Shear stress sensitizes TRPV4 in endothelium-dependent vasodilatation

Recent advances on the structure and the function relationships of the TRPV4 ion channel

The members of the superfamily of Transient Receptor Potential (TRP) ion channels are physiologically important molecules that have been studied for many years and are still being intensively researched. Among the vanilloid TRP subfamily, the TRPV4 ion channel is an interesting protein due to its involvement in several essential physiological processes and in the development of various diseases. As in other proteins, changes in its function that lead to the development of pathological states, have been closely associated with modification of its regulation by different molecules, but also by the appearance of mutations which affect the structure and gating of the channel. In the last few years, some structures for the TRPV4 channel have been solved. Due to the importance of this protein in physiology, here we discuss the recent progress in determining the structure of the TRPV4 channel, which has been achieved in three species of animals (Xenopus tropicalis, Mus musculus, and Homo sapiens), highlighting conserved features as well as key differences among them and emphasizing the binding sites for some ligands that play crucial roles in its regulation.

LIPUS regulates the progression of knee osteoarthritis in mice through primary cilia-mediated TRPV4 channels

Osteoarthritis (OA) is a common disease in middle-aged and elderly people. An imbalance in calcium ion homeostasis will contribute to chondrocyte apoptosis and ultimately lead to the progression of OA. Transient receptor potential channel 4 (TRPV4) is involved in the regulation of intracellular calcium homeostasis. TRPV4 is expressed in primary cilia, which can sense mechanical stimuli from outside the cell, and its abnormal expression is closely related to the development of OA. Low-intensity pulsed ultrasound (LIPUS) can alleviate chondrocyte apoptosis while the exact mechanism is unclear. In this project, with the aim of revealing the mechanism of action of LIPUS, we proposed to use OA chondrocytes and animal models, LIPUS intervention, inhibition of primary cilia, use TRPV4 inhibitors or TRPV4 agonist, and use Immunofluorescence (IF), Immunohistochemistry (IHC), Western Blot (WB), Quantitative Real-time PCR (QP) to detect the expression of cartilage synthetic matrix and endoplasmic reticulum stress markers. The results revealed that LIPUS altered primary cilia expression, promoted synthetic matrix metabolism in articular chondrocytes and was associated with primary cilia. In addition, LIPUS exerted a active effect on OA by activating TRPV4, inducing calcium inward flow, and facilitating the entry of NF-κB into the nucleus to regulate synthetic matrix gene transcription. Inhibition of TRPV4 altered primary cilia expression in response to LIPUS stimulation, and knockdown of primary cilia similarly inhibited TRPV4 function. These results suggest that LIPUS mediates TRPV4 channels through primary cilia to regulate the process of knee osteoarthritis in mice.

Inflammation-induced TRPV4 channels exacerbate blood-brain barrier dysfunction in multiple sclerosis

BACKGROUND

Blood-brain barrier (BBB) dysfunction and immune cell migration into the central nervous system (CNS) are pathogenic drivers of multiple sclerosis (MS). Ways to reinstate BBB function and subsequently limit neuroinflammation present promising strategies to restrict disease progression. However, to date, the molecular players directing BBB impairment in MS remain poorly understood. One suggested candidate to impact BBB function is the transient receptor potential vanilloid-type 4 ion channel (TRPV4), but its specific role in MS pathogenesis remains unclear. Here, we investigated the role of TRPV4 in BBB dysfunction in MS.

MAIN TEXT

In human post-mortem MS brain tissue, we observed a region-specific increase in endothelial TRPV4 expression around mixed active/inactive lesions, which coincided with perivascular microglia enrichment in the same area. Using in vitro models, we identified that microglia-derived tumor necrosis factor-α (TNFα) induced brain endothelial TRPV4 expression. Also, we found that TRPV4 levels influenced brain endothelial barrier formation via expression of the brain endothelial tight junction molecule claudin-5. In contrast, during an inflammatory insult, TRPV4 promoted a pathological endothelial molecular signature, as evidenced by enhanced expression of inflammatory mediators and cell adhesion molecules. Moreover, TRPV4 activity mediated T cell extravasation across the brain endothelium.

CONCLUSION

Collectively, our findings suggest a novel role for endothelial TRPV4 in MS, in which enhanced expression contributes to MS pathogenesis by driving BBB dysfunction and immune cell migration.

Flow-dependent regulation of rat mesenteric lymphatic vessel contractile response requires activation of endothelial TRPV4 channels

OBJECTIVES

The objective of our study is to evaluate the involvement of the transient receptor potential vanilloid 4 (TRPV4) in the alteration of lymphatic pumping in response to flow and determine the signaling pathways involved.

METHODS

We used immunofluorescence imaging and western blotting to assess TRPV4 expression in rat mesenteric lymphatic vessels. We examined inhibition of TRPV4 with HC067047, nitric oxide synthase (NOS) with L-NNA and cyclooxygenases (COXs) with indomethacin on the contractile response of pressurized lymphatic vessels to flow changes induced by a stepwise increase in pressure gradients, and the functionality of endothelial TRPV4 channels by measuring the intracellular Ca2+ response of primary lymphatic endothelial cell cultures to the selective agonist GSK1016790A.

RESULTS

TRPV4 protein was expressed in both the endothelial and the smooth muscle layer of rat mesenteric lymphatics with high endothelial expression around the valve sites. When maintained under constant transmural pressure, most lymphatic vessels displayed a decrease in contraction frequency under conditions of flow and this effect was ablated through inhibition of NOS, COX or TRPV4.

CONCLUSIONS

Our findings demonstrate a critical role for TRPV4 in the decrease in contraction frequency induced in lymphatic vessels by increases in flow rate via the production and action of nitric oxide and dilatory prostanoids.

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.

Endothelial basement membrane laminins - new players in mouse and human myoendothelial junctions and shear stress communication

Basement membranes (BMs) are critical but frequently ignored components of the vascular system. Using high-resolution confocal imaging of whole-mount-stained mesenteric arteries, we identify integrins, vinculin, focal adhesion kinase (FAK) and several BM proteins including laminins as novel components of myoendothelial junctions (MEJs), anatomical microdomains that are emerging as regulators of cross-talk between endothelium and smooth muscle cells (SMCs). Electron microscopy revealed multiple layers of the endothelial BM that surround endothelial projections into the smooth muscle layer as structural characteristics of MEJs. The shear-responsive calcium channel TRPV4 is broadly distributed in endothelial cells and occurs in a proportion of MEJs where it localizes to the tips of the endothelial projections that are in contact with the underlying SMCs. In mice lacking the major endothelial laminin isoform, laminin 411 (Lama4-/-), which we have previously shown over-dilate in response to shear and exhibit a compensatory laminin 511 upregulation, localization of TRPV4 at the endothelial-SMC interface in MEJs was increased. Endothelial laminins do not affect TRPV4 expression, rather in vitro electrophysiology studies using human umbilical cord arterial endothelial cells revealed enhanced TRPV4 signalling upon culturing on an RGD-motif containing domain of laminin 511. Hence, integrin-mediated interactions with laminin 511 in MEJ structures unique to resistance arteries modulate TRPV4 localization at the endothelial-smooth muscle interface in MEJs and signalling over this shear-response molecule.

Physiological levels of fluid shear stress modulate vascular function through TRPV4 sparklets

Endothelial calcium (Ca ²⁺) signaling plays a major role in regulating vasodilation in response to fluid shear stress (FSS) generated by blood flow. Local Ca ²⁺ influx through single transient receptor potential channel subfamily V member 4 (TRPV4) (termed "sparklets") activated by low concentrations of chemical and biological stimuli has been revealed to modulate vascular function. However, the range in which FSS can initiate TRPV4 sparklets to induce vasodilation is unknown. Here, we assess the activity of TPRV4 sparklets induced by various physiological levels of FSS and investigate the mechanisms involving these Ca ²⁺ signals in FSS-induced vasodilation. Intact small mesenteric arteries are used for Ca ²⁺ imaging with a GCaMP2(TRPV4-KO) mouse model and high-speed confocal systems. Markedly increased local Ca ²⁺ signals are observed in the endothelium under 4-8 dyne/cm ² FSS, whereas FSS >8 dyne/cm ² causes global Ca ²⁺ influx. Further analysis shows that TRPV4 channels form a four-channel group to mediate Ca ²⁺ sparklets under certain levels of FSS. The large Ca ²⁺ influx hyperpolarizes endothelial cells by stimulating intermediate (IK)- and small (SK)-conductance Ca ²⁺-sensitive potassium channels, leading to hyperpolarization of the surrounding smooth muscle cells and ultimately causing endothelium-dependent vasodilation. In conclusion, Ca ²⁺ influx transits through a small number of endothelial TRPV4 channels opened by certain levels of FSS, which activates the Ca ²⁺-sensitive IK and SK channels to cause vasodilation.

Translating the Force - mechano-sensing GPCRs

Incorporating mechanical cues into cellular responses allows us to experience our direct environment. Specialized cells can perceive and discriminate between different physical properties such as level of vibration, temperature, or pressure. Mechanical forces are abundant signals that also shape general cellular responses such as cytoskeletal rearrangement, differentiation, or migration and contribute to tissue development and function. The molecular structures that perceive and transduce mechanical forces are specialized cytoskeletal proteins, cell junction molecules, and membrane proteins such as ion channels and metabotropic receptors. G protein-coupled receptors (GPCRs) have attracted attention as metabotropic force receptors as they are among the most important drug targets. This review summarizes the function of mechano-sensitive GPCRs, specifically, the angiotensin II type 1 receptor and adrenergic, apelin, histamine, parathyroid hormone 1, and orphan receptors, focusing particularly on the advanced knowledge gained from adhesion-type GPCRs. We distinguish between shear stress and cell swelling/stretch as the two major types of mechano-activation of these receptors and contemplate the potential contribution of the force-from-lipid and force-from-tether models that have previously been suggested for ion channels.

Correlation of vascular change with TRPV1, TRPV4, and TRPA1 in a rat model of inferior gluteal artery perforator flap

Maximum survival area after perforator flap elevation is mainly achieved through vasodilation and angiogenesis, and endothelial Ca²⁺ signals play a pivotal role in both of them. Transient receptor potential (TRP) channels modulate many endothelial cell functions via mediating the extracellular Ca²⁺ entry. This study aims to investigate the correlation of TRPV4, TRPV1, and TRPA1 with vascular change after the inferior gluteal artery perforator flap elevation. A total of 50 adult male SD rats were used in this study. Ten rats were used in the part one to assess the flap viability on postoperative day 7. Twenty rats were used in the part two to evaluate blood flow change after flap elevation. The correlation of vascular change with TRPV1, TRPV4, and TRPA1 protein changes was investigated in 20 rats in the part three. The mean flap survival area percentage was 55 ± 5.7%. Blood flow in the overall flap and Zone II after the flap elevation markedly increased from the postoperative day 3. The most marked change of the vasodilation occurred on Days 3 and 5 after flap elevation. The angiogenesis occurred on Day 5 after flap elevation and the microvessel density peaked also on Day 5. Moreover, TRPA1 expression showed a trend towards continuous reduction over time. The expression of TRPV1 and TRPV4 reached the peak value on Day 3. The endothelial NO synthase expression showed an increasing trend at first, followed by a reduction over time, while VEGF expression reached the peak value on Day 3. The vascular changes after flap elevation might be associated with the changes in TRPV4, TRPV1, and TRPA1.

VEGFR2 in vascular smooth muscle cells mediates H2S-induced dilation of the rat cerebral basilar artery

INTRODUCTION

The aim of present study was to study whether the vascular endothelial growth factor receptor 2 (VEGFR₂) mediates hydrogen sulfide (H₂S)-induced relaxation of the rat cerebral vasculature.

METHODS

Relaxation of cerebral basilar artery (CBA) and vascular smooth muscle cells (VSMCs) was measured by using a pressure myograph system and image analysis system, respectively. The intracellular calcium concentration ([Ca²⁺]_i) in VSMCs was detected using fluorescence imaging analysis.

RESULTS

We found that H₂S donor NaHS induced significant relaxation of VSMCs from the CBA of wild type rat, but in VEGFR₂ knockdown VSMCs, NaHS-induced relaxation reduced markedly. In addition, NaHS-induced vasodilation of rat CBA also attenuated obviously when the expression of VEGFR₂ was knocked down in vivo. In addition, pretreatment with the VEGFR₂ blocker SU5416 likewise lowered the NaHS-induced relaxation of rat CBA. Nevertheless, the VEGFR₂ agonist, vascular endothelial growth factor 164 (VEGF164), induced a concentration-dependent relaxation of CBA, which is similar to the effect of NaHS. Furthermore, we found that both NaHS and VEGF164 significantly inhibited the U₄₆₆₁₉-induced increase of [Ca²⁺]_i fluorescence intensity in the VSMCs. However, the inhibitory effect of NaHS on the [Ca²⁺]_i fluorescence intensity in VSMCs was markedly inhibited by pretreatment with SU5416 or VEGFR₂ knockdown.

CONCLUSION

These findings indicated that H₂S-induced CBA dilation and reduction of [Ca²⁺]_i in VSMCs occur by acting on VEGFR₂.

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.

Lymphangiogenesis and angiogenesis rescue murine ischemic hindlimb via transient receptor potential vanilloid 4

In this study, we assessed the regulation of transient receptor potential vanilloid 4 (TRPV4) promoting lymphangio/angiogenesis to improve the ischemic hindlimb animal model, and revealed that (1) a TRPV4 agonist improved the blood flow of ischemic hindlimbs by inducing both angiogenesis and lymphangiogenesis; (2) excessive TRPV4 expression was detected on lymphatic endothelial cells (LECs) in the ischemic hindlimb; and (3) hypoxic conditions promoted Ca²⁺ influx into LECs via TRPV4. It is considered that the upregulation of both lymphatic and blood vessels by activating TRPV4 would be a promising therapeutic strategy for peripheral artery disease.

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.

Impaired TRPV4-eNOS signaling in trabecular meshwork elevates intraocular pressure in glaucoma

Primary Open Angle Glaucoma (POAG) is the most common form of glaucoma that leads to irreversible vision loss. Dysfunction of trabecular meshwork (TM) tissue, a major regulator of aqueous humor (AH) outflow resistance, is associated with intraocular pressure (IOP) elevation in POAG. However, the underlying pathological mechanisms of TM dysfunction in POAG remain elusive. In this regard, transient receptor potential vanilloid 4 (TRPV4) cation channels are known to be important Ca2+ entry pathways in multiple cell types. Here, we provide direct evidence supporting Ca2+ entry through TRPV4 channels in human TM cells and show that TRPV4 channels in TM cells can be activated by increased fluid flow/shear stress. TM-specific TRPV4 channel knockout in mice elevated IOP, supporting a crucial role for TRPV4 channels in IOP regulation. Pharmacological activation of TRPV4 channels in mouse eyes also improved AH outflow facility and lowered IOP. Importantly, TRPV4 channels activated endothelial nitric oxide synthase (eNOS) in TM cells, and loss of eNOS abrogated TRPV4-induced lowering of IOP. Remarkably, TRPV4-eNOS signaling was significantly more pronounced in TM cells compared to Schlemm's canal cells. Furthermore, glaucomatous human TM cells show impaired activity of TRPV4 channels and disrupted TRPV4-eNOS signaling. Flow/shear stress activation of TRPV4 channels and subsequent NO release were also impaired in glaucomatous primary human TM cells. Together, our studies demonstrate a central role for TRPV4-eNOS signaling in IOP regulation. Our results also provide evidence that impaired TRPV4 channel activity in TM cells contributes to TM dysfunction and elevated IOP in glaucoma.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

Flow-mediated vasodilation through mechanosensitive G protein-coupled receptors in endothelial cells

Currently, endothelium-dependent vasodilatation involves three main mechanisms: production of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS), synthesis of prostanoids by cyclooxygenase, and/or opening of calcium-sensitive potassium channels. Researchers have proposed multiple mechanosensors that may be involved in flow-mediated vasodilation (FMD), including G protein-coupled receptors (GPCRs), ion channels, and intercellular junction proteins, among others. However, GPCRs are considered the major mechanosensors that play a pivotal role in shear stress signal transduction. Among mechanosensitive GPCRs, G protein-coupled receptor 68, histamine H1 receptors, sphingosine-1-phosphate receptor 1, and bradykinin B2 receptors have been identified as endothelial sensors of flow shear stress regulating flow-mediated vasodilation. Thus, this review aims to expound on the mechanism whereby flow shear stress promotes vasodilation through the proposed mechanosensitive GPCRs in ECs.

TRPV4 channel blockade does not modulate skin vasodilation and sweating during hyperthermia or cutaneous postocclusive reactive and thermal hyperemia

Transient receptor potential vanilloid 4 (TRPV4) channels exist on vascular endothelial cells and eccrine sweat gland secretory cells in human skin. Here, we assessed whether TRPV4 channels contribute to cutaneous vasodilation and sweating during whole body passive heat stress (protocol 1) and to cutaneous vasodilation during postocclusive reactive hyperemia and local thermal hyperemia (protocol 2). Intradermal microdialysis was employed to locally deliver pharmacological agents to forearm skin sites, where cutaneous vascular conductance (CVC) and sweat rate were assessed. In protocol 1 (12 young adults), CVC and sweat rate were increased by passive whole body heating, resulting in a body core temperature elevation of 1.2 ± 0.1°C. The elevated CVC and sweat rate assessed at sites treated with TRPV4 channel antagonist (either 200 µM HC-067047 or 125 µM GSK2193874) were not different from the vehicle control site (5% dimethyl sulfoxide). After whole body heating, the TRPV4 channel agonist (100 µM GSK1016790A) was administered to each skin site, eliciting elevations in CVC. Relative to control, this response was partly attenuated by both TRPV4 channel antagonists, confirming drug efficacy. In protocol 2 (10 young adults), CVC was increased following a 5-min arterial occlusion and during local heating from 33 to 42°C. These responses did not differ between the control and the TRPV4 channel antagonist sites (200 µM HC-067047). We show that TRPV4 channels are not required for regulating cutaneous vasodilation or sweating during a whole body passive heat stress. Furthermore, they are not required for regulating cutaneous vasodilation during postocclusive reactive hyperemia and local thermal hyperemia.

The Role of Transient Receptor Potential Channels in Blood-Brain Barrier Dysfunction after Ischemic Stroke

Stroke is the leading cause of long-term disability, demanding an ever-increasing need to find treatment. Transient receptor potential (TRP) channels are nonselective Ca²⁺-permeable channels, among which TRPC, TRPM, and TRPV are widely expressed in the brain. Dysfunction of the blood brain barrier (BBB) is a core feature of stroke and is associated with severity of injury. As studies have shown, TRP channels influence various neuronal functions by regulating the BBB. Here, we briefly review the role of TRP channel in the BBB dysfunction after stroke, and explore the therapeutic potential of TRP-targeted therapy.

Transient receptor potential vanilloid 4 channels as therapeutic targets in diabetes and diabetes-related complications

With an estimated 425 million diabetes patients worldwide in 2019, type 2 diabetes has reached a pandemic proportion and represents a major unmet medical need. A key determinant of the development and progression of type 2 diabetes is pancreatic -cell dysfunction, including the loss of cell mass, the impairment of insulin biosynthesis and inadequate exocytosis. Recent studies have shown that transient receptor potential vanilloid 4 (TRPV4), a Ca2+ -permeable non-selective cation channel, is involved in -cell replication, insulin production and secretion. TRPV4 agonists have insulinotropic activity in pancreatic -cell lines, but the prolonged activation of TRPV4 leads to -cell dysfunction and death. In addition, TRPV4 is involved in a wide variety of pathophysiological activities, and has been reported to play an important role in diabetes-related complications, such as obesity, cardiovascular diseases, diabetic retinopathy, nephropathy and neuropathy. In a rodent type 2 diabetes model, Trpv4 agonists promote vasodilation and improve cardiovascular function, whereas Trpv4 antagonists reduce high-fat diet-induced obesity, insulin resistance, diabetic nephropathy, retinopathy and neuropathy. These findings raise interest in using TRPV4 as a therapeutic target for type 2 diabetes. In this review, we intend to summarize the latest findings regarding the role of TRPV4 in diabetes as well as diabetes-related conditions, and to evaluate its potential as a therapeutic target for diabetes and diabetes-related diseases.

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.