Experimental Gerontology 39 (2004) 1595-1598, www.elsevier.com/locate/expgero. Analysis of longevity in the Japanese population and polymorphic variants of genes involved in insulin and insulin-like growth factor 1 signaling pathways.

Toshio Kojima, Hidehiko Kamei, Tomoyuki Aizu, Yasumichi Arai, Michiyo Takayama, Susumu Nakazawa, Yoshinori Ebihara, Hiroki Inagaki, Yukie Masui, Yasuyuki Gondo, Yoshiyuki Sakaki, Nobuyoshi Hirose.

Abstract:

Recent studies have demonstrated a significant association between mutations in genes involved in the insulin/IGF1 signaling pathway and extension of the life span of model organisms. In this study which compared 122 Japanese semisupercentenarians (older than 105) with 122 healthy younger controls, we examined polymorphic variations of six genes which are involved in insulin/IGF1 signaling. These genes were FOXO1A, INSR, IRS1, PIK3CB, PIK3CG, and PPARGC1A. We investigated the possible association of each gene locus and longevity by haplotype-based association analyses using 18 SNPs from public databases and the published literature. One INSR haplotype, which was comprised of 2 SNPs in linkage disequilibrium, was more frequent in semisupercentenarians than in younger controls.

Keywords: Aging; Centenarian; Gene polymorphism; Insulin/IGF1 signaling; Longevity.

Introduction:

The insulin-like receptor gene (InR) was also reported in Drosophila melanogaster (Tatar et al., 2001). At almost the same time, the ablation of the D. melanogaster gene chico, which encodes an insulin receptor substrate, was reported to extend the life span of the fly (Clancy et al., 2001). Regulations of lifespan by insulin receptor and IGF1 receptor were also reported in mice (Bluher et al., 2003; Holzenberger et al., 2003). Based on these studies, genes involved in the insulin/IGF1 signaling pathway are believed to play a role in longevity throughout evolution. In fact, polymorphic variations of the genes for insulin-like growth factor 1 receptor (IGF1R) and phosphoinositide-3-kinase have been reported to affect human longevity (Bonafe et al., 2003).

Recent studies using model organisms have demonstrated a significant association between mutations in genes involved in the insulin/insulin-like growth factor 1 (IGF1) signaling pathway and extension of the life span. The first examples of such genes were found in Caenorhabditis elegans (Kenyon et al., 1993). They include daf-2, an ortholog of the insulin/IGF1 receptor gene family, and daf-16, an ortholog of the forkhead transcription factors. Another example is age-1 which is the C. elegans ortholog of the gene encoding the catalytic subunit of phosphoinositide-3-kinase, a protein involved in insulin/IGF1 signal.

In this study, we compared 122 Japanese semisupercentenarians (SSCs) (older than 105) with 122 healthy younger controls. We examined polymorphic variations of the genes for six proteins, forkhead box O1A (FOXO1A), insulin receptor (INSR), insulin receptor substrate 1 (IRS1), phosphoinositide-3-kinase, catalytic, beta polypeptide (PIK3CB), phosphoinositide-3-kinase, catalytic, gamma polypeptide (PIK3CG), and peroxisome proliferative activated receptor, gamma, coactivator 1, alpha (PPARGC1A), all of which are involved in insulin/IGF1 signaling.

Subjects:

A total of 122 Japanese SSCs (107 female, 15 male, mean age 106.8±1.0 years) were recruited from 2002 to present for this study (Table 1). Forty-six SSCs were living at home and 76 were institutionalized. None were in an acute care situation and none were receiving tube feeding. The gender-matched control subjects comprised 122 healthy volunteers (105 female, 17 male, mean age 33.3±11.4 years, range 19-63) recruited from hospital and institutional workers, medical and nursing school students, and bank clerks. The control subjects were free from diseases such as coronary artery disease, stroke, diabetes, and cancer. Smoking and alcohol consumption was moderate to nil. All subjects enrolled in this study were Japanese. Twenty milliliters of1/2Where p and q are the frequencies of the other 1 and 2 alleles at locus A and B, respectively (Hill and Robertson, 1968). Lewontin's coefficient D0 is given by D/Dmax where D = min[q p , p q] when DO0 (Lewontin, 1964). Haplotype frequencies for multiple loci were estimated by the expectation-maximization method. An additional 122 SSCs and 30 healthy younger controls were genotyped for an association analysis using 16 SNPs in six genes (Table 2). Two SNPs (IN3 and IN4) in INSR showed a weak difference between SSCs and controls. These SNPs are in LD with each other (|D0| = 0.899) and are within 2.4 kb of each other (Fig. 1). Computations were performed using SNPAlyze software (Dynacom, Mobara, Japan). Haplotypes were constructed based on the genotype data from these SNPs in INSR. The expectation-maximization algorithm, with phase-unknown samples, was used to estimate haplotype frequencies. The MM haplotype (M: major allele) was more frequent in SSCs (57.0%) than in controls (47.3%) (P = 0.030) (Table 3).

3.1. Pairwise LD in 5 genes
Among the SNPs not from the JSNP database, 3B2 in PIK3CB was not polymorphic in our 24 control samples (Table 2). Consequently, this SNP was excluded from further experiments. The 92 healthy controls were genotyped for each of the 17 selected SNPs. The strength of LD for each SNP pair within each gene was measured using the |D0| and the r2 values (Fig. 1). This figure shows that FO1 and FO4 in the FOXO1A locus are in very tight LD with each other (r2 = 0.789). FO1 was selected as the representative SNP for this SNP pair and was examined in further analysis. FO4 was excluded from further analysis.

Case-control study of SSCs and controls using estimated haplotype frequencies in INSR
Haplotype SNP ID Frequency c2 P type ID IN3 IN4 SSC Control 1 M M 0.570 0.473 4.729 0.030 2 m M 0.197 0.224 0.603 0.437 3 M m 0.000 0.011 3.019 0.082 4 m m 0.234 0.292 2.076 0.150
M, major allele; m, minor allele.