外源性硫化氢--老龄脑缺血预适应保护作用重建的关键

Cerebral ischemia/reperfusion (I/R) injury in the aged brain plays a critical role in the neurodegenerative process along with multiple behavioral alterations which affects the quality of life and health. Ischemic preconditioning (IPC) is the most powerful endogenous mechanism protecting brain from cerebral ischemia. But in aged conditions, this protective mechanism has been shown to be reduced due to triggering of neurodegenerative processes. H2S, as an endogenous neuromodulator, which has been shown to be reduced in the aged brain, has an extensive physiological role in regulating blood pressure, antioxidant, anti-inflammatory. Thus we introduce a hypothesis that H2S might act as an effective agent that may have therapeutic potential against brain damage induced by I/R through remodeling of IPC protection. In this project, we will examine the metabolic characteristics of H2S during IPC and I/R in the aged brain. We will further assess that exogenous NaHS rescue the reduction of IPC protection in the aged brain in against brain I/R injury, improving neurological and behavioral evaluation. The mechanism about NaHS recovery of IPC protection will also be explored. This study could provide a new idea, a new target and a new technology platform for I/R injury in the aged brain, and have a potential for theoretical and clinical application.

脑缺血/再灌注（I/R）损伤是危及老年人健康和生命的重要疾病。缺血预适应（IPC）是迄今发现最强的内源性脑缺血保护方法。然而，由于老龄神经细胞发生退行性变导致老龄神经元对IPC刺激的敏感性减弱或消失。硫化氢（H2S）作为一种在老龄中枢神经含量下降的内源性神经递质，具有调节血压，抗自由基，抗炎等广泛生物学作用。外源性H2S能否重建IPC对老龄中枢神经的保护作用，促进老龄脑I/R损伤后神经重塑和功能重建？本项目将从整体、器官、细胞、及分子水平上系统观察青年和老龄大鼠IPC和I/R过程中的H2S代谢特征；研究外源性NaHS重建IPC对老龄神经元的保护作用及治疗脑I/R损伤的作用，及其在改善脑缺血、神经功能评价、行为学功能检测方面的效应；并探讨NaHS重建老龄中枢神经元IPC保护作用的机制。本课题将为为老龄脑I/R损伤的防治提供一种新思路、新靶点和新的技术平台，具有重要的理论意义和应用前景。

为进一步研究外源性硫化氢（H2S）对老龄脑缺血再灌注（ Ischemia/ Reperfution, I/R）损伤的保护和重塑作用，我们进行了以下研究。.细胞水平研究显示，老龄化神经元对氧糖剥夺（oxygen glucose deprivation, OGD）损伤更敏感，外源性H2S供体硫氢化钠（NaSH）能修复或者部分修复OGD 损伤的神经元轴突数量、树突末端数量、平均长度，神经脊数量和形态，但 NaHS 对老龄化神经元的保护作用弱于普通神经元，这一保护作用有剂量依赖效应并在250uM达峰。.动物水平研究显示，给予NaHS能够改善野生型老龄小鼠学习和记忆能力。认知功能障碍的老龄小鼠脑海马胱硫醚β合酶（cystathionine β synthase, CBS）含量下降，给予NaSH能够改善其认知功能。与青年小鼠相比，CBS+/-老龄小鼠大脑中动脉梗死(middle cerebral artery occlusion, MCAO)再灌注后认知功能损伤较野生型更加严重。.外源性H2S对老龄大脑I/R损伤的保护和重塑作用可能但不仅限于与以下机制有关：抑制神经元生长相关蛋白（growth- associated protein, GAP）43表达下调，抑制氧化应激、炎症反应和核因子（nuclear factor, NF）-kB释放，增加细胞外信号调节激酶（extracellular regulated protein kinases, ERK）1/2磷酸化，而对蛋白激酶（protein kinases, PK）A的表达没有影响。其机制可能作用于蛋白质水平，而不是信使RNA（messenger RNA, mRNA）。Ca2+与NaHS诱导的代谢性谷氨酸受体依赖性长时程抑制（metabotropic glutamate receptor dependent long-term depression, mGluR-LTD）比率增加的相关性较弱。.本研究证实了外源性H2S对老龄脑I/R损伤的保护和重建作用及其可能的机制，为进一步研究奠定一定理论基础。