Intracellular signaling of the aging suppressor protein Klotho.

The Klotho protein deficiency is known to participate in premature aging. As an aging suppressor, Klotho is an important molecule in aging processes and its overexpression results in longevity. Due to many reasons, the insulin/insulin-like growth factor-1 (IGF-1) has been considered as a key pathway in aging research. The Klotho gene is closely related to this pathway. The Klotho gene encodes a transmembrane protein that after cleavage is also found as a secreted protein. Importantly, its overexpression suppresses insulin/IGF-1 signaling and thus extends the lifespan. In addition, Klotho participates in the regulation of several other intracellular signaling pathways, including regulation of FGF23 signaling, cAMP, PKC, transforming growth factor-β (TGF-β), p53/p21, and Wnt signaling. The aim of this review is to summarize current literature that shows the involvement of Klotho in the regulation of several intracellular pathways. The results of our review clearly indicate that Klotho participates in several intracellular signaling pathways, and by regulating them, Klotho is involved in aging and longevity.