Objective: In this study, we propose to decipher the role of GBA1 as a modifier of familial Parkinson’s disease (PD) using double-mutant patient-derived cellular models

Background: Mutations in more than 20 genes have been identified as being causative for PD. Nevertheless, heterogeneity in penetrance, phenotype and age of onset of patients carrying the same mutations lead to the search of modifying factors that could influence disease onset and progression. Mutations in the GBA1 gene, encoding the glucocerebrosidase (GCase), are an important and common risk factor for familial and sporadic PD. Indeed, 5-10% of all PD patients are carrying a GBA1 mutation [1]. These patients are more likely to progress to dementia, develop earlier axial motor symptoms and have a slightly earlier age of onset compared to non-carrier PD patients. Consequently, mutation in GBA1 could influence PD causal genes and modify the pathophysiology

Methods: Fibroblasts from a PD patient harbouring homozygous mutation in the PARK2 gene and a point mutation in the GBA1 gene have been donated. Patient’s fibroblasts have been reprogrammed into induced pluripotent stem cells (iPSC) using synthetic RNA encoding for reprogramming factors (Oct4, Nanog, Klf4, Glis1). These iPSC have been differentiated into small neuronal precursor cells to finally generate midbrain-specific dopaminergic neurons [2]. At iPSC stage, CRISPR Cas9 technology will be used to correct the GBA1 mutation to obtain an isogenic control free from any effect caused by this mutation and only harbouring the deletion in PARK2

Results: Three cellular models derived from patient’s fibroblasts have been successfully generated. Enriched neuronal culture were obtained, containing more than 15% of dopaminergic neurons. The characterisation of the cellular models confirmed the quality and suitability of our cell lines to study PD relevant phenotypes. Further characterisation of the cells revealed an impairment in GCase activity and a loss of Parkin. We now aim to investigate GBA1 mutation specific effect in the frame of the double mutation focusing on mitochondrial features, autophagy-lysosomal function and α-synuclein interplay

Conclusions: We have established the first double-mutant GBA1-PARK2 patient-derived cellular models. Phenotypic difference were identified and specific effect of GBA will be further studied particularly with the help of isogenic control

References: [1] Gegg ME, Schapira AHV. Mitochondrial dysfunction associated with glucocerebrosidase deficiency. Neurobiology of Disease. 2016 Jun;90:43-50.

[2] Reinhardt P, Glatza M, Hemmer K, Tsytsyura Y, Thiel CS, Hoing S, Moritz S, Parga JA, Wagner L,  Bruder JM, Wu G, Schmid B, Ropke A, Klingauf J, Schwamborn JC, Gasser T, Scholer HR, Sterneckert J. Derivation and Expansion Using Only Small Molecules of Human Neural Progenitors for Neurodegenerative Disease Modeling. PLoS One. 2013;8(3):e59252.[RK1] [ZH2] 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/patient-derived-gba1-park2-double-mutant-cellular-models-to-study-the-effect-of-gba1-as-a-modifier-of-familial-parkinsons-disease/