Abstract 301: Initial Increase of Klf5 and Ppara Expression After Myocardial Ischemia/Reperfusion in Mice Appears to be Critical for Survival

Abstract

Krüppel-like factors (KLF) have important roles in metabolism. We previously found that KLF5 is a positive transcriptional regulator of peroxisome proliferator-activated receptor α ( Ppara) , a central regulator of cardiac fatty acid oxidation (FAO). Mice with cardiomyocyte-specific Klf5 ablation ( α MHC-Klf5 -/- ) had reduced cardiac Ppara expression and FAO. At age 6-12 months these mice develop distinct cardiac dysfunction. The role of PPARα activation in I/R injury is unclear as both beneficial and detrimental effects have been reported. We aimed to study if Ppara expression changes during I/R are driven by KLF5 and explore its protective or detrimental role. Wild type mice were subjected to in vivo I/R or sham surgery. I/R resulted in an initial increase in Ppara , and its target gene pyruvate dehydrogenase kinase 4 ( Pdk4) mRNA after 2h reperfusion, followed by decreased expression after 24h reperfusion. The Ppara expression is associated with parallel changes in cardiac Klf5 mRNA expression. Concurrent, there was a decrease of cardiac FAO-related genes carnitine palmitoyl-transferase 1β ( Cpt1b), very long chain acyl-CoA dehydrogenase (Vlcad), and acyl-CoA oxidase ( Aox) in mice with I/R. To define the cell type causing the temporal changes in Klf5 and Ppara after I/R we isolated primary cardiomyocytes and fibroblasts. Our data suggest a similar effect in primary isolated cardiomyocytes only. Klf5 mRNA expression is increased after 2 hour hypoxia and normalized after 4 hour re-oxygenation in cardiomyocytes, whereas there are no changes after hypoxia/normoxia in fibroblasts. To assess the importance of cardiomyocyte KLF5 in I/R we used α MHC-Klf5 -/- mice. Interestingly, despite reduced FAO, 7 month old αMHC-Klf5 -/- mice subjected to I/R had a marked increase in mortality; 4 of 7 αMHC-Klf5 -/- mice died within the first 24h of reperfusion while no mortality was observed in age-matched wild type mice that underwent I/R. In conclusion, I/R is associated with an increase in Klf5 and Ppara in the first hours of reperfusion followed by a decrease in Klf5 and Ppara , likely accounted for by cardiomyocytes. Increased mortality for α MHC-Klf5 -/- mice with I/R injury suggests that the initial increase may be an adaptive response that is critical for survival.