Abstract
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.Impact statementTissue engineering of coculture systems containing β-cells and endothelial cells (ECs) is a promising technique to stimulate β-cell functionality. In this study, we analyzed human pancreatic islet tissue and revealed three different native distributions of β-cells and ECs. We successfully recreated these distributions in vitro by employing magnetic levitation of human β-cells and ECs, forming controlled heterotypic pseudo-islets, which enabled us to identify a significant impact of the pseudo-islet architecture on insulin secretion.
Highlights
In 2018, 425 million people were known to suffer from diabetes mellitus (DM), with millions more remaining undiagnosed.[1,2] The number of DM patients is estimated to increase to >600 million by 2045.1 DM is a chronic disease, where the physiological feedback loop of blood glucose regulation is impaired by either the reduction of b-cell mass and insulin production, type 1 DM (T1D), or by a defective response to insulin in tissues, type 2 DM.[3]
In native pancreatic tissue (Fig. 3A, H, O), we identified three major naturally occurring spatial distributions of b-cells and endothelial cells (ECs): (1) the heterogeneous distribution of both cell types (‘‘1:1,’’ Fig. 3A), (2) ECs surrounded by b-cells (‘‘ECs inside,’’ Fig. 3H), and (3) b-cells surrounded by ECs (‘‘b-cells inside,’’ Fig. 3O)
We identified that pseudo-islets composed of b-cells inside and human umbilical vein endothelial cells (HUVECs) outside secreted significantly higher amounts of insulin upon glucose stimulation, independently of the aggregation method when compared with all other cell compositions or the control group, which is pseudo-islets composed of b-cells alone formed by spontaneous aggregation (‘‘b-cells inside’’ spontaneous aggregation: 49.37 – 10 mU/L vs. ‘‘b-cells inside’’: magnetic levitation 55.09 – 5.01 mU/L, ***p < 0.001, Fig. 6A)
Summary
In 2018, 425 million people were known to suffer from diabetes mellitus (DM), with millions more remaining undiagnosed.[1,2] The number of DM patients is estimated to increase to >600 million by 2045.1 DM is a chronic disease, where the physiological feedback loop of blood glucose regulation is impaired by either the reduction of b-cell mass and insulin production, type 1 DM (T1D), or by a defective response to insulin in tissues, type 2 DM.[3]. T1D patients rely on life-long medication and treatment, such as exogeneous insulin replacement or, in more severe cases, immunosuppression after pancreatic b-cell transplantation.[4,5,6] Attempts toward the long-term treatment of T1D by b-cell transplantation frequently fails due to an impaired graft survival as a result of lost extracellular matrix (ECM)[7,8] or lack of vascularization accompanied by hypoxia after islet isolation.[4,9,10]
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