G2019S leucine-rich repeat kinase 2 causes uncoupling protein-mediated mitochondrial depolarization

3D Cultures of Parkinson's Disease-Specific Dopaminergic Neurons for High Content Phenotyping and Drug Testing

Parkinson's disease (PD)-specific neurons, grown in standard 2D cultures, typically only display weak endophenotypes. The cultivation of PD patient-specific neurons, derived from induced pluripotent stem cells carrying the LRRK2-G2019S mutation, is optimized in 3D microfluidics. The automated image analysis algorithms are implemented to enable pharmacophenomics in disease-relevant conditions. In contrast to 2D cultures, this 3D approach reveals robust endophenotypes. High-content imaging data show decreased dopaminergic differentiation and branching complexity, altered mitochondrial morphology, and increased cell death in LRRK2-G2019S neurons compared to isogenic lines without using stressor agents. Treatment with the LRRK2 inhibitor 2 (Inh2) rescues LRRK2-G2019S-dependent dopaminergic phenotypes. Strikingly, a holistic analysis of all studied features shows that the genetic background of the PD patients, and not the LRRK2-G2019S mutation, constitutes the strongest contribution to the phenotypes. These data support the use of advanced in vitro models for future patient stratification and personalized drug development.

LRRK2 and mitochondria: Recent advances and current views

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene account for most common causes of familial and sporadic Parkinson's disease (PD) and are one of the strongest genetic risk factors in sporadic PD. Pathways implicated in LRRK2-dependent neurodegeneration include cytoskeletal dynamics, vesicular trafficking, autophagy, mitochondria, and calcium homeostasis. However, the exact molecular mechanisms still need to be elucidated. Both genetic and environmental causes of PD have highlighted the importance of mitochondrial dysfunction in the pathogenesis of PD. Mitochondrial impairment has been observed in fibroblasts and iPSC-derived neural cells from PD patients with LRRK2 mutations, and LRRK2 has been shown to localize to mitochondria and to regulate its function. In this review we discuss recent discoveries relating to LRRK2 mutations and mitochondrial dysfunction.

Mitochondrial quality control and neurodegenerative diseases

Mitochondria homeostasis is sustained by the mitochondrial quality control (MQC) system, which is crucial for cellular health, especially in the maintenance of functional mitochondria. A healthy mitochondria network is essential for life as it regulates cellular metabolism processes, particularly ATP production. Mitochondrial dynamics and mitophagy are two highly integrated processes in MQC system that determines whether damaged mitochondria will be repaired or degraded. Neurons are highly differentiated cells which demand high energy consumption. Therefore, compromised MQC processes and the accumulation of dysfunctional mitochondria may be the main cause of neuronal death and lead to neurodegeneration. Here, we focus on the inseparable relationship of mitochondria dynamics and mitophagy and how their dysfunction may lead to neurodegenerative diseases.

G2019S LRRK2 Increases Stress Susceptibility Through Inhibition of DAF-16 Nuclear Translocation in a 14-3-3 Associated-Manner in Caenorhabditis elegans

Mutations in leucine-rich repeat kinase 2 (LRRK2) are common causes of familial Parkinson’s disease (PD). Oxidative stress plays a key role in the pathogenesis of PD. Mutations in LRRK2 have been shown to increase susceptibility to oxidative stress. To explore mechanisms underlying susceptibility to oxidative stress in LRRK2 mutants, we generated stable Caenorhabditis elegans (C. elegans) strains in which human LRRK2 proteins including wild type LRRK2 (WT), G2019S LRRK2 (G2019S), and G2019S-D1994A kinase-dead LRRK2 (KD) were expressed in all neurons. Human 14-3-3 β was injected into LRRK2 transgenic worms to allow co-expression of 14-3-3 β and LRRK2 proteins. We found that G2019S transgenic worms had increased sensitivity to stress (heat and juglone treatment) and impaired stress-induced nuclear translocation of DAF-16. In addition, G2019S inhibited ftt2 (a 14-3-3 gene homolog in C. elegans) knockdown-associated nuclear translocation of DAF-16. Comparably, overexpression of human 14-3-3 β could attenuate G2019S-associated toxicity in response to stress and rescued G2019S-mediated inhibition of sod-3 and dod-3 expression. Taken together, our study provides evidence suggesting that 14-3-3-associated inhibition of DAF-16 nuclear translocation could be a mechanism for G2019S LRRK2-induced oxidative stress and cellular toxicity. Our findings may give a hint that the potential of 14-3-3 proteins as neuroprotective targets in PD patients carrying LRRK2 mutations.

Ursodeoxycholic Acid Improves Mitochondrial Function and Redistributes Drp1 in Fibroblasts from Patients with Either Sporadic or Familial Alzheimer's Disease

Alzheimer's disease (AD) is the leading cause of dementia worldwide. Mitochondrial abnormalities have been identified in many cell types in AD, with deficits preceding the development of the classical pathological aggregations. Ursodeoxycholic acid (UDCA), a treatment for primary biliary cirrhosis, improves mitochondrial function in fibroblasts derived from Parkinson's disease patients as well as several animal models of AD and Parkinson's disease. In this paper, we investigated both mitochondrial function and morphology in fibroblasts from patients with both sporadic and familial AD. We show that both sporadic AD (sAD) and PSEN1 fibroblasts share the same impairment of mitochondrial membrane potential and alterations in mitochondrial morphology. Mitochondrial respiration, however, was decreased in sAD fibroblasts and increased in PSEN1 fibroblasts. Morphological changes seen in AD fibroblasts include reduced mitochondrial number and increased mitochondrial clustering around the cell nucleus as well as an increased number of long mitochondria. We show here for the first time in AD patient tissue that treatment with UDCA increases mitochondrial membrane potential and respiration as well as reducing the amount of long mitochondria in AD fibroblasts. In addition, we show reductions in dynamin-related protein 1 (Drp1) level, particularly the amount localized to mitochondria in both sAD and familial patient fibroblasts. Drp1 protein amount and localization were increased after UDCA treatment. The restorative effects of UDCA are abolished when Drp1 is knocked down. This paper highlights the potential use of UDCA as a treatment for neurodegenerative disease.

Impaired Mitophagy and Protein Acetylation Levels in Fibroblasts from Parkinson's Disease Patients

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder. While most PD cases are idiopathic, the known genetic causes of PD are useful to understand common disease mechanisms. Recent data suggests that autophagy is regulated by protein acetylation mediated by histone acetyltransferase (HAT) and histone deacetylase (HDAC) activities. The changes in histone acetylation reported to be involved in PD pathogenesis have prompted this investigation of protein acetylation and HAT and HDAC activities in both idiopathic PD and G2019S leucine-rich repeat kinase 2 (LRRK2) cell cultures. Fibroblasts from PD patients (with or without the G2019S LRRK2 mutation) and control subjects were used to assess the different phenotypes between idiopathic and genetic PD. G2019S LRRK2 mutation displays increased mitophagy due to the activation of class III HDACs whereas idiopathic PD exhibits downregulation of clearance of defective mitochondria. This reduction of mitophagy is accompanied by more reactive oxygen species (ROS). In parallel, the acetylation protein levels of idiopathic and genetic individuals are different due to an upregulation in class I and II HDACs. Despite this upregulation, the total HDAC activity is decreased in idiopathic PD and the total HAT activity does not significantly vary. Mitophagy upregulation is beneficial for reducing the ROS-induced harm in genetic PD. The defective mitophagy in idiopathic PD is inherent to the decrease in class III HDACs. Thus, there is an imbalance between total HATs and HDACs activities in idiopathic PD, which increases cell death. The inhibition of HATs in idiopathic PD cells displays a cytoprotective effect.

Mitochondrial abnormalities in Parkinson's disease and Alzheimer's disease: can mitochondria be targeted therapeutically?

Mitochondrial abnormalities have been identified as a central mechanism in multiple neurodegenerative diseases and, therefore, the mitochondria have been explored as a therapeutic target. This review will focus on the evidence for mitochondrial abnormalities in the two most common neurodegenerative diseases, Parkinson's disease and Alzheimer's disease. In addition, we discuss the main strategies which have been explored in these diseases to target the mitochondria for therapeutic purposes, focusing on mitochondrially targeted antioxidants, peptides, modulators of mitochondrial dynamics and phenotypic screening outcomes.

The Enzymatic Core of the Parkinson's Disease-Associated Protein LRRK2 Impairs Mitochondrial Biogenesis in Aging Yeast

Mitochondrial dysfunction is a prominent trait of cellular decline during aging and intimately linked to neuronal degeneration during Parkinson's disease (PD). Various proteins associated with PD have been shown to differentially impact mitochondrial dynamics, quality control and function, including the leucine-rich repeat kinase 2 (LRRK2). Here, we demonstrate that high levels of the enzymatic core of human LRRK2, harboring GTPase as well as kinase activity, decreases mitochondrial mass via an impairment of mitochondrial biogenesis in aging yeast. We link mitochondrial depletion to a global downregulation of mitochondria-related gene transcripts and show that this catalytic core of LRRK2 localizes to mitochondria and selectively compromises respiratory chain complex IV formation. With progressing cellular age, this culminates in dissipation of mitochondrial transmembrane potential, decreased respiratory capacity, ATP depletion and generation of reactive oxygen species. Ultimately, the collapse of the mitochondrial network results in cell death. A point mutation in LRRK2 that increases the intrinsic GTPase activity diminishes mitochondrial impairment and consequently provides cytoprotection. In sum, we report that a downregulation of mitochondrial biogenesis rather than excessive degradation of mitochondria underlies the reduction of mitochondrial abundance induced by the enzymatic core of LRRK2 in aging yeast cells. Thus, our data provide a novel perspective for deciphering the causative mechanisms of LRRK2-associated PD pathology.

Regulation of LRRK2: insights from structural and biochemical analysis

Leucine-rich repeat kinase 2 (LRRK2) is a multi-domain protein and its mutations can lead to Parkinson’s disease. Recent studies on LRRK2 and homologue proteins have advanced our mechanistic understanding of LRRK2 regulation. Here, we summarize the available data on the biochemistry and structure of LRRK2 and postulate three possible layers of regulation, translocation, monomer-dimer equilibrium and intramolecular activation of domains.

Exhaustion of mitochondrial and autophagic reserve may contribute to the development of LRRK2 G2019S -Parkinson's disease

Background

Mutations in leucine rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson’s disease (PD). Mitochondrial and autophagic dysfunction has been described as etiologic factors in different experimental models of PD. We aimed to study the role of mitochondria and autophagy in LRRK2^G2019S-mutation, and its relationship with the presence of PD-symptoms.

Methods

Fibroblasts from six non-manifesting LRRK2^G2019S-carriers (NM-LRRK2^G2019S) and seven patients with LRRK2^G2019S-associated PD (PD-LRRK2^G2019S) were compared to eight healthy controls (C). An exhaustive assessment of mitochondrial performance and autophagy was performed after 24-h exposure to standard (glucose) or mitochondrial-challenging environment (galactose), where mitochondrial and autophagy impairment may be heightened.

Results

A similar mitochondrial phenotype of NM-LRRK2^G2019S and controls, except for an early mitochondrial depolarization (54.14% increased, p = 0.04), was shown in glucose. In response to galactose, mitochondrial dynamics of NM-LRRK2^G2019S improved (− 17.54% circularity, p = 0.002 and + 42.53% form factor, p = 0.051), probably to maintain ATP levels over controls. A compromised bioenergetic function was suggested in PD-LRRK2^G2019S when compared to controls in glucose media. An inefficient response to galactose and worsened mitochondrial dynamics (− 37.7% mitochondrial elongation, p = 0.053) was shown, leading to increased oxidative stress. Autophagy initiation (SQTSM/P62) was upregulated in NM-LRRK2^G2019S when compared to controls (glucose + 118.4%, p = 0.014; galactose + 114.44%, p = 0.009,) and autophagosome formation increased in glucose media. Despite of elevated SQSTM1/P62 levels of PD-NM^G2019S when compared to controls (glucose + 226.14%, p = 0.04; galactose + 78.5%, p = 0.02), autophagosome formation was deficient in PD-LRRK2^G2019S when compared to NM-LRRK2^G2019S (− 71.26%, p = 0.022).

Conclusions

Enhanced mitochondrial performance of NM-LRRK2^G2019S in mitochondrial-challenging conditions and upregulation of autophagy suggests that an exhaustion of mitochondrial bioenergetic and autophagic reserve, may contribute to the development of PD in LRRK2^G2019S mutation carriers.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1526-3) contains supplementary material, which is available to authorized users.

Kinases in synaptic development and neurological diseases

Neuronal morphogenesis and synapse development is essential for building a functioning nervous system, and defects in these processes are associated with neurological disorders. Our understanding of molecular components and signalling events that contribute to neuronal development and pathogenesis is limited. Genes associated with neurodevelopmental and neurodegenerative diseases provide entry points for elucidating molecular events that contribute to these conditions. Several protein kinases, enzymes that regulate protein function by phosphorylating their substrates, are genetically linked to neurological disorders. Identifying substrates of these kinases is key to discovering their function and providing insight for possible therapies. In this review, we describe how various methods for kinase-substrate identification helped elucidate kinase signalling pathways important for neuronal development and function. We describe recent advances on roles of kinases TAOK2, TNIK and CDKL5 in neuronal development and the converging pathways of LRRK2, PINK1 and GAK in Parkinson's Disease.

Mitochondrial Dysfunction in Parkinson's Disease: New Mechanistic Insights and Therapeutic Perspectives

Purpose of Review

Parkinson’s disease (PD) is a complex neurodegenerative disorder, the aetiology of which is still largely unknown. Overwhelming evidence indicates that mitochondrial dysfunction is a central factor in PD pathophysiology. Here we review recent developments around mitochondrial dysfunction in familial and sporadic PD, with a brief overview of emerging therapies targeting mitochondrial dysfunction.

Recent Findings

Increasing evidence supports the critical role for mitochondrial dysfunction in the development of sporadic PD, while the involvement of familial PD-related genes in the regulation of mitochondrial biology has been expanded by the discovery of new mitochondria-associated disease loci and the identification of their novel functions.

Summary

Recent research has expanded knowledge on the mechanistic details underlying mitochondrial dysfunction in PD, with the discovery of new therapeutic targets providing invaluable insights into the essential role of mitochondria in PD pathogenesis and unique opportunities for drug development.

Current perspective of mitochondrial biology in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative movement disorder characterized by preferential loss of dopaminergic neurons of the substantia nigra pars compacta and the presence of Lewy bodies containing α-synuclein. Although the cause of PD remains elusive, remarkable advances have been made in understanding the possible causative mechanisms of PD pathogenesis. An explosion of discoveries during the past two decades has led to the identification of several autosomal dominant and recessive genes that cause familial forms of PD. The investigations of these familial PD gene products have shed considerable insights into the molecular pathogenesis of the more common sporadic PD. A growing body of evidence suggests that the etiology of PD is multifactorial and involves a complex interplay between genetic and environmental factors. Substantial evidence from human tissues, genetic and toxin-induced animal and cellular models indicates that mitochondrial dysfunction plays a central role in the pathophysiology of PD. Deficits in mitochondrial functions due to bioenergetics defects, alterations in the mitochondrial DNA, generation of reactive oxygen species, aberrant calcium homeostasis, and anomalies in mitochondrial dynamics and quality control are implicated in the underlying mechanisms of neuronal cell death in PD. In this review, we discuss how familial PD-linked genes and environmental factors interface the pathways regulating mitochondrial functions and thereby potentially converge both familial and sporadic PD at the level of mitochondrial integrity. We also provide an overview of the status of therapeutic strategies targeting mitochondrial dysfunction in PD. Unraveling potential pathways that influence mitochondrial homeostasis in PD may hold the key to therapeutic intervention for this debilitating neurodegenerative movement disorder.

ER-mitochondria signaling in Parkinson's disease

Mitochondria form close physical contacts with a specialized domain of the endoplasmic reticulum (ER), known as the mitochondria-associated membrane (MAM). This association constitutes a key signaling hub to regulate several fundamental cellular processes. Alterations in ER-mitochondria signaling have pleiotropic effects on a variety of intracellular events resulting in mitochondrial damage, Ca2+ dyshomeostasis, ER stress and defects in lipid metabolism and autophagy. Intriguingly, many of these cellular processes are perturbed in neurodegenerative diseases. Furthermore, increasing evidence highlights that ER-mitochondria signaling contributes to these diseases, including Parkinson's disease (PD). PD is the second most common neurodegenerative disorder, for which effective mechanism-based treatments remain elusive. Several PD-related proteins localize at mitochondria or MAM and have been shown to participate in ER-mitochondria signaling regulation. Likewise, PD-related mutations have been shown to damage this signaling. Could ER-mitochondria associations be the link between pathogenic mechanisms involved in PD, providing a common mechanism? Would this provide a pharmacological target for treating this devastating disease? In this review, we aim to summarize the current knowledge of ER-mitochondria signaling and the recent evidence concerning damage to this signaling in PD.

Transcriptional alterations in skin fibroblasts from Parkinson's disease patients with parkin mutations

Mutations in the parkin gene (PRKN) are the most common cause of autosomal-recessive juvenile Parkinson's disease (PD). PRKN encodes an E3 ubiquitin ligase that is involved in multiple regulatory functions including proteasomal-mediated protein turnover, mitochondrial function, mitophagy, and cell survival. However, the precise molecular events mediated by PRKN mutations in PRKN-associated PD (PRKN-PD) remain unknown. To elucidate the cellular impact of parkin mutations, we performed an RNA sequencing study in skin fibroblasts from PRKN-PD patients carrying different PRKN mutations (n = 4) and genetically unrelated healthy subjects (n = 4). We identified 343 differentially expressed genes in PRKN-PD fibroblasts. Gene ontology and canonical pathway analysis revealed enrichment of differentially expressed genes in processes such as cell adhesion, cell growth, and amino acid and folate metabolism among others. Our findings indicate that PRKN mutations are associated with large global gene expression changes as observed in fibroblasts from PRKN-PD patients and support the view of PD as a systemic disease affecting also non-neural peripheral tissues such as the skin.

Reduced LRRK2 in association with retromer dysfunction in post-mortem brain tissue from LRRK2 mutation carriers

Missense mutations in leucine-rich repeat kinase 2 (LRRK2) are pathogenic for familial Parkinson's disease. However, it is unknown whether levels of LRRK2 protein in the brain are altered in patients with LRRK2-associated Parkinson's disease. Because LRRK2 mutations are relatively rare, accounting for approximately 1% of all Parkinson's disease, we accessioned cases from five international brain banks to investigate levels of the LRRK2 protein, and other genetically associated Parkinson's disease proteins. Brain tissue was obtained from 17 LRRK2 mutation carriers (12 with the G2019S mutation and five with the I2020T mutation) and assayed by immunoblot. Compared to matched controls and idiopathic Parkinson's disease cases, we found levels of LRRK2 protein were reduced in the LRRK2 mutation cases. We also measured a decrease in two other proteins genetically implicated in Parkinson's disease, the core retromer component, vacuolar protein sorting associated protein 35 (VPS35), and the lysosomal hydrolase, glucocerebrosidase (GBA). Moreover, the classical retromer cargo protein, cation-independent mannose-6-phosphate receptor (MPR300, encoded by IGF2R), was also reduced in the LRRK2 mutation cohort and protein levels of the receptor were correlated to levels of LRRK2. These results provide new data on LRRK2 protein expression in brain tissue from LRRK2 mutation carriers and support a relationship between LRRK2 and retromer dysfunction in LRRK2-associated Parkinson's disease brain.

Parkinson disease-associated mutations in LRRK2 cause centrosomal defects via Rab8a phosphorylation

BACKGROUND

Mutations in LRRK2 are a common genetic cause of Parkinson's disease (PD). LRRK2 interacts with and phosphorylates a subset of Rab proteins including Rab8a, a protein which has been implicated in various centrosome-related events. However, the cellular consequences of such phosphorylation remain elusive.

METHODS

Human neuroblastoma SH-SY5Y cells stably expressing wildtype or pathogenic LRRK2 were used to test for polarity defects in the context of centrosomal positioning. Centrosomal cohesion deficits were analyzed from transiently transfected HEK293T cells, as well as from two distinct peripheral cell types derived from LRRK2-PD patients. Kinase assays, coimmunoprecipitation and GTP binding/retention assays were used to address Rab8a phosphorylation by LRRK2 and its effects in vitro. Transient transfections and siRNA experiments were performed to probe for the implication of Rab8a and its phosphorylated form in the centrosomal deficits caused by pathogenic LRRK2.

RESULTS

Here, we show that pathogenic LRRK2 causes deficits in centrosomal positioning with effects on neurite outgrowth, cell polarization and directed migration. Pathogenic LRRK2 also causes deficits in centrosome cohesion which can be detected in peripheral cells derived from LRRK2-PD patients as compared to healthy controls, and which are reversed upon LRRK2 kinase inhibition. The centrosomal cohesion and polarity deficits can be mimicked when co-expressing wildtype LRRK2 with wildtype but not phospho-deficient Rab8a. The centrosomal defects induced by pathogenic LRRK2 are associated with a kinase activity-dependent increase in the centrosomal localization of phosphorylated Rab8a, and are prominently reduced upon RNAi of Rab8a.

CONCLUSIONS

Our findings reveal a new function of LRRK2 mediated by Rab8a phosphorylation and related to various centrosomal defects.

Translational approaches to restoring mitochondrial function in Parkinson's disease

There is strong evidence of a key role for mitochondrial dysfunction in both sporadic and all forms of familial Parkinson's disease (PD). However, none of the clinical trials carried out with putative mitochondrial rescue agents have been successful. Firm establishment of a wet biomarker or a reliable readout from imaging studies detecting mitochondrial dysfunction and reflecting disease progression is also awaited. We will provide an overview of our current knowledge about mitochondrial dysfunction in PD and related drug screens. We will also summarise previously undertaken mitochondrial wet biomarker studies and relevant imaging studies with particular focus on 31P-MRI spectroscopy. We will conclude with an overview of clinical trials which tested putative mitochondrial rescue agents in PD patients.

Crosstalk between Lysosomes and Mitochondria in Parkinson's Disease

Parkinson's disease (PD) is the most common motor neurodegenerative disorder. In most cases the cause of the disease is unknown, while in about 10% of subjects, it is associated with mutations in a number of different genes. Several different mutations in 15 genes have been identified as causing familial forms of the disease, while many others have been identified as risk factors. A striking number of these genes are either involved in the regulation of mitochondrial function or of endo-lysosomal pathways. Mutations affecting one of these two pathways are often coupled with defects in the other pathway, suggesting a crosstalk between them. Moreover, PD-linked mutations in genes encoding proteins with other functions are frequently associated with defects in mitochondrial and/or autophagy/lysosomal function as a secondary effect. Even toxins that impair mitochondrial function and cause parkinsonian phenotypes, such as rotenone, also impair lysosomal function. In this review, we explore the reciprocal relationship between mitochondrial and lysosomal pathways in PD. We will discuss the impact of mitochondrial dysfunction on the lysosomal compartment and of endo-lysosomal defects on mitochondrial function, and explore the roles of both causative genes and genes that are risk factors for PD. Understanding the pathways that govern these interactions should help to define a framework to understand the roles and mechanisms of mitochondrial and lysosomal miscommunication in the pathophysiology of PD.

Mitochondria: A Common Target for Genetic Mutations and Environmental Toxicants in Parkinson's Disease

Parkinson's disease (PD) is a devastating neurological movement disorder. Since its first discovery 200 years ago, genetic and environmental factors have been identified to play a role in PD development and progression. Although genetic studies have been the predominant driving force in PD research over the last few decades, currently only a small fraction of PD cases can be directly linked to monogenic mutations. The remaining cases have been attributed to other risk associated genes, environmental exposures and gene-environment interactions, making PD a multifactorial disorder with a complex etiology. However, enormous efforts from global research have yielded significant insights into pathogenic mechanisms and potential therapeutic targets for PD. This review will highlight mitochondrial dysfunction as a common pathway involved in both genetic mutations and environmental toxicants linked to PD.

Decreased Sirtuin Deacetylase Activity in LRRK2 G2019S iPSC-Derived Dopaminergic Neurons

Mitochondrial changes have long been implicated in the pathogenesis of Parkinson's disease (PD). The glycine to serine mutation (G2019S) in leucine-rich repeat kinase 2 (LRRK2) is the most common genetic cause for PD and has been shown to impair mitochondrial function and morphology in multiple model systems. We analyzed mitochondrial function in LRRK2 G2019S induced pluripotent stem cell (iPSC)-derived neurons to determine whether the G2019S mutation elicits similar mitochondrial deficits among central and peripheral nervous system neuron subtypes. LRRK2 G2019S iPSC-derived dopaminergic neuron cultures displayed unique abnormalities in mitochondrial distribution and trafficking, which corresponded to reduced sirtuin deacetylase activity and nicotinamide adenine dinucleotide levels despite increased sirtuin levels. These data indicate that mitochondrial deficits in the context of LRRK2 G2019S are not a global phenomenon and point to distinct sirtuin and bioenergetic deficiencies intrinsic to dopaminergic neurons, which may underlie dopaminergic neuron loss in PD.

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LRRK2 G2019S iPSC-derived dopaminergic neurons have unique mitochondrial defects

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LRRK2 G2019S dopaminergic neurons have increased sirtuin levels but reduced activity

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LRRK2 G2019S dopaminergic neurons have reduced NAD⁺ levels compared with other neurons

Mitochondrial Bioenergetics Is Altered in Fibroblasts from Patients with Sporadic Alzheimer's Disease

The identification of an early biomarker to diagnose Alzheimer's disease (AD) remains a challenge. Neuropathological studies in animal and AD patients have shown that mitochondrial dysfunction is a hallmark of the development of the disease. Current studies suggest the use of peripheral tissues, like skin fibroblasts as a possibility to detect the early pathological alterations present in the AD brain. In this context, we studied mitochondrial function properties (bioenergetics and morphology) in cultured fibroblasts obtained from AD, aged-match and young healthy patients. We observed that AD fibroblasts presented a significant reduction in mitochondrial length with important changes in the expression of proteins that control mitochondrial fusion. Moreover, AD fibroblasts showed a distinct alteration in proteolytic processing of OPA1, a master regulator of mitochondrial fusion, compared to control fibroblasts. Complementary to these changes AD fibroblasts showed a dysfunctional mitochondrial bioenergetics profile that differentiates these cells from aged-matched and young patient fibroblasts. Our findings suggest that the human skin fibroblasts obtained from AD patients could replicate mitochondrial impairment observed in the AD brain. These promising observations suggest that the analysis of mitochondrial bioenergetics could represent a promising strategy to develop new diagnostic methods in peripheral tissues of AD patients.

Mitophagy in Parkinson's Disease: Pathogenic and Therapeutic Implications

Neurons affected in Parkinson’s disease (PD) experience mitochondrial dysfunction and bioenergetic deficits that occur early and promote the disease-related α-synucleinopathy. Emerging findings suggest that the autophagy-lysosome pathway, which removes damaged mitochondria (mitophagy), is also compromised in PD and results in the accumulation of dysfunctional mitochondria. Studies using genetic-modulated or toxin-induced animal and cellular models as well as postmortem human tissue indicate that impaired mitophagy might be a critical factor in the pathogenesis of synaptic dysfunction and the aggregation of misfolded proteins, which in turn impairs mitochondrial homeostasis. Interventions that stimulate mitophagy to maintain mitochondrial health might, therefore, be used as an approach to delay the neurodegenerative processes in PD.

Metabolic Dysfunction in Parkinson's Disease: Bioenergetics, Redox Homeostasis and Central Carbon Metabolism

The loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the accumulation of protein inclusions (Lewy bodies) are the pathological hallmarks of Parkinson's disease (PD). PD is triggered by genetic alterations, environmental/occupational exposures and aging. However, the exact molecular mechanisms linking these PD risk factors to neuronal dysfunction are still unclear. Alterations in redox homeostasis and bioenergetics (energy failure) are thought to be central components of neurodegeneration that contribute to the impairment of important homeostatic processes in dopaminergic cells such as protein quality control mechanisms, neurotransmitter release/metabolism, axonal transport of vesicles and cell survival. Importantly, both bioenergetics and redox homeostasis are coupled to neuro-glial central carbon metabolism. We and others have recently established a link between the alterations in central carbon metabolism induced by PD risk factors, redox homeostasis and bioenergetics and their contribution to the survival/death of dopaminergic cells. In this review, we focus on the link between metabolic dysfunction, energy failure and redox imbalance in PD, making an emphasis in the contribution of central carbon (glucose) metabolism. The evidence summarized here strongly supports the consideration of PD as a disorder of cell metabolism.

Mutations in valosin-containing protein (VCP) decrease ADP/ATP translocation across the mitochondrial membrane and impair energy metabolism in human neurons

Mutations in the gene encoding valosin-containing protein (VCP) lead to multisystem proteinopathies including frontotemporal dementia. We have previously shown that patient-derived VCP mutant fibroblasts exhibit lower mitochondrial membrane potential, uncoupled respiration, and reduced ATP levels. This study addresses the underlying basis for mitochondrial uncoupling using VCP knockdown neuroblastoma cell lines, induced pluripotent stem cells (iPSCs), and iPSC-derived cortical neurons from patients with pathogenic mutations in VCP Using fluorescent live cell imaging and respiration analysis we demonstrate a VCP mutation/knockdown-induced dysregulation in the adenine nucleotide translocase, which results in a slower rate of ADP or ATP translocation across the mitochondrial membranes. This deregulation can explain the mitochondrial uncoupling and lower ATP levels in VCP mutation-bearing neurons via reduced ADP availability for ATP synthesis. This study provides evidence for a role of adenine nucleotide translocase in the mechanism underlying altered mitochondrial function in VCP-related degeneration, and this new insight may inform efforts to better understand and manage neurodegenerative disease and other proteinopathies.

Abnormalities of Mitochondrial Dynamics in Neurodegenerative Diseases

Neurodegenerative diseases are incurable and devastating neurological disorders characterized by the progressive loss of the structure and function of neurons in the central nervous system or peripheral nervous system. Mitochondria, organelles found in most eukaryotic cells, are essential for neuronal survival and are involved in a number of neuronal functions. Mitochondrial dysfunction has long been demonstrated as a common prominent early pathological feature of a variety of common neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD). Mitochondria are highly dynamic organelles that undergo continuous fusion, fission, and transport, the processes of which not only control mitochondrial morphology and number but also regulate mitochondrial function and location. The importance of mitochondrial dynamics in the pathogenesis of neurodegenerative diseases has been increasingly unraveled after the identification of several key fusion and fission regulators such as Drp1, OPA1, and mitofusins. In this review, after a brief discussion of molecular mechanisms regulating mitochondrial fusion, fission, distribution, and trafficking, as well as the important role of mitochondrial dynamics for neuronal function, we review previous and the most recent studies about mitochondrial dynamic abnormalities observed in various major neurodegenerative diseases and discuss the possibility of targeting mitochondrial dynamics as a likely novel therapeutic strategy for neurodegenerative diseases.

Increased Oxidative Stress Markers in Cerebrospinal Fluid from Healthy Subjects with Parkinson's Disease-Associated LRRK2 Gene Mutations

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most frequent cause of inherited Parkinson’s disease (PD). The most common PD-associated LRRK2 mutation, G2019S, induces increased production of reactive oxygen species in vitro. We therefore hypothesized that individuals with PD-associated LRRK2 mutations might have increased concentrations of oxidative stress markers and/or decreased total antioxidant capacity (TAC) in their cerebrospinal fluid (CSF). We measured two oxidative stress markers, namely 8-hydroxy-2′-deoxyguanosine (8-OHdG) and 8-isoprostane (8-ISO), and TAC in CSF from LRRK2 mutation-bearing PD patients (LRRK2 PD = 19), sporadic PD patients (sPD = 31), and healthy control subjects with or without these mutations (LRRK2 CTL = 30, CTL = 27). 8-OHdG and 8-ISO levels were increased in LRRK2 CTL subjects, while TAC was similar between groups. 8-ISO was negatively correlated, and TAC was positively correlated, with Montreal Cognitive Assessment scores in LRRK2 PD, LRRK2 CTL, and CTL subjects. Correlations in both groups of PD patients between the two oxidative stress markers and Unified Parkinson Disease Rating Scale Total scores were weak, while TAC was negatively correlated with these scores. These findings suggest that oxidative stress may be increased in the CNS in healthy individuals with PD-associated LRRK2 mutations. Further, TAC may decrease in the CNS with the progression of PD, and when cognitive impairment is present regardless of the presence or absence of PD.

Screening for chemical modulators for LRRK2

After the discovery of leucine-rich repeat kinase 2 (LRRK2) as a risk factor for sporadic Parkinson's disease (PD) and mutations in LRRK2 as a cause of some forms of familial PD, there has been substantial interest in finding chemical modulators of LRRK2 function. Most of the pathogenic mutations in LRRK2 are within the enzymatic cores of the protein; therefore, many screens have focused on finding chemical modulators of this enzymatic activity. There are alternative screening approaches that could be taken to investigate compounds that modulate LRRK2 cellular functions. These screens are more often phenotypic screens. The preparation for a screen has to be rigorous and enable high-throughput accurate assessment of a compound's activity. The pipeline to beginning a drug screen and some LRRK2 inhibitor and phenotypic screens will be discussed.

Effects of LRRK2 Inhibitors on Nigrostriatal Dopaminergic Neurotransmission

INTRODUCTION

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most prevalent cause of familial and sporadic Parkinson's disease (PD). Because most pathogenic LRRK2 mutations result in enhanced kinase activity, it suggests that LRRK2 inhibitors may serve as a potential treatment for PD. To evaluate whether LRRK2 inhibitors are effective therapies for PD, it is crucial to know whether LRRK2 inhibitors will affect dopaminergic (DAergic) neurotransmission. However, to date, there is no study to investigate the impact of LRRK2 inhibitors on DAergic neurotransmission.

AIMS

To address this gap in knowledge, we examined the effects of three types of LRRK2 inhibitors (LRRK2-IN-1, GSK2578215A, and GNE-7915) on dopamine (DA) release in the dorsal striatum using fast-scan cyclic voltammetry and DA neuron firing in the substantia nigra pars compacta (SNpc) using patch clamp in mouse brain slices.

RESULTS

We found that LRRK2-IN-1 at a concentration higher than 1 μM causes off-target effects and decreases DA release, whereas GSK2578215A and GNE-7915 do not. All three inhibitors at 1 μM have no effect on DA release and DA neuron firing rate. We have further assessed the effects of the inhibitors in two preclinical LRRK2 mouse models (i.e., BAC transgenic hG2019S and hR1441G) and demonstrated that GNE-7915 enhances DA release and synaptic vesicle mobilization/recycling.

CONCLUSION

GNE-7915 can be validated for further therapeutic development for PD.

Altered Expression of EPO Might Underlie Hepatic Hemangiomas in LRRK2 Knockout Mice

Parkinson's disease (PD) is a severe neurodegenerative disorder caused by progressive loss of dopaminergic neurons in the substantia nigra pars compacta of the midbrain. The molecular mechanism of PD pathogenesis is unclear. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are a common genetic cause of familial and sporadic PD. However, studies on LRRK2 mutant mice revealed no visible dopaminergic neuronal loss in the midbrain. While surveying a LRRK2 knockout mouse strain, we found that old animals developed age-dependent hepatic vascular growths similar to cavernous hemangiomas. In livers of these hemangioma-positive LRRK2 knockout mice, we detected an increased expression of the HIF-2α protein and significant reactivation of the expression of the HIF-2α target gene erythropoietin (EPO), a finding consistent with a role of the HIF-2α pathway in blood vessel vascularization. We also found that the kidney EPO expression was reduced to 20% of the wild-type level in 18-month-old LRRK2 knockout mice. Unexpectedly, this reduction was restored to wild-type levels when the knockout mice were 22 months to 23 months old, implying a feedback mechanism regulating kidney EPO expression. Our findings reveal a novel function of LRRK2 in regulating EPO expression and imply a potentially novel relationship between PD genes and hematopoiesis.

Metallomic Biomarkers in Cerebrospinal fluid and Serum in patients with Parkinson's disease in Indian population

Parkinson's disease (PD) is a neurodegenerative disease with the absence of markers for diagnosis. Several studies on PD reported the elements imbalance in biofluids as biomarkers. However, their results remained inconclusive. This study integrates metallomics, multivariate and artificial neural network (ANN) to understand element variations in CSF and serum of PD patients from the largest cohort of Indian population to solve the inconsistent results of previous studies. Also, this study is aimed to (1) ascertain a common element signature between CSF and serum. (2) Assess cross sectional element variation with clinical symptoms. (3) Develop ANN models for rapid diagnosis. A metallomic profile of 110 CSF and 530 serum samples showed significant variations in 10 elements of CSF and six in serum of patients compared to controls. Consistent variations in elements pattern were noticed for Calcium, Magnesium and Iron in both the fluids of PD, which provides feasible diagnosis from serum. Furthermore, implementing multivariate analyses showed clear classification between normal and PD in both the fluids. Also, ANN provides 99% accuracy in detection of disease from CSF and serum. Overall, our analyses demonstrate that elements profile in biofluids of PD will be useful in development of diagnostic markers for PD.

Functional Impairment in Miro Degradation and Mitophagy Is a Shared Feature in Familial and Sporadic Parkinson's Disease

Mitochondrial movements are tightly controlled to maintain energy homeostasis and prevent oxidative stress. Miro is an outer mitochondrial membrane protein that anchors mitochondria to microtubule motors and is removed to stop mitochondrial motility as an early step in the clearance of dysfunctional mitochondria. Here, using human induced pluripotent stem cell (iPSC)-derived neurons and other complementary models, we build on a previous connection of Parkinson's disease (PD)-linked PINK1 and Parkin to Miro by showing that a third PD-related protein, LRRK2, promotes Miro removal by forming a complex with Miro. Pathogenic LRRK2G2019S disrupts this function, delaying the arrest of damaged mitochondria and consequently slowing the initiation of mitophagy. Remarkably, partial reduction of Miro levels in LRRK2G2019S human neuron and Drosophila PD models rescues neurodegeneration. Miro degradation and mitochondrial motility are also impaired in sporadic PD patients. We reveal that prolonged retention of Miro, and the downstream consequences that ensue, may constitute a central component of PD pathogenesis.

Emerging (and converging) pathways in Parkinson's disease: keeping mitochondrial wellness

The selective cell loss in the ventral component of the substantia nigra pars compacta and the presence of alpha-synuclein (α-syn)-rich intraneuronal inclusions called Lewy bodies are the pathological hallmarks of Parkinson's disease (PD), the most common motor system disorder whose aetiology remains largely elusive. Although most cases of PD are idiopathic, there are rare familial forms of the disease that can be traced to single gene mutations that follow Mendelian inheritance pattern. The study of several nuclear encoded proteins whose mutations are linked to the development of autosomal recessive and dominant forms of familial PD enhanced our understanding of biochemical and cellular mechanisms contributing to the disease and suggested that many signs of neurodegeneration result from compromised mitochondrial function. Here we present an overview of the current understanding of PD-related mitochondrial dysfunction including defects in bioenergetics and Ca²⁺ homeostasis, mitochondrial DNA mutations, altered mitochondrial dynamics and autophagy. We emphasize, in particular, the convergence of many "apparently" different pathways towards a common route involving mitochondria. Understanding whether mitochondrial dysfunction in PD represents the cause or the consequence of the disease is challenging and will help to define the pathogenic processes at the basis of the PD onset and progression.

Mitochondrial dysfunction in Parkinson's disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease, which is characterized by loss of dopaminergic (DA) neurons in the substantia nigra pars compacta and the formation of Lewy bodies and Lewy neurites in surviving DA neurons in most cases. Although the cause of PD is still unclear, the remarkable advances have been made in understanding the possible causative mechanisms of PD pathogenesis. Numerous studies showed that dysfunction of mitochondria may play key roles in DA neuronal loss. Both genetic and environmental factors that are associated with PD contribute to mitochondrial dysfunction and PD pathogenesis. The induction of PD by neurotoxins that inhibit mitochondrial complex I provides direct evidence linking mitochondrial dysfunction to PD. Decrease of mitochondrial complex I activity is present in PD brain and in neurotoxin- or genetic factor-induced PD cellular and animal models. Moreover, PINK1 and parkin, two autosomal recessive PD gene products, have important roles in mitophagy, a cellular process to clear damaged mitochondria. PINK1 activates parkin to ubiquitinate outer mitochondrial membrane proteins to induce a selective degradation of damaged mitochondria by autophagy. In this review, we summarize the factors associated with PD and recent advances in understanding mitochondrial dysfunction in PD.

LRRK2 at the Crossroad Between Autophagy and Microtubule Trafficking: Insights into Parkinson's Disease

Mutations in leucine-rich repeat kinase 2 ( lrrk2) gene cause inherited Parkinson's disease (PD), and common variants in lrrk2 are a risk factor for sporadic PD. The neuropathology associated with LRRK2-linked PD is extremely pleomorphic involving inclusions of α-synuclein (SNCA), tau or neither, therefore suggesting that LRRK2 may be central in the pathogenic pathways of PD. This large protein localizes in the cytosol, as well as, in specific membrane domains, including mitochondria and autophagosomes and interacts with a wide range of proteins such as SNCA, tau, α- and β-tubulin. For this reason LRRK2 has been associated with a variety of cellular functions, including autophagy, mitochondrial function/dynamics and microtubule/cytoskeletal dynamics. LRRK2 has been shown to interact with microtubules as well as with mitochondria interfering with their network and dynamics. Moreover, LRRK2 knock-out or mutations affect autophagic efficiency. Here, we review and discuss the literature on how LRRK2 affects mitochondrial function, autophagy, and microtubule dynamics and how this is implicated in the PD etiology.

Connecting Ca2+ and lysosomes to Parkinson disease

The neurodegenerative movement disorder Parkinson disease (PD) is prevalent in the aged population. However, the underlying mechanisms that trigger disease are unclear. Increasing work implicates both impaired Ca²⁺ signalling and lysosomal dysfunction in neuronal demise. Here I aim to connect these distinct processes by exploring the evidence that lysosomal Ca²⁺ signalling is disrupted in PD. In particular, I highlight defects in lysosomal Ca²⁺ content and signalling through NAADP-regulated two-pore channels in patient fibroblasts harbouring mutations in the PD-linked genes, GBA1 and LRRK2. As an emerging contributor to PD pathogenesis, the lysosomal Ca²⁺ signalling apparatus could represent a novel therapeutic target.

Mitochondrial DNA in CSF distinguishes LRRK2 from idiopathic Parkinson's disease

Mitochondrial DNA regulates mitochondrial function which is altered in both idiopathic and familial forms of Parkinson's disease. To investigate whether these two disease forms exhibit an altered regulation of mitochondrial DNA we measured cell free mitochondrial DNA content in cerebrospinal fluid (CSF) from idiopathic and LRRK2-related Parkinson's disease patients. The concentration of mitochondrial DNA was measured using a digital droplet polymerase chain reaction technique in a total of 98 CSF samples from a cohort of subjects including: 20 LRRK2(G2019S) mutation carriers with Parkinson's disease, 26 asymptomatic LRRK2(G2019S) mutation carriers, 31 patients with idiopathic Parkinson's disease and 21 first-degree relatives of LRRK2 Parkinson's disease patients without the mutation. Here we report that LRRK2(G2019S) mutation carriers with Parkinson's disease exhibit a high concentration of mitochondrial DNA in CSF compared with asymptomatic LRRK2(G2019S) mutation carriers and with idiopathic Parkinson's disease patients. In addition, idiopathic, but not LRRK2 Parkinson's disease is associated with low CSF concentration of α-synuclein. These results show that high mitochondrial DNA content in CSF distinguishes idiopathic from LRRK2-related Parkinson's disease suggesting that different biochemical pathways underlie neurodegeneration in these two disorders.

Activation Mechanism of LRRK2 and Its Cellular Functions in Parkinson's Disease

Human LRRK2 (Leucine-Rich Repeat Kinase 2) has been associated with both familial and idiopathic Parkinson's disease (PD). Although several LRRK2 mediated pathways and interaction partners have been identified, the cellular functions of LRRK2 and LRRK2 mediated progression of PD are still only partially understood. LRRK2 belongs to the group of Roco proteins which are characterized by the presence of a Ras-like G-domain (Roc), a C-terminal of Roc domain (COR), a kinase, and several protein-protein interaction domains. Roco proteins exhibit a complex activation mechanism involving intramolecular signaling, dimerization, and substrate/effector binding. Importantly, PD mutations in LRRK2 have been linked to a decreased GTPase and impaired kinase activity, thus providing putative therapeutic targets. To fully explore these potential targets it will be crucial to understand the function and identify the pathways responsible for LRRK2-linked PD. Here, we review the recent progress in elucidating the complex LRRK2 activation mechanism, describe the accumulating evidence that link LRRK2-mediated PD to mitochondrial dysfunction and aberrant autophagy, and discuss possible ways for therapeutically targeting LRRK2.

Phosphoproteomics reveals that Parkinson's disease kinase LRRK2 regulates a subset of Rab GTPases

Mutations in Park8, encoding for the multidomain Leucine-rich repeat kinase 2 (LRRK2) protein, comprise the predominant genetic cause of Parkinson's disease (PD). G2019S, the most common amino acid substitution activates the kinase two- to threefold. This has motivated the development of LRRK2 kinase inhibitors; however, poor consensus on physiological LRRK2 substrates has hampered clinical development of such therapeutics. We employ a combination of phosphoproteomics, genetics, and pharmacology to unambiguously identify a subset of Rab GTPases as key LRRK2 substrates. LRRK2 directly phosphorylates these both in vivo and in vitro on an evolutionary conserved residue in the switch II domain. Pathogenic LRRK2 variants mapping to different functional domains increase phosphorylation of Rabs and this strongly decreases their affinity to regulatory proteins including Rab GDP dissociation inhibitors (GDIs). Our findings uncover a key class of bona-fide LRRK2 substrates and a novel regulatory mechanism of Rabs that connects them to PD.

Leucine-rich repeat kinase 2 positively regulates inflammation and down-regulates NF-κB p50 signaling in cultured microglia cells

Background

Over-activated microglia and chronic neuroinflammation contribute to dopaminergic neuron degeneration and progression of Parkinson’s disease (PD). Leucine-rich repeat kinase 2 (LRRK2), a kinase mutated in autosomal dominantly inherited and sporadic PD cases, is highly expressed in immune cells, in which it regulates inflammation through a yet unclear mechanism.

Methods

Here, using pharmacological inhibition and cultured Lrrk2^−/− primary microglia cells, we validated LRRK2 as a positive modulator of inflammation and we investigated its specific function in microglia cells.

Results

Inhibition or genetic deletion of LRRK2 causes reduction of interleukin-1β and cyclooxygenase-2 expression upon lipopolysaccharide-mediated inflammation. LRRK2 also takes part of the signaling trigged by α-synuclein fibrils, which culminates in induction of inflammatory mediators. At the molecular level, loss of LRRK2 or inhibition of its kinase activity results in increased phosphorylation of nuclear factor kappa-B (NF-κB) inhibitory subunit p50 at S337, a protein kinase A (PKA)-specific phosphorylation site, with consequent accumulation of p50 in the nucleus.

Conclusions

Taken together, these findings point to a role of LRRK2 in microglia activation and sustainment of neuroinflammation and in controlling of NF-κB p50 inhibitory signaling. Understanding the molecular pathways coordinated by LRRK2 in activated microglia cells after pathological stimuli such us fibrillar α-synuclein holds the potential to provide novel targets for PD therapeutics.

Parkinson's disease proteins: Novel mitochondrial targets for cardioprotection

Ischemic heart disease (IHD) is the leading cause of death and disability worldwide. Therefore, novel therapeutic targets for protecting the heart against acute ischemia/reperfusion injury (IRI) are required to attenuate cardiomyocyte death, preserve myocardial function, and prevent the onset of heart failure. In this regard, a specific group of mitochondrial proteins, which have been linked to familial forms of Parkinson's disease (PD), may provide novel therapeutic targets for cardioprotection. In dopaminergic neurons of the substantia nigra, these PD proteins, which include Parkin, PINK1, DJ-1, LRRK2, and α-synuclein, play essential roles in preventing cell death-through maintaining normal mitochondrial function, protecting against oxidative stress, mediating mitophagy, and preventing apoptosis. These rare familial forms of PD may therefore provide important insights into the pathophysiology underlying mitochondrial dysfunction and the development of PD. Interestingly, these PD proteins are also present in the heart, but their role in myocardial health and disease is not clear. In this article, we review the role of these PD proteins in the heart and explore their potential as novel mitochondrial targets for cardioprotection.

Aberrant epigenome in iPSC-derived dopaminergic neurons from Parkinson's disease patients

The epigenomic landscape of Parkinson's disease (PD) remains unknown. We performed a genomewide DNA methylation and a transcriptome studies in induced pluripotent stem cell (iPSC)-derived dopaminergic neurons (DAn) generated by cell reprogramming of somatic skin cells from patients with monogenic LRRK2-associated PD (L2PD) or sporadic PD (sPD), and healthy subjects. We observed extensive DNA methylation changes in PD DAn, and of RNA expression, which were common in L2PD and sPD. No significant methylation differences were present in parental skin cells, undifferentiated iPSCs nor iPSC-derived neural cultures not-enriched-in-DAn. These findings suggest the presence of molecular defects in PD somatic cells which manifest only upon differentiation into the DAn cells targeted in PD. The methylation profile from PD DAn, but not from controls, resembled that of neural cultures not-enriched-in-DAn indicating a failure to fully acquire the epigenetic identity own to healthy DAn in PD. The PD-associated hypermethylation was prominent in gene regulatory regions such as enhancers and was related to the RNA and/or protein downregulation of a network of transcription factors relevant to PD (FOXA1, NR3C1, HNF4A, and FOSL2). Using a patient-specific iPSC-based DAn model, our study provides the first evidence that epigenetic deregulation is associated with monogenic and sporadic PD.

Fibroblast Biomarkers of Sporadic Parkinson's Disease and LRRK2 Kinase Inhibition

It has been uncertain whether specific disease-relevant biomarker phenotypes can be found using sporadic Parkinson’s disease (PD) patient-derived samples, as it has been proposed that there may be a plethora of underlying causes and pathological mechanisms. Fibroblasts derived from familial PD patients harboring leucine-rich repeat kinase 2 (LRRK2), PTEN-induced putative kinase 1 (PINK1), and Parkin mutations show clear disease-relevant mitochondrial phenotypes, which are exacerbated under conditions of pharmacological stress. We utilized fibroblasts derived from non-familial sporadic PD patients (without LRRK2 mutations) or LRRK2 mutation carriers to directly compare the cellular phenotypes during and after mitochondrial stress. We then determined the effects of pharmacological LRRK2 kinase inhibition using LRRK2-in-1. We found that there were two distinct populations of sporadic PD patient-derived fibroblast lines. One group of sporadic PD lines was highly susceptible to valinomycin-induced mitochondrial depolarization, emulating the mutant LRRK2 phenotype. These lines showed elevated mitochondrial superoxide/ nitric oxide levels, displayed increased mitochondrial and lysosome co-localization, and an increased rate of mitochondrial collapse, which corresponded with changes in mitochondrial fission and fusion proteins. The application of LRRK2-in-1 reversed decreased levels of mitochondrial and lysosome co-localization and partially restored mitochondrial network associated proteins and the mitochondrial membrane potential in the fibroblasts. This study identifies novel mitochondrial biomarkers in sporadic PD patient-derived fibroblast lines, which could be used as preclinical tools in which to test novel and known neuroprotective compounds.

UDCA exerts beneficial effect on mitochondrial dysfunction in LRRK2(G2019S) carriers and in vivo

OBJECTIVE

To further characterize mitochondrial dysfunction in LRRK2(G2019S) mutant Parkinson disease (PD) patient tissue (M-LRRK2(G2019S)), determine whether ursodeoxycholic acid (UDCA) also exerts a beneficial effect on mitochondrial dysfunction in nonmanifesting LRRK2(G2019S) mutation carriers (NM-LRRK2(G2019S)), and assess UDCA for its beneficial effect on neuronal dysfunction in vivo.

METHODS

Intracellular adenosine 5'-triphosphate (ATP) levels, oxygen consumption, and activity of the individual complexes of the mitochondrial respiratory chain as well as mitochondrial morphology were measured in M-LRRK2(G2019S), NM-LRRK2(G2019S), and controls. UDCA was assessed for its rescue effect on intracellular ATP levels in NM-LRRK2(G2019S) and in a LRRK2 transgenic fly model with dopaminergic expression of LRRK2(G2019S).

RESULTS

Crucial parameters of mitochondrial function were similarly reduced in both M-LRRK2(G2019S) and NM-LRRK2(G2019S) with a specific decrease in respiratory chain complex IV activity. Mitochondrial dysfunction precedes changes in mitochondrial morphology but is normalized after siRNA-mediated knockdown of LRRK2. UDCA improved mitochondrial function in NM-LRRK2(G2019) and rescued the loss of visual function in LRRK2(G2019S) flies.

CONCLUSION

There is clear preclinical impairment of mitochondrial function in NM-LRRK2(G2019S) that is distinct from the mitochondrial impairment observed in parkin-related PD. The beneficial effect of UDCA on mitochondrial function in both NM-LRRK2(G2019S) and M-LRRK2(G2019S) as well as on the function of dopaminergic neurons expressing LRRK2(G2019S) suggests that UDCA is a promising drug for future neuroprotective trials.

Pathogenic mechanisms of neurodegeneration in Parkinson disease

The last 2 decades represent a period of unparalleled advancement in the understanding of the pathogenesis of Parkinson disease (PD). The discovery of several forms of familial parkinsonism with mendelian inheritance has elucidated insights into the mechanisms underlying the degeneration of dopaminergic neurons of the substantia nigra that histologically characterize PD. α-Synuclein, the principal component of Lewy bodies, remains the presumed pathogen at the heart of the current model; however, concurrently, a diverse range of other mechanisms have been implicated. The creation of a coherent disease model will be crucial to the development of effective disease modifying therapies for sporadic PD.

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.

Progressive dopaminergic alterations and mitochondrial abnormalities in LRRK2 G2019S knock-in mice

Mutations in the LRRK2 gene represent the most common genetic cause of late onset Parkinson's disease. The physiological and pathological roles of LRRK2 are yet to be fully determined but evidence points towards LRRK2 mutations causing a gain in kinase function, impacting on neuronal maintenance, vesicular dynamics and neurotransmitter release. To explore the role of physiological levels of mutant LRRK2, we created knock-in (KI) mice harboring the most common LRRK2 mutation G2019S in their own genome. We have performed comprehensive dopaminergic, behavioral and neuropathological analyses in this model up to 24months of age. We find elevated kinase activity in the brain of both heterozygous and homozygous mice. Although normal at 6months, by 12months of age, basal and pharmacologically induced extracellular release of dopamine is impaired in both heterozygous and homozygous mice, corroborating previous findings in transgenic models over-expressing mutant LRRK2. Via in vivo microdialysis measurement of basal and drug-evoked extracellular release of dopamine and its metabolites, our findings indicate that exocytotic release from the vesicular pool is impaired. Furthermore, profound mitochondrial abnormalities are evident in the striatum of older homozygous G2019S KI mice, which are consistent with mitochondrial fission arrest. We anticipate that this G2019S mouse line will be a useful pre-clinical model for further evaluation of early mechanistic events in LRRK2 pathogenesis and for second-hit approaches to model disease progression.

Mitochondrial dysfunction and mitophagy in Parkinson's: from familial to sporadic disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterised by the preferential loss of dopaminergic neurons in the substantia nigra. Mitochondrial dysfunction is increasingly appreciated as a key determinant of dopaminergic neuronal susceptibility in PD and is a feature of both familial and sporadic disease, as well as in toxin-induced Parkinsonism. Recently, the mechanisms by which PD-associated mitochondrial proteins phosphatase and tensin homolog deleted on chromosome 10 (PTEN)-induced putative kinase 1 (PINK1) and parkin function and induce neurodegeneration have been identified. In addition, increasing evidence implicates other PD-associated proteins such as α-synuclein (α-syn) and leucine-rich repeat kinase 2 (LRRK2) in mitochondrial dysfunction in genetic cases of PD with the potential for a large functional overlap with sporadic disease. This review highlights how recent advances in understanding familial PD-associated proteins have identified novel mechanisms and therapeutic strategies for addressing mitochondrial dysfunction in PD.