Clinical and pathologic features of families with LRRK2-associated Parkinson's disease

Peripheral synucleinopathy in Parkinson disease with LRRK2 G2385R variants

Objective

Recent studies demonstrated cutaneous phosphorylated α synuclein (p‐syn) deposition in idiopathic and some monogenetic Parkinson disease (PD) patients, suggesting synucleinopathy identical to that in the brain. Although the LRRK2 Gly2385Arg (G2385R) variant is a common PD risk factor in the Chinese population, the pathogenesis of PD with G2385R variant has not been reported. We investigated whether synucleinopathy and small fiber neuropathy (SFN) are associated with the G2385R variant.

Methods

We performed genotyping in 59 PD patients and 30 healthy controls from the skin biopsy database. The scale of SFN was assessed, as well as bright‐field immunohistochemistry against antiprotein gene product 9.5 (PGP9.5) and double‐labeling immunofluorescence with anti‐PGP9.5 and anti‐p‐syn.

Results

(1) p‐syn deposited in the skin nerve fibers of G2385R carrier PD patients, which was a different pattern from noncarriers, without no difference observed between proximal and distal regions; (2) decreased distal intraepidermal nerve fiber density was found in both the G2385R carrier and the noncarrier PD group, and was negatively correlated with composite autonomic symptom score‐31 item (COMPASS‐31) scores; (3) PD patients with the G2385R variant showed a more peculiar clinical profile than noncarriers with a higher nonmotor symptoms scale, COMPASS‐31 score, and levodopa equivalent dose, in addition to an increased prevalence of certain autonomic symptoms or rapid eye movement sleep behavior disorders.

Interpretation

Synucleinopathy is related to the LRRK2 G2385R genotype and implies a different pathogenesis in G2385R variant carriers and noncarriers. This study also extended the clinical profiles of PD patients with the G2385R variant.

Ubiqutination via K27 and K29 chains signals aggregation and neuronal protection of LRRK2 by WSB1

A common genetic form of Parkinson's disease (PD) is caused by mutations in LRRK2. We identify WSB1 as a LRRK2 interacting protein. WSB1 ubiquitinates LRRK2 through K27 and K29 linkage chains, leading to LRRK2 aggregation and neuronal protection in primary neurons and a Drosophila model of G2019S LRRK2. Knocking down endogenous WSB1 exacerbates mutant LRRK2 neuronal toxicity in neurons and the Drosophila model, indicating a role for endogenous WSB1 in modulating LRRK2 cell toxicity. WSB1 is in Lewy bodies in human PD post-mortem tissue. These data demonstrate a role for WSB1 in mutant LRRK2 pathogenesis, and suggest involvement in Lewy body pathology in sporadic PD. Our data indicate a role in PD for ubiquitin K27 and K29 linkages, and suggest that ubiquitination may be a signal for aggregation and neuronal protection in PD, which may be relevant for other neurodegenerative disorders. Finally, our study identifies a novel therapeutic target for PD.

Leucine-rich repeat kinase 2 regulates Sec16A at ER exit sites to allow ER-Golgi export

Leucine-rich repeat kinase 2 (LRRK2) has been associated with Parkinson's disease (PD) and other disorders. However, its normal physiological functions and pathogenic properties remain elusive. Here we show that LRRK2 regulates the anterograde ER-Golgi transport through anchoring Sec16A at the endoplasmic reticulum exit sites (ERES). LRRK2 interacted and co-localized with Sec16A, a key protein in the formation of ERES. Lrrk2 depletion caused a dispersion of Sec16A from ERES and impaired ER export. In neurons, LRRK2 and Sec16A showed extensive co-localization at the dendritic ERES (dERES) that locally regulate the transport of proteins to the dendritic spines. A loss of Lrrk2 affected the association of Sec16A with dERES and impaired the activity-dependent targeting of glutamate receptors onto the cell/synapse surface. Furthermore, the PD-related LRRK2 R1441C missense mutation in the GTPase domain interfered with the interaction of LRRK2 with Sec16A and also affected ER-Golgi transport, while LRRK2 kinase activity was not required for these functions. Therefore, our findings reveal a new physiological function of LRRK2 in ER-Golgi transport, suggesting ERES dysfunction may contribute to the pathogenesis of PD.

LRRK2 kinase activity and biology are not uniformly predicted by its autophosphorylation and cellular phosphorylation site status

Missense mutations in the Leucine-Rich Repeat protein Kinase 2 (LRRK2) gene are the most common genetic predisposition to develop Parkinson's disease (PD) (Farrer et al., 2005; Skipper et al., 2005; Di Fonzo et al., 2006; Healy et al., 2008; Paisan-Ruiz et al., 2008; Lesage et al., 2010). LRRK2 is a large multi-domain phosphoprotein with a GTPase domain and a serine/threonine protein kinase domain whose activity is implicated in neuronal toxicity; however the precise mechanism is unknown. LRRK2 autophosphorylates on several serine/threonine residues across the enzyme and is found constitutively phosphorylated on Ser910, Ser935, Ser955, and Ser973, which are proposed to be regulated by upstream kinases. Here we investigate the phosphoregulation at these sites by analyzing the effects of disease-associated mutations Arg1441Cys, Arg1441Gly, Ala1442Pro, Tyr1699Cys, Ile2012Thr, Gly2019Ser, and Ile2020Thr. We also studied alanine substitutions of phosphosite serines 910, 935, 955, and 973 and specific LRRK2 inhibition on autophosphorylation of LRRK2 Ser1292, Thr1491, Thr2483 and phosphorylation at the cellular sites. We found that mutants in the Roc-COR domains, including Arg1441Cys, Arg1441His, Ala1442Pro, and Tyr1699Cys, can positively enhance LRRK2 kinase activity, while concomitantly inducing the dephosphorylation of the cellular sites. Mutation of the cellular sites individually did not affect LRRK2 intrinsic kinase activity; however, Ser910/935/955/973Ala mutations trended toward increased kinase activity of LRRK2. Increased cAMP levels did not lead to increased LRRK2 cellular site phosphorylation, 14-3-3 binding or kinase activity. In cells, inhibition of LRRK2 kinase activity leads to dephosphorylation of Ser1292 by Calyculin A and Okadaic acid sensitive phosphatases, while the cellular sites are dephosphorylated by Calyculin A sensitive phosphatases. These findings indicate that comparative analysis of both Ser1292 and Ser910/935/955/973 phosphorylation sites will provide important and distinct measures of LRRK2 kinase and biological activity in vitro and in vivo.

Evolution of neurodegeneration

A number of neurodegenerative diseases principally affect humans as they age and are characterized by the loss of specific groups of neurons in different brain regions. Although these disorders are generally sporadic, it is now clear that many of them have a substantial genetic component. As genes are the raw material with which evolution works, we might benefit from understanding these genes in an evolutionary framework. Here, I will discuss how we can understand whether evolution has shaped genes involved in neurodegeneration and the implications for practical issues, such as our choice of model systems for studying these diseases, and more theoretical concerns, such as the level of selection against these phenotypes.

Conserved role of dopamine in the modulation of behavior

Dopamine is an ancient signaling molecule. It is responsible for maintaining the adaptability of behavioral outputs and is found across taxa. The following is a summary of the role of dopamine and the mechanisms of its function and dysfunction. We discuss our recent findings on dopaminergic control of behaviors in C. elegans and discuss its potential implications for work in the fields of C. elegans and Parkinson research.

Inhibitors of leucine-rich repeat kinase-2 protect against models of Parkinson's disease

Leucine rich repeat kinase 2 (LRRK2) mutations are a common cause of Parkinson’s disease (PD). Here, we identify inhibitors of LRRK2 kinase, which are protective in in vitro and in vivo models of LRRK2-induced neurodegeneration. These results establish that LRRK2-induced degeneration of neurons in vivo is kinase dependent and that LRRK2 kinase inhibition provides a potential new neuroprotective paradigm for the treatment of PD.

Impaired dopaminergic neurotransmission and microtubule-associated protein tau alterations in human LRRK2 transgenic mice

Mutations in the Leucine Rich Repeat Kinase 2 (LRRK2) gene, first described in 2004 have now emerged as the most important genetic finding in both autosomal dominant and sporadic Parkinson's disease (PD). While a formidable research effort has ensued since the initial gene discovery, little is known of either the normal or the pathological role of LRRK2. We have created lines of mice that express human wild-type (hWT) or G2019S Lrrk2 via bacterial artificial chromosome (BAC) transgenesis. In vivo analysis of the dopaminergic system revealed abnormal dopamine neurotransmission in both hWT and G2019S transgenic mice evidenced by a decrease in extra-cellular dopamine levels, which was detected without pharmacological manipulation. Immunopathological analysis revealed changes in localization and increased phosphorylation of microtubule binding protein tau in G2019S mice. Quantitative biochemical analysis confirmed the presence of differential phospho-tau species in G2019S mice but surprisingly, upon dephosphorylation the tau isoform banding pattern in G2019S mice remained altered. This suggests that other post-translational modifications of tau occur in G2019S mice. We hypothesize that Lrrk2 may impact on tau processing which subsequently leads to increased phosphorylation. Our models will be useful for further understanding of the mechanistic actions of LRRK2 and future therapeutic screening.

Basic mechanisms of neurodegeneration: a critical update

Neurodegenerative diseases are characterized by progressive dysfunction of specific populations of neurons, determining clinical presentation. Neuronal loss is associated with extra and intracellular accumulation of misfolded proteins, the hallmarks of many neurodegenerative proteinopathies. Major basic processes include abnormal protein dynamics due to deficiency of the ubiquitin-proteosome-autophagy system, oxidative stress and free radical formation, mitochondrial dysfunction, impaired bioenergetics, dysfunction of neurotrophins, 'neuroinflammatory' processes and (secondary) disruptions of neuronal Golgi apparatus and axonal transport. These interrelated mechanisms lead to programmed cell death is a long run over many years. Neurodegenerative disorders are classified according to known genetic mechanisms or to major components of protein deposits, but recent studies showed both overlap and intraindividual diversities between different phenotypes. Synergistic mechanisms between pathological proteins suggest common pathogenic mechanisms. Animal models and other studies have provided insight into the basic neurodegeneration and cell death programs, offering new ways for future prevention/treatment strategies.

Wild-type LRRK2 but not its mutant attenuates stress-induced cell death via ERK pathway

Leucine-rich repeat kinase 2 (LRRK2) is a recently identified gene that, when mutated at specific locations, results in the onset of parkinsonian symptoms with clinical features indistinguishable from idiopathic Parkinson's disease. Based on structural and domain analysis, LRRK2 is predicted to function as a stress-responsive protein scaffold mediating the regulation of mitogen activating protein kinase (MAPK) pathways. Consistent with this notion, our results supported the notion that expression of wild-type LRRK2 but not Y1699C or G2019S mutants enhanced the tolerance of HEK293 and SH-SY5Y cells towards H(2)O(2)-induced oxidative stress. This increase in stress tolerance was dependent on the presence of the kinase domain of the LRRK2 gene and manifested through the activation of the ERK pathway. Collectively, our results indicated that cells expressing LRRK2 mutants suffer a loss of protection normally derived from wild-type LRRK2, making them more vulnerable to oxidative stress.

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.

Phenotype, genotype, and worldwide genetic penetrance of LRRK2-associated Parkinson's disease: a case-control study

BACKGROUND

Mutations in LRRK2, the gene that encodes leucine-rich repeat kinase 2, are a cause of Parkinson's disease (PD). The International LRRK2 Consortium was established to answer three key clinical questions: can LRRK2-associated PD be distinguished from idiopathic PD; which mutations in LRRK2 are pathogenic; and what is the age-specific cumulative risk of PD for individuals who inherit or are at risk of inheriting a deleterious mutation in LRRK2?

METHODS

Researchers from 21 centres across the world collaborated on this study. The frequency of the common LRRK2 Gly2019Ser mutation was estimated on the basis of data from 24 populations worldwide, and the penetrance of the mutation was defined in 1045 people with mutations in LRRK2 from 133 families. The LRRK2 phenotype was defined on the basis of 59 motor and non-motor symptoms in 356 patients with LRRK2-associated PD and compared with the symptoms of 543 patients with pathologically proven idiopathic PD.

FINDINGS

Six mutations met the consortium's criteria for being proven pathogenic. The frequency of the common LRRK2 Gly2019Ser mutation was 1% of patients with sporadic PD and 4% of patients with hereditary PD; the frequency was highest in the middle east and higher in southern Europe than in northern Europe. The risk of PD for a person who inherits the LRRK2 Gly2019Ser mutation was 28% at age 59 years, 51% at 69 years, and 74% at 79 years. The motor symptoms (eg, disease severity, rate of progression, occurrence of falls, and dyskinesia) and non-motor symptoms (eg, cognition and olfaction) of LRRK2-associated PD were more benign than those of idiopathic PD.

INTERPRETATION

Mutations in LRRK2 are a clinically relevant cause of PD that merit testing in patients with hereditary PD and in subgroups of patients with PD. However, this knowledge should be applied with caution in the diagnosis and counselling of patients.

FUNDING

UK Medical Research Council; UK Parkinson's Disease Society; UK Brain Research Trust; Internationaal Parkinson Fonds; Volkswagen Foundation; National Institutes of Health: National Institute of Neurological Disorders and Stroke and National Institute of Aging; Udall Parkinson's Disease Centre of Excellence; Pacific Alzheimer Research Foundation Centre; Italian Telethon Foundation; Fondazione Grigioni per il Morbo di Parkinson; Michael J Fox Foundation for Parkinson's Research; Safra Global Genetics Consortium; US Department of Veterans Affairs; French Agence Nationale de la Recherche.

A genome-wide scan in an Amish pedigree with parkinsonism

The identification of familial Parkinson Disease (PD) genes is yielding important molecular pathogenetic insights. In an effort to identify additional PD genes, we studied an eight generation Amish pedigree with apparent autosomal dominant parkinsonism with incomplete penetrance. Phenotypic variability ranged from idiopathic PD to progressive supranuclear palsy (PSP), with the average age at onset 53 years (range of 39 to 74 years). We identified markers on chromosome 3 and 7 that were significant at a genome-wide level by parametric and nonparametric criteria, lod > 3 and non-parametric P-value < 0.10, respectively. We also identified markers on chromosomes 10 and 22 with lod > 3. These data suggest that parkinsonism in this pedigree is genetically complex, with contributions from several loci.

Molecular pathways and genetic aspects of Parkinson's disease: from bench to bedside

Idiopathic Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by dopaminergic neuronal loss within the substantia nigra. The incidence and prevalence of PD is rising with an increasing aging population. PD is a slowly progressive condition and patients can develop debilitating motor and functional impairment. Current research has implicated oxidative stress, alpha-synucleinopathy and dysfunction of the ubiquitin-proteasome system in the pathogenesis of PD. A number of gene mutations have also been linked to the development of PD. The elucidation of these new molecular pathways has increased our knowledge of PD pathophysiology. This article reviews important molecular mechanisms and genetic causes implicated in the pathogenesis of PD, which has led to new areas of therapeutic drug research.

The role of anti-inflammatory agents in Parkinson's disease

There is ample and increasing evidence, from studies of human pathology, animal models and tissue culture, that chronic inflammation occurs in the basal ganglia in patients with Parkinson's disease. In such inflammatory states, activated glia can produce large quantities of free radicals and other neurotoxic materials. Dopaminergic neurons appear to be particularly vulnerable to these neurotoxins. The anti-inflammatory drugs that are presently in wide use act on peripheral players in the inflammatory process. Many experiments are under way to find agents that inhibit more potent contributors, such as the activated microglia or terminal complement proteins. Whether such drugs will slow the process of Parkinson's disease or reduce the high risk of dementia in such patients remains to be determined in future work.