IDENTIFICATION & CHARACTERIZATION OF PANCREATIC ENDOCRINE PROGENITOR CELLS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cell-cell interactions regulated by cell adhesion molecules (CAMs) have been recently shown to transduce a variety of signals supporting cellular functions as diverse as proliferation, differentiation, and survival. Our preliminary studies indicate that the cell adhesion molecule Ep-CAM can transduce mitogenic signals in human pancreatic islet cells. Consistently with this result, we find that over-expression of Ep-CAM in pancreatic ductal cells of a transgenic mouse model causes a significant enlargement of the pancreas, due to an increased cell number of both the exocrine (5-folds) and endocrine compartments (12-folds). These results indicate that transgenic over-expression of Ep-CAM in the ductal epithelium may cause the expansion of putative progenitors of both the exocrine and endocrine cell lineages. Importantly, despite the significant enlargement of islets, these mice show no defects of insulin production and secretion. Thus, we postulate that unlike growth factors-mediated cell proliferation, which can be associated with a decreased expression of differentiated traits, Ep-CAM-mediated cell growth of putative islet progenitors (comprised within the ductal epithelium) in these transgenic mice allows the development of a large islet mass with no apparent negative effects on beta-cell-specific genes¿ expression. The central hypothesis of our studies is that transient over-expression of Ep-CAM in human beta-cells by means of Adenoviral gene transfer may induce cell growth with minimal effects on the endocrine cell function. Thus, based on the unique molecular pathways activated by cell adhesion molecules as opposed to cell proliferation induced by classical soluble growth factors, we hypothesize that a transient growth stimulus provided by a temporally limited over-expression of Ep-CAM in human islet cells will have minimal (if any) negative effects on insulin production. Our objective is to test whether Ep-CAM can be used as a molecular switch to transiently activate human beta-cell growth in vitro. Furthermore, we plan to test whether treatment of islet beta-cells with a soluble recombinant Ep-CAM molecule (produced in our laboratory) may also stimulate cell growth, and/or improve islet beta-cells¿ survival. The proposed experimental plan focuses on the following Specific Aims: 1) To study the effects of transient over-expression of Ep-CAM in human adult beta-cells by means of Adenoviral vectors, and assess the effects on cell growth, differentiation, and survival; 2) To assess the mophoregulatory effects of Ep-CAM over-expression on the three-dimensional organization of beta-cell clusters within pancreatic islets by means of "advanced microscopic techniques" such as "two photon confocal microscopy," and "high voltage electron microscopy." Since the architectural organization of the beta-cells within the islet cell clusters has been shown to have a profound functional impact on the endocrine function of insulin-producing cells, we predict that the proposed studies will uncover novel mechanisms of cell-cell interactions mediated by the adhesion receptor Ep-CAM, and may ultimately help in the design of novel protocols of islet cell expansion for transplantation.