From patients to human pluripotent cells: elucidation of the relationship between glucocerebrosidase dysfunction and α -synuclein in Lewy body disorders
Ravi Jagasia1, Anna Lisa Gündner4, Gonzalo Duran-Pacheco1,Nadia Anastasi1, Alexandra Gherlein1, Gonzalo Duran-Pacheco1, Iris Ruf1, Tim Moors2, Wilma D.J. van de Berg2, Verdon Taylor3, Stefania Fedele3, Per-Ola Freskgard1, Karlheinz Baumann1, 1, Thomas Kremer1
1PhD, Roche Pharmaceutical Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd, Grenzacherstrasse 124, 4070 Basel, Switzerland; 2Department of Anatomy and Neurosciences, Section Quantitative Morphology, Neuroscience Campus Amsterdam, VU University Medical Center, Amsterdam, the Netherlands; 3Department of Biomedicine, University of Basel, Pestalozzistrasse 20, CH-4058, Basel, Switzerland
GBA-associated neurodegeneration is the most common known genetic risk factor for several Lewy body disorders. Accumulating evidence suggest that there is an inverse correlation that exists between levels of glucocerebrosidase and α-synuclein pathology, however the molecular basis for this reciprocal relationship remains elusive. From a therapeutic perspective, it is still debated whether glucocerbrosidase (Gcase) dysfunction is a result of a gain or loss of function and additionally whether the α-synuclein accumulation is a downstream toxic event. To this end, we aimed to assess the relationship between GCase and α-synuclein in post-mortem brain-tissue derived from subjects with Parkinson's Disease (PD), Dementia with Lewy Lodies (DLB)and age-matched controls (n=15/group). We quantified GCase enzyme activity, protein levels, its substrate glucosysphingosine and alpha-synuclein (total and phosphorylated at Serine 129) protein in three brain regions. GCase protein levels and enzymatic activity were highly correlated and protein levels were slightly decreased in the substantia nigra of PD and DLB patients versus controls. An inverse correlation between glucocerebrosidase protein/activity and α-synuclein in patients could be detected in substantia nigra, maybe reflecting lysosomal dysfunction. To better address the mechanism on a cellular/molecular neuronal level, we generated a GBA allelic series of a human embryonic stem cell line. Differentiated GBA neurons exhibit cellular and molecular phenotypes beyond α-synuclein. We are now addressing whether rescuing Gcase and/or reducing total α-synuclein levels contribute to these phenotypes. Ultimately, the elucidation of lysosomal pathomechanisms will guide the development of targeted therapeutics to several Lewy body disorders.