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

Activation of ductal progenitor-like cells from adult human pancreas requires extracellular matrix protein signaling

Ductal progenitor-like cells are a sub-population of ductal cells in the adult human pancreas that have the potential to contribute to regenerative medicine. However, the microenvironmental cues that regulate their activation are poorly understood. Here, we establish a 3-dimensional suspension culture system containing six defined soluble factors in which primary human ductal progenitor-like and ductal non-progenitor cells survive but do not proliferate. Expansion and polarization occur when suspension cells are provided with a low concentration (5% v/v) of Matrigel, a sarcoma cell product enriched in many extracellular matrix (ECM) proteins. Screening of ECM proteins identified that collagen IV can partially recapitulate the effects of Matrigel. Inhibition of integrin α1β1, a major collagen IV receptor, negates collagen IV- and Matrigel-stimulated effects. These results demonstrate that collagen IV is a key ECM protein that stimulates the expansion and polarization of human ductal progenitor-like and ductal non-progenitor cells via integrin α1β1 receptor signaling.

The collagen matrix regulates the survival and function of pancreatic islets

The extracellular matrix (ECM) provides an appropriate microenvironment for many kinds of cells, including pancreatic cells. Collagens are the most abundant components of the ECM. Type I, IV, V and VI collagen has been detected in pancreatic islets, and each type plays important role in the proliferation, survival, function and differentiation of pancreatic cells. In some cases, collagens show behaviours similar to those of growth factors and regulate the biological behaviour of β cells by binding with certain growth factors, including IGFs, EGFs and FGFs. The transcriptional coactivator YAP/TAZ has been widely recognised as a mechanosensor that senses changes in the physical characteristics of the ECM and inhibition of YAP/TAZ enhances insulin production and secretion. Type 1 diabetes mellitus (T1DM) is an autoimmune disease characterised by the destruction of insulin-producing β cells. The crosstalk between collagens and immune cells plays a key role in the development and differentiation of immune cells. Further, Supplementation with collagens during islet transplantation is a promising strategy for improving the quality of the islets. But, excessive collagen deposition results in pancreatic fibrosis and pancreatic carcinoma. Targeting inhibit Piezo, autophagy or IL-6 may reduce excessive collagen deposition-induced pancreatic fibrosis and pancreatic carcinoma. This review provides insights into the treatment of T1DM to prolong life expectancy and provides the potential targets for treating collagen deposition-induced pancreatic fibrosis and pancreatic carcinoma.

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.

Decellularized bladder as scaffold to support proliferation and functionality of insulin-secreting pancreatic cells

Loss in the number or function of insulin-producing β-cells in pancreatic islets has been associated with diabetes mellitus. Although islet transplantation can be an alternative treatment, complications such as apoptosis, ischaemia and loss of viability have been reported. The use of decellularized organs as scaffolds in tissue engineering is of interest owing to the unique ultrastructure and composition of the extracellular matrix (ECM) believed to act on tissue regeneration. In this study, a cell culture system has been designed to study the effect of decellularized porcine bladder pieces on INS-1 cells, a cell line secreting insulin in response to glucose stimulation. Porcine bladders were decellularized using two techniques: a detergent-containing and a detergent-free methods. The resulting ECMs were characterized for the removal of both cells and dsDNA. INS-1 cells were not viable on ECM produced using detergent (i.e., sodium dodecyl sulfate). INS-1 cells were visualized following 7 days of culture on detergent-free decellularized bladders using a cell viability and metabolism assay (MTT) and cell proliferation quantified (CyQUANT™ NF Cell Proliferation Assay). Further, glucose-stimulated insulin secretion and immunostaining confirmed that cells were functional in response to glucose stimulation, as well as they expressed insulin and interacted with the detergent-free produced ECM, respectively.

Unlocking the post-transplant microenvironment for successful islet function and survival

Islet transplantation (IT) offers the potential to restore euglycemia for patients with type 1 diabetes mellitus (T1DM). Despite improvements in islet isolation techniques and immunosuppressive regimes, outcomes remain suboptimal with UK five-year graft survivals (5YGS) of 55% and most patients still requiring exogenous insulin after multiple islet infusions. Native islets have a significant non-endocrine component with dense extra-cellular matrix (ECM), important for islet development, cell survival and function. Collagenase isolation necessarily disrupts this complex islet microenvironment, leaving islets devoid of a supporting framework and increasing vulnerability of transplanted islets. Following portal venous transplantation, a liver injury response is potentially induced, which typically results in inflammation and ECM deposition from liver specific myofibroblasts. The impact of this response may have important impact on islet survival and function. A fibroblast response and ECM deposition at the kidney capsule and eye chamber alongside other implantation sites have been shown to be beneficial for survival and function. Investigating the implantation site microenvironment and the interactions of transplanted islets with ECM proteins may reveal therapeutic interventions to improve IT and stem-cell derived beta-cell therapy.

Pancreatic β-cell heterogeneity in adult human islets and stem cell-derived islets

Recent studies reported that pancreatic β-cells are heterogeneous in terms of their transcriptional profiles and their abilities for insulin secretion. Sub-populations of pancreatic β-cells have been identified based on the functionality and expression of specific surface markers. Under diabetes condition, β-cell identity is altered leading to different β-cell sub-populations. Furthermore, cell-cell contact between β-cells and other endocrine cells within the islet play an important role in regulating insulin secretion. This highlights the significance of generating a cell product derived from stem cells containing β-cells along with other major islet cells for treating patients with diabetes, instead of transplanting a purified population of β-cells. Another key question is how close in terms of heterogeneity are the islet cells derived from stem cells? In this review, we summarize the heterogeneity in islet cells of the adult pancreas and those generated from stem cells. In addition, we highlight the significance of this heterogeneity in health and disease conditions and how this can be used to design a stem cell-derived product for diabetes cell therapy.

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.

A matrigel-free method for culture of pancreatic endocrine-like cells in defined protein-based hydrogels

The transplantation of pancreatic endocrine islet cells from cadaveric donors is a promising treatment for type 1 diabetes (T1D), which is a chronic autoimmune disease that affects approximately nine million people worldwide. However, the demand for donor islets outstrips supply. This problem could be solved by differentiating stem and progenitor cells to islet cells. However, many current culture methods used to coax stem and progenitor cells to differentiate into pancreatic endocrine islet cells require Matrigel, a matrix composed of many extracellular matrix (ECM) proteins secreted from a mouse sarcoma cell line. The undefined nature of Matrigel makes it difficult to determine which factors drive stem and progenitor cell differentiation and maturation. Additionally, it is difficult to control the mechanical properties of Matrigel without altering its chemical composition. To address these shortcomings of Matrigel, we engineered defined recombinant proteins roughly 41 kDa in size, which contain cell-binding ECM peptides derived from fibronectin (ELYAVTGRGDSPASSAPIA) or laminin alpha 3 (PPFLMLLKGSTR). The engineered proteins form hydrogels through association of terminal leucine zipper domains derived from rat cartilage oligomeric matrix protein. The zipper domains flank elastin-like polypeptides whose lower critical solution temperature (LCST) behavior enables protein purification through thermal cycling. Rheological measurements show that a 2% w/v gel of the engineered proteins display material behavior comparable to a Matrigel/methylcellulose-based culture system previously reported by our group to support the growth of pancreatic ductal progenitor cells. We tested whether our protein hydrogels in 3D culture could derive endocrine and endocrine progenitor cells from dissociated pancreatic cells of young (1-week-old) mice. We found that both protein hydrogels favored growth of endocrine and endocrine progenitor cells, in contrast to Matrigel-based culture. Because the protein hydrogels described here can be further tuned with respect to mechanical and chemical properties, they provide new tools for mechanistic study of endocrine cell differentiation and maturation.

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.

Bioengineering the Vascularized Endocrine Pancreas: A Fine-Tuned Interplay Between Vascularization, Extracellular-Matrix-Based Scaffold Architecture, and Insulin-Producing Cells

Intrahepatic islet transplantation is a promising β-cell replacement strategy for the treatment of type 1 diabetes. Instant blood-mediated inflammatory reactions, acute inflammatory storm, and graft revascularization delay limit islet engraftment in the peri-transplant phase, hampering the success rate of the procedure. Growing evidence has demonstrated that islet engraftment efficiency may take advantage of several bioengineering approaches aimed to recreate both vascular and endocrine compartments either ex vivo or in vivo. To this end, endocrine pancreas bioengineering is an emerging field in β-cell replacement, which might provide endocrine cells with all the building blocks (vascularization, ECM composition, or micro/macro-architecture) useful for their successful engraftment and function in vivo. Studies on reshaping either the endocrine cellular composition or the islet microenvironment have been largely performed, focusing on a single building block element, without, however, grasping that their synergistic effect is indispensable for correct endocrine function. Herein, the review focuses on the minimum building blocks that an ideal vascularized endocrine scaffold should have to resemble the endocrine niche architecture, composition, and function to foster functional connections between the vascular and endocrine compartments. Additionally, this review highlights the possibility of designing bioengineered scaffolds integrating alternative endocrine sources to overcome donor organ shortages and the possibility of combining novel immune-preserving strategies for long-term graft function.

IGF-1R/YAP signaling pathway is involved in collagen V-induced insulin biosynthesis and secretion in rat islet INS-1 cells

PURPOSE

Type V collagen (collagen V) is one of the important components of extracellular matrix (ECM) in pancreas. We previously reported that pre-coating collagen V on the culture dishes enhanced insulin production in INS-1 rat pancreatic β cells. In this study, we investigate the underlying mechanism.

RESULTS

Insulin biosynthesis and secretion are both increased in INS-1 cells cultured on collagen V-coated dishes, accompanied by the reduced nuclear translocation of Yes-associated protein (YAP), a transcriptional co-activator. YAP, the downstream effector of Hippo signaling pathway, plays an important role in the development and function of pancreas. Inhibition of YAP activation by verteporfin further up-regulates insulin biosynthesis and secretion. Silencing large tumor suppressor (LATS), a core component of Hippo pathway which inhibits activity of YAP by phosphorylation, by siRNA transfection inhibits both insulin biosynthesis and secretion. In the present study, the protein level of insulin-like growth factor 1 receptor (IGF-1 R), detected as the upstream molecule of YAP, is reduced in the INS-1 cells cultured on the dishes coated with collagen V. The silencing of IGF-1 R by siRNA transfection further enhances insulin biosynthesis and secretion. IGF-1 treatment reduces collagen V-induced up-regulation of insulin biosynthesis and secretion, accompanying the increased nuclear YAP.

CONCLUSION

Inhibition of IGF-1 R/YAP signal pathway is involved in collagen V-induced insulin biosynthesis and secretion in INS-1 cells.

Inclusion of extracellular matrix molecules and necrostatin-1 in the intracapsular environment of alginate-based microcapsules synergistically protects pancreatic β cells against cytokine-induced inflammatory stress

Immunoisolation of pancreatic islets in alginate-based microcapsules is a promising approach for grafting of islets in absence of immunosuppression. However, loss and damage to the extracellular matrix (ECM) during islet isolation enhance susceptibility of islets for inflammatory stress. In this study, a combined strategy was applied to reduce this stress by incorporating ECM components (collagen type IV/RGD) and necroptosis inhibitor, necrostatin-1 (Nec-1) in alginate-based microcapsules in vitro. To demonstrate efficacy, viability and function of MIN6 β-cells and human islets in capsules with collagen type IV/RGD and/or Nec-1 was investigated in presence and absence of IL-1β, IFN-γ and TNF-α. The combination of collagen type IV/RGD and Nec-1 had higher protective effects than the molecules alone. Presence of collagen type IV/RGD and Nec-1 in the intracapsular environment reduced cytokine-induced overproduction of free radical species and unfavorable shifts in mitochondrial dynamics. In addition, the ECM components collagen type IV/RGD prevented a cytokine induced suppression of the FAK/Akt pathway. Our data indicate that the inclusion of collagen type IV/RGD and Nec-1 in the intracapsular environment prevents islet-cell loss when exposed to inflammatory stress, which might contribute to higher survival of β-cells in the immediate period after transplantation. This approach of inclusion of stress reducing agents in the intracapsular environment of immunoisolating devices may be an effective way to enhance the longevity of encapsulated islet grafts. STATEMENT OF SIGNIFICANCE: Islet-cells in immunoisolated alginate-based microcapsules are very susceptible to inflammatory stress which impacts long-term survival of islet grafts. Here we show that incorporation of ECM components (collagen type IV/RGD) and necrostatin-1 (Nec-1) in the intracapsular environment of alginate-based capsules attenuates this susceptibility and promotes islet-cell survival. This effect induced by collagen type IV/RGD and Nec-1 was probably due to lowering free radical production, preventing mitochondrial dysfunction and by maintaining ECM/integrin/FAK/Akt signaling and Nec-1/RIP1/RIP3 signaling. Our study provides an effective strategy to extend longevity of islet grafts which might be of great potential for future clinical application of immunoisolated cells.

The Foundation for Engineering a Pancreatic Islet Niche

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

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.

Valproic Acid Initiates Transdifferentiation of the Human Ductal Adenocarcinoma Cell-line Panc-1 Into α-Like Cells

Non-mesenchymal pancreatic cells are a potential source for cell replacement. Their transdifferentiation can be achieved by triggering epigenetic remodeling through e. g. post-translational modification of histones. Valproic acid, a branched-chain saturated fatty acid with histone deacetylase inhibitor activity, was linked to the expression of key transcription factors of pancreatic lineage in epithelial cells and insulin transcription. However, the potential of valproic acid to cause cellular reprogramming is not fully understood. To shed further light on it we employed next-generation RNA sequencing, real-time PCR, and protein analyses by ELISA and western blot, to assess the impact of valproic acid on transcriptome and function of Panc-1-cells. Our results indicate that valproic acid has a significant impact on the cell cycle, cell adhesion, histone H3 acetylation, and metabolic pathways as well as the initiation of epithelial-mesenchymal transition through acetylation of histone H3 resulting in α-cell-like characteristics. We conclude that human epithelial pancreatic cells can be transdifferentiated into cells with endocrine properties through epigenetic regulation by valproic acid favoring an α-cell-like phenotype.

Adhesion Characteristics of Human Pancreatic Islets, Duct Epithelial Cells, and Acinar Cells to a Polymer Scaffold

We reported in 2018 that among several extracellular matrices, fibronectin, type I collagen, type IV collagen, laminin I, fibrinogen, and bovine serum albumin, fibronectin is particularly useful for adhesion of porcine pancreatic tissue. Subsequently, we developed a technology that enables the chemical coating of the constituent motifs of fibronectin onto cell culture dishes. In this experiment, we used islets (purity ≥ 90%), duct epithelial cells (purity ≥ 60%), and acinar cells (purity ≥ 99%) isolated from human pancreas according to the Edmonton protocol published in 2000 and achieved adhesion to the constituent motifs of fibronectin. A solution including cGMP Prodo Islet Media was used as the assay solution. In islets, adhesion was enhanced with the constitutive motifs of fibronectin compared with uncoated islets. In the functional evaluation of islets, insulin mRNA expression and insulin secretion were enhanced by the constitutive motif of fibronectin compared with non-coated islets. The stimulation index was comparable between non-coated islets and fibronectin motifs. In duct epithelial cells, adhesion was mildly promoted by the fibronectin component compared with non-coated component, while in acinar cells, adhesion was inhibited by the fibronectin component compared with the non-coated component. These data suggest that the constitutive motifs of fibronectin are useful for the adhesion of islets and duct epithelial cells.

Collagens I and V differently regulate the proliferation and adhesion of rat islet INS-1 cells through the integrin β1/E-cadherin/β-catenin pathway

Extracellular matrix (ECM) plays an important role in tissue repair, cell proliferation, and differentiation. Our previous study showed that collagen I and collagen V differently regulate the proliferation of rat pancreatic β cells (INS-1 cells) through opposite influences on the nuclear translocation of β-catenin. In this study, we investigated the β-catenin pathway in INS-1 cells on dishes coated with collagen I or V. We found that nuclear translocation of the transcription factor Yes-associated protein (YAP) was enhanced by collagen I and suppressed by collagen V, but had no effect on INS-1 cell proliferation. Morphologically, INS-1 cells on collagen V-coated dishes showed stronger cell-to-cell adhesion, while the cells on collagen I-coated dishes showed weaker cell-to-cell adhesion in comparison with the cells on non-coated dishes. E-cadherin played an inhibitory role in the proliferation of INS-1 cells cultured on collagen I or collagen V coated dishes via regulation of the nuclear translocation of β-catenin. Integrin β1 was enhanced with collagen I, while it was repressed with collagen V. The integrin β1 pathway positively regulated the cell proliferation. Inhibition of integrin β1 pathway restored the protein level of E-cadherin and inhibited the nuclear translocation of β-catenin in the cells on collagen I-coated dishes, but no effect was observed in the cells on collagen V-coated dishes. In conclusion, collagen I enhances the proliferation of INS-1 cells via the integrin β1 and E-cadherin/β-catenin signaling pathway. In INS-1 cells on collagen V-coated dishes, both integrin β1 and E-cadherin/β-catenin signal pathways are involved in the inhibition of proliferation.

Heterogeneity and Dynamics of Vasculature in the Endocrine System During Aging and Disease

The endocrine system consists of several highly vascularized glands that produce and secrete hormones to maintain body homeostasis and regulate a range of bodily functions and processes, including growth, metabolism and development. The dense and highly vascularized capillary network functions as the main transport system for hormones and regulatory factors to enable efficient endocrine function. The specialized capillary types provide the microenvironments to support stem and progenitor cells, by regulating their survival, maintenance and differentiation. Moreover, the vasculature interacts with endocrine cells supporting their endocrine function. However, the structure and niche function of vasculature in endocrine tissues remain poorly understood. Aging and endocrine disorders are associated with vascular perturbations. Understanding the cellular and molecular cues driving the disease, and age-related vascular perturbations hold potential to manage or even treat endocrine disorders and comorbidities associated with aging. This review aims to describe the structure and niche functions of the vasculature in various endocrine glands and define the vascular changes in aging and endocrine disorders.

Building Biomimetic Potency Tests for Islet Transplantation

Diabetes is a disease of insulin insufficiency, requiring many to rely on exogenous insulin with constant monitoring to avoid a fatal outcome. Islet transplantation is a recent therapy that can provide insulin independence, but the procedure is still limited by both the availability of human islets and reliable tests to assess their function. While stem cell technologies are poised to fill the shortage of transplantable cells, better methods are still needed for predicting transplantation outcome. To ensure islet quality, we propose that the next generation of islet potency tests should be biomimetic systems that match glucose stimulation dynamics and cell microenvironmental preferences and rapidly assess conditional and continuous insulin secretion with minimal manual handing. Here, we review the current approaches for islet potency testing and outline technologies and methods that can be used to arrive at a more predictive potency test that tracks islet secretory capacity in a relevant context. With the development of potency tests that can report on islet secretion dynamics in a context relevant to their intended function, islet transplantation can expand into a more widely accessible and reliable treatment option for individuals with diabetes.

Selection for CD26- and CD49A+ Cells From Pluripotent Stem Cells-Derived Islet-Like Clusters Improves Therapeutic Activity in Diabetic Mice

BACKGROUND

Cell therapy of diabetes aims at restoring the physiological control of blood glucose by transplantation of functional pancreatic islet cells. A potentially unlimited source of cells for such transplantations would be islet cells derived from an in vitro differentiation of human pluripotent stem cells (hESC/hiPSC). The islet-like clusters (ILC) produced by the known differentiation protocols contain various cell populations. Among these, the β-cells that express both insulin and the transcription factor Nkx6.1 seem to be the most efficient to restore normoglycemia in diabetes animal models. Our aim was to find markers allowing selection of these efficient cells.

METHODS

Functional Cell-Capture Screening (FCCS) was used to identify markers that preferentially capture the cells expressing both insulin and Nkx6.1, from hESC-derived ILC cells. In order to test whether selection for such markers could improve cell therapy in diabetic mouse models, we used ILC produced from a clinical-grade line of hESC by a refined differentiation protocol adapted to up-scalable bioreactors. Re-aggregated MACS sorted cells were encapsulated in microspheres made of alginate modified to reduce foreign body reaction. Implantation was done intraperitoneally in STZ-treated C57BL/6 immuno-competent mice.

RESULTS

CD49A (integrin alpha1) was identified by FCCS as a marker for cells that express insulin (or C-peptide) as well as Nkx6.1 in ILC derived by hESC differentiation. The ILC fraction enriched in CD49A ⁺ cells rapidly reduced glycemia when implanted in diabetic mice, whereas mice receiving the CD49A depleted population remained highly diabetic. CD49A-enriched ILC cells also produced higher levels of human C-peptide in the blood of transplanted mice. However, the difference between CD49A-enriched and total ILC cells remained small. Another marker, CD26 (DPP4), was identified by FCCS as binding insulin-expressing cells which are Nkx6.1 negative. Depletion of CD26 ⁺ cells followed by enrichment for CD49A ⁺ cells increased insulin⁺/Nkx6.1⁺ cells fraction to ~70%. The CD26 ^- /CD49A ⁺ enriched ILC exhibited improved function over non-sorted ILC or CD49A ⁺ cells in diabetic mice and maintain prolonged blood C-peptide levels.

CONCLUSIONS

Refining the composition of ILC differentiated from hPSC by negative selection to remove cells expressing CD26 and positive selection for CD49A expressing cells could enable more effective cell therapy of diabetes.

Recent advances in the design of implantable insulin secreting heterocellular islet organoids

Islet transplantation has proved one of the most remarkable transmissions from an experimental curiosity into a routine clinical application for the treatment of type I diabetes (T1D). Current efforts for taking this technology one-step further are now focusing on overcoming islet donor shortage, engraftment, prolonged islet availability, post-transplant vascularization, and coming up with new strategies to eliminate lifelong immunosuppression. To this end, insulin secreting 3D cell clusters composed of different types of cells, also referred as heterocellular islet organoids, spheroids, or pseudoislets, have been engineered to overcome the challenges encountered by the current islet transplantation protocols. β-cells or native islets are accompanied by helper cells, also referred to as accessory cells, to generate a cell cluster that is not only able to accurately secrete insulin in response to glucose, but also superior in terms of other key features (e.g. maintaining a vasculature, longer durability in vivo and not necessitating immunosuppression after transplantation). Over the past decade, numerous 3D cell culture techniques have been integrated to create an engineered heterocellular islet organoid that addresses current obstacles. Here, we first discuss the different cell types used to prepare heterocellular organoids for islet transplantation and their contribution to the organoids design. We then introduce various cell culture techniques that are incorporated to prepare a fully functional and insulin secreting organoids with select features. Finally, we discuss the challenges and present a future outlook for improving clinical outcomes of islet transplantation.

Genetic interactions among ADAMTS metalloproteases and basement membrane molecules in cell migration in Caenorhabditis elegans

During development of the Caenorhabditis elegans gonad, the gonadal leader cells, called distal tip cells (DTCs), migrate in a U-shaped pattern to form the U-shaped gonad arms. The ADAMTS (adisintegrin and metalloprotease with thrombospondin motifs) family metalloproteases MIG-17 and GON-1 are required for correct DTC migration. Mutations in mig-17 result in misshapen gonads due to the misdirected DTC migration, and mutations in gon-1 result in shortened and swollen gonads due to the premature termination of DTC migration. Although the phenotypes shown by mig-17 and gon-1 mutants are very different from one another, mutations that result in amino acid substitutions in the same basement membrane protein genes, emb-9/collagen IV α1, let-2/collagen IV α2 and fbl-1/fibulin-1, were identified as genetic suppressors of mig-17 and gon-1 mutants. To understand the roles shared by these two proteases, we examined the effects of the mig-17 suppressors on gon-1 and the effects of the gon-1 suppressors and enhancers on mig-17 gonadal defects. Some of the emb-9, let-2 and fbl-1 mutations suppressed both mig-17 and gon-1, whereas others acted only on mig-17 or gon-1. These results suggest that mig-17 and gon-1 have their specific functions as well as functions commonly shared between them for gonad formation. The levels of collagen IV accumulation in the DTC basement membrane were significantly higher in the gon-1 mutants as compared with wild type and were reduced to the wild-type levels when combined with suppressor mutations, but not with enhancer mutations, suggesting that the ability to reduce collagen IV levels is important for gon-1 suppression.

The role of vascular niche and endothelial cells in organogenesis and regeneration

The term vascular niche indicate the physical and biochemical microenvironment around blood vessel where endothelial cells, pericytes, and smooth muscle cells organize themselves to form blood vessels and release molecules involved in the recruitment of hematopoietic stem cells, endothelial progenitor cells and mesenchymal stem cells. The vascular niche creates a permissive environment that enables different cell types to realize their developmental or regenerative programs. In this context, the proximity between the endothelium and the new-forming cellular components of organs suggests an essential role of endothelial cells in the organs maturation. Dynamic interactions between specific organ endothelial cells and different cellular conponents are crucial for different organ morphogenesis and function. Conversely, organs provide cues shaping vascular network structure.

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

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

Beta cell dysfunction in diabetes: the islet microenvironment as an unusual suspect

Cells in different tissues, including endocrine cells in the pancreas, live in complex microenvironments that are rich in cellular and acellular components. Intricate interactions with their microenvironment dictate most cellular properties, such as their function, structure and size, and maintain tissue homeostasis. Pancreatic islets are populated by endocrine, vascular and immune cells that are immersed in the extracellular matrix. While the intrinsic properties of beta cells have been vastly investigated, our understanding of their interactions with their surroundings has only recently begun to unveil. Here, we review current research on the interplay between the islet cellular and acellular components, and the role these components play in beta cell physiology and pathophysiology. Although beta cell failure is a key pathomechanism in diabetes, its causes are far from being fully elucidated. We, thus, propose deleterious alterations of the islet niche as potential underlying mechanisms contributing to beta cell failure. In sum, this review emphasises that the function of the pancreatic islet depends on all of its components. Graphical abstract.

Generation of insulin-secreting organoids: a step toward engineering and transplanting the bioartificial pancreas

Diabetes is a major health issue of increasing prevalence. ß‐cell replacement, by pancreas or islet transplantation, is the only long‐term curative option for patients with insulin‐dependent diabetes. Despite good functional results, pancreas transplantation remains a major surgery with potentially severe complications. Islet transplantation is a minimally invasive alternative that can widen the indications in view of its lower morbidity. However, the islet isolation procedure disrupts their vasculature and connection to the surrounding extracellular matrix, exposing them to ischemia and anoikis. Implanted islets are also the target of innate and adaptive immune attacks, thus preventing robust engraftment and prolonged full function. Generation of organoids, defined as functional 3D structures assembled with cell types from different sources, is a strategy increasingly used in regenerative medicine for tissue replacement or repair, in a variety of inflammatory or degenerative disorders. Applied to ß‐cell replacement, it offers the possibility to control the size and composition of islet‐like structures (pseudo‐islets), and to include cells with anti‐inflammatory or immunomodulatory properties. In this review, we will present approaches to generate islet cell organoids and discuss how these strategies can be applied to the generation of a bioartificial pancreas for the treatment of type 1 diabetes.

White Adipose Tissue as a Site for Islet Transplantation

Although islet transplantation is recognized as a useful cellular replacement therapy for severe diabetes, surgeons face difficulties in islet engraftment. The transplant site is a pivotal factor that influences the engraftment. Although the liver is the current representative site for clinical islet transplantation, it is not the best site because of limitations in immunity, inflammation, and hypoxia. White adipose tissue, including omentum, is recognized as a useful candidate site for islet transplantation. Its effectiveness has been evaluated in not only various basic and translational studies using small and large animals but also in some recent clinical trials. In this review, we attempt to shed light on the characteristics and usefulness of white adipose tissue as a transplant site for islets.

White Adipose Tissue as a Site for Islet Transplantation

Although islet transplantation is recognized as a useful cellular replacement therapy for severe diabetes, surgeons face difficulties in islet engraftment. The transplant site is a pivotal factor that influences the engraftment. Although the liver is the current representative site for clinical islet transplantation, it is not the best site because of limitations in immunity, inflammation, and hypoxia. White adipose tissue, including omentum, is recognized as a useful candidate site for islet transplantation. Its effectiveness has been evaluated in not only various basic and translational studies using small and large animals but also in some recent clinical trials. In this review, we attempt to shed light on the characteristics and usefulness of white adipose tissue as a transplant site for islets.

Microwell Scaffolds Using Collagen-IV and Laminin-111 Lead to Improved Insulin Secretion of Human Islets

IMPACT STATEMENT

This research deals with finding a proper bioengineering strategy to improve the outcome of islets transplantation for treatment of type 1 diabetes. It is focused on the mimicking of islet extracellular matrix niche in microwell islet delivery devices to improve their endocrine function.

VEGF-A and blood vessels: a beta cell perspective

Reciprocal signalling between the endothelium and the pancreatic epithelium is crucial for coordinated differentiation of the embryonic endocrine and exocrine pancreas. In the adult pancreas, islets depend on their dense capillary network to adequately respond to changes in plasma glucose levels. Vascular changes contribute to the onset and progression of both type 1 and type 2 diabetes. Impaired revascularisation of islets transplanted in individuals with type 1 diabetes is linked to islet graft failure and graft loss. This review summarises our understanding of the role of vascular endothelial growth factor-A (VEGF-A) and endothelial cells in beta cell development, physiology and disease. In addition, the therapeutic potential of modulating VEGF-A levels in beta and beta-like cells for transplantation is discussed.

Enriched developmental biology molecular pathways impact on antipsychotics-induced weight gain

Psychotropic-induced weight gain (PIWG) may lead to increased risk for cardiovasculardiseases, metabolic disorders and treatment discontinuation. PIWG may be genetically driven. The analysis of complete molecular pathways may grant suffcient power to tackle the biologic variance of PIWG. Such identifcation would help to move a step forward in the direction of personalized treatment in psychiatry. A genetic sample from the CATIE trial (n = 765; M = 556, mean age = 40.93 ± 11.03) treated with diverse antipsychotic drugs was investigated. A molecular pathway analysis was conducted for the identifcation of the molecular pathways enriched in variations associated with PIWG. The developmental biology molecular pathway was signifcantly (P.adj = 0.018) enriched in genetic variations signifcantly (P < 0.01) associated with PIWG. A total of 18 genes were identifed and discussed. The developmental biology molecular pathway is involved in the regulation of β-cell development, and the transcriptional regulation of white adipocyte differentiation. Results from the current contribution correlate with previous evidence and it is consistent with our earlier result on the STAR*D sample. Furthermore, the involvement of the β-cell development and the transcriptional regulation of white adipocyte differentiation pathways stress the relevance of the peripheral tissue rearrangement, rather than increased food intake, in the biologic modifcations that follow psychotropic treatment and may lead to PIWG. Further research is warranted.

Informing β-cell regeneration strategies using studies of heterogeneity

BACKGROUND

Current therapeutic strategies for type 1 (T1DM) and type 2 diabetes mellitus (T2DM) rely on increasing or substituting endogenous insulin secretion in combination with lifestyle changes. β-cell regeneration, a process whereby new β-cells arise from progenitors, self-renewal or transdifferentiation, has the potential to become a viable route to insulin self-sufficiency. Current regeneration strategies capture many of the transcriptomic and protein features of native β-cells, generating cells capable of glucose-dependent insulin secretion in vitro and alleviation of hyperglycemia in vivo. However, whether novel β-cells display appreciable heterogeneity remains poorly understood, with potential consequences for long-term functional robustness.

SCOPE OF REVIEW

The review brings together crucial discoveries in the β-cell regeneration field with state-of-the-art knowledge regarding β-cell heterogeneity. Aspects that might aid production of longer-lasting and more plastic regenerated β-cells are highlighted and discussed.

MAJOR CONCLUSIONS

Different β-cell regeneration approaches result in a similar outcome: glucose-sensitive, insulin-positive cells that mimic the native β-cell phenotype but which lack normal plasticity. The β-cell subpopulations identified to date expand our understanding of β-cell survival, proliferation and function, signposting the direction for future regeneration strategies. Therefore, regenerated β-cells should exhibit stimulus-dependent differences in gene and protein expression, as well as establish a functional network with different β-cells, all while coexisting with other cell types on a three-dimensional platform.

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.

RGD-containing elastin-like polypeptide improves islet transplantation outcomes in diabetic mice

Successful islet transplantation critically depends on the isolation of healthy islets. However, the islet isolation procedure itself contributes to islet death due to the destruction of intra- and peri-islet extracellular matrices (ECMs) during digestion. We investigated whether an RGD-containing elastin-like polypeptide (REP) could function as a self-assembling matrix to replenish ECMs and protects islets from cell death. Immediately following isolation, islets were coated with REP coacervate particles via isothermal adsorption of an REP solution followed by thermal gelation. REP-coated islets displayed increased viability and insulin secretory capacity in pretransplant culture compared to untreated islets. Co-transplantation of REP-treated islets and REP beneath the renal sub-capsule in streptozotocin-induced diabetic mice restored normoglycemia and serum insulin levels. Mice that received co-transplants maintained normoglycemia for a longer period of time than those receiving untreated islets without REP. Moreover, co-transplantation sites exhibited enhanced β-cell proliferation and vascularization. Thus, the REP-based coacervation strategy improve the survival, function and therapeutic potential of transplanted islets. STATEMENT OF SIGNIFICANCE: 1). An artificial matrix polypeptide comprised of thermoresponsive elastin-like peptides and integrin-stimulatory RGD ligands (REP) to reconstitute damaged or lost matrices. 2). Through body temperature-induced coacervation, REP reconstitutes intra-islet environment and enhances islet viability and insulin secretion by activating the pro-survival and insulin signaling pathways. 3). REP-coated islets were transplanted together with the matrix polypeptide under the kidney sub-capsule of mice, it develops a new peri-insular environment, which protects the islet grafts from immune rejection thus extending islet longevity. 4). Our data suggest that in situ self-assembly of biomimetic islet environments become a new platform allowing for improved islet transplantation at extrahepatic sites.

Improved recovery of human islets from young donor pancreases utilizing increased protease dose to collagenase for digesting peri-islet extracellular matrix

Human islet isolation from young donor pancreases (YDP) utilizing the current purified standard dose of collagenase-protease enzyme mixtures often results in the release of a high percentage of mantled islets. Mantled islets are those surrounded by exocrine tissue and are difficult to purify by density gradient centrifugation, leading to poor islet recovery. Based on difference in extracellular matrix, and total collagen content between YDP and old donor pancreas (ODP, > 35 Y) led us to compare results from islet isolation using increased collagenase combination (ICC) or increased protease combination (IPC), to the standard enzyme combination (SEC) in a "trisected" pancreas model to overcome the donor-to-donor variability. These results showed a reduced percentage of mantled islets (17% ± 7.5%) and higher postpurification islet recovery (83.8% ± 5.6%) with IPC. Furthermore, these results were confirmed in 13 consecutive whole pancreas islet isolations utilizing IPC from VitaCyte, Roche, or SERVA collagenase-protease enzyme mixtures. Results obtained from in vitro and in vivo islet functional assessment indicated that islets isolated using IPC retained normal islet morphology, insulin secretion, and the ability to reverse diabetes after transplantation in diabetic nude mice. This is the first report utilizing trisected pancreas to assess the effectiveness of different enzyme combinations to improve islet recovery from young donor pancreases.

Adhesion G-protein coupled receptors: Implications for metabolic function

Adhesion G-protein coupled receptors (aGPCRs) are emerging as important actors in energy homeostasis. Recent biochemical and functional studies using transgenic mice indicate that aGPCRs play important roles in endocrine and metabolic functions including β-cell differentiation, insulin secretion, adipogenesis and whole body fuel homeostasis. Most aGPCRs are orphans, for which endogenous ligands have not yet been identified, and many of the endogenous ligands of the already de-orphanised aGPCRs are components of the extracellular matrix (ECM). In this review we focus on aGPCR expression in metabolically active tissues, their activation by ECM proteins, and current knowledge of their potential roles in islet development, insulin secretion, adipogenesis and muscle function.

Hydrogel materials for the application of islet transplantation

Type 1 diabetes mellitus is a serious disease comprising approximately 10% of all diabetes cases, and the global incidence of type 1 diabetes mellitus is steadily rising without any promise of a cure in the near future. Although islet transplantation has proven to be an effective means of treating type 1 diabetes mellitus and promoting insulin independence in patients, its widespread implementation has been severely constrained by instances of post-transplantation islet cell death, rejection, and severe adverse immune responses. Islet encapsulation is an active area of research aimed at shielding implanted islets from immunological rejection and inflammation while still allowing for effective insulin and nutrient exchange with donor cells. Given their promising physical and chemical properties, hydrogels have been a major subject of focus in the field of islet transplantation and encapsulation technology, offering promising advances towards immunologically privileged islet implants. The present review therefore summarizes the current state of research regarding the use of hydrogels in the context of islet transplantation, including both natural molecular hydrogels and artificial polymer hydrogels, with the goal of understanding the current strengths and weaknesses of this treatment strategy.

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.

Nanotechnology in cell replacement therapies for type 1 diabetes

Islet transplantation is a promising long-term, compliance-free, complication-preventing treatment for type 1 diabetes. However, islet transplantation is currently limited to a narrow set of patients due to the shortage of donor islets and side effects from immunosuppression. Encapsulating cells in an immunoisolating membrane can allow for their transplantation without the need for immunosuppression. Alternatively, "open" systems may improve islet health and function by allowing vascular ingrowth at clinically attractive sites. Many processes that enable graft success in both approaches occur at the nanoscale level-in this review we thus consider nanotechnology in cell replacement therapies for type 1 diabetes. A variety of biomaterial-based strategies at the nanometer range have emerged to promote immune-isolation or modulation, proangiogenic, or insulinotropic effects. Additionally, coating islets with nano-thin polymer films has burgeoned as an islet protection modality. Materials approaches that utilize nanoscale features manipulate biology at the molecular scale, offering unique solutions to the enduring challenges of islet transplantation.

3D-Models of Insulin-Producing β-Cells: from Primary Islet Cells to Stem Cell-Derived Islets

There is a need for physiologically relevant assay platforms to provide functionally relevant models of diabetes, to accelerate the discovery of new treatment options and boost developments in drug discovery. In this review, we compare several 3D-strategies that have been used to increase the functional relevance of ex vivo human primary pancreatic islets and developments into the generation of stem cell derived pancreatic beta-cells (β-cells). Special attention will be given to recent approaches combining the use of extracellular matrix (ECM) scaffolds with pancreatic molecular memory, which can be used to improve yield and functionality of in vitro stem cell-derived pancreatic models. The ultimate goal is to develop scalable cell-based platforms for diabetes research and drug screening. This article will critically assess key aspects related to in vitro pancreatic 3D-ECM models and highlight the most promising approaches for future research.

Fibronectin and Collagen IV Microcontact Printing Improves Insulin Secretion by INS1E Cells

IMPACT STATEMENT

This research deals with finding a proper bioengineering strategy for the creation of improved β-cell replacement therapy in type 1 diabetes. It specifically deals with the microenvironment of β-cells and its relationship to their endocrine function.

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.

Adrb2 controls glucose homeostasis by developmental regulation of pancreatic islet vasculature

A better understanding of processes controlling the development and function of pancreatic islets is critical for diabetes prevention and treatment. Here, we reveal a previously unappreciated function for pancreatic β2-adrenergic receptors (Adrb2) in controlling glucose homeostasis by restricting islet vascular growth during development. Pancreas-specific deletion of Adrb2 results in glucose intolerance and impaired insulin secretion in mice, and unexpectedly, specifically in females. The metabolic phenotypes were recapitulated by Adrb2 deletion from neonatal, but not adult, β-cells. Mechanistically, Adrb2 loss increases production of Vascular Endothelial Growth Factor-A (VEGF-A) in female neonatal β-cells and results in hyper-vascularized islets during development, which in turn, disrupts insulin production and exocytosis. Neonatal correction of islet hyper-vascularization, via VEGF-A receptor blockade, fully rescues functional deficits in glucose homeostasis in adult mutant mice. These findings uncover a regulatory pathway that functions in a sex-specific manner to control glucose metabolism by restraining excessive vascular growth during islet development.

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 scaffold and hydrogel derived from decellularized and delipidized human pancreas

Extracellular matrix (ECM) plays an important developmental role by regulating cell behaviour through structural and biochemical stimulation. Tissue-specific ECM, attained through decellularization, has been proposed in several strategies for tissue and organ replacement. Decellularization of animal pancreata has been reported, but the same methods applied to human pancreas are less effective due to higher lipid content. Moreover, ECM-derived hydrogels can be obtained from many decellularized tissues, but methods have not been reported to obtain human pancreas-derived hydrogel. Using novel decellularization methods with human pancreas we produced an acellular, 3D biological scaffold (hP-ECM) and hydrogel (hP-HG) amenable to tissue culture, transplantation and proteomic applications. The inclusion of a homogenization step in the decellularization protocol significantly improved lipid removal and gelation capability of the resulting ECM, which was capable of gelation at 37 °C in vitro and in vivo, and is cytocompatible with a variety of cell types and islet-like tissues in vitro. Overall, this study demonstrates the characterisation of a novel protocol for the decellularization and delipidization of human pancreatic tissue for the production of acellular ECM and ECM hydrogel suitable for cell culture and transplantation applications. We also report a list of 120 proteins present within the human pancreatic matrisome.

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.