Intracellular Aβ pathology and early cognitive impairments in a transgenic rat overexpressing human amyloid precursor protein: a multidimensional study

Abstract

Numerous studies have implicated the abnormal accumulation of intraneuronal amyloid-β (Aβ) as an important contributor to Alzheimer’s disease (AD) pathology, capable of triggering neuroinflammation, tau hyperphosphorylation and cognitive deficits. However, the occurrence and pathological relevance of intracellular Aβ remain a matter of controversial debate. In this study, we have used a multidimensional approach including high-magnification and super-resolution microscopy, cerebro-spinal fluid (CSF) mass spectrometry analysis and ELISA to investigate the Aβ pathology and its associated cognitive impairments, in a novel transgenic rat model overexpressing human APP. Our microscopy studies with quantitative co-localization analysis revealed the presence of intraneuronal Aβ in transgenic rats, with an immunological signal that was clearly distinguished from that of the amyloid precursor protein (APP) and its C-terminal fragments (CTFs). The early intraneuronal pathology was accompanied by a significant elevation of soluble Aβ42 peptides that paralleled the presence and progression of early cognitive deficits, several months prior to amyloid plaque deposition. Aβ38, Aβ39, Aβ40 and Aβ42 peptides were detected in the rat CSF by MALDI-MS analysis even at the plaque-free stages; suggesting that a combination of intracellular and soluble extracellular Aβ may be responsible for impairing cognition at early time points. Taken together, our results demonstrate that the intraneuronal development of AD-like amyloid pathology includes a mixture of molecular species (Aβ, APP and CTFs) of which a considerable component is Aβ; and that the early presence of these species within neurons has deleterious effects in the CNS, even before the development of full-blown AD-like pathology.Electronic supplementary materialThe online version of this article (doi:10.1186/2051-5960-2-61) contains supplementary material, which is available to authorized users.

A Bird’s-Eye View of the Multiple Biochemical Mechanisms that Propel Pathology of Alzheimer’s Disease: Recent Advances and Mechanistic Perspectives on How to Halt the Disease Progression Targeting Multiple Pathways

“…Only unprotected transgenic mice failed to explore the familiar but moved object any more than the other two unmoved objects (trial 2) but showed heightened exploration of the novel object (trial 3) as well as the wild type and protected transgenic mice. Thus, as in earlier and perhaps less controlled studies [61,73,[82][83][84][85][86][87][88][89][90], we also demonstrated that hippocampal degeneration decreased rodents' spatial but spared their non-spatial working memory. Even though we may have eliminated or reduced anxiety-induced behavior in NL/NOR by running mice in an enclosed maze rather than in an open field, we found in a subsequent research [91] that wild type mice could not be repeatedly tested on their NL/NOR performance.…”

Non-Fibrillar Oligomeric Amyloid-β within Synapses

“…Whether toxic Aβ at synapses originates from intracellular or extracellular sources is a hotly debated topic in the field [33][34][35][36]. Here we used three high-resolution imaging techniques to examine whether oAβ is present within synaptic terminals or decorating the exterior membrane of pre and postsynapses and find that NAB61 labeled oAβ is present inside synapses.…”

The keystone of Alzheimer pathogenesis might be sought in Aβ physiology

“…The main issue in detecting Aβ inside cells is represented by the method used to unravel it, which is not considered sensitive enough because of the variety of staining protocols and the use of antibodies such as 6E10 and 4G8 that cross-react with APP (Aho et al, 2010). However, different methods have been used to demonstrate that Aβ is present inside neurons (for a review see Cuello et al, 2012): i) a specific antibody recognizing the N-terminal end of Aβ that does not cross-react with APP allowed to detect intraneuronal Aβ in 3×Tg and 5×FAD mice brains (Youmans et al, 2012); ii) conformation-specific antibodies have been used to detect intraneuronal Aβ in 3×Tg (Wirths and Bayer, 2012; Wirths et al, 2012); iii) a multi-dimentional study using high-resolution microscopy, mass spectrometry analysis, and ELISAs has shown that Aβ accumulates inside neurons of an AD-like transgenic rat (Iulita et al, 2014). Recently, it has been demonstrated that intraneuronal injections of Aβ caused an impairment of basal synaptic transmission and LTP.…”