ABSTRACT: Stem cell transplantation offers much promise as a potential treatment for myocardial salvation at the end stages of coronary artery disease (CAD), and much interest has been placed in the differentiation capacity of different population of stem cells. However, little is known about the regulatory mechanisms of stem ceil differentiation In vivo, and under hostile conditions, like myocardial infarction. Myocardial infarction leads to changes In the local microenvironment and Increases oxidative stress, which can regulate cellular differentiation and survival. The long term goal of our program is to study the biology of stem cells after transplantation to the heart. Our primary hypothesis In this proposal is that changes in oxidant status play a role in stem cell differentiation and sun/ival in the mycoardium. To test that hypothesis we have the following specific aims: in Specific Aim 1 we will differentiate bone marrow stromal cells Into cells with myocyte characteristics, both in cell culture and in living subjects, and we will use molecular techniques to track this differentiation non-invasively, something that could be done until recently. For that purpose we will use reporter imaging technology and optical imaging, in Specific Aim 2, we will examine if increased oxidative stress is involved In stem ceil differentialton and sun/ival. For that, will be induced in cell culture and in living subjects (after myocardial infarction), after which stem cell differentiation and survival will be tracked using molecular imaging techniques (optical imaging). In addition, we will study pathways related to oxidative stress (i.e. nitric oxide), and examine their role in stem cell differentiation. Lastly in Specific Aim 3, we will learn from Aims 1 and 2 and "genetically engineer" stem cells so they are better prepared to differentiate and survive in hostile condition, like the one found in states of myocardial ischemia and infarction. The studies proposed in this grant will provide invaluable information on the role that the microenvironment plays in stem cell differentiation and survival and can lead to novel and improved therapeutic strategies. Stem cell therapy provides a great opportunity to re-constitute a damaged heart, but we first need to elucidate the mechanisms that regulate stem cell differentiation and sun/ival. In this study we propose that specific biological pathways (i.e. oxidant status) can be involved in such response. Understanding these mechanisms that regulate stem cell survival will lead to better and improved therapies.