The Discovery of SWI/SNF Chromatin Remodeling Activity as a Novel and Targetable Dependency in Uveal Melanoma.

Uveal melanoma is a rare and aggressive cancer that originates in the eye. Currently, there are no approved targeted therapies and very few effective treatments for this cancer. Although activating mutations in the G protein alpha subunits, GNAQ and GNA11, are key genetic drivers of the disease, few additional drug targets have been identified. Recently, studies have identified context-specific roles for the mammalian SWI/SNF chromatin remodeling complexes (also known as BAF/PBAF) in various cancer lineages. Here, we find evidence that the SWI/SNF complex is essential through analysis of functional genomics screens and further validation in a panel of uveal melanoma cell lines using both genetic tools and small-molecule inhibitors of SWI/SNF. In addition, we describe a functional relationship between the SWI/SNF complex and the melanocyte lineage-specific transcription factor Microphthalmia-associated Transcription Factor, suggesting that these two factors cooperate to drive a transcriptional program essential for uveal melanoma cell survival. These studies highlight a critical role for SWI/SNF in uveal melanoma, and demonstrate a novel path toward the treatment of this cancer.

Project DRIVE: A Compendium of Cancer Dependencies and Synthetic Lethal Relationships Uncovered by Large-Scale, Deep RNAi Screening.

Elucidation of the mutational landscape of human cancer has progressed rapidly and been accompanied by the development of therapeutics targeting mutant oncogenes. However, a comprehensive mapping of cancer dependencies has lagged behind and the discovery of therapeutic targets for counteracting tumor suppressor gene loss is needed. To identify vulnerabilities relevant to specific cancer subtypes, we conducted a large-scale RNAi screen in which viability effects of mRNA knockdown were assessed for 7,837 genes using an average of 20 shRNAs per gene in 398 cancer cell lines. We describe findings of this screen, outlining the classes of cancer dependency genes and their relationships to genetic, expression, and lineage features. In addition, we describe robust gene-interaction networks recapitulating both protein complexes and functional cooperation among complexes and pathways. This dataset along with a web portal is provided to the community to assist in the discovery and translation of new therapeutic approaches for cancer.

CRISPR Screens Provide a Comprehensive Assessment of Cancer Vulnerabilities but Generate False-Positive Hits for Highly Amplified Genomic Regions.

UNLABELLED: CRISPR/Cas9 has emerged as a powerful new tool to systematically probe gene function. We compared the performance of CRISPR to RNAi-based loss-of-function screens for the identification of cancer dependencies across multiple cancer cell lines. CRISPR dropout screens consistently identified more lethal genes than RNAi, implying that the identification of many cellular dependencies may require full gene inactivation. However, in two aneuploid cancer models, we found that all genes within highly amplified regions, including nonexpressed genes, scored as lethal by CRISPR, revealing an unanticipated class of false-positive hits. In addition, using a CRISPR tiling screen, we found that sgRNAs targeting essential domains generate the strongest lethality phenotypes and thus provide a strategy to rapidly define the protein domains required for cancer dependence. Collectively, these findings not only demonstrate the utility of CRISPR screens in the identification of cancer-essential genes, but also reveal the need to carefully control for false-positive results in chromosomally unstable cancer lines. SIGNIFICANCE: We show in this study that CRISPR-based screens have a significantly lower false-negative rate compared with RNAi-based screens, but have specific liabilities particularly in the interrogation of regions of genome amplification. Therefore, this study provides critical insights for applying CRISPR-based screens toward the systematic identification of new cancer targets. Cancer Discov; 6(8); 900-13. ©2016 AACR.See related commentary by Sheel and Xue, p. 824See related article by Aguirre et al., p. 914This article is highlighted in the In This Issue feature, p. 803.

Impact of amyloid ß aggregate maturation on antibody treatment in APP23 mice.

INTRODUCTION: The deposition of the amyloid ß protein (Aß) in the brain is a hallmark of Alzheimer's disease (AD). Removal of Aß by Aß-antibody treatment has been developed as a potential treatment strategy against AD. First clinical trials showed neither a stop nor a reduction of disease progression. Recently, we have shown that the formation of soluble and insoluble Aß aggregates in the human brain follows a hierarchical sequence of three biochemical maturation stages (B-Aß stages). To test the impact of the B-Aß stage on Aß immunotherapy, we treated transgenic mice expressing human amyloid precursor protein (APP) carrying the Swedish mutation (KM670/671NL; APP23) with the Aß-antibody ß1 or phosphate-buffered saline (PBS) beginning 1) at 3 months, before the onset of dendrite degeneration and plaque deposition, and 2) at 7 months, after the start of Aß plaque deposition and dendrite degeneration. RESULTS: At 5 months of age, first Aß aggregates in APP23 brain consisted of non-modified Aß (representing B-Aß stage 1) whereas mature Aß-aggregates containing N-terminal truncated, pyroglutamate-modified AßN3pE and phosphorylated Aß (representing B-Aß stage 3) were found at 11 months of age in both ß1- and PBS-treated animals. Protective effects on commissural neurons with highly ramified dendritic trees were observed only in 3-month-old ß1-treated animals sacrificed at 5 months. When treatment started at 7 months of age, no differences in the numbers of healthy commissural neurons were observed between ß1- and PBS-treated APP23 mice sacrificed with 11 months. CONCLUSIONS: Aß antibody treatment was capable of protecting neurons from dendritic degeneration as long as Aß aggregation was absent or represented B-Aß stage 1 but had no protective or curative effect in later stages with mature Aß aggregates (B-Aß stage 3). These data indicate that the maturation stage of Aß aggregates has impact on potential treatment effects in APP23 mice.

Amyloid-ß in the Cerebrospinal Fluid of APP Transgenic Mice Does not Show Prion-like Properties.

Early diagnosis of Alzheimer`s disease (AD) is currently difficult and involves a complex approach including clinical assessment, neuroimaging, and measurement of amyloid-ß (Aß) and tau levels in cerebrospinal fluid (CSF). A better mechanistic understanding is needed to develop more accurate and even presymptomatic diagnostic tools. It has been shown that Aß derived from amyloid-containing brain tissue has prion-like properties: it induces misfolding and aggregation of Aß when injected into human amyloid precursor protein (APP) transgenic mice. In contrast, Aß in the CSF has been less studied, and it is not clear whether it also exhibits prion-like characteristics, which might provide a sensitive diagnostic tool. Therefore, we collected CSF from APP transgenic mice carrying the Swedish mutation (APP23 mice), and injected it intracerebrally into young mice from the same transgenic line. We found that CSF derived Aß did not induce increased ß-amyloidosis, even after long incubation periods and additional concentration. This suggests that Aß present in the CSF does not have the same prion-like properties as the Aß species in the brain.

Early-onset axonal pathology in a novel P301S-Tau transgenic mouse model of frontotemporal lobar degeneration.

AIM: Tau becomes hyperphosphorylated in Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD-tau), resulting in functional deficits of neurones, neurofibrillary tangle (NFT) formation and eventually dementia. Expression of mutant human tau in the brains of transgenic mice has produced different lines that recapitulate various aspects of FTLD-tau and AD. In this study, we characterized the novel P301S mutant tau transgenic mouse line, TAU58/2. METHODS: Both young and aged TAU58/2 mice underwent extensive motor testing, after which brain tissue was analysed with immunohistochemistry, silver staining, electron microscopy and Western blotting. Tissue from various FTLD subtypes and AD patients was also analysed for comparison. RESULTS: TAU58/2 mice presented with early-onset motor deficits, which became more pronounced with age. Throughout the brains of these mice, tau was progressively hyperphosphorylated resulting in increased NFT formation with age. In addition, frequent axonal swellings that stained intensively for neurofilament (NF) were present in young TAU58/2 mice prior to NFT formation. Similar axonal pathology was also observed in human FTLD-tau and AD. Interestingly, activated microglia were found in close proximity to neurones harbouring transgenic tau, but were not associated with NF-positive axonal swellings. CONCLUSIONS: In TAU58/2 mice, early tau pathology induces functional deficits of neurones associated with NF pathology. This appears to be specific to tau, as similar changes are observed in FTLD-tau, but not in FTLD with TDP-43 inclusions. Therefore, TAU58/2 mice recapitulate aspects of human FTLD-tau and AD pathology, and will become instrumental in studying disease mechanisms and therapeutics in the future.

The type of Aß-related neuronal degeneration differs between amyloid precursor protein (APP23) and amyloid ß-peptide (APP48) transgenic mice.

BACKGROUND: The deposition of the amyloid ß-peptide (Aß) in the brain is one of the hallmarks of Alzheimer's disease (AD). It is not yet clear whether Aß always leads to similar changes or whether it induces different features of neurodegeneration in relation to its intra- and/or extracellular localization or to its intracellular trafficking routes. To address this question, we have analyzed two transgenic mouse models: APP48 and APP23 mice. The APP48 mouse expresses Aß1-42 with a signal sequence in neurons. These animals produce intracellular Aß independent of amyloid precursor protein (APP) but do not develop extracellular Aß plaques. The APP23 mouse overexpresses human APP with the Swedish mutation (KM670/671NL) in neurons and produces APP-derived extracellular Aß plaques and intracellular Aß aggregates. RESULTS: Tracing of commissural neurons in layer III of the frontocentral cortex with the DiI tracer revealed no morphological signs of dendritic degeneration in APP48 mice compared to littermate controls. In contrast, the dendritic tree of highly ramified commissural frontocentral neurons was altered in 15-month-old APP23 mice. The density of asymmetric synapses in the frontocentral cortex was reduced in 3- and 15-month-old APP23 but not in 3- and 18-month-old APP48 mice. Frontocentral neurons of 18-month-old APP48 mice showed an increased proportion of altered mitochondria in the soma compared to wild type and APP23 mice. Aß was often seen in the membrane of neuronal mitochondria in APP48 mice at the ultrastructural level. CONCLUSIONS: These results indicate that APP-independent intracellular Aß accumulation in APP48 mice is not associated with dendritic and neuritic degeneration but with mitochondrial alterations whereas APP-derived extra- and intracellular Aß pathology in APP23 mice is linked to dendrite degeneration and synapse loss independent of obvious mitochondrial alterations. Thus, Aß aggregates in APP23 and APP48 mice induce neurodegeneration presumably by different mechanisms and APP-related production of Aß may, thereby, play a role for the degeneration of neurites and synapses.

Mutant huntingtin gene-dose impacts on aggregate deposition, DARPP32 expression and neuroinflammation in HdhQ150 mice.

Huntington's disease (HD) is an autosomal dominant, progressive and fatal neurological disorder caused by an expansion of CAG repeats in exon-1 of the huntingtin gene. The encoded poly-glutamine stretch renders mutant huntingtin prone to aggregation. HdhQ150 mice genocopy a pathogenic repeat (∼150 CAGs) in the endogenous mouse huntingtin gene and model predominantly pre-manifest HD. Treating early is likely important to prevent or delay HD, and HdhQ150 mice may be useful to assess therapeutic strategies targeting pre-manifest HD. This requires appropriate markers and here we demonstrate, that pre-symptomatic HdhQ150 mice show several dramatic mutant huntingtin gene-dose dependent pathological changes including: (i) an increase of neuronal intra-nuclear inclusions (NIIs) in brain, (ii) an increase of extra-nuclear aggregates in dentate gyrus, (iii) a decrease of DARPP32 protein and (iv) an increase in glial markers of neuroinflammation, which curiously did not correlate with local neuronal mutant huntingtin inclusion-burden. HdhQ150 mice developed NIIs also in all retinal neuron cell-types, demonstrating that retinal NIIs are not specific to human exon-1 R6 HD mouse models. Taken together, the striking and robust mutant huntingtin gene-dose related changes in aggregate-load, DARPP32 levels and glial activation markers should greatly facilitate future testing of therapeutic strategies in the HdhQ150 HD mouse model.

Transgenic expression of ß1 antibody in brain neurons impairs age-dependent amyloid deposition in APP23 mice.

Heterologous expression of the functional amyloid beta (Aß) antibody ß1 in the central nervous system was engineered to maximize antibody exposure in the brain and assess the effects on Aß production and accumulation in these conditions. A single open reading frame encoding the heavy and light chains of ß1 linked by the mouth and foot virus peptide 2A was expressed in brain neurons of transgenic mice. Two of the resulting BIN66 transgenic lines were crossed with APP23 mice, which develop severe central amyloidosis. Brain concentrations at steady-state 5 times greater than those found after peripheral ß1 administration were obtained. Similar brain and plasma ß1 concentrations indicated robust antibody efflux from the brain. In preplaque mice, ß1 formed a complex with Aß that caused a modest Aß increase in brain and plasma. At 11 months of age, ß1 expression reduced amyloid by 97% compared with age-matched APP23 mice. Interference of ß1 with ß-secretase cleavage of amyloid precursor protein was relatively small. Our data suggest that severely impaired amyloid formation was primarily mediated by a complex of ß1 with soluble Aß, which might have prevented Aß aggregation or favored transport out of the brain.

The dual orexin receptor antagonist almorexant induces sleep and decreases orexin-induced locomotion by blocking orexin 2 receptors.

STUDY OBJECTIVES: Orexin peptides activate orexin 1 and orexin 2 receptors (OX(1)R and OX(2)R), regulate locomotion and sleep-wake. The dual OX(1)R/OX(2)R antagonist almorexant reduces activity and promotes sleep in multiple species, including man. The relative contributions of the two receptors in locomotion and sleep/wake regulation were investigated in mice. DESIGN: Mice lacking orexin receptors were used to determine the contribution of OX(1)R and OX(2)R to orexin A-induced locomotion and to almorexant-induced sleep. SETTING: N/A. PATIENTS OR PARTICIPANTS: C57BL/6J mice and OX(1)R(+/+), OX(1)R(-/-), OX(2)R(+/+), OX(2)R(-/-) and OX(1)R(-/-)/OX(2)R(-/-) mice. INTERVENTIONS: Intracerebroventricular orexin A; oral dosing of almorexant. MEASUREMENTS AND RESULTS: Almorexant attenuated orexin A-induced locomotion. As in other species, almorexant dose-dependently increased rapid eye movement sleep (REM) and nonREM sleep in mice. Almorexant and orexin A were ineffective in OX(1)R(-/-)/OX(2)R(-/-) mice. Both orexin A-induced locomotion and sleep induction by almorexant were absent in OX(2)R(-/-) mice. Interestingly, almorexant did not induce cataplexy in wild-type mice under conditions where cataplexy was seen in mice lacking orexins and in OX(1)R(-/-)/OX(2)R(-/-) mice. Almorexant dissociates very slowly from OX(2)R as measured functionally and in radioligand binding. Under non equilibrium conditions in vitro, almorexant was a dual antagonist whereas at equilibrium, almorexant became OX(2)R selective. CONCLUSIONS: In vivo, almorexant specifically inhibits the actions of orexin A. The two known orexin receptors mediate sleep induction by almorexant and orexin A-induced locomotion. However, OX(2)R activation mediates locomotion induction by orexin A and antagonism of OX(2)R is sufficient to promote sleep in mice.

Fragments of HdhQ150 mutant huntingtin form a soluble oligomer pool that declines with aggregate deposition upon aging.

Cleavage of the full-length mutant huntingtin (mhtt) protein into smaller, soluble aggregation-prone mhtt fragments appears to be a key process in the neuropathophysiology of Huntington's Disease (HD). Recent quantification studies using TR-FRET-based immunoassays showed decreasing levels of soluble mhtt correlating with an increased load of aggregated mhtt in the aging HdhQ150 mouse brain. To better characterize the nature of these changes at the level of native mhtt species, we developed a detection method that combines size exclusion chromatography (SEC) and time-resolved fluorescence resonance energy transfer (TR-FRET) that allowed us to resolve and define the formation, aggregation and temporal dynamics of native soluble mhtt species and insoluble aggregates in the brain of the HdhQ150 knock-in mouse. We found that mhtt fragments and not full-length mhtt form oligomers in the brains of one month-old mice long before disease phenotypes and mhtt aggregate histopathology occur. As the HdhQ150 mice age, brain levels of soluble full-length mhtt protein remain similar. In contrast, the soluble oligomeric pool of mhtt fragments slightly increases during the first two months before it declines between 3 and 8 months of age. This decline inversely correlates with the formation of insoluble mhtt aggregates. We also found that the pool-size of soluble mhtt oligomers is similar in age-matched heterozygous and homozygous HdhQ150 mouse brains whereas insoluble aggregate formation is greatly accelerated in the homozygous mutant brain. The capacity of the soluble mhtt oligomer pool therefore seems exhausted already in the heterozygous state and likely kept constant by changes in flux and, as a consequence, increased rate of insoluble aggregate formation. We demonstrate that our novel findings in mice translate to human HD brain but not HD patient fibroblasts.

Dispersible amyloid ß-protein oligomers, protofibrils, and fibrils represent diffusible but not soluble aggregates: their role in neurodegeneration in amyloid precursor protein (APP) transgenic mice.

Soluble amyloid ß-protein (Aß) aggregates have been identified in the Alzheimer's disease (AD) brain. Dispersed Aß aggregates in the brain parenchyma are different from soluble, membrane-associated and plaque-associated solid aggregates. They are in mixture with the extra- or intracellular fluid but can be separated from soluble proteins by ultracentrifugation. To clarify the role of dispersible Aß aggregates for neurodegeneration we analyzed 2 different amyloid precursor protein (APP)-transgenic mouse models. APP23 mice overexpress human mutant APP with the Swedish mutation. APP51/16 mice express high levels of human wild type APP. Both mice develop Aß-plaques. Dendritic degeneration, neuron loss, and loss of asymmetric synapses were seen in APP23 but not in APP51/16 mice. The soluble and dispersible fractions not separated from one another were received as supernatant after centrifugation of native forebrain homogenates at 14,000 × g. Subsequent ultracentrifugation separated the soluble, i.e., the supernatant, from the dispersible fraction, i.e., the resuspended pellet. The major biochemical difference between APP23 and APP51/16 mice was that APP23 mice exhibited higher levels of dispersible Aß oligomers, protofibrils and fibrils precipitated with oligomer (A11) and protofibril/fibril (B10AP) specific antibodies than APP51/16 mice. These differences, rather than soluble Aß and Aß plaque pathology were associated with dendritic degeneration, neuron, and synapse loss in APP23 mice in comparison with APP51/16 mice. Immunoprecipitation of dispersible Aß oligomers, protofibrils, and fibrils revealed that they were associated with APP C-terminal fragments (APP-CTFs). These results indicate that dispersible Aß oligomers, protofibrils, and fibrils represent an important pool of Aß aggregates in the brain that critically interact with membrane-associated APP C-terminal fragments. The concentration of dispersible Aß aggregates, thereby, presumably determines its toxicity.

TR-FRET-based duplex immunoassay reveals an inverse correlation of soluble and aggregated mutant huntingtin in huntington's disease.

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by the amplification of a polyglutamine stretch at the N terminus of the huntingtin protein. N-terminal fragments of the mutant huntingtin (mHtt) aggregate and form intracellular inclusions in brain and peripheral tissues. Aggregates are an important hallmark of the disease, translating into a high need to quantify them in vitro and in vivo. We developed a one-step TR-FRET-based immunoassay to quantify soluble and aggregated mHtt in cell and tissue homogenates. Strikingly, quantification revealed a decrease of soluble mHtt correlating with an increase of aggregated protein in primary neuronal cell cultures, transgenic R6/2, and HdhQ150 knock-in HD mice. These results emphasize the assay's efficiency for highly sensitive and quantitative detection of soluble and aggregated mHtt and its application in high-throughput screening and characterization of HD models.

Transgenic expression of intraneuronal Aß42 but not Aß40 leads to cellular Aß lesions, degeneration, and functional impairment without typical Alzheimer's disease pathology.

An early role of amyloid-ß peptide (Aß) aggregation in Alzheimer's disease pathogenesis is well established. However, the contribution of intracellular or extracellular forms of Aß to the neurodegenerative process is a subject of considerable debate. We here describe transgenic mice expressing Aß1-40 (APP47) and Aß1-42 (APP48) with a cleaved signal sequence to insert both peptides during synthesis into the endoplasmic reticulum. Although lower in transgene mRNA, APP48 mice reach a higher brain Aß concentration. The reduced solubility and increased aggregation of Aß1-42 may impair its degradation. APP48 mice develop intracellular Aß lesions in dendrites and lysosomes. The hippocampal neuron number is reduced already at young age. The brain weight decreases during aging in conjunction with severe white matter atrophy. The mice show a motor impairment. Only very few Aß1-40 lesions are found in APP47 mice. Neither APP47 nor APP48 nor the bigenic mice develop extracellular amyloid plaques. While intracellular membrane expression of Aß1-42 in APP48 mice does not lead to the AD-typical lesions, Aß aggregates develop within cells accompanied by considerable neurodegeneration.

Noninvasive magnetic resonance imaging detection of cerebral amyloid angiopathy-related microvascular alterations using superparamagnetic iron oxide particles in APP transgenic mouse models of Alzheimer's disease: application to passive Abeta immunotherapy.

Cerebral amyloid angiopathy (CAA) is a common feature of Alzheimer's disease (AD). More advanced stages are accompanied by microhemorrhages and vasculitis. Peripheral blood-borne macrophages are intimately linked to cerebrovascular pathology coincident with AD. Magnetic resonance imaging (MRI) was used to noninvasively study microvascular lesions in amyloid precursor protein transgenic mouse AD models. Foci of signal attenuation were detected in cortical and thalamic brain regions of aged APP23 mice. Their strength and number was considerably enhanced by intravenous administration of iron oxide nanoparticles, which are taken up by macrophages through absorptive endocytosis, 24 h before image acquisition. The number of cortical sites displaying signal attenuation increased with age. Histology at these sites demonstrated the presence of iron-containing macrophages in the vicinity of CAA-affected blood vessels. A fraction of the sites additionally showed thickened vessel walls and vasculitis. Consistent with the visualization of CAA-associated lesions, MRI detected a much smaller number of attenuated signal sites in APP23xPS45 mice, for which a strong presenilin mutation caused a shift toward amyloid ß(42), thus reducing vascular amyloid. Similar results were obtained with APP24 and APP51 mice, which develop significantly less CAA and microvascular pathology than APP23. In a longitudinal study, we noninvasively demonstrated the reinforced formation of microvascular pathology during passive amyloid ß immunotherapy of APP23 mice. Histology confirmed that foci of signal attenuation reflected an increase in CAA-related lesions. Our data demonstrate that MRI has the sensitivity to noninvasively monitor the development of vascular pathology and its possible enhancement by amyloid ß immunotherapy in transgenic mice modeling AD.

Microtiter plate quantification of mutant and wild-type huntingtin normalized to cell count.

Huntington's disease is caused by a gain-of-function neurotoxic mutation in normally neuroprotective huntingtin. Sensitive assays are required to discriminate mutant huntingtin from wild-type huntingtin. We have developed a normalized 384-plate assay for determination of mutant and wild-type huntingtin. Based on a single pipetting step, the sensitive assay uses two antibody pairs for simultaneous mutant and wild-type huntingtin time-resolved fluorescence resonance energy transfer detection combined with PicoGreen quantification of double-stranded DNA. The assay can be used for discovery of drugs reducing mutant huntingtin over wild-type huntingtin and for assessing the value of huntingtin as a disease progression marker, and it is adaptable to other proteins of interest.

Rapid cerebral amyloid binding by Aß antibodies infused into ß-amyloid precursor protein transgenic mice.

BACKGROUND: Passive immunization for the treatment of Alzheimer's disease (AD) was rapidly translated into clinical trials. However, basic mechanisms of AD immunotherapy remain only partially understood. METHODS: We analyzed the dynamic changes of amyloid-ß (Aß) levels in plasma, brain, and cerebrospinal fluid (CSF) as well as cerebral amyloid binding by Aß antibody after a single ß1-antibody infusion into APP(Swedish) and APP(wildtype) transgenic mice at preplaque and plaque-bearing age. RESULTS: Following intravenous Aß antibody treatment, plasma Aß increased rapidly, reaching significantly higher levels in preplaque compared with plaque-bearing mice, whereas cerebral and CSF Aß remained unchanged. Strikingly, Aß antibodies exhibited strong cerebral amyloid plaque binding rapidly after intravenous administration in a subset of animals with more severe vascular amyloid. CONCLUSIONS: Rapid plasma Aß increase after Aß antibody infusion results primarily from stabilization of Aß. Nevertheless, the smaller plasma Aß increase in plaque-bearing mice might be of diagnostic use. Importantly, intravenously administered antibodies can rapidly bind to cerebral plaques, potentially facilitated by vascular-amyloid-mediated damage of the blood-brain barrier.

Single-step detection of mutant huntingtin in animal and human tissues: a bioassay for Huntington's disease.

The genetic mutation causing Huntington's disease is a polyglutamine expansion in the huntingtin protein where more than 37 glutamines cause disease by formation of toxic intracellular fragments, aggregates, and cell death. Despite a clear pathogenic role for mutant huntingtin, understanding huntingtin expression during the presymptomatic phase of the disease or during disease progression has remained obscure. Central to clarifying the role in the pathomechanism of disease is the ability to easily and accurately measure mutant huntingtin in accessible human tissue samples as well as cell and animal models. Here we describe a highly sensitive time-resolved Förster resonance energy transfer (FRET) assay for quantification of soluble mutant huntingtin in brain, plasma, and cerebrospinal fluid. Surprisingly, in mice, soluble huntingtin levels decrease during disease progression, inversely correlating with brain aggregate load. Mutant huntingtin is easily detected in human brain and blood-derived fractions, providing a utility to assess mutant huntingtin expression during disease course as well as a pharmacodynamic marker for disease-modifying therapeutics targeting expression, cleavage, or degradation of mutant huntingtin. The design of the homogeneous one-step method for huntingtin detection is such that it can be easily applied to measure other proteins of interest.

Transmission and spreading of tauopathy in transgenic mouse brain.

Hyperphosphorylated tau makes up the filamentous intracellular inclusions of several neurodegenerative diseases, including Alzheimer's disease. In the disease process, neuronal tau inclusions first appear in the transentorhinal cortex from where they seem to spread to the hippocampal formation and neocortex. Cognitive impairment becomes manifest when inclusions reach the hippocampus, with abundant neocortical tau inclusions and extracellular beta-amyloid deposits being the defining pathological hallmarks of Alzheimer's disease. An abundance of tau inclusions, in the absence of beta-amyloid deposits, defines Pick's disease, progressive supranuclear palsy, corticobasal degeneration and other diseases. Tau mutations cause familial forms of frontotemporal dementia, establishing that tau protein dysfunction is sufficient to cause neurodegeneration and dementia. Thus, transgenic mice expressing mutant (for example, P301S) human tau in nerve cells show the essential features of tauopathies, including neurodegeneration and abundant filaments made of hyperphosphorylated tau protein. By contrast, mouse lines expressing single isoforms of wild-type human tau do not produce tau filaments or show neurodegeneration. Here we have used tau-expressing lines to investigate whether experimental tauopathy can be transmitted. We show that injection of brain extract from mutant P301S tau-expressing mice into the brain of transgenic wild-type tau-expressing animals induces assembly of wild-type human tau into filaments and spreading of pathology from the site of injection to neighbouring brain regions.

Clusters of hyperactive neurons near amyloid plaques in a mouse model of Alzheimer's disease.

The neurodegeneration observed in Alzheimer's disease has been associated with synaptic dismantling and progressive decrease in neuronal activity. We tested this hypothesis in vivo by using two-photon Ca2+ imaging in a mouse model of Alzheimer's disease. Although a decrease in neuronal activity was seen in 29% of layer 2/3 cortical neurons, 21% of neurons displayed an unexpected increase in the frequency of spontaneous Ca2+ transients. These "hyperactive" neurons were found exclusively near the plaques of amyloid beta-depositing mice. The hyperactivity appeared to be due to a relative decrease in synaptic inhibition. Thus, we suggest that a redistribution of synaptic drive between silent and hyperactive neurons, rather than an overall decrease in synaptic activity, provides a mechanism for the disturbed cortical function in Alzheimer's disease.