Regulation of human beta-cell adhesion, motility, and insulin secretion by collagen IV and its receptor alpha1beta1

Adhesion characteristics of porcine pancreatic islets and exocrine tissue to coating materials

Since the report of the Edmonton protocol in 2000, islet transplantation has been implemented worldwide, and xenotransplantation using porcine islets has also been reported. In addition, many basic experiments using pancreatic islets and exocrine tissue after isolation have been reported. Recently, exocrine cells have been found to be essential for inducing the differentiation of pancreatic islets. Therefore, the importance of the culture conditions for pancreatic tissue when conducting experiments using pancreatic tissue is also increasing. In this study, we focused on the coat material and examined the adhesive properties of porcine pancreatic islets and exocrine tissue after isolation. Porcine islet isolation was performed, and isolated islets (purity ≥95%) and exocrine tissue (purity ≥99%) were used to achieve adhesion to several extracellular matrixes, fibronectin, collagen type I, collagen type IV, laminin I, fibrinogen, and bovine serum albumin (BSA). DMEM with 0.5% FBS was used as the assay medium. For exocrine tissue, the adhesion was promoted in fibronectin, collagen type I, laminin I, and fibrinogen. The adhesive ability to fibronectin was more than twice that to BSA, while the adhesive ability to collagen type I, laminin I, and fibrinogen was less than twice that to BSA. For islets, the adhesive ability to fibronectin was weaker than that of exocrine tissue. Furthermore, the adhesion effect in fibronectin was obtained within 30 minutes and in medium containing little serum for both islets and exocrine tissues. These data suggest that fibronectin may be useful for the adhesion of pancreatic tissue.

Head-to-head comparison of two engineered cardiac grafts for myocardial repair: From scaffold characterization to pre-clinical testing

Cardiac tissue engineering, which combines cells and supportive scaffolds, is an emerging treatment for restoring cardiac function after myocardial infarction (MI), although, the optimal construct remains a challenge. We developed two engineered cardiac grafts, based on decellularized scaffolds from myocardial and pericardial tissues and repopulated them with adipose tissue mesenchymal stem cells (ATMSCs). The structure, macromechanical and micromechanical scaffold properties were preserved upon the decellularization and recellularization processes, except for recellularized myocardium micromechanics that was ∼2-fold stiffer than native tissue and decellularized scaffolds. Proteome characterization of the two acellular matrices showed enrichment of matrisome proteins and major cardiac extracellular matrix components, considerably higher for the recellularized pericardium. Moreover, the pericardial scaffold demonstrated better cell penetrance and retention, as well as a bigger pore size. Both engineered cardiac grafts were further evaluated in pre-clinical MI swine models. Forty days after graft implantation, swine treated with the engineered cardiac grafts showed significant ventricular function recovery. Irrespective of the scaffold origin or cell recolonization, all scaffolds integrated with the underlying myocardium and showed signs of neovascularization and nerve sprouting. Collectively, engineered cardiac grafts -with pericardial or myocardial scaffolds- were effective in restoring cardiac function post-MI, and pericardial scaffolds showed better structural integrity and recolonization capability.

Current advanced therapy cell-based medicinal products for type-1-diabetes treatment

In the XXI century diabetes mellitus has become one of the main threats to human health with higher incidence in regions such as Europe and North America. Type 1 diabetes mellitus (T1DM) occurs as a consequence of the immune-mediated destruction of insulin producing β-cells located in the endocrine part of the pancreas, the islets of Langerhans. The administration of exogenous insulin through daily injections is the most prominent treatment for T1DM but its administration is frequently associated to failure in glucose metabolism control, finally leading to hyperglycemia episodes. Other approaches have been developed in the past decades, such as whole pancreas and islet allotransplantation, but they are restricted to patients who exhibit frequent episodes of hypoglycemia or renal failure because the lack of donors and islet survival. Moreover, patients transplanted with either whole pancreas or islets require of immune suppression to avoid the rejection of the transplant. Currently, advanced therapy medicinal products (ATMP), such as implantable devices, have been developed in order to reduce immune rejection response while increasing cell survival. To overcome these issues, ATMPs must promote vascularization, guaranteeing the nutritional contribution, while providing O₂ until vasculature can surround the device. Moreover, it should help in the immune-protection to avoid acute and chronic rejection. The transplanted cells or islets should be embedded within biomaterials with tunable properties like injectability, stiffness and porosity mimicking natural ECM structural characteristics. And finally, an infinitive cell source that solves the donor scarcity should be found such as insulin producing cells derived from mesenchymal stem cells (MSCs), embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Several companies have registered their ATMPs and future studies envision new prototypes. In this review, we will discuss the mechanisms and etiology of diabetes, comparing the clinical trials in the last decades in order to define the main characteristics for future ATMPs.

Gene expression profiles of glucose toxicity-exposed islet microvascular endothelial cells

OBJECTIVE

Islet microcirculation is mainly composed by IMECs. The aim of the study was to investigate the differences in gene expression profiles of IMECs upon glucose toxicity exposure and insulin treatment.

METHODS

IMECs were treated with 5.6 mmol L^-1 glucose, 35 mmol L^-1 glucose, and 35 mmol L^-1 glucose plus 10^-8  mol L^-1 insulin, respectively. Gene expression profiles were determined by microarray and verified by qPCR. GO terms and KEGG analysis were performed to assess the potential roles of differentially expressed genes. The interaction and expression tendency of differentially expressed genes were analyzed by Path-Net algorithm.

RESULTS

Compared with glucose toxicity-exposed IMECs, 1574 mRNAs in control group and 2870 mRNAs in insulin-treated IMECs were identified with differential expression, respectively. GO and KEGG pathway analysis revealed that these genes conferred roles in regulation of apoptosis, proliferation, migration, adhesion, and metabolic process etc. Additionally, MAPK signaling pathway and apoptosis were the dominant nodes in Path-Net. IMECs survival and function pathways were significantly changed, and the expression tendency of genes from euglycemia and glucose toxicity exposure to insulin treatment was revealed and enriched in 7 patterns.

CONCLUSIONS

Our study provides a microcirculatory framework for gene expression profiles of glucose toxicity-exposed IMECs.

Rapid fabrication of functionalised poly(dimethylsiloxane) microwells for cell aggregate formation

Cell aggregates reproduce many features of the natural architecture of functional tissues, and have therefore become an important in vitro model of tissue function. In this study, we present an efficient and rapid method for the fabrication of site specific functionalised poly(dimethylsiloxane) (PDMS) microwell arrays that promote the formation of insulin-producing beta cell (MIN6) aggregates. Microwells were prepared using an ice templating technique whereby aqueous droplets were frozen on a surface and PDMS was cast on top to form a replica. By employing an aqueous alkali hydroxide solution, we demonstrate exclusive etching and functionalisation of the microwell inner surface, thereby allowing the selective absorption of biological factors within the microwells. Additionally, by manipulating surface wettability of the substrate through plasma polymer coating, the shape and profile of the microwells could be tailored. Microwells coated with antifouling Pluronic 123, bovine serum albumin, collagen type IV or insulin growth factor 2 were employed to investigate the formation and stability of MIN6 aggregates in microwells of different shapes. MIN6 aggregates formed with this technique retained insulin expression. These results demonstrate the potential of this platform for the rapid screening of biological factors influencing the formation and response of insulin-producing cell aggregates without the need for expensive micromachining techniques.

Collagen type VI interaction improves human islet survival in immunoisolating microcapsules for treatment of diabetes

Collagens are the most abundant fibrous protein in the human body and constitute the main structural element of the extracellular matrix. It provides mechanical and physiological support for cells. In the pancreas, collagen VI content is more than double that of collagen I or IV. It is a major component of the islet-exocrine interface and could be involved in islet-cell survival. To test the impact of collagen VI on human encapsulated pancreatic islets-cells, we tested the effects of exogenous collagen type VI on in vitro functional survival of alginate encapsulated human islet-cells. Concentrations tested ranged from 0.1 to 50 µg/ml. Islets in capsules without collagen type VI served as control. Islet-cell interaction with collagen type VI at concentrations of 0.1 and 10 µg/ml, promoted islet-cell viability (p<0.05). Although no improvement in glucose induced insulin secretion (GSIS) was observed, islets in capsules without incorporation of collagen type VI showed more dysfunction and oxygen consumption rates was improved by inclusion of collagen type VI. Our results demonstrate that incorporation of collagen type VI in immunoisolated human islets supports in vitro viability and survival of human pancreatic islets.

Transcriptomic Analysis Reveals Novel Mechanisms Mediating Islet Dysfunction in the Intrauterine Growth-Restricted Rat

Intrauterine growth restriction (IUGR) increases the risk of type 2 diabetes developing in adulthood. In previous studies that used bilateral uterine artery ligation in a rat model of IUGR, age-associated decline in glucose homeostasis and islet function was revealed. To elucidate mechanisms contributing to IUGR pathogenesis, the islet transcriptome was sequenced from 2-week-old rats, when in vivo glucose tolerance is mildly impaired, and at 10 weeks of age, when rats are hyperglycemic and have reduced β-cell mass. RNA sequencing and functional annotation with Ingenuity Pathway Analysis revealed temporal changes in IUGR islets. For instance, gene expression involving amino acid metabolism was significantly reduced primarily at 2 weeks of age, but ion channel expression, specifically that involved in cell-volume regulation, was more disrupted in adult IUGR islets. Additionally, we observed alterations in the microenvironment of IUGR islets with extracellular matrix genes being significantly increased at 2 weeks of age and significantly decreased at 10 weeks. Specifically, hyaluronan synthase 2 expression and hyaluronan staining were increased in IUGR islets at 2 weeks of age (P < 0.05). Mesenchymal stromal cell-derived factors that have been shown to preserve islet allograft function, such as Anxa1, Cxcl12, and others, also were increased at 2 weeks and decreased in adult islets. Finally, comparisons of differentially expressed genes with those of type 2 diabetic human islets support a role for these pathways in human patients with diabetes. Together, these data point to new mechanisms in the pathogenesis of IUGR-mediated islet dysfunction in type 2 diabetes.

Integrative network analysis highlights biological processes underlying GLP-1 stimulated insulin secretion: A DIRECT study

Glucagon-like peptide 1 (GLP-1) stimulated insulin secretion has a considerable heritable component as estimated from twin studies, yet few genetic variants influencing this phenotype have been identified. We performed the first genome-wide association study (GWAS) of GLP-1 stimulated insulin secretion in non-diabetic individuals from the Netherlands Twin register (n = 126). This GWAS was enhanced using a tissue-specific protein-protein interaction network approach. We identified a beta-cell protein-protein interaction module that was significantly enriched for low gene scores based on the GWAS P-values and found support at the network level in an independent cohort from Tübingen, Germany (n = 100). Additionally, a polygenic risk score based on SNPs prioritized from the network was associated (P < 0.05) with glucose-stimulated insulin secretion phenotypes in up to 5,318 individuals in MAGIC cohorts. The network contains both known and novel genes in the context of insulin secretion and is enriched for members of the focal adhesion, extracellular-matrix receptor interaction, actin cytoskeleton regulation, Rap1 and PI3K-Akt signaling pathways. Adipose tissue is, like the beta-cell, one of the target tissues of GLP-1 and we thus hypothesized that similar networks might be functional in both tissues. In order to verify peripheral effects of GLP-1 stimulation, we compared the transcriptome profiling of ob/ob mice treated with liraglutide, a clinically used GLP-1 receptor agonist, versus baseline controls. Some of the upstream regulators of differentially expressed genes in the white adipose tissue of ob/ob mice were also detected in the human beta-cell network of genes associated with GLP-1 stimulated insulin secretion. The findings provide biological insight into the mechanisms through which the effects of GLP-1 may be modulated and highlight a potential role of the beta-cell expressed genes RYR2, GDI2, KIAA0232, COL4A1 and COL4A2 in GLP-1 stimulated insulin secretion.

3D Bioprinting for Artificial Pancreas Organ

Type 1 diabetes mellitus (T1DM) results from an autoimmune destruction of insulin-producing beta cells in the islet of the endocrine pancreas. Although islet transplantation has been regarded as an ideal strategy for T1D, transplanted islets are rejected from host immune system. To immunologically protect them, islet encapsulation technology with biocompatible materials is emerged as an immuno-barrier. However, this technology has been limited for clinical trial such as hypoxia in the central core of islet bead, impurity of islet bead and retrievability from the body. Recently, 3D bioprinting has been emerged as an alternative approach to make the artificial pancreas. It can be used to position live cells in a desired location with real scale of human organ. Furthermore, constructing a vascularization of the artificial pancreas is actualized with 3D bioprinting. Therefore, it is possible to create real pancreas-mimic artificial organ for clinical application. In conclusion, 3D bioprinting can become a new leader in the development of the artificial pancreas to overcome the existed islet.

Laminin and collagen IV inclusion in immunoisolating microcapsules reduces cytokine-mediated cell death in human pancreatic islets

Extracellular matrix (ECM) molecules have several functions in pancreatic islets, including provision of mechanical support and prevention of cytotoxicity during inflammation. During islet isolation, ECM connections are damaged, and are not restored after encapsulation and transplantation. Inclusion of specific combinations of collagen type IV and laminins in immunoisolating capsules can enhance survival of pancreatic islets. Here we investigated whether ECM can also enhance survival and lower susceptibility of human islets to cytokine-mediated cytotoxicity. To this end, human islets were encapsulated in alginate with collagen IV and either RGD, LRE or PDSGR, i.e. laminin sequences. Islets in capsules without ECM served as control. The encapsulated islets were exposed to IL-1β, IFN-γ and TNF-α for 24 and 72 h. All combinations of ECM improved the islet cell survival, and reduced necrosis and apoptosis after cytokine exposure (P < 0.01). Collagen IV-RGD and collagen IV-LRE reduced danger-associated molecular patterns (DAMPs) release from islets (P < 0.05). Moreover, collagen IV-RGD and collagen IV-PDSGR, but not collagen IV-LRE, reduced NO release from encapsulated human islets (P < 0.05). This reduction correlated with a higher oxygen consumption rate (OCR) of islets in capsules containing collagen IV-RGD and collagen IV-PDSGR. Islets in capsules with collagen IV-LRE showed more dysfunction, and OCR was not different from islets in control capsules without ECM. Our study demonstrates that incorporation of specific ECM molecules such as collagen type IV with the laminin sequences RGD and PDSGR in immunoisolated islets can protect against cytokine toxicity.

Signals in the pancreatic islet microenvironment influence β-cell proliferation

The progressive loss of pancreatic β-cell mass that occurs in both type 1 and type 2 diabetes is a primary factor driving efforts to identify strategies for effectively increasing, enhancing or restoring β-cell mass. While factors that seem to influence β-cell proliferation in specific contexts have been described, reliable stimulation of human β-cell proliferation has remained a challenge. Importantly, β-cells exist in the context of a complex, integrated pancreatic islet microenvironment where they interact with other endocrine cells, vascular endothelial cells, extracellular matrix, neuronal projections and islet macrophages. This review highlights different components of the pancreatic microenvironment, and reviews what is known about how signaling that occurs between β-cells and these other components influences β-cell proliferation. Future efforts to further define the role of the pancreatic islet microenvironment on β-cell proliferation may lead to the development of successful approaches to increase or restore β-cell mass in diabetes.

Antibodies to post-translationally modified insulin as a novel biomarker for prediction of type 1 diabetes in children

AIMS/HYPOTHESIS

We have shown that autoimmunity to insulin in type 1 diabetes may result from neoepitopes induced by oxidative post-translational modifications (oxPTM). Antibodies specific to oxPTM-insulin (oxPTM-INS-Ab) are present in most newly diagnosed individuals with type 1 diabetes and are more common than autoantibodies to native insulin. In this study, we investigated whether oxPTM-INS-Ab are present before clinical onset of type 1 diabetes, and evaluated the ability of oxPTM-INS-Ab to identify children progressing to type 1 diabetes.

METHODS

We used serum samples collected longitudinally from the 'All Babies in Southeast Sweden (ABIS)' cohort tested for the gold standard islet autoantibodies to insulin (IAA), GAD (GADA), tyrosine phosphatase 2 (IA-2A) and zinc transporter 8 (ZnT8A). We studied 23 children who progressed to type 1 diabetes (progr-T1D) and 63 children who did not progress to type 1 diabetes (NP) after a median follow-up of 10.8 years (interquartile range 7.7-12.8). Of the latter group, 32 were positive for one or more islet autoantibodies (NP-AAB⁺). oxPTM-INS-Ab to insulin modified by ^•OH or HOCl were measured by our developed ELISA platform.

RESULTS

Antibodies to at least one oxPTM-INS were present in 91.3% of progr-T1D children. oxPTM-INS-Ab co-existed with GADA, IA-2A, IAA or ZnT8A in 65.2%, 56.5%, 38.9% and 33.3% progr-T1D children, respectively. In addition, oxPTM-INS-Ab were present in 17.4%, 26.1%, 38.9% and 41.6% of progr-T1D children who were negative for GADA, IA-2A, IAA and ZnT8A, respectively. ^•OH-INS-Ab were more common in progr-T1D children than in NP-AAB⁺ children (82.6% vs 19%; p < 0.001) and allowed discrimination between progr-T1D and NP-AAB⁺ children with 74% sensitivity and 91% specificity. None of the NP-AAB^- children were positive for oxPTM-INS-Ab.

CONCLUSIONS/INTERPRETATION

oxPTM-INS-Ab are present before the clinical onset of type 1 diabetes and can identify children progressing to type 1 diabetes.

Critical role of β1 integrin in postnatal beta-cell function and expansion

β1 integrin is essential for pancreatic beta-cell development and maintenance in rodents and humans. However, the effects of a temporal beta-cell specific β1 integrin knockout on adult islet function are unknown. We utilized a mouse insulin 1 promoter driven tamoxifen-inducible Cre-recombinase β1 integrin knockout mouse model (MIPβ1KO) to investigate β1 integrin function in adult pancreatic beta-cells. Adult male MIPβ1KO mice were significantly glucose intolerant due to impaired glucose-stimulated insulin secretion in vivo and ex vivo at 8 weeks post-tamoxifen. The expression of Insulin and Pancreatic and duodenal homeobox-1 mRNA was significantly reduced in MIPβ1KO islets, along with reductions in insulin exocytotic proteins. Morphological analyses demonstrated that beta-cell mass, islet density, and the number of large-sized islets was significantly reduced in male MIPβ1KO mice. Significant reductions in the phosphorylation of signaling molecules focal adhesion kinase, extracellular signal-regulated kinases 1 and 2, and v-Akt murine thymoma viral oncogene were observed in male MIPβ1KO islets when compared to controls. MIPβ1KO islets displayed a significant increase in protein levels of the apoptotic marker cleaved-Poly (ADP-ribose) polymerase and a reduction of the cell cycle marker cyclin D1. Female MIPβ1KO mice did not develop glucose intolerance or reduced beta-cell mass until 16 weeks post-tamoxifen. Glucose intolerance remained in both genders of aged MIPβ1KO mice. This data demonstrates that β1 integrin is required for the maintenance of glucose homeostasis through postnatal beta-cell function and expansion.

Intra-islet endothelial cell and β-cell crosstalk: Implication for islet cell transplantation

The intra-islet microvasculature is a critical interface between the blood and islet endocrine cells governing a number of cellular and pathophysiological processes associated with the pancreatic tissue. A growing body of evidence indicates a strong functional and physical interdependency of β-cells with endothelial cells (ECs), the building blocks of islet microvasculature. Intra-islet ECs, actively regulate vascular permeability and appear to play a role in fine-tuning blood glucose sensing and regulation. These cells also tend to behave as “guardians”, controlling the expression and movement of a number of important immune mediators, thereby strongly contributing to the physiology of islets. This review will focus on the molecular signalling and crosstalk between the intra-islet ECs and β-cells and how their relationship can be a potential target for intervention strategies in islet pathology and islet transplantation.

Individual Variation in Conditional β Cell Ablation Mice Contributes Significant Biases in Evaluating β Cell Functional Recovery

Despite the βDTA (Ins2-rtTA; Tet-DTA) mice have been developed as a valuable tool to study β cell regeneration, their individual variation in therapeutic efficacy has not been characterized. Here, we demonstrated that the βDTA mice exhibited significant variations in both spontaneous and acquired β cell regeneration. We found that doxycycline (DOX)-induced β cell death was sufficient to cause polydipsia, translating even subtle difference in drinking habit into large variations in actual DOX intake among individuals within the same group. Accumulating evidence shows that transient expression of VEGF_A enhances β cell functional recovery after injury. Therefore, we utilized the chemically modified mRNA (modRNA) technology to enable transient yet efficient VEGF_A expression in the pancreas after DOX-induced β cell death. Surprisingly, under optimized DOX dose permissive of β cell regeneration, VEGF_A modRNA only demonstrated marginal benefits on β cell functional recovery with large individual variations. We also revealed that the therapeutic efficacy of VEGF_A modRNA on β cell regeneration was dependent on the degree of β cell loss induced by the accumulated DOX intake. Therefore, our results highlight a significant contribution of individual variation in the βDTA model and call for attention in evaluating potential efficacy of therapeutic agents in β cell regeneration studies.

Insight into microenvironment remodeling in pancreatic endocrine tissue engineering: Biological and biomaterial approaches

The treatment of diabetes mellitus, as a chronic and complicated disease, is a valuable purpose. Islet transplantation can provide metabolic stability and insulin independence in type 1 diabetes patients. Diet and insulin therapy are only diabetes controllers and cannot remove all of the diabetes complications. Moreover, islet transplantation is more promising treatment than whole pancreas transplantation because of lesser invasive surgical procedure and morbidity and mortality. According to the importance of extracellular matrix for islet viability and function, microenvironment remodeling of pancreatic endocrine tissue can lead to more success in diabetes treatment by pancreatic islets. Production of bioengineered pancreas and remodeling of pancreas extracellular matrix provide essential microenvironment for re-vascularization, re-innervation and signaling cascades triggering. Therefore, islets show better viability and function in these conditions. Researchers conduct various scaffolds with different biomaterials for the improvement of islet viability, function and transplantation outcome. The attention to normal pancreas anatomy, embryology and histology is critical to understand the pancreatic Langerhans islets niche and finally to achieve efficient engineered structure. Therefore, in the present study, the status and components of the islets niche is mentioned and fundamental issues related to the tissue engineering of this structure is considered. The purpose of this review article is summarization of recent progress in the endocrine pancreas tissue engineering and biomaterials and biological aspects of it.

Extracellular matrix components supporting human islet function in alginate-based immunoprotective microcapsules for treatment of diabetes

In the pancreas, extracellular matrix (ECM) components play an import role in providing mechanical and physiological support, and also contribute to the function of islets. These ECM-connections are damaged during islet-isolation from the pancreas and are not fully recovered after encapsulation and transplantation. To promote the functional survival of human pancreatic islets, we tested different ECMs molecules in alginate-encapsulated human islets. These were laminin derived recognition sequences, IKVAV, RGD, LRE, PDSGR, collagen I sequence DGEA (0.01 - 1.0 mM), and collagen IV (50 - 200 µg/mL). Interaction with RGD and PDSGR promoted islet viability and glucose induced insulin secretion (GIIS) when it was applied at concentrations ranging from 0.01 - 1.0 mM (p < 0.05). Also the laminin sequence LRE contributed to enhanced GIIS but only at higher concentrations of 1 mM (p < 0.05). Collagen IV also had beneficial effects but only at 50 µg/ml and no further improvement was observed at higher concentrations. IKVAV and DGEA had no effects on human islets. Synergistic effects were observed by adding Collagen(IV)-RGD, Collagen(IV)-LRE, and Collagen(IV)-PDSGR to encapsulated human islets. Our results demonstrate the potential of specific ECM components in support of functional survival of human encapsulated and free islet grafts. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1788-1796, 2016.

Accelerated Maturation of Human Stem Cell-Derived Pancreatic Progenitor Cells into Insulin-Secreting Cells in Immunodeficient Rats Relative to Mice

Pluripotent human embryonic stem cells (hESCs) are a potential source of transplantable cells for treating patients with diabetes. To investigate the impact of the host recipient on hESC-derived pancreatic progenitor cell maturation, cells were transplanted into immunodeficient SCID-beige mice or nude rats. Following the transplant, basal human C-peptide levels were consistently higher in mice compared with rats, but only rats showed robust meal- and glucose-responsive human C-peptide secretion by 19-21 weeks. Grafts from rats contained a higher proportion of insulin:glucagon immunoreactivity, fewer exocrine cells, and improved expression of mature β cell markers compared with mice. Moreover, ECM-related genes were enriched, the collagen network was denser, and blood vessels were more intricately integrated into the engrafted endocrine tissue in rats relative to mice. Overall, hESC-derived pancreatic progenitor cells matured faster in nude rats compared with SCID-beige mice, indicating that the host recipient can greatly influence the fate of immature pancreatic progenitor cells post-transplantation.

Antiaging Gene Klotho Attenuates Pancreatic β-Cell Apoptosis in Type 1 Diabetes

Apoptosis is the major cause of death of insulin-producing β-cells in type 1 diabetes mellitus (T1DM). Klotho is a recently discovered antiaging gene. We found that the Klotho gene is expressed in pancreatic β-cells. Interestingly, halplodeficiency of Klotho (KL(+/-)) exacerbated streptozotocin (STZ)-induced diabetes (a model of T1DM), including hyperglycemia, glucose intolerance, diminished islet insulin storage, and increased apoptotic β-cells. Conversely, in vivo β-cell-specific expression of mouse Klotho gene (mKL) attenuated β-cell apoptosis and prevented STZ-induced diabetes. mKL promoted cell adhesion to collagen IV, increased FAK and Akt phosphorylation, and inhibited caspase 3 cleavage in cultured MIN6 β-cells. mKL abolished STZ- and TNFα-induced inhibition of FAK and Akt phosphorylation, caspase 3 cleavage, and β-cell apoptosis. These promoting effects of Klotho can be abolished by blocking integrin β1. Therefore, these cell-based studies indicated that Klotho protected β-cells by inhibiting β-cell apoptosis through activation of the integrin β1-FAK/Akt pathway, leading to inhibition of caspase 3 cleavage. In an autoimmune T1DM model (NOD), we showed that in vivo β-cell-specific expression of mKL improved glucose tolerance, attenuated β-cell apoptosis, enhanced insulin storage in β-cells, and increased plasma insulin levels. The beneficial effect of Klotho gene delivery is likely due to attenuation of T-cell infiltration in pancreatic islets in NOD mice. Overall, our results demonstrate for the first time that Klotho protected β-cells in T1DM via attenuating apoptosis.

Culture of hESC-derived pancreatic progenitors in alginate-based scaffolds

The effect of alginate-based scaffolds with added basement membrane proteins on the in vitro development of hESC-derived pancreatic progenitors was investigated. Cell clusters were encapsulated in scaffolds containing the basement membrane proteins collagen IV, laminin, fibronectin, or extracellular matrix-derived peptides, and maintained in culture for up to 46 days. The cells remained viable throughout the experiment with no signs of central necrosis. Whereas nonencapsulated cells aggregated into larger clusters, some of which showed signs of morphological changes and tissue organization, the alginate matrix stabilized the cluster size and displayed more homogeneous cell morphologies, allowing culture for long periods of time. For all conditions tested, a stable or declining expression of insulin and PDX1 and an increase in glucagon and somatostatin over time indicated a progressive reduction in beta cell-related gene expression. Alginate scaffolds can provide a chemically defined, xeno-free and easily scalable alternative for culture of pancreatic progenitors. Although no increase in insulin and PDX1 gene expression after alginate-immobilized cell culture was seen in this study, further optimization of the matrix physicochemical and biological properties and of the medium composition may still be a relevant strategy to promote the stabilization or maturation of stem cell-derived beta cells.

Extracellular Matrix and Growth Factors Improve the Efficacy of Intramuscular Islet Transplantation

Background

The efficacy of intramuscular islet transplantation is poor despite being technically simple, safe, and associated with reduced rates of severe complications. We evaluated the efficacy of combined treatment with extracellular matrix (ECM) and growth factors in intramuscular islet transplantation.

Methods

Male BALB/C mice were used for the in vitro and transplantation studies. The following three groups were evaluated: islets without treatment (islets-only group), islets embedded in ECM with growth factors (Matrigel group), and islets embedded in ECM without growth factors [growth factor-reduced (GFR) Matrigel group]. The viability and insulin-releasing function of islets cultured for 96 h were significantly improved in Matrigel and GFR Matrigel groups compared with the islets-only group.

Results

Blood glucose and serum insulin levels immediately following transplantation were significantly improved in the Matrigel and GFR Matrigel groups and remained significantly improved in the Matrigel group at postoperative day (POD) 28. On histological examination, significantly decreased numbers of TdT-mediated deoxyuridine triphosphate-biotin nick end labeling-positive islet cells and significantly increased numbers of Ki67-positive cells were observed in the Matrigel and GFR Matrigel groups at POD 3. Peri-islet revascularization was most prominent in the Matrigel group at POD 14.

Conclusions

The efficacy of intramuscular islet transplantation was improved by combination treatment with ECM and growth factors through the inhibition of apoptosis, increased proliferation of islet cells, and promotion of revascularization.

Increased Insulin Secretion from Insulin-Secreting Cells by Construction of Mixed Multicellular Spheroids

PURPOSE

We previously have shown that multicellular spheroids containing insulin-secreting cells are an effective therapy for diabetic mice. Here we attempted to increase insulin secretion by incorporating other cell types into spheroids.

MATERIALS AND METHODS

Multicellular spheroids of mouse MIN6 pancreatic β cells were formed in microwells alone and with aortic vascular endothelial MAEC cells or embryo fibroblast NIH3T3 cells. mRNA expression of insulin genes and insulin secretion of MIN6 cells in each spheroid were measured by real-time PCR and an insulin ELIZA kit. Moreover, collagen IV expression in each spheroid was analyzed by western blot.

RESULTS

In all cases, uniformly sized (about 300 μm) multicellular spheroids were obtained. MAEC or NIH3T3 cell incorporation into MIN6 spheroids significantly increased mRNA expression of insulin genes and insulin secretion. In addition, collagen IV expression, which was reported to enhance insulin secretion from pancreatic β cells, also increased in their spheroids.

CONCLUSIONS

The formation of mixed multicellular spheroids containing collagen IV-expressing cells can improve the insulin secretion from insulin-secreting MIN6 cells, and mixed multicellular spheroids can be a potent therapeutic option for patients with type I diabetes mellitus.

Controlling the blood glucose of type 1 diabetes mice by co-culturing MIN-6 β cells on 3D scaffold

T1D is an autoimmune disease, which may be caused by lack of insulin-secreting β cells due to damage of autoimmune system. Living with T1D is a challenge for the child and the family; cell transplantation is a treatment option for diabetes in children. To establish a microenvironment suitable for cell growth and proliferation as well as for sustained cellular function, we used MIN-6 β cells as seed cells and SF-IV collagen as a 3D composite scaffold to construct artificial pancreas in this experiment. The cell viabilities were determined by MTT assay, and the response of cells to different glucose concentrations was observed by glucose stimulation test. Artificial pancreas was transplanted into the abdominal cavity of T1D mice, and the changes of blood glucose were monitored. After 10 days, insulin expression was detected by immunohistochemical method, and the claybank stained area showed effectiveness of insulin secretion. A series of experiments showed that implantation of 3D cell scaffold into the abdominal cavity can effectively control the blood glucose level of T1D mice. It also had longer-lasting hypoglycemic effects than simple cell transplantation, which was expected to become a new method for the treatment of T1D.

Three-dimensional culture of mouse pancreatic islet on a liver-derived perfusion-decellularized bioscaffold for potential clinical application

The cutting-edge technology of three-dimensional liver decellularized bioscaffold has a potential to provide a microenvironment that is suitable for the resident cells and even develop a new functional organ. Liver decellularized bioscaffold preserved the native extracellular matrix and three-dimensional architecture in support of the cell culture. The goal of this study was to discover if three-dimensional extracellular matrix derived from mouse liver could facilitate the growth and maintenance of physiological functions of mouse isolated islets. We generated a whole organ liver decellularized bioscaffold which could successfully preserve extracellular matrix proteins and the native vascular channels using 1% Triton X-100/0.1% ammonium protocol. To evaluate the potential of decellularized liver as a scaffold for islets transplantation, the liver decellularized bioscaffold was infused with mouse primary pancreatic islets which were obtained through Collagenase P digestion protocol. Its yield, morphology, and quality were estimated by microscopic analysis, dithizone staining, insulin immunofluorescence and glucose stimulation experiments. Comparing the three-dimensional culture in liver decellularized bioscaffold with the orthodoxy two-dimensional plate culture, hematoxylin-eosin staining, immunohistochemistry, and insulin gene expression were tested. Our results demonstrated that the liver decellularized bioscaffold could support cellular culture and maintenance of cell functions. In contrast with the conventional two-dimensional culture, three-dimensional culture system could give rise to an up-regulated insulin gene expression. These findings demonstrated that the liver bioscaffold by a perfusion-decellularized technique could serve as a platform to support the survival and function of the pancreatic islets in vitro. Meanwhile three-dimensional culture system had a superior role in contrast with the two-dimensional culture. This study advanced the field of regenerative medicine towards the development of a liver decellularized bioscaffold capable of forming a neo-organ and could be used as potential clinical application.

Endothelium-derived essential signals involved in pancreas organogenesis

Endothelial cells (ECs) are essential for pancreas differentiation, endocrine specification, and endocrine function. They are also involved in the physiopathology of type 1 and type 2 diabetes. During embryogenesis, aortic ECs provide specific factors that maintain the expression of key genes for pancreas development such as pancreatic and duodenal homeobox-1. Other unknown factors are also important for pancreatic endocrine specification and formation of insulin-producing beta cells. Endocrine precursors proliferate interspersed with ductal cells and exocrine precursors and, at some point of development, these endocrine precursors migrate to pancreatic mesenchyme and start forming the islets of Langerhans. By the end of the gestation and close to birth, these islets contain immature beta cells with the capacity to express vascular endothelial growth factor and therefore to recruit ECs from the surrounding microenvironment. ECs in turn produce factors that are essential to maintain insulin secretion in pancreatic beta cells. Once assembled, a cross talk between endocrine cells and ECs maintain the integrity of islets toward an adequate function during the whole life of the adult individual. This review will focus in the EC role in the differentiation and maturation of pancreatic beta cells during embryogenesis as well as the current knowledge about the involvement of endothelium to derive pancreatic beta cells in vitro from mouse or human pluripotent stem cells.

Islet Endothelial Cells Induce Glycosylation and Increase Cell-surface Expression of Integrin β1 in β Cells

The co-culturing of insulinoma and islet-derived endothelial cell (iEC) lines results in the spontaneous formation of free-floating pseudoislets (PIs). We previously showed that iEC-induced PIs display improved insulin expression and secretion in response to glucose stimulation. This improvement was associated with a de novo deposition of extracellular matrix (ECM) proteins by iECs in and around the PIs. Here, iEC-induced PIs were used to study the expression and posttranslational modification of the ECM receptor integrin β1. A wide array of integrin β subunits was detected in βTC3 and NIT-1 insulinomas as well as in primary islets, with integrin β1 mRNA and protein detected in all three cell types. Interestingly, the formation of iEC-induced PIs altered the glycosylation patterns of integrin β1, resulting in a higher molecular weight form of the receptor. This form was found in native pancreas but was completely absent in monolayer β-cells. Fluorescence-activated cell sorting analysis of monolayers and PIs revealed a higher expression of integrin β1 in PIs. Antibody-mediated blocking of integrin β1 led to alterations in β-cell morphology, reduced insulin gene expression, and enhanced glucose secretion under baseline conditions. These results suggest that iEC-induced PI formation may alter integrin β1 expression and posttranslational modification by enhancing glycosylation, thereby providing a more physiological culture system for studying integrin-ECM interactions in β cells.

Islet Endothelial Cells Derived From Mouse Embryonic Stem Cells

The islet endothelium comprises a specialized population of islet endothelial cells (IECs) expressing unique markers such as nephrin and α-1 antitrypsin (AAT) that are not found in endothelial cells in surrounding tissues. However, due to difficulties in isolating and maintaining a pure population of these cells, the information on these islet-specific cells is currently very limited. Interestingly, we have identified a large subpopulation of endothelial cells exhibiting IEC phenotype, while deriving insulin-producing cells from mouse embryonic stem cells (mESCs). These cells were identified by the uptake of low-density lipoprotein (LDL) and were successfully isolated and subsequently expanded in endothelial cell culture medium. Further analysis demonstrated that the mouse embryonic stem cell-derived endothelial cells (mESC-ECs) not only express classical endothelial markers, such as platelet endothelial cell adhesion molecule (PECAM1), thrombomodulin, intercellular adhesion molecule-1 (ICAM-1), and endothelial nitric oxide synthase (eNOS) but also IEC-specific markers such as nephrin and AAT. Moreover, mESC-ECs secrete basement membrane proteins such as collagen type IV, laminin, and fibronectin in culture and form tubular networks on a layer of Matrigel, demonstrating angiogenic activity. Further, mESC-ECs not only express eNOS, but also its eNOS expression is glucose dependent, which is another characteristic phenotype of IECs. With the ability to obtain highly purified IECs derived from pluripotent stem cells, it is possible to closely examine the function of these cells and their interaction with pancreatic β-cells during development and maturation in vitro. Further characterization of tissue-specific endothelial cell properties may enhance our ability to formulate new therapeutic angiogenic approaches for diabetes.

Impact of an autologous oxygenating matrix culture system on rat islet transplantation outcome

Disruption of the pancreatic islet environment combined with the decrease in oxygen supply that occurs during isolation leads to poor islet survival. The aim of this study was to validate the benefit of using a plasma-based scaffold supplemented with perfluorodecalin to improve islet transplantation outcome. Rat islets were cultured in three conditions: i) control group, ii) plasma based-matrix (P-matrix), and iii) P-matrix supplemented with emulsified perfluorodecalin. After 24 h culture, matrix/cell contacts (Integrinβ1, p-FAK/FAK, p-Akt/Akt), survival (caspase 3, TUNEL, FDA/PI), function, and HIF-1α translocation were assessed. Afterwards, P-matrices were dissolved and the islets were intraportally transplanted. Graft function was monitored for 31 days with glycaemia and C-peptide follow up. Inflammation was assessed by histology (macrophage and granulocyte staining) and thrombin/anti-thrombin complex measurement. Islet survival correlated with an increase in integrin, FAK, and Akt activation in P-matrices and function was maintained. Perfluorodecalin supplementation decreased translocation of HIF-1α in the nucleus and post-transplantation islet structure was better preserved in P-matrices, but a quicker activation of IBMIR resulted in early loss of graft function. "Oxygenating" P-matrices provided a real benefit to islet survival and resistance in vivo. However, intraportal transplantation is not suitable for this kind of culture due to IBMIR; thus, alternative sites must be explored.

Engineering of microscale three-dimensional pancreatic islet models in vitro and their biomedical applications

Diabetes now is the most common chronic disease in the world inducing heavy burden for the people's health. Based on this, diabetes research such as islet function has become a hot topic in medical institutes of the world. Today, in medical institutes, the conventional experiment platform in vitro is monolayer cell culture. However, with the development of micro- and nano-technologies, several microengineering methods have been developed to fabricate three-dimensional (3D) islet models in vitro which can better mimic the islet of pancreases in vivo. These in vitro islet models have shown better cell function than monolayer cells, indicating their great potential as better experimental platforms to elucidate islet behaviors under both physiological and pathological conditions, such as the molecular mechanisms of diabetes and clinical islet transplantation. In this review, we present the state-of-the-art advances in the microengineering methods for fabricating microscale islet models in vitro. We hope this will help researchers to better understand the progress in the engineering 3D islet models and their biomedical applications such as drug screening and islet transplantation.

Evaluation of islets derived from human fetal pancreatic progenitor cells in diabetes treatment

Introduction

With the shortage of donor organs for islet transplantation, insulin-producing cells have been generated from different types of stem cell. Human fetal pancreatic stem cells have a better self-renewal capacity than adult stem cells and can readily differentiate into pancreatic endocrine cells, making them a potential source for islets in diabetes treatment. In the present study, the functions of pancreatic islets derived from human fetal pancreatic progenitor cells were evaluated in vitro and in vivo.

Methods

Human pancreatic progenitor cells isolated from the fetal pancreas were expanded and differentiated into islet endocrine cells in culture. Markers for endocrine and exocrine functions as well as those for alpha and beta cells were analyzed by immunofluorescent staining and enzyme-linked immunosorbent assay (ELISA). To evaluate the functions of these islets in vivo, the islet-like structures were transplanted into renal capsules of diabetic nude mice. Immunohistochemical staining for human C-peptide and human mitochondrion antigen was applied to confirm the human origin and the survival of grafted islets.

Results

Human fetal pancreatic progenitor cells were able to expand in medium containing basic fibroblast growth factor (bFGF) and leukemia inhibitor factor (LIF), and to differentiate into pancreatic endocrine cells with high efficiency upon the actions of glucagon-like peptide-1 and activin-A. The differentiated cells expressed insulin, glucagon, glucose transporter-1 (GLUT1), GLUT2 and voltage-dependent calcium channel (VDCC), and were able to aggregate into islet-like structures containing alpha and beta cells upon suspension. These structures expressed and released a higher level of insulin than adhesion cultured cells, and helped to maintain normoglycemia in diabetic nude mice after transplantation.

Conclusions

Human fetal pancreatic progenitor cells have good capacity for generating insulin producing cells and provide a promising potential source for diabetes treatment.

Tissue engineering approaches to cell-based type 1 diabetes therapy

Type 1 diabetes mellitus is an autoimmune disease resulting from the destruction of insulin-producing pancreatic β-cells. Cell-based therapies, involving the transplantation of functional β-cells into diabetic patients, have been explored as a potential long-term treatment for this condition; however, success is limited. A tissue engineering approach of culturing insulin-producing cells with extracellular matrix (ECM) molecules in three-dimensional (3D) constructs has the potential to enhance the efficacy of cell-based therapies for diabetes. When cultured in 3D environments, insulin-producing cells are often more viable and secrete more insulin than those in two dimensions. The addition of ECM molecules to the culture environments, depending on the specific type of molecule, can further enhance the viability and insulin secretion. This review addresses the different cell sources that can be utilized as β-cell replacements, the essential ECM molecules for the survival of these cells, and the 3D culture techniques that have been used to benefit cell function.

Therapeutic cell encapsulation techniques and applications in diabetes

The encapsulation of therapeutic cells permits the implantation of allogeneic and xenogeneic cells for the regulation of certain physiological processes damaged by the death or senescence of host tissues. The encapsulation of pancreatic cells for the treatment of diabetes is emphasized; however, many of the techniques are applicable to a wide array of mammalian cell applications. The summary of both established and novel encapsulation techniques, clinical trials, and commercial product developments highlights the metered but steady pace of therapeutic cell encapsulation towards implementation.

Short-term overexpression of VEGF-A in mouse beta cells indirectly stimulates their proliferation and protects against diabetes

AIMS/HYPOTHESIS

Vascular endothelial growth factor (VEGF) has been recognised by loss-of-function experiments as a pleiotropic factor with importance in embryonic pancreas development and postnatal beta cell function. Chronic, nonconditional overexpression of VEGF-A has a deleterious effect on beta cell development and function. We report, for the first time, a conditional gain-of-function study to evaluate the effect of transient VEGF-A overexpression by adult pancreatic beta cells on islet vasculature and beta cell proliferation and survival, under both normal physiological and injury conditions.

METHODS

In a transgenicmouse strain, overexpressing VEGF-A in a doxycycline-inducible and beta cell-specific manner, we evaluated the ability of VEGF-A to affect islet vessel density, beta cell proliferation and protection of the adult beta cell mass from toxin-induced injury.

RESULTS

Short-term VEGF-A overexpression resulted in islet hypervascularisation, increased beta cell proliferation and protection from toxin-mediated beta cell death, and thereby prevented the development of hyperglycaemia. Extended overexpression of VEGF-A led to impaired glucose tolerance, elevated fasting glycaemia and a decreased beta cell mass.

CONCLUSIONS/INTERPRETATION

Overexpression of VEGF-A in beta cells time-dependently affects glycometabolic control and beta cell protection and proliferation. These data nourish further studies to examine the role of controlled VEGF delivery in (pre)clinical applications aimed at protecting and/or restoring the injured beta cell mass.

The endocrine role between β cells and intra-islet endothelial cells

The islets of Langerhans is the endocrine function region of pancreas, which exist in five cell types. The majority of endocrine cells are insulin-secreting β cells, mixed up with glucagon-secreting α-cells. The islets of Langerhans are highly vascularized, and the capillary network around the islet is about five times denser than that in the exocrine tissues. It guarantees endocrine cells adequately contact with the capillary networks. Above mentioned is the basis of deep study the interaction between β cells and capillary. Increasing number of studies contribute to the consensus that endothelial cells have positive effects in the islet microenvironment. Endothelial cells can act as endocrine cells which release many active substances, such as hepatocyte growth factors (HGF), thrombospondin-1(TSP-1), laminins, and collagens by means of different molecule pathways, inducing β cells differentiation, proliferation, survivor, and insulin release next to the vessels. Apart from the effect of endothelial cells on β cells by paracrine fashion, the islets can utilize VEGF-A, angiopoietin-1 and insulin signaling to increase the interaction with endothelial cells. As the endocrine role of endothelial cells to β cells, it may be a novel target to stimulate β cells regeneration, promote vascularization post islet transplantation strategy in the treatment of diabetes mellitus.

Conditional hypovascularization and hypoxia in islets do not overtly influence adult β-cell mass or function

It is generally accepted that vascularization and oxygenation of pancreatic islets are essential for the maintenance of an optimal β-cell mass and function and that signaling by vascular endothelial growth factor (VEGF) is crucial for pancreas development, insulin gene expression/secretion, and (compensatory) β-cell proliferation. A novel mouse model was designed to allow conditional production of human sFlt1 by β-cells in order to trap VEGF and study the effect of time-dependent inhibition of VEGF signaling on adult β-cell fate and metabolism. Secretion of sFlt1 by adult β-cells resulted in a rapid regression of blood vessels and hypoxia within the islets. Besides blunted insulin release, β-cells displayed a remarkable capacity for coping with these presumed unfavorable conditions: even after prolonged periods of blood vessel ablation, basal and stimulated blood glucose levels were only slightly increased, while β-cell proliferation and mass remained unaffected. Moreover, ablation of blood vessels did not prevent β-cell generation after severe pancreas injury by partial pancreatic duct ligation or partial pancreatectomy. Our data thus argue against a major role of blood vessels to preserve adult β-cell generation and function, restricting their importance to facilitating rapid and adequate insulin delivery.

SEL1L regulates adhesion, proliferation and secretion of insulin by affecting integrin signaling

SEL1L, a component of the endoplasmic reticulum associated degradation (ERAD) pathway, has been reported to regulate the (i) differentiation of the pancreatic endocrine and exocrine tissue during the second transition of mouse embryonic development, (ii) neural stem cell self-renewal and lineage commitment and (iii) cell cycle progression through regulation of genes related to cell-matrix interaction. Here we show that in the pancreas the expression of SEL1L is developmentally regulated, such that it is readily detected in developing islet cells and in nascent acinar clusters adjacent to basement membranes, and becomes progressively restricted to the islets of Langherans in post-natal life. This peculiar expression pattern and the presence of two inverse RGD motifs in the fibronectin type II domain of SEL1L protein indicate a possible interaction with cell adhesion molecules to regulate islets architecture. Co-immunoprecipitation studies revealed SEL1L and ß1-integrin interaction and, down-modulation of SEL1L in pancreatic ß-cells, negatively influences both cell adhesion on selected matrix components and cell proliferation likely due to altered ERK signaling. Furthermore, the absence of SEL1L protein strongly inhibits glucose-stimulated insulin secretion in isolated mouse pancreatic islets unveiling an important role of SEL1L in insulin trafficking. This phenotype can be rescued by the ectopic expression of the ß1-integrin subunit confirming the close interaction of these two proteins in regulating the cross-talk between extracellular matrix and insulin signalling to create a favourable micro-environment for ß-cell development and function.

Extracellular matrix-mediated differentiation of human embryonic stem cells: differentiation to insulin-secreting beta cells

Stem cells have tremendous potential for treating various human diseases. Protocols have been established to differentiate stem cells into specific lineages through the provision of signals in the form of growth factors, cytokines, or small molecules. Herein we investigate an alternative strategy for directed differentiation of human embryonic stem cells (hESCs)--extracellular-matrix (ECM) mediated differentiation. Decellularized ECM and conditioned media from the appropriate committed cell lines are used to differentiate stem cells to the required phenotype. Applying this strategy to differentiate hESCs to pancreatic beta cells, we have obtained functional cells that secreted insulin in a glucose-responsive manner, and were able to recover normoglycemia in a streptozotocin (STZ)-induced diabetic mouse model. ECM-mediated differentiation was also demonstrated to be effective for the differentiation of hESCs into kidney tubule cells and cardiomyocytes. Gene expression studies suggested the involvement of integrins and catenins in the beta cell differentiation process; in particular, α1, αv, and β1 integrins, and β-catenin showed the highest upregulation. To further elucidate the biochemical and mechanical cues that have led to effective hESC differentiation to beta cells, we have employed an artificial system that allowed for variation of matrix stiffness and combination of individual ECM proteins at various ratios. The differentiation response of hESCs to the native ECM could be approximated by optimizing this system.

Improved MIN6 β-cell function on self-assembled peptide amphiphile nanomatrix inscribed with extracellular matrix-derived cell adhesive ligands

Understanding the role of the pancreatic extracellular matrix (ECM) in supporting islet survival and function drives the pursuit to create biomaterials that imitate and restore the pancreatic ECM microenvironment. To create an ECM mimic holding bioinductive cues for β-cells, self-assembled peptide amphiphiles (PAs) inscribed with four selected ECM-derived cell adhesive ligands are synthesized. After 7 days, compared to control groups cultured on biologically inert substrates, MIN6 β-cells cultured on PAs functionalized with YIGSR and RGDS cell adhesive ligands exhibit elevated insulin secretion in responses to glucose and also form β-cell clusters. These findings suggest that the self-assembled PA nanomatrix may be utilized to improve pancreatic islet transplantation for treating type 1 diabetes.

Relationship between vascular endothelial cells and pancreatic islet development and stem cell differentiation

As the main components of the pancreatic islet niche, endothelial cells participate in many processes of pancreatic development, including pancreatic cell fate decision, endocrine pancreatic cell differentiation and proliferation, and spatial distribution of the pancreas. On different occasions, endothelial cells play disparate roles by cross-talking with islet cells to influence endocrine pancreatic cell differentiation and islet morphology and function. Cytokines such as hepatocyte growth factor and sphingosine-1-phosphate as well as the extracellular matrixes such as laminin and collagen Ⅳ, which are produced and/or secreted by endothelial cells, play important roles in the regulation of islet development and function. Furthermore, endothelial cells are involved in the balance between self-renewal and differentiation of stem cells. Application of endothelial cells to induce the differentiation of stem cells into functional islet cells may be one of the most promising approaches to cell replacement therapy for diabetes.

Recovery from overt type 1 diabetes ensues when immune tolerance and β-cell formation are coupled with regeneration of endothelial cells in the pancreatic islets

Immune modulation of pancreatic inflammation induces recovery from type 1 diabetes (T1D), but remission was not durable, perhaps because of an inability to sustain the formation and function of new pancreatic β-cells. We have previously shown that Ig-GAD2, carrying GAD 206-220 peptide, induced in hyperglycemic mice immune modulation that was able to control pancreatic inflammation, stimulate β-cell regeneration, and prevent T1D progression. Herein, we show that the same Ig-GAD2 regimen given to mice with overt T1D was unable to reverse the course of disease despite eradication of Th1 and Th17 cells from the pancreas. However, the regimen was able to sustain recovery from T1D when Ig-GAD2 was accompanied with transfer of bone marrow (BM) cells from healthy donors. Interestingly, alongside immune modulation, there was concomitant formation of new β-cells and endothelial cells (ECs) in the pancreas. The new β-cells were of host origin while the donor BM cells gave rise to the ECs. Moreover, transfer of purified BM endothelial progenitors instead of whole BM cells sustained both β-cell and EC formation and reversal of diabetes. Thus, overcoming T1D requires both immune modulation and repair of the islet vascular niche to preserve newly formed β-cells.

Basement membrane extract preserves islet viability and activity in vitro by up-regulating α3 integrin and its signal

OBJECTIVE

Survival of transplanted islets is limited partly because of the disruption of the islet basement membrane (BM) occurring during isolation. We hypothesized that the embedment of BM extract (BME) could induce a viable cell mass and prolong islet functionality before transplantation.

METHODS

A special reconstituted BME that solidifies into a gel at 37°C was used to embed isolated islets in this study. The strategy was used to re-establish the interaction between the islets and peri-islet BM.

RESULTS

Islets embedded in BME showed lower caspase-3 levels and higher Akt activity than those in suspension. Moreover, we found for the first time that the expression of α3 integrin and focal adhesion kinase (FAK) and FAK activity was up-regulated in islets after BME embedment. The reverse effect was observed on islet apoptosis when islets rescued from a 24-hour suspension culture were embedded in BME for the next 24 hours. In addition, expression of pancreatic duodenal homeobox factor-1 and phospho-extracellular signal-regulated kinase 1/2 was partially preserved, suggesting the positive effect of BME on islet development.

CONCLUSIONS

These results indicate that BME embedment of islets can up-regulate the expression of α3 integrin and its signal transduction, which may improve islet viability.

β1 integrin is a crucial regulator of pancreatic β-cell expansion

Development of the endocrine compartment of the pancreas, as represented by the islets of Langerhans, occurs through a series of highly regulated events encompassing branching of the pancreatic epithelium, delamination and differentiation of islet progenitors from ductal domains, followed by expansion and three-dimensional organization into islet clusters. Cellular interactions with the extracellular matrix (ECM) mediated by receptors of the integrin family are postulated to regulate key functions in these processes. Yet, specific events regulated by these receptors in the developing pancreas remain unknown. Here, we show that ablation of the β1 integrin gene in developing pancreatic β-cells reduces their ability to expand during embryonic life, during the first week of postnatal life, and thereafter. Mice lacking β1 integrin in insulin-producing cells exhibit a dramatic reduction of the number of β-cells to only ∼18% of wild-type levels. Despite the significant reduction in β-cell mass, these mutant mice are not diabetic. A thorough phenotypic analysis of β-cells lacking β1 integrin revealed a normal expression repertoire of β-cell markers, normal architectural organization within islet clusters, and a normal ultrastructure. Global gene expression analysis revealed that ablation of this ECM receptor in β-cells inhibits the expression of genes regulating cell cycle progression. Collectively, our results demonstrate that β1 integrin receptors function as crucial positive regulators of β-cell expansion.

Embedding islet in a liquid scaffold increases islet viability and function

INTRODUCTION

Islet transplantation is a promising strategy to restore efficient insulin regulation in type 1 diabetes mellitus patients. However, shortage of islet donors, poor islet survival and toxicity of immunosuppressants often reduce the graft functional lifetime.

METHODS

We previously showed that a fibroblast populated-collagen matrix (CM) significantly improved engrafted islet viability/function. However, this composite was prone to gradual biodegradation and contraction. Moreover, to avoid use of systemic immunosuppressants, we proposed the use of a local immunosuppressive enzyme, indoleamine-2,3-dioxygenase (IDO). We developed a novel bioengineered crosslinked CM (CCM) to provide optimal matrix biomimetic. Viability and insulin secretory function of islets embedded within fibroblast populated CCM (FP-CCM) was evaluated in vitro and in vivo. IDO expression was transduced in fibroblasts by a lentiviral vector carrying IDO gene and islet viability was evaluated in the presence and absence of IDO producing cells.

RESULTS

Islet survival/function markedly improved within FP-CCM. Furthermore, our data shows that local lentiviral induction of IDO delivered by FP-CCM is nontoxic to the embedded islets.

CONCLUSIONS

This promising finding offers a new approach to improving islet transplant outcome.

Investigating the suspension culture on aggregation and function of mouse pancreatic β-cells

The integrity and hierarchical structure of islet influence β-cells physiology dramatically. A culture substrate which can maintain or improve β-cells aggregation shall benefit cell therapy for diabetics. In this study, nontreated, type IV collagen, Lipidure, and ultralow attachment dishes were used to culture a murine β-cell line, MIN-6. The formation and biological performances of pseudoislets were investigated. Results showed that β-cells formed loose and irregular aggregates on nontreated dishes. Oppositely, pseudoislets formed on other three substrates. Most pseudoislets on Lipidure and type IV collagen dishes had a diameter between 100-150 μm with high survival rate, while large pseudoislets (>250 μm) with seriously central necrosis were found on ultralow attachment dishes. Western blot analysis revealed that pseudoislets had relatively higher connexin 36 protein productions relative to single cells. The glucose-stimulated insulin secretion test showed pseudoislets on type IV collagen have high stimulation index. Monolayers from TCPS dishes and pseudoislets from type IV collagen or Lipidure dishes were further transplanted into diabetic mice. Animals received both single cells and pseudoislets had decreasing blood glucose level and regained body weight. Histologic examination revealed that all implants successfully engrafted with positive insulin staining. Interestingly, the area under curve for the intraperitoneal glucose tolerance test showed pseudoislets had superior glucose disappearance rate. This study reveals that isolated islets or insulin-producing cells can be cultured on type IV collagen or Lipidure dishes to improve/maintain integrity prior to transplantation.