TRP channels in oxygen physiology: distinctive functional properties and roles of TRPA1 in O2 sensing

Metal profiling in coronary ischemia-reperfusion injury: Implications for KEAP1/NRF2 regulated redox signaling

Coronary ischemia-reperfusion (IR) injury results from a blockage of blood supply to the heart followed by restoration of perfusion, leading to oxidative stress induced pathological processes. Nuclear factor erythroid 2-related factor 2 (NRF2), a master antioxidant transcription factor, plays a key role in regulating redox signaling. Over the past decades, the field of metallomics has provided novel insights into the mechanism of pro-oxidant and antioxidant pathological processes. Both redox-active (e.g. Fe and Cu) and redox-inert (e.g. Zn and Mg) metals play unique roles in establishing redox balance under IR injury. Notably, Zn protects against oxidative stress in coronary IR injury by serving as a cofactor of antioxidant enzymes such as superoxide dismutase [Cu-Zn] (SOD1) and proteins such as metallothionein (MT) and KEAP1/NRF2 mediated antioxidant defenses. An increase in labile Zn2+ inhibits proteasomal degradation and ubiquitination of NRF2 by modifying KEAP1 and glycogen synthase kinase 3β (GSK3β) conformations. Fe and Cu catalyse the formation of reactive oxygen species via the Fenton reaction and also serve as cofactors of antioxidant enzymes and can activate NRF2 antioxidant signaling. We review the evidence that Zn and redox-active metals Fe and Cu affect redox signaling in coronary cells during IR and the mechanisms by which oxidative stress influences cellular metal content. In view of the unique double-edged characteristics of metals, we aim to bridge the role of metals and NRF2 regulated redox signaling to antioxidant defenses in IR injury, with a long-term aim of informing the design and application of novel therapeutics.

Hypoxia augments TRPM3-mediated calcium influx in vagal sensory neurons

Transient receptor potential melastatin 3 (TRPM3) channels contribute to nodose afferent and brainstem nucleus tractus solitarii (nTS) activity. Exposure to short, sustained hypoxia (SH) and chronic intermittent hypoxia (CIH) enhances nTS activity, although the mechanisms are unknown. We hypothesized TRPM3 may contribute to increased neuronal activity in nTS-projecting nodose ganglia viscerosensory neurons, and its influence is elevated following hypoxia. Rats were exposed to either room air (normoxia), 24-h of 10 % O2 (SH), or CIH (episodic 6 % O2 for 10d). A subset of neurons from normoxic rats were exposed to in vitro incubation for 24-h in 21 % or 1 % O2. Intracellular Ca2+ of dissociated neurons was monitored via Fura-2 imaging. Ca2+ levels increased upon TRPM3 activation via Pregnenolone sulfate (Preg) or CIM0216. Preg responses were eliminated by the TRPM3 antagonist ononetin, confirming agonist specificity. Removal of extracellular Ca2+ also eliminated Preg response, further suggesting Ca2+ influx via membrane-bound channels. In neurons isolated from SH-exposed rats, the TRPM3 elevation of Ca2+ was greater than in normoxic-exposed rats. The SH increase was reversed following a subsequent normoxic exposure. RNAScope demonstrated TRPM3 mRNA was greater after SH than in Norm ganglia. Incubating dissociated cultures from normoxic rats in 1 % O2 (24-h) did not alter the Preg Ca2+ responses compared to their normoxic controls. In contrast to in vivo SH, 10d CIH did not alter TRPM3 elevation of Ca2+. Altogether, these results demonstrate a hypoxia-specific increase in TRPM3-mediated calcium influx.

Transient Receptor Potential Ankyrin 1 (TRPA1) Channel as a Sensor of Oxidative Stress in Cancer Cells

Moderate levels of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), fuel tumor metastasis and invasion in a variety of cancer types. Conversely, excessive ROS levels can impair tumor growth and metastasis by triggering cancer cell death. In order to cope with the oxidative stress imposed by the tumor microenvironment, malignant cells exploit a sophisticated network of antioxidant defense mechanisms. Targeting the antioxidant capacity of cancer cells or enhancing their sensitivity to ROS-dependent cell death represent a promising strategy for alternative anticancer treatments. Transient Receptor Potential Ankyrin 1 (TRPA1) is a redox-sensitive non-selective cation channel that mediates extracellular Ca²⁺ entry upon an increase in intracellular ROS levels. The ensuing increase in intracellular Ca²⁺ concentration can in turn engage a non-canonical antioxidant defense program or induce mitochondrial Ca²⁺ dysfunction and apoptotic cell death depending on the cancer type. Herein, we sought to describe the opposing effects of ROS-dependent TRPA1 activation on cancer cell fate and propose the pharmacological manipulation of TRPA1 as an alternative therapeutic strategy to enhance cancer cell sensitivity to oxidative stress.

Unraveling the Underlying Molecular Mechanism of 'Silent Hypoxia' in COVID-19 Patients Suggests a Central Role for Angiotensin II Modulation of the AT1R-Hypoxia-Inducible Factor Signaling Pathway

A few days after being infected with SARS-CoV-2, a fraction of people remain asymptomatic but suffer from a decrease in arterial oxygen saturation in the absence of apparent dyspnea. In light of our clinical investigation on the modulation of molecules belonging to the renin angiotensin system (RAS) in COVID-19 patients, we propose a model that explains 'silent hypoxia'. The RAS imbalance caused by SARS-CoV-2 results in an accumulation of angiotensin 2 (Ang II), which activates the angiotensin 2 type 1 receptor (AT1R) and triggers a harmful cascade of intracellular signals leading to the nuclear translocation of the hypoxia-inducible factor (HIF)-1α. HIF-1α transactivates many genes including the angiotensin-converting enzyme 1 (ACE1), while at the same time, ACE2 is downregulated. A growing number of cells is maintained in a hypoxic condition that is self-sustained by the presence of the virus and the ACE1/ACE2 ratio imbalance. This is associated with a progressive worsening of the patient's biological parameters including decreased oxygen saturation, without further clinical manifestations. When too many cells activate the Ang II-AT1R-HIF-1α axis, there is a 'hypoxic spillover', which marks the tipping point between 'silent' and symptomatic hypoxia in the patient. Immediate ventilation is required to prevent the 'hypoxic spillover'.

Di-(2-ethylhexyl) Phthalate Limits the Lipid-Lowering Effects of Simvastatin by Promoting Protein Degradation of Low-Density Lipoprotein Receptor: Role of PPARγ-PCSK9 and LXRα-IDOL Signaling Pathways

Dialysis prevents death from uremia in patients with end-stage renal disease (ESRD). Nevertheless, during hemodialysis, circulating levels of di-(2-ethylhexyl) phthalate (DEHP) are increased due to phthalates leaching from medical tubes. Statins are an effective therapy for reducing the risks associated with cardiovascular diseases in patients with chronic kidney disease; however, the mechanism by which statins fail to reduce cardiovascular events in hemodialysis ESRD patients remains unclear. In this study, we investigated whether DEHP and its metabolites interfere with the lipid-lowering effect of statins in hepatocytes. In Huh7 cells, treatment with DEHP and its metabolites abolished the simvastatin-conferred lipid-lowering effect. Mechanistically, DEHP down-regulated the expression of low-density lipoprotein receptor (LDLR) and led to a decrease in LDL binding, which was mediated by the activation of the PPARγ-PCSK9 and LXRα-IDOL signaling pathways. Additionally, the NOX-ROS-TRPA1 pathway is involved in the DEHP-mediated inhibition of LDLR expression and LDL binding activity. Blockage of this pathway abrogated the DEHP-mediated inhibition in the LDLR expression and LDL binding of simvastatin. Collectively, DEHP induces the activation of the NOX-ROS-TRPA1 pathway, which in turn activates PPARγ-PCSK9- and LXRα-IDOL-dependent signaling, and, ultimately, diminishes the statin-mediated lipid-lowering effect in hepatocytes.

Thermoregulation and thermal sensation during whole-body water immersion at different water temperatures in healthy individuals: A scoping review

BACKGROUND

Severe thermal discomfort may increase risk of drowning due to hypothermia or hyperthermia from prolonged exposure to noxious water temperatures. The importance of using a behavioral thermoregulation model with thermal sensation may predict the thermal load that the human body receives when exposed to various immersive water conditions. However, there is no thermal sensation "gold standard" model specific for water immersion. This scoping review aims to present a comprehensive overview regarding human physiological and behavioral thermoregulation during whole-body water immersion and explore the feasibility for an accepted defined sensation scale for cold and hot water immersion.

METHODS

A standard literary search was performed on PubMed, Google Scholar, and SCOPUS. The words "Water Immersion," "Thermoregulation," "Cardiovascular responses" were used either as independent searched terms and MeSH terms (Medical Subject Headings) or in combination with other text words. The inclusion criteria for clinical trials terms to thermoregulatory measurements (core or skin temperature), whole-body immersion, 18-60 years old and healthy individuals. The prementioned data were analyzed narratively to achieve the overall study objective.

RESULTS

Twenty-three published articles fulfilled the review inclusion/exclusion criteria (with nine measured behavioral responses). Our outcomes illustrated a homogenous thermal sensation in a variety of water temperatures ranges, that was strongly associated with thermal balance, and observed different thermoregulatory responses. This scoping review highlights the impact of water immersion duration on human thermoneutral zone, thermal comfort zone, and thermal sensation.

CONCLUSION

Our findings enlighten the significance of thermal sensation as a health indicator for establishing a behavioral thermal model applicable for water immersion. This scoping review provides insight for the needed development of subjective thermal model of thermal sensation in relation to human thermal physiology specific to immersive water temperature ranges within and outside the thermal neutral and comfort zone.

TRPA1 as Target in Myocardial Infarction

Transient receptor potential cation channel subfamily A member 1 (TRPA1), an ion channel primarily expressed on sensory neurons, can be activated by substances occurring during myocardial infarction. Aims were to investigate whether activation, inhibition, or absence of TRPA1 affects infarcts and to explore underlying mechanisms. In the context of myocardial infarction, rats received a TRPA1 agonist, an antagonist, or vehicle at different time points, and infarct size was assessed. Wild type and TRPA1 knockout mice were also compared in this regard. In vitro, sensory neurons were co-cultured with cardiomyocytes and subjected to a model of ischemia-reperfusion. Although there was a difference between TRPA1 activation or inhibition in vivo, no experimental group was different to control animals in infarct size, which also applies to animals lacking TRPA1. In vitro, survival probability of cardiomyocytes challenged by ischemia-reperfusion increased from 32.8% in absence to 45.1% in presence of sensory neurons, which depends, at least partly, on TRPA1. This study raises doubts about whether TRPA1 is a promising target to reduce myocardial damage within a 24 h period. The results are incompatible with relevant enlargements of infarcts by TRPA1 activation or inhibition, which argues against adverse effects when TRPA1 is targeted for other indications.

The role of TRPA1 channels in thermosensation

Transient receptor potential ankyrin 1 (TRPA1) is a polymodal nonselective cation channel sensitive to different physical and chemical stimuli. TRPA1 is associated with many important physiological functions in different species and thus is involved in different degrees of evolution. TRPA1 acts as a polymodal receptor for the perceiving of irritating chemicals, cold, heat, and mechanical sensations in various animal species. Numerous studies have supported many functions of TRPA1, but its temperature-sensing function remains controversial. Although TRPA1 is widely distributed in both invertebrates and vertebrates, and plays a crucial role in tempreture sensing, the role of TRPA1 thermosensation and molecular temperature sensitivity are species-specific. In this review, we summarize the temperature-sensing role of TRPA1 orthologues in terms of molecular, cellular, and behavioural levels.

The impact of COVID-19 on populations living at high altitude: Role of hypoxia-inducible factors (HIFs) signaling pathway in SARS-CoV-2 infection and replication

Cases of coronavirus disease 2019 (COVID-19) have been reported worldwide. However, one epidemiological report has claimed a lower incidence of the disease in people living at high altitude (>2,500 m), proposing the hypothesis that adaptation to hypoxia may prove to be advantageous with respect to SARS-CoV-2 infection. This publication was initially greeted with skepticism, because social, genetic, or environmental parametric variables could underlie a difference in susceptibility to the virus for people living in chronic hypobaric hypoxia atmospheres. Moreover, in some patients positive for SARS-CoV-2, early post-infection ‘happy hypoxia” requires immediate ventilation, since it is associated with poor clinical outcome. If, however, we accept to consider the hypothesis according to which the adaptation to hypoxia may prove to be advantageous with respect to SARS-CoV-2 infection, identification of the molecular rational behind it is needed. Among several possibilities, HIF-1 regulation appears to be a molecular hub from which different signaling pathways linking hypoxia and COVID-19 are controlled. Interestingly, HIF-1α was reported to inhibit the infection of lung cells by SARS-CoV-2 by reducing ACE2 viral receptor expression. Moreover, an association of the rs11549465 variant of HIF-1α with COVID-19 susceptibility was recently discovered. Here, we review the evidence for a link between HIF-1α, ACE2 and AT1R expression, and the incidence/severity of COVID-19. We highlight the central role played by the HIF-1α signaling pathway in the pathophysiology of COVID-19.

Novel oxygen sensing mechanism in the spinal cord involved in cardiorespiratory responses to hypoxia

As blood oxygenation decreases (hypoxemia), mammals mount cardiorespiratory responses, increasing oxygen to vital organs. The carotid bodies are the primary oxygen chemoreceptors for breathing, but sympathetic-mediated cardiovascular responses to hypoxia persist in their absence, suggesting additional high-fidelity oxygen sensors. We show that spinal thoracic sympathetic preganglionic neurons are excited by hypoxia and silenced by hyperoxia, independent of surrounding astrocytes. These spinal oxygen sensors (SOS) enhance sympatho-respiratory activity induced by CNS asphyxia-like stimuli, suggesting they bestow a life-or-death advantage. Our data suggest the SOS use a mechanism involving neuronal nitric oxide synthase 1 (NOS1) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX). We propose NOS1 serves as an oxygen-dependent sink for NADPH in hyperoxia. In hypoxia, NADPH catabolism by NOS1 decreases, increasing availability of NADPH to NOX and launching reactive oxygen species-dependent processes, including transient receptor potential channel activation. Equipped with this mechanism, SOS are likely broadly important for physiological regulation in chronic disease, spinal cord injury, and cardiorespiratory crisis.

Calcium Imaging Analysis of Cellular Responses to Hypercapnia and Hypoxia in the NTS of Newborn Rat Brainstem Preparation

It is supposed that the nucleus of the solitary tract (NTS) in the dorsal medulla includes gas sensor cells responsive to hypercapnia or hypoxia in the central nervous system. In the present study, we analyzed cellular responses to hypercapnia and hypoxia in the NTS region of newborn rat in vitro preparation. The brainstem and spinal cord were isolated from newborn rat (P0-P4) and were transversely cut at the level of the rostral area postrema. To detect cellular responses, calcium indicator Oregon Green was pressure-injected into the NTS just beneath the cut surface of either the caudal or rostral block of the medulla, and the preparation was superfused with artificial cerebrospinal fluid (25–26°C). We examined cellular responses initially to hypercapnic stimulation (to 8% CO₂ from 2% CO₂) and then to hypoxic stimulation (to 0% O₂ from 95% O₂ at 5% CO₂). We tested these responses in standard solution and in two different synapse blockade solutions: (1) cocktail blockers solution including bicuculline, strychnine, NBQX and MK-801 or (2) TTX solution. At the end of the experiments, the superfusate potassium concentration was lowered to 0.2 from 3 mM to classify recorded cells into neurons and astrocytes. Excitation of cells was detected as changes of fluorescence intensity with a confocal calcium imaging system. In the synaptic blockade solutions (cocktail or TTX solution), 7.6 and 8% of the NTS cells responded to hypercapnic and hypoxic stimulation, respectively, and approximately 2% of them responded to both stimulations. Some of these cells responded to low K⁺, and they were classified into astrocytes comprising 43% hypercapnia-sensitive cells, 56% hypoxia-sensitive cells and 54% of both stimulation-sensitive cells. Of note, 49% of the putative astrocytes identified by low K⁺ stimulation were sensitive to hypercapnia, hypoxia or both. In the presence of a glia preferential blocker, 5 mM fluoroacetate (plus 0.5 μM TTX), the percentage of hypoxia-sensitive cells was significantly reduced compared to those of all other conditions. This is the first study to reveal that the NTS includes hypercapnia and hypoxia dual-sensitive cells. These results suggest that astrocytes in the NTS region could act as a central gas sensor.

Di-(2-ethylhexyl) phthalate limits the pleiotropic effects of statins in chronic kidney disease patients undergoing dialysis and endothelial cells

The level of di-(2-ethylhexyl) phthalate (DEHP) is elevated in chronic kidney disease patients undergoing dialysis. However, statins are unable to reduce the cardiovascular events in chronic dialysis patients. In this study, we investigated the effects of DEHP on statin-conferred pleiotropic effects and the underlying molecular mechanism in peritoneal dialysis (PD) patients and endothelial cells (ECs). In PD patients with serum DEHP level ≥0.0687 μg/mL, statin treatment was not associated with lower risk of cardiovascular disease. In ECs, exposure to DEHP abrogated the simvastatin-induced NO bioavailability and EC-related functions. Additionally, DEHP abolished the anti-inflammatory effect of simvastatin on the tumor necrosis factor α-induced upregulation of adhesion molecules and monocyte adhesion to ECs. Mechanistically, DEHP blunted the activation of transient receptor potential vanilloid type 1 (TRPV1), which is required for NO production by simvastatin in ECs. Notably, DEHP increased the activity and expression of protein phosphatase 2B (PP2B), a negative regulator of TRPV1 activity. The effect of DEHP on PP2B activation was mediated by the activation of the NADPH oxidase/reactive oxygen species (NOX-ROS) pathway. Inhibition of PP2B activity by pharmacological antagonists prevented the inhibitory effects of DEHP on simvastatin-induced Ca²⁺ influx, NO bioavailability, and EC migration, proliferation, tube formation, and anti-inflammatory action. Collectively, DEHP activates the NOX-ROS-PP2B pathway, which in turns inhibits TRPV1/Ca²⁺-dependent signaling and abrogates the statin-conferred pleiotropic protection in ECs.

Transient receptor potential channels in pulmonary chemical injuries and as countermeasure targets

The lung is highly sensitive to chemical injuries caused by exposure to threat agents in industrial or transportation accidents, occupational exposures, or deliberate use as weapons of mass destruction (WMD). There are no antidotes for the majority of the chemical threat agents and toxic inhalation hazards despite their use as WMDs for more than a century. Among several putative targets, evidence for transient receptor potential (TRP) ion channels as mediators of injury by various inhalational chemical threat agents is emerging. TRP channels are expressed in the respiratory system and are essential for homeostasis. Among TRP channels, the body of literature supporting essential roles for TRPA1, TRPV1, and TRPV4 in pulmonary chemical injuries is abundant. TRP channels mediate their function through sensory neuronal and nonneuronal pathways. TRP channels play a crucial role in complex pulmonary pathophysiologic events including, but not limited to, increased intracellular calcium levels, signal transduction, recruitment of proinflammatory cells, neurogenic inflammatory pathways, cough reflex, hampered mucus clearance, disruption of the integrity of the epithelia, pulmonary edema, and fibrosis. In this review, we summarize the role of TRP channels in chemical threat agents-induced pulmonary injuries and how these channels may serve as medical countermeasure targets for broader indications.

O2-Dependent Protein Internalization Underlies Astrocytic Sensing of Acute Hypoxia by Restricting Multimodal TRPA1 Channel Responses

Hypoxia sensors are essential for regulating local oxygen (O₂) homeostasis within the body. This is especially pertinent within the CNS, which is particularly vulnerable to O₂ deprivation due to high energetic demand. Here, we reveal hypoxia-monitoring function exerted by astrocytes through an O₂-regulated protein trafficking mechanism within the CNS. Strikingly, cultured mouse astrocytes isolated from the parafacial respiratory group (pFRG) and retrotrapezoid nucleus (RTN) region are capable of rapidly responding to moderate hypoxia via the sensor cation channel transient receptor potential (TRP) A1 but, unlike multimodal sensory neurons, are inert to hyperoxia and other TRPA1 activators (carbon dioxide, electrophiles, and oxidants) in normoxia. Mechanistically, O₂ suppresses TRPA1 channel activity by protein internalization via O₂-dependent proline hydroxylation and subsequent ubiquitination by an E3 ubiquitin ligase, NEDD4-1 (neural precursor cell-expressed developmentally down-regulated protein 4). Hypoxia inhibits this process and instantly accumulates TRPA1 proteins at the plasma membrane, inducing TRPA1-mediated Ca²⁺ influx that triggers ATP release from pFRG/RTN astrocytes, potentiating respiratory center activity. Furthermore, astrocyte-specific Trpa1 disruption in a mouse brainstem-spinal cord preparation impedes the amplitude augmentation of the central autonomic respiratory output during hypoxia. Thus, reversible coupling of the TRPA1 channels with O₂-dependent protein translocation allows astrocytes to act as acute hypoxia sensors in the medullary respiratory center.

Selenium enhances TRPA1 channel-mediated activity of temozolomide in SH-SY5Y neuroblastoma cells

PURPOSE

Neuroblastoma is a malignant solid tumor that originates from the sympathetic nervous system in early childhood. Temozolomide is used for treatment in high-risk groups with low treatment response of neuroblastomas. TRPA1 channels in neuroblastoma cells are calcium permeable channels that can be activated by reactive oxygen species (ROT). In this study, we aimed to evaluate the level of activity of temozolomide and selenium in neuroblastoma cells via TRPA1 channels.

METHOD

Seven main groups were formed using SH-SY5Y neuroblastoma cells. The control was divided into temozolomide (TMZ) (100 μM, 24 h), TMZ+SEL+AP18, SEL (sodium selenite, 100 μM, 24 h), and SEL+AP18 groups. Intergroup calcium signaling, intracellular reactive oxygen species, caspase-3 and caspase-9, and mitochondrial depolarization analyses were performed by channel activation with TRPA1 agonist cinnamaldehyde in all groups.

RESULTS

Cytosolic calcium concentration, apoptosis, caspase-3 and caspase-9 activation, mitochondrial membrane depolarization, and ROT levels were higher in TMZ (p < 0.001), TMZ+SEL (p < 0.001), and SEL (p < 0.05) groups than the control group. TRPA1 was lower in TTMZ+AP18, TMZ+SEL+AP18, and SEL+AP18 groups with channel blockers than respectively TMZ, TMZ+SEL, and SEL groups without channel blockers (p < 0.05).

CONCLUSION

The use of selenium with temozolomide increased the apoptotic efficacy of temozolomide via TRPA1 channels on tumor cells.

Intracellular Mechanisms of Oxygen Sensing

The review describes molecular mechanisms for sensing oxygen levels in various compartments of animal cell. Several pathways for intracellular oxygen sensing are discussed together with details of functioning of the near-membrane and cytoplasmic pools of molecular components in hypoxic cells. The data on the role of mitochondria in cell sensitivity to a decreased oxygen content are presented. Details of mutual influence of the operational and chronic intracellular mechanisms for detecting the negative gradients of molecular oxygen concentration and their relationship with cell metabolism response to the oxidative stress are discussed.

Myrcene and terpene regulation of TRPV1

Nociceptive Transient Receptor Potential channels such as TRPV1 are targets for treating pain. Both antagonism and agonism of TRP channels can promote analgesia, through inactivation and chronic desensitization. Since plant-derived mixtures of cannabinoids and the Cannabis component myrcene have been suggested as pain therapeutics, we screened terpenes found in Cannabis for activity at TRPV1. We used inducible expression of TRPV1 to examine TRPV1-dependency of terpene-induced calcium flux responses. Terpenes contribute differentially to calcium fluxes via TRPV1 induced by Cannabis-mimetic cannabinoid/terpenoid mixtures. Myrcene dominates the TRPV1-mediated calcium responses seen with terpenoid mixtures. Myrcene-induced calcium influx is inhibited by the TRPV1 inhibitor capsazepine and Myrcene elicits TRPV1 currents in the whole-cell patch-clamp configuration. TRPV1 currents are highly sensitive to internal calcium. When Myrcene currents are evoked, they are distinct from capsaicin responses on the basis of Imax and their lack of shift to a pore-dilated state. Myrcene pre-application and residency at TRPV1 appears to negatively impact subsequent responses to TRPV1 ligands such as Cannabidiol, indicating allosteric modulation and possible competition by Myrcene. Molecular docking studies suggest a non-covalent interaction site for Myrcene in TRPV1 and identifies key residues that form partially overlapping Myrcene and Cannabidiol binding sites. We identify several non-Cannabis plant-derived sources of Myrcene and other compounds targeting nociceptive TRPs using a data mining approach focused on analgesics suggested by non-Western Traditional Medical Systems. These data establish TRPV1 as a target of Myrcene and suggest the therapeutic potential of analgesic formulations containing Myrcene.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

Profiling of how nociceptor neurons detect danger - new and old foes

The host evolves redundant mechanisms to preserve physiological processing and homeostasis. These functions range from sensing internal and external threats, creating a memory of the insult and generating reflexes, which aim to resolve inflammation. Impairment in such functioning leads to chronic inflammatory diseases. By interacting through a common language of ligands and receptors, the immune and sensory nervous systems work in concert to accomplish such protective functions. Whilst this bidirectional communication helps to protect from danger, it can contribute to disease pathophysiology. Thus, the somatosensory nervous system is anatomically positioned within primary and secondary lymphoid tissues and mucosa to modulate immunity directly. Upstream of this interplay, neurons detect danger, which prompts the release of neuropeptides initiating (i) defensive reflexes (ranging from withdrawal response to coughing) and (ii) chemotaxis, adhesion and local infiltration of immune cells. The resulting outcome of such neuro-immune interplay is still ill-defined, but consensual findings start to emerge and support neuropeptides not only as blockers of T_H 1-mediated immunity but also as drivers of T_H 2 immune responses. However, the modalities detected by nociceptors revealed broader than mechanical pressure and temperature sensing and include signals as various as cytokines and pathogens to immunoglobulins and even microRNAs. Along these lines, we aggregated various dorsal root ganglion sensory neuron expression profiling datasets supporting such wide-ranging sensing capabilities to help identifying new danger detection modalities of these cells. Thus, revealing unexpected aspects of nociceptor neuron biology might prompt the identification of novel drivers of immunity, means to resolve inflammation and strategies to safeguard homeostasis.

TRPA1 channels: expression in non-neuronal murine lung tissues and dispensability for hyperoxia-induced alveolar epithelial hyperplasia

Transient receptor potential A1 (TRPA1) channels were originally characterized in neuronal tissues but also identified in lung epithelium by staining with fluorescently coupled TRPA1 antibodies. Its exact function in non-neuronal tissues, however, is elusive. TRPA1 is activated in vitro by hypoxia and hyperoxia and is therefore a promising TRP candidate for sensing hyperoxia in pulmonary epithelial cells and for inducing alveolar epithelial hyperplasia. Here, we isolated tracheal, bronchial, and alveolar epithelial cells and show low but detectable TRPA1 mRNA levels in all these cells as well as TRPA1 protein by Western blotting in alveolar type II (AT II) cells. We quantified changes in intracellular Ca²⁺ ([Ca²⁺]_i) levels induced by application of hyperoxic solutions in primary tracheal epithelial, bronchial epithelial, and AT II cells isolated from wild-type (WT) and TRPA1-deficient (TRPA1-/-) mouse lungs. In all cell types, we detected hyperoxia-induced rises in [Ca²⁺]_i levels, which were not significantly different in TRPA1-deficient cells compared to WT cells. We also tested TRPA1 function in a mouse model for hyperoxia-induced alveolar epithelial hyperplasia. A characteristic significant increase in thickening of alveolar tissues was detected in mouse lungs after exposure to hyperoxia, but not in normoxic WT and TRPA1-/- controls. Quantification of changes in lung morphology in hyperoxic WT and TRPA1-/- mice, however, again revealed no significant changes. Therefore, TRPA1 expression does neither appear to be a key player for hyperoxia-induced changes in [Ca²⁺]_i levels in primary lung epithelial cells, nor being essential for the development of hyperoxia-induced alveolar epithelial hyperplasia.