Generation of human islets through expansion and differentiation of non-islet pancreatic cells discarded (pancreatic discard) after islet isolation

Recent advances in organoid culture for insulin production and diabetes therapy: methods and challenges

Breakthroughs in stem cell technology have contributed to disease modeling and drug screening via organoid technology. Organoid are defined as three-dimensional cellular aggregations derived from adult tissues or stem cells. They recapitulate the intricate pattern and functionality of the original tissue. Insulin is secreted mainly by the pancreatic β cells. Large-scale production of insulin-secreting β cells is crucial for diabetes therapy. Here, we provide a brief overview of organoids and focus on recent advances in protocols for the generation of pancreatic islet organoids from pancreatic tissue or pluripotent stem cells for insulin secretion. The feasibility and limitations of organoid cultures derived from stem cells for insulin production will be described. As the pancreas and gut share the same embryological origin and produce insulin, we will also discuss the possible application of gut organoids for diabetes therapy. Better understanding of the challenges associated with the current protocols for organoid culture facilitates development of scalable organoid cultures for applications in biomedicine.

Recent advances in organoid culture for insulin production and diabetes therapy: methods and challenges

Breakthroughs in stem cell technology have contributed to disease modeling and drug screening via organoid technology. Organoid are defined as three-dimensional cellular aggregations derived from adult tissues or stem cells. They recapitulate the intricate pattern and functionality of the original tissue. Insulin is secreted mainly by the pancreatic β cells. Large-scale production of insulin-secreting β cells is crucial for diabetes therapy. Here, we provide a brief overview of organoids and focus on recent advances in protocols for the generation of pancreatic islet organoids from pancreatic tissue or pluripotent stem cells for insulin secretion. The feasibility and limitations of organoid cultures derived from stem cells for insulin production will be described. As the pancreas and gut share the same embryological origin and produce insulin, we will also discuss the possible application of gut organoids for diabetes therapy. Better understanding of the challenges associated with the current protocols for organoid culture facilitates development of scalable organoid cultures for applications in biomedicine. [BMB Reports 2019; 52(5): 295-303].

Expansion of Adult Human Pancreatic Tissue Yields Organoids Harboring Progenitor Cells with Endocrine Differentiation Potential

Generating an unlimited source of human insulin-producing cells is a prerequisite to advance β cell replacement therapy for diabetes. Here, we describe a 3D culture system that supports the expansion of adult human pancreatic tissue and the generation of a cell subpopulation with progenitor characteristics. These cells display high aldehyde dehydrogenase activity (ALDH^hi), express pancreatic progenitors markers (PDX1, PTF1A, CPA1, and MYC), and can form new organoids in contrast to ALDH^lo cells. Interestingly, gene expression profiling revealed that ALDH^hi cells are closer to human fetal pancreatic tissue compared with adult pancreatic tissue. Endocrine lineage markers were detected upon in vitro differentiation. Engrafted organoids differentiated toward insulin-positive (INS⁺) cells, and circulating human C-peptide was detected upon glucose challenge 1 month after transplantation. Engrafted ALDH^hi cells formed INS⁺ cells. We conclude that adult human pancreatic tissue has potential for expansion into 3D structures harboring progenitor cells with endocrine differentiation potential.

(Re)generating Human Beta Cells: Status, Pitfalls, and Perspectives

Diabetes mellitus results from disturbed glucose homeostasis due to an absolute (type 1) or relative (type 2) deficiency of insulin, a peptide hormone almost exclusively produced by the beta cells of the endocrine pancreas in a tightly regulated manner. Current therapy only delays disease progression through insulin injection and/or oral medications that increase insulin secretion or sensitivity, decrease hepatic glucose production, or promote glucosuria. These drugs have turned diabetes into a chronic disease as they do not solve the underlying beta cell defects or entirely prevent the long-term complications of hyperglycemia. Beta cell replacement through islet transplantation is a more physiological therapeutic alternative but is severely hampered by donor shortage and immune rejection. A curative strategy should combine newer approaches to immunomodulation with beta cell replacement. Success of this approach depends on the development of practical methods for generating beta cells, either in vitro or in situ through beta cell replication or beta cell differentiation. This review provides an overview of human beta cell generation.

Growth of Epithelial Organoids in a Defined Hydrogel

Epithelial organoids are simplified models of organs grown in vitro from embryonic and adult stem cells. They are widely used to study organ development and disease, and enable drug screening in patient-derived primary tissues. Current protocols, however, rely on animal- and tumor-derived basement membrane extract (BME) as a 3D scaffold, which limits possible applications in regenerative medicine. This prompted us to study how organoids interact with their matrix, and to develop a well-defined hydrogel that supports organoid generation and growth. It is found that soft fibrin matrices provide suitable physical support, and that naturally occurring Arg-Gly-Asp (RGD) adhesion domains on the scaffold, as well as supplementation with laminin-111, are key parameters required for robust organoid formation and expansion. The possibility to functionalize fibrin via factor XIII-mediated anchoring also allows to covalently link fluorescent nanoparticles to the matrix for 3D traction force microscopy. These measurements suggest that the morphogenesis of budding intestinal organoids results from internal pressure combined with higher cell contractility in the regions containing differentiated cells compared to the regions containing stem cells. Since the fibrin/laminin matrix supports long-term expansion of all tested murine and human epithelial organoids, this hydrogel can be widely used as a defined equivalent to BME.

Maximizing endogenous β-cell regeneration

PURPOSE OF REVIEW

Inadequate insulin-producing pancreatic β-cell mass is a key feature of both type 1 and type 2 diabetes. Efforts to regenerate β-cell mass from pancreatic precursors may thus ameliorate absolute or relative insulin deficiency, thereby improving glucose homeostasis. A clear understanding of the processes that govern the generation of new β-cells in the mature pancreas will be fundamental to success in this effort. This review discusses the current state of knowledge regarding β-cell regeneration and emphasizes recent studies of significance.

RECENT FINDINGS

Recent reports demonstrate regenerative potential in the adult human pancreas. Further, they build on the strong existing evidence that proliferation of preexisting β-cells is the predominant source of new β-cells in adulthood by dissecting the cell cycle machinery components and critical signaling pathways required for β-cell proliferation. Finally, β-cell trophic peptides have demonstrated preclinical potential as pharmacologic regenerative agents and may form the basis for clinical interventions in the future.

SUMMARY

Efforts to augment β-cell regeneration by enhancing β-cell viability and proliferation may lead to novel therapeutic approaches for type 1 and type 2 diabetes. An intimate understanding of the molecular mechanisms underlying the regulation of β-cell proliferation and survival will be fundamental to the optimization of endogenous β-cell regeneration.

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

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

A new method for generating insulin-secreting cells from human pancreatic epithelial cells after islet isolation transformed by NeuroD1

The generation of insulin-secreting cells from nonendocrine pancreatic epithelial cells (NEPEC) has been demonstrated for potential clinical use in the treatment of diabetes. However, previous methods either had limited efficacy or required viral vectors, which hinder clinical application. In this study, we aimed to establish an efficient method of insulin-secreting cell generation from NEPEC without viral vectors. We used nonislet fractions from both research-grade human pancreata from brain-dead donors and clinical pancreata after total pancreatectomy with autologous islet transplantation to treat chronic pancreatitis. It is of note that a few islets could be mingled in the nonislet fractions, but their influence could be limited. The NeuroD1 gene was induced into NEPEC using an effective triple lipofection method without viral vectors to generate insulin-secreting cells. The differentiation was promoted by adding a growth factor cocktail into the culture medium. Using the research-grade human pancreata, the effective method showed high efficacy in the differentiation of NEPEC into insulin-positive cells that secreted insulin in response to a glucose challenge and improved diabetes after being transplanted into diabetic athymic mice. Using the clinical pancreata, similar efficacy was obtained, even though those pancreata suffered chronic pancreatitis. In conclusion, our effective differentiation protocol with triple lipofection method enabled us to achieve very efficient insulin-secreting cell generation from human NEPEC without viral vectors. This method offers the potential for supplemental insulin-secreting cell transplantation for both allogeneic and autologous islet transplantation.

In vitro reconstitution of pancreatic islets

The lack of transplantable pancreatic islets is a serious problem that affects the treatment of patients with type 1 diabetes mellitus. Beta cells can be induced from various sources of stem or progenitor cells, including induced pluripotent stem cells in the near future; however, the reconstitution of islets from β cells in culture dishes is challenging. The generation of highly functional islets may require three-dimensional spherical cultures that resemble intact islets. This review discusses recent advances in the reconstitution of islets. Several factors affect the reconstitution of pseudoislets with higher functions, such as architectural similarity, cell-to-cell contact, and the production method. The actual transplantation of naked or encapsulated pseudoislets and islet-like cell clusters from various stem cell sources is also discussed. Advancing our understanding of the methods used to reconstitute pseudoislets should expand the range of potential strategies available for developing de novo islets for therapeutic applications.

Pancreatic tissue resident mesenchymal stromal cell (MSC)-like cells as a source of in vitro islet neogenesis

Insufficient β-cell mass is a common denominator for both type 1 and type 2 diabetes. In vitro generation of β-cells from islet precursor cells, exocrine cells or ductal epithelia provide an alternative source of insulin-producing cells. However the presence of multipotent precursor cells within the pancreas is also deliberated. In this study we isolated mesenchymal stromal cell (MSC)-like cells from adult mouse pancreas by collagenase digestion. We used Knockout DMEM for our isolation procedure and the floating islets and acini were removed after 48 h. This strategy permitted the adhesion of stromal cells with typical mesenchymal morphology. These cells not only expressed MSC-specific markers like Sca-1, CD90.2, CD73, and CD44 but also generated osteocytes, adipocytes, and neurons when induced with specific growth media. Upon exposure to islet differentiation serum-free cocktail a significant upregulation of pancreatic markers like Nkx2.2, Nkx6.1, Pdx1, insulin, and somatostatin was seen. The differentiated islet-like cell aggregates (ICAs) secreted insulin which increased over the days in culture in presence of basal glucose levels. Taken together, our data strongly indicate that there is a tissue-resident precursor population within the pancreas that can be exploited for islet neogenesis in vitro.

Distinctions between the islets of mice and men: implications for new therapies for type 1 and 2 diabetes

OBJECTIVE

To elucidate why diabetes is so difficult to treat despite the present tools and pharmacologic armamentarium and to provide insights into emerging therapies by describing human and rodent data that demonstrates the ability to transform progenitor cells within the adult pancreas into new islets.

METHODS

A literature review focused on the distinctions between human and rodent islets.

RESULTS

We are beginning to elucidate important differences between the architecture and composition of the islets of Langerhans in humans and rodents. In contrast to rodent islets, human islets are more heterogeneous in cellular composition and have more prominent intra-islet vascularity, with smooth muscle-containing blood vessels that are not present in rodent islets. Some studies report that more than 70% of human beta cells have direct physical contact with other cell types, whereas others describe that smaller human islets possess features more typical of rodents, while larger islets exhibit greater vascularity and a cellular distribution distinct from centrally clustered beta cells surrounded by a mantle of alpha and delta cells found in rodents.

CONCLUSIONS

The differences between the islets of mice and men may influence why treatments hailed as reversing diabetes among rodents have not been successfully translated into humans. Increased understanding of the complexities within the human islet may yield unique insights into reversing diabetes in humans.

Incretin hormones and beta-cell mass expansion: what we know and what is missing?

Pancreatic beta-cell mass expands through beta-cell proliferation and neogenesis while it decreases mainly via apoptosis. The loss of balance between beta-cell death and regeneration leads to a reduction of beta-cell functional mass, thus contributing to the pathogenesis of type 2 diabetes mellitus (T2DM). The pathogenetic mechanisms causing T2DM are complex, and also include a significant reduction of the incretin effect. A better understanding of the role of incretin hormones in glucose homeostasis has led to the development of incretin-based therapies. Recently, incretin hormones have been shown to stimulate the beta-cell growth and differentiation from pancreas-derived stem/progenitor cells, as well as to exert cytoprotective, antiapoptotic effects on beta-cells. However, the role and the molecular mechanisms by which GLP-1 and its agonists regulate beta-cell mass have not been fully investigated. This review focuses the current findings and the missing understanding of the effects of incretin hormones on beta-cell mass expansion.

Mixed chimerism and growth factors augment β cell regeneration and reverse late-stage type 1 diabetes

Type 1 diabetes (T1D) results from an autoimmune destruction of insulin-producing β cells. Currently, islet transplantation is the only curative therapy for late-stage T1D, but the beneficial effect is limited in its duration, even under chronic immunosuppression, because of the chronic graft rejection mediated by both auto- and alloimmunity. Clinical islet transplantation is also restricted by a severe shortage of donor islets. Induction of mixed chimerism reverses autoimmunity, eliminates insulitis, and reverses new-onset but not late-stage disease in the nonobese diabetic (NOD) mouse model of T1D. Administration of gastrin and epidermal growth factor (EGF) also reverses new-onset but not late-stage T1D in this animal model. Here, we showed that combination therapy of induced mixed chimerism under a radiation-free nontoxic anti-CD3/CD8 conditioning regimen and administration of gastrin/EGF augments both β cell neogenesis and replication, resulting in reversal of late-stage T1D in NOD mice. If successfully translated into humans, this combination therapy could replace islet transplantation as a long-term curative therapy for T1D.

Purified human pancreatic duct cell culture conditions defined by serum-free high-content growth factor screening

The proliferation of pancreatic duct-like CK19+ cells has implications for multiple disease states including pancreatic cancer and diabetes mellitus. The in vitro study of this important cell type has been hampered by their limited expansion compared to fibroblast-like vimentin+ cells that overgrow primary cultures. We aimed to develop a screening platform for duct cell mitogens after depletion of the vimentin+ population. The CD90 cell surface marker was used to remove the vimentin+ cells from islet-depleted human pancreas cell cultures by magnetic-activated cell sorting. Cell sorting decreased CD90+ cell contamination of the cultures from 34±20% to 1.3±0.6%, yielding purified CK19+ cultures with epithelial morphology. A full-factorial experimental design was then applied to test the mitogenic effects of bFGF, EGF, HGF, KGF and VEGF. After 6 days in test conditions, the cells were labelled with BrdU, stained and analyzed by high-throughput imaging. This screening assay confirmed the expected mitogenic effects of bFGF, EGF, HGF and KGF on CK19+ cells and additionally revealed interactions between these factors and VEGF. A serum-free medium containing bFGF, EGF, HGF and KGF led to CK19+ cell expansion comparable to the addition of 10% serum. The methods developed in this work should advance pancreatic cancer and diabetes research by providing effective cell culture and high-throughput screening platforms to study purified primary pancreatic CK19+ cells.

Neurexin-1α contributes to insulin-containing secretory granule docking

Neurexins are a family of transmembrane, synaptic adhesion molecules. In neurons, neurexins bind to both sub-plasma membrane and synaptic vesicle-associated constituents of the secretory machinery, play a key role in the organization and stabilization of the presynaptic active zone, and help mediate docking of synaptic vesicles. We have previously shown that neurexins, like many other protein constituents of the neurotransmitter exocytotic machinery, are expressed in pancreatic β cells. We hypothesized that the role of neurexins in β cells parallels their role in neurons, with β-cell neurexins helping to mediate insulin granule docking and secretion. Here we demonstrate that β cells express a more restricted pattern of neurexin transcripts than neurons, with a clear predominance of neurexin-1α expressed in isolated islets. Using INS-1E β cells, we found that neurexin-1α interacts with membrane-bound components of the secretory granule-docking machinery and with the granule-associated protein granuphilin. Decreased expression of neurexin-1α, like decreased expression of granuphilin, reduces granule docking at the β-cell membrane and improves insulin secretion. Perifusion of neurexin-1α KO mouse islets revealed a significant increase in second-phase insulin secretion with a trend toward increased first-phase secretion. Upon glucose stimulation, neurexin-1α protein levels decrease. This glucose-induced down-regulation may enhance glucose-stimulated insulin secretion. We conclude that neurexin-1α is a component of the β-cell secretory machinery and contributes to secretory granule docking, most likely through interactions with granuphilin. Neurexin-1α is the only transmembrane component of the docking machinery identified thus far. Our findings provide new insights into the mechanisms of insulin granule docking and exocytosis.

Lineage tracing evidence for transdifferentiation of acinar to duct cells and plasticity of human pancreas

BACKGROUND & AIMS

Animal studies have indicated that pancreatic exocrine acinar cells have phenotypic plasticity. In rodents, acinar cells can differentiate into ductal precursors that can be converted to pancreatic ductal adenocarcinoma or insulin-producing endocrine cells. However, little is known about human acinar cell plasticity. We developed nongenetic and genetic lineage tracing methods to study the fate of human acinar cells in culture.

METHODS

Human exocrine tissue was obtained from organ donors, dissociated, and cultured. Cell proliferation and survival were measured, and cell phenotypes were analyzed by immunocytochemistry. Nongenetic tracing methods were developed based on selective binding and uptake by acinar cells of a labeled lectin (Ulex europaeus agglutinin 1). Genetic tracing methods were developed based on adenoviral introduction of a Cre-lox reporter system, controlled by the amylase promoter.

RESULTS

Both tracing methods showed that human acinar cells can transdifferentiate into cells that express specific ductal markers, such as cytokeratin 19, hepatocyte nuclear factor 1β, SOX9, CD133, carbonic anhydrase II, and cystic fibrosis transmembrane conductance regulator. Within 1 week of culture, all surviving acinar cells had acquired a ductal phenotype. This transdifferentiation was decreased by inhibiting mitogen-activated protein kinase signaling.

CONCLUSIONS

Human acinar cells have plasticity similar to that described in rodent cells. These results might be used to develop therapeutic strategies for patients with diabetes or pancreatic cancer.

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.

Quantitative assessment of β-cell apoptosis and cell composition of isolated, undisrupted human islets by laser scanning cytometry

BACKGROUND

Assays for assessing human islet cell quality, which provide results before transplantation, would be beneficial to improve the outcomes for islet transplantation therapy. Parameters such as percent β-cell apoptosis and cell composition are found to vary markedly between different islet preparations and may serve as markers of islet quality. We have developed fluorescence-based assays using laser scanning cytometry for assessing β-cell apoptosis and islet cell composition on serial sections of intact isolated islets.

METHODS

Isolated human islets were fixed in formalin and embedded in paraffin. Serial sections were immunostained for the pancreatic hormones and acinar and ductal cell markers. DNA fragmentation was used to label apoptotic cells. Stained cells were quantified using an iCys laser scanning cytometer.

RESULTS

Islet preparations from 102 human pancreatic islet isolations were analyzed. For the whole set of islet preparations, we found a mean islet cell composition of 54.5%±1.2% insulin-positive, 33.9%±1.2% glucagon, 12.1%±0.7% somatostatin, and 1.5%±0.2% pancreatic polypeptide-positive cells. The apoptotic β cells were 2.85%±0.4% with a range of 0.27% to 18.3%. The percentage of apoptotic β cells correlated well (P<0.0001, n=59) with results obtained in vivo by transplantation of the corresponding islets in diabetic NODscid mice.

CONCLUSIONS

The analysis of whole, nondissociated islets for cell composition and β-cell apoptosis using laser scanning cytometry gives reliable and reproducible results and could be performed both before islet transplantation and on preserved cell blocks at any time in future. Thus, they can be a powerful tool for islet quality assessment.

Rapamycin suppresses the expansion and differentiation of porcine neonatal pancreas cell clusters

BACKGROUND

The role of rapamycin in pancreas stem cells remains to be clearly elucidated. Herein, we evaluated the effects of rapamycin on porcine neonatal pancreas cell clusters (NPCCs), which primarily comprised pancreatic precursors, and attempted to find an intracellular mechanism about the harmful effects of rapamycin.

METHODS

Porcine NPCCs were treated with rapamycin in a monolayer, and the apoptosis and proliferation were determined via caspase-3 assay and H-thymidine uptake analysis. The expression of transcription factors was assessed via reverse-transcriptase polymerase chain reaction and Western blotting. For the in vivo study, the porcine NPCCs were transplanted into the kidney subcapsules of normal nude mice and treated with rapamycin.

RESULTS

Rapamycin treatment significantly reduced the number of β cells, glucose-stimulated insulin secretion, and the insulin contents in the monolayer-cultured porcine NPCCs. Furthermore, rapamycin treatment increased the apoptosis and inhibited the proliferation of β cells in the culture dishes. The expressions of the insulin, pancreatic and duodenal homeobox-1, and NeuroD/Beta2 genes were down-regulated via rapamycin treatment. The expression of insulin-like growth factor-II was significantly down-regulated, but the expression of Foxo1 was simultaneously inversely increased, and the translocation of Foxo1 from the cytoplasm to the nucleus was induced by rapamycin treatment. Moreover, rapamycin treatment induced a marked reduction in the relative volume and absolute mass of β cells in the porcine NPCCs grafts at 8 weeks after transplantation in the normal nude mice.

CONCLUSIONS

Here, we demonstrate that rapamycin treatment suppresses the expansion and differentiation of porcine NPCCs, and the alteration of Foxo1 and insulin-like growth factor-II gene expression might be the crucial factors.

Post-transcriptional up-regulation of Tsc-22 by Ybx1, a target of miR-216a, mediates TGF-{beta}-induced collagen expression in kidney cells

Increased accumulation of extracellular matrix proteins and hypertrophy induced by transforming growth factor-β1 (TGF-β) in renal mesangial cells (MC) are hallmark features of diabetic nephropathy. Although the post-transcriptional regulation of key genes has been implicated in these events, details are not fully understood. Here we show that TGF-β increased microRNA-216a (miR-216a) levels in mouse MC, with parallel down-regulation of Ybx1, a miR-216a target and RNA-binding protein. TGF-β also enhanced protein levels of Tsc-22 (TGF-β-stimulated clone 22) and collagen type I α-2 (Col1a2) expression in MC through far upstream enhancer E-boxes by interaction of Tsc-22 with an E-box regulator, Tfe3. Ybx1 colocalized with processing bodies in MC and formed a ribonucleoprotein complex with Tsc-22 mRNA, and this complex formation was reduced by TGF-β, miR-216a mimics, or Ybx1 shRNA to increase Tsc-22 protein levels but enhanced by miR-216a inhibitor oligonucleotides. Chromatin immunoprecipitation (ChIP) assays revealed that TGF-β could increase the occupancies of Tsc-22 and Tfe3 on enhancer E-boxes of Col1a2. Co-immunoprecipitation assays revealed that TGF-β promoted the interaction of Tsc-22 with Tfe3. These results demonstrate that post-transcriptional regulation of Tsc-22 mediated through Ybx1, a miR-216a target, plays a key role in TGF-β-induced Col1a2 in MC related to the pathogenesis of diabetic nephropathy.

The isolated pancreatic islet as a micro-organ and its transplantation to cure diabetes: celebrating the legacy of Paul Lacy

Over the past three decades the pancreatic islet of Langerhans has taken center stage as an endocrine micro-organ whose glucoregulatory function is highly explicable on the basis of the increasingly well understood activities of three highly interactive secretory cells. Islet dysfunction underlies both type 1 and type 2 diabetes mellitus (DM); its protection from immune attack and gluco-and lipo-toxicity may prevent the development of DM; and its replacement by non-surgical transplantation may be curative of DM. During a career marked by vision, focus and tenacity, Paul Lacy contributed substantially to the development of each of these concepts. In this review we focus on Lacy's contribution to the development of the concept of the islet as a micro-organ, how this foreshadowed our current detailed understanding of single cell function and cell-cell interactions and how this led to a reduced model of islet function encouraging islet transplantation. Next, we examine how clinical allotransplantation, first undertaken by Lacy, has contributed to a more complex view of the interaction of islet endocrine cells with its circulation and neighboring tissues, both "in situ" and after transplantation. Lastly, we consider recent developments in some alternative approaches to treatment of DM that Lacy could glimpse on the horizon but did not have the chance to participate in.

A novel alginate hollow fiber bioreactor process for cellular therapy applications

Gel-matrix culture environments provide tissue engineering scaffolds and cues that guide cell differentiation. For many cellular therapy applications such as for the production of islet-like clusters to treat Type 1 diabetes, the need for large-scale production can be anticipated. The throughput of the commonly used nozzle-based devices for cell encapsulation is limited by the rate of droplet formation to approximately 0.5 L/h. This work describes a novel process for larger-scale batch immobilization of mammalian cells in alginate-filled hollow fiber bioreactors (AHFBRs). A methodology was developed whereby (1) alginate obstruction of the intra-capillary space medium flow was negligible, (2) extra-capillary alginate gelling was complete and (3) 83 +/- 4% of the cells seeded and immobilized were recovered from the bioreactor. Chinese hamster ovary (CHO) cells were used as a model aggregate-forming cell line that grew from mostly single cells to pancreatic islet-sized spheroids in 8 days of AHFBR culture. CHO cell growth and metabolic rates in the AHFBR were comparable to small-scale alginate slab controls. Then, the process was applied successfully to the culture of primary neonatal pancreatic porcine cells, without significant differences in cell viability compared with slab controls. As expected, alginate-immobilized culture in the AHFBR increased the insulin content of these cells compared with suspension culture. The AHFBR process could be refined by adding matrix components or adapted to other reversible gels and cell types, providing a practical means for gel-matrix assisted cultures for cellular therapy.

Insulin gene expression is regulated by DNA methylation

Background

Insulin is a critical component of metabolic control, and as such, insulin gene expression has been the focus of extensive study. DNA sequences that regulate transcription of the insulin gene and the majority of regulatory factors have already been identified. However, only recently have other components of insulin gene expression been investigated, and in this study we examine the role of DNA methylation in the regulation of mouse and human insulin gene expression.

Methodology/Principal Findings

Genomic DNA samples from several tissues were bisulfite-treated and sequenced which revealed that cytosine-guanosine dinucleotide (CpG) sites in both the mouse Ins2 and human INS promoters are uniquely demethylated in insulin-producing pancreatic beta cells. Methylation of these CpG sites suppressed insulin promoter-driven reporter gene activity by almost 90% and specific methylation of the CpG site in the cAMP responsive element (CRE) in the promoter alone suppressed insulin promoter activity by 50%. Methylation did not directly inhibit factor binding to the CRE in vitro, but inhibited ATF2 and CREB binding in vivo and conversely increased the binding of methyl CpG binding protein 2 (MeCP2). Examination of the Ins2 gene in mouse embryonic stem cell cultures revealed that it is fully methylated and becomes demethylated as the cells differentiate into insulin-expressing cells in vitro.

Conclusions/Significance

Our findings suggest that insulin promoter CpG demethylation may play a crucial role in beta cell maturation and tissue-specific insulin gene expression.

Investigation and characterization of the duct cell-enriching process during serum-free suspension and monolayer culture using the human exocrine pancreas fraction

OBJECTIVES

We aimed to characterize a serum-free culture system resulting in highly enriched duct cells from human exocrine pancreas. In addition, we tested the effect of vascular endothelial growth factor (VEGF) on endothelial cell proliferation and endocrine differentiation of the duct cells.

METHODS

The exocrine pellet fraction was cultivated in suspension followed by monolayer culture. Time course analysis of multiple acinar and duct cell markers was performed using reverse transcription-polymerase chain reaction and immunocytochemistry. The effects of VEGF and placental growth factor on the quantities of endothelial, duct, and endocrine cells and fibroblasts were investigated using computerized imaging analysis.

RESULTS

Suspension culture of the exocrine material efficiently enriched the cultures for duct cells. Frequent acinar cell death as well as cell selective adherence of acinar cells to the culture dish was the underlying cause of the enrichment. Confocal microscopy demonstrated the virtual absence of cells coexpressing duct cell- and acinar cell-specific markers. The endothelial immunoreactivity of the suspension culture system could be increased 2-fold by VEGF treatment, yet no effect was observed on endocrine cell numbers.

CONCLUSIONS

We have characterized a serum-free in vitro culture system to enrich human duct cells and further show that the contribution of acinoductal transdifferentiation to the enrichment of duct cells is negligible.

Mesenchymal stem cells derived from human exocrine pancreas express transcription factors implicated in beta-cell development

OBJECTIVES

Transplantation of in vitro generated islets or insulin-producing cells represents an attractive option to overcome organ shortage. The aim of this study was to isolate, expand, and characterize cells from human exocrine pancreas and analyze their potential to differentiate into beta cells.

METHODS

Fibroblast-like cells growing out of human exocrine tissue were characterized by flow cytometry and by their capacity to differentiate into mesenchymal cell lineages. During cell expansion and after differentiation toward beta cells, expression of transcription factors of endocrine pancreatic progenitors was analyzed by reverse transcription polymerase chain reaction.

RESULTS

Cells emerged from 14/18 human pancreatic exocrine fractions and were expanded up to 40 population doublings. These cells displayed surface antigens similar to mesenchymal stem cells from bone marrow. A culture of these cells in adipogenic and chondrogenic differentiation media allowed differentiation into adipocyte- and chondrocyte-like cells. During expansion, cells expressed transcription factors implicated in islet development such as Isl1, Nkx2.2, Nkx6.1, nestin, Ngn3, Pdx1, and NeuroD. Activin A and hepatocyte growth factor induced an expression of insulin, glucagon, and glucokinase.

CONCLUSIONS

Proliferating cells with characteristics of mesenchymal stem cells and endocrine progenitors were isolated from exocrine tissue. Under specific conditions, these cells expressed little insulin. Human pancreatic exocrine tissue might thus be a source of endocrine cell progenitors.

Isolation of major pancreatic cell types and long-term culture-initiating cells using novel human surface markers

We have developed a novel panel of cell-surface markers for the isolation and study of all major cell types of the human pancreas. Hybridomas were selected after subtractive immunization of Balb/C mice with intact or dissociated human islets and assessed for cell-type specificity and cell-surface reactivity by immunohistochemistry and flow cytometry. Antibodies were identified by specific binding of surface antigens on islet (panendocrine or alpha-specific) and nonislet pancreatic cell subsets (exocrine and duct). These antibodies were used individually or in combination to isolate populations of alpha, beta, exocrine, or duct cells from primary human pancreas by FACS and to characterize the detailed cell composition of human islet preparations. They were also employed to show that human islet expansion cultures originated from nonendocrine cells and that insulin expression levels could be increased to up to 1% of normal islet cells by subpopulation sorting and overexpression of the transcription factors Pdx-1 and ngn3, an improvement over previous results with this culture system. These methods permit the analysis and isolation of functionally distinct pancreatic cell populations with potential for cell therapy.

Is pancreatic diabetes (type 3c diabetes) underdiagnosed and misdiagnosed?

Exocrine pancreatic insufficiency is frequently associated with diabetes, with high prevalence in both insulin-dependent or insulin-independent patients. Exocrine pancreatic failure has often been perceived as a complication of diabetes. In contrast, recent clinical observations lead to the notion that nonendocrine pancreatic disease is a critical factor for development rather than a sequel to diabetes. The incidence of diabetes caused by exocrine pancreatic disease appears to be underestimated and may comprise 8% or more of the general diabetic patient population. Nonendocrine pancreas disease can cause diabetes by multiple mechanisms. Genetic defects have been characterized, resulting in a syndrome of both exocrine and endocrine failure. Regulation of beta-cell mass and physiological incretin secretion are directly dependent on normal exocrine function. Algorithms for diagnosis and therapy of diabetes should therefore address both endocrine and exocrine pancreatic function.

Human marrow-derived mesodermal progenitor cells generate insulin-secreting islet-like clusters in vivo

Transplantation of pancreatic islet cells is the only known potential cure for diabetes mellitus. However, the difficulty in obtaining sufficient numbers of purified islets for transplantation severely limits its use. A renewable and clinically accessible source of stem cells capable of differentiating into insulin-secreting beta-cells might circumvent this limitation. Here, we report that human fetal bone marrow (BM)-derived mesodermal progenitor cells (MPCs) possess the potential to generate insulinsecreting islet-like clusters (ISILCs) when injected into human fetal pancreatic tissues implanted in severe combined immunodeficiency (SCID) mice. Seven essential genes involved in pancreatic endocrine development, including insulin, glucagon, somatostatin, pdx-1, glut-2, nkx 2.2, and nkx 6.1, are expressed in these BM-MPC-derived ISILCs, suggesting that ISILCs are generated through neogenesis of BM-MPCs. Our data further suggest that differentiation of BM-MPCs into ISILCs is not mediated by cell fusion. Insulin secretion from these ISILCs is regulated by glucose concentration in vitro, and transplantation of purified ISILCs normalizes hyperglycemia in streptozocin (STZ)- induced nonobese diabetic (NOD)/SCID mice.

Glucose-stimulated increment in oxygen consumption rate as a standardized test of human islet quality

Standardized assessment of islet quality is imperative for clinical islet transplantation. We have previously shown that the increment in oxygen consumption rate stimulated by glucose (DeltaOCR(glc)) can predict in vivo efficacy of islet transplantation in mice. To further evaluate the approach, we studied three factors: islet specificity, islet composition and agreement between results obtained by different groups. Equivalent perifusion systems were set up at the City of Hope and the University of Washington and the values of DeltaOCR(glc) obtained at both institutions were compared. Islet specificity was determined by comparing DeltaOCR(glc) in islet and nonislet tissue. The DeltaOCR(glc) ranged from 0.01 to 0.19 nmol/min/100 islets (n = 14), a wide range in islet quality, but the values obtained by the two centers were similar. The contribution from nonislet impurities was negligible (DeltaOCR(glc) was 0.12 nmol/min/100 islets vs. 0.007 nmol/min/100 nonislet clusters). The DeltaOCR(glc) was statistically independent of percent beta cells, demonstrating that DeltaOCR(glc) is governed more by islet quality than by islet composition. The DeltaOCR(glc), but not the absolute level of OCR, was predictive of reversal of hyperglycemia in diabetic mice. These demonstrations lay the foundation for testing DeltaOCR(glc) as a measurement of islet quality for human islet transplantation.

Mechanisms of action of glucagon-like peptide 1 in the pancreas

Glucagon-like peptide 1 (GLP-1) is a hormone that is encoded in the proglucagon gene. It is mainly produced in enteroendocrine L cells of the gut and is secreted into the blood stream when food containing fat, protein hydrolysate, and/or glucose enters the duodenum. Its particular effects on insulin and glucagon secretion have generated a flurry of research activity over the past 20 years culminating in a naturally occurring GLP-1 receptor (GLP-1R) agonist, exendin 4 (Ex-4), now being used to treat type 2 diabetes mellitus (T2DM). GLP-1 engages a specific guanine nucleotide-binding protein (G-protein) coupled receptor (GPCR) that is present in tissues other than the pancreas (brain, kidney, lung, heart, and major blood vessels). The most widely studied cell activated by GLP-1 is the insulin-secreting beta cell where its defining action is augmentation of glucose-induced insulin secretion. Upon GLP-1R activation, adenylyl cyclase (AC) is activated and cAMP is generated, leading, in turn, to cAMP-dependent activation of second messenger pathways, such as the protein kinase A (PKA) and Epac pathways. As well as short-term effects of enhancing glucose-induced insulin secretion, continuous GLP-1R activation also increases insulin synthesis, beta cell proliferation, and neogenesis. Although these latter effects cannot be currently monitored in humans, there are substantial improvements in glucose tolerance and increases in both first phase and plateau phase insulin secretory responses in T2DM patients treated with Ex-4. This review will focus on the effects resulting from GLP-1R activation in the pancreas.

Current strategies and perspectives in insulin gene therapy for diabetes

Insulin gene therapy is an approach that might overcome the weakness of islet cell therapy owing to its vulnerability to autoimmune attack. There are several mandatory conditions for successful insulin gene therapy. Efficient insulin gene therapy should have an effective insulin gene delivery mechanism, a system of regulation of the insulin biosynthesis that responds to glucose within extremely narrow physiological limits, a system of insulin processing into its active form and a choice of appropriate target cells, which possess biochemical characteristics similar to β cells, but are not targets for β-cell-specific self-reactivity. In this article, advantages and disadvantages of non-β-cell types that are most likely to be used for generating surrogate insulin-producing β cells are compared. Current achievements in insulin gene therapy are critically evaluated and future challenges are discussed.