Ext1, also known as exostosin 1, is an endoplasmic reticulum-resident transmembrane glycosyltransferase. It plays a crucial role in endoplasmic reticulum homeostasis and is involved in the biosynthesis and distribution of heparan sulfate. Mutations in Ext1 are associated with hereditary multiple exostosis (HME), indicating its importance in normal biological development and function. Genetic models such as gene knockout (KO) or conditional knockout (CKO) mouse models can be valuable tools to study its functions [2,3].

In non-alcoholic fatty liver disease (NAFLD), high-fat-diet induced mice showed decreased hepatic Ext1 expression. In vitro experiments with hepatocytes also demonstrated that Ext1 deficiency promoted free fatty acid (FFA)-induced insulin resistance and exacerbated ER stress-triggered autophagy disruption, accelerating NAFLD progression [2]. In membranous lupus nephritis, patients with EXT1-positive staining in kidney biopsies had better kidney function at diagnosis, and the EXT1 status might change during the disease course [1].

In conclusion, Ext1 is essential for maintaining endoplasmic reticulum homeostasis and is involved in multiple biological processes. Studies using KO/CKO mouse models and in vivo experiments on diseases like NAFLD and membranous lupus nephritis have revealed its significant roles in disease development and progression, providing insights into potential therapeutic targets for these diseases.