Adrenergic signaling and oxidative stress: a role for sirtuins?

Adrenergic DNA damage of embryonic pluripotent cells via β2 receptor signalling

Embryonic pluripotent cells are sensitive to genotoxicity though they need more stringent genome integrity to avoid compromising multiple cell lineages and subsequent generations. However it remains unknown whether the cells are susceptible to adrenergic stress which can induce somatic cell genome lesion. We have revealed that adrenergic stress mediators cause DNA damage of the cells through the β2 adrenergic receptor/adenylate cyclase/cAMP/PKA signalling pathway involving an induction of intracellular reactive oxygen species (ROS) accumulation. The adrenergic stress agonists adrenaline, noradrenaline, and isoprenaline caused DNA damage and apoptosis of embryonic stem (ES) cells and embryonal carcinoma stem cells. The effects were mimicked by β2 receptor-coupled signalling molecules and abrogated by selective blockade of β2 receptors and inhibition of the receptor signalling pathway. RNA interference targeting β2 receptors of ES cells conferred the cells the ability to resist the DNA damage and apoptosis. In addition, adrenergic stimulation caused a consistent accumulation of ROS in the cells and the effect was abrogated by β2 receptor blockade; quenching of ROS reversed the induced DNA damage. This finding will improve the understanding of the stem cell regulatory physiology/pathophysiology in an adrenergic receptor subtype signalling mechanism.

Aging-related changes in oxidative stress response of human endothelial cells

BACKGROUND

Oxidative stress is strongly associated with aging and age-related diseases and plays a crucial role in endothelial dysfunction development.

AIM

To better understand the molecular mechanisms of aging and stress response in humans, we examined changes to young and older human endothelial cells over time (72, 96 and 120 h), before and after H2O2-induced stress.

METHODS

We measured the expression of the deacetylase Sirtuin 1 (Sirt1) and its transcriptional target Forkhead box O3a (Foxo3a); TBARS, a well-known marker of overall oxidative stress, and catalase activity as index of antioxidation. Moreover, we quantified levels of cellular senescence by senescence-associated β galactosidase (SA-βgal) assay.

RESULTS

Under oxidative stress induction older cells showed a progressive decrease of Sirt1 and Foxo3a expression, persistently high TBARS levels with high, but ineffective Cat activity to counteract such levels. In addition cellular senescence drastically increased in older cells compared with Young cells both in presence and in the absence of oxidative stress.

DISCUSSION

By following the cell behavior during the time course, we can hypothesize that while in young cells an oxidative stress induction stimulated an adequate response through activation of molecular factor crucial to counteract oxidative stress, the older cells are not able to adequately adapt themselves to external stress stimuli.

CONCLUSIONS

During their life, endothelial cells impair the ability to defend themselves from oxidative stress stimuli. This dysfunction involves the pathway of Sirt1 a critical regulator of oxidative stress response and cellular lifespan, underlining its crucial role in endothelial homeostasis control during aging and age-associated diseases.

Sirtuins, aging, and cardiovascular risks

The sirtuins comprise a highly conserved family proteins present in virtually all species from bacteria to mammals. Sirtuins are members of the highly conserved class III histone deacetylases, and seven sirtuin genes (sirtuins 1-7) have been identified and characterized in mammals. Sirtuin activity is linked to metabolic control, apoptosis, cell survival, development, inflammation, and healthy aging. In this review, we summarize and discuss the potential mutual relations between each sirtuin and cardiovascular health and the impact of sirtuins on oxidative stress and so age-related cardiovascular disorders, underlining the possibility that sirtuins will be novel targets to contrast cardiovascular risks induced by aging.

Quantitative Proteomics Reveals the Essential Roles of Stromal Interaction Molecule 1 (STIM1) in the Testicular Cord Formation in Mouse Testis

Testicular cord formation in male gonadogenesis involves assembly of several cell types, the precise molecular mechanism is still not well known. With the high-throughput quantitative proteomics technology, a comparative proteomic profile of mouse embryonic male gonads were analyzed at three time points (11.5, 12.5, and 13.5 days post coitum), corresponding to critical stages of testicular cord formation in gonadal development. 4070 proteins were identified, and 338 were differentially expressed, of which the Sertoli cell specific genes were significant enrichment, with mainly increased expression across testis cord development. Additionally, we found overrepresentation of proteins related to oxidative stress in these Sertoli cell specific genes. Of these differentially expressed oxidative stress-associated Sertoli cell specific protein, stromal interaction molecule 1, was found to have discrepant mRNA and protein regulations, with increased protein expression but decreased mRNA levels during testis cord development. Knockdown of Stim1 in Sertoli cells caused extensive defects in gonadal development, including testicular cord disruption, loss of interstitium, and failed angiogenesis, together with increased levels of reactive oxygen species. And suppressing the aberrant elevation of reactive oxygen species could partly rescue the defects of testicular cord development. Taken together, our results suggest that reactive oxygen species regulation in Sertoli cells is important for gonadogenesis, and the quantitative proteomic data could be a rich resource to the elucidation of regulation of testicular cord development.

Sirtuin 1 and aging theory for chronic obstructive pulmonary disease

Chronic Obstructive Pulmonary disease (COPD) is an inflammatory syndrome that represents an increasing health problem, especially in the elderly population. Drug therapies are symptomatic and inadequate to contrast disease progression and mortality. Thus, there is an urgent need to clarify the molecular mechanisms responsible for this condition in order to identify new biomarkers and therapeutic targets. Processes including oxidant/antioxidant, protease/antiprotease, and proliferative/antiproliferative balance and control of inflammatory response become dysfunctional during aging as well as in COPD. Recently it was suggested that Sirtuin 1 (SIRT1), an antiaging molecule involved in the response to oxidative stress and chronic inflammation, is implicated in both development and progression of COPD. The present review focuses on the involvement of SIRT1 in the regulation of redox state, inflammation, and premature senescence, all crucial characteristics of COPD phenotypes. Recent evidence corroborating the statement of the “aging theory for COPD” was also discussed.

DPP-4 Inhibitor Linagliptin Attenuates Aβ-induced Cytotoxicity through Activation of AMPK in Neuronal Cells

AIM

It is now clear that insulin signaling has important roles in regulation of neuronal functions in the brain. Dysregulation of brain insulin signaling has been linked to neurodegenerative disease, particularly Alzheimer's disease (AD). In this regard, there is evidence that improvement of neuronal insulin signaling has neuroprotective activity against amyloid β (Aβ)-induced neurotoxicity for patients with AD. Linagliptin is an inhibitor of dipeptidylpeptidase-4 (DPP-4), which improves impaired insulin secretion and insulin downstream signaling in the in peripheral tissues. However, whether the protective effects of linagliptin involved in Aβ-mediated neurotoxicity have not yet been investigated.

METHODS

In the present study, we evaluated the mechanisms by which linagliptin protects against Aβ-induced impaired insulin signaling and cytotoxicity in cultured SK-N-MC human neuronal cells.

RESULTS

Our results showed that Aβ impairs insulin signaling and causes cell death. However, linagliptin significantly protected against Aβ-induced cytotoxicity, and prevented the activation of glycogen synthase kinase 3β (GSK3β) and tau hyperphosphorylation by restoring insulin downstream signaling. Furthermore, linagliptin alleviated Aβ-induced mitochondrial dysfunction and intracellular ROS generation, which may be due to the activation of 5' AMP-activated protein kinase (AMPK)-Sirt1 signaling. This upregulation of Sirt1 expression was also observed in diabetic patients with AD coadministration of linagliptin.

CONCLUSIONS

Taken together, our findings suggest linagliptin can restore the impaired insulin signaling caused by Aβ in neuronal cells, suggesting DPP-4 inhibitors may have therapeutic potential for reducing Aβ-induced impairment of insulin signaling and neurotoxicity in AD pathogenesis.

Norepinephrine-induced apoptotic and hypertrophic responses in H9c2 cardiac myoblasts are characterized by different repertoire of reactive oxygen species generation

Despite recent advances, the role of ROS in mediating hypertrophic and apoptotic responses in cardiac myocytes elicited by norepinephrine (NE) is rather poorly understood. We demonstrate through our experiments that H9c2 cardiac myoblasts treated with 2 µM NE (hypertrophic dose) generate DCFH-DA positive ROS only for 2 h; while those treated with 100 µM NE (apoptotic dose) sustains generation for 48 h, followed by apoptosis. Though the levels of DCFH fluorescence were comparable at early time points in the two treatment sets, its quenching by DPI, catalase and MnTmPyP suggested the existence of a different repertoire of ROS. Both doses of NE also induced moderate levels of H₂O₂ but with different kinetics. Sustained but intermittent generation of highly reactive species detectable by HPF was seen in both treatment sets but no peroxynitrite was generated in either conditions. Sustained generation of hydroxyl radicals with no appreciable differences were noticed in both treatment sets. Nevertheless, despite similar profile of ROS generation between the two conditions, extensive DNA damage as evident from the increase in 8-OH-dG content, formation of γ-H2AX and PARP cleavage was seen only in cells treated with the higher dose of NE. We therefore conclude that hypertrophic and apoptotic doses of NE generate distinct but comparable repertoire of ROS/RNS leading to two very distinct downstream responses.

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H9c2 myoblasts upon treatment with 2 and 100 µM NE induces hypertrophy and apoptosis.

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Both treatments show comparable levels of DCFH fluorescence with different kinetics.

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Both treatments show comparable levels of HPF fluorescence in an oscillating manner.

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More hydroxyl radical was generated in 100 µM NE treated set.

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DNA damage and apoptosis occurs only in 100 µM NE treated sets.

Heart failure with preserved ejection fraction in the elderly: scope of the problem

Heart failure with preserved ejection fraction (HFpEF) is the most common form of heart failure (HF) in older adults, particularly women, and is increasing in prevalence as the population ages. With morbidity and mortality on par with HF with reduced ejection fraction, it remains a most challenging clinical syndrome for the practicing clinician and basic research scientist. Originally considered to be predominantly caused by diastolic dysfunction, more recent insights indicate that HFpEF in older persons is typified by a broad range of cardiac and non-cardiac abnormalities and reduced reserve capacity in multiple organ systems. The globally reduced reserve capacity is driven by: 1) inherent age-related changes; 2) multiple, concomitant co-morbidities; 3) HFpEF itself, which is likely a systemic disorder. These insights help explain why: 1) co-morbidities are among the strongest predictors of outcomes; 2) approximately 50% of clinical events in HFpEF patients are non-cardiovascular; 3) clinical drug trials in HFpEF have been negative on their primary outcomes. Embracing HFpEF as a true geriatric syndrome, with complex, multi-factorial pathophysiology and clinical heterogeneity could provide new mechanistic insights and opportunities for progress in management. This article is part of a Special Issue entitled CV Aging.

Resveratrol prevents oxidative stress-induced senescence and proliferative dysfunction by activating the AMPK-FOXO3 cascade in cultured primary human keratinocytes

The aging process is perceived as resulting from a combination of intrinsic factors such as changes in intracellular signaling and extrinsic factors, most notably environmental stressors. In skin, the relationship between intrinsic changes and keratinocyte function is not clearly understood. Previously, we found that increasing the activity of AMP-activated protein kinase (AMPK) suppressed senescence in hydrogen peroxide (H₂O₂)-treated human primary keratinocytes, a model of oxidative stress-induced cellular aging. Using this model in the present study, we observed that resveratrol, an agent that increases the activities of both AMPK and sirtuins, ameliorated two age-associated phenotypes: cellular senescence and proliferative dysfunction. In addition, we found that treatment of keratinocytes with Ex527, a specific inhibitor of sirtuin 1 (SIRT1), attenuated the ability of resveratrol to suppress senescence. In keeping with the latter observation, we noted that compared to non-senescent keratinocytes, senescent cells lacked SIRT1. In addition to these effects on H₂O₂-induced senescence, resveratrol also prevented the H₂O₂-induced decrease in proliferation (as indicated by ³H-thymidine incorporation) in the presence of insulin. This effect was abrogated by inhibition of AMPK but not SIRT1. Compared to endothelium, we found that human keratinocytes expressed relatively high levels of Forkhead box O3 (FOXO3), a downstream target of both AMPK and SIRT1. Treatment of keratinocytes with resveratrol transactivated FOXO3 and increased the expression of its target genes including catalase. Resveratrol’s effects on both senescence and proliferation disappeared when FOXO3 was knocked down. Finally, we performed an exploratory study which showed that skin from humans over 50 years old had lower AMPK activity than skin from individuals under age 20. Collectively, these findings suggest that the effects of resveratrol on keratinocyte senescence and proliferation are regulated by the AMPK-FOXO3 pathway and in some situations, but not all, by SIRT1.

A tutorial on oxidative stress and redox signaling with application to exercise and sedentariness

Oxidative stress has been shown to play a role in the etiology of several chronic diseases, including cardiovascular disease, diabetes mellitus, and cancer. Free radicals and, most prominently, the superoxide radical, result from oxidative metabolism and several enzyme-catalyzed reactions, and endogenous cellular antioxidants dismutate many reactive oxygen species (ROS). Under certain conditions, ROS production can outpace dismutation (e.g., long-term sedentariness and positive energy balance) and the result is oxidative stress, with proteins, lipids, and DNA the most common targets of radicals. However, the molecules that contribute to oxidative stress also appear to participate in vital cell signaling activity that supports health and stimulates favorable adaptations to exercise training, such that inhibiting ROS formation prevents common adaptations to training. Furthermore, researchers have recently suggested that some proteins are not as readily formed when the redox state of the cell is insufficiently oxidative. Exercise training appears to optimize the redox environment by dramatically enhancing the capacity of the cell to neutralize ROS while regularly creating oxidative environments in which membrane and secretory proteins can be synthesized. The role that exercise plays in enhancing management of ROS likely explains many of the associated health benefits.

Oxidative stress and heart rate variability in patients with vertigo

Aims

Peripheral vertigo has been reported to result from oxidative stress or autonomic nervous dysfunction. Recently, heart rate variability has been used to evaluate autonomic nervous activity. Parasympathetic nervous dysfunction is associated with peripheral vertigo; however, the relationships between vertigo, oxidative stress, and autonomic nervous activity have not been investigated. The aim of this study was to elucidate the changes in oxidative stress and autonomic nervous activity in vertigo patients compared with healthy volunteers.

Methods

Oxidative stress was assessed by evaluating biological antioxidant potential and reactive oxygen metabolites, and heart rate variability was measured to evaluate autonomic nervous activity. Thirty-four patients who complained of peripheral vertigo and were treated in our emergency department between January and August 2011 were enrolled in study 1. Oxidative stress and heart rate variability were measured and compared with those of healthy volunteers (n = 23). In study 2, oxidative stress in 18 vertigo patients and heart rate variability in 41 vertigo patients were measured between January and August 2012 before and after conventional treatment of vertigo to evaluate the effect of the treatment on oxidative stress and autonomic nervous activity.

Results

Reactive oxygen metabolites were higher in vertigo patients than in healthy volunteers. Parasympathetic nervous activity was lower and the sympathetic/parasympathetic nervous activity ratio (autonomic nervous activity ratio) was higher in vertigo patients than in healthy volunteers. After treatment of vertigo, reactive oxygen metabolites decreased significantly and the autonomic nervous activity ratio became similar to that observed in healthy volunteers.

Conclusions

Bedside monitoring of oxidative stress and heart rate variability may be useful for the diagnosis of vertigo and evaluation of the effect of treatment.

Different effects of prolonged β-adrenergic stimulation on heart and cerebral artery

The aim of this review was to understand the effects of β-adrenergic stimulation on oxidative stress, structural remodeling, and functional alterations in the heart and cerebral artery. Diverse stimuli activate the sympathetic nervous system, leading to increased levels of catecholamines. Long-term overstimulation of the β-adrenergic receptor (βAR) in response to catecholamines causes cardiovascular diseases, including cardiac hypertrophy, stroke, coronary artery disease, and heart failure. Although catecholamines have identical sites of action in the heart and cerebral artery, the structural and functional modifications differentially activate intracellular signaling cascades. βAR-stimulation can increase oxidative stress in the heart and cerebral artery, but has also been shown to induce different cytoskeletal and functional modifications by modulating various components of the βAR signal transduction pathways. Stimulation of βAR leads to cardiac dysfunction due to an overload of intracellular Ca²⁺ in cardiomyocytes. However, this stimulation induces vascular dysfunction through disruption of actin cytoskeleton in vascular smooth muscle cells. Many studies have shown that excessive concentrations of catecholamines during stressful conditions can produce coronary spasms or arrhythmias by inducing Ca²⁺-handling abnormalities and impairing energy production in mitochondria, In this article, we highlight the different fates caused by excessive oxidative stress and disruptions in the cytoskeletal proteome network in the heart and the cerebral artery in responsed to prolonged βAR-stimulation.

Potential role of NADPH oxidase in pathogenesis of pancreatitis

Studies have demonstrated that reactive oxygen species (ROS) are closely related to inflammatory disorders. Nicotinamide adenine dinucleotide phosphate oxidase (NOX), originally found in phagocytes, is the main source of ROS in nonphagocytic cells. Besides directly producing the detrimental highly reactive ROS to act on biomolecules (lipids, proteins, and nucleic acids), NOX can also activate multiple signal transduction pathways, which regulate cell growth, proliferation, differentiation and apoptosis by producing ROS. Recently, research on pancreatic NOX is no longer limited to inflammatory cells, but extends to the aspect of pancreatic acinar cells and pancreatic stellate cells, which are considered to be potentially associated with pancreatitis. In this review, we summarize the literature on NOX protein structure, activation, function and its role in the pathogenesis of pancreatitis.

Tocopherol inhibits the relaxing effect of terbutaline in the respiratory and reproductive tracts of the rat: the role of the oxidative stress index

AIMS

Reactive oxygen species play a role in the signal transduction of beta-adrenergic receptors. We investigated whether an antioxidant (tocopherol) can reduce the effect of terbutaline in beta-2-adrenergic receptor (β2-AR)-regulated smooth muscles.

MAIN METHODS

Contractility of the tissues from nonpregnant (trachea) and 22-day-pregnant (myometrium and cervix) rats was investigated in an isolated organ bath. The tracheal and uterine β2-AR expressions were increased by 17-beta-estradiol valerate (E2) and progesterone (P4), respectively. The accumulation of cyclic-AMP (cAMP), and the total oxidant (TOS) and total antioxidant status (TAS) were also measured. The oxidative stress index (OSI) was defined as the ratio of TOS and TAS.

KEY FINDINGS

Terbutaline (10(-10)-10(-5)M) decreased the contractions in the nontreated and the P4-pretreated myometria, but tocopherol (10(-7)M) did not alter these actions. Terbutaline (10(-6)M) increased the cervical resistance both in the nontreated and in the P4-treated samples, while tocopherol reduced this action only in the P4-treated cervices. Terbutaline (10(-9)-10(-4)M) reduced the tracheal tones both in the nontreated and in the E2-treated tissues, while tocopherol reduced these effects. The changes in the intracellular cAMP levels of the tissues were in harmony with the isolated organ results. The OSI was highest in the trachea and lowest in the pregnant myometrium.

SIGNIFICANCE

A higher OSI is linked to a higher tocopherol sensitivity of beta-mimetic-induced relaxation. Our results suggest that the antiasthmatic effect of beta-mimetics may worsen, while their tocolytic effect may remain unchanged during parallel tocopherol administration.

β-adrenergic receptor responsiveness in aging heart and clinical implications

Elderly healthy individuals have a reduced exercise tolerance and a decreased left ventricle inotropic reserve related to increased vascular afterload, arterial-ventricular load mismatching, physical deconditioning and impaired autonomic regulation (the so called "β-adrenergic desensitization"). Adrenergic responsiveness is altered with aging and the age-related changes are limited to the β-adrenergic receptor density reduction and to the β-adrenoceptor-G-protein(s)-adenylyl cyclase system abnormalities, while the type and level of abnormalities change with species and tissues. Epidemiological studies have shown an high incidence and prevalence of heart failure in the elderly and a great body of evidence correlate the changes of β-adrenergic system with heart failure pathogenesis. In particular it is well known that: (a) levels of cathecolamines are directly correlated with mortality and functional status in heart failure, (b) β1-adrenergic receptor subtype is down-regulated in heart failure, (c) heart failure-dependent cardiac adrenergic responsiveness reduction is related to changes in G proteins activity. In this review we focus on the cardiovascular β-adrenergic changes involvement in the aging process and on similarities and differences between aging heart and heart failure.

Exercise training enhanced SIRT1 longevity signaling replaces the IGF1 survival pathway to attenuate aging-induced rat heart apoptosis

Cardiovascular disease is the second leading cause of death (9.1 %) in Taiwan. Heart function deteriorates with age at a rate of 1 % per year. As society ages, we must study the serious problem of cardiovascular disease. SIRT1 regulates important cellular processes, including anti-apoptosis, neuronal protection, cellular senescence, aging, and longevity. In our previous studies, rats with obesity, high blood pressure, and diabetes exhibiting slowed myocardial performance and induced cell apoptosis were reversed via sports training through IGF1 survival signaling compensation. This study designed a set of experiments with rats, in aging and exercise groups, to identify changes in myocardial cell signaling transduction pathways. Three groups of three different aged rats, 3, 12, and 18 months old, were randomly divided into aging groups (C3, A12, and A18) and exercise groups (E3, AE12, and AE18). The exercise training consisted of swimming five times a week with gradual increases from the first week from 20 to 60 min for 12 weeks. After the sports training process was completed, tissue sections were taken to observe cell organization (hematoxylin and eosin (H&E) stain) and apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays) and to observe any changes in the myocardial tissues and proteins (Western blotting). The experimental results show that cardiomyocyte apoptotic pathway protein expression increased with age in the aging groups (C3, A12, and A18), with improvement in the exercise group (E3, AE12, and AE18). However, the expression of the pro-survival p-Akt protein decreased significantly with age and reduced performance. The IGF1R/PI3K/Akt survival pathway in the heart of young rats can indeed be increased through exercise training. As rats age, this pathway loses its original function, even with increasing upstream IGF1. However, levels of SIRT1 and its downstream target PGC-1α were found to increase with age and compensatory performance. Moreover, exercise training enhanced the SIRT longevity pathway compensation instead of IGF1 survival signaling to improve cardiomyocyte survival.