Involvement of TRPV4-NO-cGMP-PKG pathways in the development of thermal hyperalgesia following chronic compression of the dorsal root ganglion in rats

Lumbar foraminal stenosis was associated with back pain and leg pain: epidemiological evidence from a population-based cohort

OBJECTIVES

To determine the characteristics of lumbar foraminal stenosis (LFS) on magnetic resonance (MR) images and their association with back pain and radiating leg pain in a population-based sample of Chinese subjects.

METHODS

This study was an extension of the Hangzhou Lumbar Spine Study, a cross-sectional study focusing on back pain and lumbar spine MR imaging findings. Questionnaire data, including demographics, lifestyle, occupational exposures, back pain and radiating leg pain were included. On lumbar spine MR images, disc degeneration was assessed using Pfirrmann grade and Modic changes were evaluated. Using Lee's scale, the L3-S1 intervertebral foramina were evaluated, with grade 2-3 representing substantial LFS and grade 0-1 no LFS. Characteristics of LFS were noted, and associations of LFS with back pain and radiating leg pain were examined.

RESULTS

Among the 644 study subjects, 141 (21.9%) had at least one LFS, and its occurrence was associated with greater age (OR = 1.93 for each 10 years, p < 0.001). Substantial LFS was associated with the presence of back pain (OR = 1.92, p = 0.001) and the intensity of the worst back pain (Coef = 8.30, p < 0.001) over the past 12 months, and disabling back pain during their lifetime (OR = 2.25, p < 0.001). Substantial LFS was also associated with leg pain (OR = 14.27, p < 0.001), with a sensitivity of 75.7% for the presence of radiating leg pain and a specificity of 81.4%.

CONCLUSION

Substantial LFS on MR images was a common age-related degenerative phenotype in adults, and appears to be an independent risk factor for back pain and leg pain.

Transient Receptor Potential (TRP) Channels in Pain, Neuropsychiatric Disorders, and Epilepsy

Pharmacomodulation of membrane channels is an essential topic in the study of physiological conditions and disease status. Transient receptor potential (TRP) channels are one such family of nonselective cation channels that have an important influence. In mammals, TRP channels consist of seven subfamilies with a total of twenty-eight members. Evidence shows that TRP channels mediate cation transduction in neuronal signaling, but the full implication and potential therapeutic applications of this are not entirely clear. In this review, we aim to highlight several TRP channels which have been shown to mediate pain sensation, neuropsychiatric disorders, and epilepsy. Recent findings suggest that TRPM (melastatin), TRPV (vanilloid), and TRPC (canonical) are of particular relevance to these phenomena. The research reviewed in this paper validates these TRP channels as potential targets of future clinical treatment and offers patients hope for more effective care.

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.

TRPV4 Role in Neuropathic Pain Mechanisms in Rodents

Neuropathic pain is a chronic pain caused by a disease or damage to the somatosensory nervous system. The knowledge about the complete mechanisms is incomplete, but the role of oxidative compounds has been evaluated. In this context, we highlight the transient potential receptor vanilloid 4 (TRPV4), a non-selective cation channel, that can be activated by oxidated compounds. In clinical trials, the TRPV4 antagonist (GSK2798745) has been well-tolerated in healthy volunteers. The TRPV4 activation by oxidative compounds, such as hydrogen peroxide (H₂O₂) and nitric oxide (NO), has been researched in neuropathic pain models. Thus, the modulation of TRPV4 activation by decreasing oxidated compounds could represent a new pharmacological approach for neuropathic pain treatment. Most models evaluated the TRPV4 using knockout mice, antagonist or antisense treatments and detected mechanical allodynia, hyposmotic solution-induced nociception and heat hyperalgesia, but this channel is not involved in cold allodynia. Only H₂O₂ and NO were evaluated as TRPV4 agonists, so one possible target to reduce neuropathic pain should focus on reducing these compounds. Therefore, this review outlines how the TRPV4 channel represents an innovative target to tackle neuropathic pain signaling in models induced by trauma, surgery, chemotherapy, cancer, diabetes and alcohol intake.

Targeting the nitric oxide/cGMP signaling pathway to treat chronic pain

Nitric oxide (NO)/cyclic guanosine 3',5'-monophosphate (cGMP) signaling has been shown to act as a mediator involved in pain transmission and processing. In this review, we summarize and discuss the mechanisms of the NO/cGMP signaling pathway involved in chronic pain, including neuropathic pain, bone cancer pain, inflammatory pain, and morphine tolerance. The main process in the NO/cGMP signaling pathway in cells involves NO activating soluble guanylate cyclase, which leads to subsequent production of cGMP. cGMP then activates cGMP-dependent protein kinase (PKG), resulting in the activation of multiple targets such as the opening of ATP-sensitive K⁺ channels. The activation of NO/cGMP signaling in the spinal cord evidently induces upregulation of downstream molecules, as well as reactive astrogliosis and microglial polarization which participate in the process of chronic pain. In dorsal root ganglion neurons, natriuretic peptide binds to particulate guanylyl cyclase, generating and further activating the cGMP/PKG pathway, and it also contributes to the development of chronic pain. Upregulation of multiple receptors is involved in activation of the NO/cGMP signaling pathway in various pain models. Notably the NO/cGMP signaling pathway induces expression of downstream effectors, exerting both algesic and analgesic effects in neuropathic pain and inflammatory pain. These findings suggest that activation of NO/cGMP signaling plays a constituent role in the development of chronic pain, and this signaling pathway with dual effects is an interesting and promising target for chronic pain therapy.

The role of TRPV4 channels in cutaneous epithelia

Transient receptor potential vanilloid 4 (TRPV4) channels are multi-modally activated cation permeable channels that are expressed most organ tissues including the skin. TRPV4 is highly expressed in the skin and functions in skin resident cells such as epidermal keratinocytes, melanocytes, immune mast cells and macrophages, and cutaneous neurons. TRPV4 plays many crucial roles in skin homeostasis to affect an extensive range of processes such as temperature sensation, osmo-sensation, hair growth, cell apoptosis, skin barrier integrity, differentiation, nociception and itch. Since TRPV4 functions in a plenitude of pathological states, TRPV4 can become a versatile therapeutic target for diseases such as chronic pain, itch and skin cancer.

Piezo1 Is a Mechanosensor Channel in Central Nervous System Capillaries

Capillaries are equipped to sense neurovascular coupling agents released onto the outer wall of a capillary, translating these external signals into electrical/Ca2+ changes that play a crucial role in blood flow regulation and ensuring that neuronal demands are met. However, control mechanisms attributable to forces imposed onto the lumen are less clear. Here, we show that Piezo1 channels act as mechanosensors in central nervous system capillaries. Electrophysiological analyses confirmed expression and function of Piezo1 channels in brain cortical and retinal capillaries. Activation of Piezo1 channels evoked currents that were sensitive to endothelial cell-specific Piezo1 deletion. Using genetically encoded Ca2+ indicator mice and an ex vivo pressurized retina preparation, we found that activation of Piezo1 channels by mechanical forces triggered Ca2+ signals in capillary endothelial cells. Collectively, these findings indicate that Piezo1 channels are capillary mechanosensors that initiate crucial Ca2+ signals and could, therefore, have a profound impact on central nervous system blood flow control.

Transient Receptor Potential (TRP) and Thermoregulation in Animals: Structural Biology and Neurophysiological Aspects

This review presents and analyzes recent scientific findings on the structure, physiology, and neurotransmission mechanisms of transient receptor potential (TRP) and their function in the thermoregulation of mammals. The aim is to better understand the functionality of these receptors and their role in maintaining the temperature of animals, or those susceptible to thermal stress. The majority of peripheral receptors are TRP cation channels formed from transmembrane proteins that function as transductors through changes in the membrane potential. TRP are classified into seven families and two groups. The data gathered for this review include controversial aspects because we do not fully know the mechanisms that operate the opening and closing of the TRP gates. Deductions, however, suggest the intervention of mechanisms related to G protein-coupled receptors, dephosphorylation, and ligands. Several questions emerge from the review as well. For example, the future uses of these data for controlling thermoregulatory disorders and the invitation to researchers to conduct more extensive studies to broaden our understanding of these mechanisms and achieve substantial advances in controlling fever, hyperthermia, and hypothermia.

The Emerging Pro-Algesic Profile of Transient Receptor Potential Vanilloid Type 4

Transient receptor potential vanilloid type 4 (TRPV4) channels are Ca²⁺-permeable non-selective cation channels which mediate a wide range of physiological functions and are activated and modulated by a diverse array of stimuli. One of this ion channel's least discussed functions is in relation to the generation and maintenance of certain pain sensations. However, in the two decades which have elapsed since the identification of this ion channel, considerable data has emerged concerning its function in mediating pain sensations. TRPV4 is a mediator of mechanical hyperalgesia in the various contexts in which a mechanical stimulus, comprising trauma (at the macro-level) or discrete extracellular pressure or stress (at the micro-level), results in pain. TRPV4 is also recognised as constituting an essential component in mediating inflammatory pain. It also plays a role in relation to many forms of neuropathic-type pain, where it functions in mediating mechanical allodynia and hyperalgesia.Here, we review the role of TRPV4 in mediating pain sensations.

Role of TRPV4-P2X7 Pathway in Neuropathic Pain in Rats with Chronic Compression of the Dorsal Root Ganglion

Transient receptor potential vanilloid 4 (TRPV4) is a Ca2+-permeable non-selective cation channel that is involved in the development of neuropathic pain. P2X7 receptor (P2X7) belongs to a class of ATP-gated nonselective cation channels that plays an important role in neuropathic pain. Nevertheless, little is known about the interaction between them for neuropathic pain. In this paper, we investigated role of TRPV4-P2X7 pathway in neuropathic pain. We evaluated the effect of TRPV4-P2X7 pathway on neuropathic pain in a chronic compression of the dorsal root ganglion (DRG) (hereafter termed CCD) model. We analyzed the effect of P2X7 on mechanical and thermal hyperalgesia mediated by TRPV4 in CCD. Furthermore, we assessed the effect of TRPV4 on the expression of P2X7 and the release of IL-1β and IL-6 in DRG after CCD. We found that intraperitoneal injection of TRPV4 agonist GSK-1016790A led to a significant increase of mechanical and thermal hyperalgesia in CCD, which was partially suppressed by P2X7 blockade with antagonist Brilliant Blue G (BBG). Then, we further noticed that GSK-1016790A injection increased the P2X7 expression of CCD, which was decreased by TRPV4 blockade with antagonist RN-1734 and HC-067047. Furthermore, we also discovered that the expressions of IL-1β and IL-6 were upregulated by GSK-1016790A injection but reduced by RN-1734 and HC-067047. Our results provide evidence that P2X7 contributes to development of neuropathic pain mediated by TRPV4 in the CCD model, which may be the basis for treatment of neuropathic pain relief.

Identification of Key Genes and Pathways in Mouse Spinal Cord Involved in ddC-Induced Neuropathic Pain by Transcriptome Sequencing

Highly active antiretroviral therapy (HAART) works effectively in inhibiting HIV replication in patients. However, the use of nucleoside reverse transcriptase inhibitors (NRTIs) often causes side effects of neuropathic pain, and its mechanism remains to be elucidated. Therefore, we aim to explore the mechanism of NRTIs-induced neuropathic pain at the transcriptome level. C57BL/6 J mice were given intraperitoneal injection of zalcitabine (ddC) or saline (control) for 2 weeks, during which the mechanical pain threshold of the mice was detected by von Frey test. Then the L3~L5 spinal segments of the mice were isolated and subsequently used for RNA sequencing (RNA-seq) on the last day of treatment. The mechanical pain threshold of mice given ddC decreased significantly. Compared with the control group, ddC caused significant changes in the expression of 135 genes, of which 66 upregulated and 69 downregulated. Enrichment analysis showed that the functions of these genes are mainly enriched in regulation of transcription, multicellular organism development, and cell differentiation, and the pathway is mainly enriched in the cGMP-PKG signaling pathway and AMPK signaling pathway. Furthermore, key genes such as Gabrd, Kcnd3, Npcd, Insr, Lypd6, Scd2, and Mef2d were also identified. These may serve as drug targets for the prevention or treatment of NRTI-induced neuropathic pain.

Role of Transient Receptor Potential Vanilloid 4 Channel in Skin Physiology and Pathology

Transient receptor potential vanilloid 4 (TRPV4) channel responds to temperature, as well as various mechanical and chemical stimuli. This non-selective cation channel is expressed in several organs, including the blood vessels, kidneys, oesophagus and skin. In the skin, TRPV4 channel is present in various cell types such as keratinocytes, melanocytes and sensory neurons, as well as immune and inflammatory cells, and engages in several physiological actions, from skin homeostasis to sensation. In addition, there is substantial evidence implicating dysfunctional TRPV4 channel—in the form of either deficient or excessive channel activity—in pathological cutaneous conditions such as skin barrier compromise, pruritus, pain, skin inflammation and carcinogenesis. These varied functions, combined with the fact that TRPV4 channel owns pharmacologically-accessible sites, make this channel an attractive therapeutic target for skin disorders. In this review, we summarize the different physiological and pathophysiological effects of TRPV4 in the skin.

Sini-San Regulates the NO-cGMP-PKG Pathway in the Spinal Dorsal Horn in a Modified Rat Model of Functional Dyspepsia

The present study investigated the effect of Chinese medicine Sini-San (SNS) on visceral hypersensitivity in a rat model of functional dyspepsia (FD), and it explored related underlying mechanisms. The rat model of FD was developed by combining neonatal iodoacetamide (IA) treatment and adult tail-clamping. After SNS treatment, the behavior and electromyographic testing were performed to evaluate the visceromotor responses of rats to gastric distention. Immunofluorescence was used to detect the distribution of iNOS-positive cells in the spinal dorsal horn, while the real-time quantitative PCR and western blot were used for detection of the gene expression of c-fos, iNOS, and GABAb and protein levels of iNOS and GABAb in the spinal dorsal horn, respectively. The protein concentration of cGMP and PKG proteins in the spinal dorsal horn were quantified by enzyme-linked immunosorbent assay. In this study, SNS treatment significantly reduced the behavioral score and electromyographic response to graded intragastric distension pressure. The middle-dose of SNS treatment significantly reduced the distribution of iNOS-positive cells in the spinal dorsal horn of FD model rats. The gene expression of c-fos, iNOS, and GABAb and the protein contents of iNOS, GABAb, cGMP, and PKG in the spinal dorsal horn of FD model rats were restored to a normal level by middle-dose of SNS treatment. Our results suggest that Sini-San may alleviate the visceral hypersensitivity in FD model rats via regulation of the NO/cGMP/PKG pathway in the spinal dorsal horn.

Distinct functions of soluble guanylyl cyclase isoforms NO-GC1 and NO-GC2 in inflammatory and neuropathic pain processing

A large body of evidence indicates that nitric oxide (NO)/cGMP signaling essentially contributes to the processing of chronic pain. In general, NO-induced cGMP formation is catalyzed by 2 isoforms of guanylyl cyclase, NO-sensitive guanylyl cyclase 1 (NO-GC1) and 2 (NO-GC2). However, the specific functions of the 2 isoforms in pain processing remain elusive. Here, we investigated the distribution of NO-GC1 and NO-GC2 in the spinal cord and dorsal root ganglia, and we characterized the behavior of mice lacking either isoform in animal models of pain. Using immunohistochemistry and in situ hybridization, we demonstrate that both isoforms are localized to interneurons in the spinal dorsal horn with NO-GC1 being enriched in inhibitory interneurons. In dorsal root ganglia, the distribution of NO-GC1 and NO-GC2 is restricted to non-neuronal cells with NO-GC2 being the major isoform in satellite glial cells. Mice lacking NO-GC1 demonstrated reduced hypersensitivity in models of neuropathic pain, whereas their behavior in models of inflammatory pain was normal. By contrast, mice lacking NO-GC2 exhibited increased hypersensitivity in models of inflammatory pain, but their neuropathic pain behavior was unaltered. Cre-mediated deletion of NO-GC1 or NO-GC2 in spinal dorsal horn neurons recapitulated the behavioral phenotypes observed in the global knockout. Together, these results indicate that cGMP produced by NO-GC1 or NO-GC2 in spinal dorsal horn neurons exert distinct, and partly opposing, functions in chronic pain processing.

Cyclic nucleotide signaling in sensory neuron hyperexcitability and chronic pain after nerve injury

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Activation of cAMP-PKA and cGMP-PKG pathways contributes to injury-induced sensory neuron hyperexcitability.

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Activation of cAMP and cGMP contributes to the development of bone cancer pain.

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PAR2 activation mediates injury-induced cAMP-dependent sensory neuron hyperexcitability.

The cyclic nucleotide signaling, including cAMP-PKA and cGMP-PKG pathways, has been well known to play critical roles in regulating cellular growth, metabolism and many other intracellular processes. In recent years, more and more studies have uncovered the roles of cAMP and cGMP in the nervous system. The cAMP and cGMP signaling mediates chronic pain induced by different forms of injury and stress. Here we summarize the roles of cAMP-PKA and cGMP-PKG signaling pathways in the pathogenesis of chronic pain after nerve injury. In addition, acute dissociation and chronic compression of the dorsal root ganglion (DRG) neurons, respectively, leads to neural hyperexcitability possibly through PAR2 activation-dependent activation of cAMP-PKA pathway. Clinically, radiotherapy can effectively alleviate bone cancer pain at least partly through inhibiting the cancer cell-induced activation of cAMP-PKA pathway. Roles of cyclic nucleotide signaling in neuropathic and inflammatory pain are also seen in many other animal models and are involved in many pro-nociceptive mechanisms including the activation of hyperpolarization-activated cyclic nucleotide (HCN)-modulated ion channels and the exchange proteins directly activated by cAMP (EPAC). Further understanding the roles of cAMP and cGMP signaling in the pathogenesis of chronic pain is theoretically significant and clinically valuable for treatment of chronic pain.

TRPV4: a Sensor for Homeostasis and Pathological Events in the CNS

Transient receptor potential vanilloid type 4 (TRPV4) was originally described as a calcium-permeable nonselective cation channel. TRPV4 is now recognized as a polymodal ionotropic receptor: it is a broadly expressed, nonselective cation channel (permeable to calcium, potassium, magnesium, and sodium) that plays an important role in a multitude of physiological processes. TRPV4 is involved in maintaining homeostasis, serves as an osmosensor and thermosensor, can be activated directly by endogenous or exogenous chemical stimuli, and can be activated or sensitized indirectly via intracellular signaling pathways. Additionally, TRPV4 is upregulated in a variety of pathological conditions. In this review, we focus on the role of TRPV4 in mediating homeostasis and pathological events in the central nervous system (CNS). This review is composed of three parts. Section 1 describes the role of TRPV4 in maintaining homeostatic processes, including the volume of body water, ionic concentrations, volume, and the temperature. Section 2 describes the effects of activation and inhibition of TRPV4 in the CNS. Section 3 focuses on the role of TRPV4 during pathological events in CNS.

Regulation of Pain and Itch by TRP Channels

Nociception is an important physiological process that detects harmful signals and results in pain perception. In this review, we discuss important experimental evidence involving some TRP ion channels as molecular sensors of chemical, thermal, and mechanical noxious stimuli to evoke the pain and itch sensations. Among them are the TRPA1 channel, members of the vanilloid subfamily (TRPV1, TRPV3, and TRPV4), and finally members of the melastatin group (TRPM2, TRPM3, and TRPM8). Given that pain and itch are pro-survival, evolutionarily-honed protective mechanisms, care has to be exercised when developing inhibitory/modulatory compounds targeting specific pain/itch-TRPs so that physiological protective mechanisms are not disabled to a degree that stimulus-mediated injury can occur. Such events have impeded the development of safe and effective TRPV1-modulating compounds and have diverted substantial resources. A beneficial outcome can be readily accomplished via simple dosing strategies, and also by incorporating medicinal chemistry design features during compound design and synthesis. Beyond clinical use, where compounds that target more than one channel might have a place and possibly have advantageous features, highly specific and high-potency compounds will be helpful in mechanistic discovery at the structure-function level.

A Functional Kinase Short Interfering Ribonucleic Acid Screen Using Protease-Activated Receptor 2-Dependent Opening of Transient Receptor Potential Vanilloid-4

Protease-activated receptor 2 (PAR₂) is a proinflammatory G-protein coupled receptor (GPCR) that is activated by inflammatory proteases, and its activation initiates signaling pathways that modulate the nonselective cation channel transient receptor potential vanilloid-4 (TRPV4). PAR₂-dependent opening of TRPV4 has been attributed to kinase activation, but the identity of the responsible enzymes is unknown. Deciphering the signaling pathways involved in the PAR₂-dependent opening of TRPV4 may yield new targets for pain treatment. This study has identified specific kinases that are involved in opening TRPV4, using a selective screen of short interfering ribonucleic acid (siRNA) SMARTpools, which individually targeted all human kinases, in human embryonic kidney 293 (HEK293) cells that stably express inducible TRPV4. This screen is unique because it uses a real-time assay measuring intracellular calcium with Fura-2AM dye. From the primary screen, subsequent confirmation screen, and on-target messenger ribonucleic acid expression analysis, we identified two kinases as crucial to the PAR₂-dependent opening of TRPV4 in HEK293 cells, mitogen-activated protein kinase 13 and with no lysine kinase 4. In conclusion, this study describes a powerful new application of siRNA knockdown to identity signaling molecules that are responsible for the PAR₂-dependent opening of TRPV4, which will help elucidate this signaling process.

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

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

TRPV4: Molecular Conductor of a Diverse Orchestra

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

The NO-cGMP-PKG signal transduction pathway is involved in the analgesic effect of early hyperbaric oxygen treatment of neuropathic pain

Background

Hyperbaric oxygen (HBO) has the potential to relieve neuropathic pain. The purpose of this study was to determine whether the NO-cGMP-PKG signaling pathway is involved in the analgesic effects of early hyperbaric oxygen treatment of neuropathic pain in rats.

Methods

Rats were randomly grouped for establishment of chronic constriction injury (CCI) models. Intrathecal catheters were inserted and 2.5ATA HBO therapy was administered from day 1 post-surgery for 60 minutes daily, continuously for 5 days; menstruum NS, DMSO, NO synthase(NOS) nonspecific inhibitor (L-NAME), soluble guanylyl cyclase(sGC) inhibitor (ODQ) and protein kinase G(PKG) inhibitor (KT5823) were administered intrathecally 30 minutes prior to HBO therapy. Pain-related behaviors in rats were observed at specific time points. Western blot and real-time RT-PCR were used to observe the expressions of PKG1 mRNA and protein in the spinal dorsal horn.

Results

Compared with the CCI group, HBO could significantly relieve mechanical and thermal hyperalgesia in rats. After intrathecal administration of L-NAME, ODQ and KT5823, effects of HBO on relieving hyperalgesia in rats were reversed (P < 0.05 vs. HBO), and expression of PKG1 mRNA and protein decreased in the spinal dorsal horn of the animals (P < 0.05 vs. HBO).

Conclusions

Early HBO therapy could significantly improve symptoms of hyperalgesia of neuropathic pain in rats, possibly via activation of the NO-cGMP-PKG signaling transduction pathway.

TRP Channels in Skin Biology and Pathophysiology

Ion channels of the Transient Receptor Potential (TRP) family mediate the influx of monovalent and/or divalent cations into cells in response to a host of chemical or physical stimuli. In the skin, TRP channels are expressed in many cell types, including keratinocytes, sensory neurons, melanocytes, and immune/inflammatory cells. Within these diverse cell types, TRP channels participate in physiological processes ranging from sensation to skin homeostasis. In addition, there is a growing body of evidence implicating abnormal TRP channel function, as a product of excessive or deficient channel activity, in pathological skin conditions such as chronic pain and itch, dermatitis, vitiligo, alopecia, wound healing, skin carcinogenesis, and skin barrier compromise. These diverse functions, coupled with the fact that many TRP channels possess pharmacologically accessible sites, make this family of proteins appealing therapeutic targets for skin disorders.

MAPK Pathways Are Involved in Neuropathic Pain in Rats with Chronic Compression of the Dorsal Root Ganglion

The aim of the present study was to investigate whether the MAPK pathways were involved in the mechanism of neuropathic pain in rats with chronic compression of the dorsal root ganglion. We determined the paw withdrawal mechanical threshold (PWMT) of rats before and after CCD surgery and then after p38, JNK, or ERK inhibitors administration. Western blotting, RT-PCR, and immunofluorescence of dorsal root ganglia were performed to investigate the protein and mRNA level of MAPKs and also the alternation in distributions of positive neurons in dorsal root ganglia. Intrathecal administration of MAPKs inhibitors, SB203580 (p38 inhibitor), SP600125 (JNK inhibitor), and U0126 (ERK inhibitor), resulted in a partial reduction in CCD-induced mechanical allodynia. The reduction of allodynia was associated with significant depression in the level of both MAPKs mRNA and protein expression in CCD rats and also associated with the decreased ratios of large size MAPKs positive neurons in dorsal root ganglia. In conclusion, the specific inhibitors of MAPKs contributed to the attenuation of mechanical allodynia in CCD rats and the large size MAPKs positive neurons in dorsal root ganglia were crucial.

Transient Receptor Potential Channel and Interleukin-17A Involvement in LTTL Gel Inhibition of Bone Cancer Pain in a Rat Model

Cancer pain management is a challenge for which Chinese herbal medicine might be useful. To study the spinal mechanisms of the Chinese medicated gel Long-Teng-Tong-Luo (LTTL), a 7-herb compound, on bone cancer pain, a bone cancer pain model was made by inoculating the tibias of female rats with Walker 256 cells. LTTL gel or inert gel, 0.5 g/cm(2)/d, was applied to the skin of tumor-bearing tibias for 21 days beginning a day after the inoculation. Mechanical threshold and paw withdrawal latency to thermal stimulation was measured. Transient receptor potential (TRP) cation channels in lumbar dorsal root ganglia (DRG) were immunostained and counted, and lumbar spinal cord interleukin-17A (IL-17A) was measured with real-time polymerase chain reaction and enzyme-linked immunosorbent assay. TRP antagonists and interleukin (IL)-17A antibodies were intrathecally administered to determine their effects on bone cancer pain. The gel significantly (P < .05) alleviated cancer-induced mechanical allodynia and thermal hyperalgesia and inhibited cancer-enhanced expression of IL-17A in spinal astrocytes and the TRP subfamily members V1, A1, and V4 in lumbar DRG. Intrathecal TRP antagonists at 10 µg significantly (P < .05) attenuated mechanical allodynia, thermal hyperalgesia, and IL-17A expression, indicating that TRP channels facilitate spinal IL-17 expression and cancer pain. IL-17A antibodies inhibited cancer pain, suggesting that IL-17A promotes such pain. The data show that LTTL gel inhibits cancer pain, and this might be accounted for by the decrease in expression of DRG TRP channels and spinal astrocyte IL-17A.

Transient receptor potential vanilloid 4 inhibits mouse colonic motility by activating NO-dependent enteric neurotransmission

Recent studies implicate TRPV4 receptors in visceral pain signaling and intestinal inflammation. Our aim was to evaluate the role of TRPV4 in the control of gastrointestinal (GI) motility and to establish the underlying mechanisms. We used immunohistochemistry and PCR to study TRPV4 expression in the GI tract. The effect of TRPV4 activation on GI motility was characterized using in vitro and in vivo motility assays. Calcium and nitric oxide (NO) imaging were performed to study the intracellular signaling pathways. Finally, TRPV4 expression was examined in the colon of healthy human subjects. We demonstrated that TRPV4 can be found on myenteric neurons of the colon and is co-localized with NO synthase (NOS-1). In vitro, the TRPV4 agonist GSK1016790A reduced colonic contractility and increased inhibitory neurotransmission. In vivo, TRPV4 activation slowed GI motility and reduced stool production in mouse models mimicking pathophysiological conditions. We also showed that TRPV4 activation inhibited GI motility by reducing NO-dependent Ca(2+) release from enteric neurons. In conclusion, TRPV4 is involved in the regulation of GI motility in health and disease.

KEY MESSAGES

• Recent studies implicate TRPV4 in pain signaling and intestinal inflammation. • Our aim was to characterize the role of TRPV4 in the control of GI motility. • We found that TRPV4 activation reduced colonic contractility. • Our studies also showed altered TRPV4 mRNA expression in IBS-C patients. • TRPV4 may be a novel pharmacological target in functional GI diseases.

Analgesic Effect of Electroacupuncture in a Mouse Fibromyalgia Model: Roles of TRPV1, TRPV4, and pERK

Fibromyalgia (FM) is among the most common chronic pain syndromes encountered in clinical practice, but there is limited understanding of FM pathogenesis. We examined the contribution of transient receptor potential vanilloid 1 (TRPV1) and TRPV4 channels to chronic pain in the repeated acid injection mouse model of FM and the potential therapeutic efficacy of electroacupuncture. Electroacupuncture (EA) at the bilateral Zusanli (ST36) acupoint reduced the long-lasting mechanical hyperalgesia induced by repeated acid saline (pH 4) injection in mouse hindpaw. Isolated L5 dorsal root ganglion (DRG) neurons from FM model mice (FM group) were hyperexcitable, an effect reversed by EA pretreatment (FM + EA group). The increase in mechanical hyperalgesia was also accompanied by upregulation of TRPV1 expression and phosphoactivation of extracellular signal regulated kinase (pERK) in the DRG, whereas DRG expression levels of TRPV4, p-p38, and p-JNK were unaltered. Blockade of TRPV1, which was achieved using TRPV1 knockout mice or via antagonist injection, and pERK suppressed development of FM-like pain. Both TRPV1 and TRPV4 protein expression levels were increased in the spinal cord (SC) of model mice, and EA at the ST36 acupoint decreased overexpression. This study strongly suggests that DRG TRPV1 overexpression and pERK signaling, as well as SC TRPV1 and TRPV4 overexpression, mediate hyperalgesia in a mouse FM pain model. The therapeutic efficacy of EA may result from the reversal of these changes in pain transmission pathways.

TRPV4 activates autonomic and behavioural warmth-defence responses in Wistar rats

AIM

In this study, we aimed at investigating the involvement of the warmth-sensitive channel - TRPV4 (in vitro sensitive to temperatures in the range of approx. 24-34 °C) - on the thermoregulatory mechanisms in rats.

METHODS

We treated rats with a chemical selective agonist (RN-1747) and two antagonists (RN-1734 and HC-067047) of the TRPV4 channel and measured core body temperature, metabolism, heat loss index and preferred ambient temperature.

RESULTS

Our data revealed that chemical activation of TRPV4 channels by topical application of RN-1747 on the skin leads to hypothermia and this effect was blocked by the pre-treatment with the selective antagonist of this channel. Intracerebroventricular treatment with RN-1747 did not cause hypothermia, indicating that the observed response was indeed due to activation of TRPV4 channels in the periphery. Intravenous blockade of this channel with HC-067047 caused an increase in core body temperature at ambient temperature of 26 and 30 °C, but not at 22 and 32 °C. At 26 °C, HC-067047-induced hyperthermia was accompanied by increase in oxygen consumption (an index of thermogenesis), while chemical stimulation of TRPV4 increased tail heat loss, indicating that these two autonomic thermoeffectors in the rat are modulated through TRPV4 channels. Furthermore, rats chemically stimulated with TRPV4 agonist choose colder ambient temperatures and cold-seeking behaviour after thermal stimulation (28-31 °C) was inhibited by TRPV4 antagonist.

CONCLUSION

Our results suggest, for the first time, that TRPV4 channel is involved in the recruitment of behavioural and autonomic warmth-defence responses to regulate core body temperature.

Ca(2+) influx mediates the TRPV4-NO pathway in neuropathic hyperalgesia following chronic compression of the dorsal root ganglion

Chronic compression of the dorsal root ganglion (DRG) (CCD) in rats is a typical model of neuropathic pain. TRPV4 contributed to mechanical allodynia induced by the CCD model. Our previous study demonstrated that TRPV4 enhances neuropathic hyperalgesia through a NO-cGMP-PKG cascade. However, the underlying mechanism(s) is still largely unknown. Therefore, the aim of the present study was to test whether TRPV4-mediated Ca(2+) influx is involved in the TRPV4-NO pathway. Regulation of intracellular calcium concentration by intrathecal injection of TRPV4-targeted siRNA significantly decreased the behavioural hyperalgesia, NF-κB activity, and NO content in CCD rats. Intraperitoneal (i.p.) injection of mibefradil significantly induced dose-dependent increases in the paw withdrawal latency (PWL) and mechanical withdrawal thresholds (MWT), as well as decreases in NF-κB activity and NO content in DRG of CCD rats. Moreover, pre-treatment with 4α-PDD attenuated the suppressive effects of mibefradil on CCD-induced neuropathic hyperalgesia, NF-κB activity, and NO production. The data showed that TRPV4-mediated Ca(2+) influx might be engaged in the TRPV4-NO pathway in neuropathic hyperalgesia in the CCD model.

Oxidant-induced activation of cGMP-dependent protein kinase Iα mediates neuropathic pain after peripheral nerve injury

AIMS

Emerging lines of evidence indicate that oxidants such as hydrogen peroxide exert specific signaling functions during the processing of chronic pain. However, the mechanisms by which oxidants regulate pain processing in vivo remain poorly understood. Here, we investigated whether cyclic guanosine monophosphate (cGMP)-dependent protein kinase Iα (cGKIα), which can be activated by oxidants independently of cGMP, serves as a primary redox target during pain processing.

RESULTS

After peripheral nerve injury, oxidant-induced cGKIα activation is increased in dorsal root ganglia of mice. Knock-in (KI) mice in which cGKIα cannot transduce oxidant signals demonstrated reduced neuropathic pain behaviors after peripheral nerve injury, and reduced pain behaviors after intrathecal delivery of oxidants. In contrast, acute nociceptive, inflammatory, and cGMP-induced pain behaviors were not impaired in these mice.

INNOVATION

Studying cGKIα KI mice, we provide the first evidence that oxidants activate cGKIα in sensory neurons after peripheral nerve injury in vivo.

CONCLUSION

Our results suggest that oxidant-induced activation of cGKIα specifically contributes to neuropathic pain processing, and that prevention of cGKIα redox activation could be a potential novel strategy to manage neuropathic pain.

Remote intrathecal morphine preconditioning confers cardioprotection via spinal cord nitric oxide/cyclic guanosine monophosphate/protein kinase G pathway

BACKGROUND

Remote intrathecal morphine preconditioning (RMPC) induces cardioprotection, but the underlying mechanisms of this effect is unknown. The aim of this study was to investigate the role of spinal cord nitric oxide/cyclic guanosine monophosphate/protein kinase G (NO/cGMP/PKG) signal pathway in the cardioprotection of RMPC in rats.

MATERIALS AND METHODS

Anesthetized, open chest, male Sprague-Dawley rats were assigned to one of eight treatment groups 3 d after intrathecal catheter placement. Before ischemia and reperfusion, RMPC received intrathecal morphine (3 μg/kg) by three cycles of 5-min infusions interspersed with 5-min infusion free periods. Intrathecally administrated a nonspecific nitric oxide synthase (NOS) inhibitor Nω-Nitro-L-arginine methyl ester (30 nmol), a specific guanylate cyclase inhibitor oxadiazolo [4,3-a] quinoxalin-1-one (11 nmol) and PKG inhibitor KT-5823 (20 pmol) 10 min before RMPC was used to evaluate the role of NO/cGMP/PKG of spinal cord. Ischemia and reperfusion injury were then induced by 30 min of left coronary artery occlusion, followed by 120 min of reperfusion. Infarct size, as a percentage of the area at risk, was determined by 2,3,5-triphenyltetrazolium staining. The content of cyclic guanosine monophosphate in the thoracic spinal cord was determined by radioimmunity protocol; the contents of nitric oxide and activity of NOS in the thoracic spinal cord were determined by nitrate reductase reduction and colorimetric methods; the expression of neuronal NOS (nNOS) and PKG in the thoracic spinal cord were determined by immunohistochemical and Western blotting method; the expression of nNOS messenger RNA was determined by reverse transcription-polymerase chain reaction method.

RESULTS

RMPC group markedly reduced the infarct size compared with the control group. However, the cardioprotection of RMPC could be abolished by pretreatment with Nω-Nitro-L-arginine methyl ester, Oxadiazolo [4,3-a] quinoxalin-1-one, and KT-5823. RMPC enhanced nitric oxide , NOS, and cyclic guanosine monophosphate levels in the spinal cord. Meanwhile, RMPC increased PKG and nNOS protein or messenger RNA expression in the spinal cord.

CONCLUSIONS

Spinal cord NO/cGMP/PKG signaling pathway mediates RMPC-induced cardioprotective effect.

Role of colchicine-induced microtubule depolymerization in hyperalgesia via TRPV4 in rats with chronic compression of the dorsal root ganglion

The aim of this study is to investigate the effect of microtubule depolymerization by colchicine on hyperalgesia mediated by transient receptor potential vanilloid 4 (TRPV4) in a neuropathic pain model of chronic compression of the dorsal root ganglion (DRG) (hereafter termed CCD) in rat. Intrathecal administration of microtubule-depolymerizing agent, colchicine, attenuated the activated effect of 4alpha-phorbol 12, 13-didecanoate (4alpha-PDD, TRPV4 specific agonist) on mechanical and thermal hyperalgesia in CCD rats. This observation is in agreement with our in vitro experiments with DRG cells that showed a significant attenuation of 4alpha-PDD-activated Ca(2+)-influx and substance P (SP) release with the colchicine treatment. We conclude that microtubule depolymerization by colchicine can regulate pain sensitivity by depressing the hyperalgesia mediated by TRPV4.

TRPV4 and the regulation of vascular tone

Recent studies have introduced the importance of transient receptor potential vanilloid subtype 4 (TRPV4) channels in the regulation of vascular tone. TRPV4 channels are expressed in both endothelium and vascular smooth muscle cells and can be activated by numerous stimuli including mechanical (eg, shear stress, cell swelling, and heat) and chemical (eg, epoxyeicosatrienoic acids, endocannabinoids, and 4α-phorbol esters). In the brain, TRPV4 channels are primarily localized to astrocytic endfeet processes, which wrap around blood vessels. Thus, TRPV4 channels are strategically localized to sense hemodynamic changes and contribute to the regulation of vascular tone. TRPV4 channel activation leads to smooth muscle cell hyperpolarization and vasodilation. Here, we review recent findings on the cellular mechanisms underlying TRPV4-mediated vasodilation; TRPV4 channel interaction with other proteins including transient receptor potential channel 1, small conductance (K(Ca)2.3), and large conductance (K(Ca)1.1) calcium-activated potassium-selective channels; and the importance of caveolin-rich domains for these interactions to take place.

A genetically engineered thermally responsive sustained release curcumin depot to treat neuroinflammation

Radiculopathy, a painful neuroinflammation that can accompany intervertebral disc herniation, is associated with locally increased levels of the pro-inflammatory cytokine tumor necrosis factor alpha (TNFα). Systemic administration of TNF antagonists for radiculopathy in the clinic has shown mixed results, and there is growing interest in the local delivery of anti-inflammatory drugs to treat this pathology as well as similar inflammatory events of peripheral nerve injury. Curcumin, a known antagonist of TNFα in multiple cell types and tissues, was chemically modified and conjugated to a thermally responsive elastin-like polypeptide (ELP) to create an injectable depot for sustained, local delivery of curcumin to treat neuroinflammation. ELPs are biopolymers capable of thermally-triggered in situ depot formation that have been successfully employed as drug carriers and biomaterials in several applications. ELP-curcumin conjugates were shown to display high drug loading, rapidly release curcumin in vitro via degradable carbamate bonds, and retain in vitro bioactivity against TNFα-induced cytotoxicity and monocyte activation with IC50 only two-fold higher than curcumin. When injected proximal to the sciatic nerve in mice via intramuscular (i.m.) injection, ELP-curcumin conjugates underwent a thermally triggered soluble-insoluble phase transition, leading to in situ formation of a depot that released curcumin over 4days post-injection and decreased plasma AUC 7-fold.

Astrocyte regulation of cerebral vascular tone

Cerebral blood flow is controlled by two crucial processes, cerebral autoregulation (CA) and neurovascular coupling (NVC) or functional hyperemia. Whereas CA ensures constant blood flow over a wide range of systemic pressures, NVC ensures rapid spatial and temporal increases in cerebral blood flow in response to neuronal activation. The focus of this review is to discuss the cellular mechanisms by which astrocytes contribute to the regulation of vascular tone in terms of their participation in NVC and, to a lesser extent, CA. We discuss evidence for the various signaling modalities by which astrocytic activation leads to vasodilation and vasoconstriction of parenchymal arterioles. Moreover, we provide a rationale for the contribution of astrocytes to pressure-induced increases in vascular tone via the vasoconstrictor 20-HETE (a downstream metabolite of arachidonic acid). Along these lines, we highlight the importance of the transient receptor potential channel of the vanilloid family (TRPV4) as a key molecular determinant in the regulation of vascular tone in cerebral arterioles. Finally, we discuss current advances in the technical tools available to study NVC mechanisms in the brain as it relates to the participation of astrocytes.

Human skeletal dysplasia caused by a constitutive activated transient receptor potential vanilloid 4 (TRPV4) cation channel mutation

The transient receptor potential vanilloid 4 (TRPV4) cation channel, a member of the TRP vanilloid subfamily, is expressed in a broad range of tissues where it participates in the generation of Ca²⁺ signals and/or depolarization of the membrane potential. Regulation of TRPV4 abundance at the cell surface is critical for osmo- and mechanotransduction. Defects in TRPV4 are the cause of several human diseases, including brachyolmia type 3 (MIM:113500) (also known as brachyrachia or spondylometaphyseal dysplasia Kozlowski type [MIM:118452]), and metatropic dysplasia (MIM:156530) (also called metatropic dwarfism or parastremmatic dwarfism [MIM:168400]). These bone dysplasia mutants are characterized by severe dwarfism, kyphoscoliosis, distortion and bowing of the extremities, and contractures of the large joints. These diseases are characterized by a combination of decreased bone density, bowing of the long bones, platyspondyly, and striking irregularities of endochondral ossification with areas of calcific stippling and streaking in radiolucent epiphyses, metaphyses, and apophyses. In this review, we discuss the potential effect of the mutation on the regulation of TRPV4 functions, which are related to human diseases through deviated function. In particular, we emphasize how the constitutive active TRPV4 mutant affects endochondral ossification with a reduced number of hypertrophic chondrocytes and the presence of cartilage islands within the zone of primary mineralization. In addition, we summarize current knowledge about the role of TRPV4 in the pathogenesis of several diseases.

Attenuation of TRPV1 and TRPV4 Expression and Function in Mouse Inflammatory Pain Models Using Electroacupuncture

Although pain is a major human affliction, our understanding of pain mechanisms is limited. TRPV1 (transient receptor potential vanilloid subtype 1) and TRPV4 are two crucial receptors involved in inflammatory pain, but their roles in EA- (electroacupuncture-) mediated analgesia are unknown. We injected mice with carrageenan (carra) or a complete Freund's adjuvant (CFA) to model inflammatory pain and investigated the analgesic effect of EA using animal behavior tests, immunostaining, Western blotting, and a whole-cell recording technique. The inflammatory pain model mice developed both mechanical and thermal hyperalgesia. Notably, EA at the ST36 acupoint reversed these phenomena, indicating its curative effect in inflammatory pain. The protein levels of TRPV1 and TRPV4 in DRG (dorsal root ganglion) neurons were both increased at day 4 after the initiation of inflammatory pain and were attenuated by EA, as demonstrated by immunostaining and Western blot analysis. We verified DRG electrophysiological properties to confirm that EA ameliorated peripheral nerve hyperexcitation. Our results indicated that the AP (action potential) threshold, rise time, and fall time, and the percentage and amplitude of TRPV1 and TRPV4 were altered by EA, indicating that EA has an antinociceptive role in inflammatory pain. Our results demonstrate a novel role for EA in regulating TRPV1 and TRPV4 protein expression and nerve excitation in mouse inflammatory pain models.

Dorsal root ganglion compression as an animal model of sciatica and low back pain

As sciatica and low back pain are among the most common medical complaints, many studies have duplicated these conditions in animals. Chronic compression of the dorsal root ganglion (CCD) is one of these models. The surgery is simple: after exposing the L4/L5 intervertebral foramina, stainless steel rods are implanted unilaterally, one rod for each vertebra, to chronically compress the lumbar dorsal root ganglion (DRG). Then, CCD can be used to simulate the clinical conditions caused by stenosis, such as a laterally herniated disc or foraminal stenosis. As the intraforaminal implantation of a rod results in neuronal somal hyperexcitability and spontaneous action potentials associated with hyperalgesia, spontaneous pain, and mechanical allodynia, CCD provides an animal model that mimics radicular pain in humans. This review concerns the mechanisms of neuronal hyperexcitability, focusing on various patterns of spontaneous discharge including one possible pain signal for mechanical allodynia - evoked bursting. Also, new data regarding its significant property of maintaining peripheral input are also discussed. Investigations using this animal model will enhance our understanding of the neural mechanisms for low back pain and sciatica. Furthermore, the peripheral location of the DRG facilitates its use as a locus for controlling pain with minimal central effects, in the hope of ultimately uncovering analgesics that block neuropathic pain without influencing physiological pain.

The negative feedback regulation of TRPV4 Ca2+ ion channel function by its C-terminal cytoplasmic domain

The transient receptor potential vanilloid 4 (TRPV4) cation channel, a member of the TRP vanilloid subfamily, is expressed in a broad range of tissues where it participates in the generation of a Ca(2+) signal and/or depolarization of the membrane potential. Regulation of the abundance of TRPV4 at the cell surface is critical in osmo- and mechanotransduction. In this review, we discussed that the potential effect of Ca(2+) occurs via its action at an intracellular site in the C-terminus of the channel protein by the effect of the modulation on TRPV4 (such as 824 Ser residue phosphorylation), and its regulation for TRPV4 functions related with cell surface spread, wound healing or its polarity reorientation through its differential affinity with actin or tubulin.

Nuclear factor-kappa B mediates TRPV4-NO pathway involved in thermal hyperalgesia following chronic compression of the dorsal root ganglion in rats

The aim of this study was to test the hypothesis that nuclear factor-kappa B (NF-κB) is involved in TRPV4-NO pathway in thermal hyperalgesia following chronic compression of the dorsal root ganglion (DRG) (the procedure hereafter termed CCD) in rat. Intrathecal administration of two NF-κB inhibitors, pyrrolidine dithiocarbamate (PDTC; 10(-1) to 10(-2)M) and BAY (100-50 μM), both induced significantly dose-dependent increase in the paw withdrawal latency (PWL) and decrease in nitric oxide (NO) content in DRG when compared with control rats. Pretreatment with 4α-phorbol 12,13-didecanoate (4α-PDD, transient receptor potential vanilloid 4 (TRPV4) synthetic activator, 1 nm) attenuated the suppressive effects of PDTC (10(-1)M) and BAY (100 μM) on CCD-induced thermal hyperalgesia and NO production. In addition, Western blot analysis indicated that CCD rats exhibited nuclear NF-κB protein expression and low levels of cytoplasmic inhibitory-kappa B (I-κB) expression; the increase in NF-κB expression and decrease in I-κB expression were reversed after intrathecal injection of PDTC. In conclusion, our data suggested that NF-κB could be involved in TRPV4-NO pathway in CCD-induced thermal hyperalgesia.

CMT2C with vocal cord paresis associated with short stature and mutations in the TRPV4 gene

BACKGROUND

Recently, mutations in the transient receptor potential cation channel, subfamily V, member 4 gene (TRPV4) have been reported in Charcot-Marie-Tooth Type 2C (CMT2C) with vocal cord paresis. Other mutations in this same gene have been described in separate families with various skeletal dysplasias. Further clarification is needed of the different phenotypes associated with this gene.

METHODS

We performed clinical evaluation, electrophysiology, and genetic analysis of the TRPV4 gene in 2 families with CMT2C.

RESULTS

Two multigenerational families had a motor greater than sensory axonal neuropathy associated with variable vocal cord paresis. The vocal cord paresis varied from absent to severe, requiring permanent tracheotomy in 2 subjects. One family with mild neuropathy also manifested pronounced short stature, more than 2 SD below the average height for white Americans. There was one instance of dolichocephaly. A novel S542Y mutation in the TRPV4 gene was identified in this family. The other family had a more severe, progressive, motor neuropathy with sensory loss, but less remarkable short stature and an R315W mutation in TRPV4. Third cranial nerve involvement and sleep apnea occurred in one subject in each family.

CONCLUSION

CMT2C with axonal neuropathy, vocal cord paresis, and short stature is a unique syndrome associated with mutations in the TRPV4 gene. Mutations in TRPV4 can cause abnormalities in bone, peripheral nerve, or both and may result in highly variable orthopedic and neurologic phenotypes.