A marked paucity of granule cells in the developing cerebellum of the Npc1−/− mouse is corrected by a single injection of hydroxypropyl-β-cyclodextrin

Abstract

In this study we show that postnatal development of cerebellar granule neurons (GNs) is defective in Npc1−/− mice. Compared to age-matched wild-type littermates, there is an accelerated disappearance of the external granule layer (EGL) in these mice. This is due to a premature exit from the cell cycle of GN precursors residing at the level of the EGL. As a consequence, the size of cerebellar lobules of these mice displays a 20%–25% reduction compared to that of age-matched wild-type mice. This size reduction is detectable at post-natal day 28 (PN28), when cerebellar GN development is completed while signs of neuronal atrophy are not yet apparent.Based on the analysis of EGL thickness and the determination of proliferating GN fractions at increasing developmental times (PN8–PN14), we trace the onset of this GN developmental defect during the second postnatal week. We also show that during this developmental time Shh transcripts undergo a significant reduction in Npc1−/− mice compared to age-matched wild-type mice. In light of the mitogenic activity of Shh on GNs, this observation further supports the presence of defective GN proliferation in Npc1−/− mice. A single injection of hydroxypropyl-β-cyclodextrin at PN7 rescues this defect, restoring the normal patterns of granule neuron proliferation and cerebellar lobule size.To our knowledge, these findings identify a novel developmental defect that was underappreciated in previous studies. This defect was probably overlooked because Npc1 loss-of-function does not affect cerebellar foliation and causes the internal granule layer and molecular layer to decrease proportionally, giving rise to a normally appearing, yet harmoniously smaller, cerebellum.

NPC1 Deficiency in Mice is Associated with Fetal Growth Restriction, Neonatal Lethality and Abnormal Lung Pathology

“…In support of this, abnormal expression and localization of SHH and its receptor Patched has been shown in the cerebellum of Npc1 mutant mice at P14 as well as in NPC1 patient-derived fibroblasts [63,64]. These data along with other studies highlighting the importance of cholesterol for SHH function in the developing cerebellum suggest that important connections may exist between NPC1 and SHH signaling pathways [58,65,66].…”

Identification of Novel Pathways Associated with Patterned Cerebellar Purkinje Neuron Degeneration in Niemann-Pick Disease, Type C1

“…The Sonic Hedgehog (SHH) Signaling pathway (Supplementary Materials Figure S7C), known to be critical for cerebellar patterning [67], is predicted to be increased in lobule X. Additionally, NPC1-specific abnormalities in SHH signaling have been described, leading to a reduction of ciliated cells in the Npc1 −/− mice mouse brain [68]. During development, mRNA levels of Shh are decreased in Npc1 −/− mice and likely results in defective proliferation of granule neurons within the cerebellum, as granule neuron proliferation is sustained by consistent levels of SHH [69]. Granule neuron function is important in the context of NPC1 and Purkinje neuron degeneration because they are the only excitatory neurons within the cerebellum and their parallel fibers within the molecular layer directly activate Purkinje neurons [70].…”

The physiological basis of therapies for cerebellar ataxias

“…A randomized controlled study showed that miglustat, an inhibitor of glucosylceramide synthesis, improves saccadic eye movements, swallowing capacity, and ambulatory capacity [Patterson et al 2007]. Recently, 2-hydroxypropyl-beta-cyclodextrins (HPBCD) has gained attention as a promising candidate [Camargo et al 2001;Nusca et al 2014;Vite et al 2015]. HPBCD increases the solubility of poorly water-soluble compounds such as cholesterol [Vite et al 2015].…”