Megakaryocytic Leukemia 1 (MKL1) Bridges Epigenetic Activation of NADPH Oxidase in Macrophages to Cardiac Ischemia-Reperfusion Injury [Original Research Article]

Background—Excessive accumulation of reactive oxygen species (ROS), catalyzed by the NADPH oxidases (NOX), is involved in the pathogenesis of ischemia-reperfusion (I/R) injury. The underlying epigenetic mechanism remains elusive.Methods—We evaluated the potential role of megakaryocytic leukemia 1, or MKL1, as a bridge linking epigenetic activation of NOX to ROS production and cardiac ischemia-reperfusion injury.Results—Following I/R injury, MKL1 deficient (KO) mice exhibited smaller myocardial infarction along with improved heart function compared to wild type (WT) littermates. Similarly, pharmaceutical inhibition of MKL1 with CCG-1423 also attenuated myocardial infarction and improved heart function in mice. Amelioration of I/R injury as a result of MKL1 deletion or inhibition was accompanied by reduced ROS in vivo and in vitro. In response to I/R, MKL1 levels were specifically elevated in macrophages, but not in cardiomyocytes, in the heart. Of note, macrophage-specific deletion (MφcKO), instead of cardiomyocyte-restricted ablation (CMcKO), of MKL1 in mice led to similar improvements of infarct size, heart function, and myocardial ROS generation. Reporter assay and ChIP assay revealed that MKL1 directly bound to the promoters of NADPH oxidase (NOX) genes to activate NOX transcription. Mechanistically, MKL1 recruited the histone acetyltransferase MOF to modify the chromatin structure surrounding the NOX promoters. Knockdown of MOF in macrophages blocked hyoxia/re-oxygenation-induced NOX transactivation and ROS accumulation. Of importance, pharmaceutical inhibition of MOF with MG-149 significantly down-regulated NOX1/NOX4 expression, dampened ROS production, and normalized myocardial function in mice exposed to I/R injury. Finally, administration of a specific NOX1/4 inhibitor GKT137831 dampened ROS generation and rescued heart function following I/R in mice.Conclusions—Our data delineate an MKL1-MOF-NOX axis in macrophages that contributes to I/R injury and as such have provided novel therapeutic targets in the treatment of ischemic heart disease.