The Avian Endocrine Pancreas

The avian endocrine pancreas is comprised of A-islets containingA₁- and A₂- cell types, and B-islets containing A₁- and B-celltypes. The function of the A₂- and B-cells is the secretionof glucagon and insulin, respectively, while that of the A₂-cellsis uncertain. The avian pancreas contains small amounts of insulin, has poorinsulinogenic potential, and releases the hormone "sluggishly"in response to high glucose load. Fasting, hormones, and/orvagal stimulation do not alter insulin release. Avian insulinis not anti-lipolytic and is poorly lipogenic in in vitro aviansystems. Both avian pancreas and plasma contain 5-10 times more glucagonthan observed in mammals; however, no studies have been reportedemploying the avian hormone. Birds are extremely sensitive tomammalian glucagon, exhibiting a rapid and marked hyperglycemia,hepatic glycogenolysis, hyperglycerolemia, and hypertriglyceridemia.The lipolytic effects of glucagon are intensified in ‘vitro’by insulin. A pancreatic polypeptide (APP) containing 36 amino acid residueshas been isolated from the avian pancreas, but not from gut,liver, proventriculus, or gizzard. APP circulates normally,fluctuates with nutritional manipulation, and is found in allavian species investigated. At high levels APP induces hepaticglycogenolysis and hypoglycerolemia. At low levels APP is apowerful "gastric" secretogogue, encouraging rapid proventricularvolume, acid, pepsin, and protein release.     

In Vitro Pancreas Organogenesis from Dispersed Mouse Embryonic Progenitors

The pancreas is an essential organ that regulates glucose homeostasis and secretes digestive enzymes. Research on pancreas embryogenesis has led to the development of protocols to produce pancreatic cells from stem cells ¹. The whole embryonic organ can be cultured at multiple stages of development ^2-4. These culture methods have been useful to test drugs and to image developmental processes. However the expansion of the organ is very limited and morphogenesis is not faithfully recapitulated since the organ flattens. We propose three-dimensional (3D) culture conditions that enable the efficient expansion of dissociated mouse embryonic pancreatic progenitors. By manipulating the composition of the culture medium it is possible to generate either hollow spheres, mainly composed of pancreatic progenitors expanding in their initial state, or, complex organoids which progress to more mature expanding progenitors and differentiate into endocrine, acinar and ductal cells and which spontaneously self-organize to resemble the embryonic pancreas. We show here that the in vitro process recapitulates many aspects of natural pancreas development. This culture system is suitable to investigate how cells cooperate to form an organ by reducing its initial complexity to few progenitors. It is a model that reproduces the 3D architecture of the pancreas and that is therefore useful to study morphogenesis, including polarization of epithelial structures and branching. It is also appropriate to assess the response to mechanical cues of the niche such as stiffness and the effects on cell´s tensegrity.     

Endocrine Cell Clustering During Human Pancreas Development

The development of efficient, reproducible protocols for directed in vitro differentiation of human embryonic stem (hES) cells into insulin-producing β cells will benefit greatly from increased knowledge regarding the spatiotemporal expression profile of key instructive factors involved in human endocrine cell generation. Human fetal pancreases 7 to 21 weeks of gestational age, were collected following consent immediately after pregnancy termination and processed for immunostaining, in situ hybridization, and real-time RT-PCR expression analyses. Islet-like structures appear from approximately week 12 and, unlike the mixed architecture observed in adult islets, fetal islets are initially formed predominantly by aggregated insulin- or glucagon-expressing cells. The period studied (7–22 weeks) coincides with a decrease in the proliferation and an increase in the differentiation of the progenitor cells, the initiation of NGN3 expression, and the appearance of differentiated endocrine cells. The present study provides a detailed characterization of islet formation and expression profiles of key intrinsic and extrinsic factors during human pancreas development. This information is beneficial for the development of efficient protocols that will allow guided in vitro differentiation of hES cells into insulin-producing cells. (J Histochem Cytochem 57:811–824, 2009)     

Studies on the Endocrine Pancreas of Amphibians and Reptiles

At this time, it can be said that the available data obtainedfrom amphibians and reptiles as regards the endocrine pancreasis consistent with the much more extensive data known for themetabolic effects of insuilin and glucagon in mammals. Thereremain, however, many unexplored facets of the specific responsesof the pancreas and the target tissues in lower animals.     

Follicles in the Endocrine Pancreas of Some Myxinoid Species

A light microscopic study of the endocrine pancreas in some myxinoids has revealed a striking difference in the occurrence of follicles. Islet tissue follicles are regularly occurring and also abundant in Myxine glutinosa, but are sparse or absent in Eptatretus burgeri and Eptatretus stouti. Whether this is caused by a decreased need for insulin in Myxine glutinosa is discussed but remains an open question.     

Pancreas and Kidney Transplantation Using Embryonic Donor Organs

One novel solution to the shortage of human organs available for transplantation envisions ‘growing’ new organs in situ. This can be accomplished by transplantation of developing organ anlagen/primordia. We and others have shown that renal anlagen (metanephroi) transplanted into animal hosts undergo differentiation and growth, become vascularized by blood vessels of host origin and exhibit excretory function. Metanephroi can be stored for up to 3 days in vitro prior to transplantation with no impairment in growth or function post-implantation. Metanephroi can be transplanted across both concordant (rat to mouse) and highly disparate (pig to rodent) xenogeneic barriers. Similarly, pancreatic anlagen can be transplanted across concordant and highly disparate barriers, and undergo growth, differentiation and secrete insulin in a physiological manner following intra-peritoneal placement. Implantation of the embryonic pancreas, is followed by selective differentiation of islet components. Here we review studies exploring the potential therapeutic applicability for organogenesis of the kidney or endocrine pancreas.     

Pancreas and Kidney Transplantation Using Embryonic Donor Organs

One novel solution to the shortage of human organs available for transplantation envisions ‘growing’ new organs in situ. This can be accomplished by transplantation of developing organ anlagen/primordia. We and others have shown that renal anlagen (metanephroi) transplanted into animal hosts undergo differentiation and growth, become vascularized by blood vessels of host origin and exhibit excretory function. Metanephroi can be stored for up to 3 days in vitro prior to transplantation with no impairment in growth or function post-implantation. Metanephroi can be transplanted across both concordant (rat to mouse) and highly disparate (pig to rodent) xenogeneic barriers. Similarly, pancreatic anlagen can be transplanted across concordant and highly disparate barriers, and undergo growth, differentiation and secrete insulin in a physiological manner following intra-peritoneal placement. Implantation of the embryonic pancreas, is followed by selective differentiation of islet components. Here we review studies exploring the potential therapeutic applicability for organogenesis of the kidney or endocrine pancreas.Key Words: cell therapy, diabetes mellitus, end-stage renal disease, metanephros, organogenesis, xenotransplantation     

Midkine Promotes Selective Expansion of the Nephrogenic Mesenchyme during Kidney Organogenesis

During kidney development, the growth and development of the stromal and nephrogenic mesenchyme cell populations and the ureteric bud epithelium is tightly coupled through intricate reciprocal signaling mechanisms between these three tissue compartments. Midkine, a target gene activated by retinoid signaling in the metanephros, encodes a secreted polypeptide with mitogenic and anti-apoptotic activities in a wide variety of cell types. Using immmunohistochemical methods we demonstrated that Midkine is found in the uninduced mesenchyme at the earliest stages of metanephric kidney development and only subsequently concentrated in the ureteric bud epithelium and basement membrane. The biological effects of purified recombinant Midkine were analyzed in metanephric organ culture experiments carried out in serum-free defined media. These studies revealed that Midkine selectively promoted the overgrowth of the Pax-2 and N-CAM positive nephrogenic mesenchymal cells, failed to stimulate expansion of the stromal compartment and suppressed branching morphogenesis of the ureteric bud. Midkine suppressed apoptosis and stimulated cellular proliferation of the nephrogenic mesenchymal cells, and was capable of maintaining the viability of isolated mesenchymes cultured in the absence of the ureteric bud. These results suggest that Midkine may regulate the balance of epithelial and stromal progenitor cell populations of the metanephric mesenchyme during renal organogenesis.     

Midkine Promotes Selective Expansion of the Nephrogenic Mesenchyme During Kidney Organogenesis

During kidney development, the growth and development of the stromal and nephrogenic mesenchyme cell populations and the ureteric bud epithelium is tightly coupled through intricate reciprocal signaling mechanisms between these three tissue compartments. Midkine, a target gene activated by retinoid signaling in the metanephros, encodes a secreted polypeptide with mitogenic and anti-apoptotic activities in a wide variety of cell types. Using immmunohistochemical methods we demonstrated that Midkine is found in the uninduced mesenchyme at the earliest stages of metanephric kidney development and only subsequently concentrated in the ureteric bud epithelium and basement membrane. The biological effects of purified recombinant Midkine were analyzed in metanephric organ culture experiments carried out in serum-free defined media. These studies revealed that Midkine selectively promoted the overgrowth of the Pax-2 and N-CAM positive nephrogenic mesenchymal cells, failed to stimulate expansion of the stromal compartment and suppressed branching morphogenesis of the ureteric bud. Midkine suppressed apoptosis and stimulated cellular proliferation of the nephrogenic mesenchymal cells, and was capable of maintaining the viability of isolated mesenchymes cultured in the absence of the ureteric bud. These results suggest that Midkine may regulate the balance of epithelial and stromal progenitor cell populations of the metanephric mesenchyme during renal organogenesis.Key Words: growth factor, proliferation, apoptosis, ureteric bud, branching morphogenesis, epithelial progenitor, development, signaling     

The Chondrichthyean Endocrine Pancreas: What are its Functions?

The limited studies on chondrichthyean islet function are discussedand evaluated. The only certain effect is that of insulin-inducedhypoglycemia in all species studied. Bovine and chondrichthyeaninsulin preparations both have pronounced effects. The evidencealso indicates that glucagon is hyperglycemic in some species,but the source of the mobilized glucose is unknown. Blood glucoselevels in the Chondrichthyes show wide variations, even withina species, and are apparently not closely regulated. To thepresent time the effects of pancreatic hormones on carbohydratemetabolism have been investigated, but other possible effectsof these hormones on intermediary metabolism (e.g., proteinand lipid) have not been studied. The sparse information onthe immunology of chondrichthyean insulins is also discussed.     

Elimination of Von Hippel-Lindau Function Perturbs Pancreas Endocrine Homeostasis in Mice

Mutations in the human homolog of the Vhlh gene [encoding the von-Hippel Lindau (VHL) protein] lead to tumor development. In mice, depletion of Vhlh in pancreatic ß-cells causes perturbed glucose homeostasis, but the role of this gene in other pancreatic cells is poorly understood. To investigate the function of VHL/HIF pathway in pancreatic cells, we inactivated Vhlh in the pancreatic epithelium as well as in the endocrine and exocrine lineages. Our results show that embryonic depletion of Vhlh within the pancreatic epithelium causes postnatal lethality due to severe hypoglycemia. The hypoglycemia is recapitulated in mice with endocrine-specific removal of Vhlh, while animals with loss of Vhlh predominantly in the exocrine compartment survive to adulthood with no overt defects in glucose metabolism. Mice with hypoglycemia display diminished insulin release in response to elevated glucose. Significantly, the glucagon response is impaired both in vivo (circulating glucagon levels) as well as in an in vitro secretion assay in isolated islets. Hypoxia also impairs glucagon secretion in a glucagon-expressing cell line in culture. Our results reveal a novel role for the hypoxia/HIF pathway in islet hormone secretion and maintenance of the fine balance that allows for the establishment of normoglycemia.     

Control of Gastric Acid Secretion and the Endocrine Pancreas by Gastrointestinal Regulatory Peptides

Gastrointestinal peptides that perform the dual functions ofregulating gastric acid secretion and secretion by the endocrinepancreas are reviewed. The regulation of release ofgastrin andgastrin releasing peptide and their roles in stimulating acidsecretion are first considered. Inhibitory regulation of acidsecretion is then outlined, with particular emphasis on candidateenterogastrones, such as gastric inhibitory polypeptide (GIP),and the enterogastric reflex. Finally, the contribution of GIP,and other incretins, and the neural component of the enteroinsularaxis to the regulation of insulin secretion by the endocrinepancreas is discussed. Although the major emphasis is on studiesperformed in mammals, the more limited information on thesepathways in non-mammalian vertebrates is also considered.     

Histochimie du Pancreas du Chat Avec Discussion du Tissu Langerhansien Endocrine

Résumé Des recherches histologiques et histochimiques sont faites sur le pancréas du chat avec discussion surtout au sujet du tissu endocrine. Quelques particularités sont signalées: la richesse en îlots ganglionnaires, en corpuscules de Pacini et en complexes neuro-insulaires, aussi bien que l'existence dans la partie apicale de l'épithélium des canaux excréteurs de granulations paraldéhyde positives. En principe l'histoenzymologie du pancréas du chat est semblable à celle des autres mammifères mais ne lui est pas toujours identique. Certaines considérations sont faites sur le rôle probable des enzymes étudiées et du Zn dans la cytophysiologie insulaire.

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Summary Morphological and histochemical investigations on the pancreas of cat have been carried out and discussion on the question of the endocrine tissue. Some particularities are marked down: abundance of ganglion islets, of corpuscules of Pacini and neuro-insular complexes, as well as existence of positive paraldehyde granulations in the top portion of the epithelium of the excretory ducts. In general the histoenzymology of the pancreas of the cat is similar to other mammals, but is not always identical. Some considerations on the probable role of the enzymes investigated and on the zinc in the insular cytophysiology are made.

     

Functional and Morphological Changes in Endocrine Pancreas following Cola Drink Consumption in Rats

Aim

We report the effects of long-term cola beverage drinking on glucose homeostasis, endocrine pancreas function and morphology in rats.

Methods

Wistar rats drank: water (group W), regular cola beverage (group C, sucrose sweetened) or “light” cola beverage (group L, artificially sweetened). After 6 months, 50% of the animals in each group were euthanized and the remaining animals consumed water for the next 6 months when euthanasia was performed. Biochemical assays, insulinemia determination, estimation of insulin resistance (HOMA-IR), morphometry and immunohistochemistry evaluations were performed in pancreas.

Results

Hyperglycemia (16%, p<0.05), CoQ₁₀ (coenzyme-Q₁₀) decrease (−52%,p<0.01), strong hypertriglyceridemia (2.8-fold, p<0.01), hyperinsulinemia (2.4 fold, p<0.005) and HOMA-IR increase (2.7 fold, p<0.01) were observed in C. Group C showed a decrease in number of α cells (−42%, p<0.01) and β cells (−58%, p<0.001) and a moderate increase in α cells’ size after wash-out (+14%, p<0.001). Group L showed reduction in β cells’ size (−9%, p<0.001) and only after wash-out (L₁₂) a 19% increase in size (p<0.0001) with 35% decrease in number of α cells (p<0.01). Groups C and L showed increase in α/β-cell ratio which was irreversible only in C (α/β = +38% in C₆,+30% in C₁₂, p<0.001vs.W₆). Regular cola induced a striking increase in the cytoplasmic expression of Trx1 (Thioredoxin-1) (2.25-fold in C₆ vs. W₆; 2.7-fold in C₁₂ vs. W_12, p<0.0001) and Prx2 (Peroxiredoxin-2) (3-fold in C₆ vs. W₆; 2-fold in C₁₂ vs. W_12, p<0.0001). Light cola induced increase in Trx1 (3-fold) and Prx2 (2-fold) after wash-out (p<0.0001, L₁₂ vs. W₁₂).

Conclusion

Glucotoxicity may contribute to the loss of β cell function with depletion of insulin content. Oxidative stress, suggested by increased expression of thioredoxins and low circulating levels of CoQ₁₀, may follow sustained hyperglycemia. A likely similar panorama may result from the effects of artificially sweetened cola though via other downstream routes.     

Cell Degeneration and Cavity Formation in the Endocrine Pancreas of the Hagfish Myxine glutinosa

Abstract Cell degeneration within the islet lobules of the pancreas of Myxine glutinosa appears to be a natural feature of the gland in this species. Degenerating cells bordering a lobule cavity discharge debris directly into the cavity, while cells undergoing degeneration at sites distant from such cavities discharge debris into the surrounding intercellular space. The latter process may well act as a locus for local degeneration within the lobule and the formation of a lobule cavity.     

Follicles in the Endocrine Pancreas of Myxine glutinosa Studied by Scanning Electron Microscopy

Abstract Scanning electron microscopic studies of the inner surfaces of the follicular cavities in the endocrine pancreas of Myxine glutinosa have revealed two types of follicles. The predominant type of follicles is lined by cells bearing microvilli, while the rare second type has smooth surfaced cavities. It is postulated, that the microvillous cells absorb material stored in these follicles, while the smooth surfaced follicles are disintegrating.     

The Ultrastructure of the Endocrine Pancreas of the Grass Lizard,Mabuya quinquetaeniata*

Four endocrine cell types were identified ultrastructurally in the pancreas of the grass lizard, Mabuya quinquetaeniata. These cells were similar in shape, location and frequency to the previously described B-, A-, D- and PP-cells. The secretory granules of the B-cells were round or oval in profile, with an internal core of variable shape. The mean diameter of the B-cell granules was 780 nm (range 350–1000 nm). The A-cell granules were round, oval or irregular in shape and highly electron dense, with a narrow electron lucent space between the core and the limiting membrane. The mean diameter of these granules was 450 nm (range 200–750 nm). The D-cell granules were round, oval or irregular and of moderate electron density, with an average diameter of 340 nm (range 200–500 nm). The limiting membrane was closely apposed to the core or separated from it by a narrow lucent space. PP-cell granules were round with high electron density and with a narrow space between the core and the limiting membrane, and their average diameter was 150 nm (range 50–350 nm); these secretory granules accumulated at the cytoplasmic process. Tracing of the cytoplasmic processes of PP-cells in serially cut ultrathin sections revealed that most of these processes ended in the vicinity of blood capillaries, indicating that the PP-cells were endocrine rather than paracrine.     

PERK Regulates the Proliferation and Development of Insulin-Secreting Beta-Cell Tumors in the Endocrine Pancreas of Mice

Background

PERK eIF2α kinase is required for the proliferation of the insulin-secreting beta- cells as well as insulin synthesis and secretion. In addition, PERK signaling has been found to be an important factor in determining growth and angiogenesis of specific types of tumors, and was attributed to PERK-dependent regulation of the hypoxic stress response. In this report we examine the role of PERK in regulating proliferation and angiogenesis of transformed beta-cells in the development of insulinomas.

Methodology

The SV40 Large T-antigen (Tag) was genetically introduced into the insulin secreting beta-cells of Perk KO mice under the control of an inducible promoter. Tumor growth and the related parameters of cell proliferation were measured. In late stage insulinomas the degree of vascularity was determined.

Principal Findings

The formation and growth of insulinomas in Perk-deficient mice was dramatically ablated with much fewer tumors, which averaged 38-fold smaller than seen in wild-type control mice. Beta-cell proliferation was ablated in Perk-deficient mice associated with reduced tumor growth. In the small number of large encapsulated insulinomas that developed in Perk-deficient mice, we found a dramatic reduction in tumor vascularity compared to similar sized insulinomas in wild-type mice. Although insulinoma growth in Perk-deficient mice was largely impaired, beta-cell mass was increased sufficiently by T-antigen induction to rescue the hypoinsulinemia and diabetes in these mice.

Conclusions

We conclude that PERK has two roles in the development of beta-cell insulinomas, first to support rapid cell proliferation during the initial transition to islet hyperplasia and later to promote angiogenesis during the progression to late-stage encapsulated tumors.