Abstract P044: Activation of Interferon Regulatory Factor-3 Prolongs Stress-Induced Cardiomyocyte Apoptosis and Decreases Survival Post Myocardial Infarction

Background. The innate immune response is critical in mediating host protection from foreign antigen or stress. It is evident that multiple innate immune pathways also tightly regulate the remodeling process post-myocardial infarction (MI), however it is not clear how this process is mediated. In order to further elucidate the underlying mechanism of this process, we screened both mouse and human post-MI microarray databases and identified a common, significantly upregulated transcription factor of interest, interferon regulatory factor-3 (IRF3). To assess its function in vivo, we tested the hypothesis that activation of IRF3 post-MI coordinates maladaptive repair by promoting cardiomyocyte apoptosis. Methods/Results. We randomly allocated IRF-3 knockout (IRF-3-/-) mice and their wild-type (WT) counterparts to either left anterior descending (LAD) coronary artery ligation or sham operation. Four weeks post-MI, deficiency in IRF3 led to improved survival [88% (44/50) vs. 29% (14/49) in WT, p<0.0001], preserved cardiac function via echocardiography [Fractional Shortening: 37% vs. 22.9% in WT, LVEDD: 5.15mm vs. 5.85mm in WT, LVESD: 4.15mm vs. 5.14mm in WT; p<0.057#x005D;, and attenuated infarct size [27% vs. 44% in WT, p<0.05]. Assessing the stress response 1-week post-MI, we found that NFkB signaling (IKKa, Ikba, p65) as well as pan-ubiquitination of proteins, were both significantly downregulated in the border infarct zone of IRF3-/- mice. These findings were complemented with increased protein and mRNA expression of de-ubiquitinating enzyme A20. Interestingly, in IRF3-/- mice these results were linked with decreased apoptosis (Caspases, TUNEL staining), however with a more specific attenuation of the mitochondrial-specific apoptotic pathway (Bid, Cytochrome C, Caspase9). Conclusions. These data establish a novel link between the innate immune transcription factor IRF3 and maladaptive regulation of cardiomyocyte apoptosis through mitochondrial apoptotic pathway activation. As an acute responder coordinating maladaptive remodeling, IRF3 may prove to be an efficacious therapeutic target to improve outcome following MI.