GLP1R and diabetes mellitus: In this review, we summarize the latest advances in using optogenetics‐based synthetic biology approach for treating diabetes and its related complications, which include engineering β‐cells or non‐β‐cells for insulin or GLP‐1 production, enhancement of insulin sensitivity for glucose disposal, the delivery strategies for engineered cell therapy, as well as discussing the challenges in optogenetics‐based therapies for DM.