Parkinson Phenotype in Aged PINK1-Deficient Mice Is Accompanied by Progressive Mitochondrial Dysfunction in Absence of Neurodegeneration

Parkinson's disease (PD) is an adult-onset movement disorder of largely unknown etiology. We have previously shown that loss-of-function mutations of the mitochondrial protein kinase PINK1 (PTEN induced putative kinase 1) cause the recessive PARK6 variant of PD. Now we generated a PINK1 deficient mouse and observed several novel phenotypes: A progressive reduction of weight and of locomotor activity selectively for spontaneous movements occurred at old age. As in PD, abnormal dopamine levels in the aged nigrostriatal projection accompanied the reduced movements. Possibly in line with the PARK6 syndrome but in contrast to sporadic PD, a reduced lifespan, dysfunction of brainstem and sympathetic nerves, visible aggregates of alpha-synuclein within Lewy bodies or nigrostriatal neurodegeneration were not present in aged PINK1-deficient mice. However, we demonstrate PINK1 mutant mice to exhibit a progressive reduction in mitochondrial preprotein import correlating with defects of core mitochondrial functions like ATP-generation and respiration. In contrast to the strong effect of PINK1 on mitochondrial dynamics in Drosophila melanogaster and in spite of reduced expression of fission factor Mtp18, we show reduced fission and increased aggregation of mitochondria only under stress in PINK1-deficient mouse neurons. Thus, aging Pink1-/- mice show increasing mitochondrial dysfunction resulting in impaired neural activity similar to PD, in absence of overt neuronal death. Transcriptome microarray data of Pink1-/- mouse brains in absence of a stressor, even at old age, show remarkably sparse dysregulations. See Gispert-S et al 2009 PLOS ONE. Factorial design comparing Pink1 knock-out mice with wild type littermates in three different tissues (striatum, midbrain, cerebellum at four different timepoints (6, 12, 14 weeks, and 18 month)帕金森病（Parkinson's disease, PD）是一类病因尚未完全阐明的成人起病性运动障碍疾病。本团队既往研究证实，线粒体蛋白激酶PINK1（PTEN诱导的假定激酶1，PTEN induced putative kinase 1）的功能丧失性突变可引发隐性遗传的PARK6型帕金森病。本研究构建了PINK1基因缺陷型小鼠，并观察到多项全新表型：老年小鼠出现进行性体重下降，且自发性运动相关的运动活性出现选择性减退；与帕金森病患者的表现一致，老年黑质纹状体投射通路的多巴胺水平异常与运动能力减退相伴出现。值得注意的是，尽管该表型与PARK6综合征的特征相符，但与散发性帕金森病不同，老年PINK1缺陷小鼠未出现寿命缩短、脑干及交感神经功能障碍、路易小体内α-突触核蛋白可见聚集，亦未发生黑质纹状体通路神经退行性变。不过，本研究证实PINK1突变小鼠存在线粒体前体蛋白导入能力的进行性降低，该现象与ATP生成、呼吸作用等核心线粒体功能缺陷密切相关。与果蝇（Drosophila melanogaster）中PINK1对线粒体动态的强烈调控作用不同，尽管裂变因子Mtp18的表达水平下调，本研究仅在应激状态下的PINK1缺陷小鼠神经元中观察到线粒体裂变减少及聚集增加。因此，衰老的Pink1-/-小鼠会出现进行性线粒体功能障碍，进而引发类似帕金森病的神经活性受损，但并未出现明显的神经元死亡。在无应激条件下（即使处于老年阶段），Pink1-/-小鼠大脑的转录组微阵列数据显示异常调控的基因数量极少。相关研究详情参见Gispert-S等于2009年发表于《PLOS ONE》的论文。本研究采用析因实验设计，将Pink1基因敲除小鼠与其野生型同窝仔鼠在三种不同组织（纹状体、中脑、小脑）以及四个不同时间点（6、12、14周龄及18月龄）下开展对比分析。