Scientists at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), one of the National Institutes of Health (NIH), have induced human insulin-producing cells of the pancreas to revert to islet precursor cells. These precursor cells are capable of expansion and appear to naturally and efficiently differentiate into clusters of islet-like cells. This work may help to clarify the natural lifecycle of the beta cell and may eventually have applications for diabetes treatment. The study appears on-line today in Science Express, the rapid publication web site of the journal Science.
Insulin-producing beta cells exist in spherical clusters, called islets, in the pancreas. Research shows that beta cells are born, die, and are replaced by other beta cells throughout a person's lifetime, but little is known about the process. When the body cannot produce or replace beta cells, insulin levels fall causing blood glucose levels to rise and diabetes results. This study's findings may eventually have implications for islet transplantation, an experimental treatment for type 1 diabetes.
"This is a step forward in the field, but we're still a long way from using this knowledge to develop a therapy for diabetes," says lead author, Marvin C. Gershengorn, M.D., Scientific Director of NIDDK's Division of Intramural Research and Chief of the institute's Clinical Endocrinology Branch. "For one thing these differentiated cells do not function as well as the original cells. They don't produce as much insulin and they are not as adaptable to changes in the environment. For another thing, we grew these cells in a culture that is not optimal for use in humans, so we are not ready to transplant these cells into people. Still, I am encouraged."
The researchers removed islets from human cadaver pancreata, as is done before islet transplantation, and exposed these islets to a medium containing fetal bovine serum. Over 17 days the cells in the clusters migrated out until the original islets were depleted. These migrating islet cells, identified as insulin-expressing cells, then transformed into more primitive precursor cells that do not produce insulin.
These new cells, called human islet-derived precursor cells (hIPCs), reproduce easily. The researchers observed that the hIPCs showed substantial proliferative potential, doubling in number about every 60 hours, and by 90 days had expanded by almost a billion fold. Not stem cells, these precursor cells are transitional cells since they originated from insulin-producing islets. The authors note, however, that this finding does not preclude the possible existence of islet stem cells, as yet undiscovered.
"We knew that islets regenerate," says Gershengorn. "When old islets die out, the pancreas produces new ones to take their place. So, we thought, there must be cells within the pancreas that can reproduce and efficiently differentiate into hormone-producing cells or even intact islets. The challenge was to identify them and make them work."
After isolating significant numbers of hIPCs and showing that they are highly proliferative, the researchers wanted to see if they could reverse the process and induce the new cells to become insulin-producing again. In the second stage of their study, the researchers exposed cultures of hIPCs to a serum-free medium. They saw a highly efficient, gradual transition from precursor hIPCs to epithelial islet-like cell aggregates over a period of several weeks. The cell aggregates produced insulin and other hormones, but at much lower levels than that of human islets — about 0.02 percent of the level of insulin produced by healthy islets. Still, the islet-like cells did show many of the characteristics of the original beta cells. "It appears, therefore, that hIPCs are pre-determined to transition back into hormone-producing cells under minimal conditions in culture," added Gershengorn.
One of NIDDK's goals for long-term diabetes research is to better understand the beta cell and how it regenerates. These findings may eventually have implications for diabetes treatments, including islet transplantation. Islet transplantation involves the infusion of islets derived from donor pancreata into a person with complicated type 1 diabetes. The hope is that some of the transplanted cells will survive in the pancreas and continue producing insulin. A major obstacle to the wider use of islet transplantation as a treatment for type 1 diabetes is the small number of donor pancreata that become available for use each year and the large number of islets needed for transplantation. The NIDDK is focusing its research on understanding the beta cell and its regeneration and on efforts to develop alternative sources of beta cells.
The researchers hope that future studies will corroborate their findings and address some of the unanswered questions. For example, the researchers plan to conduct studies to try to define the optimal environmental conditions to grow precursor cells and to stimulate them to differentiate into hormone-producing cells. Their goal is to design a cellular environment as close as possible to the natural environment of a healthy human pancreas. Another challenge is to develop a culture medium that does not rely on animal serum, so cells grown in the lab can be transplanted back into people with a minimum risk of side effects.
More information on islet transplantation can be found on the NIDDK web site: http://diabetes.niddk.nih.gov/dm/pubs/pancreaticislet/
(C) 2004 - NIH
Gershengorn MC, Hardikar AA, Hardikar A, Wei C, Geras-Raaka E, Marcus-Samuels B, Raaka BM.
Epithelial-to-Mesenchymal Transition Generates Proliferative Human Islet Precursor Cells.
Science. 2004 Nov 25; [Epub ahead of print]
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