Defining the role of peripheral Adrb3 in chronic pain and inflammation

摘要 功能性疼痛综合征影响着1亿多人，但仍然没有得到有效的治疗，因为 在很大程度上是未知的。越来越多的证据表明，这些症状在很大程度上是由于低血压 儿茶酚氧甲基转移酶(COMT)的活性，这是一种代谢儿茶酚胺的酶。据估计 66%的功能性疼痛综合征患者，如纤维肌痛，在COMT基因中存在变异， 导致COMT酶活性低。COMT活性低的个体报告更大的疼痛 应激事件加强儿茶酚胺释放后的基线和增强的疼痛 交感神经。与临床症状一致，我们的实验室已经表明，药物抑制 啮齿类动物的COMT会在多个身体部位产生疼痛，并在反复应激后加剧疼痛。在……里面 随后的研究表明，COMT依赖的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而发挥作用。疼痛是由 随后脊髓组织中促炎症细胞因子的增加和丝裂原激活 痛觉痛觉感受器胞体和中央终末的蛋白激酶(MAPK)。加在一起，这些 数据显示，儿茶酚胺水平升高通过外周ADRB3及其下游导致慢性疼痛 效应器。然而，表达ADRB3和介导疼痛的细胞类型仍然需要确定，并且 分子机制已确定。我们假设ADRB3在脂肪细胞(脂肪细胞， 围绕外周伤害性感受器和交感神经末梢)通过 促进炎症和伤害性感受器激活的细胞因子和MAPK增加。此外，我们 假设应激诱导的儿茶酚胺释放放大ADRB3信号对炎症的影响 和痛苦。初步数据显示，COMT依赖的促炎细胞因子的增加是由 定位于脂肪细胞上的ADRB3。更多数据显示，ADRB3的持续激活会导致 MiR-133a的水平，这是一种在脂肪细胞中表达的能够阻断MAPK信号的微型RNA。建议数 研究将扩展这项工作，以直接确定1)ADRB3和miR-133a在脂肪和 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在介导COMT依赖的炎症和神经性炎症中的作用 外周血ADRB3和miR-133a在COMT依赖的心肌细胞活性增加中的作用 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 受压力的影响。这些研究的结果将促进我们对其机制的了解 外周ADRB3驱动慢性疼痛并阐明外周受限发展的新靶点 治疗功能性疼痛综合征的特异度和副作用改善的疗法。

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.