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

Extracellular electrophysiology on clonal human β-cell spheroids

Background

Pancreatic islets are important in nutrient homeostasis and improved cellular models of clonal origin may very useful especially in view of relatively scarce primary material. Close 3D contact and coupling between β-cells are a hallmark of physiological function improving signal/noise ratios. Extracellular electrophysiology using micro-electrode arrays (MEA) is technically far more accessible than single cell patch clamp, enables dynamic monitoring of electrical activity in 3D organoids and recorded multicellular slow potentials (SP) provide unbiased insight in cell-cell coupling.

Objective

We have therefore asked whether 3D spheroids enhance clonal β-cell function such as electrical activity and hormone secretion using human EndoC-βH1, EndoC-βH5 and rodent INS-1 832/13 cells.

Methods

Spheroids were formed either by hanging drop or proprietary devices. Extracellular electrophysiology was conducted using multi-electrode arrays with appropriate signal extraction and hormone secretion measured by ELISA.

Results

EndoC-βH1 spheroids exhibited increased signals in terms of SP frequency and especially amplitude as compared to monolayers and even single cell action potentials (AP) were quantifiable. Enhanced electrical signature in spheroids was accompanied by an increase in the glucose stimulated insulin secretion index. EndoC-βH5 monolayers and spheroids gave electrophysiological profiles similar to EndoC-βH1, except for a higher electrical activity at 3 mM glucose, and exhibited moreover a biphasic profile. Again, physiological concentrations of GLP-1 increased AP frequency. Spheroids also exhibited a higher secretion index. INS-1 cells did not form stable spheroids, but overexpression of connexin 36, required for cell-cell coupling, increased glucose responsiveness, dampened basal activity and consequently augmented the stimulation index.

Conclusion

In conclusion, spheroid formation enhances physiological function of the human clonal β-cell lines and these models may provide surrogates for primary islets in extracellular electrophysiology.

Evaluation of Pancreatic β-cell Differentiation Efficiency of Human iPSC Lines for Clinical Use

BACKGROUND

Transplantation of pancreatic β-cells generated from human induced pluripotent stem cells (hiPSCs) has great potential as a root treatment for type 1 diabetes. However, their current level of efficiency to differentiate into β-cells is still not at par for clinical use. Previous research has shown that differentiation efficiency varies among human embryonic stem cells and mouse-induced pluripotent stem cell lines. Therefore, selecting a suitable cell line for efficient induction into desired tissues and organs is crucial.

METHODS

In this study, we have evaluated the efficiency of 15 hiPSC lines available for clinical use to differentiate into pancreatic β-cells.

RESULTS

Our investigation has revealed induction efficiency to differ among the hiPSC lines, even when derived from the same donor. Among the hiPSC lines tested, the 16A01 cell line exhibited the highest Insulin expression and low Glucagon expression, suggesting that this cell line is suitable for differentiation into β-cells.

CONCLUSION

Our study has demonstrated the importance of selecting a suitable hiPSC line for effective differentiation into β-cells.

Vascularized pancreas-on-a-chip device produced using a printable simulated extracellular matrix

The extracellular matrix (ECM) influences cellular behavior, function, and fate. The ECM surrounding Langerhans islets has not been investigated in detail to explain its role in the development and maturation of pancreatic β-cells. Herein, a complex combination of the simulated ECM (sECM) has been examined with a comprehensive analysis of cell response and a variety of controls. The most promising results were obtained from group containing fibrin, collagen type I, Matrigel®, hyaluronic acid, methylcellulose, and two compounds of functionalized, ionically crosslinking bacterial cellulose (sECMbc). Even though the cell viability was not significantly impacted, the performance of group of sECMbc showed 2 to 4x higher sprouting number and length, 2 to 4x higher insulin secretion in static conditions, and 2 to 10x higher gene expression of VEGF-A, Endothelin-1, and NOS3 than the control group of fibrin matrix (sECMf). Each material was tested in a hydrogel-based, perfusable, pancreas-on-a-chip device and the best group - sECMbc has been tested with the drug Sunitinib to show the extended possibilities of the device for both diabetes-like screening as well as PDAC chemotherapeutics screening for potential personal medicine approach. It proved its functionality in 7 days dynamic culture and is suitable as a physiological tissue model. Moreover, the device with the pancreatic-like spheroids was 3D bioprintable and perfusable.

Organ-specific endothelial cell heterogenicity and its impact on regenerative medicine and biomedical engineering applications

Endothelial cells (ECs) are a key cellular component of the vascular system as they form the inner lining of the blood vessels. Recent findings highlight that ECs express extensive phenotypic heterogenicity when following the vascular tree from the major vasculature down to the organ capillaries. However, in vitro models, used for drug development and testing, or to study the role of ECs in health and disease, rarely acknowledge this EC heterogenicity. In this review, we highlight the main differences between different EC types, briefly summarize their different characteristics and focus on the use of ECs in in vitro models. We introduce different approaches on how ECs can be utilized in co-culture test systems in the field of brain, pancreas, and liver research to study the role of the endothelium in health and disease. Finally, we discuss potential improvements to current state-of-the-art in vitro models and future directions.

An Overview of Engineered Hydrogel-Based Biomaterials for Improved β-Cell Survival and Insulin Secretion

Islet transplantation provides a promising strategy in treating type 1 diabetes as an autoimmune disease, in which damaged β-cells are replaced with new islets in a minimally invasive procedure. Although islet transplantation avoids the complications associated with whole pancreas transplantations, its clinical applications maintain significant drawbacks, including long-term immunosuppression, a lack of compatible donors, and blood-mediated inflammatory responses. Biomaterial-assisted islet transplantation is an emerging technology that embeds desired cells into biomaterials, which are then directly transplanted into the patient, overcoming the aforementioned challenges. Among various biomaterials, hydrogels are the preferred biomaterial of choice in these transplants due to their ECM-like structure and tunable properties. This review aims to present a comprehensive overview of hydrogel-based biomaterials that are engineered for encapsulation of insulin-secreting cells, focusing on new hydrogel design and modification strategies to improve β-cell viability, decrease inflammatory responses, and enhance insulin secretion. We will discuss the current status of clinical studies using therapeutic bioengineering hydrogels in insulin release and prospective approaches.

In vitro Characterization of Insulin-Producing β-Cell Spheroids

Over the years, immortalized rodent β-cell lines such as RIN, HIT, MIN, βTC, and INS-1 have been used to investigate pancreatic β-cell physiology using conventional two-dimensional (2D) culture techniques. However, physical and physiological limitations inherent to 2D cell culture necessitates confirmatory follow up studies using sentient animals. Three-dimensional (3D) culture models are gaining popularity for their recapitulation of key features of in vivo organ physiology, and thus could pose as potential surrogates for animal experiments. In this study, we aimed to develop and characterize a rat insulinoma INS-1 3D spheroid model to compare with 2D monolayers of the same cell line. Ultrastructural verification was done by transmission electron microscopy and toluidine blue staining, which showed that both 2D monolayers and 3D spheroids contained highly granulated cells with ultrastructural features synonymous with mature pancreatic β-cells, with increased prominence of these features observed in 3D spheroids. Viability, as assessed by cellular ATP quantification, size profiling and glucose utilization, showed that our spheroids remained viable for the experimental period of 30 days, compared to the limiting 5-day passage period of INS-1 monolayers. In fact, increasing ATP content together with spheroid size was observed over time, without adverse changes in glucose utilization. Additionally, β-cell function, assessed by determining insulin and amylin secretion, showed that the 3D spheroids retained glucose sensing and insulin secretory capability, that was more acute when compared to 2D monolayer cultures. Thus, we were able to successfully demonstrate that our in vitro INS-1 β-cell 3D spheroid model exhibits in vivo tissue-like structural features with extended viability and lifespan. This offers enhanced predictive capacity of the model in the study of metabolic disease, β-cell pathophysiology and the potential treatment thereof.

Pancreatic extracellular matrix and platelet-rich plasma constructing injectable hydrogel for pancreas tissue engineering

The development of pancreatic extracellular matrices enriched with insulin-secreting β-cells is a promising tissue engineering approach to treat type 1 diabetes. However, its long-term therapeutic efficacy is restricted by the defensive mechanism of host immune response and the lack of developed vascularization as appropriate after transplantation. Platelet-rich plasma (PRP), as an autologous platelet concentrate, contains a large number of active factors that are essential for the cell viability, vascularization, and immune regulation. In this study, we have incorporated pancreatic extracellular matrix (PEM) with PRP to develop a three-dimensional (3D) injectable PEM-PRP hydrogel to coculture and transplant rat insulinoma cells (INS-1) and human umbilical vein endothelial cells (HUVECs). Results from this study demonstrated that PEM-PRP hydrogel mimicked the biochemical compositions of native extracellular matrices, and possessed the enhanced elastic modulus and resistance to enzymatic degradation that enabled biomaterials to maintain its volume and slowly degrade. Additionally, PEM-PRP hydrogel could release growth factors in a sustained manner. In vitro, PEM-PRP hydrogel significantly promoted the viability, insulin-secreting function, and insulin gene expression of gel encapsulated INS-1 cells. Moreover, HUVECs encapsulated in PEM-PRP hydrogel were found to constitute many lumen-like structures and exhibited high expression of proangiogenic genes. In vivo transplantation of PEM-PRP hydrogel encapsulated with INS-1 cells and HUVECs improved the viability of INS-1 cells, promoted vascularization, inhibited the host inflammatory response, and reversed hyperglycemia of diabetic rats. Our study suggests that the PEM-PRP hydrogel offers excellent biocompatibility and proangiogenic property, and may serve as an effective biomaterial platform to maintain the long-term survival and function of insulin-secreting β cells.

Controlled Heterotypic Pseudo-Islet Assembly of Human β-Cells and Human Umbilical Vein Endothelial Cells Using Magnetic Levitation

β-Cell functionality and survival are highly dependent on the cells' microenvironment and cell–cell interactions. Since the pancreas is a highly vascularized organ, the crosstalk between β-cells and endothelial cells (ECs) is vital to ensure proper function. To understand the interaction of pancreatic β-cells with vascular ECs, we sought to investigate the impact of the spatial distribution on the interaction of human cell line-based β-cells (EndoC-βH3) and human umbilical vein endothelial cells (HUVECs). We focused on the evaluation of three major spatial distributions, which can be found within human islets in vivo, in tissue-engineered heterotypic cell spheroids, so-called pseudo-islets, by controlling the aggregation process using magnetic levitation. We report that heterotypic spheroids formed by spontaneous aggregation cannot be maintained in culture due to HUVEC disassembly over time. In contrast, magnetic levitation allows the formation of stable heterotypic spheroids with defined spatial distribution and significantly facilitated HUVEC integration. To the best of our knowledge, this is the first study that introduces a human-only cell line-based in vitro test system composed of a coculture of β-cells and ECs with a successful stimulation of β-cell secretory function monitored by a glucose-stimulated insulin secretion assays. In addition, we systematically investigate the impact of the spatial distribution on cocultures of human β-cells and ECs, showing that the architecture of pseudo-islets significantly affects β-cell functionality.

Sprouting angiogenesis in engineered pseudo islets

Despite the recent achievements in cell-based therapies for curing type-1 diabetes (T1D), capillarization in beta (β)-cell clusters is still a major roadblock as it is essential for long-term viability and function of β-cells in vivo. In this research, we report sprouting angiogenesis in engineered pseudo islets (EPIs) made of mouse insulinoma βTC3 cells and rat heart microvascular endothelial cells (RHMVECs). Upon culturing in three-dimensional (3D) constructs under angiogenic conditions, EPIs sprouted extensive capillaries into the surrounding matrix. Ultra-morphological analysis through histological sections also revealed presence of capillarization within EPIs. EPIs cultured in 3D constructs maintained their viability and functionality over time while non-vascularized EPIs, without the presence of RHMVECs, could not retain their viability nor functionality. Here we demonstrate angiogenesis in engineered islets, where patient specific stem cell-derived human beta cells can be combined with microvascular endothelial cells in the near future for long-term graft survival in T1D patients.

Endothelial and beta cell composite aggregates for improved function of a bioartificial pancreas encapsulation device

INTRODUCTION

Encapsulation of pancreatic islets or beta cells is a promising strategy for treatment of type 1 diabetes by providing an immune isolated environment and allowing for transplantation in a different location than the liver. However, islets used for encapsulation often show lower functionality due to the damaging of islet endothelial cells during the isolation procedure. Factors produced by endothelial cells have great impact on beta cell insulin secretion. Therefore, mutual signaling between endothelial cells and beta cells should be considered for the development of encapsulation systems to achieve high insulin secretion and maintain beta cell viability. Here, we investigate whether co-culture of beta cells with endothelial cells could improve beta cell function within encapsulation devices.

MATERIALS AND METHODS

Mouse insulinoma MIN6 cells and human umbilical vein endothelial cells were used for creating composite aggregates on agarose microwell platform. The composite aggregates were encapsulated within flat poly(ether sulfone)/polyvinylpyrrolidone device. Their functionality was assessed by glucose-induced insulin secretion test and compared to non-encapsulated free-floating aggregates.

RESULTS

We created composite aggregates of 80-100 µm in diameter, closely mimicking pancreatic islets. Upon glucose stimulation, their insulin secretion is improved in comparison to aggregates consisting of only MIN6 cells. Moreover, the composite aggregates encapsulated within a device secrete more insulin than aggregates consisting of only MIN6 cells.

CONCLUSION

Composite aggregates of MIN6 cells with human umbilical vein endothelial cells have improved insulin secretion in comparison to MIN6 aggregates showing that the interaction of beta cell and endothelial cell is crucial for a functional encapsulation system.

Effective endothelial cell and human pluripotent stem cell interactions generate functional insulin-producing beta cells

AIMS/HYPOTHESIS

Endothelial cells (ECs) play an essential role in pancreatic organogenesis. We hypothesise that effective in vitro interactions between human microvascular endothelial cells (HMECs) and human pluripotent stem cells (hPSCs) results in the generation of functional pancreatic beta cells.

METHODS

Embryoid bodies (EBs) derived from hPSCs were cultured alone (controls) or with ECs in collagen gels. Subsequently, cells were analysed for pancreatic beta cell markers, and then isolated and expanded. Insulin secretion in response to glucose was evaluated in vitro by static and dynamic (perifusion) assays, and in vivo by EB transplantation into immunodeficient mice.

RESULTS

Co-cultured EBs had a higher expression of mature beta cells markers and enhanced insulin secretion in vitro, compared with controls. In mice, transplanted EBs had higher levels of human C-peptide secretion with a significant reduction in hyperglycaemia after the selective destruction of native pancreatic beta cells. In addition, there was significant in vitro upregulation of bone morphogenetic proteins 2 and 4 (BMP-2, 4) in co-cultured cells, compared with controls.

CONCLUSIONS/INTERPRETATION

ECs provide essential signalling in vitro, such as activation of the BMP pathway, for derivation of functional insulin-producing beta cells from hPSCs.

Endothelium-derived essential signals involved in pancreas organogenesis

Endothelial cells (ECs) are essential for pancreas differentiation, endocrine specification, and endocrine function. They are also involved in the physiopathology of type 1 and type 2 diabetes. During embryogenesis, aortic ECs provide specific factors that maintain the expression of key genes for pancreas development such as pancreatic and duodenal homeobox-1. Other unknown factors are also important for pancreatic endocrine specification and formation of insulin-producing beta cells. Endocrine precursors proliferate interspersed with ductal cells and exocrine precursors and, at some point of development, these endocrine precursors migrate to pancreatic mesenchyme and start forming the islets of Langerhans. By the end of the gestation and close to birth, these islets contain immature beta cells with the capacity to express vascular endothelial growth factor and therefore to recruit ECs from the surrounding microenvironment. ECs in turn produce factors that are essential to maintain insulin secretion in pancreatic beta cells. Once assembled, a cross talk between endocrine cells and ECs maintain the integrity of islets toward an adequate function during the whole life of the adult individual. This review will focus in the EC role in the differentiation and maturation of pancreatic beta cells during embryogenesis as well as the current knowledge about the involvement of endothelium to derive pancreatic beta cells in vitro from mouse or human pluripotent stem cells.

Endothelial cells mediate islet-specific maturation of human embryonic stem cell-derived pancreatic progenitor cells

It is well recognized that in vitro differentiation of embryonic stem cells (ESC) can be best achieved by closely recapitulating the in vivo developmental niche. Thus, implementation of directed differentiation strategies has yielded encouraging results in the area of pancreatic islet differentiation. These strategies have concentrated on direct addition of chemical signals, however, other aspect of the developmental niche are yet to be explored. During development, pancreatic progenitor (PP) cells grow as an epithelial sheet, which aggregates with endothelial cells (ECs) during the final stages of maturation. Several findings suggest that the interactions with EC play a role in pancreatic development. In this study, we recapitulated this phenomenon in an in vitro environment by maturing the human ESC (hESC)-derived PP cells in close contact with ECs. We find that co-culture with different ECs (but not fibroblast) alone results in pancreatic islet-specific differentiation of hESC-derived PP cells even in the absence of additional chemical induction. The differentiated cells responded to exogenous glucose levels by enhanced C-peptide synthesis. The co-culture system aligned well with endocrine development as determined by comprehensive analysis of involved signaling pathways. By recapitulating cell-cell interaction aspects of the developmental niche we achieved a differentiation model that aligns closely with islet organogenesis.

Fibrin, a scaffold material for islet transplantation and pancreatic endocrine tissue engineering

Fibrin is derived from fibrinogen during injury to produce a blood clot and thus promote wound repair. Composed of different domains, including Arg-Gly-Asp amino acid motifs, fibrin is used extensively as a hydrogel and sealant in the clinic. By binding to cell surface receptors like integrins and acting as a supportive 3D scaffold, fibrin has been useful in promoting cell differentiation, proliferation, function, and survival. In particular, fibrin has been able to maintain islet cell architecture, promote beta cell insulin secretion, and islet angiogenesis, as well as inducing a protective effect against cell death. During islet transplantation, fibrin improved neovascularization and islet function. These improvements resulted in reduced number of transplanted islets necessary to reverse diabetes. Therefore, fibrin, as a biocompatible and biodegradable scaffold, should be considered during subcutaneous islet transplantation and beta cell expansion in vitro to ensure maintenance of islet cell function, proliferation, and survival to develop effective cell-based therapies for the treatment of diabetes.

Tissue engineering approaches to cell-based type 1 diabetes therapy

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