291-OR: CREG1 Regulates Hepatic Insulin Sensitivity and Insulin Receptor Trafficking

CREG1 is a small glycoprotein in the endosomal-lysosomal system involved in endocytic trafficking. It contains 3 N-linked glycosylation sites and is highly expressed in the liver. To elucidate its physiological functions, we generated Creg1fl/fl mice using CRISPR technology. Whole-body and hepatocyte-specific deletion of Creg1 was achieved by crossing Creg1fl/fl with UBC-cre-ERT2 and Albumin-cre mice, respectively. Both knockout mice developed elevated glycemia, glucose intolerance, and resistance to the blood glucose-lowering effect of insulin. Loss of hepatic CREG1 also aggravated high-fat diet-induced insulin resistance and hyperinsulinemia. This is likely caused by impaired insulin receptor (IR) trafficking because IR expression on the hepatocyte surface was significant reduced in hepatocyte specific Creg1 knockout mice. In in vitro studies using cultured hepatocytes, CREG1 overexpression increased IR recycling to the cell surface and enhanced insulin signaling, whereas its knockdown had the opposite effect. These findings indicate a cell autonomous role of CREG1 in hepatocyte IR trafficking and insulin signaling. Furthermore, SNP database survey identified 3 missense mutations of CREG1 at the N216 glycosylation site (N216I, N216K, and N216Y). When overexpressed in human hepatocytes, the N216I mutant inhibited insulin signaling in a dominant negative fashion. Taken together, these results suggest CREG1 regulates hepatic insulin sensitivity and signaling likely through its effect on IR trafficking. CREG1 glycosylation at N216 may be required for its function in these processes.