Voltage-gated sodium channels (VGSCs) play a key role in the initiation and propagation of action potentials in neurons. Na(V)1.8 is a tetrodotoxin (TTX) resistant VGSC expressed in nociceptors, ...peripheral small-diameter neurons able to detect noxious stimuli. Na(V)1.8 underlies the vast majority of sodium currents during action potentials. Many studies have highlighted a key role for Na(V)1.8 in inflammatory and chronic pain models. Lipid rafts are microdomains of the plasma membrane highly enriched in cholesterol and sphingolipids. Lipid rafts tune the spatial and temporal organisation of proteins and lipids on the plasma membrane. They are thought to act as platforms on the membrane where proteins and lipids can be trafficked, compartmentalised and functionally clustered. In the present study we investigated Na(V)1.8 sub-cellular localisation and explored the idea that it is associated with lipid rafts in nociceptors. We found that Na(V)1.8 is distributed in clusters along the axons of DRG neurons in vitro and ex vivo. We also demonstrated, by biochemical and imaging studies, that Na(V)1.8 is associated with lipid rafts along the sciatic nerve ex vivo and in DRG neurons in vitro. Moreover, treatments with methyl-β-cyclodextrin (MβCD) and 7-ketocholesterol (7KC) led to the dissociation between rafts and Na(V)1.8. By calcium imaging we demonstrated that the lack of association between rafts and Na(V)1.8 correlated with impaired neuronal excitability, highlighted by a reduction in the number of neurons able to conduct mechanically- and chemically-evoked depolarisations. These findings reveal the sub-cellular localisation of Na(V)1.8 in nociceptors and highlight the importance of the association between Na(V)1.8 and lipid rafts in the control of nociceptor excitability.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
VGF (nonacronymic) is a neuropeptide precursor that plays multiple roles in regulation of energy balance, reproduction, hippocampal synaptic plasticity, and pain. Data from a number of pain models ...showed significant up-regulation of VGF in sensory neurons. TLQP-21, one of the VGF-derived neuropeptides, has been shown to induce a hyperalgesic response when injected subcutaneously into the hind paw of mice. However, the precise role of VGF-derived neuropeptides in neuropathic pain and the molecular identity of the receptor for VGF-derived peptides are yet to be investigated. Here we identified gC1qR, the globular heads of the C1q receptor, as the receptor for TLQP-21 using chemical cross-linking combined with mass spectrometry analysis. TLQP-21 caused an increase in intracellular Ca2+ levels in rat macrophages and microglia. Inoculation of TLQP-21-stimulated macrophages into rat hind paw caused mechanical hypersensitivity. The increase in intracellular Ca2+ levels in macrophages was attenuated by either siRNA or neutralizing antibodies against gC1qR. Furthermore, application of the gC1qR-neutralizing antibody to rats with partial sciatic nerve ligation resulted in a delayed onset of nerve injury-associated mechanical hypersensitivity. These results indicate that gC1qR is the receptor for TLQP-21 and plays an important role in chronic pain through activation of macrophages. Because direct association between TLQP-21 and gC1qR is required for activation of macrophages and causes hypersensitivity, disrupting this interaction may be a useful new approach to develop novel analgesics.
Background: VGF is a neuropeptide involved in chronic pain.
Results: VGF-derived peptide TLQP-21 activates macrophages. We identified gC1qR as a receptor for TLQP-21.
Conclusion: TLQP-21 and gC1qR are involved in chronic pain pathways.
Significance: TLQP-21 and gC1qR may be drug targets for chronic pain treatment.
Neuropathic pain (NP) remains an area of considerable unmet medical need. A persistent challenge in the management of NP is to target the specific mechanisms leading to a change from normal to ...abnormal sensory perception while ensuring that the defensive pain perception remains intact. Targeting VGF-derived neuropeptides may offer this opportunity. VGF was first identified in 1985 and is highly expressed after nerve injury and inflammation in neurons of both the peripheral and central nervous system. Subsequent studies implicate the
gene and its products in pain pathways. This narrative review was supported by a systematic search to identify, select, and critically appraise all relevant research investigating the role of VGF-derived neuropeptides in pain pathways. It predominantly focuses on in vivo investigations of the role of VGF in the initiation and maintenance of NP. VGF expression levels are very low under normal physiological conditions and nerve injury results in rapid and robust upregulation, increasing mechanical and thermal hypersensitivity. The identification of the 2 complement receptors with which VGF neuropeptides interact suggests a novel interplay of neuronal and immune signalling mediators. The understanding of the molecular mechanisms and signalling events by which VGF-derived active neuropeptides exert their physiological actions is in its infancy. Future work should aim to improve understanding of the downstream consequences of VGF neuropeptides thereby providing novel insights into pain mechanisms potentially leading to the identification of novel therapeutic targets.
Neuropathic pain arises as a debilitating consequence of nerve injury. The etiology of such pain is poorly understood, and existing treatment is largely ineffective. We demonstrate here that glial ...cell line-derived neurotrophic factor (GDNF) both prevented and reversed sensory abnormalities that developed in neuropathic pain models, without affecting pain-related behavior in normal animals. GDNF reduces ectopic discharges within sensory neurons after nerve injury. This may arise as a consequence of the reversal by GDNF of the injury-induced plasticity of several sodium channel subunits. Together these findings provide a rational basis for the use of GDNF as a therapeutic treatment for neuropathic pain states.
To test the hypothesis that trkA (the high-affinity NGF receptor) is selectively expressed in nociceptive dorsal root ganglion (DRG) neurons, we examined the intensity of trkA immunoreactivity in ...single dye-injected rat DRG neurons, the sensory receptor properties of which were identified in vivo with mechanical and thermal stimuli. We provide the first evidence in single identified neurons that strong trkA expression in DRGs is restricted to nociceptive neurons, probably accounting for the profound influence of NGF on these neurons. Furthermore, we demonstrate that trkA expression is as high in rapidly conducting (Aalpha/beta) as in more slowly conducting (Adelta and C) nociceptors. All Aalpha/beta low-threshold mechanoreceptors (LTMs) are trkA negative, although weak but detectable trkA is present in some C and Adelta LTMs. NGF can influence electrophysiological properties of DRG neurons, probably by binding to trkA. We found positive correlations for single identified Aalpha/beta (but not C or Adelta) nociceptors between trkA immunocytochemical intensity and electrophysiological properties typical of nociceptors, namely long action potential and afterhyperpolarization durations and large action potential amplitudes. Furthermore, for Aalpha/beta (notCorAdelta) nociceptors, trkA intensity is inversely correlated with conduction velocity. Similar relationships, again only in Aalpha/beta nociceptors, between electrophysiological properties and trkA expression exist for sodium channel Nav1.8 but not Nav1.9 immunoreactivities. These findings suggest that in Aalpha/beta nociceptors, influences of NGF on expression levels of Nav1.8 are related to, and perhaps limited by, expression levels of trkA. This view is supported by a positive correlation between immuno-intensities of trkA and Nav1.8 in A-fiber, but not C-fiber, nociceptors.
Acid-sensing ion channels (ASICs) have been implicated in a wide variety of physiological functions. We have used a rat dorsal root ganglion cDNA library in a yeast two-hybrid assay to identify ...sensory neuron proteins that interact with ASICs. We found that annexin II light chain p11 physically interacts with the N terminus of ASIC1a, but not other ASIC isoforms. Immunoprecipitation studies confirmed an interaction between p11 and ASIC1 in rat dorsal root ganglion neurons in vivo. Coexpression of p11 and ASIC1a in CHO-K1 cells led to a 2-fold increase in expression of the ion channel at the cell membrane as determined by membrane-associated immunoreactivity and cell-surface biotinylation. Consistent with these findings, peak ASIC1a currents in transfected CHO-K1 cells were up-regulated 2-fold in the presence of p11, whereas ASIC3-mediated currents were unaffected by p11 expression. Neither the pH dependence of activation nor the rates of desensitization were altered by p11, suggesting that its primary role in regulating ASIC1a activity is to enhance cell-surface expression of ASIC1a. These data demonstrate that p11, already known to traffic members of the voltage-gated sodium and potassium channel families as well as transient receptor potential and chloride channels, also plays a selective role in enhancing ASIC1a functional expression.
Many damage-sensing neurons express tetrodotoxin (TTX)-resistant voltage-gated sodium channels. Here we examined the role of the sensory-neuron-specific (SNS) TTX-resistant sodium channel alpha ...subunit in nociception and pain by constructing sns-null mutant mice. These mice expressed only TTX-sensitive sodium currents on step depolarizations from normal resting potentials, showing that all slow TTX-resistant currents are encoded by the sns gene. Null mutants were viable, fertile and apparently normal, although lowered thresholds of electrical activation of C-fibers and increased current densities of TTX-sensitive channels demonstrated compensatory upregulation of TTX-sensitive currents in sensory neurons. Behavioral studies demonstrated a pronounced analgesia to noxious mechanical stimuli, small deficits in noxious thermoreception and delayed development of inflammatory hyperalgesia. These data show that SNS is involved in pain pathways and suggest that blockade of SNS expression or function may produce analgesia without side effects.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The tetrodotoxin-resistant sodium channel NaV1.8/SNS is expressed exclusively in sensory neurons and appears to have an important role in pain pathways. Unlike other sodium channels, NaV1.8 is poorly ...expressed in cell lines even in the presence of accessory β-subunits. Here we identify annexin II light chain (p11) as a regulatory factor that facilitates the expression of NaV1.8. p11 binds directly to the amino terminus of NaV1.8 and promotes the translocation of NaV1.8 to the plasma membrane, producing functional channels. The endogenous NaV1.8 current in sensory neurons is inhibited by antisense downregulation of p11 expression. Because direct association with p11 is required for functional expression of NaV1.8, disrupting this interaction may be a useful new approach to downregulating NaV1.8 and effecting analgesia.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract To elucidate the mechanisms underlying peripheral neuropathic pain in the context of HIV infection and antiretroviral therapy, we measured gene expression in dorsal root ganglia (DRG) of ...rats subjected to systemic treatment with the anti-retroviral agent, ddC (Zalcitabine) and concomitant delivery of HIV-gp120 to the rat sciatic nerve. L4 and L5 DRGs were collected at day 14 (time of peak behavioural change) and changes in gene expression were measured using Affymetrix whole genome rat arrays. Conventional analysis of this data set and Gene Set Enrichment Analysis (GSEA) was performed to discover biological processes altered in this model. Transcripts associated with G protein coupled receptor signalling and cell adhesion were enriched in the treated animals, while ribosomal proteins and proteasome pathways were associated with gene down-regulation. To identify genes that are directly relevant to neuropathic mechanical hypersensitivity, as opposed to epiphenomena associated with other aspects of the response to a sciatic nerve lesion, we compared the gp120 + ddC-evoked gene expression with that observed in a model of traumatic neuropathic pain (L5 spinal nerve transection), where hypersensitivity to a static mechanical stimulus is also observed. We identified 39 genes/expressed sequence tags that are differentially expressed in the same direction in both models. Most of these have not previously been implicated in mechanical hypersensitivity and may represent novel targets for therapeutic intervention. As an external control, the RNA expression of three genes was examined by RT-PCR, while the protein levels of two were studied using western blot analysis.
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