Comparison of insulin release from MIN6 pseudoislets and pancreatic islets of Langerhans reveals importance of homotypic cell interactions

Objectives: Cellular communication is required for normal patterns of insulin secretion from β cells. Experiments using isolated islets of Langerhans are hampered by lack of supply and the consuming isolation process. Pseudoislets comprising clonal cells have emerged as an alternative to study islet-cell interactions and insulin secretion. The current study compared MIN6 pseudoislets and freshly isolated mouse islets. Methods: Insulin content and release were measured by insulin radioimmunoassay. Reverse transcription polymerase chain reaction and Western blot analysis of adhesion molecule expression were performed on MIN6 monolayers and pseudoislets. MIN6 cellular proliferation and viability were measured by 5-bromo-2-deoxyuridine (BrdU) enzyme-linked immunosorbent assay, 3-(4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT), and lactate dehydrogenase assays. Results: Mouse islets were found to have greater insulin content than pseudoislets. However, insulin release was comparable between the 2 groups. With the use of MIN6 monolayers as a control, the expression of the adhesion molecule E-cadherin and connexin 36 were found to be enhanced in cells cultured as pseudoislets. Moreover, connexin 43 was shown to be absent from MIN6 cells irrespective of configuration. Finally, MIN6 pseudoislets seem able to manage their rate of proliferation with apoptosis resulting in a static size in the culture for extended periods. Conclusions: The current study found that MIN6 pseudoislets share many important functional and molecular features with islets of Langerhans.