Functional Significance of hESC Glycotype Diversity: Fate Specification & Immune Tolerance
Biological molecules, the building blocks of cells, exist in many forms. Commonly, scientists study the role of proteins in normal and disease processes. As a result, the functions of other types of molecules are less well studied. Consequently, significant gaps in knowledge exist. For example, the role of sugars is often ignored. Until now, this has been largely the case in the human embryonic stem cell (hESC) field. Why is this a significant omission? There is a great deal of evidence that suggests sugars could play important roles in the basic biology of these cells and their suitability for patient therapies. Some of these data come from the field of medicine that deals with blood transfusions. Attempts to treat the illness of one individual using donated blood has been documented for hundreds of years, but prior to the early 1900s, there was no explanation for why this procedure benefited some patients and not others. In 1901, a physician described a code based on sugar structures that distinguishes groups of individuals. Matching the code of the donor and the recipient cells prevented rejection and enabled routine blood transfusions. It is now understood that the biosynthetic machinery for producing these determinants is heritable. As a result, various groups within the population express different codes (blood types), the reason that blood banks need many donors. Subsequent work has shown that these structures are present on many other types of cells. Preliminary experimental evidence from our group shows that hESCs also have this sugar code. As with blood cells, they can be grouped according to type. Additionally, the work of others suggests that the expression patterns of these determinants change as the cells differentiate. In this context, we propose two sets of studies. The first focuses on undifferentiated hESCs that are in a constant state of self-renewal. We want to create a bank of cells that is representative of the sugar codes of United States citizens. We also want to precisely define the nature of the sugar determinants and the proteins that carry them. In addition, we will focus on hESCs that have been induced to differentiate into cells that make up the pancreas, heart, and nervous systems. We think that the distribution of the sugars and the protein scaffolds that present these structures change during the differentiation process. The second study is comprised of functional analyses. In these experiments, we will test the hypothesis that the sugar code influences the basic biological properties of hESCs. Specifically, we will determine if these structures play a role in their ability to self-renew or differentiate. We will also determine if, like blood cells, the body is able to recognize and destroy stem cells based on mismatches in the sugar code. Thus, at the conclusion of these experiments we will know whether it will be important to consider these sugar structures in differentiation and/or transplantation procedures.
It is envisioned that human embryonic stem cells (hESCs) will be the foundation on which regenerative medicine therapies will be built. Investigative teams are working hard to translate research findings into cell-based treatments for patients with a wide variety of chronic and/or fatal diseases. While the importance of these efforts cannot be overstated, it is essential to realize that hESC biology is a very young field, slightly more than a decade old. In general, it takes many years for new discoveries to be fully understood. Accordingly, it is important to keep learning about the basic properties of these cells as gaps in our knowledge could create major delays in developing and implementing clinical applications.
The project we propose in this application benefits the citizens of California by investigating early on, during the development phases when treatment strategies are being devised, an issue that might become a confounding factor when clinical trials begin in earnest. Specifically, we are investigating the role of sugar structures that are matched between donors and recipients in blood transfusions. We think that these molecular signatures might play important roles in governing basic aspects of hESC biology. This phenomenon could account for, at least in part, the differences in behavior that have been observed among the lines. Additionally, their sugar codes could play a role in the response of patients’ immune systems to cell replacement therapies that utilize hESCs. If these determinants are mismatched in blood transfusions, the donor cells are often destroyed, which illustrates the possible hazards.
What can we do with the information that emerges from this study? We can take preventative measures now so that, in the future, therapeutic applications do not encounter costly delays in both human and financial terms. For example, if we know that it is important to match the sugar type of the donor and the recipient, then we can take this information into consideration. This would allow investigators to use the strategies that have been developed for blood banking to create the collections of cells that will be needed for hESC-based therapies. Since the development of lines that grow continuously in culture and differentiate in predictable ways is a long process, these efforts should begin as soon as possible.
By sponsoring projects that are designed to advance stem cell science, the California Institute for Regenerative Medicine is one of the most exciting ventures in state history. Citizens voted for this initiative because they believe that it is important to put tax dollars into research that has the potential to develop novel therapies and cures for major human diseases. Accordingly, the benefits of this work will accrue not only locally, within the state, but to all patients who have medical conditions that are amenable to these types of therapies.