Dawkins Edgar, Gasperini Robert, Hu Yanling, Cui Hao, Vincent Adele J, Bolós Marta, Young Kaylene M, Foa Lisa, Small David H
Menzies Research Institute Tasmania, University of Tasmania, Hobart, Tasmania, Australia.
J Neurosci Res. 2014 Nov;92(11):1478-89. doi: 10.1002/jnr.23422. Epub 2014 Jun 11.
The function of the β-amyloid precursor protein (APP) of Alzheimer's disease is poorly understood. The secreted ectodomain fragment of APP (sAPPα) can be readily cleaved to produce a small N-terminal fragment (N-APP) that contains heparin-binding and metal-binding domains and that has been found to have biological activity. In the present study, we examined whether N-APP can bind to lipids. We found that N-APP binds selectively to phosphoinositides (PIPs) but poorly to most other lipids. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2 )-rich microdomains were identified on the extracellular surface of neurons and glia in primary hippocampal cultures. N-APP bound to neurons and colocalized with PIPs on the cell surface. Furthermore, the binding of N-APP to neurons increased the level of cell-surface PI(4,5)P2 and phosphatidylinositol 3,4,5-trisphosphate. However, PIPs were not the principal cell-surface binding site for N-APP, because N-APP binding to neurons was not inhibited by a short-acyl-chain PIP analogue, and N-APP did not bind to glial cells which also possessed PI(4,5)P2 on the cell surface. The data are explained by a model in which N-APP binds to two distinct components on neurons, one of which is an unidentified receptor and the second of which is a PIP lipid, which binds more weakly to a distinct site within N-APP. Our data provide further support for the idea that N-APP may be an important mediator of APP's biological activity.
阿尔茨海默病β-淀粉样前体蛋白（APP）的功能目前仍知之甚少。APP分泌的胞外域片段（sAPPα）可被轻易切割，产生一个小的N端片段（N-APP），该片段含有肝素结合域和金属结合域，且已发现具有生物活性。在本研究中，我们检测了N-APP是否能与脂质结合。我们发现N-APP选择性地与磷酸肌醇（PIPs）结合，但与大多数其他脂质的结合较弱。在原代海马培养物中，神经元和神经胶质细胞的细胞外表面鉴定出富含磷脂酰肌醇4,5-二磷酸（PI(4,5)P2）的微结构域。N-APP与神经元结合，并在细胞表面与PIPs共定位。此外，N-APP与神经元的结合增加了细胞表面PI(4,5)P2和磷脂酰肌醇3,4,5-三磷酸的水平。然而，PIPs并非N-APP的主要细胞表面结合位点，因为N-APP与神经元的结合不受短酰基链PIP类似物的抑制，且N-APP不与细胞表面也含有PI(4,5)P2的神经胶质细胞结合。这些数据可用一个模型来解释，即N-APP与神经元上的两个不同成分结合，其中一个是未鉴定的受体，另一个是PIP脂质，它与N-APP内的一个不同位点结合较弱。我们的数据为N-APP可能是APP生物活性的重要介质这一观点提供了进一步支持。
