Department of Demyelinating Disease and Aging, National Institute of Neuroscience, NCNP, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187-8502, Japan.
Curr Alzheimer Res. 2013 Feb;10(2):135-42. doi: 10.2174/1567205011310020003.
Inhibition of the β-secretase, BACE1, which cleaves amyloid precursor protein (APP) to produce β-amyloid protein (Aβ), is thought to be a feasible therapeutic strategy for Alzheimer's disease. Reticulon (RTN) proteins such as RTN3 have been identified as membrane proteins that interact with BACE1 and inhibit its Aβ-generating activity. In this study, we investigated whether RTN3 can regulate Aβ production in vivo, using transgenic (Tg) mice expressing APP with Swedish and London mutations (APP Tg mice) and those expressing RTN3; the latter mice showed ~1.4-fold higher expression levels of RTN3 protein in the cerebral cortex than non-Tg controls. We analyzed the brains of single APP Tg and double APP/RTN3 Tg mice at the age of approximately 15 months. The levels of secreted APP-β, a direct BACE1 cleavage product of APP, in Tris-soluble fraction were considerably reduced in the hippocampus and cerebral cortex of APP/RTN3 Tg mice relative to those in APP Tg mice. Immunohistochemical analyses demonstrated that Aβ burden and plaques were significantly (by approximately 50%) decreased in both the hippocampus and cerebral cortex of double Tg mice compared to APP Tg mice. Furthermore, the levels of guanidine-soluble Aβ40 and Aβ42 in these brain regions of APP/RTN3 Tg mice were relatively lower than those in APP Tg mice. These findings indicate that even a small increase in RTN3 expression exerts suppressive effects on amyloidogenic processing of APP and Aβ accumulation through modulation of BACE1 activity in vivo, and suggest that induction of RTN3 might be an effective therapeutic strategy against Alzheimer's disease.
β-分泌酶（BACE1）可切割淀粉样前体蛋白（APP）生成β-淀粉样蛋白（Aβ），抑制 BACE1 被认为是治疗阿尔茨海默病的可行策略。现已鉴定出 RTN 蛋白（如 RTN3）是与 BACE1 相互作用并抑制其 Aβ生成活性的膜蛋白。在本研究中，我们通过转 APP 基因（Tg）小鼠（携带瑞典和伦敦突变的 APP Tg 小鼠）和转 RTN3 基因（Tg）小鼠（后者大脑皮质中 RTN3 蛋白表达水平约高 1.4 倍）来研究 RTN3 能否在体内调节 Aβ的生成。我们分析了约 15 月龄的 APP 单 Tg 鼠和 APP/RTN3 双 Tg 鼠的大脑。APP/RTN3 Tg 鼠海马和大脑皮质中的 APP-β（APP 被 BACE1 直接切割的产物）可溶部分的分泌水平明显低于 APP Tg 鼠。免疫组化分析显示，与 APP Tg 鼠相比，双 Tg 鼠的海马和大脑皮质中 Aβ负荷和斑块减少了约 50%。此外，APP/RTN3 Tg 鼠这些脑区的胍溶性 Aβ40 和 Aβ42 水平也相对较低。这些发现表明，即使 RTN3 表达略有增加，也能通过调节体内 BACE1 活性，对 APP 的淀粉样生成和 Aβ的积累产生抑制作用，并提示诱导 RTN3 可能是治疗阿尔茨海默病的有效策略。
