Multiple pieces of evidence converge on the notion that accumulation of the protein alpha-synuclein is important for Parkinson’s disease (PD) pathogenesis. One of the ways through which such accumulation could occur is through impairment of the mechanisms that normally degrade alpha-synuclein. We and others have shown that in cultured neuronal cells a major mechanism for alpha-synuclein degradation is that of chaperone-mediated autophagy (CMA), which occurs in lysosomes. Whether this occurs in the setting of a pre-clinical model, and whether induction of this degradation system in vivo can be used to get rid of excess alpha-synuclein, and thus confer therapeutic benefit in PD, is unknown.
We will use a system of viral delivery, in which the gene of interest is expressed via an Adeno-Assocaited Virus (AAV), which infects the nigral dopaminergic neurons affected in PD with high efficiency. We will inject such viruses in the substantia nigra of a pre-clinical model using a stereotaxic approach for correct targeting, and thus express the protein products of 3 genes: EGFP, which is used as a control, Lamp-2a, whose expression has been shown to induce CMA, and alpha-synuclein. We will examine whether combined expression of Lamp2a together with alpha-synuclein diminishes the accumulation and aggregation of alpha-synuclein, as well as its toxic effects on nigral dopaminergic neurons.
Relevance to Diagnosis/Treatment of Parkinson’s Disease, Combined with Outcome:
This project will test the hypothesis that induction of CMA and subsequent enhanced clearance of alpha-synuclein may have beneficial effects in a relevant PD animal model. Should we be successful, this may pave the way for the use of such approaches, of enhancing CMA function, in order to diminish alpha-synuclein accumulation in PD. Such approaches could either be of the type of gene therapy employed here, or of the type of specific drugs that enhance CMA function. First, however, a proof of principle study, like the one proposed here, is needed in order to test that this strategy can be safe and effective in a pre-clinical model.
We have found that overexpression of Lamp-2a, a protein that drives degradation of substrates through the lysosomes in a process known as chaperone-mediated autophagy (CMA), ameliorates the toxicity induced by overexpression of alpha-synuclein in a pre-clinical model substantia nigra. Importantly, using this approach, both nigral cell bodies and nigrostriatal terminals, as well as levels of dopamine, were preserved. Furthermore, total levels of alpha-synuclein, as well as specific aberrant species, were reduced when Lamp-2a was co-expressed. This implies that Lamp-2a overexpression enhanced the clearance of alpha-synuclein. Overall, these results support the idea that enhancement of CMA through Lamp-2a overexpression or other means, possibly pharmacological, may represent a therapeutic avenue to treat Parkinson’s disease and related synucleinopathies, in which excess and aberrant alpha-synuclein contributes to neurodegeneration.