Year 3

The clinical potential of pluripotent stem cells for use in regenerative medicine will be realized only when the process by which tissues are generated from these cells is significantly more efficient and controlled than is currently the case. Fundamental questions remain about the mechanisms by which pluripotent stem cells differentiate into mature tissue. The overall goal of this research proposal is to discover if the cell types produced during differentiation of PSC produce the microenvironment needed for specialized tissue stem cells to develop.

To approach this question we use the hematopoietic (“blood-forming”) system as our model, as it is the best characterized tissue in terms of differentiation pathways and offers a range of unique technical tools with which to rigorously study questions of differentiation. Adult hematopoietic stem cells (HSC) survive and grow in the bone marrow only if they are physically close to specialized cell types, the so-called hematopoietic stem cell “niche”. We hypothesize that hematopoietic stem cells are not produced from pluripotent cells because the cells that form the niche and provide the necessary signals are not present during this early stage of differentiation.

Our research proposal has three specific aims. The first aim is to determine if a single cell type derived from pluripotent cells can generate both blood cells and the cells of the hematopoietic niche. The second aim is to identify the types of niche cells produced from pluripotent cells and define how each of them affect the growth of adult stem cells. In the third aim, the cell types that are found in aim 2 to best support adult hematopoiesis, will then be tested for their ability to promote the production of hematopoietic stem cells from pluripotent stem cells.

During the third year of support, we have made significant progress in all three specific aims. We have now completed our studies that track the common origin of the blood forming cells and their microenvironment. We have performed functional studies to identify which of the cell types that we generate from pluripotent cells support HSC when grown in culture, and which do not. Finally we have performed gene expression analyses on these different cell types to understand the molecular pathways that they use to support HSC in culture.