The authors have declared that no competing interests exist.
Conceived and designed the experiments: DC RB. Performed the experiments: MC PC CR DC. Analyzed the data: FDR AM. Wrote the paper: FC GR DC GP.
¶ These authors also contributed equally to this work.
Several studies have shown that genetic factors account for 25% of the variation in human life span. On the basis of published molecular, genetic and epidemiological data, we hypothesized that genetic polymorphisms of taste receptors, which modulate food preferences but are also expressed in a number of organs and regulate food absorption processing and metabolism, could modulate the aging process. Using a tagging approach, we investigated the possible associations between longevity and the common genetic variation at the three bitter taste receptor gene clusters on chromosomes 5, 7 and 12 in a population of 941 individuals ranging in age from 20 to 106 years from the South of Italy. We found that one polymorphism, rs978739, situated 212 bp upstream of the
Several studies including various genome wide association studies have demonstrated the existence of an important familial and genetic component of longevity
The importance of nutrients in the aging process is also witnessed by overwhelming epidemiologic evidences that diet and nutrition can affect growth, the development of the body during childhood, the risk of acute and chronic diseases during adulthood, the maintenance of physiological processes and the biological process of aging
For example, the
On the other hand, new evidence strongly suggests that taste genes play a much broader role in human health. Genes of the
The value inside each diamond represents the linkage disequilibrium (r2) between each SNP. The values inside the black arrows represent the distance between the SNPs. SNPs situated in a coding region are written in red, while SNPs in non coding regions are in black. The red arrows show the direction in which the gene is transcribed.
Symbols are as in
Symbols are as in
Samples were collected within the framework of several recruitment campaigns carried out for monitoring the quality of aging in Calabria (Southern Italy) from 2002. The recruitment campaigns and subsequent analyses received the approval of the Ethical committee of the University of Calabria. All subjects provided written informed consent for studies on aging carried out by our research group. White blood cells (WBC) from blood buffy coats were used as a source of DNA.
ID_Gene | SNP | ≥85 yrs |
<85 yrs |
OR (95%CI) |
Pvalue | Ptrend |
|
rs6466849 | |||||
G/G | 233 | 316 | 1 | 0.043 | ||
A/G | 86 | 172 | 0.69 (0.50–0.94) | 0.018 | ||
A/A | 14 | 22 | 0.89 (0.44–1.77) | 0.730 | ||
(A/G+A/A) | 0.71 (0.53–0.95) | 0.023 | ||||
|
rs860170 | |||||
A/A | 139 | 253 | 1 | 0.042 | ||
A/G | 153 | 224 | 1.25 (0.93–1.67) | 0.135 | ||
G/G | 39 | 46 | 1.51 (0.94–2.43) | 0.090 | ||
(A/G+G/G) | 1.29 (0.98–1.71) | 0.069 | ||||
|
rs978739 | |||||
A/A | 185 | 245 | 1 |
|
||
A/G | 125 | 284 | 0.59 (0.45–0.79) |
|
||
G/G | 30 | 54 | 0.76 (0.46–1.23) | 0.262 | ||
(A/G+G/G) | 0.62 (0.47–0.81) |
|
||||
|
rs2233998 | |||||
C/C | 118 | 159 | 1 | 0.057 | ||
C/T | 146 | 282 | 0.71 (0.52–0.97) | 0.029 | ||
T/T | 78 | 146 | 0.74 (0.51–1.06) | 0.102 | ||
(C/T+T/T) | 0.72 (0.54–0.96) | 0.024 | ||||
|
rs2227264 | |||||
T/T | 114 | 158 | 1 | 0.047 | ||
G/T | 148 | 287 | 0.72 (0.53–0.99) | 0.044 | ||
G/G | 74 | 146 | 0.72 (0.50–1.04) | 0.081 | ||
(G/T+G/G) | 0.72 (0.54–0.97) | 0.029 |
Numbers may not add up to 100% of subjects due to genotyping failure. Data points that were still not filled after this procedure were left blank.
OR: odds ratio; CI: confidence interval.
Subjects were recruited between 1994 and 2008 in Calabria and included 941 unrelated individuals, of which 348 were very elderly cases (≥85 years, range 85–106 years, mean age 93.82±4.44 years, median age 92) and 593 were non-elderly controls (<85 years, range 20–84 years, mean age 59.17±19.45 years, median age 67 years). We chose 85 as a cut-off point because it has been shown that genetic factors contribute to the variation in human life span minimally before age 60 years and most profoundly from age 85 years onwards
Younger subjects were contacted through general physicians. Subjects older than 90 years were identified by screening of population registers in different municipalities distributed across the Calabria region. It is important to note that we can exclude the fact that older and younger people in Calabria are of two different ethnicities. Calabria is not subject to immigration from other parts of Italy and all the subjects in the study were of Caucasian origin excluding the possibility that the observed effect is due to ethnicity Eligible subjects were contacted and invited to participate in the study. Written informed consent was obtained from all participants before the enrolment in the study. The health status was ascertained through a medical examination carried out by a geriatrician. Subjects with dementia and/or neurologic disorders were not included. At the time of the visit, peripheral venous blood samples were also obtained.
The A/A genotype frequency is about 40.5% in the young and adult classes (20–50 and 51–70 years). Thereafter the A/A frequency increases through older classes reaching the 55.5% in the oldest (χ2 = 17,08, p<0.029).
We sought to survey the entire set of common genetic variants in the selected bitter taste receptors situated at chromosome 5, 7 and 12. To this end, we followed a hybrid tagging-functional approach. We used the algorithm described by Carlson and coworkers
DNA was extracted from blood samples with standard proteinase K digestion followed by phenol/chloroform extraction and ethanol precipitation. The order of DNAs of cases (age≥85) and controls (age<85) was randomized on PCR plates in order to ensure that an equal number of cases and controls could be analyzed simultaneously. All genotyping was carried out using Kaspar (Kbioscience, Heddesdon, UK) or Taqman (Applied Biosystems, Foster City, CA, USA) assays. PCR plates were read on an ABI PRISM 7900HT instrument (Applied Biosystems).
Haplotype blocks were identified from the genotyping data of this study using SNPtool (
The frequency distribution of genotypes was examined for the cases and the controls. HWE was tested for each of the SNP by chi-square test. logistic regression for multivariate analyses to assess the main effects of the genetic polymorphism on longevity was used. In these models the genetic data was coded using a co-dominant and a dominant inheritance model using the most common genotype in the controls as the reference category. All analyses were adjusted for gender. For haplotype analysis unconditional logistic regression was used to estimate the “risk of longevity”. The most frequent haplotype was set as reference, while haplotypes with a frequency below 1% were declared as rare and combined in a single category. In order to take into account the large number of tests performed in this study, we calculated for each gene the number of effective independent variables, Meff, by use of the SNP Spectral Decomposition approach
All analysis were performed using STATGRAPHICS
SNP-SNP interactions were tested using nonparametric Multifactor Dimensionality Reduction (MDR,
The genotype distributions at all loci were in HWE with non-significant chi square values (p>0.05) (
The distribution of the genotypes and their odds ratios (ORs) for association with longevity are shown in
To take into account multiple testing, we calculated for each region the number of effective independent variables (Meff). The Meff values for the regions on chromosome 5, chromosome 7 and chromosome 12 were 2, 11 and 8, respectively. The experiment-wise significance threshold was therefore set at 0.05/(2+11+8) = 0.0024. After correction for multiple testing, only the carriers of the G allele of rs978739 variation showed a statistically significant association.
Haplotype analysis was performed for each LD block in the study. None of the haplotypes showed a study-wise statistically significant association with longevity. However, the haplotype (rs1357949–rs6466849–rs860170–rs978739: T_A_A_G) of the
In the present study, we have investigated possible associations between longevity and 41 SNPs in 20 candidate genes involved in bitter taste perception. Our intensive SNP tagging approach along with the analyses of haplotypes provides a close to exhaustive analysis of the possible associations of longevity with the known common polymorphic variants at these bitter taste receptor loci.
We found that five polymorphisms were associated with longevity: three in the
The
Polymorphic variants in TAS2R16 confer differential response
These observations point to a role of variation in the TAS2R16 receptor in recognizing and therefore modulating the effect of both beneficial and harmful molecules with which the organism interacts during life. It is possible that the fine tuning of the receptor function due to the genetic polymorphisms along with the environment may modulate how many beneficial and how many harmful compounds are recognized by the receptor throughout the life span and that this could, in the long term, modify the chances to reach very old ages. However there is also another possible, even though highly speculative, explanation of the involvement of TAS2R16 genetic variability in healthy aging. Numerous recent reports investigated non-gustatory actions of taste receptors. They have been shown to be expressed in a plethora of tissues such as the respiratory system where they affect respiratory functions in response to noxious stimuli
(DOC)
(DOCX)
(DOCX)
(DOCX)
(DOCX)
(DOCX)
(DOCX)
(DOCX)
(DOCX)
(DOCX)
(DOCX)
We would like to thank Prof. Dennis Drayna for his precious help and support.