In 2004 it was first shown that mutations in LRRK2 can cause Parkinson's disease. This initial discovery was quickly followed by the observation that a single particular mutation is a relatively common cause of Parkinson's disease across varied populations. Further genetic investigation has revealed a variety of genetic ties to Parkinson's disease across this gene. These include common alleles with quite broad effects on risk, likely through both alterations at the protein sequence level, and in the context of expression. A great deal of functional characterization of LRRK2 and disease-causing mutations in this protein has occurred over the last 9 years, and considerable progress has been made. Particular attention has been paid to the kinase activity of LRRK2 as a therapeutic target, and while it is no means certain that this is viable target it is likely that this hypothesis will be tested in clinical trials sooner rather than later. We believe that the future goals for LRRK2 research are, while challenging, relatively clear and that the next 10 years of research promises to be perhaps more exciting than the last.
LRRK2; associated phenotype; disease risk; biology; future challenges; Parkinson's disease; parkinsonism; genetics
Compelling evidence indicates that two autosomal recessive Parkinson’s disease genes, PINK1 (PARK6) and Parkin (PARK2), co-operate to mediate the autophagic clearance of damaged mitochondria (mitophagy). Mutations in the F-box domain containing protein Fbxo7 (PARK15) also cause early onset autosomal recessive Parkinson’s disease by an unknown mechanism. Here we show that Fbxo7 participates in mitochondrial maintenance through direct interaction with PINK1 and Parkin and plays a role in Parkin-mediated mitophagy. Cells with reduced Fbxo7 expression show deficiencies in Parkin mitochondrial translocation, ubiquitination of mitofusin 1 and mitophagy. In Drosophila, ectopic overexpression of Fbxo7 rescued loss of Parkin supporting a functional relationship between the two proteins. Parkinson’s disease-causing mutations in Fbxo7 interfere with this process, emphasising the importance of mitochondrial dysfunction in Parkinson’s disease pathogenesis.
Fbxo7; Parkin; PINK1; mitofusin 1; mitophagy; Drosophila; Parkinson’s disease
We use a combination of cytochrome b sequence data and karyological evidence to confirm the presence of Mus indutus and Mus minutoides in Botswana. Our data include sampling from five localities from across the country, including one site in northwestern Botswana where both species were captured in syntopy. Additionally, we find evidence for two mitochondrial lineages of M. minutoides in northwestern Botswana that differ by 5% in sequence variation. Also, we report that M. minutoides in Botswana have the 2n=34 karyotype with the presence of a (X.1) sex-autosome translocation.
Africa; rodent; distribution; karyotype; sex-autosome translocation; cytochrome b
Leucine Rich Repeat Kinase 2 (LRRK2) is one of the most important genetic contributors to Parkinson's disease. LRRK2 has been implicated in a number of cellular processes, including macroautophagy. To test whether LRRK2 has a role in regulating autophagy, a specific inhibitor of the kinase activity of LRRK2 was applied to human neuroglioma cells and downstream readouts of autophagy examined. The resulting data demonstrate that inhibition of LRRK2 kinase activity stimulates macroautophagy in the absence of any alteration in the translational targets of mTORC1, suggesting that LRRK2 regulates autophagic vesicle formation independent of canonical mTORC1 signaling. This study represents the first pharmacological dissection of the role LRRK2 plays in the autophagy/lysosomal pathway, emphasizing the importance of this pathway as a marker for LRRK2 physiological function. Moreover it highlights the need to dissect autophagy and lysosomal activities in the context of LRRK2 related pathologies with the final aim of understanding their aetiology and identifying specific targets for disease modifying therapies in patients.
•Inhibiting the kinase activity of LRRK2 induces autophagy•This induction is independent of an impact on the translational targets of mTORC1•Inhibition of LRRK2 kinase activity results in a translation dependent increase in p62 levels
LRRK2, Leucine Rich Repeat Kinase 2; mTOR, Mammalian target of rapamycin; ROC, Ras of Complex Proteins; COR, C-terminal of ROC domain; SDS, Sodium dodecyl sulphate; EDTA, Ethylene di-ammonium tetra acetic acid; DPBS, Dulbecco's phosphate buffered saline; DMSO, Dimethylsulfoxide; LRRK2; Macroautophagy; Parkinson's disease; LC3; p62; WIPI2
•Mutations in the ROC, COR and Kinase domain of LRRK2 alter the autophagic response to starvation.•LC3-I/II ratio following starvation is altered by mutations, as well as p62 and WIPI2 positive puncta.•This occurs independently of any alteration in downstream targets of mTORC1.
LRRK2 is one of the most important genetic contributors to Parkinson’s disease (PD). Point mutations in this gene cause an autosomal dominant form of PD, but to date no cellular phenotype has been consistently linked with mutations in each of the functional domains (ROC, COR and Kinase) of the protein product of this gene. In this study, primary fibroblasts from individuals carrying pathogenic mutations in the three central domains of LRRK2 were assessed for alterations in the autophagy/lysosomal pathway using a combination of biochemical and cellular approaches. Mutations in all three domains resulted in alterations in markers for autophagy/lysosomal function compared to wild type cells. These data highlight the autophagy and lysosomal pathways as read outs for pathogenic LRRK2 function and as a marker for disease, and provide insight into the mechanisms linking LRRK2 function and mutations.
LRRK2, leucine rich repeat kinase 2; ROC, ras of complex proteins; COR, C-terminal of ROC; PD, Parkinson’s disease; ICC, Immunocytochemistry; LRRK2; Parkinson’s disease; Autophagy; Lysosomes; Signaling pathways
Approximately 20 % of individuals with Parkinson's disease (PD) report a positive family history. Yet, a large portion of causal and disease-modifying variants is still unknown. We used exome sequencing in two affected individuals from a family with late-onset PD to identify 15 potentially causal variants. Segregation analysis and frequency assessment in 862 PD cases and 1,014 ethnically matched controls highlighted variants in EEF1D and LRRK1 as the best candidates. Mutation screening of the coding regions of these genes in 862 cases and 1,014 controls revealed several novel non-synonymous variants in both genes in cases and controls. An in silico multi-model bioinformatics analysis was used to prioritize identified variants in LRRK1 for functional follow-up. However, protein expression, subcellular localization, and cell viability were not affected by the identified variants. Although it has yet to be proven conclusively that variants in LRRK1 are indeed causative of PD, our data strengthen a possible role for LRRK1 in addition to LRRK2 in the genetic underpinnings of PD but, at the same time, highlight the difficulties encountered in the study of rare variants identified by next-generation sequencing in diseases with autosomal dominant or complex patterns of inheritance.
Electronic supplementary material
The online version of this article (doi:10.1007/s10048-013-0383-8) contains supplementary material, which is available to authorized users.
Parkinson's disease; LRRK1; EEF1D; Exome sequencing
Mutations in LRRK2 are the most common genetic cause of Parkinson's disease (PD). The most prevalent LRRK2 mutation is the G2019S coding change, located in the kinase domain of this complex multi-domain protein. The majority of G2019S autopsy cases feature typical Lewy Body pathology with a clinical phenotype almost indistinguishable from idiopathic PD (iPD). Here we have investigated the biochemical characteristics of α-synuclein in G2019S LRRK2 PD post-mortem material, in comparison to pathology-matched iPD. Immunohistochemistry with pS129 α-synuclein antibody showed that the medulla is heavily affected with pathology in G2019S PD whilst the basal ganglia (BG), limbic and frontal cortical regions demonstrated comparable pathology scores between G2019S PD and iPD. Significantly lower levels of the highly aggregated α-synuclein species in urea–SDS fractions were observed in G2019S cases compared to iPD in the BG and limbic cortex. Our data, albeit from a small number of cases, highlight a difference in the biochemical properties of aggregated α-synuclein in G2019S linked PD compared to iPD, despite a similar histopathological presentation. This divergence in solubility is most notable in the basal ganglia, a region that is affected preclinically and is damaged before overt dopaminergic cell death.
•We compared α-synuclein biochemistry from LRRK2 G2019S and idiopathic PD brains.•We used four G2019S PD post-mortem brains and pathology matched idiopathic PD cases.•G2019S PD and idiopathic PD cases show comparable Limbic stage Lewy Body pathology.•Minimal SDS-insoluble α-synuclein seen in G2019S PD in contrast to idiopathic PD•We propose a divergent nature of α-synuclein pathogenic species in G2019S PD.
LRRK2; G2019S; α-Synuclein; Differential solubility; Immunohistochemistry
Association studies have identified several signals at the LRRK2 locus for Parkinson's disease (PD), Crohn's disease (CD) and leprosy. However, little is known about the molecular mechanisms mediating these effects. To further characterize this locus, we fine-mapped the risk association in 5,802 PD and 5,556 controls using a dense genotyping array (ImmunoChip). Using samples from 134 post-mortem control adult human brains (UK Human Brain Expression Consortium), where up to ten brain regions were available per individual, we studied the regional variation, splicing and regulation of LRRK2. We found convincing evidence for a common variant PD association located outside of the LRRK2 protein coding region (rs117762348, A>G, P = 2.56×10−8, case/control MAF 0.083/0.074, odds ratio 0.86 for the minor allele with 95% confidence interval [0.80–0.91]). We show that mRNA expression levels are highest in cortical regions and lowest in cerebellum. We find an exon quantitative trait locus (QTL) in brain samples that localizes to exons 32–33 and investigate the molecular basis of this eQTL using RNA-Seq data in n = 8 brain samples. The genotype underlying this eQTL is in strong linkage disequilibrium with the CD associated non-synonymous SNP rs3761863 (M2397T). We found two additional QTLs in liver and monocyte samples but none of these explained the common variant PD association at rs117762348. Our results characterize the LRRK2 locus, and highlight the importance and difficulties of fine-mapping and integration of multiple datasets to delineate pathogenic variants and thus develop an understanding of disease mechanisms.
•We map all five missense SNCA mutations on the proposed α-synuclein protein models.•4 mutations cluster around the protein loop linking the two legs of the hairpin.•4 mutations cluster around the point of hairpin convergence for tetramer formation.
With the recent identification of two new pathogenic mutations in α-synuclein, we map the five known pathogenic mutations onto the best available models of the protein structure. We show that four of the five mutations map to a potential fold in the protein with the exception being the A30P mutation in which the substitution would be expected to have a profound effect on protein structure. We discuss this localisation in terms of the proposed mechanisms for mutation pathogenicity.
α-Synuclein; SNCA; Genetics; Parkinson's disease
We report a British family with young-onset Parkinson’s disease (PD) and a G51D SNCA mutation that segregates with the disease. Family history was consistent with autosomal dominant inheritance as both the father and sister of the proband developed levodopa-responsive parkinsonism with onset in their late thirties. Clinical features show similarity to those seen in families with SNCA triplication and to cases of A53T SNCA mutation. Post-mortem brain examination of the proband revealed atrophy affecting frontal and temporal lobes in addition to the caudate, putamen, globus pallidus and amygdala. There was severe loss of pigmentation in the substantia nigra and pallor of the locus coeruleus. Neuronal loss was most marked in frontal and temporal cortices, hippocampal CA2/3 subregions, substantia nigra, locus coeruleus and dorsal motor nucleus of the vagus. The cellular pathology included widespread and frequent neuronal α-synuclein immunoreactive inclusions of variable morphology and oligodendroglial inclusions similar to the glial cytoplasmic inclusions of multiple system atrophy (MSA). Both inclusion types were ubiquitin and p62 positive and were labelled with phosphorylation-dependent anti-α-synuclein antibodies In addition, TDP-43 immunoreactive inclusions were observed in limbic regions and in the striatum. Together the data show clinical and neuropathological similarities to both the A53T SNCA mutation and multiplication cases. The cellular neuropathological features of this case share some characteristics of both PD and MSA with additional unique striatal and neocortical pathology. Greater understanding of the disease mechanism underlying the G51D mutation could aid in understanding of α-synuclein biology and its impact on disease phenotype.
Electronic supplementary material
The online version of this article (doi:10.1007/s00401-013-1096-7) contains supplementary material, which is available to authorized users.
Parkinson’s disease; Multiple system atrophy; α-Synuclein; SNCA
Goals of this study were to: (1) develop distributional maps of modern rodent genera throughout the countries of South Africa, Lesotho, and Swaziland by georeferencing museum specimens; (2) assess habitat preferences for genera by cross-referencing locality position with South African vegetation; and (3) identify mean annual precipitation and temperature range where the genera are located. Conterminous South Africa including the countries of Lesotho and Swaziland Digital databases of rodent museum specimens housed in the Ditsong National Museum of Natural History, South Africa (DM), and the Division of Mammals, National Museum of Natural History, Smithsonian Institution, United States (NMNH), were acquired and then sorted into a subset of specimens with associated coordinate data. The coordinate data were then used to develop distributional maps for the rodent genera present within the study area. Percent habitat occupation and descriptive statistics for six climatic variables were then determined for each genus by cross-referencing locality positions with vegetation and climatic maps. This report presents a series of maps illustrating the distribution of 35 rodent genera based on 19,471 geo-referenced specimens obtained from two major collections. Inferred habitat use by taxon is provided for both locality and specimen percent occurrence at three hierarchical habitat levels: biome, bioregion, and vegetation unit. Descriptive statistics for six climatic variables are also provided for each genus based on locality and specimen percent incidence. As rodent faunas are commonly used in paleoenvironmental reconstructions, an accurate assessment of rodent environmental tolerance ranges is necessary before confidence can be placed in an actualistic model. While the data presented here represent only a subset of the modern geographic distributions for many of the taxa examined, a wide range of environmental regimes are observed, suggesting that more research is necessary in order to accurately reconstruct an environmental signature when these taxa are found in the fossil record.
Distribution maps; environmental tolerances; GIS; rodents; South Africa; vegetation
Two gammaherpesviruses, Epstein-Barr virus (EBV) (Lymphocryptovirus genus) and Kaposi's sarcoma-associated herpesvirus (KSHV) (Rhadinovirus genus) have been implicated in the etiology of AIDS-associated lymphomas. Homologs of these viruses have been identified in macaques and other non-human primates. In order to assess the association of these viruses with non-human primate disease, archived lymphoma samples were screened for the presence of macaque lymphocryptovirus (LCV) homologs of EBV, and macaque rhadinoviruses belonging to the RV1 lineage of KSHV homologs or the more distant RV2 lineage of Old World primate rhadinoviruses. Viral loads were determined by QPCR and infected cells were identified by immunolabeling for different viral proteins. The lymphomas segregated into three groups. The first group (n = 6) was associated with SIV/SHIV infections, contained high levels of LCV (1–25 genomes/cell) and expressed the B-cell antigens CD20 or BLA.36. A strong EBNA-2 signal was detected in the nuclei of the neoplastic cells in one of the LCV-high lymphomas, indicative of a type III latency stage. None of the lymphomas in this group stained for the LCV viral capsid antigen (VCA) lytic marker. The second group (n = 5) was associated with D-type simian retrovirus-2 (SRV-2) infections, contained high levels of RV2 rhadinovirus (9–790 genomes/cell) and expressed the CD3 T-cell marker. The third group (n = 3) was associated with SIV/SHIV infections, contained high levels of RV2 rhadinovirus (2–260 genomes/cell) and was negative for both CD20 and CD3. In both the CD3-positive and CD3/CD20-negative lymphomas, the neoplastic cells stained strongly for markers of RV2 lytic replication. None of the lymphomas had detectable levels of retroperitoneal fibromatosis herpesvirus (RFHV), the macaque RV1 homolog of KSHV. Our data suggest etiological roles for both lymphocryptoviruses and RV2 rhadinoviruses in the development of simian AIDS-associated lymphomas and indicate that the virus-infected neoplastic lymphoid cells are derived from different lymphocyte lineages and differentiation stages.
The incidence of Kaposi's sarcoma (KS) and non-Hodgkin's lymphoma increased in conjunction with the epidemic of HIV disease and AIDS. These malignancies are now known to be associated with secondary infections with a gammaherpesvirus; KS, with the Kaposi's sarcoma-associated herpesvirus (KSHV) and lymphoma, with both KSHV and Epstein-Barr virus (EBV). Similar AIDS-related malignancies have been observed in monkeys with simian AIDS and monkey gammaherpesviruses related to KSHV and EBV have been implicated in the development of disease. The study of monkey models of AIDS-related malignancies provides important approaches for understanding the role of gammaherpesviruses in AIDS-related tumorigenesis. Here we have used a combined molecular and immunological approach to identify, quantitate and localize infections of gammaherpesviruses in AIDS-associated lymphomas in macaques. We found high levels of macaque viruses related to EBV and KSHV in the tumor cells of distinct types of macaque lymphomas, suggesting that the virus-infected tumor cells belong to different lymphocyte lineages and differentiation stages.
The ROCO proteins are a family of large, multidomain proteins characterised by the presence of a Ras of complex proteins (ROC) domain followed by a COR, or C-terminal of ROC, domain. It has previously been shown that the ROC domain of the human ROCO protein Leucine Rich Repeat Kinase 2 (LRRK2) controls its kinase activity. Here, the ability of the ROC domain of another human ROCO protein, Death Associated Protein Kinase 1 (DAPK1), to bind GTP and control its kinase activity has been evaluated. In contrast to LRRK2, loss of GTP binding by DAPK1 does not result in loss of kinase activity, instead acting to modulate this activity. These data highlight the ROC domain of DAPK1 as a target for modifiers of this proteins function, and casts light on the role of ROC domains as intramolecular regulators in complex proteins with implications for a broad range of human diseases.
Our understanding of the molecular mechanisms of many neurological disorders has been greatly enhanced by the discovery of mutations in genes linked to familial forms of these diseases. These have facilitated the generation of cell and animal models that can be used to understand the underlying molecular pathology. Recently, there has been a surge of interest in the use of patient-derived cells, due to the development of induced pluripotent stem cells and their subsequent differentiation into neurons and glia. Access to patient cell lines carrying the relevant mutations is a limiting factor for many centres wishing to pursue this research. We have therefore generated an open-access collection of fibroblast lines from patients carrying mutations linked to neurological disease. These cell lines have been deposited in the National Institute for Neurological Disorders and Stroke (NINDS) Repository at the Coriell Institute for Medical Research and can be requested by any research group for use in in vitro disease modelling. There are currently 71 mutation-defined cell lines available for request from a wide range of neurological disorders and this collection will be continually expanded. This represents a significant resource that will advance the use of patient cells as disease models by the scientific community.
► Summary of the existing literature on gene expression in Parkinson's disease, concentrating on alterations in gene expression in the brain. ► Analysis of the strengths and weaknesses of a genome wide approach to assessing gene expression in Parkinson's. ► A preview of what lies ahead for gene expression in Parkinson's disease as technology advances.
The study of gene expression has undergone a transformation in the past decade as the benefits of the sequencing of the human genome have made themselves felt. Increasingly, genome wide approaches are being applied to the analysis of gene expression in human disease as a route to understanding the underlying pathogenic mechanisms. In this review, we will summarise current state of gene expression studies of the brain in Parkinson's disease, and examine how these techniques can be used to gain an insight into aetiology of this devastating disorder.
Parkinson's disease; Microarray; Gene expression; Neuropathology; Genome wide
The colorimetric properties of resorcinarene solutions had not been investigated since Baeyer’s initial synthesis. We recently reported that solutions containing resorcinarene macrocycles develop color upon heating or standing. In the presence of saccharides, these solutions exhibit significant color changes which are easily seen. We herein present strong evidence that the solution color is due to macrocycle ring opening and oxidation. The optical responses to saccharides are due to complexation of the sugar with the acyclic chromophores. We apply these mechanistic insights toward the challenging problem of the visual detection of neutral oligosaccharides by simple chromogens. In addition, we also report the first single-crystal X-ray crystal structure determination of a rarely observed “diamond” resorcinarene stereoisomer.
A major barrier to research on Parkinson's disease is inaccessibility of diseased tissue for study. One solution is to derive induced pluripotent stem cells from patients and differentiate them into neurons affected by disease. Triplication of SNCA, encoding α-synuclein, causes a fully penetrant, aggressive form of Parkinson's disease with dementia. α-Synuclein dysfunction is the critical pathogenic event in Parkinson's disease, multiple system atrophy and dementia with Lewy bodies. Here we produce multiple induced pluripotent stem cell lines from an SNCA triplication patient and an unaffected first-degree relative. When these cells are differentiated into midbrain dopaminergic neurons, those from the patient produce double the amount of α-synuclein protein as neurons from the unaffected relative, precisely recapitulating the cause of Parkinson's disease in these individuals. This model represents a new experimental system to identify compounds that reduce levels of α-synuclein, and to investigate the mechanistic basis of neurodegeneration caused by α-synuclein dysfunction.
Pluripotent stem cells can be generated from the somatic cells of humans and are a useful model to study disease. Here, pluripotent stem cells are made from a patient with familial Parkinson's disease, and the resulting neurons exhibit elevated levels of α-synuclein, recapitulating the molecular features of the patient's disease.
Leucine Rich Repeat Kinase 2 (LRRK2) is a 2527 amino acid member of the ROCO family of proteins, possessing a complex, multidomain structure including a GTPase domain (termed ROC, for Ras of Complex proteins) and a kinase domain1. The discovery in 2004 of mutations in LRRK2 that cause Parkinson's disease (PD) resulted in LRRK2 being the focus of a huge volume of research into its normal function and how the protein goes awry in the disease state2,3. Initial investigations into the function of LRRK2 focused on its enzymatic activities4-6. Although a clear picture has yet to emerge of a consistent alteration in these due to mutations, data from a number of groups has highlighted the importance of the kinase activity of LRRK2 in cell death linked to mutations7,8. Recent publications have reported inhibitors targeting the kinase activity of LRRK2, providing a key experimental tool9-11. In light of these data, it is likely that the enzymatic properties of LRRK2 afford us an important window into the biology of this protein, although whether they are potential drug targets for Parkinson's is open to debate.
A number of different approaches have been used to assay the kinase activity of LRRK2. Initially, assays were carried out using epitope tagged protein overexpressed in mammalian cell lines and immunoprecipitated, with the assays carried out using this protein immobilised on agarose beads4,5,7. Subsequently, purified recombinant fragments of LRRK2 in solution have also been used, for example a GST tagged fragment purified from insect cells containing residues 970 to 2527 of LRRK212. Recently, Daniëls et al. reported the isolation of full length LRRK2 in solution from human embryonic kidney cells, however this protein is not widely available13. In contrast, the GST fusion truncated form of LRRK2 is commercially available (from Invitrogen, see table 1 for details), and provides a convenient tool for demonstrating an assay for LRRK2 kinase activity. Several different outputs for LRRK2 kinase activity have been reported. Autophosphorylation of LRRK2 itself, phosphorylation of Myelin Basic Protein (MBP) as a generic kinase substrate and phosphorylation of an artificial substrate - dubbed LRRKtide, based upon phosphorylation of threonine 558 in Moesin - have all been used, as have a series of putative physiological substrates including α-synuclein, Moesin and 4-EBP14-17. The status of these proteins as substrates for LRRK2 remains unclear, and as such the protocol described below will focus on using MBP as a generic substrate, noting the utility of this system to assay LRRK2 kinase activity directed against a range of potential substrates.
Molecular Biology; Issue 59; Kinase; LRRK2; Parkinson's disease
Biomarkers derived from gene expression profiling data may have a high false-positive rate and must be rigorously validated using independent clinical data sets, which are not always available. Although animal model systems could provide alternative data sets to formulate hypotheses and limit the number of signatures to be tested in clinical samples, the predictive power of such an approach is not yet proven. The present study aims to analyze the molecular signatures of liver cancer in a c-MET-transgenic mouse model and investigate its prognostic relevance to human hepatocellular carcinoma (HCC). Tissue samples were obtained from tumor (TU), adjacent non-tumor (AN) and distant normal (DN) liver in Tet-operator regulated (TRE) human c-MET transgenic mice (n = 21) as well as from a Chinese cohort of 272 HBV- and 9 HCV-associated HCC patients. Whole genome microarray expression profiling was conducted in Affymetrix gene expression chips, and prognostic significances of gene expression signatures were evaluated across the two species. Our data revealed parallels between mouse and human liver tumors, including down-regulation of metabolic pathways and up-regulation of cell cycle processes. The mouse tumors were most similar to a subset of patient samples characterized by activation of the Wnt pathway, but distinctive in the p53 pathway signals. Of potential clinical utility, we identified a set of genes that were down regulated in both mouse tumors and human HCC having significant predictive power on overall and disease-free survival, which were highly enriched for metabolic functions. In conclusions, this study provides evidence that a disease model can serve as a possible platform for generating hypotheses to be tested in human tissues and highlights an efficient method for generating biomarker signatures before extensive clinical trials have been initiated.
Point mutations in LRRK2 cause autosomal dominant Parkinson's disease. Despite extensive efforts to determine the mechanism of cell death in patients with LRRK2 mutations, the aetiology of LRRK2 PD is not well understood. To examine possible alterations in gene expression linked to the presence of LRRK2 mutations, we carried out a case versus control analysis of global gene expression in three systems: fibroblasts isolated from LRRK2 mutation carriers and healthy, non-mutation carrying controls; brain tissue from G2019S mutation carriers and controls; and HEK293 inducible LRRK2 wild type and mutant cell lines. No significant alteration in gene expression was found in these systems following correction for multiple testing. These data suggest that any alterations in basal gene expression in fibroblasts or cell lines containing mutations in LRRK2 are likely to be quantitatively small. This work suggests that LRRK2 is unlikely to play a direct role in modulation of gene expression, although it remains possible that this protein can influence mRNA expression under pathogenic cicumstances.
Parkinson's disease (PD) represents a major challenge for health care systems around the world: it is the most common degenerative movement disorder of old age, affecting over 100,000 people in the UK alone (Schrag et al., 2000). Despite the remarkable success of treatments directed at potentiating or replacing dopamine within the brain, which can relieve symptoms for over a decade, PD remains an incurable and invariably fatal disorder. As such, efforts to understand the processes that lead to cell death in the brains of patients with PD are a priority for neurodegenerative researchers. A great deal of progress has been made in this regard by taking advantage of advances in genetics, initially by the identification of genes responsible for rare Mendelian forms of PD (outlined in Table 1), and more recently by applying genome wide association studies (GWAS) to the sporadic form of the disease (Hardy et al., 2009). Several such GWAS have now been carried out, with a meta-analysis currently under way. Using over 6000 cases and 10,000 controls, two of these studies have identified variation at a number of loci as being associated with an increased risk of disease (Satake et al., 2009; Simon-Sanchez et al., 2009). Three genes stand out as candidates from these studies – the SNCA gene, coding for α-synuclein, the LRRK2 gene, coding for leucine rich repeat kinase 2, and MAPT, coding for the microtubule-associated protein tau. Mutations at all three of these loci have been associated with Mendelian forms of disease presenting with the clinical syndrome of Parkinsonism, however only SNCA and LRRK2 have been previously associated with pathologically defined PD (Hardy et al., 2009). Point mutations in α-synuclein, along with gene multiplication events, result in autosomal dominant PD, often with a significant dementia component. In addition to this, α-synuclein is the principle component of the main pathological hallmark of idiopathic PD, the Lewy body, making it an unsurprising hit in the GWAS (Spillantini et al., 1997). Mutations in LRRK2 are the most common genetic cause of PD, and so again made this gene a likely candidate as a susceptibility locus for the sporadic form of disease (Kumari and Tan, 2009). More surprising, perhaps, was the identification of tau as a susceptibility factor for Parkinson's. In this review we will outline the role of tau in neurodegeneration and in different forms of Parkinsonism, and speculate as to what the functional basis of the association between MAPT and PD might be.
genome wide association study; Parkinson's disease; synuclein; tau
Cancer and neurodegeneration are often thought of as disease mechanisms at opposite ends of a spectrum; one due to enhanced resistance to cell death and the other due to premature cell death. There is now accumulating evidence to link these two disparate processes. An increasing number of genetic studies add weight to epidemiological evidence suggesting that sufferers of a neurodegenerative disorder have a reduced incidence for most cancers, but an increased risk for other cancers. Many of the genes associated with either cancer and/or neurodegeneration play a central role in cell cycle control, DNA repair, and kinase signalling. However, the links between these two families of diseases remain to be proven. In this review, we discuss recent and sometimes as yet incomplete genetic discoveries that highlight the overlap of molecular pathways implicated in cancer and neurodegeneration.
LRRK2 is a 250kDa multidomain protein, mutations in which cause familial Parkinson’s disease. Previously, we have demonstrated that the R1441C mutation in the ROC domain decreases GTPase activity. Here we show that the R1441C alters the folding properties of the ROC domain, lowering its thermodynamic stability. Similar to small GTPases, binding of different guanosine nucleotides alters the stability of the ROC domain, suggesting that there is an alteration in conformation dependent on GDP or GTP occupying the active site. GTP/GDP bound state also alters the self-interaction of the ROC domain, accentuating the impact of the R1441C mutation on this property. These data suggest a mechanism whereby the R1441C mutation can reduce the GTPase activity of LRRK2, and highlights the possibility of targeting the stability of the ROC domain as a therapeutic avenue in LRRK2 disease.
LRRK2; ROCO protein; GTPase; Parkinson’s disease; differential scanning fluorimetry; circular dichroism
Parkinson's disease (PD) has long been considered to be a sporadic entity, perhaps with an environmental etiology. However, recent genetic discoveries have challenged this view, as there are many families with diseases of Mendelian inheritance that clinically resemble PD. Here, we will review in detail the neuropathological data relating to familial cases of PD. We will discuss the complicated relationships between the genetically defined cases and the two key pathological events seen in PD, namely loss of dopaminergic neurons in the substantia nigra pars compacta and the formation of protein inclusions, Lewy bodies, in the neurons that survive to the end stage of the disease course. These observations will be synthesized into an overall scheme that emphasizes the two key aspects of the neuropathology as distinct events and suggest that each gene tells us something a little different about the neuropathology of PD.
Parkinson's disease; parkinsonism; α-synuclein; LRRK2; parkin; tau; neuropathology