Jorge D. Erusalimsky

Does nitric oxide modulate mitochondrial energy generation and apoptosis

The physiological role of nitric oxide (NO) in the maintenance of vascular tone, in synaptic transmission and in cellular defence is now firmly established. Recent evidence indicates that NO can also affect mitochondrial function. Here, we review findings indicating that NO — through its interaction with components of the electron-transport chain — might function not only as a physiological regulator of cell respiration, but also to augment the generation of reactive oxygen species by mitochondria, and thereby trigger mechanisms of cell survival or death.

Nitric oxide and mitochondrial signaling from physiology to pathophysiology

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.

Megakaryocyte Ploidy and Platelet Changes in Human Diabetes and Atherosclerosis

Altered platelet morphology and function have been reported in patients with diabetes. They are likely to be associated with the pathological processes and increased risk of vascular disease seen in these patients. Mean platelet volume (MPV), platelet count, and megakaryocyte (MK) ploidy (DNA content) were measured in (1) nondiabetics with normal coronary arteries, (2) nondiabetics with coronary artery atherosclerosis, (3) diabetics without evidence of vascular complications, and (4) diabetics with vascular disease. The platelet count (+/- SD) was increased in all groups but only significantly in the diabetics with vascular disease (236 +/- 65 versus 250 +/- 54 versus 257 +/- 64 versus 295 +/- 90 [P < or = .05] x 10(9)/L, for groups, I, II, II, and IV, respectively). The MPV was significantly increased in patients with atherosclerosis (7.0 +/- 0.4 versus 8.0 +/- 1.2 [P < or = .05] versus 7.2 +/- 0.9 versus 8.1 +/- 0.9 [P < or = .05] IL). Geometric mean MK ploidy was significantly increased in all groups compared with controls (16 +/- 1.5 versus 18.7 +/- 1.8 [P < or = .05] versus 19.8 +/- 1.6 [P < or = .05] versus 20.1 +/- 2.7 [P < or = .05]). Furthermore, some patients with vascular disease and/or diabetes had a modal ploidy shift from 16 (the normal mammalian modal ploidy) to 32, with a concomitant reduction of MKs in the 8 and 16 ploidy classes. This shift was seen particularly in the diabetics with vascular disease (P = .007). Interleukin-6 (IL-6) levels were measured and were elevated in patients with atherosclerosis; the highest levels were found in the diabetic patients (0.7 +/- 0.9 versus 5.3 +/- 5.5 [P < or = .05] versus 2.5 +/- 2.8 versus 6.7 +/- 5.5 [P < or = .05] ng/L). In the diabetic patients with atherosclerosis, fibrinogen levels were also increased (2.85 +/- 0.76 versus 3.34 +/- 1.32 versus 2.43 +/- 1.50 versus 5.59 +/- 1.72 [P < or = .05] g/L). Furthermore, IL-6 levels correlated with MK ploidy (r = .45, P = .009) and fibrinogen levels (r = .5, P = .0001). This study demonstrates that patients with vascular disease, particularly diabetics, have an altered MK ploidy distribution, showing a shift toward higher ploidy in association with an increased platelet mass (count x volume). Changes in platelets in diabetes probably reflect MK changes, which themselves are a response to systemic change.

SIRT6 protects human endothelial cells from DNA damage, telomere dysfunction, and senescence

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. Conclusion 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.

Educational attainment but not measures of current socioeconomic circumstances are associated with leukocyte telomere length in healthy older men and women

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.

Mechanisms of endothelial senescence

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.

Shorter telomeres with high telomerase activity are associated with raised allostatic load and impoverished psychosocial resources

Significance These findings indicate that the combination of shorter leukocyte telomeres with high telomerase activity is associated with stress-related impairment of function at both the biological and psychological levels. Slow poststress recovery in cardiovascular activity in inflammatory responses and reduced stress responsivity in blood pressure and cortisol are indicative of a state of heightened allostatic load. Older men with the shorter telomere/high telomerase phenotype also show impoverished resources for dealing with stress, including low levels of social support and optimism and higher levels of hostility. The integrated approach taken in this study advances our understanding of the cellular substrate of stress-related processes and documents the dynamic interplay between social environmental exposures and the mechanisms underlying chromosomal integrity. 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.

Endothelial cell senescence.

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.

Short sleep duration is associated with shorter telomere length in healthy men: findings from the Whitehall II cohort study.

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.

Hostility and cellular aging in men from the Whitehall II cohort.

Background 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. Methods 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. Results 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. Conclusions 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 mens health.