Klotho deficiency is an early biomarker of renal ischemia–reperfusion injury and its replacement is protective

Abstract

Klotho is an antiaging substance with pleiotropic actions including regulation of mineral metabolism. It is highly expressed in the kidney and is present in the circulation and urine but its role in acute kidney injury (AKI) is unknown. We found that ischemia–reperfusion injury (IRI) in rodents reduced Klotho in the kidneys, urine, and blood, all of which were restored upon recovery. Reduction in kidney and plasma Klotho levels were earlier than that of neutrophil gelatinase-associated lipocalin (NGAL), a known biomarker of kidney injury. Patients with AKI were found to have drastic reductions in urinary Klotho. To examine whether Klotho has a pathogenic role, we induced IRI in mice with different endogenous Klotho levels ranging from heterozygous Klotho haploinsufficient, to wild-type (WT), to transgenic mice overexpressing Klotho. Klotho levels in AKI were lower in haploinsufficient and higher in transgenic compared with WT mice. The haploinsufficient mice had more extensive functional and histological alterations compared with WT mice, whereas these changes were milder in overexpressing transgenic mice, implying that Klotho is renoprotective. Rats with AKI given recombinant Klotho had higher Klotho protein, less kidney damage, and lower NGAL than rats with AKI given vehicle. Hence, AKI is a state of acute reversible Klotho deficiency, low Klotho exacerbates kidney injury and its restoration attenuates renal damage and promotes recovery from AKI. Thus, endogenous Klotho not only serves as an early biomarker for AKI but also functions as a renoprotective factor with therapeutic potential.

FGF-23 Levels in Patients with AKI and Risk of Adverse Outcomes

“…We did not have access to data on urine output, which might have allowed earlier identification of AKI and would have been another traditional biomarker (other than serum creatinine) with which to compare the prognostic use of FGF-23. We did not measure circulating or soluble Klotho, which has recently been reported as an early AKI biomarker and renoprotective factor in rodents (20). Finally, although most enrollment laboratory collections in the AKI group were obtained within 24 hours after the clinical diagnosis was established, occasionally, the laboratory collections were delayed up to 48 hours, which may have altered the prognostic use of other serum parameters relative to FGF-23.…”

The Inflammatory Cytokines TWEAK and TNFα Reduce Renal Klotho Expression through NFκB

“…Decreased renal, circulating, and urine Klotho was recently reported in ischemia-reperfusion-induced AKI. 42 Patients with kidney disease have progressive injury to multiple organs, among them the cardiovascular system, resulting in a mortality rate which is ten times that of age-matched controls, resulting in effective accelerated BASIC RESEARCH www.jasn.org aging. 14,43 Interestingly, systemic inflammation also promotes cardiovascular morbidity and mortality and has been associated with other age-dependent diseases such as osteoporosis and dementia.…”

“…However we can speculate on a nephroprotective role of Klotho based on the beneficial effect of Klotho overexpression on progressive renal injury 55 and in AKI. 42,56 In summary, the inflammatory cytokines TWEAK and TNF␣ downregulate Klotho in renal tubular cells through an NFBdependent mechanism. These results are of interest to kidney injury and to the accelerated aging observed in uremic patients.…”

Renal Production, Uptake, and Handling of Circulating αKlotho

“…This signal likely came from free 125 I released from 125 I-aKlotho which we detected (data not shown) and is largely unavoidable. To independently confirm the high signal in the kidney, we covalently labeled recombinant aKlotho with infrared dye 42 and examined aKlotho distribution in several organs in normal rats. Similar to the radioactive labeling, exogenous infrared labeled aKlotho protein was prominently distributed in the kidney and spleen, sparsely in the heart ( Figure 3D), and not detectable in aorta, brain, and muscle (data not shown).…”

“…There is no information on how this 130 kD protein is cleared from the circulation. We previously demonstrated the presence of intravenously injected exogenous extracellular domain of recombinant aKlotho protein in animal urine 42 but how aKlotho gets into the urine is not known.…”