Abstract 321: LRP6 Regulates LDL Receptor Internalization and LDL Uptake

Abstract

Genetic variations in LRP6 gene are associated with high serum LDL cholesterol levels and atherosclerosis. We examined the role of LRP6 in LDL receptor (LDLR) mediated LDL uptake. LDL uptake was increased when LRP6 was overexpressed and reduced when it was knocked down in LDLR deficient CHO cells. Interestingly, LRP6 knockdown in wildtype CHO cells resulted in a much greater decline in LDL uptake compared to ldlA7 cells. This finding suggested interaction between LRP6 and other proteins involved in LDL uptake. Strikingly, LDL receptor internalization was severely diminished when LRP6 was knocked down and was restored after LRP6 was reintroduced. Further investigations showed that LRP6 forms a complex with the LDL endocytic machinery including LDLR, clathrin and ARH and undergoes endocytosis after stimulation with LDL. LDLR internalization was defective in skin fibroblasts of the LRP6 R611C mutation carriers. LDLR and LRP6 internalizations as well as LDL uptake were significantly impaired in wildtype CHO cells expressing LRP6 R611C mutation(figa,b). These studies introduce LRP6 as a critical modulator of receptor-mediated LDL endocytosis and identify a mechanism by which variation in LRP6 may contribute to high serum LDL levels and atherosclerosis.