Pharmacochaperoning in a Drosophila model system rescues human dopamine transporter variants associated with infantile/juvenile parkinsonism

Point mutations in the gene encoding the human dopamine transporter (hDAT, SLC6A3) cause a syndrome of infantile/juvenile dystonia and parkinsonism. To unravel the molecular mechanism underlying these disorders and investigate possible pharmacological therapies, here we examined 13 disease-causing DAT mutants that were retained in the endoplasmic reticulum (ER) when heterologously expressed in HEK293 cells. In three of these mutants - i.e. hDAT-V158F, hDAT-G327R and hDAT-L368Q- the folding deficit was remedied with the pharmacochaperonenoribogaineor the heat shock protein 70 (HSP70)-inhibitor pifithrin-μ such that ER export of and radioligand binding and substrate uptake by these DAT mutants were restored. In Drosophila melanogaster, DAT deficiency results in reduced sleep. We therefore exploited the power of targeted transgene expression of mutant hDAT in Drosophila to explore, whether these hDAT mutants could also be pharmacologically rescued in an intact organism. Noribogaine or pifithrin-μ treatment supported hDAT delivery to the presynaptic terminals of dopaminergic neurons and restored sleep to normal length in DAT-deficient (fumin) Drosophilalines expressinghDAT-V158F or hDAT-G327R. In contrast, expression of hDAT-L368Qin the Drosophila DAT mutant background caused developmental lethality indicating a toxic action not remedied by pharmacochaperoning. Our observations identified those mutations most likely amenable to pharmacological rescue in the affected children. In addition, our findings also highlight the challenges of translating insights from pharmacochaperoning in cell culture to the clinical situation. Because of the evolutionary conservation in dopaminergic neurotransmission between Drosophila and people, pharmacocha-peroning of DAT in Drosophila melanogaster may allow to bridge that gap.