Objective: To determine age-dependent accumulation of oligomeric alpha-synuclein in the brain of aged LRRK2(R1441G) knockin mice; and to explore whether activation of chaperone-mediated autophagy (CMA) can attenuate accumulation of alpha-synuclein oligomers in mutant LRRK2 neurons.

Background: Progressive accumulation and propagation of misfolded alpha-synuclein in the aging brains is a key feature of Parkinson’s disease (PD). Impaired alpha-synuclein degradation potentiates aggregation and formation of its toxic pre-fibrillar oligomers. Leucine-rich repeat kinase 2 (LRRK2) mutations form a common cause of familial PD which shares similar features to idiopathic PD. We previously generated a knockin mouse colony carrying the homozygous LRRK2(R1441G) mutation as an in vivo experimental model of PD [1,2]. LRRK2 mutation has shown to perturb lysosomal processes in chaperone-mediated autophagy (CMA) which degrades alpha-synuclein. Here we hypothesize that LRRK2 mutation contributes to alpha-synuclein aggregation into toxic oligomers via impairment of alpha-synuclein degradation.

Methods: Levels of oligomeric alpha-synuclein in mouse brain lysates at different ages were quantified using oligomer-specific ELISA and dot-blotting. Matured primary cortical neurons from mutant mice were treated with CMA activator, AR7, over 21 days and the amount of oligomers were quantified in both cell lysates and conditioned medium. A novel cell-based flow cytometry assay was developed to measure alpha-synuclein degradation.

Results: There is a greater age-dependent accumulation of oligomeric alpha-synuclein in striatum and cortex of aged LRRK2(R1441G) knockin mice as compared to age-matched wildtype mice. In mutant neurons, AR7 treatment significantly reduced intra- and extracellular alpha-synuclein oligomer levels in a dose-dependent manner. The amount of intracellular oligomers in mutant neurons treated with AR7 was markedly reduced by 44% compared to those without treatment.

Conclusions: Pathogenic LRRK2(R1441G) mutation together with aging resulted in age-dependent accumulation of alpha-synuclein oligomers in the brain. CMA activation to reduce accumulation of alpha-synuclein oligomers in neurons with age may be a viable therapeutic strategy to address LRRK2-associated synucleinopathies in PD.

References: Liu HF, Ho PWL, Leung GC, Lam CS, Pang SY, Li LF, Kung MHW, Ramsden DB, Ho SL*. Combined LRRK2 mutation, aging and chronic low dose oral rotenone as a model of Parkinson’s disease. Sci Rep. 2017; 7:40887. doi:10.1038/srep40887. 2. Liu HF, Lu S, Ho PWL, Tse ZHM, Pang S, Kung MHW, Ho JWM, Ramsden DB, Zhou ZJ, Ho SL*. LRRK2 R1441G mice are more liable to dopamine depletion and locomotor inactivity. Ann Clin Transl Neurol. 2014; 1(3):199-208.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/activation-of-chaperone-mediated-autophagy-reduces-oligomeric-alpha-synuclein-accumulation-in-lrrk2r1441g-knockin-mouse-model-of-parkinsons-disease-pd/