Histone deacetylase 4 deletion broadly affects cardiac epigenetic repression and regulates transcriptional susceptibility via H3K9 methylation.

Histone deacetylase 4 (HDAC4) is a member of class IIa histone deacetylases (class IIa HDACs) and is believed to possess a low intrinsic deacetylase activity. However, HDAC4 sufficiently represses distinct transcription factors (TFs) such as the myocyte enhancer factor 2 (MEF2). Transcriptional repression by HDAC4 has been suggested to be mediated by the recruitment of other chromatin-modifying enzymes, such as methyltransferases or class I histone deacetylases. However, this concept has not been investigated by an unbiased approach. Therefore, we studied the histone modifications H3K4me3, H3K9ac, H3K27ac, H3K9me2 and H3K27me3 in a genome-wide approach using HDAC4-deficient cardiomyocytes. We identified a general epigenetic shift from a 'repressive' to an 'active' status, characterized by an increase of H3K4me3, H3K9ac and H3K27ac and a decrease of H3K9me2 and H3K27me3. In HDAC4-deficient cardiomyocytes, MEF2 binding sites were considerably overrepresented in upregulated promoter regions of H3K9ac and H3K4me3. For example, we identified the promoter of Adprhl1 as a new genomic target of HDAC4 and MEF2. Overexpression of HDAC4 in cardiomyocytes was able to repress the transcription of the Adprhl1 promoter in the presence of the methyltransferase SUV39H1. On a genome-wide level, the decrease of H3K9 methylation did not change baseline expression but was associated with exercise-induced gene expression. We conclude that HDAC4, on the one hand, associates with activating histone modifications, such as H3K4me3 and H3K9ac. A functional consequence, on the other hand, requires an indirect regulation of H3K9me2. H3K9 hypomethylation in HDAC4 target genes ('first hit') plus a 'second hit' (e.g., exercise) determines the transcriptional response.

HDAC5 catalytic activity suppresses cardiomyocyte oxidative stress and NRF2 target gene expression.

Histone deacetylase 5 (HDAC5) and HDAC9 are class IIa HDACs that function as signal-responsive repressors of the epigenetic program for pathological cardiomyocyte hypertrophy. The conserved deacetylase domains of HDAC5 and HDAC9 are not required for inhibition of cardiac hypertrophy. Thus, the biological function of class IIa HDAC catalytic activity in the heart remains unknown. Here we demonstrate that catalytic activity of HDAC5, but not HDAC9, suppresses mitochondrial reactive oxygen species generation and subsequent induction of NF-E2-related factor 2 (NRF2)-dependent antioxidant gene expression in cardiomyocytes. Treatment of cardiomyocytes with TMP195 or TMP269, which are selective class IIa HDAC inhibitors, or shRNA-mediated knockdown of HDAC5 but not HDAC9 leads to stimulation of NRF2-mediated transcription in a reactive oxygen species-dependent manner. Conversely, ectopic expression of catalytically active HDAC5 decreases cardiomyocyte oxidative stress and represses NRF2 activation. These findings establish a role of the catalytic domain of HDAC5 in the control of cardiomyocyte redox homeostasis and define TMP195 and TMP269 as a novel class of NRF2 activators that function by suppressing the enzymatic activity of an epigenetic regulator.

CaM Kinase II-δ Is Required for Diabetic Hyperglycemia and Retinopathy but Not Nephropathy.

Type 2 diabetes has become a pandemic and leads to late diabetic complications of organs, including kidney and eye. Lowering hyperglycemia is the typical therapeutic goal in clinical medicine. However, hyperglycemia may only be a symptom of diabetes but not the sole cause of late diabetic complications; instead, other diabetes-related alterations could be causative. Here, we studied the role of CaM kinase II-δ (CaMKIIδ), which is known to be activated through diabetic metabolism. CaMKIIδ is expressed ubiquitously and might therefore affect several different organ systems. We crossed diabetic leptin receptor-mutant mice to mice lacking CaMKIIδ globally. Remarkably, CaMKIIδ-deficient diabetic mice did not develop hyperglycemia. As potential underlying mechanisms, we provide evidence for improved insulin sensing with increased glucose transport into skeletal muscle and also reduced hepatic glucose production. Despite normoglycemia, CaMKIIδ-deficient diabetic mice developed the full picture of diabetic nephropathy, but diabetic retinopathy was prevented. We also unmasked a retina-specific gene expression signature that might contribute to CaMKII-dependent retinal diabetic complications. These data challenge the clinical concept of normalizing hyperglycemia in diabetes as a causative treatment strategy for late diabetic complications and call for a more detailed analysis of intracellular metabolic signals in different diabetic organs.

The lipid droplet-associated protein ABHD5 protects the heart through proteolysis of HDAC4.

Catecholamines stimulate the first step of lipolysis by PKA-dependent release of the lipid droplet-associated protein ABHD5 from perilipin to co-activate the lipase ATGL. Here, we unmask a yet unrecognized proteolytic and cardioprotective function of ABHD5. ABHD5 acts in vivo and in vitro as a serine protease cleaving HDAC4. Through the production of an N-terminal polypeptide of HDAC4 (HDAC4-NT), ABHD5 inhibits MEF2-dependent gene expression and thereby controls glucose handling. ABHD5-deficiency leads to neutral lipid storage disease in mice. Cardiac-specific gene therapy of HDAC4-NT does not protect from intra-cardiomyocyte lipid accumulation but strikingly from heart failure, thereby challenging the concept of lipotoxicity-induced heart failure. ABHD5 levels are reduced in failing human hearts and murine transgenic ABHD5 expression protects from pressure-overload induced heart failure. These findings represent a conceptual advance by connecting lipid with glucose metabolism through HDAC4 proteolysis and enable new translational approaches to treat cardiometabolic disease.

CaM Kinase II mediates maladaptive post-infarct remodeling and pro-inflammatory chemoattractant signaling but not acute myocardial ischemia/reperfusion injury.

CaMKII was suggested to mediate ischemic myocardial injury and adverse cardiac remodeling. Here, we investigated the roles of different CaMKII isoforms and splice variants in ischemia/reperfusion (I/R) injury by the use of new genetic CaMKII mouse models. Although CaMKIIδC was upregulated 1 day after I/R injury, cardiac damage 1 day after I/R was neither affected in CaMKIIδ-deficient mice, CaMKIIδ-deficient mice in which the splice variants CaMKIIδB and C were re-expressed, nor in cardiomyocyte-specific CaMKIIδ/γ double knockout mice (DKO). In contrast, 5 weeks after I/R, DKO mice were protected against extensive scar formation and cardiac dysfunction, which was associated with reduced leukocyte infiltration and attenuated expression of members of the chemokine (C-C motif) ligand family, in particular CCL3 (macrophage inflammatory protein-1α, MIP-1α). Intriguingly, CaMKII was sufficient and required to induce CCL3 expression in isolated cardiomyocytes, indicating a cardiomyocyte autonomous effect. We propose that CaMKII-dependent chemoattractant signaling explains the effects on post-I/R remodeling. Taken together, we demonstrate that CaMKII is not critically involved in acute I/R-induced damage but in the process of post-infarct remodeling and inflammatory processes.