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Immunofluorescence staining of DRG neurons. DRG neurons from the control and the CCI groups are stained using a marker for IB4 (green) and TREK (red). (A) Double immunofluorescence indicates a partial colocalization between the IB4+ neuron and TREK-1. (B) The expression of TREK-2 was weak on both control and CCI groups, and little colocalization was observed between IB4+ and TREK-2. The expression of TREK-1 was stronger compared to TREK-2 on IB4+ CCI DRG neurons.
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Neuropathic pain is a complex state showing increased pain response with dysfunctional inhibitory neurotransmission. The TREK family, one of the two pore domain K+ (K2P) channel subgroups were focused among various mechanisms of neuropathic pain. These channels influence neuronal excitability and are thought to be related in mechano/thermosensation...
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... staining intensity was increased in the DRG of CCI mice compared to the DRG of shame mice. The merged image of DRG of CCI mice revealed partial colocalization between IB4 and TREK-1. TREK-1 expression was also observed on IB4-neurons (Fig. 3A). The expression of TREK-2 was weak on both control and the CCI groups, only slightly increased in the DRG of CCI mice. There was little colocalization between IB4 and TREK-2, much weaker than that of TREK-1 and IB4 (Fig. ...
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... DRG of CCI mice revealed partial colocalization between IB4 and TREK-1. TREK-1 expression was also observed on IB4-neurons (Fig. 3A). The expression of TREK-2 was weak on both control and the CCI groups, only slightly increased in the DRG of CCI mice. There was little colocalization between IB4 and TREK-2, much weaker than that of TREK-1 and IB4 (Fig. ...
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... such as rilu- zole; and some volatile anesthetics (Kim and Chung, 1992; For comparison, the control group was tested at pH 7.3, without any pressure or activator. The TREK-1-like channel was easily activated by TREK-1 activators. *p<0.05, **p<0.01 vs. the control value (n=5, Low pH: p=0.005, Negative pressure: p=0.02, Riluzole treatment: p=0.003, Fig. 3). Saadé et al., 2002). The release of unsaturated free fatty ac- ids, local heat or fever, acidosis, and mechanical stretch due to edema are common findings of the inflammatory process and nerve damage. The TREK subfamily is a group of tem- perature sensitive K + channels, and within the 24-37°C range, there is progressive increase in ...
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P2X7 receptor is a crucial receptor related to neuronal activation, neurosensitization, and pain transmission, and increasing evidences indicated that glial cells is thought to be a major contributor to the chronic neuropathic pain after nerve injury. In present study, we designed to investigate whether the P2X7R in glial plays a role in chronic ne...
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... Експериментально було показано, що мРНК каналів TREK-1 присутні в дорзальних гангліях. Їх рівні підвищуються внаслідок хронічної інфравезикальної обструкції [55], а також після хронічного стиснення нерва [56]. Встановлено, що при запаленні передміхурової залози експресія теплових каналів K2P посилюється в грудо-поперекових і попереково-крижових відділах [57]. ...
Introduction. The need to understand the pathophysiology of prostatitis is determined by its prevalence, usually chronic progressive course, significant impact on quality of life, fertility and sexuality. The modern arsenal of medicines allows us to achieve a clinically significant effect. Along with this, non-pharmacological methods are widely used to increase the effectiveness of treatment. However, despite significant successes in the treatment of prostatitis, the problems of insufficient efficiency remain unsolved by modern urology, and it is extremely difficult to help these patients. Understanding the pathophysiology of the disease has always been the key to successful diagnosis and treatment. That is why it is important to determine the mechanisms of development of painful manifestations of prostatitis. The aim. To describe the main molecular mechanisms of tissue damage reception, in particular of the prostate gland, which are perceived as pain sensations. Materials and methods. An evaluation of modern literature devoted to the mechanisms of creation of nerve impulses due to damage and inflammation of the prostate gland was carried out. The search was conducted in the MEDLINE and databases of the National Library of Ukraine named after V.I. Vernadsky. Results. The main molecular mechanisms of nociception in chronic prostatitis have been determined. A review of modern literature devoted to the study of pain mechanisms as a biologically significant signal of damage at the molecular level of reception is presented. Attention is focused on the features of nociception in prostatitis, its connection with the production of inflammatory mediators, possible mechanisms of hyperalgesia and allodynia. As a result of stress and tissue damage, the production and release of inflammatory mediators such as interleukins, interferon, prostaglandins, bradykinin, adenosine triphosphate, protons and nerve growth factor increase. These mediators activate pain receptors located on nerve endings and are ion channels of various types: transient receptor potential, acid, purinergic, and potassium ion leak channels. Conclusions. The presented literature data describe the mechanisms of nociception, hyperalgesia and allodynia in chronic prostatitis, the understanding of which can be the basis for the development of new methods of diagnosis and treatment.
... Many studies reported that chronic pain downregulated Kv1.4 and BKCa and upregulated other peripheral nociceptive nerve ICs [37][38][39][40][41]. Moreover, a study of a chronic pain model showed that BKCa blockade suppressed afterhyperpolarization [42], and a separate study showed that pruritus-related pathways were associated with a lower AP frequency than pain pathways [43]. ...
Background: Expression levels of voltage-dependent T-type calcium channel subunit alfa 1H (Cav3.2), big conductance calcium-activated potassium channel (BKCa), and anoctamin 1 in the skin, including in peripheral nerve endings were previously found to be significantly elevated in patients with chronic kidney disease (CKD)–associated pruritus (CKD-aP). On the other hand, the expression of transient receptor potential 1 was significantly reduced.
Methods: We further compared CKD patients with and without CKD-aP in terms of the expression levels of several ion channels Based on CKD-aP severity, subjects were divided into two groups: non-CKD-aP (no or slight pruritus; n = 16) and CKD-aP (mild, moderate, or severe pruritus; n = 16). Skin samples were obtained from the forearm or elbow during arteriovenous fistula surgery. We used quantitative reverse transcriptional polymerase chain reaction (RT-PCR)to measure the skin expression levels of the following ion channels in the skin: voltage gated sodium channel 1.7 (Nav1.7), voltage gated potassium channel 7.2 (Kv7.2), TWIK-related K+ channel 1 (TREK1), hyperpolarization-activated cyclic nucleotide-gated channel type 2 (HCN2), tyrosine kinase receptor A (TrkA), and piezo-type mechano-sensitive ion channel component 2 (Piezo2).
Results: RT-PCR analyses showed that CKD-aP patients had significantly higher levels of TREK1 and Piezo2 transcripts and significantly lower levels of HCN2 transcripts than non–CKD-aP patients. No significant differences were noted between groups in the expression of Nav1.7 or TrkA. Moreover, Kv7.2 transcripts were not detected in either group.
Conclusion: In skin samples collected from CKD-aP patients, ion channel expression patterns were altered to enhance hyperpolarization of pruriceptive neurons.
... Riluzole is the only drug to prolong survival for amyotrophic lateral sclerosis [26]; however, increasing evidences have shown that riluzole has antinociceptive benefit [12,[34][35][36][37][38]. But the underlying mechanism is still obscure. ...
Neuropathic pain since early diabetes swamps patients’ lives, and diabetes mellitus has become an increasingly worldwide epidemic. No agent, so far, can terminate the ongoing diabetes. Therefore, strategies that delay the process and the further complications are preferred, such as diabetic neuropathic pain (DNP). Dysfunction of ion channels is generally accepted as the central mechanism of diabetic associated neuropathy, of which hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) ion channel has been verified the involvement of neuropathic pain in dorsal root ganglion (DRG) neurons. Riluzole is a benzothiazole compound with neuroprotective properties on intervention to various ion channels, including hyperpolarization-activated voltage-dependent channels. To investigate the effect of riluzole within lumbar (L3-5) DRG neurons from DNP models, streptozocin (STZ, 70 mg/kg) injection was recruited subcutaneously followed by paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL), which both show significant reduction, whilst relieved by riluzole (4 mg/kg/d) administration, which was performed once daily for 7 consecutive days for 14 days. HCN2 expression was also decreased in line with alleviated behavioral tests. Our results indicate riluzole as the alleviator to STZ-induced DNP with involvement of downregulated HCN2 in lumbar DRG by continual systemic administration in rats.
... The role of TREK-1 in acute nociception [5,8] and neuropathic pain [19][20][21] is well known. However, its participation in acute and chronic inflammatory pain remains unclear. ...
... Formalin injection enhanced TREK-1 protein expression in the ipsilateral DRG and dorsal region of the spinal cord, sites related to the peripheral and spinal processing of pain. Our results agree with previous studies demonstrating that TREK-1 is up-regulated in inflammatory [2] and nerve injury [5,[19][20][21] conditions in rodents. However, data contrast with some reports showing that TREK-1 expression is downregulated in DRG in a colon inflammatory model [43] or oxaliplatin-induced neuropathic pain [44]. ...
TREK-1 channels are expressed in small nociceptive dorsal root ganglion (DRG) neurons where they participate in acute inflammatory and neuropathic pain. However, the role of TREK-1 in persistent pain is not well understood. The aim of this study was to investigate the local peripheral and spinal participation of TREK-1 in formalin-induced acute and long-lasting nociceptive hypersensitivity. Local peripheral or intrathecal pre-treatment with spadin, selective blocker of TREK-1, increased acute flinching behavior and secondary mechanical allodynia and hyperalgesia behavior observed 6 days after formalin injection. Local peripheral or intrathecal pre-treatment with BL-1249, selective opener of TREK-1, decreased long-lasting secondary mechanical allodynia and hyperalgesia induced by formalin. Pre-treatment with BL-1249 prevented the pro-nociceptive effect of spadin on acute nociception and long-lasting mechanical allodynia and hyperalgesia in rats. Pre-treatment with two recombinant channels that produce a high TREK-1 current, S300A and S333A (non-phosphorylated state of TREK-1), reduced formalin-induced acute pain and long-lasting mechanical allodynia and hyperalgesia. Besides, post-treatment with S300A, S333A or BL-1249 reversed long-lasting mechanical allodynia and hyperalgesia induced by formalin. Formalin increased TREK-1 expression at 1 and 6 days in DRG and dorsal spinal cord in rats, whereas that it increased c-fos expression at the DRG. Intrathecal repeated transfection of rats with S300A and S333A or injection with BL-1249 reduced formalin-induced enhanced c-fos expression. Data suggest that TREK-1 activity at peripheral and spinal sites reduces neuronal excitability in the process of acute and long-lasting nociception induced by formalin in rats.
... In the peripheral nervous system, several K2P channels are highly expressed in dorsal root ganglion (DRG) and trigeminal ganglion (TG) [35][36][37][38] and play a crucial role in acute or chronic nociceptive processing by hyperpolarizing the RMP or counteracting the AP of nociceptive neurons [39]. Their mRNA and protein levels are also altered during inflammatory and neuropathic pain conditions [35,36,[40][41][42][43][44][45][46][47]. After K2P gene knockout or knockdown in rodents, animals showed increased sensitivity to thermal, and mechanical stimuli compared to wild type animals [40,41,[47][48][49][50][51][52]. ...
... In acute pancreatitis, the mRNA levels of TREK-1 and TREK-2 in DRG neurons were also downregulated [76]. In other pain models, including chronic constriction injury [46,47], spinal nerve axotomy [37] or complete Freund's adjuvant induced inflammatory pain [35,40], changes in the mRNA levels of TREK channels were contradictory. The underlying mechanisms for the altered protein or mRNA expression remain to be investigated in pathological pain. ...
Two-pore domain potassium (K2P) channels are a diverse family of potassium channels. K2P channels generate background leak potassium currents to regulate cellular excitability and are thereby involved in a wide range of neurological disorders. K2P channels are modulated by a variety of physicochemical factors such as mechanical stretch, temperature, and pH. In the the peripheral nervous system (PNS), K2P channels are widely expressed in nociceptive neurons and play a critical roles in pain perception. In this review, we summarize the recent advances in the pharmacological properties of K2P channels, with a focus on the exogenous small-molecule activators targeting K2P channels. We emphasize the subtype-selectivity, cellular and in vivo pharmacological properties of all the reported small-molecule activators. The key underlying analgesic mechanisms mediated by K2P are also summarized based on the data in the literature from studies using small-molecule activators and genetic knock-out animals. We discuss advantages and limitations of the translational perspectives of K2P in pain medicine and provide outstanding questions for future studies in the end.
... Accordingly, TREK-1 knockout mice show thermal and mechanical hypersensitivity (Alloui et al., 2006;Noël et al., 2009). Recent studies have shown that nerve injury increases expression of TREK-1 in rats and mice (Han et al., 2016;Shi et al., 2018), whereas treatment with a non-selective activator of TREK-1 reduces oxaliplatin-induced pain (Poupon et al., 2018). However, the function and modulation of TREK-1 channels in neuropathic pain remains to be determined. ...
... Our results agree with those showing that oxaliplatin decreases TREK-1 mRNA in DRG of mice (Descoeur et al., 2011). In contrast, other reports have demonstrated that nerve injury up-regulates TREK-1 mRNA in mice and rats (Han et al., 2016;Shi et al., 2018). Differences could be due to the different primers to determine TREK-1 mRNA, as there are several alternative splicing TREK-1 variants (Rinné et al., 2014;Veale et al., 2010). ...
... versus SNL rats, by one-way ANOVA followed by Dunnett test and uninjured L4 DRG at 7 and 14 days after surgery. Other reports also have demonstrated that nerve injury increases TREK-1 protein expression in mice and rats (Han et al., 2016;Shi et al., 2018). Of note, antibody used for western blot analysis detects the amino terminal region of the TREK-1 1 and 2 isoforms. ...
PKC and PKA phosphorylation inhibit TREK‐1 channels downstream of Gs protein‐coupled receptor activation in vitro. However, the role of phosphorylation of TREK‐1 in neuropathic pain is unknown. The purpose of this study was to investigate whether altered TREK‐1 channel function by PKA and PKC modulators contributes to antiallodynia in neuropathic rats. Furthermore, we investigated if the in vitro described sites for PKC and PKA phosphorylation (S300 and S333, respectively) participate in the modulation of TREK‐1 in naïve and neuropathic rats. L5/L6 spinal nerve ligation (SNL) induced tactile allodynia. Intrathecal injection of BL‐1249 (TREK‐1 activator) reversed nerve injury‐induced tactile allodynia, whereas spadin (TREK‐1 blocker) produced tactile allodynia in naïve rats and reversed the antiallodynic effect induced by BL‐1249 in neuropathic rats. Intrathecal administration of rottlerin or Rp‐cAMPs (PKC and PKA inhibitors, respectively) enhanced the antiallodynia observed with BL‐1249 in neuropathic rats. In contrast, pretreatment with PdBu or forskolin (PKC and PKA activators, respectively) reduced the BL‐1249‐induced antiallodynia. Intrathecal injection of two high‐activity TREK‐1 recombinant channels, using a in vivo transfection method with lipofectamine, with mutations at PKC/PKA phosphosites (S300A and S333A) reversed tactile allodynia in neuropathic rats, with no effect in naïve rats. In contrast, transfection of two low‐activity TREK‐1 recombinant channels with phosphomimetic mutations at those sites (S300D and S333D) produced tactile allodynia in naïve rats and interfered with antiallodynic effects of rottlerin/BL‐1249 or Rp‐cAMPs/BL‐1249. Data suggest that TREK‐1 channel activity can be dynamically tuned in vivo by PKC/PKA to provoke allodynia and modulate its antiallodynic role in neuropathic pain.
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... In DRG neurons treated in vitro with oxaliplatin, we observed an early and transient negative regulation of both spontaneous and capsaicin-evoked electrical activity. In mice, TREK channels are highly expressed in both peptidergic and nonpeptidergic small sensory neurons [8,42]. Furthermore, TREK-1 extensively co-localizes with TRPV1 [8], the capsaicin-activated nonselective ion channel. ...
Oxaliplatin-induced peripheral neuropathy is characterized by an acute hyperexcitability syndrome triggered/exacerbated by cold. The mechanisms underlying oxaliplatin-induced peripheral neuropathy are unclear, but the alteration of ion channel expression and activity plays a well-recognized central role. Recently, we found that oxaliplatin leads to cytosolic acidification in dorsal root ganglion (DRG) neurons. Here, we investigated the early impact of oxaliplatin on the proton-sensitive TREK potassium channels. Following a 6-h oxaliplatin treatment, both channels underwent a transcription upregulation that returned to control levels after 42 h. The overexpression of TREK channels was also observed after in vivo treatment in DRG cells from mice exposed to acute treatment with oxaliplatin. Moreover, both intracellular pH and TREK channel transcription were similarly regulated after incubation with amiloride, an inhibitor of the Na + /H + exchanger. In addition, we studied the role of oxaliplatin-induced acidification on channel behavior, and, as expected, we observed a robust positive modulation of TREK channel activity. Finally, we focused on the impact of this complex modulation on capsaicin-evoked neuronal activity finding a transient decrease in the average firing rate following 6 h of oxaliplatin treatment. In conclusion, the early activation of TREK genes may represent a mechanism of protection against the oxaliplatin-related perturbation of neuronal excitability.
... In the present study, CurDG, at the lowest dose tested (equimolar to 25 mg/kg curcumin), demonstrated a significant reduction in both mechanical and thermal pain hypersensitivities compared to the CCI-control group (p < 0.05). Though many studies reported the baseline PWT of mice lying below 1.4 g, the baseline PWT value of ≈ 4 g, obtained in this study, was consistent with several previous studies [38,39]. Moreover, as per the AUC data obtained for the entire time-course, a dose-dependent reduction in both mechanical and thermal pain-hypersensitivities was observed with 25, 50, and 100 CurDG (p < 0.05), while 200 CurDG showed comparable analgesia with 100 CurDG. ...
The drug treatment for neuropathic pain remains a challenge due to poor efficacy and patient satisfaction. Curcumin has been reported to alleviate neuropathic pain, but its clinical application is hindered by its low solubility and poor oral bioavailability. Curcumin diglutaric acid (CurDG) is a curcumin prodrug with improved water solubility and in vivo antinociceptive effects. In this study, we investigated the anti-inflammatory mechanisms underlying the analgesic effect of CurDG in the chronic constriction injury (CCI)-induced neuropathy mouse model. Repeated oral administration of CurDG at a low dose equivalent to 25 mg/kg/day produced a significant analgesic effect in this model, both anti-allodynic activity and anti-hyperalgesic activity appearing at day 3 and persisting until day 14 post-CCI surgery (p < 0.001) while having no significant effect on the motor performance. Moreover, the repeated administration of CurDG diminished the increased levels of the pro-inflammatory cytokines: TNF-α and IL-6 in the sciatic nerve and the spinal cord at the lowest tested dose (equimolar to 25 mg/kg curcumin). This study provided pre-clinical evidence to substantiate the potential of pursuing the development of CurDG as an analgesic agent for the treatment of neuropathic pain.
... Importantly, after CFAinduced inflammation, spontaneous foot lifting, a measure of spontaneous pain, was increased in animals where TREK2 had been lowered by siRNA and in animals with naturally lower levels of TREK2 [9]. In chronic constriction injury models of neuropathic pain, an increase in TREK2 mRNA was also observed compared to non-injured animals [12]. ...
TREK2 (KCNK10, K2P10.1) is a two-pore domain potassium (K2P) channel and a potential target for the treatment of pain. Like the majority of the K2P superfamily, there is currently a lack of useful pharmacological tools to study TREK2. Here we present a strategy for identifying novel TREK2 activators. A cell-based thallium flux assay was developed and used to screen a library of drug-like molecules, from which we identified the CysLT1 antagonist Pranlukast as a novel activator of TREK2. This compound was selective for TREK2 versus TREK1 and showed no activity at TRAAK. Pranlukast was also screened against other members of the K2P superfamily. Several close analogues of Pranlukast and other CysLT1 antagonists were also tested for their ability to activate K2P channels. Consistent with previous work, structure activity relationships showed that subtle structural changes to these analogues completely attenuated the activation of TREK2, whereas for TREK1, analogues moved from activators to inhibitors. Pranlukast's activity was also confirmed using whole-cell patch clamp electrophysiology. Studies using mutant forms of TREK2 suggest Pranlukast does not bind in the K2P modulator pocket or the BL-1249 binding site. Pranlukast therefore represents a novel tool by which to study the mechanism of TREK2 activation.
... Furthermore, TREK-1 deficiency enhanced astrogliosis, neuronal apoptosis, demyelination and retarded motor recovery (Fang et al., 2017). Nevertheless, in other reported studies, in the DRG, the microRNA miR-183 expression was decreased and TREK-1 expression was increased in neuropathic pain induced by chronic constriction of sciatic nerve (CCI) ( Table 3; Han et al., 2016;Shi et al., 2018). Intrathecal injection of miR-183 alleviated pain in rat model of CCI and downregulated TREK-1 expression (Shi et al., 2018). ...
TREK-1 is the most studied background K2P channel. Its main role is to control cell excitability and maintain the membrane potential below the threshold of depolarization. TREK-1 is multi-regulated by a variety of physical and chemical stimuli which makes it a very promising and challenging target in the treatment of several pathologies. It is mainly expressed in the brain but also in heart, smooth muscle cells, endocrine pancreas, and prostate. In the nervous system, TREK-1 is involved in many physiological and pathological processes such as depression, neuroprotection, pain, and anesthesia. These properties explain why many laboratories and pharmaceutical companies have been focusing their research on screening and developing highly efficient modulators of TREK-1 channels. In this review, we summarize the different roles of TREK-1 that have been investigated so far in attempt to characterize pharmacological tools and new molecules to modulate cellular functions controlled by TREK-1.
