Wild type alpha-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: Beatrice Macchi[Show abstract] [Hide abstract]
ABSTRACT: Evidence has been accumulated showing that inflammatory and cell death pathways are altered both in brain and periphery during Parkinson disease (PD). Neuronal loss in PD is associated with chronic neuroinflammation characterized by microglia activation through the release of reactive oxygen radicals, cytokines, and Prostaglandin E2. The release of these inflammatory mediators in addition to deprivation in growth factors and increase of calcium and dopamine seem implicated in triggering apoptosis. The interaction of leucine-rich repeat kinase and Fas-Associated protein with Death Domain has been implicated in the switching-on of the extrinsic apoptotic pathway via caspase-8 activation, while deficiency in PTEN induced putative kinase 1 has been shown to cause Ca2+ accumulation in mitochondria, increased generation of reactive oxygen species and intrinsic cell death. Autophagy/mitophagy appears to be impaired in the brain during PD; this impairment could be related to defective degradation of mutant α-synuclein and consequent apoptotic cell death. Regarding to the peripheral blood, reduced amounts of dopamine, reduced levels of immunoreactivity for tyrosine hydroxylase and dopamine active transporter, and alterations of dopamine receptor expression have been detected in mononuclear cells from PD patients. In addition, mononuclear cells from PD patients show mitochondrial, ubiquitin-proteasome system dysfunction and up-regulation of α-synuclein gene, associated to high expression of the Fas molecule, activation of caspase-3 and -9 and proneness to apoptosis. These and other observations reported in this mini-review suggest that a better understanding of molecular dysfunctions in inflammatory and cell death/autophagy pathways, both in brain and peripheral blood, could provide useful targets for future investigation on drug-discovery and biomarker identification in PD.CNS & Neurological Disorders - Drug Targets (Formerly Current Drug Targets - CNS & Neurological Disorders) 02/2015; 14(3). · 2.70 Impact Factor
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ABSTRACT: Although Parkinson's disease is the most common neurodegenerative movement disorder, the mechanisms of pathogenesis remain poorly understood. Recent findings have shown that deregulation of the autophagy-lysosome pathway is involved in the pathogenesis of Parkinson's disease. This review summarizes the most recent findings and discusses the unique role of the autophagy-lysosome pathway in Parkinson's disease to highlight the possibility of Parkinson's disease treatment strategies that incorporate autophagy-lysosome pathway modulation.Neural Regeneration Research 01/2012; 7(2):141-145. DOI:10.3969/j.issn.1673-5374.2012.02.011 · 0.23 Impact Factor
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ABSTRACT: Mammalian cells remove misfolded proteins using various proteolytic systems, including the ubiquitin (Ub)-proteasome system (UPS), chaperone mediated autophagy (CMA) and macroautophagy. The majority of misfolded proteins are degraded by the UPS, in which Ub-conjugated substrates are deubiquitinated, unfolded and cleaved into small peptides when passing through the narrow chamber of the proteasome. The substrates that expose a specific degradation signal, the KFERQ sequence motif, can be delivered to and degraded in lysosomes via the CMA. Aggregation-prone substrates resistant to both the UPS and the CMA can be degraded by macroautophagy, in which cargoes are segregated into autophagosomes before degradation by lysosomal hydrolases. Although most misfolded and aggregated proteins in the human proteome can be degraded by cellular protein quality control, some native and mutant proteins prone to aggregation into β-sheet-enriched oligomers are resistant to all known proteolytic pathways and can thus grow into inclusion bodies or extracellular plaques. The accumulation of protease-resistant misfolded and aggregated proteins is a common mechanism underlying protein misfolding disorders, including neurodegenerative diseases such as Huntington’s disease (HD), Alzheimer’s disease (AD), Parkinson’s disease (PD), prion diseases and Amyotrophic Lateral Sclerosis (ALS). In this review, we provide an overview of the proteolytic pathways in neurons, with an emphasis on the UPS, CMA and macroautophagy, and discuss the role of protein quality control in the degradation of pathogenic proteins in neurodegenerative diseases. Additionally, we examine existing putative therapeutic strategies to efficiently remove cytotoxic proteins from degenerating neurons.03/2015; 47(3):e147. DOI:10.1038/emm.2014.117