[Show abstract][Hide abstract] ABSTRACT: Recent work has linked psychological stress with premature cellular aging as indexed by reduced leukocyte telomere length. The combination of shorter telomeres with high telomerase activity (TA) may be indicative of active cell stress. We hypothesized that older individuals characterized by shorter telomeres with high TA in unstimulated leukocytes would show signs of high allostatic load and low levels of protective psychosocial resources. We studied 333 healthy men and women aged 54-76 y who underwent laboratory testing in which we measured cardiovascular, neuroendocrine, and inflammatory responses to standardized mental stress tasks. The tasks elicited prompt increases in blood pressure (BP), heart rate, cortisol, and mediators of inflammation and reductions in heart rate variability, returning toward baseline levels following stress. However, men having shorter telomeres with high TA showed blunted poststress recovery in systolic BP, heart rate variability, and monocyte chemoattractant protein-1, together with reduced responsivity in diastolic BP, heart rate, and cortisol, in comparison to men with longer telomeres or men with shorter telomeres and low TA. Shorter telomeres with high TA were also associated with reduced social support, lower optimism, higher hostility, and greater early life adversity. These effects were independent of age, socioeconomic status, and body mass index. We did not observe differences among older women. Our findings suggest that active cell stress is associated with impaired physiological stress responses and impoverished psychosocial resources, reflecting an integration of cellular, systemic, and psychological stress processes potentially relevant to health in older men.
Proceedings of the National Academy of Sciences 03/2014; · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: AIMS: Although endothelial cell senescence is known to play an important role in the development of cardiovascular pathologies, mechanisms that attenuate this process have not been extensively investigated. The aim of this study was to investigate whether SIRT6, a member of the sirtuin family of NAD(+)-dependent protein deacetylases/ADP-ribosyltransferases, protects endothelial cells from premature senescence and dysfunction, and if so which is its mode of action. METHODS AND RESULTS: mRNA expression analysis demonstrated comparable levels of SIRT1 and SIRT6 transcripts in endothelial cells derived from different vascular beds and significantly higher levels of SIRT6 in these cells relative to those in haematopoietic progenitor cells. SIRT6 depletion by RNA interference in human umbilical vein endothelial cells (HUVEC) and aortic endothelial cells reduced cell proliferation, increased the fraction of senescence-associated-β-galactosidase positive cells and diminished the ability of the cells to form tubule networks on Matrigel. Further examination of SIRT6-depleted HUVEC demonstrated higher intercellular-adhesion molecule-1 (ICAM-1) and plasminogen-activator inhibitor-1 mRNA, lower levels of endothelial nitric oxide synthase mRNA and protein, higher ICAM-1 surface expression and up-regulation of p21. Fluorescence microscopy of SIRT6-depleted HUVEC stained with anti-Phospho-histone H2A.X and anti-telomere-repeat-binding-factor-1 antibodies showed evidence of increased nuclear DNA damage and the formation of telomere dysfunction-induced foci. CONCLUSIONS: This work demonstrates that the presence of SIRT6 in endothelial cells confers protection from telomere and genomic DNA damage, thus preventing a decrease in replicative capacity and the onset of premature senescence. These findings suggest that SIRT6 may be important to maintain endothelial homeostatic functions and delay vascular ageing.
Cardiovascular research 12/2012; · 5.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Shorter telomere length and poor sleep are more prevalent at older ages, but their relationship is uncertain. This study explored associations between sleep duration and telomere length in a sample of healthy middle and early old age people. METHODS: Participants were 434 men and women aged 63.3 years on average drawn from the Whitehall II cohort study. Sleep duration was measured by self-report. RESULTS: There was a linear association between sleep duration and leukocyte telomere length in men but not in women (P = 0.035). Men reporting shorter sleep duration had shorter telomeres, independently of age, body mass index, smoking, educational attainment, current employment, cynical hostility scores and depressive symptoms. Telomeres were on average 6% shorter in men sleeping 5 hours or fewer compared with those sleeping more than 7 hours per night. CONCLUSION: This study adds to the growing literature relating sleep duration with biomarkers of aging, and suggests that shortening of telomeres might reflect mechanisms through which short sleep contributes to pathological conditions in older men.
PLoS ONE 01/2012; 7(10):e47292. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hostility is associated with a significantly increased risk of age-related disease and mortality, yet the pathophysiological mechanisms involved remain unclear. Here we investigated the hypothesis that hostility might impact health by promoting cellular aging.
We tested the relationship between cynical hostility and two known markers of cellular aging, leukocyte telomere length (TL) and leukocyte telomerase activity (TA), in 434 men and women from the Whitehall II cohort.
High-hostile men had significantly shorter leukocyte TL than their low-hostile counterparts. They also had elevated leukocyte TA, with a significantly increased likelihood of having both short TL and high TA, compared with low-hostile individuals.
Because telomerase is known to counteract telomere shortening by synthesizing telomeric DNA repeats, particularly in the context of shortened telomeres, heightened TA might represent a compensatory response in high-hostile individuals. The relationship between hostility and disease is stronger in men than in women, and men generally have a shorter life expectancy than women. Our findings suggest that telomere attrition might represent a novel mechanism mediating the detrimental effects of hostility on men's health.
[Show abstract][Hide abstract] ABSTRACT: Low socioeconomic status (SES) may be associated with accelerated biological aging, but findings relating SES with telomere length have been inconsistent. We tested the hypotheses that shorter telomere length and telomerase activity would be related more robustly to education, an early life indicator of socioeconomic position, than to current indicators of socioeconomic circumstances. Healthy men and women aged 53-76 years from the Whitehall II epidemiological cohort provided blood samples from which telomere length was assessed in 448 and telomerase activity in 416. Educational attainment was classified into four levels, while household income and grade of employment were measured as indicators of current socioeconomic circumstances. Age, gender, blood pressure, glycated hemoglobin, high density lipoprotein cholesterol, smoking, body mass index and physical activity were included as covariates. We found that lower educational attainment was associated with shorter telomere length after controlling statistically for biological and behavioral covariates. Neither household income nor employment grade was related to telomere length. The association between telomere length and education remained significant after adjusting for current socioeconomic circumstances. In men, highest levels of telomerase activity were found in the lowest education group. We conclude that low SES defined in terms of education but not current socioeconomic circumstances is associated with shortened telomeres. Low educational attainment may be an indicator of long-term SES trajectories, and be associated with accumulated allostatic load resulting in telomere shortening. Education may also promote problem-solving skills leading to reduced biological stress responsivity, with favorable consequences for biological aging.
Brain Behavior and Immunity 04/2011; 25(7):1292-8. · 5.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Anagrelide is a selective inhibitor of megakaryocytopoiesis used to treat thrombocytosis in patients with chronic myeloproliferative disorders. The effectiveness of anagrelide in lowering platelet counts is firmly established, but its primary mechanism of action remains elusive.
Here, we have evaluated whether anagrelide interferes with the major signal transduction cascades stimulated by thrombopoietin in the hematopoietic cell line UT-7/mpl and in cultured CD34(+) -derived human hematopoietic cells. In addition, we have used quantitative mRNA expression analysis to assess whether the drug affects the levels of known transcription factors that control megakaryocytopoiesis.
In UT-7/mpl cells, anagrelide (1μm) did not interfere with MPL-mediated signaling as monitored by its lack of effect on JAK2 phosphorylation. Similarly, the drug did not affect the phosphorylation of STAT3, ERK1/2 or AKT in either UT-7/mpl cells or primary hematopoietic cells. In contrast, during thrombopoietin-induced megakaryocytic differentiation of normal hematopoietic cultures, anagrelide (0.3μm) reduced the rise in the mRNA levels of the transcription factors GATA-1 and FOG-1 as well as those of the downstream genes encoding FLI-1, NF-E2, glycoprotein IIb and MPL. However, the drug showed no effect on GATA-2 or RUNX-1 mRNA expression. Furthermore, anagrelide did not diminish the rise in GATA-1 and FOG-1 expression during erythropoietin-stimulated erythroid differentiation. Cilostamide, an exclusive and equipotent phosphodiesterase III (PDEIII) inhibitor, did not alter the expression of these genes.
Anagrelide suppresses megakaryocytopoiesis by reducing the expression levels of GATA-1 and FOG-1 via a PDEIII-independent mechanism that is differentiation context-specific and does not involve inhibition of MPL-mediated early signal transduction events.
Journal of Thrombosis and Haemostasis 10/2010; 8(10):2252-61. · 6.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Normal cells can permanently lose the ability to proliferate when challenged by potentially oncogenic stress, a process termed cellular senescence. Senescence-associated beta-galactosidase (SA-betagal) activity, detectable at pH 6.0, permits the identification of senescent cells in culture and mammalian tissues. Here we describe first a cytochemical protocol suitable for the histochemical detection of individual senescent cells both in culture and tissue biopsies. The second method is based on the alkalinization of lysosomes, followed by the use of 5-dodecanoylaminofluorescein di-beta-D-galactopyranoside (C12FDG), a fluorogenic substrate for betagal activity. The cytochemical method takes about 30 min to execute, and several hours to a day to develop and score. The fluorescence methods take between 4 and 8 h to execute and can be scored in a single day. The cytochemical method is applicable to tissue sections and requires simple reagents and equipment. The fluorescence-based methods have the advantages of being more quantitative and sensitive.
[Show abstract][Hide abstract] ABSTRACT: Most mitotically competent mammalian cell types can react to stress by undergoing a phenotypically distinctive and permanent form of growth arrest called "cellular senescence." This response has been extensively characterized in cell culture and more recently it has been found to occur also in vivo in a number of tissues. In this review I will present the case for the occurrence of senescence in the vascular endothelium. I will also discuss the mechanisms and factors that modulate endothelial cell replicative capacity and the onset of senescence. Finally, I will examine the senescent phenotype and its possible consequences for the development and progression of vascular diseases.
Journal of Applied Physiology 12/2008; 106(1):326-32. · 3.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: When endothelial cells from different vascular beds are grown in culture they show a limited capacity to divide, eventually entering into a permanent and phenotypically distinctive non-dividing state referred to as 'replicative senescence'. Replicative senescence is thought to result from progressive shortening of telomeric DNA and consequent telomere dysfunction. More recently, it has been realised that senescence can also be induced by a variety of insults, including those causing intracellular oxidative stress. In this report, we review evidence for the occurrence of endothelial cell senescence in vivo. We will also examine the causes, mechanisms and regulation of this process as they emerge from our studies in cell culture, focusing in particular on the roles of oxidative stress, telomerase, growth factors and nitric oxide.
[Show abstract][Hide abstract] ABSTRACT: Nitric oxide (NO) has been known for many years to bind to cytochrome C oxidase, the terminal acceptor in the mitochondrial electron transport chain, in competition with oxygen. This interaction may be significant in vivo and explain some of the biological actions of NO. In this article we review the evidence showing that binding of NO to cytochrome C oxidase elicits intracellular signaling events, including the diversion of oxygen to nonrespiratory substrates and the generation of reactive oxygen species. We discuss findings indicating that these NO-elicited events act as triggers by which mitochondria modulate signal transduction cascades involved in the induction of cellular defense mechanisms and adaptive responses. We also discuss instances in which the effects of NO on the electron transport chain might lead to mitochondrial dysfunction and pathology.
[Show abstract][Hide abstract] ABSTRACT: Telomerase, a reverse transcriptase involved in the maintenance of telomere function and cellular replicative capacity, is thought to be regulated by nitric oxide (NO). Here, we have used pharmacological tools and RNA interference to re-assess the role of NO in the regulation of telomerase and senescence of human umbilical vein endothelial cells. Acute or chronic treatment of these cells with the NO donors diethylenetriamine/NO (DETA-NO) or S-nitroso-N-acetylpenicillamine (SNAP) at concentrations which generated NO in the 1-300 nM range did not modulate telomerase activity. Similarly these agents did not affect cellular replicative capacity during long-term sub-cultivation. The NO synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (1 mM) reduced basal levels of c-GMP by 50% but had no effect on telomerase activity or replicative capacity. Withdrawal of ascorbic acid increased the intracellular pro-oxidant capacity, reduced telomerase activity and increased the accumulation of senescent cells upon serial passage in culture. However, this shift to a more oxidative redox state did not unmask the putative capacity of NO to modulate telomerase or senescence. Infection of cells with a lentiviral vector expressing a small hairpin RNA targeted against endothelial NOS inhibited endogenous NO production completely but failed to affect the decrease of telomerase activity or the accumulation of senescent cells observed with passage in culture. Our findings suggest that physiological concentrations of NO do not modulate telomerase levels or replicative capacity of endothelial cells, regardless of their cellular oxidative status.
[Show abstract][Hide abstract] ABSTRACT: Tea drinking appears to protect against the development of coronary heart disease (CHD), but the mediating pathways are uncertain. We studied the effects of 6 weeks of black tea or placebo on platelet activation, C-reactive protein (CRP), total antioxidant status, and soluble (s) P-Selectin in a randomized double-blind trial.
Healthy non-smoking men aged 18-55 years were randomized to black tea (N=37) or placebo (N=38) following a 4-week washout period during which they drank no tea, coffee or caffeinated beverages, but consumed caffeinated placebo tea. Bloods were drawn after 6 weeks of treatment. Platelet activation was assessed by measuring leukocyte-platelet aggregates using whole blood flow cytometry.
Following treatment, the tea group had fewer monocyte-platelet aggregates (means 5.84 versus 6.60%, P=0.027), neutrophil-platelet aggregates (P=0.017), total leukocyte-platelet aggregates (P=0.027), and lower plasma C-reactive protein (means 0.76 versus 0.97 mg/L, P=0.05) than the placebo group. There were no differences in total antioxidant status or soluble P-Selectin.
Chronic tea consumption reduces platelet activation and plasma C-reactive protein in healthy men. Effects cannot be attributed to observer bias or lifestyle confounders. These effects of tea may contribute to sustained cardiovascular health.
[Show abstract][Hide abstract] ABSTRACT: Tea has anecdotally been associated with stress relief, but this has seldom been tested scientifically.
To investigate the effects of 6 weeks of black tea consumption, compared with matched placebo, on subjective, cardiovascular, cortisol and platelet responses to acute stress, in a parallel group double-blind randomised design.
Seventy-five healthy nonsmoking men were withdrawn from tea, coffee and caffeinated beverages for a 4-week wash-out phase during which they drank four cups per day of a caffeinated placebo. A pretreatment laboratory test session was carried out, followed by either placebo (n = 38) or active tea treatment (n = 37) for 6 weeks, then, a final test session. Cardiovascular measures were obtained before, during and after two challenging behavioural tasks, while cortisol, platelet and subjective measures were assessed before and after tasks.
The tasks induced substantial increases in blood pressure, heart rate and subjective stress ratings, but responses did not differ between tea and placebo treatments. Platelet activation (assessed using flow cytometry) was lower following tea than placebo treatment in both baseline and post-stress samples (P < 0.005). The active tea group also showed lower post-task cortisol levels compared with placebo (P = 0.032), and a relative increase in subjective relaxation during the post-task recovery period (P = 0.036).
Compared with placebo, 6 weeks of tea consumption leads to lower post-stress cortisol and greater subjective relaxation, together with reduced platelet activation. Black tea may have health benefits in part by aiding stress recovery.
[Show abstract][Hide abstract] ABSTRACT: Anagrelide (ANA) and hydroxycarbamide (HC) are two distinct pharmacological agents used to treat thrombocythaemia associated with myeloproliferative disorders. Although both drugs have been in clinical use for a number of years, comparative studies of their selectivity and mode of action are still lacking. Here, we have evaluated the activities of ANA and HC on the growth and differentiation of human haematopoietic progenitor cells in liquid culture. Both drugs inhibited thrombopoietin-induced megakaryocytopoiesis in a dose-dependent manner, but with strikingly different potencies (IC(50)=26 nM for ANA and 30 muM for HC) and modes of action. Whereas HC inhibited cell proliferation, ANA acted primarily on the differentiation process. At doses that abrogated megakaryocytopoiesis, HC also inhibited the expansion of CD34(+) cells stimulated by stem cell factor, interleukin-3 and Flt-3 ligand and also induced apoptosis. Furthermore, HC inhibited erythroid and myelomonocytic cell growth, induced by erythropoietin or granulocyte-macrophage colony-stimulating factor, respectively. In contrast, ANA showed none of these additional effects. Taken together, these results demonstrate that ANA is a potent and selective inhibitor of megakaryocytopoiesis, having no significant activity against haematopoietic progenitor cell expansion or differentiation into other lineages. In contrast, the anti-megakaryocytopoietic activity of HC cannot be dissociated from its more general cytoreductive and cytotoxic actions.
[Show abstract][Hide abstract] ABSTRACT: The wear and tear processes that are thought to contribute to human ageing may play an important role in the development of vascular diseases. One such process is cellular senescence. In endothelial cells the senescent phenotype can be induced by a number of factors, including telomere damage, oxidative stress and sustained mitogenic stimulation. Several lines of evidence indicate that endothelial cell senescence maybe relevant to vascular disease. In this chapter we examine the causes, mechanisms and regulation of endothelial cell senescence as they emerge from studies in cell culture. We also describe the senescent phenotype and discuss its pathophysiological implications. We review the evidence for the occurrence of endothelial cell senescence in vivo and examine findings in animal models of ageing and human genetic disorders that argue for and against a role of endothelial cell senescence in age-related vascular pathology. Finally, we address the particular case of endothelial progenitor cell senescence and discuss the relevance of this phenomenon for angiogenesis and vascular repair.
[Show abstract][Hide abstract] ABSTRACT: Previous studies have demonstrated shortened bleeding times in patients with acute coronary syndromes, especially in myocardial infarction (MI). In this study we have investigated platelet hyper-function using the PFA-100 with collagen/adenosine diphosphate and collagen/epinephrine cartridges in 78 patients presenting with acute chest pain. Patients were classified into MI, unstable angina (UA) and non-specific chest pain. All patients received 300 mg aspirin (ASA) more than 2 h before blood samples were collected. Twenty healthy normal subjects were also tested before and 2 h after 300 mg ASA (n = 10). The collagen/adenosine diphosphate closure time was significantly shorter in MI patients (median, 71 s; P = 0.0237) but not in UA patients (median, 81 s; P > 0.05) compared with normal subjects (median, 92.5 s). The collagen/epinephrine closure times were significantly longer in UA patients (median, 233 s) than in untreated controls (median, 125 s; P < 0.0001), as expected, but there was no difference in MI patients (median, 149.24 s; P > 0.05), suggesting that the MI patients were not all responding to ASA. Analysis of a subset of the apparent ASA non-responders (n = 5) by platelet aggregation demonstrated that this was not related to failure of ASA to block cyclo-oxygenase activity. Von Willebrand factor levels were significantly elevated in both UA and MI patients compared with normal subjects (mean, 175.5 and 248.9 versus 89.1 s; P < 0.0001 and P < 0.0001, respectively) and were also significantly higher in the MI group compared with the UA group (P < 0.05). There is evidence for platelet hyper-function and elevated von Willebrand factor levels in the MI group that could explain their decreased responsiveness to ASA on the collagen/epinephrine cartridge.
Blood Coagulation and Fibrinolysis 11/2005; 16(8):557-62. · 1.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The platelet-lowering drug anagrelide inhibits bone marrow megakaryocytopoiesis by an unknown mechanism. Recently, it was found that anagrelide is bio-transformed in humans into two major metabolites (6,7-dichloro-3-hydroxy-1,5 dihydro-imidazo[2,1-b]quinazolin-2-one (BCH24426) and 2-amino-5,6-dichloro-3,4,-dihydroquinazoline (RL603). Whether these metabolites have biological activities that may underlie the mode of action of the parent drug is presently unclear. To clarify this question here we have compared the activities of anagrelide, BCH24426 and RL603 on the growth and differentiation of CD34(+) haematopoietic progenitor cells in liquid culture and on the migration of differentiated megakaryocytes. Incubation with either anagrelide, BCH24426 or RL603 did not affect the early expansion of CD34(+) cells stimulated by thrombopoietin. In contrast, both anagrelide and BCH24426 potently inhibited the development of megakaryocytes (IC(50) +/- s.e.m. = 26 +/- 4 and 44 +/- 6 nM, respectively), whereas RL603 showed no significant effect. Anagrelide and BCH24426 did not affect erythroid or myelomonocytic differentiation stimulated by erythropoietin or granulocyte-macrophage colony-stimulating factor, demonstrating the selectivity of these compounds against the megakaryocytic lineage. Neither anagrelide nor its metabolites showed a significant effect on the migratory response of megakaryocytes towards stromal cell-derived factor-1alpha. Although BCH24426 was shown to be considerably more potent than anagrelide as an inhibitor of phosphodiesterase type III (PDEIII) (IC(50) = 0.9 vs 36 nM) this activity did not correlate with the potency of inhibition of megakaryocyte development. Furthermore, other PDEIII inhibitors of widely differing potency were shown to have negligible effects on megakaryocytopoiesis. Taken together our results demonstrate that anagrelide and BCH24426 target a cellular event involved specifically in the megakaryocyte differentiation programme, which is independent of PDEIII inhibition.
British Journal of Pharmacology 11/2005; 146(3):324-32. · 5.07 Impact Factor