Coronary heart disease is the leading cause of death in the developed world. This disease results from atherosclerosis or fatty deposits in the vessel wall that causes blockage of coronary arteries. Blockage of these arteries cut off supplies of nutrients and oxygen to the heart muscle, causing heart attacks, heart failure or sudden death. To restore coronary blood supply, physicians use guide-wires to position an inflatable balloon at the blockage site of the artery, where the balloon is inflated to open up the artery. This procedure is called percutaneous transluminal coronary angioplasty or PTCA, which is usually accompanied by the placement of a metal tube (or stent) at the diseased site to maintain vessel opening. PTCA is the dominant procedure to restore blood flow in coronary arteries- in the United States alone nearly 1.3 million PTCA procedures were performed in 2004. However, as a response to PTCA-related vessel wall damage, cells from the vessel wall are activated to divide and grow into the vessel lumen, causing re-narrowing or restenosis of the artery. Restenosis of the vessel lumen is the major hurdle limiting the success of PTCA. It occurs in 20-50% of cases within six months of the initial PTCA procedure and requires repeated PTCA to open up the re-narrowed artery, leading to tremendous human and social expenses. Stents which contain drug inhibitors of cell growth (drug eluting stents, or DES) reduce restenosis; however, considerable concerns have emerged regarding the safety of DES due to an increased risk of sudden stent occlusion by platelet aggregates (or thrombosis). This sudden occlusion is caused by a concomitant drug inhibition of cells that cover the raw surface of metal stents to prevent platelet aggregation. This complication is frequently lethal, resulting in death or heart attack in 85% of cases. The safety concerns over DES have created an urgent need to define the mechanisms underlying the biology of restenosis. A population of cells resident in the vessel wall consists of progenitor cells that divide and grow into the vessel lumen when vessels are injured. The repair process mediated by these cells directly contributes to vessel restenosis. Our goal is to understand the biology of these stem cells in the repair of injured arteries- how vessel injury signals these cells to divide and invade the vessel lumen, what molecular effectors control the cellular responses, and how to intercept these signals and effectors to prevent vessel restenosis. This will provide a solid scientific basis for new therapeutic targets and strategies for vessel restenosis after PTCA. The proposal is a targeted response to CIRM New Faculty Awards II. It seeks to extend my research expertise into the field of stem cell biology related to clinically important vascular diseases. We are confident that our proposed studies will generate significant progress in this field, in both scientific knowledge and useful therapies.
Coronary heart disease is the leading cause of death in California. This disease results from atherosclerosis or fatty deposits in the vessel wall that causes blockage of coronary arteries of the heart, causing heart attacks, heart failure or sudden death. Physicians use wires and balloons to open up the blocked artery (angioplasty) and a metal tube (stent) to keep the artery open and restore blood flow. Although effective, angioplasty and stenting cause some damages to the blood vessel, which leads to a recurrent blockage (or restenosis) of the vessel in 20-50% of patients within 6 months of the procedure. This vessel restenosis requires repeated angioplasties and stenting for restoration of blood flow. Given the large number of patients with coronary heart disease in California, the need for repeated surgical procedures has resulted in tremendous human, social and economic costs in our state. An attempt to reduce vessel restenosis is the placement of drug-eluting stents (or DES) in angioplastied vessels. Although drugs released from the stents reduce vessel restenosis, this approach creates a new and frequently fatal complication- sudden occlusion of the stented arteries. This complication is because drugs in the stents delay the repair of inner lining of the artery, whose function is to prevent platelet aggregation within the lumen of the artery. Sudden platelet aggregation (or thrombosis) within the vessel lumen causes instantaneous obstruction of the artery, leading to acute heart attacks or death. Thus, the safety concerns over DES have created an urgent need to define the mechanisms underlying the biology of restenosis. A population of cells present at the vessel wall possess stem cell characteristics. After vessel injury, these cells increase in number and turn into different kinds of cells, which then migrate from the vessel wall into the lumen, causing blockage of the vessel. Thus, understanding how these cells behave will inspire new ideas for treating recurrent vessel blockage or restenosis. We propose to study how and what molecular signals activate these cells when vessels are injured. Our goal is to provide a scientific strategy of intercepting these signals for the treatment of vessel restenosis. We believe that understanding the biology of vascular stem cells will lead to significant advances in the research and novel therapies of vessel injury and restenosis. Given the scope of this problem , an improved therapy of vessel restenosis will have a significant economic and social impact. We have proposed to use modern methods in genetics, cell biology, and molecular biology to attack the challenges of this project. At the same time, we will train a new generation of bright students and junior scientists in the areas of stem cell biology highly relevant to human disease. This ensures that an essential knowledge base will be preserved, passed on and expanded in California for the foreseeable future.
This proposal focuses on the role of adventitial cells (a connective tissue layer in blood vessel walls) in the vascular remodeling that occurs during repair of injured arteries. The clinical scenario most relevant to this proposal in humans is that following percutaneous transluminal coronary angioplasty (PTCA), a procedure in which physicians use a guidewire to position a balloon where it can be inflated to open up the lumen of an atherosclerotic artery. In 20-50% of cases, restenosis (re-occlusion of the vessel lumen) occurs. As a response to the vessel wall damage during PTCA, cells are activated to divide and cause obstruction of the arterial blood flow.
The applicant’s preliminary results suggest that adventitial cells are activated by an angiogenic cytokine to causes restenosis after vascular injury. In order to study the mechanism of restenosis, the applicant proposes three aims. In the first aim, the applicant seeks to examine the cellular responses of adventitial cells to angiogenic cytokine-mediated signaling by purifying these cells and then analyzing proliferation/apoptosis, differentiation and migration. In the second aim, the applicant attempts to define the roles of specific angiogenic receptors in adventitial cells by studying knock out mice, and assessing the ability of mice with particular gene deletions to repair wire-injured vessels. Finally, in the third aim, the applicant seeks to define the molecular pathways downstream of the angiogenic receptors in adventitial cells by transcriptionally profiling isolated cells that have been treated with anti-receptor antibodies following angiogenesis, and further observing changes of the expression of candidate genes in injured vessels when receptor signaling is inhibited in the knock out mice.
Reviewers judged the application to be a logical and well thought out research plan, focusing on a significant clinical problem that is relatively under-investigated. Overall, the reviewers felt the experimental design was well written and within the expertise of the team. The applicant demonstrated availability of the necessary tools to complete to proposed work, notably appropriate mouse models and vectors to dissect the signaling pathways, and the necessary reagents for isolation of cells. A few weaknesses were identified with the proposal. Reviewers were divided in their assessment on whether the adventitial cells were adequately established as stem cells. Two reviewers felt that the preliminary data were weak in this aspect, and would have been more convincing with lineage tracing or classical self-renewal and differentiation experiments proposed. One reviewer expressed concern that the adventitial cell population isolated by the proposed markers could represent a heterogeneous population of cells, and that further work should be done to define the phenotype, localization, and function of these cells in vivo. However, one reviewer expressed great excitement that the applicant could identify a resident stem cell in the adventitia, and that the potential for this research is enormous. This point was underscored by the fact that this area of cell biology is relatively understudied.
Reviewers felt the applicant was well trained and qualified to conduct the proposed studies. The candidate has trained in cardiovascular medicine and developmental biology, which are both relevant to the proposed research. The PI has a number of high quality publications, both as a trainee and in the first two years as an independent investigator. The applicant has recruited two senior stem cell scientists as mentors, but no letters accompany the application. One reviewer commented that a mentor with vascular biology expertise would also have been desirable. A career development plan is present, but lacked detail.
The institutional supported was judged to be strong. A letter of commitment co-authored by the Chief of Research in the Cardiovascular Division and the Chief of Medicine of the Department of Medicine is included in the application. The candidate has been awarded sufficient laboratory space and funds to equip the laboratory as a start up package. Reviewers noted that the institution has an excellent track record of developing its young faculty.
A motion was made to recommend this application be moved to Tier 1 - Recommended for Funding. During programmatic discussion, the panel highlighted the significance of the clinical problem being addressed, and emphasized that the proposal focused on a translational target that was “within reach” of development toward a potential therapeutic. The PI was judged to be a strong physician-scientist candidate who is at the earlier stage of an independent career, and therefore is an excellent candidate for this RFA. The motion to move this application to Tier 1 carried.