A genetic mutation in the Vps35 subunit of retromer has recently been linked to late onset Parkinson's disease. We observed that the distribution and maturation of Vps35 D620N positive endosomes are ...altered. While Vps35 D620N containing retromer still binds CI‐M6PR, its trafficking is perturbed as shown by secretion of its ligand cathepsin D. As cathepsin D is involved in processing of α‐synuclein, a well‐established causative agent of Parkinson's disease, its altered trafficking may therefore represent the underlying cause of disease.
The retromer is a trimeric cargo‐recognition protein complex composed of Vps26, Vps29 and Vps35 associated with protein trafficking within endosomes. Recently, a pathogenic point mutation within the Vps35 subunit (D620N) was linked to the manifestation of Parkinson's disease (PD). Here, we investigated details underlying the molecular mechanism by which the D620N mutation in Vps35 modulates retromer function, including examination of retromer's subcellular localization and its capacity to sort cargo. We show that expression of the PD‐linked Vps35 D620N mutant redistributes retromer‐positive endosomes to a perinuclear subcellular localization and that these endosomes are enlarged in both model cell lines and fibroblasts isolated from a PD patient. Vps35 D620N is correctly folded and binds Vps29 and Vps26A with the same affinity as wild‐type Vps35. While PD‐linked point mutant Vps35 D620N interacts with the cation‐independent mannose‐6‐phosphate receptor (CI‐M6PR), a known retromer cargo, we find that its expression disrupts the trafficking of cathepsin D, a CI‐M6PR ligand and protease responsible for degradation of α‐synuclein, a causative agent of PD. In summary, we find that the expression of Vps35 D620N leads to endosomal alterations and trafficking defects that may partly explain its action in PD.
Retromer core complex is an endosomal scaffold that plays a critical role in orchestrating protein trafficking within the endosomal system. Here we characterized the effect of the Parkinson's ...disease‐linked Vps35 D620N in the endo‐lysosomal system using Vps35 D620N rescue cell models. Vps35 D620N fully rescues the lysosomal and autophagy defects caused by retromer knock‐out. Analogous to Vps35 knock out cells, the endosome‐to‐trans‐Golgi network transport of cation‐independent mannose 6‐phosphate receptor (CI‐M6PR) is impaired in Vps35 D620N rescue cells because of a reduced capacity to form endosome transport carriers. Cells expressing the Vps35 D620N variant have altered endosomal morphology, resulting in smaller, rounder structures with less tubule‐like branches. At the molecular level retromer incorporating Vps35 D620N variant has a decreased binding to retromer associated proteins wiskott–aldrich syndrome protein and SCAR homologue (WASH) and SNX3 which are known to associate with retromer to form the endosome transport carriers. Hence, the partial defects on retrograde protein trafficking carriers in the presence of Vps35 D620N represents an altered cellular state able to cause Parkinson's disease.
Synopsis
Retromer plays a critical role in orchestrating the sorting and trafficking of transmembrane receptors within the endosomal system. We demonstrate that Parkinson disease‐linked Vps35 D620N variant is defective in the formation of retromer‐mediated CI‐M6PR‐loaded endosomal transport carriers that are tethered at the trans‐Golgi network by GCC88. We also demonstrate that the endosomal recruitment of proteins associated with this retrograde trafficking pathway, SNX3 and WASH complex subunit FAM21 is impaired in the presence of Vps35 D620N variant.
Biallelic DNAJC12 mutations were described in children with hyperphenylalaninemia, neurodevelopmental delay, and dystonia. We identified DNAJC12 homozygous null variants (c.187A>T;p.K63* and ...c.79‐2A>G;p.V27Wfs*14) in two kindreds with early‐onset parkinsonism. Both probands had mild intellectual disability, mild nonprogressive, motor symptoms, sustained benefit from small dose of levodopa, and substantial worsening of symptoms after levodopa discontinuation. Neuropathology (Proband‐A) revealed no alpha‐synuclein pathology, and substantia nigra depigmentation with moderate cell loss. DNAJC12 transcripts were reduced in both patients. Our results suggest that DNAJC12 mutations (absent in 500 early‐onset patients with Parkinson's disease) rarely cause dopa‐responsive nonprogressive parkinsonism in adulthood, but broaden the clinical spectrum of DNAJC12 deficiency. Ann Neurol 2017;82:640–646
•Parkinson’s disease causing mutation (DNAJC13 p.Asn855Ser) does not alter DNAJC13/RME-8 levels.•SNX1 membrane dynamics are altered in a DNAJC13 p.Asn855Ser knock-in (DKI) mouse model.•DNAJC13 ...p.Asn855Ser does not disrupt RME-8 binding to SNX1 or Retromer-WASH complexes.
DNAJC13 (RME-8) is a core co-chaperone that facilitates membrane recycling and cargo sorting of endocytosed proteins. DNAJ/Hsp40 (heat shock protein 40) proteins are highly conserved throughout evolution and mediate the folding of nascent proteins, and the unfolding, refolding or degradation of misfolded proteins while assisting in associated-membrane translocation. DNAJC13 is one of five DNAJ ‘C’ class chaperone variants implicated in monogenic parkinsonism. Here we examine the effect of the DNAJC13 disease-linked mutation (p.Asn855Ser) on its interacting partners, focusing on sorting nexin 1 (SNX1) membrane dynamics in primary cortical neurons derived from a novel Dnajc13 p.Asn855Ser knock-in (DKI) mouse model. Dnajc13 p.Asn855Ser mutant and wild type protein expression were equivalent in mature heterozygous cultures (DIV21). While SNX1-positive puncta density, area, and WASH-retromer assembly were comparable between cultures derived from DKI and wild type littermates, the formation of SNX1-enriched tubules in DKI neuronal cultures was significantly increased. Thus, Dnajc13 p.Asn855Ser disrupts SNX1 membrane-tubulation and trafficking, analogous to results from RME-8 depletion studies. The data suggest the mutation confers a dominant-negative gain-of-function in RME-8. Implications for the pathogenesis of Parkinson’s disease are discussed.
Dysregulation of dopamine neurotransmission profoundly affects motor, motivation and learning behaviors, and can be observed during the prodromal phase of Parkinson's disease (PD). However, the ...mechanism underlying these pathophysiological changes remains to be elucidated. Mutations in vacuolar protein sorting 35 (VPS35) and leucine-rich repeat kinase 2 (LRRK2) both lead to autosomal dominant PD, and VPS35 and LRRK2 may physically interact to govern the trafficking of synaptic cargos within the endo-lysosomal network in a kinase-dependent manner. To better understand the functional role of VPS35 and LRRK2 on dopamine physiology, we examined Vps35 haploinsufficient (Haplo) and Vps35 p.D620N knock-in (VKI) mice and how their behavior, dopamine kinetics and biochemistry are influenced by LRRK2 kinase inhibitors. We found Vps35 p.D620N significantly elevates LRRK2-mediated phosphorylation of Rab10, Rab12 and Rab29. In contrast, Vps35 haploinsufficiency reduces phosphorylation of Rab12. While striatal dopamine transporter (DAT) expression and function is similarly impaired in both VKI and Haplo mice, that physiology is normalized in VKI by treatment with the LRRK2 kinase inhibitor, MLi-2. As a corollary, VKI animals show a significant increase in amphetamine induced hyperlocomotion, compared to Haplo mice, that is also abolished by MLi-2. Taken together, these data show Vps35 p.D620N confers a gain-of-function with respect to LRRK2 kinase activity, and that VPS35 and LRRK2 functionally interact to regulate DAT function and striatal dopamine transmission.
•Genetic variability in LRRK2 confers significant genotypic and population-attributable risk for parkinsonism.•Facets of leucine-rich repeat kinase 2 (LRRK2) biology may influence synaptic-axonal ...dysfunction.•LRRK2 may orchestrate changes in vesicular and long-range axonal trafficking by binding to microtubules.•Increasing microtubule dynamics may limit the toxicity of mutant LRRK2 and restore axonal transport.
Parkinson’s disease (PD) represents the second most common neurodegenerative disorder, characterized clinically by bradykinesia, resting tremor, rigidity and postural instability, and a variety of non-motor features. The etiology of PD is unknown, however genetic, environmental and inflammatory factors may influence disease onset and progression. Genetic variability in leucine-rich repeat kinase 2 confers significant genotypic and population-attributable risk for LRRK2-parkinsonism that is clinically indistinguishable from idiopathic PD. Nevertheless, the age-associated midbrain pathology observed post-mortem in LRRK2-parkinsonism may involve the abnormal accumulation of either α-synuclein or tau, or just the loss of dopaminergic neurons and gliosis. While diverse biological functions have been described for this multi-domain protein in many cell types, evidence suggests LRRK2 may sense endosomal trafficking to orchestrate dynamic changes in vesicular flux and cytoskeletal architecture. This review posits the long-held belief that synaptic-axonal dysfunction and terminal degeneration may precede dopaminergic cell loss, and provocatively questions how facets of LRRK2 biology may influence this molecular pathogenesis.
Leucine-rich repeat kinase 2 (LRRK2) c.6055G>A (p.G2019S) is a frequent cause of Parkinson’s disease (PD), accounting for >30% of Tunisian Arab-Berber patients. LRRK2 is widely expressed in the ...immune system and its kinase activity confers a survival advantage against infection in animal models. Here, we assess haplotype variability in cis and in trans of the LRRK2 c.6055G>A mutation, define the age of the pathogenic allele, explore its relationship to the age of disease onset (AOO), and provide evidence for its positive selection.
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