INS and diabetes mellitus: GPCRs can control glucose homeostasis through modulation of insulin and incretin secretion, with potential targets for diabetes treatment including free fatty acid receptor 1 (FFAR1), also known as G-protein coupled receptor 40 (GPR40), free fatty acid receptor 4 (FFA4, also known as GPR120), and glucose-dependent insulinotropic receptor (GPR119) (24).