Lipid receptors and islet function: therapeutic implications?

G-protein coupled receptors (GPCRs) are targets of approximately 30% of currently marketed drugs. Over the last few years, a number of GPCRs expressed in pancreatic beta-cells and activated by lipids have been discovered. GPR40 was shown to be activated by medium- to long-chain fatty acids (FAs). It has since been shown that GPR40 contributes to FA amplification of glucose-induced insulin secretion. Although some controversy still exists as to whether GPR40 agonists or antagonists should be designed as novel type 2 diabetes drugs, data obtained in our laboratory and others strongly suggest that GPR40 agonism might represent a valuable therapeutic approach. GPR119 is expressed in pancreatic beta-cells and enteroendocrine L-cells, and augments circulating insulin levels both through its direct insulinotropic action on beta-cells and through FA stimulation of glucagon-like peptide 1 (GLP-1) secretion. GPR120 is expressed in L-cells and was also shown to mediate FA-stimulated GLP-1 release. Finally, GPR41 and GPR43 are receptors for short-chain FAs and may indirectly regulate beta-cell function via adipokine secretion. Although the discovery of these various lipid receptors opens new and exciting avenues of research for drug development, a number of questions regarding their mechanisms of action and physiological roles remain to be answered.