Cardiac-Specific Inhibition of Kinase Activity in Calcium/Calmodulin-Dependent Protein Kinase Kinase-β Leads to Accelerated Left Ventricular Remodeling and Heart Failure after Transverse Aortic Constriction in Mice

Background

The mechanism of cardiac energy production against sustained pressure overload remains to be elucidated.

Methods and Results

We generated cardiac-specific kinase-dead (kd) calcium/calmodulin-dependent protein kinase kinase-β (CaMKKβ) transgenic (α-MHC CaMKKβ^kd TG) mice using α-myosin heavy chain (α-MHC) promoter. Although CaMKKβ activity was significantly reduced, these mice had normal cardiac function and morphology at baseline. Here, we show that transverse aortic binding (TAC) in α-MHC CaMKKβ^kd TG mice led to accelerated death and left ventricular (LV) dilatation and dysfunction, which was accompanied by significant clinical signs of heart failure. CaMKKβ downstream signaling molecules, including adenosine monophosphate-activated protein kinase (AMPK), were also suppressed in α-MHC CaMKKβ^kd TG mice compared with wild-type (WT) mice. The expression levels of peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α, which is a downstream target of both of CaMKKβ and calcium/calmodulin kinases, were also significantly reduced in α-MHC CaMKKβ^kd TG mice compared with WT mice after TAC. In accordance with these findings, mitochondrial morphogenesis was damaged and creatine phosphate/β-ATP ratios assessed by magnetic resonance spectroscopy were suppressed in α-MHC CaMKKβ^kd TG mice compared with WT mice after TAC.

Conclusions

These data indicate that CaMKKβ exerts protective effects on cardiac adaptive energy pooling against pressure-overload possibly through phosphorylation of AMPK and by upregulation of PGC-1α. Thus, CaMKKβ may be a therapeutic target for the treatment of heart failure.     

G9a/GLP-sensitivity of H3K9me2 Demarcates Two Types of Genomic Compartments

In the nucleus, chromatin is folded into hierarchical architecture that is tightly linked to various nuclear functions. However, the underlying molecular mechanisms that confer these architectures remain incompletely understood. Here, we investigated the functional roles of H3 lysine 9 dimethylation (H3K9me2), one of the abundant histone modifications, in three-dimensional (3D) genome organization. Unlike in mouse embryonic stem cells, inhibition of methyltransferases G9a and GLP in differentiated cells eliminated H3K9me2 predominantly at A-type (active) genomic compartments, and the level of residual H3K9me2 modifications was strongly associated with B-type (inactive) genomic compartments. Furthermore, chemical inhibition of G9a/GLP in mouse hepatocytes led to decreased chromatin-nuclear lamina interactions mainly at G9a/GLP-sensitive regions, increased degree of genomic compartmentalization, and up-regulation of hundreds of genes that were associated with alterations of the 3D chromatin. Collectively, our data demonstrated essential roles of H3K9me2 in 3D genome organization.     

Downregulation of JMJD2a and LSD1 is involved in CK2 inhibition-mediated cellular senescence through the p53-SUV39h1 pathway

Lysine methylation is one of the most important histone modifications that modulate chromatin structure. In the present study, the roles of the histone lysine demethylases JMJD2a and LSD1 in CK2 downregulation-mediated senescence were investigated. The ectopic expression of JMJD2a and LSD1 suppressed the induction of senescence-associated β-galactosidase activity and heterochromatin foci formation as well as the reduction of colony-forming and cell migration ability mediated by CK2 knockdown. CK2 downregulation inhibited JMJD2a and LSD1 expression by activating the mammalian target of rapamycin (mTOR)-ribosomal p70 S6 kinase (p70S6K) pathway. In addition, the down-regulation of JMJD2a and LSD1 was involved in activating the p53-p21^Cip1/WAF1-SUV39h1-trimethylation of the histone H3 Lys9 (H3K9me3) pathway in CK2-downregulated cells. Further, CK2 downregulation-mediated JMJD2a and LSD1 reduction was found to stimulate the dimethylation of Lys370 on p53 (p53K370me2) and nuclear import of SUV39h1. Therefore, this study indicated that CK2 downregulation reduces JMJD2a and LSD1 expression by activating mTOR, resulting in H3K9me3 induction by increasing the p53K370me2-dependent nuclear import of SUV39h1. These results suggest that CK2 is a potential therapeutic target for age-related diseases.     

Cardiac genes show contextual SWI/SNF interactions with distinguishable gene activities

Recent experimental evidence indicates that cardiac and chromatin remodeling are associated with changes in gene expression mediated by Brahma-related gene 1 (Brg1), a member of the large group of SWI/SNF subunits. The second catalytic member of this family is Brahma (Brm), which shares close sequence homology to Brg1. Despite the sequence similarities, these determinants are found in distinct regulatory complexes; however, the precise nature and role of these remodeling enzymes in the failing heart remains unknown. Here we have hypothesized that Brg1 and Brm form distinct complexes in regulating gene expression in an animal model of cardiac hypertrophy. We have identified that the hypertrophic myocardium is characterized by profound morphological changes associated with increased expression of ANP (Nppa), BNP (Nppb) and β-MHC (Myh7) genes, correlating with reduced expression of the α-MHC (Myh6) and SERCA2A (Atp2a2) genes. Histone deacetylase inhibition prevented left ventricular hypertrophy indicating that the re-expression of gene activity can be associated with both contextual and distinct SWI/SNF interactions. We hypothesize that cardiac hypertrophy and the fetal gene expression program are associated with distinguishable binding of Brm and Brg1 on genes present in distinct complexes, suggesting possible independent-regulatory roles.