Blood vessels of human islets of Langerhans are surrounded by a double basement membrane

Aetiology of type 1 diabetes: Physiological growth in children affects disease progression

The prevailing view is that type 1 diabetes (T1D) develops as a consequence of a severe decline in β-cell mass resulting from T-cell-mediated autoimmunity; however, progression from islet autoantibody seroconversion to overt diabetes and finally to total loss of C-peptide production occurs in most affected individuals only slowly over many years or even decades. This slow disease progression should be viewed in relation to the total β-cell mass of only 0.2 to 1.5 g in adults without diabetes. Focal lesions of acute pancreatitis with accumulation of leukocytes, often located around the ducts, are frequently observed in people with recent-onset T1D, and most patients display extensive periductal fibrosis, the end stage of inflammation. An injurious inflammatory adverse event, occurring within the periductal area, may have negative implications for islet neogenesis, dependent on stem cells residing within or adjacent to the ductal epithelium. This could in part prevent the 30-fold increase in β-cell mass that would normally occur during the first 20 years of life. This increase occurs in order to maintain glucose metabolism during the physiological increases in insulin production that are required to balance the 20-fold increase in body weight during childhood and increased insulin resistance during puberty. Failure to expand β-cell mass during childhood would lead to clinically overt T1D and could help to explain the apparently more aggressive form of T1D occurring in growing children when compared with that observed in affected adults.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Signals in the pancreatic islet microenvironment influence β-cell proliferation

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

Enzyme Development for Human Islet Isolation: Five Decades of Progress or Stagnation?

In comparison to procedures used for the separation of individual cell types from other organs, the process of human pancreatic islet isolation aims to digest the pancreatic exocrine matrix completely without dispersing the individual cells within the endocrine cell cluster. This objective is unique within the field of tissue separation, and outlines the challenge of islet isolation to balance two opposing priorities. Although significant progress has been made in the characterization and production of enzyme blends for islet isolation, there are still numerous areas which require improvement. The ultimate goal of enzyme production, namely the routine production of a consistent and standardized enzyme blend, has still not been realized. This seems to be mainly the result of a lack of detailed knowledge regarding the structure of the pancreatic extracellular matrix and the synergistic interplay between collagenase and different supplementary proteases during the degradation of the extracellular matrix. Furthermore, the activation of intrinsic proteolytic enzymes produced by the pancreatic acinar cells, also impacts on the chance of a successful outcome of human islet isolation. This overview discusses the challenges of pancreatic enzymatic digestion during human islet isolation, and outlines the developments in this field over the past 5 decades.

The Different Faces of the Pancreatic Islet

Type 1 diabetes (T1D) patients who receive pancreatic islet transplant experience significant improvement in their quality-of-life. This comes primarily through improved control of blood sugar levels, restored awareness of hypoglycemia, and prevention of serious and potentially life-threatening diabetes-associated complications, such as kidney failure, heart and vascular disease, stroke, nerve damage, and blindness. Therefore, beta cell replacement through transplantation of isolated islets is an important option in the treatment of T1D. However, lasting success of this promising therapy depends on durable survival and efficacy of the transplanted islets, which are directly influenced by the islet isolation procedures. Thus, isolating pancreatic islets with consistent and reliable quality is critical in the clinical application of islet transplantation.Quality of isolated islets is important in pre-clinical studies as well, as efforts to advance and improve clinical outcomes of islet transplant therapy have relied heavily on animal models ranging from rodents, to pigs, to nonhuman primates. As a result, pancreatic islets have been isolated from these and other species and used in a variety of in vitro or in vivo applications for this and other research purposes. Protocols for islet isolation have been somewhat similar across species, especially, in mammals. However, given the increasing evidence about the distinct structural and functional features of human and mouse islets, using similar methods of islet isolation may contribute to inconsistencies in the islet quality, immunogenicity, and experimental outcomes. This may also contribute to the discrepancies commonly observed between pre-clinical findings and clinical outcomes. Therefore, it is prudent to consider the particular features of pancreatic islets from different species when optimizing islet isolation protocols.In this chapter, we explore the structural and functional features of pancreatic islets from mice, pigs, nonhuman primates, and humans because of their prevalent use in nonclinical, preclinical, and clinical applications.

Vessel Network Architecture of Adult Human Islets Promotes Distinct Cell-Cell Interactions In Situ and Is Altered After Transplantation

Islet-cell hormone release is modulated by signals from endothelial and endocrine cells within the islet. However, models of intraislet vascularization and paracrine cell signaling are mostly based on the rodent pancreas. We assessed the architecture and endocrine cell interaction of the vascular network in unperturbed human islets in situ and their potential to re-establish their endogenous vascular network after transplantation in vivo. We prepared slices of fresh pancreas tissue obtained from nondiabetic patients undergoing partial pancreatectomy. In addition, we transplanted human donor islets into the anterior chamber of the mouse eye. Next, we performed three-dimensional in situ and in vivo imaging of islet cell and vessel architecture at cellular resolution and compared our findings with mouse and porcine islets. Our data reveal a significantly different vascular architecture with decreased vessel diameter, reduced vessel branching, and shortened total vessel network in human compared with mouse islets. Together with the distinct cellular arrangement in human islets, this limits β to endothelial cell interactions, facilitates connection of α and β cells, and promotes the formation of independent β-cell clusters within islets. Furthermore, our results show that the endogenous vascular network of islets is significantly altered after transplantation in a donor age-related mechanism. Thus, our study provides insight into the vascular architecture and cellular arrangement of human islets with apparent consequences for intercellular islet signaling. Moreover, our findings suggest that human islet engraftment after transplantation can be improved by using alternative, less mature islet-cell sources.

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

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

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.

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

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

Sex Differences in Androgen Regulation of Metabolism in Nonhuman Primates

The in-depth characterization of sex differences relevant to human physiology requires the judicious use of a variety of animal models and human clinical data. Nonhuman primates (NHPs) represent an important experimental system that bridges rodent studies and clinical investigations. NHP studies have been especially useful in understanding the role of sex hormones in development and metabolism and also allow the elucidation of the effects of pertinent dietary influences on physiology pertinent to disease states such as obesity and diabetes. This chapter summarizes the current state of our understanding of androgen effects on male and female NHP metabolism relevant to hypogonadism in human males and polycystic ovary syndrome in human females. This review will also focus on the interaction between altered androgen levels and dietary restriction and excess, in particular the Western-style diet that underlies significant human pathophysiology.

A holistic approach to dissecting SPARC family protein complexity reveals FSTL-1 as an inhibitor of pancreatic cancer cell growth

SPARC is a matricellular protein that is involved in both pancreatic cancer and diabetes. It belongs to a wider family of proteins that share structural and functional similarities. Relatively little is known about this extended family, but evidence of regulatory interactions suggests the importance of a holistic approach to their study. We show that Hevin, SPOCKs, and SMOCs are strongly expressed within islets, ducts, and blood vessels, suggesting important roles for these proteins in the normal pancreas, while FSTL-1 expression is localised to the stromal compartment reminiscent of SPARC. In direct contrast to SPARC, however, FSTL-1 expression is reduced in pancreatic cancer. Consistent with this, FSTL-1 inhibited pancreatic cancer cell proliferation. The complexity of SPARC family proteins is further revealed by the detection of multiple cell-type specific isoforms that arise due to a combination of post-translational modification and alternative splicing. Identification of splice variants lacking a signal peptide suggests the existence of novel intracellular isoforms. This study underlines the importance of addressing the complexity of the SPARC family and provides a new framework to explain their controversial and contradictory effects. We also demonstrate for the first time that FSTL-1 suppresses pancreatic cancer cell growth.

Composition and organization of the pancreatic extracellular matrix by combined methods of immunohistochemistry, proteomics and scanning electron microscopy

The epidemic expansion of diabetes is a major concern of public health. A promising treatment is the transplantation of islets of Langerhans isolated from the whole pancreas but the yields of islets isolation and the rates of successful engraftments still have to be improved to make this therapy effective. The extracellular matrix (ECM) of the pancreatic tissue is partially lost during the isolation process and a comprehensive knowledge of the pancreatic ECM composition and organization could identify targets to improve islets isolation and transplantation or highlight new therapeutics for pancreatic diseases. The organization, composition and three-dimensional architecture of the pancreatic ECM were analysed in mouse and pig by three different techniques. Laminin α-4 and β-2 chains are localized by immunohistochemistry in the exocrine tissue and inside islets of mouse pancreas but not around islets that are surrounded by an ECM made of collagen type IV and type V. Collagen type I, III, and VI were identified by proteomics as specific constituents of the pig pancreatic ECM along with the low-abundance isoforms α3(IV) α4(IV) α5(IV) and α1(V) α2(V) α3(V) of collagen type IV and type V respectively. The three-dimensional ECM architecture is analysed on decellularized mouse pancreas by scanning electron microscopy and is organized in honeycomb structures made of thin ECM fibers assembled in thicker bundles. The combination of immunohistochemistry, proteomics and scanning electron microscopy gives complementary perspective on the pancreatic ECM composition and organization. It represents a valuable toolbox for deeper investigations of ECMs and proposes clues in tissue engineering of the pancreas.

Beta Cells Secrete Significant and Regulated Levels of Insulin for Long Periods when Seeded onto Acellular Micro-Scaffolds

The aim of this work is to obtain significant and regulated insulin secretion from human beta cells ex vivo. Long-term culture of human pancreatic islets and attempts at expanding human islet cells normally result in loss of beta-cell phenotype. We propose that to obtain proper ex vivo beta cell function, there is a need to develop three-dimensional structures that mimic the natural islet tissue microenvironment. We here describe the preparation of endocrine micro-pancreata (EMPs) that are made up of acellular organ-derived micro-scaffolds seeded with human intact or enzymatically dissociated islets. We show that EMPs constructed by seeding whole islets, freshly enzymatically-dissociated islets or even dissociated islets grown first in standard monolayer cultures express high levels of key beta-cell specific genes and secrete quantities of insulin per cell similar to freshly isolated human islets in a glucose-regulated manner for more than 3 months in vitro.

All-trans retinoic acid ameliorates glycemic control in diabetic mice via modulating pancreatic islet production of vascular endothelial growth factor-A

Patients with type 1 diabetes mellitus are associated with impairment in vitamin A metabolism. This study evaluated whether treatment with retinoic acid, the biologically active metabolite of vitamin A, can ameliorate diabetes. All-trans retinoic acid (atRA) was used to treat streptozotocin (STZ)-induced diabetic mice which revealed atRA administration ameliorated blood glucose levels of diabetic mice. This hyperglycemic amelioration was accompanied by an increase in the amount of β cells co-expressed Pdx1 and insulin and by restoration of the vascular laminin expression. The atRA-induced production of vascular endothelial growth factor-A from the pancreatic islets was possibly the key factor that mediated the restoration of islet vascularity and recovery of β-cell mass. Furthermore, the combination of islet transplantation and atRA administration significantly rescued hyperglycemia in diabetic mice. These findings suggest that vitamin A derivatives can potentially be used as a supplementary treatment to improve diabetes management and glycemic control.

An Apparent Deficiency of Lymphatic Capillaries in the Islets of Langerhans in the Human Pancreas

The lymphatic system is crucial for efficient immune surveillance and for the maintenance of a physiological pressure in the interstitial space. Even so, almost no information is available concerning the lymph drainage of the islets of Langerhans in the human pancreas. Immunohistochemical staining allowed us to distinguish lymphatic capillaries from blood capillaries. Almost no lymphatic capillaries were found within the islets in pancreatic biopsy specimens from subjects without diabetes or from subjects with type 1 or type 2 diabetes. Lymphatic capillaries were, however, found at the islet-exocrine interface, frequently located along blood capillaries and other fibrotic structures within or close to the islet capsule. Lymphatic capillaries were regularly found in the exocrine pancreas, with small lymphatic vessels located close to and around acini. Larger collecting lymphatic vessels were located in fibrotic septa between the exocrine lobules and adjacent to the ductal system of the pancreas. In summary, we report a pronounced deficiency of lymphatic capillaries in human islets, a finding with implications for immune surveillance and the regulation of interstitial fluid transport in the endocrine pancreas as well as for the pathophysiology of both type 1 and type 2 diabetes.

Cell rearrangement in transplanted human islets

The major feature of the human pancreatic islet architecture is the organization of endocrine cells into clusters comprising central β cells and peripheral α cells surrounded by vasculature. To have an insight into the mechanisms that govern this unique islet architecture, islet cells were isolated, and reaggregation of α and β cells into islet-like structures (pseudoislets) after culture or transplantation into mice was studied by immunohistology. The pseudoislets formed in culture displayed an unusual cell arrangement, contrasting with the transplanted pseudoislets, which exhibited a cell arrangement similar to that observed in native pancreatic islet subunits. The pattern of revascularization and the distribution of extracellular matrix around transplanted pseudoislets were alike to those observed in native pancreatic islets. This organization of transplanted pseudoislets occurred also when revascularization was abolished by treating mice with an anti-VEGF antibody, but not when contact with extracellular matrix was prevented by encapsulation of pseudoislets within alginate hydrogel. These results indicate that the maintenance of islet cell arrangement is dependent on in vivo features such as extracellular matrix but independent of vascularization.

Necessities for a Clinical Islet Program

For more than two decades we have been refining advances in islet cell transplantation as a clinical therapy for patients suffering from type 1 diabetes. A great deal of effort has gone to making this a viable therapy for a broader range of patients with type 1 diabetes. Clinical results have progressively improved, demonstrating clinical outcomes on par with other organ transplants, specifically in terms of insulin independence, graft and patient survival. We are now at the point where islet cell transplantation, in the form of allotransplantation, has become accepted as a clinical therapy in adult patients affected by type 1 diabetes, in particular those suffering from severe hypoglycaemic unawareness. This chapter provides an overview on how this has been undertaken over the years to provide outcomes on par with other organ transplantation results. In particular this chapter focuses on the processes and facilities that are required to establish a clinical islet isolation and transplantation program. It also outlines the very important underpinning processes of selection of the organ donor for islet isolation, the processes of organ donor operation and preservation of the pancreas by various means and the ideal ways to best improve outcomes for human islet cell isolation. Providing these more optimal conditions we can underpin the isolation processes to provide islets for transplantation and as such a safe, effective and feasible therapeutic option for an increasing number of patients suffering from type 1 diabetes with severe hypoglycaemic unawareness.

Human pluripotent stem cell based islet models for diabetes research

Although similar, mouse and human pancreatic development and beta cell physiology have significant differences. For this reason, mouse models present shortcomings that can obscure the understanding of human diabetes pathology. Progress in the field of human pluripotent stem cell (hPSC) differentiation now makes it possible to derive unlimited numbers of human beta cells in vitro. This constitutes an invaluable approach to gain insight into human beta cell development and physiology and to generate improved disease models. Here we summarize the main differences in terms of development and physiology of the pancreatic endocrine cells between mouse and human, and describe the recent progress in modeling diabetes using hPSC. We highlight the need of developing more physiological hPSC-derived beta cell models and anticipate the future prospects of these approaches.

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

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

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

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

Human Islets Have Fewer Blood Vessels than Mouse Islets and the Density of Islet Vascular Structures Is Increased in Type 2 Diabetes

Human and rodent islets differ substantially in several features, including architecture, cell composition, gene expression and some aspects of insulin secretion. Mouse pancreatic islets are highly vascularized with interactions between islet endothelial and endocrine cells being important for islet cell differentiation and function. To determine whether human islets have a similar high degree of vascularization and whether this is altered with diabetes, we examined the vascularization of islets from normal human subjects, subjects with type 2 diabetes (T2D), and normal mice. Using an integrated morphometry approach to quantify intra-islet capillary density in human and mouse pancreatic sections, we found that human islets have five-fold fewer vessels per islet area than mouse islets. Islets in pancreatic sections from T2D subjects showed capillary thickening, some capillary fragmentation and had increased vessel density as compared with non-diabetic controls. These changes in islet vasculature in T2D islets appeared to be associated with amyloid deposition, which was noted in islets from 8/9 T2D subjects (and occupied 14% ± 4% of islet area), especially around the intra-islet capillaries. The physiological implications of the differences in the angioarchitecture of mouse and human islets are not known. Islet vascular changes in T2D may exacerbate β cell/islet dysfunction and β cell loss.

New insights into the architecture of the islet of Langerhans: a focused cross-species assessment

The human genome project and its search for factors underlying human diseases has fostered a major human research effort. Therefore, unsurprisingly, in recent years we have observed an increasing number of studies on human islet cells, including disease approaches focusing on type 1 and type 2 diabetes. Yet, the field of islet and diabetes research relies on the legacy of rodent-based investigations, which have proven difficult to translate to humans, particularly in type 1 diabetes. Whole islet physiology and pathology may differ between rodents and humans, and thus a comprehensive cross-species as well as species-specific view on islet research is much needed. In this review we summarise the current knowledge of interspecies islet cytoarchitecture, and discuss its potential impact on islet function and future perspectives in islet pathophysiology research.

Enzymatically degradable poly(ethylene glycol) hydrogels for the 3D culture and release of human embryonic stem cell derived pancreatic precursor cell aggregates

This study aimed to develop a three dimensional culture platform for aggregates of human embryonic stem cell (hESC)-derived pancreatic progenitors that enables long-term culture, maintains aggregate size and morphology, does not adversely affect differentiation and provides a means for aggregate recovery. A platform was developed with poly(ethylene glycol) hydrogels containing collagen type I, for cell-matrix interactions, and peptide crosslinkers, for facile recovery of aggregates. The platform was first demonstrated with RIN-m5F cells, showing encapsulation and subsequent release of single cells and aggregates without adversely affecting viability. Aggregates of hESC-derived pancreatic progenitors with an effective diameter of 82 (15)μm were either encapsulated in hydrogels or cultured in suspension for 28 days. At day 14, aggregate viability was maintained in the hydrogels, but significantly reduced (88%) in suspension culture. However by day 28, viability was reduced under both culture conditions. Aggregate size was maintained in the hydrogels, but in suspension was significantly higher (∼ 2-fold) by day 28. The ability to release aggregates followed by a second enzyme treatment to achieve single cells enabled assessment by flow cytometry. Prior to encapsulation, there were 39% Pdx1(+)/Nkx6.1(+) cells, key endocrine markers required for β-cell maturation. The fraction of doubly positive cells was not affected in hydrogels but was slightly and significantly lower in suspension culture by 28 days. In conclusion, we demonstrate that a MMP-sensitive PEG hydrogel containing collagen type I is a promising platform for hESC-derived pancreatic progenitors that maintains viable aggregates, aggregate size, and progenitor state and offers facile recovery of aggregates.

Pancreatic Islet Survival and Engraftment Is Promoted by Culture on Functionalized Spider Silk Matrices

Transplantation of pancreatic islets is one approach for treatment of diabetes, however, hampered by the low availability of viable islets. Islet isolation leads to disruption of the environment surrounding the endocrine cells, which contributes to eventual cell death. The reestablishment of this environment is vital, why we herein investigated the possibility of using recombinant spider silk to support islets in vitro after isolation. The spider silk protein 4RepCT was formulated into three different formats; 2D-film, fiber mesh and 3D-foam, in order to provide a matrix that can give the islets physical support in vitro. Moreover, cell-binding motifs from laminin were incorporated into the silk protein in order to create matrices that mimic the natural cell environment. Pancreatic mouse islets were thoroughly analyzed for adherence, necrosis and function after in vitro maintenance on the silk matrices. To investigate their suitability for transplantation, we utilized an eye model which allows in vivo imaging of engraftment. Interestingly, islets that had been maintained on silk foam during in vitro culture showed improved revascularization. This coincided with the observation of preserved islet architecture with endothelial cells present after in vitro culture on silk foam. Selected matrices were further evaluated for long-term preservation of human islets. Matrices with the cell-binding motif RGD improved human islet maintenance (from 36% to 79%) with preserved islets architecture and function for over 3 months in vitro. The islets established cell-matrix contacts and formed vessel-like structures along the silk. Moreover, RGD matrices promoted formation of new, insulin-positive islet-like clusters that were connected to the original islets via endothelial cells. On silk matrices with islets from younger donors (<35 year), the amount of newly formed islet-like clusters found after 1 month in culture were almost double compared to the initial number of islets added.

Islet Endothelial Cells Derived From Mouse Embryonic Stem Cells

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

Extracellular matrix components in the pathogenesis of type 1 diabetes

Type 1 diabetes (T1D) results from progressive immune cell-mediated destruction of pancreatic β cells. As immune cells migrate into the islets, they pass through the extracellular matrix (ECM). This ECM is composed of different macromolecules localized to different compartments within and surrounding islets; however, the involvement of this ECM in the development of human T1D is not well understood. Here, we summarize our recent findings from human and mouse studies illustrating how specific components of the islet ECM that constitute basement membranes and interstitial matrix of the islets, and surprisingly, the intracellular composition of islet β cells themselves, are significantly altered during the pathogenesis of T1D. Our focus is on the ECM molecules laminins, collagens, heparan sulfate/heparan sulfate proteoglycans, and hyaluronan, as well as on the enzymes that degrade these ECM components. We propose that islet and lymphoid tissue ECM composition and organization are critical to promoting immune cell activation, islet invasion, and destruction of islet β cells in T1D.

Distinct cell clusters touching islet cells induce islet cell replication in association with over-expression of Regenerating Gene (REG) protein in fulminant type 1 diabetes

BACKGROUND

Pancreatic islet endocrine cell-supporting architectures, including islet encapsulating basement membranes (BMs), extracellular matrix (ECM), and possible cell clusters, are unclear.

PROCEDURES

The architectures around islet cell clusters, including BMs, ECM, and pancreatic acinar-like cell clusters, were studied in the non-diabetic state and in the inflamed milieu of fulminant type 1 diabetes in humans.

RESULT

Immunohistochemical and electron microscopy analyses demonstrated that human islet cell clusters and acinar-like cell clusters adhere directly to each other with desmosomal structures and coated-pit-like structures between the two cell clusters. The two cell-clusters are encapsulated by a continuous capsule composed of common BMs/ECM. The acinar-like cell clusters have vesicles containing regenerating (REG) Iα protein. The vesicles containing REG Iα protein are directly secreted to islet cells. In the inflamed milieu of fulminant type 1 diabetes, the acinar-like cell clusters over-expressed REG Iα protein. Islet endocrine cells, including beta-cells and non-beta cells, which were packed with the acinar-like cell clusters, show self-replication with a markedly increased number of Ki67-positive cells.

CONCLUSION

The acinar-like cell clusters touching islet endocrine cells are distinct, because the cell clusters are packed with pancreatic islet clusters and surrounded by common BMs/ECM. Furthermore, the acinar-like cell clusters express REG Iα protein and secrete directly to neighboring islet endocrine cells in the non-diabetic state, and the cell clusters over-express REG Iα in the inflamed milieu of fulminant type 1 diabetes with marked self-replication of islet cells.

Tissue engineering approaches to cell-based type 1 diabetes therapy

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

Pancreatic pathology in type 1 diabetes mellitus

Type 1 diabetes is a multifactorial disease resulting from a complex interplay between host genetics, the immune system and the environment, that culminates in the destruction of insulin-producing beta cells. The incidence of type 1 diabetes is increasing at an alarming rate, especially in children under the age of 5 (Gepts in Diabetes 14(10):619-613, 1965; Foulis et al. in Lancet 29(5):267-274, 1986; Gamble, Taylor and Cumming in British Medical Journal 4(5887):260-262 1973). Genetic predisposition, although clearly important, cannot explain this rise, and so, it has been proposed that changes in the 'environment' and/or changes in 'how we respond to our environment' must contribute to this rising incidence. In order to gain an improved understanding of the factors influencing the disease process, it is important, firstly, to focus on the organ at the centre of the illness-the pancreas. This review summarises our knowledge of the pathology of the endocrine pancreas in human type 1 diabetes and, in particular, explores the progression of this understanding over the past 25 years.

Destruction of tissue, cells and organelles in type 1 diabetic rats presented at macromolecular resolution

Finding alternatives for insulin therapy and making advances in etiology of type 1 diabetes benefits from a full structural and functional insight into Islets of Langerhans. Electron microscopy (EM) can visualize Islet morphology at the highest possible resolution, however, conventional EM only provides biased snapshots and lacks context. We developed and employed large scale EM and compiled a resource of complete cross sections of rat Islets during immuno-destruction to provide unbiased structural insight of thousands of cells at macromolecular resolution. The resource includes six datasets, totalling 25.000 micrographs, annotated for cellular and ultrastructural changes during autoimmune diabetes. Granulocytes are attracted to the endocrine tissue, followed by extravasation of a pleiotrophy of leukocytes. Subcellullar changes in beta cells include endoplasmic reticulum stress, insulin degranulation and glycogen accumulation. Rare findings include erythrocyte extravasation and nuclear actin-like fibers. While we focus on a rat model of autoimmune diabetes, our approach is general applicable.

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

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

Extracellular Matrix Scaffold Technology for Bioartificial Pancreas Engineering: State of the Art and Future Challenges

Emergent technologies in regenerative medicine may soon overcome the limitations of conventional diabetes therapies. Collaborative efforts across the subfields of stem cell technology, islet encapsulation, and biomaterial carriers seek to produce a bioengineered pancreas capable of restoring endocrine function in patients with insulin-dependent diabetes. These technologies rely on a robust understanding of the extracellular matrix (ECM), the supportive 3-dimensional network of proteins necessary for cellular attachment, proliferation, and differentiation. Although these functions can be partially approximated by biosynthetic carriers, novel decellularization protocols have allowed researchers to discover the advantages afforded by the native pancreatic ECM. The native ECM has proven to be an optimal platform for recellularization and whole-organ pancreas bioengineering, an exciting new field with the potential to resolve the dire shortage of transplantable organs. This review seeks to contextualize recent findings, discuss current research goals, and identify future challenges of regenerative medicine as it applies to diabetes management.

Controlled local presentation of matrix proteins in microparticle-laden cell aggregates

Multi-cellular aggregates are found in healthy and diseased tissues, and while cell-cell contact is important for regulating many cell functions, cells also interact, to varying degrees, with extra-cellular matrix (ECM) proteins. Islets of Langerhans are one such example of cell aggregates in contact with ECM, both at the periphery of the cluster and dispersed throughout. While several studies have investigated the effect of reintroducing contact with ECM proteins on islet cell survival and function, the majority of these experiments only allow contact with the exterior cells. Thus, cell-culture platforms that enable the study of ECM-cell interactions throughout multi-cellular aggregates are of interest. Here, local presentation of ECM proteins was achieved using hydrogel microwell arrays to incorporate protein-laden microparticles during formation of MIN6 β-cell aggregates. Varying the microparticle seeding density reproducibly controlled the number of microparticles incorporated within three-dimensional aggregates (i.e., total amount of protein). Further, a relatively uniform spatial distribution of laminin- and fibronectin-coated microparticles was achieved throughout the x-, y-, and z-directions. Multiple ECM proteins were presented to β-cells in concert by incorporating two distinct populations of microparticles throughout the aggregates. Finally, scaling the microwell device dimensions allowed for the formation of two different sized cell-particle aggregates, ∼80 and 160 µm in diameter. While the total number of microparticles incorporated per aggregate varied with size, the fraction of the aggregate occupied by microparticles was affected only by the microparticle seeding density, indicating that uniform local concentrations of proteins can be preserved while changing the overall aggregate dimensions.

Early immunotherapy using autologous adult stem cells reversed the effect of anti-pancreatic islets in recently diagnosed type 1 diabetes mellitus: preliminary results

BACKGROUND

Bone marrow stem cell treatment has been proven a promising therapeutic strategy and showed significant results given the strong immune modulating properties. We have investigated the safety and efficacy of autologous bone marrow stem cell transplantation through liver puncture in two patients with recently diagnosed type 1 diabetes mellitus.

MATERIAL AND METHODS

The procedure was approved by the Institutional Ethics Committee. In 2011, in three young patients, type 1 diabetes mellitus diagnosis was confirmed, with the presence of positive antibodies and ketoacidosis. Two patients was treated with autologous bone marrow stem cell stimulated with filgrastim and transplantation, through liver puncture, as immune modulators. One patients was treated with conventional treatment and participate in this experiment as a control group. The families of the patients signed the informed consent. No specific statistical analysis was performed. The patients had less than 8 years old, diagnosis of type 1 diabetes for less than 60 days, body mass index less than 22 kg/m2, normal complete blood count, coagulation and renal function, no lesions in target organs, glycosylated hemoglobin (HbA1c) level less than 13.70%, c-peptide level less than 0.67 ng/ml, positive results of Islets Cells Antibody (ICA), Glutamic Acid Decarboxylase (GAD) and insulin antibody.

RESULTS

In two patients treated, the follow up at 12 months showed negative value in ICA, GAD and anti insulin antibody levels, with an increased levels of c peptide and decreased levels of blood glucose and HbA1c.

CONCLUSIONS

Treatment with autologous bone marrow stem cells is easy and effective as it reversed the production and effect of anti pancreatic islet antibody and significantly resulted in an increased c-peptide concentration.

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

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

Current understanding of the molecular biology of pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (PanNETs) are complicated and often deadly neoplasms. A recent increased understanding of their molecular biology has contributed to expanded treatment options. DNA sequencing of samples derived from patients with PanNETs and rare genetic syndromes such as multiple endocrine neoplasia type 1 (MEN1) and Von Hippel-Lindau (VHL) syndrome reveals the involvement of MEN1, DAXX/ATRX, and the mammalian target of rapamycin (mTOR) pathways in PanNET tumorigenesis. Gene knock-out/knock-in studies indicate that inactivation of factors including MEN1 and abnormal PI3K/mTOR signaling uncouples endocrine cell cycle progression from the control of environmental cues such as glucose, leading to islet cell overgrowth. In addition, accumulating evidence suggests that further impairment of endothelial-endocrine cell interactions contributes to tumor invasion and metastasis. Recent phase III clinical trials have shown that therapeutic interventions, such as sunitinib and everolimus, targeting those signal transduction pathways improve disease-free survival rates. Yet, cure in the setting of advanced disease remains elusive. Further advances in our understanding of the molecular mechanisms of PanNETs and improved preclinical models will assist in developing personalized therapy utilizing novel drugs to provide prolonged control or even cure the disease.

The peri-islet basement membrane, a barrier to infiltrating leukocytes in type 1 diabetes in mouse and human

We provide the first comprehensive analysis of the extracellular matrix (ECM) composition of peri-islet capsules, composed of the peri-islet basement membrane (BM) and subjacent interstitial matrix (IM), in development of type 1 diabetes in NOD mice and in human type 1 diabetes. Our data demonstrate global loss of peri-islet BM and IM components only at sites of leukocyte infiltration into the islet. Stereological analyses reveal a correlation between incidence of insulitis and the number of islets showing loss of peri-islet BM versus islets with intact BMs, suggesting that leukocyte penetration of the peri-islet BM is a critical step. Protease- and protease inhibitor-specific microarray analyses (CLIP-CHIP) of laser-dissected leukocyte infiltrated and noninfiltrated pancreatic islets and confirmatory quantitative real time PCR and protein analyses identified cathepsin S, W, and C activity at sites of leukocyte penetration of the peri-islet BM in association with a macrophage subpopulation in NOD mice and human type 1 diabetic samples and, hence, potentially a novel therapeutic target specifically acting at the islet penetration stage. Interestingly, the peri-islet BM and underlying IM are reconstituted once inflammation subsides, indicating that the peri-islet BM-producing cells are not lost due to the inflammation, which has important ramifications to islet transplantation studies.

Porous scaffolds support extrahepatic human islet transplantation, engraftment, and function in mice

Islet transplantation as a therapy or cure for type 1 diabetes has significant promise but has been limited by islet mass requirements and long-term graft failure. The intrahepatic and intravascular site may be responsible for significant loss of transplanted islets. Nonencapsulating biomaterial scaffolds provide a strategy for architecturally defining and modulating extrahepatic sites beyond the endogenous milieu to enhance islet survival and function. We utilized scaffolds to transplant human islets into the intraperitoneal fat of immunodeficient mice. A smaller human islet mass than previously reported reversed murine diabetes and restored glycemic control at human blood glucose levels. Graft function was highly dependent on the islet number transplanted and directly correlated to islet viability, as determined by the ATP-to-DNA ratio. Islets engrafted and revascularized in host tissue, and glucose tolerance testing indicated performance equivalent to healthy mice. Addition of extracellular matrix, specifically collagen IV, to scaffold surfaces improved graft function compared to serum-supplemented media. Porous scaffolds can facilitate efficient human islet transplantation and provide a platform for modulating the islet microenvironment, in ways not possible with current clinical strategies, to enhance islet engraftment and function.

Pancreatic islet basement membrane loss and remodeling after mouse islet isolation and transplantation: impact for allograft rejection

The isolation of islets by collagenase digestion can cause damage and impact the efficiency of islet engraftment and function. In this study, we assessed the basement membranes (BMs) of mouse pancreatic islets as a molecular biomarker for islet integrity, damage after isolation, and islet repair in vitro as well as in the absence or presence of an immune response after transplantation. Immunofluorescence staining of BM matrix proteins and the endothelial cell marker platelet endothelial cell adhesion molecule-1 (PECAM-1) was performed on pancreatic islets in situ, isolated islets, islets cultured for 4 days, and islet grafts at 3-10 days posttransplantation. Flow cytometry was used to investigate the expression of BM matrix proteins in isolated islet β-cells. The islet BM, consisting of collagen type IV and components of Engelbreth-Holm-Swarm (EHS) tumor laminin 111, laminin α2, nidogen-2, and perlecan in pancreatic islets in situ, was completely lost during islet isolation. It was not reestablished during culture for 4 days. Peri- and intraislet BM restoration was identified after islet isotransplantation and coincided with the migration pattern of PECAM-1(+) vascular endothelial cells (VECs). After islet allotransplantation, the restoration of VEC-derived peri-islet BMs was initiated but did not lead to the formation of the intraislet vasculature. Instead, an abnormally enlarged peri-islet vasculature developed, coinciding with islet allograft rejection. The islet BM is a sensitive biomarker of islet damage resulting from enzymatic isolation and of islet repair after transplantation. After transplantation, remodeling of both peri- and intraislet BMs restores β-cell-matrix attachment, a recognized requirement for β-cell survival, for isografts but not for allografts. Preventing isolation-induced islet BM damage would be expected to preserve the intrinsic barrier function of islet BMs, thereby influencing both the effector mechanisms required for allograft rejection and the antirejection strategies needed for allograft survival.

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.

Syndecan-4 is associated with beta-cells in the pancreas and the MIN6 beta-cell line

Basement membranes (BM) in the pancreatic islet are important for islet survival and function, but supplementation of isolated islets with these components have had limited success. Currently, little is understood about which BM components and proteoglycans are essential to maintaining islet homeostasis. This study therefore aimed to characterize the BM components and proteoglycans of the islet in the mouse, rat and rabbit species. The BM of the mouse islet was varied in continuity around the islet and was discontinuous in the rat and rabbit islets. The BM consisted of collagen IV, laminin, fibronectin and perlecan in the mouse and was in tight association with the underlying islet endothelium. None of these components were found directly associated with the β-cells in tissue and in the MIN6 β-cell line. In contrast, heparan sulfate (HS) was distributed throughout the islet in all three species in a pattern distinctly different to that of perlecan and was observed mainly on the β-cells and not the α-cells in the mouse and rat. Similarly, syndecan-4 showed a staining pattern almost identical to that of HS and was mostly observed on the β-cells, not α-cells, in the mouse and rat. Both HS and syndecan-4 were also observed in the MIN6 β-cell line. The mouse islet and MIN6 syndecan-4 were both ~37 kDa in size, after deglycosylation with heparitinase. These results indicate that syndecan-4 may play an important role in β-cell function and that the cell-surface HS proteoglycans may be the missing link to maintaining islet longevity after isolation.

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.