Neonatal pig pancreatic duct–derived insulin-producing cells: preliminary in vitro studies

Isolation, cultivation and identification of pancreatic stem/progenitor cells in rabbit

Pancreases obtained from 1–9-day-old rabbits were digested with 1 mg/ml ?? collagenase and cultivated with low-glucose Dulbecco's modified Eagle's medium (DMEM). The cells were subcultured almost until confluence. They were identified as pancreatic stem/progenitor cells using two methods: an immunohistochemical staining technique and the response of glucose-stimulated insulin secretion after β-cell induction. Results showed that the cells of rabbits acquired strong proliferation ability, and expressed the markers of pancreatic stem/progenitor cells: PDX-1, CK19 and nestin. After β-cell induction for 2 days, 20% of cells were dithizone (DTZ) positive, rapidly increasing to 80% after 6 days. Insulin secretion was stimulated by a high glucose concentration (26 mmol/l). These powerful tests demonstrated that isolated and cultivated cells in rabbits were pancreatic stem/progenitor cells. This result has not yet been reported elsewhere.

Mechanism of prolonged gene expression by Epstein-Barr virus-based plasmid in porcine cells

BACKGROUND

We previously showed that an Epstein-Barr virus (EBV)-based plasmid, pEBVGFP, exerts prolonged gene expression in porcine neonatal pancreatic cell clusters (NPCCs). In this study, the mechanism underlying this was investigated.

METHODS

GFP expression was analyzed in porcine cells transfected with pEBVGFP by FACS analysis and confocal microscopy. The possible integration of pEBVGFP into the chromosomal DNA was analyzed by Southern blot. Self-replication of the EBV-based plasmid in porcine cells was investigated by PCR. The NPCCs were immunostained to characterize cells transfected with pEBVGFP.

RESULTS

The EBV based plasmid provided prolonged GFP expression in porcine cells and duct cells were the main cells transfected among NPCCs. Southern blot showed that the transfected pEBVGFP stayed for a long time as an episome rather than integrating into the chromosomal DNA. pEBVGFP isolated from the transfected porcine cells had methylated CpG suggesting that they self-replicated in those cells.

CONCLUSIONS

The EBV-based plasmid may be useful for genetically manipulating porcine cells to enhance their value as xenotransplantation sources.

Transdifferentiation molecular pathways of neonatal pig pancreatic duct cells into endocrine cell phenotypes

Restrictions in availability of cadaveric human donor pancreata have intensified the search for alternate sources of pancreatic endocrine tissue. We have undertaken to assess whether nonendocrine pancreatic tissue, with special regard to ducts, including epithelial cells, and retrieved from neonatal pig pancreata that are used for islet isolation, may under special in vitro culture conditions generate endocrine cell phenotypes. Special care was taken to identify the time-related appearance of molecular and biochemical markers associated with beta-cell specificity, in terms of glucose-sensing apparatus and insulin secretion. For this purpose, established ductal origin monolayer cell cultures were incubated with a battery of mono- or polyvalent growth factors. Morphological, immunocytochemical, molecular, and functional assays indicated that under special culture conditions ductal origin cells acquired an endocrine identity, based upon expression of key gene transcripts that govern the stimulus-coupled insulin secretory activity. Among factors eliciting transdifferentiation of ductal epithelial into endocrine cells, Sertoli cell (SC)-conditioned medium seemed to be the most powerful inducer of this process. In fact, the resulting cultures not only expressed beta-cell-oriented metabolic markers but also were associated with insulin and C-peptide output at equimolar ratios. This finding indicates that SC coincubation, more than other conditions, caused originally ductal cell cultures to gradually differentiate and mature into beta-cell-like elements. In vivo studies with this early cell differentiation product will test whether our approach may be suitable for correction of hyperglycemia in diabetic animal models.

Short-term Stimulation Studies on Neonatal Pig Pancreatic Duct-derived Cell Monolayers

Short-term stimulation with insulinotropic factors may induce morphologic and functional changes in primary ductal cell cultures as a potential source of stem cells. We sought to assess the capacity of hepatocyte growth factor (HGF) to induce expression and maturation of proteins--PDX-1 and GLUT-2--and the subsequent beta-cell secretory profiles. HGF, which is involved in pancreatic development, may induce islet beta-cell neogenesis. Primary ductal cell monolayers were cultured in Click's + FBS 10% at 37 degrees C until tissue confluence. The medium was enriched with HGF (10 ng/mL for different periods); controls were treated for similar times with normal culture medium. At the end of the study, three-dimensional islet-like cell aggregates were observed in both conditions. In all conditions immunostaining studies showed positivity for the major endocrine-phenotype cell markers: insulin, PDX-1, glucokinase, and GLUT-2. Furthermore, treatment with HGF for short periods induced the expression of a functionally active, phosphorylated isoform of PDX-1. Finally, we observed that under basal conditions the cells initially and progressively released proinsulin throughout 5 days in all settings. Thereafter proinsulin was gradually replaced by insulin in the culture medium, reflecting a maturation progress. This pattern of insulin maturation and release was more evident when the cells were continuously stimulated with HGF for 12 days. The employed stimuli seemed to differentiate the original ductal cell layers toward endocrine cell phenotypes that synthesize and release proinsulin and subsequently insulin. HGF seems to provide a more efficient differentiation.