Reestablishment of microenvironment is necessary to maintain in vitro and in vivo human islet function

Microphysiological pancreas-on-chip platform with integrated sensors to model endocrine function and metabolism

Pancreatic in vitro research is of major importance to advance mechanistic understanding and development of treatment options for diseases such as diabetes mellitus. We present a thermoplastic-based microphysiological system aiming to model the complex microphysiological structure and function of the endocrine pancreas with concurrent real-time read-out capabilities. The specifically tailored platform enables self-guided trapping of single islets at defined locations: β-cells are assembled to pseudo-islets and injected into the tissue chamber using hydrostatic pressure-driven flow. The pseudo-islets can further be embedded in an ECM-like hydrogel mimicking the native microenvironment of pancreatic islets in vivo. Non-invasive real-time monitoring of the oxygen levels on-chip is realized by the integration of luminescence-based optical sensors to the platform. To monitor insulin secretion kinetics in response to glucose stimulation in a time-resolved manner, an automated cycling of different glucose conditions is implemented. The model's response to glucose stimulation can be monitored via offline analysis of insulin secretion and via specific changes in oxygen consumption due to higher metabolic activity of pseudo-islets at high glucose levels. To demonstrate applicability for drug testing, the effects of antidiabetic medications are assessed and changes in dynamic insulin secretion are observed in line with the respective mechanism of action. Finally, by integrating human pancreatic islet microtissues, we highlight the flexibility of the platform and demonstrate the preservation of long-term functionality of human endocrine pancreatic tissue.

A vascularized 3D model of the human pancreatic islet forex vivostudy of immune cell-islet interaction

Insulin is an essential regulator of blood glucose homeostasis that is produced exclusively byβcells within the pancreatic islets of healthy individuals. In those affected by diabetes, immune inflammation, damage, and destruction of isletβcells leads to insulin deficiency and hyperglycemia. Current efforts to understand the mechanisms underlyingβcell damage in diabetes rely onin vitro-cultured cadaveric islets. However, isolation of these islets involves removal of crucial matrix and vasculature that supports islets in the intact pancreas. Unsurprisingly, these islets demonstrate reduced functionality over time in standard culture conditions, thereby limiting their value for understanding native islet biology. Leveraging a novel, vascularized micro-organ (VMO) approach, we have recapitulated elements of the native pancreas by incorporating isolated human islets within a three-dimensional matrix nourished by living, perfusable blood vessels. Importantly, these islets show long-term viability and maintain robust glucose-stimulated insulin responses. Furthermore, vessel-mediated delivery of immune cells to these tissues provides a model to assess islet-immune cell interactions and subsequent islet killing-key steps in type 1 diabetes pathogenesis. Together, these results establish the islet-VMO as a novel,ex vivoplatform for studying human islet biology in both health and disease.

The Foundation for Engineering a Pancreatic Islet Niche

Progress in diabetes research is hindered, in part, by deficiencies in current experimental systems to accurately model human pathophysiology and/or predict clinical outcomes. Engineering human-centric platforms that more closely mimic in vivo physiology, however, requires thoughtful and informed design. Summarizing our contemporary understanding of the unique and critical features of the pancreatic islet can inform engineering design criteria. Furthermore, a broad understanding of conventional experimental practices and their current advantages and limitations ensures that new models address key gaps. Improving beyond traditional cell culture, emerging platforms are combining diabetes-relevant cells within three-dimensional niches containing dynamic matrices and controlled fluidic flow. While highly promising, islet-on-a-chip prototypes must evolve their utility, adaptability, and adoptability to ensure broad and reproducible use. Here we propose a roadmap for engineers to craft biorelevant and accessible diabetes models. Concurrently, we seek to inspire biologists to leverage such tools to ask complex and nuanced questions. The progenies of such diabetes models should ultimately enable investigators to translate ambitious research expeditions from benchtop to the clinic.

Basement membrane proteins improve human islet survival in hypoxia: Implications for islet inflammation

Enzymatic digestion of the pancreas during islet isolation is associated with disintegration of the islet basement membrane (IBM) that can cause reduction of functional and morphological islet integrity. Attempts to re-establish IBM by coating the surface of culture vessels with various IBM proteins (IBMP) have resulted in loss of islet phenotype and function. This study investigated the capability of Collagen-IV, Laminin-521 and Nidogen-1, utilised as single or combined media supplements, to protect human islets cultured in hypoxia. When individually supplemented to media, all IBMP significantly improved islet survival and in-vitro function, finally resulting in as much as a two-fold increase of islet overall survival. In contrast, combining IBMP enhanced the production of chemokines and reactive oxygen species diminishing all positive effects of individually added IBMP. This impact was concentration-dependent and concerned nearly all parameters of islet integrity. Predictive extrapolation of these findings to data from 116 processed human pancreases suggests that more than 90% of suboptimal pancreases could be rescued for clinical islet transplantation increasing the number of transplantable preparations from actual 25 to 40 when adding Nidogen-1 to pretransplant culture. This study suggests that media supplementation with essential IBMP protects human islets from hypoxia. Amongst those, certain IBMP may be incompatible when combined or applied at higher concentrations. STATEMENT OF SIGNIFICANCE: Pancreatic islet transplantation is a minimally-invasive treatment that can reverse type 1 diabetes in certain patients. It involves infusing of insulin-producing cell-clusters (islets) from donor pancreases. Unfortunately, islet extraction is associated with damage of the islet basement membrane (IBM) causing reduced islet function and cell death. Attempts to re-establish the IBM by coating the surface of culture vessels with IBM proteins (IBMP) have been unsuccessful. Instead, we dissolved the most relevant IBM components Collagen-IV, Laminin-521 and Nidogen-1 in media routinely used for clinical islet culture and transplantation. We found human islet survival and function was substantially improved by IBMP, particularly Nidogen-1, when exposed to a hypoxic environment as found in vivo. We also investigated IBMP combinations. Our present findings have important clinical implications.

The Transcriptome and Epigenome Reveal Novel Changes in Transcription Regulation During Pancreatic Rat Islet Maturation

Islet function is critical for normal glucose homeostasis. Unlike adult β cells, fetal and neonatal islets are more proliferative and have decreased insulin secretion in response to stimuli. However, the underlying mechanisms governing functional maturity of islets have not been completely elucidated. Pancreatic islets comprise different cell types. The microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. Thus, the study of intact islets is optimal to identify novel molecular mechanisms controlling islet functional development. Transcriptomes and genome-wide histone landscapes of H3K4me3, H3K27me3, and H3K27Ac from intact islets isolated from 2- and 10-week-old Sprague-Dawley rats were integrated to elucidate genes and pathways modulating islet development, as well as the contribution of epigenetic regulation. A total of 4489 differentially expressed genes were identified; 2289 and 2200 of them were up- and down-regulated in 10-week islets, respectively. Ingenuity Pathway Analysis revealed critical pathways regulating functional maturation of islets, including nutrient sensing, neuronal function, immune function, cell replication, and extracellular matrix. Furthermore, we identified significant changes in enrichment of H3K4me3, H3K27me3, and H3K27Ac marks, which correlated with expression changes of genes critical for islet function. These histone marks were enriched at critical transcription factor-binding motifs, such as Hoxa9, C/EBP-β, Gata1, Foxo1, E2f1, E2f3, and Mafb. In addition, our chromatin immunoprecipitation sequencing data revealed multiple potential bivalent genes whose poised states changed with maturation. Collectively, our current study identified critical novel pathways for mature islet function and suggested a role for histone modifications in regulating islet development and maturation.

Decellularized Matrix Bioscaffolds: Implementation of Native Microenvironment in Pancreatic Tissue Engineering

ABSTRACT

Type 1 diabetes is an autoimmune disease, and its incidence is usually estimated in the range of 5% to 10%. Currently, the administration of exogenous insulin is the standard of care therapy. However, this therapy is not effective in some patients who may develop some chronic complications. Islet transplantation into the liver is another therapy with promising outcomes; however, the long-term efficacy of this therapeutic option is limited to a small number of patients. Because native extracellular matrix (ECM) components provide a suitable microenvironment for islet functions, engineering a 3-dimensional construct that recapitulates the native pancreatic environment could address these obstacles. Many attempts have been conducted to mimic an in vivo microenvironment to increase the survival of islets or islet-like clusters. With the advent of decellularization technology, it is possible to use a native ECM in organ engineering. Pancreatic decellularized bioscaffold provides proper cell-cell and cell-ECM interactions and retains growth factors that are critical in the determination of cell fate within a native organ. This review summarizes the current knowledge of decellularized matrix technology and addresses its possible limitations before use in the clinic.

Extracellular matrix requirements for gastrointestinal organoid cultures

Organoids are a new class of biological model systems that have garnered significant interest in the life sciences. When provided with the proper 3D matrix and biochemical factors, stem cells can self-organize and form tissue-specific organoids. Thus far, there has been a substantial effort to identify soluble niche components essential for organoid culture; however, the role of the solid extracellular matrix (ECM) as an essential element of the niche is still largely lacking. In this review, we discuss the importance of the ECM in intestinal, hepatic, and pancreatic organoid culture and how biomaterial-based approaches can be used to probe different ECM properties required for more physiologically and translationally relevant organoid models.

Transcriptomic and Quantitative Proteomic Profiling Reveals Signaling Pathways Critical for Pancreatic Islet Maturation

Pancreatic β-cell dysfunction and reduced insulin secretion play a key role in the pathogenesis of diabetes. Fetal and neonatal islets are functionally immature and have blunted glucose responsiveness and decreased insulin secretion in response to stimuli and are far more proliferative. However, the mechanisms underlying functional immaturity are not well understood. Pancreatic islets are composed of a mixture of different cell types, and the microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. RNA sequencing and quantitative proteomic data from intact islets isolated from fetal (embryonic day 19) and 2-week-old Sprague-Dawley rats were integrated to compare their gene and protein expression profiles. Ingenuity Pathway Analysis (IPA) was also applied to elucidate pathways and upstream regulators modulating functional maturation of islets. By integrating transcriptome and proteomic data, 917 differentially expressed genes/proteins were identified with a false discovery rate of less than 0.05. A total of 411 and 506 of them were upregulated and downregulated in the 2-week-old islets, respectively. IPA revealed novel critical pathways associated with functional maturation of islets, such as AMPK (adenosine monophosphate-activated protein kinase) and aryl hydrocarbon receptor signaling, as well as the importance of lipid homeostasis/signaling and neuronal function. Furthermore, we also identified many proteins enriched either in fetal or 2-week-old islets related to extracellular matrix and cell communication, suggesting that these pathways play critical roles in islet maturation. Our present study identified novel pathways for mature islet function in addition to confirming previously reported mechanisms, and provided new mechanistic insights for future research on diabetes prevention and treatment.

Collagen and Endothelial Cell Coculture Improves β-Cell Functionality and Rescues Pancreatic Extracellular Matrix

The use of biomaterials and biomaterial functionalization is a promising approach to support pancreatic islet viability posttransplantation in an effort to reduce insulin dependence for patients afflicted with diabetes mellitus type 1. Extracellular matrix (ECM) proteins are known to impact numerous reparative functions in the body. Assessing how endogenously expressed pancreatic ECM proteins are affected by posttransplant-like hypoxic conditions may provide significant insights toward the development of tissue-engineered therapeutic strategies to positively influence β-cell survival, proliferation, and functionality. Here, we investigated the expression of three relevant groups of pancreatic ECM proteins in human native tissue, including basement membrane (BM) proteins (collagen type 4 [COL4], laminins [LAM]), proteoglycans (decorin [DCN], nidogen-1 [NID1]), and fibril-forming proteins (fibronectin [FN], collagen type 1 [COL1]). In an in vitro hypoxia model, we identified that ECM proteins were differently affected by hypoxic conditions, contributing to an overall loss of β-cell functionality. The use of a COL1 hydrogel as carrier material demonstrated a protective effect on β-cells mitigating the effect of hypoxia on proteoglycans as well as fibril-forming protein expression, supporting β-cell functionality in hypoxia. We further showed that providing endothelial cells (ECs) into the COL1 hydrogel improves β-cell response as well as the expression of relevant BM proteins. Our data show that β-cells benefit from a microenvironment composed of structure-providing COL1 with the incorporation of ECs to withstand the harsh conditions of hypoxia. Such hydrogels support β-cell survival and can serve as an initial source of ECM proteins to allow cell engraftment while preserving cell functionality posttransplantation. Impact statement Expression analysis identifies hypoxia-induced pathological changes in extracellular matrix (ECM) homeostasis as potential targets to support β-cell transplants by encapsulation in biomaterials for the treatment of diabetes mellitus. A collagen-1 hydrogel is shown to attenuate the effect of hypoxia on β-cells and their ECM expression. The functionalization of the hydrogel with endothelial cells increases the β-cell response to glucose and rescues essential basement membrane proteins.

Functionalization of Alginate with Extracellular Matrix Peptides Enhances Viability and Function of Encapsulated Porcine Islets

Translation of transplanted alginate-encapsulated pancreatic islets to treat type 1 diabetes has been hindered by inconsistent long-term efficacy. This loss of graft function can be partially attributed to islet dysfunction associated with the destruction of extracellular matrix (ECM) interactions during the islet isolation process as well as immunosuppression-associated side effects. This study aims at recapitulating islet-ECM interactions by the direct functionalization of alginate with the ECM-derived peptides RGD, LRE, YIGSR, PDGEA, and PDSGR. Peptide functionalization is controlled in a concentration-dependent manner and its presentation is found to be homogeneous across the microcapsule environment. Preweaned porcine islets are encapsulated in peptide-functionalized alginate microcapsules, and those encapsulated in RGD-functionalized alginate displays enhanced viability and glucose-stimulated insulin release. Effects are RGD-specific and not observed with its scrambled control RDG nor with LRE, YIGSR, PDGEA, and PDSGR. This study supports the sustained presentation of ECM-derived peptides in helping to maintain health of encapsulated pancreatic islets and may aid in prolonging longevity of encapsulated islet grafts.

Decellularized and solubilized pancreatic stroma promotes the in vitro proliferation, migration and differentiation of BMSCs into IPCs

Bone marrow-derived mesenchymal stem cells (BMSCs) have the ability to differentiate into insulin-producing cells (IPCs). Bio-scaffolds derived from decellularized organs can act as a carrier for seed cells and may have broad applications in regenerative medicine. This study investigated the effect of native pancreatic stroma obtained from decellularized pancreas on the proliferation, migration and differentiation of BMSCs into IPCs, and explored the potential underlying molecular mechanism. The decellularized pancreas bio-scaffold was obtained by perfusion with Triton X-100/ammonium hydroxide, followed by digestion with a mixture of pepsin and hydrochloric acid to prepare the stroma solution. Islet-like cells were differentiated from BMSCs by a three-step induction method. The differences on the cytological behavior with or without stroma were evaluated by morphological observation, insulin release assay, qRT-PCR assay and western blot analysis. Our results showed that, stroma derived from decellularized pancreas could promote the proliferation and migration of BMSCs. Furthermore, the formation of IPCs could also be promoted, which possessed similar morphology to endogenous islets. During the induced differentiation process, the presence of stroma significantly increased the expression of insulin 1, insulin 2 and Pdx-1, as well as insulin release. This was accompanied by an increase in the phosphorylation of Akt and ERK in third stage cell clusters, which was prevented by the addition of the inhibitors PD98059 and LY294002, respectively. In summary, decellularized pancreatic stroma could promote the proliferation, migration and differentiation of BMSCs into IPCs, and this involved the activation of Akt and ERK signal pathways.

Adipose tissue-derived mesenchymal stem cells rescue the function of islets transplanted in sub-therapeutic numbers via their angiogenic properties

A significant proportion of islets are lost following transplantation due to hypoxia and inflammation. We hypothesize that adipose tissue-derived mesenchymal stem cells (AD-MSCs) can rescue a sub-therapeutic number of transplanted islets by helping them establish a new blood supply and reducing inflammation. Diabetic mice received syngeneic transplantation with 75 (minimal), 150 (sub-therapeutic), or 225 (therapeutic) islets, with or without 1 × 10⁶ mouse AD-MSCs. Fasting blood glucose (FBG) values were measured over 6 weeks with tissue samples collected for islet structure and morphology (H&E, insulin/glucagon staining). Histological and immunohistochemical analyses of islets were also performed at 2 weeks in animals transplanted with a sub-therapeutic number of islets, with and without AD-MSCs, to determine new blood vessel formation, the presence of pro-angiogenic factors facilitating revascularization, and the degree of inflammation. AD-MSCs had no beneficial effect on FBG values when co-transplanted with a minimal or therapeutic number of islets. However, AD-MSCs significantly reduced FBG values and restored glycemic control in diabetic animals transplanted with a sub-therapeutic number of islets. Islets co-transplanted with AD-MSCs preserved their native morphology and organization and exhibited less aggregation when compared to islets transplanted alone. In the sub-therapeutic group, AD-MSCs significantly increased islet revascularization and the expression of angiogenic factors including hepatocyte growth factor (HGF) and angiopoietin-1 (Ang-1) while also reducing inflammation. AD-MSCs can rescue the function of islets when transplanted in a sub-therapeutic number, for at least 6 weeks, via their ability to maintain islet architecture while concurrently facilitating islet revascularization and reducing inflammation.

Can We Re-Engineer the Endocrine Pancreas?

PURPOSE OF REVIEW

Engineering endocrine pancreatic tissue is an emerging topic in type 1 diabetes with the intent to overcome the current limitation of β cell transplantation. During islet isolation, the vascularized structure and surrounding extracellular matrix (ECM) are completely disrupted. Once implanted, islets slowly engraft and mostly are lost for the initial avascular phase. This review discusses the main building blocks required to engineer the endocrine pancreas: (i) islet niche ECM, (ii) islet niche vascular network, and (iii) new available sources of endocrine cells.

RECENT FINDINGS

Current approaches include the following: tissue engineering of endocrine grafts by seeding of native or synthetic ECM scaffolds with human islets, vascularization of native or synthetic ECM prior to implantation, vascular functionalization of ECM structures to enhance angiogenesis after implantation, generation of engineered animals as human organ donors, and embryonic and pluripotent stem cell-derived endocrine cells that may be encapsulated or genetically engineered to be immunotolerated. Substantial technological improvements have been made to regenerate or engineer endocrine pancreatic tissue; however, significant hurdles remain, and more research is needed to develop a technology to integrate all components of viable endocrine tissue for clinical application.

Extracellular matrix and the maintenance and loss of peripheral immune tolerance in autoimmune insulitis

There is a growing appreciation that the extracellular matrix (ECM) contributes to both the maintenance of immune tolerance in healthy tissues and to its loss at sites of autoimmunity. Here, we review recent literature on the role of ECM and particularly the glycosaminoglycans hyaluronan and heparan sulfate in the development of autoimmune, type 1 diabetes (T1D). Data from transplant models suggest that healthy islets are embedded within an intact ECM that supports beta-cell homeostasis and provides physical and immunoregulatory barriers against immune infiltration. However, studies of human insulitis as well as the non-obese diabetic (NOD) and DORmO mouse models of T1D indicate that autoimmune insulitis is associated with the degradation of basement membrane structures, the catabolism of the islet interstitium, and the accumulation of a hyaluronan-rich, pro-inflammatory ECM. Moreover, in these models of autoimmune diabetes, either the pharmacologic inhibition of heparan sulfate catabolism, the reduction of hyaluronan synthesis, or the targeting of the pathways that sense these ECM changes can all prevent beta-cell destruction. Together these data support an emerging paradigm that in healthy islets the local ECM contributes to both immune tolerance and beta-cell homeostasis while in chronic inflammation the islet ECM is permissive to immune infiltration and beta-cell destruction. Therapies that support ECM-mediated 'barrier tolerance' may have potential as adjunctive agents in combination regimens designed to prevent or treat autoimmunity.

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.

Differentiation potential of Pluripotent Stem Cells correlates to the level of CHD7

Embryonic Stem Cells (ESC) possesses two distinct features; self-renewal and the potential to differentiate. Here we show the differentiation potential and growth rate of ESC correlates positively with the expression level of the gene encoding chromodomain helicase DNA binding protein 7 (CHD7). When ESCs are maintained in feeder-free conditions and single cell seeding, ESC KhES-1 having 4520 copies or more of CHD7 in 5 ng total RNA show differentiation potential, but this is lost when the CHD7 copy number is reduced in KhES-1 to less than 696 by alternative culture conditions. Introduction of siCHD7 reduced differentiation potential and growth rate of KhES-1. Interestingly, KhES-1 underwent spontaneous differentiation when mCHD7 was introduced and we could not obtain CHD7-overexpressing ESC in culture. These data suggest that CHD7 drives differentiation, and there is a lower limit for CHD7 to initiate differentiation and an upper limit for CHD7 if maintained in undifferentiated state, and such upper limit varies depending on culture condition. As CHD7 drives cell growth, ESC with the highest permissible CHD7 level in the given culture become dominant in a couple of passages. Thus, we can select differentiation resistance-free cell clones by optimizing the culture system using CHD7 as an index.

Human islet xenotransplantation in rodents: A literature review of experimental model trends

Among the innovations for the treatment of type 1 diabetes, islet transplantation is a less invasive method of treatment, although it is still in development. One of the greatest barriers to this technique is the low number of pancreas donors and the low number of pancreases that are available for transplantation. Rodent models have been chosen in most studies of islet rejection and type 1 diabetes prevention to evaluate the quality and function of isolated human islets and to identify alternative solutions to the problem of islet scarcity. The purpose of this study is to conduct a review of islet xenotransplantation experiments from humans to rodents, to organize and analyze the parameters of these experiments, to describe trends in experimental modeling and to assess the viability of this procedure. In this study, we reviewed recently published research regarding islet xenotransplantation from humans to rodents, and we summarized the findings and organized the relevant data. The included studies were recent reports that involved xenotransplantation using human islets in a rodent model. We excluded the studies that related to isotransplantation, autotransplantation and allotransplantation. A total of 34 studies that related to xenotransplantation were selected for review based on their relevance and current data. Advances in the use of different graft sites may overcome autoimmunity and rejection after transplantation, which may solve the problem of the scarcity of islet donors in patients with type 1 diabetes.

Key Matrix Proteins Within the Pancreatic Islet Basement Membrane Are Differentially Digested During Human Islet Isolation

Clinical islet transplantation achieves insulin independence in selected patients, yet current methods for extracting islets from their surrounding pancreatic matrix are suboptimal. The islet basement membrane (BM) influences islet function and survival and is a critical marker of islet integrity following rodent islet isolation. No studies have investigated the impact of islet isolation on BM integrity in human islets, which have a unique duplex structure. To address this, samples were taken from 27 clinical human islet isolations (donor age 41-59, BMI 26-38, cold ischemic time < 10 h). Collagen IV, pan-laminin, perlecan and laminin-α5 in the islet BM were significantly digested by enzyme treatment. In isolated islets, laminin-α5 (found in both layers of the duplex BM) and perlecan were lost entirely, with no restoration evident during culture. Collagen IV and pan-laminin were present in the disorganized BM of isolated islets, yet a significant reduction in pan-laminin was seen during the initial 24 h culture period. Islet cytotoxicity increased during culture. Therefore, the human islet BM is substantially disrupted during the islet isolation procedure. Islet function and survival may be compromised as a consequence of an incomplete islet BM, which has implications for islet survival and transplanted graft longevity.

Epithelial cells from oral mucosa: How to cultivate them?

Epithelial cells from oral mucosa (EOM) are responsible for important functions, like the primary protection of oral mucosa against external aggressions building a mechanical barrier against microorganisms, mechanical damage, toxic material, thermal regulation and secretion of different classes of inflammatory mediators. EOM could be an interesting tool for cellular and molecular biology research. Usually, EOM are collected by a painful and invasive process. In this study, we propose an alternative method to cultivate EOM collected by non-invasive scraping method of oral mucosa. Papanicolaou staining showed mainly two kinds of epithelial cell population after EOM scraping. As result of the five culture methods tested here, our results revealed that the EOM were successfully cultured on a murine feeder layer. In addition, EOM could be frozen and thawed, without morphology changes and loss of viability. Our findings suggest that EOM can be considered as a good cell source for many purposes, such as genetic studies, diagnosis and cell therapy.

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.

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hESC-derived pancreatic progenitor cells matured faster in nude rats than in SCID-bg mice

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Human C-peptide secretion was meal-regulated in rats but not in mice at 19 weeks

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Grafts from rats expressed more mature β cell markers compared with mice

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Grafts from rats had a denser ECM and greater vasculature than grafts from mice

Hyaluronan: A Mediator of Islet Dysfunction and Destruction in Diabetes?

Hyaluronan (HA) is an extracellular matrix (ECM) component that is present in mouse and human islet ECM. HA is localized in peri-islet and intra-islet regions adjacent to microvessels. HA normally exists in a high molecular weight form, which is anti-inflammatory. However, under inflammatory conditions, HA is degraded into fragments that are proinflammatory. HA accumulates in islets of human subjects with recent onset type 1 diabetes (T1D), and is associated with myeloid and lymphocytic islet infiltration, suggesting a possible role for HA in insulitis. A similar accumulation of HA, in amount and location, occurs in non-obese diabetic (NOD) and DORmO mouse models of T1D. Furthermore, HA accumulates in follicular germinal centers and in T-cell areas in lymph nodes and spleen in both human and mouse models of T1D, as compared with control tissues. Whether HA accumulates in islets in type 2 diabetes (T2D) or models thereof has not been previously described. Here we show evidence that HA accumulates in a mouse model of islet amyloid deposition, a well-known component of islet pathology in T2D. In summary, islet HA accumulation is a feature of both T1D and a model of T2D, and may represent a novel inflammatory mediator of islet pathology.

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.

Young porcine endocrine pancreatic islets cultured in fibrin and alginate gels show improved resistance towards human monocytes

AIM

To investigate the protective function of alginate and fibrin gels used to embed porcine endocrine pancreatic islets towards human monocytes.

METHODS

Groups of 200 islet equivalents from young pigs were embedded in either a fibrin or in an alginate gel, and as a control seeded in tissue culture polystyrene (TCPS) well plates. The islet cultures were incubated with 2×10(5) human monocytes for 24h. In addition, both islets and monocytes were separately cultured in TCPS, fibrin and alginate. Islet morphology, viability and function were investigated as well as the secretion of cytokines TNFα, IL-6, and IL-1β.

RESULTS

When freely-floating in TCPS, non-encapsulated islets were surrounded by monocytes and started to disperse after 24h. In fibrin, monocytes could be found in close proximity to embedded islets, indicating monocyte migration through the gel. In contrast, after 24h, few monocytes were found close to islets in alginate. Immunofluorescence staining and manual counting showed that integrin expression was higher in fibrin-embedded islet cultures. A TUNEL assay revealed elevated numbers of apoptotic cells for islets in TCPS wells compared to fibrin and alginate cultures. Insulin secretion was higher with islets embedded in fibrin and alginate when compared to non-encapsulated islets. TNFα, IL-6 and IL-1β were found in high concentrations in the media of co-cultures and monocyte mono-culture in fibrin.

CONCLUSION

Both alginate and fibrin provide key structural support and offer some protection for the islets towards human monocytes. Fibrin itself triggers the cytokine secretion from monocytes.

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.

Young porcine endocrine pancreatic islets cultured in fibrin show improved resistance toward hydrogen peroxide

AIM

To study the protective effect of a fibrin scaffold toward embedded young porcine endocrine pancreatic islets from hydrogen peroxide within the context of islet encapsulation in transplantation.

METHODS

After isolation and in vitro maturation, groups of 200 young porcine islet equivalents (IEQ) were embedded in a 200 µL fibrin gel and exposed to 2 concentrations (10 and 100 µM) of hydrogen peroxide (H2O2) to investigate the ability of fibrin to protect islets against apoptotic stimuli. As a control, young porcine islets were seeded in tissue culture polystyrene (TCPS) well plates and exposed to the same H2O2 concentrations. Islet integrity, viability and function were then investigated.

RESULTS

Morphologically, the integrity of islets embedded in fibrin gels was better preserved compared with that of islets cultured in TCPS plates, when exposed to H2O2. Immunofluorescence staining showed that insulin and glucagon expression was higher in islets cultured in fibrin. Overall, H2O2 incubation led to decreased insulin and glucagon expression. A TUNEL assay revealed elevated numbers of apoptotic cells for islets cultured in TCPS plates when compared with those embedded in fibrin. Islets cultured in TCPS plates and exposed to H2O2 had diminished ability to secrete insulin in response to glucose stimulation, whereas islets embedded in fibrin maintained their glucose responsiveness. Insulin trapped in fibrin was extracted and quantified, revealing insulin in the extract.

CONCLUSIONS/INTERPRETATION

Fibrin has a protective effect on young porcine endocrine pancreatic islets exposed to hydrogen peroxide.

Collagen IV-modified scaffolds improve islet survival and function and reduce time to euglycemia

Islet transplantation on extracellular matrix (ECM) protein-modified biodegradable microporous poly(lactide-co-glycolide) scaffolds is a potential curative treatment for type 1 diabetes mellitus (T1DM). Collagen IV-modified scaffolds, relative to control scaffolds, significantly decreased the time required to restore euglycemia from 17 to 3 days. We investigated the processes by which collagen IV-modified scaffolds enhanced islet function and mediated early restoration of euglycemia post-transplantation. We characterized the effect of collagen IV-modified scaffolds on islet survival, metabolism, and insulin secretion in vitro and early- and intermediate-term islet mass and vascular density post-transplantation and correlated these with early restoration of euglycemia in a syngeneic mouse model. Control scaffolds maintained native islet morphologies and architectures as well as collagen IV-modified scaffolds in vivo. The islet size and vascular density increased, while β-cell proliferation decreased from day 16 to 113 post-transplantation. Collagen IV-modified scaffolds promoted islet cell viability and decreased early-stage apoptosis in islet cells in vitro-phenomena that coincided with enhanced islet metabolic function and glucose-stimulated insulin secretion. These findings suggest that collagen IV-modified scaffolds promote the early restoration of euglycemia post-transplantation by enhancing islet metabolism and glucose-stimulated insulin secretion. These studies of ECM proteins, in particular collagen IV, and islet function provide key insights for the engineering of a microenvironment that would serve as a platform for enhancing islet transplantation as a viable clinical therapy for T1DM.

Protein-mediated interactions of pancreatic islet cells

The islets of Langerhans collectively form the endocrine pancreas, the organ that is soley responsible for insulin secretion in mammals, and which plays a prominent role in the control of circulating glucose and metabolism. Normal function of these islets implies the coordination of different types of endocrine cells, noticeably of the beta cells which produce insulin. Given that an appropriate secretion of this hormone is vital to the organism, a number of mechanisms have been selected during evolution, which now converge to coordinate beta cell functions. Among these, several mechanisms depend on different families of integral membrane proteins, which ensure direct (cadherins, N-CAM, occludin, and claudins) and paracrine communications (pannexins) between beta cells, and between these cells and the other islet cell types. Also, other proteins (integrins) provide communication of the different islet cell types with the materials that form the islet basal laminae and extracellular matrix. Here, we review what is known about these proteins and their signaling in pancreatic β -cells, with particular emphasis on the signaling provided by Cx36, given that this is the integral membrane protein involved in cell-to-cell communication, which has so far been mostly investigated for effects on beta cell functions.

Three-dimensional scaffolds reduce islet amyloid formation and enhance survival and function of cultured human islets

Islet transplantation provides a promising approach for treatment of type 1 diabetes mellitus. Amyloid formation and loss of extracellular matrix are two nonimmune factors contributing to death of isolated human islets. We tested the effects of two types of three-dimensional scaffolds, collagen matrix (CM) and fibroblast-populated collagen matrix (FPCM), on amyloid formation, viability, and function of isolated islets. Islets from cadaveric donors were cultured in FPCM, CM, or two-dimensional plate (2D) for 7 days. After 7 days, compared with the 2D culture condition, CM and FPCM markedly reduced amyloid formation of cultured islets and decreased apoptotic β-cell rate by ∼75%. IL-1β and Fas levels were also reduced in scaffold-embedded islets. Furthermore, β/α cell ratios were increased by ∼18% and ∼36% in CM- and FPCM-embedded islets, respectively. Insulin content and insulin response to elevated glucose were also enhanced by both three-dimensional scaffolds. Moreover, culture in CM and FPCM (but not 2D) preserved insulin, GLUT-2, and PDX-1 mRNA expression. FPCM-embedded islets had significantly higher insulin response and lower amyloid formation than CM-embedded islets. These findings suggest that three-dimensional scaffolds reduce amyloid formation and improve viability and function of human islets in vitro, and that CM and fibroblasts have additive effects in enhancing islet function and reducing amyloid formation. Using this strategy is likely to improve outcome in human islet transplantation.

A human islet cell culture system for high-throughput screening

A small-molecule inducer of beta-cell proliferation in human islets represents a potential regeneration strategy for treating type 1 diabetes. However, the lack of suitable human beta cell lines makes such a discovery a challenge. Here, we adapted an islet cell culture system to high-throughput screening to identify such small molecules. We prepared microtiter plates containing extracellular matrix from a human bladder carcinoma cell line. Dissociated human islets were seeded onto these plates, cultured for up to 7 days, and assessed for proliferation by simultaneous Ki67 and C-peptide immunofluorescence. Importantly, this environment preserved beta-cell physiological function, as measured by glucose-stimulated insulin secretion. Adenoviral overexpression of cdk-6 and cyclin D(1), known inducers of human beta cell proliferation, was used as a positive control in our assay. This induction was inhibited by cotreatment with rapamycin, an immunosuppressant often used in islet transplantation. We then performed a pilot screen of 1280 compounds, observing some phenotypic effects on cells. This high-throughput human islet cell culture method can be used to assess various aspects of beta-cell biology on a relatively large number of compounds.

Targeting Uncoupling Protein-2 Improves Islet Graft Function

Preserving and enhancing the primary function of transplanted islets is not only crucial for improving the outcome of the islet transplantation, but is also important for reducing the islet mass required to achieve insulin independence. Uncoupling protein 2 (UCP2) is a member of the uncoupling protein family, which is localized to the inner mitochondrial membrane and negatively regulates insulin secretion in the pancreatic β-cells. In this study, we assessed the importance of UCP2 in improving islet graft primary function by using UCP2 gene-knockout (UCP2-KO) mice in a syngeneic islet transplantation model. Islets were isolated from UCP2-KO or wild-type (WT) C57BL/6J mice. The effects of deficiency of UCP2 on islet transplantation and islet function were determined. Two hundred islets from UCP2-KO, but not from WT, donors were capable of completely restoring normoglycemia in 1 week in all syngeneic diabetic recipients. Islets harvested from UCP2-KO mice secreted onefold more insulin in GSIS assay than that from WT mice, and maintained normal GSIS after 72-h exposure to high glucose challenge. In addition, UCP2-KO islets expressed twohold higher Bcl-2 mRNA than that from WT islets, and were resistant to high glucose and proinflammatory cytokine induced death. Our study explored a potential mechanism that may explain the benefit of UCP2-KO islets in islet transplantation. Targeting UCP2 may provide a novel strategy to improve primary function of transplanted islets and reduce the number of islets required in transplantation.

Feeder-free derivation of induced pluripotent stem cells from human immature dental pulp stem cells

Induced pluripotent stem cells (iPSCs) can be created by forcing expression of certain genes in fibroblasts or other somatic cell types, reversing them to a pluripotent state similar to that of embryonic stem cells (ESC). Here, we used human immature dental pulp stem cells (hIDPSCs) as an alternative source for creating iPSC. hIDPSCs can be easily isolated from accessible tissue of young and adult patients. hIDPSCs possess a fibroblast-like morphology, retaining characteristics of adult multipotent stem cells. Reprogramming of hIDPSCs was fast, producing primary hIDPSC-iPSC colonies even under feeder-free conditions. hIDPSCs acquired ESC-like morphology, expressed pluripotent markers, possessed stable, normal karyotypes, and demonstrated the ability to differentiated in vitro and in vivo. Our data demonstrate that hIDPSCs-iPSCs offer an advantageous cell system for future cell therapy and basic studies, particularly as a model for pediatric developmental disorders.

Self-assembling nanostructures to deliver angiogenic factors to pancreatic islets

Supramolecular self-assembly of nanoscale filaments offers a vehicle to signal cells within dense cell aggregates such as pancreatic islets. We previously developed a heparin-binding peptide amphiphile (HBPA) that self-assembles into nanofiber gels at concentrations of 1% by weight when mixed with heparin and activates heparin-binding, angiogenic growth factors. We report here on the use of these molecules at concentrations 100 times lower to drive delivery of the nanofibers into the dense islet interior. Using fluorescent markers, HBPA molecules, heparin, and FGF2 were shown to be present in and on the surface of murine islets. The intraislet nanofibers were found to be necessary to retain FGF2 within the islet for 48 h and to increase cell viability significantly for at least 7 days in culture. Furthermore, enhanced insulin secretion was observed with the nanofibers for 3 days in culture. Delivery of FGF2 and VEGF in conjunction with the HBPA/heparin nanofibers also induced a significant amount of islet endothelial cell sprouting from the islets into a peptide amphiphile 3-D matrix. We believe the infiltration of bioactive nanofibers in the interior of islets as an artificial ECM can improve cell viability and function in vitro and enhance their vascularization in the presence of growth factors such as FGF2 and VEGF. The approach described here may have significant impact on islet transplantation to treat type 1 diabetes.

Polymer nanofibrous structures: Fabrication, biofunctionalization, and cell interactions

Extracellular matrix fibers (ECM) such as collagen, elastin, and keratin provide biological and physical support for cell attachment, proliferation, migration, differentiation and ultimately cell fate. Therefore, ECM fibers are an important component in tissue and organ development and regeneration. Meanwhile, polymer nanofibers could play the same critical role in tissue regeneration process. Fibrous structures can be fabricated from a variety of materials and methods with diameters ranging throughout the size scale where cells can sense individual fibers (several nanometers to several microns). Polymer nanofiber scaffolds can be designed in a way that predictably modulates a variety of important cell behaviors towards a desired overall function. The nanofibrous topography itself, independent of the fiber material, has demonstrated the potential to modulate cell behaviors desirable in tissue engineering such as: unidirectional alignment; increased viability, attachment, and ECM production; guided migration; and controlled differentiation. The versatility of polymer nanofibers for functionalization with biomolecules opens the door to vast opportunities for the design of tissue engineering scaffolds with even greater control over cell incorporation and function. Despite the promise of polymer nanofibers as tissue engineering scaffolds there have been few clinically relevant successes because no single fabrication technique currently combines control over structural arrangement, material composition, and biofunctionalization, while maintaining reasonable cost and yield. Promising strategies are currently being investigated to allow for the fabrication of optimal polymer nanofiber tissue engineering scaffolds with the goal of treating damaged and degenerated tissues in a clinical setting.

Engineering of an hepatic organoid to develop liver assist devices

Cell-based technologies to support/restore liver function represent one of the most promising opportunities in the treatment of acute liver failure. However, the understanding of the constituent cell types that interact to achieve liver-specific structure and function has not been achieved in the development of liver assist devices (LADs). Here we show that hepatocytes migrated toward and adhered and formed sinusoids-like structures in conjunction with liver nonparenchymal cells, and that this liver organoid formed sophisticated tissue after 7 days in an implanted LAD in rodents. Hepatocytes only or in combination with human nonparenchymal liver cell lines (endothelial, cholangiocytes, and stellate cells) were cultured in Matrigel. Ultrastructural analysis showed that the hepatocyte-decorated endothelial vascular structures resemble in vivo sinusoids containing plate-like structures, bile canaliculi, and lumen. The sinusoid-like structures retained albumin secretion and drug metabolism capabilities. In addition, LADs containing cocultures of human liver nonparenchymal cells were transplanted in animals for a week; the liver tissue formed sophisticated structures resembling the liver. These results demonstrate the importance of nonparenchymal cells in the cellular composition of LADs. The novelty of the culture's sinusoid-like organization and function strongly support the integration of liver nonparenchymal units into hepatocyte coculture-based LADs as a potential destination therapy for liver failure.

Cell delivery: from cell transplantation to organ engineering

Cell populations derived from adult tissue and stem cells possess a great expectation for the treatment of several diseases. Great efforts have been made to generate cells with therapeutic impact from stem cells. However, it is clear that the development of systems to deliver such cells to induce efficient engraftment, growth, and function is a real necessity. Biologic and artificial scaffolds have received significant attention for their potential therapeutic application when use to form tissues in vitro and facilitate engraftment in vivo. Ultimately more sophisticated methods for decellularization of organs have been successfully used in tissue engineering and regenerative medicine applications. These decellularized tissues and organs appear to provide bioactive molecules and bioinductive properties to induce homing, differentiation, and proliferation of cells. The combination of decellularized organs and stem cells may dramatically improve the survival, engraftment, and fate control of transplanted stem cells and their ultimate clinical utility, opening the doors to a new era of organ engineering.

Angiostatic factors normally restrict islet endothelial cell proliferation and migration: implications for islet transplantation

New blood vessel formation in transplanted islets occurs within 7-14 days post-transplantation through both the expansion of donor islet endothelium and ingrowth of blood vessels from the implantation organ. However, several studies indicate that although the islets attract recipient blood vessels, the formed intra-islet vascular network is insufficient, which affects islet post-transplant function. This study aimed to develop an in vitro model to investigate the migration and proliferation properties of isolated liver and islet endothelium.Rat islet or liver endothelium was purified using Bandeiraea simplicifolia(BS-1)-coated Dynabeads. The liver endothelium displayed an increased migration and proliferation to islet-conditioned medium. These effects were fully prevented by adding a neutralizing vascular endothelial growth factor (VEGF)-antibody. In contrast, islet-produced VEGF failed to induce islet endothelial cell migration and only had marginal effects on islet endothelial cell proliferation.These properties could, however, be activated through blocking the effects of either endostatin, thrombospondin-1 or alpha(1)-antitrypsin. In conclusion, VEGF may attract recipient blood vessels towards intrahepatically transplanted islets,but intra-islet vascular expansion is hampered by angiostatic factors present within the islets and the islet endothelium. Inhibition of angiostatic factors early after transplantation may provide a strategy to restore the islet vascular network and improve islet graft function.

Extracellular matrix in pancreatic islets: relevance to scaffold design and transplantation

Intrahepatic islet transplantation provides a potentially more benign alternative to pancreatic transplantation. However, islet transplants are associated with limited engraftment potential. This inefficiency is likely at least partially attributable to the isolation process, which removes islets from their native environment. Isolation not only disrupts the internal vascularization and innervation of islets, but also fundamentally changes interactions between islet cells and macromolecules of the extracellular matrix (ECM). Signaling interactions between islet cells and ECM are known to regulate multiple aspects of islet physiology, including survival, proliferation, and insulin secretion. Although it is highly likely that disruptions to these interactions during isolation significantly affect transplant outcomes, the true implications of these conditions are not well understood. The following article reviews current understandings and uncertainties in islet-ECM interactions and explains their potential impact on posttransplant engraftment. Topics covered include matrix and receptor compositions in native islets, effects of isolation and culture on islet-ECM interactions, and potential for postisolation restoration of islet-ECM interactions. Greater understanding in these areas may help to reduce isolation and transplantation stresses and improve islet engraftment.

Beneficial role of pancreatic microenvironment for angiogenesis in transplanted pancreatic islets

Pancreatic islets implanted heterotopically (i.e., into the kidney, spleen, or liver) become poorly revascularized following transplantation. We hypothesized that islets implanted into the pancreas would become better revascularized. Islets isolated from transgenic mice expressing enhanced yellow fluorescent protein (EYFP) in all somatic cells were cultured before they were implanted into the pancreas or beneath the renal capsule of athymic mice. Vascular density was evaluated in histological sections 1 month posttransplantation. EYFP was used as reporter for the transgene to identify the transplanted islets. Islet endothelial cells were visualized by staining with the lectin Bandeiraea simplicifolia (BS-1). Capillary numbers in intrapancreatically implanted islets were only slightly lower than those counted in endogenous islets, whereas islets implanted beneath the renal capsule had a markedly lower vascular density. In order to determine if this high graft vascular density at the intrapancreatic site reflected expansion of remnant donor endothelial cells or increased ingrowth of blood vessels from the host, also islets from Tie2-green fluorescent protein (GFP) mice (i.e., islets with fluorescent endothelial cells) were transplanted into the pancreas or beneath the renal capsule of athymic mice. These islet grafts revealed that the new vascular structures formed in the islet grafts contained very few GFP-positive cells, and thus mainly were of recipient origin. The reason(s) for the much better ingrowth of blood vessels at the intrapancreatic site merits further studies, because this may help us form strategies to overcome the barrier for ingrowth of host vessels also into islets in heterotopic implantation sites.

Neovascularization Induced around an Artificial Device Implanted in the Abdomen by the Use of Gelatinized Fibroblast Growth Factor 2

The development of a bioartificial pancreas (BAP) with immunoisolating fashion has been gaining attention as a new method for treating diabetes. We have been proceeding with the development of a bag-type BAP that can be easily implanted and that allows for the optional injection or rejection of cells at any time. If fibrosis develops around a BAP device, then the permeability of substances transmitted through a semipermeable membrane will decrease, thereby reducing the reactivity with glucose, so it is necessary for the material of the device to have an excellent histocompatibility. Furthermore, in order to improve the efficacy of BAP treatment, it is important to maintain an environment of ample blood flow around the device. We have created a bag-type device for BAP that is 20 × 20 mm in size and comprises two layers of membranes. We have used an EVAL membrane for the outer membrane of the two layers. The EVAL membrane is a semipermeable membrane with good insulin permeability, which functions as an immunoisolation membrane. The inner membrane consists of PAU-coated HD-PE (nonwoven material processed with polyaminourethan) and it is designed to function as a scaffold for cells. We used Lewis rats to determine whether the effectiveness of fibroblast growth factor 2 (bFGF) can be improved by concomitantly using bFGF with a capacity for blood vessel regeneration as well as bFGF immersed in a sheet of gelatin. We placed the BAP in the abdominal cavity and covered it with the greater omentum. We were able to significantly increase the blood flow and the number of new blood vessels in the tissue surrounding the BAP device by using gelatinized bFGF. There were only a few instances of fibrosis as a biological reaction to the EVAL membrane, and the infiltration of inflammatory cells was mild. There were no adverse effects related to implantation of the device. We confirmed in this study that the use of an implantable BAP device and bFGF allowed for a better blood flow around the BAP device. There were only minor instances of fibrosis and inflammation reaction around the BAP, thus indicating the BAP that we are currently developing to have an excellent histocompatibility.

NF-kappaB activity in endothelial cells is modulated by cell substratum interactions and influences chemokine-mediated adhesion of natural killer cells

Because changes in subendothelial matrix composition are associated with alterations of the endothelial immune phenotype, we sought to understand if cytokine-induced NF-kappaB activity and downstream effects depend on substrate adherence of endothelial cells (EC). We compared the upstream phosphorylation cascade, activation of NF-kappaB, and expression/secretion of downstream effects of EC grown on tissue culture polystyrene plates (TCPS) with EC embedded within collagen-based matrices (MEEC). Adhesion of natural killer (NK) cells was quantified in vitro and in vivo. NF-kappaB subunit p65 nuclear levels were significantly lower and p50 significantly higher in cytokine-stimulated MEEC than in EC-TCPS. Despite similar surface expression of TNF-alpha receptors, MEEC had significantly decreased secretion and expression of IL-6, IL-8, MCP-1, VCAM-1, and ICAM-1. Attenuated fractalkine expression and secretion in MEEC (two to threefold lower than in EC-TCPS; p < 0.0002) correlated with 3.7-fold lower NK cell adhesion to EC (6,335 +/- 420 vs. 1,735 +/- 135 cpm; p < 0.0002). Furthermore, NK cell infiltration into sites of EC implantation in vivo was significantly reduced when EC were embedded within matrix. Matrix embedding enables control of EC substratum interaction. This in turn regulates chemokine and surface molecule expression and secretion, in particular of those compounds within NF-kappaB pathways, chemoattraction of NK cells, local inflammation, and tissue repair.