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

Matrix design for optimal pancreatic β cells transplantation

New therapeutic approaches to treat type 1 diabetes mellitus relies on pancreatic islet transplantation. Here, developing immuno-isolation strategies is essential to eliminate the need for systemic immunosuppression after pancreatic islet grafts. A solution is the macro-encapsulation of grafts in semipermeable matrixes with a double function: separating islets from host immune cells and facilitating the diffusion of insulin, glucose, and other metabolites. This study aims to synthesize and characterize different types of gelatin-collagen matrixes to prepare a macro-encapsulation device for pancreatic islets that fulfill these functions. While natural polymers exhibit superior biocompatibility compared to synthetic ones, their mechanical properties are challenging to reproduce. To address this issue, we conducted a comparative analysis between photo-crosslinked gelatin matrixes and chemically crosslinked collagen matrixes. We show that the different crosslinkers and polymerization methods influence the survival and glucose-stimulated insulin production of pancreatic β cells (INS1) in vitro, as well as the in vitro and in vivo stability of the matrix and the immuno-isolation in vivo. Among the matrixes, the stiff multilayer GelMA matrixes (8.5 kPa), fabricated by digital light processing, were the best suited for pancreatic β cells macro-encapsulation regarding these parameters. Within the alveoli of this matrix, pancreatic β cells spontaneously formed aggregates.

ECM-based bioactive microencapsulation significantly improves islet function and graft performance

Microencapsulation is a promising strategy to prolong the survival and function of transplanted pancreatic islets for diabetes therapy, albeit its translation has been impeded by incoherent graft performance. The use of decellularized ECM has lately gained substantial research momentum due to its innate capacity to augment the function of cells originating from the same tissue type. In the present study, the advantages of both these approaches are leveraged in a porcine pancreatic ECM (pECM)-based microencapsulation platform, thus significantly enhancing murine pancreatic islet performance. pECM-encapsulated islets sustain high insulin secretion levels in vitro, surpassing those of islets encapsulated in conventional alginate microcapsules. Moreover, pECM-encapsulated islet cells proliferate and produce an enriched intra-islet ECM framework, displaying a distinctive structural rearrangement. The beneficial effect of pECM encapsulation is further reinforced by the temporary protection against cytokine-induced cytotoxicity. In-vivo, this platform significantly improves glucose tolerance and achieves glycemic correction in 100% of immunocompetent diabetic mice without any immunosuppression, compared to only 50% mice achieved glycemic correction by alginate encapsulation. Altogether, the results presented herein reveal that pECM-based microencapsulation offers a natural pancreatic niche that can restore the function of isolated pancreatic islets and deliver them safely, avoiding the need for immunosuppression. STATEMENT OF SIGNIFICANCE: Aiming to improve pancreatic islet transplantation outcomes in diabetic patients, we developed a microencapsulation platform based on pancreatic extracellular matrix (pECM). In these microcapsules the islets are entrapped within a pECM hydrogel that mimics the natural pancreatic microenvironment. We show that pECM encapsulation supports the islets' viability and function in culture, and provides temporal protection against cytokine-induced stress. In a diabetic mouse model, pECM encapsulation significantly improved glucose tolerance and achieved glycemic correction without any immunosuppression. These results reveal the potential of pECM encapsulation as a viable treatment for diabetes, providing a solid scientific basis for more advanced preclinical studies.

Insulin secretion hot spots in pancreatic β cells as secreting adhesions

Pancreatic β cell secretion of insulin is crucial to the maintenance of glucose homeostasis and prevention of diseases related to glucose regulation, including diabetes. Pancreatic β cells accomplish efficient insulin secretion by clustering secretion events at the cell membrane facing the vasculature. Regions at the cell periphery characterized by clustered secretion are currently termed insulin secretion hot spots. Several proteins, many associated with the microtubule and actin cytoskeletons, are known to localize to and serve specific functions at hot spots. Among these proteins are the scaffolding protein ELKS, the membrane-associated proteins LL5β and liprins, the focal adhesion-associated protein KANK1, and other factors typically associated with the presynaptic active zone in neurons. These hot spot proteins have been shown to contribute to insulin secretion, but many questions remain regarding their organization and dynamics at hot spots. Current studies suggest microtubule- and F-actin are involved in regulation of hot spot proteins and their function in secretion. The hot spot protein association with the cytoskeleton networks also suggests a potential role for mechanical regulation of these proteins and hot spots in general. This perspective summarizes the existing knowledge of known hot spot proteins, their cytoskeletal-mediated regulation, and discuss questions remaining regarding mechanical regulation of pancreatic beta cell hot spots.

β1-Integrin-A Key Player in Controlling Pancreatic Beta-Cell Insulin Secretion via Interplay With SNARE Proteins

Shortcomings in cell-based therapies for patients with diabetes have been revealed to be, in part, a result of an improper extracellular matrix (ECM) environment. In vivo, pancreatic islets are emersed in a diverse ECM that provides physical support and is crucial for healthy function. β1-Integrin receptors have been determined to be responsible for modulation of beneficial interactions with ECM proteins influencing beta-cell development, proliferation, maturation, and function. β1-Integrin signaling has been demonstrated to augment insulin secretion by impacting the actin cytoskeleton via activation of focal adhesion kinase and downstream signaling pathways. In other secretory cells, evidence of a bidirectional relationship between integrins and exocytotic machinery has been demonstrated, and, thus, this relationship could be present in pancreatic beta cells. In this review, we will discuss the role of ECM-β1-integrin interplay with exocytotic proteins in controlling pancreatic beta-cell insulin secretion through their dynamic and unique signaling pathway.

Collagen IV-β1-Integrin Influences INS-1 Cell Insulin Secretion via Enhanced SNARE Protein Expression

β1-integrin is a key receptor that regulates cell-ECM interactions and is important in maintaining mature beta-cell functions, including insulin secretion. However, there is little reported about the relationship between ECM-β1-integrin interactions and exocytotic proteins involved in glucose-stimulated insulin secretion (GSIS). This study examined the effect of collagen IV-β1-integrin on exocytotic proteins (Munc18-1, Snap25, and Vamp2) involved in insulin secretion using rat insulinoma (INS-1) cell line. Cells cultured on collagen IV (COL IV) had promoted INS-1 cell focal adhesions and GSIS. These cells also displayed changes in levels and localization of β1-integrin associated downstream signals and exocytotic proteins involved in insulin secretion. Antibody blocking of β1-integrin on INS-1 cells cultured on COL IV showed significantly reduced cell adhesion, spreading and insulin secretion along with reduced exocytotic protein levels. Blocking of β1-integrin additionally influenced the cellular localization of exocytotic proteins during the time of GSIS. These results indicate that specific collagen IV-β1-integrin interactions are critical for proper beta-cell insulin secretion.

Insulin enhances neurite extension and myelination of diabetic neuropathy neurons

Background

The authors established an in vitro model of diabetic neuropathy based on the culture system of primary neurons and Schwann cells (SCs) to mimic similar symptoms observed in in vivo models of this complication, such as impaired neurite extension and impaired myelination. The model was then utilized to investigate the effects of insulin on enhancing neurite extension and myelination of diabetic neurons.

Methods

SCs and primary neurons were cultured under conditions mimicking hyperglycemia prepared by adding glucose to the basal culture medium. In a single culture, the proliferation and maturation of SCs and the neurite extension of neurons were evaluated. In a co-culture, the percentage of myelination of diabetic neurons was investigated. Insulin at different concentrations was supplemented to culture media to examine its effects on neurite extension and myelination.

Results

The cells showed similar symptoms observed in in vivo models of this complication. In a single culture, hyperglycemia attenuated the proliferation and maturation of SCs, induced apoptosis, and impaired neurite extension of both sensory and motor neurons. In a co-culture of SCs and neurons, the percentage of myelinated neurites in the hyperglycemia-treated group was significantly lower than that in the control group. This impaired neurite extension and myelination was reversed by the introduction of insulin to the hyperglycemic culture media.

Conclusions

Insulin may be a potential candidate for improving diabetic neuropathy. Insulin can function as a neurotrophic factor to support both neurons and SCs. Further research is needed to discover the potential of insulin in improving diabetic neuropathy.

Organization and dynamics of the cortical complexes controlling insulin secretion in β-cells

Insulin secretion in pancreatic β-cells is regulated by cortical complexes that are enriched at the sites of adhesion to extracellular matrix facing the vasculature. Many components of these complexes, including bassoon, RIM, ELKS and liprins, are shared with neuronal synapses. Here, we show that insulin secretion sites also contain the non-neuronal proteins LL5β (also known as PHLDB2) and KANK1, which, in migrating cells, organize exocytotic machinery in the vicinity of integrin-based adhesions. Depletion of LL5β or focal adhesion disassembly triggered by myosin II inhibition perturbed the clustering of secretory complexes and attenuated the first wave of insulin release. Although previous analyses in vitro and in neurons have suggested that secretory machinery might assemble through liquid–liquid phase separation, analysis of endogenously labeled ELKS in pancreatic islets indicated that its dynamics is inconsistent with such a scenario. Instead, fluorescence recovery after photobleaching and single-molecule imaging showed that ELKS turnover is driven by binding and unbinding to low-mobility scaffolds. Both the scaffold movements and ELKS exchange were stimulated by glucose treatment. Our findings help to explain how integrin-based adhesions control spatial organization of glucose-stimulated insulin release.

Summary: Characterization of the composition of cortical complexes controlling insulin secretion, showing that their dynamics is inconsistent with assembly through liquid–liquid phase separation.

TUDCA receptors and their role on pancreatic beta cells

Bile acids have received increasing attention over the past years as their multiple alternative roles became clearer. Tauroursodeoxycholic Acid (TUDCA) in specific has generated special interest due to its ability to promote pancreatic survival and function, as well as reduce endoplasmic reticulum stress. However, there are few studies explaining the molecular mechanisms behind TUDCA's beneficial actions on pancreatic beta cells. In this review, we decided to review the literature in order to craft a primer for researchers on what is known about TUDCA's receptors and the molecular pathways involved in this bile acid's function in the endocrine pancreas. We review the studies that focused on G protein-coupled bile acid receptor (TGR5), Sphingosine-1-phosphate receptor 2 (S1PR2) and α5β1 Integrin function in pancreatic cells. Our hope is to provide a basis for future studies to expand upon, especially considering the current lack of studies focusing on the importance of these receptors, either through TUDCA signaling or other signaling molecules.

Activation of Pancreatic Stellate Cells Is Beneficial for Exocrine but Not Endocrine Cell Differentiation in the Developing Human Pancreas

Pancreatic stellate cells (PaSCs) are non-endocrine, mesenchymal-like cells that reside within the peri-pancreatic tissue of the rodent and human pancreas. PaSCs regulate extracellular matrix (ECM) turnover in maintaining the integrity of pancreatic tissue architecture. Although there is evidence indicating that PaSCs are involved in islet cell survival and function, its role in islet cell differentiation during human pancreatic development remains unclear. The present study examines the expression pattern and functional role of PaSCs in islet cell differentiation of the developing human pancreas from late 1st to 2nd trimester of pregnancy. The presence of PaSCs in human pancreata (8–22 weeks of fetal age) was characterized by ultrastructural, immunohistological, quantitative RT-PCR and western blotting approaches. Using human fetal PaSCs derived from pancreata at 14–16 weeks, freshly isolated human fetal islet-epithelial cell clusters (hIECCs) were co-cultured with active or inactive PaSCs in vitro. Ultrastructural and immunofluorescence analysis demonstrated a population of PaSCs near ducts and newly formed islets that appeared to make complex cell-cell dendritic-like contacts. A small subset of PaSCs co-localized with pancreatic progenitor-associated transcription factors (PDX1, SOX9, and NKX6-1). PaSCs were highly proliferative, with significantly higher mRNA and protein levels of PaSC markers (desmin, αSMA) during the 1st trimester of pregnancy compared to the 2nd trimester. Isolated human fetal PaSCs were identified by expression of stellate cell markers and ECM. Suppression of PaSC activation, using all-trans retinoic acid (ATRA), resulted in reduced PaSC proliferation and ECM proteins. Co-culture of hIECCs, directly on PaSCs or indirectly using Millicell^® Inserts or using PaSC-conditioned medium, resulted in a reduction the number of insulin⁺ cells but a significant increase in the number of amylase⁺ cells. Suppression of PaSC activation or Notch activity during the co-culture resulted in an increase in beta-cell differentiation. This study determined that PaSCs, abundant during the 1st trimester of pancreatic development but decreased in the 2nd trimester, are located near ductal and islet structures. Direct and indirect co-cultures of hIECCs with PaSCs suggest that activation of PaSCs has opposing effects on beta-cell and exocrine cell differentiation during human fetal pancreas development, and that these effects may be dependent on Notch signaling.

Beta-cell β1 integrin deficiency affects in utero development of islet growth and vascularization

The β1 integrin subunit contributes to pancreatic beta cell growth and function through communication with the extracellular matrix (ECM). The effects of in vitro and in vivo β1 integrin knockout have been extensively studied in mature islets, yet no study to date has examined how the loss of β1 integrin during specific stages of pancreatic development impacts beta cell maturation. Beta-cell-specific tamoxifen-inducible Cre recombinase (MIP-CreERT) mice were crossed with mice containing floxed Itgb1 (β1 integrin) to create an inducible mouse model (MIPβ1KO) at the second transition stage (e13.5) of pancreas development. By e19.5-20.5, the expression of beta-cell β1 integrin in fetal MIPβ1KO mice was significantly reduced and these mice displayed decreased beta cell mass, density and proliferation. Morphologically, fetal MIPβ1KO pancreata exhibited reduced islet vascularization and nascent endocrine cells in the ductal region. In addition, decreased ERK phosphorylation was observed in fetal MIPβ1KO pancreata. The expression of transcription factors needed for beta-cell development was unchanged in fetal MIPβ1KO pancreata. The findings from this study demonstrate that β1 integrin signaling is required during a transition-specific window in the developing beta-cell to maintain islet mass and vascularization.

Silibinin's regulation of proliferation and collagen gene expressions of rat pancreatic β-cells cultured on types I and V collagen involves β-catenin nuclear translocation

Extracellular matrix (ECM) molecules have multiple functions; prevention of cytotoxicity, provision of mechanical support, cell adhesive substrates and structural integrity in addition to mediation of cellular signaling. In this study, we report that the proliferation of INS-1 cells cultured on collagen I-coated dishes is enhanced, but it is inhibited on collagen V-coated dishes. Inhibitory proliferation on collagen V-coated is not due to apoptosis induction. Silibinin decreases hepatic glucose production and protects pancreatic β-cells, as a potential medicine for type II diabetes. Silibinin up-regulates the proliferation of cells cultured on both collagen I- and V-coated dishes. Collagen-coating regulates gene expression of collagen in a collagen type-related manner. Silibinin increases mRNA expression of collagen I in the cells on collagen I- and V-coated dishes; however, silibinin decreases collagen V mRNA expression on collagen I- and V-coated dishes. Collagen I-coating significantly enhances nuclear translocation of β-catenin, while collagen V-coating reduces it. Differential effects of silibinin on collagen I mRNA and collagen V mRNA can be accounted for by the finding that silibinin enhances nuclear translocation of β-catenin on both collagen I- and V-coated dishes, since phenomenologically nuclear translocation of β-catenin enhances collagen I mRNA but represses collagen V mRNA. These results demonstrate that nuclear translocation of β-catenin up-regulates proliferation and collagen I gene expression, whereas it down-regulates collagen V gene expression of INS-1 cells. Differential gene expressions of collagen I and V by nuclear β-catenin could be important for understanding fibrosis where collagen I and V may have differential effects.

Extracellular Matrix-Associated Factors Play Critical Roles in Regulating Pancreatic β-Cell Proliferation and Survival

This review describes formation of the islet basement membrane and the function of extracellular matrix (ECM) components in β-cell proliferation and survival. Implications for islet transplantation are discussed. The insulin-producing β-cell is key for maintaining glucose homeostasis. The islet microenvironment greatly influences β-cell survival and proliferation. Within the islet, β-cells contact the ECM, which is deposited primarily by intraislet endothelial cells, and this interaction has been shown to modulate proliferation and survival. ECM-localized growth factors, such as vascular endothelial growth factor and cellular communication network 2, signal through specific receptors and integrins on the β-cell surface. Further understanding of how the ECM functions to influence β-cell proliferation and survival will provide targets for enhancing functional β-cell mass for the treatment of diabetes.

Stem-cell based organ-on-a-chip models for diabetes research

Diabetes mellitus (DM) ranks among the severest global health concerns of the 21st century. It encompasses a group of chronic disorders characterized by a dysregulated glucose metabolism, which arises as a consequence of progressive autoimmune destruction of pancreatic beta-cells (type 1 DM), or as a result of beta-cell dysfunction combined with systemic insulin resistance (type 2 DM). Human cohort studies have provided evidence of genetic and environmental contributions to DM; yet, these studies are mostly restricted to investigating statistical correlations between DM and certain risk factors. Mechanistic studies, on the other hand, aimed at re-creating the clinical picture of human DM in animal models. A translation to human biology is, however, often inadequate owing to significant differences between animal and human physiology, including the species-specific glucose regulation. Thus, there is an urgent need for the development of advanced human in vitro models with the potential to identify novel treatment options for DM. This review provides an overview of the technological advances in research on DM-relevant stem cells and their integration into microphysiological environments as provided by the organ-on-a-chip technology.

SPARC is required for the maintenance of glucose homeostasis and insulin secretion in mice

Obesity, metabolic syndrome, and type 2 diabetes, three strongly interrelated diseases, are associated to increased morbidity and mortality worldwide. The pathogenesis of obesity-associated disorders is still under study. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular glycoprotein expressed in many cell types including adipocytes, parenchymal, and non-parenchymal hepatic cells and pancreatic cells. Studies have demonstrated that SPARC inhibits adipogenesis and promotes insulin resistance; in addition, circulating SPARC levels were positively correlated with body mass index in obese individuals. Therefore, SPARC is being proposed as a key factor in the pathogenesis of obesity-associated disorders. The aim of this study is to elucidate the role of SPARC in glucose homeostasis. We show here that SPARC null (SPARC−/−) mice displayed an abnormal insulin-regulated glucose metabolism. SPARC−/− mice presented an increased adipose tissue deposition and an impaired glucose homeostasis as animals aged. In addition, the absence of SPARC worsens high-fat diet-induced diabetes in mice. Interestingly, although SPARC−/− mice on high-fat diet were sensitive to insulin they showed an impaired insulin secretion capacity. Of note, the expression of glucose transporter 2 in islets of SPARC−/− mice was dramatically reduced. The present study provides the first evidence that deleted SPARC expression causes diabetes in mice. Thus, SPARC deficient mice constitute a valuable model for studies concerning obesity and its related metabolic complications, including diabetes.

The adhesion receptor GPR56 is activated by extracellular matrix collagen III to improve β-cell function

AIMS

G-protein coupled receptor 56 (GPR56) is the most abundant islet-expressed G-protein coupled receptor, suggesting a potential role in islet function. This study evaluated islet expression of GPR56 and its endogenous ligand collagen III, and their effects on β-cell function.

METHODS

GPR56 and collagen III expression in mouse and human pancreas sections was determined by fluorescence immunohistochemistry. Effects of collagen III on β-cell proliferation, apoptosis, intracellular calcium ([Ca2+]i) and insulin secretion were determined by cellular BrdU incorporation, caspase 3/7 activities, microfluorimetry and radioimmunoassay, respectively. The role of GPR56 in islet vascularisation and innervation was evaluated by immunohistochemical staining for CD31 and TUJ1, respectively, in pancreases from wildtype (WT) and Gpr56-/- mice, and the requirement of GPR56 for normal glucose homeostasis was determined by glucose tolerance tests in WT and Gpr56-/- mice.

RESULTS

Immunostaining of mouse and human pancreases revealed that GPR56 was expressed by islet β-cells while collagen III was confined to the peri-islet basement membrane and islet capillaries. Collagen III protected β-cells from cytokine-induced apoptosis, triggered increases in [Ca2+]i and potentiated glucose-induced insulin secretion from WT islets but not from Gpr56-/- islets. Deletion of GPR56 did not affect glucose-induced insulin secretion in vitro and it did not impair glucose tolerance in adult mice. GPR56 was not required for normal islet vascularisation or innervation.

CONCLUSION

We have demonstrated that collagen III improves islet function by increasing insulin secretion and protecting against apoptosis. Our data suggest that collagen III may be effective in optimising islet function to improve islet transplantation outcomes, and GPR56 may be a target for the treatment of type 2 diabetes.

Identification of novel high-impact recessively inherited type 2 diabetes risk variants in the Greenlandic population

AIMS/HYPOTHESIS

In a recent study using a standard additive genetic model, we identified a TBC1D4 loss-of-function variant with a large recessive impact on risk of type 2 diabetes in Greenlanders. The aim of the current study was to identify additional genetic variation underlying type 2 diabetes using a recessive genetic model, thereby increasing the power to detect variants with recessive effects.

METHODS

We investigated three cohorts of Greenlanders (B99, n = 1401; IHIT, n = 3115; and BBH, n = 547), which were genotyped using Illumina MetaboChip. Of the 4674 genotyped individuals passing quality control, 4648 had phenotype data available, and type 2 diabetes association analyses were performed for 317 individuals with type 2 diabetes and 2631 participants with normal glucose tolerance. Statistical association analyses were performed using a linear mixed model.

RESULTS

Using a recessive genetic model, we identified two novel loci associated with type 2 diabetes in Greenlanders, namely rs870992 in ITGA1 on chromosome 5 (OR 2.79, p = 1.8 × 10-8), and rs16993330 upstream of LARGE1 on chromosome 22 (OR 3.52, p = 1.3 × 10-7). The LARGE1 variant did not reach the conventional threshold for genome-wide significance (p < 5 × 10-8) but did withstand a study-wide Bonferroni-corrected significance threshold. Both variants were common in Greenlanders, with minor allele frequencies of 23% and 16%, respectively, and were estimated to have large recessive effects on risk of type 2 diabetes in Greenlanders, compared with additively inherited variants previously observed in European populations.

CONCLUSIONS/INTERPRETATION

We demonstrate the value of using a recessive genetic model in a historically small and isolated population to identify genetic risk variants. Our findings give new insights into the genetic architecture of type 2 diabetes, and further support the existence of high-effect genetic risk factors of potential clinical relevance, particularly in isolated populations.

DATA AVAILABILITY

The Greenlandic MetaboChip-genotype data are available at European Genome-Phenome Archive (EGA; https://ega-archive.org/ ) under the accession EGAS00001002641.

Extracellular matrix molecules and their potential contribution to the function of transplanted pancreatic islets

Extracellular matrix (ECM) molecules are responsible for structural and biochemical support, as well as for regulation of molecular signalling and tissue repair in many organ structures, including the pancreas. In pancreatic islets, collagen type IV and VI, and laminins are the most abundant molecules, but other ECM molecules are also present. The ECM interacts with specific combinations of integrin α/β heterodimers on islet cells and guides many cellular processes. More specifically, some ECM molecules are involved in beta cell survival, function and insulin production, while others can fine tune the susceptibility of islet cells to cytokines. Further, some ECM induce release of growth factors to facilitate tissue repair. During enzymatic isolation of islets for transplantation, the ECM is damaged, impacting islet function. However, restoration of the ECM in human islets (for example by adding ECM to the interior of immunoprotective capsules) has been shown to enhance islet function. Here, we provide current insight into the role of ECM molecules in islet function and discuss the clinical potential of ECM manipulation to enhance pancreatic islet function and survival.

Therapeutic Strategies for Modulating the Extracellular Matrix to Improve Pancreatic Islet Function and Survival After Transplantation

PURPOSES OF REVIEW

Extracellular matrix (ECM) components modulate the interaction between pancreatic islet cells. During the islet isolation prior to transplantation as treatment for type 1 diabetes, the ECM is disrupted impacting functional graft survival. Recently, strategies for restoring ECM have shown to improve transplantation outcomes. This review discusses the current therapeutic strategies to modulate ECM components to improve islet engraftment.

RECENT FINDINGS

Approaches applied are seeding islets in ECM of decellularized organs, supplementation of specific ECM components in polymeric scaffolds or immunoisolating capsules, and stimulating islet ECM production with specific growth factors or ECM-producing cells. These strategies have shown success in improving functional islet survival. However, the same experiments show that caution should be taken as some ECM components may negatively impact islet function and engraftment. ECM restoration resulted in improved transplantation outcomes, but careful selection of beneficial ECM components and strategies is warranted.

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

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

Role and impact of the extracellular matrix on integrin-mediated pancreatic β-cell functions

Understanding the organisation and role of the extracellular matrix (ECM) in islets of Langerhans is critical for maintaining pancreatic β-cells, and to recognise and revert the physiopathology of diabetes. Indeed, integrin-mediated adhesion signalling in response to the pancreatic ECM plays crucial roles in β-cell survival and insulin secretion, two major functions, which are affected in diabetes. Here, we would like to present an update on the major components of the pancreatic ECM, their role during integrin-mediated cell-matrix adhesions and how they are affected during diabetes. To treat diabetes, a promising approach consists in replacing β-cells by transplantation. However, efficiency is low, because β-cells suffer of anoikis, due to enzymatic digestion of the pancreatic ECM, which affects the survival of insulin-secreting β-cells. The strategy of adding ECM components during transplantation, to reproduce the pancreatic microenvironment, is a challenging task, as many of the regulatory mechanisms that control ECM deposition and turnover are not sufficiently understood. A better comprehension of the impact of the ECM on the adhesion and integrin-dependent signalling in β-cells is primordial to improve the healthy state of islets to prevent the onset of diabetes as well as for enhancing the efficiency of the islet transplantation therapy.

Maintaining human fetal pancreatic stellate cell function and proliferation require β1 integrin and collagen I matrix interactions

Pancreatic stellate cells (PaSCs) are cells that are located around the acinar, ductal, and vasculature tissue of the rodent and human pancreas, and are responsible for regulating extracellular matrix (ECM) turnover and maintaining the architecture of pancreatic tissue. This study examines the contributions of integrin receptor signaling in human PaSC function and survival. Human PaSCs were isolated from pancreata collected during the 2nd trimester of pregnancy and identified by expression of stellate cell markers, ECM proteins and associated growth factors. Multiple integrins are found in isolated human PaSCs, with high levels of β1, α3 and α5. Cell adhesion and migration assays demonstrated that human PaSCs favour collagen I matrix, which enhanced PaSC proliferation and increased TGFβ1, CTGF and α3β1 integrin. Significant activation of FAK/ERK and AKT signaling pathways, and up-regulation of cyclin D1 protein levels, were observed within PaSCs cultured on collagen I matrix. Blocking β1 integrin significantly decreased PaSC adhesion, migration and proliferation, further complementing the aforementioned findings. This study demonstrates that interaction of β1 integrin with collagen I is required for the proliferation and function of human fetal PaSCs, which may contribute to the biomedical engineering of the ECM microenvironment needed for the efficient regulation of pancreatic development.

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

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

Maintenance of ischemic β cell viability through delivery of lipids and ATP by targeted liposomes

Islet transplantation is a promising treatment for type 1 diabetes, but despite the successes, existing challenges prevent widespread application. Ischemia, occurring during pancreas preservation and isolation, as well as after islet transplantation, decreases islet viability and function. We hypothesized that the liposomal delivery of adenosine triphosphate (ATP) could prevent the loss of cell viability during an ischemic insult. In this work we use a model β cell line, INS-1 to probe the liposome/cell interactions and examined the ability of liposomes functionalized with the fibronectin-mimetic peptide PR_b to facilitate the delivery of ATP to ischemic β cells. We demonstrate that PR_b increases the binding and internalization of liposomes to the β cells. Unexpectedly, when comparing the ability of PR_b liposomes with and without ATP to protect INS-1 cells from ischemia we found that both formulations increased cell survival. By probing the functional activity of ischemic cells treated with PR_b functionalized liposomes with and without ATP we find that both lipids and ATP play a role in maintaining cell metabolic activity after an ischemic insult and preventing cell necrosis. This approach may be beneficial for preventing ischemia related damage to islet cells, especially in the organ preservation stage.

Microenvironmental stimuli for proliferation of functional islet β-cells

Diabetes is characterized by high blood glucose level due to either autoimmune destruction of islet β-cells or insufficient insulin secretion or glucose non-responsive production of insulin by β-cells. It is highly desired to replace biological functional β-cells for the treatment of diabetes. Unfortunately, β-cells proliferate with an extremely low rate. This cellular property hinders cell-based therapy for clinical application. Many attempts have been made to develop techniques that allow production of large quantities of clinically relevant islet β-cells in vitro. A line of studies evidently demonstrate that β-cells can proliferate under certain circumstances, giving the hopes for generating and expanding these cells in vitro and transplanting them to the recipient. In this review, we discuss the requirements of microenvironmental stimuli that stimulate β-cell proliferation in cell cultures. We highlight advanced approaches for augmentation of β-cell expansion that have recently emerged in this field. Furthermore, knowing the signaling pathways and molecular mechanisms would enable manipulating cell proliferation and optimizing its insulin secretory function. Thus, signaling pathways involved in the enhancement of cell proliferation are discussed as well.

Fibrin improves beta (INS-1) cell function, proliferation and survival through integrin αvβ3

Extracellular matrix (ECM)-integrin stimulation can promote beta cell differentiation, proliferation and function. However, beta cells lose their insulin secretion function in response to glucose stimulation, and senesce when cultured with ECM proteins for a long time. Fibrin is a provisional ECM protein that is capable of maintaining beta cell function, yet the mechanisms by which this occurs is unknown. The present study examined how fibrin interacts with integrin receptors to promote beta cell cluster formation, proliferation and function. The rat insulinoma cell line, INS-1, was cultured on tissue-culture polystyrene, or with 2-D or 3-D fibrin gels for up to 4 weeks. Cells cultured with fibrin formed islet-like clusters and showed direct contacts with fibrin determined by scanning electron microscopy. Fibrin-cultured INS-1 cells also had significantly increased glucose-stimulated insulin secretion. A significant increase in integrin αvβ3 protein and phosphorylated FAK, Erk1/2 and Akt levels was observed in fibrin-cultured INS-1 cells, which was associated with significantly increased cell proliferation and decreased cell apoptosis. Integrin αvβ3 blockade affected INS-1 cell spreading on fibrin gels, and resulted in significantly decreased FAK phosphorylation and increased cleaved caspase-3 levels. These results show that fibrin promotes beta cell function, proliferation and survival via integrin αvβ3 interactions.

Co-culture of neural crest stem cells (NCSC) and insulin producing beta-TC6 cells results in cadherin junctions and protection against cytokine-induced beta-cell death

Purpose

Transplantation of pancreatic islets to Type 1 diabetes patients is hampered by inflammatory reactions at the transplantation site leading to dysfunction and death of insulin producing beta-cells. Recently we have shown that co-transplantation of neural crest stem cells (NCSCs) together with the islet cells improves transplantation outcome. The aim of the present investigation was to describe in vitro interactions between NCSCs and insulin producing beta-TC6 cells that may mediate protection against cytokine-induced beta-cell death.

Procedures

Beta-TC6 and NCSC cells were cultured either alone or together, and either with or without cell culture inserts. The cultures were then exposed to the pro-inflammatory cytokines IL-1β and IFN-γ for 48 hours followed by analysis of cell death rates (flow cytometry), nitrite production (Griess reagent), protein localization (immunofluorescence) and protein phosphorylation (flow cytometry).

Results

We observed that beta-TC6 cells co-cultured with NCSCs were protected against cytokine-induced cell death, but not when separated by cell culture inserts. This occurred in parallel with (i) augmented production of nitrite from beta-TC6 cells, indicating that increased cell survival allows a sustained production of nitric oxide; (ii) NCSC-derived laminin production; (iii) decreased phospho-FAK staining in beta-TC6 cell focal adhesions, and (iv) decreased beta-TC6 cell phosphorylation of ERK(T202/Y204), FAK(Y397) and FAK(Y576). Furthermore, co-culture also resulted in cadherin and beta-catenin accumulations at the NCSC/beta-TC6 cell junctions. Finally, the gap junction inhibitor carbenoxolone did not affect cytokine-induced beta-cell death during co-culture with NCSCs.

Conclusion

In summary, direct contacts, but not soluble factors, promote improved beta-TC6 viability when co-cultured with NCSCs. We hypothesize that cadherin junctions between NCSC and beta-TC6 cells promote powerful signals that maintain beta-cell survival even though ERK and FAK signaling are suppressed. It may be that future strategies to improve islet transplantation outcome may benefit from attempts to increase beta-cell cadherin junctions to neighboring cells.

INS-1 cell glucose-stimulated insulin secretion is reduced by the downregulation of the 67 kDa laminin receptor

Understanding β cell-extracellular matrix (ECM) interactions can advance our knowledge of the mechanisms that control glucose homeostasis and improve culture methods used in islet transplantation for the treatment of diabetes. Laminin is the main constituent of the basement membrane and is involved in pancreatic β cell survival and function, even enhancing glucose-stimulated insulin secretion. Most of the studies on cell responses towards laminin have focused on integrin-mediated interactions, while much less attention has been paid on non-integrin receptors, such as the 67 kDa laminin receptor (67LR). The specificity of the receptor-ligand interaction through the adhesion of INS-1 cells (a rat insulinoma cell line) to CDPGYIGSR-, GRGDSPC- or CDPGYIGSR + GRGDSPC-covered surfaces was evaluated. Also, the effects of the 67LR knocking down over glucose-stimulated insulin secretion were investigated. Culture of the INS-1 cells on the bioactive surfaces was improved compared to the low-fouling carboxymethyl dextran (CMD) surfaces, while downregulation of the 67LR resulted in reduced cell adhesion to surfaces bearing the CDPGYIGSR peptide. Glucose-stimulated insulin secretion was hindered by downregulation of the 67LR, regardless of the biological motif available on the biomimetic surfaces on which the cells were cultured. This finding illustrates the importance of the 67LR in glucose-stimulated insulin secretion and points to a possible role of the 67LR in the mechanisms of insulin secretion.

A 3D cell culture system: separation distance between INS-1 cell and endothelial cell monolayers co-cultured in fibrin influences INS-1 cells insulin secretion

The aim of this study was to develop an in vitro cell culture system allowing studying the effect of separation distance between monolayers of rat insulinoma cells (INS-1) and human umbilical vein endothelial cells (HUVEC) co-cultured in fibrin over INS-1 cell insulin secretion. For this purpose, a three-dimensional (3D) cell culture chamber was designed, built using micro-fabrication techniques and validated. The co-culture was successfully carried out and the effect on INS-1 cell insulin secretion was investigated. After 48 and 72 h, INS-1 cells co-cultured with HUVEC separated by a distance of 100 µm revealed enhanced insulin secretion compared to INS-1 cells cultured alone or co-cultured with HUVEC monolayers separated by a distance of 200 µm. These results illustrate the importance of the separation distance between two cell niches for cell culture design and the possibility to further enhance the endocrine function of beta cells when this factor is considered.

Inhibition of Gsk3β activity improves β-cell function in c-KitWv/+ male mice

Previous studies have shown that the stem cell marker, c-Kit, is involved in glucose homeostasis. We recently reported that c-Kit(Wv/+) male mice displayed the onset of diabetes at 8 weeks of age; however, the mechanisms by which c-Kit regulates β-cell proliferation and function are unknown. The purpose of this study is to examine if c-Kit(Wv/+) mutation-induced β-cell dysfunction is associated with downregulation of the phospho-Akt/Gsk3β pathway in c-Kit(Wv/+) male mice. Histology and cell signaling were examined in C57BL/6J/Kit(Wv/+) (c-Kit(Wv/+)) and wild-type (c-Kit(+/+)) mice using immunofluorescence and western blotting approaches. The Gsk3β inhibitor, 1-azakenpaullone (1-AKP), was administered to c-Kit(Wv/+) and c-Kit(+/+) mice for 2 weeks, whereby alterations in glucose metabolism were examined and morphometric analyses were performed. A significant reduction in phosphorylated Akt was observed in the islets of c-Kit(Wv/+) mice (P<0.05) along with a decrease in phosphorylated Gsk3β (P<0.05), and cyclin D1 protein level (P<0.01) when compared with c-Kit(+/+) mice. However, c-Kit(Wv/+) mice that received 1-AKP treatment demonstrated normal fasting blood glucose with significantly improved glucose tolerance. 1-AKP-treated c-Kit(Wv/+) mice also showed increased β-catenin, cyclin D1 and Pdx-1 levels in islets, demonstrating that inhibition of Gsk3β activity led to increased β-cell proliferation and insulin secretion. These data suggest that c-Kit(Wv/+) male mice had alterations in the Akt/Gsk3β signaling pathway, which lead to β-cell dysfunction by decreasing Pdx-1 and cyclin D1 levels. Inhibition of Gsk3β could prevent the onset of diabetes by improving glucose tolerance and β-cell function.

Culturing INS-1 cells on CDPGYIGSR-, RGD- and fibronectin surfaces improves insulin secretion and cell proliferation

Rat insulinoma cells (INS-1), an immortalized pancreatic beta cell line, were cultured on low-fouling carboxymethyl-dextran (CMD) layers bearing fibronectin, the tripeptide Arg-Gly-Asp (RGD) or CDPGYIGSR, a laminin nonapeptide. INS-1 cells were non-adherent on CMD and RGE but adhered to fibronectin- and peptide-coated CMD surfaces and to tissue culture polystyrene (TCPS). On CMD bearing fibronectin and the peptides, INS-1 cells showed higher glucose-stimulated insulin secretion compared to those on TCPS, bare CMD and RGE. INS-1 cells experienced a net cell growth, with the lowest found after 7 days on CMD and the highest on fibronectin. Similarly, cells on RGD and CDPGYIGSR showed lower net growth rates than those on fibronectin. Expression of E-cadherin and integrins αvβ3 and α5 were similar between the conditions, except for α5 expression on fibronectin, RGD and CDPGYIGSR. Larger numbers of Ki-67-positive cells were found on CDPGYIGSR, TCPS, fibronectin and RGD. Cells in all conditions expressed Pdx1.

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.

Patterning of mono- and multilayered pancreatic beta-cell clusters

Cluster-size dependent behavior of pancreatic beta-cells has direct implications in islet transplantation therapy for type I diabetes treatment. Control over the cluster size enables evaluation of cluster-size-dependent function, ultimately leading to the production of beta-cell clusters with improved transplant efficacy. This work for the first time demonstrates the use of microcontact-printing-based cell patterning of discrete two- and three-dimensional clusters of pancreatic beta-cells. Both single and multiple cell layers are confined to a 2D area by attaching to patterns of covalently linked laminin and not adhering to surrounding polyethylene glycol. Cell clusters were successfully formed within 24 h for printed patterns in the range 40-120 microm, and simple modulation of the initial cell seeding density leads to the formation of multiple cell layers. Semiquantitative fluorescence microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were used to extensively characterize the surface chemistry. This technique offers exceptional control over cell cluster shape and size, and not only provides an effective tool to study the cluster-size-dependent behavior of pancreatic beta-cells but also has potential applicability to numerous other cell lines.

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.