Functional beta-cell mass after transplantation of human fetal pancreatic cells: differentiation or proliferation?

Potential therapeutic roles of stem cells in ischemia-reperfusion injury

Ischemia-reperfusion injury (I/RI), produced by an initial interruption of organ blood flow and its subsequent restoration, contributes significantly to the pathophysiologies of stroke, myocardial infarction, renal I/RI, intestinal I/RI and liver I/RI, which are major causes of disability (including transplant failure) and even mortality. While the restoration of blood flow is required to restore oxygen and nutrient requirements, reperfusion often triggers local and systemic inflammatory responses and subsequently elevate the ischemic insult where the duration of ischemia determines the magnitude of I/RI damage. I/RI increases vascular leakage, changes transcriptional and cell death programs, drives leukocyte entrapment and inflammation and oxidative stress in tissues. Therapeutic approaches which reduce complications associated with I/RI are desperately needed to address the clinical and economic burden created by I/RI. Stem cells (SC) represent ubiquitous and uncommitted cell populations with the ability to self-renew and differentiate into one or more developmental 'fates'. Like immune cells, stem cells can home to and penetrate I/R-injured tissues, where they can differentiate into target tissues and induce trophic paracrine signaling which suppress injury and maintain tissue functions perturbed by ischemia-reperfusion. This review article summarizes the present use and possible protective mechanisms underlying stem cell protection in diverse forms of ischemia-reperfusion.

Mitigating Ischemic Injury of Stem Cell-Derived Insulin-Producing Cells after Transplant

The advent of large-scale in vitro differentiation of human stem cell-derived insulin-producing cells (SCIPC) has brought us closer to treating diabetes using stem cell technology. However, decades of experiences from islet transplantation show that ischemia-induced islet cell death after transplant severely limits the efficacy of the therapy. It is unclear to what extent human SCIPC are susceptible to ischemia. In this study, we show that more than half of SCIPC die shortly after transplantation. Nutrient deprivation and hypoxia acted synergistically to kill SCIPC in vitro. Amino acid supplementation rescued SCIPC from nutrient deprivation, likely by providing cellular energy. Generating SCIPC under physiological oxygen tension of 5% conferred hypoxia resistance without affecting their differentiation or function. A two-pronged strategy of physiological oxygen acclimatization during differentiation and amino acid supplementation during transplantation significantly improved SCIPC survival after transplant.

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Stem cell-derived insulin-producing cells (SCIPC) are susceptible to ischemic injury

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Amino acid supplementation prevents nutrient-deprivation-induced SCIPC death

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Generation of SCIPC at physiological oxygen levels protects them against hypoxia

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Both strategies combined preserve SCIPC graft viability in vivo upon transplant

Systematic single-cell analysis provides new insights into heterogeneity and plasticity of the pancreas

Background

Diabetes mellitus is characterized by loss or dysfunction of insulin-producing β-cells in the pancreas, resulting in failure of blood glucose regulation and devastating secondary complications. Thus, β-cells are currently the prime target for cell-replacement and regenerative therapy. Triggering endogenous repair is a promising strategy to restore β-cell mass and normoglycemia in diabetic patients. Potential strategies include targeting specific β-cell subpopulations to increase proliferation or maturation. Alternatively, transdifferentiation of pancreatic islet cells (e.g. α- or δ-cells), extra-islet cells (acinar and ductal cells), hepatocytes, or intestinal cells into insulin-producing cells might improve glycemic control. To this end, it is crucial to systematically characterize and unravel the transcriptional program of all pancreatic cell types at the molecular level in homeostasis and disease. Furthermore, it is necessary to better determine the underlying mechanisms of β-cell maturation, maintenance, and dysfunction in diabetes, to identify and molecularly profile endocrine subpopulations with regenerative potential, and to translate the findings from mice to man. Recent approaches in single-cell biology started to illuminate heterogeneity and plasticity in the pancreas that might be targeted for β-cell regeneration in diabetic patients.

Scope of review

This review discusses recent literature on single-cell analysis including single-cell RNA sequencing, single-cell mass cytometry, and flow cytometry of pancreatic cell types in the context of mechanisms of endogenous β-cell regeneration. We discuss new findings on the regulation of postnatal β-cell proliferation and maturation. We highlight how single-cell analysis recapitulates described principles of functional β-cell heterogeneity in animal models and adds new knowledge on the extent of β-cell heterogeneity in humans as well as its role in homeostasis and disease. Furthermore, we summarize the findings on cell subpopulations with regenerative potential that might enable the formation of new β-cells in diseased state. Finally, we review new data on the transcriptional program and function of rare pancreatic cell types and their implication in diabetes.

Major conclusion

Novel, single-cell technologies offer high molecular resolution of cellular heterogeneity within the pancreas and provide information on processes and factors that govern β-cell homeostasis, proliferation, and maturation. Eventually, these technologies might lead to the characterization of cells with regenerative potential and unravel disease-associated changes in gene expression to identify cellular and molecular targets for therapy.

Comparison of Fetal Porcine Aggregates of Purified β-Cells versus Islet-Like Cell Clusters as a Treatment of Diabetes

Fetal pig islet-like cell clusters (ICCs) have the potential to reverse diabetes 1–5 months after transplantation. In a fetal ICC, however, β-cells constitute only 6–8% of the cells, in contrast to 65% in an adult pig islet. Attempts to purify fetal β-cells from cell clusters and compare their function to that of ICCs have not been shown previously. β-Cells were purified from ICCs isolated from the fetal pig pancreas. These were then aggregated and maintained in culture for 3 days. ICCs were isolated from fetal pig pancreas and allowed to round up in culture for 3 days. Transplantation of aggregates and ICCs (10,000 and 12,600, respectively) into diabetic immunoincompetent mice resulted in normoglycemia at 18 ± 2 and 8 ± 1 weeks, respectively (p = 0.0006). Removal of grafts after normalization of blood glucose levels resulted in rapid return of hyperglycemia in both groups. In conclusion, a purified population of immature β-cells can be produced from the fetal pig pancreas. The reason these cells take longer than ICCs to reverse diabetes when transplanted is postulated to be because of the relative lack of precursor cells from which β-cells differentiate. This finding may have implications for stem cell therapy, as other cell types, other than purified β-cells, may be necessary for appropriate function in vivo.

Brief review: cell replacement therapies to treat type 1 diabetes mellitus

Human embryonic stem cells (hESCs) and induced pluripotent cells (iPSCs) have the potential to differentiate into any somatic cell, making them ideal candidates for cell replacement therapies to treat a number of human diseases and regenerate damaged or non-functional tissues and organs. Key to the promise of regenerative medicine is developing standardized protocols that can safely be applied in patients. Progress towards this goal has occurred in a number of fields, including type 1 diabetes mellitus (T1D). During the past 10 years, significant technological advances in hESC/iPSC biochemistry have provided a roadmap to generate sufficient quantities of glucose-responsive, insulin-producing cells capable of eliminating diabetes in rodents. Although many of the molecular mechanisms underlying the genesis of these cells remain to be elucidated, the field of cell-based therapeutics to treat T1D has advanced to the point where the first Phase I/II trials in humans have begun. Here, we provide a concise review of the history of cell replacement therapies to treat T1D from islet transplantations and xenotranplantation, to current work in hESC/iPSC. We also highlight the latest advances in efforts to employ insulin-producing, glucose-responsive β-like cells derived from hESC as therapeutics.

Arginine is preferred to glucagon for stimulation testing of β-cell function

A key aspect of research into the prevention and treatment of type 2 diabetes is the availability of reproducible clinical research methodology to assess β-cell function. One commonly used method employs nonglycemic secretagogues like arginine (arg) or glucagon (glgn). This study was designed to quantify the insulin response to arg and glgn and determine test repeatability and tolerability. Obese overnight-fasted subjects with normal glucose tolerance were studied on 4 separate days: twice using arg (5 g iv) and twice with glgn (1 mg iv). Pre- and postinfusion samples for plasma glucose, insulin, and C-peptide were acquired. Arg and glgn challenges were repeated in the last 10 min of a 60-min glucose (900 mg/min) infusion. Insulin and C-peptide secretory responses were estimated under baseline fasting glucose conditions (AIRarg and AIRglgn) and hyperglycemic (AIRargMAX AIRglgnMAX) states. Relative repeatability was estimated by intraclass correlation coefficient (ICC). Twenty-three (12 men and 11 women) subjects were studied (age: 42.4 ± 8.3 yr; BMI: 31.4 ± 2.8 kg/m²). Geometric means (95% CI) for baseline-adjusted values AIRarg and AIRglgn were 84 (75-95) and 102 (90-115) μU/ml, respectively. After the glucose infusion, AIRargMAX and AIRglgnMAX were 395 (335-466) and 483 (355-658) μU/ml, respectively. ICC values were >0.90 for AIRarg andAIRargMAX. Glucagon ICCs were 0.83, 0.34, and 0.36, respectively, although the exclusion of one outlier increased the latter two values (to 0.84 and 0.86). Both glgn and arg induced mild adverse events that were transient. Glucagon, but not arginine, induced moderate adverse events due to nausea. Taken together, arginine is preferred to glucagon for assessment of β-cell function.

The SDF-1α/CXCR4 axis is required for proliferation and maturation of human fetal pancreatic endocrine progenitor cells

The chemokine receptor CXCR4 and ligand SDF-1α are expressed in fetal and adult mouse islets. Neutralization of CXCR4 has previously been shown to diminish ductal cell proliferation and increase apoptosis in the IFNγ transgenic mouse model in which the adult mouse pancreas displays islet regeneration. Here, we demonstrate that CXCR4 and SDF-1α are expressed in the human fetal pancreas and that during early gestation, CXCR4 colocalizes with neurogenin 3 (ngn3), a key transcription factor for endocrine specification in the pancreas. Treatment of islet like clusters (ICCs) derived from human fetal pancreas with SDF-1α resulted in increased proliferation of epithelial cells in ICCs without a concomitant increase in total insulin expression. Exposure of ICCs in vitro to AMD3100, a pharmacological inhibitor of CXCR4, did not alter expression of endocrine hormones insulin and glucagon, or the pancreatic endocrine transcription factors PDX1, Nkx6.1, Ngn3 and PAX4. However, a strong inhibition of β cell genesis was observed when in vitro AMD3100 treatment of ICCs was followed by two weeks of in vivo treatment with AMD3100 after ICC transplantation into mice. Analysis of the grafts for human C-peptide found that inhibition of CXCR4 activity profoundly inhibits islet development. Subsequently, a model pancreatic epithelial cell system (CFPAC-1) was employed to study the signals that regulate proliferation and apoptosis by the SDF-1α/CXCR4 axis. From a selected panel of inhibitors tested, both the PI 3-kinase and MAPK pathways were identified as critical regulators of CFPAC-1 proliferation. SDF-1α stimulated Akt phosphorylation, but failed to increase phosphorylation of Erk above the high basal levels observed. Taken together, these results indicate that SDF-1α/CXCR4 axis plays a critical regulatory role in the genesis of human islets.

Inhibition of gamma-secretase activity promotes differentiation of embryonic pancreatic precursor cells into functional islet-like clusters in poly(ethylene glycol) hydrogel culture

We assessed the ability of a gamma-secretase inhibitor to promote the in vitro differentiation of induced embryonic pancreatic precursor cell aggregates into functional islet-like clusters when encapsulated within a three-dimensional hydrogel. Undifferentiated pancreatic precursor cells were isolated from E.15 rat embryos, dissociated into single cells, and aggregated in suspension-rotation culture. Aggregates were photoencapsulated into poly(ethylene glycol) hydrogels with entrapped collagen type 1 and cultured for 14 days with or without a gamma-secretase inhibitor. Gene expression, proinsulin content, and C-peptide release were measured to determine differentiation and maturation of encapsulated precursor cell aggregates. In the control medium, scattered breakthrough beta cell differentiation was observed; however, cells remained largely insulin negative. Upon addition of a gamma-secretase inhibitor the majority of cells in clusters became insulin positive, and insulin per DNA and glucose-stimulated insulin release measurements for these cultures were comparable with those for adult rat islets. Cluster counts after culture day 14 were 88% of those initially encapsulated, demonstrating excellent cluster survival in hydrogel culture. These results indicate that concerted differentiation of pancreatic precursor cell aggregates into functionally mature islet-like clusters can be achieved in poly(ethylene glycol)-based hydrogel cultures by blocking cell contact-mediated Notch signaling with a gamma-secretase inhibitor.

Human beta-cell precursors mature into functional insulin-producing cells in an immunoisolation device: implications for diabetes cell therapies. Transplantation. 2009;87:983-991. [PMID: 19352116 DOI: 10.1097/tp.0b013e31819c86ea]

BACKGROUND

Islet transplantation is limited by the need for chronic immunosuppression and the paucity of donor tissue. As new sources of human beta-cells are developed (e.g., stem cell-derived tissue), transplanting them in a durable device could obviate the need for immunosuppression, while also protecting the patient from any risk of tumorigenicity. Here, we studied (1) the survival and function of encapsulated human beta-cells and their progenitors and (2) the engraftment of encapsulated murine beta-cells in allo- and autoimmune settings.

METHODS

Human islets and human fetal pancreatic islet-like cell clusters were encapsulated in polytetrafluorethylene devices (TheraCyte) and transplanted into immunodeficient mice. Graft survival and function was measured by immunohistochemistry, circulating human C-peptide levels, and blood glucose levels. Bioluminescent imaging was used to monitor encapsulated neonatal murine islets.

RESULTS

Encapsulated human islet-like cell clusters survived, replicated, and acquired a level of glucose responsive insulin secretion sufficient to ameliorate hyperglycemia in diabetic mice. Bioluminescent imaging of encapsulated murine neonatal islets revealed a dynamic process of cell death followed by regrowth, resulting in robust long-term allograft survival. Further, in the non-obese diabetic (NOD) mouse model of type I diabetes, encapsulated primary beta-cells ameliorated diabetes without stimulating a detectable T-cell response.

CONCLUSIONS

We demonstrate for the first time that human beta-cells function is compatible with encapsulation in a durable, immunoprotective device. Moreover, our study suggests that encapsulation of beta-cells before terminal differentiation will be a successful approach for new cell-based therapies for diabetes, such as those derived from stem cells.

Stem cell therapy to treat diabetes mellitus

Transplantation of pancreatic islets offers a direct treatment for type 1 diabetes and in some cases, insulin-dependent type 2 diabetes. However, its widespread use is hampered by a shortage of donor organs. Many extant studies have focused on deriving beta-cell progenitors from pancreas and pluripotent stem cells. Efforts to generate beta-cells in vitro will help elucidate the mechanisms of beta-cell formation and thus provide a versatile in vivo system to evaluate the therapeutic potential of these cells to treat diabetes. Various successful experiments using beta-cells in animal models have generated extensive interest in using human embryonic stem cells to restore normoglycemia in diabetic patients. While new techniques are continually unveiled, the success of beta-cell generation rests upon successful manipulation of culture conditions and the induction of key regulatory genes implicated in pancreas development. In this review, we compare successfully conducted protocols, highlight essential steps and identify some of the remarkable shortfalls common to these methods. In addition, we discuss recent advancements in the derivation of patient-specific pluripotent stem cells that may facilitate the use of autologous beta-cells in stem cell therapy.

Beta cells within single human islets originate from multiple progenitors

Background

In both humans and rodents, glucose homeostasis is controlled by micro-organs called islets of Langerhans composed of beta cells, associated with other endocrine cell types. Most of our understanding of islet cell differentiation and morphogenesis is derived from rodent developmental studies. However, little is known about human islet formation. The lack of adequate experimental models has restricted the study of human pancreatic development to the histological analysis of different stages of pancreatic development. Our objective was to develop a new experimental model to (i) transfer genes into developing human pancreatic cells and (ii) validate gene transfer by defining the clonality of developing human islets.

Methods and Findings

In this study, a unique model was developed combining ex vivo organogenesis from human fetal pancreatic tissue and cell type-specific lentivirus-mediated gene transfer. Human pancreatic progenitors were transduced with lentiviruses expressing GFP under the control of an insulin promoter and grafted to severe combined immunodeficient mice, allowing human beta cell differentiation and islet morphogenesis. By performing gene transfer at low multiplicity of infection, we created a chimeric graft with a subpopulation of human beta cells expressing GFP and found both GFP-positive and GFP-negative beta cells within single islets.

Conclusion

The detection of both labeled and unlabeled beta cells in single islets demonstrates that beta cells present in a human islet are derived from multiple progenitors thus providing the first dynamic analysis of human islet formation during development. This human transgenic-like tool can be widely used to elucidate dynamic genetic processes in human tissue formation.

A novel human stem cell coculture system that maintains the survival and function of culture islet-like cell clusters

Islet-like cell clusters (ICCs) have been suggested to be a source of insulin-producing tissue for xenotransplantation in type 1 diabetes. We designed an approach to maintain the cultured rat pancreatic ICC survival and function, when cocultured with human umbilical cord mesenchymal stem cells (HUMSCs). HUMSCs in coculture have the ability to maintain ICC survival and function, for which number and insulin secretion of ICCs are increasing and lasting for 3 months, while ICCs gradually crash, which results in cell death after a period of 12 days of culture without HUMSCs. Cytokine protein array showed it has more than a twofold increase in levels of several cytokines (interleukin-6, tissue inhibitor of metalloproteinases-1, tissue inhibitor of metalloproteinases-2, monocyte chemoattractant protein-1, growth related oncogene, hepatocyte growth factor, insulin-like growth factor binding proteins 4, and interleukin-8) on coculture medium, implying an important role of these cytokines in this coculture system. These findings suggest that coculture with HUMSCs may have a significant potential to protect ICCs from damage during culture, and may be employed in a novel culture approach to maintain islet cell survival and function before transplantation.

Overexpression of pre-pro-cholecystokinin stimulates beta-cell proliferation in mouse and human islets with retention of islet function

Type 1 and type 2 diabetes result from a deficit in insulin production and beta-cell mass. Methods to expand beta-cell mass are under intensive investigation for the treatment of type 1 and type 2 diabetes. We tested the hypothesis that cholecystokinin (CCK) can promote beta-cell proliferation. We treated isolated mouse and human islets with an adenovirus containing the CCK cDNA (AdCMV-CCK). We measured [(3)H]thymidine and BrdU incorporation into DNA and additionally, performed flow cytometry analysis to determine whether CCK overexpression stimulates beta-cell proliferation. We studied islet function by measuring glucose-stimulated insulin secretion and investigated the cell cycle regulation of proliferating beta-cells by quantitative RT-PCR and Western blot analysis. Overexpression of CCK stimulated [(3)H]thymidine incorporation into DNA 5.0-fold and 15.8-fold in mouse and human islets, respectively. AdCMV-CCK treatment also stimulated BrdU incorporation into DNA 10-fold and 21-fold in mouse and human beta-cells, respectively. Glucose-stimulated insulin secretion was unaffected by CCK expression. Analysis of cyclin and cdk mRNA and protein abundance revealed that CCK overexpression increased cyclin A, cyclin B, cyclin E, cdk1, and cdk2 with no change in cyclin D1, cyclin D2, cyclin D3, cdk4, or cdk6 in mouse and human islets. Additionally, AdCMV-CCK treatment of CCK receptor knockout and wild-type mice resulted in equal [(3)H]thymidine incorporation. CCK is a beta-cell proliferative factor that is effective in both mouse and human islets. CCK triggers beta-cell proliferation without disrupting islet function, up-regulates a distinct set of cell cycle regulators in islets, and signals independently of the CCK receptors.

Effects of antidiabetic treatment with metformin and insulin on serum and adipose tissue adiponectin levels in db/db mice

Decreased circulating levels of adiponectin, a novel adipose-derived adipocytokine, in obesity possibly contribute to the development of insulin resistance which is a major factor in the pathogenesis of type 2 diabetes. The present study was conducted to examine whether circulating and adipose tissue adiponectin levels are modulated by chronic treatment with metformin and intensive treatment with insulin in murine models of obesity and type 2 diabetes, db/db mice with a C57BL/KsJ genetic background. Nine-week-old male db/db mice were treated with metformin, insulin, and vehicle for 4 weeks. Expectedly, metformin treatment led to inhibition of weight gain and improvement of hyperinsulinemia. Insulin treatment lowered fasting blood glucose levels to normal values, although it sustained hyperinsulinemic state. However, after 4 weeks of treatment, serum adiponectin levels were not significantly elevated in either metformin-treated or insulin-treated db/db mouse group (14.2 +/- 0.7 and 16.7 +/- 1.0 microg/ml, respectively) compared to vehicle-treated group (14.9 +/- 0.6 microg/ml). Similarly, adipose tissue adiponectin levels determined by Western blot analysis were not increased in either metformin-treated or insulin-treated group relative to vehicle-treated group. Recent studies have shown that adiponectin possibly has the same physiological effects on lipid and glucose metabolism that metformin has. Therefore, an elevation in blood concentration of metformin following the treatment might lead to suppression in adiponectin synthesis in adipose tissue, independent of inhibition in weight gain and improvement in hyperinsulinemia by metformin treatment. The present results indicate that adiponectin is not involved in the mechanism by which metformin treatment enhances insulin sensitivity. Moreover, our results suggest that adiponectin synthesis in adipose tissue may be suppressed under hyperinsulinemic state sustained by insulin treatment, even though hyperglycemia is markedly reduced. We conclude that antidiabetic treatment with metformin and insulin does not affect circulating and adipose tissue adiponectin levels.

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.

In search of endocrine progenitor/stem cells in the human pancreas

Motives to isolate endocrine precursor cells vary between clinical and basic research needs. In our case, the object has been to identify cell populations that could be used for cell replacement in situations of beta-cell deficiency, such as type 1 diabetes. Initially, as was the case with most laboratories oriented toward translational islet research, experimentation was geared more toward cell replication than to the identification and isolation of putative endocrine cell precursors.

Embryonic pig liver, pancreas, and lung as a source for transplantation: optimal organogenesis without teratoma depends on distinct time windows

Pig embryonic tissues represent an attractive option for organ transplantation. However, the achievement of optimal organogenesis after transplantation, namely, maximal organ growth and function without teratoma development, represents a major challenge. In this study, we determined distinct gestational time windows for the growth of pig embryonic liver, pancreas, and lung precursors. Transplantation of embryonic-tissue precursors at various gestational ages [from E (embryonic day) 21 to E100] revealed a unique pattern of growth and differentiation for each embryonic organ. Maximal liver growth and function were achieved at the earliest teratoma-free gestational age (E28), whereas the growth and functional potential of the pancreas gradually increased toward E42 and E56 followed by a marked decline in insulin-secreting capacity at E80 and E100. Development of mature lung tissue containing essential respiratory system elements was observed at a relatively late gestational age (E56). These findings, showing distinct, optimal gestational time windows for transplantation of embryonic pig liver, pancreas, and lung, might explain, in part, the disappointing results in previous transplantation trials and could help enhance the chances for successful implementation of embryonic pig tissue in the treatment of a wide spectrum of human diseases.

Human embryonic stem cells: possibilities for human cell transplantation

Human embryonic stem (ES) cells serve as a potentially unlimited renewable source for cell transplantation targeted to treat several diseases. One advantage of embryonic stem (ES) cells over other stem cells under research is their apparently indefinite self-renewal capacity if cultured appropriately, and their ready differentiation into various cell phenotypes of all three germ layers. To date, a number of studies have reported the derivation of specific functional derivatives from human ES cells in vitro. While there have been clinical trials of human embryonal carcinoma (EC) cell-derived neurons in humans there has been no attempt as yet using human ES cell derivatives. However, the latter have been transplanted into recipient animals. In some cases ES-derived cells were shown to undergo further maturation, displayed integration with host tissue and even ameliorated the disease condition in the animal model. Recently, it has been reported that human ES cells can be genetically manipulated. Such procedures could be used to direct differentiation to a specific cell type or to reduce graft rejections by the modification of immune responses. This review highlights some of the recent advances in the field and the challenges that lie ahead before clinical trials using ES-derived cells can be contemplated.

Xenogeneic transplantation of porcine islets: an overview

The extreme demand for human organs or tissues for transplantation has driven the search for viable alternatives. Pigs are considered a possible source of tissue for a number of reasons including shared physiology, plentiful supply, short gestation, and, more recently, the generation of transgenic animals. Porcine islets show promise as a source of islets for the treatment of type 1 diabetes mellitus. Porcine islets regulate glucose levels in the same physiologic range as humans, and porcine insulin has been used for years as an exogenous source of insulin for glucose control. In this review, we discuss the advantages and disadvantages of the use of adult or neonatal porcine islets, the immunologic challenges facing transplantation of xenogeneic islets, and the concerns regarding transmission of infectious agents between species. Porcine islets isolated from both adult and neonatal pigs are capable of restoring euglycemia in experimental animal models of diabetes. Adult islets are more difficult to isolate, whereas neonatal islets have great proliferation potential but require several weeks to function posttransplantation. Xenogeneic islets are susceptible to complement-mediated lysis after the binding of preformed natural antibodies and cellular immunity involving both macrophages and CD4+ T cells. In addition, the potential for transmission of porcine endogenous retroviruses, porcine cytomegalovirus, and porcine lymphotropic herpesvirus type 1 are all concerns that must be addressed. Despite the challenges facing xenotransplantation, the extreme need for donor organs and tissues continues to drive progress toward overcoming the unique issues associated with transplantation between species.

Keratinocyte growth factor and beta-cell differentiation in human fetal pancreatic endocrine precursor cells

AIMS AND HYPOTHESIS

Keratinocyte growth factor (KGF) is a member of the heparin-binding fibroblast growth factor family with a high degree of specificity for epithelial cells in vitro and in vivo. Our aim was to study the effect of KGF on beta-cell growth and differentiation on islet-like cell clusters derived from human fetal pancreas.

METHODS

We investigated the effects of KGF, in vitro, on beta-cell differentiation from undifferentiated pancreatic precursor cells and in vivo after transplantating human fetal pancreatic cells into athymic rats treated with KGF.

RESULTS

Treatment of islet-like cell clusters with KGF in vitro did not change the number of insulin producing cells, as measured by the measurement of insulin content or DNA. The in vivo treatment of recipient rats with KGF increased the number of beta cells within the grafts 8 weeks after transplantation. At this time, glucose-stimulated insulin secretion was evaluated by glucose stimulation tests in rats bearing the transplants. Measurements of human C-peptide concentrations after glucose challenge showed that the newly differentiated beta cells in the KGF-treated group were functionally competent as opposed to the control group, where the graft failed to release insulin appropriately.

CONCLUSION/INTERPRETATION

These findings suggest that in vivo, KGF is capable of inducing human fetal beta-cell expansion. The growth promoting effect of KGF on beta cells occurred mainly through the activation of ductal cell proliferation and their subsequent differentiation into beta cells.

Development and retroviral transduction of porcine neonatal pancreatic islet cells in monolayer culture

To learn more about the potential of neonatal porcine pancreatic duct and islet cells for xenotransplantation, the development of these cells when cultured as monolayers was evaluated. Immunostaining for islet hormones and cytokeratin-7 revealed that day eight monolayers consisted of approximately 70% duct cells and less than 10% beta cells. Using Ki-67 immunostaining as a proliferation marker, the fraction of beta cells in the cell cycle was shown to decrease from 20% at day three to 10% at day eight, and for duct cells from 36 to 19%. Insulin secretion increased 2.4-fold upon glucose stimulation, and 38-fold when 10 mm theophylline was added, showing the responsiveness of the neonatal beta cells. Reaggregated monolayers consisted mostly of duct cells, but 4 weeks after transplantation, grafts contained predominantly endocrine cells, with duct cells being almost absent, suggesting in vivo differentiation of duct cells to endocrine cells. Monolayer susceptibility to retroviral transduction was also investigated using a Moloney Murine Leukemia Virus-based vector. Approximately 60% of duct cells but less than 5% of beta cells expressed the transgene, indicating that precursor duct cells are better targets for transgene expression. These results show that porcine neonatal pancreatic cells can be cultured as monolayers in preparation for transplantation. Furthermore, in such a culture setting, precursor duct cells have a high rate of proliferation and are more efficiently transduced with a retrovirus-based reporter gene than are beta cells.

Alternatives to unmodified human islets for transplantation

Islet transplantation as a procedure to induce insulin independence is still a long way from benefitting the population of more than I million type I diabetic patients in the United States. In addition to the problems involved with immune suppression, the most significant obstacle is a scarcity of human organs for transplantation. In 1999, only 5882 donated pancreases were available, of which only 50% could be expected to produce islet yields suitable for clinical purposes. In this article, we review various sources with the potential to provide tissue for transplantation. These sources include islet and nonislet cells derived from both human and nonhuman sources, with an emphasis on human cells.

Pluripotent stem cells--model of embryonic development, tool for gene targeting, and basis of cell therapy

Embryonic stem (ES) cells are pluripotent cell lines with the capacity of self-renewal and a broad differentiation plasticity. They are derived from pre-implantation embryos and can be propagated as a homogeneous, uncommitted cell population for an almost unlimited period of time without losing their pluripotency and their stable karyotype. Murine ES cells are able to reintegrate fully into embryogenesis when returned into an early embryo, even after extensive genetic manipulation. In the resulting chimeric offspring produced by blastocyst injection or morula aggregation, ES cell descendants are represented among all cell types, including functional gametes. Therefore, mouse ES cells represent an important tool for genetic engineering, in particular via homologous recombination, to introduce gene knock-outs and other precise genomic modifications into the mouse germ line. Because of these properties ES cell technology is of high interest for other model organisms and for livestock species like cattle and pigs. However, in spite of tremendous research activities, no proven ES cells colonizing the germ line have yet been established for vertebrate species other than the mouse (Evans and Kaufman, 1981; Martin, 1981) and chicken (Pain et al., 1996). The in vitro differentiation capacity of ES cells provides unique opportunities for experimental analysis of gene regulation and function during cell commitment and differentiation in early embryogenesis. Recently, pluripotent stem cells were established from human embryos (Thomson et al., 1998) and early fetuses (Shamblott et al., 1998), opening new scenarios both for research in human developmental biology and for medical applications, i.e. cell replacement strategies. At about the same time, research activities focused on characteristics and differentiation potential of somatic stem cells, unravelling an unexpected plasticity of these cell types. Somatic stem cells are found in differentiated tissues and can renew themselves in addition to generating the specialized cell types of the tissue from which they originate. Additional to discoveries of somatic stem cells in tissues that were previously not thought to contain these kinds of cells, they also appear to be capable of developing into cell types of other tissues, but have a reduced differentiation potential as compared to embryo-derived stem cells. Therefore, somatic stem cells are referred to as multipotent rather than pluripotent. This review summarizes characteristics of pluripotent stem cells in the mouse and in selected livestock species, explains their use for genetic engineering and basic research on embryonic development, and evaluates their potential for cell therapy as compared to somatic stem cells.

Methods for measuring glycogen cycling

Simultaneous synthesis and breakdown of glycogen is called glycogen cycling. The extent of hyperglycemia and decreased glycogen stores in diabetes mellitus may relate in part to the extent cycling occurs. Four methods have been introduced to estimate its extent in liver in humans. 1) In the fasted state, the rate of net hepatic glycogenolysis, i.e., glycogen breakdown minus synthesis, is estimated using NMR, and the rate of glycogenolysis is estimated from deuterium labeling of blood glucose on (2)H(2)O ingestion. 2) The rate of glycogen synthesis is estimated from the rate of labeling of carbon 1 of glycogen on [1-(13)C]glucose infusion, monitored by NMR, and the rate of breakdown from the rate of disappearance of that labeling on unlabeled glucose infusion. 3) The rate of synthesis from glucose-1-P, formed by glycogenolysis, is measured by the decrease in the (3)H/(14)C ratio in acetaminophen glucuronide on acetaminophen and [2-(3)H,6-(14)C]galactose administration. 4) The rate of synthesis is estimated from the dilution of label from labeled galactose in its conversion to the acetaminophen glucuronide, and the rate of glycogenolysis is estimated from the amount of label in blood glucose. In the first method, the fate of glucose-6-P is assumed to be only to glycogen and glucose. In the second, only glucose-6-P molecules formed by breakdown that are not cycled back to glycogen are measured. In the third, (3)H is assumed to be removed completely during cycling, and only the molecules cycled back to glycogen are measured. In the fourth, galactose conversion to glucose is assumed to be via glycogen. Quantitations in all four methods depend on assuming the order in which the molecules deposited in glycogen are released.

Increase in beta-cell mass in transplanted porcine neonatal pancreatic cell clusters is due to proliferation of beta-cells and differentiation of duct cells

A 20-fold increase in beta-cell mass has been found after transplantation of porcine neonatal pancreatic cell clusters (NPCCs). Here the mechanisms leading to this increased beta-cell mass were studied. NPCCs (4000 islet equivalents) generated after 8 days culture of digested neonatal pig pancreas were transplanted beneath the renal capsule of streptozotocin (STZ) diabetic and normoglycemic nude mice. Grafts were removed at 10 days, 6 weeks, and 20 weeks after transplantation for immunostaining and insulin content. Proliferation of beta-cells and duct cells was assessed morphometrically using double immunostaining for Ki-67 with insulin or cytokeratin 7 (CK7). Graft maturation was assessed with double immunostaining of CK7 and insulin. Apoptosis was determined using propidium iodide staining. beta-cell proliferation in NPCCs was higher after 8 days of culture compared with that found in neonatal pig pancreas. After transplantation, beta-cell proliferation remained high at 10 days, decreased somewhat at 6 weeks, and was much lower 20 weeks after transplantation. Diabetic recipients not cured at 6 weeks after transplantation had significantly higher beta-cell proliferation compared with those cured and to normoglycemic recipients. The size of individual beta-cells, as determined by cross-sectional area, increased as the grafts matured. Graft insulin content was 20-fold increased at 20 weeks after transplantation compared with 8 days cultured NPCCS: The proliferation index of duct cells was significantly higher in neonatal pig pancreas than in 8 days cultured NPCCs and in 10-day-old grafts. The incidence of apoptosis in duct cells appeared to be low. About 20% of duct cells 10 days post transplantation showed costaining for CK7 and insulin, a marker of protodifferentiation. In conclusion, the increase in beta-cell mass after transplantation of NPCCs is due to both proliferation of differentiated beta-cells and differentiation of duct cells into beta-cells.

A role for activin A and betacellulin in human fetal pancreatic cell differentiation and growth

Activin A (Act.A), a member of the transforming growth factor beta family of secreted proteins, has been implicated in the regulation of growth and differentiation of various cell types. Betacellulin (BTC), a member of the epidermal growth factor family, converts exocrine AR42J cells to insulin-expressing cells when combined with Act.A. We have used primary cultures of human fetal pancreatic tissue to identify the effects of Act.A and/or BTC on islet development and growth. Exposure to Act.A resulted in a 1.5-fold increase in insulin content (P < 0.005) and a 2-fold increase in the number of cells immunopositive for insulin (P < 0.005). The formation of islet-like cell clusters, containing mainly epithelial cells, during a 5-day culture, was stimulated 1.4-fold by BTC (P < 0.05). BTC alone caused a 2.6-fold increase in DNA synthesis (P < 0.005). These data suggest that Act.A induces endocrine differentiation, whereas BTC has a mitogenic effect on human undifferentiated pancreatic epithelial cells.

Glucose-responsive gene delivery in pancreatic Islet cells via recombinant adeno-associated viral vectors

PURPOSE

Recent progress in genetic engineering presents the possibility of providing physiologically regulated glucose metabolism in individuals with diabetes. The objective of this study is to explore the feasibility of obtaining glucose dependent gene expression in the pancreatic beta-cell lines via recombinant adeno-associated virus type 2 (rAAV) mediated gene transfer.

METHODS

Two transcription cassettes containing the luciferase gene under the control of the rat insulin I gene promoter and the enhanced green fluorescent protein (EGFP) open reading frame under the control of the immediate early gene promoter of human cytomegalovirus (CMV) were placed in series between the inverted terminal repeats (ITRs) of AAV. The rAAV vectors produced were used to transduce pancreatic beta-cell line grown in the absence or presence of various concentrations of glucose. Luciferase activity assays were performed at 72 hr post-transduction.

RESULTS

Glucose-responsive reporter gene expression was obtained in both calcium phosphate transfected HIT-T15 and betaHC-9 cells, demonstrating regulated luciferase gene expression under control of the insulin gene promoter. At MOI of 100, rAAV-transduced betaHC-9 cells exhibited glucose-dependent luciferase activities, which were approximately 4.3 fold higher than those transfected by the calcium phosphate coprecipitation method at 20 mM glucose.

CONCLUSIONS

Delivery of the insulin gene promoter via rAAV was shown in this study to result in glucose-dependent control of the reporter gene expression. The results suggest that rAAV is an efficient viral vector for gene transfer into the pancreatic islet cells.

KSA antigen Ep-CAM mediates cell-cell adhesion of pancreatic epithelial cells: morphoregulatory roles in pancreatic islet development

Cell adhesion molecules (CAMs) are important mediators of cell-cell interactions and regulate cell fate determination by influencing growth, differentiation, and organization within tissues. The human pancarcinoma antigen KSA is a glycoprotein of 40 kD originally identified as a marker of rapidly proliferating tumors of epithelial origin. Interestingly, most normal epithelia also express this antigen, although at lower levels, suggesting that a dynamic regulation of KSA may occur during cell growth and differentiation. Recently, evidence has been provided that this glycoprotein may function as an epithelial cell adhesion molecule (Ep-CAM). Here, we report that Ep-CAM exhibits the features of a morphoregulatory molecule involved in the development of human pancreatic islets. We demonstrate that Ep-CAM expression is targeted to the lateral domain of epithelial cells of the human fetal pancreas, and that it mediates calcium-independent cell-cell adhesion. Quantitative confocal immunofluorescence in fetal pancreata identified the highest levels of Ep-CAM expression in developing islet-like cell clusters budding from the ductal epithelium, a cell compartment thought to comprise endocrine progenitors. A surprisingly reversed pattern was observed in the human adult pancreas, displaying low levels of Ep-CAM in islet cells and high levels in ducts. We further demonstrate that culture conditions promoting epithelial cell growth induce upregulation of Ep-CAM, whereas endocrine differentiation of fetal pancreatic epithelial cells, transplanted in nude mice, is associated with a downregulation of Ep-CAM expression. In addition, a blockade of Ep-CAM function by KS1/4 mAb induced insulin and glucagon gene transcription and translation in fetal pancreatic cell clusters. These results indicate that developmentally regulated expression and function of Ep-CAM play a morphoregulatory role in pancreatic islet ontogeny.

Experimental transplantation of human fetal and adult pancreatic islets

We examined morphology and function following transplantation of human fetal islet-like clusters (ICCs) in nude mice and compared the functional efficiency of human adult islets and fetal ICCs after transplantation. To assess the optimal site we first transplanted ICCs under the kidney capsule, pancreas, lung, and liver in nude mice. Grafts to the kidney and pancreas matured functionally and morphologically, as evidenced by a 4-fold increase in C peptide after glucose stimulation and the presence of insulin in the grafts of all animals. Grafts to the lung, liver, and spleen did poorly; C peptide was only measurable in two of eight, two of five, or three of five of mice grafted to the lung, liver, or spleen, respectively. Using chemically diabetic nude rats as recipients, we were able to restore normoglycemia using 15,000 ICCs/kg. Lastly, when transplanted under the kidney capsule of normal nude mice, ICCs had significantly higher insulin contents and C peptide release than equivalent grafts of adult islets. In summary, ICCs are an efficient source of insulin-producing cells of potential use in clinical transplantation. In nude mice, both the kidney and the pancreas provide suitable environments for the growth and maturation of undifferentiated human beta-cells.

Phosphatidylinositol 3-kinase is a negative regulator of cellular differentiation

Phosphatidylinositol 3-kinase (PI3K) has been shown to be an important mediator of intracellular signal transduction in mammalian cells. We show here, for the first time, that the blockade of PI3K activity in human fetal undifferentiated cells induced morphological and functional endocrine differentiation. This was associated with an increase in mRNA levels of insulin, glucagon, and somatostatin, as well as an increase in the insulin protein content and secretion in response to secretagogues. Blockade of PI3K also increased the proportion of pluripotent precursor cells coexpressing multiple hormones and the total number of terminally differentiated cells originating from these precursor cells. We examined whether any of the recently described modulators of endocrine differentiation could participate in regulating PI3K activity in fetal islet cells. The activity of PI3K was inversely correlated with the hepatocyte growth factor/scatter factor-induced downregulation or nicotinamideinduced upregulation of islet-specific gene expression, giving support to the role of PI3K, as a negative regulator of endocrine differentiation. In conclusion, our results provide a mechanism for the regulation of hormone-specific gene expression during human fetal neogenesis. They also suggest a novel function for PI3K, as a negative regulator of cellular differentiation.