INVOLVEMENT OF PROSTAGLANDIN E_2 IN PRODUCTION OF AMYLOID-b PEPTIDES BOTH IN VITRO AND IN VIVO

淀粉样多肽(A-β-β.)是由β淀粉样前体蛋白(APP)在β-和γ-分泌酶的作用下产生的，在阿尔茨海默病(AD)的发病机制中起着重要作用。炎症也被认为是阿尔茨海默病发病过程中不可或缺的因素。我们发现，前列腺素E_2(PGE_2)是一种强烈的炎症诱导剂，它能刺激培养的人胚胎肾(HEK293)或人神经母细胞瘤(SH-SY5Y)细胞产生A-β，这两种细胞都表达一种突变型APP。我们用亚型特异性激动剂证明，在PGE_2受体的四种主要亚型(EP_4受体)中，EP_4受体单独或EP_2和EP_4受体共同作用于PGE_2刺激HEK293或SH-SY5Y细胞产生Aβ。EP_4受体拮抗剂可抑制前列腺素E_2刺激的HEK293细胞产生A-β。这种刺激伴随着细胞内cAMP水平的升高，并且cAMP的类似物刺激Aβ的产生，表明细胞内cAMP水平的增加是PGE_2刺激Aβ产生的原因。免疫印迹实验和γ分泌酶活性的直接测定表明，PGE_2刺激A-β的产生是通过激活γ-分泌酶而不是β-分泌酶来实现的。当表达突变型APP的转基因小鼠与缺乏EP_2或EP_4受体的小鼠杂交时，它们的脑中Aβ水平较低，提示PGE_2介导的EP_2和EP_4受体的激活参与了体内Aβ的产生和AD的发病。

Amyloid-β peptides (Aβ., generated by proteolysis of the βamyloid precursor protein (APP) by β- and γ-secretases, play an important role in the pathogenesis of Alzheimer's disease (AD). Inflammation is also believed to be integral to the pathogenesis of AD. Here we show that prostaglandin E_2 (PGE_2), a strong inducer of inflammation, stimulates the production of Aβ in cultured human embryonic kidney (HEK) 293 or human neuroblastoma (SH-SY5Y) cells, both of which express a mutant type of APP. We have demonstrated using subtype-specific agonists that, of the four main subtypes of PGE_2 receptors (EP_<1-4>), EP_4 receptors alone or EP_2 and EP_4 receptors together are responsible for this PGE_2-stimulated production of Aβ in HEK293 or SH-SY5Y cells, respectively. An EP_4 receptor antagonist suppressed the PGE_2-stimulated production of Aβ in HEK293 cells. This stimulation was accompanied by an increase in cellular cAMP levels and an analogue of cAMP stimulated the production of Aβ, demonstrating that an increases in the cellular level of cAMP are responsible for the PGE_2-stimulated production of Aβ. Immunoblotting experiments and direct measurement of γsecretase activity suggested that PGE_2-stimulated production of Aβ is mediated by activation of γ-secretase but not of β-secretase. Transgenic mice expressing the mutant type of APP showed lower levels of Aβ in the brain, when they were crossed with mice lacking either EP_2 or EP_4 receptors, suggesting that PGE_2-mediated activation of EP_2 and EP_4 receptors is involved in the production of Aβ in vivo and in the pathogenesis of AD.