Abstract 17196: Genetic and Acquired DHCR7 Deficiency Upregulates 7β-hydroxycholesterol to Drive Endothelial Apoptosis and Pulmonary Hypertension

Abstract

Introduction: Pulmonary hypertension (PH) is a fatal disease without a cure, in which endothelial dysfunction drives pathologic remodeling of the pulmonary vasculature. Individuals with Smith-Lemli-Opitz syndrome (SLOS) develop PH, but the underlying mechanisms remain undefined. SLOS is an autosomal recessive disorder of cholesterol synthesis, resulting from loss-of-function mutations in 7-dehydrocholesterol reductase (DHCR7)-the terminal enzyme in the de novo synthesis of cholesterol- that leads to accumulation of 7-dehydrocholesterol (7-DHC) and cytotoxic oxysterol species. The role of DHCR7 in PH, however, is unknown. Hypothesis: Elevated cytotoxic oxysterols resulting from genetic or acquired DHCR7 deficiency promotes endothelial dysfunction and the development of PH. Methods & Results: DHCR7 mRNA and protein expression was decreased in pulmonary artery endothelial cells (ECs) in cellular (P=0.0089), rodent, and human PH models, mirroring DHCR7 reduction in SLOS. Both genetic loss of DHCR7 and hypoxia promoted a global shutdown of de novo cholesterol synthesis, resulting in an accumulation of cholesterol intermediates and increased derivative oxysterols. Specifically, 7β-hydroxycholesterol (7β-HC) was elevated in DHCR7-deficient ECs (P<0.0001), and 7β-HC drove endothelial apoptosis (P<0.0001) via downregulation of insulin-like growth factor 1 (IGF1) in ECs (fold change=0.101 ± 0.034, FDR=6.65E-11). Conversely, overexpression of DHCR7 upregulated IGF1 expression (P<0.0007), and IGF1 delivery reversed apoptosis (P<0.0001). Correspondingly, ECs derived from SLOS patient stem cells with DHCR7 mutations (p.T93M/c.964-1G>C) exhibited IGF1-dependent apoptosis. Finally, EC-specific DHCR7 deletion in chronically hypoxic mice induced more severe PH in vivo (right ventricular systolic pressure 36.4 mmHg vs. 30.8 mmHg, P<0.0130). Conclusions: Resulting either from hypoxic or genetic causes, DHCR7 deficiency promoted EC apoptosis and PH via 7β-HC accumulation and subsequent IGF1 downregulation. Our work is the first to define an oxysterol-dependent mechanism underlying the link between genetic and acquired DHCR7 deficiency and PH.