Platelets as a peripheral district where to study pathogenetic mechanisms of Alzheimer disease: The case of amyloid precursor protein

Alzheimer disease is a progressive neurodegenerative disease, characterised by a progressive cognitive and memory decline. From a neuropathological point of view, Alzheimer disease is defined by the presence of characteristic lesions, i.e. mature senile plaques, neurofibrillary tangles (NFTs) and amyloid angiopathy. In particular, accumulation of the amyloid β-peptide in the brain parenchyma and vasculature is an invariant event in the pathogenesis of both sporadic and familial Alzheimer cases. Amyloid β-peptide originates from a larger precursor, the amyloid precursor protein (APP) ubiquitously expressed. Among the different peripheral cells expressing APP forms, platelets are particularly interesting since they show concentrations of its isoforms equivalent to those found in brain. Moreover, a number of laboratories independently described alterations in APP metabolism/concentration in platelets of Alzheimer patients when compared to control subjects matched for demographic characteristics. These observations defined the frame of our work aimed to investigate if a correlation between levels of platelet APP forms and Alzheimer disease could be detected. We have reported that patients affected by Alzheimer disease show a differential level of platelet APP forms. This observation has several implications: APP processing abnormalities, believed to be a very early change in Alzheimer disease in neuronal compartment, do occur in extraneuronal tissues, such as platelets, thus, suggesting that Alzheimer disease is a systemic disorder; further, our data strongly indicate that a differential level of platelet APP isoforms can be considered a potential peripheral marker of Alzheimer disease allowing for discrimination between Alzheimer and other types of dementia