Platelet Proteomic Analysis Revealed Differential Pattern of Cytoskeletal- and Immune-Related Proteins at Early Stages of Alzheimer's Disease

Platelets are considered a good model system to study a number of elements associated with neuronal pathways as they share biochemical similarities. Platelets represent the major source of amyloid- (A) in blood contributing to the A accumulation in the brain parenchyma and vasculature. Peripheral blood platelet alterations including cytoskeletal abnormalities, abnormal cytoplasmic calcium fluxes or increased oxidative stress levels have been related to Alzheimer's disease (AD) pathology. Therefore, platelets can be considered a peripheral model to study metabolic mechanisms occurring in AD. To investigate peripheral molecular alterations, we examined platelet protein expression in a cohort of 164 subjects, including mild cognitive impairment (MCI), and AD patients, and healthy aged-matched controls. A two-dimensional difference gel electrophoresis (2D-DIGE) discovery phase revealed significant differences between patients and controls in five proteins: talin, vinculin, moesin, complement C3b and Rho GDP, which are known to be involved in cytoskeletal regulation including focal adhesions, inflammation and immune functions. Western blot analysis verified that talin was found to be increased in mild and moderate AD groups versus control, while the other three were found to be decreased. We also analysed amyloid precursor protein (APP), amyloid- 1-40 (A(40)) and 1-42 (A(42)) levels in platelets from the same groups of subjects. Upregulation of platelet APP and A peptides was found in AD patients compared to controls. These findings complement and expand previous reports concerning the morphological and functional alterations in AD platelets, and provide more insights into possible mechanisms that participate in the multifactorial and systemic damage in AD.