低糖后处理对缺血性脑损伤的保护作用及机制

Endogenous strategies for neuroprotection provide novel therapeutic strategies for ischemic stroke, which mobilize a variety of self-protection mechanisms against lethal cerebral ischemia by giving a sub-threshold insult including preconditioning and postconditioning. However, an effective and feasible therapeutic approach has not been formulated yet. Our previous study found that hypoxic preconditioning and ischemic postconditioning have neuroprotective effects. Based on these results, we proposed to substitute hypoxia or glucose deprivation (GD) for ischemia in postconditioning, since hypoxia and GD are key factors in ischemia. In theory, if hypoxia or GD postconditioning alone is neuroprotective, it may be safer and more feasible than ischemic postconditioning in clinical application. Surprisingly, hypoxic postconditioning aggravated ischemia/reperfusion injury. In contrast, GD postconditioning had stronger neuroprotection and wider time window than ischemic postconditioning. In addition, we also demonstrated the protective effect of low-glucose postconditioning in vivo. These results imply that low-glucose postconditioning is a novel therapeutic strategie which has practical value in clinic. Therefore, it is necessary to investigate the concrete role and mechanisms of low-glucose postconditioning. In this study, we will further confirm the neuroprotection of low-glucose postconditioning against cerebral ischemia in vivo and in vitro. And using pharmacological approaches, RNA interference and cell electrophysiological techniques, its neuroprotective mechanisms will be clarified by investigating whether low-glucose postconditioning can regulate glutamate transport and metabolism through reducing reactive oxygen species and activating PI3K/AKT/mTOR pathway. The achievement of this project will provide a new therapeutic strategy for ischemic stroke.

内源性保护策略通过给予一个亚损伤刺激调动多种自身保护机制来减轻严重缺血所造成的损伤，为脑缺血治疗提供了新途径，但至今尚未形成有效可行的治疗方案。课题组在前期研究发现低氧预处理和缺血后处理具有神经保护作用的基础上，试图验证更具有实际意义的低氧后处理的保护作用，但意外发现低氧后处理反而加重了损伤，而缺血另一重要因素缺糖后处理的保护作用比缺血后处理更强，且有效时间窗更宽，预实验还发现在整体动物上利用胰岛素进行低糖后处理也有明显保护作用，强烈提示低糖后处理是一种有实际应用价值的治疗新策略，但其具体作用及机制尚不清楚。因此，本课题首先拟在整体、脑片和细胞水平明确低糖后处理对脑缺血的保护作用；并利用药理学方法、RNA干扰、细胞电生理等手段，通过研究减少氧自由基产生、调控PI3K/AKT/mTOR信号通路对谷氨酸转运代谢的调节作用等机制来阐明低糖后处理的保护机制。本项目的完成将为脑缺血提供新的治疗策略。

内源性保护策略通过给予一个亚损伤刺激调动多种自身保护机制来减轻严重缺血所造成的损伤，为脑缺血治疗提供了新途径，但至今尚未形成有效可行的治疗方案。短暂性低糖是缺血后处理的重要因素之一，我们推测，在脑缺血再灌后给予短暂的低糖处理，可能减轻脑损伤，其作为一种非手术形式的后处理策略对于脑缺血的治疗更具有临床意义。因此，本研究着重探索了两个科学问题：（1）明确了低糖后处理对脑缺血再灌注损伤的保护作用及特点。（2）阐明了谷氨酸代谢通路及线粒体自噬是否参与了后处理诱导的神经保护机制。通过本课题的实施，课题组首次发现了低糖后处理可抑制脑缺血/复灌诱发的神经损伤，并且其保护作具有“时间窗”效应和作用时程及浓度依赖性。同时，我们意外的发现，作为缺血另一重要组成因素的组织酸化可能也是缺血后处理发挥神经保护作用的重要机制之一。利用药理学方法、基因敲除小鼠及RNA干扰技术等手段，课题组进一步对其保护机制进行了探索。结果发现，调节谷氨酸代谢通路及Parkin依赖的线粒体自噬是低糖后处理和酸后处理在脑缺血后的复灌过程中发挥了神经保护作用的重要机制。这些研究结果为脑缺血治疗提供了新的治疗策略和潜在的治疗靶点。