Development of embryonic chick insulin cells in culture: beneficial effects of serum-free medium, raised nutrients, and biomatrix

Islet-derived stellate-like cells as a novel source for islet neogenesis in chicks

The therapeutic potential of stem cells has led to renewed interest in regenerative biology. Pancreatic stellate cells have been reported in the mammalian pancreas; however, there are very few reports on stellate cells in the chicken pancreas. The intercalated duct epithelial cells observed in the A and B islets of the chicken pancreas have been claimed to be stellate cells from their morphological appearance. While isolating islets and acinar cells from the chick pancreas, we have found a population of stellate-like cells, which has been successfully propagated in a defined nutrient medium. These cells were immunopositive for vimentin, desmin, and fibronectin and also expressed alkaline phosphatase, indicating their undifferentiated state. On exposure to serum-free medium containing specific nutrients and differentiating agents, these stellate-like-cells gave rise to islet-like cell clusters. Islet-like clusters stained positive for the islet specific stain diphenyl thiocarbazone and were immunopositive for C-peptide indicating de novo insulin synthesis. These clusters secreted insulin in response to glucose challenge, thus suggesting their similarity to islets. Thus stellate cells found in chick pancreatic islets exhibit potential to differentiate into islet-like clusters. Taken together, our study documents for the first time the presence of a stellate-like cell population in chick pancreatic islets providing a source for islet neogenesis.

TGF-beta1 and high levels of glucose do not increase insulin cell proportions in the avian embryonic pancreas

TGF-beta1 is thought to decrease the proportion of embryonic pancreatic beta-cells with respect to alpha-cells, whereas glucose is thought to enhance beta-cell proportions in rats. However, chick pancreatic cells may respond in a dissimilar way to glucose. Thus, the effect of TGF-beta1 on the proportion of beta-cells in embryonic chick dorsal pancreatic buds (DPBs) in vitro was tested with short-term exposure to high levels of glucose. Five-day-old chick DPBs were cultured on growth factor-reduced Matrigel, which contains reduced levels of growth factors including TGF-beta1, and a variety of culture media with and without high levels of glucose. TGF-beta1 reduced the proportion of beta-cells, as expected. A similar decrease in the proportion of beta-cells occurred in the presence of high levels of glucose.

Regulation of the proportion of insulin cells in embryonic chick pancreas: effect of a growth factor-reduced extracellular matrix in combination with retinoic acid

Both retinoic acid (RA) and transforming growth factor (TGF)-beta1 are known to be influential in the development of insulin cells. Respectively, they increase and decrease the proportion of insulin cells when added to cultures of embryonic chick dorsal pancreatic buds. The aim of this study was to define the action of RA in the presence of decreased levels of TGF-beta1, as are found in growth factor-reduced Matrigel (GFRM), on the proportion of insulin cells. The endodermal component of 5-d chick dorsal pancreatic buds was explanted on to GFRM. Retinoic acid (10(-6) M) was added to Ham's F12 culture medium containing insulin (5 microg/ml), transferrin (5 microg/ml), and selenium (10(-10) M) (F12.ITS). Control explants were cultured in F12.ITS alone or in F12.ITS containing dimethyl sulfoxide (DMSO). After 7 d in culture, insulin and glucagon cells were localized immunocytochemically; changes in numbers of insulin cells were expressed as a percentage of insulin plus glucagon cells. Medium containing RA or DMSO increased the proportion of insulin cells significantly compared with the proportion in the explants cultured in F12.ITS medium alone.

Morphogenesis of gut and distribution of the progenitors of gut endocrine cells at cranial somite levels of the chick embryo

The primary objective of this study was to establish the distribution of the progenitors of selected gut endocrine cell types at cranial somite levels. In addition, analysis of the material has provided new information about the location of the presumptive territories of certain gut regions and of the pancreas. Narrow transverse strips of full-thickness blastoderm two or three somites in length were excised at the levels of somites 1 to 5 of 8.5- to 18-somite chick embryos and cultured as chorioallantoic grafts to an age equivalent to 20 days of incubation. The grafts were analysed by immunocytochemistry, and their morphology was evaluated. Individual grafts exhibited up to five different types of gut morphology, including those of oesophagus, proventriculus, gizzard, pyloric region, small intestine, and pancreas. The morphologic survey yielded new information about the location, extent, or both, of the territories of the pyloric region, the small intestine, and the pancreas. In general, the progenitors of gut endocrine cell types identified were those expected for the different morphologic regions: in only a few instances were ectopic endocrine cell types detected. The available evidence points to the progenitors of bombesin/gastrin-releasing peptide cells being located cranial to somite 5 at the stages studied. Based on the morphology and the proportion of insulin cells, the development of pancreas in grafts appeared compromised compared with grafts of the intact dorsal pancreatic bud: this may relate to the likely exclusion of dorsal pancreatic bud mesoderm from the graft area. The results show that presumptive small intestinal endoderm in grafts can differentiate in the absence of homologous (i.e., small intestinal) mesoderm: this accords with the view that the primary source of positional information in the gut is in the endoderm.

Isolation, maintenance, and characterization of human pancreatic islet tumor cells expressing vasoactive intestinal peptide

Tissue from a vasoactive intestinal peptide (VIP)-secreting human tumor has been used to establish and characterize human neuroendocrine primary cell cultures from which permanent, clone-derived cell lines have been established. Viable cells were obtained by enzymatic and mechanical dissociation of freshly resected pancreatic islet tumor and hepatic metastatic tumor tissues. Aliquots of tumor cells were established ex vivo under culture conditions including porous substrata coated with type IV collagen and laminin and a low serum, hormonally defined culture medium. The small (<10 microm) rounded, grape-like cells had a very slow growth rate of doubling times estimated at several weeks or more. After several passages, morphologically uniform cells were derived that strongly expressed neuroendocrine markers of synaptophysin and synaptobrevin. Although chromogranin A and VIP had somewhat weaker expression, both demonstrated phorbol ester-stimulated secretion. The morphologic and secretory properties were maintained by the cells for nearly 2 years in culture. The establishment of this novel VIP-secreting human neuroendocrine cell line (HuNET) makes available a culture model with which to study a transformed version of this pancreatic islet cell type and offers approaches by which to establish islet tumor cell lines.

Beneficial effect of nicotinamide on the proportion of insulin cells in developing chick pancreas

Previous studies have suggested that nicotinamide increases the number of insulin cells both in vivo and in vitro. However, the question remains as to whether there is in fact an increase and whether this increase is caused by the proliferation of progenitor cells, or by replication of existing insulin cells. In order to investigate this, the endodermal component of dorsal pancreatic buds of 5-day-old chick embryos was cultured on Matrigel in a serum-free medium (Ham's F12-ITS) to which nicotinamide, at a concentration of 5 and 10 mM, respectively, was added. Control explants were cultured in Ham's F12-ITS medium without nicotinamide. After 7 days in culture the buds were incubated with bromodeoxyuridine (BrdU) and then processed for immunocytochemistry. Localization of insulin, BrdU and glucagon was carried out on adjacent serial sections. The proportion of insulin cells was 6.76, 11.32 and 16.86% in control, 5 and 10 mM nicotinamide-treated explants, respectively. Hence adding nicotinamide to the culture medium induced a 1.7- and 2.5-fold increase in the proportion of insulin cells when compared to the controls. These proportions were significantly different from that of control explants (P < 0.05). However, a very small number of insulin cells were found to be proliferating, suggesting that the increase in the proportion of insulin cells had resulted from stimulation of progenitor cells and not proliferation of existing insulin cells.

Manipulation of pancreatic stem cells for cell replacement therapy

The demonstration of the existence of tissue-specific adult stem cells has had a great impact on our understanding of stem cell biology and its application in clinical medicine. Their existence has revolutionized the implications for the treatment of many degenerative diseases characterized by either the loss or malfunction of discrete cell types. However, successful exploitation of this opportunity requires that we have sufficient know-how of stem cell manipulation. Because stem cells are the founders of virtually all tissues during embryonic development, we believe that understanding the cellular and molecular mechanisms of embryogenesis and organogenesis will ultimately serve as a platform to identify factors and conditions that regulate stem cell behavior. Discovery of stem cell regulatory factors will create potential pharmaceutical opportunities for treatment of degenerative diseases, as well as providing critical knowledge of the processes by which stem cells can be expanded in vitro, differentiated, and matured into desired functional cells for implantation into humans. A well-characterized example of this is the hematopoietic system where the discovery of erythropoietin (EPO) and granulocyte-colony stimulating factor (G-CSF), which regulate hematopoietic progenitor cell behavior, have provided significant clinical success in disease treatment as well as providing important insights into hematopoiesis. In contrast, little is known about the identity of pancreatic stem cells, the focus of this review. Recent reports of the potential existence of pancreatic stem cells and their utility in rescuing the diabetic state now raise the same possibilities of generating insulin-producing beta cells as well as other cell types of the pancreatic islet from a stem cell. In this review, we will focus on the potential of these new developments and how our understanding of pancreas development can help design strategies and approaches by which a cell replacement therapy can be implemented for the treatment of insulin-dependent diabetes which is manifested by the loss of beta cells in the pancreas.

The effect of retinoic acid on the proportion of insulin cells in the developing chick pancreas

We assessed the potential role of all-trans-retinoic acid on the developing chick pancreas, specifically with regard to the proportions of insulin cells. The endodermal component of the dorsal pancreatic bud of 5-d-old chick embryos was cultured on Matrigel. Retinoic acid (10(-6) or 10(-5) M) was added to a standard serum-free medium, Ham's F12 containing insulin, transferrin and selenium (F12.ITS). Control grafts were cultured in F12.ITS alone or in F12.ITS with DMSO (the diluent for retinoic acid). After 7 d the explants were retrieved, freeze-dried, vapor-fixed, and embedded in resin. Endocrine cell types were identified by immunocytochemistry. The numbers of insulin cells were expressed as a proportion of the sum of insulin plus glucagon cells. Retinoic acid had a dose-related effect; the proportion of insulin cells in explants treated with the lower dose of retinoic acid (10(-6) M) was more than twice the proportion of insulin cells in explants treated with the higher dose (10(-5) M) of retinoic acid and more than three times that of the control grafts.

Morphogenesis and differentiation of the avian endocrine pancreas, with particular reference to experimental studies on the chick embryo

The avian pancreas has three or four lobes and develops from a dorsal and two ventral buds. The cells that will contribute to formation of the dorsal bud are at first located in the mid-dorsal endoderm, those of the ventral buds in the floor of the foregut. The determination of endoderm to form dorsal and ventral bud derivatives occurs before formation of the buds. The highest concentration of endocrine tissue is in the splenic lobe. The lobes contain A and B islets in which glucagon and insulin cells, respectively, predominate. Islets contain somatostatin and pancreatic polypeptide (PP) cells, both of which also occur scattered in the exocrine parenchyma. Pancreatic endocrine cells arise from endoderm: glucagon, insulin, and somatostatin cells differentiate early, PP cells later. To establish culture conditions suitable for avian insulin cells, the epithelial component of dorsal buds of 5-day chick embryos was cultured under various conditions. At the end of 7 days the proportion of insulin cells was determined. In raising the proportion of insulin cells, Matrigel was superior to collagen gel and a serum-free medium (incorporating insulin, transferrin, and selenium) was superior to a serum-containing medium. Modifications to the serum-free medium were tested. Raising the level of glucose or of glucose and essential amino acids increased the proportion of insulin cells. This proportion was also increased by replacement of insulin by insulin-like growth factor-I, whereas addition of transforming growth factor beta1 reduced the proportion. Transfer of explants from poor to favourable culture conditions showed that the improved conditions stimulated quiescent insulin progenitor cells to develop.