This research proposal is aimed at gaining a better understanding of the factors that control the differentiation of human embryonic stem cells into one or another cell type. We propose a research program that focuses on the roles of a particular class of soluble, extracellular differentiation factors, i.e. the TGF-beta family, and the signaling molecules that they activate in cells. This class of differentiation factors is known to function as key regulators of many types of cell differentiation, and to play key roles in the generation of many tissues. Remarkably, these soluble factors have the ability to redirect differentiation from one cell type to another, raising the distinct possibility that changes in signaling by these factors may redirect the differentiation potential of embryonic stem cells, allowing them to give rise to cell types with different properties. Yet, very little is known about their effects in human embryonic stem cells, and how changes in signaling by TGF-beta family proteins affect embryonic stem cell differentiation. We are exceptionally well-positioned to study the role of these factors and their signaling molecules, as this lab has been at the basis of much of the current knowledge on what roles these factors play in cell dfferentiation. In the proposed research program, we will tinker with the embryonic stem cells to introduce changes in the signaling networks that are activated by TGF-beta family proteins, and then ask how these changes affect the potential of these cells to become different cell types. Furthermore, we will study the effects of such changes on the potential of cells, derived from embryonic stem cells, to become pluripotent again and to give rise to the full spectrum of cells. Finally, we will address whether changes in the cells that form the niche for embryonic stem cells affect the ability of embryonic stem cells to become many different cell types. Taken together, these studies should provide a basis for targeted manipulations of embryonic stem cells that will then result in directed changes in the cell types that can be generated from embryonic stem cells.
This research proposal addresses basic research questions and therefore does not directly address the potential use of human embryonic stem cells for therapeutic purposes or toward a particular disease. Nevertheless, we believe that this proposal may have important implications for future uses of embryonic stem cells, in particular for our desire to instruct the cells at will to differentiate into a particular cell type. Through our research on other cell types, e.g. fat cells, muscle cells and bone cells, we have found that we can enhance the potential of precursor cells to differentiate into one or another cell type by modifying the signaling pathways of TGF-beta family proteins. Thus, we have been able to enhance bone cell differentiation and muscle cell differentiation using such approaches. In addition, we are even able to redirect differentiation by modifying the signaling by TGF-beta proteins. For example, using this approach, we have been able to redirect pre-fat cells to become bona fide bone cells or muscle cells, thus providing a possible basis for the use of pre-fat cells, obtained through liposuction, for bone and muscle regenerative therapy. We now propose to study the role of these same TGF-beta family signaling pathways in embryonic stem cells, and to evaluate whether changes in these signaling pathways will change the capacity of the embryonic cells to differentiate into one or another cell type. If successful, this approach may have substantial implications for the derivation of various cell types from embryonic stem cells.