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Role of the lysosomal dysfunction during aging, and implication for Parkinson’s Disease

Final Report Summary - AGELYSPARK (Role of the lysosomal dysfunction during aging, and implication for Parkinson’s Disease.)

The AGELYSPARK research project aims at developing clinically relevant models in mouse and primate species by studying the interaction of multiple likely causes of cell death in PD.
This frontier-breaking research project is organized in parallel research projects that will reach a succession of specific milestones, which in themselves constitute frontier research objectives. Achieving these intermediate keystones will allow the progressive transfer of increasingly-complex, multi- dimensional, hopefully heuristic, models that will be able to improve the translational value of preclinical development of therapeutic strategies, not mentioning the gain in knowledge of intrinsic cell death, protein aggregation and prion-like mechanisms.
In SO I and II, we analyzed the role of aging and the lysosomal dysfunction in PD. The working hypothesis was: Impairment of the lysosomal-mediated degradation pathway associated with other PD-related genes and aging contributes to inclusion formation and neuron cell death in PD. We analyzed also the role of Parkinson’s disease associated gene (PARK9) in the pathogenesis of PD and the study of senescence-accelerated cells and PD-derived senescence-accelerated cells to pharmacological and genetic inhibition of the lysosomal-mediated degradation pathway. Following the publication in PNAS in 2012 describing for the first time the role of ATP13A2 in the lysosomal function and its role in PD, we currently pursue the characterization of this pathway.
IN SO III, mounting evidence suggests that α-synuclein, a major protein component of Lewy bodies (LB), may be responsible for initiating and spreading the pathological process in PD. Supporting this concept, intracerebral inoculation of synthetic recombinant α-synuclein fibrils can trigger a-synuclein pathology in mice. However, it remains uncertain whether the pathogenic effects of recombinant synthetic a-synuclein may apply to PD- linked pathological a-synuclein and occur in species closer to humans. To answer to this question, nigral LB-enriched fractions containing pathological α-synuclein were purified from postmortem PD brains by sucrose gradient fractionation and subsequently inoculated into the substantia nigra or striatum of wild-type mice and macaque monkeys. Control animals received non-LB fractions containing soluble α-synuclein derived from the same nigral PD tissue. We observed in both mice and monkeys, intranigral or intrastriatal inoculations of PD-derived LB extracts resulted in progressive nigrostriatal neurodegeneration starting at striatal dopaminergic terminals. No neurodegeneration was observed in animals receiving non-LB fractions from the same patients. In LB-injected animals, exogenous human α-synuclein was quickly internalized within host neurons and triggered the pathological conversion of endogenous α-synuclein. At the onset of LB-induced degeneration, host pathological α-synuclein diffusely accumulated within nigral neurons and anatomically interconnected regions, both anterogradely and retrogradely. LB-induced pathogenic effects required both human α-synuclein present in LB extracts and host expression of α-synuclein. Overall, our results support the concept that α-synuclein species contained in PD-derived LB are pathogenic and have the capacity to initiate a PD-like pathological process, including intracellular and presynaptic accumulations of pathological a-synuclein in different brain areas and slowly progressive axon-initiated dopaminergic nigrostriatal neurodegeneration. Overall, the results presented here indicate that insoluble α-synuclein forms contained in PD-derived LB are pathogenic. These results may have important implications for the development of disease-modifying therapies for PD aimed at targeting expression levels, pathological conversion and/or cell-to-cell transmission of α-synuclein. The study was published in Annals of Neurology as co-first authorship
The fundamental basis and main objective of my research project was to abolish the current roadblock towards successful development of neuroprotective and neurorestorative approaches for PD. An original comprehensive multi-hit approach shall be needed to model PD neurodegeneration to identify new molecular targets for potential therapeutic intervention. The relationship between aging and inhibition of the lysosomal-mediated degradation pathway in neuronal death and process of aggregate formation has never been emphasized, deeply studied and is now of growing of interest. This program allowed establishing new in vitro and in vivo experimental model combining aging and lysosomal impairment, in which the etiology, mechanisms of formation and potential significance of LB-like inclusion formation relevant to Parkinson’s disease could be experimentally tested. Furthermore, the potential beneficial effect of pharmacologically restoring or stimulating lysosomal-mediated degradation will be tested in these models. Identifying molecular pathways that may be common to other neurodegenerative disorders with protein aggregates, such as Alzheimer’s or Huntington’s diseases. Increasingly, experimental evidence and clinical data suggest that the mechanisms responsible for initiating the degenerative process in PD are still present at late stages of the disease and are capable of affecting grafted healthy neurons, implicating a “prion-like” mechanism in PD.