin-based boundaries function in the context of a living embryo and/or tissue. These in vivo manipulations have pointed to roles for claudins in maintaining the epithelial integrity of cell layers, establishing micro-environments and contributing to the overall shape of an embryo or tissue. In addition, loss-of-function mutations in combination with the characterization of mutations in human disease have demonstrated the importance of claudins in regulating paracellular transport of solutes and water during normal physiological states. In this review, we will discuss specific examples of in vivo studies that illustrate the function of claudin family members during development and in disease.

Branching morphogenesis in the fetal mouse submandibular gland is codependent on growth factors and extracellular matrix

Branching morphogenesis (BrM) is a basic developmental process for the formation of the lung, kidney, and all exocrine glands, including the salivary glands. This process proceeds as follows. An epithelial downgrowth invaginates into underlying mesenchyme, and forms a cleft at its distal end, which is the site of dichotomous branching and elongation; this process of clefting and elongation is repeated many times at the distal ends of the invading epithelium until the desired final extent of branching is reached. The distal ends of the epithelium differentiate into the secretory endpieces, and the elongated segments become the ducts. This presentation is a brief historical review of studies on BrM during the development of the submandibular gland (SMG).

Tight junctions in salivary epithelium

Epithelial cell tight junctions (TJs) consist of a narrow belt-like structure in the apical region of the lateral plasma membrane that circumferentially binds each cell to its neighbor. TJs are found in tissues that are involved in polarized secretions, absorption functions, and maintaining barriers between blood and interstitial fluids. The morphology, permeability, and ion selectivity of TJ vary among different types of tissues and species. TJs are very dynamic structures that assemble, grow, reorganize, and disassemble during physiological or pathological events. Several studies have indicated the active role of TJ in intestinal, renal, and airway epithelial function; however, the functional significance of TJ in salivary gland epithelium is poorly understood. Interactions between different combinations of the TJ family (each with their own unique regulatory proteins) define tissue specificity and functions during physiopathological processes; however, these interaction patterns have not been studied in salivary glands. The purpose of this review is to analyze some of the current data regarding the regulatory components of the TJ that could potentially affect cellular functions of the salivary epithelium.

Claudin-10 exists in six alternatively spliced isoforms that exhibit distinct localization and function

The tight junction protein claudin-10 is known to exist in two isoforms, resulting from two alternative exons, 1a and 1b (Cldn10a, Cldn10b). Here, we identified and characterized another four claudin-10 splice variants in mouse and human. One (Cldn10a_v1) results from an alternative splice donor site, causing a deletion of the last 57 nucleotides of exon 1a. For each of these three variants one further splice variant was identified (Cldn10a_v2, Cldn10a_v3, Cldn10b_v1), lacking exon 4. When transfected into MDCK cells, Cldn10a, Cldn10a_v1 and Cldn10b were inserted into the tight junction, whereas isoforms of splice variants lacking exon 4 were retained in the endoplasmic reticulum. Cldn10a transfection into MDCK cells confirmed the previously described increase in paracellular anion permeability. Cldn10a_v1 transfection had no direct effect, but modulated Cldn10a-induced organic anion permeability. At variance with previous reports in MDCK-II cells, transfection of high-resistance MDCK-C7 cells with Cldn10b dramatically decreased transepithelial resistance, increased cation permeability, and changed monovalent cation selectivity from Eisenman sequence IV to X, indicating the presence of a high field-strength binding site that almost completely removes the hydration shell of the permeating cations. The extent of all these effects strongly depended on the endogenous claudins of the transfected cells.

Protective role of Lactobacillus plantarun in regulating intestinal epithelial cells response to pathogenic bacteria

AIM: To investigate the alteration of intestinal epithelial tight junction proteins after infection with enteroinvasive Escherichia coli and to study mechanism underlying protective effect of Lactobacillus plantarun on Caco-2 cells.

METHODS: Caco-2 models were established and divided into normal group, infection group, Lactobacillus treatment group and gentamicin treatment group. Ultrastructure of tight junction structure was observed using immuno-gold labeling. The distribution and structure of tight junction proteins, such as Claudin-1, Occludin, ZO-1, JAM-1 as well as F-actin were examined using immunofluorescence assay.

RESULTS: The tight junction structure was at the top of intestine epithelial cells. After infection with EIEC, the structure of tight junction was destroyed and the expression of F-actin and tight junction proteins (such as Claudin-1, Occludin, JAM-1, ZO-1) were diminished. But Lactobacillus plantarun prevented the damage induced by EIEC.

CONCLUSION: The Lactobacillus plantarun exerts a protective effect against the damage to the F-actin and distribution of TJ proteins promoted by enteroinvasive Escherichia coli infection.

Enhancement of barrier function by overexpression of claudin-4 in tight junctions of submandibular gland cells

In salivary glands, primary saliva is produced by acini and is modified by the reabsorption and secretion of ions in the ducts. Thus, the permeability of intercellular junctions in the ducts is considered to be lower than in the acini. We have examined the relationship between the expressed claudin isotypes and the barrier functions of tight junctions in a submandibular gland epithelial cell line, SMIE. SMIE cells were originally derived from rat submandibular duct cells, but their barrier functions are not as efficient as those of Madin-Darby canine kidney cells. Large molecules, such as 70-kDa dextran, diffuse across the monolayers, although E-cadherin and occludin, adherens junction and tight junction proteins, respectively, are expressed in SMIE cells. Claudin-3 protein has also been detected, but the expression level of claudin-3 mRNA is much lower than in the original submandibular glands. Other claudins including claudin-4 (originally expressed in the duct cells) have not been detected. Because of the limited expression of claudins, SMIE cells are suitable for studying the role(s) of claudins. To examine the function of claudin-4 in submandibular glands, we have overexpressed green fluorescence protein (GFP)-fused claudin-4 in SMIE cells. Cells that express GFP-fused claudin-4 have a higher transepithelial electrical resistance and a lower permeability of 70-kDa dextran, although the expression levels of occludin and claudin-3 are hardly affected. Therefore, claudin-4 plays a role in the regulation of the barrier function of tight junctions in submandibular glands.

Inhibition of Src and p38 MAP kinases suppresses the change of claudin expression induced on dedifferentiation of primary cultured parotid acinar cells

Sjögren's syndrome and therapeutic radiation for head and neck cancers result in irreversible changes in the parenchyma of salivary glands, loss of acinar cells, prominence of duct cells, and fibrosis. To clarify mechanisms of salivary gland dysfunction, we identified a signaling pathway involved in the dedifferentiation of primary cultures of parotid acinar cells. We reported previously that the expression pattern of claudins changes during culture, is related to the three-dimensional organization of the cells, and reflects their ability to function as acinar cells. In this study, we found that this change of claudin expression is a process of dedifferentiation, because expression of other differentiation markers also changes during culture. The expression levels of claudins-4 and -6, cytokeratin 14, and vimentin are increased, and those of claudin-10, aquaporin 5, and amylase are decreased. Inhibitors of Src and p38 MAP kinases suppress these changes and increase the expression of acinar marker proteins. Differences in extracellular matrix components have no effect. Activation of p38 MAP kinase occurs during cell isolation from the parotid glands and is retained up to 6 h after the isolation. In contrast, activation of Src kinases does not increase during the cell isolation. The Src inhibitor PP1 suppresses the activation of p38 MAP kinase. Therefore, cellular stresses induced during cell isolation cause dedifferentiation and transition to duct-like cells through activation of p38 MAP kinase and constitutively active Src kinases.

Human salivary gland branching morphogenesis: morphological localization of claudins and its parallel relation with developmental stages revealed by expression of cytoskeleton and secretion markers

Development of salivary glands is a highly complex and dynamic process termed branching morphogenesis, where branched structures differentiate into mature glands. Tight junctions (TJ) are thought to play critical roles in physiological functions of tubular organs, contributing to cell polarity and preventing lateral movement of membrane proteins. Evidence demonstrated that claudins are directly involved in TJ formation and function. Using immunohistochemistry and immunofluorescence we have mapped the distribution of claudins-1, 2, 3, 4, 5, 7 and 11 and compared it with the expression of differentiation markers in human salivary glands obtained from foetuses ranging from weeks 4 to 24 of gestation. Expression of all claudins, except claudin-2 was detected in the various phases of human salivary gland development, up to fully mature salivary gland. The expression of all claudins increased according to the progression of salivary gland maturation evidenced by the classical markers-cytokeratin 14, cytokeratin low molecular weight, smooth muscle actin and human secretory component. Tight junction proteins-claudins appear to be important in the final shape and physiological functions of human salivary glands and are parallel related with markers of salivary gland differentiation.

Expression of claudins in murine tooth development

Claudins belong to a family of transmembrane proteins that were identified as components of tight junction strands. We carried out comparative in situ hybridization analysis of 11 claudin genes (claudin1 - claudin11) during murine odontogenesis from the formation of the epithelial thickening to the cytodifferentiation stage. We identify dynamic spatiotemporal expression of 9 of the 11 claudins. At the early bell stage, two claudins (claudin1 and 4) are specifically expressed in stratum intemedium, whereas only one claudin is expressed in each of the preameloblasts (claudin2) and preodontoblasts (claudin10). At the bud stage, when the first epithelial differentiation pathways are being established, localized expression of six claudins (claudin1, 3, 4, 6, 7, and 10) identify spatial specific interactions, suggesting a hitherto unobserved complexity of epithelial organization, within the early tooth primordium.