Role of PGE2-induced up-regulation of TRPV1 channel in prolonged nociceptor sensitization and potentiation

外周和中枢伤害性神经元对疼痛传递通路的敏化在慢性疼痛的发生中起着至关重要的作用。伤害性背根神经节(DRG)神经元(伤害性感受器)在转录和翻译水平的可塑性事件有助于持续的外周敏化。我们的长期目标集中在炎性介质诱导的神经可塑性在延长伤害性感受器敏化和增强中的作用。前列腺素E_2(PGE_2)是一种广泛存在于损伤组织中的炎性介质，它不仅能敏化伤害性感受器，还能在功能水平上增强其他痛觉介质如瞬时电位受体香草素-1(TRPV1)的敏化作用。TRPV1是多种伤害性刺激的整合因子，参与炎症性和神经病理性慢性疼痛。然而，目前尚不清楚PGE2是否通过刺激DRG神经元的转录和翻译来增强TRPV1的活性，以及PGE2诱导的TRPV1合成是否有助于持续的伤害性感受器敏化和增强。我们的初步数据表明，PGE2参与了炎症和神经损伤后DRG神经元中TRPV1的上调。此外，PGE2暴露不仅延长了TRPV1激动剂辣椒素引起的疼痛，而且还增加了DRG神经元中TRPV1的水平。这些数据使我们假设，促进DRG神经元合成TRPV1是PGE2延长伤害性感受器敏化和增强的新机制。在这项研究计划中，我们将在体外和体内模型中使用多学科方法针对三个特定的短期目标。*特定目标1：使用分子、神经化学和形态方法，我们将确定在体外和体内模型中，PGE2是否在基因和蛋白质水平上诱导DRG神经元中TRPV1的合成，以及PGE2是否有助于延长敏感性疼痛、炎症性疼痛和神经病理性疼痛动物模型中TRPV1的上调。*特定目的2：利用选择性CDK5抑制剂和siRNA技术，我们将在体外和体内确定细胞周期蛋白依赖性激酶5(CDK5)信号是否介导PGE2诱导的DRG神经元合成TRPV1。*具体目标3：利用电生理学、药理学和行为学方法，我们将确定PGE2诱导的TRPV1合成是否与培养的DRG神经元中TRPV1的活性增强有关，PGE2诱导的TRPV1上调是否有助于野生型大鼠延长敏化痛，以及TRPV1基因敲除大鼠是否取消PGE2延长的敏化痛。*意义：预期的结果将促进我们对慢性疼痛发生的新机制的理解，即促进DRG神经元中TRPV1的合成有助于PGE2增强的TRPV1活性和延长的伤害性感受器敏化。

Sensitization of peripheral and central nociceptive neurons along pain transmission pathway is essential to the genesis of chronic pain. Plastic events at transcriptional and translational levels in nociceptive dorsal root ganglion (DRG) neurons (nociceptors) contribute to persistent peripheral sensitization. Our long term goal focuses on role of neuroplasticity induced by inflammatory mediators in prolonged nociceptor sensitization and potentiation. Prostaglandin E2 (PGE2), a well-known inflammatory mediator enriched in injured tissue, not only sensitizes nociceptors, but also potentiates the sensitizing effects of other pain mediators such as transient potential receptor vanilloid-1 (TRPV1) at functional level. TRPV1 is an integrator of diverse noxious stimuli and involved in chronic pain of inflammatory and neuropathic origins. However, it remains unknown whether PGE2 potentiates TRPV1 activity by stimulating its transcription and translation in DRG neurons and whether PGE2-induced TRPV1 synthesis contributes to persistent nociceptor sensitization and potentiation. Our pilot data suggest that PGE2 is involved in TRPV1 up-regulation in DRG neurons after inflammation and nerve injury. Moreover, PGE2 exposure not only prolongs pain evoked by subsequent challenge of TRPV1 agonist capsaicin, but also increases TRPV1 levels in DRG neurons. These data let us hypothesize that facilitating TRPV1 synthesis in DRG neurons is a novel mechanism underlying PGE2 prolonged nociceptor sensitization and potentiation. In this research program, we will target three specific short term goals using multidisciplinary approaches in both in vitro and in vivo models.*** Specific aim 1: Using molecular, neurochemical and morphological approaches, we will determine whether PGE2 induces TRPV1 synthesis at the gene and protein levels in DRG neurons in both in vitro and in vivo models and whether PGE2 contributes to TRPV1 up-regulation in animal models of prolonged sensitization pain, inflammatory pain and neuropathic pain. *** Specific aim 2: Using selective Cdk5 inhibitor and siRNA technique, we will determine whether cyclin dependent kinase 5 (Cdk5) signaling mediates PGE2-induced TRPV1 synthesis in in vitro and in vivo DRG neurons. *** Specific aim 3: Using electrophysiological, pharmacological and behavioral approaches, we will determine whether PGE2-induced TRPV1 synthesis is coupled to enhanced TRPV1 activity in cultured DRG neurons, whether PGE2-induced TRPV1 up-regulation contributes to prolonged sensitization pain in wild type rats and whether PGE2-prolonged sensitization pain is abolished in TRPV1 knockout rats.*** Significance: The anticipated outcome will advance our understanding of a novel mechanism governing development of chronic pain, i. e, facilitating TRPV1 synthesis in DRG neurons contributes to PGE2 potentiated TRPV1 activity and prolonged nociceptor sensitization.