Accumulation of high molecular weight kininogen in the brains of Alzheimer's disease patients may affect microglial function by altering phagocytosis and lysosomal cathepsin activity.

Increased activation of the contact system protein high molecular weight kininogen (HK) has been shown in plasma and cerebrospinal fluid of Alzheimer's disease (AD) patients, but its potential role in the brain has not been explored. We assessed HK levels in brain tissue from 20 AD patients and controls and modeled the effects of HK on microglia-like cells in culture. We show increased levels of HK in the hippocampus of AD patients, which colocalized with amyloid beta (Aß) deposits and activated microglia. Treatment of microglia with HK led to cell clustering and elevated levels of phagocytosed Aß. We demonstrate that microglia internalize HK and traffic it to lysosomes, which is accompanied by reduced activity of lysosomal cathepsins L and S. Our results suggest that HK accumulation in the AD hippocampus may alter microglial uptake and degradation of Aß fibrils, possibly contributing to microglial dysfunction in AD.

AdRoit is an accurate and robust method to infer complex transcriptome composition.

Bulk RNA sequencing provides the opportunity to understand biology at the whole transcriptome level without the prohibitive cost of single cell profiling. Advances in spatial transcriptomics enable to dissect tissue organization and function by genome-wide gene expressions. However, the readout of both technologies is the overall gene expression across potentially many cell types without directly providing the information of cell type constitution. Although several in-silico approaches have been proposed to deconvolute RNA-Seq data composed of multiple cell types, many suffer a deterioration of performance in complex tissues. Here we present AdRoit, an accurate and robust method to infer the cell composition from transcriptome data of mixed cell types. AdRoit uses gene expression profiles obtained from single cell RNA sequencing as a reference. It employs an adaptive learning approach to alleviate the sequencing technique difference between the single cell and the bulk (or spatial) transcriptome data, enhancing cross-platform readout comparability. Our systematic benchmarking and applications, which include deconvoluting complex mixtures that encompass 30 cell types, demonstrate its preferable sensitivity and specificity compared to many existing methods as well as its utilities. In addition, AdRoit is computationally efficient and runs orders of magnitude faster than most methods.

The impact of the SARS-CoV-2 pandemic on the mental health of hemodialysis patients in Lebanon.

Hemodialysis is a necessary treatment for end-stage kidney disease patients. It imposes undergoing three sessions of dialysis per week in a specialized center. Amid the SARS-CoV-2 pandemic, precautionary measures were mandatory in all dialysis facilities and may have negatively impacted patients' well-being. This study aimed to uncover the scale of this effect. We performed a cross-sectional study of all patients undergoing chronic hemodialysis in two dialysis units (one urban and another rural). Patients with Alzheimer's disease were excluded. Patients filled a questionnaire including information on socio-demographics, factors related to the dialysis facility, and the impact of the COVID-19 epidemic on their mental health. A total of 72 patients responded. Their median age was 70 (60.79) years. Of them, 68% were males, 71% were married, and 10% were living alone. Following the pandemic, 35% felt more anxious, with a higher incidence of anxiety in the rural unit (p=0.021). Half of them felt very limited in their relationships, and 29% were isolated from their families. In total, 98% of patients were satisfied with the staff support. The imposed preventive measures were perceived as very strict in 27% of the surveyed patients. The majority of the urban group were bothered for not eating during the session, and they felt significantly more stress than the rural group (p=0.001). The SARS-CoV-2 pandemic increased anxiety among hemodialysis patients from a rural setting. Stress was more prevalent in the urban group and most probably related to limitations in eating during sessions. The majority were satisfied with staff support.

A Short Isoform of Coagulation Factor XII mRNA Is Expressed by Neurons in the Human Brain.

Coagulation factor XII (FXII) is synthesized in the liver and secreted into the circulation, where it initiates the contact activation system. Although typically thought to be restricted to the circulation, FXII protein has been found in the brain of Alzheimer's disease (AD) and multiple sclerosis patients. Moreover, activation of the contact system has been detected in the cerebrospinal fluid of these patients as well as in the brain of healthy and AD individuals. While FXII protein has been detected in the brain, its source and its potential role in brain physiology and/or pathology have not been elucidated. Using in situ hybridization, we show that a shorter FXII mRNA isoform is expressed by neurons in human brain and in the brain of FXII humanized mice, with the highest expression observed in pyramidal neurons. This shorter FXII transcript contains an open reading frame coding for the portion of FXII that spans its proline-rich and catalytic domains (FXII297-596). We show that a recombinant version of this shorter FXII protein is activated by plasma kallikrein, reciprocally activates prekallikrein, and converts pro-hepatocyte growth factor (HGF) to active HGF in vitro. HGF-Met signaling plays a role in neuronal development and survival, and its dysregulation has been implicated in neurodevelopmental disorders and neurodegeneration. Taken together, our results show that a short isoform of FXII mRNA is expressed in the brain and raise the possibility that brain-derived FXII may be involved in HGF-Met signaling in neurons.

Evaluation of antibiotic prescriptions for urinary tract infections in a geriatric rehabilitation unit.

Prescription of antibiotic in elderly patients must follow guidelines. to study the quality of antibiotic prescriptions for urinary tract infections (UTI) in the geriatric rehabilitation unit. Over a four-month period, all the antibiotics treatments prescribed for UTI in the rehabilitation ward were analyzed prospectively by medical experts and confronted with the recommendations of the local antibiotic guidelines. The methodology was based on Gyssens' algorithm. Treatments were considered appropriate if indication, choice of the molecule, duration and dose were approved by the experts, unnecessary if the indication was incorrect, and inappropriate in all other cases. The re-assessment of the prescription between 48 and 72 h was also evaluated. We reviewed 39 prescriptions. About half of all prescriptions (51.3%) was found to be unnecessary due to misdiagnosis, 16 prescriptions (41%) were considered inappropriate (2 for inadequate duration and 14 for inappropriate spectrum of activity, mainly with ceftriaxone prescriptions (9 cases)). Ten prescriptions (25.6%) were re-assessed between 48 and 72 hours after treatment initiation. According to this study, an improvement program was implemented. A diagnostic algorithm for UTI in elderly was drafted and will be integrated into the local guidelines. A supporting document for the re-assessment of the prescriptions 48-72h after treatment initiation was created. We decided to perform an evaluation of antibiotic prescriptions by the subcutaneous route.

Generation of a pain memory in the primary afferent nociceptor triggered by PKCε activation of CPEB.

Isolectin B(4)-positive [IB(4)(+)] primary afferent nociceptors challenged with an inflammatory or neuropathic insult develop a PKCε-dependent long-lasting hyperalgesic response to a subsequent challenge by the proinflammatory cytokine prostaglandin E(2) (PGE(2)), a phenomenon known as hyperalgesic priming. Here we demonstrate that the neuroplasticity underlying nociceptor priming requires 72 h to be established; rats that have been challenged with the inflammatory mediator TNFα 24 or 48 h ahead of PGE(2) do not show the enhanced and prolonged hyperalgesic response by which primed IB(4)(+)-nociceptors are being characterized. Moreover, as the underlying plasticity can be interrupted by the peripheral administration of the protein translation inhibitor anisomycin it is reflected by changes in the peripheral protein expression pattern. Finally, the induction of priming by the selective PKCε agonist, psi ε receptor for activated c kinase (ψεRACK) can be prevented, but not reversed by intrathecal injections of antisense oligodeoxynucleotides for the cytoplasmic polyadenylation element binding protein (CPEB) mRNA, a master regulator of protein translation that coimmunoprecipitated with PKCε and is almost exclusively expressed by IB(4)(+)-nociceptors. Our results suggest that CPEB is downstream of PKCε in the cellular signaling cascade responsible for the induction of priming, raising the intriguing possiblity that prion-like misfolding could be a responsible mechanism for the chronification of pain.

Delay in diagnosis of influenza virus in an elderly hospitalized patient: a fatal outcome.

Influenza is a well established cause of seasonal hospitalizations and deaths among older persons. However, influenza is frequently underdiagnosed by physicians, because its clinical presentations are often complex, particularly in elderly patients. We report the case of a 78-year-old woman admitted to the emergency department in January 2008 with fever, vomiting, and a history of asthenia and falls in the preceding three days. Diagnosis of influenza at admission was missed. Influenza was diagnosed by direct fluorescent antibody in a sputum specimen four days later, but the evolution was rapidly unfavorable with fatal respiratory distress syndrome. This case illustrates that, during the influenza season, influenza should be suspected in elderly patients admitted to hospital even if they do not present with classical symptoms. Immunofluorescence testing on sputum specimens can provide a rapid diagnosis and merits further evaluation.

TRPC1 and TRPC6 channels cooperate with TRPV4 to mediate mechanical hyperalgesia and nociceptor sensitization.

The transient receptor potential vanilloid 4 (TRPV4) contributes to mechanical hyperalgesia of diverse etiologies, presumably as part of a mechanoreceptor signaling complex (Alessandri-Haber et al., 2008). To investigate the hypothesis that a functional interaction between TRPV4 and stretch-activated ion channels (SACs) is involved in this mechanical transduction mechanism, we used a selective SACs inhibitor, GsMTx-4. Intradermal injection of GsMTx-4 in the rat hindpaw reversed the mechanical hyperalgesia induced by intradermal injection of inflammatory mediators. In vivo single fiber recordings showed that GsMTx-4 reversed inflammatory mediator-induced decrease in mechanical threshold in half of sensitized C-fibers. Furthermore, GsMTx-4 reduced hyperalgesia to both mechanical and hypotonic stimuli in different models of inflammatory and neuropathic pain, although it had no effect on baseline mechanical nociceptive thresholds. TRPC1 and TRPC6, two GsMTx-4-sensitive SACs, are expressed in dorsal root ganglion (DRG) neurons. Single-cell reverse transcription-PCR showed that messenger RNAs for TRPV4, TRPC1, and TRPC6 are frequently coexpressed in DRG neurons. Spinal intrathecal administration of oligodeoxynucleotides antisense to TRPC1 and TRPC6, like that to TRPV4, reversed the hyperalgesia to mechanical and hypotonic stimuli induced by inflammatory mediators without affecting baseline mechanical nociceptive threshold. However, antisense to TRPC6, but not to TRPC1, reversed the mechanical hyperalgesia induced by a thermal injury or the TRPV4-selective agonist 4alpha-PDD (4 alpha-phorbol 12,13-didecanoate). We conclude that TRPC1 and TRPC6 channels cooperate with TRPV4 channels to mediate mechanical hyperalgesia and primary afferent nociceptor sensitization, although they may have distinctive roles.

[Lower respiratory tract infections with influenza and respiratory syncytial viruses in hospitalized elderly patients during the 2005-2006 winter season]. / Etude des infections respiratoires basses à virus grippal et virus respiratoire syncytial au cours d'une saison hivernale chez des sujets âgés hospitalisés.

OBJECTIVES: To assess the proportion of lower respiratory tract infections (LRTI) attributable to influenza virus and respiratory syncytial virus (RSV) during the 2005-2006 winter period, among hospitalized elderly in a geriatric unit of a French hospital near Paris and and describe the characteristics of these infections. METHODS: In a geriatric unit with 115 beds, distributed as 14 in acute care (ACF), 21 in rehabilitation and intermediate-care (RICF) and 80 in long-term-care-facilities (LTCF), all patients over age 65 with LRTI were enrolled during a winter. Clinical and biological parameters were recorded including paired serology for influenza virus and RSV. RESULTS: 54 LRTI concerned 47 patients were recorded. 50 paired serums were analysed. Influenza virus or RSV were found in 17 cases (34%). The distribution of the cases was as follows: Influenza A in 5 cases, Influenza B in 3 cases, a co-infection with influenza A and B in 4 cases, RSV in 3 cases and co-infections with influenza and RSV in 2 cases (influenza A and RSV in one case and influenza A and B and RSV in the other case). 7 cases concerned patients in ACF, in 3 cases patients were in RICF and in 7 cases patients were in LTCF. 15 cases were nosocomial infections. 11 patients infected by influenza virus were vaccined. It was concluded as bronchitis in 8 cases, interstitial pneumonia in 6 cases and alveolar pneumonia in 3 cases. Antibiotics were prescribed in 11 cases. In one case the evolution was unfavourable with death. Patients with influenza or RSV infections had significantly more rales and rhonchi compared with patients non infected by these virus (p<0.05). CONCLUSION: Influenza and RSV are an important cause of LRTI in elderly during the winter months, influenza infections can occurring among vaccinated elderly. It seems necessary to achieve further clinical studies about LRTI in elderly and to study the impact of rapid diagnostic tests to improve the management of these infections.

Neurotoxic catecholamine metabolite in nociceptors contributes to painful peripheral neuropathy.

The neurotoxic effects of catecholamine metabolites have been implicated in neurodegenerative diseases. As some sensory neurons express tyrosine hydroxylase and monoamine oxidase (MAO), we investigated the potential contribution of catecholamine metabolites to neuropathic pain in a model of alcoholic neuropathy. The presence of catecholamines in sensory neurons is supported by capsaicin-stimulated epinephrine release, an effect enhanced in ethanol-fed rats. mRNA for enzymes in dorsal root ganglia involved in catecholamine uptake and metabolism, dopamine beta-hydroxylase and MAO-A, were decreased by neonatal administration of capsaicin. Ethanol-induced hyperalgesia was attenuated by systemic and local peripheral administration of inhibitors of MAO-A, reduction of norepinephrine transporter (NET) in sensory neurons and a NET inhibitor. Finally, intradermal injection of 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), a neurotoxic MAO-A catecholamine metabolite, produced robust mechanical hyperalgesia. These observations suggest that catecholamines in nociceptors are metabolized to neurotoxic products by MAO-A, which can cause neuronal dysfunction underlying neuropathic pain.

Stress induces a switch of intracellular signaling in sensory neurons in a model of generalized pain.

Stress dramatically exacerbates pain in diseases such as fibromyalgia and rheumatoid arthritis, but the underlying mechanisms are unknown. We tested the hypothesis that stress causes generalized hyperalgesia by enhancing pronociceptive effects of immune mediators. Rats exposed to nonhabituating sound stress exhibited no change in mechanical nociceptive threshold, but showed a marked increase in hyperalgesia evoked by local injections of prostaglandin E(2) or epinephrine. This enhancement, which developed more than a week after exposure to stress, required concerted action of glucocorticoids and catecholamines at receptors located in the periphery on sensory afferents. The altered response to pronociceptive mediators involved a switch in coupling of their receptors from predominantly stimulatory to inhibitory G-proteins (G(s) to G(i)), and for prostaglandin E(2), emergence of novel dependence on protein kinase C epsilon. Thus, an important mechanism in generalized pain syndromes may be stress-induced coactivation of the hypothalamo-pituitary-adrenal and sympathoadrenal axes, causing a long-lasting alteration in intracellular signaling pathways, enabling normally innocuous levels of immune mediators to produce chronic hyperalgesia.

Interaction of transient receptor potential vanilloid 4, integrin, and SRC tyrosine kinase in mechanical hyperalgesia.

Although the transient receptor potential vanilloid 4 (TRPV4) has been implicated in the process of osmomechanical transduction, it appears to make little contribution to the normal somatosensory detection of mechanical stimuli. However, evidence suggests that it may play an important role in mechanical hyperalgesia. In the present study, we examined the common requirement for TRPV4 in mechanical hyperalgesia associated with diverse pain models and investigated whether the very close association observed between TRPV4 and mechanical hyperalgesia, regardless of etiology, reflects a close functional connection of TRPV4 with other molecules implicated in mechanical transduction. In models of painful peripheral neuropathy associated with vincristine chemotherapy, alcoholism, diabetes, and human immunodeficiency virus/acquired immune deficiency syndrome therapy, mechanical hyperalgesia was markedly reduced by spinal intrathecal administration of oligodeoxynucleotides antisense to TRPV4. Similarly, mechanical hyperalgesia induced by paclitaxel, vincristine, or diabetes was strongly reduced in TRPV4 knock-out mice. We also show that alpha2beta1 integrin and Src tyrosine kinase, which have been implicated in mechanical transduction, are important for the development of mechanical hyperalgesia, and that their contribution requires TRPV4. Furthermore, we establish a direct interaction between TRPV4, alpha2 integrin, and the Src tyrosine kinase Lyn in sensory neurons. We suggest that TRPV4 plays a role in mechanotransduction, as a component of a molecular complex that functions only in the setting of inflammation or nerve injury.

Alcohol-induced stress in painful alcoholic neuropathy.

Chronic alcohol consumption induces a painful small-fiber peripheral neuropathy, the severity of which increases during alcohol withdrawal. Chronic alcohol consumption also produces a sustained increase in stress hormones, epinephrine and corticosterone, that is exacerbated during alcohol withdrawal. We report that adrenal medullectomy and administration of a glucocorticoid receptor antagonist, mifepristone (RU 38486), both prevented and reversed a model of painful peripheral neuropathy in alcohol binge-drinking rats. Chronic administration of stress levels of epinephrine to rats that had undergone adrenal medullectomy and were being fed the alcohol diet reconstituted this phenotype. Intrathecal administration of oligodeoxynucleotides antisense to the beta(2)-adrenergic- or glucocorticoid-receptor also prevented and reversed the pro-nociceptive effects of ethanol. Our results suggest a convergence of the effects of mediators of the hypothalamic-pituitary- and sympathoadrenal-stress axes on sensory neurons in the induction and maintenance of alcohol-induced painful peripheral neuropathy.

Marked attenuation of inflammatory mediator-induced C-fiber sensitization for mechanical and hypotonic stimuli in TRPV4-/- mice.

Inflammatory mediators can directly sensitize primary afferent nociceptors to mechanical and osmotic stimuli. Sensitized nociceptors have a lowered threshold of activation and increased spontaneous activity, which result in symptoms of hyperalgesia and pain, respectively. The transient receptor potential vanilloid 4 (TRPV4) ligand-gated ion channel has been implicated in the hyperalgesia for mechanical and osmotic stimuli associated with inflammatory states. To investigate whether TRPV4 directly contributes to the mechanisms of inflammatory mediator sensitization of C-fiber nociceptors, we compared the effect of the injection of simplified inflammatory soup (prostaglandin E2 and serotonin) into the mechanical receptive fields of C-fibers in TRPV4+/+ and TRPV4-/- mice in vivo. Following the injection of the soup, the percentage of C-fibers responding to a hypotonic stimulus and the magnitude of the response was significantly greater in TRPV4+/+ mice compared to TRPV4-/- mice. Moreover, in response to simplified inflammatory soup only C-fibers from TRPV4+/+ mice exhibited increased spontaneous activity and decreased mechanical threshold. These marked impairments in the response of C-fibers in TRPV4-/- mice demonstrate the importance of TRPV4 in nociceptor sensitization; we suggest that TRPV4, as TRPV1, underlies the nociceptive effects of multiple inflammatory mediators on primary afferent.

PLC-beta 3 signals upstream of PKC epsilon in acute and chronic inflammatory hyperalgesia.

While protein kinase C epsilon has been shown to contribute to acute and chronic mechanical hyperalgesia, its upstream signaling pathway has received little attention. Since phospholipase C can signal to PKC epsilon and has been implicated in nociceptor sensitization, we tested if it is upstream of PKC epsilon in mechanisms underlying primary mechanical hyperalgesia. In the rat, the PKC epsilon-dependent mechanical hyperalgesia and hyperalgesic priming (i.e., a form of chronic latent enhanced hyperalgesia) induced by carrageenan were attenuated by a non-selective PLC inhibitor U-73122. A lipid mediator of PLC signaling, l-alpha-lysophosphatidylcholine produced dose-dependent mechanical hyperalgesia and hyperalgesic priming, which was attenuated by EAVSLKPT, a selective PKC epsilon inhibitor. However, U-73122 did not attenuate hyperalgesia induced by psi epsilon RACK, a selective PKC epsilon activator. Antisense to PLC-beta 3 isoform, which was found in small-diameter dorsal root ganglion neurons, also attenuated carrageenan-induced acute and chronic-latent hyperalgesia. These studies support the suggestion that PLC-beta 3 is an important upstream signaling molecule for PKC epsilon-mediated acute and chronic inflammatory pain.

TRP channels: targets for the relief of pain.

Patients with inflammatory or neuropathic pain experience hypersensitivity to mechanical, thermal and/or chemical stimuli. Given the diverse etiologies and molecular mechanisms of these pain syndromes, an approach to developing successful therapies may be to target ion channels that contribute to the detection of thermal, mechanical and chemical stimuli and promote the sensitization and activation of nociceptors. Transient Receptor Potential (TRP) channels have emerged as a family of evolutionarily conserved ligand-gated ion channels that contribute to the detection of physical stimuli. Six TRPs (TRPV1, TRPV2, TRPV3, TRPV4, TRPM8 and TRPA1) have been shown to be expressed in primary afferent nociceptors, pain sensing neurons, where they act as transducers for thermal, chemical and mechanical stimuli. This short review focuses on their contribution to pain hypersensitivity associated with peripheral inflammatory and neuropathic pain states.

A transient receptor potential vanilloid 4-dependent mechanism of hyperalgesia is engaged by concerted action of inflammatory mediators.

The transient receptor potential vanilloid 4 (TRPV4) is a primary afferent transducer that plays a crucial role in neuropathic hyperalgesia for osmotic and mechanical stimuli, as well as in inflammatory mediator-induced hyperalgesia for osmotic stimuli. In view of the clinical importance of mechanical hyperalgesia in inflammatory states, the present study investigated the role of TRPV4 in mechanical hyperalgesia induced by inflammatory mediators and the second-messenger pathways involved. Intradermal injection of either the inflammogen carrageenan or a soup of inflammatory mediators enhanced the nocifensive paw-withdrawal reflex elicited by hypotonic or mechanical stimuli in rat. Spinal administration of TRPV4 antisense oligodeoxynucleotide blocked the enhancement without altering baseline nociceptive threshold. Similarly, in TRPV4(-/-) knock-out mice, inflammatory soup failed to induce any significant mechanical or osmotic hyperalgesia. In vitro investigation showed that inflammatory mediators engage the TRPV4-mediated mechanism of sensitization by direct action on dissociated primary afferent neurons. Additional behavioral observations suggested that multiple mediators are necessary to achieve sufficient activation of the cAMP pathway to engage the TRPV4-dependent mechanism of hyperalgesia. In addition, direct activation of protein kinase A or protein kinase C epsilon, two pathways that mediate inflammation-induced mechanical hyperalgesia, also induced hyperalgesia for both hypotonic and mechanical stimuli that was decreased by TRPV4 antisense and absent in TRPV4(-/-) mice. We conclude that TRPV4 plays a crucial role in the mechanical hyperalgesia that is generated by the concerted action of inflammatory mediators present in inflamed tissues.

TRPV4 mediates pain-related behavior induced by mild hypertonic stimuli in the presence of inflammatory mediator.

The ligand-gated ion channel, TRPV4, functions as a transducer of hypotonic stimuli in primary afferent nociceptive neurons and contributes to inflammatory and neuropathic pain. Hypertonic saline also stimulates primary afferent nociceptors and the injection of mild hypertonic saline (2-5%) is widely used as an experimental model of pain in humans. Therefore, we tested whether TRPV4 participates in the transduction of hypertonic stimuli. Intradermal injection of 2% (607 mOsm) or 10% (3,250 mOsm) saline solution in the hind paw of rats induced a concentration-dependent pain-related behavior, flinching. Sensitization with prostaglandin E(2) (PGE(2)) caused a 7-fold increase in the number of flinches induced by 2% saline but failed to increase those caused by 10% saline. Spinal administration of antisense oligodeoxynucleotides to TRPV4 caused a 46% decrease in the number of flinches induced by 2% saline, but there was no change in flinching induced by 10% saline. Similarly, only the nociceptive behavior caused by 2% saline was reduced in TRPV4(-/-) knockout mice. The TRPV4-mediated nociceptive behaviors induced by hyper- and hypotonic stimuli were dependent on Src tyrosine kinase. We suggest TRPV4 is a transducer in primary afferents that mediates nociceptive behavior induced by small increases or decreases in osmolarity. Such changes in osmolarity might contribute to pain in inflammatory and neuropathic states.

Transient receptor potential vanilloid 4 is essential in chemotherapy-induced neuropathic pain in the rat.

The development of treatments for neuropathic pain has been hindered by our limited understanding of the basic mechanisms underlying abnormalities in nociceptor hyperexcitability. We recently showed that the polymodal receptor transient receptor potential vanilloid 4 (TRPV4), a member of the transient receptor potential (TRP) family of ion channels, may play a role in inflammatory pain (Alessandri-Haber et al., 2003). The present study tested whether TRVP4 also contributes to neuropathic pain, using a rat model of Taxol-induced painful peripheral neuropathy. Taxol is the most widely used drug for the treatment of a variety of tumor types, but the dose of Taxol that can be tolerated is limited by the development of a small-fiber painful peripheral neuropathy. We found that Taxol treatment enhanced the nociceptive behavioral responses to both mechanical and hypotonic stimulation of the hind paw. Spinal administration of antisense oligodeoxynucleotides to TRPV4, which reduced the expression of TRPV4 in sensory nerve, abolished Taxol-induced mechanical hyperalgesia and attenuated hypotonic hyperalgesia by 42%. The enhancement of osmotic nociception involves sensitization of osmotransduction in primary afferents because osmotransduction was enhanced in cultured sensory neurons isolated from Taxol-treated rats. Taxol-induced TRPV4-mediated hyperalgesia and the enhanced osmotransduction in cultured nociceptors were dependent on integrin/Src tyrosine kinase signaling. These results suggest that TRPV4 plays a crucial role in a painful peripheral neuropathy, making it a very promising target for the development of a novel class of analgesics.

Hypotonicity induces TRPV4-mediated nociception in rat.

We hypothesized that TRPV4, a member of the transient receptor family of ion channels, functions as a sensory transducer for osmotic stimulus-induced nociception. We found that, as expected for a transducer molecule, TRPV4 protein is transported in sensory nerve distally toward the peripheral nerve endings. In vivo single-fiber recordings in rat showed that hypotonic solution activated 54% of C-fibers, an effect enhanced by the hyperalgesic inflammatory mediator prostaglandin E2. This osmotransduction causes nociception, since administration of a small osmotic stimulus into skin sensitized by PGE2 produced pain-related behavior. Antisense-induced decrease in expression of TRPV4 confirmed that the channel is required for hypotonic stimulus-induced nociception. Thus, we conclude that TRPV4 can function as an osmo-transducer in primary afferent nociceptive nerve fibers. Because this action is enhanced by an inflammatory mediator, TRPV4 may be important in pathological states and may be an attractive pharmacological target for the development of novel analgesics.