A microsatellite polymorphism in the promoter of the IGF1 gene and its association with longevity in Han Chinese

Liang Xie1,2,3, Yuan-ying Gong1,3, Shi-gang Lian4, Juan Yang4, Shou-jun Gao5, Liang-you Xu5, Ya-ping

Abstract

Background: Previous studies have suggested a probable association between the polymorphism of a microsatellite locus located in the promoter of the IGF1 (Insulin-like growth factor 1) gene and the serum level of, as well as many age-related diseases. Based on these results, we hypothesized that this polymorphism may influence longevity in humans. We performed an association study in a Han Chinese population to test this hypothesis.

Findings: We recruited 493 elderly Han Chinese individuals (females 94; males 90) and 425 young (controls) from Dujiangyan (Sichuan province, China). The genotype distributions and allele frequencies of the microsatellite site in the elderly and control groups were compared by chi-square test. Our results suggested that there was no association between the microsatellite polymorphism and longevity in the Han Chinese population. However, there were more male individuals with 18/21 genotype in the elderly group than in the control group (11.11 vs. 5.45%, p = 0.011). As the difference was not significant when corrected by Bonferroni method, we speculate that the 18/21 genotype cannot be functional in longevity; however, it may be linked with the real functional loci as there is a long haplotype block embracing the microsatellite locus.

Conclusions: There was no association between polymorphism of the microsatellite in promoter of IGF1 gene and longevity in our study. Future association studies containing the long haplotype block are deserved and can test our speculation of the potential linkage of 18/21 genotype and functional loci.

Background

Insulin-like growth factor 1 (IGF1) plays a number of important roles in the human body. It is involved in physiological processes such as growth, development, and metabolism, and has been implicated as a factor in the development of common diseases. Meanwhile, a conserved insulin/IGF1 signal pathway which may affect ageing and longevity is known in yeast, drosophila, mice, and humans. Elucidating the functions of insulin/IGF1 pathway in ageing and longevity is a current hotspot in longevity research.

A cytosine-adenine (CA) repeat polymorphism in IGF1 gene promoter region (1 kilobase pairs upstream from the transcription start site) has been associated with serum IGF1 level. At the same time, many studies have related this microsatellite polymorphism to age-related diseases such as diabetes, cancers, and cardiovascular diseases. These results are disputed by several other studies. However, they suggest that this microsatellite locus might be a potential functional site for serum IGF1 level regulation and might therefore function in ageing and longevity. Therefore, exploring the association of this microsatellite polymorphism and longevity is urgent.

Thermocycling parameters included an initial denaturation of 5 min at 95°C; 35 cycles of: 95°C for 30 s, 62°C for 1 min, and 72°C for 1 min; and a final extension at 72°C for 10 min. PCR products were denatured and size fractionated on a 6% denaturing polyacrylamide gel run on an ABI 3730 automated sequencer (Applied Biosystems, Foster City, CA). Alleles were read and scored by GeneMapper V4.0 software (ABI Perkin Elmer) using Liz500 as size standard. Alleles were verified artificially twice by two different persons. The number of repeats contained in alleles of different lengths was confirmed by cloning and sequencing two differently sized PCR products (i.e., two alleles). We replicated PCR amplification and genotyping of 30% of the samples, ensuring that replicates were performed by a different researcher. Ambiguous results were confirmed by another PCR and fragment analysis.

To our knowledge, there have been no reports on the association between the microsatellite polymorphism and longevity in the Han Chinese people. In this study, we conducted an association study in a Han Chinese population to investigate the potential function of this microsatellite locus in predicting longevity.

Methods

Subjects

A total of 493 elderly individuals (94 females; 90 males) from Dujiangyan (Sichuan province, China) agreed to participate in this study. Ages were authenticated by the official certification of the Fifth National Census in China as well as by the inference of the number of generations and the memories of these, their offspring, and other local elderly people. The age was confirmed when the certification and theof Contents:
1. Introduction
2. Methods
3. Results
4. Discussion

1. Introduction 

The aim of this study was to investigate the potential association between a microsatellite polymorphism in the IGF1 gene promoter and longevity in a Han Chinese population. The study included 493 elderly individuals and 425 control individuals, and genotyping was performed using DNA extracted from white blood cells in whole blood. 

2. Methods 

PCR primers were used for genotyping according to a previous study [21]. The PCR reactions included 20 ng genomic DNA as template, 2.5 μL 10 PCR buffer, 1.0 μL dNTP (2.5 mmol L-1), 0.5 μL BSA (bovine serum albumin, 200 μg ml-1), 0.5 μL forward primer (10 pmol L-1), 0.5 μL reverse primer (10 pmol L-1), 0.125 μL rTaq polymerase (Takara, Dalian, China) and distilled water to a total volume of 25 microliter (μL). Chi square tests were performed to compare the genotype frequencies and allele distribution between the elderly and control groups, as well as between genders within each group.

3. Results