Endothelial cell senescence and age-related vascular diseases

GPR120 Agonist GW9508 Ameliorated Cellular Senescence Induced by ox-LDL

Introduction Oxidized low-density lipoprotein (ox-LDL)-induced endothelial senescence is involved in the pathogenesis of atherosclerosis and many cardiovascular diseases. G-protein-coupled receptor 120 (GPR120), a type of orphan G-protein-coupled receptors (GPRs), plays a vital role in mediating anti-inflammatory and insulin-sensitizing effects. The biological function of GPR120 in vascular endothelial cells is largely unknown. Methods The human aortic endothelial cells (HAECs) were treated with ox-LDL (100 μg/mL) in the presence or absence of GW9508 (50 μM) or AH9614 (1 μM) for 24 h. The LDH assay was used to determine cell death. The dihydroethidium (DHE) staining assay was used to measure intracellular levels of reactive oxidative species (ROS), and a senescence β-galactosidase assay kit was used to determine endothelial senescence. Gene and protein expressions were measured using real-time polymerase chain reaction (PCR) and western blot analysis, respectively. Results Ox-LDL treatment decreased the expression of GPR120 by more than half in HAECs. Typically, 100 μg/mL of ox-LDL- induced 35.2% LDH release, which was reduced to 16.9% by 50 μM GW9508, the agonist of GPR120. Importantly, GW9508 relieved cytotoxicity and suppressed the ox-LDL-induced increase in the activity of senescence-associated β-galactosidase (SA-β-Gal) (from 3.3-fold to 1.6-fold of the control group) and the generation of cellular reactive oxidative species (ROS) (from 3.8-fold to 1.6-fold of the control group). Furthermore, we found that GW9508 ameliorated ox-LDL-induced endothelial cell cycle arrest at the G0/G1 phase and the expression of key senescence proteins, including p53 and plasminogen activator inhibitor-1(PAI-1). Mechanistically, we showed that GW9508 promoted ox-LDL-induced transcriptional factor NF-E2-related factor 2 (NRF2) (increase by 47.3%) translocation into the nucleus. The effect of GW9508 is dependent on its receptor GPR120, the blockage of which by its specific antagonist, AH7614, abolished the antisenescence effect of GW9508. Conclusion Collectively, this study revealed the protective effect of GPR120 activation in vascular endothelial cells, implying that GPR120 is a promising therapeutic target for the treatment of cardiovascular diseases.

Microvascular disease in chronic kidney disease: the base of the iceberg in cardiovascular comorbidity

Chronic kidney disease (CKD) is a relentlessly progressive disease with a very high mortality mainly due to cardiovascular complications. Endothelial dysfunction is well documented in CKD and permanent loss of endothelial homeostasis leads to progressive organ damage. Most of the vast endothelial surface area is part of the microcirculation, but most research in CKD-related cardiovascular disease (CVD) has been devoted to macrovascular complications. We have reviewed all publications evaluating structure and function of the microcirculation in humans with CKD and animals with experimental CKD. Microvascular rarefaction, defined as a loss of perfused microvessels resulting in a significant decrease in microvascular density, is a quintessential finding in these studies. The median microvascular density was reduced by 29% in skeletal muscle and 24% in the heart in animal models of CKD and by 32% in human biopsy, autopsy and imaging studies. CKD induces rarefaction due to the loss of coherent vessel systems distal to the level of smaller arterioles, generating a typical heterogeneous pattern with avascular patches, resulting in a dysfunctional endothelium with diminished perfusion, shunting and tissue hypoxia. Endothelial cell apoptosis, hypertension, multiple metabolic, endocrine and immune disturbances of the uremic milieu and specifically, a dysregulated angiogenesis, all contribute to the multifactorial pathogenesis. By setting the stage for the development of tissue fibrosis and end organ failure, microvascular rarefaction is a principal pathogenic factor in the development of severe organ dysfunction in CKD patients, especially CVD, cerebrovascular dysfunction, muscular atrophy, cachexia, and progression of kidney disease. Treatment strategies for microvascular disease are urgently needed.

Cerebrovascular Senescence Is Associated With Tau Pathology in Alzheimer's Disease

Alzheimer's Disease (AD) is associated with neuropathological changes, including aggregation of tau neurofibrillary tangles (NFTs) and amyloid-beta plaques. Mounting evidence indicates that vascular dysfunction also plays a key role in the pathogenesis and progression of AD, in part through endothelial dysfunction. Based on findings in animal models that tau pathology induces vascular abnormalities and cellular senescence, we hypothesized that tau pathology in the human AD brain leads to vascular senescence. To explore this hypothesis, we isolated intact microvessels from the dorsolateral prefrontal cortex (PFC, BA9) from 16 subjects with advanced Braak stages (Braak V/VI, B3) and 12 control subjects (Braak 0/I/II, B1), and quantified expression of 42 genes associated with senescence, cell adhesion, and various endothelial cell functions. Genes associated with endothelial senescence and leukocyte adhesion, including SERPINE1 (PAI-1), CXCL8 (IL8), CXCL1, CXCL2, ICAM-2, and TIE1, were significantly upregulated in B3 microvessels after adjusting for sex and cerebrovascular pathology. In particular, the senescence-associated secretory phenotype genes SERPINE1 and CXCL8 were upregulated by more than 2-fold in B3 microvessels after adjusting for sex, cerebrovascular pathology, and age at death. Protein quantification data from longitudinal plasma samples for a subset of 13 (n = 9 B3, n = 4 B1) subjects showed no significant differences in plasma senescence or adhesion-associated protein levels, suggesting that these changes were not associated with systemic vascular alterations. Future investigations of senescence biomarkers in both the peripheral and cortical vasculature could further elucidate links between tau pathology and vascular changes in human AD.

Histone methyltransferase Smyd3 is a new regulator for vascular senescence

Endothelial cell senescence is one of the main risk factors contributing to vascular diseases. As increasing number of “epigenetic drugs” entering clinical trials, understanding the mechanism of epigenetic regulation in vascular aging has significant implications in finding targets to cure vascular diseases. However, the epigenetic regulation of endothelial senescence remains unclear. Based on the findings that increased protein level of histone H3 lysine 4 (H3K4) methyltransferase Smyd3 and elevated H3K4me3 modification happened in angiotensin II (Ang II)‐induced senescence in rat endothelial cells, we are curious about whether and how Smyd3 can regulate endothelial senescence. We found that an increase of Smyd3 alone promoted senescence‐associated phenotypes, while knockdown of Smyd3 blocked senescence in endothelial cells. Furthermore, Smyd3‐specific inhibitor reversed vascular senescence‐associated phenotypes at cellular level. Importantly, Ang II‐induced vascular senescence can be greatly alleviated in Smyd3 knockout (KO) mice and those treated with Smyd3 inhibitor. Mechanistically, Smyd3 directly bound to the promoter region of Cdkn1a (coding for p21), then caused its increased H3K4me3 level and elevated gene expression, and ultimately gave rise to senescence‐associated phenotypes. Intriguingly, Smyd3‐mediated p21 upregulated expression also exists in human tissues of vascular disease, indicating it is probably an evolutionarily conserved mechanism in regulating vascular senescence. Thus, Smyd3 can act as a novel factor regulating endothelial senescence through transcriptionally promoting p21 expression. Blocking the Smyd3‐p21 signaling axis may also have potential medical implications in treating diseases related to vascular aging.

Myocyte enhancer factor 2A delays vascular endothelial cell senescence by activating the PI3K/p-Akt/SIRT1 pathway

Myocyte enhancer factor 2A (MEF2A) dysfunction is closely related to the occurrence of senile diseases such as cardiocerebrovascular diseases, but the underlying molecular mechanism is unclear. Here, we studied the effects of MEF2A on the senescent phenotype of vascular endothelial cells (VEC) and downstream signaling pathway, and the association between plasma MEF2A levels and coronary artery disease (CAD). Results showed that MEF2A silencing promoted cell senescence and down-regulated PI3K/p-AKT/Sirtuin 1 (SIRT1) expression. MEF2A overexpression delayed cell senescence and up-regulated PI3K/p-AKT/SIRT1. Hydrogen peroxide (H₂O₂) treatment induced cellular senescence and down-regulated the expression of MEF2A and PI3K/p-AKT/SIRT1. MEF2A overexpression inhibited cellular senescence and the down-regulation of PI3K/p-AKT/SIRT1 induced by H₂O₂. Further study revealed that MEF2A directly up-regulated the expression of PIK3CA and PIK3CG through MEF2 binding sites in the promoter region. Pearson correlation and logistic regression analysis showed that the plasma level of MEF2A was negatively correlated with CAD, and with age in the controls. These results suggested that MEF2A can directly up-regulate PI3K gene expression, and one of the molecular mechanisms of delaying effect of MEF2A on VEC cell senescence was SIRT1-expression activation through the PI3K/p-Akt pathway. Moreover, the plasma MEF2A levels may be a potential biomarker for CAD risk prediction.

Alternative polyadenylation dependent function of splicing factor SRSF3 contributes to cellular senescence

Down-regulated splicing factor SRSF3 is known to promote cellular senescence, an important biological process in preventing cancer and contributing to individual aging, via its alternative splicing dependent function in human cells. Here we discovered alternative polyadenylation (APA) dependent function of SRSF3 as a novel mechanism explaining SRSF3 downregulation induced cellular senescence. Knockdown of SRSF3 resulted in preference usage of proximal poly(A) sites and thus global shortening of 3′ untranslated regions (3′ UTRs) of mRNAs. SRSF3-depletion also induced senescence-related phenotypes in both human and mouse cells. These 3′ UTR shortened genes were enriched in senescence-associated pathways. Shortened 3′ UTRs tended to produce more proteins than the longer ones. Simulating the effects of 3′ UTR shortening by overexpression of three candidate genes (PTEN, PIAS1 and DNMT3A) all led to senescence-associated phenotypes. Mechanistically, SRSF3 has higher binding density near proximal poly(A) site than distal one in 3′ UTR shortened genes. Further, upregulation of PTEN by either ectopic overexpression or SRSF3-knockdown induction both led to reduced phosphorylation of AKT and ultimately senescence-associated phenotypes. We revealed for the first time that reduced SRSF3 expression could promote cellular senescence through its APA-dependent function, largely extending our mechanistic understanding in splicing factor regulated cellular senescence.

CR6 interacting factor 1 deficiency induces premature senescence via SIRT3 inhibition in endothelial cells

Vascular endothelial cell senescence is an important cause of cardiac-related diseases. Mitochondrial reactive oxygen species (mtROS) have been implicated in cellular senescence and multiple cardiovascular disorders. CR6 interacting factor 1 (CRIF1) deficiency has been shown to increase mtROS via the inhibition of mitochondrial oxidative phosphorylation; however, the mechanisms by which mtROS regulates vascular endothelial senescence have not been thoroughly explored. The goal of this study was to investigate the effects of CRIF1 deficiency on endothelial senescence and to elucidate the underlying mechanisms. CRIF1 deficiency was shown to increase the activity of senescence-associated β-galactosidase along with increased expression of phosphorylated p53, p21, and p16 proteins. Cell cycle arrested in the G0/G1 phase were identified in CRIF1-deficient cells using the flow cytometry. Furthermore, CRIF1 deficiency was also shown to increase cellular senescence by reducing the expression of Sirtuin 3 (SIRT3) via ubiquitin-mediated degradation of transcription factors PGC1α and NRF2. Downregulation of CRIF1 also attenuated the function of mitochondrial antioxidant enzymes including manganese superoxide dismutase (MnSOD), Foxo3a, nicotinamide-adenine dinucleotide phosphate, and glutathione via the suppression of SIRT3. Interestingly, overexpression of SIRT3 in CRIF1-deficient endothelial cells not only reduced mtROS levels by elevating expression of the antioxidant enzyme MnSOD but also decreased the expression of cell senescence markers. Taken together, these results suggest that CRIF1 deficiency induces vascular endothelial cell senescence via ubiquitin-mediated degradation of the transcription coactivators PGC1α and NRF2, resulting in decreased expression of SIRT3.

Connexin43 Hemichannel Targeting With TAT-Gap19 Alleviates Radiation-Induced Endothelial Cell Damage

BACKGROUND

Emerging evidence indicates an excess risk of late occurring cardiovascular diseases, especially atherosclerosis, after thoracic cancer radiotherapy. Ionizing radiation (IR) induces cellular effects which may induce endothelial cell dysfunction, an early marker for atherosclerosis. In addition, intercellular communication through channels composed of transmembrane connexin proteins (Cxs), i.e. Gap junctions (direct cell-cell coupling) and hemichannels (paracrine release/uptake pathway) can modulate radiation-induced responses and therefore the atherosclerotic process. However, the role of endothelial hemichannel in IR-induced atherosclerosis has never been described before.

MATERIALS AND METHODS

Telomerase-immortalized human Coronary Artery/Microvascular Endothelial cells (TICAE/TIME) were exposed to X-rays (0.1 and 5 Gy). Production of reactive oxygen species (ROS), DNA damage, cell death, inflammatory responses, and senescence were assessed with or without applying a Cx43 hemichannel blocker (TAT-Gap19).

RESULTS

We report here that IR induces an increase in oxidative stress, cell death, inflammatory responses (IL-8, IL-1β, VCAM-1, MCP-1, and Endothelin-1) and premature cellular senescence in TICAE and TIME cells. These effects are significantly reduced in the presence of the Cx43 hemichannel-targeting peptide TAT-Gap19.

CONCLUSION

Our findings suggest that endothelial Cx43 hemichannels contribute to various IR-induced processes, such as ROS, cell death, inflammation, and senescence, resulting in an increase in endothelial cell damage, which could be protected by blocking these hemichannels. Thus, targeting Cx43 hemichannels may potentially exert radioprotective effects.

Vascular endothelium-targeted Sirt7 gene therapy rejuvenates blood vessels and extends life span in a Hutchinson-Gilford progeria model

Vascular dysfunction is a typical characteristic of aging, but its contributing roles to systemic aging and the therapeutic potential are lacking experimental evidence. Here, we generated a knock-in mouse model with the causative Hutchinson-Gilford progeria syndrome (HGPS) Lmna^G609G mutation, called progerin. The Lmna^f/f ;TC mice with progerin expression induced by Tie2-Cre exhibit defective microvasculature and neovascularization, accelerated aging, and shortened life span. Single-cell transcriptomic analysis of murine lung endothelial cells revealed a substantial up-regulation of inflammatory response. Molecularly, progerin interacts and destabilizes deacylase Sirt7; ectopic expression of Sirt7 alleviates the inflammatory response caused by progerin in endothelial cells. Vascular endothelium-targeted Sirt7 gene therapy, driven by an ICAM2 promoter, improves neovascularization, ameliorates aging features, and extends life span in Lmna^f/f ;TC mice. These data support endothelial dysfunction as a primary trigger of systemic aging and highlight gene therapy as a potential strategy for the clinical treatment of HGPS and age-related vascular dysfunction.

Aspirin Enhances the Protection of Hsp90 from Heat-Stressed Injury in Cardiac Microvascular Endothelial Cells Through PI3K-Akt and PKM2 Pathways

Heat stress (HS) often causes sudden death of humans and animals due to heart failure, mainly resulting from the contraction of cardiac microvasculature followed by myocardial ischemia. Cardiac microvascular endothelial cells (CMVECs) play an important role in maintaining vasodilatation. Aspirin (ASA) is well known for its protective abilities of febrile animals. However, there is little knowledge about molecular resistance mechanisms of CMVECs and which role ASA may play in this context. Therefore, we used a heat stress model of rat cardiac microvascular endothelial cell cultures in vitro and investigated the cell injuries and molecular resistance mechanism of CMVECs caused by heat stress, and the effect of aspirin (ASA) on it. HS induced severe pathological damage of CMVECs and cellular oxidative stress and dysfunction of NO release. Hsp90 was proven to be indispensable for resisting HS-injury of CMVECs through PI3K-Akt and PKM2 signaling pathways. Meanwhile, PKM2 functioned in reducing Akt phosphorylation. ASA treatment of CMVECs induced a significant expression of Hsp90, which promoted both Akt and PKM2 signals, which are beneficial for relieving HS damage and maintaining the function of CMVECs. Akt activation also promoted HSF-1 that regulates the expression of Hsp70, which is known to assist Hsp90′s molecular chaperone function and when released to the extracellular liquid to protect myocardial cells from HS damage. To the best of our knowledge, this is the first study to show that HS damages CMVECs and the protection mechanism of Hsp90 on it, and that ASA provides a new potential strategy for regulating cardiac microcirculation preventing HS-induced heart failure.

Noncoding RNAs in Vascular Aging

Increases in age are accompanied by vascular aging, which can lead to a variety of chronic diseases, including atherosclerosis and hypertension. Noncoding RNAs (ncRNAs) have become a research hotspot in different fields of life sciences in recent years. For example, these molecules have been found to have regulatory roles in many physiological and pathological processes. Many studies have shown that microRNAs (miRNAs) and long ncRNAs (lncRNAs) also play a regulatory role in vascular aging. Endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) are important components of blood vessels, and the senescence of both cell types promotes the occurrence of vascular aging. This review provides a contemporary update on the molecular mechanisms underlying the senescence of ECs and VSMCs and the regulatory role of miRNAs and lncRNAs in this process.

Endothelial Aldehyde Dehydrogenase 2 as a Target to Maintain Vascular Wellness and Function in Ageing

Endothelial cells are the main determinants of vascular function, since their dysfunction in response to a series of cardiovascular risk factors is responsible for disease progression and further consequences. Endothelial dysfunction, if not resolved, further aggravates the oxidative status and vessel wall inflammation, thus igniting a vicious cycle. We have furthermore to consider the physiological manifestation of vascular dysfunction and chronic low-grade inflammation during ageing, also known as inflammageing. Based on these considerations, knowledge of the molecular mechanism(s) responsible for endothelial loss-of-function can be pivotal to identify novel targets of intervention with the aim of maintaining endothelial wellness and vessel trophism and function. In this review we have examined the role of the detoxifying enzyme aldehyde dehydrogenase 2 (ALDH2) in the maintenance of endothelial function. Its impairment indeed is associated with oxidative stress and ageing, and in the development of atherosclerosis and neurodegenerative diseases. Strategies to improve its expression and activity may be beneficial in these largely diffused disorders.

Where Metabolism Meets Senescence: Focus on Endothelial Cells

Despite the decline in their proliferative potential, senescent cells display a high metabolic activity. Senescent cells have been shown to acquire a more glycolytic state even in presence of high oxygen levels, in a way similar to cancer cells. The diversion of pyruvate, the final product of glycolysis, away from oxidative phosphorylation results in an altered bioenergetic state and may occur as a response to the enhanced oxidative stress caused by the accumulation of dysfunctional mitochondria. This metabolic shift leads to increased AMP/ATP and ADP/ATP ratios, to the subsequent AMPK activation, and ultimately to p53-mediated growth arrest. Mounting evidences suggest that metabolic reprogramming is critical to direct considerable amounts of energy toward specific activities related to the senescent state, including the senescence-associated secretory phenotype (SASP) and the modulation of immune responses within senescent cell tissue microenvironment. Interestingly, despite the relative abundance of oxygen in the vascular compartment, healthy endothelial cells (ECs) produce most of their ATP content from the anaerobic conversion of glucose to lactate. Their high glycolytic rate further increases during senescence. Alterations in EC metabolism have been identified in age-related diseases (ARDs) associated with a dysfunctional vasculature, including atherosclerosis, type 2 diabetes and cardiovascular diseases. In particular, higher production of reactive oxygen species deriving from a variety of enzymatic sources, including uncoupled endothelial nitric oxide synthase and the electron transport chain, causes DNA damage and activates the NAD+-consuming enzymes polyADP-ribose polymerase 1 (PARP1). These non-physiological mechanisms drive the impairment of the glycolytic flux and the diversion of glycolytic intermediates into many pathological pathways. Of note, accumulation of senescent ECs has been reported in the context of ARDs. Through their pro-oxidant, pro-inflammatory, vasoconstrictor, and prothrombotic activities, they negatively impact on vascular physiology, promoting both the onset and development of ARDs. Here, we review the current knowledge on the cellular senescence-related metabolic changes and their contribution to the mechanisms underlying the pathogenesis of ARDs, with a particular focus on ECs. Moreover, current and potential interventions aimed at modulating EC metabolism, in order to prevent or delay ARD onset, will be discussed.

ASK1 Mediates Apoptosis and Autophagy during oxLDL-CD36 Signaling in Senescent Endothelial Cells

Vessel damage by oxidized low-density lipoprotein (oxLDL) increases reactive oxygen species (ROS) and the membrane receptor cluster of differentiation 36 (CD36), involving various vascular pathological processes. In this study, the role of apoptosis signal-regulating kinase 1 (ASK1) as a cellular effector via the oxLDL-CD36 signaling axis, and its related mechanism as a downstream responder of CD36, was investigated in senescent human aortic endothelial cells (HAECs). To inhibit oxLDL-triggered vascular damage, HAECs and monocytes were treated with the CD36-neutralizing antibody or the ASK1 inhibitor NQDI-1. The oxLDL-triggered increases in ROS and CD36 elevated active ASK1 in the senescent HAECs. The ROS increase induced apoptosis, whereas CD36 neutralization or ASK1 inhibition protected against cell death. The blocking of CD36 increased senescent HAEC autophagy. In monocytes, oxLDL also induced CD36 expression and autophagy, the latter of which still occurred following ASK1 inhibition but not after CD36 neutralization. These findings suggest that oxLDL exposure activates ASK1, as a CD36 downstream responder, to accelerate apoptosis, particularly in senescent HAECs. ASK1's involvement in monocytic autophagy was due to endoplasmic reticulum stress resulting from the oxLDL load, suggesting that oxLDL loading on aged vessels causes atherosclerotic endothelial dysfunction mediated by active ASK1.

Autoantibodies against AT1 Receptor Contribute to Vascular Aging and Endothelial Cell Senescence

Vascular aging predisposes the elderly to the progression of many aging-related vascular disorders and leads to deterioration of cardiovascular diseases (CVD). However, the underlying mechanisms have not been clearly elucidated. Agonistic autoantibodies against angiotensin II type 1 (AT1) receptor (AT1-AAs) have been demonstrated to be pro-inflammatory and contribute to the progression of atherosclerosis. However, the association between AT1-AAs and vascular aging has not been defined. Peripheral arterial disease (PAD) is an acknowledged vascular aging-related disease. In this study, AT1-AAs were detected in the sera of patients with PAD and the positive rate was 44.44% (n=63) vs. 17.46% in non-PAD volunteers (n=63). In addition, case-control analysis showed that AT1-AAs level was positively correlated with PAD. To reveal the causal relationship between AT1-AAs and vascular aging, an AT1-AAs-positive rat model was established by active immunization. The carotid pulse wave velocity was higher, and the aortic endothelium-dependent vasodilatation was attenuated significantly in the immunized rats. Morphological staining showed thickening of the aortic wall. Histological examination showed that levels of the senescent markers were increased in the aortic tissue, mostly located at the endothelium. In addition, purified AT1-AAs-IgGs from both the immunized rats and PAD patients induced premature senescence in cultured human umbilical vein endothelial cells. These effects were significantly blocked by the AT1 receptor blocker. Taken together, our study demonstrates that AT1-AAs contribute to the progression of vascular aging and induce EC senescence through AT1 receptor. AT1-AA is a novel biomarker of vascular aging and aging-related CVD that acts to accelerate EC senescence.

Effects of senescence and angiotensin II on expression and processing of amyloid precursor protein in human cerebral microvascular endothelial cells

The present study was designed to determine the effects of senescence and angiotensin II (Ang II) on expression and processing of amyloid precursor protein (APP) in human brain microvascular endothelial cells (BMECs). Senescence caused a decrease in APP expression thereby resulting in reduced secretion of soluble APPα (sAPPα). In contrast, β-site APP cleaving enzyme (BACE1) expression and production of amyloid β (Aβ)40 were increased in senescent endothelium. Importantly, in senescent human BMECs, treatment with BACE1 inhibitor IV inhibited Aβ generation and increased sAPPα production by enhancing a disintegrin and metalloprotease (ADAM)10 expression. Furthermore, Ang II impaired expression of ADAM10 and significantly reduced generation of sAPPα in senescent human BMECs. This inhibitory effect of Ang II was prevented by treatment with BACE1 inhibitor IV. Our results suggest that impairment of α-processing and shift to amyloidogenic pathway of APP contribute to endothelial dysfunction induced by senescence. Loss of sAPPα in senescent cells treated with Ang II exacerbates detrimental effects of senescence on APP processing. Notably, inhibition of BACE1 has beneficial effects on senescence induced endothelial dysfunction. Reported findings may help to explain contributions of senescent cerebral microvascular endothelium to development of cerebral amyloid angiopathy and Alzheimer’s disease (AD) pathology.

A Unique SUMO-Interacting Motif of Trx2 Is Critical for Its Mitochondrial Presequence Processing and Anti-oxidant Activity

OBJECTIVE

Mitochondrial thioredoxin 2 (Trx2) is a vital mitochondrial redox protein that mediates normal protein thiol reduction and provides electrons to peroxiredoxin 3 (Prx3) to scavenge H2O2 in mitochondria. It has been widely reported that Trx2 deletion in cells or mice generates massive reactive oxygen species (ROS) which have been implicated in many pathological processes. On the contrary, how ROS regulate Trx2 processing and activity remains to be elucidated.

APPROACH AND RESULTS

Here we show that excess ROS induce endothelial cell senescence concomitant with an attenuation of Trx2 processing in which Trx2 presequence [i.e., mitochondrial targeting signal peptide (MTS)] is cleaved to generate a mature form. Mutation analyses indicate that Trx2 processing is mediated by mitochondrial processing peptidase (MPP) and mitochondrial intermediate peptidase (MIP)-recognition sites within the MTS. Interestingly, a mutation at a SUMO- interacting motif (SIM), but not the catalytic sites within the mature Trx2 protein, completely blocks Trx2 processing with no effect on Trx2 mitochondrial targeting. Consistently, chemical inhibition of protein SUMOylation attenuates, while SUMOylation agonist promotes, Trx2 processing. Moreover, we identify the α-MPP subunit is a SUMOylated protein that potentially mediates Trx2-binding and cleavage. Furthermore, the unprocessed form of Trx2-SIM is unable to protect cells from both ROS generation and oxidative stress-induced cellular senescence.

CONCLUSION

Our study reveals that a unique SUMO-interacting motif of Trx2 is critical for its mitochondrial processing and subsequent anti-oxidant/antisenescence activities.

Re-thinking the Etiological Framework of Neurodegeneration

Neurodegenerative diseases are among the leading causes of disability and death worldwide. The disease-related socioeconomic burden is expected to increase with the steadily increasing life expectancy. In spite of decades of clinical and basic research, most strategies designed to manage degenerative brain diseases are palliative. This is not surprising as neurodegeneration progresses "silently" for decades before symptoms are noticed. Importantly, conceptual models with heuristic value used to study neurodegeneration have been constructed retrospectively, based on signs and symptoms already present in affected patients; a circumstance that may confound causes and consequences. Hence, innovative, paradigm-shifting views of the etiology of these diseases are necessary to enable their timely prevention and treatment. Here, we outline four alternative views, not mutually exclusive, on different etiological paths toward neurodegeneration. First, we propose neurodegeneration as being a secondary outcome of a primary cardiovascular cause with vascular pathology disrupting the vital homeostatic interactions between the vasculature and the brain, resulting in cognitive impairment, dementia, and cerebrovascular events such as stroke. Second, we suggest that the persistence of senescent cells in neuronal circuits may favor, together with systemic metabolic diseases, neurodegeneration to occur. Third, we argue that neurodegeneration may start in response to altered body and brain trophic interactions established via the hardwire that connects peripheral targets with central neuronal structures or by means of extracellular vesicle (EV)-mediated communication. Lastly, we elaborate on how lifespan body dysbiosis may be linked to the origin of neurodegeneration. We highlight the existence of bacterial products that modulate the gut-brain axis causing neuroinflammation and neuronal dysfunction. As a concluding section, we end by recommending research avenues to investigate these etiological paths in the future. We think that this requires an integrated, interdisciplinary conceptual research approach based on the investigation of the multimodal aspects of physiology and pathophysiology. It involves utilizing proper conceptual models, experimental animal units, and identifying currently unused opportunities derived from human data. Overall, the proposed etiological paths and experimental recommendations will be important guidelines for future cross-discipline research to overcome the translational roadblock and to develop causative treatments for neurodegenerative diseases.

Nrf2 exerts mixed inflammation and glucose metabolism regulatory effects on murine RAW264.7 macrophages

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a transcription factor that mediates a broad range of cellular antioxidative, detoxification and anti-inflammatory effects. However, the precise mechanism by which Nrf2 regulates inflammation and metabolism in macrophages remains controversial and unclear. To further clarify the roles of Nrf2 in inflammation and glucose metabolism regulation, retrovirus-mediated knockdown of Nrf2 was performed in murine RAW264.7 macrophages, and the cells were stimulated with 100 ng/mL lipopolysaccharide for 24 h for M1 activation. qPCR and western blotting results indicated that Nrf2 knockdown significantly enhanced expression of the inflammatory genes Il1a and Il1b in unstimulated macrophages and increased expression of the inflammatory genes Il1a, Il1b, Il6, Il10, Ccl2, Ccl22, and CD38 but decreased that of Tnfa and Tgfb1 in M1 macrophages. Nrf2 knockdown also significantly elevated IL6 and IL10 secretion by M1 macrophages. Western blotting showed that Nrf2 knockdown reduced iNOS protein levels in resting macrophages and enhanced CD38 protein levels in both resting and M1 macrophages. The differential regulation of these macrophage inflammation and polarization markers by Nrf2 reveals multiple roles for Nrf2 in regulating inflammation in macrophages. Moreover, Nrf2 knockdown increased the Glu4 protein level and decreased AKT and GSK3β protein phosphorylation in M1 macrophages, suggesting multiple roles for Nrf2 in regulating glucose metabolism in macrophages. Overall, our results are the first to demonstrate mixed inflammation and glucose metabolism regulatory effects of Nrf2 in macrophages that may occur independent of its classic function in redox regulation. These findings support the potential of Nrf2 as a therapeutic target for the prevention and treatment of inflammation- and obesity-associated syndromes, including diabetes and atherosclerosis.

The senescent status of endothelial cells affects proliferation, inflammatory profile and SOX2 expression in bone marrow-derived mesenchymal stem cells

Human aging is a physiological process characterized by a chronic low-grade inflammation. Senescence may affect endothelial cells, subsequently involved in the most common age-related diseases (ARDs), as well as mesenchymal stem cells (MSCs) with an impairment of their properties in tissues regeneration. Endothelial cells seem to be able to exert a paracrine effect on BM-MSCs through the secretion of pro-inflammatory factors. This work is aimed to evaluate if the senescent status of human umbilical vein endothelial cells (HUVECs) could affect bone marrow derived MSCs (BM-MSCs) proliferative ability and stemness. HUVECs were cultured until the senescence status. Young (passage 3) and senescent HUVECs (passage 13) were indirectly co-cultured with BM-MSCs for 8 days in order to evaluate the effect of their senescence status on proliferative ability and stemness of MSCs. The co-culture of senescent HUVECs with BM-MSCs was associated with a reduced proliferative ability of BM-MSCs, an enforced pro-inflammatory phenotype of BM-MSCs (increased synthesis of proinflammatory cytokines such as IL-6 and TNF-α) and an increased expression of miR-126a-3p, in association with a significant decrease of SOX2, a stemmness- associated gene, targeted by miR-126a-3p. A more general IPA analysis, revealed as miR-126a-3p also modulates the expression of IRS1, IRS2, IL6ST and PIK3R2, all targets that enforce the hypothesis that senescent endothelial cells may reduce the proliferative ability and the stemness phenotype of bone marrow-derived mesenchymal stem cells.

Expert consensus on clinical assessment and intervention of vascular aging in China (2018)

With the development of geriatric medicine, more and more reported research has found that as humans grow old, their blood vessels also age. Blood vessels are vital components of various organs. Vascular aging is an important physiological and pathological basis for the aging of organs and systems of the human body and is the common pathogenesis of various chronic diseases in the elderly. Early detection of vascular aging and the use of correct methods to delay and treat vascular aging are of great significance to prevent and control chronic diseases in the elderly and to deal with the increasingly serious problems of population aging. For this purpose, this consensus is formulated for use by geriatric doctors and related personnel.

ALDH2 Activity Reduces Mitochondrial Oxygen Reserve Capacity in Endothelial Cells and Induces Senescence Properties

Endothelial cells (ECs) are dynamic cells that turn from growth into senescence, the latter being associated with cellular dysfunction, altered metabolism, and age-related cardiovascular diseases. Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme metabolizing acetaldehyde and other toxic aldehydes, such as 4-hydroxynonenal (4-HNE). In conditions in which lipid peroxidation products and reactive oxygen species (ROS) are accumulated, ECs become dysfunctional and significantly contribute to the progression of vascular-dependent diseases. The aim of the present study has been to investigate whether inhibition of ALDH2 alters endothelial functions together with the impairment of bioenergetic functions, accelerating the acquisition of a senescent phenotype. HUVECs transfected with siRNA targeting ALDH2 or treated with daidzin, an ALDH2 inhibitor, were used in this study. We observed an alteration in cell morphology associated with endothelial dysfunctions. Loss of ALDH2 reduced cell proliferation and migration and increased paracellular permeability. To assess bioenergetic function in intact ECs, extracellular flux analysis was carried out to establish oxygen consumption rates (OCR). We observed a decrease in mitochondrial respiration and reserve capacity that coincided with SA-β-Gal accumulation and an increase in p21 and p53 expression in siALDH2 or daidzin-treated HUVECs. Treatment with N-acetyl-L-cysteine (NAC) reduced endothelial dysfunctions mediated by siALDH2, indicating that oxidative stress downstream to siALDH2 plays an instrumental role. Our results highlight that ALDH2 impairment accelerates the acquisition of a premature senescent phenotype, a change likely to be associated with the observed reduction of mitochondrial respiration and reserve capacity.

Metabolic Stress, Autophagy, and Cardiovascular Aging: from Pathophysiology to Therapeutics

Recent advances in health care have improved the management of cardiometabolic disorders, and prolonged lifespan. However, the ever-rising prevalence of metabolic stress related to obesity (insulin resistance, diabetes, hypertension, and dyslipidemia) has greatly challenged geriatric care. The ubiquitin-proteasome system and autophagy-lysosomal pathways represent two major, yet distinct cellular machineries, for degradation and removal of damaged or long-lived proteins and organelles; the function of which declines with aging. To seek new strategies for cardiovascular aging under various metabolic diseases, it is imperative to understand the precise role for metabolic stress and protein quality control, in particular autophagy, in premature cardiovascular aging. Targeting metabolic stress and autophagy may offer exciting new avenues for the management of cardiovascular aging.

Conserved signaling pathways genetically associated with longevity across the species

Advanced age is an independent risk factor for natural death and common diseases, such as cardiovascular diseases, dementia, and cancers, which are life-threatening and cause disabilities. On the other hand, individual with healthy longevity is a plausible model for successful aging. Thus, search for longevity-associated genes and pathways likely provides a unique approach to understand the genetic mechanisms underlying aging and healthspan, and emerging evidence from model organisms has highlighted the significance of genetic components in longevity. Here we reviewed the uses of model organisms including yeast, ciliate, nematode, arthropod, fish, rodent, and primate as well as human to identify the genetic determinants of longevity and discussed the genetic contributions of conserved longevity pathways, such as adrenergic system, AMPK, insulin/IGF-1, and mTOR signaling pathways.

β-Hydroxybutyrate Prevents Vascular Senescence through hnRNP A1-Mediated Upregulation of Oct4

β-hydroxybutyrate (β-HB) elevation during fasting or caloric restriction is believed to induce anti-aging effects and alleviate aging-related neurodegeneration. However, whether β-HB alters the senescence pathway in vascular cells remains unknown. Here we report that β-HB promotes vascular cell quiescence, which significantly inhibits both stress-induced premature senescence and replicative senescence through p53-independent mechanisms. Further, we identify heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) as a direct binding target of β-HB. β-HB binding to hnRNP A1 markedly enhances hnRNP A1 binding with Octamer-binding transcriptional factor (Oct) 4 mRNA, which stabilizes Oct4 mRNA and Oct4 expression. Oct4 increases Lamin B1, a key factor against DNA damage-induced senescence. Finally, fasting and intraperitoneal injection of β-HB upregulate Oct4 and Lamin B1 in both vascular smooth muscle and endothelial cells in mice in vivo. We conclude that β-HB exerts anti-aging effects in vascular cells by upregulating an hnRNP A1-induced Oct4-mediated Lamin B1 pathway.

Endothelial progenitor cells in age-related vascular remodeling

Accumulating evidence has demonstrated that endothelial progenitor cells (EPCs) could facilitate the reendothelialization of injured arteries by replacing the dysfunctional endothelial cells, thereby suppressing the formation of neointima. Meanwhile, other findings suggest that EPCs may be involved in the pathogenesis of age-related vascular remodeling. This review is presented to summarize the characteristics of EPCs and age-related vascular remodeling. In addition, the role of EPCs in age-related vascular remodeling and possible solutions for improving the therapeutic effects of EPCs in the treatment of age-related diseases are discussed.

Genetic profiling of young and aged endothelial progenitor cells in hypoxia

Age is a major risk factor for diseases caused by ischemic hypoxia, such as stroke and coronary artery disease. Endothelial progenitor cells (EPCs) are the major cells respond to ischemic hypoxia through angiogenesis and vascular remodeling. However, the effect of aging on EPCs and their responses to hypoxia are not well understood. CD34⁺ EPCs were isolated from healthy volunteers and aged by replicative senescence, which was to passage cells until their doubling time was twice as long as the original cells. Young and aged CD34⁺ EPCs were exposed to a hypoxic environment (1% oxygen for 48hrs) and their gene expression profiles were evaluated using gene expression array. Gene array results were confirmed using quantitative polymerase chain reaction, Western blotting, and BALB/c female athymic nude mice hindlimb ischemia model. We identified 115 differentially expressed genes in young CD34⁺ EPCs, 54 differentially expressed genes in aged CD34⁺ EPCs, and 25 common genes between normoxia and hypoxia groups. Among them, the expression of solute carrier family 2 (facilitated glucose transporter), member 1 (SLC2A1) increased the most by hypoxia in young cells. Gene set enrichment analysis indicated the pathways affected by aging and hypoxia most, including genes “response to oxygen levels” in young EPCs and genes involved “chondroitin sulfate metabolic process” in aged cells. Our study results indicate the key factors that contribute to the effects of aging on response to hypoxia in CD34⁺ EPCs. With the potential applications of EPCs in cardiovascular and other diseases, our study also provides insight on the impact of ex vivo expansion might have on EPCs.

3' UTR lengthening as a novel mechanism in regulating cellular senescence

Cellular senescence has been viewed as a tumor suppression mechanism and also as a contributor to individual aging. Widespread shortening of 3' untranslated regions (3' UTRs) in messenger RNAs (mRNAs) by alternative polyadenylation (APA) has recently been discovered in cancer cells. However, the role of APA in the process of cellular senescence remains elusive. Here, we found that hundreds of genes in senescent cells tended to use distal poly(A) (pA) sites, leading to a global lengthening of 3' UTRs and reduced gene expression. Genes that harbor longer 3' UTRs in senescent cells were enriched in senescence-related pathways. Rras2, a member of the Ras superfamily that participates in multiple signal transduction pathways, preferred longer 3' UTR usage and exhibited decreased expression in senescent cells. Depletion of Rras2 promoted senescence, while rescue of Rras2 reversed senescence-associated phenotypes. Mechanistically, splicing factor TRA2B bound to a core "AGAA" motif located in the alternative 3' UTR of Rras2, thereby reducing the RRAS2 protein level and causing senescence. Both proximal and distal poly(A) signals showed strong sequence conservation, highlighting the vital role of APA regulation during evolution. Our results revealed APA as a novel mechanism in regulating cellular senescence.

Endothelial transplantation rejuvenates aged hematopoietic stem cell function

Age-related changes in the hematopoietic compartment are primarily attributed to cell-intrinsic alterations in hematopoietic stem cells (HSCs); however, the contribution of the aged microenvironment has not been adequately evaluated. Understanding the role of the bone marrow (BM) microenvironment in supporting HSC function may prove to be beneficial in treating age-related functional hematopoietic decline. Here, we determined that aging of endothelial cells (ECs), a critical component of the BM microenvironment, was sufficient to drive hematopoietic aging phenotypes in young HSCs. We used an ex vivo hematopoietic stem and progenitor cell/EC (HSPC/EC) coculture system as well as in vivo EC infusions following myelosuppressive injury in mice to demonstrate that aged ECs impair the repopulating activity of young HSCs and impart a myeloid bias. Conversely, young ECs restored the repopulating capacity of aged HSCs but were unable to reverse the intrinsic myeloid bias. Infusion of young, HSC-supportive BM ECs enhanced hematopoietic recovery following myelosuppressive injury and restored endogenous HSC function in aged mice. Coinfusion of young ECs augmented aged HSC engraftment and enhanced overall survival in lethally irradiated mice by mitigating damage to the BM vascular microenvironment. These data lay the groundwork for the exploration of EC therapies that can serve as adjuvant modalities to enhance HSC engraftment and accelerate hematopoietic recovery in the elderly population following myelosuppressive regimens.

The Antioxidant Machinery of Young and Senescent Human Umbilical Vein Endothelial Cells and Their Microvesicles

We examine the antioxidant role of young and senescent human umbilical vein endothelial cells (HUVECs) and their microvesicles (MVs). Proteomic and Western blot studies have shown young HUVECs to have a complete and well-developed antioxidant system. Their MVs also contain antioxidant molecules, though of a smaller and more specific range, specialized in the degradation of hydrogen peroxide and the superoxide anion via the thioredoxin-peroxiredoxin system. Senescence was shown to be associated with a large increase in the size of the antioxidant machinery in both HUVECs and their MVs. These responses might help HUVECs and their MVs deal with the more oxidising conditions found in older cells. Functional analysis confirmed the antioxidant machinery of the MVs to be active and to increase in size with senescence. No glutathione or nonpeptide antioxidant (ascorbic acid and vitamin E) activity was detected in the MVs. Endothelial cells and MVs seem to adapt to higher ROS concentrations in senescence by increasing their antioxidant machinery, although this is not enough to recover completely from the senescence-induced ROS increase. Moreover, MVs could be involved in the regulation of the blood plasma redox status by functioning as ROS scavengers.

Catheter Failure and Mortality in Hemodialysis Patients with Tunneled Cuffed Venous Catheters in a Single Center

Background: As of now, only a few studies have focused on the failure of tunneled cuffed venous catheter (tCVC) and mortality of hemodialysis (HD) patients using tCVC as long-term vascular access, whose vascular condition for arteriovenous fistula was not very satisfactory. In this study, we aimed to provide information about the first tCVC failure and survival rates of patients in this population. Methods: Fifty-nine patients who used tCVC from January 1, 2009 to December 31, 2014 in our HD center were analyzed in this retrospective study and followed up either until their death or until December 31, 2015. The first tCVC and patient survival rates were analyzed. Results: The incidence of catheter-related infections was 0.3 per 1,000 patient-days. The median survival duration of first tCVC was 45.0 (95% CI 29.3-69.7) months and the median survival time of all patients was 56.3 (95% CI 34.1-78.5) months by Kaplan-Meier analysis. Advanced age (hazard ratio [HR] 1.055, p < 0.05) and diabetic mellitus (HR 4.147, p < 0.05) at the initiation of HD were significant risk factors of first tCVC failure, while male (HR 2.712, p < 0.05) and cardiovascular diseases (CVDs; HR 4.139, p < 0.05) were significant risk factors for patient mortality as deduced by Cox proportional hazards methods. Conclusions: The study highlighted that first tCVC survival rates and patient survival rates were high in HD patients who were using tCVCs as long-term vascular access, with low incidence of catheter-related infections. In the study it was found that advanced age and diabetic mellitus at the initiation of HD influenced first tCVC failure, whereas male and CVDs seemed to be risk factors for patient mortality.

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.

Serum from Varicose Patients Induces Senescence-Related Dysfunction of Vascular Endothelium Generating Local and Systemic Proinflammatory Conditions

Although the role of endothelium in varicose vein development is indisputable, the effect of the pathology on biological properties of endothelial cells remains unclear. Here we examined if the presence of varicose veins affects senescence of endothelial cells (HUVECs) and, if so, what will be the local and systemic outcome of this effect. Experiments showed that HUVECs subjected to serum from varicose patients display improved proliferation, increased expression of senescence marker, SA-β-Gal, and increased generation of reactive oxygen species (ROS), as compared with serum from healthy donors. Both increased SA-β-Gal activity and ROS release were mediated by TGF-β1, the concentration of which in varicose serum was elevated and the activity of which in vitro was prevented using specific neutralizing antibody. Senescent HUVECs exposed to varicose serum generated increased amounts of ICAM-1, VCAM-1, P-selectin, uPA, PAI-1, and ET-1. Direct comparison of sera from varicose and healthy donors showed that pathological serum contained increased level of ICAM-1, VCAM-1, P-selectin, uPA, and ET-1. Calendar age of healthy subjects correlated positively with serum uPA and negatively with P-selectin. Age of varicose patients correlated positively with ICAM-1, VCAM-1, and ET-1. Collectively, our findings indicate that the presence of varicose veins causes a senescence-related dysfunction of vascular endothelium, which leads to the development of local and systemic proinflammatory environment.

Age-associated downregulation of vasohibin-1 in vascular endothelial cells

Vasohibin-1 (VASH1) is an angiogenesis-inhibiting factor synthesized by endothelial cells (ECs) and it also functions to increase stress tolerance of ECs, which function is critical for the maintenance of vascular integrity. Here, we examined whether the expression of VASH1 would be affected by aging. We passaged human umbilical vein endothelial cells (HUVECs) and observed that VASH1 was downregulated in old HUVECs. This decrease in VASH1 expression with aging was confirmed in mice. To explore the mechanism of this downregulation, we compared the expression of microRNAs between old and young HUVECs by performing microarray analysis. Among the top 20 microRNAs that were expressed at a higher level in old HUVECs, the third highest microRNA, namely miR-22-3p, had its binding site on the 3' UTR of VASH1 mRNA. Experiments with microRNA mimic and anti-miR revealed that miR-22-3p was involved at least in part in the downregulation of VASH1 in ECs during replicative senescence. We then clarified the significance of this defective expression of VASH1 in the vasculature. When a cuff was placed around the femoral arteries of wild-type mice and VASH1-null mice, neointimal formation was augmented in the VASH1-null mice accompanied by an increase in adventitial angiogenesis, macrophage accumulation in the adventitia, and medial/neointimal proliferating cells. These results indicate that in replicative senescence, the downregulation of VASH1 expression in ECs was caused, at least in part, by the alteration of microRNA expression. Such downregulation of VASH1 might be involved in the acceleration of age-associated vascular diseases.

Substrate Stiffness Combined with Hepatocyte Growth Factor Modulates Endothelial Cell Behavior

Endothelial cells (ECs) play a crucial role in regulating various physiological and pathological processes. The behavior of ECs is modulated by physical (e.g., substrate stiffness) and biochemical cues (e.g., growth factors). However, the synergistic influence of these cues on EC behavior has rarely been investigated. In this study, we constructed poly(l-lysine)/hyaluronan (PLL/HA) multilayer films with different stiffness and exposed ECs to these substrates with and without hepatocyte growth factor (HGF)-supplemented culture medium. We demonstrated that EC adhesion, migration, and proliferation were positively correlated with substrate stiffness and that these behaviors were further promoted by HGF. Interestingly, ECs on the lower stiffness substrates showed stronger responses to HGF in terms of migration and proliferation, suggesting that HGF can profoundly influence stiffness-dependent EC behavior correlated with EC growth. After the formation of an EC monolayer, EC behaviors correlated with endothelial function were evaluated by characterizing monolayer integrity, nitric oxide production, and gene expression of endothelial nitric oxide synthase. For the first time, we demonstrated that endothelial function displayed a negative correlation with substrate stiffness. Although HGF improved endothelial function, HGF was not able to change the stiffness-dependent manner of endothelial functions. Taken together, this study provides insights into the synergetic influence of physical and biochemical cues on EC behavior and offers great potential in the development of optimized biomaterials for EC-based regenerative medicine.

Senescent endothelial cells: Potential modulators of immunosenescence and ageing

Recent studies have demonstrated that the accumulation of senescent endothelial cells may be the primary cause of cardiovascular diseases. Because of their multifunctional properties, endothelial cells actively take part in stimulating the immune system and inflammation. In addition, ageing is characterized by the progressive deterioration of immune cells and a decline in the activation of the immune response. This results in a loss of the primary function of the immune system, which is eliminating damaged/senescent cells and neutralizing potential sources of harmful inflammatory reactions. In this review, we discuss cellular senescence and the senescence-associated secretory phenotype (SASP) of endothelial cells and summarize the link between endothelial cells and immunosenescence. We describe the possibility that age-related changes in Toll-like receptors (TLRs) and microRNAs can affect the phenotypes of senescent endothelial cells and immune cells via a negative feedback loop aimed at restraining the excessive pro-inflammatory response. This review also addresses the following questions: how do senescent endothelial cells influence ageing or age-related changes in the inflammatory burden; what is the connection between ECs and immunosenescence, and what are the crucial hypothetical pathways linking endothelial cells and the immune system during ageing.

Mutant LRP6 Impairs Endothelial Cell Functions Associated with Familial Normolipidemic Coronary Artery Disease

Mutations in the genes low-density lipoprotein (LDL) receptor-related protein-6 (LRP6) and myocyte enhancer factor 2A (MEF2A) were reported in families with coronary artery disease (CAD). We intend to determine the mutational spectrum of these genes among hyperlipidemic and normolipidemic CAD families. Forty probands with early-onset CAD were recruited from 19 hyperlipidemic and 21 normolipidemic Chinese families. We sequenced all exons and intron-exon boundaries of LRP6 and MEF2A, and found a novel heterozygous variant in LRP6 from a proband with normolipidemic CAD. This variant led to a substitution of histidine to tyrosine (Y418H) in an evolutionarily conserved domain YWTD in exon 6 and was not found in 1025 unrelated healthy individuals. Co-segregated with CAD in the affected family, LRP6Y418H significantly debilitated the Wnt3a-associated signaling pathway, suppressed endothelial cell proliferation and migration, and decreased anti-apoptotic ability. However, it exhibited no influences on low-density lipoprotein cholesterol uptake. Thus, mutation Y418H in LRP6 likely contributes to normolipidemic familial CAD via impairing endothelial cell functions and weakening the Wnt3a signaling pathway.

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.

New Insights into the Role of Autophagy in Ovarian Cryopreservation by Vitrification

Ovarian cryopreservation by vitrification is a highly useful method for preserving female fertility during radiotherapy and chemotherapy. However, cryoinjury, osmotic stress during vitrification, and ischemia/reperfusion during transplantation lead to loss of ovarian follicles. Ovarian follicle loss may be partially reduced by several methods; however, studies regarding the mechanism of ovarian follicle loss have only investigated cell apoptosis, which consists of type I programmed cell death. Autophagy is type II programmed cell death, and cell homeostasis is maintained by autophagy during conditions of stress. The role of autophagy during cryopreservation by vitrification has rarely been reported. The potential role of autophagy during ovarian cryopreservation by vitrification is reviewed in this article.

Molecular and biological hallmarks of ageing

BACKGROUND

Ageing is the inevitable time-dependent decline in physiological organ function that eventually leads to death. Age is a major risk factor for many of the most common medical conditions, such as cardiovascular disease, cancer, diabetes and Alzheimer's disease. This study reviews currently known hallmarks of ageing and their clinical implications.

METHODS

A literature search of PubMed/MEDLINE was conducted covering the last decade.

RESULTS

Average life expectancy has increased dramatically over the past century and is estimated to increase even further. Maximum longevity, however, appears unchanged, suggesting a universal limitation to the human organism. Understanding the underlying molecular processes of ageing and health decline may suggest interventions that, if used at an early age, can prevent, delay, alleviate or even reverse age-related diseases. Hallmarks of ageing can be grouped into three main categories. The primary hallmarks cause damage to cellular functions: genomic instability, telomere attrition, epigenetic alterations and loss of proteostasis. These are followed by antagonistic responses to such damage: deregulated nutrient sensing, altered mitochondrial function and cellular senescence. Finally, integrative hallmarks are possible culprits of the clinical phenotype (stem cell exhaustion and altered intercellular communication), which ultimately contribute to the clinical effects of ageing as seen in physiological loss of reserve, organ decline and reduced function.

CONCLUSION

The sum of these molecular hallmarks produces the clinical picture of the elderly surgical patient: frailty, sarcopenia, anaemia, poor nutrition and a blunted immune response system. Improved understanding of the ageing processes may give rise to new biomarkers of risk or prognosis, novel treatment targets and translational approaches across disciplines that may improve outcomes.

MicroRNA-33 promotes the replicative senescence of mouse embryonic fibroblasts by suppressing CDK6

MicroRNAs are a large class of tiny noncoding RNAs, which have emerged as critical regulators of gene expression, and thus are involved in multiple cellular processes, including cellular senescence. MicroRNA-33 has previously been established to exert crucial effect on cell proliferation, lipid metabolism and cholesterol metabolism. Nonetheless, the association between microRNA-33 and cellular senescence and its underlying molecular mechanism are far to be elucidated. The present study has attempted to probe into the effect of microRNA-33 on MEFs senescence. Our data unveiled that microRNA-33 was dramatically down-regulated in senescent MEFs compared to the young MEFs, and ectopic expression of microRNA-33 promoted MEFs senescence, while knock-down of microRNA-33 exhibited a protective effect against senescence phenotype. Moreover, we verified CDK6 as a direct target of microRNA-33 in mouse. Silencing of CDK6 induced the premature senescence phenotype of MEFs similarly as microRNA-33, while enforced expression of CDK6 significantly reverse the senescence-induction effect of microRNA-33. Taken together, our results suggested that microRNA-33 enhanced the replicative senescence of MEFs potentially by suppressing CDK6 expression.

Endothelial progenitor cells (EPCs) in ageing and age-related diseases: How currently available treatment modalities affect EPC biology, atherosclerosis, and cardiovascular outcomes

Endothelial progenitor cells (EPCs) are mononuclear cells that circulate in the blood and are derived from different tissues, expressing cell surface markers that are similar to mature endothelial cells. The discovery of EPCs has lead to new insights in vascular repair and atherosclerosis and also a new theory for ageing. EPCs from the bone marrow and some other organs aid in vascular repair by migrating to distant vessels where they differentiate into mature endothelial cells and replace old and injured endothelial cells. The ability of EPCs to repair vascular damage depends on their number and functionality. Currently marketed drugs used in a variety of diseases can modulate these characteristics. In this review, the effect of currently available treatment options for cardiovascular and metabolic disorders on EPC biology will be discussed. The various EPC-based therapies that will be discussed include lipid-lowering agents, antihypertensive agents, antidiabetic drugs, phosphodiesteraze inhibitors, hormones, as well as EPC capturing stents.

The role of oxysterols in vascular ageing

The ageing endothelium progressively loses its remarkable and crucial ability to maintain homeostasis of the vasculature, as it acquires a proinflammatory phenotype. Cellular and structural changes gradually accumulate in the blood vessels, and markedly in artery walls. Most changes in aged arteries are comparable to those occurring during the atherogenic process, the latter being more marked: pro-oxidant and proinflammatory molecules, mainly deriving from or triggered by oxidized low density lipoproteins (oxLDLs), are undoubtedly a major driving force of this process. Oxysterols, quantitatively relevant components of oxLDLs, are likely candidate molecules in the pathogenesis of vascular ageing, because of their marked pro-oxidant, proinflammatory and proapoptotic properties. An increasing bulk of experimental data point to the contribution of a variety of oxysterols of pathophysiological interest, also in the age-related genesis of endothelium dysfunction, intimal thickening due to lipid accumulation, and smooth muscle cell migration and arterial stiffness due to increasing collagen deposition and calcification. This review provides an updated analysis of the molecular mechanisms whereby oxysterols accumulating in the wall of ageing blood vessels may 'activate' endothelial and monocytic cells, through expression of an inflammatory phenotype, and 'convince' smooth muscle cells to proliferate, migrate and, above all, to act as fibroblast-like cells.

Systemic Vascular Transduction by Capsid Mutant Adeno-Associated Virus After Intravenous Injection

The ability to effectively deliver genetic material to vascular endothelial cells remains one of the greatest unmet challenges facing the development of gene therapies to prevent diseases with underlying vascular etiology, such as diabetes, atherosclerosis, and age-related macular degeneration. Herein, we assess the effectiveness of an rAAV2-based capsid mutant vector (Y272F, Y444F, Y500F, Y730F, T491V; termed QuadYF+TV) with strong endothelial cell tropism at transducing the vasculature after systemic administration. Intravenous injection of QuadYF+TV resulted in widespread transduction throughout the vasculature of several major organ systems, as assessed by in vivo bioluminescence imaging and postmortem histology. Robust transduction of lung tissue was observed in QuadYF+TV-injected mice, indicating a role for intravenous gene delivery in the treatment of chronic diseases presenting with pulmonary complications, such as α1-antitrypsin deficiency. The QuadYF+TV vector cross-reacted strongly with AAV2 neutralizing antibodies, however, indicating that a targeted delivery strategy may be required to maximize clinical translatability.

Klotho, stem cells, and aging

Aging is an inevitable and progressive biological process involving dysfunction and eventually destruction of every tissue and organ. This process is driven by a tightly regulated and complex interplay between genetic and acquired factors. Klotho is an antiaging gene encoding a single-pass transmembrane protein, klotho, which serves as an aging suppressor through a wide variety of mechanisms, such as antioxidation, antisenescence, antiautophagy, and modulation of many signaling pathways, including insulin-like growth factor and Wnt. Klotho deficiency activates Wnt expression and activity contributing to senescence and depletion of stem cells, which consequently triggers tissue atrophy and fibrosis. In contrast, the klotho protein was shown to suppress Wnt-signaling transduction, and inhibit cell senescence and preserve stem cells. A better understanding of the potential effects of klotho on stem cells could offer novel insights into the cellular and molecular mechanisms of klotho deficiency-related aging and disease. The klotho protein may be a promising therapeutic agent for aging and aging-related disorders.

Imaging of cellular aging in human retinal blood vessels

To date two main aging vascular lesions have been reported in elderly human retinas: acellular capillaries and microaneurysms. However, their exact mechanism of formation remains unclear. Using high resolution microscopy techniques we revise cellular alterations observed in aged human retinal vessels, such as lipofuscin accumulation, caveolae malfunction, blood basement membrane disruption and enhanced apoptosis that could trigger the development of these aging vascular lesions. Moreover, we have generated a set of original images comparing retinal vasculature between middle and old aged healthy humans to show in a comprehensive manner the main structural and ultrastructural alterations occurred during age in retinal blood vessels.