Mutations in the lysosomal
enzyme glucocerebrosidase (GCase, GBA1 gene) are the most common genetic risk factor for developing
Parkinson's disease (PD). GCase metabolizes the
glycosphingolipids glucosylceramide (GlcCer) and
glucosylsphingosine (
GlcSph). Mutations in GBA1 reduce
enzyme activity and the resulting accumulation of
glycosphingolipids may contribute to the underlying pathology of PD, possibly via altering lysosomal function. While reduction of GCase activity exacerbates α-
synuclein (α-syn) aggregation, it has not been determined that this effect is the result of altered
glycosphingolipid levels and lysosome function or some other effect of altering GCase. The
glycosphingolipid GlcCer is synthesized by a single
enzyme,
glucosylceramide synthase (GCS), and small molecule inhibitors (
GCSi) reduce cellular
glycosphingolipid levels. In the present studies, we utilize a preformed fibril (PFF) rodent primary neuron in vitro model of α-syn pathology to investigate the relationship between
glycosphingolipid levels, α-syn pathology, and lysosomal function. In primary cultures, pharmacological inhibition of GCase and D409V GBA1 mutation enhanced accumulation of
glycosphingolipids and insoluble phosphorylated α-syn. Administration of a novel small molecule
GCSi,
benzoxazole 1 (BZ1), significantly decreased
glycosphingolipid concentrations in rodent primary neurons and reduced α-syn pathology. BZ1 rescued lysosomal deficits associated with the D409V GBA1 mutation and α-syn PFF administration, and attenuated α-syn induced neurodegeneration of dopamine neurons. In vivo studies revealed BZ1 had pharmacological activity and reduced
glycosphingolipids in the mouse brain to a similar extent observed in neuronal cultures. These data support the hypothesis that reduction of
glycosphingolipids through GCS inhibition may impact progression of
synucleinopathy and BZ1 is useful tool to further examine this important biology.