IDE-mediated GLP-1 degradation as the basis for designing long-acting and CNS-stable GLP-1 receptor agonists.

Glucagon-like peptide-1 (GLP-1) is a key incretin hormone rapidly degraded by circulating proteases such as DPP-4. The metabolism of GLP-1 by other proteases, particularly tissue-resident proteases, remains largely unexplored. Here, we identify insulin-degrading enzyme (IDE) as a previously unknown GLP-1-degrading protease with two cleavage sites. We show that IDE-mediated degradation of GLP-1, but not insulin, represents a major mechanism regulating glucose control. To resist IDE, we engineered GLP-1 and Semaglutide with D-amino acid substitutions at these sites. These peptides exhibit enhanced stability in plasma, liver and intestinal secretomes, peritoneal fluid, and central nervous system (CNS). D-Ser-Semaglutide shows prolonged plasma retention and sustained glucose-lowering effects in mice. Moreover, IDE knockdown and intracerebral injection of D-Ser-Semaglutide confirm IDE's physiological role in GLP-1 degradation, particularly in the CNS. These findings reveal a previously unidentified regulatory mechanism of GLP-1 metabolism and provide a strategy for designing long-acting agonists with improved metabolic and CNS therapeutic potential.