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

外周和中枢痛觉神经元沿疼痛传递途径的敏化对慢性疼痛的发生至关重要。伤害性背根神经节（DRG）神经元（伤害感受器）在转录和翻译水平上的可塑性事件有助于持续的外周致敏。我们的长期目标集中在炎症介质诱导的神经可塑性在延长伤害感受器敏化和增强中的作用。前列腺素E2 （PGE2）是一种众所周知的炎症介质，在损伤组织中丰富，不仅使痛觉感受器增敏，而且在功能水平上增强了其他疼痛介质如瞬时电位受体香草素-1 （TRPV1）的增敏作用。TRPV1是多种有害刺激的整合者，参与炎症性和神经性慢性疼痛。然而，目前尚不清楚PGE2是否通过刺激TRPV1在DRG神经元中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感受器致敏和增强。我们的实验数据表明PGE2参与炎症和神经损伤后DRG神经元中TRPV1的上调。此外，PGE2暴露不仅延长了TRPV1激动剂辣椒素随后刺激引起的疼痛，而且增加了DRG神经元中TRPV1的水平。这些数据让我们假设促进DRG神经元中TRPV1的合成是PGE2延长伤害感受器敏化和增强的新机制。在本研究项目中，我们将利用多学科方法在体外和体内模型中实现三个特定的短期目标。***具体目的1：通过分子、神经化学和形态学方法，在体外和体内模型中，研究PGE2是否在基因和蛋白水平上诱导DRG神经元中TRPV1的合成，以及PGE2是否有助于延长致敏性疼痛、炎症性疼痛和神经性疼痛动物模型中TRPV1的上调。***特异性目的2：利用选择性Cdk5抑制剂和siRNA技术，我们将确定细胞周期蛋白依赖性激酶5 （cyclin dependent kinase 5, Cdk5）信号是否介导pge2诱导的TRPV1在体外和体内DRG神经元的合成。***具体目的3：我们将通过电生理、药理学和行为学方法，确定pge2诱导的TRPV1合成是否与培养DRG神经元中TRPV1活性增强相关联，pge2诱导的TRPV1上调是否有助于野生型大鼠延长致敏性疼痛，以及pge2基因敲除大鼠是否消除pge2延长的致敏性疼痛。***意义：预期结果将促进我们对慢性疼痛发展的新机制的理解，即促进DRG神经元中TRPV1的合成有助于PGE2增强TRPV1活性和延长伤害感受器的敏化。

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.