The impact of phosphodiesterase 2 on cardiac epigenetic regulation in diabetic cardiomyopathy

Cardiovascular diseases are the most prevalent cause of morbidity and mortality among patients with diabetes. The metabolic disease leads to abnormal energy metabolism, oxidative stress, cardiac inflammation, fibrosis and altered Ca²⁺ signaling in the heart resulting in left ventricular dysfunction, arrhythmia and sudden cardiac death (SCD). Epigenetic control mechanisms play an important role in tissue homeostasis. Posttranslational modifications of histones like histone phosphorylation or acetylation contribute to the regulation of gene expression. Epigenetic mechanisms were shown to be involved in heart failure (HF) and arrhythmia pathogenesis. Recently, we revealed significant higher levels of phosphorylated histone 3 in patients with endstage HF as well as upon β-AR stimulation in experimental models. We showed that β-adrenergic stimulation resulted in the elevation of H3 phosphorylation, which was mediated by Ca²⁺/calmodulin-dependent kinase II (CaMKII) and prevented by pharmacological β-AR blockade. Other studies demonstrated that the phosphorylation of H3 by nuclear CaMKII is associated with cardiac hypertrophy. CaMKII-dependent phosphorylation of class IIa histone deacetylase 4 (HDAC4) was shown to prevent its nuclear transport mediating the depression of HDAC target genes and hypertrophic growth. Phosphodiesterases (PDEs) are hydrolyzing enzymes that degrade the second messengers cAMP and cGMP. In contrast to other cardiac PDEs, PDE2 is upregulated in human heart failure (HF) and in models of experimental diabetic cardiomyopathy. A key mechanism involved in HF is the permanent stimulation of β-adrenoreceptors (β-AR) mediating high levels of cAMP and chronic activation of downstream-kinases like CaMKII.

Here, we aim to investigate the impact of PDE2 on epigenetic mechanisms in diabetic cardiomyopathy using cardiac specific PDE2 overexpression (OE) or knockout (KO) mouse models. Our first results indicate an important role of PDE2 in these CaMKII-mediated H3 modifications. Western blot analysis revealed that cardiac specific PDE2 OE resulted in significant reduction of CaMKII phosphorylation and H3 phosphorylation. To evaluate the role of PDE2 on CaMKII-dependent epigenetic mechanisms in heart failure, we will further detect levels of histone phosphorylation and acetylation in cardiac specific PDE2 KO and control mice developing diabetic cardiomyopathy using western blot with site-specific antibodies or ELISA-based quantification kits. We will analyze subcellular localizations of HDACs using immunofluorescence staining. In PDE2A KO mice, we expect increased levels of H3 phosphorylation mediating changes in cardiac gene expression. The epigenetic regulation of the cardiac excitation genes and its contribution to arrhythmia development is largely unknown. Therefore, we will quantify expression levels of selected genes in diabetic cardiomyopathy of PDE2 KO and control mice.

As a proof-of-concept, we will test our hypothesis that augmenting myocardial PDE2 activity via natriuretic peptides is cardioprotective, reduces lethal arrhythmia in diabetic heart disease and may serve as a new therapeutic antiarrhythmic strategy.

Publications:

Cellular Mechanisms of the Anti-Arrhythmic Effect of Cardiac PDE2 Overexpression.  M. Wagner, M.S. Sadek, N. Dybkova, F.E. Mason, J. Klehr, R. Firneburg, E. Cachorro, K. Richter, E. Klapproth, S.R. Kuenzel, K. Lorenz, J. Heijman, D. Dobrev, A. El-Armouche, S. Sossalla, S. Kämmerer. Int J Mol Sci. 2021;22(9):4816.