Effect of Oxidized LDL on the Amount of Insulin Receptor and Gi-proteins in the Caveolae of Bovine Aortic Endothelial Cells (BAEC)

Jeon, Sung Yoon; Son, Hyun Shik; Lee, Jung Min; Moon, Sung Dae; Yoon, Kun Ho; Cha, Bong Yun; Lee, Kwang Woo; Son, Ho Young; Kang, Sung Koo

Abstract

BACKGROUND AND AIMS: Oxidized LDL (ox-LDL) may induce endothelial cell dysfunction and suggested to have an association with atherosclerosis or insulin resistance. Several studies have shown that ox-LDL inhibits signaling pathways mediated by inhibitory GTP-binding proteins (Gi-proteins). G-protein coupled receptors (GPCRs) can be internalized via caveolae. Caveolae are small flask-shaped invaginations of the plasma membrane, characterized by high levels of cholesterol and glycosphingolipids and also by the presence of caveolin, a 20-24 kDa integral membrane protein. G-proteins are enriched within caveolae membranes, where caveolin-1 directly interacts with the -subunits of G-proteins. It is reported that functional changes of G-proteins such as mutational or pharmacological activation of G-proteins affect direct interaction between G-proteins and caveolin-1. Thus, we investigated the effect of ox-LDL on the change of the amount of insulin receptor and Gi proteins in the caveolae. MATERIALS AND METHODS: ox-LDL was prepared by exposing samples of native LDL (n-LDL) to CuSO4 for 24 hours. Caveolae were extracted after treating BAECs at several concentrations of ox-LDL (10, 50, 100 g/mL) for various durations (0-48 hr), and we investigated the changes of the amount of caveolin-1, Gi -proteins and insulin receptor using immunoblot.
RESULTS
While the amount of caveolin-1 was decreased, the amount of insulin receptor, Gi 2 and Gi 3 proteins in caveolae were also decreased after treatment of ox-LDL on the BAECs (insulin receptor: 66%; Gi 2 protein: 33%; Gi 3 protein: 66%, p<0.05). The amount of caveolin-1 was increased for the first 6 hours and then decreased, however, the amount of Gi -proteins and insulin receptor were vice versa during 48 hours incubation.
CONCLUSION
These results indicate that ox-LDL can affect the change of the amount of insulin receptor and Gi-proteins in caveolae and it may induce endothelial cell dysfunction.