Angiotensin II Induces Premature Senescence of Vascular Smooth Muscle Cells and Accelerates the Development of Atherosclerosis via a p21-Dependent Pathway

Proinflammation of aging central arteries: a mini-review

Arterial aging is a cornerstone of organismal aging. The central arterial wall structurally and functionally remodels under chronic proinflammatory stress over a lifetime. The low-grade proinflammation that accompanies advancing age causes arterial wall thickening and stiffening. These structural and functional alterations are consequences of adverse molecular and cellular events, e.g. an increase in local angiotensin II signaling that induces an inflammatory phenotypic shift of endothelial and smooth muscle cells. Thus, interventions to restrict proinflammatory signaling are a rational approach to delay or prevent age-associated adverse arterial remodeling.

Vitamin D puts the brakes on angiotensin II-induced oxidative stress and vascular smooth muscle cell senescence

Signaling via both vitamin D (VitD) and the renin-angiotensin system (RAS) plays important roles in physiological processes. Evidence has mounted linking cardiovascular disease to both increased activity of the RAS and VitD deficiency. Although several studies have established functional relationships between the RAS and VitD, many aspects of their complex interaction remain unknown. In this issue of Atherosclerosis, Valcheva and colleagues show that defective VitD signaling can promote vascular damage by inducing premature senescence of smooth muscle cells due to elevated local production of angiotensin II and reactive oxygen species, and upregulation of the tumor suppressor p57(Kip2).

Smoking cessation reverses DNA double-strand breaks in human mononuclear cells

OBJECTIVE

Cigarette smoking is a major risk factor for atherosclerotic cardiovascular disease, which is responsible for a significant proportion of smoking-related deaths. However, the precise mechanism whereby smoking induces this pathology has not been fully delineated. Based on observation of DNA double-strand breaks (DSBs), the most harmful type of DNA damage, in atherosclerotic lesions, we hypothesized that there is a direct association between smoking and DSBs. The goal of this study was to investigate whether smoking induces DSBs and smoking cessation reverses DSBs in vivo through examination of peripheral mononuclear cells (MNCs).

APPROACH AND RESULTS

Immunoreactivity of oxidative modification of DNA and DSBs were increased in human atherosclerotic lesions but not in the adjacent normal area. DSBs in human MNCs isolated from the blood of volunteers can be detected as cytologically visible "foci" using an antibody against the phosphorylated form of the histone H2AX (γ-H2AX). Young healthy active smokers (n = 15) showed increased γ-H2AX foci number when compared with non-smokers (n = 12) (foci number/cell: median, 0.37/cell; interquartile range [IQR], 0.31-0.58 vs. 4.36/cell; IQR, 3.09-7.39, p<0.0001). Smoking cessation for 1 month reduced the γ-H2AX foci number (median, 4.44/cell; IQR, 4.36-5.24 to 0.28/cell; IQR, 0.12-0.53, p<0.05). A positive correlation was noted between γ-H2AX foci number and exhaled carbon monoxide levels (r = 0.75, p<0.01).

CONCLUSIONS

Smoking induces DSBs in human MNCs in vivo, and importantly, smoking cessation for 1 month resulted in a decrease in DSBs to a level comparable to that seen in non-smokers. These data reinforce the notion that the cigarette smoking induces DSBs and highlight the importance of smoking cessation.

A crucial role for CDC42 in senescence-associated inflammation and atherosclerosis

Risk factors for atherosclerosis accelerate the senescence of vascular endothelial cells and promote atherogenesis by inducing vascular inflammation. A hallmark of endothelial senescence is the persistent up-regulation of pro-inflammatory genes. We identified CDC42 signaling as a mediator of chronic inflammation associated with endothelial senescence. Inhibition of CDC42 or NF-κB signaling attenuated the sustained up-regulation of pro-inflammatory genes in senescent human endothelial cells. Endothelium-specific activation of the p53/p21 pathway, a key mediator of senescence, also resulted in up-regulation of pro-inflammatory molecules in mice, which was reversed by Cdc42 deletion in endothelial cells. Likewise, endothelial-specific deletion of Cdc42 significantly attenuated chronic inflammation and plaque formation in atherosclerotic mice. While inhibition of NF-κB suppressed the pro-inflammatory responses in acute inflammation, the influence of Cdc42 deletion was less marked. Knockdown of cdc-42 significantly down-regulated pro-inflammatory gene expression and restored the shortened lifespan to normal in mutant worms with enhanced inflammation. These findings indicate that the CDC42 pathway is critically involved in senescence-associated inflammation and could be a therapeutic target for chronic inflammation in patients with age-related diseases without compromising host defenses.

Cellular senescence and the senescent secretory phenotype in age-related chronic diseases

PURPOSE OF REVIEW

Possible mechanisms in cellular senescence and the senescence-associated secretory phenotype (SASP) that drive and promote chronic inflammation in multiple age-related chronic diseases are considered.

RECENT FINDINGS

A series of studies about the SASP indicate that senescent cells may be involved in the development of chronic inflammatory diseases associated with aging.

SUMMARY

Aging is a complex biological process accompanied by a state of chronic, low-grade, 'sterile' inflammation, which is a major contributor to the development of many age-related chronic disorders including atherosclerosis, osteoarthritis, Alzheimer's disease, type 2 diabetes, cancers, and others. It appears that cellular senescence plays a role in causing inflammation through the SASP. A better understanding of the contribution of senescent cells to the pathologies of chronic inflammatory disorders could have potentially profound diagnostic and therapeutic implications.

Blood pressure variability, impaired autonomic function and vascular senescence in aged spontaneously hypertensive rats are ameliorated by angiotensin blockade

OBJECTIVE

Elderly hypertensive patients are characterized by blood pressure (BP) variability, impaired autonomic function, and vascular endothelial dysfunction and stiffness. However, the mechanisms causing these conditions are unclear. The present study examined the effect of angiotensin receptor blockers (ARBs) on aged spontaneously hypertensive rats (SHR).

METHODS

We surgically implanted telemetry devices in SHR and WKY at the age of 15 weeks (Young) and 80 weeks (Aged). Aged SHR were orally administered either olmesartan or valsartan once daily at 19:00 h (at the beginning of the dark period (active phase)) for 4 weeks to examine the effects on BP variability, impaired autonomic function, and vascular senescence.

RESULTS

Aging and hypertension in SHR additively caused the following: increased low frequency (LF) power of systolic BP, a decreased spontaneous baroreceptor reflex gain (sBRG), increased BP variability, increased urinary norepinephrine excretion, increased vascular senescence-related beta-galactosidase positive cells and oxidative stress. Treatment with olmesartan or valsartan significantly ameliorated these changes in aged SHR. However, olmesartan ameliorated these changes in aged SHR better than valsartan. The reductions in BP caused by olmesartan in aged SHR were sustained longer than reductions by valsartan. This result indicates longer-lasting inhibition of the AT1 receptor by olmesartan than by valsartan.

CONCLUSION

ARBs ameliorated autonomic dysfunction, BP variability, and vascular senescence in aged SHR. Olmesartan ameliorated the aging-related disorders better than valsartan and was associated with longer-lasting AT1 receptor inhibition by olmesartan. Thus, the magnitude of improvement of these aging-related abnormalities differs for ARBs.

Lack of vitamin D receptor causes stress-induced premature senescence in vascular smooth muscle cells through enhanced local angiotensin-II signals

OBJECTIVES

The inhibition of the renal renin-angiotensin system by the active form of vitamin D contributes to the cardiovascular health benefits of a normal vitamin D status. Local production of angiotensin-II in the vascular wall is a potent mediator of oxidative stress, prompting premature senescence. Herein, our objective was to examine the impact of defective vitamin D signalling on local angiotensin-II levels and arterial health.

METHODS

Primary cultures of aortic vascular smooth muscle cells (VSMC) from wild-type and vitamin D receptor-knockout (VDRKO) mice were used for the assessment of cell growth, angiotensin-II and superoxide anion production and expression levels of cathepsin D, angiotensin-II type 1 receptor and p57(Kip2). The in vitro findings were confirmed histologically in aortas from wild-type and VDRKO mice.

RESULTS

VSMC from VDRKO mice produced more angiotensin-II in culture, and elicited higher levels of cathepsin D, an enzyme with renin-like activity, and angiotensin-II type 1 receptor, than wild-type mice. Accordingly, VDRKO VSMC showed higher intracellular superoxide anion production, which could be suppressed by cathepsin D, angiotensin-II type 1 receptor or NADPH oxidase antagonists. VDRKO cells presented higher levels of p57(Kip2), impaired proliferation and premature senescence, all of them blunted upon inhibition of angiotensin-II signalling. In vivo studies confirmed higher levels of cathepsin D, angiotensin-II type 1 receptor and p57(Kip2) in aortas from VDRKO mice.

CONCLUSION

The beneficial effects of active vitamin D in vascular health could be a result of the attenuation of local production of angiotensin-II and downstream free radicals, thus preventing the premature senescence of VSMC.

Analysis of disease progression-associated gene expression profile in fibrillin-1 mutant mice: new insight into molecular pathogenesis of marfan syndrome

Marfan syndrome (MFS) is a dominantly inherited connective tissue disorder caused by mutations in the gene encoding fibrillin-1 (FBN1) and is characterized by aortic dilatation and dissection, which is the primary cause of death in untreated MFS patients. However, disease progression-associated changes in gene expression in the aortic lesions of MFS patients remained unknown. Using a mouse model of MFS, FBN1 hypomorphic mouse (mgR/mgR), we characterized the aortic gene expression profiles during the progression of the MFS. Homozygous mgR mice exhibited MFS-like phenotypic features, such as fragmentation of elastic fibers throughout the vessel wall and were graded into mgR1–4 based on the pathological severity in aortic walls. Comparative gene expression profiling of WT and four mgR mice using microarrays revealed that the changes in the transcriptome were a direct reflection of the severity of aortic pathological features. Gene ontology analysis showed that genes related to oxidation/reduction, myofibril assembly, cytoskeleton organization, and cell adhesion were differentially expressed in the mgR mice. Further analysis of differentially expressed genes identified several candidate genes whose known roles were suggestive of their involvement in the progressive destruction of aorta during MFS. This study is the first genome-wide analysis of the aortic gene expression profiles associated with the progression of MFS. Our findings provide valuable information regarding the molecular pathogenesis during MFS progression and contribute to the development of new biomarkers as well as improved therapeutic strategies.

Collagenase-resistant collagen promotes mouse aging and vascular cell senescence

Collagen fibrils become resistant to cleavage over time. We hypothesized that resistance to type I collagen proteolysis not only marks biological aging but also drives it. To test this, we followed mice with a targeted mutation (Col1a1^r/r) that yields collagenase-resistant type I collagen. Compared with wild-type littermates, Col1a1^r/r mice had a shortened lifespan and developed features of premature aging including kyphosis, weight loss, decreased bone mineral density, and hypertension. We also found that vascular smooth muscle cells (SMCs) in the aortic wall of Col1a1^r/r mice were susceptible to stress-induced senescence, displaying senescence-associated ß-galactosidase (SA-ßGal) activity and upregulated p16^INK4A in response to angiotensin II infusion. To elucidate the basis of this pro-aging effect, vascular SMCs from twelve patients undergoing coronary artery bypass surgery were cultured on collagen derived from Col1a1^r/r or wild-type mice. This revealed that mutant collagen directly reduced replicative lifespan and increased stress-induced SA-ßGal activity, p16^INK4A expression, and p21^CIP1 expression. The pro-senescence effect of mutant collagen was blocked by vitronectin, a ligand for αvß3 integrin that is presented by denatured but not native collagen. Moreover, inhibition of αvß3 with echistatin or with αvß3-blocking antibody increased senescence of SMCs on wild-type collagen. These findings reveal a novel aging cascade whereby resistance to collagen cleavage accelerates cellular aging. This interplay between extracellular and cellular compartments could hasten mammalian aging and the progression of aging-related diseases.

Proinflammation: the key to arterial aging

Arterial aging is the major contributing factor to increases in the incidence and prevalence of cardiovascular disease, due mainly to the presence of chronic, low-grade, 'sterile' arterial inflammation. Inflammatory signaling driven by the angiotensin II cascade perpetrates adverse age-associated arterial structural and functional remodeling. The aged artery is characterized by endothelial disruption, enhanced vascular smooth muscle cell (VMSC) migration and proliferation, extracellular matrix (ECM) deposition, elastin fracture, and matrix calcification/amyloidosis/glycation. Importantly, the molecular mechanisms of arterial aging are also relevant to the pathogenesis of hypertension and atherosclerosis. Age-associated arterial proinflammation is to some extent mutable, and interventions to suppress or delay it may have the potential to ameliorate or retard age-associated arterial diseases.

Overexpression of SIRT1 in vascular smooth muscle cells attenuates angiotensin II-induced vascular remodeling and hypertension in mice

Angiotensin II (AngII) induces the development of vascular hypertrophy and hypertension. We have shown previously that overexpression of class III deacetylase SIRT1 inhibits AngII-induced hypertrophy in vascular smooth muscle cells (VSMCs). However, the direct role of SIRT1 in VSMCs in response to AngII infusion in vivo remains unclear. Here, we found that the expression and activity of SIRT1 in mouse aortas was decreased significantly by AngII infusion. VSMC-specific SIRT1 transgene (SV-Tg) prevented the increase in systolic blood pressure (SBP) caused by AngII infusion without affecting heart function in mice. SIRT1 overexpression alleviated vascular remodeling in mouse thoracic and renal aortas induced by AngII infusion, and significantly inhibited reactive oxygen species (ROS) generation, vascular inflammation, and collagen synthesis in arterial walls. Reduced expression of transforming growth factor-β 1 (TGF-β1) was also observed in the aortas of AngII-infused SV-Tg mice. Moreover, SIRT1 overexpression decreased AngII-increased binding of nuclear factor-κB on its specific binding sites on TGF-β1 promoter. Taken together, these data demonstrate that SIRT1 overexpression in VSMCs reduces SBP and inhibits AngII-induced vascular remodeling in mice. The inhibition of vascular remodeling contributes, at least in part, to the antihypertensive effect of SIRT1.

KEY MESSAGE

SIRT1 is reduced in aortas of AngII-infused hypertensive mice. SIRT1 VSMC transgene alleviates AngII-increased systolic blood pressure. SIRT1 VSMC transgene attenuates AngII-induced vascular remodeling. VSMC SIRT1 overexpression inhibits remodeling-related pathological changes. VSMC SIRT1 overexpression reduces AngII-induced TGF-β1 expression.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

p53/p21 Pathway involved in mediating cellular senescence of bone marrow-derived mesenchymal stem cells from systemic lupus erythematosus patients

Our and other groups have found that bone marrow-derived mesenchymal stem cells (BM-MSCs) from systemic lupus erythematosus (SLE) patients exhibited senescent behavior and are involved in the pathogenesis of SLE. Numerous studies have shown that activation of the p53/p21 pathway inhibits the proliferation of BM-MSCs. The aim of this study was to determine whether p53/p21 pathway is involved in regulating the aging of BM-MSCs from SLE patients and the underlying mechanisms. We further confirmed that BM-MSCs from SLE patients showed characteristics of senescence. The expressions of p53 and p21 were significantly increased, whereas levels of Cyclin E, cyclin-dependent kinase-2, and phosphorylation of retinoblastoma protein were decreased in the BM-MSCs from SLE patients and knockdown of p21 expression reversed the senescent features of BM-MSCs from SLE patients. Our results demonstrated that p53/p21 pathway played an important role in the senescence process of BM-MSCs from SLE.

A role for mitochondrial oxidants in stress-induced premature senescence of human vascular smooth muscle cells

Mitochondria are a major source of cellular oxidants and have been implicated in aging and associated pathologies, notably cardiovascular diseases. Vascular cell senescence is observed in experimental and human cardiovascular pathologies. Our previous data highlighted a role for angiotensin II in the induction of telomere-dependent and -independent premature senescence of human vascular smooth muscle cells and suggested this was due to production of superoxide by NADPH oxidase. However, since a role for mitochondrial oxidants was not ruled out we hypothesise that angiotensin II mediates senescence by mitochondrial superoxide generation and suggest that inhibition of superoxide may prevent vascular smooth muscle cell aging in vitro. Cellular senescence was induced using a stress-induced premature senescence protocol consisting of three successive once-daily exposure of cells to 1×10⁻⁸ mol/L angiotensin II and was dependent upon the type-1 angiotensin II receptor. Angiotensin stimulated NADPH-dependent superoxide production as estimated using lucigenin chemiluminescence in cell lysates and this was attenuated by the mitochondrial electron transport chain inhibitor, rotenone. Angiotensin also resulted in an increase in mitoSOX fluorescence indicating stimulation of mitochondrial superoxide. Significantly, the induction of senescence by angiotensin II was abrogated by rotenone and by the mitochondria-targeted superoxide dismutase mimetic, mitoTEMPO. These data suggest that mitochondrial superoxide is necessary for the induction of stress-induced premature senescence by angiotensin II and taken together with other data suggest that mitochondrial cross-talk with NADPH oxidases, via as yet unidentified signalling pathways, is likely to play a key role.

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Angiotensin II causes stress-induced premature senescence in hVSMC.

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Mitochondrial superoxide is necessary for premature senescence.

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Mitochondrial cross-talk with NADPH oxidases is implicated in this mechanism.

Peroxisome proliferator-activated receptor γ coactivator-1α is a central negative regulator of vascular senescence

OBJECTIVE

Cellular senescence influences organismal aging and increases predisposition to age-related diseases, in particular cardiovascular disease, a leading cause of death and disability worldwide. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a master regulator of mitochondrial biogenesis and function, oxidative stress, and insulin resistance. Senescence is associated with telomere and mitochondrial dysfunction and oxidative stress, implying a potential causal role of PGC-1α in senescence pathogenesis.

APPROACH AND RESULTS

We generated a PGC-1α(+/-)/apolipoprotein E(-/-) mouse model and showed that PGC-1α deficiency promotes a vascular senescence phenotype that is associated with increased oxidative stress, mitochondrial abnormalities, and reduced telomerase activity. PGC-1α disruption results in reduced expression of the longevity-related deacetylase sirtuin 1 (SIRT1) and the antioxidant catalase, and increased expression of the senescence marker p53 in aortas. Further, angiotensin II, a major hormonal inducer of vascular senescence, induces prolonged lysine acetylation of PGC-1α and releases the PGC-1α-FoxO1 complex from the SIRT1 promoter, thus reducing SIRT1 expression. The phosphorylation-defective mutant PGC-1α S570A is not acetylated, is constitutively active for forkhead box O1-dependent SIRT1 transcription, and prevents angiotensin II-induced senescence. Acetylation of PGC-1α by angiotensin II interrupts the PGC-1α-forkhead box O1-SIRT1 feed-forward signaling circuit leading to SIRT1 and catalase downregulation and vascular senescence.

CONCLUSIONS

PGC-1α is a primary negative regulator of vascular senescence. Moreover, the central role of posttranslational modification of PGC-1α in regulating angiotensin II-induced vascular senescence may inform development of novel therapeutic strategies for mitigating age-associated diseases, such as atherosclerosis.

Role of p16(INK4A) in Replicative Senescence and DNA Damage-Induced Premature Senescence in p53-Deficient Human Cells

The p16(INK4A) (hereafter p16) tumor suppressor is encoded by the INK4A/ARF locus which is among the most commonly dysregulated sequences in human cancer. By inhibiting cyclin-dependent kinases, p16 activates the G1-S checkpoint, and this response is often considered to be critical for establishing a senescence-like growth arrest. Not all studies support a universal role for p16 in senescence. Single-cell analysis of noncancerous human fibroblast cultures undergoing senescence as a function of culture age (replicative senescence) has revealed that p16 is not expressed in the majority (>90%) of cells that exhibit features of senescence (e.g., flattened and enlarged morphology coupled with senescence-associated β-galactosidase expression), ruling out a requirement for p16 in this process. In addition, ionizing radiation triggers premature senescence in human cancer cell lines that do not express p16. These observations are made with cells that express wild-type p53, a key mediator of the DNA damage response. In this paper, we examine the growing evidence suggesting a negative regulatory relationship between p16 and p53 and discuss recent reports that implicate a role for p16 in replicative senescence and ionizing radiation-induced premature senescence in human cells that lack wild-type p53 function.

Indoxyl sulfate promotes vascular smooth muscle cell senescence with upregulation of p53, p21, and prelamin A through oxidative stress

We previously demonstrated that indoxyl sulfate (IS), a uremic toxin, induces aortic calcification in hypertensive rats and induces oxidative stress and the expression of osteoblast-specific proteins in vascular smooth muscle cells. This study aimed to clarify whether IS stimulates senescence of cultured human aortic smooth muscle cells (HASMCs) and aorta in Dahl salt-sensitive hypertensive rats and whether AST-120, an oral sorbent, prevents senescence of aorta in subtotally nephrectomized uremic rats. IS increased the mRNA expression of p53 and p21 in HASMCs, whereas it did not change that of p16 and retinoblastoma protein (pRb). The IS-induced expression of p53 and p21 was suppressed by N-acetylcysteine, an antioxidant. IS promoted protein expression of p53, p21, and senescence-associated β-galactosidase (SA-β-gal) activity in HASMCs, and N-acetylcysteine and pifithrin-α,p-nitro, a p53 inhibitor, blocked these effects. IS upregulated prelamin A, a hallmark of vascular smooth muscle cell senescence, and downregulated FACE1/Zempste24 protein expression in HASMCs, and N-acetylcysteine suppressed these effects. Administration of IS to hypertensive rats increased expression of SA-β-gal, p53, p21, prelamin A, and oxidative stress markers such as 8-hydroxyl-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA) in the cells embedded in the calcification area of arcuate aorta. Further, the uremic rat model showed positive staining for SA-β-gal, p53, p21, prelamin A, 8-OHdG, and MDA in the cells embedded in the calcification area of arcuate aorta, whereas AST-120 reduced the expression of these biomarkers. Taken together, IS accelerates vascular smooth muscle cell senescence with upregulation of p53, p21, and prelamin A and downregulation of FACE1 through oxidative stress.

Emergence of the erythropoietin/erythropoietin receptor system as a novel cardiovascular therapeutic target

Although hypoxia and ischemia are known to be involved in the pathogenesis of cardiovascular disease, specific therapeutic targets still remain elusive. To address this important issue, we have performed 2 series of experimental studies, aiming at erythropoietin (Epo)/Epo receptor (EpoR) based on the following backgrounds. Epo has long been regarded as a hematopoietic hormone that acts exclusively in the proliferation and differentiation of erythroid progenitors. Although recent studies have demonstrated that EpoR is expressed in the cardiovascular system, the potential protective role of the vascular Epo/EpoR system in vivo remains to be examined. We hypothesized that the vascular Epo/EpoR system plays an important protective role against the development of cardiovascular disease. Using vascular EpoR-deficient mouse, we demonstrated that the vascular Epo/EpoR system plays a crucial role for endothelial function and vascular homeostasis. The vascular Epo/EpoR system is important for the activation of the vascular endothelial growth factor/vascular endothelial growth factor receptor-2 system, inhibits hypoxia-induced pulmonary endothelial damage and promotes ischemia-induced angiogenesis in vivo. These results indicate that the vascular Epo/EpoR system plays an important protective role against hypoxia/ischemia, demonstrating that this system is a novel therapeutic target in cardiovascular medicine.

Angiotensin II requires zinc and downregulation of the zinc transporters ZnT3 and ZnT10 to induce senescence of vascular smooth muscle cells

Senescence, a hallmark of mammalian aging, is associated with the onset and progression of cardiovascular disease. Angiotensin II (Ang II) signaling and zinc homeostasis dysfunction are increased with age and are linked to cardiovascular disease, but the relationship among these processes has not been investigated. We used a model of cellular senescence induced by Ang II in vascular smooth muscle cells (VSMCs) to explore the role of zinc in vascular dysfunction. We found that Ang II-induced senescence is a zinc-dependent pathway mediated by the downregulation of the zinc transporters ZnT3 and ZnT10, which work to reduce cytosolic zinc. Zinc mimics Ang II by increasing reactive oxygen species (ROS), activating NADPH oxidase activity and Akt, and by downregulating ZnT3 and ZnT10 and inducing senescence. Zinc increases Ang II-induced senescence, while the zinc chelator TPEN, as well as overexpression of ZnT3 or ZnT10, decreases ROS and prevents senescence. Using HEK293 cells, we found that ZnT10 localizes in recycling endosomes and transports zinc into vesicles to prevent zinc toxicity. Zinc and ZnT3/ZnT10 downregulation induces senescence by decreasing the expression of catalase. Consistently, ZnT3 and ZnT10 downregulation by siRNA increases ROS while downregulation of catalase by siRNA induces senescence. Zinc, siZnT3 and siZnT10 downregulate catalase by a post-transcriptional mechanism mediated by decreased phosphorylation of ERK1/2. These data demonstrate that zinc homeostasis dysfunction by decreased expression of ZnT3 or ZnT10 promotes senescence and that Ang II-induced senescence is a zinc and ROS-dependent process. Our studies suggest that zinc might also affect other ROS-dependent processes induced by Ang II, such as hypertrophy and migration of smooth muscle cells.

Aldosterone does not contribute to renal p21 expression during the development of angiotensin II-induced hypertension in mice

BACKGROUND

We recently reported that aldosterone-induced cellular senescence via an increase in p21, a cyclin-dependent kinase (CDK) inhibitor, in rat kidney and cultured human proximal tubular cells. In the present study, we investigated the contribution of aldosterone to the renal p21 expression and senescence during the development of angiotensin II (AngII)-induced hypertension.

METHODS

Mice received 1% salt in drinking water and vehicle or AngII, and were divided into five groups: 1, vehicle; 2, AngII; 3, AngII+olmesartan; 4, AngII+eplerenone; and 5, AngII+hydralazine.

RESULTS

Plasma aldosterone levels were increased by AngII infusion. Eplerenone further elevated the plasma aldosterone level, but olmesartan and hydralazine did not. AngII group showed significant increase in blood pressure compared to vehicle. Olmesartan and hydralazine, but not eplerenone, suppressed the AngII-salt hypertension. The increase in urinary protein excretion by AngII-salt was suppressed only by olmesartan. AngII with high salt induced a greater expression of p21 mRNA in the kidney than vehicle. Olmesartan abolished the increase in p21 expression, whereas neither eplerenone nor hydralazine affected it. AngII with high salt did not change the expression of p16, another CDK inhibitor. The mice lacking p21 showed identical changes on blood pressure and albuminuria in response to AngII with high salt compared to wild type.

CONCLUSION

These results suggest that aldosterone does not predominantly contribute to renal p21 expression and senescence during the development of AngII-salt hypertension, and that the increase in p21 in the kidney is not likely involved in the development of hypertension and albuminuria.

Angiotensin II type 2 receptor-interacting protein prevents vascular senescence

Angiotensin II type 2 (AT(2)) receptor-interacting protein (ATIP), which interacts with the C-terminal tail of the AT(2) receptor, regulates the functions of the AT(2) receptor. We have reported that AT(2) receptor stimulation attenuated vascular senescence. Therefore, we examined the possible negative role of ATIP in regulating vascular senescence. We generated ATIP-transgenic (Tg) mice, and cultured vascular smooth muscle cells (VSMCs). Persistent angiotensin II stimulation induced increases in SA-β-gal-positive cells and the level of a DNA damage marker, 8-OHdG in VSMC, whereas these effects of angiotensin II were attenuated in VSMC prepared from ATIP-Tg mice. Angiotensin II treatment also upregulated the expression of methyl methanesulfonate-sensitive 2 (MMS2), a DNA repair factor, and Src homology 2 domain-containing protein-tyrosine phosphatase 1 (SHP-1) activity, whereas these effects of angiotensin II were further enhanced in ATIP-Tg VSMC. In vivo, x-ray irradiation to mice caused increases in SA-β-gal-positive area and 8-OHdG level in the thoracic aorta; however, these effects were reduced in ATIP-Tg mice, with a significant increase in MMS2 expression. These results suggest that ATIP could inhibit VSMC senescence, involving MMS2 expression and SHP-1 activity. ATIP might be a new therapeutic molecule to treat vascular aging and age-related vascular diseases.

Empowering adult stem cells for myocardial regeneration

Treatment strategies for heart failure remain a high priority for ongoing research due to the profound unmet need in clinical disease coupled with lack of significant translational progress. The underlying issue is the same whether the cause is acute damage, chronic stress from disease, or aging: progressive loss of functional cardiomyocytes and diminished hemodynamic output. To stave off cardiomyocyte losses, a number of strategic approaches have been embraced in recent years involving both molecular and cellular approaches to augment myocardial structure and performance. Resultant excitement surrounding regenerative medicine in the heart has been tempered by realizations that reparative processes in the heart are insufficient to restore damaged myocardium to normal functional capacity and that cellular cardiomyoplasty is hampered by poor survival, proliferation, engraftment, and differentiation of the donated population. To overcome these limitations, a combination of molecular and cellular approaches must be adopted involving use of genetic engineering to enhance resistance to cell death and increase regenerative capacity. This review highlights biological properties of approached to potentiate stem cell-mediated regeneration to promote enhanced myocardial regeneration, persistence of donated cells, and long-lasting tissue repair. Optimizing cell delivery and harnessing the power of survival signaling cascades for ex vivo genetic modification of stem cells before reintroduction into the patient will be critical to enhance the efficacy of cellular cardiomyoplasty. Once this goal is achieved, then cell-based therapy has great promise for treatment of heart failure to combat the loss of cardiac structure and function associated with acute damage, chronic disease, or aging.

Blockade of the nuclear factor-κB pathway in the endothelium prevents insulin resistance and prolongs life spans

BACKGROUND

Nuclear factor-κB (NF-κB) signaling plays critical roles in physiological and pathological processes such as responses to inflammation and oxidative stress.

METHODS AND RESULTS

To examine the role of endothelial NF-κB signaling in vivo, we generated transgenic mice expressing dominant-negative IκB under the Tie2 promoter/enhancer (E-DNIκB mice). These mice exhibited functional inhibition of NF-κB signaling specifically in endothelial cells. Although E-DNIκB mice displayed no overt phenotypic changes when young and lean, they were protected from the development of insulin resistance associated with obesity, whether diet- or genetics-induced. Obesity-induced macrophage infiltration into adipose tissue and plasma oxidative stress markers were decreased and blood flow and mitochondrial content in muscle and active-phase locomotor activity were increased in E-DNIκB mice. In addition to inhibition of obesity-related metabolic deteriorations, blockade of endothelial NF-κB signaling prevented age-related insulin resistance and vascular senescence and, notably, prolonged life span. These antiaging phenotypes were also associated with decreased oxidative stress markers, increased muscle blood flow, enhanced active-phase locomotor activity, and aortic upregulation of mitochondrial sirtuin-related proteins.

CONCLUSIONS

The endothelium plays important roles in obesity- and age-related disorders through intracellular NF-κB signaling, thereby ultimately affecting life span. Endothelial NF-κB signaling is a potential target for treating the metabolic syndrome and for antiaging strategies.

Losartan inhibits STAT1 activation and protects human glomerular mesangial cells from angiotensin II induced premature senescence

Human glomerular mesangial cells (HMCs) have a finite lifespan, and eventually enter irreversible growth arrest known as cellular senescence, which is thought to contribute to kidney ageing and age-related kidney disorders, such as chronic kidney disease. The signal transducer and activator of transcription 1 (STAT1) is a latent transcription factor involved in a variety of signal transduction pathways, including cell proliferation, apoptosis, and differentiation, but whether it could regulate HMC senescence still remains to be explored. In our study, the induction of angiotensin II (Ang II)-accelerated HMC senescence, as judged by increased senescence-associated β-galactosidase (SA-β-gal)-positive staining cells, morphological changes, and G0/G1 cell cycle arrest. STAT1 activity and the expression of p53 and p21Cip1 were increased after Ang II treatment. STAT1 knockdown using RNA interference significantly inhibited the progression of HMC senescence and decreased the elevated expression of p53 and p21Cip1. Pretreating HMCs with Ang II receptor blocker losartan also inhibited the progression of HMC senescence and STAT1 activity. Our results indicate that STAT1 is implicated in the mediation of Ang II-induced HMC senescence through p53/ p21Cip1 pathway, and that losartan could attenuate HMC senescence by regulating STAT1. The antioxidant N-acetyl-L-cysteine reduced ROS production and STAT1 activity induced by Ang II, indicating that Ang II uses ROS as a second messenger to regulate STAT1 activity.

Is cellular senescence important in pediatric kidney disease?

Somatic cellular senescence (SCS) describes the limited ability of cells to divide. Normally, SCS is associated with physiological aging, but evidence suggests that it may play a role in disease progression, even in young patients. Stressors such as acute injury or chronic inflammation may induce SCS, which in turn exhausts organ regenerative potential. This review summarizes what is known about SCS in the kidney with aging and disease. As most patients with chronic kidney disease (CKD) also develop cardiovascular complications, a second focus of this review deals with the role of SCS in cardiovascular disease. Also, as SCS seems to accelerate CKD and cardiovascular disease progression, developing strategies for new treatment options that overcome SCS or protect a patient from it represents an exciting challenge.

PPARδ coordinates angiotensin II-induced senescence in vascular smooth muscle cells through PTEN-mediated inhibition of superoxide generation

Cellular senescence-associated changes in blood vessels have been implicated in aging and age-related cardiovascular disorders. Here, we demonstrate that peroxisome proliferator-activated receptor (PPAR) δ coordinates angiotensin (Ang) II-induced senescence of human vascular smooth muscle cells (VSMCs). Activation of PPARδ by GW501516, a specific ligand for PPARδ, significantly attenuated Ang II-induced generation of superoxides and suppressed senescence of VSMCs. A marked increase in the levels of p53 and p21 induced by Ang II was blunted by the treatment with GW501516. Ligand-activated PPARδ up-regulated expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and suppressed the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Knockdown of PTEN with siRNA abrogated the effects of PPARδ on cellular senescence, on PI3K/Akt signaling, and on generation of ROS in VSMCs treated with Ang II. Finally, administration of GW501516 to apoE-deficient mice treated with Ang II significantly reduced the number of senescent cells in the aorta, where up-regulation of PTEN with reduced levels of phosphorylated Akt and ROS was demonstrated. Thus, ligand-activated PPARδ confers resistance to Ang II-induced senescence by up-regulation of PTEN and ensuing modulation of the PI3K/Akt signaling to reduce ROS generation in vascular cells.

New and old mechanisms associated with hypertension in the elderly

Hypertension is a widely prevalent and important risk factor for cardiovascular diseases that increase with aging. The hallmark of hypertension in the elderly is increased vascular dysfunction. However, the molecular mechanisms by which increased blood pressure leads to vascular injury and impaired endothelial function are not well defined. In the present paper, we will analyze several mechanisms described in the scientific literature involved in hypertension in the elderly as endothelial dysfunction, increased oxygen delivery to tissues, inflammation, cellular apoptosis, and increased concentration of active metabolites. Also, we will focus on new molecular mechanisms involved in hypertension such as telomeres shortening, progenitor cells, circulating microparticles, and epigenetic factors that have appeared as possible causes of hypertension in the elderly. These molecular mechanisms may elucidate different origin for hypertension in the elderly and provide us with new targets for hypertension treatment.

The association of ACE I/D gene polymorphism with severe carotid atherosclerosis in patients undergoing carotid endarterectomy

Introduction: The ACE I/D polymorphism was mostly investigated in association with intima-media thickness, rarely with severe atherosclerotic phenotype.

Materials and methods: We investigated the association of I/D polymorphism with severe carotid atherosclerosis (CA) (stenosis > 70%) in asymptomatic and symptomatic patients undergoing carotid endarterectomy. The 504 patients subjected to endarterectomy and 492 healthy controls from a population in Serbia were investigated as a case-control study.

Results: The univariate logistic regression analysis revealed ACE DD as a significant risk factor for severe CA (odds ratio [OR] = 1.3, 95% confidence interval [CI] 1.0–1.7, p = 0.04). After adjustment for the common risk factors (age, hypertension, smoking, and HDL) ACE was no longer significant. However, we found a significant independent influence of DD genotype on plaque presence in a normotensive subgroup of patients (OR 1.8, CI 1.2–3.0, p = 0.01, corrected for multiple testing). In symptomatic patients D allele carriers were significantly more frequent compared with asymptomatic patients (OR 1.6 CI 1.0–2.6, p = 0.05).

Conclusions: Our data suggests that ACE I/D is not an independent risk factor for severe CA. On the other hand, a significant independent genetic influence of ACE I/D appeared in normotensive and symptomatic patients with severe CA. This should be considered in further research toward resolving the complex genetic background of severe CA phenotype.

HDAC2 phosphorylation-dependent Klf5 deacetylation and RARα acetylation induced by RAR agonist switch the transcription regulatory programs of p21 in VSMCs

Abnormal proliferation of vascular smooth muscle cells (VSMCs) occurs in hypertension, atherosclerosis and restenosis after angioplasty, leading to pathophysiological vascular remodeling. As an important growth arrest gene, p21 plays critical roles in vascular remodeling. Regulation of p21 expression by retinoic acid receptor (RAR) and its ligand has important implications for control of pathological vascular remodeling. Nevertheless, the mechanism of RAR-mediated p21 expression in VSMCs remains poorly understood. Here, we show that, under basal conditions, RARα forms a complex with histone deacetylase 2 (HDAC2) and Krüppel-like factor 5 (Klf5) at the p21 promoter to inhibit its expression. Upon RARα agonist stimulation, HDAC2 is phosphorylated by CK2α. Phosphorylation of HDAC2, on the one hand, promotes its dissociation from RARα, thus allowing the liganded-RARα to interact with co-activators; on the other hand, it increases its interaction with Klf5, thus leading to deacetylation of Klf5. Deacetylation of Klf5 facilitates its dissociation from the p21 promoter, relieving its repressive effect on the p21 promoter. Interference with HDAC2 phosphorylation by either CK2α knockdown or the use of phosphorylation-deficient mutant of HDAC2 prevents the dissociation of Klf5 from the p21 promoter and impairs RAR agonist-induced p21 activation. Our results reveal a novel mechanism involving a phosphorylation-deacetylation cascade that functions to remove the basal repression complex from the p21 promoter upon RAR agonist treatment, allowing for optimum agonist-induced p21 expression.

Renal oxidative stress, oxygenation, and hypertension

Hypertension is closely associated with progressive kidney dysfunction, manifested as glomerulosclerosis, interstitial fibrosis, proteinuria, and eventually declining glomerular filtration. The postulated mechanism for development of glomerulosclerosis is barotrauma caused by increased capillary pressure, but the reason for development of interstitial fibrosis and the subsequently reduced kidney function is less clear. However, it has been hypothesized that tissue hypoxia induces fibrogenesis and progressive renal failure. This is very interesting, since recent reports highlight several different mechanisms resulting in altered oxygen handling and availability in the hypertensive kidney. Such mechanisms include decreased renal blood flow due to increased vascular tone induced by ANG II that limits oxygen delivery and increases oxidative stress, resulting in increased mitochondrial oxygen usage, increased oxygen usage for tubular electrolyte transport, and shunting of oxygen from arterial to venous blood in preglomerular vessels. It has been shown in several studies that interventions to prevent oxidative stress and to restore kidney tissue oxygenation prevent progression of kidney dysfunction. Furthermore, inhibition of ANG II activity, by either blocking ANG II type 1 receptors or angiotensin-converting enzyme, or by preventing oxidative stress by administration of antioxidants also results in improved blood pressure control. Therefore, it seems likely that tissue hypoxia in the hypertensive kidney contributes to progression of kidney damage, and perhaps also persistence the high blood pressure.

Delaying vascular aging with Chinese medicine: implications from an overview of the p53 and miR-34s family

p53 is an important target for studying vascular aging. However, as people gradually learned more about the miR-34s and the relationship between miR-34s and p53, new research idea emerged. This paper tries to elaborate the feature of p53, microRNA and miR-34s in-depth, analyze the regulatory action of miR-34s on p53, and offer some new prevention and treatment prospects about vascular aging in Chinese medicine.

Rho-kinase: important new therapeutic target in cardiovascular diseases

Rho-kinase (ROCKs) belongs to the family of serine/threonine kinases and is an important downstream effector of the small GTP-binding protein RhoA. There are two isoforms of Rho-kinase, ROCK1 and ROCK2, and they have different functions with ROCK1 for circulating inflammatory cells and ROCK2 for vascular smooth muscle cells. It has been demonstrated that the RhoA/Rho-kinase pathway plays an important role in various fundamental cellular functions, including contraction, motility, proliferation, and apoptosis, leading to the development of cardiovascular disease. The important role of Rho-kinase in vivo has been demonstrated in the pathogenesis of vasospasm, arteriosclerosis, ischemia-reperfusion injury, hypertension, pulmonary hypertension, stroke, and heart failure. Furthermore, the beneficial effects of fasudil, a selective Rho-kinase inhibitor, have been demonstrated for the treatment of several cardiovascular diseases in humans. Thus the Rho-kinase pathway is an important new therapeutic target in cardiovascular medicine.

Early inflammatory reactions in atherosclerosis are induced by proline-rich tyrosine kinase/reactive oxygen species-mediated release of tumor necrosis factor-alpha and subsequent activation of the p21Cip1/Ets-1/p300 system

OBJECTIVE

Reactive oxygen species (ROS) are involved in the initial process of atherosclerosis, whereas it remains to be determined how atherogenic stimulus causes ROS-mediated proinflammatory reactions. Here, we focused on proline-rich tyrosine kinase (PYK2)-mediated ROS generation and examined how atherogenic stimulus causes early proinflammatory reactions.

METHODS AND RESULTS

PYK2-deficient (knockout [KO]) (PYK2-KO) mice were crossbred with apolipoprotein E (ApoE)-deficient (PYK2-KO/ApoE-KO) mice. PYK2-KO/ApoE-KO mice and endothelial cells (EC) were used for the study. Aortic atherogenic lesions in PYK2-KO/ApoE-KO mice were markedly decreased (55% versus ApoE-KO) after 8 weeks of a Western diet. Aortic PYK2 was activated as early as 7 days after the Western diet, when inflammatory cells were not yet activated. Addition of the proatherogenic oxidized phospholipid lysophosphatidylcholine caused activation of endothelial PYK2. Lysophosphatidylcholine-activated PYK2 induced NADPH oxidase-mediated ROS generation and ROS-mediated synthesis of tumor necrosis factor-α (TNFα), vascular cell adhesion molecule-1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1), and p21Cip1/Ets-1. Neutralizing anti-TNFα antibody or knockdown of p21Cip1/Ets-1 system blocked the induction of VCAM-1 and MCP-1. PYK2 deficiency abolished these ROS-mediated proinflammatory reactions. Further analysis revealed that PYK2/ROS-mediated p21Cip1/Ets-1 activation upregulated the transcription of the MCP-1 gene in collaboration with p300 transcription coactivator.

CONCLUSIONS

PYK2 is a key tyrosine kinase activated by high cholesterol exposure, which causes ROS-mediated TNFα release and induces TNFα-dependent expression of proinflammatory molecules via the p21Cip1/Ets-1/p300 transcription system.

Dual effects of estrogen on vascular smooth muscle cells: receptor-mediated proliferative vs. metabolite-induced pro-senescent actions

OBJECTIVE

To investigate the mechanism for the dual effects of estrogen on vascular smooth muscle cells (VSMCs).

METHODS

Cultured rat VSMCs were exposed to gradient concentrations (10(-9)-10(-5)M) of 17β-estradiol (E(2)) with or without pre-administration of a broad-spectrum CYP450 inhibitor 1-aminobenzotriazole (ABT) (10×10(-6)M) and an estrogen receptor (ER) antagonist ICI 182,780 (10(-6)M), respectively. The growth, cell cycle progression, premature senescence, estrogen metabolites, reactive oxygen species (ROS) and DNA damage of the cells were analyzed with cell counting assay, flow cytometry, Western blot, liquid chromatography-mass spectrometry and comet assay, respectively.

RESULTS

E(2) in its physiological levels from 10(-9)M to 10(-8)M had a concentration-dependent promoting effect on growth of VSMCs. However, when the concentration increased over 10(-8)M, the growth-promoting effect gradually reversed to a growth-inhibiting action. When the activity of CYP450s was blocked by ABT, the growth-promoting effect of E(2) increased and did not reverse at high concentrations. Whereas when the ERs were blocked by ICI 182,780, E(2) showed a pure growth-inhibiting effect. The E(2) metabolites 2- and 4-hydroxyestradiols accumulated with the increase of E(2) over 10(-8)M, which accompanied by increased ROS, DNA damage and cellular senescence. All of these changes were eliminated by block of CYP450s, indicating that the VSMC growth inhibition by E(2) is due to an increased production of ROS from accumulated E(2) metabolites which induces DNA damage, leading to VSMC premature senescence.

CONCLUSION

The complex effect of E(2) is due to two opposite actions: one ER-mediated and proliferative, and the other estrogen metabolite-induced and pro-senescent.

Effects of estrogen on stress-induced premature senescence of vascular smooth muscle cells: a novel mechanism for the "time window theory" of menopausal hormone therapy

OBJECTIVES

To investigate the effects of estrogen on stress-induced premature senescence of vascular smooth muscle cells (VSMCs) and the underlying mechanisms.

METHODS

VSMCs of passage 2-3 cultured from young (2 months) and old (18 months) female SD rats were induced into premature senescence by exposure to 150 μmol/L H(2)O(2) in the presence or absence of different concentrations of 17β-estradiol (E(2)). The expression or activation of senescence-associated beta-galactosidase (SA-β-Gal), DcR2, oncogene Ras, p38, PRAK, p53, p21, p16 and Rb was detected by flow cytometry, pull-down assay or Western blot.

RESULTS

Flow cytometry analysis showed that in the VSMCs from young rats pre-administration of E(2) significantly suppressed the H(2)O(2)-induced premature senescence (reducing both percentage of SA-β-Gal positive cells and cellular expression of DcR2) in a dose-dependent manner; these senescent-inhibiting effects of E(2) could be blocked by an estrogen receptor antagonist ICI 182,780 (10(-5)mol/L). Pull-down assay or Western blot analysis revealed that pre-administration of 10(-8)mol/L E(2) significantly reduced the H(2)O(2)-induced activation of oncogene Ras, as well as activity of p16 and p38 MAPK, and expression of PRAK, p53, p21 and p-Rb. Unexpectedly, in the VSMCs from old rats the senescent-inhibiting effect of E(2) disappeared and switched to a senescent-promoting action at 10(-8)mol/L. This senescent-promoting effect could be enhanced by ICI 182,780 and eliminated by a cytochrome P450s inhibitor ABT.

CONCLUSION

Estrogen inhibits stress-induced premature senescence of VSMCs from young female through its receptor-mediated suppression of both Ras-p38-PRAK-p53-p21-Rb and Ras-p16-Rb pathways, but this effect disappeared and even more switched to a senescent-promoting action in the cells from old body probably due to a side effect of estrogen metabolites.

Early endosomal antigen 1 (EEA1) is an obligate scaffold for angiotensin II-induced, PKC-alpha-dependent Akt activation in endosomes

Akt/protein kinase B (PKB) activation/phosphorylation by angiotensin II (Ang II) is a critical signaling event in hypertrophy of vascular smooth muscle cells (VSMCs). Conventional wisdom asserts that Akt activation occurs mainly in plasma membrane domains. Recent evidence that Akt activation may take place within intracellular compartments challenges this dogma. The spatial identity and mechanistic features of these putative signaling domains have not been defined. Using cell fractionation and fluorescence methods, we demonstrate that the early endosomal antigen-1 (EEA1)-positive endosomes are a major site of Ang II-induced Akt activation. Akt moves to and is activated in EEA1 endosomes. The expression of EEA1 is required for phosphorylation of Akt at both Thr-308 and Ser-473 as well as for phosphorylation of its downstream targets mTOR and S6 kinase, but not for Erk1/2 activation. Both Akt and phosphorylated Akt (p-Akt) interact with EEA1. We also found that PKC-α is required for organizing Ang II-induced, EEA1-dependent Akt phosphorylation in VSMC early endosomes. EEA1 expression enables PKC-α phosphorylation, which in turn regulates Akt upstream signaling kinases, PDK1 and p38 MAPK. Our results indicate that PKC-α is a necessary regulator of EEA1-dependent Akt signaling in early endosomes. Finally, EEA1 down-regulation or expression of a dominant negative mutant of PKC-α blunts Ang II-induced leucine incorporation in VSMCs. Thus, EEA1 serves a novel function as an obligate scaffold for Ang II-induced Akt activation in early endosomes.

Role of cellular senescence in lifestyle-related disease

Epidemiological studies have shown that age is the chief risk factor for lifestyle-related diseases such as cardiovascular disease and diabetes, but the molecular mechanisms that underlie the increase in the risk of such diseases conferred by aging remain unclear. Recently, genetic analyses using various animal models have identified molecules that are crucial for aging. These include components of the DNA repair system, the tumor suppressor pathway, the telomere maintenance system, the insulin/Akt pathway, and other metabolic pathways. Interestingly, most of the molecules that influence the phenotypic changes of aging also regulate cellular senescence, suggesting a causative link between cellular senescence and aging. This review examines the hypothesis that cellular senescence might contribute to lifestyle-related disease.

Senescence and dysfunction of proximal tubular cells are associated with activated p53 expression by indoxyl sulfate

Various uremic toxins accumulate in patients with chronic renal failure (CRF) and one of them is indoxyl sulfate, which accelerates the progression of CRF through unknown mechanisms. The present study investigates how indoxyl sulfate promotes CRF using the proximal tubular cell line HK-2 and CRF rats. Indoxyl sulfate inhibited serum-induced cell proliferation and promoted the activation of senescence-associated β-galactosidase, a marker of cellular senescence, and the expression of α-smooth muscle actin (α-SMA), a marker of fibrosis, through inducing p53 expression and phosphorylation. Pifithrin-α, p-nitro, a p53 inhibitor, blocked these effects. Indoxyl sulfate evoked reactive oxygen species (ROS), and the antioxidant N-acetylcysteine inhibited indoxyl sulfate-induced p53 expression and phosphorylation, as well as indoxyl sulfate-induced α-SMA expression. We previously demonstrated that although cellular senescence and fibrosis are detectable in the kidneys of CRF rats, the oral adsorbent AST-120 repressed these effects. Here, we found that β-galactosidase, p53 and α-SMA were expressed and colocalized in the renal tubules of CRF rats, whereas AST-120 decreased the expression of these genes. Taken together, these findings indicate that indoxyl sulfate induces the expression and phosphorylation of p53 though ROS production, thus inhibiting cell proliferation and promoting cellular senescence and renal fibrosis.