Abstract P499: Histone H4K20 Trimethylation Is Differentially Regulated In Heart Disease

It has been well established that many cardiac pathologies result from dynamic changes in gene expression and conversely that modulating key epigenetic factors in murine models is capable of preventing or abrogating ischemic injury and pathological remodeling. One epigenetic mechanism is the post-translational modification of histones, which are reversibly methylated on lysine (K) residues and can accept up to three methyl groups (Me1, Me2 and Me3). In the heart, significant changes in global levels of histone H3K4Me3 and H3K9Me3 have been previously reported to be upregulated and downregulated, respectively, during hypertrophy and failure in mice. However, the majority of post-translational modifications on histones have never been examined to quantify global abundance in the heart during disease. In particular, histone H4K20Me3 is important in heterochromatin formation and gene repression in non-cardiac cells but has never been evaluated in the heart. Therefore, we utilized cardiac tissue from three animal models of cardiac stress and employed western blotting and mass spectrometry to quantify the global abundance of total histone H4 and H4K20 methylation. We specifically evaluated tissue from mice subjected to LAD ligation, transverse aortic banding and isoproterenol infusion (via mini-osmotic pump). In addition, we also utilized primary neonatal cardiomyocytes treated with the hypertrophic agonist phenylephrine to quantify H4K20 methylation. Our data show that global levels of histone H4K20Me3 are differentially regulated in some models of cardiac dysfunction, but not all (i.e. isoproterenol infusion). In addition, we measured the abundance of histone methyltransferases and demethylases (via western blotting and qPCR) which are responsible for adding or removing this methyl mark in mouse cardiac tissue, and compared this to published data from human heart failure patients. These analyses allowed us to identify two enzymes, the methyltransferase Smyd5 and demethylase KDM7B, which are also differentially expressed in cardiac tissue during disease. Together these results are the first analysis of histone H4K20 methylation in the heart and suggest a novel role for this methylation site in the pathophysiology of cardiovascular disease.