KL and renal fibrosis: Kl−/− deficient mice with unilateral ureteral obstruction (UUO) had higher TGF-β1 levels and more renal fibrosis than WT wild type mice with UUO (13, 15) in human kidney, decreased Klotho expression occurs in early stages of CKD, and could be responsible for early increase in serum FGF23 level (16).