Changes in the distribution of ZO-1, occludin, and claudins in the rat uterine epithelium during the estrous cycle

Tissue regression-related changes in connexin 43 and zonula occludens 1 gene and protein expression in the hen oviduct

A growing body of evidence has highlighted the involvement of intercellular junctions in the remodeling of various tissues in physiological and pathological conditions. In this study, the hypothesis was that the expression of connexin 43 (Cx43 protein/GJA1 gene) and zonula occludens 1 (ZO1), crucial molecules of gap junctions and tight junctions, respectively, changes in the regressing oviduct of non-laying hens. Accordingly, the mRNA transcript and protein abundance of Cx43 and ZO1 and their protein localization in the oviduct of hens subjected to a fasting-induced pause in egg laying were examined. All oviductal parts (the infundibulum, magnum, isthmus, shell gland, and vagina) were harvested on the sixth day of the experiment from the control (laying) hens and hens that had been fasted for five consecutive days (non-laying). qRT-PCR, western blotting, and immunofluorescence were applied to examine gene expression, protein abundance, and protein localization, respectively. Fasting caused a decrease in the oviduct weight, concomitantly with histological changes in the oviductal wall, including epithelial thinning, tubular gland degeneration, and disorganization of tissue architecture. Segment-specific expression patterns of Cx43 and ZO1 genes were observed, with the lowest mRNA transcript and protein abundance being noted in the magnum. In the fasted hens, GJA1 mRNA transcript abundance did not change in the oviductal parts compared to the control hens; however, an increase in ZO1 mRNA level was observed in the shell gland. Cx43 protein abundance was reduced in the infundibulum and shell gland, whereas ZO1 protein abundance was increased in the shell gland of the fasted birds. Reduced and irregular immunoreactivity of Cx43 and ZO1 proteins was observed in the oviduct of the non-laying hens. The results demonstrate that fasting-induced oviductal tissue regression was accompanied by alterations in the expression and localization of Cx43 and ZO1 proteins, indicating the potential role of these proteins in the control of cell-cell communication, paracellular permeability, and mucosal barrier formation in the hen oviduct.

Uterine Microbiota and Bisphenols: Novel Influencers in Reproductive Health

Infertility affects 8-12% of couples worldwide, and 30-75% of preclinical pregnancy losses are due to a failure during the implantation process. Exposure to endocrine disruptors, like bisphenols, among others, has been associated with the increase in infertility observed in the past decades. An increase in infertility has correlated with exposure to endocrine disruptors like bisphenols. The uterus harbors its own microbiota, and changes in this microbiota have been linked to several gynecological conditions, including reproductive failure. There are no studies on the effects of bisphenols on the uterine-microbiota composition, but some inferences can be gleaned by looking at the gut. Bisphenols can alter the gut microbiota, and the molecular mechanism by which gut microbiota regulates intestinal permeability involves Toll-like receptors (TLRs) and tight junction (TJ) proteins. TJs participate in embryo implantation in the uterus, but bisphenol exposure disrupts the expression and localization of TJ proteins. The aim of this review is to summarize the current knowledge on the microbiota of the female reproductive tract (FRT), its association with different reproductive diseases-particularly reproductive failure-the effects of bisphenols on microbiota composition and reproductive health, and the molecular mechanisms regulating uterine-microbiota interactions crucial for embryo implantation. This review also highlights existing knowledge gaps and outlines research needs for future risk assessments regarding the effects of bisphenols on reproduction.

Subacute Ruminal Acidosis as a Potential Factor that Induces Endometrium Injury in Sheep

The demand for economic benefits has led to an increase in the proportion of high-concentrate (HC) feed in the ruminant diet, resulting in an increased incidence of subacute ruminal acidosis (SARA). During SARA, a high concentration of lipopolysaccharide (LPS) translocated in the rumen induces a systemic inflammatory response. Inflammatory diseases, such as endometritis and mastitis, are often associated with SARA; however, in sheep, the mechanism of the effect of SARA on the endometrium has rarely been reported. Therefore, the aim of this study was to investigate, for the first time, the influence of LPS translocation on endometrial tight junctions (TJs) during SARA in sheep. The results showed that LPS and TNFα levels in the ruminal fluid, serum, and endometrial tissue supernatant during SARA increased, transcription levels of TLR4, NFκB, and TNFα in the endometrium increased, the protein expression level of claudin-1 in the endometrium increased, and the protein expression level of occludin decreased. 17β-estradiol (E₂) inhibits claudin-1 protein expression and promotes occludin expression, and progesterone (P₄) promotes claudin-1 protein expression and inhibits occludin protein expression. E₂ and P₄ regulate claudin-1 and occludin protein expression through their receptor pathways. Here, we found that LPS hindered the regulatory effect of E₂ and P₄ on endometrial TJs by inhibiting their receptor expression. The results of this study indicate that HC feeding can cause SARA-induced LPS translocation in sheep, increase susceptibility to systemic inflammation, induce the endometrial inflammatory response, and cause endometrial epithelial TJ damage directly and/or by obstructing E₂ and P₄ function. LPS translocation caused by SARA has also been suggested to induce an endometrial inflammatory response, resulting in endometrial epithelial barrier damage and physiological dysfunction, which seriously affects ruminant production. Therefore, this study provides new evidence that SARA is a potential factor that induces systemic inflammation in ruminants. It provides theoretical support for research on the prevention of endometritis in ruminants.

Clipping EpCAM to release Claudin-7 for the greater good of the epithelial barrier

Maintenance of epithelial barrier function requires dynamic repair and remodeling of tight junctions. In this issue, Higashi et al. (2022. J. Cell Biol.https://doi.org/10.1083/jcb.202204079) demonstrate that the proteolytic cleavage of EpCAM by membrane-anchored serine proteinases releases Claudin-7 to join tight junctions, suggesting a novel mechanism that couples sensing with repair of damaged tight junctions.

Impact of endometrial claudin-3 deletion on murine implantation, decidualization and embryo development

The composition of cell contacts in the endometrium plays an important role in the process of embryo implantation and the establishment of pregnancy. In previous studies, we showed an induction of the tight junction protein claudin-3 in the developing decidua from 6.5 dpc onwards. To evaluate the role if this specific claudin-3 distribution, we here evaluated the effect of an endometrial claudin-3 deletion in implantation and embryo development in claudin-3 knockout mice. Claudin-3 KO mice were fertile but revealed a slightly reduced amount of implantation sites as well as of litter size. Though implantation sites showed morphologically regularly developed embryos and deciduas, depth of ectoplacental cone invasion was reduced in tendency compared to controls. The weight of the implantation sites on 6.5 and 8.5 dpc as well as the weight of the embryos on 17.5 dpc, but not of the placentas, was significantly reduced in claudin-3 KO mice due to a maternal effect. This could be due to an impairment of decidualization as substantiated by a downregulation of the transcription of various decidua-associated genes in the early implantation sites of claudin-3 KO mice. The fact that claudin-3 KO mice are nevertheless fertile possibly may be compensated by the presence of other claudins like claudin-4 and claudin-10.

Protective Effect of the Abelmoschus manihot Flower Extract on DSS-Induced Ulcerative Colitis in Mice

Background

The flower of Abelmoschus manihot (AM) has been widely used in the treatment of chronic inflammatory diseases, including ulcerative colitis. This paper aimed to confirm the therapeutic effect of AM on ulcerative colitis (UC) and explore its mechanism.

Methods

Mouse models were induced by 2.5% dextran sulfate sodium (DSS) and treated with AM. UC signs, symptoms, colon macroscopic lesion scores, and disease activity index (DAI) scores were observed. Colon levels of interleukin- (IL-) 6, IL-1β, IL-18, IL-17, tumor necrosis factor- (TNF-) α, and IL-10 were quantified by ELISA. The colon protein expression levels of NLRP3, ASC, caspase 1 p10, β-arrestin1, ZO-1, occludin-1, and claudin-1 were examined by immunohistochemistry and western blotting. The mRNA levels of IL-1β, IL-18, NLRP3, ASC, and caspase 1 p10 in the colon were determined by real-time quantitative polymerase chain reaction (qPCR).

Results

After treatment with AM, the mortality of mice, pathological damage to the colon, splenomegaly, and the spleen coefficient were decreased. AM reduced the levels of proinflammatory cytokines (IL-6, IL-1β, IL-18, IL-17, and TNF-α) and increased the level of IL-10. The mRNA expression levels of NLRP3, ASC, and caspase 1 in colon tissue were decreased by AM in a dose-dependent manner. In addition, AM also reduced the protein expression of NLRP3, ASC, caspase 1 p10, IL-1β, IL-18, and β-arrestin1 in the colon tissue of model mice. Western blot analysis confirmed that AM increased the expression of occludin-1, claudin-1, and ZO-1 in a dose-dependent manner.

Conclusion

This study shows that AM has a significant therapeutic effect on mice with UC, and the mechanism may be related to the inhibition of the β-arrestin1/NLRP3 inflammasome signaling pathway and the protection of intestinal barrier function.

Changes in the expression and distribution of junction and polarity proteins in the porcine endometrium during early pregnancy period

The maternal endometrium undergoes transformations during early pregnancy period to regulate the paracellular permeability across the epithelium and to enable adhesion between the trophoblast and endometrial epithelial cells. These transformations, under the influence of ovarian hormones, are associated with a partial loss in polarity of epithelial cell that is regulated by tight junctions (TJ), adherens junctions (AJ) and associated polarity protein complexes. This study examined the change in expression and distribution of proteins associated with TJs, AJs and apical partition defective (PAR) complex in porcine endometrium on Days 10, 13 and 16 of estrous cycle and pregnancy. Moreover, effect of hormones, progesterone (P4) and 17-β estradiol (E2) on polar phenotype of endometrial epithelial cells was also investigated in vitro. There was pregnancy induced increase in gene and protein expression of TJ associated claudin-1 (CLDN1) on Day 13 of pregnancy as compared to corresponding day of estrous cycle and a decrease in TJ protein, zona occludens-1 (ZO-1) and PAR complex associated PAR6 expression levels on Day 16 of pregnancy (P < 0.05). Immunofluorescence studies revealed that on Days 10 and 13, TJ proteins occludin (OCLN) and ZO-1were primarily present in the apical region of lateral epithelial membrane. On Day 16 of pregnancy, whereas, OCLN redistributed into cytoplasm, ZO-1 decreased apically but was found to localize in the basal epithelium. The AJ proteins cadherin and β-catenin were located at the apical epithelium on Day 10 of estrous cycle and pregnancy and Day 13 of estrous cycle. On Days 13 and 16 of pregnancy both proteins were expressed in the lateral membrane and co-localization between these proteins was observed on Day 16. On Day 10, PAR complex proteins PAR3, cell division control protein 42 (CDC42) and atypical protein kinase C (aPKC) ζ were observed in apical epithelium and in lateral membrane and CDC42 was also present in the cytoplasm of epithelium. Pregnancy induced redistribution of aPKCζ to cytoplasm and CDC42 to apical surface of luminal epithelium was observed on Days 13 and 16. The in vitro P4 and E2 treatment of epithelial cells mimicked in vivo results. These results indicate that P4 and E2 regulate alterations in epithelium that may facilitate embryo implantation and given the role of cadherin, catenin and CDC42 in embryo invasion, change in distribution of these proteins may limit the invasiveness of porcine conceptuses into the stroma.

Abundances and localizations of Claudin-1 and Claudin-5 in the domestic cat (Felis catus) ovary during the estrous cycle

Claudins (CLDNs) are major Ca²⁺-independent cell adhesion molecules functioning at tight junctions (TJ). The presence and localization of cell adhesion molecules are important for understanding the mechanisms associated with follicular and luteal development in the ovary. In this study, there was an examination of whether CLDN-1 and CLDN-5 are present in a cell- and stage-specific manner during follicular and luteal development in the domestic cat ovary using immunohistochemistry and Western blot analysis. While results from immunoblot analyses revealed there were relatively similar abundances of CLDN-5 protein in three phases of the ovarian cycle, the abundance of CLDN-1 in the luteal phase was greater than those measured in the follicular and anestrous phases (P < 0.01). Results with immunohistochemistry indicate CLDN-1 and -5 are mainly localized in the cell nuclei and cytoplasm of all tissues of the cat ovary. In follicles, throughout the development from primordial to large antral follicles, CLDN-1 and -5 were present in oocytes, and the granulosa and theca cell layers. In follicles at all stages of atresia, there were cell-type and stage-specific protein distributions with immunostaining present in granulosa, thecal interstitial, and fibroblast-like cells. In corpora lutea, both small and large luteal cells stained positively for both claudins. In conclusion, the specific presence and localization patterns of CLDN-1 and -5 in the cat ovary is suggestive that these TJ proteins could have local functions in the regulation of most ovarian functions such as follicle development and atresia, ovulation, and corpus luteum formation and regression.

Parental perinatal exposure to bisphenol A reduces the threshold to disrupt blastocyst implantation via decreasing talin, occudin and E-cadherin levels

The aim was to evaluate the effect of perinatal BPA exposure of one or both parents on the implantation index and expression of talin, occludin and E-cadherin in the uterine epithelial cells (UEC) of the offspring. Pregnant Wistar dams (F0) received BPA or vehicle from gestational day (GD) 6 to lactation day 21. F1 animals were mated forming four groups: Control dam-Control sire (C♀-C♂), BPA dam -Control sire (B♀-C♂), Control dam -BPA sire (C♀-B♂), BPA dam -BPA sire (B♀-B♂). F1 dams were sacrificed at GD 6. Significantly decreased number of implantation sites was observed in the B♀-B♂ group as compared to the C♀-C♂ group, which correlated with decreased talin apical/basal expression ratio, occludin apical expression, and E-cadherin apical/lateral expression ratio in the UEC. Furthermore, decreased E-cadherin expression in the blastocyst was observed. Our data suggest that reduced protein expressions in F1 BPA offspring could result from decreased progesterone serum levels.

Direct Cell⁻Cell Interactions in the Endometrium and in Endometrial Pathophysiology

Cell contacts exhibit a considerable influence on tissue physiology and homeostasis by controlling paracellular and intercellular transport processes, as well as by affecting signaling pathways. Since they maintain cell polarity, they play an important role in cell plasticity. The knowledge about the junctional protein families and their interactions has increased considerably during recent years. In contrast to most other tissues, the endometrium undergoes extensive physiological changes and reveals an extraordinary plasticity due to its crucial role in the establishment and maintenance of pregnancy. These complex changes are accompanied by changes in direct cell–cell contacts to meet the various requirements in the respective developmental stage. Impairment of this sophisticated differentiation process may lead to failure of implantation and embryo development and may be involved in the pathogenesis of endometrial diseases. In this article, we focus on the knowledge about the distribution and regulation of the different junctional proteins in the endometrium during cycling and pregnancy, as well as in pathologic conditions such as endometriosis and cancer. Decoding these sophisticated interactions should improve our understanding of endometrial physiology as well as of the mechanisms involved in pathological conditions.

Severe Intestinal Inflammation in the Small Intestine of Mice Induced by Controllable Deletion of Claudin-7

BACKGROUND

As a potential tumor suppressor gene, Claudin-7 (Cldn7), which is a component of tight junctions, may play an important role in colorectal cancer occurrence and development.

AIMS

To generate a knockout mouse model of inducible conditional Cldn7 in the intestine and analyze the phenotype of the mice after induction with tamoxifen.

METHODS

We constructed Cldn7-flox transgenic mice and crossed them with Villin-CreERT2 mice. The Cldn7 inducible conditional knockout mice appeared normal and were well developed at birth. We induced Cldn7 gene deletion by injecting different dosages of tamoxifen into the mice and then conducted a further phenotypic analysis.

RESULTS

After induction for 5 days in succession at a dose of 200 µl tamoxifen in sunflower oil at 10 mg/ml per mouse every time, the mice appeared dehydrated, had a lower temperature, and displayed inactivity or death. The results of hematoxylin-eosin staining showed that the intestines of the Cldn7 inducible conditional knockout mice had severe intestinal defects that included epithelial cell sloughing, necrosis, inflammation and hyperplasia. Owing to the death of ICKO mice, we adjusted the dose of tamoxifen to a dose of 100 µl in sunflower oil at 10 mg/ml per mouse (aged more than 8 weeks old) every 4 days. And we could induce atypical hyperplasia and adenoma in the intestine. Immunofluorescent staining indicated that the intestinal epithelial structure was destroyed. Electron microscopy experimental analysis indicated that the intercellular gap along the basolateral membrane of Cldn7 inducible conditional knockout mice in the intestine was increased and that contact between the cells and matrix was loosened.

CONCLUSIONS

We generated a model of intestinal Cldn7 inducible conditional knockout mice. Intestinal Cldn7 deletion induced by tamoxifen initiated inflammation and hyperplasia in mice.

Perinatal administration of bisphenol A alters the expression of tight junction proteins in the uterus and reduces the implantation rate

We studied the effect of bisphenol-A (BPA) administration to rats, during the perinatal period, on the fertility of F1 generation and on the expression of tight junction (TJ) proteins in the uterus during early pregnancy. Pregnant Wistar dams (F0) received: BPA-L (0.05mg/kg/day), BPA-H (20mg/kg/day) or vehicle, from gestational day (GD) 6 to lactation day 21. F1 female pups were mated at 3 months of age and sacrificed at GD 1, 3, 6, and 7. Serum hormonal levels, ovulation rate, number of implantation sites and expression of TJ proteins in the uterus of F1 females were evaluated. BPA treatment induced no change in ovulation rate, but induced alterations in progesterone (P₄) and estradiol (E₂) serum levels, and in implantation rate. With regards to TJ proteins, BPA-H increased claudin-1 during all GDs; eliminated the peaks of claudins -3 and -4 at GD 3 and 6, respectively; and decreased claudin-7 at GD 6, ZO-1 from GD 1-6, and claudin-3 at GD 7 in stromal cells. BPA-L instead, eliminated claudin-3 peak at GD 3, increased claudin-4 and decreased claudin-7 from GD 1-6, decreased claudin-1 at GD 3 and 7 and claudin-4 at GD 7 in stromal cells. BPA-L also decreased ZO-1 at GDs 1 and 3 and increased ZO-1 at GD 6. Thus, BPA treatment during perinatal period perturbed, when the animals reached adulthood and became pregnant, the particular expression of TJ proteins in the uterine epithelium and reduced in consequence the number of implantation sites.

Loss of CD73-mediated actin polymerization promotes endometrial tumor progression

Ecto-5'-nucleotidase (CD73) is central to the generation of extracellular adenosine. Previous studies have highlighted a detrimental role for extracellular adenosine in cancer, as it dampens T cell-mediated immune responses. Here, we determined that, in contrast to other cancers, CD73 is markedly downregulated in poorly differentiated and advanced-stage endometrial carcinoma compared with levels in normal endometrium and low-grade tumors. In murine models, CD73 deficiency led to a loss of endometrial epithelial barrier function, and pharmacological CD73 inhibition increased in vitro migration and invasion of endometrial carcinoma cells. Given that CD73-generated adenosine is central to regulating tissue protection and physiology in normal tissues, we hypothesized that CD73-generated adenosine in endometrial carcinoma induces an innate reflex to protect epithelial integrity. CD73 associated with cell-cell contacts, filopodia, and membrane zippers, indicative of involvement in cell-cell adhesion and actin polymerization-dependent processes. We determined that CD73-generated adenosine induces cortical actin polymerization via adenosine A1 receptor (A1R) induction of a Rho GTPase CDC42-dependent conformational change of the actin-related proteins 2 and 3 (ARP2/3) actin polymerization complex member N-WASP. Cortical F-actin elevation increased membrane E-cadherin, β-catenin, and Na(+)K(+) ATPase. Together, these findings reveal that CD73-generated adenosine promotes epithelial integrity and suggest why loss of CD73 in endometrial cancer allows for tumor progression. Moreover, our data indicate that the role of CD73 in cancer is more complex than previously described.

Claudin-3, claudin-7, and claudin-10 show different distribution patterns during decidualization and trophoblast invasion in mouse and human

Implantation of the mammalian embryo requires profound endometrial changes for successful pregnancy, including epithelial-mesenchymal transition of the luminal epithelium and stromal-epithelial transition of the stromal cells resulting in decidualization. Claudins (Cldn) determine the variability in tight junction paracellular permeability and may play a role during these epithelial and decidual changes. We here localized Cldn3, Cldn7 and Cldn10 proteins in the different compartments of murine endometrium up to day 8.5 of pregnancy (dpc) as well as in human endometrium and first trimester decidua. In murine estrous endometrium, luminal and glandular epithelium exhibited Cldn3 and Cldn7, whereas Cldn10 was only detectable in glandular epithelium. At 4.5 dpc, Cldn3 protein shifted to an apical localization, whereas Cldn7 vanished in the epithelium of the implantation chamber. At this stage, there was no stromal signal for Cldn3 and Cldn7, but a strong induction of Cldn10 in the primary decidual zone. Cldn3 proteins emerged at 5.5 dpc spreading considerably from 6.5 dpc onward in the endothelial cells of the decidual blood sinusoids and in the decidual cells of the compact antimesometrial region. In addition to Cldn3, Cldn10 was identified in human endometrial epithelia. Both proteins were not detected in human first trimester decidual cells. Cldn3 was shown in murine trophoblast giant cells as well as in human extravillous trophoblast cells and thus may have an impact on trophoblast invasion in both species. We here showed a specific claudin signature during early decidualization pointing to a role in decidual angiogenesis and regulation of trophoblast invasion.

A non-tight junction function of claudin-7-Interaction with integrin signaling in suppressing lung cancer cell proliferation and detachment

BACKGROUND

Claudins are a family of tight junction (TJ) membrane proteins involved in a broad spectrum of human diseases including cancer. Claudin-7 is a unique TJ membrane protein in that it has a strong basolateral membrane distribution in epithelial cells and in tissues. Therefore, this study aims to investigate the functional significance of this non-TJ localization of claudin-7 in human lung cancer cells.

METHODS

Claudin-7 expression was suppressed or deleted by lentivirus shRNA or by targeted-gene deletion. Cell cycle analysis and antibody blocking methods were employed to assay cell proliferation and cell attachment, respectively. Electron microscopy and transepthelial electrical resistance measurement were performed to examine the TJ ultrastructure and barrier function. Co-immunolocalization and co-immunoprecipitation was used to study claudin-7 interaction with integrin β1. Tumor growth in vivo were analyzed using athymic nude mice.

RESULTS

Claudin-7 co-localizes and forms a stable complex with integrin β1. Both suppressing claudin-7 expression by lentivirus shRNA in human lung cancer cells (KD cells) and deletion of claudin-7 in mouse lungs lead to the reduction in integrin β1 and phospho-FAK levels. Suppressing claudin-7 expression increases cell growth and cell cycle progression. More significantly, claudin-7 KD cells have severe defects in cell-matrix interactions and adhere poorly to culture plates with a remarkably reduced integrin β1 expression. When cultured on uncoated glass coverslips, claudin-7 KD cells grow on top of each other and form spheroids while the control cells adhere well and grow as a monolayer. Reintroducing claudin-7 reduces cell proliferation, upregulates integrin β1 expression and increases cell-matrix adhesion. Integrin β1 transfection partially rescues the cell attachment defect. When inoculated into nude mice, claudin-7 KD cells produced significantly larger tumors than control cells.

CONCLUSION

In this study, we identified a previously unrecognized function of claudin-7 in regulating cell proliferation and maintaining epithelial cell attachment through engaging integrin β1.

Regulation of paracellular permeability: factors and mechanisms

Epithelial permeability is composed of transcellular permeability and paracellular permeability. Paracellular permeability is controlled by tight junctions (TJs). Claudins and occludin are two major transmembrane proteins in TJs, which directly determine the paracellular permeability to different ions or large molecules. Intracellular signaling pathways including Rho/Rho-associated protein kinase, protein kinase Cs, and mitogen-activated protein kinase, modulate the TJ proteins to affect paracellular permeability in response for diverse stimuli. Cytokines, growth factors and hormones in organism can regulate the paracellular permeability via signaling pathway. The transcellular transporters such as Na-K-ATPase, Na(+)-coupled transporters and chloride channels, can interact with paracellular transport and regulate the TJs. In this review, we summarized the factors affecting paracellular permeability and new progressions of the related mechanism in recent studies, and pointed out further research areas.

Immune aspects of embryo-maternal cross-talk in the bovine uterus

This mini-review summarizes the results of recent transcriptome studies of bovine endometrium during the estrous cycle and during the pre-implantation phase, with a focus on immune response genes. Gene expression changes in the bovine endometrium during the estrous cycle were compared to a similar study in equine endometrium. The results indicate species-specific expression patterns, particularly for genes with immune functions. These are presumably the consequence of adaptations to differences in the physiology of reproduction in each species, including development of the conceptus, hormone profiles during the estrous cycle, and insemination. The results from a number of transcriptome studies during the pre-implantation phase, as well as comparison to the effects of human interferon alpha on bovine endometrial gene expression, suggest that during pregnancy there is no general suppression of the maternal immune system, but rather a fine-tuned regulation of immune cells. This presumably facilitates tolerance to the immunologically 'foreign' conceptus and at the same time activation of the immune system to defend against microbial and viral infections. Furthermore, comparison of differentially expressed genes in bovine endometrium to similar studies in human endometrial samples reveals a number of similar changes, indicating the existence of shared mechanisms in preparation for embryo implantation.

Papillomavirus E6 oncoprotein up-regulates occludin and ZO-2 expression in ovariectomized mice epidermis

We have studied the expression of the tight junction proteins (TJ) occludin, claudin-1 and ZO-2 in the epidermis of female mice. We observed a peak of expression of these proteins at postnatal day 7 and a decrease in 6 week-old mice to values similar to those found in newborn animals. We explored if the expression of the E6 oncoprotein from high-risk human papilloma virus type 16 (HPV16) in the skin of transgenic female mice (K14E6), altered TJ protein expression in a manner sensitive to ovarian hormones. We observed that in ovariectomized mice E6 up-regulates the expression of occludin and ZO-2 in the epidermis and that this effect was canceled by 17β-estradiol. Progesterone instead induced occludin and ZO-2 over-expression. However, the decreased expression of occludin and ZO-2 induced by 17β-estradiol in the epidermis was not overturned by E6 or progesterone. In addition, we employed MDCK cells transfected with E6, and observed that ZO-2 delocalizes from TJs and accumulates in the cell nuclei due to a decrease in the turnover rate of the protein. These results reinforce the view of 17β-estradiol and E6 as risk factors for the development of cancer through effects on expression and mislocalization of TJ proteins.

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.

Inflammation and disruption of the mucosal architecture in claudin-7-deficient mice

BACKGROUND & AIMS

Integrity of the intestinal epithelium is required for nutrition absorption and defense against pathogens. Claudins are cell adhesion molecules that localize at tight junctions (TJs); many are expressed in the intestinal tract, but little is known about their functions. Claudin-7 is unique in that it has a stronger basolateral membrane distribution than other claudins, which localize primarily to apical TJs in the intestinal epithelium. We investigated the basolateral functions of claudin-7 and assessed the effects of disruption of Cldn7 in intestines of mice.

METHODS

We generated Cldn7(-/-) mice and examined their intestines by histology, molecular and cellular biology, and biochemistry approaches. We performed gene silencing experiments in epithelial cell lines using small interfering RNAs (siRNAs).

RESULTS

The Cldn7(-/-) mice had severe intestinal defects that included mucosal ulcerations, epithelial cell sloughing, and inflammation. Intestines of Cldn7(-/-) mice produced significantly higher levels of cytokines, the nuclear factor κB p65 subunit, and cyclooxygenase 2; they also up-regulated expression of matrix metalloproteinases (MMPs)-3 and -7. siRNA in epithelial cell lines showed that the increased expression of MMP-3 resulted directly from claudin-7 depletion, whereas that of MMP-7 resulted from inflammation. Electron microscopy analysis showed that intestines of Cldn7(-/-) mice had intercellular gaps below TJs and cell matrix loosening. Deletion of Cldn7 reduced expression and altered localization of the integrin α2 subunit in addition to disrupting formation of complexes of claudin-7, integrin α2, and claudin-1 that normally form in epithelial basolateral compartments of intestines.

CONCLUSIONS

In mice, claudin-7 has non-TJ functions, including maintenance of epithelial cell-matrix interactions and intestinal homeostasis.

Identification of claudins by western blot and immunofluorescence in different cell lines and tissues

Claudins are integral proteins of the TJ. Each epithelia in the organism expresses a unique set of claudins that determines the degree of sealing of the paracellular pathway and the ionic selectivity of the tissue. TJs are dynamic structures whose organization and composition change in response to alterations in the environment as well as under physiological and pathological conditions. Changes in claudin expression and subcellular distribution can be analyzed in western blot and immunofluorescence experiments, employing a wide array of available specific antibodies against claudins. In this chapter, we describe in detail protocols used for western blot and immunofluorescence detection of claudins in epithelial cell lines and in various tissue samples.

Ovarian hormones control the changing expression of claudins and occludin in rat uterine epithelial cells during early pregnancy

Regulation of the uterine luminal environment is important for successful attachment and implantation of the blastocyst. The contents and volume of luminal fluid are regulated in part by the tight junctions. Using immunofluorescence microscopy, protein and RNA analysis, the cellular distributions of tight junction components claudins and occludin were observed during early pregnancy and under various hormonal regimens. Results indicate that occludin and claudin-4 distribution changed during early pregnancy and in response to ovarian hormones. At the time of implantation and in response to progesterone administration to ovariectomised rats, occludin and claudin-4 showed increased immunolabelling in luminal epithelium. Interestingly, occludin protein detection in uterine luminal epithelial cells at the time of implantation was statistically significantly decreased at the time of implantation compared to day 1 of pregnancy. This suggests that a cytoplasmic pool of occludin is present at day 1 of pregnancy and is redistributed to the tight junctions at the time of implantation. The presence of occludin and claudin-4 in the tight junctions at the time of implantation and in response to progesterone suggests that the paracellular pathway is impermeable to water and Na(+) at this time, and that the transport of such substances takes place via the transcellular pathway.

Differential expression of claudins in human endometrium and endometriosis

Membrane proteins of the claudin superfamily are important components of cellular tight and adherens junctions. Although their exact function remains unclear, these proteins may play a role in tissue remodeling, a process which is associated with several diseases including endometriosis. In the present work we analyzed the expression of 13 members of the claudin family in the endometrium and peritoneum by microarray analysis. Real-time polymerase chain reaction and immunohistochemistry in human endometrium and peritoneal endometriotic lesions were performed for validation of the expression of claudin-1, -3, -4, -5 and -7. Diminished expression of claudin-3, -4 and -7 in ectopic endometrium was frequently observed as indicated by all three methods. In contrast to a higher expression of claudin-5 mRNA detected in bulk biopsies of ectopic endometrium, immunohistochemistry revealed no alteration of claudin-5 protein expression in glandular cells of endometriosis samples. The downregulation of various members of the claudin family may contribute to endometrial cell detachment and increase the number of cells invading pelvic organs.

Localization of claudin-5 and ZO-1 in rat spleen sinus endothelial cells

Splenic sinus endothelial cells, which adhere through tight and adherens junctions, regulate the passage of blood cells through the splenic cord. The objective of this study was to assess the localization of tight junctional proteins, claudin-5 and ZO-1 in the sinus endothelial cells of rat spleen and to characterize spatial and functional relationships between tight and adherens junctions. Immunofluorescence microscopy of tissue cryosections demonstrated that claudin-5, ZO-1, and alpha-catenin were distinctly localized in the junctional regions of adjacent endothelial cells. Immunogold electron microscopy demonstrated claudin-5 localized in the tight-junctional fused membranes of adjacent endothelial cells. Immunogold labeling for ZO-1 was localized not only in the tight-junctional-fused membranes of endothelial cells but also in the junctional membrane. alpha-Catenin was intermittently localized along the juxtaposed junctional membranes of adjacent endothelial cells. Double-staining immunogold microscopy for claudin-5 and ZO-1, claudin-5 and VE-cadherin, ZO-1 and VE-cadherin, and ZO-1 and alpha-catenin demonstrated that ZO-1 was closely localized to VE-cadherin and alpha-catenin in their juxtaposed membranes of endothelial cells. Thus, ZO-1 might play an important role in regulating the cell-cell junctions of sinus endothelial cells for blood-cell passage through splenic cords.

Dynamic changes in the cervical epithelial tight junction complex and differentiation occur during cervical ripening and parturition

Cervical epithelia have numerous functions that include proliferation, differentiation, maintenance of fluid balance, protection from environmental hazards, and paracellular transport of solutes via tight junctions (TJs). Epithelial functions must be tightly regulated during pregnancy and parturition as the cervix undergoes extensive growth and remodeling. This study evaluated TJ proteins, as well as markers of epithelial cell differentiation in normal and cervical ripening defective mice to gain insights into how the permeability barrier is regulated during pregnancy and parturition. Although numerous TJ proteins are expressed in the nonpregnant cervix, claudins 1 and 2 are temporally regulated in pregnancy. Claudin 1 mRNA expression is increased, whereas claudin 2 expression declines. The cellular localization of claudin 1 shifts at the end of pregnancy (gestation d 18.75) to the plasma membrane in a lattice pattern, consistent with TJs in the apical cells. The timing of claudin 1-enriched TJs coincides with initiation of terminal differentiation of cervical squamous epithelia as evidenced by the increased expression of genes by differentiated epithelia late on gestation d 18. The cervical ripening defective steroid 5alpha-reductase type 1 deficient mouse, which has an elevated local progesterone concentration, also has aberrant claudin 1 and 2 expressions, fails to form claudin 1-enriched TJs, and lacks normal expression of genes involved in epithelial terminal differentiation. These data suggest that changes in permeability barrier properties during cervical ripening are, in part, negatively regulated by progesterone, and that dynamic changes in barrier properties of the cervix occur during pregnancy and parturition.

The tight junction proteins claudin-7 and -8 display a different subcellular localization at Henle's loops and collecting ducts of rabbit kidney

BACKGROUND

The tight junction (TJ) regulates the passage of ions and molecules through the paracellular pathway. In multicellular organisms, epithelial sheets function as a barrier between a variety of environments and the internal media. Therefore, TJs are required to control the passage of diverse molecules in different epithelia. The mammalian nephron constitutes a particularly relevant model of this diversity, since the paracellular transport in this organ is significantly different along the various tubular segments. Here, we have analysed the distribution of claudins-7 and -8 in Henle's loops and collecting ducts isolated from rabbit kidneys.

METHODS

Renal segments were manually isolated from newborn and adult rabbit kidneys and processed for immunofluorescence. The distribution of claudins-7 and -8 was studied by confocal microscopy.

RESULTS

The localization of claudins-7 and -8 along Henle's loops and collecting ducts is remarkably different. While claudin-8 displays a clear cell border distribution in Henle's segment, claudin-7 shows a non-specific cytosolic staining. Moreover, in the collecting ducts, claudin-8 localizes at the TJ region, while claudin-7 shows a basolateral staining. This pattern is present from the newborn stage. The distribution of claudins along the mammalian kidney has been found to vary in different mammalian species. Accordingly, in the rabbit, we have found the expression of claudin-8 at the descending and ascending thin limbs of Henle, a distribution that differs from that found in the mouse by others.

CONCLUSION

In the rabbit Henle's loop, claudin-8 is present at the cellular borders of the descending and ascending thin limbs, while claudin-7 displays no specific labelling. Instead, at the collecting duct, both claudins are present but exhibit a different subcellular distribution.

Endothelia of term human placentae display diminished expression of tight junction proteins during preeclampsia

This study explores the molecular composition of the tight junction (TJ) in human term placenta from normal women and from patients with preeclampsia, a hypertensive disorder of pregnancy. Maternal endothelial dysfunction is a critical characteristic of preeclampsia; hence, we have analyzed its impact on placental vessels. The study concentrates on the TJ because this structure regulates the sealing of the paracellular route. We have found that, in placental endothelial vessels, TJ components include the peripheral protein ZO-1 and the integral proteins occludin and claudins 1, 3, and 5. During preeclampsia, the amounts of occludin and ZO-1 exhibit no significant variation, whereas those of claudins 1, 3, and 5 diminish, suggesting the presence of leakier TJs in the endothelia of the preeclamptic placenta, possibly in response to the decreased perfusion of this organ during preeclampsia. We have unexpectedly found that, in normal placentae, the multinucleated syncytiotrophoblast layer displays claudin 4 at the basal surface of the plasma membrane, and claudin 16 along the apical and basolateral surfaces. The presence of membrane-lined channels that cross the syncytiotrophoblast constituting a paracellular pathway has been determined by transmission electron microscopy and by the co-immunolocalization of claudin 16 with the plasma membrane proteins Na+K+-ATPase and GP135. Since claudin 16 functions as a paracellular channel for Mg2+, its diffuse pattern in preeclamptic placentae suggests the altered paracellular transport of Mg2+ between the maternal blood and the placental tissue.