A role for the gut-to-brain GLP-1-dependent axis in the control of metabolism

Over the past years tremendous amounts of clinical and fundamental data have been generated about GLP-1 and related therapeutic strategies for the treatment of type 2 diabetes. However, the cellular and physiological mechanisms through which GLP-1 is secreted, controls glycemia, and behaves as a therapeutic agent are certainly unclear. This is due to the dogma that proposes that upon glucose absorption GLP-1 is secreted into the hepatoportal blood flow, binds to its receptor at the surface of the insulin secreting β cells, and triggers the secretion of insulin to control glycemia. However, these events have never been demonstrated sequentially for the control of glycemia. This conclusion is supported by a growing number of evidences that point out that the enteric and the central nervous systems are main actors in the control of GLP-1 action. This involves the triggering of the gut-to-brain and to periphery axis where nutrients regulate the release of GLP-1 and activate the tightly regulated enteric and cerebral neuronal circuits. These integrate and redistribute the GLP-1-dependent signals toward numerous targeted tissues. We will review some of them.