For the millions of Americans who are born with or develop heart disease, stem cell research offers the first real hope of reversing or repairing heart muscle damage. In addition to their regenerative potential, human stem cells offer an unprecedented opportunity to study mechanisms of human disease and develop and test novel therapies. However, these new applications are limited by the lack of culture conditions that replicate complex tissue structures. Theses limitations are particularly apparent for many cardiovascular diseases. Thus, there is a great need for laboratory biotechnologies that replicate the 3-D microenvironment and conditions seen in patients. We propose to create synthetic human heart muscle in culture with perfused bioreactors. Bioreactors are contained reaction vessels for the controlled culture of cells to create tissues in a dish. The models and knowledge gained from these studies will facilitate the creation of cardiovascular disease-in-a-dish models and systems to reliably screen new therapies.
Statement of Benefit to California:
Heart disease, stroke and other cardiovascular diseases are the #1 killer in California. Despite medical advances, heart disease remains a leading cause of disability and death. Recent estimates of its cost to the U.S. healthcare system amounts to almost $300 billion dollars. Although current therapies slow the progression of heart disease, there are few, if any options, to reverse or repair damage. Thus, regenerative therapies that restore normal heart function would have an enormous societal and financial impact not only on Californians, but the U.S. more generally. The research that is proposed in this application could lead to new therapies that would restore heart function after and heart attack and prevent the development of heart failure and death. We will develop the techniques and models that will allow the development and testing of cardiovascular therapies. Combining tissue engineering with disease-specific human pluripotent stem cells will facilitate the creation of cardiovascular disease-in-a-dish models and systems to reliably screen new therapies.
The goal of this proposal is to develop a bioreactor for three-dimensional (3-D) cardiovascular tissue engineering, thereby overcoming the limitations of 2-D culture systems and more accurately modeling native cardiac physiology and pathophysiology. The bioreactor consists of a scaffold prepared from decellularized animal tissue, which is vascularized using human endothelial (blood vessel) cells to enable metabolite exchange within the tissue construct. This vascularized construct is then seeded with human pluripotent stem cell (hPSC)-derived cardiac cells. In the first aim, the applicants will create and characterize the physiologic properties of this engineered human cardiac tissue system. In aim 2, the applicants will optimize the vascularized bioreactor to best recapitulate the properties of human heart tissue. The goal of aim 3 is to create and characterize a 3-D model of human cardiac disease in vitro, using this system.
The reviewers believed this application focuses on an important goal and has the potential to advance the utility of hPSCs in the study of cardiac development, drug screening, and cardiac regenerative therapies. Reviewers differed in their opinion regarding the novelty of the proposed bioengineering technology, and found the approaches for cardiac cell generation to be neither novel nor especially up-to-date. However, they did appreciate that the preliminary data demonstrate the investigators’ ability to generate and characterize cardiac cells.
The reviewers raised several criticisms about the application’s feasibility and experimental design. Concerns were expressed regarding the composition of the cell population that will be incorporated into the tissue construct. Though the preliminary data show the applicant’s ability to generate a highly purified cardiac progenitor population, a substantial fraction of these cells become a cell type other than cardiomyocytes (CM). These non-CMs may have positive or negative effects on cardiac tissue development, and reviewers felt the omission of a systematic examination of the contribution of supporting cell types, like endothelial cells or cardiac fibroblasts, was a critical flaw in experimental design. Reviewers noted a lack of experimental detail regarding cell seeding parameters in general, and for aim 2 specifically, and were unclear if uniform cell coverage within the tissue construct can be achieved. A systematic approach toward overcoming potential limitations was lacking in the application and raised concern. Reviewers considered the size of the engineered cardiac tissue and the many potential sources of variability a considerable challenge, and cautioned that decellularized tissue-based bioreactors create poorly defined environments that would be difficult to extend into high throughput and high-content approaches necessary for disease modeling. Reviewers commended the premise and design of aim 3, and considered access to tissue samples from patients with cardiac disease a strength.
The Principal Investigator (PI) is an accomplished clinical cardiologist with a large number of high impact publications that address the analysis of normal and PSC-derived cardiomyocytes. A Partner-PI funded through a collaborative funding partner provides critical expertise in bioengineering, and reviewers appreciated that this working relationship is already in existence. Additional collaborations support the team’s cell and tissue electrophysiology and stem cell expertise. Overall, the budget seems appropriate and well justified for the scope of the proposed work.
In summary, the PI proposes to develop an in vitro 3-D cardiac tissue model with hPSC-derived CM using a vascularized bioreactor. Though the reviewers appreciated the PI’s and team’s expertise and the potential impact of the proposed studies, a lack of innovation and limitations in the experimental approach diminished their enthusiasm. Thus, the application was not recommended for funding.