MiR-181a Negatively Regulates Claudin-3 to Facilitate Lateolabrax maculatus Iridovirus Replication in Lateolabrax maculatus Astroglia Cells.

Lateolabrax maculatus iridovirus (LMIV) is a variant strain of red sea bream iridovirus (RSIV), causing serious economic losses in aquaculture. Claudins (CLDNs) are major components of tight junctions (TJs) forming an important line of defense against pathogens. Our pilot miRNA-mRNA joint analysis indicated the degradation of CLDN3, as well as its interaction with miR-181a during LMIV infection. To elucidate the miR-181a/CLDN3/LMIV interactions, in vitro assays were carried out on LMB-L cells. We first confirmed that LMIV infection could decrease the expression of CLDN3, accompanied by the enhancement of permeability, suggesting the dysfunction of TJs. Contrary to the inhibition of CLDN3, the activation of miR-181a was proved, presenting a negative correlation between miR-181a and CLDN3 (Pearson r = -0.773 and p < 0.01). In addition, the influence of CLDN3 on LMIV replication was analyzed by knockdown and over-expression of CLDN3. When CLDN3 was silenced in LMB-L cells with siCLDN3-623 at 9 days post transfection (dpt), LMIV copies and titers were significantly up-regulated by 1.59-fold and 13.87-fold, respectively. By contrast, LMIV replication in LMB-L cells was reduced by 60% and 71%, post transfection with pcDNA3.1-CLDN3 over-expressed plasmid at 6 dpt and 9 dpt, respectively. Ultimately, the regulatory relationship between miR-181a and CLDN3 was further validated by dual luciferase reporter assays. Taking into account the above-described results, we proposed a "miR-181a/CLDN3/LMIV" regulatory relationship. This study provides a new insight for understanding the mechanism of LMIV replication.

Claudin and transmembrane receptor protein gene expressions are reversely correlated in peritumoral brain edema.

INTRODUCTION: Peritumoral brain edema (PTBE) has been widely reported with many brain tumors, especially with glioma. Since the blood-brain barrier (BBB) is essential for maintaining minimal permeability, any alteration in the interaction of BBB components, specifically in astrocytes and tight junctions (TJ), can result in disrupting the homeostasis of the BBB and making it severely leaky, which subsequently generates edema. OBJECTIVE: This study aimed to evaluate the functional gliovascular unit of the BBB by examining changes in the expression of claudin (CLDN) genes and the expression of transient receptor potential (TRP) membrane channels, additionally to define the correlation between their expressions. The evaluation was conducted using in vitro spheroid swelling models and tumor samples from glioma patients with PTBE. RESULTS: The results of the spheroid model showed that the genes TRPC3, TRPC4, TRPC5, and TRPV1 were upregulated in glioma cells either wild-type isocitrate dehydrogenase 1 (IDH1) or the IDH1 R132H mutant, with or without NaCl treatment. Furthermore, TRP genes appeared to adversely correlate with the up regulation of CLDN1, CLDN3, and CLDN5 genes. Besides, the upregulation of TRPC1 and TRPC4 in IDH1mt-R132H glioma cells. On the other hand, the correlation analysis revealed different correlations between different proteins in PTBE. CLDN1 exhibits a slight positive correlation with CLDN3. Similarly, TRPV1 displays a slight positive correlation with TRPC1. In contrast, TRPC4 shows a slight negative correlation with TRPC5. On the other hand, TRPC3 demonstrates a slight positive correlation with TRPC5, while the non-PTBE analysis highlights a moderate positive correlation between CLDN1 and TRPM4 while CLDN3 exhibits a moderate negative correlation with TRPC4. Additionally, CLDN5 demonstrates a slight negative correlation with TRPC4 but a moderate positive correlation with TRPC3. Furthermore, TRPC1 have a slight negative correlation with TRPV1, TRPC3 exhibiting a slight positive correlation with TRPC4, and TRPV1 showing a slight negative correlation with TRPC5. CONCLUSION: As a conclusion, the current study provided evidence of a slight negative correlation between TRPs and CLDN gene expression in PTBE patients and confirmatory results with some of the genes in cell model of edema.

Absence of claudin-3 does not alter intestinal absorption of phosphate in mice.

Intestinal absorption of phosphate is bimodal, consisting of a transcellular pathway and a poorly characterized paracellular mode, even though the latter one contributes to the bulk of absorption under normal dietary conditions. Claudin-3 (Cldn3), a tight junction protein present along the whole intestine in mice, has been proposed to tighten the paracellular pathway for phosphate. The aim of this work was to characterize the phosphate-related phenotype of Cldn3-deficient mice. Cldn3-deficient mice and wildtype littermates were fed standard diet or challenged for 3 days with high dietary phosphate. Feces, urine, blood, intestinal segments and kidneys were collected. Measurements included fecal, urinary, and plasma concentrations of phosphate and calcium, plasma levels of phosphate-regulating hormones, evaluation of trans- and paracellular phosphate transport across jejunum and ileum, and analysis of intestinal phosphate and calcium permeabilities. Fecal and urinary excretion of phosphate as well as its plasma concentration was similar in both genotypes, under standard and high-phosphate diet. However, Cldn3-deficient mice challenged with high dietary phosphate had a reduced urinary calcium excretion and increased plasma levels of calcitriol. Intact FGF23 concentration was also similar in both groups, regardless of the dietary conditions. We found no differences either in intestinal phosphate transport (trans- or paracellular) and phosphate and calcium permeabilities between genotypes. The intestinal expression of claudin-7 remained unaltered in Cldn3-deficient mice. Our data do not provide evidence for a decisive role of Cldn3 for intestinal phosphate absorption and phosphate homeostasis. In addition, our data suggest a novel role of Cldn3 in regulating calcitriol levels.

Improved Preservation of Rat Small Intestine Transplantation Graft by Introduction of Mesenchymal Stem Cell-Secreted Fractions.

Segmental grafts from living donors have advantages over grafts from deceased donors when used for small intestine transplantation. However, storage time for small intestine grafts can be extremely short and optimal graft preservation conditions for short-term storage remain undetermined. Secreted factors from mesenchymal stem cells (MSCs) that allow direct activation of preserved small intestine grafts. Freshly excised Luc-Tg LEW rat tissues were incubated in preservation solutions containing MSC-conditioned medium (MSC-CM). Preserved Luc-Tg rat-derived grafts were then transplanted to wild-type recipients, after which survival, injury score, and tight junction protein expression were examined. Luminance for each graft was determined using in vivo imaging. The findings indicated that 30-100 and 3-10 kDa fractions of MSC-CM have superior activating effects for small intestine preservation. Expression of the tight-junction proteins claudin-3, and zonula occludens-1 preserved for 24 h in University of Wisconsin (UW) solution containing MSC-CM with 50-100 kDa, as shown by immunostaining, also indicated effectiveness. Reflecting the improved graft preservation, MSC-CM preloading of grafts increased survival rate from 0% to 87%. This is the first report of successful transplantation of small intestine grafts preserved for more than 24 h using a rodent model to evaluate graft preservation conditions that mimic clinical conditions.

Intestinal Ketogenesis and Permeability.

Consumption of a high-fat diet (HFD) has been suggested as a contributing factor behind increased intestinal permeability in obesity, leading to increased plasma levels of microbial endotoxins and, thereby, increased systemic inflammation. We and others have shown that HFD can induce jejunal expression of the ketogenic rate-limiting enzyme mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCS). HMGCS is activated via the free fatty acid binding nuclear receptor PPAR-α, and it is a key enzyme in ketone body synthesis that was earlier believed to be expressed exclusively in the liver. The function of intestinal ketogenesis is unknown but has been described in suckling rats and mice pups, possibly in order to allow large molecules, such as immunoglobulins, to pass over the intestinal barrier. Therefore, we hypothesized that ketone bodies could regulate intestinal barrier function, e.g., via regulation of tight junction proteins. The primary aim was to compare the effects of HFD that can induce intestinal ketogenesis to an equicaloric carbohydrate diet on inflammatory responses, nutrition sensing, and intestinal permeability in human jejunal mucosa. Fifteen healthy volunteers receiving a 2-week HFD diet compared to a high-carbohydrate diet were compared. Blood samples and mixed meal tests were performed at the end of each dietary period to examine inflammation markers and postprandial endotoxemia. Jejunal biopsies were assessed for protein expression using Western blotting, immunohistochemistry, and morphometric characteristics of tight junctions by electron microscopy. Functional analyses of permeability and ketogenesis were performed in Caco-2 cells, mice, and human enteroids. Ussing chambers were used to analyze permeability. CRP and ALP values were within normal ranges and postprandial endotoxemia levels were low and did not differ between the two diets. The PPARα receptor was ketone body-dependently reduced after HFD. None of the tight junction proteins studied, nor the basal electrical parameters, were different between the two diets. However, the ketone body inhibitor hymeglusin increased resistance in mucosal biopsies. In addition, the tight junction protein claudin-3 was increased by ketone inhibition in human enteroids. The ketone body ß-Hydroxybutyrate (ßHB) did not, however, change the mucosal transition of the large-size molecular FD4-probe or LPS in Caco-2 and mouse experiments. We found that PPARα expression was inhibited by the ketone body ßHB. As PPARα regulates HMGCS expression, the ketone bodies thus exert negative feedback signaling on their own production. Furthermore, ketone bodies were involved in the regulation of permeability on intestinal mucosal cells in vitro and ex vivo. We were not, however, able to reproduce these effects on intestinal permeability in vivo in humans when comparing two weeks of high-fat with high-carbohydrate diet in healthy volunteers. Further, neither the expression of inflammation markers nor the aggregate tight junction proteins were changed. Thus, it seems that not only HFD but also other factors are needed to permit increased intestinal permeability in vivo. This indicates that the healthy gut can adapt to extremes of macro-nutrients and increased levels of intestinally produced ketone bodies, at least during a shorter dietary challenge.

Transcriptional Levels of Intercellular Junction Proteins in an Alveolar Epithelial Cell Line Exposed to Irradiation or Bleomycin.

We performed a comparative study of the effects of X-ray irradiation and bleomycin on the mRNA levels of E-cadherin and tight junction proteins (claudin-3, claudin-4, claudin-18, ZO-2, and occludin) in an alveolar epithelial cell line L2. Irradiation decreased claudin-4 levels and increased occludin levels, while the levels of other mRNAs remained unchanged. Bleomycin increased the expression levels of all proteins examined except claudin-3. Irradiation and bleomycin have different effects on the expression level of intercellular junction proteins, indicating different reactions triggered in alveolar epithelial cells and a great prospects of further comparative studies.

Effect and mechanism of Prunella vulgaris L. extract on alleviating lipopolysaccharide-induced acute mastitis in protecting the blood-milk barrier and reducing inflammation.

ETHNOPHARMACOLOGICAL RELEVANCE: According to ancient literature, Prunella vulgaris L. (P vulgaris) alleviates mastitis and has been used in China for many years; however, there are no relevant reports that confirm this or the mechanism of its efficacy. AIM OF THE STUDY: To explore the anti-acute mastitis effect and potential mechanism of P vulgaris extract. MATERIALS AND METHODS: First, the active ingredients and targets of P vulgaris against mastitis were predicted using network pharmacology. Next, the relevant active ingredients were enriched using macroporous resins and verified using UV and UPLC-Q-TOF-MS/MS. Lastly, a mouse model of acute mastitis was established by injecting lipopolysaccharides into the mammary gland and administering P vulgaris extract by oral gavage. The pathological changes in mammary tissue were observed by HE staining. Serum and tissue inflammatory factors were measured by ELISA method. MPO activity in mammary tissue was measured using colorimetry and MPO expression was detected by immunohistochemistry. The expression of tight junction proteins (ZO-1, claudin-3, and occludin) in mammary tissue was detected by immunofluorescence and Western blot. iNOS and COX-2 in mammary tissue were detected by Western blot. MAPK pathway and NF-κB pathway related proteins were also detected by Western blot. RESULTS: Network pharmacology predicted that phenolic acids and flavonoids in P vulgaris had anti-mastitis effects. The contents of total flavonoids and total phenolic acids in P vulgaris extract were 64.5% and 29.4%, respectively. UPLC-Q-TOF-MS/MS confirmed that P vulgaris extract contained phenolic acids and flavonoids. The results of animal experiments showed that P vulgaris extract reduced lipopolysaccharide-induced inflammatory edema, inflammatory cell infiltration, and interstitial congestion of mammary tissue. It also reduced the levels of serum and tissue inflammatory factors TNF-α, IL-6, and IL-1ß, and inhibited the activation of MPO. Furthermore, it downregulated the expression of MAPK and NF-κB pathway-related proteins. The expressions of ZO-1, occludin, and claudin-3 in mammary gland tissues were upregulated. CONCLUSIONS: P vulgaris extract can maintain the integrity of mammary connective tissue and reduce its inflammatory response to prevent acute mastitis. Its mechanism probably involves regulating NF-κB and MAPK pathways.

Computational Models of Claudin Assembly in Tight Junctions and Strand Properties.

Claudins are one of the major components of tight junctions (TJs) that polymerize within the cell membrane and form interactions between cells. Some claudins seal the paracellular space, limiting paracellular flux, while others form selectively permeable ion channels that control the paracellular permeability of small ions. Claudin strands are known to be dynamic and reshape within TJs to accommodate large-scale movements and rearrangements of epithelial tissues. Here, we summarize the recent computational and modeling studies on claudin assembly into tetrameric ion channels and their polymerization into µm long strands within the membrane. Computational studies ranging from all-atom molecular dynamics, coarse-grained simulations, and hybrid-resolution simulations elucidate the molecular nature of claudin assembly and function and provide a framework that describes the lateral flexibility of claudin strands.

Canonical and Non-Canonical Localization of Tight Junction Proteins during Early Murine Cranial Development.

This study investigates the intricate composition and spatial distribution of tight junction complex proteins during early mouse neurulation. The analyses focused on the cranial neural tube, which gives rise to all head structures. Neurulation brings about significant changes in the neuronal and non-neuronal ectoderm at a cellular and tissue level. During this process, precise coordination of both epithelial integrity and epithelial dynamics is essential for accurate tissue morphogenesis. Tight junctions are pivotal for epithelial integrity, yet their complex composition in this context remains poorly understood. Our examination of various tight junction proteins in the forebrain region of mouse embryos revealed distinct patterns in the neuronal and non-neuronal ectoderm, as well as mesoderm-derived mesenchymal cells. While claudin-4 exhibited exclusive expression in the non-neuronal ectoderm, we demonstrated a neuronal ectoderm specific localization for claudin-12 in the developing cranial neural tube. Claudin-5 was uniquely present in mesenchymal cells. Regarding the subcellular localization, canonical tight junction localization in the apical junctions was predominant for most tight junction complex proteins. ZO-1 (zona occludens protein-1), claudin-1, claudin-4, claudin-12, and occludin were detected at the apical junction. However, claudin-1 and occludin also appeared in basolateral domains. Intriguingly, claudin-3 displayed a non-canonical localization, overlapping with a nuclear lamina marker. These findings highlight the diverse tissue and subcellular distribution of tight junction proteins and emphasize the need for their precise regulation during the dynamic processes of forebrain development. The study can thereby contribute to a better understanding of the role of tight junction complex proteins in forebrain development.

Effect of Infliximab on Radiation-Induced Submandibular Gland Dysfunction in Rats.

Inflammatory response is one of the essential parts of various pathogenic mechanisms of radiation-induced salivary dysfunction. The effect of decreasing the levels of inflammatory cytokines on alleviating submandibular gland injuries after irradiation is unclear. This study aimed to explore the effect of the antibody against tumor necrosis factor-alpha, infliximab, on radiation-induced submandibular gland dysfunction in rats. Male Wistar rats received a single 20 Gy dose to the right submandibular gland region or sham irradiated. Meanwhile, the irradiated group was divided into infliximab treatment groups or untreated groups. Animals were euthanized at 1, 6, and 12 weeks postirradiation, and the irradiated submandibular gland was dissected for subsequent detection. Submandibular gland exposure caused obvious pathological changes. The increased levels of inflammatory cytokines, including tumor necrosis factor-alpha, interleukin-1ß, and interleukin-6, represent an aggravated inflammatory response. The results of the western blot, reverse transcription-quantitative polymerase chain reaction, and immunofluorescence staining showed upregulated levels of claudin-1, claudin-3, and aquaporin 5 and downregulated levels of claudin-4. Moreover, nuclear factor kappa-B phosphorylation levels were also up-regulated. In subsequent experiments, we found that infliximab alleviated inflammatory response, up-regulated tumor necrosis factor-alpha, interleukin-1ß, and interleukin-6 levels, and improved claudin-1, claudin-3, claudin-4, and aquaporin 5 expression. Our results indicate that infliximab might improve the para-cellular pathway and trans-cellular pathway destruction by reducing the inflammatory.

Epithelial Tight Junction Anomalies in Nasal Inverted Papilloma.

OBJECTIVES: As a critical component of the epithelial barrier, tight junctions (TJs) are essential in nasal mucosa against pathogen invasion. However, the function of TJs has rarely been reported in nasal inverted papilloma (NIP). This study aims to investigate the potential factors of TJs' abnormality in NIP. METHODS: We assessed the expression of ZO-1, occludin, claudin-1, claudin-3, and claudin-7 in healthy controls and NIP by real-time quantitative polymerase chain reaction and immunofluorescent staining. The correlation between TJs expression and neutrophil count, TH 1/TH 2/TH 17 and regulatory T cell biomarkers, and the proportion of nasal epithelial cells was investigated. RESULTS: Upregulation of ZO-1, occludin, claudin-1, and claudin-7, along with downregulation of claudin-3, was found in NIP compared to control (all p < 0.05). An abnormal proportion with a lower number of ciliated cells (control vs. NIP: 37.60 vs. 8.67) and goblet cells (12.52 vs. 0.33) together with a higher number of basal cells (45.58 vs. 124.00) in NIP. Meanwhile, claudin-3 was positively correlated with ciliated and goblet cells (all p < 0.01). Additionally, neutrophils were excessively infiltrated in NIP, negatively correlated with ZO-1, but positively with claudin-3 (all p < 0.05). Furthermore, FOXP3, IL-10, TGF-ß1, IL-5, IL-13, and IL-22 levels were induced in NIP (all p < 0.01). Occludin level was negatively correlated with IL-10, IL-5, IL-13, and IL-22, whereas ZO-1 was positively with TGF-ß1 (all p < 0.05). CONCLUSION: Nasal epithelial barrier dysfunction with TJs anomalies is commonly associated with abnormal proliferation and differentiation of epithelial cells and imbalance of immune and inflammatory patterns in NIP. LEVEL OF EVIDENCE: NA Laryngoscope, 134:552-561, 2024.

Claudin-3 in the non-neural ectoderm is essential for neural fold fusion in chicken embryos.

The neural tube, the embryonic precursor to the brain and spinal cord, begins as a flat sheet of epithelial cells, divided into non-neural and neural ectoderm. Proper neural tube closure requires that the edges of the neural ectoderm, the neural folds, to elevate upwards and fuse along the dorsal midline of the embryo. We have previously shown that members of the claudin protein family are required for the early phases of chick neural tube closure. Claudins are transmembrane proteins, localized in apical tight junctions within epithelial cells where they are essential for regulation of paracellular permeability, strongly involved in apical-basal polarity, cell-cell adhesion, and bridging the tight junction to cytoplasmic proteins. Here we explored the role of Claudin-3 (Cldn3), which is specifically expressed in the non-neural ectoderm. We discovered that depletion of Cldn3 causes folic acid-insensitive primarily spinal neural tube defects due to a failure in neural fold fusion. Apical cell surface morphology of Cldn3-depleted non-neural ectodermal cells exhibited increased membrane blebbing and smaller apical surfaces. Although apical-basal polarity was retained, we observed altered Par3 and Pals1 protein localization patterns within the apical domain of the non-neural ectodermal cells in Cldn3-depleted embryos. Furthermore, F-actin signal was reduced at apical junctions. Our data presents a model of spina bifida, and the role that Cldn3 is playing in regulating essential apical cell processes in the non-neural ectoderm required for neural fold fusion.

Increase in Paracellular Leakage of Amino Acids Mediated by Aging-Induced Reduction of Claudin-4 Expression.

BACKGROUND: Claudins (CLDNs), major components of tight junctions, control paracellular permeabilities of mineral ions and wastes. The absorption of nutrients including glucose and amino acids (AAs) is regulated by intestinal epithelial cells. However, the role of CLDNs is not fully understood. OBJECTIVES: The purpose of this study was to clarify the effect of AA deprivation on the expression of AA transporters and CLDNs, as well as the role of CLDNs in the regulation of paracellular AA fluxes. METHODS: The messenger RNA and protein expression of various CLDNs were examined by real-time quantitative polymerase chain reaction and Western blot analyses, respectively. The AA selectivity of CLDNs was estimated using liquid chromatography-tandem mass spectrometry (LC-MS) analysis. RESULTS: The expression levels of some AA transporters, CLDN4, and CLDN15 were increased by AA deprivation in normal mouse colon-derived MCE301 cells. The expression of AA transporters and CLDN15 in the mouse colon was positively correlated with aging but the expression of CLDN4 was not. The AA deprivation-induced elevation of CLDN4 expression was inhibited by MHY1485, a mammalian target of rapamycin (mTOR) activator. Furthermore, CLDN4 expression was increased by rapamycin, an mTOR inhibitor. mTOR may be involved in the transcriptional activation of CLDN4. The fluxes of AAs from the basal to apical compartments were decreased and increased by CLDN4 overexpression and silencing, respectively. LC-MS analysis showed that the fluxes of all AAs, especially Lys, His, and Arg, were enhanced by CLDN4 silencing. CONCLUSIONS: CLDN4 is suggested to form a paracellular barrier to AAs, especially alkaline AAs, which is attenuated with aging.

Claudin-3 facilitates the progression and mediates the tumorigenic effects of TGF-ß in glioblastoma multiforme.

Glioblastoma multiforme (GBM) is a significantly malignant and lethal brain tumor with an average survival time of less than 12 months. Several researches had shown that Claudin-3 (CLDN3) is overexpressed in various cancers and might be important in their growth and spread. In this study, we used qRT-PCR, western blotting, immunohistochemistry, and immunofluorescence staining assays to investigate the expression levels of various proteins. To explore the proliferation abilities of GBM cells, we conducted the CCK-8 and EdU-DNA formation assays. Wound healing and transwell assays were used to investigate the capacities of invasion and migration of GBM cells. Additionally, we constructed an intracranial xenograft model of GBM to study the in vivo role of CLDN3. Our study devoted to investigate the function of CLDN3 in the pathogenesis and progression of GBM. Our study revealed that CLDN3 was upregulated in GBM and could stimulate tumor cell growth and epithelial-mesenchymal transition (EMT) in both laboratory and animal models. We also discovered that CLDN3 expression could be triggered by transforming growth factor-ß (TGF-ß) and reduced by specific inhibitors of the TGF-ß signaling pathway, such as ITD-1. Further analysis revealed that increased CLDN3 levels enhanced TGF-ß-induced growth and EMT in GBM cells, while reducing CLDN3 levels weakened these effects. Our study demonstrated the function of CLDN3 in facilitating GBM growth and metastasis and indicated its involvement in the tumorigenic effects of TGF-ß. Developing specific inhibitors of CLDN3 might, therefore, represent a promising new approach for treating this devastating disease.

X-ray radiation-induced intestinal barrier dysfunction in human epithelial Caco-2 cell monolayers.

Radiation therapy and unwanted radiological or nuclear exposure, such as nuclear plant accidents, terrorist attacks, and military conflicts, pose serious health issues to humans. Dysfunction of the intestinal epithelial barrier and the leakage of luminal antigens and bacteria across the barrier have been linked to various human diseases. Intestinal permeability is regulated by intercellular structures, termed tight junctions (TJs), which are disrupted after radiation exposure. In this study, we investigated radiation-induced alterations in TJ-related proteins in an intestinal epithelial cell model. Caco-2 cells were irradiated with 2, 5, and 10 Gy and harvested 1 and 24 h after X-ray exposure. The trypan blue assay revealed that cell viability was reduced in a dose-dependent manner 24 h after X-ray exposure compared to that of non-irradiated cells. However, the WST-8 assay revealed that cell proliferation was significantly reduced only 24 h after radiation exposure to 10 Gy compared to that of non-irradiated cells. In addition, a decreased growth rate and increased doubling time were observed in cells irradiated with X-rays. Intestinal permeability was significantly increased, and transepithelial electrical resistance values were remarkably reduced in Caco-2 cell monolayers irradiated with X-rays compared to non-irradiated cells. X-ray irradiation significantly decreased the mRNA and protein levels of ZO-1, occludin, claudin-3, and claudin-4, with ZO-1 and claudin-3 protein levels decreasing in a dose-dependent manner. Overall, the present study reveals that exposure to X-ray induces dysfunction of the human epithelial intestinal barrier and integrity via the downregulation of TJ-related genes, which may be a key factor contributing to intestinal barrier damage and increased intestinal permeability.

Picroside III, an Active Ingredient of Picrorhiza scrophulariiflora, Ameliorates Experimental Colitis by Protecting Intestinal Barrier Integrity.

This study aims to explore the protective effects of Picroside III, an active ingredient of Picrorhiza scrophulariiflora, on the intestinal epithelial barrier in tumor necrosis factor-α (TNF-α) induced Caco-2 cells and dextran sulfate sodium (DSS) induced colitis in mice. Results show that Picroside III significantly alleviated clinical signs of colitis including body weight loss, disease activity index increase, colon shortening, and colon tissue damage. It also increased claudin-3, ZO-1 and occludin expressions and decreased claudin-2 expression in the colon tissues of mice with colitis. In vitro, Picroside III also significantly promoted wound healing, decreased the permeability of cell monolayer, upregulated the expressions of claudin-3, ZO-1 and occludin and downregulated the expression of claudin-2 in TNF-α treated Caco-2 cells. Mechanism studies show that Picroside III significantly promoted AMP-activated protein kinase (AMPK) phosphorylation in vitro and in vivo, and blockade with AMPK could significantly attenuate the upregulation of Picroside III in ZO-1 and occludin expressions and the downregulation of claudin-2 expression in TNF-α treated Caco-2 cells. In conclusion, this study demonstrates that Picroside III attenuated DSS-induced colitis by promoting colonic mucosal wound healing and epithelial barrier function recovery via the activation of AMPK.

Double mutation of claudin-1 and claudin-3 causes alopecia in infant mice.

Hair follicles (HFs) undergo cyclic phases of growth, regression, and rest in association with hair shafts to maintain the hair coat. Nonsense mutations in the tight junction protein claudin (CLDN)-1 cause hair loss in humans. Therefore, we evaluated the roles of CLDNs in hair retention. Among the 27 CLDN family members, CLDN1, CLDN3, CLDN4, CLDN6, and CLDN7 were expressed in the inner bulge layer, isthmus, and sebaceous gland of murine HFs. Hair phenotypes were observed in Cldn1 weaker knockdown and Cldn3-knockout (Cldn1Δ/Δ Cldn3-/- ) mice. Although hair growth was normal, Cldn1Δ/Δ Cldn3-/- mice showed striking hair loss in the first telogen. Simultaneous deficiencies in CLDN1 and CLDN3 caused abnormalities in telogen HFs, such as an aberrantly layered architecture of epithelial cell sheets in bulges with multiple cell layers, mislocalization of bulges adjacent to sebaceous glands, and dilated hair canals. Along with the telogen HF abnormalities, which shortened the hair retention period, there was an enhanced proliferation of the epithelium surrounding HFs in Cldn1Δ/Δ Cldn3-/- mice, causing accelerated hair regrowth in adults. Our findings suggested that CLDN1 and CLDN3 may regulate hair retention in infant mice by maintaining the appropriate layered architecture of HFs, a deficiency of which can lead to alopecia.

PPARγ activation inhibits endocytosis of claudin-4 and protects against deoxynivalenol-induced intestinal barrier dysfunction in IPEC-J2 cells and weaned piglets.

The role of peroxisome proliferator activated receptor gamma (PPARγ) in the regulation of adipocyte differentiation has been well characterized. Besides adipose tissue, PPARγ is also highly expressed in the intestine. However, the functional role of PPARγ in the regulation of intestinal function still remains poorly understood. In the present study, we sought to understand the role of PPARγ activation on regulation of intestinal barrier function in intestinal porcine epithelial cells (IPEC-J2) and weaned piglets exposed to the mycotoxin, deoxynivalenol (DON). PPARγ activation by rosiglitazone and troglitazone, two pharmacological PPARγ ligands, increased the protein expression of tight junction proteins (TJP), claudin-3 and 4. PPARγ inhibition increased endocytosis of claudin-4 which was reversed by its activation with troglitazone. DON exposure decreased the protein expression of TJP, and also significantly suppressed PPARγ transcriptional activity. Interestingly, PPARγ activation reversed the reduction of claudin-3 and 4 caused by DON in vitro and in vivo. PPARγ activation also partially restored the transepithelial electrical resistance (TEER) and reduced the permeability of fluorescein isothiocyanate-dextran (FITC-dextran) that have been negatively impacted by DON. These effects were lost in the presence of a specific PPARγ antagonist or in PPARγ knockout cells, confirming the importance of PPARγ in the regulation of intestinal barrier function and integrity. Likewise, in weaned pigs exposed to DON, the PPARγ agonist pioglitazone mitigated the impaired villus-crypt morphology caused by DON. Therefore, pharmacological and natural bioactive compounds with PPARγ stimulatory activities could be effective in preventing DON-induced gut barrier dysfunction.

Construction of a Lactobacillus plantarum-based claudin-3 targeting delivery system for the development of vaccines against Eimeria tenella.

Avian coccidiosis causes huge economic losses to the poultry industry worldwide and currently lacks effective live vector vaccines. Achieving efficient antigen delivery to mucosa-associated lymphoid tissue (MALT) is critical for improving the effectiveness of vaccines. Here, chicken claudin-3 (CLDN3), a tight junction protein expressed in MALT, was identified as a target, and the C-terminal region of Clostridium perfringens enterotoxin (C-CPE) was proven to bind to chicken CLDN3. Then, a CLDN3-targeting Lactobacillus plantarum NC8-expressing C-CPE surface display system (NC8/GFP-C-CPE) was constructed to successfully express the heterologous protein on the surface of L. plantarum. The colonization level of NC8/GFP-C-CPE was significantly increased compared to the non-targeting strain and could persist in the intestine for at least 72 h. An oral vaccine strain expressing five EGF domains of Eimeria tenella microneme protein 8 (EtMIC8-EGF) (NC8/EtMIC8-EGF-C-CPE) was constructed to evaluate the protective efficacy against E. tenella infection. The results revealed that CLDN3-targeting L. plantarum induced stronger mucosal immunity in gut-associated lymphoid tissues (GALT) as well as humoral responses and conferred better protection in terms of parasite replication and pathology than the non-targeting strain. Overall, we successfully constructed a CLDN3-targeting L. plantarum NC8 surface display system characterized by MALT-targeting, which is an efficient antigen delivery system to confer enhanced protective efficacy in chickens against E. tenella infection.

Artesunate delays the dysfunction of age-related intestinal epithelial barrier by mitigating endoplasmic reticulum stress/unfolded protein response.

The impairment of the intestinal epithelial barrier and subsequent bacterial translocation are common in aging individuals, contributory to several local and systematic disorders. However, the underlying mechanism of the age-related degeneration has not been fully understood. In this study, we demonstrated that the intestinal KIT signaling declined and de-activated with aging, parallel with epithelial barrier dysfunction. Endoplasmic reticulum stress (ERS)/unfolded protein response (UPR) was obviously increased during aging. The ERS and its downstream IRE1α were highly activated in the aging colonic epithelium. Furthermore, by the use of Tunicamycin (Tm)-induced ERS mouse and cell models, we uncovered that the activity of the ERS/IRE1α accelerated the protein degradation of KIT via ubiquitin-proteasome pathway. The deficiency of KIT signaling further reduced the transcription of the tight junction protein Claudin-3. Of significance, Artesunate (ART) could be capable of ameliorating the detrimental effect of ERS/IRE1α, indicated by the re-gained KIT and Claudin-3 expressions and the restoration of the intestinal epithelial barrier. In conclusion, our present study provided novel evidence elucidating the ERS/IRE1α-induced loss of KIT and Claudin-3 in the aging colonic epithelium and also shed light on the protective effect of Artesunate on the intestinal epithelial barrier by blocking ERS/IRE1α activity during aging.