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Vascular endothelial cells (ECs) play a critical role in angiogenesis and organogenesis, especially in embryonic liver development. Hypoxia-inducible transcription factors (Hifs) are a key trigger of hypoxic signals, a primary stimulus of angiogenesis. The aryl hydrocarbon receptor nuclear translocator (Arnt), also called Hif-1β, serves as an obligate heterodimerization partner of Hif-1α and Hif-2α. Using Cre-Lox technology, the mouseArntgene was specifically disrupted in endothelial cells. The resulting mice, designated ArntΔEC, developed impaired hepatic vasculature, liver necrosis, and degenerative lesions in cardiac myocytes at the late embryonic stage (E16.5-E18.5), leading to approximately 90% neonatal lethality. Low serum glucose, downregulation of glucose transporter-1 and glucose-6-phosphatase mRNA, and hepatocyte proliferation were observed in ArntΔEC embryos. Magnetic resonance imaging on E16.5 embryonic livers revealed that ArntΔEC mice had a significant volume of avascular region. ArntΔEC mice that survived to the adult stage were fertile, showed normal behavioral activity, but had smaller livers with mild portal fibrosis, dilated blood vessels, abnormal collagen accumulation, and remarkable iron deposition. ArntΔEC mice had reduced adiposity, impaired serum lipid homeostasis, and a higher respiratory exchange ratio, indicating they utilized relatively more carbohydrates than their ArntF/F counterparts.In conclusion, endothelial Arnt plays a pivotal role in embryonic liver development. Adult ArntΔEC mice carrying embryonic hepatic defects developed what was possibly an early stage of cirrhosis with consequences of limited oxygen availability and altered lipid metabolism.