Cell interactions during the in vitro neoformation of fetal rat pancreatic islets

Distribution of N-cadherin and NCAM in neurons and endocrine cells of the human embryonic and fetal gastroenteropancreatic system

For the first time, the distribution of N-cadherin and neural cell adhesion molecule (NCAM) as well as some neuropeptides in nerve cells and endocrine cells of the human embryonic and fetal gastroenteropancreatic system has been detected in early stages (from the 6th postovulatory week onwards). Epithelial cells of the stomach and small intestine contained gastrin and somatostatin and the epithelium of the small intestine also bombesin-positive cells. Myenteric ganglionic cells showed both bombesin and VIP and were NCAM- and N-cadherin-positive at all ages studied. Some basally granulated epithelial cells of stomach, duodenum and the upper part of jejunum contained N-cadherin. The number of these cells increased from 6th to 10th postovulatory weeks. Nerve cells and the cytoplasm of individual epithelial cells of pancreatic ducts were immunoreactive for NCAM and N-cadherin. NCAM- and N-cadherin-positive cells also appeared in Langerhans islets (> 10 weeks), mainly in their peripheral part. NCAM- and N-cadherin-positive endocrine cells were less numerous than endocrine cells producing somatostatin, bombesin, and VIP, probably reflecting the features of embryonic/fetal histogenesis of Langerhans islets from epithelial endocrine cells of pancreatic ducts. NCAM and N-cadherin were localized on the surface of endocrine islets cells as well as in the cytoplasm of single islet cells. This suggests the involvement of both membrane and soluble forms of adhesion proteins in embryonic/fetal histogenesis of human pancreatic islets. The early occurrence of N-cadherin (6th postovulatory week) in enteroendocrine cells supports the existence of a common precursor. The expression of NCAM and N-cadherin in nerve cells and endocrine cells of the human fetal gastroenteropancreatic system may indicate the involvement of neuronal adhesion mechanisms in the development of neuro-endocrine complexes of fetal stomach, small intestine and pancreas.

Culture of endocrine pancreatic cells in protein-free, chemically defined media

Cell suspensions prepared by collagenase digestion of pancreata obtained from 21.5-d-old rat fetuses were preincubated in RPMI medium containing 10% fetal bovine serum (FBS), to ensure cell adhesion. Twenty hours later, this medium was replaced by a chemically defined medium. Dulbecco's modified Eagle's (DME)-F12 was used alone or supplemented with various combinations of transferrin, sodium selenite, or Ultroser G. The evolution of the culture and the islet ultrastructure were similar in defined and serum-containing media. However, in the defined medium, the neoformed islets seemed less numerous, and the fibroblast layer less dense, when compared to the RPMI + 10% FBS control medium. At Day 7, in defined media, the total insulin content per dish was half that of control cultures. None of the tested additives improved the yield of the cultures. The fractional insulin release per day was elevated in defined media. In subsequent incubations, glucose and leucine stimulated insulin release in a way characteristic of these cells of fetal origin. The labeling index of islet cells cultured in DME-F12 reached 10.7%, which is not far from that observed in RPMI + 10% FBS. Such a defined medium is useful to study B cell physiology, avoiding the possible interaction of serum components with substances to be tested.

Enhancement of pancreatic islet cell monolayer growth by endothelial cell matrix and insulin

The roles of glucose and insulin in the promotion of DNA synthesis in pancreatic islet cell monolayers were assessed using a variety of in vitro conditions. Several substrates including collagen, poly-l-lysine, Matrigel, and the extracellular matrix produced by cultured bovine endothelial cells (BCEM) were compared for their ability to promote monolayer growth. Islets grown on BCEM in combination with medium RPMI 1640 supplemented with 22.2 mM glucose or 10 micrograms/ml insulin gave the best results as determined by new DNA synthesis. The new-form monolayers were free of contaminating fibroblasts. These results suggest that insulin is critical to pancreatic islet growth when the cells are attached to biocompatible matrices.

Immunocytochemical evidence for the presence of S-100 protein in insulin-containing cells of cultured fetal rat islets

S-100 protein was long considered to be specific to glial and Schwann cells, but was subsequently proved to be present in various organs. In particular, S-100 proteinimmunoreactivity was demonstrated in the parathyroid gland, adenohypophysis and endocrine pancreas. In the present study cultured fetal rat islets were investigated in view of the possible presence of S-100 protein immunoreactivity in their cells. In the initial 5-day period, continuity between islets and ducts could be demonstrated, and the islets appeared to bud from the ducts. During this time, S-100 protein-immunoreactive cells were found in either the budding islets or ducts. The colocalization of S-100 protein and insulin was demonstrated immunocytochemically. In contrast, the newly formed islets from endocrine monolayers did not display S-100 protein immunoreactivity. After this initial period, numerous free-floating islets were observed, but only some of them contained S-100 protein immunoreactivity. S-100 protein-immunoreactive cells had the same distribution as those storing insulin, again suggesting the coexistence of the two peptides. The results suggest that S-100 protein might be involved in the regulation of islet function.

In vitro cytodifferentiation of perinatal rat islet cells within a tridimensional matrix of collagen

Cell suspensions prepared by collagenase digestion of pancreases obtained from rat fetuses (21.5 d old) and newborns (2.5 d old) were mixed with a collagen solution and inoculated on a collagen base layer. At the onset of the culture, most acinar cells became necrotic, whereas other epithelial cells proliferated. Most of the cell clusters arranged themselves into simple polarized structures composed of epithelial cells forming hollow spheres, and from these budded neoformed endocrine islets. Scarce fibroblasts were located close to these structures. Immunocytochemical localization of insulin and glucagon, as well as ultrastructural characteristics of the cell types revealed an intrainsular distribution similar to the in vivo localization. Tridimensional matrix of collagen offers, to perinatal pancreatic cells in culture, an environment close to the in vivo conditions: cells reorganize themselves in tissuelike structures and cell interactions concerned in the cytodifferentiation of pancreatic islets occur. This system allows for the study of undifferentiated epithelial cells--the presumed stem cells--differentiating and differentiated endocrine cells in the same preparation.

Ultrastructural aspects of streptozotocin cytotoxicity on rat pancreatic islets in vitro. Test of a protective effect of zinc

Pancreatic islets, newly formed in vitro were incubated in the presence of streptozotocin (STZ; 0.4 mM) for up to 6 h. Ultrastructural changes first appeared between 2 and 4 h; heterochromatization, was followed by swelling of nuclear and reticular membranes, vesiculation of the Golgi apparatus, fragmentation of cell membranes and finally mitochondrial destruction. At the end of the experiment all the B cells were destroyed, whereas the other cell types remained intact. Exogenous ZnSO4 was added during preincubation periods to increase the intrainsular zinc content and to determine any protective effect against STZ-cytotoxicity. Since the addition of zinc had no obvious effect, it is suggested that STZ cytotoxicity on B cells cannot be attributed to competition for zinc between copper-zinc superoxide dismutase (Cu-Zn-SOD) and the crystallization of insulin.