Studies on the tau lysosomal proteolytic pathway

Tau是阿尔茨海默病（AD）脑中成对螺旋丝（PHF）的主要成分。tau蛋白免疫反应，PHF样原纤维的存在下，在肌肉中的包涵体肌炎（IBM）的影响，和无定形tau蛋白沉积物最近发现氯喹肌病（CM），一个实验模型IBM.We调查CM获得洞察PHF形成AD脑。在CM中，tau mRNA水平在早期瞬时上调，而tau本身在晚期缓慢积累。tau mRNA水平及其积累的时间分布与β-淀粉样蛋白前体（APP）及其羧基末端片段非常相似，已知两者均在溶酶体中降解。免疫细胞化学显示tau蛋白在有缘空泡中进行性积累，酸性磷酸酶活性增加，免疫电镜显示tau蛋白位于空泡内。这些结果表明tau蛋白被降解 ...更多信息 为了证实溶酶体中的tau降解途径，我们分析了来自在鸡β-肌动蛋白启动子的转录控制下过表达最短形式的人tau的转基因大鼠的肝脏的自噬溶酶体。我们发现，tau蛋白存在于亮抑酶肽处理的肝脏的自噬溶酶体中，而在亮抑酶肽未处理的肝脏中未检测到。这些结果表明，tau在肝脏的溶酶体中也被降解。在肌肉和肝脏中的观察结果促使我们在大鼠脑溶酶体中寻找tau的受体。通过SDS聚丙烯酰胺凝胶电泳分离大鼠脑溶酶体膜，转移到硝酸纤维素膜上，并与tau孵育。我们发现分子量为130，100和76 kDa的蛋白质特异性结合tau蛋白。另一方面，我们确定MP5 O（谷氨酸脱氢酶）在溶酶体部分作为一个可能的tau结合蛋白，通过使用tau亲和层析。少

Tau is the major component of paired helical filaments (PHF) in Alzheimer's disease (AD) brain. The presence of tau-immunoreactive, PHF-like fibrils was reported in the muscle affected by inclusion body myositis (IBM), and amorphous tau deposits were recently found in chloroquine myopathy (CM), an experimental model for IBM.We investigated CM to obtain insight into PHF formation in AD brain. In CM tau mRNA level was transiently upregulated in the early phase, while tau itself slowly accumulated in the late phase. The temporal profiles of tau mRNA levels and its accumulation were very similar to those of beta-amyloid protein precursor (APP) and its carboxyl-terminal fragments, both of which have been known to be degraded in lysosomes. Immunocytochemistry showed that tau progressively accumulated in the rimmed vacuoles with increased acid phosphatase activities, and immunoelectron microscopy demonstrated that tau was located within the vacuoles. These results suggest that tau is degraded … More in lysosomes or their functional equivalents in the muscle.To confirm the tau degradation pathway in lysosome we analyzed the autophagolysosomes from liver of the transgenic rat overexpressing the shortest form of human tau under transcriptional control of the chicken beta-actin promoter. We found that tau was present in autophagolysosomes from leupeptin-treated liver, whereas it was not detected in those from leupeptin-untreated liver. These results suggest that tau is also degraded in lysosomes in liver. The observations in both muscle and liver prompted us to search for a receptor for tau in rat brain lysosomes. Rat brain lysosomal membranes were separated by SDS polyacrylamide gel electrophoresis, transferred to nitrocellulose membrane, and incubated with tau. We found that the proteins with the molecular weight of 130, 100, and 76 kDa specifically bound tau. On the other hand, we identified MP5O (glutamate dehydrogenase) in the lysosomal fraction as a possible tau-binding protein by use of tau affinity chromatography. Less