1 2066 114 EPIGENETIC CONTROL OF ION CHANNEL EXPRESSION AND CELL-SPECIFIC SPLICING IN NOCICEPTORS: CHRONIC PAIN MECHANISMS AND POTENTIAL THERAPEUTIC TARGETS. ION CHANNELS UNDERLIE ALL FORMS FOR ELECTRICAL SIGNALING INCLUDING THE TRANSMISSION OF INFORMATION ABOUT HARMFUL EVENTS. VOLTAGE-GATED CALCIUM ION CHANNELS HAVE DUAL FUNCTION, THEY SUPPORT ELECTRICAL SIGNALING AS WELL AS INTRACELLULAR CALCIUM SIGNALING THROUGH EXCITATION-DEPENDENT CALCIUM ENTRY ACROSS THE PLASMA MEMBRANE. MECHANISMS THAT REGULATE ION CHANNEL FORMS AND ACTIONS ARE ESSENTIAL FOR MYRIAD CELL FUNCTIONS AND THESE ARE TARGETED BY DRUGS AND THERAPEUTICS. WHEN DISRUPTED, THE CELLULAR MECHANISMS THAT CONTROL ION CHANNEL ACTIVITY CAN CONTRIBUTE TO DISEASE PATHOPHYSIOLOGY. FOR EXAMPLE, ALTERNATIVE PRE-MRNA SPLICING IS A MAJOR STEP IN DEFINING THE PRECISE COMPOSITION OF THE TRANSCRIPTOME ACROSS DIFFERENT CELL TYPES FROM EARLY CELLULAR DIFFERENTIATION TO PROGRAMMED APOPTOSIS. AN ESTIMATED 30% OF DISEASE-CAUSING MUTATIONS ARE ASSOCIATED WITH ALTERED ALTERNATIVE SPLICING, AND MIS-SPLICING IS A FEATURE OF NUMEROUS HIGHLY PREVALENT DISEASES INCLUDING NEURODEGENERATIVE, CANCER, AND CHRONIC PAIN. HERE WE DISCUSS THE IMPORTANT ROLE OF EPIGENETIC REGULATION OF GENE EXPRESSION AND CELL-SPECIFIC ALTERNATIVE SPLICING OF CALCIUM ION CHANNELS IN NOCICEPTORS, WITH EMPHASIS ON HOW THESE PROCESSES ARE DISRUPTED IN CHRONIC PAIN, THE POTENTIAL THERAPEUTIC BENEFIT OF CORRECTING OR COMPENSATING FOR ABERRANT ION CHANNEL SPLICING IN CHRONIC PAIN. 2021 2 5778 32 SPINAL CORD INJURY INDUCED NEUROPATHIC PAIN: MOLECULAR TARGETS AND THERAPEUTIC APPROACHES. NEUROPATHIC PAIN, ESPECIALLY THAT RESULTING FROM SPINAL CORD INJURY, IS A TREMENDOUS CLINICAL CHALLENGE. A MYRIAD OF BIOLOGICAL CHANGES HAVE BEEN IMPLICATED IN PRODUCING THESE PAIN STATES INCLUDING CELLULAR INTERACTIONS, EXTRACELLULAR PROTEINS, ION CHANNEL EXPRESSION, AND EPIGENETIC INFLUENCES. PHYSIOLOGICAL CONSEQUENCES OF THESE CHANGES ARE VARIED AND INCLUDE FUNCTIONAL DEFICITS AND PAIN RESPONSES. DEVELOPING THERAPIES THAT EFFECTIVELY ADDRESS THE CAUSE OF THESE SYMPTOMS REQUIRE A DEEPER KNOWLEDGE OF ALTERATIONS IN THE MOLECULAR PATHWAYS. MATRIX METALLOPROTEINASES AND TISSUE INHIBITORS OF METALLOPROTEINASES ARE TWO PROMISING THERAPEUTIC TARGETS. MATRIX METALLOPROTEINASES INTERACT WITH AND INFLUENCE MANY OF THE STUDIED PAIN PATHWAYS. GENE EXPRESSION OF ION CHANNELS AND INFLAMMATORY MEDIATORS CLEARLY CONTRIBUTES TO NEUROPATHIC PAIN. LOCALIZED AND TIME DEPENDENT TARGETING OF THESE PROTEINS COULD ALLEVIATE AND EVEN PREVENT NEUROPATHIC PAIN FROM DEVELOPING. CURRENT THERAPEUTIC OPTIONS FOR NEUROPATHIC PAIN ARE LIMITED PRIMARILY TO ANALGESICS TARGETING THE OPIOID PATHWAY. THERAPIES DIRECTED AT MOLECULAR TARGETS ARE HIGHLY DESIRABLE AND IN EARLY STAGES OF DEVELOPMENT. THESE INCLUDE TRANSPLANTATION OF EXOGENOUSLY ENGINEERED CELL POPULATIONS AND TARGETED GENE MANIPULATION. THIS REVIEW DESCRIBES SPECIFIC MOLECULAR TARGETS AMENABLE TO THERAPEUTIC INTERVENTION USING CURRENTLY AVAILABLE DELIVERY SYSTEMS. 2015 3 2194 36 EPIGENETIC MODIFICATION IN NEUROPATHIC PAIN. NEUROPATHIC PAIN IS CHARACTERIZED BY COMPLICATED COMBINATION OF POSITIVE (E.G., HYPERALGESIA AND ALLODYNIA) AND NEGATIVE (E.G., HYPOESTHESIA AND HYPOALGESIA) SYMPTOMS, AND IS OFTEN REFRACTORY TO CONVENTIONAL PHARMACOLOGICAL AGENTS, INCLUDING MORPHINE. ALTHOUGH THE MOLECULAR MECHANISMS FOR POSITIVE SYMPTOMS ARE EXTENSIVELY STUDIED, THOSE FOR NEGATIVE SYMPTOMS ARE POORLY UNDERSTOOD. THERE IS CONVINCING EVIDENCE THAT ALTERED GENE EXPRESSION WITHIN PERIPHERAL AND CENTRAL NERVOUS SYSTEMS IS A KEY MECHANISM FOR NEUROPATHIC PAIN; HOWEVER, ITS TRANSCRIPTIONAL MECHANISMS ARE POORLY UNDERSTOOD. EPIGENETIC MODIFICATIONS, SUCH AS DNA METHYLATION AND HISTONE MODIFICATIONS (E.G., ACETYLATION, METHYLATION, AND PHOSPHORYLATION), ARE KNOWN TO CAUSE STABLE GENE EXPRESSION VIA CHROMATIN REMODELING. THESE MECHANISMS HAVE A ROLE NOT ONLY IN THE DETERMINATION OF DEVELOPMENTAL CELL FATES, BUT ALSO IN THE PHYSIOLOGICAL AND PATHOLOGICAL PROCESSES IN NERVOUS SYSTEM. MOREOVER, EPIGENETIC THERAPIES USING EPIGENETIC MODIFYING COMPOUNDS ARE PROGRESSIVELY ADVANCED IN THE TREATMENTS OF DIVERSE DISEASES, INCLUDING CANCER AND NEUROLOGICAL DISEASES. IMPORTANTLY, THERE IS EMERGING EVIDENCE THAT A VARIETY OF GENES UNDERGO EPIGENETIC REGULATION VIA DNA METHYLATION AND HISTONE MODIFICATIONS WITHIN PERIPHERAL AND CENTRAL NERVOUS SYSTEMS, THEREBY CONTRIBUTING TO THE ALTERATIONS IN BOTH PAIN SENSITIVITY AND PHARMACOLOGICAL EFFICACY IN NEUROPATHIC PAIN. IN THIS REVIEW, WE WILL HIGHLIGHT THE EPIGENETIC GENE REGULATION UNDERLYING NEUROPATHIC PAIN, ESPECIALLY FOCUSING ON THE NEGATIVE SYMPTOMS. MOREOVER, WE WILL DISCUSS WHETHER EPIGENETIC MECHANISMS CAN SERVE AS A POTENTIAL TARGET TO TREAT NEUROPATHIC PAIN. 2015 4 5369 29 RECENT ADVANCES IN UNDERSTANDING NEUROPATHIC PAIN: GLIA, SEX DIFFERENCES, AND EPIGENETICS. NEUROPATHIC PAIN RESULTS FROM DISEASES OR TRAUMA AFFECTING THE NERVOUS SYSTEM. THIS PAIN CAN BE DEVASTATING AND IS POORLY CONTROLLED. THE PATHOPHYSIOLOGY IS COMPLEX, AND IT IS ESSENTIAL TO UNDERSTAND THE UNDERLYING MECHANISMS IN ORDER TO IDENTIFY THE RELEVANT TARGETS FOR THERAPEUTIC INTERVENTION. IN THIS ARTICLE, WE FOCUS ON THE RECENT RESEARCH INVESTIGATING NEURO-IMMUNE COMMUNICATION AND EPIGENETIC PROCESSES, WHICH GAIN PARTICULAR ATTENTION IN THE CONTEXT OF NEUROPATHIC PAIN. SPECIFICALLY, WE ANALYZE THE ROLE OF GLIAL CELLS, INCLUDING MICROGLIA, ASTROCYTES, AND OLIGODENDROCYTES, IN THE MODULATION OF THE CENTRAL NERVOUS SYSTEM INFLAMMATION TRIGGERED BY NEUROPATHY. CONSIDERING EPIGENETICS, WE ADDRESS DNA METHYLATION, HISTONE MODIFICATIONS, AND THE NON-CODING RNAS IN THE REGULATION OF ION CHANNELS, G-PROTEIN-COUPLED RECEPTORS, AND TRANSMITTERS FOLLOWING NEURONAL DAMAGE. THE GOAL WAS NOT ONLY TO HIGHLIGHT THE EMERGING CONCEPTS BUT ALSO TO DISCUSS CONTROVERSIES, METHODOLOGICAL COMPLICATIONS, AND INTRIGUING OPINIONS. 2016 5 5926 32 TARGETING EPIGENETIC MECHANISMS FOR CHRONIC PAIN: A VALID APPROACH FOR THE DEVELOPMENT OF NOVEL THERAPEUTICS. CHRONIC PAIN IS A MULTIFACETED AND COMPLEX CONDITION. BROADLY CLASSIFIED INTO SOMATIC, VISCERAL, OR NEUROPATHIC PAIN, IT IS POORLY MANAGED DESPITE ITS PREVALENCE. CURRENT DRUGS USED FOR THE TREATMENT OF CHRONIC PAIN ARE LIMITED BY TOLERANCE WITH LONG-TERM USE, ABUSE POTENTIAL, AND MULTIPLE ADVERSE SIDE EFFECTS. THE PERSISTENT NATURE OF PAIN SUGGESTS THAT EPIGENETIC MACHINERY MAY BE A CRITICAL FACTOR DRIVING CHRONIC PAIN. IN THIS REVIEW, WE DISCUSS THE LATEST INSIGHTS INTO EPIGENETIC PROCESSES, INCLUDING DNA METHYLATION, HISTONE MODIFICATIONS, AND MICRORNAS, AND WE DESCRIBE THEIR INVOLVEMENT IN THE PATHOPHYSIOLOGY OF CHRONIC PAIN AND WHETHER EPIGENETIC MODIFICATIONS COULD BE APPLIED AS FUTURE THERAPEUTIC TARGETS FOR CHRONIC PAIN. WE PROVIDE EVIDENCE FROM EXPERIMENTAL MODELS AND TRANSLATIONAL RESEARCH IN HUMAN TISSUE THAT HAVE ENHANCED OUR UNDERSTANDING OF EPIGENETIC PROCESSES MEDIATING NOCICEPTION, AND WE THEN SPECULATE ON THE POTENTIAL FUTURE USE OF MORE SPECIFIC AND SELECTIVE AGENTS THAT TARGET EPIGENETIC MECHANISMS TO ATTENUATE PAIN. 2016 6 5419 39 REGULATION OF GENE EXPRESSION AND PAIN STATES BY EPIGENETIC MECHANISMS. THE INDUCTION OF INFLAMMATORY OR NEUROPATHIC PAIN STATES IS KNOWN TO INVOLVE MOLECULAR ACTIVITY IN THE SPINAL SUPERFICIAL DORSAL HORN AND DORSAL ROOT GANGLIA, INCLUDING INTRACELLULAR SIGNALING EVENTS WHICH LEAD TO CHANGES IN GENE EXPRESSION. THESE CHANGES ULTIMATELY CAUSE ALTERATIONS IN MACROMOLECULAR SYNTHESIS, SYNAPTIC TRANSMISSION, AND STRUCTURAL ARCHITECTURE WHICH SUPPORT CENTRAL SENSITIZATION, A PROCESS REQUIRED FOR THE ESTABLISHMENT OF LONG-TERM PAIN STATES. EPIGENETIC MECHANISMS ARE ESSENTIAL FOR LONG-TERM SYNAPTIC PLASTICITY AND MODULATION OF GENE EXPRESSION. THIS IS BECAUSE EPIGENETIC MODIFICATIONS ARE KNOWN TO REGULATE GENE TRANSCRIPTION BY AIDING THE PHYSICAL RELAXATION OR CONDENSATION OF CHROMATIN. THESE PROCESSES ARE THEREFORE POTENTIAL REGULATORS OF THE MOLECULAR CHANGES UNDERLYING PERMANENT PAIN STATES. A HANDFUL OF STUDIES HAVE EMERGED IN THE FIELD OF PAIN EPIGENETICS; HOWEVER, THE FIELD IS STILL VERY MUCH IN ITS INFANCY. THIS CHAPTER DRAWS UPON OTHER SPECIALITIES WHICH HAVE EXTENSIVELY INVESTIGATED EPIGENETIC MECHANISMS, SUCH AS LEARNING AND MEMORY AND ONCOLOGY. AFTER DEFINING EPIGENETICS AS WELL AS THE RECENT FIELD OF "NEUROEPIGENETICS" AND THE MAIN MOLECULAR MECHANISMS INVOLVED, THIS CHAPTER DESCRIBES THE ROLE OF THESE MECHANISMS IN THE SYNAPTIC PLASTICITY SEEN IN LEARNING AND MEMORY, AND ADDRESS THOSE EPIGENETIC MECHANISMS THAT HAVE BEEN LINKED WITH THE DEVELOPMENT OF ACUTE AND PROLONGED PAIN STATES. FINALLY, THE IDEA THAT LONG-LASTING EPIGENETIC MODIFICATIONS COULD CONTRIBUTE TO THE TRANSITION FROM ACUTE TO CHRONIC PAIN STATES BY SUPPORTING MALADAPTIVE MOLECULAR CHANGES IS DISCUSSED. 2015 7 1509 24 DNA METHYLATION AND NON-CODING RNAS DURING TISSUE-INJURY ASSOCIATED PAIN. WHILE ABOUT HALF OF THE POPULATION EXPERIENCE PERSISTENT PAIN ASSOCIATED WITH TISSUE DAMAGES DURING THEIR LIFETIME, CURRENT SYMPTOM-BASED APPROACHES OFTEN FAIL TO REDUCE SUCH PAIN TO A SATISFACTORY LEVEL. TO PROVIDE BETTER PATIENT CARE, MECHANISM-BASED ANALGESIC APPROACHES MUST BE DEVELOPED, WHICH NECESSITATES A COMPREHENSIVE UNDERSTANDING OF THE NOCICEPTIVE MECHANISM LEADING TO TISSUE INJURY-ASSOCIATED PERSISTENT PAIN. EPIGENETIC EVENTS LEADING THE ALTERED TRANSCRIPTION IN THE NERVOUS SYSTEM ARE PIVOTAL IN THE MAINTENANCE OF PAIN IN TISSUE INJURY. HOWEVER, THE MECHANISMS THROUGH WHICH THOSE EVENTS CONTRIBUTE TO THE PERSISTENCE OF PAIN ARE NOT FULLY UNDERSTOOD. THIS REVIEW PROVIDES A SUMMARY AND CRITICAL EVALUATION OF TWO EPIGENETIC MECHANISMS, DNA METHYLATION AND NON-CODING RNA EXPRESSION, ON TRANSCRIPTIONAL MODULATION IN NOCICEPTIVE PATHWAYS DURING THE DEVELOPMENT OF TISSUE INJURY-ASSOCIATED PAIN. WE ASSESS THE PRE-CLINICAL DATA AND THEIR TRANSLATIONAL IMPLICATION AND EVALUATE THE POTENTIAL OF CONTROLLING DNA METHYLATION AND NON-CODING RNA EXPRESSION AS NOVEL ANALGESIC APPROACHES AND/OR BIOMARKERS OF PERSISTENT PAIN. 2022 8 842 39 CHEMOKINES IN CHRONIC PAIN: CELLULAR AND MOLECULAR MECHANISMS AND THERAPEUTIC POTENTIAL. CHRONIC PAIN RESULTING FROM NERVE INJURY, TISSUE INFLAMMATION, AND TUMOR INVASION OR TREATMENT, IS A MAJOR HEALTH PROBLEM IMPACTING THE QUALITY OF LIFE AND PRODUCING A SIGNIFICANT ECONOMIC AND SOCIAL BURDEN. HOWEVER, THE CURRENT ANALGESIC DRUGS INCLUDING NON-STEROIDAL ANTI-INFLAMMATORY DRUGS AND OPIOIDS ARE INADEQUATE TO RELIEVE CHRONIC PAIN DUE TO THE LACK OF EFFICACY OR SEVERE SIDE-EFFECTS. CHEMOKINES ARE A FAMILY OF SMALL SECRETED PROTEINS THAT BIND TO G PROTEIN-COUPLED RECEPTORS TO TRIGGER INTRACELLULAR SIGNALING PATHWAYS AND DIRECT CELL MIGRATION, PROLIFERATION, SURVIVAL, AND INFLAMMATION UNDER HOMEOSTATIC AND PATHOLOGICAL CONDITIONS. ACCUMULATING EVIDENCE SUPPORTS THE IMPORTANT ROLE OF CHEMOKINES AND CHEMOKINE RECEPTORS IN THE PERIPHERAL AND CENTRAL NERVOUS SYSTEM IN MEDIATING CHRONIC PAIN VIA ENHANCING NEUROINFLAMMATION. IN THIS REVIEW, WE FOCUS ON RECENT PROGRESS IN UNDERSTANDING THE COMPREHENSIVE ROLES OF CHEMOKINES AND CHEMOKINE RECEPTORS IN THE GENERATION AND MAINTENANCE OF DIFFERENT TYPES OF CHRONIC PAIN, INCLUDING NEUROPATHIC PAIN, INFLAMMATORY PAIN, CANCER PAIN, AND VISCERAL PAIN. THE CURRENT REVIEW ALSO SUMMARIZES THE UPSTREAM SIGNALING OF TRANSCRIPTIONAL AND EPIGENETIC REGULATION ON THE EXPRESSION OF CHEMOKINES AND CHEMOKINE RECEPTORS AS WELL AS THE DOWNSTREAM SIGNALING OF CHEMOKINE RECEPTORS UNDERLYING CHRONIC PAIN. AS CHRONIC ITCH AND CHRONIC PAIN SHARE SOME COMMON MECHANISMS, WE ALSO DISCUSS THE EMERGING ROLES OF CHEMOKINES AND CHEMOKINE RECEPTORS IN CHRONIC ITCH. TARGETING SPECIFIC CHEMOKINES OR CHEMOKINE RECEPTORS BY SIRNAS, BLOCKING ANTIBODIES, OR SMALL-MOLECULE ANTAGONISTS MAY OFFER NEW THERAPEUTIC POTENTIAL FOR THE MANAGEMENT OF CHRONIC PAIN. 2020 9 5928 24 TARGETING EPIGENETIC MECHANISMS FOR PAIN RELIEF. EPIGENETIC CHANGES ARE CHEMICAL MODIFICATIONS TO CHROMATIN THAT MODULATE GENE ACTIVITY WITHOUT ALTERING THE DNA SEQUENCE. WHILE RESEARCH ON EPIGENETICS HAS GROWN EXPONENTIALLY OVER THE PAST FEW YEARS, VERY FEW STUDIES HAVE INVESTIGATED EPIGENETIC MECHANISMS IN RELATION TO PAIN STATES. HOWEVER, EPIGENETIC MECHANISMS ARE CRUCIAL TO MEMORY FORMATION THAT REQUIRES SIMILAR SYNAPTIC PLASTICITY TO PAIN PROCESSING, INDICATING THAT THEY MAY PLAY A KEY ROLE IN THE CONTROL OF PAIN STATES. THIS ARTICLE REVIEWS THE EARLY EVIDENCE SUGGESTING THAT EPIGENETIC MECHANISMS ARE ENGAGED AFTER INJURY AND IN CHRONIC PAIN STATES, AND THAT DRUGS USED CLINICALLY TO TARGET THE EPIGENETIC MACHINERY FOR THE TREATMENT OF CANCER MIGHT BE USEFUL FOR THE MANAGEMENT OF CHRONIC PAIN. 2012 10 2551 31 EPIGENETICS IN PAIN AND ANALGESIA: AN IMMINENT RESEARCH FIELD. HERITABLE PHENOTYPES RESULTING FROM ENVIRONMENT-CAUSED CHANGES IN A CHROMOSOME WITHOUT ALTERATIONS IN THE DNA SEQUENCE ARE INCREASINGLY RECOGNIZED AS A BASIS OF PERSONALIZED THERAPY. EPIGENETIC MECHANISMS INCLUDE COVALENT MODIFICATIONS OF THE DNA (METHYLATION) OR OF THE DNA-PACKAGING HISTONES (E.G., DEACETYLATION OR PHOSPHORYLATION). IN ADDITION, REGULATORY NON-CODING RNA MOLECULES (MICRO-RNAS) EXERT EPIGENETIC ACTIONS. THIS LEADS TO DISRUPTION OR OTHERWISE MODIFIED EXPRESSION OF GENES. ENVIRONMENTAL INFLUENCES SUCH AS NUTRITIONAL FACTORS, EXPOSURE TO CHEMICALS OR DRUGS, BUT ALSO SOCIAL FACTORS APPEAR TO EXERT EPIGENETIC ACTIONS. HISTONE MODIFICATIONS AND DNA METHYLATION ARE ASSOCIATED WITH THE SUBJECT'S AGE. EPIGENETIC MECHANISMS CAN SILENCE THE EXPRESSION OF PRO- OR ANTINOCICEPTIVE GENES. TO THE EPIGENETIC CONTROL OF NOCICEPTION ADDS ITS CONTROL OF THE PHARMACODYNAMICS OR PHARMACOKINETICS OF ANALGESICS BY EPIGENETIC CONTROL OF DRUG TARGETS AND ANALGESICS METABOLIZING ENZYMES. ALTHOUGH EPIGENETICS-BASED STRATEGIES FOR PAIN THERAPY ARE NOT YET AVAILABLE, EXPERIMENTS IN RODENTS SUGGEST THAT RNA INTERFERENCE MAY BECOME A NEW THERAPY APPROACH FOR NEUROPATHIC AND OTHER PAIN. ANOTHER EPIGENETIC APPROACH TO ANALGESIC TREATMENT EMPLOYS INHIBITORS OF HISTONE DEACETYLASE THAT ACT ON THE EPIGENOME BY INDIRECTLY REMODELING THE SPATIAL CONFORMATION OF THE CHROMATIN. FINALLY, EPIGENETIC TECHNIQUES SUCH AS RNA INTERFERENCE HAVE BEEN EMPLOYED IN PAIN RESEARCH TO PROOF THE CONTRIBUTION OF CERTAIN PROTEINS TO NOCICEPTION. THUS, THE NEW FIELD OF EPIGENETICS BECOMES INCREASINGLY USED IN RESEARCH AND MANAGEMENT OF PAIN AND WILL COMPLEMENT GENETICS. THIS ARTICLE INTRODUCES EPIGENETICS TO PAIN AND SUMMARIZES THE CURRENT AND FUTURE UTILITY. 2011 11 2214 40 EPIGENETIC MODIFICATIONS ASSOCIATED TO NEUROINFLAMMATION AND NEUROPATHIC PAIN AFTER NEURAL TRAUMA. ACCUMULATING EVIDENCE SUGGESTS THAT EPIGENETIC ALTERATIONS LIE BEHIND THE INDUCTION AND MAINTENANCE OF NEUROPATHIC PAIN. NEUROPATHIC PAIN IS USUALLY A CHRONIC CONDITION CAUSED BY A LESION, OR PATHOLOGICAL CHANGE, WITHIN THE NERVOUS SYSTEM. NEUROPATHIC PAIN APPEARS FREQUENTLY AFTER NERVE AND SPINAL CORD INJURIES OR DISEASES, PRODUCING A DEBILITATION OF THE PATIENT AND A DECREASE OF THE QUALITY OF LIFE. AT THE CELLULAR LEVEL, NEUROPATHIC PAIN IS THE RESULT OF NEURONAL PLASTICITY SHAPED BY AN INCREASE IN THE SENSITIVITY AND EXCITABILITY OF SENSORY NEURONS OF THE CENTRAL AND PERIPHERAL NERVOUS SYSTEM. ONE OF THE MECHANISMS THOUGHT TO CONTRIBUTE TO HYPEREXCITABILITY AND THEREFORE TO THE ONTOGENY OF NEUROPATHIC PAIN IS THE ALTERED EXPRESSION, TRAFFICKING, AND FUNCTIONING OF RECEPTORS AND ION CHANNELS EXPRESSED BY PRIMARY SENSORY NEURONS. BESIDES, NEURONAL AND GLIAL CELLS, SUCH AS MICROGLIA AND ASTROCYTES, TOGETHER WITH BLOOD BORNE MACROPHAGES, PLAY A CRITICAL ROLE IN THE INDUCTION AND MAINTENANCE OF NEUROPATHIC PAIN BY RELEASING POWERFUL NEUROMODULATORS SUCH AS PRO-INFLAMMATORY CYTOKINES AND CHEMOKINES, WHICH ENHANCE NEURONAL EXCITABILITY. ALTERED GENE EXPRESSION OF NEURONAL RECEPTORS, ION CHANNELS, AND PRO-INFLAMMATORY CYTOKINES AND CHEMOKINES, HAVE BEEN ASSOCIATED TO EPIGENETIC ADAPTATIONS OF THE INJURED TISSUE. WITHIN THIS REVIEW, WE DISCUSS THE INVOLVEMENT OF THESE EPIGENETIC CHANGES, INCLUDING HISTONE MODIFICATIONS, DNA METHYLATION, NON-CODING RNAS, AND ALTERATION OF CHROMATIN MODIFIERS, THAT HAVE BEEN SHOWN TO TRIGGER MODIFICATION OF NOCICEPTION AFTER NEURAL LESIONS. IN PARTICULAR, THE FUNCTION ON THESE PROCESSES OF EZH2, JMJD3, MECP2, SEVERAL HISTONE DEACETYLASES (HDACS) AND HISTONE ACETYL TRANSFERASES (HATS), G9A, DNMT, REST AND DIVERSE NON-CODING RNAS, ARE DESCRIBED. DESPITE THE EFFORT ON DEVELOPING NEW THERAPIES, CURRENT TREATMENTS HAVE ONLY PRODUCED LIMITED RELIEF OF THIS PAIN IN A PORTION OF PATIENTS. THUS, THE PRESENT REVIEW AIMS TO CONTRIBUTE TO FIND NOVEL TARGETS FOR CHRONIC NEUROPATHIC PAIN TREATMENT. 2018 12 2354 25 EPIGENETIC REGULATION OF PERSISTENT PAIN. PERSISTENT OR CHRONIC PAIN IS TIGHTLY ASSOCIATED WITH VARIOUS ENVIRONMENTAL CHANGES AND LINKED TO ABNORMAL GENE EXPRESSION WITHIN CELLS PROCESSING NOCICEPTIVE SIGNALING. EPIGENETIC REGULATION GOVERNS GENE EXPRESSION IN RESPONSE TO ENVIRONMENTAL CUES. RECENT ANIMAL MODEL AND CLINICAL STUDIES INDICATE THAT EPIGENETIC REGULATION PLAYS AN IMPORTANT ROLE IN THE DEVELOPMENT OR MAINTENANCE OF PERSISTENT PAIN AND POSSIBLY THE TRANSITION OF ACUTE PAIN TO CHRONIC PAIN, THUS SHEDDING LIGHT IN A DIRECTION FOR DEVELOPMENT OF NEW THERAPEUTICS FOR PERSISTENT PAIN. 2015 13 6866 33 [PAIN AND EMOTIONAL DYSREGULATION: CELLULAR MEMORY DUE TO PAIN]. GENETIC FACTORS ARE INVOLVED IN DETERMINANTS FOR THE RISK OF PSYCHIATRIC DISORDERS, AND NEUROLOGICAL AND NEURODEGENERATIVE DISEASES. CHRONIC PAIN STIMULI AND INTENSE PAIN HAVE EFFECTS AT A CELLULAR AND/OR GENE EXPRESSION LEVEL, AND WILL EVENTUALLY INDUCE "CELLULAR MEMORY DUE TO PAIN", WHICH MEANS THAT TISSUE DAMAGE, EVEN IF ONLY TRANSIENT, CAN ELICIT EPIGENETICALLY ABNORMAL TRANSCRIPTION/TRANSLATION AND POST-TRANSLATIONAL MODIFICATION IN RELATED CELLS DEPENDING ON THE DEGREE OR KIND OF INJURY OR ASSOCIATED CONDITIONS. SUCH CELL MEMORY/TRANSFORMATION DUE TO PAIN CAN CAUSE AN ABNORMALITY IN A FUNDAMENTAL INTRACELLULAR RESPONSE, SUCH AS A CHANGE IN THE THREE-DIMENSIONAL STRUCTURE OF DNA, TRANSCRIPTION, OR TRANSLATION. ON THE OTHER HAND, PAIN IS A MULTIDIMENSIONAL EXPERIENCE WITH SENSORY-DISCRIMINATIVE AND MOTIVATIONAL-AFFECTIVE COMPONENTS. RECENT HUMAN BRAIN IMAGING STUDIES HAVE EXAMINED DIFFERENCES IN ACTIVITY IN THE NUCLEUS ACCUMBENS BETWEEN CONTROLS AND PATIENTS WITH CHRONIC PAIN, AND HAVE REVEALED THAT THE NUCLEUS ACCUMBENS PLAYS A ROLE IN PREDICTING THE VALUE OF A NOXIOUS STIMULUS AND ITS OFFSET, AND IN THE CONSEQUENT CHANGES IN THE MOTIVATIONAL STATE. IN THIS REVIEW, WE PROVIDE A VERY BRIEF OVERVIEW OF A COMPREHENSIVE UNDERSTANDING OF CHRONIC PAIN ASSOCIATED WITH EMOTIONAL DYSREGULATION DUE TO TRANSCRIPTIONAL REGULATION, EPIGENETIC MODIFICATION AND MIRNA REGULATION. 2015 14 2523 37 EPIGENETICS AND THE TRANSITION FROM ACUTE TO CHRONIC PAIN. OBJECTIVE: THE OBJECTIVE OF THIS STUDY WAS TO REVIEW THE EPIGENETIC MODIFICATIONS INVOLVED IN THE TRANSITION FROM ACUTE TO CHRONIC PAIN AND TO IDENTIFY POTENTIAL TARGETS FOR THE DEVELOPMENT OF NOVEL, INDIVIDUALIZED PAIN THERAPEUTICS. BACKGROUND: EPIGENETICS IS THE STUDY OF HERITABLE MODIFICATIONS IN GENE EXPRESSION AND PHENOTYPE THAT DO NOT REQUIRE A CHANGE IN GENETIC SEQUENCE TO MANIFEST THEIR EFFECTS. ENVIRONMENTAL TOXINS, MEDICATIONS, DIET, AND PSYCHOLOGICAL STRESSES CAN ALTER EPIGENETIC PROCESSES SUCH AS DNA METHYLATION, HISTONE ACETYLATION, AND RNA INTERFERENCE. AS EPIGENETIC MODIFICATIONS POTENTIALLY PLAY AN IMPORTANT ROLE IN INFLAMMATORY CYTOKINE METABOLISM, STEROID RESPONSIVENESS, AND OPIOID SENSITIVITY, THEY ARE LIKELY KEY FACTORS IN THE DEVELOPMENT OF CHRONIC PAIN. ALTHOUGH OUR KNOWLEDGE OF THE HUMAN GENETIC CODE AND DISEASE-ASSOCIATED POLYMORPHISMS HAS GROWN SIGNIFICANTLY IN THE PAST DECADE, WE HAVE NOT YET BEEN ABLE TO ELUCIDATE THE MECHANISMS THAT LEAD TO THE DEVELOPMENT OF PERSISTENT PAIN AFTER NERVE INJURY OR SURGERY. DESIGN: THIS IS A FOCUSED LITERATURE REVIEW OF EPIGENETIC SCIENCE AND ITS RELATIONSHIP TO CHRONIC PAIN. RESULTS: SIGNIFICANT LABORATORY AND CLINICAL DATA SUPPORT THE NOTION THAT EPIGENETIC MODIFICATIONS ARE AFFECTED BY THE ENVIRONMENT AND LEAD TO DIFFERENTIAL GENE EXPRESSION. SIMILAR TO MECHANISMS INVOLVED IN THE DEVELOPMENT OF CANCER, NEURODEGENERATIVE DISEASE, AND INFLAMMATORY DISORDERS, THE LITERATURE ENDORSES AN IMPORTANT POTENTIAL ROLE FOR EPIGENETICS IN CHRONIC PAIN. CONCLUSIONS: EPIGENETIC ANALYSIS MAY IDENTIFY MECHANISMS CRITICAL TO THE DEVELOPMENT OF CHRONIC PAIN AFTER INJURY, AND MAY PROVIDE NEW PATHWAYS AND TARGET MECHANISMS FOR FUTURE DRUG DEVELOPMENT AND INDIVIDUALIZED MEDICINE. 2012 15 1686 33 DRUGGING THE PAIN EPIGENOME. MORE THAN 20% OF ADULTS WORLDWIDE EXPERIENCE DIFFERENT TYPES OF CHRONIC PAIN, WHICH ARE FREQUENTLY ASSOCIATED WITH SEVERAL COMORBIDITIES AND A DECREASE IN QUALITY OF LIFE. SEVERAL APPROVED PAINKILLERS ARE AVAILABLE, BUT CURRENT ANALGESICS ARE OFTEN HAMPERED BY INSUFFICIENT EFFICACY AND/OR SEVERE ADVERSE EFFECTS. CONSEQUENTLY, NOVEL STRATEGIES FOR SAFE, HIGHLY EFFICACIOUS TREATMENTS ARE HIGHLY DESIRABLE, PARTICULARLY FOR CHRONIC PAIN. EPIGENETIC MECHANISMS SUCH AS DNA METHYLATION, HISTONE MODIFICATIONS AND MICRORNAS (MIRNAS) STRONGLY AFFECT THE REGULATION OF GENE EXPRESSION, POTENTIALLY FOR LONG PERIODS OVER YEARS OR EVEN GENERATIONS, AND HAVE BEEN ASSOCIATED WITH PATHOPHYSIOLOGICAL PAIN. SEVERAL STUDIES, MOSTLY IN ANIMALS, REVEALED THAT INHIBITORS OF DNA METHYLATION, ACTIVATORS AND INHIBITORS OF HISTONE MODIFICATION AND MODULATORS OF MIRNAS REVERSE A NUMBER OF PATHOLOGICAL CHANGES IN THE PAIN EPIGENOME, WHICH ARE ASSOCIATED WITH ALTERED EXPRESSION OF PAIN-RELEVANT GENES. THIS EPIGENETIC MODULATION MIGHT THEN REDUCE THE NOCICEPTIVE RESPONSE AND PROVIDE NOVEL THERAPEUTIC OPTIONS FOR ANALGESIC THERAPY OF CHRONIC PAIN STATES. HOWEVER, A NUMBER OF CHALLENGES, SUCH AS NONSPECIFIC EFFECTS AND POOR DELIVERY TO TARGET CELLS AND TISSUES, HINDER THE RAPID DEVELOPMENT OF SUCH ANALGESICS. IN THIS REVIEW, WE CRITICALLY SUMMARIZE DATA ON EPIGENETICS AND PAIN, FOCUSING ON CHALLENGES IN CLINICAL DEVELOPMENT AS WELL AS POSSIBLE NEW APPROACHES TO THE DRUG MODULATION OF THE PAIN EPIGENOME. 2017 16 6124 33 THE EPIGENETIC MECHANISMS INVOLVED IN CHRONIC PAIN IN RODENTS: A MINI- REVIEW. CHRONIC PAIN IS A COMMON DISTRESSING NEUROLOGICAL DISORDER AND ABOUT 30% OF THE GLOBAL POPULATION SUFFERS FROM IT. IN ADDITION TO BEING HIGHLY PREVALENT, CHRONIC PAIN CAUSES A HEAVY ECONOMIC AND SOCIAL BURDEN. ALTHOUGH SUBSTANTIAL PROGRESS HAS BEEN ACHIEVED TO DISSECT THE UNDERLYING MECHANISM OF CHRONIC PAIN IN THE PAST FEW DECADES, THE INCIDENCE AND TREATMENT OF THIS NEUROLOGICAL ILLNESS IS YET NOT PROPERLY MANAGED IN CLINICAL PRACTICE. WHILE NERVE INJURY-, CHEMOTHERAPY- OR INFLAMMATION-INDUCED FUNCTIONAL REGULATION OF GENE EXPRESSION IN THE DORSAL ROOT GANGLION AND SPINAL CORD ARE EXTENSIVELY REPORTED TO BE INVOLVED IN THE PATHOGENIC PROCESS OF CHRONIC PAIN, THE SPECIFIC MECHANISM OF THESE ALTERED TRANSCRIPTIONAL PROFILE STILL REMAINS UNCLEAR. RECENT STUDIES HAVE SHOWN THAT EPIGENETIC MECHANISMS, INCLUDING DNA/RNA METHYLATION, HISTONE MODIFICATION AND CIRCULAR RNAS REGULATION, ARE INVOLVED IN THE OCCURRENCE AND DEVELOPMENT OF CHRONIC PAIN. IN THIS REVIEW, WE PROVIDE A DESCRIPTION OF RESEARCH ON THE ROLE OF EPIGENETIC MECHANISM IN CHRONIC PAIN, SUMMARIZE THE LATEST CLINICAL AND PRECLINICAL ADVANCE IN THIS FIELD, AND PROPOSE THE POTENTIAL DIRECTIONS FOR FURTHER RESEARCH TO ELUCIDATE THE MOLECULAR MECHANISM UNDERLYING THE PATHOGENESIS OF CHRONIC PAIN. 2022 17 789 38 CELLULAR AND MOLECULAR MECHANISMS DRIVING NEUROPATHIC PAIN: RECENT ADVANCEMENTS AND CHALLENGES. CURRENT PHARMACOTHERAPEUTICS FOR NEUROPATHIC PAIN OFFER ONLY SYMPTOMATIC RELIEF WITHOUT TREATING THE UNDERLYING PATHOPHYSIOLOGY. ADDITIONALLY, THEY ARE ASSOCIATED WITH VARIOUS DOSE-LIMITING SIDE EFFECTS. PAIN RESEARCH IN THE PAST FEW DECADES HAS REVOLVED AROUND THE ROLE OF OXIDATIVE-NITROSATIVE STRESS, PROTEIN KINASES, GLIAL CELL ACTIVATION, AND INFLAMMATORY SIGNALING CASCADES BUT HAS FAILED TO PRODUCE SPECIFIC AND EFFECTIVE THERAPIES. AREAS COVERED: THIS REVIEW FOCUSES ON RECENT ADVANCES IN CELLULAR AND MOLECULAR MECHANISMS OF NEUROPATHIC PAIN THAT MAY BE TRANSLATED INTO FUTURE THERAPIES. WE DISCUSS EMERGING TARGETS SUCH AS WNT SIGNALING MECHANISMS, THE TETRAHYDROBIOPTERIN PATHWAY, MRG RECEPTORS, ENDOGENOUS LIPID MEDIATORS, MICRO-RNAS AND THEIR ROLES IN PAIN REGULATION. RECENT EVIDENCE IS ALSO PRESENTED REGARDING GENETIC AND EPIGENETIC MECHANISMS OF PAIN MODULATION. EXPERT OPINION: DURING CHRONIC NEUROPATHIC PAIN, MALADAPTATION OCCURS IN THE PERIPHERAL AND CENTRAL NERVOUS SYSTEMS, INCLUDING A SHIFT IN MICROGLIAL PHENOTYPE FROM A SURVEILLANCE STATE TO AN ACTIVATED STATE. MICROGLIAL ACTIVATION LEADS TO AN ALTERED EXPRESSION OF CELL SURFACE PROTEINS, GROWTH FACTORS, AND INTRACELLULAR SIGNALING MOLECULES THAT CONTRIBUTE TO DEVELOPMENT OF A NEUROINFLAMMATORY CASCADE AND CHRONIC PAIN SENSITIZATION. SPECIFIC TARGETING OF THESE CELLULAR AND MOLECULAR MECHANISMS MAY PROVIDE THE KEY TO DEVELOPMENT OF EFFECTIVE NEUROPATHIC PAIN THERAPIES THAT HAVE MINIMAL SIDE EFFECTS. 2018 18 3675 27 INFLAMMATION AND HISTONE MODIFICATION IN CHRONIC PAIN. INCREASING EVIDENCE SUGGESTS THAT EPIGENETIC MECHANISMS HAVE GREAT POTENTIAL IN THE FIELD OF PAIN. THE CHANGES AND ROLES OF EPIGENETICS OF THE SPINAL CORD AND DORSAL ROOT GANGLIA IN THE CHRONIC PAIN PROCESS MAY PROVIDE BROAD INSIGHTS FOR FUTURE PAIN MANAGEMENT. PRO-INFLAMMATORY CYTOKINES AND CHEMOKINES RELEASED BY MICROGLIA AND ASTROCYTES, AS WELL AS BLOOD-DERIVED MACROPHAGES, PLAY CRITICAL ROLES IN INDUCING AND MAINTAINING CHRONIC PAIN, WHILE HISTONE MODIFICATIONS MAY PLAY AN IMPORTANT ROLE IN INFLAMMATORY METABOLISM. THIS REVIEW PROVIDES AN OVERVIEW OF NEUROINFLAMMATION AND CHRONIC PAIN, AND WE SYSTEMATICALLY DISCUSS THE REGULATION OF NEUROINFLAMMATION AND HISTONE MODIFICATIONS IN THE CONTEXT OF CHRONIC PAIN. SPECIFICALLY, WE ANALYZED THE ROLE OF EPIGENETICS IN ALLEVIATING OR EXACERBATING CHRONIC PAIN BY MODULATING MICROGLIA, ASTROCYTES, AND THE PROINFLAMMATORY MEDIATORS THEY RELEASE. THIS REVIEW AIMED TO CONTRIBUTE TO THE DISCOVERY OF NEW THERAPEUTIC TARGETS FOR CHRONIC PAIN. 2022 19 5626 30 SELECTIVE REPRESSION OF GENE EXPRESSION IN NEUROPATHIC PAIN BY THE NEURON-RESTRICTIVE SILENCING FACTOR/REPRESSOR ELEMENT-1 SILENCING TRANSCRIPTION (NRSF/REST). NEUROPATHIC PAIN OFTEN DEVELOPS FOLLOWING NERVE INJURY AS A RESULT OF MALADAPTIVE CHANGES THAT OCCUR IN THE INJURED NERVE AND ALONG THE NOCICEPTIVE PATHWAYS OF THE PERIPHERAL AND CENTRAL NERVOUS SYSTEMS. MULTIPLE CELLULAR AND MOLECULAR MECHANISMS LIKELY ACCOUNT FOR THESE CHANGES; HOWEVER, THE EXACT NATURE OF THESE MECHANISMS REMAIN LARGELY UNKNOWN. A GROWING NUMBER OF STUDIES SUGGEST THAT ALTERATION IN GENE EXPRESSION IS AN IMPORTANT STEP IN THE PROGRESSION FROM ACUTE TO CHRONIC PAIN STATES AND EPIGENETIC REGULATION HAS BEEN PROPOSED TO DRIVE THIS CHANGE IN GENE EXPRESSION. IN THIS REVIEW, WE DISCUSS RECENT EVIDENCE THAT THE DNA-BINDING PROTEIN NEURON-RESTRICTIVE SILENCING FACTOR/REPRESSOR ELEMENT-1 SILENCING TRANSCRIPTION FACTOR (NRSF/REST) IS AN IMPORTANT COMPONENT IN THE DEVELOPMENT AND MAINTENANCE OF NEUROPATHIC PAIN THROUGH ITS ROLE AS A TRANSCRIPTIONAL REGULATOR FOR A SELECT SUBSET OF GENES THAT IT NORMALLY REPRESSES DURING DEVELOPMENT. 2016 20 2611 27 EPIGENETICS: A PROMISING PARADIGM FOR BETTER UNDERSTANDING AND MANAGING PAIN. EPIGENETIC REGULATION OF GENE EXPRESSION IS A RAPIDLY GROWING AREA OF RESEARCH. CONSIDERING THE LONGEVITY AND PLASTICITY OF NEURONS, THE STUDIES ON EPIGENETIC PATHWAYS IN THE NERVOUS SYSTEM SHOULD BE OF SPECIAL INTEREST FOR BOTH EPIGENETICISTS AND NEUROSCIENTISTS. ACTIVATION OR INACTIVATION OF DIFFERENT EPIGENETIC PATHWAYS BECOMES MORE PRONOUNCED WHEN THE CELLS EXPERIENCE RAPID CHANGES IN THEIR ENVIRONMENT, AND SUCH CHANGES CAN BE EASILY CAUSED BY INJURY AND INFLAMMATION, RESULTING IN PAIN PERCEPTION OR DISTORTION OF PAIN PERCEPTION (EG, HYPERALGESIA). THEREFORE, IN THIS REGARD, THE FIELD OF PAIN IS AT AN ADVANTAGE TO STUDY THE EPIGENETIC PATHWAYS. MORE IMPORTANTLY, UNDERSTANDING PAIN FROM AN EPIGENETICS POINT OF VIEW WOULD PROVIDE A NEW PARADIGM FOR DEVELOPING DRUGS OR STRATEGIES FOR PAIN MANAGEMENT. IN THIS REVIEW, WE INTRODUCE BASIC CONCEPTS OF EPIGENETICS, INCLUDING CHROMATIN DYNAMICS, HISTONE MODIFICATIONS, DNA METHYLATION, AND RNA-INDUCED GENE SILENCING. IN ADDITION, WE PROVIDE EVIDENCE FROM PUBLISHED STUDIES SUGGESTING WIDE IMPLICATION OF DIFFERENT EPIGENETIC PATHWAYS WITHIN PAIN PATHWAYS. PERSPECTIVE: THIS ARTICLE PROVIDES A BRIEF OVERVIEW OF EPIGENETIC PATHWAYS FOR GENE REGULATION AND HIGHLIGHTS THEIR INVOLVEMENT IN PAIN. OUR GOAL IS TO EXPOSE THE READERS TO THESE CONCEPTS SO THAT PAIN-RELATED PHENOTYPES CAN BE INVESTIGATED FROM THE EPIGENETIC POINT OF VIEW. 2013