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。慢性阿片暴露后发生的背角神经元可塑性的变化被认为是阿片诱导的耐受性和痛觉过敏的诱导和维持的基础。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物（如4E-BP1和S6K1）来控制蛋白质翻译。我们的初步研究表明，在慢性吗啡暴露过程中，mu受体/PI3K/Akt介导的背角mTOR激活通过mTOR触发的蛋白翻译启动参与神经元可塑性的形成。这些新发现表明，背角mTOR的激活是吗啡诱导的耐受性和痛觉过敏的发展和维持所必需的。本研究将确定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促进吗啡诱导的镇痛耐受和痛觉过敏的发展和维持。在Specific Aim 1中，我们将检验(a)反复注射吗啡后，mTOR、S6K1、4E-BP1、PI3K和Akt是否通过背角mu受体激活而被激活；(b)慢性吗啡暴露时，PI3K和Akt是否介导mu受体触发的背角神经元mTOR、S6K1和4E-BP1的激活；(c)反复注射吗啡后，表达mu受体和痛觉性背角神经元中PI3K/Akt/mTOR通路是否被激活。在Specific Aim 2中，我们将确定脊髓mu受体依赖的PI3K/Akt/mTOR通路的激活是否通过mTOR触发的背角蛋白合成参与吗啡耐受和痛觉过敏的机制。我们将研究(a)长期吗啡暴露后，背角神经元中翻译起始活性、新生蛋白合成和一些已知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mu受体触发的PI3K/Akt/mTOR通路的激活来阻断。在Specific Aim 3中，我们将确定脊髓mTOR及其触发的翻译起始是否需要吗啡诱导的耐受性和痛觉过敏的发展和维持。我们将研究脊髓mTOR的药理抑制、脊髓mTOR和S6K1的基因敲低或背角4E-BP1的过度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。提出的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进展。由于mTOR抑制剂是fda批准的药物，我们的研究也可能在治疗和/或预防阿片类药物引起的镇痛耐受性和慢性疼痛方面具有强大的潜在临床应用

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.