Abstract 113: Klf5 and Ppara Expression is Increased at the Early Stage and Reduced at the Late Stage of Myocardial Ischemia/Reperfusion in Mice

Abstract

Inhibition of cardiac fatty acid oxidation (FAO) is considered beneficial after ischemia reperfusion (I/R). Krüppel-like factors (KLF) have an important role in metabolism. In a model of cardiac energetic deficiency (LPS-treated mice), in silico promoter analysis and whole genome array analysis indicated cardiac KLF5 as important regulator of Ppara . Gene expression analysis in human ventricular myocytes (AC16) treated with Ad-Klf5 followed by ChIP analysis confirmed that KLF5 is a positive transcriptional regulator of Ppara . Mice with cardiomyocyte-specific Klf5 ablation (αMHC-Klf5 -/- ) that we made had reduced cardiac Ppara expression and other FAO-related genes. The role of PPARα activation in I/R injury is unclear as both beneficial and detrimental effects have been reported. We aimed to gain insight in the effects of KLF5 and PPARα on acute I/R injury. To mimic I/R in vitro , AC16 cells were subjected to hypoxia (9.5 h) followed by short (1h) or prolonged (14h) normoxia. Ppara expression was initially (1h) increased (p<0.05) and then (14 h) decreased (p<0.05). Klf5 expression pattern showed a trend of similar changes . Infarction was performed by 30 min of left coronary artery occlusion followed by 2 or 24 hours of reperfusion in wild type mice. I/R resulted in a trend for an initial increase in Klf5 (2-fold, p=0.05), Ppara (3-fold, p=0.08), and Pdk4 (8-fold, p<0.01) mRNA at 2h post-surgery. Klf5 (2-fold; p<0.01) and Ppara (9-fold; p<0.05) expression were decreased 24h post-surgery. Consistent with Ppara changes, there was a 2-fold decrease of Cpt1 (p<0.01) and Vlcad (p<0.01) and a trend for decreased Aox (2-fold), Lcad (2-fold), and Pdk4 (6-fold) compared to sham. Echocardiography indicated normal cardiac function after 24h post-surgery. Despite reduced FAO, αMHC-Klf5 -/- mice subjected to I/R had a marked increase in mortality; 40% (4 of 10) of αMHC-Klf5 -/- mice died within the first 24h of reperfusion while no mortality was observed in 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 . Increased mortality for αMHC-Klf5 -/- mice with I/R injury suggests that the initial increase may be an adaptive response that is critical for survival.