Mitochondrial polymorphisms are associated both with increased and decreased longevity

Mitochondrial haplogroups and lifespan in a population isolate

Physiochemical differences between mitochondrial DNA (mtDNA) haplogroups that favor oxidative phosphorylation efficiency during periods of caloric limitation can lead to lifespan lengthening when food calories are less abundant. For example, prior work demonstrated that older female haplogroup H carriers had modestly lengthened lifespans beyond 60 years during the Great Depression, a time of caloric limitation in North America. The objective of the current study is to replicate the prior findings in an independent cohort that includes both sexes and younger ages. By determining and cross-referencing the mtDNA genotypes of a culturally homogeneous population isolate to the lifespans of their ancestors, we found that between 1930 and 1939, haplogroup H compared to haplogroup U carriers had a modestly lengthened lifespan (3 years) past 60 years (hazard ratio 2.35; CI₉₅ 1.41-3.90; p-value: 0.0029). The lifespan-lengthening association was apparent in both sexes but only after the age of 60. Our results provide further support for the role of mitochondrial genetics in lengthening human lifespan.

A mitochondrial haplogroup is associated with decreased longevity in a historic new world population

Interest in mitochondrial influences on extended longevity has been mounting, as evidenced by a growing literature. Such work has demonstrated that some haplogroups are associated with increased longevity and that such associations are population specific. Most previous work, however, suffers from the methodological shortcoming that long-lived individuals are compared with "controls" who are born decades after the aged individuals. The only true controls of the elderly are people who were born in the same time period but who did not have extended longevity. Here we present results of a study in which we are able to test whether longevity is independent of haplogroup type, controlling for time period, by using mtDNA genealogies. Since mtDNA does not recombine, we know the mtDNA haplogroup of the maternal ancestors of our living participants. Thus, we can compare the haplogroup of people with and without extended longevity who were born during the same time period. Our sample is an admixed New World population that has haplogroups of Amerindian, European, and African origin. We show that women who belong to Amerindian, European, and African haplogroups do not differ in their mean longevity. Therefore, to the extent that ethnicity was tied in this population to mtDNA make-up, such ethnicity did not impact longevity. In support of previous suggestions that the link between mtDNA haplogroups and longevity is specific to the population being studied, we found an association between haplogroup C and decreased longevity. Interestingly, the lifetime reproductive success and the number of grandchildren produced via a daughter of women with haplogroup C are not reduced. Our diachronic approach to the mtDNA and longevity link allowed us to determine that the same haplogroup is associated with decreased longevity during different time periods and allowed us to compare the haplogroup of short- and long-lived individuals born during the same time period. By controlling for time period, we minimized the effect of different cultural and ecological environments on differential longevity. With our diachronic approach, we investigated the mtDNA and longevity link with a biocultural perspective.

Mitochondrial Variations in Non-Small Cell Lung Cancer (NSCLC) Survival

Mutations in the mtDNA genome have long been suspected to play an important role in cancer. Although most cancer cells harbor mtDNA mutations, the question of whether such mutations are associated with clinical prognosis of lung cancer remains unclear. We resequenced the entire mitochondrial genomes of tumor tissue from a population of 250 Korean patients with non-small cell lung cancer (NSCLC). Our analysis revealed that the haplogroup (D/D4) was associated with worse overall survival (OS) of early-stage NSCLC [adjusted hazard ratio (AHR), 1.95; 95% CI, 1.14–3.33; P_trend = 0.03]. By comparing the mtDNA variations between NSCLC tissues and matched blood samples, we found that haplogroups M/N and/or D/D4 were hotspots for somatic mutations, suggesting a more complicated mechanism of mtDNA somatic mutations other than the commonly accepted mechanism of sequential accumulation of mtDNA mutations.

Aging: A mitochondrial DNA perspective, critical analysis and an update

The mitochondrial theory of aging, a mainstream theory of aging which once included accumulation of mitochondrial DNA (mtDNA) damage by reactive oxygen species (ROS) as its cornerstone, has been increasingly losing ground and is undergoing extensive revision due to its inability to explain a growing body of emerging data. Concurrently, the notion of the central role for mtDNA in the aging process is being met with increased skepticism. Our progress in understanding the processes of mtDNA maintenance, repair, damage, and degradation in response to damage has largely refuted the view of mtDNA as being particularly susceptible to ROS-mediated mutagenesis due to its lack of “protective” histones and reduced complement of available DNA repair pathways. Recent research on mitochondrial ROS production has led to the appreciation that mitochondria, even in vitro, produce much less ROS than previously thought, automatically leading to a decreased expectation of physiologically achievable levels of mtDNA damage. New evidence suggests that both experimentally induced oxidative stress and radiation therapy result in very low levels of mtDNA mutagenesis. Recent advances provide evidence against the existence of the “vicious” cycle of mtDNA damage and ROS production. Meta-studies reveal no longevity benefit of increased antioxidant defenses. Simultaneously, exciting new observations from both comparative biology and experimental systems indicate that increased ROS production and oxidative damage to cellular macromolecules, including mtDNA, can be associated with extended longevity. A novel paradigm suggests that increased ROS production in aging may be the result of adaptive signaling rather than a detrimental byproduct of normal respiration that drives aging. Here, we review issues pertaining to the role of mtDNA in aging.

mtDNA mutations in human aging and longevity: controversies and new perspectives opened by high-throughput technologies

The last 30 years of research greatly contributed to shed light on the role of mitochondrial DNA (mtDNA) variability in aging, although contrasting results have been reported, mainly due to bias regarding the population size and stratification, and to the use of analysis methods (haplogroup classification) that resulted to be not sufficiently adequate to grasp the complexity of the phenomenon. A 5-years European study (the GEHA EU project) collected and analyzed data on mtDNA variability on an unprecedented number of long-living subjects (enriched for longevity genes) and a comparable number of controls (matched for gender and ethnicity) in Europe. This very large study allowed a reappraisal of the role of both the inherited and the somatic mtDNA variability in aging, as an association with longevity emerged only when mtDNA variants in OXPHOS complexes co-occurred. Moreover, the availability of data from both nuclear and mitochondrial genomes on a large number of subjects paves the way for an evaluation at a very large scale of the epistatic interactions at a higher level of complexity. This scenario is expected to be even more clarified in the next future with the use of next generation sequencing (NGS) techniques, which are becoming applicable to evaluate mtDNA variability and, then, new mathematical/bioinformatic analysis methods are urgently needed. Recent advances of association studies on age-related diseases and mtDNA variability will also be discussed in this review, taking into account the bias hidden by population stratification. Finally, very recent findings in terms of mtDNA heteroplasmy (i.e. the coexistence of wild type and mutated copies of mtDNA) and aging as well as mitochondrial epigenetic mechanisms will also be discussed.

Genetics of healthy aging and longevity

Longevity and healthy aging are among the most complex phenotypes studied to date. The heritability of age at death in adulthood is approximately 25 %. Studies of exceptionally long-lived individuals show that heritability is greatest at the oldest ages. Linkage studies of exceptionally long-lived families now support a longevity locus on chromosome 3; other putative longevity loci differ between studies. Candidate gene studies have identified variants at APOE and FOXO3A associated with longevity; other genes show inconsistent results. Genome-wide association scans (GWAS) of centenarians vs. younger controls reveal only APOE as achieving genome-wide significance (GWS); however, analyses of combinations of SNPs or genes represented among associations that do not reach GWS have identified pathways and signatures that converge upon genes and biological processes related to aging. The impact of these SNPs, which may exert joint effects, may be obscured by gene-environment interactions or inter-ethnic differences. GWAS and whole genome sequencing data both show that the risk alleles defined by GWAS of common complex diseases are, perhaps surprisingly, found in long-lived individuals, who may tolerate them by means of protective genetic factors. Such protective factors may ‘buffer’ the effects of specific risk alleles. Rare alleles are also likely to contribute to healthy aging and longevity. Epigenetics is quickly emerging as a critical aspect of aging and longevity. Centenarians delay age-related methylation changes, and they can pass this methylation preservation ability on to their offspring. Non-genetic factors, particularly lifestyle, clearly affect the development of age-related diseases and affect health and lifespan in the general population. To fully understand the desirable phenotypes of healthy aging and longevity, it will be necessary to examine whole genome data from large numbers of healthy long-lived individuals to look simultaneously at both common and rare alleles, with impeccable control for population stratification and consideration of non-genetic factors such as environment.

Mitochondrial DNA polymorphisms are associated with the longevity in the Guangxi Bama population of China

Human longevity is an interesting and complicated subject, with many associated variations, geographic and genetic, including some known mitochondrial variations. The population of the Bama County of Guangxi Province of China is well known for its longevity and serves as a good model for studying a potential molecular mechanism. In this study, a full sequence analysis of mitochondrial DNA (mtDNA) has been done in ten Bama centenarians using direct sequencing. Polymorphisms of the displacement loop (D-loop) region of mtDNA and several serum parameters were analyzed for a total of 313 Bama individuals with ages between 10 and 110 years. The results showed that there were seven mitochondrial variations, A73G, A263G, A2076G, A8860G, G11719A, C14766T, and A15326G, and four haplogroups, M(*), F1, D* and D(4) in 10 Bama centenarians. In the D-loop region of mtDNA, the mt146T occurred at a significantly lower frequency in those is the older age group (90-110 years) than in the middle (80-89 years) and in the younger (10-79 years) groups (P < 0.05). The mt146T also had lower systolic blood pressure and serum markers such as total cholesterol, triglyceride and low density lipoprotein than did mt146C in the older age group (P < 0.05). No significant differences were observed between the mt146C and the mt146T individuals in the middle and the younger groups (P > 0.05). The mt5178C/A polymorphisms did not show any significant differences among the three age-groups (P > 0.05), but different nationalities in the Bama County did show a significant difference in the mt5178C/A polymorphisms (P < 0.05). These results suggest that the mt146T/C polymorphisms in Guangxi Bama individuals may partly account for the Bama longevity whereas the mt5178C/A polymorphisms are strongly associated with the nationalities in the Guangxi Bama population.

High mitochondrial mutation rates estimated from deep-rooting Costa Rican pedigrees

Estimates of mutation rates for the noncoding hypervariable Region I (HVR-I) of mitochondrial DNA vary widely, depending on whether they are inferred from phylogenies (assuming that molecular evolution is clock-like) or directly from pedigrees. All pedigree-based studies so far were conducted on populations of European origin. In this article, we analyzed 19 deep-rooting pedigrees in a population of mixed origin in Costa Rica. We calculated two estimates of the HVR-I mutation rate, one considering all apparent mutations, and one disregarding changes at sites known to be mutational hot spots and eliminating genealogy branches which might be suspected to include errors, or unrecognized adoptions along the female lines. At the end of this procedure, we still observed a mutation rate equal to 1.24 × 10(-6) , per site per year, i.e., at least threefold as high as estimates derived from phylogenies. Our results confirm that mutation rates observed in pedigrees are much higher than estimated assuming a neutral model of long-term HVRI evolution. We argue that until the cause of these discrepancies will be fully understood, both lower estimates (i.e., those derived from phylogenetic comparisons) and higher, direct estimates such as those obtained in this study, should be considered when modeling evolutionary and demographic processes.

Association of mtDNA haplogroup F with healthy longevity in the female Chuang population, China

Human longevity is a complex heritable genetic trait. Based on substantial evidence from model organisms, it is clear that mitochondria play a pivotal role in aging and lifespan. However, the effects that mitochondrial genome variations have upon longevity and longevity-related phenotypes in Chuang people in China have yet to be established. By genotyping 15 variants for 10 haplogroups in 738 Chuang subjects, including 367 long-lived individuals and 371 controls, we found that haplogroup F was significantly associated with longevity in females of Zhuang population of China (p=0.003, OR: 2.01, 95%CI: 1.263-3.197). Additionally, haplogroup F was related to higher HDL levels (p<0.05) in long-lived individuals. Further analysis suggests that the non-synonymous variant m.13928G>C in haplogroup F was also associated with longevity in female Zhuang Chinese which might account for the beneficial effect of F.

Mitochondria-wide association study of common variants in osteoporosis

Mitochondrial DNA (mtDNA) variants are involved in the pathogenesis of human complex diseases, especially for age-related disorders, including osteoporosis. However, the role of mtDNA variants in osteoporosis is largely unknown. In this study, we performed a mitochondria-wide association study for osteoporosis in a large sample of 2286 unrelated Caucasian subjects. A total of 445 mtSNPs were genotyped and 72 mtSNPs survived the quality control. We first examined association between mtSNPs and bone mineral density (BMD), and identified that an mtSNP, mt4823 within the ND2 gene, was strongly associated with hip BMD (P= 2.05 × 10(-4)), even after Bonferroni correction. The C allele of mt4823 was associated with reduced hip BMD and the effect size (β) was ∼0.044. Another SNP mt15885 within the MT-CYB gene was associated both with spine (P= 1.66 × 10(-3)) and hip BMD (P= 0.023). The T allele of mt15885 had a protective effect on spine (β= 0.064) and hip BMD (β= 0.038). Next, we classified subjects into the nine common European haplogroups and conducted association analyses. Subjects classified as haplogroup X had significantly lower hip BMD values than others (P= 0.040). Our results highlighted the importance of mtDNA variants in osteoporosis.

May "mitochondrial eve" and mitochondrial haplogroups play a role in neurodegeneration and Alzheimer's disease?

Mitochondria, the powerhouse of the cell, play a critical role in several metabolic processes and apoptotic pathways. Multiple evidences suggest that mitochondria may be crucial in ageing-related neurodegenerative diseases. Moreover, mitochondrial haplogroups have been linked to multiple area of medicine, from normal ageing to diseases, including neurodegeneration. Polymorphisms within the mitochondrial genome might lead to impaired energy generation and to increased amount of reactive oxygen species, having either susceptibility or protective role in several diseases. Here, we highlight the role of the mitochondrial haplogroups in the pathogenetic cascade leading to diseases, with special attention to Alzheimer's disease.

Is there more to aging than mitochondrial DNA and reactive oxygen species?

With the aging of the population, we are seeing a global increase in the prevalence of age-related disorders, especially in developed countries. Chronic diseases disproportionately affect the older segment of the population, contributing to disability, a diminished quality of life and an increase in healthcare costs. Increased life expectancy reflects the success of contemporary medicine, which must now respond to the challenges created by this achievement, including the growing burden of chronic illnesses, injuries and disabilities. A well-developed theoretical framework is required to understand the molecular basis of aging. Such a framework is a prerequisite for the development of clinical interventions that will constitute an efficient response to the challenge of age-related health issues. This review critically analyzes the experimental evidence that supports and refutes the Free Radical/Mitochondrial Theory of Aging, which has dominated the field of aging research for almost half a century.