Telomere length and replicative aging in human vascular tissues

Generation of human pulmonary microvascular endothelial cell lines

The limited lifespan of human microvascular endothelial cells in cell culture represents a major obstacle for the study of microvascular pathobiology. To date, no endothelial cell line is available that demonstrates all of the fundamental characteristics of microvascular endothelial cells. We have generated endothelial cell lines from human pulmonary microvascular endothelial cells (HPMEC) isolated from adult donors. HPMEC were cotransfected with a plasmid encoding the catalytic component of telomerase (hTERT) and a plasmid encoding the simian virus 40 (SV40) large T antigen. Cells transfected with either plasmid alone had an extended lifespan, but the cultures eventually entered crisis after several months of proliferation. Only those cells that were transfected with both plasmids acquired the capacity to grow in vitro without demonstrating major crisis, and these cells have been in culture for 24 months. HPMEC isolated from two different donors were used, generating two populations of immortalized cells, HPMEC-ST1 and HPMEC-ST2. Single cell-derived clones of the immortalized cells HPMEC-ST1 exhibited growth characteristics that were similar to those of the parental HPMEC. One selected clone, HPMEC-ST1.6R, displayed all major constitutively expressed and inducible endothelial phenotypic markers, including platelet endothelial cell adhesion molecule (PECAM-1, CD31), von Willebrand factor (vWF), and the adhesion molecules, intercellular adhesion molecule (ICAM-1), vascular adhesion molecule (VCAM-1), and E-selectin. In addition, an angiogenic response was demonstrated by sprout formation on a biological extracellular matrix (Matrigel). The HPMEC-ST1.6R cells did not form tumors in nude mice. The microvascular endothelial cell line, HPMEC-ST1.6R, will be a valuable tool for the study of microvascular endothelial physiology and pathology including gene expression, angiogenesis, and tumorigenesis.

Vasculoprotective effects of oestrogens

1. The rationale for preclinical research on the atheroprotective effect of oestrogens is based on the epidemiological evidence that women are protected against the clinical complications of atherosclerosis until menopause. However, this protection, probably due to sex hormones, is progressively lost within the years following menopause. 2. In addition, numerous studies have clearly demonstrated the atheroprotective effect of oestrogens in all animal models. 3. In the present paper, we first summarize our understanding of the pathophysiology of atherosclerosis. We then focus on the recognized target of oestradiol (E2) in the vessel wall: the classical target, namely the endothelium, and a recently characterized target, namely cells of the inflammatory-immune system. Finally, we discuss how unknown mechanisms in atherosclerosis could be responsible for the absence of effect of hormone-replacement therapy in the Heart and Estrogen/ progestin Replacement Study (HERS).

Cellular senescence, cancer and aging: the telomere connection

Telomeres are the repetitive DNA sequences and specialized proteins that form the distinctive structure that caps the ends of linear chromosomes. Telomeres allow cells to distinguish the chromosome ends from double strand DNA breaks. The telomeric structure prevents the degradation or fusion of chromosome ends, and thus is essential for maintaining the integrity and stability of eukaryotic genomes. In addition, and perhaps less widely appreciated, telomeres may also indirectly influence gene expression. The length, structure and organization of telomeres are regulated by a host of telomere-associated proteins, and can be influenced by basic cellular processes such as cell proliferation, differentiation, and DNA damage. In mammalian cells, telomere length and/or telomere structure have been linked to both cancer and aging. Here, we briefly review what is known about mammalian telomeres and the proteins that associate with them, and discuss the cellular and organismal consequences of telomere dysfunction and the evidence that cells with dysfunctional telomeres can contribute to cancer and aging phenotypes.

eNOS activity is reduced in senescent human endothelial cells: Preservation by hTERT immortalization

Advanced age is associated with endothelial dysfunction and increased risk for atherosclerosis. However, the mechanisms for these observed effects are not clear. To clarify the association between aging and loss of endothelial function, young human aortic endothelial cells (HAECs), senescent HAECs transfected with control vector, and immortalized HAECs containing human telomerase reverse transcriptase (hTERT) were compared for expression of endothelial nitric oxide synthase (eNOS) and production of NO. To investigate a specific function modulated by endothelial NO, adhesion of monocytes under basal conditions as well as after exposure to TNF-alpha was assessed. A decrease in eNOS mRNA, protein, and activity was observed in endothelial cells at senescence as compared with young HAEC; this effect was blunted in hTERT cells. In all cells, shear stress induced a greater increase in the expression of eNOS protein with the final result being higher levels in hTERT compared with senescent cells. Basal monocyte binding was significantly elevated on aged endothelial cells compared with parental and hTERT cells. Exposure of TNF-alpha resulted in a 2-fold increase in monocyte adhesion in senescent cells, whereas this effect was reduced in cells transfected with hTERT. Prior exposure to fluid flow significantly reduced subsequent monocyte adhesion in all groups. These studies demonstrate that replicative aging results in decreased endothelial expression of eNOS accompanied by enhanced monocyte binding. Stable expression of hTERT results in endothelial cells with a younger phenotype with greater amount of eNOS and NO activity. Thus, telomerase transfection may have important functional consequences on endothelial cells.

Telomere shortening and decline in replicative potential as a function of donor age in human adrenocortical cells

Telomere shortening is the cause of replicative senescence of mammalian cells in culture and may be a cause of cellular aging in vivo. Some tissues clearly show telomere shortening during aging in humans, but the relationship between replication history and telomere length is obscured by complex relationships between stem cells and more differentiated cell types. Previous experiments on the adrenal cortex and human adrenocortical cells in culture indicate that the proliferative biology of this tissue is relatively simple; cell division occurs continuously throughout life, without evidence for a distinct stem cell compartment. In this tissue we investigated the relationship between telomere biology and replicative senescence by measuring replicative capacity and telomere length as a function of donor age. Cells cultured from adrenal tissue from donors of different ages showed a strong age-related decline in total replicative capacity, falling from about 50 population doublings for fetal cells to an almost total lack of division in culture for cells from older donors. Telomere restriction fragment (TRF) length was analyzed in the same sets of cells and decreased from a value of about 12 kb in fetal cells to approximately 7 kb in cells from older donors. The latter value is consistent with that in fibroblasts which have reached replicative senescence. Furthermore, there was a good correlation in individual donor samples between TRF length and replicative capacity in culture. To confirm the relationship between telomere length, telomerase, and replicative capacity, we measured telomere length in cells before and after infection with a retrovirus encoding hTERT, the catalytic component of human telomerase. The adult adrenal cortex does not have telomerase activity; cells after transduction with the hTERT retrovirus had high telomerase activity. Whereas control cells underwent a replication-dependent shortening in telomeres during long-term growth in culture, hTERT-modified cells maintained telomere length and are probably immortalized. Symmetric cell division in human adrenocortical cells, occurring slowly over the life span, is associated with progressive telomere shortening and may result in proliferative defects in vivo in old age, which could partly account for the age-related changes in the structure and function of the human adrenal cortex.

Alterations of telomerase activity and terminal restriction fragment in gastric cancer and its premalignant lesions

AIMS

In order to explore the role of alterations of telomerase activity and terminal restriction fragment (TRF) length in the development and progression of gastric cancer.

METHODS

Telomerase activity was detected in 176 specimens of gastric mucosa obtained through an operation or endoscopical biopsy by using the telomeric repeat amplification protocol (TRAP) assay. Meanwhile, the mean length of TRF was measured with the use of a Southern blot in part of those samples.

RESULTS

Telomerase activity was detected in 14 of 57 (24.6%) chronic atrophy gastritis patients, six of 18 (33.3%) intestinal metaplasia patients, three of eight (37.5%) dysplasia patients and 60 of 65 (92.3%) gastric cancer patients, respectively. Normal gastric mucosa revealed no telomerase activity. No association was found between telomerase activity and any clinicopathological parameters. The mean TRF length was decreased gradually with age in normal mucosa and in gastric cancer tissue. Regression analysis demonstrated that the reduction rate in these tissues was 41 +/- 12 base pairs/year. Among 35 gastric cancers, TRF length was shown to be shorter in 20 cases (57.1%), similar in 12 cases (34.3%) and elongated in three cases (7.6%), compared to the corresponding adjacent tissues. The mean TRF length tended to decrease as the mucosa underwent chronic atrophy gastritis, intestinal metaplasia, dysplasia and into gastric cancer. The mean TRF length in gastric cancer was not statistically correlated with clinicopathological parameters and telomerase activity.

CONCLUSIONS

Our results suggest that telomerase is expressed during the early stage of gastric carcinogenesis, and that the clinical significance of TRF length appears to be limited in gastric cancer.

Stress, DNA damage and ageing -- an integrative approach

Ageing is highly complex, involving multiple mechanisms at different levels. Nevertheless, recent evidence suggests that several of the most important mechanisms are linked via endogenous stress-induced DNA damage caused by reactive oxygen species (ROS). Understanding how such damage contributes to age-related changes requires that we explain how these different mechanisms relate to each other and potentially interact. In this article, we review the contributions of stress-induced damage to cellular DNA through (i) the role of damage to nuclear DNA and its repair mediated via the actions of poly(ADP-ribose) polymerase-1, (ii) the role of damage to telomeric DNA and its contribution to telomere-driven cell senescence, and (iii) the role of damage to and the accumulation of mutations in mitochondrial DNA. We describe how an integrative approach to studying these mechanisms, coupled with computational modelling, may be of considerable importance in resolving some of the complexity of cellular ageing.

E2F-1 represses transcription of the human telomerase reverse transcriptase gene

The ends of human chromosomes (telomeres) lose up to 200 bp of DNA per cell division. Chromosomal shortening ultimately leads to senescence and death in normal cells. Many human carcinoma lines are immortal in vitro, suggesting that these cells have a mechanism for maintaining the ends of their chromosomes. Telomerase is a ribonucleoprotein complex that synthesizes telomeric DNA onto chromosomes using its RNA component as template. Telomerase activity is found in most tumor cells, but is absent from normal cells. Little is known about how normal human cells repress telomerase (hTERT) gene expression. Mice carrying an E2F-1 null mutation develop a variety of malignant tumors, suggesting that this transcription factor has a tumor suppressor function. To determine mechanisms by which E2F-1 suppresses tumor formation, we examined the role of this transcription factor in regulation of the hTERT promoter in human cells. We identified two putative E2F-1-binding sites proximal to the transcriptional start site of the hTERT promoter. Mutation of these sites produced dramatic increases in promoter activity. Overexpression of E2F-1 but not a mutant E2F-1 repressed hTERT promoter activity in reporter gene assays. This repression was abolished by mutation of the E2F-1-binding sites in the hTERT promoter. Human cancer cell lines stably overexpressing E2F-1 exhibited decreased hTERT mRNA expression and telomerase activity. We conclude that E2F-1 has an atypical function as a transcriptional repressor of the hTERT gene in human cells.

Telomere lengths and telomerase activity in dog tissues: a potential model system to study human telomere and telomerase biology

Studies on telomere and telomerase biology are fundamental to the understanding of aging and age-related diseases such as cancer. However, human studies have been hindered by differences in telomere biology between humans and the classical murine animal model system. In this paper, we describe basic studies of telomere length and telomerase activity in canine normal and neoplastic tissues and propose the dog as an alternative model system. Briefly, telomere lengths were measured in normal canine peripheral blood mononuclear cells (PBMCs), a range of normal canine tissues, and in a panel of naturally occurring soft tissue tumours by terminal restriction fragment (TRF) analysis. Further, telomerase activity was measured in canine cell lines and multiple canine tissues using a combined polymerase chain reaction/enzyme-linked immunosorbent assay method. TRF analysis in canine PBMCs and tissues demonstrated mean TRF lengths to range between 12 and 23 kbp with heterogeneity in telomere lengths being observed in a range of normal somatic tissues. In soft tissue sarcomas, two subgroups were identified with mean TRFs of 22.2 and 18.2 kbp. Telomerase activity in canine tissue was present in tumour tissue and testis with little or no activity in normal somatic tissues. These results suggest that the dog telomere biology is similar to that in humans and may represent an alternative model system for studying telomere biology and telomerase-targeted anticancer therapies.

How long should telomeres be?

What began as a study of the "end-replication problem" took on a new dimension as it became clear that telomeres are a "molecular clock" of replication in human somatic cells. Here we review the biology of telomeres in vitro and in vivo, in mice and humans. We suggest that, in humans, telomeres are involved in the biology of aging and pathobiology of disorders of aging, including cancer and cardiovascular disease. We also propose that the underlying dynamics of telomere biology is in line with broad principles of evolutionary theories.

Hypothesis: pulse pressure and human longevity

In exploration of the association between pulse pressure and longevity in humans, 3 hypotheses are briefly discussed: the fetal origin hypothesis, antagonistic pleiotropy, and the telomere hypothesis of cellular aging. The implications of these hypotheses serve to draw a critical distinction between biologic age (aging) and chronological age and, thereby, offer an answer to a question that presently matters most in the field of hypertension: Why has it been so difficult to disentangle the genetic components of essential hypertension and to identify the variant genes responsible for elevated blood pressure in a large segment of the human population?

Telomere erosion and senescence in human articular cartilage chondrocytes

Aging and the degeneration of articular cartilage in osteoarthritis are distinct processes, but a strong association exists between age and the incidence and prevalence of osteoarthritis. We hypothesized that this association is due to in vivo replicative senescence, which causes age-related declines in the ability of chondrocytes to maintain articular cartilage. For this hypothesis to be tested, senescence-associated markers were measured in human articular chondrocytes from donors ranging in age from 1 to 87 years. These measures included in situ staining for senescence-associated beta-galactosidase activity, (3)H-thymidine incorporation assays for mitotic activity, and Southern blots for telomere length determinations. We found that senescence-associated beta-galactosidase activity increased with age, whereas both mitotic activity and mean telomere length declined. These findings indicate that chondrocyte replicative senescence occurs in vivo and support the hypothesis that the association between osteoarthritis and aging is due in part to replicative senescence. The data also imply that transplantation procedures performed to restore damaged articular surfaces could be limited by the inability of older chondrocytes to form new cartilage after transplantation.

From cells to organisms: can we learn about aging from cells in culture?

Can studying cultured cells inform us about the biology of aging? The idea that this may be was stimulated by the first formal description of replicative senescence. Replicative senescence limits the proliferation of normal human cells in culture, causing them to irreversibly arrest growth and adopt striking changes in cell function. We now know that telomere shortening, which occurs in most somatic cells as a consequence of DNA replication, drives replicative senescence in human cells. However, rodent cells also undergo replicative senescence, despite very long telomeres, and DNA damage, the action of certain oncogenes and changes in chromatin induce a phenotype similar to that of replicatively senescent cells. Thus, replicative senescence is an example of the more general process of cellular senescence, indicating that the telomere hypothesis of aging is a misnomer, Cellular senescence appears to be a response to potentially oncogenic insults, including oxidative stress. The growth arrest almost certainly suppresses tumorigenesis, at least in young organisms, whereas the functional changes may contribute to aging, although this has yet to be critically tested. Thus, cellular senescence may be an example of antagonistic pleiotropy. Cross-species comparisons suggest there is a relationship between the senescence of cells in culture and organismal life span, but the relationship is neither quantitative nor direct.

Rb and E2F-1 regulate telomerase activity in human cancer cells

The ends of human chromosomes (telomeres) lose up to 200 bp of DNA per cell division. Chromosomal shortening ultimately leads to senescence and death in normal cells. Many human carcinoma lines are immortal in vitro, suggesting that these cells have a mechanism for maintaining the ends of their chromosomes. Telomerase is a ribonucleoprotein complex that synthesizes telomeric DNA onto chromosomes using its RNA component as a template. Recent studies have shown that inactivation of the retinoblastoma gene product pRb and the cyclin dependent kinase inhibitor p16(INK4A) is required for telomerase activity in epithelial cells. We have demonstrated previously that restoration of functional retinoblastoma (Rb) expression is sufficient to downregulate telomerase activity in carcinoma cells. To determine mechanisms by which Rb regulates telomerase expression, we examined the effects of cyclin dependent kinase (cdk) mediated Rb inactivation and the release of E2F-1 on telomerase activity in human carcinoma cells. Overexpression of cdk2 and cdk4 but not a dominant negative cdk2 rescued Rb mediated downregulation of telomerase activity. Overexpression of the cdk regulatory subunit cyclin D1 also rescued telomerase downregulation and p16 expression alone was sufficient to ablate activity. E2F-1 overexpression was sufficient to rescue Rb mediated reduction of telomerase activity, but an E2F-1 mutant defective in DNA and Rb binding activities failed to produce this effect. Tumor tissue from E2F-1 -/- mice was negative for telomerase activity, indicating a key regulatory role for this transcription factor.

Telomerized human microvasculature is functional in vivo

Previously we showed the superior in vitro survival of human telomerase reverse transcriptase (hTERT)-transduced human endothelial cells (EC). Here we show that retroviral-mediated transduction of hTERT in human dermal microvascular EC (HDMEC) results in cell lines that form microvascular structures when subcutaneously implanted in severe combined immunodeficiency (SCID) mice. Anti-human type IV collagen basement membrane immunoreactivity and visualization of enhanced green fluorescent protein (eGFP)-labeled microvessels confirmed the human origin of these capillaries. No human vasculature was observed after implantation of HT1080 fibrosarcoma cells, 293 human embryonic kidney cells, or human skin fibroblasts. Intravascular red fluorescent microspheres injected into host circulation were found within green "telomerized" microvessels, indicating functional murine-human vessel anastamoses. Whereas primary HDMEC-derived vessel density decreased with time, telomerized HDMEC maintained durable vessels six weeks after xenografting. Modulation of implant vessel density by exposure to different angiogenic and angiostatic factors demonstrated the utility of this system for the study of human microvascular remodeling in vivo.

Replicative senescence in normal liver, chronic hepatitis C, and hepatocellular carcinomas

There is growing evidence that senescent cells accumulate in vivo and are associated with the aging process in parallel with the progressive erosion of telomeres. Because recent data show that telomere shortening is involved in the pathogenesis of liver cirrhosis, we looked for replicative senescence cells in normal livers, chronic hepatitis C, and hepatocellular carcinoma (HCC). Replicative senescent cells were detected on liver tissue cryosections using expression of a specific marker, senescence-associated beta-galactosidase, a cytoplasmic enzyme detected at pH 6. A total of 57 frozen liver samples (15 normal liver, 32 chronic hepatitis C, and 10 HCCs) were studied. Replicative senescence was graded as absent in 56% of cases (32 of 57) and present in 44% (25 of 57). Replicative senescence was considered present in 3 of 15 normal livers (20%), 16 of 32 chronic hepatitis cases (50%), and 6 of 10 HCCs (60%). In the group of nontumoral livers, the presence of senescent cells in liver was associated with older age (P =.03). In the group with chronic hepatitis C, fibrosis stage, but not activity grade, was significantly correlated with the accumulation of replicative senescent cells (P <.001). Finally, beta-Gal staining in nontumoral tissue was strongly correlated with the presence of HCC in the surrounding liver (P <.001). These results suggest that chronic hepatitis C represents a relevant model of accelerated replicative senescence and that accumulation of replicative senescent cells predispose to HCC development. Detection of replicative senescent cells may then serve as a predictive marker of a hepatocellular carcinoma in the surrounding tissue. HUM PATHOL 32:327-332.

Telomeres, replicative senescence and human ageing

Ageing concerns the extracellular environment and cells that are either post-mitotic or capable of division during life. Primary human cells have a finite division capacity in culture before they enter a state of viable cell cycle arrest termed senescence. Cell division occurs during life in many tissues, either as part of normal tissue function or in response to tissue damage. The accumulation of cells at the end of their replicative lifespan in the elderly might contribute to aged tissue either because of a reduced ability to undergo proliferation or because of the known altered gene-expression patterns of senescent cells. This has been illustrated experimentally using a transgenic telomerase-negative mouse, which shows some premature ageing phenotypes. The mechanism whereby cells count divisions uses the gradual erosion of the ends of chromosomes (telomeres) with cell division caused by the repression of the telomere-maintenance enzyme telomerase in most human cells. Telomere erosion ultimately triggers replicative senescence in many cell types; this can be prevented experimentally by forcibly expressing telomerase. This extends the lifespan of normal human cells and those from progeroid syndromes such as Werner's. Telomere-driven senescence did not evolve to cause ageing, but is instead a by-product of a system devised to provide a tumour-suppression function, a concept that fits well with evolutionary arguments regarding trade-offs between somatic maintenance and reproduction. Work in the future will focus on the development of new animal models to critically address the quantitative significance of this ageing mechanism.

IFN-gamma-dependent transcription of MHC class II IA is impaired in macrophages from aged mice

To determine the effect of aging on IFN-gamma-induced MHC class II antigen expression, we produced bone marrow-derived macrophages in vitro. In these conditions, we analyzed the effect of aging on the genomic expression of macrophages without the influence of other cell types that may be affected by aging. Although macrophages from young and aged mice showed an identical degree of differentiation, after incubation with IFN-gamma, the expression at the cell surface of the IA complex and the levels of IAbeta protein and mRNA were lower in aged macrophages. Moreover, the transcription of the IAbeta gene was impaired in aged macrophages. The amount of transcription factors that bound to the W and X, but not to the Y, boxes of the IAbeta promoter gene was lower in aged macrophages. Similar levels of CIITA mRNA were found after IFN-gamma treatment of both young and aged macrophages. This shows that neither the initial cascade that starts after the interaction of IFN-gamma with the receptor nor the second signals involved in the expression of CIITA are impaired in aged macrophages. These data indicate that aging is associated with low levels of MHC class II gene induction by IFN-gamma because of impaired transcription.

Workshop: excess growth and apoptosis: is hypertension a case of accelerated aging of cardiovascular cells?

Several groups including ours have demonstrated cardiac hyperplasia in neonates from genetically hypertensive rat strains. We have shown that similar problems exist in the kidney as well. More recently, we found that excessive heart and kidney weight is neonatally related to inhibition of apoptosis. Using recombinant inbred strains derived from a reciprocal cross between Brown Norway and spontaneously hypertensive rat progenitor strains, we mapped the inhibition of neonatal apoptosis to 2 distinct loci on chromosomes 1 (Myl 2) and 18 (Abrb 2). Positional candidate genes at these loci are being explored. These studies have also demonstrated that the loci determining kidney and heart weights in neonates are distinct from those determining increased organ weight in adults. The impact of blood pressure per se is also divergent because adult kidney weight is negatively correlated whereas heart weight is positively correlated with it. Analyses by extremes of low and high percentiles from fetal life to adulthood identified a single locus determining heart weight at Acaa on chromosome 8 in newborn (P=0.0003) and adult (P=0.016) rats. The Acaa region contains a DNA mismatch repair gene (hMLH1). The kinetics of neonatal growth through adulthood by prelabeling DNA with [(3)H]thymidine in pregnant mares showed that although the growth process is complex and nonlinear in the kidney of hypertensive rats, there is an increased turnover of cells, that is, reduced half-life of DNA. This observation is supported by the presence of shorter telomere fragments in kidneys of spontaneously hypertensive rats. These studies suggest that cardiovascular cells from hypertensive animals are subject to accelerated turnover, potentially leading to their accelerated aging.

Cellular senescence after single and repeated balloon catheter denudations of rabbit carotid arteries

The hypothesis that increased cellular proliferation in the vasculature may lead to replicative senescence has been tested in a model of neointima formation. We have used a biomarker of replicative senescence, senescence-associated beta-galactosidase (SA-beta-gal), to detect senescence in rabbit carotid arteries subjected to single and double balloon denudations. We found an accumulation of senescent cells in the neointima and media of all injured vessels, in contrast to the near absence of such cells in control vessels. The relative area occupied by SA-beta-gal-positive cells was higher in vessels subjected to double denudation than in those subjected to single denudation, both in the neointima (0.99% versus 0.06%, respectively; P:<0.001) and in the media (0.11% versus 0.01%, respectively; P:<0.02). The majority of SA-beta-gal-positive cells were vascular smooth muscle cells, and a minority were endothelial cells. SA-beta-gal-positive cells showed no evidence of apoptosis by use of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling. Our results indicate that the proliferative response that follows intraluminal injury to the artery leads to the emergence of senescent endothelial and smooth muscle cells. The demonstration that vascular cell senescence can occur in vivo suggests that this process may be involved in cardiovascular pathologies that have a proliferative component.

Telomere length as an indicator of biological aging: the gender effect and relation with pulse pressure and pulse wave velocity

Chronological age is the primary determinant of stiffness of central arteries. Increased stiffness is an independent indicator of cardiovascular risk. The aim of this study was to determine whether telomere length, a possible index of biological aging, provides a better account than chronological age for variation in arterial stiffness, evaluated by measuring pulse pressure and aortic pulse wave velocity. The study population included 193 French subjects (120 men, 73 women), with a mean age of 56+/-11 years, who were not on any antihypertensive medications. Telomere length was evaluated in white blood cells by measuring the mean length of the terminal restriction fragments. Age-adjusted telomere length was longer in women than in men (8.67+/-0.09 versus 8.37+/-0.07 kb; P=0.016). In both genders, telomere length was inversely correlated with age (P<0.01). Multivariate analysis showed that in men, but not in women, telomere length significantly contributed to pulse pressure and pulse wave velocity variations. In conclusion, telomere length provides an additional account to chronological age of variations in both pulse pressure and pulse wave velocity among men, such that men with shorter telomere length are more likely to exhibit high pulse pressure and pulse wave velocity, which are indices of large artery stiffness. The longer telomere length in women suggests that for a given chronological age, biological aging of men is more advanced than that of women.

Telomere length in different tissues of elderly patients

Telomeres are supposed to play a role in cellular aging and might contribute to the genetic background of human aging and longevity. During the past few years telomere length has been measured in various human tissues. However, very little is known about the individual telomere loss in different tissues from the same donor. Therefore we have measured telomere restriction fragment (TRF) length in three unrelated tissues (leukocytes, skin and synovial tissue) of nine elderly patients (age range 73-95 years old). Dependent on the tissue specific proliferation rate we have found significantly shorter telomeres (6546+/-519 bp, mean +/- S.D.) in leukocytes compared to skin (7792+/-596 bp, P<0.01) and synovial tissue (7910+/-420 bp, P<0.001). In general, we have observed an inverse relationship between donor age and TRF length which becomes significant in leukocytes (P=0.04, R(2)=0.49) and skin specimens (P=0.006, R(2)=0.81). Interestingly, linear correlations (P values between 0.017 and 0.038, R(2) values between 0.54 and 0.79) were also obtained on comparison of telomere length in each pair of two different tissues from the same donor without taking donor age into account. This suggests that genetic determination of the regulation of telomere length is tissue-independent. Furthermore, our results indicate that TRF measurement in easily accessible tissues such as blood could serve as a surrogate parameter for the relative telomere length in other tissues.

Loss of chromosome 13 in cultured human vascular endothelial cells

In the vascular endothelium of human beings, telomere length is negatively related while the frequency of aneuploidy is positively related to donor age. Both in culture and in vivo the frequency of aneuploidy increases as telomere length is shortened. In this study we explored the relation between telomere length and aneuploidy in cultured human umbilical vein endothelial cells (HUVEC) by: (a) karyotype analysis and fluorescent in situ hybridization (FISH), (b) measurement of the terminal restriction fragments (TRF), and (c) assessment of replicative senescence by the expression of beta-galactosidase. Of 8 HUVEC strains, 7 cell strains lost chromosome 13, as shown by metaphase analysis and FISH of interphase cells. Five strains gained chromosome 11. In addition, five HUVEC strains became hypotetraploid shortly after the loss of chromosome 13. The loss of chromosome 13 was observed as early as PD 20, when mean TRF length was greater than 9 kb and the percentage of cells positive for beta-galactosidase was relatively low. The almost uniform loss of chromosome 13 suggests that this unique type of aneuploidy of HUVEC is the result of a progressive expression of clones with survival advantage.

Telomere shortening with aging in human liver

Progressive telomere shortening with aging was studied in the normal liver tissue of 94 human subjects aged between 0 and 101 years old to determine the rate of telomere loss in 1 year. Telomere length demonstrated accelerated shortening with reduction of 55 base pairs (bp) per year. The mean telomere length in five neonates was 12.9 +/- 2.6 kilobase pairs (kbp), and that in one centenarian was 8.3 kbp. Mean telomere lengths by age group were 13.2 +/- 2.0 kbp (< or = 8 years; 10 subjects), 7.8 +/- 1.9 kbp (40-79 years; 29 subjects), and 7.5 +/- 2.0 kbp (> or = 80 years; 53 subjects), with reduction thus appearing to show slowing on the attainment of middle age. The difference of mean telomere lengths for two groups with or without advanced malignancies of other than liver origin was not significant in the older two groups. Despite the slow turnover of liver tissue, the overall reduction rate of telomere length decrease in 1 year was almost the same as that of digestive tract mucosa, with its very rapid renewal.

Short telomeres in patients with vascular dementia: an indicator of low antioxidative capacity and a possible risk factor?

Progressive cerebrovascular atherosclerosis and consecutive stroke are among the most common causes of dementia. However, specific risk factors for vascular dementia are still not known. Human telomeres shorten with each cell division in vitro and with donor age in vivo. In human fibroblasts in vitro, the telomere shortening rate decreased with increasing antioxidative capacity. There was a good intra-individual correlation between the age-corrected telomere lengths in fibroblasts and peripheral blood mononuclear cells. In 186 individuals including 149 geriatric patients (age range, 55-98 yr), leukocyte telomeres in patients with probable or possible vascular dementia were significantly shorter than in three age-matched control groups, namely in cognitively competent patients suffering from cerebrovascular or cardiovascular disease alone, in patients with probable Alzheimer's dementia, and in apparently healthy control subjects. No correlation was found to polymorphisms in the apolipoprotein E and glutathione-S-transferase genes. Telomere length may be an independent predictor for the risk of vascular dementia.

Telomere attrition of the human abdominal aorta: relationships with age and atherosclerosis

Little is known about the turnover rate (i.e. the rate of replication and death) of cells in the intima and media of human arteries as a function of age and atherosclerosis. One indicator of the replicative history of cells is telomere length. In this work we explored the rate of telomere attrition as a function of age and atherosclerosis in cells of the human abdominal aorta. Telomere length, measured by the terminal restriction fragment using Southern analysis, was determined in the intima and media of the distal (infrarenal) versus proximal (suprarenal) segments of the abdominal aorta. Telomere length was then correlated with age and atherosclerotic grade. The rate of age-dependent telomere attrition was higher in both the intima and media of the distal versus proximal abdominal aorta. In addition, telomere length was negatively correlated with atherosclerotic grade. However, after adjustment for age, this relationship was not statistically significant. The high rate of age-dependent telomere attrition in the distal abdominal aorta probably reflects enhanced cellular turnover rate due to local factors such as an increase in shear wall stress in this vascular segment.

Repair of telomeric DNA prior to replicative senescence

The average length of telomere repeats at the ends of chromosomes in most normal human somatic cells has been found to decrease by 50-200 base pairs with each cell division. The loss of telomere repeats has been causally linked to replicative senescence by the demonstration that overexpression of the enzyme telomerase can result in the elongation or maintenance of telomeres and immortalization of somatic cells with a diploid and apparently normal karyotype. Major questions that remain are related to the actual mechanism by which telomere shortening induces replicative senescence and the importance of telomere shortening and replicative senescence in the homeostasis of cells in renewal tissues and aging. This perspective is concerned with the consequences of telomere shortening at individual chromosomes in individual cells. Experimental evidence indicates that short telomeres accumulate prior to senescence and that replicative senescence is not triggered by the first telomere to reach a critical minimal threshold length. These observations are compatible with limited repair of short telomeres by telomerase-dependent or telomerase-independent DNA repair pathways. Deficiencies in telomere repair may result in accelerated senescence and aging as well as genetic instability that facilitates malignant transformation. Examples of molecules that may have a role in the repair of telomeric DNA prior to replicative senescence include ATM, p53, PARP, DNA-PK, Ku70/80, the human hRad50-hMre11-p95 complex, BRCA 1 and 2 and the helicases implicated in Bloom's and Werner's syndrome.

Telomere length inversely correlates with pulse pressure and is highly familial

There is evidence that telomeres, the ends of chromosomes, serve as clocks that pace cellular aging in vitro and in vivo. In industrialized nations, pulse pressure rises with age, and it might serve as a phenotype of biological aging of the vasculature. We therefore conducted a twin study to investigate the relation between telomere length in white blood cells and pulse pressure while simultaneously assessing the role of genetic factors in determining telomere length. We measured by Southern blot analysis the mean length of the terminal restriction fragments (TRF) in white blood cells of 49 twin pairs from the Danish Twin Register and assessed the relations of blood pressure parameters with TRF. TRF length showed an inverse relation with pulse pressure. Both TRF length and pulse pressure were highly familial. We conclude that telomere length, which is under genetic control, might play a role in mechanisms that regulate pulse pressure, including vascular aging.

Phenotypic alterations in senescent large-vessel and microvascular endothelial cells

Endothelial cell senescence likely plays a key role in age-associated vascular diseases. A close relationship between in vitro and in vivo senescence of endothelial cells has been established. Therefore, elucidating the structural and functional changes occurring during long-term cultures of endothelial cells would contribute to clarifying the pathogenesis of vascular disorders in the elderly. We investigated the effects of replicative senescence on the architecture of bovine aortic vs microvascular endothelial cells. A marked increase in cell area was observed in both cell types, whereas dramatic morphological alterations were detected in microvascular endothelial cells only. The latter also showed age-associated reorganization of the actin cytoskeleton. Finally, both aortic and microvascular endothelial cells lost their migratory response to basic fibroblast growth factor with age. Our results highlight dramatic structural and functional alterations in senescent endothelial cells. Such rearrangements might account for in vivo endothelial cell alterations involved in age-associated vascular dysfunction.

The role of telomerase expression and telomere length maintenance in human and mouse

The molecular regulation of telomere length has been well elucidated by a series of elegant studies over the past decade. More recently, experimental evidence has accrued that addresses the challenging question of if and how telomere length regulation may contribute to normal human aging or to human disease. Recent studies in mice have provided a mammalian precedent indicating that telomerase deficiency can lead to in vivo dysfunction, most probably as a consequence of progressive telomere shortening. In humans, the evidence that telomere shortening might lead to in vivo dysfunction is far less direct, although the recent description of telomerase deficiency and telomere shortening associated with the DKC syndrome is suggestive of such a link. Methodologies exist and continue to be developed that are increasingly capable of manipulating telomerase activity and telomere length in human cells. It remains to be determined whether scientifically rigorous and (equally important) medically ethical approaches will emerge to directly assess the ability of telomere length modulation to correct functional disorders of human cellular function ex vivo or more challenging still, in vivo.

Some new directions for research on the biology of aging

A highly selective, eclectic, and personal view of new directions and new opportunities for research on the biology of aging is briefly outlined. Some concern is raised regarding the present emphasis on the use of centenarians for the definition of genetic loci responsible for unusually robust retention of structure and function. More progress is likely to be made were we to focus on the genetic basis for "elite" aging in middle-aged subjects examined for very specific phenotypes, as these are likely to be far less polygenic. Descriptive gerontology is entering a renaissance, given such new clinical tools as functional MRI and basic science tools such as functional genomics and proteomics. Advances in genomics should expedite answers to such questions as why some avian species have exceptionally long lifespans despite unusual loads of oxidative stress. One hopes to see renewed mechanistic studies, using such tools, at the systems levels. New methodologies are permitting the evaluation of stochastic alterations in gene structure and function in postreplicative cells. The exciting work on molecular misreading should prompt us to reexplore the Orgel hypothesis as it applies to such cell types. Epigenetic shifts in gene expression that occur in association with sexual maturation and the cessation of growth may have deleterious consequences late in the life course. It will therefore be important for gerontologists to investigate the molecular biology of pubescence. Finally, our community should investigate the impact of environmental "gerontogens," agents that accelerate specific processes of aging and specific senescent phenotypes.

Homocysteine accelerates endothelial cell senescence

In this study we demonstrate that exposure of cultured endothelial cells to homocysteine significantly accelerates the rate of endothelial senescence. Examination of telomere length demonstrates that homocysteine increases the amount of telomere length lost per population doubling. The effects of homocysteine on both senescence and telomere length are inhibited by treatment with the peroxide scavenger catalase. Chronic exposure of endothelial cells to homocysteine also increases the expression of two surface molecules linked to vascular disease, intracellular adhesion molecule-1 (ICAM-1) and plasminogen activator inhibitor-1 (PAI-1). Interestingly, the level of expression of both ICAM-1 and PAI-1 correlates with the degree of endothelial senescence. Taken together, these results suggest that homocysteine accelerates the rate of cellular senescence through a redox-dependent pathway. In addition, it suggests that chronic oxidative stress in the vessel wall may hasten the rate of senescence and that the senescent endothelial cell may in turn be pro-atherogenic.

Telomere shortening in kidneys with age

The histology and function of the kidney deteriorates with age and age-related diseases, but the mechanisms involved in renal aging are not known. In vitro studies suggest that telomere shortening is important in replicative senescence, and is accelerated by stresses that increase replication. This study explored the relationship between age and telomere length in surgical samples from 24 human kidneys, which were either histologically normal (17) or displayed histologic abnormalities (7). Telomere loss was assessed by two independent methods: Southern blotting of terminal restriction fragments (TRF) and slot blotting using telomere-specific probes. The results of these methods correlated with each other. The mean TRF length determined by Southern blotting in cortex was about 12 kb pairs (kbp) in infancy and was shorter in older kidneys. The slope of the regression line was about 0.029 kbp (0.24%, P = 0.023) per year. Telomere DNA loss in cortex by the slot blot method was 0.25% per year (P = 0.011). By both methods, the telomere loss in medulla was not significant and was less than in cortex. Comparisons of TRF length from 20 paired samples from cortex and medulla showed that TRF was greater in cortex than medulla, with the differences being greater in young kidneys and lessening with age due to telomere loss in cortex. These findings indicate that telomeres shorten in an age-dependent manner in the kidney, either due to developmental factors or aging, particularly in renal cortex.

Somatic mutations and aging: a re-evaluation

Aging has been explained in terms of an accumulation of mutations in the genome of somatic cells, leading to tissue atrophy and neoplasms, as well as increased loss of function. Recent advances in transgenic mouse modeling and genomics technology have created, for the first time, the opportunity to begin testing this theory. In this paper the existing evidence for a possible role of somatic mutation accumulation in aging will be re-evaluated on the basis of the evolutionary logic of aging and recent insights in genome structure and function. New strategies for investigating the relationship between genome instability, mutation accumulation and aging will be discussed.

Alternative pathways for the extension of cellular life span: inactivation of p53/pRb and expression of telomerase

Telomere shortening may be one of several factors that contribute to the onset of senescence in human cells. The p53 and pRb pathways are involved in the regulation of cell cycle progression from G1 into S phase and inactivation of these pathways leads to extension of life span. Short dysfunctional telomeres may be perceived as damaged DNA and may activate these pathways, leading to prolonged arrest in G1, typical of cells in senescence. Inactivation of the p53 and pRb pathways, however, does not lead to cell immortalization. Cells that overcome senescence and have an extended life span continue to lose telomeric DNA and subsequently enter a second phase of growth arrest termed 'crisis'. Forced expression of telomerase in human cells leads to the elongation of telomeres and immortalization. The development of human cancer is frequently associated with the inactivation of the pRb and p53 pathways, attesting to the importance of senescence in restricting the tumor-forming ability of human cells. Cancer cells must also maintain telomere length and, in the majority of cases, this is associated with expression of telomerase activity.

Human endothelial cell life extension by telomerase expression

Normal human endothelial cells, like other somatic cells in culture, divide a limited number of times before entering a nondividing state called replicative senescence. Expression of the catalytic component of human telomerase, human telomerase reverse transcriptase (hTERT), extends the life span of human fibroblasts and retinal pigment epithelial cells beyond senescence without causing neoplastic transformation (Bodnar, A. G., Ouellette, M., Frolkis, M., Holt, S. E., Chiu, C. P., Morin, G. B., Harley, C. B., Shay, J. W., Lichtsteiner, S., and Wright, W. E. (1998) Science 279, 349-352; Jiang, X., Jimenez, G., Chang, E., Frolkis, M., Kusler, B., Sage, M., Beeche, M., Bodnar, A., Wahl, G., Tlsty, T., and Chiu, C.-P. (1999) Nat. Genet. 21, 111-114). Here, we show that both human large vessel and microvascular endothelial cells also bypass replicative senescence after introduction of hTERT. For the first time, we report that hTERT expression in these life-extended vascular cells does not affect their differentiated and functional phenotype and that these cells maintain their angiogenic potential in vitro. Furthermore, hTERT(+) microvascular endothelial cells have normal karyotype, and hTERT(+) endothelial cell strains do not exhibit a transformed phenotype. Relative to parental cells at senescence, hTERT-expressing endothelial cells exhibit resistance to induction of apoptosis by a variety of different conditions. Such characteristics are highly desirable for designing vascular transplantation and gene therapy delivery systems in vivo.

Age-dependent changes in DNA polymerase fidelity and proofreading activity during cellular aging

DNA polymerase alpha and the 3'-->5' exonuclease involved in the proofreading of DNA synthesis were isolated from human diploid fetal lung fibroblast (TIG-1) cells at various population doubling levels (PDL). The final PDL of the TIG-1 cells used in these experiments was 70. The fidelity of DNA polymerase alpha remained high until late passage and fell suddenly just before the end of the life span between 65 and 69 PDL. The activities of the 3'-->5' exonuclease related to proofreading remained unchanged from 21 to 61 PDL, but the activity decreased rapidly in more aged cells. The 3'-->5' exonuclease activity at 69 PDL was about 50% of that in TIG cells at 21 PDL. In vitro DNA synthesis by DNA polymerase alpha from TIG-1 cells harvested at 69 PDL showed the amount of non-complementary nucleotides incorporated to be decreased by the addition of the 3'-->5' exonuclease from the same cells. However, not all errors were edited out since the ratio of DNA polymerase activity to 3'-->5' exonuclease activity was adjusted to reflect that in vivo and the infidelity of DNA synthesis by error-prone DNA polymerase alpha from aged cells was improved by the addition of the highly active 3'-->5' exonuclease from cells at 41 PDL. These results suggested that the mutation frequency rises just before the end of the life span of TIG-1 cells.

Resistance to apoptosis in human CD8+ T cells that reach replicative senescence after multiple rounds of antigen-specific proliferation

We have established an in vitro culture model of cellular aging in which antigen-specific T cells are stimulated repeatedly to divide until they reach the irreversible state of growth arrest known as "replicative senescence." T lymphocytes that reach replicative senescence in culture show complete loss of CD28 expression, shortened telomeres, undetectable telomerase, and reduced ability to produce heat shock proteins. We now document that in response to treatment with apoptotic stimuli, senescent CD8+ T-cell cultures show reduced apoptosis and diminished caspase 3 activity compared with quiescent early passage cultures from the same donor. Our results suggest that the progressive accumulation of T cells showing many of the hallmarks of replicative senescence during aging, chronic infection, and autoimmune disease may, in part, reflect the diminished capacity of such cells to undergo normal programmed cell death.

Telomerase activation in human fibroblasts during escape from crisis

The immortalization of human diploid fibroblasts requires the circumvention of both the senescence (M1) and crisis (M2) mechanisms of growth control. Cells expressing the SV40 T antigen virtually always bypass senescence, but only rarely escape crisis. The low frequency of this latter event indicates that cellular mutations are necessary to escape crisis. Thirteen subpopulations of T antigen-expressing human fibroblasts were cultured into crisis. Colonies that appeared to resume growth were assayed for telomerase activity, telomere maintenance, and the immortal phenotype. Our results show that 33 of 35 colonies were telomerase negative and were not immortal. Two colonies were telomerase positive when assayed in the first approximately 15 population doublings after crisis. The first was strongly positive, maintained telomeres at a stable short length, and was later determined to be immortal. The second initially had a weak telomerase signal, grew extremely slowly, and when examined had greatly elongated telomeres consistent with the ALT (alternative lengthening of telomeres) mechanism of telomere maintenance. These cells eventually grew faster and were later determined to be immortal. Additionally, two subpopulations had initially weak and later strong telomerase activity and the cells never entered a defined crisis period. We observed a perfect correlation between telomere maintenance and escape from crisis, supporting the hypothesis that the lack of stable telomeres causes crisis and that the ability to maintain telomeres abrogates crisis.

Telomere shortening with aging in human esophageal mucosa

Progressive telomere shortening with aging was studied using normal esophageal mucosal specimens from 177 human subjects aged between 0 and 102 years (yrs). We observed age-related shortening of the telomere, at a rate of 60 base pairs (bp) per year (yr). The mean telomere length of 12 neonates was 15.2 kilobase pairs (kbp) and that of 2 centenarians was 9.3 kbp. Mean (±SD) telomere lengths were 14.9±1.3, 14.0±1.8, 10.1±3.7, 10.4±3.3 and 9.5±3.1 kbp for the age groups less than 2 yrs, 2-20 yrs, 21-60 yrs, 61-80 yrs and 81-102 yrs, respectively. The variation in telomere length among individuals in the same age group was greater for the 3 older groups than for the 2 younger groups, as shown by the SDs. Furthermore, older individuals had greater telomere length variation than younger individuals, based on the lengths of DNA digested smears. Although the telomere length decreased significantly with aging at the rate of 60 bp per yr, differences in the mean telomere lengths between the 3 older age groups were not significant. Rapid shortening occurred in the young generations and there was no further substantial decrease in the esophageal mucosa after 60 yrs of age. Compared to the very rapid renewal rate of the esophageal epithelial cells, the annual reduction rate in telomere length was very low. These findings support the hypothesis that germ cells in the esophageal epithelium have a mechanism to lengthen telomeres.

Absence of correlation between telomerase activity and hepatic neoplasia in B6C3F1 mice

Telomeres are the physical ends of eukaryotic chromosomes, which maintain chromosome stability and are progressively shortened with aging in somatic cells. The enzyme telomerase elongates telometric DNA and while not usually detectable in human somatic cells is expressed in most human tumors. The present study was conducted to determine if telomerase activity is a marker for spontaneous hepatic neoplastic changes in B6C3F1 mice, a strain frequently used in rodent carcinogenicity studies. Telomerase activity was generally higher in microscopically normal liver tissue from 8-week-old compared to aged mice (110-week-old); however, telomerase activity was not consistently increased in hepatocellular adenomas and carcinomas. It is proposed that, while elevated telomerase activity may modulate human tumor development, modulation of telomerase activity is not a feature of hepatic tumors in B6C3F1 mice and therefore is unlikely to have utility as a molecular marker for hepatic neoplasia in this mouse strain.

Intact functional domains of the retinoblastoma gene product (pRb) are required for downregulation of telomerase activity

The ends of human chromosomes (telomeres) consist of tandem repeats of the sequence TTAGGG. Telomeres lose up to 200 base pairs of DNA per cell division due to the inability of DNA polymerase to completely replicate the chromosomal ends. Chromosomal shortening ultimately leads to senescence and cell death in normal cells. However, some immortal cells do not lose telomeric sequence during DNA replication. Many human carcinoma lines are immortal in vitro, suggesting that these cells have a mechanism for maintaining the ends of their chromosomes. Telomerase is a ribonucleoprotein complex that synthesizes telomeric DNA onto chromosomes using its RNA component as a template. To elucidate potential mechanisms for telomerase regulation, we tested human squamous cell carcinoma lines (SCCs) for telomerase activity. All SCC lines expressed high levels of telomerase activity. Synchronization in specific cell cycle phases caused marked reduction in telomerase activity in G0 and S, but not in G1 or M. Reduction in telomerase activity correlated with induction of Rb protein in these phases. Overexpression of full length Rb resulted in significant downregulation of telomerase activity. However, expression of an Rb N-terminal oligomerization domain deletion construct, a C-terminal DNA binding domain deletion construct, or a pocket domain mutant failed to downregulate telomerase activity. We concluded that functionally intact Rb was required for cell cycle-dependent downregulation of telomerase activity in SCC lines.

Telomeric instability and reduced proliferative potential in ovarian surface epithelial cells from women with a family history of ovarian cancer

OBJECTIVE

Increased telomeric instability in normal ovarian surface epithelium may contribute to ovarian carcinogenesis in women from families with a high frequency of breast/ovarian cancer. To test this hypothesis, we compared proliferative potential, mean telomeric length, and telomerase activity in SV-40 large T-antigen transfected cell lines derived from normal ovarian surface epithelium of women with and without a familial history of breast/ovarian cancer.

METHODS

Telomeric instability was examined in SV-40 large T-antigen transfected cell lines of normal ovarian surface epithelium from patients with (FHIOSE, N = 5) and without (NFHIOSE, N = 11) a history of familial breast/ovarian cancer. The duration and total attainable number of population doublings, mean telomeric length, rate of telomeric loss, and telomerase activity were determined by cell counts, Southern blot analysis, and PCR ELISA.

RESULTS

FHIOSE cells attained fewer population doublings than NFHIOSE cells and doubled at approximately half the rate of NFHIOSE cells, indicating a reduced proliferative capacity in FHIOSE cells. While telomerase activity was not detected in FHIOSE or NFHIOSE cell lines, mean telomeric lengths in FHIOSE were generally 1 kb shorter than in NFHIOSE cells and the rate of telomeric loss as a function of population doublings was up to threefold greater in FHIOSE cells.

CONCLUSIONS

Increased telomeric instability and reduced growth potential suggest greater proximity to replicative senescence in ovarian surface epithelium from women with a familial history of breast/ovarian cancer. Consequently, an accumulation of genetic aberrations due to accelerated cellular aging may contribute to the enhanced susceptibility for malignant transformation and earlier onset in heritable ovarian cancer.

Telomere length in fibroblasts and blood cells from healthy centenarians

Several lines of evidence indicate that telomere shortening during in vitro aging of human somatic cells plays a causal role in cellular senescence. A critical telomere length seems to be associated with the replicative block characterizing senescent cells. In this paper we analyzed the mean length of the terminal restriction fragments (TRF) in fibroblast strains from 4 healthy centenarians, that is, in cells aged in vivo, and from 11 individuals of different ages. No correlation between mean TRF length and donor age was found. As expected, telomere shortening was detected during in vitro propagation of centenarian fibroblasts, suggesting that in fibroblasts aged in vivo telomeres can be far from reaching a critical length. Accordingly, chromosome analysis did not show the presence of telomeric associations in early passage centenarian fibroblasts. In blood cells from various individuals, the expected inverse correlation between mean TRF length and donor age was found. In particular, a substantial difference (about 2 kb) between telomere length in the two cell types was observed in the same centenarian. Expression analysis of three senescence-induced genes, i.e., fibronectin, apolipoprotein J, and p21, revealed for only the fibronectin expression levels a clear positive correlation with donor age. Our results suggest that (1) telomere shortening could play a different role in the aging of different cell types and (2) the characteristics of fibroblasts aged in vitro might not be representative of what occurs in vivo.

Early growth determines longevity in male rats and may be related to telomere shortening in the kidney

Maternal protein undernutrition can influence the growth and longevity of male offspring in the rat. We tested the hypothesis that these differences in longevity were associated with changes in the rate of telomere shortening. We found age-related shortening of telomeres in the liver and kidney but not in the brain of male rats. Growth retardation in postnatal life was associated with significantly longer kidney telomeres and an increased longevity. Conversely, growth retardation during the foetal life followed by postnatal catch-up growth was associated with a shorter life span and shorter kidney telomeres. These findings may provide a mechanistic basis for epidemiological studies linking early growth retardation to adult degenerative diseases.