A strategy for restoring cholesterol-dependent Shh signalling in a lipid storage neurodevelopmental disorder

Loss-of-function mutations of Niemann Pick C1 intracellular cholesterol transporter (NPC1) cause a rare genetic condition (NPC1 disease, NPCD) in which cholesterol and sphingolipids are entrapped in late endosomes/lysosomes. This lipid imbalance disrupts membrane microdomain organization, impairs autophagic flux, and interferes with key signalling pathways, including the Sonic Hedgehog (Shh) cascade, which is essential for neuronal differentiation, glial maturation, ciliogenesis, and synaptic integration. Here, we report that the olfactory bulb's (OB) lifetime supply of neurons derived from lateral ventricle progenitors is compromised by deficient Shh. Shh levels were significantly lower within the OB and along the rostral migratory stream, which was associated with glomerular structural abnormalities, altered periglomerular interneuron production, decreased granule cell stimulus-response dynamics, and fine odor discrimination. We investigated whether modulating sphingolipid metabolism could improve cellular abnormalities associated with impaired Shh signalling by reestablishing the availability of bioactive cholesterol. Myriocin, a serine palmitoyl-transferase inhibitor, decreases the production of sphingomyelin and is expected to raise the metabolically active cholesterol needed for the covalent modification of Shh and Smoothened. Myriocin treatment of Npc1⁻/⁻ mouse embryonic fibroblasts (MEFs) greatly rescued typical NPCD characteristics, including shortened primary cilia, increased p62 and LC3bII/I ratio, and cholesterol accumulation. Additionally, myriocin boosted Gli2's ciliary localization and largely restored Gli1's reduced expression, suggesting improved Shh pathway responsiveness. Overall, our findings uncover a mechanistic link between cholesterol dyshomeostasis, autophagy, ciliary defects, and Shh signalling failure in NPCD and highlight sphingomyelin metabolism as a promising therapeutic target.