LOX-1, an oxidized LDL endothelial receptor, induces CD40/CD40L signaling in human coronary artery endothelial cells

Background - Despite increasing appreciation that atherogenesis involves participation of inflammatory cells, information on mediators of communication between different constituents of atherosclerotic plaque remain incomplete. We examined the role of LOX-1, a receptor for oxidized ( ox) LDL, in the expression of CD40/CD40L in cultured human coronary artery endothelial cells (HCAECs). Methods and Results - We observed that ox-LDL increased the expression of CD40 and CD40L in a concentration ( 10 to 80 mug/mL)- and time (1 to 24 hours)- dependent manner. These effects of ox-LDL were mediated by activation of LOX-1, because pretreatment of HCAECs with a blocking antibody to LOX-1 (JTX92) prevented the expression of CD40 and CD40L in response to ox-LDL (P < 0.01). In parallel experiments, HCAECs were incubated with the protein kinase C (PKC) inhibitor bisindolylmaleimide I, and the cells were then exposed to ox-LDL. Both LOX-1 antibody and the PKC inhibitor inhibited PKC activation in response to ox-LDL (P < 0.01). The PKC inhibitor also blocked the effects of ox-LDL on the expression of CD40 and CD40L (P < 0.01). In additional experiments, we found that it is the PKC alpha, but not PKC beta and PKC gamma, isoform that mediated ox-LDL-induced CD40 and CD40L upregulation. Further experiments showed that upregulation of CD40 mediated induction of proinflammatory genes, because CD40 antibody markedly reduced ox-LDL-induced TNF-alpha generation and P-selectin expression, whereas nonspecific mouse IgG had no effect. Conclusions - These findings indicate that ox-LDL through its receptor LOX-1 triggers the CD40/CD40L signaling pathway that activates the inflammatory reaction in HCAECs. These observations provide novel insight into ox-LDL-mediated inflammation in atherosclerosis.