APOB and fatty liver disease: Mice with hepatocyte-specific deletion of IRE1α exhibit increased hepatic steatosis and decreased plasma lipids under ER stress conditions due to altered expression of key metabolic factors such as C/EBPβ, C/EBPδ, PPARγ, and enzymes involved in triglyceride biosynthesis (31), and IRE1α is also required for the efficient synthesis of ApoB (32).