Abstract 1559: Inflammatory Cytokine Interleukin-1beta Upregulates Novel Junctional Components in the Epicardial Border Zone of Ischemic Hearts
Myocardial function is maintained by 3 of the 4 primary junction types, adherens junctions, desmosomes, and gap junctions. Normal myocardium does not contain tight junctions (TJs) which function as resistivity barriers (e.g. in epithelial cells of skin and gut). Previous work in glia has shown that the proinflammatory cytokine Interleukin 1beta (IL-1β) causes upregulation of Claudin-1 (Cln-1), the primary component of TJs, and produces the de novo formation of TJs in these cells. In ischemic hearts, inflammatory cells and myofibroblasts produce high levels of IL-1b within regions of injury. Thus, we hypothesized that IL-1β in the surviving epicardial border zone (EBZ) of the ischemic and infarcting heart upregulates Cln-1 and forms TJs between myocytes, thus increasing tissue resistivity in the EBZ. In a canine model of myocardial infarction caused by occlusion of the left anterior descending coronary artery (LAD), rtPCR of surviving EBZ tissue showed Cln-1 mRNA upregulation at 1 hr post coronary occlusion while western blot analysis of EBZ indicated that the Cln-1 protein accumulated significantly by 3 hrs post occlusion. Immunohistochemistry and confocal microscopy of tissue sections showed that Cln-1 protein localized to lateral membranes of EBZ myocytes adjacent to but not co-localized with lateralized Cx43 gap junctions. Electron microscopy showed that tight junctions were formed between myocytes in the EBZ, occluding the extracellular space. To determine if IL-1β was involved in this upregulation, we directly perfused active IL-1β into the LAD in the absence of arterial occlusion. Western blot analysis of EBZ 3 hrs post-IL-1β perfusion showed an upregulation of Cln-1, similar to that seen post-coronary occlusion. Pre-infusion of the IL-1β receptor antagonist, IL-1ra, blocked upregulation of Cln-1. These data indicate that signal transduction through activation of IL-1 receptors upregulates the tight junction-associated protein Claudin-1 leading to formation of TJs in the EBZ of the ischemic/infarcting heart that are predicted to increase tissue resistivity. These molecular changes would be expected to contribute to slowed conduction in the EBZ, and the occurrence of arrhythmias.