Aggregates In Human Brain Research Articles

Specific post-translational modifications of soluble tau protein distinguishes Alzheimer’s disease and primary tauopathies

Tau protein aggregates in several neurodegenerative disorders, referred to as tauopathies. The tau isoforms observed in post mortem human brain aggregates is used to classify tauopathies. However, distinguishing tauopathies ante mortem remains challenging, potentially due to differences between insoluble tau in aggregates and soluble tau in body fluids. Here, we demonstrated that tau isoforms differ between tauopathies in insoluble aggregates, but not in soluble brain extracts. We therefore characterized post-translational modifications of both the aggregated and the soluble tau protein obtained from post mortem human brain tissue of patients with Alzheimer’s disease, cortico-basal degeneration, Pick’s disease, and frontotemporal lobe degeneration. We found specific soluble signatures for each tauopathy and its specific aggregated tau isoforms: including ubiquitination on Lysine 369 for cortico-basal degeneration and acetylation on Lysine 311 for Pick’s disease. These findings provide potential targets for future development of fluid-based biomarker assays able to distinguish tauopathies in vivo.

Physiological Consequences of Targeting 14-3-3 and Its Interacting Partners in Neurodegenerative Diseases.

The mammalian 14-3-3 family comprises seven intrinsically unstructured, evolutionarily conserved proteins that bind >200 protein targets, thereby modulating cell-signaling pathways. The presence of 14-3-3 proteins in cerebrospinal fluid provides a sensitive and specific biomarker of neuronal damage associated with Alzheimer’s disease (AD), Creutzfeldt−Jakob disease (CJD), spongiform encephalitis, brain cancers, and stroke. We observed significant enrichment of 14-3-3 paralogs G, S, and Z in human brain aggregates diagnostic of AD. We used intra-aggregate crosslinking to identify 14-3-3 interaction partners, all of which were significantly enriched in AD brain aggregates relative to controls. We screened FDA-approved drugs in silico for structures that could target the 14-3-3G/hexokinase interface, an interaction specific to aggregates and AD. C. elegans possesses only two 14-3-3 orthologs, which bind diverse proteins including DAF-16 (a FOXO transcription factor) and SIR-2.1 (a sensor of nutrients and stress), influencing lifespan. Top drug candidates were tested in C. elegans models of neurodegeneration-associated aggregation and in a human neuroblastoma cell-culture model of AD-like amyloidosis. Several drugs opposed aggregation in all models assessed and rescued behavioral deficits in C. elegans AD-like neuropathy models, suggesting that 14-3-3 proteins are instrumental in aggregate accrual and supporting the advancement of drugs targeting 14-3-3 protein complexes with their partners.

Developing therapeutic protein disaggregases for Neurodegenerative Disease

The accumulation of abnormal protein aggregates in human brain is connected with neurodegenerative diseases. The mammalian protein‐disaggregase system comprised of Hsp110, Hsp70, and Hsp40 can protect cells from proteinopathies. However, this disaggregase system has limitations and its activity declines with age. As a therapeutic strategy for neurodegenerative disease we propose to introduce an exogenous, synthetic disaggregase machinery, based on Hsp104 that converts amyloid to soluble, functional protein. Hsp104 is a hexameric AAA+ ATPase that is critical for stress tolerance in yeast by facilitating the resolubilization of stress‐damaged, aggregated proteins. The homologues of Hsp104 are highly conserved in bacteria, fungi, and plants, but absent from metazoa. The disaggregase activity of Hsp104 can be enhanced by the presence Hsp70 and Hsp40. Hsp104 can dissolve α‐synuclein, β‐amyloid, and TDP‐43 aggregates, but impractically high Hsp104 concentrations are needed. We aim to rationally design potentiated Hsp104 variants that can reverse protein misfolding at low concentrations. One potential problem for the currently discovered potentiated Hsp104 variants is their “off‐target” effects, where expression potentiated Hsp104 variant in ∆hsp104 yeast causes cell death possibly by unfolding metastable proteins at 37°C. By investigating the mechanism of Hsp104 disaggregation and its structural basis, we will engineer and evolve potentiated Hsp104 variants with minimized “off‐target” effect that eradicate α‐synuclein, β‐amyloid, or TDP‐43 misfolding and toxicity. We have exploited new cryo‐EM structures of Hsp104 to engineer key interfaces to yield several novel Hsp104 variants with tunable activity, which can reverse protein aggregation in the presence or absence of human Hsp70 and Hsp40. These novel Hsp104 variants effectively rescue the aggregation and toxicity of diverse human neurodegenerative disease proteins and could have therapeutic utility. Moreover, our engineered Hsp104 variants provide key mechanistic insights into disaggregase function.

Developing therapeutic protein disaggregases for neurodegenerative disease

AbstractBackgroundThe accumulation of abnormal protein aggregates in human brain is connected with neurodegenerative diseases. The mammalian protein‐disaggregase system comprised of Hsp110, Hsp70, and Hsp40 can protect cells from proteinopathies. However, this disaggregase system has limitations and its activity declines with age. As a therapeutic strategy for neurodegenerative disease we propose to introduce an exogenous, synthetic disaggregase machinery, based on Hsp104 that converts amyloid to soluble, functional protein. Hsp104 is a hexameric AAA+ ATPase that is critical for stress tolerance in yeast by facilitating the resolubilization of stress‐damaged, aggregated proteins. The homologues of Hsp104 are highly conserved in bacteria, fungi, and plants, but absent from metazoa. The disaggregase activity of Hsp104 can be enhanced by the presence Hsp70 and Hsp40. Hsp104 can dissolve α‐synuclein, β‐amyloid, and TDP‐43 aggregates, but impractically high Hsp104 concentrations are needed.MethodNimble yeast models are used to perform an initial evaluation to enhance experimental efficiency. Promising variants will be purified for further characterization and will be advanced to neuronal and glial cell models.ResultWe have engineered and evolved potentiated Hsp104 variants with minimized “off‐target” effect that eradicate α‐synuclein, β‐amyloid, or TDP‐43 misfolding and toxicity. We have discovered Hsp104 variant that reverse TDP‐43 toxicity specifically with no "off‐target" effect. We have exploited new cryo‐EM structures of Hsp104 to engineer key interfaces to yield several novel Hsp104 variants with tunable activity, which can reverse protein aggregation in the presence or absence of human Hsp70 and Hsp40.ConclusionThese novel Hsp104 variants effectively rescue the aggregation and toxicity of diverse human neurodegenerative disease proteins and could have therapeutic utility.

STochastic Optical Reconstruction Microscopy (STORM) reveals the nanoscale organization of pathological aggregates in human brain.

AimsHistological analysis of brain tissue samples provides valuable information about the pathological processes leading to common neurodegenerative disorders. In this context, the development of novel high‐resolution imaging approaches is a current challenge in neuroscience.MethodsTo this end, we used a recent super‐resolution imaging technique called STochastic Optical Reconstruction Microscopy (STORM) to analyse human brain sections. We combined STORM cell imaging protocols with neuropathological techniques to image cryopreserved brain samples from control subjects and patients with neurodegenerative diseases.ResultsThis approach allowed us to perform 2D‐, 3D‐ and two‐colour‐STORM in neocortex, white matter and brainstem samples. STORM proved to be particularly effective at visualizing the organization of dense protein inclusions and we imaged with a <50 nm resolution pathological aggregates within the central nervous system of patients with Alzheimer’s disease, Parkinson’s disease, Lewy body dementia and fronto‐temporal lobar degeneration. Aggregated Aβ branches appeared reticulated and cross‐linked in the extracellular matrix, with widths from 60 to 240 nm. Intraneuronal Tau and TDP‐43 inclusions were denser, with a honeycomb pattern in the soma and a filamentous organization in the axons. Finally, STORM imaging of α‐synuclein pathology revealed the internal organization of Lewy bodies that could not be observed by conventional fluorescence microscopy.ConclusionsSTORM imaging of human brain samples opens further gates to a more comprehensive understanding of common neurological disorders. The convenience of this technique should open a straightforward extension of its application for super‐resolution imaging of the human brain, with promising avenues to current challenges in neuroscience.

Molecular Cloning of Synucleins in River Lamprey Lampetra fluviatilis

Synaptic proteins synucleins are found in pathologic aggregates in human brain during neurodegenerative diseases and in some tumors. Normal functions of these proteins in synapses are still unclear. In the present study, we used cDNA cloning to determine amino acid sequences of synucleins in the central nervous system of river lamprey (Lampetra fluviatilis), which is used as a model organism to study molecular mechanisms of synaptic transmission. Three genes are identified. High similarity in amino acid sequences as compared to other vertebrate species is revealed. The bioinformatic analysis predicts that the river lamprey synucleins relate to the group of gamma-synucleins. High homology with human alpha-synuclein is reported. The hydrophobic region required for the formation of alpha-synuclein amyloid fibers is also present in the river lamprey synucleins. The latter suggests that this region appeared at early stages of evolution. The obtained amino acid sequences of synucleins in the river lamprey brain will allow generating novel molecular tools for dissecting physiological functions of these proteins.

Prion Disease Induces Alzheimer Disease-Like Neuropathologic Changes.

We examined the brains of 266 patients with prion disease (PrionD) and found that 46 patients (17%) had Alzheimer disease (AD)-like changes. To explore potential mechanistic links between PrionD and AD, we exposed human brain aggregates (BrnAggs) to a brain homogenate from a patient with sporadic Creutzfeldt-Jakob disease and found that neurons in human BrnAggs produced many β-amyloid (Aβ; Aβ42) inclusions, whereas uninfected control-exposed human BrnAggs did not. Western blot analysis of 20 pooled Creutzfeldt-Jakob disease-infected BrnAggs verified Aβ42 levels higher than those in controls. We next examined the CA1 region of the hippocampus from 14 patients with PrionD and found that 5 patients had low levels of scrapie-associated prion protein (PrP), many Aβ42 intraneuronal inclusions, low apolipoprotein E-4 (APOE-4), and no significant nerve cell loss. Seven patients had high levels of PrP, low Aβ42, high APOE-4, and 40% nerve cell loss, suggesting that APOE-4 and PrP together cause neuron loss in PrionD. There were also increased levels of hyperphosphorylated tau protein (Hτ) and Hτ-positive neuropil threads and neuron bodies in both PrionD and AD groups. The brains of 6 age-matched control patients without dementia did not contain Aβ42 deposits; however, there were rare Hτ-positive threads in 5 controls, and 2 controls had few Hτ-positive nerve cell bodies. We conclude that PrionD may trigger biochemical changes similar to those triggered by AD and suggest that PrionD is a disease involving PrP, Aβ42, APOE-4, and abnormal tau.

Upregulation of NRG-1 and VAMP-1 in human brain aggregates exposed to clozapine

Growing genetic evidence has implicated a role for neuregulin-1 (NRG-1) in schizophrenia pathogenesis as well as alterations in SNAP receptor (SNARE) proteins at both gene and protein levels in post-mortem investigations. In relation to a potential therapeutic mechanism for atypical antipsychotic medications, clozapine has been shown to increase both NRG-1 levels and synaptic markers in rodents. As evidence continues to mount for a potential restoration in connectivity by antipsychotic medications being a mode of efficacy we chose to examine the effects of the atypical antipsychotic clozapine and the typical antipsychotic haloperidol on NRG-1 and SNARE protein transcripts in human brain aggregates exposed to plasma levels chronically for a period of three weeks. At the end of this exposure period we performed quantitative real-time PCR to investigate the mRNA levels of NRG-1, VAMP-1 and SNAP-25. Overall we found that clozapine had the ability to upregulate NRG-1 (+3.58 fold change) and VAMP-1 (+1.92) while SNAP-25 remained unchanged. Changes for haloperidol exposed aggregates were below our cut-off of +1.5. Overall the results of our investigation lend further support to atypical antipsychotic medications having the potential to increase levels of neurotrophic and synaptic markers such as NRG-1 and VAMP-1, the former being a strong candidate susceptibility gene for schizophrenia. In the absence of frank neuronal loss in schizophrenia, restoration of neuronal and synaptic functions by atypical antipsychotics in the brains of schizophrenics maybe a key mechanism of therapeutic efficacy by re-establishing normal connectivity and functioning.

Microarray analysis of cultured human brain aggregates following cortisol exposure: Implications for cellular functions relevant to mood disorders

Increased cortisol levels in humans are often observed in patients suffering from mood disorders. In this study human fetal brain aggregates were exposed to cortisol at 500 nM for 3 weeks, as an in-vitro model of chronic cortisol exposure. Microarray analysis on extracted mRNA using the Affymetrix U133A platform was then performed. Our results demonstrated a significant effect of cortisol on 1648 transcripts; 736 up-regulated and 912 down-regulated genes. The most differentially regulated biological categories were: RNA processing, protein metabolism, and cell growth. Within these categories we observed a down-regulation of fibroblast growth factor 2 (FGF2) (-1.5-fold) and aquaporin4 (AQP4) (-1.7-fold), alongside an up-regulation of fibroblast growth factor 9 (FGF9) (+1.7-fold) and vesicle associated membrane protein2 (VAMP2) (+1.7-fold). FGF2, FGF9, AQP4 and VAMP2 changes were confirmed at the protein level by immunohistochemistry. Alterations in FGF transcripts are in keeping with recent literature demonstrating such effects in patients with mood disorders.

HIV-1 Tat inhibits neprilysin and elevates amyloid β

Aging is a risk factor for amyloid beta (Abeta) accumulation and dementia. Since highly active antiretroviral therapies have effectively lengthened the life expectancy of individuals infected with HIV-1, we investigated the affect of HIV-1 Tat, a viral transactivating transcription factor, on Abeta degradation in the brain by neprilysin (NEP), a neuronal endopeptidase. Using neural cell membrane fractions from human brain aggregates, Tat inhibition of NEP activity was assessed in a fluorescence assay. Following treatment with Tat, conditioned medium of human brain aggregate cultures was assayed for Abeta1-40 by ELISA. We evaluated the potential consequence of Tat inhibition of NEP by immunostaining cortex sections from postmortem human brain for Abeta. In an in vitro assay, Tat inhibited NEP activity by 80%. The cysteine-rich domain of Tat was essential for NEP inhibition. Recombinant Tat added directly to brain cultures, resulted in a 125% increase in soluble Abeta. Postmortem human brain sections from patients with HIV-1 infection (n = 14; 31-58 years old) had a significant increase in Abeta, compared to controls (n = 5; 30-52 years old). Correlative analysis identified a statistically significant relationship between Abeta load and duration of HIV-1 seropositive status. We have shown that Tat, which is found in the brains of patients with HIV-1 infection, inhibits the Abeta-degrading enzyme, NEP. Abeta staining was significantly increased in human brain sections from individuals with HIV-1 infection compared to controls. These results have important implications for individuals living and aging with HIV-1 infection.

Granulocyte-macrophage colony-stimulating factor enhances viral load in human brain tissue: amelioration with stavudine.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is elevated in cerebrospinal fluid in HIV- associated dementia; in addition, therapeutic GM-CSF elevates plasma viral load. To assess the effect of GM-CSF on viral replication and the potential ameliorative effect of antiretroviral therapy. A primary human brain aggregate system is used as a model of the in vivo situation. Cultured aggregates were infected with the macrophage tropic strain HIV-1SF162 and then exposed to varying GM-CSF concentrations and 0.3 micromol/l stavudine. Viral replication was assessed by p24 expression in the supernatant and aggregates. Immunohistochemistry identified neurons, astrocytes, microglia and oligodendrocytes. A GM-CSF concentration of 1 ng/ml resulted in a fivefold increase in microglial cells, the main HIV cellular reservoir (P = 0.0001). Prior GM-CSF exposure before infection of the aggregates resulted in sixfold increase in p24 levels compared with non-GM-CSF-exposed infected aggregates. Infected aggregates with or without GM-CSF had significant neuronal loss of 50% and 45%, respectively, and astrocytosis. Addition of stavudine to the infected aggregates, even in the presence of GM-CSF, reduced p24 levels to zero and prevented neuronal loss and astrocytosis. This study demonstrates that GM-CSF enhances viral replication while addition of stavudine prevents this potentially detrimental process.

Interleukin-1beta up-regulates expression of neurofilament light in human neuronal cells.

Elevated expression of interleukin-1 (IL-1beta), a pro-inflammatory cytokine secreted by activated microglia, is a pathogenic marker of numerous neurodegenerative processes including Alzheimer's disease (AD). We have characterized a link between IL-1beta and the 68-kDa neurofilament light (NF-L) protein, which is a major component of the neuronal cytoskeleton. Using human brain aggregate cultures, we found that IL-1beta treatment significantly increased NF-L expression in primary neurons. Analysis of mRNA levels demonstrated elevated NF-L expression within 72 h while imaging of neurons by immunofluorescent staining for NF-L confirmed IL-1beta-induced NF-L protein expression. These observations suggest a potential inflammatory-induced mechanism for deregulation of an important cytoskeletal protein, NF-L, possibly leading to neuronal dysfunction.

Differential modulation of cell death proteins in human brain cells by tumor necrosis factor alpha and platelet activating factor.

Programmed cell death contributes to the morbidity and mortality of several neurological disorders including stroke, Alzheimer's disease and human immunodeficiency virus (HIV)-associated dementia. Patients with HIV dementia show evidence of programmed cell death in brain. In vitro data demonstrates several neurotoxic products of macrophage infection that cause neural cell death, including tumor necrosis factor alpha (TNFalpha) and platelet activating factor (PAF). We treated human brain aggregate cultures with these cytokines and determined their effect on the mRNA and protein levels for Bcl-2, Bcl(x) and Bax alpha. TNFalpha and PAF differentially regulate the Bcl-2 family of proteins at a post-transcriptional level. Following TNFalpha treatment, Bcl-2 protein is significantly decreased, and at least one additional Bax isomer emerges. Bcl(xL) protein is slightly increased after treatment with either cytokine. We demonstrated that overexpression of Bcl-2 in brain aggregate cultures protects cells from TNFalpha-induced damage but has no effect on cell damage induced by PAF. We conclude that Bcl-2 and Bax alpha proteins play significant roles in modulating neural cell death from TNFalpha- but not from PAF-induced cell damage.

Human cytomegalovirus induces IL-6 and TNF alpha from macrophages and microglial cells: possible role in neurotoxicity.

Human cytomegalovirus (HCMV) can frequently infect the central nervous system (CNS) in the setting of immunosuppression such as transplantation and infection with the human immunodeficiency virus (HIV). Our laboratory previously reported that HCMV infection of human brain aggregates preferentially infected a microglial/macrophage (M/M) and caused a neuropathology that differed between strains and could occur in the absence of antigen expression. We extended these studies by infecting a human brain cell aggregate model with four low passage clinical isolates of HCMV. Two patterns of cytopathology emerged after infection; a lacy eosinophilic appearance or a glial nodular formation concomitant with a decreased aggregate size. None of the infections were positive for HCMV antigen; however, all were positive for HCMV DNA. We also infected primary macrophages and microglial cells with the same HCMV isolates. Microglial cells were more susceptible to HCMV infection resulting in a lytic infection. Production of potentially neurotoxic cytokines, IL-1, IL-6 and TNF alpha, from HCMV-infected macrophages and microglial cells were evaluated to explain brain aggregate cytopathology. Supernatants from HCMV-infected macrophages and microglial cells produced similar levels of TNF alpha (< 30 pg ml-1) but showed strain and cell source variation in the production of IL-6; microglial cultures produced > 4 fold higher levels. None of the supernatants contained IL-1. Treatment of brain aggregates with either IL-6 or TNF alpha resulted in morphologic alterations and/or a decrease in size consistent with HCMV infection or supernatant treatment.

Purified trichosanthin (GLQ223®) exacerbation of indirect HIV-associated neurotoxicity in vitro

A formulated preparation of trichosanthin (GLQ223, Pharmaceutical Development Group, Genelabs Inc., Redwood City, California, USA) has been shown to selectively inhibit HIV replication in vitro in lymphocytes and macrophages. In view of recent anecdotal reports of central nervous system (CNS) complications associated with trichosanthin use in some HIV-infected patients, we evaluated any potential drug effects leading to neurotoxicity using a human brain cell aggregate model. Brain cell aggregate cultures were incubated with dilutions of purified trichosanthin alone (trichosanthin), supernatants of HIV-infected macrophage cultures (S-HIV), supernatants of uninfected macrophage cultures (S-U), supernatants of purified trichosanthin-treated uninfected macrophage cultures (S-trichosanthin), or supernatants of purified trichosanthin-treated HIV-infected macrophage cultures (S-HIV-trichosanthin). Treatment with purified trichosanthin alone at up to 2 micrograms/ml, with S-U or with S-trichosanthin, produced no morphological signs of toxicity to brain cell aggregate cultures. S-trichosanthin treatment at 2 micrograms/ml did not result in a significant change in cyclic nucleoside phosphorylase (CNP) activity. Treatment of the brain aggregates with S-HIV and S-HIV-trichosanthin did, however, result in morphological alteration of the brain aggregates, with S-HIV-trichosanthin-treated brain aggregates showing the most severe damage. Although purified trichosanthin did not appear to be directly toxic to human brain aggregate cultures, trichosanthin treatment of infected macrophages may have increased the morphological alterations caused by supernatants of HIV-infected macrophages. These experimental observations may explain anecdotal reports of adverse CNS reactions in association with trichosanthin treatment of HIV-infected patients and emphasize the neurotoxic potential of any therapy targeted at HIV-infected macrophages.

Human immunodeficiency virus-infected macrophages produce soluble factors that cause histological and neurochemical alterations in cultured human brains.

We wanted to establish an in vitro human model for AIDS-associated dementia and pursue the hypothesis that this disease process may be a result of soluble factors produced by HIV-infected macrophages. Human brain aggregates were prepared from nine different brain specimens, and were treated with supernatants from in vitro HIV-infected macrophages (SI), uninfected macrophages (SU), infected T cells, or macrophage-conditioned media from four AIDS patients. Seven of nine treated brains exposed to SI showed peripheral rarefaction after 1 wk of incubation that by ultrastructural analysis showed cytoplasmic vacuolation. Aggregates from two of three brain cultures treated with SI for 3 wk became smaller, an approximately 50% decrease in size. The degree of apparent toxicity in brains exposed to patient-derived macrophage supernatants paralleled the proportion of macrophages found to be expressing HIV p24. Ultrastructural abnormalities were not observed in brains treated with supernatants from HIV-infected T cells, uninfected macrophages, or LPS-activated macrophages. Levels of five neurotransmitter amino acids were decreased in comparison to the structural amino acid leucine. These findings suggest that HIV-infected macrophages, infected both in vitro as well as derived from AIDS patients' peripheral blood, produce factors that cause reproducible histochemical, ultrastructural, and functional abnormalities in human brain aggregates.