Roles of Aβ42 secreted in the lumen of the endoplasmic reticulum played in the disease course of Alzheimer'disease

众所周知，作为阿尔茨海默病(AD)病理损害的主要成分，AP/APP和tau之间的相互作用对AD的发病机制有重要影响。我们假设APP的胞浆结构域和胞浆蛋白tau相互作用，在Thr668处调节APP的磷酸化，并在几个潜在的磷酸化位点调控tau。在本研究中，我们聚焦于APP的蛋白降解产物C99，并检测C99是否调节tau的磷酸化。在转导C99和tau的COS7细胞中，与未转导C99的tau相比，共转染C99的COS7细胞中tau在Thr181和Thr231处的磷酸化水平降低。用磷酸酶抑制剂进行的去磷酸化抑制试验表明，PP1参与了tau的去磷酸化。Tau和C99的阴性免疫沉淀表明Tau和C99不直接相互结合，提供了第三种试剂…的可能性More可介导tau和C99的相互作用。第三种试剂必须同时与tau和app结合，结合tau的磷酸化Thr231和APP的Thr668的Pin 1可能是这样的候选者。我们检测了与tau和C99共转染的Pin^&lt；-/-&gt；MEF。在Pin1；+/+&gt；MEF和Pin1^&lt；-/-&gt；MEF中，在有或没有Pin1表达的情况下，tau的Thr181和Thr231处的磷酸化水平没有变化。在与tau和C99共转染的MEF中，Pin1的表达增加了tau的去磷酸化，而Pin1的缺失不仅取消了tau的去磷酸化，而且还增加了tau的磷酸化。因此，tau在Pin1和C99同时存在的情况下被去磷酸化，而tau在C99存在和没有Pin1的情况下被磷酸化。这些结果表明，C99和Pin1与tau的磷酸化有关，这种机制可能是AD疾病过程的基础，因为Pin1的表达在缠结形成过程中降低。较少

It is known that the interaction between AP/APP and tau, the main components of the pathologic lesions of Alzheimer's disease (AD), has significant influence on the pathogenesis of the disease. We have hypothesized that the cytosol domain of APP and the cytosol protein tau interact each other, modulating the phosphorylation of APP at Thr668 and tau at several potential phosphorylation sites. In the present study we focused on C99, the proteolytic product of APP, and examined whether C99 modulates the phosphorylation of tau.In COS7 cells transfected with C99 and tau, the phosphorylations at Thr181 and Thr231 of tau were reduced when co-transfected with C99 compared to that given by transfection of tau without C99. The dephosphorylation-inhibition test with phosphatase inhibitors showed that PP1 is implicated in the dephosphorylation of tau. Negative immunoprecipitation of tau and C99 indicates that tau and C99 do not directly bind each other, providing a possibility that the third agent … More could mediate the interaction of tau and C99. The third agent must bind both tau and APP, and Pin 1 that binds phosphorylated Thr231 of tau and Thr668 of APP could be such a candidate. We examined Pin^<-/->MEF co-transfected with tau and C99. In Pin1^<+/+>MEF and Pin1^<-/->MEF transfected with tau only, the phosphorylation level at Thr181 and Thr231 of tau remained unchanged between the presence and absence of Pin1 expression. In MEF co-transfected with tau and C99, the presence of Pin1 expression increases dephosphorylation of tau, whereas the absence of Pin1 expression not only abrogates dephosphorylation of tau but also increases phosphorylation of tau. Thus tau is dephosphorylated in the concomitant presence of Pin1 and C99, while tau is phosphorylated in the presence of C99 and in the absence of Pin1. These results indicate that C99 and Pin1 are associated with phosphorylation of tau, and such mechanism might underlie the disease course of AD since Pin1 expression is diminished in association of tangle formation. Less