The world is experiencing and epidemic of diabetes mellitus, a serious disease characterized by the body’s inability to secrete adequate amounts of insulin. Diabetes is the leading cause of blindness, kidney failure, amputations and nerve disease and the seventh leading cause of death in America. Recent work suggests that one way to treat diabetes is to surgically transplant those very cells that normally produce and secrete insulin. These cells, called pancreatic beta cells, normally secrete insulin after a meal, when blood sugar rises. However, the transplanted beta cells must be obtained from organ donors, and there are too few donors to treat everyone who needs treatment.
A promising way to produce a potentially unlimited supply of transplantable tissue for diabetes treatment would be to use human embryonic stem cells. Human embryonic stem cells can turn into any other cell of the body, as occurs normally during development. The problem is that there is no known laboratory technique to completely turn these special cells into fully functional beta cells. We can make cells that produce insulin, but they do not secrete it, in response to a rise in blood sugar, as would be needed to function normally. Scientists have shown, curiously, that when these cells are transplanted into mice, they do learn to secrete insulin when sugar rises, but it takes months for the change to occur, and we do not know whether this would happen, if the cells were transplanted into humans.
We aim to find the genetic switches, called "microRNAs" that will turn on the production of the cell machinery that enables beta cells normally to know when blood sugar is higher than normal and to respond by secreting insulin. If we can find these genetic switches, we may be able to speed up the production of cells useful for transplantation treatment of diabetes. The approach we are pioneering may have broader application to turn human embryonic stem cells into almost any other desired tissue, which would then be useful for transplantation treatment of other diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease, for example.
The genetic switches we are looking at, microRNAs, are normally present in all cells and participate in the turning on and off of cellular machinery at strategic times during development. If we could compare the laboratory-produced cells (that make insulin but do not secrete it when sugar is high) with real beta cells (that both make insulin and secrete it when sugar is high), we may be able to identify which microRNAs need to be there (or may not there), and use this knowledge to get cells to turn on the sugar-response machinery.
We have an outstanding team includes scientists who are the experts needed (1) to identify the key microRNAs, (2) to check the microRNAs' ability to turn on the sugar-response machinery, and (3) to transplant the treated cells to see whether they can treat diabetes in mice.
Statement of Benefit to California:
California is the largest state and has the largest economy of the USA. It, therefore, suffers the lion's share of the health and economic costs of diabetes -- a devastating disease of sugar metabolism. The total cost of diabetes has been estimated at over $170 billion for the USA (diabetes fact sheet, ADA). Scaled to the GDP of California, the total cost can be estimated to be on the order of $20 billion. The total number of people in California suffering from diabetes is estimated at over 3 million, of which about 300,000 suffer from type 1 diabetes, the kind of diabetes that has been shown to be treatable by human islet transplantation. Any advances in treatment of diabetes, such as might result if our project is successful, would have the important potential to dramatically reduce the disease burden on the state of California.
Our proposal is designed to address the major bottleneck for islet transplantation therapy of type 1 diabetes, which is an inadequate supply of transplantable tissue. We aim to identify the genetic switches to turn on the machinery that will enable laboratory-treated human embryonic stem cells to become fully functional pancreatic beta cells. While the approach of identifying and manipulating genetic switches of beta cells has obvious medical and economic payoffs specifically for diabetes treatment, the general approach may have much broader significance for stem cell therapy, as it may point the way to speed differentiation of stem cells into any particular cell type.
As the approach here is novel, and it is being applied to create tissues that can be used for medical treatment, the proposed work has the potential to spawn a completely new biotechnology industry, which would therefore benefit California not only by providing efficacious medical treatment for a major disease, but also provide jobs to a burgeoning industry.
Current in vitro methods for generating insulin-producing pancreatic beta cells from human embryonic stem cells (hESCs) result in cells lacking the ability to respond to glucose. The goal of this project is to identify specific genetic regulators, known as microRNAs (miRNAs), involved in turning on the set of genes during differentiation of beta cells that enables them to respond to blood sugar levels. This project has as its specific aims to: 1) develop a relevant reporter protein to facilitate the proposed studies; 2) use the reporter protein to purify hESC-derived insulin-positive cells and compare their miRNA profile to that of primary human beta cells to identify possible candidate miRNAs involved in regulating glucose-response genes; 3) manipulate candidate miRNA expression levels and test for expression of glucose response machinery and 4) compare in vitro and in vivo differentiation to validate the miRNA model.
Significance and Innovation:
- Reviewers agreed that the proposal addresses an important research topic.
- Achieving glucose responsiveness of pancreatic beta cells has been a major roadblock, and, if successful, the proposed research could make a major impact and significantly advance the field.
- Although aspects of the study are novel, overall the approach lacks innovation, as others have investigated miRNA expression in developing pancreatic islet cells.
Feasibility and Experimental Design:
- Reviewers expressed concern that the project depends upon the development and optimization of the reporter in Aim 1, and if there were problems with the reporter, the entire project would fail.
- The proposal contains some supportive preliminary data.
- Reviewers were skeptical that enough cells can be produced to conduct the proposed studies, since only a limited proportion of hESC-derived cells express insulin, and reporter gene transduction will likely be inefficient.
- Reviewers raised questions about how the PI will prioritize candidate miRNAs and why already-identified candidates were not being pursued.
- Reviewers doubted that studies proposed in Aim 4 would be informative.
- Although the proposal follows a systematic approach, makes use of cutting-edge technology, and would generate a large amount of data, the study lacks a clear hypothesis.
Principal Investigator (PI) and Research Team:
- Reviewers expressed some doubts as to whether the research team was appropriately qualified to execute the proposed studies.
- The PI has a strong track record in studying beta cells but lacks expertise in stem cell research.
- Reviewers felt that letters of support from collaborators should have been stronger.
Responsiveness to the RFA:
- The proposal is responsive to the RFA, as the proposed work focuses on the molecular mechanism of differentiating hESCs into a specific cell type related to human disease (glucose-responsive beta-like cells).