Wild Type -Synuclein Is Degraded by Chaperone-mediated Autophagy and Macroautophagy in Neuronal Cells
ABSTRACT 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.
- SourceAvailable from: Ianai Fishbein
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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. "
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.Brain 12/2014; 137(12):3235. DOI:10.1093/brain/awu291 · 9.20 Impact Factor
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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. "
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.Virus Research 11/2014; 42. DOI:10.1016/j.virusres.2014.10.016 · 2.32 Impact Factor
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- "As for the contribution of other proteolytic machineries in the degradation of ASYN, there is significant evidence that both macroautophagy  and the proteasome [18-20] contribute to the removal of various ASYN species (from monomers to oligomers). However, it should be mentioned that in our experimental setting (SH-SY5Y cell line) the contribution of the proteasome to the degradation of monomeric ASYN was not found to be significant . However, it is also believed that the latter mechanism could be impaired by specific ASYN species of higher molecular weight (oligomeric and fibrillar) [18,20-24]. "
ABSTRACT: Background Alpha-synuclein (ASYN) is central in Parkinson's disease (PD) pathogenesis. Converging pieces of evidence suggest that the levels of ASYN expression play a critical role in both familial and sporadic Parkinson's disease. ASYN fibrils are the main component of inclusions called Lewy Bodies (LBs) which are found mainly in the surviving neurons of the substantia nigra. Despite the accumulated knowledge regarding the involvement of ASYN in molecular mechanisms underlying the development of PD, there is much information missing which prevents understanding the causes of the disease and how to stop its progression. Results Using a Systems Biology approach, we develop a biomolecular reactions model that describes the intracellular ASYN dynamics in relation to overexpression, post-translational modification, oligomerization and degradation of the protein. Especially for the proteolysis of ASYN, the model takes into account the biological knowledge regarding the contribution of Chaperone Mediated Autophagy (CMA), macro-autophagic and proteasome pathways in the protein's degradation. Importantly, inhibitory phenomena, caused by ASYN, concerning CMA (more specifically the lysosomal-associated membrane protein 2a, abbreviated as Lamp2a receptor, which is the rate limiting step of CMA) and the proteasome are carefully modeled. The model is validated by simulation studies of known experimental overexpression data from SH-SY5Y cells and the unknown model parameters are estimated either computationally or by experimental fitting. The calibrated model is then tested under three hypothetical intervention scenarios and in all cases predicts increased cell viability that agrees with experimental evidence. The biomodel has been annotated and is made available in SBML format. Conclusions The mathematical model presented here successfully simulates the dynamic phenomena of ASYN overexpression and oligomerization and predicts the biological system's behavior in a number of scenarios not used for model calibration. It allows, for the first time, to qualitatively estimate the protein levels that are capable of deregulating proteolytic homeostasis. In addition, it can help form new hypotheses for intervention that could be tested experimentally.BMC Systems Biology 05/2014; 8(1):54. DOI:10.1186/1752-0509-8-54 · 2.44 Impact Factor