Transient receptor potential ankyrin1 channel is endogenously expressed in T cells and is involved in immune functions

Upregulation, Functional Association, and Correlated Expressions of TRPV1 and TRPA1 During Telmisartan-Driven Immunosuppression of T Cells

TRPV1 and TRPA1, are known to be functionally expressed in T cells, where these two channels differentially regulate effector immune responses. Telmisartan (TM), an anti-hypertension drug, has been recently repurposed to suppress various inflammatory responses. However, the possible involvement of TRP channels during TM-driven suppression of T cells responses has not been explored yet. In this study, we investigated the potential role of TRPV1 and TRPA1 during TM-driven immunosuppression of T cells in vitro. We observed a significant elevation of both TRPV1 and TRPA1 during TM-induced immunosuppression of T cells.We found that TRPA1 activation-driven suppression of T cell activation and effector cytokine responses during TM treatment is partially, yet significantly overridden by TRPV1 activation. Moreover, the expressions of TRPV1 and TRPA1 were highly correlated in various conditions of T cell. Mechanistically, it might be suggested that TRPV1 and TRPA1 are differentially involved in regulating T cell activation despite the co-elevation of both these TRP channels' expressions in the presence of TM. T cell activation was delineated by CD69 and CD25 expressions along with the effector cytokine levels (IFN-γ and TNF) in TM-driven suppression of T cell. These findings could have broad implications for designing possible future immunotherapeutic strategies, especially in the repurposing of TM for T cell-TRP-directed immune disorders.

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.

TRP Ion Channels in Immune Cells and Their Implications for Inflammation

The transient receptor potential (TRP) ion channels act as cellular sensors and mediate a plethora of physiological processes, including somatosensation, proliferation, apoptosis, and metabolism. Under specific conditions, certain TRP channels are involved in inflammation and immune responses. Thus, focusing on the role of TRPs in immune system cells may contribute to resolving inflammation. In this review, we discuss the distribution of five subfamilies of mammalian TRP ion channels in immune system cells and how these ion channels function in inflammatory mechanisms. This review provides an overview of the current understanding of TRP ion channels in mediating inflammation and may offer potential avenues for therapeutic intervention.

Senso-immunology: the past, present, and future

Pain and mechanical stimulation are thought to be alarm systems that alert the brain to physical abnormalities. When we experience unpleasant feelings in infected or traumatized tissues, our awareness is directed to the afflicted region, prompting activities such as resting or licking the tissue. Despite extensive research into the molecular biology of nociceptors, it was unclear whether their role was limited to the generation and transmission of unpleasant feelings or whether they actively modulate the pathogenesis of infected or traumatized tissues. Recently, it has become clear how the sensory and immune systems interact with one another and share similar receptors and ligands to modify the pathogenesis of various diseases. In this paper, we summarize the mechanisms of crosstalk between the sensory and immune systems and the impact of this new interdisciplinary field, which should be dubbed 'senso-immunology,' on medical science.

Mechanosensitive Ion Channels: Their Physiological Importance and Potential Key Role in Cancer

Mechanosensitive ion channels comprise a broad group of proteins that sense mechanical extracellular and intracellular changes, translating them into cation influx to adapt and respond to these physical cues. All cells in the organism are mechanosensitive, and these physical cues have proven to have an important role in regulating proliferation, cell fate and differentiation, migration and cellular stress, among other processes. Indeed, the mechanical properties of the extracellular matrix in cancer change drastically due to high cell proliferation and modification of extracellular protein secretion, suggesting an important contribution to tumor cell regulation. In this review, we describe the physiological significance of mechanosensitive ion channels, emphasizing their role in cancer and immunity, and providing compelling proof of the importance of continuing to explore their potential as new therapeutic targets in cancer research.

TRPA1 activation and Hsp90 inhibition synergistically downregulate macrophage activation and inflammatory responses in vitro

BACKGROUND

Transient receptor potential ankyrin 1 (TRPA1) channels are known to be actively involved in various pathophysiological conditions, including neuronal inflammation, neuropathic pain, and various immunological responses. Heat shock protein 90 (Hsp90), a cytoplasmic molecular chaperone, is well-reported for various cellular and physiological processes. Hsp90 inhibition by various molecules has garnered importance for its therapeutic significance in the downregulation of inflammation and are proposed as anti-cancer drugs. However, the possible role of TRPA1 in the Hsp90-associated modulation of immune responses remains scanty.

RESULTS

Here, we have investigated the role of TRPA1 in regulating the anti-inflammatory effect of Hsp90 inhibition via 17-(allylamino)-17-demethoxygeldanamycin (17-AAG) in lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA) stimulation in RAW 264.7, a mouse macrophage cell lines and PMA differentiated THP-1, a human monocytic cell line similar to macrophages. Activation of TRPA1 with Allyl isothiocyanate (AITC) is observed to execute an anti-inflammatory role via augmenting Hsp90 inhibition-mediated anti-inflammatory responses towards LPS or PMA stimulation in macrophages, whereas inhibition of TRPA1 by 1,2,3,6-Tetrahydro-1,3-dimethyl-N-[4-(1-methylethyl)phenyl]-2,6-dioxo-7 H-purine-7-acetamide,2-(1,3-Dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7 H-purin-7-yl)-N-(4-isopropylphenyl)acetamide (HC-030031) downregulates these developments. LPS or PMA-induced macrophage activation was found to be regulated by TRPA1. The same was confirmed by studying the levels of activation markers (major histocompatibility complex II (MHCII), cluster of differentiation (CD) 80 (CD80), and CD86, pro-inflammatory cytokines (tumor necrosis factor (TNF) and interleukin 6 (IL-6)), NO (nitric oxide) production, differential expression of mitogen-activated protein kinase (MAPK) signaling pathways (p-p38 MAPK, phospho-extracellular signal-regulated kinase 1/2 (p-ERK 1/2), and phosphor-stress-activated protein kinase/c-Jun N-terminal kinase (p-SAPK/JNK)), and induction of apoptosis. Additionally, TRPA1 has been found to be an important contributor to intracellular calcium levels toward Hsp90 inhibition in LPS or PMA-stimulated macrophages.

CONCLUSION

This study indicates a significant role of TRPA1 in Hsp90 inhibition-mediated anti-inflammatory developments in LPS or PMA-stimulated macrophages. Activation of TRPA1 and inhibition of Hsp90 has synergistic roles towards regulating inflammatory responses associated with macrophages. The role of TRPA1 in Hsp90 inhibition-mediated modulation of macrophage responses may provide insights towards designing future novel therapeutic approaches to regulate various inflammatory responses.

Transient receptor potential Ankyrin-1 (TRPA1) agonists suppress myelination and induce demyelination in organotypic cortical slices

Oligodendrocytes are highly specialized glial cells characterized by their production of multilayer myelin sheaths that wrap axons to speed up action potential propagation. It is due to their specific role in supporting axons that impairment of myelin structure and function leads to debilitating symptoms in a wide range of degenerative diseases, including Multiple Sclerosis and Leukodystrophies. It is known that myelin damage can be receptor-mediated and recently oligodendrocytes have been shown to express Ca2+ -permeable Transient Receptor Potential Ankyrin-1 (TRPA1) channels, whose activation can result in myelin damage in ischemia. Here, we show, using organotypic cortical slice cultures, that TRPA1 activation, by TRPA1 agonists JT010 and Carvacrol for varying lengths of time, induces myelin damage. Although TRPA1 activation does not appear to affect oligodendrocyte progenitor cell number or proliferation, it prevents myelin formation and after myelination causes internodal shrinking and significant myelin degradation. This does not occur when the TRPA1 antagonist, A967079, is also applied. Of note is that when TRPA1 agonists are applied for either 24 h, 3 days or 7 days, axon integrity appears to be preserved while mature myelinated oligodendrocytes remain but with significantly shortened internodes. These results provide further evidence that TRPA1 inhibition could be protective in demyelination diseases and a promising therapy to prevent demyelination and promote remyelination.

TRPV4 regulates mitochondrial Ca2+-status and physiology in primary murine T cells based on their immunological state

T cell activation process is critically affected by temperature and intracellular Ca²⁺-signalling. Yet, the nature and the key molecules involved in such complex Ca²⁺-signalling is poorly understood. It is mostly assumed that ion channels present in the plasma membrane primarily regulate the cytosolic Ca²⁺-levels exclusively. TRPV4 is a non-selective Ca²⁺ channel which can be activated at physiological temperature. TRPV4 is involved in several physiological, pathophysiological process as well as different forms of pain. Here we demonstrate that TRPV4 is endogenously expressed in T cell and is present in the mitochondria of T cells. TRPV4 activation increases mitochondrial Ca²⁺-levels, and alters mitochondrial temperature as well as specific metabolisms. The TRPV4-dependent increment in the mitochondrial Ca²⁺ is context-dependent and not just passively due to the increment in the cytosolic Ca²⁺. Our work also indicates that mitochondrial Ca²⁺-level correlates positively with a series of essential factors, such as mitochondrial membrane potential, mitochondrial ATP production and negatively correlates with certain factors such as mitochondrial temperature. We propose that TRPV4-mediated mitochondrial Ca²⁺-signalling and other metabolisms has implications in the immune activation process including immune synapse formation. Our data also endorse the re-evaluation of Ca²⁺-signalling in T cell, especially in the light of mitochondrial Ca²⁺-buffering and in higher body temperature, such as in case of fever. Presence of TRPV4 in the mitochondria of T cell is relevant for proper and optimum immune response and may provide evolutionary adaptive benefit. These findings may also have broad implications in different pathophysiological process, neuro-immune cross-talks, and channelopathies involving TRPV4.

Understanding the role of Ca2+ via transient receptor potential (TRP) channel in viral infection: Implications in developing future antiviral strategies

Transient receptor potential (TRP) channels are a superfamily of cation-specific permeable channels primarily conducting Ca2+ions across various membranes of the cell. The perturbation of the Ca2+ homeostasis is the hallmark of viral infection. Viruses hijack the host cell Ca2+ signaling, employing tailored Ca2+ requirements via TRP channels to meet their own cellular demands. This review summarizes the importance of Ca2+ across diverse viruses based on the Baltimore classification and focuses on the associated role of Ca2+-conducting TRP channels in viral pathophysiology. More emphasis has been given to the role of the TRP channel in viral life-cycle events such as viral fusion, viral entry, viral replication, virion maturation, and egress. Additionally, this review highlights the TRP channel as a store-operated channel which has been discussed vividly. The TRP channels form an essential aspect of host-virus interaction by virtue of its Ca2+ permeability. These channels are directly involved in regulating the viral calcium dynamics in host cells and thereby affect the viral infection. Considering its immense potential in regulating viral infection, the TRP channels may act as a target for antiviral therapeutics.

Inflammation-the role of TRPA1 channel

Recently, increasing numbers of studies have demonstrated that transient receptor potential ankyrin 1 (TRPA1) can be used as a potential target for the treatment of inflammatory diseases. TRPA1 is expressed in both neuronal and non-neuronal cells and is involved in diverse physiological activities, such as stabilizing of cell membrane potential, maintaining cellular humoral balance, and regulating intercellular signal transduction. TRPA1 is a multi-modal cell membrane receptor that can sense different stimuli, and generate action potential signals after activation via osmotic pressure, temperature, and inflammatory factors. In this study, we introduced the latest research progress on TRPA1 in inflammatory diseases from three different aspects. First, the inflammatory factors released after inflammation interacts with TRPA1 to promote inflammatory response; second, TRPA1 regulates the function of immune cells such as macrophages and T cells, In addition, it has anti-inflammatory and antioxidant effects in some inflammatory diseases. Third, we have summarized the application of antagonists and agonists targeting TRPA1 in the treatment of some inflammatory diseases.

Concanavalin A as a promising lectin-based anti-cancer agent: the molecular mechanisms and therapeutic potential

Concanavalin A (ConA), the most studied plant lectin, has been known as a potent anti-neoplastic agent for a long time. Since initial reports on its capacity to kill cancer cells, much attention has been devoted to unveiling the lectin's exact molecular mechanism. It has been revealed that ConA can bind to several receptors on cancerous and normal cells and modulate the related signaling cascades. The most studied host receptor for ConA is MT1-MMP, responsible for most of the lectin's modulations, ranging from activating immune cells to killing tumor cells. In this study, in addition to studying the effect of ConA on signaling and immune cell function, we will focus on the most up-to-date advancements that unraveled the molecular mechanisms by which ConA can induce autophagy and apoptosis in various cancer cell types, where it has been found that P73 and JAK/STAT3 are the leading players. Moreover, we further discuss the main signaling molecules causing liver injury as the most significant side effect of the lectin injection. Altogether, these findings may shed light on the complex signaling pathways controlling the diverse responses created via ConA treatment, thereby modulating these complex networks to create more potent lectin-based cancer therapy.

Impact of Δ9-Tetrahydrocannabinol on Rheumatoid Arthritis Synovial Fibroblasts Alone and in Co-Culture with Peripheral Blood Mononuclear Cells

δ9-Tetrahydrocannabinol (THC) has demonstrated anti-inflammatory effects in animal models of arthritis, but its mechanism of action and cellular targets are still unclear. The purpose of this study is to elucidate the effects of THC (0.1-25 µM) on synovial fibroblasts from patients with rheumatoid arthritis (RASF) and peripheral blood mononuclear cells (PBMC) from healthy donors in respect to proliferation, calcium mobilization, drug uptake, cytokine and immunoglobulin production. Intracellular calcium and drug uptake were determined by fluorescent dyes Cal-520 and PoPo3, respectively. Cytokine and immunoglobulin production were evaluated by ELISA. Cannabinoid receptors 1 and 2 (CB1 and CB2) were detected by flow cytometry. RASF express CB1 and CB2 and the latter was increased by tumor necrosis factor (TNF). In RASF, THC (≥5 µM) increased intracellular calcium levels/PoPo3 uptake in a TRPA1-dependent manner and reduced interleukin-8 (IL-8) and matrix metalloprotease 3 (MMP-3) production at high concentrations (25 µM). Proliferation was slightly enhanced at intermediate THC concentrations (1-10 µM) but was completely abrogated at 25 µM. In PBMC alone, THC decreased interleukin-10 (IL-10) production and increased immunoglobulin G (IgG). In PBMC/RASF co-culture, THC decreased TNF production when cells were stimulated with interferon-γ (IFN-γ) or CpG. THC provides pro- and anti-inflammatory effects in RASF and PBMC. This is dependent on the activating stimulus and concentration of THC. Therefore, THC might be used to treat inflammation in RA but it might need titrating to determine the effective concentration.

An Overview of the TRP-Oxidative Stress Axis in Metabolic Syndrome: Insights for Novel Therapeutic Approaches

Metabolic syndrome (MS) is a complex pathology characterized by visceral adiposity, insulin resistance, arterial hypertension, and dyslipidaemia. It has become a global epidemic associated with increased consumption of high-calorie, low-fibre food and sedentary habits. Some of its underlying mechanisms have been identified, with hypoadiponectinemia, inflammation and oxidative stress as important factors for MS establishment and progression. Alterations in adipokine levels may favour glucotoxicity and lipotoxicity which, in turn, contribute to inflammation and cellular stress responses within the adipose, pancreatic and liver tissues, in addition to hepatic steatosis. The multiple mechanisms of MS make its clinical management difficult, involving both non-pharmacological and pharmacological interventions. Transient receptor potential (TRP) channels are non-selective calcium channels involved in a plethora of physiological events, including energy balance, inflammation and oxidative stress. Evidence from animal models of disease has contributed to identify their specific contributions to MS and may help to tailor clinical trials for the disease. In this context, the oxidative stress sensors TRPV1, TRPA1 and TRPC5, play major roles in regulating inflammatory responses, thermogenesis and energy expenditure. Here, the interplay between these TRP channels and oxidative stress in MS is discussed in the light of novel therapies to treat this syndrome.

Presence of TRPA1 Modifies CD4+/CD8+ T Lymphocyte Ratio and Activation

Transient Receptor Potential Ankyrin 1 (TRPA1) has been reported to influence neuroinflammation and lymphocyte function. We analysed the immune phenotype and activation characteristics of TRPA1-deficient mice (knockout—KO) generated by targeted deletion of the pore-loop domain of the ion channel. We compared TRPA1 mRNA and protein expression in monocyte and lymphocyte subpopulations isolated from primary and secondary lymphatic organs of wild type (WT) and KO mice. qRT-PCR and flow cytometric studies indicated a higher level of TRPA1 in monocytes than in lymphocytes, but both were orders of magnitude lower than in sensory neurons. We found lower CD4+/CD8+ thymocyte ratios, diminished CD4/CD8 rates, and B cell numbers in the KO mice. Early activation marker CD69 was lower in CD4+ T cells of KO, while the level of CD8+/CD25+ cells was higher. In vitro TcR-mediated activation did not result in significant differences in CD69 level between WT and KO splenocytes, but lower cytokine (IL-1β, IL-6, TNF-α, IL-17A, IL-22, and RANTES) secretion was observed in KO splenocytes. Basal intracellular Ca²⁺ level and TcR-induced Ca²⁺ signal in T lymphocytes did not differ significantly, but interestingly, imiquimod-induced Ca²⁺ level in KO thymocytes was higher. Our results support the role of TRPA1 in the regulation of activation, cytokine production, and T and B lymphocytes composition in mice.

TRPA1 Expression and Pathophysiology in Immune Cells

The non-selective cation channel TRPA1 is best known as a broadly-tuned sensor expressed in nociceptive neurons, where it plays key functions in chemo-, thermo-, and mechano-sensing. However, in this review we illustrate how this channel is expressed also in cells of the immune system. TRPA1 has been detected, mainly with biochemical techniques, in eosinophils, mast cells, macrophages, dendritic cells, T cells, and B cells, but not in neutrophils. Functional measurements, in contrast, remain very scarce. No studies have been reported in basophils and NK cells. TRPA1 in immune cells has been linked to arthritis (neutrophils), anaphylaxis and atopic dermatitis (mast cells), atherosclerosis, renal injury, cardiac hypertrophy and inflammatory bowel disease (macrophages), and colitis (T cells). The contribution of TRPA1 to immunity is dual: as detector of cell stress, tissue injury, and exogenous noxious stimuli it leads to defensive responses, but in conditions of aberrant regulation it contributes to the exacerbation of inflammatory conditions. Future studies should aim at characterizing the functional properties of TRPA1 in immune cells, an essential step in understanding its roles in inflammation and its potential as therapeutic target.

The Hypothermic Effect of Hydrogen Sulfide Is Mediated by the Transient Receptor Potential Ankyrin-1 Channel in Mice

Hydrogen sulfide (H₂S) has been shown in previous studies to cause hypothermia and hypometabolism in mice, and its thermoregulatory effects were subsequently investigated. However, the molecular target through which H₂S triggers its effects on deep body temperature has remained unknown. We investigated the thermoregulatory response to fast-(Na₂S) and slow-releasing (GYY4137) H₂S donors in C57BL/6 mice, and then tested whether their effects depend on the transient receptor potential ankyrin-1 (TRPA1) channel in Trpa1 knockout (Trpa1^−/−) and wild-type (Trpa1^+/+) mice. Intracerebroventricular administration of Na₂S (0.5–1 mg/kg) caused hypothermia in C57BL/6 mice, which was mediated by cutaneous vasodilation and decreased thermogenesis. In contrast, intraperitoneal administration of Na₂S (5 mg/kg) did not cause any thermoregulatory effect. Central administration of GYY4137 (3 mg/kg) also caused hypothermia and hypometabolism. The hypothermic response to both H₂S donors was significantly (p < 0.001) attenuated in Trpa1^−/− mice compared to their Trpa1^+/+ littermates. Trpa1 mRNA transcripts could be detected with RNAscope in hypothalamic and other brain neurons within the autonomic thermoeffector pathways. In conclusion, slow- and fast-releasing H₂S donors induce hypothermia through hypometabolism and cutaneous vasodilation in mice that is mediated by TRPA1 channels located in the brain, presumably in hypothalamic neurons within the autonomic thermoeffector pathways.

Metformin strengthens uroepithelial immunity against E. coli infection

Urinary tract infection frequently caused by E. coli is one of the most common bacterial infections. Increasing antibiotic resistance jeopardizes successful treatment and alternative treatment strategies are therefore mandatory. Metformin, an oral antidiabetic drug, has been shown to activate macrophages in the protection against certain infecting microorganisms. Since epithelial cells often form the first line of defense, we here investigated the effect on uroepithelial cells during E. coli infection. Metformin upregulated the human antimicrobial peptides cathelicidin LL-37 and RNase7 via modulation of the TRPA1 channel and AMPK pathway. Interestingly, metformin stimulation enriched both LL-37 and TRPA1 in lysosomes. In addition, metformin specifically increased nitric oxide and mitochondrial, but not cytosolic ROS. Moreover, metformin also triggered mRNA expression of the proinflammatory cytokines IL1B, CXCL8 and growth factor GDF15 in human uroepithelial cells. The GDF15 peptide stimulated macrophages increased LL-37 expression, with increased bacterial killing. In conclusion, metformin stimulation strengthened the innate immunity of uroepithelial cells inducing enhanced extracellular and intracellular bacterial killing suggesting a favorable role of metformin in the host defense.

Transient Receptor Potential (TRP) Channels in Haematological Malignancies: An Update

Transient receptor potential (TRP) channels are improving their importance in different cancers, becoming suitable as promising candidates for precision medicine. Their important contribution in calcium trafficking inside and outside cells is coming to light from many papers published so far. Encouraging results on the correlation between TRP and overall survival (OS) and progression-free survival (PFS) in cancer patients are available, and there are as many promising data from in vitro studies. For what concerns haematological malignancy, the role of TRPs is still not elucidated, and data regarding TRP channel expression have demonstrated great variability throughout blood cancer so far. Thus, the aim of this review is to highlight the most recent findings on TRP channels in leukaemia and lymphoma, demonstrating their important contribution in the perspective of personalised therapies.

An Immunometabolic Shift Modulates Cytotoxic Lymphocyte Activation During Melanoma Progression in TRPA1 Channel Null Mice

Melanoma skin cancer is extremely aggressive with increasing incidence and mortality. Among the emerging therapeutic targets in the treatment of cancer, the family of transient receptor potential channels (TRPs) has been reported as a possible pharmacological target. Specifically, the ankyrin subfamily, representing TRPA1 channels, can act as a pro-inflammatory hub. These channels have already been implicated in the control of intracellular metabolism in several cell models, but little is known about their role in immune cells, and how it could affect tumor progression in a process known as immune surveillance. Here, we investigated the participation of the TRPA1 channel in the immune response against melanoma tumor progression in a mouse model. Using Trpa1 ^+/+ and Trpa1 ^-/- animals, we evaluated tumor progression using murine B16-F10 cells and assessed isolated CD8+ T cells for respiratory and cytotoxic functions. Tumor growth was significantly reduced in Trpa1 ^-/- animals. We observed an increase in the frequency of circulating lymphocytes. Using a dataset of CD8+ T cells isolated from metastatic melanoma patients, we found that TRPA1 reduction correlates with several immunological pathways. Naïve CD8+ T cells from Trpa1 ^+/+ and Trpa1 ^-/- animals showed different mitochondrial respiration and glycolysis profiles. However, under CD3/CD28 costimulatory conditions, the absence of TRPA1 led to an even more extensive metabolic shift, probably linked to a greater in vitro killling ability of Trpa1 ^-/- CD8+ T cells. Therefore, these data demonstrate an unprecedented role of TRPA1 channel in the metabolism control of the immune system cells during carcinogenesis.

Network Pharmacology-Based Strategy for Elucidating the Molecular Basis Forthe Pharmacologic Effects of Licorice (Glycyrrhiza spp.)

Licorice (Glycyrrhiza spp.) is used widely in traditional Chinese medicine (TCM) due to its numerous pharmacologic effects. However, the mechanisms of action of the chemical constituents of licorice and their structure–function relationships are not fully understood. To address these points, we analyzed the chemical compounds in licorice listed in the TCM Systems Pharmacology database and TCM Integrated database. Target proteins of the compounds were predicted using Integrative Pharmacology-based Research Platform of TCM v2.0. Information on the pharmacologic effects of licorice was obtained from the 2020 Chinese Pharmacopoeia, and disease-related genes that have been linked to these effects were identified from the Encyclopedia of TCM database. Pathway analyses using the Kyoto Encyclopedia of Genes and Genomes database were carried out for target proteins, and pharmacologic networks were constructed based on drug target–disease-related gene and protein–protein interactions. A total of 451 compounds were analyzed, of which 211 were from the medicinal parts of the licorice plant. The 241 putative targets of 106 bioactive compounds in licorice comprised 52 flavonoids, 47 triterpenoids, and seven coumarins. Four distinct pharmacologic effects of licorice were defined: 61 major hubs were the putative targets of 23 compounds in heat-clearing and detoxifying effects; 68 were targets of six compounds in spleen-invigorating and qi-replenishing effects; 28 were targets of six compounds in phlegm-expulsion and cough-suppressant effects; 25 compounds were targets of six compounds in spasm-relieving and analgesic effects. The major bioactive compounds of licorice were identified by ultra-high-performance liquid chromatography–quadrupole time-of-flight–tandem mass spectrometry. The anti-inflammatory properties of liquiritin apioside, liquiritigenin, glycyrrhizic acid and isoliquiritin apioside were demonstrated by enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. Liquiritin apioside, liquiritigenin, isoliquiritin, isoliquiritin apioside, kaempferol, and kumatakenin were the main active flavonoids, and 18α- and 18β-glycyrrhetinic acid were the main active triterpenoids of licorice. The former were associated with heat-clearing and detoxifying effects, whereas the latter were implicated in the other three pharmacologic effects. Thus, the compounds in licorice have distinct pharmacologic effects according to their chemical structure. These results provide a reference for investigating the potential of licorice in treatment of various diseases.

Dimethyl Trisulfide Diminishes Traumatic Neuropathic Pain Acting on TRPA1 Receptors in Mice

Pharmacotherapy of neuropathic pain is still challenging. Our earlier work indicated an analgesic effect of dimethyl trisulfide (DMTS), which was mediated by somatostatin released from nociceptor nerve endings acting on SST₄ receptors. Somatostatin release occurred due to TRPA1 ion channel activation. In the present study, we investigated the effect of DMTS in neuropathic pain evoked by partial ligation of the sciatic nerve in mice. Expression of the mRNA of Trpa1 in murine dorsal-root-ganglion neurons was detected by RNAscope. Involvement of TRPA1 ion channels and SST₄ receptors was tested with gene-deleted animals. Macrophage activity at the site of the nerve lesion was determined by lucigenin bioluminescence. Density and activation of microglia in the spinal cord dorsal horn was verified by immunohistochemistry and image analysis. Trpa1 mRNA is expressed in peptidergic and non-peptidergic neurons in the dorsal root ganglion. DMTS ameliorated neuropathic pain in Trpa1 and Sstr4 WT mice, but not in KO ones. DMTS had no effect on macrophage activity around the damaged nerve. Microglial density in the dorsal horn was reduced by DMTS independently from TRPA1. No effect on microglial activation was detected. DMTS might offer a novel therapeutic opportunity in the complementary treatment of neuropathic pain.

Functional Expression of TRPV1 Ion Channel in the Canine Peripheral Blood Mononuclear Cells

TRPV1, known as a capsaicin receptor, is the best-described transient receptor potential (TRP) ion channel. Recently, it was shown to be expressed by non-excitable cells such as lymphocytes. However, the data regarding the functional expression of the TRPV1 channel in the immune cells are often contradictory. In the present study, we performed a phylogenetical analysis of the canine TRP ion channels, we assessed the expression of TRPV1 in the canine peripheral blood mononuclear cells (PBMC) by qPCR and Western blot, and we determined the functionality of TRPV1 by whole-cell patch-clamp recordings and calcium assay. We found high expression of TRPV2, -M2, and -M7 in the canine PBMCs, while expression of TRPV1, -V4 and, -M5 was relatively low. We confirmed that TRPV1 is expressed on the protein level in the PBMC and it localizes in the plasma membrane. The whole-cell patch-clamp recording revealed that capsaicin application caused a significant increase in the current density. Similarly, the results from the calcium assay show a dose-dependent increase in intracellular calcium level in the presence of capsaicin that was partially abolished by capsazepine. Our study confirms the expression of TRPV1 ion channel on both mRNA and protein levels in the canine PBMC and indicates that the ion channel is functional.

A TRiP Through the Roles of Transient Receptor Potential Cation Channels in Type 2 Upper Airway Inflammation

PURPOSE OF REVIEW

Despite their high prevalence, the pathophysiology of allergic rhinitis (AR) and chronic rhinosinusitis (CRS) remains unclear. Recently, transient receptor potential (TRP) cation channels emerged as important players in type 2 upper airway inflammatory disorders. In this review, we aim to discuss known and yet to be explored roles of TRP channels in the pathophysiology of AR and CRS with nasal polyps.

RECENT FINDINGS

TRP channels participate in a plethora of cellular functions and are expressed on T cells, mast cells, respiratory epithelial cells, and sensory neurons of the upper airways. In chronic upper airway inflammation, TRP vanilloid 1 is mostly studied in relation to nasal hyperreactivity. Several other TRP channels such as TRP vanilloid 4, TRP ankyrin 1, TRP melastatin channels, and TRP canonical channels also have important functions, rendering them potential targets for therapy. The role of TRP channels in type 2 inflammatory upper airway diseases is steadily being uncovered and increasingly recognized. Modulation of TRP channels may offer therapeutic perspectives.

Involvement of Neuro-Immune Interactions in Pruritus With Special Focus on Receptor Expressions

Pruritus is a common, but very challenging symptom with a wide diversity of underlying causes like dermatological, systemic, neurological and psychiatric diseases. In dermatology, pruritus is the most frequent symptom both in its acute and chronic form (over 6 weeks in duration). Treatment of chronic pruritus often remains challenging. Affected patients who suffer from moderate to severe pruritus have a significantly reduced quality of life. The underlying physiology of pruritus is very complex, involving a diverse network of components in the skin including resident cells such as keratinocytes and sensory neurons as well as transiently infiltrating cells such as certain immune cells. Previous research has established that there is a significant crosstalk among the stratum corneum, nerve fibers and various immune cells, such as keratinocytes, T cells, basophils, eosinophils and mast cells. In this regard, interactions between receptors on cutaneous and spinal neurons or on different immune cells play an important role in the processing of signals which are important for the transmission of pruritus. In this review, we discuss the role of various receptors involved in pruritus and inflammation, such as TRPV1 and TRPA1, IL-31RA and OSMR, TSLPR, PAR-2, NK1R, H1R and H4R, MRGPRs as well as TrkA, with a focus on interaction between nerve fibers and different immune cells. Emerging evidence shows that neuro-immune interactions play a pivotal role in mediating pruritus-associated inflammatory skin diseases such as atopic dermatitis, psoriasis or chronic spontaneous urticaria. Targeting these bidirectional neuro-immune interactions and the involved pruritus-specific receptors is likely to contribute to novel insights into the underlying pathogenesis and targeted treatment options of pruritus.

TRPM8 channel augments T-cell activation and proliferation

The transient receptor potential melastatin 8 (TRPM8) is an ion channel that has been widely studied as a cold-sensitive nociceptor. However, its importance in nonneuronal cells is mostly unexplored. Here, we describe the presence and functional significance of endogenous TRPM8, a nonselective Ca²⁺ -channel in T cell functions. The major pool of TRPM8 resides at the T cell surface and its surface accumulation significantly increases in activated T cells. TRPM8 activation synergizes with T-cell receptor (TCR) stimulation to increase CD25, CD69 levels and enhances secretion of proinflammatory cytokine tumor necrosis factor. However, TRPM8 inhibition does not restrict TCR stimulation mediated activation of T cells, indicating that unlike the heat-sensitive TRPV1 and TRPV4 channels, the cold-sensitive TRPM8 channel may be dispensable during T-cell activation, at least in mice. In this study, we demonstrate that TRPM8 promotes TCR-induced intracellular calcium increase. TRPM8 activation is beneficial for T-cell activation and differentiation into effector cells. TRPM8 inhibition during the T-cell activation process may lead to altered phenotype and reduced proliferation, without affecting cell viability. These results collectively establish TRPM8 as a functional calcium channel whose activation may be utilized for mounting an effective immune response. The findings of this study will be relevant to the regulation and response of T cells during cell-mediated immunity. These results will likely further our understanding on the role of ion channels in T-cell activation.

Inhibition of transient receptor potential vanilloid 1 (TRPV1) channel regulates chikungunya virus infection in macrophages

Chikungunya virus (CHIKV), a virus that induces pathogenic inflammatory host immune responses, is re-emerging worldwide, and there are currently no established antiviral control measures. Transient receptor potential vanilloid 1 (TRPV1), a non-selective Ca²⁺-permeable ion channel, has been found to regulate various host inflammatory responses including several viral infections. Immune responses to CHIKV infection in host macrophages have been reported recently. However, the possible involvement of TRPV1 during CHIKV infection in host macrophages has not been studied. Here, we investigated the possible role of TRPV1 in CHIKV infection of the macrophage cell line RAW 264.7. It was found that CHIKV infection upregulates TRPV1 expression in macrophages. To confirm this observation, the TRPV1-specific modulators 5'-iodoresiniferatoxin (5'-IRTX, a TRPV1 antagonist) and resiniferatoxin (RTX, a TRPV1 agonist) were used. Our results indicated that TRPV1 inhibition leads to a reduction in CHIKV infection, whereas TRPV1 activation significantly enhances CHIKV infection. Using a plaque assay and a time-of-addition assay, it was observed that functional modulation of TRPV1 affects the early stages of the viral lifecycle in RAW 264.7 cells. Moreover, CHIKV infection was found to induce of pNF-κB (p65) expression and nuclear localization. However, both activation and inhibition of TRPV1 were found to enhance the expression and nuclear localization of pNF-κB (p65) and production of pro-inflammatory TNF and IL-6 during CHIKV infection. In addition, it was demonstrated by Ca²⁺ imaging that TRPV1 regulates Ca²⁺ influx during CHIKV infection. Hence, the current findings highlight a potentially important regulatory role of TRPV1 during CHIKV infection in macrophages. This study might also have broad implications in the context of other viral infections as well.

A Rapid Shift from Chronic Hyperoxia to Normoxia Induces Systemic Anaphylaxis via Transient Receptor Potential Ankyrin 1 Channels on Mast Cells

Extensive activation of mast cells is the major switch that triggers systemic anaphylaxis, resulting in the subsequent release of anaphylactic mediators into circulation. We previously demonstrated that rapid changes in oxygen tension lead to mast cell degranulation, and the released tryptase triggers retinal angiogenesis in a murine oxygen-induced retinopathy model. However, whether a rapid shift from hyperoxia to normoxia (relative hypoxic stress) is a risk factor for systemic anaphylaxis remains unknown. In this study, we demonstrated that the relative hypoxia stress induces systemic mast cell activation via transient receptor potential ankyrin 1 (TRPA1) channels, which immediately leads to hypothermia and increased vascular permeability in adult mice. Although mast cell-deficient or TRPA1-deficient mice did not exhibit anaphylactic symptoms following a rapid sift to normoxia, preinjection with bone marrow-derived cultured mast cells (BMCMCs) derived from wild-type TRPA1-expressing mice restored anaphylactic responses. In addition, we found that the rapid reductions in oxygen tension in a culture atmosphere triggered the degranulation of BMCMCs derived from wild-type TRPA1-expressing mice but not that of BMCMCs derived from TRPA1-deficient mice. In human LAD2 mast cells, the relative hypoxic stress led to the degranulation, which was suppressed by the addition of a TRPA1 inhibitor. Gradual reductions from hyperoxia to normoxia led to no anaphylactic symptoms. Our results demonstrated that TRPA1-triggered mast cell degranulation is a novel pathway that induces anaphylactic shock without Ag-Ab reactions. These findings introduce a potential role for oxygen in inducing mast cell-dependent anaphylaxis and highlight the need to reconsider chronic pure oxygen therapy for anoxic diseases.

In Vivo Pharmacokinetic Analysis Utilizing Non-Targeted and Targeted Mass Spectrometry and In Vitro Assay against Transient Receptor Potential Channels of Maobushisaishinto and Its Constituent Asiasari Radix

The Japanese traditional medicine maobushisaishinto (MBST) has been prescribed for treating upper respiratory tract infections, such as a common cold. However, its mode of action is poorly understood, especially concerning the MBST constituent Asiasari Radix (AR). In this study, we focused on AR, with an objective of clarifying its bioavailable active ingredients and role within MBST by performing pharmacokinetic and pharmacological studies. Firstly, we performed qualitative non-targeted analysis utilizing high-resolution mass spectrometry to explore the bioavailable ingredients of AR as well as quantitative targeted analysis to reveal plasma concentrations following oral administration of MBST in rats. Secondly, we performed in vitro pharmacological study of bioavailable AR ingredients in addition to other ingredients of MBST to confirm any agonistic activities against transient receptor potential (TRP) channels. As a result, methyl kakuol and other compounds derived from AR were detected in the rat plasma and showed agonistic activity against TRPA1. This study suggests that methyl kakuol as well as other compounds have the potential to be an active ingredient in AR and thus presumably would contribute in part to the effects exerted by MBST.

Cannabidiol (CBD): a killer for inflammatory rheumatoid arthritis synovial fibroblasts

Cannabidiol (CBD) is a non-intoxicating phytocannabinoid from cannabis sativa that has demonstrated anti-inflammatory effects in several inflammatory conditions including arthritis. However, CBD binds to several receptors and enzymes and, therefore, its mode of action remains elusive. In this study, we show that CBD increases intracellular calcium levels, reduces cell viability and IL-6/IL-8/MMP-3 production of rheumatoid arthritis synovial fibroblasts (RASF). These effects were pronounced under inflammatory conditions by activating transient receptor potential ankyrin (TRPA1), and by opening of the mitochondrial permeability transition pore. Changes in intracellular calcium and cell viability were determined by using the fluorescent dyes Cal-520/PoPo3 together with cell titer blue and the luminescent dye RealTime-glo. Cell-based impedance measurements were conducted with the XCELLigence system and TRPA1 protein was detected by flow cytometry. Cytokine production was evaluated by ELISA. CBD reduced cell viability, proliferation, and IL-6/IL-8 production of RASF. Moreover, CBD increased intracellular calcium and uptake of the cationic viability dye PoPo3 in RASF, which was enhanced by pre-treatment with TNF. Concomitant incubation of CBD with the TRPA1 antagonist A967079 but not the TRPV1 antagonist capsazepine reduced the effects of CBD on calcium and PoPo3 uptake. In addition, an inhibitor of the mitochondrial permeability transition pore, cyclosporin A, also blocked the effects of CBD on cell viability and IL-8 production. PoPo3 uptake was inhibited by the voltage-dependent anion-selective channel inhibitor DIDS and Decynium-22, an inhibitor for all organic cation transporter isoforms. CBD increases intracellular calcium levels, reduces cell viability, and IL-6/IL-8/MMP-3 production of RASF by activating TRPA1 and mitochondrial targets. This effect was enhanced by pre-treatment with TNF suggesting that CBD preferentially targets activated, pro-inflammatory RASF. Thus, CBD possesses anti-arthritic activity and might ameliorate arthritis via targeting synovial fibroblasts under inflammatory conditions.

Complex Regulatory Role of the TRPA1 Receptor in Acute and Chronic Airway Inflammation Mouse Models

The Transient Receptor Potential Ankyrin 1 (TRPA1) cation channel expressed on capsaicin-sensitive afferents, immune and endothelial cells is activated by inflammatory mediators and exogenous irritants, e.g., endotoxins, nicotine, crotonaldehyde and acrolein. We investigated its involvement in acute and chronic pulmonary inflammation using Trpa1 gene-deleted (Trpa1^-/-) mice. Acute pneumonitis was evoked by intranasal Escherichia coli endotoxin (lipopolysaccharide: LPS) administration, chronic bronchitis by daily cigarette smoke exposure (CSE) for 4 months. Frequency, peak inspiratory/expiratory flows, minute ventilation determined by unrestrained whole-body plethysmography were significantly greater, while tidal volume, inspiratory/expiratory/relaxation times were smaller in Trpa1^-/- mice. LPS-induced bronchial hyperreactivity, myeloperoxidase activity, frequency-decrease were significantly greater in Trpa1^-/- mice. CSE significantly decreased tidal volume, minute ventilation, peak inspiratory/expiratory flows in wildtypes, but not in Trpa1^-/- mice. CSE remarkably increased the mean linear intercept (histopathology), as an emphysema indicator after 2 months in wildtypes, but only after 4 months in Trpa1^-/- mice. Semiquantitative histopathological scores were not different between strains in either models. TRPA1 has a complex role in basal airway function regulation and inflammatory mechanisms. It protects against LPS-induced acute pneumonitis and hyperresponsiveness, but is required for CSE-evoked emphysema and respiratory deterioration. Further research is needed to determine TRPA1 as a potential pharmacological target in the lung.

Nociception in a Progressive Multiple Sclerosis Model in Mice Is Dependent on Spinal TRPA1 Channel Activation

Central neuropathic pain is a common untreated symptom in progressive multiple sclerosis (PMS) and is associated with poor quality of life and interference with patients' daily activities. The neuroinflammation process and mitochondrial dysfunction in the PMS lesions generate reactive species. The transient potential receptor ankyrin 1 (TRPA1) has been identified as one of the major mechanisms that contribute to neuropathic pain signaling and can be activated by reactive compounds. Thus, the goal of our study was to evaluate the role of spinal TRPA1 in the central neuropathic pain observed in a PMS model in mice. We used C57BL/6 female mice (20-30 g), and the PMS model was induced by the experimental autoimmune encephalomyelitis (EAE) using mouse myelin oligodendrocyte glycoprotein (MOG_35-55) antigen and CFA (complete Freund's adjuvant). Mice developed progressive clinical score, with motor impairment observed after 15 days of induction. This model induced mechanical and cold allodynia and heat hyperalgesia which were measured up to 14 days after induction. The hypersensitivity observed was reduced by the administration of selective TRPA1 antagonists (HC-030031 and A-967079, via intrathecal and intragastric), antioxidants (α-lipoic acid and apocynin, via intrathecal and intragastric), and TRPA1 antisense oligonucleotide (via intrathecal). We also observed an increase in TRPA1 mRNA levels, NADPH oxidase activity, and 4-hydroxinonenal (a TRPA1 agonist) levels in spinal cord samples of PMS-EAE induced animals. In conclusion, these results support the hypothesis of the TRPA1 receptor involvement in nociception observed in a PMS-EAE model in mice.

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.

Association between neuropathic pain characteristics and DNA methylation of transient receptor potential ankyrin 1 in human peripheral blood

Elucidation of epigenetic mechanisms correlating with neuropathic pain in humans is crucial for the prevention and treatment of this treatment-resistant pain state. In the present study, associations between neuropathic pain characteristics and DNA methylation of the transient receptor potential ankyrin 1 (TRPA1) gene were evaluated in chronic pain patients and preoperative patients. Pain and psychological states were prospectively assessed in patients who suffered chronic pain or were scheduled for thoracic surgery. Neuropathic characteristics were assessed using the Douleur Neuropathique 4 (DN4) questionnaire. DNA methylation levels of the CpG islands in the TRPA1 gene were examined using whole blood. Forty-eight adult patients were enrolled in this study. Increases in DNA methylation rates at CpG -51 showed positive correlations with increases in the DN4 score both in preoperative and chronic pain patients. Combined methylation rates at CpG -51 in these patients also significantly increased together with increase in DN4 scores. Neuropathic pain characteristics are likely associated with methylation rates at the promoter region of the TRPA1 gene in human peripheral blood.