Hardy, J. Expression of normal sequence pathogenic proteins for neurodegenerative disease contributes to disease risk: 'permissive templating' as a general mechanism underlying neurodegeneration. Biochem. Soc. Trans. 33, 578-581

Laboratory of Neurogenetics, National Institute on Aging, Porter Neuroscience Building, 35, Convent Drive, Bethesda, MD 20892, USA.
Biochemical Society Transactions (Impact Factor: 3.19). 09/2005; 33(Pt 4):578-81. DOI: 10.1042/BST0330578
Source: PubMed


Loci underlying autosomal dominant forms of most neurodegenerative disease have been identified: prion mutations cause Gerstmann Straussler syndrome and hereditary Creutzfeldt-Jakob disease, tau mutations cause autosomal dominant frontal temporal dementia and alpha-synuclein mutations cause autosomal dominant Parkinson's disease. In these cases, the pathogenic mutation is in the protein that is deposited in the diseased tissue and the whole protein is deposited. In Alzheimer's disease, mutations in amyloid precursor protein or in the presenilins cause autosomal dominant disease. These are the substrate and proteases responsible for the production of the deposited peptide Abeta. Thus, in all the cases, the mutations lead to the disease by a mechanism that involves the deposition process. Furthermore, sporadic forms of all these diseases are predisposed by genetic variability at the same loci, implying that the quantity of the normal protein influences the risk of this form of disease. These results show that the amount of pathogenic protein expression is a key factor in determining disease initiation. Recent work on transgenic models of these diseases is consistent with the view that there are two stages of pathogenesis: a concentration-dependent formation of a pathogenic protein oligomer followed by aggregation on to this oligomeric template by a process that is less dependent on the concentration of the protein.

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    • "Thus, there has been a major effort to develop agents that reduce Aβ production for the prevention and treatment of AD. This effort has been further justified by the finding that numerous mutations on APP, PS1 and PS2 increase Aβ42 production even in cell cultures [37]. "
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    ABSTRACT: BACE1 (β-secretase) and α-secretase cleave the Alzheimer's amyloid β protein (Aβ) precursor (APP) to C-terminal fragments of 99 aa (CTFβ) and 83 aa (CTFα), respectively, which are further cleaved by γ-secretase to eventually secrete Aβ and Aα (a.k.a. P3) that terminate predominantly at residues 40 and 42. A number of γ-secretase inhibitors (GSIs), such as N-[N-(3,5-Difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester (DAPT), have been developed with the goal of reducing Aβ to treat Alzheimer's disease (AD). Although most studies show that DAPT inhibits Aβ in a dose-dependent manner several studies have also detected a biphasic effect with an unexpected increase at low doses of DAPT in cell cultures, animal models and clinical trials. In this article, we confirm the increase in Aβ40 and Aβ42 in SH-SY5Y human neuroblastoma cells treated with low doses of DAPT and identify one of the mechanisms for this paradox. We studied the pathway by first demonstrating that stimulation of Aβ, a product of γ-secretase, was accompanied by a parallel increase of its substrate CTFβ, thereby demonstrating that the inhibitor was not anomalously stimulating enzyme activity at low levels. Secondly, we have demonstrated that inhibition of an Aβ degrading activity, endothelin converting enzyme (ECE), yielded more Aβ, but abolished the DAPT-induced stimulation. Finally, we have demonstrated that Aα, which is generated in the secretory pathway before endocytosis, is not subject to the DAPT-mediated stimulation. We therefore conclude that impairment of γ-secretase can paradoxically increase Aβ by transiently skirting Aβ degradation in the endosome. This study adds to the growing body of literature suggesting that preserving γ-secretase activity, rather than inhibiting it, is important for prevention of neurodegeneration.
    Full-text · Article · Mar 2014 · PLoS ONE
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    • "Thereby the protein acts as a template for misfolding that transmits the disease process from one cell to another. This intercellular transfer of misfolded α-syn is hypothesized to contribute to the progressive spread of Lewy pathology in the nervous system in PD and other synucleinopathies [1, 11, 22, 30]. Earlier post-mortem studies of Lewy pathology in PD brains had led to the proposal that it gradually spreads throughout the nervous system following a predictable anatomical pattern [6, 8]. "
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    ABSTRACT: α-Synuclein (α-syn) is a protein prevalent in neural tissue and known to undergo axonal transport. Intracellular α-syn aggregates are a hallmark of Parkinson’s disease (PD). Braak and collaborators have suggested that in people who are destined to eventually develop PD, α-syn aggregate pathology progresses following a stereotypic pattern, starting in the olfactory bulb (OB) and the gut. α-Synuclein aggregates are postulated to spread to interconnected brain regions over several years. Thus, propagation of the pathology via neural pathways can potentially explain how α-syn aggregates spread in PD. We have now studied if α-syn can transfer from the OB to other brain structures through neural connections, by injecting different molecular species of human α-syn (monomers, oligomers, fibrils) into the OB of wild-type mice. We found that non-fibrillar human α-syn is taken up very quickly by OB neurons. Within minutes to hours, it is also found in neurons in structures connected to the OB. Conversely, when we injected bovine serum albumin used as a control protein, we found that it does not diffuse beyond the OB, is rarely taken up by OB cells, and does not transfer to other structures. Taken together, our results show that OB cells readily take up α-syn, and that monomeric and oligomeric, but not fibrillar, forms of α-syn are rapidly transferred to interconnected structures within the timeframe we explored. Our results support the idea that α-syn can transfer along neural pathways and thereby contribute to the progression of the α-syn-related pathology. Electronic supplementary material The online version of this article (doi:10.1007/s00401-013-1160-3) contains supplementary material, which is available to authorized users.
    Full-text · Article · Aug 2013 · Acta Neuropathologica
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    • "Somatic mutations occurring later in neurodevelopment and therefore restricted to a small region could modify protein conformation locally, and this could still lead to spread by permissive templating48 and prion-like propagation of pathology.49 The concept of spread of neurodegenerative disease from a small focus of cells with a somatic mutation has already been proposed, with particular emphasis on amyotrophic lateral sclerosis.12,50 "
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    ABSTRACT: Alpha-synuclein (SNCA) is crucial in the pathogenesis of Parkinson's disease (PD), yet mutations in the SNCA gene are rare. Evidence for somatic genetic variation in normal humans, also involving the brain, is increasing, but its role in disease is unknown. Somatic SNCA mutations, arising in early development and leading to mosaicism, could contribute to PD pathogenesis and yet be absent or undetectable in DNA derived from peripheral lymphocytes. Such mutations could underlie the widespread pathology in PD, with the precise clinical outcome dependent on their type and the timing and location of their occurrence. We recently reported a novel SNCA mutation (c.150T>G, p.H50Q) in PD brain-derived DNA. To determine if there was mosaicism for this, a PCR and cloning strategy was used to take advantage of a nearby heterozygous intronic polymorphism. No evidence of mosaicism was found. High-resolution melting curve analysis of SNCA coding exons, which was shown to be sensitive enough to detect low proportions of 2 known mutations, did not reveal any further mutations in DNA from 28 PD brain-derived samples. We outline the grounds that make the somatic SNCA mutation hypothesis consistent with genetic, embryological, and pathological data. Further studies of brain-derived DNA are warranted and should include DNA from multiple regions and methods for detecting other types of genomic variation. © 2013 Movement Disorder Society.
    Full-text · Article · Jun 2013 · Movement Disorders
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