Stephenson D T, Clemens J A
Eli Lilly and Company, CNS Division, Lilly Corporate Center, Indianapolis, IN 46285, USA.
Neurochem Int. 1998 Jul;33(1):83-93. doi: 10.1016/s0197-0186(05)80012-9.
Stimulation of metabotropic glutamate receptors in vitro has been shown to accelerate the breakdown of amyloid precursor protein (APP) to form increased production of non-amyloidogenic secreted APP (sAPP). The mechanism whereby this occurs is not entirely clear but it is presumed to be linked to generation of diacylglycerol and activation of protein kinase C because other neurotransmitter receptors such as m1 and m3 muscarinic receptors, known to be coupled to this second messenger cascade, likewise increase sAPP production. Although it is presumed that a reciprocal relationship exists between the formation of amyloid beta protein (Abeta) and the production of sAPP, recent evidence suggests alternative processing can occur. Given the fact that much of the observations on APP metabolism have been made in vitro we sought to investigate the effect of metabotropic receptor activation on Abeta in vivo in a species known to contain the same amino acid sequence of Abeta as found in humans. Intrahippocampal injection of the mGluR agonist 1S,3R-ACPD in guinea pigs produced neurodegeneration of CA1 hippocampal pyramidal neurons at 12 h postinjection. Immunocytochemistry of sections from ACPD injected animals using selective antibodies to Abeta revealed the presence of punctate intraneuronal granules in pyramidal neurons of the hippocampus. These structures appeared to be localized within the nucleus and were particularly prominent in neurons within the region of neurodegeneration. Immunoreactivity was not observed in vehicle injected controls nor in sections from ACPD injected animals stained with preadsorbed antiserum. Abeta immunodetection was correlated with the onset of neurodegeneration since animals evaluated at 1 h and 4 h postinjection lacked both Abeta immunoreactivity as well as neurodegeneration. Evaluation of animals injected with NMDA revealed neurodegeneration but no Abeta immunoreactivity suggesting Abeta formation did not appear to be due to non-selective excitotoxicity. Staining of sections with antibodies directed to various regions of APP demonstrated increased C-terminal APP immunoreactivity in pyramidal neurons in the vicinity of degeneration. These data support recent in vitro studies illustrating that Abeta can be found intracellularly within neurons.
体外实验表明，代谢型谷氨酸受体的激活可加速淀粉样前体蛋白（APP）的分解，从而增加非淀粉样生成性分泌型APP（sAPP）的产生。这一过程发生的机制尚不完全清楚，但据推测与二酰基甘油的生成和蛋白激酶C的激活有关，因为其他已知与该第二信使级联反应偶联的神经递质受体，如M1和M3毒蕈碱受体，同样会增加sAPP的产生。虽然推测淀粉样β蛋白（Aβ）的形成与sAPP的产生之间存在相互关系，但最近的证据表明可能存在其他加工途径。鉴于许多关于APP代谢的观察是在体外进行的，我们试图在一种已知其Aβ氨基酸序列与人类相同的物种中，研究代谢型受体激活对体内Aβ的影响。豚鼠海马内注射mGluR激动剂1S,3R-ACPD后12小时，CA1海马锥体神经元发生神经变性。使用针对Aβ的选择性抗体对注射ACPD动物的切片进行免疫细胞化学分析，结果显示海马锥体神经元中存在点状细胞内颗粒。这些结构似乎定位于细胞核内，在神经变性区域的神经元中尤为突出。在注射溶剂的对照动物中未观察到免疫反应性，在用预吸附抗血清染色的注射ACPD动物的切片中也未观察到免疫反应性。Aβ免疫检测与神经变性的发生相关，因为在注射后1小时和4小时评估的动物既没有Aβ免疫反应性，也没有神经变性。对注射NMDA的动物进行评估，结果显示有神经变性，但没有Aβ免疫反应性，这表明Aβ的形成似乎不是由于非选择性兴奋性毒性。用针对APP不同区域的抗体对切片进行染色，结果显示变性附近的锥体神经元中C端APP免疫反应性增加。这些数据支持了最近的体外研究，表明Aβ可以在神经元细胞内被发现。
