The biology of replicative senescence

Role of cellular senescence in lifestyle-related disease

Epidemiological studies have shown that age is the chief risk factor for lifestyle-related diseases such as cardiovascular disease and diabetes, but the molecular mechanisms that underlie the increase in the risk of such diseases conferred by aging remain unclear. Recently, genetic analyses using various animal models have identified molecules that are crucial for aging. These include components of the DNA repair system, the tumor suppressor pathway, the telomere maintenance system, the insulin/Akt pathway, and other metabolic pathways. Interestingly, most of the molecules that influence the phenotypic changes of aging also regulate cellular senescence, suggesting a causative link between cellular senescence and aging. This review examines the hypothesis that cellular senescence might contribute to lifestyle-related disease.

Telomere/telomerase dynamics within the human immune system: effect of chronic infection and stress

Aging of the immune system is a major factor responsible for the increased severity of infections, reduced responses to vaccines, and higher cancer incidence in the elderly. A major category of stressors that contribute to the alterations within the T lymphocyte compartment is the family of herpes viruses. These viruses, usually acquired early in life, persist for many decades and drive certain T cells to the end stage of replicative senescence, which is characterized by a variety of phenotypic and functional changes, including altered cytokine profile, resistance to apoptosis, and shortened telomeres. Indeed, high proportions of senescent CD8 (cytotoxic) T lymphocytess are associated with latent cytomegalovirus (CMV) infection in the elderly, and are part of a cluster of immune biomarkers that are associated with early mortality. Similar cells accumulate at younger ages in persons chronically infected with HIV-1. In addition to persistent viral infection, psychological stress as well as oxidative stress can also contribute to the generation of senescent dysfunctional T lymphocytes. Strategies such as cell culture manipulation of replicative senescence, as well as lifestyle and stress reduction techniques are discussed in terms of possible approaches to enhance immune function in older persons. This review highlights the importance of using humans in studies on immunosenescence and telomere/telomerase dynamics, since model organisms employed in other facets of aging research are not subject to the particular factors that cause the striking age-related reconfiguration of the human immune system.

Establishment of immortalized mesenchymal stromal cells with red fluorescence protein expression for in vivo transplantation and tracing in the rat model with traumatic brain injury

BACKGROUND AIMS

Human mesenchymal stromal cells (hMSC) play a crucial role in tissue engineering and regenerative medicine, and have important clinical potential for cell therapy. However, many hMSC studies have been restricted by limited cell numbers and difficult detection in vivo. To expand the lifespan, hMSC are usually immortalized by virus-mediated gene transfer. However, these genetically modified cells easily lose critical phenotypes and stable genotypes because of insertional mutagenesis.

METHODS

We used a non-viral transfection method to establish human telomerase reverse transcriptase-immortalized cord blood hMSC (hTERT-cbMSC). We also established red fluorescent protein (RFP)-expressing hTERT-cbMSC (hTERT/RFP-cbMSC) by the same non-viral transfection method, and these cells were injected into a rat model with traumatic brain injury for in vivo detection analysis.

RESULTS

The hTERT-cbMSC could grow more than 200 population doublings with a stable doubling time and maintained differentiation capacities. hTERT/RFP-cbMSC could proliferate efficiently within 2 weeks at the injury location and could be detected easily under a fluorescent microscope. Importantly, both hTERT-cbMSC and hTERT/RFP-cbMSC showed no chromosomal abnormalities by karyotype analysis and no tumor formation in severe combined immunodeficient (SCID) mice by transplantation assay.

CONCLUSIONS

We have developed immortalized cbMSC with hTERT expression and RFP expression, which will be useful tools for stem cell research and translational study.

Proliferation and osteogenesis of immortalized bone marrow-derived mesenchymal stem cells in porous polylactic glycolic acid scaffolds under perfusion culture

Human bone marrow mesenchymal stem cells (hMSCs) are promising candidates for cell therapy and tissue engineering. However, the life span of hMSCs during in vitro culture is limited. Human telomerase catalytic subunit (hTERT) gene transduction could prolong the life span of hMSCs and maintain their potential of osteogenic differentiation. Therefore, hMSCs transduced with hTERT (hTERT-hMSCs) could be used as a cell model for in vitro tissue engineering experiment because of its prolonged life span and normal cellular properties. A perfusion culture system for proliferation and osteogenesis of hTERT-hMSCs or primary hMSCs in porous polylactic glycolic acid (PLGA) scaffolds is described here. A cell suspension of hTERT-hMSCs or primary hMSCs (5 x 10(5) cells/250 microL) was seeded and then cultured for 12 days in porous PLGA scaffolds (10 mm in diameter, 3 mm in height) under both static and perfusion culture systems. The seeding efficiency, proliferation, distribution and viability, and osteogenesis of cells in scaffolds were evaluated. The perfusion method generated higher scaffold cellularity and proliferation of cells in scaffolds, and hTERT-hMSCs showed the higher proliferation potential than primary hMSCs. Results from fluorescein diacetate (FDA) staining and scanning electron microscopy (SEM) demonstrated homogeneous seeding, proliferation, and viability of hTERT-hMSCs throughout the scaffolds in the perfusion culture system. On the contrary, the static culture yielded polarized proliferation favoring the outer and upper scaffold surfaces, and resulted in decreasing of cells in the central section of the scaffolds. A flow rate of 0.5 mL/min had an effect on osteogenic differentiation of cells in scaffolds. However, the osteogenic medium promoted the osteogenic efficiency of cells. Scaffolds with hTERT-hMSCs had the higher osteogenesis than scaffolds with primary hMSCs. Thus, these results suggest that the flow condition not only allow a better seeding efficiency and homogeneity but also facilitate uniform proliferation and osteogenic differentiation of hTERT-hMSCs in scaffolds. hTERT-hMSCs could be used as stem cell candidates for bone tissue engineering experiments.

Senescent vs. non-senescent cells in the human annulus in vivo: cell harvest with laser capture microdissection and gene expression studies with microarray analysis

BACKGROUND

Senescent cells are well-recognized in the aging/degenerating human disc. Senescent cells are viable, cannot divide, remain metabolically active and accumulate within the disc over time. Molecular analysis of senescent cells in tissue offers a special challenge since there are no cell surface markers for senescence which would let one use fluorescence-activated cell sorting as a method for separating out senescent cells.

METHODS

We employed a novel laser capture microdissection (LCM) design to selectively harvest senescent and non-senescent annulus cells in paraffin-embedded tissue, and compared their gene expression with microarray analysis. LCM was used to separately harvest senescent and non-senescent cells from 11 human annulus specimens.

RESULTS

Microarray analysis revealed significant differences in expression levels in senescent cells vs non-senescent cells: 292 genes were upregulated, and 321 downregulated. Genes with established relationships to senescence were found to be significantly upregulated in senescent cells vs. non-senescent cells: p38 (MPAK14), RB-Associated KRAB zinc finger, Discoidin, CUB and LCCL domain, growth arrest and DNA-damage inducible beta, p28ING5, sphingosine-1-phosphate receptor 2 and somatostatin receptor 3; cyclin-dependent kinase 8 showed significant downregulation in senescent cells. Nitric oxidase synthase 1, and heat shock 70 kDa protein 6, both of which were significantly down-regulated in senescent cells, also showed significant changes. Additional genes related to cytokines, cell proliferation, and other processes were also identified.

CONCLUSIONS

Our LCM-microarray analyses identified a set of genes associated with senescence which were significantly upregulated in senescent vs non-senescent cells in the human annulus. These genes include p38 MAP kinase, discoidin, inhibitor of growth family member 5, and growth arrest and DNA-damage-inducible beta. Other genes, including genes associated with cell proliferation, extracellular matrix formation, cell signaling and other cell functions also showed significant modulation in senescent vs non-senescent cells. The aging/degenerating disc undergoes a well-recognized loss of cells; understanding senescent cells is important since their presence further reduces the disc's ability to generate new cells to replace those lost to necrosis or apoptosis.

Increased cell senescence is associated with decreased cell proliferation in vivo in the degenerating human annulus

BACKGROUND CONTEXT

During disc degeneration, there is a well-recognized loss of cells. This puts the remaining cell population at high risk for any further decrease in cell function or cell numbers. Cell senescence has recently been shown to be present in the aging/degenerating human disc. Senescent cell are viable, metabolically active, persist, and accumulate over time, but cannot divide. Little is known about the relationship between renewal of the disc cell population via cell proliferation and disc cell senescence.

PURPOSE

To determine the percentage of senescent cells and proliferating cells in the human annulus in vivo.

STUDY DESIGN/SETTING

Human annulus specimens were obtained from surgical subjects and control donors in a study approved by the authors' Human Subjects Institutional Review Board.

PATIENT SAMPLE

One Thompson Grade I disc, 4 Grade II discs, 9 Grade III discs, and 12 Grade IV discs were studied.

OUTCOME MEASURES

The percentages of senescent cells and the percentage of proliferating cells.

METHODS

Immunohistochemistry was used to detect senescent cells using an antisenescence-associated beta-galactosidase antibody, and an antiproliferation antibody (Ki67). An average of 410 cells/specimens was counted to determine the percent senescence, and an average of 229 cells was counted to determine the percent proliferation.

RESULTS

Cell proliferation was low in both surgical and control normal donor annulus tissue (4.09%+1.77 (26), mean+SD (n)). There was no significant difference in the percentage of proliferating cells for more degenerate discs versus healthier discs (4.7%+1.6 (21) for Grades III and IV vs. 5.3%+1.9 (5) for Grades I and II). More degenerated Grades III and IV discs contained significantly greater percentages of senescent annulus cells than did the healthier Grades I and II discs (44.4%+20.0 (21) vs. 18.8%+11.0 (5), respectively; p=.011). A significant negative correlation was present between the percentage of senescent cells versus the percentage of proliferating cells, r=-0.013, p=.013. No correlation was present between age and the percentage of senescent cells or age and the percentage of proliferating cells.

CONCLUSIONS

Because senescent cells cannot divide, senescence may reduce the disc's ability to generate new cells to replace cells lost to necrosis or apoptosis. Senescent cells also accumulate in the disc over time, such that their metabolic patterns may contribute to the pathologic changes seen in degenerating discs. Novel data presented here show a significant negative correlation between the percentage of senescent cells and the percentage of proliferating cells during disc degeneration. Molecular work is underway in our lab to help us determine whether senescent cells in the disc secrete factors that can result in decreased proliferation in neighboring cells.

Cellular senescence, ageing and disease

Cellular senescence is the irreversible growth arrest of individual mitotic cells, which as a consequence display a radically altered phenotype that is thought to impair tissue function and predispose tissues to disease development and/or progression as they gradually accumulate. However, in the past, research into mechanisms of ageing has commonly been researched and treated separately from disease development. This may partly be due to the lack of understanding concerning mechanisms of ageing and the difficulty in implementing what was known into models of disease development. Only in the last 10 years, with increasing knowledge of the senescent phenotype and the ability to detect senescent cells in human tissues, have biologists been able to investigate the relationship between cellular senescence and disease. This review therefore brings together and discusses recent findings which suggest that cellular senescence does contribute to ageing and the development/progression of disease.

Using naturally occurring tumours in dogs and cats to study telomerase and cancer stem cell biology

The recently described cancer stem cell theory opens up many new challenges and opportunities to identify targets for therapeutic intervention. However, the majority of cancer related therapeutic studies rely upon rodent models of human cancer that rarely translate into clinical success in human patients. Naturally occurring cancers in dogs, cats and humans share biological features, including molecular targets, telomerase biology and tumour genetics. Studying cancer stem cell biology and telomere/telomerase dynamics in the cancer bearing pet population may offer the opportunity to develop a greater understanding of cancer biology in the natural setting and evaluate the development of novel therapies targeted at these systems.

Cell proliferation in the presence of telomerase

Background

Telomerase, which is active early in development and later in stem and germline cells, is also active in the majority of human cancers. One of the known functions of telomerase is to extend the ends of linear chromosomes, countering their gradual shortening at each cell division due to the end replication problem and postreplication processing. Telomerase concentration levels vary between different cell types as well as between different tumors. In addition variable telomerase concentrations will exist in different cells in the same tumor when telomerase inhibitors are used, because of limitations of drug delivery in tissue. Telomerase extends short telomeres more frequently than long telomeres and the relation between the extension frequency and the telomere length is nonlinear.

Methodolgy/Principal Findings

Here, the biological data of the nonlinear telomerase-telomere dynamics is incorporated in a mathematical theory to relate the proliferative potential of a cell to the telomerase concentration in that cell. The main result of the paper is that the proliferative capacity of a cell grows exponentially with the telomerase concentration.

Conclusions/Significance

The theory presented here suggests that long term telomerase inhibition in every cancer progenitor or cancer stem cell is needed for successful telomere targeted cancer treatment. This theory also can be used to plan and asses the results of clinical trials targeting telomerase.

Kleemeier Award Lecture 2008--the canary in the coal mine: telomeres and human healthspan

Telomeres, the repeated series of DNA sequences that cap the ends of linear chromosomes, become shorter during cell division and oxidative stress. Shortened telomeres have been documented in a wide variety of pathologies associated with aging and are also predictive of early mortality in the very old. However, telomere shortening--like the canary in the coal mine--is not the cause of the deleterious effects, but rather, the harbinger of increased health risk. Using immune responses to infection as a model system to further analyze the link between telomeres and age-related disease, we have demonstrated that the end-stage T cell with shortened telomeres is reduced in antiviral immune function and secretes large amounts of so-called proinflammatory factors. Our research has documented that maintaining high levels of the telomere-extending enzyme, telomerase, by either genetic manipulation or exposure of T cells to chemical telomerase activators, not only retards telomere loss but also restores a more youthful functional profile to the T cells. These observations suggest possible novel telomerase-based therapeutic approaches to enhancing healthspan in the elderly population.

Stable knockdown of PASG enhances DNA demethylation but does not accelerate cellular senescence in TIG-7 human fibroblasts

Demethylation of 5-methylcytosine in genomic DNA is believed to be one of the mechanisms underlying replicative life-span of mammalian cells. Both proliferation associated SNF2-like gene (PASG, also termed Lsh) and DNA methyltransferase 3B (Dnmt3b) knockout mice result in embryonic genomic hypomethylation and a replicative senescent phenotype. However, it is unclear whether gradual demethylation of DNA during somatic cell division is directly involved in senescence. In this study, we retrovirally transduced TIG-7 human fibroblasts with a shRNA against PASG and compared the rate of change in DNA methylation as well as the replicative life-span to control cells under low (3%) and ambient (20%) oxygen. Expression of PASG protein was decreased by approximately 80% compared to control cells following transduction of PASG shRNA gene. The rate of cell growth was the same in both control and PASG-suppressed cells. The rate of demethylation of DNA was significantly increased in PASG-suppressed cells as compared control cells. However, decreased PASG expression did not shorten the replicative life-span of TIG-7 cells. Culture under low oxygen extended the life-span of TIG-7 cells but did not alter the rate of DNA demethylation. While knockout of PASG during development results in genomic hypomethylation and premature senescence, our results show that while downregulation of PASG expression in a somatic cell also leads to DNA hypomethylation, there is no associated senescent phenotype. These results suggest differences in cellular consequences of hypomethylation mediated by PASG during development compared to that in somatic cells.

Gene expression of types I, II, and VI collagen, aggrecan, and chondroitin-6-sulfotransferase in the human annulus: in situ hybridization findings

BACKGROUND CONTEXT

Within each lamellar bundle in the annulus, disc cells produce a complex and sophisticated architectural organization which acts to meet the unique biomechanical needs of the disc. How cells coordinate expression of genes throughout the disc is an important but as yet poorly understood process. For the annulus, such coordination probably involves cell-cell communication as well as growth factor and mechanoreceptor signaling to appropriately maintain the disc extracellular matrix (ECM) for the prevention of annular tears.

PURPOSE

To determine the percentage and patterns of gene expression for types I, II, and VI collagen, aggrecan, and chondroitin-6-sulfotransferase in the human annulus.

STUDY DESIGN/SETTING

Human annulus specimens were obtained from surgical subjects and a control donor in a study approved by the authors' Human Subjects Institutional Review Board.

PATIENT SAMPLE

Four Thompson grade II, three grade III, and four grade IV annulus specimens were evaluated with in situ hybridization to determine gene expression.

OUTCOME MEASURES

The percentages of cells in the human annulus expressing type I, II, and VI collagen, aggrecan, and chondroitin-6-sulfotransferase.

METHODS

In situ hybridization, a technique with high temporal and spatial resolution, was used to detect gene expression of types I, II, and VI collagen, aggrecan, and chondroitin-6 sulfotransferase in cells in adjacent sections of annulus from discs with Thompson grades of II, III, and IV.

RESULTS

Overall, 30.8% of cells expressed aggrecan, 38.4% type I collagen, 45.6% type II collagen, 48.1% type VI collagen, and 57.7% chondroitin-6-sulfotransferase. An important finding was that adjacent cells could be expressing, or not expressing, the gene of interest. These data could not have been gained from other global molecular techniques such as microarray analysis or reverse transcription polymerase chain reaction (RT-PCR). Information on gene expression by individual disc cells is important to better understand disc matrix homeostasis, the pathogenesis of disc degeneration, and to formulate potential biologic therapies for disc degeneration.

CONCLUSIONS

This in situ hybridization study revealed the important finding that adjacent cells differ in their gene expression patterns for specific genes. Factors that could contribute to this difference in adjacent cell gene expression include cellular heterogeneity within the annulus, the presence of senescent cells with altered gene expression, and/or loss of coordinated disc cell function as a result of disruption of cell-cell communication.

CSIG inhibits PTEN translation in replicative senescence

Using a suppressive subtractive hybridization system, we identified CSIG (cellular senescence-inhibited gene protein; RSL1D1) that was abundant in young human diploid fibroblast cells but declined upon replicative senescence. Overexpression or knockdown of CSIG did not influence p21(Cip1) and p16(INK4a) expressions. Instead, CSIG negatively regulated PTEN and p27(Kip1) expressions, in turn promoting cell proliferation. In PTEN-silenced HEK 293 cells and PTEN-deficient human glioblastoma U87MG cells, the effect of CSIG on p27(Kip1) expression and cell division was abolished, suggesting that PTEN was required for the role of CSIG on p27(Kip1) regulation and cell cycle progression. Investigation into the underlying mechanism revealed that the regulation of PTEN by CSIG was achieved through a translational suppression mechanism. Further study showed that CSIG interacted with PTEN mRNA in the 5' untranslated region (UTR) and that knockdown of CSIG led to increased luciferase activity of a PTEN 5' UTR-luciferase reporter. Moreover, overexpression of CSIG significantly delayed the progression of replicative senescence, while knockdown of CSIG expression accelerated replicative senescence. Knockdown of PTEN diminished the effect of CSIG on cellular senescence. Our findings indicate that CSIG acts as a novel regulatory component of replicative senescence, which requires PTEN as a mediator and involves in a translational regulatory mechanism.

IGF-1 rescues human intervertebral annulus cells from in vitro stress-induced premature senescence

The aging human intervertebral disc contains a sizeable population of senescent cells. Since senescent cells cannot divide, senescence reduces the disc's ability to generate new cells to replace existing ones lost to necrosis or apoptosis. The objectives of the present work were: (1) to develop a reliable in vitro model for stress-induced premature senescence in human annulus cells, and (2) to investigate the potential for insulin-like growth factor-1 (IGF-1) to prevent or ameliorate senescence in vitro. The developed experimental model employs a 2 h exposure to 50 microM hydrogen peroxide; immunocytochemical localization of senescence associated-beta-galactosidase at pH 6.0 was used as the marker for senescent cells, and the percentage of senescent cells quantified after 3 days of culture. Nine sets of annulus cells were obtained from eight human surgical disc specimens; cells were tested with 0, 50, 100 or 500 ng/ml IGF-1. Although 50 or 100 ng/ml IGF-1 did not significantly alter the percentage of senescent cells, a significant reduction was present following exposure to 500 ng/ml IGF-1 (control, 56.3% +/- 8.5 (9); mean +/- SEM, (n) vs. treated, 39.6% +/- 6.6 (9), p = 0.0009). These novel findings point to the value of continued research towards development of future biologic therapies designed to reduce cell senescence in degenerating human discs.

Proteomic analysis of human bone marrow mesenchymal stem cells transduced with human telomerase reverse transcriptase gene during proliferation

OBJECTIVES

Previous studies have reported immortalization and tumorigenicity of human mesenchymal stem cells (hMSCs) transduced with exogenous human telomerase reverse transcriptase (hTERT). We also have established a line of hMSCs transduced with hTERT (hTERT-hMSCs) and we have cultured these cells for 290 population doublings (PDs) during which they demonstrated a large proliferation potential but with no tumorigenicity. The aim of this study was to investigate the protein expression profile of hTERT-hMSCs with two-dimensional gel electrophoresis and peptide mass fingerprinting by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, to be able to analyse the effects of exogenous hTERT on protein expression in hMSCs.

MATERIALS AND METHODS

We generated proteome maps of primary hMSCs and hTERT-hMSCs at PD 95 and PD 275.

RESULTS

A total of 1543 +/- 145 protein spots in gels of primary MSCs at PD 12, 1611 +/- 186 protein spots in gels of hTERT-hMSCs at PD 95 and 1451 +/- 126 protein spots in gels of hTERT-hMSCs at 275 PD were detected. One hundred of these were successfully identified, including 20 which were differentially expressed.

CONCLUSIONS

The results suggest that sustaining levels of prohibitin and p53 expression along with differential expression of proteins in hTERT-hMSCs provide an insight into lack of transforming activity of hTERT-hMSCs during cell proliferation.

Stabilization of cellular properties and differentiation mutilpotential of human mesenchymal stem cells transduced with hTERT gene in a long-term culture

Human bone marrow mesenchymal stem cells (hMSCs) are promising candidates for cell therapy and tissue engineering. The life span of hMSCs during in vitro culture is limited. Human telomerase catalytic subunit (hTERT) gene transduction can prolong the life span of hMSCs and maintain their potential of osteogenic differentiation. We established a line of hMSCs transduced with exogenous hTERT (hTERT-hMSCs) and investigated its sustaining cellular properties in a long-term culture. This line of hTERT-hMSCs was cultured for 290 population doublings (PDs) without loss of contact inhibition. Under adipogenic, chondrogenic and osteogenic induction, hTERT-hMSCs at PD 95 and PD 275 could differentiate respectively into adipocytes, chondrocytes, and osteocytes. hTERT-hMSCs at these PDs showed no transforming activity through both in vitro assay of cell growth in soft agar and in vivo assay of tumorigenicity in NOD-SCID mice. Karyotype analyses showed no significant chromosomal abnormalities in hTERT-hMSCs at these PDs. These results suggested that the hTERT-hMSCs at lower population doubling levels (PDLs) should be considered as a cell model for studies of cellular senescence, differentiation and in vitro tissue engineering experiment because of its prolonged life span and normal cellular properties.

p16(INK4a) translation suppressed by miR-24

Background

Expression of the tumor suppressor p16^INK4a increases during aging and replicative senescence.

Methodology/Principal Findings

Here, we report that the microRNA miR-24 suppresses p16 expression in human diploid fibroblasts and cervical carcinoma cells. Increased p16 expression with replicative senescence was associated with decreased levels of miR-24, a microRNA that was predicted to associate with the p16 mRNA coding and 3′-untranslated regions. Ectopic miR-24 overexpression reduced p16 protein but not p16 mRNA levels. Conversely, introduction of antisense (AS)-miR-24 blocked miR-24 expression and markedly enhanced p16 protein levels, p16 translation, and the production of EGFP-p16 reporter bearing the miR-24 target recognition sites.

Conclusions/Significance

Together, our results suggest that miR-24 represses the initiation and elongation phases of p16 translation.

Evidence-based roads to the promotion of health in old age

The increase in life expectancy, along with the accompanying ongoing increase in the proportion and absolute numbers of nonagenarians and centenarians have set forth the curiosity regarding the question of the quality of health in very old age. Studies on that issue have pointed to the fact that the very old people are actually healthier than originally predicted on the basis of the earlier studies on aging. Current efforts are thus invested in elucidating the possible basis of health in the very old people, as well as better understanding of potential causes of frailty and common diseases in old age. This review recounts on the various aspects underlying evidence-based recommendations for healthy life in old age. We focus on the genetic and non-genetic bases of aging and longevity, and the various directions towards the promotion of health, both via avoiding, or eliminating risk factors and deleterious effects, as well as conducting healthy lifestyle - in terms of proper nutrition and physical exercise. Next, we touch upon preventive medicine, particularly as related to vaccination, with a note also on the need for a reasonable use of medications. In addition, we report about the developing area of regenerative medicine and its potential in relation to the prevention of damage and possible strategies towards tissue repair in cases of age-related degenerative processes.

Correlation between proliferative activity and cellular thickness of human mesenchymal stem cells

A cell's shape is known to be related to its proliferative activity. In particular, large and flat mammalian adult stem cells seem to show slow proliferation, however using quantitative analysis to prove the phenomenon is difficult. We measured the proliferation and cellular thickness of human mesenchymal stem cells (MSCs) by atomic force microscopy and found that MSCs with high proliferative activity were thick while those with low proliferative activity were thin, even though these MSCs were early passage cells. Further, low proliferative MSCs contained many senescence-associated beta-galactosidase positive cells together with high senescence-associated gene expression. These findings suggest that the measurement of cellular thickness is useful for estimating the proliferative activity of human MSCs and is expected to be a practical tool for MSC applications in regenerative medicine.

Influence of aging on biological properties of periodontal ligament cells

The majority of patients eligible for periodontal regenerative therapies are aged subjects. Since periodontal ligament cells (PDLC) are essential for periodontal regeneration, the aim of the present study was to determine the effect of cellular aging on PDLC, including genes associated with extracellular matrix metabolism and growth-associated factors. PDLC cultures were obtained from subjects aged 15 to 20 years and subjects aged more than 60 years. Proliferation, cell viability, mineralization assays, and mRNA levels were assessed for type I and III collagen, platelet-derived growth factor (PDGF)-1, basic fibroblast growth factor (bFGF), metalloproteinase (MMP)-2 and-8, and tissue inhibitor of metalloproteinases (TIMP)-1 and-2. Data analysis demonstrated that aging negatively influenced cell proliferation and mineral nodule formation (p < 0.05). Gene expression analysis further showed that mRNA levels for bFGF, PDGF-1, and TIMP-2 were not affected by aging (p > 0.05). In addition, mRNA levels for type I and III collagen were significantly lower in aged cells (p < 0.05), whereas MMP-2 and-8 and TIMP-1 mRNA levels were higher (p < 0.05). Within the limits of the present study, data analysis suggests that aging modulates important biological properties of periodontal ligament cells, diminishes the potential for mineral nodule formation, and favors extracellular matrix degradation.

Telomere exchange and asymmetric segregation of chromosomes can account for the unlimited proliferative potential of ALT cell populations

Telomerase-negative cancer cells show increased telomere sister chromatid exchange (T-SCE) rates, a phenomenon that has been associated with an alternative lengthening of telomeres (ALT) mechanism for maintaining telomeres in this subset of cancers. Here we examine whether or not T-SCE can maintain telomeres in human cells using a combinatorial model capable of describing how telomere lengths evolve over time. Our results show that random T-SCE is unlikely to be the mechanism of telomere maintenance of ALT human cells, but that increased T-SCE rates combined with a recently proposed novel mechanism of non-random segregation of chromosomes with long telomeres preferentially into the same daughter cell during cell division can stabilize chromosome ends in ALT cancers. At the end we discuss a possible experiment that can validate the findings of this study.

Ageing and atherosclerosis: Mechanisms and therapeutic options

Atherosclerosis is the cause of most heart attacks and strokes, and is par excellence, a disease of ageing. Whilst disease prevalence and incidence increases with increasing decade of life, there is also evidence of accelerated cellular ageing in atherosclerosis. Such evidence includes impaired cell proliferation, early culture senescence and cell cycle markers of senescence in vitro and in vivo. Cell senescence is also characterised by loss of telomeres from the ends of chromosomes. Cellular ageing increases with disease severity, acting as a marker for disease, but also directly promotes atherosclerosis. Cellular ageing appears to be due to both abnormal proliferation of cells in an attempt to repair vessel damage, and a response to the damage itself. This review summarises the evidence of vascular cell senescence in atherosclerosis, the causes and consequences of accelerated cellular ageing in atherosclerosis, and identifies potential therapeutic options for both prevention and treatment.

Aging and immortality in a cell proliferation model

We investigate a model of cell division in which the length of telomeres within a cell regulates its proliferative potential. At each division, telomeres undergo a systematic length decrease as well as a superimposed fluctuation due to exchange of telomere DNA between the two daughter cells. A cell becomes senescent when one or more of its telomeres become shorter than a critical length. We map this telomere dynamics onto a biased branching-diffusion process with an absorbing boundary condition whenever any telomere reaches the critical length. Using first-passage ideas, we find a phase transition between finite lifetime and immortality (infinite proliferation) of the cell population as a function of the influence of telomere shortening, fluctuations, and cell division.

The cell biology of intervertebral disc aging and degeneration

Intervertebral disc degeneration, which mimics disc aging but occurs at an accelerated rate, is considered to be related to neck or low back pain and disc herniation. Degenerated discs show breakdown of the extracellular matrix and thus fail to bear the daily loadings exerted on the spine. Rather than a passive process of wear and tear, disc degeneration is an aberrant, cell-mediated response to progressive structural failure due to aging and other environmental factors such as abnormal mechanical stress. With aging and degeneration, disc cells undergo substantially biologic changes, including alternation of cell type in the nucleus pulposus, increased cell density but decreased number of viable cells as a result of increased cell death and increased cell proliferation, increased cell senescence, and altered cell phenotype which is characterized by compromised capability of synthesizing correct matrix components and by enhanced catabolic metabolism. These changes are involved in the process of disc degeneration through the complicated interactions among them. To retard or reverse disc degeneration, the abnormal conditions of the decreased viable cell population and the altered cell phenotype should be corrected. As potential therapies for disc degeneration, intradiscal protein injection, gene transfer and cell implantation are being understudied in vivo. Suppression of excessive apoptosis and accelerated senescence of disc cells may be other choices for treating disc degeneration. When performing a biologic therapy in order to repair or regenerate the degenerated disc, nutrient and biomechanical factors should also be incorporated, because they are the major causes of the biologic changes experienced by disc cells. Moreover, a very early intervention is indicated by the finding that the onset of human disc degeneration occurs as early as by adolescence.

Human telomerase reverse transcriptase (hTERT) extends the lifespan of canine chondrocytes in vitro without inducing neoplastic transformation

To determine if the exogenous expression of the human telomerase reverse transcriptase (hTERT) protein can extend the in vitro lifespan of chondrocytes from normal and osteoarthritic canine donors, articular chondrocytes were harvested and expanded initially in monolayer culture. Cells were transfected with pCIneo or pCIneo-hTERT and selected using G418. Transfectants were cultured either in monolayer or alginate beads and telomerase activity, replicative lifespan and the tumourogenic potential of the transfected cells were assessed. hTERT expression in canine chondrocytes prolonged the replicative lifespan of these cells but did not permit growth in low serum conditions or promote the formation of foci in anchorage independence assays. In addition, hTERT expression resulted in the down-regulation of MMP-1. This suggests that hTERT may represent a tool for the generation of tissue engineered chondrocytes suitable for autologous re-implantation into the affected areas of osteoarthritic joints.

Cyclosporine A induces senescence in renal tubular epithelial cells

The nephrotoxic potential of the widely used immunosuppressive agent cyclosporine A (CsA) is well recognized. However, the mechanism of renal tubular toxicity is not yet fully elucidated. Chronic CsA nephropathy and renal organ aging share some clinical features, such as renal fibrosis and tubular atrophy, raising the possibility that CsA may exert some of its deleterious effects via induction of a stress-induced senescent phenotype. We investigated this hypothesis in HK-2 cells and primary proximal tubular cells in vitro. CsA induced the production of H2O2, caused cell cycle arrest in the G0/G1 phase, and inhibited DNA synthesis. Furthermore, CsA exposure lead to a reduction of telomere length, increased p53 serine 15 phosphorylation, and caused an upregulation of the cell cycle inhibitor p21Kip1 (CDKN1A) mRNA levels. CsA caused an increase in p16INK4a (CDKN2A) expression after a 13-day exposure in primary proximal tubular cells but not in HK-2 cells. Coincubation of cells with CsA and catalase was able to prevent telomere shortening and partially restored DNA synthesis. In summary, CsA induces cellular senescence in human renal tubular epithelial cells, which can be attenuated by scavenging reactive oxygen species.

Premature senescence of mesothelial cells is associated with non-telomeric DNA damage

Human peritoneal mesothelial cells (HPMCs) senesce in vitro after barely few population doublings. In this report, we show that senescence of HPMCs is associated with increased accumulation of gamma-H2A.X foci, which reveal DNA double-strand breaks. Of note, already early-passage cultures contain a considerable fraction (44+/-10%) of cells bearing gamma-H2A.X foci. The gamma-H2A.X foci localize predominantly to non-telomeric DNA, either in young or senescent cells. Moreover, HPMCs seem to have unusually short telomeres (approximately 3.5 kbp) despite the presence of active telomerase. These telomeres do not shorten during senescence, but the activity of telomerase decreases to undetectable levels. In addition, senescence of HPMCs is associated with mitochondrial dysfunction, as manifested by increased production of reactive oxygen species and reduced mitochondrial membrane potential. These results may indicate that premature senescence of HPMCs is largely related to oxidative stress-induced DNA damage in non-telomeric regions of the genome.

Stress chaperones, mortalin, and pex19p mediate 5-aza-2' deoxycytidine-induced senescence of cancer cells by DNA methylation-independent pathway

DNA demethylating agents are used to reverse epigenetic silencing of tumor suppressors in cancer therapeutics. Understanding of the molecular and cellular factors involved in DNA demethylation-induced gene desilencing and senescence is still limited. We have tested the involvement of two stress chaperones, Pex19p and mortalin, in 5-Aza-2' deoxycytidine (5AZA-dC; DNA demethylating agent)-induced senescence. We found that the cells overexpressing these chaperones were highly sensitive to 5AZA-dC, and their partial silencing eliminated 5AZA-dC-induced senescence in human osteosarcoma cells. We demonstrate that these chaperones modulate the demethylation and chromatin remodeling-dependent (as accessed by p16(INK4A) expression) and remodeling-independent (such as activation of tumor suppressor p53 pathway) senescence response of cells. Furthermore, we found the direct interactions of 5AZA-dC with these chaperones that may alter their functions. We conclude that both mortalin and Pex19p are important mediators, prognostic indicators, and tailoring tools for 5AZA-dC-induced senescence in cancer cells.

Telomeres and telomerase: Biological and clinical importance in dogs

In recent years in human oncology the enzyme telomerase has emerged as an ideal target for cancer therapy. This has led to the assessment of telomerase in cancers in companion animals, mainly dogs and these studies confirm that in dogs, like humans, telomere maintenance by telomerase is the primary mechanism by which cancer cells overcome their mortality and extend their lifespan. This review aims to provide an introduction to the biology of telomeres and telomerase and to discuss some of the telomere/telomerase directed therapeutic methodologies currently under development which may be of benefit to the canine cancer patient.

Presence of human circulating progenitor cells for cancer stromal fibroblasts in the blood of lung cancer patients

Recent animal data have suggested that cancer-induced stroma consists of blood-borne fibroblasts as well as tissue-derived fibroblasts. In this study, mononuclear cells isolated from the pulmonary vein blood of lungs resected from lung cancer patients were cultured to confirm the presence of blood-borne fibroblast. In 34% (16 of 47) of the cases, spindle cells with fibroblast morphology proliferated in a disarrayed fashion and were positive for vimentin and collagen type I but negative for both specific myogenic and endothelial markers. The cDNA profiles of blood-borne fibroblasts, tissue-derived (lung) fibroblasts, human vascular smooth muscle cells (HSMCs), and umbilical vein endothelial cells (HUVECs) were clustered with a hierarchical classification algorithm. The profiles of the blood-borne fibroblasts were clearly isolated from those of the tissue-derived fibroblasts, HSMCs, and HUVECs. When carboxyfluorescein succinyl ester (CFSE)-labeled human mononuclear cells from the blood of lung cancer patients were transferred into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice engrafted with a human lung cancer xenograft, CFSE-labeled fibroblasts were found around the cancer nests. We investigated the several clinicopathological factors of blood-borne fibroblast-positive patients. The blood-borne fibroblast-positive cases had a significantly larger central fibrotic area in primary lung cancer than in the negative cases (123 +/- 29 vs. 59 +/- 13 mm(2); p = .02). Our results indicated that the blood in the vicinity of human lung cancer contains fibroblast progenitor cells that have the capacity to migrate into the cancer stroma and differentiate into fibroblasts having biological characteristics different from those of tissue-derived fibroblasts. Disclosure of potential conflicts of interest is found at the end of this article.

Epigenetic control of hematopoietic stem cell aging the case of Ezh2

Hematopoietic stem cells have potent, but not unlimited, selfrenewal potential. The mechanisms that restrict selfrenewal are likely to play a role during aging. Recent data suggest that the regulation of histone modifications by Polycomb group genes may be of crucial relevance to balance selfrenewal and aging. We provide evidence for the involvement of one of these Polycomb group genes, Ezh2, in aging of the hematopoietic stem cell system.

Skeletal muscle aging

Average world life expectancy has seen a dramatic rise over the last two centuries although active life expectancy remains relatively unchanged. One reason for this is that aging results in skeletal muscle becoming smaller, weaker and more susceptible to contraction-induced injury. By the age of 70, muscle strength is reduced by around 30–40% and this can have catastrophic effects on quality of life. Despite a vast amount of research into age-related changes in skeletal muscle, the exact mechanisms responsible for this is still unclear and thus treatments to preserve muscle function with aging remain elusive.

Senescence in cells of the aging and degenerating intervertebral disc: immunolocalization of senescence-associated beta-galactosidase in human and sand rat discs

STUDY DESIGN

Human intervertebral disc anulus tissue was obtained in a prospective study of cell senescence. Localization of the senescence biomarker beta-galactosidase (senescence associated beta-galactosidase, SA-beta-gal) was used for quantitative determination of the % senescent cells. Discs were obtained from surgical specimens or control donors. Discs were also studied from the lumbar spine of the sand rat. Experimental studies were approved by the authors' Human Subjects Institutional Review Board and animal use committee.

OBJECTIVES

To determine the incidence of cell senescence in human discs with Thompson Grades I through V using immunocytochemistry to quantify the percentage of cells positive for the senescence biomarker SA-beta-gal.

SUMMARY OF BACKGROUND DATA

Cell senescence has been recognized as a potential factor playing a role age-related disc degeneration. Senescent cells are viable but have lost the ability to divide. Senescence cells, however, are metabolically active.

METHODS

Fifty-seven discs specimens from 54 subjects were examined with immunocytochemistry for anti-SA-beta-gal immunocytochemical localization to identify senescent cells. The fraction of positive cells was determined with quantitative histomorphometry.

RESULTS

Quantitative histomorphometry of human discs show an overall incidence of SA-beta-gal-positive cells of 29.9% (+/-24.8, SD), with a range from 0 to 92.01%. Analysis by ANOVA of the % senescent cells grouped by Thompson grade showed significant increases in senescence with increasing disc degeneration (P < 0.0001). Further analysis with Tukey's test showed significant differences between the % senescent cells in Grades I/II versus IV, and versus V. SA-beta-gal-positive cells were also present in discs of the aging sand rat spine.

CONCLUSIONS

Quantitative analysis of immunohistochemical localization of SA-beta-gal identified a sizeable population of senescent cells in the aging/degenerating disc. It is important to discover more about the senescent disc cell population because these cells persist and accumulate over time within the disc. Since senescent cells cannot divide, senescence may reduce the disc's ability to generate new cells to replace existing ones lost to necrosis or apoptosis.

Human embryonic stem cell stability

Human embryonic stem cells (hESCs) are derived from human preimplantation embryos, and exhibit the defining characteristics of immortality and pluripotency. Indeed, these cell populations can be maintained for several years in continuous culture, and undergo hundreds of population doublings. hESCs are thus likely candidates for source of cells for cell replacement therapies. Although hESC lines appear stable in their expression of cytokine markers, expression of telomerase, ability to differentiate, and maintenance of a stable karyotype, several other aspects of stability have not yet been addressed, including mitochondrial sequencing, methylation patterns, and fine resolution cytogenetic analysis. Because of the potential utility of hESCs, it will be of utmost importance to evaluate the stability of these aspects of ESC biology.

Cloning in companion animal, non-domestic and endangered species: can the technology become a practical reality?

Somatic cell nuclear transfer (SCNT) can provide a unique alternative for the preservation of valuable individuals, breeds and species. However, with the exception of a handful of domestic animal species, successful production of healthy cloned offspring has been challenging. Progress in species that have little commercial or research interest, including many companion animal, non-domestic and endangered species (CANDES), has lagged behind. In this review, we discuss the current and future status of SCNT in CANDES and the problems that must be overcome to improve pre- and post-implantation embryo survival in order for this technology to be considered a viable tool for assisted reproduction in these species.

Bone marrow-derived cells: the influence of aging and cellular senescence

During the course of an entire lifespan, tissue repair and regeneration is made possible by the presence of adult stem cells. Stem cell expansion, maintenance, and differentiation must be tightly controlled to assure longevity. Hematopoietic stem cells (HSC) are greatly solicited given the daily high blood cell turnover. Moreover, several bone marrow-derived cells including HSC, mesenchymal stromal cells (MSC), and endothelial progenitor cells (EPC) also significantly contribute to peripheral tissue repair and regeneration, including tumor formation. Therefore, factors influencing bone marrow-derived cell proliferation and functions are likely to have a broad impact. Aging has been identified as one of these factors. One hypothesis is that aging directly affects stem cells as a consequence of exhaustive proliferation. Alternatively, it is also possible that aging indirectly affects stem cells by acting on their microenvironment. Cellular senescence is believed to have evolved as a tumor suppressor mechanism capable of arresting growth to reduce risk of malignancy. In opposition to apoptosis, senescent cells accumulate in tissues. Recent evidence suggests their accumulation contributes to the phenotype of aging. Senescence can be activated by both telomere-dependent and telomere-independent pathways. Genetic alteration, genome-wide DNA damage, and oxidative stress are inducers of senescence and have recently been identified as occurring in bone marrow-derived cells. Below is a review of the link between cellular senescence, aging, and bone marrow-derived cells, and the possible consequences aging may have on bone marrow trans plantation procedures and emerging marrow-derived cell-based therapies.

Cigarette smoke induces cellular senescence

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States, and cigarette smoking is the major risk factor for COPD. Fibroblasts play an important role in repair and lung homeostasis. Recent studies have demonstrated a reduced growth rate for lung fibroblasts in patients with COPD. In this study we examined the effect of cigarette smoke extract (CSE) on fibroblast proliferative capacity. We found that cigarette smoke stopped proliferation of lung fibroblasts and upregulated two pathways linked to cell senescence (a biological process associated with cell longevity and an inability to replicate), p53 and p16-retinoblastoma protein pathways. We compared a single exposure of CSE to multiple exposures over an extended time course. A single exposure to CSE led to cell growth inhibition at multiple phases of the cell cycle without killing the cells. The decrease in proliferation was accompanied by increased ATM, p53, and p21 activity. However, several important senescent markers were not present in the cells at an earlier time point. When we examined multiple exposures to CSE, we found that the cells had profound growth arrest, a flat and enlarged morphology, upregulated p16, and senescence-associated beta-galactosidase activity, which is consistent with a classic senescent phenotype. These observations suggest that while a single exposure to cigarette smoke inhibits normal fibroblast proliferation (required for lung repair), multiple exposures to cigarette smoke move cells into an irreversible state of senescence. This inability to repair lung injury may be an essential feature of emphysema.

Identification of p38MAPK-dependent genes with changed transcript abundance in H2O2-induced premature senescence of IMR-90 hTERT human fibroblasts

Premature senescence of IMR-90 human diploid fibroblasts expressing telomerase (hTERT) establishes after exposure to an acute sublethal concentration of H2O2. We showed herein that p38(MAPK) was phosphorylated after exposure of IMR-90 hTERT cells to H2O2. Selective inhibition of p38(MAPK) activity attenuated the increase in the proportion of cells positive for senescence associated beta-galactosidase activity. We generated a low density DNA array to study gene expression profiles of 240 senescence-related genes. Using this array, p38(MAPK) inhibitor and p38(MAPK) small interferent RNA, we identified several p38(MAPK)-target genes differentially expressed in H2O2-stressed IMR-90 hTERT fibroblasts.

The telomere-telomerase axis and the heart

The preservation of myocyte number and cardiac mass throughout life is dependent on the balance between cell death and cell division. Rapidly emerging evidence indicates that new myocytes can be formed through the activation and differentiation of resident cardiac progenitor cells. The critical issue is the identification of mechanisms that define the aging of cardiac progenitor cells and, ultimately, their inability to replace dying myocytes. The most reliable marker of cellular senescence is the modification of the telomere-telomerase axis, together with the expression of the cell cycle inhibitors p16INK4a and p53. Cellular senescence is characterized by biochemical events that occur within the cell. In this regard, one of the most relevant processes is represented by repeated oxidative stress that may evolve into the activation of the cell death program or result in the development of a senescent phenotype. Thus, the modulation of telomerase activity and the control of telomeric length, together with the attenuation of the formation of reactive oxygen species, may represent important therapeutic tools in regenerative medicine and in prevention of aging and diabetic cardiomyopathies.

Vascular Smooth Muscle Cells Undergo Telomere-Based Senescence in Human Atherosclerosis

Although human atherosclerosis is associated with aging, direct evidence of cellular senescence and the mechanism of senescence in vascular smooth muscle cells (VSMCs) in atherosclerotic plaques is lacking. We examined normal vessels and plaques by histochemistry, Southern blotting, and fluorescence in situ hybridization for telomere signals. VSMCs in fibrous caps expressed markers of senescence (senescence-associated β-galactosidase [SAβG] and the cyclin-dependent kinase inhibitors [cdkis] p16 and p21) not seen in normal vessels. In matched samples from the same individual, plaques demonstrated markedly shorter telomeres than normal vessels. Fibrous cap VSMCs exhibited markedly shorter telomeres compared with normal medial VSMCs. Telomere shortening was closely associated with increasing severity of atherosclerosis. In vitro, plaque VSMCs demonstrated morphological features of senescence, increased SAβG expression, reduced proliferation, and premature senescence. VSMC senescence was mediated by changes in cyclins D/E, p16, p21, and pRB, and plaque VSMCs could reenter the cell cycle by hyperphosphorylating pRB. Both plaque and normal VSMCs expressed low levels of telomerase. However, telomerase expression alone rescued plaque VSMC senescence despite short telomeres, normalizing the cdki/pRB changes. In vivo, plaque VSMCs exhibited oxidative DNA damage, suggesting that telomere damage may be induced by oxidant stress. Furthermore, oxidants induced premature senescence in vitro, with accelerated telomere shortening and reduced telomerase activity. We conclude that human atherosclerosis is characterized by senescence of VSMCs, accelerated by oxidative stress-induced DNA damage, inhibition of telomerase and marked telomere shortening. Prevention of cellular senescence may be a novel therapeutic target in atherosclerosis.

Venous ulcer fibroblasts respond to basic fibroblast growth factor at the cell cycle protein level

Fibroblasts cultured from venous ulcers demonstrate phenotypic characteristics of cellular senescence including slow growth, altered morphology, upregulation of fibronectin, and increased senescence-associated beta-galactosidase activity. In senescent cells, arrest of cell replication is related to overexpression of p21 and underexpression of phosphorylated tumor-suppressor protein retinoblastoma (ppRb). The regulatory mechanisms for cell proliferation in venous ulcer fibroblasts are unknown. In this study, venous ulcer fibroblasts are examined for cell cycle protein expression and modulation by basic fibroblast growth factor (bFGF). Fibroblasts were isolated from the venous ulcer of the distal lower extremity (fb-D) of patients with chronic venous insufficiency. A control biopsy was obtained from the proximal ipsilateral thigh (fb-P). Paired cultures were plated at 100,000 cells/plate and the cells synchronized. After 24 hr, one culture set was treated with bFGF (20 ng/mL) and the other was kept in culture medium only (untreated). All cultures, treated and untreated, were lysed following 24 hr of incubation, and the lysate was used to perform immunoblot analysis for p21, ppRb, and cyclin D1. Immunoblot samples were standardized to protein content. In all patients analyzed (n = 4), at basal levels (untreated) fb-D demonstrated significant overexpression of p21 versus fb-P (p = 0.016). Treatment with bFGF resulted in significant downregulation of p21 levels for fb-D (p = 0.008) and fb-P (p = 0.037) compared to untreated fibroblasts. ppRb was underexpressed in fb-D versus fb-P (p = 0.069). Treatment with bFGF increased ppRb significantly in fb-D (p = 0.030) and in fb-P (p = 0.027) compared to untreated fibroblasts. No differences were observed in cyclin D1 with respect to basal levels in fb-P versus fb-D or in treated versus untreated groups. Venous ulcer fibroblasts show phenotypic similarity to senescent cells, with overexpression of p21 as well as down regulation of phosphorylated pRb. The aberrations seen in the cell cycle proteins in fb-D are similar to those seen in senescent cells; however, bFGF can modulate important cell cycle regulatory proteins, promoting a proliferative environment in fb-D that is not possible in a senescent cell. The role of bFGF may be useful in the clinical treatment of venous ulcer pathology.

No Association Between Telomere Length and Survival Among the Elderly and Oldest Old

BACKGROUND

The consistent findings of a negative correlation between telomere length and replicative potential of cultured cells, as well as a decreasing telomere length in a number of different tissues in humans with age, have led to the suggestion that telomeres play a role in cellular aging in vivo and ultimately even in organismal aging. Furthermore, one small longitudinal study of elderly individuals has suggested that longer telomeres are associated with better survival.

METHODS

Telomere length was measured as mean terminal restriction fragment length on blood cells from 812 persons, age 73 to 101 years, who participated in population-based surveys in 1997-1998. Among the participants were 652 twins. The participants were followed up through the Danish Civil Registration system until January 2005, at which time 412 (51%) were dead.

RESULTS

Univariate Cox regression analyses revealed that longer telomeres were associated with better survival (hazard ratios = 0.89 [95% confidence interval = 0.76-1.04] per 1 kb in males and 0.79 [0.72-0.88] per 1 kb in females, respectively). However, including age in the analyses changed the estimates to 0.97 (0.83-1.14) and 0.93 (0.85-1.03), respectively. Intrapair comparison showed that among 175 twin pairs in which at least one died during follow up, it was the twin with the shorter telomere length who died first in 97 (55%) of the pairs (95% confidence interval = 48-63%). We could not confirm the recently reported negative correlation between telomere length and obesity or between telomere length and smoking.

CONCLUSION

This longitudinal study of the elderly and oldest old does not support the hypothesis that telomere length is a predictor for remaining lifespan once age is controlled for.

Selective pharmacologic inhibition of c-Jun NH2-terminal kinase radiosensitizes thyroid anaplastic cancer cell lines via induction of terminal growth arrest

CONTEXT

The high radioresistance of anaplastic thyroid cancer (ATC) and cultured ATC cells stipulates for the means of increasing their radiosensitivity. It has been shown that c-Jun NH(2)-terminal kinase (JNK) activation is one of the manifestations of radiation response in ATC cells.

OBJECTIVE

Assessment of the effect of selective JNK inhibition on ATC cell radiosensitivity and clarification of the associated mechanisms.

RESULTS

The JNK inhibitor markedly suppressed ATC cell growth in a reversible cytostatic manner. The combination treatment with JNK inhibitor plus ionizing radiation induced a significant decrease in clonogenic survival of irradiated cells as compared with either singular treatment. The effect was not due to apoptosis of exposed cells but to a profound senescence-like terminal growth arrest occurring irrespectively of cells' p53 mutational status. Postradiational DNA damage repair was also significantly compromised in the presence of SP600125.

CONCLUSIONS

JNK signaling is an essential component of ATC cell proliferation and survival after radiation therapy. Hence, pharmacological interference with JNK pathway in combination with radiotherapy may be a promising treatment of ATC.

Human fibroblast reactions to standard and electropolished titanium and Ti-6Al-7Nb, and electropolished stainless steel

Stainless steel (SS), titanium (cpTi), and Ti-6Al-7Nb (TAN) are frequently used metals in orthopedic internal fracture fixation. Although reactivity to SS and cpTi are noted in reference, the soft tissue compatibility of TAN has not been comprehensively studied. This study focuses on the in vitro soft tissue compatibility of TAN in comparison to SS and cpTi using a human fibroblast model. The industrial standard surface finishes of these three materials vary considerably in view of their use in similar applications. To distinguish between material parameters of topography and chemistry, we have included electropolished (e.p) counterparts of the standard preparations of cpTi and TAN in the study (standard SS is e.p). All materials were characterized using atomic force microscopy, profilometry, and scanning electron microscopy. Our findings demonstrate that cell morphology and growth rate was similar for SS, and e.p. cpTi and TAN, with cells well spread and forming a confluent monolayer by 10 days. Cell growth on standard cpTi was similar to the electropolished samples; however, they showed a less spread morphology with more filopodia and surface ruffling present. Cell morphology on standard TAN was rounded or elongated and proliferation was inhibited at all time points, with possible cell necrosis by day 10. We found evidence of endocytosis of beta-phase particles originating from the standard TAN surface. We believe that the particle uptake coupled with the characteristic surface topography contribute to the noncytocompatibility of fibroblasts on standard TAN.

Requirement of E7 oncoprotein for viability of HeLa cells

Most human papillomavirus (HPV)-positive cervical cancers contain integrated copies of the viral genome in their chromosomes and express the viral oncoproteins E6 and E7. A virus-encoded transcription factor, E2, is known to repress E6/E7 expression in HPV-positive cancer cells, leading to growth inhibition, which indicates that E6/E7 is required for the survival of the cells. We found that the E2-mediated growth inhibition of HeLa cells, an HPV18-positive cancer cell line, was coupled with a reduction in telomerase activity, an effect which was rescued by the complementation of E7 expression, but not E6 expression, indicating that the cell viability and the telomerase activity in HeLa cells are maintained by an E7-associated function. Analysis of E7 mutants suggested that the binding to the pRB family of pocket proteins was involved in the ability of E7 to rescue the growth potential and telomerase activity inhibited by E2 expression. We also showed that the telomerase activity upregulated by E7 expression was determined by the hTERT promoter activity, and that c-Myc upregulation caused by pRB inactivation could account for the promoter activity. The activation of p53 and consequent accumulation of p21Cip1, which were triggered by the downregulation of E6, appeared not to be essential for the E2-mediated growth arrest.