Expression and cellular distribution of transient receptor potential vanilloid 4 in cortical tubers of the tuberous sclerosis complex

TRPV4 modulation participates in paraoxon-induced brain injury via NMDA and NLRP3 regulation

BACKGROUND

Organophosphorus pesticide poisoning can lead to severe brain damage, but the specific mechanisms involved are not fully understood. Our research aims to elucidate the function of the TRPV4 ion channel in the development of brain injury induced by paraoxon (POX).

METHODS

In vivo, we examined the survival rate, behavioral seizures, histopathological alterations, NMDA receptor phosphorylation, as well as the expression of the NLRP3-ASC-caspase-1 complex and downstream inflammatory factors in the POX poisoning model following intervention with the TRPV4 antagonist GSK2193874. In vitro, we investigated the effects of GSK2193874 on NMDA-induced inward current, cell viability, cell death rate, and Ca2+ accumulation in primary hippocampal neurons.

RESULTS

The treatment with the TRPV4 antagonist increased the survival rate, suppressed the status epilepticus, improved pathological damage, and reduced the phosphorylation level of NMDA receptors after POX exposure. Additionally, it inhibited the upregulation of NLRP3 inflammasome and inflammatory cytokines expression after POX exposure. Moreover, the TRPV4 antagonist corrected the NMDA-induced increase in inward current and cell death rate, decrease in cell viability, and Ca2+ accumulation.

CONCLUSION

TRPV4 participates in the mechanisms of brain injury induced by POX exposure through NMDA-mediated excitotoxicity and NLRP3-mediated inflammatory response.

Blockage of TRPV4 Downregulates the Nuclear Factor-Kappa B Signaling Pathway to Inhibit Inflammatory Responses and Neuronal Death in Mice with Pilocarpine-Induced Status Epilepticus

The blockage of transient receptor potential vanilloid 4 (TRPV4) inhibits inflammation and reduces hippocampal neuronal injury in a pilocarpine-induced mouse model of temporal lobe epilepsy. However, the underlying mechanisms remain largely unclear. NF-κB signaling pathway is responsible for the inflammation and neuronal injury during epilepsy. Here, we explored whether TRPV4 blockage could affect the NF-κB pathway in mice with pilocarpine-induced status epilepticus (PISE). Application of a TRPV4 antagonist markedly attenuated the PISE-induced increase in hippocampal HMGB1, TLR4, phospho (p)-IκK (p-IκK), and p-IκBα protein levels, as well as those of cytoplasmic p-NF-κB p65 (p-p65) and nuclear NF-κB p65 and p50; in contrast, the application of GSK1016790A, a TRPV4 agonist, showed similar changes to PISE mice. Administration of the TLR4 antagonist TAK-242 or the NF-κB pathway inhibitor BAY 11-7082 led to a noticeable reduction in the hippocampal protein levels of cleaved IL-1β, IL-6 and TNF, as well as those of cytoplasmic p-p65 and nuclear p65 and p50 in GSK1016790A-injected mice. Finally, administration of either TAK-242 or BAY 11-7082 greatly increased neuronal survival in hippocampal CA1 and CA2/3 regions in GSK1016790A-injected mice. Therefore, TRPV4 activation increases HMGB1 and TLR4 expression, leading to IκK and IκBα phosphorylation and, consequently, NF-κB activation and nuclear translocation. The resulting increase in pro-inflammatory cytokine production is responsible for TRPV4 activation-induced neuronal injury. We conclude that blocking TRPV4 can downregulate HMGB1/TLR4/IκK/κBα/NF-κB signaling following PISE onset, an effect that may underlie the anti-inflammatory response and neuroprotective ability of TRPV4 blockage in mice with PISE.

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.

Progress of clinical research studies on tuberous sclerosis complex-related epilepsy in China

Tuberous sclerosis complex (TSC) is an autosomal dominant neurocutaneous syndrome, with 75.6%-83.5% and 54.1% patients presenting with epilepsy and drug-resistant epilepsy (DRE), respectively. Clinical studies on TSC, particularly surgical interventions, have achieved rapid and substantial progress. The TSC-Task Force Committee of the China Association Against Epilepsy (CAAE-TFTSC) was founded in 2012, and annual academic conferences on the surgical treatment of TSC-related epilepsy have been held since 2013. 'China experts' consensus on surgical treatment of TSC-related epilepsy' was published in 2019. This review focuses on surgical treatment, including resective surgery, neuromodulations, corpus callosotomy and mini-invasive ablations, as well as studies on phenotype, genotype and anti-seizure therapies of mammalian target of rapamycin inhibitor, vigabatrin and ketogenic diet in patients with TSC-related DRE in China.

Activation of TRPV4 Induces Exocytosis and Ferroptosis in Human Melanoma Cells

TRPV4 (transient receptor potential vanilloid 4), a calcium permeable TRP ion channel, is known to play a key role in endocytosis. However, whether it contributes to exocytosis remains unclear. Here, we report that activation of TRPV4 induced massive exocytosis in both melanoma A375 cell and heterologous expression systems. We show here that, upon application of TRPV4-specific agonists, prominent vesicle priming from endoplasmic reticulum (ER) was observed, followed by morphological changes of mitochondrial crista may lead to cell ferroptosis. We further identified interactions between TRPV4 and folding/vesicle trafficking proteins, which were triggered by calcium entry through activated TRPV4. This interplay, in turn, enhanced TRPV4-mediated activation of folding and vesicle trafficking proteins to promote exocytosis. Our study revealed a signaling mechanism underlying stimulus-triggered exocytosis in melanoma and highlighted the role of cellular sensor TRPV4 ion channel in mediating ferroptosis.

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.

Involvement of TRPV4 in changes in rapidly inactivating potassium channels in the early stage of pilocarpine-induced status epilepticus in mice

The rapidly inactivating potassium current (I_A ) is important in controlling neuronal action potentials. Altered I_A function and K⁺ channel expression have been found in epilepsy, and activation of the transient receptor potential vanilloid 4 (TRPV4) channel is involved in epilepsy pathogenesis. This study examined whether TRPV4 affects Kv4.2 and K⁺ channel interacting protein (KCHIP) expression and I_A changes following pilocarpine-induced status epilepticus (PISE) in mice. Herein, hippocampal protein levels of Kv4.2 and KCHIP2 increased 3 h-3 d and decreased 7-30 d; that of KCHIP1 increased 3-24 h and decreased 3-30 d post-PISE. The TRPV4 antagonist HC-067047 attenuated the increased protein levels of Kv4.2 and KCHIP2 but not that of KCHIP1 post-PISE. The TRPV4 agonist GSK1016790A increased hippocampal protein levels of Kv4.2 and KCHIP2 but had no effect on KCHIP1 expression. HC-067047 attenuated the increased I_A in hippocampal pyramidal neurons 24 h and 3 d post-PISE. GSK1016790A increased I_A in hippocampal pyramidal neurons, shifting the voltage-dependent inactivation curve toward depolarization. The GSK1016790A-induced increase of I_A was blocked by protein kinase A and calcium/calmodulin-dependent kinase II antagonists but was unaffected by protein kinase C antagonists. We conclude that TRPV4 activation may be responsible for the increases of Kv4.2 and KCHIP2 expression in hippocampi and I_A in hippocampal pyramidal neurons in PISE mice, which are likely compensatory measures for hyperexcitability at the early stage of epilepsy.

TRPV4 Regulates Soman-Induced Status Epilepticus and Secondary Brain Injury via NMDA Receptor and NLRP3 Inflammasome

Nerve agents are used in civil wars and terrorist attacks, posing a threat to public safety. Acute exposure to nerve agents such as soman (GD) causes serious brain damage, leading to death due to intense seizures induced by acetylcholinesterase inhibition and neuronal injury resulting from increased excitatory amino-acid levels and neuroinflammation. However, data on the anticonvulsant and neuroprotective efficacies of currently-used countermeasures are limited. Here, we evaluated the potential effects of transient receptor vanilloid 4 (TRPV4) in the treatment of soman-induced status epilepticus (SE) and secondary brain injury. We demonstrated that TRPV4 expression was markedly up-regulated in rat hippocampus after soman-induced seizures. Administration of the TRPV4 antagonist GSK2193874 prior to soman exposure significantly decreased the mortality rate in rats and reduced SE intensity. TRPV4-knockout mice also showed lower incidence of seizures and higher survival rates than wild-type mice following soman exposure. Further in vivo and in vitro experiments demonstrated that blocking TRPV4 prevented NMDA receptor-mediated glutamate excitotoxicity. The protein levels of the NLRP3 inflammasome complex and its downstream cytokines IL-1β and IL-18 increased in soman-exposed rat hippocampus. However, TRPV4 inhibition or deletion markedly reversed the activation of the NLRP3 inflammasome pathway. In conclusion, our study suggests that the blockade of TRPV4 protects against soman exposure and reduces brain injury following SE by decreasing NMDA receptor-mediated excitotoxicity and NLRP3-mediated neuroinflammation. To our knowledge, this is the first study regarding the "dual-switch" function of TRPV4 in the treatment of soman intoxication.

Transient receptor potential vanilloid 4 activation inhibits the delayed rectifier potassium channels in hippocampal pyramidal neurons: An implication in pathological changes following pilocarpine-induced status epilepticus

Activation of transient receptor potential vanilloid 4 (TRPV4) can increase hippocampal neuronal excitability. TRPV4 has been reported to be involved in the pathogenesis of epilepsy. Voltage-gated potassium channels (VGPCs) play an important role in regulating neuronal excitability and abnormal VGPCs expression or function is related to epilepsy. Here, we examined the effect of TRPV4 activation on the delayed rectifier potassium current (I_K ) in hippocampal pyramidal neurons and on the Kv subunits expression in male mice. We also explored the role of TRPV4 in changes in Kv subunits expression in male mice following pilocarpine-induced status epilepticus (PISE). Application of TRPV4 agonists, GSK1016790A and 5,6-EET, markedly reduced I_K in hippocampal pyramidal neurons and shifted the voltage-dependent inactivation curve to the hyperpolarizing direction. GSK1016790A- and 5,6-EET-induced inhibition of I_K was blocked by TRPV4 specific antagonists, HC-067047 and RN1734. GSK1016790A-induced inhibition of I_K was markedly attenuated by calcium/calmodulin-dependent kinase II (CaMKII) antagonist. Application of GSK1016790A for up to 1 hr did not change the hippocampal protein levels of Kv1.1, Kv1.2, or Kv2.1. Intracerebroventricular injection of GSK1016790A for 3 d reduced the hippocampal protein levels of Kv1.2 and Kv2.1, leaving that of Kv1.1 unchanged. Kv1.2 and Kv2.1 protein levels as well as I_K reduced markedly in hippocampi on day 3 post PISE, which was significantly reversed by HC-067047. We conclude that activation of TRPV4 inhibits I_K in hippocampal pyramidal neurons, possibly by activating CaMKII. TRPV4-induced decrease in Kv1.2 and Kv2.1 expression and I_K may be involved in the pathological changes following PISE.

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.

Transient receptor potential vanilloid 4 is involved in the upregulation of connexin expression following pilocarpine-induced status epilepticus in mice

Epilepsy is characterized by spontaneous seizures. Changes in the expression of the connexins (Cxs) have been reported to be involved in epileptogenesis. It has previously been shown that the transient receptor potential vanilloid 4 (TRPV4) plays an important role in the modulation of neuronal excitability, and that application of a TRPV4 antagonist blocks hyperthermia-induced seizures. Accordingly, in the present study, we sought to explore whether TRPV4 is involved in the regulation of Cx expression following pilocarpine-induced status epilepticus (PISE) in mice. We observed that TRPV4 protein levels in hippocampi increased 3 h to 30 d following PISE, peaking 1-3 d after induction, and that pre-application of the TRPV4 antagonist HC-067047 increased the latency to develop SE induced by pilocarpine and reduced the success rate of PISE preparation. We demonstrated that Cx43 protein levels followed a time profile similar to that of TRPV4, and further showed that the increase in Cx43 protein levels on 3 d post-PISE was markedly attenuated by HC-067047. In contrast, the corresponding increase in Cx32 protein levels lagged substantially behind, and these levels were unaffected by HC-067047. Similarly, the TRPV4 agonist GSK1016790A increased the mRNA and protein levels of Cx43, but not those of Cx32. We thus conclude that the upregulation of Cx43 expression by TRPV4 may be involved in the pathophysiology of epilepsy.

Sensitization of TRPV1 receptors by TNF-α orchestrates the development of vincristine-induced pain

Vincristine is one of the most common anticancer drugs clinically employed in the treatment of various malignancies. A major side effect associated with vincristine is the development of neuropathic pain, which is not readily relieved by available analgesics. Although efforts have been made to identify the pathogenesis of vincristine-induced neuropathic pain, the mechanisms underlying its pathogenesis have not been fully elucidated. In the present study, a neuropathic pain model was established in Sprague-Dawley rats by intraperitoneal injection of vincristine sulfate. The results demonstrated that vincristine administration induced the upregulation of transient receptor potential cation channel subfamily V member 1 (TRPV1) protein expression and current density in dorsal root ganglion (DRG) nociceptive neurons. Consistently, inhibition of TRPV1 with capsazepine alleviated vincristine-induced mechanical allodynia and thermal hyperalgesia in rats. Furthermore, vincristine administration induced the upregulation of tumor necrosis factor (TNF)-α production in DRGs, and inhibition of TNF-α synthesis with thalidomide in vivo reversed TRPV1 protein expression, as well as pain hypersensitivity induced by vincristine in rats. The present results suggested that TNF-α could sensitize TRPV1 by promoting its expression, thus leading to mechanical allodynia and thermal hyperalgesia in vincristine-treated rats. Taken together, these findings may enhance our understanding of the pathophysiological mechanisms underlying vincristine-induced pain.