Restoring Parkin Function: An AAV Gene Therapy Approach for Early-Onset Parkinson's Disease

Biallelic loss-of-function mutations in PRKN gene (encoding Parkin protein) cause early-onset Parkinson's disease (EOPD). Parkin is a crucial component of PINK1-Parkin pathway, which marks damaged mitochondria for degradation via mitophagy. Without functional Parkin, damaged mitochondria accumulate, causing oxidative stress and neurodegeneration.

Investigate Parkin gene replacement via AAV gene therapy as a potential treatment for Parkin-dependent EOPD.

We initially validated phosphorylated ubiquitin Ser65 (pUb ^Ser65 ) as an indicator of Parkin-mediated mitophagy initiation. We evaluated AAV-mediated PRKN replacement (hereafter, AAV-Parkin) in a Parkin knockout neuroblastoma cell line (SH-SY5Y cells) and feasibility of delivery in mouse and rat models.

Our research showed pUb ^Ser65 signal was reduced in Parkin-KO SH-SY5Y cells when compared to wild-type cells after mitochondrial stress, indicating deficiency in initiation of mitophagy. AAV-mediated human PRKN gene replacement successfully restored these pUb ^Ser65 levels in knockout cells. We saw restoration in patient-derived fibroblasts following AAV-Parkin overexpression. We developed a translatable gene therapy approach using rodents. We demonstrated the feasibility of delivering AAV-Parkin directly into the substantia nigra (SN) of wild-type rats. Using an AAV1 capsid with Ef1a promoter, we achieved dose-dependent Parkin expression and identified a well-tolerated dose. We also evaluated multiple promoters in a proprietary Spark100 capsid, finding Ef1a and Synapsin1 (Syn1) were most effective for transducing dopaminergic neurons in the SN of mice without causing adverse effects. These findings established a well-tolerated vector dose and an optimal capsid-promoter combination.

Our results support the potential of AAV-Parkin gene therapy as a disease-modifying approach for Parkin-deficient EOPD.