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Background: Cardiac kinases play a critical role in the development of heart failure, and represent potential tractable therapeutic targets. However, only a very small fraction of the cardiac kinome has been investigated. To identify novel cardiac kinases involved in heart failure, we used an integrated transcriptomics and bioinformatics analysis and identified Homeodomain-Interacting Protein Kinase 2 (HIPK2) as a novel candidate kinase. The role of HIPK2 in cardiac biology is unknown.Methods: We used the Expression2Kinase algorithm for the screening of kinase targets. To determine the role of HIPK2 in the heart, we generated cardiomyocyte (CM)-specific HIPK2 knockout and heterozygous mice. Heart function was examined by echocardiography, and related cellular and molecular mechanisms were examined. Adeno-associated virus serotype 9 carrying cardiac-specific constitutively active MEK1 (TnT-MEK1-CA) was administrated to rescue cardiac dysfunction in CM-HIPK2 knockout mice.Results: To our knowledge, this is the first study to define the role of HIPK2 in cardiac biology. Using multiple HIPK2 loss-of-function mouse models, we demonstrated that reduction of HIPK2 in CMs leads to cardiac dysfunction, suggesting a causal role in heart failure. It is important to note that cardiac dysfunction in HIPK2 knockout mice developed with advancing age, but not during development. In addition, CM-HIPK2 knockout mice and CM-HIPK2 heterozygous mice exhibited a gene dose-response relationship of CM-HIPK2 on heart function. HIPK2 expression in the heart was significantly reduced in human end-stage ischemic cardiomyopathy in comparison to nonfailing myocardium, suggesting a clinical relevance of HIPK2 in cardiac biology. In vitro studies with neonatal rat ventricular CMscorroborated the in vivo findings. Specifically, adenovirus-mediated overexpression of HIPK2 suppressed the expression of heart failure markers, NPPA and NPPB, at basal condition and abolished phenylephrine-induced pathological gene expression. An array of mechanistic studies revealed impaired extracellular signal-regulated kinase 1/2 signaling in HIPK2-deficient hearts. An in vivo rescue experiment with adeno-associated virus serotype 9 TnT-MEK1-CA nearly abolished the detrimental phenotype of knockout mice, suggesting that impaired extracellular signal-regulated kinase signaling mediated apoptosis as the key factor driving the detrimental phenotype in CM-HIPK2 knockout mice hearts.Conclusions: Taken together, these findings suggest that CM-HIPK2 is required to maintain normal cardiac function via extracellular signal-regulated kinase signaling. [ABSTRACT FROM AUTHOR]

Rationale: Cardiac myocyte-specific deletion of either glycogen synthase kinase (GSK)-3α and GSK-3β leads to cardiac protection after myocardial infarction, suggesting that deletion of both isoforms may provide synergistic protection. This is an important consideration because of the fact that all GSK-3-targeted drugs, including the drugs already in clinical trial target both isoforms of GSK-3, and none are isoform specific., Objective: To identify the consequences of combined deletion of cardiac myocyte GSK-3α and GSK-3β in heart function., Methods and Results: We generated tamoxifen-inducible cardiac myocyte-specific mice lacking both GSK-3 isoforms (double knockout). We unexpectedly found that cardiac myocyte GSK-3 is essential for cardiac homeostasis and overall survival. Serial echocardiographic analysis reveals that within 2 weeks of tamoxifen treatment, double-knockout hearts leads to excessive dilatative remodeling and ventricular dysfunction. Further experimentation with isolated adult cardiac myocytes and fibroblasts from double-knockout implicated cardiac myocytes intrinsic factors responsible for observed phenotype. Mechanistically, loss of GSK-3 in adult cardiac myocytes resulted in induction of mitotic catastrophe, a previously unreported event in cardiac myocytes. Double-knockout cardiac myocytes showed cell cycle progression resulting in increased DNA content and multinucleation. However, increased cell cycle activity was rivaled by marked activation of DNA damage, cell cycle checkpoint activation, and mitotic catastrophe-induced apoptotic cell death. Importantly, mitotic catastrophe was also confirmed in isolated adult cardiac myocytes., Conclusions: Together, our findings suggest that cardiac myocyte GSK-3 is required to maintain normal cardiac homeostasis, and its loss is incompatible with life because of cell cycle dysregulation that ultimately results in a severe fatal dilated cardiomyopathy., (© 2016 American Heart Association, Inc.)

Background: Myocardial infarction-induced remodeling includes chamber dilatation, contractile dysfunction, and fibrosis. Of these, fibrosis is the least understood. After myocardial infarction, activated cardiac fibroblasts deposit extracellular matrix. Current therapies to prevent fibrosis are inadequate, and new molecular targets are needed., Methods and Results: Herein we report that glycogen synthase kinase-3β (GSK-3β) is phosphorylated (inhibited) in fibrotic tissues from ischemic human and mouse heart. Using 2 fibroblast-specific GSK-3β knockout mouse models, we show that deletion of GSK-3β in cardiac fibroblasts leads to fibrogenesis, left ventricular dysfunction, and excessive scarring in the ischemic heart. Deletion of GSK-3β induces a profibrotic myofibroblast phenotype in isolated cardiac fibroblasts, in post-myocardial infarction hearts, and in mouse embryonic fibroblasts deleted for GSK-3β. Mechanistically, GSK-3β inhibits profibrotic transforming growth factor-β1/SMAD-3 signaling via interactions with SMAD-3. Moreover, deletion of GSK-3β resulted in the significant increase of SMAD-3 transcriptional activity. This pathway is central to the pathology because a small-molecule inhibitor of SMAD-3 largely prevented fibrosis and limited left ventricular remodeling., Conclusions: These studies support targeting GSK-3β in myocardial fibrotic disorders and establish critical roles of cardiac fibroblasts in remodeling and ventricular dysfunction., (© 2014 American Heart Association, Inc.)