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

Long non-coding RNAs: novel regulators of cellular physiology and function

Long non-coding RNAs were once considered as “junk” RNA produced by aberrant DNA transcription. They are now understood to play central roles in diverse cellular processes from proliferation and migration to differentiation, senescence and DNA damage control. LncRNAs are classed as transcripts longer than 200 nucleotides that do not encode a peptide. They are relevant to many physiological and pathophysiological processes through their control of fundamental molecular functions. This review summarises the recent progress in lncRNA research and highlights the far-reaching physiological relevance of lncRNAs. The main areas of lncRNA research encompassing their characterisation, classification and mechanisms of action will be discussed. In particular, the regulation of gene expression and chromatin landscape through lncRNA control of proteins, DNA and other RNAs will be introduced. This will be exemplified with a selected number of lncRNAs that have been described in numerous physiological contexts and that should be largely representative of the tens-of-thousands of mammalian lncRNAs. To some extent, these lncRNAs have inspired the current thinking on the central dogmas of epigenetics, RNA and DNA mechanisms.

Serum anti-inflammatory and inflammatory markers have no causal impact on telomere length: a Mendelian randomization study

INTRODUCTION

The relationship between inflammatory and anti-inflammatory markers and telomere length (TL), a biological index of aging, is still poorly understood. By applying a 2-sample Mendelian randomization (MR), we investigated the causal associations between adiponectin, bilirubin, C-reactive protein (CRP), leptin, and serum uric acid (SUA) with TL.

MATERIAL AND METHODS

MR was implemented by using summary-level data from the largest ever genome-wide association studies (GWAS) conducted on our interested exposure and TL. Inverse variance weighted method (IVW), weighted median (WM)-based method, MR-Egger, MR-Robust Adjusted Profile Score (RAPS), and MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were applied. Sensitivity analysis was conducted using the leave-one-out method.

RESULTS

With regard to adiponectin, CRP, leptin, and SUA levels, we found no effect on TL for all 4 types of tests (all p > 0.108). Results of the MR-Egger (p = 0.892) and IVW (p = 0.124) showed that bilirubin had no effect on telomere maintenance, whereas the results of the WM (p = 0.030) and RAPS (p = 0.022) were negative, with higher bilirubin concentrations linked to shorter TL. There was a low likelihood of heterogeneity for all the estimations, except for bilirubin (IVW p = 0.026, MR Egger p = 0.018). MR-PRESSO highlighted no outlier. For all the estimations, we observed negligible intercepts that were indicative of low likelihood of the pleiotropy (all p > 0.161). The results of leave-one-out method demonstrated that the links are not driven because of single nucleotide polymorphisms (SNPs).

CONCLUSIONS

Our results highlight that neither the anti-inflammatory nor pro-inflammatory markers tested have any significant causal effect on TL. The casual role of bilirubin on TL still needs to be investigated.

Both in vitro T cell proliferation and telomere length are decreased, but CD25 expression and IL-2 production are not affected in aged men

INTRODUCTION

Aging is a natural process involving dysfunction of multiple organs and is characterized by increased susceptibility to infections, cancer and autoimmune diseases. The functionality of the immune system depends on the capacity of lymphocytes to proliferate in response to antigenic challenges, and telomere length has an important role regulating the number of cell divisions. The aim of this study was to determine the possible relationship between telomere length, interleukin 2 (IL-2) production, CD25 expression and proliferation of peripheral blood mononuclear cells (PBMCs) in aged men.

MATERIAL AND METHODS

Telomere length was measured by RT-PCR in PBMCs from young and aged men. IL-2 production and CD25 expression were determined by ELISA and flow cytometry, respectively. Cell proliferation was measured by CFSE dilution assays upon in vitro stimulation with concanavalin A (Con A).

RESULTS

PBMCs from aged men showed a shorter telomere length and a reduced capacity to proliferate in vitro, compared to young men. In contrast, no significant differences in the level of CD25 expression on T lymphocytes, and in vitro production of IL-2 were detected in both groups. In addition, no significant correlation was detected between levels of CD25 expression, IL-2 production, cell proliferation, and telomere length in aged men.

CONCLUSIONS

In aged men the telomere length shortening and the reduced T cell proliferation are not related to the capacity of IL-2 production and CD25 expression on T lymphocytes.

Correlation Between Differentiation of Adrenocortical Zones and Telomere Lengths Measured by Q-FISH

CONTEXT

Adrenocortical zonation is associated with a markedly complex developmental process, and the pathogenesis and/or etiology of many disorders of adrenocortical zonal development have remained unknown. Cells from the three adrenocortical zones are morphologically and functionally differentiated, and the mature stage of cell development or senescence has been recently reported to be correlated with telomere length. However, the telomere length of each adrenocortical zonal cell has not yet been studied in human adrenal glands.

OBJECTIVE

We aimed to study the telomere lengths of adrenocortical parenchymal cells from three different zones of the adrenal glands present during childhood, adolescence, and adulthood.

METHODS

Adrenal glands of 30 autopsied subjects, aged between 0 and 68 years, were retrieved from pathology files. The normalized telomere to centromere ratio (NTCR), an index of telomere length, was determined in the parenchymal cells of the zona glomerulosa, zona fasciculata, and zona reticularis (ZR), using quantitative fluorescence in situ hybridization.

RESULTS

NTCR of ZR cells was the longest, followed in decreasing order by that of zona glomerulosa and zona fasciculata cells in subjects aged 20 to 68 years, but no substantial differences in NTCR were detected among these three zones in the group <20 years of age. NTCR of ZR increased with age in subjects aged 20 to 68 years, whereas no important age-dependent changes in NTCR were detected in the group <20 years of age.

CONCLUSION

The telomere lengths for three zones in adrenal cortex were correlated with their differentiation in adulthood but not in childhood and adolescence.

Vimentin Plays a Crucial Role in Fibroblast Ageing by Regulating Biophysical Properties and Cell Migration

Ageing is the result of changes in biochemical and biophysical processes at the cellular level that lead to progressive organ decline. Here we focus on the biophysical changes that impair cellular function of human dermal fibroblasts using donors of increasing age. We find that cell motility is impaired in cells from older donors, which is associated with increased Young’s modulus, viscosity, and adhesion. Cellular morphology also displays parallel increases in spread area and cytoskeletal assembly, with a threefold increase in vimentin filaments alongside a decrease in its remodelling rate. Treatments with withaferin A or acrylamide show that cell motility can be modulated by regulating vimentin assembly. Crucially, decreasing vimentin amount in cells from older individuals to levels displayed by the neonatal donor rescues their motility. Our results suggest that increased vimentin assembly may underlay the aberrant biophysical properties progressively observed at the cellular level in the course of human ageing and propose vimentin as a potential therapeutic target for ageing-related diseases.

Significant SNPs Related to Telomere Length and Hepatocellular Carcinoma Risk in Chronic Hepatitis B Carriers

Chronic hepatitis B virus (HBV) infection increases the risk of developing cirrhosis and hepatocellular carcinoma (HCC) with suspected interactions between virus replication and host immune responses. A number of reports have suggested that telomerase function may be involved in chronic hepatitis B (CHB) pathogenesis, but positive or negative associations with HCC risk remain for discussion. Mean telomere length is an indicator of biological aging and it has been reported that reduction in NBV carriers compared to normal individuals. In somatic cells, telomeres contain simple, tandemly repeated G-rich sequences that frequently are reduced by 50 to 200 base pairs at each cell division. Several genome-wide association studies (GWAS) in diverse ethnic populations have revealed eleven single nucleotide polymorphisms (SNPs) linked to telomere length. Two of these, rs398652 and rs621559, have prognostic value and could be used as genetic markers. This review describes current knowledge concerning telomerase activity and telomere length as well as significant polymorphisms in HBV-related HCC patients. In particular, to cast light on genotype-phenotype interactions, we used SNPnexus to evaluate effects of the two SNPs on risk of disease and complex disorders.

Anticancer effects of methanol extract of Myrmecodia platytyrea Becc. leaves against human hepatocellular carcinoma cells via inhibition of ERK and STAT3 signaling pathways

Myrmecodia platytyrea Becc., a member of the Rubiaceae family, is found throughout Southeast Asia and has been traditionally used to treat cancer. However, there is limited pharmacological information on this plant. We investigated the anticancer effects of the methanol extract of Myrmecodia platytyrea Becc. leaves (MMPL) and determined the molecular mechanisms underlying the effects of MMPL on metastasis in human hepatocellular carcinoma (HCC) cells. MMPL dose-dependently inhibited cell migration and invasion in SK‑Hep1 and Huh7 cells. In addition, MMPL strongly suppressed the enzymatic activity of matrix metalloproteinases (MMP‑2 and MMP‑9). Diminished telomerase activity by MMPL resulted in the suppression of both telomerase activity and telomerase-associated gene expression. The levels of urokinase-type plasminogen activator receptor (uPAR) expression as well as the phosphorylation levels of signal transducer and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase (ERK) were also attenuated by MMPL. The above results collectively suggest that MMPL has anticancer effects in HCC and that MMPL can serve as an effective therapeutic agent for treating human liver cancer.

A quantitative model of cellular senescence influence on cancer and longevity

Contrary to the paradigm that cancer incidence increases indefinitely with age, significant data now suggest cancer incidence may markedly reduce beyond age 80 years for humans and beyond 800 days for mice, and is not inevitable. We show that increasing cellular senescence with age is a possible cause of this reduction, since senescent cells are removed from the pool of cells that retain proliferative ability necessary for cancer. We further show that animal interventions appearing to alter senescence, p53 mutation and melatonin dosing, support the prediction that increasing senescence rate reduces cancer while reducing lifespan, and vice versa. Studies of environmental agents associated with increased cancer might be re-examined to find if there is an association with longevity increases, which may markedly alter our view of such agents. We also show that if an agent functions by slowing both senescence and carcinogenesis, longevity is increased while reducing cancer. Dietary restriction is the only known intervention that accomplishes this, but there may be others.

Effects of age, replicative lifespan and growth rate of human nucleus pulposus cells on selecting age range for cell-based biological therapies for degenerative disc diseases

Autologous disc cell implantation, growth factors and gene therapy appear to be promising therapies for disc regeneration. Unfortunately, the replicative lifespan and growth kinetics of human nucleus pulposus (NP) cells related to host age are unclear. We investigated the potential relations among age, replicative lifespan and growth rate of NP cells, and determined the age range that is suitable for cell-based biological therapies for degenerative disc diseases. We used NP tissues classified by decade into five age groups: 30s, 40s, 50s, 60s and 70s. The mean cumulative population doubling level (PDL) and population doubling rate (PDR) of NP cells were assessed by decade. We also investigated correlations between cumulative PDL and age, and between PDR and age. The mean cumulative PDL and PDR decreased significantly in patients in their 60s. The mean cumulative PDL and PDR in the younger groups (30s, 40s and 50s) were significantly higher than those in the older groups (60s and 70s). There also were significant negative correlations between cumulative PDL and age, and between PDR and age. We found that the replicative lifespan and growth rate of human NP cells decreased with age. The replicative potential of NP cells decreased significantly in patients 60 years old and older. Young individuals less than 60 years old may be suitable candidates for NP cell-based biological therapies for treating degenerative disc diseases.

Quantifying replicative senescence as a tumor suppressor pathway and a target for cancer therapy

To study quantitatively replicative senescence as a tumor suppressor mechanism, we investigate the distribution of a growing clonal cell population restricted by Hayflick’s limit. We find that in the biologically relevant range of parameters, if the imbalance between cell division and death is moderate or low (high death-to-birth ratio), senescence offers significant protection against cancer by halting abnormal cell proliferation at early pre-diagnostic stages of tumor development. We also find that by the time tumors are typically detected, there is a high probability that telomerase is activated, even if the cell of origin was telomerase negative. Hence, the fact that most cancers are positive for telomerase is not necessarily an indication that cancer originated in a telomerase positive cell. Finally, we discuss how the population dynamics of cells can determine the outcomes of anti-telomerase cancer therapies, and provide guidelines on how the model could potentially be applied to develop clinically useful tools to predict the response to treatment by telomerase inhibitors in individual patients.

Relationship between Initial Telomere Length, Initial Telomerase Activity, Age, and Replicative Capacity of Nucleus Pulposus Chondrocytes in Human Intervertebral Discs: What Is a Predictor of Replicative Potential?

There is evidence that telomere length (TL), telomerase activity (TA), and age are related to the replicative potential of human nucleus pulposus chondrocytes (NPCs). However, it has not yet been established if any of these factors can serve as predictors of the replicative potential of NPCs. To establish predictors of the replicative potential of NPCs, we evaluated potential relationships between replicative capacity of NPCs, initial TL (telomere length at the first passage), initial TA (telomerase activity at the first passage), and age. Nucleus pulposus specimens were obtained from 14 patients of various ages undergoing discectomy. NPCs were serially cultivated until the end of their replicative lifespans. Relationships among cumulative population doubling level (PDL), initial TL, initial TA, and age were analyzed. Initial TA was negatively correlated with age (r = -0.674, P = 0.008). However, no correlation between initial TL and age was observed. Cumulative PDL was also negatively correlated with age (r = -0.585, P = 0.028). Although the cumulative PDL appeared to increase with initial TL or initial TA, this trend was not statistically significant. In conclusion, age is the sole predictor of the replicative potential of human NPCs, and replicative potential decreases with age. Initial TL and initial TA are not predictors of replicative potential, and can serve only as reference values.

The DNA structure and sequence preferences of WRN underlie its function in telomeric recombination events

Telomeric abnormalities caused by loss of function of the RecQ helicase WRN are linked to the multiple premature ageing phenotypes that characterize Werner syndrome. Here we examine WRN's role in telomeric maintenance, by comparing its action on a variety of DNA structures without or with telomeric sequences. Our results show that WRN clearly prefers to act on strand invasion intermediates in a manner that favours strand invasion and exchange. Moreover, WRN unwinding of these recombination structures is further enhanced when the invading strand contains at least three G-rich single-stranded telomeric repeats. These selectivities are most pronounced at NaCl concentrations within the reported intranuclear monovalent cation concentration range, and are partly conferred by WRN's C-terminal region. Importantly, WRN's specificity for the G-rich telomeric sequence within this precise structural context is particularly relevant to telomere metabolism and strongly suggests a physiological role in telomeric recombination processes, including T-loop dynamics.

Cell-Free Fetal DNA, Telomeres, and the Spontaneous Onset of Parturition

Multiple previous reports have provided compelling support for the premise that spontaneous parturition is mediated by activation of inflammation-related signaling pathways leading to increased secretion of cytokines and chemokines, the influx of neutrophils and macrophages into the pregnant uterus, increased production of uterine activation proteins (eg, connexin-43, cyclo-oxygenase-2, oxytocin receptors, etc), activation of matrix metalloproteinases, and the release of uterotonins leading to cervical ripening, membrane rupture, and myometrial contractions. The missing link has been the fetal/placental signal that triggers these proinflammatory events in the absence of microbial invasion and intrauterine infection. This article reviews the biomedical literature regarding the increase in cell-free fetal DNA (cffDNA), which is released during apoptosis in the placenta and fetal membranes at term, the ability of apoptosis modified vertebrate DNA to stimulate toll-like receptor-9 (TLR9) leading to increased release of cytokines and chemokines, and the potential "fail-safe" role for the anti-inflammatory cytokine IL-10. This article also reviews the literature supporting the key role that telomere loss plays in regard to increasing the ability of vertebrate (including placental) DNA to stimulate TLR9, and in regard to signaling the onset of apoptosis in the placenta and fetal membranes, thereby providing a biologic clock that determines the length of gestation and the timing for the onset of parturition. In summary, this literature review provides a strong rationale for future research to test the hypothesis that telomere loss and increased cffDNA levels trigger the proinflammatory events leading to the spontaneous onset of parturition in mammals: the "cffDNA/telomere hypothesis."

Increased telomere length and proliferative potential in peripheral blood mononuclear cells of adults of different ages stimulated with concanavalin A

BACKGROUND

Recently, a direct correlation with telomere length, proliferative potential and telomerase activity has been found in the process of aging in peripheral blood cells. The objective of the study was to evaluate telomere length and proliferative potential in peripheral blood mononuclear cells (PBMCs) after stimulation with Concanavalin A (ConA) of young adults compared with older adults.

METHODS

Blood samples were obtained from 20 healthy young males (20-25 years old) (group Y) and 20 males (60-65 years old) (group O). We compared PBMC proliferation before and after stimulation with ConA. DNA was isolated from cells separated before and after culture with ConA for telomeric measurement by real-time polymerase chain reaction.

RESULTS

In vitro stimulation of PBMCs from young subjects induced an increase of telomere length as well as a higher replicative capacity of cell proliferation. Samples from older adults showed higher loss of telomeric DNA (p = 0.03) and higher levels of senescent (≤6.2 kb) telomeric DNA (p = 0.02) and displayed a marked decrease of proliferation capacity. Viability cell counts and CFSE tracking in 72-h-old cell cultures indicated that group O PBMCs (CD8+ and CD4+ T cells) underwent fewer mitotic cycles and had shorter telomeres than group Y (p = 0.04).

CONCLUSIONS

Our findings confirm that telomere length in older-age adults is shorter than in younger subjects. After stimulation with ConA, cells are not restored to the previous telomere length and undergo replicative senescence. This is in sharp contrast to the response observed in young adults after ConA stimulation where cells increase in telomere length and replicative capacity. The mechanisms involved in this phenomenon are not yet clear and merit further investigation.

Endogenous oxidative stress prevents telomerase-dependent immortalization of human endothelial cells

INTRODUCTION

With aging, oxidative stress accelerates vascular endothelial cell (EC) telomere shortening-induced senescence, and may promote atherosclerosis in humans. Our aim was to investigate whether an antioxidant treatment combined with telomerase (hTERT) over-expression would prevent senescence of EC isolated from patients with severe atherosclerosis.

METHODS

Cells were isolated from internal mammary arteries (n=11 donors), cultured until senescence with or without N-acetylcystein (NAC) and infected, or not, with a lentivirus over-expressing hTERT.

RESULTS

Compared to control EC, hTERT-NAC cells had increased telomerase activity, longer telomeres and underwent more cell divisions. According to the donor, hTERT-NAC either delayed (n=5) or prevented (n=4) EC senescence, the latter leading to cell immortalization. Lack of cell immortalization by hTERT-NAC was accompanied by an absence of beneficial effect of NAC alone in paired EC. Accordingly, lack of EC immortalization by hTERT-NAC was associated with high endogenous susceptibility to oxidation. In EC where hTERT-NAC did not immortalize EC, p53, p21 and p16 expression increased with senescence, while oxidative-dependent DNA damage associated with senescence was not prevented.

CONCLUSION

Our data suggest that irreversible oxidative stress-dependent damages associated with cardiovascular risk factors are responsible for senescence of EC from atherosclerotic patients.

Correlation of donor age and telomerase activity with in vitro cell growth and replicative potential for dermal fibroblasts and keratinocytes

Previous studies suggested telomerase activity as a determinant of cell replicative capacity by delaying cell senescence. This study aimed to evaluate the feasibility of adopting telomerase activity as a selection criterion for in vitro expanded skin cells before autologous transplantation. Fibroblasts and keratinoctyes were derived from the same consenting patients aged 9-69 years, and cultured separately in serum-supplemented and serum-free media, respectively. Telomerase activity of fresh and cultured cells were measured and correlated with cell growth rate, donor age and passage number. The results showed that telomerase activity and cell growth were independent of donor age for both cell types. Telomerase was expressed in freshly digested epidermis and dermis and continued expressing in vitro. Keratinocytes consistently showed 3-12 folds greater telomerase activity than fibroblast both in vivo and in vitro. Conversely, growth rate for fibroblast exceeded that of keratinocyte. Telomerase activity decreased markedly at Passage 6 for keratinocytes and ceased by Passage 3 for fibroblasts. The decrease or cessation of telomerase activity coincided with senescence for keratinocyte but not for fibroblast, implying a telomerase-regulated cell senescence for the former and hence a predictor of replicative capacity for this cell type. Relative telomerase activity for fibroblasts from the younger age group was significantly higher than that from the older age group; 69.7% higher for fresh isolates and 31.1% higher at P0 (p<0.05). No detectable telomerase activity was to be found at later subcultures for both age groups. Similarly for keratinocytes, telomerase activity in the younger age group was significantly higher (p<0.05) compared to that in the older age group; 507.7% at P0, 36.8% at P3 and the difference was no longer significant at P6. In conclusion, the study provided evidence that telomerase sustained the proliferation of keratinocytes but not fibroblasts. Telomerase activity is an important criterion for continued survival and replication of keratinocytes, hence its positive detection before transplantation is desirable. Inferring from our results, the use of keratinocytes from Passage 3 or lesser for construction of skin substitute or cell-based therapy is recommended owing to their sustained telomerase expression.

Cellular senescence in pretransplant renal biopsies predicts postoperative organ function

Older and marginal donors have been used to meet the shortfall in available organs for renal transplantation. Post-transplant renal function and outcome from these donors are often poorer than chronologically younger donors. Some organs, however, function adequately for many years. We have hypothesized that such organs are biologically younger than poorer performing counterparts. We have tested this hypothesis in a cohort of preimplantation human renal allograft biopsies ( n = 75) that have been assayed by real-time polymerase chain reaction for the expression of known markers of cellular damage and biological aging, including CDKN2A, CDKN1A, SIRT2 and POT1. These have been investigated for any associations with traditional factors affecting transplant outcome (donor age, cold ischaemic time) and organ function posttransplant (serum creatinine levels). Linear regression analyses indicated a strong association for serum creatinine with pre-transplant CDKN2A levels ( p = 0.001) and donor age ( p = 0.004) at 6 months post-transplant. Both these markers correlated significantly with urinary protein to creatinine ratios ( p = 0.002 and p = 0.005 respectively), an informative marker for subsequent graft dysfunction. POT1 expression also showed a significant association with this parameter ( p = 0.05). Multiple linear regression analyses for CDKN2A and donor age accounted for 24.6% ( p = 0.001) of observed variability in serum creatinine levels at 6 months and 23.7% ( p = 0.001) at 1 year posttransplant. Thus, these data indicate that allograft biological age is an important novel prognostic determinant for renal transplant outcome.

Improving cell therapy--experiments using transplanted telomerase-immortalized cells in immunodeficient mice

Cell therapy is the use of stem cells and other types of cells in various therapies for age-related diseases. Two issues that must be addressed before cell therapy could be used routinely in medicine are improved efficacy of the transplanted cells and demonstrated long-term safety. Desirable genetic modifications that could be made to cells to be used for cell therapy include immortalization with human telomerase reverse transcriptase (hTERT). We have used a model for cell therapy in which transplantation of adrenocortical cells restores glucocorticoid and mineralocorticoid hormone levels in adrenalectomized immunodeficient mice. In this model, clones of cells that had been immortalized with hTERT were shown to be able to replace the function of the animals' adrenal glands by forming vascularized tissue structures when cells were transplanted beneath the capsule of the kidney. hTERT-modified cells showed no tendency for neoplastic changes. Moreover, a series of experiments showed that hTERT does not cooperate with known oncoproteins in tumorigenesis either in adrenocortical cells or in human fibroblasts. Nevertheless, hTERT was required for tumorigenesis when cells were implanted subcutaneously rather than in the subrenal capsule space. Changes in gene expression make hTERT-modified cells more robust. Understanding these changes is important so as to be able to separately control immortalization and other desirable properties of cells that could be used in cell therapy. Alternatively, desirable properties of transplants might be provided by co-transplanted mesenchymal cells: mesenchymal cell-assisted cell therapy. For both hTERT modification and mesenchymal cell-assisted cell therapy, genomics approaches will be needed to define what genetic modifications are desirable and safe in cells used in cell therapy.

Fat depot-specific characteristics are retained in strains derived from single human preadipocytes

Fat depots vary in size, function, and potential contribution to disease. Since fat tissue turns over throughout life, preadipocyte characteristics could contribute to this regional variation. To address whether preadipocytes from different depots are distinct, we produced preadipocyte strains from single abdominal subcutaneous, mesenteric, and omental human preadipocytes by stably expressing human telomere reverse transcriptase (hTERT). These strains could be subcultured repeatedly and retained capacity for differentiation, while primary preadipocyte adipogenesis and replication declined with subculturing. Primary omental preadipocytes, in which telomeres were longest, replicated more slowly than mesenteric or abdominal subcutaneous preadipocytes. Even after 40 population doublings, replication, abundance of the rapidly replicating preadipocyte subtype, and resistance to tumor necrosis factor alpha-induced apoptosis were highest in subcutaneous, intermediate in mesenteric, and lowest in omental hTERT-expressing strains, as in primary preadipocytes. Subcutaneous hTERT-expressing strains accumulated more lipid and expressed more adipocyte fatty acid-binding protein (aP2), peroxisome proliferator-activated receptor gamma2, and CCAAT/enhancer-binding protein alpha than omental cells, as in primary preadipocytes, while hTERT abundance was similar. Thus, despite dividing 40 population doublings, hTERT strains derived from single preadipocytes retained fat depot-specific cell dynamic characteristics, consistent with heritable processes contributing to regional variation in fat tissue function.

Human adult olfactory neuroepithelial derived progenitors retain telomerase activity and lack apoptotic activity

Olfactory epithelium (OE) contains a population of progenitors responsible for its life-long regenerative capacity. Procedures for the isolation of these progenitors have been established [F.J. Roisen, K.M. Klueber, C.L. Lu, L.M. Hatcher, A. Dozier, C.B. Shields, Adult human olfactory stem cells, Brain Res., 890 (2001) 11-12.] and over 40 patient-specific cell lines from adult postmortem OE and endoscopic biopsy from patients undergoing nasal sinus surgery have been obtained. As these cells emerged in primary cultures, they formed neurospheres (NSFCs). The purpose of the present study was to further characterize these adult human olfactory-derived progenitors. Subcultures of the NSFCs have been passaged nearly 200 times, with a mitotic cycle of 18-20 h. Telomerase activity remains in stem cells; therefore, ELISA was employed to determine the telomerase activity of different lines and passages. Since progenitors undergo low levels of apoptosis, the levels of apoptosis were also examined in these populations. The levels of telomerase and apoptotic activity in 12 NSFC lines remained relatively constant irrespective of donor age, culture duration, or sex. To further study the apoptotic characteristics of the NSFCs, nine different caspases (cysteine proteases) known to be critical in apoptosis were evaluated using gene-microarrays comparing cells from a single line at passages 14, 88, and 183. No increases were found in caspase activity in all passages studied. ELISA confirmed the absence of caspase activity over the entire range of passages. This study further suggests that NSFCs can be obtained and used from patients, irrespective of age, sex, or time in culture without altered viability expanding the potential utility of these cells for autologous transplantation and possible diagnostic testing.

Telomere length assessment in tissue sections by quantitative FISH: image analysis algorithms

BACKGROUND

Telomeres are tandem repeated DNA sequences at the ends of every chromosome, which cap, stabilize, and prevent chromosome fusions and instability. Telomere regulation is an important mechanism in cellular proliferation and senescence in normal diploid and neoplastic cells. Quantitative methods to assess telomere lengths are essential to understanding how telomere dynamics play a role in these processes.

METHODS

Telomere lengths have been conventionally measured using terminal restriction fragment (TRF), quantitative fluorescence in situ hybridization (QFISH), and flow FISH. In this study, we have applied QFISH to measure average telomere lengths in cultured cells and human tissues of the GI tract. Importantly, this method can be used to analyze telomere lengths in sections using confocal microscopy. We describe and compare three image analysis algorithms: a simple pixel histogram calculation of background corrected fluorescence, a telomere spot-finding method, and a background curve subtraction algorithm.

RESULTS

Using normal human diploid fibroblasts (NHDF) either dropped on slides or sectioned after agar embedding, similar telomere length shortening is evident with increasing population doubling levels (PDLs), using peptide nucleic acid (PNA) and an N3'-P5'-phosphoamidate (PA) oligonucleotide probe for all three methods. Validation of these in situ telomere quantification methods showed excellent agreement with the commonly used telomere repeat fragment-Southern blot method. Telomere length reductions can also be demonstrated in tissue sections from histologically normal mucosa from patients with chronic ulcerative colitis (with dysplasia or cancer elsewhere in the colon), in colon adenomas, and in mucosal biopsies from patients with Barrett's esophagus. Both on slides and in tissue sections, the telomere spot-finding method has the greatest variability, while intra- and inter-biopsy variability in telomere length assessment using the other methods is relatively low.

CONCLUSIONS

Accurate and reproducible telomere length measurements can be made in tissue sections using QFISH and confocal microscopy. The simplest methods proved the most reliable and make these methods readily accessible to many laboratories. The use of these methods will enhance the ability to measure telomere lengths in tissue samples and aid in the understanding of the role of telomere length in aging and disease.

Progressive loss of malignant behavior in telomerase-negative tumorigenic adrenocortical cells and restoration of tumorigenicity by human telomerase reverse transcriptase

Replicative senescence/crisis is thought to act as a tumor suppressor mechanism. Although recent data indicate that normal human cells cannot be converted into cancer cells without telomerase, the original concept of senescence as a tumor suppressor mechanism is that senescence/crisis would act to limit the growth of telomerase-negative tumors. We show here that this concept is valid when oncogene-expressing human and bovine cells are introduced into immunodeficient mice using tissue reconstruction techniques, as opposed to conventional subcutaneous injection. Primary human and bovine adrenocortical cells were transduced with retroviruses encoding Ha-Ras(G12V) and SV40 large T antigen and transplanted in immunodeficient mice using tissue reconstruction techniques. Transduced cells were fully malignant (invasive and metastatic) in this model. They had negligible telomerase activity both before transplantation and when recovered from tumors. When serially transplanted, tumors showed progressively slower growth, decreased invasion and metastasis, shortened telomeres, and morphological features of crisis. Whereas telomerase was not essential for malignant behavior, expression of human telomerase reverse transcriptase enabled cells from serially transplanted tumors that had ceased growth to reacquire tumorigenicity. Moreover, telomerase-negative oncogene-expressing cells were tumorigenic only when transplanted using tissue reconstruction techniques; human telomerase reverse transcriptase was required for cells to form tumors when cells were injected subcutaneously. This work provides a new model to study crisis in an in vivo setting and its effects on malignancy; despite having invasive and metastatic properties, cells are eventually driven into crisis by proliferation in the absence of a telomere maintenance mechanism.

Aging of the Human Adrenal Cortex

The most striking age-related change in the human adrenal cortex is the decline in secretion of dehydroepiandrosterone and its sulfate, steroids synthesized by the inner zone of the cortex, the zona reticularis. Because these steroids are of essentially unknown function, the importance of this age-related change is the subject of considerable debate. It is likely that the age-related change in these steroids results from loss of zona reticularis cells or impairment of their function. During aging, cumulative damage to the zona reticularis could occur through ischemia-related infarcts and other causes of cell death. Cellular senescence could contribute to a loss of the ability of the tissue to replace lost cells. In contrast, feedback mechanisms that regulate adrenocortical growth cause compensatory local tissue hyperplasias called nodules. The effect of imperfect repair of damage combined with compensatory overgrowth in the form of nodules leads to an increasingly abnormal tissue architecture.

Ageing–apoptosis relation in murine spleen

Relatively few studies have been published with regard to modification of apoptosis in normal tissues as a function of ageing. The majority of these studies demonstrated an increase in programmed cell death (PCD) with age. However, opposite results, namely loss of apoptotic control with age, have also been reported. In the present study, we examined proliferation and apoptotic cell death in spleens of C57/BL mice of different ages. A tendency towards decrease in cell proliferative capacity was seen with age. By contrast, apoptosis was increased in spleens from aged animals. Moreover, the proliferative cell/apoptotic cell ratio decreased in function of age. Ladder type DNA degradation was much more pronounced in DNA derived from splenocytes of old mice. These results were supported by a decrease of Bcl-2 and an increase in Fas receptor expression as well as by increased activation of caspases 8, 3 and 9 in splenocytes from aged animals. In addition, cell surface molecular markers recognizable by macrophages in apoptotic cells, namely decreased sialic acid concomitant with increased unmasking of galactose residues, were more pronounced on splenocytes from old mice than on those from young animals. In addition to the experimental evidence which supports a role of apoptotic cell death in ageing, a series of theoretical reasoning, which could also favor this possibility, are discussed.

Demethylation of the human telomerase catalytic subunit (hTERT) gene promoter reduced hTERT expression and telomerase activity and shortened telomeres

Telomerase is the ribonucleoproteic complex involved in maintaining telomere size. It is expressed in germ and stem cells but not in normal somatic cells. In most tumors, telomerase is reactivated. In humans, telomerase activity is tightly regulated by expression of the hTERT gene. In a previous study, we found a direct correlation between methylation of the hTERT promoter and hTERT gene expression. In order to demonstrate this correlation, demethylation experiments were performed with the demethylating agent 5aza-2'-deoxycytidine (5azadC). Three telomerase-positive tumor cell lines (Lan-1, HeLa, and Co115), presenting a hypermethylated hTERT promoter, were treated with different doses and types of treatment for a long period. Analysis of methylation revealed a final hTERT promoter demethylation up to 95%. Quantification of hTERT mRNA showed that transcription was strongly repressed during drug exposure. In contrast, expression of c-Myc, an activator of hTERT promoter, was barely down-regulated or increased by the treatment. Using a TRAP assay, telomerase activity was semiquantified in all experiments. It strongly decreased or was suppressed after two to four passages. Finally, telomere length was measured by Southern blot. Their averages were not modified, but ranges concentrated around the mean. Thus, it is likely that hTERT promoter hypermethylation would be necessary for its expression.

Growth, telomere dynamics and successful and unsuccessful human aging

This paper links mass trajectories with telomere dynamics to construct theoretical models of successful and unsuccessful aging in human beings. It couples parameters of telomere length in somatic cells, as expressed by the terminal restriction fragment (TRF), at birth and the rate of telomere attrition thereafter with nonlinear models of somatic growth to predict the probability of surviving disease free, based on the assumption that telomere length in replicating somatic cells is a surrogate indicator of aging determinants in humans. The models capture aspects of individual variation in successful and unsuccessful aging and the long-term consequences of rapid growth early in life.

Duration of senescent cell survival in vitro as a characteristic of organism longevity, an additional to the proliferative potential of fibroblasts

More than 40 years have passed since the original publication by Hayflick and Moorhead led to the concept of the 'Hayflick limit' of the maximum number of divisions which somatic cells undergo in vitro. This concept is still regarded as a fundamental characteristic of species longevity. Here we want to emphasize another characteristic of somatic cells, namely, the duration of their survival in vitro in the non-dividing state after cessation of proliferation. This is suggested on the basis of results of recent experiments with so-called Japanese accelerated senescent mice. Results of these experiments reveal a good correlation between the longevity of the mice, the number of duplications of their fibroblasts in vitro, and the survival time of these cells in the non-dividing state. In routine culture conditions, cell survival time may be very long, as much as a few years. However, when the cells are grown under conditions of oxidative stress, cellular longevity is markedly shortened. This new test may serve as an additional marker of organismic longevity. The comparative value of both tests, the classical 'Hayflick limit' and the new test, is discussed.

Analysis of telomerase activity and detection of its catalytic subunit, hTERT

The discovery of the enzyme telomerase and its subunits has led to major advances in understanding the mechanisms of cellular proliferation, immortalization, aging, and neoplastic transformation. The expression of telomerase in more than 85% of tumors provides an excellent tool for the diagnosis, prognosis, and treatment of cancer. However, the techniques employed in its detection appear to play a significant role in the interpretation of the results. The telomeric repeat amplification protocol (TRAP assay) has been the standard assay in the detection of telomerase activity and many variations of this technique have been reported. Recent advances in the development of the TRAP assay and the incorporation of techniques that provide a quantitative and qualitative estimate of telomerase activity are assessed in this review. In addition to histological and cytological examination of tissues, distribution patterns of the catalytic subunit of telomerase, hTERT, are frequently used in the prognosis of tumors. The methods involved in the detection of hTERT as a biomarker of cellular transformation are also analyzed.

Telomere shortening and cellular senescence in a model of chronic renal allograft rejection

Cellular senescence has been suggested to play a role in the deterioration of renal graft function and has been linked to telomere shortening. We have investigated markers of cellular senescence in the F344 to LEW rat model of chronic renal transplant rejection. Syngeneic and LEW to F344 transplants were used as controls. Substantial telomere shortening was observed in all transplants, including allogeneic and syngeneic grafts from day 7 post-transplant onwards. Ischemia of native F344 kidneys was already sufficient to induce telomere shortening. It is known that shortened telomeres can activate cell cycle regulators, such as p21 and p16. Accordingly, all cases showed a transient p21 increase, with a maximum at day 7 and a sustained expression of p16. Importantly, senescence-associated beta-galactosidase staining, a cytological marker for senescence, was only observed in tubular epithelial cells of chronically rejecting F344 allografts from day 30 post-transplantation onwards. Long-term surviving LEW allografts or syngeneic F344 grafts were negative for senescence-associated beta-galactosidase. In conclusion, ischemia during transplantation results in telomere shortening and subsequent activation of p21 and p16, whereas senescence-associated beta-galactosidase staining is only present in chronically rejecting kidney grafts.

Assessment of telomere length and factors that contribute to its stability

Short strands of tandem hexameric repeats known as telomeres cap the ends of linear chromosomes. These repeats protect chromosomes from degradation and prevent chromosomal end-joining, a phenomenon that could occur due to the end-replication problem. Telomeres are maintained by the activity of the enzyme telomerase. The total number of telomeric repeats at the terminal end of a chromosome determines the telomere length, which in addition to its importance in chromosomal stabilization is a useful indicator of telomerase activity in normal and malignant tissues. Telomere length stability is one of the important factors that contribute to the proliferative capacity of many cancer cell types; therefore, the detection and estimation of telomere length is extremely important. Until relatively recently, telomere lengths were analyzed primarily using the standard Southern blot technique. However, the complexities of this technique have led to the search for more simple and rapid detection methods. Improvements such as the use of fluorescent probes and the ability to sort cells have greatly enhanced the ease and sensitivity of telomere length measurements. Recent advances, and the limitations of these techniques are evaluated. Drugs that assist in telomere shortening may contribute to tumor regression. Therefore, factors that contribute to telomere stability may influence the efficiency of the drugs that have potential in cancer therapy. These factors in relation to telomere length are also examined in this analysis.

Adrenocortical cell proliferation in a cell transplantation model: the role of SV40 T antigen

Bovine adrenocortical cells immortalized by human telomerase reverse transcriptase (hTERT) are capable of forming functional vascularized tissue structures when transplanted in immunodeficient mice. These tissues maintain the life of adrenalectomized animals, show normal cell proliferation rates, and maintain a constant tissue size. These experiments were performed by co-transfection of an hTERT-encoding plasmid with an SV40 T antigen-encoding plasmid, but in tissues formed from clones derived in this way SV40 T Ag was not expressed. However, when tissues were formed from nonclonal heterogeneous populations of transfected cells, nodules of SV40 TAg-expressing cells arose that showed a high proliferation rate. These structures resembled nodules formed from transplanted bovine adrenocortical cells in which SV40 TAg was introduced by retroviral transduction rather than transfection. The reasons for these phenomena are discussed; in a nonclonal mixed population of cells, some may have much higher levels of SV40 TAg, which perturbs the normal histology and behavior of tissues formed from hTERT-immortalized adrenocortical cells.

The Sam and Ann Barshop Center for Longevity and Aging Studies: the University of Texas Health Science Center at San Antonio

The Sam and Ann Barshop Center for Longevity and Aging Studies is a focal point for advanced research designed exclusively to study the genes involved in aging and the diseases of aging. The research performed at the Barshop Center is based on a solid foundation of nearly twenty-five years of aging research at The University of Texas Health Science Center at San Antonio. Internationally recognized scientists in aging are now leading innovative research programs using state-of-the-art technologies in molecular and cellular biology to explore aging processes at the gene level in the four major programs that comprise the research at the Barshop Center: the Cellular Aging Program, the Invertebrate Aging Program, the Rodent Models of Aging Program, and the Human Genetics of Aging Program. The researchers involved in these programs share a common purpose in an atmosphere of collaboration to gain the scientific insights necessary to understand the molecular basis of aging. Their long-term goal is to gain the knowledge that will give rise to the development of interventions that retard or arrest the debilitating conditions associated with aging. February or March 2003 marks the groundbreaking for the first building of Barshop Center's new stand-alone facility. This is the initial step toward a $70 million, world-class research complex dedicated to the study of aging and healthy longevity.

Historical claims and current interpretations of replicative aging

Replicative aging is the process by which most normal human cells "count" the number of times they have divided, eventually undergoing a growth arrest termed cellular senescence. This process is dependent on the shortening of telomeres, repeated sequences at the ends of the chromosomes. The loss of telomeric sequences with each cell division eventually induces a growth arrest that has a similar phenotype to that of cells stressed by inadequate culture or other conditions. Experiments over the past several years have identified species in which replicative aging does not occur and many examples in which a failure to proliferate has been misinterpreted as replicative senescence. Insights from these studies now permit a reevaluation of much of the seemingly contradictory data concerning replicative aging. There are good theoretical reasons for believing a limited proliferative capacity contributes to declining tissue homeostasis with increasing age. Although the presence of telomere shortening provides strong circumstantial evidence that replicative aging is occurring in vivo, thus far there is only very limited direct evidence for actual physiological effects of replicative aging.

Cellular senescence and tissue aging in vivo

A long-standing controversy concerns the relevance of cellular senescence, defined and observed as a cell culture phenomenon, to tissue aging in vivo. Here the evidence on this topic is reviewed. The main conclusions are as follows. First, telomere shortening, the principal known mediator of cellular senescence, occurs in many human tissues in aging. Second, it is not clear whether this results in cellular senescence or in some other cell fate (e.g., crisis). Third, rodents probably are not appropriate experimental models for these questions, because of important differences in telomere biology between rodent cells and cells from long-lived mammals (e.g., human or bovine cells). Fourth, better and more comprehensive observations on aging human tissues are needed to answer the question of the occurrence of senescent cells in tissues, and new experimental approaches are needed to elucidate the consequences of telomere shortening in tissues in aging.

Human fibroblasts in vitro senesce with a donor-specific telomere length

In human fibroblasts, replicative senescence, telomere length and donor age are closely interrelated. We analyzed these relationships for fibroblast strains from 14 healthy human donors in the age range of 28-90 years. In vitro replicative capacity was correlated more closely with donor age than with telomere length ex vivo, especially for healthy donors. Telomere length at senescence was as variable as at cell explantation and increased with donor age. The data suggest a donor-specific, age-dependent regulation of the telomere length threshold that triggers senescence in human fibroblasts.

Telomeres, aging and cancer: in search of a happy ending

Telomeres are distinctive structures, composed of a repetitive DNA sequence and associated proteins, that cap the ends of linear chromosomes. Telomeres are essential for maintaining the integrity and stability of eukaryotic genomes. In addition, under some circumstances, telomeres can influence cellular gene expression. In mammals, the length, structure, and function of telomeres have been proposed to contribute to cellular and organismal phenotypes associated with cancer and aging. Here, we discuss what is known about the basis for the links between telomeres, aging and cancer, and some of the known and proposed consequences of telomere dysfunction and maintenance for mammalian cells and organisms.