Inflammatory hyperalgesia due to TRPV1, the pepper spray receptor in the cornea

描述（由申请人提供）：我们的工作目标是阐明细胞表面受体调节离子通道的功能、运输和表达的细胞和分子机制。我们对疼痛传导中离子通道的受体调节特别感兴趣，因为炎症期间对疼痛刺激的敏化（炎症性痛觉过敏）深刻地影响着我们的身心健康，以及我们的经济和社会福祉。我们选择Ca2+可渗透通道TRPV1作为我们的模型，因为它的特性使它特别合适，也因为它在传导疼痛刺激和调节疼痛传导神经元的兴奋性方面的重要性。在美国，慢性疼痛是一个重大的公共卫生和经济问题。一项针对美国工人的全国性调查——2003年美国生产力审计的分析显示，在给定的两周内，13%的劳动力由于无法控制的疼痛而失去了工作时间，平均每周损失4.6小时。2003年国家卫生统计中心报告发现，26%的成年人报告有持续24小时以上的疼痛问题。2006年对慢性疼痛患者的一项研究发现，超过一半的人感到他们几乎无法控制自己的疼痛。头痛、背痛、关节炎痛、牙痛、癌症痛和术后疼痛只是导致整个美国人口生活质量下降和经济损失的几种常见疾病。目前的治疗显然不足以满足广泛的止痛需求，并且存在与特异性和成瘾性相关的进一步问题。神经生长因子（NGF）是由Rita Levi-Montalcini和Stanley Cohen在20世纪50年代末发现的。从一开始，他们就了解了它调节感觉神经元分化和生长的能力。NGF参与感觉神经元的引导和存活，并在损伤和炎症期间释放到表达trpv1的神经元上。在过去的几年中，我们对NGF如何使炎症性痛觉过敏的TRPV1增敏的理解激增。在之前的研究中，我们发现NGF通过增加质膜上TRPV1通道的数量来增加TRPV1电流。我们进一步发现，在伤害感受器中存在一个信号转导复合物，该复合物由NGF受体（TrkA）、TRPV1和PI3K酶组成，可将磷酸肌肽4,5-二磷酸（PIP2）磷酸化为磷酸肌肽3,4,5-三磷酸（PIP3）。我们和其他人进一步表明，PI3K活性是致敏所必需的。对于本建议的其余部分，使用术语TRPV1的“敏化”来指代质膜中TRPV1通道数量的增加。虽然细胞表面受体刺激的膜脂和膜蛋白运输在生物学上具有广泛的意义，但其发生的分子机制尚不清楚。其中一个研究得最好的例子是，葡萄糖转运蛋白Glut4转运到脂肪细胞和肌肉细胞的质膜，以响应胰岛素，揭示了许多重要的参与者，我们基于这些参与者建立了ngf诱导TRPV1转运到疼痛受体神经元的质膜的模型。然而，即使在脂肪细胞和肌肉中，这一过程的许多关键步骤也没有得到充分的了解。鉴定TRPV1致敏过程中的主要参与者及其相互作用可能有助于阐明细胞分化、代谢和生存所必需的信号通路，并有助于了解TRPV1对炎症性疼痛的重要调节。

DESCRIPTION (provided by applicant): The goal of our work is to elucidate the cellular and molecular mechanisms by which cell-surface receptors regulate the function, trafficking, and expression of ion channels. We are particularly interested in receptor regulation of ion channels in pain transduction, as sensitization to painful stimuli during inflammation (inflammatory hyperalgesia) profoundly influences our physical and mental health, as well as our economic and social well-being. We have chosen the Ca2+-permeable channel TRPV1 as our model both because its properties make it especially suitable and because of its importance in transducing painful stimuli and in tuning the excitability of pain-transducing neurons. Chronic pain is a significant public health and economic problem in the US. An analysis of the 2003 American Productivity Audit, a national survey of US workers, showed that, in a given two-week period, 13% of the workforce lost work time due to uncontrolled pain, with a mean loss of 4.6 hours per week. The 2003 National Center for Health Statistics Report found that 26% of adults report having a problem with pain lasting more than 24 hours. A 2006 study of chronic pain patients found that more than half felt they had little or no control over their pain. Headache, back pain, arthritis pain, tooth pain, cancer pain, and post-operative pain are just a few of the common conditions contributing to decreased quality of life and economic loss across the whole spectrum of the US population. Current treatments are clearly not sufficient to address the wide-spread need for pain relief, and have further problems related to specificity and addiction. Nerve Growth Factor (NGF) was discovered by Rita Levi-Montalcini and Stanley Cohen in the late 1950's. From the first, they understood its power to regulate the differentiation and growth of sensory neurons. NGF is involved in the guidance and survival of sensory neurons and is released onto TRPV1-expressing neurons during injury and inflammation. Our understanding of how NGF sensitizes TRPV1 in inflammatory hyperalgesia exploded in the last several years. In the previous funding period we showed that NGF increases TRPV1 currents by increasing the number of the TRPV1 channels in the plasma membrane. We further showed that a signal-transduction complex is present in nociceptors, composed of the NGF receptor (TrkA), TRPV1, and the enzyme PI3K, which phosphorylates phosphoinositide 4,5-bisphosphate (PIP2) to phosphoinositide 3,4,5-trisphosphate (PIP3). We and others further showed that PI3K activity is required for sensitization. For the remainder of this proposal use the term "sensitization" of TRPV1 to refer to the increase in the number of TRPV1 channels in the plasma membrane. Although cell surface receptor-stimulated trafficking of membrane lipids and membrane proteins is of broad significance to biology, the molecular mechanisms by which it occurs are poorly understood. One of the best-studied examples, trafficking of the Glut4 glucose transporter to the plasma membrane of adipocytes and muscle cells in response to insulin, has revealed a number of important players on which we based our model for NGF-induced trafficking of TRPV1 to the plasma membrane of pain-receptor neurons. Even in adipocytes and muscles, however, many critical steps in this process are not fully understood. Identification of the main players and their interactions in sensitization of TRPV1 may shed light on a signaling pathway essential to cell differentiation, metabolism, and survival in addition to leading to an understanding of TRPV1 regulation important for inflammatory pain.