Optogenetic Engineering of Pancreatic Beta-Cells for Modulation of Insulin Release By Light

Diabetes is characterized by abnormal blood sugar levels linked to damage or ablation of pancreatic beta-cells due to autoimmunity (type 1 diabetes; T1D) or insulin resistance (type 2 diabetes; T2D). Over 30 million people in the US suffer from diabetes. Insulin administration is essential for the treatment of all T1D patients and those with late stage T2D. Given the limited supply of donor islet cells, an appealing alternative is the engineering of beta-cells aiming at increasing the specific rate glucose-stimulated insulin secretion (GSIS) thereby reducing the total number of cells needed for reconstituting normoglycemia. In the present study, we implemented optogenetic engineering for enhancing GSIS in beta-cells via photostimulation rather than pharmacological agents. This was accomplished by ectopic expression of a photoactivated adenylyl cyclase (PAC) gene in beta-cells followed by extensive testing of their function in vitro and in vivo. Rodent β-cell lines and primary islet cells expressing PAC and exposed to blue light exhibited increased intracellular cyclic adenosine monophosphate (cAMP) and GSIS rate compared to their counterparts without PAC expression and/or photostimulation. Stable PAC expression and successive rounds of stimulation with light had no adverse effect on cell growth and viability over multiple passages. Cyclic AMP was also elevated with light in the absence of glucose but insulin secretion did not increase in agreement with the role of cAMP as an amplifier not an inducer of GSIS and the preservation of GSIS dependence on glucose. Encapsulated PIs were implanted in streptozotocin-treated diabetic mice. Animals receiving engineered cells displayed improved glucose tolerance and higher plasma insulin with light vs. those kept in dark. These findings support further development of optogenetic augmentation of beta-cell GSIS to enable cell therapy technologies for diabetes and tools for studying beta-cell physiology in normal and disease states.