TRANSDIFFERENTIATION OF HUMAN ISLETS TO PANCREATIC DUCTAL CELLS IN COLLAGEN MATRIX CULTURE

Transdifferentiation is a change from one differentiated phenotype to another, involving morphological and functional phenotypic markers. St ability of the cellular phenotype is probably related to the extracell ular milieu, as well as cytoplasmic and nuclear components that intera ct to control gene expression, and the conversion of cell phenotype is likely to be accomplished by selective enhancement of gene expression , which controls the terminal developmental commitment of cells. In th is paper, we show the induction of cultured human islets cells to alte r their usual phenotypic expression and attain morphological and funct ional characteristics of duct cells. Islets were isolated by collagena se digestion of pancreata that were removed from cadaveric organ donor s. The islets were purified on a two-step density gradient of bovine s erum albumin and were then placed into a three-dimensional rat-tail co llagen gel matrix supplemented with NuSerum epithelial growth factor a nd cholera toxin. During the initial 96 h of culture, the islets under went a cystic transformation that was associated with (1) the maintena nce of immunoreactivity for neuron-specific enolase, an endocrine cell marker, but a progressive loss of insulin gene expression, (2) a loss of immunoreactivity for insulin protein, and (3) the appearance of CK -19, a marker for ductal cells. After the transformation was complete, the cells had the ultrastructural appearance of primitive duct-like c ells. Cyst enlargement after the initial 96 h was associated, at least in part, with cell replication, as reflected in the 1500% increase in the incorporation of tritiated thymidine. These experiments are consi stent with the transdifferentiation of an islet cell to a ductal cell. The exact mechanisms involved still need to be fully elucidated.