THE KEYSTONE OF ALZHEIMER PATHOGENESIS MIGHT BE SOUGHT IN Aβ PHYSIOLOGY

For several years Amyloid-beta peptide (A beta) has been considered the main pathogenetic factor of Alzheimer's disease (AD). According to the so called Amyloid Cascade Hypothesis the increase of A beta triggers a series of events leading to synaptic dysfunction and memory loss as well as to the structural brain damage in the later stage of the disease. However, several evidences suggest that this hypothesis is not sufficient to explain AD pathogenesis, especially considering that most of the clinical trials aimed to decrease A beta levels have been unsuccessful. Moreover, A beta is physiologically produced in the healthy brain during neuronal activity and it is needed for synaptic plasticity and memory. Here we propose a model interpreting AD pathogenesis as an alteration of the negative feedback loop between A beta and its physiological receptors, focusing on alpha7 nicotinic acetylcholine receptors (alpha 7-nAchRs). According to this vision, when A beta cannot exert its physiological function a negative feedback mechanism would induce a compensatory increase of its production leading to an abnormal accumulation that reduces alpha 7-nAchR function, leading to synaptic dysfunction and memory loss. In this perspective, the indiscriminate A beta removal might worsen neuronal homeostasis, causing a further impoverishment of learning and memory. Even if further studies are needed to better understand and validate these mechanisms, we believe that to deepen the role of A beta in physiological conditions might represent the keystone to elucidate important aspects of AD pathogenesis. (C) 2015 IBRO. Published by Elsevier Ltd. All rights reserved.