Pancreatic Stem Cells

Stem cells in the pancreas are produced during adulthood, but their origin is not clear. It is not known what role the B-cell progenitors play during pancreas maintenance and regeneration, or whether the adult pancreas contains a population of true stem cells. This chapter reviews evidence for the existence and identity of pancreatic progenitor and stem cells and describe the criteria for experimental demonstration of such cells. The search for pancreatic stem or progenitor cells may provide insights into the basic mechanisms of organ homeostasis, as well as a promising therapeutic approach for diabetes. It is clear that pancreatic progenitor cells exist and play a major role during embryonic development, although much has to be learned about the mechanisms and molecules controlling them. There is no evidence for pancreatic stem cells capable of self-renewal. As for the adult pancreas, no conclusive evidence shows the importance or mere existence of pancreatic progenitor or stem cells in the adult organism. It appears that, at least for pancreatic beta cells, the major mechanism for tissue maintenance is self-duplication rather than stem cell differentiation. It is possible that under certain stresses progenitor cells appear and may contribute to the maintenance of the pancreas. Most evidence points to the pancreatic ducts as the likely niche of such "facultative" progenitors. Development of culture conditions that support the growth and differentiation of dissociated pancreatic tissue, as well as in vivo lineage analysis systems, are the tools most needed for tackling this problem.