GCG and Osteopenia: Since GLP-1R is expressed in thyroid C cells and GLP-1 directly stimulates the secretion of calcitonin, which is a potent inhibitor of bone resorption in osteoclasts, GLP-1 may contribute to the nutrient-mediated reduction in bone resorption.369,370 Genetic disruption of GLP-1R signaling leads to cortical osteopenia and heightened bone fragility, primarily caused by increased bone resorption by osteoclasts.