Objective: Evaluate PARKIN gene replacement by adeno-associated virus (AAV) vector as a therapeutic modality in relevant disease models of early-onset Parkinson’s Disease (EOPD).

Background: Biallelic loss of function mutations in the PARKIN (PRKN) gene cause familial EOPD. Parkin, a ubiquitin E3 ligase, is a crucial element of the PTEN-induced kinase 1 (PINK1)-Parkin pathway, which acts as a cellular stress response to mark damaged mitochondria for autophagy. In absence of Parkin, the accumulation of damaged mitochondria and oxidative stress results in neurodegeneration. In this study, we evaluated AAV-mediated expression of human Parkin in PARKIN-deficient cells and in wild-type (WT) rodents.

Method: To assess Parkin-pathway activation, we measured phospho-Ubiquitin Ser65 (pUb^Ser65), a residue specific phosphorylation by PINK1, which is subsequently amplified by Parkin to trigger degradation of damaged mitochondria. We also demonstrated the feasibility of Parkin overexpression via intraparenchymal substantia nigra (SN) delivery of AAV-Parkin in rodents.

Results: In PARKIN knock-out (KO) SH-SY5Y cells, pUb^Ser65 signal is decreased in PARKIN KO vs. WT SH-SY5Y cells following mitochondrial stress.  AAV carrying a Parkin transgene under the control of a ubiquitous promoter corrected the pUb^Ser65 deficiency in KO cells. Moreover, we observed similar restoration of pUb^Ser65 signal in PRKN-PD patient-derived fibroblasts following Parkin replacement by an AAV-Parkin. Additionally, WT Sprague-Dawley rats, injected with AAV carrying a Parkin transgene at different doses, expressed Parkin in a dose-dependent manner after 8 weeks without any significant impact on the levels of dopamine or dopamine turnover. A concurrent study in C57BL/6 mice testing multiple promoter candidates in a Spark proprietary capsid showed that both a ubiquitous and a pan-neuronal promoter transduced tyrosine hydroxylase positive dopaminergic neurons in the SN.

Conclusion: These data together form the basis for a potential disease-modifying approach in Parkin-deficient EOPD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/parkin-gene-replacement-by-aav-mediated-gene-delivery-as-a-therapeutic-modality-for-parkin-deficient-early-onset-familial-parkinsons-disease/