LRRK2 in Parkinson's disease – drawing the curtain of penetrance: a commentary

Parkinson's disease is the most common neurodegenerative movement disorder and affects about 2% of the population over the age of 60 years. In 2004, mutations in the LRRK2 gene were first described and turned out to be the most frequent genetic cause of familial and sporadic Parkinson's disease and may account for up to 40% of patients in distinct populations. Based on these findings, Latourelle and colleagues show that the penetrance of the most common LRRK2 mutation is higher in patients with familial compared with sporadic Parkinson's disease and identified a substantial number of affected relatives of mutation carriers not presenting with a LRRK2 mutation themselves. This commentary discusses the role of genetic and/or environmental susceptibility factors modulating the expressivity of the disease trait, how these factors may contribute to the phenomenon of phenocopies in genetically defined Parkinson's disease pedigrees, and how the findings of Latourelle and colleagues, published this month in BMC Medicine, relate to current concepts of genetic counselling

LRRK2 at the interface of autophagosomes, endosomes and lysosomes

Over the past 20 years, substantial progress has been made in identifying the underlying genetics of Parkinson’s disease (PD). Of the known genes, LRRK2 is a major genetic contributor to PD. However, the exact function of LRRK2 remains to be elucidated. In this review, we discuss how familial forms of PD have led us to hypothesize that alterations in endomembrane trafficking play a role in the pathobiology of PD. We will discuss the major observations that have been made to elucidate the role of LRRK2 in particular, including LRRK2 animal models and high-throughput proteomics approaches. Taken together, these studies strongly support a role of LRRK2 in vesicular dynamics. We also propose that targeting these pathways may not only be beneficial for developing therapeutics for LRRK2-driven PD, but also for other familial and sporadic cases

LRRK2 Phosphorylates Tubulin-Associated Tau but Not the Free Molecule: LRRK2-Mediated Regulation of the Tau-Tubulin Association and Neurite Outgrowth

Leucine-rich repeat kinase 2 (LRRK2), a large protein kinase containing multi-functional domains, has been identified as the causal molecule for autosomal-dominant Parkinson's disease (PD). In the present study, we demonstrated for the first time that (i) LRRK2 interacts with tau in a tubulin-dependent manner; (ii) LRRK2 directly phosphorylates tubulin-associated tau, but not free tau; (iii) LRRK2 phosphorylates tau at Thr181 as one of the target sites; and (iv) The PD-associated LRRK2 mutations, G2019S and I2020T, elevated the degree of tau-phosphorylation. These results provide direct proof that tau is a physiological substrate for LRRK2. Furthermore, we revealed that LRRK2-mediated phosphorylation of tau reduces its tubulin-binding ability. Our results suggest that LRRK2 plays an important role as a physiological regulator for phosphorylation-mediated dissociation of tau from microtubules, which is an integral aspect of microtubule dynamics essential for neurite outgrowth and axonal transport

A comparative study of Lrrk2 function in primary neuronal cultures.

OBJECTIVE: To assess the contribution of wild-type, mutant and loss of leucine-rich repeat kinase-2 (LRRK2; Lrrk2) on dendritic neuronal arborization. BACKGROUND: LRRK2 mutations are recognized as the major genetic determinant of susceptibility to Parkinson's disease for which a cellular assay of Lrrk2 mutant function would facilitate the development of targeted molecular therapeutics. METHODS: Dendritic neuronal arborization (neurite length, branching and the number of processes per cell) was quantified in primary hippocampal and midbrain cultures derived from five lines of recombinant LRRK2 mice, including human BAC wild-type and mutant overexpressors (Y1699C and G2019S), murine knock-out and G2019S knock-in animals. RESULTS: Neuronal arborization in cultures from BAC Lrrk2 wild-type animals is comparable to non-transgenic littermate controls, despite high levels of human transgene expression. In contrast, primary neurons from both BAC mutant overexpressors presented with significantly reduced neuritic outgrowth and branching, although the total number of processes per cell remained comparable. The mutant-specific toxic gain-of-function observed in cultures from BAC mutant mice may be partially rescued by staurosporine treatment, a non-specific kinase inhibitor. In contrast, neuronal arborization is far more extensive in neuronal cultures derived from murine knock-out mice that lack endogenous Lrrk2 expression. In Lrrk2 G2019S knock-in mice, arguably the most physiologically relevant system, neuritic arborization is not impaired. CONCLUSIONS: Impairment of neuritic arborization is an exaggerated, albeit mutant specific, consequence of Lrrk2 over-expression in primary cultures. The phenotype and assay described provides a means to develop therapeutic agents that modulate the toxic gain-of-function conferred by mutant Lrrk2

LRRK2 knockout mice have an intact dopaminergic system but display alterations in exploratory and motor co-ordination behaviors.

Mutations in the LRRK2 gene are the most common cause of genetic Parkinson's disease. Although the mechanisms behind the pathogenic effects of LRRK2 mutations are still not clear, data emerging from in vitro and in vivo models suggests roles in regulating neuronal polarity, neurotransmission, membrane and cytoskeletal dynamics and protein degradation.We created mice lacking exon 41 that encodes the activation hinge of the kinase domain of LRRK2. We have performed a comprehensive analysis of these mice up to 20 months of age, including evaluation of dopamine storage, release, uptake and synthesis, behavioral testing, dendritic spine and proliferation/neurogenesis analysis.Our results show that the dopaminergic system was not functionally comprised in LRRK2 knockout mice. However, LRRK2 knockout mice displayed abnormal exploratory activity in the open-field test. Moreover, LRRK2 knockout mice stayed longer than their wild type littermates on the accelerated rod during rotarod testing. Finally, we confirm that loss of LRRK2 caused degeneration in the kidney, accompanied by a progressive enhancement of autophagic activity and accumulation of autofluorescent material, but without evidence of biphasic changes

An informatics approach to analyzing the incidentalome

PURPOSE: Next-generation sequencing (NGS) has transformed genetic research and is poised to revolutionize clinical diagnosis. However, the vast amount of data and inevitable discovery of incidental findings require novel analytic approaches. We therefore implemented for the first time a strategy that utilizes an a priori structured framework and a conservative threshold for selecting clinically relevant incidental findings. METHODS: We categorized 2016 genes linked with Mendelian diseases into “bins” based on clinical utility and validity, and used a computational algorithm to analyze 80 whole genome sequences in order to explore the use of such an approach in a simulated real-world setting. RESULTS: The algorithm effectively reduced the number of variants requiring human review and identified incidental variants with likely clinical relevance. Incorporation of the Human Gene Mutation Database (HGMD) improved the yield for missense mutations, but also revealed that a substantial proportion of purported disease-causing mutations were misleading. CONCLUSIONS: This approach is adaptable to any clinically relevant bin structure, scalable to the demands of a clinical laboratory workflow, and flexible with respect to advances in genomics. We anticipate that application of this strategy will facilitate pre-test informed consent, laboratory analysis, and post-test return of results in a clinical context

Characterization of a selective inhibitor of the Parkinson's disease kinase LRRK2

Mutations in leucine-rich repeat kinase 2 (LRRK2) are strongly associated with late-onset autosomal dominant Parkinson’s disease. We employed a novel, parallel, compound-centric approach to identify a potent and selective LRRK2 inhibitor LRRK2-IN-1, and demonstrated that inhibition of LRRK2 induces dephosphorylation of Ser910/Ser935 and accumulation of LRRK2 within aggregate structures. LRRK2-IN-1 will serve as a versatile tool to pharmacologically interrogate LRRK2 biology and study its role in Parkinson’s disease