RESUMO
Amyloid-ß (Aß) oligomers consist of fibrillar and non-fibrillar soluble assemblies of the Aß peptide. Aß∗56 is a non-fibrillar Aß assembly that is linked to memory deficits. Previous studies did not decipher specific forms of Aß present in Aß∗56. Here, we confirmed the memory-impairing characteristics of Aß∗56 and extended its biochemical characterization. We used anti-Aß(1-x), anti-Aß(x-40), anti-Aß(x-42), and A11 anti-oligomer antibodies in conjunction with western blotting, immunoaffinity purification, and size-exclusion chromatography to probe aqueous brain extracts from Tg2576, 5xFAD, and APP/TTA mice. In Tg2576, Aß∗56 is a â¼56-kDa, SDS-stable, A11-reactive, non-plaque-dependent, water-soluble, brain-derived oligomer containing canonical Aß(1-40). In 5xFAD, Aß∗56 is composed of Aß(1-42), whereas in APP/TTA, it contains both Aß(1-40) and Aß(1-42). When injected into the hippocampus of wild-type mice, Aß∗56 derived from Tg2576 mice impairs memory. The unusual stability of this oligomer renders it an attractive candidate for studying relationships between molecular structure and effects on brain function.
RESUMO
Amyloid-ß (Aß) oligomers consist of fibrillar and non-fibrillar soluble assemblies of the Aß peptide. Tg2576 human amyloid precursor protein (APP)-expressing transgenic mice modeling Alzheimer's disease produce Aß*56, a non-fibrillar Aß assembly that has been shown by several groups to relate more closely to memory deficits than plaques. Previous studies did not decipher specific forms of Aß present in Aß*56. Here, we confirm and extend the biochemical characterization of Aß*56. We used anti-Aß(1-x), anti-Aß(x-40), and A11 anti-oligomer antibodies in conjunction with western blotting, immunoaffinity purification, and size-exclusion chromatography to probe aqueous brain extracts from Tg2576 mice of different ages. We found that Aß*56 is a â¼56-kDa, SDS-stable, A11-reactive, non-plaque-related, water-soluble, brain-derived oligomer containing canonical Aß(1-40) that correlates with age-related memory loss. The unusual stability of this high molecular-weight oligomer renders it an attractive candidate for studying relationships between molecular structure and effects on brain function.
RESUMO
Studies have recently demonstrated that a caspase-2-mediated cleavage of human tau (htau) at asparate-314 (D314) is responsible for cognitive deficits and neurodegeneration in mice modeling frontotemporal dementia (FTD). However, these animal studies may be confounded by flaws in their model systems, such as endogenous functional gene disruption and inequivalent transgene expression. To avoid these weaknesses, we examined the pathogenic role of this site-specific htau cleavage in FTD using genetically matched htau targeted-insertion mouse lines: rT2 and rT3. Both male and female mice were included in this study. rT2 mice contain a single copy of the FTD-linked htau proline-to-leucine mutation at amino acid 301 (htau P301L), inserted into a neutral site to avoid dysregulation of host gene expression. The similarly constructed rT3 mice harbor an additional D314-to-glutamate (D314E) mutation that blocks htau cleavage. We demonstrate that htau transgene expression occurs primarily in the forebrain at similar levels in rT2 and rT3 mice. Importantly, expression of the cleavage-resistant D314E mutant delays transgene-induced tau accumulation in the postsynaptic density, brain atrophy, hippocampal neurodegeneration, and spatial memory impairment, without altering age-related progression of pathologic tau conformation and phosphorylation. Our comprehensive investigation of age-dependent disease phenotypes associated with the htau P301L variant in precisely engineered FTD-modeling mice unveils a transiently protective effect of blocking htau cleavage at D314. Findings of this study advance our understanding of the contribution of this tau cleavage to the pathogenesis of FTD, and aid the development of effective dementia-targeting therapies.SIGNIFICANCE STATEMENT A site-specific and caspase-2-mediated cleavage of human tau plays a pathologic role in dementia. In this study, we investigate the contribution of this cleavage to the pathogenesis of frontotemporal dementia (FTD) using two genetically matched, tau-transgene targeted-insertion mouse lines that differ only by a cleavage-resistant mutation. The use of these mice avoids confounding effects associated with the random integration of tau transgenes to the mouse genome and allows us to comprehensively evaluate the impact of the tau cleavage on FTD phenotypes. Our data reveal that blocking this tau cleavage delays memory impairment and neurodegeneration of FTD-modeling mice. These findings improve our understanding of the pathogenic mechanisms underlying FTD and will facilitate the development of effective therapeutics.
Assuntos
Demência Frontotemporal , Animais , Caspase 2/genética , Modelos Animais de Doenças , Feminino , Demência Frontotemporal/genética , Humanos , Masculino , Transtornos da Memória , Camundongos , Camundongos Transgênicos , Fenótipo , Proteínas tau/genética , Proteínas tau/metabolismoRESUMO
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
RESUMO
Neurofibrillary tangles are a pathological hallmark of Alzheimer's disease, and their levels correlate with the severity of cognitive dysfunction in humans. However, experimental evidence suggests that soluble tau species cause cognitive deficits and memory impairment. Our recent study suggests that caspase-2 (Casp2)-catalyzed tau cleavage at aspartate 314 mediates synaptic dysfunction and memory impairment in mouse and cellular models of neurodegenerative disorders. Δtau314, the C-terminally-truncated cleavage products, are soluble and present in human brain. In addition, levels of Δtau314 proteins are elevated in the brain of the cognitively impaired individuals compared to the cognitively normal individuals, indicating a possible role for Δtau314 proteins in cognitive deterioration. Here we show that (1) Δtau314 proteins are present in the inferior temporal gyrus of human brains; (2) Δtau314 proteins are generated from all six tau splicing isoforms, (3) levels of both Casp2 and Δtau314 proteins are elevated in cognitively impaired individuals compared to cognitively normal individuals, and (4) levels of Δtau314 proteins show a modest predictive value for dementia. These findings advance our understanding of the characteristics of Δtau314 proteins and their relevance to cognitive dysfunction and shed light on the contribution of Casp2-mediated Δtau314 production to cognitive deterioration.
Assuntos
Doença de Alzheimer/metabolismo , Disfunção Cognitiva/metabolismo , Lobo Temporal/metabolismo , Proteínas tau/metabolismo , Doença de Alzheimer/genética , Doença de Alzheimer/patologia , Animais , Caspase 2/genética , Caspase 2/metabolismo , Disfunção Cognitiva/genética , Disfunção Cognitiva/patologia , Cisteína Endopeptidases/genética , Cisteína Endopeptidases/metabolismo , Feminino , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Lobo Temporal/patologia , Proteínas tau/genéticaRESUMO
Lewy body diseases are neurodegenerative disorders characterized by Lewy bodies in the brain. Lewy body dementia (LBD) refers to two forms of Lewy body disease: Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB). Tau is a cytoskeletal protein found in neurofibrillary tangles, but not Lewy bodies. The gene encoding tau, MAPT, is a well-established genetic risk factor for LBD; odds ratios of the H1:H2 MAPT haplotypes have been reported in the range of 2 to 4. Despite this genetic association, the mechanism by which tau contributes to dementia is unclear. Recently, a soluble form of tau, Δtau314, which is generated when caspase-2 (Casp2) cleaves tau at Asp314, was reported to be associated with impaired cognition in mice modeling frontotemporal dementia, and with mild cognitive impairment and Alzheimer's disease (AD) in humans. To investigate whether Δtau314 is associated with dementia in Lewy body disease, we compared Δtau314 levels in aqueous extracts from the superior temporal gyrus of pathologically confirmed LBD (n = 21) and non-dementia Parkinson's disease (PD) (n = 12). We excluded subjects with AD or microvascular pathology, which could mask potential associations of Δtau314 with LBD.Using a Δtau314-specific ELISA, we found ~ 2-fold higher levels of Δtau314 in LBD relative to PD (p = 0.009). Additionally, we found ~40% lower levels of soluble total tau and the neuronal marker ß-III-tubulin in LBD. These results suggest that in LBD, there is substantial neuron loss or axonal degeneration in the neocortex but disproportionately high levels of Δtau314 in the surviving neurons.Our results indicate an association between Δtau314 and dementia in Lewy body disease. Cleavage of tau by Casp2 promotes the mislocalization of tau to dendritic spines leading to a reduction in postsynaptic AMPA receptors and excitatory neurotransmission, which suggests a mechanism of the synaptic dysfunction underlying cognitive impairment in LBD. These findings support the potential of Casp2 as a novel drug target for treating LBD.
Assuntos
Encéfalo/metabolismo , Encéfalo/patologia , Caspase 2/metabolismo , Cisteína Endopeptidases/metabolismo , Doença por Corpos de Lewy/metabolismo , Doença por Corpos de Lewy/patologia , Proteínas tau/metabolismo , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Masculino , Emaranhados Neurofibrilares/metabolismo , Emaranhados Neurofibrilares/patologia , Neurônios/metabolismo , Neurônios/patologiaRESUMO
Amyloid-ß (Aß) oligomers, found in the brains of Alzheimer's disease (AD) patients and transgenic mouse models of AD, cause synaptotoxicity and memory impairment. Grape seed polyphenolic extract (GSPE) inhibits Aß oligomerization in vitro and attenuates cognitive impairment and AD-related neuropathology in the brains of transgenic mice. In the current study, GSPE was administered to Tg2576 mice for a period of five months. Treatment significantly decreased brain levels of Aß*56, a 56-kDa Aß oligomer previously shown to induce memory dysfunction in rodents, without changing the levels of transgenic amyloid-ß protein precursor, monomeric Aß, or other Aß oligomers. These results thus provide the first demonstration that a safe and affordable intervention can lower the levels of a memory-impairing Aß oligomer in vivo and strongly suggest that GSPE should be further tested as a potential prevention and/or therapy for AD.