Endothelial progenitor cell cotransplantation enhances islet engraftment by rapid revascularization

Toward a 3D Printed Perfusable Islet Embedding Structure: Technical Notes and Preliminary Results

To date, islet transplantation to treat type 1 diabetes mellitus remains unsuccessful in long-term follow-up, mainly due to failed engraftment and reconstruction of the islet niche. Alternative approaches, such as islet embedding structures (IESs) based on 3D printing have been developed. However, most of them have been implanted subcutaneously and only a few are intended for direct integration into the vascular system through anastomosis. In this study, we 3D printed a proof-of-concept IES using gelatin methacrylate biocompatible ink. This structure consisted of a branched vascular system surrounding both sides of a central cavity dedicated to islets of Langerhans. Furthermore, we designed a bioreactor optimized for these biological structures. This bioreactor allows seeding and perfusion experiments under sterile and physiological conditions. Preliminary experiments aimed to analyze if the vascular channel could successfully be seeded with mature endothelial cells and the central cavity with rat islets. Subsequently, the structures were used for a humanized model seeding human endothelial progenitor cells (huEPC) within the vascular architecture and human islets co-cultured with huEPC within the central cavity. The constructs were tested for hemocompatibility, suture strength, and anastomosability. The 3D printed IES appeared to be hemocompatible and anastomosable using an alternative cuff anastomosis in a simple ex vivo perfusion model. While rat islets alone could not successfully be embedded within the 3D printed structure for 3 days, human islets co-cultivated with huEPC successfully engrafted within the same time. This result emphasizes the importance of co-culture, nursing cells, and islet niche. In conclusion, we constructed a proof-of-concept 3D printed islet embedding device consisting of a vascular channel that is hemocompatible and perspectively anastomosable to clinical scale blood vessels. However, there are numerous limitations in this model that need to be overcome to transfer this technology to the bedside.

No Time to Die-How Islets Meet Their Demise in Transplantation

Islet transplantation represents an effective treatment for patients with type 1 diabetes mellitus (T1DM) and severe hypoglycaemia unawareness, capable of circumventing impaired counterregulatory pathways that no longer provide protection against low blood glucose levels. The additional beneficial effect of normalizing metabolic glycaemic control is the minimisation of further complications related to T1DM and insulin administration. However, patients require allogeneic islets from up to three donors, and the long-term insulin independence is inferior to that achieved with solid organ (whole pancreas) transplantation. This is likely due to the fragility of islets caused by the isolation process, innate immune responses following portal infusion, auto- and allo-immune-mediated destruction and β-cell exhaustion following transplantation. This review covers the specific challenges related to islet vulnerability and dysfunction that affect long-term cell survival following transplantation.

A porcine islet-encapsulation device that enables long-term discordant xenotransplantation in immunocompetent diabetic mice

Islet transplantation is an effective treatment for type 1 diabetes (T1D). However, a shortage of donors and the need for immunosuppressants are major issues. The ideal solution is to develop a source of insulin-secreting cells and an immunoprotective method. No bioartificial pancreas (BAP) devices currently meet all of the functions of long-term glycemic control, islet survival, immunoprotection, discordant xenotransplantation feasibility, and biocompatibility. We developed a device in which porcine islets were encapsulated in a highly stable and permeable hydrogel and a biocompatible immunoisolation membrane. Discordant xenotransplantation of the device into diabetic mice improved glycemic control for more than 200 days. Glycemic control was also improved in new diabetic mice "relay-transplanted" with the device after its retrieval. The easily retrieved devices exhibited almost no adhesion or fibrosis and showed sustained insulin secretion even after the two xenotransplantations. This device has the potential to be a useful BAP for T1D.

Type 1 diabetes and engineering enhanced islet transplantation

The development of new therapeutic approaches to treat type 1 diabetes mellitus (T1D) relies on the precise understanding and deciphering of insulin-secreting β-cell biology, as well as the mechanisms responsible for their autoimmune destruction. β-cell or islet transplantation is viewed as a potential long-term therapy for the millions of patients with diabetes. To advance the field of insulin-secreting cell transplantation, two main research areas are currently investigated by the scientific community: (1) the identification of the developmental pathways that drive the differentiation of stem cells into insulin-producing cells, providing an inexhaustible source of cells; and (2) transplantation strategies and engineered transplants to provide protection and enhance the functionality of transplanted cells. In this review, we discuss the biology of pancreatic β-cells, pathology of T1D and current state of β-cell differentiation. We give a comprehensive view and discuss the different possibilities to engineer enhanced insulin-secreting cell/islet transplantation from a translational perspective.

Targeting Pancreatic Islet NLRP3 Improves Islet Graft Revascularization

Hypoxia-induced islet cell death, caused by an insufficient revascularization of the grafts, is a major obstacle for successful pancreatic islet transplantation. Recently, it has been reported that the nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is expressed in pancreatic islets and that its loss protects against hypoxia-induced cell death. Therefore, we hypothesized that the inhibition of NLRP3 in islets improves the survival and endocrine function of the grafts. The transplantation of Nlrp3-/- islets or wild-type (WT) islets exposed to the NLRP3 inhibitor CY-09 into mouse dorsal skinfold chambers resulted in an improved revascularization compared with controls. An increased insulin release after NLRP3 inhibition caused the enhanced angiogenic response. Moreover, the inhibition of NLRP3 in hypoxic β-cells triggered insulin gene expression by inducing the shuttling of MafA and pancreatic and duodenal homeobox-1 into the nucleus. This was mediated by a reduced interaction of NLRP3 with the thioredoxin-interacting protein (TXNIP). Transplantation of Nlrp3-/- islets or WT islets exposed to CY-09 under the kidney capsule of diabetic mice markedly improved the restoration of normoglycemia. These findings indicate that the inhibition of NLRP3 in isolated islets represents a promising therapeutic strategy to improve engraftment and function of the islets.

Biophysical quantification of reorganization dynamics of human pancreatic islets during co-culture with adipose-derived stem cells

Reorganization dynamics of human islets during co-culture with adipose stem cells depends on islet size and the heterogeneity can be assessed based on biomechanical opacity of individual islets.

Recapitulating pancreatic cell-cell interactions through bioengineering approaches: the momentous role of non-epithelial cells for diabetes cell therapy

Over the past few years, extensive efforts have been made to generate in-vitro pancreatic micro-tissue, for disease modeling or cell replacement approaches in pancreatic related diseases such as diabetes mellitus. To obtain these goals, a closer look at the diverse cells participating in pancreatic development is necessary. Five major non-epithelial pancreatic (pN-Epi) cell populations namely, pancreatic endothelium, mesothelium, neural crests, pericytes, and stellate cells exist in pancreas throughout its development, and they are hypothesized to be endogenous inducers of the development. In this review, we discuss different pN-Epi cells migrating to and existing within the pancreas and their diverse effects on pancreatic epithelium during organ development mediated via associated signaling pathways, soluble factors or mechanical cell-cell interactions. In-vivo and in-vitro experiments, with a focus on N-Epi cells' impact on pancreas endocrine development, have also been considered. Pluripotent stem cell technology and multicellular three-dimensional organoids as new approaches to generate pancreatic micro-tissues have also been discussed. Main challenges for reaching a detailed understanding of the role of pN-Epi cells in pancreas development in utilizing for in-vitro recapitulation have been summarized. Finally, various novel and innovative large-scale bioengineering approaches which may help to recapitulate cell-cell interactions and are crucial for generation of large-scale in-vitro multicellular pancreatic micro-tissues, are discussed.

Tissue engineering and 3D printing of bioartificial pancreas for regenerative medicine in diabetes

Diabetes is a severe chronic disease worldwide. In various types of diabetes, the pancreatic beta cells fail to secrete sufficient insulin, at some point, to regulate blood glucose levels. Therefore, the replacement of dysfunctional pancreas, islets of Langerhans, or even the insulin-secreting beta cells facilitates physiological regulation of blood glucose levels. However, the current lack of sufficient donor human islets for cell replacement therapy precludes a routine and absolute cure for most of the existing diabetes cases globally. It is envisioned that tissue engineering of a bioartificial pancreas will revolutionize regenerative medicine and the treatment of diabetes. In this review, we discuss the anatomy and physiology of the pancreas, and identify the clinical considerations for engineering a bioartificial pancreas. Subsequently, we dissect the bioengineering problem based on the design of the device, the biomaterial used, and the cells involved. Last but not least, we highlight current tissue engineering challenges and explore potential directions for future work.

Neovascularization of engineered tissues for clinical translation: Where we are, where we should be?

One of the key challenges in engineering three-dimensional tissue constructs is the development of a mature microvascular network capable of supplying sufficient oxygen and nutrients to the tissue. Recent angiogenic therapeutic strategies have focused on vascularization of the constructed tissue, and its integration in vitro; these strategies typically combine regenerative cells, growth factors (GFs) with custom-designed biomaterials. However, the field needs to progress in the clinical translation of tissue engineering strategies. The article first presents a detailed description of the steps in neovascularization and the roles of extracellular matrix elements such as GFs in angiogenesis. It then delves into decellularization, cell, and GF-based strategies employed thus far for therapeutic angiogenesis, with a particularly detailed examination of different methods by which GFs are delivered in biomaterial scaffolds. Finally, interdisciplinary approaches involving advancement in biomaterials science and current state of technological development in fabrication techniques are critically evaluated, and a list of remaining challenges is presented that need to be solved for successful translation to the clinics.

The Role of Vascular Cells in Pancreatic Beta-Cell Function

Insulin-producing β-cells constitute the majority of the cells in the pancreatic islets. Dysfunction of these cells is a key factor in the loss of glucose regulation that characterizes type 2 diabetes. The regulation of many of the functions of β-cells relies on their close interaction with the intra-islet microvasculature, comprised of endothelial cells and pericytes. In addition to providing islet blood supply, cells of the islet vasculature directly regulate β-cell activity through the secretion of growth factors and other molecules. These factors come from capillary mural pericytes and endothelial cells, and have been shown to promote insulin gene expression, insulin secretion, and β-cell proliferation. This review focuses on the intimate crosstalk of the vascular cells and β-cells and its role in glucose homeostasis and 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.

Microvessel Network Formation and Interactions with Pancreatic Islets in Three-Dimensional Chip Cultures

The pancreatic islet is a highly vascularized micro-organ, and rapid revascularization postislet transplantation is important for islet survival and function. However, the various mechanisms involved in islet revascularization are not fully understood, and we currently lack good in vitro platforms to explore this. Our aim for this study was to generate perfusable microvascular networks in a microfluidic chip device, in which islets could be easily integrated, to establish an in vitro platform for investigations on islet-microvasculature interactions. We compared the ability of mesenchymal stem cells (MSCs) and fibroblasts to support microvascular network formation by human umbilical vein endothelial cells (HUVECs) and human induced pluripotent stem cell-derived endothelial colony-forming cell in two-dimensional and three-dimensional models of angiogenesis, and tested the effect of different culture media on microvessel formation. HUVECs that were supported by MSCs formed patent and perfusable networks in a fibrin gel, whereas networks supported by fibroblasts rapidly regressed. Network morphology could be controlled by adjusting relative cell numbers and densities. Incorporation of isolated rat islets demonstrated that islets recruit local microvasculature in vitro, but that the microvessels did not invade islets, at least during the course of these studies. This in vitro microvascularization platform can provide a useful tool to study how various parameters affect islet integration with microvascular networks and could also be utilized for studies of vascularization of other organ systems. Impact statement To improve pancreatic islet graft survival and function posttransplantation, rapid and adequate revascularization is critical. Efforts to improve islet revascularization are demanding due to an insufficient understanding of the mechanisms involved in the process. We have applied a microfluidics platform to generate microvascular networks, and by incorporating pancreatic islets, we were able to study microvasculature-islet interactions in real time. This platform can provide a useful tool to study islet integration with microvascular networks, and could be utilized for studies of vascularization of other organ systems. Moreover, this work may be adapted toward developing a prevascularized islet construct for transplantation.

Evaluating Vascularization of Heterotopic Islet Constructs for Type 1 Diabetes Using an In Vitro Platform

Type 1 diabetes (T1D) results from the autoimmune destruction of β-cells within the pancreatic islets of Langerhans. Clinical islet transplantation from healthy donors is proposed to ameliorate symptoms, improve quality of life, and enhance the life span of afflicted T1D patients. However, post-transplant outcomes are dependent on the survival of the transplanted islets, which relies on the engraftment of the islets with the recipient's vasculature among other factors. Treatment strategies to improve engraftment include combining islets with supporting cells including endothelial cells (EC) and mesenchymal stem cells (MSC), dynamic cells capable of robust immunomodulatory and vasculogenic effects. In this study, we developed an in vitro model of transplantation to investigate the cellular mechanisms that enhance rapid vascularization of heterotopic islet constructs. Self-assembled vascular beds of fluorescently stained EC served as reproducible in vitro transplantation sites. Heterotopic islet constructs composed of islets, EC, and MSC were transferred to vascular beds for modeling transplantation. Time-lapsed imaging was performed for analysis of the vascular bed remodeling for parameters of neo-vascularization. Moreover, sampling of media following modeled transplantation showed secretory profiles that were correlated with imaging analyses as well as with islet function using glucose-stimulated insulin secretion. Together, evidence revealed that heterotopic constructs consisting of islets, EC, and MSC exhibited the most rapid recruitment and robust branching of cells from the vascular beds suggesting enhanced neo-vascularization compared to islets alone and control constructs. Together, this evidence supports a promising cell transplantation strategy for T1D and also demonstrates a valuable tool for rapidly investigating candidate cellular therapies for transplantation.

Small Molecule-Induced Pancreatic β-Like Cell Development: Mechanistic Approaches and Available Strategies

Diabetes is a metabolic disease which affects not only glucose metabolism but also lipid and protein metabolism. It encompasses two major types: type 1 and 2 diabetes. Despite the different etiologies of type 1 and 2 diabetes mellitus (T1DM and T2DM, respectively), the defining features of the two forms are insulin deficiency and resistance, respectively. Stem cell therapy is an efficient method for the treatment of diabetes, which can be achieved by differentiating pancreatic β-like cells. The consistent generation of glucose-responsive insulin releasing cells remains challenging. In this review article, we present basic concepts of pancreatic organogenesis, which intermittently provides a basis for engineering differentiation procedures, mainly based on the use of small molecules. Small molecules are more auspicious than any other growth factors, as they have unique, valuable properties like cell-permeability, as well as a nonimmunogenic nature; furthermore, they offer immense benefits in terms of generating efficient functional beta-like cells. We also summarize advances in the generation of stem cell-derived pancreatic cell lineages, especially endocrine β-like cells or islet organoids. The successful induction of stem cells depends on the quantity and quality of available stem cells and the efficient use of small molecules.

Integration of Primary Endocrine Cells and Supportive Cells Using Functionalized Silk Promotes the Formation of Prevascularized Islet-like Clusters

Pancreatic islet transplantation has not yet succeeded as an overall treatment for type 1 diabetes because of limited access to donor islets, as well as low efficacy and poor reproducibility of the current procedure. Herein, a method to create islets-like composite clusters (coclusters) from dispersed endocrine cells and supportive cells is described, attempting to improve compatibility with the recipient and more efficiently make use of the donor-derived material. To mimic the extracellular matrix environment, recombinant spider silk functionalized with cell binding motifs are used as 3D support for the coclusters. A cell binding motif derived from fibronectin (FN) was found superior in promoting cell adherence, while a plain RGD-motif incorporated in the repetitive part of the silk protein (2R) increased the mobility and cluster formation of endocrine cells. Self-assembly of a mixture of FN/2R silk is utilized to integrate endocrine cells together with endothelial and mesenchymal cells into islet-like coclusters. Both xenogenic and allogenic versions of these coclusters were found to be viable and were able to respond to dynamic glucose stimulation with insulin release. Moreover, the endothelial cells were found to be colocalized with the endocrine cells, showing that the silk combined with supportive cells may promote vascularization. This method to engineer combined islet-like coclusters allows donor-derived endocrine cells to be surrounded by supportive cells from the recipient, which have the potential to further promote engraftment in the host and considerably reduce risk of rejection.

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.

Pancreatic ductal cells may have a negative effect on human islet transplantation

AIM

To evaluate the effect of pancreatic ductal cells on experimental human islet transplantation.

MATERIALS AND METHODS

Isolated islets were additionally purified by handpicking. Ductal cells were purified by magnetic cell sorting and then clustered into ductal pancreatospheres (DPS). Islets, DPS, and islets + DPS (100 islets + 75 DPS, or 100 islets + 200 DPS) were cultured and glucose-stimulated insulin secretion, β-cell apoptosis, and gene expression was determined. Islets and islets + DPS preparations (800 islets + 600 DPS) were transplanted to streptozotocin-treated immunodeficient mice and glycemia, graft morphometry, and gene expression were determined.

RESULTS

Insulin stimulation index was higher in islets than in islets co-cultured with DPS (5.59 ± 0.93 vs 4.02 ± 0.46; p<0.05). IL1B and CXCL11 expression was higher in 100 islets + 200 DPS than in islets (p<0.01), and IL-1β was detected in supernatants collected from DPS and islets + DPS preparations, but not in islets. Hyperglycemia developed in 33% and 67% of mice transplanted with islets or with islets + DPS respectively. β-cell mass was 26% lower in islets + DPS than in islets grafts (p>0.05), and the ratio β-/endocrine non-β-cell mass was lower in islets + DPS grafts (islets: 2.05 ± 0.18, islets + DPS: 1.35 ± 0.15; p<0.01). IL1B and IL1RN expression was significantly higher in islets + DPS grafts.

CONCLUSIONS

Islet preparations enriched with ductal cells have a lower insulin stimulation index in vitro and achieved a worse metabolic outcome after transplantation. Inflammation may mediate the deleterious effects of ductal cells on islet cells.

Bioprinting an Artificial Pancreas for Type 1 Diabetes

PURPOSE OF REVIEW

Pancreatic islet cell transplantation is currently the only curative cell therapy for type 1 diabetes mellitus. However, its potential to treat many more patients is limited by several challenges. The emergence of 3D bioprinting technology from recent advances in 3D printing, biomaterials, and cell biology has provided the means to overcome these challenges.

RECENT FINDINGS

3D bioprinting allows for the precise fabrication of complex 3D architectures containing spatially distributed cells, biomaterials (bioink), and bioactive factors. Different strategies to capitalize on this ability have been investigated for the 3D bioprinting of pancreatic islets. In particular, with co-axial bioprinting technology, the co-printability of islets with supporting cells such as endothelial progenitor cells and regulatory T cells, which have been shown to accelerate revascularization of islets and improve the outcome of various transplantations, respectively, has been achieved. 3D bioprinting of islets for generation of an artificial pancreas is a newly emerging field of study with a vast potential to improve islet transplantation.

Unsurpassed Intrahepatic Islet Engraftment - the Quest for New Sites for Beta Cell Replacement

The liver is currently the site of choice for clinical islet transplantation, even though many alternative implantation sites have lately been proposed as more ideal for graft survival. The suggested sites, for example intramuscular space, omentum, bone marrow, and spleen, are sometimes difficult to compare due to differences in animal model, islet isolation procedure, and islet quality. In addition, the variation in transplanted islet mass is vast. The aim of this commentary is to review alternative implantation sites tested experimentally as well as in clinical islet transplantation. Although many sites have been investigated, none have convincingly proved better suited for clinical islet transplantation than intraportal injection to the liver, regardless of whether it is autologous or allogeneic transplantation. However, in order to fully evaluate upcoming bioengineering techniques, such as scaffolds containing insulin-producing cells derived from stem cells, the need of an alternative site has arisen to enable cellular monitoring, which currently cannot be achieved within the liver.

Mesenchymal Stem Cells from Chronic Pancreatitis Patients Show Comparable Potency Compared to Cells from Healthy Donors

Mesenchymal stem cells (MSCs) are proven to be beneficial in islet transplantation, suggesting a potential therapeutic role of them in total pancreatectomy with islet autotransplantation (TP-IAT) for chronic pancreatitis (CP) patients. We investigated whether MSCs derived from CP patients are suitable for use in autologous cell therapy. MSCs from healthy donors (H-MSCs) and CP patients (CP-MSCs) were studied for phenotype, colony formation potential, multilineage differentiation ability, proliferation, senescence, secretory characters, and immunosuppressive functions. The potential protective effect of CP-MSCs was evaluated on hypoxia-induced islet cell death. Cell surface markers were similar between H-MSCs and CP-MSCs, as well as the ability of colony formation, multilineage differentiation, secretion of vascular endothelial growth factor and transforming growth factor (TGF-β), senescence, and inhibition of T cells proliferation in vitro. We found that growth differentiation factor 6 and hepatocyte growth factor (HGF) were significantly downregulated, whereas TGFβ and matrix metalloproteinase-2 were significantly upregulated in CP-MSCs compared with H-MSCs, among 84 MSC-related genes investigated in this study. MSCs from CP patients secreted less HGF, compared with the H-MSCs. A higher interferon-γ-induced indoleamine 2,3-dioxygenase expression was observed in CP-MSCs compared to H-MSCs. Moreover, CP-MSCs prevented hypoxia-induced β cell deaths to a similar extent as H-MSCs. Regardless of moderate difference in gene expression, CP-MSCs possess similar immunomodulatory and prosurvival functions to H-MSCs, and may be suitable for autologous cell therapy in CP patients undergoing TP-IAT. Stem Cells Translational Medicine 2019;8:418-429.

β-Cell-Derived Angiopoietin-1 Regulates Insulin Secretion and Glucose Homeostasis by Stabilizing the Islet Microenvironment

Islets are highly vascularized for prompt insulin secretion. Although angiopoietin-1 (Ang1) is a well-known angiogenic factor, its role in glucose homeostasis remains largely unknown. The objective of this study was to investigate whether and how Ang1 contributes to glucose homeostasis in response to metabolic challenge. We used inducible systemic Ang1 knockout (Ang1^sys-/-) and β-cell-specific Ang1 knockout (Ang1^β-cell-/-) mice fed a high-fat diet for 24 weeks. Although the degree of insulin sensitivity did not differ between Ang1^sys-/- and Ang1^sys+/+ mice, serum insulin levels were lower in Ang1^sys-/- mice, resulting in significant glucose intolerance. Similar results were observed in Ang1^β-cell-/- mice, suggesting a critical role of β-cell-derived Ang1 in glucose homeostasis. There were no differences in β-cell area or vasculature density, but glucose-stimulated insulin secretion was significantly decreased, and PDX-1 expression and GLUT2 localization were altered in Ang1^β-cell-/- compared with Ang1^β-cell+/+ mice. These effects were associated with less pericyte coverage, disorganized endothelial cell ultrastructure, and enhanced infiltration of inflammatory cells and upregulation of adhesion molecules in the islets of Ang1^β-cell-/- mice. In conclusion, β-cell-derived Ang1 regulates insulin secretion and glucose homeostasis by stabilizing the blood vessels in the islet and may be a novel therapeutic target for diabetes treatment in the future.

The role of the vasculature niche on insulin-producing cells generated by transdifferentiation of adult human liver cells

Background

Insulin-dependent diabetes is a multifactorial disorder that could be theoretically cured by functional pancreatic islets and insulin-producing cell (IPC) implantation. Regenerative medicine approaches include the potential for growing tissues and organs in the laboratory and transplanting them when the body cannot heal itself. However, several obstacles remain to be overcome in order to bring regenerative medicine approach for diabetes closer to its clinical implementation; the cells generated in vitro are typically of heterogenic and immature nature and the site of implantation should be readily vascularized for the implanted cells to survive in vivo. The present study addresses these two limitations by analyzing the effect of co-implanting IPCs with vasculature promoting cells in an accessible site such as subcutaneous. Secondly, it analyzes the effects of reconstituting the in vivo environment in vitro on the maturation and function of insulin-producing cells.

Methods

IPCs that are generated by the transdifferentiation of human liver cells are exposed to the paracrine effects of endothelial colony-forming cells (ECFCs) and human bone marrow mesenchymal stem cells (MSCs), which are the “building blocks” of the blood vessels. The role of the vasculature on IPC function is analyzed upon subcutaneous implantation in vivo in immune-deficient rodents. The paracrine effects of vasculature on IPC maturation are analyzed in culture.

Results

Co-implantation of MSCs and ECFCs with IPCs led to doubling the survival rates and a threefold increase in insulin production, in vivo. ECFC and MSC co-culture as well as conditioned media of co-cultures resulted in a significant increased expression of pancreatic-specific genes and an increase in glucose-regulated insulin secretion, compared with IPCs alone. Mechanistically, we demonstrate that ECFC and MSC co-culture increases the expression of CTGF and ACTIVINβα, which play a key role in pancreatic differentiation.

Conclusions

Vasculature is an important player in generating regenerative medicine approaches for diabetes. Vasculature displays a paracrine effect on the maturation of insulin-producing cells and their survival upon implantation. The reconstitution of the in vivo niche is expected to promote the liver-to-pancreas transdifferentiation and bringing this cell therapy approach closer to its clinical implementation.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1157-5) contains supplementary material, which is available to authorized users.

Hidradenitis suppurativa and diabetes mellitus: updated systematic review and adjusted meta-analysis

BACKGROUND

Hidradenitis suppurativa (HS) is a debilitating and distressing chronic inflammatory skin disease. There is also evolving evidence supporting the association between HS and cardiovascular risk factors, including smoking, obesity, hyperlipidaemia and metabolic syndrome. Notably, these are clinical features and risk factors that are closely associated with type 2 diabetes mellitus (DM).

AIMS

We performed a pooled adjusted meta-analysis of comparative studies to investigate the relationship between HS and DM.

METHODS

A systematic review and meta-analysis was performed according to recommended Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. OR was used as the summary effect size.

RESULTS

From pooled analysis of unadjusted data from 12 studies, we found a significantly higher proportion of DM in HS cases compared with non-HS healthy controls (16.1% vs. 15.7%; OR = 2.17; 95% CI 1.85-2.55; P < 0.001). Adjusted effect sizes from five studies were also pooled. A significantly higher proportion of DM was found for HS compared with healthy controls, although the effect size was attenuated compared with unadjusted analyses (OR 1.69; 95% CI 1.50-1.91; P < 0.001).

CONCLUSIONS

To our knowledge, our systematic review and meta-analysis is the first to pool adjusted effect sizes. We found that HS was associated with a 1.69-fold increased odds of diabetes; however, the absolute risk difference was small (16.1% vs. 15.7%) and is probably not clinically relevant. Treating clinicians should be aware of this association, but there may not be an urgent need to perform screening for impaired glucose tolerance or diabetes.

Replica moulded poly(dimethylsiloxane) microwell arrays induce localized endothelial cell immobilization for coculture with pancreatic islets

PolyJet three-dimensional (3D) printing allows for the rapid manufacturing of 3D moulds for the fabrication of cross-linked poly(dimethylsiloxane) microwell arrays (PMAs). As this 3D printing technique has a resolution on the micrometer scale, the moulds exhibit a distinct surface roughness. In this study, the authors demonstrate by optical profilometry that the topography of the 3D printed moulds can be transferred to the PMAs and that this roughness induced cell adhesive properties to the material. In particular, the topography facilitated immobilization of endothelial cells on the internal walls of the microwells. The authors also demonstrate that upon immobilization of endothelial cells to the microwells, a second population of cells, namely, pancreatic islets could be introduced, thus producing a 3D coculture platform.

An important step towards a prevascularized islet microencapsulation device: in vivo prevascularization by combination of mesenchymal stem cells on micropatterned membranes

Extrahepatic transplantation of islets of Langerhans could aid in better survival of islets after transplantation. When islets are transfused into the liver 60-70% of them are lost immediately after transplantation. An important factor for a successful extrahepatic transplantation is a well-vascularized tissue surrounding the implant. There are many strategies known for enhancing vessel formation such as adding cells with endothelial potential, the combination with angiogenic factors and / or applying surface topography at the exposed surface of the device. Previously we developed porous, micropatterned membranes which can be applied as a lid for an islet encapsulation device and we showed that the surface topography induces human umbilical vein endothelial cell (HUVEC) alignment and interconnection. This was achieved without the addition of hydrogels, often used in angiogenesis assays. In this work, we went one step further towards clinical implementation of the device by combining this micropatterned lid with Mesenchymal Stem Cells (MSCs) to facilitate prevascularization in vivo. As for HUVECs, the micropatterned membranes induced MSC alignment and organization in vitro, an important contributor to vessel formation, whereas in vivo (subcutaneous rat model) they contributed to improved implant prevascularization. In fact, the combination of MSCs seeded on the micropatterned membrane induced the highest vessel formation score in 80% of the sections.

The Role of Accessory Cells in Islet Homeostasis

PURPOSES OF REVIEW

Scattered throughout the pancreas, the endocrine islets rely on neurovascular support for signal relay to regulate hormone secretion and for maintaining tissue homeostasis. The islet accessory cells (or components) of neurovascular tissues include the endothelial cells, pericytes, smooth muscle cells, neurons (nerve fibers), and glia. Research results derived from experimental diabetes and islet transplantation indicate that the accessory cells are reactive in islet injury and can affect islet function and homeostasis in situ or in an ectopic environment.

RECENT FINDINGS

Recent advances in cell labeling and tissue imaging have enabled investigation of islet accessory cells to gain insights into their network structures, functions, and remodeling in disease. It has become clear that in diabetes, the islet neurovascular tissues are not just bystanders damaged in neuropathy and vascular complications; rather, they participate in islet remodeling in response to changes in the microenvironment. Because of the fundamental differences between humans and animal models in neuroinsular cytoarchitecture and cell proliferation, examination of islet accessory cells in clinical specimens and donor pancreases warrants further attention.

Tissue-engineering approaches in pancreatic islet transplantation

Pancreatic islet transplantation is a promising alternative to whole-pancreas transplantation as a treatment of type 1 diabetes mellitus. This technique has been extensively developed during the past few years, with the main purpose of minimizing the complications arising from the standard protocols used in organ transplantation. By using a variety of strategies used in tissue engineering and regenerative medicine, pancreatic islets have been successfully introduced in host patients with different outcomes in terms of islet survival and functionality, as well as the desired normoglycemic control. Here, we describe and discuss those strategies to transplant islets together with different scaffolds, in combination with various cell types and diffusible factors, and always with the aim of reducing host immune response and achieving islet survival, regardless of the site of transplantation.

Bioengineering with Endothelial Progenitor Cells Improves the Vascular Engraftment of Transplanted Human Islets

Pancreatic islets isolated for transplantation are disconnected from their vascular supply and need to establish a new functional network posttransplantation. Due to poor revascularization, prevailing hypoxia with correlating increased apoptosis rates in experimental studies can be observed for months posttransplantation. Endothelial progenitor cells (EPCs) are bone marrow-derived cells that promote neovascularization. The present study tested the hypothesis that EPCs, isolated from human umbilical cord blood, could be coated to human islet surfaces and be used to promote islet vascular engraftment. Control or EPC bioengineered human islets were transplanted into the renal subcapsular space of nonobese diabetic/severe combined immunodeficiency mice. Four weeks posttransplantation, graft blood perfusion and oxygen tension were measured using laser Doppler flowmetry and Clark microelectrodes, respectively. Vessel functionality was also assessed by in vivo confocal imaging. The vascular density and the respective contribution of human and recipient endothelium were assessed immunohistochemically by staining for human and mouse CD31. Islet grafts with EPCs had substantially higher blood perfusion and oxygen tension than control transplants. Furthermore, analysis of the vascular network of the grafts revealed that grafts containing EPC bioengineered islets had a superior vascular density compared with control grafts, with functional chimeric blood vessels. We conclude that a simple procedure of surface coating with EPCs provides a possibility to improve the vascular engraftment of transplanted human islets. Established protocols are also easily applicable for intraportal islet transplantation in order to obtain a novel directed cellular therapy at the site of implantation in the liver.

Self-Condensation Culture Enables Vascularization of Tissue Fragments for Efficient Therapeutic Transplantation

Clinical transplantation of tissue fragments, including islets, faces a critical challenge because of a lack of effective strategies that ensure efficient engraftment through the timely integration of vascular networks. We recently developed a complex organoid engineering method by "self-condensation" culture based on mesenchymal cell-dependent contraction, thereby enabling dissociated heterotypic lineages including endothelial cells to self-organize in a spatiotemporal manner. Here, we report the successful adaptation of this method for generating complex tissues from diverse tissue fragments derived from various organs, including pancreatic islets. The self-condensation of human and mouse islets with endothelial cells not only promoted functionalization in culture but also massively improved post-transplant engraftment. Therapeutically, fulminant diabetic mice were more efficiently treated by a vascularized islet transplant compared with the conventional approach. Given the general limitations of post-transplant vascularization associated with 3D tissue-based therapy, our approach offers a promising means of enhancing efficacy in the context of therapeutic tissue transplantation.

Highly Angiogenic, Nonthrombogenic Bone Marrow Mononuclear Cell-Derived Spheroids in Intraportal Islet Transplantation

Highly angiogenic bone marrow mononuclear cell-derived spheroids (BM-spheroids), formed by selective proliferation of the CD31⁺CD14⁺CD34⁺ monocyte subset via three-dimensional (3D) culture, have had robust angiogenetic capacity in rodent syngeneic renal subcapsular islet transplantation. We wondered whether the efficacy of BM-spheroids could be demonstrated in clinically relevant intraportal islet transplantation models without increasing the risk of portal thrombosis. The thrombogenic potential of intraportally infused BM-spheroids was compared with that of mesenchymal stem cells (MSCs) and MSC-derived spheroids (MSC-spheroids). The angiogenic efficacy and persistence in portal sinusoids of BM-spheroids were examined in rodent syngeneic and primate allogeneic intraportal islet transplantation models. In contrast to MSCs and MSC-spheroids, intraportal infusion of BM-spheroids did not evoke portal thrombosis. BM-spheroids had robust angiogenetic capacity in both the rodent and primate intraportal islet transplantation models and improved posttransplant glycemic outcomes. MRI and intravital microscopy findings revealed the persistence of intraportally infused BM-spheroids in portal sinusoids. Intraportal cotransplantation of allogeneic islets with autologous BM-spheroids in nonhuman primates further confirmed the clinical feasibility of this approach. In conclusion, cotransplantation of BM-spheroids enhances intraportal islet transplantation outcome without portal thrombosis in mice and nonhuman primates. Generating BM-spheroids by 3D culture prevented the rapid migration and disappearance of intraportally infused therapeutic cells.

Inflammation-Associated Cytokines IGFBP1 and RANTES Impair the Megakaryocytic Potential of HSCs in PT Patients after Allo-HSCT

Prolonged isolated thrombocytopenia (PT) is a severe complication in patients after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Whether the megakaryoctic potential of hematopoietic stem cells (HSCs) in bone marrow is intact and what factors drive the pathological process of PT remain elusive. A retrospective study in patients (n = 285) receiving HSCT revealed that the occurrence of PT was approximately 8% and the number of platelets and megakaryocytes in PT patients is much lower compared with control subjects. To test whether the deficiency of thrombopoiesis was caused by the activities of HSCs, the megakaryocytic differentiation potential of HSCs before or after transplantation was assessed. Interestingly, a substantial decrease of megakaryocytic differentiation was observed 2 weeks after transplantation of HSCs in all of the allo-HSCT recipients. However, 4 weeks after transplantation, the ability of HSCs to generate CD41⁺CD42b⁺ megakaryocytes in successful platelet engraftment patients recovered to the same level as those of HSCs before implantation. In contrast, HSCs derived from PT patients throughout the postimplantation period exhibited poor survival and failed to differentiate properly. A protein array analysis demonstrated that multiple inflammation-associated cytokines were elevated in allo-HSCT recipients with PT. Among them, insulin-like growth factor-binding protein 1 and regulated on activation, normal T cell expressed and secreted were found to significantly suppress the proliferation and megakaryocytic differentiation of HSCs in vitro. Our results suggested that the occurrence of PT may be attributed, at least partially, to the damage to HSC function caused by inflammation-associated cytokines after HSCT. These findings shed light on the mechanism underlying HSC megakaryocytic differentiation in PT patients and may provide potential new strategies for treating PT patients after HSCT.

Culturing with modified EGM2 medium enhances porcine neonatal islet-like cell clusters resistance to apoptosis in islet xenotransplantation

BACKGROUND

Neonatal pig islet-like cell clusters (NICC) are an attractive source of insulin-producing tissue for potential transplantation treatment of type 1 diabetic patients. However, a considerable loss of NICC after their transplantation due to apoptosis resulted from islet isolation and instant blood-mediated inflammatory reaction remains to be overcome.

METHODS

EGM2 medium depleted with hydrocortisone and supplemented with 50 mmol/L isobutylmethylxanthine, 10 mmol/L nicotinamide, and 10 mmol/L glucose was used to culture NICC at day 1, the day after isolation and changed every other day. NICC cultured with EGM2 or control Ham's F-10 medium were collected at day 7 of culture for the following assays. The viability of NICC was evaluated by AO/EB staining and FACS. Static assay and oxygen consumption rate analysis were performed to assess the function of NICC. Insulin and glucagon gene expression were measured by real-time PCR. Tubing loops model and TUNEL assay were performed to confirm the apoptosis-resistant ability of NICC cultured with modified EGM2 medium. Serum starvation and hypoxia treatment were used to test the tolerant capability of NICC in the microenvironment of hypoxia/nutrient deficiency in vitro. The molecules involved in apoptosis pathways in NICC were analyzed by Western blotting.

RESULTS

Compared with Ham's F-10 medium, culturing NICC with EGM2 medium led to increased number and viability of NICC with higher stimulation index, upregulated gene expression of both insulin and glucagon, and enhanced mitochondria function. Furthermore, fewer modified EGM2 medium cultured NICC were found under apoptosis when evaluated in an in vitro tubing loop model of IBMIR. Moreover, EGM2 medium cultured NICC demonstrated much less apoptotic cells under either serum starvation or hypoxia condition than their Ham's F-10 medium cultured counterparts. The enhanced capability of EGM2 cultured NICC to resist apoptosis was associated with their elevated protein levels of anti-apoptotic Bcl-2 family member Mcl-1.

CONCLUSION

Culturing NICC with EGM2 provides a simple and effective approach not only to increase NICC yield, viability, and maturation but also to enhance their resistance to apoptosis to preserve the initial graft mass for successful islet xenotransplantation.

Local Sphingosine Kinase 1 Activity Improves Islet Transplantation

Pancreatic islet transplantation is a promising clinical treatment for type 1 diabetes, but success is limited by extensive β-cell death in the immediate posttransplant period and impaired islet function in the longer term. Following transplantation, appropriate vascular remodeling is crucial to ensure the survival and function of engrafted islets. The sphingosine kinase (SK) pathway is an important regulator of vascular beds, but its role in the survival and function of transplanted islets is unknown. We observed that donor islets from mice deficient in SK1 (Sphk1 knockout) contain a reduced number of resident intraislet vascular endothelial cells. Furthermore, we demonstrate that the main product of SK1, sphingosine-1-phosphate, controls the migration of intraislet endothelial cells in vitro. We reveal in vivo that Sphk1 knockout islets have an impaired ability to cure diabetes compared with wild-type controls. Thus, SK1-deficient islets not only contain fewer resident vascular cells that participate in revascularization, but likely also a reduced ability to recruit new vessels into the transplanted islet. Together, our data suggest that SK1 is important for islet revascularization following transplantation and represents a novel clinical target for improving transplant outcomes.

Individual Variation in Conditional β Cell Ablation Mice Contributes Significant Biases in Evaluating β Cell Functional Recovery

Despite the βDTA (Ins2-rtTA; Tet-DTA) mice have been developed as a valuable tool to study β cell regeneration, their individual variation in therapeutic efficacy has not been characterized. Here, we demonstrated that the βDTA mice exhibited significant variations in both spontaneous and acquired β cell regeneration. We found that doxycycline (DOX)-induced β cell death was sufficient to cause polydipsia, translating even subtle difference in drinking habit into large variations in actual DOX intake among individuals within the same group. Accumulating evidence shows that transient expression of VEGF_A enhances β cell functional recovery after injury. Therefore, we utilized the chemically modified mRNA (modRNA) technology to enable transient yet efficient VEGF_A expression in the pancreas after DOX-induced β cell death. Surprisingly, under optimized DOX dose permissive of β cell regeneration, VEGF_A modRNA only demonstrated marginal benefits on β cell functional recovery with large individual variations. We also revealed that the therapeutic efficacy of VEGF_A modRNA on β cell regeneration was dependent on the degree of β cell loss induced by the accumulated DOX intake. Therefore, our results highlight a significant contribution of individual variation in the βDTA model and call for attention in evaluating potential efficacy of therapeutic agents in β cell regeneration studies.

Pivotal Cytoprotective Mediators and Promising Therapeutic Strategies for Endothelial Progenitor Cell-Based Cardiovascular Regeneration

Cardiovascular diseases (CVDs), including atherosclerosis, stroke, and myocardial infarction, is a major cause of death worldwide. In aspects of cell therapy against CVD, it is generally accepted that endothelial progenitor cells (EPCs) are potent neovascular modulators in ischemic tissues. In response to ischemic injury signals, EPCs located in a bone marrow niche migrate to injury sites and form new vessels by secreting various vasculogenic factors including VEGF, SDF-1, and FGF, as well as by directly differentiating into endothelial cells. Nonetheless, in ischemic tissues, most of engrafted EPCs do not survive under harsh ischemic conditions and nutrient depletion. Therefore, an understanding of diverse EPC-related cytoprotective mediators underlying EPC homeostasis in ischemic tissues may help to overcome current obstacles for EPC-mediated cell therapy for CVDs. Additionally, to enhance EPC's functional capacity at ischemic sites, multiple strategies for cell survival should be considered, that is, preconditioning of EPCs with function-targeting drugs including natural compounds and hormones, virus mediated genetic modification, combined therapy with other stem/progenitor cells, and conglomeration with biomaterials. In this review, we discuss multiple cytoprotective mediators of EPC-based cardiovascular repair and propose promising therapeutic strategies for the treatment of CVDs.

Endothelial Progenitor Cells in Diabetic Microvascular Complications: Friends or Foes?

Despite being featured as metabolic disorder, diabetic patients are largely affected by hyperglycemia-induced vascular abnormality. Accumulated evidence has confirmed the beneficial effect of endothelial progenitor cells (EPCs) in coronary heart disease. However, antivascular endothelial growth factor (anti-VEGF) treatment is the main therapy for diabetic retinopathy and nephropathy, indicating the uncertain role of EPCs in the pathogenesis of diabetic microvascular disease. In this review, we first illustrate how hyperglycemia induces metabolic and epigenetic changes in EPCs, which exerts deleterious impact on their number and function. We then discuss how abnormal angiogenesis develops in eyes and kidneys under diabetes condition, focusing on “VEGF uncoupling with nitric oxide” and “competitive angiopoietin 1/angiopoietin 2” mechanisms that are shared in both organs. Next, we dissect the nature of EPCs in diabetic microvascular complications. After we overview the current EPCs-related strategies, we point out new EPCs-associated options for future exploration. Ultimately, we hope that this review would uncover the mysterious nature of EPCs in diabetic microvascular disease for therapeutics.

A hybrid of cells and pancreatic islets toward a new bioartificial pancreas

Cell surface engineering using single-stranded DNA-poly(ethylene glycol)-conjugated phospholipid (ssDNA-PEG-lipid) is useful for inducing cell-cell attachment two and three dimensionally. In this review, we summarize our recent techniques for cell surface engineering and their applications to islet transplantation. Because any DNA sequence can be immobilized onto the cell surface by hydrophobic interactions between ssDNA-PEG-lipid and the cellular membrane without impairing cell function, a cell-cell hybrid can be formed through the DNA hybridization. With this technique, it would be possible to create three-dimensional hybrid structures of pancreatic islets coated with various accessory cells, such as patients' own cells, mesenchymal and adipose-derived stem cells, endothelial progenitor cells, neural crest stem cells or regulatory T cells, which might significantly improve the outcome of islet transplantation in diabetic patients.

Accessory cells for β-cell transplantation

Despite recent advances, insulin therapy remains a treatment, not a cure, for diabetes mellitus with persistent risk of glycaemic alterations and life-threatening complications. Restoration of the endogenous β-cell mass through regeneration or transplantation offers an attractive alternative. Unfortunately, signals that drive β-cell regeneration remain enigmatic and β-cell replacement therapy still faces major hurdles that prevent its widespread application. Co-transplantation of accessory non-islet cells with islet cells has been shown to improve the outcome of experimental islet transplantation. This review will highlight current travails in β-cell therapy and focuses on the potential benefits of accessory cells for islet transplantation in diabetes.

Coculturing Human Islets with Proangiogenic Support Cells to Improve Islet Revascularization at the Subcutaneous Transplantation Site

While subcutaneous tissue has been proposed as a clinically relevant site for pancreatic islet transplantation, a major issue of concern remains, which is its poor vascular state. In an effort to overcome this limitation, we present an efficient and reproducible method to form human composite islets (CIs) with proangiogenic cell types in a controlled manner using nonadherent agarose microwell templates. In this study, we assessed the three-dimensional structure, function, and angiogenic potential of human CIs with human mesenchymal stromal cells (hMSCs), with or without human umbilical vein endothelial cells (HUVECs), and preconditioned hMSCs (PC-hMSCs) in EGM-2 under shear stress. Distinct cellular rearrangements could be observed in CIs, but islet functionality was maintained. In vitro angiogenesis assays found significantly enhanced sprout formation in case of CIs. In particular, the number of sprouts emanating from CIs with PC-hMSCs was significantly increased compared to other conditions. Subsequent in vivo assessment confirmed the proangiogenic potential of CIs. However, in contrast to our in vitro angiogenesis assays, CIs with hMSCs and HUVECs exhibited a higher in vivo angiogenic potential compared to control islets or islets combined with hMSCs or PC-hMSCs. These findings highlight the importance and necessity of verifying in vitro studies with in vivo models to reliably predict, in this case, revascularization outcomes. Regardless, we demonstrate here the therapeutic potential of CIs with proangiogenic support cells to enhance islet revascularization at a clinically relevant, although poorly vascularized, transplantation site.

Improved revascularization of islet grafts using an angiogenic monocyte subpopulation derived from spheroid culture of bone marrow mononuclear cells

The spheroid culture method is an effective strategy for ex vivo expansion of an autologous therapeutic cell population. We investigated if cotransplantation of bone marrow-derived spheroids (BM-spheroid) formed using 3D culture of BM-derived mononuclear cells (BM-MNCs) could improve the posttransplant outcome of islet grafts using a mouse syngeneic marginal mass renal subcapsular islet transplantation model. Using green fluorescent protein transgenic (GFP-Tg) mice, the role of the BM-spheroids and the contribution of vessels derived from donors and recipients in grafted areas were assessed by immunohistochemistry. Compared to fresh BM-MNCs and nonspheroid remnant cells (BM-nonspheroid), the BM-spheroids, mainly composed of CXCR4(+) CD14(+) myeloid cells, showed higher angiogenic capacity, such as in vitro self-formed vessel structures; increased expression of angiogenic and chemoattractive factors; and incorporation into new vessel formation in basement membrane matrix plugs. BM-spheroid cotransplantation with islets improved the posttransplant outcomes in terms of glucose tolerance, serum insulin level, and diabetes reversal rate when compared with cotransplantation of BM-nonspheroids. Immunohistochemistry revealed that cotransplantation of the BM-spheroids increased vessel density, area of grafted endocrine and non-endocrine tissue, and β cell proliferation. In conclusion, cotransplantation of islets and BM-spheroids improved islet function through facilitation of revascularization and an increase in cell proliferation and islet cell mass.

Surface coating of pancreatic islets with neural crest stem cells improves engraftment and function after intraportal transplantation

The present study aimed to develop techniques for surface coating of islets with neural crest stem cells (NCSCs) in order to enable cotransplantation to the clinically used liver site and then investigate engraftment and function intraportally of such bioengineered islets. Mouse islets were coated during incubation with enhanced green fluorescent protein (EGFP)-expressing mouse NCSCs and transplanted into the portal vein to cure diabetic mice. An intravenous glucose tolerance test was performed at 1 month posttransplantation. Islet grafts were retrieved and evaluated for vascular density, nerves, and glial cells. NCSCs expressed a vast number of key angiogenic and neurotrophic factors. Mice transplanted with NCSC-bioengineered islets responded better to the glucose load than recipient mice with control islets. NCSCs remained present in the vicinity or had often migrated into the NCSC-coated islets, and an improved islet graft reinnervation and revascularization was observed. Transplanted NCSCs differentiated into both glial and neural cells in the islet grafts. We conclude that bioengineering of islets with NCSCs for intraportal transplantation provides a possibility to improve islet engraftment and function. Pending successful establishment of protocols for expansion of NCSCs from, for example, human skin or bone marrow, this strategy may be applied to clinical islet transplantation.

Association between an impaired bone marrow vascular microenvironment and prolonged isolated thrombocytopenia after allogeneic hematopoietic stem cell transplantation

Prolonged isolated thrombocytopenia (PT) is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, it remains unclear whether abnormalities of the bone marrow (BM) microenvironment are involved in the pathogenesis of PT. This prospective, nested case-control study included 20 patients with PT, 40 matched patients with good graft function (GGF) after allo-HSCT, and 16 healthy donors (HDs). Cellular elements of the BM microenvironment, including BM endothelial cells (BMECs), perivascular cells, and endosteal cells, were analyzed via flow cytometry and via hematoxylin-eosin and immunohistochemical staining in situ. Moreover, stromal-derived factor 1 (SDF-1) and vascular endothelial growth factor (VEGF) were measured in the plasma of BM via an enzyme-linked immunosorbent assay. No significant differences in endosteal cells (15 per high-power field [hpf] versus 16 per hpf versus 20 per hpf, P > .05) were demonstrated among the patients with PT, GGF, and the HDs. The PT patients exhibited remarkable decreases in cellular elements of the vascular microenvironment, including BMECs (.01% versus .18% versus .20%, P < .0001) and perivascular cells (.01% versus .12% versus .13%, P < .0001), compared with the GGF allo-HSCT recipients and the HDs, respectively. Moreover, significantly lower levels of SDF-1 (3163 pg/mL versus 3928 pg/mL, P = .0002) and VEGF (56 pg/mL versus 123 pg/mL, P < .0001) were found in the BM plasma of the PT patients compared with the BM of the GGF patients. A multivariate analysis revealed that BMECs (odds ratio [OR] = 171.57, P = .002) and cytomegalovirus infection after HSCT (OR = 4.35, P = .009) were independent risk factors for PT. Our data suggested that an impaired BM vascular microenvironment and megakaryocyte-active factors may contribute to the occurrence of PT after HSCT.

Co-transplantation of endothelial progenitor cells and pancreatic islets to induce long-lasting normoglycemia in streptozotocin-treated diabetic rats

Graft vascularization is a crucial step to obtain stable normoglycemia in pancreatic islet transplantation. Endothelial progenitor cells (EPCs) contribute to neoangiogenesis and to the revascularization process during ischaemic events and play a key role in the response to pancreatic islet injury. In this work we co-transplanted EPCs and islets in the portal vein of chemically-induced diabetic rats to restore islet vascularization and to improve graft survival. Syngenic islets were transplanted, either alone or with EPCs derived from green fluorescent protein (GFP) transgenic rats, into the portal vein of streptozotocin-induced diabetic rats. Blood glucose levels were monitored and intraperitoneal glucose tolerance tests were performed. Real time-PCR was carried out to evaluate the gene expression of angiogenic factors. Diabetic-induced rats showed long-lasting (6 months) normoglycemia upon co-transplantation of syngenic islets and EPCs. After 3–5 days from transplantation, hyperglycaemic levels dropped to normal values and lasted unmodified as long as they were checked. Further, glucose tolerance tests revealed the animals' ability to produce insulin on-demand as indexed by a prompt response in blood glucose clearance. Graft neovascularization was evaluated by immunohistochemistry: for the first time the measure of endothelial thickness revealed a donor-EPC-related neovascularization supporting viable islets up to six months after transplant. Our results highlight the importance of a newly formed viable vascular network together with pancreatic islets to provide de novo adequate supply in order to obtain enduring normoglycemia and prevent diabetes-related long-term health hazards.

Omentum is better site than kidney capsule for growth, differentiation, and vascularization of immature porcine β-cell implants in immunodeficient rats

BACKGROUND

Rapid revascularization of islet cell implants is important for engraftment and subsequent survival and function. Development of an adequate vascular network is expected to allow adaptive growth of the β-cell mass. The present study compares omentum and kidney capsule as sites for growth and differentiation of immature β-cell grafts.

METHODS

Perinatal porcine islet cell grafts were implanted in omentum or under kidney capsule of nondiabetic nude rats. Implants were compared over 10 weeks for their respective growth, cellular composition, number and size of β cells, their proliferative activity, and implant blood vessel density.

RESULTS

In both sites, the β-cell volume increased fourfold between weeks 1 and 10 reflecting a rise in β-cell number. In the omental implants, however, the cellular insulin reserves and the percent of proliferating cells were twofold higher than in kidney implants. In parallel, the blood vessel density in omental implants increased twofold, reaching a density comparable with islets in adult pig pancreas. A positive correlation was found between the percent bromodeoxyuridine-positive β cells and the vessel density.

CONCLUSIONS

Growth of the β-cell volume proceeds similarly in the omentum and under the kidney capsule. However, the omentum leads to higher insulin reserves and an increased pool of proliferating cells, which might be related to a more extended vascular network. Our observations support the omentum as an alternative site for immature porcine islet cells, with beneficial effects on proliferation and implant revascularization.

The β-cell/EC axis: how do islet cells talk to each other?

Within the pancreatic islet, the β-cell represents the ultimate biosensor. Its central function is to accurately sense glucose levels in the blood and consequently release appropriate amounts of insulin. As the only cell type capable of insulin production, the β-cell must balance this crucial workload with self-preservation and, when required, regeneration. Evidence suggests that the β-cell has an important ally in intraislet endothelial cells (ECs). As well as providing a conduit for delivery of the primary input stimulus (glucose) and dissemination of its most important effector (insulin), intraislet blood vessels deliver oxygen to these dense clusters of metabolically active cells. Furthermore, it appears that ECs directly impact insulin gene expression and secretion and β-cell survival. This review discusses the molecules and pathways involved in the crosstalk between β-cells and intraislet ECs. The evidence supporting the intraislet EC as an important partner for β-cell function is examined to highlight the relevance of this axis in the context of type 1 and type 2 diabetes. Recent work that has established the potential of ECs or their progenitors to enhance the re-establishment of glycemic control following pancreatic islet transplantation in animal models is discussed.