Antioxidant effect of estrogen on cytomegalovirus-induced gene expression in coronary artery smooth muscle cells

Abstract

Background - Pathogens infecting the arterial wall with resultant intimation may contribute to atherogenesis. Human coronary artery smooth muscle cells (SMCs) infected with human cytomegalovirus (CMV) demonstrate a rapid increase in reactive oxygen species (ROSs), with activation of genes involved in viral replication and inflammation. Because estrogen appears to have antioxidant properties, we wished to determine whether this hormone attenuates SMC responses to CMV infection. Methods and Results - Using confocal microscopy and an intracellular fluorescent dye activated by ROSs, we found that 17β-estradiol (0.1 to 10 nmol/L) and its stereoisomer 17α-estradiol (which has low affinity for the estrogen receptor) dose-dependently inhibited ROS generation in CMV-infected SMCs. These effects were not blocked by the estrogen receptor inhibitor ICI 182,780.3-Methoxyestrone, which lacks the phenolic hydroxyl group, did not interfere with ROS generation. We found that 17β-estradiol and 17α-estradiol, but not 3-methoxyestrone, prevented binding of nuclear factor (NF)-κB to DNA. Furthermore, in SMCs transfected with the reporter constructs 3XκB-CAT, MIEP-CAT, or ICAM-CAT, cotransfection with a CMV-IE72 expression plasmid caused promoter and CAT activation. Treatment with 17β-estradiol and 17α-estradiol, but not 3-methoxyestrone, inhibited CAT activity and, in CMV-infected SMCs, prevented IE72 and ICAM-1 protein expression and cytopathic effects. Conclusions -These findings indicate that estrogen molecules with an A-ring hydroxyl group have estrogen receptor-independent anti-CMV effects at physiological concentrations by inhibiting ROS generation, NF-κB activation, NF-κB-dependent transcription, and viral replication. To the extent that chronic infection of the vascular wall with CMV contributes to atherogenesis, these antioxidant actions of estrogen may be of therapeutic importance.