1 2885 97 G9A PARTICIPATES IN NERVE INJURY-INDUCED KCNA2 DOWNREGULATION IN PRIMARY SENSORY NEURONS. NERVE INJURY-INDUCED DOWNREGULATION OF VOLTAGE-GATED POTASSIUM CHANNEL SUBUNIT KCNA2 IN THE DORSAL ROOT GANGLION (DRG) IS CRITICAL FOR DRG NEURONAL EXCITABILITY AND NEUROPATHIC PAIN GENESIS. HOWEVER, HOW NERVE INJURY CAUSES THIS DOWNREGULATION IS STILL ELUSIVE. EUCHROMATIC HISTONE-LYSINE N-METHYLTRANSFERASE 2, ALSO KNOWN AS G9A, METHYLATES HISTONE H3 ON LYSINE RESIDUE 9 TO PREDOMINANTLY PRODUCE A DYNAMIC HISTONE DIMETHYLATION, RESULTING IN CONDENSED CHROMATIN AND GENE TRANSCRIPTIONAL REPRESSION. WE SHOWED HERE THAT BLOCKING NERVE INJURY-INDUCED INCREASE IN G9A RESCUED KCNA2 MRNA AND PROTEIN EXPRESSION IN THE AXOTOMIZED DRG AND ATTENUATED THE DEVELOPMENT OF NERVE INJURY-INDUCED PAIN HYPERSENSITIVITY. MIMICKING THIS INCREASE DECREASED KCNA2 MRNA AND PROTEIN EXPRESSION, REDUCED KV CURRENT, AND INCREASED EXCITABILITY IN THE DRG NEURONS AND LED TO SPINAL CORD CENTRAL SENSITIZATION AND NEUROPATHIC PAIN-LIKE SYMPTOMS. G9A MRNA IS CO-LOCALIZED WITH KCNA2 MRNA IN THE DRG NEURONS. THESE FINDINGS INDICATE THAT G9A CONTRIBUTES TO NEUROPATHIC PAIN DEVELOPMENT THROUGH EPIGENETIC SILENCING OF KCNA2 IN THE AXOTOMIZED DRG. 2016 2 5574 48 ROLE OF MICRORNA-143 IN NERVE INJURY-INDUCED UPREGULATION OF DNMT3A EXPRESSION IN PRIMARY SENSORY NEURONS. PERIPHERAL NERVE INJURY INCREASED THE EXPRESSION OF THE DNA METHYLTRANSFERASE 3A (DNMT3A) MRNA AND ITS ENCODING DNMT3A PROTEIN IN INJURED DORSAL ROOT GANGLIA (DRG). THIS INCREASE IS CONSIDERED AS AN ENDOGENOUS INSTIGATOR IN NEUROPATHIC PAIN GENESIS THROUGH EPIGENETIC SILENCING OF PAIN-ASSOCIATED GENES (SUCH AS OPRM1) IN INJURED DRG. HOWEVER, HOW DRG DNMT3A IS INCREASED FOLLOWING PERIPHERAL NERVE INJURY IS STILL ELUSIVE. WE REPORTED HERE THAT PERIPHERAL NERVE INJURY CAUSED BY THE FIFTH SPINAL NERVE LIGATION (SNL) DOWNREGULATED MICRORNA (MIR)-143 EXPRESSION IN INJURED DRG. THIS DOWNREGULATION WAS REQUIRED FOR SNL-INDUCED DRG DNMT3A INCREASE AS RESCUING MIR-143 DOWNREGULATION THROUGH MICROINJECTION OF MIR-143 MIMICS INTO INJURED DRG BLOCKED THE SNL-INDUCED INCREASE IN DNMT3A AND RESTORED THE SNL-INDUCED DECREASES IN OPRM1 MRNA AND ITS ENCODING MU OPIOID RECEPTOR (MOR) IN INJURED DRG, IMPAIRED SPINAL CORD CENTRAL SENSITIZATION AND NEUROPATHIC PAIN, AND IMPROVED MORPHINE ANALGESIC EFFECTS FOLLOWING SNL. MIMICKING SNL-INDUCED DRG MIR-143 DOWNREGULATION THROUGH DRG MICROINJECTION OF MIR143 INHIBITORS IN NAIVE RATS INCREASED THE EXPRESSION OF DNMT3A AND REDUCED THE EXPRESSION OF OPRM1 MRNA AND MOR IN INJECTED DRG AND PRODUCED NEUROPATHIC PAIN-LIKE SYMPTOMS. THESE FINDINGS SUGGEST THAT MIR-143 IS A NEGATIVE REGULATOR IN DNMT3A EXPRESSION IN THE DRG UNDER NEUROPATHIC PAIN CONDITIONS AND MAY BE A POTENTIAL TARGET FOR THERAPEUTIC MANAGEMENT OF NEUROPATHIC PAIN. 2017 3 4615 47 NERVE INJURY DIMINISHES OPIOID ANALGESIA THROUGH LYSINE METHYLTRANSFERASE-MEDIATED TRANSCRIPTIONAL REPRESSION OF MU-OPIOID RECEPTORS IN PRIMARY SENSORY NEURONS. THE MU-OPIOID RECEPTOR (MOR, ENCODED BY OPRM1) AGONISTS ARE THE MAINSTAY ANALGESICS FOR TREATING MODERATE TO SEVERE PAIN. NERVE INJURY CAUSES DOWN-REGULATION OF MORS IN THE DORSAL ROOT GANGLION (DRG) AND DIMINISHES THE OPIOID EFFECT ON NEUROPATHIC PAIN. HOWEVER, THE EPIGENETIC MECHANISMS UNDERLYING THE DIMINISHED MOR EXPRESSION CAUSED BY NERVE INJURY ARE NOT CLEAR. G9A (ENCODED BY EHMT2), A HISTONE 3 AT LYSINE 9 METHYLTRANSFERASE, IS A KEY CHROMATIN REGULATOR RESPONSIBLE FOR GENE SILENCING. IN THIS STUDY, WE DETERMINED THE ROLE OF G9A IN DIMINISHED MOR EXPRESSION AND OPIOID ANALGESIC EFFECTS IN ANIMAL MODELS OF NEUROPATHIC PAIN. WE FOUND THAT NERVE INJURY IN RATS INDUCED A LONG-LASTING REDUCTION IN THE EXPRESSION LEVEL OF MORS IN THE DRG BUT NOT IN THE SPINAL CORD. NERVE INJURY CONSISTENTLY INCREASED THE ENRICHMENT OF THE G9A PRODUCT HISTONE 3 AT LYSINE 9 DIMETHYLATION IN THE PROMOTER OF OPRM1 IN THE DRG. G9A INHIBITION OR SIRNA KNOCKDOWN FULLY REVERSED MOR EXPRESSION IN THE INJURED DRG AND POTENTIATED THE MORPHINE EFFECT ON PAIN HYPERSENSITIVITY INDUCED BY NERVE INJURY. IN MICE LACKING EHMT2 IN DRG NEURONS, NERVE INJURY FAILED TO REDUCE THE EXPRESSION LEVEL OF MORS AND THE MORPHINE EFFECT. IN ADDITION, G9A INHIBITION OR EHMT2 KNOCKOUT IN DRG NEURONS NORMALIZED NERVE INJURY-INDUCED REDUCTION IN THE INHIBITORY EFFECT OF THE OPIOID ON SYNAPTIC GLUTAMATE RELEASE FROM PRIMARY AFFERENT NERVES. OUR FINDINGS INDICATE THAT G9A CONTRIBUTES CRITICALLY TO TRANSCRIPTIONAL REPRESSION OF MORS IN PRIMARY SENSORY NEURONS IN NEUROPATHIC PAIN. G9A INHIBITORS MAY BE USED TO ENHANCE THE OPIOID ANALGESIC EFFECT IN THE TREATMENT OF CHRONIC NEUROPATHIC PAIN. 2016 4 4618 43 NERVE INJURY-INDUCED EPIGENETIC SILENCING OF OPIOID RECEPTORS CONTROLLED BY DNMT3A IN PRIMARY AFFERENT NEURONS. OPIOIDS ARE THE GOLD STANDARD FOR PHARMACOLOGICAL TREATMENT OF NEUROPATHIC PAIN, BUT THEIR ANALGESIC EFFECTS ARE UNSATISFACTORY IN PART DUE TO NERVE INJURY-INDUCED DOWNREGULATION OF OPIOID RECEPTORS IN DORSAL ROOT GANGLIA (DRG) NEURONS. HOW NERVE INJURY DRIVES SUCH DOWNREGULATION REMAINS ELUSIVE. DNA METHYLTRANSFERASE (DNMT)-TRIGGERED DNA METHYLATION REPRESSES GENE EXPRESSION. WE SHOW HERE THAT BLOCKING THE NERVE INJURY-INDUCED INCREASE IN DRG DNMT3A (A DE NOVO DNMT) RESCUED THE EXPRESSION OF OPRM1 AND OPRK1 MRNAS AND THEIR RESPECTIVE ENCODING MU-OPIOID RECEPTOR (MOR) AND KAPPA-OPIOID RECEPTOR (KOR) PROTEINS IN THE INJURED DRG. BLOCKING THIS INCREASE ALSO PREVENTED THE NERVE INJURY-INDUCED INCREASE IN DNA METHYLATION IN THE PROMOTER AND 5'-UNTRANSLATED REGION OF THE OPRM1 GENE IN THE INJURED DRG, RESTORED MORPHINE OR LOPERAMIDE (A PERIPHERAL ACTING MOR PREFERRING AGONIST) ANALGESIC EFFECTS, AND ATTENUATED THE DEVELOPMENT OF THEIR ANALGESIC TOLERANCE UNDER NEUROPATHIC PAIN CONDITIONS. MIMICKING THIS INCREASE REDUCED THE EXPRESSION OF OPRM1 AND OPRK1 MRNAS AND THEIR CODING MOR AND KOR IN DRG AND AUGMENTED MOR-GATED NEUROTRANSMITTER RELEASE FROM THE PRIMARY AFFERENTS. MECHANISTICALLY, DNMT3A REGULATION OF OPRM1 GENE EXPRESSION REQUIRED THE METHYL-CPG-BINDING PROTEIN 1, MBD1, AS MBD1 KNOCKOUT RESULTED IN THE DECREASED BINDING OF DNMT3A TO THE OPRM1 GENE PROMOTER AND BLOCKED THE DNMT3A-TRIGGERED REPRESSION OF OPRM1 GENE EXPRESSION IN DRG NEURONS. THESE DATA SUGGEST THAT DNMT3A IS REQUIRED FOR NERVE INJURY-INDUCED AND MBD1-MEDIATED EPIGENETIC SILENCING OF THE MOR AND KOR IN THE INJURED DRG. DNMT3A INHIBITION MAY SERVE AS A PROMISING ADJUVANT THERAPY FOR OPIOID USE IN NEUROPATHIC PAIN MANAGEMENT. 2017 5 4616 44 NERVE INJURY INCREASES BRAIN-DERIVED NEUROTROPHIC FACTOR LEVELS TO SUPPRESS BK CHANNEL ACTIVITY IN PRIMARY SENSORY NEURONS. ABNORMAL HYPEREXCITABILITY OF PRIMARY SENSORY NEURONS CONTRIBUTES TO NEUROPATHIC PAIN DEVELOPMENT AFTER NERVE INJURY. NERVE INJURY PROFOUNDLY REDUCES THE EXPRESSION OF BIG CONDUCTANCE CA(2+) -ACTIVATED K(+) (BK) CHANNELS IN THE DORSAL ROOT GANGLION (DRG). HOWEVER, LITTLE IS KNOWN ABOUT HOW NERVE INJURY AFFECTS BK CHANNEL ACTIVITY IN DRG NEURONS. IN THIS STUDY, WE DETERMINED THE CHANGES IN BK CHANNEL ACTIVITY IN DRG NEURONS IN A RAT MODEL OF NEUROPATHIC PAIN AND THE CONTRIBUTION OF BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) TO REDUCED BK CHANNEL ACTIVITY. THE BK CHANNEL ACTIVITY WAS PRESENT PREDOMINANTLY IN SMALL AND MEDIUM DRG NEURONS, AND LIGATION OF L5 AND L6 SPINAL NERVES PROFOUNDLY DECREASED THE BK CURRENT DENSITY IN THESE NEURONS. BLOCKING BK CHANNELS SIGNIFICANTLY INCREASED NEURONAL EXCITABILITY IN SHAM CONTROL, BUT NOT IN NERVE-INJURED, RATS. THE BDNF CONCENTRATION IN THE DRG WAS SIGNIFICANTLY GREATER IN NERVE-INJURED RATS THAN IN CONTROL RATS. BDNF TREATMENT LARGELY REDUCED BK CURRENTS IN DRG NEURONS IN CONTROL RATS, WHICH WAS BLOCKED BY EITHER ANTI-BDNF ANTIBODY OR K252A, A TRK RECEPTOR INHIBITOR. FURTHERMORE, EITHER ANTI-BDNF ANTIBODY OR K252A REVERSED REDUCTION IN BK CURRENTS IN INJURED DRG NEURONS. BDNF TREATMENT REDUCED THE MRNA LEVELS OF BKALPHA1 SUBUNIT IN DRG NEURONS, AND ANTI-BDNF ANTIBODY ATTENUATED THE REDUCTION IN THE BKALPHA1 MRNA LEVEL IN INJURED DRG NEURONS. THESE FINDINGS SUGGEST THAT NERVE INJURY PRIMARILY DIMINISHES THE BK CHANNEL ACTIVITY IN SMALL AND MEDIUM DRG NEURONS. INCREASED BDNF LEVELS CONTRIBUTE TO REDUCED BK CHANNEL ACTIVITY IN DRG NEURONS THROUGH EPIGENETIC AND TRANSCRIPTIONAL MECHANISMS IN NEUROPATHIC PAIN. 2012 6 1166 43 CONTRIBUTION OF DNMT1 TO NEUROPATHIC PAIN GENESIS PARTIALLY THROUGH EPIGENETICALLY REPRESSING KCNA2 IN PRIMARY AFFERENT NEURONS. EXPRESSIONAL CHANGES OF PAIN-ASSOCIATED GENES IN PRIMARY SENSORY NEURONS OF DRG ARE CRITICAL FOR NEUROPATHIC PAIN GENESIS. DNA METHYLTRANSFERASE (DNMT)-TRIGGERED DNA METHYLATION SILENCES GENE EXPRESSION. WE SHOW HERE THAT DNMT1, A CANONICAL MAINTENANCE METHYLTRANSFERASE, ACTS AS THE DE NOVO DNMT AND IS REQUIRED FOR NEUROPATHIC PAIN GENESIS LIKELY THROUGH REPRESSING AT LEAST DRG KCNA2 GENE EXPRESSION IN MALE MICE. PERIPHERAL NERVE INJURY UPREGULATED DNMT1 EXPRESSION IN THE INJURED DRG THROUGH THE TRANSCRIPTION FACTOR CAMP RESPONSE ELEMENT BINDING PROTEIN-TRIGGERED TRANSCRIPTIONAL ACTIVATION OF DNMT1 GENE. BLOCKING THIS UPREGULATION PREVENTED NERVE INJURY-INDUCED DNA METHYLATION WITHIN THE PROMOTER AND 5'-UNTRANSLATED REGION OF KCNA2 GENE, RESCUED KCNA2 EXPRESSION AND TOTAL KV CURRENT, ATTENUATED HYPEREXCITABILITY IN THE INJURED DRG NEURONS, AND ALLEVIATED NERVE INJURY-INDUCED PAIN HYPERSENSITIVITIES. GIVEN THAT KCNA2 IS A KEY PLAYER IN NEUROPATHIC PAIN, OUR FINDINGS SUGGEST THAT DRG DNMT1 MAY BE A POTENTIAL TARGET FOR NEUROPATHIC PAIN MANAGEMENT.SIGNIFICANCE STATEMENT IN THE PRESENT STUDY, WE REPORTED THAT DNMT1, A CANONICAL DNA MAINTENANCE METHYLTRANSFERASE, IS UPREGULATED VIA THE ACTIVATION OF THE TRANSCRIPTION FACTOR CREB IN THE INJURED DRG AFTER PERIPHERAL NERVE INJURY. THIS UPREGULATION WAS RESPONSIBLE FOR NERVE INJURY-INDUCED DE NOVO DNA METHYLATION WITHIN THE PROMOTER AND 5'-UNTRANSLATED REGION OF THE KCNA2 GENE, REDUCTIONS IN KCNA2 EXPRESSION AND KV CURRENT AND INCREASES IN NEURONAL EXCITABILITY IN THE INJURED DRG. SINCE PHARMACOLOGICAL INHIBITION OR GENETIC KNOCKDOWN OF DRG DNMT1 ALLEVIATED NERVE INJURY-INDUCED PAIN HYPERSENSITIVITIES, DRG DNMT1 CONTRIBUTES TO NEUROPATHIC PAIN GENESIS PARTIALLY THROUGH REPRESSION OF DRG KCNA2 GENE EXPRESSION. 2019 7 4172 26 MELATONIN IMPEDES TET1-DEPENDENT MGLUR5 PROMOTER DEMETHYLATION TO RELIEVE PAIN. MELATONIN (N-ACETYL-5-METHOXYTRYPTAMINE)/MT2 RECEPTOR-DEPENDENT EPIGENETIC MODIFICATION REPRESENTS A NOVEL PATHWAY IN THE TREATMENT OF NEUROPATHIC PAIN. BECAUSE SPINAL TEN-ELEVEN TRANSLOCATION METHYLCYTOSINE DIOXYGENASE 1 (TET1)-DEPENDENT EPIGENETIC DEMETHYLATION HAS RECENTLY BEEN LINKED TO PAIN HYPERSENSITIVITY, WE HYPOTHESIZED THAT MELATONIN/MT2-DEPENDENT ANALGESIA INVOLVES SPINAL TET1-DEPENDENT DEMETHYLATION. HERE, WE SHOWED THAT SPINAL TET1 GENE TRANSFER BY INTRATHECAL DELIVERY OF TET1-ENCODING VECTORS TO NAIVE RATS PRODUCED PROFOUND AND LONG-LASTING NOCICEPTIVE HYPERSENSITIVITY. IN ADDITION, ENHANCED TET1 EXPRESSION, TET1-METABOTROPIC GLUTAMATE RECEPTOR SUBTYPE 5 (MGLUR5) PROMOTER COUPLING, DEMETHYLATION AT THE MGLUR5 PROMOTER, AND MGLUR5 EXPRESSION IN DORSAL HORN NEURONS WERE OBSERVED. RATS SUBJECTED TO SPINAL NERVE LIGATION AND INTRAPLANTAR COMPLETE FREUND'S ADJUVANT INJECTION DISPLAYED TACTILE ALLODYNIA AND BEHAVIORAL HYPERALGESIA ASSOCIATED WITH SIMILAR CHANGES IN THE DORSAL HORN. NOTABLY, INTRATHECAL MELATONIN INJECTION REVERSED THE PROTEIN EXPRESSION, PROTEIN-PROMOTER COUPLING, PROMOTER DEMETHYLATION, AND PAIN HYPERSENSITIVITY INDUCED BY TET1 GENE TRANSFER, SPINAL NERVE LIGATION, AND INTRAPLANTAR COMPLETE FREUND'S ADJUVANT INJECTION. ALL THE EFFECTS CAUSED BY MELATONIN WERE BLOCKED BY PRETREATMENT WITH A MT2 RECEPTOR-SELECTIVE ANTAGONIST. IN CONCLUSION, MELATONIN RELIEVES PAIN BY IMPEDING TET1-DEPENDENT DEMETHYLATION OF MGLUR5 IN DORSAL HORN NEURONS THROUGH THE MT2 RECEPTOR. OUR FINDINGS LINK MELATONIN/MT2 SIGNALING TO TET1-DEPENDENT EPIGENETIC DEMETHYLATION OF NOCICEPTIVE GENES FOR THE FIRST TIME AND SUGGEST MELATONIN AS A PROMISING THERAPY FOR THE TREATMENT OF PAIN. 2017 8 1654 36 DORSAL ROOT GANGLIA COACTIVATOR-ASSOCIATED ARGININE METHYLTRANSFERASE 1 CONTRIBUTES TO PERIPHERAL NERVE INJURY-INDUCED PAIN HYPERSENSITIVITIES. NEUROPATHIC PAIN IS ASSOCIATED WITH GENE EXPRESSION CHANGES WITHIN THE DORSAL ROOT GANGLION (DRG) AFTER PERIPHERAL NERVE INJURY, WHICH INVOLVES EPIGENETIC MECHANISMS. COACTIVATOR-ASSOCIATED ARGININE METHYLTRANSFERASE 1 (CARM1), AN EPIGENETIC ACTIVATOR, REGULATES GENE TRANSCRIPTIONAL ACTIVITY BY PROTEIN POSTTRANSLATIONAL MODIFICATIONS. HOWEVER, WHETHER CARM1 PLAYS AN ESSENTIAL ROLE IN THE DEVELOPMENT AND MAINTENANCE OF NEUROPATHIC PAIN IS UNKNOWN. WE REPORT HERE THAT PERIPHERAL NERVE INJURY INDUCED THE UPREGULATION OF THE MRNA AND PROTEIN EXPRESSION OF CARM1 IN THE INJURED DRG, AND BLOCKING ITS EXPRESSION THROUGH SMALL INTERFERING RNA (SIRNA) IN THE INJURED DRG ATTENUATED THE DEVELOPMENT AND MAINTENANCE OF NEUROPATHIC PAIN. FURTHERMORE, PHARMACOLOGICAL INHIBITION OF CARM1 MITIGATED PERIPHERAL NERVE INJURY-INDUCED MECHANICAL ALLODYNIA AND THERMAL HYPERALGESIA. GIVEN THAT CARM1 INHIBITION OR KNOCKDOWN ATTENUATED THE INDUCTION AND MAINTENANCE OF NEUROPATHIC PAIN AFTER PERIPHERAL NERVE INJURY, OUR FINDINGS SUGGEST THAT CARM1 MAY SERVE AS A PROMISING THERAPEUTIC TARGET FOR NEUROPATHIC PAIN TREATMENT IN CLINICAL APPLICATIONS. 2018 9 742 41 CANNABINOID CB2 RECEPTORS ARE UPREGULATED VIA BIVALENT HISTONE MODIFICATIONS AND CONTROL PRIMARY AFFERENT INPUT TO THE SPINAL CORD IN NEUROPATHIC PAIN. TYPE-2 CANNABINOID RECEPTORS (CB2, ENCODED BY THE CNR2 GENE) ARE MAINLY EXPRESSED IN IMMUNE CELLS, AND CB2 AGONISTS NORMALLY HAVE NO ANALGESIC EFFECT. HOWEVER, NERVE INJURY UPREGULATES CB2 IN THE DORSAL ROOT GANGLION (DRG), FOLLOWING WHICH CB2 STIMULATION REDUCES NEUROPATHIC PAIN. IT IS UNCLEAR HOW NERVE INJURY INCREASES CB2 EXPRESSION OR HOW CB2 ACTIVITY IS TRANSFORMED IN NEUROPATHIC PAIN. IN THIS STUDY, IMMUNOBLOTTING SHOWED THAT SPINAL NERVE LIGATION (SNL) INDUCED A DELAYED AND SUSTAINED INCREASE IN CB2 EXPRESSION IN THE DRG AND DORSAL SPINAL CORD SYNAPTOSOMES. RNASCOPE IN SITU HYBRIDIZATION ALSO SHOWED THAT SNL SUBSTANTIALLY INCREASED CB2 MRNA LEVELS, MOSTLY IN MEDIUM AND LARGE DRG NEURONS. FURTHERMORE, WE FOUND THAT THE SPECIFIC CB2 AGONIST JWH-133 SIGNIFICANTLY INHIBITS THE AMPLITUDE OF DORSAL ROOT-EVOKED GLUTAMATERGIC EXCITATORY POSTSYNAPTIC CURRENTS IN SPINAL DORSAL HORN NEURONS IN SNL RATS, BUT NOT IN SHAM CONTROL RATS; INTRATHECAL INJECTION OF JWH-133 REVERSED PAIN HYPERSENSITIVITY IN SNL RATS, BUT HAD NO EFFECT IN SHAM CONTROL RATS. IN ADDITION, CHROMATIN IMMUNOPRECIPITATION-QPCR ANALYSIS SHOWED THAT SNL INCREASED ENRICHMENT OF TWO ACTIVATING HISTONE MARKS (H3K4ME3 AND H3K9AC) AND DIMINISHED OCCUPANCY OF TWO REPRESSIVE HISTONE MARKS (H3K9ME2 AND H3K27ME3) AT THE CNR2 PROMOTER IN THE DRG. IN CONTRAST, SNL HAD NO EFFECT ON DNA METHYLATION LEVELS AROUND THE CNR2 PROMOTER. OUR FINDINGS SUGGEST THAT PERIPHERAL NERVE INJURY PROMOTES CB2 EXPRESSION IN PRIMARY SENSORY NEURONS VIA EPIGENETIC BIVALENT HISTONE MODIFICATIONS AND THAT CB2 ACTIVATION REDUCES NEUROPATHIC PAIN BY ATTENUATING NOCICEPTIVE TRANSMISSION FROM PRIMARY AFFERENT NERVES TO THE SPINAL CORD. 2022 10 2751 31 EXPRESSION OF ACETYL-HISTONE H3 AND ACETYL-HISTONE H4 IN DORSAL ROOT GANGLION AND SPINAL DORSAL HORN IN RAT CHRONIC PAIN MODELS. AIMS: HISTONE ACETYLATION AND DEACETYLATION ARE TWO HISTONE POSTTRANSLATIONAL MODIFICATIONS THAT ARE USUALLY CONTROLLED BY HISTONE ACETYLTRANSFERASES (HATS) AND HISTONE DEACETYLASES (HDACS). ALTHOUGH HATS OR HDACS INHIBITORS COULD RELIEVE PAIN HYPERSENSITIVITIES IN CHRONIC PAIN ANIMAL MODELS, IT IS NOT CLEAR ON THE EXPRESSION OF GLOBAL HISTONE ACETYLATION IN THE DORSAL ROOT GANGLION (DRG) OR SPINAL DORSAL HORN IN CHRONIC PAIN CONDITIONS. MAIN METHODS: A SPINAL NERVE LIGATION (SNL)-INDUCED NEUROPATHIC PAIN MODEL AND A COMPLETE FREUND'S ADJUVANT (CFA)-INDUCED INFLAMMATORY PAIN MODEL IN RATS WERE USED TO EXAMINE THE EXPRESSION OF TOTAL ACETYL-HISTONE H3 (ACH3) AND TOTAL ACETYL-HISTONE H4 (ACH4) BY IMMUNOFLUORESCENCE OR WESTERN BLOT. KEY FINDINGS: ACH3 AND ACH4 NOT ONLY LOCALIZED IN NEURONAL NUCLEI, BUT ALSO IN NUCLEI OF GLIAL CELLS IN THE DRG. UNILATERAL SNL INDUCED THE INCREASE OF ACH3 AND ACH4 EXPRESSION IN THE INJURED LUMBAR 5 (L5) DRG, BUT NOT IN THE UNINJURED L5 DRG OR THE SPINAL DORSAL HORN, WHILE UNILATERAL INTRAPLANTAR INJECTION OF CFA INCREASED ACH3 AND ACH4 EXPRESSION IN THE IPSILATERAL L4/5 SPINAL DORSAL HORN, BUT NOT IN THE L4/5 DRG. SIGNIFICANCE: THESE RESULTS PROVIDE MORPHOLOGICAL EVIDENCE FOR GLOBAL HISTONE ACETYLATION EXPRESSION IN THE DRG AND SPINAL CORD AND INDICATE THE DIFFERENTIAL EXPRESSION IN THE DRG AND SPINAL DORSAL HORN IN DIFFERENT CHRONIC PAIN MODELS. MORE PRECISE EPIGENETIC MECHANISMS OF HISTONE ACETYLATION ON THE TARGET GENES NEED TO BE REVEALED. 2018 11 2884 42 G9A IS ESSENTIAL FOR EPIGENETIC SILENCING OF K(+) CHANNEL GENES IN ACUTE-TO-CHRONIC PAIN TRANSITION. NEUROPATHIC PAIN IS A DEBILITATING CLINICAL PROBLEM AND DIFFICULT TO TREAT. NERVE INJURY CAUSES A LONG-LASTING REDUCTION IN K(+) CHANNEL EXPRESSION IN THE DORSAL ROOT GANGLION (DRG), BUT LITTLE IS KNOWN ABOUT THE EPIGENETIC MECHANISMS INVOLVED. WE FOUND THAT NERVE INJURY INCREASED DIMETHYLATION OF LYS9 ON HISTONE H3 (H3K9ME2) AT KCNA4, KCND2, KCNQ2 AND KCNMA1 PROMOTERS BUT DID NOT AFFECT LEVELS OF DNA METHYLATION ON THESE GENES IN DRGS. NERVE INJURY INCREASED ACTIVITY OF EUCHROMATIC HISTONE-LYSINE N-METHYLTRANSFERASE-2 (G9A), HISTONE DEACETYLASES AND ENHANCER OF ZESTE HOMOLOG-2 (EZH2), BUT ONLY G9A INHIBITION CONSISTENTLY RESTORED K(+) CHANNEL EXPRESSION. SELECTIVE KNOCKOUT OF THE GENE ENCODING G9A IN DRG NEURONS COMPLETELY BLOCKED K(+) CHANNEL SILENCING AND CHRONIC PAIN DEVELOPMENT AFTER NERVE INJURY. REMARKABLY, RNA SEQUENCING ANALYSIS REVEALED THAT G9A INHIBITION NOT ONLY REACTIVATED 40 OF 42 SILENCED GENES ASSOCIATED WITH K(+) CHANNELS BUT ALSO NORMALIZED 638 GENES DOWN- OR UPREGULATED BY NERVE INJURY. THUS G9A HAS A DOMINANT FUNCTION IN TRANSCRIPTIONAL REPRESSION OF K(+) CHANNELS AND IN ACUTE-TO-CHRONIC PAIN TRANSITION AFTER NERVE INJURY. 2015 12 3332 27 HISTONE DEACETYLASE INHIBITOR-INDUCED EMERGENCE OF SYNAPTIC DELTA-OPIOID RECEPTORS AND BEHAVIORAL ANTINOCICEPTION IN PERSISTENT NEUROPATHIC PAIN. THE EFFICACY OF OPIOIDS IN PATIENTS WITH CHRONIC NEUROPATHIC PAIN REMAINS CONTROVERSIAL. ALTHOUGH ACTIVATION OF DELTA-OPIOID RECEPTORS (DORS) IN THE BRAINSTEM REDUCES INFLAMMATION-INDUCED PERSISTENT HYPERALGESIA, IT IS NOT EFFECTIVE UNDER PERSISTENT NEUROPATHIC PAIN CONDITIONS AND THESE CLINICAL PROBLEMS REMAIN LARGELY UNKNOWN. IN THIS STUDY, BY USING A CHRONIC CONSTRICTION INJURY (CCI) OF THE SCIATIC NERVE IN RATS, WE FOUND THAT IN THE BRAINSTEM NUCLEUS RAPHE MAGNUS (NRM), DORS EMERGED ON THE SURFACE MEMBRANE OF CENTRAL SYNAPTIC TERMINALS ON DAY 3 AFTER CCI SURGERY AND DISAPPEARED ON DAY 14. HISTONE DEACETYLASE (HDAC) INHIBITORS MICROINJECTED INTO THE NRM IN VIVO INCREASED THE LEVEL OF SYNAPTOSOMAL DOR PROTEIN AND NRM INFUSION OF DOR AGONISTS PRODUCING AN ANTINOCICEPTIVE EFFECT IN A NERVE GROWTH FACTOR (NGF) SIGNALING-DEPENDENT MANNER. IN VITRO, IN CCI RAT SLICES INCUBATED WITH HDAC INHIBITORS, DOR AGONISTS SIGNIFICANTLY INHIBITED EPSCS. THIS EFFECT WAS BLOCKED BY TYROSINE RECEPTOR KINASE A ANTAGONISTS. CHROMATIN IMMUNOPRECIPITATION ANALYSIS REVEALED THAT NRM INFUSION OF HDAC INHIBITORS IN CCI RATS INCREASED THE LEVEL OF HISTONE H4 ACETYLATION AT NGF GENE PROMOTER REGIONS. NGF WAS INFUSED INTO THE NRM OR INCUBATED CCI RAT SLICES DROVE DORS TO THE SURFACE MEMBRANE OF SYNAPTIC TERMINALS. TAKEN TOGETHER, EPIGENETIC UPREGULATION OF NGF ACTIVITY BY HDAC INHIBITORS IN THE NRM PROMOTES THE TRAFFICKING OF DORS TO PAIN-MODULATING NEURONAL SYNAPSES UNDER NEUROPATHIC PAIN CONDITIONS, LEADING TO DELTA-OPIOID ANALGESIA. THESE FINDINGS INDICATE THAT THERAPEUTIC USE OF DOR AGONISTS COMBINED WITH HDAC INHIBITORS MIGHT BE EFFECTIVE IN CHRONIC NEUROPATHIC PAIN MANAGEMENTS. 2016 13 4160 44 MECP2 EPIGENETIC SILENCING OF OPRM1 GENE IN PRIMARY SENSORY NEURONS UNDER NEUROPATHIC PAIN CONDITIONS. OPIOIDS ARE THE LAST OPTION FOR THE PHARMACOLOGICAL TREATMENT OF NEUROPATHIC PAIN, BUT THEIR ANTINOCICEPTIVE EFFECTS ARE LIMITED. DECREASED MU OPIOID RECEPTOR (MOR) EXPRESSION IN THE PERIPHERAL NERVOUS SYSTEM MAY CONTRIBUTE TO THIS. HERE, WE SHOWED THAT NERVE INJURY INDUCED HYPERMETHYLATION OF THE OPRM1 GENE PROMOTER AND AN INCREASED EXPRESSION OF METHYL-CPG BINDING PROTEIN 2 (MECP2) IN INJURED DORSAL ROOT GANGLION (DRG). THE DOWNREGULATION OF MOR IN THE DRG IS CLOSELY RELATED TO THE AUGMENTATION OF MECP2, AN EPIGENETIC REPRESSOR, WHICH COULD RECRUIT HDAC1 AND BIND TO THE METHYLATED REGIONS OF THE OPRM1 GENE PROMOTER. MECP2 KNOCKDOWN RESTORED THE EXPRESSION OF MOR IN INJURED DRG AND ENHANCED THE ANALGESIC EFFECT OF MORPHINE, WHILE THE MIMICKING OF THIS INCREASE VIA THE INTRATHECAL INFUSION OF VIRAL VECTOR-MEDIATED MECP2 WAS SUFFICIENT TO REDUCE MOR IN THE DRG. MOREOVER, HDAC1 INHIBITION WITH SUBEROYLANILIDE HYDROXAMIC ACID, AN HDAC INHIBITOR, ALSO PREVENTED MOR REDUCTION IN THE DRG OF NEUROPATHIC PAIN MICE, CONTRIBUTING TO THE AUGMENTATION OF MORPHINE ANALGESIA EFFECTS. MECHANISTICALLY, UPREGULATED MECP2 PROMOTES THE BINDING OF A HIGH LEVEL OF HDCA1 TO HYPERMETHYLATED REGIONS OF THE OPRM1 GENE PROMOTER, REDUCES THE ACETYLATION OF HISTONE H3 (ACH3) LEVELS OF THE OPRM1 GENE PROMOTER, AND ATTENUATES OPRM1 TRANSCRIPTION IN INJURED DRG. THUS, UPREGULATED MECP2 AND HDAC1 IN OPRM1 GENE PROMOTER SITES, NEGATIVELY REGULATES MOR EXPRESSION IN INJURED DRG, MITIGATING THE ANALGESIC EFFECT OF THE OPIOIDS. TARGETING MECP2/HDAC1 MAY THUS PROVIDE A NEW SOLUTION FOR IMPROVING THE THERAPEUTIC EFFECT OF OPIOIDS IN A CLINICAL SETTING. 2021 14 2407 39 EPIGENETIC RESTORATION OF VOLTAGE-GATED POTASSIUM CHANNEL KV1.2 ALLEVIATES NERVE INJURY-INDUCED NEUROPATHIC PAIN. VOLTAGE-GATED POTASSIUM CHANNELS (KV) ARE IMPORTANT REGULATORS OF NEURONAL EXCITABILITY FOR ITS ROLE OF REGULATING RESTING MEMBRANE POTENTIAL AND REPOLARIZATION. RECENT STUDIES SHOW THAT KV CHANNELS PARTICIPATE IN NEUROPATHIC PAIN, BUT THE DETAILED UNDERLYING MECHANISMS ARE FAR FROM BEING CLEAR. IN THIS STUDY, WE USED SIRNA, MIR-137 AGOMIR, AND ANTAGOMIR TO REGULATE THE EXPRESSION OF KV1.2 IN SPINAL CORD AND DORSAL ROOT GANGLIA (DRG) OF NAIVE AND CHRONIC CONSTRICTION INJURY (CCI) RATS. KV CURRENTS AND NEURON EXCITABILITY IN DRG NEURONS WERE EXAMINED BY PATCH-CLAMP WHOLE-CELL RECORDING TO VERIFY THE CHANGE IN KV1.2 FUNCTION. THE RESULTS SHOWED THAT KV1.2 WAS DOWN-REGULATED IN DRG AND SPINAL DORSAL HORN (SDH) BY CCI. KNOCKDOWN OF KV1.2 BY INTRATHECALLY INJECTING KCNA2 SIRNA INDUCED SIGNIFICANT MECHANICAL AND THERMAL HYPERSENSITIVITY IN NAIVE RATS. CONCOMITANT WITH THE DOWN-REGULATION OF KV1.2 WAS AN INCREASE IN THE EXPRESSION OF THE MIR-137. THE TARGETING AND REGULATING OF MIR-137 ON KCNA2 WAS VERIFIED BY DUAL-LUCIFERASE REPORTER SYSTEM AND INTRATHECAL INJECTING MIR-137 AGOMIR. FURTHERMORE, RESCUING THE EXPRESSION OF KV1.2 IN CCI RATS, ACHIEVED THROUGH INHIBITING MIR-137, RESTORED THE ABNORMAL KV CURRENTS AND EXCITABILITY IN DRG NEURONS, AND ALLEVIATED MECHANICAL ALLODYNIA AND THERMAL HYPERALGESIA. THESE RESULTS INDICATE THAT THE MIR-137-MEDIATED KV1.2 IMPAIRMENT IS A CRUCIAL ETIOPATHOGENESIS FOR THE NERVE INJURY-INDUCED NEUROPATHIC PAIN AND CAN BE A NOVEL POTENTIAL THERAPEUTIC TARGET FOR NEUROPATHIC PAIN MANAGEMENT. 2021 15 687 34 BRAINSTEM BRAIN-DERIVED NEUROTROPHIC FACTOR SIGNALING IS REQUIRED FOR HISTONE DEACETYLASE INHIBITOR-INDUCED PAIN RELIEF. OUR PREVIOUS STUDY DEMONSTRATED THAT PERSISTENT PAIN CAN EPIGENETICALLY SUPPRESS THE TRANSCRIPTION OF GAD2 [ENCODING GLUTAMIC ACID DECARBOXYLASE 65 (GAD65)] AND CONSEQUENTLY IMPAIR THE INHIBITORY FUNCTION OF GABAERGIC SYNAPSES IN CENTRAL PAIN-MODULATING NEURONS. THIS CONTRIBUTES TO THE DEVELOPMENT OF PERSISTENT PAIN SENSITIZATION. HISTONE DEACETYLASE (HDAC) INHIBITORS INCREASED GAD65 ACTIVITY CONSIDERABLY, RESTORED GABA SYNAPTIC FUNCTION, AND RENDERED SENSITIZED PAIN BEHAVIOR LESS PRONOUNCED. HOWEVER, THE MOLECULAR MECHANISMS BY WHICH HDAC REGULATES GABAERGIC TRANSMISSION THROUGH GAD65 UNDER PAIN CONDITIONS ARE UNKNOWN. THIS WORK SHOWED THAT HDAC INHIBITOR-INDUCED INCREASES IN COLOCALIZATION OF GAD65 AND SYNAPTIC PROTEIN SYNAPSIN I ON THE PRESYNAPTIC AXON TERMINALS OF THE NUCLEUS RAPHE MAGNUS (NRM) WERE BLOCKED BY A TRKB RECEPTOR ANTAGONIST K252A [(9S,10R,12R)-2,3,9,10,11,12-HEXAHYDRO-10-HYDROXY-9-METHYL-1-OXO-9,12-EPOXY-1H-DIINDOLO[1,2,3-FG:3',2',1'-KL]PYRROLO[3,4-I][1,6]BENZODIAZOCINE-10-CARBOXYLIC ACID METHYL ESTER], INDICATING THAT BDNF-TRKB SIGNALING MAY BE REQUIRED IN GAD65 MODULATION OF GABA SYNAPTIC FUNCTION. AT THE BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) PROMOTER, HDAC INHIBITORS INDUCED SIGNIFICANT INCREASES IN H3 HYPERACETYLATION, CONSISTENT WITH THE INCREASE IN BDNF MRNA AND TOTAL PROTEINS. ALTHOUGH EXOGENOUS BDNF FACILITATED GABA MINIATURE INHIBITORY POSTSYNAPTIC CURRENTS AND GAD65 ACCUMULATION IN NRM NEURONAL SYNAPSES IN NORMAL RATS, IT FAILED TO DO SO IN ANIMALS SUBJECTED TO PERSISTENT INFLAMMATION. IN ADDITION, BLOCKADE OF THE TRKB RECEPTOR WITH K252A HAS NO EFFECT ON MINIATURE INHIBITORY POSTSYNAPTIC CURRENTS AND SYNAPTIC GAD65 ACCUMULATION UNDER NORMAL CONDITIONS. IN ADDITION, THE ANALGESIC EFFECTS OF HDAC INHIBITORS ON BEHAVIOR WERE BLOCKED BY NRM INFUSION OF K252A. THESE FINDINGS SUGGEST THAT BDNF-TRKB SIGNALING IS REQUIRED FOR DRUGS THAT REVERSE THE EPIGENETIC EFFECTS OF CHRONIC PAIN AT THE GENE LEVEL, SUCH AS HDAC INHIBITORS. 2015 16 6424 46 THE TRANSCRIPTION FACTOR C/EBPBETA IN THE DORSAL ROOT GANGLION CONTRIBUTES TO PERIPHERAL NERVE TRAUMA-INDUCED NOCICEPTIVE HYPERSENSITIVITY. CHANGES IN GENE TRANSCRIPTION IN THE DORSAL ROOT GANGLION (DRG) AFTER NERVE TRAUMA CONTRIBUTE TO THE GENESIS OF NEUROPATHIC PAIN. WE REPORT THAT PERIPHERAL NERVE TRAUMA CAUSED BY CHRONIC CONSTRICTION INJURY (CCI) INCREASED THE ABUNDANCE OF THE TRANSCRIPTION FACTOR C/EBPBETA (CCAAT/ENHANCER BINDING PROTEIN BETA) IN THE DRG. BLOCKING THIS INCREASE MITIGATED THE DEVELOPMENT AND MAINTENANCE OF CCI-INDUCED MECHANICAL, THERMAL, AND COLD PAIN HYPERSENSITIVITIES WITHOUT AFFECTING BASAL RESPONSES TO ACUTE PAIN AND LOCOMOTOR ACTIVITY. CONVERSELY, MIMICKING THIS INCREASE PRODUCED HYPERSENSITIVITY TO MECHANICAL, THERMAL, OR COLD PAIN. IN THE IPSILATERAL DRG, C/EBPBETA PROMOTED A DECREASE IN THE ABUNDANCE OF THE VOLTAGE-GATED POTASSIUM CHANNEL SUBUNIT KV1.2 AND MU OPIOID RECEPTOR (MOR) AT THE MRNA AND PROTEIN LEVELS, WHICH WOULD BE PREDICTED TO INCREASE EXCITABILITY IN THE IPSILATERAL DRG NEURONS AND REDUCE THE EFFICACY OF MORPHINE ANALGESIA. THESE EFFECTS REQUIRED C/EPBBETA-MEDIATED TRANSCRIPTIONAL ACTIVATION OF EHMT2 (EUCHROMATIC HISTONE-LYSINE N-METHYLTRANSFERASE 2), WHICH ENCODES G9A, AN EPIGENETIC SILENCER OF THE GENES ENCODING KV1.2 AND MOR. BLOCKING THE INCREASE IN C/EBPBETA IN THE DRG IMPROVED MORPHINE ANALGESIA AFTER CCI. THESE RESULTS SUGGEST THAT C/EBPBETA IS AN ENDOGENOUS INITIATOR OF NEUROPATHIC PAIN AND COULD BE A POTENTIAL TARGET FOR THE PREVENTION AND TREATMENT OF THIS DISORDER. 2017 17 1320 33 DEMETHYLATION REGULATION OF BDNF GENE EXPRESSION IN DORSAL ROOT GANGLION NEURONS IS IMPLICATED IN OPIOID-INDUCED PAIN HYPERSENSITIVITY IN RATS. REPEATED ADMINISTRATION OF MORPHINE MAY RESULT IN OPIOID-INDUCED HYPERSENSITIVITY (OIH), WHICH INVOLVES ALTERED EXPRESSION OF NUMEROUS GENES, INCLUDING BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) IN DORSAL ROOT GANGLION (DRG) NEURONS. YET, IT REMAINS UNCLEAR HOW BDNF EXPRESSION IS INCREASED IN DRG NEURONS AFTER REPEATED MORPHINE TREATMENT. DNA METHYLATION IS AN IMPORTANT MECHANISM OF EPIGENETIC CONTROL OF GENE EXPRESSION. IN THE CURRENT STUDY, WE HYPOTHESIZED THAT THE DEMETHYLATION REGULATION OF CERTAIN BDNF GENE PROMOTERS IN DRG NEURONS MAY CONTRIBUTE TO THE DEVELOPMENT OF OIH. REAL-TIME RT-PCR WAS USED TO ASSESS CHANGES IN THE MRNA TRANSCRIPTION LEVELS OF MAJOR BDNF EXONS INCLUDING EXON I, II, IV, VI, AS WELL AS TOTAL BDNF MRNA IN DRGS FROM RATS AFTER REPEATED MORPHINE ADMINISTRATION. THE LEVELS OF EXON IV AND TOTAL BDNF MRNA WERE SIGNIFICANTLY UPREGULATED BY REPEATED MORPHINE ADMINISTRATION, AS COMPARED TO THAT IN SALINE CONTROL GROUP. FURTHER, ELISA ARRAY AND IMMUNOCYTOCHEMISTRY STUDY REVEALED A ROBUST UPREGULATION OF BDNF PROTEIN EXPRESSION IN DRG NEURONS AFTER REPEATED MORPHINE EXPOSURE. CORRESPONDINGLY, THE METHYLATION LEVELS OF BDNF EXON IV PROMOTER SHOWED A SIGNIFICANT DOWNREGULATION BY MORPHINE TREATMENT. IMPORTANTLY, INTRATHECAL ADMINISTRATION OF A BDNF ANTIBODY, BUT NOT CONTROL IGG, SIGNIFICANTLY INHIBITED MECHANICAL HYPERSENSITIVITY THAT DEVELOPED IN RATS AFTER REPEATED MORPHINE TREATMENT. CONVERSELY, INTRATHECAL ADMINISTRATION OF AN INHIBITOR OF DNA METHYLATION, 5-AZA-2'-DEOXYCYTIDINE (5-AZA-DC) MARKEDLY UPREGULATED THE BDNF PROTEIN EXPRESSION IN DRG NEURONS AND ENHANCED THE MECHANICAL ALLODYNIA AFTER REPEATED MORPHINE EXPOSURE. TOGETHER, OUR FINDINGS SUGGEST THAT DEMETHYLATION REGULATION OF BDNF GENE PROMOTER MAY BE IMPLICATED IN THE DEVELOPMENT OF OIH THROUGH EPIGENETIC CONTROL OF BDNF EXPRESSION IN DRG NEURONS. 2016 18 1630 42 DNMT3A CONTRIBUTES TO THE DEVELOPMENT AND MAINTENANCE OF BONE CANCER PAIN BY SILENCING KV1.2 EXPRESSION IN SPINAL CORD DORSAL HORN. METASTATIC BONE TUMOR-INDUCED CHANGES IN GENE TRANSCRIPTION AND TRANSLATION IN PAIN-RELATED REGIONS OF THE NERVOUS SYSTEM MAY PARTICIPATE IN THE DEVELOPMENT AND MAINTENANCE OF BONE CANCER PAIN. EPIGENETIC MODIFICATIONS INCLUDING DNA METHYLATION REGULATE GENE TRANSCRIPTION. HERE, WE REPORT THAT INTRATHECAL INJECTION OF DECITABINE, A DNA METHYLTRANSFERASE (DNMT) INHIBITOR, DOSE DEPENDENTLY ATTENUATED THE DEVELOPMENT AND MAINTENANCE OF BONE CANCER PAIN INDUCED BY INJECTING PROSTATE CANCER CELLS INTO THE TIBIA. THE LEVEL OF THE DE NOVO DNMT3A, BUT NOT DNMT3B, TIME DEPENDENTLY INCREASED IN THE IPSILATERAL L4/5 DORSAL HORN (NOT L4/5 DORSAL ROOT GANGLION) AFTER PROSTATE CANCER CELLS INJECTION. BLOCKING THIS INCREASE THROUGH MICROINJECTION OF RECOMBINANT ADENO-ASSOCIATED VIRUS 5 (AAV5) EXPRESSING DNMT3A SHRNA INTO DORSAL HORN RESCUED PROSTATE CANCER CELLS-INDUCED DOWNREGULATION OF DORSAL HORN KV1.2 EXPRESSION AND IMPAIRED PROSTATE CANCER CELLS-INDUCED PAIN HYPERSENSITIVITY. IN TURN, MIMICKING THIS INCREASE THROUGH MICROINJECTION OF AAV5 EXPRESSING FULL-LENGTH DNMT3A INTO DORSAL HORN REDUCED DORSAL HORN KV1.2 EXPRESSION AND PRODUCED PAIN HYPERSENSITIVITY IN THE ABSENCE OF PROSTATE CANCER CELLS INJECTION. ADMINISTRATION OF NEITHER DECITABINE NOR VIRUS AFFECTED LOCOMOTOR FUNCTION AND ACUTE RESPONSES TO MECHANICAL, THERMAL, OR COLD STIMULI. GIVEN THAT DNMT3A MRNA IS CO-EXPRESSED WITH KCNA2 MRNA (ENCODING KV1.2) IN INDIVIDUAL DORSAL HORN NEURONS, OUR FINDINGS SUGGEST THAT INCREASED DORSAL HORN DNMT3A CONTRIBUTES TO BONE CANCER PAIN THROUGH SILENCING DORSAL HORN KV1.2 EXPRESSION. DNMT3A MAY REPRESENT A POTENTIAL NEW TARGET FOR CANCER PAIN MANAGEMENT. 2017 19 2300 39 EPIGENETIC REGULATION OF BDNF EXPRESSION IN THE PRIMARY SENSORY NEURONS AFTER PERIPHERAL NERVE INJURY: IMPLICATIONS IN THE DEVELOPMENT OF NEUROPATHIC PAIN. BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) IS KNOWN TO BE UP-REGULATED IN THE DORSAL ROOT GANGLION (DRG) AFTER PERIPHERAL NERVE INJURY, AND TO CONTRIBUTE TO NEUROPATHIC PAIN. HERE, WE FOUND THAT THERMAL HYPERALGESIA AND MECHANICAL ALLODYNIA AT DAY 7 POST-INJURY WERE INHIBITED ONLY WHEN ANTI-BDNF ANTIBODY WAS INTRATHECALLY ADMINISTRATED AT DAY 2 POST-INJURY. CONSISTENT WITH BEHAVIORAL RESULTS, WESTERN BLOT ANALYSIS SHOWED THAT THE EXPRESSION LEVELS OF BDNF PROTEIN IN THE SPINAL DORSAL HORN WERE MARKEDLY INDUCED DURING EARLY STAGE POST-INJURY. MOREOVER, THE MAXIMAL INCREASE IN BDNF MRNA EXPRESSION IN THE DRG WAS OBSERVED AT DAY 1 POST-INJURY, AND SIGNIFICANTLY ELEVATED LEVELS WERE SUSTAINED FOR AT LEAST 14 DAYS. FOUR OF FIVE BDNF MRNA TRANSCRIPTS WERE UP-REGULATED AFTER NERVE INJURY, AND THE MOST INDUCIBLE TRANSCRIPT WAS EXON I. USING A CHROMATIN IMMUNOPRECIPITATION (CHIP) ASSAY, WE FOUND THAT NERVE INJURY PROMOTES HISTONE H3 AND H4 ACETYLATION, TRANSCRIPTIONALLY ACTIVE MODIFICATIONS, AT BDNF PROMOTER I AT DAY 1 POST-INJURY, AND THE LEVELS OF HISTONE ACETYLATION REMAIN ELEVATED FOR AT LEAST 7 DAYS. TAKEN TOGETHER, OUR FINDINGS SUGGEST THAT AN INITIAL INCREASE IN BDNF EXON I EXPRESSION CONTROLLED BY EPIGENETIC MECHANISMS MIGHT HAVE A CRUCIAL ROLE IN THE DEVELOPMENT OF NEUROPATHIC PAIN. 2013 20 3201 45 HDAC2 IN PRIMARY SENSORY NEURONS CONSTITUTIVELY RESTRAINS CHRONIC PAIN BY REPRESSING ALPHA2DELTA-1 EXPRESSION AND ASSOCIATED NMDA RECEPTOR ACTIVITY. ALPHA2DELTA-1 (ENCODED BY THE CACNA2D1 GENE) IS A NEWLY DISCOVERED NMDA RECEPTOR-INTERACTING PROTEIN AND IS THE THERAPEUTIC TARGET OF GABAPENTINOIDS (E.G., GABAPENTIN AND PREGABALIN) FREQUENTLY USED FOR TREATING PATIENTS WITH NEUROPATHIC PAIN. NERVE INJURY CAUSES SUSTAINED ALPHA2DELTA-1 UPREGULATION IN THE DORSAL ROOT GANGLION (DRG), WHICH PROMOTES NMDA RECEPTOR SYNAPTIC TRAFFICKING AND ACTIVATION IN THE SPINAL DORSAL HORN, A HALLMARK OF CHRONIC NEUROPATHIC PAIN. HOWEVER, LITTLE IS KNOWN ABOUT HOW NERVE INJURY INITIATES AND MAINTAINS THE HIGH EXPRESSION LEVEL OF ALPHA2DELTA-1 TO SUSTAIN CHRONIC PAIN. HERE, WE SHOW THAT NERVE INJURY CAUSED HISTONE HYPERACETYLATION AND DIMINISHED ENRICHMENT OF HISTONE DEACETYLASE-2 (HDAC2), BUT NOT HDAC3, AT THE CACNA2D1 PROMOTER IN THE DRG. STRIKINGLY, HDAC2 KNOCKDOWN OR CONDITIONAL KNOCKOUT IN DRG NEURONS IN MALE AND FEMALE MICE CONSISTENTLY INDUCED LONG-LASTING MECHANICAL PAIN HYPERSENSITIVITY, WHICH WAS READILY REVERSED BY BLOCKING NMDA RECEPTORS, INHIBITING ALPHA2DELTA-1 WITH GABAPENTIN OR DISRUPTING THE ALPHA2DELTA-1-NMDA RECEPTOR INTERACTION AT THE SPINAL CORD LEVEL. HDAC2 DELETION IN DRG NEURONS INCREASED HISTONE ACETYLATION LEVELS AT THE CACNA2D1 PROMOTER, UPREGULATED ALPHA2DELTA-1 IN THE DRG, AND POTENTIATED ALPHA2DELTA-1-DEPENDENT NMDA RECEPTOR ACTIVITY AT PRIMARY AFFERENT CENTRAL TERMINALS IN THE SPINAL DORSAL HORN. CORRESPONDINGLY, HDAC2 KNOCKDOWN-INDUCED PAIN HYPERSENSITIVITY WAS BLUNTED IN CACNA2D1 KNOCKOUT MICE. THUS, OUR FINDINGS REVEAL THAT HDAC2 FUNCTIONS AS A PIVOTAL TRANSCRIPTIONAL REPRESSOR OF NEUROPATHIC PAIN VIA CONSTITUTIVELY SUPPRESSING ALPHA2DELTA-1 EXPRESSION AND ENSUING PRESYNAPTIC NMDA RECEPTOR ACTIVITY IN THE SPINAL CORD. HDAC2 ENRICHMENT LEVELS AT THE CACNA2D1 PROMOTER IN DRG NEURONS CONSTITUTE A UNIQUE EPIGENETIC MECHANISM THAT GOVERNS ACUTE-TO-CHRONIC PAIN TRANSITION.SIGNIFICANCE STATEMENT EXCESS ALPHA2DELTA-1 PROTEINS PRODUCED AFTER NERVE INJURY DIRECTLY INTERACT WITH GLUTAMATE NMDA RECEPTORS TO POTENTIATE SYNAPTIC NMDA RECEPTOR ACTIVITY IN THE SPINAL CORD, A PROMINENT MECHANISM OF NERVE PAIN. BECAUSE ALPHA2DELTA-1 UPREGULATION AFTER NERVE INJURY IS LONG LASTING, GABAPENTINOIDS RELIEVE PAIN SYMPTOMS ONLY TEMPORARILY. OUR STUDY DEMONSTRATES FOR THE FIRST TIME THE UNEXPECTED ROLE OF INTRINSIC HDAC2 ACTIVITY AT THE ALPHA2DELTA-1 GENE PROMOTER IN LIMITING ALPHA2DELTA-1 GENE TRANSCRIPTION, NMDA RECEPTOR-DEPENDENT SYNAPTIC PLASTICITY, AND CHRONIC PAIN DEVELOPMENT AFTER NERVE INJURY. THESE FINDINGS CHALLENGE THE PREVAILING VIEW ABOUT THE ROLE OF GENERAL HDAC ACTIVITY IN PROMOTING CHRONIC PAIN. RESTORING THE REPRESSIVE HDAC2 FUNCTION AND/OR REDUCING HISTONE ACETYLATION AT THE ALPHA2DELTA-1 GENE PROMOTER IN PRIMARY SENSORY NEURONS COULD LEAD TO LONG-LASTING RELIEF OF NERVE PAIN. 2022