1683-P: High-Fat Diet Downregulates CREG1 in the Liver via DNA Methylation

CREG1 is an endosomal-lysosomal protein which is highly expressed in the liver. Hepatocyte-specific deletion of Creg1 in mice causes insulin resistance and elevated glycemia. To test if CREG1 is nutritionally regulated, we fed mice for 10 weeks with a high-fat diet (HFD) which progressively downregulated CREG1 in the liver at both protein and mRNA levels. The CREG1 expression was restored after switch back to a standard chow diet for two weeks. The diet-induced CREG1 changes negatively correlated with blood glucose levels. Sequence analysis revealed enrichment of CpG islands in exon 1 of both human and mouse CREG1 genes. To test if methylation of these CpG islands contributes to HFD-induced CREG1 reduction, we fed mice with a HFD for 10 weeks and treated them with the DNA methyltransferase inhibitor 5-aza-deoxycytidine, which reversed HFD-induced CREG1 downregulation in the liver. At the cellular level, overload of cultured human hepatocytes with fatty acids reduced CREG1 expression, and this was reversed by inhibiting DNA methylation. Furthermore, removal of all CpG islands in the first exon with sense mutations abolished lipid overload-induced CREG1 downregulation. These results suggest that HFD downregulates CREG1 via DNA methylation of the CpG islands in the first exon. It would be interesting to test if CREG1 reduction mediates HFD-induced insulin resistance.