The Role of Alpha Cells in the Self-Assembly of Bioengineered Islets

Impact statementPancreatic pseudoislets, which are three-dimensional spheroids composed of alpha, beta, and endothelial cells, can be formed in microwells and used as a model system to study how the different cell types organize and interact. In this study, we showed that including the glucagon-producing alpha cells (and not only the insulin-producing beta cells) could positively influence the number of endothelial cells in the pseudoislet. This is important for tissue engineers who aim to generate a de novo cell source of bioengineered islets for transplantation.Vascularization is undoubtedly one of the greatest challenges in tissue engineering. Its importance is particularly evident when considering the transplantation of (bioengineered) pancreatic islets of Langerhans, which are highly sensitive to the delivery of oxygen and nutrients for their survival and function. Here we studied pseudoislets of Langerhans, which are three-dimensional spheroids composed of beta (INS1E), alpha (alpha TC-1), and endothelial (HUVEC) cells, and were interested in how the location and prevalence of the different cell types affected the presence of endothelial cells in the pseudoislet. We hypothesized that alpha (alpha) cells play an essential role in islet self-assembly and the incorporation of endothelial cells into the pseudoislet, and are thus important to consider in tissue engineering or regenerative medicine strategies, which typically focuses on the insulin-producing beta (beta) cells alone. We first determined the effect of changing the relative ratios of the cells and found the cell distribution converged on a steady state of similar to 21% alpha cells, 74% beta cells, and 5% endothelial cells after 10 days of culture regardless of their respective ratios at seeding. We also found that the incorporation of endothelial cells was related to the pseudoislet size, with more endothelial cells found in the core of larger pseudoislets following a concomitant increase of alpha cells and a decrease in beta cells. Finally, we observed that both endothelial and beta cells were found adjacent to alpha cells significantly more frequently than to each other. In conclusion, this study demonstrates that the self-assembly of a pseudoislet is an intrinsically cell-regulated process. The endothelial cells had preferential proximity to the alpha cells, and this persisted even when challenged with changing the cell ratios and numbers. This study gives insight into the rules governing the self-organization of pseudoislets and suggests an important role for alpha cells to promote the incorporation of endothelial cells.