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Dysfunction of glucagon-secreting α-cells participates in the progression of diabetes, and glucagon receptor (GCGR) antagonism is regarded as a novel strategy for diabetes therapy. GCGR antagonism upregulates glucagon and glucagon-like peptide 1 (GLP-1) secretion and, notably, promotes β-cell regeneration in diabetic mice. Here, we aimed to clarify the role of GLP-1 receptor (GLP-1R) activated by glucagon and/or GLP-1 in the GCGR antagonism–induced β-cell regeneration. We showed that in db/db mice and type 1 diabetic wild-type or Flox/cre mice, GCGR monoclonal antibody (mAb) improved glucose control, upregulated plasma insulin level, and increased β-cell area. Notably, blockage of systemic or pancreatic GLP-1R signaling by exendin 9-39 (Ex9) or Glp1r knockout diminished the above effects of GCGR mAb. Furthermore, glucagon-neutralizing antibody (nAb), which prevents activation of GLP-1R by glucagon, also attenuated the GCGR mAb–induced insulinotropic effect and β-cell regeneration. In cultured primary mouse islets isolated from normal mice and db/db mice, GCGR mAb action to increase insulin release and to upregulate β-cell–specific marker expression was reduced by a glucagon nAb, by the GLP-1R antagonist Ex9, or by a pancreas-specific Glp1r knockout. These findings suggest that activation of GLP-1R by glucagon participates in β-cell regeneration induced by GCGR antagonism in diabetic mice. Article Highlights: Glucagon receptor (GCGR) antagonism promotes β-cell regeneration in type 1 and type 2 diabetic mice and in euglycemic nonhuman primates. Glucagon and glucagon-like peptide 1 (GLP-1) can activate the GLP-1 receptor (GLP-1R), and their levels are upregulated following GCGR antagonism. We investigated whether GLP-1R activated by glucagon and/or GLP-1 contributed to β-cell regeneration induced by GCGR antagonism. We found that blockage of glucagon–GLP-1R signaling attenuated the GCGR monoclonal antibody–induced insulinotropic effect and β-cell regeneration in diabetic mice. Our study reveals a novel mechanism of β-cell regeneration and uncovers the communication between α-cells and β-cells in regulating β-cell mass. [ABSTRACT FROM AUTHOR]