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Ongtanasup T, Tawanwongsri W, Manaspon C, Srisang S, Eawsakul K. Comprehensive investigation of niosomal red palm wax gel encapsulating ginger (Zingiber officinale Roscoe): Network pharmacology, molecular docking, In vitro studies and phase 1 clinical trials. Int J Biol Macromol 2024; 277:134334. [PMID: 39094890 DOI: 10.1016/j.ijbiomac.2024.134334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2024] [Revised: 07/24/2024] [Accepted: 07/29/2024] [Indexed: 08/04/2024]
Abstract
Ginger, a Zingeberaceae family member, is notable for its anti-inflammatory properties. This study explores the pharmaceutical mechanisms of ginger and red palm wax co-extract, developing novel niosomal formulations for enhanced transdermal delivery. Evaluations included physical characteristics, drug loading, in vitro release, network pharmacology, molecular docking, and biocompatibility. The niosomal ginger with red palm wax gel (NGPW) exhibited non-Newtonian fluid properties. The optimized niosome formulation (cholesterol: Tween80: Span60 = 12.5: 20: 5 w/w) showed a high yield (93.23 %), high encapsulation efficiency (54.71 %), and small size (264.33 ± 5.84 nm), prolonging in vitro anti-inflammatory activity. Human skin irritation and biocompatibility tests on 1 % NGPW showed favorable cytotoxicity and hemocompatibility results (ISO10993). Network pharmacology identified potential targets, while molecular docking highlighted high affinities between gingerol and red palm wax compounds with TRPM8 and TRPV1 proteins, suggesting pain inhibition via serotonergic synapse pathways. NGPW presents a promising transdermal pain inhibitory drug delivery strategy.
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Affiliation(s)
- Tassanee Ongtanasup
- School of Medicine, Walailak University, Nakhon Si Thammarat 80160, Thailand
| | | | - Chawan Manaspon
- Biomedical Engineering Institute, Chiang Mai University, Chiang Mai 50200, Thailand; Biomedical Engineering and Innovation Research Center, Chiang Mai University, Chiang Mai 50200, Thailand
| | - Siriwan Srisang
- Energy Engineering Division, Department of Engineering, King Mongkut's Institute of Technology Lad-krabang, Prince of Chumphon Campus, Chumphon 86160, Thailand
| | - Komgrit Eawsakul
- School of Medicine, Walailak University, Nakhon Si Thammarat 80160, Thailand; Research Excellence Center for Innovation and Health Products (RECIHP), Walailak University, Nakhon Si Thammarat 80160, Thailand.
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Garza-Carbajal A, Bavencoffe A, Herrera JJ, Johnson KN, Walters ET, Dessauer CW. Mechanism of gabapentinoid potentiation of opioid effects on cyclic AMP signaling in neuropathic pain. Proc Natl Acad Sci U S A 2024; 121:e2405465121. [PMID: 39145932 PMCID: PMC11348325 DOI: 10.1073/pnas.2405465121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2024] [Accepted: 07/10/2024] [Indexed: 08/16/2024] Open
Abstract
Over half of spinal cord injury (SCI) patients develop opioid-resistant chronic neuropathic pain. Safer alternatives to opioids for treatment of neuropathic pain are gabapentinoids (e.g., pregabalin and gabapentin). Clinically, gabapentinoids appear to amplify opioid effects, increasing analgesia and overdose-related adverse outcomes, but in vitro proof of this amplification and its mechanism are lacking. We previously showed that after SCI, sensitivity to opioids is reduced by fourfold to sixfold in rat sensory neurons. Here, we demonstrate that after injury, gabapentinoids restore normal sensitivity of opioid inhibition of cyclic AMP (cAMP) generation, while reducing nociceptor hyperexcitability by inhibiting voltage-gated calcium channels (VGCCs). Increasing intracellular Ca2+ or activation of L-type VGCCs (L-VGCCs) suffices to mimic SCI effects on opioid sensitivity, in a manner dependent on the activity of the Raf1 proto-oncogene, serine/threonine-protein kinase C-Raf, but independent of neuronal depolarization. Together, our results provide a mechanism for potentiation of opioid effects by gabapentinoids after injury, via reduction of calcium influx through L-VGCCs, and suggest that other inhibitors targeting these channels may similarly enhance opioid treatment of neuropathic pain.
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Affiliation(s)
- Anibal Garza-Carbajal
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX77030
| | - Alexis Bavencoffe
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX77030
| | - Juan J. Herrera
- Department of Diagnostic and Interventional Imaging, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX77030
| | - Kayla N. Johnson
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX77030
| | - Edgar T. Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX77030
| | - Carmen W. Dessauer
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX77030
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Sankaranarayanan I, Kume M, Mohammed A, Mwirigi JM, Inturi NN, Munro G, Petersen KA, Tavares-Ferreira D, Price TJ. Persistent changes in nociceptor translatomes govern hyperalgesic priming in mouse models. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.08.07.606891. [PMID: 39149295 PMCID: PMC11326310 DOI: 10.1101/2024.08.07.606891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 08/17/2024]
Abstract
Hyperalgesic priming is a model system that has been widely used to understand plasticity in painful stimulus-detecting sensory neurons, called nociceptors. A key feature of this model system is that following priming, stimuli that do not normally cause hyperalgesia now readily provoke this state. We hypothesized that hyperalgesic priming occurs due to reorganization of translation of mRNA in nociceptors. To test this hypothesis, we used paclitaxel treatment as the priming stimulus and translating ribosome affinity purification (TRAP) to measure persistent changes in mRNA translation in Nav1.8+ nociceptors. TRAP sequencing revealed 161 genes with persistently altered mRNA translation in the primed state. We identified Gpr88 as upregulated and Metrn as downregulated. We confirmed a functional role for these genes, wherein a GPR88 agonist causes pain only in primed mice and established hyperalgesic priming is reversed by Meteorin. Our work demonstrates that altered nociceptor translatomes are causative in producing hyperalgesic priming.
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Affiliation(s)
- Ishwarya Sankaranarayanan
- Pain Neurobiology Research Group, Department of Neuroscience, Center for Advanced Pain Studies, School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas
| | - Moeno Kume
- Pain Neurobiology Research Group, Department of Neuroscience, Center for Advanced Pain Studies, School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas
| | - Ayaan Mohammed
- Pain Neurobiology Research Group, Department of Neuroscience, Center for Advanced Pain Studies, School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas
| | - Juliet M Mwirigi
- Pain Neurobiology Research Group, Department of Neuroscience, Center for Advanced Pain Studies, School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas
| | - Nikhil Nageswar Inturi
- Pain Neurobiology Research Group, Department of Neuroscience, Center for Advanced Pain Studies, School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas
| | | | | | - Diana Tavares-Ferreira
- Pain Neurobiology Research Group, Department of Neuroscience, Center for Advanced Pain Studies, School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas
| | - Theodore J Price
- Pain Neurobiology Research Group, Department of Neuroscience, Center for Advanced Pain Studies, School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas
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Bavencoffe A, Zhu MY, Neerukonda SV, Johnson KN, Dessauer CW, Walters ET. Induction of long-term hyperexcitability by memory-related cAMP signaling in isolated nociceptor cell bodies. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.13.603393. [PMID: 39071414 PMCID: PMC11275899 DOI: 10.1101/2024.07.13.603393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/30/2024]
Abstract
Persistent hyperactivity of nociceptors is known to contribute significantly to long-lasting sensitization and ongoing pain in many clinical conditions. It is often assumed that nociceptor hyperactivity is mainly driven by continuing stimulation from inflammatory mediators. We have tested an additional possibility: that persistent increases in excitability promoting hyperactivity can be induced by a prototypical cellular signaling pathway long known to induce late-phase long-term potentiation (LTP) of synapses in brain regions involved in memory formation. This cAMP-PKA-CREB-gene transcription-protein synthesis pathway was tested using whole-cell current clamp methods on small dissociated sensory neurons (primarily nociceptors) from dorsal root ganglia (DRGs) excised from previously uninjured ("naïve") rats. Six-hour treatment with the specific Gαs-coupled 5-HT4 receptor agonist, prucalopride, or with the adenylyl cyclase activator, forskolin, induced long-term hyperexcitability (LTH) in DRG neurons that manifested 12-24 hours later as action potential (AP) discharge (ongoing activity, OA) during artificial depolarization to -45 mV, a membrane potential that is normally subthreshold for AP generation. Prucalopride treatment also induced significant long-lasting depolarization of resting membrane potential (from -69 to -66 mV), enhanced depolarizing spontaneous fluctuations (DSFs) of membrane potential, and indications of reduced AP threshold and rheobase. LTH was prevented by co-treatment of prucalopride with inhibitors of PKA, CREB, gene transcription, and protein synthesis. As in the induction of synaptic memory, many other cellular signals are likely to be involved. However, the discovery that this prototypical memory induction pathway can induce nociceptor LTH, along with reports that cAMP signaling and CREB activity in DRGs can induce hyperalgesic priming, suggest that early, temporary, cAMP-induced transcriptional and translational mechanisms can induce nociceptor LTH that might last for long periods. An interesting possibility is that these mechanisms can also be reactivated by re-exposure to inflammatory mediators such as serotonin during subsequent challenges to bodily integrity, "reconsolidating" the cellular memory and thereby extending the duration of persistent nociceptor hyperexcitability.
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Affiliation(s)
- Alexis Bavencoffe
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas, USA 77030
| | - Michael Y. Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas, USA 77030
| | - Sanjay V. Neerukonda
- Medical Scientist Training Program, McGovern Medical School at UTHealth, Houston, Texas, USA 77030
| | - Kayla N. Johnson
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas, USA 77030
| | - Carmen W. Dessauer
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas, USA 77030
| | - Edgar T. Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas, USA 77030
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Tian J, Bavencoffe AG, Zhu MX, Walters ET. Readiness of nociceptor cell bodies to generate spontaneous activity results from background activity of diverse ion channels and high input resistance. Pain 2024; 165:893-907. [PMID: 37862056 PMCID: PMC10950548 DOI: 10.1097/j.pain.0000000000003091] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Accepted: 08/09/2023] [Indexed: 10/21/2023]
Abstract
ABSTRACT Nociceptor cell bodies generate "spontaneous" discharge that can promote ongoing pain in persistent pain conditions. Little is known about the underlying mechanisms. Recordings from nociceptor cell bodies (somata) dissociated from rodent and human dorsal root ganglia have shown that previous pain in vivo is associated with low-frequency discharge controlled by irregular depolarizing spontaneous fluctuations of membrane potential (DSFs), likely produced by transient inward currents across the somal input resistance. Using mouse nociceptors, we show that DSFs are associated with high somal input resistance over a wide range of membrane potentials, including depolarized levels where DSFs approach action potential (AP) threshold. Input resistance and both the amplitude and frequency of DSFs were increased in neurons exhibiting spontaneous activity. Ion substitution experiments indicated that the depolarizing phase of DSFs is generated by spontaneous opening of channels permeable to Na + or Ca 2+ and that Ca 2+ -permeable channels are especially important for larger DSFs. Partial reduction of the amplitude or frequency of DSFs by perfusion of pharmacological inhibitors indicated small but significant contributions from Nav1.7, Nav1.8, TRPV1, TRPA1, TRPM4, and N-type Ca 2+ channels. Less specific blockers suggested a contribution from NALCN channels, and global knockout suggested a role for Nav1.9. The combination of high somal input resistance plus background activity of diverse ion channels permeable to Na + or Ca 2+ produces DSFs that are poised to reach AP threshold if resting membrane potential depolarizes, AP threshold decreases, or DSFs become enhanced-all of which can occur under painful neuropathic and inflammatory conditions.
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Affiliation(s)
- Jinbin Tian
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Alexis G. Bavencoffe
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Michael X. Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Edgar T. Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
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Weng HR. Emerging Molecular and Synaptic Targets for the Management of Chronic Pain Caused by Systemic Lupus Erythematosus. Int J Mol Sci 2024; 25:3602. [PMID: 38612414 PMCID: PMC11011483 DOI: 10.3390/ijms25073602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Revised: 03/13/2024] [Accepted: 03/19/2024] [Indexed: 04/14/2024] Open
Abstract
Patients with systemic lupus erythematosus (SLE) frequently experience chronic pain due to the limited effectiveness and safety profiles of current analgesics. Understanding the molecular and synaptic mechanisms underlying abnormal neuronal activation along the pain signaling pathway is essential for developing new analgesics to address SLE-induced chronic pain. Recent studies, including those conducted by our team and others using the SLE animal model (MRL/lpr lupus-prone mice), have unveiled heightened excitability in nociceptive primary sensory neurons within the dorsal root ganglia and increased glutamatergic synaptic activity in spinal dorsal horn neurons, contributing to the development of chronic pain in mice with SLE. Nociceptive primary sensory neurons in lupus animals exhibit elevated resting membrane potentials, and reduced thresholds and rheobases of action potentials. These changes coincide with the elevated production of TNFα and IL-1β, as well as increased ERK activity in the dorsal root ganglion, coupled with decreased AMPK activity in the same region. Dysregulated AMPK activity is linked to heightened excitability in nociceptive sensory neurons in lupus animals. Additionally, the increased glutamatergic synaptic activity in the spinal dorsal horn in lupus mice with chronic pain is characterized by enhanced presynaptic glutamate release and postsynaptic AMPA receptor activation, alongside the reduced activity of glial glutamate transporters. These alterations are caused by the elevated activities of IL-1β, IL-18, CSF-1, and thrombin, and reduced AMPK activities in the dorsal horn. Furthermore, the pharmacological activation of spinal GPR109A receptors in microglia in lupus mice suppresses chronic pain by inhibiting p38 MAPK activity and the production of both IL-1β and IL-18, as well as reducing glutamatergic synaptic activity in the spinal dorsal horn. These findings collectively unveil crucial signaling molecular and synaptic targets for modulating abnormal neuronal activation in both the periphery and spinal dorsal horn, offering insights into the development of analgesics for managing SLE-induced chronic pain.
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Affiliation(s)
- Han-Rong Weng
- Department of Basic Sciences, California Northstate University College of Medicine, Elk Grove, CA 95757, USA
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Jiang C, Zhao J, Zhang Y, Zhu X. Role of EPAC1 in chronic pain. Biochem Biophys Rep 2024; 37:101645. [PMID: 38304575 PMCID: PMC10832381 DOI: 10.1016/j.bbrep.2024.101645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2023] [Revised: 01/08/2024] [Accepted: 01/10/2024] [Indexed: 02/03/2024] Open
Abstract
Chronic pain usually lasts over three months and commonly occurs in chronic diseases (cancer, arthritis, and diabetes), injuries (herniated discs, torn ligaments), and many major pain disorders (neuropathic pain, fibromyalgia, chronic headaches). Unfortunately, there is currently a lack of effective treatments to help people with chronic pain to achieve complete relief. Therefore,it is particularly important to understand the mechanism of chronic pain and find new therapeutic targets. The exchange protein directly activated by cyclic adenosine monophosphate(cAMP) (EPAC) has been recognized for its functions in nerve regeneration, stimulating insulin release, controlling vascular pressure, and controlling other metabolic activities. In recent years, many studies have found that the subtype of EPAC, EPAC1 is involved in the regulation of neuroinflammation and plays a crucial role in the regulation of pain, which is expected to become a new therapeutic target for chronic pain. This article reviews the major contributions of EPAC1 in chronic pain.
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Affiliation(s)
- Chenlu Jiang
- Department of Anesthesiology, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, 226001, China
- Medical School of Nantong University, Nantong, 226001, China
| | - Jiacheng Zhao
- Department of Anesthesiology, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, 226001, China
- Medical School of Nantong University, Nantong, 226001, China
| | - Yihang Zhang
- Medical School of Nantong University, Nantong, 226001, China
| | - Xiang Zhu
- Department of Anesthesiology, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, 226001, China
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Bavencoffe AG, Lopez ER, Johnson KN, Tian J, Gorgun FM, Shen BQ, Zhu MX, Dessauer CW, Walters ET. Widespread latent hyperactivity of nociceptors outlasts enhanced avoidance behavior following incision injury. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.30.578108. [PMID: 38352319 PMCID: PMC10862851 DOI: 10.1101/2024.01.30.578108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/24/2024]
Abstract
Nociceptors with somata in dorsal root ganglia (DRGs) exhibit an unusual readiness to switch from an electrically silent state to a hyperactive state of tonic, nonaccommodating, low-frequency, irregular discharge of action potentials (APs). Ongoing activity (OA) during this state is present in vivo in rats months after spinal cord injury (SCI), and has been causally linked to SCI pain. OA induced by various neuropathic conditions in rats, mice, and humans is retained in nociceptor somata after dissociation and culturing, providing a powerful tool for investigating its mechanisms and functions. An important question is whether similar nociceptor OA is induced by painful conditions other than neuropathy. The present study shows that probable nociceptors dissociated from DRGs of rats subjected to postsurgical pain (induced by plantar incision) exhibit OA. The OA was most apparent when the soma was artificially depolarized to a level within the normal range of membrane potentials where large, transient depolarizing spontaneous fluctuations (DSFs) can approach AP threshold. This latent hyperactivity persisted for at least 3 weeks, whereas behavioral indicators of affective pain - hindpaw guarding and increased avoidance of a noxious substrate in an operant conflict test - persisted for 1 week or less. An unexpected discovery was latent OA in neurons from thoracic DRGs that innervate dermatomes distant from the injured tissue. The most consistent electrophysiological alteration associated with OA was enhancement of DSFs. Potential in vivo functions of widespread, low-frequency nociceptor OA consistent with these and other findings are to amplify hyperalgesic priming and to drive anxiety-related hypervigilance.
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Affiliation(s)
- Alexis G. Bavencoffe
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Elia R. Lopez
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Kayla N. Johnson
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Jinbin Tian
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Falih M. Gorgun
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Breanna Q. Shen
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Michael X. Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Carmen W. Dessauer
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
| | - Edgar T. Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston
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Walters ET. Exaptation and Evolutionary Adaptation in Nociceptor Mechanisms Driving Persistent Pain. BRAIN, BEHAVIOR AND EVOLUTION 2023; 98:314-330. [PMID: 38035556 PMCID: PMC10922759 DOI: 10.1159/000535552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 11/23/2023] [Indexed: 12/02/2023]
Abstract
BACKGROUND Several evolutionary explanations have been proposed for why chronic pain is a major clinical problem. One is that some mechanisms important for driving chronic pain, while maladaptive for modern humans, were adaptive because they enhanced survival. Evidence is reviewed for persistent nociceptor hyperactivity (PNH), known to promote chronic pain in rodents and humans, being an evolutionarily adaptive response to significant bodily injury, and primitive molecular mechanisms related to cellular injury and stress being exapted (co-opted or repurposed) to drive PNH and consequent pain. SUMMARY PNH in a snail (Aplysia californica), squid (Doryteuthis pealeii), fruit fly (Drosophila melanogaster), mice, rats, and humans has been documented as long-lasting enhancement of action potential discharge evoked by peripheral stimuli, and in some of these species as persistent extrinsically driven ongoing activity and/or intrinsic spontaneous activity (OA and SA, respectively). In mammals, OA and SA are often initiated within the protected nociceptor soma long after an inducing injury. Generation of OA or SA in nociceptor somata may be very rare in invertebrates, but prolonged afterdischarge in nociceptor somata readily occurs in sensitized Aplysia. Evidence for the adaptiveness of injury-induced PNH has come from observations of decreased survival of injured squid exposed to predators when PNH is blocked, from plausible survival benefits of chronic sensitization after severe injuries such as amputation, and from the functional coherence and intricacy of mammalian PNH mechanisms. Major contributions of cAMP-PKA signaling (with associated calcium signaling) to the maintenance of PNH both in mammals and molluscs suggest that this ancient stress signaling system was exapted early during the evolution of nociceptors to drive hyperactivity following bodily injury. Vertebrates have retained core cAMP-PKA signaling modules for PNH while adding new extracellular modulators (e.g., opioids) and cAMP-regulated ion channels (e.g., TRPV1 and Nav1.8 channels). KEY MESSAGES Evidence from multiple phyla indicates that PNH is a physiological adaptation that decreases the risk of attacks on injured animals. Core cAMP-PKA signaling modules make major contributions to the maintenance of PNH in molluscs and mammals. This conserved signaling has been linked to ancient cellular responses to stress, which may have been exapted in early nociceptors to drive protective hyperactivity that can persist while bodily functions recover after significant injury.
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Affiliation(s)
- Edgar T Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas, USA
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10
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Viatchenko-Karpinski V, Kong L, Weng HR. Deficient AMPK activity contributes to hyperexcitability in peripheral nociceptive sensory neurons and thermal hyperalgesia in lupus mice. PLoS One 2023; 18:e0288356. [PMID: 37440542 PMCID: PMC10343046 DOI: 10.1371/journal.pone.0288356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Accepted: 06/23/2023] [Indexed: 07/15/2023] Open
Abstract
Patients with systemic lupus erythematosus (SLE) often suffer from chronic pain. Little is known about the peripheral mechanisms underlying the genesis of chronic pain induced by SLE. The aim of this study was to investigate whether and how membrane properties in nociceptive neurons in the dorsal root ganglions (DRGs) are altered by SLE. We found elevation of resting membrane potentials, smaller capacitances, lower action potential thresholds and rheobases in nociceptive neurons in the DRGs from MRL/lpr mice (an SLE mouse model) with thermal hyperalgesia. DRGs from MRL/lpr mice had increased protein expressions in TNFα, IL-1β, and phosphorylated ERK but suppressed AMPK activity, and no changes in sodium channel 1.7 protein expression. We showed that intraplantar injection of Compound C (an AMPK inhibitor) induced thermal hyperalgesia in normal mice while intraplantar injection of AICAR (an AMPK activator) reduced thermal hyperalgesia in MRL/Lpr mice. Upon inhibition of AMPK membrane properties in nociceptive neurons from normal control mice could be rapidly switched to those found in SLE mice with thermal hyperalgesia. Our study indicates that increased excitability in peripheral nociceptive sensory neurons contributes to the genesis of thermal hyperalgesia in mice with SLE, and AMPK regulates membrane properties in nociceptive sensory neurons as well as thermal hyperalgesia in mice with SLE. Our study provides a basis for targeting signaling pathways regulating membrane properties of peripheral nociceptive neurons as a means for conquering chronic pain caused by SLE.
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Affiliation(s)
| | - Lingwei Kong
- Department of Biomedical Sciences, Mercer University School of Medicine, Macon, GA, United States of America
| | - Han-Rong Weng
- Department of Biomedical Sciences, Mercer University School of Medicine, Macon, GA, United States of America
- Department of Basic Sciences, California Northstate University College of Medicine, Elk Grove, CA, United States of America
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Gabriel KA, Streicher JM. HSP90 inhibition in the mouse spinal cord enhances opioid signaling by suppressing an AMPK-mediated negative feedback loop. Sci Signal 2023; 16:eade2438. [PMID: 37040443 PMCID: PMC11010773 DOI: 10.1126/scisignal.ade2438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 03/22/2023] [Indexed: 04/13/2023]
Abstract
Opioids and other agonists of the μ-opioid receptor are effective at managing acute pain, but their chronic use can lead to tolerance that limits their efficacy. We previously reported that inhibiting the chaperone protein HSP90 in the spinal cords of mice promotes the antinociceptive effects of opioids in a manner that involved increased activation of the kinase ERK. Here, we found that the underlying mechanism involves the relief of a negative feedback loop mediated by the kinase AMPK. Intrathecal treatment of male and female mice with the HSP90 inhibitor 17-AAG decreased the abundance of the β1 subunit of AMPK in the spinal cord. The antinociceptive effects of 17-AAG with morphine were suppressed by intrathecal administration of AMPK activators and enhanced by an AMPK inhibitor. Opioid treatment increased the abundance of phosphorylated AMPK in the dorsal horn of the spinal cord, where it colocalized with a neuronal marker and the neuropeptide CGRP. Knocking down AMPK in CGRP-positive neurons enhanced the antinociceptive effects of morphine and demonstrated that AMPK mediated the signal transduction between HSP90 inhibition and ERK activation. These data suggest that AMPK mediates an opioid-induced negative feedback loop in CGRP neurons of the spinal cord and that this loop can be disabled by HSP90 inhibition to enhance the efficacy of opioids.
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Affiliation(s)
- Katherin A. Gabriel
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson AZ USA
| | - John M. Streicher
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson AZ USA
- Comprehensive Pain and Addiction Center, University of Arizona, Tucson AZ USA
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Walters ET, Crook RJ, Neely GG, Price TJ, Smith ESJ. Persistent nociceptor hyperactivity as a painful evolutionary adaptation. Trends Neurosci 2023; 46:211-227. [PMID: 36610893 PMCID: PMC9974896 DOI: 10.1016/j.tins.2022.12.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 12/05/2022] [Accepted: 12/16/2022] [Indexed: 01/07/2023]
Abstract
Chronic pain caused by injury or disease of the nervous system (neuropathic pain) has been linked to persistent electrical hyperactivity of the sensory neurons (nociceptors) specialized to detect damaging stimuli and/or inflammation. This pain and hyperactivity are considered maladaptive because both can persist long after injured tissues have healed and inflammation has resolved. While the assumption of maladaptiveness is appropriate in many diseases, accumulating evidence from diverse species, including humans, challenges the assumption that neuropathic pain and persistent nociceptor hyperactivity are always maladaptive. We review studies indicating that persistent nociceptor hyperactivity has undergone evolutionary selection in widespread, albeit selected, animal groups as a physiological response that can increase survival long after bodily injury, using both highly conserved and divergent underlying mechanisms.
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Affiliation(s)
- Edgar T Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
| | - Robyn J Crook
- Department of Biology, San Francisco State University, San Francisco, CA 94132, USA
| | - G Gregory Neely
- Charles Perkins Centre and School of Life and Environmental Sciences, The University of Sydney, NSW 2006, Australia
| | - Theodore J Price
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX 75080, USA
| | - Ewan St John Smith
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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13
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Ray PR, Shiers S, Caruso JP, Tavares-Ferreira D, Sankaranarayanan I, Uhelski ML, Li Y, North RY, Tatsui C, Dussor G, Burton MD, Dougherty PM, Price TJ. RNA profiling of human dorsal root ganglia reveals sex differences in mechanisms promoting neuropathic pain. Brain 2023; 146:749-766. [PMID: 35867896 PMCID: PMC10169414 DOI: 10.1093/brain/awac266] [Citation(s) in RCA: 47] [Impact Index Per Article: 47.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 05/16/2022] [Accepted: 06/22/2022] [Indexed: 11/12/2022] Open
Abstract
Neuropathic pain is a leading cause of high-impact pain, is often disabling and is poorly managed by current therapeutics. Here we focused on a unique group of neuropathic pain patients undergoing thoracic vertebrectomy where the dorsal root ganglia is removed as part of the surgery allowing for molecular characterization and identification of mechanistic drivers of neuropathic pain independently of preclinical models. Our goal was to quantify whole transcriptome RNA abundances using RNA-seq in pain-associated human dorsal root ganglia from these patients, allowing comprehensive identification of molecular changes in these samples by contrasting them with non-pain-associated dorsal root ganglia. We sequenced 70 human dorsal root ganglia, and among these 50 met inclusion criteria for sufficient neuronal mRNA signal for downstream analysis. Our expression analysis revealed profound sex differences in differentially expressed genes including increase of IL1B, TNF, CXCL14 and OSM in male and CCL1, CCL21, PENK and TLR3 in female dorsal root ganglia associated with neuropathic pain. Coexpression modules revealed enrichment in members of JUN-FOS signalling in males and centromere protein coding genes in females. Neuro-immune signalling pathways revealed distinct cytokine signalling pathways associated with neuropathic pain in males (OSM, LIF, SOCS1) and females (CCL1, CCL19, CCL21). We validated cellular expression profiles of a subset of these findings using RNAscope in situ hybridization. Our findings give direct support for sex differences in underlying mechanisms of neuropathic pain in patient populations.
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Affiliation(s)
- Pradipta R Ray
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA
| | - Stephanie Shiers
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA
| | - James P Caruso
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA.,Department of Neurological Surgery, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Diana Tavares-Ferreira
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA
| | - Ishwarya Sankaranarayanan
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA
| | - Megan L Uhelski
- Department of Pain Medicine, Division of Anesthesiology, MD Anderson Cancer Center, Houston, TX, USA
| | - Yan Li
- Department of Pain Medicine, Division of Anesthesiology, MD Anderson Cancer Center, Houston, TX, USA
| | - Robert Y North
- Department of Neurosurgery, MD Anderson Cancer Center, Houston, TX, USA
| | - Claudio Tatsui
- Department of Neurosurgery, MD Anderson Cancer Center, Houston, TX, USA
| | - Gregory Dussor
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA
| | - Michael D Burton
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA
| | - Patrick M Dougherty
- Department of Pain Medicine, Division of Anesthesiology, MD Anderson Cancer Center, Houston, TX, USA
| | - Theodore J Price
- Department of Neuroscience and Center for Advanced Pain Studies, University of Texas at Dallas, Richardson, TX, USA
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14
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Chai-Hu-San-Shen Capsule Ameliorates Ventricular Arrhythmia Through Inhibition of the CaMKII/FKBP12.6/RyR2/Ca 2+ Signaling Pathway in Rats with Myocardial Ischemia. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2022; 2022:2670473. [PMID: 36225189 PMCID: PMC9550443 DOI: 10.1155/2022/2670473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Accepted: 08/18/2022] [Indexed: 11/18/2022]
Abstract
Ventricular arrhythmia is one of the main causes of sudden cardiac death, especially after myocardial ischemia. Previous studies have shown that Chai-Hu-San-Shen capsule (CHSSC) can reduce the incidence of ventricular arrhythmias following myocardial ischemia, however, the mechanisms of it are unclear. In present study, we explored the mechanism of CHSSC ameliorates ventricular arrhythmia following myocardial ischemia via inhibiting the CaMKII/FKBP12.6/RyR2/Ca2+ signaling pathway. In vivo, a myocardial ischemia rat model was established and treated with CHSSC to evaluate the therapeutic effect of CHSSC. In vitro, we established an ischemia model in H9C2 cells and treated with CHSSC, KN-93, or H-89. Then, intracellular Ca2+ content, the expression of RyR2, and the interaction between FKBP12.6 and RyR2 were detected. The results showed that CHSSC could delay the occurrence of ventricular arrhythmias and shorten the duration of ventricular arrhythmias. After myocardial ischemia, the intracellular Ca2+ content was increased, and CHSSC treatment mitigated this increase, down-regulated the levels of p-CaMKII, CaMKII, p-RyR2, and RyR2, and up-regulated the levels of p-RyR2 (Ser2808) and p-RyR2 (Ser2814). Co-immunoprecipitation showed an interaction between FKBP12.6 and RyR2, and CHSSC up-regulated the content of the FKBP12.6-RyR2 complex in ischemic cells. In conclusion, our study showed that CaMKII activation led to hyperphosphorylation of RyR2 (Ser2814) and RyR2 (Ser2808) during cardiomyocyte ischemia, which resulted in dissociation of the FKBP12.6-RyR2 complex, and increased intracellular Ca2+ content, which may contribute to the development of ventricular arrhythmias. CHSSC may reduce the incidence of ventricular arrhythmias following myocardial ischemia through inhibition of the CaMKII/RyR2/FKBP12.6/Ca2+ signaling pathway.
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15
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Bavencoffe A, Spence EA, Zhu MY, Garza-Carbajal A, Chu KE, Bloom OE, Dessauer CW, Walters ET. Macrophage Migration Inhibitory Factor (MIF) Makes Complex Contributions to Pain-Related Hyperactivity of Nociceptors after Spinal Cord Injury. J Neurosci 2022; 42:5463-5480. [PMID: 35610050 PMCID: PMC9270921 DOI: 10.1523/jneurosci.1133-21.2022] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 05/12/2022] [Accepted: 05/19/2022] [Indexed: 02/08/2023] Open
Abstract
Neuropathic pain is a major, inadequately treated challenge for people with spinal cord injury (SCI). While SCI pain mechanisms are often assumed to be in the CNS, rodent studies have revealed mechanistic contributions from primary nociceptors. These neurons become chronically hyperexcitable after SCI, generating ongoing electrical activity that promotes ongoing pain. A major question is whether extrinsic chemical signals help to drive ongoing electrical activity after SCI. People living with SCI exhibit acute and chronic elevation of circulating levels of macrophage migration inhibitory factor (MIF), a cytokine implicated in preclinical pain models. Probable nociceptors isolated from male rats and exposed to an MIF concentration reported in human plasma (1 ng/ml) showed hyperactivity similar to that induced by SCI, although, surprisingly, a 10-fold higher concentration failed to increase excitability. Conditioned behavioral aversion to a chamber associated with peripheral MIF injection suggested that MIF stimulates affective pain. A MIF inhibitor, Iso-1, reversed SCI-induced hyperexcitability. Unlike chronic SCI-induced hyperexcitability, acute MIF-induced hyperexcitability was only partially abrogated by inhibiting ERK signaling. Unexpectedly, MIF concentrations that induced hyperactivity in nociceptors from naive animals, after SCI induced a long-lasting conversion from a highly excitable nonaccommodating type to a rapidly accommodating, hypoexcitable type, possibly as a homeostatic response to prolonged depolarization. Treatment with conditioned medium from cultures of DRG cells obtained after SCI was sufficient to induce MIF-dependent hyperactivity in neurons from naive rats. Thus, changes in systemic and DRG levels of MIF may help to maintain SCI-induced nociceptor hyperactivity that persistently promotes pain.SIGNIFICANCE STATEMENT Chronic neuropathic pain is a major challenge for people with spinal cord injury (SCI). Pain can drastically impair quality of life, and produces substantial economic and social burdens. Available treatments, including opioids, remain inadequate. This study shows that the cytokine macrophage migration inhibitory factor (MIF) can induce pain-like behavior and plays an important role in driving persistent ongoing electrical activity in injury-detecting sensory neurons (nociceptors) in a rat SCI model. The results indicate that SCI produces an increase in MIF release within sensory ganglia. Low MIF levels potently excite nociceptors, but higher levels trigger a long-lasting hypoexcitable state. These findings suggest that therapeutic targeting of MIF in neuropathic pain states may reduce pain and sensory dysfunction by curbing nociceptor hyperactivity.
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Affiliation(s)
- Alexis Bavencoffe
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas 77030
| | - Emily A Spence
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas 77030
| | - Michael Y Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas 77030
| | - Anibal Garza-Carbajal
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas 77030
| | - Kerry E Chu
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas 77030
| | - Ona E Bloom
- Laboratory of Spinal Cord Injury Research, Feinstein Institutes for Medical Research, Manhasset, New York 11030
| | - Carmen W Dessauer
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas 77030
| | - Edgar T Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UTHealth, Houston, Texas 77030
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16
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Abstract
This paper is the forty-third consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2020 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY, 11367, United States.
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17
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Wang Q, Gong L, Mao S, Yao C, Liu M, Wang Y, Yang J, Yu B, Chen G, Gu X. Klf2-Vav1-Rac1 axis promotes axon regeneration after peripheral nerve injury. Exp Neurol 2021; 343:113788. [PMID: 34147481 DOI: 10.1016/j.expneurol.2021.113788] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 05/03/2021] [Accepted: 06/16/2021] [Indexed: 11/28/2022]
Abstract
Increasing the intrinsic regeneration potential of neurons is the key to promote axon regeneration and repair of nerve injury. Therefore, identifying the molecular switches that respond to nerve injury may play critical role in improving intrinsic regeneration ability. The mechanisms by which injury unlocks the intrinsic axonal growth competence of mature neurons are not well understood. The present study identified the key regulatory genes after sciatic nerve crush injury by RNA sequencing (RNA-Seq) and found that the hub gene Vav1 was highly expressed at both early response and regenerative stages of sciatic nerve injury. Furthermore, Vav1 was required for axon regeneration of dorsal root ganglia (DRG) neurons and functional recovery. Krüppel-like factor 2 (Klf2) was induced by retrograde Ca2+ signaling from injured axons and could directly promote Vav1 transcription in adult DRG neurons. The increased Vav1 then promoted axon regeneration by activating Rac1 GTPase independent of its tyrosine phosphorylation. Collectively, these findings break through previous limited cognition of Vav1, and first reveal a crucial role of Vav1 as a molecular switch in response to axonal injury for promoting axon regeneration, which might further serve as a novel molecular therapeutic target for clinical nerve injury repair.
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Affiliation(s)
- Qihui Wang
- Ministry of Education (MOE) Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210061, China; Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Leilei Gong
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Susu Mao
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Chun Yao
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Mingwen Liu
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Yaxian Wang
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Jian Yang
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Bin Yu
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China
| | - Guiquan Chen
- Ministry of Education (MOE) Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210061, China.
| | - Xiaosong Gu
- Ministry of Education (MOE) Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210061, China; Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Co-innovation Center of Neuroregeneration, Nantong University, Nantong 226001, China.
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18
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Lopez ER, Carbajal AG, Tian JB, Bavencoffe A, Zhu MX, Dessauer CW, Walters ET. Serotonin enhances depolarizing spontaneous fluctuations, excitability, and ongoing activity in isolated rat DRG neurons via 5-HT 4 receptors and cAMP-dependent mechanisms. Neuropharmacology 2020; 184:108408. [PMID: 33220305 DOI: 10.1016/j.neuropharm.2020.108408] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 11/10/2020] [Accepted: 11/16/2020] [Indexed: 12/18/2022]
Abstract
Ongoing activity in nociceptors, a driver of spontaneous pain, can be generated in dorsal root ganglion neurons in the absence of sensory generator potentials if one or more of three neurophysiological alterations occur - prolonged depolarization of resting membrane potential (RMP), hyperpolarization of action potential (AP) threshold, and/or increased amplitude of depolarizing spontaneous fluctuations of membrane potential (DSFs) to bridge the gap between RMP and AP threshold. Previous work showed that acute, sustained exposure to serotonin (5-HT) hyperpolarized AP threshold and potentiated DSFs, leading to ongoing activity if a separate source of maintained depolarization was present. Cellular signaling pathways that increase DSF amplitude and promote ongoing activity acutely in nociceptors are not known for any neuromodulator. Here, isolated DRG neurons from male rats were used to define the pathway by which low concentrations of 5-HT enhance DSFs, hyperpolarize AP threshold, and promote ongoing activity. A selective 5-HT4 receptor antagonist blocked these 5-HT-induced hyperexcitable effects, while a selective 5-HT4 agonist mimicked the effects of 5-HT. Inhibition of cAMP effectors, protein kinase A (PKA) and exchange protein activated by cAMP (EPAC), attenuated 5-HT's hyperexcitable effects, but a blocker of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels had no significant effect. 5-HT4-dependent PKA activation was specific to DRG neurons that bind isolectin B4 (a nonpeptidergic nociceptor marker). 5-HT's effects on AP threshold, DSFs, and ongoing activity were mimicked by a cAMP analog. Sustained exposure to 5-HT promotes ongoing activity in nonpeptidergic nociceptors through the Gs-coupled 5-HT4 receptor and downstream cAMP signaling involving both PKA and EPAC.
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Affiliation(s)
- Elia R Lopez
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UT Health, Houston, TX, 77030, USA.
| | - Anibal Garza Carbajal
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UT Health, Houston, TX, 77030, USA.
| | - Jin Bin Tian
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UT Health, Houston, TX, 77030, USA.
| | - Alexis Bavencoffe
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UT Health, Houston, TX, 77030, USA.
| | - Michael X Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UT Health, Houston, TX, 77030, USA.
| | - Carmen W Dessauer
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UT Health, Houston, TX, 77030, USA.
| | - Edgar T Walters
- Department of Integrative Biology and Pharmacology, McGovern Medical School at UT Health, Houston, TX, 77030, USA.
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