BK通道的SUMO化修饰在缺血性神经元死亡中的作用及其调控机制

Neuroprotective drugs are used in an attempt to reduce ischemic neuronal damage; however, most drugs have failed in clinical trials because of side-effects, causing normal brain function to become compromised. New strategies are designed based on the principle that drugs should interact with their targets only during states of pathological and not physiological activation; one of the strategy is to targeting the modulation mechanism of pathological activated protein. Our previous work shows that over-activity of BK channels mediates hippocampal neuronal death after reoxygenation and reperfusion; however, the underlying mechanisms are largely unknown. SUMOylation has recently been shown to modulate ion-channel function; while whether BK channel is modulated by SUMOylation has not been reported. Using Abgent SUMOplot algorithm and SUMOsp 2.0, we identified that BK channel is a candidate protein regulated by SUMOylation. In the past few years, it was found that SUMOyation level increased after neuronal ischemia in vitro and in vivo. The present project will firstly detect the SUMOylation of BK channel in cell-free system, cultured hippocampal neurons and rat hippocampal tissue. Then, the underlying mechanisms of BK channel modulation by SUMOylation will be studied using methods of molecular biology and electrophysiology. Furthermore, the effects of SUMOylation of BK channel on neuronal death will be investigated under the condition of neuronal ischemia in vitro and in vivo. The result are expected to provide the theoretical and experimental basis for new strategy of neuroprotection.

神经保护剂治疗缺血性脑卒中时，因影响靶蛋白正常生理功能而导致严重副作用是目前临床试验神经保护治疗效果不佳的重要原因；针对靶蛋白的调控机制而特异性阻断靶蛋白病理性激活是新的神经保护研究焦点。我们发现BK通道活动增强介导缺血性海马神经元死亡，然而BK通道在缺血过程中的调控机制还知之甚少。SUMO化修饰调控神经元离子通道的新发现使得这种动态、可逆的翻译后调控机制备受瞩目。新近文献报道脑缺血后SUMO化水平升高，我们用软件预测发现BK通道是SUMO化修饰的候选靶蛋白。SUMO化修饰如何调控BK通道活动及其在缺血性神经元死亡中的作用是本项目研究的核心问题。我们将在cell-free系统、培养细胞及海马组织三个层次确认BK通道被SUMO化修饰；结合分子生物学和电生理学手段阐明SUMO化修饰对BK通道的调控机制；探索干预缺血条件下BK通道的SUMO化修饰对神经元死亡的影响，为神经保护治疗探索新途径。

神经保护剂治疗缺血性脑卒中时，因影响靶蛋白正常生理功能而导致严重副作用是目前临床试验神经保护治疗效果不佳的重要原因；针对靶蛋白的调控机制而特异性阻断靶蛋白病理性激活是新的神经保护研究焦点。BK通道在神经元上具有重要功能，其活动影响神经元兴奋性、动作电位发放频率以及神经递质释放。BK通道的分子结构由alpha亚单位（孔道形成）和beta亚单位（调节通道门控和药理学特性）构成，在神经元，其beta亚单位则主要是beta4亚型。我们已有的工作表明，BK通道活动增强介导了缺血缺氧性神经元死亡，提示干预其病理条件下的活动增强是缺血缺氧性神经元保护的可能策略。SUMO化修饰是一种翻译后修饰，SUMO化/去SUMO化修饰是调节通道活动的重要机制，已经发现在不同病理情况下不同类型的钾通道发生SUMO化/去SUMO化修饰进而参与了发病机制，因此了解BK通道在缺血缺氧条件下是否受到SUMO化调控以及这种调控是否在介导神经元死亡中起作用对发展新的缺血缺氧神经元保护策略非常重要。我们对组成BK通道的alpha亚单位和beta亚单位能否被SUMO化修饰进行了研究，发现BK通道alpha亚单位可被SUMO化修饰，而未检测到beta亚单位发生SUMO化修饰。我们进一步研究了哪种SUMO亚型能够修饰BK通道alpha亚单位，发现在SUMO1、SUMO2、SUMO3三种亚型中，只有SUMO3可将BK通道alpha亚单位SUMO化修饰；我们还进一步筛选了其修饰位点。我们在离体和在体缺血性神经元死亡模型上检测了BK通道的SUMO化水平，发现SUMO化修饰水平增加增强了BK通道活性并进一步介导了神经元死亡。本研究揭示并阐明了BK 通道的新的调控机制——SUMO 化修饰，发现了BK 通道的SUMO 化修饰在缺血性神经元死亡中的作用，为神经保护治疗寻找到新的干预靶点提供了理论和实验依据。