Transient receptor potential vanilloid 4 (TRPV4) activation by arachidonic acid requires protein kinase A-mediated phosphorylation

TRPV4 Channel Modulators as Potential Drug Candidates for Cystic Fibrosis

Cystic fibrosis (CF) is a genetic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, resulting in defective chloride ion channels. This leads to thick, dehydrated mucus that severely disrupts mucociliary clearance in the respiratory system and triggers infection that eventually is the cause of death of CF patients. Current therapeutic strategies primarily focus on restoring CFTR function, blocking epithelial sodium channels to prevent mucus dehydration, or directly targeting mucus to reduce its viscosity. Among the ion channels expressed in ciliated bronchial epithelial cells, the transient receptor potential vanilloid 4 (TRPV4) channel emerges as a significant channel in CF pathogenesis. Activation of TRPV4 channels affects the regulation of airway surface liquid by modulating sodium absorption and intracellular calcium levels, which indirectly influences CFTR activity. TRPV4 is also involved in the regulatory volume decrease (RVD) process and enhances inflammatory responses in CF patients. Here, we combine current findings on TRPV4 channel modulation as a promising therapeutic approach for CF. Although limited studies have directly explored TRPV4 in CF, emerging evidence indicates that TRPV4 activation can significantly impact key pathological processes in the disease. Further investigation into TRPV4 modulators could lead to innovative treatments that alleviate severe respiratory complications and improve outcomes for CF patients.

Phenotypic switch of vascular smooth muscle cells in COVID-19: Role of cholesterol, calcium, and phosphate

Although the novel coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), primarily manifests as severe respiratory distress, its impact on the cardiovascular system is also notable. Studies reveal that COVID-19 patients often suffer from certain vascular diseases, partly attributed to increased proliferation or altered phenotype of vascular smooth muscle cells (VSMCs). Although the association between COVID-19 and VSMCs is recognized, the precise mechanism underlying SARS-CoV-2's influence on VSMC phenotype remains largely under-reviewed. In this context, while there is a consistent body of literature dissecting the effect of COVID-19 on the cardiovascular system, few reports delve into the potential role of VSMC switching in the pathophysiology associated with COVID-19 and the molecular mechanisms involved therein. This review dissects and critiques the link between COVID-19 and VSMCs, with particular attention to pathways involving cholesterol, calcium, and phosphate. These pathways underpin the interaction between the virus and VSMCs. Such interaction promotes VSMC proliferation, and eventually potentiates vascular calcification as well as worsens prognosis in patients with COVID-19.

A CatSper-Uninvolved Mechanism to Induce Forward Sperm Motility in the Internal Fertilization

Sperm-specific cation channel (CatSper), sperm-specific Na + /H + exchanger (sNHE), and soluble adenylyl cyclase (sAC) are necessary in the signaling pathways to control sperm motility in many animals, whereas some animals have lost some or all of them. In the present study, we examined CatSper-uninvolved signaling for vigorous undulation of the undulating membrane that is attached to the sperm tail and gives thrust for forward motility in the internally fertilizing newt Cynops pyrrhogaster. Reverse-transcription PCR failed to detect sNHE in the newt sperm. However, the pH of sperm cytoplasm was raised under a high extracellular pH equivalent to that of egg jelly, where sperm motility is initiated by sperm motility-initiating substance (SMIS). Carbonic anhydrase XII/ XVI and SLC4A4/8 were suggested to be present in the sperm, and transported bicarbonates raised the intracellular pH. In egg jelly extract that contained SMIS, the anion transporter inhibitor DIDS weakened the undulation of the undulating membrane, while bicarbonates enhanced it. The cyclic AMP concentration was found to increase in sperm cytoplasm in the egg-jelly extract. An inhibitor of sAC (KH7) weakened the undulation of the undulating membrane, and dibutyryl cyclic AMP blocked the inhibitory effect. Inhibitor of transmembrane AC (DDA) limitedly affected the undulation. The undulation was weakened by an inhibitor of protein kinase A (H89), and by an inhibitor of transient receptor potential (TRP) channels (RN1747). Our results support the conclusions that the high pH of the egg jelly triggers a signaling pathway through sAC, PKA, and TRP channels, and coacts with SMIS to induce forward sperm motility.

WNK kinase is a vasoactive chloride sensor in endothelial cells

Endothelial cells (ECs) line the wall of blood vessels and regulate arterial contractility to tune regional organ blood flow and systemic pressure. Chloride (Cl-) is the most abundant anion in ECs and the Cl- sensitive With-No-Lysine (WNK) kinase is expressed in this cell type. Whether intracellular Cl- signaling and WNK kinase regulate EC function to alter arterial contractility is unclear. Here, we tested the hypothesis that intracellular Cl- signaling in ECs regulates arterial contractility and examined the signaling mechanisms involved, including the participation of WNK kinase. Our data obtained using two-photon microscopy and cell-specific inducible knockout mice indicated that acetylcholine, a prototypical vasodilator, stimulated a rapid reduction in intracellular Cl- concentration ([Cl-]i) due to the activation of TMEM16A, a Cl- channel, in ECs of resistance-size arteries. TMEM16A channel-mediated Cl- signaling activated WNK kinase, which phosphorylated its substrate proteins SPAK and OSR1 in ECs. OSR1 potentiated transient receptor potential vanilloid 4 (TRPV4) currents in a kinase-dependent manner and required a conserved binding motif located in the channel C terminus. Intracellular Ca2+ signaling was measured in four dimensions in ECs using a high-speed lightsheet microscope. WNK kinase-dependent activation of TRPV4 channels increased local intracellular Ca2+ signaling in ECs and produced vasodilation. In summary, we show that TMEM16A channel activation reduces [Cl-]i, which activates WNK kinase in ECs. WNK kinase phosphorylates OSR1 which then stimulates TRPV4 channels to produce vasodilation. Thus, TMEM16A channels regulate intracellular Cl- signaling and WNK kinase activity in ECs to control arterial contractility.

Modulating TRPV4 Channel Activity in Pro-Inflammatory Macrophages within the 3D Tissue Analog

Investigating macrophage plasticity emerges as a promising strategy for promoting tissue regeneration and can be exploited by regulating the transient receptor potential vanilloid 4 (TRPV4) channel. The TRPV4 channel responds to various stimuli including mechanical, chemical, and selective pharmacological compounds. It is well documented that treating cells such as epithelial cells and fibroblasts with a TRPV4 agonist enhances the Ca2+ influx to the cells, which leads to secretion of pro-inflammatory cytokines, while a TRPV4 antagonist reduces both Ca2+ influx and pro-inflammatory cytokine secretion. In this work, we investigated the effect of selective TRPV4 modulator compounds on U937-differentiated macrophages encapsulated within three-dimensional (3D) matrices. Despite offering a more physiologically relevant model than 2D cultures, pharmacological treatment of macrophages within 3D collagen matrices is largely overlooked in the literature. In this study, pro-inflammatory macrophages were treated with an agonist, 500 nM of GSK1016790A (TRPV4(+)), and an antagonist, 10 mM of RN-1734 (TRPV4(-)), to elucidate the modulation of the TRPV4 channel at both cellular and extracellular levels. To evaluate macrophage phenotypic alterations within 3D collagen matrices following TRPV4 modulator treatment, we employed structural techniques (SEM, Masson's trichrome, and collagen hybridizing peptide (CHP) staining), quantitative morphological measures for phenotypic assessment, and genotypic methods such as quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC). Our data reveal that pharmacological modulation of the macrophage TRPV4 channel alters the cytoskeletal structure of macrophages and influences the 3D structure encapsulating them. Moreover, we proved that treating macrophages with a TRPV4 agonist and antagonist enhances the expression of pro- and anti-inflammatory genes, respectively, leading to the upregulation of surface markers CD80 and CD206. In the TRPV4(-) group, the CD206 gene and CD206 surface marker were significantly upregulated by 9- and 2.5-fold, respectively, compared to the control group. These findings demonstrate that TRPV4 modulation can be utilized to shift macrophage phenotype within the 3D matrix toward a desired state. This is an innovative approach to addressing inflammation in musculoskeletal tissues.

PAR2-dependent phosphorylation of TRPV4 at the trigeminal nerve terminals contributes to tongue cancer pain

OBJECTIVE

This study aimed to clarify the interactions between the tongue and primary afferent fibers in tongue cancer pain.

METHODS

A pharmacological analysis was conducted to evaluate mechanical hypersensitivity of the tongues of rats with squamous cell carcinoma (SCC). Changes in trigeminal ganglion (TG) neurons projecting to the tongue were analyzed using immunohistochemistry and western blotting.

RESULTS

SCC inoculation of the tongue caused persistent mechanical sensitization and tumor formation. Trypsin expression was significantly upregulated in cancer lesions. Continuous trypsin inhibition or protease-activated receptor 2 (PAR2) antagonism in the tongue significantly inhibited SCC-induced mechanical sensitization. No changes were observed in PAR2 and transient receptor potential vanilloid 4 (TRPV4) levels in the TG or the number of PAR2-and TRPV4-expressing TG neurons after SCC inoculation. In contrast, the relative amount of phosphorylated TRPV4 in the TG was significantly increased after SCC inoculation and abrogated by PAR2 antagonism in the tongue. TRPV4 antagonism in the tongue significantly ameliorated the mechanical sensitization caused by SCC inoculation.

CONCLUSIONS

Our findings indicate that tumor-derived trypsin sensitizes primary afferent fibers by PAR2 stimulation and subsequent TRPV4 phosphorylation, resulting in severe tongue pain.

Role of TRPV4 on vascular tone regulation in pathophysiological states

Vascular tone regulation is a key event in controlling blood flow in the body. Endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) help regulate the vascular tone. Abnormal vascular responsiveness to various stimuli, including constrictors and dilators, has been observed in pathophysiological states although EC and VSMC coordinate to maintain the exquisite balance between contraction and relaxation in vasculatures. Thus, investigating the mechanisms underlying vascular tone abnormality is very important in maintaining vascular health and treating vasculopathy. Increased intracellular free Ca2+ concentration ([Ca2+]i) is one of the major triggers initiating each EC and VSMC response. Transient receptor potential vanilloid family member 4 (TRPV4) is a Ca2+-permeable non-selective ion channel, which is activated by several stimuli, and is presented in both ECs and VSMCs. Therefore, TRPV4 plays an important role in vascular responses. Emerging evidence indicates the role of TRPV4 on the functions of ECs and VSMCs in various pathophysiological states, including hypertension, diabetes, and obesity. This review focused on the link between TRPV4 and the functions of ECs/VSMCs, particularly its role in vascular tone and responsiveness to vasoactive substances.

Signaling Roleplay between Ion Channels during Mammalian Sperm Capacitation

In order to accomplish their primary goal, mammalian spermatozoa must undergo a series of physiological, biochemical, and functional changes crucial for the acquisition of fertilization ability. Spermatozoa are highly polarized cells, which must swiftly respond to ionic changes on their passage through the female reproductive tract, and which are necessary for male gametes to acquire their functional competence. This review summarizes the current knowledge about specific ion channels and transporters located in the mammalian sperm plasma membrane, which are intricately involved in the initiation of changes within the ionic milieu of the sperm cell, leading to variations in the sperm membrane potential, membrane depolarization and hyperpolarization, changes in sperm motility and capacitation to further lead to the acrosome reaction and sperm-egg fusion. We also discuss the functionality of selected ion channels in male reproductive health and/or disease since these may become promising targets for clinical management of infertility in the future.

Role of TRP Channels in Liver-Related Diseases

The liver plays a crucial role in preserving the homeostasis of an entire organism by metabolizing both endogenous and exogenous substances, a process that relies on the harmonious interactions of hepatocytes, hepatic stellate cells (HSCs), Kupffer cells (KCs), and vascular endothelial cells (ECs). The disruption of the liver's normal structure and function by diverse pathogenic factors imposes a significant healthcare burden. At present, most of the treatments for liver disease are palliative in nature, rather than curative or restorative. Transient receptor potential (TRP) channels, which are extensively expressed in the liver, play a crucial role in regulating intracellular cation concentration and serve as the origin or intermediary stage of certain signaling pathways that contribute to liver diseases. This review provides an overview of recent developments in liver disease research, as well as an examination of the expression and function of TRP channels in various liver cell types. Furthermore, we elucidate the molecular mechanism by which TRP channels mediate liver injury, liver fibrosis, and hepatocellular carcinoma (HCC). Ultimately, the present discourse delves into the current state of research and extant issues pertaining to the targeting of TRP channels in the treatment of liver diseases and other ailments. Despite the numerous obstacles encountered, TRP channels persist as an extremely important target for forthcoming clinical interventions aimed at treating liver diseases.

Inhibition of TRPV4 remodels single cell polarity and suppresses the metastasis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a malignant tumor, frequently causing both intrahepatic and extrahepatic metastases. The overall prognosis of patients with metastatic HCC is poor. Recently, single-cell (sc) polarity is proved to be an innate feature of some tumor cells in liquid phase, and directly involved in the cell adhesion to blood vessel and tumor metastasis. Here, we characterize the maintained sc polarity of HCC cells in a suspension culture, and investigate its roles and regulatory mechanisms during metastasis. We demonstrate that transient receptor potential vanilloid 4 (TRPV4) is a promoting regulator of sc polarity via activating Ca²⁺-dependent AMPK/MLC/ERM pathway. This attenuates the adhesion of metastatic HCC cells to vascular endothelial cells. The reduction of cancer metastases can result from TRPV4 inhibition, which not only impacts the migration and invasion of tumor cells, but also prevents the adhesion to vascular endothelial cells. Additionally, we discover a brand-new TRPV4 inhibitor called GL-V9 that modifies the degree of sc polarization and significantly decreases the metastatic capacity of HCC cells. Taken together, our data shows that TRPV4 and calcium signal are significant sc polarity regulators in metastatic HCC, and that the pharmacological intervention that results in HCC cells becoming depolarized suggests a promising treatment for cancer metastasis.

Structure of human TRPV4 in complex with GTPase RhoA

Transient receptor potential (TRP) channel TRPV4 is a polymodal cellular sensor that responds to moderate heat, cell swelling, shear stress, and small-molecule ligands. It is involved in thermogenesis, regulation of vascular tone, bone homeostasis, renal and pulmonary functions. TRPV4 is implicated in neuromuscular and skeletal disorders, pulmonary edema, and cancers, and represents an important drug target. The cytoskeletal remodeling GTPase RhoA has been shown to suppress TRPV4 activity. Here, we present a structure of the human TRPV4-RhoA complex that shows RhoA interaction with the membrane-facing surface of the TRPV4 ankyrin repeat domains. The contact interface reveals residues that are mutated in neuropathies, providing an insight into the disease pathogenesis. We also identify the binding sites of the TRPV4 agonist 4α-PDD and the inhibitor HC-067047 at the base of the S1-S4 bundle, and show that agonist binding leads to pore opening, while channel inhibition involves a π-to-α transition in the pore-forming helix S6. Our structures elucidate the interaction interface between hTRPV4 and RhoA, as well as residues at this interface that are involved in TRPV4 disease-causing mutations. They shed light on TRPV4 activation and inhibition and provide a template for the design of future therapeutics for treatment of TRPV4-related diseases.

Female mice are protected from impaired parenchymal arteriolar TRPV4 function and impaired cognition in hypertension

Hypertension is a leading modifiable risk factor for cerebral small vessel disease. Our laboratory has shown that endothelium-dependent dilation in cerebral parenchymal arterioles (PAs) is dependent on transient receptor potential vanilloid 4 (TRPV4) activation, and this pathway is impaired in hypertension. This impaired dilation is associated with cognitive deficits and neuroinflammation. Epidemiological evidence suggests that women with midlife hypertension have an increased dementia risk that does not exist in age-matched men, though the mechanisms responsible for this are unclear. This study aimed to determine the sex differences in young, hypertensive mice to serve as a foundation for future determination of sex differences at midlife. We tested the hypothesis that young hypertensive female mice would be protected from the impaired TRPV4-mediated PA dilation and cognitive dysfunction observed in male mice. Angiotensin II (ANG II)-filled osmotic minipumps (800 ng/kg/min, 4 wk) were implanted in 16- to 19-wk-old male C56BL/6 mice. Age-matched female mice received either 800 ng/kg/min or 1,200 ng/kg/min ANG II. Sham-operated mice served as controls. Systolic blood pressure was elevated in ANG II-treated male mice and in 1,200 ng ANG II-treated female mice versus sex-matched shams. PA dilation in response to the TRPV4 agonist GSK1016790A (10-9-10-5 M) was impaired in hypertensive male mice, which was associated with cognitive dysfunction and neuroinflammation, reproducing our previous findings. Hypertensive female mice exhibited normal TRPV4-mediated PA dilation and were cognitively intact. Female mice also showed fewer signs of neuroinflammation than male mice. Determining the sex differences in cerebrovascular health in hypertension is critical for developing effective therapeutic strategies for women.NEW & NOTEWORTHY Vascular dementia is a significant public health concern, and the effect of biological sex on dementia development is not well understood. TRPV4 channels are essential regulators of cerebral parenchymal arteriolar function and cognition. Hypertension impairs TRPV4-mediated dilation and memory in male rodents. Data presented here suggest female sex protects against impaired TRPV4 dilation and cognitive dysfunction during hypertension. These data advance our understanding of the influence of biological sex on cerebrovascular health in hypertension.

Skeletal dysplasia-causing TRPV4 mutations suppress the hypertrophic differentiation of human iPSC-derived chondrocytes

Mutations in the TRPV4 ion channel can lead to a range of skeletal dysplasias. However, the mechanisms by which TRPV4 mutations lead to distinct disease severity remain unknown. Here, we use CRISPR-Cas9-edited human-induced pluripotent stem cells (hiPSCs) harboring either the mild V620I or lethal T89I mutations to elucidate the differential effects on channel function and chondrogenic differentiation. We found that hiPSC-derived chondrocytes with the V620I mutation exhibited increased basal currents through TRPV4. However, both mutations showed more rapid calcium signaling with a reduced overall magnitude in response to TRPV4 agonist GSK1016790A compared to wildtype (WT). There were no differences in overall cartilaginous matrix production, but the V620I mutation resulted in reduced mechanical properties of cartilage matrix later in chondrogenesis. mRNA sequencing revealed that both mutations up-regulated several anterior HOX genes and down-regulated antioxidant genes CAT and GSTA1 throughout chondrogenesis. BMP4 treatment up-regulated several essential hypertrophic genes in WT chondrocytes; however, this hypertrophic maturation response was inhibited in mutant chondrocytes. These results indicate that the TRPV4 mutations alter BMP signaling in chondrocytes and prevent proper chondrocyte hypertrophy, as a potential mechanism for dysfunctional skeletal development. Our findings provide potential therapeutic targets for developing treatments for TRPV4-mediated skeletal dysplasias.

Flipping Off and On the Redox Switch in the Microcirculation

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

Remodeling of Adipose Tissues by Fatty Acids: Mechanistic Update on Browning and Thermogenesis by n-3 Polyunsaturated Fatty Acids

Enhancing thermogenesis by increasing the amount and activity of brown and brite adipocytes is a potential therapeutic target for obesity and its associated diseases. Diet plays important roles in energy metabolism and a myriad of dietary components including lipids are known to regulate thermogenesis through recruitment and activation of brown and brite adipocytes. Depending on types of fatty acids (FAs), the major constituent in lipids, their health benefits differ. Long-chain polyunsaturated FAs (PUFAs), especially n-3 PUFAs remodel adipose tissues in a healthier manner with reduced inflammation and enhanced thermogenesis, while saturated FAs exhibit contrasting effects. Lipid mediators derived from FAs act as autocrine/paracrine as well as endocrine factors to regulate thermogenesis. We discuss lipid mediators that may contribute to the differential effects of FAs on adipose tissue remodeling and hence, cardiometabolic diseases. We also discuss current understanding of molecular and cellular mechanisms through which n-3 PUFAs enhance thermogenesis. Elucidating molecular details of beneficial effects of n-3 PUFAs on thermogenesis is expected to provide information that can be used for development of novel therapeutics for obesity and its associated diseases.

Modulation of transient receptor potential (TRP) channels by plant derived substances used in over-the-counter cough and cold remedies

BACKGROUND

Upper respiratory tract infections (URTIs) impact all age groups and have a significant economic and social burden on society, worldwide. Most URTIs are mild and self-limiting, but due to the wide range of possible causative agents, including Rhinovirus (hRV), Adenovirus, Respiratory Syncytial Virus (RSV), Coronavirus and Influenza, there is no single and effective treatment. Over-the-counter (OTC) remedies, including traditional medicines and those containing plant derived substances, help to alleviate symptoms including inflammation, pain, fever and cough.

PURPOSE

This systematic review focuses on the role of the major plant derived substances in several OTC remedies used to treat cold symptoms, with a particular focus on the transient receptor potential (TRP) channels involved in pain and cough.

METHODS

Literature searches were done using Pubmed and Web of Science, with no date limitations, using the principles of the PRISMA statement. The search terms used were 'TRP channel AND plant compound', 'cough AND plant compound', 'cough AND TRP channels AND plant compound', 'cough AND P2X3 AND plant compound' and 'P2X3 AND plant compound' where plant compound represents menthol or camphor or eucalyptus or turpentine or thymol.

RESULTS

The literature reviewed showed that menthol activates TRPM8 and may inhibit respiratory reflexes reducing irritation and cough. Menthol has a bimodal action on TRPA1, but inhibition may have an analgesic effect. Eucalyptus also activates TRPM8 and inhibits TRPA1 whilst down regulating P2X3, aiding in the reduction of cough, pain and airway irritation. Camphor inhibits TRPA1 and the activation of TRPM8 may add to the effects of menthol. Activation of TRPV1 by camphor, may also have an analgesic effect.

CONCLUSIONS

The literature suggests that these plant derived substances have multifaceted actions and can interact with the TRP 'cough' receptors. The plant derived substances used in cough and cold medicines have the potential to target multiple symptoms experienced during a cold.

Modulating cell signalling in vivo with magnetic nanotransducers

Weak magnetic fields offer nearly lossless transmission of signals within biological tissue. Magnetic nanomaterials are capable of transducing magnetic fields into a range of biologically relevant signals in vitro and in vivo. These nanotransducers have recently enabled magnetic control of cellular processes, from neuronal firing and gene expression to programmed apoptosis. Effective implementation of magnetically controlled cellular signalling relies on careful tailoring of magnetic nanotransducers and magnetic fields to the responses of the intended molecular targets. This primer discusses the versatility of magnetic modulation modalities and offers practical guidelines for selection of appropriate materials and field parameters, with a particular focus on applications in neuroscience. With recent developments in magnetic instrumentation and nanoparticle chemistries, including those that are commercially available, magnetic approaches promise to empower research aimed at connecting molecular and cellular signalling to physiology and behaviour in untethered moving subjects.

Silybin induces endothelium-dependent vasodilation via TRPV4 channels in mouse mesenteric arteries

Silybin is a flavonolignan extracted from the seeds of Silybum marianum that has been used as a dietary supplement for treating hepatic diseases and components of metabolic syndrome such as diabetes, obesity and hypertension. Transient receptor potential vanilloid 4 (TRPV4) channels are Ca²⁺-permeable, nonselective cation channels that regulate vascular endothelial function and blood flow. However, the relationship between silybin and TRPV4 channels in small mesenteric arteries remains unknown. In our study, we carried out a molecular docking experiment by using Discovery Studio v3.5 to predict the binding of silybin to TRPV4. Activation of TRPV4 with silybin was detected via intracellular Ca²⁺ concentration ([Ca²⁺]_i) measurement and patch clamp experiments. The molecular docking results showed that silybin was likely to bind to the ankyrin repeat domain of TPRV4. [Ca²⁺]_i measurements in mesenteric arterial endothelial cells (MAECs) and TRPV4-overexpressing HEK293 (TRPV4-HEK293) cells demonstrated that silybin induced Ca²⁺ influx by activating TRPV4 channels. The patch clamp experiments indicated that in TRPV4-HEK293 cells, silybin induced TRPV4-mediated cation currents. In addition, in high-salt-induced hypertensive mice, oral administration of silybin decreased systolic blood pressure (SBP) and significantly improved the arterial dilatory response to acetylcholine. Our findings provide the first evidence that silybin could induce mesenteric endothelium-dependent vasodilation and reduce blood pressure in high-salt-induced hypertensive mice via TRPV4 channels, thereby revealing the potential effect of silybin on preventing endothelial dysfunction-related cardiovascular diseases.

Protein Kinase A in cellular migration—Niche signaling of a ubiquitous kinase

Cell migration requires establishment and maintenance of directional polarity, which in turn requires spatial heterogeneity in the regulation of protrusion, retraction, and adhesion. Thus, the signaling proteins that regulate these various structural processes must also be distinctly regulated in subcellular space. Protein Kinase A (PKA) is a ubiquitous serine/threonine kinase involved in innumerable cellular processes. In the context of cell migration, it has a paradoxical role in that global inhibition or activation of PKA inhibits migration. It follows, then, that the subcellular regulation of PKA is key to bringing its proper permissive and restrictive functions to the correct parts of the cell. Proper subcellular regulation of PKA controls not only when and where it is active but also specifies the targets for that activity, allowing the cell to use a single, promiscuous kinase to exert distinct functions within different subcellular niches to facilitate cell movement. In this way, understanding PKA signaling in migration is a study in context and in the elegant coordination of distinct functions of a single protein in a complex cellular process.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

NADPH oxidase 4 contributes to TRPV4-mediated endothelium-dependent vasodilation in human arterioles by regulating protein phosphorylation of TRPV4 channels

Impaired endothelium-dependent vasodilation has been suggested to be a key component of coronary microvascular dysfunction (CMD). A better understanding of endothelial pathways involved in vasodilation in human arterioles may provide new insight into the mechanisms of CMD. The goal of this study is to investigate the role of TRPV4, NOX4, and their interaction in human arterioles and examine the underlying mechanisms. Arterioles were freshly isolated from adipose and heart tissues obtained from 71 patients without coronary artery disease, and vascular reactivity was studied by videomicroscopy. In human adipose arterioles (HAA), ACh-induced dilation was significantly reduced by TRPV4 inhibitor HC067047 and by NOX 1/4 inhibitor GKT137831, but GKT137831 did not further affect the dilation in the presence of TRPV4 inhibitors. GKT137831 also inhibited TRPV4 agonist GSK1016790A-induced dilation in HAA and human coronary arterioles (HCA). NOX4 transcripts and proteins were detected in endothelial cells of HAA and HCA. Using fura-2 imaging, GKT137831 significantly reduced GSK1016790A-induced Ca²⁺ influx in the primary culture of endothelial cells and TRPV4-WT-overexpressing human coronary artery endothelial cells (HCAEC). However, GKT137831 did not affect TRPV4-mediated Ca²⁺ influx in non-phosphorylatable TRPV4-S823A/S824A-overexpressing HCAEC. In addition, treatment of HCAEC with GKT137831 decreased the phosphorylation level of Ser824 in TRPV4. Finally, proximity ligation assay (PLA) revealed co-localization of NOX4 and TRPV4 proteins. In conclusion, both TRPV4 and NOX4 contribute to ACh-induced dilation in human arterioles from patients without coronary artery disease. NOX4 increases TRPV4 phosphorylation in endothelial cells, which in turn enhances TRPV4-mediated Ca²⁺ entry and subsequent endothelium-dependent dilation in human arterioles.

The amino-terminal domain of TRPV4 channel is involved in its trafficking to the nucleus

Transient Receptor Potential Vanilloid 4 (TRPV4) ion channel is a sensor for multiple physical and chemical stimuli of ubiquitous expression that participates in various functions either in differentiated tissues or during differentiation. We recently demonstrated the nuclear localization of the full-length TRPV4 in the renal epithelial cells MDCK and its interaction with the transcriptional regulator β-catenin. Here, we describe the presence of a functional nuclear localization signals (NLS) in the N-terminal domain of TRPV4. Simultaneous substitution R404Q, K405Q, and K407Q, produces a channel that fail to reach the nucleus, while K177Q, K178Q, and R179Q mutant channel reaches the nucleus but does not arrive to the plasma membrane (PM). Similar result was observed with the S824D phosphomimetic mutant and the K407E mutation associated with skeletal dysplasia. Structural analysis of these mutants showed important remodeling in their C-terminal domains. Our observations suggest that nucleus-PM trafficking of TRPV4 is important for its cellular functions and may help to explain some deleterious effect of mutations causing TRPV4 channelopathies.

Pannexin 1-a novel regulator of acute hypoxic pulmonary vasoconstriction

AIMS

Hypoxic pulmonary vasoconstriction (HPV) is a physiological response to alveolar hypoxia that diverts blood flow from poorly ventilated to better aerated lung areas to optimize ventilation-perfusion matching. Yet, the exact sensory and signaling mechanisms by which hypoxia triggers pulmonary vasoconstriction remain incompletely understood. Recently, ATP release via pannexin 1 (Panx1) and subsequent signaling via purinergic P2Y receptors has been identified as regulator of vasoconstriction in systemic arterioles. Here, we probed for the role of Panx1-mediated ATP release in HPV and chronic hypoxic pulmonary hypertension (PH).

METHODS AND RESULTS

Pharmacological inhibition of Panx1 by probenecid, spironolactone, the Panx1 specific inhibitory peptide (10Panx1) and genetic deletion of Panx1 specifically in smooth muscle attenuated HPV in isolated perfused mouse lungs. In pulmonary artery smooth muscle cells (PASMC), both spironolactone and 10Panx1 attenuated the increase in intracellular Ca2+ concentration ([Ca2+]i) in response to hypoxia. Yet, genetic deletion of Panx1 in either endothelial or smooth muscle cells did not prevent the development of PH in mice. Unexpectedly, ATP release in response to hypoxia was not detectable in PASMC, and inhibition of purinergic receptors or ATP degradation by ATPase failed to attenuate HPV. Rather, transient receptor potential vanilloid 4 (TRPV4) antagonism and Panx1 inhibition inhibited the hypoxia-induced [Ca2+]i increase in PASMC in an additive manner, suggesting that Panx1 regulates [Ca2+]i independently of the ATP-P2Y-TRPV4 pathway. In line with this notion, Panx1 overexpression increased the [Ca2+]i response to hypoxia in HeLa cells.

CONCLUSION

In the present study we identify Panx1 as novel regulator of HPV. Yet, the role of Panx1 in HPV was not attributable to ATP release and downstream signaling via P2Y receptors or TRPV4 activation, but relates to a role of Panx1 as direct or indirect modulator of the PASMC Ca2+ response to hypoxia. Panx1 did not affect the development of chronic hypoxic PH.

TRANSLATIONAL PERSPECTIVE

Hypoxic pulmonary vasoconstriction (HPV) optimizes lung ventilation-perfusion matching, but also contributes to pulmonary pathologies including high altitude pulmonary edema (HAPE) or chronic hypoxic pulmonary hypertension. Here, we demonstrate that pharmaceutical inhibition as well as genetic deletion of the hemichannel pannexin-1 (Panx1) in pulmonary artery smooth muscle cells attenuates the physiological HPV response. Panx1 deficiency did, however, not prevent the development of chronic hypoxic pulmonary hypertension in mice. Panx1 inhibitors such as the mineralocorticoid receptor antagonist spironolactone may thus present a putative strategy for the prevention or treatment of HAPE, yet not for chronic hypoxic lung disease.

The Transient Receptor Potential Vanilloid 4 Channel and Cardiovascular Disease Risk Factors

Vascular endothelial cells regulate arterial tone through the release of nitric oxide and other diffusible factors such as prostacyclin and endothelium derived hyperpolarizing factors. Alongside these diffusible factors, contact-mediated electrical propagation from endothelial cells to smooth muscle cells via myoendothelial gap junctions, termed endothelium-dependent hyperpolarization (EDH), plays a critical role in endothelium-dependent vasodilation in certain vascular beds. A rise in intracellular Ca²⁺ concentration in endothelial cells is a prerequisite for both the production of diffusible factors and the generation of EDH, and Ca²⁺ influx through the endothelial transient receptor potential vanilloid 4 (TRPV4) ion channel, a nonselective cation channel of the TRP family, plays a critical role in this process in various vascular beds. Emerging evidence suggests that the dysregulation of endothelial TRPV4 channels underpins endothelial dysfunction associated with cardiovascular disease (CVD) risk factors, including hypertension, obesity, diabetes, and aging. Because endothelial dysfunction is a precursor to CVD, a better understanding of the mechanisms underlying impaired TRPV4 channels could lead to novel therapeutic strategies for CVD prevention. In this mini review, we present the current knowledge of the pathophysiological changes in endothelial TRPV4 channels associated with CVD risk factors, and then explore the underlying mechanisms involved.

Heteromeric TRP Channels in Lung Inflammation

Activation of Transient Receptor Potential (TRP) channels can disrupt endothelial barrier function, as their mediated Ca²⁺ influx activates the CaM (calmodulin)/MLCK (myosin light chain kinase)-signaling pathway, and thereby rearranges the cytoskeleton, increases endothelial permeability and thus can facilitate activation of inflammatory cells and formation of pulmonary edema. Interestingly, TRP channel subunits can build heterotetramers, whereas heteromeric TRPC1/4, TRPC3/6 and TRPV1/4 are expressed in the lung endothelium and could be targeted as a protective strategy to reduce endothelial permeability in pulmonary inflammation. An update on TRP heteromers and their role in lung inflammation will be provided with this review.

Mutations in calmodulin-binding domains of TRPV4/6 channels confer invasive properties to colon adenocarcinoma cells

Transient receptor potential (TRP) channels form a family of polymodal cation channels gated by thermal, mechanical, or chemical stimuli, with many of them involved in the control of proliferation, apoptosis, or cell cycle. From an evolutionary point of view, TRP family is characterized by high conservation of duplicated genes originating from whole-genome duplication at the onset of vertebrates. The conservation of such “ohnolog” genes is theoretically linked to an increased probability of generating phenotypes deleterious for the organism upon gene mutation. We aimed to test experimentally the hypothesis that TRP mutations, in particular gain-of-function, could be involved in the generation of deleterious phenotypes involved in cancer, such as gain of invasiveness. Indeed, a number of TRP channels have been linked to cancer progression, and exhibit changes in expression levels in various types of cancers. However, TRP mutations in cancer have been poorly documented. We focused on 2 TRPV family members, TRPV4 and TRPV6, and studied the effect of putative gain-of-function mutations on invasiveness properties. TRPV channels have a C-terminal calmodulin-binding domain (CaMBD) that has important functions for regulating protein function, through different mechanisms depending on the channel (channel inactivation/potentiation, cytoskeleton regulation). We studied the effect of mutations mimicking constitutive phosphorylation in TRPV4 and TRPV6 CaMBDs: TRPV4 S823D, S824D and T813D, TRPV6 S691D, S692D and T702. We found that most of these mutants induced a strong gain of invasiveness of colon adenocarcinoma SW480 cells, both for TRPV4 and TRPV6. While increased invasion with TRPV6 S692D and T702D mutants was correlated to increased mutant channel activity, it was not the case for TRPV4 mutants, suggesting different mechanisms with the same global effect of gain in deleterious phenotype. This highlights the potential importance to search for TRP mutations involved in cancer.

Selective blockade of transient receptor potential vanilloid 4 reduces cyclophosphamide-induced bladder pain in mice

Transient receptor potential vanilloid 4 (TRPV4) is a non-selective cation channel activated by various physical stimuli such as cell swelling and shear stress. TRPV4 is expressed in bladder sensory nerves and epithelium, and its activation produces urinary dysfunction in rodents. However, there have been few reports regarding its involvement in bladder pain. Therefore, we investigated whether TRPV4 is involved in bladder pain in mouse cystitis model. Intraperitoneal injection of cyclophosphamide (CYP; 300 mg/kg) produced mechanical hypersensitivity in the lower abdomen associated with a severe inflammatory bladder in mice. The mechanical threshold was reversed significantly in Trpv4-knockout (KO) mice. Repeated injections of CYP (150 mg/kg) daily for 4 days provoked mild bladder inflammation and persistent mechanical hypersensitivity in mice. Trpv4-KO mice prevented a reduction of the mechanical threshold without an alteration in bladder inflammation. A selective TRPV4 antagonist also reversed the mechanical threshold in chronic cystitis mice. Although expression of Trpv4 was unchanged in the bladders of chronic cystitis mice, the level of phosphorylated TRPV4 was increased significantly. These results suggest involvement of TRPV4 in bladder pain of cystitis mice. A TRPV4 antagonist might be useful for patients with irritable bladder pain such as those with interstitial cystitis/painful bladder syndrome.

Role of Transient Receptor Potential Vanilloid 4 in Vascular Function

Transient receptor potential vanilloid 4 (TRPV4) channels are widely expressed in systemic tissues and can be activated by many stimuli. TRPV4, a Ca²⁺-permeable cation channel, plays an important role in the vasculature and is implicated in the regulation of cardiovascular homeostasis processes such as blood pressure, vascular remodeling, and pulmonary hypertension and edema. Within the vasculature, TRPV4 channels are expressed in smooth muscle cells, endothelial cells, and perivascular nerves. The activation of endothelial TRPV4 contributes to vasodilation involving nitric oxide, prostacyclin, and endothelial-derived hyperpolarizing factor pathways. TRPV4 activation also can directly cause vascular smooth muscle cell hyperpolarization and vasodilation. In addition, TRPV4 activation can evoke constriction in some specific vascular beds or under some pathological conditions. TRPV4 participates in the control of vascular permeability and vascular damage, particularly in the lung capillary endothelial barrier and lung injury. It also participates in vascular remodeling regulation mainly by controlling vasculogenesis and arteriogenesis. This review examines the role of TRPV4 in vascular function, particularly in vascular dilation and constriction, vascular permeability, vascular remodeling, and vascular damage, along with possible mechanisms, and discusses the possibility of targeting TRPV4 for therapy.

Structure and Function of Ion Channels Regulating Sperm Motility-An Overview

Sperm motility is linked to the activation of signaling pathways that trigger movement. These pathways are mainly dependent on Ca²⁺, which acts as a secondary messenger. The maintenance of adequate Ca²⁺ concentrations is possible thanks to proper concentrations of other ions, such as K⁺ and Na⁺, among others, that modulate plasma membrane potential and the intracellular pH. Like in every cell, ion homeostasis in spermatozoa is ensured by a vast spectrum of ion channels supported by the work of ion pumps and transporters. To achieve success in fertilization, sperm ion channels have to be sensitive to various external and internal factors. This sensitivity is provided by specific channel structures. In addition, novel sperm-specific channels or isoforms have been found with compositions that increase the chance of fertilization. Notably, the most significant sperm ion channel is the cation channel of sperm (CatSper), which is a sperm-specific Ca²⁺ channel required for the hyperactivation of sperm motility. The role of other ion channels in the spermatozoa, such as voltage-gated Ca²⁺ channels (VGCCs), Ca²⁺-activated Cl-channels (CaCCs), SLO K⁺ channels or voltage-gated H⁺ channels (VGHCs), is to ensure the activation and modulation of CatSper. As the activation of sperm motility differs among metazoa, different ion channels may participate; however, knowledge regarding these channels is still scarce. In the present review, the roles and structures of the most important known ion channels are described in regard to regulation of sperm motility in animals.

Apoptosis in resistance arteries induced by hydrogen peroxide: greater resilience of endothelium versus smooth muscle

Reactive oxygen species (ROS) are implicated in cardiovascular and neurologic disorders including atherosclerosis, heart attack, stroke, and traumatic brain injury. Although oxidative stress can lead to apoptosis of vascular cells, such findings are largely based upon isolated vascular smooth muscle cells (SMCs) and endothelial cells (ECs) studied in culture. Studying intact resistance arteries, we have focused on understanding how SMCs and ECs in the blood vessel wall respond to acute oxidative stress induced by hydrogen peroxide, a ubiquitous, membrane-permeant ROS. We find that apoptosis induced by H₂O₂ is far greater in SMCs compared to ECs. For both cell types, apoptosis is associated with a rise in intracellular calcium concentration ([Ca²⁺]_i) during H₂O₂ exposure. Consistent with their greater death, the rise in [Ca²⁺]_i for SMCs exceeds that in ECs. Finding that disruption of the endothelium increases SMC death, we address how myoendothelial coupling and paracrine signaling attenuate apoptosis. Remarkably, conditions associated with chronic oxidative stress (advanced age, Western-style diet) protect SMCs during H₂O₂ exposure, as does female sex. In light of intracellular Ca²⁺ handling, we consider how glycolytic versus oxidative pathways for ATP production and changes in mitochondrial structure and function impact cellular resilience to H₂O₂-induced apoptosis. Gaining new insight into protective signaling within and between SMCs and ECs of the arterial wall can be applied to promote vascular cell survival (and recovery of blood flow) in tissues subjected to acute oxidative stress as occurs during reperfusion following myocardial infarction and thrombotic stroke.

Modulating the Mechanical Activation of TRPV4 at the Cell-Substrate Interface

Ion channels activated by mechanical inputs are important force sensing molecules in a wide array of mammalian cells and tissues. The transient receptor potential channel, TRPV4, is a polymodal, nonselective cation channel that can be activated by mechanical inputs but only if stimuli are applied directly at the interface between cells and their substrate, making this molecule a context-dependent force sensor. However, it remains unclear how TRPV4 is activated by mechanical inputs at the cell-substrate interface, which cell intrinsic and cell extrinsic parameters might modulate the mechanical activation of the channel and how mechanical activation differs from TRPV4 gating in response to other stimuli. Here we investigated the impact of substrate mechanics and cytoskeletal components on mechanically evoked TRPV4 currents and addressed how point mutations associated with TRPV4 phosphorylation and arthropathy influence mechanical activation of the channel. Our findings reveal distinct regulatory modulation of TRPV4 from the mechanically activated ion channel PIEZO1, suggesting the mechanosensitivity of these two channels is tuned in response to different parameters. Moreover, our data demonstrate that the effect of point mutations in TRPV4 on channel activation are profoundly dependent on the gating stimulus.

TRPing to the Point of Clarity: Understanding the Function of the Complex TRPV4 Ion Channel

The transient receptor potential vanilloid 4 channel (TRPV4) belongs to the mammalian TRP superfamily of cation channels. TRPV4 is ubiquitously expressed, activated by a disparate array of stimuli, interacts with a multitude of proteins, and is modulated by a range of post-translational modifications, the majority of which we are only just beginning to understand. Not surprisingly, a great number of physiological roles have emerged for TRPV4, as have various disease states that are attributable to the absence, or abnormal functioning, of this ion channel. This review will highlight structural features of TRPV4, endogenous and exogenous activators of the channel, and discuss the reported roles of TRPV4 in health and disease.

Platelet-derived microvesicles induce calcium oscillations and promote VSMC migration via TRPV4

Rationale: Abnormal migration of vascular smooth muscle cells (VSMCs) from the media to the interior is a critical process during the intimal restenosis caused by vascular injury. Here, we determined the role of platelet-derived microvesicles (PMVs) released by activated platelets in VSMC migration. Methods: A percutaneous transluminal angioplasty balloon dilatation catheter was used to establish vascular intimal injury. Collagen I was used to activate PMVs, mimicking collagen exposure during intimal injury. To determine the effects of PMVs on VSMC migration in vitro, scratch wound healing assays were performed. Fluorescence resonance energy transfer was used to detect variations of calcium dynamics in VSMCs. Results: Morphological results showed that neointimal hyperplasia was markedly increased after balloon injury of the carotid artery in rats, and the main component was VSMCs. PMVs significantly promoted single cell migration and wound closure in vitro. Fluorescence resonance energy transfer revealed that PMVs induced temporal and dynamic calcium oscillations in the cytoplasms of VSMCs. The influx of extracellular calcium, but not calcium from intracellular stores, was involved in the process described above. The channel antagonist GSK219 and specific siRNA revealed that a membrane calcium channel, transient receptor potential vanilloid 4 (TRPV4), participated in the calcium oscillations and VSMC migration induced by PMVs. Conclusions: TRPV4 participated in the calcium oscillations and VSMC migration induced by PMVs. PMVs and the related molecules might be novel therapeutic targets for vascular remodeling during vascular injury.

Piezo1 acts upstream of TRPV4 to induce pathological changes in endothelial cells due to shear stress

The ion channels Piezo1 and TRPV4 have both, independently, been implicated in high venous pressure- and fluid shear stress-induced vascular hyperpermeability in endothelial cells. However, the mechanism by which Piezo1 and TRPV4 channels execute the same function is poorly understood. Here we demonstrate that Piezo1 regulates TRPV4 channel activation in endothelial cells and that Piezo1-mediated TRPV4 channel opening is a function of the strength and duration of fluid shear stress. We first confirmed that either fluid shear stress or the Piezo1 agonist, Yoda1, led to an elevation in intracellular calcium ([Ca²⁺]_i) and that application of the Piezo1 antagonist, GsMTx4, completely blocked this change. We discovered that high and prolonged shear stress caused sustained [Ca²⁺]_i elevation that was blocked by inhibition of TRPV4 channel opening. Moreover, Piezo1 stimulated TRPV4 opening through activation of phospholipase A2. TRPV4-dependent sustained [Ca²⁺]_i elevation was responsible for fluid shear stress-mediated and Piezo1-mediated disruption of adherens junctions and actin remodeling. Blockade of TRPV4 channels with the selective TRPV4 blocker, HC067047, prevented the loss of endothelial cell integrity and actin disruption induced by Yoda1 or shear stress and prevented Piezo1-induced monocyte adhesion to endothelial cell monolayers. These findings demonstrate that Piezo1 activation by fluid shear stress initiates a calcium signal that causes TRPV4 opening, which in turn is responsible for the sustained phase calcium elevation that triggers pathological events in endothelial cells. Thus, deleterious effects of shear stress are initiated by Piezo1 but require TRPV4.

Vasoconstrictor Mechanisms in Chronic Hypoxia-Induced Pulmonary Hypertension: Role of Oxidant Signaling

Elevated resistance of pulmonary circulation after chronic hypoxia exposure leads to pulmonary hypertension. Contributing to this pathological process is enhanced pulmonary vasoconstriction through both calcium-dependent and calcium sensitization mechanisms. Reactive oxygen species (ROS), as a result of increased enzymatic production and/or decreased scavenging, participate in augmentation of pulmonary arterial constriction by potentiating calcium influx as well as activation of myofilament sensitization, therefore mediating the development of pulmonary hypertension. Here, we review the effects of chronic hypoxia on sources of ROS within the pulmonary vasculature including NADPH oxidases, mitochondria, uncoupled endothelial nitric oxide synthase, xanthine oxidase, monoamine oxidases and dysfunctional superoxide dismutases. We also summarize the ROS-induced functional alterations of various Ca2+ and K+ channels involved in regulating Ca2+ influx, and of Rho kinase that is responsible for myofilament Ca2+ sensitivity. A variety of antioxidants have been shown to have beneficial therapeutic effects in animal models of pulmonary hypertension, supporting the role of ROS in the development of pulmonary hypertension. A better understanding of the mechanisms by which ROS enhance vasoconstriction will be useful in evaluating the efficacy of antioxidants for the treatment of pulmonary hypertension.

Investigational drugs in early phase clinical trials targeting thermotransient receptor potential (thermoTRP) channels

INTRODUCTION

Thermo transient receptor potential (thermoTRP) channels are some of the most intensely pursued therapeutic targets of the past decade. They are considered promising targets of numerous diseases including chronic pain and cancer. Modulators of these proteins, in particular TRPV1-4, TRPM8 and TRPA1, have reached clinical development, but none has been approved for clinical practice yet.

AREAS COVERED

The therapeutic potential of targeting thermoTRP channels is discussed. The discussion is centered on our experience and on available data found in SciFinder, PubMed, and ClinicalTrials.gov database from the past decade. This review focuses on the therapeutic progress concerning this family of channels, including strategies to improve their therapeutic index for overcoming adverse effects.

EXPERT OPINION

Although thermoTRPs are pivotal drug targets, translation to the clinic has faced two key problems, (i) unforeseen side effects in Phase I trials and, (ii) poor clinical efficacy in Phase II trials. Thus, there is a need for (i) an enhanced understanding of the physiological role of these channels in tissues and organs and (ii) the development of human-based pre-clinical models with higher clinical translation. Furthermore, progress in nanotechnology-based delivery strategies will positively impact thermoTRP human pharmacology.

Ionic Channels as Potential Therapeutic Targets for Erectile Dysfunction: A Review

Erectile dysfunction (ED) is a prevalent condition, especially in men over 40 years old, characterized by the inability to obtain and/or maintain penile erection sufficient for satisfactory sexual intercourse. Several psychological and/or organic factors are involved in the etiopathogenesis of ED. In this context, we gathered evidence of the involvement of Large-conductance, Ca2+-activated K+ channels (BKCa), Small-conductance, Ca2+-activated K+ channels (SKCa), KCNQ-encoded voltage-dependent K+ channels (KV7), Transient Receptor Potential channels (TRP), and Calcium-activated Chloride channels (CaCC) dysfunctions on ED. In addition, the use of modulating agents of these channels are involved in relaxation of the cavernous smooth muscle cell and, consequent penile erection, suggesting that these channels are promising therapeutic targets for the treatment of erectile dysfunction.

PAR2-Mediated cAMP Generation Suppresses TRPV4-Dependent Ca2+ Signaling in Alveolar Macrophages to Resolve TLR4-Induced Inflammation

Alveolar macrophages (AMs), upon sensing pathogens, trigger host defense by activating toll-like receptor 4 (TLR4), but the counterbalancing mechanisms that deactivate AM inflammatory signaling and prevent lethal edema, the hallmark of acute lung injury (ALI), remain unknown. Here, we demonstrate the essential role of AM protease-activating receptor 2 (PAR2) in rapidly suppressing inflammation to prevent long-lasting injury. We show that thrombin, released during TLR4-induced lung injury, directly activates PAR2 to generate cAMP, which abolishes Ca²⁺ entry through the TRPV4 channel. Deletion of PAR2 and thus the accompanying cAMP generation augments Ca²⁺ entry via TRPV4, causing sustained activation of the transcription factor NFAT to produce long-lasting TLR4-mediated inflammatory lung injury. Rescuing thrombin-sensitive PAR2 expression or blocking TRPV4 activity in PAR2-null AMs restores their capacity to resolve inflammation and reverse lung injury. Thus, activation of the thrombin-induced PAR2-cAMP cascade in AMs suppresses TLR4 inflammatory signaling to reinstate tissue integrity.

TRPV4 channel opening mediates pressure-induced pancreatitis initiated by Piezo1 activation

Elevated pressure in the pancreatic gland is the central cause of pancreatitis following abdominal trauma, surgery, endoscopic retrograde cholangiopancreatography, and gallstones. In the pancreas, excessive intracellular calcium causes mitochondrial dysfunction, premature zymogen activation, and necrosis, ultimately leading to pancreatitis. Although stimulation of the mechanically activated, calcium-permeable ion channel Piezo1 in the pancreatic acinar cell is the initial step in pressure-induced pancreatitis, activation of Piezo1 produces only transient elevation in intracellular calcium that is insufficient to cause pancreatitis. Therefore, how pressure produces a prolonged calcium elevation necessary to induce pancreatitis is unknown. We demonstrate that Piezo1 activation in pancreatic acinar cells caused a prolonged elevation in intracellular calcium levels, mitochondrial depolarization, intracellular trypsin activation, and cell death. Notably, these effects were dependent on the degree and duration of force applied to the cell. Low or transient force was insufficient to activate these pathological changes, whereas higher and prolonged application of force triggered sustained elevation in intracellular calcium, leading to enzyme activation and cell death. All of these pathological events were rescued in acinar cells treated with a Piezo1 antagonist and in acinar cells from mice with genetic deletion of Piezo1. We discovered that Piezo1 stimulation triggered transient receptor potential vanilloid subfamily 4 (TRPV4) channel opening, which was responsible for the sustained elevation in intracellular calcium that caused intracellular organelle dysfunction. Moreover, TRPV4 gene-KO mice were protected from Piezo1 agonist- and pressure-induced pancreatitis. These studies unveil a calcium signaling pathway in which a Piezo1-induced TRPV4 channel opening causes pancreatitis.

Ion channels as effectors of cyclic nucleotide pathways: Functional relevance for arterial tone regulation

Numerous mediators and drugs regulate blood flow or arterial pressure by acting on vascular tone, involving cyclic nucleotide intracellular pathways. These signals lead to regulation of several cellular effectors, including ion channels that tune cell membrane potential, Ca²⁺ influx and vascular tone. The characterization of these vasocontrictive or vasodilating mechanisms has grown in complexity due to i) the variety of ion channels that are expressed in both vascular endothelial and smooth muscle cells, ii) the heterogeneity of responses among the various vascular beds, and iii) the number of molecular mechanisms involved in cyclic nucleotide signalling in health and disease. This review synthesizes key data from literature that highlight ion channels as physiologically relevant effectors of cyclic nucleotide pathways in the vasculature, including the characterization of the molecular mechanisms involved. In smooth muscle cells, cation influx or chloride efflux through ion channels are associated with vasoconstriction, whereas K⁺ efflux repolarizes the cell membrane potential and mediates vasodilatation. Both categories of ion currents are under the influence of cAMP and cGMP pathways. Evidence that some ion channels are influenced by CN signalling in endothelial cells will also be presented. Emphasis will also be put on recent data touching a variety of determinants such as phosphodiesterases, EPAC and kinase anchoring, that complicate or even challenge former paradigms.

Endothelial TRPV4 channels and vasodilator reactivity

Transient receptor potential vanilloid 4 (TRPV4) ion channels on the endothelial cell membrane are widely regarded as a crucial Ca²⁺ influx pathway that promotes endothelium-dependent vasodilation. The downstream vasodilatory targets of endothelial TRPV4 channels vary among different vascular beds, potentially contributing to endothelial cell heterogeneity. Although numerous studies have examined the role of endothelial TRPV4 channels using specific pharmacological tools over the past decade, their physiological significance remains unclear, mainly due to a lack of endothelium-specific knockouts. Moreover, the loss of endothelium-dependent vasodilation is a significant contributor to vascular dysfunction in cardiovascular disease. The activity of endothelial TRPV4 channels is impaired in cardiovascular disease; therefore, strategies targeting the mechanisms that reduce endothelial TRPV4 channel activity may restore vascular function and provide therapeutic benefit. In this chapter, we discuss endothelial TRPV4 channel-dependent signaling mechanisms, the heterogeneity in endogenous activators and targets of endothelial TRPV4 channels, and the role of endothelial TRPV4 channels in the pathogenesis of cardiovascular diseases. We also discuss potentially interesting future research directions that may provide novel insights into the physiological and pathological roles of endothelial TRPV4 channels.

Cytokine and inflammatory mediator effects on TRPV4 function in choroid plexus epithelial cells

The choroid plexus (CP), composed of capillaries surrounded by a barrier epithelium, is the main producer of cerebrospinal fluid (CSF). The CP epithelium regulates the transport of ions and water between the blood and the ventricles, contributing to CSF production and composition. Several studies suggest a connection between the cation channel transient receptor potential vanilloid-4 (TRPV4) and transepithelial ion movement. TRPV4 is a nonselective, calcium-permeable cation channel present in CP epithelia reported to be activated by cytokines and inflammatory mediators. Utilizing the PCP-R (porcine choroid plexus-Riems) cell line, we investigated the effects of various cytokines and inflammatory mediators on TRPV4-mediated activity. Select proinflammatory cytokines (TNF-α, IL-1β, TGF-β1) had inhibitory effects on TRPV4-stimulated transepithelial ion flux and permeability changes, whereas anti-inflammatory cytokines (IL-10, IL-4, and IL-6) had none. Quantitative mRNA analysis showed that these cytokines had no effect on TRPV4 transcription levels. Inhibition of the transcription factor NF-κB, involved in the production and regulation of several inflammatory cytokines, inhibited TRPV4-mediated activity, suggesting a link between TRPV4 and cytokine production. Contrary to published studies, the proinflammatory mediator arachidonic acid (AA) had inhibitory rather than stimulatory effects on TRPV4-mediated responses. However, inhibition of AA metabolism also caused inhibitory effects on TRPV4, suggesting a complex interaction of AA and its metabolites in the regulation of TRPV4 activity. Together these data imply that TRPV4 activity is involved in the inflammatory response; it is negatively affected by proinflammatory mediators. Furthermore, arachidonic acid metabolites, but not arachidonic acid itself, are positive regulators of TRPV4.

TRP Channels in Angiogenesis and Other Endothelial Functions

Angiogenesis is the growth of blood vessels mediated by proliferation, migration, and spatial organization of endothelial cells. This mechanism is regulated by a balance between stimulatory and inhibitory factors. Proangiogenic factors include a variety of VEGF family members, while thrombospondin and endostatin, among others, have been reported as suppressors of angiogenesis. Transient receptor potential (TRP) channels belong to a superfamily of cation-permeable channels that play a relevant role in a number of cellular functions mostly derived from their influence in intracellular Ca²⁺ homeostasis. Endothelial cells express a variety of TRP channels, including members of the TRPC, TRPV, TRPP, TRPA, and TRPM families, which play a relevant role in a number of functions, including endothelium-induced vasodilation, vascular permeability as well as sensing hemodynamic and chemical changes. Furthermore, TRP channels have been reported to play an important role in angiogenesis. This review summarizes the current knowledge and limitations concerning the involvement of particular TRP channels in growth factor-induced angiogenesis.

Endothelin receptor A and p66Shc regulate spontaneous Ca2+ oscillations in smooth muscle cells controlling renal arterial spontaneous motion

Adaptor protein p66Shc is overexpressed in smooth muscle cells of renal resistance vessels of hypertensive salt-sensitive rats and is involved in the regulation of renal vascular tone. We applied 2-photon laser scanning fluorescence microscopy to analyze spontaneous dynamic fluctuations in intracellular calcium concentrations ([Ca²⁺]_i) in smooth muscle cells embedded in the walls of freshly isolated renal resistance arteries. The amplitude, number of events, and frequency of spontaneous [Ca²⁺]_i oscillations triggered by endogenously released endothelin-1 were recorded in smooth muscle cells of the renal arteries. Endothelin receptor A antagonist BQ123 dramatically reduced the amplitude and frequency of spontaneous Ca²⁺ events, producing marked inhibition of renal vessels spontaneous motion. Spontaneous Ca²⁺ fluctuations in smooth muscle cells of p66Shc knockout (p66ShcKO) rats had significantly higher amplitude than in control rats. The frequency of spontaneous [Ca²⁺]_i oscillations did not change in p66ShcKO rats, suggesting that p66Shc expression did not affect endothelin-1 release from resident endothelial cells. Acute application of endothelin-1 revealed significantly elevated production of the total [Ca²⁺]_i in p66ShcKO rats. Spontaneous cytosolic Ca²⁺ oscillations in smooth muscle cells of renal vessels mediate their spontaneous motion via the endothelin-1/endothelin receptor A pathway. p66Shc decreases the amplitude of individual changes in [Ca²⁺]_i, which mitigates the spontaneous motion of renal vessels.-Palygin, O., Miller, B. S., Nishijima, Y., Zhang, D. X., Staruschenko, A., Sorokin, A. Endothelin receptor A and p66Shc regulate spontaneous Ca²⁺ oscillations in smooth muscle cells controlling renal arterial spontaneous motion.