Abstract 17: Nuclear Calcium/Calmodulin-dependent Protein Kinase II Signaling Enhances Cardiac Progenitor Cell Survival and Cardiac Lineage Commitment

Ca2+/Calmodulin-dependent protein kinase II (CaMKII) signaling in the heart regulates cardiomyocyte contractility and growth in response to elevated intracellular Ca2+. The δB isoform of CaMKII is the predominant nuclear splice variant in the adult heart and regulates cardiomyocyte hypertrophic gene expression by signaling to the histone deacetylase HDAC4. However, the role of CaMKIIδ in cardiac progenitor cells (CPCs) has not been explored. During developmental growth endogenous CPCs display primarily cytosolic CaMKIIδ, which localizes to the nuclear compartment of CPCs after myocardial infarction injury. CPCs undergoing early differentiation in vitro increase levels of CaMKIIδB in the nuclear compartment where the kinase may contribute to the regulation of CPC commitment. CPCs modified with an established lentiviral based constructs to overexpress CaMKIIδB (CPCeδB) have reduced proliferative rate compared to lentiviral transduction of CPCs with eGFP alone (CPCe). Additionally, stable expression of CaMKIIδB promotes distinct morphological changes such as increased cell surface area and increased length of cells compared to CPCe. CPCeδB are resistant to oxidative stress induced by H2O2 relative to CPCe, whereas a knockdown of CaMKIIδB using small hairpin RNA resulted in an up regulation of cell death compared to scrambled treated controls. Dexamethasone treatment to promote cardiac differentiation increased cardiomyogenic markers cardiac troponin T and α-smooth muscle actin measured by RT-PCR and immunoblot analyses in CPCeδB compared to control CPCe. Therefore, CaMKIIδB may serve as a novel modulatory protein to enhance CPC survival and commitment into the cardiac and smooth muscle lineage.