Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains.

Interactome maps are valuable resources to elucidate protein function and disease mechanisms. Here, we report on an interactome map that focuses on neurodegenerative disease (ND), connects ∼5,000 human proteins via ∼30,000 candidate interactions and is generated by systematic yeast two-hybrid interaction screening of ∼500 ND-related proteins and integration of literature interactions. This network reveals interconnectivity across diseases and links many known ND-causing proteins, such as α-synuclein, TDP-43, and ATXN1, to a host of proteins previously unrelated to NDs. It facilitates the identification of interacting proteins that significantly influence mutant TDP-43 and HTT toxicity in transgenic flies, as well as of ARF-GEP100 that controls misfolding and aggregation of multiple ND-causing proteins in experimental model systems. Furthermore, it enables the prediction of ND-specific subnetworks and the identification of proteins, such as ATXN1 and MKL1, that are abnormally aggregated in postmortem brains of Alzheimer's disease patients, suggesting widespread protein aggregation in NDs.

Cloning of the gene containing mutations that cause PARK8-linked Parkinson's disease.

Parkinson's disease (PD; OMIM #168600) is the second most common neurodegenerative disorder in the Western world and presents as a progressive movement disorder. The hallmark pathological features of PD are loss of dopaminergic neurons from the substantia nigra and neuronal intracellular Lewy body inclusions. Parkinsonism is typically sporadic in nature; however, several rare familial forms are linked to genetic loci, and the identification of causal mutations has provided insight into the disease process. PARK8, identified in 2002 by Funayama and colleagues, appears to be a common cause of familial PD. We describe here the cloning of a novel gene that contains missense mutations segregating with PARK8-linked PD in five families from England and Spain. Because of the tremor observed in PD and because a number of the families are of Basque descent, we have named this protein dardarin, derived from the Basque word dardara, meaning tremor.

Discovery and functional prioritization of Parkinson's disease candidate genes from large-scale whole exome sequencing.

BACKGROUND: Whole-exome sequencing (WES) has been successful in identifying genes that cause familial Parkinson's disease (PD). However, until now this approach has not been deployed to study large cohorts of unrelated participants. To discover rare PD susceptibility variants, we performed WES in 1148 unrelated cases and 503 control participants. Candidate genes were subsequently validated for functions relevant to PD based on parallel RNA-interference (RNAi) screens in human cell culture and Drosophila and C. elegans models. RESULTS: Assuming autosomal recessive inheritance, we identify 27 genes that have homozygous or compound heterozygous loss-of-function variants in PD cases. Definitive replication and confirmation of these findings were hindered by potential heterogeneity and by the rarity of the implicated alleles. We therefore looked for potential genetic interactions with established PD mechanisms. Following RNAi-mediated knockdown, 15 of the genes modulated mitochondrial dynamics in human neuronal cultures and four candidates enhanced α-synuclein-induced neurodegeneration in Drosophila. Based on complementary analyses in independent human datasets, five functionally validated genes-GPATCH2L, UHRF1BP1L, PTPRH, ARSB, and VPS13C-also showed evidence consistent with genetic replication. CONCLUSIONS: By integrating human genetic and functional evidence, we identify several PD susceptibility gene candidates for further investigation. Our approach highlights a powerful experimental strategy with broad applicability for future studies of disorders with complex genetic etiologies.

Genetic screening for a single common LRRK2 mutation in familial Parkinson's disease.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause some forms of autosomal dominant Parkinson's disease. We measured the frequency of a novel mutation (Gly2019 ser) in familial Parkinson's disease by screening genomic DNA of patients and controls. Of 767 affected individuals from 358 multiplex families, 35 (5%) individuals were either heterozygous (34) or homozygous (one) for the mutation, and had typical clinical findings of idiopathic Parkinson's disease. Thus, our results suggest that a single LRRK2 mutation causes Parkinson's disease in 5% of individuals with familial disease. Screening for this mutation should be a component of genetic testing for Parkinson's disease.

A common LRRK2 mutation in idiopathic Parkinson's disease.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been shown to cause autosomal dominant Parkinson's disease. Few mutations in this gene have been identified. We investigated the frequency of a common heterozygous mutation, 2877510 g-->A, which produces a glycine to serine aminoacid substitution at codon 2019 (Gly2019 ser), in idiopathic Parkinson's disease. We assessed 482 patients with the disorder, of whom 263 had pathologically confirmed disease, by direct sequencing for mutations in exon 41 of LRRK2. The mutation was present in eight (1.6%) patients. We have shown that a common single Mendelian mutation is implicated in sporadic Parkinson's disease. We suggest that testing for this mutation will be important in the management and genetic counselling of patients with Parkinson's disease.

Analysis of IFT74 as a candidate gene for chromosome 9p-linked ALS-FTD.

BACKGROUND: A new locus for amyotrophic lateral sclerosis--frontotemporal dementia (ALS-FTD) has recently been ascribed to chromosome 9p. METHODS: We identified chromosome 9p segregating haplotypes within two families with ALS-FTD (F476 and F2) and undertook mutational screening of candidate genes within this locus. RESULTS: Candidate gene sequencing at this locus revealed the presence of a disease segregating stop mutation (Q342X) in the intraflagellar transport 74 (IFT74) gene in family 476 (F476), but no mutation was detected within IFT74 in family 2 (F2). While neither family was sufficiently informative to definitively implicate or exclude IFT74 mutations as a cause of chromosome 9-linked ALS-FTD, the nature of the mutation observed within F476 (predicted to truncate the protein by 258 amino acids) led us to sequence the open reading frame of this gene in a large number of ALS and FTD cases (n = 420). An additional sequence variant (G58D) was found in a case of sporadic semantic dementia. I55L sequence variants were found in three other unrelated affected individuals, but this was also found in a single individual among 800 Human Diversity Gene Panel samples. CONCLUSION: Confirmation of the pathogenicity of IFT74 sequence variants will require screening of other chromosome 9p-linked families.

Mutations in the gene LRRK2 encoding dardarin (PARK8) cause familial Parkinson's disease: clinical, pathological, olfactory and functional imaging and genetic data.

We have established that the frequency of LRRK2 mutations in a series of 118 cases of familial Parkinson's disease is 5.1%. In the largest family with autosomal dominant, late-onset Parkinson's disease where affected subjects share a Y1699C missense mutation we provide a detailed clinical, pathological and imaging report. The phenotype in this large British kindred included asymmetrical, levodopa-responsive parkinsonism where unilateral leg tremor at onset and foot dystonia were prominent features. There was no significant abnormality of cognition but there was prominent behavioural disorder. We observed a lower age of onset in successive generations. Histopathology in one patient showed substantia nigra cell loss and Lewy body formation, with small numbers of cortical Lewy bodies. 18F-dopa positron emission tomography (PET) in another patient showed a pattern of nigrostriatal dysfunction typical of idiopathic Parkinson's disease. 18F-dopa-PET scans in unaffected family members prior to identifying the disease locus did not detect subclinical nigrostriatal dysfunction. Olfaction was assessed in affected subjects and Lewy bodies were identified in the olfactory bulb as well as cortex and brainstem of one deceased patient. In order to assess the role of mutations in this gene in other familial cases we undertook a mutation screen of all 51 exons of LRRK2 in 117 other smaller British kindreds with familial Parkinson's disease. The commonest mutation was G2019S and we also identified two novel mutations, R1941H and T2356I, in the coding sequence. These data suggest that parkinsonism caused by mutations in LRRK2 is likely to represent the commonest locus for autosomal dominant Parkinson's disease with a phenotype, pathology and in vivo imaging similar to idiopathic, late-onset Parkinson's disease.

High content screening in neurodegenerative diseases.

The functional annotation of genomes, construction of molecular networks and novel drug target identification, are important challenges that need to be addressed as a matter of great urgency. Multiple complementary 'omics' approaches have provided clues as to the genetic risk factors and pathogenic mechanisms underlying numerous neurodegenerative diseases, but most findings still require functional validation. For example, a recent genome wide association study for Parkinson's Disease (PD), identified many new loci as risk factors for the disease, but the underlying causative variant(s) or pathogenic mechanism is not known. As each associated region can contain several genes, the functional evaluation of each of the genes on phenotypes associated with the disease, using traditional cell biology techniques would take too long. There is also a need to understand the molecular networks that link genetic mutations to the phenotypes they cause. It is expected that disease phenotypes are the result of multiple interactions that have been disrupted. Reconstruction of these networks using traditional molecular methods would be time consuming. Moreover, network predictions from independent studies of individual components, the reductionism approach, will probably underestimate the network complexity. This underestimation could, in part, explain the low success rate of drug approval due to undesirable or toxic side effects. Gaining a network perspective of disease related pathways using HT/HC cellular screening approaches, and identifying key nodes within these pathways, could lead to the identification of targets that are more suited for therapeutic intervention. High-throughput screening (HTS) is an ideal methodology to address these issues. but traditional methods were one dimensional whole-well cell assays, that used simplistic readouts for complex biological processes. They were unable to simultaneously quantify the many phenotypes observed in neurodegenerative diseases such as axonal transport deficits or alterations in morphology properties. This approach could not be used to investigate the dynamic nature of cellular processes or pathogenic events that occur in a subset of cells. To quantify such features one has to move to multi-dimensional phenotypes termed high-content screening (HCS). HCS is the cell-based quantification of several processes simultaneously, which provides a more detailed representation of the cellular response to various perturbations compared to HTS. HCS has many advantages over HTS, but conducting a high-throughput (HT)-high-content (HC) screen in neuronal models is problematic due to high cost, environmental variation and human error. In order to detect cellular responses on a 'phenomics' scale using HC imaging one has to reduce variation and error, while increasing sensitivity and reproducibility. Herein we describe a method to accurately and reliably conduct shRNA screens using automated cell culturing and HC imaging in neuronal cellular models. We describe how we have used this methodology to identify modulators for one particular protein, DJ1, which when mutated causes autosomal recessive parkinsonism. Combining the versatility of HC imaging with HT methods, it is possible to accurately quantify a plethora of phenotypes. This could subsequently be utilized to advance our understanding of the genome, the pathways involved in disease pathogenesis as well as identify potential therapeutic targets.

The complete automation of cell culture: improvements for high-throughput and high-content screening.

Genomic approaches provide enormous amounts of raw data with regard to genetic variation, the diversity of RNA species, and protein complement. High-throughput (HT) and high-content (HC) cellular screens are ideally suited to contextualize the information gathered from other "omic" approaches into networks and can be used for the identification of therapeutic targets. Current methods used for HT-HC screens are laborious, time-consuming, and prone to human error. The authors thus developed an automated high-throughput system with an integrated fluorescent imager for HC screens called the AI.CELLHOST. The implementation of user-defined culturing and assay plate setup parameters allows parallel operation of multiple screens in diverse mammalian cell types. The authors demonstrate that such a system is able to successfully maintain different cell lines in culture for extended periods of time as well as significantly increasing throughput, accuracy, and reproducibility of HT and HC screens.

SFRS7-mediated splicing of tau exon 10 is directly regulated by STOX1A in glial cells.

BACKGROUND: In this study, we performed a genome-wide search for effector genes bound by STOX1A, a winged helix transcription factor recently demonstrated to be involved in late onset Alzheimer's disease and affecting the amyloid processing pathway. METHODOLOGY/PRINCIPAL FINDINGS: Our results show that out of 218 genes bound by STOX1A as identified by chromatin-immunoprecipitation followed by sequencing (ChIP-Seq), the serine/arginine-rich splicing factor 7 (SFRS7) was found to be induced, both at the mRNA and protein levels, by STOX1A after stable transfection in glial cells. The increase in SFRS7 was followed by an increase in the 4R/3R ratios of the microtubule-associated protein tau (MAPT) by differential exon 10 splicing. Secondly, STOX1A also induced expression of total tau both at the mRNA and protein levels. Upregulation of total tau expression (SFRS7-independent) and tau exon 10 splicing (SFRS7-dependent), as shown in this study to be both affected by STOX1A, is known to have implications in neurodegeneration. CONCLUSIONS: Our data further supports the functional importance and central role of STOX1A in neurodegeneration.

From single genes to gene networks: high-throughput-high-content screening for neurological disease.

Neuronal development, function, and the subsequent degeneration of the brain are still an enigma in both the normal and pathologic states, and there is an urgent need to find better targets for developing therapeutic intervention. Current techniques to deconstruct the architecture of brain and disease-related pathways are best suited for following up on single genes but would take an impractical amount of time for the leads from the current wave of genetic and genomic data. New technical developments have made combined high-throughput-high-content (HT-HC) cellular screens possible, which have the potential to contextualize the information, gathered from a combination of genetic and genomic approaches, into networks and functional biology and can be utilized for the identification of therapeutic targets. Herein we discuss the potential impact of HT-HC cellular screens on medical neuroscience.

The Parkinson disease-associated leucine-rich repeat kinase 2 (LRRK2) is a dimer that undergoes intramolecular autophosphorylation.

Mutations in leucine-rich repeat kinase 2 (LRRK2) are a common cause of familial and apparently sporadic Parkinson disease. LRRK2 is a multidomain protein kinase with autophosphorylation activity. It has previously been shown that the kinase activity of LRRK2 is required for neuronal toxicity, suggesting that understanding the mechanism of kinase activation and regulation may be important for the development of specific kinase inhibitors for Parkinson disease treatment. Here, we show that LRRK2 predominantly exists as a dimer under native conditions, a state that appears to be stabilized by multiple domain-domain interactions. Furthermore, an intact C terminus, but not N terminus, is required for autophosphorylation activity. We identify two residues in the activation loop that contribute to the regulation of LRRK2 autophosphorylation. Finally, we demonstrate that LRRK2 undergoes intramolecular autophosphorylation. Together, these results provide insight into the mechanism and regulation of LRRK2 kinase activity.

The R1441C mutation of LRRK2 disrupts GTP hydrolysis.

Mutations in Leucine Rich Repeat Kinase 2 (LRRK2) are the leading genetic cause of Parkinson's disease (PD). LRRK2 is predicted to contain kinase and GTPase enzymatic domains, with recent evidence suggesting that the kinase activity of LRRK2 is central to the pathogenic process associated with this protein. The GTPase domain of LRRK2 plays an important role in the regulation of kinase activity. To investigate how the GTPase domain might be related to disease, we examined the GTP binding and hydrolysis properties of wild type and a mutant form of LRRK2. We show that LRRK2 immunoprecipitated from cells has a detectable GTPase activity that is disrupted by a familial mutation associated with PD located within the GTPase domain, R1441C.

Comprehensive screening of a North American Parkinson's disease cohort for LRRK2 mutation.

BACKGROUND: Recently, mutations in LRRK2 encoding the protein dardarin have been linked to an autosomal dominant form of parkinsonism. OBJECTIVE: To identify mutations causing Parkinson's disease (PD) in a cohort of North Americans with familial PD. METHODS: We sequenced exons 1-51 of LRRK2 in 79 unrelated North American PD patients reporting a family history of the disease. RESULTS: One patient had a missense mutation (Thr2356Ile) while two others had the common Gly2019Ser mutation. In addition, 1 patient had a 4-bp deletion in close proximity to the exon 19 splice donor (IVS20+4delGTAA) that in vitro abrogates normal splicing. CONCLUSIONS: Our observations in the 79 North American patients indicate that mutations in LRRK2 are associated with approximately 5% of PD cases with a positive family history. The results also show that G2019S represents approximately half of the LRRK2 mutations in United States PD cases with a family history of the disease. We have identified two novel mutations in LRRK2.

Kinase activity is required for the toxic effects of mutant LRRK2/dardarin.

Mutations in the LRRK2 gene, coding for dardarin, cause dominantly inherited Parkinson's disease (PD). Dardarin is a large protein, and mutations are found throughout the gene including the kinase domain. However, it is not clear if kinase activity is important for the damaging effects of pathogenic mutations. In this study, we noted two cellular phenotypes associated with mutant dardarin. First, pathogenic mutations increase the tendency of dardarin to form inclusion bodies. Secondly, neurons and neuronal cell lines undergo cell death after expression of mutant protein. Manipulating activity by replacing the kinase domain with a 'kinase-dead' version blocks inclusion body formation and strongly delays cell death. This predicts that kinase inhibitors will be useful therapeutic agents in patients with LRRK2 mutations and, perhaps, in sporadic PD. We also show that dardarin protein is expressed within human midbrain neurons and that C-terminal epitopes are also found in some Lewy bodies.

Molecular genetic pathways in Parkinson's disease: a review.

Major progress has been made in the last decade in understanding the genetic basis of PD (Parkinson's disease) with five genes unequivocally associated with disease. As a result, multiple pathways have been implicated in the pathogenesis of PD, including proteasome impairment and mitochondrial dysfunction. Although Mendelian genetics has been successful in establishing a genetic predisposition for familial PD, this has not been reiterated in the sporadic form. In fact no genetic factors have been unequivocally associated with increased risk for sporadic PD. The difficulty in identifying susceptibility factors in PD has not only been because of numerous underpowered studies, but we have been unable to dissect out the genetic component in a multifactorial disease. This review aims to summarize the genetic findings within PD.

Clinical and positron emission tomography of Parkinson's disease caused by LRRK2.

We have recently identified mutations in a gene leucine-rich repeat kinase-2 (LRRK2), which cause autosomal dominant Parkinson's disease. Here, we describe two families with autosomal dominant Parkinson's disease caused by a LRRK2 G2019S mutation. We present here a clinical description of patients, including 6-(18)F-fluoro-L-dopa positron emission tomography and discuss the potential implications of this mutation, which alters a conserved residue in a domain required for kinase activation.

Elevated amyloid beta protein (Abeta42) and late onset Alzheimer's disease are associated with single nucleotide polymorphisms in the urokinase-type plasminogen activator gene.

Plasma amyloid beta protein (Abeta42) levels and late onset Alzheimer's disease (LOAD) have been linked to the same region on chromosome 10q. The PLAU gene within this region encodes urokinase-type plasminogen activator, which converts plasminogen to plasmin. Abeta aggregates induce PLAU expression thereby increasing plasmin, which degrades both aggregated and non-aggregated forms of Abeta. We evaluated single nucleotide polymorphisms (SNPs) in PLAU for association with Abeta42 and LOAD. PLAU SNP compound genotypes composed of haplotype pairs showed significant association with AD in three independent case-control series. PLAU SNP haplotypes associated significantly with plasma Abeta42 in 10 extended LOAD families. One of the SNPs analyzed was a missense C/T polymorphism in exon 6 of PLAU (PLAU_1=rs2227564), which causes a proline to leucine change (P141L). We analyzed PLAU_1 for association with AD in six case-control series and 24 extended LOAD families. The CT and TT PLAU_1 genotypes showed association (P=0.05) with an overall estimated odds ratio of 1.2 (1.0-1.5). The CT and TT genotypes of PLAU_1 were also associated with significant age-dependent elevation of plasma Abeta42 in 24 extended LOAD families (P=0.0006). In knockout mice lacking the PLAU gene, plasma--but not brain--Abeta42 as well as Abeta40 was significantly elevated, also in an age-dependent manner. The PLAU_1 associations were independent of the associations we found among plasma Abeta42, LOAD and variants in the IDE or VR22 region. These results provide strong evidence that PLAU or a nearby gene is involved in the development of LOAD. PLAU_1 is a plausible pathogenic mutation that could act by increasing Abeta42, but additional biological experiments are required to show this definitively.

Fine mapping of the alpha-T catenin gene to a quantitative trait locus on chromosome 10 in late-onset Alzheimer's disease pedigrees.

Using plasma amyloid beta protein (Abeta42) levels as an intermediate, quantitative phenotype for late onset Alzheimer's disease (LOAD), we previously obtained significant linkage at approximately 80 cM on chromosome 10. Linkage to the same region was obtained independently in a study of affected LOAD sib-pairs. Together, these two studies provide strong evidence for a novel LOAD locus on chromosome 10 that acts to increase Abeta42. VR22 is a large (1.7 Mb) gene located at 80 cM that encodes alpha-T catenin, which is a binding partner of beta catenin. This makes VR22 an attractive candidate gene because beta catenin interacts with presenilin 1, which has many mutations that elevate Abeta42 and cause early onset familial AD. We identified two intronic VR22 SNPs (4360 and 4783) in strong linkage disequilibrium (LD) that showed highly significant association (P=0.0001 and 0.0006) with plasma Abeta42 in 10 extended LOAD families. This association clearly contributed to the linkage at approximately 80 cM because the lod scores decreased when linkage analysis was performed conditional upon the VR22 association. This association replicated in another independent set of 12 LOAD families (P=0.04 for 4783 and P=0.08 for 4360). Bounding of the association region using multiple SNPs showed VR22 to be the only confirmed gene within the region of association. These findings indicate that VR22 has variant(s) which influence Abeta42 and contribute to the previously reported linkage for plasma Abeta42 in LOAD families.