Optogenetic Excitation of the Pancreatic β-Cell

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The β-cell is a subunit of the Islet of Langerhans, a micro-organ of the pancreas which maintains glucose homeostasis. This endocrine cell senses changes in blood glucose levels and releases the hormone insulin. An electrophysiological process governing insulin release occurs through initial uptake of blood glucose and generation of ATP which binds the K-ATP channel causing inhibition and subsequent membrane depolarization. Influx of calcium from voltage-gated channels then interact with insulin secretory vesicles to promote exocystosis into the blood stream. In order to directly influence calcium dynamics, insulin release, and to study the electrophysical properties of the β-cell we used Channelrhodopsin-2 (ChR2), a light activated cation channel capable of creating membrane depolarization with light stimulation. Transient transfection of the MIN6 β-cell line using ChR2-YFP was carried out followed by calcium imaging using Fura2-AM. Following ChR2 stimulation at 490nm we observed local depolarization events in positively transfected cells. We demonstrated the creation of new oscillatory behavior at high glucose levels that can be set at specified frequencies and demonstrate that ChR2 can be used to overcome disruption in the K-ATP channel. Next, we isolated intact islets from a mouse model with β-cell specific expression of ChR2-YFP. We demonstrated global depolarization events upon ChR2 stimulation and performed insulin secretion assays to demonstrate enhanced insulin secretion. In addition, a computational multi-cellular islet model including ChR2 was used for comparison between in-vitro and in-silico experiments. This work demonstrates the ability of cell-specific electrophysiological control in the islet of Langerhans which will give further insight into β-cell behavior. Future work will include analyzing local depolarization on global islet behavior, examining the effect of ChR2 on islet-islet coupling, and developing an in-vivo model; which will include testing the feasibility for reversing diabetes.