Inhibition of LRRK2 kinase activity stimulates macroautophagy

Association of the LRRK2 genetic polymorphisms with leprosy in Han Chinese from Southwest China

Leprosy is a chronic infectious and neurological disease that is caused by infection of Mycobacterium leprae (M. leprae). A recent genome-wide association study indicated a suggestive association of LRRK2 genetic variant rs1873613 with leprosy in Chinese population. To validate this association and further identify potential causal variants of LRRK2 with leprosy, we genotyped 13 LRRK2 variants in 548 leprosy patients and 1078 healthy individuals from Yunnan Province and (re-)analyzed 3225 Han Chinese across China. Variants rs1427267, rs3761863, rs1873613, rs732374 and rs7298930 were significantly associated with leprosy per se and/or paucibacillary leprosy (PB). Haplotype A-G-A-C-A was significantly associated with leprosy per se (P=0.018) and PB (P=0.020). Overexpression of the protective allele (Thr2397) of rs3761863 in HEK293 cells led to a significantly increased nuclear factor of activated T-cells' activity compared with allele Met2397 after lipopolysaccharides stimulation. Allele Thr2397 could attenuate 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine-induced autophagic activity in U251 cells. These data suggest that the protective effect of LRRK2 variant p.M2397T on leprosy might be mediated by increasing immune response and decreasing neurotoxicity after M. leprae loading. Our findings confirm that LRRK2 is a susceptible gene to leprosy in Han Chinese population.

Fluorescence-based imaging of autophagy progression by human WIPI protein detection

Central to the process of macroautophagy (hereafter autophagy) is the formation of autophagosomes, double-membrane vesicles that sequester cytoplasmic cargo, including proteins, lipids and organelles, for lysosomal degradation and macromolecule recycling. Tight regulation of both autophagic activity and capacity is crucial to secure cellular homeostasis and aberrant autophagy is tightly linked to the development of many human diseases. Hence it is of great importance to accurately measure autophagy progression in health and disease. Members of the human WIPI β-propeller proteins associate with autophagosomal membranes due to specific phosphatidylinositol 3-phosphate (PtdIns3P) binding at the onset of autophagy. The specific autophagosomal localization of both WIPI1 and WIPI2 (refered to as WIPI puncta) has been employed to assess autophagy using fluorescence microscopy methods, such as confocal and live-cell video microscopy and was extended for automated high-throughput image acquisition and analyses procedures. We here provide an overview on the employment of human WIPI members for the assessment of autophagy in higher eukaryotic cells, suitable for systems biology approaches such as mathematical modelling.

The role of the LRRK2 gene in Parkinsonism

Parkinson’s disease (PD), like many common age-related conditions, has been recognized to have a substantial genetic component. Multiple lines of evidence suggest that Leucine-rich repeat kinase 2 (LRRK2) is a crucial factor to understanding the etiology of PD. LRRK2 is a large, widely expressed, multi-domain and multifunctional protein. LRRK2 mutations are the major cause to inherited and sporadic PD. In this review, we discuss the pathology and clinical features which show diversity and variability of LRRK2-associated PD. In addition, we do a thorough literature review and provide theoretical data for gene counseling. Further, we present the evidence linking LRRK2 to various possible pathogenic mechanism of PD such as α-synuclein, tau, inflammatory response, oxidative stress, mitochondrial dysfunction, synaptic dysfunction as well as autophagy-lysosomal system. Based on the above work, we investigate activities both within GTPase and outside enzymatic regions in order to obtain a potential therapeutic approach to solve the LRRK2 problem.

Advances in kinase targeting: current clinical use and clinical trials

Phosphotransferases, also known as kinases, are the most intensively studied protein drug target category in current pharmacological research, as evidenced by the vast number of kinase-targeting agents enrolled in active clinical trials. This development has emerged following the great success of small-molecule, orally available protein kinase inhibitors for the treatment of cancer, starting with the introduction of imatinib (Gleevec®) in 2003. The pharmacological utility of kinase-targeting has expanded to include treatment of inflammatory diseases, and rapid development is ongoing for kinase-targeted therapies in a broad array of indications in ophthalmology, analgesia, central nervous system (CNS) disorders, and the complications of diabetes, osteoporosis, and otology. In this review we highlight specifically the kinase drug targets and kinase-targeting agents being explored in current clinical trials. This analysis is based on a recent estimate of all established and clinical trial drug mechanisms of action, utilizing private and public databases to create an extensive dataset detailing aspects of more than 3000 approved and experimental drugs.

Impaired mitochondrial homeostasis and neurodegeneration: towards new therapeutic targets?

The sustained integrity of the mitochondrial population of a cell is critical for maintained cell health, and disruption of that integrity is linked strongly to human disease, especially to the neurodegenerative diseases. These are appalling diseases causing untold levels of suffering for which treatment is woefully inadequate. Understanding the mechanisms that disturb mitochondrial homeostasis may therefore prove key to identification of potential new therapeutic pathways. Mechanisms causing mitochondrial dysfunction include the acute catastrophic loss of function caused by opening of the mitochondrial permeability transition pore (mPTP), which collapses bioenergetic function and initiates cell death. This is best characterised in ischaemic reperfusion injury, although it may also contribute to a number of other diseases. More insidious disturbances of mitochondrial homeostasis may result from impaired balance in the pathways that promote mitochondrial repair (biogenesis) and pathways that remove dysfunctional mitochondria (mitophagy). Impaired coordination between these processes is emerging as a key feature of a number of neurodegenerative and neuromuscular disorders. Here we review pathways that may prove to be valuable potential therapeutic targets, focussing on the molecular mechanisms that govern the coordination of these processes and their involvement in neurodegenerative diseases.

The LRRK2 inhibitor GSK2578215A induces protective autophagy in SH-SY5Y cells: involvement of Drp-1-mediated mitochondrial fission and mitochondrial-derived ROS signaling

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been associated with Parkinson's disease, and its inhibition opens potential new therapeutic options. Among the drug inhibitors of both wild-type and mutant LRRK2 forms is the 2-arylmethyloxy-5-subtitutent-N-arylbenzamide GSK257815A. Using the well-established dopaminergic cell culture model SH-SY5Y, we have investigated the effects of GSK2578215A on crucial neurodegenerative features such as mitochondrial dynamics and autophagy. GSK2578215A induces mitochondrial fragmentation of an early step preceding autophagy. This increase in autophagosome results from inhibition of fusion rather than increases in synthesis. The observed effects were shared with LRRK2-IN-1, a well-described, structurally distinct kinase inhibitor compound or when knocking down LRRK2 expression using siRNA. Studies using the drug mitochondrial division inhibitor 1 indicated that translocation of the dynamin-related protein-1 has a relevant role in this process. In addition, autophagic inhibitors revealed the participation of autophagy as a cytoprotective response by removing damaged mitochondria. GSK2578215A induced oxidative stress as evidenced by the accumulation of 4-hydroxy-2-nonenal in SH-SY5Y cells. The mitochondrial-targeted reactive oxygen species scavenger MitoQ positioned these species as second messengers between mitochondrial morphologic alterations and autophagy. Altogether, our results demonstrated the relevance of LRRK2 in mitochondrial-activated pathways mediating in autophagy and cell fate, crucial features in neurodegenerative diseases.

Genetic causes of Parkinson's disease and their links to autophagy regulation

Genetic studies over the past 15 years have revolutionized our understanding towards the etiology of Parkinson's disease (PD). These studies have discovered many disease-linked genetic loci (PARK 1 to 18), which are now being interrogated for cellular pathways contributing to PD. Various pathogenic pathways were proposed but validation of each pathway awaits rigorous experimental testing. Here we review recent progress in understanding the influence of disease risk genes on cellular functions, specifically, autophagy pathways. Autophagy is a cell self-eating, lysosomal degradation system that plays an important role in cell homeostasis and survival. Neurons are post-mitotic cells and particularly vulnerable to the impairment of autophagic degradation due to their inability to redistribute damaged proteins and organelles to daughter cells. Emerging evidence has implicated dysfunctional autophagy in a growing number of neurodegenerative diseases including PD. We will also discuss the prospect of intervening autophagy pathways as a potential strategy to treat PD.

Defective autophagy in Parkinson's disease: lessons from genetics

Parkinson's disease (PD) is the most prevalent neurodegenerative movement disorder. Genetic studies over the past two decades have greatly advanced our understanding of the etiological basis of PD and elucidated pathways leading to neuronal degeneration. Recent studies have suggested that abnormal autophagy, a well conserved homeostatic process for protein and organelle turnover, may contribute to neurodegeneration in PD. Moreover, many of the proteins related to both autosomal dominant and autosomal recessive PD, such as α-synuclein, PINK1, Parkin, LRRK2, DJ-1, GBA, and ATPA13A2, are also involved in the regulation of autophagy. We propose that reduced autophagy enhances the accumulation of α-synuclein, other pathogenic proteins, and dysfunctional mitochondria in PD, leading to oxidative stress and neuronal death.

LRRK2, a puzzling protein: insights into Parkinson's disease pathogenesis

Leucine-rich repeat kinase 2 (LRRK2) is a large, ubiquitous protein of unknown function. Mutations in the gene encoding LRRK2 have been linked to familial and sporadic Parkinson's disease (PD) cases. The LRRK2 protein is a single polypeptide that displays GTPase and kinase activity. Kinase and GTPase domains are involved in different cellular signaling pathways. Despite several experimental studies associating LRRK2 protein with various intracellular membranes and vesicular structures such as endosomal/lysosomal compartments, the mitochondrial outer membrane, lipid rafts, microtubule-associated vesicles, the golgi complex, and the endoplasmic reticulum its broader physiologic function(s) remain unidentified. Additionally, the cellular distribution of LRRK2 may indicate its role in several different pathways, such as the ubiquitin-proteasome system, the autophagic-lysosomal pathway, intracellular trafficking, and mitochondrial dysfunction. This review discusses potential mechanisms through which LRRK2 may mediate neurodegeneration and cause PD.

Membrane recruitment of endogenous LRRK2 precedes its potent regulation of autophagy

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial and idiopathic Parkinson's disease. However, the mechanisms for activating its physiological function are not known, hindering identification of the biological role of endogenous LRRK2. The recent discovery that LRRK2 is highly expressed in cells of the innate immune system and genetic association is a risk factor for autoimmune disorders implies an important role for LRRK2 in pathology outside of the central nervous system. Thus, an examination of endogenous LRRK2 in immune cells could provide insight into the protein's function. Here, we establish that stimulation of specific Toll-like receptors results in a complex biochemical activation of endogenous LRRK2, with early phosphorylation of LRRK2 preceding its dimerization and membrane translocation. Membrane-associated LRRK2 co-localized to autophagosome membranes following either TLR4 stimulation or mTOR inhibition with rapamycin. Silencing of endogenous LRRK2 expression resulted in deficits in the induction of autophagy and clearance of a well-described macroautophagy substrate, demonstrating the critical role of endogenous LRRK2 in regulating autophagy. Inhibition of LRRK2 kinase activity also reduced autophagic degradation and suggested the importance of the kinase domain in the regulation of autophagy. Our results demonstrate a well-orchestrated series of biochemical events involved in the activation of LRRK2 important to its physiological function. With similarities observed across multiple cell types and stimuli, these findings are likely relevant in all cell types that natively express endogenous LRRK2, and provide insights into LRRK2 function and its role in human disease.

LRRK2 and neuroinflammation: partners in crime in Parkinson's disease?

It is now well established that chronic inflammation is a prominent feature of several neurodegenerative disorders including Parkinson’s disease (PD). Growing evidence indicates that neuroinflammation can contribute greatly to dopaminergic neuron degeneration and progression of the disease. Recent literature highlights that leucine-rich repeat kinase 2 (LRRK2), a kinase mutated in both autosomal-dominantly inherited and sporadic PD cases, modulates inflammation in response to different pathological stimuli. In this review, we outline the state of the art of LRRK2 functions in microglia cells and in neuroinflammation. Furthermore, we discuss the potential role of LRRK2 in cytoskeleton remodeling and vesicle trafficking in microglia cells under physiological and pathological conditions. We also hypothesize that LRRK2 mutations might sensitize microglia cells toward a pro-inflammatory state, which in turn results in exacerbated inflammation with consequent neurodegeneration.

Pathogenic Parkinson's disease mutations across the functional domains of LRRK2 alter the autophagic/lysosomal response to starvation

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.

ERKed by LRRK2: a cell biological perspective on hereditary and sporadic Parkinson's disease

The leucine rich repeat kinase 2 (LRRK2/dardarin) is implicated in autosomal dominant familial and sporadic Parkinson's disease (PD); mutations in LRRK2 account for up to 40% of PD cases in some populations. LRRK2 is a large protein with a kinase domain, a GTPase domain, and multiple potential protein interaction domains. As such, delineating the functional pathways for LRRK2 and mechanisms by which PD-linked variants contribute to age-related neurodegeneration could result in pharmaceutically tractable therapies. A growing number of recent studies implicate dysregulation of mitogen activated protein kinases 3 and 1 (also known as ERK1/2) as possible downstream mediators of mutant LRRK2 effects. As these master regulators of growth, differentiation, neuronal plasticity and cell survival have also been implicated in other PD models, a set of common cell biological pathways may contribute to neuronal susceptibility in PD. Here, we review the literature on several major cellular pathways impacted by LRRK2 mutations--autophagy, microtubule/cytoskeletal dynamics, and protein synthesis--in context of potential signaling crosstalk involving the ERK1/2 and Wnt signaling pathways. Emerging implications for calcium homeostasis, mitochondrial biology and synaptic dysregulation are discussed in relation to LRRK2 interactions with other PD gene products. It has been shown that substantia nigra neurons in human PD and Lewy body dementia patients exhibit cytoplasmic accumulations of ERK1/2 in mitochondria, autophagosomes and bundles of intracellular fibrils. Both experimental and human tissue data implicate pathogenic changes in ERK1/2 signaling in sporadic, toxin-based and mutant LRRK2 settings, suggesting engagement of common cell biological pathways by divergent PD etiologies.