术后疼痛介导的海马神经可塑性改变诱发老年POCD—IGF-2基因失调的作用及机制研究

Postoperative dysfunction (POCD) is a common postoperative complication which severely affects the life quality of the aging people. More and more evidence has shown that postoperative pain contributes to the development of aging POCD. However, the underlying mechanism is still elusive. Our preliminary study confirmed that postoperative pain after laparotomy decreased learning and memory in the aging but not young rats as determined by Morris Water Maze experiments. The decreased spatial learning and memory was concomittant with the dendritic retraction and decreased expression of MAP-2 and PSD-95 in the aging but not young rats. These findings suggest that pain-related hippocampal neuroplasticity mediates the development of aging POCD. More interestingly, we observed that in response to postoperative pain, hippocampal IGF-2 gene and protein expression were upregulated in the young, but not aging rats. Given that hippocampal IGF-2 could promote dendritic spine maturation, neurogenesis and improve cognitive function, the present study hypothesized that upregulation of IGF-2 in response to pain plays a critical role in the fact that young rats do not develop cognitive impairment after surgery. However, in the aging rats, the compensatory mechanism have lost due to epigenetic disability and therefore resulted in the nerve fibers retraction, and subsequently the development of POCD. In order to test the hypothesis, we firstly assess whether neuroplasticity plays a critical role in the development of aging POCD. Furthermore, the present study will examine the role of IGF-2 signaling in the nerve fibers' retraction and cognitive impairment. Finally, the study will explore the role of DNA methylation in the differential expression of IGF-2 in the aging and young rats after laparotomy. The project will provide a noverl mechanism of aging POCD, and may have potential clinical application for the treatment of POCD since IGF-2 is a nutrient which can taken orally.

术后认知功能障碍（POCD）是严重影响老年病人术后生活质量的常见并发症。研究表明术后疼痛可诱发老年POCD，但其作用机制尚不清楚。课题组预实验发现剖腹探查手术后疼痛导致老年、而非年轻大鼠的认知功能下降以及海马神经纤维萎缩；手术后年轻、而非老年大鼠海马胰岛素样生长因子（IGF）-2表达上调。本课题遂假设IGF-2代偿性上调是年轻大鼠抵消术后疼痛导致的海马神经纤维萎缩和认知功能下降的重要机制；老年大鼠缺乏此代偿机制而诱发POCD。为此，本课题拟首先明确神经可塑性改变在术后疼痛诱发老年POCD中的作用；通过观察IGF-2信号通路的表达以及干预海马IGF-2信号对术后疼痛诱发老年POCD的影响，明确IGF-2调控失代偿在老年POCD产生中的作用；最后探讨DNA甲基化在老年和年轻大鼠术后IGF-2差异性表达的调控作用。本课题的实施将为POCD的产生机制提供新理论，为临床上防治POCD提供新思路。

本研究主要探讨手术麻醉对术后情绪，学习记忆以及认知功能的影响。我们前期结果提示，手术疼痛相关的焦虑样情绪和前扣带回区ERK的双向激活相关，于是我们研究了不同麻醉药七氟烷，丙泊酚，戊巴比妥对福尔马林足底注射疼痛的焦虑样情绪的影响，结果发现七氟烷具有改善疼痛引起焦虑样情绪的作用，这种效果可能是和七氟烷抑制前扣带回ERK的激活相关，此项工作发表在Psychopharmacology杂志上。同时我们研究了幼年期多次麻醉之后的认知行为的影响，我们选择了出生后21天的小鼠作为研究对象，发现幼年小鼠多次七氟烷麻醉暴露会导致恐惧记忆的损伤，即“遗忘”，这种遗忘的会持续到成年；进一步和湖南大学覃宏涛教授，采用果蝇这一模式生物，探讨多次七氟醚麻醉对果蝇嗅觉恐惧记忆的影响。发现蘑菇体多巴胺神经元过渡兴奋在七氟醚暴露导致的幼年果蝇的记忆力下降的重要机制，从而为婴幼儿麻醉对神经发育的影响提供了新的理论依据。本课题也从临床上选取髋关节置换老年患者，从表观遗传学角度，检测术后认知功能障碍患者的外周血的甲基化水平，以找到和临床POCD致病的相关“生物标志物”。我们发现白细胞DNA低甲基化是POCD独立的危险因素，这将为临床POCD的防治提供一定的理论依据。此外我们还研究了proBDNF在抑郁症和焦虑症中的作用。我们发现在在炎性疼痛致焦虑模型和慢性束缚性应激致抑郁模型的大鼠海马中proBDNF都显著上调，并且伴随着齿状回区神经元树突形态的萎缩，使用proBDNF抗体中和后可以缓解焦虑和抑郁样情绪，该工作发表在frontiers in Psychiatry杂志上（In press），这一工作将为抑郁症和焦虑症等精神疾病的发病机制和治疗提供一定的线索。本项目也改进传统高尔基银染神经元的方法，这扩大了高尔基染色的应用，使得该方法更方便便捷，目前已获得国家专利（专利号：ZL 2017 1 0568588.4）。在本课题资助下，已有4篇SCI论文发表（最高IF：5.67），还有3篇在撰写中，获得中华医学会麻醉学分会中青年优秀论文竞赛一等奖1次，三等奖3次。

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