Loss of glucocerebrosidase 1 activity causes lysosomal dysfunction and α-synuclein aggregation

Lysosomal dysfunction is a common pathological feature of neurodegenerative diseases. GTP-binding protein type A1 (GBA1) encodes β-glucocerebrosidase 1 (GCase 1), a lysosomal hydrolase. Homozygous mutations in GBA1 cause Gaucher disease, the most common lysosomal storage disease, while heterozygous mutations are strong risk factors for Parkinson’s disease. However, whether loss of GCase 1 activity is sufficient for lysosomal dysfunction has not been clearly determined. Here, we generated human neuroblastoma cell lines with nonsense mutations in the GBA1 gene using zinc-finger nucleases. Depending on the site of mutation, GCase 1 activity was lost or maintained. The cell line with GCase 1 deficiency showed indications of lysosomal dysfunction, such as accumulation of lysosomal substrates, reduced dextran degradation and accumulation of enlarged vacuolar structures. In contrast, the cell line with C-terminal truncation of GCase 1 but with intact GCase 1 activity showed normal lysosomal function. When α-synuclein was overexpressed, accumulation and secretion of insoluble aggregates increased in cells with GCase 1 deficiency but did not change in mutant cells with normal GCase 1 activity. These results demonstrate that loss of GCase 1 activity is sufficient to cause lysosomal dysfunction and accumulation of α-synuclein aggregates. Loss of activity of the β-glucocerebrosidase 1 enzyme is sufficient to cause the defects responsible for Gaucher and Parkinson's diseases. Mutations in the GBA1 gene that encodes β-glucocerebrosidase 1 are known to cause Gaucher disease, an inherited lysosomal storage disorder, and to be risk factors for Parkinson's disease. Yet, despite the strong association between GBA1 mutations and these diseases, the mechanism responsible for pathology was not well understood. A research team led by Seung-Jae Lee of Konkuk University in Seoul, South Korea, generated human neuroblastoma cells harboring mutations in the GBA1 gene. The cell line without glucocerebrosidase 1 activity showed signs of lysosomal dysfunction, consistent with Gaucher disease, and a build-up of α-synuclein protein aggregates, a hallmark of Parkinson's disease. Mutant cells with normal enzyme activity did not show these problems.