Transient receptor potential vanilloid 4 channel regulates vascular endothelial permeability during colonic inflammation in dextran sulphate sodium-induced murine colitis

Zinc pyrithione ameliorates colitis in mice by interacting on intestinal epithelial TRPA1 and TRPV4 channels

AIMS

Although zinc pyrithione (ZPT) has been studied as topical antimicrobial and cosmetic consumer products, little is known about its pharmacological actions in gastrointestinal (GI) health and inflammation. Our aims were to investigate the effects of ZPT on transient receptor potential (TRP) channels and Ca2+ signaling in intestinal epithelial cells (IECs) and its therapeutic potential for colitis.

MAIN METHODS

Digital Ca2+ imaging and patch-clamp electrophysiology were performed on human colonic epithelial cells (HCoEpiC) and rat small intestinal epithelial cells (IEC-6). The transcription levels of proinflammatory cytokines such as IL-1β were detected by RTq-PCR. Dextran sulfate sodium (DSS) was used to induce colitis in mice.

KEY FINDINGS

ZPT dose-dependently induced Ca2+ signaling and membrane currents in IECs, which were attenuated by selective blockers of transient receptor potential ankyrin 1 (TRPA1) and transient receptor potential vanilloid 4 (TRPV4) channels, respectively. Interestingly, Ca2+ entry via TRPA1 channels inhibited the activity of TRPV4 channels in HCoEpiC, but not vice versa. ZPT significantly promoted migration of IECs by activating TRPA1 and TRPV4 channels. ZPT reversed lipopolysaccharides (LPS)-induced changes in mRNA expression of TRPA1 and TRPV4. Moreover, ZPT decreased mRNA levels of pro-inflammatory factors promoted by LPS in HCoEpiC, which were restored by selective TRPA1 blocker. In whole animal studies in vivo, ZPT significantly ameliorated DSS-induced body weight loss, colon shortening and increases in stool score, serum calprotectin and lactic acid (LD) in mouse model of colitis.

SIGNIFICANCE

ZPT exerts anti-colitic action likely by anti-inflammation and pro-mucosal healing through TRP channels in IECs. The present study not only expands pharmacology spectrum of ZPT in GI tract, but also repurposes it to a potential drug for colitis therapy.

Gut mechanoimmunology: Shaping immune response through physical cues

The gut immune system embodies a complex interplay between the gut mucosal barrier, the host's immune cells, and gut microbiota. These components exist within a dynamic environment characterized by a variety of physical cues, e.g., compression, tension, shear stress, stiffness, and viscoelasticity. The physical cues can be modified under specific pathological conditions. Given their dynamic nature, comprehending the specific effects of these physical cues on the gut immune system is critical for pathological and therapeutic studies of intestinal immune-related diseases. This review aims to discuss how physical cues influence gut immunology by affecting the gut mucosal barrier, host immune cells, and gut microbiota, defining this concept as gut mechanoimmunology. This review seeks to highlight that an enhanced understanding of gut mechanoimmunology carries therapeutic implications, not only for intestinal diseases but also for extraintestinal diseases.

Role of transient receptor potential vanilloid 4 channels in an ovalbumin-induced murine food allergic model

The prevalence of food allergy (FA) has increased worldwide but an effective therapeutic strategy has not been established. Transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive nonselective cation channel, is mainly expressed in the epithelium of various organs. The present study investigated the role of TRPV4 in the pathogenesis of an ovalbumin (OVA)-induced FA model in mice. Wild-type (WT) and TRPV4-deficient (TRPV4KO) mice were sensitized and challenged by OVA to establish FA model. Intestinal tissue samples were processed for biochemical, molecular, and image analyses. Intestinal permeability and antigen uptake assay were conducted using FITC-dextran and OVA-FITC, respectively. TRPV4 was expressed in the colonic epithelium in normal and OVA-treated WT mice. Repeated oral administration of OVA to mice induced systemic allergic symptoms, diarrhea, upregulation of T helper 2 cytokines, OVA-specific immunoglobulin, and FA-related inflammatory cells. These responses were significantly augmented in TRPV4KO mice compared with WT mice. After the induction of FA, the intestinal permeability was significantly increased in TRPV4KO mice compared with WT mice. The expressions of the tight junction protein occludin and adherence junction protein E-cadherin in the colon were significantly lower in TRPV4KO mice compared with WT mice under normal and FA conditions. In addition, the uptake of OVA by CD11c-positive cells was significantly increased in TRPV4KO mice compared with WT mice under FA conditions. These results suggest that epithelial TRPV4 protects against OVA-induced FA symptoms by suppressing the penetration of allergens by maintaining epithelial barrier functions.

Gain-of-function mutations of TRPV4 acting in endothelial cells drive blood-CNS barrier breakdown and motor neuron degeneration in mice

Blood-CNS barrier disruption is a hallmark of numerous neurological disorders, yet whether barrier breakdown is sufficient to trigger neurodegenerative disease remains unresolved. Therapeutic strategies to mitigate barrier hyperpermeability are also limited. Dominant missense mutations of the cation channel transient receptor potential vanilloid 4 (TRPV4) cause forms of hereditary motor neuron disease. To gain insights into the cellular basis of these disorders, we generated knock-in mouse models of TRPV4 channelopathy by introducing two disease-causing mutations (R269C and R232C) into the endogenous mouse Trpv4 gene. TRPV4 mutant mice exhibited weakness, early lethality, and regional motor neuron loss. Genetic deletion of the mutant Trpv4 allele from endothelial cells (but not neurons, glia, or muscle) rescued these phenotypes. Symptomatic mutant mice exhibited focal disruptions of blood-spinal cord barrier (BSCB) integrity, associated with a gain of function of mutant TRPV4 channel activity in neural vascular endothelial cells (NVECs) and alterations of NVEC tight junction structure. Systemic administration of a TRPV4-specific antagonist abrogated channel-mediated BSCB impairments and provided a marked phenotypic rescue of symptomatic mutant mice. Together, our findings show that mutant TRPV4 channels can drive motor neuron degeneration in a non-cell autonomous manner by precipitating focal breakdown of the BSCB. Further, these data highlight the reversibility of TRPV4-mediated BSCB impairments and identify a potential therapeutic strategy for patients with TRPV4 mutations.

Honokiol targeting ankyrin repeat domain of TRPV4 ameliorates endothelial permeability in mice inflammatory bowel disease induced by DSS

ETHNOPHARMACOLOGICAL RELEVANCE

As a classic traditional Chinese medicine, Magnolia officinalis (M. officinalis) is widely used in digestive diseases. It has rich gastrointestinal activity including inflammatory bowel disease (IBD) treatment, but the mechanism is not clear.

AIM OF THE STUDY

In recent years, there has been a growing interest in investigating the regulatory effects of herbal compounds on transient receptor potential (TRP) channel proteins. Transient receptor potential vanilloid 4 (TRPV4), a subtype involved in endothelial permeability regulation, was discussed as the target of M. officinalis in the treatment of IBD in the study. Based on the targeting effect of TRPV4, this study investigated the active ingredients and mechanism of M. officinalis extract in treating IBD.

MATERIALS AND METHODS

To reveal the connection between the active ingredients in M. officinalis and TRPV4, a bioactivity-guided high performance liquid chromatography system coupled with mass spectrometry identification was utilized to screen for TRPV4 antagonists. TRPV4 siRNA knockdown experiment was employed to validate the significance of TRPV4 as a crucial target in regulating endothelial permeability by honokiol (HON). The interaction of the active ingredient representing HON with TRPV4 was confirmed by molecular docking, fluorescence-based thermal shift and live cell calcium imaging experiments. The potential binding sites and inhibitory mechanisms of HON in TRPV4 were analyzed by molecular dynamics simulation and microscale thermophoresis. The therapeutic effect of HON based on TRPV4 was discussed in DSS-IBD mice.

RESULTS

Our finding elucidated that the inhibitory activity of M. officinalis against TRPV4 is primarily attributed to HON analogues. The knockdown of TRPV4 expression significantly impaired the calcium regulation and permeability protection in endothelial cells. The mechanism study revealed that HON specifically targets the Q239 residue located in the ankyrin repeat domain of TRPV4, and competitively inhibits channel opening with adenosine triphosphate (ATP) binding. The immunofluorescence assay demonstrated that the administration of HON enhances the expression and location of VE-Cadherin to protect the endothelial barrier and attenuates immune cell infiltration.

CONCLUSIONS

The finding suggested that HON alleviates IBD by improving endothelial permeability through TRPV4. The discovery provides valuable insights into the potential therapeutic strategy of active natural products for alleviating IBD.

The Role of TRP Channels in Sepsis and Colitis

To date, several members of the transient receptor potential (TRP) channels which provide a wide array of roles have been found in the gastrointestinal tract (GI). The goal of earlier research was to comprehend the intricate signaling cascades that contribute to TRP channel activation as well as how these receptors' activity affects other systems. Moreover, there is a large volume of published studies describing the role of TRP channels in a number of pathological disorders, including inflammatory bowel disease (IBD) and sepsis. Nevertheless, the generalizability of these results is subject to certain limitations. For instance, the study of IBD relies on various animal models and experimental methods, which are unable to precisely imitate the multifactorial chronic disease. The diverse pathophysiological mechanisms and unique susceptibility of animals may account for the inconsistency of the experimental data collected. The main purpose of this study was to conduct a comprehensive review and analysis of existing studies on transient receptor potential (TRP) channels implicating specific models of colitis and sepsis, with particular emphasis on their involvement in pathological disorders such as IBD and sepsis. Furthermore, the text endeavors to evaluate the generalizability of experimental findings, taking into consideration the limitations posed by animal models and experimental methodologies. Finally, we also provide an updated schematic of the most important and possible molecular signaling pathways associated with TRP channels in IBD and sepsis.

Roles of TRP and PIEZO receptors in autoimmune diseases

Autoimmune diseases are pathological autoimmune reactions in the body caused by various factors, which can lead to tissue damage and organ dysfunction. They can be divided into organ-specific and systemic autoimmune diseases. These diseases usually involve various body systems, including the blood, muscles, bones, joints and soft tissues. The transient receptor potential (TRP) and PIEZO receptors, which resulted in David Julius and Ardem Patapoutian winning the Nobel Prize in Physiology or Medicine in 2021, attracted people's attention. Most current studies on TRP and PIEZO receptors in autoimmune diseases have been carried out on animal model, only few clinical studies have been conducted. Therefore, this study aimed to review existing studies on TRP and PIEZO to understand the roles of these receptors in autoimmune diseases, which may help elucidate novel treatment strategies.

Non-electrophysiological techniques targeting transient receptor potential (TRP) gene of gastrointestinal tract

Transient receptor potential (TRP) channels are cation channels related to a wide range of physical and chemical stimuli, they are expressed all along the gastrointestinal system, and a myriad of diseases are often associated with aberrant expression or mutation of the TRP gene, suggesting that TRPs are promising targets for drug therapy. Therefore, a better understanding of the information of TRPs in health and disease could facilitate the development of effective drugs for the treatment of gastrointestinal diseases like IBD. But there are very few generalizations about the experimental techniques studied in this field. In view of the promise of TRP as a therapeutic target, we discuss experimental methods that can be used for TRPs including their distribution, function and interaction with other proteins, as well as some promising emerging technologies to provide experimental methods for future studies.

TRPV4 is expressed by enteric glia and muscularis macrophages of the colon but does not play a prominent role in colonic motility

Background

Mechanosensation is an important trigger of physiological processes in the gastrointestinal tract. Aberrant responses to mechanical input are associated with digestive disorders, including visceral hypersensitivity. Transient Receptor Potential Vanilloid 4 (TRPV4) is a mechanosensory ion channel with proposed roles in visceral afferent signaling, intestinal inflammation, and gut motility. While TRPV4 is a potential therapeutic target for digestive disease, current mechanistic understanding of how TRPV4 may influence gut function is limited by inconsistent reports of TRPV4 expression and distribution.

Methods

In this study we profiled functional expression of TRPV4 using Ca2+ imaging of wholemount preparations of the mouse, monkey, and human intestine in combination with immunofluorescent labeling for established cellular markers. The involvement of TRPV4 in colonic motility was assessed in vitro using videomapping and contraction assays.

Results

The TRPV4 agonist GSK1016790A evoked Ca2+ signaling in muscularis macrophages, enteric glia, and endothelial cells. TRPV4 specificity was confirmed using TRPV4 KO mouse tissue or antagonist pre-treatment. Calcium responses were not detected in other cell types required for neuromuscular signaling including enteric neurons, interstitial cells of Cajal, PDGFRα+ cells, and intestinal smooth muscle. TRPV4 activation led to rapid Ca2+ responses by a subpopulation of glial cells, followed by sustained Ca2+ signaling throughout the enteric glial network. Propagation of these waves was suppressed by inhibition of gap junctions or Ca2+ release from intracellular stores. Coordinated glial signaling in response to GSK1016790A was also disrupted in acute TNBS colitis. The involvement of TRPV4 in the initiation and propagation of colonic motility patterns was examined in vitro.

Conclusions

We reveal a previously unappreciated role for TRPV4 in the initiation of distension-evoked colonic motility. These observations provide new insights into the functional role of TRPV4 activation in the gut, with important implications for how TRPV4 may influence critical processes including inflammatory signaling and motility.

Research hotspots and trend analysis of abdominal pain in inflammatory bowel disease: a bibliometric and visualized analysis

Aims: The study aimed to provide a bibliometric and visual analysis of research on abdominal pain in inflammatory bowel disease and discuss the current status, research hotspots, and future developments. Methods: We used the Web of Science Core Collection to comprehensively search the literature on abdominal pain-related research in IBD published between 2003 and 2022. The bibliometric and visual analysis was performed through CiteSpace, VOSviewer software, R language, and the bibliometric online analysis platform, including authors, institutions, countries, journals, references, and keywords in the literature. Results: A total of 3,503 relevant articles are included, indicating that the number of articles in this field has increased in recent years. The United States leads the way with a dominant position in terms of article output, followed by China and JAPAN. United States (967 articles), University of Calgary (98 articles), and World Journal of Gastroenterology (127 articles) are the top publishing countries, institutions, and journals, respectively; keyword analysis shows that gut microbiota, depression, stress, visceral hypersensitivity, and multidisciplinary approach are the hot spots and trends in this research area. Conclusion: Abdominal pain-related studies in IBD have received increasing attention in the past two decades. This study provides the first bibliometric analysis of papers in this research area using visualization software and data information mining. It provides insights into this field's current status, hot spots, and trends. However, many outstanding issues in this research area still need further exploration to provide a theoretical basis for its clinical application.

Contribution of Blood Vessel Activation, Remodeling and Barrier Function to Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs) consist of a group of chronic inflammatory disorders with a complex etiology, which represent a clinical challenge due to their often therapy-refractory nature. In IBD, inflammation of the intestinal mucosa is characterized by strong and sustained leukocyte infiltration, resulting in the loss of epithelial barrier function and subsequent tissue destruction. This is accompanied by the activation and the massive remodeling of mucosal micro-vessels. The role of the gut vasculature in the induction and perpetuation of mucosal inflammation is receiving increasing recognition. While the vascular barrier is considered to offer protection against bacterial translocation and sepsis after the breakdown of the epithelial barrier, endothelium activation and angiogenesis are thought to promote inflammation. The present review examines the respective pathological contributions of the different phenotypical changes observed in the microvascular endothelium during IBD, and provides an overview of potential vessel-specific targeted therapy options for the treatment of IBD.

Ion channel regulation of gut immunity

Mounting evidence indicates that gastrointestinal (GI) homeostasis hinges on communications among many cellular networks including the intestinal epithelium, the immune system, and both intrinsic and extrinsic nerves innervating the gut. The GI tract, especially the colon, is the home base for gut microbiome which dynamically regulates immune function. The gut's immune system also provides an effective defense against harmful pathogens entering the GI tract while maintaining immune homeostasis to avoid exaggerated immune reaction to innocuous food and commensal antigens which are important causes of inflammatory disorders such as coeliac disease and inflammatory bowel diseases (IBD). Various ion channels have been detected in multiple cell types throughout the GI tract. By regulating membrane properties and intracellular biochemical signaling, ion channels play a critical role in synchronized signaling among diverse cellular components in the gut that orchestrates the GI immune response. This work focuses on the role of ion channels in immune cells, non-immune resident cells, and neuroimmune interactions in the gut at the steady state and pathological conditions. Understanding the cellular and molecular basis of ion channel signaling in these immune-related pathways and initial testing of pharmacological intervention will facilitate the development of ion channel-based therapeutic approaches for the treatment of intestinal inflammation.

Repeated psychological stress, chronic vicarious social defeat stress, evokes irritable bowel syndrome-like symptoms in mice

Increasing evidence has demonstrated that emotional states and intestinal conditions are inter-connected in so-called “brain–gut interactions.” Indeed, many psychiatric disorders are accompanied by gastrointestinal symptoms, such as the irritable bowel syndrome (IBS). However, the functional connection remains elusive, partly because there are few useful experimental animal models. Here, we focused on a highly validated animal model of stress-induced psychiatric disorders, such as depression, known as the chronic vicarious social defeat stress (cVSDS) model mice, which we prepared using exposure to repeated psychological stress, thereafter examining their intestinal conditions. In the charcoal meal test and the capsaicin-induced hyperalgesia test, cVSDS model mice showed a significantly higher intestinal transit ratio and increased visceral pain-related behaviors, respectively. These changes persisted over one month after the stress session. On the other hand, the pathological evaluations of the histological and inflammatory scores of naive and cVSDS model mice did not differ. Furthermore, keishikashakuyakuto—a kampo medicine clinically used for the treatment of IBS—normalized the intestinal motility change in cVSDS model mice. Our results indicate that cVSDS model mice present IBS-like symptoms such as chronic intestinal peristaltic changes and abdominal hyperalgesia without organic lesion. We therefore propose the cVSDS paradigm as a novel animal model of IBS with wide validity, elucidating the correlation between depressive states and intestinal abnormalities.

Capsaicin inhibits intestinal Cl- secretion and promotes Na+ absorption by blocking TRPV4 channels in healthy and colitic mice

Although capsaicin has been studied extensively as an activator of the transient receptor potential vanilloid cation channel subtype 1 (TRPV1) channels in sensory neurons, little is known about its TRPV1-independent actions in gastrointestinal health and disease. Here, we aimed to investigate the pharmacological actions of capsaicin as a food additive and medication on intestinal ion transporters in mouse models of ulcerative colitis (UC). The short-circuit current (Isc) of the intestine from WT, TRPV1-, and TRPV4-KO mice were measured in Ussing chambers, and Ca2+ imaging was performed on small intestinal epithelial cells. We also performed Western blots, immunohistochemistry, and immunofluorescence on intestinal epithelial cells and on intestinal tissues following UC induction with dextran sodium sulfate. We found that capsaicin did not affect basal intestinal Isc but significantly inhibited carbachol- and caffeine-induced intestinal Isc in WT mice. Capsaicin similarly inhibited the intestinal Isc in TRPV1 KO mice, but this inhibition was absent in TRPV4 KO mice. We also determined that Ca2+ influx via TRPV4 was required for cholinergic signaling-mediated intestinal anion secretion, which was inhibited by capsaicin. Moreover, the glucose-induced jejunal Iscvia Na+/glucose cotransporter was suppressed by TRPV4 activation, which could be relieved by capsaicin. Capsaicin also stimulated ouabain- and amiloride-sensitive colonic Isc. Finally, we found that dietary capsaicin ameliorated the UC phenotype, suppressed hyperaction of TRPV4 channels, and rescued the reduced ouabain- and amiloride-sensitive Isc. We therefore conclude that capsaicin inhibits intestinal Cl- secretion and promotes Na+ absorption predominantly by blocking TRPV4 channels to exert its beneficial anti-colitic action.

The Emerging Pro-Algesic Profile of Transient Receptor Potential Vanilloid Type 4

Transient receptor potential vanilloid type 4 (TRPV4) channels are Ca²⁺-permeable non-selective cation channels which mediate a wide range of physiological functions and are activated and modulated by a diverse array of stimuli. One of this ion channel's least discussed functions is in relation to the generation and maintenance of certain pain sensations. However, in the two decades which have elapsed since the identification of this ion channel, considerable data has emerged concerning its function in mediating pain sensations. TRPV4 is a mediator of mechanical hyperalgesia in the various contexts in which a mechanical stimulus, comprising trauma (at the macro-level) or discrete extracellular pressure or stress (at the micro-level), results in pain. TRPV4 is also recognised as constituting an essential component in mediating inflammatory pain. It also plays a role in relation to many forms of neuropathic-type pain, where it functions in mediating mechanical allodynia and hyperalgesia.Here, we review the role of TRPV4 in mediating pain sensations.

The rich pharmacological activities of Magnolia officinalis and secondary effects based on significant intestinal contributions

ETHNOPHARMACOLOGICAL RELEVANCE

Magnolia officinalis Cortex (M. officinalis) is a traditional herbal drug widely used in Asian countries. Depending on its multiple biological activities, M. officinalis is used to regulate gastrointestinal (GI) motility, relieve cough and asthma, prevent cardiovascular and cerebrovascular diseases, and treat depression and anxiety.

AIM OF THE REVIEW

We aimed to review the abundant form of pharmacodynamics activity and potential mechanisms of action of M. officinalis and the characteristics of the internal processes of the main components. The potential mechanisms of local and distance actions of M. officinalis based on GI tract was provided, and it was used to reveal the interconnections between traditional use, phytochemistry, and pharmacology.

MATERIALS AND METHODS

Published literatures about M. officinalis and its main components were collected from several scientific databases, including PubMed, Elsevier, ScienceDirect, Google Scholar and Web of Science etc. RESULTS: M. officinalis was shown multiple effects including effects on digestive system, respiratory system, central system, which is consistent with traditional applications, as well as some other activities such as cardiovascular system, anticancer, anti-inflammatory and antioxidant effects and so on. The mechanisms of these activities are abundant. Its chief ingredients such as magnolol and honokiol can be metabolized into active metabolites in vivo, which can increase water solubility and bioavailability and exert pharmacological activity in the whole body. In the GI tract, M. officinalis and its main ingredient can regulate GI hormones and substance metabolism, protect the intestinal barrier and affect the gut microbiota (GM). These actions are effective to improve local discomfort and some distal symptoms such as depression, asthma, or metabolic disorders.

CONCLUSIONS

Although M. officinalis has rich pharmacological effects, the GI tract makes great contributions to it. The GI tract is not only an important place for absorption and metabolism but also a key site to help M. officinalis exert local and distal efficacy. Pharmacodynamical studies on the efficacies of distal tissues based on the contributions of the GI tract hold great potential for understanding the benefits of M. officinalis and providing new ideas for the treatment of important diseases.

Beneficial effect of capsaicin via TRPV4/EDH signals on mesenteric arterioles of normal and colitis mice

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Capsaicin induced vasorelaxation of human colonic submucosal arterioles in vitro and in vitro.

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Capsaicin induced an endothelium-dependent vasorelaxation of human submucosal arterioles.

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Capsaicin induced an endothelium-dependent vasorelaxation of mouse mesenteric arterioles.

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Capsaicin induced vasorelaxation minily by TRPV1-mediated endothelial nitric oxide release.

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Capsaicin induced vasorelaxation mainly by TRPV4/endothelium-dependent hyperpolarization.

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Capsaicin exerted anti-colitis action in wide-type mice, but not in TRPV4 knock-out mice.

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Capsaicin rescued the impaired endothelium-dependent vasorelaxation via TRPV4/EDH pathway.

Introduction

Although capsaicin has long been used as food additive and medication worldwide, its actions on gastrointestinal tract as its most delivery pathway have not been well addressed.

Objectives

In the present study, we aimed to study GI actions of capsaicin on mesenteric arterioles in normal and colitis mice and to elucidate the underlying mechanisms.

Methods

Vasorelaxation of human submucosal arterioles and the mesenteric arterioles from wide-type (WT) mice, TRPV1^−/− and TRPV4^−/− (KO) mice were measured. The expression and function of TRPV channels in endothelial cells were examined by q-PCR, immunostaining, Ca²⁺ imaging and membrane potential measurements.

Results

Capsaicin dose-dependently induced vasorelaxation of human submucosal arterioles and mouse mesenteric arterioles in vitro and in vivo through endothelium-dependent hyperpolarization (EDH), nitric oxide (NO), and prostacyclin (PGI₂). Using TRPV1 and TRPV4 KO mice, we found that capsaicin-induced vasorelaxation was predominately through TRPV4/EDH, but marginally through TRPV1/NO/PGI₂. Capsaicin induced hyperpolarization through activation of endothelial TRPV4 channels and intermediate-conductance of Ca²⁺-activated K⁺ channels to finally stimulate vasorelaxation. Importantly, capsaicin exerted anti-colitis action by rescuing the impaired ACh-induced vasorelaxation in WT colitis mice but not in TRPV4 KO colitis mice.

Conclusions

Capsaicin increases intestinal mucosal blood perfusion to potentially prevent/treat colitis through a novel TRPV4/EDH-dependent vasorelaxation of submucosal arterioles in health and colitis. This study further supports our previous notion that TRPV4/EDH in mesenteric circulation plays a critical role in the pathogenesis of colitis.

Post-inflammatory Abdominal Pain in Patients with Inflammatory Bowel Disease During Remission: A Comprehensive Review

Patients with inflammatory bowel disease often experience ongoing pain even after achieving mucosal healing (i.e., post-inflammatory pain). Factors related to the brain-gut axis, such as peripheral and central sensitization, altered sympatho-vagal balance, hypothalamic-pituitary-adrenal axis activation, and psychosocial factors, play a significant role in the development of post-inflammatory pain. A comprehensive study investigating the interaction between multiple predisposing factors, including clinical psycho-physiological phenotypes, molecular mechanisms, and multi-omics data, is still needed to fully understand the complex mechanism of post-inflammatory pain. Furthermore, current treatment options are limited and new treatments consistent with the underlying pathophysiology are needed to improve clinical outcomes.

Retardant effect of dihydroartemisinin on ulcerative colitis in a JAK2/STAT3-dependent manner

Dihydroartemisinin (DHA) is a semi-synthetic derivative and the main active metabolite of artemisinin. The purpose of this study was to investigate the effect of DHA on the ulcerative colitis (UC) in both in vivo and in vitro models. Weight, survival rate, colon length, and Disease Activity Index score were used to evaluate the severity of colitis. Reverse transcription quantitative polymerase chain reaction and enzyme-linked immunosorbent assay were used to detect the expressions of cytokines interleukin (IL)-1, IL-1β, IL-4, IL-6, IL-10, IL-12, and tumor necrosis factor-α (TNF-α). The expressions of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3), and the phosphorylation of JAK2 (p-JAK2) and STAT3 (p-STAT3), were measured by western blot analysis. Western blot analysis and immunohistochemistry were used to detect the expressions of tight junction proteins. We found that the weights and colon lengths of mice in dextran sodium sulfate (DSS)+DHA group were significantly lower and longer than those in the DSS group, respectively. Compared with those in the DSS group, the expressions of IL-1β, IL-6, IL-17, and TNF-α in the DSS+DHA and DSS+5-aminosalicylic acid (5-ASA) groups were decreased, while the expressions of IL-4 and IL-10 were significantly upregulated. DHA largely increased the expressions of zonula occludens-1 and occludin. Western blot analysis and/or immunohistochemical staining analysis showed that the expressions of JAK2, STAT3, p-JAK2, and p-STAT3 in DSS+DHA and DSS+5-ASA groups were significantly lower than those in DSS group. DHA has a specific therapeutic effect on UC. The anti-inflammatory mechanism of DHA is related to the blockage of the JAK2/STAT3 signaling pathway. These findings provide evidence that DHA may be a useful drug and is expected to become a promising new treatment for human UC.

Efficient Attenuation of Dextran Sulfate Sodium-Induced Colitis by Oral Administration of 5,6-Dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic Acid in Mice

5,6-dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic acid (5,6-DiHETE) is an eicosapentaenoic acid-derived newly discovered bioactive anti-inflammatory lipid mediator having diverse functions. Here, we assessed the potential of orally administered 5,6-DiHETE in promoting healing of dextran sulfate sodium (DSS)-induced colitis in mice. We measured the plasma concentrations of 5,6-DiHETE in untreated mice before and 0.5, 1, 3, and 6 h after its oral administration (150 or 600 μg/kg) in mice. Mice developed colitis by DSS (2% in drinking water for 4 days), and 5,6-DiHETE (150 or 600 μg/kg/day) was orally administered from day 9 to 14. Next, the faecal hardness and bleeding were assessed, and the dissected colons on day 14 via H&E staining. The plasma concentration of 5,6-DiHETE reached 25.05 or 44.79 ng/mL 0.5 h after the administration of 150 or 600 μg/kg, respectively, followed by a gradual decrease. The half-life of 5,6-DiHETE was estimated to be 1.25-1.63 h. Diarrhoea deteriorated after day 3 and peaked on day 5, followed by a gradual recovery. Histological assessment on day 14 showed DSS-mediated granulocyte infiltration, mucosal erosion, submucosal edema, and cryptal abscesses in mice. Oral administration of 150 or 600 μg/kg/day of 5,6-DiHETE accelerated the recovery from the DSS-induced diarrhoea and significantly ameliorated colon inflammation. The therapeutic effect of 600 μg/kg/day 5,6-DiHETE was slightly stronger than that by 150 μg/kg/day. Our study reveals attenuation of DSS-induced colitis in mice by the oral administration of 5,6-DiHETE dose-dependently, thereby suggesting a therapeutic potential of 5,6-DiHETE for inflammatory bowel disease.

Role of transient receptor potential vanilloid subtype 2 in lower oesophageal sphincter in rat acid reflux oesophagitis

Gastroesophageal reflux disease (GERD) is a common gastrointestinal disorder. In the present study, we investigated TRP vanilloid subfamily member 2 (TRPV2) expression in lower oesophageal sphincter (LES) and its involvement in acid reflux oesophagitis in rats. Expression of TRPV2 and nerve growth factor mRNAs was significantly enhanced in LES of rats with reflux oesophagitis compared with normal rats. TRPV2 was mainly expressed in inhibitory motor neurons, and partly in intrinsic and extrinsic primary afferent neurons, and macrophages in LES of normal and reflux oesophagitis rats. Number of TRPV2-immunopositive nerve fibres was significantly increased, but that of nNOS-, CGRP-, and PGP9.5-nerve fibres was not changed in reflux oesophagitis compared with normal group. Probenecid produced nitric oxide production and relaxation in LES and this response was significantly enhanced in oesophagitis compared with normal group. Probenecid-induced relaxant effect was blocked by a TRPV2 inhibitor, tranilast, and a NOS inhibitor, NG-nitro-l-arginine methyl ester, in reflux oesophagitis rats. Oral administration of tranilast significantly improved body weight loss, oesophageal lesions, and epithelial thickness in oesophagitis model. These results suggest that up-regulation of TRPV2 in inhibitory motor neurons is involved in LES relaxation in oesophagitis model. TRPV2 inhibition might be beneficial for treatment of GERD.

Role of Transient Receptor Potential Vanilloid 4 in Vascular Function

Transient receptor potential vanilloid 4 (TRPV4) channels are widely expressed in systemic tissues and can be activated by many stimuli. TRPV4, a Ca²⁺-permeable cation channel, plays an important role in the vasculature and is implicated in the regulation of cardiovascular homeostasis processes such as blood pressure, vascular remodeling, and pulmonary hypertension and edema. Within the vasculature, TRPV4 channels are expressed in smooth muscle cells, endothelial cells, and perivascular nerves. The activation of endothelial TRPV4 contributes to vasodilation involving nitric oxide, prostacyclin, and endothelial-derived hyperpolarizing factor pathways. TRPV4 activation also can directly cause vascular smooth muscle cell hyperpolarization and vasodilation. In addition, TRPV4 activation can evoke constriction in some specific vascular beds or under some pathological conditions. TRPV4 participates in the control of vascular permeability and vascular damage, particularly in the lung capillary endothelial barrier and lung injury. It also participates in vascular remodeling regulation mainly by controlling vasculogenesis and arteriogenesis. This review examines the role of TRPV4 in vascular function, particularly in vascular dilation and constriction, vascular permeability, vascular remodeling, and vascular damage, along with possible mechanisms, and discusses the possibility of targeting TRPV4 for therapy.

5,6-dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic acid accelerates the healing of colitis by inhibiting transient receptor potential vanilloid 4-mediated signaling

5,6-dihydroxy-8Z,11Z,14Z,17Z-eicosatetraenoic acid (5,6-DiHETE) is an eicosapentaenoic acid-derived lipid metabolite, which we previously detected in inflamed mouse colon. In this study, we investigated the pathophysiological roles of 5,6-DiHETE in murine colitis and its underlying mechanisms of action, focusing on the effects on transient receptor potential vanilloid (TRPV) channel activity. Oral administration of dextran sodium sulfate (DSS, 2%, for 4 days) caused colon inflammation, which peaked on day 7 and gradually declined by day 18. 5,6-DiHETE concentration in colon tissue was significantly increased during the healing phase of colitis (days 9 to 18). In vitro study showed that pretreatment with 5,6-DiHETE (0.1-1 μM, 30 minutes) significantly inhibited endothelial barrier disruption induced by a TRPV4 agonist (GSK1016790A, 50 nM). Intracellular Ca²⁺ imaging also showed that pretreatment with 5,6-DiHETE (1 μM, 10 minutes) reduced GSK1016790A-induced intracellular Ca²⁺ increase in HEK293T cells overexpressing TRPV4. In vivo, intraperitoneal administration of 5,6-DiHETE (50 µg kg^-1  day^-1 ) during the healing phase accelerated the recovery from DSS-induced colitis. Pathological studies showed that the administration of 5,6-DiHETE inhibited edema formation and leukocyte infiltration in inflamed colon tissue. In conclusion, we identified 5,6-DiHETE as a novel endogenous TRPV4 antagonist, and we also demonstrated that its administration promotes the healing of colitis by inhibiting inflammatory responses.

A venous-specific purinergic signaling cascade initiated by Pannexin 1 regulates TNFα-induced increases in endothelial permeability

The endothelial cell barrier regulates the passage of fluid between the bloodstream and underlying tissues, and barrier function impairment exacerbates the severity of inflammatory insults. To understand how inflammation alters vessel permeability, we studied the effects of the proinflammatory cytokine TNFα on transendothelial permeability and electrophysiology in ex vivo murine veins and arteries. We found that TNFα specifically decreased the barrier function of venous endothelium without affecting that of arterial endothelium. On the basis of RNA expression profiling and protein analysis, we found that claudin-11 (CLDN11) was the predominant claudin in venous endothelial cells and that there was little, if any, CLDN11 in arterial endothelial cells. Consistent with a difference in claudin composition, TNFα increased the permselectivity of Cl^- over Na⁺ in venous but not arterial endothelium. The vein-specific effects of TNFα also required the activation of Pannexin 1 (Panx1) channels and the CD39-mediated hydrolysis of ATP to adenosine, which subsequently stimulated A_2A adenosine receptors. Moreover, the increase in vein permeability required the activation of the Ca²⁺ channel TRPV4 downstream of Panx1 activation. Panx1-deficient mice resisted the pathologic effects of sepsis induced by cecal ligation and puncture on life span and lung vascular permeability. These data provide a targetable pathway with the potential to promote vein barrier function and prevent the deleterious effects of vascular leak in response to inflammation.

TRPV4 channel activation induces the transition of venous and arterial endothelial cells toward a pro-inflammatory phenotype

The Transient Receptor Potential Vanilloid 4 (TRPV4) of endothelial cells contributes to many important functions including the regulation of Ca2+ homeostasis, cell volume, endothelial barrier permeability, and smooth muscle tone. However, its role in the transition of endothelial cells toward a pro-inflammatory phenotype has not been studied so far. Using both arterial and venous endothelial cells, we first show that the pharmacological activation of TRPV4 channels with GSK1016790A, a potent TRPV4 agonist, triggers robust and sustained Ca2+ increases, which are blocked by both TRPV4 antagonists HC067047 and RN9893. TRPV4 activation also triggers the actin cytoskeleton and adherens junction (VE-Cadherin) rearrangement in both arterial and venous endothelial cells and leads to rapid decreases of trans-endothelial electrical resistance. In addition to its effect on endothelial barrier integrity, TRPV4 activation selectively increases ICAM-1 surface expression in arterial and venous endothelial cells, due to the stimulation of ICAM-1 gene expression through the NF-κB transcription factor. TRPV4 channel activation also induced apoptosis of venous and arterial endothelial cells, while TRPV4 blockade reduced apoptosis, even in the absence of TRPV4 activation. As altered barrier integrity, increased adhesion molecule expression and apoptosis are hallmarks of the pro-inflammatory state of endothelial cells, our results indicate that TRPV4 channel activity can induce the transition of both venous and arterial endothelial cells toward a pro-inflammatory phenotype.

Protective Effect of TRPM8 against Indomethacin-Induced Small Intestinal Injury via the Release of Calcitonin Gene-Related Peptide in Mice

Transient receptor potential melastatin 8 (TRPM8) is a non-selective cation channel activated by mild cooling and chemical agents including menthol. Nonsteroidal anti-inflammatory drugs have antipyretic, analgesic effects, and they can cause stomach and small intestinal injury. The current study investigated the role of TRPM8 in the pathogenesis of indomethacin-induced small intestinal injury. In male TRPM8-deficient (TRPM8KO) and wild-type (WT) mice, intestinal injury was induced via the subcutaneous administration of indomethacin. In addition, the effect of WS-12, a specific TRPM8 agonist, was examined in TRPM8KO and WT mice with indomethacin-induced intestinal injury. TRPM8KO mice had a significantly higher intestinal ulcerogenic response to indomethacin than WT mice. The repeated administration of WS-12 significantly attenuated the severity of intestinal injury in WT mice. However, this response was abrogated in TRPM8KO mice. Furthermore, in TRPM8-enhanced green fluorescent protein (EGFP) transgenic mice, which express EGFP under the direction of TRPM8 promoter, the EGFP signals in the indomethacin-treated intestinal mucosa were upregulated. Further, the EGFP signals were commonly found in calcitonin gene-related peptide (CGRP)-positive sensory afferent neurons and partly colocalized with substance P (SP)-positive neurons in the small intestine. The intestinal CGRP-positive neurons were significantly upregulated after the administration of indomethacin in WT mice. Nevertheless, this response was abrogated in TRPM8KO mice. In contrast, indomethacin increased the expression of intestinal SP-positive neurons in not only WT mice but also TRPM8KO mice. Thus, TRPM8 has a protective effect against indomethacin-induced small intestinal injury. This response may be mediated by the upregulation of CGRP, rather than SP.

Fibrinogen/AKT/Microfilament Axis Promotes Colitis by Enhancing Vascular Permeability

BACKGROUND & AIMS

Increased vascular permeability (VP) has been indicated to play an important role in the pathogenesis of inflammatory bowel disease (IBD). However, the pathological causes of increased intestinal VP in IBD remain largely unknown.

METHOD

Fibrinogen level was measured in dextran sulphate sodium (DSS)-induced colitis and patients with ulcerative colitis. Gly-Pro-Arg-Pro acetate (GPRP), an Fg inhibitor, was used to detect the effect of Fg inhibition on the pathogenesis of DSS-induced colitis, as indicated by tissue damage, cytokine release and inflammatory cell infiltration. Miles assay was used to detect vascular permeability.

RESULTS

Through tandem mass tag-based quantitative proteomics, fibrinogen (Fg) was found to be upregulated in the colon of DSS-treated mice, which was consistent with increased Fg level in colon sample of patients with ulcerative colitis. Gly-Pro-Arg-Pro acetate (GPRP), an Fg inhibitor, significantly alleviated DSS-induced colitis as indicated by improvement of body weight loss and mortality. GPRP decreased colonic inflammation and VP in DSS-treated mice. In vivo, Fg enhanced VP as indicated by Miles assay, which was significantly inhibited by GRPR, AKT (serine/threonine kinase 1) inhibitors and low doses of Jasplakinolide which induced actin polymerization, while was dramatically enhanced by Cytochalasin D (an actin polymerization inhibitor). Moreover, activation of AKT was found in vessels of DSS-treated mice. In vitro, Fg induced activation of AKT and depolymerization of microfilament and promoted cell-to-cell disaggregation. Furthermore, inhibition of AKT decreased Fg-induced microfilament depolymerization.

CONCLUSIONS

Our findings highlight the importance of Fg in regulating colitis by modulation of VP via activating AKT and subsequent depolymerization of microfilament and suggest Fg as an attractive target for anti-colitis treatment.

TRPV4-Mediated Regulation of the Blood Brain Barrier Is Abolished During Inflammation

Blood-brain barrier (BBB) dysfunction is critically involved in determining the extent of several central nervous systems (CNS) pathologies and here in particular neuroinflammatory conditions. Inhibiting BBB breakdown could reduce the level of vasogenic edema and the number of immune cells invading the CNS, thereby counteracting neuronal injury. Transient receptor potential (TRP) channels have an important role as environmental sensors and constitute attractive therapeutic targets that are involved in calcium homeostasis during pathologies of the CNS. Transient receptor potential vanilloid 4 (TRPV4) is a calcium permeable, non-selective cation channel highly expressed in endothelial cells. As it is involved in the regulation of the blood brain barrier permeability and consequently cerebral edema formation, we anticipated a regulatory role of TRPV4 in CNS inflammation and subsequent neuronal damage. Here, we detected an increase in transendothelial resistance in mouse brain microvascular endothelial cells (MbMECs) after treatment with a selective TRPV4 inhibitor. However, this effect was abolished after the addition of IFNγ and TNFα indicating that inflammatory conditions override TRPV4-mediated permeability. Accordingly, we did not observe a protection of Trpv4-deficient mice when compared to wildtype controls in a preclinical model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), and no differences in infarct sizes following transient middle cerebral artery occlusion (tMCAO), the experimental stroke model, which leads to an acute postischemic inflammatory response. Furthermore, Evans Blue injections did not show differences in alterations of the blood brain barrier (BBB) permeability between genotypes in both animal models. Together, TRPV4 does not regulate brain microvascular endothelial permeability under inflammation.

Transient receptor potential vanilloid 4 channels as therapeutic targets in diabetes and diabetes-related complications

With an estimated 425 million diabetes patients worldwide in 2019, type 2 diabetes has reached a pandemic proportion and represents a major unmet medical need. A key determinant of the development and progression of type 2 diabetes is pancreatic -cell dysfunction, including the loss of cell mass, the impairment of insulin biosynthesis and inadequate exocytosis. Recent studies have shown that transient receptor potential vanilloid 4 (TRPV4), a Ca2+ -permeable non-selective cation channel, is involved in -cell replication, insulin production and secretion. TRPV4 agonists have insulinotropic activity in pancreatic -cell lines, but the prolonged activation of TRPV4 leads to -cell dysfunction and death. In addition, TRPV4 is involved in a wide variety of pathophysiological activities, and has been reported to play an important role in diabetes-related complications, such as obesity, cardiovascular diseases, diabetic retinopathy, nephropathy and neuropathy. In a rodent type 2 diabetes model, Trpv4 agonists promote vasodilation and improve cardiovascular function, whereas Trpv4 antagonists reduce high-fat diet-induced obesity, insulin resistance, diabetic nephropathy, retinopathy and neuropathy. These findings raise interest in using TRPV4 as a therapeutic target for type 2 diabetes. In this review, we intend to summarize the latest findings regarding the role of TRPV4 in diabetes as well as diabetes-related conditions, and to evaluate its potential as a therapeutic target for diabetes and diabetes-related diseases.

TRPV Subfamily (TRPV2, TRPV3, TRPV4, TRPV5, and TRPV6) Gene and Protein Expression in Patients with Ulcerative Colitis

Introduction

TRPVs are a group of receptors with a channel activity predominantly permeable to Ca²⁺. This subfamily is involved in the development of gastrointestinal diseases such as ulcerative colitis (UC). The aim of the study was to characterize the gene and protein expression of the TRPV subfamily in UC patients and controls.

Methods

We determined by quantitative PCR the gene expression of TRPV2, TRPV3, TRPV4, TRPV5, and TRPV6 in 45 UC patients (29 active UC and 16 remission UC) and 26 noninflamed controls. Protein expression was evaluated in 5 μm thick sections of formalin-fixed, paraffin-embedded tissue from 5 customized severe active UC patients and 5 control surgical specimens.

Results

TRPV2 gene expression was increased in the control group compared with active UC and remission patients (P = 0.002 and P = 0.05, respectively). TRPV3 gene expression was significantly higher in controls than in active UC patients (P = 0.002). The gene expression of TRPV4 was significantly higher in colonic tissue from patients with remission UC compared with active UC patients (P = 0.05) and controls (P = 0.005). TRPV5 had significantly higher mRNA levels in a control group compared with active UC patients (P = 0.02). The gene expression of TRPV6 was significantly higher in the colonic tissue from patients with active UC compared with the control group (P = 0.05). The protein expression of TRPV2 was upregulated in the mucosa and submucosa from the controls compared with the UC patients (P ≤ 0.003). The protein expression of TRPV3 and TRPV4 was upregulated in all intestinal layers from the controls compared with the UC patients (P < 0.001). TRPV5 was upregulated in the submucosa and serosa from the controls vs. UC patients (P < 0.001). TRPV6 was upregulated in all intestinal layers from the UC patients vs. controls (P ≤ 0.001).

Conclusion

The TRPV subfamily clearly showed a differential expression in the UC patients compared with the controls, suggesting their role in the pathophysiology of UC.

Leukotriene B4 Receptor Type 2 Accelerates the Healing of Intestinal Lesions by Promoting Epithelial Cell Proliferation

Leukotriene B₄ receptor type 2 (BLT2) is a low-affinity leukotriene B₄ receptor that is highly expressed in intestinal epithelial cells. Previous studies demonstrated the protective role of BLT2 in experimentally induced colitis. However, its role in intestinal lesion repair is not fully understood. We investigated the role of BLT2 in the healing of indomethacin-induced intestinal lesions in mice. There was no significant different between wild-type (WT) and BLT2-deficient (BLT2KO) mice in terms of the development of indomethacin-induced intestinal lesions. However, healing of these lesions was significantly impaired in BLT2KO mice compared with WT mice. In contrast, transgenic mice with intestinal epithelium-specific BLT2 overexpression presented with superior ileal lesion healing relative to WT mice. An immunohistochemical study showed that the number of Ki-67-proliferative cells was markedly increased during the healing of intestinal lesions in WT mice but significantly attenuated in BLT2KO mice. Exposure of cultured mouse intestinal epithelial cells to CAY10583, a BLT2 agonist, promoted wound healing and cell proliferation in a concentration-dependent manner. Nevertheless, these responses were abolished under serum-free conditions. The CAY10583-induced proliferative effect was also negated by Go6983, a protein kinase C (PKC) inhibitor, U-73122, a phospholipase C (PLC) inhibitor, LY255283, a BLT2 antagonist, and pertussis toxin that inhibits G protein-coupled receptor signaling via G_i/o proteins. Thus, BLT2 plays an important role in intestinal wound repair. Moreover, this effect is mediated by the promotion of epithelial cell proliferation via the G_i/o protein-dependent and PLC/PKC signaling pathways. The BLT2 agonists are potential therapeutic agents for the treatment of intestinal lesions. SIGNIFICANCE STATEMENT: The healing of indomethacin-induced Crohn's disease-like intestinal lesions was impaired in mice deficient in low-affinity leukotriene B₄ receptor type 2 (BLT2). They presented with reduced epithelial cell proliferation during the healing. In contrast, healing was promoted in mice overexpressing intestinal epithelial BLT2. In cultured intestinal epithelial cells, the BLT2 agonist CAY10583 substantially accelerated wound repair by enhancing cell proliferation rather than migration. Thus, BLT2 plays an important role in the intestinal lesions via acceleration of epithelial cell proliferation.

Transient Receptor Potential Channels and Inflammatory Bowel Disease

The transient receptor potential (TRP) cation channels are present in abundance across the gastrointestinal (GI) tract, serving as detectors for a variety of stimuli and secondary transducers for G-protein coupled receptors. The activation of TRP channels triggers neurogenic inflammation with related neuropeptides and initiates immune reactions by extra-neuronally regulating immune cells, contributing to the GI homeostasis. However, under pathological conditions, such as inflammatory bowel disease (IBD), TRP channels are involved in intestinal inflammation. An increasing number of human and animal studies have indicated that TRP channels are correlated to the visceral hypersensitivity (VHS) and immune pathogenesis in IBD, leading to an exacerbation or amelioration of the VHS or intestinal inflammation. Thus, TRP channels are a promising target for novel therapeutic methods for IBD. In this review, we comprehensively summarize the functions of TRP channels, especially their potential roles in immunity and IBD. Additionally, we discuss the contradictory findings of prior studies and offer new insights with regard to future research.

Role of transient receptor potential vanilloid subtype 4 in the regulation of azoymethane/dextran sulphate sodium-induced colitis-associated cancer in mice

Ca²⁺-permeable ion channels, such as transient receptor channels, are one of the potential therapeutic targets in cancer. Transient receptor potential vanilloid subtype 4 (TRPV4) is a nonselective cation channel associated with cancer progression. This study investigates the roles of TRPV4 in the pathogenesis of colitis-associated cancer (CAC) in mice. The role of TRPV4 was examined in azoxymethane (AOM)/dextran sulphate sodium (DSS)-induced murine CAC model. The formation of colon tumours induced by AOM/DSS treatment was significantly attenuated in TRPV4-deficient mice (TRPV4KO). TRPV4 was co-localised with markers of angiogenesis and macrophages. AOM/DSS treatment upregulated the expression of CD105, vascular endothelial growth factor receptor 2, and TRPV4 in wildtype, but the upregulation of CD105 was significantly attenuated in TRPV4KO. Bone marrow chimera experiments indicated that TRPV4, expressed in both vascular endothelial cells and bone marrow-derived macrophages, played a significant role in colitis-associated tumorigenesis. There was no significant difference in the population of hematopoietic cells, neutrophils, and monocytes between untreated and AOM/DSS-treated WT and TRPV4KO on flow cytometric analysis. TRPV4 activation by a selective agonist induced TNF-α and CXCL2 release in macrophages. Furthermore, TRPV4 activation enhanced the proliferation of human umbilical vein endothelial cells. These results suggest that TRPV4 expressed in neovascular endothelial cells and bone marrow-derived macrophages contributes to the progression of CAC in mice.

Beneficial effects of nutritional supplements on intestinal epithelial barrier functions in experimental colitis models in vivo

Acute and chronic colitis affect a huge proportion of the population world-wide. The etiology of colitis cases can be manifold, and diet can significantly affect onset and outcome of colitis. While many forms of acute colitis are easily treatable, chronic forms of colitis such as ulcerative colitis and Crohn's disease (summarized as inflammatory bowel diseases) are multifactorial with poorly understood pathogenesis. Inflammatory bowel diseases are characterized by exacerbated immune responses causing epithelial dysfunction and bacterial translocation. There is no cure and therapies aim at reducing inflammation and restoring intestinal barrier function. Unfortunately, most drugs can have severe side effects. Changes in diet and inclusion of nutritional supplements have been extensively studied in cell culture and animal models, and some supplements have shown promising results in clinical studies. Most of these nutritional supplements including vitamins, fatty acids and phytochemicals reduce oxidative stress and inflammation and have shown beneficial effects during experimental colitis in rodents induced by dextran sulphate sodium or 2,4,6-trinitrobenzene sulfonic acid, which remain the gold standard in pre-clinical colitis research. Here, we summarize the mechanisms through which such nutritional supplements contribute to epithelial barrier stabilization.

Autoinflammatory characteristics and short-term effects of delivering high-dose steroids to the surface of the intact endolymphatic sac and incus in refractory Ménière's disease

Objective

To investigate immune-related genetic background in intractable Meniere’s disease (MD) and the immediate results of a novel therapy by delivering steroids to the surface of the intact endolymphatic sac (ES) and incus in a sustainable manner.

Case report and methods

Candidate genes involved in immune regulation were sequenced using a next-generation sequencing method in a patient with intractable MD. Mutations were confirmed using the Sanger sequencing method. The ES was exposed, and gelatin sponge particles were immersed in high-dose methylprednisolone solution and placed onto the surface of ES. “L”-shaped gelatin sponge strips were immersed in dexamethasone solution and served as a guiding device for the steroids by touching the incus and gelatin sponge particles on the surface of the ES. Gelatin sponge particles immersed in dexamethasone solution were placed around the gelatin sponge strips and sealed using fibrin glue.

Results

Autoinflammation in the refractory MD case was indicated by genotype, including novel heterozygous mutations of PRF1, UNC13D, SLC29A3, ITCH, and JAK3, as well as phenotype. The vertigo was fully relieved immediately after operation. Tinnitus and aural fullness were resolved 3 weeks after operation, whereas hearing improved in 2 mon postoperation. No recurrence was noted during the 5-monfollow-up, and the final MRI supported the novel therapeutic hypothesis.

Conclusion

Autoinflammation was involved in a refractory MD. This novel therapy, which involves the delivery of steroids to the surface of the intact ES and incus, is effective in relieving vertigo and tinnitus and improves hearing function of refractory MD.

TRPV4 inhibition prevents increased water diffusion and blood-retina barrier breakdown in the retina of streptozotocin-induced diabetic mice

A better understanding of the molecular and cellular mechanisms involved in retinal hydro-mineral homeostasis imbalance during diabetic macular edema (DME) is needed to gain insights into retinal (patho-)physiology that will help elaborate innovative therapies with lower health care costs. Transient receptor potential cation channel subfamily vanilloid member 4 (TRPV4) plays an intricate role in homeostatic processes that needs to be deciphered in normal and diabetic retina. Based on previous findings showing that TRPV4 antagonists resolve blood-retina barrier (BRB) breakdown in diabetic rats, we evaluated whether TRPV4 channel inhibition prevents and reverts retinal edema in streptozotocin(STZ)-induced diabetic mice. We assessed retinal edema using common metrics, including retinal morphology/thickness (histology) and BRB integrity (albumin-associated tracer), and also by quantifying water mobility through apparent diffusion coefficient (ADC) measures. ADC was measured by diffusion-weighted magnetic resonance imaging (DW-MRI), acquired ex vivo at 4 weeks after STZ injection in diabetes and control groups. DWI images were also used to assess retinal thickness. TRPV4 was genetically ablated or pharmacologically inhibited as follows: left eyes were used as vehicle control and right eyes were intravitreally injected with TRPV4-selective antagonist GSK2193874, 24 h before the end of the 4 weeks of diabetes. Histological data show that retinal thickness was similar in nondiabetic and diabetic wt groups but increased in diabetic Trpv4^-/- mice. In contrast, DWI shows retinal thinning in diabetic wt mice that was absent in diabetic Trpv4^-/- mice. Disorganized outer nuclear layer was observed in diabetic wt but not in diabetic Trpv4^-/- retinas. We further demonstrate increased water diffusion, increased distances between photoreceptor nuclei, reduced nuclear area in all nuclear layers, and BRB hyperpermeability, in diabetic wt mice, effects that were absent in diabetic Trpv4^-/- mice. Retinas of diabetic mice treated with PBS showed increased water diffusion that was not normalized by GSK2193874. ADC maps in nondiabetic Trpv4^-/- mouse retinas showed restricted diffusion. Our data provide evidence that water diffusion is increased in diabetic mouse retinas and that TRPV4 function contributes to retinal hydro-mineral homeostasis and structure under control conditions, and to the development of BRB breakdown and increased water diffusion in the retina under diabetes conditions. A single intravitreous injection of TRPV4 antagonist is however not sufficient to revert these alterations in diabetic mouse retinas.

Transient receptor potential vanilloid 4 mediates sour taste sensing via type III taste cell differentiation

Taste buds are comprised of taste cells, which are classified into types I to IV. Transient receptor potential (TRP) channels play a significant role in taste perception. TRP vanilloid 4 (TRPV4) is a non-selective cation channel that responds to mechanical, thermal, and chemical stimuli. The present study aimed to define the function and expression of TRPV4 in taste buds using Trpv4-deficient mice. In circumvallate papillae, TRPV4 colocalized with a type IV cell and epithelial cell marker but not type I, II, or III markers. Behavioural studies showed that Trpv4 deficiency reduced sensitivity to sourness but not to sweet, umami, salty, and bitter tastes. Trpv4 deficiency significantly reduced the expression of type III cells compared with that in wild type (WT) mice in vivo and in taste bud organoid experiments. Trpv4 deficiency also significantly reduced Ki67-positive cells and β-catenin expression compared with those in WT circumvallate papillae. Together, the present results suggest that TRPV4 contributes to sour taste sensing by regulating type III taste cell differentiation in mice.

TRPV4: a Sensor for Homeostasis and Pathological Events in the CNS

Transient receptor potential vanilloid type 4 (TRPV4) was originally described as a calcium-permeable nonselective cation channel. TRPV4 is now recognized as a polymodal ionotropic receptor: it is a broadly expressed, nonselective cation channel (permeable to calcium, potassium, magnesium, and sodium) that plays an important role in a multitude of physiological processes. TRPV4 is involved in maintaining homeostasis, serves as an osmosensor and thermosensor, can be activated directly by endogenous or exogenous chemical stimuli, and can be activated or sensitized indirectly via intracellular signaling pathways. Additionally, TRPV4 is upregulated in a variety of pathological conditions. In this review, we focus on the role of TRPV4 in mediating homeostasis and pathological events in the central nervous system (CNS). This review is composed of three parts. Section 1 describes the role of TRPV4 in maintaining homeostatic processes, including the volume of body water, ionic concentrations, volume, and the temperature. Section 2 describes the effects of activation and inhibition of TRPV4 in the CNS. Section 3 focuses on the role of TRPV4 during pathological events in CNS.

Transient receptor potential vanilloid 4 channel regulates vascular endothelial permeability during colonic inflammation in dextran sulphate sodium-induced murine colitis

BACKGROUND AND PURPOSE

The transient receptor potential vanilloid 4 (TRPV4) channel is a non-selective cation channel involved in physical sensing in various tissue types. The present study aimed to elucidate the function and expression of TRPV4 channels in colonic vascular endothelial cells during dextran sulphate sodium (DSS)-induced colitis.

EXPERIMENTAL APPROACH

The role of TRPV4 channels in the progression of colonic inflammation was examined in a murine DSS-induced colitis model using immunohistochemical analysis, Western blotting and Evans blue dye extrusion assay.

KEY RESULTS

DSS-induced colitis was significantly attenuated in TRPV4-deficient (TRPV4 KO) as compared to wild-type mice. Repeated intrarectal administration of GSK1016790A, a TRPV4 agonist, exacerbated the severity of DSS-induced colitis. Bone marrow transfer experiments demonstrated the important role of TRPV4 in non-haematopoietic cells for DSS-induced colitis. DSS treatment up-regulated TRPV4 expression in the vascular endothelia of colonic mucosa and submucosa. DSS treatment increased vascular permeability, which was abolished in TRPV4 KO mice. This DSS-induced increase in vascular permeability was further enhanced by i.v. administration of GSK1016790A, and this effect was abolished by the TRPV4 antagonist RN1734. TRPV4 was co-localized with vascular endothelial (VE)-cadherin, and VE-cadherin expression was decreased by repeated i.v. administration of GSK1016790A during colitis. Furthermore, GSK106790A decreased VE-cadherin expression in mouse aortic endothelial cells exposed to TNF-α.

CONCLUSION AND IMPLICATIONS

These findings indicate that an up-regulation of TRPV4 channels in vascular endothelial cells contributes to the progression of colonic inflammation by increasing vascular permeability. Thus, TRPV4 is an attractive target for the treatment of inflammatory bowel diseases.