How to reduce the accumulation of autophagic vacuoles in NPC1-deficient neurons: a comparison of two pharmacological strategies.

A disturbed autophagic pathway leads to chronically increased levels of autophagic vacuoles in Niemann Pick Type-C 1 (NPC1) deficient neurons. Since these accumulations potentially contribute to neuronal cell death associated with the disease, we investigated two pharmacological strategies which potentially reduce the number of autophagic structures under following aspects: efficiency, sustainability and effect on neuronal cell viability. The strategies comprised (i) an interruption of the autophagic flux by the class III PI3K inhibitor 3-methyladenine (3-MA) and (ii) an acceleration of the autophagic execution by 2-hydroxypropyl-β-cyclodextrin (pCD). Our data show that the inhibition of autophagy with 3-MA only initially reduced the number of autophagic vacuoles in cultured neurons. Prolonged treatments with the PI3K-inhibitor reversed this lowering effect. The re-increase in the number of autophagic vacuoles was combined with a defect in the integrity of lysosomes which endangered further survival of cells. The treatment with pCD evoked a slow but sustained reduction of autophagic structures and had no negative effects on neuronal survival.