Carbonic anhydrase II-positive pancreatic cells are progenitors for both endocrine and exocrine pancreas after birth. Proc Natl Acad Sci U S A. 2008;105:19915-19919. [PMID: 19052237 DOI: 10.1073/pnas.0805803105]

Combinatorial human progenitor cell transplantation optimizes islet regeneration through secretion of paracrine factors

Transplanted human bone marrow (BM) and umbilical cord blood (UCB) progenitor cells activate islet-regenerative or revascularization programs depending on the progenitor subtypes administered. Using purification of multiple progenitor subtypes based on a conserved stem cell function, high aldehyde dehydrogenase (ALDH) activity (ALDH(hi)), we have recently shown that transplantation of BM-derived ALDH(hi) progenitors improved systemic hyperglycemia and augmented insulin secretion by increasing islet-associated proliferation and vascularization, without increasing islet number. Conversely, transplantation of culture-expanded multipotent-stromal cells (MSCs) derived from BM ALDH(hi) cells augmented total beta cell mass via formation of beta cell clusters associated with the ductal epithelium, without sustained islet vascularization. To identify paracrine effectors produced by islet-regenerative MSCs, culture-expanded BM ALDH(hi) MSCs were transplanted into streptozotocin-treated nonobese diabetic/severe combine immune deficient (SCID) mice and segregated into islet-regenerative versus nonregenerative cohorts based on hyperglycemia reduction, and subsequently compared for differential production of mRNA and secreted proteins. Regenerative MSCs showed increased expression of matrix metalloproteases, epidermal growth factor receptor (EGFR)-activating ligands, and downstream effectors of Wnt signaling. Regenerative MSC supernatant also contained increased levels of pro-angiogenic versus pro-inflammatory cytokines, and augmented the expansion of ductal epithelial but not beta cells in vitro. Conversely, co-culture with UCB ALDH(hi) cells induced beta cell but not ductal epithelial cell proliferation. Sequential transplantation of MSCs followed by UCB ALDH(hi) cells improved hyperglycemia and glucose tolerance by increasing beta cell mass associated with the ductal epithelium and by augmenting intra-islet capillary densities. Thus, combinatorial human progenitor cell transplantation stimulated both islet-regenerative and revascularization programs. Understanding the progenitor-specific pathways that modulate islet-regenerative and revascularization processes may provide new approaches for diabetes therapy.

Tamoxifen-Induced Cre-loxP Recombination Is Prolonged in Pancreatic Islets of Adult Mice

Tamoxifen (Tm)-inducible Cre recombinases are widely used to perform gene inactivation and lineage tracing studies in mice. Although the efficiency of inducible Cre-loxP recombination can be easily evaluated with reporter strains, the precise length of time that Tm induces nuclear translocation of CreER^Tm and subsequent recombination of a target allele is not well defined, and difficult to assess. To better understand the timeline of Tm activity in vivo, we developed a bioassay in which pancreatic islets with a Tm-inducible reporter (from Pdx1^PB-CreER^Tm;R26R^lacZ mice) were transplanted beneath the renal capsule of adult mice previously treated with three doses of 1 mg Tm, 8 mg Tm, or corn oil vehicle. Surprisingly, recombination in islet grafts, as assessed by expression of the β-galactosidase (β-gal) reporter, was observed days or weeks after Tm treatment, in a dose-dependent manner. Substantial recombination occurred in islet grafts long after administration of 3×8 mg Tm: in grafts transplanted 48 hours after the last Tm injection, 77.9±0.4% of β-cells were β-gal+; in β-cells placed after 1 week, 46.2±5.0% were β-gal+; after 2 weeks, 26.3±7.0% were β-gal+; and after 4 weeks, 1.9±0.9% were β-gal+. Islet grafts from mice given 3×1 mg Tm showed lower, but notable, recombination 48 hours (4.9±1.7%) and 1 week (4.5±1.9%) after Tm administration. These results show that Tm doses commonly used to induce Cre-loxP recombination may continue to label significant numbers of cells for weeks after Tm treatment, possibly confounding the interpretation of time-sensitive studies using Tm-dependent models. Therefore, investigators developing experimental approaches using Tm-inducible systems should consider both maximal recombination efficiency and the length of time that Tm-induced Cre-loxP recombination occurs.

FoxO1 as a double-edged sword in the pancreas: analysis of pancreas- and β-cell-specific FoxO1 knockout mice

Diabetes is characterized by an absolute or relative deficiency of pancreatic β-cells. New strategies to accelerate β-cell neogenesis or maintain existing β-cells are desired for future therapies against diabetes. We previously reported that forkhead box O1 (FoxO1) inhibits β-cell growth through a Pdx1-mediated mechanism. However, we also reported that FoxO1 protects against β-cell failure via the induction of NeuroD and MafA. Here, we investigate the physiological roles of FoxO1 in the pancreas by generating the mice with deletion of FoxO1 in the domains of the Pdx1 promoter (P-FoxO1-KO) or the insulin 2 promoter (β-FoxO1-KO) and analyzing the metabolic parameters and pancreatic morphology under two different conditions of increased metabolic demand: high-fat high-sucrose diet (HFHSD) and db/db background. P-FoxO1-KO, but not β-FoxO1-KO, showed improved glucose tolerance with HFHSD. Immunohistochemical analysis revealed that P-FoxO1-KO had increased β-cell mass due to increased islet number rather than islet size, indicating accelerated β-cell neogenesis. Furthermore, insulin-positive pancreatic duct cells were increased in P-FoxO1-KO but not β-FoxO1-KO. In contrast, db/db mice crossed with P-FoxO1-KO or β-FoxO1-KO showed more severe glucose intolerance than control db/db mice due to decreased glucose-responsive insulin secretion. Electron microscope analysis revealed fewer insulin granules in FoxO1 knockout db/db mice. We conclude that FoxO1 functions as a double-edged sword in the pancreas; FoxO1 essentially inhibits β-cell neogenesis from pancreatic duct cells but is required for the maintenance of insulin secretion under metabolic stress.

Adenosine kinase inhibition selectively promotes rodent and porcine islet β-cell replication

Diabetes is a pathological condition characterized by relative insulin deficiency, persistent hyperglycemia, and, consequently, diffuse micro- and macrovascular disease. One therapeutic strategy is to amplify insulin-secretion capacity by increasing the number of the insulin-producing β cells without triggering a generalized proliferative response. Here, we present the development of a small-molecule screening platform for the identification of molecules that increase β-cell replication. Using this platform, we identify a class of compounds [adenosine kinase inhibitors (ADK-Is)] that promote replication of primary β cells in three species (mouse, rat, and pig). Furthermore, the replication effect of ADK-Is is cell type-selective: treatment of islet cell cultures with ADK-Is increases replication of β cells but not that of α cells, PP cells, or fibroblasts. Short-term in vivo treatment with an ADK-I also increases β-cell replication but not exocrine cell or hepatocyte replication. Therefore, we propose ADK inhibition as a strategy for the treatment of diabetes.

COUP-TFII controls mouse pancreatic β-cell mass through GLP-1-β-catenin signaling pathways

Background

The control of the functional pancreatic β-cell mass serves the key homeostatic function of releasing the right amount of insulin to keep blood sugar in the normal range. It is not fully understood though how β-cell mass is determined.

Methodology/Principal Findings

Conditional chicken ovalbumin upstream promoter transcription factor II (COUP-TFII)-deficient mice were generated and crossed with mice expressing Cre under the control of pancreatic duodenal homeobox 1 (pdx1) gene promoter. Ablation of COUP-TFII in pancreas resulted in glucose intolerance. Beta-cell number was reduced at 1 day and 3 weeks postnatal. Together with a reduced number of insulin-containing cells in the ductal epithelium and normal β-cell proliferation and apoptosis, this suggests decreased β-cell differentiation in the neonatal period. By testing islets isolated from these mice and cultured β-cells with loss and gain of COUP-TFII function, we found that COUP-TFII induces the expression of the β-catenin gene and its target genes such as cyclin D1 and axin 2. Moreover, induction of these genes by glucagon-like peptide 1 (GLP-1) via β-catenin was impaired in absence of COUP-TFII. The expression of two other target genes of GLP-1 signaling, GLP-1R and PDX-1 was significantly lower in mutant islets compared to control islets, possibly contributing to reduced β-cell mass. Finally, we demonstrated that COUP-TFII expression was activated by the Wnt signaling-associated transcription factor TCF7L2 (T-cell factor 7-like 2) in human islets and rat β-cells providing a feedback loop.

Conclusions/Significance

Our findings show that COUP-TFII is a novel component of the GLP-1 signaling cascade that increases β-cell number during the neonatal period. COUP-TFII is required for GLP-1 activation of the β-catenin-dependent pathway and its expression is under the control of TCF7L2.

Stem cell-based treatments for Type 1 diabetes mellitus: bone marrow, embryonic, hepatic, pancreatic and induced pluripotent stem cells

Type 1 diabetes mellitus--characterized by the permanent destruction of insulin-secreting β-cells--is responsive to cell-based treatments that replace lost β-cell populations. The current gold standard of pancreas transplantation provides only temporary independence from exogenous insulin and is fraught with complications, including increased mortality. Stem cells offer a number of theoretical advantages over current therapies. Our review will focus on the development of treatments involving tissue stem cells from bone marrow, liver and pancreatic cells, as well as the potential use of embryonic and induced pluripotent stem cells for Type 1 diabetes therapy. While the body of research involving stem cells is at once promising and inconsistent, bone marrow-derived mesenchymal stem cell transplantation seems to offer the most compelling evidence of efficacy. These cells have been demonstrated to increase endogenous insulin production, while partially mitigating the autoimmune destruction of newly formed β-cells. However, recently successful experiments involving induced pluripotent stem cells could quickly move them into the foreground of therapeutic research. We address the limitations encountered by present research and look toward the future of stem cell treatments for Type 1 diabetes.

Lineage tracing of pancreatic stem cells and beta cell regeneration

Restoring a functional β cell mass in diabetes patients by β cell transplantation or stimulation of β cell regeneration are promising approaches. It requires knowledge on the mechanisms of β cell neogenesis, an issue that is still quite controversial. Postnatal islet regeneration may or may not depend on an influx of new islet cells from adult progenitors. To solve this issue in animal models, genetic lineage tracing has become a crucial research method. This method allows to test the various hypotheses that have been proposed concerning β cell neogenesis and regeneration.

Formation of pancreatic islets involves coordinated expansion of small islets and fission of large interconnected islet-like structures

The islets of Langerhans, micro-organs for maintaining glucose homeostasis, range in size from small clusters of <10 cells to large islets consisting of several thousand endocrine cells. Islet size distributions among various species are similar and independent of body size, suggesting an intrinsic limit to islet size. Little is known about the mechanisms regulating islet size. We have carried out a comprehensive analysis of changes of islet size distribution in the intact mouse pancreas from birth to eight months, including mathematical modeling to quantify this dynamic biological process. Islet growth was size-dependent during development, with preferential expansion of smaller islets and fission of large interconnected islet-like structures occurring most actively at approximately three weeks of age at the time of weaning. The process of islet formation was complete by four weeks with little or no new islet formation thereafter, and all the β-cells had low proliferation potential in the adult, regardless of islet size. Similarly, in insulinoma-bearing mice, the early postnatal developmental process including fission followed the same time course with no new islet formation in adults. However, tumor progression led to uncontrolled islet growth with accelerated expansion of larger islets. Thus, islet formation and growth is a tightly regulated process involving preferential expansion of small islets and fission of large interconnected islet-like structures.

Pancreatic ductal cells in development, regeneration, and neoplasia

The pancreas is a complex organ comprised of three critical cell lineages: islet (endocrine), acinar, and ductal. This review will focus upon recent insights and advances in the biology of pancreatic ductal cells. In particular, emphasis will be placed upon the regulation of ductal cells by specific transcriptional factors during development as well as the underpinnings of acinar-ductal metaplasia as an important adaptive response during injury and regeneration. We also address the potential contributions of ductal cells to neoplastic transformation, specifically in pancreatic ductal adenocarcinoma.

Pancreatic ductal cells in development, regeneration, and neoplasia

The pancreas is a complex organ comprised of three critical cell lineages: islet (endocrine), acinar, and ductal. This review will focus upon recent insights and advances in the biology of pancreatic ductal cells. In particular, emphasis will be placed upon the regulation of ductal cells by specific transcriptional factors during development as well as the underpinnings of acinar-ductal metaplasia as an important adaptive response during injury and regeneration. We also address the potential contributions of ductal cells to neoplastic transformation, specifically in pancreatic ductal adenocarcinoma.

Pancreatic progenitors: The shortest route to restore islet cell mass

The regenerative process of the pancreas is of interest because the main pathogenesis of diabetes mellitus is an inadequate number of insulin-producing β-cells. The functional mass of β-cells is decreased in most forms of diabetes, so replacing missing β-cells or triggering their regeneration may allow for improved diabetes treatment. Therefore, expansion of the β-cell mass from endogenous sources, either in vivo or in vitro, represents an area of increasing interest. The mechanism of islet regeneration remains poorly understood, but the identification of islet progenitor sources is critical for understanding β-cell regeneration. One potential source is the islet proper, via the de-differentiation, proliferation and redifferentiation of facultative progenitors residing within the islet. The new pancreatic islets derived from progenitor cells present within the ducts have been reported, but the existence and identity of the progenitor cells have been debated. In this mini-review, we focus primarily on pancreatic progenitors, which are islet progenitors capable of differentiating into insulin producing cells. We also emphasize the importance of pancreatic progenitors as a target for stem cell therapy for diabetes.

Transplanted human bone marrow progenitor subtypes stimulate endogenous islet regeneration and revascularization

Transplanted murine bone marrow (BM) progenitor cells recruit to the injured pancreas and induce endogenous beta cell proliferation to improve islet function. To enrich for analogous human progenitor cell types that stimulate islet regeneration, we purified human BM based on high-aldehyde dehydrogenase activity (ALDH(hi)), an enzymatic function conserved in hematopoietic, endothelial, and mesenchymal progenitor lineages. We investigated the contributions of ALDH(hi) mixed progenitor cells or culture-expanded, ALDH-purified multipotent stromal cell (MSC) subsets to activate endogenous programs for islet regeneration after transplantation into streptozotocin-treated NOD/SCID mice. Intravenous injection of uncultured BM ALDH(hi) cells improved systemic hyperglycemia and augmented insulin secretion by increasing islet size and vascularization, without increasing total islet number. Augmented proliferation within regenerated endogenous islets and associated vascular endothelium indicated the induction of islet-specific proliferative and pro-angiogenic programs. Although cultured MSC from independent human BM samples showed variable capacity to improve islet function, and prolonged expansion diminished hyperglycemic recovery, transplantation of ALDH-purified regenerative MSC reduced hyperglycemia and augmented total beta cell mass by stimulating the formation of small beta cell clusters associated with the ductal epithelium, without evidence of increased islet vascularization or Ngn3(+) endocrine precursor activation. Thus, endogenous islet recovery after progenitor cell transplantation can occur via distinct regenerative mechanisms modulated by subtypes of progenitor cells administered. Further, understanding of how these islet regenerative and pro-angiogenic programs are activated by specific progenitor subsets may provide new approaches for combination cellular therapies to combat diabetes.

β-Cell Generation: Can Rodent Studies Be Translated to Humans?

β-cell replacement by allogeneic islet transplantation is a promising approach for patients with type 1 diabetes, but the shortage of organ donors requires new sources of β cells. Islet regeneration in vivo and generation of β-cells ex vivo followed by transplantation represent attractive therapeutic alternatives to restore the β-cell mass. In this paper, we discuss different postnatal cell types that have been envisaged as potential sources for future β-cell replacement therapy. The ultimate goal being translation to the clinic, a particular attention is given to the discrepancies between findings from studies performed in rodents (both ex vivo on primary cells and in vivo on animal models), when compared with clinical data and studies performed on human cells.

Duct cells contribute to regeneration of endocrine and acinar cells following pancreatic damage in adult mice

BACKGROUND & AIMS

There have been conflicting results on a cell of origin in pancreatic regeneration. These discrepancies predominantly stem from lack of specific markers for the pancreatic precursors/stem cells, as well as differences in the targeted cells and severity of tissue injury in the experimental models so far proposed. We attempted to create a model that used diphtheria toxin receptor (DTR) to ablate specific cell populations, control the extent of injury, and avoid induction of the inflammatory response.

METHODS

To target specific types of pancreatic cells, we crossed R26DTR or R26DTR/lacZ mice with transgenic mice that express the Cre recombinase in the pancreas, under control of the Pdx1 (global pancreatic) or elastase (acinar-specific) promoters.

RESULTS

Exposure of PdxCre;R26DTR mice to diphtheria toxin resulted in extensive ablation of acinar and endocrine tissues but not ductal cells. Surviving cells within the ductal compartment contributed to regeneration of endocrine and acinar cells via recapitulation of the embryonic pancreatic developmental program. However, following selective ablation of acinar tissue in ElaCreERT2;R26DTR mice, regeneration likely occurred by reprogramming of ductal cells to acinar lineage.

CONCLUSIONS

In the pancreas of adult mice, epithelial cells within the ductal compartment contribute to regeneration of endocrine and acinar cells. The severity of injury determines the regenerative mechanisms and cell types that contribute to this process.

Potential pathways to restore β-cell mass: pluripotent stem cells, reprogramming, and endogenous regeneration

Currently available β-cell replacement therapies for patients with diabetes, including islet and pancreas transplantation, are largely successful in restoring normal glucose metabolism, but the scarcity of organ donors restricts their more widespread use. To solve this supply problem, several different strategies for achieving β-cell mass restoration are being pursued. These include the generation of β cells from stem cells and their subsequent transplantation, or regeneration-type approaches, such as stimulating endogenous regenerative mechanisms or inducing reprogramming of non-β cells into β cells. Because these strategies would ultimately generate allogeneic or syngeneic β cells in humans, the control of alloimmunity and/or autoimmunity in addition to replacing lost β cells will be of utmost importance. We briefly review the recent literature on these three promising strategies toward β-cell replacement or restoration and point out the major issues impacting their translation to treating human diabetes.

Stem cell approaches for diabetes: towards beta cell replacement

Stem cells hold great promise for pancreatic beta cell replacement therapy for diabetes. In type 1 diabetes, beta cells are mostly destroyed, and in type 2 diabetes beta cell numbers are reduced by 40% to 60%. The proof-of-principle that cellular transplants of pancreatic islets, which contain insulin-secreting beta cells, can reverse the hyperglycemia of type 1 diabetes has been established, and there is now a need to find an adequate source of islet cells. Human embryonic stem cells can be directed to become fully developed beta cells and there is expectation that induced pluripotent stem (iPS) cells can be similarly directed. iPS cells can also be generated from patients with diabetes to allow studies of the genomics and pathogenesis of the disease. Some alternative approaches for replacing beta cells include finding ways to enhance the replication of existing beta cells, stimulating neogenesis (the formation of new islets in postnatal life), and reprogramming of pancreatic exocrine cells to insulin-producing cells. Stem-cell-based approaches could also be used for modulation of the immune system in type 1 diabetes, or to address the problems of obesity and insulin resistance in type 2 diabetes. Herein, we review recent advances in our understanding of diabetes and beta cell biology at the genomic level, and we discuss how stem-cell-based approaches might be used for replacing beta cells and for treating diabetes.

Pancreatic β-cells are generated by neogenesis from non-β-cells after birth

The mass of pancreatic β-cells is maintained throughout lifetime to control blood glucose levels. Although the major mechanism of the maintenance of β-cell mass after birth is thought to be selfreplication of pre-existing β-cells, it is possible that pancreatic β-cells are also generated from non-β-cells. Here, we address this issue by using the inducible Cre/loxP system to trace β-cells. We generated Ins2-CreERT2/R26R-YFP double knock-in mice, in which pancreatic β-cells can be labeled specifically and permanently upon injection of the synthetic estrogen analog tamoxifien, and then traced the β-cells by pulse and chase experiment in several different conditions. When β-cells were labeled in adults under physiological and untreated conditions, the frequency of the labeling (labeling index) was not altered significantly throughout the 12-month experimental period. In addition, the labeling index was not changed after ablation of β-cells by streptozotocin treatment. However, when tamoxifen was injected to pregnant mothers just before they gave birth, the labeling index in the neonates was decreased significantly around weaning, suggesting that β-cells are generated from non-β-cells. These results indicate that various mechanisms are involved in the maintenance of β-cells after birth, and that the present system using knock-in mice is useful for investigation of β-cell fate.

R-spondin1 deficiency in mice improves glycaemic control in association with increased beta cell mass

AIMS/HYPOTHESIS

Roof plate-specific spondin (R-spondin1; RSPO1) is a modulator of canonical Wg (wingless) plus Int1 (chromosomal integration site of mouse mammary tumour virus on mouse chromosome 15) (cWNT) signalling that induces cWNT target genes. We have demonstrated that Rspo1 is expressed in murine beta cells, and that it stimulates proliferation and insulin secretion, and inhibits cytokine-induced apoptosis, in mouse insulinoma (MIN6) and beta cells. We thus investigated the role of RSPO1 in beta cells in vivo using Rspo1 ( -/- ) mice.

METHODS

The effects of Rspo1 deficiency were assessed by determination of cWNT signalling, glucose tolerance and beta cell mass.

RESULTS

Rspo1 ( -/- ) mice demonstrated an 82% reduction in RSPO1 transcripts and a 61% reduction in the signal detected by an RSPO1 antibody, as well as a 47% decrease in islet cWNT signalling. Despite no differences in body and pancreatic weights or in fasting glycaemia and insulinaemia compared with Rspo1 (+/+) mice, Rspo1 ( -/- ) animals had improved glycaemic control after oral glucose challenge (p < 0.05), with no difference in insulin sensitivity, but an enhanced insulin response over 30 min (p < 0.05); glucagon responses were normal. Rspo1 deficiency also resulted in a twofold increase in beta cell mass (p < 0.05) in association with 2- and 12-fold increases in the number of beta cells positive for antigen identified by monoclonal antibody Ki67 (Ki67) (p < 0.01) and insulin-positive ductal cells (p < 0.05), respectively. No change in the number of TUNEL-positive beta cells was detected. Islets isolated from Rspo1 ( -/- ) animals displayed no differences in glucose-induced insulin secretion or in glucose suppression of glucagon.

CONCLUSIONS/INTERPRETATION

The present study reveals an unexpected role for RSPO1 as a regulator of both beta cell proliferation and neogenesis in vivo, and reinforces the importance of cWNT signalling for the maintenance of normal pancreatic beta cell behaviour.

Gastrin treatment stimulates β-cell regeneration and improves glucose tolerance in 95% pancreatectomized rats

β-Cell mass reduction is a central aspect in the development of type 1 and type 2 diabetes, and substitution or regeneration of the lost β-cells is a potentially curative treatment of diabetes. To study the effects of gastrin on β-cell mass in rats with 95% pancreatectomy (95%-Px), a model of pancreatic regeneration, rats underwent 95% Px or sham Px and were treated with [15 leu] gastrin-17 (Px+G and S+G) or vehicle (Px+V and S+V) for 15 d. In 95% Px rats, gastrin treatment reduced hyperglycemia (280 ± 52 mg vs. 436 ± 51 mg/dl, P < 0.05), and increased β-cell mass (1.15 ± 0.15 mg)) compared with vehicle-treated rats (0.67 ± 0.15 mg, P < 0.05). Gastrin treatment induced β-cell regeneration by enhancing β-cell neogenesis (increased number of extraislet β-cells in Px+G: 0.42 ± 0.05 cells/mm(2) vs. Px+V: 0.27 ± 0.07 cells/mm(2), P < 0.05, and pancreatic and duodenal homeobox 1 expression in ductal cells of Px+G: 1.21 ± 0.38% vs. Px+V: 0.23 ± 0.10%, P < 0.05) and replication (Px+G: 1.65 ± 0.26% vs. S+V: 0.64 ± 0.14%; P < 0.05). In addition, reduced β-cell apoptosis contributed to the increased β-cell mass in gastrin-treated rats (Px+G: 0.07 ± 0.02%, Px+V: 0.23 ± 0.05%; P < 0.05). Gastrin action on β-cell regeneration and survival increased β-cell mass and improved glucose tolerance in 95% Px rats, supporting a potential role of gastrin in the treatment of diabetes.

Epidermal growth factor (EGF)-receptor signalling is needed for murine beta cell mass expansion in response to high-fat diet and pregnancy but not after pancreatic duct ligation

AIMS/HYPOTHESIS

Epidermal growth factor receptor (EGFR) signalling is essential for the proper fetal development of pancreatic islets and in the postnatal formation of an adequate beta cell mass. In this study we investigated the role of EGFR signalling in the physiological states of beta cell mass expansion in adults during metabolic syndrome and pregnancy, as well as in regeneration after pancreatic duct ligation.

METHODS

Heterozygous Pdx1-EGFR-dominant-negative (E1-DN) mice, which have a kinase-negative EGFR under the Pdx1 promoter, and wild-type mice were both subjected to a high-fat diet, pregnancy and pancreatic duct ligation.

RESULTS

The beta cell mass of wild-type mice fed the high-fat diet increased by 70% and the mice remained normoglycaemic; the E1-DN mice became diabetic and failed to show any compensatory beta cell mass expansion. Similarly, pregnant wild-type mice had four times more proliferating beta cells and a 75% increase in beta cell mass at mid-gestation, in contrast to the pregnant E1-DN mice, which did not show any significant beta cell compensation and were hyperglycaemic in an intraperitoneal glucose tolerance test. However, after pancreatic duct ligation, both the wild-type and E1-DN mice showed similar expression of Ngn3 (also known as Neurog3) and beta cell proliferation increased to a similar level in the ligated part of pancreas.

CONCLUSIONS/INTERPRETATIONS

EGFR signalling is essential in beta cell mass expansion during a high-fat diet and pregnancy where replication is the primary mechanism for compensatory beta cell mass expansion. In contrast, EGFR signalling appears not to be crucial to increased beta cell proliferation after pancreatic duct ligation.

Progenitor cell domains in the developing and adult pancreas

Unlike organs with defined stem cell compartments, such as the intestine, the pancreas has limited capacity to regenerate. The question of whether the adult pancreas harbors facultative stem/progenitor cells has been a prime subject of debate. Cumulative evidence from recent genetic lineage tracing studies, in which specific cell populations were marked and traced in adult mice, suggests that endocrine and acinar cells are no longer generated from progenitors in the adult pancreas. These studies further indicate that adult pancreatic ductal cells are not a source for endocrine cells following pancreatic injury, as previously suggested. Our own studies have shown that adult ductal cells reinitiate expression of some endocrine progenitor markers, including Ngn3, after injury by partial duct ligation (PDL), but that these cells do not undergo endocrine cell differentiation. Here, we present additional evidence that endocrine cells do not arise from ducts following b-cell ablation by streptozotocin or by a diphtheria toxin-expressing transgene or when b-cell ablation is combined with PDL. In this review, we discuss findings from recent lineage tracing studies of embryonic and adult pancreatic ductal cells. Based upon the combined evidence from these studies, we propose that multipotency is associated with a specific transcriptional signature.

Multiple phenotypes in adult mice following inactivation of the Coxsackievirus and Adenovirus Receptor (Car) gene

To determine the normal function of the Coxsackievirus and Adenovirus Receptor (CAR), a protein found in tight junctions and other intercellular complexes, we constructed a mouse line in which the CAR gene could be disrupted at any chosen time point in a broad spectrum of cell types and tissues. All knockouts examined displayed a dilated intestinal tract and atrophy of the exocrine pancreas with appearance of tubular complexes characteristic of acinar-to-ductal metaplasia. The mice also exhibited a complete atrio-ventricular block and abnormal thymopoiesis. These results demonstrate that CAR exerts important functions in the physiology of several organs in vivo.

Regenerative medicine for insulin deficiency: creation of pancreatic islets and bioartificial pancreas

Recent advances in pancreas organogenesis have greatly improved the understanding of cell lineage from inner cell mass to fully differentiated β-cells. Based upon such knowledge, insulin-producing cells similar to β-cells to a certain extent have been generated from various cell sources including embryonic stem cells (ESCs) and induced pluripotent stem (iPS) cells, although fully differentiated cells comparable to β-cells are not yet available. The bioartificial pancreas is a therapeutic approach to enable allo- and xenotransplantation of islets without immune suppression. Among several types of bioartificial pancreases (BAPs), micro-encapsulated porcine islets are already in use in clinical trials and may, perhaps, replace islet transplantation in the near future. Some types of bioartificial pancreas such as macro-encapsulation are also useful for keeping transplanted cells enclosed in case retrieval is necessary. Therefore, early clinical applications of artificially generated β-like cells, especially those from ESCs or iPS cells, will be considered in combination with retrievable BAPs.

Genetic lineage tracing, a powerful tool to investigate the embryonic organogenesis and adult organ maintenance of the pancreas

Revealing the mechanism of adult organ maintenance and regeneration after injury is fundamental to our understanding of the pathogenesis of diseases. Considering the results of pulse and chase experiments using inducible insulin-Cre or Elastase-Cre, and more recently HNF1b-Cre, adult pancreatic cells (beta, acinar, and duct cells) seem to be maintained by the self-duplication of the existing cells, while there is still a dispute about whether adult beta-cells are supplied from the duct cells. Here we describe the advantages and pitfalls of Cre-mediated genetic lineage tracing experiments in the analysis of embryonic organogenesis and adult organ maintenance of the pancreas. This experimental technique enables us to visualize the specific cells and their progeny in vivo, and the combination of lineage tracing and other experimental procedures provides us with more detailed information on the mechanism of organogenesis and adult organ homeostasis.

Stem cell-based approaches for the treatment of diabetes

The incidence of diabetes and the associated debilitating complications are increasing at an alarming rate worldwide. Current therapies for type 1 diabetes focus primarily on administration of exogenous insulin to help restore glucose homeostasis. However, such treatment rarely prevents the long-term complications of this serious metabolic disorder, including neuropathy, nephropathy, retinopathy, and cardiovascular disease. Whole pancreas or islet transplantations have enjoyed limited success in some individuals, but these approaches are hampered by the shortage of suitable donors and the burden of lifelong immunosuppression. Here, we review current approaches to differentiate nonislet cell types towards an islet-cell phenotype which may be used for larger-scale cell replacement strategies. In particular, the differentiation protocols used to direct embryonic stem cells, progenitor cells of both endocrine and nonendocrine origin, and induced pluripotent stem cells towards an islet-cell phenotype are discussed.

Generating mouse models of degenerative diseases using Cre/lox-mediated in vivo mosaic cell ablation

Most degenerative diseases begin with a gradual loss of specific cell types before reaching a threshold for symptomatic onset. However, the endogenous regenerative capacities of different tissues are difficult to study, because of the limitations of models for early stages of cell loss. Therefore, we generated a transgenic mouse line (Mos-iCsp3) in which a lox-mismatched Cre/lox cassette can be activated to produce a drug-regulated dimerizable caspase-3. Tissue-restricted Cre expression yielded stochastic Casp3 expression, randomly ablating a subset of specific cell types in a defined domain. The limited and mosaic cell loss led to distinct responses in 3 different tissues targeted using respective Cre mice: reversible, impaired glucose tolerance with normoglycemia in pancreatic β cells; wound healing and irreversible hair loss in the skin; and permanent moderate deafness due to the loss of auditory hair cells in the inner ear. These mice will be important for assessing the repair capacities of tissues and the potential effectiveness of new regenerative therapies.

Control of pancreatic β cell regeneration by glucose metabolism

Recent studies revealed a surprising regenerative capacity of insulin-producing β cells in mice, suggesting that regenerative therapy for human diabetes could in principle be achieved. Physiologic β cell regeneration under stressed conditions relies on accelerated proliferation of surviving β cells, but the factors that trigger and control this response remain unclear. Using islet transplantation experiments, we show that β cell mass is controlled systemically rather than by local factors such as tissue damage. Chronic changes in β cell glucose metabolism, rather than blood glucose levels per se, are the main positive regulator of basal and compensatory β cell proliferation in vivo. Intracellularly, genetic and pharmacologic manipulations reveal that glucose induces β cell replication via metabolism by glucokinase, the first step of glycolysis, followed by closure of K(ATP) channels and membrane depolarization. Our data provide a molecular mechanism for homeostatic control of β cell mass by metabolic demand.

Δ40 Isoform of p53 controls β-cell proliferation and glucose homeostasis in mice

OBJECTIVE

Investigating the dynamics of pancreatic β-cell mass is critical for developing strategies to treat both type 1 and type 2 diabetes. p53, a key regulator of the cell cycle and apoptosis, has mostly been a focus of investigation as a tumor suppressor. Although p53 alternative transcripts can modulate p53 activity, their functions are not fully understood. We hypothesized that β-cell proliferation and glucose homeostasis were controlled by Δ40p53, a p53 isoform lacking the transactivation domain of the full-length protein that modulates total p53 activity and regulates organ size and life span in mice.

RESEARCH DESIGN AND METHODS

We phenotyped metabolic parameters in Δ40p53 transgenic (p44tg) mice and used quantitative RT-PCR, Western blotting, and immunohistochemistry to examine β-cell proliferation.

RESULTS

Transgenic mice with an ectopic p53 gene encoding Δ40p53 developed hypoinsulinemia and glucose intolerance by 3 months of age, which worsened in older mice and led to overt diabetes and premature death from ∼14 months of age. Consistent with a dramatic decrease in β-cell mass and reduced β-cell proliferation, lower expression of cyclin D2 and pancreatic duodenal homeobox-1, two key regulators of proliferation, was observed, whereas expression of the cell cycle inhibitor p21, a p53 target gene, was increased.

CONCLUSIONS

These data indicate a significant and novel role for Δ40p53 in β-cell proliferation with implications for the development of age-dependent diabetes.

Sox9+ ductal cells are multipotent progenitors throughout development but do not produce new endocrine cells in the normal or injured adult pancreas

One major unresolved question in the field of pancreas biology is whether ductal cells have the ability to generate insulin-producing β-cells. Conclusive examination of this question has been limited by the lack of appropriate tools to efficiently and specifically label ductal cells in vivo. We generated Sox9CreER(T2) mice, which, during adulthood, allow for labeling of an average of 70% of pancreatic ductal cells, including terminal duct/centroacinar cells. Fate-mapping studies of the Sox9(+) domain revealed endocrine and acinar cell neogenesis from Sox9(+) cells throughout embryogenesis. Very small numbers of non-β endocrine cells continue to arise from Sox9(+) cells in early postnatal life, but no endocrine or acinar cell neogenesis from Sox9(+) cells occurs during adulthood. In the adult pancreas, pancreatic injury by partial duct ligation (PDL) has been suggested to induce β-cell regeneration from a transient Ngn3(+) endocrine progenitor cell population. Here, we identify ductal cells as a cell of origin for PDL-induced Ngn3(+) cells, but fail to observe β-cell neogenesis from duct-derived cells. Therefore, although PDL leads to activation of Ngn3 expression in ducts, PDL does not induce appropriate cues to allow for completion of the entire β-cell neogenesis program. In conclusion, although endocrine cells arise from the Sox9(+) ductal domain throughout embryogenesis and the early postnatal period, Sox9(+) ductal cells of the adult pancreas no longer give rise to endocrine cells under both normal conditions and in response to PDL.

Ongoing beta-cell turnover in adult nonhuman primates is not adaptively increased in streptozotocin-induced diabetes

OBJECTIVE

β-Cell turnover and its potential to permit β-cell regeneration in adult primates are unknown. Our aims were 1) to measure β-cell turnover in adult nonhuman primates; 2) to establish the relative contribution of β-cell replication and formation of new β-cells from other precursors (defined thus as β-cell neogenesis); and 3) to establish whether there is an adaptive increase in β-cell formation (attempted regeneration) in streptozotocin (STZ)-induced diabetes in adult nonhuman primates.

RESEARCH DESIGN AND METHODS

Adult (aged 7 years) vervet monkeys were administered STZ (45-55 mg/kg, n = 7) or saline (n = 9). Pancreas was obtained from each animal twice, first by open surgical biopsy and then by euthanasia. β-Cell turnover was evaluated by applying a mathematic model to measured replication and apoptosis rates.

RESULTS

β-Cell turnover is present in adult nonhuman primates (3.3 ± 0.9 mg/month), mostly (~80%) derived from β-cell neogenesis. β-Cell formation was minimal in STZ-induced diabetes. Despite marked hyperglycemia, β-cell apoptosis was not increased in monkeys administered STZ.

CONCLUSIONS

There is ongoing β-cell turnover in adult nonhuman primates that cannot be accounted for by β-cell replication. There is no evidence of β-cell regeneration in monkeys administered STZ. Hyperglycemia does not induce β-cell apoptosis in nonhuman primates in vivo.

Stem cell therapy for diabetes: progress and prospects

Stem cells can supply sufficient islet cells for cell replacement therapy in patients with diabetes. Many types of stem cells, including embryonic stem (ES) cells, induced pluripotent stem (iPS) cells, and somatic stem cells, have been shown to be able to differentiate into insulin-producing cells either in vitro or in vivo, which could ameliorate hyperglycemia in diabetic animal models. Furthermore, several small-scale pilot clinical studies have demonstrated the potential efficacy of autologous hematopoietic stem cell transplantation in treating diabetes. Great progress has been made in basic research on the differentiation of insulin-producing cells from human ES cells, in which the ethical debate and immunological rejection are unavoidable. Use of human iPS cells and autologous somatic stem cells can avoid such problems. However, the safety of iPS cells in future clinical application and the amplification, identification and differentiation of somatic stem cells deserve further investigation. This paper aims to present an overview of different types of stem cells, strategies for differentiation into islet cells, and the problems and prospects of stem cell therapy for diabetes.

Facultative stem cells in liver and pancreas: fact and fancy

Tissue turnover is a regular feature of higher eukaryotes, either as part of normal wear and tear (homeostasis) or in response to injury (regeneration). Cell replacement is achieved either through replication of existing cells or differentiation from a self-renewing pool of stem cells. The major distinction regards cellular potential, because stem cells by definition have a capacity to differentiate, while replication implies that cells adopt a single fate under physiologic conditions. A hybrid model, the facultative stem cell (FSC) model, posits that tissues contain cells that normally exhibit unipotency but have the capacity to function as stem cells upon injury. The FSC paradigm is well established in urodele amphibians, but the nature and role of FSCs in mammals is less defined. Here, we review the evidence for FSCs in two mammalian organs, the liver and the pancreas, and discuss alternative models that could account for regeneration in these organs.

Essential role of clusterin in pancreas regeneration

Based on our previous observations that clusterin induction accompanies pancreas regeneration in the rat, we sought to determine if regeneration might be impaired in mice that lacked clusterin. We studied the impact of absent clusterin on morphogenic and functional features of regenerating pancreas. Clusterin induction was accompanied in the regenerating pancreas by a robust development of new lobules with ductules, acini, and endocrine islets in wild type after partial pancreatectomy. In clusterin knock-out mice, however, pancreatectomy resulted in a poor formation of regenerating lobule. In particular, regeneration of beta-cells was also significantly reduced and was associated with persistent hyperglycemia. Duct cells obtained from pancreatectomized clusterin knock-out mice exhibited impaired beta-cell formation in vitro; this was restored by administration of exogenous clusterin. We suggest that clusterin plays a critical role to promote both exocrine and endocrine regeneration following pancreas injury, as well as for in vitro beta-cell regeneration.

Lineage tracing reveals the dynamic contribution of Hes1+ cells to the developing and adult pancreas

Notch signaling regulates numerous developmental processes, often acting either to promote one cell fate over another or else to inhibit differentiation altogether. In the embryonic pancreas, Notch and its target gene Hes1 are thought to inhibit endocrine and exocrine specification. Although differentiated cells appear to downregulate Hes1, it is unknown whether Hes1 expression marks multipotent progenitors, or else lineage-restricted precursors. Moreover, although rare cells of the adult pancreas express Hes1, it is unknown whether these represent a specialized progenitor-like population. To address these issues, we developed a mouse Hes1(CreERT2) knock-in allele to inducibly mark Hes1(+) cells and their descendants. We find that Hes1 expression in the early embryonic pancreas identifies multipotent, Notch-responsive progenitors, differentiation of which is blocked by activated Notch. In later embryogenesis, Hes1 marks exocrine-restricted progenitors, in which activated Notch promotes ductal differentiation. In the adult pancreas, Hes1 expression persists in rare differentiated cells, particularly terminal duct or centroacinar cells. Although we find that Hes1(+) cells in the resting or injured pancreas do not behave as adult stem cells for insulin-producing beta (β)-cells, Hes1 expression does identify stem cells throughout the small and large intestine. Together, these studies clarify the roles of Notch and Hes1 in the developing and adult pancreas, and open new avenues to study Notch signaling in this and other tissues.

Tracking adult stem cells

The maintenance of stem-cell-driven tissue homeostasis requires a balance between the generation and loss of cell mass. Adult stem cells have a close relationship with the surrounding tissue--known as their niche--and thus, stem-cell studies should preferably be performed in a physiological context, rather than outside their natural environment. The mouse is an attractive model in which to study adult mammalian stem cells, as numerous experimental systems and genetic tools are available. In this review, we describe strategies commonly used to identify and functionally characterize adult stem cells in mice and discuss their potential, limitations and interpretations, as well as how they have informed our understanding of adult stem-cell biology. An accurate interpretation of physiologically relevant stem-cell assays is crucial to identify adult stem cells and elucidate how they self-renew and give rise to differentiated progeny.

Neurogenic differentiation 1 directs differentiation of cytokeratin 19-positive human pancreatic nonendocrine cells into insulin-producing cells

BACKGROUND

It has been reported that the human pancreatic nonendocrine fraction, which remains after islet isolation, can be differentiated toward beta cells. However, the optimal method to accomplish this goal has not been established. In this study, we introduced the human neurogenic differentiation 1 (NeuroD1) gene into human nonendocrine pancreatic epithelial cells (NEPECs) and promoted insulin-producing cells in vitro.

METHODS

The human pancreatic nonislet fractions were obtained from brain-dead donors and cultured in suspension for 2-3 days followed by culture with G418 for 4 days. These cells (NEPECs) were then plated on dishes. The NEPECs spread into a cell monolayer within 7 days and all of the cells were cytokeratin-19 (CK19) positive. Seven days after plating, plasmids encoding human NeuroD1 gene under human CK19 promoter were transfected 3 times every other day (termed NEPEC+ND). Seven days after starting induction, these cells were characterized.

RESULTS

Seven days after starting the induction of human NeuroD1, NEPEC+ND strongly expressed NeuroD1 and insulin mRNA. The ratio of NeuroD1-positive cells in NEPEC+ND was significantly higher than in NEPEC. Human insulin-positive cells in NEPEC+ND were also significantly greater than in NEPEC. Human insulin and C-peptide levels in culture medium in NEPEC+ND were significantly higher than in NEPEC.

CONCLUSIONS

These findings demonstrated that human NeuroD1 under control of the CK19 promoter can induce the differentiation of CK19-positive NEPECs into insulin-producing cells.

Genetic inducible fate mapping in larval zebrafish reveals origins of adult insulin-producing β-cells

The Notch-signaling pathway is known to be fundamental in controlling pancreas differentiation. We now report on using Cre-based fate mapping to indelibly label pancreatic Notch-responsive cells (PNCs) at larval stages and follow their fate in the adult pancreas. We show that the PNCs represent a population of progenitors that can differentiate to multiple lineages, including adult ductal cells, centroacinar cells (CACs) and endocrine cells. These endocrine cells include the insulin-producing β-cells. CACs are a functional component of the exocrine pancreas; however, our fate-mapping results indicate that CACs are more closely related to endocrine cells by lineage as they share a common progenitor. The majority of the exocrine pancreas consists of the secretory acinar cells; however, we only detect a very limited contribution of PNCs to acinar cells. To explain this observation we re-examined early events in pancreas formation. The pancreatic anlage that gives rise to the exocrine pancreas is located in the ventral gut endoderm (called the ventral bud). Ptf1a is a gene required for exocrine pancreas development and is first expressed as the ventral bud forms. We used transgenic marker lines to observe both the domain of cells expressing ptf1a and cells responding to Notch signaling. We do not detect any overlap in expression and demonstrate that the ventral bud consists of two cell populations: a ptf1-expressing domain and a Notch-responsive progenitor core. As pancreas organogenesis continues, the ventral bud derived PNCs align along the duct, remain multipotent and later in development differentiate to form secondary islets, ducts and CACs.

Isolation and culture of human multipotent stromal cells from the pancreas

Mesenchymal stem cells, also termed multipotent mesenchymal stromal cells (MSCs), can be isolated from most adult tissues. Although the exact origin of MSCs expanded from the human pancreas has not been resolved, we have developed protocols to isolate and expand MSCs from human pancreatic tissue that remains after islet procurement. Similar to techniques used to isolate MSCs from bone marrow, pancreatic MSCs are isolated based on their cell adherence, expression of several cell surface antigens, and multilineage differentiation. The protocols for isolating, characterizing, and differentiating MSCs from the pancreas are presented in this chapter.

β-cell regeneration: the pancreatic intrinsic faculty

Type I diabetes (T1D) patients rely on cumbersome chronic injections of insulin, making the development of alternate durable treatments a priority. The ability of the pancreas to generate new β-cells has been described in experimental diabetes models and, importantly, in infants with T1D. Here we discuss recent advances in identifying the origin of new β-cells after pancreatic injury, with and without inflammation, revealing a surprising degree of cell plasticity in the mature pancreas. In particular, the inducible selective near-total destruction of β-cells in healthy adult mice uncovers the intrinsic capacity of differentiated pancreatic cells to spontaneously reprogram to produce insulin. This opens new therapeutic possibilities because it implies that β-cells can differentiate endogenously, in depleted adults, from heterologous origins.

A mouse model for monitoring islet cell genesis and developing therapies for diabetes

Transient expression of the transcription factor neurogenin-3 marks progenitor cells in the pancreas as they differentiate into islet cells. We developed a transgenic mouse line in which the surrogate markers secreted alkaline phosphatase (SeAP) and enhanced green florescent protein (EGFP) can be used to monitor neurogenin-3 expression, and thus islet cell genesis. In transgenic embryos, cells expressing EGFP lined the pancreatic ducts. SeAP was readily detectable in embryos, in the media of cultured embryonic pancreases and in the serum of adult animals. Treatment with the γ-secretase inhibitor DAPT, which blocks Notch signaling, enhanced SeAP secretion rates and increased the number of EGFP-expressing cells as assayed by fluorescence-activated cell sorting (FACS) and immunohistochemistry in cultured pancreases from embryos at embryonic day 11.5, but not in pancreases harvested 1 day later. By contrast, treatment with growth differentiation factor 11 (GDF11) reduced SeAP secretion rates. In adult mice, partial pancreatectomy decreased, whereas duct ligation increased, circulating SeAP levels. This model will be useful for studying signals involved in islet cell genesis in vivo and developing therapies that induce this process.

Differential effects of prenatal and postnatal nutritional environment on ß-cell mass development and turnover in male and female rats

Fetal nutrient and growth restriction is associated with development of type 2 diabetes. Although the exact mechanisms responsible for this association remain debated, intrauterine and/or postnatal maldevelopment of β-cell mass has been proposed as a potential mechanism. To address this hypothesis, β-cell mass development and turnover was assessed in rats exposed to either intrauterine and/or postnatal caloric/growth restriction. In total, four groups of male and female Sprague Dawley rats (n = 69) were developed and studied: 1) control rats, i.e. control mothers rearing control pups; 2) intrauterine calorically and growth-restricted rats, i.e. 50% prenatal calorically restricted pups cross-fostered to control mothers; 3) postnatal calorically and growth-restricted rats, i.e. 50% calorically restricted mothers rearing pups born to control mothers; and 4) prenatal and postnatal calorically and growth restricted rats, i.e. 50% calorically restricted mothers rearing intrauterine 50% calorically restricted pups. Intrauterine growth restriction resulted in approximately 45% reduction of postnatal β-cell fractional area and mass characterized by reduced rate of β-cell replication and decreased evidence of neogenesis. In contrast, β-cell fractional area and weight-adjusted β-cell mass in postnatal growth restriction was approximately 30% higher than in control rats. Rats exposed to both intrauterine and postnatal caloric and growth restriction demonstrated approximately 80% decrease in β-cell mass, reduction in β-cell replication, and decreased evidence of neogenesis compared with control. Neither intrauterine nor postnatal caloric restriction significantly affected the rate of β-cell apoptosis. These data support the hypothesis that intrauterine maldevelopment of β-cell mass may predict the increased risk of type 2 diabetes in adult life.

Stem cell-based strategies for the treatment of type 1 diabetes mellitus

IMPORTANCE OF THE FIELD

β-Cell regeneration and β-cell preservation are two promising therapeutic approaches for the management of patients with type 1 diabetes (T1D). Stem cell-based strategies to address the problems of shortage in β cells, autoimmune and alloimmune responses have become an area of intense study.

AREAS COVERED IN THIS REVIEW

This review focuses on the progress that has been made in obtaining functional, insulin-producing cells from various types of stem/progenitor cells, including the current knowledge on the immunomodulatory roles of hematopoietic stem cell and multipotent stromal cell in the therapies for T1D.

WHAT THE READER WILL GAIN

A broad overview of recent advancements in this field is provided. The hurdles that remain in the path of using stem cell-based strategies for the treatment of T1D and possible approaches to overcome these challenges are discussed.

TAKE HOME MESSAGE

Stem cell-based strategies hold great promise for the treatment of T1D. In spite of the progress that has been made over the last decade, a number of obstacles and concerns need to be cleared before widespread clinical application is possible. In particular, the mechanism of ESC and iPSC-derived β-cell maturation in vivo is poorly understood.

Continuous cell supply from a Sox9-expressing progenitor zone in adult liver, exocrine pancreas and intestine

The liver and exocrine pancreas share a common structure, with functioning units (hepatic plates and pancreatic acini) connected to the ductal tree. Here we show that Sox9 is expressed throughout the biliary and pancreatic ductal epithelia, which are connected to the intestinal stem-cell zone. Cre-based lineage tracing showed that adult intestinal cells, hepatocytes and pancreatic acinar cells are supplied physiologically from Sox9-expressing progenitors. Combination of lineage analysis and hepatic injury experiments showed involvement of Sox9-positive precursors in liver regeneration. Embryonic pancreatic Sox9-expressing cells differentiate into all types of mature cells, but their capacity for endocrine differentiation diminishes shortly after birth, when endocrine cells detach from the epithelial lining of the ducts and form the islets of Langerhans. We observed a developmental switch in the hepatic progenitor cell type from Sox9-negative to Sox9-positive progenitors as the biliary tree develops. These results suggest interdependence between the structure and homeostasis of endodermal organs, with Sox9 expression being linked to progenitor status.

Pancreatic β-cell neogenesis by direct conversion from mature α-cells

Because type 1 and type 2 diabetes are characterized by loss of β-cells, β-cell regeneration has garnered great interest as an approach to diabetes therapy. Here, we developed a new model of β-cell regeneration, combining pancreatic duct ligation (PDL) with elimination of pre-existing β-cells with alloxan. In this model, in which virtually all β-cells observed are neogenic, large numbers of β-cells were generated within 2 weeks. Strikingly, the neogenic β-cells arose primarily from α-cells. α-cell proliferation was prominent following PDL plus alloxan, providing a large pool of precursors, but we found that β-cells could form from α-cells by direct conversion with or without intervening cell division. Thus, classical asymmetric division was not a required feature of the process of α- to β-cell conversion. Intermediate cells coexpressing α-cell- and β-cell-specific markers appeared within the first week following PDL plus alloxan, declining gradually in number by 2 weeks as β-cells with a mature phenotype, as defined by lack of glucagon and expression of MafA, became predominant. In summary, these data revealed a novel function of α-cells as β-cell progenitors. The high efficiency and rapidity of this process make it attractive for performing the studies required to gain the mechanistic understanding of the process of α- to β-cell conversion that will be required for eventual clinical translation as a therapy for diabetes.

Contribution of postnatally formed small beta cell aggregates to functional beta cell mass in adult rat pancreas

AIMS/HYPOTHESIS

Neogenesis of beta cells and their clustering to small aggregates is a key process in prenatal development of beta cell mass. We investigated the contribution of postnatally formed small aggregates to functional beta cell mass in adult rats.

METHODS

Conditions were defined for (1) counting total beta cell number in pancreases with relative error of <10% and (2) determining their distribution over aggregates of different size and over functionally different subpopulations.

RESULTS

Pancreases of 10-week-old male Wistar rats contained 2.8 ± 0.2 × 10⁶ beta cells, of which >90% was generated postnatally, involving: (1) neo-formation of 30,000 aggregates with diameter <50 μm including single cells; and (2) growth of 5,500 aggregates to larger sizes, accounting for 90% of the increase in cell number, with number of growing aggregates in the tail 50% greater than elsewhere. At 10 weeks, 86% of aggregates were <50 μm; compared with aggregates >200 μm, their beta cells exhibited a higher basal insulin content that was also resistant to glibenclamide-induced degranulation. The pool of Ki67-positive beta cells was sixfold larger than at birth and distributed over all aggregate sizes.

CONCLUSIONS/INTERPRETATION

We describe a method for in situ counting of beta cell numbers and subpopulations with low relative error. In adult rats, >90% of beta cells and beta cell aggregates are formed after birth. Aggregates <50 μm are more than 100-fold more abundant than aggregates >200 μm, which are selected for isolated islet studies. Their topographic and functional properties contribute to the functional heterogeneity of the beta cell population; their growth to larger aggregates with characteristic beta cell functions may serve future metabolic needs.

Gastrointestinal hormones and the regulation of β-cell mass

Type 2 diabetes occurs due to a relative deficit in β-cell mass or function. Glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), and gastrin are gastrointestinal hormones that are secreted in response to nutrient intake, regulating digestion, insulin secretion, satiety, and β-cell mass. In this review, we focus upon β-cell mass regulation. β-cell mass expands through β-cell proliferation and islet neogenesis; β-cell mass is lost via apoptosis. GLP-1 and GIP are well-studied gastrointestinal hormones and influence β-cell proliferation, apoptosis, and islet neogenesis. CCK regulates β-cell apoptosis and mitogenesis, and gastrin stimulates islet neogenesis. GLP-1 and GIP bind to G protein-coupled receptors and regulate β-cell mass via multiple signaling pathways. The protein kinase A pathway is central to this process because it directly regulates proliferative and anti-apoptotic genes and transactivates several signaling cascades, including Akt and mitogen-activated protein kinases. However, the signaling pathways downstream of G protein-coupled CCK receptors that influence β-cell mass remain unidentified. Gastrointestinal hormones integrate nutrient signals from the gut to the β-cell, regulating insulin secretion and β-cell mass adaptation.

Adaptive changes in pancreatic beta cell fractional area and beta cell turnover in human pregnancy

AIMS/HYPOTHESIS

We sought to establish the extent and basis for adaptive changes in beta cell numbers in human pregnancy.

METHODS

Pancreas was obtained at autopsy from women who had died while pregnant (n = 18), post-partum (n = 6) or were not pregnant at or shortly before death (controls; n = 20). Pancreases were evaluated for fractional pancreatic beta cell area, islet size and islet fraction of beta cells, beta cell replication (Ki67) and apoptosis (TUNEL), and indirect markers of beta cell neogenesis (insulin-positive cells in ducts and scattered beta cells in pancreas).

RESULTS

The pancreatic fractional beta cell area was increased by approximately 1.4-fold in human pregnancy, with no change in mean beta cell size. In pregnancy there were more small islets rather than an increase in islet size or beta cells per islet. No increase in beta cell replication or change in beta cell apoptosis was detected, but duct cells positive for insulin and scattered beta cells were increased with pregnancy.

CONCLUSIONS/INTERPRETATION

The adaptive increase in beta cell numbers in human pregnancy is not as great as in most reports in rodents. This increase in humans is achieved by increased numbers of beta cells in apparently new small islets, rather than duplication of beta cells in existing islets, which is characteristic of pregnancy in rodents.