Laboratory for Alzheimer's Disease and Aging Research, Kansas City Veterans Affairs Medical Center, Kansas City, Missouri 64128, USA.
J Biol Chem. 2010 Dec 31;285(53):41541-8. doi: 10.1074/jbc.M110.170894. Epub 2010 Nov 1.
Membrane G protein-coupled receptor kinase 5 (GRK5) deficiency is linked to Alzheimer disease, yet its precise roles in the disease pathogenesis remain to be delineated. We have previously demonstrated that GRK5 deficiency selectively impairs desensitization of presynaptic M2 autoreceptors, which causes presynaptic M2 hyperactivity and inhibits acetylcholine release. Here we report that inactivation of one copy of Grk5 gene in transgenic mice overexpressing β-amyloid precursor protein (APP) carrying Swedish mutations (Tg2576 or APPsw) resulted in significantly increased β-amyloid (Aβ) accumulation, including increased Aβ(+) plaque burdens and soluble Aβ in brain lysates and interstitial fluid (ISF). In addition, secreted β-APP fragment (sAPPβ) also increased, whereas full-length APP level did not change, suggesting an alteration in favor of β-amyloidogenic APP processing in these animals. Reversely, perfusion of methoctramine, a selective M2 antagonist, fully corrected the difference between the control and GRK5-deficient APPsw mice for ISF Aβ. In contrast, a cholinesterase inhibitor, eserine, although significantly decreasing the ISF Aβ in both control and GRK5-deficient APPsw mice, failed to correct the difference between them. However, combining eserine with methoctramine additively reduced the ISF Aβ further in both animals. Altogether, these findings indicate that GRK5 deficiency accelerates β-amyloidogenic APP processing and Aβ accumulation in APPsw mice via impaired cholinergic activity and that presynaptic M2 hyperactivity is the specific target for eliminating the pathologic impact of GRK5 deficiency. Moreover, a combination of an M2 antagonist and a cholinesterase inhibitor may reach the maximal disease-modifying effect for both amyloid pathology and cholinergic dysfunction.
膜 G 蛋白偶联受体激酶 5（GRK5）缺乏与阿尔茨海默病有关，但它在疾病发病机制中的确切作用仍需阐明。我们之前已经证明，GRK5 缺乏选择性地损害了突触前 M2 自身受体的脱敏作用，导致突触前 M2 过度活跃并抑制乙酰胆碱释放。在这里，我们报告在过表达携带瑞典突变的β-淀粉样前体蛋白（APP）的转基因小鼠中，一个 Grk5 基因的失活导致β-淀粉样蛋白（Aβ）积累显著增加，包括脑裂解物和间质液（ISF）中 Aβ（+）斑块负担和可溶性 Aβ增加。此外，分泌的β-淀粉样前体蛋白片段（sAPPβ）也增加，而全长 APP 水平没有变化，表明这些动物中有利于β-淀粉样蛋白生成的 APP 加工的改变。相反，M2 拮抗剂甲硫胺完全纠正了对照组和 GRK5 缺陷型 APPsw 小鼠之间 ISF Aβ 的差异。相比之下，乙酰胆碱酯酶抑制剂毒扁豆碱虽然显著降低了对照组和 GRK5 缺陷型 APPsw 小鼠的 ISF Aβ，但未能纠正它们之间的差异。然而，毒扁豆碱与甲硫胺联合使用可进一步增加两种动物的 ISF Aβ。总之，这些发现表明，GRK5 缺乏通过受损的胆碱能活性加速 APPsw 小鼠中的β-淀粉样蛋白生成 APP 加工和 Aβ 积累，并且突触前 M2 过度活跃是消除 GRK5 缺乏的病理影响的特定靶标。此外，M2 拮抗剂和乙酰胆碱酯酶抑制剂的联合使用可能会对淀粉样蛋白病理和胆碱能功能障碍产生最大的疾病修饰作用。
