Plasma Fibrinogen Is a Natural Deterrent to Amyloid Beta-Induced Platelet Activation.

ABSTRACT

Alzheimer's disease (AD) is a devastating neurodegenerative disorder, characterized by extensive loss of neurons, and deposition of amyloid beta (Aß) in the form of extracellular plaques. Aß is considered to have critical role in synaptic loss and neuronal death underlying cognitive decline. Platelets contribute to 95% of circulating amyloid-precursor protein that releases Aß into circulation. We have recently demonstrated that, Aß active fragment containing amino acid sequence 25-35 (Aß25-35) is highly thrombogenic in nature, and elicits strong aggregation of washed human platelets in RhoA-dependent manner. In the present study we evaluated the influence of fibrinogen on Aß-induced platelet activation. Intriguingly, Aß failed to induce aggregation of platelets suspended in plasma but not in buffer. Fibrinogen brought about dose-dependent decline in aggregatory response of washed human platelets elicited by Aß25-35, which could be reversed by increasing doses of Aß. Fibrinogen also attenuated Aß-induced platelet responses like secretion, clot retraction, rise in cytosolic Ca+2 and reactive oxygen species (ROS). Fibrinogen prevented intracellular accumulation of full length amyloid beta peptide (Aß42) in platelets as well as neuronal cells. We conclude that fibrinogen serves as a physiological check against the adverse effects of Aß by preventing its interaction with cells.