Recombinant human betacellulin promotes the neogenesis of beta-cells and ameliorates glucose intolerance in mice with diabetes induced by selective alloxan perfusion

Betacellulin overexpression in transgenic mice causes disproportionate growth, pulmonary hemorrhage syndrome, and complex eye pathology

The EGF family comprises a network of ligands and receptors that regulate proper development and elicit diverse functions in physiology and pathology. Betacellulin (BTC) is a rather poorly characterized member of the EGF family whose in vivo effects have been linked mainly to endocrine pancreas, intestine, and mammary gland function. In vitro studies revealed that this growth factor is a potent mitogen for diverse cell types and suggested unique receptor-binding properties. Genetic ablation of BTC in mice yielded a mild phenotype, probably because of opportunistic compensation by other EGF receptor ligands. To study the biological capabilities of BTC in vivo, we generated transgenic mice overexpressing BTC ubiquitously, with highest expression levels in heart, lung, brain, and pancreas. Mice overexpressing BTC exhibit high early postnatal mortality, reduced body weight gain, and impaired longitudinal growth. In addition, a variety of pathological alterations were observed. Cataract and abnormally shaped retinal layers as well as bone alterations leading to a dome-shaped, round head form were hallmarks of BTC transgenic mice. The most important finding and the cause of reduced life expectancy of BTC transgenic mice were severe alterations of the lung. Pulmonary pathology was primarily characterized by alveolar hemorrhage, thickening of the alveolar septa, intraalveolar accumulation of hemosiderin-containing macrophages, and nodular pulmonary remodeling. Thus, our model uncovers multiple consequences of BTC overexpression in vivo. These transgenic mice provide a useful model for examining the effects of BTC excess on different organs.

A functional variant in the human betacellulin gene promoter is associated with type 2 diabetes

Betacellulin (BTC) plays an important role in differentiation, growth, and antiapoptosis of pancreatic beta-cells. We characterized about 2.3 kb of the 5'-flanking region of human BTC gene and identified six polymorphisms (-2159A>G, -1449G>A, -1388C>T, -279C>A, -233G>C, and -226A>G). The G allele in the -226A>G polymorphism was more frequent in type 2 diabetic patients (n = 250) than in nondiabetic subjects (n = 254) (35.6% vs. 27.8%, P = 0.007), and the -2159G, -1449A, and -1388T alleles were in complete linkage disequilibrium with the -226G allele. The frequencies of the -279A and -233C alleles were low (7.0 and 2.0% in diabetic patients), and no significant differences were observed. In the diabetic group, insulin secretion ability, assessed by the serum C-peptide response to intravenous glucagon stimulation, was lower in patients with the -226G allele (G/G, 2.96 +/- 0.16 ng/ml; G/A, 3.65 +/- 0.18 ng/ml; A/A, 3.99 +/- 0.16 ng/ml at 5 min after stimulation; P = 0.008). Furthermore, in vitro functional analyses indicated that both the -226G and the -233C alleles caused an approximately 50% decrease in the promoter activity, but no effects of the -2159A>G, -1449G>A, -1388C>T, and -279C>A polymorphisms were observed. These results suggest that the -226A/G polymorphism of the BTC gene may contribute to the development of diabetes.

Betacellulin-delta4, a novel differentiation factor for pancreatic beta-cells, ameliorates glucose intolerance in streptozotocin-treated rats

We previously described a novel alternatively spliced mRNA transcript of the betacellulin (BTC) gene. This splice isoform, termed BTC-delta4, lacks the C-loop of the epidermal growth factor motif and the transmembrane domain as a result of exon 4 'skipping'. In this study, we expressed BTC-delta4 recombinantly to explore its biological function. When BTC-delta4 was expressed in COS-7 cells, it was secreted largely into the culture medium, in contrast to BTC. Unlike BTC, highly purified recombinant BTC-delta4 produced in Escherichia coli failed to bind or induce tyrosine phosphorylation of either ErbB1 or ErbB4, nor did it antagonize the binding of BTC to these receptors. Consistent with this, BTC-delta4 failed to stimulate DNA synthesis in Balb/c 3T3 and INS-1 cells. However, BTC-delta4 induced differentiation of pancreatic beta-cells; BTC-delta4 converted AR42J cells to insulin-producing cells. When recombinant BTC-delta4 was administered to streptozotocin-treated neonatal rats, it reduced the plasma glucose concentration and improved glucose tolerance. Importantly, BTC-delta4 significantly increased the insulin content, the beta-cell mass, and the numbers of islet-like cell clusters and PDX-1-positive ductal cells. Thus, BTC-delta4 is a secreted protein that stimulates differentiation of beta-cells in vitro and in vivo in an apparent ErbB1- and ErbB4-independent manner. The mechanism by which BTC-delta4 exerts this action on beta-cells remains to be defined but presumably involves an, as yet, unidentified unique receptor.

Regulation of pancreatic beta-cell mass

Beta-cell mass regulation represents a critical issue for understanding diabetes, a disease characterized by a near-absolute (type 1) or relative (type 2) deficiency in the number of pancreatic beta cells. The number of islet beta cells present at birth is mainly generated by the proliferation and differentiation of pancreatic progenitor cells, a process called neogenesis. Shortly after birth, beta-cell neogenesis stops and a small proportion of cycling beta cells can still expand the cell number to compensate for increased insulin demands, albeit at a slow rate. The low capacity for self-replication in the adult is too limited to result in a significant regeneration following extensive tissue injury. Likewise, chronically increased metabolic demands can lead to beta-cell failure to compensate. Neogenesis from progenitor cells inside or outside islets represents a more potent mechanism leading to robust expansion of the beta-cell mass, but it may require external stimuli. For therapeutic purposes, advantage could be taken from the surprising differentiation plasticity of adult pancreatic cells and possibly also from stem cells. Recent studies have demonstrated that it is feasible to regenerate and expand the beta-cell mass by the application of hormones and growth factors like glucagon-like peptide-1, gastrin, epidermal growth factor, and others. Treatment with these external stimuli can restore a functional beta-cell mass in diabetic animals, but further studies are required before it can be applied to humans.

Identification and expansion of pancreatic stem/progenitor cells

Pancreatic islet transplantation represents an attractive approach for the treatment of diabetes. However, the limited availability of donor islets has largely hampered this approach. In this respect, the use of alternative sources of islets such as the ex vivo expansion and differentiation of functional endocrine cells for treating diabetes has become the major focus of diabetes research. Adult pancreatic stem cells /progenitor cells have yet to be recognized because limited markers exist for their identification. While the pancreas has the capacity to regenerate under certain circumstances, questions where adult pancreatic stem/progenitor cells are localized, how they are regulated, and even if the pancreas harbors a stem cell population need to be resolved. In this article, we review the recent achievements both in the identification as well as in the expansion of pancreatic stem/progenitor cells.

Combination therapy with epidermal growth factor and gastrin increases beta-cell mass and reverses hyperglycemia in diabetic NOD mice

Combination therapy with epidermal growth factor (EGF) and gastrin induces beta-cell regeneration in rodents with chemically induced diabetes. We investigated whether EGF plus gastrin could correct hyperglycemia in NOD mice with autoimmune diabetes. Combined treatment with EGF (1 mug/kg) and gastrin (3 mug/kg) for 2 weeks restored normoglycemia after diabetes onset in NOD mice, whereas EGF or gastrin alone did not. Fasting blood glucose remained normal (3.5-6.5 mmol/l) or mildly elevated (<11 mmol/l) in five of six mice (83%) for 10 weeks after EGF plus gastrin treatment was stopped, whereas all mice treated with vehicle or EGF or gastrin alone became severely hyperglycemic (12-35 mmol/l). Pancreatic beta-cell mass was increased threefold and insulin content was increased eightfold in mice treated with EGF plus gastrin compared with pretreatment values. The correction of hyperglycemia correlated significantly with increases in pancreatic beta-cell mass and insulin content. In addition, splenic cells from mice treated with EGF plus gastrin delayed diabetes induction by adoptive transfer of diabetogenic cells into immunodeficient NOD-scid mice, suggesting the induction of immunoregulatory cells in NOD mice treated with EGF plus gastrin. We conclude that a short course of combined EGF and gastrin therapy increases pancreatic beta-cell mass and reverses hyperglycemia in acutely diabetic NOD mice; the impact of this combined therapy may result from the effects of EGF and gastrin on beta-cells, immune cells, or both.

The transcription factor Stat3 is dispensable for pancreatic β-cell development and function

The transcription factor Stat3 is activated by multiple cytokines, including leptin and those signaling through the gp130 receptor. In two independent studies, mice in which the Stat3 gene was inactivated using a RIP-Cre transgene led to glucose intolerance, defects in early-phase insulin secretion, and mild obesity [S. Gorogawa, Y. Fujitani, H. Kaneto, Y. Hazama, H. Watada, Y. Miyamoto, K. Takeda, S. Akira, M. Magnuson, Y. Yamasaki, Y. Kajimoto, M. Hori, Insulin secretory defects and impaired islet architecture in pancreatic beta-cell-specific STAT3 knockout mice, Biochem. Biophys. Res. Commun. 319 (2004) 1159; Y. Cui, L. Huang, F. Elefteriou, G. Yang, J. Shelton, J. Giles, O. Oz, T. Pourbahrami, C. Lu, J. Richardson, G. Karsenty, C. Li, Essential role of STAT3 in body weight and glucose homeostasis, Mol. Cell. Biol. 24 (2004) 258]. However, since the RIP-Cre transgene is also expressed in the hypothalamus, and thereby Stat3 was deleted from neurons expressing the leptin receptor, it was not clear as to which of the metabolic defects were due to the loss of Stat3 from beta-cells or the hypothalamus. We have addressed this issue through the inactivation of Stat3 from pancreatic beta-cells using a Pdx1-Cre transgene. Complete loss of Stat3 was observed in islets from mice, which carry two floxed Stat3 alleles and the Pdx1-Cre transgene. However, these mice did not develop glucose intolerance or obesity over a period of 6 months, demonstrating that Stat3 is dispensable for the generation and physiology of beta-cells. Similarly, mice that express only the Pdx1-Cre transgene display a normal physiology. In contrast, mice that expressed only the RIP-Cre transgene developed glucose intolerance as early as 6 weeks of age. The finding that RIP-Cre transgenic mice in a C57B/6 dominated background develop glucose intolerance is important as this line has been used in several studies.

Regenerative and therapeutic effects of heparin-binding epidermal growth factor-like growth factor on diabetes by gene transduction through retrograde pancreatic duct injection of adenovirus vector

OBJECTIVES

In the adult pancreas, pre-existing beta cells, stem cells, and endocrine progenitor cells residing in the duct lining are considered important sources for beta-cell regeneration. A member of the epidermal growth factor (EGF) family, heparin binding (HB)-EGF, may promote this process. We examined whether HB-EGF gene transduction into duct cells could promote beta-cell regeneration.

METHODS

We administered an HB-EGF adenovirus vector construct to male Institute of Cancer Research mice by retrograde injection through the pancreatic duct. We also performed HB-EGF gene transduction into cultured duct cells.

RESULTS

On immunohistochemical and histomorphometric analysis of the experimental group, insulin-positive cells differentiated from duct cells, and the 5-bromo-2-deoxyuridine labeling index of beta cells was significantly increased. beta-cell mass was also increased, and the glucose tolerance of diabetic mice was improved at 12 weeks after injection. Using cultured pancreatic duct cells, we confirmed that HB-EGF gene transduction induced both insulin gene expression and insulin production by these cells.

CONCLUSIONS

These results indicate that HB-EGF gene transduction into adult pancreatic duct cells not only promotes the proliferation of pre-existing beta cells but also leads to beta-cell differentiation from duct cells, and the resulting increase in beta-cell mass improves glucose tolerance.

Molecular targeting of pancreatic disorders

During the last decade significant advances in gene therapy have made it possible to treat various pancreatic disorders in both animal models and in humans. For example, insulin gene delivery to non-beta-cell tissues has been shown to reverse hyperglycemia in diabetic mice, and islet transplantation, based on in vitro differentiation of beta cells and concomitant gene targeting to prevent host autoimmune responses, has become more feasible. Additionally, introduction of the glucokinase regulatory protein and protein kinase C-zeta have been shown to improve glucose tolerance in non-insulin-dependent diabetes mellitus animal models. Pancreatic cancer studies utilize several DNA-based strategies for tumor treatment including introduction of tumor suppressor genes, suppression of oncogenes, suicide gene/prodrug therapy, and restricted replication-competent virus therapy. Tumor-specific targeting is an important part of suicide gene therapy, and tumor-specific promoters are used for cell-specific targeting. Tumor-specific suicide gene therapy directed by the rat insulin promoter has been used to eliminate insulinoma tumors in a mouse model. This review compiles a compendium of information related to the treatment of pancreatic disorders using gene therapy.

Combination therapy with epidermal growth factor and gastrin induces neogenesis of human islet {beta}-cells from pancreatic duct cells and an increase in functional {beta}-cell mass

Pancreatic islet transplantation is a viable treatment for type 1 diabetes, but is limited by human donor tissue availability. The combination of epidermal growth factor (EGF) and gastrin induces islet beta-cell neogenesis from pancreatic exocrine duct cells in rodents. In this study we investigated whether EGF and gastrin could expand the beta-cell mass in adult human isolated islets that contain duct as well as endocrine cells. Human islet cells were cultured for 4 wk in serum-free medium (control) or in medium with EGF (0.3 mug/ml), gastrin (1.0 mug/ml), or the combination of EGF and gastrin. beta-Cell numbers were increased in cultures with EGF plus gastrin (+118%) and with EGF (+81%), but not in cultures with gastrin (-3%) or control medium (-62%). After withdrawal of EGF and gastrin and an additional 4 wk in control medium, beta-cell numbers continued to increase only in cultures previously incubated with both EGF and gastrin (+232%). EGF plus gastrin also significantly increased cytokeratin 19-positive duct cells (+678%) in the cultures. Gastrin, alone or in combination with EGF, but not EGF alone, increased the expression of pancreatic and duodenal homeobox factor-1 as well as insulin and C peptide in the cytokeratin 19-positive duct cells. Also, EGF plus gastrin significantly increased beta-cells and insulin content in human islets implanted in immunodeficient nonobese diabetic-severe combined immune deficiency mice as well as insulin secretory responses of the human islet grafts to glucose challenge. In conclusion, combination therapy with EGF and gastrin increases beta-cell mass in adult human pancreatic islets in vitro and in vivo, and this appears to result from the induction of beta-cell neogenesis from pancreatic exocrine duct cells.

Molecular scanning of the betacellulin gene for mutations in type 2 diabetic patients

Betacellulin (BTC), a member of the epidermal growth factor (EGF) family, is an important factor in the growth and/or differentiation of pancreatic beta cells. In this point of view, we determined the transcriptional start site of the human BTC gene and screened the protein-coding region for mutations. The transcriptional start site was located 347 bp upstream from the translational initiation codon. After screening the protein coding exons (exons 1-5), we identified two novel missense mutations, Cys (TGC) to Gly (GGC) at codon 7 (C7G) and Leu (TTG) to Met (ATG) at codon 124 (L124M), and a single nucleotide substitution (-31c/t) in the intron 2. The C7G was located in the signal peptide and the L124M in the transmembrane domain and this Leu at codon 124 was conserved among human, bovine, rat, and mouse. The frequencies of these variants, however, were similar between type 2 diabetic patients (n = 228) and non-diabetic control subjects (n = 170). These data suggest that genetic variations in the protein-coding region of the human BTC gene are unlikely to be a major contributor to development of type 2 diabetes.

The pancreatic ductal epithelium serves as a potential pool of progenitor cells

With the increasing success of islet transplantation, beta-cell replacement therapy has had renewed interest. To make such a therapy available to more than a few of the thousands of patients with diabetes, new sources of insulin-producing cells must become readily available. The most promising sources are stem cells, whether embryonic or adult stem cells. Clearly identifiable adult pancreatic stem cells have yet to be characterized. Although considerable evidence suggests their possibility, recent lineage-tracing experiments challenge their existence. Even in light of these lineage-tracing experiments, we suggest that evidence for neogenesis or new islet formation after birth remains strong. Our work has suggested that the pancreatic duct epithelium itself serves as a pool for progenitors for both islet and acinar tissues after birth and into adulthood and, thus, that the duct epithelium can be considered 'facultative stem cells'. We will develop our case for this hypothesis in this perspective.

The exon 1 Cys7Gly polymorphism within the betacellulin gene is associated with type 2 diabetes in African Americans

In vitro and in vivo studies suggest a role for betacellulin in islet neogenesis and regeneration. Since abnormalities in beta-cell function play a role in the development of type 2 diabetes, a mutation in the betacellulin gene could potentially contribute to the development of type 2 diabetes. Using RT-PCR, we initially determined that betacellulin was expressed in 9- to 24-week-old human fetal pancreas. We then screened the betacellulin gene for mutations in subjects with type 2 diabetes and identified seven polymorphisms in segments encompassing the 5' untranslated region (G-233C, A-226G), exon 1 (TGC19GGC, Cys7Gly), exon 2 (CTC130TTC, Leu44Phe), exon 4 (TTG370ATG, Leu124Met), intron 2 (T-31C), and intron 4 (C-4T). These polymorphisms were genotyped in an expanded set of diabetic case and control subjects. Among African Americans (n = 334), the frequency of the Gly7 allele in exon 1 was 31.9% in diabetic case subjects compared with 45.1% in nondiabetic control subjects (P = 0.0004). Allele frequencies for the other polymorphisms did not differ significantly between African-American case and control subjects. Additionally, there were no significant differences in allele frequencies between case and control subjects among the Caucasian sample (n = 426) for any of the seven polymorphisms, including the Gly7 variant. Further studies will be needed to understand the different roles that betacellulin polymorphisms play in susceptibility to type 2 diabetes in Caucasians and African Americans.

In vitro transdifferentiation of hepatoma cells into functional pancreatic cells

We have characterised the transdifferentiation of human HepG2 (hepatoma) cells to pancreatic cells following introduction of an activated version of the pancreatic transcription factor Pdx1 (XlHbox8-VP16). The following questions are addressed: (1) are all types of pancreatic cells produced? (2) is the requirement for expression of the transgene temporary or permanent? (3) are the transdifferentiated beta-cells responsive to physiological stimuli? The results showed that both pancreatic exocrine cells (by detection of amylase protein), and endocrine cells (by detecting insulin, glucagon and somatostatin proteins) are induced after XlHbox8VP16 transfection. Moreover, the hepatic phenotype becomes suppressed during transdifferentiation of hepatocytes to pancreatic cells. Requirement for the transgene is only temporary and it is no longer required once the pancreatic differentiation program is activated. Finally, we provided results to suggest that the transdifferentiated cells are functional by detecting: (1) functional markers for pancreatic beta-cells including prohormone convertase 1/3 (PC1/3), insulin C-peptide and glucagon-like peptide 1 receptor (GLP-1R), (2) increased insulin mRNA expression after treatment of cells with GLP-1 and betacellulin, physiological stimuli that regulate pancreatic function and (3) elevated insulin secretion after glucose challenge. The transdifferentiation of hepatic to pancreatic cells represents one possible source of beta-cells for human islet transplantation and this study shows that such a transdifferentiation can be achieved in vitro.

In vitro generation of insulin-producing beta cells from adult exocrine pancreatic cells

AIMS/HYPOTHESIS

Transplantation of insulin-producing beta cells from donors can cure diabetes, but they are available in insufficient quantities. In this study, we investigated the possibility of generating insulin-producing cells from adult rat exocrine cells cultured in the presence of growth factors.

METHODS

Rat exocrine pancreatic cells were isolated and treated in vitro with epidermal growth factor (EGF) and leukaemia inhibitory factor (LIF). Analysis was performed by immunocytochemistry, DNA measurement and radioimmunoassay. Cells were transplanted to alloxan-treated (70 mg/kg) nude mice and glycaemia was monitored for 21 days. Nephrectomy was performed on day 15.

RESULTS

In a 3-day culture period, addition of LIF plus EGF to the medium resulted in an 11-fold increase of the beta cell mass. This could not be attributed to the very low mitotic activity of contaminating beta cells. Furthermore, when contaminating beta cells were initially destroyed with alloxan, this effect was even more pronounced. The newly formed cells secreted insulin in response to glucose and were immunoreactive for C-peptide-I, Pdx-1 and GLUT-2, which are characteristics of mature beta cells. Electron microscopy showed that they also contained insulin-immunoreactive secretory granules. Some insulin-positive cells were immunoreactive for amylase and cytokeratin-20, or were binucleated, which are characteristics of exocrine cells. The cells were able to restore normoglycaemia when transplanted to alloxan-diabetic mice, and hyperglycaemia recurred upon removal of the graft.

CONCLUSIONS/INTERPRETATION

Our study shows that functional beta cells can be generated from exocrine tissue by transdifferentiation and thereby may offer a new perspective for beta cell therapy.

Stem cell-based approaches to solving the problem of tissue supply for islet transplantation in type 1 diabetes

Type 1 diabetes is a debilitating condition, affecting millions worldwide, that is characterized by the autoimmune destruction of insulin-producing pancreatic islets of Langerhans. Although exogenous insulin administration has traditionally been the mode of treatment for this disease, recent advancements in the transplantation of donor-derived insulin-producing cells have provided new hope for a cure. However, in order for islet transplantation to become a widely used technique, an alternative source of cells must be identified to supplement the limited supply currently available from cadaveric donor organs. Stem cells represent a promising solution to this problem, and current research is being aimed at the creation of islet-endocrine tissue from these undifferentiated cells. This review presents a summary of the research to date involving stem cells and cell replacement therapy for type 1 diabetes. The potential for the differentiation of embryonic stem (ES) cells to islet phenotype is discussed, as well as the possibility of identifying and exploiting a pancreatic progenitor/stem cell from the adult pancreas. The possibility of creating new islets from adult stem cells derived from other tissues, or directly form other terminally differentiated cell types is also addressed. Finally, a model for the isolation and maturation of islets from the neonatal porcine pancreas is discussed as evidence for the existence of an islet precursor cell in the pancreas.

Insulin secretory defects and impaired islet architecture in pancreatic β-cell-specific STAT3 knockout mice

Normal islet formation and function depends on the action of various growth factors operating in pre- and postnatal development; however, the specific physiological function of each factor is largely unknown. Loss-of-function analyses in mice have provided little information so far, perhaps due to functional redundancies of the growth factors acting on the pancreas. The present study focuses on the role of the transcription factor STAT3 in insulin-producing cells. STAT3 is one of the potential downstream mediators for multiple growth factors acting on the pancreatic beta-cells, including betacellulin, hepatocyte growth factor, growth hormone, and heparin-binding EGF-like growth factor. To elucidate its role in the beta-cells, the STAT3 gene was disrupted in insulin-producing cells in mice (STAT3-insKO), using a cre-mediated gene recombination approach. Unexpectedly, STAT3-insKO mice exhibited an increase in appetite and obesity at 8 weeks of age or older. The mice showed partial leptin resistance, suggesting that expression of the RIP (rat insulin promoter)-cre transgene in hypothalamus partially inhibited the appetite-regulating system. Intraperitoneal glucose tolerance tests, performed in non-obese 5-week-old mice, showed that the STAT3-insKO mice were glucose intolerant. Islet perifusion experiments further revealed a deficiency in early-phase insulin secretion. Whereas islet insulin content or islet mass was not affected, expression levels of GLUT2, SUR1, and VEGF-A were significantly reduced in STAT3-insKO islets. Interestingly, STAT3-insKO mice displayed impaired islet morphology: alpha-cells were frequently seen in central regions of islets. Our present observations demonstrate a unique role of STAT3 in maintaining glucose-mediated early-phase insulin secretion and normal islet morphology.

Adult pancreatic beta-cells are formed by self-duplication rather than stem-cell differentiation

How tissues generate and maintain the correct number of cells is a fundamental problem in biology. In principle, tissue turnover can occur by the differentiation of stem cells, as is well documented for blood, skin and intestine, or by the duplication of existing differentiated cells. Recent work on adult stem cells has highlighted their potential contribution to organ maintenance and repair. However, the extent to which stem cells actually participate in these processes in vivo is not clear. Here we introduce a method for genetic lineage tracing to determine the contribution of stem cells to a tissue of interest. We focus on pancreatic beta-cells, whose postnatal origins remain controversial. Our analysis shows that pre-existing beta-cells, rather than pluripotent stem cells, are the major source of new beta-cells during adult life and after pancreatectomy in mice. These results suggest that terminally differentiated beta-cells retain a significant proliferative capacity in vivo and cast doubt on the idea that adult stem cells have a significant role in beta-cell replenishment.

Activin A and betacellulin: effect on regeneration of pancreatic beta-cells in neonatal streptozotocin-treated rats

Activin A and betacellulin (BTC) are thought to regulate differentiation of pancreatic beta-cells during development and regeneration of beta-cells in adults. In the present study, we used neonatal rats treated with streptozotocin (STZ) to investigate the effects of activin A and BTC on regeneration of pancreatic beta-cells. One-day-old Sprague-Dawley rats were injected with STZ (85 micro g/g) and then administered for 7 days with activin A and/or BTC. Treatment with activin A and BTC significantly reduced the plasma glucose concentration and the plasma glucose response to intraperitoneal glucose loading. The pancreatic insulin content and beta-cell mass in rats treated with activin A and BTC were significantly increased compared with the control group on day 8 and at 2 months. Treatment with activin A and BTC significantly increased the DNA synthesis in preexisting beta-cells, ductal cells, and delta-cells. The number of islet cell-like clusters (ICCs) and islets was significantly increased by treatment with activin A and BTC. In addition, the number of insulin/somatostatin-positive cells and pancreatic duodenal homeobox-1/somatostatin-positive cells was significantly increased. These results indicate that, in neonatal STZ-treated rats, a combination of activin A and BTC promoted regeneration of pancreatic beta-cells and improved glucose metabolism in adults.

Stem cells: a promising source of pancreatic islets for transplantation in type 1 diabetes

Diabetes is a disease that affects millions and causes a major burden on the health care system. Type 1 diabetes has traditionally been managed with exogenous insulin therapy, however factors such as cost, lifestyle restriction, and life threatening complications necessitate the development of a more efficient treatment alternative. Pancreas transplantation, and more recently transplant of purified pancreatic islets, has offered the potential for independence from insulin injections. Islet transplantation is gaining acceptance as it has been shown to be effective for certain patients with type 1 diabetes. One obstacle, however, is the fact that there is an inadequate supply of cadaveric human islets to implement this procedure on a widespread clinical basis. A promising source of transplantable islets in the future will come through the use of adult or embryonic stem cells. This chapter presents an overview of the advancements made in the development of a stem cell based application to islet transplantation. Advantages and limitations are discussed regarding the use of embryonic stem cells, adult pancreatic stem/progenitor cells, and the use of nonpancreatic tissues based on current experimental models in the literature. It is concluded that stem cells offer the greatest potential for the development of an abundant source of pancreatic islets, although specific obstacles must be overcome before this can become a reality.

Combined gastrin and epidermal growth factor treatment induces islet regeneration and restores normoglycaemia in C57Bl6/J mice treated with alloxan

AIMS/HYPOTHESIS

Increasing beta-cell mass and/or function could restore glucose homeostasis in diabetes mellitus. Hitherto, trophic factors for beta-cell regeneration after toxic events have been difficult to identify. We evaluated the application of gastrin and epidermal growth factor after alloxan-induced pancreatic beta-cell damage.

METHODS

After alloxan treatment (70 mg/kg), mice were implanted with Alzet osmotic minipumps releasing gastrin and epidermal growth factor for one week. We monitored glycaemia, did histological analyses of the pancreata and quantified pancreatic beta-cell mass and insulin content.

RESULTS

Alloxan treatment alone resulted in a persisting hyperglycaemic state. Combined gastrin and epidermal growth factor treatment restored normoglycaemia in 3 days, an effect which seemed permanent. Glucose tolerance tests showed normal glucose responsiveness. Gastrin on its own and epidermal growth factor on its own did not alleviate hyperglycaemia. Islet mass, islet density and pancreatic insulin content were higher in mice treated with gastrin and epidermal growth factor than in untreated mice with persisting hyperglycaemia. In normoglycaemic control mice treatment with gastrin and epidermal growth factor did not affect these parameters. We detected transitional cytokeratin-positive ductal to endocrine insulin-expressing cells and noted increased ductal but not beta-cell proliferation.

CONCLUSIONS/INTERPRETATION

Our results show that combined treatment with gastrin and epidermal growth factor can induce sufficient regeneration of a functional islet mass to restore glucose homeostasis.

New organs from our own tissues: liver-to-pancreas transdifferentiation

Recent advances in pancreatic islet transplantation emphasize the potential of this approach for the long-term control of blood glucose levels in diabetic patients. However, tissue-replacement therapy will become widely available as a treatment for diabetes only when new sources of islets and insulin-producing cells are found. Here, we review recent evidence that documents the potential of mature liver as a source of tissue for generating a functional endocrine pancreas, by ectopic expression of pancreatic transcription and differentiation factors. When key events in the transconversion process have been identified, using the liver as a source of pancreatic tissue might provide a valuable approach for replacing impaired beta cell function in diabetics.

Betacellulin improves glucose metabolism by promoting conversion of intraislet precursor cells to beta-cells in streptozotocin-treated mice

Betacellulin (BTC) induces differentiation of pancreatic beta-cells and promotes regeneration of beta-cells in experimental diabetes. The present study was conducted to determine if BTC improved glucose metabolism in severe diabetes induced by a high dose of streptozotocin (STZ) in mice. Male ICR mice were injected with 200 microg/g ip STZ, and various doses of BTC were administered daily for 14 days. The plasma glucose concentration increased to a level of >500 mg/dl in STZ-injected mice. BTC (0.2 microg/g) significantly reduced the plasma glucose concentration, but a higher concentration was ineffective. The effect of BTC was marked by day 4 but became smaller on day 6 or later. The plasma insulin concentration and the insulin content were significantly higher in mice treated with 0.1 and 0.2 microg/g BTC. BTC treatment significantly increased the number of beta-cells in each islet as well as the number of insulin-positive islets. Within islets, the numbers of 5-bromo-2-deoxyuridine/somatostatin-positive cells and pancreatic duodenal homeobox-1/somatostatin-positive cells were significantly increased by BTC. These results indicate that BTC improved hyperglycemia induced by a high dose of STZ by promoting neoformation of beta-cells, mainly from somatostatin-positive islet cells.

Defective valvulogenesis in HB-EGF and TACE-null mice is associated with aberrant BMP signaling

Heparin-binding epidermal growth factor (HB-EGF) and betacellulin (BTC) are activating ligands for EGF receptor (EGFR/ErbB1) and ErbB4. To identify their physiological functions, we disrupted mouse HB-EGF and BTC alleles by homologous recombination. Most HB-EGF(-/-) mice died before weaning, and survivors had enlarged, dysfunctional hearts and reduced lifespans. Although BTC(-/-) mice were viable and fertile and displayed no overt defects, the lifespan of double null HB-EGF(-/-)/BTC(-/-) mice was further reduced, apparently due to accelerated heart failure. HB-EGF(-/-) newborns had enlarged and malformed semilunar and atrioventricular heart valves, and hypoplastic, poorly differentiated lungs. Defective cardiac valvulogenesis was the result of abnormal mesenchymal cell proliferation during remodeling, and was associated with dramatic increases in activated Smad1/5/8. Consistent with the phenotype, HB-EGF transcripts were localized to endocardial cells lining the margins of wild-type valves. Similarly defective valvulogenesis was observed in newborn mice lacking EGFR and tumor necrosis factor-alpha converting enzyme (TACE). These results suggest that cardiac valvulogenesis is dependent on EGFR activation by TACE-derived soluble HB-EGF, and that EGFR signaling is required to regulate bone morphogenetic protein signaling in this context.

Prospects for the prevention and reversal of type 1 diabetes mellitus

Type 1 (insulin-dependent) diabetes mellitus results from selective immune-mediated destruction of pancreatic islet beta cells. Strategies to prevent or reverse the development of diabetes can be divided into three groups, depending on whether they focus on beta-cell protection, regeneration or replacement. Prevention of immune beta-cell destruction involves either halting the immune attack directed against beta cells or making beta cells better able to withstand immune attack, for example, by making them resistant to free radical damage. The recent identification of beta-cell growth factors and development of stem cell technologies provides an alternative route to the reversal of diabetes, namely beta-cell regeneration. Interestingly, stem cell-derived islets appear to be less sensitive to recurrent immune destruction that is normally seen in response to islet transplantation. The last alternative is beta-cell replacement or substitution. This covers a wide range of interventions including human whole pancreas transplantation, xenotransplantation, genetically modified beta cells, mechanical insulin sensing and delivery devices, and the artificial pancreas. This review describes recent advances in each of these research areas and aims to provide clinicians with an idea of where and when an effective strategy to prevent or reverse diabetes development will become available.

Betacellulin induces angiogenesis through activation of mitogen-activated protein kinase and phosphatidylinositol 3'-kinase in endothelial cell

Betacellulin (BTC) is a member of the epidermal growth factor (EGF) family, and it acts through EGF receptors. We asked whether BTC could be an angiogenic factor. Using human umbilical vein endothelial cells (HUVECs), we examined the effect of BTC on kinases and angiogenic processes. BTC induced ERK1/2 and Akt phosphorylation in a dose- and time-dependent manner. BTC induced phosphorylation of all three EGF receptors present on HUVECs: ErbB2, ErbB3, and ErbB4. Pretreatment with effective concentrations of ErbB1 inhibitor did not suppress BTC-induced kinase phosphorylation. BTC, EGF, VEGF (all at 10 ng/ml) produced similar increases in DNA synthesis. BTC, EGF, and VEGF all significantly increased endothelial cell migration. In addition, BTC promoted survival in a dose-dependent manner, and its effect was inhibited by pretreatment with PtdIns 3'-kinase inhibitor wortmannin or MEK1/2 inhibitor PD98059. Both BTC and EGF produced similar increases in tube formation in collagen gels. BTC-induced tube formation was suppressed by PD98059, wortmannin, and LY294002. In the mouse Matrigel plug assay, BTC (100 ng/ml) promoted neovessel formation, and its effect was suppressed by a combination of wortmannin and PD98059. Taken together, these data show that BTC exerts potent angiogenic activity through activation of EGF receptors, mitogen-activated protein kinase, and PtdIns 3'-kinase/Akt in endothelial cells.

PDX-1 induces differentiation of intestinal epithelioid IEC-6 into insulin-producing cells

A homeodomain containing transcription factor PDX-1 can induce beta-cell-specific gene expressions in some non-beta-cells and may therefore be useful for future diabetes gene/cell therapy. Among the potential target organs or tissues for transcription factor-mediated induction of beta-cell-like differentiation are the intestinal epithelial cells. They have certain merits over other tissues and organs in terms of accessibility for gene delivery and of similarity in developmental background to the pancreatic primordium. In this study, we used an intestinal epithelium-derived cell line, IEC-6 cells, and investigated the possible effects of PDX-1 expression in those cells. By exogenous expression of the PDX-1 gene, IEC-6 cells started expressing multiple beta-cell-specific genes such as amylin, glucokinase, and Nkx6.1, which were not found in the original IEC-6 cells. Insulin gene expression, which was missing initially even in the PDX-1-transfected IEC-6 cells, became detectable when the cells were transplanted under the renal capsule of a rat. When the PDX-1(+) IEC-6 cells were kept in vitro, treatment with betacellulin could also confer insulin gene expression to them. Although insulin secretory granules became visible by electron microscopy, they were secreted regardless of glucose concentration. The in vivo or in vitro inductions of the insulin gene expression were not observed in the PDX-1(-) IEC-6 cells. Thus, our present observations demonstrate the potency of intestinal epithelial cells as a tool for diabetes gene/cell therapy and provide further support for the potency of PDX-1 in driving beta-cell-like differentiation in non-beta-cells.

Functional and histochemical analysis on pancreatic islets of APA hamsters with SZ-induced hyperglycemia and hyperlipidemia

To clarify how Syrian hamsters of the APA strain (APA hamsters) keep a diabetic condition for a long period, the functional and histochemical changes in the pancreatic islets of diabetic APA hamsters were examined. By glucose tolerance test, no glucose-induced insulin secretion was seen in the diabetic APA hamsters. By immunohistochemistry, it was revealed that at 24 hr after SZ-injection, the number of islets had decreased and that remnant islets had become markedly smaller. The islets had hardly any insulin-immunoreactive cells and consisted of cells stained by anti-glucagon and somatostatin antibodies. One, three and six months after SZ-injection, a small number of cells with vacuolative changes, which were positive for PAS staining, were observed in most islets and the vacuolated cells were stained mainly by anti-insulin antibody. In addition, a number of PCNA-positive cells were observed, especially in the periphery of the vacuolated cells, while TUNEL-positive cells were not detected. This data suggests that beta-cells proliferating as a result of the replication of the resident beta-cells in islets had fallen into degeneration and necrosis by a stress, such as the glycogen deposition in hyperglycemia and hyperlipidemia. Consequently, secretion of insulin was maintained at low levels, which allowed the hamsters to live without insulin therapy in the diabetic condition for over 6 months.

Promotion of beta-cell regeneration by betacellulin in ninety percent-pancreatectomized rats

Betacellulin is thought to promote growth and differentiation of pancreatic beta-cells. We investigated the effect of betacellulin on regeneration of pancreatic beta-cells in 90%-pancreatectomized rats. Ninety percent pancreatectomy was performed in male Wistar rats and betacellulin (0.5 microg/g body weight) or saline was administered daily for 10 d starting immediately after pancreatectomy. In pancreatectomized rats, the morning-fed plasma glucose was significantly lower and the plasma insulin concentration was significantly higher in betacellulin-treated rats than those in control rats for up to 4 wk. Thirty days after pancreatectomy, a glucose tolerance test was performed. Betacellulin reduced the plasma glucose response to ip glucose loading. In control rats, the plasma insulin concentration was significantly lower and did not respond to glucose. In contrast, the plasma insulin concentration increased slightly but significantly in betacellulin-treated rats. Thirty days after pancreatectomy, the beta-cell mass was greater and the insulin content was significantly higher in betacellulin-treated rats than those in control rats. The numbers of islet cell-like cluster and bromodeoxy uridine/insulin double- positive cells in both islet cell-like cluster and islets were significantly higher in betacellulin-treated rats. These results indicate that administration of betacellulin improves glucose metabolism by promoting beta-cell regeneration in 90%-pancreatectomized rats.

Novel betacellulin derivatives. Separation of the differentiation activity from the mitogenic activity

Betacellulin (BTC) is a member of the epidermal growth factor family. It has two biological activities: mitogenic activity in fibroblasts and vascular smooth muscle cells, and differentiation activity for the differentiation of pancreatic acinar AR42J cells into insulin-secreting cells. The previous finding that recombinant BTC promotes the neogenesis of beta-cells in a mouse model supports the possibility that BTC is a therapeutic protein. However, the mitogenic activity of BTC may not be needed for differentiation into beta-cells and may cause a side effect in clinical use. We prepared several derivatives of BTC to segregate the two activities, to decrease the mitogenic activity, and to maintain the differentiation activity. We succeeded in obtaining BTC derivatives segregated by the two biological activities by preparing truncated-type derivatives. A derivative of BTC, BTC24-76, with a truncated N-terminal 23 amino acids and C-terminal 4 amino acids, was 2.5-fold more active in differentiation and had one-tenth of the mitogenic activity. The derivatives described in the present study should be helpful in future applications as therapeutic proteins and in basic research for discovery of a BTC-specific receptor.