Klotho is an enzyme that in humans is encoded by the KL gene.[5]
This gene encodes a type-I membrane protein that is related to β-glucuronidases. Reduced production of this protein has been observed in patients with chronic renal failure (CRF), and this may be one of the factors underlying the degenerative processes (e.g., arteriosclerosis, osteoporosis, and skin atrophy) seen in CRF. Also, mutations within this protein have been associated with ageing, bone loss and alcohol consumption.[6][7]Transgenic mice that overexpress Klotho live longer than wild-type mice.[8]
Function
Klotho is a transmembrane protein that, in addition to other effects, provides some control over the sensitivity of the organism to insulin and appears to be involved in aging. Its discovery was documented in 1997 by Kuro-o et al.[9] The name of the gene comes from Klotho or Clotho, one of the Moirai, or Fates, in Greek mythology.
The Klotho protein is a novel β-glucuronidase (EC number 3.2.1.31) capable of hydrolyzing steroid β-glucuronides. Genetic variants in KLOTHO have been associated with human aging,[10][11] and Klotho protein has been shown to be a circulating factor detectable in serum that declines with age.[12]
The binding of certain fibroblast growth factors (FGF’s) viz., FGF19, FGF20, and FGR23, to their Fibroblast growth factor receptors, is promoted by their interaction with Klotho.[13]
Klotho-deficient mice manifest a syndrome resembling accelerated human aging and display extensive and accelerated arteriosclerosis. Additionally, they exhibit impaired endothelium dependent vasodilation and impaired angiogenesis, suggesting that Klotho protein may protect the cardiovascular system through endothelium-derived NO production.
Although the vast majority of research has been based on lack of Klotho, it was demonstrated that an overexpression of Klotho in mice might extend their average life span between 19% and 31% compared to normal mice.[8] In addition, variations in the Klotho gene (SNP Rs9536314) are associated with both life extension and increased cognition in human populations.[14]
The mechanism of action of klotho is not fully understood, but it changes cellular calcium homeostasis, by both increasing the expression and activity of TRPV5 and decreasing that of TRPC6.[15] Additionally, klotho increases membrane expression of the inward rectifier channel ROMK.[15]
Klotho-deficient mice show increased production of vitamin D, and altered mineral-ion homeostasis is suggested to be a cause of premature aging‑like phenotypes.