We report duplication of the APP locus on chromosome 21 in five families with autosomal dominant early-onset Alzheimer disease (ADEOAD) and cerebral amyloid angiopathy (CAA). Among these families, the duplicated segments had a minimal size ranging from 0.58 to 6.37 Mb. Brains from individuals with APP duplication showed abundant parenchymal and vascular deposits of amyloid-beta peptides. Duplication of the APP locus, resulting in accumulation of amyloid-beta peptides, causes ADEOAD with CAA.
Tauopathies, including Alzheimer's disease and fronto-temporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), are a group of neurodegenerative disorders characterized by the presence of intraneuronal filamentous inclusions of aberrantly phosphorylated-tau. Tau is a neuronal microtubule-associated protein involved in microtubule assembly and stabilization. Currently, the molecular mechanisms underlying tau-mediated cellular toxicity remain elusive. To address the determinants of tau neurotoxicity, we first characterized the cellular alterations resulting from the over-expression of a mutant form of human tau associated with FTDP-17 (tau V337M) in Drosophila. We found that the over-expression of tau V337M, in Drosophila larval motor neurons, induced disruption of the microtubular network at presynaptic nerve terminals and changes in neuromuscular junctions morphological features. Secondly, we performed a misexpression screen to identify genetic modifiers of the tau V337M-mediated rough eye phenotype. The screening of 1250 mutant Drosophila lines allowed us to identify several components of the cytoskeleton, and particularly from the actin network, as specific modifiers of tau V337M-induced neurodegeneration. Furthermore, we found that numerous tau modulators identified in our screen were involved in the maintenance of synaptic function. Taken together, these findings suggest that disruption of the microtubule network in presynaptic nerve terminals could constitute early events in the pathological process leading to synaptic dysfunction in tau V337M pathology.
J. Neurochem. (2010) 113, 895–903.
Abstract
Tau is a neuronal microtubule‐associated protein involved in microtubules assembly and stabilization. Tauopathies, including Alzheimer’s disease and fronto‐temporal dementia with parkinsonism linked to chromosome 17, are a group of neurodegenerative disorders characterized by the presence of intraneuronal filamentous inclusions of abnormally and hyperphosphorylated Tau. Currently, the molecular mechanisms underlying Tau‐mediated cellular toxicity remain elusive. To address the determinants of Tau neurotoxicity, we used Drosophila models of human tauopathies to study the microtubule‐binding properties of human Tau proteins in vivo. We showed that, in contrast to endogenous Drosophila Tau, human Tau proteins bind very poorly to microtubules in Drosophila, and are mostly recovered as soluble cytosolic hyperphosphorylated species. This weak binding of human Tau to microtubules is neither because of microtubules saturation nor competition with endogenous Drosophila Tau, but clearly depends on its phosphorylation degree. We also reported that accumulation of cytosolic hyperphosphorylated forms of human Tau proteins correlates with human Tau‐mediated neurodegeneration in flies, supporting the key role of soluble cytosolic hyperphosphorylated Tau proteins as toxic species in vivo.
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