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Cholesterol serves as a building material for cellular membranes and plays an important role in cellular metabolism. The brain relies on its own cholesterol biosynthesis, which starts during embryonic development. Cholesterol is synthesized from two immediate precursors, desmosterol and 7-dehydrocholesterol (7-DHC). Mutations in the DHCR24 enzyme, which converts desmosterol into cholesterol, lead to desmosterolosis, an autosomal recessive developmental disorder. In this study, we assessed the brain content of desmosterol, 7-DHC, and cholesterol from development to adulthood, and analyzed the biochemical, molecular, and anatomical consequences of Dhcr24 mutations on the sterol profile in a mouse model of desmosterolosis and heterozygous Dhcr24 +/- carriers. Our HPLC-MS/MS studies revealed that by P0 desmosterol almost entirely replaced cholesterol in the Dhcr24-KO brain. The greatly elevated desmosterol levels were also present in the Dhcr24-Het brains irrespective of maternal genotype, persisting into adulthood. Furthermore, Dhcr24-KO mice brains showed complex changes in expression of lipid and sterol transcripts, nuclear receptors, and synaptic plasticity transcripts. Cultured Dhcr24-KO neurons showed increased arborization, which was also present in the Dhcr24-KO mouse brains. Finally, we observed a shared pathophysiological mechanism between the mouse models of desmosterolosis and Smith-Lemli-Opitz syndrome (a genetic disorder of conversion of 7-DHC to cholesterol)., (© 2019 SSIEM.)

7-Dehydrocholesterol (7-DHC) accumulates in tissues and fluids of patients with Smith-Lemli-Opitz syndrome (SLOS), which is caused by mutations in the gene encoding 3β-hydroxysterol-Δ(7)-reductase (DHCR7). We recently reported that 7-DHC is the most reactive lipid molecule toward free radical oxidation (lipid peroxidation) and 14 oxysterols have been identified as products of oxidation of 7-DHC in solution. As the high oxidizability of 7-DHC may lead to systemic oxidative stress in SLOS patients, we report here lipid biomarkers of oxidative stress in a Dhcr7-KO mouse model of SLOS, including oxysterols, isoprostanes (IsoPs), and neuroprostanes (NeuroPs) that are formed from the oxidation of 7-DHC, arachidonic acid and docosahexaenoic acid, respectively. In addition to a previously described oxysterol, 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), we provide evidence for the chemical structures of three new oxysterols in the brain and/or liver tissue of Dhcr7-KO mice, two of which were quantified. We find that levels of IsoPs and NeuroPs are also elevated in brain and/or liver tissues of Dhcr7-KO mice relative to matching WT mice. While IsoPs and NeuroPs have been established as a reliable measurement of lipid peroxidation and oxidative stress in vivo, we show that in this genetic SLOS mouse model, 7-DHC-derived oxysterols are present at much higher levels than IsoPs and NeuroPs and thus are better markers of lipid oxidation and related oxidative stress.