FGF21 and type 2 diabetes mellitus: In addition, β-cell-specific knockout of β-klotho (coreceptor of FGF21) led to impaired glucose-stimulated insulin secretion (GSIS) and glucose intolerance in mice, while adenovirus-mediated β-klotho overexpression alleviated the defect of islet GSIS in type 2 diabetic mice (81).