SIRT1-mediated epigenetic downregulation of plasminogen activator inhibitor-1 prevents vascular endothelial replicative senescence

Fibroblast growth factor 21 delayed endothelial replicative senescence and protected cells from H2O2-induced premature senescence through SIRT1

Vascular aging is an independent risk factor for age-related diseases, including atherosclerosis. Fibroblast growth factor 21 (FGF21) has been widely recognized as a metabolic regulator that is elevated in response to caloric and nutritional restrictions. Recent studies have demonstrated its emerging role as a pro-longevity hormone, but its effects on the senescence of human umbilical vascular endothelial cells (HUVECs) remain unclear. In the present study, we explored the anti-senescence effects and underlying mechanism of FGF21 on HUVECs. Co-cultivation of HUVECs with 5 ng/mL FGF21 significantly attenuated the phenotype changes of cells during in vitro subculture, including increased senescent population, decreased proliferation rate, decreased SIRT1 and elevated P53 and P21 protein levels. FGF21 also protected HUVECs from H₂O₂-induced cell damage, including premature cell senescence, intracellular accumulation of reactive oxygen species, increased DNA damage, decreased SIRT1 protein level and elevated protein levels of VCAM-1, ICAM-1, P53 and P21. Transient knockdown of SIRT1 in HUVECs significantly suppressed the protective effects of FGF21 for the rescue of H₂O₂-induced premature senescence and DNA damage, which suggests that the anti-senescence effect of FGF21 on HUVECs is SIRT1-dependent. These results support the potential of FGF21 as a therapeutic target for postponing vascular aging and preventing age-related vascular diseases.

Vascular Smooth Muscle Cells and Arterial Stiffening: Relevance in Development, Aging, and Disease

The cushioning function of large arteries encompasses distension during systole and recoil during diastole which transforms pulsatile flow into a steady flow in the microcirculation. Arterial stiffness, the inverse of distensibility, has been implicated in various etiologies of chronic common and monogenic cardiovascular diseases and is a major cause of morbidity and mortality globally. The first components that contribute to arterial stiffening are extracellular matrix (ECM) proteins that support the mechanical load, while the second important components are vascular smooth muscle cells (VSMCs), which not only regulate actomyosin interactions for contraction but mediate also mechanotransduction in cell-ECM homeostasis. Eventually, VSMC plasticity and signaling in both conductance and resistance arteries are highly relevant to the physiology of normal and early vascular aging. This review summarizes current concepts of central pressure and tensile pulsatile circumferential stress as key mechanical determinants of arterial wall remodeling, cell-ECM interactions depending mainly on the architecture of cytoskeletal proteins and focal adhesion, the large/small arteries cross-talk that gives rise to target organ damage, and inflammatory pathways leading to calcification or atherosclerosis. We further speculate on the contribution of cellular stiffness along the arterial tree to vascular wall stiffness. In addition, this review provides the latest advances in the identification of gene variants affecting arterial stiffening. Now that important hemodynamic and molecular mechanisms of arterial stiffness have been elucidated, and the complex interplay between ECM, cells, and sensors identified, further research should study their potential to halt or to reverse the development of arterial stiffness.

Biogenesis of Pro-senescent Microparticles by Endothelial Colony Forming Cells from Premature Neonates is driven by SIRT1-Dependent Epigenetic Regulation of MKK6

Senescent cells may exert detrimental effect on microenvironment through the secretion of soluble factors and the release of extracellular vesicles, such as microparticles, key actors in ageing and cardiovascular diseases. We previously reported that sirtuin-1 (SIRT1) deficiency drives accelerated senescence and dysfunction of endothelial colony-forming cells (ECFC) in PT neonates. Because preterm birth (PT) increases the risk for cardiovascular diseases during neonatal period as well as at adulthood, we hypothesized that SIRT1 deficiency could control the biogenesis of microparticles as part of a senescence–associated secretory phenotype (SASP) of PT-ECFC and investigated the related molecular mechanisms. Compared to control ECFC, PT-ECFC displayed a SASP associated with increased release of endothelial microparticles (EMP), mediating a paracrine induction of senescence in naïve endothelial cells. SIRT1 level inversely correlated with EMP release and drives PT-ECFC vesiculation. Global transcriptomic analysis revealed changes in stress response pathways, specifically the MAPK pathway. We delineate a new epigenetic mechanism by which SIRT1 deficiency regulates MKK6/p38^MAPK/Hsp27 pathway to promote EMP biogenesis in senescent ECFC. These findings deepen our understanding of the role of ECFC senescence in the disruption of endothelial homeostasis and provide potential new targets towards the control of cardiovascular risk in individuals born preterm.

Plasminogen Activator Inhibitor Type-1 as a Regulator of Fibrosis

Fibrosis is known as a frequent and irreversible pathological condition which is associated with organ failure. Tissue fibrosis is a central process in a variety of chronic progressive diseases such as diabetes, hypertension, and persistent inflammation. This state could contribute to chronic injury and the initiation of tissue repair. Fibrotic disorders represent abnormal wound healing with defective matrix turnover and clearance that lead to excessive accumulation of extracellular matrix components. A variety of identified growth factors, cytokines, and persistently activated myofibroblasts have critical roles in the pathogenesis of fibrosis. Irrespective of etiology, the transforming growth factor-β pathway is the major driver of fibrotic response. Plasminogen activator inhibitor-1 (PAI-1) is a crucial downstream target of this pathway. Transforming growth factor-β positively regulates PAI-1 gene expression via two main pathways including Smad-mediated canonical and non-canonical pathways. Overexpression of PAI-1 reduces extracellular matrix degradation via perturbing the plasminogen activation system. Indeed, elevated PAI-1 levels inhibit proteolytic activity of tissue plasminogen activator and urokinase plasminogen activator which could contribute to a variety of inflammatory elements in the injury site and to excessive matrix deposition. This review summarizes the current knowledge of critical pathways that regulate PAI-1 gene expression and suggests effective approaches for the treatment of fibrotic disease. J. Cell. Biochem. 119: 17-27, 2018. © 2017 Wiley Periodicals, Inc.

Generation of human iPSCs from urine derived cells of patient with a novel heterozygous PAI-1 mutation

We have generated a human induced pluripotent stem cell (iPSC) line under feeder-free culture conditions using the urine derived cells (UCs) collected from subjects heterozygous for a novel Plasminogen Activator Inhibitor-1 (PAI-1) mutation. The Sendai Virus (SeV) vector encoding pluripotent Yamanaka transcription factors was used at a low multiplicity of infection to reprogram the PAI-1 UCs.

Long-term nicotine exposure induces dysfunction of mouse endothelial progenitor cells

Endothelial progenitor cells (EPCs) have an important role in maintaining endothelial homeostasis. Previous studies reported that smoking has detrimental effects on EPCs; however, recent studies revealed that short-term nicotine exposure may benefit EPCs. As most smokers are exposed to nicotine over an extended time period, the present study aimed to investigate the long-term effects of nicotine on EPCs. Mice were administered nicotine orally for 1, 3 or 6 months. The mice exposed to nicotine for 1 month demonstrated increased EPC counts and telomerase activity and reduced cell senescence compared with control mice, consistent with previous reports. However, long-term nicotine exposure resulted in opposing effects on EPCs, causing decreased counts, functional impairment and reduced telomerase activity. Furthermore, the effects of nicotine exposure were correlated with changes in sirtuins type 1 (SIRT1) protein expression. The current study indicated that long-term nicotine exposure induces dysfunction and senescence of EPCs, which may be associated with impairment of telomerase activity through SIRT1 downregulation. The present results emphasize the necessity of smoking cessation to prevent dysfunction of EPCs.

Generation of human iPSCs from urine derived cells of a patient with a novel homozygous PAI-1 mutation

We have generated a human induced pluripotent stem cell (iPSC) line under feeder-free culture conditions using the urine derived cells (UCs) collected from subject with a novel homozygous Plasminogen Activator Inhibitor-1 (PAI-1 null) mutation. The Sendai virus (SeV) vector encoding pluripotent Yamanaka transcription factors was used at a low multiplicity of infection to reprogram the PAI-1 UCs.

Calorie restriction protects against experimental abdominal aortic aneurysms in mice

Abdominal aortic aneurysm (AAA), characterized by a localized dilation of the abdominal aorta, is a life-threatening vascular pathology. Because of the current lack of effective treatment for AAA rupture, prevention is of prime importance for AAA management. Calorie restriction (CR) is a nonpharmacological intervention that delays the aging process and provides various health benefits. However, whether CR prevents AAA formation remains untested. In this study, we subjected Apoe^-/- mice to 12 wk of CR and then examined the incidence of angiotensin II (AngII)-induced AAA formation. We found that CR markedly reduced the incidence of AAA formation and attenuated aortic elastin degradation in Apoe^-/- mice. The expression and activity of Sirtuin 1 (SIRT1), a key metabolism/energy sensor, were up-regulated in vascular smooth muscle cells (VSMCs) upon CR. Importantly, the specific ablation of SIRT1 in smooth muscle cells abolished the preventive effect of CR on AAA formation in Apoe^-/- mice. Mechanistically, VSMC-SIRT1-dependent deacetylation of histone H3 lysine 9 on the matrix metallopeptidase 2 (Mmp2) promoter was required for CR-mediated suppression of AngII-induced MMP2 expression. Together, our findings suggest that CR may be an effective intervention that protects against AAA formation.

Age-Associated Sirtuin 1 Reduction in Vascular Smooth Muscle Links Vascular Senescence and Inflammation to Abdominal Aortic Aneurysm

RATIONALE

Uncontrolled growth of abdominal aortic aneurysms (AAAs) is a life-threatening vascular disease without an effective pharmaceutical treatment. AAA incidence dramatically increases with advancing age in men. However, the molecular mechanisms by which aging predisposes individuals to AAAs remain unknown.

OBJECTIVE

In this study, we investigated the role of SIRT1 (Sirtuin 1), a class III histone deacetylase, in AAA formation and the underlying mechanisms linking vascular senescence and inflammation.

METHODS AND RESULTS

The expression and activity of SIRT1 were significantly decreased in human AAA samples. SIRT1 in vascular smooth muscle cells was remarkably downregulated in the suprarenal aortas of aged mice, in which AAAs induced by angiotensin II infusion were significantly elevated. Moreover, vascular smooth muscle cell-specific knockout of SIRT1 accelerated angiotensin II-induced formation and rupture of AAAs and AAA-related pathological changes, whereas vascular smooth muscle cell-specific overexpression of SIRT1 suppressed angiotensin II-induced AAA formation and progression in Apoe^-/- mice. Furthermore, the inhibitory effect of SIRT1 on AAA formation was also proved in a calcium chloride (CaCl₂)-induced AAA model. Mechanistically, the reduction of SIRT1 was shown to increase vascular cell senescence and upregulate p21 expression, as well as enhance vascular inflammation. Notably, inhibition of p21-dependent vascular cell senescence by SIRT1 blocked angiotensin II-induced nuclear factor-κB binding on the promoter of monocyte chemoattractant protein-1 and inhibited its expression.

CONCLUSIONS

These findings provide evidence that SIRT1 reduction links vascular senescence and inflammation to AAAs and that SIRT1 in vascular smooth muscle cells provides a therapeutic target for the prevention of AAA formation.

TEL2 suppresses metastasis by down-regulating SERPINE1 in nasopharyngeal carcinoma

Metastasis is the major cause of treatment failure in patients with nasopharyngeal carcinoma (NPC). However, the molecular mechanisms of NPC metastasis are poorly understood. Here, using our customized gene microarray containing all of the known human transcription factors and the current markers for epithelial-mesenchymal transition, we report that TEL2 was down-regulated in highly metastatic NPC cells and the metastatic tissues in lymph node. Mechanistically, TEL2 inhibits the cell migration and invasion in vitro and metastasis in vivo by releasing its direct suppression on the SERPINE1 promoter in NPC. Consistently, an inverse correlation was observed between the protein levels of TEL2 and SERPINE1 using clinical NPC samples. Collectively, we have provided the first evidence that TEL2 plays a key role in NPC metastasis by directly down-regulating SERPINE1, and that this novel axis of TEL2 / SERPINE1 may be valuable to develop new strategies for treating NPC patients with metastasis.

Ionizing Radiation-Induced Endothelial Cell Senescence and Cardiovascular Diseases

Exposure to ionizing radiation induces not only apoptosis but also senescence. While the role of endothelial cell apoptosis in mediating radiation-induced acute tissue injury has been extensively studied, little is known about the role of endothelial cell senescence in the pathogenesis of radiation-induced late effects. Senescent endothelial cells exhibit decreased production of nitric oxide and expression of thrombomodulin, increased expression of adhesion molecules, elevated production of reactive oxygen species and inflammatory cytokines and an inability to proliferate and form capillary-like structures in vitro. These findings suggest that endothelial cell senescence can lead to endothelial dysfunction by dysregulation of vasodilation and hemostasis, induction of oxidative stress and inflammation and inhibition of angiogenesis, which can potentially contribute to radiation-induced late effects such as cardiovascular diseases (CVDs). In this article, we discuss the mechanisms by which radiation induces endothelial cell senescence, the roles of endothelial cell senescence in radiation-induced CVDs and potential strategies to prevent, mitigate and treat radiation-induced CVDs by targeting senescent endothelial cells.

Decreased expression of the plasminogen activator inhibitor type 1 is involved in degradation of extracellular matrix surrounding cervical cancer stem cells

The plasminogen activator (PA) system consists of plasminogen activator inhibitor type 1 (PAI-1), urokinase-type plasminogen activator and its receptor (uPA and uPAR). PAI-1 inhibits the activation of uPA (which converts plasminogen to plasmin), and is involved in cancer invasion and metastasis, by remodeling the extracellular matrix (ECM) through regulating plasmin. Cancer stem cells (CSCs) are a small subset of cells within tumors, and are thought to be involved in tumor recurrence and metastasis. Considering these facts, we investigated the relationship between PAI-1 and cervical CSCs. We used ALDH1 as a marker of cervical CSCs. First, we demonstrated that culturing ALDH1-high cells and ALDH-low cells on collagen IV-coted plates increased their expression of active PAI-1 (ELISA), and these increases were suggested to be at mRNA expression levels (RT-qPCR). Secondly, we demonstrated PAI-1 was indeed involved in the ECM maintenance. With gelatin zymography assays, we found that ALDH1-high cells and ALDH-low cells expressed pro-matrix metalloproteinase-2 (pro-MMP-2) irrespective of their coatings. With gelatinase/collagenase assay kit, we confirmed that collagenase activity was increased when ALDH1-low cells were exposed to TM5275, a small molecule inhibitor of PAI-1. Putting the data together, we hypothesized that cancer cells adhered to basal membrane secrete abundant PAI-1, on the other hand, cancer cells (especially CSCs rather than non-CSCs) distant from basal membrane secrete less PAI-1, which makes the ECM surrounding CSCs more susceptible to degradation. Our study could be an explanation of conflicting reports, where some researchers found negative impacts of PAI-1 expression on clinical outcomes and others not, by considering the concept of CSCs.

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.

Epigenetics in the Vascular Endothelium: Looking From a Different Perspective in the Epigenomics Era

Cardiovascular diseases are commonly thought to be complex, non-Mendelian diseases that are influenced by genetic and environmental factors. A growing body of evidence suggests that epigenetic pathways play a key role in vascular biology and might be involved in defining and transducing cardiovascular disease inheritability. In this review, we argue the importance of epigenetics in vascular biology, especially from the perspective of endothelial cell phenotype. We highlight and discuss the role of epigenetic modifications across the transcriptional unit of protein-coding genes, especially the role of intragenic chromatin modifications, which are underappreciated and not well characterized in the current era of genome-wide studies. Importantly, we describe the practical application of epigenetics in cardiovascular disease therapeutics.

Cellular Senescence in Type 2 Diabetes: A Therapeutic Opportunity

Cellular senescence is a fundamental aging mechanism that has been implicated in many age-related diseases and is a significant cause of tissue dysfunction. Accumulation of senescent cells occurs during aging and is also seen in the context of obesity and diabetes. Senescent cells may play a role in type 2 diabetes pathogenesis through direct impact on pancreatic β-cell function, senescence-associated secretory phenotype (SASP)-mediated tissue damage, and involvement in adipose tissue dysfunction. In turn, metabolic and signaling changes seen in diabetes, such as high circulating glucose, altered lipid metabolism, and growth hormone axis perturbations, can promote senescent cell formation. Thus, senescent cells might be part of a pathogenic loop in diabetes, as both a cause and consequence of metabolic changes and tissue damage. Therapeutic targeting of a basic aging mechanism such as cellular senescence may have a large impact on disease pathogenesis and could be more effective in preventing the progression of diabetes complications than currently available therapies that have limited impact on already existing tissue damage. Therefore, senescent cells and the SASP represent significant opportunities for advancement in the prevention and treatment of type 2 diabetes and its complications.

Sirtuins in vascular diseases: Emerging roles and therapeutic potential

Silent information regulator-2 (Sir-2) proteins, or sirtuins, are a highly conserved protein family of histone deacetylases that promote longevity by mediating many of the beneficial effects of calorie restriction which extends life span and reduces the incidence of cancer, cardiovascular disease (CVD), and diabetes. Here, we review the role of sirtuins (SIRT1-7) in vascular homeostasis and diseases by providing an update on the latest knowledge about their roles in endothelial damage and vascular repair mechanisms. Among all sirtuins, in the light of the numerous functions reported on SIRT1 in the vascular system, herein we discuss its roles not only in the control of endothelial cells (EC) functionality but also in other cell types beyond EC, including endothelial progenitor cells (EPC), smooth muscle cells (SMC), and immune cells. Furthermore, we also provide an update on the growing field of compounds under clinical evaluation for the modulation of SIRT1 which, at the state of the art, represents the most promising target for the development of novel drugs against CVD, especially when concomitant with type 2 diabetes.