Proper heart development requires patterning across the myocardial wall. Early myocardial patterning is characterized by a transmural subdivision of the myocardium into an outer, highly mitotic, compact zone and an inner, trabecular zone with lower mitotic activity. We have shown previously that fibroblast growth factor receptor (FGFR) -mediated signaling is central to myocyte proliferation in the developing heart. Consistent with this, FGFR-1 and FGF2 are more highly expressed in myocytes of the compact zone. However, the mechanism that regulates the transmural pattern of myocyte proliferation and expression of these mitogenic factors is unknown. The present study examined whether this transmural patterning occurs in a myocardium-autonomous manner or by signals from the epicardium. Microsurgical inhibition of epicardium formation in the embryonic chick gives rise to a decrease in myocyte proliferation, accounting for a thinner compact myocardium. We show that the transmural pattern of myocyte mitotic activity is maintained in these hearts. Consistent with this, the expression patterns of FGF1, FGF2, and FGFR-1 across the myocardium persist in the absence of the epicardium. However, FGF2 and FGFR-1 mRNA levels are reduced in proportion to the depletion of epicardium. The results suggest that epicardium-derived signals are essential for maintenance of the correct amount of myocyte proliferation in the compact myocardium, by means of levels of mitogen expression in the myocardium. However, initiation and maintenance of transmural patterning of the myocardium occurs largely independently of the epicardium. Developmental Dynamics 228:161-172, 2003.

Percutaneous coronary intervention is first-line therapy for acute coronary syndromes (ACS) but can promote cardiomyocyte death and cardiac dysfunction via reperfusion injury, a phenomenon driven in large part by oxidative stress. Therapies to limit this progression have proven elusive, with no major classes of new agents since the development of anti-platelets/anti-thrombotics. We report that cardiac troponin I–interacting kinase (TNNI3K), a cardiomyocyte-specific kinase, promotes ischemia/reperfusion injury, oxidative stress, and myocyte death. TNNI3K-mediated injury occurs through increased mitochondrial superoxide production and impaired mitochondrial function and is largely dependent on p38 mitogen-activated protein kinase (MAPK) activation. We developed a series of small-molecule TNNI3K inhibitors that reduce mitochondrial-derived superoxide generation, p38 activation, and infarct size when delivered at reperfusion to mimic clinical intervention. TNNI3K inhibition also preserves cardiac function and limits chronic adverse remodeling. Our findings demonstrate that TNNI3K modulates reperfusion injury in the ischemic heart and is a tractable therapeutic target for ACS. Pharmacologic TNNI3K inhibition would be cardiac-selective, preventing potential adverse effects of systemic kinase inhibition.

Abstract-It is well established that cardiovascular repair mechanisms become progressively impaired with age and that advanced age is itself a significant risk factor for cardiovascular disease. Although therapeutic developments have improved the prognosis for those with cardiovascular disease, mortality rates have nevertheless remained virtually unchanged in the last twenty years. Clearly, there is a need for alternative strategies for the treatment of cardiovascular disease. In recent years, the idea that the heart is capable of regeneration has raised the possibility that cell-based therapies may provide such an alternative to conventional treatments. Cells that have the potential to generate cardiomyocytes and vascular cells have been identified in both the adult heart and peripheral tissues, and in vivo experiments suggest that these cardiovascular stem cells and cardiovascular progenitor cells, including endothelial progenitor cells, are capable of replacing damaged myocardium and vascular tissues. Despite these findings, the endogenous actions of cardiovascular stem cells and cardiovascular progenitor cells appear to be insufficient to protect against cardiovascular disease in older individuals. Because recent evidence suggests that cardiovascular stem cells and cardiovascular progenitor cells are subject to age-associated changes that impair their function, these changes may contribute to the dysregulation of endogenous cardiovascular repair mechanisms in the aging heart and vasculature. Here we present the evidence for the impact of aging on cardiovascular stem cell/cardiovascular progenitor cell function and its potential importance in the increased severity of cardiovascular pathophysiology observed in the geriatric population. Key Words: cardiac stem cell Ⅲ endothelial progenitor cell Ⅲ regeneration Ⅲ aging C ardiovascular disease (CVD) is the leading cause of morbidity and mortality in the United States. 1 CVD risk increases with age and, in older patients, is associated with increased rates of complications and poorer clinical outcomes. As a consequence, CVD is predominant within the elderly population, with approximately 85% of all deaths attributable to CVD in the United States occurring in individuals more than 65 years of age. 1 Age-associated changes in many aspects of cardiovascular function appear to contribute to this increased risk. These include: (1) impairment in the regulation of vascular tone that is attributable, for example, to decreased NO production and increased levels of angioten-

Microenvironmental cues mediate postnatal neovascularization via modulation of endothelial cell and bone marrow-derived endothelial progenitor cell (EPC) activity. Numerous signals regulate the activity of both of these cell types in response to vascular injury, which suggests that parallel mechanisms regulate angiogenesis in the vascular beds of both the heart and bone marrow. To identify mediators of such shared pathways, in vivo bone marrow/cardiac phage display biopanning was performed and led to the identification of tenascin-C as a candidate protein. Functionally, tenascin-C inhibits cardiac endothelial cell spreading and enhances migration in response to angiogenic growth factors. Analysis of human coronary thrombi revealed tenascin-C protein expression colocalized with the endothelial cell/EPC marker Tie-2 in intrathrombi vascular channels. Immunostains in the rodent heart demonstrated that tenascin-C also colocalizes with EPCs homing to sites of cardiac angiogenic induction. To determine the importance of tenascin-C in cardiac neovascularization, we used an established cardiac transplantation model and showed that unlike wild-type mice, tenascin-C-/- mice fail to vascularize cardiac allografts. This demonstrates for the first time that tenascin-C is essential for postnatal cardiac angiogenic function. Together, our data highlight the role of tenascin-C as a microenvironmental regulator of cardiac endothelial/EPC activity.