Geranylgeranyl pyrophosphate is crucial for neuronal survival but has no special role in Purkinje cell degeneration in Niemann Pick type C1 disease

Niemann Pick type C (NPC1) is a rare fatal hereditary cholesterol storage disease associated with a massive Purkinje cells loss. The mechanisms leading to neurodegeneration are still poorly understood. Different laboratories pointed to hypersensitivity to cytotoxic effects of statins (HMG-CoA reductase inhibitors) in NPC1 and suggested an underlying lack of geranylgeranyl pyrophosphate (GGPP). GGPP is a non-sterol isoprenoid essential for cell survival and differentiation. We measured GGPP levels in cerebella of a NPC1 mouse model and of wild-type littermates and found a physiological increase of GGPP levels between post-natal days 21 and 49 in wild-type mice but not in NPC mice. This further supports the hypothesis that Purkinje cell loss may be due to an extremely low level of GGPP. The progressive Purkinje cell loss in NPC starts between p21 and p49. To test the hypothesis, we used long-term organotypic slice cultures of NPC1 mice that display the natural history of NPC1 disease in vitro and tested if chronic administration of GGPP might prevent Purkinje cell loss. We did not see a beneficial effect. This suggests, in contrast to the expectations, that the relative lack of GGPP may not significantly contribute to mechanisms of Purkinje cell loss in NPC1.