Summary In the past 15 years there has been substantial progress in our understanding of the genetics of Parkinson's disease (PD). Highly-penetrant mutations in different genes ( SNCA, LRRK2, VPS35, ...Parkin, PINK1, and DJ-1 ) are known to cause rare monogenic forms of the disease. Furthermore, different variants with incomplete penetrance in the LRRK2 and the GBA gene are strong risk factors for PD, and are especially prevalent in some populations. Last, common variants of small effect size, modulating the risk for PD, have been identified by genome-wide association studies in more than 20 chromosomal loci. Here, I first outline the evolution of the research strategies to find PD-related genes, and then focus on recent advances in the field of the monogenic forms, including VPS35 mutations in autosomal dominant PD, and DNAJC6 and SYNJ1 mutations in recessive forms of juvenile parkinsonism. Additional genetic determinants of PD likely remain to be identified, as the currently known mutations and variants only explain a minor fraction of the disease burden. There is great expectation that the new DNA sequencing technologies (exome and whole-genome sequencing) will bring us closer to the full resolution of the genetic landscape of PD.
Mitochondrial dysfunction and oxidative stress occur in Parkinson's disease (PD), but the molecular mechanisms controlling these events are not completely understood. Peroxisome ...proliferator-activated receptor-gamma coactivator-1α (PGC-1α) is a transcriptional coactivator known as master regulator of mitochondrial functions and oxidative metabolism. Recent studies, including one from our group, have highlighted altered PGC-1α activity and transcriptional deregulation of its target genes in PD pathogenesis suggesting it as a new potential therapeutic target. Resveratrol, a natural polyphenolic compound proved to improve mitochondrial activity through the activation of several metabolic sensors resulting in PGC-1α activation. Here we have tested in vitro the effect of resveratrol treatment on primary fibroblast cultures from two patients with early-onset PD linked to different Park2 mutations. We show that resveratrol regulates energy homeostasis through activation of AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1) and raise of mRNA expression of a number of PGC-1α's target genes resulting in enhanced mitochondrial oxidative function, likely related to a decrease of oxidative stress and to an increase of mitochondrial biogenesis. The functional impact of resveratrol treatment encompassed an increase of complex I and citrate synthase activities, basal oxygen consumption, and mitochondrial ATP production and a decrease in lactate content, thus supporting a switch from glycolytic to oxidative metabolism. Moreover, resveratrol treatment caused an enhanced macro-autophagic flux through activation of an LC3-independent pathway. Our results, obtained in early-onset PD fibroblasts, suggest that resveratrol may have potential clinical application in selected cases of PD-affected patients.
•Park2 mutations linked to early onset Parkinson disease cause mitochondrial dysfunction.•Partial rescue of the mitochondrial defects by resveratrol treatment in Park2 mutant fibroblasts.•The effect of resveratrol is attained throughout activation of the AMPK/SIRT1/PGC-1α axis.
Presynaptic terminals are metabolically active and accrue damage through continuous vesicle cycling. How synapses locally regulate protein homeostasis is poorly understood. We show that the ...presynaptic lipid phosphatase synaptojanin is required for macroautophagy, and this role is inhibited by the Parkinson's disease mutation R258Q. Synaptojanin drives synaptic endocytosis by dephosphorylating PI(4,5)P2, but this function appears normal in SynaptojaninRQ knock‐in flies. Instead, R258Q affects the synaptojanin SAC1 domain that dephosphorylates PI(3)P and PI(3,5)P2, two lipids found in autophagosomal membranes. Using advanced imaging, we show that SynaptojaninRQ mutants accumulate the PI(3)P/PI(3,5)P2‐binding protein Atg18a on nascent synaptic autophagosomes, blocking autophagosome maturation at fly synapses and in neurites of human patient induced pluripotent stem cell‐derived neurons. Additionally, we observe neurodegeneration, including dopaminergic neuron loss, in SynaptojaninRQ flies. Thus, synaptojanin is essential for macroautophagy within presynaptic terminals, coupling protein turnover with synaptic vesicle cycling and linking presynaptic‐specific autophagy defects to Parkinson's disease.
Synopsis
Parkinson's disease‐related human synaptojanin 1 (SYNJ1) or Drosophila synaptojanin (Synj) SAC1 function drives autophagosome biogenesis within synapses by dephosphorylating PI(3)P/PI(3,5)P2, releasing WIPI2/Atg18a from immature autophagosomes, independent from Synj function in endocytosis.
Parkinson's disease related synaptojanin RQ SAC1 mutation does not affect synaptic vesicle endocytosis at fly excitatory glutamatergic neurons and photoreceptors.
Synaptojanin is required for autophagosome formation in presynaptic terminals, analogous to synaptic vesicle uncoating by synaptojanin.
The PI(3)P/PI(3,5)P2‐binding protein, WIPI2/Atg18a accumulates in Synj mutant flies and SYNJ1 R258Q patient‐derived human induced neurons.
Synaptojanin regulates Atg18a mobility at autophagosomal membranes.
Synaptojanin RQ knock‐in flies show neurodegeneration.
The Parkinson's disease‐associated lipid phosphatase synaptojanin promotes synaptic autophagosome formation, a function that is impaired by pathogenic mutations.
Manganese is essential for several metabolic pathways but becomes toxic in excessive amounts. Manganese levels in the body are therefore tightly regulated, but the responsible protein(s) remain ...incompletely known. We studied two consanguineous families with neurologic disorders including juvenile-onset dystonia, adult-onset parkinsonism, severe hypermanganesemia, polycythemia, and chronic hepatic disease, including steatosis and cirrhosis. We localized the genetic defect by homozygosity mapping and then identified two different homozygous frameshift SLC30A10 mutations, segregating with disease. SLC30A10 is highly expressed in the liver and brain, including in the basal ganglia. Its encoded protein belongs to a large family of membrane transporters, mediating the efflux of divalent cations from the cytosol. We show the localization of SLC30A10 in normal human liver and nervous system, and its depletion in liver from one affected individual. Our in silico analyses suggest that SLC30A10 possesses substrate specificity different from its closest (zinc-transporting) homologs. We also show that the expression of SLC30A10 and the levels of the encoded protein are markedly induced by manganese in vitro. The phenotype associated with SLC30A10 mutations is broad, including neurologic, hepatic, and hematologic disturbances. Intrafamilial phenotypic variability is also present. Chelation therapy can normalize the manganesemia, leading to marked clinical improvements. In conclusion, we show that SLC30A10 mutations cause a treatable recessive disease with pleomorphic phenotype, and provide compelling evidence that SLC30A10 plays a pivotal role in manganese transport. This work has broad implications for understanding of the manganese biology and pathophysiology in multiple human organs.
A variant in the GBA1 gene is one of the most common genetic risk factors to develop Parkinson's disease (PD). Here the serendipitous finding is reported of a polymerase dependent allelic imbalance ...when using next generation sequencing, potentially resulting in false-negative results when the allele frequency falls below the variant calling threshold (by default commonly at 30%). The full GBA1 gene was sequenced using next generation sequencing on saliva derived DNA from PD patients. Four polymerase chain reaction conditions were varied in twelve samples, to investigate the effect on allelic imbalance: (1) the primers (n = 4); (2) the polymerase enzymes (n = 2); (3) the primer annealing temperature (T
) specified for the used polymerase; and (4) the amount of DNA input. Initially, 1295 samples were sequenced using Q5 High-Fidelity DNA Polymerase. 112 samples (8.6%) had an exonic variant and an additional 104 samples (8.0%) had an exonic variant that did not pass the variant frequency calling threshold of 30%. After changing the polymerase to TaKaRa LA Taq DNA Polymerase Hot-Start Version: RR042B, all samples had an allele frequency passing the calling threshold. Allele frequency was unaffected by a change in primer, annealing temperature or amount of DNA input. Sequencing of the GBA1 gene using next generation sequencing might be susceptible to a polymerase specific allelic imbalance, which can result in a large amount of flase-negative results. This was resolved in our case by changing the polymerase. Regions displaying low variant calling frequencies in GBA1 sequencing output in previous and future studies might warrant additional scrutiny.
Summary Background Mutations in LRRK2 , the gene that encodes leucine-rich repeat kinase 2, are a cause of Parkinson's disease (PD). The International LRRK2 Consortium was established to answer three ...key clinical questions: can LRRK2 -associated PD be distinguished from idiopathic PD; which mutations in LRRK2 are pathogenic; and what is the age-specific cumulative risk of PD for individuals who inherit or are at risk of inheriting a deleterious mutation in LRRK2 ? Methods Researchers from 21 centres across the world collaborated on this study. The frequency of the common LRRK2 Gly2019Ser mutation was estimated on the basis of data from 24 populations worldwide, and the penetrance of the mutation was defined in 1045 people with mutations in LRRK2 from 133 families. The LRRK2 phenotype was defined on the basis of 59 motor and non-motor symptoms in 356 patients with LRRK2 -associated PD and compared with the symptoms of 543 patients with pathologically proven idiopathic PD. Findings Six mutations met the consortium's criteria for being proven pathogenic. The frequency of the common LRRK2 Gly2019Ser mutation was 1% of patients with sporadic PD and 4% of patients with hereditary PD; the frequency was highest in the middle east and higher in southern Europe than in northern Europe. The risk of PD for a person who inherits the LRRK2 Gly2019Ser mutation was 28% at age 59 years, 51% at 69 years, and 74% at 79 years. The motor symptoms (eg, disease severity, rate of progression, occurrence of falls, and dyskinesia) and non-motor symptoms (eg, cognition and olfaction) of LRRK2 -associated PD were more benign than those of idiopathic PD. Interpretation Mutations in LRRK2 are a clinically relevant cause of PD that merit testing in patients with hereditary PD and in subgroups of patients with PD. However, this knowledge should be applied with caution in the diagnosis and counselling of patients. Funding UK Medical Research Council; UK Parkinson's Disease Society; UK Brain Research Trust; Internationaal Parkinson Fonds; Volkswagen Foundation; National Institutes of Health: National Institute of Neurological Disorders and Stroke and National Institute of Aging; Udall Parkinson's Disease Centre of Excellence; Pacific Alzheimer Research Foundation Centre; Italian Telethon Foundation; Fondazione Grigioni per il Morbo di Parkinson; Michael J Fox Foundation for Parkinson's Research; Safra Global Genetics Consortium; US Department of Veterans Affairs; French Agence Nationale de la Recherche.
Familial Parkinson's disease (PD) protein DJ-1 mutations are linked to early onset PD. We have found that DJ-1 binds directly to the F
F
ATP synthase β subunit. DJ-1's interaction with the β subunit ...decreased mitochondrial uncoupling and enhanced ATP production efficiency while in contrast mutations in DJ-1 or DJ-1 knockout increased mitochondrial uncoupling, and depolarized neuronal mitochondria. In mesencephalic DJ-1 KO cultures, there was a progressive loss of neuronal process extension. This was ameliorated by a pharmacological reagent, dexpramipexole, that binds to ATP synthase, closing a mitochondrial inner membrane leak and enhancing ATP synthase efficiency. ATP synthase c-subunit can form an uncoupling channel; we measured, therefore, ATP synthase F
(β subunit) and c-subunit protein levels. We found that ATP synthase β subunit protein level in the DJ-1 KO neurons was approximately half that found in their wild-type counterparts, comprising a severe defect in ATP synthase stoichiometry and unmasking c-subunit. We suggest that DJ-1 enhances dopaminergic cell metabolism and growth by its regulation of ATP synthase protein components.
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