First neuropathological description of a patient with Parkinson's disease and LRRK2 p.N1437H mutation

LRRK2 kinase activity is necessary for development and regeneration in Nematostella vectensis

BACKGROUND

The starlet sea anemone, Nematostella vectensis, is an emerging model organism with a high regenerative capacity, which was recently found to possess an orthologue to the human Leucine Rich Repeat Kinase 2 (LRRK2) gene. Mutations in this gene are the most common cause of inherited Parkinson's Disease (PD), highlighting the importance of understanding its function. Despite two decades of research, however, the function of LRRK2 is not well established.

METHODS

To investigate the function of LRRKs in Nematostella vectensis, we applied small molecule inhibitors targeting the kinase activity of LRRK2 to examine its function in development, homeostasis and regeneration in Nematostella vectensis.

RESULTS

In vivo analyses inhibiting the kinase function of this enzyme demonstrated a role of nvLRRK2 in development and regeneration of N. vectensis. These findings implicate a developmental role of LRRK2 in Nematostella, adding to the expanding knowledge of its physiological function.

CONCLUSIONS

Our work introduces a new model organism with which to study LRRK biology. We report that LRRK kinase activity is necessary for the development and regeneration of Nematostella. Given the short generation time, genetic trackability and in vivo imaging capabilities, this work introduces Nematostella vectensis as a new model in which to study genes linked to neurodegenerative diseases such as Parkinson's.

Emerging perspectives on precision therapy for Parkinson's disease: multidimensional evidence leading to a new breakthrough in personalized medicine

PD is a prevalent and progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Genes play a significant role in the onset and progression of the disease. While the complexity and pleiotropy of gene expression networks have posed challenges for gene-targeted therapies, numerous pathways of gene variant expression show promise as therapeutic targets in preclinical studies, with some already in clinical trials. With the recognition of the numerous genes and complex pathways that can influence PD, it may be possible to take a novel approach to choose a treatment for the condition. This approach would be based on the symptoms, genomics, and underlying mechanisms of the disease. We discuss the utilization of emerging genetic and pathological knowledge of PD patients to categorize the disease into subgroups. Our long-term objective is to generate new insights for the therapeutic approach to the disease, aiming to delay and treat it more effectively, and ultimately reduce the burden on individuals and society.

Peripheral cutaneous synucleinopathy characteristics in genetic Parkinson's disease

Background

Cutaneous phosphorylated alpha-synuclein (p-α-syn) deposition is an important biomarker of idiopathic Parkinson's disease (iPD). Recent studies have reported synucleinopathies in patients with common genetic forms of PD.

Objective

This study aimed to detect p-α-syn deposition characteristic in rare genetic PD patients with CHCHD2 or RAB39B mutations. Moreover, this study also aimed to describe peripheral alpha-synuclein prion-like activity in genetic PD patients, and acquire whether the cutaneous synucleinopathy characteristics of genetic PD are consistent with central neuropathologies.

Methods

We performed four skin biopsy samples from the distal leg (DL) and proximal neck (C7) of 161 participants, including four patients with CHCHD2 mutations, two patients with RAB39B mutations, 16 patients with PRKN mutations, 14 patients with LRRK2 mutations, five patients with GBA mutations, 100 iPD patients, and 20 healthy controls. We detected cutaneous synucleinopathies using immunofluorescence staining and a seeding amplification assay (SAA). A systematic literature review was also conducted, involving 64 skin biopsies and 205 autopsies of genetic PD patients with synucleinopathy.

Results

P-α-syn was deposited in the peripheral cutaneous nerves of PD patients with CHCHD2, LRRK2, or GBA mutations but not in those with RAB39B or PRKN mutations. There were no significant differences in the location or rate of α-syn-positive deposits between genetic PD and iPD patients. Peripheral cutaneous synucleinopathy appears to well represent brain synucleinopathy of genetic PD, especially autosomal dominant PD (AD-PD). Cutaneous α-synuclein SAA analysis of iPD and LRRK2 and GBA mutation patients revealed prion-like activity.

Conclusion

P-α-syn deposition in peripheral cutaneous nerves, detected using SAA and immunofluorescence staining, may serve as an accurate biomarker for genetic PD and iPD in the future.

LRRK2 kinase activity is necessary for development and regeneration in Nematostella vectensis

Background

The starlet sea anemone, Nematostella vectensis, is an emerging model organism with a high regenerative capacity, which was recently found to possess an orthologue to the human LRRK2 gene (nvLRRK2). The leucine rich repeat kinase 2 (LRRK2) gene, when mutated, is the most common cause of inherited Parkinson's Disease (PD). Its protein product (LRRK2) has implications in a variety of cellular processes, however, the full function of LRRK2 is not well established. Current research is focusing on understanding the function of LRRK2, including both its physiological role as well as its pathobiological underpinnings.

Methods

We used bioinformatics to determine the cross-species conservation of LRRK2, then applied drugs targeting the kinase activity of LRRK2 to examine its function in development, homeostasis and regeneration in Nematostella vectensis.

Results

An in-silico characterization and phylogenetic analysis of nvLRRK2 comparing it to human LRRK2 highlighted key conserved motifs and residues. In vivo analyses inhibiting the kinase function of this enzyme demonstrated a role of nvLRRK2 in development and regeneration of N. vectensis. These findings implicate a developmental role of LRRK2 in Nematostella, adding to the expanding knowledge of its physiological function.

Conclusions

Our work introduces a new model organism with which to study LRRK biology. We show a necessity for LRRK2 in development and regeneration. Given the short generation time, genetic trackability and in vivo imaging capabilities, this work introduces Nematostella vectensis as a new model in which to study genes linked to neurodegenerative diseases such as Parkinson's.

Pain in monogenic Parkinson's disease: a comprehensive review

Pain, a challenging symptom experienced by individuals diagnosed with Parkinson's disease (PD), still lacks a comprehensive understanding of its underlying pathophysiological mechanisms. A systematic investigation of its prevalence and impact on the quality of life in patients affected by monogenic forms of PD has yet to be undertaken. This comprehensive review aims to provide an overview of the association between pain and monogenic forms of PD, specifically focusing on pathogenic variants in SNCA, PRKN, PINK1, PARK7, LRRK2, GBA1, VPS35, ATP13A2, DNAJC6, FBXO7, and SYNJ1. Sixty-three articles discussing pain associated with monogenic PD were identified and analyzed. The included studies exhibited significant heterogeneity in design, sample size, and pain outcome measures. Nonetheless, the findings of this review suggest that patients with monogenic PD may experience specific types of pain depending on the pathogenic variant present, distinguishing them from non-carriers. For instance, individuals with SNCA pathogenic variants have reported painful dystonia, lower extremity pain, dorsal pain, and upper back pain. However, these observations are primarily based on case reports with unclear prevalence. Painful lower limb dystonia and lower back pain are prominent symptoms in PRKN carriers. A continual correlation has been noted between LRRK2 mutations and the emergence of pain, though the conflicting research outcomes pose challenges in reaching definitive conclusions. Individuals with PINK1 mutation carriers also frequently report experiencing pain. Pain has been frequently reported as an initial symptom and the most troublesome one in GBA1-PD patients compared to those with idiopathic PD. The evidence regarding pain in ATP13A2, PARK7, VPS35, DNAJC6, FBXO7, and SYNJ1pathogenic variants is limited and insufficient. The potential linkage between genetic profiles and pain outcomes holds promising clinical implications, allowing for the potential stratification of patients in clinical trials and the development of personalized treatments for pain in monogenic PD. In conclusion, this review underscores the need for further research to unravel the intricate relationship between pain and monogenic forms of PD. Standardized methodologies, larger sample sizes, and longitudinal studies are essential to elucidate the underlying mechanisms and develop targeted therapeutic interventions for pain management in individuals with monogenic PD.

LRRK2 and Parkinson's disease: from genetics to targeted therapy

LRRK2 variants are implicated in both familial and sporadic PD. LRRK2-PD has a generally benign clinical presentation and variable pathology, with inconsistent presence of Lewy bodies and marked Alzheimer's disease pathology. The mechanisms underlying LRRK2-PD are still unclear, but inflammation, vesicle trafficking, lysosomal homeostasis, and ciliogenesis have been suggested, among others. As novel therapies targeting LRRK2 are under development, understanding the role and function of LRRK2 in PD is becoming increasingly important. Here, we outline the epidemiological, pathophysiological, and clinical features of LRRK2-PD, and discuss the arising therapeutic approaches targeting LRRK2 and possible future directions for research.

Autosomal dominant Parkinson's disease caused by the recently identified LRRK2 N1437D mutation in a Chinese family: Clinical features, imaging findings, and functional impact

INTRODUCTION

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of autosomal dominantly inherited Parkinson's disease (PD). Recently, a novel pathogenic variant (N1437D; c.4309A > G; NM_98578) in the LRRK2 gene has been identified in three Chinese families with PD. In this study, we describe a Chinese family with autosomal dominant PD that segregated with the N1437D mutation. A detailed clinical and neuroimaging characterization of the affected family members is reported. We also sought to investigate the functional mechanisms by which the detected mutation could cause PD.

METHODS

We characterized the clinical and imaging phenotype of a Chinese pedigree with autosomal dominant PD. We searched for a disease-causing mutation by targeted sequencing and multiple ligation-dependent probe amplification. The functional impact of the mutation was investigated in terms of LRRK2 kinase activity, guanosine triphosphate (GTP) binding, and guanosine triphosphatase (GTPase) activity.

RESULTS

The disease was found to co-segregate with the LRRK2 N1437D mutation. Patients in the pedigree exhibited typical parkinsonism (age at onset: 54.0 ± 5.9 years). One affected family member - who had evidence of abnormal tau accumulation in the occipital lobe on tau PET imaging - developed PD dementia at follow-up. The mutation markedly increased LRRK2 kinase activity and promoted GTP binding, without affecting GTPase activity.

CONCLUSIONS

This study describes the functional impact of a recently identified LRRK2 mutation, N1437D, that causes autosomal dominant PD in the Chinese population. Further research is necessary to investigate the contribution of this mutation to PD in multiple Asian populations.

Overview of the Impact of Pathogenic LRRK2 Mutations in Parkinson's Disease

Leucine-rich repeat kinase 2 (LRRK2) is a large protein kinase that physiologically phosphorylates and regulates the function of several Rab proteins. LRRK2 is genetically implicated in the pathogenesis of both familial and sporadic Parkinson's disease (PD), although the underlying mechanism is not well understood. Several pathogenic mutations in the LRRK2 gene have been identified, and in most cases the clinical symptoms that PD patients with LRRK2 mutations develop are indistinguishable from those of typical PD. However, it has been shown that the pathological manifestations in the brains of PD patients with LRRK2 mutations are remarkably variable when compared to sporadic PD, ranging from typical PD pathology with Lewy bodies to nigral degeneration with deposition of other amyloidogenic proteins. The pathogenic mutations in LRRK2 are also known to affect the functions and structure of LRRK2, the differences in which may be partly attributable to the variations observed in patient pathology. In this review, in order to help researchers unfamiliar with the field to understand the mechanism of pathogenesis of LRRK2-associated PD, we summarize the clinical and pathological manifestations caused by pathogenic mutations in LRRK2, their impact on the molecular function and structure of LRRK2, and their historical background.

The Relationship between Iron and LRRK2 in a 6-OHDA-Induced Parkinson's Disease Model

The pathogenesis of Parkinson's disease (PD) is very complex and still needs further exploration. Leucine-rich repeat kinase 2 (LRRK2) is associated with familial PD in mutant forms and sporadic PD in the wild-type form. Abnormal iron accumulation is found in the substantia nigra of PD patients, but its exact effects are not very clear. Here, we show that iron dextran exacerbates the neurological deficit and loss of dopaminergic neurons in 6-OHDA lesioned rats. 6-OHDA and ferric ammonium citrate (FAC) significantly increase the activity of LRRK2 as reflected by the phosphorylation of LRRK2, at S935 and S1292 sites. 6-OHDA-induced LRRK2 phosphorylation is attenuated by the iron chelator deferoxamine, especially at the S1292 site. 6-OHDA and FAC markedly induce the expression of pro-apoptotic molecules and the production of ROS by activating LRRK2. Furthermore, G2019S-LRRK2 with high kinase activity showed the strongest absorptive capacity for ferrous iron and the highest intracellular iron content among WT-LRRK2, G2019S-LRRK2, and kinase-inactive D2017A-LRRK2 groups. Taken together, our results demonstrate that iron promotes the activation of LRRK2, and active LRRK2 accelerates ferrous iron uptake, suggesting that there exists an interplay between iron and LRRK2 in dopaminergic neurons, providing a new perspective to uncover the underlying mechanisms of PD occurrence.

Brain and Cerebrospinal Fluid α-Synuclein Real-Time Quaking-Induced Conversion Identifies Lewy Body Pathology in LRRK2-PD

BACKGROUND

The neuropathology of Parkinson's disease (PD) associated with leucine-rich repeat kinase 2 (LRRK2) mutations (LRRK2-PD) is heterogeneous and varies with the type of mutation. There are only a few studies evaluating seeding aggregation assays to detect α-synuclein (α-syn) in patients with LRRK2-PD.

OBJECTIVE

We aimed to investigate whether α-syn real-time quaking induced conversion (RT-QuIC) is a sensitive biomarker of synucleinopathy in LRRK2-PD.

METHODS

We studied α-syn RT-QuIC in brain tissue and postmortem ventricular cerebrospinal fluid (CSF) of LRRK2-PD cases with and without Lewy-type pathology.

RESULTS

The accuracy of α-syn RT-QuIC in substantia nigra and CSF samples of patients with LRRK2-PD was 100%. The test also obtained 100% sensitivity to detect misfolded α-syn in substantia nigra of cases with idiopathic PD and was negative in the substantia nigra of all the control brains without Lewy-type pathology.

CONCLUSIONS

Substantia nigra and ventricular CSF RT-QuIC discriminates with high sensitivity and specificity LRRK2 cases with Lewy-type pathology from those without it. RT-QuIC assay could be of particular interest in the selection of cases for clinical trials in this genetic form of PD. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Human Induced Pluripotent Stem Cell Phenotyping and Preclinical Modeling of Familial Parkinson's Disease

Parkinson's disease (PD) is primarily idiopathic and a highly heterogenous neurodegenerative disease with patients experiencing a wide array of motor and non-motor symptoms. A major challenge for understanding susceptibility to PD is to determine the genetic and environmental factors that influence the mechanisms underlying the variations in disease-associated traits. The pathological hallmark of PD is the degeneration of dopaminergic neurons in the substantia nigra pars compacta region of the brain and post-mortem Lewy pathology, which leads to the loss of projecting axons innervating the striatum and to impaired motor and cognitive functions. While the cause of PD is still largely unknown, genome-wide association studies provide evidence that numerous polymorphic variants in various genes contribute to sporadic PD, and 10 to 15% of all cases are linked to some form of hereditary mutations, either autosomal dominant or recessive. Among the most common mutations observed in PD patients are in the genes LRRK2, SNCA, GBA1, PINK1, PRKN, and PARK7/DJ-1. In this review, we cover these PD-related mutations, the use of induced pluripotent stem cells as a disease in a dish model, and genetic animal models to better understand the diversity in the pathogenesis and long-term outcomes seen in PD patients.

Review of the epidemiology and variability of LRRK2 non-p.Gly2019Ser pathogenic mutations in Parkinson’s disease

Parkinson’s disease (PD) is a heterogenous neurodegenerative disorder. Genetic factors play a significant role, especially in early onset and familial cases. Mutations are usually found in the LRRK2 gene, but their importance varies. Some mutations, such as p.Arg1441Cys or other alterations in the 1441 codon, show clear correlation with PD, whereas others are risk factors found also in healthy populations or have neglectable consequences. They also exhibit various prevalence among different populations. The aim of this paper is to sum up the current knowledge regarding the epidemiology and pathogenicity of LRRK2 mutations, other than the well-established p.Gly2019Ser. We performed a review of the literature using PubMed database. 103 publications met our inclusion criteria. p.Arg1441Cys, p.Arg1441Gly, p.Arg1441His, p.Arg1441Ser are the most common pathogenic mutations in European populations, especially Hispanic. p.Asn1437His is pathogenic and occurs mostly in the Scandinavians. p.Asn1437Ser and p.Asn1437Asp have been reported in German and Chinese cohorts respectively. p.Ile2020Thr is a rare pathogenic mutation described only in a Japanese cohort. p.Met1869Thr has only been reported in Caucasians. p.Tyr1699Cys, p.Ile1122Val have only been found in one family each. p.Glu1874Ter has been described in just one patient. We found no references concerning mutation p.Gln416Ter. We also report the first case of a Polish PD family whose members carried p.Asn1437His.

Mind the Gap: LRRK2 Phenotypes in the Clinic vs. in Patient Cells

Mutations in the Parkinson's disease (PD) protein Leucine Rich Repeat Kinase 2 (LRRK2) have been under study for more than 15 years and our understanding of the cellular phenotypes for the pathogenic mutant forms of LRRK2 has significantly advanced. In parallel to research on LRRK2 mutations in experimental systems, clinical characterization of patients carrying LRRK2 mutations has advanced, as has the analysis of cells that are derived from these patients, including fibroblasts, blood-derived cells, or cells rendered pluripotent. Under the hypothesis that patient clinical phenotypes are a consequence of a cascade of underlying molecular mechanisms gone astray, we currently have a unique opportunity to compare findings from patients and patient-derived cells to ask the question of whether the clinical phenotype of LRRK2 Parkinson's disease and cellular phenotypes of LRRK2 patient-derived cells may be mutually informative. In this review, we aim to summarize the available information on phenotypes of LRRK2 mutations in the clinic, in patient-derived cells, and in experimental models in order to better understand the relationship between the three at the molecular and cellular levels and identify trends and gaps in correlating the data.

Effects of α-Synuclein-Associated Post-Translational Modifications in Parkinson's Disease

α-Synuclein (α-syn), a small highly conserved presynaptic protein containing 140 amino acids, is thought to be the main pathological hallmark in related neurodegenerative disorders. Although the normal function of α-syn is closely involved in the regulation of vesicular neurotransmission in these diseases, the underlying mechanisms of post-translational modifications (PTMs) of α-syn in the pathogenesis of Parkinson's disease (PD) have not been fully characterized. The pathological accumulation of misfolded α-syn has a critical role in PD pathogenesis. Recent studies of factors contributing to α-syn-associated aggregation and misfolding have expanded our understanding of the PD disease process. In this Review, we summarize the structure and physiological function of α-syn, and we further highlight the major PTMs (namely phosphorylation, ubiquitination, nitration, acetylation, truncation, SUMOylation, and O-GlcNAcylation) of α-syn and the effects of these modifications on α-syn aggregation, which may elucidate mechanisms for PD pathogenesis and lay a theoretical foundation for clinical treatment of PD.

Genetic and Environmental Factors Influence the Pleomorphy of LRRK2 Parkinsonism

Missense mutations in the LRRK2 gene were first identified as a pathogenic cause of Parkinson's disease (PD) in 2004. Soon thereafter, a founder mutation in LRRK2, p.G2019S (rs34637584), was described, and it is now estimated that there are approximately 100,000 people worldwide carrying this risk variant. While the clinical presentation of LRRK2 parkinsonism has been largely indistinguishable from sporadic PD, disease penetrance and age at onset can be quite variable. In addition, its neuropathological features span a wide range from nigrostriatal loss with Lewy body pathology, lack thereof, or atypical neuropathology, including a large proportion of cases with concomitant Alzheimer's pathology, hailing LRRK2 parkinsonism as the "Rosetta stone" of parkinsonian disorders, which provides clues to an understanding of the different neuropathological trajectories. These differences may result from interactions between the LRRK2 mutant protein and other proteins or environmental factors that modify LRRK2 function and, thereby, influence pathobiology. This review explores how potential genetic and biochemical modifiers of LRRK2 function may contribute to the onset and clinical presentation of LRRK2 parkinsonism. We review which genetic modifiers of LRRK2 influence clinical symptoms, age at onset, and penetrance, what LRRK2 mutations are associated with pleomorphic LRRK2 neuropathology, and which environmental modifiers can augment LRRK2 mutant pathophysiology. Understanding how LRRK2 function is influenced and modulated by other interactors and environmental factors-either increasing toxicity or providing resilience-will inform targeted therapeutic development in the years to come. This will allow the development of disease-modifying therapies for PD- and LRRK2-related neurodegeneration.

Are genetic and idiopathic forms of Parkinson's disease the same disease?

Genetic forms represent a small fraction of Parkinson's disease (PD) but their discovery has revolutionized research in the field, putting α-synuclein in the spotlight, and uncovering other key neuropathological mechanisms of the disease. The question of whether genetic and idiopathic PD (iPD) correspond to a same disease entity is not simply philosophical, has implications for the discovery of the biological background of PD and for the development of novel therapeutic strategies that may also be applicable to the larger iPD group. Here, we review the current landscape of what has been labeled genetic PD and critically discuss the rational for merging or separating genetic and idiopathic forms of PD as the same or different disease entities. We conclude by addressing the potential implications for future research.

Deep brain stimulation and genetic variability in Parkinson's disease: a review of the literature

Deep brain stimulation is offered as symptomatic treatment in advanced Parkinson's disease, depending on a clinical assessment of the individual patient's risk-benefit profile. Genetics contribute to phenotypic variability in Parkinson's disease, suggesting that genetic testing could have clinical relevance for personalized therapy. Aiming to review current evidence linking genetic variation to deep brain stimulation treatment and outcomes in Parkinson's disease we performed systematic searches in the Embase and PubMed databases to identify relevant publications and summarized the findings. We identified 39 publications of interest. Genetic screening studies indicate that monogenic forms of Parkinson's disease and high-risk variants of GBA may be more common in cohorts treated with deep brain stimulation. Studies assessing deep brain stimulation outcomes in patients carrying mutations in specific genes are limited in size. There are reports suggesting that the phenotype associated with parkin mutations could be suitable for early surgery. In patients with LRRK2 mutations, outcomes of deep brain stimulation seem at least as good as in mutation-negative patients, whereas less favorable outcomes are seen in patients carrying mutations in GBA. Careful assessment of clinical symptoms remains the primary basis for clinical decisions associated with deep brain stimulation surgery in Parkinson's disease, although genetic information could arguably be taken into account in special cases. Current evidence is scarce, but highlights a promising development where genetic profiling may be increasingly relevant for clinicians tailoring personalized medical or surgical therapy to Parkinson's disease patients.

Deep brain stimulation and genetic variability in Parkinson's disease: a review of the literature

Deep brain stimulation is offered as symptomatic treatment in advanced Parkinson’s disease, depending on a clinical assessment of the individual patient’s risk-benefit profile. Genetics contribute to phenotypic variability in Parkinson’s disease, suggesting that genetic testing could have clinical relevance for personalized therapy. Aiming to review current evidence linking genetic variation to deep brain stimulation treatment and outcomes in Parkinson’s disease we performed systematic searches in the Embase and PubMed databases to identify relevant publications and summarized the findings. We identified 39 publications of interest. Genetic screening studies indicate that monogenic forms of Parkinson’s disease and high-risk variants of GBA may be more common in cohorts treated with deep brain stimulation. Studies assessing deep brain stimulation outcomes in patients carrying mutations in specific genes are limited in size. There are reports suggesting that the phenotype associated with parkin mutations could be suitable for early surgery. In patients with LRRK2 mutations, outcomes of deep brain stimulation seem at least as good as in mutation-negative patients, whereas less favorable outcomes are seen in patients carrying mutations in GBA. Careful assessment of clinical symptoms remains the primary basis for clinical decisions associated with deep brain stimulation surgery in Parkinson’s disease, although genetic information could arguably be taken into account in special cases. Current evidence is scarce, but highlights a promising development where genetic profiling may be increasingly relevant for clinicians tailoring personalized medical or surgical therapy to Parkinson’s disease patients.

Low prevalence of known pathogenic mutations in dominant PD genes: A Swedish multicenter study

OBJECTIVE

To determine the frequency of mutations known to cause autosomal dominant Parkinson disease (PD) in a series with more than 10% of Sweden's estimated number of PD patients.

METHODS

The Swedish Parkinson Disease Genetics Network was formed as a national multicenter consortium of clinical researchers who together have access to DNA from a total of 2,206 PD patients; 85.4% were from population-based studies. Samples were analyzed centrally for known pathogenic mutations in SNCA (duplications/triplications, p.Ala30Pro, p.Ala53Thr) and LRRK2 (p.Asn1437His, p.Arg1441His, p.Tyr1699Cys, p.Gly2019Ser, p.Ile2020Thr). We compared the frequency of these mutations in Swedish patients with published PD series and the gnomAD database.

RESULTS

A family history of PD in first- and/or second-degree relatives was reported by 21.6% of participants. Twelve patients (0.54%) carried LRRK2 p.(Gly2019Ser) mutations, one patient (0.045%) an SNCA duplication. The frequency of LRRK2 p.(Gly2019Ser) carriers was 0.11% in a matched Swedish control cohort and a similar 0.098% in total gnomAD, but there was a marked difference between ethnicities in gnomAD, with 42-fold higher frequency among Ashkenazi Jews than all others combined.

CONCLUSIONS

In relative terms, the LRRK2 p.(Gly2019Ser) variant is the most frequent mutation among Swedish or international PD patients, and in gnomAD. SNCA duplications were the second most common of the mutations examined. In absolute terms, however, these known pathogenic variants in dominant PD genes are generally very rare and can only explain a minute fraction of familial aggregation of PD. Additional genetic and environmental mechanisms may explain the frequent co-occurrence of PD in close relatives.

Mutant LRRK2 mediates peripheral and central immune responses leading to neurodegeneration in vivo

Missense mutations in the leucine rich repeat kinase 2 (LRRK2) gene result in late-onset Parkinson's disease. The incomplete penetrance of LRRK2 mutations in humans and LRRK2 murine models of Parkinson's disease suggests that the disease may result from a complex interplay of genetic predispositions and persistent exogenous insults. Since neuroinflammation is commonly associated with the pathogenesis of Parkinson's disease, we examine a potential role of mutant LRRK2 in regulation of the immune response and inflammatory signalling in vivo. Here, we show that mice overexpressing human pathogenic LRRK2 mutations, but not wild-type mice or mice overexpressing human wild-type LRRK2 exhibit long-term lipopolysaccharide-induced nigral neuronal loss. This neurodegeneration is accompanied by an exacerbated neuroinflammation in the brain. The increased immune response in the brain of mutant mice subsequently has an effect on neurons by inducing intraneuronal LRRK2 upregulation. However, the enhanced neuroinflammation is unlikely to be triggered by dysfunctional microglia or infiltrated T cells and/or monocytes, but by peripheral circulating inflammatory molecules. Analysis of cytokine kinetics and inflammatory pathways in the peripheral immune cells demonstrates that LRRK2 mutation alters type II interferon immune response, suggesting that this increased neuroinflammatory response may arise outside the central nervous system. Overall, this study suggests that peripheral immune signalling plays an unexpected-but important-role in the regulation of neurodegeneration in LRRK2-associated Parkinson's disease, and provides new targets for interfering with the onset and progression of the disease.

Leucine-rich repeat kinase 2 (LRRK2) inhibitors differentially modulate glutamate release and Serine935 LRRK2 phosphorylation in striatal and cerebrocortical synaptosomes

Mutations in leucine-rich repeat kinase 2 (LRRK2) gene have been pathogenically linked to Parkinson's disease, and pharmacological inhibition of LRRK2 is being pursued to tackle nigro-striatal dopaminergic neurodegeneration. However, LRRK2 kinase inhibitors may have manifold actions, affecting not only pathological mechanisms in dopaminergic neurons but also physiological functions in nondopaminergic neurons. Therefore, we investigated whether LRRK2 kinase inhibitors differentially modulate dopamine and glutamate release from the mouse striatum and cerebral cortex. Spontaneous and KCl-evoked [3H]-dopamine and glutamate release from superfused synaptosomes obtained from wild-type and LRRK2 knock-out, kinase-dead or G2019S knock-in mice was measured. Two structurally unrelated inhibitors, LRRK2-IN-1 and GSK2578215A, were tested. LRRK2, phosphoSerine1292 and phosphoSerine935 LRRK2 levels were measured in all genotypes, and target engagement was evaluated by monitoring phosphoSerine935 LRRK2. LRRK2-IN-1 inhibited striatal glutamate but not dopamine release; GSK2578215A inhibited striatal dopamine and cortical glutamate but enhanced striatal glutamate release. LRRK2-IN-1 reduced striatal and cortical phosphoSerine935 levels whereas GSK2578215A inhibited only the former. Neither LRRK2 inhibitor affected neurotransmitter release in LRRK2 knock-out and kinase-dead mice; however, they facilitated dopamine without affecting striatal glutamate in G2019S knock-in mice. GSK2578215A inhibited cortical glutamate release in G2019S knock-in mice. We conclude that LRRK2-IN-1 and GSK2578215A modulate exocytosis by blocking LRRK2 kinase activity, although their effects vary depending on the nerve terminal examined. The G2019S mutation unravels a dopamine-promoting action of LRRK2 inhibitors while blunting their effects on glutamate release, which highlights their positive potential for the treatment of PD, especially of LRRK2 mutation carriers.

Deep brain stimulation for monogenic Parkinson's disease: a systematic review

Deep brain stimulation (DBS) is an effective treatment for Parkinson’s disease (PD) patients with motor fluctuations and dyskinesias. The key DBS efficacy studies were performed in PD patients with unknown genotypes; however, given the estimated monogenic mutation prevalence of approximately 5–10%, most commonly LRRK2, PRKN, PINK1 and SNCA, and risk-increasing genetic factors such as GBA, proper characterization is becoming increasingly relevant. We performed a systematic review of 46 studies that reported DBS effects in 221 genetic PD patients. The results suggest that monogenic PD patients have variable DBS benefit depending on the mutated gene. Outcome appears excellent in patients with the most common LRRK2 mutation, p.G2019S, and good in patients with PRKN mutations but poor in patients with the more rare LRRK2 p.R1441G mutation. The overall benefit of DBS in SNCA, GBA and LRRK2 p.T2031S mutations may be compromised due to rapid progression of cognitive and neuropsychiatric symptoms. In the presence of other mutations, the motor changes in DBS-treated monogenic PD patients appear comparable to those of the general PD population.

The Parkinson's disease-associated mutation N1437H impairs conformational dynamics in the G domain of LRRK2

Parkinson disease-associated mutations within the GTPase domain Ras of complex proteins (ROC) of leucine rich repeat kinase 2 (LRRK2) result in an abnormal over-activation of its kinase domain. However, the mechanisms involved remain unclear. Recent study has shown that LRRK2 G-domain cycles between monomeric and dimeric conformations upon binding to GTP or guanosine diphosphate, and that the Parkinson's disease (PD)-associated R1441C/G/H mutations impair the G-domain monomer-dimer dynamics and trap the G-domain in a constitutive monomeric conformation. That led us to question whether other disease-associated mutations in G-domain would also affect its conformation. Here, we report that another PD-associated N1437H mutation also impairs its monomer-dimer conformational dynamics and GTPase activity. In contrast with mutations at R1441, ROC_N1437H was found to be locked in a stable dimeric conformation in solution and its GTPase activity was ∼4-fold lower than that of the wild-type. Furthermore, the N1437H mutation reduced the GTP binding affinity by ∼2.5-fold when compared with other pathogenic G-domain mutations. Moreover, ROC_N1437H was found to have a slower GTP dissociation rate, indicating that N1437H might interrupt the nucleotide exchange cycle. Taken together, our data support that conformational dynamics is important for LRRK2 GTPase activity and that the N1437H mutation impairs GTPase activity by locking the ROC domain in a persistently dimeric state.-Huang, X., Wu, C., Park, Y., Long, X., Hoang, Q. Q., Liao, J. The Parkinson's disease-associated mutation N1437H impairs conformational dynamics in the G domain of LRRK2.

Physiological and pathological functions of LRRK2: implications from substrate proteins

Leucine-rich repeat kinase 2 (LRRK2) encodes a 2527-amino acid (aa) protein composed of multiple functional domains, including a Ras of complex proteins (ROC)-type GTP-binding domain, a carboxyl terminal of ROC (COR) domain, a serine/threonine protein kinase domain, and several repeat domains. LRRK2 is genetically involved in the pathogenesis of both sporadic and familial Parkinson's disease (FPD). Parkinson's disease (PD) is the second most common neurodegenerative disorder, manifesting progressive motor dysfunction. PD is pathologically characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta, and the presence of intracellular inclusion bodies called Lewy bodies (LB) in the remaining neurons. As the most frequent PD-causing mutation in LRRK2, G2019S, increases the kinase activity of LRRK2, an abnormal increase in LRRK2 kinase activity is believed to contribute to PD pathology; however, the precise biological functions of LRRK2 involved in PD pathogenesis remain unknown. Although biochemical studies have discovered several substrate proteins of LRRK2 including Rab GTPases and tau, little is known about whether excess phosphorylation of these substrates is the cause of the neurodegeneration in PD. In this review, we summarize latest findings regarding the physiological and pathological functions of LRRK2, and discuss the possible molecular mechanisms of neurodegeneration caused by LRRK2 and its substrates.

The LRRK2 signalling system

The LRRK2 gene is a major contributor to genetic risk for Parkinson's disease and understanding the biology of the leucine-rich repeat kinase 2 (LRRK2, the protein product of this gene) is an important goal in Parkinson's research. LRRK2 is a multi-domain, multi-activity enzyme and has been implicated in a wide range of signalling events within the cell. Because of the complexities of the signal transduction pathways in which LRRK2 is involved, it has been challenging to generate a clear idea as to how mutations and disease associated variants in this gene are altered in disease. Understanding the events in which LRRK2 is involved at a systems level is therefore critical to fully understand the biology and pathobiology of this protein and is the subject of this review.

Leucine-Rich Repeat Kinase 2 in Parkinson's Disease: Updated from Pathogenesis to Potential Therapeutic Target

BACKGROUND

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the midbrain. The pathogenesis of PD is not fully understood but is likely caused by a combination of genetic and environmental factors. Several genes are associated with the onset and progression of familial PD. There is increasing evidence that leucine-rich repeat kinase 2 (LRRK2) plays a significant role in PD pathophysiology.

SUMMARY

Many studies have been conducted to elucidate the functions of LRRK2 and identify effective LRRK2 inhibitors for PD treatment. In this review, we discuss the role of LRRK2 in PD and recent progress in the use of LRRK2 inhibitors as therapeutic agents. Key Messages: LRRK2 plays a significant role in the pathophysiology of PD, and pharmacological inhibition of LRRK2 has become one of the most promising potential therapies for PD. Further research is warranted to determine the functions of LRRK2 and expand the applications of LRRK2 inhibitors in PD treatment.

Neuropathology of genetic synucleinopathies with parkinsonism: Review of the literature

Clinical-pathological studies remain the gold-standard for the diagnosis of Parkinson's disease (PD). However, mounting data from genetic PD autopsies challenge the diagnosis of PD based on Lewy body pathology. Most of the confirmed genetic risks for PD show heterogenous neuropathology, even within kindreds, which may or may not include Lewy body pathology. We review the literature of genetic PD autopsies from cases with molecularly confirmed PD or parkinsonism and summarize main findings on SNCA (n = 25), Parkin (n = 20, 17 bi-allelic and 3 heterozygotes), PINK1 (n = 5, 1 bi-allelic and 4 heterozygotes), DJ-1 (n = 1), LRRK2 (n = 55), GBA (n = 10 Gaucher disease patients with parkinsonism), DNAJC13, GCH1, ATP13A2, PLA2G6 (n = 8 patients, 2 with PD), MPAN (n = 2), FBXO7, RAB39B, and ATXN2 (SCA2), as well as on 22q deletion syndrome (n = 3). Findings from autopsies of heterozygous mutation carriers of genes that are traditionally considered recessively inherited are also discussed. Lewy bodies may be present in syndromes clinically distinctive from PD (eg, MPAN-related neurodegeneration) and absent in patients with clinical PD syndrome (eg, LRRK2-PD or Parkin-PD). Therefore, the authors can conclude that the presence of Lewy bodies are not specific to the diagnosis of PD and that PD can be diagnosed even in the absence of Lewy body pathology. Interventions that reduce alpha-synuclein load may be more justified in SNCA-PD or GBA-PD than in other genetic forms of PD. The number of reported genetic PD autopsies remains small, and there are limited genotype-clinical-pathological-phenotype studies. Therefore, larger series of autopsies from genetic PD patients are required. © 2017 International Parkinson and Movement Disorder Society.

Interaction of LRRK2 and α-Synuclein in Parkinson's Disease

Parkinson's disease (PD) is a progressively debilitating neurodegenerative syndrome. It is best described as a movement disorder characterized by motor dysfunctions, progressive degeneration of dopaminergic neurons of the substantia nigra pars compacta, and abnormal intraneuronal protein aggregates, named Lewy bodies and Lewy neurites. Nevertheless, knowledge of the molecular events leading to this pathophysiology is incomplete. To date, only mutations in the α-synuclein and LRRK2-encoding genes have been associated with typical findings of clinical and pathologic PD. LRRK2 appears to have a central role in the pathogenesis of PD as it is associated with α-synuclein pathology and other proteins implicated in neurodegeneration. Thus, LRRK2 dysfunction may influence the accumulation of α-synuclein and its pathology through diverse pathomechanisms altering cellular functions and signaling pathways, including immune system, autophagy, vesicle trafficking, and retromer complex modulation. Consequently, development of novel LRRK2 inhibitors can be justified to treat the neurodegeneration associated with abnormal α-synuclein accumulation.

Multisystem Lewy body disease and the other parkinsonian disorders

Here we prioritize as multisystem Lewy body disease (MLBD) those genetic forms of Parkinson's disease that point the way toward a mechanistic understanding of the majority of sporadic disease. Pathological diagnosis of genetic subtypes offers the prospect of distinguishing different mechanistic trajectories with a common mutational etiology, differing outcomes from varying allelic bases, and those disease-associated variants that can be used in gene-environment analysis. Clearly delineating parkinsonian disorders into subclasses on the basis of molecular mechanisms with well-characterized outcome expectations is the basis for refining these forms of neurodegeneration as research substrate through the use of cell models derived from affected individuals while ensuring that clinically collected data can be used for therapeutic decisions and research without increasing the noise and confusion engendered by the collection of data against a range of historically defined criteria.

Cellular processes associated with LRRK2 function and dysfunction

Mutations in the leucine-rich repeat kinase 2 (LRRK2)-encoding gene are the most common cause of monogenic Parkinson's disease. The identification of LRRK2 polymorphisms associated with increased risk for sporadic Parkinson's disease, as well as the observation that LRRK2-Parkinson's disease has a pathological phenotype that is almost indistinguishable from the sporadic form of disease, suggested LRRK2 as the culprit to provide understanding for both familial and sporadic Parkinson's disease cases. LRRK2 is a large protein with both GTPase and kinase functions. Mutations segregating with Parkinson's disease reside within the enzymatic core of LRRK2, suggesting that modification of its activity impacts greatly on disease onset and progression. Although progress has been made since its discovery in 2004, there is still much to be understood regarding LRRK2's physiological and neurotoxic properties. Unsurprisingly, given the presence of multiple enzymatic domains, LRRK2 has been associated with a diverse set of cellular functions and signalling pathways including mitochondrial function, vesicle trafficking together with endocytosis, retromer complex modulation and autophagy. This review discusses the state of current knowledge on the role of LRRK2 in health and disease with discussion of potential substrates of phosphorylation and functional partners with particular emphasis on signalling mechanisms. In addition, the use of immune cells in LRRK2 research and the role of oxidative stress as a regulator of LRRK2 activity and cellular function are also discussed.

Chemical genetic approach identifies microtubule affinity-regulating kinase 1 as a leucine-rich repeat kinase 2 substrate

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of autosomal-dominant forms of Parkinson's disease. LRRK2 is a modular, multidomain protein containing 2 enzymatic domains, including a kinase domain, as well as several protein-protein interaction domains, pointing to a role in cellular signaling. Although enormous efforts have been made, the exact pathophysiologic mechanisms of LRRK2 are still not completely known. In this study, we used a chemical genetics approach to identify LRRK2 substrates from mouse brain. This approach allows the identification of substrates of 1 particular kinase in a complex cellular environment. Several of the identified peptides are involved in the regulation of microtubule (MT) dynamics, including microtubule-associating protein (MAP)/microtubule affinity-regulating kinase 1 (MARK1). MARK1 is a serine/threonine kinase known to phosphorylate MT-binding proteins such as Tau, MAP2, and MAP4 at KXGS motifs leading to MT destabilization. In vitro kinase assays and metabolic-labeling experiments in living cells confirmed MARK1 as an LRRK2 substrate. Moreover, we also showed that LRRK2 and MARK1 are interacting in eukaryotic cells. Our findings contribute to the identification of physiologic LRRK2 substrates and point to a potential mechanism explaining the reported effects of LRRK2 on neurite morphology.

Phosphatases of α-synuclein, LRRK2, and tau: important players in the phosphorylation-dependent pathology of Parkinsonism

An important challenge in the field of Parkinson’s disease (PD) is to develop disease modifying therapies capable of stalling or even halting disease progression. Coupled to this challenge is the need to identify disease biomarkers, in order to identify pre-symptomatic hallmarks of disease and monitor disease progression. The answer to these challenges lies in the elucidation of the molecular causes underlying PD, for which important leads are disease genes identified in studies investigating the underlying genetic causes of PD. LRRK2 and α-syn have been both linked to familial forms of PD as well as associated to sporadic PD. Another gene, microtubule associated protein tau (MAPT), has been genetically linked to a dominant form of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) and genome-wide association studies report a strong association between MAPT and sporadic PD. Interestingly, LRRK2, α-syn, and tau are all phosphorylated proteins, and their phosphorylation patterns are linked to disease. In this review, we provide an overview of the evidence linking LRRK2, α-syn, and tau phosphorylation to PD pathology and focus on studies which have identified phosphatases responsible for dephosphorylation of pathology-related phosphorylations. We also discuss how the LRRK2, α-syn, and tau phosphatases may point to separate or cross-talking pathological pathways in PD. Finally, we will discuss how the study of phosphatases of dominant Parkinsonism proteins opens perspectives for targeting pathological phosphorylation events.

Heterogeneity of leucine-rich repeat kinase 2 mutations: genetics, mechanisms and therapeutic implications

Variation within and around the leucine-rich repeat kinase 2 (LRRK2) gene is associated with familial and sporadic Parkinson's disease (PD). Here, we discuss the prevalence of LRRK2 substitutions in different populations and their association with PD, as well as molecular and cellular mechanisms of pathologically relevant LRRK2 mutations. Kinase activation was proposed as a universal molecular mechanism for all pathogenic LRRK2 mutations, but later reports revealed heterogeneity in the effect of mutations on different activities of LRRK2. One mutation (G2019S) increases kinase activity, whereas mutations in the Ras of complex proteins (ROC)-C-terminus of ROC (COR) bidomain impair the GTPase function of LRRK2. Some risk factor variants, including G2385R in the WD40 domain, actually decrease the kinase activity of LRRK2. We suggest a model where LRRK2 mutations exert different molecular mechanisms but interfere with normal cellular function of LRRK2 at different levels of the same downstream pathway. Finally, we discuss the current state of therapeutic approaches for LRRK2-related PD.

Pharmacological inhibition of LRRK2 cellular phosphorylation sites provides insight into LRRK2 biology

Mutations in LRRK2 (leucine-rich repeat kinase 2) have been linked to inherited forms of PD (Parkinson's disease). Substantial pre-clinical research and drug discovery efforts have focused on LRRK2 with the hope that small-molecule inhibitors of the enzyme may be valuable for the treatment or prevention of the onset of PD. The pathway to develop therapeutic or neuroprotective agents based on LRRK2 function (i.e. kinase activity) has been facilitated by the development of both biochemical and cell-based assays for LRRK2. LRRK2 is phosphorylated on Ser910, Ser935, Ser955 and Ser973 in the N-terminal domain of the enzyme, and these sites of phosphorylation are likely to be regulated by upstream enzymes in an LRRK2 kinase-activity-dependent manner. Knowledge of these phosphorylation sites and their regulation can be adapted to high-throughput-screening-amenable platforms. The present review describes the utilization of LRRK2 phosphorylation as indicators of enzyme inhibition, as well as how such assays can be used to deconvolute the pathways in which LRRK2 plays a role.

Monogenic Parkinson's disease and parkinsonism: clinical phenotypes and frequencies of known mutations

Mutations in seven genes are robustly associated with autosomal dominant (SNCA, LRRK2, EIF4G1, VPS35) or recessive (parkin/PARK2, PINK1, DJ1/PARK7) Parkinson's disease (PD) or parkinsonism. Changes in a long list of additional genes have been suggested as causes for parkinsonism or PD, including genes for hereditary ataxias (ATXN2, ATXN3, FMR1), frontotemporal dementia (C9ORF72, GRN, MAPT, TARDBP), DYT5 (GCH1, TH, SPR), and others (ATP13A2, CSF1R, DNAJC6, FBXO, GIGYF2, HTRA2, PLA2G6, POLG, SPG11, UCHL1). This review summarizes the clinical features of diseases caused by mutations in these genes, and their frequencies. Point mutations and multiplications in SNCA cause cognitive or psychiatric symptoms, parkinsonism, dysautonomia and myoclonus with widespread alpha-synuclein pathology in the central and peripheral nervous system. LRRK2 mutations may lead to a clinical phenotype closely resembling idiopathic PD with a puzzling variety in neuropathology. Mutations in parkin/PARK2, PINK1 or DJ1/PARK7 may cause early-onset parkinsonism with a low risk for cognitive decline and a pathological process usually restricted to the brainstem. Carriers of mutations in the other genes may develop parkinsonism with or without additional symptoms, but rarely a disease resembling PD. The pathogenicity of several mutations remains unconfirmed. Although some mutations occur with high frequency in specific populations, worldwide all are very rare. The genetic cause of the majority of patients with sporadic or hereditary PD remains unknown in most populations. Clinical genetic testing is useful for selected patients. Testing strategies need to be adapted individually based on clinical phenotype and estimated frequency of the mutation in the patient's population.

LRRK2: cause, risk, and mechanism

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.

The neuropathology of genetic Parkinson's disease

Pathological data from autopsies genotyped for Parkinson's disease (PD)-related mutations in alpha-synuclein, Parkin, PINK1, DJ1, LRRK2, and glucocerebrosidase have accumulated in recent years. The aim of this review is to systematically review all pathological reports of mutation carriers and to identify pathological patterns and gaps in the currently available data. A systematic review of the English literature was done using the terms "Parkinson's disease," "brain pathology," "autopsy," the specific gene nomenclature, and any combination of the above. Most studies included reports of convenience samples: either cases that were preidentified as mutation carriers before autopsy or screens of Lewy body brain banks. Nineteen autopsies of alpha-synuclein mutation carriers, 49 of LRRK2 mutation carriers, nine of Parkin mutation carriers, one of a PINK1 mutation carrier, and 86 of glucocerebrosidase mutation carriers were identified. Most autopsies of alpha-synuclein, LRRK2 G2019S, and glucocerebrosidase mutation carriers demonstrated Lewy body pathology, as opposed to Parkin and LRRK2 non-G2019S mutation carriers. However, there was a marked variability in pathological findings, even among carriers of identical mutations. Pathological data from DJ1 mutation carriers, nonmanifesting mutation carriers (e.g., of LRRK2 mutations), and carriers of a single Parkin mutation were lacking. In gathering together all studies of PD autopsies with an identified genetic risk, this review highlights the wealth of information generated as well as shortcomings in the available data. In particular, there is a need for larger, unbiased pathological studies. Differential association of Lewy pathology with specific mutations may reflect heterogeneity in pathogenic mechanisms among the different PD-related genes.