Premature senescence of endothelial cells: Methusaleh's dilemma

SIRT-associated attenuation of cellular senescence in vascular wall

This review focuses on the vital function that SIRT1 and other sirtuins play in promoting cellular senescence in vascular smooth muscle cells, which is a key element in the pathogenesis of vascular aging and associated cardiovascular diseases. Vascular aging is a gradual process caused by the accumulation of senescent cells, which results in increased vascular remodeling, stiffness, and diminished angiogenic ability. Such physiological alterations are characterized by a complex interplay of environmental and genetic variables, including oxidative stress and telomere attrition, which affect gene expression patterns and trigger cell growth arrest. SIRT1 has been highlighted for its potential to reduce cellular senescence through modulation of multiple signaling cascades, particularly the endothelial nitric oxide (eNOS)/NO signaling pathway. It also modulates cell cycle through p53 inactivation and suppresses NF-κB mediated expression of adhesive molecules at the vascular level. The study also examines the therapeutic potential of sirtuin modulation in vascular health, identifying SIRT1 and its sirtuin counterparts as potential targets for reducing vascular aging. This study sheds light on the molecular basis of vascular aging and the beneficial effects of sirtuins, paving the way for the development of tailored therapies aimed at enhancing vascular health and prolonging life.

The Relationship of Birth Size and Postnatal Growth with Cellular Senescence in Adults: Data from the New Delhi Birth Cohort

OBJECTIVE

To assess the effect of birth size and postnatal body mass index (BMI) gain from birth to adulthood on leucocytes cellular senescence in adult life.

METHODS

Participants were aged 43.04 (± 0.92) y, and were enrolled from the New Delhi Birth Cohort study, who participated in phase 7 of the study (n = 210). Cellular senescence markers, p16 and p21 gene expression were determined by RT-qPCR in leucocytes and their association with birth size and conditional BMI gain at 2, 11, and 29 y were assessed in univariate and multivariate regression models.

RESULTS

Birth weight (regression coefficient; B = -0.087, p = 0.011) and birth BMI (unadjusted B = -0.024, p = 0.026; adjusted B = -0.032, p = 0.022) were inversely associated with p21 gene expression in adult life. The p16 gene expression was not associated with any birth parameters. Conditional BMI gain at 2 y, 11 y, and 29 y was not associated with either p16 or p21 gene expression. The p21 gene expression was inversely associated with circulating insulin (B = -0.065, p = 0.026) and C-peptide levels (unadjusted B = -0.097, p = 0.014; adjusted B = -0.133, p = 0.003).

CONCLUSION

Small size at birth is associated with accelerated cellular senescence in adult life. An altered senescent state is likely to be one of the links between LBW and adult chronic diseases.

Sirtuins and chemokines as markers of replicative and induced senescence of human endotheliocytes

Background. One of the factors of the pathogenesis of atherosclerosis and other cardiovascular diseases is induced endothelial senescence. In this regard, the urgent task of molecular biology and medicine is the search for molecules that affect the process of vascular endotheliocytes senescence.The aim. To assess the expression of Sirt-1,3,6 and chemokines IL-4, CXCL11 in the replicative and induced senescence of human endotheliocytes.Materials and methods. The study was conducted on the primary culture of isolated human umbilical vein endothelial cells (HUVECs). HUVECs were cultured under conditions of replicative (natural) and lipopolysaccharide induced senescence.Results. The synthesis of Sirt-1,3,6, IL-4 and CXCL11 was evaluated using western blot analysis. We revealed a decrease in Sirt-1,3,6 synthesis by 1.6–1.8 times (р < 0.05) in the conditions of HUVEC replicative senescence. Induced senescence of endotheliocytes is characterized by a more pronounced decrease (1.7–3.4 times; р < 0.05) in the Sirt-1,3,6 synthesis. CXCL11 synthesis increases by 1.4 times (р < 0.05) in replicative and by 3.4 times (р < 0.05) in induced HUVEC senescence. IL-4 synthesis increases by 4.7 times in conditions of induced HUVEC senescence and doesn’t have changes in replicative senescence of endotheliocytes.Conclusion. These data obtained indicate that sirtuins and chemokines play an important role in the development of endothelial dysfunction observed in natural and induced senescence.

Oxidative Stress-Induced Cellular Senescence in Aging Retina and Age-Related Macular Degeneration

Aging leads to a gradual decline of function in multiple organs. Cataract, glaucoma, diabetic retinopathy, and age-related macular degeneration (AMD) are age-related ocular diseases. Because their pathogenesis is unclear, it is challenging to combat age-related diseases. Cellular senescence is a cellular response characterized by cell cycle arrest. Cellular senescence is an important contributor to aging and age-related diseases through the alteration of cellular function and the secretion of senescence-associated secretory phenotypes. As a driver of stress-induced premature senescence, oxidative stress triggers cellular senescence and age-related diseases by inducing senescence markers via reactive oxygen species and mitochondrial dysfunction. In this review, we focused on the mechanism of oxidative stress-induced senescence in retinal cells and its role in the pathogenesis of AMD.

Factors and Pathways Modulating Endothelial Cell Senescence in Vascular Aging

Aging causes a progressive decline in the structure and function of organs. With advancing age, an accumulation of senescent endothelial cells (ECs) contributes to the risk of developing vascular dysfunction and cardiovascular diseases, including hypertension, diabetes, atherosclerosis, and neurodegeneration. Senescent ECs undergo phenotypic changes that alter the pattern of expressed proteins, as well as their morphologies and functions, and have been linked to vascular impairments, such as aortic stiffness, enhanced inflammation, and dysregulated vascular tone. Numerous molecules and pathways, including sirtuins, Klotho, RAAS, IGFBP, NRF2, and mTOR, have been implicated in promoting EC senescence. This review summarizes the molecular players and signaling pathways driving EC senescence and identifies targets with possible therapeutic value in age-related vascular diseases.

Time course of capillary regression and an expression balance between vascular endothelial growth factor-A and thrombospondin-1 in the soleus muscle of hindlimb unloaded rats

INTRODUCTION/AIMS

Skeletal muscle capillaries regress with disuse; however, information on time-dependent changes in the expression of pro- and anti-angiogenic factors in disused muscle is limited. This study aimed to clarify time-dependent changes in skeletal muscle capillarization, pro-angiogenic vascular endothelial growth factor-A (VEGF-A), and anti-angiogenic thrombospondin-1 (TSP-1) in the soleus muscle of hindlimb unloaded rat.

METHODS

Eight-week-old male Sprague Dawley rats were randomly divided into four groups corresponding to different hindlimb unloading (HU) duration at 0, 1, 2, and 3 weeks.

RESULTS

Muscle atrophy and capillary regression worsened in the soleus muscle with longer periods of HU. The VEGF-A protein expression level was lower at week 1 than at week 0. In addition, the value at week 3 was also lower than those at weeks 0, 1, and 2. The TSP-1 protein expression level was higher at week 1 than that at week 0 but was similar at weeks 2 and 3. Moreover, reactive oxygen species, assessed by dihydroethidium fluorescence intensity on cryosection, were higher at weeks 2 and 3 than that at week 0.

DISCUSSION

Depending on the HU period, VEGF-A and TSP-1 showed different expression patterns. In the early HU phase, TSP-1 may play an important role in capillary regression. However, when HU extends for a longer period, decreased VEGF-A, and/or increased oxidative stress may be more involved in capillary regression. This article is protected by copyright. All rights reserved.

Endothelial cells from umbilical cord of women affected by gestational diabetes: A suitable in vitro model to study mechanisms of early vascular senescence in diabetes

Human umbilical cord endothelial cells (HUVECs) obtained from women affected by gestational diabetes (GD-HUVECs) display durable pro-atherogenic modifications and might be considered a valid in vitro model for studying chronic hyperglycemia effects on early endothelial senescence. Here, we demonstrated that GD- compared to C-HUVECs (controls) exhibited oxidative stress, altered both mitochondrial membrane potential and antioxidant response, significant increase of senescent cells characterized by a reduced NAD-dependent deacetylase sirtuin-1 (SIRT1) activity together with an increase in cyclin-dependent kinase inhibitor-2A (P16), cyclin-dependent kinase inhibitor-1 (P21), and tumor protein p53 (P53) acetylation. This was associated with the p300 activation, and its silencing significantly reduced the GD-HUVECs increased protein levels of P300 and Ac-P53 thus indicating a persistent endothelial senescence via SIRT1/P300/P53/P21 pathway. Overall, our data suggest that GD-HUVECs can represent an "endothelial hyperglycemic memory" model to investigate in vitro the early endothelium senescence in cells chronically exposed to hyperglycemia in vivo.

LRRK2 Kinase Inhibitor Rejuvenates Oxidative Stress-Induced Cellular Senescence in Neuronal Cells

Background

Leucine-rich repeat kinase 2 (LRRK2) plays a critical role in the pathogenesis of Parkinson's disease (PD). Aging is the most critical risk factor for the progression of PD. The correlation between aging and cellular senescence has been established. Cellular senescence is correlated with the dysregulation of the proteolytic pathway and mitochondrial dysfunction, which are also associated with the aggregation of α-synuclein (α-syn).

Methods

Human dopaminergic neuron-like cells (differentiated SH-SY5Y cells) were treated with rotenone in the presence or absence of the LRRK2 kinase inhibitor GSK2578215A (GSK-KI) for 48 h. The markers of cellular senescence, including p53, p21^Waf1/Cip1 (p21), β-galactosidase (β-gal), Rb phosphorylation, senescence-associated (SA) β-gal activity, and lysosomal activity, were examined. The dSH cells and rat primary cortical neurons were treated with α-syn fibrils 30 min before treatment with rotenone in the presence or absence of GSK-KI for 48 h. Mice were intraperitoneally injected with rotenone and MLi-2 (LRRK2 kinase inhibitor) once every two days for two weeks.

Results

Rotenone upregulated LRRK2 phosphorylation and β-gal levels through the activation of the p53-p21 signaling axis and downregulated Rb phosphorylation. Additionally, rotenone upregulated SA β-gal activity, reactive oxygen species levels, and LRRK2 phosphorylation and inhibited lysosome activity. Rotenone-induced LRRK2 upregulation impaired the clearance of α-syn fibrils. Treatment with LRRK2 inhibitor mitigated rotenone-induced cellular senescence and α-syn accumulation.

Conclusions

Rotenone-induced upregulation of LRRK2 kinase activity promoted cellular senescence, which enhanced α-syn accumulation. However, the administration of an LRRK2 kinase inhibitor rejuvenated rotenone-induced cellular senescence.

Cellular senescence and the senescence-associated secretory phenotype: Potential therapeutic targets for renal fibrosis

Renal fibrosis plays a crucial role in the progression of chronic kidney disease and end-stage renal disease. However, because the aetiology of this pathological process is complex and remains unclear, there is still no effective treatment. Cellular senescence and the senescence-associated secretory phenotype (SASP) have been reported to lead to renal fibrosis. This review first discusses the relationships among cellular senescence, the SASP and renal fibrosis. Then, the key role of the SASP in irreversible renal fibrosis, including fibroblast activation and abnormal extracellular matrix accumulation, is discussed, with the results of studies having indicated that inhibiting cellular senescence and the SASP might be a potential preventive and therapeutic strategy for renal fibrosis. Finally, we summarize promising therapeutic strategies revealed by existing research on senescent cells and the SASP, including emerging interventions targeting the SASP, caloric restriction and mimetics, and novel regeneration therapies with stem cells.

Cell senescence: basic mechanisms and the need for computational networks in vascular ageing

This review seeks to provide an update of the mechanisms of vascular cell senescence, from newly identified molecules to arterial ageing phenotypes, and finally to present a computational approach to connect these selected proteins in biological networks. We will discuss current key signalling and gene expression pathways by which these focus proteins and networks drive normal and accelerated vascular ageing. We also review the possibility that senolytic drugs, designed to restore normal cell differentiation and function, could effectively treat multiple age-related vascular diseases. Finally, we discuss how cell senescence is both a cause and a consequence of vascular ageing because of the possible feedback controls between identified networks.

Protective effects of Brazilian propolis supplementation on capillary regression in the soleus muscle of hindlimb-unloaded rats

The protective effects of Brazilian propolis on capillary regression induced by chronically neuromuscular inactivity were investigated in rat soleus muscle. Four groups of male Wistar rat were used in this study; control (CON), control plus Brazilian propolis supplementation (CON + PP), 2-week hindlimb unloading (HU), and 2-week hindlimb unloading plus Brazilian propolis supplementation (HU + PP). The rats in the CON + PP and HU + PP groups received two oral doses of 500 mg/kg Brazilian propolis daily (total daily dose 1000 mg/kg) for 2 weeks. Unloading resulted in a decrease in capillary number, luminal diameter, and capillary volume, and an increase in the expression of anti-angiogenic factors, such as p53 and TSP-1, within the soleus muscle. Brazilian propolis supplementation, however, prevented these changes in capillary structure due to unloading through the stimulation of pro-angiogenic factors and suppression of anti-angiogenic factors. These results suggest that Brazilian propolis is a potential non-drug therapeutic agent against capillary regression induced by chronic unloading.

Glutathione depletion induces ferroptosis, autophagy, and premature cell senescence in retinal pigment epithelial cells

Glutathione (GSH) protects against oxidative damage in many tissues, including retinal pigment epithelium (RPE). Oxidative stress-mediated senescence and death of RPE and subsequent death of photoreceptors have been observed in age-related macular degeneration (AMD). Although the consequences of GSH depletion have been described previously, questions remain regarding the molecular mechanisms. We herein examined the downstream effects of GSH depletion on stress-induced premature senescence (SIPS) and cell death in human RPE cells. Briefly, cultured ARPE-19 cells were depleted of GSH using: (1) incubation in cystine (Cys₂)-free culture medium; (2) treatment with buthionine sulphoximine (BSO, 1000 µM) to block de novo GSH synthesis for 24-48 h; or (3) treatment with erastin (10 µM for 12-24 h) to inhibit Cys₂/glutamate antiporter (system x_c^-). These treatments decreased cell viability and increased both soluble and lipid reactive oxygen species (ROS) generation but did not affect mitochondrial ROS or mitochondrial mass. Western blot analysis revealed decreased expression of ferroptotic modulator glutathione peroxidase 4 (GPX4). Increased autophagy was apparent, as reflected by increased LC3 expression, autophagic vacuoles, and autophagic flux. In addition, GSH depletion induced SIPS, as evidenced by increased percentage of the senescence-associated β-galactosidase-positive cells, increased senescence-associated heterochromatin foci (SAHF), as well as cell cycle arrest at the G1 phase. GSH depletion-dependent cell death was prevented by selective ferroptosis inhibitors (8 μM Fer-1 and 600 nM Lip-1), iron chelator DFO (80 μM), as well as autophagic inhibitors Baf-A1 (75 nM) and 3-MA (10 mM). Inhibiting autophagy with Baf-A1 (75 nM) or 3-MA (10 mM) promoted SIPS. In contrast, inducing autophagy with rapamycin (100 nM) attenuated SIPS. Our findings suggest that GSH depletion induces ferroptosis, autophagy, and SIPS. In addition, we found that autophagy is activated in the process of ferroptosis and reduces SIPS, suggesting an essential role of autophagy in ferroptosis and SIPS.

Mycophenolic acid induces senescence of vascular precursor cells

OBJECTIVE

Endothelial dysfunction is central to the pathogenesis of many rheumatic diseases, typified by vascular inflammation and damage. Immunosuppressive drugs induce disease remission and lead to improved patient survival. However, there remains a higher incidence of cardiovascular disease in these patients even after adequate disease control. The purpose of this study was to determine the effect of mycophenolic acid (MPA), a commonly used immunosuppressive drug in rheumatology, on blood vessel or circulating endothelial colony forming cell number and function.

METHODS

We tested whether mycophenolic acid exerts an inhibitory effect on proliferation, clonogenic potential and vasculogenic function of endothelial colony forming cell. We also studied potential mechanisms involved in the observed effects.

RESULTS

Treatment with MPA decreased endothelial colony forming cell proliferation, clonogenic potential and vasculogenic function in a dose-dependent fashion. MPA increased senescence-associated β-galactosidase expression, p21 gene expression and p53 phosphorylation, indicative of activation of cellular senescence. Exogenous guanosine supplementation rescued diminished endothelial colony forming cell proliferation and indices of senescence, consistent with the known mechanism of action of MPA.

CONCLUSION

Our findings show that clinically relevant doses of MPA have potent anti-angiogenic and pro-senescent effects on vascular precursor cells in vitro, thus indicating that treatment with MPA can potentially affect vascular repair and regeneration. This warrants further studies in vivo to determine how MPA therapy contributes to vascular dysfunction and increased cardiovascular disease seen in patients with inflammatory rheumatic disease.

TNFα-senescence initiates a STAT-dependent positive feedback loop, leading to a sustained interferon signature, DNA damage, and cytokine secretion

Cellular senescence is a cell fate program that entails essentially irreversible proliferative arrest in response to damage signals. Tumor necrosis factor-alpha (TNFα), an important pro-inflammatory cytokine secreted by some types of senescent cells, can induce senescence in mouse and human cells. However, downstream signaling pathways linking TNFα-related inflammation to senescence are not fully characterized. Using human umbilical vein endothelial cells (HUVECs) as a model, we show that TNFα induces permanent growth arrest and increases p21^CIP1, p16^INK4A, and SA-β-gal, accompanied by persistent DNA damage and ROS production. By gene expression profiling, we identified the crucial involvement of inflammatory and JAK/STAT pathways in TNFα-mediated senescence. We found that TNFα activates a STAT-dependent autocrine loop that sustains cytokine secretion and an interferon signature to lock cells into senescence. Furthermore, we show STAT1/3 activation is necessary for cytokine and ROS production during TNFα-induced senescence. However, inhibition of STAT1/3 did not rescue cells from proliferative arrest, but rather suppressed cell cycle regulatory genes and altered TNFα-induced senescence. Our findings suggest a positive feedback mechanism via the STAT pathway that sustains cytokine production and reveal a reciprocal regulatory role of JAK/STAT in TNFα-mediated senescence.

Activation of Nrf2-mediated anti-oxidant genes by antrodin C prevents hyperglycemia-induced senescence and apoptosis in human endothelial cells

In the present study, we investigated the effects of antrodin C (ADC), a maleimide derivative isolated from mycelia of Antrodia cinnamomea, on high glucose (HG, 30 mM)-accelerated endothelial dysfunction in vitro. HG-induced cytotoxicity in human umbilical vein endothelial cells (HUVECs) was significantly ameliorated by ADC. In addition, treatment with ADC significantly prevented HG-induced senescence, growth arrest at the G₁-S transition phase and apoptosis in HUVECs. Moreover, the increased level of intracellular reactive oxygen species (ROS) under HG condition was significantly ameliorated by ADC. Further analysis revealed that ADC-mediated anti-oxidant effects were due to up-regulation of cellular anti-oxidant genes, such as HO-1 and NQO-1 via promotion of the transcriptional activity of Nrf2, which was further confirmed by the failure of ADC to protect HUVECs from HG-induced dysfunction under HO-1 inhibition or Nrf2 silencing. Furthermore, hyperosmotic glucose (HOG, 60 mM)-induced uncontrolled production of ROS, rapid apoptotic cell death and HUVEC injury were significantly prevented by ADC, whereas these preventive effects were barely observed in HO-1 inhibited or Nrf2 silenced cells. Taken together, these results suggest that ADC may represent a promising intervention in diabetic-associated cardiovascular diseases by activating the Nrf2-dependent cellular anti-oxidant defense system.

[Role of the mechanisms of replicative cellular senescence in structural and functional changes of the vascular wall in chronic kidney disease]

This review considers the mechanisms and risk factors for the development of replicative cellular senescence of the vascular wall in patients with CKD and discusses therapeutic approaches to slowing the accelerated vascular aging.

Long-Term Treatment of Native LDL Induces Senescence of Cultured Human Endothelial Cells

The study aimed to evaluate whether the treatment of primary cultured human endothelial cells with native low-density lipoprotein (nLDL) could induce their senescence and to uncover some of the putative mechanisms involved. For this purpose, human umbilical vein endothelial cells (HUVECs) were subcultured and/or continuously cultured with nLDL (0, 2, 5, and 10 μg protein/mL), for up to 9 days. The results indicated that nLDL inhibited the proliferation of HUVECs by arresting the cell cycle at G1 phase. The G1-arrested cells showed increase in cytosolic senescence-associated-β-galactosidase (SA-β-Gal) activity, a biomarker of cellular senescence. The causative factor of the cellular senescence was nLDL itself and not oxidized LDL (oxLDL), since blocking LDL receptor (LDLR) with the anti-LDLR antibody opposed the nLDL-induced increase of SA-β-Gal activity and decrease of cellular proliferation. In addition, nLDL-induced cellular senescence by inhibiting the phosphorylation of pRb (G1 arrest) via p53 as well as p16 signal transduction pathways. G1 phase arrest of the senescent cells was not overcome by nLDL removal from the culture medium. Moreover, the nLDL-treated cells produced reactive oxygen species (ROS) dose- and time-dependently. These results suggested, for the first time, that long-term treatment of nLDL could induce the premature senescence of endothelial cells.

Endothelial sirtuin 1 inactivation enhances capillary rarefaction and fibrosis following kidney injury through Notch activation

Peritubular capillary (PTC) rarefaction along with tissue fibrosis is a hallmark of chronic kidney disease (CKD). However, molecular mechanisms of PTC loss have been poorly understood. Previous studies have demonstrated that functional loss of endothelial sirtuin 1 (SIRT1) impairs angiogenesis during development and tissue damage. Here, we found that endothelial SIRT1 dysfunction causes activation of endothelial Notch1 signaling, which leads to PTC rarefaction and fibrosis following kidney injury. In mice lacking functional SIRT1 in the endothelium (Sirt1 mutant), kidney injury enhanced apoptosis and senescence of PTC endothelial cells with impaired endothelial proliferation and expanded myofibroblast population and collagen deposition. Compared to wild-type kidneys, Sirt1 mutant kidneys up-regulated expression of Delta-like 4 (DLL4, a potent Notch1 ligand), Hey1 and Hes1 (Notch target genes), and Notch intracellular domain-1 (NICD1, active form of Notch1) in microvascular endothelial cells (MVECs) post-injury. Sirt1 mutant primary kidney MVECs reduced motility and vascular assembly and enhanced senescence compared to wild-type kidney MVECs. This difference in the phenotype was negated with Notch inhibition. Concurrent stimulation of DLL4 and transforming growth factor (TGF)-β1 increased trans-differentiation of primary kidney pericytes into myofibroblast more than TGF-β1 treatment alone. Collectively, these results indicate that endothelial SIRT1 counteracts PTC rarefaction by repression of Notch1 signaling and antagonizes fibrosis via suppression of endothelial DLL4 expression.

Bradykinin inhibits oxidative stress-induced senescence of endothelial progenitor cells through the B2R/AKT/RB and B2R/EGFR/RB signal pathways

Circulating endothelial progenitor cells (EPCs) have multiple protective effects that facilitate repair of damage to tissues and organs. However, while various stressors are known to impair EPC function, the mechanisms of oxidative stress-induced EPC senescence remains unknown. We demonstrated that B2 receptor (B2R) expression on circulating CD34⁺ cells was significantly reduced in patients with diabetes mellitus (DM) as compared to healthy controls. Furthermore, CD34⁺ cell B2R expression in patients with DM was inversely correlated with plasma myeloperoxidase concentrations. Bradykinin (BK) treatment decreased human EPC (hEPC) senescence and intracellular oxygen radical production, resulting in reduced retinoblastoma 1 (RB) RNA expression in H₂O₂-induced senescent hEPCs and a reversal of the B2R downregulation that is normally observed in senescent cells. Furthermore, BK treatment of H₂O₂-exposed cells leads to elevated phosphorylation of RB, AKT, and cyclin D1 compared with H₂O₂-treatment alone. Antagonists of B2R, PI3K, and EGFR signaling pathways and B2R siRNA blocked BK protective effects. In summary, this study demonstrates that BK significantly inhibits oxidative stress-induced hEPC senescence though B2R-mediated activation of PI3K and EGFR signaling pathways.

Metabolic response of lung cancer cells to radiation in a paper-based 3D cell culture system

This work demonstrates the application of a 3D culture system-Cells-in-Gels-in-Paper (CiGiP)-in evaluating the metabolic response of lung cancer cells to ionizing radiation. The 3D tissue-like construct-prepared by stacking multiple sheets of paper containing cell-embedded hydrogels-generates a gradient of oxygen and nutrients that decreases monotonically in the stack. Separating the layers of the stack after exposure enabled analysis of the cellular response to radiation as a function of oxygen and nutrient availability; this availability is dictated by the distance between the cells and the source of oxygenated medium. As the distance between the cells and source of oxygenated media increased, cells show increased levels of hypoxia-inducible factor 1-alpha, decreased proliferation, and reduced sensitivity to ionizing radiation. Each of these cellular responses are characteristic of cancer cells observed in solid tumors. With this setup we were able to differentiate three isogenic variants of A549 cells based on their metabolic radiosensitivity; these three variants have known differences in their metastatic behavior in vivo. This system can, therefore, capture some aspects of radiosensitivity of populations of cancer cells related to mass-transport phenomenon, carry out systematic studies of radiation response in vitro that decouple effects from migration and proliferation of cells, and regulate the exposure of oxygen to subpopulations of cells in a tissue-like construct either before or after irradiation.

Challenges and opportunities for stem cell therapy in patients with chronic kidney disease

Chronic kidney disease (CKD) is a global health care burden affecting billions of individuals worldwide. The kidney has limited regenerative capacity from chronic insults, and for the most common causes of CKD, no effective treatment exists to prevent progression to end-stage kidney failure. Therefore, novel interventions, such as regenerative cell-based therapies, need to be developed for CKD. Given the risk of allosensitization, autologous transplantation of cells to boost regenerative potential is preferred. Therefore, verification of cell function and vitality in CKD patients is imperative. Two cell types have been most commonly applied in regenerative medicine. Endothelial progenitor cells contribute to neovasculogenesis primarily through paracrine angiogenic activity and partly by differentiation into mature endothelial cells in situ. Mesenchymal stem cells also exert paracrine effects, including proangiogenic, anti-inflammatory, and antifibrotic activity. However, in CKD, multiple factors may contribute to reduced cell function, including older age, coexisting cardiovascular disease, diabetes, chronic inflammatory states, and uremia, which may limit the effectiveness of an autologous cell-based therapy approach. This Review highlights current knowledge on stem and progenitor cell function and vitality, aspects of the uremic milieu that may serve as a barrier to therapy, and novel methods to improve stem cell function for potential transplantation.

Sirtuins, Cell Senescence, and Vascular Aging

The sirtuins (SIRTs) constitute a class of proteins with nicotinamide adenine dinucleotide-dependent deacetylase or adenosine diphosphate-ribosyltransferase activity. Seven SIRT family members have been identified in mammals, from SIRT1, the best studied for its role in vascular aging, to SIRT7. SIRT1 and SIRT2 are localized in the nucleus and cytoplasm. SIRT3, SIRT4, and SIRT5 are mitochondrial, and SIRT6 and SIRT7 are nuclear. Extensive studies have clearly revealed that SIRT proteins regulate diverse cell functions and responses to stressors. Vascular aging involves the aging process (senescence) of endothelial and vascular smooth muscle cells. Two types of cell senescence have been identified: (1) replicative senescence with telomere attrition; and (2) stress-induced premature senescence without telomere involvement. Both types of senescence induce vascular cell growth arrest and loss of vascular homeostasis, and contribute to the initiation and progression of cardiovascular diseases. Previous mechanistic studies have revealed in detail that SIRT1, SIRT3, and SIRT6 show protective functions against vascular aging, and definite vascular function of other SIRTs is under investigation. Thus, direct SIRT modulation and nicotinamide adenine dinucleotide stimulation of SIRT are promising candidates for cardiovascular disease therapy. A small number of pilot studies have been conducted to assess SIRT modulation in humans. These clinical studies have not yet provided convincing evidence that SIRT proteins alleviate morbidity and mortality in patients with cardiovascular diseases. The outcomes of multiple ongoing clinical trials are awaited to define the efficacy of SIRT modulators and SIRT activators in cardiovascular diseases, along with the potential adverse effects of chronic SIRT modulation.

Pathogenesis of endothelial cell dysfunction in chronic kidney disease: a retrospective and what the future may hold

Cardiovascular complications dominate the landscape of chronic kidney diseases (CKD). Endothelial cell dysfunction (ECD) is a well-known culprit of cardiovascular morbidity and it develops in CKD with remarkable frequency. This brief overview of ECD in CKD scans two decades of studies performed in my laboratory, from genetic analyses to proteomic and metabolomics screens. I provide a detailed description of findings related to the premature senescence of endothelial cells, cell transition from the endothelial to mesenchymal phenotype, and stages of development of ECD. Clinical utility of some of these findings is illustrated with data on laser-Doppler flowmetry and imaging in patients with CKD. Some currently available and emerging therapeutic options for the management of ECD are briefly presented.

Cellular senescence and autophagy of myoepithelial cells are involved in the progression of in situ areas of carcinoma ex-pleomorphic adenoma to invasive carcinoma. An in vitro model

During tumor invasion, benign myoepithelial cells of carcinoma ex-pleomorphic adenoma (CXPA) surround malignant epithelial cells and disappear. The mechanisms involved in the death and disappearance of these myoepithelial cells were investigated via analysis of the expression of regulatory proteins for apoptosis, autophagy and cellular senescence in an in situ in vitro model. Protein expression relating to apoptosis (Bax, Bcl-2, Survivin), autophagy (Beclin-1, LC3B) and cellular senescence (p21, p16) was evaluated using indirect immunofluorescence. β-galactosidase expression was assessed via histochemistry. Biopsies of CXPA (ex vivo) allowed immunhistochemical evaluation of p21 and p16, whilst LC3B, p21 and p16 protein expression was analyzed by western blotting. In the in vitro model, the myoepithelial cells were positive for LC3B (cytoplasm) and p21 (nucleus), whilst in vivo positivity for p21 and p16 was observed. In vitro, β-galactosidase activity increased in the myoepithelial cells over time. Western blotting analysis revealed an increased LC3B, p16 and p21 expression in the myoepithelial cells with previous contact with the malignant cells when compared with those without contact. The investigation of behavior of benign myoepithelial cells in ductal areas of CXAP revealed that the myoepithelial cells are involved in the autophagy-senescence phenotype that subsequently leads to their disappearance.

Foam cell-derived 4-hydroxynonenal induces endothelial cell senescence in a TXNIP-dependent manner

Vascular endothelial cell (VEC) senescence is considered an early event in the development of atherosclerotic lesions. Stressful stimuli, in particular oxidative stress, have been linked to premature senescence in the vasculature. Foam cells are a major source of reactive oxygen species and may play a role in the induction of VEC senescence; hence, we investigated their involvement in the induction of VEC senescence in a co-culture transwell system. Primary bovine aortic endothelial cells, exposed to the secretome of THP-1 monocyte-derived foam cells, were analysed for the induction of senescence. Senescence associated β-galactosidase activity and the expression of p16 and p21 were increased, whereas phosphorylated retinoblastoma protein was reduced. This senescent phenotype was mediated by 4-hydroxnonenal (4-HNE), a lipid peroxidation product secreted from foam cells; scavenging of 4-HNE in the co-culture medium blunted this effect. Furthermore, both foam cells and 4-HNE increased the expression of the pro-oxidant thioredoxin-interacting protein (TXNIP). Molecular manipulation of TXNIP expression confirmed its involvement in foam cell-induced senescence. Previous studies showed that peroxisome proliferator-activated receptor (PPAR)δ was activated by 4-hydroalkenals, such as 4-HNE. Pharmacological interventions supported the involvement of the 4-HNE-PPARδ axis in the induction of TXNIP and VEC senescence. The association of TXNIP with VEC senescence was further supported by immunofluorescent staining of human carotid plaques in which the expression of both TXNIP and p21 was augmented in endothelial cells. Collectively, these findings suggest that foam cell-released 4-HNE activates PPARδ in VEC, leading to increased TXNIP expression and consequently to senescence.

New approaches to radiation protection

Radioprotectors are compounds that protect against radiation injury when given prior to radiation exposure. Mitigators can protect against radiation injury when given after exposure but before symptoms appear. Radioprotectors and mitigators can potentially improve the outcomes of radiotherapy for cancer treatment by allowing higher doses of radiation and/or reduced damage to normal tissues. Such compounds can also potentially counteract the effects of accidental exposure to radiation or deliberate exposure (e.g., nuclear reactor meltdown, dirty bomb, or nuclear bomb explosion); hence they are called radiation countermeasures. Here, we will review the general principles of radiation injury and protection and describe selected examples of radioprotectors/mitigators ranging from small-molecules to proteins to cell-based treatments. We will emphasize agents that are in more advanced stages of development.

Dysfunction of endothelial progenitor cells from smokers and chronic obstructive pulmonary disease patients due to increased DNA damage and senescence

Cardiovascular disease (CVD) is a major cause of death in smokers, particularly in those with chronic obstructive pulmonary disease (COPD). Circulating endothelial progenitor cells (EPC) are required for endothelial homeostasis, and their dysfunction contributes to CVD. To investigate EPC dysfunction in smokers, we isolated and expanded blood outgrowth endothelial cells (BOEC) from peripheral blood samples from healthy nonsmokers, healthy smokers, and COPD patients. BOEC from smokers and COPD patients showed increased DNA double-strand breaks and senescence compared to nonsmokers. Senescence negatively correlated with the expression and activity of sirtuin-1 (SIRT1), a protein deacetylase that protects against DNA damage and cellular senescence. Inhibition of DNA damage response by silencing of ataxia telangiectasia mutated (ATM) kinase resulted in upregulation of SIRT1 expression and decreased senescence. Treatment of BOEC from COPD patients with the SIRT1 activator resveratrol or an ATM inhibitor (KU-55933) also rescued the senescent phenotype. Using an in vivo mouse model of angiogenesis, we demonstrated that senescent BOEC from COPD patients are dysfunctional, displaying impaired angiogenic ability and increased apoptosis compared to cells from healthy nonsmokers. Therefore, this study identifies epigenetic regulation of DNA damage and senescence as pathogenetic mechanisms linked to endothelial progenitors' dysfunction in smokers and COPD patients. These defects may contribute to vascular disease and cardiovascular events in smokers and could therefore constitute therapeutic targets for intervention.

NaDC3 Induces Premature Cellular Senescence by Promoting Transport of Krebs Cycle Intermediates, Increasing NADH, and Exacerbating Oxidative Damage

High-affinity sodium-dependent dicarboxylate cotransporter 3 (NaDC3) is a key metabolism-regulating membrane protein responsible for transport of Krebs cycle intermediates. NaDC3 is upregulated as organs age, but knowledge regarding the underlying mechanisms by which NaDC3 modulates mammalian aging is limited. In this study, we showed that NaDC3 overexpression accelerated cellular senescence in young human diploid cells (MRC-5 and WI-38) and primary renal tubular cells, leading to cell cycle arrest in G1 phase and increased expression of senescent biomarkers, senescence-associated β-galactosidase and p16. Intracellular levels of reactive oxygen species, 8-hydroxy-2'-deoxyguanosine, malondialdehyde, and carbonyl were significantly enhanced, and activities of respiratory complexes I and III and ATP level were significantly decreased in NaDC3-infected cells. Stressful premature senescent phenotypes induced by NaDC3 were markedly ameliorated via treatment with the antioxidants Tiron and Tempol. High expression of NaDC3 caused a prominent increase in intracellular levels of Krebs cycle intermediates and NADH. Exogenous NADH and NAD(+) may aggravate and attenuate the aging phenotypes induced by NaDC3, respectively. These results suggest that NaDC3 can induce premature cellular senescence by promoting the transport of Krebs cycle intermediates, increasing generation of NADH and reactive oxygen species and leading to oxidative damage. Our results clarify the aging signaling pathway regulated by NaDC3.

eEOC-mediated modulation of endothelial autophagy, senescence, and EnMT in murine diabetic nephropathy

Diabetic nephropathy is the most frequent single cause of end-stage renal disease in our society. Microvascular damage is a key event in diabetes-associated organ malfunction. Early endothelial outgrowth cells (eEOCs) act protective in murine acute kidney injury. The aim of the present study was to analyze consequences of eEOC treatment of murine diabetic nephropathy with special attention on endothelial-to-mesenchymal transdifferentiation, autophagy, senescence, and apoptosis. Male C57/Bl6N mice (8–12 wk old) were treated with streptozotocin for 5 consecutive days. Animals were injected with untreated or bone morphogenetic protein (BMP)-5-pretreated syngeneic murine eEOCs on days 2 and 5 after the last streptozotocin administration. Four, eight, and twelve weeks later, animals were analyzed for renal function, proteinuria, interstitial fibrosis, endothelial-to-mesenchymal transition, endothelial autophagy, and senescence. In addition, cultured mature murine endothelial cells were investigated for autophagy, senescence, and apoptosis in the presence of glycated collagen. Diabetes-associated renal dysfunction (4 and 8 wk) and proteinuria (8 wk) were partly preserved by systemic cell treatment. At 8 wk, antiproteinuric effects were even more pronounced after the injection of BMP-5-pretreated cells. The latter also decreased mesenchymal transdifferentiation of the endothelium. At 8 wk, intrarenal endothelial autophagy (BMP-5-treated cells) and senescence (native and BMP-5-treated cells) were reduced. Autophagy and senescence in/of cultured mature endothelial cells were dramatically reduced by eEOC supernatant (native and BMP-5). Endothelial apoptosis decreased after incubation with eEOC medium (native and BMP-5). eEOCs act protective in diabetic nephropathy, and such effects are significantly stimulated by BMP-5. The cells modulate endothelial senescence, autophagy, and apoptosis in a protective manner. Thus, the renal endothelium could serve as a therapeutic target in diabetes-associated kidney dysfunction.

Endothelial cell senescence and age-related vascular diseases

Advanced age is an independent risk factor for ageing-related complex diseases, such as coronary artery disease, stroke, and hypertension, which are common but life threatening and related to the ageing-associated vascular dysfunction. On the other hand, patients with progeria syndromes suffer from serious atherosclerosis, suggesting that the impaired vascular functions may be critical to organismal ageing, or vice versa. However, it remains largely unknown how vascular cells, particularly endothelial cell, become senescent and how the senescence impairs the vascular functions and contributes to the age-related vascular diseases over time. Here, we review the recent progress on the characteristics of vascular ageing and endothelial cell senescence in vitro and in vivo, evaluate how genetic and environmental factors as well as autophagy and stem cell influence endothelial cell senescence and how the senescence contributes to the age-related vascular phenotypes, such as atherosclerosis and increased vascular stiffness, and explore the possibility whether we can delay the age-related vascular diseases through the control of vascular ageing.

Cerebral abnormalities in adults with ataxia-telangiectasia

Ataxia-telangiectasia, an autosomal recessive disorder caused by defect of the ataxia-telangiectasia mutated gene, is characterized by progressive neurologic impairment with cerebellar atrophy, ocular and cutaneous telangiectasia, immunodeficiency, heightened sensitivity to ionizing radiation and susceptibility to developing lymphoreticular malignancy. Supratentorial brain abnormalities have been reported only rarely. In this study, brain MRI was performed in 10 adults with ataxia-telangiectasia having stable neurologic impairment. Intracerebral telangiectasia with multiple punctate hemosiderin deposits were identified in 60% of subjects. These lesions were apparently asymptomatic. They are similar in appearance to radiation-induced telangiectasia and to cryptogenic vascular malformations. Also noted, in the 2 oldest subjects, was extensive white matter T2 hyperintensity, and in 1 of these a space-occupying fluid collection consistent with transudative capillary leak and edema as evidenced by reduced levels of metabolites on MR spectroscopic imaging. Asymptomatic supratentorial vascular abnormalities appear to be common in adults with ataxia-telangiectasia.

Icariin delays homocysteine-induced endothelial cellular senescence involving activation of the PI3K/AKT-eNOS signaling pathway

CONTEXT

Homocysteine-induced endothelial cellular senescence may contribute to some cardiovascular disorders. Icariin (ICA), a flavonoid derived from Epimedium sagittatum Maxim. (Berberidaceae), has been reported to increase production of nitric oxide (NO) and reduce reactive oxygen species (ROS) levels in human umbilical vein endothelial cells (HUVECs).

OBJECTIVE

To observe the effects of ICA on homocysteine-induced senescence and the underlying mechanisms in HUVECs.

MATERIALS AND METHODS

ICA at concentrations of 0.1, 1, and 5 μM was added into homocysteine pretreated HUVECs. Cellular senescence was assayed by senescence-associated β-galactosidase (SA-β-gal) staining and cumulative population doublings (CPDs). ICA (5 μM) was given orally to homocysteine-treated rats, luminal surface of aortic artery of rats was subjected to SA-β-gal staining. Protein expression was measured by western blot.

RESULTS

Homocysteine significantly increased cellular senescence both in vitro and in vivo. After treatment by ICA, the percentage of SA-β-gal-positive cells, and the ROS level significantly decreased. The CPDs were partially restored. ICA also significantly reduced the mean density of SA-β-gal staining in vivo. We found that NO production and phosphorylation of AKT, ERK, and endothelial NO synthase (eNOS) were elevated by ICA in HUVECs. Furthermore, the increased level of NO production was fully abolished by the phosphatidylinositol-3-kinase (PI3K) inhibitor wortmannin. The mitogen-activated protein kinase (MEK) inhibitor PD98059, which can inhibit phosphorylation of ERK, did not show this ability.

DISCUSSION AND CONCLUSION

Our results indicate that ICA delays homocyteine-induced endothelial senescence in vitro and in vivo. Activation of PI3K/Akt-eNOS-dependent signaling pathway may be responsible for this efficacy of ICA.

Vitiligo: a possible model of degenerative diseases

Vitiligo is characterized by the progressive disappearance of pigment cells from skin and hair follicle. Several in vitro and in vivo studies show evidence of an altered redox status, suggesting that loss of cellular redox equilibrium might be the pathogenic mechanism in vitiligo. However, despite the numerous data supporting a pathogenic role of oxidative stress, there is still no consensus explanation underlying the oxidative stress-driven disappear of melanocytes from the epidermis. In this study, in vitro characterization of melanocytes cultures from non-lesional vitiligo skin revealed at the cellular level aberrant function of signal transduction pathways common with neurodegenerative diseases including modification of lipid metabolism, hyperactivation of mitogen-activated protein kinase (MAPK) and cAMP response element-binding protein (CREB), constitutive p53-dependent stress signal transduction cascades, and enhanced sensibility to pro-apoptotic stimuli. Notably, these long-term effects of subcytotoxic oxidative stress are also biomarkers of pre-senescent cellular phenotype. Consistent with this, vitiligo cells showed a significant increase in p16 that did not correlate with the chronological age of the donor. Moreover, vitiligo melanocytes produced many biologically active proteins among the senescence-associated secretory phenotype (SAPS), such as interleukin-6 (IL-6), matrix metallo proteinase-3 (MMP3), cyclooxygenase-2 (Cox-2), insulin-like growth factor-binding protein-3 and 7 (IGFBP3, IGFBP7). Together, these data argue for a complicated pathophysiologic puzzle underlying melanocytes degeneration resembling, from the biological point of view, neurodegenerative diseases. Our results suggest new possible targets for intervention that in combination with current therapies could correct melanocytes intrinsic defects.

Vascular aging: chronic oxidative stress and impairment of redox signaling-consequences for vascular homeostasis and disease

Characteristic morphological and molecular alterations such as vessel wall thickening and reduction of nitric oxide occur in the aging vasculature leading to the gradual loss of vascular homeostasis. Consequently, the risk of developing acute and chronic cardiovascular diseases increases with age. Current research of the underlying molecular mechanisms of endothelial function demonstrates a duality of reactive oxygen and nitrogen species in contributing to vascular homeostasis or leading to detrimental effects when formed in excess. Furthermore, changes in function and redox status of vascular smooth muscle cells contribute to age-related vascular remodeling. The age-dependent increase in free radical formation causes deterioration of the nitric oxide signaling cascade, alters and activates prostaglandin metabolism, and promotes novel oxidative posttranslational protein modifications that interfere with vascular and cell signaling pathways. As a result, vascular dysfunction manifests. Compensatory mechanisms are initially activated to cope with age-induced oxidative stress, but become futile, which results in irreversible oxidative modifications of biological macromolecules. These findings support the 'free radical theory of aging' but also show that reactive oxygen and nitrogen species are essential signaling molecules, regulating vascular homeostasis.

Biological effects of cigarette smoke in cultured human retinal pigment epithelial cells

The goal of the present study was to determine whether treatment with cigarette smoke extract (CSE) induces cell loss, cellular senescence, and extracellular matrix (ECM) synthesis in primary human retinal pigment epithelial (RPE) cells. Primary cultured human RPE cells were exposed to 2, 4, 8, and 12% of CSE concentration for 24 hours. Cell loss was detected by cell viability assay. Lipid peroxidation was assessed by loss of cis-parinaric acid (PNA) fluorescence. Senescence-associated ß-galactosidase (SA-ß-Gal) activity was detected by histochemical staining. Expression of apolipoprotein J (Apo J), connective tissue growth factor (CTGF), fibronectin, and laminin were examined by real-time PCR, western blot, or ELISA experiments. The results showed that exposure of cells to 12% of CSE concentration induced cell death, while treatment of cells with 2, 4, and 8% CSE increased lipid peroxidation. Exposure to 8% of CSE markedly increased the number of SA-ß-Gal positive cells to up to 82%, and the mRNA expression of Apo J, CTGF, and fibronectin by approximately 3–4 fold. Treatment with 8% of CSE also increased the protein expression of Apo J and CTGF and the secretion of fibronectin and laminin. Thus, treatment with CSE can induce cell loss, senescent changes, and ECM synthesis in primary human RPE cells. It may be speculated that cigarette smoke could be involved in cellular events in RPE cells as seen in age-related macular degeneration.

CDK inhibitors (p16/p19/p21) induce senescence and autophagy in cancer-associated fibroblasts, "fueling" tumor growth via paracrine interactions, without an increase in neo-angiogenesis

Here, we investigated the compartment-specific role of cell cycle arrest and senescence in breast cancer tumor growth. For this purpose, we generated a number of hTERT-immortalized senescent fibroblast cell lines overexpressing CDK inhibitors, such as p16(INK4A), p19(ARF) or p21(WAF1/CIP1). Interestingly, all these senescent fibroblast cell lines showed evidence of increased susceptibility toward the induction of autophagy (either at baseline or after starvation), as well as significant mitochondrial dysfunction. Most importantly, these senescent fibroblasts also dramatically promoted tumor growth (up to ~2-fold), without any comparable increases in tumor angiogenesis. Conversely, we generated human breast cancer cells (MDA-MB-231 cells) overexpressing CDK inhibitors, namely p16(INK4A) or p21(WAF1/CIP1). Senescent MDA-MB-231 cells also showed increased expression of markers of cell cycle arrest and autophagy, including β-galactosidase, as predicted. Senescent MDA-MB-231 cells had retarded tumor growth, with up to a near 2-fold reduction in tumor volume. Thus, the effects of CDK inhibitors are compartment-specific and are related to their metabolic effects, which results in the induction of autophagy and mitochondrial dysfunction. Finally, induction of cell cycle arrest with specific inhibitors (PD0332991) or cellular stressors [hydrogen peroxide (H₂O₂) or starvation] indicated that the onset of autophagy and senescence are inextricably linked biological processes. The compartment-specific induction of senescence (and hence autophagy) may be a new therapeutic target that could be exploited for the successful treatment of human breast cancer patients.

Heat shock induces apoptosis in human embryonic stem cells but a premature senescence phenotype in their differentiated progeny

Embryonic stem cells (ESC) are able to self-renew and to differentiate into any cell type. To escape error transmission to future cell progeny, ESC require robust mechanisms to ensure genomic stability. It was stated that stress defense of mouse and human ESC against oxidative stress and irradiation is superior compared with differentiated cells. Here, we investigated heat shock response of human ESC (hESC) and their differentiated progeny. Fibroblast-like cells were generated by spontaneous hESC differentiation via embryoid bodies. Like normal human diploid fibroblasts, these cells have a finite lifespan in culture, undergo replicative senescence and die. We found that sublethal heat shock affected survival of both cell types, but in hESC it induced apoptosis, whereas in differentiated cells it produced cell cycle arrest and premature senescence phenotype. Heat shock survived hESC and differentiated cells restored the properties of initial cells. Heated hESC progeny exhibited pluripotent markers and the capacity to differentiate into the cells of three germ layers. Fibroblast-like cells resisted heat shock, proliferated for a limited number of passages and entered replicative senescence as unheated parental cells. Taken together, these results show for the first time that both hESC and their differentiated derivatives are sensitive to heat shock, but the mechanisms of their stress response are different: hESC undergo apoptosis, whereas differentiated cells under the same conditions exhibit stress-induced premature senescence (SIPS) phenotype. Both cell types that survived sublethal heat shock sustain parental cell properties.

Autophagy and senescence in cancer-associated fibroblasts metabolically supports tumor growth and metastasis via glycolysis and ketone production

Senescent fibroblasts are known to promote tumor growth. However, the exact mechanism remains largely unknown. An important clue comes from recent studies linking autophagy with the onset of senescence. Thus, autophagy and senescence may be part of the same physiological process, known as the autophagy-senescence transition (AST). To test this hypothesis, human fibroblasts immortalized with telomerase (hTERT-BJ1) were stably transfected with autophagy genes (BNIP3, CTSB or ATG16L1). Their overexpression was sufficient to induce a constitutive autophagic phenotype, with features of mitophagy, mitochondrial dysfunction and a shift toward aerobic glycolysis, resulting in L-lactate and ketone body production. Autophagic fibroblasts also showed features of senescence, with increased p21(WAF1/CIP1), a CDK inhibitor, cellular hypertrophy and increased β-galactosidase activity. Thus, we genetically validated the existence of the autophagy-senescence transition. Importantly, autophagic-senescent fibroblasts promoted tumor growth and metastasis, when co-injected with human breast cancer cells, independently of angiogenesis. Autophagic-senescent fibroblasts stimulated mitochondrial metabolism in adjacent cancer cells, when the two cell types were co-cultured, as visualized by MitoTracker staining. In particular, autophagic ATG16L1 fibroblasts, which produced large amounts of ketone bodies (3-hydroxy-butyrate), had the strongest effects and promoted metastasis by up to 11-fold. Conversely, expression of ATG16L1 in epithelial cancer cells inhibited tumor growth, indicating that the effects of autophagy are compartment-specific. Thus, autophagic-senescent fibroblasts metabolically promote tumor growth and metastasis, by paracrine production of high-energy mitochondrial fuels. Our current studies provide genetic support for the importance of “two-compartment tumor metabolism” in driving tumor growth and metastasis via a simple energy transfer mechanism. Finally, β-galactosidase, a known lysosomal enzyme and biomarker of senescence, was localized to the tumor stroma in human breast cancer tissues, providing in vivo support for our hypothesis. Bioinformatic analysis of genome-wide transcriptional profiles from tumor stroma, isolated from human breast cancers, also validated the onset of an autophagy-senescence transition. Taken together, these studies establish a new functional link between host aging, autophagy, the tumor microenvironment and cancer metabolism.

Endothelial progenitor cells in atherosclerosis

Endothelial progenitor cells (EPCs) are involved in the maintenance of endothelial homoeostasis and in the process of new vessel formation. Experimental and clinical studies have shown that atherosclerosis is associated with reduced numbers and dysfunction of EPCs; and that medications alone are able to partially reverse the impairment of EPCs in patients with atherosclerosis. Therefore, novel EPC-based therapies may provide enhancement in restoring EPCs' population and improvement of vascular function. Here, for a better understanding of the molecular mechanisms underlying EPC impairment in atherosclerosis, we provide a comprehensive overview on EPC characteristics, phenotypes, and the signaling pathways underlying EPC impairment in atherosclerosis.

Notch activation induces endothelial cell senescence and pro-inflammatory response: implication of Notch signaling in atherosclerosis

OBJECTIVE

Notch signaling plays pivotal roles in the pathogenesis of vascular disease. However, little is known about its role in atherosclerosis. We sought to investigate the potential involvement of the Notch signaling in atherosclerosis.

METHODS

Expression of Notch pathway components in mouse and human aorta with or without atherosclerosis plaque was examined by immunohistochemistry. Expression of Notch target genes in young versus aged human endothelial cells (EC) was examined by PCRArray and immunoblot. In vitro loss- and gain-of-function approaches were utilized to evaluate the role of Notch signaling in inducing EC senescence and secretion of pro-inflammatory cytokines by ProteinArray. Notch gene profile was studied in 1054 blood samples of patients with coronary artery disease (CAD). Genotyping was performed using the Genome-Wide Single Nucleotide Polymorphism (SNP) Array.

RESULTS

Notch pathway components were upregulated in luminal EC at atherosclerotic lesions from mouse and human aortas. In addition, the Notch pathway was activated in aged but not young human EC. Enforced Notch activation resulted in EC senescence and significantly upregulated expression of several molecules implicated in the inflammatory response (IL-6/IL-8/IL-1α/RANTES/ICAM-1). The upregulated IL-6 was partially responsible for mediating leukocyte transendothelial migration. Genetic association analysis detected, of 82 SNPs across 6 Notch pathway genes analyzed, 4 SNPs with nominal association with CAD burden.

CONCLUSION

Notch pathway is activated in luminal EC at atherosclerotic plaques and results in pro-inflammatory response and senescence of EC. Notch signaling may be linked to human CAD risk. These findings implicate a potential involvement of Notch signaling in atherosclerosis.

Resveratrol reduces vascular cell senescence through attenuation of oxidative stress by SIRT1/NADPH oxidase-dependent mechanisms

OBJECTIVE

Senescence of vascular cells contributes to the development of cardiovascular diseases and the overall aging. This study was undertaken to investigate the effects of resveratrol (Res) on amelioration of vascular cell aging and the role of SIRT1/nicotinamide adenine dinucleotide phosphate (NADPH) oxidase pathway.

METHODS AND RESULTS

Adult male Wistar rats were treated with a high-fat/sucrose diet (HFS) in the presence or absence of Res for 3 months. HFS and in vitro treatment with high glucose increased the senescence cells and reactive oxygen species production in rat aorta and cultured bovine aortic endothelial cells (BAECs), respectively, which was attenuated by Res treatment. Res protected against HFS- or high-glucose-induced increase in NADPH oxidase p47phox expression and decrease in SIRT1 level. Apocynin, a NADPH oxidase inhibitor, down-regulated p47phox protein expression, but had no influence on SIRT1 protein; sirtinol, a SIRT1 inhibitor, aggravated the decrease in SIRT1 protein level and the increase in p47phox protein expression induced by high glucose.

CONCLUSION

Our studies suggested that Res was able to reverse the senescence process in aorta induced by HFS in rats or induced by the exposure to high glucose in cultured BAECs. The underlying mechanism is at least SIRT1/NADPH oxidase pathway dependent.

Senescent endothelial dysfunction is attributed to the up-regulation of sphingosine-1-phosphate receptor-2 in aged rats

Sphingosine-1-phosphate (S1P) regulates an array of biological activities in various cell types. Many S1P-regulated functions are mediated by S1P receptor subtypes. Previous studies have shown that the S1P receptor-2 (S1P(2) receptor) is involved in senescence of endothelial cells in vitro. However, the functional outcomes of S1P(2) receptor-mediated signaling pathways in a physiological environment are currently unknown. The main aim of this study was to explore the underlying mechanisms of senescent-associated impairments in pulmonary microvascular endothelial cells (PMECs) isolated from young and aged rats in vivo. The expression of S1P receptor subtypes in PMECs was detected using RT-PCR and Western blot analyses. The chemotaxis of PMECs was measured using the transwell migration assay. The endothelial morphogenesis assay was performed in three-dimensional Matrigel. The wound-healing assay was performed using a scratch wound model on primary PMEC monolayers. We observed that the S1P(2) receptor was markedly increased and S1P-regulated responses were significantly inhibited in PMECs isolated from aged rats. Furthermore, the senescent-associated impairments were revoked by the down-regulation of the S1P(2) receptor in senescent PMECs. These results indicate that the impaired functions (such as chemotactic, wound healing, and morphogenetic responses) in senescent PMECs in vivo are mediated by the S1P(2) receptor.

Aging and the kidney

PURPOSE OF REVIEW

Aging in most species is associated with impaired adaptive and homeostatic mechanisms, leading to susceptibility to environmental or internal stresses with increasing rates of disease. A number of different theories of primarily disease-independent renal aging, which can be categorized as evolutionary, molecular, cellular and systemic, have been put forward in the past decades, and recent studies have provided evidence for some of them.

RECENT FINDINGS

This review is focused on the several mechanisms that are considered to underlie the primary aging process and contribute to age-related changes and adaptive responses in the kidney. These mechanisms include genetic modulations, telomere shortening, oxidative stress and mitochondrial dysfunction, all markers of cell senescence. Moreover, we also highlight new advances in understanding functions of angiotensin II type 1 (AT1) receptor that contribute to the renal aging process.

SUMMARY

Here we review recent advances in understanding the role of Klotho, sirtuins, cell senescence through oxidative stress and mitochondrial dysfunction, as well as of the renin-angiotensin system in modulating age-related kidney damage.

Mitochondrial gene expression in the human annulus: in vivo data from annulus cells and selectively harvested senescent annulus cells

BACKGROUND CONTEXT

Mitochondrial dysfunction is recognized during cell senescence and apoptosis, two important components of human disc aging/degeneration. We hypothesize that mitochondrial dysfunction is present in the degenerating and senescent annulus cells. The objective of the present study was to analyze gene expression profiles related to mitochondrial function in vivo.

PURPOSE

This study had two objectives in the analysis of gene expression patterns related to mitochondria in the human annulus: First, to assess human annulus cells in a genome-wide microarray analysis approach to evaluate mitochondrial gene expression in annulus tissue from degenerated compared with healthier discs. Second, to use laser capture microdissection (LCM) to selectively isolate senescent versus nonsenescent annulus cells to evaluate their mitochondrial gene expression patterns.

STUDY DESIGN

Following approval by our Human Subjects Institutional Review Board, annulus cells from 20 human lumbar discs were analyzed for gene groups related to mitochondrial function; a subset was also analyzed, which focused on senescent versus nonsenescent annulus cells in a study of annulus cells from 10 lumbar discs.

PATIENT SAMPLE

Human annulus tissue was used in molecular studies following institutional review board approval.

OUTCOME MEASURES

Gene expression levels identified with microarray analyses were statistically evaluated using GeneSifter Web-based software (VizX Labs, Seattle, WA, USA).

METHODS

Human annulus specimens were assessed for gene expression related to mitochondrial function. Approaches used whole annulus tissue and senescent or nonsenescent annulus cells selectively harvested using LCM. Microarray data were analyzed using gene ontology searches and GeneSifter Web-based software.

RESULTS

Analysis of annulus cells compared mitochondrial gene expression patterns in annulus cells from more degenerated discs with patterns in annulus cells derived from healthier discs. Important findings included significant upregulation of p53 and several proapoptotic genes (including apoptosis-inducing factor, mitochondrion-associated 1, BCL2-like 11 [an apoptosis facilitator]; caspase 7 apoptosis-related cysteine peptidase; proteasome 26S subunit nonadenosine triphosphatase 10, programmed cell death 6, and reticulon 3). Methionine sulfoxide reductase (Msr), a repair enzyme that reduces methionine sulfoxide residues in proteins damaged by oxidation, was also significantly upregulated (2.02-fold increase). The gene "membrane-associated ring finger (C3HC4) 5" was significantly upregulated and relevant because it is believed to play a role in preventing cell senescence acting to regulate mitochondrial quality control. Nitric oxide synthase 3 (endothelial nitric oxide synthase [eNOS]) showed a 5.9-fold downregulation in more degenerated versus healthier annulus cells. In LCM-harvested senescent cells, Msr was significantly downregulated in senescent versus nonsenescent cells, a finding previously recognized in other types of senescent cells.

CONCLUSIONS

Novel data showed that significant gene expression patterns are present in the human annulus related to mitochondrial dysfunction; changes were identified in important genes involving apoptosis, eNOS and Msr expressions, and solute carrier genes. Because current research efforts are focusing on bioactive compounds for mitochondria, we suggest that future biologic cell-based therapies for annulus degeneration should also consider mitochondrial-focused therapies.