Cardiomyocyte HIPK2 Maintains Basal Cardiac Function via ERK Signaling

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 employed 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-specific HIPK2 knockout (CM-KO) and heterozygous (CM-Het) mice. Heart function was examined by echocardiography and related cellular and molecular mechanisms were examined. Adeno-associated virus serotype 9 (AAV9) carrying cardiac-specific constitutively active MEK1 (TnT-MEK1-CA) were administrated to rescue cardiac dysfunction in CM-KOs. 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 cardiomyocytes leads to cardiac dysfunction—suggesting a causal role in heart failure. Importantly, cardiac dysfunction in HIPK2 KOs developed with advancing age, but not during development. In addition, CM-KO and CM-Het exhibited a gene dose-response relationship of cardiomyocyte HIPK2 on heart function. HIPK2 expression in the heart was significantly reduced in human end-stage ischemic cardiomyopathy compared to non-failing myocardium, suggesting a clinical relevance of HIPK2 in cardiac biology. In vitro studies with neonatal rat ventricular cardiomyocytes corroborated 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 ERK1/2 signaling in HIPK2 deficient hearts. In vivo rescue experiment with AAV9 TnT-MEK1-CA nearly abolished the detrimental phenotype of KOs suggesting that impaired ERK signaling mediated apoptosis as the key factor driving the detrimental phenotype in CM-KO hearts. CONCLUSIONS: Taken together, these findings suggest that cardiomyocyte HIPK2 is required to maintain normal cardiac function via ERK signaling.