Boosting chaperone-mediated autophagy in vivo mitigates -synuclein-induced neurodegeneration

1 Division of Basic Neurosciences, Biomedical Research Foundation of the Academy of Athens (BRFAA), Athens, Greece.
Brain (Impact Factor: 9.2). 06/2013; 136(7). DOI: 10.1093/brain/awt131
Source: PubMed


α-Synuclein levels are critical to Parkinson's disease pathogenesis. Wild-type α-synuclein is degraded partly by chaperone-mediated autophagy, and aberrant α-synuclein may act as an inhibitor of the pathway. To address whether the induction of chaperone-mediated autophagy may represent a potential therapy against α-synuclein-induced neurotoxicity, we overexpressed lysosomal-associated membrane protein 2a, the rate-limiting step of chaperone-mediated autophagy, in human neuroblastoma SH-SY5Y cells, rat primary cortical neurons in vitro, and nigral dopaminergic neurons in vivo. Overexpression of the lysosomal-associated membrane protein 2a in cellular systems led to upregulation of chaperone-mediated autophagy, decreased α-synuclein turnover, and selective protection against adenoviral-mediated wild-type α-synuclein neurotoxicity. Protection was observed even when the steady-state levels of α-synuclein were unchanged, suggesting that it occurred through the attenuation of α-synuclein-mediated dysfunction of chaperone-mediated autophagy. Overexpression of the lysosomal receptor through the nigral injection of recombinant adeno-associated virus vectors effectively ameliorated α-synuclein-induced dopaminergic neurodegeneration by increasing the survival of neurons located in the substantia nigra as well as the axon terminals located in the striatum, which was associated with a reduction in total α-synuclein levels and related aberrant species. We conclude that induction of chaperone-mediated autophagy may provide a novel therapeutic strategy in Parkinson's disease and related synucleinopathies through two different mechanisms: amelioration of dysfunction of chaperone-mediated autophagy and lowering of α-synuclein levels.

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    • "For example, in the MPTP-treated mouse model, pharmacological activation of ALP with the mammalian target of rapamycin (mTOR) inhibitor, rapamycin, attenuates neurodegeneration and lysosomal dysfunction (Dehay et al., 2010; Malagelada et al., 2010). Consistent with this approach, viral-mediated overexpression of ALP components, such as transcription factor EB (TFEB), LAMP2a or Beclin-1, provided neuroprotection in viral-mediated α-syn-overexpressing rodent models of PD (Spencer et al., 2009; Decressac et al., 2013; Xilouri et al., 2013). With regards to the development of therapeutic approaches, we must keep in mind that a balance needs to be maintained between boosting and inhibiting processes of autophagy. "
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    ABSTRACT: Neurodegenerative diseases are (i) characterized by a selective neuronal vulnerability to degeneration in specific brain regions; and (ii) likely to be caused by disease-specific protein misfolding. Parkinson's disease (PD) is characterized by the presence of intraneuronal proteinacious cytoplasmic inclusions, called Lewy Bodies (LB). α-Synuclein, an aggregation prone protein, has been identified as a major protein component of LB and the causative for autosomal dominant PD. Lysosomes are responsible for the clearance of long-lived proteins, such as α-synuclein, and for the removal of old or damaged organelles, such as mitochondria. Interestingly, PD-linked α-synuclein mutants and dopamine-modified wild-type α-synuclein block its own degradation, which result in insufficient clearance, leading to its aggregation and cell toxicity. Moreover, both lysosomes and lysosomal proteases have been found to be involved in the activation of certain cell death pathways. Interestingly, lysosomal alterations are observed in the brains of patients suffering from sporadic PD and also in toxic and genetic rodent models of PD-related neurodegeneration. All these events have unraveled a causal link between lysosomal impairment, α-synuclein accumulation, and neurotoxicity. In this review, we emphasize the pathophysiological mechanisms connecting α-synuclein and lysosomal dysfunction in neuronal cell death.
    Frontiers in Neuroanatomy 08/2014; 8(83). DOI:10.3389/fnana.2014.00083 · 3.54 Impact Factor
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    • "In conclusion, our model predicts an increased cell survival probability, and this agrees with experimental findings in our lab showing a higher turnover of ASYN species (monomeric as well as oligomeric) and significantly reduced ASYN-mediated neurotoxicity when Lamp2a is overexpressed. This was tested in three different experimental models: SH-SY5Y cells, primary rat cortical neurons and the living rat brain [37]. The in vivo data in particular are striking, in that the dopamine deficiency state was completely reversed, indicating that both the predictions of cellular and computational models are supported by the in vivo findings. "
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    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
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    ABSTRACT: Heterozygous mutations in the glucocerebrosidase gene (GBA1) are associated with increased risk for α-synuclein aggregation disorders ('synucleinopathies'), which include Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Homozygous GBA1 mutations lead to reduced GBA1 lysosomal activity underlying three variants of Gaucher disease (GD). Despite the wealth of clinical and genetic evidence supporting the association between mutant genotypes and synucleinopathy risk, the precise mechanisms by which GBA1 mutations lead to PD and DLB remain unclear. Here, we summarize recent findings that highlight the complexity of this pathogenetic link. In neural cells, both gain and loss of function mechanisms, as conferred by mutant GBA1 expression and activity loss, respectively, seem to promote aberrant α-synuclein processing. In addition, we draw attention to recent insights gleaned from GD animal models regarding axonal pathology, brain inflammation and memory dysfunction. From a translational perspective, we discuss the concepts of neural enzyme replacement therapy and pharmacological agents as potential treatment strategies for GBA1-associated synucleinopathies. Finally, we touch on the issue whether aberrant α-synuclein species may coregulate GBA1 activity in the vertebrate brain, thereby providing a reverse link, i.e., between an important synucleinopathy risk factor and the enzyme's lysosomal function. In summary, several leads connecting GBA1 mutations with α-synuclein misprocessing have emerged as potential targets for the treatment of GBA1-related synucleinopathies, and possibly, for non-GBA1-associated neurodegenerative diseases.
    Neurodegenerative Diseases 02/2012; 10(1-4):195-202. DOI:10.1159/000335038 · 3.51 Impact Factor
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