Reestablishment of Glucose Inhibition of Glucagon Secretion in Small Pseudoislets

Abstract

Misregulated hormone secretion from the islet of Langerhans is central to the pathophysiology of diabetes. Although insulin plays a key role in glucose regulation, the importance of glucagon is increasingly acknowledged. However, the mechanisms that regulate glucagon secretion from α-cells are still unclear. We used pseudoislets reconstituted from dispersed islet cells to study α-cells with and without various indirect effects from other islet cells. Dispersed islet cells secrete aberrant levels of glucagon and insulin at basal and elevated glucose levels. When cultured, murine islet cells reassociate to form pseudoislets, which recover normal glucose-regulated hormone secretion, and human islet cells follow a similar pattern. We created small (∼40-µm) pseudoislets using all of the islet cells or only some of the cell types, which allowed us to characterize novel aspects of regulated hormone secretion. The recovery of regulated glucagon secretion from α-cells in small pseudoislets depends upon the combined action of paracrine factors, such as insulin and somatostatin, and juxtacrine signals between EphA4/7 on α-cells and ephrins on β-cells. Although these signals modulate different pathways, both appear to be required for proper inhibition of glucagon secretion in response to glucose. This improved understanding of the modulation of glucagon secretion can provide novel therapeutic routes for the treatment of some individuals with diabetes.

Delivery of shRNA via lentivirus in human pseudoislets provides a model to test dynamic regulation of insulin secretion and gene function in human islets

“…), human pseudoislets mirror the original intact islets well for both nonendocrine and endocrine cells. When sorted mouse beta, alpha, and delta cells were used, alpha and delta cells were incapable to form aggregates implicating beta cells are critical for the formation of pseudoislets (Reissaus and Piston ). Although it remains to be determined whether beta cell drives formation of pseudoislets in humans, our data indicate that the formation of pseudoislets have little selectivity in inclusion or exclusion of cell types to be incorporated for both endocrine and nonendocrine cells.…”

“…). As the three‐dimensional structure of pancreatic islets supports viability and function of beta cells through cell‐cell and cell‐matrix communications (Rutter and Hodson ; Arous and Wehrle‐Haller ; Reissaus and Piston ; Briant et al. ), it is critical to address beta cell pathophysiology in pancreatic islets.…”

“…The loss of functional beta cell mass is the central pathology for both type 1 and type 2 diabetes (Kahn 2001;Atkinson et al 2014;Chen et al 2017). As the threedimensional structure of pancreatic islets supports viability and function of beta cells through cell-cell and cell-matrix communications (Rutter and Hodson 2015;Arous and Wehrle-Haller 2017;Reissaus and Piston 2017;Briant et al 2018), it is critical to address beta cell pathophysiology in pancreatic islets. Rodent islets are readily available, cost effective, can be easily genetically manipulated, and can be compared with syngeneic animals to connect in vitro observations to in vivo phenotype.…”

Stem Cell Therapy for Diabetes: Beta Cells versus Pancreatic Progenitors

“…However, fractionating the differentiated pancreatic organoids into individual cells for the purpose of isolating only beta cells would disrupt the islet architecture generated in the dish that is sought to recapitulate in vivo development. To this extent, it has been demonstrated that isolated pancreatic beta cells underperform those in intact islets in insulin secretion response [54][55][56], indicating that establishment of the strategic cell-cell and cell-matrix contacts by beta cells with the islet is rather crucial to conferring its functional properties. In contrast, isolation of pure beta cells generated within the hPSC-derived pancreatic organoid and their re-aggregation to establish beta cell-beta cell contact improved their metabolic maturation and glucose-responsiveness [20].…”

“…Pancreatic islet architecture with appropriate distribution of different endocrine cell types has been shown to contribute towards beta cell functionality and glucose responsiveness. Resonating from the findings that beta cells within an intact islet are more precise in their secretory and calcium response to elevated glucose levels than those in dissociated or dispersed islets [54][55][56], it is important to consider that intra-islet cell-cell communication between beta cells and other endocrine cells as well as amongst different subpopulations of beta cells is crucial for paracrine signaling and enhanced electrical coupling [59][60][61].…”