Adult human cytokeratin 19-positive cells reexpress insulin promoter factor 1 in vitro - Further evidence for pluripotent pancreatic stem cells in humans

Human pancreatic cells with a typical ductal phenotype and potential to pro liferate can be obtained in vitro, but the differentiation capacity of thes e putative human pancreatic stem cells remains to be documented. We investi gated the protein and mRNA expression of insulin promoter factor 1 (IPF-1) (or pancreas/duodenal homeobox 1), a transcription factor critical for panc reatic development and endocrine cell neogenesis, in human pancreatic ducta l cells derived from cultured exocrine tissue. In vitro, exocrine cells rap idly adhered (within 12 h) and were de-/transdifferentiated to ductal cells after 3 days with a dramatic loss of amylase protein (n = 4, 92 +/- 3,3%, P < 0.05 vs. day 1) and a simultaneous increase of ductal cytokeratin 19 pr otein (n = 4, 3.4-fold on day 3 and 7-fold on day 9, P 4 0.05 vs, day 1), I PF-1 protein and mRNA levels were low to undetectable in exocrine preparati ons before culture. After 2 days of culture, a 3.2-fold increase in IPF-1 p rotein was observed, corresponding to the characteristic 46kDa protein in W estern blots. Reverse transcriptase-polymerase chain reaction confirmed a 1 0.5-fold increase in IPF-1 mRNA levels after 3 days of culture (n = 5, P < 0.001 vs. day 1), Double immunocytochemistry showed direct evidence that IP F-1 appeared during culture in these exocrine-derived ductal cells (cytoker atin 7-positive) and was not merely in contaminating endocrine cells (chrom ogranin A-positive). In conclusion, we describe herein the first converging evidence on both the molecular and protein level that human cells with a t ypical ductal phenotype derived ex vivo from pancreatic exocrine tissue (ob tained from healthy donors) can reexpress IPF-1 in culture, suggesting thei r pancreatic precursor/stem cell potential.