脂质运载蛋白-2在帕金森病黑质铁聚积中的作用及调控机制研究

Parkinson’s disease (PD) is a common neurodegenerative disorder characterized by progressive degeneration of dopamine (DA) neurons in the substantia nigra (SN). Increasing evidence suggests that nigral iron overload and neuroinflammatory processes, which are mainly mediated by activated microglia and astrocytes, are crucial for the initiation and progression of PD. Lipocalin-2 (LCN2), also known as 24p3 and neutrophil gelatinase-associated lipocalin (NAGL), is a member of the highly heterogeneous secretory protein family of lipocalins and participates in the innate immune response, cellular influx of iron, neuroinflammation and regulation of neurodegeneration. Evidence has shown that LCN2 expression was increased in the SN of patients with PD and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD animal models. Further study showed that the increased LCN2 levels contributed to neurotoxicity and neuroinflammation, resulting in disruption of the nigrostriatal DA neurons and abnormal locomotor behaviors. However, the mechanisms underlying the upregulation of LCN2 in PD and its involvement in nigral iron accumulation and degeneration of DA neurons are not fully understood. Therefore, in this study, using different technological methods, we will elucidate the possible mechanisms underlying the elevated expression of LCN2 in PD animal models and cell models. We hypothesize that inflammation and the feedback regulation of iron might be responsible for the upregulation of LCN2 in PD brain. In addition, we also hypothesize that LCN2 upregulation can directly affect iron accumulation of DA neurons in PD due to its function of iron transport, and LCN2 can also promote activation of glial cells, enhance the secretion of inflammatory factors whereby aggravating iron accumulation of DA neurons. This study will provide powerful evidence on etiology of PD and promising strategies on prevention and therapy of PD.

帕金森病（PD）是中老年人常见的神经退行性疾病，日益增多的证据表明黑质铁聚积及胶质细胞激活介导的炎症反应是PD多巴胺（DA）能神经元损伤的重要原因。脂质运载蛋白-2（LCN2）是一种分泌型糖蛋白，参与机体固有免疫反应，细胞铁离子转运，炎症反应及神经退行性变的调节等。实验证实PD病人及动物模型中黑质LCN2的表达上调，并证实其上调参与DA能神经元的损伤。但其在PD中的上调及其在黑质DA能神经元铁聚积并损伤DA能神经元的作用机制尚不清楚。本项目拟在PD动物和细胞模型及LCN2基因敲除小鼠上，深入研究LCN2在PD中的作用和调控机制，阐明炎症因子、铁的反馈性调节在PD脑内LCN2上调中的作用机制；证实LCN2的上调通过受体介导的铁转运直接影响DA能神经元铁聚积，并通过激活胶质细胞的炎症表型，促进炎症因子的分泌加重DA能神经元铁聚积。本实验将为阐明PD的发生发展机制及防治提供新思路。

帕金森病（PD）黑质铁沉积和胶质细胞激活介导的炎症反应是多巴胺能神经元退变的重要机制。脂质运载蛋白-2（LCN2）是主要由胶质细胞释放的神经炎症和铁代谢的重要调节因子，但其在PD中的上调与炎症反应和铁沉积之间的关系及机制尚不清楚。本项目探索了PD动物和细胞模型中LCN2及其受体24p3R的表达变化和可能机制；阐明了星形胶质细胞中LCN2受铁水平的调控及机制；提出了自噬激活可能是减少LCN2释放和某些神经保护因素发挥作用的重要靶点。研究结果揭示：（1）携带A53T型α-突触核蛋白（α-syn）转基因小鼠模型中血清LCN2水平增加，但其受体24p3R在转基因小鼠模型、MPTP小鼠模型和侧脑室注射脂多糖（LPS）小鼠模型黑质区均表达下降；LPS或α-syn均可作为致炎因素诱导原代培养的星形胶质细胞LCN2表达增加，但LCN2表达与细胞内炎症反应无关，铁调素—铁蛋白比值变化是星形胶质细胞炎症反应中的关键环节；（2）铁负载不影响星形胶质细胞中LPS或α-syn诱导的LCN2表达上调，但去铁胺（DFO）可显著抑制LPS诱导的LCN2表达上调。这种抑制与自噬途径、尤其是分泌型自噬的激活有关，而与蛋白酶体和NF-κB途径无关；（3）自噬激活是脑肠肽apelin、中草药钩藤有效成分柯诺辛等发挥神经保护作用的关键靶点。上述研究结果针对铁沉积和神经炎症两大重要的PD发病机制，探讨了LCN2在多巴胺能神经元退变中的作用及受铁水平调控的机制。从胶质细胞而不是神经元的角度出发，首次提出了减轻铁沉积、抑制神经炎症和激活自噬三者之间的复杂关系和崭新靶点。本研究为进一步阐明PD的发病机制，以及寻找新型药物治疗靶点提供了非常重要而有力的实验依据。