Enzyme Activity-Based Genome-wide Screening for Modifiers of Lysosomal Glucocerebrosidase Uncovers Candidate Risk Factors for Parkinson’s Disease

Mutations in GBA1, the gene encoding
the lysosomal
hydrolase glucocerebrosidase (GCase), are the strongest common genetic
risk factor for Parkinson’s Disease (PD). However, these mutations
are incompletely penetrant, which suggests that there are likely genetic
modifiers of GCase function. To identify such genes, we implemented
a live cell GCase activity-based CRISPR-platform to enable genome-wide
screening for novel regulators of lysosomal GCase activity. Among
the screening hits, we find significant enrichment of genes linked
to development and progression of PD through genome-wide association
studies (GWAS). Moreover, we identify two lysosomal lipid transporter
genes, including those encoding the lysosphospholipid transporter
SPNS1 and the cholesterol transporter NPC1, and find an allele of
SPNS1 that is associated with increased risk of PD. We show that disruption
of SPNS1 does not affect GCase protein levels but impairs its lysosomal
function. Collectively, these data suggest that dysfunction of many
PD-associated genes converge to impact lysosomal GCase activity and
thereby contribute to disease pathogenesis. A better understanding
of the impacts of these and the other GCase modulators identified
here should help unravel the important, yet complex, relationship
between GBA1 and PD.