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.

Mitochondrial DNA haplogroups and APOE4 allele are non-independent variables in sporadic Alzheimer's disease.

Allele epsilon4 of the nuclear APOE gene is a leading genetic risk factor for sporadic Alzheimer's disease (AD). Moreover, an allele-specific effect of APOE isoforms on neuronal cell oxidative death is known. Because of the role of the mitochondrial genome (mtDNA) in oxidative phosphorylation and oxidative stress, an interaction between APOE polymorphism and mtDNA inherited variability in the genetic susceptibility to sporadic AD can be hypothesized. We have explored this hypothesis by analyzing mtDNA germline variants (mtDNA haplogroups) in a sample of AD patients (213 subjects) genotyped for APOE and classified as APOE epsilon4 carriers and non-carriers. We found that the frequency distribution of mtDNA haplogroups is different between epsilon4 carriers and non-carriers (P=0.018), thus showing non-random association between APOE and mtDNA polymorphisms. The same analysis, carried out in two samples of healthy subjects (179 age-matched and 210 individuals aged more than 100 years), showed independence between epsilon4 allele and mtDNA haplogroups. Therefore, the APOE/mtDNA interaction is restricted to AD and may affect susceptibility to the disease. In particular, some mtDNA haplogroups (K and U) seem to neutralize the harmful effect of the APOE epsilon4 allele, lowering the epsilon4 odds ratio from statistically significant to non-significant values.

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.

Inherited variability of the mitochondrial genome and successful aging in humans.

Increasing data indicate that polymorphic variants of nuclear loci can affect rate and quality of aging in humans. However, the mitochondrial genome is another good candidate, because of the central role played by mitochondrial genes in oxidative phosphorylation (OXPHOS) and cell metabolism. A characteristic of the mitochondrial genome (mtDNA) is the high level of interindividual variability that ensues from high mutation rate and unilinear inheritance. Related groups of germline/inherited mtDNA polymorphisms (haplogroups) have been identified as continent-specific sets of stable/ancient/associated restriction fragment length polymorphisms in the mtDNA coding region, representing markers capable of exactly depicting the mtDNA pool of a specific population. The hypothesis can be put forward that mtDNA variants included in a haplogroup may have similar OXPHOS efficiency and therefore act as genetic factors predisposing to individual successful or unsuccessful aging. This idea can be explored by sampling groups of individuals of different ages from a well-defined population and comparing the pools of mtDNA haplogroups between samples. The results obtained by screening mtDNA haplogroups in about 800 Italians of different ages, including more than 200 centenarians, agree with the hypothesis that the inherited variability of the mitochondrial genome is associated with the chance of successful aging and longevity in humans.