α-Klotho (hereafter Klotho) was discovered as an aging-suppressor protein whose function is intrinsically dependent on the kidney. Its shed ectodomain, soluble Klotho (sKlotho), is detectable in blood and urine. As an obligate co-receptor for endocrine fibroblast growth factor 23, Klotho operates at the intersection of mineral metabolism and chronic kidney disease (CKD). Within the kidney, Klotho expression is moderate in the...