Peptides come to the rescue of pancreatic β cells

Abstract

Insulin and glucagon are well-known peptide hormones that keep glucose levels within a healthy range in the body. But they are only part of a complex network that controls concentrations of this ubiquitous sugar in blood and tissues. Other molecules regulate glucose by controlling insulin secretion from the pancreas or protecting pancreatic β cells against stresses that lead to cellular dysfunction or cell death (1). One of these protective regulators is glucagon-like peptide 1 (GLP-1), a 30-amino-acid-long peptide produced in specialized epithelial cells of the intestine, called L cells, and also in the brain and other organs and tissues (2). GLP-1 belongs to a group of peptides that mediate the “incretin effect,” an endocrine response to glucose arising from food digestion in the intestines (2, 3). This response helps regulate food intake and the fate of dietary glucose. Specifically, GLP-1 is released from the intestinal cells when food is ingested and then binds to and activates the GLP-1 receptor (GLP-1R), a G protein–coupled receptor on many cell types, including β cells in which GLP-1R signaling stimulates insulin synthesis and secretion (3). Notably, the incretin effect stimulates insulin secretion from pancreatic β cells more strongly than exposure to glucose alone. An article published in the Journal of Biological Chemistry (4), recognized as a Classic here, added to our understanding of the incretin effect by showing that GLP-1R signaling protects β cells from cell death (Fig. 1). This finding was significant for preventing or managing type 2 diabetes, in which β-cell apoptosis occurs (5) and may contribute to insufficient pancreatic insulin production (6). Open in a separate window Figure 1. Li et al. (4) have shown that binding of the receptor agonist exendin-4 to GLP-1R on pancreatic β cells protects the cells from cellular injury and cytokine-induced apoptosis and thereby preserves glucose homeostasis in mice. Binding of GLP-1 to its cognate receptor on pancreatic β cells up-regulates intracellular cAMP levels, in turn reducing streptozotocin-induced β-cell death. Images of exendin-4 and GLP-1R (with GLP-1 bound) are from Ref. 7; image of cAMP is from Wikimedia, used under Creative Commons.