A novel lysosome-to-mitochondria signaling pathway disrupted by amyloid-? oligomers.
ABSTRACT: The mechanisms of mitochondrial dysfunction in Alzheimer's disease are incompletely understood. Using two-photon fluorescence lifetime microscopy of the coenzymes, NADH and NADPH, and tracking brain oxygen metabolism with multi-parametric photoacoustic microscopy, we show that activation of lysosomal mechanistic target of rapamycin complex 1 (mTORC1) by insulin or amino acids stimulates mitochondrial activity and regulates mitochondrial DNA synthesis in neurons. Amyloid-? oligomers, which are precursors of amyloid plaques in Alzheimer's disease brain and stimulate mTORC1 protein kinase activity at the plasma membrane but not at lysosomes, block this Nutrient-induced Mitochondrial Activity (NiMA) by a mechanism dependent on tau, which forms neurofibrillary tangles in Alzheimer's disease brain. NiMA was also disrupted in fibroblasts derived from two patients with tuberous sclerosis complex, a genetic disorder that causes dysregulation of lysosomal mTORC1. Thus, lysosomal mTORC1 couples nutrient availability to mitochondrial activity and links mitochondrial dysfunction to Alzheimer's disease by a mechanism dependent on the soluble building blocks of the poorly soluble plaques and tangles.
Project description:The mechanisms of mitochondrial dysfunction in Alzheimer's disease are incompletely understood. Using two-photon fluorescence lifetime microscopy of the coenzymes, NADH and NADPH, and tracking brain oxygen metabolism with multi-parametric photoacoustic microscopy, we show that activation of lysosomal mechanistic target of rapamycin complex 1 (mTORC1) by insulin or amino acids stimulates mitochondrial activity and regulates mitochondrial DNA synthesis in neurons. Amyloid-β oligomers, which are precursors of amyloid plaques in Alzheimer's disease brain and stimulate mTORC1 protein kinase activity at the plasma membrane but not at lysosomes, block this Nutrient-induced Mitochondrial Activity (NiMA) by a mechanism dependent on tau, which forms neurofibrillary tangles in Alzheimer's disease brain. NiMA was also disrupted in fibroblasts derived from two patients with tuberous sclerosis complex, a genetic disorder that causes dysregulation of lysosomal mTORC1. Thus, lysosomal mTORC1 couples nutrient availability to mitochondrial activity, and links mitochondrial dysfunction to Alzheimer's disease by a mechanism dependent on the soluble building blocks of the poorly soluble plaques and tangles.
Project description:A major obstacle to presymptomatic diagnosis and disease-modifying therapy for Alzheimer's disease (AD) is inadequate understanding of molecular mechanisms of AD pathogenesis. For example, impaired brain insulin signaling is an AD hallmark, but whether and how it might contribute to the synaptic dysfunction and neuron death that underlie memory and cognitive impairment has been mysterious. Neuron death in AD is often caused by cell cycle reentry (CCR) mediated by amyloid-? oligomers (A?Os) and tau, the precursors of plaques and tangles. We now report that CCR results from A?O-induced activation of the protein kinase complex, mTORC1, at the plasma membrane and mTORC1-dependent tau phosphorylation, and that CCR can be prevented by insulin-stimulated activation of lysosomal mTORC1. A?Os were also shown previously to reduce neuronal insulin signaling. Our data therefore indicate that the decreased insulin signaling provoked by A?Os unleashes their toxic potential to cause neuronal CCR, and by extension, neuron death.
Project description:We studied Alzheimer's disease (AD) pathology in the precuneus and surrounding brain areas. Anatomically, the precuneus corresponds to the medial portion of human cerebral cortical Brodmann Area 7. This study utilized patients from the University of Kentucky Alzheimer's Disease Center autopsy cohort. Data from 47 brains were used comprising patients of differing antemortem cognitive impairment severities, each with longitudinal clinical data and extensive neuropathological data. We assessed whether the precuneus and surrounding areas are differentially vulnerable to AD-type pathological lesions (diffuse amyloid plaques, neuritic amyloid plaques, and neurofibrillary tangles). Eleven areas of brain were evaluated for each case: amygdala, hippocampal CA1, subiculum, entorhinal cortex, frontal cortex, superior and middle temporal gyri, inferior parietal lobule, occipital cortex, posterior cingulate gyrus, Brodmann Area 31, and the precuneus proper. Like other areas of neocortex, the precuneus demonstrated increased diffuse and neuritic amyloid plaques early in the evolution in AD, and increased neurofibrillary tangles late in AD. Correcting for the antemortem cognitive status of the patients, there was no evidence of an increase in the density of AD-type pathology in the precuneus or neighboring areas relative to other areas of cerebral neocortex. Our results are not consistent with the idea that the precuneus is involved in a special way with plaques or tangles relative to other areas of neocortex.
Project description:Alzheimer's disease is the commonest cause of dementia in the elderly, but its pathological determinants are still debated. Amyloid-? plaques and neurofibrillary tangles have been implicated either directly as disruptors of neural function, or indirectly by precipitating neuronal death and thus causing a reduction in neuronal number. Alternatively, the initial cognitive decline has been attributed to subtle intracellular events caused by amyloid-? oligomers, resulting in dementia after massive synaptic dysfunction followed by neuronal degeneration and death. To investigate whether Alzheimer's disease is associated with changes in the absolute cell numbers of ageing brains, we used the isotropic fractionator, a novel technique designed to determine the absolute cellular composition of brain regions. We investigated whether plaques and tangles are associated with neuronal loss, or whether it is dementia that relates to changes of absolute cell composition, by comparing cell numbers in brains of patients severely demented with those of asymptomatic individuals-both groups histopathologically diagnosed as Alzheimer's-and normal subjects with no pathological signs of the disease. We found a great reduction of neuronal numbers in the hippocampus and cerebral cortex of demented patients with Alzheimer's disease, but not in asymptomatic subjects with Alzheimer's disease. We concluded that neuronal loss is associated with dementia and not the presence of plaques and tangles, which may explain why subjects with histopathological features of Alzheimer's disease can be asymptomatic; and exclude amyloid-? deposits as causes for the reduction of neuronal numbers in the brain. We found an increase of non-neuronal cell numbers in the cerebral cortex and subcortical white matter of demented patients with Alzheimer's disease when compared with asymptomatic subjects with Alzheimer's disease and control subjects, suggesting a reactive glial cell response in the former that may be related to the symptoms they present.
Project description:In Alzheimer's disease, aggregates of A? and tau in amyloid plaques and neurofibrillary tangles spread progressively across brain tissues following a characteristic pattern, implying a tissue-specific vulnerability to the disease. We report a transcriptional analysis of healthy brains and identify an expression signature that predicts-at ages well before the typical onset-the tissue-specific progression of the disease. We obtain this result by finding a quantitative correlation between the histopathological staging of the disease and the expression patterns of the proteins that coaggregate in amyloid plaques and neurofibrillary tangles, together with those of the protein homeostasis components that regulate A? and tau. Because this expression signature is evident in healthy brains, our analysis provides an explanatory link between a tissue-specific environmental risk of protein aggregation and a corresponding vulnerability to Alzheimer's disease.
Project description:Alzheimer's disease (AD) is a uniquely human brain disorder characterized by the accumulation of amyloid-beta protein (A?) into extracellular plaques, neurofibrillary tangles (NFT) made from intracellular, abnormally phosphorylated tau, and selective neuronal loss. We analyzed a large group of aged chimpanzees (n = 20, age 37-62 years) for evidence of A? and tau lesions in brain regions affected by AD in humans. A? was observed in plaques and blood vessels, and tau lesions were found in the form of pretangles, NFT, and tau-immunoreactive neuritic clusters. A? deposition was higher in vessels than in plaques and correlated with increases in tau lesions, suggesting that amyloid build-up in the brain's microvasculature precedes plaque formation in chimpanzees. Age was correlated to greater volumes of A? plaques and vessels. Tangle pathology was observed in individuals that exhibited plaques and moderate or severe cerebral amyloid angiopathy, a condition in which amyloid accumulates in the brain's vasculature. Amyloid and tau pathology in aged chimpanzees suggests these AD lesions are not specific to the human brain.
Project description:Alzheimer's disease is the most common form of dementia, characterized by two pathological hallmarks: amyloid-? plaques and neurofibrillary tangles. The amyloid hypothesis of Alzheimer's disease posits that the excessive accumulation of amyloid-? peptide leads to neurofibrillary tangles composed of aggregated hyperphosphorylated tau. However, to date, no single disease model has serially linked these two pathological events using human neuronal cells. Mouse models with familial Alzheimer's disease (FAD) mutations exhibit amyloid-?-induced synaptic and memory deficits but they do not fully recapitulate other key pathological events of Alzheimer's disease, including distinct neurofibrillary tangle pathology. Human neurons derived from Alzheimer's disease patients have shown elevated levels of toxic amyloid-? species and phosphorylated tau but did not demonstrate amyloid-? plaques or neurofibrillary tangles. Here we report that FAD mutations in ?-amyloid precursor protein and presenilin 1 are able to induce robust extracellular deposition of amyloid-?, including amyloid-? plaques, in a human neural stem-cell-derived three-dimensional (3D) culture system. More importantly, the 3D-differentiated neuronal cells expressing FAD mutations exhibited high levels of detergent-resistant, silver-positive aggregates of phosphorylated tau in the soma and neurites, as well as filamentous tau, as detected by immunoelectron microscopy. Inhibition of amyloid-? generation with ?- or ?-secretase inhibitors not only decreased amyloid-? pathology, but also attenuated tauopathy. We also found that glycogen synthase kinase 3 (GSK3) regulated amyloid-?-mediated tau phosphorylation. We have successfully recapitulated amyloid-? and tau pathology in a single 3D human neural cell culture system. Our unique strategy for recapitulating Alzheimer's disease pathology in a 3D neural cell culture model should also serve to facilitate the development of more precise human neural cell models of other neurodegenerative disorders.
Project description:Alzheimer's disease (AD) is an age-related neurodegenerative disorder. The pathology of AD includes amyloid-β (Aβ) deposits in neuritic plaques and neurofibrillary tangles composed of hyperphosphorylated tau, as well as neuronal loss in specific brain regions. Increasing epidemiological and functional neuroimaging evidence indicates that global and regional disruptions in brain metabolism are involved in the pathogenesis of this disease. Aβ precursor protein is cleaved to produce both extracellular and intracellular Aβ, accumulation of which might interfere with the homeostasis of cellular metabolism. Mitochondria are highly dynamic organelles that not only supply the main energy to the cell but also regulate apoptosis. Mitochondrial dysfunction might contribute to Aβ neurotoxicity. In this review, we summarize the pathways of Aβ generation and its potential neurotoxic effects on cellular metabolism and mitochondrial dysfunction.
Project description:Progranulin (PGRN) is a protein encoded by the GRN gene with multiple identified functions including as a neurotrophic factor, tumorigenic growth factor, anti-inflammatory cytokine and regulator of lysosomal function. A single mutation in the human GRN gene resulting in reduced PGRN expression causes types of frontotemporal lobar degeneration resulting in frontotemporal dementia. Prosaposin (PSAP) is also a multifunctional neuroprotective secreted protein and regulator of lysosomal function. Interactions of PGRN and PSAP affect their functional properties. Their roles in Alzheimer's disease (AD), the leading cause of dementia, have not been defined. In this report, we examined in detail the cellular expression of PGRN in middle temporal gyrus samples of a series of human brain cases (n =?45) staged for increasing plaque pathology. Immunohistochemistry showed PGRN expression in cortical neurons, microglia, cerebral vessels and amyloid beta (A?) plaques, while PSAP expression was mainly detected in neurons and A? plaques, and to a limited extent in astrocytes. We showed that there were increased levels of PGRN protein in AD cases and corresponding increased levels of PSAP. Levels of PGRN and PSAP protein positively correlated with amyloid beta (A?), with PGRN levels correlating with phosphorylated tau (serine 205) levels in these samples. Although PGRN colocalized with lysosomal-associated membrane protein-1 in neurons, most PGRN associated with A? plaques did not. A? plaques with PGRN and PSAP deposits were identified in the low plaque non-demented cases suggesting this was an early event in plaque formation. We did not observe PGRN-positive neurofibrillary tangles. Co-immunoprecipitation studies of PGRN from brain samples identified only PSAP associated with PGRN, not sortilin or other known PGRN-binding proteins, under conditions used. Most PGRN associated with A? plaques were immunoreactive for PSAP showing a high degree of colocalization of these proteins that did not change between disease groups. As PGRN supplementation has been considered as a therapeutic approach for AD, the possible involvement of PGRN and PSAP interactions in AD pathology needs to be further considered.
Project description:Alzheimer's disease is characterized by the accumulation of amyloid-beta in plaques, aggregation of hyperphosphorylated tau in neurofibrillary tangles and neuroinflammation, together resulting in neurodegeneration and cognitive decline1. The NLRP3 inflammasome assembles inside of microglia on activation, leading to increased cleavage and activity of caspase-1 and downstream interleukin-1? release2. Although the NLRP3 inflammasome has been shown to be essential for the development and progression of amyloid-beta pathology in mice3, the precise effect on tau pathology remains unknown. Here we show that loss of NLRP3 inflammasome function reduced tau hyperphosphorylation and aggregation by regulating tau kinases and phosphatases. Tau activated the NLRP3 inflammasome and intracerebral injection of fibrillar amyloid-beta-containing brain homogenates induced tau pathology in an NLRP3-dependent manner. These data identify an important role of microglia and NLRP3 inflammasome activation in the pathogenesis of tauopathies and support the amyloid-cascade hypothesis in Alzheimer's disease, demonstrating that neurofibrillary tangles develop downstream of amyloid-beta-induced microglial activation.