1 4854 101 OPRM1 METHYLATION CONTRIBUTES TO OPIOID TOLERANCE IN CANCER PATIENTS. CANCER PATIENTS IN PAIN REQUIRE HIGH DOSES OF OPIOIDS AND QUICKLY BECOME OPIOID-TOLERANT. PREVIOUS STUDIES HAVE SHOWN THAT CHRONIC CANCER PAIN AS WELL AS HIGH-DOSE OPIOID USE LEAD TO MU-OPIOID RECEPTOR DOWNREGULATION. IN THIS STUDY WE EXPLORE DOWNREGULATION OF THE MU-OPIOID RECEPTOR GENE (OPRM1), AS A MECHANISM FOR OPIOID TOLERANCE IN THE SETTING OF OPIOID USE FOR CANCER PAIN. WE DEMONSTRATE IN A COHORT OF 84 CANCER PATIENTS THAT HIGH-DOSE OPIOID USE CORRELATES WITH OPRM1 HYPERMETHYLATION IN PERIPHERAL LEUKOCYTES OF THESE PATIENTS. WE THEN REVERSE-TRANSLATE OUR CLINICAL FINDINGS BY CREATING A MOUSE CANCER PAIN MODEL; WE CREATE OPIOID TOLERANCE IN THE MOUSE CANCER MODEL TO MIMIC OPIOID TOLERANCE IN THE CANCER PATIENTS. USING THIS MODEL WE DETERMINE THE FUNCTIONAL SIGNIFICANCE OF OPRM1 METHYLATION ON CANCER PAIN AND OPIOID TOLERANCE. WE FOCUS ON 2 MAIN CELLS WITHIN THE CANCER MICROENVIRONMENT: THE CANCER CELL AND THE NEURON. WE SHOW THAT TARGETED RE-EXPRESSION OF MU-OPIOID RECEPTOR ON CANCER CELLS INHIBITS MECHANICAL AND THERMAL HYPERSENSITIVITY, AND PREVENTS OPIOID TOLERANCE, IN THE MOUSE MODEL. THE RESULTANT ANALGESIA AND PROTECTION AGAINST OPIOID TOLERANCE ARE LIKELY DUE TO PRESERVATION OF MU-OPIOID RECEPTOR EXPRESSION ON THE CANCER-ASSOCIATED NEURONS. PERSPECTIVE: WE DEMONSTRATE THAT EPIGENETIC REGULATION OF OPRM1 CONTRIBUTES TO OPIOID TOLERANCE IN CANCER PATIENTS, AND THAT TARGETED GENE THERAPY COULD TREAT CANCER-INDUCED NOCICEPTION AND OPIOID TOLERANCE IN A MOUSE CANCER MODEL. 2017 2 976 37 CHRONIC OPIOID USE IS ASSOCIATED WITH INCREASED DNA METHYLATION CORRELATING WITH INCREASED CLINICAL PAIN. ENVIRONMENTALLY CAUSED CHANGES IN CHROMOSOMES THAT DO NOT ALTER THE DNA SEQUENCE BUT CAUSE PHENOTYPIC CHANGES BY ALTERING GENE TRANSCRIPTION ARE SUMMARIZED AS EPIGENETICS. A MAJOR EPIGENETIC MECHANISM IS METHYLATION OR DEMETHYLATION AT CPG-RICH DNA ISLANDS. DNA METHYLATION TRIGGERED BY DRUGS HAS LARGELY UNEXPLORED THERAPEUTIC CONSEQUENCES. HERE WE REPORT INCREASED METHYLATION AT A CPG RICH ISLAND IN THE OPRM1 GENE CODING FOR MU-OPIOID RECEPTORS AND AT A GLOBAL METHYLATION SITE (LINE-1) IN LEUKOCYTES OF METHADONE-SUBSTITUTED FORMER OPIATE ADDICTS COMPARED WITH MATCHED HEALTHY CONTROLS. HIGHER DNA METHYLATION ASSOCIATED WITH CHRONIC OPIOID EXPOSURE WAS REPRODUCED IN AN INDEPENDENT COHORT OF OPIOID-TREATED AS COMPARED TO NON-OPIOID-TREATED PAIN PATIENTS. THIS SUGGESTS THAT OPIOIDS MAY STIMULATE DNA METHYLATION. THE OPRM1 METHYLATION HAD NO IMMEDIATE EFFECT ON MU-OPIOID RECEPTOR TRANSCRIPTION AND WAS NOT ASSOCIATED WITH OPIOID DOSING REQUIREMENTS. HOWEVER, THE GLOBAL DNA METHYLATION AT LINE-1 WAS SIGNIFICANTLY CORRELATED WITH INCREASED CHRONIC PAIN. THIS SUGGESTS INHIBITORY EFFECTS ON THE TRANSCRIPTION OF STILL UNSPECIFIED NOCIFENSIVE GENE PRODUCTS. IT FURTHER IMPLIES THAT OPIOIDS MAY BE CAUSALLY ASSOCIATED WITH INCREASED GENOME-WIDE DNA METHYLATION, ALTHOUGH CURRENTLY THERE IS NO DIRECT EVIDENCE OF THIS. THIS HAS PHENOTYPIC CONSEQUENCES FOR PAIN AND MAY PROVIDE A NEW, EPIGENETICS-ASSOCIATED MECHANISM OF OPIOID-INDUCED HYPERALGESIA. THE RESULTS INDICATE A POTENTIAL INFLUENCE OF OPIOID ANALGESICS ON THE PATIENTS' EPIGENOME. THEY EMPHASIZE THE NEED FOR RELIABLE AND COST-EFFECTIVE SCREENING TOOLS AND MAY IMPLY THAT HIGH-THROUGHPUT SCREENING FOR LEAD COMPOUNDS IN ARTIFICIAL EXPRESSION SYSTEMS MAY NOT PROVIDE THE BEST TOOLS FOR IDENTIFYING NEW PAIN MEDICATIONS. 2013 3 4604 31 NEGATIVE EVIDENCE FOR A FUNCTIONAL ROLE OF NEURONAL DNMT3A IN PERSISTENT PAIN. TRADITIONALLY, NEUROSCIENCE HAS HAD TO RELY ON MIXED TISSUE ANALYSIS TO EXAMINE TRANSCRIPTIONAL AND EPIGENETIC CHANGES IN THE CONTEXT OF NERVOUS SYSTEM FUNCTION OR PATHOLOGY. HOWEVER, PARTICULARLY WHEN STUDYING CHRONIC PAIN CONDITIONS, THIS APPROACH CAN BE FLAWED, SINCE IT NEGLECTS TO TAKE INTO ACCOUNT THE SHIFTING CONTRIBUTION OF DIFFERENT CELL TYPES ACROSS EXPERIMENTAL CONDITIONS. HERE, WE DEMONSTRATE THIS USING THE EXAMPLE OF DNA METHYLTRANSFERASES (DNMTS) - A GROUP OF EPIGENETIC MODIFIERS CONSISTING OF DNMT1, DNMT3A, AND DNMT3B IN MAMMALIAN CELLS. WE USED SENSORY NEURON-SPECIFIC KNOCKOUT MICE FOR DNMT3A/3B AS WELL AS PHARMACOLOGICAL BLOCKADE OF DNMT1 TO STUDY THEIR ROLE IN NOCICEPTION. IN CONTRAST TO PREVIOUS ANALYSES ON WHOLE TISSUE, WE FIND THAT DNMT3A AND 3B PROTEIN IS NOT EXPRESSED IN ADULT DRG NEURONS, THAT NONE OF THE DNA METHYLTRANSFERASES ARE REGULATED WITH INJURY AND THAT INTERFERING WITH THEIR FUNCTION HAS NO EFFECT ON NOCICEPTION. OUR RESULTS THEREFORE CURRENTLY DO NOT SUPPORT A ROLE FOR NEURONAL DNA METHYLTRANSFERASES IN PAIN PROCESSING IN ADULT ANIMALS. 2018 4 5034 26 PHARMACOEPIGENETICS OF THE ROLE OF DNA METHYLATION IN MU-OPIOID RECEPTOR EXPRESSION IN DIFFERENT HUMAN BRAIN REGIONS. AIM: EXPOSURE TO OPIOIDS HAS BEEN ASSOCIATED WITH EPIGENETIC EFFECTS. STUDIES IN RODENTS SUGGESTED A ROLE OF VARYING DEGREES OF DNA METHYLATION IN THE DIFFERENTIAL REGULATION OF MU-OPIOID RECEPTOR EXPRESSION ACROSS THE BRAIN. METHODS: IN A TRANSLATIONAL INVESTIGATION, USING TISSUE ACQUIRED POSTMORTEM FROM 21 BRAIN REGIONS OF FORMER OPIATE ADDICTS, REPRESENTING A HUMAN COHORT WITH CHRONIC OPIOID EXPOSURE, MU-OPIOID RECEPTOR EXPRESSION WAS ANALYZED AT THE LEVEL OF DNA METHYLATION, MRNA AND PROTEIN. RESULTS & CONCLUSION: WHILE HIGH OR LOW MU-OPIOID RECEPTOR EXPRESSION SIGNIFICANTLY CORRELATED WITH LOCAL OPRM1 MRNA LEVELS, THERE WAS NO CORRESPONDING ASSOCIATION WITH OPRM1 METHYLATION STATUS. ADDITIONAL EXPERIMENTS IN HUMAN CELL LINES SHOWED THAT CHANGES IN DNA METHYLATION ASSOCIATED WITH CHANGES IN MU-OPIOID EXPRESSION WERE AN ORDER OF MAGNITUDE GREATER THAN DIFFERENCES IN BRAIN. HENCE, DIFFERENT DEGREES OF DNA METHYLATION ASSOCIATED WITH CHRONIC OPIOID EXPOSURE ARE UNLIKELY TO EXERT A MAJOR ROLE IN THE REGION-SPECIFICITY OF MU-OPIOID RECEPTOR EXPRESSION IN THE HUMAN BRAIN. 2016 5 405 29 ANALYSIS OF EPIGENETIC MECHANISMS REGULATING OPIOID RECEPTOR GENE TRANSCRIPTION. OPIOID DRUGS ARE GENERALLY USED FOR MODERATE AND SEVERE PAIN REDUCTIONS WHICH ACT THROUGH OPIOID RECEPTORS. STUDIES ON TRANSCRIPTIONAL REGULATION OF OPIOID RECEPTORS ARE STILL INVALUABLE BECAUSE NOT ONLY TRANSCRIPTION IS THE FIRST STEP TO PRODUCE PROTEIN PRODUCTS IN CELLS, BUT THE RECEPTOR TRANSCRIPTION LEVELS ALSO AFFECT THE PAIN REDUCTION BY OPIOIDS, AS OBSERVED IN STUDIES OF HETEROZYGOUS OPIOID RECEPTOR KNOCKOUT MICE.THERE ARE GROWING EVIDENCES THAT EPIGENETIC REGULATION HAS PLAYED SIGNIFICANT ROLES IN TRANSCRIPTIONAL REGULATION OF GENES, INCLUDING OPIOID RECEPTORS. IN GENERAL, EPIGENETIC MECHANISMS INCLUDE THREE MAIN REGULATORY FACTORS: DNA METHYLATION, CHROMATIN MODIFICATION, AND NONCODING RNAS (SUCH AS MICRORNA). FROM PREVIOUS STUDIES OF OURS AND OTHERS ON OPIOID RECEPTORS, THOSE EPIGENETIC FACTORS WERE CLEARLY INVOLVED IN REGULATING OPIOID RECEPTOR EXPRESSION IN VIVO AND IN VITRO. IN THIS CHAPTER, AMONG THOSE THREE TECHNIQUES WE DESCRIBE MORE DETAILS OF DNA METHYLATION METHODS BECAUSE OF EMERGING CONCEPTS OF DNA METHYLATION WITH THE RECENT DISCOVERY OF 5-HYDROXYMETHYLCYTOSINE CONVERTING ENZYME, TET1. ANOTHER ANALYTICAL METHOD OF THE EPIGENETIC FACTORS, CHROMATIN MODIFICATION, WILL BE DESCRIBED BRIEFLY AND INFORMATION OF ANALYZING NONCODING RNAS IS BRIEFLY MENTIONED IN SUBHEADING 1. 2015 6 5007 29 PERIPHERAL NERVE INJURY IS ASSOCIATED WITH CHRONIC, REVERSIBLE CHANGES IN GLOBAL DNA METHYLATION IN THE MOUSE PREFRONTAL CORTEX. CHANGES IN BRAIN STRUCTURE AND CORTICAL FUNCTION ARE ASSOCIATED WITH MANY CHRONIC PAIN CONDITIONS INCLUDING LOW BACK PAIN AND FIBROMYALGIA. THE MAGNITUDE OF THESE CHANGES CORRELATES WITH THE DURATION AND/OR THE INTENSITY OF CHRONIC PAIN. MOST STUDIES REPORT CHANGES IN COMMON AREAS INVOLVED IN PAIN MODULATION, INCLUDING THE PREFRONTAL CORTEX (PFC), AND PAIN-RELATED PATHOLOGICAL CHANGES IN THE PFC CAN BE REVERSED WITH EFFECTIVE TREATMENT. WHILE THE MECHANISMS UNDERLYING THESE CHANGES ARE UNKNOWN, THEY MUST BE DYNAMICALLY REGULATED. EPIGENETIC MODULATION OF GENE EXPRESSION IN RESPONSE TO EXPERIENCE AND ENVIRONMENT IS REVERSIBLE AND DYNAMIC. EPIGENETIC MODULATION BY DNA METHYLATION IS ASSOCIATED WITH ABNORMAL BEHAVIOR AND PATHOLOGICAL GENE EXPRESSION IN THE CENTRAL NERVOUS SYSTEM. DNA METHYLATION MIGHT ALSO BE INVOLVED IN MEDIATING THE PATHOLOGIES ASSOCIATED WITH CHRONIC PAIN IN THE BRAIN. WE THEREFORE TESTED A) WHETHER ALTERATIONS IN DNA METHYLATION ARE FOUND IN THE BRAIN LONG AFTER CHRONIC NEUROPATHIC PAIN IS INDUCED IN THE PERIPHERY USING THE SPARED NERVE INJURY MODAL AND B) WHETHER THESE INJURY-ASSOCIATED CHANGES ARE REVERSIBLE BY INTERVENTIONS THAT REVERSE THE PATHOLOGIES ASSOCIATED WITH CHRONIC PAIN. SIX MONTHS FOLLOWING PERIPHERAL NERVE INJURY, ABNORMAL SENSORY THRESHOLDS AND INCREASED ANXIETY WERE ACCOMPANIED BY DECREASED GLOBAL METHYLATION IN THE PFC AND THE AMYGDALA BUT NOT IN THE VISUAL CORTEX OR THE THALAMUS. ENVIRONMENTAL ENRICHMENT ATTENUATED NERVE INJURY-INDUCED HYPERSENSITIVITY AND REVERSED THE CHANGES IN GLOBAL PFC METHYLATION. FURTHERMORE, GLOBAL PFC METHYLATION CORRELATED WITH MECHANICAL AND THERMAL SENSITIVITY IN NEUROPATHIC MICE. IN SUMMARY, INDUCTION OF CHRONIC PAIN BY PERIPHERAL NERVE INJURY IS ASSOCIATED WITH EPIGENETIC CHANGES IN THE BRAIN. THESE CHANGES ARE DETECTED LONG AFTER THE ORIGINAL INJURY, AT A LONG DISTANCE FROM THE SITE OF INJURY AND ARE REVERSIBLE WITH ENVIRONMENTAL MANIPULATION. CHANGES IN BRAIN STRUCTURE AND CORTICAL FUNCTION THAT ARE ASSOCIATED WITH CHRONIC PAIN CONDITIONS MAY THEREFORE BE MEDIATED BY EPIGENETIC MECHANISMS. 2013 7 3008 25 GENETIC-EPIGENETIC INTERACTION MODULATES MU-OPIOID RECEPTOR REGULATION. GENETIC AND EPIGENETIC MECHANISMS PLAY IMPORTANT ROLES IN PROTEIN EXPRESSION, ALTHOUGH AT DIFFERENT LEVELS. GENETIC VARIATIONS CAN ALTER CPG SITES AND THUS INFLUENCE THE EPIGENETIC REGULATION OF MRNA EXPRESSION, PROVIDING AN INCREASINGLY RECOGNIZED MECHANISM OF FUNCTIONAL CONSEQUENCES OF GENETIC POLYMORPHISMS. ONE OF THOSE GENETIC EFFECTS IS THE ASSOCIATION OF REDUCED MU-OPIOID RECEPTOR EXPRESSION WITH THE FUNCTIONAL GENETIC VARIANT N40D (OPRM1 118A>G, RS1799971) THAT CAUSES AN AMINO ACID EXCHANGE IN THE EXTRACELLULAR TERMINAL OF THE MU-OPIOID RECEPTOR. WE REPORT THAT THE NUCLEOTIDE EXCHANGE AT GENE POSITION +118 INTRODUCES A NEW CPG-METHYLATION SITE INTO THE OPRM1 DNA AT POSITION +117. THIS LEADS TO AN ENHANCED METHYLATION OF THE OPRM1 DNA AT THIS SITE AND DOWNSTREAM. THIS EPIGENETIC MECHANISM IMPEDES MU-OPIOID RECEPTOR UPREGULATION IN BRAIN TISSUE OF CAUCASIAN CHRONIC OPIATE ADDICTS, ASSESSED POSTMORTEM. WHILE IN WILD-TYPE SUBJECTS, A REDUCED SIGNALLING EFFICIENCY ASSOCIATED WITH CHRONIC HEROIN EXPOSURE WAS COMPENSATED BY AN INCREASED RECEPTOR DENSITY, THIS UPREGULATION WAS ABSENT IN CARRIERS OF THE 118G RECEPTOR VARIANT DUE TO A DIMINISHED OPRM1 MRNA TRANSCRIPTION. THUS, THE OPRM1 118A>G SNP VARIANT NOT ONLY REDUCES MICRO-OPIOID RECEPTOR SIGNALLING EFFICIENCY, BUT, BY A GENETIC-EPIGENETIC INTERACTION, REDUCES OPIOID RECEPTOR EXPRESSION AND THEREFORE, DEPLETES THE OPIOID SYSTEM OF A COMPENSATORY REACTION TO CHRONIC EXPOSURE. THIS DEMONSTRATES THAT A CHANGE IN THE GENOTYPE CAN CAUSE A CHANGE IN THE EPIGENOTYPE WITH MAJOR FUNCTIONAL CONSEQUENCES. 2012 8 4619 32 NERVE TRAUMA-CAUSED DOWNREGULATION OF OPIOID RECEPTORS IN PRIMARY AFFERENT NEURONS: MOLECULAR MECHANISMS AND POTENTIAL MANAGEMENTS. NEUROPATHIC PAIN IS THE MOST COMMON CLINICAL DISORDER DESTROYING THE QUALITY OF PATIENT LIFE AND LEADING TO A MARKED ECONOMIC AND SOCIAL BURDEN. OPIOIDS ARE STILL LAST OPTION FOR PHARMACOLOGICAL TREATMENT OF THIS DISORDER, BUT THEIR ANTINOCICEPTIVE EFFECTS ARE LIMITED IN PART DUE TO THE DOWNREGULATION OF OPIOID RECEPTORS IN THE PRIMARY AFFERENT NEURONS AFTER PERIPHERAL NERVE TRAUMA. HOW THIS DOWNREGULATION OCCURS IS NOT COMPLETELY UNDERSTOOD, BUT RECENT STUDIES HAVE DEMONSTRATED THAT PERIPHERAL NERVE TRAUMA DRIVES THE ALTERATIONS IN EPIGENETIC MODIFICATIONS (INCLUDING DNA METHYLATION, HISTONE METHYLATION AND MCIRORNAS), EXPRESSION OF TRANSCRIPTION FACTORS, POST-TRANSCRIPTIONAL MODIFICATIONS (E.G., RNA METHYLATION) AND PROTEIN TRANSLATION INITIATION IN THE NEURONS OF NERVE TRAUMA-RELATED DORSAL ROOT GANGLION (DRG) AND THAT THESE ALTERNATIONS MAY BE ASSOCIATED WITH NERVE TRAUMA-CAUSED DOWNREGULATION OF DRG OPIOID RECEPTORS. THIS REVIEW PRESENTS HOW OPIOID RECEPTORS ARE DOWNREGULATED IN THE DRG AFTER PERIPHERAL NERVE TRAUMA, SPECIFICALLY FOCUSING ON DISTINCT MOLECULAR MECHANISMS UNDERLYING TRANSCRIPTIONAL AND TRANSLATIONAL PROCESSES. THIS REVIEW ALSO DISCUSSES HOW THIS DOWNREGULATION CONTRIBUTES TO THE INDUCTION AND MAINTENANCE OF NEUROPATHIC PAIN. A DEEPER UNDERSTANDING OF THESE MOLECULAR MECHANISMS LIKELY PROVIDES A NOVEL AVENUE FOR PREVENTION AND/OR TREATMENT OF NEUROPATHIC PAIN. 2021 9 5645 28 SEX DEPENDENT ALTERATION OF EPIGENETIC MARKS AFTER CHRONIC MORPHINE TREATMENT IN MICE ORGANS. EPIGENETIC MARKS MAY BE ALSO AFFECTED BY SEVERAL FACTORS, SUCH AS AGE, LIFESTYLE, EARLY LIFE EXPERIENCES AND EXPOSURE TO CHEMICALS OR DRUGS, SUCH AS OPIOIDS. PREVIOUS STUDIES HAVE FOCUSED ON HOW MORPHINE EPIGENETICALLY REGULATES DIFFERENT REGIONS OF THE BRAIN THAT ARE IMPLICATED IN TOLERANCE, DEPENDENCE AND OTHER PSYCHIATRIC DISORDERS MORE RELATED TO THE PHYSIO-PATHOLOGICAL EFFECTS OF OPIOIDS. NEVERTHELESS, A SIGNIFICANT KNOWLEDGE GAP REMAINS REGARDING THE EFFECT OF CHRONIC TREATMENT ON OTHER ORGANS AND BIOLOGICAL SYSTEMS. THEREFORE, THE AIM OF THIS WORK IS TO INCREASE OUR KNOWLEDGE ABOUT THE IMPACT OF CHRONIC MORPHINE EXPOSURE ON DNA METHYLATION AND HISTONE MODIFICATION LEVELS IN EACH OF THE ORGANS OF MALE AND FEMALE MODEL MICE IN VIVO. OUR RESULTS REVEAL, FOR THE FIRST TIME, THAT CHRONIC MORPHINE TREATMENT INDUCED CHANGES IN DNA METHYLATION/HYDROXYMETHYLATION AND HISTONE MODIFICATION IN-VIVO AT THE SYSTEMIC LEVEL, REVEALING A POTENTIAL PHYSIOLOGICAL EFFECT ON THE REGULATION OF GENE EXPRESSION. NOTABLY, MORPHINE-INDUCED EPIGENETIC MODIFICATION OCCURS IN A SEX-DEPENDENT MANNER, REVEALING THE EXISTENCE OF DIFFERENT UNDERLYING MECHANISMS OF EPIGENETIC MODIFICATION IN MALE AND FEMALE MICE. 2021 10 6427 25 THE TRANSITION FROM ACUTE TO CHRONIC PAIN: DYNAMIC EPIGENETIC REPROGRAMMING OF THE MOUSE PREFRONTAL CORTEX UP TO 1 YEAR AFTER NERVE INJURY. CHRONIC PAIN IS ASSOCIATED WITH PERSISTENT STRUCTURAL AND FUNCTIONAL CHANGES THROUGHOUT THE NEUROAXIS, INCLUDING IN THE PREFRONTAL CORTEX (PFC). THE PFC IS IMPORTANT IN THE INTEGRATION OF SENSORY, COGNITIVE, AND EMOTIONAL INFORMATION AND IN CONDITIONED PAIN MODULATION. WE PREVIOUSLY REPORTED WIDESPREAD EPIGENETIC REPROGRAMMING IN THE PFC MANY MONTHS AFTER NERVE INJURY IN RODENTS. EPIGENETIC MODIFICATIONS, INCLUDING DNA METHYLATION, CAN DRIVE CHANGES IN GENE EXPRESSION WITHOUT MODIFYING DNA SEQUENCES. TO DATE, LITTLE IS KNOWN ABOUT EPIGENETIC DYSREGULATION AT THE ONSET OF ACUTE PAIN OR HOW IT PROGRESSES AS PAIN TRANSITIONS FROM ACUTE TO CHRONIC. WE HYPOTHESIZE THAT ACUTE PAIN AFTER INJURY RESULTS IN RAPID AND PERSISTENT EPIGENETIC REMODELLING IN THE PFC THAT EVOLVES AS PAIN BECOMES CHRONIC. WE FURTHER PROPOSE THAT UNDERSTANDING EPIGENETIC REMODELLING WILL PROVIDE INSIGHTS INTO THE MECHANISMS DRIVING PAIN-RELATED CHANGES IN THE BRAIN. EPIGENOME-WIDE ANALYSIS WAS PERFORMED IN THE MOUSE PFC 1 DAY, 2 WEEKS, 6 MONTHS, AND 1 YEAR AFTER PERIPHERAL INJURY USING THE SPARED NERVE INJURY IN MICE. SPARED NERVE INJURY RESULTED IN RAPID AND PERSISTENT CHANGES IN DNA METHYLATION, WITH ROBUST DIFFERENTIAL METHYLATION OBSERVED BETWEEN SPARED NERVE INJURY AND SHAM-OPERATED CONTROL MICE AT ALL TIME POINTS. HUNDREDS OF DIFFERENTIALLY METHYLATED GENES WERE IDENTIFIED, INCLUDING MANY WITH KNOWN FUNCTION IN PAIN. PATHWAY ANALYSIS REVEALED ENRICHMENT IN GENES RELATED TO STIMULUS RESPONSE AT EARLY TIME POINTS, IMMUNE FUNCTION AT LATER TIME POINTS, AND ACTIN AND CYTOSKELETAL REGULATION THROUGHOUT THE TIME COURSE. THESE RESULTS EMPHASIZE THE IMPORTANCE OF CONSIDERING PAIN CHRONICITY IN BOTH PAIN RESEARCH AND IN TREATMENT OPTIMIZATION. 2020 11 2003 24 EPIGENETIC AND TRANSCRIPTIONAL CONTROL OF THE OPIOID PRODYNORPHINE GENE: IN-DEPTH ANALYSIS IN THE HUMAN BRAIN. NEUROPEPTIDES SERVE AS NEUROHORMONES AND LOCAL PARACRINE REGULATORS THAT CONTROL NEURAL NETWORKS REGULATING BEHAVIOR, ENDOCRINE SYSTEM AND SENSORIMOTOR FUNCTIONS. THEIR EXPRESSION IS CHARACTERIZED BY EXCEPTIONALLY RESTRICTED PROFILES. CIRCUIT-SPECIFIC AND ADAPTIVE EXPRESSION OF NEUROPEPTIDE GENES MAY BE DEFINED BY TRANSCRIPTIONAL AND EPIGENETIC MECHANISMS CONTROLLED BY CELL TYPE AND SUBTYPE SEQUENCE-SPECIFIC TRANSCRIPTION FACTORS, INSULATORS AND SILENCERS. THE OPIOID PEPTIDE DYNORPHINS PLAY A CRITICAL ROLE IN NEUROLOGICAL AND PSYCHIATRIC DISORDERS, PAIN PROCESSING AND STRESS, WHILE THEIR MUTATIONS CAUSE PROFOUND NEURODEGENERATION IN THE HUMAN BRAIN. IN THIS REVIEW, WE FOCUS ON THE PRODYNORPHIN GENE AS A MODEL FOR THE IN-DEPTH EPIGENETIC AND TRANSCRIPTIONAL ANALYSIS OF EXPRESSION OF THE NEUROPEPTIDE GENES. PRODYNORPHIN STUDIES MAY PROVIDE A FRAMEWORK FOR ANALYSIS OF MECHANISMS RELEVANT FOR REGULATION OF NEUROPEPTIDE GENES IN NORMAL AND PATHOLOGICAL HUMAN BRAIN. 2021 12 2194 31 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 13 2310 30 EPIGENETIC REGULATION OF CHRONIC PAIN. CHRONIC PAIN ARISING FROM PERIPHERAL INFLAMMATION AND TISSUE OR NERVE INJURY IS A COMMON CLINICAL SYMPTOM. ALTHOUGH INTENSIVE RESEARCH ON THE NEUROBIOLOGICAL MECHANISMS OF CHRONIC PAIN HAS BEEN CARRIED OUT DURING PREVIOUS DECADES, THIS DISORDER IS STILL POORLY MANAGED BY CURRENT DRUGS SUCH AS OPIOIDS AND NONSTEROIDAL ANTI-INFLAMMATORY DRUGS. INFLAMMATION, TISSUE INJURY AND/OR NERVE INJURY-INDUCED CHANGES IN GENE EXPRESSION IN SENSORY NEURONS OF THE DORSAL ROOT GANGLION, SPINAL CORD DORSAL HORN AND PAIN-ASSOCIATED BRAIN REGIONS ARE THOUGHT TO PARTICIPATE IN CHRONIC PAIN GENESIS; HOWEVER, HOW THESE CHANGES OCCUR IS STILL ELUSIVE. EPIGENETIC MODIFICATIONS INCLUDING DNA METHYLATION AND COVALENT HISTONE MODIFICATIONS CONTROL GENE EXPRESSION. RECENT STUDIES HAVE SHOWN THAT PERIPHERAL NOXIOUS STIMULATION CHANGES DNA METHYLATION AND HISTONE MODIFICATIONS AND THAT THESE CHANGES MAY BE RELATED TO THE INDUCTION OF PAIN HYPERSENSITIVITY UNDER CHRONIC PAIN CONDITIONS. THIS REVIEW SUMMARIZES THE CURRENT KNOWLEDGE AND PROGRESS IN EPIGENETIC RESEARCH IN CHRONIC PAIN AND DISCUSSES THE POTENTIAL ROLE OF EPIGENETIC MODIFICATIONS AS THERAPEUTIC ANTINOCICEPTIVE TARGETS IN THIS DISORDER. 2015 14 2250 28 EPIGENETIC MODULATION OF OPIOID RECEPTORS BY DRUGS OF ABUSE. CHRONIC EXPOSURE TO DRUGS OF ABUSE PRODUCES PROFOUND CHANGES IN GENE EXPRESSION AND NEURAL ACTIVITY ASSOCIATED WITH DRUG-SEEKING AND TAKING BEHAVIOR. DYSREGULATION OF OPIOID RECEPTOR GENE EXPRESSION IS COMMONLY OBSERVED ACROSS A VARIETY OF ABUSED SUBSTANCES INCLUDING OPIOIDS, COCAINE, AND ALCOHOL. EARLY STUDIES IN CULTURED CELLS SHOWED THAT THE SPATIAL AND TEMPORAL GENE EXPRESSION OF OPIOID RECEPTORS ARE REGULATED BY EPIGENETIC MECHANISMS INCLUDING DNA AND HISTONE MODIFICATIONS AND NON-CODING RNAS. ACCUMULATING EVIDENCE INDICATE THAT DRUGS OF ABUSE CAN MODULATE OPIOID RECEPTOR GENE EXPRESSION BY TARGETING VARIOUS EPIGENETIC REGULATORY NETWORKS. BASED ON CURRENT CELLULAR AND ANIMAL MODELS OF SUBSTANCE USE DISORDER AND CLINICAL EVIDENCE, THIS REVIEW SUMMARIZES HOW CHRONIC DRUG EXPOSURE ALTERS THE GENE EXPRESSION OF MU, DELTA, KAPPA, AND NOCICEPTIN RECEPTORS VIA DNA AND HISTONE MODIFICATIONS. THE INFLUENCE OF DRUGS OF ABUSE ON EPIGENETIC MODULATORS, SUCH AS NON-CODING RNAS AND TRANSCRIPTION FACTORS, IS ALSO PRESENTED. FINALLY, THE THERAPEUTIC POTENTIAL OF MANIPULATING EPIGENETIC PROCESSES AS AN AVENUE TO TREAT SUBSTANCE USE DISORDER IS DISCUSSED. 2022 15 5624 28 SELECTIVE BOOSTING OF TRANSCRIPTIONAL AND BEHAVIORAL RESPONSES TO DRUGS OF ABUSE BY HISTONE DEACETYLASE INHIBITION. HISTONE ACETYLATION AND OTHER MODIFICATIONS OF THE CHROMATIN ARE IMPORTANT REGULATORS OF GENE EXPRESSION AND, CONSEQUENTLY, MAY CONTRIBUTE TO DRUG-INDUCED BEHAVIORS AND NEUROPLASTICITY. EARLIER STUDIES HAVE SHOWN THAT A REDUCTION IN HISTONE DEACETYLASE (HDAC) ACTIVITY RESULTS IN THE ENHANCEMENT OF SOME PSYCHOSTIMULANT-INDUCED BEHAVIORS. IN THIS STUDY, WE EXTEND THOSE SEMINAL FINDINGS BY SHOWING THAT THE ADMINISTRATION OF THE HDAC INHIBITOR SODIUM BUTYRATE ENHANCES MORPHINE-INDUCED LOCOMOTOR SENSITIZATION AND CONDITIONED PLACE PREFERENCE. IN CONTRAST, THIS COMPOUND HAS NO EFFECTS ON THE DEVELOPMENT OF MORPHINE TOLERANCE AND DEPENDENCE. SIMILAR EFFECTS WERE OBSERVED FOR COCAINE AND ETHANOL-INDUCED BEHAVIORS. THESE BEHAVIORAL CHANGES WERE ACCOMPANIED BY A SELECTIVE BOOSTING OF A COMPONENT OF THE TRANSCRIPTIONAL PROGRAM ACTIVATED BY CHRONIC MORPHINE ADMINISTRATION THAT INCLUDED CIRCADIAN CLOCK GENES AND OTHER GENES RELEVANT TO ADDICTIVE BEHAVIOR. OUR RESULTS SUPPORT A SPECIFIC FUNCTION FOR HISTONE ACETYLATION AND THE EPIGENETIC MODULATION OF TRANSCRIPTION AT A REDUCED NUMBER OF BIOLOGICALLY RELEVANT LOCI ON NON-HOMEOSTATIC, LONG-LASTING, DRUG-INDUCED BEHAVIORAL PLASTICITY. 2009 16 2297 25 EPIGENETIC REGULATION OF ACUTE INFLAMMATORY PAIN. ACUTE PAIN IS ASSOCIATED WITH TISSUE DAMAGE, WHICH RESULTS IN THE RELEASE OF INFLAMMATORY MEDIATORS. RECENT STUDIES POINT TO THE INVOLVEMENT OF EPIGENETIC MECHANISMS (DNA METHYLATION) IN THE DEVELOPMENT OF PAIN. WE HAVE FOUND THAT DURING ACUTE INFLAMMATORY PAIN INDUCED BY THE APPLICATION OF 10% MUSTARD OIL ON THE TONGUES OF RATS, LEVELS OF DNMT3A AND 3B WERE ELEVATED MARKEDLY (36 AND 42 % RESPECTIVELY), WHEREAS THE LEVEL OF DNMT1 WAS NOT CHANGED SIGNIFICANTLY. PREVIOUS INJECTION OF XEFOCAM WITH 0,4 MG/KG DOSE DECREASED LEVELS OF DNMT3A AND 3B (25 AND 24% RESPECTIVELY). THE LEVEL OF DNMT1 WAS NOT CHANGED SIGNIFICANTLY COMPARED TO THE CONTROL GROUP. THE FINDINGS SUPPORT THE IDEA THAT INHIBITORS OF DNA-METHYLTRANSFERASES COULD BE USEFUL FOR PAIN MANAGEMENT. OUR DATA SUGGEST THAT NSAIDS (ALONE OR IN COMBINATION WITH DNMT INHIBITORS) MAY BE PROPOSED AS POSSIBLE EPIGENETIC REGULATORY AGENTS, WHICH MAY PLAY A ROLE IN EPIGENETIC MECHANISMS INDIRECTLY THROUGH ALTERING THE ACTIVITY OF INFLAMMATORY MEDIATORS INVOLVED IN PAIN DEVELOPMENT. 2014 17 3754 25 INTEGRATED ANALYSIS OF OMICS DATA REVEAL AP-1 AS A POTENTIAL REGULATION HUB IN THE INFLAMMATION-INDUCED HYPERALGESIA RAT MODEL. INFLAMMATION-ASSOCIATED CHRONIC PAIN IS A GLOBAL CLINICAL PROBLEM, AFFECTING MILLIONS OF PEOPLE WORLDWIDE. HOWEVER, THE UNDERLYING MECHANISMS THAT MEDIATE INFLAMMATION-ASSOCIATED CHRONIC PAIN REMAIN UNCLEAR. A RAT MODEL OF CUTANEOUS INFLAMMATION INDUCED BY COMPLETE FREUND'S ADJUVANT (CFA) HAS BEEN WIDELY USED AS AN INFLAMMATION-INDUCED PAIN HYPERSENSITIVITY MODEL. WE PRESENT THE TRANSCRIPTOMICS PROFILE OF CFA-INDUCED INFLAMMATION IN THE RAT DORSAL ROOT GANGLION (DRG) VIA AN APPROACH THAT TARGETS GENE EXPRESSION, DNA METHYLATION, AND POST-TRANSCRIPTIONAL REGULATION. WE IDENTIFIED 418 DIFFERENTIALLY EXPRESSED MRNAS, 120 DIFFERENTIALLY EXPRESSED MICRORNAS (MIRNAS), AND 2,670 DIFFERENTIALLY METHYLATED REGIONS (DMRS), WHICH WERE ALL HIGHLY ASSOCIATED WITH MULTIPLE INFLAMMATION-RELATED PATHWAYS, INCLUDING NUCLEAR FACTOR KAPPA B (NF-KAPPAB) AND INTERFERON (IFN) SIGNALING PATHWAYS. AN INTEGRATED ANALYSIS FURTHER DEMONSTRATED THAT THE ACTIVATOR PROTEIN 1 (AP-1) NETWORK, WHICH MAY ACT AS A REGULATOR OF THE INFLAMMATORY RESPONSE, IS REGULATED AT BOTH THE TRANSCRIPTOMIC AND EPIGENETIC LEVELS. WE BELIEVE OUR DATA WILL NOT ONLY PROVIDE DRUG SCREENING TARGETS FOR THE TREATMENT OF CHRONIC PAIN AND INFLAMMATION BUT WILL ALSO SHED LIGHT ON THE MOLECULAR NETWORK ASSOCIATED WITH INFLAMMATION-INDUCED HYPERALGESIA. 2021 18 5626 24 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 19 2214 34 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 20 1509 20 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