ER Stress and Autophagic Perturbations Lead to Elevated Extracellular α-Synuclein in GBA-N370S Parkinson's iPSC-Derived Dopamine Neurons.

Hugo J R Fernandes ,Heather Booth,William James,Kostas Vekrellis,Samuel Evetts,Jane Vowles,Helle Bogetofte,Kevin Talbot,Jennifer Badger,Evangelia Emmanoulidou,Ying Zheng,Charmaine Lang,Michèle Hu ,Sally A Cowley ,Elizabeth M Hartfield ,Helen C Christian ,Brent J Ryan ,George K Tofaris ,S Pablo Sardi ,Richard Wade‐Martins

doi:10.1016/j.stemcr.2016.01.013

Abstract

SummaryHeterozygous mutations in the glucocerebrosidase gene (GBA) represent the strongest common genetic risk factor for Parkinson's disease (PD), the second most common neurodegenerative disorder. However, the molecular mechanisms underlying this association are still poorly understood. Here, we have analyzed ten independent induced pluripotent stem cell (iPSC) lines from three controls and three unrelated PD patients heterozygous for the GBA-N370S mutation, and identified relevant disease mechanisms. After differentiation into dopaminergic neurons, we observed misprocessing of mutant glucocerebrosidase protein in the ER, associated with activation of ER stress and abnormal cellular lipid profiles. Furthermore, we observed autophagic perturbations and an enlargement of the lysosomal compartment specifically in dopamine neurons. Finally, we found increased extracellular α-synuclein in patient-derived neuronal culture medium, which was not associated with exosomes. Overall, ER stress, autophagic/lysosomal perturbations, and elevated extracellular α-synuclein likely represent critical early cellular phenotypes of PD, which might offer multiple therapeutic targets.

Highlights

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, characterized by the preferential degeneration of dopamine neurons in the substantia nigra pars compacta (SNpc)
The association of GBA with PD first emerged from clinical studies that demonstrated that relatives of patients with Gaucher’s disease (GD), a lysosomal storage disease caused by homozygous GBA mutations, had an increased incidence of PD (Goker-Alpan et al, 2004)
Our results suggest that the heterozygous GBA-N370S mutation leads to a cellular gain of function, shown by misprocessing of misfolded GCase protein in the ER resulting in ER stress upregulation and autophagic/lysosomal dysfunction leading to an enlargement of the lysosomal compartment in individually identified vulnerable dopamine neurons

Summary

Introduction

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, characterized by the preferential degeneration of dopamine neurons in the substantia nigra pars compacta (SNpc). Heterozygous mutations in the glucocerebrosidase gene (GBA) encoding the lysosomal enzyme GCase represent the strongest common genetic risk factor for PD (Sidransky et al, 2009) and have been associated with other related Lewy body disorders (Goker-Alpan et al, 2006); the underlying molecular mechanisms are still poorly understood. More recent studies exploring the pathogenic role of homozygous GBA mutations in GD have highlighted a role of GCase in mitochondria function, a-synuclein aggregation, and autophagic machinery (Mazzulli et al, 2011; Sardi et al, 2011). Mutations in GBA and in LRRK2, known to play a role in regulating autophagy (Alegre-Abarrategui et al, 2009), have emphasized the role for the autophagic/lysosomal pathway as central to the pathogenesis of PD (Tofaris, 2012)

Results

Discussion

Conclusion