Permeable Nonselective Cation Channel Research Articles

Blockade of Transient Receptor Potential Vanilloid 4 Enhances Antioxidative Activity and Attenuates Hypoxia/Reoxygenation Injury in Cardiomyocytes: Involvement of Akt/Nrf2/ARE

Antioxidative stress provided the cardioprotective effects in myocardial ischemia/reperfusion (I/R). Transient receptor potential vanilloid 4 (TRPV4) is a Ca2+-permeable nonselective cation channel and widely expressed in the cardiovascular system. We previously demonstrated blockage of TRPV4 attenuates hypoxia/reoxygenation (H/R) induces Ca2+ influx and decreases reactive oxygen species (ROS) release, and finally alleviates injury in cardiomyocytes. The current study focused on whether blockade of TRPV4 reduced the injury via the antioxidative activity during H/R and explored the molecular mechanisms in cardiomyocytes. Our results reveal that H/R induced cell injury as evidenced by the cell viability, the release of lactate dehydrogenase (LDH) and apoptosis, which were obviously alleviated by a selective TRPV4 blocker HC-067047 or specific TRPV4-siRNA. Moreover, H/R also increased the contents of ROS and malondialdehyde (MDA) and decreased the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), which were reversed by HC-067047 or specific TRPV4-siRNA. Furthermore, HC-067047 treatment increased the expression of P-Akt, and the translocation of nuclear factor E2-related factor 2 (Nrf2) and related antioxidant response element (ARE) mainly including SOD, GSH-Px and hemeoxygenase-1(HO-1) after H/R. In addition, the Akt inhibitor, LY294002, absolutely hampered these cardioprotective effects of HC-067047. Finally, we confirmed the antioxidative stress roles of blockade of TRPV4 in myocardial I/R or application of exogenous H2O2. In conclusion, inhibition of TRPV4 exerts protective effects against oxidative stress induced cardiomyocyte injury possibly related to the up-regulated Akt/Nrf2/ARE pathway.

Regulation of Ciliary Length in LLC-PK1 Renal Epithelial Cells

Polycystin-2 (PC2, TRPP2) is a Ca2+ permeable nonselective cation channel whose dysfunction generates autosomal dominant polycystic kidney disease (ADPKD). PC2 is present in different cellular locations, including the primary cilium of LLC-PK1 renal epithelial cells, where it may contribute to ciliary Ca2+ transport. Little is known, however, as to how renal epithelial cells control the length of the primary cilium, and in particular how PC2 function may contribute to this regulation. Here, we explored the effect of maneuvers that either control Ca2+ transport through PC2 or modulate its function, on the ciliary length of LLC-PK1 cells. Cells (2-3 wk old) were labeled with a specific antibody against α-acetylated tubulin to identify primary cilia, and DAPI to locate cellular nuclei. Images were collected after overnight exposure of cells to the various experimental conditions. The length of the primary cilium was obtained with the ImageJ software. Primary cilia length measurements did not follow a normal distribution, in any of the conditions tested. Comparisons between groups were conducted either by group (Mann-Whitney) or in between groups (Kruskall Wallis) rendering significant differences for all conditions respect to Control (normal Ca2+, 1.2 mM, n = 199). Cells exposed either to low Ca2+ (n = 212) or high Ca2+ (n = 331) had a decreased primary cilium length by 23.8% and 14.4%, respectively (p < 0.001). Amiloride (200 μM, n = 287) and LiCl (10 mM, n = 92), two chemicals that reduce PC2 function, both induced an increase in primary cilium length of 12.1% and 20.0% (p < 0.001), respectively. The data indicate that PC2 function controls ciliary length in renal epithelial cells, suggesting a Ca2+-mediated regulatory mechanism. Dysregulation of this mechanism may be essential in the onset of ADPKD.

Functional Characterization of a Calcium-Sensing Receptor-Polycystin-2 Channel Complex in the Plasma Membrane of LLC-PK1 Cells

Polycystin-2 (PC2, TRPP2) is a Ca2+-permeable nonselective cation channel from the TRP superfamily. PC2 is encoded by the PKD2 gene, whose mutations are responsible for autosomal dominant polycystic kidney disease (ADPKD). Recent studies from our laboratory (Dai et al, Exp Cell Res, 2017), determined that the PC2 contribution to the whole cell conductance of wild type LLC-PK1 renal epithelial cells is regulated by changes in external Ca2+ concentration, in a mechanism that implicates the Calcium-Sensing Receptor (CaSR). The present study explored the effect of Ca2+ and CaSR agonists in the regulation of PC2 from isolated LLC-PK1 plasma membranes reconstituted in a lipid bilayer system (BLM). Addition of the CaSR agonist R-568 (5 μM) to the “external” side of the bilayer, activated single channel currents consistent with a functional PC2 by 84 ± 12% (n = 4, p < 0.01). These cation-selective currents were subsequently inhibited (91.3 ± 1.1%, p < 0.0001) by addition to the “cytosolic” side of the BLM, of a commercially available anti-PC2 C-terminal antibody to the “cytosolic” or “internal” side of the BLM. Interestingly, similar findings were observed with the material obtained by co-immunoprecipitation of LLC-PK1 cell lysate with anti-CaSR antibody crosslinked in agarose beads. The data indicate the presence of a membrane locate CaSR-PC2 functional complex in LLC-PK1 renal epithelial cells. The presence of the receptor/channel complex is in agreement with the regulatory role external Ca2+ plays in the modulation of PC2 channel function in the plasma membrane of renal epithelial cells. This receptor-channel complex may be part of a regulatory mechanism connecting Ca2+ signals and PC2 function to onset of ADPKD.

TRPM8 activation improves energy expenditure in skeletal muscle and exercise endurance in mice

Skeletal muscle serving as the major organ is responsible for energy expenditure and exercise endurance, which directly influence cardiometabolic risk factors. Transient receptor potential melastatin 8 (TRPM8), a Ca2+-permeable non-selective cation channel, plays vital roles in the regulation of various cellular functions. It has been reported that TRPM8 activation enhanced the energy metabolism of adipocytes. However, the involvement of TRPM8 in the energy metabolism of skeletal muscle remains unexplored. Our data revealed that TRPM8 was expressed in cultured C2C12 myocytes. Menthol treatment increased uncoupling protein 1 (UCP1) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) expression in C2C12 myotubes through TRPM8 activation. Moreover, dietary menthol upregulated the expression of UCP1 and PGC1α in skeletal muscle of mice. In addition, dietary menthol enhanced exercise endurance and reduced blood lactic acid and triglycerides through TRPM8 activation. It is concluded that dietary menthol improves energy metabolism and exercise endurance by increasing UCP1 and PGC1α in skeletal muscles, suggesting dietary menthol might be a novel therapeutic approach for cardiometabolic diseases management and prevention.

TRPM8 is required for survival and radioresistance of glioblastoma cells.

TRPM8 is a Ca2+-permeable nonselective cation channel belonging to the melastatin sub-group of the transient receptor potential (TRP) family. TRPM8 is aberrantly overexpressed in a variety of tumor entities including glioblastoma multiforme where it reportedly contributes to tumor invasion. The present study aimed to disclose further functions of TRPM8 in glioma biology in particular upon cell injury by ionizing radiation. To this end, TCGA data base was queried to expose the TRPM8 mRNA abundance in human glioblastoma specimens and immunoblotting was performed to analyze the TRPM8 protein abundance in primary cultures of human glioblastoma. Moreover, human glioblastoma cell lines were irradiated with 6 MV photons and TRPM8 channels were targeted pharmacologically or by RNA interference. TRPM8 abundance, Ca2+ signaling and resulting K+ channel activity, chemotaxis, cell migration, clonogenic survival, DNA repair, apoptotic cell death, and cell cycle control were determined by qRT-PCR, fura-2 Ca2+ imaging, patch-clamp recording, transfilter migration assay, wound healing assay, colony formation assay, immunohistology, flow cytometry, and immunoblotting. As a result, human glioblastoma upregulates TRPM8 channels to variable extent. TRPM8 inhibition or knockdown slowed down cell migration and chemotaxis, attenuated DNA repair and clonogenic survival, triggered apoptotic cell death, impaired cell cycle and radiosensitized glioblastoma cells. Mechanistically, ionizing radiation activated and upregulated TRPM8-mediated Ca2+ signaling that interfered with cell cycle control probably via CaMKII, cdc25C and cdc2. Combined, our data suggest that TRPM8 channels contribute to spreading, survival and radioresistance of human glioblastoma and, therefore, might represent a promising target in future anti-glioblastoma therapy.

TRPC3 Channels in Cardiac Fibrosis.

Cardiac stiffness, caused by interstitial fibrosis due to deposition of extracellular matrix proteins, is thought as a major clinical outcome of heart failure with preserved ejection fraction (HFpEF). Canonical transient receptor potential (TRPC) subfamily proteins are components of Ca2+-permeable non-selective cation channels activated by receptor stimulation and mechanical stress, and have been attracted attention as a key mediator of maladaptive cardiac remodeling. How TRPC-mediated local Ca2+ influx encodes a specific signal to induce maladaptive cardiac remodeling has been long obscure, but our recent studies suggest a pathophysiological significance of channel activity-independent function of TRPC proteins for amplifying redox signaling in heart. This review introduces the current understanding of the physiological and pathophysiological roles of TRPCs, especially focuses on the role of TRPC3 as a positive regulator of reactive oxygen species (PRROS) in heart. We have revealed that TRPC3 stabilizes NADPH oxidase 2 (Nox2), a membrane-bound reactive oxygen species (ROS)-generating enzyme, by forming stable protein complex with Nox2, which leads to amplification of mechanical stress-induced ROS signaling in cardiomyocytes, resulting in induction of fibrotic responses in cardiomyocytes and cardiac fibroblasts. Thus, the TRPC3 function as PRROS will offer a new therapeutic strategy for the prevention or treatment of HFpEF.

Abstract 003: Role of Transient Receptor Potential Ankyrin 1 in Monocyte Activation and Hypertensive Kidney Injury

It has been shown that monocyte activation and infiltration occur during the development of hypertensive kidney disease, a condition newly recognized as an inflammatory disorder. Indeed, monocytosis is linked to chronic kidney disease. Transient receptor potential ankyrin 1 (TRPA1), a Ca 2+ -permeable non-selective cation channel, has been shown to be an oxidative stress sensor that regulates neurogenic inflammation due to its abundant expression in sensory nerves. With the use of qPCR and immunostaining, we identified that the TRPA1 is also expressed in human and murine monocytes. The gene expression of TRPA1 is decreased in peripheral monocytes in hypertensive patients compared to normotensive subjects (-6-fold, p&lt;0.05) and in kidney tissues in angiotensin II (1000ng/kg/min, s.c., 14 days)-induced hypertensive compared to control mice (-9-fold, p&lt;0.01). The differentiation of human monocytic leukemia cells (THP-1) into macrophages induced by phorbol 12-myristate 13-acetate (PMA, 100nM, 48h) was accompanied with decreases in TRPA1 expression (-8-fold, p&lt;0.05) and increases in pro-inflammatory cytokines, including interleukin (IL)-1β (+705-fold, p&lt;0.01), monocyte chemotactic protein (MCP)-1 (+16-fold, p&lt;0.01), and CD36 (+7-fold, p&lt;0.01). Treatment with supercinnamaldehyde (SCA), a TRPA1 agonist, decreased the expression of IL-1β (-12-fold, p&lt;0.01), MCP-1 (-3.5-fold, p&lt;0.01), and CD36 (-2-fold, p&lt;0.05) in THP-1-derived macrophages, whereas these effects were abolished by pre-treatment with the selective TRPA1 antagonist, HC-030031 (HC). Additionally, HC promoted the proliferation of THP-1 cells while SCA suppressed THP-1 cell growth and variability. SCA induced the apoptosis of THP-1 cells (Annexin V positive cells: 8.5±1.4% vs. 30.1±2.4%, p&lt;0.01), which can be blocked by HC (30.1±2.4% vs. 15.6±1.9%, p&lt;0.01). These results show that TRPA1 activation inhibits monocyte activation and differentiation, and that suppressed expression of TRPA1 occurs in monocytes and kidneys in hypertensive patients and animals, respectively. These findings indicate that impaired expression and function of TRPA1 may contribute to monocytosis and pro-inflammatory state during hypertension, leading to hypertension related kidney injury.

Effects of Different Doses of Curcumin on Apoptosis, Mitochondrial Oxidative Stress and Calcium Ion Influx in DBRG Glioblastoma Cells

Transient Receptor Potential (TRP) channels superfamily has mostly calcium ion (Ca2+) permeable non-selective cation channels. Transient receptor potential melastatin subfamily 2 (TRPM2) is widely expressed in central nervous system. Intracellular Ca2+ concentration ([Ca2+]i) may change depend on TRPM2 and TRPM8 activations from extracellular liquid to cytosol. Curcumin as natural antioxidant shows phenolic structure, synthesized by Curcuma longa L. (Indian saffron, turmeric), has powerful non-enzymatically antioxidant effects. Low dose curcumin treatment can decrease calcium signaling via TRPM2 channel inhibition and prevent elevation of [Ca2+]i levels. Hence, we investigated effects of four different concentrations (5, 10, 25 and 50 µM) of curcumin on apoptosis and cell viability (MTT), reactive oxygen species (ROS) production, mitochondrial membrane potential levels, caspase 3 and caspase 9 values in DBRG glioblastoma cells. We found that curcumin reduces cell viability by concentration dependent manner. It was also observed that curcumin induces apoptosis via caspase 3 and 9 related pathways. However, it was not found any direct relationship between the effect of increased concentrations of curcumin and inhibition or activation of TRPM2 mediated Ca2+ signaling in the DBTRG cells. The [Ca2+]i concentration was lower in 5 µM group as compare to control group. Curcumin acted important role on decrease of mitochondrial membrane potential and intracellular ROS production in the cells. Moreover, curcumin treatment markedly supported GSH concentration levels in the cells. In conclusion, it was firstly assessed the effects of different doses of curcumin on TRPM2 mediated calcium signaling and interaction with various apoptosis parameters in DBTRG glioblastoma cells.

Dietary menthol-induced TRPM8 activation enhances WAT "browning" and ameliorates diet-induced obesity.

Beige adipocytes are a new type of recruitable brownish adipocytes, with highly mitochondrial membrane uncoupling protein 1 expression and thermogenesis. Beige adipocytes were found among white adipocytes, especially in subcutaneous white adipose tissue (sWAT). Therefore, beige adipocytes may be involved in the regulation of energy metabolism and fat deposition. Transient receptor potential melastatin 8 (TRPM8), a Ca2+-permeable non-selective cation channel, plays vital roles in the regulation of various cellular functions. It has been reported that TRPM8 activation enhanced the thermogenic function of brown adiposytes. However, the involvement of TRPM8 in the thermogenic function of WAT remains unexplored. Our data revealed that TRPM8 was expressed in mouse white adipocytes at mRNA, protein and functional levels. The mRNA expression of Trpm8 was significantly increased in the differentiated white adipocytes than pre-adipocytes. Moreover, activation of TRPM8 by menthol enhanced the expression of thermogenic genes in cultured white aidpocytes. And menthol-induced increases of the thermogenic genes in white adipocytes was inhibited by either KT5720 (a protein kinase A inhibitor) or BAPTA-AM. In addition, high fat diet (HFD)-induced obesity in mice was significantly recovered by co-treatment with menthol. Dietary menthol enhanced WAT “browning” and improved glucose metabolism in HFD-induced obesity mice as well. Therefore, we concluded that TRPM8 might be involved in WAT “browning” by increasing the expression levels of genes related to thermogenesis and energy metabolism. And dietary menthol could be a novel approach for combating human obesity and related metabolic diseases.

Role of canonical transient receptor potential channel-3 in acetylcholine-induced mouse airway smooth muscle cell proliferation

AimsCanonical transient receptor potential channel-3 (TRPC3)-encoded Ca2+-permeable nonselective cation channel (NSCC) has been proven to be an important native constitutively active channel in airway smooth muscle cell (ASMC), which plays significant roles in physiological and pathological conditions by controlling Ca2+ homeostasis in ASMC. Acetylcholine (ACh) is generally accepted as a contractile parasympathetic neurotransmitter in the airway. Recently studies have revealed the pathological role of ACh in airway remodeling, however, the mechanisms remain unclear. Here, we investigated the role of TRPC3 in ACh-induced ASMC proliferation. Materials and methodsPrimary mouse ASMCs were cultured with or without ACh treatment, then cell viability, TRPC3 expression, NSCC currents and [Ca2+]i changes were examined by MTT assay, cell counting, Western blotting, standard whole-cell patch clamp recording and calcium imaging, respectively. Small interfering RNA (siRNA) technology was used to confirm the contribution of TRPC3 to ACh-induced ASMC proliferation. Key findingsTRPC3 blocker Gd3+, antibody or siRNA largely inhibited ACh-induced up-regulation of TRPC3 protein, enhancement of NSCC currents, resting [Ca2+]i and KCl-induced changes in [Ca2+]i, eventually inhibiting ACh-induced ASMC proliferation. SignificanceOur data suggested ACh could induce ASMC proliferation, and TRPC3 may be involved in ACh-induced ASMC proliferation that occurs with airway remodeling.

Tumor necrosis factor α accelerates Hep-2 cells proliferation by suppressing TRPP2 expression.

TRPP2, a Ca2+-permeable non-selective cation channel, has been shown to negatively regulate cell cycle, but the mechanism underlying this regulation is unknown. Tumor necrosis factor α (TNF-α) is a proinflammatory cytokine extensively involved in immune system regulation, cell proliferation and cell survival. However, the effects and mechanisms for the role of TNF-α in laryngeal cancer remain unclear. Here, we demonstrated using western blot analyses and intracellular Ca2+ concentration measurements that TNF-α treatment suppressed both TRPP2 expression and ATP-induced Ca2+ release in a laryngeal cancer cell line (Hep-2). Knockdown of TRPP2 by a specific siRNA significantly decreased ATP-induced Ca2+ release and abolished the effect of TNF-α on the ATP-induced Ca2+ release. TNF-α treatment also enhanced Hep-2 cell proliferation and growth, as determined using cell counting and flow cytometry cell cycle assays. Moreover, TNF-α treatment down-regulated phosphorylated protein kinase R-like endoplasmic reticulum kinase (p-PERK) and phosphorylated eukaryotic translation initiation factor (p-eIF2α) expression levels, without affecting PERK and eIF2α expression levels in Hep-2 cells. We concluded that suppressing TRPP2 expression and TRPP2-mediated Ca2+ signaling may be one mechanism underlying TNF-α-enhanced Hep-2 cell proliferation. These results offer new insights into the mechanisms of TNF-α-mediated laryngeal cancer cell proliferation, and provide evidences showing a potential role of TNF-α in the development of laryngeal cancer.

2'-Deoxyadenosine 5'-diphosphoribose is an endogenous TRPM2 superagonist.

Transient receptor potential melastatin 2 (TRPM2) is a ligand-gated Ca2+-permeable nonselective cation channel. Whereas physiological stimuli, such as chemotactic agents, evoke controlled Ca2+ signals via TRPM2, pathophysiological stimuli such as reactive oxygen species and genotoxic stress result in prolonged TRPM2-mediated Ca2+ entry and, consequently, apoptosis. To date, adenosine 5'-diphosphoribose (ADPR) has been assumed to be the main agonist for TRPM2. Here we show that 2'-deoxy-ADPR was a significantly better TRPM2 agonist, inducing 10.4-fold higher whole-cell currents at saturation. Mechanistically, this increased activity was caused by a decreased rate of inactivation and higher average open probability. Using high-performance liquid chromatography (HPLC) and mass spectrometry, we detected endogenous 2'-deoxy-ADPR in Jurkat T lymphocytes. Consistently, cytosolic nicotinamide mononucleotide adenylyltransferase 2 (NMNAT-2) and nicotinamide adenine dinucleotide (NAD)-glycohydrolase CD38 sequentially catalyzed the synthesis of 2'-deoxy-ADPR from nicotinamide mononucleotide (NMN) and 2'-deoxy-ATP in vitro. Thus, 2'-deoxy-ADPR is an endogenous TRPM2 superagonist that may act as a cell signaling molecule.

The Role of Transient Receptor Potential Channel 6 Channels in the Pulmonary Vasculature.

Canonical or classical transient receptor potential channel 6 (TRPC6) is a Ca2+-permeable non-selective cation channel that is widely expressed in the heart, lung, and vascular tissues. The use of TRPC6-deficient (“knockout”) mice has provided important insights into the role of TRPC6 in normal physiology and disease states of the pulmonary vasculature. Evidence indicates that TRPC6 is a key regulator of acute hypoxic pulmonary vasoconstriction. Moreover, several studies implicated TRPC6 in the pathogenesis of pulmonary hypertension. Furthermore, a unique genetic variation in the TRPC6 gene promoter has been identified, which might link the inflammatory response to the upregulation of TRPC6 expression and ultimate development of pulmonary vascular abnormalities in idiopathic pulmonary arterial hypertension. Additionally, TRPC6 is critically involved in the regulation of pulmonary vascular permeability and lung edema formation during endotoxin or ischemia/reperfusion-induced acute lung injury. In this review, we will summarize latest findings on the role of TRPC6 in the pulmonary vasculature.

Ligand-induced activation of human TRPM2 requires the terminal ribose of ADPR and involves Arg1433 and Tyr1349.

TRPM2 (transient receptor potential channel, subfamily melastatin, member 2) is a Ca2+-permeable non-selective cation channel activated by the binding of adenosine 5′-diphosphoribose (ADPR) to its cytoplasmic NUDT9H domain (NUDT9 homology domain). Activation of TRPM2 by ADPR downstream of oxidative stress has been implicated in the pathogenesis of many human diseases, rendering TRPM2 an attractive novel target for pharmacological intervention. However, the structural basis underlying this activation is largely unknown. Since ADP (adenosine 5′-diphosphate) alone did not activate or antagonize the channel, we used a chemical biology approach employing synthetic analogues to focus on the role of the ADPR terminal ribose. All novel ADPR derivatives modified in the terminal ribose, including that with the seemingly minor change of methylating the anomeric-OH, abolished agonist activity at TRPM2. Antagonist activity improved as the terminal substituent increasingly resembled the natural ribose, indicating that gating by ADPR might require specific interactions between hydroxyl groups of the terminal ribose and the NUDT9H domain. By mutating amino acid residues of the NUDT9H domain, predicted by modelling and docking to interact with the terminal ribose, we demonstrate that abrogating hydrogen bonding of the amino acids Arg1433 and Tyr1349 interferes with activation of the channel by ADPR. Taken together, using the complementary experimental approaches of chemical modification of the ligand and site-directed mutagenesis of TRPM2, we demonstrate that channel activation critically depends on hydrogen bonding of Arg1433 and Tyr1349 with the terminal ribose. Our findings allow for a more rational design of novel TRPM2 antagonists that may ultimately lead to compounds of therapeutic potential.

TRPC6-mediated ERK1/2 phosphorylation prevents dentate granule cell degeneration via inhibiting mitochondrial elongation

Transient receptor potential canonical channel-6 (TRPC6) is one of Ca2+-permeable non-selective cation channels. In the rat hippocampus, TRPC6 expression is predominantly observed in dentate granule cells (DGC) rather than other hippocampal components. Interestingly, TRPC6 knockdown results in the massive DGC degeneration following status epilepticus (SE), although DGC is one of the resistant neuronal populations to various harmful stresses. However, the molecular events underlying the DGC degeneration induced by TRPC6 knockdown are still unclear. In the present study, TRPC6 knockdown resulted in mitochondrial elongation accompanied by reduction in dynamin-related proteins 1 (DRP1)-S616 phosphorylation. Furthermore, TRPC6 knockdown selectively decreased extracellular-signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Similar to TRPC6 knockdown, ERK1/2 inhibition by U0126 evoked mitochondrial elongation with diminished DRP1-S616 phosphorylation, and facilitated SE-induced DGC degeneration independent of seizure severity. These findings indicate that TRPC6 may regulate mitochondrial dynamics via ERK1/2-mediaed DRP1 activation, which would be involved in DGC invulnerability to SE. Therefore, TRPC6 will be an interesting and important therapeutic target for neurological diseases related to impaired mitochondrial dynamics.

The Ca2+-Permeable Cation Transient Receptor Potential TRPV3 Channel: An Emerging Pivotal Target for Itch and Skin Diseases.

Temperature-sensitive transient receptor potential (TRP) channels such as TRPA1 and TRPV1 have been identified as downstream ion channel targets in the transduction of itch. As a member of the temperature-sensitive TRP family, the Ca2+-permeable nonselective cation channel TRPV3 is expressed abundantly in skin keratinocytes. Recent identification of gain-of-function mutations of human TRPV3 from patients with Olmsted syndrome, which is characterized by severe itching and palmoplantar and periorificial keratoderma, unveils its crucial role in chronic itch and skin diseases. In this review, we will focus on recent progress made in the understanding of TRPV3 that emerges as an attractive target for developing effective antipruritic therapy for chronic itch or skin-related diseases.

Blockage of transient receptor potential vanilloid 4 alleviates myocardial ischemia/reperfusion injury in mice

Transient receptor potential vanilloid 4 (TRPV4) is a Ca2+-permeable nonselective cation channel and can be activated during ischemia/reperfusion (I/R). This study tested whether blockade of TRPV4 can alleviate myocardial I/R injury in mice. TRPV4 expression began to increase at 1 h, reached statistically at 4 h, and peaked at 24–72 h. Treatment with the selective TRPV4 antagonist HC-067047 or TRPV4 knockout markedly ameliorated myocardial I/R injury as demonstrated by reduced infarct size, decreased troponin T levels and improved cardiac function at 24 h after reperfusion. Importantly, the therapeutic window for HC-067047 lasts for at least 12 h following reperfusion. Furthermore, treatment with HC-067047 reduced apoptosis, as evidenced by the decrease in TUNEL-positive myocytes, Bax/Bcl-2 ratio, and caspase-3 activation. Meanwhile, treatment with HC-067047 attenuated the decrease in the activation of reperfusion injury salvage kinase (RISK) pathway (phosphorylation of Akt, ERK1/2, and GSK-3β), while the activation of survival activating factor enhancement (SAFE) pathway (phosphorylation of STAT3) remained unchanged. In addition, the anti-apoptotic effects of HC-067047 were abolished by the RISK pathway inhibitors. We conclude that blockade of TRPV4 reduces apoptosis via the activation of RISK pathway, and therefore might be a promising strategy to prevent myocardial I/R injury.

Voltage- and receptor-mediated activation of a non-selective cation channel in rat carotid body glomus cells

A recent study showed that hypoxia activates a Ca2+-sensitive, Na+-permeable non-selective cation channel (NSC) in carotid body glomus cells. We studied the effects of mitochondrial inhibitors that increase Ca2+ influx via Ca2+ channel (Cav), and receptor agonists that release Ca2+ from endoplasmic reticulum (ER) on NSC. Mitochondrial inhibitors (NaCN, FCCP, H2S, NO) elevated [Ca2+]i and activated NSC. Angiotensin II and acetylcholine that elevate [Ca2+]i via the Gq-IP3 pathway activated NSC. However, endothelin-1 (Gq) and 5-HT (Gq) showed little or no effect on [Ca2+]i and did not activate NSC. Adenosine (Gs) caused a weak rise in [Ca2+]i but did not activate NSC. Dopamine (Gs) and γ-aminobytyric acid (Gi) were ineffective in raising [Ca2+]i and failed to activate NSC. Store-operated Ca2+ entry (SOCE) produced by depletion of Ca2+ stores with cyclopiazonic acid activated NSC. Our results show that Ca2+ entry via Cav, ER Ca2+ release and SOCE can activate NSC. Thus, NSC contributes to both voltage- and receptor-mediated excitation of glomus cells.

Targeting TRPM2 in ROS-Coupled Diseases.

Under pathological conditions such as inflammation and ischemia-reperfusion injury large amounts of reactive oxygen species (ROS) are generated which, in return, contribute to the development and exacerbation of disease. The second member of the transient receptor potential (TRP) melastatin subfamily, TRPM2, is a Ca2+-permeable non-selective cation channel, activated by ROS in an ADP-ribose mediated fashion. In other words, TRPM2 functions as a transducer that converts oxidative stress into Ca2+ signaling. There is good evidence that TRPM2 plays an important role in ROS-coupled diseases. For example, in monocytes the influx of Ca2+ through TRPM2 activated by ROS contributes to the aggravation of inflammation via chemokine production. In this review, the focus is on TRPM2 as a molecular linker between ROS and Ca2+ signaling in ROS-coupled diseases.

Resiniferatoxin: The Evolution of the "Molecular Scalpel" for Chronic Pain Relief.

Control of chronic pain is frequently inadequate or can be associated with debilitating side effects. Ablation of certain nociceptive neurons, while retaining all other sensory modalities and motor function, represents a new therapeutic approach to controlling severe pain while avoiding off-target side effects. transient receptor potential cation channel subfamily V member 1 (TRPV1) is a calcium permeable nonselective cation channel expressed on the peripheral and central terminals of small-diameter sensory neurons. Highly selective chemoablation of TRPV1-containing peripheral nerve endings, or the entire TRPV1-expressing neuron itself, can be used to control chronic pain. Administration of the potent TRPV1 agonist resiniferatoxin (RTX) to neuronal perikarya or nerve terminals induces calcium cytotoxicity and selective lesioning of the TRPV1-expressing nociceptive primary afferent population. This selective neuroablation has been coined “molecular neurosurgery” and has the advantage of sparing motor, proprioceptive, and other somatosensory functions that are so important for coordinated movement, performing activities of daily living, and maintaining quality of life. This review examines the mechanisms and preclinical data underlying the therapeutic use of RTX and examples of such use for the management of chronic pain in clinical veterinary and human pain states.