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Evidence for depletion of CASP5 Ala90Thr heterozygous genotype in aged subjects

Yulia M. Ulybina a, Ekatherina Sh. Kuligina a, Nathalia V. Mitiushkina a, Nathalia Yu. Sherina a, Grigoriy A. Yanus a,b, Tatiana V. Gorodnova a,b, Anna S. Katanugina a, Andrey V. Koloskov c, ⁎ Alexandr V. Togo a, Evgeny N. Imyanitov a,b,d,

a N.N. Petrov Institute of Oncology, Pesochny-2, St.-Petersburg, Russia b St.-Petersburg Pediatric Medical Academy, Russia c 26th City Hospital, St.-Petersburg, Russia d St.-Petersburg Medical Academy for Postgraduate Studies, Russia



Our previous studies, which included genotyping of multiple coding apoptotic gene polymorphisms, unexpectedly demonstrated a depletion of heterozygous CASP5 Ala90Thr (rs507879, c.268 GNA) genotypes in elderly subjects. Present investigation was aimed to validate this trend. An analysis of 510 subjects aged 75–103 years revealed 205 (40%) CASP5 Ala90Thr heterozygotes as compared to 254 (50%) expected from the minor allele frequency 0.470 (p=0.000014). This deviation was not observed in 549 middle-aged (18– 50 years) controls (270 (49%) heterozygotes observed vs. 274 (50%) expected; minor allele frequency 0.475; p=0.743). Unfavorable significance of CASP5 heterozygous genotype may be explained by the role of the caspase-5 in inflammation-related processes. Almost all prior gene-longevity association studies focused on discrimination between “good” and “bad” gene variants. Here we present a distinct situation, where the combination of alternative alleles (i.e., heterozygosity) appears to be unfavorable as compared to the

© 2010 Elsevier Inc. All rights reserved.

a single case-control comparison. GWAS already led to the identifi- cation of new genetic determinants for common age-related diseases (Kronenberg, 2008), however their immediate use in genuine longevity research is compromised by the requirement for an extremely large study size (Franceschi et al., 2007; Lunetta et al.,

1. Introduction

expectancy is beyond any reasonable doubt. Several allelic variants related to either longevity per se or resistance to common age-related diseases, have been identified within recent decade, and many more remain to be discovered in the future years (Franceschi et al., 2007; Lunetta et al., 2007). Contribution of ApoE polymorphism in the risk of Alzheimer's disease, cardiovascular diseases and overall life span is frequently quoted as the most reproducible observation in molecular epidemiology of ageing (Lewis and Brunner, 2004). Some studies demonstrated age-related differences in p53 Arg/Pro allele distribu- tion (Bojesen and Nordestgaard, 2008). The analysis of IGF1 signaling pathway genes led to the identification of highly reproducible association between FOXO3A gene polymorphism and survival chances (Flachsbart et al., 2009). Previous research in this field was based on a candidate gene approach and included participants of lipid metabolism, energy production and storage, DNA repair, oxidative stress, inflammation and other relevant pathways. Recent invention of so-called genome-wide association studies (GWAS) provided a possibility to assess the distribution of nearly all known SNPs within

Almost all “positive” gene-longevity association studies reported distinct frequencies of at-risk allele containing genotypes in elderly subjects vs. controls, i.e. they discriminated between “good” and “bad” gene variants (Franceschi et al., 2007; Lunetta et al., 2007). Here we present an unusual observation, where the presence of either of alternative homozygous genotypes appears to be neutral or favorable, whereas the combination of the variant alleles (i.e., heterozygosity) shows reduced frequency in aged subjects.

This study originated from our activities in of cancer- associated gene polymorphisms. While comparing allele frequencies in cancer patients vs. non-affected subjects, we use elderly tumor-free individuals as a “supercontrol”, i.e. an example of pronounced cancer tolerance (Imyanitov, 2009). Previously, we performed a systematic analysis of cancer-predisposing relevance of coding polymorphisms in apoptotic genes. We initially analyzed 19 coding apoptotic gene SNPs in lung cancer patients vs. elderly tumor-free smokers and in breast cancer cases vs. elderly tumor-free females. The groups of elderly tumor-free subjects, which served as a reference in this com- parison, demonstrated agreement with Hardy–Weinberg genotype

⁎ Corresponding author. N.N. Petrov Institute of Oncology, Pesochny-2, 197758 St.-Petersburg, Russia. Tel.: +7 812 5968951; fax: +7 812 5968947. E-mail address: evgeny@imyanitov.spb.ru (E.N. Imyanitov).

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distribution for 18 out of 19 tested SNPs. The remaining gene polymorphism, CASP5 Ala90Thr (rs507879, c.268 GNA), showed statistically significant depletion of heterozygotes in both series of aged non-affected individuals, but not in the middle-aged breast or lung cancer patients (Ulybina et al., 2009; Ulybina et al., manuscript in preparation). CASP5 gene codes for caspase-5 protease, a protein specifically involved in the process of inflammation (Martinon and Tschopp, 2007). We hypothesized that the heterozygosity for the above polymorphism negatively affects chances to achieve elderly age, and designed the validation study to test this assumption.