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

Salivary Gland Transplantation as a Promising Approach for Tear Film Restoration in Severe Dry Eye Disease

With increased awareness of dry eye disease (DED), a multitude of therapeutic options have become available. Nevertheless, the treatment of severe DED remains difficult. In a patient whose DED is related to the loss of lacrimal function without severe destruction of the salivary glands, autologous transplantation of the latter as functioning exocrine tissue to rebuild a stable tear film is an attractive idea. All three major and minor salivary glands have been used for such transplantation. Due to the complications associated with and unfavorable prognosis of parotid duct and sublingual gland transplantation, surgeons now prefer to use the submandibular gland (SMG) for such procedures. The transplantation of the SMG not only has a high survival rate, but also improves dry eye symptoms and signs for more than 20 years post-surgery. The regulation of the secretion of the transplanted SMG is critical because the denervated SMG changes its mechanism of secretion. Innovative procedures have been developed to stimulate secretion in order to prevent the obstruction of the Wharton's duct and to decrease secretion when postoperative "epiphora" occurs. Among the minor salivary glands, the transplantation of the labial salivary glands is the most successful in the long-term. The measurement of the flow rates of minor salivary glands and donor-site selection are critical steps before surgery.

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.

SHED-derived exosomes ameliorate hyposalivation caused by Sjögren's syndrome via Akt/GSK-3β/Slug-mediated ZO-1 expression

BACKGROUND

Sjögren's syndrome (SS) is an autoimmune disorder characterized by sicca syndrome and/or systemic manifestations. The treatment is still challenging. This study aimed to explore the therapeutic role and mechanism of exosomes obtained from the supernatant of stem cells derived from human exfoliated deciduous teeth (SHED-exos) in sialadenitis caused by SS.

METHODS

SHED-exos were administered to the submandibular glands (SMGs) of 14-week-old non-obese diabetic (NOD) mice, an animal model of the clinical phase of SS, by local injection or intraductal infusion. The saliva flow rate was measured after pilocarpine intraperitoneal injection in 21-week-old NOD mice. Protein expression was examined by western blot analysis. Exosomal microRNA (miRNAs) were identified by microarray analysis. Paracellular permeability was evaluated by transepithelial electrical resistance measurement.

RESULTS

SHED-exos were injected into the SMG of NOD mice and increased saliva secretion. The injected SHED-exos were taken up by glandular epithelial cells, and further increased paracellular permeability mediated by zonula occluden-1 (ZO-1). A total of 180 exosomal miRNAs were identified from SHED-exos, and Kyoto Encyclopedia of Genes and Genomes analysis suggested that the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) pathway might play an important role. SHED-exos treatment down-regulated phospho-Akt (p-Akt)/Akt, phospho-glycogen synthase kinase 3β (p-GSK-3β)/GSK-3β, and Slug expressions and up-regulated ZO-1 expression in SMGs and SMG-C6 cells. Both the increased ZO-1 expression and paracellular permeability induced by SHED-exos were abolished by insulin-like growth factor 1, a PI3K agonist. Slug bound to the ZO-1 promoter and suppressed its expression. For safer and more effective clinical application, SHED-exos were intraductally infused into the SMGs of NOD mice, and saliva secretion was increased and accompanied by decreased levels of p-Akt/Akt, p-GSK-3β/GSK-3β, and Slug and increased ZO-1 expression.

CONCLUSION

Local application of SHED-exos in SMGs can ameliorate Sjögren syndrome-induced hyposalivation by increasing the paracellular permeability of glandular epithelial cells through Akt/GSK-3β/Slug pathway-mediated ZO-1 expression.

Effects of Houpo Mahuang Decoction on serum metabolism and TRPV1/Ca2+/TJs in asthma

ETHNOPHARMACOLOGICAL RELEVANCE

Houpo Mahuang Decoction (HPMHD is one of the classic traditional Chinese prescriptions that has been used in the treatment of asthma. The therapeutic effects and mechanism of HPMHD in aggravated asthma remain to be explored, especially from the perspective of metabolomics and Transient Receptor Potential Vanilloid-1 (TRPV1)/Ca²⁺/Tight junction (TJ) regulation.

AIM OF THE STUDY

To investigate the therapeutic and metabolic regulatory effects and the underlying mechanism of HPMHD in asthmatic rats.

MATERIALS AND METHODS

The asthmatic rats were administered with the corresponding HPMHD (at dosages of 5.54, 11.07, 22.14 mg/kg). Then inflammatory cells in peripheral blood and bronchoalveolar lavage fluid (BALF) were counted, the levels of interleukin (IL)-4 and IL-13 in BALF were measured, and the changes in enhanced pause (Penh) and pathological damage of lung tissues were also detected to evaluate the protective effects of HPMHD. The serum metabolic profile of HPMHD in asthmatic rats was explored using Ultra-High-Performance Liquid Chromatography-mass spectrometer (UHPLC-MS), and the regulatory effects on TRPV1 and TJs of HPMHD in asthmatic rats were detected by Western blotting analysis. In vitro, 16HBE cells were stimulated with IL-4 plus SO₂ derivatives and then administered HPMHD. The intracellular Ca²⁺ regulated by TRPV1, and the expression levels of TRPV1 and TJ proteins (TJs) were then detected by calcium imaging and Western blotting. The effects were verified by inhibition of TRPV1 and in short hairpin RNA (shRNA)-mediated TRPV1 silencing cells.

RESULTS

HPMHD significantly attenuated the airway inflammation of asthmatic rats, and reduced the levels of inflammatory cells in peripheral blood and BALF as well as the levels of IL-4 plus IL-13 in BALF. In addition, the airway hyperresponsiveness and lung pathological damage were alleviated. Serum metabolomic analysis showed that 31 metabolites were differentially expressed among the normal saline-, model-, and HPMHD-treated rats. Pathway enrichment analysis showed that the metabolites were involved in 45 pathways, among which, TJs regulation-relevant pathway was associated with the Ca²⁺ concentration change mediated by the TRP Vanilloid channel. In vivo and in vitro experiments indicated that HPMHD reduced the concentration of intracellular Ca²⁺ via suppressing the expression and activation of TRPV1, increased the expression of ZO-1, Occludin, and Claudin-3, and protected the integrity of TJs.

CONCLUSION

The current study indicates that HPMHD alleviates rat asthma and participates in the regulation of serum metabolism. The anti-asthma effects of HPMHD might be related to the protection of TJs by inhibiting the intracellular Ca²⁺ concentration via TRPV1.

Targeting endothelial tight junctions to predict and protect thoracic aortic aneurysm and dissection

AIMS

Whether changes in endothelial tight junctions (TJs) lead to the formation of thoracic aortic aneurysm and dissection (TAAD) and serve as an early indicator and therapeutic target remains elusive.

METHODS AND RESULTS

Single-cell RNA sequencing analysis showed aberrant endothelial TJ expressions in the thoracic aortas of patients with TAAD. In a β-aminopropionitrile (BAPN)-induced TAAD mouse model, endothelial TJ function was disrupted in the thoracic aortas at an early stage (5 and 10 days) as observed by a vascular permeability assay, while the intercellular distribution of crucial TJ components was significantly decreased by en face staining. For the non-invasive detection of endothelial TJ function, two dextrans of molecular weights 4 and 70 kDa were conjugated with the magnetic resonance imaging (MRI) contrast agent Gd-DOTA to synthesize FITC-dextran-DOTA-Gd and rhodamine B-dextran-DOTA-Gd. MRI images showed that both probes accumulated in the thoracic aortas of the BAPN-fed mice. Particularly, the mice with increased accumulated signals from 5 to 10 days developed TAAD at 14 days, whereas the mice with similar signals between the two time points did not. Furthermore, the protease-activated receptor 2 inhibitor AT-1001, which seals TJs, alleviated the BAPN-induced impairment of endothelial TJ function and expression and subsequently reduced TAAD incidence. Notably, endothelial-targeted ZO-1 conditional knockout increased TAAD incidence. Mechanistically, vascular inflammation and edema were observed in the thoracic aortas of the BAPN-fed mice, whereas these phenomena were attenuated by AT-1001.

CONCLUSION

The disruption of endothelial TJ function is an early event prior to TAAD formation, herein serving as a potential indicator and a promising target for TAAD.

The Utility of Capsicum annuum L. in Internal Medicine and In Dentistry: A Comprehensive Review

Capsaicin is a chili peppers extract, genus Capsicum, commonly used as a food spice. Since ancient times, Capsaicin has been used as a "homeopathic remedy" for treating a wild range of pathological conditions but without any scientific knowledge about its action. Several studies have demonstrated its potentiality in cardiovascular, nephrological, nutritional, and other medical fields. Capsaicin exerts its actions thanks to the bond with transient receptor potential vanilloid subtype 1 (TRPV1). TRPV1 is a nociceptive receptor, and its activation starts with a neurosensitive impulse, responsible for a burning pain sensation. However, constant local application of Capsaicin desensitized neuronal cells and leads to relief from neuropathic pain. In this review, we analyze the potential adjuvant role of Capsaicin in the treatment of different pathological conditions either in internal medicine or dentistry. Moreover, we present our experience in five patients affected by oro-facial pain consequent to post-traumatic trigeminal neuropathy, not responsive to any remedy, and successfully treated with topical application of Capsaicin. The topical application of Capsaicin is safe, effective, and quite tolerated by patients. For these reasons, in addition to the already-proven beneficial actions in the internal field, it represents a promising method for the treatment of neuropathic oral diseases.

Alteration of tight junctions during botulinum toxin type A-inhibited salivary secretion

OBJECTIVES

Tight junctions (TJs) are involved in the regulation of salivary secretion via paracellular pathway. Botulinum toxin type A (BTXA) is widely used for the treatment of hypersecretion diseases such as sialorrhea. This study aimed to investigate the role of TJs in BTXA-inhibited secretion of the submandibular gland (SMG).

MATERIALS AND METHODS

BTXA was injected into the SMGs of rats, and the same amount of saline was injected as a control. Western blot, real-time PCR and immunofluorescence staining were used to detect the expression and distribution of TJ proteins. Paracellular permeability was evaluated using the transepithelial electrical resistance (TER) measurements and fluorescent tracer detection in BTXA-stimulated SMG-C6 cells.

RESULTS

BTXA injection into the SMGs of rats led to increased expression of claudin (Cldn) -1 and Cldn3. Immunofluorescence staining showed no significant changes in the distribution of TJ proteins. In vitro, BTXA increased the TER values and significantly reduced the permeability of fluorescent tracer, suggesting that BTXA decreased the paracellular permeability. The expression levels of Cldn1, Cldn3 and Cldn4 were upregulated after BTXA treatment.

CONCLUSION

The expression of TJ proteins changed in both animal models and SMG-C6 cells after BTXA treatment, which may contribute to the inhibition of salivary secretion.

High Glucose Reduces the Paracellular Permeability of the Submandibular Gland Epithelium via the MiR-22-3p/Sp1/Claudin Pathway

Tight junctions (TJs) play an important role in water, ion, and solute transport through the paracellular pathway of epithelial cells; however, their role in diabetes-induced salivary gland dysfunction remains unknown. Here, we found that the TJ proteins claudin-1 and claudin-3 were significantly increased in the submandibular glands (SMGs) of db/db mice and high glucose (HG)-treated human SMGs. HG decreased paracellular permeability and increased claudin-1 and claudin-3 expression in SMG-C6 cells. Knockdown of claudin-1 or claudin-3 reversed the HG-induced decrease in paracellular permeability. MiR-22-3p was significantly downregulated in diabetic SMGs and HG-treated SMG-C6 cells. A miR-22-3p mimic suppressed claudin-1 and claudin-3 expression and abolished the HG-induced increases in claudin-1 and claudin-3 levels in SMG-C6 cells, whereas a miR-22-3p inhibitor produced the opposite effects. Specificity protein-1 (Sp1) was enhanced in diabetic SMGs and HG-treated SMG-C6 cells, which promoted claudin-1 and claudin-3 transcription through binding to the corresponding promoters. A luciferase reporter assay confirmed that miR-22-3p repressed Sp1 by directly targeting the Sp1 mRNA 3′-untranslated region (3′-UTR). Consistently, the miR-22-3p mimic suppressed, whereas the miR-22-3p inhibitor enhanced, the effects of HG on Sp1 expression. Taken together, our results demonstrate a new regulatory pathway through which HG decreases the paracellular permeability of SMG cells by inhibiting miR-22-3p/Sp1-mediated claudin-1 and claudin-3 expression.

Ultrastructural intestinal mucosa change after prolonged inhibition of gastric acid secretion by omeprazole in male rats

Omeprazole is a potent inhibitor of gastric acid secretion. It was reported that omeprazole induced dramatic gastric mucosa morphologic changes from the resting state to the stimulated state. However, the effect of omeprazole administration on the ultrastructure and absorptive function of small intestines was largely unknown. Here, male Sprague-Dawley rats were daily treated with a single dose of omeprazole for 12 or 24 weeks. Ultrastructure intestinal mucosal change in duodenum, jejunum, and ileum was observed. We also determined small intestine inflammation, using intraepithelial lymphocytes activation. Finally, magnesium levels were measured in plasma, urine, feces, muscle, and bone to determine systemic magnesium balance. Omeprazole-treated rats had significantly decreased the width of tight junction, villous length, and absorptive area of duodenum, jejunum, and ileum compared to control rats. The small intestine of the omeprazole-treated group showed significantly higher intraepithelial lymphocytes activation levels compared with the control group. Lower secretory granules of Paneth cells at the base of the crypts were showed in omeprazole-treated rats. They also had significantly lower plasma, urinary, bone, and muscle Mg2+ contents indicating hypomagnesemia with systemic magnesium deficiency. In conclusion, prolonged omeprazole treatment-induced small intestinal inflammation and villous atrophy, which led to decrease small intestinal magnesium absorption in the condition of proton pump inhibitor-induced hypomagnesemia.

Water treadmill training attenuates blood-spinal cord barrier disruption in rats by promoting angiogenesis and inhibiting matrix metalloproteinase-2/9 expression following spinal cord injury

Background

The permeability of the blood-spinal cord barrier (BSCB) is mainly determined by junction complexes between adjacent endothelial cells (ECs), including tight junctions (TJs) and adherens junctions (AJs), which can be severely damaged after spinal cord injury (SCI). Exercise training is a recognized method for the treatment of SCI. The destruction of the BSCB mediated by matrix metalloproteinases (MMPs) leads to inflammation, neurotoxin production, and neuronal apoptosis. The failure of new blood vessels to effectively regenerate is also an important cause of delayed recovery after SCI. For the first time, we introduced water treadmill training (TT) to help SCI rats successfully exercise and measured the effects of TT in promoting recovery after SCI and the possible mechanisms involved.

Methods

Sprague-Dawley (200–250 g) rats were randomly divided into the following three groups: sham operated, SCI, and SCI + TT. Animals were sacrificed at 7 or 14 days post-surgery. The degree of neurological deficit, tissue morphology and BSCB permeability were assessed by the Basso-Beattie-Bresnahan (BBB) motor function scale and appropriate staining protocols, and apoptosis, protein expression and vascular EC ultrastructure were assessed by TUNEL staining, Western blotting, immunofluorescence and transmission electron microscopy (TEM).

Results

Our experiments showed that TT reduced permeability of the BSCB and decreased structural tissue damage. TT significantly improved functional recovery when compared with that in the SCI group; TJ and AJ proteins expression increased significantly after TT, and training reduced apoptosis induced by SCI. TT could promote angiogenesis, and MMP-2 and MMP-9 expression was significantly inhibited by TT.

Conclusions

The results of this study indicate that TT promotes functional recovery for the following reasons: TT (1) protects residual BSCB structure from further damage, (2) promotes vascular regeneration, and (3) inhibits MMP-2/9 expression to mitigate BSCB damage.

Disruption of tight junctions contributes to hyposalivation of salivary glands in a mouse model of type 2 diabetes

Tight junction (TJ) plays an important role in regulating paracellular fluid transport in salivary glands; however, little is known about the involvement of TJs in diabetes salivary glands. This study aimed to investigate the alterations of TJs and their possible contribution in diabetes-induced hyposalivation. Here, we observed that the morphologies of submandibular glands (SMGs) were impaired, characterized by enlarged acini accumulation with giant secretory granules, which were significantly reduced in atrophic ducts in SMGs of db/db mice, a spontaneous model of type-2 diabetes. However, the secretory granules were increased and scattered in the acini of diabetes parotid glands (PGs). Other ultrastructural damages including swollen mitochondria, expansive endoplasmic reticulum, and autophagosomes were observed in the diabetes group. The levels of TJ proteins including claudin-1 (Cldn1) and claudin-3 (Cldn3) were increased, whereas those of claudin-4 (Cldn4), occludin (Ocln), and zonula occludens-1 (ZO-1) were decreased in SMGs of db/db mice. Higher Cldn1 and Cldn3 and lower claudin-10 (Cldn10) and Ocln levels were observed in PGs of diabetes mice. Taken together, the structures of SMGs and PGs were impaired in diabetes mice, and the disruption of TJ integrity in both SMGs and PGs may contribute to diabetes-induced hyposalivation.

Tricellulin Modulates Transport of Macromolecules in the Salivary Gland

Volume and composition of saliva are crucial for oral and systemic health. How substances, particularly macromolecules, are transported across the salivary gland epithelium has not been established in detail. Tricellulin is a component of tricellular tight junctions that form a central tube to serve as an important route for macromolecule transport. Whether tricellulin is expressed in the submandibular gland (SMG) and involved in salivation has been unknown. Here, by using Western blotting and immunofluorescence, tricellulin was found to be characteristically localized at tricellular contacts of human, rat, and mouse SMGs. Knockdown of tricellulin significantly increased, whereas overexpression of tricellulin decreased, paracellular permeability for 40-kDa but not for 4-kDa fluorescein isothiocyanate–dextran, while transepithelial electrical resistance was unaffected. Conversely, claudin-4 knockdown and overexpression affected transepithelial electrical resistance but not 40-kDa fluorescein isothiocyanate–dextran transport, suggesting that tricellulin regulated transport of macromolecules but not ions, which were mainly regulated by bicellular tight junctions (bTJs). Moreover, tricellulin was dynamically redistributed from tri- to bicellular membranes in cholinergically stimulated SMG tissues and cells. Immunoglobulin-like domain-containing receptor 1 (ILDR1) recruits tricellulin to tricellular contacts. The proportion of macromolecules in the saliva was increased, whereas the amount of stimulated saliva was unchanged in Ildr1-/- mice, which displayed abnormal tricellulin distribution in SMGs. Furthermore, tricellulin interacted with bTJ proteins, such as occludin, claudin-1, claudin-3, claudin-4, and ZO-1, in rat SMG epithelial polarized cell line SMG-C6. Knockdown of tricellulin decreased occludin levels. Thus, we revealed a specific expression pattern of tricellulin in SMG epithelium. Tricellulin not only functioned as a barrier for macromolecules but also modulated the connection of bTJs to the tight junction complex. Alterations in tricellulin expression and distribution could thereby change salivary composition. Our study provided novel insights on salivary gland tight junction organization and function.

Endothelial tight junctions and their regulatory signaling pathways in vascular homeostasis and disease

Endothelial tight junctions (TJs) regulate the transport of water, ions, and molecules through the paracellular pathway, serving as an important barrier in blood vessels and maintaining vascular homeostasis. In endothelial cells (ECs), TJs are highly dynamic structures that respond to multiple external stimuli and pathological conditions. Alterations in the expression, distribution, and structure of endothelial TJs may lead to many related vascular diseases and pathologies. In this review, we provide an overview of the assessment methods used to evaluate endothelial TJ barrier function both in vitro and in vivo and describe the composition of endothelial TJs in diverse vascular systems and ECs. More importantly, the direct phosphorylation and dephosphorylation of TJ proteins by intracellular kinases and phosphatases, as well as the signaling pathways involved in the regulation of TJs, including and the protein kinase C (PKC), PKA, PKG, Ras homolog gene family member A (RhoA), mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/Akt, and Wnt/β-catenin pathways, are discussed. With great advances in this area, targeting endothelial TJs may provide novel treatment for TJ-related vascular pathologies.

[Role and mechanism of muscarinic acetylcholine receptor in the regulation of submandibular gland secretion]

Muscarinic acetylcholine receptors (mAChRs), including M1-M5 subtypes, are classic receptors in regulating water, ion, and solute transport in salivary gland. Our work focuses on the studies on the expression pattern and function of mAChR in the submandibular gland (SMG), and the underlying mechanism involved in the mAChR-regulated secretion, together with the effect of parasympathectomy on the salivary secretion. Microvascular autotransplantation of SMG into the temporal fossa provides a continuous and endogenous source of fluids, and is currently an effective method for treating severe keratoconjunctivitis sicca. By using RT-PCR, Western blotting, and immunofluorescence, our data demonstrated that the expression of M1 and M3 subtypes were decreased in latent period in rabbit SMG autotransplantation model, whereas carbachol stimulation promoted the salivary secretion, as well as M1 and M3 expressions. By contrast, mAChRs were hypersensitive in epiphora SMGs, whereas atropine gel and botulinum toxin A application significantly inhibited the hypersecretion in both animal models and patients. Furthermore, the possible intracellular signal molecules involved in the mAChR-modulated salivary secretion were explored. Activation of mAChR upregulated the expression of aquaporin 5 (AQP5), the main transporter that mediated water secretion through transcellular pathway, and led to AQP5 trafficking from lipid rafts to non-lipid microdomain. Extracellular signal-regulated kinase 1/2 (ERK1/2) was involved in the mAChR-regulated AQP5 content. mAChR activation also modulated the expression, distribution, and function of tight junction proteins, and increased paracellular permeability. ERK1/2/β-arrestin2/clathrin/ubiquitin signaling pathway was responsible for the mAChR-regulated downregulation of tight junction molecule claudin-4. Cytoskeleton filamentous actin (F-actin) was also involved in the distribution and barrier function of epithelial tight junctions. Besides, endothelial tight junctions were opened by mAChR agonist-evoked salivation in the mice. Furthermore, parasympathetic denervation increased resting salivary secretion in the long terminrats and minipigs. Taken together, our work demonstrated that mAChR regulated saliva secretion via transcellular and paracellular pathways in SMG epithelium as well as tight junction opening in SMG endothelium. Modulation of mAChR might be a promising strategy to ameliorate SMG dysfunction.

Upregulation of the WNK4 Signaling Pathway Inhibits Epithelial Sodium Channels of Mouse Tracheal Epithelial Cells After Influenza A Infection

Influenza virus has a significant impact on the respiratory system. The mechanism of how influenza virus impairs the fluid transport in airway is not fully understood. We examined its effects on epithelial sodium channels (ENaC), which are very important for water and salt transport in the respiratory system. We focused on the impacts of influenza virus on ENaC activity in mouse tracheal epithelial cells (MTECs) and applied Ussing chamber apparatus for recording the short-circuit currents in primary cultured MTECs. Expressions of α and γ-ENaC were measured at the protein and mRNA levels by western blot and quantitative real-time polymerase chain reaction, respectively. Roles of the with-no-lysine-kinase-4 (WNK4) pathway were considered in participating influenza virus-involved ENaC regulation by using siRNA to knockdown WNK4 and the physical properties of airway surface liquid (ASL) were detected by confocal microscopy. Our results showed that influenza virus reduced ENaC activity, and the expressions of α and γ-ENaC were decreased at the protein and mRNA levels, respectively. WNK4 expression increased time-dependently at the protein level after influenza virus infection, while knockdown of WNK4 rescued the impact of influenza virus on ENaC and ASL height increased obviously after MTECs were treated with influenza virus. Taken together, these results suggest that influenza virus causes the changes of biophysical profile in the airway by altering the ENaC activity at least partly via facilitating the expression of WNK4.

A 90-day toxicity and genotoxicity study with high-purity phenylcapsaicin

To evaluate the safety of the synthetic capsaicin analogue phenylcapsaicin (PheCap; 7-phenylhept-6-yne-acid-hydroxy-3-mathoxylbenzylamide, CAS no 848127-67-3), a 90-day repeated dose oral gavage of 0, 30, 100 or 250 mg/kg body weight (bw)/day toxicity study with a 28-day recovery period was conducted using Wistar rats. Examinations of clinical signs, body and organ weight, haematology, urinalysis, clinical chemistry, food consumption and macroscopic, as well as histopathological tissue examinations were carried out for signs of toxicity. Degenerative, but reversible changes in the liver at 250 mg/kg bw/day, and local irritating effects in the stomach at 100 and 250 mg/kg bw/day were found. These findings were associated with test item-related clinical symptoms, that is, diarrhoea, salivation and moving of bedding material. PheCap did neither cause gene mutations by base pair changes or frame shifts in the genome of the tester stains Salmonella typhimurium TA 98, TA 100, TA 1535, TA 1537 or TA 102 nor induce structural and/or numerical chromosomal damage in human lymphocytes. Therefore, it can be concluded that PheCap is not genotoxic. The No Observed Adverse Effect Level (NOAEL) of PheCap for systemic toxicity is considered to be at 100 mg/kg bw/day which is based on degenerative changes in the liver. Due to irritating effects in the stomach, the NOAEL for local effects was established at 30 mg/kg bw/day.

Role of TRPV1 receptor in inflammation and impairment of esophageal mucosal integrity in a murine model of nonerosive reflux disease

BACKGROUND

Microscopic inflammation and impairment of the esophageal epithelial barrier are considered relevant for perception of symptoms in patients with nonerosive reflux disease (NERD). In these patients, the receptor transient receptor potential vanilloid 1 (TRPV1) is overexpressed in the esophageal mucosa, but its role is not yet fully understood. We evaluated the role of TRPV1 in esophageal inflammation and mucosal barrier impairment in a murine model of NERD.

METHODS

Nonerosive reflux disease was surgically induced in Swiss mice by pyloric substenosis and ligature of the gastric fundus, and the mice were killed 7 days post surgery. The experimental groups were: I, sham surgery (negative control); II, NERD untreated; III and IV, NERD + SB366791 or capsazepine (TRPV1 antagonists); and V, NERD + resiniferatoxin (for long-term desensitization of TRPV1). The esophagus was collected for western blotting and histopathology and for evaluation of wet weight, myeloperoxidase (MPO), keratinocyte-derived chemokine (KC), transepithelial electrical resistance (TEER), and basal permeability to fluorescein.

KEY RESULTS

Compared to sham, NERD mice had increased esophageal wet weight and MPO and KC levels. The mucosa had no ulcers but exhibited inflammation. NERD mice showed mucosal TRPV1 overexpression, a more pronounced decrease in TEER at pH 0.5 (containing pepsin and taurodeoxycholic acid), and increased basal permeability. Pharmacological modulation of TRPV1 prevented esophageal inflammation development, TEER changes by acidic exposure, and increase in esophageal permeability.

CONCLUSIONS & INFERENCES

The TRPV1 receptor has a critical role in esophageal inflammation and mucosal barrier impairment in NERD mice, suggesting that TRPV1 might be a pharmacological target in patients with NERD.

Roles of transient receptor potential channels in regulation of vascular and epithelial barriers

Transient receptor potential (TRP) channels are a ubiquitously expressed multi-family group of cation channels that are critical to signaling events in many tissues. Their roles have been documented in many physiologic and pathologic conditions. Nevertheless, direct studies of their roles in maintain barrier function in endothelial and epithelia are relatively infrequent. This seems somewhat surprising considering that calcium ion concentrations are known to regulate barrier function. This short review provides an introduction to TRP channels and reviews some of the work in which investigators directly studied the role of TRP channels in endothelial permeability to electric current, solute, or leukocytes during the inflammatory response.

Decreased interaction between ZO-1 and occludin is involved in alteration of tight junctions in transplanted epiphora submandibular glands

Tight junctions (TJs) in salivary epithelium play an important role in regulating saliva secretion. Autologous transplantation of submandibular glands (SMGs) is an effective method to treat severe dry eye syndrome. However, epiphora occurs in some patients 6 months after transplantation. We previously found that the acinar TJs are enlarged in rabbit SMGs after long-term transplantation, but the exact TJ components involved in the epiphora are still unknown. Here, we found that the mRNA and protein expression of ZO-1 and occludin were increased in the transplanted SMGs obtained from epiphora patients, while other TJs were unchanged. The intensity of ZO-1 and occludin at the apicolateral membranes as well as occludin in the cytoplasm were increased in epiphora SMGs, but the interaction between ZO-1 and occludin was decreased as evidenced by both co-immunoprecipitation assay and co-immunofluorescence staining. Mechanically, the expression of casein kinase 2α (CK2α) and CK2β, which was reported to affect occludin modification and the interaction of occludin with ZO-1 in previous literatures, were increased in epiphora glands. Moreover, activation of muscarinic acetylcholine receptor (mAChR) by carbachol directly decreased the interaction between ZO-1 and occludin and increased the acinar TJ width in the freshly isolated human SMGs, whereas these effects were abolished by pretreatment with CK2 inhibitor. Taken together, our findings suggest that decreased interaction between ZO-1 and occludin might contribute to the epiphora occurred in the transplanted SMGs, and mAChR together with the intracellular molecule CK2 might be responsible for the alteration of TJs in epiphora glands.

Endothelial Tight Junctions Are Opened in Cholinergic-Evoked Salivation In Vivo

Blood vessels provide the original supplies for the formation of primary saliva, which is regulated by the tight junctions (TJs) between endothelial cells. Previous studies have shown that blood flow increases with vasodilatation during cholinergic-evoked salivation. However, changes in vascular paracellular permeability and the role of endothelial TJs in salivation are unknown. Here, we established an in vivo paracellular permeability detection system and observed that the endothelial TJs were permeable to 4-kDa fluorescein isothiocyanate (FITC)-dextran while impermeable to 40- and 70-kDa FITC-dextran under an unstimulated condition in mouse submandibular glands (SMGs). Pilocarpine increased the flux of 4- and 40-kDa FITC-dextran out of blood vessels but did not affect 70-kDa FITC-dextran. Claudin 5, a TJ protein specifically localized in salivary endothelial cells, was redistributed from the apicolateral membranes to the lateral and basolateral membranes and cytoplasm in cholinergic-stimulated mouse SMGs and freshly cultured human SMG tissues. In the transplanted SMGs from epiphora patients, we found that claudin 5 was present in the basolateral membranes and cytoplasm, instead of the apical region in control SMGs. Moreover, the level of phospho-myosin light chain 2 increased within the blood vessels of the pilocarpine-stimulated mouse SMGs and transplanted human SMGs, while the downstream molecule F-actin was reorganized in the endothelial cells of the transplanted human SMGs. Taken together, our findings provide direct visual evidence that the opening of endothelial TJs and the redistribution of claudin 5 are essential events contributing to cholinergic-evoked salivation, thus enriching our understanding of the secretory mechanisms that link blood flow to primary saliva formation by regulating the endothelial paracellular permeability.

Muscarinic acetylcholine receptor-mediated tight junction opening is involved in epiphora in late phase of submandibular gland transplantation

Submandibular gland (SMG) autotransplantation is an effective therapy for treating severe dry eye syndrome. However, epiphora occurs in more than 40% of patients 6 months after operation. We previously found that muscarinic acetylcholine receptor (mAChR) plays a crucial role in regulating SMG secretion partially through the modulation on tight junction (TJ)-based paracellular pathway. Therefore, the present study aimed to investigate the possible involvement of mAChR and TJ in a rabbit long-term model of SMG transplantation. We found that SMG secretion was significantly increased on postoperative days 90 and 180, which imitated epiphora observed in the patients with SMG transplantation. Although the mRNA expression and fluorescence intensity of M1 and M3 mAChR subtypes were reversed to control levels on postoperative days 30, 90, and 180, the content of β-arrestin2, but not β-arrestin1, was gradually decreased after transplantation, which suggests that mAChR may be hypersensitive in late phase of SMG transplantation. The width of acinar TJs was enlarged and fluorescence intensity of F-actin in peri-apicolateral membranes were remarkably increased on postoperative days 90 and 180. Topical treatment with atropine gel significantly reduced SMG secretion, TJ width, as well as F-actin intensity in peri-apicolateral membranes on postoperative days 180. Moreover, in a perfused rabbit SMG, carbachol increased salivary secretion, enlarged TJ width, and induced F-actin rearrangement, whereas these responses were inhibited by atropine pretreatment. Taken together, our findings suggest that the hypersensitive mAChR may contribute to epiphora in late phase of SMG transplantation through modulating TJ-based paracellular permeability.

TRPV4 Regulates Tight Junctions and Affects Differentiation in a Cell Culture Model of the Corneal Epithelium

TRPV4 (transient receptor potential vanilloid 4) is a cation channel activated by hypotonicity, moderate heat, or shear stress. We describe the expression of TRPV4 during the differentiation of a corneal epithelial cell model, RCE1(5T5) cells. TRPV4 is a late differentiation feature that is concentrated in the apical membrane of the outmost cell layer of the stratified epithelia. Ca²⁺ imaging experiments showed that TRPV4 activation with GSK1016790A produced an influx of calcium that was blunted by the specific TRPV4 blocker RN-1734. We analyzed the involvement of TRPV4 in RCE1(5T5) epithelial differentiation by measuring the development of transepithelial electrical resistance (TER) as an indicator of the tight junction (TJ) assembly. We showed that TRPV4 activity was necessary to establish the TJ. In differentiated epithelia, activation of TRPV4 increases the TER and the accumulation of claudin-4 in cell-cell contacts. Epidermal Growth Factor (EGF) up-regulates the TER of corneal epithelial cultures, and we show here that TRPV4 activation mimicked this EGF effect. Conversely, TRPV4 inhibition or knock down by specific shRNA prevented the increase in TER. Moreover, TRPP2, an EGF-activated channel that forms heteromeric complexes with TRPV4, is also concentrated in the outmost cell layer of differentiated RCE1(5T5) sheets. This suggests that the EGF regulation of the TJ may involve a heterotetrameric TRPV4-TRPP2 channel. These results demonstrated TRPV4 activity was necessary for the correct establishment of TJ in corneal epithelia and as well as the regulation of both the barrier function of TJ and its ability to respond to EGF. J. Cell. Physiol. 232: 1794-1807, 2017. © 2016 Wiley Periodicals, Inc.

Neuronal TRPV1 activation regulates alveolar bone resorption by suppressing osteoclastogenesis via CGRP

The transient receptor potential vanilloid 1 (TRPV1) channel is abundantly expressed in peripheral sensory neurons where it acts as an important polymodal cellular sensor for heat, acidic pH, capsaicin, and other noxious stimuli. The oral cavity is densely innervated by afferent sensory neurons and is a highly specialized organ that protects against infections as well as physical, chemical, and thermal stresses in its capacity as the first part of the digestive system. While the function of TRPV1 in sensory neurons has been intensively studied in other organs, its physiological role in periodontal tissues is unclear. In this study we found that Trpv1^−/− mice developed severe bone loss in an experimental model of periodontitis. Chemical ablation of TRPV1-expressing sensory neurons recapitulated the phenotype of Trpv1^−/− mice, suggesting a functional link between neuronal TRPV1 signaling and periodontal bone loss. TRPV1 activation in gingival nerves induced production of the neuropeptide, calcitonin gene-related peptide (CGRP), and CGRP treatment inhibited osteoclastogenesis in vitro. Oral administration of the TRPV1 agonist, capsaicin, suppressed ligature-induced bone loss in mice with fewer tartrate-resistant acid phosphatase (TRAP)-positive cells in alveolar bone. These results suggest that neuronal TRPV1 signaling in periodontal tissue is crucial for the regulation of osteoclastogenesis via the neuropeptide CGRP.

The Effect of Capsaicin on Salivary Gland Dysfunction

Capsaicin (trans-8-methyl-N-vanilyl-6-nonenamide) is a unique alkaloid isolated from hot chili peppers of the capsicum family. Capsaicin is an agonist of transient receptor potential vanilloid subtype 1 (TRPV1), which is expressed in nociceptive sensory neurons and a range of secretory epithelia, including salivary glands. Capsaicin has analgesic and anti-inflammatory properties in sensory neurons. Recently, increasing evidence has indicated that capsaicin also affects saliva secretion and inflammation in salivary glands. Applying capsaicin increases salivary secretion in human and animal models. Capsaicin appears to increase salivation mainly by modulating the paracellular pathway in salivary glands. Capsaicin activates TRPV1, which modulates the permeability of tight junctions (TJ) by regulating the expression and function of putative intercellular adhesion molecules in an ERK (extracelluar signal-regulated kinase) -dependent manner. Capsaicin also improved dysfunction in transplanted salivary glands. Aside from the secretory effects of capsaicin, it has anti-inflammatory effects in salivary glands. The anti-inflammatory effect of capsaicin is, however, not mediated by TRPV1, but by inhibition of the NF-κB pathway. In conclusion, capsaicin might be a potential drug for alleviating dry mouth symptoms and inflammation of salivary glands.

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.

Ischemia preconditioning protects rat submandibular glands from ischemia/reperfusion injuries

To investigate the effects of ischemia/reperfusion on rat submandibular glands without denervation and the possible protective effects of ischemia preconditioning on the glands that experienced ischemia/reperfusion, in-situ ischemia/reperfusion and ischemia preconditioning experimental models of submandibular glands of healthy male Wistar rats were conducted. For ischemia/reperfusion groups, the glands were subjected to 90 min of ischemia without denervation, followed by 1, 12, 24, or 72 h of reperfusion. Ischemia preconditioning was achieved by 3 min of ischemia following 3 min of reperfusion, performed three times before ischemia/reperfusion. Salivary secretion, histological changes, alterations of tight junctions, myeloperoxidase activity, cellular apoptosis, and reactive oxygen species levels were detected. In ischemia/reperfusion glands, rising acute-inflammation responses, reduced tight-junction width, and increased myeloperoxidase activity, reactive oxygen species levels, and apoptotic cell numbers were observed, along with secretory dysfunction, especially at 1 and 12 h post-reperfusion, which seemed to gradually return to normal by 72 h post-reperfusion. In contrast, ischemia preconditioning showed the potential to ameliorate the injury-stress responses caused by ischemia/reperfusion. Our study revealed that ischemia/reperfusion could cause a series of injury-stress responses and ultimately lead to hyposecretion, independently of the parasympathetic nerve supply, which might play an important role in the early-phase dysfunction of the transplanted glands. Ischemia preconditioning could protect the involved glands and improve ischemia/reperfusion-induced hyposecretion.

Dysbiosis gut microbiota associated with inflammation and impaired mucosal immune function in intestine of humans with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) has recently been considered to be under the influence of the gut microbiota, which might exert toxic effects on the human host after intestinal absorption and delivery to the liver via the portal vein. In this study, the composition of the gut microbiota in NAFLD patients and healthy subjects was determined via 16S ribosomal RNA Illumina next-generation sequencing. Among those taxa displaying greater than 0.1% average abundance in all samples, five genera, including Alistipes and Prevotella, were significantly more abundant in the gut microbiota of healthy subjects compared to NAFLD patients. Alternatively, Escherichia, Anaerobacter, Lactobacillus and Streptococcus were increased in the gut microbiota of NAFLD patients compared to healthy subjects. In addition, decreased numbers of CD4+ and CD8+ T lymphocytes and increased levels of TNF-α, IL-6 and IFN-γ were detected in the NAFLD group compared to the healthy group. Furthermore, irregularly arranged microvilli and widened tight junctions were observed in the gut mucosa of the NAFLD patients via transmission electron microscopy. We postulate that aside from dysbiosis of the gut microbiota, gut microbiota-mediated inflammation of the intestinal mucosa and the related impairment in mucosal immune function play an important role in the pathogenesis of NAFLD.

TRPV1 in Salivary Gland Epithelial Cells Is Not Involved in Salivary Secretion via Transcellular Pathway

Transient receptor potential vanilloid subtype 1 (TRPV1) was originally found in sensory neurons. Recently, it has been reported that TRPV1 is expressed in salivary gland epithelial cells (SGEC). However, the physiological role of TRPV1 in salivary secretion remains to be elucidated. We found that TRPV1 is expressed in mouse and human submandibular glands (SMG) and HSG cells, originated from human submandibular gland ducts at both mRNA and protein levels. However, capsaicin (CAP), TRPV1 agonist, had little effect on intracellular free calcium concentration ([Ca²⁺]_i) in these cells, although carbachol consistently increased [Ca²⁺]_i. Exposure of cells to high temperature (>43℃) or acidic bath solution (pH5.4) did not increase [Ca²⁺]_i, either. We further examined the role of TRPV1 in salivary secretion using TRPV1 knock-out mice. There was no significant difference in the pilocarpine (PILO)-induced salivary flow rate between wild-type and TRPV1 knock-out mice. Saliva flow rate also showed insignificant change in the mice treated with PILO plus CAP compared with that in mice treated with PILO alone. Taken together, our results suggest that although TRPV1 is expressed in SGEC, it appears not to play any direct roles in saliva secretion via transcellular pathway.

Adiponectin increases secretion of rat submandibular gland via adiponectin receptors-mediated AMPK signaling

Adiponectin and adiponectin receptors (AdipoR1/2) are expressed in various tissues and are involved in the regulation of multiple functions such as energy metabolism and inflammatory responses. However, the effect of adiponectin and AdipoRs in submandibular glands has not been fully evaluated. In the present study, we found that mRNA and protein of both adiponectin and AdipoR1/2 were expressed in rat submandibular glands and in the SMG-C6 cell line, as evidenced by RT-PCR and Western blot analysis. Immunofluorescence staining showed that adiponectin was diffused in the cytoplasm, while AdipoR1/2 was concentrated in the membrane of acinar cells. Saliva flow was significantly increased by full length adiponectin (fAd) or globular adiponectin (gAd) perfusion in isolated rat submandibular glands. 5-Aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR), an adenosine monophosphate activated protein kinase (AMPK) activator, also increased saliva secretion. fAd, gAd, and AICAR all increased the average width of apical tight junctions in perfused submandibular glands, and decreased transepithelial electrical resistance (TER) in SMG-C6 cells, suggesting that adiponectin promoted secretion by modulating paracellular permeability. fAd and gAd increased p-AMPK levels, while AraA, an AMPK antagonist, abolished fAd- and gAd-induced changes in secretion, tight junction ultrastructure, and TER. Moreover, both AdipoR1 and AdipoR2 were required for fAd- or gAd-induced p-AMPK and TER responses, suggesting from their inhibition following AdipoR1 or AdipoR2 knockdown, and co-knockdown of AdipoRs by RNA interference. Our results suggest that adiponectin functions as a promoter of salivary secretion in rat submandibular glands via activation of AdipoRs, AMPK, and paracellular permeability.

Occludin is required for TRPV1-modulated paracellular permeability in the submandibular gland

Occludin plays an important role in maintaining tight junction barrier function in many types of epithelia. We previously reported that activation of transient receptor potential vanilloid subtype 1 (TRPV1) in rabbit submandibular gland promoted salivary secretion, partly by an increase in paracellular permeability. We have now explored the role of occludin in TRPV1-modulated paracellular permeability in a rat submandibular gland cell line SMG-C6. Both TRPV1 and occludin were expressed in SMG-C6 cells, and capsaicin induced redistribution of occludin, but not claudin-3, claudin-4 or E-cadherin, from the cell membrane into the cytoplasm. Capsaicin also decreased transepithelial electrical resistance (TER) and increased the Trypan Blue and FITC-dextran flux. Capsazepine (CPZ), a TRPV1 antagonist, inhibited the capsaicin-induced occludin redistribution and TER decrease. Moreover, occludin knockdown by shRNA suppressed, whereas occludin re-expression restored, the TER response to capsaicin. Mechanistically, TRPV1 activation increased ERK1/2 and MLC2 phosphorylation. PD98059, an ERK1/2 kinase inhibitor, abolished the capsaicin-induced MLC2 phosphorylation, whereas ML-7, an MLC2 kinase inhibitor, did not affect ERK1/2 phosphorylation, suggesting that ERK1/2 is the upstream signaling molecule of MLC2. Capsaicin also induced F-actin reorganization, which was abolished by CPZ, PD98059 and ML-7, indicating that TRPV1 activation altered F-actin organization in an ERK1/2- and MLC2-dependent manner. Furthermore, either PD98059 or ML-7 could abolish the capsaicin-induced TER response and occludin redistribution, whereas knockdown of ERK1/2 further confirmed that the TRPV1-modulated paracellular permeability was ERK1/2 dependent. Taken together, these results identified a crucial role of occludin in submandibular epithelial cells, and more importantly, demonstrated that occludin was required to mediate TRPV1-modulated paracellular permeability.

Decreased adiponectin level is associated with aggressive phenotype of tongue squamous cell carcinoma

Circulating adiponectin levels are inversely associated with risk of various obesity-related cancers. However, the effect of adiponectin on carcinogenesis and progression of tongue squamous cell carcinoma (TSCC) remains unknown. We measured serum adiponectin levels in 59 patients with TSCC and 50 healthy controls. Expression of adiponectin and its receptors in paired tumor and paracancerous specimens were determined by immunohistochemical staining (n = 37) and western blot (n = 30), respectively. Serum adiponectin level was lower in patients than in controls (5.0 ± 2.4 vs 8.4 ± 3.5 μg/mL, P < 0.01), and was inversely associated with histological grade and lymph node metastasis but not tumor size. Local adiponectin levels in tumor tissue gradually decreased as tumor-node-metastasis stage increased, while the expression of adiponectin receptors was unchanged. In addition, serum adiponectin levels in the TSCC patients without metabolic and cardiovascular diseases, or without smoking and drinking habits, were still lower than in controls. Furthermore, adiponectin inhibited the migration, but not proliferation, of SCC15 cells in vitro. These results indicate that a decreased adiponectin level is associated with risk of TSCC. Hypoadiponectinemia might be used as a biomarker to predict an aggressive phenotype of TSCC.