Accelerated telomere shortening in response to life stress

Numerous studies demonstrate links between chronic stress and indices of poor health, including risk factors for cardiovascular disease and poorer immune function. Nevertheless, the exact mechanisms of how stress gets "under the skin" remain elusive. We investigated the hypothesis that stress impacts health by modulating the rate of cellular aging. Here we provide evidence that psychological stress--both perceived stress and chronicity of stress--is significantly associated with higher oxidative stress, lower telomerase activity, and shorter telomere length, which are known determinants of cell senescence and longevity, in peripheral blood mononuclear cells from healthy premenopausal women. Women with the highest levels of perceived stress have telomeres shorter on average by the equivalent of at least one decade of additional aging compared to low stress women. These findings have implications for understanding how, at the cellular level, stress may promote earlier onset of age-related diseases.     

Accelerated telomere shortening and telomerase activation in Fanconi's anaemia

Fanconi's anaemia (FA) is an autosomal recessive disorder characterized by progressive bone marrow failure that often evolves towards acute leukaemia. FA also belongs to a group of chromosome instability diseases. Because telomeres are directly involved in chromosomal stability and in cell proliferation capacity, we examined telomere metabolism in peripheral blood mononuclear cells (PBMC). Telomere length was significantly shorter in 54 FA patient samples, compared to 51 controls (P<0.0001). In addition, mean telomere terminal restriction fragment lengths (TRF) in nine heterozygous patient samples did not differ from those of controls. In 14 samples from FA patients with severe aplastic anaemia (SFA), telomere length was significantly shorter than in 22 samples of age-matched FA patients with moderate haematological abnormalities (NSFA) (P<0.001). However, no correlation was found between TRF length and the presence of bone marrow clonal abnormalities in 16 additional, separately analysed, patient samples. Sequential measurement of TRF in six FA patients showed an accelerated rate of telomere shortening. Accordingly, telomere shortening rate was inversely correlated with clinical status. Telomerase, the enzyme that counteracts telomere shortening, was 4.8-fold more active in 25 FA patients than in 15 age-matched healthy controls. A model for the FA disease process is proposed.     

Inhibition of human telomerase in immortal human cells leads to progressive telomere shortening and cell death

The correlation between telomerase activity and human tumors has led to the hypothesis that tumor growth requires reactivation of telomerase and that telomerase inhibitors represent a class of chemotherapeutic agents. Herein, we examine the effects of inhibition of telomerase inside human cells. Peptide nucleic acid and 2'-O-MeRNA oligomers inhibit telomerase, leading to progressive telomere shortening and causing immortal human breast epithelial cells to undergo apoptosis with increasing frequency until no cells remain. Telomere shortening is reversible: if inhibitor addition is terminated, telomeres regain their initial lengths. Our results validate telomerase as a target for the discovery of anticancer drugs and supply general insights into the properties that successful agents will require regardless of chemical type. Chemically similar oligonucleotides are in clinical trials and have well characterized pharmacokinetics, making the inhibitors we describe practical lead compounds for testing for an antitelomerase chemotherapeutic strategy.     

Human pancreatic islet tumor cells maintained in vitro

Summary Tumor cells from two human insulinomas were maintained in culture for more than 6 months. The cultured cells synthesized and secreted proinsulin and insulin; and responded to cyclic AMP (1 mM) and tolbutamide (1 mM) stimulation with increased insulin release. In culture, these cells did not respond to stimulation by high concentrations of glucose (300 mg%) or by glucagon (10 g/ml).     

Abrupt telomere shortening in normal human fibroblasts

Aging is one of the most basic properties of living organisms. Abundant evidence supports the idea that cell senescence underlies organismal aging in higher mammals. Therefore, examining the molecular mechanisms that control cell and replicative senescence is of great interest for biology and medicine. Several discoveries strongly support telomere shortening as the main molecular mechanism that limits the growth of normal cells. Although cultures gradually approach their growth limit, appearance of individual senescent cells is sudden and stochastic. A theoretical model of abrupt telomere shortening has been proposed in order to explain this phenomenon, but until now there was no reliable experimental evidence supporting this idea. Here, we have employed novel methodology to provide evidence for the generation of extrachromosomal circular telomeric DNA as a result of abrupt telomere shortening in normal human fibroblasts. This mechanism ensures heterogeneity in growth potential among individual cells, which is crucial for gradual progression of the aging process.     

Accelerated telomere length shortening in granulocytes: a diagnostic marker for myeloproliferative diseases

OBJECTIVE: The telomere in mature myeloid cells derived from abnormal progenitor cells of myeloproliferative diseases (MPDs) may shorten more rapidly than that in T lymphocytes, which are considered to be derived from normal clones. To test this hypothesis, we measured telomere lengths in granulocytes and T lymphocytes from patients with MPDs and compared them with those from normal individuals. MATERIALS AND METHODS: Granulocytes and T lymphocytes were separated from the peripheral blood of 65 patients with MPDs (25 chronic myelogenous leukemia [CML], 16 polycythemia vera, 19 essential thrombocythemia, 5 chronic idiopathic myelofibrosis) and 35 normal individuals. Genomic DNA from each cell fraction was subjected to Southern blot hybridization to determine the mean telomere length. RESULTS: Telomere lengths in granulocytes from patients with MPDs were significantly shorter than those from normal individuals (vs CML, p = 0.002; vs other MPDs, p < 0.0001). However, there was no statistical difference in telomere length in T lymphocytes between MPD patients and normal individuals (vs CML, p = 0.35; vs other MPDs, p = 0.85). DeltaTRF (terminal restriction fragment) in patients with MPDs, which is defined as the difference in telomere length between granulocytes and T lymphocytes, was significantly longer than that in normal individuals. CONCLUSIONS: The results support the disease theory that MPDs result from extensive proliferation of myeloid progenitor cells, leading to accelerated telomere length shortening in mature granulocytes. An increase in DeltaTRF over the standard value (>1.74 kb) may be useful for discriminating leukocytosis due to MPDs from reactive leukocytosis.     

Accelerated telomere shortening in hematological lineages is limited to the first year following stem cell transplantation

Using quantitative fluorescence in situ hybridization and flow cytometry, the telomere length of telomere repeat sequences after stem cell transplantation (SCT) were measured. The study included the telomeres of peripheral blood monocytes that should reflect the length of telomeres in stem cells and the telomeres of T lymphocytes that could shorten as a result of peripheral expansion. The loss of telomeres in monocytes and in memory T cells, although accelerated initially, became comparable to the loss of telomeres in healthy controls from the second year after transplantation. In addition, the telomere length in the naive T cells that were produced by the thymus was comparable to the telomere length in the naive T cells of the donor. Compared to the total length of telomeres available, the loss of telomere repeats in leukocytes after SCT resembles the accelerated shortening seen in early childhood and remains, therefore, relatively insignificant.     

Enterovirus infection in human pancreatic islet cells,islet tropism in vivo and receptor involvement in cultured islet beta cells

Aims/hypothesis It is thought that enterovirus infections cause beta-cell damage and contribute to the development of Type 1 diabetes by replicating in the pancreatic islets. We sought evidence for this through autopsy studies and by investigating known enterovirus receptors in cultured human islets.Methods Autopsy pancreases from 12 newborn infants who died of fulminant coxsackievirus infections and from 65 Type 1 diabetic patients were studied for presence of enteroviral ribonucleic acid by in situ hybridisation. Forty non-diabetic control pancreases were included in the study. The expression and role of receptor candidates in cultured human islets were investigated with receptor-specific antibodies using immunocytochemistry and functional assays.Results Enterovirus-positive islet cells were found in some of both autopsy specimen collections, but not in control pancreases. No infected cells were seen in exocrine tissue. The cell surface molecules, poliovirus receptor and integrin v₃, which act as enterovirus receptors in established cell lines, were expressed in beta cells. Antibodies to poliovirus receptor, human coxsackievirus and adenovirus receptor and integrin v₃ protected islets and beta cells from adverse effects of poliovirus, coxsackie B viruses, and several of the arginine-glycine-aspartic acid motifs containing enteroviruses and human parechovirus 1 respectively. No evidence was found for expression of the decay-accelerating factor which acts as a receptor for several islet-cell-replicating echoviruses in established cell lines.Conclusions/interpretation The results show a definite islet-cell tropism of enteroviruses in the human pancreas. Some enteroviruses seem to use previously identified cell surface molecules as receptors in beta cells, whereas the identity of receptors used by other enteroviruses remains unknown.Abbreviations A-549 Human lung carcinoma cell line - CAV coxsackie A virus - CBV coxsackie B virus - DAF decay-accelerating factor - EV echovirus - HBSS Hanks balanced salt solution - FITC fluorescein isothiocyanate - GMK a green monkey kidney cell line - HCAR human coxsackievirus and adenovirus receptor - HPEV-1 human parechovirus 1 - PV-1 poliovirus type 1 - PVR poliovirus receptor - RGD arginine-glycine-aspartic acid - RNA ribonucleic acid P. Ylipaasto and K. Klingel contributed equally to the study     

Cell-mediated cytotoxic islet cell surface antibodies to human pancreatic beta cells

Summary Sera containing islet cell surface antibodies show a complement-dependent cytotoxic reaction against islet cells, but it has not yet been clarified whether islet cell surface antibodies exhibit cell-mediated cytotoxicity to these cells. By ⁵¹Cr release assay we investigated whether islet cell surface antibodies showed a cytotoxic reaction to human pancreatic B cells (JHPI-1 clone) in the presence of normal human lymphocytes. The sera from 14 islet cell surface antibody-positive, 16 islet cell surface antibody-negative Type 1 (insulin-dependent) diabetic patients and 18 islet cell surface antibody-negative healthy subjects were studied. Four sera containing islet cell surface antibodies showed specific cytotoxicity above the mean +3SD value of healthy subjects, and the mean specific cytotoxicity of islet cell surface antibody-positive sera differed significantly from that of both islet cell surface antibody-negative groups. These results suggest that this cell-mediated cytotoxic mechanism may play an important role in the pathogenesis of Type 1 diabetes.     

Gene disruption of a G4-DNA-dependent nuclease in yeast leads to cellular senescence and telomere shortening.

The yeast gene KEM1 (also named SEP1/DST2/XRN1/RAR5) produces a G4-DNA-dependent nuclease that binds to G4 tetraplex DNA structure and cuts in a single-stranded region 5' to the G4 structure. G4-DNA generated from yeast telomeric oligonucleotides competitively inhibits the cleavage reaction, suggesting that this enzyme may interact with yeast telomeres in vivo. Homozygous deletions of the KEM1 gene in yeast block meiosis at the pachytene stage, which is consistent with the hypothesis that G4 tetraplex DNA may be involved in homologous chromosome pairing during meiosis. We conjectured that the mitotic defects of kem1/sep1 mutant cells, such as a higher chromosome loss rate, are also due to failure in processing G4-DNA, especially at telomeres. Here we report two phenotypes associated with a kem1-null allele, cellular senescence and telomere shortening, that provide genetic evidence that G4 tetraplex DNA may play a role in telomere functioning. In addition, our results reveal that chromosome ends in the same cells behave differently in a fashion dependent on the KEM1 gene product.     

Simulated shortening of proliferation-restricting telomeres during clonal proliferation and senescence of human cells

In the absence of telomerase or other mechanisms to maintain their length, telomeres in human cells shorten at each round of cell division. This has been suggested to ultimately cause cell cycle exit when a critical telomere length is reached, leading to replicative senescence of the cell. At present, it is not clear whether the division potential of human cells is limited by the overall shortening of telomeres at all chromosomes or the shortening of specific telomeres on certain particular chromosomes. By computer simulations, my previous work has suggested that if the telomere theory is correct, the shortening of only a few, most likely two, telomeres might be preferentially involved in restricting the division of human cells. In this work, the length dynamics of individual telomeres in simulated cell clones were examined over their life span. It is shown that if the shortening of only two telomeres is responsible for restricting the proliferation of a cell, these two specific telomeres will shorten at different rates and have different length distributions from those of the rest telomeres. The unique pattern of length dynamics associated with the proliferation-restricting telomeres (PRT) provides a possibility of experimentally identifying these particular telomeres in human cells.     

Cell senescence and telomere shortening induced by a new series of specific G-quadruplex DNA ligands

Telomeres of human chromosomes contain a G-rich 3'-overhang that adopts an intramolecular G-quadruplex structure in vitro which blocks the catalytic reaction of telomerase. Agents that stabilize G-quadruplexes have the potential to interfere with telomere replication by blocking the elongation step catalyzed by telomerase and can therefore act as antitumor agents. We have identified by Fluorescence Resonance Energy Transfer a new series of quinoline-based G-quadruplex ligands that also exhibit potent and specific anti-telomerase activity with IC50 in the nanomolar concentration range. Long term treatment of tumor cells at subapoptotic dosage induces a delayed growth arrest that depends on the initial telomere length. This growth arrest is associated with telomere erosion and the appearance of the senescent cell phenotype (large size and expression of beta-galactosidase activity). Our data show that a G-quadruplex interacting agent is able to impair telomerase function in a tumor cell thus providing a basis for the development of new anticancer agents.     

Effects of C-peptide on isolated human pancreatic islet cells

BACKGROUND: Recent data have demonstrated that pro-insulin-derived C-peptide can affect the function of several different cell types. We hypothesized that C-peptide might have an influence on the function and survival of isolated human islets. METHODS: Islets were prepared by combining enzymatic digestion and density gradient centrifugation, and the effects of human C-peptide were evaluated acutely and after 24-h incubation. Insulin secretion, apoptosis, quantitative RT-PCR and western-blotting experiments were then performed. RESULTS: Glucose-stimulated insulin secretion was not affected by C-peptide and, accordingly, mRNA expression of glucose transporter 2 and glucokinase did not differ between islets pre-cultured or not with the hormone. However, apoptosis was significantly lower in islets exposed to C-peptide than in control islets. This was accompanied by a significant increase of mRNA and protein expression of Bcl2, an anti-apoptotic molecule, with no change in the expression of Bax, a pro-apoptotic molecule. CONCLUSION: These results show that in human islets pro-insulin C-peptide has no direct effects on insulin secretion, but it decreases islet cell apoptosis. A direct role of C-peptide on beta-cell mass regulation is therefore suggested.     

Adult human pancreatic islet cells in tissue culture: function and immunoreactivity

In order to obtain an appropriate tissue model to study human diabetes we isolated islet cells from pancreata obtained from brain-dead, heart-beating kidney donor subjects by collagenase dispersion and tissue culture. The presence of viable islet cells was confirmed by both immunofluorescence staining and hormone release experiments. Insulin and somatostatin release were determined on culture day 3 or 4 when amylase measurements indicated an absence of functional exocrine cells. Glucose, alpha-ketoisocaproic acid, theophylline, glucagon, and tolbutamide each stimulated insulin release 2- to 3-fold and somatostatin release 1.5- to 2-fold. Epinephrine and somatostatin both inhibited glucose-stimulated insulin release. Successful subculture of islet cells was achieved after dispersion of primary cultures with dispase. Subcultured islet cells released insulin into the medium during a subsequent 8-day period and when challenged with glucose responded with a 1.6-fold increase in insulin output. Cells cultured on glass coverslips were used to detect, by indirect immunofluorescence, islet cell surface antibodies (ICSA) in the sera of patients with insulin-dependent diabetes mellitus. Of 15 sera from patients with newly diagnosed insulin-dependent diabetes mellitus 9 were ICSA positive, whereas all of 10 control sera were negative; in contrast, using rat insulinoma cells only 4 diabetic sera were positive, as well as 2 control sera. These findings demonstrate the functional viability of adult human islet cells in primary and secondary culture. Cultured human islet cells are a novel, sensitive, and specific system for detecting ICSA and for studying autoimmune effects, and provide a potential source of islet cells for transplantation.