Involvement of prostaglandin E2 in production of beta-amyloid peptides both in vitro and in vivo

Abstract

Amyloid-β peptides (Aβ, generated by proteolysis of the β-amyloid 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 examined the effect of prostaglandin E2 (PGE2), a strong inducer of inflammation, on the production of Aβ in vitro. We also examined the role of PGE2 in pathogenesis of AD in vivo. The production of Aβ in cells expressing a mutant type of APP (APPsw) was examined by ELISA. Cognitive performance was assessed by a hidden-platform Morris-type water maze. PGE2 stimulated production of Aβ and, of the four main subtypes of PGE2 receptors (EP1-4), EP2 and EP4 receptors are responsible for this PGE2-stimulated production of Aβ. Activation of EP2 and EP4 receptors is coupled to an increase in cellular cAMP levels and activation of protein kinase A (PKA). We found that inhibitors of adenylate cyclase and PKA suppress EP2 receptor-mediated but not EP4 receptor-mediated stimulation of the production of Aβ by PGE2. In contrast, inhibitors of endocytosis suppressed EP4 receptor-mediated but not EP2 receptor-mediated stimulation. PGE2-dependent internalization of EP4 receptor was observed and cells expressing a mutant EP4 receptor lacking the internalization activity did not exhibit PGE2-stimulated production of Aβ. A surface biotinylation assay revealed that the γ-secretase internalizes in a manner dependent on both PGE2 and EP4 receptors. On the other hand, in vivo, transgenic mice expressing APPsw showed lower levels of Aβ in the brain and less apparent cognitive deficit, when they were crossed with mice lacking EP4 receptors. Administration of antagonist for EP4 receptor also improved cognitive deficit of transgenic mice expressing APPsw. These results suggest that PGE2-stimulated production of Aβ involves EP4 receptor-mediated endocytosis of γ-secretase, and EP2 receptor-dependent activation of adenylate cyclase and PKA, both of which are important in the inflammation-mediated progression of AD. Results also suggest that PGE2-mediated activation of EP4 receptor is involved in the production of Aβ in vivo and in the pathogenesis of AD and that antagonists for EP4 receptor are therapeutically beneficial for AD.