GBA1 mutations alter neuronal excitability and ultrastructure in Parkinson´s disease, regulating VGLUT2 and CRYAB in dopaminergic neurons

Mutations in the glucocerebrosidase 1 ( GBA1 ) gene are major risk factors for Parkinson´s disease (PD), but their role in PD etiopathology is not fully understood. The impact of GBA1 mutations on neuronal maturation, function and degeneration was investigated in dopaminergic (DA) neurons obtained from induced pluripotent stem cells (iPS cells/iPSCs) derived from PD patients carrying the heterozygous N370S or L444P mutation in GBA1 . DA neurons co-expressing TH and VGLUT2 were detected in the cultures, and their number and/or expression of VGLUT2 / SLC17A6 mRNA was markedly reduced in both N370S and L444P cultures compared to controls. Electrophysiological recordings revealed a significant increase in the firing rate of N370S but not L444P neurons, whereas evoked dopamine release was stronger from neurons carrying either mutation than from the controls. Furthermore, there was a significant accumulation of α-synuclein aggregates in the cell body and dendrites of N370S neurons. Remarkably, neurons carrying either GBA1 mutation accumulated abundant Lewy body-like inclusions, multilamellar bodies, Golgi apparatus vacuolated dictyosomes and autophagosomes. Notably, a significant upregulation of the chaperone CRYAB/HSPB5/alpha-crystallin-B was found early in DA neuron differentiation and in the substantia nigra of PD patients. Therefore, our cellular model allows clear features of neurodegeneration to be detected in neurons derived from PD patients. Our findings indicate that N370S and L444P GBA1 mutations impair midbrain DA neurons expressing VGLUT2, and provoke molecular, functional and ultrastructural changes, possibly involved in PD etiopathology. They suggest that VGLUT2 and CRYAB may potentially serve as early molecular targets and/or biomarkers in GBA1 -PD.