TRPV4 partially participates in proliferation of human brain capillary endothelial cells

Mechanotransduction in Development: A Focus on Angiogenesis

Cells respond to external mechanical cues and transduce these forces into biological signals. This process is known as mechanotransduction and requires a group of proteins called mechanosensors. This peculiar class of receptors include extracellular matrix proteins, plasma membrane proteins, the cytoskeleton and the nuclear envelope. These cell components are responsive to a wide spectrum of physical cues including stiffness, tensile force, hydrostatic pressure and shear stress. Among mechanotransducers, the Transient Receptor Potential (TRP) and the PIEZO family members are mechanosensitive ion channels, coupling force transduction with intracellular cation transport. Their activity contributes to embryo development, tissue remodeling and repair, and cell homeostasis. In particular, vessel development is driven by hemodynamic cues such as flow direction and shear stress. Perturbed mechanotransduction is involved in several pathological vascular phenotypes including hereditary hemorrhagic telangiectasia. This review is conceived to summarize the most recent findings of mechanotransduction in development. We first collected main features of mechanosensitive proteins. However, we focused on the role of mechanical cues during development. Mechanosensitive ion channels and their function in vascular development are also discussed, with a focus on brain vessel morphogenesis.

Peptide Lv and Angiogenesis: A Newly Discovered Angiogenic Peptide

Peptide Lv is a small endogenous secretory peptide with ~40 amino acids and is highly conserved among certain several species. While it was first discovered that it augments L-type voltage-gated calcium channels (LTCCs) in neurons, thus it was named peptide "Lv", it can bind to vascular endothelial growth factor receptor 2 (VEGFR2) and has VEGF-like activities, including eliciting vasodilation and promoting angiogenesis. Not only does peptide Lv augment LTCCs in neurons and cardiomyocytes, but it also promotes the expression of intermediate-conductance KCa channels (KCa3.1) in vascular endothelial cells. Peptide Lv is upregulated in the retinas of patients with early proliferative diabetic retinopathy, a disease involving pathological angiogenesis. This review will provide an overview of peptide Lv, its known bioactivities in vitro and in vivo, and its clinical relevance, with a focus on its role in angiogenesis. As there is more about peptide Lv to be explored, this article serves as a foundation for possible future developments of peptide Lv-related therapeutics to treat or prevent diseases.

Identification and Properties of TRPV4 Mutant Channels Present in Polycystic Kidney Disease Patients

Polycystic kidney disease (PKD), a disease characterized by the enlargement of the kidney through cystic growth is the fourth leading cause of end-stage kidney disease world-wide. Transient receptor potential Vanilloid 4 (TRPV4), a calcium-permeable TRP, channel participates in kidney cell physiology and since TRPV4 forms complexes with another channel whose malfunction is associated to PKD, TRPP2 (or PKD2), we sought to determine whether patients with PKD, exhibit previously unknown mutations in TRPV4. Here, we report the presence of mutations in the TRPV4 gene in patients diagnosed with PKD and determine that they produce gain-of-function (GOF). Mutations in the sequence of the TRPV4 gene have been associated to a broad spectrum of neuropathies and skeletal dysplasias but not PKD, and their biophysical effects on channel function have not been elucidated. We identified and examined the functional behavior of a novel E6K mutant and of the previously known S94L and A217S mutant TRVP4 channels. The A217S mutation has been associated to mixed neuropathy and/or skeletal dysplasia phenotypes, however, the PKD carriers of these variants had not been diagnosed with these reported clinical manifestations. The presence of certain mutations in TRPV4 may influence the progression and severity of PKD through GOF mechanisms. PKD patients carrying TRVP4 mutations are putatively more likely to require dialysis or renal transplant as compared to those without these mutations.

Drug Discovery Research for Traumatic Brain Injury Focused on Functional Molecules in Astrocytes

Traumatic brain injury (TBI) is severe damage to the head caused by traffic accidents, falls, and sports. Because TBI-induced disruption of the blood-brain barrier (BBB) causes brain edema and neuroinflammation, which are major causes of death or serious disabilities, protection and recovery of BBB function may be beneficial therapeutic strategies for TBI. Astrocytes are key components of BBB integrity, and astrocyte-derived bioactive factors promote and suppress BBB disruption in TBI. Therefore, the regulation of astrocyte function is essential for BBB protection. In the injured cerebrum of TBI model mice, we found that the endothelin ETB receptor, histamine H2 receptor, and transient receptor potential vanilloid 4 (TRPV4) were predominantly expressed in reactive astrocytes. We also showed that repeated administration of an ETB receptor antagonist, H2 receptor agonist, and TRPV4 antagonist alleviated BBB disruption and brain edema in a TBI mouse model. Furthermore, these drugs decreased the expression levels of astrocyte-derived factors promoting BBB disruption and increased the expression levels of astrocyte-derived protective factors in the injured cerebrum after TBI. These results suggest that the ETB receptor, H2 receptor, and TRPV4 are molecules that regulate astrocyte function, and might be attractive candidates for the development of therapeutic drugs for TBI.

Hyperoside ameliorates cerebral ischaemic-reperfusion injury by opening the TRPV4 channel in vivo through the IP3-PKC signalling pathway

CONTEXT

Hyperoside (Hyp), one of the active flavones from Rhododendron (Ericaceae), has beneficial effects against cerebrovascular disease. However, the effect of Hyp on vasodilatation has not been elucidated.

OBJECTIVE

To explore the effect of Hyp on vasodilatation in the cerebral basilar artery (CBA) of Sprague-Dawley (SD) rats suffering with ischaemic-reperfusion (IR) injury.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into sham, model, Hyp, Hyp + channel blocker and channel blocker groups. Hyp (50 mg/kg, IC₅₀ = 18.3 μg/mL) and channel blocker were administered via tail vein injection 30 min before ischaemic, followed by 20 min of ischaemic and 2 h of reperfusion. The vasodilation, hyperpolarization, ELISA assay, haematoxylin-eosin (HE), Nissl staining and channel-associated proteins and qPCR were analysed. Rat CBA smooth muscle cells were isolated to detect the Ca²⁺ concentration and endothelial cells were isolated to detect apoptosis rate.

RESULTS

Hyp treatment significantly ameliorated the brain damage induced by IR and evoked endothelium-dependent vasodilation rate (47.93 ± 3.09% vs. 2.99 ± 1.53%) and hyperpolarization (-8.15 ± 1.87 mV vs. -0.55 ± 0.42 mV) by increasing the expression of IP3R, PKC, transient receptor potential vanilloid channel 4 (TRPV4), IK_Ca and SK_Ca in the CBA. Moreover, Hyp administration significantly reduced the concentration of Ca²⁺ (49.08 ± 7.74% vs. 83.52 ± 6.93%) and apoptosis rate (11.27 ± 1.89% vs. 23.44 ± 2.19%) in CBA. Furthermore, these beneficial effects of Hyp were blocked by channel blocker.

DISCUSSION AND CONCLUSIONS

Although Hyp showed protective effect in ischaemic stroke, more clinical trial certification is needed due to the difference between animals and humans.

Astrocytic TRPV4 Channels and Their Role in Brain Ischemia

Transient receptor potential cation channels subfamily V member 4 (TRPV4) are non-selective cation channels expressed in different cell types of the central nervous system. These channels can be activated by diverse physical and chemical stimuli, including heat and mechanical stress. In astrocytes, they are involved in the modulation of neuronal excitability, control of blood flow, and brain edema formation. All these processes are significantly impaired in cerebral ischemia due to insufficient blood supply to the tissue, resulting in energy depletion, ionic disbalance, and excitotoxicity. The polymodal cation channel TRPV4, which mediates Ca²⁺ influx into the cell because of activation by various stimuli, is one of the potential therapeutic targets in the treatment of cerebral ischemia. However, its expression and function vary significantly between brain cell types, and therefore, the effect of its modulation in healthy tissue and pathology needs to be carefully studied and evaluated. In this review, we provide a summary of available information on TRPV4 channels and their expression in healthy and injured neural cells, with a particular focus on their role in ischemic brain injury.

Transient Receptor Potential Vanilloid 4: a Double-Edged Sword in the Central Nervous System

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel that can be activated by diverse stimuli, such as heat, mechanical force, hypo-osmolarity, and arachidonic acid metabolites. TRPV4 is widely expressed in the central nervous system (CNS) and participates in many significant physiological processes. However, accumulative evidence has suggested that deficiency, abnormal expression or distribution, and overactivation of TRPV4 are involved in pathological processes of multiple neurological diseases. Here, we review the latest studies concerning the known features of this channel, including its expression, structure, and its physiological and pathological roles in the CNS, proposing an emerging therapeutic strategy for CNS diseases.

Ion Channels in Gliomas-From Molecular Basis to Treatment

Ion channels provide the basis for the nervous system's intrinsic electrical activity. Neuronal excitability is a characteristic property of neurons and is critical for all functions of the nervous system. Glia cells fulfill essential supportive roles, but unlike neurons, they also retain the ability to divide. This can lead to uncontrolled growth and the formation of gliomas. Ion channels are involved in the unique biology of gliomas pertaining to peritumoral pathology and seizures, diffuse invasion, and treatment resistance. The emerging picture shows ion channels in the brain at the crossroads of neurophysiology and fundamental pathophysiological processes of specific cancer behaviors as reflected by uncontrolled proliferation, infiltration, resistance to apoptosis, metabolism, and angiogenesis. Ion channels are highly druggable, making them an enticing therapeutic target. Targeting ion channels in difficult-to-treat brain tumors such as gliomas requires an understanding of their extremely heterogenous tumor microenvironment and highly diverse molecular profiles, both representing major causes of recurrence and treatment resistance. In this review, we survey the current knowledge on ion channels with oncogenic behavior within the heterogeneous group of gliomas, review ion channel gene expression as genomic biomarkers for glioma prognosis and provide an update on therapeutic perspectives for repurposed and novel ion channel inhibitors and electrotherapy.

Pharmacological activation of transient receptor potential vanilloid 4 promotes triggering of the swallowing reflex in rats

The swallowing reflex is an essential physiological reflex that allows food or liquid to pass into the esophagus from the oral cavity. Delayed triggering of this reflex is a significant health problem in patients with oropharyngeal dysphagia for which no pharmacological treatments exist. Transient receptor potential channels have recently been discovered as potential targets to facilitate triggering of the swallowing reflex. However, the ability of transient receptor potential vanilloid 4 (TRPV4) to trigger the swallowing reflex has not been studied. Here, we demonstrate the involvement of TRPV4 in triggering the swallowing reflex in rats. TRPV4 immunoreactive nerve fibers were observed in the superior laryngeal nerve (SLN)-innervated swallowing-related regions. Retrograde tracing with fluorogold revealed localization of TRPV4 on approximately 25% of SLN-afferent neurons in the nodose-petrosal-jugular ganglionic complex. Among them, approximately 49% were large, 35% medium, and 15% small-sized SLN-afferent neurons. Topical application of a TRPV4 agonist (GSK1016790A) to the SLN-innervated regions dose-dependently facilitated triggering of the swallowing reflex, with the highest number of reflexes triggered at a concentration of 250 μM. The number of agonist-induced swallowing reflexes was significantly reduced by prior topical application of a TRPV4 antagonist. These findings indicate that TRPV4 is expressed on sensory nerves innervating the swallowing-related regions, and that its activation by an agonist can facilitate swallowing. TRPV4 is a potential pharmacological target for the management of oropharyngeal dysphagia.

The Effect of Global Warming on Complex Disorders (Mental Disorders, Primary Hypertension, and Type 2 Diabetes)

Multiple studies imply a strong relationship between global warming (GW) and complex disorders. This review summarizes such reports concentrating on three disorders-mental disorders (MD), primary hypertension, and type 2 diabetes (T2D). We also attempt to point at potential mechanisms mediating the effect of GW on these disorders. Concerning mental disorders, immediate candidates are brain levels of heat-shock proteins (HSPs). In addition, given that heat stress increases reactive oxygen species (ROS) levels which may lead to blood-brain barrier (BBB) breakdown and, hence, enhanced protein extravasation in the brain, this might finally cause, or exacerbate mental health. As for hypertension, since its causes are incompletely understood, the mechanism(s) by which heat exposure affects blood pressure (BP) is an open question. Since the kidneys participate in regulating blood volume and BP they are considered as a site of heat-associated disease, hence, we discuss hyperosmolarity as a potential mediator. In addition, we relate to autoimmunity, inflammation, sodium excretion, and HSP70 as risk factors that might play a role in the effect of heat on hypertension. In the case of T2D, we raise two potential mediators of the effect of exposure to ambient hot environment on the disease's incidence-brown adipose tissue metabolism and HSPs.

Pharmacological Inhibition of Transient Receptor Potential Vanilloid 4 Reduces Vasogenic Edema after Traumatic Brain Injury in Mice

Vasogenic edema results from blood-brain barrier (BBB) disruption after traumatic brain injury (TBI), and although it can be fatal, no promising therapeutic drugs have been developed as yet. Transient receptor potential vanilloid 4 (TRPV4) is a calcium-permeable channel that is sensitive to temperature and osmotic pressure. As TRPV4 is known to be responsible for various pathological conditions following brain injury, we investigated the effects of pharmacological TRPV4 antagonists on TBI-induced vasogenic edema in this study. A TBI model was established by inflicting fluid percussion injury (FPI) in the mouse cerebrum and cultured astrocytes. Vasogenic brain edema and BBB disruption were assessed based on brain water content and Evans blue (EB) extravasation into brain tissue, respectively. After FPI, brain water content and EB extravasation increased. Repeated intracerebroventricular administration of the specific TRPV4 antagonists HC-067047 and RN-1734 dose-dependently reduced brain water content and alleviated EB extravasation in FPI mice. Additionally, real-time PCR analysis indicated that administration of HC-067047 and RN-1734 reversed the FPI-induced increase in mRNA levels of endogenous causal factors for BBB disruption, including matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor-A (VEGF-A), and endothelin-1 (ET-1). In astrocytes, TRPV4 level was observed to be higher than that in brain microvascular endothelial cells. Treatment with HC-067047 and RN-1734 inhibited the increase in mRNA levels of MMP-9, VEGF-A, and ET-1 in cultured astrocytes subjected to in vitro FPI. These results suggest that pharmacological inhibition of TRPV4 is expected to be a promising therapeutic strategy for treating TBI-induced vasogenic edema.

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.

Puerarin induces mouse mesenteric vasodilation and ameliorates hypertension involving endothelial TRPV4 channels

Puerarin (Pue) is an isoflavone derived from the root of Pueraria lobata, which has been widely used as food and a herb for treating cardiovascular and cerebrovascular diseases. Transient receptor potential vanilloid 4 (TRPV4), a Ca2+-permeable channel with multiple modes of activation, plays an important role in vascular endothelial function and vasodilation. However, no reports have shown the effects of Pue on TRPV4 channels and mouse small mesenteric arteries. In the present study, we performed a molecular docking assay by using Discovery Studio 3.5 software to predict the binding of Pue to TRPV4 protein. The activation of TRPV4 by Pue was determined by intracellular Ca2+ concentration ([Ca2+]i), live-cell fluorescent Ca2+ imaging and patch clamp assays. Molecular docking results indicated a high possibility of Pue-TPRV4 binding. [Ca2+]i and Ca2+ imaging assays showed that Pue activated TRPV4 channels and increased [Ca2+]i in TRPV4-overexpressing HEK293 (TRPV4-HEK293) cells and primary mouse mesenteric artery endothelial cells (MAECs). Patch clamp assay demonstrated that Pue stimulated the TRPV4-mediated cation currents. Additionally, Pue relaxed mouse mesenteric arteries involving the TRPV4-small-conductance Ca2+-activated K+ channel (SKCa)/intermediate-conductance Ca2+-activated K+ channel (IKCa) pathway, and reduced systolic blood pressure (SBP) in high-salt-induced hypertensive mice. Our study found for the first time that Pue acts as a TRPV4 agonist, induces endothelium-dependent vasodilation in mouse mesenteric arteries, and attenuates blood pressure in high-salt-induced hypertensive mice, highlighting the beneficial effect of Pue in treating endothelial dysfunction-related cardiovascular diseases.

Role of TRPV4 channel in vasodilation and neovascularization

The transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca²⁺ -permeable nonselective cation channel, is widely distributed in the circulatory system, particularly in vascular endothelial cells (ECs) and smooth muscle cells (SMCs). The TRPV4 channel is activated by various endogenous and exogenous stimuli, including shear stress, low intravascular pressure, and arachidonic acid. TRPV4 has a role in mediating vascular tone and arterial blood pressure. The activation of the TRPV4 channel induces Ca²⁺ influx, thereby resulting in endothelium-dependent hyperpolarization and SMC relaxation through SK_Ca and IK_Ca activation on ECs or through BK_Ca activation on SMCs. Ca²⁺ binds to calmodulin, which leads to the production of nitric oxide, causing vasodilation. Furthermore, the TRPV4 channel plays an important role in angiogenesis and arteriogenesis and is critical for tumor angiogenesis and growth, since it promotes or inhibits the development of various types of cancer. The TRPV4 channel is involved in the active growth of collateral arteries induced by flow shear stress, which makes it a promising therapeutic target in the occlusion or stenosis of the main arteries. In this review, we explore the role and the potential mechanism of action of the TRPV4 channel in the regulation of vascular tone and in the induction of neovascularization to provide a reference for future research.

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.

TRP Channels in Brain Tumors

Malignant glioma including glioblastoma (GBM) is the most common group of primary brain tumors. Despite standard optimized treatment consisting of extensive resection followed by radiotherapy/concomitant and adjuvant therapy, GBM remains one of the most aggressive human cancers. GBM is a typical example of intra-heterogeneity modeled by different micro-environmental situations, one of the main causes of resistance to conventional treatments. The resistance to treatment is associated with angiogenesis, hypoxic and necrotic tumor areas while heterogeneity would accumulate during glioma cell invasion, supporting recurrence. These complex mechanisms require a focus on potential new molecular actors to consider new treatment options for gliomas. Among emerging and underexplored targets, transient receptor potential (TRP) channels belonging to a superfamily of non-selective cation channels which play critical roles in the responses to a number of external stimuli from the external environment were found to be related to cancer development, including glioma. Here, we discuss the potential as biological markers of diagnosis and prognosis of TRPC6, TRPM8, TRPV4, or TRPV1/V2 being associated with glioma patient overall survival. TRPs-inducing common or distinct mechanisms associated with their Ca²⁺-channel permeability and/or kinase function were detailed as involving miRNA or secondary effector signaling cascades in turn controlling proliferation, cell cycle, apoptotic pathways, DNA repair, resistance to treatment as well as migration/invasion. These recent observations of the key role played by TRPs such as TRPC6 in GBM growth and invasiveness, TRPV2 in proliferation and glioma-stem cell differentiation and TRPM2 as channel carriers of cytotoxic chemotherapy within glioma cells, should offer new directions for innovation in treatment strategies of high-grade glioma as GBM to overcome high resistance and recurrence.

Transient Receptor Potential Vanilloid in the Brain Gliovascular Unit: Prospective Targets in Therapy

The gliovascular unit (GVU) is composed of the brain microvascular endothelial cells forming blood–brain barrier and the neighboring surrounding “mural” cells (e.g., pericytes) and astrocytes. Modulation of the GVU/BBB features could be observed in a variety of vascular, immunologic, neuro-psychiatric diseases, and cancers, which can disrupt the brain homeostasis. Ca²⁺ dynamics have been regarded as a major factor in determining BBB/GVU properties, and previous studies have demonstrated the role of transient receptor potential vanilloid (TRPV) channels in modulating Ca²⁺ and BBB/GVU properties. The physiological role of thermosensitive TRPV channels in the BBB/GVU, as well as their possible therapeutic potential as targets in treating brain diseases via preserving the BBB are reviewed. TRPV2 and TRPV4 are the most abundant isoforms in the human BBB, and TRPV2 was evidenced to play a main role in regulating human BBB integrity. Interspecies differences in TRPV2 and TRPV4 BBB expression complicate further preclinical validation. More studies are still needed to better establish the physiopathological TRPV roles such as in astrocytes, vascular smooth muscle cells, and pericytes. The effect of the chronic TRPV modulation should also deserve further studies to evaluate their benefit and innocuity in vivo.

Ca2+ homeostasis in brain microvascular endothelial cells

Blood brain barrier (BBB) is formed by the brain microvascular endothelial cells (BMVECs) lining the wall of brain capillaries. Its integrity is regulated by multiple mechanisms, including up/downregulation of tight junction proteins or adhesion molecules, altered Ca²⁺ homeostasis, remodeling of cytoskeleton, that are confined at the level of BMVECs. Beside the contribution of BMVECs to BBB permeability changes, other cells, such as pericytes, astrocytes, microglia, leukocytes or neurons, etc. are also exerting direct or indirect modulatory effects on BBB. Alterations in BBB integrity play a key role in multiple brain pathologies, including neurological (e.g. epilepsy) and neurodegenerative disorders (e.g. Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis etc.). In this review, the principal Ca²⁺ signaling pathways in brain microvascular endothelial cells are discussed and their contribution to BBB integrity is emphasized. Improving the knowledge of Ca²⁺ homeostasis alterations in BMVECa is fundamental to identify new possible drug targets that diminish/prevent BBB permeabilization in neurological and neurodegenerative disorders.

Molecular and Functional Study of Transient Receptor Potential Vanilloid 1-4 at the Rat and Human Blood-Brain Barrier Reveals Interspecies Differences

Transient receptor potential vanilloid 1-4 (TRPV1-4) expression and functionality were investigated in brain microvessel endothelial cells (BMEC) forming the blood-brain barrier (BBB) from rat and human origins. In rat, Trpv1-4 were detected by qRT-PCR in the brain cortex, brain microvessels, and in primary cultures of brain microvessel endothelial cells [rat brain microvessel endothelial cells (rPBMEC)]. A similar Trpv1-4 expression profile in isolated brain microvessels and rPBMEC was found with the following order: Trpv4 > Trpv2 > Trpv3 > Trpv1. In human, TRPV1-4 were detected in the BBB cell line human cerebral microvessel endothelial cells D3 cells (hCMEC/D3) and in primary cultures of BMEC isolated from human adult and children brain resections [human brain microvascular endothelial cells (hPBMEC)], showing a similar TRPV1-4 expression profile in both hCMEC/D3 cells and hPBMECs as follow: TRPV2 > > TRPV4 > TRPV1 > TRPV3. Western blotting and immunofluorescence experiments confirmed that TRPV2 and TRPV4 are the most expressed TRPV isoforms in hCMEC/D3 cells with a clear staining at the plasma membrane. A fluorescent dye Fluo-4 AM ester was applied to record intracellular Ca2+ levels. TRPV4 functional activity was demonstrated in mediating Ca2+ influx under stimulation with the specific agonist GSK1016790A (ranging from 3 to 1000 nM, EC50 of 16.2 ± 4.5 nM), which was inhibited by the specific TRPV4 antagonist, RN1734 (30 μM). In contrast, TRPV1 was slightly activated in hCMEC/D3 cells as shown by the weak Ca2+ influx induced by capsaicin at a high concentration (3 μM), a highly potent and specific TRPV1 agonist. Heat-induced Ca2+ influx was not altered by co-treatment with a selective potent TRPV1 antagonist capsazepine (20 μM), in agreement with the low expression of TRPV1 as assessed by qRT-PCR. Our present study reveals an interspecies difference between Rat and Human. Functional contributions of TRPV1-4 subtype expression were not identical in rat and human tissues reflective of BBB integrity. TRPV2 was predominant in the human whereas TRPV4 had a larger role in the rat. This interspecies difference from a gene expression point of view should be taken into consideration when modulators of TRPV2 or TRPV4 are investigated in rat models of brain disorders.

Endothelial Transient Receptor Potential Channels and Vascular Remodeling: Extracellular Ca2 + Entry for Angiogenesis, Arteriogenesis and Vasculogenesis

Vasculogenesis, angiogenesis and arteriogenesis represent three crucial mechanisms involved in the formation and maintenance of the vascular network in embryonal and post-natal life. It has long been known that endothelial Ca²⁺ signals are key players in vascular remodeling; indeed, multiple pro-angiogenic factors, including vascular endothelial growth factor, regulate endothelial cell fate through an increase in intracellular Ca²⁺ concentration. Transient Receptor Potential (TRP) channel consist in a superfamily of non-selective cation channels that are widely expressed within vascular endothelial cells. In addition, TRP channels are present in the two main endothelial progenitor cell (EPC) populations, i.e., myeloid angiogenic cells (MACs) and endothelial colony forming cells (ECFCs). TRP channels are polymodal channels that can assemble in homo- and heteromeric complexes and may be sensitive to both pro-angiogenic cues and subtle changes in local microenvironment. These features render TRP channels the most versatile Ca²⁺ entry pathway in vascular endothelial cells and in EPCs. Herein, we describe how endothelial TRP channels stimulate vascular remodeling by promoting angiogenesis, arteriogenesis and vasculogenesis through the integration of multiple environmental, e.g., extracellular growth factors and chemokines, and intracellular, e.g., reactive oxygen species, a decrease in Mg²⁺ levels, or hypercholesterolemia, stimuli. In addition, we illustrate how endothelial TRP channels induce neovascularization in response to synthetic agonists and small molecule drugs. We focus the attention on TRPC1, TRPC3, TRPC4, TRPC5, TRPC6, TRPV1, TRPV4, TRPM2, TRPM4, TRPM7, TRPA1, that were shown to be involved in angiogenesis, arteriogenesis and vasculogenesis. Finally, we discuss the role of endothelial TRP channels in aberrant tumor vascularization by focusing on TRPC1, TRPC3, TRPV2, TRPV4, TRPM8, and TRPA1. These observations suggest that endothelial TRP channels represent potential therapeutic targets in multiple disorders featured by abnormal vascularization, including cancer, ischemic disorders, retinal degeneration and neurodegeneration.

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.

Role of transient receptor potential vanilloid subtype 4 in the regulation of azoymethane/dextran sulphate sodium-induced colitis-associated cancer in mice

Ca²⁺-permeable ion channels, such as transient receptor channels, are one of the potential therapeutic targets in cancer. Transient receptor potential vanilloid subtype 4 (TRPV4) is a nonselective cation channel associated with cancer progression. This study investigates the roles of TRPV4 in the pathogenesis of colitis-associated cancer (CAC) in mice. The role of TRPV4 was examined in azoxymethane (AOM)/dextran sulphate sodium (DSS)-induced murine CAC model. The formation of colon tumours induced by AOM/DSS treatment was significantly attenuated in TRPV4-deficient mice (TRPV4KO). TRPV4 was co-localised with markers of angiogenesis and macrophages. AOM/DSS treatment upregulated the expression of CD105, vascular endothelial growth factor receptor 2, and TRPV4 in wildtype, but the upregulation of CD105 was significantly attenuated in TRPV4KO. Bone marrow chimera experiments indicated that TRPV4, expressed in both vascular endothelial cells and bone marrow-derived macrophages, played a significant role in colitis-associated tumorigenesis. There was no significant difference in the population of hematopoietic cells, neutrophils, and monocytes between untreated and AOM/DSS-treated WT and TRPV4KO on flow cytometric analysis. TRPV4 activation by a selective agonist induced TNF-α and CXCL2 release in macrophages. Furthermore, TRPV4 activation enhanced the proliferation of human umbilical vein endothelial cells. These results suggest that TRPV4 expressed in neovascular endothelial cells and bone marrow-derived macrophages contributes to the progression of CAC in mice.

PIEZO1 and TRPV4, which Are Distinct Mechano-Sensors in the Osteoblastic MC3T3-E1 Cells, Modify Cell-Proliferation

Mechanical-loading and unloading can modify osteoblast functioning. Ca²⁺ signaling is one of the earliest events in osteoblasts to induce a mechanical stimulus, thereby demonstrating the importance of the underlying mechanical sensors for the sensation. Here, we examined the mechano-sensitive channels PIEZO1 and TRPV4 were involved in the process of mechano-sensation in the osteoblastic MC3T3-E1 cells. The analysis of mRNA expression revealed a high expression of Piezo1 and Trpv4 in these cells. We also found that a PIEZO1 agonist, Yoda1, induced Ca²⁺ response and activated cationic currents in these cells. Ca²⁺ response was elicited when mechanical stimulation (MS), with shear stress, was induced by fluid flow in the MC3T3-E1 cells. Gene knockdown of Piezo1 in the MC3T3-E1 cells, by transfection with siPiezo1, inhibited the Yoda1-induced response, but failed to inhibit the MS-induced response. When MC3T3-E1 cells were transfected with siTrpv4, the MS-induced response was abolished and Yoda1 response was attenuated. Moreover, the MS-induced response was inhibited by a TRPV4 antagonist HC-067047 (HC). Yoda1 response was also inhibited by HC in MC3T3-E1 cells and HEK cells, expressing both PIEZO1 and TRPV4. Meanwhile, the activation of PIEZO1 and TRPV4 reduced the proliferation of MC3T3-E1, which was reversed by knockdown of PIEZO1, and TRPV4, respectively. In conclusion, TRPV4 and PIEZO1 are distinct mechano-sensors in the MC3T3-E1 cells. However, PIEZO1 and TRPV4 modify the proliferation of these cells, implying that PIEZO1 and TRPV4 may be functional in the osteoblastic mechano-transduction. Notably, it is also found that Yoda1 can induce TRPV4-dependent Ca²⁺ response, when both PIEZO1 and TRPV4 are highly expressed.

Transient Receptor Potential Channels and Endothelial Cell Calcium Signaling

The vascular endothelium is a broadly distributed and highly specialized organ. The endothelium has a number of functions including the control of blood vessels diameter through the production and release of potent vasoactive substances or direct electrical communication with underlying smooth muscle cells, regulates the permeability of the vascular barrier, stimulates the formation of new blood vessels, and influences inflammatory and thrombotic processes. Endothelial cells that make up the endothelium express a variety of cell-surface receptors and ion channels on the plasma membrane that are capable of detecting circulating hormones, neurotransmitters, oxygen tension, and shear stress across the vascular wall. Changes in these stimuli activate signaling cascades that initiate an appropriate physiological response. Increases in the global intracellular Ca²⁺ concentration and localized Ca²⁺ signals that occur within specialized subcellular microdomains are fundamentally important components of many signaling pathways in the endothelium. The transient receptor potential (TRP) channels are a superfamily of cation-permeable ion channels that act as a primary means of increasing cytosolic Ca²⁺ in endothelial cells. Consequently, TRP channels are vitally important for the major functions of the endothelium. In this review, we provide an in-depth discussion of Ca²⁺ -permeable TRP channels in the endothelium and their role in vascular regulation. © 2019 American Physiological Society. Compr Physiol 9:1249-1277, 2019.

Cannabidiol Increases Proliferation, Migration, Tubulogenesis, and Integrity of Human Brain Endothelial Cells through TRPV2 Activation

The effect of cannabidiol (CBD), a high-affinity agonist of the transient receptor potential vanilloid-2 (TRPV2) channel, has been poorly investigated in human brain microvessel endothelial cells (BMEC) forming the blood-brain barrier (BBB). TRPV2 expression and its role on Ca²⁺ cellular dynamics, trans-endothelial electrical resistance (TEER), cell viability and growth, migration, and tubulogenesis were evaluated in human primary cultures of BMEC (hPBMEC) or in the human cerebral microvessel endothelial hCMEC/D3 cell line. Abundant TRPV2 expression was measured in hCMEC/D3 and hPBMEC by qRT-PCR, Western blotting, nontargeted proteomics, and cellular immunofluorescence studies. Intracellular Ca²⁺ levels were increased by heat and CBD and blocked by the nonspecific TRP antagonist ruthenium red (RR) and the selective TRPV2 inhibitor tranilast (TNL) or by silencing cells with TRPV2 siRNA. CBD dose-dependently induced the hCMEC/D3 cell number (EC₅₀ 0.3 ± 0.1 μM), and this effect was fully abolished by TNL or TRPV2 siRNA. A wound healing assay showed that CBD induced cell migration, which was also inhibited by TNL or TRPV2 siRNA. Tubulogenesis of hCMEC/D3 cells in 3D matrigel cultures was significantly increased by 41 and 73% after a 7 or 24 h CBD treatment, respectively, and abolished by TNL. CBD also increased the TEER of hPBMEC monolayers cultured in transwell, and this was blocked by TNL. Our results show that CBD, at extracellular concentrations close to those observed in plasma of patients treated by CBD, induces proliferation, migration, tubulogenesis, and TEER increase in human brain endothelial cells, suggesting CBD might be a potent target for modulating the human BBB.

Expression of trpv channels during Xenopus laevis embryogenesis

Transient receptor potential (TRP) cation channel genes code for an extensive family of conserved proteins responsible for a variety of physiological processes, including sensory perception, ion homeostasis, and chemical signal transduction. The TRP superfamily consists of seven subgroups, one of which is the transient receptor potential vanilloid (trpv) channel family. While trpv channels are relatively well studied in adult vertebrate organisms given their role in functions such as nociception, thermoregulation, and osmotic regulation in mature tissues and organ systems, relatively little is known regarding their function during embryonic development. Although there are some reports of the expression of specific trpv channels at particular stages in various organisms, there is currently no comprehensive analysis of trpv channels during embryogenesis. Here, performing in situ hybridization, we examined the spatiotemporal expression of trpv channel mRNA during early Xenopus laevis embryogenesis. Trpv channels exhibited unique patterns of embryonic expression at distinct locations including the trigeminal ganglia, spinal cord, cement gland, otic vesicle, optic vesicle, nasal placode, notochord, tailbud, proctodeum, branchial arches, epithelium, somite and the animal pole during early development. We have also observed the colocalization of trpv channels at the animal pole (trpv 2/4), trigeminal ganglia (trpv 1/2), and epithelium (trpv 5/6). These localization patterns suggest that trpv channels may play diverse roles during early embryonic development.

TRPV4 Blockade Preserves the Blood-Brain Barrier by Inhibiting Stress Fiber Formation in a Rat Model of Intracerebral Hemorrhage

Blood–brain barrier (BBB) disruption and subsequent brain edema play important roles in the secondary neuronal death and neurological dysfunction that are observed following intracerebral hemorrhage (ICH). In previous studies, transient receptor potential vanilloid 4 (TRPV4), a calcium-permeable mechanosensitive channel, was shown to induce cytotoxicity in many types of cells and to play a role in orchestrating barrier functions. In the present study, we explored the role of TRPV4 in ICH-induced brain injury, specifically investigating its effect on BBB disruption. Autologous arterial blood was injected into the basal ganglia of rats to mimic ICH. Adult male Sprague Dawley rats were randomly assigned to sham and experimental groups for studies on the time course of TRPV4 expression after ICH. The selective TRPV4 antagonist HC-067047 and TRPV4 siRNA were administered to evaluate the effects of TRPV4 inhibition. GSK1016790A, a TRPV4 agonist, was administered to naive rats to verify the involvement of TRPV4-induced BBB disruption. A PKC inhibitor, dihydrochloride (H7), and a selective RhoA inhibitor, C3 transferase, were administered to clarify the involvement of the PKCα/RhoA/MLC2 pathway following ICH. Post-ICH assessments including functional tests, brain edema measurements, Evans blue extravasation, western blotting and immunohistochemical assays were performed. TRPV4 inhibition remarkably ameliorated neurological symptoms, brain edema, and neuronal death, as well as BBB disruption, 24–72 h following ICH. Meanwhile, TRPV4 blockade preserved the expression of adherens and tight junction proteins, as well as BBB integrity, by inhibiting stress fiber formation, which might be correlated with the regulation of components of the PKCα/RhoA/MLC2 pathway. Furthermore, adherens and tight junction protein degradation induced by GSK1016790A treatment in naive rats was also related to PKCα/RhoA/MLC2-pathway-mediated stress fiber formation. Based on these findings, therapeutic interventions targeting TRPV4 may represent a novel approach to ameliorate secondary brain injury following ICH.

Endothelial Ca2+ Signaling and the Resistance to Anticancer Treatments: Partners in Crime

Intracellular Ca²⁺ signaling drives angiogenesis and vasculogenesis by stimulating proliferation, migration, and tube formation in both vascular endothelial cells and endothelial colony forming cells (ECFCs), which represent the only endothelial precursor truly belonging to the endothelial phenotype. In addition, local Ca²⁺ signals at the endoplasmic reticulum (ER)-mitochondria interface regulate endothelial cell fate by stimulating survival or apoptosis depending on the extent of the mitochondrial Ca²⁺ increase. The present article aims at describing how remodeling of the endothelial Ca²⁺ toolkit contributes to establish intrinsic or acquired resistance to standard anti-cancer therapies. The endothelial Ca²⁺ toolkit undergoes a major alteration in tumor endothelial cells and tumor-associated ECFCs. These include changes in TRPV4 expression and increase in the expression of P2X7 receptors, Piezo2, Stim1, Orai1, TRPC1, TRPC5, Connexin 40 and dysregulation of the ER Ca²⁺ handling machinery. Additionally, remodeling of the endothelial Ca²⁺ toolkit could involve nicotinic acetylcholine receptors, gasotransmitters-gated channels, two-pore channels and Na⁺/H⁺ exchanger. Targeting the endothelial Ca²⁺ toolkit could represent an alternative adjuvant therapy to circumvent patients' resistance to current anti-cancer treatments.

Dual contribution of TRPV4 antagonism in the regulatory effect of vasoinhibins on blood-retinal barrier permeability: diabetic milieu makes a difference

Breakdown of the blood-retinal barrier (BRB), as occurs in diabetic retinopathy and other chronic retinal diseases, results in vasogenic edema and neural tissue damage, causing vision loss. Vasoinhibins are N-terminal fragments of prolactin that prevent BRB breakdown during diabetes. They modulate the expression of some transient receptor potential (TRP) family members, yet their role in regulating the TRP vanilloid subtype 4 (TRPV4) remains unknown. TRPV4 is a calcium-permeable channel involved in barrier permeability, which blockade has been shown to prevent and resolve pulmonary edema. We found TRPV4 expression in the endothelium and retinal pigment epithelium (RPE) components of the BRB, and that TRPV4-selective antagonists (RN-1734 and GSK2193874) resolve BRB breakdown in diabetic rats. Using human RPE (ARPE-19) cell monolayers and endothelial cell systems, we further observed that (i) GSK2193874 does not seem to contribute to the regulation of BRB and RPE permeability by vasoinhibins under diabetic or hyperglycemic-mimicking conditions, but that (ii) vasoinhibins can block TRPV4 to maintain BRB and endothelial permeability. Our results provide important insights into the pathogenesis of diabetic retinopathy that will further guide us toward rationally-guided new therapies: synergistic combination of selective TRPV4 blockers and vasoinhibins can be proposed to mitigate diabetes-evoked BRB breakdown.

TRPV4 Activation Contributes Functional Recovery from Ischemic Stroke via Angiogenesis and Neurogenesis

The endothelial transient receptor potential cation channel subfamily V member 4 (TRPV4) plays a crucial role in vascular remodeling; however, TRPV4-mediated angiogenesis after ischemic neuronal death as a neurorestorative strategy has not yet been thoroughly examined. In this study, we first tested whether TRPV4 activation can improve functional recovery in rats subjected to transient brain ischemia. The possible mechanisms for TRPV4 activation-promoted functional recovery were explored. A TRPV4 agonist, 4α-phorbol 12,13-didecanoate (4α-PDD), was intravenously injected via the tail vein at 6 h and 1, 2, 3, 4 days after ischemic stroke. The treatment reduced infarct volume by almost 50% (14.7 ± 3.7 vs. 29.2 ± 6.2%; p < 0.0001) and improved functional outcomes (p = 0.03) on day 5. To explore the therapeutic mechanism, we measured endothelial nitric oxide synthase (eNOS) expression and phosphorylation, vascular endothelial growth factor A (VEGFA) signaling, and neural stem/progenitor cells (NPCs). TRPV4 activation significantly increased eNOS expression and phosphorylation (serine 1177) by more than 2-fold in the ischemic region. The expressions of VEGFA and VEGF receptor-2 were significantly higher in the treated animals, especially an increase of the proangiogenic VEGFA_164a isoform while a decrease of the antiangiogenic VEGFA_165b isoform. We evaluated angiogenesis by detecting microvessel density in ischemic region. Using the immunohistochemistry staining, we found that 4α-PDD treatment caused a 3.4-fold increase of microvessel density (p < 0.0001). In addition, NPC proliferation and migration in the ischemic hemisphere were increased by 3-fold and 5-fold, respectively. In conclusion, our data suggest that TRPV4 activation by 4α-PDD may improve poststroke functional improvement through angiogenesis and neurogenesis.

TRPV4: Molecular Conductor of a Diverse Orchestra

Transient receptor potential vanilloid type 4 (TRPV4) is a calcium-permeable nonselective cation channel, originally described in 2000 by research teams led by Schultz (Nat Cell Biol 2: 695-702, 2000) and Liedtke (Cell 103: 525-535, 2000). TRPV4 is now recognized as being a polymodal ionotropic receptor that is activated by a disparate array of stimuli, ranging from hypotonicity to heat and acidic pH. Importantly, this ion channel is constitutively expressed and capable of spontaneous activity in the absence of agonist stimulation, which suggests that it serves important physiological functions, as does its widespread dissemination throughout the body and its capacity to interact with other proteins. Not surprisingly, therefore, it has emerged more recently that TRPV4 fulfills a great number of important physiological roles and that various disease states are attributable to the absence, or abnormal functioning, of this ion channel. Here, we review the known characteristics of this ion channel's structure, localization and function, including its activators, and examine its functional importance in health and disease.

Activation of Transient Receptor Potential Vanilloid 4 Promotes the Proliferation of Stem Cells in the Adult Hippocampal Dentate Gyrus

Neurogenesis plays an important role in adult hippocampal function, and this process can be modulated by intracellular calcium. The activation of transient receptor potential vanilloid 4 (TRPV4) induces an increase in intracellular calcium concentration, but whether neurogenesis can be modulated by TRPV4 activation remains unclear. Here, we report that intracerebroventricular injection of the TRPV4 agonist GSK1016790A for 5 days enhanced the proliferation of stem cells in the hippocampal dentate gyrus (DG) of adult mice without affecting neurite growth, differentiation, or survival of newborn cells. GSK1016790A induced increases in the hippocampal protein levels of cyclin-dependent kinase (CDK) 6, CDK2, cyclin E1, and cyclin A2 but did not affect CDK4 and cyclin D1 expression. The phosphorylation of retinoblastoma protein (Rb) in hippocampi was enhanced in GSK1016790A-injected mice compared with control mice. Moreover, hippocampal protein levels of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation were enhanced by GSK1016790A. Finally, GSK1016790A-enhanced proliferation was markedly blocked by a MAPK/ERK kinase or p38 MAPK antagonist (U0126 or SB203580, respectively). The increased protein levels of CDK2 and CDK6, as well as those of cyclin E1 and cyclin A2, in GSK1016790A-injected mice were substantially reduced by co-injection of U0126 or SB203580. We conclude that TRPV4 activation results in the proliferation of stem cells in the adult hippocampal DG, which is likely mediated through ERK1/2 and p38 MAPK signaling to increase the expression of CDKs (CDK6 and CDK2) and cyclins (cyclin E1 and A2), phosphorylate Rb consequently, and accelerate the cell cycle ultimately.

Basal cells express functional TRPV4 channels in the mouse nasal epithelium

Basal cells in the nasal epithelium (olfactory and airway epithelia) are stem/progenitor cells that are capable of dividing, renewing and differentiating into specialized cells. These stem cells can sense their biophysical microenvironment, but the underlying mechanism of this process remains unknown. Here, we demonstrate the prominent expression of the transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca²⁺-permeable channel that is known to act as a sensor for hypo-osmotic and mechanical stresses, in the basal cells of the mouse nasal epithelium. TRPV4 mRNA was expressed in the basal portions of the prenatal mouse nasal epithelium, and this expression continued into adult mice. The TRPV4 protein was also detected in the basal layers of the nasal epithelium in wild-type but not in TRPV4-knockout (TRPV4-KO) mice. The TRPV4-positive immunoreactions largely overlapped with those of keratin 14 (K14), a marker of basal cells, in the airway epithelium, and they partially overlapped with those of K14 in the olfactory epithelium. Ca²⁺ imaging analysis revealed that hypo-osmotic stimulation and 4α-phorbol 12,13 didecanoate (4α-PDD), both of which are TRPV4 agonists, caused an increase in the cytosolic Ca²⁺ concentration in a subset of primary epithelial cells cultured from the upper parts of the nasal epithelium of the wild-type mice. This response was barely noticeable in cells from similar parts of the epithelium in TRPV4-KO mice. Finally, there was no significant difference in BrdU-labeled proliferation between the olfactory epithelia of wild-type and TRPV4-KO mice under normal conditions. Thus, TRPV4 channels are functionally expressed in basal cells throughout the nasal epithelium and may act as sensors for the development and injury-induced regeneration of basal stem cells.

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TRPV4 is expressed in basal stem cells of the nasal airway and olfactory epithelium.

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TRPV4 expression appears in the nasal epithelium during the late prenatal stages.

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TRPV4 activation causes an increase in cytosolic Ca²⁺ concentration.

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TRPV4 may be involved in a variety of cellular functions in progenitor/stem cells.

Polymodal Transient Receptor Potential Vanilloid (TRPV) Ion Channels in Chondrogenic Cells

Mature and developing chondrocytes exist in a microenvironment where mechanical load, changes of temperature, osmolarity and acidic pH may influence cellular metabolism. Polymodal Transient Receptor Potential Vanilloid (TRPV) receptors are environmental sensors mediating responses through activation of linked intracellular signalling pathways. In chondrogenic high density cultures established from limb buds of chicken and mouse embryos, we identified TRPV1, TRPV2, TRPV3, TRPV4 and TRPV6 mRNA expression with RT-PCR. In both cultures, a switch in the expression pattern of TRPVs was observed during cartilage formation. The inhibition of TRPVs with the non-selective calcium channel blocker ruthenium red diminished chondrogenesis and caused significant inhibition of proliferation. Incubating cell cultures at 41 °C elevated the expression of TRPV1, and increased cartilage matrix production. When chondrogenic cells were exposed to mechanical load at the time of their differentiation into matrix producing chondrocytes, we detected increased mRNA levels of TRPV3. Our results demonstrate that developing chondrocytes express a full palette of TRPV channels and the switch in the expression pattern suggests differentiation stage-dependent roles of TRPVs during cartilage formation. As TRPV1 and TRPV3 expression was altered by thermal and mechanical stimuli, respectively, these are candidate channels that contribute to the transduction of environmental stimuli in chondrogenic cells.

Hyperglycemia and Diabetes Downregulate the Functional Expression of TRPV4 Channels in Retinal Microvascular Endothelium

Retinal endothelial cell dysfunction is believed to play a key role in the etiology and pathogenesis of diabetic retinopathy. Numerous studies have shown that TRPV4 channels are critically involved in maintaining normal endothelial cell function. In the current paper, we demonstrate that TRPV4 is functionally expressed in the endothelium of the retinal microcirculation and that both channel expression and activity is downregulated by hyperglycaemia. Quantitative PCR and immunostaining demonstrated molecular expression of TRPV4 in cultured bovine retinal microvascular endothelial cells (RMECs). Functional TRPV4 activity was assessed in cultured RMECs from endothelial Ca2+-responses recorded using fura-2 microfluorimetry and electrophysiological recordings of membrane currents. The TRPV4 agonist 4α-phorbol 12,13-didecanoate (4-αPDD) increased [Ca2+]i in RMECs and this response was largely abolished using siRNA targeted against TRPV4. These Ca2+-signals were completely inhibited by removal of extracellular Ca2+, confirming their dependence on influx of extracellular Ca2+. The 4-αPDD Ca2+-response recorded in the presence of cyclopiazonic acid (CPA), which depletes the intracellular stores preventing any signal amplification through store release, was used as a measure of Ca2+-influx across the cell membrane. This response was blocked by HC067047, a TRPV4 antagonist. Under voltage clamp conditions, the TRPV4 agonist GSK1016790A stimulated a membrane current, which was again inhibited by HC067047. Following incubation with 25 mM D-glucose TRPV4 expression was reduced in comparison with RMECs cultured under control conditions, as were 4αPDD-induced Ca2+-responses in the presence of CPA and ion currents evoked by GSK1016790A. Molecular expression of TRPV4 in the retinal vascular endothelium of 3 months' streptozotocin-induced diabetic rats was also reduced in comparison with that in age-matched controls. We conclude that hyperglycaemia and diabetes reduce the molecular and functional expression of TRPV4 channels in retinal microvascular endothelial cells. These changes may contribute to diabetes induced endothelial dysfunction and retinopathy.

A functional transient receptor potential vanilloid 4 (TRPV4) channel is expressed in human endothelial progenitor cells

Endothelial progenitor cells (EPCs) are mobilized into circulation to replace damaged endothelial cells and recapitulate the vascular network of injured tissues. Intracellular Ca(2+) signals are key to EPC activation, but it is yet to be elucidated whether they are endowed with the same blend of Ca(2+) -permeable channels expressed by mature endothelial cells. For instance, endothelial colony forming cells (ECFCs), the only EPC subset truly committed to acquire a mature endothelial phenotype, lack canonical transient receptor potential channels 3, 5 and 6 (TRPC3, 5 and 6), which are widely distributed in vascular endothelium; on the other hand, they express a functional store-operated Ca(2+) entry (SOCE). The present study was undertaken to assess whether human circulating EPCs possess TRP vanilloid channel 4 (TRPV4), which plays a master signalling role in mature endothelium, by controlling both vascular remodelling and arterial pressure. We found that EPCs express both TRPV4 mRNA and protein. Moreover, both GSK1016790A (GSK) and phorbol myristate acetate and, two widely employed TRPV4 agonists, induced intracellular Ca(2+) signals uniquely in presence of extracellular Ca(2+). GSK- and PMA-induced Ca(2+) elevations were inhibited by RN-1734 and ruthenium red, which selectively target TRPV4 in mature endothelium. However, TRPV4 stimulation with GSK did not cause EPC proliferation, while the pharmacological blockade of TRPV4 only modestly affected EPC growth in the presence of a growth factor-enriched culture medium. Conversely, SOCE inhibition with BTP-2, La(3+) and Gd(3+) dramatically decreased cell proliferation. These data indicate that human circulating EPCs possess a functional TRPV4 protein before their engraftment into nascent vessels.

TRPV4 channel inhibits TGF-β1-induced proliferation of hepatic stellate cells

TRPV4, one of the TRP channels, is implicated in diverse physiological and pathological processes including cell proliferation. However, the role of TRPV4 in liver fibrosis is largely unknown. Here, we characterized the role of TRPV4 in regulating HSC-T6 cell proliferation. TRPV4 mRNA and protein were measured by RT-PCR and Western blot in patients and rat model of liver fibrosis in vivo and TGF-β1-activated HSC-T6 cells in vitro. Both mRNA and protein of TRPV4 were dramatically increased in liver fibrotic tissues of both patients and CCl₄-treated rats. Stimulation of HSC-T6 cells with TGF-β1 resulted in increase of TRPV4 mRNA and protein. However, TGF-β1-induced HSC-T6 cell proliferation was inhibited by Ruthenium Red (Ru) or synthetic siRNA targeting TRPV4, and this was accompanied by downregulation of myofibroblast markers including α-SMA and Col1α1. Moreover, our study revealed that miR-203 was downregulated in liver fibrotic tissues and TGF-β1-treated HSC-T6 cell. Bioinformatics analyses predict that TRPV4 is the potential target of miR-203. In addition, overexpression of miR-203 in TGF-β1-induced HSC significantly reduced TRPV4 expression, indicating TRPV4, which was regulated by miR-203, may function as a novel regulator to modulate TGF-β1-induced HSC-T6 proliferation.

Endothelial calcium dynamics, connexin channels and blood-brain barrier function

Situated between the circulation and the brain, the blood-brain barrier (BBB) protects the brain from circulating toxins while securing a specialized environment for neuro-glial signaling. BBB capillary endothelial cells exhibit low transcytotic activity and a tight, junctional network that, aided by the cytoskeleton, restricts paracellular permeability. The latter is subject of extensive research as it relates to neuropathology, edema and inflammation. A key determinant in regulating paracellular permeability is the endothelial cytoplasmic Ca(2+) concentration ([Ca(2+)]i) that affects junctional and cytoskeletal proteins. Ca(2+) signals are not one-time events restricted to a single cell but often appear as oscillatory [Ca(2+)]i changes that may propagate between cells as intercellular Ca(2+) waves. The effect of Ca(2+) oscillations/waves on BBB function is largely unknown and we here review current evidence on how [Ca(2+)]i dynamics influence BBB permeability.