Defining the role of peripheral Adrb3 in chronic pain and inflammation

摘要 功能性疼痛综合症影响着超过1亿人，但由于病因复杂，治疗效果不佳 大部分都是未知的。越来越多的证据表明，这些综合征在很大程度上是由于低， 儿茶酚-O-甲基转移酶（COMT）的活性，一种代谢儿茶酚胺的酶。估计 66%的功能性疼痛综合征患者，如纤维肌痛，具有COMT基因变异， 导致COMT酶的低活性。具有“低COMT活性”基因型的个体报告更大的疼痛 在基线和增强疼痛后的压力事件，加强儿茶酚胺释放从 交感神经与临床症状一致，我们的实验室已经表明， 啮齿类动物中的COMT在多个身体部位产生疼痛，并在重复压力后增强疼痛。在 随后的研究表明，COMT依赖性疼痛是由外周肾上腺素能受体启动的， β-3（Adrb3）通过在局部组织中释放促炎细胞因子。疼痛是由 脊髓组织中促炎细胞因子的随后增加和促分裂原活化 蛋白激酶（MAPKs）在痛觉感受器的细胞体和中央终端。所有这些 数据显示升高的儿茶酚胺张力通过外周Adrb3及其下游导致慢性疼痛， 效应器然而，表达Adrb3并介导疼痛的细胞类型仍需要鉴定， 分子机制确定。我们假设Adrb3在脂肪细胞（脂肪细胞， 周围伤害感受器和交感神经末梢）通过 促进炎症和伤害感受器激活的细胞因子和MAPK增加。我们还 假设应激诱导的儿茶酚胺释放放大了Adrb3信号对炎症的作用 和痛苦.初步数据显示，促炎细胞因子的COMT依赖性增加介导 Adrb3定位于脂肪细胞。额外的数据显示，Adrb3的持续激活导致了细胞凋亡的减少。 miR-133a是一种在脂肪细胞中表达的微小RNA，能够阻断MAPK信号传导。拟议 研究将扩展这项工作，以直接确定1）Adrb3和miR-133a在脂肪组织中的表达模式， 其他外周组织随时间的变化及其与COMT依赖性功能性疼痛的关系，2） 外周Adrb3和miR-133a介导COMT依赖性炎症和神经炎症，3） 外周Adrb3和miR-133a在介导COMT依赖性的细胞凋亡活性增加中的作用 机械敏感和温度敏感的伤害感受器，以及4）这些分子和行为表型是如何 受到压力的影响。这些研究的结果将促进我们对机制的了解， 外周Adrb3驱动慢性疼痛并阐明外周限制性疼痛发展的新靶点 用于治疗功能性疼痛综合征的具有改善的特异性和副作用特征的疗法。

ABSTRACT Functional pain syndromes affect over 100 million people, yet remain ineffectively treated because the causes are largely unknown. Accumulating evidence suggests that these syndromes are due, in large part, to low activity of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines. An estimated 66% of patients with functional pain syndromes, such as fibromyalgia, possess variants in the COMT gene that lead to low activity of the COMT enzyme. Individuals with the ‘low COMT activity’ genotype report greater pain at baseline and enhanced pain following stressful events that potentiate catecholamine release from sympathetic nerves. Consistent with clinical syndromes, our lab has shown that pharmacologic inhibition of COMT in rodents produces pain at multiple body sites and enhances pain following repeated stress. In subsequent studies, we demonstrated that COMT-dependent pain is initiated by peripheral adrenergic receptor beta-3 (Adrb3) through the release of pro-inflammatory cytokines in local tissues. The pain is maintained by subsequent increases in pro-inflammatory cytokines in spinal tissues and activation of mitogen activated protein kinases (MAPKs) in the cell bodies and central terminals of pain-sensing nociceptors. Together, these data show that heightened catecholamine tone leads to chronic pain via peripheral Adrb3 and its downstream effectors. However, the cell types that express Adrb3 and mediate pain still need to be identified and the molecular mechanisms determined. We hypothesize that activation of Adrb3 on adipocytes (fat cells that surround peripheral nociceptor and sympathetic nerve terminals) drives chronic COMT-dependent pain via increases in cytokines and MAPKs that promote inflammation and nociceptor activation. Further, we hypothesize that stress-induced catecholamine release amplifies the effects of Adrb3 signaling on inflammation and pain. Preliminary data reveal that COMT-dependent increases in pro-inflammatory cytokines are mediated by Adrb3 located on adipocytes. Additional data reveal that sustained activation of Adrb3 leads to decreased levels of miR-133a, a microRNA expressed in adipocytes that is able to block MAPK signaling. The proposed studies will extend this work to directly determine 1) Adrb3 and miR-133a expression patterns in adipose vs other peripheral tissues over time and their relationship to COMT-dependent functional pain, 2) the role of peripheral Adrb3 and miR-133a in mediating COMT-dependent inflammation and neuroinflammation, 3) the role of peripheral Adrb3 and miR-133a in mediating COMT-dependent increases in the activity of mechosensitive and thermosensitive nociceptors, and 4) how these molecular and behavioral phenotypes are influenced by stress. Results from these studies will advance our knowledge about the mechanisms whereby peripheral Adrb3 drives chronic pain and elucidate new targets for the development of peripherally-restricted therapies with improved specificity and side-effect profiles for the treatment of functional pain syndromes.