The frequency of Klotho KL-VS polymorphism in a large Italian population, from young subjects to centenarians, suggests the presence of specific time windows for its effect

Laura Invidia Æ Stefano Salvioli Æ Serena Altilia Æ Michela Pierini Æ Maria P. Panourgia Æ Daniela Monti Æ Francesco De Rango Æ Giuseppe Passarino Æ Claudio

Received: 24 February 2009/Accepted: 21 April 2009/Published online: 7 May 2009  Springer Science+Business Media B.V. 2009

Abstract In mice a defect of Klotho gene expression resultsinmultipleaging-likephenotypesincludingshort lifespan, osteoporosis and atherosclerosis, while its over-expression suppresses aging and extends lifespan. Contrasting data have been reported as far as the importance of the functional variant of Klotho termed ‘‘KL-VS’’ on human longevity, depending on the average age of the old subjects that were compared with young controls. We therefore performed a study on a large Italian population sample including people from very young to very old age (centenarians). A total of

from 19 to 109 years, born and residing in northern and central Italy, were subdivided into three age classes defined on the basis of the survival curve constructed using Italian demographic mortality data, and geno- typed for the KL-VS allele. We found a significant increase of the heterozygous Klotho genotype in the class of elderly people compared to young controls. On the contrary, no difference was present between cente- narians and young controls. Such a non monotonic trajectory is evident only when a large, comprehensive age range is investigated, and is compatible with the hypothesis that this KL-VS heterozygous genotype is favorable for survival in old people, its beneficial effect decreasing thereafter, and becoming no more evident at the extreme ages. Such unusual age-related changes in the Klotho KL-VS genotype frequency is compatible with the hypothesis that alleles and genotypes involved in aging and longevity may exert their biological effect at specific time windows.

L. Invidia   S. Salvioli   S. Altilia   M. Pierini  M. P. Panourgia   C. Franceschi (&) Department of Experimental Pathology, University of Bologna, via S. Giacomo

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Bologna, Italy e-mail: claudio.franceschi@unibo.it

S. Salvioli   C. Franceschi ER-GenTech Laboratory, via Saragat 1, 44100 Ferrara, Italy

Department of Experimental Pathology and Oncology, University of Florence, V. Morgagni 50, 50134 Florence, Italy

Department of Cell Biology, University of Calabria, 87030 Rende, Italy

Klotho (MIM 604824), originally identified by inser- tional mutation in a transgenic mouse, is an aging

depending on the different age of the groups of old subjects analysed and their controls. In particular, a survival advantage was observed for the heterozygous but not homozygous genotype in a population of Bohemian Czech elderly subjects (Arking et al. 2002, 2005). However, these results were not confirmed in Baltimore Caucasian and Baltimore African-American subjects (Arking et al. 2002, 2005). In another study performed in two independent populations (Ashke- nazi-Jewish and Czech) the advantage for the hetero- zygous genotype was observed in subjects aged C79 years (Arking et al. 2005). Recently, Puca et al. tested the frequency of KL-VS variant in Caucasian long-lived (C93 years) and young control subjects (\35 years). This study reported no association between the functional variant of the Klotho gene and exceptional longevity (Novelli et al. 2008).

results in aging-like phenotypes including short life span, hypoactivity, infertility, osteoporosis and ath- erosclerosis (Kuro-o et al. 1997). On the other hand, its over-expression extends mice lifespan by about 20–30% (Kurosu et al. 2005). Mouse Klotho gene encodes a 130 kDa protein with a single transmem- brane domain and an extracellular domain that contains two repeats (KL1 and KL2), both of which have up to 40% homology to b-glycosidase family-1. Klotho is expressed predominantly in the choroid plexus of the brain and the distal convoluted tubule of the kidney (Kuro-o et al. 1997; Tohyama et al. 2004). An alternatively spliced transcript that lacks the trans- membrane domain also exists (Shiraki-Iida et al. 1998). Klotho can be found as either transmembrane or secreted protein, this latter form being predominant in humans (Matsumura et al. 1998). Secreted Klotho is detectable in the blood and cerebrospinal fluid of mice and humans, which suggests that Klotho could function as a hormone (Kurosu et al. 2005; Imura et al. 2004). The secreted Klotho protein can regulate multiple growth factor signaling pathways, including insulin/ IGF-1 and Wnt, and the activity of multiple ion channels. Klotho protein also protects cells and tissues from oxidative stress, yet the precise mechanism underlying this antioxidant activity remains to be determined (Kuro-o 2008). It has been hypothesized that Klotho-mediated resistance to oxidative stress may explain, at least in part, the anti-aging effects of this protein (Bartke 2006; Kuro-o et al. 1997; Yamam-

In order to clarify the importance of Klotho KL-VS genotype in human longevity, we performed a study on a large Italian population sample, including people from very young to very old age (centenarians).

Materials and methods