Identification of Targets of Neurotoxic Sphingolipids Using iPSCs from People with GBA-associated Parkinson’s Disease

Study Rationale:
GBA encodes the enzyme beta-glucocerebrosidase (GCase), which is required to maintain function of the cell’s lysosomes, which break down unnecessary cellular parts. Mutations in GBA are a risk factor for Gaucher disease and Parkinson’s disease. Using induced pluripotent stem cell (iPSC)-derived neuron cells from patients with Gaucher, we found that elevation in sphingolipids (a class of fatty acids) caused by GBA deficiency deregulates lysosomal function through hyperactivation of the mTOR protein. In this study we will identify the molecular targets of sphingolipids, and determine whether drugs that inhibit mTOR or restore sphingolipid balance can rescue lysosomal functions in dopamine neurons from patients with GBA-associated PD.

Hypothesis:
We hypothesize that the accumulation of sphingolipids in dopaminergic neurons caused by GBA deficiency results in hyperactivation of mTOR, lysosomal dysfunction, alpha-synuclein accumulation and aggregation, and dopaminergic neuronal death.

Study Design:
We will analyze the effect of GBA deficiency on lysosomal function in a panel of iPSC-derived dopamine neurons from patients with GBA-associated PD. The dopamine neurons will be examined by lysosome marker and autophagic flux analysis, and by assaying for accumulation/aggregation of alpha-synuclein. Then we will determine whether pharmacological reversal of sphingolipid imbalance and mTOR hyperactivity by treatment with drugs that inhibit glucosylceramide synthetase (GCS) or mTOR, can reverse the lysosomal abnormalities caused by mutant GBA.

Impact on Diagnosis/Treatment of Parkinson’s Disease:
Identification of the molecular mechanisms that are disrupted by sphingolipids will point to new therapeutic targets and early markers of GBA-associated PD. The iPSC-based assays developed in our laboratory provide a relevant human platform for evaluating the therapeutic efficacy of GCS or mTOR inhibitors as they become available.

Next Steps for Development:
If this study is successful, the next step will be to test the therapeutic effect of mTOR and GCS inhibitors in a model of GBA-associated PD. Another goal is to carry out a stratified study with more samples from GBA-associated PD patients, to identify patient populations that are responsive to these drugs.