TRPV4 is functionally expressed in oligodendrocyte precursor cells and increases their proliferation

ITPR2 Mediated Calcium Homeostasis in Oligodendrocytes is Essential for Myelination and Involved in Depressive-Like Behavior in Adolescent Mice

Ca2+ signaling is essential for oligodendrocyte (OL) development and myelin formation. Inositol 1,4,5-trisphosphate receptor type 2 (ITPR2) is an endoplasmic reticulum calcium channel and shows stage-dependent high levels in postmitotic oligodendrocyte precursor cells (OPCs). The role and potential mechanism of ITPR2 in OLs remain unclear. In this study, it is revealed that loss of Itpr2 in OLs disturbs Ca2+ homeostasis and inhibits myelination in adolescent mice. Animals with OL-specific deletion of Itpr2 exhibit anxiety/depressive-like behaviors and manifest with interrupted OPC proliferation, leading to fewer mature OLs in the brain. Detailed transcriptome profiling and signal pathway analysis suggest that MAPK/ERK-CDK6/cyclin D1 axis underlies the interfered cell cycle progression in Itpr2 ablated OPCs. Besides, blocking MAPK/ERK pathway significantly improves the delayed OPC differentiation and myelination in Itpr2 mutant. Notably, the resting [Ca2+]i is increased in Itpr2 ablated OPCs, with the elevation of several plasma calcium channels. Antagonists against these plasma calcium channels can normalize the resting [Ca2+]i level and enhance lineage progression in Itpr2-ablated OPCs. Together, the findings reveal novel insights for calcium homeostasis in manipulating developmental transition from OPCs to pre-OLs; additionally, the involvement of OLs-originated ITPR2 in depressive behaviors provides new therapeutic strategies to alleviate myelin-associated psychiatric disorders.

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

Astrocytic TRPV4 Channels and Their Role in Brain Ischemia

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

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

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

Vitamin D supplementation is effective for olanzapine-induced dyslipidemia

Olanzapine is an atypical antipsychotic drug that is clinically applied in patients with schizophrenia. It increases the risk of dyslipidemia, a disturbance of lipid metabolic homeostasis, usually characterized by increased low-density lipoprotein (LDL) cholesterol and triglycerides, and accompanied by decreased high-density lipoprotein (HDL) in the serum. In this study, analyzing the FDA Adverse Event Reporting System, JMDC insurance claims, and electronic medical records from Nihon University School of Medicine revealed that a co-treated drug, vitamin D, can reduce the incidence of olanzapine-induced dyslipidemia. In the following experimental validations of this hypothesis, short-term oral olanzapine administration in mice caused a simultaneous increase and decrease in the levels of LDL and HDL cholesterol, respectively, while the triglyceride level remained unaffected. Cholecalciferol supplementation attenuated these deteriorations in blood lipid profiles. RNA-seq analysis was conducted on three cell types that are closely related to maintaining cholesterol metabolic balance (hepatocytes, adipocytes, and C2C12) to verify the direct effects of olanzapine and the functional metabolites of cholecalciferol (calcifediol and calcitriol). Consequently, the expression of cholesterol-biosynthesis-related genes was reduced in calcifediol- and calcitriol-treated C2C12 cells, which was likely to be mediated by activating the vitamin D receptor that subsequently inhibited the cholesterol biosynthesis process via insulin-induced gene 2 regulation. This clinical big-data-based drug repurposing approach is effective in finding a novel treatment with high clinical predictability and a well-defined molecular mechanism.

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.

The regulatory and modulatory roles of TRP family channels in malignant tumors and relevant therapeutic strategies

Transient receptor potential (TRP) channels are one primary type of calcium (Ca²⁺) permeable channels, and those relevant transmembrane and intracellular TRP channels were previously thought to be mainly associated with the regulation of cardiovascular and neuronal systems. Nowadays, however, accumulating evidence shows that those TRP channels are also responsible for tumorigenesis and progression, inducing tumor invasion and metastasis. However, the overall underlying mechanisms and possible signaling transduction pathways that TRP channels in malignant tumors might still remain elusive. Therefore, in this review, we focus on the linkage between TRP channels and the significant characteristics of tumors such as multi-drug resistance (MDR), metastasis, apoptosis, proliferation, immune surveillance evasion, and the alterations of relevant tumor micro-environment. Moreover, we also have discussed the expression of relevant TRP channels in various forms of cancer and the relevant inhibitors' efficacy. The chemo-sensitivity of the anti-cancer drugs of various acting mechanisms and the potential clinical applications are also presented. Furthermore, it would be enlightening to provide possible novel therapeutic approaches to counteract malignant tumors regarding the intervention of calcium channels of this type.

Inhibition of Transient Receptor Potential Vanilloid 4 (TRPV4) Mitigates Seizures

Astrocytes are critical regulators of the immune/inflammatory response in several human central nervous system (CNS) diseases. Emerging evidence suggests that dysfunctional astrocytes are crucial players in seizures. The objective of this study was to investigate the role of transient receptor potential vanilloid 4 (TRPV4) in 4-aminopyridine (4-AP)-induced seizures and the underlying mechanism. We also provide evidence for the role of Yes-associated protein (YAP) in seizures. 4-AP was administered to mice or primary cultured astrocytes. YAP-specific small interfering RNA (siRNA) was administered to primary cultured astrocytes. Mouse brain tissue and surgical specimens from epileptic patient brains were examined, and the results showed that TRPV4 was upregulated, while astrocytes were activated and polarized to the A1 phenotype. The levels of glial fibrillary acidic protein (GFAP), cytokine production, YAP, signal transducer activator of transcription 3 (STAT3), intracellular Ca2+([Ca2+]i) and the third component of complement (C3) were increased in 4-AP-induced mice and astrocytes. Perturbations in the immune microenvironment in the brain were balanced by TRPV4 inhibition or the manipulation of [Ca2+]i in astrocytes. Knocking down YAP with siRNA significantly inhibited 4-AP-induced pathological changes in astrocytes. Our study demonstrated that astrocytic TRPV4 activation promoted neuroinflammation through the TRPV4/Ca2+/YAP/STAT3 signaling pathway in mice with seizures. Astrocyte TRPV4 inhibition attenuated neuroinflammation, reduced neuronal injury, and improved neurobehavioral function. Targeting astrocytic TRPV4 activation may provide a promising therapeutic approach for managing epilepsy.

Can Enhancing Neuronal Activity Improve Myelin Repair in Multiple Sclerosis?

Enhanced neuronal activity in the healthy brain can induce de novo myelination and behavioral changes. As neuronal activity can be achieved using non-invasive measures, it may be of interest to utilize the innate ability of neuronal activity to instruct myelination as a novel strategy for myelin repair in demyelinating disorders such as multiple sclerosis (MS). Preclinical studies indicate that stimulation of neuronal activity in demyelinated lesions indeed has the potential to improve remyelination and that the stimulation paradigm is an important determinant of success. However, future studies will need to reveal the most efficient stimulation protocols as well as the biological mechanisms implicated. Nonetheless, clinical studies have already explored non-invasive brain stimulation as an attractive therapeutic approach that ameliorates MS symptomatology. However, whether symptom improvement is due to improved myelin repair remains unclear. In this mini-review, we discuss the neurobiological basis and potential of enhancing neuronal activity as a novel therapeutic approach in MS.

Transient Receptor Potential Melastatin 3 Is Functionally Expressed in Oligodendrocyte Precursor Cells and Is Upregulated in Ischemic Demyelinated Lesions

Oligodendrocyte precursor cells (OPCs) are glial cells that differentiate into oligodendrocytes and myelinate axons. The number of OPCs is reportedly increased in brain lesions in some demyelinating diseases and during ischemia; however, these cells also secrete cytokines and elicit both protective and deleterious effects in response to brain injury. The mechanism regulating the behaviors of OPCs in physiological and pathological conditions must be elucidated to control these cells and to treat demyelinating diseases. Here, we focused on transient receptor potential melastatin 3 (TRPM3), a Ca²⁺-permeable channel that is activated by the neurosteroid pregnenolone sulfate (PS) and body temperature. Trpm3⁺/Pdgfra⁺ OPCs were detected in the cerebral cortex (CTX) and corpus callosum (CC) of P4 and adult rats by in situ hybridization. Trpm3 expression was detected in primary cultured rat OPCs and was increased by treatment with tumor necrosis factor α (TNFα). Application of PS (30-100 µM) increased the Ca²⁺ concentration in OPCs and this effect was inhibited by co-treatment with the TRP channel blocker Gd³⁺ (100 µM) or the TRPM3 inhibitor isosakuranetin (10 µM). Stimulation of TRPM3 with PS (50 µM) did not affect the differentiation or migration of OPCs. The number of Trpm3⁺ OPCs was markedly increased in demyelinated lesions in an endothelin-1 (ET-1)-induced ischemic rat model. In conclusion, TRPM3 is functionally expressed in OPCs in vivo and in vitro and is upregulated in inflammatory conditions such as ischemic insults and TNFα treatment, implying that TRPM3 is involved in the regulation of specific behaviors of OPCs in pathological conditions.

Heterogeneity and Proliferative and Differential Regulators of NG2-glia in Physiological and Pathological States

NG2-glia, also called Oligodendrocyte Precursor Cells (OPCs), account for approximately 5%-10% of the cells in the developing and adult brain and constitute the fifth major cell population in the central nervous system. NG2-glia express receptors and ion channels involved in rapid modulation of neuronal activities and signaling with neuronal synapses, which have functional significance in both physiological and pathological states. NG2-glia participate in quick signaling with peripheral neurons via direct synaptic touches in the developing and mature central nervous system. These distinctive glia perform the unique function of proliferating and differentiating into oligodendrocytes in the early developing brain, which is critical for axon myelin formation. In response to injury, NG2-glia can proliferate, migrate to the lesions, and differentiate into oligodendrocytes to form new myelin sheaths, which wrap around damaged axons and result in functional recovery. The capacity of NG2-glia to regulate their behavior and dynamics in response to neuronal activity and disease indicate their critical role in myelin preservation and remodeling in the physiological state and in repair in the pathological state. In this review, we provide a detailed summary of the characteristics of NG2-glia, including their heterogeneity, the regulators of their proliferation, and the modulators of their differentiation into oligodendrocytes.

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.

Increased TRPV4 expression in non-myelinating Schwann cells is associated with demyelination after sciatic nerve injury

Transient receptor potential vanilloid 4 (TRPV4) is a non-selective calcium-permeable cation channel that is widely expressed and activated in various neurons and glial cells in the nervous system. Schwann cells (SCs) are primary glia cells that wrap around axons to form the myelin sheath in the peripheral nervous system. However, whether TRPV4 is expressed and functions in SCs is unclear. Here, we demonstrate functional expression of TRPV4 in mouse SCs and investigated its physiological significance. Deletion of TRPV4 did not affect normal myelin development for SCs in sciatic nerves in mice. However, after sciatic nerve cut injury, TRPV4 expression levels were remarkably increased in SCs following nerve demyelination. Ablation of TRPV4 expression impaired the demyelinating process after nerve injury, resulting in delayed remyelination and functional recovery of sciatic nerves. These results suggest that local activation of TRPV4 could be an attractive pharmacological target for therapeutic intervention after peripheral nerve injury.

Feng et al. report that TRPV4 plays an important role in Schwann cells (SCs) during nerve demyelination and remyelination in mice. Using sciatic nerve cut injury mouse models, they find that TRPV4 expression is remarkably increased in demyelinating SCs during sciatic nerve injury; and ablation of TRPV4 expression impairs the demyelinating process after nerve injury, resulting in their delayed remyelination and functional recovery.

Modulation of TRPV4 and BKCa for treatment of brain diseases

As a member of transient receptor potential family, the transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium-permeable cation channel, which belongs to non-voltage gated Ca²⁺ channel. Large-conductance Ca²⁺-activated K⁺ channel (BKCa) represents a unique superfamily of Ca²⁺-activated K⁺ channel (KCa) that is both voltage and intracellular Ca²⁺ dependent. Not surprisingly, aberrant function of either TRPV4 or BKCa in neurons has been associated with brain disorders, such as Alzheimer's disease, cerebral ischemia, brain tumor, epilepsy, as well as headache. In these diseases, vascular dysfunction is a common characteristic. Notably, endothelial and smooth muscle TRPV4 can mediate BKCa to regulate cerebral blood flow and pressure. Therefore, in this review, we not only discuss the diverse functions of TRPV4 and BKCa in neurons to integrate relative signaling pathways in the context of cerebral physiological and pathological situations respectively, but also reveal the relationship between TRPV4 and BKCa in regulation of cerebral vascular tone as an etiologic factor. Based on these analyses, this review demonstrates the effective mechanisms of compounds targeting these two channels, which may be potential therapeutic strategies for diseases in the brain.

Strategies for Neuroprotection in Multiple Sclerosis and the Role of Calcium

Calcium ions are vital for maintaining the physiological and biochemical processes inside cells. The central nervous system (CNS) is particularly dependent on calcium homeostasis and its dysregulation has been associated with several neurodegenerative disorders including Parkinson’s disease (PD), Alzheimer’s disease (AD) and Huntington’s disease (HD), as well as with multiple sclerosis (MS). Hence, the modulation of calcium influx into the cells and the targeting of calcium-mediated signaling pathways may present a promising therapeutic approach for these diseases. This review provides an overview on calcium channels in neurons and glial cells. Special emphasis is put on MS, a chronic autoimmune disease of the CNS. While the initial relapsing-remitting stage of MS can be treated effectively with immune modulatory and immunosuppressive drugs, the subsequent progressive stage has remained largely untreatable. Here we summarize several approaches that have been and are currently being tested for their neuroprotective capacities in MS and we discuss which role calcium could play in this regard.

Transient receptor potential ion-channel subfamily V member 4: a potential target for cancer treatment

The transient receptor potential ion-channel superfamily consists of nonselective cation channels located mostly on the plasma membranes of numerous animal cell types, which are closely related to sensory information transmission (e.g., vision, pain, and temperature perception), as well as regulation of intracellular Ca2+ balance and physiological activities of growth and development. Transient receptor potential ion channel subfamily V (TRPV) is one of the largest and most diverse subfamilies, including TRPV1-TRPV6 involved in the regulation of a variety of cellular functions. TRPV4 can be activated by various physical and chemical stimuli, such as heat, mechanical force, and phorbol ester derivatives participating in the maintenance of normal cellular functions. In recent years, the roles of TRPV4 in cell proliferation, differentiation, apoptosis, and migration have been extensively studied. Its abnormal expression has also been closely related to the onset and progression of multiple tumors, so TRPV4 may be a target for cancer diagnosis and treatment. In this review, we focused on the latest studies concerning the role of TRPV4 in tumorigenesis and the therapeutic potential. As evidenced by the effects on cancerogenesis, TRPV4 is a potential target for anticancer therapy.

Physiology of Oligodendroglia

Oligodendrocytes are the myelinating cells of the CNS, producing the insulating myelin sheath that facilitates rapid electrical conduction of axonal action potentials. Oligodendrocytes arise from oligodendrocyte progenitor cells (OPCs) under the control of multiple factors, including neurotransmitters and other neuron-derived factors. A significant population of OPCs persists in the adult CNS, where they are often referred to as NG2-glia, because they are identified by their expression of the NG2 chondroitin sulphate proteoglycan (CSPG4). In the adult brain, the primary function of NG2-glia is the life-long generation of oligodendrocytes to replace myelin lost through natural 'wear and tear' and pathology, as well as to provide new oligodendrocytes to myelinate new connections formed in response to new life experiences. NG2-glia contact synapses and respond to neurotransmitters and potassium released during neuronal transmission; to this end, NG2-glia (OPCs) express multiple neurotransmitter receptors and ion channels, with prominent roles being identified for glutamatergic signalling and potassium channels in oligodendrocyte differentiation. Myelinating oligodendrocytes also express a wide range of neurotransmitter receptors and ion channels, together with transporters and gap junctions; together, these have critical functions in cellular ion and water homeostasis, as well as metabolism, which is essential for maintaining myelin and axon integrity. An overriding theme is that oligodendrocyte function and myelination is not only essential for rapid axonal conduction, but is essential for learning and the long-term integrity of axons and neurones. Hence, myelination underpins cognitive function and the massive computing power of the human brain and myelin loss has devastating effects on CNS function. This chapter focuses on normal oligodendrocyte physiology.

TRPV4 Inhibition Improved Myelination and Reduced Glia Reactivity and Inflammation in a Cuprizone-Induced Mouse Model of Demyelination

The inhibition of demyelination and the promotion of remyelination are both considerable challenges in the therapeutic process for many central nervous system (CNS) diseases. Increasing evidence has demonstrated that neuroglial activation and neuroinflammation are responsible for myelin sheath damage during demyelinating disorders. 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 demyelination have remained unclear. Here, for the first time, we found that there was a significant increase in TRPV4 in the corpus callosum in a demyelinated mouse model induced by cuprizone (CPZ). RN-1734, a TRPV4-antagonist, clearly alleviated demyelination and inhibited glial activation and the production of tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) without altering the number of olig2-positive cells. In vitro, RN-1734 treatment clearly inhibited the influx of calcium and decreased the levels of IL-1β and TNF-α in lipopolysaccharide (LPS)-activated microglial cells by suppressing NF-κB P65 phosphorylation. Apoptosis of oligodendrocyte induced by LPS-activated microglia was also alleviated by RN-1734. The results suggest that activation of TRPV4 in microglia is involved in oligodendrocyte apoptosis through the activation of the NF-κB signaling pathway, thus revealing a new mechanism of CNS demyelination.

The role of TRP channels in white matter function and ischaemia

Transient receptor potential (TRP) proteins are a large family of tetrameric non-selective cation channels that are widely expressed in the grey and white matter of the CNS, and are increasingly considered as potential therapeutic targets in brain disorders. Here we briefly review the evidence for TRP channel expression in glial cells and their possible role in both glial cell physiology and stroke. Despite their contribution to important functions, our understanding of the roles of TRP channels in glia is still in its infancy. The evidence reviewed here indicates that further investigation is needed to determine whether TRP channel inhibition can decrease damage or increase repair in stroke and other diseases affecting the white matter.