Activation of NFκB and expression of ICAM-1 in ischemic-reperfused canine myocardium

Although redox-sensitive transcription factors, including nuclear factor κB (NFκB) and activator protein-1 (AP-1), have been shown to induce intercellular adhesion molecule-1 (ICAM-1) gene transcription in isolated cells, little is known about their involvement in the regulation of the ICAM-1 gene in vivo during ischemia-reperfusion. Anesthetized closed-chest dogs underwent 90 min coronary artery occlusion, followed by reperfusion for 0, 15, 30, 60, 180, or 360 min. Blood flow (fluorescent or radioactive microspheres), ICAM-1 protein expression (immunohistochemistry), ICAM-1 gene activation (Northern blotting), and nuclear DNA-binding activity of NFκB and AP-1 (electrophoretic mobility shift assays) were assessed in myocardial tissue samples. ICAM-1 protein was expressed constitutively on vascular endothelium, but expression levels decreased markedly during ischemia. Within 15 min reperfusion, endothelial ICAM-1 protein increased, associated with a rapid appearance of ICAM-1 mRNA. Activation of both NFκB and AP-1 occurred following ischemia-reperfusion, but did not coincide temporally with early post-reperfusion ICAM-1 gene induction. NFκB was activated during ischemia, when ICAM-1 mRNA was undetectable, and did not increase further until 60 min reperfusion, well after the increase in ICAM-1 mRNA had begun. Similarly, AP-1 did not increase until 60 min reperfusion. In non-ischemic myocardium, NFκB and AP-1 were both activated, but ICAM-1 mRNA did not appear until 6 h later. By immunohistology, NFκB (p65 subunit) and the c-Fos subunit of AP-1 were localized primarily in vascular endothelium. Reperfusion of ischemic myocardium is associated with very rapid ICAM-1 gene induction in the context of prior NFκB activation, without new activation of NFκB. In non-ischemic myocardium, ICAM-1 transcription begins hours after NFκB is activated. These findings support a role for NFκB in ICAM-1 induction in vivo, but suggest that other processes, such as oxygen-radical generation, may combine with NFκB to trigger an accelerated transcription of ICAM-1 following ischemia-reperfusion.