Lipoprotein genotype and conserved pathway for exceptional longevity in humans

Proteomic analysis of human very low-density lipoprotein by two-dimensional gel electrophoresis and MALDI-TOF/TOF

Biochemical studies of lipoproteins have shed light on their composition, highly contributing to the comprehension of their function. Due to the complexity of their structure, however, an in-depth structural analysis, in terms of components and PTMs, may still unravel important players in physiological and pathological processes of lipid metabolism. In this study, we performed a protein map of very low-density lipoprotein (VLDL) using a 2-DE MALDI-TOF/TOF proteomic approach. Several VLDL-associated apolipoproteins were identified, including five isoforms of apoE, three isoforms of apoC-IV, and one isoform each of apoC-III, apoM, apoA-I, and apoA-IV. Notably, we also identified seven isoforms of apoL-I and two isoforms of prenylcysteine lyase as new VLDL-associated proteins. Furthermore, we were able to identify PTM of apoE, which was found to be differently O-glycosylated at Thr212 residue, and PTM of apoL-I which we described, for the first time, to be phosphorylated at Ser296. While the physiological relevance of our finding remains to be assessed, we believe that our results will be useful as reference for future studies of VLDL structure in specific physiopathological conditions.

Longevity network: Construction and implications

The vast majority of studies on longevity have focused on individual genes/proteins, without adequately addressing the possible role of interactions between them. This study is the first attempt towards constructing a "longevity network" via analysis of human protein-protein interactions (PPIs). For this purpose, we (i) compiled a complete list of established longevity genes from different species, including those that most probably affect the longevity in humans, (ii) defined the human orthologs of the longevity genes, and (iii) determined whether the encoded proteins could be organized as a network. The longevity gene-encoded proteins together with their interacting proteins form a continuous network, which fits the criteria for a scale-free network with an extremely high contribution of hubs to the network connectivity. Most of them have never been annotated before in connection with longevity. Remarkably, almost all of the hubs of the "longevity network" were reported to be involved in at least one age-related disease (ARD), with many being involved in several ARDs. This may be one of the ways by which the proteins with multiple interactions affect the longevity. The hubs offer the potential of being primary targets for longevity-promoting interventions.

Sex and Age Specificity of Susceptibility Genes Modulating Survival at Old Age

OBJECTIVE

We aimed to investigate the influence of the genetic variability of candidate genes on survival at old age in good health.

METHODS

First, on the basis of a synthetic survival curve constructed using historic mortality data taken from the Italian population from 1890 onward, we defined three age classes ranging from 18 to 106 years. Second, we assembled a multinomial logistic regression model to evaluate the effect of dichotomous variables (genotypes) on the probability to be assigned to a specific category (age class). Third, we applied the regression model to a cross-sectional dataset (10 genes; 972 subjects selected for healthy status) categorized according to age and sex.

RESULTS

We found that genetic factors influence survival at advanced age in good health in a sex- and age-specific way. Furthermore, we found that genetic variability plays a stronger role in males than in females and that, in both genders, its impact is especially important at very old ages.

CONCLUSIONS

The analyses presented here underline the age-specific effect of the gene network in modulating survival at advanced age in good health.

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.

How genetic analysis tests theories of animal aging

Each animal species displays a specific life span, rate of aging and pattern of development of age-dependent diseases. The genetic bases of these related features are being studied experimentally in invertebrate and vertebrate model systems as well as in humans through medical records. Three types of mutants are being analyzed: (i) short-lived mutants that are prone to age-dependent diseases and might be models of accelerated aging; (ii) mutants that show overt molecular defects but that do not live shorter lives than controls, and can be used to test specific theories about the molecular causes of aging and age-dependent diseases; and (iii) long-lived mutants that might advance the understanding of the molecular physiology of slow-aging animals and aid the discovery of molecular targets that could be used to manipulate rates of aging to benefit human health. Here, I analyze some of what we know today and discuss what we should try to find out in the future to understand the aging phenomenon.

Characterization of a bidirectional promoter shared between two human genes related to aging: SIRT3 and PSMD13

The human SIRT3 gene contains an intronic VNTR enhancer whose variability is correlated with life span. The SIRT3 5' flanking region encompasses the PSMD13 gene encoding the p40.5 regulator subunit of the 26S proteasome. Proteasome is a multicatalytic proteinase whose function declines with aging. SIRT3 and PSMD13 are linked in a head-to-head configuration (788-bp intergenic region). The molecular configuration of two genes that are both related to aging prompted us to search for shared regulatory mechanisms between them. Transfection experiments carried out in HeLa cells by deletion mutants of the PSMD13-SIRT3 intergenic region showed a complex pathway of coregulation acting in both directions. Furthermore, linkage disequilibrium (LD) analyses carried out in a sample of 710 subjects (18-108 years of age) screened for A21631G (marker of PSMD13), and for G477T and VNTR(intron5) (markers of SIRT3), revealed high LD, with significantly different PSMD13-SIRT3 haplotype pools between samples of centenarians and younger people.

The adversities of aging

The aging process is evolutionarily conserved and subject to quantitative modification by both genetic and environmental factors. Fundamental mechanisms of aging result in progressive deficits in the function of cells and organs, often leading to diseases that ultimately kill the organism such as cancers, cardiovascular disease and neurodegenerative disorders. Oxidative stress and damage to all of the major classes of molecules in cells are involved in aging and age-related diseases. The widely pursued approach of targeting disease-specific processes to develop therapeutic interventions has not had a major impact on healthspan. A more productive approach would be to target the fundamental mechanisms of aging throughout adult life so as to extend healthspan. Caloric restriction and regular exercise are two such approaches.

Family clustering in Sardinian longevity: a genealogical approach

This paper aims to discuss the validation and family determinants affecting the longevity of Sardinian centenarians, using a genealogical approach. This preliminary study presents the first results of a genealogical tree reconstruction of selected centenarians aged 105 and over, from certain areas. These are mostly situated in the province of Nuoro, an area with the highest rate of centenarians and where the female-to-male sex ratio tends to be male-biased. An accurate centenarian age validation was performed that required a meticulous examination of numerous civil status records and parish registers. An important finding was that longevity occurs among the ascendants of a particular branch of the family. The data used are still provisional but, should it apply to other validated cases, it would provide empirical evidence of a genetic component in longevity. A more thorough examination of the data available may yield deeper insights into the role played by endogamy and consanguinity.

The quest for genetic determinants of human longevity: challenges and insights

Twin studies show that genetic differences account for about a quarter of the variance in adult human lifespan. Common polymorphisms that have a modest effect on lifespan have been identified in one gene, APOE, providing hope that other genetic determinants can be uncovered. However, although variants with substantial beneficial effects have been proposed to exist and several candidates have been put forward, their effects have yet to be confirmed. Human studies of longevity face numerous theoretical and logistical challenges, as the determinants of lifespan are extraordinarily complex. However, large-scale linkage studies of long-lived families, longitudinal candidate-gene association studies and the development of analytical methods provide the potential for future progress.

Aging at the interface of stem cell renewal, apoptosis, senescence, and cancer

The aging-related research field has focused on the detection of genetic factors that affect the aging process, but more recently scientists have started to shift their attention to novel and more integrative ways of studying cellular and organismal function. Such approaches allow them to uncover and explore unexpected patterns and themes, resulting in a more comprehensive knowledge of the complex regulatory pathways and networks involved in aging and age-related diseases. Eventually, this knowledge will lead to a systems-level understanding of aging. The third "Functional Genomics of Aging" conference held in Palermo, Italy, in March/April 2006 highlighted some of the more exciting work in this area.