Tao Wenjuan, Chen Quan, Wang Lu, Zhou Wenjie, Wang Yunping, Zhang Zhi
Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, Department of Neurobiology and Biophysics, University of Science and Technology of China, Hefei, Anhui, China.
Chinese Academy of Sciences Key Laboratory of Brain Function and Disease, Department of Neurobiology and Biophysics, University of Science and Technology of China, Hefei, Anhui, China
Mol Pharmacol. 2015 Jun;87(6):1035-41. doi: 10.1124/mol.115.098186. Epub 2015 Apr 7.
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.
我们之前的研究表明，持续性疼痛可通过表观遗传方式抑制Gad2（编码谷氨酸脱羧酶65，即GAD65）的转录，进而损害中枢疼痛调节神经元中GABA能突触的抑制功能。这促使了持续性疼痛敏化的发展。组蛋白脱乙酰酶（HDAC）抑制剂可显著提高GAD65活性，恢复GABA突触功能，并使敏化的疼痛行为减轻。然而，在疼痛条件下HDAC通过GAD65调节GABA能传递的分子机制尚不清楚。这项研究表明，HDAC抑制剂诱导的GAD65与突触蛋白突触素I在中缝大核（NRM）突触前轴突终末的共定位增加被TrkB受体拮抗剂K252a [（9S，10R，12R）-2,3,9,10,11,12-六氢-10-羟基-9-甲基-1-氧代-9,12-环氧-1H-二吲哚并[1,2,3-fg:3',2',1'-kl]吡咯并[3,4-i][1,6]苯并二氮杂卓-10-羧酸甲酯]阻断，这表明BDNF-TrkB信号可能参与GAD65对GABA突触功能的调节。在脑源性神经营养因子（BDNF）启动子处，HDAC抑制剂可诱导H3高度乙酰化显著增加，这与BDNF mRNA和总蛋白的增加一致。虽然外源性BDNF可促进正常大鼠NRM神经元突触中GABA微小抑制性突触后电流和GAD65的积累，但在遭受持续性炎症的动物中却无法做到这一点。此外，用K252a阻断TrkB受体在正常条件下对微小抑制性突触后电流和突触GAD65的积累没有影响。另外，HDAC抑制剂对行为的镇痛作用被向NRM注射K252a所阻断。这些发现表明，BDNF-TrkB信号对于在基因水平逆转慢性疼痛表观遗传效应的药物（如HDAC抑制剂）是必需的。
