Basic Biology I
Diabetes is a disorder in which the cells of the body are not able to properly use the sugar glucose as a source of energy. This results in high levels of glucose circulating in the blood. Prolonged high levels of glucose are toxic, resulting in the many problems that patients with diabetes can develop over time, including kidney disease, blindness, and heart disease. A major part of the glucose regulatory system in the body is the beta-cell, which is located in the pancreas and produces a protein called insulin that functions as a key to unlock the insulin receptor, which functions to regulate other molecules that serve as a door on many cells in the body to allow glucose to enter. Regardless of the type of diabetes, it is clear that dysfunction and eventual loss of the beta-cells plays a central role in the development of diabetes. In type I diabetes, also known as juvenile diabetes, the beta-cell are destroyed by the body's immune system, resulting in a almost complete lack of beta-cells and consequent insulin deficiency. In type II diabetes, which is strongly associated with obesity, the situation is more complex, with a combination of two major processes- resistance to the action of insulin combined with gradual dysfunction and loss of beta-cells- combining to produce a diabetic state. Thus, in both major forms of diabetes, beta-cell dysfunction and loss plays a central role and much effort is consequently being devoted to increasing the number of beta-cells, including from adult stem/progenitor cells, as proposed in this grant. Recently, it has been demonstrated that stem/progenitor cells that can form new beta-cells are present in the adult human pancreas. To advance that finding into a therapy for diabetes requires a greater understanding of the nature of those cells and the process by which they become beta-cells. The experiments proposed in this grant are directed at just those issues. We propose to study the mechanism by which adult stem/progenitor cells become beta-cells and also to study possible markers expressed by those cells, which would facilitate their identification and manipulation.
Statement of Benefit to California:
Diabetes is epidemic in our society, including California, due in large part to the increase in obesity. It is estimated that more than six percent of all Californians are afflicted with diabetes. For minority populations, the number is up to ten percent, reflecting the higher levels of obesity in those populations, as well as genetic predispositions that are just beginning to be understood. Achieving the goal of this project, which is to develop a new treatment for diabetes based on inducing the formation of new beta-cells from stem cells, would have an enormous impact on the quality of life of those citizens.
The goal of this proposal is to gain a better understanding of the mechanisms involved in adult beta cell formation from non-insulin-producing pancreatic exocrine cells. Throughout this study, the experimental paradigm consists of exposure of human adult exocrine pancreas (hAExP) cells to various treatments in vitro, followed by transplantation of these cells into an in vivo environment permissive for beta cell differentiation in immune compromised mice. The first two aims will assess whether generation of beta cells from exocrine cells recapitulates beta cell formation in the embryo. In Aim 1, the function of a transcription factor thought to be involved in the exocrine to beta cell transition will be further investigated by either up or down regulation in hAExP cells. In Aim 2, the authors will use lineage tracing to determine if Ngn3, a transcription factor known to be transiently activated during embryonic beta cell differentiation, is activated in hAExP cells undergoing beta cell differentiation. Aim 3 seeks to confirm that cell free extracts isolated from a rat pancreas regeneration model function similarly to those obtained in a mouse model in facilitating transdifferentiation of hAExP cells to insulin-producing beta cells. Reviewers unanimously stressed the clear need to understand the mechanisms regulating differentiation of beta cells from other pancreatic cells. Ultimately, this area of research could help with the development of protocols that promote such transdifferentiation and thus have a major impact on regenerative medicine approaches for diabetes. Experiments are clearly described with discussion of potential problems and future plans. Despite the potential impact of the proposed research, reviewers' concerns with several aspects of the preliminary data left them less enthusiastic about the project's outcome. Although reviewers found many aspects of the preliminary data to be intriguing and supportive of the proposed aims, they were concerned that the applicant had only demonstrated partial differentiation of hAExP cells towards beta cell fate, and that insulin expression had not been established. In light of published work by others that certain pancreatic cells differentiate only into glucagon-producing cells, reviewers felt that differentiation of hAExP cells into endocrine cell types other than beta cells should have been considered. Similarly, published data describing unsuccessful transdifferentiation using soluble factors isolated in a different model of pancreatic regeneration than that proposed in Aim 3 should have been discussed. More importantly, reviewers felt the potential impact of Aim 3 was minimal, since no analysis of the cell free extract was proposed. Furthermore, some of the preliminary data appear to be internally inconsistent; experiments indicate that the transcription factor pursued in Aim1 is elevated in an in vivo model of transdifferentiation yet must be diminished for beta cell transdifferentiation to occur in vitro. This inconsistency was not addressed in the proposal. Finally, reviewers mentioned that the lineage tracing construct required to accomplish Aim 2 was not yet generated, raising further concerns about feasibility. Reviewers praised the principal investigator's publication record, qualifications and commitment to generating cell therapies for diabetes. However, there was concern that he/she may be overcommitted. The applicant has assembled an excellent team possessing all the expertise required to accomplish this project. In summary, reviewers felt that the proposed program has promise and addresses a large unmet medical need. However, concerns about the preliminary data and a lack of appropriate consideration of previously published, related studies lessened reviewers' enthusiasm about the application.