Parkin Mutations Research Articles

Parkin mutation and deep brain stimulation outcome

Patients with parkin mutations are expected to be good candidates for deep brain stimulation (DBS) because of an excellent levodopa response and frequent occurrence of levodopa-induced dyskinesia. However, there are insufficient data on surgical outcome in patients with parkin mutations. This study aimed to compare the outcome of subthalamic nucleus DBS in patients with early-onset Parkinson’s disease with and without parkin mutations. Fourteen patients with early-onset Parkinson’s disease who underwent bilateral subthalamic nucleus DBS surgery were screened for parkin mutations and assessed for surgical outcomes at baseline and 2–5years after surgery. Three patients had homozygote/compound heterozygote mutations; two had single heterozygote mutations; and nine had no mutations. Patients with homozygote/compound heterozygote mutations were younger at disease onset and had longer disease duration than patients without a parkin mutation. Postoperatively, there were no significant differences in improvement on the Unified Parkinson’s Disease Rating Scale part II, III, and IV, or the reduction of levodopa equivalent daily doses between patients with and without parkin mutations. The therapeutic effect of DBS did not differ between patients with and without parkin mutations.

Next-Generation Phenotyping Using theParkinExample

Two decades of intense research have led to important insights into the pathophysiology of neurodegenerative diseases, with limited direct clinical impact. While next-generation sequencing has emerged as a powerful research tool, we hypothesized that systematic exploitation of phenotypic data are lagging behind genetic advances. To use the 15-year experience with parkin-associated Parkinson disease (PD) to evaluate type, quality, and quantity of genetic and phenotypic data and to elucidate clinical or genetic features impacting genetic testing and counseling. We searched MEDLINE: (1998-2012) using the term parkin AND mutation for English publications about proved parkin-associated PD and at least minimal, individual clinical information excluding digenic cases, and redundant articles. This approach identified 877 articles, of which 196 described patients with PD with confirmed parkin mutations and 127 articles fulfilled our inclusion criteria. Information was extracted using predefined criteria and a consensus approach for questionable details. To evaluate study method differences, we devised a quality score representing the completeness of clinical, demographic, and genetic information. In the data about 1184 patients, the quality score increased steadily and was driven exclusively by improvements in genetic analyses. By contrast, demographic and clinical content stagnated. The mean age at onset was 9 years lower in index patients with 2 mutant parkin alleles than in heterozygotes. Genotype-phenotype correlation was observed for the number of mutated alleles and dystonia. By contrast, dementia was rare in all parkin-mutation carriers (<3%), despite long disease duration. Notwithstanding large gaps in phenotypic information content, we identified dystonia and the absence of dementia as "red flags" to be incorporated in counseling guidelines. We propose mandatory minimal criteria for genotype-phenotype studies to facilitate the next breakthrough-following genetics-toward more personalized medicine for genetic conditions, extending well beyond the parkin example.

Detection of copy number changes in genes associated with Parkinson's disease in Iranian patients

Parkinson's disease (PD) is the second most common neurodegenerative disorder, after Alzheimer's disease. Genomic rearrangements are common mutations reported in PD patients. In this study, we investigated the prevalence of genomic rearrangements in a total of 232 Iranian PD patients, out of which 102 were sporadic early-onset (age-at-onset ≤45 years) and 51 had a family history. We used multiplex ligation-dependent probe amplification (MLPA) method to detect exon dosage changes. Two new improved probe kits, SALSA P051 and P052, were used and altogether α-synuclein, parkin, UCHL1, PINK1, DJ-1, LRRK2, GCH1, ATP13A2, CAV1, CAV2, LPA and TNFRSF9 genes were analyzed. Exon or whole-gene rearrangements were identified in 14 (13.7%) sporadic early-onset PD patients in parkin, α-synuclein and PINK1. Of familial PD patients 46 cases from 18 families (35.3%) showed exon or whole-gene rearrangements in parkin, α-synuclein, PINK1, DJ-1, and ATP13A2 genes. All changes were verified by quantitative PCR (qPCR). Novel mutations and unusual clinical features are reported in this study. Mutations in parkin were the predominant genetic cause in both early-onset and familial PD groups. Also the mutations observed in family PD group are more in number and diversity than the sporadic early-onset PD group.

Variability in clinical phenotypes of heterozygous and homozygous cases of Parkin-related Parkinson's disease

Parkin mutations are a common cause of early-onset Parkinson's disease. To study the clinical features and treatment responses of patients with homozygous or heterozygous Parkin mutations, we performed a retrospective chart review in six early-onset parkinsonism patients with pathogenic Parkin mutations. The clinical phenotypes observed in this cohort, all drawn from different families, were variable. All patients had a slowly progressive form of parkinsonism that responded well to dopaminergic therapy with the exception of one advanced case. Homozygous patients had an earlier age at disease onset than heterozygous patients. Two of our patients underwent bilateral deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus leading to a sustained positive response. Our observations support an earlier age of onset for homozygous cases and possible beneficial effects of DBS in Parkin-related parkinsonism.

Genotype and phenotype in Parkinson's disease: lessons in heterogeneity from deep brain stimulation.

Variation in the genetic risk(s) of developing Parkinson's disease (PD) undoubtedly contributes to the subsequent phenotypic heterogeneity. Although patients with PD who undergo deep brain stimulation (DBS) are a skewed population, they represent a valuable resource for exploring the relationships between heterogeneous phenotypes and PD genetics. In this series, 94 patients who underwent DBS were screened for mutations in the most common genes associated with PD. The consequent genetic subgroups of patients were compared with respect to phenotype, levodopa (l-dopa), and DBS responsiveness. An unprecedented number (29%) of patients tested positive for at least 1 of the currently known PD genes. Patients with Parkin mutations presented at the youngest age but had many years of disease before needing DBS, whereas glucocerebrosidase (GBA) mutation carriers reached the threshold of needing DBS earlier, and developed earlier cognitive impairment after DBS. DBS cohorts include large numbers of gene positive PD patients and can be clinically instructive in the exploration of genotype-phenotype relationships.

A molecular explanation for the recessive nature of parkin-linked Parkinson’s disease

Mutations in the park2 gene, encoding the RING-inBetweenRING-RING E3 ubiquitin ligase parkin, cause 50% of autosomal recessive juvenile Parkinsonism cases. More than 70 known pathogenic mutations occur throughout parkin, many of which cluster in the inhibitory amino-terminal ubiquitin-like domain, and the carboxy-terminal RING2 domain that is indispensable for ubiquitin transfer. A structural rationale showing how autosomal recessive juvenile Parkinsonism mutations alter parkin function is still lacking. Here we show that the structure of parkin RING2 is distinct from canonical RING E3 ligases and lacks key elements required for E2-conjugating enzyme recruitment. Several pathogenic mutations in RING2 alter the environment of a single surface-exposed catalytic cysteine to inhibit ubiquitination. Native parkin adopts a globular inhibited conformation in solution facilitated by the association of the ubiquitin-like domain with the RING-inBetweenRING-RING C-terminus. Autosomal recessive juvenile Parkinsonism mutations disrupt this conformation. Finally, parkin autoubiquitinates only in cis, providing a molecular explanation for the recessive nature of autosomal recessive juvenile Parkinsonism.

Parkin overexpression during aging reduces proteotoxicity, alters mitochondrial dynamics, and extends lifespan

Aberrant protein aggregation and mitochondrial dysfunction have each been linked to aging and a number of age-onset neurodegenerative disorders, including Parkinson disease. Loss-of-function mutations in parkin, an E3 ubiquitin ligase that functions to promote the ubiquitin-proteasome system of protein degradation and also in mitochondrial quality control, have been implicated in heritable forms of Parkinson disease. The question of whether parkin can modulate aging or positively impact longevity, however, has not been addressed. Here, we show that ubiquitous or neuron-specific up-regulation of Parkin, in adult Drosophila melanogaster, increases both mean and maximum lifespan without reducing reproductive output, physical activity, or food intake. Long-lived Parkin-overexpressing flies display an increase in K48-linked polyubiquitin and reduced levels of protein aggregation during aging. Recent evidence suggests that Parkin interacts with the mitochondrial fission/fusion machinery to mediate the turnover of dysfunctional mitochondria. However, the relationships between parkin gene activity, mitochondrial dynamics, and aging have not been explored. We show that the mitochondrial fusion-promoting factor Drosophila Mitofusin, a Parkin substrate, increases in abundance during aging. Parkin overexpression results in reduced Drosophila Mitofusin levels in aging flies, with concomitant changes in mitochondrial morphology and an increase in mitochondrial activity. Together, these findings reveal roles for Parkin in modulating organismal aging and provide insight into the molecular mechanisms linking aging to neurodegeneration.

Glioma tumor grade correlates with parkin depletion in mutant p53-linked tumors and results from loss of function of p53 transcriptional activity

Gliomas represent the most frequent form of primary brain tumors in adults, the prognosis of which remains extremely poor. Inactivating mutations on the tumor suppressor TP53 were proposed as a key etiological trigger of glioma development. p53 has been recently identified as a transcriptional target of parkin. Interestingly, somatic mutations on parkin have also been linked to glioma genesis. We examined the possibility that a disruption of a functional interaction between p53 and parkin could contribute to glioma development in samples devoid of somatic parkin mutations or genetic allele deletion. We show here that parkin levels inversely correlate to brain tumor grade and p53 levels in oligodendrogliomas, mixed gliomas and glioblastomas. We demonstrate that p53 levels negatively and positively correlate to bax and Bcl2 respectively, underlying a loss of p53 transcriptional activity in all types of glial tumors. Using various cell models lacking p53 or harboring either transcriptionally inactive or dominant negative p53, as well as in p53 knockout mice brain, we establish that p53 controls parkin promoter transactivation, mRNA and protein levels. Furthermore, we document an increase of parkin expression in mice brain after p53-bearing viral infection. Finally, both cancer-related p53 inactivating mutations and deletion of a consensus p53 binding sequence located on parkin promoter abolish p53-mediated control of parkin transcription, demonstrating that p53 regulates parkin transcription via its DNA binding properties. In conclusion, our work delineates a functional interplay between mutated p53 and parkin in glioma genesis that is disrupted by cancer-linked pathogenic mutations. It also allows envisioning parkin as a novel biomarker of glioma biopsies enabling to follow the progression of this type of cancers.

Lewy body pathology in a patient with a homozygous Parkin deletion

We report neuropathologic findings in a patient with homozygous deletions of exons 2 to 4 of parkin. Although the absence of Lewy bodies has been considered a neuropathologic characteristic of parkin mutation, here we report a pathologic finding with the presence of Lewy bodies. The patient was a 72-year-old woman with onset of the disease at age 61. Her autopsy revealed marked decrease in melanized neurons in the substantia nigra and the locus coeruleus. Lewy bodies were found in the substantia nigra, the locus coeruleus, the dorsal motor nucleus of the vagus, the basal nucleus of Meynert, the amygdaloid nucleus, and the sympathetic nerve bundles in the myocardium. Only 3 previous case reports described Lewy body formation in patients carrying parkin mutations. The distribution of Lewy bodies in our patient appeared to be reminiscent of sporadic Parkinson's disease.

Parkin acts as a transcription factor modulating presenilin-1 and presenilin-2 promoter transactivations

Background Parkin is associated to autosomal recessive early-onset Parkinson’s disease. Parkin acts as an E3-ubiquitin ligase involved in the proteasome-mediated degradation of various substrates. It has been suggested that pathogenic mutations of parkin, abolishing its ubiquitin-ligase activity, could explain the accumulation of proteins and lead to neuronal death by apoptosis. However, besides this function, additional parkin-dependent cellular pathways exist. We demonstrated that parkin is a direct transcriptional repressor of the tumor suppressor p53 [1]. p53 regulates the expression and functions of presenilin-1 (PS1) and presenilin-2 (PS2), two members of the gamma secretase complex involved in the production of the amyloid b peptide (Ab) and parkin could control the homeostasis of intracellular Ab. These findings prompted us to investigate whether parkin could control presenilins and if so, whether it is via a direct transcriptional control of PS promoters or indirectly, via p53.

ER-stress-associated functional link between Parkin and DJ-1 via a transcriptional cascade involving the tumor suppressor p53 and the spliced X-box binding protein XBP-1

Parkin and DJ-1 are two multi-functional proteins linked to autosomal recessive early-onset Parkinson's disease (PD) that have been shown to functionally interact by as-yet-unknown mechanisms. We have delineated the mechanisms by which parkin controls DJ-1. Parkin modulates DJ-1 transcription and protein levels via a signaling cascade involving p53 and the endoplasmic reticulum (ER)-stress-induced active X-box-binding protein-1S (XBP-1S). Parkin triggers the transcriptional repression of p53 while p53 downregulates DJ-1 protein and mRNA expressions. We show that parkin-mediated control of DJ-1 is fully p53-dependent. Furthermore, we establish that p53 lowers the protein and mRNA levels of XBP-1S. Accordingly, we show that parkin ultimately upregulates XBP-1 levels. Subsequently, XBP-1S physically interacts with the DJ-1 promoter, thereby enhancing its promoter trans-activation, mRNA levels and protein expression. This data was corroborated by the examination of DJ-1 in both parkin- and p53-null mice brains. This transcriptional cascade is abolished by pathogenic parkin mutations and is independent of its ubiquitin-ligase activity. Our data establish a parkin-dependent ER-stress-associated modulation of DJ-1 and identifies p53 and XBP-1 as two major actors acting downstream of parkin in this signaling cascade in cells and in vivo. This work provides a mechanistic explanation for the increase in the unfolded protein response observed in PD pathology, i.e. that it is due to a defect in parkin-associated control of DJ-1.

Young‐onset parkinsonism due to homozygous duplication of α‐synuclein in a consanguineous family

With a growing list of monogenetic causes of Parkinson's disease (PD),1–3 prioritization of genetic testing is made on the presumed mode of inheritance. In patients with early-onset PD from consanguineous families, the most common mode of inheritance is autosomal recessive. Rarely, an individual may be homozygous for a mutation inherited in an autosomal dominant manner, complicating the diagnostic process. The proband is a 36-year-old female from a consanguineous Pakistani family (Fig. 1A). She presented with a 5-year history of left-sided stiffness, micrographia, festinant gait, tremor, and falls. Past medical history included postpartum psychosis and severe depression. There were no symptoms of autonomic dysfunction. Neurological examination at the age of 35 years revealed severe bilateral bradykinesia, rigidity, worse on the left, and mild bilateral upper limb rest tremor. Gait was shuffling, with freezing and complete loss of postural reflexes. Bilateral ankle clonus was noted. Initially, there was a poor response to dopamine agonists. She responded well to 100/25 mg co-careldopa 3 times per day, but developed wearing offs and peak-dose dyskinesias after 4 months of treatment. There was no family history of parkinsonism. The proband's mother's neurological examination at the age of 72 years was normal. The proband's father, who died at age 64 years from a stroke, had no symptoms or signs of parkinsonism as described by his family. Her siblings and children were asymptomatic, but were unavailable for examination. Figure 1 A: Pedigree and clinical information on the family. A half filled symbol represents the proband (arrow), who is the only individual affected by parkinsonism. Clinically unaffected but confirmed mutation carrier (the proband's mother) is represented by ... Investigations in the proband included routine blood work, copper studies, and white cell enzymes, and were all normal. Dopamine transporter scan (DAT-SCAN) showed bilateral reduction in tracer uptake in the striatum, more significant on the right. Formal neuropsychological examination revealed a mild degree of intellectual under-functioning from premorbid estimates, with anterior/subcortical dysfunction. Mutations in PARKIN, PINK1, and common LRRK2 mutations were excluded. Multiplex ligation-dependent probe amplification (MLPA) showed 4 copies of SNCA (Fig. 1B). Comparative genomic hybridization (Nimblegen 135 K array Roche-Niblegen) showed copy number gain of 0.928 Mb, containing 5 genes including SNCA (Fig. 1C). Single-nucleotide polymorphism (SNP) array showed this to be homozygous. Fluorescent in situ-hybridization demonstrated duplication of SNCA on both alleles (Supplemental Figure 1). The proband's mother's MLPA showed SNCA duplication. Considering the proband's homozygosity for SNCA duplication, her father is likely to have had an SNCA duplication. Less likely, de novo duplication (in addition to duplication inherited from mother) occurred in the proband. SNCA multiplication is a rare cause of autosomal dominant PD.4,5 SNCA triplications (4 copies of SNCA) are fully penetrant; with early-onset and rapidly progressive parkinsonism associated with dementia, autonomic dysfunction, and psychiatric features.4 With SNCA duplications (3 SNCA copies), the disease clinically resembles idiopathic PD5 and reduced penetrance is recognized.6 Our patient has 4 SNCA copies and her clinical phenotype closely matches that of patients with SNCA triplications4 and is in keeping with the single previously described case of SNCA double duplication.7 Homozygous SNCA duplications are a rare cause of young-onset parkinsonism and should be considered in the patients with a family history compatible with recessive inheritance. Early cognitive dysfunction and depression are consistently reported in patients with 4 SNCA copies and may be regarded as “red flags” for SNCA multiplications.

A case of α‐synuclein gene duplication presenting with head‐shaking movements

PARK4 is a candidate locus for familial Parkinson's disease (PD), combined with multiplication of the α-synuclein gene (SNCA). The eventual phenotype is dependent on the copy number of SNCA. Mutations in leucine-rich repeat kinase 2 (LRRK2) are also causative of parkinsonism. This report describes a man who presented at our hospital complaining of a stagger after running and difficulty in handling the mouse of a personal computer, having suffered tremors since his twenties. Nine months after treatment and discharge, he developed titubation and began to drag his right foot. We examined the patient's family pedigree for SNCA dosage, using quantitative polymerase chain reaction. We also screened this pedigree for mutations in parkin and LRRK2, using gene-sequencing techniques. We identified the proband, his sister, and his paternal uncle as carrying a duplication of SNCA. In addition, we found that the proband and his mother carried the G2385R variant of the LRRK2, a strong risk factor for PD in Asians and the rare V1450I variant, although only the proband showed symptoms of parkinsonism. No mutations were found in parkin. The combination of SNCA gene duplication and LRRK2 G2385R variant may explain the early onset of disease in this patient.

AMP Kinase Activation Mitigates Dopaminergic Dysfunction and Mitochondrial Abnormalities inDrosophilaModels of Parkinson's Disease

Mutations in parkin and LRRK2 together account for the majority of familial Parkinson's disease (PD) cases. Interestingly, recent evidence implicates the involvement of parkin and LRRK2 in mitochondrial homeostasis. Supporting this, we show here by means of the Drosophila model system that, like parkin, LRRK2 mutations induce mitochondrial pathology in flies when expressed in their flight muscles, the toxic effects of which can be rescued by parkin coexpression. When expressed specifically in fly dopaminergic neurons, mutant LRRK2 results in the appearance of significantly enlarged mitochondria, a phenotype that can also be rescued by parkin coexpression. Importantly, we also identified in this study that epigallocatechin gallate (EGCG), a green tea-derived catechin, acts as a potent suppressor of dopaminergic and mitochondrial dysfunction in both mutant LRRK2 and parkin-null flies. Notably, the protective effects of EGCG are abolished when AMP-activated protein kinase (AMPK) is genetically inactivated, suggesting that EGCG-mediated neuroprotection requires AMPK. Consistent with this, direct pharmacological or genetic activation of AMPK reproduces EGCG's protective effects. Conversely, loss of AMPK activity exacerbates neuronal loss and associated phenotypes in parkin and LRRK mutant flies. Together, our results suggest the relevance of mitochondrial-associated pathway in LRRK2 and parkin-related pathogenesis, and that AMPK activation may represent a potential therapeutic strategy for these familial forms of PD.

Lack of association between cancer history and PARKIN genotype: A family based study in PARKIN/Parkinson's Families

A number of publications have attributed a tumor suppressive (TS) function to PARKIN, a gene associated with recessive familial early onset Parkinson's disease (EOPD). Discoveries of PARKIN deletions and point mutations in tumors, functional studies, and data from mouse models have been presented to support the hypothesis. We have asked whether PARKIN mutations are associated with history of cancer in humans. We interviewed 431 participants who were screened for PARKIN mutations, including 149 EOPD cases and their family members, who were unaware of mutation status. We found no significant difference in self-reported history of cancer among carriers of one or two PARKIN mutations and noncarriers, odds ratio 0.75 (95% confidence interval 0.27-1.83). In particular, no increase in cancer history was seen among homozygous and compound heterozygous mutation carriers compared to noncarriers. Therefore, we hypothesize that published studies attributing TS capability to PARKIN merit further exploration and we present a reevaluation of these data with respect to patterns of mutation frequencies in normal and cancer cells. We conclude that although Parkin may exert a suppressive effect in mice, further studies are required prior to assigning a TS function to PARKIN in humans.

Manganese-induced toxicity in normal and human B lymphocyte cell lines containing a homozygous mutation in parkin

Mutations in the parkin gene are linked to development of juvenile onset of Parkinson’s disease and recent studies have reported that parkin can protect against increased oxidative stress and mitochondrial dysfunction caused by a variety of oxidative and toxic insults. Overexpression of parkin has also been reported to selectively protect dopaminergic neurons from Mn toxicity. Accordingly, in this paper we compare the effect that mutations in parkin have on Mn toxicity and associated apoptotic signals in normal and human B lymphocyte cell lines containing a homozygous mutation in the gene. Results of these studies reveal that Mn toxicity was similar in both control and mutant parkin lymphocyte cells indicating that cell death caused by Mn was not altered in cells devoid of parkin activity. In contrast, Mn did inhibit mitochondrial function to a greater extent in cells devoid of active parkin as indicated by a decrease in ATP production although mitochondrial membrane potential was essentially unaffected. Consistent with inactive parkin influencing the Mn response is the observation of increased activity in the down-stream apoptotic signal, caspase 3. In summary, results reported in this paper demonstrate that mutations in parkin can lead to functional changes in potential signaling processes known to provoke Mn toxicity. The selectivity and magnitude of this response, however, does not necessarily lead to cell death in lymphocytes which are devoid of dopamine.

Phenotypic variability of parkin mutations in single kindred

Mutations in parkin have been associated with autosomal recessive early-onset Parkinson's disease (PD). Here, we report on unusual phenotypic variability within a family with mutations in parkin. The proband and her parents were clinically assessed. Mutation analysis was performed using genomic DNA and complementary DNA. The protein expression of Parkin and Mitofusin 2 was examined by western blotting. The proband was a compound heterozygote with no detectable Parkin and presented with early-onset PD. The father, a single heterozygote with reduced expression of Parkin, had mild loss of arm swing. The mother, who had only very mild rigidity, was unexpectedly found to be a homozygote with no Parkin expression. The proband, but not the parents, met the Queen Square Brain Bank criteria for PD. Parkin-dependent ubiquitination of Mitofusin 2 was impaired in the mother and the proband. We report the first case of a homozygous mutation carrier in parkin who had no functional protein and only mild signs of parkinsonism in her seventh decade, whereas her daughter developed typical early-onset PD. This family demonstrates phenotypic variability in parkin-related parkinsonism. © 2012 Movement Disorder Society.

High frequency of Parkin exon rearrangements in Mexican‐mestizo patients with early‐onset Parkinson's disease

Parkin mutations in patients with early-onset Parkinson's disease (EOPD) are estimated to occur in 49% of familial cases and 18% of sporadic cases. We analyzed the entire sequence-coding region and dosage mutations of parkin in 63 Mexican-mestizo EOPD patients and 120 controls. Parkin mutations were present in 34 patients (54.0%). Exon rearrangements, predominantly spanning exons 9 and 12 (31.7% and 19.0%, respectively) were present in 32 patients, with 17.5% carrying simple heterozygous and 25.4% carrying compound heterozygous parkin mutations. A higher frequency of parkin exon rearrangements than of sequence mutations was observed. Patients with parkin exons 9 and 12 rearrangements showed a later age at onset than did cases with other regions affected (40.3 ± 4.5 vs 30.1 ± 8.8; P = .005), suggesting a mutational hot spot in the etiology of Mexican-mestizo patients with EOPD. To our knowledge, this study represents the largest sampling of Mexican-mestizo patients with EOPD cases for which parkin sequence and dosage alterations were analyzed. .

The Role of Parkin in Parkinson’s Disease: A Stem Cell Perspective

ISSN 1758-2024 10.2217/NMT.12.25 © 2012 Future Medicine Ltd Neurodegen. Dis. Manage. (2012) 2(3), 239–241 part of Parkinson’s disease (PD) is a movement disorder characterized by the degeneration of nigral dopaminergic (DA) neurons. The defining locomotor symptoms (i.e., rest tremor, rigidity, bradykinesia and postural instability) are caused by a relatively selective loss of nigral DA neurons [1]. Current pharmacological treatments focus on augmenting DA levels in the brain (e.g., levodopa, monoamine oxidase [MAO]-B inhibitors and catechol-O-methyltransferase inhibitors) or mimicking the actions of DA (e.g., DA agonists). These drugs mostly provide symptomatic relief; the unabated degeneration of nigral DA neurons and other cells invariably kills PD patients. Surgical interventions such as deep-brain stimulation are similar in that they only alleviate locomotor symptoms and have no impact on the neuro degeneration process. Thus, the central problems for PD research are to understand the cause for the degeneration of nigral DA neurons and to identify a strategy to intervene, preferably as early as possible. Mechanistic studies on PD-linked monogenic mutations have revealed significant insights into the unique vulnerabilities of nigral DA neurons and how mutations of a single gene, such as parkin, expose these vulnerabilities. A variety of mouse genetic models of PD have revealed surprisingly little information on the human disease [2]. For example, parkin knockout mice do not exhibit any robust phenotype [3], in sharp contrast with PD patients with parkin mutations [4]. It suggests that human nigral DA neurons are quite different from the murine counterpart. The landmark discovery of induced pluripotent stem cells (iPSCs) [5,6] has made it possible for us to generate patient-specific midbrain DA neurons from PD patients with parkin mutations and normal controls [7]. Our study shows that parkin mutations significantly disrupt the precision of DA transmission by increasing spontaneous DA release and decreasing DA reuptake. In addition, parkin mutations greatly elevate DA-induced oxidative stress by increasing the transcription of MAOs, which catalyze the oxidative deamination of DA – a reaction that produces a large amount of reactive oxygen species. Overexpression of wild-type parkin, but not its PD-linked mutant, significantly rescues all these phenotypes. Thus, mimicking the beneficial actions of parkin, for example, with small-molecule

Microtubule destabilization is shared by genetic and idiopathic Parkinson's disease patient fibroblasts.

Data from both toxin-based and gene-based models suggest that dysfunction of the microtubule system contributes to the pathogenesis of Parkinson’s disease, even if, at present, no evidence of alterations of microtubules in vivo or in patients is available. Here we analyze cytoskeleton organization in primary fibroblasts deriving from patients with idiopathic or genetic Parkinson’s disease, focusing on mutations in parkin and leucine-rich repeat kinase 2. Our analyses reveal that genetic and likely idiopathic pathology affects cytoskeletal organization and stability, without any activation of autophagy or apoptosis. All parkinsonian fibroblasts have a reduced microtubule mass, represented by a higher fraction of unpolymerized tubulin in respect to control cells, and display significant changes in microtubule stability-related signaling pathways. Furthermore, we show that the reduction of microtubule mass is so closely related to the alteration of cell morphology and behavior that both pharmacological treatment with microtubule-targeted drugs, and genetic approaches, by transfecting the wild type parkin or leucine-rich repeat kinase 2, restore the proper microtubule stability and are able to rescue cell architecture. Taken together, our results suggest that microtubule destabilization is a point of convergence of genetic and idiopathic forms of parkinsonism and highlight, for the first time, that microtubule dysfunction occurs in patients and not only in experimental models of Parkinson’s disease. Therefore, these data contribute to the knowledge on molecular and cellular events underlying Parkinson’s disease and, revealing that correction of microtubule defects restores control phenotype, may offer a new therapeutic target for the management of the disease.