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S Bonner-Weir

Publications and source records attributed to S Bonner-Weir.

At least 37 records · Page 2Linked to original sources
PubMed2001

beta-cell turnover: its assessment and implications.

The pancreatic beta-cells are responsible for the maintenance of the body's glucose levels within a very narrow range; their population is dynamic and undergoes compensatory changes to maintain euglycemia. The structural parameters that allow mass changes (replication, neogenesis, cell volume changes, and cell death) can now be assessed and have proved to be powerful tools. Changes in one parameter can dramatically affect the beta-cell mass. Unfortunately, conclusions are often drawn on measurements that do not assess beta-cell mass but only relative volumes. Throughout the lifetime of a mammal, low levels of beta-cell replication and apoptosis are balanced and result in a slowly increasing mass. The balance allows gradual replacement of the beta-cell population; thus, beta-cells should be considered a slowly renewed tissue. Two major implications of beta-cell turnover are that 1) at any time, the beta-cells would be at different ages and 2) any limitation on replacement could have dire consequences for glucose homeostasis.

Animals↗
PubMed2000

In vitro cultivation of human islets from expanded ductal tissue.

A major obstacle to successful islet transplantation for both type 1 and 2 diabetes is an inadequate supply of insulin-producing tissue. This need for transplantable human islets has stimulated efforts to expand existing pancreatic islets and/or grow new ones. To test the hypothesis that human adult duct tissue could be expanded and differentiated in vitro to form islet cells, digested pancreatic tissue that is normally discarded from eight human islet isolations was cultured under conditions that allowed expansion of the ductal cells as a monolayer whereupon the cells were overlaid with a thin layer of Matrigel. With this manipulation, the monolayer of epithelial cells formed three-dimensional structures of ductal cysts from which 50-to 150- micrometer diameter islet-like clusters of pancreatic endocrine cells budded. Over 3-4 weeks culture the insulin content per flask increased 10- to 15-fold as the DNA content increased up to 7-fold. The cultivated human islet buds were shown by immunofluorescence to consist of cytokeratin 19-positive duct cells and hormone-positive islet cells. Double staining of insulin and non-beta cell hormones in occasional cells indicated immature cells still in the process of differentiation. Insulin secretion studies were done over 24 h in culture. Compared with their basal secretion at 5 mM glucose, cysts/cultivated human islet buds exposed to stimulatory 20 mM glucose had a 2.3-fold increase in secreted insulin. Thus, duct tissue from human pancreas can be expanded in culture and then be directed to differentiate into glucose responsive islet tissue in vitro. This approach may provide a potential new source of pancreatic islet cells for transplantation.

Adult↗
PubMed2000

Effects of diabetes and hypoxia on gene markers of angiogenesis (HGF, cMET, uPA and uPAR, TGF-alpha, TGF-beta, bFGF and Vimentin) in cultured and transplanted rat islets.

AIMS/HYPOTHESIS: The vascularisation of newly transplanted islets originates from the recipients. Because islets transplanted into a diabetic do less well than those transplanted into a euglycaemic environment, we examined the hypothesis that gene expression of angiogenic factors in grafts is delayed in diabetes. These factors include hepatocyte growth factor (HGF) and its receptor c-MET, and urokinase plasminogen activator (uPA) and its receptor uPAR, basic fibroblast growth factor (bFGF), TGF-alpha and TGF beta-1. METHODS: Isolated rat islets were studied in vitro under normoxic and hypoxic culture conditions and gene expression was determined with semi-quantitative multiplex RT-PCR. We found that HGF but not c-MET expression was induced by hypoxia in vitro. Using syngeneic Lewis rats, gene expression was also studied in grafts on days 1, 3, 5, 7 and 14 after transplantation. RESULTS: In grafts of normoglycaemic rats, HGF expression was enhanced on day 3 and maintained whereas expression of c-MET fell and remained down until day 14. Expression of uPA was up at day 3 and remained high; expression of uPAR was also up at day 3 but then fell to control levels at day 14. Expression of bFGF, TGF-alpha and TGF beta-1 persisted throughout. Vimentin, a marker of fibroblasts, had increased expression at day 1 which was further enhanced in subsequent days. In the grafts of diabetic recipients the expression of HGF, uPA and uPAR were delayed, being clearly expressed at day 5 rather than day 3. Vimentin expression was similarly delayed. CONCLUSION/INTERPRETATION: This apparent delay in angiogenesis provides a potential mechanism for the less favourable outcomes of islets transplanted into diabetic recipients.

Animals↗
PubMed2000

Life and death of the pancreatic beta cells.

Pancreatic beta cells are responsible for maintaining the body's glucose levels within a very narrow range; their population is dynamic, with compensatory changes to maintain euglycemia. Throughout the lifetime of a mammal, low levels of beta-cell replication and apoptosis are balanced and result in a slowly increasing mass of beta cells. The emphasis in this review is on recent insights on the natural history of the beta cell in a normal pancreas: sources of renewal, survival and changes in differentiation.

Animals↗
PubMed2000

Improved glucose and lipid metabolism in genetically obese mice lacking aP2.

Adipocyte fatty acid-binding protein, aP2, is a member of the intracellular fatty acid binding protein family. Previously, studies have shown increased insulin sensitivity in aP2-deficient mice with dietary obesity. Here, we asked whether aP2-related alterations in lipolytic response and insulin production are features of obesity-induced insulin resistance and investigated the effects of aP2-deficiency on glucose homeostasis and lipid metabolism in ob/ob mice, a model of extreme obesity. ob/ob mice homozygous for the aP2 null allele (ob/ ob-aP2-/-) became more obese than ob/ob mice as indicated by significantly increased body weight and fat pad size but unaltered body length. However, despite their extreme adiposity, ob/ob-aP2-/- animals were more insulin-sensitive compared with ob/ob controls, as demonstrated by significantly lower plasma glucose and insulin levels and better performance in both insulin and glucose tolerance tests. These animals also showed improvements in dyslipidemia and had lower plasma triglyceride and cholesterol levels. Lipolytic response to beta-adrenergic stimulation and lipolysis-associated insulin secretion was significantly reduced in ob/ob-aP2-/- mice. Interestingly, glucose-stimulated insulin secretion, while virtually abolished in ob/ob controls, was significantly improved in ob/ob-aP2-/- animals. There were no apparent morphological differences in the structure or size of the pancreatic islets between genotypes. Taken together, the data indicate that in obesity, aP2-deficiency not only improves peripheral insulin resistance but also preserves pancreatic beta cell function and has beneficial effects on lipid metabolism.

Adipose Tissue↗
PubMed2000

Insulinotropic glucagon-like peptide 1 agonists stimulate expression of homeodomain protein IDX-1 and increase islet size in mouse pancreas.

Diabetes is caused by a failure of the pancreas to produce insulin in amounts sufficient to meet the body's needs. A hallmark of diabetes is an absolute (type 1) or relative (type 2) reduction in the mass of pancreatic beta-cells that produce insulin. Mature beta-cells have a lifespan of approximately 48-56 days (rat) and are replaced by the replication of preexisting beta-cells and by the differentiation and proliferation of new beta-cells (neogenesis) derived from the pancreatic ducts. Here, we show that the insulinotropic hormone glucagon-like peptide (GLP)-1, which is produced by the intestine, enhances the pancreatic expression of the homeodomain transcription factor IDX-1 that is critical for pancreas development and the transcriptional regulation of the insulin gene. Concomitantly, GLP-1 administered to diabetic mice stimulates insulin secretion and effectively lowers their blood sugar levels. GLP-1 also enhances beta-cell neogenesis and islet size. Thus, in addition to stimulating insulin secretion, GLP-1 stimulates the expression of the transcription factor IDX-1 while stimulating beta-cell neogenesis and may thereby be an effective treatment for diabetes.

Animals↗
PubMed1999

Prolonged xenograft survival of islets infected with small doses of adenovirus expressing CTLA4Ig.

BACKGROUND: Systemic administration of the inhibitor of costimulation, CTLA4Ig, has been shown to prolong islet graft survival. The purpose of this study was to compare local and systemic expression of murine CTLA4Ig in transplants of rat islets into mice. METHODS: Murine CTLA4Ig was made by joining two polymerase chain reaction products, the extracellular portion of CTLA4 and the Fc portion of IgG2a. Recombinant adenovirus expressing CTLA4Ig (AdCTLA4Ig) was generated using the strategy of Cre-lox recombination. Isolated rat islets infected with AdCTLA4Ig at multiplicities of infection (MOIs) ranging from 0.1 to 10 were transplanted into streptozocin diabetic male B6AF1 mice. Control islets were mock infected or infected with AdLacZ or AdsIg, a recombinant adenovirus expressing only the Fc portion of IgG2a. Also, AdCTLA4Ig and control viruses were injected intramuscularly into mouse transplant recipients at the time of islet transplantation to provide CTLA4Ig systemically. RESULTS: Control islets transplanted into diabetic mice were rejected in 13-17 days. Islets infected with AdCTLA4Ig had dose-dependent prolongation of graft survival. Prolonged survival was even found with very low MOIs of 0.1 and 0.5, with survivals of 24+/-4.2 and 25+/-2.2 days, respectively. Survival with an MOI of 10 was 39+/-8.7 days. With intramuscular injection, no prolongation was found at the lowest relative MOIs of 0.2 and 1, but there was dose-dependent prolongation of graft survival with larger doses. At the highest relative MOI of 400, survival was prolonged to 58+/-10 days. CONCLUSIONS: Rat islets infected with AdCTLA4Ig transplanted into mice had prolonged graft survival. Prolonged survival with MOIs as low as 0.1 and 0.5 indicates that only a minority of islet cells need to express CTLA4Ig to exert an effect. Moreover, the results suggest that the improved islet graft survival is due to a local influence of CTLA4Ig.

Abatacept↗
PubMed1999

In situ electrochemical oxygen generation with an immunoisolation device.

The viability and function of transplanted tissue encapsulated in immunobarrier devices is subject to oxygen transport limitation. In this study, we have designed and used an in situ electrochemical oxygen generator which decomposes water electrolyticaly to provide oxygen to the adjacent planer immunobarrier diffusion chamber. The rate of oxygen generation, which increases linearly with electrical current, was accurately controlled. A theoretical model of oxygen diffusion was also developed and was used to calculate the oxygen profiles in some of the experimental systems. In vitro culture experiments were carried out with beta TC3 cells encapsulated in titanium ring devices. The growth and viability of cells with or without in situ oxygen generation was studied. We found that under otherwise similar culturing conditions, the thickness of the cell layer and the viability of cells was the highest in devices cultured in stirred media with oxygen generation, even though the thickness had not reached the theoretically predicted value, and lowest in those unstirred and without oxygen generation.

Animals↗
PubMed1999

Chronic hyperglycemia triggers loss of pancreatic beta cell differentiation in an animal model of diabetes.

Differentiated pancreatic beta cells are unique in their ability to secrete insulin in response to a rise in plasma glucose. We have proposed that the unique constellation of genes they express may be lost in diabetes due to the deleterious effect of chronic hyperglycemia. To test this hypothesis, Sprague-Dawley rats were submitted to a 85-95% pancreatectomy or sham pancreatectomy. One week later, the animals developed mild to severe chronic hyperglycemia that was stable for the next 3 weeks, without significant alteration of plasma nonesterified fatty acid levels. Expression of many genes important for glucose-induced insulin release decreased progressively with increasing hyperglycemia, in parallel with a reduction of several islet transcription factors involved in beta cell development and differentiation. In contrast, genes barely expressed in sham islets (lactate dehydrogenase A and hexokinase I) were markedly increased, in parallel with an increase in the transcription factor c-Myc, a potent stimulator of cell growth. These abnormalities were accompanied by beta cell hypertrophy. Changes in gene expression were fully developed 2 weeks after pancreatectomy. Correction of blood glucose by phlorizin for the next 2 weeks normalized islet gene expression and beta cell volume without affecting plasma nonesterified fatty acid levels, strongly suggesting that hyperglycemia triggers these abnormalities. In conclusion, chronic hyperglycemia leads to beta cell hypertrophy and loss of beta cell differentiation that is correlated with changes in c-Myc and other key transcription factors. A similar change in beta cell differentiation could contribute to the profound derangement of insulin secretion in human diabetes.

Animals↗
PubMed1999

Reversal of hyperglycemia in mice after subcutaneous transplantation of macroencapsulated islets.

BACKGROUND: Macroencapsulated islets can reverse hyperglycemia in diabetic animals when transplanted i.p. or into the fat pad. The s.c. space is an attractive site for such transplantation because macrocapsules can be implanted with local anesthesia and be easily removed or reloaded with fresh islets. METHODS: Immunoprotective 20 microl ported devices were transplanted under the skin of Streptozocin-diabetic nude mice. Devices were loaded with 1200 rat islets in culture medium or in alginate. Empty devices were implanted for 2 weeks and then loaded with islets. Normal mice and mice with islets transplanted under the renal capsule or under the skin were used as controls. Seven weeks after transplantation, an intraperitoneal glucose tolerance test (IPGTT) was performed, followed by implant removal. RESULTS: Three weeks after transplantation, normal blood glucose levels were observed in all animals. Compared with those of normal controls, IPGTTs showed accelerated blood glucose clearance in mice transplanted with islets either within devices or beneath the kidney capsule. Fasted transplanted mice were hypoglycemic before glucose injection and 2 hr later. After removal of the implants, all recipient mice returned to hyperglycemia. Histological evaluation revealed viable islet cells and a network of close vascular structures outside the devices. CONCLUSIONS: Macroencapsulated islets transplanted into the s.c. space were able to survive and regulate blood glucose levels in mice. The observed differences in glucose metabolism between normal and transplanted mice may be attributed to the site of transplantation and to the use of rat islets, which have a different set point for glucose induced insulin release.

Animals↗
PubMed1999

The neuroendocrine protein 7B2 is required for peptide hormone processing in vivo and provides a novel mechanism for pituitary Cushing's disease.

The neuroendocrine protein 7B2 has been implicated in activation of prohormone convertase 2 (PC2), an important neuroendocrine precursor processing endoprotease. To test this hypothesis, we created a null mutation in 7B2 employing a novel transposon-facilitated technique and compared the phenotypes of 7B2 and PC2 nulls. 7B2 null mice have no demonstrable PC2 activity, are deficient in processing islet hormones, and display hypoglycemia, hyperproinsulinemia, and hypoglucagonemia. In contrast to the PC2 null phenotype, these mice show markedly elevated circulating ACTH and corticosterone levels, with adrenocortical expansion. They die before 9 weeks of severe Cushing's syndrome arising from pituitary intermediate lobe ACTH hypersecretion. We conclude that 7B2 is indeed required for activation of PC2 in vivo but has additional important functions in regulating pituitary hormone secretion.

Adipose Tissue↗
PubMed1999

Prior streptozotocin treatment does not inhibit pancreas regeneration after 90% pancreatectomy in rats.

The effects of residual beta-cell mass and glycemia on regeneration of endocrine pancreas after 90% pancreatectomy were investigated. Streptozotocin or buffer alone was injected into 4-wk-old male Lewis rats (day 0). On day 7, varying numbers of syngeneic islets were transplanted under the kidney capsule to achieve varying degrees of glucose normalization. On day 14, a 90% pancreatectomy or sham pancreatectomy was performed. On day 19, rats were killed and the pancreas was fixed for quantitative morphometric determination of beta-cell mass. Focal areas of regenerating pancreas were observed in all animals that underwent partial pancreatectomy. The percentage of remnant pancreas classified as foci was unaffected by streptozotocin treatment or by plasma glucose. Moderate to severe hyperglycemia did not promote regeneration of the pancreatic beta-cell mass; rather the total endocrine cell mass was inversely related to the plasma glucose level (r = -0.5, P < 0.01). These data suggest that the precursor population for both endocrine and exocrine tissue is not susceptible to damage by streptozotocin and that local effects of residual beta-cell mass are not important to regeneration after a 90% pancreatectomy.

Animals↗