mTOR, A new target for opioid-induced togerance and hyperalgesia

描述（由申请人提供）：了解阿片类药物诱导的镇痛耐受和痛觉过敏的机制对于开发新的治疗策略以实现更有效的疼痛管理非常重要。慢性阿片类药物暴露后背角神经元可塑性的变化被认为是诱导和维持阿片类药物诱导的耐受和痛觉过敏的基础。哺乳动物雷帕霉素靶蛋白（mTOR）是一种丝氨酸-苏氨酸蛋白激酶，通过磷酸化特定的下游效应子（如4 E-BP 1和S6 K1）来控制蛋白质翻译。我们的初步工作表明，在慢性吗啡暴露期间，mu受体/PI 3 K/Akt介导的背角mTOR激活通过mTOR触发的蛋白质翻译起始参与神经元可塑性的形成。这些新发现表明，背角mTOR激活是吗啡诱导的耐受和痛觉过敏的发展和维持所必需的。该提案将确定在慢性吗啡暴露下背角神经元中mTOR及其下游效应物是否以及如何被激活，以及这种激活是否以及如何有助于吗啡诱导的镇痛耐受和痛觉过敏的发展和维持。在具体目标1中，我们将检查（a）在重复吗啡注射后，mTOR、S6 K1、4 E-BP 1、PI 3 K和Akt是否通过背角中的mu受体激活而被激活;（B）在慢性吗啡暴露期间，PI 3 K和Akt是否介导背角神经元中的mu受体触发的mTOR、S6 K1和4 E-BP 1的激活;和（c）在重复注射吗啡后，在μ受体表达和伤害感受背角神经元中是否激活PI 3 K/Akt/mTOR通路。在具体目标2中，我们将确定脊髓μ受体依赖性PI 3 K/Akt/mTOR通路的激活是否通过mTOR触发的背角蛋白合成而有助于吗啡耐受和痛觉过敏的机制。我们将研究（a）慢性吗啡暴露后背角神经元中翻译起始活性、新生蛋白质合成和一些已知的耐受相关关键蛋白的时间依赖性增加，以及（B）这些增加是否可以通过抑制脊髓μ受体触发的PI 3 K/Akt/mTOR通路激活来阻断。在具体目标3中，我们将确定脊髓mTOR及其引发的翻译起始是否是吗啡诱导的耐受和痛觉过敏的发展和维持所必需的。将检查脊髓mTOR的药理学抑制、脊髓mTOR和S6 K1的遗传敲低或背角4 E-BP 1的过表达对吗啡诱导的耐受性和痛觉过敏的发展和维持的影响。这些研究将为我们理解吗啡诱导的镇痛耐受和痛觉过敏的分子机制提供重要的概念性进展。因为mTOR抑制剂是FDA批准的药物，所以我们的研究也可能在治疗和/或预防阿片类药物诱导的镇痛耐受和/或神经毒性中具有很强的潜在临床应用。 痛觉过敏

DESCRIPTION (provided by applicant): Understanding the mechanisms that underlie opioid-induced analgesic tolerance and hyperalgesia is important for developing novel therapeutic strategies to achieve more effective pain management. The changes in dorsal horn neuronal plasticity that occur after chronic opioid exposure are believed to underlie the induction and maintenance of opioid-induced tolerance and hyperalgesia. Mammalian target of rapamycin (mTOR), a serine-threonine protein kinase, controls protein translation via phosphorylation of specific downstream effectors, such as 4E-BP1 and S6K1. Our preliminary work indicates that mu receptor/PI3K/Akt- mediated activation of dorsal horn mTOR participates in the formation of neuronal plasticity through mTOR- triggered initiation of protein translation during chronic morphine exposure. These novel discoveries suggest that dorsal horn mTOR activation is required for the development and maintenance of morphine-induced tolerance and hyperalgesia. This proposal will determine whether and how mTOR and its downstream effectors are activated in dorsal horn neurons under chronic morphine exposure and whether and how this activation contributes to the development and maintenance of morphine-induced analgesic tolerance and hyperalgesia. In Specific Aim 1, we will examine (a) whether mTOR, S6K1, 4E-BP1, PI3K, and Akt are activated through mu receptor activation in dorsal horn following repeated morphine injections; (b) whether PI3K and Akt mediate mu receptor-triggered activation of mTOR, S6K1, and 4E-BP1 in dorsal horn neurons during chronic morphine exposure; and (c) whether the PI3K/Akt/mTOR pathway is activated in mu receptor-expressing and nociceptive dorsal horn neurons following repeated morphine injection. In Specific Aim 2, we will define whether spinal mu receptor-dependent activation of the PI3K/Akt/mTOR pathway contributes to mechanism of morphine tolerance and hyperalgesia through mTOR-triggered dorsal horn protein synthesis. We will examine (a) time-dependent increases in translation initiation activity, nascent protein synthesis, and some known tolerance-associated key proteins in dorsal horn neurons following chronic morphine exposure and (b) whether these increases could be blocked by inhibition of spinal mu receptor-triggered activation of the PI3K/Akt/mTOR pathway. In Specific Aim 3, we will determine whether spinal mTOR and the translation initiation that it triggers are required for the development and maintenance of morphine-induced tolerance and hyperalgesia. The effects of pharmacologic inhibition of spinal mTOR, genetic knockdown of spinal mTOR and S6K1, or over- expression of dorsal horn 4E-BP1 on the development and maintenance of morphine-induced tolerance and hyperalgesia will be examined. The proposed studies will provide major conceptual advances to our understanding of the molecular mechanism of morphine-induced analgesic tolerance and hyperalgesia. Because mTOR inhibitors are FDA-approved drugs, our studies may also have a strong potential clinical application in treating and/or preventing opioid-induced analgesic tolerance and hyperalgesia.