ß-Amyloid Orchestrates Factor XII and Platelet Activation Leading to Endothelial Dysfunction and Abnormal Fibrinolysis in Alzheimer Disease.

Alzheimer disease (AD) is the most common form of dementia in humans. However, to date, the cause of sporadic AD (SAD), which is the most frequent form, is still unknown. Although it has not been possible to determine the origin of this disease, the amyloid hypothesis is one of the most accepted to explain the etiology of AD. This hypothesis proposes that the pathogenesis of AD is derived from the toxic effect produced by the amyloid-ß (Aß) peptide in the brain parenchyma, but it does not make clear how Aß is capable of producing such damage. Furthermore, it has been observed that SAD is accompanied by disruptions in the vascular system, such as damage to the blood-brain barrier. This facilitates the transfer of some systemic proteins, such as fibrinogen, to the brain parenchyma, where Aß is abundant. Therefore, this Aß interacts with fibrinogen, which favors the formation of clots resistant to fibrinolysis, inducing a risk of thrombosis and neuroinflammation. Notably, Aß is not only of neuronal origin; platelets also contribute to high Aß production in the circulation. The Aß present in circulation favors the activation of coagulation factor XII, which leads to the generation of thrombin and bradykinin. In addition to Aß-induced platelet activation, all these events favor the development of inflammatory processes that cause damage to the brain vasculature. This damage represents the beginning of the toxic effects of Aß, which supports the amyloid hypothesis. This review addresses the relationship between alterations in the vascular and hemostatic systems caused by Aß and how both alterations contribute to the progression of SAD.

Platelet activation as a trigger factor for inflammation and atherosclerosis.

Platelets, in addition to participating in atherosclerosis, play a very active role in the immune response of this disease since they have the ability to interact with various inflammatory cells, in addition to secreting cytokines, chemokines, growth factors, etc. The functions of platelets go beyond their interaction with the endothelium, as they participate in creating an inflammatory environment, which contributes to the loss of homeostasis. On the other hand, platelet-derived microparticles induce the activation of other platelets, of endothelial cells and in recruiting leukocytes. For all the above, platelets and the inflammatory environment can be considered as possible therapeutic targets to prevent the development of atherosclerosis and the events associated with it.

Las plaquetas, además de participar en la ateroesclerosis, desempeñan un papel muy activo en la respuesta inmunitaria de esta enfermedad, ya que tienen la capacidad de interaccionar con diversas células inflamatorias, además de secretar citocinas, quimiocinas, factores de crecimiento, etc. Las funciones de las plaquetas van más allá de su interacción con el endotelio, pues participan en crear un ambiente inflamatorio, lo que contribuye a la pérdida de la homeostasis. Por otra parte, las micropartículas derivadas de plaquetas inducen la activación de otras plaquetas y de células endoteliales, y el reclutamiento de leucocitos. Por todo lo anterior, las plaquetas y el ambiente inflamatorio pueden considerarse como posibles blancos terapéuticos para evitar el desarrollo de la ateroesclerosis y los eventos asociados a esta.