Interactions of dopamine, iron, and alpha-synuclein linked to dopaminergic neuron vulnerability in Parkinson's disease and Neurodegeneration with Brain Iron Accumulation disorders.

Dopamine metabolism, alpha-synuclein pathology, and iron homeostasis have all been implicated as potential contributors to the unique vulnerability of substantia nigra dopaminergic neurons which preferentially decline in Parkinson's disease and some rare neurodegenerative disorders with shared pathological features. However, the mechanisms contributing to disease progression and resulting in dopaminergic neuron loss in the substantia nigra are still not completely understood. Increasing evidence demonstrates that disrupted dopamine, alpha-synuclein, and/or iron pathways, when combined with the unique morphological, physiological, and metabolic features of this neuron population, may culminate in weakened resilience to multiple stressors. This review analyzes the involvement of each of these pathways in dopamine neuron physiology and function, and discusses how disrupted interplay of dopamine, alpha-synuclein, and iron pathways may synergize to promote pathology and drive the unique vulnerability to disease states. We suggest that elucidating the interactions of dopamine with iron and alpha-synuclein, and the role of dopamine metabolism in driving pathogenic phenotypes will be critical for developing therapeutics to prevent progression in diseases that show degeneration of nigral dopamine neurons such as Parkinson's disease and the rare family of disorders known as Neurodegeneration with Brain Iron Accumulation.

Modeling Brain Pathology of Niemann-Pick Disease Type C Using Patient-Derived Neurons.

BACKGROUND: Niemann-Pick disease type C (NPC) is a rare autosomal-recessive lysosomal storage disease that is also associated with progressive neurodegeneration. NPC shares many pathological features with Alzheimer's disease, including neurofibrillary tangles, axonal spheroids, ß-amyloid deposition, and dystrophic neurites. Here, we examined if these pathological features could be detected in induced pluripotent stem cell (iPSC)-derived neurons from NPC patients. METHODS: Brain tissues from 8 NPC patients and 5 controls were analyzed for histopathological and biochemical markers of pathology. To model disease in culture, iPSCs from NPC patients and controls were differentiated into cortical neurons. RESULTS: We found hyperphosphorylated tau, altered processing of amyloid precursor protein, and increased Aß42 in NPC postmortem brains and in iPSC-derived cortical neurons from NPC patients. CONCLUSION: Our findings demonstrated that the main pathogenic phenotypes typically found in NPC brains were also observed in patient-derived neurons, providing a useful model for further mechanistic and therapeutic studies of NPC. © 2021 International Parkinson and Movement Disorder Society.

Acid ceramidase inhibition ameliorates α-synuclein accumulation upon loss of GBA1 function.

GBA1 encodes the lysosomal enzyme ß-glucocerebrosidase (GCase) which converts glucosylceramide into ceramide and glucose. Mutations in GBA1 lead to Gaucher's disease and are a major risk factor for Parkinson's disease (PD) and Dementia with Lewy bodies (DLB), synucleinopathies characterized by accumulation of intracellular α-synuclein. In this study, we examined whether decreased ceramide that is observed in GCase-deficient cells contributes to α-synuclein accumulation. We demonstrated that deficiency of GCase leads to a reduction of C18-ceramide species and altered intracellular localization of Rab8a, a small GTPase implicated in secretory autophagy, that contributed to impaired secretion of α-synuclein and accumulation of intracellular α-synuclein. This secretory defect was rescued by exogenous C18-ceramide or chemical inhibition of lysosomal enzyme acid ceramidase that converts lysosomal ceramide into sphingosine. Inhibition of acid ceramidase by carmofur resulted in increased ceramide levels and decreased glucosylsphingosine levels in GCase-deficient cells, and also reduced oxidized α-synuclein and levels of ubiquitinated proteins in GBA1-PD patient-derived dopaminergic neurons. Together, these results suggest that decreased ceramide generation via the catabolic lysosomal salvage pathway in GCase mutant cells contributes to α-synuclein accumulation, potentially due to impaired secretory autophagy. We thus propose that acid ceramidase inhibition which restores ceramide levels may be a potential therapeutic strategy to target synucleinopathies linked to GBA1 mutations including PD and DLB.

The role of dopamine in the pathogenesis of GBA1-linked Parkinson's disease.

Our understanding of the molecular mechanisms underlying differential vulnerability of substantia nigra dopamine neurons in Parkinson's disease (PD) remains limited, and previous therapeutic efforts targeting rodent nigral neurons have not been successfully translated to humans. However, recent emergence of induced pluripotent stem cell technology has highlighted some fundamental differences between human and rodent midbrain dopamine neurons that may at least in part explain relative resistance of rodent neurons to degeneration in genetic models of PD. Using GBA1-linked PD as an example, we discuss cellular pathways that may predispose human neurons to degeneration in PD, including mitochondrial oxidant stress, elevated intracellular calcium, altered synaptic vesicle endocytosis, accumulation of oxidized dopamine and neuromelanin. Recent studies have suggested that a combination of mitochondrial oxidant stress and accumulation of oxidized dopamine contribute to dysfunction of nigral neurons in various genetic and sporadic forms of PD. We also briefly summarize the development of targeted therapies for GBA1-associated synucleinopathies and highlight that modulation of wild-type GCase activity serves as an important target for the treatment of genetic and idiopathic forms of PD and dementia with Lewy bodies.

Iron overload is accompanied by mitochondrial and lysosomal dysfunction in WDR45 mutant cells.

Beta-propeller protein-associated neurodegeneration is a subtype of monogenic neurodegeneration with brain iron accumulation caused by de novo mutations in WDR45. The WDR45 protein functions as a beta-propeller scaffold and plays a putative role in autophagy through its interaction with phospholipids and autophagy-related proteins. Loss of WDR45 function due to disease-causing mutations has been linked to defects in autophagic flux in patient and animal cells. However, the role of WDR45 in iron homeostasis remains elusive. Here we studied patient-specific WDR45 mutant fibroblasts and induced pluripotent stem cell-derived midbrain neurons. Our data demonstrated that loss of WDR45 increased cellular iron levels and oxidative stress, accompanied by mitochondrial abnormalities, autophagic defects, and diminished lysosomal function. Restoring WDR45 levels partially rescued oxidative stress and the susceptibility to iron treatment, and activation of autophagy reduced the observed iron overload in WDR45 mutant cells. Our data suggest that iron-containing macromolecules and organelles cannot effectively be degraded through the lysosomal pathway due to loss of WDR45 function.

Activation of ß-Glucocerebrosidase Reduces Pathological α-Synuclein and Restores Lysosomal Function in Parkinson's Patient Midbrain Neurons.

UNLABELLED: Parkinson's disease (PD) is characterized by the accumulation of α-synuclein (α-syn) within Lewy body inclusions in the nervous system. There are currently no disease-modifying therapies capable of reducing α-syn inclusions in PD. Recent data has indicated that loss-of-function mutations in the GBA1 gene that encodes lysosomal ß-glucocerebrosidase (GCase) represent an important risk factor for PD, and can lead to α-syn accumulation. Here we use a small-molecule modulator of GCase to determine whether GCase activation within lysosomes can reduce α-syn levels and ameliorate downstream toxicity. Using induced pluripotent stem cell (iPSC)-derived human midbrain dopamine (DA) neurons from synucleinopathy patients with different PD-linked mutations, we find that a non-inhibitory small molecule modulator of GCase specifically enhanced activity within lysosomal compartments. This resulted in reduction of GCase substrates and clearance of pathological α-syn, regardless of the disease causing mutations. Importantly, the reduction of α-syn was sufficient to reverse downstream cellular pathologies induced by α-syn, including perturbations in hydrolase maturation and lysosomal dysfunction. These results indicate that enhancement of a single lysosomal hydrolase, GCase, can effectively reduce α-syn and provide therapeutic benefit in human midbrain neurons. This suggests that GCase activators may prove beneficial as treatments for PD and related synucleinopathies. SIGNIFICANCE STATEMENT: The presence of Lewy body inclusions comprised of fibrillar α-syn within affected regions of PD brain has been firmly documented, however no treatments exist that are capable of clearing Lewy bodies. Here, we used a mechanistic-based approach to examine the effect of GCase activation on α-syn clearance in human midbrain DA models that naturally accumulate α-syn through genetic mutations. Small molecule-mediated activation of GCase was effective at reducing α-syn inclusions in neurons, as well as associated downstream toxicity, demonstrating a therapeutic effect. Our work provides an example of how human iPSC-derived midbrain models could be used for testing potential treatments for neurodegenerative disorders, and identifies GCase as a critical therapeutic convergence point for a wide range of synucleinopathies.

Detection of Free and Protein-Bound ortho-Quinones by Near-Infrared Fluorescence.

Aging and oxidative stress are two prominent pathological mechanisms for Parkinson's disease (PD) that are strongly associated with the degeneration of dopamine (DA) neurons in the midbrain. DA and other catechols readily oxidize into highly reactive o-quinone species that are precursors of neuromelanin (NM) pigment and under pathological conditions can modify and damage macromolecules. The role of DA oxidation in PD pathogenesis remains unclear in part due to the lack of appropriate disease models and the absence of a simple method for the quantification of DA-derived oxidants. Here, we describe a rapid, simple, and reproducible method for the quantification of o-quinones in cells and tissues that relies on the near-infrared fluorescent properties of these species. Importantly, we demonstrate that catechol-derived oxidants can be quantified in human neuroblastoma cells and midbrain dopamine neurons derived from induced pluripotent stem cells, providing a novel model to study the downstream actions of o-quinones. This method should facilitate further study of oxidative stress and DA oxidation in PD and related diseases that affect the dopaminergic system.

A novel heterozygous OPA3 mutation located in the mitochondrial target sequence results in altered steady-state levels and fragmented mitochondrial network.

BACKGROUND: Mutations in OPA3 have been reported in patients with autosomal dominant optic atrophy plus cataract and Costeff syndrome. Here, we report the results of a comprehensive study on OPA3 mutations, including the mutation spectrum and its prevalence in a large cohort of OPA1-negative autosomal dominant optic atrophy (ADOA) patients, the associated clinical phenotype and the functional characterisation of a newly identified OPA3 mutant. METHODS: Mutation analysis was carried out in a patient cohort of 121 independent ADOA patients. To characterise a novel OPA3 mutation, we analysed the mitochondrial import, steady-state levels and the mitochondrial localisation of the mutated protein in patients' fibroblasts. Furthermore, the morphology of mitochondria harbouring the mutated OPA3 was monitored. RESULTS: We identified four independent cases (representing families with multiple affected members) with OPA3 mutations. Besides the known p.Q105E mutation, we observed a novel insertion, c.10_11insCGCCCG/p.V3_G4insAP which is located in the mitochondrial presequence. Detailed functional analysis of mitochondria harbouring this novel mutation demonstrates a fragmented mitochondrial network with a decreased mitochondrial mass in patient fibroblasts. In addition, quantification of the OPA3 protein reveals decreased steady-state levels of the mutant protein compared with the native one. Comparison of the clinical phenotypes suggests that OPA3 mutations can additionally evoke hearing loss and by that extend the clinical manifestation of OPA3-associated optic atrophy. This finding is supported by expression analysis of OPA3 in murine cochlear tissue. CONCLUSIONS: In summary, our study provides new insights into the clinical spectrum and the pathogenesis of dominant optic atrophy caused by mutations in the OPA3 gene.

Genome-wide association study of copy number variations in Parkinson's disease.

Objective: Our study investigates the impact of copy number variations (CNVs) on Parkinson's disease (PD) pathogenesis using genome-wide data, aiming to uncover novel genetic mechanisms and improve the understanding of the role of CNVs in sporadic PD. Methods: We applied a sliding window approach to perform CNV-GWAS and conducted genome-wide burden analyses on CNV data from 11,035 PD patients (including 2,731 early-onset PD (EOPD)) and 8,901 controls from the COURAGE-PD consortium. Results: We identified 14 genome-wide significant CNV loci associated with PD, including one deletion and 13 duplications. Among these, duplications in 7q22.1, 11q12.3 and 7q33 displayed the highest effect. Two significant duplications overlapped with PD-related genes SNCA and VPS13C, but none overlapped with recent significant SNP-based GWAS findings. Five duplications included genes associated with neurological disease, and four overlapping genes were dosage-sensitive and intolerant to loss-of-function variants. Enriched pathways included neurodegeneration, steroid hormone biosynthesis, and lipid metabolism. In early-onset cases, four loci were significantly associated with EOPD, including three known duplications and one novel deletion in PRKN. CNV burden analysis showed a higher prevalence of CNVs in PD-related genes in patients compared to controls (OR=1.56 [1.18-2.09], p=0.0013), with PRKN showing the highest burden (OR=1.47 [1.10-1.98], p=0.026). Patients with CNVs in PRKN had an earlier disease onset. Burden analysis with controls and EOPD patients showed similar results. Interpretation: This is the largest CNV-based GWAS in PD identifying novel CNV regions and confirming the significant CNV burden in EOPD, primarily driven by the PRKN gene, warranting further investigation.

Dissecting the role of the mitochondrial chaperone mortalin in Parkinson's disease: functional impact of disease-related variants on mitochondrial homeostasis.

The mitochondrial chaperone mortalin has been linked to neurodegeneration in Parkinson's disease (PD) based on reduced protein levels in affected brain regions of PD patients and its interaction with the PD-associated protein DJ-1. Recently, two amino acid exchanges in the ATPase domain (R126W) and the substrate-binding domain (P509S) of mortalin were identified in Spanish PD patients. Here, we identified a separate and novel variant (A476T) in the substrate-binding domain of mortalin in German PD patients. To define a potential role as a susceptibility factor in PD, we characterized the functions of all three variants in different cellular models. In vitro import assays revealed normal targeting of all mortalin variants. In neuronal and non-neuronal human cell lines, the disease-associated variants caused a mitochondrial phenotype of increased reactive oxygen species and reduced mitochondrial membrane potential, which were exacerbated upon proteolytic stress. These functional impairments correspond with characteristic alterations of the mitochondrial network in cells overexpressing mutant mortalin compared with wild-type (wt), which were confirmed in fibroblasts from a carrier of the A476T variant. In line with a loss of function hypothesis, knockdown of mortalin in human cells caused impaired mitochondrial function that was rescued by wt mortalin, but not by the variants. Our genetic and functional studies of novel disease-associated variants in the mortalin gene define a loss of mortalin function, which causes impaired mitochondrial function and dynamics. Our results support the role of this mitochondrial chaperone in neurodegeneration and underscore the concept of impaired mitochondrial protein quality control in PD.

Genome-wide Association and Meta-analysis of Age at Onset in Parkinson Disease: Evidence From the COURAGE-PD Consortium.

BACKGROUND AND OBJECTIVES: Considerable heterogeneity exists in the literature concerning genetic determinants of the age at onset (AAO) of Parkinson disease (PD), which could be attributed to a lack of well-powered replication cohorts. The previous largest genome-wide association studies (GWAS) identified SNCA and TMEM175 loci on chromosome (Chr) 4 with a significant influence on the AAO of PD; these have not been independently replicated. This study aims to conduct a meta-analysis of GWAS of PD AAO and validate previously observed findings in worldwide populations. METHODS: A meta-analysis was performed on PD AAO GWAS of 30 populations of predominantly European ancestry from the Comprehensive Unbiased Risk Factor Assessment for Genetics and Environment in Parkinson's Disease (COURAGE-PD) Consortium. This was followed by combining our study with the largest publicly available European ancestry dataset compiled by the International Parkinson Disease Genomics Consortium (IPDGC). RESULTS: The COURAGE-PD Consortium included a cohort of 8,535 patients with PD (91.9%: Europeans and 9.1%: East Asians). The average AAO in the COURAGE-PD dataset was 58.9 years (SD = 11.6), with an underrepresentation of females (40.2%). The heritability estimate for AAO in COURAGE-PD was 0.083 (SE = 0.057). None of the loci reached genome-wide significance (p < 5 × 10-8). Nevertheless, the COURAGE-PD dataset confirmed the role of the previously published TMEM175 variant as a genetic determinant of the AAO of PD with Bonferroni-corrected nominal levels of significance (p < 0.025): (rs34311866: ß(SE)COURAGE = 0.477(0.203), p COURAGE = 0.0185). The subsequent meta-analysis of COURAGE-PD and IPDGC datasets (Ntotal = 25,950) led to the identification of 2 genome-wide significant association signals on Chr 4, including the previously reported SNCA locus (rs983361: ß(SE)COURAGE+IPDGC = 0.720(0.122), p COURAGE+IPDGC = 3.13 × 10-9) and a novel BST1 locus (rs4698412: ß(SE)COURAGE+IPDGC = -0.526(0.096), p COURAGE+IPDGC = 4.41 × 10-8). DISCUSSION: Our study further refines the genetic architecture of Chr 4 underlying the AAO of the PD phenotype through the identification of BST1 as a novel AAO PD locus. These findings open a new direction for the development of treatments to delay the onset of PD.

Identification of ASCL1 as a determinant for human iPSC-derived dopaminergic neurons.

During cellular specification, transcription factors orchestrate cellular decisions through gene regulation. By hijacking these transcriptional networks, human pluripotent stem cells (hPSCs) can be specialized into neurons with different molecular identities for the purposes of regenerative medicine and disease modeling. However, molecular fine tuning cell types to match their in vivo counterparts remains a challenge. Directing cell fates often result in blended or incomplete neuron identities. A better understanding of hPSC to neuron gene regulation is needed. Here, we used single cell RNA sequencing to resolve some of these graded molecular identities during human neurogenesis from hPSCs. Differentiation platforms were established to model neural induction from stem cells, and we characterized these differentiated cell types by 10x single cell RNA sequencing. Using single cell trajectory and co-expression analyses, we identified a co-regulated transcription factor module expressing achaete-scute family basic helix-loop-helix transcription factor 1 (ASCL1) and neuronal differentiation 1 (NEUROD1). We then tested the function of these transcription factors in neuron subtype differentiation by gene knockout in a novel human system that reports the expression of tyrosine hydroxylase (TH), the rate limiting enzyme in dopamine synthesis. ASCL1 was identified as a necessary transcription factor for regulating dopaminergic neurotransmitter selection.

Mitochondrial Phenotypes in Parkinson's Diseases-A Focus on Human iPSC-Derived Dopaminergic Neurons.

Established disease models have helped unravel the mechanistic underpinnings of pathological phenotypes in Parkinson's disease (PD), the second most common neurodegenerative disorder. However, these discoveries have been limited to relatively simple cellular systems and animal models, which typically manifest with incomplete or imperfect recapitulation of disease phenotypes. The advent of induced pluripotent stem cells (iPSCs) has provided a powerful scientific tool for investigating the underlying molecular mechanisms of both familial and sporadic PD within disease-relevant cell types and patient-specific genetic backgrounds. Overwhelming evidence supports mitochondrial dysfunction as a central feature in PD pathophysiology, and iPSC-based neuronal models have expanded our understanding of mitochondrial dynamics in the development and progression of this devastating disorder. The present review provides a comprehensive assessment of mitochondrial phenotypes reported in iPSC-derived neurons generated from PD patients' somatic cells, with an emphasis on the role of mitochondrial respiration, morphology, and trafficking, as well as mitophagy and calcium handling in health and disease. Furthermore, we summarize the distinguishing characteristics of vulnerable midbrain dopaminergic neurons in PD and report the unique advantages and challenges of iPSC disease modeling at present, and for future mechanistic and therapeutic applications.

Direct targeting of wild-type glucocerebrosidase by antipsychotic quetiapine improves pathogenic phenotypes in Parkinson's disease models.

Current treatments for Parkinson's disease (PD) provide only symptomatic relief, with no disease-modifying therapies identified to date. Repurposing FDA-approved drugs to treat PD could significantly shorten the time needed for and reduce the costs of drug development compared with conventional approaches. We developed an efficient strategy to screen for modulators of ß-glucocerebrosidase (GCase), a lysosomal enzyme that exhibits decreased activity in patients with PD, leading to accumulation of the substrate glucosylceramide and oxidized dopamine and α-synuclein, which contribute to PD pathogenesis. Using a GCase fluorescent probe and affinity-based fluorescence polarization assay, we screened 1280 structurally diverse, bioactive, and cell-permeable FDA-approved drugs and found that the antipsychotic quetiapine bound GCase with high affinity. Moreover, quetiapine treatment of induced pluripotent stem cell-derived (iPSC-derived) dopaminergic neurons from patients carrying mutations in GBA1 or LRRK2 led to increased wild-type GCase protein levels and activity and partially lowered accumulation of oxidized dopamine, glucosylceramide, and α-synuclein. Similarly, quetiapine led to activation of wild-type GCase and reduction of α-synuclein in a GBA mutant mouse model (Gba1D409V/+ mice). Together, these results suggest that repurposing quetiapine as a modulator of GCase may be beneficial for patients with PD exhibiting decreased GCase activity.

Balance is the challenge--the impact of mitochondrial dynamics in Parkinson's disease.

Impaired mitochondrial function has been implicated in neurodegeneration in Parkinson's disease (PD) based on biochemical and pathoanatomical studies in brains of PD patients. This observation was further substantiated by the identification of exogenic toxins, i.e. complex I inhibitors that directly affect mitochondrial energy metabolism and cause Parkinsonism in humans and various animal models. Recently, insights into the underlying molecular signalling pathways leading to alterations in mitochondrial homeostasis were gained based on the functional characterization of mitoprotective genes identified in rare forms of inherited PD. Using in vitro and in vivo loss of function models of the Parkin, PINK1, DJ-1 and Omi/HtrA2 gene, the emerging field of mitochondrial dynamics in PD was established as being critical for the maintenance of mitochondrial function in neurons. This underscored the concept that mitochondria are highly dynamic organelles, which are tightly regulated to continuously adapt shape to functional and anatomical requirements during axonal transport, synaptic signalling, organelle degradation and cellular energy supply. The dissection of pathways involved in mitochondrial quality control clearly established the PINK1/Parkin-pathway in the clearance of dysfunctional mitochondria by autophagy and hints to a complex interplay between PD-associated proteins acting at the mitochondrial interface. The elucidation of this mitoprotective signalling network may help to define novel therapeutic targets for PD via molecular modelling of mitochondria and/or pharmacological modulation of mitochondrial dynamics.

The Convergence of Alpha-Synuclein, Mitochondrial, and Lysosomal Pathways in Vulnerability of Midbrain Dopaminergic Neurons in Parkinson's Disease.

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by progressive bradykinesia, rigidity, resting tremor, and gait impairment, as well as a spectrum of non-motor symptoms including autonomic and cognitive dysfunction. The cardinal motor symptoms of PD stem from the loss of substantia nigra (SN) dopaminergic (DAergic) neurons, and it remains unclear why SN DAergic neurons are preferentially lost in PD. However, recent identification of several genetic PD forms suggests that mitochondrial and lysosomal dysfunctions play important roles in the degeneration of midbrain dopamine (DA) neurons. In this review, we discuss the interplay of cell-autonomous mechanisms linked to DAergic neuron vulnerability and alpha-synuclein homeostasis. Emerging studies highlight a deleterious feedback cycle, with oxidative stress, altered DA metabolism, dysfunctional lysosomes, and pathological alpha-synuclein species representing key events in the pathogenesis of PD. We also discuss the interactions of alpha-synuclein with toxic DA metabolites, as well as the biochemical links between intracellular iron, calcium, and alpha-synuclein accumulation. We suggest that targeting multiple pathways, rather than individual processes, will be important for developing disease-modifying therapies. In this context, we focus on current translational efforts specifically targeting lysosomal function, as well as oxidative stress via calcium and iron modulation. These efforts could have therapeutic benefits for the broader population of sporadic PD and related synucleinopathies.

Gelator length precisely tunes supramolecular hydrogel stiffness and neuronal phenotype in 3D culture.

The brain is one of the softest tissues in the body with storage moduli (G') that range from hundreds to thousands of pascals (Pa) depending upon the anatomic region. Furthermore, pathological processes such as injury, aging and disease can cause subtle changes in the mechanical properties throughout the central nervous system. However, these changes in mechanical properties lie within an extremely narrow range of moduli and there is great interest in understanding their effect on neuron biology. We report here the design of supramolecular hydrogels based on anionic peptide amphiphile nanofibers using oligo-L-lysines of different molecular lengths to precisely tune gel stiffness over the range of interest and found that G' increases by 10.5 Pa for each additional lysine monomer in the oligo-L-lysine chain. We found that small changes in storage modulus on the order of 70 Pa significantly affect survival, neurite growth and tyrosine hydroxylase-positive population in dopaminergic neurons derived from induced pluripotent stem cells. The work reported here offers a strategy to tune mechanical stiffness of hydrogels for use in 3D neuronal cell cultures and transplantation matrices for neural regeneration.

Dopamine metabolism by a monoamine oxidase mitochondrial shuttle activates the electron transport chain.

Monoamine oxidase (MAO) metabolizes cytosolic dopamine (DA), thereby limiting auto-oxidation, but is also thought to generate cytosolic hydrogen peroxide (H2O2). We show that MAO metabolism of DA does not increase cytosolic H2O2 but leads to mitochondrial electron transport chain (ETC) activity. This is dependent upon MAO anchoring to the outer mitochondrial membrane and shuttling electrons through the intermembrane space to support the bioenergetic demands of phasic DA release.

Author Correction: Dopamine metabolism by a monoamine oxidase mitochondrial shuttle activates the electron transport chain.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A patient-based model of RNA mis-splicing uncovers treatment targets in Parkinson's disease.

Parkinson's disease (PD) is a heterogeneous neurodegenerative disorder with monogenic forms representing prototypes of the underlying molecular pathology and reproducing to variable degrees the sporadic forms of the disease. Using a patient-based in vitro model of PARK7-linked PD, we identified a U1-dependent splicing defect causing a drastic reduction in DJ-1 protein and, consequently, mitochondrial dysfunction. Targeting defective exon skipping with genetically engineered U1-snRNA recovered DJ-1 protein expression in neuronal precursor cells and differentiated neurons. After prioritization of candidate drugs, we identified and validated a combinatorial treatment with the small-molecule compounds rectifier of aberrant splicing (RECTAS) and phenylbutyric acid, which restored DJ-1 protein and mitochondrial dysfunction in patient-derived fibroblasts as well as dopaminergic neuronal cell loss in mutant midbrain organoids. Our analysis of a large number of exomes revealed that U1 splice-site mutations were enriched in sporadic PD patients. Therefore, our study suggests an alternative strategy to restore cellular abnormalities in in vitro models of PD and provides a proof of concept for neuroprotection based on precision medicine strategies in PD.