Dewachter I, Van Dorpe J, Smeijers L, Gilis M, Kuipéri C, Laenen I, Caluwaerts N, Moechars D, Checler F, Vanderstichele H, Van Leuven F
Experimental Genetics Group, Center for Human Genetics, Flemish Institute for Biotechnology, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.
J Neurosci. 2000 Sep 1;20(17):6452-8. doi: 10.1523/JNEUROSCI.20-17-06452.2000.
Aging of transgenic mice that overexpress the London mutant of amyloid precursor protein (APP/V717I) (Moechars et al., 1999a) was now demonstrated not to affect the normalized levels of alpha- or beta-cleaved secreted APP nor of the beta-C-terminal stubs. This indicated that aging did not markedly disturb either alpha- or beta-secretase cleavage of APP and failed to explain the origin of the massive amounts of amyloid peptides Abeta40 and Abeta42, soluble and precipitated as amyloid plaques in the brain of old APP/V717I transgenic mice. We tested the hypothesis that aging acted on presenilin1 (PS1) to affect gamma-secretase-mediated production of amyloid peptides by comparing aged APP/V717I transgenic mice to double transgenic mice coexpressing human PS1 and APP/V717I. In double transgenic mice with mutant (A246E) but not wild-type human PS1, brain amyloid peptide levels increased and resulted in amyloid plaques when the mice were only 6-9 months old, much earlier than in APP/V717I transgenic mice (12-15 months old). Mutant PS1 increased mainly brain Abeta42 levels, whereas in aged APP/V717I transgenic mice, both Abeta42 and Abeta40 increased. This resulted in a dramatic difference in the Abeta42/Abeta40 ratio of precipitated or plaque-associated amyloid peptides, i.e., 3.11+/-0.22 in double APP/V717I x PS1/A246E transgenic mice compared with 0.43 +/- 0.07 in aged APP/V717I transgenic mice, and demonstrated a clear difference between the effect of aging and the effect of the insertion of a mutant PS1 transgene. In conclusion, we demonstrate that aging did not favor amyloidogenic over nonamyloidogenic processing of APP, nor did it exert a mutant PS1-like effect on gamma-secretase. Therefore, the data are interpreted to suggest that parenchymal and vascular accumulation of amyloid in aging brain resulted from failure to clear the amyloid peptides rather than from increased production.
现已证明，过表达淀粉样前体蛋白伦敦突变体（APP/V717I）的转基因小鼠（Moechars等人，1999a）的衰老不会影响α-或β-切割的分泌型APP以及β- C末端残基的标准化水平。这表明衰老并未显著干扰APP的α-或β-分泌酶切割，也无法解释在老年APP/V717I转基因小鼠大脑中大量淀粉样肽Aβ40和Aβ42以淀粉样斑块形式溶解和沉淀的来源。我们通过将老年APP/V717I转基因小鼠与共表达人早老素1（PS1）和APP/V717I的双转基因小鼠进行比较，来检验衰老作用于早老素1（PS1）以影响γ-分泌酶介导的淀粉样肽产生这一假设。在携带突变型（A246E）而非野生型人PS1的双转基因小鼠中，当小鼠仅6至9个月大时，脑淀粉样肽水平就会升高并形成淀粉样斑块，这比APP/V717I转基因小鼠（12至15个月大）要早得多。突变型PS1主要增加脑Aβ42水平，而在老年APP/V717I转基因小鼠中，Aβ42和Aβ40均增加。这导致沉淀的或与斑块相关的淀粉样肽的Aβ42/Aβ40比值出现显著差异，即在双APP/V717I×PS1/A246E转基因小鼠中为3.11±0.22，而在老年APP/V717I转基因小鼠中为0.43±0.07，这表明衰老的影响与插入突变型PS1转基因的影响之间存在明显差异。总之，我们证明衰老并不倾向于APP的淀粉样生成而非非淀粉样生成加工，也不会对γ-分泌酶产生类似突变型PS1的作用。因此，这些数据被解释为表明衰老大脑中淀粉样物质在实质和血管中的积累是由于未能清除淀粉样肽而非产量增加所致。
