Abstractβ-Amyloid precursor protein (APP) mutations cause familial Alzheimer's disease with nearly complete penetrance. We found an APP mutation [alanine-673→valine-673 (A673V)] that causes disease only in the homozygous state, whereas heterozygous carriers were unaffected, consistent with a recessive Mendelian trait of inheritance. The A673V mutation affected APP processing, resulting in enhanced β-amyloid (Aβ) production and formation of amyloid fibrils in vitro. Coincubation of mutated and wild-type peptides conferred instability on Aβ aggregates and inhibited amyloidogenesis and neurotoxicity. The highly amyloidogenic effect of the A673V mutation in the homozygous state and its anti-amyloidogenic effect in the heterozygous state account for the autosomal recessive pattern of inheritance and have implications for genetic screening and the potential treatment of Alzheimer's disease.Acentral pathological feature of Alzheimer's disease (AD) is the accumulation of β-Aβ in the form of oligomers and amyloid fibrils in the brain (1). Aβ is generated by sequential cleavage of the APP by β-and γ-secretases and exists as short and long isoforms, Aβ1-40 and Aβ1-42 (2). Aβ1-42 is especially prone to misfolding and builds up aggregates that are thought to be the primary neurotoxic species involved in AD pathogenesis (2,3). AD is usually sporadic, but *To whom correspondence should be addressed. E-mail: ftagliavini@istituto-besta.it. Publisher's Disclaimer: This manuscript has been accepted for publication in Science. This version has not undergone final editing. Please refer to the complete version of record at http://www.sciencemag.org/. The manuscript may not be reproduced or used in any manner that does not fall within the fair use provisions of the Copyright Act without the prior, written permission of AAAS. NIH Public Access Author ManuscriptScience. Author manuscript; available in PMC 2010 March 13. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript a small fraction of cases is familial (4). The familial forms show an autosomal dominant pattern of inheritance with virtually complete penetrance and are linked to mutations in the APP, presenilin 1, and presenilin 2 genes (5). The APP mutations close to the sites of β-or γ-secretase cleavage flanking the Aβ sequence overproduce total Aβ or only Aβ1-42, respectively, whereas those that alter amino acids within Aβ result in greater propensity to aggregation in vitro (6, 7).We have identified an APP mutation [Ala 673 →Val 673 (A673V)] that causes disease only in the homozygous state. The mutation consists of a C-to-T transition that results in an alanineto-valine substitution at position 673 (APP770 numbering) corresponding to position 2 of Aβ ( Fig. 1A and fig. S1) (8). The genetic defect was found in a patient with early-onset dementia and in his younger sister, who now shows multiple-domain mild cognitive impairment (MCI) In the patient, the disease presented with behavioral changes and cognitive deficits at the age of 36 years and evolved towar...
Background The cerebrospinal fluid (CSF) biomarkers amyloid beta 1–42, total tau, and phosphorylated tau are used increasingly for Alzheimer’s disease (AD) research and patient management. However, there are large variations in biomarker measurements among and within laboratories. Methods Data from the first nine rounds of the Alzheimer’s Association quality control program was used to define the extent and sources of analytical variability. In each round, three CSF samples prepared at the Clinical Neurochemistry Laboratory (Mölndal, Sweden) were analyzed by single-analyte enzyme-linked immunosorbent assay (ELISA), a multiplexing xMAP assay, or an immunoassay with electrochemoluminescence detection. Results A total of 84 laboratories participated. Coefficients of variation (CVs) between laboratories were around 20% to 30%; within-run CVs, less than 5% to 10%; and longitudinal within-laboratory CVs, 5% to 19%. Interestingly, longitudinal within-laboratory CV differed between biomarkers at individual laboratories, suggesting that a component of it was assay dependent. Variability between kit lots and between laboratories both had a major influence on amyloid beta 1–42 measurements, but for total tau and phosphorylated tau, between-kit lot effects were much less than between-laboratory effects. Despite the measurement variability, the between-laboratory consistency in classification of samples (using prehoc-derived cutoffs for AD) was high (>90% in 15 of 18 samples for ELISA and in 12 of 18 samples for xMAP). Conclusions The overall variability remains too high to allow assignment of universal biomarker cutoff values for a specific intended use. Each laboratory must ensure longitudinal stability in its measurements and use internally qualified cutoff levels. Further standardization of laboratory procedures and improvement of kit performance will likely increase the usefulness of CSF AD biomarkers for researchers and clinicians.
Atypical neuropathological and molecular phenotypes of bovine spongiform encephalopathy (BSE) have recently been identified in different countries. One of these phenotypes, named bovine “amyloidotic” spongiform encephalopathy (BASE), differs from classical BSE for the occurrence of a distinct type of the disease-associated prion protein (PrP), termed PrPSc, and the presence of PrP amyloid plaques. Here, we show that the agents responsible for BSE and BASE possess different biological properties upon transmission to transgenic mice expressing bovine PrP and inbred lines of nontransgenic mice. Strikingly, serial passages of the BASE strain to nontransgenic mice induced a neuropathological and molecular disease phenotype indistinguishable from that of BSE-infected mice. The existence of more than one agent associated with prion disease in cattle and the ability of the BASE strain to convert into the BSE strain may have important implications with respect to the origin of BSE and spongiform encephalopathies in other species, including humans.
BACKGROUND Prions, the infectious agents responsible for transmissible spongiform encephalopathies, consist mainly of the misfolded prion protein (PrPSc). The unique mechanism of transmission and the appearance of a variant form of Creutzfeldt–Jakob disease, which has been linked to consumption of prion-contaminated cattle meat, have raised concerns about public health. Evidence suggests that variant Creutzfeldt–Jakob disease prions circulate in body fluids from people in whom the disease is silently incubating. METHODS To investigate whether PrPSc can be detected in the urine of patients with variant Creutzfeldt–Jakob disease, we used the protein misfolding cyclic amplification (PMCA) technique to amplify minute quantities of PrPSc, enabling highly sensitive detection of the protein. We analyzed urine samples from several patients with various transmissible spongiform encephalopathies (variant and sporadic Creutzfeldt–Jakob disease and genetic forms of prion disease), patients with other degenerative or nondegenerative neurologic disorders, and healthy persons. RESULTS PrPSc was detectable only in the urine of patients with variant Creutzfeldt–Jakob disease and had the typical electrophoretic profile associated with this disease. PrPSc was detected in 13 of 14 urine samples obtained from patients with variant Creutzfeldt–Jakob disease and in none of the 224 urine samples obtained from patients with other neurologic diseases and from healthy controls, resulting in an estimated sensitivity of 92.9% (95% confidence interval [CI], 66.1 to 99.8) and a specificity of 100.0% (95% CI, 98.4 to 100.0). The PrPSc concentration in urine calculated by means of quantitative PMCA was estimated at 1×10−16 g per milliliter, or 3×10−21 mol per milliliter, which extrapolates to approximately 40 to 100 oligomeric particles of PrPSc per milliliter of urine. CONCLUSIONS Urine samples obtained from patients with variant Creutzfeldt–Jakob disease contained minute quantities of PrPSc. (Funded by the National Institutes of Health and others.)
Based on in vitro observations in scrapie-infected neuroblastoma cells, quinacrine has recently been proposed as a treatment for Creutzfeldt-Jakob disease (CJD), including a new variant CJD which is linked to contamination of food by the bovine spongiform encephalopathy (BSE) agent. The present study investigated possible mechanisms of action of quinacrine on prions. The ability of quinacrine to interact with and to reduce the protease resistance of PrP peptide aggregates and PrPres of human and animal origin were analyzed, together with its ability to inhibit the in vitro conversion of the normal prion protein (PrPc) to the abnormal form (PrPres). Furthermore, the efficiencies of quinacrine and chlorpromazine, another tricyclic compound, were examined in different in vitro models and in an experimental murine model of BSE. Quinacrine efficiently hampered de novo generation of fibrillogenic prion protein and PrPres accumulation in ScN2a cells. However, it was unable to affect the protease resistance of preexisting PrP fibrils and PrPres from brain homogenates, and a "curing" effect was obtained in ScGT1 cells only after lengthy treatment. In vivo, no detectable effect was observed in the animal model used, consistent with other recent studies and preliminary observations in humans. Despite its ability to cross the blood-brain barrier, the use of quinacrine for the treatment of CJD is questionable, at least as a monotherapy. The multistep experimental approach employed here could be used to test new therapeutic regimes before their use in human trials.Transmissible spongiform encephalopathies are a group of neurodegenerative disorders including sporadic, genetic, and acquired forms of Creutzfeldt-Jakob disease (CJD) in humans, scrapie in sheep, and spongiform encephalopathy in cattle (bovine spongiform encephalopathy [BSE]). These diseases are characterized by the accumulation of a pathological form of the cellular prion protein (PrPc), called scrapie prion protein (PrPres), in the central nervous system and, in many instances, in the lymphoreticular system. PrPres shows several differences from PrPc: a high percentage of -sheet secondary structure, resistance to proteolysis, insolubility in detergents, and a propensity to polymerize into amyloid-like fibrils (4, 27, 28). The disease-related form of PrPc, PrPres, is the only specific molecular marker of the infection, and the inhibition of its accumulation is often used to evaluate the efficacy of therapeutic drugs.To date, several compounds have been described which decrease the PrPres concentration in different scrapie-infected cell lines or prolong the incubation period in animal models. These drugs belong to different classes, including sulfated
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