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Published on: June 8, 2016
by MedicalResearch.com with Prof. Margitta Elvers, PhD:
Platelets are the main players in hemostasis and thrombosis, but are also recognized to be involved in the pathology of different neurodegenerative diseases. It is well known that amyloid-beta is able to activate platelets and to induce platelet activation. In Alzheimer’s Disease (AD) patients, platelet activation is enhanced and a correlation between AD and vascular diseases such as stroke and atherosclerosis was shown in different studies However, a direct contribution of platelets to the progression of Alzheimer’s disease (AD) was an open question for many years.
In the last years our group in Düsseldorf, Germany, provided strong evidence for platelets to play a relevant role in the progression of AD, because AD transgenic mice showed enhanced platelet signaling that translated into almost unlimited thrombus formation in vitro and accelerated carotid artery occlusion in vivo suggesting that these mice are at high risk of arterial thrombosis leading to cerebrovascular and unexpectedly to cardiovascular complications that might be also relevant in AD patients.
In the recent study, we analyzed the contribution of platelets, which accumulate at vascular Abeta deposits, to cerebral amyloid angiopathy (CAA), a vascular dysfunction in most of Alzheimer’s disease patients, characterized by deposits of Abeta in the wall of cerebral vessels. We found that synthetic monomeric Abeta is able to bind to integrin alphaIIbbeta3 via its RHDS (Arg-His-Asp-Ser) sequence thereby stimulating the release of adenosine diphosphate (ADP) and clusterin from platelets.
ADP enhanced integrin activation via the ADP receptors P2Y1 and P2Y12 and further increased platelet clusterin release and Abeta fibril formation. Clopidogrel, an antiplatelet drug which irreversible inhibits P2Y12, inhibited Abeta aggregation in human and murine platelet cell cultures. Treatment of AD transgenic mice with clopidogrel for three months reduced clusterin plasma levels and the incidence of CAA.
Our findings indicate a direct contribution of platelets to CAA by promoting the formation of Abeta aggregates and that Abeta, in turn, activates platelets, creating a feed-forward loop. In conclusion, Alzheimer’s disease patients might benefit from anti-thrombotic therapy because platelet inhibitors may alleviate fibril formation in cerebral vessels of AD patients.
Recommendations For Future Research
Future studies are needed to analyze if platelets also modulate the formation of parenchymal Abeta plaques in AD. The potential mechanism how platelets contribute to CAA in mice should be assessed in Alzheimer’s disease patients to confirm that AD patients benefit from anti-platelet therapy.
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