Dysregulation of cholesterol homeostasis

Thesis

Cholesterol plays a critical role in the health and normal function of every mammalian cell. Cholesterol has multiple cellular functions including maintenance of cell membrane stability and fluidity, steroid hormone and bile acid synthesis, and membrane receptor signaling. As with any critical metabolite, cholesterol is highly regulated. I will detail my research focusing on the two prevalent disorders of cholesterol homeostasis. The first is a disorder of cholesterol biosynthesis, Smith-Lemli-Opitz syndrome (SLOS), and the second a disorder of cholesterol trafficking, Niemann-Pick disease, type C1 (NPC). I have identified a unique cellular phenotypic overlap between these two previously unrelated disorders. Specifically, increasing concentrations of the precursor sterol present in SLOS, 7-dehydrocholesterol, leads to the induction of an NPC-like cellular phenotype. Aspects of the NPC cellular phenotype that can be induced in SLOS fibroblasts include lysosomal storage of unesterified cholesterol, sphingosine, and glycosphingolipids. Also, similar to what is observed in NPC, dysregulation of acidic calcium stores is present in SLOS. Further research indicates that this cellular phenotype extends into both the mouse models of SLOS and the patients. The dysregulation of cholesterol trafficking in SLOS cells likely decreases cellular cholesterol bioavailabilty and thus potentially limits the therapeutic efficacy of dietary cholesterol supplementation in SLOS patients. I also show that treatment of SLOS cells with miglustat, an established therapy for NPC, ameliorates the NPC-like cellular phenotype and thus may have therapeutic benefit in SLOS. The incidence of both SLOS and NPC has been the subject of debate. Thus, using data generated from massively parallel sequencing of the human exome, I demonstrate that the previously predicted incidence of SLOS of 1:40,000 births is likely correct, but call into question the predicted NPC rate of 1:120,000 . In fact, NPC maybe closer to a rate of 1:40,000. The role of oxysterols in the teratogenicity of SLOS and the underlying secondary storage of lipids in the phenotypic presentation of SLOS has been investigated.

Authors: Wassif, C

• Publication date: 2015
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: Cholesterol; NPC; Smith-Lemli-Opitz
• Subjects: Biology (medical sciences)