Activation of TRPV1 mediates thymic stromal lymphopoietin release via the Ca2+/NFAT pathway in airway epithelial cells

The extract from Quzhou Aurantii Fructus attenuates cough variant asthma through inhibiting the TRPV1/Ca2+/NFAT/TSLP pathway and ferroptosis via TRPV1 mediation in ovalbumin-induced mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cough variant asthma (CVA), a prevalent chronic inflammatory disease, is the most common cause of chronic cough. Over the years, the aqueous extract of Quzhou Aurantii Fructus (QAFA) has been widely used to treat respiratory diseases, particularly cough.

AIM OF THE STUDY

This study aimed to elucidate the therapeutic effect of QAFA on allergen-induced CVA, providing deep insights into the underlying mechanisms.

MATERIALS AND METHODS

Ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) was employed to characterize the compositions, while UPLC was used to quantify the contents of its major components in QAFA. CVA model was established via sensitization and atomization with ovalbumin (OVA), and received 600 and 1200 mg/kg of QAFA via intragastric gavage. Cough response was assessed by stimulation with capsaicin (CAP). Then, airway hyperresponsiveness (AHR), ELISA, western blotting, RT-qPCR, and histological analyses, were applied to assess pulmonary function, pathological changes, and investigate mechanisms in CVA mice following QAFA treatment through the TRPV1/Ca2+-dependent NFAT-induced expression of TSLP and ferroptosis. Additionally, the effects and mechanisms of QAFA were validated using IL-4, CAP for stimulation, capsazepine (CPZ) for inhibition, and TRPV1 siRNA transfection in cells.

RESULTS

Chemical analysis revealed that QAFA primarily contained sixteen compounds, with four main components including narirutin, naringin, hesperidin, and neohesperidin. In vivo, QAFA treatment alleviated cough and AHR, while concurrently reducing airway inflammation and mucus secretion in CVA mice. These effects were achieved by suppressing the TRPV1/NFAT/TSLP pathway and modulating the expression of ferroptosis-related proteins. In vitro, siTRPV1-transfected BEAS-2B cells demonstrated the involvement of the TRPV1 channel in IL-4-mediated Ca2+ influxes, ferroptosis, and regulation of TSLP production. QAFA and CPZ suppressed IL-4-induced TSLP production via the TRPV1/NFAT pathway and regulated the levels of ferroptosis-related proteins, while CAP counteracted the effect of QAFA on TSLP production in BEAS-2B cells. Furthermore, QAFA reduced IL-4 or CAP induced Ca2+ influx and IL-4 induced ferroptosis through TRPV1 mediation.

CONCLUSIONS

This study demonstrated that QAFA improved pulmonary function and alleviated asthmatic inflammatory response in treating CVA probably through suppressing the TRPV1/Ca2+/NFAT/TSLP pathway and ferroptosis via TRPV1 mediation.

Bleomycin triggers chronic mechanical nociception by activating TRPV1 and glial reaction-mediated neuroinflammation via TSLP/TSLPR/pSTAT5 signals

Chronic pain is a universal public health problem with nearly one third of global human involved, which causes significant distressing personal burden. After painful stimulus, neurobiological changes occur not only in peripheral nervous system but also in central nervous system where somatosensory cortex is important for nociception. Being an ion channel, transient receptor potential vanilloid 1 (TRPV1) act as an inflammatory detector in the brain. Thymic stromal lymphopoietin (TSLP) is a potent neuroinflammation mediator after nerve injury. Bleomycin is applied to treat dermatologic diseases, and its administration elicits local painful sensation. However, whether bleomycin administration can cause chronic pain remains unknown. In the present study, we aimed to investigate how mice develop chronic pain after receiving repeated bleomycin administration. In addition, the relevant neurobiological brain changes after noxious stimuli were clarified. C57BL/6 mice aged five- to six-weeks were randomly classified into two group, PBS (normal) group and bleomycin group which bleomycin was intradermally administered to back five times a week over a three-week period. Calibrated forceps testing was used to measure mouse pain threshold. Western blots were used to assess neuroinflammatory response; immunofluorescence assay was used to measure the status of neuron apoptosis, glial reaction, and neuro-glial communication. Bleomycin administration induced mechanical nociception and activated both TRPV1 and TSLP/TSLPR/pSTAT5 signals in mouse somatosensory cortex. Through these pathways, bleomycin not only activates glial reaction but also causes neuronal apoptosis. TRPV1 and TSLP/TSLPR/pSTAT5 signaling had co-labeled each other by immunofluorescence assay. Taken together, our study provides a new chronic pain model by repeated intradermal bleomycin injection by activating TRPV1 and glial reaction-mediated neuroinflammation via TSLP/TSLPR/pSTAT5 signals.

Development and dysfunction of structural cells in eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a disorder characterized by dysfunction and chronic local inflammation of the esophagus. The incidence and prevalence of EoE are increasing worldwide. The mechanisms responsible are poorly understood, and effective treatment options are limited. From the lumen outward, the esophagus comprises stratified squamous epithelium, lamina propria, and muscle. The tissue-specific nature of EoE strongly suggests that structural cells in the esophagus are involved in the EoE diathesis. Epithelial basal cell hyperplasia and dilated intercellular spaces are cardinal features of EoE. Some patients with EoE develop lamina propria fibrosis, strictures, or esophageal muscle dysmotility. Clinical symptoms of EoE are only weakly correlated with peak eosinophil count, implying that other cell types contribute to EoE pathogenesis. Epithelial, endothelial, muscle, and fibroblast cells can each initiate inflammation and repair, regulate tissue resident immune cells, recruit peripheral leukocytes, and tailor adaptive immune cell responses. A better understanding of how structural cells maintain tissue homeostasis, respond to cell-intrinsic and cell-extrinsic stressors, and exacerbate and/or resolve inflammatory responses in the esophagus is needed. This knowledge will facilitate the development of more efficacious treatment strategies for EoE that can restore homeostasis of both hematopoietic and structural elements in the esophagus.

Role of TRPV1 and TRPA1 in TSLP production in nasal epithelial cells

BACKGROUND

TRP protein is sensitive to external temperature changes, but its pathogenic mechanism in the upper airway mucosa is still unclear.

OBJECTIVE

To investigate the mechanism of TRPV1and TRPA1 in regulating the secretion of inflammatory factors in nasal epithelial cells.

METHODS

The expression of TRPV1 and TRPA1 in nasal mucosal epithelial cells was investigated using immunofluorescence assays. Epithelial cells were stimulated with TRPV1 and TRPA1 agonists and antagonists, and changes in Ca2+ release and inflammatory factor secretion in epithelial cells were detected. TSLP secretion stimulated with the calcium chelating agent EGTA was evaluated. The transcription factor NFAT was observed by immunofluorescence staining.

RESULTS

TRPV1 and TRPA1 expression was detected in nasal epithelial cells, and Ca2+ influx was increased after stimulation with agonists. After the activation of TRPV1 and TRPA1, the gene expression of TSLP, IL-25, and IL-33 and the protein expression levels of TSLP and IL-33 were increased, and only TSLP could be inhibited by antagonists and siRNAs. After administration of EGTA, the secretion of TSLP was inhibited significantly, and the expression of the transcription factor NFAT in the nucleus was observed after activation of the TRPV1 and TRPA1 proteins in epithelial cells.

CONCLUSION

Activation of TRPV1 and TRPA1 on nasal epithelial cells stimulates the generation of TSLP through the Ca2+/NFAT pathway. It also induces upregulation of IL-25 and IL-33 gene expression levels and increased levels of IL-33 protein, leading to the development of airway inflammation.

Multifactorial Causes and Consequences of TLSP Production, Function, and Release in the Asthmatic Airway

Disruption of the airway epithelium triggers a defensive immune response that begins with the production and release of alarmin cytokines. These epithelial-derived alarmin cytokines, including thymic stromal lymphopoietin (TSLP), are produced in response to aeroallergens, viruses, and toxic inhalants. An alarmin response disproportionate to the inhaled trigger can exacerbate airway diseases such as asthma. Allergens inhaled into previously sensitized airways are known to drive a T2 inflammatory response through the polarization of T cells by dendritic cells mediated by TSLP. Harmful compounds found within air pollution, microbes, and viruses are also triggers causing airway epithelial cell release of TSLP in asthmatic airways. The release of TSLP leads to the development of inflammation which, when unchecked, can result in asthma exacerbations. Genetic and inheritable factors can contribute to the variable expression of TSLP and the risk and severity of asthma. This paper will review the various triggers and consequences of TSLP release in asthmatic airways.

Heme oxygenase-1 alleviates allergic airway inflammation by suppressing NF-κB-mediated pyroptosis of bronchial epithelial cells

Allergic asthma development and pathogenesis are influenced by airway epithelial cells in response to allergens. Heme oxygenase-1 (HO-1), an inducible enzyme responsible for the breakdown of heme, has been considered an appealing target for the treatment of chronic inflammatory diseases. Herein, we report that alleviation of allergic airway inflammation by HO-1-mediated suppression of pyroptosis in airway epithelial cells (AECs). Using house dust mite (HDM)-induced asthma models of mice, we found increased gasdermin D (GSDMD) in the airway epithelium. In vivo administration of disulfiram, a specific inhibitor of pore formation by GSDMD, decreased thymic stromal lymphopoietin (TSLP) release, T helper type 2 immune response, alleviated airway inflammation, and reduced airway hyperresponsiveness (AHR). HO-1 induction by hemin administration reversed these phenotypes. In vitro studies revealed that HO-1 restrained GSDMD-mediated pyroptosis and cytokine TSLP release in AECs by binding Nuclear Factor-Kappa B (NF-κB) p65 RHD domain and thus controlling NF-κB-dependent pyroptosis. These data provide new therapeutic indications for purposing HO-1 to counteract inflammation, which contributes to allergic inflammation control.

Total alkaloids of Fritillaria unibracteata var. wabuensis bulbus ameliorate chronic asthma via the TRPV1/Ca2+/NFAT pathway

BACKGROUND

Asthma is a chronic inflammatory disease that is challenging to treat. Fritillaria unibracteata var. wabuensis (FUW) is the plant origin for the famous Chinese antitussive medicine Fritillaria Cirrhosae Bulbus. The total alkaloids of Fritillaria unibracteata var. wabuensis bulbus (TAs-FUW) have anti-inflammatory properties and may be used to treat asthma.

PURPOSE

To explore whether TAs-FUW have bioactivity against airway inflammation and a therapeutic effect on chronic asthma.

METHODS

The alkaloids were extracted via ultrasonication in a cryogenic chloroform-methanol solution after ammonium-hydroxide percolation of the bulbus. UPLC-Q-TOF/MS was used to characterize the composition of TAs-FUW. An ovalbumin (OVA)-induced asthmatic mouse model was established. We used whole-body plethysmography, ELISA, western blotting, RT-qPCR, and histological analyses to assess the pulmonary pathological changes in these mice after TAs-FUW treatment. Additionally, TNF-α/IL-4-induced inflammation in BEAS-2B cells was used as an in vitro model, whereby the effects of various doses of TAs-FUW on the TRPV1/Ca²⁺-dependent NFAT-induced expression of TSLP were assessed. Stimulation and inhibition of TRPV1 receptors by capsaicin (CAP) and capsazepine (CPZ), respectively, were used to validate the effect of TAs-FUW.

RESULTS

The UPLC-Q-TOF/MS analysis revealed that TAs-FUW mainly contain six compounds (peiminine, peimine, edpetiline, khasianine, peimisine, and sipeimine). TAs-FUW improved airway inflammation and obstruction, mucus secretion, collagen deposition, and leukocyte and macrophage infiltration, and downregulated TSLP by inhibiting the TRPV1/NFAT pathway in asthmatic mice. In vitro, the application of CPZ demonstrated that the TRPV1 channel is involved in TNF-α/IL-4-mediated regulation of TSLP. TAs-FUW suppressed TNF-α/IL-4-induced TSLP generation expression by regulating the TRPV1/Ca²⁺/NFAT pathway. Furthermore, TAs-FUW reduced CAP-induced TSLP release by inhibiting TRPV1 activation. Notably, sipeimine and edpetiline each were sufficient to block the TRPV1-mediated Ca²⁺ influx.

CONCLUSION

Our study is the first to demonstrate that TNF-α/IL-4 can activate the TRPV1 channel. TAs-FUW can alleviate asthmatic inflammation by suppressing the TRPV1 pathway and thereby preventing the increase in cellular Ca²⁺ influx and the subsequent NFAT activation. The alkaloids in FUW may be used for complementary or alternative therapies in asthma.

Cooperation of Complement MASP-1 with Other Proinflammatory Factors to Enhance the Activation of Endothelial Cells

Endothelial cells play an important role in sensing danger signals and regulating inflammation. Several factors are capable of inducing a proinflammatory response (e.g., LPS, histamine, IFNγ, and bradykinin), and these factors act simultaneously during the natural course of the inflammatory reaction. We have previously shown that the complement protein mannan-binding lectin-associated serine protease-1 (MASP-1) also induces a proinflammatory activation of the endothelial cells. Our aim was to investigate the possible cooperation between MASP-1 and other proinflammatory mediators when they are present in low doses. We used HUVECs and measured Ca²⁺ mobilization, IL-8, E-selectin, VCAM-1 expression, endothelial permeability, and mRNA levels of specific receptors. LPS pretreatment increased the expression of PAR2, a MASP-1 receptor, and furthermore, MASP-1 and LPS enhanced each other's effects in regulating IL-8, E-selectin, Ca²⁺ mobilization, and changes in permeability in a variety of ways. Cotreatment of MASP-1 and IFNγ increased the IL-8 expression of HUVECs. MASP-1 induced bradykinin and histamine receptor expression, and consequently, increased Ca²⁺ mobilization was found. Pretreatment with IFNγ enhanced MASP-1-induced Ca²⁺ mobilization. Our findings highlight that well-known proinflammatory mediators and MASP-1, even at low effective doses, can strongly synergize to enhance the inflammatory response of endothelial cells.

Similarities and Differences between the Orai1 Variants: Orai1α and Orai1β

Orai1, the first identified member of the Orai protein family, is ubiquitously expressed in the animal kingdom. Orai1 was initially characterized as the channel responsible for the store-operated calcium entry (SOCE), a major mechanism that allows cytosolic calcium concentration increments upon receptor-mediated IP₃ generation, which results in intracellular Ca²⁺ store depletion. Furthermore, current evidence supports that abnormal Orai1 expression or function underlies several disorders. Orai1 is, together with STIM1, the key element of SOCE, conducting the Ca²⁺ release-activated Ca²⁺ (CRAC) current and, in association with TRPC1, the store-operated Ca²⁺ (SOC) current. Additionally, Orai1 is involved in non-capacitative pathways, as the arachidonate-regulated or LTC4-regulated Ca²⁺ channel (ARC/LRC), store-independent Ca²⁺ influx activated by the secretory pathway Ca²⁺-ATPase (SPCA2) and the small conductance Ca²⁺-activated K⁺ channel 3 (SK3). Furthermore, Orai1 possesses two variants, Orai1α and Orai1β, the latter lacking 63 amino acids in the N-terminus as compared to the full-length Orai1α form, which confers distinct features to each variant. Here, we review the current knowledge about the differences between Orai1α and Orai1β, the implications of the Ca²⁺ signals triggered by each variant, and their downstream modulatory effect within the cell.

Protease-activated receptor-2: Role in asthma pathogenesis and utility as a biomarker of disease severity

PAR₂, a receptor activated by serine proteases, has primarily pro-inflammatory roles in the airways and may play a role in asthma pathogenesis. PAR₂ exerts its effects in the lungs through activation of a variety of airway cells, but also activation of circulating immune cells. There is evidence that PAR₂ expression increases in asthma and other inflammatory diseases, although the regulation of PAR₂ expression is not fully understood. Here we review the available literature on the potential role of PAR₂ in asthma pathogenesis and propose a model of PAR₂-mediated development of allergic sensitization. We also propose, based on our previous work, that PAR₂ expression on peripheral blood monocyte subsets has the potential to serve as a biomarker of asthma severity and/or control.

Alarmin Cytokines as Central Regulators of Cutaneous Immunity

Skin acts as the primary interface between the body and the environment. The skin immune system is composed of a complex network of immune cells and factors that provide the first line of defense against microbial pathogens and environmental insults. Alarmin cytokines mediate an intricate intercellular communication between keratinocytes and immune cells to regulate cutaneous immune responses. Proper functions of the type 2 alarmin cytokines, thymic stromal lymphopoietin (TSLP), interleukin (IL)-25, and IL-33, are paramount to the maintenance of skin homeostasis, and their dysregulation is commonly associated with allergic inflammation. In this review, we discuss recent findings on the complex regulatory network of type 2 alarmin cytokines that control skin immunity and highlight the mechanisms by which these cytokines regulate skin immune responses in host defense, chronic inflammation, and cancer.

Transient Receptor Potential Vanilloid 1 Plays a Major Role in Low Temperature-Mediated Skin Barrier Dysfunction

BACKGROUND

Children born in the fall and winter are at increased risk for developing atopic dermatitis (AD) and food allergy (FA). Since these seasons are associated with low temperature, we hypothesized that low temperature exposure may compromise keratinocyte differentiation and contribute to skin barrier dysfunction.

OBJECTIVE

To examine whether low temperature causes skin barrier dysfunction.

METHODS

Primary human epidermal keratinocytes (HEKs) were differentiated in 1.3mM CaCl₂ media and cultured at different temperatures. The cells were transfected with transient receptor potential cation channel subfamily V member 1 (TRPV1) or signal transducer and activator of transcription (STAT) 3 small-interfering RNA (siRNA) to examine the effects of these gene targets in HEKs exposed to low temperature. Gene expression of TRPV1, epidermal barrier proteins, and keratinocyte-derived cytokines were evaluated. Organotypic skin equivalents were generated using HEKs transfected with control or TRPV1 siRNA and grown at 25^oC or 37^oC. Transepidermal water loss (TEWL) and levels of epidermal barrier proteins were evaluated.

RESULTS

Filaggrin (FLG) and loricrin (LOR) expression, but not keratin (KRT)-1 and KRT-10 expression, was downregulated in HEKs incubated at 25^oC while TRPV1 silencing increased intracellular Ca²⁺ influx (keratinocyte differentiation signal) and enhanced the expression of epidermal differentiation proteins. Interleukin (IL)-1β and thymic stromal lymphopoietin (TSLP) induced by low temperature inhibited FLG expression in keratinocytes through the TRPV1/STAT3 pathway. Moreover, low temperature-mediated inhibition of FLG and LOR was recovered, and TEWL was decreased in organotypic skin transfected with TRPV1 siRNA.

CONCLUSION

TRPV1 is critical in low temperature-mediated skin barrier dysfunction. Low temperature exposure induced TSLP, an alarmin implicated in epicutaneous allergen sensitization.

CLINICAL IMPLICATIONS

Low temperature causes skin barrier dysfunction through TRPV1 and TSLP, which may explain the pathways involved in promoting allergic sensitization through the skin.

Transient receptor potential cation channel subfamily V (TRPV) and its importance in asthma

Transient receptor potential (TRP) ion channels play critical roles in physiological and pathological conditions. Increasing evidence has unveiled the contribution of TRP vanilloid (TRPV) family in the development of asthma. The TRPV family is a group (TRPV1-TRPV6) of polymodal channels capable of sensing thermal, acidic, mechanical stress, and osmotic stimuli. TRPVs can be activated by endogenous ligands including, arachidonic acid derivatives or endocannabinoids. While TRPV1-TRPV4 are non-selective cation channels showing a predominance for Ca2+ over Na + influx, TRPV5 and TRPV6 are only Ca2+ permeable selective channels. Asthma is a chronic inflammatory bronchopulmonary disorder involving airway hyperresponsiveness (AHR) and airway remodeling. Patients suffering from allergic asthma display an inflammatory pattern driven by cytokines produced in type-2 helper T cells (Th2) and type 2 innate lymphoid cells (ILC2s). Ion channels are essential regulators in airway smooth muscle (ASM) and immune cells physiology. In this review, we summarize the contribution of TRPV1, TRPV2, and TRPV4 to the pathogenesis of asthma. TRPV1 is associated with hypersensitivity to environmental pollutants and chronic cough, inflammation, AHR, and remodeling. TRPV2 is increased in peripheral lymphocytes of asthmatic patients. TRPV4 contributes to ASM cells proliferation, and its blockade leads to a reduced eosinophilia, neutrophilia, as well as an abolished AHR. In conclusion, TRPV2 may represent a novel biomarker for asthma in children; meanwhile, TRPV1 and TRPV4 seem to be essential contributors to the development and exacerbations of asthma. Moreover, these channels may serve as novel therapeutic targets for this ailment.

The ion channel TRPV1 gain-of-function reprograms the immune microenvironment to facilitate colorectal tumorigenesis

Transient receptor potential vanilloid 1 (TRPV1) is a Ca²⁺-permeable ion channel that acts as cellular sensor and is implicated in the tumor microenvironment cross talk. However, the functional role of TRPV1 in colorectal cancer (CRC) is still controversial. By using a TRPV1 gain-of-function model, we previously reported that hyperfunctional TRPV1 exacerbated experimental colitis by modulating mucosal immunity. Here, we found that TRPV1 gain-of-function significantly promoted tumor initiation and progression in colitis-associated cancer, as evidenced by the increase in the number and size of tumor. Systemic TRPV1 hyperactivation fostered a tumor permissive microenvironment through altering macrophage activation status and shifting the Th1/Th2 balance towards Th2 phenotype. Mechanistically, TRPV1 gain-of-function directly potentiated M1 cytokine production in macrophage and enhanced Th2 immune response by promoting Calcineurin/nuclear factor of activated T cells (NFATc2) signaling activation. In patients with CRC, TRPV1 expression was increased in tumor immune infiltrating cells. TRPV1 level was associated with CRC progression and could impact clinical outcome. Our study reveals an important role for TRPV1 in regulating the immune microenvironment during colorectal tumorigenesis. TRPV1 might be a potential target for CRC immunotherapy.

Gain of Function of Ion Channel TRPV1 Exacerbates Experimental Colitis by Promoting Dendritic Cell Activation

Dysregulated mucosal immunity plays an essential role in the pathophysiology of inflammatory bowel disease (IBD). Transient receptor potential vanilloid 1 (TRPV1) is a Ca²⁺-permeable ion channel that is implicated in modulating immune responses. However, its role in the pathogenesis of intestinal inflammation remains elusive. Here, we found that TRPV1 gain of function significantly increased the susceptibility of mice to experimental colitis, and that was associated with excessive recruitment of dendritic cells and enhanced Th17 immune responses in the lamina propria of colon. TRPV1 gain of function promoted dendritic cell activation and cytokine production upon inflammatory stimuli, and consequently enhanced dendritic cell-mediated Th17 cell differentiation. Further mechanistic studies showed that TRPV1 gain of function in dendritic cells enhanced activation of calcineurin/nuclear factor of activated T cells (NFATc2) signaling induced by inflammatory stimuli. Moreover, in patients with IBD, TRPV1 expression was increased in lamina propria cells of inflamed colon compared with healthy controls. Our findings identify an important role for TRPV1 in modulating dendritic cell activation and sustaining Th17 responses to inflammatory stimuli, which suggest that TRPV1 might be a potential therapeutic target in controlling mucosal immunity and IBD.

The potential role of TRPV1 in pulmonary hypertension: Angel or demon?

Pulmonary hypertension (PH) is a pathological state defined by increased pulmonary artery pressure, the pathogenesis of which is related to genetic mutations, intracellular calcium ([Ca²⁺]_i), inflammation and proliferation. Transient receptor potential vanilloid subfamily member 1 (TRPV1) is a nonselective cation channel expressed in neural and nonneural cells, including pulmonary vessels and nerves. As a calcium channel, TRPV1 can make vessels contracted, and promote smooth muscle cells proliferation through calcium-dependent transcription factors. Activation of TRPV1 in sensory nerves can release neuropeptides, including calcitonin gene-related peptide (CGRP), substance P (SP), and somatostatin (SST), which can regulate inflammation via transcription factor NF-kB. Considering the increased level of [Ca²⁺]_i and inflammation in the pathogenesis of PH, our review summarizes the role of TRPV1 in PH with regard to [Ca²⁺]_i, neuropeptides, and inflammation. In view of the limited research illustrating the relationship between TRPV1 and PH directly, our review also considers the role of TRPV1 in other types of vascular inflammation. Through this review, we hope to raise awareness about the function of TRPV1 in PH.

Thymic stromal lymphopoietin: its role and potential as a therapeutic target in asthma

INTRODUCTION

Thymic stromal lymphopoietin (TSLP), an epithelial cytokine (alarmin), is a central regulator of the immune response to inhaled environmental insults such as allergens, viruses and pollutants, initiating a cascade of downstream inflammation. There is compelling evidence that TSLP plays a major role in the pathology of asthma, and therapies that aim to block its activity are in development.

AREAS COVERED

We review studies conducted in humans and human cells, largely published in PubMed January 2010-October 2019, that investigated the innate and adaptive immune mechanisms of TSLP in asthma relevant to type 2-driven (eosinophilic/allergic) inflammation and non-type 2-driven (non-eosinophilic/non-allergic) inflammation, and the role of TSLP as a mediator between immune cells and structural cells in the airway. Clinical data from studies evaluating TSLP blockade are also discussed.

EXPERT OPINION

The position of TSLP at the top of the inflammatory cascade makes it a promising therapeutic target in asthma. Systemic anti-TSLP monoclonal antibody therapy with tezepelumab has yielded positive results in clinical trials to date, reducing exacerbations and biomarkers of inflammation in patients across the spectrum of inflammatory endotypes. Inhaled anti-TSLP is an alternative route currently under evaluation. The long-term safety and efficacy of TSLP blockade need to be evaluated.

Post-Burn Pruritus

Post-burn pruritus is the pruritus that occurs after burn during the rehabilitation and healing process of burn wounds. The post-burn pruritus is a common and serious complication of burn injury, which severely lowers the quality of life of the patient. Many potential treatments are available for pruritus but there is no consensus of the best single treatment yet. The precise mechanism of post-burn pruritus has not been elucidated, but it appears to have pruritogenic and neuropathic aspects. Clinically, post-burn pruritus tends to be intractable to conventional treatment but rather responds to neuroleptic agents, such as gabapentin and pregabalin. During wound healing, various neuropeptides secreted from the nerves of the skin control epidermal and vascular proliferation and connective tissue cells. When keratinocytes are activated by an itch-inducing substance, they secrete a variety of inflammatory substances that increase the susceptibility of the itch receptor. There are two mechanisms underlying post-burn neuropathic pruritus. The first one is peripheral sensitization. The second one is the intact nociceptor hypothesis. An effective treatment for post-burn pruritus will also be effective in other neuropathic and intractable itching. In this review, we summarized the interaction and mechanism of keratinocytes, immune cells, and nerve fibers related to post-burn pruritus.

Gene expression of TMEM178, which encodes a negative regulator of NFATc1, decreases with the progression of asthma severity

In two independent microarray studies involving primary airway epithelial cells, the relative gene expression of TMEM178 decreases with the progression of asthma severity. Our manuscript creates a paradigm for future studies dissecting the role of Tmem178 in the pathogenesis of severe asthma.

Role of transient receptor potential cation channel subfamily V member 1 (TRPV1) on ozone-exacerbated allergic asthma in mice

Around the globe, worsening air pollution is spawning major public health and environmental concerns, especially in the poorest and most populous cities. As a major secondary air pollutant, ozone is a potential risk factor for exacerbated asthma, although the underlying mechanisms remain uncertain. In this study, we aim to investigate the role of ozone on asthma exacerbation using a classic asthmatic model with allergic airway inflammation by treating Balb/c mice with ovalbumin (OVA). Our study shows ozone exposure significantly exacerbated OVA-induced asthmatic phenotypes, including serum immunoglobulin, Th cytokines, inflammatory cell counts, mucus production, airway remodeling, and airway hyper-responsiveness (AHR). Interestingly, expression of transient receptor potential cation channel subfamily V member1 (TRPV1) was also significantly elevated in ozone-exacerbated asthmatic mice and that treatment with TRPV1 antagonist effectively suppressed AHR, airway inflammation and remodeling. The underlying mechanisms of these effects may be associated with suppression of neuropeptide calcitonin gene-related peptide (CGRP) and thymic stromal lymphopoietin (TSLP), an epithelial cell-derived cytokine. Base on the role of TRPV1 in allergic asthma, this study further revealed that inhibition of TRPV1 by TRPV1 antagonist has significant anti-inflammatory effects on ozone-induced asthma exacerbation in this study. Induction of TRPV1 expression may be an important mechanism underlying the increased risks for asthma after exposure to environmental pollutants.

TRPV3 Channel in Keratinocytes in Scars with Post-Burn Pruritus

Post-burn pruritus is a common and distressing sequela of burn scars. Empirical antipruritic treatments usually fail to have a satisfactory outcome because of their limited selectivity and possible side effects. Therefore, novel drug targets need to be identified. Here, we aimed to investigate the possible role of protease-activated receptor 2 (PAR2) and transient receptor potential vanniloid 3 (TRPV3), along with the relation of TRPV3 to thymic stromal lymphopoietin (TSLP). Specimens from normal (unscarred) or burn-scarred (with or without pruritus) tissue were obtained from burn patients for this study. In each sample, the keratinocytes were isolated and cultured, and the intracellular Ca²⁺ level at the time of stimulation of each factor was quantified and the interaction was screened. PAR2 function was reduced by antagonism of TRPV3. Inhibiting protein kinase A (PKA) and protein kinase C (PKC) reduced TRPV3 function. TSLP mRNA and protein, and TSLPR protein expressions, increased in scars with post-burn pruritus, compared to scars without it or to normal tissues. In addition, TRPV1 or TRPV3 activation induced increased TSLP expression. Conclusively, TRPV3 may contribute to pruritus in burn scars through TSLP, and can be considered a potential therapeutic target for post-burn pruritus.

Analysis of chromatin accessibility in human epidermis identifies putative barrier dysfunction-sensing enhancers

To identify putative gene regulatory regions that respond to epidermal injury, we mapped chromatin dynamics in a stratified human epidermis during barrier maturation and disruption. Engineered skin substitutes (ESS) cultured at the air-liquid interface were used as a model of developing human epidermis with incomplete barrier formation. The epidermal barrier stabilized following engraftment onto immunocompromised mice, and was compromised again upon injury. Modified formaldehyde-assisted isolation of regulatory elements (FAIRE) was used to identify accessible genomic regions characteristic of monolayer keratinocytes, ESS in vitro, grafted ESS, and tape-stripped ESS graft. We mapped differentiation- and maturation-associated changes in transcription factor binding sites enriched at each stage and observed overrepresentation of AP-1 gene family motifs in barrier-deficient samples. Transcription of TSLP, an important effector of immunological memory in response to allergen exposure, was dramatically elevated in our barrier-deficient samples. We identified dynamic DNA elements that correlated with TSLP induction and may contain enhancers that regulate TSLP. Two dynamic regions were located near the TSLP promoter and overlapped with allergy-associated SNPs rs17551370 and rs2289877, strongly implicating these loci in the regulation of TSLP expression in allergic disease. Additional dynamic chromatin regions ~250kb upstream of the TSLP promoter were found to be in high linkage disequilibrium with allergic disease SNPs. Taken together, these results define dynamic chromatin accessibility changes during epidermal development and dysfunction.

Regulation of Gene Transcription Following Stimulation of Transient Receptor Potential (TRP) Channels

Transient receptor potential (TRP) channels belong to a heterogeneous superfamily of cation channels that are involved in the regulation of numerous biological functions, including regulation of Ca²⁺ and glucose homeostasis, tumorigenesis, temperature, and pain sensation. To understand the functions of TRP channels, their associated intracellular signaling pathways and molecular targets have to be identified on the cellular level. Stimulation of TRP channels frequently induces an influx of Ca²⁺ ions into the cells and the subsequent activation of protein kinases. These intracellular signal transduction pathways ultimately induce changes in the gene expression pattern of the cells. Here, we review the effects of TRPC6, TRPM3, and TRPV1 channel stimulation on the activation of the stimulus-responsive transcription factors AP-1, CREB, Egr-1, Elk-1, and NFAT. Following activation, these transcription factors induce the transcription of delayed response genes. We propose that many biological functions of TRP channels can be explained by the activation of stimulus-responsive transcription factors and their delayed response genes. The proteins encoded by those delayed response genes may be responsible for the biochemical and physiological changes following TRP channel activation.

The emerging role of transient receptor potential channels in chronic lung disease

Chronic lung diseases such as asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis are a major and increasing global health burden with a high unmet need. Drug discovery efforts in this area have been largely disappointing and so new therapeutic targets are needed. Transient receptor potential ion channels are emerging as possible therapeutic targets, given their widespread expression in the lung, their role in the modulation of inflammatory and structural changes and in the production of respiratory symptoms, such as bronchospasm and cough, seen in chronic lung disease.

TRPV1 and TRPA1 in cutaneous neurogenic and chronic inflammation: pro-inflammatory response induced by their activation and their sensitization

Cutaneous neurogenic inflammation (CNI) is inflammation that is induced (or enhanced) in the skin by the release of neuropeptides from sensory nerve endings. Clinical manifestations are mainly sensory and vascular disorders such as pruritus and erythema. Transient receptor potential vanilloid 1 and ankyrin 1 (TRPV1 and TRPA1, respectively) are non-selective cation channels known to specifically participate in pain and CNI. Both TRPV1 and TRPA1 are co-expressed in a large subset of sensory nerves, where they integrate numerous noxious stimuli. It is now clear that the expression of both channels also extends far beyond the sensory nerves in the skin, occuring also in keratinocytes, mast cells, dendritic cells, and endothelial cells. In these non-neuronal cells, TRPV1 and TRPA1 also act as nociceptive sensors and potentiate the inflammatory process. This review discusses the role of TRPV1 and TRPA1 in the modulation of inflammatory genes that leads to or maintains CNI in sensory neurons and non-neuronal skin cells. In addition, this review provides a summary of current research on the intracellular sensitization pathways of both TRP channels by other endogenous inflammatory mediators that promote the self-maintenance of CNI.

Topical Tetracycline Improves MC903-induced Atopic Dermatitis in Mice through Inhibition of Inflammatory Cytokines and Thymic Stromal Lymphopoietin Expression

Background:

Tetracycline (TET) has been found to have both antibiotic and anti-inflammatory properties. The anti-inflammatory effect of topical TET on atopic dermatitis (AD) has not been reported. The purpose of this study was to explore the potential role of topical TET and its anti-inflammatory effects in a mouse model of AD.

Methods:

The 2% TET was applied topically to ears of MC903-induced AD-like BALB/c mice once a day. AD-like symptoms and severity were evaluated by assessing skin scoring of dermatitis, ear thickness, and frequency of scratching. Serum IgE and thymic stromal lymphopoietin (TSLP) levels were measured by enzyme-linked immunosorbent assay. Western blot was used for analyzing the expressions of TSLP, protease-activated receptor 2 (PAR2), and nuclear factor-kappa B (NF-κB) in skin lesions. Real-time polymerase chain reaction was performed to assess the mRNA levels of TSLP and inflammatory cytokines including interleukin (IL)-4, IL-13, tumor necrosis factor (TNF)-α, and IL-1β in skin lesions.

Results:

Scoring of dermatitis (9.00 ± 0.63 vs. 6.67 ± 1.03, P = 0.001), ear thickness (0.44 ± 0.02 mm vs. 0.40 ± 0.03 mm, P = 0.018), and serum IgE level (421.06 ± 212.13 pg/ml vs. 244.15 ± 121.39 pg/ml, P = 0.047) were all improved in the 2% TET treatment group compared with AD group. Topical TET significantly reduced the serum level of TSLP (119.04 ± 38.92 pg/ml vs. 65.95 ± 54.61 pg/ml, P = 0.011) and both mRNA and protein expressions of TSLP in skin lesions compared with AD group (P = 0.003 and 0.011, respectively), and NF-κB and PAR2 expression in skin lesions were also suppressed (P = 0.016 and 0.040, respectively). Furthermore, expressions of inflammatory cytokines IL-4, IL-13, and TNF-α in skin lesions were down-regulated in 2% TET group compared with AD group (P = 0.035, 0.008, and 0.044, respectively).

Conclusions:

Topical TET exerted anti-inflammatory effects through suppression of TSLP and inflammatory cytokines in AD mouse model, suggesting TET as a potential agent for the topical treatment of AD in the future.

The role of TRPV1 in the CD4+ T cell-mediated inflammatory response of allergic rhinitis

Transient receptor potential vanilloid 1 (TRPV1), which has been identified as a molecular target for the activation of sensory neurons by various painful stimuli, was reported to regulate the signaling and activation of CD4⁺ T cells. However, the role of TRPV1 in CD4⁺ T cell in allergic rhinitis remains poorly understood. In this study, TRPV1 expression was localized in CD4⁺ T cells. Both knockout and chemical inhibition of TRPV1 suppressed Th2/Th17 cytokine production in CD4 T cells and Jurkat T cells, respectively, and can suppress T cell receptor signaling pathways including NF-κB, MAP kinase, and NFAT. In TRPV1 knockout allergic rhinitis (AR) mice, eosinophil infiltration, Th2/Th17 cytokines in the nasal mucosa, and total and ova-specific IgE levels in serum decreased, compared with wild-type AR mice. The TRPV1 antagonists, BCTC or theobromine, showed similar inhibitory immunologic effects on AR mice models. In addition, the number of TRPV1⁺/CD4⁺ inflammatory cells increased in the nasal mucosa of patients with AR, compared with that of control subjects. Thus, TRPV1 activation on CD4⁺ T cells is involved in T cell receptor signaling, and it could be a novel therapeutic target in AR.

Role of the ion channel, transient receptor potential cation channel subfamily V member 1 (TRPV1), in allergic asthma

BACKGROUND

Asthma prevalence has increased world-wide especially in children; thus there is a need to develop new therapies that are safe and effective especially for patients with severe/refractory asthma. CD4(+) T cells are thought to play a central role in disease pathogenesis and associated symptoms. Recently, TRPV1 has been demonstrated to regulate the activation and inflammatory properties of CD4(+) cells. The aim of these experiments was to demonstrate the importance of CD4(+) T cells and the role of TRPV1 in an asthma model using a clinically ready TRPV1 inhibitor (XEN-D0501) and genetically modified (GM) animals.

METHODS

Mice (wild type, CD4 (-/-) or TRPV1 (-/-)) and rats were sensitised with antigen (HDM or OVA) and subsequently topically challenged with the same antigen. Key features associated with an allergic asthma type phenotype were measured: lung function (airway hyperreactivity [AHR] and late asthmatic response [LAR]), allergic status (IgE levels) and airway inflammation.

RESULTS

CD4(+) T cells play a central role in both disease model systems with all the asthma-like features attenuated. Targeting TRPV1 using either GM mice or a pharmacological inhibitor tended to decrease IgE levels, airway inflammation and lung function changes.

CONCLUSION

Our data suggests the involvement of TRPV1 in allergic asthma and thus we feel this target merits further investigation.

Andrographolide suppresses thymic stromal lymphopoietin in phorbol myristate acetate/calcium ionophore A23187-activated mast cells and 2,4-dinitrofluorobenzene-induced atopic dermatitis-like mice model

BACKGROUND

Atopic dermatitis (AD) is one of the most common inflammatory cutaneous diseases. Thymic stromal lymphopoietin (TSLP) has been demonstrated to be an important immunologic factor in the pathogenesis of AD. The production of TSLP can be induced by a high level of intracellular calcium concentration and activation of the receptor-interacting protein 2/caspase-1/NF-κB pathway. Andrographolide (ANDRO), a natural bicyclic diterpenoid lactone, has been found to exert anti-inflammatory effects in gastrointestinal inflammatory disorders through suppressing the NF-κB pathway.

OBJECTIVE

To explore the effect of ANDRO on the production of TSLP in human mast cells and AD mice model.

METHODS

We utilized enzyme-linked immunosorbent assay, real-time reverse transcription polymerase chain reaction analysis, Western blot analysis, and immunofluorescence staining assay to investigate the effects of ANDRO on AD.

RESULTS

ANDRO ameliorated the increase in the intracellular calcium, protein, and messenger RNA levels of TSLP induced by phorbol myristate acetate/calcium ionophore A23187, through the blocking of the receptor-interacting protein 2/caspase-1/NF-κB pathway in human mast cell line 1 cells. ANDRO, via oral or local administration, also attenuated clinical symptoms in 2,4-dinitrofluorobenzene-induced AD mice model and suppressed the levels of TSLP in lesional skin.

CONCLUSION

Taken together, ANDRO may be a potential therapeutic agent for AD through suppressing the expression of TSLP.

Cannabinoid-based drugs targeting CB1 and TRPV1, the sympathetic nervous system, and arthritis

Chronic inflammation in rheumatoid arthritis (RA) is accompanied by activation of the sympathetic nervous system, which can support the immune system to perpetuate inflammation. Several animal models of arthritis already demonstrated a profound influence of adrenergic signaling on the course of RA. Peripheral norepinephrine release from sympathetic terminals is controlled by cannabinoid receptor type 1 (CB1), which is activated by two major endocannabinoids (ECs), arachidonylethanolamine (anandamide) and 2-arachidonylglycerol. These ECs also modulate function of transient receptor potential channels (TRPs) located on sensory nerve fibers, which are abundant in arthritic synovial tissue. TRPs not only induce the sensation of pain but also support inflammation via secretion of pro-inflammatory neuropeptides. In addition, many cell types in synovial tissue express CB1 and TRPs. In this review, we focus on CB1 and transient receptor potential vanilloid 1 (TRPV1)-mediated effects on RA since most anti-inflammatory mechanisms induced by cannabinoids are attributed to cannabinoid receptor type 2 (CB2) activation. We demonstrate how CB1 agonism or antagonism can modulate arthritic disease. The concept of functional antagonism with continuous CB1 activation is discussed. Since fatty acid amide hydrolase (FAAH) is a major EC-degrading enzyme, the therapeutic possibility of FAAH inhibition is studied. Finally, the therapeutic potential of ECs is examined since they interact with cannabinoid receptors and TRPs but do not produce central side effects.

The importance of TSLP in allergic disease and its role as a potential therapeutic target

Thymic stromal lymphopoietin (TSLP) is an epithelial-derived cytokine similar to IL- 7, whose gene is located on chromosome 5q22.1 and it exerts its biological function through the TSLP-Receptor (TSLP-R). TSLP is expressed primarily by epithelial cells at barrier surfaces such as the skin, gut and lung in response to danger signals. Since it was cloned in 1994, there has been accumulating evidence that TSLP is crucial for the maturation of antigen presenting cells and hematopoietic cells. TSLP genetic variants and its dysregulated expression have been linked to atopic diseases such as atopic dermatitis, asthma, allergic rhinitis and eosinophilic esophagitis.

TRPV4 as a therapeutic target for joint diseases

Biomechanical factors play a critical role in regulating the physiology as well as the pathology of multiple joint tissues and have been implicated in the pathogenesis of osteoarthritis. Therefore, the mechanisms by which cells sense and respond to mechanical signals may provide novel targets for the development of disease-modifying osteoarthritis drugs (DMOADs). Transient receptor potential vanilloid 4 (TRPV4) is a Ca(2+)-permeable cation channel that serves as a sensor of mechanical or osmotic signals in several musculoskeletal tissues, including cartilage, bone, and synovium. The importance of TRPV4 in joint homeostasis is apparent in patients harboring TRPV4 mutations, which result in the development of a spectrum of skeletal dysplasias and arthropathies. In addition, the genetic knockout of Trpv4 results in the development of osteoarthritis and decreased osteoclast function. In engineered cartilage replacements, chemical activation of TRPV4 can reproduce many of the anabolic effects of mechanical loading to accelerate tissue growth and regeneration. Overall, TRPV4 plays a key role in transducing mechanical, pain, and inflammatory signals within joint tissues and thus is an attractive therapeutic target to modulate the effects of joint diseases. In pathological conditions in the joint, when the delicate balance of TRPV4 activity is altered, a variety of different tools could be utilized to directly or indirectly target TRPV4 activity.