Abstract 219: Obligatory Role of Nrf2-Dependent Upregulation of Extracellular Superoxide Dismutase in Cardioprotection Afforded by Heme Oxygenase-1 Gene Therapy
Upregulation of HO-1 leads to elevated expression of Ec-SOD, a major defense of cellular armamentarium against excess levels of ROS, which in turn protects against myocardial ischemic injury. However, the mechanism of crosslink between HO-1 and Ec-SOD is unknown. Recently, Nrf2 has been manifested to be a key transcription factor that regulates antioxidant genes as an adaptive response to ROS stress. Thus, we hypothesized that protection afforded by HO-1 gene therapy involves upregulation of Ec-SOD via Nrf2 signaling pathway. Mice received injections in LV anterior wall of Ad5/LacZ (LacZ group) or Ad5/HO-1 (HO-1 group); 3 days later, they were subjected to a 30-min coronary occlusion followed by 4 h of reperfusion. In WT mice 48 h after HO-1 gene transfer (confirmed by HO-1 immunoblotting), cardiac Nrf2 protein content in nuclear fraction increased significantly (2.2-fold vs. LacZ group, P<0.05; Fig⇓), indicating translocation (i.e., activation) of this factor. Sequentially, robust Ec-SOD proteins expressed in myocardium 3 days after HO-1 gene transfer in WT mice (3.4-fold vs. LacZ group, P<0.05; Fig⇓). Conversely, disruption of Nrf2 (Nrf2 KO) completely abrogated both upregulation of Ec-SOD expression (n=4) and infarct-sparing effects of HO-1 gene therapy (Fig⇓). We conclude that 1) Ec-SOD is a downstream effector of HO-1-dependent cardioprotection; 2) activation of Nrf2 as a potential molecular target links the crosstalk between HO-1 and Ec-SOD; and 3) targeted disruption of Nrf2 gene completely extinguishes cardioprotection of HO-1 gene transfer, providing unequivocal molecular genetic attestation for a necessary role of Nrf2 in protection afforded by HO-1 gene therapy.