The increased activity of TRPV4 channel in the astrocytes of the adult rat hippocampus after cerebral hypoxia/ischemia

Graphene oxide electrodes enable electrical stimulation of distinct calcium signalling in brain astrocytes

Astrocytes are responsible for maintaining homoeostasis and cognitive functions through calcium signalling, a process that is altered in brain diseases. Current bioelectronic tools are designed to study neurons and are not suitable for controlling calcium signals in astrocytes. Here, we show that electrical stimulation of astrocytes using electrodes coated with graphene oxide and reduced graphene oxide induces respectively a slow response to calcium, mediated by external calcium influx, and a sharp one, exclusively due to calcium release from intracellular stores. Our results suggest that the different conductivities of the substrate influence the electric field at the cell-electrolyte or cell-material interfaces, favouring different signalling events in vitro and ex vivo. Patch-clamp, voltage-sensitive dye and calcium imaging data support the proposed model. In summary, we provide evidence of a simple tool to selectively control distinct calcium signals in brain astrocytes for straightforward investigations in neuroscience and bioelectronic medicine.

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.

The Multifaceted Functions of TRPV4 and Calcium Oscillations in Tissue Repair

The transient receptor potential vanilloid 4 (TRPV4) specifically functions as a mechanosensitive ion channel and is responsible for conveying changes in physical stimuli such as mechanical stress, osmotic pressure, and temperature. TRPV4 enables the entry of cation ions, particularly calcium ions, into the cell. Activation of TRPV4 channels initiates calcium oscillations, which trigger intracellular signaling pathways involved in a plethora of cellular processes, including tissue repair. Widely expressed throughout the body, TRPV4 can be activated by a wide array of physicochemical stimuli, thus contributing to sensory and physiological functions in multiple organs. This review focuses on how TRPV4 senses environmental cues and thereby initiates and maintains calcium oscillations, critical for responses to organ injury, tissue repair, and fibrosis. We provide a summary of TRPV4-induced calcium oscillations in distinct organ systems, along with the upstream and downstream signaling pathways involved. In addition, we delineate current animal and disease models supporting TRPV4 research and shed light on potential therapeutic targets for modulating TRPV4-induced calcium oscillation to promote tissue repair while reducing tissue fibrosis.

Pregabalin inhibits purinergic P2Y2 receptor and TRPV4 to suppress astrocyte activation and to relieve neuropathic pain

BACKGROUNDS

Transient receptor potential vanilloid 4 (TRPV4)-mediated astrocyte activation is critical to neuropathic pain. Pregabalin, a widely used drug to treat chronic pain, is reported to lower the intracellular calcium level. However, the molecular mechanism by which pregabalin decreases the intracellular calcium level remains unknown. Purinergic P2Y2 receptor-a member of the G protein-coupled receptor (GPCR) family-regulates calcium-related signal transduction in astrocyte activation. We investigated whether P2Y2 receptor is involved in the pharmacological effects of pregabalin on neuropathic pain.

METHODS

Neuropathic pain was induced by chronic compression of the dorsal root ganglion (CCD) in rats. Paw withdrawal mechanical threshold (PWMT) was used for behavioral testing. Intracellular calcium concentration was measured using a fluorescent calcium indicator (Fluo-4 AM).

RESULTS

We found that P2Y2 receptor protein was upregulated and astrocytes were activated in the experimental rats after CCD surgery. Lipopolysaccharide (LPS) increased the intracellular calcium concentration and induced astrocyte activation in cultured astrocytes but was prevented via P2Y2 receptor inhibitor AR-C118925 or pregabalin. Furthermore, plasmid-mediated P2Y2 receptor overexpression induced an elevation of the intracellular calcium levels and inflammation in astrocytes, which was abolished by the TRPV4 inhibitor HC-067047. AR-C118925, HC-067047, and pregabalin relieved neuropathic pain and inflammation in rats after CCD surgery. Finally, plasmid-mediated P2Y2 receptor overexpression induced neuropathic pain in rats, which was abolished by pregabalin administration.

CONCLUSIONS

Pathophysiological variables that upregulated the P2Y2 receptor/TRPV4/calcium axis contribute to astrocyte activation in neuropathic pain. Pregabalin exerts an analgesic effect by inhibiting this pathway.

TRP Channels in Stroke

Ischemic stroke is a devastating disease that affects millions of patients worldwide. Unfortunately, there are no effective medications for mitigating brain injury after ischemic stroke. TRP channels are evolutionally ancient biosensors that detect external stimuli as well as tissue or cellular injury. To date, many members of the TRP superfamily have been reported to contribute to ischemic brain injury, including the TRPC subfamily (1, 3, 4, 5, 6, 7), TRPV subfamily (1, 2, 3, 4) and TRPM subfamily (2, 4, 7). These TRP channels share structural similarities but have distinct channel functions and properties. Their activation during ischemic stroke can be beneficial, detrimental, or even both. In this review, we focus on discussing the interesting features of stroke-related TRP channels and summarizing the underlying cellular and molecular mechanisms responsible for their involvement in ischemic brain injury.

AQP4-independent TRPV4 modulation of plasma membrane water permeability

Despite of the major role of aquaporin (AQP) water channels in controlling transmembrane water fluxes, alternative ways for modulating water permeation have been proposed. In the Central Nervous System (CNS), Aquaporin-4 (AQP4) is reported to be functionally coupled with the calcium-channel Transient-Receptor Potential Vanilloid member-4 (TRPV4), which is controversially involved in cell volume regulation mechanisms and water transport dynamics. The present work aims to investigate the selective role of TRPV4 in regulating plasma membrane water permeability in an AQP4-independent way. Fluorescence-quenching water transport experiments in Aqp4-/- astrocytes revealed that cell swelling rate is significantly increased upon TRPV4 activation and in the absence of AQP4. The biophysical properties of TRPV4-dependent water transport were therefore assessed using the HEK-293 cell model. Calcein quenching experiments showed that chemical and thermal activation of TRPV4 overexpressed in HEK-293 cells leads to faster swelling kinetics. Stopped-flow light scattering water transport assay was used to measure the osmotic permeability coefficient (Pf, cm/s) and activation energy (Ea, kcal/mol) conferred by TRPV4. Results provided evidence that although the Pf measured upon TRPV4 activation is lower than the one obtained in AQP4-overexpressing cells (Pf of AQP4 = 0.01667 ± 0.0007; Pf of TRPV4 = 0.002261 ± 0.0004; Pf of TRPV4 + 4αPDD = 0.007985 ± 0.0006; Pf of WT = 0.002249 ± 0.0002), along with activation energy values (Ea of AQP4 = 0.86 ± 0.0006; Ea of TRPV4 + 4αPDD = 2.73 ± 1.9; Ea of WT = 8.532 ± 0.4), these parameters were compatible with a facilitated pathway for water movement rather than simple diffusion. The possibility to tune plasma membrane water permeability more finely through TRPV4 might represent a protective mechanism in cells constantly facing severe osmotic challenges to avoid the potential deleterious effects of the rapid cell swelling occurring via AQP channels.

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.

The emerging science of Glioception: Contribution of glia in sensing, transduction, circuit integration of interoception

Interoception is the process by which the nervous system regulates internal functions to achieve homeostasis. The role of neurons in interoception has received considerable recent attention, but glial cells also contribute. Glial cells can sense and transduce signals including osmotic, chemical, and mechanical status of extracellular milieu. Their ability to dynamically communicate "listening" and "talking" to neurons is necessary to monitor and regulate homeostasis and information integration in the nervous system. This review introduces the concept of "Glioception" and focuses on the process by which glial cells sense, interpret and integrate information about the inner state of the organism. Glial cells are ideally positioned to act as sensors and integrators of diverse interoceptive signals and can trigger regulatory responses via modulation of the activity of neuronal networks, both in physiological and pathological conditions. We believe that understanding and manipulating glioceptive processes and underlying molecular mechanisms provide a key path to develop new therapies for the prevention and alleviation of devastating interoceptive dysfunctions, among which pain is emphasized here with more focused details.

Effects of Aloe-Emodin on the Expression of Brain Aquaporins and Secretion of Neurotrophic Factors in a Rat Model of Post-Stroke Depression

Post-stroke depression (PSD) is a common complication of stroke that can damage patients’ brains. More and more studies have been conducted on PSD in recent years, but the exact mechanism is still not understood. Currently, animal models provide an alternative approach to better understand the pathophysiology of PSD and may also pave the way for the discovery of new treatments for depression. This study investigated the therapeutic effect and mechanism of aloe-emodin (AE) on PSD rats. Previous studies have shown that AE positively affects PSD in rats by improving depression, increasing their activities and curiosities, enhancing the number of neurons, and ameliorating damage to brain tissue. Meanwhile, AE could up-regulate the expression of brain-derived neurotrophic factor (BDNF) and neurotrophic 3 (NTF3), but it could also down-regulate the expression of aquaporins (AQP3, AQP4, and AQP5), glial fibrillary acidic protein (GFAP), and transient receptor potential vanilloid 4 (TRPV4), which is helpful in maintaining homeostasis and alleviating encephaledema. AE may be a prospective solution in the future for the treatment of PSD patients.

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.

Transient receptor potential ion channels and cerebral stroke

METHODS

The databases Pubmed, and the National Library of Medicine were searched for literature. All papers on celebral stroke and transient receptor potential ion channels were considered.

RESULTS

Stroke is the second leading cause of death and disability, with an increasing incidence in developing countries. About 75 per cent of strokes are caused by occlusion of cerebral arteries, and substantial advances have been made in elucidating mechanisms how stroke affects the brain. Transient receptor potential (TRP) ion channels are calcium-permeable channels highly expressed in brain that drives Ca²⁺ entry into multiple cellular compartments. TRPC1/3/4/6, TRPV1/2/4, and TRPM2/4/7 channels have been implicated in stroke pathophysiology.

CONCLUSIONS

Although the precise mechanism of transient receptor potential ion channels in cerebral stroke is still unclear, it has the potential to be a therapeutic target for patients with stroke if developed appropriately. Hence, more research is needed to prove its efficacy in this context.

Retinal TRP channels: Cell-type-specific regulators of retinal homeostasis and multimodal integration

Transient receptor potential (TRP) channels are a widely expressed family of 28 evolutionarily conserved cationic ion channels that operate as primary detectors of chemical and physical stimuli and secondary effectors of metabotropic and ionotropic receptors. In vertebrates, the channels are grouped into six related families: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. As sensory transducers, TRP channels are ubiquitously expressed across the body and the CNS, mediating critical functions in mechanosensation, nociception, chemosensing, thermosensing, and phototransduction. This article surveys current knowledge about the expression and function of the TRP family in vertebrate retinas, which, while dedicated to transduction and transmission of visual information, are highly susceptible to non-visual stimuli. Every retinal cell expresses multiple TRP subunits, with recent evidence establishing their critical roles in paradigmatic aspects of vertebrate vision that include TRPM1-dependent transduction of ON bipolar signaling, TRPC6/7-mediated ganglion cell phototransduction, TRP/TRPL phototransduction in Drosophila and TRPV4-dependent osmoregulation, mechanotransduction, and regulation of inner and outer blood-retina barriers. TRP channels tune light-dependent and independent functions of retinal circuits by modulating the intracellular concentration of the 2nd messenger calcium, with emerging evidence implicating specific subunits in the pathogenesis of debilitating diseases such as glaucoma, ocular trauma, diabetic retinopathy, and ischemia. Elucidation of TRP channel involvement in retinal biology will yield rewards in terms of fundamental understanding of vertebrate vision and therapeutic targeting to treat diseases caused by channel dysfunction or over-activation.

The absence of AQP4/TRPV4 complex substantially reduces acute cytotoxic edema following ischemic injury

Introduction

Astrocytic Aquaporin 4 (AQP4) and Transient receptor potential vanilloid 4 (TRPV4) channels form a functional complex that likely influences cell volume regulation, the development of brain edema, and the severity of the ischemic injury. However, it remains to be fully elucidated whether blocking these channels can serve as a therapeutic approach to alleviate the consequences of having a stroke.

Methods and results

In this study, we used in vivo magnetic resonance imaging (MRI) to quantify the extent of brain lesions one day (D1) and seven days (D7) after permanent middle cerebral artery occlusion (pMCAO) in AQP4 or TRPV4 knockouts and mice with simultaneous deletion of both channels. Our results showed that deletion of AQP4 or TRPV4 channels alone leads to a significant worsening of ischemic brain injury at both time points, whereas their simultaneous deletion results in a smaller brain lesion at D1 but equal tissue damage at D7 when compared with controls. Immunohistochemical analysis 7 days after pMCAO confirmed the MRI data, as the brain lesion was significantly greater in AQP4 or TRPV4 knockouts than in controls and double knockouts. For a closer inspection of the TRPV4 and AQP4 channel complex in the development of brain edema, we applied a real-time iontophoretic method in situ to determine ECS diffusion parameters, namely volume fraction (α) and tortuosity (λ). Changes in these parameters reflect alterations in cell volume, and tissue structure during exposure of acute brain slices to models of ischemic conditions in situ, such as oxygen-glucose deprivation (OGD), hypoosmotic stress, or hyperkalemia. The decrease in α was comparable in double knockouts and controls when exposed to hypoosmotic stress or hyperkalemia. However, during OGD, there was no decrease in α in the double knockouts as observed in the controls, which suggests less swelling of the cellular components of the brain.

Conclusion

Although simultaneous deletion of AQP4 and TRPV4 did not improve the overall outcome of ischemic brain injury, our data indicate that the interplay between AQP4 and TRPV4 channels plays a critical role during neuronal and non-neuronal swelling in the acute phase of ischemic injury.

Glia as a key factor in cell volume regulation processes of the central nervous system

Brain edema is a pathological condition with potentially fatal consequences, related to cerebral injuries such as ischemia, chronic renal failure, uremia, and diabetes, among others. Under these pathological states, the cell volume control processes are fully compromised, because brain cells are unable to regulate the movement of water, mainly regulated by osmotic gradients. The processes involved in cell volume regulation are homeostatic mechanisms that depend on the mobilization of osmolytes (ions, organic molecules, and polyols) in the necessary direction to counteract changes in osmolyte concentration in response to water movement. The expression and coordinated function of proteins related to the cell volume regulation process, such as water channels, ion channels, and other cotransport systems in the glial cells, and considering the glial cell proportion compared to neuronal cells, leads to consider the astroglial network the main regulatory unit for water homeostasis in the central nervous system (CNS). In the last decade, several studies highlighted the pivotal role of glia in the cell volume regulation process and water homeostasis in the brain, including the retina; any malfunction of this astroglial network generates a lack of the ability to regulate the osmotic changes and water movements and consequently exacerbates the pathological condition.

Cell Confluence Modulates TRPV4 Channel Activity in Response to Hypoxia

Transient receptor potential vanilloid 4 (TRPV4) is a polymodal Ca²⁺-permeable channel involved in various hypoxia-sensitive pathophysiological phenomena. Different tools are available to study channel activity, requiring cells to be cultured at specific optimal densities. In the present study, we examined if cell density may influence the effect of hypoxia on TRPV4 activity. Transiently TRPV4-transfected HEK293T cells were seeded at low or high densities corresponding to non-confluent or confluent cells, respectively, on the day of experiments, and cultured under in vitro normoxia or hypoxia. TRPV4-mediated cytosolic Ca²⁺ responses, single-channel currents, and Ca²⁺ influx through the channel were measured using Ca²⁺ imaging/microspectrofluorimetric assay, patch-clamp, and Bioluminescence Resonance Energy Transfer (BRET), respectively. TRPV4 plasma membrane translocation was studied using confocal microscopy, biotinylation of cell surface proteins, and BRET. Our results show that hypoxia exposure has a differential effect on TRPV4 activation depending on cell confluence. At low confluence levels, TRPV4 response is increased in hypoxia, whereas at high confluence levels, TRPV4 response is strongly inhibited, due to channel internalization. Thus, cell density appears to be a crucial parameter for TRPV4 channel activity.

Ca2+ Signalling and Hypoxia/Acidic Tumour Microenvironment Interplay in Tumour Progression

Solid tumours are characterised by an altered microenvironment (TME) from the physicochemical point of view, displaying a highly hypoxic and acidic interstitial fluid. Hypoxia results from uncontrolled proliferation, aberrant vascularization and altered cancer cell metabolism. Tumour cellular apparatus adapts to hypoxia by altering its metabolism and behaviour, increasing its migratory and metastatic abilities by the acquisition of a mesenchymal phenotype and selection of aggressive tumour cell clones. Extracellular acidosis is considered a cancer hallmark, acting as a driver of cancer aggressiveness by promoting tumour metastasis and chemoresistance via the selection of more aggressive cell phenotypes, although the underlying mechanism is still not clear. In this context, Ca²⁺ channels represent good target candidates due to their ability to integrate signals from the TME. Ca²⁺ channels are pH and hypoxia sensors and alterations in Ca²⁺ homeostasis in cancer progression and vascularization have been extensively reported. In the present review, we present an up-to-date and critical view on Ca²⁺ permeable ion channels, with a major focus on TRPs, SOCs and PIEZO channels, which are modulated by tumour hypoxia and acidosis, as well as the consequent role of the altered Ca²⁺ signals on cancer progression hallmarks. We believe that a deeper comprehension of the Ca²⁺ signalling and acidic pH/hypoxia interplay will break new ground for the discovery of alternative and attractive therapeutic targets.

Statins Inhibit the Gliosis of MIO-M1, a Müller Glial Cell Line Induced by TRPV4 Activation

We characterized Müller cell gliosis induced by the activation of transient receptor potential vanilloid-type 4 (TRPV4) and assessed whether statins could modulate the gliosis. The human Müller cell line, MIO-M1, was used to analyze the gliosis caused by glaucomatous stimulation. To induce Müller gliosis in MIO-M1 cells, GSK101 was used to activate TRPV4, and Müller gliosis was evaluated by analyzing vimentin, nestin, and glial fibrillary acidic protein (GFAP) expression. The expression level of TNF-α was determined by ELISA. To evaluate the GSK101 activation of the NF-κB pathway, p65 phosphorylation was measured by Western blotting, and the nuclear translocation of p65 and IκBα phosphorylation were assessed by immunostaining. To assess the effect of statins on MIO-M1 gliosis, cells were pretreated for 24 h with statins before GSK101 treatment. Vimentin, nestin, and GFAP expression were upregulated by GSK101, while statins effectively inhibited them. The expression of TNF-α was increased by GSK101. The phosphorylation and nuclear translocation of p65 and IκBα phosphorylation, which occurs prior to p65 activation, were induced. Statins suppressed the GSK101-mediated phosphorylation of IκBα and p65 translocation. Statins can mitigate gliosis in the human Müller cell line. Because TRPV4 activation in Müller cells reflects glaucoma pathophysiology, statins may have the potential to prevent RGC death.

A novel antagonist of TRPM2 and TRPV4 channels: Carvacrol

The overload cytosolic free Ca²⁺ (cCa²⁺) influx-mediated excessive generation of oxidative stress in the pathophysiological conditions induces neuronal and cellular injury via the activation of cation channels. TRPM2 and TRPV4 channels are activated by oxidative stress, and their specific antagonists have not been discovered yet. The antioxidant and anti-Covid-19 properties of carvacrol (CARV) were recently reported. Hence, I suspected possible antagonist properties of CARV against oxidative stress (OS)/ADP-ribose (ADPR)-induced TRPM2 and GSK1016790A (GSK)-mediated TRPV4 activations in neuronal and kidney cells. I investigated the antagonist role of CARV on the activations of TRPM2 and TRPV4 in SH-SY5Y neuronal, BV-2 microglial, and HEK293 cells. The OS/ADPR and GSK in the cells caused to increase of TRPM2/TRPV4 current densities and overload cytosolic free Ca²⁺ (cCa²⁺) influx with an increase of mitochondrial membrane potential, cytosolic (cROS), and mitochondrial (mROS) ROS. The changes were not observed in the absence of TRPM2 and TRPV4 or the presence of Ca²⁺ free extracellular buffer and PARP-1 inhibitors (PJ34 and DPQ). When OS-induced TRPM2 and GSK-induced TRPV4 activations were inhibited by the treatment of CARV, the increase of cROS, mROS, lipid peroxidation, apoptosis, cell death, cCa²⁺ concentration, caspase -3, and caspase -9 levels were restored via upregulation of glutathione and glutathione peroxidase. In conclusion, the treatment of CARV modulated the TRPM2 and TRPV4-mediated overload Ca²⁺ influx and may provide an avenue for protecting TRPM2 and TRPV4-mediated neurodegenerative diseases associated with the increase of mROS and cCa²⁺. The possible TRPM2 and TRPV4 blocker action of carvacrol (CARV) via the modulation oxidative stress and apoptosis in the SH-SY5Y neuronal cells. TRPM2 is activated by DNA damage-induced (via PARP-1 activation) ADP-ribose (ADPR) and reactive oxygen species (ROS) (H₂O₂), although it is inhibited by nonspecific inhibitors (ACA and 2-APB). TRPV4 is activated by the treatments of GSK1016790A (GSK), although it is inhibited by a nonspecific inhibitor (ruthenium red, RuRe). The treatment of GSK induces excessive generation of ROS. The accumulation of free cytosolic Ca²⁺ (cCa²⁺) via the activations of TRPM2 and TRPV4 in the mitochondria causes the increase of mitochondrial membrane depolarization (ΔΨm). In turn, the increase of ΔΨm causes the excessive generation of ROS. The TRPM2 and TRPV4-induced the excessive generations of ROS result in the increase of apoptosis and cell death via the activations of caspase -3 (Casp-3) and caspase -9 (Casp-9) in the neuronal cells, although their oxidant actions decrease the glutathione (GSH) and glutathione peroxidase (GSHPx) levels. The oxidant and apoptotic adverse actions of TRPM2 and TRPV4 are modulated by the treatment of CARV.

Therapeutic Potential of Astrocyte Transplantation

Cell transplantation is an attractive treatment strategy for a variety of brain disorders, as it promises to replenish lost functions and rejuvenate the brain. In particular, transplantation of astrocytes has come into light recently as a therapy for amyotrophic lateral sclerosis (ALS); moreover, grafting of astrocytes also showed positive results in models of other conditions ranging from neurodegenerative diseases of older age to traumatic injury and stroke. Despite clear differences in etiology, disorders such as ALS, Parkinson's, Alzheimer's, and Huntington's diseases, as well as traumatic injury and stroke, converge on a number of underlying astrocytic abnormalities, which include inflammatory changes, mitochondrial damage, calcium signaling disturbance, hemichannel opening, and loss of glutamate transporters. In this review, we examine these convergent pathways leading to astrocyte dysfunction, and explore the existing evidence for a therapeutic potential of transplantation of healthy astrocytes in various models. Existing literature presents a wide variety of methods to generate astrocytes, or relevant precursor cells, for subsequent transplantation, while described outcomes of this type of treatment also differ between studies. We take technical differences between methodologies into account to understand the variability of therapeutic benefits, or lack thereof, at a deeper level. We conclude by discussing some key requirements of an astrocyte graft that would be most suitable for clinical applications.

TRPV4 inhibitor HC067047 produces antidepressant-like effect in LPS-induced depression mouse model

Inflammation is a crucial component that contributes to the pathogenesis of major depressive disorder. It has been revealed that the nonselective cation channel transient receptor potential vanilloid 4 (TRPV4) profoundly affects a variety of physiological processes, including inflammation. However, its roles and mechanisms in LPS-induced depression are still unclear. Here, for the first time, we found that there was a significant increase in TRPV4 in the hippocampus in a depression mouse model induced by LPS. TRPV4 inhibitor HC067047 or knockdown the hippocampal TRPV4 with TRPV4 shRNA could effectively rescue the aberrant behaviors. Furthermore, TRPV4 inhibitor HC067047 reduced the activation of astrocyte and microglia, decreased expression of CaMKII-NLRP3 inflammasome and increased the expression of neurogenesis marker DCX in the hippocampus. In addition, enhanced neuroinflammation in the serum was also reversed by TRPV4 inhibitor HC067047. Thus, we consider that TRPV4 has an important role in contributing to the depression-like behavior following LPS-induced systemic inflammation.

Astrocytes: The Housekeepers and Guardians of the CNS

Astroglia are a diverse group of cells in the central nervous system. They are of the ectodermal, neuroepithelial origin and vary in morphology and function, yet, they can be collectively defined as cells having principle function to maintain homeostasis of the central nervous system at all levels of organisation, including homeostasis of ions, pH and neurotransmitters; supplying neurones with metabolic substrates; supporting oligodendrocytes and axons; regulating synaptogenesis, neurogenesis, and formation and maintenance of the blood-brain barrier; contributing to operation of the glymphatic system; and regulation of systemic homeostasis being central chemosensors for oxygen, CO₂ and Na⁺. Their basic physiological features show a lack of electrical excitability (inapt to produce action potentials), but display instead a rather active excitability based on variations in cytosolic concentrations of Ca²⁺ and Na⁺. It is expression of neurotransmitter receptors, pumps and transporters at their plasmalemma, along with transports on the endoplasmic reticulum and mitochondria that exquisitely regulate the cytosolic levels of these ions, the fluctuation of which underlies most, if not all, astroglial homeostatic functions.

Astrocytic potassium and calcium channels as integrators of the inflammatory and ischemic CNS microenvironment

Astrocytes are key regulators of their surroundings by receiving and integrating stimuli from their local microenvironment, thereby regulating glial and neuronal homeostasis. Cumulating evidence supports a plethora of heterogenic astrocyte subpopulations that differ morphologically and in their expression patterns of receptors, transporters and ion channels, as well as in their functional specialisation. Astrocytic heterogeneity is especially relevant under pathological conditions. In experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis (MS), morphologically distinct astrocytic subtypes were identified and could be linked to transcriptome changes during different disease stages and regions. To allow for continuous awareness of changing stimuli across age and diseases, astrocytes are equipped with a variety of receptors and ion channels allowing the precise perception of environmental cues. Recent studies implicate the diverse repertoire of astrocytic ion channels - including transient receptor potential channels, voltage-gated calcium channels, inwardly rectifying K+ channels, and two-pore domain potassium channels - in sensing the brain state in physiology, inflammation and ischemia. Here, we review current evidence regarding astrocytic potassium and calcium channels and their functional contribution in homeostasis, neuroinflammation and stroke.

Membrane cholesterol regulates TRPV4 function, cytoskeletal expression, and the cellular response to tension

Despite the association of cholesterol with debilitating pressure-related diseases such as glaucoma, heart disease, and diabetes, its role in mechanotransduction is not well understood. We investigated the relationship between mechanical strain, free membrane cholesterol, actin cytoskeleton, and the stretch-activated transient receptor potential vanilloid isoform 4 (TRPV4) channel in human trabecular meshwork (TM) cells. Physiological levels of cyclic stretch resulted in time-dependent decreases in membrane cholesterol/phosphatidylcholine ratio and upregulation of stress fibers. Depleting free membrane cholesterol with m-β-cyclodextrin (MβCD) augmented TRPV4 activation by the agonist GSK1016790A, swelling and strain, with the effects reversed by cholesterol supplementation. MβCD increased membrane expression of TRPV4, caveolin-1, and flotillin. TRPV4 did not colocalize or interact with caveolae or lipid rafts, apart from a truncated ∼75 kDa variant partially precipitated by a caveolin-1 antibody. MβCD induced currents in TRPV4-expressing Xenopus laevis oocytes. Thus, membrane cholesterol regulates trabecular transduction of mechanical information, with TRPV4 channels mainly located outside the cholesterol-enriched membrane domains. Moreover, the biomechanical milieu itself shapes the lipid content of TM membranes. Diet, cholesterol metabolism, and mechanical stress might modulate the conventional outflow pathway and intraocular pressure in glaucoma and diabetes in part by modulating TM mechanosensing.

Extracellular Calcium Influx Pathways in Astrocyte Calcium Microdomain Physiology

Astrocytes are complex glial cells that play many essential roles in the brain, including the fine-tuning of synaptic activity and blood flow. These roles are linked to fluctuations in intracellular Ca2+ within astrocytes. Recent advances in imaging techniques have identified localized Ca2+ transients within the fine processes of the astrocytic structure, which we term microdomain Ca2+ events. These Ca2+ transients are very diverse and occur under different conditions, including in the presence or absence of surrounding circuit activity. This complexity suggests that different signalling mechanisms mediate microdomain events which may then encode specific astrocyte functions from the modulation of synapses up to brain circuits and behaviour. Several recent studies have shown that a subset of astrocyte microdomain Ca2+ events occur rapidly following local neuronal circuit activity. In this review, we consider the physiological relevance of microdomain astrocyte Ca2+ signalling within brain circuits and outline possible pathways of extracellular Ca2+ influx through ionotropic receptors and other Ca2+ ion channels, which may contribute to astrocyte microdomain events with potentially fast dynamics.

The involvement of TRPV4 on the hypoxia-induced oxidative neurotoxicity and apoptosis in a neuronal cell line: Protective role of melatonin

The hypoxia (HYPX)-mediated excessive generation of mitochondrial free reactive oxygen species (mROS) and the overload Ca²⁺ influx via the inhibition of TRPV4 are controlled by the treatment of antioxidants. However, the molecular mechanisms underlying melatonin (MLT)'s neuroprotection remains elusive. We investigated the role of MLT via modulation of TRPV4 on oxidative neurodegeneration and death in SH-SY5Y neuronal cells. The SH-SY5Y cells were divided into five groups as follows: control, MLT (1 mM for 2 h), HYPX (200 μM CoCl₂ for 24 h), HYPX + MLT, and HYPX + TRPV4 blockers (ruthenium red-1 μM for 30 min). The HYPX caused to the increase of TRPV4 current density and overload Ca²⁺ influx with an increase of mitochondrial membrane potential and mROS generation. The changes were not observed in the absence of TRPV4. When HYPX exposure and TRPV4 agonist (GSK1016790A)-induced TRPV4 activity were inhibited by the treatment of ruthenium red or MLT, the increase of mROS, lipid peroxidation, apoptosis, Zn²⁺ concentrations, TRPV4, caspase -3, caspase -9, Bax, and Bcl-2 expressions were restored via upregulation of reduced glutathione, glutathione peroxidase, and total antioxidant status. The levels of apoptosis and cell death in the cells were enriched with increases of caspase -3 and -9 activations, although they were decreased by MLT treatment. In conclusion, the treatment of MLT modulates HYPX-mediated mROS, apoptosis, and TRPV4-mediated overload Ca²⁺ influx and may provide an avenue for protecting HYPX-mediated neurological diseases associated with the increase of mROS, Ca²⁺, and Zn²⁺ concentration.

On the Common Journey of Neural Cells through Ischemic Brain Injury and Alzheimer's Disease

Ischemic brain injury and Alzheimer's disease (AD) both lead to cell death in the central nervous system (CNS) and thus negatively affect particularly the elderly population. Due to the lack of a definitive cure for brain ischemia and AD, it is advisable to carefully study, compare, and contrast the mechanisms that trigger, and are involved in, both neuropathologies. A deeper understanding of these mechanisms may help ameliorate, or even prevent, the destructive effects of neurodegenerative disorders. In this review, we deal with ischemic damage and AD, with the main emphasis on the common properties of these CNS disorders. Importantly, we discuss the Wnt signaling pathway as a significant factor in the cell fate determination and cell survival in the diseased adult CNS. Finally, we summarize the interesting findings that may improve or complement the current sparse and insufficient treatments for brain ischemia and AD, and we delineate prospective directions in regenerative medicine.

Advancement in research on the role of the transient receptor potential vanilloid channel in cerebral ischemic injury (Review)

Stroke is a common critical disease occurring in middle-aged and elderly individuals, and is characterized by high morbidity, lethality and mortality. As such, it is of great concern to medical professionals. The aim of the present review was to investigate the effects of transient receptor potential vanilloid (TRPV) subtypes during cerebral ischemia in ischemia-reperfusion animal models, oxygen glucose deprivation and in other administration cell models in vitro to explore new avenues for stroke research and clinical treatments. TRPV1, TRPV2 and TRPV4 employ different methodologies by which they confer protection against cerebral ischemic injury. TRPV1 and TRPV4 are likely related to the inhibition of inflammatory reactions, neurotoxicity and cell apoptosis, thus promoting nerve growth and regulation of intracellular calcium ions (Ca2+). The mechanisms of neuroprotection of TRPV1 are the JNK pathway, N-methyl-D-aspartate (NMDA) receptor and therapeutic hypothermia. The mechanisms of neuroprotection of TRPV4 are the PI3K/Akt pathways, NMDA receptor and p38 MAPK pathway, amongst others. The mechanisms by which TRPV2 confers its protective effects are predominantly connected with the regulation of nerve growth factor, MAPK and JNK pathways, as well as JNK-dependent pathways. Thus, TRPVs have the potential for improving outcomes associated with cerebral ischemic or reperfusion injuries. The protection conferred by TRPV1 and TRPV4 is closely related to cellular Ca2+ influx, while TRPV2 has a different target and mode of action, possibly due to its expression sites. However, in light of certain contradictory research conclusions, further experimentation is required to clarify the mechanisms and specific pathways by which TRPVs act to alleviate nerve injuries.

Decreased parenchymal arteriolar tone uncouples vessel-to-neuronal communication in a mouse model of vascular cognitive impairment

Chronic hypoperfusion is a key contributor to cognitive decline and neurodegenerative conditions, but the cellular mechanisms remain ill-defined. Using a multidisciplinary approach, we sought to elucidate chronic hypoperfusion-evoked functional changes at the neurovascular unit. We used bilateral common carotid artery stenosis (BCAS), a well-established model of vascular cognitive impairment, combined with an ex vivo preparation that allows pressurization of parenchymal arterioles in a brain slice. Our results demonstrate that mild (~ 30%), chronic hypoperfusion significantly altered the functional integrity of the cortical neurovascular unit. Although pial cerebral perfusion recovered over time, parenchymal arterioles progressively lost tone, exhibiting significant reductions by day 28 post-surgery. We provide supportive evidence for reduced adenosine 1 receptor-mediated vasoconstriction as a potential mechanism in the adaptive response underlying the reduced baseline tone in parenchymal arterioles. In addition, we show that in response to the neuromodulator adenosine, the action potential frequency of cortical pyramidal neurons was significantly reduced in all groups. However, a significant decrease in adenosine-induced hyperpolarization was observed in BCAS 14 days. At the microvascular level, constriction-induced inhibition of pyramidal neurons was significantly compromised in BCAS mice. Collectively, these results suggest that BCAS uncouples vessel-to-neuron communication-vasculo-neuronal coupling-a potential early event in cognitive decline.

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.

Modulation of photosynthesis and other proteins during water-stress

Protein changes under drought or water stress conditions have been widely investigated. These investigations have given us enormous understanding of how drought is manifested in plants and how plants respond and adopt to such conditions. Chlorophyll fluoroescence, gas exchange, OMICS, biochemical and molecular analyses have shed light on regulation of physiology and photosynthesis of plants under drought. Use of proteomics has greatly increased the repertoire of drought-associated proteins which nevertheless, need to be investigated for their mechanistic and functional roles. Roles of such proteins have been succinctly discussed in various review articles, however more information on their functional role in countering drought is needed. In this review, recent developments in the field, alterations in the abundance of plant proteins in response to drought, monitored through numerous proteomic and immuno-blot analyses, and how these could affect plants growth and development, are discussed.

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.

Graphene glial-interfaces: challenges and perspectives

Graphene nanosheets are mechanically strong but flexible, electrically conductive and bio-compatible. Thus, due to these unique properties, they are being intensively studied as materials for the next generation of neural interfaces. Most of the literature focused on optimizing the interface between these materials and neurons. However, one of the most common causes of implant failure is the adverse inflammatory reaction of glial cells. These cells are not, as previously considered, just passive and supportive cells, but play a crucial role in the physiology and pathology of the nervous system, and in the interaction with implanted electrodes. Besides providing structural support to neurons, glia are responsible for the modulation of synaptic transmission and control of central and peripheral homeostasis. Accordingly, knowledge on the interaction between glia and biomaterials is essential to develop new implant-based therapies for the treatment of neurological disorders, such as epilepsy, brain tumours, and Alzheimer's and Parkinson's disease. This work provides an overview of the emerging literature on the interaction of graphene-based materials with glial cells, together with a complete description of the different types of glial cells and problems associated with them. We believe that this description will be important for researchers working in materials science and nanotechnology to develop new active materials to interface, measure and stimulate these cells.

The Role of TRP Channels and PMCA in Brain Disorders: Intracellular Calcium and pH Homeostasis

Brain disorders include neurodegenerative diseases (NDs) with different conditions that primarily affect the neurons and glia in the brain. However, the risk factors and pathophysiological mechanisms of NDs have not been fully elucidated. Homeostasis of intracellular Ca²⁺ concentration and intracellular pH (pH_i) is crucial for cell function. The regulatory processes of these ionic mechanisms may be absent or excessive in pathological conditions, leading to a loss of cell death in distinct regions of ND patients. Herein, we review the potential involvement of transient receptor potential (TRP) channels in NDs, where disrupted Ca²⁺ homeostasis leads to cell death. The capability of TRP channels to restore or excite the cell through Ca²⁺ regulation depending on the level of plasma membrane Ca²⁺ ATPase (PMCA) activity is discussed in detail. As PMCA simultaneously affects intracellular Ca²⁺ regulation as well as pH_i, TRP channels and PMCA thus play vital roles in modulating ionic homeostasis in various cell types or specific regions of the brain where the TRP channels and PMCA are expressed. For this reason, the dysfunction of TRP channels and/or PMCA under pathological conditions disrupts neuronal homeostasis due to abnormal Ca²⁺ and pH levels in the brain, resulting in various NDs. This review addresses the function of TRP channels and PMCA in controlling intracellular Ca²⁺ and pH, which may provide novel targets for treating NDs.

Glial Interfaces: Advanced Materials and Devices to Uncover the Role of Astroglial Cells in Brain Function and Dysfunction

Research over the past four decades has highlighted the importance of certain brain cells, called glial cells, and has moved the neurocentric vision of structure, function, and pathology of the nervous system toward a more holistic perspective. In this view, the demand for technologies that are able to target and both selectively monitor and control glial cells is emerging as a challenge across neuroscience, engineering, chemistry, and material science. Frequently neglected or marginally considered as a barrier to be overcome between neural implants and neuronal targets, glial cells, and in particular astrocytes, are increasingly considered as active players in determining the outcomes of device implantation. This review provides a concise overview not only of the previously established but also of the emerging physiological and pathological roles of astrocytes. It also critically discusses the most recent advances in biomaterial interfaces and devices that interact with glial cells and thus have enabled scientists to reach unprecedented insights into the role of astroglial cells in brain function and dysfunction. This work proposes glial interfaces and glial engineering as multidisciplinary fields that have the potential to enable significant advancement of knowledge surrounding cognitive function and acute and chronic neuropathologies.

Trpv4 regulates Nlrp3 inflammasome via SIRT1/PGC-1α pathway in a cuprizone-induced mouse model of demyelination

Increasing evidence has demonstrated that the Nod-like receptor pyrin domain containing 3 (Nlrp3) inflammasome overactivated during demyelinating disorders. It has been implicated that transient receptor potential type 4 (Trpv4) is regarded as a polymodal ionotropic receptor that plays an important role in a multitude of pathological conditions, including inflammation. The aim of this study was to investigate whether the Trpv4 channel regulates Nlrp3 inflammasome in the corpus callosum of mice with demyelination. Our results showed that CPZ treatment significantly increased the expression of Trpv4, activated Nlrp3 inflammasome, reduced peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) and decreased mitochondrial function. siRNA-mediated Nlrp3 knockdown inhibited glial activation and alleviated demyelination. Whereas knockdown of Trpv4 by siRNA markedly ameliorated Nlrp3 inflammasome activation and restored mitochondrial function as well as reducing the level of reactive oxygen species (ROS). Meanwhile, glial activation, demyelination and behavioral impairment induced by CPZ were also alleviated by siRNA-mediated Trpv4 knockdown. Furthermore, immunoprecipitation and use of a lysine acetylation assay showed that Sirtuin1 (SIRT1) mediated the PGC-1α deacetylation, which is involved in Nlrp3 inflammasome activation. These findings suggest that Trpv4 regulates mitochondrial function through the SIRT1/PGC-1α pathway, which further trigger Nlrp3 inflammasome activation in the CPZ-induced demyelination in mice.

Involvement of Neural Transient Receptor Potential Channels in Peripheral Inflammation

Transient receptor potential (TRP) channels are a superfamily of non-selective cation channels that act as polymodal sensors in many tissues throughout mammalian organisms. In the context of ion channels, they are unique for their broad diversity of activation mechanisms and their cation selectivity. TRP channels are involved in a diverse range of physiological processes including chemical sensing, nociception, and mediating cytokine release. They also play an important role in the regulation of inflammation through sensory function and the release of neuropeptides. In this review, we discuss the functional contribution of a subset of TRP channels (TRPV1, TRPV4, TRPM3, TRPM8, and TRPA1) that are involved in the body’s immune responses, particularly in relation to inflammation. We focus on these five TRP channels because, in addition to being expressed in many somatic cell types, these channels are also expressed on peripheral ganglia and nerves that innervate visceral organs and tissues throughout the body. Activation of these neural TRP channels enables crosstalk between neurons, immune cells, and epithelial cells to regulate a wide range of inflammatory actions. TRP channels act either through direct effects on cation levels or through indirect modulation of intracellular pathways to trigger pro- or anti-inflammatory mechanisms, depending on the inflammatory disease context. The expression of TRP channels on both neural and immune cells has made them an attractive drug target in diseases involving inflammation. Future work in this domain will likely yield important new pathways and therapies for the treatment of a broad range of disorders including colitis, dermatitis, sepsis, asthma, and pain.

Roles of TRP Channels in Neurological Diseases

Transient receptor potential (TRP) proteins consist of a superfamily of cation channels that have been involved in diverse physiological processes in the brain as well as in the pathogenesis of neurological disease. TRP channels are widely expressed in the brain, including neurons and glial cells, as well as in the cerebral vascular endothelium and smooth muscle. Members of this channel superfamily show a wide variety of mechanisms ranging from ligand binding to voltage, physical, and chemical stimuli, implying the promising therapeutic potential of TRP in neurological diseases. In this review, we focus on the physiological functions of TRP channels in the brain and the pathological roles in neurological disorders to explore future potential neuroprotective strategies.

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.

Channels that Cooperate with TRPV4 in the Brain

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective Ca²⁺-permeable cation channel that is a member of the TRP channel family. It is clear that TRPV4 channels are broadly expressed in the brain. As they are expressed on the plasma membrane, they interact with other channels and play a crucial role in nervous system activity. Under some pathological conditions, TRPV4 channels are upregulated and sensitized via cellular signaling pathways, and this can cause nervous system diseases. In this review, we focus on receptors that cooperate with TRPV4, including large-conductance Ca²⁺-activated K⁺(BKca) channels, N-methyl-D-aspartate receptors (NMDARs), α-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors (AMPARs), inositol 1,4,5-trisphosphate receptors (IP3Rs), ryanodine receptors (RyRs), aquaporin 4 (AQP4), and other potential cooperative receptors in the brain. The data demonstrate how these channels work together to cause nervous system diseases under pathological conditions. The aim of this review was to discuss the receptors and signaling pathways related to TRPV4 based on recent data on the important physiological functions of TRPV4 channels to provide new clues for future studies and prospective therapeutic targets for related brain diseases.

Stimulation of water and calcium dynamics in astrocytes with pulsed infrared light

Astrocytes are non-neuronal cells that govern the homeostatic regulation of the brain through ions and water transport, and Ca2+ -mediated signaling. As they are tightly integrated into neural networks, label-free tools that can modulate cell function are needed to evaluate the role of astrocytes in brain physiology and dysfunction. Using live-cell fluorescence imaging, pharmacology, electrophysiology, and genetic manipulation, we show that pulsed infrared light can modulate astrocyte function through changes in intracellular Ca2+ and water dynamics, providing unique mechanistic insight into the effect of pulsed infrared laser light on astroglial cells. Water transport is activated and, IP3 R, TRPA1, TRPV4, and Aquaporin-4 are all involved in shaping the dynamics of infrared pulse-evoked intracellular calcium signal. These results demonstrate that astrocyte function can be modulated with infrared light. We expect that targeted control over calcium dynamics and water transport will help to study the crucial role of astrocytes in edema, ischemia, glioma progression, stroke, and epilepsy.

Kidins220/ARMS controls astrocyte calcium signaling and neuron-astrocyte communication

Through their ability to modulate synaptic transmission, glial cells are key regulators of neuronal circuit formation and activity. Kidins220/ARMS (kinase-D interacting substrate of 220 kDa/ankyrin repeat-rich membrane spanning) is one of the key effectors of the neurotrophin pathways in neurons where it is required for differentiation, survival, and plasticity. However, its role in glial cells remains largely unknown. Here, we show that ablation of Kidins220 in primary cultured astrocytes induced defects in calcium (Ca2+) signaling that were linked to altered store-operated Ca2+ entry and strong overexpression of the transient receptor potential channel TRPV4. Moreover, Kidins220-/- astrocytes were more sensitive to genotoxic stress. We also show that Kidins220 expression in astrocytes is required for the establishment of proper connectivity of cocultured wild-type neurons. Altogether, our data reveal a previously unidentified role for astrocyte-expressed Kidins220 in the control of glial Ca2+ dynamics, survival/death pathways and astrocyte-neuron communication.

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

A plethora of neurological disorders shares a final common deadly pathway known as excitotoxicity. Among these disorders, ischemic injury is a prominent cause of death and disability worldwide. Brain ischemia stems from cardiac arrest or stroke, both responsible for insufficient blood supply to the brain parenchyma. Glucose and oxygen deficiency disrupts oxidative phosphorylation, which results in energy depletion and ionic imbalance, followed by cell membrane depolarization, calcium (Ca²⁺) overload, and extracellular accumulation of excitatory amino acid glutamate. If tight physiological regulation fails to clear the surplus of this neurotransmitter, subsequent prolonged activation of glutamate receptors forms a vicious circle between elevated concentrations of intracellular Ca²⁺ ions and aberrant glutamate release, aggravating the effect of this ischemic pathway. The activation of downstream Ca²⁺-dependent enzymes has a catastrophic impact on nervous tissue leading to cell death, accompanied by the formation of free radicals, edema, and inflammation. After decades of “neuron-centric” approaches, recent research has also finally shed some light on the role of glial cells in neurological diseases. It is becoming more and more evident that neurons and glia depend on each other. Neuronal cells, astrocytes, microglia, NG2 glia, and oligodendrocytes all have their roles in what is known as glutamate excitotoxicity. However, who is the main contributor to the ischemic pathway, and who is the unsuspecting victim? In this review article, we summarize the so-far-revealed roles of cells in the central nervous system, with particular attention to glial cells in ischemia-induced glutamate excitotoxicity, its origins, and consequences.

Physiology of Astroglia

Astrocytes are principal cells responsible for maintaining the brain homeostasis. Additionally, these glial cells are also involved in homocellular (astrocyte-astrocyte) and heterocellular (astrocyte-other cell types) signalling and metabolism. These astroglial functions require an expression of the assortment of molecules, be that transporters or pumps, to maintain ion concentration gradients across the plasmalemma and the membrane of the endoplasmic reticulum. Astrocytes sense and balance their neurochemical environment via variety of transmitter receptors and transporters. As they are electrically non-excitable, astrocytes display intracellular calcium and sodium fluctuations, which are not only used for operative signalling but can also affect metabolism. In this chapter we discuss the molecules that achieve ionic gradients and underlie astrocyte signalling.

Sensing and regulation of cell volume - we know so much and yet understand so little: TRPV4 as a sensor of volume changes but possibly without a volume-regulatory role?

Cellular volume changes lead to initiation of cell volume regulatory events, the molecular identity of which remains unresolved. We here discuss experimental challenges associated with investigation of volume regulation during application of large, non-physiological osmotic gradients. The TRPV4 ion channel responds to volume increase irrespectively of the molecular mechanism underlying cell swelling, and is thus considered a sensor of volume changes. Evidence pointing towards the involvement of TRPV4 in subsequent volume regulatory mechanisms is intriguing, yet far from conclusive. We here present an experimental setting with astrocytic cell swelling in the absence of externally applied osmotic gradients, and the lack of evidence for involvement of TRPV4 in this regulatory volume response. Our aim with these new data and the preceding discussion is to stimulate further experimental effort in this area of research to clarify the role of TRPV4 and other channels and transporters in regulatory volume responses.