鼻腔胰岛素对术后认知功能障碍的作用及tau蛋白相关作用机制研究

Postoperative cognitive dysfunction (POCD) is popular after general anesthesia in elder people, which is believed to be one of the risk factors for Alzheimer’s disease (AD).It is well documented that POCD can accelerate and aggravate further AD. Studies in the last decade have demonstrated that insulin signaling plays an important role in neural plasticity, learning and memory. Deficient brain insulin signaling is observed in AD brain. These observations suggest that impaired brain insulin signaling may be one of the etiological factors for POCD and sporadic AD. In consistent with this, intranasal administration of insulin, which bypasses the blood-brain barrier and delivers insulin directly into the brain, improves general behavioral performance and cognition in normal and diabetic mice. Intranasal insulin also improves memory in healthy humans and in individuals with mild cognitive impairment(MCI) and AD.Our early studies suggest that anesthesia may increase the risk for POCD and AD through promoting abnormal hyperphosphorylation of tau, which is crucial to neurodegeneration in AD. However, how insulin treatment improves cognitive function is poorly understood. There is no research on intranasal insulin treatment in POCD. So we treated 3xTg-AD mice, which are a commonly used transgenic mouse model of AD and develop both amyloid pathology and tau pathology in the brain as well as cognitive deficits, with propofol, a commonly used intravenous anesthetic in clinical practice, and found that propofol strongly promoted hyperphosphorylation of tau at several AD-related phosphorylation sites. We further demonstrated that daily intranasal administration of insulin attenuated propofol-induced hyperphosphorylation of tau. Biochemical analyses indicated that intranasal insulin promoted brain insulin signaling and led to up-regulation of protein phosphatase 2A, a major tau phosphatase in the brain. Intranasal insulin also resulted in down-regulation of several tau kinases. These findings provide the first evidence supporting that intranasal insulin administration might be a potential treatment for the prevention of anesthesia-induced cognitive decline and increased risk for AD and dementia. In this project we introduce tau phosphorylation mechanism in intranasal insulin treatment in POCD. We mainly studied the effect of intranasal insulin on tau phosphorylation in POCD in wild type and 3xTg-AD mouse; the protect effect of intranasal insulin to recognition function after anesthesia. We observed if intranasal insulin can improve recognize and memory function after anesthesia, if intranasal insulin can reduce and abate further AD. The above study was designed about intranasal insulin treatment mechanism related to tau phosphorylation in POCD, and provide a new theoretic proof and technical means for clinical intranasal treatment.

术后认知功能障碍(POCD)是广泛发生于老年患者麻醉后的一系列认知功能损害。临床观察到鼻腔内胰岛素能提高MCI，AD甚至是无认知功能损害患者的认知功能。目前还没有研究涉及鼻腔内胰岛素是否对POCD有防治作用。我们之前的国家自然基金项目已经证实麻醉后脑组织中tau蛋白异常高磷酸化(AD的特征性病理改变之一)是POCD发生的重要机制。我们的预试验首次证实对AD模型小鼠行鼻腔内胰岛素给药能有效抑制麻醉后脑组织tau蛋白的异常高磷酸化。因此我们假设，鼻腔内胰岛素对POCD有防治作用，此作用可能是通过抑制麻醉后tau蛋白的异常高磷酸化来实现的。本课题拟把tau蛋白磷酸化机制引入到鼻腔胰岛素对POCD作用研究中来，通过观察鼻腔内胰岛素不同给药时程对小鼠麻醉后tau蛋白磷酸化的影响，对麻醉后小鼠中期及远期认知功能的影响，探讨鼻腔内胰岛素对POCD的作用及作用机制，为POCD的临床防治提供新的策略。

临床前和临床实验表明，老年人在全身麻醉后认知功能下降的风险增加。全身麻醉也被认为是阿尔茨海默氏病（AD）的危险因素。在动物研究和小型临床试验中，胰岛素的鼻内给药是将药物直接递送至大脑，可改善记忆力和认知能力。然而，胰岛素治疗如何改善认知功能知之甚少。在这里，我们将胰岛素治疗分为两组，然后对两组老年小鼠（17〜18个月）进行每日鼻内胰岛素治疗（1.75U /天），分别给药11天和26天。异丙酚（160mg /天）腹腔内注射诱导全身麻醉，每天麻醉2小时，持续5天（第7至11日）。第26天后进行旷场实验、新事物识别实验和恐惧条件反射实验，我们发现鼻内胰岛素可以预防麻醉引起的认知障碍。并增加了突触后密度蛋白95（PSD95）的水平，以及上调海马齿状回中的微管相关蛋白2（MAP-2）的水平。此外，我们还发现胰岛素治疗通过PI3K / PDK1 / AKT途径恢复了胰岛素信号传导，然后通过增加GSK3β-Ser9磷酸化的水平来减弱麻醉诱导的多个AD相关位点的tau过度磷酸化。总之，我们的数据表明，鼻内注射胰岛素可能是老年患者麻醉引起的认知功能下降的有应用前景的治疗方法。