Analysis of an early-onset Parkinson's disease cohort for DJ-1 mutations

The Role of Structural Variants in the Genetic Architecture of Parkinson's Disease

Parkinson's disease (PD) significantly impacts millions of individuals worldwide. Although our understanding of the genetic foundations of PD has advanced, a substantial portion of the genetic variation contributing to disease risk remains unknown. Current PD genetic studies have primarily focused on one form of genetic variation, single nucleotide variants (SNVs), while other important forms of genetic variation, such as structural variants (SVs), are mostly ignored due to the complexity of detecting these variants with traditional sequencing methods. Yet, these forms of genetic variation play crucial roles in gene expression and regulation in the human brain and are causative of numerous neurological disorders, including forms of PD. This review aims to provide a comprehensive overview of our current understanding of the involvement of coding and noncoding SVs in the genetic architecture of PD.

Pathogenesis of DJ-1/PARK7-Mediated Parkinson's Disease

Parkinson's disease (PD) is a common movement disorder associated with the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Mutations in the PD-associated gene PARK7 alter the structure and function of the encoded protein DJ-1, and the resulting autosomal recessively inherited disease increases the risk of developing PD. DJ-1 was first discovered in 1997 as an oncogene and was associated with early-onset PD in 2003. Mutations in DJ-1 account for approximately 1% of all recessively inherited early-onset PD occurrences, and the functions of the protein have been studied extensively. In healthy subjects, DJ-1 acts as an antioxidant and oxidative stress sensor in several neuroprotective mechanisms. It is also involved in mitochondrial homeostasis, regulation of apoptosis, chaperone-mediated autophagy (CMA), and dopamine homeostasis by regulating various signaling pathways, transcription factors, and molecular chaperone functions. While DJ-1 protects neurons against damaging reactive oxygen species, neurotoxins, and mutant α-synuclein, mutations in the protein may lead to inefficient neuroprotection and the progression of PD. As current therapies treat only the symptoms of PD, the development of therapies that directly inhibit oxidative stress-induced neuronal cell death is critical. DJ-1 has been proposed as a potential therapeutic target, while oxidized DJ-1 could operate as a biomarker for PD. In this paper, we review the role of DJ-1 in the pathogenesis of PD by highlighting some of its key neuroprotective functions and the consequences of its dysfunction.

Genetics of cognitive dysfunction in Parkinson's disease

Presentation and progression of cognitive symptoms in Parkinson's disease are highly variable. PD is a genetically complex disorder with multiple genetic risk factors and understanding the role that genes play in cognitive outcomes is important for patient counseling and treatment. Currently, there are seven well-described genes that increase the risk for PD, with variable levels of penetrance: SNCA, LRRK2, VPS35, PRKN, PINK1, DJ1 and GBA. In addition, large, genome-wide association studies have identified multiple loci in our DNA which increase PD risk. In this chapter, we summarize what is currently known about each of the seven strongly-associated PD genes and select PD risk variants, including PITX3, TMEM106B, SNCA Rep1, APOɛ4, COMT and MAPT H1/H1, along with their respective relationships to cognition.

Neurodegenerative Disorders and the Current State, Pathophysiology, and Management of Parkinson's Disease

In the last few decades, major knowledge has been gained about pathophysiological aspects and molecular pathways behind Parkinson's Disease (PD). Based on neurotoxicological studies and postmortem investigations, there is a general concept of how environmental toxicants (neurotoxins, pesticides, insecticides) and genetic factors (genetic mutations in PD-associated proteins) cause depletion of dopamine from substantia nigra pars compacta region of the midbrain and modulate cellular processes leading to the pathogenesis of PD. α-Synuclein, a neuronal protein accumulation in oligomeric form, called protofibrils, is associated with cellular dysfunction and neuronal death, thus possibly contributing to PD propagation. With advances made in identifying loci that contribute to PD, molecular pathways involved in disease pathogenesis are now clear, and introducing therapeutic strategy at the right time may delay the progression. Biomarkers for PD have helped monitor PD progression; therefore, personalized therapeutic strategies can be facilitated. In order to further improve PD diagnostic and prognostic accuracy, independent validation of biomarkers is required.

Mitochondrial LonP1 protease is implicated in the degradation of unstable Parkinson's disease-associated DJ-1/PARK 7 missense mutants

DJ-1/PARK7 mutations are linked with familial forms of early-onset Parkinson's disease (PD). We have studied the degradation of untagged DJ-1 wild type (WT) and missense mutants in mouse embryonic fibroblasts obtained from DJ-1-null mice, an approach closer to the situation in patients carrying homozygous mutations. The results showed that the mutants L10P, M26I, A107P, P158Δ, L166P, E163K, and L172Q are unstable proteins, while A39S, E64D, R98Q, A104T, D149A, A171S, K175E, and A179T are as stable as DJ-1 WT. Inhibition of proteasomal and autophagic-lysosomal pathways had little effect on their degradation. Immunofluorescence and biochemical fractionation studies indicated that M26I, A107P, P158Δ, L166P, E163K, and L172Q mutants associate with mitochondria. Silencing of mitochondrial matrix protease LonP1 produced a strong reduction of the degradation of the mitochondrial-associated DJ-1 mutants A107P, P158Δ, L166P, E163K, and L172Q but not of mutant L10P. These results demonstrated a mitochondrial pathway of degradation of those DJ-1 missense mutants implicated in PD pathogenesis.

Long-Term Outcomes of Genetic Parkinson's Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder that affects 1–2% of people by the age of 70 years. Age is the most important risk factor, and most cases are sporadic without any known environmental or genetic causes. Since the late 1990s, mutations in the genes SNCA, PRKN, LRRK2, PINK1, DJ-1, VPS35, and GBA have been shown to be important risk factors for PD. In addition, common variants with small effect sizes are now recognized to modulate the risk for PD. Most studies in genetic PD have focused on finding new genes, but few have studied the long-term outcome of patients with the specific genetic PD forms. Patients with known genetic PD have now been followed for more than 20 years, and we see that they may have distinct and different prognoses. New therapeutic possibilities are emerging based on the genetic cause underlying the disease. Future medication may be based on the pathophysiology individualized to the patient’s genetic background. The challenge is to find the biological consequences of different genetic variants. In this review, the clinical patterns and long-term prognoses of the most common genetic PD variants are presented.

Running wheel exercise reduces α-synuclein aggregation and improves motor and cognitive function in a transgenic mouse model of Parkinson's disease

Exercise has been recommended to improve motor function in Parkinson patients, but its value in altering progression of disease is unknown. In this study, we examined the neuroprotective effects of running wheel exercise in mice. In adult wild-type mice, one week of running wheel activity led to significantly increased DJ-1 protein concentrations in muscle and plasma. In DJ-1 knockout mice, running wheel performance was much slower and Rotarod performance was reduced, suggesting that DJ-1 protein is required for normal motor activity. To see if exercise can prevent abnormal protein deposition and behavioral decline in transgenic animals expressing a mutant human form of α-synuclein in all neurons, we set up running wheels in the cages of pre-symptomatic animals at 12 months old. Activity was monitored for a 3-month period. After 3 months, motor and cognitive performance on the Rotarod and Morris Water Maze were significantly better in running animals compared to control transgenic animals with locked running wheels. Biochemical analysis revealed that running mice had significantly higher DJ-1, Hsp70 and BDNF concentrations and had significantly less α-synuclein aggregation in brain compared to control mice. By contrast, plasma concentrations of α-synuclein were significantly higher in exercising mice compared to control mice. Our results suggest that exercise may slow the progression of Parkinson's disease by preventing abnormal protein aggregation in brain.

Mutation analysis of the PARKIN, PINK1, DJ1, and SNCA genes in Turkish early-onset Parkinson's patients and genotype-phenotype correlations

OBJECTIVE

Variations in PARK genes (PRKN, PINK1, DJ-1, and SNCA) cause early-onset Parkinson's disease (EOPD) in different populations. In the current study, we aimed to evaluate the frequencies of variations in PARK genes and the effects of these variations on the phenotypes of Turkish EOPD patients.

METHODS

All coding regions and exon-intron boundaries of the PRKN, PINK1, DJ-1, and SNCA genes were screened by heteroduplex analysis followed by direct sequencing of the detected variants in 50 Turkish EOPD patients. These variants were evaluated using SIFT, PolyPhen, HSF, and LOVD web-based programs.

RESULTS

The frequency of EOPD-associated variations in the PRKN gene was 34%. Among these variations, p.A82E in exon 3 and p.Q409X in exon 11 was determined to be pathogenic. We also defined previously unknown cryptic variations, including c.872-35 G>A and c.872-28T>G in exon 8 of PRKN and c.252+30 T>G and c.322+4 A>G in exons 4 and 5 of DJ1, respectively, that were associated with EOPD. Although no significant association was observed between the PARK gene mutations and clinical features (P>0.05), the alterations were related to the clinical symptoms in each patient.

CONCLUSION

An increasing number of studies report that PRKN, PINK1, DJ1 and SNCA mutations are associated with early-onset Parkinson's disease; however, a limited number of studies have been conducted in Turkey. Additionally, our study is the first to evaluate the frequency of SNCA mutations in a Turkish population. The aim of this study was determine the frequency distributions of the PRKN, PINK1, DJ1, and SNCA gene mutations and to analyze the relationships between these genetic variations and the clinical phenotype of EOPD in Turkish patients.

Amyloid Precursor Protein (APP) May Act as a Substrate and a Recognition Unit for CRL4CRBN and Stub1 E3 Ligases Facilitating Ubiquitination of Proteins Involved in Presynaptic Functions and Neurodegeneration

The amyloid precursor protein (APP), whose mutations cause Alzheimer disease, plays an important in vivo role and facilitates transmitter release. Because the APP cytosolic region (ACR) is essential for these functions, we have characterized its brain interactome. We found that the ACR interacts with proteins that regulate the ubiquitin-proteasome system, predominantly with the E3 ubiquitin-protein ligases Stub1, which binds the NH2 terminus of the ACR, and CRL4(CRBN), which is formed by Cul4a/b, Ddb1, and Crbn, and interacts with the COOH terminus of the ACR via Crbn. APP shares essential functions with APP-like protein-2 (APLP2) but not APP-like protein-1 (APLP1). Noteworthy, APLP2, but not APLP1, interacts with Stub1 and CRL4(CRBN), pointing to a functional pathway shared only by APP and APLP2. In vitro ubiquitination/ubiquitome analysis indicates that these E3 ligases are enzymatically active and ubiquitinate the ACR residues Lys(649/650/651/676/688) Deletion of Crbn reduces ubiquitination of Lys(676) suggesting that Lys(676) is physiologically ubiquitinated by CRL4(CRBN) The ACR facilitated in vitro ubiquitination of presynaptic proteins that regulate exocytosis, suggesting a mechanism by which APP tunes transmitter release. Other dementia-related proteins, namely Tau and apoE, interact with and are ubiquitinated via the ACR in vitro This, and the evidence that CRBN and CUL4B are linked to intellectual disability, prompts us to hypothesize a pathogenic mechanism, in which APP acts as a modulator of E3 ubiquitin-protein ligase(s), shared by distinct neuronal disorders. The well described accumulation of ubiquitinated protein inclusions in neurodegenerative diseases and the link between the ubiquitin-proteasome system and neurodegeneration make this concept plausible.

Activation of endogenous antioxidants as a common therapeutic strategy against cancer, neurodegeneration and cardiovascular diseases: A lesson learnt from DJ-1

This review aims at presenting a new concept pertaining to the development of antioxidants, namely, to evolve from disease-oriented therapy to mechanism-oriented therapy. Using as our illustrative example is DJ-1, a homodimeric protein that is ubiquitously expressed in a variety of mammalian tissues, including the brain, and is found in the matrix and the intermembrane space of the mitochondria. DJ-1 is known to be an endogenous antioxidant against cancer, neurodegeneration and cardiovascular diseases, of which oxidative stress plays a causal role. Interestingly, the mechanistic targets of DJ-1 as an antioxidant, including Daxx, Nrf2, thioredoxin, glutathione, α-synuclein, PTEN/PI3K/Akt, and Pink/Parkin are also associated with those oxidative stress-related diseases. Furthermore, activators of DJ-1 are available in the form of mortalin, phenylbutyrate and

NAD(P)H

quinone oxidoreductase 1. It follows that activation of DJ-1 as a common endogenous antioxidant provides a new strategy against cancer, neurodegeneration and cardiovascular diseases. Since clinical trials on exogenous application of the known antioxidants have basically failed, an alternative approach would logically be to activate the endogenous antioxidants that are already present in the appropriate cellular locale where elevated oxidative stress is the culprit for the disease. At the same time, since oxidative stress is a common denominator among cancer, neurodegeneration and cardiovascular diseases, development of antioxidant therapy should target the reduction in reactive oxygen species. Instead of focusing on disease-oriented therapy, pharmaceutical companies should concentrate on developing agents and dosing schemes for effective activation of the endogenous antioxidants that are associated with a multitude of oxidative stress-related diseases (mechanism-oriented therapy).

Age- and manganese-dependent modulation of dopaminergic phenotypes in a C. elegans DJ-1 genetic model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, yet its etiology and pathogenesis are poorly understood. PD is characterized by selective dopaminergic (DAergic) degeneration and progressive hypokinetic motor impairment. Mutations in dj-1 cause autosomal recessive early-onset PD. DJ-1 is thought to protect DAergic neurons via an antioxidant mechanism, but the precise basis of this protection has not yet been resolved. Aging and manganese (Mn) exposure are significant non-genetic risk factors for PD. Caenorhabditis elegans (C. elegans) is an optimal model for PD and aging studies because of its simple nervous system, conserved DAergic machinery, and short 20-day lifespan. Here we tested the hypothesis that C. elegans DJ-1 homologues were protective against Mn-induced DAergic toxicity in an age-dependent manner. We showed that the deletion of C. elegans DJ-1 related (djr) genes, djr-1.2, decreased survival after Mn exposure. djr-1.2, the DJ-1 homologue was expressed in DAergic neurons and its deletion decreased lifespan and dopamine (DA)-dependent dauer movement behavior after Mn exposure. We also tested the role of DAF-16 as a regulator of dj-1.2 interaction with Mn toxicity. Lifespan defects resulting from djr-1.2 deletion could be restored to normal by overexpression of either DJR-1.2 or DAF-16. Furthermore, dauer movement alterations after djr-1.2 deletion were abolished by constitutive activation of DAF-16 through mutation of its inhibitor, DAF-2 insulin receptor. Taken together, our results reveal PD-relevant interactions between aging, the PD environmental risk factor manganese, and homologues of the established PD genetic risk factor DJ-1. Our data demonstrate a novel role for the DJ-1 homologue, djr-1.2, in mitigating Mn-dependent lifespan reduction and DA signaling alterations, involving DAF-2/DAF-16 signaling.

Genetic insights into sporadic Parkinson's disease pathogenesis

Intensive research over the last 15 years has led to the identification of several autosomal recessive and dominant genes that cause familial Parkinson’s disease (PD). Importantly, the functional characterization of these genes has shed considerable insights into the molecular mechanisms underlying the etiology and pathogenesis of PD. Collectively; these studies implicate aberrant protein and mitochondrial homeostasis as key contributors to the development of PD, with oxidative stress likely acting as an important nexus between the two pathogenic events. Interestingly, recent genome-wide association studies (GWAS) have revealed variations in at least two of the identified familial PD genes (i.e. α-synuclein and LRRK2) as significant risk factors for the development of sporadic PD. At the same time, the studies also uncovered variability in novel alleles that is associated with increased risk for the disease. Additionally, in-silico meta-analyses of GWAS data have allowed major steps into the investigation of the roles of gene-gene and gene-environment interactions in sporadic PD. The emergent picture from the progress made thus far is that the etiology of sporadic PD is multi-factorial and presumably involves a complex interplay between a multitude of gene networks and the environment. Nonetheless, the biochemical pathways underlying familial and sporadic forms of PD are likely to be shared.

Incidence of mutations in the PARK2, PINK1, PARK7 genes in Polish early-onset Parkinson disease patients

BACKGROUND AND PURPOSE

Parkinson disease (PD) is a complex disease, comprising genetic and environmental factors. Despite the vast majority of sporadic cases, three genes, i.e. PARK2, PINK1 and PARK7 (DJ-1), have been identified as responsible for the autosomal recessive form of early-onset Parkinson disease (EO-PD). Identified changes of these genes are homozygous or compound heterozygous mutations. The frequency of PARK2, PINK1 and PARK7 mutations is still under debate, as is the significance and pathogenicity of the single heterozygous mutations/variants, which are also detected among PD patients. The aim of the study was to analyze the incidence of autosomal recessive genes PARK2, PINK1, PARK7 mutations in Polish EO-PD patients.

MATERIAL AND METHODS

The analysis of the PARK2, PINK1 and PARK7 genes was performed in a group of 150 Polish EO-PD patients (age of onset < 45 years). Mutation analysis was based on sequencing and gene dosage abnormality identification.

RESULTS

Mutations were identified only in the PARK2 and PINK1 genes with the frequency of 4.7% and 2.7% of subjects, respectively. In PARK2, point mutations and exons' rearrangements, and in PINK1 only missense mutations were detected. In both genes mutations were found as compound heterozygous/homozygous and single heterozygous. EO-PD patients' genotype-phenotype correlation revealed similarities of clinical features in mutation carriers and non-carriers.

CONCLUSIONS

The frequency of the PARK2, PINK1, PARK7 mutations among Polish EO-PD patients seems to be low. The role of single heterozygous mutations remains a matter of debate and needs further investigations.

DJ1 analysis in a large cohort of Italian early onset Parkinson Disease patients

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DJ1 is a recessive gene involved in early onset PD.

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We tested 163 Italian EOPD.

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We did not find any mutation in our population.

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DJ1 PD causing mutations are very rare in Italian population.

We analyzed the DJ1 gene in a large consecutive series (N = 163) of Italian unrelated Early Onset Parkinson Disease (EOPD: onset ≤40 years of age) patients and 100 healthy controls (mean age 64 ± 7 years). No homozygous or compound heterozygous mutations with an obvious pathogenic effect were found. Several variants were identified, some of which were novels. All variants had similar frequency in patients and in controls. Our data suggest that DJ1 mutations are very rare in Italian EOPD. Other genes and risk factors for PD are still to be identified.

Molecular insights into Parkinson's disease

Mutations in SNCA, PINK1, parkin, and DJ-1 are associated with autosomal-dominant or autosomal-recessive forms of Parkinson's disease (PD), the second most common neurodegenerative disorder. Studies on the structural and functional properties of the corresponding gene products have provided significant insights into the molecular underpinnings of familial PD and the much more common sporadic forms of the disease. Here, we review recent advances in our understanding of four PD-related gene products: α-synuclein, parkin, PINK1, and DJ-1. In Part 1, we review new insights into the role of α-synuclein in PD. In Part 2, we summarize the latest developments in understanding the role of mitochondrial dysfunction in PD, emphasizing the role of the PINK1/parkin pathway in regulating mitochondrial dynamics and mitophagy. The role of DJ-1 is also discussed. In Part 3, we point out converging pathways and future directions.

What genetics tells us about the causes and mechanisms of Parkinson's disease

Parkinson's disease (PD) is a common motor disorder of mysterious etiology. It is due to the progressive degeneration of the dopaminergic neurons of the substantia nigra and is accompanied by the appearance of intraneuronal inclusions enriched in α-synuclein, the Lewy bodies. It is becoming increasingly clear that genetic factors contribute to its complex pathogenesis. Over the past decade, the genetic basis of rare PD forms with Mendelian inheritance, representing no more than 10% of the cases, has been investigated. More than 16 loci and 11 associated genes have been identified so far; genome-wide association studies have provided convincing evidence that polymorphic variants in these genes contribute to sporadic PD. The knowledge acquired of the functions of their protein products has revealed pathways of neurodegeneration that may be shared between inherited and sporadic PD. An impressive set of data in different model systems strongly suggest that mitochondrial dysfunction plays a central role in clinically similar, early-onset autosomal recessive PD forms caused by parkin and PINK1, and possibly DJ-1 gene mutations. In contrast, α-synuclein accumulation in Lewy bodies defines a spectrum of disorders ranging from typical late-onset PD to PD dementia and including sporadic and autosomal dominant PD forms due to mutations in SCNA and LRRK2. However, the pathological role of Lewy bodies remains uncertain, as they may or may not be present in PD forms with one and the same LRRK2 mutation. Impairment of autophagy-based protein/organelle degradation pathways is emerging as a possible unifying but still fragile pathogenic scenario in PD. Strengthening these discoveries and finding other convergence points by identifying new genes responsible for Mendelian forms of PD and exploring their functions and relationships are the main challenges of the next decade. It is also the way to follow to open new promising avenues of neuroprotective treatment for this devastating disorder.

Gene-environment interactions: key to unraveling the mystery of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. The gradual, irreversible loss of dopamine neurons in the substantia nigra is the signature lesion of PD. Clinical symptoms of PD become apparent when 50-60% of nigral dopamine neurons are lost. PD progresses insidiously for 5-7 years (preclinical period) and then continues to worsen even under the symptomatic treatment. To determine what triggers the disease onset and what drives the chronic, self-propelling neurodegenerative process becomes critical and urgent, since lack of such knowledge impedes the discovery of effective treatments to retard PD progression. At present, available therapeutics only temporarily relieve PD symptoms. While the identification of causative gene defects in familial PD uncovers important genetic influences in this disease, the majority of PD cases are sporadic and idiopathic. The current consensus suggests that PD develops from multiple risk factors including aging, genetic predisposition, and environmental exposure. Here, we briefly review research on the genetic and environmental causes of PD. We also summarize very recent genome-wide association studies on risk gene polymorphisms in the emergence of PD. We highlight the new converging evidence on gene-environment interplay in the development of PD with an emphasis on newly developed multiple-hit PD models involving both genetic lesions and environmental triggers.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Phenylbutyrate up-regulates the DJ-1 protein and protects neurons in cell culture and in animal models of Parkinson disease

Parkinson disease is caused by the death of midbrain dopamine neurons from oxidative stress, abnormal protein aggregation, and genetic predisposition. In 2003, Bonifati et al. (23) found that a single amino acid mutation in the DJ-1 protein was associated with early-onset, autosomal recessive Parkinson disease (PARK7). The mutation L166P prevents dimerization that is essential for the antioxidant and gene regulatory activity of the DJ-1 protein. Because low levels of DJ-1 cause Parkinson, we reasoned that overexpression might stop the disease. We found that overexpression of DJ-1 improved tolerance to oxidative stress by selectively up-regulating the rate-limiting step in glutathione synthesis. When we imposed a different metabolic insult, A53T mutant α-synuclein, we found that DJ-1 turned on production of the chaperone protein Hsp-70 without affecting glutathione synthesis. After screening a number of small molecules, we have found that the histone deacetylase inhibitor phenylbutyrate increases DJ-1 expression by 300% in the N27 dopamine cell line and rescues cells from oxidative stress and mutant α-synuclein toxicity. In mice, phenylbutyrate treatment leads to a 260% increase in brain DJ-1 levels and protects dopamine neurons against 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP) toxicity. In a transgenic mouse model of diffuse Lewy body disease, long-term administration of phenylbutyrate reduces α-synuclein aggregation in brain and prevents age-related deterioration in motor and cognitive function. We conclude that drugs that up-regulate DJ-1 gene expression may slow the progression of Parkinson disease by moderating oxidative stress and protein aggregation.

Frequency of known mutations in early-onset Parkinson disease: implication for genetic counseling: the consortium on risk for early onset Parkinson disease study

OBJECTIVE

To assess the frequency and clinical characteristics of carriers of previously identified mutations in 6 genes associated with early-onset Parkinson disease (PD) and provide empirical data that can be used to inform genetic counseling.

DESIGN

Cross-sectional observational study.

SETTING

Thirteen movement disorders centers.

PATIENTS

Nine hundred fifty-three individuals with early-onset PD defined as age at onset (AAO) younger than 51 years. Participants included 77 and 139 individuals of Hispanic and Jewish ancestry, respectively. Intervention Mutations in SNCA, PRKN, PINK1, DJ1, LRRK2, and GBA were assessed. A validated family history interview and the Unified Parkinson Disease Rating Scale were administered. Demographic and phenotypic characteristics were compared among groups defined by mutation status. Main Outcome Measure Mutation carrier frequency stratified by AAO and ethnic background.

RESULTS

One hundred fifty-eight (16.6%) participants had mutations, including 64 (6.7%) PRKN, 35 (3.6%) LRRK2 G2019S, 64 (6.7%) GBA, and 1 (0.2%) DJ1. Mutation carriers were more frequent in those with an AAO of 30 years or younger compared with those with AAO between 31 and 50 years (40.6% vs 14.6%, P < .001), in individuals who reported Jewish ancestry (32.4% vs 13.7%, P < .001), and in those reporting a first-degree family history of PD (23.9% vs 15.1%, P = .01). Hispanic individuals were more likely to be PRKN carriers than non-Hispanic individuals (15.6% vs 5.9%, P = .003). The GBA L444P mutation was associated with a higher mean Unified Parkinson Disease Rating Scale III score after adjustment for covariates.

CONCLUSION

Individuals of Jewish or Hispanic ancestry with early-onset PD, those with AAO of 30 years or younger, and those with a history of PD in a first-degree relative may benefit from genetic counseling.

Engineered disulfide bonds restore chaperone-like function of DJ-1 mutants linked to familial Parkinson's disease

Loss-of-function mutations such as L166P, A104T, and M26I in the DJ-1 gene (PARK7) have been linked to autosomal-recessive early onset Parkinson's disease (PD). Cellular and structural studies of the familial mutants suggest that these mutations may destabilize the dimeric structure. To look for common dynamical signatures among the DJ-1 mutants, short MD simulations of up to 1000 ps were conducted to identify the weakest region of the protein (residues 38-70). In an attempt to stabilize the protein, we mutated residue Val 51 to cysteine (V51C) to make a symmetry-related disulfide bridge with the preexisting Cys 53 on the opposite subunit. We found that the introduction of this disulfide linkage stabilized the mutants A104T and M26I against thermal denaturation, improved their ability to scavenge reactive oxygen species (ROS), and restored a chaperone-like function of blocking alpha-synuclein aggregation. The L166P mutant was far too unstable to be rescued by introduction of the V51C mutation. The results presented here point to the possible development of pharmacological chaperones, which may eventually lead to PD therapeutics.

Genetic etiology of Parkinson disease associated with mutations in the SNCA, PARK2, PINK1, PARK7, and LRRK2 genes: a mutation update

To date, molecular genetic analyses have identified over 500 distinct DNA variants in five disease genes associated with familial Parkinson disease; alpha-synuclein (SNCA), parkin (PARK2), PTEN-induced putative kinase 1 (PINK1), DJ-1 (PARK7), and Leucine-rich repeat kinase 2 (LRRK2). These genetic variants include approximately 82% simple mutations and approximately 18% copy number variations. Some mutation subtypes are likely underestimated because only few studies reported extensive mutation analyses of all five genes, by both exonic sequencing and dosage analyses. Here we present an update of all mutations published to date in the literature, systematically organized in a novel mutation database (http://www.molgen.ua.ac.be/PDmutDB). In addition, we address the biological relevance of putative pathogenic mutations. This review emphasizes the need for comprehensive genetic screening of Parkinson patients followed by an insightful study of the functional relevance of observed genetic variants. Moreover, while capturing existing data from the literature it became apparent that several of the five Parkinson genes were also contributing to the genetic etiology of other Lewy Body Diseases and Parkinson-plus syndromes, indicating that mutation screening is recommendable in these patient groups.

Pathogenesis of familial Parkinson's disease: new insights based on monogenic forms of Parkinson's disease

Parkinson's disease (PD) is one of the most common movement disorders caused by the loss of dopaminergic neuronal cells. The molecular mechanisms underlying neuronal degeneration in PD remain unknown; however, it is now clear that genetic factors contribute to the pathogenesis of this disease. Approximately, 5% of patients with clinical features of PD have clear familial etiology, which show a classical recessive or dominant Mendelian mode of inheritance. Over the decade, more than 15 loci and 11 causative genes have been identified so far and many studies shed light on their implication in not only monogenic but also sporadic form of PD. Recent studies revealed that PD-associated genes play important roles in cellular functions, such as mitochondrial functions, ubiquitin-proteasomal system, autophagy-lysosomal pathway and membrane trafficking. Furthermore, the proteins encoded by PD-associated genes can interact with each other and such gene products may share a common pathway that leads to nigral degeneration. However, their precise roles in the disease and their normal functions remain poorly understood. In this study, we review recent progress in knowledge about the genes associated with familial PD.

Dissembled DJ-1 high molecular weight complex in cortex mitochondria from Parkinson's disease patients

The PARK7 gene encodes a protein, DJ-1, with several functions such as protection of cells from oxidative stress, sperm maturation and fertilization, and chaperone activity. Mutations in the PARK7 gene are associated with autosomal recessive early-onset Parkinson's disease (PD). DJ-1 has been reported to be expressed in multiple cells in the central nerve system. Here, by using both native and denatured Western blots, we examined levels of total DJ-1 and high molecular weight complexes of DJ-1 (HMW) in both the substantia nigra and cortex from rapidly autopsied 18 PD and 9 non-pathological control (NPC) brains. We have discovered that the level of total DJ-1 protein is significantly reduced in the substantia nigra in brains of sporadic PD patients. Moreover, in the PD cortex mitochondria fraction, the HMW DJ-1 complex is significantly lower than in the NPC. These results suggest abnormal DJ-1 expression levels and DJ-1 complex changes may contribute to PD pathogenesis.

A critical evaluation of the ubiquitin-proteasome system in Parkinson's disease

The evidence for impairment in the ubiquitin proteasome system (UPS) in Parkinson's disease (PD) is mounting and becoming increasingly more convincing. However, it is presently unclear whether UPS dysfunction is a cause or result of PD pathology, a crucial distinction which impedes both the understanding of disease pathogenesis and the development of effectual therapeutic approaches. Recent findings discussed within this review offer new insight and provide direction for future research to conclusively resolve this debate.

Ordered-subset analysis (OSA) for family-based association mapping of complex traits

Association analysis provides a powerful tool for complex disease gene mapping. However, in the presence of genetic heterogeneity, the power for association analysis can be low since only a fraction of the collected families may carry a specific disease susceptibility allele. Ordered-subset analysis (OSA) is a linkage test that can be powerful in the presence of genetic heterogeneity. OSA uses trait-related covariates to identify a subset of families that provide the most evidence for linkage. A similar strategy applied to genetic association analysis would likely result in increased power to detect association. Association in the presence of linkage (APL) is a family-based association test (FBAT) for nuclear families with multiple affected siblings that properly infers missing parental genotypes when linkage is present. We propose here APL-OSA, which applies the OSA method to the APL statistic to identify a subset of families that provide the most evidence for association. A permutation procedure is used to approximate the distribution of the APL-OSA statistic under the null hypothesis that there is no relationship between the family-specific covariate and the family-specific evidence for allelic association. We performed a comprehensive simulation study to verify that APL-OSA has the correct type I error rate under the null hypothesis. This simulation study also showed that APL-OSA can increase power relative to other commonly used association tests (APL, FBAT and FBAT with covariate adjustment) in the presence of genetic heterogeneity. Finally, we applied APL-OSA to a family study of age-related macular degeneration, where cigarette smoking was used as a covariate.

Genetic findings in Parkinson's disease and translation into treatment: a leading role for mitochondria?

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder and in most patients its aetiology remains unknown. Molecular genetic studies in familial forms of the disease identified key proteins involved in PD pathogenesis, and support a major role for mitochondrial dysfunction, which is also of significant importance to the common sporadic forms of PD. While current treatments temporarily alleviate symptoms, they do not halt disease progression. Drugs that target the underlying pathways to PD pathogenesis, including mitochondrial dysfunction, therefore hold great promise for neuroprotection in PD. Here we summarize how the proteins identified through genetic research (alpha-synuclein, parkin, PINK1, DJ-1, LRRK2 and HTRA2) fit into and add to our current understanding of the role of mitochondrial dysfunction in PD. We highlight how these genetic findings provided us with suitable animal models and critically review how the gained insights will contribute to better therapies for PD.

Structural impact of three Parkinsonism-associated missense mutations on human DJ-1

A number of missense mutations in the oxidative stress response protein DJ-1 are implicated in rare forms of familial Parkinsonism. The best-characterized Parkinsonian DJ-1 missense mutation, L166P, disrupts homodimerization and results in a poorly folded protein. The molecular basis by which the other Parkinsonism-associated mutations disrupt the function of DJ-1, however, is incompletely understood. In this study we show that three different Parkinsonism-associated DJ-1 missense mutations (A104T, E163K, and M26I) reduce the thermal stability of DJ-1 in solution by subtly perturbing the structure of DJ-1 without causing major folding defects or loss of dimerization. Atomic resolution X-ray crystallography shows that the A104T substitution introduces water and a discretely disordered residue into the core of the protein, E163K disrupts a key salt bridge with R145, and M26I causes packing defects in the core of the dimer. The deleterious effect of each Parkinsonism-associated mutation on DJ-1 is dissected by analysis of engineered substitutions (M26L, A104V, and E163K/R145E) that partially alleviate each of the defects introduced by the A104T, E163K and M26I mutations. In total, our results suggest that the protective function of DJ-1 can be compromised by diverse perturbations in its structural integrity, particularly near the junctions of secondary structural elements.

Mutations in the glucocerebrosidase gene are associated with early-onset Parkinson disease

OBJECTIVE

To evaluate the frequency of glucocerebrosidase (GBA) mutations in cases and controls enrolled in the Genetic Epidemiology of Parkinson's Disease (GEPD) study.

METHODS

We sequenced all exons of the GBA gene in 278 Parkinson disease (PD) cases and 179 controls enrolled in GEPD, with a wide range of age at onset (AAO), and that included a subset of 178 Jewish cases and 85 Jewish controls. Cases and controls were recruited without knowledge of family history of PD, and cases were oversampled in the AAO < 50 years category.

RESULTS

13.7% of PD cases (38/278) carried GBA mutations, compared with 4.5% of controls (8/179) (odds ratio [OR] 3.4, 95% CI 1.5 to 7.4). The frequency of GBA mutations was 22.2% in 90 cases with AAO < or = 50 years, compared with 9.7% in 185 cases with AAO > 50 years (OR 2.7, 95% CI 1.3 to 5.3). Adjusting for age at the time of evaluation, sex, family history of PD, and Jewish ancestry, GBA carriers had a 1.7-year-earlier AAO of PD (95% CI 0.5 to 3.3, p < 0.04) than noncarriers. The average AAO of PD was 2.5 years earlier in carriers with an AAO < or = 50 years compared with noncarriers (95% CI 0.6 to 4.5, p < 0.01) and this was not seen in the AAO > 50 years group. The frequency of GBA mutations was higher in a subset of 178 cases that reported four Jewish grandparents (16.9%) than in cases who did not report Jewish ancestry (8.0%) (p < 0.01). Nine different GBA mutations were identified in PD cases, including 84insGG, E326K, T369M, N370S, D409H, R496H, L444P, RecNciI, and a novel mutation, P175P.

CONCLUSIONS

This study suggests that the Glucocerebrosidase gene may be a susceptibility gene for Parkinson disease and that Glucocerebrosidase mutations may modify age at onset.

Porcine DJ-1: cloning of PARK7 cDNA, sequence comparison, expression analysis and chromosomal localization

The PARK7 gene encodes a protein, DJ-1, with several functions such as protection of cells from oxidative stress, sperm maturation and fertilization and chaperone activity. Mutations in the PARK7 gene are associated with autosomal recessive early-onset Parkinson's disease (Parkinsonism). This work reports the cloning and analysis of the porcine (Sus scrofa) homologue of DJ-1. The porcine PARK7 cDNA was amplified by reverse transcriptase polymerase chain reaction (RT-PCR) using oligonucleotide primers derived from in silico sequences. The porcine PARK7 cDNA (SsPARK7) encodes a protein of 189 amino acids which shows a very high similarity to bovine (97%), to human (96%) and to canine (95%) DJ-1. Protein structure comparison of human and porcine DJ-1 sequences revealed that amino acid changes were few between the two species and not likely to alter DJ-1 structure and function. Quantitative real-time RT-PCR detection exhibited SsPARK7 mRNA expression in all analyzed porcine tissues, although at different levels. Furthermore, expression analysis showed that SsPARK7 transcripts could be detected early in embryo development in different brain regions. The PARK7 gene was demonstrated to be located on porcine chromosome 6. Single-nucleotide polymorphism (SNP) analysis revealed one SNP in the porcine PARK7 gene, giving rise to a silent mutation in exon 6.

Identification of a risk haplotype of the alpha-synuclein gene in Japanese with sporadic Parkinson's disease

alpha-Synuclein is one of the main components of Lewy bodies, a pathological marker of Parkinson's disease (PD). Certain missense mutations of the alpha-synuclein gene cause familial PD, but the role of the gene in sporadic PD is still controversial. We scrutinized polymorphisms of the alpha-synuclein gene in a Japanese population and investigated their associations with sporadic cases of PD. The 5' flanking region to intron 2 of the alpha-synuclein gene (3.8 kb) and two polymorphisms in intron 4 previously reported in Caucasian sporadic cases of PD were analyzed in 185 sporadic PD and 191 controls. Five novel single nucleotide polymorphisms (SNPs), 16 reported SNPs, and one reported polynucleotide polymorphism (PNP) were found. Most of the polymorphisms examined were in linkage disequilibrium. Significant associations with PD were found in 15 of 21 SNPs, especially in intron 1 (IVS1+155 TmAn PNP and the IVS1+719 C>T SNP, P < 0.0001). Haplotype analysis showed that T10A7-A-A and T11A6-G-G haplotypes at three loci (IVS1+155 - IVS1+273 - IVS1+608) were strongly negative and positive risk factors of sporadic PD, respectively (odds ratios were 0.23 [95% confidence interval, 0.16-0.32] and 1.51 [95% confidence interval, 1.29-1.75]). In conclusion, our findings indicate that genetic variations of the alpha-synuclein gene affect the development of sporadic PD.

Role of DJ-1 in Parkinson's disease

Parkinson's disease (PD), one of the most common neurodegenerative diseases, is a multifactorial disease caused by both genetic and environmental factors. Although most patients suffering from PD have a sporadic disease, several genetic causes have been identified in recent years, including alpha-synuclein, parkin, PINK1, dardarin (LRRK2), and DJ-1. DJ-1 deletions and point mutations have been found worldwide, and loss of functional protein was shown to cause autosomal recessive PD. Moreover, DJ-1 immunoreactive inclusions are found in other alpha-synucleopathies and tauopathies, indicating that different neurodegenerative diseases might share a common mechanism in which DJ-1 might play a key role. The function of DJ-1 is still unknown; however, it is associated with various cellular processes, including response to oxidative stress, cellular transformation, RNAbinding, androgen-receptor signaling, spermatogenesis, and fertilization. This article reviews the current knowledge on DJ-1, focusing on its importance in the pathogenesis of PD.

Pathogenic mutations in Parkinson disease

Parkinson disease (PD; Parkinson's) is the second most common neurodegenerative disease, characterized by the progressive loss of dopamine neurons and the accumulation of Lewy bodies. Increasing evidence suggests that deficits in mitochondrial function, oxidative and nitrosative stress, the accumulation of aberrant or misfolded proteins, and ubiquitin-proteasome system (UPS) dysfunction may represent the principal molecular pathways that commonly underlie the pathogenesis. The relative role of genetic and environmental factors has been the focus of research and debate. The recent discovery of a number of disease-causing genes (SNCA, Parkin/PARK2, UCHL1, PINK1, DJ1/PARK7, and LRRK2) in familial and sporadic forms of PD has provided considerable insights into the pathophysiology of this complex disorder. The frequency of these gene mutations may vary according to ethnicity and to the specific gene. A gene dosage effect is observed in some cases, and the phenotype of some of the mutation carriers closely resembles typical PD. Penetrance of some of the recurrent mutations is incomplete and may vary with age. Further research to unravel the etiopathology could identify biochemical or genetic markers for potential neuroprotective trials.

WC. Mutations in DJ-1 are rare in familial Parkinson disease

Mutations in DJ-1 (PARK7) are one cause of early-onset autosomal-recessive parkinsonism. We screened for DJ-1 mutations in 93 affected individuals from the 64 multiplex Parkinson disease (PD) families in our sample that had the highest family-specific multipoint LOD scores at the DJ-1 locus. In addition to sequencing all coding exons for alterations, we used multiplex ligation-dependent probe amplification (MLPA) to examine the genomic copy number of DJ-1 exons. A known polymorphism (R98Q) was found in five PD subjects, once as a homozygote and in the other four cases as heterozygotes. No additional missense mutations and no exon deletions or duplications were detected. Our results, in combination with those of previous studies, suggest that alterations in DJ-1 are not a common cause of familial PD.

Parkinson's disease: the genetics of a heterogeneous disorder

Since the first description of Parkinson's disease (PD) in 1817 attempts have been made to resolve the etiology of this common neurodegenerative disorder. In the last century the influence of heredity in PD was controversial. The identification of mutations in six genes responsible for Mendelian forms of PD; alpha-synuclein (SNCA), parkin (PRKN), ubiquitin C-terminal hydrolase L1 (UCH-L1), oncogene DJ-1, PTEN-induced putative kinase 1 (PINK1), and most recently leucine-rich repeat kinase 2 (LRRK2), has confirmed the role of genetics in familial forms of the disease. The exact relationship of these familial disorders and related genes to the more common sporadic form is currently uncertain. The identification of LRRK2 mutations and the association of common variants in SNCA and UCH-L1 in apparently sporadic late-onset disease indicate these genes may be of greater importance than previously believed. The protein products of the six genes are involved in different pathways of neurodegeneration and have opened new avenues of research. This focused research will lead to the development of novel targeted therapies, which may revolutionize the treatment of PD for a substantial proportion of patients.

Recessive Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease caused by loss of dopaminergic neurons in the substantia nigra pars compacta. Although the etiology of PD remains unclear, it is now clear that genetic factors contribute to the pathogenesis of the disease. Recently, several causative genes have been identified in monogenic forms of PD. Accumulating evidence indicates that their gene products play important roles in mitochondrial function, oxidative stress response, and the ubiquitin-proteasome system, which are also implicated in sporadic PD, suggesting that these gene products share a common pathway to nigral degeneration in both familial and sporadic PD. Here, we review recent advances in knowledge about genes associated with recessive PD, including parkin, PINK1, and DJ-1.

PINK1, Parkin, and DJ-1 mutations in Italian patients with early-onset parkinsonism

Recessively inherited early-onset parkinsonism (EOP) has been associated with mutations in the Parkin, DJ-1, and PINK1 genes. We studied the prevalence of mutations in all three genes in 65 Italian patients (mean age of onset: 43.2+/-5.4 years, 62 sporadic, three familial), selected by age at onset equal or younger than 51 years. Clinical features were compatible with idiopathic Parkinson's disease in all cases. To detect small sequence alterations in Parkin, DJ-1, and PINK1, we performed a conventional mutational analysis (SSCP/dHPLC/sequencing) of all coding exons of these genes. To test for the presence of exon rearrangements in PINK1, we established a new quantitative duplex PCR assay. Gene dosage alterations in Parkin and DJ-1 were excluded using previously reported protocols. Five patients (8%; one woman/four men; mean age at onset: 38.2+/-9.7 (range 25-49) years) carried mutations in one of the genes studied: three cases had novel PINK1 mutations, one of which occurred twice (homozygous c.1602_1603insCAA; heterozygous c.1602_1603insCAA; heterozygous c.836G>A), and two patients had known Parkin mutations (heterozygous c.734A>T and c.924C>T; heterozygous c.924C>T). Family history was negative for all mutation carriers, but one with a history of tremor. Additionally, we detected one novel polymorphism (c.344A>T) and four novel PINK1 changes of unknown pathogenic significance (-21G/A; IVS1+97A/G; IVS3+38_40delTTT; c.852C>T), but no exon rearrangements. No mutations were found in the DJ-1 gene. The number of mutation carriers in both the Parkin and the PINK1 gene in our cohort is low but comparable, suggesting that PINK1 has to be considered in EOP.

DJ-1 up-regulates glutathione synthesis during oxidative stress and inhibits A53T alpha-synuclein toxicity

DJ-1 is the third gene that has been linked to Parkinson disease. Mutations in the DJ-1 gene cause early onset PD with autosomal recessive inheritance. To clarify the mechanism of DJ-1 protection, we have overexpressed the gene in cultured dopaminergic cells that were then subjected to chemical stress. In the rat dopaminergic cell line, N27, and in primary dopamine neurons, overexpression of wild type DJ-1 protected cells from death induced by hydrogen peroxide and 6-hydroxydopamine. Overexpressing the L166P mutant DJ-1 had no protective effect. By contrast, knocking down endogenous DJ-1 with antisense DJ-1 rendered cells more susceptible to oxidative damage. We have found that DJ-1 improves survival by increasing cellular glutathione levels through an increase in the rate-limiting enzyme glutamate cysteine ligase. Blocking glutathione synthesis eliminated the beneficial effect of DJ-1. Protection could be restored by adding exogenous glutathione. Wild type DJ-1 reduced cellular reactive oxygen species and reduced the levels of protein oxidation caused by oxidative stress. By a separate mechanism, overexpressing wild type DJ-1 inhibited the protein aggregation and cytotoxicity usually caused by A53T human alpha-synuclein. Under these circumstances, DJ-1 increased the level of heat shock protein 70 but did not change the glutathione level. Our data indicate that DJ-1 protects dopaminergic neurons from oxidative stress through up-regulation of glutathione synthesis and from the toxic consequences of mutant humanalpha-synuclein through increased expression of heat shock protein 70. We conclude that DJ-1 has multiple specific mechanisms for protecting dopamine neurons from cell death.