Hypomorphic ASGR1 Modulates Lipid Homeostasis via SREBPs Network

A population genetic study identified that the asialoglycoprotein receptor 1 (ASGR1) mutation carriers had significantly lower non-HDL-c levels and reduced risks of cardiovascular diseases. However, the mechanism behind this phenomenon remained unclear. Here, we established Asgr1 knockout mice that represented a plasma lipid profile with significantly lower non-HDL-c and triglyceride caused by decreased secretion and increased uptake of VLDL/LDL. These two phenotypes were linked with the decreased expression of microsomal triglyceride transfer protein (MTTP) and proprotein convertase subtilisin/kexin type 9 (PCSK9), two key target genes of the sterol regulatory element-binding proteins (SREBPs). Furthermore, there were less nSREBPs on account of more SREBPs being trapped in endoplasmic reticulum, which was caused by an increased expression of insulin-induced gene 1 (INSIG1), an anchor of SREBPs. Logically, two rescue experiments were conducted in ASGR1 deficient condition. Both INSIG1 knockdown and ASGR1 rescue independently reversed the ASGR1-mutated phenotypes, restoring the SREBP signaling manifested by improved APOB secretion and reduced LDL uptake. Our observation demonstrated a novel axis of ASGR1-INSIG1-SREBPs regulating lipid hemostasis, and hypomorphic manipulation of ASGR1 leads to significant reduction of lipid content via less nSREBPs. It provides multiple potential targets, including ASGR, for lipid-lowering drug development. Overall design: Male mice of WT and Asgr1-/- were fasted overnight and collected the liver tissues. A total of 6 mice's samples were applied to the sequencing, among which 3 were WT, and the other were Asgr1-/-. WT samples were used as control when analyzed the data.