Amyloid imaging in aging and dementia: testing the amyloid hypothesis in vivo.

Amyloid imaging represents a major advance in neuroscience, enabling the detection and quantification of pathologic protein aggregations in the brain. In this review we survey current amyloid imaging techniques, focusing on positron emission tomography (PET) with (11)carbon-labelled Pittsburgh Compound-B ((11)C-PIB), the most extensively studied and best validated tracer. PIB binds specifically to fibrillar beta-amyloid (Abeta) deposits, and is a sensitive marker for Abeta pathology in cognitively normal older individuals and patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD). PIB-PET provides us with a powerful tool to examine in vivo the relationship between amyloid deposition, clinical symptoms, and structural and functional brain changes in the continuum between normal aging and AD. Amyloid imaging studies support a model in which amyloid deposition is an early event on the path to dementia, beginning insidiously in cognitively normal individuals, and accompanied by subtle cognitive decline and functional and structural brain changes suggestive of incipient AD. As patients progress to dementia, clinical decline and neurodegeneration accelerate and proceed independently of amyloid accumulation. In the future, amyloid imaging is likely to supplement clinical evaluation in selecting patients for anti-amyloid therapies, while MRI and FDG-PET may be more appropriate markers of clinical progression

Increasing the Receptor Tyrosine Kinase EphB2 Prevents Amyloid-β-induced Depletion of Cell Surface Glutamate Receptors by a Mechanism That Requires the PDZ-binding Motif of EphB2 and Neuronal Activity.

Diverse lines of evidence suggest that amyloid-β (Aβ) peptides causally contribute to the pathogenesis of Alzheimer disease (AD), the most frequent neurodegenerative disorder. However, the mechanisms by which Aβ impairs neuronal functions remain to be fully elucidated. Previous studies showed that soluble Aβ oligomers interfere with synaptic functions by depleting NMDA-type glutamate receptors (NMDARs) from the neuronal surface and that overexpression of the receptor tyrosine kinase EphB2 can counteract this process. Through pharmacological treatments and biochemical analyses of primary neuronal cultures expressing wild-type or mutant forms of EphB2, we demonstrate that this protective effect of EphB2 depends on its PDZ-binding motif and the presence of neuronal activity but not on its kinase activity. We further present evidence that the protective effect of EphB2 may be mediated by the AMPA-type glutamate receptor subunit GluA2, which can become associated with the PDZ-binding motif of EphB2 through PDZ domain-containing proteins and can promote the retention of NMDARs in the membrane. In addition, we show that the Aβ-induced depletion of surface NMDARs does not depend on several factors that have been implicated in the pathogenesis of Aβ-induced neuronal dysfunction, including aberrant neuronal activity, tau, prion protein (PrP(C)), and EphB2 itself. Thus, although EphB2 does not appear to be directly involved in the Aβ-induced depletion of NMDARs, increasing its expression may counteract this pathogenic process through a neuronal activity- and PDZ-dependent regulation of AMPA-type glutamate receptors

Without magic bullets: the biological basis for public health interventions against protein folding disorders

Protein folding disorders of aging like Alzheimer's and Parkinson's diseases currently present intractable medical challenges. 'Small molecule' interventions - drug treatments - often have, at best, palliative impact, failing to alter disease course. The design of individual or population level interventions will likely require a deeper understanding of protein folding and its regulation than currently provided by contemporary 'physics' or culture-bound medical magic bullet models. Here, a topological rate distortion analysis is applied to the problem of protein folding and regulation that is similar in spirit to Tlusty's (2010a) elegant exploration of the genetic code. The formalism produces large-scale, quasi-equilibrium 'resilience' states representing normal and pathological protein folding regulation under a cellular-level cognitive paradigm similar to that proposed by Atlan and Cohen (1998) for the immune system. Generalization to long times produces diffusion models of protein folding disorders in which epigenetic or life history factors determine the rate of onset of regulatory failure, in essence, a premature aging driven by familiar synergisms between disjunctions of resource allocation and need in the context of socially or physiologically toxic exposures and chronic powerlessness at individual and group scales. Application of an HPA axis model is made to recent observed differences in Alzheimer's onset rates in White and African American subpopulations as a function of an index of distress-proneness

Phenotypic heterogeneity and genetic modification of P102L inherited prion disease in an international series

The largest kindred with inherited prion disease P102L, historically Gerstmann-Sträussler-Scheinker syndrome, originates from central England, with émigrés now resident in various parts of the English-speaking world. We have collected data from 84 patients in the large UK kindred and numerous small unrelated pedigrees to investigate phenotypic heterogeneity and modifying factors. This collection represents by far the largest series of P102L patients so far reported. Microsatellite and genealogical analyses of eight separate European kindreds support multiple distinct mutational events at a cytosine-phosphate diester-guanidine dinucleotide mutation hot spot. All of the smaller P102L kindreds were linked to polymorphic human prion protein gene codon 129M and were not connected by genealogy or microsatellite haplotype background to the large kindred or each other. While many present with classical Gerstmann-Sträussler-Scheinker syndrome, a slowly progressive cerebellar ataxia with later onset cognitive impairment, there is remarkable heterogeneity. A subset of patients present with prominent cognitive and psychiatric features and some have met diagnostic criteria for sporadic Creutzfeldt-Jakob disease. We show that polymorphic human prion protein gene codon 129 modifies age at onset: the earliest eight clinical onsets were all MM homozygotes and overall age at onset was 7 years earlier for MM compared with MV heterozygotes (P = 0.02). Unexpectedly, apolipoprotein E4 carriers have a delayed age of onset by 10 years (P = 0.02). We found a preponderance of female patients compared with males (54 females versus 30 males, P = 0.01), which probably relates to ascertainment bias. However, these modifiers had no impact on a semi-quantitative pathological phenotype in 10 autopsied patients. These data allow an appreciation of the range of clinical phenotype, modern imaging and molecular investigation and should inform genetic counselling of at-risk individuals, with the identification of two genetic modifiers

The challenges of purely mechanistic models in biology and the minimum need for a 'mechanism-plus-X' framework

Ever since the advent of molecular biology in the 1970s, mechanical models have become the dogma in the field, where a "true" understanding of any subject is equated to a mechanistic description. This has been to the detriment of the biomedical sciences, where, barring some exceptions, notable new feats of understanding have arguably not been achieved in normal and disease biology, including neurodegenerative disease and cancer pathobiology. I argue for a "mechanism-plus-X" paradigm, where mainstay elements of mechanistic models such as hierarchy and correlation are combined with nomological principles such as general operative rules and generative principles. Depending on the question at hand and the nature of the inquiry, X could range from proven physical laws to speculative biological generalizations, such as the notional principle of cellular synchrony. I argue that the "mechanism-plus-X" approach should ultimately aim to move biological inquiries out of the deadlock of oft-encountered mechanistic pitfalls and reposition biology to its former capacity of illuminating fundamental truths about the world

Alzheimer's disease pathology and the unfolded protein response : Prospective pathways and therapeutic targets

The authors would like to thank Alzheimer's Research UK (Grant refs: ARUK-PPG2014A-21 and ARUK-NSG2015-1 to BP and DK) who have provided support for relevant projects leading to this review.Peer reviewedPostprin

Tau-aggregation inhibitor therapy for Alzheimer's disease

Article Accepted Date: 9 December 2013 Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.Peer reviewedPublisher PD

New light on prions : putative role of co-operation of PrPcPrP^{c} and AβA\beta proteins in cognition

A seminal article of Takahashi et al. reporting concomitant accumulation of cellular prion protein ($PrP^{c}$) and $\beta$ -amyloid ($A\beta$) in dystrophic neurites, within neuritic plaques raised an exciting issue that is important for our understanding of mechanisms of neurodegeneration. The mentioned authors interpreted their findings rather cautiously, however since the time of their publication, several reports representing different approaches and methods have seemed to indicate that both proteins appear to co-operate more intrinsically than it could have been imagined earlier. The goal of the review is to sum up the accruing research data with special attention to evidence pointing to the co-operative role of $PrP^{c}$ and $A\beta$ in cognitive impairment