Wild Type -Synuclein Is Degraded by Chaperone-mediated Autophagy and Macroautophagy in Neuronal Cells

Division of Basic Neurosciences, Biomedical Research Foundation of the Academy of Athens, Soranou Efesiou 4, Athens, Greece.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2008; 283(35):23542-56. DOI: 10.1074/jbc.M801992200
Source: PubMed


Alpha-synuclein (ASYN) is crucial in Parkinson disease (PD) pathogenesis. Increased levels of wild type (WT) ASYN expression are sufficient to cause PD in humans. The manner of post-transcriptional regulation of ASYN levels is controversial. Previously, we had shown that WT ASYN can be degraded by chaperone-mediated autophagy (CMA) in isolated liver lysosomes. Whether this occurs in a cellular and, in particular, in a neuronal cell context is unclear. Using a mutant ASYN form that lacks the CMA recognition motif and RNA interference against the rate-limiting step in the CMA pathway, Lamp2a, we show here that CMA is indeed involved in WT ASYN degradation in PC12 and SH-SY5Y cells, and in primary cortical and midbrain neurons. However, the extent of involvement varies between cell types, potentially because of differences in compensatory mechanisms. CMA inhibition leads to an accumulation of soluble high molecular weight and detergent-insoluble species of ASYN, suggesting that CMA dysfunction may play a role in the generation of such aberrant species in PD. ASYN and Lamp2a are developmentally regulated in parallel in cortical neuron cultures and in vivo in the central nervous system, and they physically interact as indicated by co-immunoprecipitation. In contrast to previous reports, inhibition of macroautophagy, but not the proteasome, also leads to WT ASYN accumulation, suggesting that this lysosomal pathway is also involved in normal ASYN turnover. These results indicate that CMA and macroautophagy are important pathways for WT ASYN degradation in neurons and underline the importance of CMA as degradation machinery in the nervous system.

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    • "Specifically, phosphorylated a-synuclein (Martinez-Vicente et al. 2008), A53T mutant (Cuervo et al. 2004; Xilouri et al. 2009), and dopamine-modified forms of the wild-type protein (Martinez-Vicente et al. 2008; Xilouri et al. 2009) lead to CMA dysfunction, and may induce compensatory macroautophagy (Xilouri et al. 2009). Indeed, pharmacological inhibition of macroautophagy resulted in a-synuclein accumulation in the lysosome (Webb et al. 2003; Vogiatzi et al. 2008) and activation of macroautophagy facilitated the degradation of both wild-type and mutant forms of asynuclein (Webb et al. 2003; Spencer et al. 2009). A study in transgenic mice over-expressing a-synuclein under the regulatory control of the Thy-1 promoter provided evidence that CMA provides a major mechanism for a-synuclein degradation in vivo. "
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    ABSTRACT: Substantial progress has been made in the genetic basis of Parkinson's disease (PD). In particular, by identifying genes that segregate with inherited PD or show robust association with sporadic disease, and by showing the same genes are found on both lists, we have generated an outline of the cause of this condition. Here, we will discuss what those genes tell us about the underlying biology of PD. We specifically discuss the relationships between protein products of PD genes and show that common links include regulation of the autophagy-lysosome system, an important way by which cells recycle proteins and organelles. We also discuss whether all PD genes should be considered to be in the same pathway and propose that in some cases the relationships are closer while in other cases the interactions are more distant and might be considered separate. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Preview · Article · Jul 2015 · Journal of Neurochemistry
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    • "It may arise from either the gain of a new toxic function by the mutated GBA protein, or by a decrease in its enzymatic efficiency, or by both. The second and third possibilities are supported by the fact that the lysosomal-autophagy pathway is considered to be the main pathway through which SNCA is degraded (Vogiatzi et al., 2008; Machiya et al., 2010). Although Gaucher disease is a recessive disorder and heterozygous carriers of the disease are asymptomatic , lysosomal function might not be optimal in Gaucher disease heterozygotes. "
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    ABSTRACT: The involvement of the protein a-synuclein (SNCA) in the pathogenesis of Parkinson's disease is strongly supported by the facts that (i) missense and copy number mutations in the SNCA gene can cause inherited Parkinson's disease; and (ii) Lewy bodies in sporadic Parkinson's disease are largely composed of aggregated SNCA. Unaffected heterozygous carriers of Gaucher disease mutations have an increased risk for Parkinson's disease. As mutations in the GBA gene encoding glucocerebrosidase (GBA) are known to interfere with lysosomal protein degradation, GBA heterozygotes may demonstrate reduced lysosomal SNCA degradation , leading to increased steady-state SNCA levels and promoting its aggregation. We have created mouse models to investigate the interaction between GBA mutations and synucleinopathies. We investigated the rate of SNCA degradation in cultured primary cortical neurons from mice expressing wild-type mouse SNCA, wild-type human SNCA, or mutant A53T SNCA, in a background of either wild-type Gba or heterozygosity for the L444P GBA mutation associated with Gaucher disease. We also tested the effect of this Gaucher mutation on motor and enteric nervous system function in these transgenic animals. We found that human SNCA is stable, with a half-life of 61 h, and that the A53T mutation did not significantly affect its half-life. Heterozygosity for a naturally occurring Gaucher mutation, L444P, reduced GBA activity by 40%, reduced SNCA degradation and triggered accumulation of the protein in culture. This mutation also resulted in the exacerbation of motor and gastrointes-tinal deficits found in the A53T mouse model of Parkinson's disease. This study demonstrates that heterozygosity for a Gaucher disease-associated mutation in Gba interferes with SNCA degradation and contributes to its accumulation, and exacerbates the phenotype in a mouse model of Parkinson's disease.
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    • "Other studies have focused on trying to understand what changes can be triggered by alpha-synuclein aggregation in cell metabolism. Some groups have reported than promoting apoptosis, energy depriving the cells and impairing proteasome degradation, among other cell insults, increase the levels of aggregated alpha-synuclein, suggesting that maintaining cellular homeostasis is critical for alpha-synuclein (Bellucci et al., 2008; Gentile et al., 2008; Vogiatzi et al., 2008). More importantly, primary cultures have been an invaluable model to study the seeding of alpha-synuclein pathological forms and the prion-like transmission from cell to cell. "
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    ABSTRACT: Parkinson's disease is one of several neurodegenerative diseases associated with a misfolded, aggregated and pathological protein. In Parkinson's disease this protein is alpha-synuclein and its neuronal deposits in the form of Lewy bodies are considered a hallmark of the disease. In this review we describe the clinical and experimental data that have led to think of alpha-synuclein as a prion-like protein and we summarize data from in vitro, cellular and animal models supporting this view. (C) 2014 Published by Elsevier B.V.
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