Objective: To elucidate how GBA1 deficiency promotes the spread of Lewy pathology from cell to cell.

Background: Mutations in the gene glucosidase, beta acid 1 (GBA1) not only increase risk for Parkinson’s Disease (PD) but also accelerate disease progression. As PD clinical progression is correlated with the spatial distribution of Lewy pathology, we hypothesize that GBA1 deficiency accelerates the spread of Lewy pathology from cell to cell.

Method: We developed a Drosophila GBA1 deficient model that has locomotor deficits, accelerated protein aggregation and neurodegeneration (Davis MY et al. 2016). To complement this model, human induced pluripotent stem cells (iPSCs) were generated from an individual with PD carrying the IVS2+1G>A GBA mutation (GBA^IVS). Dopaminergic neurons and astrocytes were differentiated from GBA^IVS and age- and sex-matched healthy control iPSCs. Control or GBA^IVS neurons or astrocytes were co-cultured, by culturing donor cells with lentivirus-mediated expression of alpha-synuclein-GFP (syn-GFP) in Transwell inserts over recipient cells plated on glass-bottom wells, allowing immunostaining of recipient cells for endolysosomal trafficking. Imaris software was used to 3D reconstruct z-stacks and obtain volumetric measurements of stained endolysosomal vesicles. Lysates of recipient cells were also analyzed by Western blot.

Results: Expression of human a-syn in flight muscle of our Drosophila GBA1 deficient model results in increased oligomerization of alpha-synuclein in heads. Neuronal expression of a-syn in GBA1 mutant flies also resulted in detecting oligomerized a-syn in thorax. Accelerated spread of alpha-synuclein was confirmed in GBA1deficient donor astrocytes expressing syn-GFP co-cultured with control recipient astrocytes, compared to control donor astrocytes expressing syn-GFP co-cultured with control recipient astrocytes, as measured by the number of recipient cells with GFP-positive inclusions.

Conclusion: Our Drosophila and cell culture models support the hypothesis that GBA1 deficiency accelerates the propagation of Lewy pathology from cell to cell. We will further test this by co-culturing GBA deficient and control neurons using the Transwell system, and examine a-syn oligomerization in recipient cells by Western blot. Understanding how GBA deficiency modulates the spread of Lewy pathology will elucidate novel therapeutic targets to slow progression of PD.

References: Davis MY, Trinh K, Thomas RE, Yu S, Germanos AA, Whitley B, Sardi SP, Montine TJ, Pallanck LJ. Glucocerebrosidase deficiency in Drosophila results in α-synuclein-independent protein aggregation and neurodegeneration. PLoS Genetics, 2016; 12(3):e1005944. PMID: 27019408

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MDS Abstracts - https://www.mdsabstracts.org/abstract/gba1-deficiency-promotes-the-spread-of-lewy-pathology/