KL and Cognitive impairment: Klotho−/− mice exhibit multiple phenotypes resembling human premature aging, including extremely shortened life span, cognitive impairment, hippocampal neurodegeneration, hair loss, muscle atrophy, hypoglycemia, etc. To investigate the effect of linagliptin on these aging-related phenotypes, male klotho−/− mice were divided into two groups: (1) control group fed the standard diet, and (2) linagliptin group fed the standard diet containing linagliptin.