Our laboratory includes three general areas of research: a) stem cells, plasticity, and differentiation, b) cell characterization, isolation, and/or selection to achieve high levels of cell purity, and c) development of vascular tissue products. In many ways these three areas are very much related, and, while cutting edge, are built on the heritage of mammalian cell culture.

All these areas have significant impact and/or relationship to the general area of tissue engineering. Tissue engineering has been defined as a sub/cross discipline that focuses on the design, development, and maintenance of tissue products that can be used to repair, improve, or restore tissue function. However, this field is still very much in its infancy and many problems and challenges still exist that have yet to be overcome before we will see safe, high quality, tissue engineered products in the marketplace. My current research interests address two particularly important concerns in using stem cells to make tissue engineered materials or in using stem cell-derived cells for therapeutic applications, in general. One concern is the ability to achieve purified cell populations. The second concern has to do with the quality of the cells derived from stem cells. Tissue-specific cells derived from stem cells in vitro have a very different history compared to cells derived in vivo. Stem cell therapies will only become clinically relevant if the stem cells differentiated in vitro function as their in vivo counterparts. Therefore, the focus of our research is to derive pure populations from stem cells in vitro, characterize these cells and compare their function with mature cells derived in vivo and then to use these cells towards regenerative medicine applications including tissue engineering and cell therapy approaches. Our laboratory currently focuses on the vascular cell lineages, but we plan to expand into other cell systems long-term.

Projects

1. Assay and characterize the stem cell-derived vascular cells. Not unlike the age-old, but classic, question “Is it nature or nurture?” for identifying the source of our health, temperament, intelligence, and personality, we ask an analogous question on the cellular level. How much of a cell’s behavior is a function of its history and how important are the current environmental cues? And can we mimic/replace nature with nurture? Endothelial cells derived from stem cells in vitro will need to be thoroughly investigated to ensure that these cells will function as their mature endothelial counterparts. Standard characteristics such as cell proliferation capacity, number of population doublings, cell migration, adhesion, and cell-cell signals, will be addressed. In addition, a variety of in vitro assays may be employed to test endothelial cell function including cell surface marker expression, nitric oxide synthesis, low density lipoprotein uptake, von Willebrand’s Factor, cytoskeletal rearrangement in response to shear stress, and the ability to inhibit platelet adhesion and clotting. In addition, the gene expression of stem cell-derived and mature endothelial cells should be compared. These assays will also need to be tested for endothelial cells derived from the different stem cell sources for comparison.

2. Characterize the stages of vascular differentiation and compare these between cell sources. The word “endothelial progenitor cell” is used often in the literature, yet this cell is almost completely undefined. The word seems to apply to any cell that has differentiated beyond a stem cell, but has not yet become a mature endothelial cell. I would like to answer question regarding the origins of an endothelial progenitor cell, identify some consistent characteristics of an endothelial progenitor cell, and define and assign a precise stage of differentiation, level of maturation, vasculogenesis capabilities, and surface markers.

3. Part1: Investigate the potential plasticity (transdifferentiation) of stem cell derived- and mature endothelial cells. There has been some evidence that endothelial cells have the capacity to transdifferentiate into cardiomyoctyes and smooth muscle cells. I would like to first verify this level of plasticity in vitro. Are these cells really transdifferentiating, or are they simply immature cells that share a common precursor? Also, environmental cues that might signal the transdifferentiation need to be identified, and further evidence of transdifferentiation needs to be investigated. The transdifferentiation potential should also be compared between stem cell-derived and mature endothelial cells. Part 2: Test the tumorogenicity (or dedifferentiation) of stem cell-derived endothelial cells. Tissues derived from embryonic stem cells could potentially form teratomas in vivo. Deriving homogeneous populations of cells might eliminate the tumorogenic potential of these cells, but before these cells could have any clinical applications, they need to be thoroughly tested. The cell populations could be tested in vitro using some tumorogenic markers, and then more thoroughly tested in vivo.

4. Investigate the ideal stage of vascular differentiation for implantations, other cell therapies, or in vitro tissue assembly. Once the endothelial cells have been characterized, it will be important investigate and optimize the stage of differentiation for each individual application. A mature endothelial cell might not integrate and adapt to its new environment as well as an endothelial progenitor cell, since an endothelial progenitor cell is still partially uncommitted, and therefore, much more susceptible to environmental stimuli. Alternatively, an endothelial progenitor cell might have a greater tumorogenic capacity than a more mature endothelial cell. The cells will need to be tested for adaptability and integration into the host tissue.

5. Design and develop an in vitro bioreactor for whole tissue perfusion. This model would be used to incorporate perfusion into neovasculature to assess the effect of fluid flow on the stability of neovessel structures.

6. Develop a cardiac patch for myocardial repair. Embryonic stem cells, endothelial progenitor cells, bone-marrow derived stem cells, skeletal myoblasts, mesenchymal stem cells, side-populations cells, fibroblasts, etc. have been directly injected into myocardial infarcts to enhance regeneration of the infarcted tissue. Most cells enhance cardiac output, but evidence of cell integration is weak. I hypothesize that a cardiac patch would enhance the number of cells in the infracted region, as well as provide some mechanical support to the weakened tissue.