Transient Receptor Potential A1 Research Articles

TRPA1 Influences Staphylococcus Aureus Skin Infection in Mice and Associates with HIF-1a and MAPK Pathway Modulation

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a major public health burden. Emerging antibiotic resistance has heightened the need for new treatment approaches for MRSA infection such as developing novel antimicrobial agents and enhancing the host’s defense response. The thermo-ion channels Transient Receptor Potential (TRP-) A1 and V1 have been identified as modulators of S. aureus quorum sensing in cell culture models. However, their effects on in vivo infection control are unknown. In this study, we investigated the therapeutic effect of natural TRP ion channel inhibitors on MRSA skin infection in mice. While deletion of TRPV1 did not affect lesion size or inflammatory markers, TRPA1−/− mice demonstrated significantly reduced infection severity and abscess size. Treatment with natural inhibitors of TRPA1 with or without blockade of TRPV1 also reduced abscess size. Tissue transcriptomic data coupled with immunohistochemistry revealed that TRPA1 inhibition impacted heat shock protein expression (HSP), modulated the HIF-1a and MAPK pathways, and reduced IL4 expression. Additionally, metabolomics data showed an impact on purine and glycosaminoglycan pathways. Multi-omic integration of transcriptomic and metabolic data revealed that diacylglycerol metabolism was the likely bridge between metabolic and immunological impacts. Our findings suggest that TRPA1 antagonism could provide a promising and cost-effective therapeutic approach for reducing the severity of MRSA infection, and presents a novel underlying molecular mechanism.

The role of TRPA1 and TRPV1 in the perception of astringency.

Astringency, commonly described as a drying, roughening, and/or puckering sensation associated with polyphenol-rich foods affects their palatability. While the compounds eliciting astringency are known, its mechanism of action is debated. This study investigated the role of transient receptor potential (TRP) channels A1 and V1 in astringency perception. If TRP A1 or V1 have a functional role in astringency perception, then desensitizing these receptors should decrease perceived astringency. Thirty-seven panelists underwent unilateral lingual desensitization of TRP A1 and V1 channels using mustard oil and capsaicin, respectively. Panelists then evaluated four astringent stimuli: epicatechin (EC), epigallocatechin gallate (EGCG), tannic acid (TA) and potassium alum (Alum), via 2-AFC and intensity ratings. When TRPA1 receptors were desensitized on one half of the tongue via mustard oil, no significant differences were observed between the treated and untreated sides for both 2-AFC and intensity ratings. Similarly, when TRPV1 receptors were desensitized on one half of the tongue via capsaicin, no significant differences were observed between the treated and untreated sides for both 2-AFC and intensity ratings. These findings challenge the notion that TRP channels play a pivotal role in astringency perception.

Mono-2-ethylhexylphthalate (MEHP) is a potent agonist of human TRPA1 channel

Phthalates are extensively used as plasticizers in diverse consumer care products but have been reported to cause adverse health effects in humans. A commonly used phthalate, di-2-ethylhexylphthalate (DEHP) causes developmental and reproductive toxicities in humans, but the associated molecular mechanisms are not fully understood. Mono-2-ethylhexylphthalate (MEHP), a hydrolytic product of DEHP generated by cellular esterases, is proposed to be the active toxicant. We conducted a screen for sensory irritants among compounds used in consumer care using an assay for human Transient Receptor Potential A1 (hTRPA1). We have identified MEHP as a potent agonist of hTRPA1. MEHP-induced hTRPA1 activation was blocked by the TRPA1 inhibitor A-967079. Patch clamp assays revealed that MEHP induced inward currents in cells expressing hTRPA1. In addition, the N855S mutation in hTRPA1 associated with familial episodic pain syndrome decreased MEHP-induced hTRPA1 activation. In summary, we report that MEHP is a potent agonist of hTRPA1 which generates new possible mechanisms for toxic effects of phthalates in humans.

H2O2 enhances the spontaneous phasic contractions of isolated human-bladder strips via activation of TRPA1 channels on sensory nerves and the release of substance P and PGE2

Several studies have indicated that reactive oxygen species (ROS) can lead to detrusor overactivity (DO), but the underlying mechanisms are not known. Hydrogen dioxide (H2O2) is used commonly to investigate the effects of ROS. In present study, we investigated the effects of H2O2 on phasic spontaneous bladder contractions (SBCs) of isolated human-bladder strips (iHBSs) and the underlying mechanisms. Samples of bladder tissue were obtained from 26 patients undergoing cystectomy owing to bladder cancer. SBCs of iHBSs were recorded in organ-bath experiments. H2O2 (1μM–10mM) concentration-dependently increased the SBCs of iHBSs. These enhancing effects could be mimicked by an agonist of transient receptor potential (TRP)A1 channels (allyl isothiocyanate) and blocked with an antagonist of TRPA1 channels (HC030031; 10 μM). H2O2 induced enhancing effects also could be attenuated by desensitizing sensory afferents with capsaicin (10 μM), blocking nerve firing with TTX (1 μM), blocking neurokinin effects with NK2 receptor antagonist (SR48968, 10 μM), and blocking PGE2 synthesis with indomethacin (10 μM), respectively. Our study: (i) suggests activation of TRPA1 channels on bladder sensory afferents, and then release of substance P or PGE2 from sensory nerve terminals, contribute to the H2O2-induced enhancing effects on SBCs of iHBSs; (ii) provides insights for the mechanisms underlying ROS leading to DO; (iii) indicates that targeting TRPA1 channels might be the promising strategy against overactive bladder in conditions associated with excessive production of ROS.

An experimental study of acute toxicity and pharmacology of fermented Platycodonis Radix

This study investigated the acute toxicity of fermented Platycodonis Radix on mice and its effect on coughing in mice infected with Mycoplasma pneumoniae. The maximum dosage(MAD) was used in the acute toxicity experiment on mice to observe the signs of mice. After 14 days, dissection, blood biochemical examination, and pathological tissue section observation were conducted. In the pharmacological experiment of fermented Platycodonis Radix, 60 healthy BALB/c mice, 30 males and 30 females, were randomly divided into a blank group, a model group, a carbetapentane group(0.013 g·kg~(-1)·d~(-1)), and high-, medium-, and low-dose fermented Platycodonis Radix groups(5.2, 2.6, and 1.3 g·kg~(-1)·d~(-1)), with 10 mice in each group. Except for the blank group, the mice in the other five groups underwent model induction by intranasally instilling 20 μL of 1×10~6 CCU M. pneumoniae for 3 days, and the mice in each group were orally administered the corresponding drugs for 7 days. Cough induction experiment was conducted to observe and record the cough latency and total cough count within 3 min for each group. Hematoxylin-eosin(HE) staining and Masson staining were used to observe the pathological changes in lung tissues. Immunohistochemistry was performed to observe the protein expression of transient receptor potential A1(TRPA1), calcitonin gene-related peptide(CGRP), and substance P(SP) in the lung tissues of mice in each group. Real-time fluorescence-based quantitative polymerase chain reaction(qRT-PCR) was used to elucidate the changes in the mRNA levels of cough-related factors TRPA1, CGRP, and SP in mice treated with fermented Platycodonis Radix. No mice died in the acute toxicity experiment, and there were no changes in general behavior and major organ histopathological examinations. Compared with the blank group, there were no statistically significant differences in blood biochemical indexes. In the pharmacological experiment of fermented Platycodonis Radix, compared with the model group, the high-and medium-dose fermented Platycodonis Radix groups showed improved lung tissue structure of mice, with clear structure and regular tissue morphology. The qRT-PCR and immunohistochemical detection showed a decrease in the expression of TRPA1, CGRP, and SP in the fermented Platycodonis Radix groups. Fermented Platycodonis Radix can exert an inhibitory effect on cough by suppressing the expression of TRPA1, CGRP, and SP in lung tissues, thereby identifying the target of the drug.

Lipopolysaccharide-Induced TRPA1 Upregulation in Trigeminal Neurons is Dependent on TLR4 and Vesicular Exocytosis.

Pain from bacterial infection was believed to be the consequence of inflammation induced by bacterial products. However recent studies have shown that bacterial products can directly activate sensory neurons and induce pain. The mechanisms by which bacteria induce pain are poorly understood, but toll-like receptor (TLR)4 and transient receptor potential A1 (TRPA1) receptors are likely important integrators of pain signaling induced by bacteria. Using male and female mice we show that sensory neuron activation by bacterial lipopolysaccharides (LPS) is mediated by both TRPA1 and TLR4 and involves the mobilization of extracellular and intracellular calcium. We also show that LPS induces neuronal sensitization in a process dependent on TLR4 receptors. Moreover, we show that TLR4 and TRPA1 are both involved in sensory neurons response to LPS stimulation. Activation of TLR4 in a subset of sensory neurons induces TRPA1 upregulation at the cell membrane through vesicular exocytosis, contributing to the initiation of neuronal sensitization and pain. Collectively these data highlight the importance of sensory neurons to pathogen detection, and their activation by bacterial products like LPS as potentially important to early immune and nociceptive responses.SIGNIFICANCE STATEMENT Bacterial infections are often painful and the recent discovery that bacteria can directly stimulate sensory neurons leading to pain sensation and modulation of immune system have highlighted the importance of nervous system in the response to bacterial infection. Here, we showed that lipopolysaccharide, a major bacterial by-product, requires both toll-like receptor (TLR)4 and transient receptor potential A1 (TRPA1) receptors for neuronal activation and acute spontaneous pain, but only TLR4 mediates sensory neurons sensitization. Moreover, we showed for the first time that TLR4 sensitize sensory neurons through a rapid upregulation of TRPA1 via vesicular exocytosis. Our data highlight the importance of sensory neurons to pathogen detection and suggests that TLR4 would be a potential therapeutic target to modulate early stage of bacteria-induced pain and immune response.

TrpA1 is a shear stress mechanosensing channel regulating intestinal stem cell proliferation in Drosophila

Adult stem cells are essential for tissue maintenance and repair. Although genetic pathways for controlling adult stem cells are extensively investigated in various tissues, much less is known about how mechanosensing could regulate adult stem cells and tissue growth. Here, we demonstrate that shear stress sensing regulates intestine stem cell proliferation and epithelial cell number in adult Drosophila. Ca2+ imaging in ex vivo midguts shows that shear stress, but not other mechanical forces, specifically activates enteroendocrine cells among all epithelial cell types. This activation is mediated by transient receptor potential A1 (TrpA1), a Ca2+-permeable channel expressed in enteroendocrine cells. Furthermore, specific disruption of shear stress, but not chemical, sensitivity of TrpA1 markedly reduces proliferation of intestinal stem cells and midgut cell number. Therefore, we propose that shear stress may act as a natural mechanical stimulation to activate TrpA1 in enteroendocrine cells, which, in turn, regulates intestine stem cell behavior.

Flavonoids in Amomum tsaoko Crevost et Lemarie Ameliorate Loperamide-Induced Constipation in Mice by Regulating Gut Microbiota and Related Metabolites.

Amomum tsaoko (AT) is a dietary botanical with laxative properties; however, the active ingredients and mechanisms are still unclear. The active fraction of AT aqueous extract (ATAE) for promoting defecation in slow transit constipation mice is the ethanol-soluble part (ATES). The total flavonoids of ATES (ATTF) were the main active component. ATTF significantly increased the abundance of Lactobacillus and Bacillus and reduced the dominant commensals, such as Lachnospiraceae, thereby changing the gut microbiota structure and composition. Meanwhile, ATTF changed the gut metabolites mainly enriched in pathways such as the serotonergic synapse. In addition, ATTF increased the serum serotonin (5-HT) content and mRNA expression of 5-hydroxytryptamine receptor 2A (5-HT2A), Phospholipase A2 (PLA2), and Cyclooxygenase-2 (COX2), which are involved in the serotonergic synaptic pathway. ATTF increased Transient receptor potential A1 (TRPA1), which promotes the release of 5-HT, and Myosin light chain 3(MLC3), which promotes smooth muscle motility. Notably, we established a network between gut microbiota, gut metabolites, and host parameters. The dominant gut microbiota Lactobacillus and Bacillus, prostaglandin J2 (PGJ2) and laxative phenotypes showed the most significant associations. The above results suggest that ATTF may relieve constipation by regulating the gut microbiota and serotonergic synaptic pathway and has great potential for laxative drug development in the future.

Camphor Attenuates Hyperalgesia in Neuropathic Pain Models in Mice.

The treatment of neuropathic pain is still a majortroublesomeclinicalproblem. The existing therapeutic drugs have limited analgesic effect and obvious adverse reactions, which presents opportunities and challenges for the development of new analgesic drugs. Camphor, a kind of monoterpene, has been shown anti-inflammatory and analgesic effects in traditional Chinese medicine. But we know little about its effect in neuropathic pain. In this article, We have verified the reliable analgesic effect of camphor in the neuropathic pain model caused by different predispositions. The nociceptive response of mice was induced by transient receptor potential A1 (TRPA1) agonist to verify the effect of camphor on the nociceptive response. Multiple paclitaxel (PTX) injection models, Single oxaliplatin (OXA) injection models, Chronic constriction injury (CCI) models and Streptozotocin-induced (STZ) diabetic neuropathic pain models were used in this study. We verified the analgesic effect of camphor in mice by acetone test and conditioned place aversion test. At the same time, comparing the adverse reaction of nervous system between camphor and pregabalin at equivalent dose in locomotor activity test and rotarod test. Using patch clamp to verify the effect of camphor on dorsal root ganglion (DRG) excitability. In behavioral test, compared with vehicle group, camphor significantly reduced the spontaneous nociception caused by TRPA1 agonist-formalina and allyl isothiocyanate (AITC). Compared with vehicle group, camphor significantly reduced the flinching and licking time in neuropathic pain model mice, including PTX, OXA, STZ and CCI induced peripheral neuralgia models. Compared with vehicle group, pregabalin significantly increased the resting time and reduced the average speed without resting and distance in locomotor activity test, reduced the time stayed on rotarod in rotarod test. In patch clamp test, compared with vehicle group, camphor significantly reduced the action potential (AP) firing frequency of DRG. Camphor can alleviate the symptoms of hyperalgesia in various neuropathic pain models, and has no obvious adverse reactions compared with pregabalin. This effect is related to the down-regulation of DRG neuron excitability.

In silico affinity between analgesic/anti-inflammatory drugs and the transient receptor potential A1 to predict potential pharmacological managing approaches for bleaching sensitivity.

Reducing in-office tooth bleaching sensitivity represents a challenge for professionals. Researchers have associated the block of the pain receptor TRPA1 with reducing bleaching sensitivity. However, the chemical affinity of analgesic/anti-inflammatory drugs to the TRPA1 needs to be verified. To perform a virtual screening of multiple drugs (analgesic and anti-inflammatory drugs) to verify chemical affinity for the TRPA1 receptor. The crystal structure of the TRPA1 receptor proteins was retrieved from the Protein Data Bank. The SMILES codes of the ligands were extracted from PubChem. The binding energy of the complex was obtained in ∆G - kcal/mol by AutoDock Vina© and replicated in the webservers SwissDock©, Dockthor©, and CbDock©. LigPlus© confirmed the binding sites. Codeine and dexamethasone showed regularity among all servers, even showing binding energy values of -7.9 kcal/mol for codeine and -8.1 kcal/mol for dexamethasone. Codeine and dexamethasone may be potential drugs to manage tooth bleaching sensitivity if they reach the dental pulp TRPA1 receptor.

Water extract of Notopterygium incisum alleviates cold allodynia in neuropathic pain by regulation of TRPA1

Ethnopharmacological relevanceNeuropathic pain can be debilitating and drastically affects the quality of life of those patients suffering from this condition. The Chinese herb Notopterygium incisum Ting ex H.T. Chang has long been used to disperse “cold”. One under examined clinical feature of neuropathic pain is sensitivity to cold. Patients with neuropathic pain or arthritis usually describe a worsening of symptoms during the winter. Aims of this studyWe proposed to test the hypothesis that Notopterygium incisum has a positive effect on the cold sensitivity found in neuropathic pain. Materials and methodsIn this study, we established chronic constriction injury (CCI) and cisplatin induced neuropathic pain mice models. Behavioral experiments and physiological examination methods were employed to investigate the effect of water extract of Notopterygium incisum (WN) on cold pain. ResultsWe found WN reduced cold pain and allyl isothiocyanate (AITC, Transient Receptor Potential A1 (TRPA1 agonist)) induced pain. WN inhibited AITC induced calcium response in HEK 293 cells transfected with TRPA1 and dorsal root ganglion (DRG) neurons. Moreover, we found that oral administration of WN reduced cold allodynia and mechanical allodynia caused by (CCI) and cisplatin induced neuropathic pain. We also observed that oral administration of WN decreased responses to AITC in DRG neurons as well as expression of TRPA1 in the WN treated neuropathic pain model. ConclusionsThe present study provide evidence that Notopterygium incisum alleviates cold allodynia in CCI and cisplatin induced neuropathic pain mouse models. WN alleviated neuropathic pain induced cold allodynia via directly modulating TRPA1. Our findings identify WN as a promising candidate for treating neuropathic pain that highlights a new mechanism of Notopterygium incisum on ‘disperse cold’.

Targeting ROS-sensitive TRP ion channels for relieving oxidative stress-related diseases based on nanomaterials

Reactive oxygen species (ROS) play an important role in regulating various physiological functions by activating specific ion channels to mediate cell growth, proliferation, regeneration, and apoptosis. ROS sensitive ion channels in the transient receptor potential (TRP) channel family are closely related to oxidative stress-related diseases. Therefore, it is of great significance to regulate ROS levels and their related ion channels. This review summarizes the role of five ROS sensitive ion channels, transient receptor potential M2 (TRPM2), transient receptor potential A1 (TRPA1), transient receptor potential V1 (TRPV1), transient receptor potential M7 (TRPM7) and transient receptor potential C5 (TRPC5), in oxidative stress-related diseases. In addition, the recent research progress of using nanomaterials to regulate oxidative stress-related diseases by targeting ROS-sensitive ion channels is summarized. It is hoped that this review will provide insights for researchers to regulate ROS-sensitive ion channels to alleviate related diseases.

Therapeutic effect of Baimai Ointment on peripheral sensitization of chronic inflammatory pain in mice

Chronic inflammatory pain is mainly manifested by peripheral sensitization. Baimai Ointment(BMO), a classical Tibetan medicine for external use, has good clinical efficacy in the treatment of chronic inflammatory pain, while its pharmacodynamics and mechanism for relieving peripheral sensitization remain unclear. This study established an animal model of chronic inflammatory pain induced by complete Freund's adjuvant to explore the mechanism of BMO in the treatment of chronic inflammatory pain by behavioral test, side effect assessment, network analysis, and experimental verification. The pharmacodynamics experiment showed that BMO increased the thresholds of mechanical pain sensitivity and thermal radiation pain sensitivity of chronic inflammatory pain mice in a dose-dependent manner, and had inhibitory effect on foot swelling, inflammatory mediator, and the expression of transient receptor potential vanilloid-1(TRPV1) and transient receptor potential A1(TRPA1). The results of body weight monitoring, pain sensitivity threshold detection in normal mice, rotarod performance test, and forced swimming test showed that BMO had no obvious toxic or side effect. The network analysis of 51 candidate active molecules selected according to the efficacy of BMO, content of main components, and ADME parameters showed that the inhibitory effect of BMO on chronic inflammatory pain was associated with the core regulatory elements of tumor necrosis factor(TNF) and T cell receptor signaling pathways. BMO down-regulated the protein levels of mitogen-activated protein kinase 14(MAPK14), MAPK1, and prostaglandin-endoperoxide synthase 2(PTGS2), and up-regulated the phosphorylation le-vel of glycogen synthase kinase 3 beta(GSK3 B) in the plantar tissue of mice. In conclusion, BMO can effectively relieve peripheral sensitization of chronic inflammatory pain without inducing tolerance and obvious toxic and side effects. The relevant mechanism may be related to the regulation of BMO on core regulatory elements of TNF and T cell receptor signaling pathways in surrounding tissues.

Involvement of the transient receptor potential A1 in morphine-induced conditioned place preference and physical dependence in mice.

The main side effects of opioid use are physiological and psychological dependence. The transient receptor potential channels, including transient receptor potential ankyrin 1 (TRPA1), are involved in various neurological disorders. We aimed to evaluate the effect of TRPA1 inhibition on morphine-induced conditioned place preference (CPP) and physical dependence. For induction of CPP, morphine (10 and 20mg/kg) was administrated for four consecutive days to male BALB/c mice. The effects of HC030031 (TRPA1 antagonist, 10, 25, and 50mg/kg) on the expression and reinstatement of morphine-induced CPP were evaluated. For induction of physical dependence, morphine was injected three times a day for 3 days. Withdrawal-related behaviors such as jumping and defecation were precipitated by the administration of naloxone to morphine-dependent mice. The effect of HC030031 on jumping and defecation was assessed. The results showed that 20mg/kg of morphine elicited a significant CPP. HC030031 reduced the expression of morphine CPP without any change in the locomotor activity. It also decreased the reinstatement of morphine CPP. HC030031 mitigated morphine withdrawal via reducing jumping and defecation. The present study demonstrated that HC030031 decreased morphine-associated CPP and physical dependence. It is presumed that TRPA1 has interaction with the main pharmacological effects of morphine.

Shear stress activates nociceptors to drive Drosophila mechanical nociception

Mechanical nociception is essential for animal survival. However, the forces involved in nociceptor activation and the underlying mechanotransduction mechanisms remain elusive. Here, we address these problems by investigating nocifensive behavior in Drosophila larvae. We show that strong poking stimulates nociceptors with a mixture of forces including shear stress and stretch. Unexpectedly, nociceptors are selectively activated by shear stress, but not stretch. Both the shear stress responses of nociceptors and nocifensive behavior require transient receptor potential A1 (TrpA1), which is specifically expressed in nociceptors. We further demonstrate that expression of mammalian or Drosophila TrpA1 in heterologous cells confers responses to shear stress but not stretch. Finally, shear stress activates TrpA1 in a membrane-delimited manner, through modulation of membrane fluidity. Together, our study reveals TrpA1 as an evolutionarily conserved mechanosensitive channel specifically activated by shear stress and suggests a critical role of shear stress in activating nociceptors to drive mechanical nociception.

The Effectiveness of Wogonin on Treating Cough Mice With Mycoplasma Pneumoniae Infection.

Background: Cough is the main symptom of mycoplasma pneumoniae (MP) infection. Cough potential protein transient receptor potential A1 (TRPA1) plays an important role in cough reflex. The purpose of this study was to clarify the mechanism of wogonin, the effective component of Qinbai Qingfei concentrated pellet (Qinbai), in the treatment of cough after MP infection. Methods: The Biacore™ system was used to detect whether there was specific binding between Qinbai and cough potential protein TRPA1. Biacore™ fishing technology and UPLC-Q-TOF-MS technology were used during fishing combined active components and identification and analysis of recovered samples. The expression levels of TRPA1, substance P (SP), calcitonin gene-related peptide (CGRP), cough-related proteins, and mRNA in the lung tissues from each group were detected by immunohistochemistry, Western blot, and real-time PCR. Results: Biacore™ results showed that Qinbai had strong specific binding to TRPA1 protein with a binding value of 99.0 resonance unit (RU). The samples obtained from angling were identified and analyzed by UPLC-Q-TOF-MS as wogonin. The results of immunohistochemistry, Western blot, and real-time PCR showed that compared with the model group, the wogonin group had lower expressions of mRNA, TRPA1, SP, and CGRP in the lung tissue of cough mice with MP infection (p < 0.01 or p < 0.05), and the effects were superior to those of azithromycin and pentoxyverine control groups. Conclusion: Wogonin can treat cough after MP infection by affecting the expressions of cough-related proteins, such as TRPA1, SP, and CGRP. This study provided a theoretical foundation for the clinical research of Qinbai.

Sonogenetic control of mammalian cells using exogenous Transient Receptor Potential A1 channels

Ultrasound has been used to non-invasively manipulate neuronal functions in humans and other animals. However, this approach is limited as it has been challenging to target specific cells within the brain or body. Here, we identify human Transient Receptor Potential A1 (hsTRPA1) as a candidate that confers ultrasound sensitivity to mammalian cells. Ultrasound-evoked gating of hsTRPA1 specifically requires its N-terminal tip region and cholesterol interactions; and target cells with an intact actin cytoskeleton, revealing elements of the sonogenetic mechanism. Next, we use calcium imaging and electrophysiology to show that hsTRPA1 potentiates ultrasound-evoked responses in primary neurons. Furthermore, unilateral expression of hsTRPA1 in mouse layer V motor cortical neurons leads to c-fos expression and contralateral limb responses in response to ultrasound delivered through an intact skull. Collectively, we demonstrate that hsTRPA1-based sonogenetics can effectively manipulate neurons within the intact mammalian brain, a method that could be used across species.

The Role of Transient Receptor Potential A1 and G Protein-Coupled Receptor 39 in Zinc-Mediated Acute and Chronic Itch in Mice.

Itching is a common symptom of many skin or systemic diseases and has a negative impact on the quality of life. Zinc, one of the most important trace elements in an organism, plays an important role in the regulation of pain. Whether and how zinc regulates itching is largely unclear. Herein, we explored the role of Zn2+ in the regulation of acute and chronic itch in mice. It is found that intradermal injection (i.d.) of Zn2+ dose-dependently induced acute itch and transient receptor potential A1 (TRPA1) participated in Zn2+-induced acute itch in mice. Moreover, the pharmacological analysis showed the involvement of histamine, mast cells, opioid receptors, and capsaicin-sensitive C-fibers in Zn2+-induced acute itch in mice. Systemic administration of Zn2+ chelators, such as N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), pyrithione, and clioquinol were able to attenuate both acute itch and dry skin-induced chronic itch in mice. Quantitative polymerase chain reaction (Q-PCR) analysis showed that the messenger RNA (mRNA) expression levels of zinc transporters (ZIPs and ZnTs) significantly changed in the dorsal root ganglia (DRG) under dry skin-induced chronic itch condition in mice. Activation of extracellular signal-regulated kinase (ERK) pathway was induced in the DRG and skin by the administration of zinc or under dry skin condition, which was inhibited by systemic administration of Zn2+ chelators. Finally, we found that the expression of GPR39 (a zinc-sensing GPCR) was significantly upregulated in the dry skin mice model and involved in the pathogenesis of chronic itch. Together, these results indicated that the TRPA1/GPR39/ERK axis mediated the zinc-induced itch and, thus, targeting zinc signaling may be a promising strategy for anti-itch therapy.

Inherent P2X7 Receptors Regulate Macrophage Functions during Inflammatory Diseases.

Macrophages are mononuclear phagocytes which derive either from blood-borne monocytes or reside as resident macrophages in peripheral (Kupffer cells of the liver, marginal zone macrophages of the spleen, alveolar macrophages of the lung) and central tissue (microglia). They occur as M1 (pro-inflammatory; classic) or M2 (anti-inflammatory; alternatively activated) phenotypes. Macrophages possess P2X7 receptors (Rs) which respond to high concentrations of extracellular ATP under pathological conditions by allowing the non-selective fluxes of cations (Na+, Ca2+, K+). Activation of P2X7Rs by still higher concentrations of ATP, especially after repetitive agonist application, leads to the opening of membrane pores permeable to ~900 Da molecules. For this effect an interaction of the P2X7R with a range of other membrane channels (e.g., P2X4R, transient receptor potential A1 [TRPA1], pannexin-1 hemichannel, ANO6 chloride channel) is required. Macrophage-localized P2X7Rs have to be co-activated with the lipopolysaccharide-sensitive toll-like receptor 4 (TLR4) in order to induce the formation of the inflammasome 3 (NLRP3), which then activates the pro-interleukin-1β (pro-IL-1β)-degrading caspase-1 to lead to IL-1β release. Moreover, inflammatory diseases (e.g., rheumatoid arthritis, Crohn’s disease, sepsis, etc.) are generated downstream of the P2X7R-induced upregulation of intracellular second messengers (e.g., phospholipase A2, p38 mitogen-activated kinase, and rho G proteins). In conclusion, P2X7Rs at macrophages appear to be important targets to preserve immune homeostasis with possible therapeutic consequences.

Dysfunctional TRPM8 signalling in the vascular response to environmental cold in ageing.

Ageing is associated with increased vulnerability to environmental cold exposure. Previously, we identified the role of the cold-sensitive transient receptor potential (TRP) A1, M8 receptors as vascular cold sensors in mouse skin. We hypothesised that this dynamic cold-sensor system may become dysfunctional in ageing. We show that behavioural and vascular responses to skin local environmental cooling are impaired with even moderate ageing, with reduced TRPM8 gene/protein expression especially. Pharmacological blockade of the residual TRPA1/TRPM8 component substantially diminished the response in aged, compared with young mice. This implies the reliance of the already reduced cold-induced vascular response in ageing mice on remaining TRP receptor activity. Moreover, sympathetic-induced vasoconstriction was reduced with downregulation of the α2c adrenoceptor expression in ageing. The cold-induced vascular response is important for sensing cold and retaining body heat and health. These findings reveal that cold sensors, essential for this neurovascular pathway, decline as ageing onsets.