Hydroxysteroid (17β) Dehydrogenase 7 Activity Is Essential for Fetal de Novo Cholesterol Synthesis and for Neuroectodermal Survival and Cardiovascular Differentiation in Early Mouse Embryos

Hydroxysteroid (17β) dehydrogenase 7 (HSD17B7) has been shown to catalyze the conversion of both estrone to estradiol (17-ketosteroid reductase activity) and zymosterone to zymosterol (3-ketosteroid reductase activity involved in cholesterol biosynthesis) in vitro. To define the metabolic role of the enzyme in vivo, we generated knockout mice deficient in the enzyme activity (HSD17B7KO). The data showed that the lack of HSD17B7 results in a blockage in the de novo cholesterol biosynthesis in mouse embryos in vivo, and HSD17BKO embryos die at embryonic day (E) 10.5. Analysis of neural structures revealed a defect in the development of hemispheres of the front brain with an increased apoptosis in the neuronal tissues. Morphological defects in the cardiovascular system were also observed from E9.5 onward. Mesodermal, endodermal, and hematopoietic cells were all detected by the histological analysis of the visceral yolk sac, whereas no organized vessels were observed in the knockout yolk sac. Immunohistologic...