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

Vascular instruction of pancreas development

Blood vessels course through organs, providing them with essential nutrient and gaseous exchange. However, the vasculature has also been shown to provide non-nutritional signals that play key roles in the control of organ growth, morphogenesis and homeostasis. Here, we examine a decade of work on the contribution of vascular paracrine signals to developing tissues, with a focus on pancreatic β-cells. During the early stages of embryonic development, blood vessels are required for pancreas specification. Later, the vasculature constrains pancreas branching, differentiation and growth. During adult life, capillaries provide a vascular niche for the maintenance of β-cell function and survival. We explore the possibility that the vasculature constitutes a dynamic and regionalized signaling system that carries out multiple and changing functions as it coordinately grows with the pancreatic epithelial tree.

Impact of common variation in bone-related genes on type 2 diabetes and related traits

Exploring genetic pleiotropy can provide clues to a mechanism underlying the observed epidemiological association between type 2 diabetes and heightened fracture risk. We examined genetic variants associated with bone mineral density (BMD) for association with type 2 diabetes and glycemic traits in large well-phenotyped and -genotyped consortia. We undertook follow-up analysis in ∼19,000 individuals and assessed gene expression. We queried single nucleotide polymorphisms (SNPs) associated with BMD at levels of genome-wide significance, variants in linkage disequilibrium (r(2) > 0.5), and BMD candidate genes. SNP rs6867040, at the ITGA1 locus, was associated with a 0.0166 mmol/L (0.004) increase in fasting glucose per C allele in the combined analysis. Genetic variants in the ITGA1 locus were associated with its expression in the liver but not in adipose tissue. ITGA1 variants appeared among the top loci associated with type 2 diabetes, fasting insulin, β-cell function by homeostasis model assessment, and 2-h post-oral glucose tolerance test glucose and insulin levels. ITGA1 has demonstrated genetic pleiotropy in prior studies, and its suggested role in liver fibrosis, insulin secretion, and bone healing lends credence to its contribution to both osteoporosis and type 2 diabetes. These findings further underscore the link between skeletal and glucose metabolism and highlight a locus to direct future investigations.

Hyaluronan and hyaluronan binding proteins are normal components of mouse pancreatic islets and are differentially expressed by islet endocrine cell types

The pancreatic islet comprises endocrine, vascular, and neuronal cells. Signaling among these cell types is critical for islet function. The extracellular matrix (ECM) is a key regulator of cell-cell signals, and while some islet ECM components have been identified, much remains unknown regarding its composition. We investigated whether hyaluronan, a common ECM component that may mediate inflammatory events, and molecules that bind hyaluronan such as versican, tumor necrosis factor-stimulated gene 6 (TSG-6), and components of inter-α-trypsin inhibitor (IαI), heavy chains 1 and 2 (ITIH1/ITIH2), and bikunin, are normally produced in the pancreatic islet. Mouse pancreata and isolated islets were obtained for microscopy (with both paraformaldehyde and Carnoy's fixation) and mRNA. Hyaluronan was present predominantly in the peri-islet ECM, and hyaluronan synthase isoforms 1 and 3 were also expressed in islets. Versican was produced in α cells; TSG-6 in α and β cells; bikunin in α, β, and δ cells; and ITIH1/ITIH2 predominantly in β cells. Our findings demonstrate that hyaluronan, versican, TSG-6, and IαI are normal islet components and that different islet endocrine cell types contribute these ECM components. Thus, dysfunction of either α or β cells likely alters islet ECM composition and could thereby further disrupt islet function.

Encapsulation of protein microfiber networks supporting pancreatic islets

Networks of discrete, genipin-crosslinked gelatin microfibers enveloping pancreatic islets were incorporated within barium alginate microcapsules. This novel technique enabled encapsulation of cellular aggregates in a spherical fibrous matrix <300 μm in diameter. Microfibers were produced by vortex-drawn extrusion within an alginate support matrix. Optimization culminated in a hydrated fiber diameter of 22.3 ± 0.4 μm, a significant reduction relative to that available through current gelatin microfiber spinning techniques, while making the process more reliable and less labor intensive. Microfibers were encapsulated at 40 vol % within 294 ± 4 μm 1.6% barium alginate microparticles by electrostatic-mediated dropwise extrusion. Pancreatic islets extracted from Sprague Dawley rats were encapsulated within the microparticles and analyzed over 21 days. Acridine orange and propidium iodide fluorescent viability staining and light microscopy indicated a significant increase in viability for islets within the fiber-embedded particles relative to fiber-free controls at days 7, 14, and 21. The fiber-embedded system also promoted cellular aggregate cohesion, reducing the incidence of dispersed islet morphologies within the capsules from 31 to 8% at day 21. Further enquiry into benefits of islet encapsulation within a protein fiber network will be the subject of future investigation.

Enhanced function of pancreatic islets co-encapsulated with ECM proteins and mesenchymal stromal cells in a silk hydrogel

Pancreatic islet encapsulation within biosynthetic materials has had limited clinical success due to loss of islet function and cell death. As an alternative encapsulation material, a silk-based scaffold was developed to reestablish the islet microenvironment lost during cell isolation. Islets were encapsulated with ECM proteins (laminin and collagen IV) and mesenchymal stromal cells (MSCs), known to have immunomodulatory properties or to enhance islet cell graft survival and function. After a 7 day in vitro encapsulation, islets remained viable and maintained insulin secretion in response to glucose stimulation. Islets encapsulated with collagen IV, or laminin had increased insulin secretion at day 2 and day 7, respectively. A 3.2-fold synergistic improvement in islet insulin secretion was observed when islets were co-encapsulated with MSCs and ECM proteins. Furthermore, encapsulated islets had increased gene expression of functional genes; insulin I, insulin II, glucagon, somatostatin, and PDX-1, and lower expression of the de-differentiation genes cytokeratin 19 and vimentin compared to non-encapsulated cells. This work demonstrates that encapsulation in silk with both MSCs and ECM proteins enhances islet function and with further development may have potential as a suitable platform for islet delivery in vivo.

Tissue architecture in the Caenorhabditis elegans gonad depends on interactions among fibulin-1, type IV collagen and the ADAMTS extracellular protease

Molecules in the extracellular matrix (ECM) regulate cellular behavior in both development and pathology. Fibulin-1 is a conserved ECM protein. The Caenorhabditis elegans ortholog, FBL-1, regulates gonad-arm elongation and expansion by acting antagonistically to GON-1, an ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) family protease. The elongation of gonad arms is directed by gonadal distal tip cells (DTCs). Here we report that a dominant mutation in the EMB-9/type IV collagen α1 subunit can compensate for loss of FBL-1 activity in gonadogenesis. A specific amino acid substitution in the noncollagenous 1 (NC1) domain of EMB-9 suppressed the fbl-1 null mutant. FBL-1 was required to maintain wild-type EMB-9 in the basement membrane (BM), whereas mutant EMB-9 was retained in the absence of FBL-1. EMB-9 (either wild type or mutant) localization in the BM enhanced PAT-3/β-integrin expression in DTCs. In addition, overexpression of PAT-3 partially rescued the DTC migration defects in fbl-1 mutants, suggesting that EMB-9 acts in part through PAT-3 to control DTC migration. In contrast to the suppression of fbl-1(tk45), mutant EMB-9 enhanced the gonadal defects of gon-1(e1254), suggesting that it gained a function similar to that of wild-type FBL-1, which promotes DTC migration by inhibiting GON-1. We propose that FBL-1 and GON-1 control EMB-9 accumulation in the BM and promote PAT-3 expression to control DTC migration.

Novel mechanistic link between focal adhesion remodeling and glucose-stimulated insulin secretion

Actin cytoskeleton remodeling is well known to be positively involved in glucose-stimulated pancreatic β cell insulin secretion. We have observed glucose-stimulated focal adhesion remodeling at the β cell surface and have shown this to be crucial for glucose-stimulated insulin secretion. However, the mechanistic link between such remodeling and the insulin secretory machinery remained unknown and was the major aim of this study. MIN6B1 cells, a previously validated model of primary β cell function, were used for all experiments. Total internal reflection fluorescence microscopy revealed the glucose-responsive co-localization of focal adhesion kinase (FAK) and paxillin with integrin β1 at the basal cell surface after short term stimulation. In addition, blockade of the interaction between β1 integrins and the extracellular matrix with an anti-β1 integrin antibody (Ha2/5) inhibited short term glucose-induced phosphorylation of FAK (Tyr-397), paxillin (Tyr-118), and ERK1/2 (Thr-202/Tyr-204). Pharmacological inhibition of FAK activity blocked glucose-induced actin cytoskeleton remodeling and glucose-induced disruption of the F-actin/SNAP-25 association at the plasma membrane as well as the distribution of insulin granules to regions in close proximity to the plasma membrane. Furthermore, FAK inhibition also completely blocked short term glucose-induced activation of the Akt/AS160 signaling pathway. In conclusion, these results indicate 1) that glucose-induced activation of FAK, paxillin, and ERK1/2 is mediated by β1 integrin intracellular signaling, 2) a mechanism whereby FAK mediates glucose-induced actin cytoskeleton remodeling, hence allowing docking and fusion of insulin granules to the plasma membrane, and 3) a possible functional role for the Akt/AS160 signaling pathway in the FAK-mediated regulation of glucose-stimulated insulin secretion.

Advancing islet transplantation: from engraftment to the immune response

The promise and progress of islet transplantation for treating type 1 diabetes has been challenged by obstacles to patient accessibility and long-term graft function that may be overcome by integrating emerging technologies in biomaterials, drug delivery and immunomodulation. The hepatic microenvironment and traditional systemic immunosuppression stress the vulnerable islets and contribute to the limited success of transplantation. Locally delivering extracellular matrix proteins and trophic factors can enhance transplantation at extrahepatic sites by promoting islet engraftment, revascularisation and long-term function while avoiding unintended systemic effects. Cell- and cytokine-based therapies for immune cell recruitment and reprogramming can inhibit local and systemic immune system activation that normally attacks transplanted islets. Combined with antigen-specific immunotherapies, states of operational tolerance may be achievable, reducing or eliminating the long-term pharmaceutical burden. Integration of these technologies to enhance engraftment and combat rejection may help to advance the therapeutic efficacy and availability of islet transplantation.

Endothelium-derived Netrin-4 supports pancreatic epithelial cell adhesion and differentiation through integrins α2β1 and α3β1

BACKGROUND

Netrins have been extensively studied in the developing central nervous system as pathfinding guidance cues, and more recently in non-neural tissues where they mediate cell adhesion, migration and differentiation. Netrin-4, a distant relative of Netrins 1-3, has been proposed to affect cell fate determination in developing epithelia, though receptors mediating these functions have yet to be identified.

METHODOLOGY/PRINCIPAL FINDINGS

Using human embryonic pancreatic cells as a model of developing epithelium, here we report that Netrin-4 is abundantly expressed in vascular endothelial cells and pancreatic ductal cells, and supports epithelial cell adhesion through integrins α2β1 and α3β1. Interestingly, we find that Netrin-4 recognition by embryonic pancreatic cells through integrins α2β1 and α3β1 promotes insulin and glucagon gene expression. In addition, full genome microarray analysis revealed that fetal pancreatic cell adhesion to Netrin-4 causes a prominent down-regulation of cyclins and up-regulation of negative regulators of the cell cycle. Consistent with these results, a number of other genes whose activities have been linked to developmental decisions and/or cellular differentiation are up-regulated.

CONCLUSIONS/SIGNIFICANCE

Given the recognized function of blood vessels in epithelial tissue morphogenesis, our results provide a mechanism by which endothelial-derived Netrin-4 may function as a pro-differentiation cue for adjacent developing pancreatic cell populations expressing adhesion receptors α2β1 and α3β1 integrins.

Fibroblast populated collagen matrix promotes islet survival and reduces the number of islets required for diabetes reversal

Islet transplantation represents a viable treatment for type 1 diabetes. However, due to loss of substantial mass of islets early after transplantation, islets from two or more donors are required to achieve insulin independence. Islet-extracellular matrix disengagement, which occurs during islet isolation process, leads to subsequent islet cell apoptosis and is an important contributing factor to early islet loss. In this study, we developed a fibroblast populated collagen matrix (FPCM) as a novel scaffold to improve islet cell viability and function post-transplantation. FPCM was developed by embedding fibroblasts within type-I collagen and used as scaffold for islet grafts. Viability and insulin secretory function of islets embedded within FPCM was evaluated in vitro and in a syngeneic murine islet transplantation model. Islets embedded within acellular matrix or naked islets were used as control. Islet cell survival and function was markedly improved particularly after embedding within FPCM. The composite scaffold significantly promoted islet isograft survival and reduced the critical islet mass required for diabetes reversal by half (from 200 to 100 islets per recipient). Fibroblast embedded within FPCM produced fibronectin and growth factors and induced islet cell proliferation. No evidence of fibroblast over-growth within composite grafts was noticed. These results confirm that FPCM significantly promotes islet viability and functionality, enhances engraftment of islet grafts and decreases the critical islet mass needed to reverse hyperglycemia. This promising finding offers a new approach to reducing the number of islet donors per recipient and improving islet transplant outcome.

Matrix components and scaffolds for sustained islet function

The clinical treatment of diabetes by islet transplantation is limited by low islet survival rates. A fundamental reason for this inefficiency is likely due to the removal of islets from their native environment. The isolation process not only disrupts interactions between blood vessels and endocrine cells, but also dramatically changes islet cell interaction with the extracellular matrix (ECM). Biomolecular cues from the ECM are important for islet survival, proliferation, and function; however, very little is known about the composition of islet ECM and the role each component plays. Without a thorough understanding of islet ECM, current endeavors to prolong islet survival via scaffold engineering lack a systematic basis. The following article reviews current knowledge of islet ECM and attempts to explain the roles they play in islet function. In addition, the effects of in vitro simulations of the native islet scaffold will be evaluated. Greater understanding in these areas will provide a preliminary platform from which a sustainable bioartificial pancreas may be developed.

Preservation of islet survival by upregulating α3 integrin signaling: the importance of 3-dimensional islet culture in basement membrane extract

AIM

Islet transplantation is a promising treatment to cure diabetes, but is associated with a high rate of early graft failure. The isolation process leads to the loss of the surrounding extracellular matrix, resulting in eventual islet disintegration and apoptosis. The purpose of this study was to determine the effects on the viability of isolated islets of embedding islets in reconstituted basement membrane extract (BME), which is similar to the normal peri-islet BM composition in vivo.

METHODS

Isolated mouse islets were embedded in BME gel for 24 or 48 hours. Expression of caspase-3, α3, and α5, focal adhesion kinase (FAK), phosphor-FAK, and pancreatic duodenal homeobox factor (PDX)-1 were detected with Western immunoblotting.

RESULTS

Impaired aggregation of single islet cells could only be observed in non-BME medium. Islets embedded in BME gel were partially protected from anoikis showed decreased caspase-3 compared with non-BME islets. We also observed an increase of α3 integrin, FAK protein level, and FAK activity. Furthermore, expression of PDX-1 was preserved at 48 hours, suggesting a positive contribution of BME to β-cell activity.

CONCLUSION

These results indicated that embedding islets in BME can upregulate α3 integrin, which may result in preservation of viability and function of isolated islets.

TGF-beta i promotes islet beta-cell function and regeneration

TGF-βi is a secreted protein and is capable of binding to both extracellular matrix (ECM) and cells. It thus acts as a bifunctional molecule enhancing ECM and cell interactions, a lack of which results in dysfunction of many cell types. In this study, we investigated the role of TGF-βi in the function and survival of islets. Based on DNA microarray followed by quantitative PCR confirmation, TGFβi gene showed drastic increase in expression in islets after culture. We demonstrated that recombinant TGF-βi could preserve the integrity and enhance the function of cultured islets. Such a beneficial effect was mediated via signaling through FAK. Exogenous TGF-βi was capable of sustaining high-level FAK phosphorylation in isolated islets, and FAK knockdown by small interfering RNA in islets resulted in compromised islet function. TGF-βi transgenic (Tg) islets showed better integrity and insulin release after in vitro culture. In vivo, β-cell proliferation was detectable in Tg but not wild-type pancreata. At age above 12 mo, Tg pancreata contained giant islets. Tg mice displayed better glucose tolerance than that of the controls. Tg islets were more potent in lowering blood glucose when transplanted into syngeneic mice with streptozotocin-induced diabetes, and these transplanted islets also underwent regeneration. Our results indicate that TGF-βi is a vital trophic factor promoting islet survival, function, and regeneration. At least some of its beneficial effect was mediated by signaling through FAK.

α3(V) collagen is critical for glucose homeostasis in mice due to effects in pancreatic islets and peripheral tissues

Collagen V, broadly expressed as α1(V)2 α2(V) heterotrimers that regulate collagen fibril geometry and strength, also occurs in some tissues, such as white adipose tissue (WAT), pancreatic islets, and skeletal muscle, as the poorly characterized α1(V) α2(V) α3(V) heterotrimer. Here, we investigate the role of α3(V) collagen chains by generating mice with a null allele of the α3(V) gene Col5a3 (Col5a3–/– mice). Female Col5a3–/– mice had reduced dermal fat and were resistant to high-fat diet–induced weight gain. Male and female mutant mice were glucose intolerant, insulin-resistant, and hyperglycemic, and these metabolic defects worsened with age. Col5a3–/– mice demonstrated decreased numbers of pancreatic islets, which were more susceptible to streptozotocin-induced apoptosis, and islets isolated from mutant mice displayed blunted glucose-stimulated insulin secretion. Moreover, Col5a3–/– WAT and skeletal muscle were defective in glucose uptake and mobilization of intracellular GLUT4 glucose transporter to the plasma membrane in response to insulin. Our results underscore the emerging view of the importance of ECM to the microenvironments that inform proper development/functioning of specialized cells, such as adipocytes, β cells, and skeletal muscle.

Conditional β1-integrin-deficient mice display impaired pancreatic β cell function

β1-Integrin, a critical regulator of β cell survival and function, has been shown to protect against cell death and promote insulin expression and secretion in rat and human islet cells in vitro. The aim of the present study was to examine whether the knockout of β1-integrin in collagen I-producing cells would have physiological and functional implications in pancreatic endocrine cells in vivo. Using adult mice with a conditional knockout of β1-integrin in collagen I-producing cells, the effects of β1-integrin deficiency on glucose metabolism and pancreatic endocrine cells were examined. Male β1-integrin-deficient mice display impaired glucose tolerance, with a significant reduction in pancreatic insulin content (p < 0.01). Morphometric analysis revealed a significant reduction in β cell mass (p < 0.001) in β1-integrin-deficient mice, along with a significant decrease in β cell proliferation, Pdx-1 and Nkx6.1 expression when compared with controls. Interestingly, these physiological and morphometric alterations in female β1-integrin-deficient mice were less significant. Furthermore, β1-integrin-deficient mice displayed decreased FAK (p < 0.05) and ERK1/2 (p < 0.001) phosphorylation, reduced cyclin D1 levels (p < 0.001) and increased caspase 3 cleavage (p < 0.01), while no changes in Akt phosphorylation were observed, indicating that the β1-integrin signals through the FAK-MAPK-ERK pathway in vivo. Our results demonstrate that β1-integrin is involved in the regulation of glucose metabolism and contributes to the maintenance of β cell survival and function in vivo.

Integrin {alpha}3, but not {beta}1, regulates islet cell survival and function via PI3K/Akt signaling pathways

β1-integrin is a well-established regulator of β-cell activities; however, the role of its associated α-subunits is relatively unknown. Previously, we have shown that human fetal islet and INS-1 cells highly express α3β1-integrin and that collagens I and IV significantly enhance their survival and function; in addition, blocking β1 function in the fetal islet cells decreased adhesion on collagen I and increased apoptosis. The present study investigates the effect of blocking α3. Using α3 blocking antibody or small interfering RNA, the effects of α3-integrin blockade were examined in isolated human fetal or adult islet cells or INS-1 cells, cultured on collagens I or IV. In parallel, β1 blockade was analyzed in INS-1 cells. Perturbing α3 function in human islet or INS-1 cells resulted in significant decreases in cell function (adhesion, spreading, proliferation and Pdx1 and insulin expression/secretion), primarily on collagen IV. A significant decrease in focal adhesion kinase and ERK1/2 phosphorylation and increased caspase3 cleavage were observed on both collagens. These effects were similar to changes after β1 blockade. Interestingly, only α3 blockade reduced expression of phospho-Akt and members of its downstream signaling cascades (glycogen synthase kinase β and X-linked inhibitor of apoptosis), demonstrating a specific effect of α3 on the phosphatidylinositol 3-kinase/Akt pathway. These results suggest that α3- as well as β1-integrin-extracellular matrix interactions are critical for modulating β-cell survival and function through specialized signaling cascades and enhance our understanding of how to improve islet microenvironments for cell-based treatments of diabetes.

Long-term in vitro human pancreatic islet culture using three-dimensional microfabricated scaffolds

Human pancreatic islet in vitro culture is very challenging and requires the presence of various extra cellular matrix (ECM) components in a three-dimensional environment, which provides mechanical and biological support. The development of such an environment is vital in providing favourable conditions to preserve human islets in long-term culture. In this study, we investigated the effects of human islet culture within various three-dimensional environments; collagen I gel, collagen I gel supplemented with ECM components fibronectin and collagen IV, and microfabricated scaffold with ECM-supplemented gel. The cultured human islets were analyzed for functionality, gene expression and hormone content following long-term in vitro culture. It was clear the incorporation of ECM components within the three-dimensional support improved prolonged culture. However, long-term and highly uniform human islet culture within a microfabricated scaffold, with controlled pore structures, coupled with the presence of ECM components, displayed an insulin release profile similar to freshly isolated islets, yielding a stimulation index of approximately 1.8. Moreover, gene expression was markedly increased for all pancreatic genes, giving a approximately 50-fold elevation of insulin gene expression with respect to suspension culture. The distribution and presence of pancreatic hormones was also highly elevated. These findings provide a platform for the long-term maintenance and preservation of human pancreatic islets in vitro.

Bone marrow and pancreatic islets: an old story with new perspectives

In the past years, in the field of β-cell replacement for diabetes therapy, the easy availability of bone marrow (BM) and the widely consolidated clinical experience in the field of hematology have contributed to the development of strategy to achieve donor-specific transplantation tolerance. Recently, the potential role of BM in diabetes therapy has been reassessed from a different point of view. Diverse groups investigated the contribution of BM cells to β-cell replacement as direct differentiation into insulin-producing cells. More importantly, while direct differentiation is highly unlikely, a wide array of experimental evidences indicates that cells of BM origin are capable of facilitating the survival or the endogenous regeneration of β-cells through an as yet well-defined regeneration process. These new experimental in vitro and in vivo data will expand in the near future the clinical trials involving BM or BM-derived cells to cure both type 1 and type 2 diabetes in humans. In this review we recapitulate the history of use of BM in diabetes therapy and we provide clinically relevant actual information about the participation of BM and BM-derived stem cells in islet cell regeneration processes. Furthermore, new aspects such as employing BM as "feeder tissue" for pancreatic islets and new clinical use of BM in diabetes therapy are discussed.

Mesenchymal stem cells as feeder cells for pancreatic islet transplants

Allogeneic islet transplantation serves as a source of insulin-secreting beta-cells for the maintenance of normal glucose levels and treatment of diabetes. However, limited availability of islets, high rates of islet graft failure, and the need for life-long non-specific immunosuppressive therapy are major obstacles to the widespread application of this therapeutic approach. To overcome these problems, pancreatic islet transplantation was recently suggested as a potential target of the "therapeutic plasticity" of adult stem cells. In fact, new results suggest that stem/precursor cells, and mesenchymal stem cells in particular, co-transplanted with islets can promote tissue engraftment and beta-cell survival via bystander mechanisms, mainly exerted by creating a milieu of cytoprotective and immunomodulatory molecules. This evidence consistently challenges the limited view that stem/precursor cells work exclusively through beta-cell replacement in diabetes therapy. It proposes that stem cells also act as "feeder" cells for islets, and supporter of graft protection, tissue revascularization, and immune acceptance. This article reviews the experience of using stem cell co-transplantation as strategy to improve islet transplantation. It highlights that comprehension of the mechanisms involved will help to identify new molecular targets and promote development of new pharmacological strategies to treat type 1 and type 2 diabetes patients.

'Giving and taking': endothelial and beta-cells in the islets of Langerhans

The beta-cells of the islets of Langerhans are embedded in a dense capillary network. The blood vessels supply the islet cells with nutrients and oxygen, and in turn take up the secreted islet hormones to deliver them to target tissues. In addition, vessels provide a basement membrane, which optimizes islet function. In this review we focus on the dynamic interactions between blood vessels and beta-cells, which are pivotal for enhancing insulin expression and beta-cell proliferation in response to increased insulin demand during body growth, pregnancy, and virtually all conditions associated with insulin resistance. Importantly, a failure in this adaptive response might contribute to the onset of type 2 diabetes mellitus.

Impact of integrin-matrix interaction and signaling on insulin gene expression and the mesenchymal transition of human beta-cells

A critical shortage of donor pancreata currently prevents the development of a universal cell-based therapy for type I diabetes. The ex vivo expansion of insulin-producing beta-cells offers a potential solution but is problematic due to the inherent tendency of these cells to transition into mesenchymal-like cells that are devoid of function. Here, we demonstrate for the first time that exposure to elements of the extracellular matrix (ECM) directly potentiates the mesenchymal transition of cultured fetal beta-cells and causes associated declines in insulin gene expression. Individual ECM constituents varied in their ability to induce such responses, with collagen-IV (C-IV) and fibronectin inducing strong responses, whereas laminin-1 had no significant effect. Mesenchymal transition and concomitant losses in insulin gene expression observed on C-IV were found to be dependent on beta(1)-integrin ligation and were augmented in the presence of hepatocyte growth factor. Importantly, selective inhibition of c-Src, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) prior to exposure to C-IV prevented mesenchymal transition and effectively preserved insulin expression. Fetal beta-cells undergoing mesenchymal transition were found to acquire alpha(1)beta(1) expression, and ligation of this integrin then promotes declines in insulin gene expression and a marked increase in beta-cell motility. Inhibition of Src-, ERK-, or JNK-dependent signaling combined with the selective regulation of matrix exposure may ultimately facilitate the development of more effective beta-cell expansion protocols.

Changes in islet microvasculature following streptozotocin-induced beta-cell loss and subsequent replacement in the neonatal rat

Neonatal rats undergo considerable beta-cell regeneration after depletion with streptozotocin (STZ). Since the intraislet vasculature is necessary for both beta-cell growth and function, we examined changes in vascular morphology following STZ. Neonatal Wistar rats (4 days) were injected with 70 mg/kg STZ, or buffer, and were examined between days 4 and 40 postinjection. Animals receiving STZ were relatively hyperglycemic for eight days, but became normoglycemic subsequent to a partial recovery of beta-cell mass. However, glucose tolerance remained impaired. The intraislet area occupied by capillaries was significantly reduced by approximately 20% following STZ, mainly within the beta-cell-rich islet core, but had recovered by day 40. Vascular endothelial growth factor (VEGF) was localized to beta-cells, and pancreatic VEGF mRNA levels in control animals showed a progressive increase between days 4 and 20. This rise was delayed following STZ, but by day 20 VEGF mRNA abundance exceeded that in control pancreas. Hepatocyte growth factor (HGF) was localized to intraislet endothelial cells. Levels of HGF mRNA increased until day 16 in control rats, but subsequently declined to low levels. Following STZ, HGF mRNA had declined prematurely after day 12. Type IV collagen was localized to the extracellular matrix around the intraislet vasculature. The islet area immunopositive for collagen was significantly reduced at all times following STZ. Results indicate that there is a relative loss of intraislet vasculature following STZ, which may limit subsequent beta-cell regeneration through both local growth factor and extracellular matrix interactions.

Basement membrane in pancreatic islet function

Clinical treatment of diabetic patients by islet transplantation faces various complications. At present, in vitro expansion of islets occurs at the cost of their essential features, which are insulin production and release. However, the recent discovery of blood vessel/beta-cell interactions as an important aspect of insulin transcription, secretion, and proliferation might point us to ways of how this problem could be overcome. The correct function of beta-cells depends on the presence of a basement membrane, a specialized extracellular matrix located around the blood vessel wall in mouse and human pancreatic islets. In this chapter, we summarize how the vascular basement membrane influences insulin transcription, insulin secretion, and beta-cell proliferation. In addition, a brief overview about basement membrane components and their interactions with cell surface receptors is given.

Effect of renin angiotensin system blockade on the islet microvessel density of diabetic rats and its relationship with islet function

To investigate the effects of rennin angiotensin system blockade on the microvessel density in islets of diabetic rats and its relationship with islet function, diabetes model was created by feeding of high-caloric laboratory chow plus intraperitoneal injection of a small dose of streptozotocin (30 mg/kg). After 8 weeks intervention with perindopril (AE, n=10) or valsartan (AR, n=10), the islet function of the animals was evaluated by intravenous insulin release test (IVIRT). The pancreases were immunohistochemically stained to analyze the content of insulin and vascular endothelial growth factor (VEGF) in the islets. The microvessel density (MVD) of islets was detected by counting CD34 positive cells. The hypoxia inducible factor (HIF)-1alpha mRNA expression in the islets was detected by RT-PCR. Compared with normal control group (NC, n=10), the area under the curve for insulin from 0 to 30 min (AUCI(0-30)) of diabetes group (DM, n=8) was decreased by 66.3%; the insulin relative concentration (IRC) of betacell was decreased significantly; the relative content of VEGF was increased obviously [(-4.21+/-0.13) vs (-4.06+/-0.29)]; MVD in islets was decreased by 71.4%; the relative expression of HIF-1alpha mRNA was increased by 1.19 times (all P<0.01). Compared with DM group, the AUCI(0-30) of AE and AR group was increased by 44.6% and 34.9% respectively; IRC was also increased significantly; the relative content of VEGF was decreased by 21.2% and 21.7% respectively; MVD was increased by 62.5% and 75.0% respectively; the relative expression of HIF-1alpha was decreased by 27.2% and 29.0% respectively (all P<0.01 or P<0.05). There were no significant differences in the said indexes between group AE and AR. It is concluded that the blockade of RAS may ameliorate islets function of diabetic rats by increasing the MVD in islets.

The effect of extracellular matrix components on the preservation of human islet function in vitro

Human islet isolation leads to the loss of the ECM basement membrane which contributes to eventual apoptosis in vitro. The reestablishment of this environment is vital in understanding the mechanism of islet interaction with its surroundings in order to arrive at conditions favourable to islet culture in vitro. In this study, we investigated the effects of the main ECM components collagen I and IV, fibronectin, and laminin on human islet adhesion, survival, and functionality. Results have provided insight into integrin-mediated effects and behaviour. Collagen I/IV and fibronectin induced adhesion, while fibronectin was the only ECM protein capable of maintaining islet structural integrity and insulin content distribution. Furthermore, islet phenotype was eventually lost, but insulin gene expression was highest in islets cultured on collagen I and IV. However, insulin release was highest on fibronectin, along with a decrease in SUR1 expression, while glucose metabolism, along with GLUT2 and GCK expression, was highest on collagen I and IV surfaces. These findings provide a basis for the future establishment of a modified three-dimensional construct for the culture of human pancreatic islets in vitro.

beta1 integrin/FAK/ERK signalling pathway is essential for human fetal islet cell differentiation and survival

beta1 integrin and collagen matrix interactions regulate the survival of cells by associating with focal adhesion kinase (FAK) and initiating MAPK/ERK signalling, but little is known about these signalling pathways during human fetal islet ontogeny. The purpose of this study was to investigate whether beta1 integrin/FAK activation of the MAPK/ERK pathway regulates human fetal islet cell expression of endocrine cell markers and survival. Isolated human (18-21 weeks fetal age) islet-epithelial cell clusters, cultured on collagen I, were examined using beta1 integrin blocking antibody, beta1 integrin siRNA and FAK expression vector. Perturbing beta1 integrin function in the human fetal islet-epithelial cell clusters resulted in a marked decrease in cell adhesion, in parallel with a reduction in the number of cells expressing PDX-1, insulin and glucagon (p < 0.05). beta1 integrin blockade disorganized focal adhesion contacts in the PDX-1(+) cells and decreased activation of FAK and ERK1/2 signalling in parallel with an increase in expression of cleaved caspases 9 and 3 (p < 0.01). Similar results were obtained following an siRNA knock-down of beta1 integrin expression. In contrast, over-expression of FAK not only increased phospho-ERK and the expression of PDX-1, insulin and glucagon (p < 0.05) but also abrogated the decreases in phospho-ERK and PDX-1 by beta1 integrin blockade. This study demonstrates that activation of the FAK/ERK signalling cascade by beta1 integrin is involved in the differentiation and survival of human fetal pancreatic islet cells.

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.

Vascular niche of pancreatic islets

Pancreatic islets are highly vascularized micro-organs. Approximately 10% of an islet consists of blood vessels. The induction and maintenance of the islet vascular system depend on VEGF secreted from β-cells. VEGF is also critical for the phenotype of the islet vasculature by induction of a vast number of fenestrae. The islet vasculature serves the role of supplying the endocrine cells with oxygen and nutrients, but may also be important for proper glucose sensing of the cells, for paracrine support of endocrine function and growth, and for drainage of metabolites and secreted islet hormones into the systemic circulation. Emerging evidence suggests an important role of islet endothelial cells to maintain β-cell function and growth by secretion of molecules such as hepatocyte growth factor, thrombospondin-1 and laminins, thereby forming a vascular niche for the endocrine cells.

Cell-matrix interactions improve beta-cell survival and insulin secretion in three-dimensional culture

Controlled matrix interactions were presented to pancreatic beta-cells in three-dimensional culture within poly(ethylene glycol) hydrogels. Dispersed MIN6 beta-cells were encapsulated in gel environments containing the following entrapped extracellular matrix (ECM) proteins: collagen type I, collagen type IV, fibrinogen, fibronectin, laminin, and vitronectin. In ECM-containing gels, beta-cell survival was significantly better than in gels without ECM over 10 days. Correspondingly, apoptosis in encapsulated beta-cells was less in the presence of each matrix protein, suggesting the ability of individual matrix interactions to prevent matrix signaling-related apoptosis (anoikis). MIN6 beta-cells cultured in gels containing collagen type IV or laminin secreted more insulin in response to glucose stimulation than beta-cells in all other experimental conditions. Variations in collagen type IV or laminin concentration between 10 microg/mL and 250 microg/mL did not affect insulin secretion. Finally, beta-cell function in hydrogels presenting both collagen type IV and laminin revealed synergistic interactions. With a total protein concentration of 100 microg/mL, three gel compositions of varying ratios of collagen type IV to laminin (25:75, 50:50, and 75:25) were tested. In the presence of 25 microg/mL of collagen type IV and 75 microg/mL of laminin, beta-cell insulin secretion was greater than with laminin or collagen type IV individually. These results demonstrate that specific, rationally designed extracellular environments promote isolated beta-cell survival and function.

Matrix metalloproteinases, T cell homing and beta-cell mass in type 1 diabetes

The pathogenesis of type 1 diabetes begins with the activation of autoimmune T killer cells and is followed by their homing into the pancreatic islets. After penetrating the pancreatic islets, T cells directly contact and destroy insulin-producing beta cells. This review provides an overview of the dynamic interactions which link T cell membrane type-1 matrix metalloproteinase (MT1-MMP) and the signaling adhesion CD44 receptor with T cell transendothelial migration and the subsequent homing of the transmigrated cells to the pancreatic islets. MT1-MMP regulates the functionality of CD44 in diabetogenic T cells. By regulating the functionality of T cell CD44, MT1-MMP mediates the transition of T cell adhesion to endothelial cells to the transendothelial migration of T cells, thus, controlling the rate at which T cells home into the pancreatic islets. As a result, the T cell MT1-MMP-CD44 axis controls the severity of the disease. Inhibition of MT1-MMP proteolysis of CD44 using highly specific and potent synthetic inhibitors, which have been clinically tested in cancer patients, reduces the rate of transendothelial migration and the homing of T cells. Result is a decrease in the net diabetogenic efficiency of T cells and a restoration of beta cell mass and insulin production in NOD mice. The latter is a reliable and widely used model of type I diabetes in humans. Overall, existing experimental evidence suggests that there is a sound mechanistic rationale for clinical trials of the inhibitors of T cell MT1-MMP in human type 1 diabetes patients.

Expression and function of alphabeta1 integrins in pancretic beta (INS-1) cells

Integrin-extracellular matrix interactions are important determinants of beta cell behaviours. The β1 integrin is a well-known regulator of beta cell activities; however, little is known of its associated α subunits. In the present study, αβ1 integrin expression was examined in the rat insulinoma cell line (INS-1) to identify their role in beta cell survival and function. Seven α subunits associated with β1 integrin were identified, including α1-6 and αV. Among these heterodimers, α3β1 was most highly expressed. Common ligands for the α3β1 integrin, including fibronectin, laminin, collagen I and collagen IV were tested to identify the most suitable matrix for INS-1 cell proliferation and function. Cells exposed to collagen I and IV demonstrated significant increases in adhesion, spreading, cell viability, proliferation, and FAK phosphorylation when compared to cells cultured on fibronectin, laminin and controls. Integrin-dependent attachment also had a beneficial effect on beta cell function, increasing Pdx-1 and insulin gene and protein expression on collagens I and IV, in parallel with increased basal insulin release and enhanced insulin secretion upon high glucose challenge. Furthermore, functional blockade of α3β1 integrin decreased cell adhesion, spreading and viability on both collagens and reduced Pdx-1 and insulin expression, indicating that its interactions with collagen matrices are important for beta cell survival and function. These results demonstrate that specific αβ1 integrin-ECM interactions are critical regulators of INS-1 beta cell survival and function and will be important in designing optimal conditions for cell-based therapies for diabetes treatment.

Molecular composition of the peri-islet basement membrane in NOD mice: a barrier against destructive insulitis

AIMS/HYPOTHESIS

This study examined whether the capsule which encases islets of Langerhans in the NOD mouse pancreas represents a specialised extracellular matrix (ECM) or basement membrane that protects islets from autoimmune attack.

METHODS

Immunofluorescence microscopy using a panel of antibodies to collagens type IV, laminins, nidogens and perlecan was performed to localise matrix components in NOD mouse pancreas before diabetes onset, at onset of diabetes and after clinical diabetes was established (2-8.5 weeks post-onset).

RESULTS

Perlecan, a heparan sulphate proteoglycan that is characteristic of basement membranes and has not previously been investigated in islets, was localised in the peri-islet capsule and surrounding intra-islet capillaries. Other components present in the peri-islet capsule included laminin chains alpha2, beta1 and gamma1, collagen type IV alpha1 and alpha2, and nidogen 1 and 2. Collagen type IV alpha3-alpha6 were not detected. These findings confirm that the peri-islet capsule represents a specialised ECM or conventional basement membrane. The islet basement membrane was destroyed in islets where intra-islet infiltration of leucocytes marked the progression from non-destructive to destructive insulitis. No changes in basement membrane composition were observed before leucocyte infiltration.

CONCLUSIONS/INTERPRETATION

These findings suggest that the islet basement membrane functions as a physical barrier to leucocyte migration into islets and that degradation of the islet basement membrane marks the onset of destructive autoimmune insulitis and diabetes development in NOD mice. The components of the islet basement membrane that we identified predict that specialised degradative enzymes are likely to function in autoimmune islet damage.

Hydrogel encapsulation environments functionalized with extracellular matrix interactions increase islet insulin secretion

The individual and synergistic effects of extracellular matrix interactions on isolated islet function in culture were investigated within a three-dimensional poly(ethylene glycol) (PEG) hydrogel encapsulation environment. First, we observed similar glucose-stimulated insulin secretion from unencapsulated murine islets and islets photoencapsulated in PEG gels. Then islets were encapsulated in gels containing the basement membrane proteins collagen type IV and laminin, individually and in combination, at a total protein concentration of 100 microg/ml, and islet insulin secretion in response to high glucose was measured over time. Specific laminin interactions were investigated via islet encapsulation with adhesive peptide sequences found in laminin as well as via functional blocking of cell surface receptors known to bind laminin. Over 32 days, islet interactions with collagen type IV and laminin localized within the three-dimensional extracellular environment contributed to two-fold and four-fold increases in insulin secretion, respectively, relative to islets encapsulated without matrix proteins. Hydrogel compositions containing both matrix proteins and >75% laminin further increased islet insulin secretion to approximately six-fold that of islets encapsulated in the absence of matrix proteins. Encapsulation with the peptide sequence IKVAV resulted in increased islet insulin secretion, but not to the extent observed in the presence of whole laminin. Increased insulin secretion in the presence of laminin was eliminated when islets were exposed to functionally blocking anti-alpha6 integrin antibody prior to islet encapsulation with laminin. Our results demonstrate the potential of specific matrix interactions within an islet encapsulation microenvironment to promote encapsulated islet function.

Extracellular matrix protein-coated scaffolds promote the reversal of diabetes after extrahepatic islet transplantation

BACKGROUND

The survival and function of transplanted pancreatic islets is limited, owing in part to disruption of islet-matrix attachments during the isolation procedure. Using polymer scaffolds as a platform for islet transplantation, we investigated the hypothesis that replacement of key extracellular matrix components known to surround islets in vivo would improve graft function at an extrahepatic implantation site.

METHODS

Microporous polymer scaffolds fabricated from copolymers of lactide and glycolide were adsorbed with collagen IV, fibronectin, laminin-332 or serum proteins before seeding with 125 mouse islets. Islet-seeded scaffolds were then implanted onto the epididymal fat pad of syngeneic mice with streptozotocin-induced diabetes. Nonfasting glucose levels, weight gain, response to glucose challenges, and histology were used to assess graft function for 10 months after transplantation.

RESULTS

Mice transplanted with islets seeded onto scaffolds adsorbed with collagen IV achieved euglycemia fastest and their response to glucose challenge was similar to normal mice. Fibronectin and laminin similarly promoted euglycemia, yet required more time than collagen IV and less time than serum. Histopathological assessment of retrieved grafts demonstrated that coating scaffolds with specific extracellular matrix proteins increased total islet area in the sections and vessel density within the transplanted islets, relative to controls.

CONCLUSIONS

Extracellular matrix proteins adsorbed to microporous scaffolds can enhance the function of transplanted islets, with collagen IV maximizing graft function relative to the other proteins tested. These scaffolds enable the creation of well-defined microenvironments that promote graft efficacy at extrahepatic sites.

Hyperglycemia induces apoptosis of human pancreatic islet endothelial cells: effects of pravastatin on the Akt survival pathway

Pancreatic islet microendothelium and beta cells exhibit an interdependent physical and functional relationship. In this study, we analyzed the effect of chronic hyperglycemia on human pancreatic islet microendothelial cells as well as the involvement of the phosphatidylinositol 3-kinase/Akt and nephrin pathways, interleukin-1beta, and nitric oxide production. In addition, whether 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors can reverse the response to high-glucose conditions was investigated. Proliferation of purified islet microendothelial cells cultured under hyperglycemic conditions (28 mmol/L glucose) decreased compared to that of normoglycemic cells (from 12.7% after 2 days to 47.7% after 30 days, P < 0.05). In parallel, apoptosis progressively increased from 7% after 2 days to 79% after 30 days in high glucose (P < 0.05) concomitant with an early increase of caspase-3 activity. Intermittent hyperglycemia induced greater apoptosis than sustained hyperglycemia. Apoptosis was accompanied by a reduced p-Akt/Akt ratio and inhibition of nephrin tyrosine phosphorylation. Pravastatin (1 mumol/L) decreased apoptosis induced by high glucose or oxidized LDL and increased Akt phosphorylation. Hyperglycemia significantly increased the production of the proinflammatory cytokine interleukin-1beta and stimulated the expression of inducible nitric oxide synthase and the production of nitric oxide, possibly relevant to beta cell mass and function. Thus, chronic hyperglycemia reduces islet microendothelial cell survival by inhibiting the serine-threonine kinase Akt pathway, and the effect of pravastatin on this pathway represents a potential tool to improve islet vascularization and, indirectly, islet function.

Mammalian collagen IV

Four decades have passed since the first discovery of collagen IV by Kefalides in 1966. Since then collagen IV has been investigated extensively by a large number of research laboratories around the world. Advances in molecular genetics have resulted in identification of six evolutionary related mammalian genes encoding six different polypeptide chains of collagen IV. The genes are differentially expressed during the embryonic development, providing different tissues with specific collagen IV networks each having unique biochemical properties. Newly translated alpha-chains interact and assemble in the endoplasmic reticulum in a chain-specific fashion and form unique heterotrimers. Unlike most collagens, type IV collagen is an exclusive member of the basement membranes and through a complex inter- and intramolecular interactions form supramolecular networks that influence cell adhesion, migration, and differentiation. Collagen IV is directly involved in a number of genetic and acquired disease such as Alport's and Goodpasture's syndromes. Recent discoveries have also highlighted a new and direct role for collagen IV in the development of rare genetic diseases such as cerebral hemorrhage and porencephaly in infants and hemorrhagic stroke in adults. Years of intensive investigations have resulted in a vast body of information about the structure, function, and biology of collagen IV. In this review article, we will summarize essential findings on the structural and functional relationships of different collagen IV chains and their roles in health and disease.

Beyond angiogenesis: the role of endothelium in the bone marrow vascular niche

Specific tissue microenvironments, or niches, are critical for homing and maintenance of both stem cells and tumor cells in vivo. Little is known, however, about the molecular interactions between individual cells within these microenvironments. Recent studies that describe a newly identified hematopoietic stem and tumor cell vascular niche in the bone marrow (BM) suggest a critical role for vascular endothelial cell signaling and raise the possibility that bidirectional interactions of these cells with the vasculature regulate the niche dynamically. The mechanisms that govern hematopoietic stem cell (HSC)/tumor cell cross-talk with endothelial cells provide a promising new direction for future studies. Here we review recent advances that open new avenues of study in this field.

Conversion of embryonic stem cells into pancreatic beta-cell surrogates guided by ontogeny

Cellular therapies to treat Type 1 diabetes are being devised and the use of human embryonic stem cells (hESCs) offers a solution to the issue of supply, because hESCs can be maintained in a pluripotent state indefinitely. Furthermore, hESCs have advantages in terms of their plasticity and reduced immunogenicity. Several strategies that have so far been investigated indicate that hESCs are capable of differentiating into insulin producing beta-cell surrogates. However the efficiency of the differentiation procedures used is generally quite low and the cell populations derived are often highly heterogenous. A strategy that appears to have long term potential is to design differentiation procedures based on the ontogeny of the beta-cell. The focus of this strategy is to replicate signaling processes that are known to be involved in the maturation of a beta-cell. The earliest pancreatic progenitors found in the developing vertebrate fetus are produced via a process known as gastrulation and form part of the definitive endoderm germ layer. hESCs have recently been differentiated into definitive endoderm with high efficiency using a differentiation procedure that mimics the signaling that occurs during gastrulation and the formation of the definitive endoderm. Subsequent events during pancreas development involve a section of the definitive endoderm forming into pancreatic epithelium, which then branches into the pancreatic mesenchyme to form islet clusters of endocrine cells. A proportion of the endocrine precursor cells within islets develop into insulin producing beta-cells. The challenge currently is to design hESC differentiation procedures that mimic the combined events of these stages of beta-cell development.

CUTL1 promotes tumor cell migration by decreasing proteasome-mediated Src degradation

Recently, we identified the homeodomain transcription factor CUTL1 as important mediator of cell migration and tumor invasion downstream of transforming growth factor beta (TGFbeta). The molecular mechanisms and effectors mediating the pro-migratory and pro-invasive phenotype induced by CUTL1 have not been elucidated so far. Therefore, the aim of this study was to identify signaling pathways downstream of CUTL1 which are responsible for its effects on tumor cell migration. We found that the reduced motility seen after knock down of CUTL1 by RNA interference is accompanied by a delay in tumor cell spreading. This spreading defect is paralleled by a marked reduction of Src protein levels. We show that CUTL1 leads to Src protein stabilization and activation of Src-regulated downstream signaling molecules such as RhoA, Rac1, Cdc42 and ROCK. In addition, we demonstrate that CUTL1 decreases proteasome-mediated Src protein degradation, possibly via transcriptionally upregulating C-terminal Src kinase (Csk). Based on experiments using Src knockout cells (SYF), we present evidence that Src plays a crucial role in CUTL1-induced tumor cell migration. In conclusion, our findings linking the pro-invasive transcription factor CUTL1 and the Src pathway provide important new insights in the molecular effector pathways mediating CUTL-induced migration and invasion.

The effects of cell-matrix interactions on encapsulated beta-cell function within hydrogels functionalized with matrix-derived adhesive peptides

The influence of matrix-derived adhesive peptide sequences on encapsulated beta-cell survival and glucose-stimulated insulin release was explored by covalently incorporating synthetic peptide sequences within a model encapsulation environment. Photopolymerized poly(ethylene glycol) (PEG) hydrogels were functionalized via the addition of acrylate-PEG-peptide conjugates to the polymer precursor solution prior to beta-cell photoencapsulation. Individual MIN6 beta-cells were encapsulated in the presence of the laminin-derived recognition sequences, IKLLI, IKVAV, LRE, PDSGR, RGD, and YIGSR, and the collagen type I sequence, DGEA. In the absence of cell-cell and cell-matrix contacts, encapsulated MIN6 beta-cell survival diminishes within one week; however, in PEG hydrogel derivatives including the laminin sequences IKLLI and IKVAV, encapsulated beta-cells exhibit preserved viability, reduced apoptosis, and increased insulin secretion. Interactions with the laminin sequences LRE, PDSGR, RGD, and YIGSR contribute to improved viability, but insulin release from these samples was not statistically greater than that from controls. MIN6 beta-cells were also encapsulated with various concentrations of IKLLI and IKVAV (0.05-5.0mm), individually, and the peptide combinations IKLLI-IKVAV, IKVAV-YIGSR, and PDSGR-YIGSR to explore synergistic effects. The presented results give evidence that synthetic peptide epitopes may be useful in the design of an islet encapsulation environment that promotes cell survival and function via targeted cell-matrix interactions.

The vascular niche and its basement membrane

Over the past few years, scientists have realized that many cellular and developmental processes, including pancreatic beta-cell growth and differentiation, stem cell and progenitor cell proliferation and cancer cell metastasis, occur in what are known as 'vascular niches'. Despite increasing numbers of reports on these niches, few common mechanisms have been identified to explain their various effects. Here, we define the term 'vascular niche' and suggest that a common and conserved feature of this niche is to provide a basement membrane to cells that are unable to form their own. We further propose that these cells require a vascular niche when they retain a high degree of plasticity.

Impact of defined matrix interactions on insulin production by cultured human beta-cells: effect on insulin content, secretion, and gene transcription

The impact of extracellular matrix on insulin production needs to be understood both to optimize the derivation of functional beta-cells for transplantation and to understand mechanisms controlling islet neogenesis and glucose homeostasis. In this study, we present evidence that adhesion to some common matrix constituents has a profound impact on the transcription, secretion, and storage of insulin by human beta-cells. The integrin-dependent adhesion of fetal beta-cells to both collagen IV and vitronectin induces significant glucose-independent insulin secretion and a substantial reciprocal decline in insulin content. Collagen IV, but not vitronectin, induces comparable responses in adult beta-cells. Inhibition of extracellular signal-regulated kinase activation abrogates matrix-induced insulin secretion and effectively preserves the insulin content of adherent beta-cells. Using real-time PCR, we demonstrate that adhesion of both fetal and adult beta-cells to collagen IV and vitronectin also results in the marked suppression of insulin gene transcription. Based on these findings, we contend that integrin-dependent adhesion and signaling in response to certain matrices can have a significant negative impact on insulin production by primary human beta-cells. Such responses were not found to be associated with cell death but may precede beta-cell dedifferentiation.

Gene expression changes in SNAP-stimulated and iNOS-transfected tenocytes--expression of extracellular matrix genes and its implications for tendon-healing

Nitric oxide (NO) has a variety of physiological roles, including acting as a key mediator in various phases of tendon healing, but its importance as a modulator of gene expression during tendon healing has not been well studied. The current study used microarray analysis to elucidate global gene expression after transfection with inducible nitric oxide synthase (iNOS) in tenocytes isolated from the injured rotator cuff tendons of human patients. We show that the expression of a wide range of genes is affected by NO, with many activated genes having known roles in healing. Of particular significance is that NOS overexpression stimulates the transcription and translation of a range of extracellular matrix genes important to the structure of connective tissues such as tendons, including collagen Ialpha1, collagen IIIalpha1, collagen IValpha5, biglycan, decorin, laminin, and matrix metalloproteinase 10 (MMP10). These genes were also shown to respond to stimulation by the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) in a dose-dependent manner. We further show that varying levels of NO significantly affect cellular adhesion in tenocytes, a critical process during tendon repair. These findings will be of use when optimizing the dose of NO delivery in further work investigating NO as potential treatment of tendon injuries.

Perinatal development of the pancreatic islet microvasculature in rats

The aim of the present study was to investigate possible changes in the islet microvasculature during the period of pronounced beta-cell growth seen perinatally in rats. We studied islet endothelial and beta-cell proliferation, as well as islet vascular density, in rats during this period. There was a progressive increase in islet vascular density from day -1 to day 7 postpartum, with values similar to those in adult rats seen at the latter time point. (3)H-thymidine-labelled islet endothelial cells were extremely rare in adult rats, whereas such cells were much more frequent perinatally. The beta-cell labelling index was higher in all perinatal animals than in adult rats, with peak values seen on day 2. The proliferating endocrine cells were located very close to blood vessels at day 2 after birth. In conclusion, the pronounced growth of islet endocrine cells seen during the first week after birth coincides and co-localizes with an even more pronounced increase in islet endothelial cell proliferation, which results in a marked increase in intra-islet vascular density. This perinatal increase in islet blood vessel density may facilitate glucose sensing and islet hormonal delivery to the systemic circulation.

The pancreatic islet endothelial cell: emerging roles in islet function and disease

The pancreatic islets are one of the most vascularized organs of the body. This likely reflects the requirements of the organ for a rich supply of nutrients and oxygen to the tissue, as well as the need for rapid disposal of metabolites and secreted hormones. The islet endothelium is richly fenestrated to facilitate trans-endothelial transport of secreted hormones, has a unique expression of surface markers, and produces a number of vasoactive substances and growth factors. The islet endothelial cells play a critical role in the early phase of type 1 diabetes mellitus by increasing the expression of surface leucocyte-homing receptors, thereby enabling immune cells to enter the endocrine tissue and cause beta-cell destruction. Following transplantation, pancreatic islets lack a functional capillary system and need to be properly revascularized. Insufficient revascularization may severely affect the transport properties of the islet endothelial system, resulting in a dysfunctional islet graft.

Blockade of beta1 integrin-laminin-5 interaction affects spreading and insulin secretion of rat beta-cells attached on extracellular matrix

When attached on a matrix produced by a rat bladder carcinoma cell line (804G matrix), rat pancreatic beta-cells spread in response to glucose and secrete more insulin compared with cells attached on poly-l-lysine. The aim of this study was to determine whether laminin-5 and its corresponding cell receptor beta1 integrin are implicated in these phenomena. By using specific blocking antibodies, we demonstrated that laminin-5 is the component present in 804G matrix responsible for the effect of 804G matrix on beta-cell function and spreading. When expression of two well-known laminin-5 ligands, beta1 and beta4 integrin, was assessed by Western blot and RT-PCR, only the beta1 integrin was detected in beta-cells. Anti-beta1 integrin antibody reduced the spreading of beta-cells on 804G matrix. Blockade of the interaction between beta1 integrins and laminin-5 resulted in a reduction in glucose-stimulated insulin secretion. Blocking anti-beta1 integrin antibody also inhibited focal adhesion kinase phosphorylation induced by 804G matrix. In conclusion, anti-beta1 integrin and -laminin-5 antibodies interfere with spreading of beta-cells, resulting in decreased insulin secretion in response to glucose. Our findings indicate that outside-in signaling via engagement of beta1 integrins by laminin-5 is an important component of normal beta-cell function.

Rigidity sensing at the leading edge through alphavbeta3 integrins and RPTPalpha

Cells require optimal substrate stiffness for normal function and differentiation. The mechanisms for sensing matrix rigidity and durotaxis, however, are not clear. Here we showed that control, Shp2-/-, integrin beta1-/-, and talin1-/- cell lines all spread to a threefold greater area on fibronectin (FN)-coated rigid polyacrylamide surfaces than soft. In contrast, RPTPalpha-/- cells spread to the same area irrespective of rigidity on FN surfaces but spread 3x greater on rigid collagen IV-coated surfaces than soft. RPTPalpha and alphavbeta3 integrins were shown previously to be colocalized at leading edges and antibodies to alphavbeta3 blocked FN rigidity sensing. When FN beads were held with a rigid laser trap at the leading edge, stronger bonds to the cytoskeleton formed than when held with a soft trap; whereas back from the leading edge and in RPTPalpha-/- cells, weaker bonds were formed with both rigid and soft laser traps. From the rigidity of the trap, we calculate that a force of 10 pN generated in 1 s is sufficient to activate the rigidity response. We suggest that RPTPalpha and alphavbeta3 at the leading edge are critical elements for sensing FN matrix rigidity possibly through SFK activation at the edge and downstream signaling.

Activation of NF-kappaB by extracellular matrix is involved in spreading and glucose-stimulated insulin secretion of pancreatic beta cells

Laminin-5-rich extracellular matrix derived from 804G cells (804G-ECM) engages beta1 integrins to induce spreading, improve glucose-stimulated insulin secretion (GSIS), and increase survival of pancreatic beta cells. The present study examines whether 804G-ECM activates the transcriptional activity of NF-kappaB and the involvement of NF-kappaB in those effects of 804G-ECM on pancreatic beta cells. 804G-ECM induces nuclear translocation and the DNA binding activity of the p65 subunit of NF-kappaB. 804G-ECM-induced nuclear translocation of NF-kappaB was weak as compared with that induced by interleukin-1beta. Transient 804G-ECM-induced DNA binding activity of NF-kappaB (peak at 2 h) and overexpression of NF-kappaB target genes IkappaB alpha and NF-kappaB1(p105) (peak at 4 h) were observed. When NF-kappaB was inhibited by an inhibitor of IkappaB alpha phosphorylation (Bay 11-7082) or by a recombinant adenovirus expressing the nonphosphorylatable form of IkappaB alpha, 804G-ECM-induced cell spreading and actin cytoskeleton organization were reduced. GSIS from cells on 804G-ECM was inhibited 5-fold, whereas cell survival was not affected. In summary, the results indicate that 804G-ECM induces a transient and moderate NF-kappaB activity. This study shows for the first time that ECM-induced NF-kappaB activity is necessary in maintaining GSIS, although it does not affect survival of pancreatic beta cells. The effects of ECM-induced NF-kappaB activity contrast with the deleterious effects of cytokine-induced NF-kappaB activity. It is proposed that transient and moderate NF-kappaB activity is essential for proper function of the pancreatic beta cell.