1) To study the cell cycle withdrawal program in skeletal and cardiac myocytes, we have developed methods for differentiating rodent and avian myoblasts into myocytes with spontaneous contractile activity, and for establishing and manipulating primary myoblast cultures. Using microarrays, we have identified several regulatory proteins that are differentially expressed in proliferating myoblasts versus post-mitotic myotubes. We have demonstrated that one of these proteins, Stem cell antigen-1 (Sca-1), specifically regulates the proliferation/differentiation transition during skeletal myogenesis. Current efforts in primary myoblasts and mouse models are focused on determining the mechanisms by which Sca-1 specifically controls myoblast proliferation and regulates myogenic precursor cell self-renewal.

2) To examine the regulation of human cardiac fate determination, our lab is identifying human embryonic stem cells (hESCs) that preferentially differentiate into cardiomyocytes, and developing methods for isolating developmentally-synchronized hESC-derived myocardial precursors. This will facilitate efforts to determine the contributions of genetic programming and environmental stimuli to subspecialization of human cardiomyocytes into atrial and ventricular myocardium, and conduction tissue. We also are examining the role of microRNAs in cardiac fate determination in hESCs.

3) We have demonstrated that hypertrophic stimuli cause a transient burst of Cdk4 activity, remodeling of the retinoblastoma protein complex, and activation of a subset of E2F-1 target genes in murine myoblasts. This has led us to identify a physiological role for both E2F-1-mediated activation and repression of genes involved in cell growth versus division, respectively. Currently, we are investigating the mechanism(s) by which Cip1/Kip1 and INK4 classes of Cdk-inhibitors facilitate this burst of Cdk4 activity, and the role of chromatin remodeling in the hypertrophic response.

4) Over the past several years, the identification of heterogeneous populations of muscle stem cells in the heart and bone marrow has generated great enthusiasm for new approaches to muscle repair and regeneration. However, these studies also have exposed the limitations of current strategies. Taking cues from the highly plastic, developing human heart, our lab is exploring hESC-based therapies for heart failure. Using a mouse model of myocardial injury and cell delivery, we are determining the developmental stage at which hESC-derived myocardial cells engraft in vivo , and examining the effects of hESC transplant therapy on cardiac function.

5) To complement our efforts toward cell-based therapies for heart failure, our group also is investigating better ways to monitor heart failure and the response to therapy in children with single ventricle heart disease, the most difficult congenital heart defect to manage. We have initiated a human research protocol to measure the levels of four proteins found in blood in children with single ventricle compared to children with structurally normal hearts, to determine whether any of these potential biomarkers predict the presence or degree of heart failure in these children. New efforts will be directed toward using proteomics to establish biomarker arrays for pediatric heart failure.