Ghrelin对黑质多巴胺能神经元A型钾通道的调控机制研究及其在帕金森病中的应用

The excitability of dopaminergic neurons in the substantia nigra pars compacta (SNc) plays an important role in the function of nigrostriatal system and Parkinson’s disease (PD) motor symptoms. Our previous studies showed that the brain-gut peptide ghrelin could enhance pacemaker firing of nigral dopaminergic neurons by inhibiting voltage-gated potassium Kv7/KCNQ/M-channels, which have been published in Nat Commun (2013). However, the native KCNQ current recorded in nigral dopaminergic neurons is less than 40 pA, and the A-type potassium channels (IA) has been demonstrated to play a key role in pacemaker control. In addition, we also observed that ghrelin could significantly inhibit IA. To explore the underlying mechanisms as well as the role of IA inhibition by ghrelin during the process of PD, we utilize the IA knockout mice and PKCδ knockout mice to detect the changes of IA and dopaminergic neuronal excitability. We hypothesize that ghrelin enhances dopaminergic neuronal pacemaker firing by inhibiting IA through ghrelin receptor (GHSR)-PLC-PKCδ pathway. We also detect the changes of IA and dopaminergic neuronal excitability in the different stages of PD transgenic mice expressing the prion promoter driven human A53T mutation (A53T mice). Meanwhile, the changes of striatal dopamine release and motor activity are also observed. Since ghrelin is a novel neuroprotective agent in PD, it is also applied to the A53T mice in the very early stage. Our study could demonstrate that ghrelin inhibits IA to enhance the excitability of nigral dopaminergic neurons, thus plays an important role in the prevention and treatment of PD. This will provide new evidence for the usage of ghrelin to treat PD.

黑质多巴胺（DA）能神经元电活动在帕金森病（PD）的运动调控中起到重要作用。我们研究发现脑肠肽ghrelin通过抑制KCNQ通道增强黑质DA能神经元的起搏放电（Nat Commun，2013）。但黑质KCNQ电流过小，虽参与DA能神经元的起搏放电，但A型钾通道（IA）被认为是更关键因素。并且ghrelin对IA也有明显的抑制作用，但其机制尚不清楚。为了阐明ghrelin对IA的调控机制及其在PD中的应用，本项目将利用IA敲除小鼠和PKCδ敲除小鼠证实ghrelin通过激活受体GHSR-PLC-PKCδ通路，抑制IA，进而增强DA能神经元兴奋性。在PD转基因小鼠上，观察DA能神经元IA和黑质纹状体系统电活动的变化，早期给予ghrelin，是否可通过影响IA，从而改善PD的运动行为。本研究将阐明ghrelin通过调控IA，影响黑质纹状体系统的电生理，从而为其在PD中的应用提供新的实验依据。

Ghrelin是一种含28个氨基酸残基的生物活性肽，是生长激素促分泌素受体（GHS-R）唯一的内源性配体，在摄食、能量代谢平衡、生长激素释放、学习记忆以及神经保护等多方面发挥重要调节作用。前期研究工作证实ghrelin可以通过抑制Kv7/KCNQ/M通道提高黑质多巴胺能神经元的兴奋性，提示电压依赖钾通道可能是ghrelin调控神经元电活动的重要作用靶点。但是黑质Kv7/KCNQ/M通道电流较小，只有大约30pA左右，其可能并不是ghrelin调节多巴胺能神经元兴奋性的唯一影响因素。A型钾通道是在黑质多巴胺能神经元上广泛存在的一种电压依赖型钾通道，被认为是影响多巴胺能神经元自发放电的关键因素。本项目在黑质脑片上，进一步证实了生理条件下A型钾通道是ghrelin调控多巴胺能神经元电活动的重要的作用靶点，ghrelin通过激活GHS-R1a-PLC-PKCδ信号通路抑制A型钾通道，提高神经元的兴奋性。致PD经典神经毒素MPP+可以抑制多巴胺能神经元的自发及诱发放电，而ghrelin可明显改善MPP+的上述抑制作用。鉴于离子通道的开放或关闭将直接影响神经元的电活动，进而改变神经递质的释放，我们也初步观察了A型钾通道阻断剂4-AP对PD的多巴胺能神经元损伤中的保护作用。本研究主要阐明了ghrelin在生理及病理条件下对黑质纹状体系统的电生理活动的影响，为其在PD中的应用提供新的实验依据。