Hung A Y, Koo E H, Haass C, Selkoe D J
Department of Neurology, Harvard Medical School, Boston, MA.
Proc Natl Acad Sci U S A. 1992 Oct 15;89(20):9439-43. doi: 10.1073/pnas.89.20.9439.
Despite increasing evidence for a pathogenetic role for the beta-amyloid precursor protein (beta APP) in Alzheimer disease, the physiological function of the protein remains unclear. The expression of the neural-specific isoform containing 695 amino acids, beta APP695, is consistent with a role for the protein in neuronal development. In this study, we analyzed the expression of beta APP during the retinoic acid-induced neuronal differentiation of P19 murine embryonal carcinoma cells. Northern blot and RNase protection analyses show a selective increase in beta APP695 expression, concomitant with the morphologic differentiation of P19-derived neurons. Moreover, the time course of increase observed for the beta APP695 mRNA is paralleled by other neuronal-specific transcripts. A similar increase in beta APP695 is observed at the protein level. Furthermore, we show that levels of beta APP695 protein progressively increase during the in vitro differentiation of primary hippocampal neurons. The finding that beta APP695 increases selectively and progressively during neuronal differentiation in two different cell culture systems suggests that this isoform has an important cellular function during this process in the brain. Unlike beta APP in most peripheral cell types, the increased levels of beta APP found in terminally differentiated neuronal cells are not processed in significant amounts by secretory cleavage. Thus, differentiation of neurons is accompanied by increased beta APP695 expression and membrane retention of the protein as intact, full-length molecules that could serve as potential substrates for amyloidogenesis.
尽管越来越多的证据表明β-淀粉样前体蛋白（βAPP）在阿尔茨海默病中具有致病作用，但该蛋白的生理功能仍不清楚。含695个氨基酸的神经特异性同工型βAPP695的表达，与该蛋白在神经元发育中的作用一致。在本研究中，我们分析了维甲酸诱导P19小鼠胚胎癌细胞神经元分化过程中βAPP的表达。Northern印迹和核糖核酸酶保护分析表明，βAPP695表达选择性增加，同时伴随着P19衍生神经元的形态学分化。此外，βAPP695 mRNA观察到的增加时间进程与其他神经元特异性转录本平行。在蛋白质水平也观察到βAPP695有类似的增加。此外，我们表明，在原代海马神经元的体外分化过程中，βAPP695蛋白水平逐渐增加。在两种不同细胞培养系统中，βAPP695在神经元分化过程中选择性且逐渐增加，这一发现表明该同工型在大脑这一过程中具有重要的细胞功能。与大多数外周细胞类型中的βAPP不同，终末分化神经元细胞中发现的βAPP水平增加，并未通过分泌性切割大量加工。因此，神经元分化伴随着βAPP695表达增加以及该蛋白以完整全长分子形式保留在膜上，这些分子可能作为淀粉样蛋白生成的潜在底物。
