Gut-derived GLP-1 released by rare sugar D-allulose cooperates with insulin to activate left-sided vagal afferents and enhance insulin sensitivity

ABSTRACT Glucagon-like peptide-1 receptor agonists (GLP-1RAs) ameliorate hyperglycemia by directly stimulating insulin secretion from the pancreas. In contrast, the physiological role of short-lived endogenous GLP-1 remains unclear, largely because of its limited access to pancreatic β cells. Here, we show that D-allulose-induced intestinal GLP-1 secretion (AIGS) cooperates with insulin to reduce blood glucose levels by enhancing insulin action, rather than insulin secretion, in male mice. This cooperation and remote signaling require left-sided vagal afferents forming the common hepatic branch, but not right-sided afferents. AIGS-enhanced insulin action required both GLP-1 receptors and insulin receptor substrate 2 in these neurons. Remarkably, AIGS improved insulin resistance and hyperglycemia more rapidly and potently than the GLP-1RA exendin-4. These findings reveal that a subclass of vagal afferent neurons synergistically activated by endogenous intestinal GLP-1 and insulin does not stimulate insulin secretion but augments insulin action to improve glucose tolerance. This novel extra-pancreatic GLP-1 action mediated by vagal afferents provides a promising basis for innovative type 2 diabetes therapies. ARTICLE HIGHLIGHT Compared with GLP-1 receptor agonists, the physiological roles and mechanisms of endogenous, short-lived GLP-1 in glucose metabolism remain poorly understood. We utilized the rare sugar D-allulose, a noncaloric GLP-1 secretagogue, as a tool to elucidate the physiological actions of endogenous GLP-1. D-allulose–induced intestinal GLP-1 release cooperates with insulin to activate left-sided vagal afferents, enhancing insulin action rather than insulin secretion and thereby regulating glycemic control. Because this acute mechanism improved hyperglycemia in type 2 diabetes more effectively than GLP-1 receptor agonists, targeting GLP-1/insulin–vagal signaling may inform novel therapies and dietary or nutritional interventions for T2DM.