Intensity-dependent activation of extracellular signal-regulated protein kinase 5 in sensory neurons contributes to pain hypersensitivity

Research progress of the role and mechanism of extracellular signal-regulated protein kinase 5 (ERK5) pathway in pathological pain

Extracellular signal-regulated protein kinase 5 (ERK5), also known as big mitogen-activated protein kinase 1 (MAPK1), is an important member of ERK family, which is a subfamily of the large MAPK family. ERK5 is expressed in many tissues, including the dorsal root ganglion (DRG) neurons and the spinal cord. In this review, we focus on elaborating ERK5-associated pathway in pathological pain, in which the ERK5/CREB (cyclic adenosine monophosphate (cAMP)-response element-binding protein) pathway plays a crucial role in the transduction of pain signal and contributes to pain hypersensitivity. ERK5 activation in the spinal dorsal horn occurs mainly in microglia. The activation of ERK5 can be mediated by N-methyl-D-aspartate (NMDA) receptors. We also elaborate the relationship between ERK5 activation and nerve growth factor-tyrosine kinase A (NGF-TrkA), and the connection between ERK5 activation and brain-derived neurotrophic factor (BDNF) in pathological pain in detail.

[Role of Transient Receptor Potential Channels in Paclitaxel- and Oxaliplatin-induced Peripheral Neuropathy]

Peripheral neuropathy is a common adverse effect of paclitaxel and oxaliplatin treatment. The major dose-limiting side effect of these drugs is peripheral sensory neuropathy. The symptoms of paclitaxel-induced neuropathy are mostly sensory and peripheral in nature, consisting of mechanical allodynia/hyperalgesia, tingling, and numbness. Oxaliplatin-induced neurotoxicity manifests as rapid-onset neuropathic symptoms that are exacerbated by cold exposure and as chronic neuropathy that develops after several treatment cycles. Although many basic and clinical researchers have studied anticancer drug-induced peripheral neuropathy, the mechanism is not well understood. In this review, we focus on (1) analysis of transient receptor potential vanilloid 1 (TRPV1) channel expression in the rat dorsal root ganglion (DRG) after paclitaxel treatment and (2) analysis of transient receptor potential ankyrin 1 (TRPA1) channel in the DRG after oxaliplatin treatment. This review describes that (1) paclitaxel-induced neuropathic pain may be the result of up-regulation of TRPV1 in small- and medium-diameter DRG neurons. In addition, paclitaxel treatment increases the release of substance P, but not calcitonin gene-related peptide, in the superficial layers of the spinal dorsal horn. (2) TRPA1 expression via activation of p38 mitogen-activated protein kinase in small-diameter DRG neurons, at least in part, contributes to the development of oxaliplatin-induced acute cold hyperalgesia. We suggest that TRPV1 or TRPA1 antagonists may be potential therapeutic lead compounds for treating anticancer drug-induced peripheral neuropathy.

Capsaicin and Its Role in Chronic Diseases

A significant number of experimental and clinical studies published in peer-reviewed journals have demonstrated promising pharmacological properties of capsaicin in relieving signs and symptoms of non-communicable diseases (chronic diseases). This chapter provides an overview made from basic and clinical research studies of the potential therapeutic effects of capsaicin, loaded in different application forms, such as solution and cream, on chronic diseases (e.g. arthritis, chronic pain, functional gastrointestinal disorders and cancer). In addition to the anti-inflammatory and analgesic properties of capsaicin largely recognized via, mainly, interaction with the TRPV1, the effects of capsaicin on different cell signalling pathways will be further discussed here. The analgesic, anti-inflammatory or apoptotic effects of capsaicin show promising results in arthritis, neuropathic pain, gastrointestinal disorders or cancer, since evidence demonstrates that the oral or local application of capsaicin reduce inflammation and pain in rheumatoid arthritis, promotes gastric protection against ulcer and induces apoptosis of the tumour cells. Sadly, these results have been paralleled by conflicting studies, which indicate that high concentrations of capsaicin are likely to evoke deleterious effects, thus suggesting that capsaicin activates different pathways at different concentrations in both human and rodent tissues. Thus, to establish effective capsaicin doses for chronic conditions, which can be benefited from capsaicin therapeutic effects, is a real challenge that must be pursued.

Extracellular signal-regulated kinase 5 in the cerebrospinal fluid-contacting nucleus contributes to morphine physical dependence in rats

The cerebrospinal fluid-contacting nucleus (CSF-CN) may influence actual composition of the CSF for non-synaptic signal transmission via releasing or absorbing bioactive substances, which distributes and localizes in the ventral periaqueductal central gray of the brainstem. Previous studies demonstrated that CSF-CN was involved in neuropathic pain and morphine dependence. Thus, to identify whether extracellular signal-regulated kinase 5 (ERK5) distributed in the CSF-CN and its function on the formation and development of morphine physical dependence, morphine withdrawal-like behavioral test and immunofluorescent technique were used in this research. Morphine was subcutaneously injected by an intermittent and escalating procedure to induce physical dependence, which was measured by withdrawal symptoms. In this study, we found that horseradish peroxidase-conjugated toxin subunit B/p-ERK5 double-labeled neurons expressed in the CSF-CN of normal rats. ERK5 signaling pathway was remarkably activated by naloxone-precipitated withdrawal in the CSF-CN. Moreover, selective attenuation of p-ERK5 expression in the CSF-CN by lateral ventricle injection of BIX02188 could significantly relieve morphine withdrawal symptom. These findings confirmed that the activation of p-ERK5 in the CSF-CN might contribute to morphine physical dependence.

Protein kinase C modulation of thermo-sensitive transient receptor potential channels: Implications for pain signaling

A variety of molecules are reported to be involved in chronic pain. This review outlines the specifics of protein kinase C (PKC), its isoforms and their role in modulating thermo-sensitive transient receptor potential (TRP) channels TRPV1-4, TRPM8, and TRPA1. Anatomically, PKC and thermo-sensitive TRPs are co-expressed in cell bodies of nociceptive dorsal root ganglion (DRG) neurons, which are used as physiological correlates of peripheral and central projections involved in pain transmission. In the past decade, modulation of painful heat-sensitive TRPV1 by PKC has received the most attention. Recently, PKC modulation of other newly discovered thermo-sensitive pain-mediating TRPs has come into focus. Such modulation may occur under conditions of chronic pain resulting from nerve damage or inflammation. Since thermo-TRPs are primary detectors of acute pain stimuli, their modulation by PKC can severely alter their function, resulting in chronic pain. Comprehensive knowledge of pain signaling involving interaction of specific isoforms of PKC with specific thermo-sensitive TRP channels is incomplete. Such information is necessary to dissect out modality specific mechanisms to better manage the complex polymodal nature of chronic pain. This review is an attempt to update the readers on current knowledge of PKC modulation of thermo-sensitive TRPs and highlight implications of such modulation for pain signaling

Inflammation-induced shift in spinal GABA(A) signaling is associated with a tyrosine kinase-dependent increase in GABA(A) current density in nociceptive afferents

To account for benzodiazepine-induced spinal analgesia observed in association with an inflammation-induced shift in the influence of the GABA(A) receptor antagonist gabazine on nociceptive threshold, the present study was designed to determine whether persistent inflammation is associated with the upregulation of high-affinity GABA(A) receptors in primary afferents. The cell bodies of afferents innervating the glabrous skin of the rat hind paw were retrogradely labeled, acutely dissociated, and studied before and after the induction of persistent inflammation. A time-dependent increase in GABA(A) current density was observed that was more than twofold by 72 h after the initiation of inflammation. This increase in current density included both high- and low-affinity currents and was restricted to neurons in which GABA increased intracellular Ca(2+). No increases in GABA(A) receptor subunit mRNA or protein were detected in whole ganglia. In contrast, the increased current density was completely reversed by 20-min preincubation with the tyrosine kinase inhibitor genistein and partially reversed with the Src kinase inhibitor PP2. Genistein reversal was partially blocked by the dynamin inhibitor peptide P4. Changes in nociceptive threshold following spinal administration of genistein and muscimol to inflamed rats indicated that the pronociceptive actions of muscimol observed in the presence of inflammation were reversed by genistein. These results suggest that persistent changes in relative levels of tyrosine kinase activity following inflammation provide not only a sensitive way to dynamically regulate spinal nociceptive signaling but a viable target for the development of novel therapeutic interventions for the treatment of inflammatory pain.

TRP channels and analgesia

Since cloning and characterizing the first nociceptive ion channel Transient Receptor Potential (TRP) Vanilloid 1 (TRPV1), other TRP channels involved in nociception have been cloned and characterized, which include TRP Vanilloid 2 (TRPV2), TRP Vanilloid 3 (TRPV3), TRP Vanilloid 4 (TRPV4), TRP Ankyrin 1 (TRPA1) and TRP Melastatin 8 (TRPM8), more recently TRP Canonical 1, 5, 6 (TRPC1, 5, 6), TRP Melastatin 2 (TRPM2) and TRP Melastatin 3 (TRPM3). These channels are predominantly expressed in C and Aδ nociceptors and transmit noxious thermal, mechanical and chemical sensitivities. TRP channels are modulated by pro-inflammatory mediators, neuropeptides and cytokines. Significant advances have been made targeting these receptors either by antagonists or agonists to treat painful conditions. In this review, we will discuss TRP channels as targets for next generation analgesics and the side effects that may ensue as a result of blocking/activating these receptors, because they are also involved in physiological functions such as release of vasoactive neuropeptides and regulation of vascular tone, maintenance of the body temperature, gastrointestinal motility, urinary bladder control, etc.

Activation of mitogen-activated protein kinase in descending pain modulatory system

The descending pain modulatory system is thought to undergo plastic changes following peripheral tissue injury and exerts bidirectional (facilitatory and inhibitory) influence on spinal nociceptive transmission. The mitogen-activated protein kinases (MAPKs) superfamily consists of four main members: the extracellular signal-regulated protein kinase1/2 (ERK1/2), the c-Jun N-terminal kinases (JNKs), the p38 MAPKs, and the ERK5. MAPKs not only regulate cell proliferation and survival but also play important roles in synaptic plasticity and memory formation. Recently, many studies have demonstrated that noxious stimuli activate MAPKs in several brain regions that are components of descending pain modulatory system. They are involved in pain perception and pain-related emotional responses. In addition, psychophysical stress also activates MAPKs in these brain structures. Greater appreciation of the convergence of mechanisms between noxious stimuli- and psychological stress-induced neuroplasticity is likely to lead to the identification of novel targets for a variety of pain syndromes.

Extracellular signal-regulated kinases in pain of peripheral origin

Activation of members of the family of enzymes known as extracellular signal-regulated kinases (ERKs) is now known to be involved in the development and/or maintenance of the pain associated with many inflammatory conditions, such as herniated spinal disc pain, chronic inflammatory articular pain, and the pain associated with bladder inflammation. Moreover, ERKs are implicated in the development of neuropathic pain signs in animals which are subjected to the lumbar 5 spinal nerve ligation model and the chronic constriction injury model of neuropathic pain. The position has now been reached where all scientists working on pain subjects ought to be aware of the importance of ERKs, if only because certain of these enzymes are increasingly employed as experimental markers of nociceptive processing. Here, we introduce the reader, first, to the intracellular context in which these enzymes function. Thereafter, we consider the involvement of ERKs in mediating nociceptive signalling to the brain resulting from noxious stimuli at the periphery which will be interpreted by the brain as pain of peripheral origin.

p75 neurotrophin receptor is implicated in the ability of neurotrophin-3 to negatively modulate activated ERK1/2 signaling in TrkA-expressing adult sensory neurons

Neurotrophin-3 (NT-3) can negatively modulate trkA and associated phenotype in intact sensory neurons, while positively regulating trkC and associated phenotype. How NT-3 effects this response is not clear. Whether NT-3 exerts a differential influence on levels of activated ERK1/2 signaling in trkA- versus trkC-mRNA-positive subpopulations of neurons and the role that the common neurotrophin receptor, p75NTR, plays in this response was assessed by examining alterations in the levels of phospho-ERK1/2 immunofluorescence signal over nuclei of sensory neurons expressing trkA alone, trkC alone, or both trkA and trkC mRNA. NT-3 intrathecal infusion differentially modulated nuclear phospho-ERK1/2 levels detected over neurons expressing trkA alone or trkC alone. Levels were significantly decreased over nuclei of neurons expressing trkA alone and significantly increased over the nuclei of neurons expressing trkC alone. Neurons expressing both trkA and trkC or neurons expressing neither trkA nor trkC had no significant alteration in phospho-ERK1/2. Antisense oligonucleotides directed against p75NTR were infused intrathecally with or without NT-3 infusion to examine the impact of suppressing p75NTR expression on the ability of NT-3 to diminish phospho-ERK1/2 signaling in neurons expressing only trkA. NT-3 did not significantly attenuate levels of phospho-ERK1/2 when p75NTR expression was suppressed by antisense infusion, despite being able to do so when NT-3 was infused alone. In conclusion, NT-3's ability to negatively modulate ERK1/2 signaling in a p75-dependent manner in sensory neurons that express trkA to the exclusion of trkC provides a feasible mechanism by which it negatively modulates other aspects of nociceptive phenotype in these neurons.

Activation of extracellular signal-regulated protein kinases 5 in the spinal cord contributes to the neuropathic pain behaviors induced by CCI in rats

OBJECTIVE

To investigate whether activation and translocation of extracellular signal-regulated kinase 5 (ERK5) is involved in the induction and maintenance of neuropathic pain and observe the effects of activation and translocation of ERK5 on the expression of phosphorylated cAMP response element binding (pCREB) in the chronic neuropathic pain.

METHODS

Lumbar intrathecal catheters were chronically implanted in male Sprague-Dawley rats. The left sciatic nerve was loosely ligated proximal to the sciatica's trifurcation at approximately 1.0 mm intervals with 4-0 silk sutures. The phosphorothioate-modified antisense oligonucleotides (AS-ODNs) were intrathecally administered every 12 hours, 1 day pre-chronic constriction injury (CCI) and 3 day post-CCI. Thermal and mechanical nociceptive thresholds were assessed with the paw withdrawal latency to a radiant heat and von Frey filaments. Expressions of phosphorylated ERK5 (pERK5), pCREB, were assessed by both Western blotting and immunohistochemical analysis.

RESULTS

Intrathecal injection of ERK5 AS-ODN significantly attenuated CCI-induced mechanical allodynia and thermal hyperalgesia. CCI significantly increased the expression of pERK5 neurons in the ipsilateral spinal dorsal horn to injury, not in the contralateral spinal dorsal horn. The time courses of pERK5 expression showed that the levels of both cytosol and nuclear pERK5 were increased at all points after CCI and reached a peak level on post-operative day 5. CCI significantly increased the expression of pERK5 neurons in the laminae I and II of ipsilateral spinal dorsal horn to injury, not in the contralateral spinal dorsal horn. Phospho-CREB-positive neurons were distributed in all laminae of the bilateral spinal cord. Intrathecal injection AS-ODN markedly suppressed the increase of CCI-induced pERK5, pCREB expression in the spinal cord.

CONCLUSION

The activation of ERK5 pathways contributes to neuropathic pain in CCI rats, and the function of pERK5 may partly be accomplished via the CREB protein-dependent gene expression.

The activation of extracellular signal-regulated protein kinase 5 in spinal cord and dorsal root ganglia contributes to inflammatory pain

Activation of mitogen-activated protein kinases (MAPKs) in dorsal root ganglia (DRG) and the spinal dorsal horn contributes to inflammatory pain by transcription-dependent and -independent means. In this study, we investigated extracellular signal-regulated protein kinase 5 (ERK5) activation by peripheral inflammation in the spinal cord and DRG of rats and whether this activation contributes to a heat and mechanical hyperalgesia response. Injection of complete Freund's adjuvant (CFA) into a hindpaw produced persistent inflammation and sustained ERK5 activation in DRG and the spinal dorsal horn. Knockdown of the ERK5 by antisense oligonucleotides suppressed the heat and mechanical hyperalgesia. In addition, the antisense knockdown of ERK5 reduced CFA-induced phosphorylation of cAMP response-element binding protein (CREB), a downstream substrate of the ERK5 pathway, and expression of Fos, a marker for neuronal activation in the central nervous system. Our study suggests that activation of the ERK5 signaling pathway contributes to persistent hyperalgesia induced by peripheral inflammation.

ThermoTRP channels in nociceptors: taking a lead from capsaicin receptor TRPV1

Nociceptors with peripheral and central projections express temperature sensitive transient receptor potential (TRP) ion channels, also called thermoTRP's. Chemosensitivity of thermoTRP's to certain natural compounds eliciting pain or exhibiting thermal properties has proven to be a good tool in characterizing these receptors. Capsaicin, a pungent chemical in hot peppers, has assisted in the cloning of the first thermoTRP, TRPV1. This discovery initiated the search for other receptors encoding the response to a wide range of temperatures encountered by the body. Of these, TRPV1 and TRPV2 encode unique modalities of thermal pain when exposed to noxious heat. The ability of TRPA1 to encode noxious cold is presently being debated. The role of TRPV1 in peripheral inflammatory pain and central sensitization during chronic pain is well known. In addition to endogenous agonists, a wide variety of chemical agonists and antagonists have been discovered to activate and inhibit TRPV1. Efforts are underway to determine conditions under which agonist-mediated desensitization of TRPV1 or inhibition by antagonists can produce analgesia. Also, identification of specific second messenger molecules that regulate phosphorylation of TRPV1 has been the focus of intense research, to exploit a broader approach to pain treatment. The search for a role of TRPV2 in pain remains dormant due to the lack of suitable experimental models. However, progress into TRPA1's role in pain has received much attention recently. Another thermoTRP, TRPM8, encoding for the cool sensation and also expressed in nociceptors, has recently been shown to reduce pain via a central mechanism, thus opening a novel strategy for achieving analgesia. The role of other thermoTRP's (TRPV3 and TRPV4) encoding for detection of warm temperatures and expressed in nociceptors cannot be excluded. This review will discuss current knowledge on the role of nociceptor thermoTRPs in pain and therapy and describes the activator and inhibitor molecules known to interact with them and modulate their activity.

Nociceptors--noxious stimulus detectors

In order to deal effectively with danger, it is imperative to know about it. This is what nociceptors do--these primary sensory neurons are specialized to detect intense stimuli and represent, therefore, the first line of defense against any potentially threatening or damaging environmental inputs. By sensing noxious stimuli and contributing to the necessary reactions to avoid them--rapid withdrawal and the experience of an intensely unpleasant or painful sensation, nociceptors are essential for the maintenance of the body's integrity. Although nociceptive pain is clearly an adaptive alarm system, persistent pain is maladaptive, essentially an ongoing false alarm. Here, we highlight the genesis of nociceptors during development and the intrinsic properties of nociceptors that enable them to transduce, conduct, and transmit nociceptive information and also discuss how their phenotypic plasticity contributes to clinical pain.