Neogenesis and proliferation of beta-cells induced by human betacellulin gene transduction via retrograde pancreatic duct injection of an adenovirus vector

HB-EGF Signaling Is Required for Glucose-Induced Pancreatic β-Cell Proliferation in Rats

The molecular mechanisms of β-cell compensation to metabolic stress are poorly understood. We previously observed that nutrient-induced β-cell proliferation in rats is dependent on epidermal growth factor receptor (EGFR) signaling. The aim of this study was to determine the role of the EGFR ligand heparin-binding EGF-like growth factor (HB-EGF) in the β-cell proliferative response to glucose, a β-cell mitogen and key regulator of β-cell mass in response to increased insulin demand. We show that exposure of isolated rat and human islets to HB-EGF stimulates β-cell proliferation. In rat islets, inhibition of EGFR or HB-EGF blocks the proliferative response not only to HB-EGF but also to glucose. Furthermore, knockdown of HB-EGF in rat islets blocks β-cell proliferation in response to glucose ex vivo and in vivo in transplanted glucose-infused rats. Mechanistically, we demonstrate that HB-EGF mRNA levels are increased in β-cells in response to glucose in a carbohydrate-response element-binding protein (ChREBP)-dependent manner. In addition, chromatin immunoprecipitation studies identified ChREBP binding sites in proximity to the HB-EGF gene. Finally, inhibition of Src family kinases, known to be involved in HB-EGF processing, abrogated glucose-induced β-cell proliferation. Our findings identify a novel glucose/HB-EGF/EGFR axis implicated in β-cell compensation to increased metabolic demand.

Impact of proton pump inhibitor treatment on pancreatic beta-cell area and beta-cell proliferation in humans

INTRODUCTION

Gastrin has been shown to promote beta-cell proliferation in rodents, but its effects in adult humans are largely unclear. Proton pump inhibitors (PPIs) lead to endogenous hypergastrinaemia, and improved glucose control during PPI therapy has been reported in patients with diabetes. Therefore, we addressed whether PPI treatment is associated with improved glucose homoeostasis, islet cell hyperplasia or increased new beta-cell formation in humans.

PATIENTS AND METHODS

Pancreatic tissue specimens from 60 patients with and 33 patients without previous PPI therapy were examined. The group was subdivided into patients without diabetes (n = 27), pre-diabetic patients (n = 31) and patients with diabetes (n = 35).

RESULTS

Fasting glucose and HbA1c levels were not different between patients with and without PPI therapy (P = 0.34 and P = 0.30 respectively). Beta-cell area was higher in patients without diabetes than in patients with pre-diabetes or diabetes (1.33 ± 0.12%, 1.05 ± 0.09% and 0.66 ± 0.07% respectively; P < 0.0001). There was no difference in beta-cell area between patients with and without PPI treatment (1.05 ± 0.08% vs 0.87 ± 0.08%, respectively; P = 0.16). Beta-cell replication was rare and not different between patients with and without PPI therapy (P = 0.20). PPI treatment was not associated with increased duct-cell replication (P = 0.18), insulin expression in ducts (P = 0.28) or beta-cell size (P = 0.63).

CONCLUSIONS

These results suggest that in adult humans, chronic PPI treatment does not enhance beta-cell mass or beta-cell function to a relevant extent.

Stem cells versus plasticity in liver and pancreas regeneration

Cell replacement in adult organs can be achieved through stem cell differentiation or the replication or transdifferentiation of existing cells. In the adult liver and pancreas, stem cells have been proposed to replace tissue cells, particularly following injury. Here we review how specialized cell types are produced in the adult liver and pancreas. Based on current evidence, we propose that the plasticity of differentiated cells, rather than stem cells, accounts for tissue repair in both organs.

β-cell replacement sources for type 1 diabetes: a focus on pancreatic ductal cells

Thorough research on the capacity of human islet transplantation to cure type 1 diabetes led to the achievement of 3- to 5-year-long insulin independence in nearly half of transplanted patients. Yet, translation of this technique to clinical routine is limited by organ shortage and the need for long-term immunosuppression, restricting its use to adults with unstable disease. The production of new bona fide β cells in vitro was thus investigated and finally achieved with human pluripotent stem cells (PSCs). Besides ethical concerns about the use of human embryos, studies are now evaluating the possibility of circumventing the spontaneous tumor formation associated with transplantation of PSCs. These issues fueled the search for cell candidates for β-cell engineering with safe profiles for clinical translation. In vivo studies revealed the regeneration capacity of the exocrine pancreas after injury that depends at least partially on facultative progenitors in the ductal compartment. These stimulated subpopulations of pancreatic ductal cells (PDCs) underwent β-cell transdifferentiation through reactivation of embryonic signaling pathways. In vitro models for expansion and differentiation of purified PDCs toward insulin-producing cells were described using cocktails of growth factors, extracellular-matrix proteins and transcription factor overexpression. In this review, we will describe the latest findings in pancreatic β-cell mass regeneration due to adult ductal progenitor cells. We will further describe recent advances in human PDC transdifferentiation to insulin-producing cells with potential for clinical translational studies.

Human β-cell proliferation and intracellular signaling part 2: still driving in the dark without a road map

Enhancing β-cell proliferation is a major goal for type 1 and type 2 diabetes research. Unraveling the network of β-cell intracellular signaling pathways that promote β-cell replication can provide the tools to address this important task. In a previous Perspectives in Diabetes article, we discussed what was known regarding several important intracellular signaling pathways in rodent β-cells, including the insulin receptor substrate/phosphatidylinositol-3 kinase/Akt (IRS-PI3K-Akt) pathways, glycogen synthase kinase-3 (GSK3) and mammalian target of rapamycin (mTOR) S6 kinase pathways, protein kinase Cζ (PKCζ) pathways, and their downstream cell-cycle molecular targets, and contrasted that ample knowledge to the small amount of complementary data on human β-cell intracellular signaling pathways. In this Perspectives, we summarize additional important information on signaling pathways activated by nutrients, such as glucose; growth factors, such as epidermal growth factor, platelet-derived growth factor, and Wnt; and hormones, such as leptin, estrogen, and progesterone, that are linked to rodent and human β-cell proliferation. With these two Perspectives, we attempt to construct a brief summary of knowledge for β-cell researchers on mitogenic signaling pathways and to emphasize how little is known regarding intracellular events linked to human β-cell replication. This is a critical aspect in the long-term goal of expanding human β-cells for the prevention and/or cure of type 1 and type 2 diabetes.

Enhanced expression of VEGF-A in β cells increases endothelial cell number but impairs islet morphogenesis and β cell proliferation

There is a reciprocal interaction between pancreatic islet cells and vascular endothelial cells (EC) in which EC-derived signals promote islet cell differentiation and islet development while islet cell-derived angiogenic factors promote EC recruitment and extensive islet vascularization. To examine the role of angiogenic factors in the coordinated development of islets and their associated vessels, we used a "tet-on" inducible system (mice expressing rat insulin promoter-reverse tetracycline activator transgene and a tet-operon-angiogenic factor transgene) to increase the β cell production of vascular endothelial growth factor-A (VEGF-A), angiopoietin-1 (Ang1), or angiopoietin-2 (Ang2) during islet cell differentiation and islet development. In VEGF-A overexpressing embryos, ECs began to accumulate around epithelial tubes residing in the central region of the developing pancreas (associated with endocrine cells) as early as embryonic day 12.5 (E12.5) and increased dramatically by E16.5. While α and β cells formed islet cell clusters in control embryos at E16.5, the increased EC population perturbed endocrine cell differentiation and islet cell clustering in VEGF-A overexpressing embryos. With continued overexpression of VEGF-A, α and β cells became scattered, remained adjacent to ductal structures, and never coalesced into islets, resulting in a reduction in β cell proliferation and β cell mass at postnatal day 1. A similar impact on islet morphology was observed when VEGF-A was overexpressed in β cells during the postnatal period. In contrast, increased expression of Ang1 or Ang2 in β cells in developing or adult islets did not alter islet differentiation, development, or morphology, but altered islet EC ultrastructure. These data indicate that (1) increased EC number does not promote, but actually impairs β cell proliferation and islet formation; (2) the level of VEGF-A production by islet endocrine cells is critical for islet vascularization during development and postnatally; (3) angiopoietin-Tie2 signaling in endothelial cells does not have a crucial role in the development or maintenance of islet vascularization.

Betacellulin-induced beta cell proliferation and regeneration is mediated by activation of ErbB-1 and ErbB-2 receptors

Background

Betacellulin (BTC), a member of the epidermal growth factor family, is known to play an important role in regulating growth and differentiation of pancreatic beta cells. Growth-promoting actions of BTC are mediated by epidermal growth factor receptors (ErbBs), namely ErbB-1, ErbB-2, ErbB-3 and ErbB-4; however, the exact mechanism for beta cell proliferation has not been elucidated. Therefore, we investigated which ErbBs are involved and some molecular mechanisms by which BTC regulates beta cell proliferation.

Methodology/Principal Findings

The expression of ErbB-1, ErbB-2, ErbB-3, and ErbB-4 mRNA was detected by RT-PCR in both a beta cell line (MIN-6 cells) and C57BL/6 mouse islets. Immunoprecipitation and western blotting analysis showed that BTC treatment of MIN-6 cells induced phosphorylation of only ErbB-1 and ErbB-2 among the four EGF receptors. BTC treatment resulted in DNA synthetic activity, cell cycle progression, and bromodeoxyuridine (BrdU)-positive staining. The proliferative effect was blocked by treatment with AG1478 or AG825, specific tyrosine kinase inhibitors of ErbB-1 and ErbB-2, respectively. BTC treatment increased mRNA and protein levels of insulin receptor substrate-2 (IRS-2), and this was blocked by the ErbB-1 and ErbB-2 inhibitors. Inhibition of IRS-2 by siRNA blocked cell cycle progression induced by BTC treatment. Streptozotocin-induced diabetic mice injected with a recombinant adenovirus expressing BTC and treated with AG1478 or AG825 showed reduced islet size, reduced numbers of BrdU-positive cells in the islets, and did not attain BTC-mediated remission of diabetes.

Conclusions/Significance

These results suggest that BTC exerts proliferative activity on beta cells through the activation of ErbB-1 and ErbB-2 receptors, which may increase IRS-2 expression, contributing to the regeneration of beta cells.

Intra-arterial targeted islet-specific expression of Sirt1 protects β cells from streptozotocin-induced apoptosis in mice

Gene therapy provides a promising approach to curing diabetes. However, an effective route for islet-specific targeting has yet to be established. Toward this end, the pancreatic blood circulation system in Balb/c mice was determined by the injection of rhodamine-containing beads. The efficiency of islet targeting was then measured by the injection of adenoviral vectors carrying a green fluorescence gene via the celiac trunk (C.T.). The results showed that >95% of islets and about 60% of β cells within the pancreatic body and tail could be labeled 3 days after surgery. α-Cell labeling was not as efficient, whereas labeling of nonendocrine tissues was barely detectable. For proof of principle, adenoviral vectors carrying a Sirtuin transgene were injected similarly to test the islet protection effect in the streptozotocin (STZ)-induced type 1 diabetic model. The results demonstrated that overexpression of Sirtuin in STZ-treated mice reduced the level of β-cell death and extent of glucose intolerance. This study reports on efficient islet-specific targeting by using adenoviral injection. This procedure could be invaluable to the treatment of diabetes and the study of islet biology.

Adult pancreatic acinar cells give rise to ducts but not endocrine cells in response to growth factor signaling

Studies in both humans and rodents have found that insulin(+) cells appear within or near ducts of the adult pancreas, particularly following damage or disease, suggesting that these insulin(+) cells arise de novo from ductal epithelium. We have found that insulin(+) cells are continuous with duct cells in the epithelium that makes up the hyperplastic ducts of both chronic pancreatitis and pancreatic cancer in humans. Therefore, we tested the hypothesis that both hyperplastic ductal cells and their associated insulin(+) cells arise from the same cell of origin. Using a mouse model that develops insulin(+) cell-containing hyperplastic ducts in response to the growth factor TGFalpha, we performed genetic lineage tracing experiments to determine which cells gave rise to both hyperplastic ductal cells and duct-associated insulin(+) cells. We found that hyperplastic ductal cells arose largely from acinar cells that changed their cell fate, or transdifferentiated, into ductal cells. However, insulin(+) cells adjacent to acinar-derived ductal cells arose from pre-existing insulin(+) cells, suggesting that islet endocrine cells can intercalate into hyperplastic ducts as they develop. We conclude that apparent pancreatic plasticity can result both from the ability of acinar cells to change fate and of endocrine cells to reorganize in association with duct structures.

Heterogeneity in mitotic activity and telomere length implies an important role of young islets in the maintenance of islet mass in the adult pancreas

Understanding the mechanisms of beta-cell dynamics in postnatal animals is central to cure diabetes. A major obstacle in evaluating the status of pancreatic cells is the lack of surface markers. Here we performed quantitative measurements of two internal markers to follow the developmental history of islets. One marker, cell-cycle activity, was established by measuring expression of Ki67 and the incorporation of 5-bromodeoxyuridine. The other marker, the aging process, was delineated by the determination of telomere length. Moreover, islet neogenesis, possibly from ductal precursors, was monitored by pancreatic duct labeling with an enhanced green fluorescence protein (EGFP) transgene. We found that islets from younger animals, on average, expressed higher Ki67 transcripts, displayed elevated 5-bromodeoxyuridine incorporation, and had longer telomeres. However, significant heterogeneity of these parameters was observed among islets from the same mouse. In contrast, the levels of proinsulin-1 transcripts in islets of different ages did not change significantly. Moreover, mitotic activities correlated significantly with telomere lengths of individual islets. Lastly, after 5.5 d pancreatic duct labeling, a few EGFP-positive islets could be identified in neonatal but not from adult pancreases. Compared with unlabeled control islets, EGFP-positive islets had higher mitotic activities and longer telomeres. The results suggest that islets are born at different time points during the embryonic and neonatal stages and imply that young islets might play an important role in the maintenance of islet mass in the adult pancreas.

Weighing up beta-cell mass in mice and humans: self-renewal, progenitors or stem cells?

Understanding how beta-cells maintain themselves in the adult pancreas is important for prioritizing strategies aimed at ameliorating or ideally curing different forms of diabetes. There has been much debate over whether beta-cell proliferation, as a means of self-renewal, predominates over the existence and differentiation of a pancreatic stem cell or progenitor cell population. This article describes the two opposing positions based largely on research in laboratory rodents and its extrapolation to humans.

Development of β-Cells in the Native Pancreas After Pancreas Allo-Transplantation in the Spontaneously Diabetic Torii Rat

BACKGROUND

We previously demonstrated the development of beta-cells in the native pancreas after syngeneic pancreas transplantation (PTx) in a model of type 2 diabetes, namely the Spontaneously Diabetic Torii (SDT; RT1 a) rat. In this study, we evaluated the effect of fully allogeneic PTx (allo-PTx) under immunosuppression on the native pancreases in the recipients.

MATERIALS AND METHODS

Diabetic 25-week-old SDT rats were divided into two groups: untreated controls and PTx-treated recipients. Dark Agouti (RT1 a) pancreases were then transplanted into the SDT rats. FK506 was administered daily postoperatively. Each group was examined for 15 weeks.

RESULTS

Control SDT rats showed a disappearance of the pancreatic and duodenal homeobox-1 (PDX-1) expression of the pancreases with the development of diabetes. In addition, the islets were gradually replaced by fibrosis, thus resulting in a marked decrease in the beta-cell mass at 40 weeks of age. On the other hand, in PTx recipients, islet-like cell clusters were found in the native pancreases. The beta-cell mass significantly increased in the native pancreases in the recipients at 10 and 15 weeks posttransplantation in comparison to the age-matched controls. Moreover, we observed the re-expression of PDX-1 in the islet-like cell clusters. Interestingly, insulin and glucagon double-positive stained cells in the mesenchyme and insulin single-positive cells in the ductal epithelium were also observed.

CONCLUSIONS

Our results indicated that the benefits of avoiding glucose toxicity by allo-PTx under immunosuppression could therefore induce the PDX-1 expression in the native pancreases, thus potentially resulting in the development of beta-cells in type 2 diabetic recipients.