KL and chronic kidney disease: Increased serum phosphate level is reported to be universal in patients with advanced CKD or end-stage renal disease (ESRD) [16], and ESRD patients are known to show aging-like phenotypes including vascular calcification and metabolic bone disease [12] induced by decreased Klotho expression in the kidneys [38] as well as increased serum FGF-23 levels [39].