Cardiovascular diseases are the leading cause of death in the United States. Blood vessel replacement is a common treatment for vascular diseases such as atherosclerosis, restenosis and aneurysm, with over 300,000 artery bypass procedures performed each year. However, vein grafts are limited to their availability and the additional cost and surgeries, and small-diameter synthetic vascular grafts have frequent clogging due to thrombogenesis. Tissue engineering is a promising approach to the fabrication of non-thrombogenic vascular grafts, but the reliable and expandable cell sources for tissue-engineered vascular graft (TEVG) have not been established. Our long-term objectives are to engineer stem cells and nanostructured biomaterials for the repair and regeneration of cardiovascular tissues. In this project, we will investigate the differentiation of human embryonic stem cells (hESCs) into vascular cells, and use hESC-derived cells and nanostructured scaffolds to construct TEVGs that are non-thrombogenic, are capable of self-remodeling, and have long-term patency. This study will generate insights into the differentiation and regeneration potential of hESCs and their derived cells in vascular microenvironment, and help to establish a stable cell source for cardiovascular repair and therapies, which will benefit our health care in the near future.
Statement of Benefit to California:
Cardiovascular diseases are the leading cause of death in the United States. Our long-term objectives are to engineer stem cells and nanostructured biomaterials for the repair and regeneration of cardiovascular tissues. In this project, we will investigate the differentiation of human embryonic stem cells (hESCs) into vascular cells, and use hESC-derived cells and nanostructured scaffolds to construct tissue-engineered vascular grafts (TEVGs) that are non-thrombogenic, are capable of self-remodeling, and have long-term patency. This study will generate insights into the differentiation and regeneration potential of hESCs and their derived cells in vascular microenvironment, and help to establish a stable cell source for cardiovascular repair and therapies. TEVGs will benefit patients and reduce our cost for health care. For example, the additional surgeries, cost and morbidity for harvesting autologous blood vessels can be avoided, and the clogging of synthetic vascular grafts can be minimized. Furthermore, hESC-derived vascular progenitors could be used to fabricate TEVGs that are available off-the-shelf.
SYNOPSIS: The goal of this proposal is to use hESCs to develop tissue-engineered vascular grafts (TEVGs) for treatment of vascular diseases, such as atherosclerosis, restenosis, and aneurysm. The first aim relates to investigation of the effects of vascular chemical and mechanical factors on the production of endothelial precursor cells (EPCs) from hESC. Preliminary experiments have been carried out in H9 cells. A second aim is to determine the roles of hES derived cells in TEVG patency and remodeling in vivo in the rat carotid artery. For the first aim, the culture media will contain stem cell factor and VEGF. Mechanical effects (oscillatory shear stress) on EPCs from hES cells will be tested on a dispersed collagen type IV substrate. In the second aim, Flk+VEcad-CD31- cells will be isolated by FACS and further differentiated upon seeding to nanofibrous scaffolds coated with ECM proteins. Carotid surgeries will be performed and patency assessed along with antithrombogenic properties. SIGNIFICANCE AND INNOVATION: The study addresses an important biomedical problem that is approached in unique ways that incorporate principles of stem cell biology, biomechanics, and tissue engineering. The proposal could lead to the development of more suitable endothelial coated devices for cardiovascular interventions and surgery down the road, particularly if this can be done in an autologous manner. Early data suggests that ES cell and embryo-derived endothelial cells have enhanced capabilities for grafting and forming new blood vessels versus putative circulating endothelial progenitors that have markers that actually suggest that they may be monocytic in origin. In summary, this proposal addresses a significant medical problem (vascular disease)although using a conventional approach in the vascular field. STRENGTHS: One strength of this proposal is the experience of investigators and collaborators, which bring unique interdisciplinary expertise in bioengineering, tissue engineering and biomechanics. The proposal addresses an important problem that the investigators are uniquely positioned to address. Preliminary data is suggestive that critical apsects of the proposal are likely to be feasible. The PI has an excellent track record. WEAKNESSES: It is unclear that there are new ideas to be exploited in this proposal. The purity of the cells to be produced is not addressed - it is not entirely clear if the investigators can isolate pure populations of ES cell-derived endothelial cells. Mechanical stimulation enhances the formation of endothelial cells from murine ES cells, but it is not yet clear if this can be translated into human ES cells. Additonal expertise in human ES cell biology and FACS strategies for purifying the cells could enhance the proposal. Comparisons of hESC-derived endothelial cells to authentic human endothelial cells would be helpful. Molecular characterization of the endothelial subtype would also seem appropriate. Attention should be paid to the purity of the cell populations to be studied. For the in vitro work, it is likely that results of mechanical manipulations may be influenced by the mix of cells in the culture. Similarly, the population to be used for the carotid studies may not be sufficiently "clean". DISCUSSION: This proposal looks at the potential for use of hESCs in cardiovascular tissue engineering. The goal is to generate hESC-derived tissue-engineered vascular grafts which will be tested in a rat carotid artery model in order to look at the effect of shear stress on tissue engineered grafts. The proposal addresses an important problem - vascular disease - using a conventional, well-developed system for studying effects of shear. This group is good at studying mechanical stress/shear effects, and they have a developed a good assay. The PI could profit from collaborations with stem cell experts and from a stronger rationale that such mechanical effects would be important. The transition from mouse ES to human ES could be interesting, and while one reviewer does want to see bioengineering work done on VE cells, the investigators would benefit from more expertise on hESC and human endothelial cells. It is not clear that mechannical stimulation can effect hESC differentiation, and there is a major flaw in the lack of studies on the purity of the cells. It would help to better characterize the cells because if the PI is unable to isolate pure cell populations, then the data may not be interpretable. As written, the approach is not innovative, and the expected information not predicted to be of value. One reviewer felt that characterization of the cells by biologists, not just bioengineers, is important -- mechanical stimuli can have effects on differentiation (see recent Lee Sweeny Science paper). While conventional aspects of bioengineering are employed, this is one of the groups who invented the techniques. The applicant is a pioneer in biomechanical effects on phenotype. Characterizing the assay could be a benefit to an unknown system like hESCs. However there is concern as to how cells will be characterized since the investigators are not stem cell scientists. It is imperative to compare the real thing with hESC-derived products. Such comparative studies would strengthen this proposal. Although not quite ready for prime time, the reviewers want to encourage involvement of bioengineers in the hESC field and to provide positive reinforcement to the applicant.