Genetic analysis of TOR complex gene variation with human longevity: a nested case-control study of American men of Japanese ancestry

Role of Raptor Gene Variants in Hypertension: Influence on Blood Pressure Independent of Salt Intake in White Population

BACKGROUND

The mTOR (mechanistic target of rapamycin) is an essential regulator of fundamental biological processes. mTOR forms 2 distinct complexes, mTORC1 (mTOR complex 1) when it binds with RAPTOR (Regulatory-associated Protein of mTOR) and mTORC2 (mTOR complex 2) when it associates with RICTOR (Rapamycin-insesitive companion of mTOR). Due to the previous link between the mTOR pathway, aldosterone, and blood pressure (BP), we anticipated that variants in the mTOR complex might be associated with salt-sensitive BP.

METHODS

BP and other parameters were assessed after a one-week liberal Na+ (200 mmol/d) and a one-week restricted Na+ (10 mmol/d) diet in 608 White subjects from the Hypertensive Pathotype cohort, single-nucleotide variants in MTOR, RPTOR, and RICTOR genes were obtained for candidate genes analyses.

RESULTS

The analysis revealed a significant association between a single nucleotide variants within the RPTOR gene and BP. Individuals carrying the RPTOR rs9901846 homozygous risk allele (AA) and heterozygous risk allele (GA) exhibited a 5 mm Hg increase in systolic BP on a liberal diet compared with nonrisk allele individuals (GG), but only in women. This single nucleotide variants effect was more pronounced on the restricted diet and present in both sexes, with AA carriers having a 9 mm Hg increase and GA carriers having a 5 mm Hg increase in systolic BP compared with GG. Interestingly, there were no significant associations between MTOR or RICTOR gene variants and BP.

CONCLUSIONS

The RPTOR gene variation is associated with elevated BP in White participants, regardless of salt intake, specifically in females.

DNA methylation in genes of longevity-regulating pathways: association with obesity and metabolic complications

Aging is the main risk factor for most chronic diseases. Epigenetic mechanisms, such as DNA methylation (DNAm) plays a pivotal role in the regulation of physiological responses that can vary along lifespan. The aim of this research was to analyze the association between leukocyte DNAm in genes involved in longevity and the occurrence of obesity and related metabolic alterations in an adult population. Subjects from the MENA cohort (n=474) were categorized according to age (<45 vs 45>) and the presence of metabolic alterations: increased waist circumference, hypercholesterolemia, insulin resistance, and metabolic syndrome. The methylation levels of 58 CpG sites located at genes involved in longevity-regulating pathways were strongly correlated (FDR-adjusted< 0.0001) with BMI. Fifteen of them were differentially methylated (p<0.05) between younger and older subjects that exhibited at least one metabolic alteration. Six of these CpG sites, located at MTOR (cg08862778), ULK1 (cg07199894), ADCY6 (cg11658986), IGF1R (cg01284192), CREB5 (cg11301281), and RELA (cg08128650), were common to the metabolic traits, and CREB5, RELA, and ULK1 were statistically associated with age. In summary, leukocyte DNAm levels of several CpG sites located at genes involved in longevity-regulating pathways were associated with obesity and metabolic syndrome traits, suggesting a role of DNAm in aging-related metabolic alterations.

Analysis of Polymorphisms in 59 Potential Candidate Genes for Association With Human Longevity

Longevity is a polygenic trait in which genetic predisposition is particularly important. We hypothesized that among genes differentially expressed in response to caloric restriction, several may be candidate longevity genes. We tested 459 single-nucleotide polymorphisms (SNPs) in 47 genes differentially expressed in calorically restricted mice and 12 other genes for association with longevity. Subjects were American men of Japanese ancestry, 440 aged ≥95 years and 374 with an average life span. Based on a dominant model of inheritance, an association with longevity at the p < .05 level was seen for SNPs in 13 of the genes. Testing by all possible models increased the number of genes to 18. After correction for multiple testing, four genes retained significance, namely, MAP3K5 (p = .00004), SIRT7 (p = .00004), SIRT5 (p = .0007), and PIK3R1 (p = .01). In a dominant model, association with longevity was seen for multiple adjacent SNPs within two of these genes (MAP3K5 and PIK3R1), as well as in FLT1, consistent with linkage disequilibrium with a causative variant in the vicinity of each respective SNP set. MAP3K5 and FLT1 haplotypes were associated with longevity. In conclusion, the present study implicates variation in MAP3K5, FLT1, PIK3R1, SIRT7, and SIRT5 in human longevity.

Genetic background, epigenetic factors and dietary interventions which influence human longevity

Longevity is mainly conditioned by genetic, epigenetic and environmental factors. Different genetic modifications seem to be positively associated to longevity, including SNPs in SIRT1, APOE, FOXO3A, ACE, ATM, NOS1 and NOS2 gene. Epigenetic changes as DNA hyper- and hypo-methylation influence significantly human longevity by activating/deactivating different genes involved in physiological mechanisms. Several studies have confirmed that centenarians have a lower DNA methylation content compared to young subjects, which showed more homogeneously methylated DNA region. Also the up-regulation of miR-21 seems to be more associated with longevity in different populations of long-lived subjects, suggesting its role as potential epigenetic biomarkers. A non-pharmacological treatment that seems to contrast age-related diseases and promote longevity is represented by dietary intervention. It has been evaluated the effects of dietary restriction of both single nutrients or total calories to extend lifespan. However, in daily practice it is very difficult to guarantee adherence/compliance of the subjects to dietary restriction and at the same time avoid dangerous nutritional deficiencies. As consequence, the attention has focused on a variety of substances both drugs and natural compounds able to mime the beneficial effects of caloric restriction, including resveratrol, quercetin, rapamycin, metformin and 2-deoxy-D-glucose.

Genetic and epigenetic regulation of human aging and longevity

Here we summarize the latest data on genetic and epigenetic contributions to human aging and longevity. Whereas environmental and lifestyle factors are important at younger ages, the contribution of genetics appears more important in reaching extreme old age. Genome-wide studies have implicated ~57 gene loci in lifespan. Epigenomic changes during aging profoundly affect cellular function and stress resistance. Dysregulation of transcriptional and chromatin networks is likely a crucial component of aging. Large-scale bioinformatic analyses have revealed involvement of numerous interaction networks. As the young well-differentiated cell replicates into eventual senescence there is drift in the highly regulated chromatin marks towards an entropic middle-ground between repressed and active, such that genes that were previously inactive "leak". There is a breakdown in chromatin connectivity such that topologically associated domains and their insulators weaken, and well-defined blocks of constitutive heterochromatin give way to generalized, senescence-associated heterochromatin, foci. Together, these phenomena contribute to aging.

Genetic cartography of longevity in humans and mice: Current landscape and horizons

Aging is a complex and highly variable process. Heritability of longevity among humans and other species is low, and this finding has given rise to the idea that it may be futile to search for DNA variants that modulate aging. We argue that the problem in mapping longevity genes is mainly one of low power and the genetic and environmental complexity of aging. In this review we highlight progress made in mapping genes and molecular networks associated with longevity, paying special attention to work in mice and humans. We summarize 40 years of linkage studies using murine cohorts and 15 years of studies in human populations that have exploited candidate gene and genome-wide association methods. A small but growing number of gene variants contribute to known longevity mechanisms, but a much larger set have unknown functions. We outline these and other challenges and suggest some possible solutions, including more intense collaboration between research communities that use model organisms and human cohorts. Once hundreds of gene variants have been linked to differences in longevity in mammals, it will become feasible to systematically explore gene-by-environmental interactions, dissect mechanisms with more assurance, and evaluate the roles of epistasis and epigenetics in aging. A deeper understanding of complex networks-genetic, cellular, physiological, and social-should position us well to improve healthspan.

Exome-wide Association Study Identifies CLEC3B Missense Variant p.S106G as Being Associated With Extreme Longevity in East Asian Populations

Life span is a complex trait regulated by multiple genetic and environmental factors; however, the genetic determinants of extreme longevity have been largely unknown. To identify the functional coding variants associated with extreme longevity, we performed an exome-wide association study (EWAS) on a Japanese population by using an Illumina HumanExome Beadchip and a focused replication study on a Chinese population. The EWAS on two independent Japanese cohorts consisting of 530 nonagenarians/centenarians demonstrated that the G allele of CLEC3B missense variant p.S106G was associated with extreme longevity at the exome-wide level of significance (p = 2.33×10^–7, odds ratio [OR] = 1.50). The CLEC3B gene encodes tetranectin, a protein implicated in the mineralization process in osteogenesis as well as in the prognosis and metastasis of cancer. The replication study consisting of 448 Chinese nonagenarians/centenarians showed that the G allele of CLEC3B p.S106G was also associated with extreme longevity (p = .027, OR = 1.51), and the p value of this variant reached 1.87×10^–8 in the meta-analysis of Japanese and Chinese populations. In conclusion, the present study identified the CLEC3B p.S106G as a novel longevity-associated variant, raising the novel hypothesis that tetranectin, encoded by CLEC3B, plays a role in human longevity and aging.

Association of Polymorphisms in Connective Tissue Growth Factor and Epidermal Growth Factor Receptor Genes With Human Longevity

Growth pathways play key roles in longevity. The present study tested single-nucleotide polymorphisms (SNPs) in the connective tissue growth factor gene (CTGF) and the epidermal growth factor receptor gene (EGFR) for association with longevity. Comparison of allele and genotype frequencies of 12 CTGF SNPs and 41 EGFR SNPs between 440 American men of Japanese ancestry aged ≥95 years and 374 men of average life span revealed association with longevity at the p < .05 level for 2 SNPs in CTGF and 7 in EGFR. Two in CTGF and two in EGFR remained significant after Bonferroni correction. The SNPs of both CTGF and EGFR were in a haplotype block in each respective gene. Haplotype analysis confirmed the suggestive association found by χ2 analysis. We noted an excess of heterozygotes among the longevity cases, consistent with heterozygote advantage in living to extreme old age. No associations of the most significant SNPs were observed in whites or Koreans. In conclusion, the present findings indicate that genetic variation in CTGF and EGFR may contribute to the attainment of extreme old age in Japanese. More research is needed to confirm that genetic variation in CTGF and EGFR contributes to the attainment of extreme old age across human populations.

The impact of nutrients on the aging rate: A complex interaction of demographic, environmental and genetic factors

Nutrition has a strong influence on the health status of the elderly, with many dietary components associated to either an increased risk of disease or to an improvement of the quality of life and to a delay of age-related pathologies. A direct effect of a reduced caloric intake on the delay of aging phenotypes is documented in several organisms. The role of nutrients in the regulation of human lifespan is not easy to disentangle, influenced by a complex interaction of nutrition with environmental and genetic factors. The individual genetic background is fundamental for mediating the effects of nutritional components on aging. Classical genetic factors able to influence nutrient metabolism are considered those belonging to insulin/insulin growth factor (INS/IGF-1) signaling, TOR signaling and Sirtuins, but also genes involved in inflammatory/immune response and antioxidant activity can have a major role. Considering the worldwide increasing interest in nutrition to prevent age related diseases and achieve a healthy aging, in this review we will discuss this complex interaction, in the light of metabolic changes occurring with aging, with the aim of shedding a light on the enormous complexity of the metabolic scenario underlying longevity phenotype.

How the effects of aging and stresses of life are integrated in mortality rates: insights for genetic studies of human health and longevity

Increasing proportions of elderly individuals in developed countries combined with substantial increases in related medical expenditures make the improvement of the health of the elderly a high priority today. If the process of aging by individuals is a major cause of age related health declines then postponing aging could be an efficient strategy for improving the health of the elderly. Implementing this strategy requires a better understanding of genetic and non-genetic connections among aging, health, and longevity. We review progress and problems in research areas whose development may contribute to analyses of such connections. These include genetic studies of human aging and longevity, the heterogeneity of populations with respect to their susceptibility to disease and death, forces that shape age patterns of human mortality, secular trends in mortality decline, and integrative mortality modeling using longitudinal data. The dynamic involvement of genetic factors in (i) morbidity/mortality risks, (ii) responses to stresses of life, (iii) multi-morbidities of many elderly individuals, (iv) trade-offs for diseases, (v) genetic heterogeneity, and (vi) other relevant aging-related health declines, underscores the need for a comprehensive, integrated approach to analyze the genetic connections for all of the above aspects of aging-related changes. The dynamic relationships among aging, health, and longevity traits would be better understood if one linked several research fields within one conceptual framework that allowed for efficient analyses of available longitudinal data using the wealth of available knowledge about aging, health, and longevity already accumulated in the research field.

Longevity GWAS Using the Drosophila Genetic Reference Panel

We used 197 Drosophila melanogaster Genetic Reference Panel (DGRP) lines to perform a genome-wide association analysis for virgin female lifespan, using ~2M common single nucleotide polymorphisms (SNPs). We found considerable genetic variation in lifespan in the DGRP, with a broad-sense heritability of 0.413. There was little power to detect signals at a genome-wide level in single-SNP and gene-based analyses. Polygenic score analysis revealed that a small proportion of the variation in lifespan (~4.7%) was explicable in terms of additive effects of common SNPs (≥2% minor allele frequency). However, several of the top associated genes are involved in the processes previously shown to impact ageing (eg, carbohydrate-related metabolism, regulation of cell death, proteolysis). Other top-ranked genes are of unknown function and provide promising candidates for experimental examination. Genes in the target of rapamycin pathway (TOR; Chrb, slif, mipp2, dredd, RpS9, dm) contributed to the significant enrichment of this pathway among the top-ranked 100 genes (p = 4.79×10(-06)). Gene Ontology analysis suggested that genes involved in carbohydrate metabolism are important for lifespan; including the InterPro term DUF227, which has been previously associated with lifespan determination. This analysis suggests that our understanding of the genetic basis of natural variation in lifespan from induced mutations is incomplete.

Genetic variation in the raptor gene is associated with overweight but not hypertension in American men of Japanese ancestry

BACKGROUND

The mechanistic target of rapamycin (mTOR) pathway is pivotal for cell growth. Regulatory associated protein of mTOR complex I (Raptor) is a unique component of this pro-growth complex. The present study tested whether variation across the raptor gene (RPTOR) is associated with overweight and hypertension.

METHODS

We tested 61 common (allele frequency ≥ 0.1) tagging single nucleotide polymorphisms (SNPs) that captured most of the genetic variation across RPTOR in 374 subjects of normal lifespan and 439 subjects with a lifespan exceeding 95 years for association with overweight/obesity, essential hypertension, and isolated systolic hypertension. Subjects were drawn from the Honolulu Heart Program, a homogeneous population of American men of Japanese ancestry, well characterized for phenotypes relevant to conditions of aging. Hypertension status was ascertained when subjects were 45-68 years old. Statistical evaluation involved contingency table analysis, logistic regression, and the powerful method of recursive partitioning.

RESULTS

After analysis of RPTOR genotypes by each statistical approach, we found no significant association between genetic variation in RPTOR and either essential hypertension or isolated systolic hypertension. Models generated by recursive partitioning analysis showed that RPTOR SNPs significantly enhanced the ability of the model to accurately assign individuals to either the overweight/obese or the non-overweight/obese groups (P = 0.008 by 1-tailed Z test).

CONCLUSION

Common genetic variation in RPTOR is associated with overweight/obesity but does not discernibly contribute to either essential hypertension or isolated systolic hypertension in the population studied.

Effect of age on basal muscle protein synthesis and mTORC1 signaling in a large cohort of young and older men and women

The rate of muscle loss with aging is higher in men than women. However, women have smaller muscles throughout the adult life. Protein content is a major determinant of skeletal muscle size. This study was designed to determine if age and sex differentially impact basal muscle protein synthesis and mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling. We performed a secondary data analysis on a cohort of 215 healthy, non-obese (BMI<30kg·m(-2)) young (18-40y; 74 men, 52 women) and older (60-87y; 57 men, 32 women) adults. The database contained information on physical characteristics, basal muscle protein fractional synthetic rate (FSR; n=215; stable isotope methodology) and mTORC1 signaling (n=125, Western blotting). FSR and mTORC1 signaling were measured at rest and after an overnight fast. mTORC1 and S6K1 phosphorylation were higher (p<0.05) in older subjects with no sex differences. However, there were no age or sex differences or interaction for muscle FSR (p>0.05). Body mass index, fat free mass, or body fat was not a significant covariate and did not influence the results. We conclude that age and sex do not influence basal muscle protein synthesis. However, basal mTORC1 hyperphosphorylation in the elderly may contribute to insulin resistance and the age-related anabolic resistance of skeletal muscle protein metabolism to nutrition and exercise.