Developmental delay in motor skill acquisition in Niemann-Pick C1 mice reveals abnormal cerebellar morphogenesis.

Paola Caporali,Robert P Erickson,Franco Mangia,Sonia Canterini,Jessica Dragotto,Maria Teresa Fiorenza,Giampiero Palladino,Laura Petrosini,Francesco Bruno

doi:10.1186/s40478-016-0370-z

Abstract

Niemann-Pick type C1 (NPC1) disease is a lysosomal storage disorder caused by defective intracellular trafficking of exogenous cholesterol. Purkinje cell (PC) degeneration is the main sign of cerebellar dysfunction in both NPC1 patients and animal models. It has been recently shown that a significant decrease in Sonic hedgehog (Shh) expression reduces the proliferative potential of granule neuron precursors in the developing cerebellum of Npc1−/− mice. Pursuing the hypothesis that this developmental defect translates into functional impairments, we have assayed Npc1-deficient pups belonging to the milder mutant mouse strain Npc1nmf164 for sensorimotor development from postnatal day (PN) 3 to PN21. Npc1nmf164/ Npc1nmf164 pups displayed a 2.5-day delay in the acquisition of complex motor abilities compared to wild-type (wt) littermates, in agreement with the significant disorganization of cerebellar cortex cytoarchitecture observed between PN11 and PN15. Compared to wt, Npc1nmf164 homozygous mice exhibited a poorer morphological differentiation of Bergmann glia (BG), as indicated by thicker radial shafts and less elaborate reticular pattern of lateral processes. Also BG functional development was defective, as indicated by the significant reduction in GLAST and Glutamine synthetase expression. A reduced VGluT2 and GAD65 expression also indicated an overall derangement of the glutamatergic/GABAergic stimulation that PCs receive by climbing/parallel fibers and basket/stellate cells, respectively. Lastly, Npc1-deficiency also affected oligodendrocyte differentiation as indicated by the strong reduction of myelin basic protein. Two sequential 2-hydroxypropyl-β-cyclodextrin administrations at PN4 and PN7 counteract these defects, partially preventing functional impairment of BG and fully restoring the normal patterns of glutamatergic/GABAergic stimulation to PCs.These findings indicate that in Npc1nmf164 homozygous mice the derangement of synaptic connectivity and dysmyelination during cerebellar morphogenesis largely anticipate motor deficits that are typically observed during adulthood.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0370-z) contains supplementary material, which is available to authorized users.

Highlights

Niemann-Pick type C (NPC) is an inherited lysosomal storage disorder, fatal and presenting with variable neurovisceral symptoms, age of onset and life span [1]
The defect is due to mutations in the genes Niemann-Pick type C1 (NPC1) (95 % of cases) or NPC2, encoding for proteins that cooperatively mediate the egress from endosomes/lysosomes of exogenous cholesterol brought to the cells by the low density lipoprotein (LDL)/clathrin-coated pit pathway [4]
In conclusion, we correlate the delay of complex motor skills acquisition by Npc1nmf164 mice to a number of glial cell differentiation anomalies and derangement of synaptic input to Purkinje cell (PC)

Summary

Introduction

Niemann-Pick type C (NPC) is an inherited lysosomal storage disorder, fatal and presenting with variable neurovisceral symptoms, age of onset and life span [1]. The most recent incidence estimate is 1.12 affected patients per 100,000 live births, this value is likely underestimated because of misdiagnosis [3]. The defect is due to mutations in the genes NPC1 (95 % of cases) or NPC2, encoding for proteins that cooperatively mediate the egress from endosomes/lysosomes of exogenous cholesterol brought to the cells by the low density lipoprotein (LDL)/clathrin-coated pit pathway [4]. The role of NPC1/NPC2 proteins is important in neural cells because cholesterol does not cross the blood–brain barrier once it is fully established after birth [5], making the adult brain mostly dependent on endogenouslyderived cholesterol. Cholesterol de novo synthesis occurs in both neurons and astrocytes during early postnatal neurogenesis, thereafter becoming most prominent in astrocytes [6]

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