Effects of staurosporine, U-73122, wortmannin, 4-hydroxynonenal and sodium azide upon the release of secreted beta-amyloid precursor protein from human platelets in response to thrombin stimulation

Estrogen receptor α promotes non-amyloidogenic processing of platelet amyloid precursor protein via the MAPK/ERK pathway

Deposition of amyloid β peptide (Aβ), a proteolytic product of amyloid precursor protein (APP), in senile plaques and in the walls of cerebral blood vessels is a hallmark of Alzheimer's disease (AD). Platelets contain high levels of APP and Aβ and may contribute to amyloid deposits seen in AD. However, the biochemical mechanism(s) involved in the regulation of platelet APP metabolism are largely unknown. The estrogen receptor α (ERα) is found to be expressed in platelets. It has not been elucidated whether ERα-mediated non-genomic signaling intervenes with platelet APP processing. Using ERα knock-out (α-ERKO) mice and wild type (WT) littermates, the present study demonstrated that ERα-specific agonist propylpyrazole triol (PPT) promoted non-amyloidogenic processing of platelet APP via the mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) pathway. The underlying basis involves direct association of activated ERK with a disintegrin and metalloprotease domain 17 (ADAM17, an α-secretase candidate) and ERK-dependent threonine phosphorylation of ADAM17. These results suggest that selective modulation of ERα in peripheral target tissues may serve as an anti-amyloidogenic strategy for AD and other amyloidogenic diseases.

Estrogenic effect of ginsenoside Rg1 on APP processing in post-menopausal platelets

Ginsenoside Rg1, an active component of high abundance in ginseng, has recently been reported to possess neuroprotective properties and also identified as a potent phytoestrogen. However, it is unknown whether Rg1 intervenes in amyloid precursor protein (APP) processing, and whether such intervention is associated with its estrogenic activity. Using human platelets, this study demonstrated that Rg1 promoted α-secretase cleavage of APP via estrogenic activity. The mitogen-activated protein kinases (MAPK)/extracellular signal-regulated kinases (ERK) pathway may be involved in the effect of Rg1 on APP metabolism as a downstream effector of estrogen receptor (ER) extranuclear signaling. Estrogen withdrawal is a risk factor for the onset of Alzheimer's disease (AD). Rg1 exerts estrogenic activity in APP processing in platelets supporting the use of this compound in the prevention of AD, in particular in postmenopausal females.