Insulin sensor cells for the analysis of insulin secretion responses in single living pancreatic β cells

Investigation of the functions of insulin-secreting cells in response to glucose in single-living cells is essential for improving our knowledge on the pathogenesis of diabetes. Therefore, it is desired to develop a new convenient method that enables the direct detection of insulin secreted from single-living cells. Here, insulin-sensor-cells expressing a protein-based insulin-detecting probe immobilized on the extracellular membrane were developed to evaluate the insulin-secretion response in single-living pancreatic β cells. The protein-based insulin-detecting probe (NαLY) was composed of a bioluminescent protein (nano-luc), the αCT segment of the insulin receptor, L1 and CR domains of the insulin receptor, and a fluorescent protein (YPet). NαLY exhibited a bioluminescence resonance energy transfer (BRET) signal in response to insulin; thus, cells of Hepa1-6 line were genetically engineered to express NαLY on the extracellular membrane. The cells were found to act as insulin-sensor-cells, exhibiting a BRET signal in response to insulin. When the insulin-sensor-cells and pancreatic β cells (MIN6 cell line) were cocultured and stimulated with glucose, insulin-sensor-cells nearby pancreatic β cells showed the spike-shaped BRET signal response, whereas the insulin-sensor-cells close to one pancreatic β cell did not exhibit such signal response. However, all the insulin-sensor-cells showed a gradual increase in BRET signals, which were presumably attributed to the increase in insulin concentrations in the culture dish, confirming the function of these insulin-sensor-cells. Therefore, we demonstrated that heterogenetic insulin secretion in single-living pancreatic β cells could be measured directly using the insulin sensor cells.