The influences on human longevity by HUMTHO1.STR polymorphism (Tyrosine Hydroxylase gene). A relative risk approach.

A new method based on the recently developed relative risk approach is introduced, and applied to data from Italian centenarian study (965 subjects aged from 13 to 109 years old) for investigating influences on longevity by Tyrosine Hydroxylase (TH) gene variability. The strategic parameterization enables the model to disentangle the various ways by which HUMTHO1.STR alleles (alleles 6, 7, 8, 9, 10*, 10, as defined according to the number of repeats) may contribute in reducing or increasing the hazard of death with different patterns of influences. Among all the alleles, we have found that allele 10* (10 imperfect repeats) shows a remarkable dominant and beneficial effect that reduces the log hazard of death in an additive manner. The results confirm that HUMTHO1.STR polymorphism is involved in the modulation of human longevity.

Sex-specific longevity associations defined by Tyrosine Hydroxylase-Insulin-Insulin Growth Factor 2 haplotypes on the 11p15.5 chromosomal region.

By studies in centenarians, it was recently found that an STR marker of the Tyrosine Hydroxylase (TH, 11p15.5) gene is associated with human longevity. The aim of the present study was to continue the exploration of the 11p15.5 chromosomal region in human longevity by analyzing two additional RFLP markers, which lie in the Insulin (INS) and Insulin Growth Factor 2 (IGF2) genes. Both the genes, which are localized downstream TH, are indeed good candidates in longevity, as ascertained on the basis of laboratory studies in experimental models. Neither INS nor IGF2 markers did reveal association with longevity. Nevertheless, linkage disequilibrium analyses showed sex-specific longevity associations defined by both TH-INS and TH-IGF2 haplotypes. On the whole, the results reinforce the involvement of the chromosomal region spanning from TH to IGF2 loci in controlling the longevity phenotype in humans.

Does a retrograde response in human aging and longevity exist?

The retrograde response (RR) is a compensatory mechanism by which mutant strains of yeast are able to cope with mitochondrial DNA (mtDNA) impairments by up-regulating the expression of the stress-responder nuclear genes and significantly increasing lifespan. Starting from the observation that both mtDNA variability and Tyrosine hydroxylase (THO, stress-responder gene) variability are correlated with human longevity, we asked ourselves whether mechanisms similar to RR may exist in humans. As a first investigative step we have analyzed the distribution of the mtDNA inherited variants (haplogroups) according to THO genotypes in three sample groups of increasing ages (20-49 years; 50-80 years; centenarians). We found that the mtDNA haplogroups and the THO genotypes are associated randomly in the first group, while in the second group, and particularly in the centenarians, a non-random association is observed between the mtDNA and nuclear DNA variability. Moreover, in centenarians the U haplogroup is over-represented (p=0.012) in subjects carrying the THO genotype unfavorable to longevity. On the whole these findings are in line with the hypothesis that longevity requires particular interactions between mtDNA and nuclear DNA and do not exclude the possibility that an RR has been maintained throughout evolution and it is present in higher organisms.

Variability of the SIRT3 gene, human silent information regulator Sir2 homologue, and survivorship in the elderly.

The human sirtuin 3 (SIRT3) gene encodes a putative mitochondrial NAD-dependent deacetylase (SIRT3) which belongs to the evolutionary conserved family of sirtuin 2 proteins. Studies in model organisms have demonstrated that SIR2 genes control lifespan, while no data are available regarding a possible role of SIRT3 in human longevity. By analysing the genotype-specific survival function relevant to the G477T marker of SIRT3, we found that in males the TT genotype increases (p=0.0272), while the GT genotype decreases (p=0.0391) survival in the elderly. Since SIRT3 lies in a chromosomal region (11p15.5) where four genes potentially associated with longevity are located (HRAS1, Insulin-like Growth Factor 2, Proinsulin, and Tyrosine Hydroxylase) we tested for linkage-disequilibrium between G477T alleles and alleles of the above genes. The disequilibrium was not significant in any case, thus suggesting that SIRT3 itself, or a gene strictly linked to SIRT3, may have a role in human longevity.

A cluster analysis to define human aging phenotypes.

The definition of a precise and consistent aging phenotype that allows to measure the physical and cognitive decline, as well as the increase of mortality hazard late in life, is a major problem for studies aimed at finding the genetic factors modulating rate and quality of human aging. In this frame, it seems promising the concept of frailty which tends to figure out the subjects who are more vulnerable and more prone to negative outcomes, such as death or hospitalization. Cognitive, functional and psychological measures turned out to be the most effective measures to define frailty, as they condense most of the frailty cycle that occurs in the elderly and is probably responsible of the aging related physical decline. We used MMSE, Hand Grip strength, and GDS as variable parameters in a hierarchical Cluster Analysis (CA) in order to recognise aging phenotypes. By using a sample of 65-85 years old subjects we identified three frailty phenotypes that were consistent from both geriatric and genetic perspectives. Therefore, the method we propose may provide unbiased phenotypes suitable for the identification of genetic variants affecting the quality of aging in this age range. The CA method was less effective in ultranonagenarians, probably due to the high prevalence of frail subjects in this age group that makes difficult to distinguish discrete phenotypes.

The study of APOA1, APOC3 and APOA4 variability in healthy ageing people reveals another paradox in the oldest old subjects.

The genes coding for apolipoprotein A1 (APOA1), apolipoprotein C3 (APOC3) and apolipoprotein A4 (APOA4) are tandemly organised within a short region on chromosome 11q23-q24. Polymorphisms of these genes have been extensively investigated in lipoprotein disorders and cardiovascular diseases, but poorly investigated in healthy ageing. The aim of this study was to describe possible modifications of the APOA1, APOC3, and APOA4 gene pool by cross-sectional studies carried out in a healthy ageing population whose ages ranged from 18 to 109 years (800 subjects, 327 males and 473 females, free of clinically manifested disease, and with emato-chemical parameters in the norm). APOA1-MspI-RFLP (-75 nt from the transcription starting site), APOC3-SstI-RFLP (3'UTR, 3238 nt), and APOA4-HincII-RFLP (Asp127/Ser127) were analysed according to age and sex. A significant age-related variation of the APOA1 gene pool was observed in males. An analysis of the allele average effect exerted by APOA1-MspI-RFLP A/P alleles (Absence/Presence of the restriction site) on lipidemic parameters in 46-80 year old males showed that allele A decreased, while allele P significantly increased, serum LDL-cholesterol. Unexpectedly, the P allele was over-represented in the group of the oldest old subjects, thus giving evidence of another "genetic paradox of centenarians".

The allele (A)(-110) in the promoter region of the HSP70-1 gene is unfavorable to longevity in women.

Heat shock proteins (HSPs) are crucial for maintenance of cell homeostasis and survival both during and after various stresses. The capability to cope with stress is believed to affect the chance of health and survival at organismal level. We have investigated whether the gene pool relevant to the (A/C)(-110) polymorphism in the promoter region of the HSP70-1 gene changes as the population ages and survival selection occurs. A total of 591 southern Italian subjects were enrolled in the study (263 males and 328 females; age range 18-109 years), free of clinically manifest diseases and with normal haemato-chemical parameters. A significant age-related decrease of the frequency of allele (A)(-110) was observed in females. The probability ratio of 0.403 (95% confidence interval [0.163, 0.910]) computed by considering female centenarians as cases and young women (18-49 years old) as controls showed that the (A)(-110) allele is unfavorable to longevity in females.

Replication studies in longevity: puzzling findings in Danish centenarians at the 3'APOB-VNTR locus.

In Danes we replicated the 3'APOB-VNTR gene/longevity association study previously carried out in Italians, by which the Small alleles (less than 35 repeats) had been identified as frailty alleles for longevity. In Danes, neither genotype nor allele frequencies differed between centenarians and 20-64-year-old subjects. However, when Danish and Italian data were compared, a significant difference (p = 0.0004) was found between the frequencies of Small alleles in youths, which disappeared in centenarians (p = 0.290). Furthermore, the demographic-genetic approach revealed in Danes a significant gene-sex interaction relevant to Long alleles (more than 37 repeats). The different findings in Denmark and Italy suggest that gene/longevity associations are population-specific, and heavily affected by the population-specific genetic and environmental history.