The genetics of aging

Once thought to be an extremely complex conundrum of weak genetic and environmental effects, exceptional longevity is beginning to yield genetic findings. Numerous lower organism and mammalian models demonstrate genetic mutations that increase life-span markedly. These variations, some of them evolutionarily conserved, inform us about biochemical pathways that significantly impact upon longevity. Centenarian studies have also proven useful as they are a cohort that, relative to younger age groups, lacks genotypes linked to age-related lethal diseases and premature mortality. Pedigree studies have demonstrated a significant familial component to the ability to survive to extreme old age and a recent study demonstrates a locus on chromosome 4 linked to exceptional longevity indicating the likely existence of at least one longevity enabling gene in humans. Thus, a number of laboratories are making substantial and exciting strides in the understanding of the genetics of aging and longevity which should lead to the discovery of genes and ultimately drugs that slow down the aging process and facilitate people's ability to delay and perhaps escape age-associated diseases.     

Genetic signatures of exceptional longevity in humans

Like most complex phenotypes, exceptional longevity is thought to reflect a combined influence of environmental (e.g., lifestyle choices, where we live) and genetic factors. To explore the genetic contribution, we undertook a genome-wide association study of exceptional longevity in 801 centenarians (median age at death 104 years) and 914 genetically matched healthy controls. Using these data, we built a genetic model that includes 281 single nucleotide polymorphisms (SNPs) and discriminated between cases and controls of the discovery set with 89% sensitivity and specificity, and with 58% specificity and 60% sensitivity in an independent cohort of 341 controls and 253 genetically matched nonagenarians and centenarians (median age 100 years). Consistent with the hypothesis that the genetic contribution is largest with the oldest ages, the sensitivity of the model increased in the independent cohort with older and older ages (71% to classify subjects with an age at death>102 and 85% to classify subjects with an age at death>105). For further validation, we applied the model to an additional, unmatched 60 centenarians (median age 107 years) resulting in 78% sensitivity, and 2863 unmatched controls with 61% specificity. The 281 SNPs include the SNP rs2075650 in TOMM40/APOE that reached irrefutable genome wide significance (posterior probability of association = 1) and replicated in the independent cohort. Removal of this SNP from the model reduced the accuracy by only 1%. Further in-silico analysis suggests that 90% of centenarians can be grouped into clusters characterized by different “genetic signatures” of varying predictive values for exceptional longevity. The correlation between 3 signatures and 3 different life spans was replicated in the combined replication sets. The different signatures may help dissect this complex phenotype into sub-phenotypes of exceptional longevity.     

Cell type-specific β2-adrenergic receptor clusters identified using photoactivated localization microscopy are not lipid raft related, but depend on actin cytoskeleton integrity

Recent developments in the field of optical super-resolution techniques allow both a 10-fold increase in resolution as well as an increased ability to quantify the number of labeled molecules visualized in the fluorescence measurement. By using photoactivated localization microscopy (PALM) and an experimental approach based on the systematic comparison with a nonclustering peptide as a negative control, we found that the prototypical G protein-coupled receptor β2-adrenergic receptor is partially preassociated in nanoscale-sized clusters only in the cardiomyocytes, such as H9C2 cells, but not in other cell lines, such as HeLa and Chinese hamster ovary (CHO). The addition of the agonist for very short times or the addition of the inverse agonist did not significantly affect the organization of receptor assembly. To investigate the mechanism governing cluster formation, we altered plasma membrane properties with cholesterol removal and actin microfilament disruption. Although cholesterol is an essential component of cell membranes and it is supposed to be enriched in the lipid rafts, its sequestration and removal did not affect receptor clustering, whereas the inhibition of actin polymerization did decrease the number of clusters. Our findings are therefore consistent with a model in which β2 receptor clustering is influenced by the actin cytoskeleton, but it does not rely on lipid raft integrity, thus ruling out the possibility that cell type-specific β2 receptor clustering is associated with the raft.     

Human longevity and common variations in the LMNA gene: a meta-analysis

A mutation in the LMNA gene is responsible for the most dramatic form of premature aging, Hutchinson-Gilford progeria syndrome (HGPS). Several recent studies have suggested that protein products of this gene might have a role in normal physiological cellular senescence. To explore further LMNA's possible role in normal aging, we genotyped 16 SNPs over a span of 75.4 kb of the LMNA gene on a sample of long-lived individuals (LLI) (US Caucasians with age ≥ 95 years, N=873) and genetically matched younger controls (N=443). We tested all common nonredundant haplotypes (frequency ≥ 0.05) based on subgroups of these 16 SNPs for association with longevity. The most significant haplotype, based on four SNPs, remained significant after adjustment for multiple testing (OR=1.56, P=2.5 × 10(-5) , multiple-testing-adjusted P=0.0045). To attempt to replicate these results, we genotyped 3619 subjects from four independent samples of LLI and control subjects from (i) the New England Centenarian Study (NECS) (N=738), (ii) the Southern Italian Centenarian Study (SICS) (N=905), (iii) France (N=1103), and (iv) the Einstein Ashkenazi Longevity Study (N= 702). We replicated the association with the most significant haplotype from our initial analysis in the NECS sample (OR=1.60, P=0.0023), but not in the other three samples (P > 0.15). In a meta-analysis combining all five samples, the best haplotype remained significantly associated with longevity after adjustment for multiple testing in the initial and follow-up samples (OR=1.18, P=7.5 × 10(-4) , multiple-testing-adjusted P=0.037). These results suggest that LMNA variants may play a role in human lifespan.     

Micronutrients (Other than iron) and Helicobacter pylori infection: a systematic review

Background: Many micronutrients depend on a healthy stomach for absorption. Helicobacter pylori chronic gastritis may alter gastric physiology affecting homeostasis of vitamins and minerals. Objectives: Systematic review to assess whether H. pylori infection is associated with reduced micronutrient levels (other than iron) in the plasma or gastric juice and whether low micronutrient levels are modified by eradication treatment. Method: Medline was searched for relevant publications from inception to June 2010. Studies describing micronutrient levels in H. pylori‐infected and not‐infected adults and/or the effect of eradication treatment on micronutrient levels were included. Findings: Fifty‐two publications were selected: 46 investigated the association between H. pylori infection and reduced micronutrient levels and 14 the effect of eradication treatment on micronutrient levels. Sixty‐four studies investigated vitamins (23 ascorbic acid, four ß‐carotene, 21 cobalamin, 11 folate, and five α‐tocopherol) and 10 addressed minerals (one calcium, one copper, one magnesium, one phosphorus, three selenium, and three zinc). Pooled standardized mean differences in micronutrient levels showed positive associations with H. pylori infection for ascorbic acid (gastric juice, ?1.087) and cobalamin (?0.744), and a positive effect of eradication treatment, which increased ascorbic acid in the gastric juice (?1.408) and serum cobalamin (?1.910). No significant association between infection and low folate levels was observed. Meta‐analyses for other micronutrients were not performed owing to insufficient data. Conclusions: Meta‐analyses indicate that H. pylori infection is associated with reduced levels of ascorbic acid and cobalamin, supported by the positive effect of eradication treatment. For other micronutrients, further studies are needed.     

Evaluation of the MicroSeq 500 16S rDNA-based gene sequencing for the diagnosis of culture-negative bacterial meningitis

Gene amplification using 16S rDNA primers has been proposed as a strategy for the diagnosis of bacterial meningitis. The aim of this study was to evaluate the performance of the MicroSeq 500 16S ribosomal DNA test (Applied Biosystems) from patients with suspected bacterial meningitis and CSF negative-culture in comparison to traditional methods. Twelve purulent culture-negative CSF samples were collected between January 2005 and January 2007. For DNA extraction, 500 microl of CSF samples were treated using the QIAamp mini kit (QIAGEN). The extracted DNA was examined amplifying 500 bp at the 5' end of 16S rRNA gene using MicroSeq500 16S rDNA Bacterial Identification PCR kit and the sequencing reactions were performed with the MicroSeq500 16S rDNA Bacterial Identification Sequencing kit (Applied Biosystems). The sequences were compared with those available in GenBank. For the culture-negative CSF samples the MicroSeq 500 16S rDNA yielded a positive result in 9 cases (75.0%): three samples were identified as Streptococcus. pneumoniae, three as Neisseria meningitidis, and the remaining 3 as Haemophilus influenzae, Abiotrophia defectiva and Porphyromonas gingivalis. The MicroSeq 500 16S ribosomal DNA test may improve the microbiological diagnosis of bacterial meningitis, especially when spinal fluid samples are obtained after the administration of antimicrobial therapy.     

Role of noninvasive tests (C-urea breath test and stool antigen test) as additional tools in diagnosis of Helicobacter pylori infection in patients with atrophic body gastritis

BACKGROUND: Detection of Helicobacter pylori infection in atrophic body gastritis (ABG) is difficult, as during progression of body atrophy, H. pylori disappears. AIM: To increase the diagnostic yield of detection of active H. pylori infection in atrophic body gastritis patients by using noninvasive tests such as (13)C-Urea Breath Test ((13)C-UBT) and H. pylori stool antigen test (HpSA) would be useful. PATIENTS: 27 consecutive patients with newly-diagnosed atrophic body gastritis (19F/7M, age 27-73 years). METHODS: Gastroscopy with biopsies (antrum n = 3, body n = 3) and histology according to updated Sydney system, H. pylori IgG serology, (13)C-UBT, and HpSA. RESULTS: All tests used in the diagnosis of H. pylori infection were in agreement in 9/27 atrophic body gastritis patients (33.3%), being all positive in four (14.8%) and all negative in five patients (18.5%). Ten of the 27 (37%) patients were Giemsa stain-positive and serology-positive (group I). Seventeen of the 27 (63%) patients were Giemsa stain-negative: 5/17 with positive serology (group II) and 12/17 with negative serology (group III). In group I, 5/10 (50%) were (13)C-UBT positive and 4/10 (40%) HpSA positive. In group II, two patients were (13)C-UBT positive, but all were HpSA negative. Also in group III, all patients were HpSA negative, but one had a positive (13)C-UBT. CONCLUSIONS: In atrophic body gastritis patients, neither (13)C-UBT nor HpSA per se add useful information regarding active H. pylori infection, but these noninvasive tests may be important in combination with histology and serology to define the H. pylori status in some atrophic body gastritis patients.     

CagA and VacA are immunoblot markers of past Helicobacter pylori infection in atrophic body gastritis

BACKGROUND AND AIM: Atrophic body gastritis (ABG) may be induced by H. pylori infection. It is difficult to diagnose H. pylori infection in this condition, since during progression of body atrophy the bacterium disappears. In 30% of patients with ABG no sign of H. pylori infection is detectable. We aimed to investigate whether patients with ABG, classified as H. pylori-negative by conventional methods (ELISA serology and Giemsa stain histology), have been previously exposed to the infection. METHODS: Case series consisted of 138 outpatients with ABG, of whom 31 are H. pylori negative (histology and ELISA serology), and 107 are H. pylori related (histology and ELISA serology positive: active infection, n = 29; only serology positive: past infection, n = 78). Thirty control subjects who were H. pylori negative at histology and ELISA serology were investigated. Immunoblotting of sera against H. pylori whole-cell protein lysate was performed. RESULTS: None of the control sera recognized CagA, VacA, heat-shock protein B, and urease B, yielding a specificity of 100%. All H. pylori-negative patients with ABG showed immunoblotting seroreactivity, including in each case either CagA or VacA. The concomitant seroreactivity against CagA and VacA was highly prevalent in the H. pylori-negative patients with ABG, comparable to those with active infection (77.4% vs. 86.2%) and with past infection (vs. 61.5%). CONCLUSIONS: Immunoblotting against CagA and VacA is able to prove past exposure to H. pylori infection in all patients with ABG defined as H. pylori-negative by conventional methods, suggesting a hidden role of H. pylori infection in gastric atrophy also in these patients.