Background: Recently, CD40 ligand (CD40L) and its receptor CD40 have been implicated in atherosclerosis. Clinical data showed that elevated CD40L levels are associated with a high risk of cardiovascular events. The aim of this study was to investigate whether CD40L could affect the expression of its membrane receptor CD40 as a feedback mechanism by which CD40L could enhance its functions in human coronary artery endothelial cells (HCAECs).
Methods: The HCAECs were treated with human soluble CD40L, and the messenger RNA (mRNA) and protein levels of CD40 were determined by real-time polymerase chain reaction and Western blot analysis, respectively. The specific effect of CD40L was confirmed by a blocking experiment with antibody against CD40L. Involvements of oxidative stress and mitogen-activated protein kinases (MAPKs) were also studied with antioxidant seleno-L-methionine (SeMet) and MAPK inhibitors such as extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor.
Results: When HCAECs were cultured with CD40L (5 microg/mL) for 24 hours, CD40 mRNA levels were increased by 79% compared with controls (P < .05). Similarly, Western blot analysis showed an 80% increase in CD40 protein levels (P < .05). The CD40L-induced increase in CD40 mRNA levels were blocked specifically by anti-CD40L antibody. Antioxidant SeMet and specific ERK1/2 inhibitor (PD98059) also effectively blocked CD40L-induced CD40 mRNA increase.
Conclusions: These data demonstrate that clinically relevant concentration of CD40L increased the expression of its receptor CD40 in HCAECs. The CD40L-induced upregulation of CD40 may be mediated by oxidative stress and ERK1/2 activation. This study suggests a new mechanism by which CD40L could enhance its biologic functions in the vascular system and contribute to endothelial dysfunction and vascular disease.