Cellular and molecular mechanisms of stress-induced premature senescence (SIPS) of human diploid fibroblasts and melanocytes

Cr(VI) induces premature senescence through ROS-mediated p53 pathway in L-02 hepatocytes

Hexavalent Chromium [Cr(VI)], which can be found of various uses in industries such as metallurgy and textile dying, can cause a number of human disease including inflammation and cancer. Unlike previous research that focused on Cr(VI)-induced oxidative damage and apoptosis, this study placed emphasis on premature senescence that can be induced by low-dose and long-term Cr(VI) exposure. We found Cr(VI) induced premature senescence in L-02 hepatocytes, as confirmed by increase in senescence associated-β-galactosidase (SA-β-Gal) activity. Cr(VI) stabilized p53 through phosphorylation at Ser15 and increased expression of p53-transcriptional target p21. Mechanism study revealed Cr(VI) targeted and inhibited mitochondrial respiratory chain complex (MRCC) I and II to enhance reactive oxygen species (ROS) production. By applying antioxidant Trolox, we also confirmed that ROS mediated p53 activation. A tetracycline-inducible lentiviral expression system containing shRNA to p53 was used to knockout p53. We found p53 could inhibit pro-survival genes B-cell lymphoma-2 (Bcl-2), myeloid leukemia-1 (Mcl-1) and S phase related cell cycle proteins cyclin-dependent kinase 2 (CDK2), Cyclin E to induce premature senescence, and the functional role of ROS in Cr(VI)-induced premature senescence is depend on p53. The results suggest that Cr(VI) has a role in premature senescence by promoting ROS-dependent p53 activation in L-02 hepatocytes.

A steroid like phytochemical Antcin M is an anti-aging reagent that eliminates hyperglycemia-accelerated premature senescence in dermal fibroblasts by direct activation of Nrf2 and SIRT-1

The present study revealed the anti-aging properties of antcin M (ANM) and elucidated the molecular mechanism underlying the effects. We found that exposure of human normal dermal fibroblasts (HNDFs) to high-glucose (HG, 30 mM) for 3 days, accelerated G0/G1 phase arrest and senescence. Indeed, co-treatment with ANM (10 µM) significantly attenuated HG-induced growth arrest and promoted cell proliferation. Further molecular analysis revealed that ANM blocked the HG-induced reduction in G1-S transition regulatory proteins such as cyclin D, cyclin E, CDK4, CDK6, CDK2 and protein retinoblastoma (pRb). In addition, treatment with ANM eliminated HG-induced reactive oxygen species (ROS) through the induction of anti-oxidant genes, HO-1 and NQO-1 via transcriptional activation of Nrf2. Moreover, treatment with ANM abolished HG-induced SIPS as evidenced by reduced senescence-associated β-galactosidase (SA-β-gal) activity. This effect was further confirmed by reduction in senescence-associated marker proteins including, p21CIP1, p16INK4A, and p53/FoxO1 acetylation. Also, the HG-induced decline in aging-related marker protein SMP30 was rescued by ANM. Furthermore, treatment with ANM increased SIRT-1 expression, and prevented SIRT-1 depletion. This protection was consistent with inhibition of SIRT-1 phosphorylation at Ser47 followed by blocking its upstream kinases, p38 MAPK and JNK/SAPK. Further analysis revealed that ANM partially protected HG-induced senescence in SIRT-1 silenced cells. A similar effect was also observed in Nrf2 silenced cells. However, a complete loss of protection was observed in both Nrf2 and SIRT-1 knockdown cells suggesting that both induction of Nrf2-mediated anti-oxidant defense and SIRT-1-mediated deacetylation activity contribute to the anti-aging properties of ANM in vitro. Result of in vivo studies shows that ANM-treated C. elegens exhibits an increased survival rate during HG-induced oxidative stress insult. Furthermore, ANM significantly extended the life span of C. elegans. Taken together, our results suggest the potential application of ANM in age-related diseases or as a preventive reagent against aging process.

Low doses of X-rays induce prolonged and ATM-independent persistence of γH2AX foci in human gingival mesenchymal stem cells

Diagnostic imaging delivering low doses of radiation often accompany human mesenchymal stem cells (MSCs)-based therapies. However, effects of low dose radiation on MSCs are poorly characterized. Here we examine patterns of phosphorylated histone H2AX (γH2AX) and phospho-S1981 ATM (pATM) foci formation in human gingiva-derived MSCs exposed to X-rays in time-course and dose-response experiments. Both γH2AX and pATM foci accumulated linearly with dose early after irradiation (5–60 min), with a maximum induction observed at 30–60 min (37 ± 3 and 32 ± 3 foci/cell/Gy for γH2AX and pATM, respectively). The number of γH2AX foci produced by intermediate doses (160 and 250 mGy) significantly decreased (40–60%) between 60 and 240 min post-irradiation, indicating rejoining of DNA double-strand breaks. In contrast, γH2AX foci produced by low doses (20–80 mGy) did not change after 60 min. The number of pATM foci between 60 and 240 min decreased down to control values in a dose-independent manner. Similar kinetics was observed for pATM foci co-localized with γH2AX foci. Collectively, our results suggest differential DNA double-strand break signaling and processing in response to low vs. intermediate doses of X-rays in human MSCs. Furthermore, mechanisms governing the prolonged persistence of γH2AX foci in these cells appear to be ATM-independent.

Accelerated leukocyte telomere erosion in schizophrenia: Evidence from the present study and a meta-analysis

Human telomeres consist of tandem nucleotide repeats (TTAGGG) and associated proteins, and telomere length (TL) is reduced progressively with cell division over the lifespan. Telomere erosion might be accelerated or prevented to varying degrees when exposure to serious medical illnesses. In previous studies, an association between TL decrease and schizophrenia has been extensively reported; however, the results remain largely controversial. To further investigate TL in schizophrenia patients and reconcile this controversy, we first measured leucocyte TL (LTL) in our samples (52 paranoid schizophrenia, 89 non-paranoid patients and 120 controls), and then conducted a comprehensive meta-analysis of the existing results of LTL in patients of schizophrenia compared to healthy subjects. Totally, 11 studies encompassing 1243 patients of schizophrenia and 1274 controls were included in the final meta-analysis model. In our samples, significant reduction of LTL in paranoid schizophrenia was observed compared to controls (F = 50.88, P < 0.001); whereas there was no significant difference in LTL between non-paranoid schizophrenia and controls (F = 0.842, P = 0.360). For meta-analysis, random-effects model showed significant LTL decrease in patients of schizophrenia when compared to controls (Z = 2.07, P = 0.039, SMD = -0.48, 95% CI = -0.94 to -0.03). Moreover, a marginal decrease in LTL was observed in medicated patients (Z = 1.92, P = 0.055, SMD = -0.58, 95% CI = -1.18-0.01) and those patients with poor response to antipsychotics (Z = 1.76, P = 0.078, SMD = -0.60, 95% CI = -1.27-0.07). In conclusion, we observed significant reduction of LTL in individuals with schizophrenia compared with controls. However, all the studies included in the meta-analysis were cross-sectional, and better controlled long-term studies are needed to replicate this result.

Biomarkers to identify and isolate senescent cells

Aging is the main risk factor for many degenerative diseases and declining health. Senescent cells are part of the underlying mechanism for time-dependent tissue dysfunction. These cells can negatively affect neighbouring cells through an altered secretory phenotype: the senescence-associated secretory phenotype (SASP). The SASP induces senescence in healthy cells, promotes tumour formation and progression, and contributes to other age-related diseases such as atherosclerosis, immune-senescence and neurodegeneration. Removal of senescent cells was recently demonstrated to delay age-related degeneration and extend lifespan. To better understand cell aging and to reap the benefits of senescent cell removal, it is necessary to have a reliable biomarker to identify these cells. Following an introduction to cellular senescence, we discuss several classes of biomarkers in the context of their utility in identifying and/or removing senescent cells from tissues. Although senescence can be induced by a variety of stimuli, senescent cells share some characteristics that enable their identification both in vitro and in vivo. Nevertheless, it may prove difficult to identify a single biomarker capable of distinguishing senescence in all cell types. Therefore, this will not be a comprehensive review of all senescence biomarkers but rather an outlook on technologies and markers that are most suitable to identify and isolate senescent cells.

Conserved genes and pathways in primary human fibroblast strains undergoing replicative and radiation induced senescence

Background

Cellular senescence is induced either internally, for example by replication exhaustion and cell division, or externally, for example by irradiation. In both cases, cellular damages accumulate which, if not successfully repaired, can result in senescence induction. Recently, we determined the transcriptional changes combined with the transition into replicative senescence in primary human fibroblast strains. Here, by γ-irradiation we induced premature cellular senescence in the fibroblast cell strains (HFF and MRC-5) and determined the corresponding transcriptional changes by high-throughput RNA sequencing.

Results

Comparing the transcriptomes, we found a high degree of similarity in differential gene expression in replicative as well as in irradiation induced senescence for both cell strains suggesting, in each cell strain, a common cellular response to error accumulation. On the functional pathway level, “Cell cycle” was the only pathway commonly down-regulated in replicative and irradiation-induced senescence in both fibroblast strains, confirming the tight link between DNA repair and cell cycle regulation. However, “DNA repair” and “replication” pathways were down-regulated more strongly in fibroblasts undergoing replicative exhaustion. We also retrieved genes and pathways in each of the cell strains specific for irradiation induced senescence.

Conclusion

We found the pathways associated with “DNA repair” and “replication” less stringently regulated in irradiation induced compared to replicative senescence. The strong regulation of these pathways in replicative senescence highlights the importance of replication errors for its induction.

Electronic supplementary material

The online version of this article (doi:10.1186/s40659-016-0095-2) contains supplementary material, which is available to authorized users.

A quantitative model of cellular senescence influence on cancer and longevity

Contrary to the paradigm that cancer incidence increases indefinitely with age, significant data now suggest cancer incidence may markedly reduce beyond age 80 years for humans and beyond 800 days for mice, and is not inevitable. We show that increasing cellular senescence with age is a possible cause of this reduction, since senescent cells are removed from the pool of cells that retain proliferative ability necessary for cancer. We further show that animal interventions appearing to alter senescence, p53 mutation and melatonin dosing, support the prediction that increasing senescence rate reduces cancer while reducing lifespan, and vice versa. Studies of environmental agents associated with increased cancer might be re-examined to find if there is an association with longevity increases, which may markedly alter our view of such agents. We also show that if an agent functions by slowing both senescence and carcinogenesis, longevity is increased while reducing cancer. Dietary restriction is the only known intervention that accomplishes this, but there may be others.

AMPK and HIF signaling pathways regulate both longevity and cancer growth: the good news and the bad news about survival mechanisms

The AMP-activated protein kinase (AMPK) and hypoxia-inducible factor (HIF) signaling pathways are evolutionarily-conserved survival mechanisms responding to two fundamental stresses, energy deficiency and/or oxygen deprivation. The AMPK and HIF pathways regulate the function of a survival network with several transcription factors, e.g. FOXO, NF-κB, NRF2, and p53, as well as with protein kinases and other factors, such as mTOR, ULK1, HDAC5, and SIRT1. Given that AMPK and HIF activation can enhance not only healthspan and lifespan but also cancer growth in a context-dependent manner; it seems that cancer cells can hijack certain survival factors to maintain their growth in harsh conditions. AMPK activation improves energy metabolism, stimulates autophagy, and inhibits inflammation, whereas HIF-1α increases angiogenesis and helps cells to adapt to severe conditions. First we will review how AMPK and HIF signaling mechanisms control the function of an integrated survival network which is able not only to improve the regulation of longevity but also support the progression of tumorigenesis. We will also describe distinct crossroads between the regulation of longevity and cancer, e.g. specific regulation through the AMPKα and HIF-α isoforms, the Warburg effect, mitochondrial dynamics, and cellular senescence.

Cristacarpin promotes ER stress-mediated ROS generation leading to premature senescence by activation of p21(waf-1)

Stress-induced premature senescence (SIPS) is quite similar to replicative senescence that is committed by cells exposed to various stress conditions viz. ultraviolet radiation (DNA damage), hydrogen peroxide (oxidative stress), chemotherapeutic agents (cytotoxic threat), etc. Here, we report that cristacarpin, a natural product obtained from the stem bark of Erythrina suberosa, promotes endoplasmic reticulum (ER) stress, leading to sub-lethal reactive oxygen species (ROS) generation and which eventually terminates by triggering senescence in pancreatic and breast cancer cells through blocking the cell cycle in the G1 phase. The majority of cristacarpin-treated cells responded to conventional SA-β-gal stains; showed characteristic p21(waf1) upregulation along with enlarged and flattened morphology; and increased volume, granularity, and formation of heterochromatin foci-all of these features are the hallmarks of senescence. Inhibition of ROS generation by N-acetyl-L-cysteine (NAC) significantly reduced the expression of p21(waf1), confirming that the modulation in p21(waf1) by anti-proliferative cristacarpin was ROS dependent. Further, the elevation in p21(waf1) expression in PANC-1 and MCF-7 cells was consistent with the decrease in the expression of Cdk-2 and cyclinD1. Here, we provide evidence that cristacarpin promotes senescence in a p53-independent manner. Moreover, cristacarpin treatment induced p38MAPK, indicating the ROS-dependent activation of the MAP kinase pathway, and thus abrogates the tumor growth in mouse allograft tumor model.

AMPK activation protects cells from oxidative stress-induced senescence via autophagic flux restoration and intracellular NAD(+) elevation

AMPK activation is beneficial for cellular homeostasis and senescence prevention. However, the molecular events involved in AMPK activation are not well defined. In this study, we addressed the mechanism underlying the protective effect of AMPK on oxidative stress‐induced senescence. The results showed that AMPK was inactivated in senescent cells. However, pharmacological activation of AMPK by metformin and berberine significantly prevented the development of senescence and, accordingly, inhibition of AMPK by Compound C was accelerated. Importantly, AMPK activation prevented hydrogen peroxide‐induced impairment of the autophagic flux in senescent cells, evidenced by the decreased p62 degradation, GFP‐RFP‐LC3 cancellation, and activity of lysosomal hydrolases. We also found that AMPK activation restored the NAD⁺ levels in the senescent cells via a mechanism involving mostly the salvage pathway for NAD⁺ synthesis. In addition, the mechanistic relationship of autophagic flux and NAD⁺ synthesis and the involvement of mTOR and Sirt1 activities were assessed. In summary, our results suggest that AMPK prevents oxidative stress‐induced senescence by improving autophagic flux and NAD⁺ homeostasis. This study provides a new insight for exploring the mechanisms of aging, autophagy and NAD⁺ homeostasis, and it is also valuable in the development of innovative strategies to combat aging.

Conserved Senescence Associated Genes and Pathways in Primary Human Fibroblasts Detected by RNA-Seq

Cellular senescence correlates with changes in the transcriptome. To obtain a complete view on senescence-associated transcription networks and pathways, we assessed by deep RNA sequencing the transcriptomes of five of the most commonly used laboratory strains of human fibroblasts during their transition into senescence. In a number of cases, we verified the RNA-seq data by real-time PCR. By determining cellular protein levels we observed that the age-related expression of most but not all genes is regulated at the transcriptional level. We found that 78% of the age-affected differentially expressed genes were commonly regulated in the same direction (either up- or down-regulated) in all five fibroblast strains, indicating a strong conservation of age-associated changes in the transcriptome. KEGG pathway analyses confirmed up-regulation of the senescence-associated secretory phenotype and down-regulation of DNA synthesis/repair and most cell cycle pathways common in all five cell strains. Newly identified senescence-induced pathways include up-regulation of endocytotic/phagocytic pathways and down-regulation of the mRNA metabolism and the mRNA splicing pathways. Our results provide an unprecedented comprehensive and deep view into the individual and common transcriptome and pathway changes during the transition into of senescence of five human fibroblast cell strains.

Reflections on the role of senescence during development and aging

New and stimulating results have challenged the concept that cellular senescence might not be synonymous with aging. It is indisputable that during aging, senescent cell accumulation has an impact on organismal health. Nevertheless, senescent cells are now known to display physiological roles during embryonic development, during wound healing repair and as a cellular response to stress. The fact that senescence has been found in cells that did not attain their maximal round of replications, nor have metabolic alterations or DNA damage, also challenges the paradigm that senescence is cellular aging, and it is in favor of the idea that cellular senescence is a phenomenon that has a function by itself. Therefore, in order to understand this phenomenon it is important to analyze the relationship between senescence and other cellular responses that have many features in common, such as apoptosis, cancer and autophagy, particularly highlighting their role during development and adulthood.

Malvidin Protects WI-38 Human Fibroblast Cells Against Stress-induced Premature Senescence

Background:

Malvidin is one of the most abundant components in red wines and black rice. The effects of malvidin on aging and lifespan under oxidative stress have not been fully understood. This study focused on the anti-aging effect of malvidin on stress-induced premature senescence (SIPS) in WI-38 human lung-derived diploid fibroblasts.

Methods:

In order to determine the viability of WI-38 cells, MTT assay was conducted, and malondialdehyde level was determined using thiobarbituric acid-reactive substance assay. Protein expression of inflammation-related factors was also evaluated by Western blot analysis.

Results:

Acute and chronic oxidative stress via hydrogen peroxide (H₂O₂) treatment led to SIPS in WI-38 cells, which showed decreased cell viability, increased lipid peroxidation, and a shortened lifespan in comparison with non-H₂O₂-treated WI-38 cells. However, malvidin treatment significantly attenuated H₂O₂-induced oxidative stress by inhibiting lipid peroxidation and increasing cell viability. Furthermore, the lifespan of WI-38 cells was prolonged by malvidin treatment. In addition, malvidin downregulated the expression of oxidative stress-related proteins, including NF-κB, COX-2, and inducible nitric oxide synthase. Furthermore, protein expression levels of p53, p21, and Bax were also regulated by malvidin treatment in WI-38 cells undergoing SIPS.

Conclusions:

Malvidin may potentially inhibit the aging process by controlling oxidative stress.

Senescence associated secretory phenotype profile from primary lung mice fibroblasts depends on the senescence induction stimuli

Cellular senescence is a multifactorial phenomenon of growth arrest and distorted function, which has been recognized as an important feature during tumor suppression mechanisms and a contributor to aging. Senescent cells have an altered secretion pattern called Senescence-Associated Secretory Phenotype (SASP) that comprises a complex mix of factors including cytokines, growth factors, chemokines, and matrix metalloproteinases. SASP has been related with local inflammation that leads to cellular transformation and neurodegenerative diseases. Various pathways for senescence induction have been proposed; the most studied is replicative senescence due to telomere attrition called replicative senescence (RS). However, senescence can be prematurely achieved when cells are exposed to diverse stimuli such as oxidative stress (stress-induced premature senescence, SIPS) or proteasome inhibition (proteasome inhibition-induced premature senescence, PIIPS). SASP has been characterized in RS and SIPS but not in PIIPS. Hence, our aim was to determine SASP components in primary lung fibroblasts obtained from CD-1 mice induced to senescence by PIIPS and compare them to RS and SIPS. Our results showed important variations in the 62 cytokines analyzed, while SIPS and RS showed an increase in the secretion of most cytokines, and in PIIPS only 13 were incremented. Variations in glutathione-redox balance were also observed in SIPS and RS, and not in PIIPS. All senescence types SASP displayed a pro-inflammatory profile and increased proliferation in L929 mice fibroblasts exposed to SASP. However, the behavior observed was not exactly the same, suggesting that the senescence induction pathway might encompass dissimilar responses in adjacent cells and promote different outcomes.

Defective DNA single-strand break repair is responsible for senescence and neoplastic escape of epithelial cells

The main characteristic of senescence is its stability which relies on the persistence of DNA damage. We show that unlike fibroblasts, senescent epithelial cells do not activate an ATM-or ATR-dependent DNA damage response (DDR), but accumulate oxidative-stress-induced DNA single-strand breaks (SSBs). These breaks remain unrepaired because of a decrease in PARP1 expression and activity. This leads to the formation of abnormally large and persistent XRCC1 foci that engage a signalling cascade involving the p38MAPK and leading to p16 upregulation and cell cycle arrest. Importantly, the default in SSB repair also leads to the emergence of post-senescent transformed and mutated precancerous cells. In human-aged skin, XRCC1 foci accumulate in the epidermal cells in correlation with a decline of PARP1, whereas DDR foci accumulate mainly in dermal fibroblasts. These findings point SSBs as a DNA damage encountered by epithelial cells with aging which could fuel the very first steps of carcinogenesis.

Oxidative stress and age-related changes in T cells: is thalassemia a model of accelerated immune system aging?

Iron overload in β-thalassemia major occurs mainly due to blood transfusion, an essential treatment for β-thalassemia major patients, which results in oxidative stress. It has been thought that oxidative stress causes elevation of immune system senescent cells. Under this condition, cells normally enhance in aging, which is referred to as premature immunosenescence. Because there is no animal model for immunosenescence, most knowledge on the immunosenescence pattern is based on induction of immunosenescence. In this review, we describe iron overload and oxidative stress in β-thalassemia major patients and how they make these patients a suitable human model for immunosenescence. We also consider oxidative stress in some kinds of chronic virus infections, which induce changes in the immune system similar to β-thalassemia major. In conclusion, a therapeutic approach used to improve the immune system in such chronic virus diseases, may change the immunosenescence state and make life conditions better for β-thalassemia major patients.

Suppressive effects of sirtinol on human cytomegalovirus (hCMV) infection and hCMV-induced activation of molecular mechanisms of senescence and production of reactive oxygen species

Substantial evidence suggests that chronic human cytomegalovirus (hCMV) infection contributes significantly to T-cell immunosenescence and adverse health outcomes in older adults. As such, it is important to search for compounds with anti-hCMV properties. Studies have shown that resveratrol, a sirtuin activator, suppresses hCMV infection. Here we report suppressive effects of sirtinol, a sirtuin antagonist, on hCMV infection and its cellular and molecular consequences. Human diploid fibroblast WI-38 cells were infected by hCMV Towne strain in the absence or presence of sirtinol. hCMV replication was measured using qPCR. Senescent phenotype was determined by senescence-associated β galactosidase (SA-β-Gal) activity. Expression of hCMV immediate early (IE) and early (E) proteins and senescence-associated proteins (pRb and Rb, p16(INK4), and p53) and production of reactive oxygen species (ROS) were assessed using standard laboratory assays. The results demonstrated that sirtinol suppressed hCMV infection as well as hCMV-induced activation of molecular mechanisms of senescence and ROS production. While underlying molecular mechanisms remain to be elucidated, these findings indicate sirtinol as a novel and potent anti-hCMV agent with the potential to be developed as an effective treatment for chronic hCMV infection and its cellular and molecular consequences that are important to ageing and health of older adults.

CBX8 antagonizes the effect of Sirtinol on premature senescence through the AKT-RB-E2F1 pathway in K562 leukemia cells

Although tyrosine kinase inhibitor (TKI) therapies are highly effective in the treatment of chronic myeloid leukemia (CML), frequent recurrence limits their usage and demands new approaches for CML therapy. Stress-induced premature senescence (SIPS) is considered a potential anticancer treatment, but the underlying mechanism remains elusive. Here, we report that Sirtinol, a known SIRT1 inhibitor, induces premature senescence and growth arrest in K562 CML cells. Chromobox homolog 8 (CBX8) suppresses the Sirtinol-induced premature senescence, which is reversed by CBX8 knockdown. Upon Sirtinol treatment, the phosphorylation of AKT1, p27KIP1 and RB is severely downregulated. However, CBX8 overexpression enhances phosphorylation and, thereby, promotes the transcriptional activity of E2F1, both of which are impaired upon CBX depletion. These data suggest that CBX8 modulates SIPS through the RB-E2F1 pathway in CML cells and provide important insight into its application in CML treatment.

A three-dimensional skin equivalent reflecting some aspects of in vivo aged skin

Human skin undergoes morphological, biochemical and functional modifications during the ageing process. This study was designed to produce a 3-dimensional (3D) skin equivalent in vitro reflecting some aspects of in vivo aged skin. Reconstructed skin was generated by co-culturing skin fibroblasts and keratinocytes on a collagen-glycosaminoglycan-chitosan scaffold, and ageing was induced by the exposition of fibroblasts to Mitomycin-C (MMC). Recently published data showed that MMC treatment resulted in a drug-induced accelerated senescence (DIAS) in human dermal fibroblast cultures. Next to established ageing markers, histological changes were analysed in comparison with in vivo aged skin. In aged epidermis, the filaggrin expression is reduced in vivo and in vitro. Furthermore, in dermal tissue, the amount of elastin and collagen is lowered in aged skin in vivo as well as after the treatment of 3D skin equivalents with MMC in vitro. Our results show histological signs and some aspects of ageing in a 3D skin equivalent in vitro, which mimics aged skin in vivo.

The zebrafish as a gerontology model in nervous system aging, disease, and repair

Considering the increasing number of elderly in the world's population today, developing effective treatments for age-related pathologies is one of the biggest challenges in modern medical research. Age-related neurodegeneration, in particular, significantly impacts important sensory, motor, and cognitive functions, seriously constraining life quality of many patients. Although our understanding of the causal mechanisms of aging has greatly improved in recent years, animal model systems still have much to tell us about this complex process. Zebrafish (Danio rerio) have gained enormous popularity for this research topic over the past decade, since their life span is relatively short but, like humans, they are still subject to gradual aging. In addition, the extensive characterization of its well-conserved molecular and cellular physiology makes the zebrafish an excellent model to unravel the underlying mechanisms of aging, disease, and repair. This review provides a comprehensive overview of the progress made in zebrafish gerontology, with special emphasis on nervous system aging. We review the evidence that classic hallmarks of aging can also be recognized within this small vertebrate, both at the molecular and cellular level. Moreover, we illustrate the high level of similarity with age-associated human pathologies through a survey of the functional deficits that arise as zebrafish age.

Glucose Oxidase Induces Cellular Senescence in Immortal Renal Cells through ILK by Downregulating Klotho Gene Expression

Cellular senescence can be prematurely induced by oxidative stress involved in aging. In this work, we were searching for novel intermediaries in oxidative stress-induced senescence, focusing our interest on integrin-linked kinase (ILK), a scaffold protein at cell-extracellular matrix (ECM) adhesion sites, and on the Klotho gene. Cultured renal cells were treated with glucose oxidase (GOx) for long time periods. GOx induced senescence, increasing senescence associated β-galactosidase activity and the expression of p16. In parallel, GOx increased ILK protein expression and activity. Ectopic overexpression of ILK in cells increased p16 expression, even in the absence of GOx, whereas downregulation of ILK inhibited the increase in p16 due to oxidative stress. Additionally, GOx reduced Klotho gene expression and cells overexpressing Klotho protein did not undergo senescence after GOx addition. We demonstrated a direct link between ILK and Klotho since silencing ILK expression in cells and mice increases Klotho expression and reduces p53 and p16 expression in renal cortex. In conclusion, oxidative stress induces cellular senescence in kidney cells by increasing ILK protein expression and activity, which in turn reduces Klotho expression. We hereby present ILK as a novel downregulator of Klotho gene expression.

Density-gradient centrifugation enables the purification of cultured corneal endothelial cells for cell therapy by eliminating senescent cells

The corneal endothelium is essential for maintaining corneal transparency; therefore, corneal endothelial dysfunction causes serious vision loss. Tissue engineering-based therapy is potentially a less invasive and more effective therapeutic modality. We recently started a first-in-man clinical trial of cell-based therapy for treating corneal endothelial dysfunction in Japan. However, the senescence of corneal endothelial cells (CECs) during the serial passage culture needed to obtain massive quantities of cells for clinical use is a serious technical obstacle preventing the push of this regenerative therapy to clinical settings. Here, we show evidence from an animal model confirming that senescent cells are less effective in cell therapy. In addition, we propose that density-gradient centrifugation can eliminate the senescent cells and purify high potency CECs for clinical use. This simple technique might be applicable for other types of cells in the settings of regenerative medicine.

Senescence as a general cellular response to stress: A mini-review

Cellular senescence was initially described as the phenomenon of limited cell divisions that normal cells in culture can undergo during long-term-cultivation. Later it was found that senescence may be induced by various stress factors. The intriguing resemblance between stress-induced and replicative senescence makes questionable the distinction between both types and suggests that the cellular senescence is a common outcome of stress response. Growing evidences support the idea that stress-induced senescence is the cell-type specific.

Suppression of the senescence-associated secretory phenotype (SASP) in human fibroblasts using small molecule inhibitors of p38 MAP kinase and MK2

Senescent cells show an altered secretome profile termed the senescence-associated secretory phenotype (SASP). There is an increasing body of evidence that suggests that the accumulation of SASP-positive senescent cells in humans is partially causal in the observed shift to a low-level pro-inflammatory state in aged individuals. This in turn suggests the SASP as a possible therapeutic target to ameliorate inflammatory conditions in the elderly, and thus a better understanding of the signalling pathways underlying the SASP are required. Prior studies using the early generation p38 MAPK inhibitor SB203580 indicated that p38 signalling was required for the SASP. In this study, we extend these observations using two next-generation p38 inhibitors (UR-13756 and BIRB 796) that have markedly improved selectivity and specificity compared to SB203580, to strengthen the evidence that the SASP is p38-dependent in human fibroblasts. BIRB 796 has an efficacy and toxicity profile that has allowed it to reach Phase III clinical trials, suggesting its possible use to suppress the SASP in vivo. We also demonstrate for the first time a requirement for signalling through the p38 downstream MK2 kinase in the regulation of the SASP using two MK2 inhibitors. Finally, we demonstrate that a commercially-available multiplex cytokine assay technology can be used to detect SASP components in the conditioned medium of cultured fibroblasts from both young and elderly donors. This assay is a high-throughput, multiplex microtitre-based assay system that is highly sensitive, with very low sample requirements, allowing it to be used for low-volume human biological fluids. Our initial studies using existing multiplex plates form the basis for a “SASP signature” assay that could be used as a high-throughput system in a clinical study setting. Our findings therefore provide important steps towards the study of, and intervention in, the SASP in human ageing and age-related disease.

Human Dermal Stem/Progenitor Cell-Derived Conditioned Medium Improves Senescent Human Dermal Fibroblasts

Adult skin stem cells are recognized as potential therapeutics to rejuvenate aged skin. We previously demonstrated that human dermal stem/progenitor cells (hDSPCs) with multipotent capacity could be enriched from human dermal fibroblasts using collagen type IV. However, the effects of hDSPCs on cellular senescence remain to be elucidated. In the present study, we investigated whether conditioned medium (CM) collected from hDSPC cultures (hDSPC-CM) exhibits beneficial effects on senescent fibroblasts. We found that hDSPC-CM promoted proliferation and decreased the expression level of senescence-associated β-galactosidase in senescent fibroblasts. In addition, p53 phosphorylation and p21 expression were significantly reduced in senescent fibroblasts treated with hDSPC-CM. hDSPC-CM restored the expression levels of collagen type I, collagen type III, and tissue inhibitor of metalloproteinase, and antagonized the increase of matrix metalloproteinase 1 expression. Finally, we demonstrated that hDSPC-CM significantly reduced reactive oxygen species levels by specifically up-regulating the expression level of superoxide dismutase 2. Taken together, these data suggest that hDSPC-CM can be applied as a potential therapeutic agent for improving human aged skin.

Similarities in Gene Expression Profiles during In Vitro Aging of Primary Human Embryonic Lung and Foreskin Fibroblasts

Replicative senescence is of fundamental importance for the process of cellular aging, since it is a property of most of our somatic cells. Here, we elucidated this process by comparing gene expression changes, measured by RNA-seq, in fibroblasts originating from two different tissues, embryonic lung (MRC-5) and foreskin (HFF), at five different time points during their transition into senescence. Although the expression patterns of both fibroblast cell lines can be clearly distinguished, the similar differential expression of an ensemble of genes was found to correlate well with their transition into senescence, with only a minority of genes being cell line specific. Clustering-based approaches further revealed common signatures between the cell lines. Investigation of the mRNA expression levels at various time points during the lifespan of either of the fibroblasts resulted in a number of monotonically up- and downregulated genes which clearly showed a novel strong link to aging and senescence related processes which might be functional. In terms of expression profiles of differentially expressed genes with age, common genes identified here have the potential to rule the transition into senescence of embryonic lung and foreskin fibroblasts irrespective of their different cellular origin.

Protein Oxidation in Aging: Does It Play a Role in Aging Progression?

SIGNIFICANCE

A constant accumulation of oxidized proteins takes place during aging. Oxidation of proteins leads to a partial unfolding and, therefore, to aggregation. Protein aggregates impair the activity of cellular proteolytic systems (proteasomes, lysosomes), resulting in further accumulation of oxidized proteins. In addition, the accumulation of highly crosslinked protein aggregates leads to further oxidant formation, damage to macromolecules, and, finally, to apoptotic cell death. Furthermore, protein oxidation seems to play a role in the development of various age-related diseases, for example, neurodegenerative diseases.

RECENT ADVANCES

The highly oxidized lipofuscin accumulates during aging. Lipofuscin formation might cause impaired lysosomal and proteasomal degradation, metal ion accumulation, increased reactive oxygen species formation, and apoptosis.

CRITICAL ISSUES

It is still unclear to which extent protein oxidation is involved in the progression of aging and in the development of some age-related diseases.

FUTURE DIRECTIONS

An extensive knowledge of the effects of protein oxidation on the aging process and its contribution to the development of age-related diseases could enable further strategies to reduce age-related impairments. Strategies aimed at lowering aggregate formation might be a straightforward intervention to reduce age-related malfunctions of organs.

The emerging role of senescent cells in tissue homeostasis and pathophysiology

Cellular senescence is a state of permanent growth arrest and is thought to play a pivotal role in tumor suppression. Cellular senescence may play an important role in tumor suppression, wound healing, and protection against tissue fibrosis in physiological conditions in vivo. However, accumulating evidence that senescent cells may have harmful effects in vivo and may contribute to tissue remodeling, organismal aging, and many age-related diseases also exists. Cellular senescence can be induced by various intrinsic and extrinsic factors. Both p53/p21 and p16/RB pathways are important for irreversible growth arrest in senescent cells. Senescent cells secret numerous biologically active factors. This specific secretion phenotype by senescent cells may largely contribute to physiological and pathological consequences in organisms. Here I review the molecular basis of cell cycle arrest and the specific secretion phenotype in cellular senescence. I also summarize the current knowledge of the role of cellular senescence in vivo in physiological and pathological settings.

Could caveolae be acting as warnings of mitochondrial ageing?

Ageing is a cellular process with many facets, some of which are currently undergoing a paradigm change. It is the case of "mitochondrial theory of ageing", which, interestingly, has been found lately to cross paths with another ageing dysfunctional process - intracellular signalling - in an unexpected point (or place) - caveolae. The latter represent membrane microdomains altered in senescent cells, scaffolded by proteins modified (posttranslational or as expression) with ageing. An important determinant of these alterations is oxidative stress, through increased production of reactive oxygen species that originate at mitochondrial site. Spanning from physical contact points, to shared structural proteins and similar function domains, caveolae and mitochondria might have more in common than originally thought. By reviewing recent data on oxidative stress impact on caveolae and caveolins, as well as possible interactions between caveolae and mitochondria, we propose a hypothesis for senescence-related involvement of caveolins.

Oxidative stress in aging human skin

Oxidative stress in skin plays a major role in the aging process. This is true for intrinsic aging and even more for extrinsic aging. Although the results are quite different in dermis and epidermis, extrinsic aging is driven to a large extent by oxidative stress caused by UV irradiation. In this review the overall effects of oxidative stress are discussed as well as the sources of ROS including the mitochondrial ETC, peroxisomal and ER localized proteins, the Fenton reaction, and such enzymes as cyclooxygenases, lipoxygenases, xanthine oxidases, and NADPH oxidases. Furthermore, the defense mechanisms against oxidative stress ranging from enzymes like superoxide dismutases, catalases, peroxiredoxins, and GSH peroxidases to organic compounds such as L-ascorbate, α-tocopherol, beta-carotene, uric acid, CoQ10, and glutathione are described in more detail. In addition the oxidative stress induced modifications caused to proteins, lipids and DNA are discussed. Finally age-related changes of the skin are also a topic of this review. They include a disruption of the epidermal calcium gradient in old skin with an accompanying change in the composition of the cornified envelope. This modified cornified envelope also leads to an altered anti-oxidative capacity and a reduced barrier function of the epidermis.

The protective effects of berry-derived anthocyanins against visible light-induced damage in human retinal pigment epithelial cells

BACKGROUND

Studies have shown that anthocyanins (ACNs) in berries contribute to eye health. However, information on the relationship between the chemical structures and visual functions of ACNs is scarce. This study investigated the protection effects of ACNs with different structures against visible light-induced damage in human retinal pigment epithelial (RPE) cells.

RESULTS

Four ACNs with different aglycones, namely, pelargonidin-3-glucoside (Pg-3-glu), cyanidin-3-glucoside (Cy-3-glu), delphinidin-3-glucoside, and malvidin-3-glucoside (Mv-3-glu), were isolated from three berries (blueberry, blackberry and strawberry). Of these ACNs, Cy-3-glu exhibited the highest reactive oxygen species inhibitory capacity in RPE cells, with 40 µg mL(-1) Cy-3-glu showing a ROS clearance of 57.5% ± 4.2%. The expression of vascular endothelial growth factor levels were significantly (P < 0.05) down-regulated by Cy-3-glu and Mv-3-glu in a visible light-induced damage RPE cell model. Cy-3-glu and Pg-3-glu treatments significantly (P < 0.05) inhibited the increase in β-galactosidase during the RPE cell ageing caused by visible light exposure.

CONCLUSION

Our findings suggest that the biological properties of different ACNs significantly vary. Cy-3-glu, which contains an ortho hydroxyl group in its B ring, possibly exerts multiple protective effects (antioxidant, anti-angiogenic and anti-ageing) in RPE cells. Therefore, Cy-3-glu may prove useful as a prophylactic health food for the prevention of retinal diseases.

Hepatocyte Turnover in Chronic HCV-Induced Liver Injury and Cirrhosis

Chronic hepatitis C virus (HCV) infection may eventually lead to progressive liver fibrosis and cirrhosis through a complex, multistep process involving hepatocyte death and regeneration. Despite common pathogenetic pathways present in all forms of liver cirrhosis irrespective of etiology, hepatocyte turnover and related molecular events in HCV-induced cirrhosis are increasingly being distinguished from even “similar” causes, such as hepatitis B virus- (HBV-) related cirrhosis. New insights in HCV-induced hepatocellular injury, differential gene expression, and regenerative pathways have recently revealed a different pattern of progression to irreversible parenchymal liver damage. A shift to the significant role of the host immune response rather than the direct effect of HCV on hepatocytes and the imbalance between antiapoptotic and proapoptotic signals have been investigated in several studies but need to be further elucidated. The present review aims to comprehensively summarize the current evidence on HCV-induced hepatocellular turnover with a view to outline the significant trends of ongoing research.

Characterization of Skin Aging-Associated Secreted Proteins (SAASP) Produced by Dermal Fibroblasts Isolated from Intrinsically Aged Human Skin

Most molecular hallmarks of cellular senescence have been identified in studies of cells aged in vitro by driving them into replicative or stress-induced senescence. Comparatively, less is known about the characteristic features of cells that have aged in vivo. Here we provide a systematic molecular analysis of normal human dermal fibroblasts (NHDFs) that were isolated from intrinsically aged human skin of young versus middle aged versus old donors. Intrinsically aged NHDFs in culture exhibited more frequently nuclear foci positive for p53 binding protein 1 and promyelocytic leukemia protein reminiscent of 'DNA segments with chromatin alterations reinforcing senescence (DNA-SCARS)'. Formation of such foci was neither accompanied by increased DNA double strand breaks, nor decreased cell viability, nor telomere shortening. However, it was associated with the development of a secretory phenotype, indicating incipient cell senescence. By quantitative analysis of the entire secretome present in conditioned cell culture supernatant, combined with a multiplex cytokine determination, we identified 998 proteins secreted by intrinsically aged NHDFs in culture. Seventy of these proteins exhibited an age-dependent secretion pattern and were accordingly denoted 'skin aging-associated secreted proteins (SAASP)'. Systematic comparison of SAASP with the classical senescence-associated secretory phenotype (SASP) revealed that matrix degradation as well as proinflammatory processes are common aspects of both conditions. However, secretion of 27 proteins involved in the biological processes of 'metabolism' and 'adherens junction interactions' was unique for NHDFs isolated from intrinsically aged skin. In conclusion, fibroblasts isolated from intrinsically aged skin exhibit some, but not all, molecular hallmarks of cellular senescence. Most importantly, they secrete a unique pattern of proteins that is distinct from the canonical SASP and might reflect specific processes of skin aging.

Cellular senescence: from growth arrest to immunogenic conversion

Cellular senescence was first reported in human fibroblasts as a state of stable in vitro growth arrest following extended culture. Since that initial observation, a variety of other phenotypic characteristics have been shown to co-associate with irreversible cell cycle exit in senescent fibroblasts. These include (1) a pro-inflammatory secretory response, (2) the up-regulation of immune ligands, (3) altered responses to apoptotic stimuli and (4) promiscuous gene expression (stochastic activation of genes possibly as a result of chromatin remodeling). Many features associated with senescent fibroblasts appear to promote conversion to an immunogenic phenotype that facilitates self-elimination by the immune system. Pro-inflammatory cytokines can attract and activate immune cells, the presentation of membrane bound immune ligands allows for specific recognition and promiscuous gene expression may function to generate an array of tissue restricted proteins that could subsequently be processed into peptides for presentation via MHC molecules. However, the phenotypes of senescent cells from different tissues and species are often assumed to be broadly similar to those seen in senescent human fibroblasts, but the data show a more complex picture in which the growth arrest mechanism, tissue of origin and species can all radically modulate this basic pattern. Furthermore, well-established triggers of cell senescence are often associated with a DNA damage response (DDR), but this may not be a universal feature of senescent cells. As such, we discuss the role of DNA damage in regulating an immunogenic response in senescent cells, in addition to discussing less established "atypical" senescent states that may occur independent of DNA damage.

Anti-ageing effects of Sonchus oleraceus L. (pūhā) leaf extracts on H₂O₂-induced cell senescence

Antioxidants protect against damage from free radicals and are believed to slow the ageing process. Previously, we have reported the high antioxidant activity of 70% methanolic Sonchus oleraceus L. (Asteraceae) leaf extracts. We hypothesize that S. oleraceus extracts protect cells against H₂O₂-induced senescence by mediating oxidative stress. Premature senescence of young WI-38 cells was induced by application of H₂O₂. Cells were treated with S. oleraceus extracts before or after H₂O₂ stress. The senescence- associated β-galactosidase (SA-β-gal) activity was used to indicate cell senescence. S. oleraceus extracts showed higher cellular antioxidant activity than chlorogenic acid in WI-38 cells. S. oleraceus extracts suppressed H₂O₂ stress-induced premature senescence in a concentration-dependent manner. At 5 and 20 mg/mL, S. oleraceus extracts showed better or equivalent effects of reducing stress-induced premature senescence than the corresponding ascorbic acid treatments. These findings indicate the potential of S. oleraceus extracts to be formulated as an anti-ageing agent.

mTOR: a potential therapeutic target in osteoarthritis?

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by the progressive loss of articular cartilage, remodeling of the subchondral bone, and synovial inflammation. Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that controls critical cellular processes such as growth, proliferation, and protein synthesis. Recent studies suggest that mTOR plays a vital role in cartilage growth and development and in altering the articular cartilage homeostasis as well as contributing to the process of cartilage degeneration associated with OA. Both pharmacological inhibition and genetic deletion of mTOR have been shown to reduce the severity of OA in preclinical mouse models. In this review article, we discuss the roles of mTOR in cartilage development, in maintaining articular cartilage homeostasis, and its potential as an OA therapeutic target.

Acrylamide Induces Senescence in Macrophages through a Process Involving ATF3, ROS, p38/JNK, and a Telomerase-Independent Pathway

Senescence, which is irreversible cell cycle arrest, is induced by various types of DNA damage, including genotoxic stress. Senescent cells show dysregulation of tumor suppressor genes and other regulators of cellular proliferation. Activating transcription factor 3 (ATF3) plays a pleiotropic role in biological processes through genotoxic stress. In this study, we examined the effects of acrylamide (ACR), a genotoxic carcinogen, on cellular senescence and the molecular mechanisms of ATF3 function in macrophages. Treatment of macrophages with ACR at low concentrations (<1.0 mM) resulted in senescence-like morphology and an increase in senescence-associated β-galactosidase (SA-β-gal) activity. Exposure of macrophages to ACR led to stress-induced, telomerase-independent senescence. In addition, ACR treatment for 1, 3, or 5 days showed a concentration-dependent increase in ATF3 expression and G0/G1 phase arrest. To better understand the role of ATF3 in controlling the senescence response to ACR, SA-β-gal activity was examined using ATF3 knockdown and overexpression. ACR-mediated senescence was significantly decreased by knockdown of ATF3, whereas it was increased with ATF3 overexpression. We found that ATF3 regulated p53 and p21 levels. ATF3 also played an important role in regulating intracellular reactive oxygen species (ROS) production in response to ACR treatment. Moreover, phosphorylation of p38 and JNK kinases, which were activated during ATF3-mediated senescence, was observed in ACR-treated macrophages. Taken together, these results suggest that ATF3 contributes to ACR-induced senescence by enhancing ROS production, activating p38 and JNK kinases, and promoting the ATF3-dependent expression of p53, resulting in regulation of cellular senescence in macrophages.

The unfolded protein response and cellular senescence. A review in the theme: cellular mechanisms of endoplasmic reticulum stress signaling in health and disease

The endoplasmic reticulum (ER) is a multifunctional organelle critical for the proper folding and assembly of secreted and transmembrane proteins. Perturbations of ER functions cause ER stress, which activates a coordinated system of transcriptional and translational controls called the unfolded protein response (UPR), to cope with accumulation of misfolded proteins and proteotoxicity. It results in ER homeostasis restoration or in cell death. Senescence is a complex cell phenotype induced by several stresses such as telomere attrition, DNA damage, oxidative stress, and activation of some oncogenes. It is mainly characterized by a cell enlargement, a permanent cell-cycle arrest, and the production of a secretome enriched in proinflammatory cytokines and components of the extracellular matrix. Senescent cells accumulate with age in tissues and are suspected to play a role in age-associated diseases. Since senescence is a stress response, the question arises of whether an ER stress could occur concomitantly with senescence and participate in the onset or maintenance of the senescent features. Here, we described the interconnections between the UPR signaling and the different aspects of the cellular senescence programs and discuss the implication of UPR modulations in this context.

Long-term quiescent fibroblast cells transit into senescence

Cellular senescence is described to be a consequence of telomere erosion during the replicative life span of primary human cells. Quiescence should therefore not contribute to cellular aging but rather extend lifespan. Here we tested this hypothesis and demonstrate that cultured long-term quiescent human fibroblasts transit into senescence due to similar cellular mechanisms with similar dynamics and with a similar maximum life span as proliferating controls, even under physiological oxygen conditions. Both, long-term quiescent and senescent fibroblasts almost completely fail to undergo apoptosis. The transition of long-term quiescent fibroblasts into senescence is also independent of HES1 which protects short-term quiescent cells from becoming senescent. Most significantly, DNA damage accumulates during senescence as well as during long-term quiescence at physiological oxygen levels. We suggest that telomere-independent, potentially maintenance driven gradual induction of cellular senescence during quiescence is a counterbalance to tumor development.

Level of macroautophagy drives senescent keratinocytes into cell death or neoplastic evasion

Senescence is a non-proliferative state reached by normal cells in response to various stresses, including telomere uncapping, oxidative stress or oncogene activation. In previous reports, we have highlighted that senescent human epidermal keratinocytes have two opposite outcomes: either they die by autophagic programmed cell death or they evade in the form of neoplastic postsenescence emergent (PSNE) cells. Herein, we show that partially reducing macroautophagy in senescent keratinocytes using 3-methyl adenine or anti-Atg5 siRNAs increases the PSNE frequency, suggesting that senescent keratinocytes have to escape autophagic cell death to generate PSNE cells. However, totally inhibiting macroautophagy impairs PSNE and leads to a huge accumulation of oxidative damages, indicating that senescent keratinocytes need to achieve quality-control macroautophagy for PSNE to occur. In accordance, we demonstrate that the progenitors of PSNE cells display a level of macroautophagy slightly lower than that of the average senescent population, which is directly dictated by their level of reactive oxygen species, their level of upregulation of MnSOD, their level of activation of NF-κB transcription factors and their level of dysfunctional mitochondria. Macroautophagy thus has antagonistic roles during senescence, inducing cell death or promoting neoplastic transformation, depending on its level of activation. Taken together, these data suggest that levels of oxidative damages and ensuing macroautophagic activity could be two main determinants of the very initial phases of neoplastic transformation by senescence evasion.

Ionizing irradiation inhibits keloid fibroblast cell proliferation and induces premature cellular senescence

Keloids are one of the common refractory conditions in dermatology and aesthetic plastic surgery. The most effective treatment is superficial radiotherapy followed by surgical removal. The rate of recurrence is strongly associated with the total dose of ionizing irradiation, and the underlying mechanism remains unclear. In this study, we used primary keloid fibroblasts (KFb) isolated from patient samples to investigate the effects of X-ray radiation on cell proliferation, cell toxicity and cell cycle, as detected by CCK-8 assay kit and flow cytometer. In addition, we examined senescence-associated β-galactosidase activity and the associated gene expression using real-time polymerase chain reaction and western blot in KFb exposed to X-ray radiation. X-ray radiation inhibited cell proliferation and induced cell senescence in KFb in a dose-dependent manner. Inhibition of cell proliferation and induction of cellular senescence were mediated by interruption of the cell cycle with an extended G0/G1 phase. Furthermore, the expressions of senescence-associated genes p21, p16 and p27 were upregulated both at mRNA and protein levels in KFb exposed to X-ray radiation. Taken together, our data indicate that X-ray radiation may prevent the recurrence of keloids by controlling fibroblast proliferation, arresting the cell cycle and inducing premature cellular senescence.

Ginsenoside Rb1 prevents H2O2-induced HUVEC senescence by stimulating sirtuin-1 pathway

Purposes

We have previously reported that Ginsenoside Rb1 may effectively prevent HUVECs from senescence, however, the detailed mechanism has not demonstrated up to now. Recent studies have shown that sirtuin-1 (Sirt1) plays an important role in the development of endothelial senescence. The purpose of this study was to explore whether Sirt1 is involved in the action of Ginsenoside Rb1 regarding protection against H₂O₂-induced HUVEC Senescence.

Methods and Results

Senescence induced by hydrogen peroxide (H₂O₂) in human umbilical vein endothelial cells (HUVECs) was examined by analyzing plasminogen activator inhibitor-1 (PAI-1) expression, cell morphology, and senescence-associated beta-galactosidase (SA-β-gal) activity. The results revealed that 42% of control-treated HUVECs were SA-β-gal positive after treatment by 60 µmol/L H₂O₂, however, this particular effect of H₂O₂ was decreased more than 2-fold (19%) in the HUVECs when pretreated with Rb1 (20 µmol/L) for 30 min. Additionally, Rb1 decreased eNOS acetylation, as well as promoted more NO production that was accompanied by an increase in Sirt1 expression. Furthermore, upon knocking down Sirt1, the effect of Rb1 on HUVEC senescence was blunted.

Conclusions

The present study indicated that Ginsenoside Rb1 acts through stimulating Sirt1 in order to protect against endothelial senescence and dysfunction. As such, Sirt1 appears to be of particular importance in maintaining endothelial functions and delaying vascular aging.

Comparison of biological properties of umbilical cord-derived mesenchymal stem cells from early and late passages: immunomodulatory ability is enhanced in aged cells

Mesenchymal stem cells (MSCs) are a potential source of adult stem cells for cell-based therapeutics due to their substantial multilineage differentiation capacity and secretory functions. No information is presently available regarding the maintenance of immunosuppressive properties of this cell type with repeated passages. It was therefore the aim of the present study to analyze the biological properties, particularly the immunoregulatory effect, of MSCs from late passages. The differences between young and old MSCs in morphology, cell surface antigen phenotype, proliferation, gene expression and immunomodulatory ability were investigated. The results of the current study demonstrated that with the passage of cells, senescent MSCs displayed a characteristically enlarged and flattened morphology, different gene expression profiles and stronger immunosuppressive activities. Increased interleukin-6 production may be a possible underlying mechanism for this enhanced immunomodulatory ability of MSCs. These findings suggest that aged MSCs may provide a treatment option for patients with graft versus host disease and other diseases associated with dysregulation of the immune system.

Exploiting tumor cell senescence in anticancer therapy

Cellular senescence is a physiological process of irreversible cell-cycle arrest that contributes to various physiological and pathological processes of aging. Whereas replicative senescence is associated with telomere attrition after repeated cell division, stress-induced premature senescence occurs in response to aberrant oncogenic signaling, oxidative stress, and DNA damage which is independent of telomere dysfunction. Recent evidence indicates that cellular senescence provides a barrier to tumorigenesis and is a determinant of the outcome of cancer treatment. However, the senescence-associated secretory phenotype, which contributes to multiple facets of senescent cancer cells, may influence both cancer-inhibitory and cancer-promoting mechanisms of neighboring cells. Conventional treatments, such as chemo- and radiotherapies, preferentially induce premature senescence instead of apoptosis in the appropriate cellular context. In addition, treatment-induced premature senescence could compensate for resistance to apoptosis via alternative signaling pathways. Therefore, we believe that an intensive effort to understand cancer cell senescence could facilitate the development of novel therapeutic strategies for improving the efficacy of anticancer therapies. This review summarizes the current understanding of molecular mechanisms, functions, and clinical applications of cellular senescence for anticancer therapy.

Phloroglucinol Attenuates Free Radical-induced Oxidative Stress

The protective role of phloroglucinol against oxidative stress and stress-induced premature senescence (SIPS) was investigated in vitro and in cell culture. Phloroglucinol had strong and concentration-dependent radical scavenging effects against nitric oxide (NO), superoxide anions (O₂⁻), and hydroxyl radicals. In this study, free radical generators were used to induce oxidative stress in LLC-PK1 renal epithelial cells. Treatment with phloroglucinol attenuated the oxidative stress induced by peroxyl radicals, NO, O₂⁻, and peroxynitrite. Phloroglucinol also increased cell viability and decreased lipid peroxidation in a concentration-dependent manner. WI-38 human diploid fibroblast cells were used to investigate the protective effect of phloroglucinol against hydrogen peroxide (H₂O₂)-induced SIPS. Phloroglucinol treatment attenuated H₂O₂-induced SIPS by increasing cell viability and inhibited lipid peroxidation, suggesting that treatment with phloroglucinol should delay the aging process. The present study supports the promising role of phloroglucinol as an antioxidative agent against free radical-induced oxidative stress and SIPS.

Exendin-4 alleviates angiotensin II-induced senescence in vascular smooth muscle cells by inhibiting Rac1 activation via a cAMP/PKA-dependent pathway

Vascular aging has been implicated in the progression of diabetes and age-related cardiovascular disorders. Glucagon-like peptide-1 (GLP-1) is an incretin hormone capable of cytoprotective actions in addition to its glucose-lowering effect. The present study was undertaken to examine whether Exendin-4, a specific ligand for the GLP-1 receptor, could prevent angiotensin (ANG) II-induced premature senescence in vascular smooth muscle cells (VSMCs) and to determine the underlying mechanism involved. Senescence-associated β-galactosidase (SA β-gal) assay showed that ANG II induced premature senescence of VSMCs. Pretreatment with Exendin-4 significantly attenuated ANG II-induced generation of H2O2 and the subsequent VSMC senescence. These effects were, however, reversed in the presence of exendin fragment 9-39, a GLP-1 receptor antagonist, or PKI14-22. Moreover, a marked increase in the levels of p53 and p21 induced by ANG II was blunted by the treatment with Exendin-4. Nevertheless, Exendin-4 failed to decrease ANG II-induced expression of NAD(P)H oxidase 1 (Nox1), NAD(P)H oxidase 4 (Nox4), p22(phox), or p47(phox) in VSMCs. Mechanistically, Exendin-4 blocked ANG II-induced Rac1 activation through the cAMP/PKA signaling cascade. Specifically, NSC23766, a Rac1 inhibitor, abrogated the suppressive effects of Exendin-4 on ANG II-induced premature senescence and H2O2 generation, respectively. Thus Exendin-4 confers resistance to ANG II-induced superoxide anion generation from NAD(P)H oxidase and the resultant VSMC senescence by inhibiting Rac1 activation via a cAMP/PKA-dependent pathway. These findings demonstrate that GLP-1 as well as its analogs (GLP-1-related reagents) may hold therapeutic potential in the treatment of diabetes with cardiovascular disease.

Cellular senescence and the aging brain

Cellular senescence is a potent anti-cancer mechanism that arrests the proliferation of mitotically competent cells to prevent malignant transformation. Senescent cells accumulate with age in a variety of human and mouse tissues where they express a complex 'senescence-associated secretory phenotype' (SASP). The SASP includes many pro-inflammatory cytokines, chemokines, growth factors and proteases that have the potential to cause or exacerbate age-related pathology, both degenerative and hyperplastic. While cellular senescence in peripheral tissues has recently been linked to a number of age-related pathologies, its involvement in brain aging is just beginning to be explored. Recent data generated by several laboratories suggest that both aging and age-related neurodegenerative diseases are accompanied by an increase in SASP-expressing senescent cells of non-neuronal origin in the brain. Moreover, this increase correlates with neurodegeneration. Senescent cells in the brain could therefore constitute novel therapeutic targets for treating age-related neuropathologies.

FOXO1, TGF-β regulation and wound healing

Re-epithelialization is a complex process that involves migration and proliferation of keratinocytes, in addition to the production of cytokines and growth factors that affect other cells. The induction of transcription factors during these processes is crucial for successful wound healing. The transcription factor forkhead boxO-1 (FOXO1) has recently been found to be an important regulator of wound healing. In particular, FOXO1 has significant effects through regulation of transforming growth factor-beta (TGF-β) expression and protecting keratinocytes from oxidative stress. In the absence of FOXO1, there is increased oxidative damage, reduced TGF-β1 expression, reduced migration and proliferation of keratinocytes and increased keratinocytes apoptosis leading to impaired re-epithelialization of wounds.

Bisphenol A disrupts transcription and decreases viability in aging vascular endothelial cells

Bisphenol A (BPA) is a widely utilized endocrine disruptor capable of mimicking endogenous hormones, employed in the manufacture of numerous consumer products, thereby interfering with physiological cellular functions. Recent research has shown that BPA alters epigenetic cellular mechanisms in mammals and may be correlated to enhanced cellular senescence. Here, the effects of BPA at 10 ng/mL and 1 µg/mL, concentrations found in human samples, were analyzed on HT29 human colon adenocarcinona cell line and Human Umbilical Vein Endothelial Cells (HUVEC). Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) transcriptional analysis of the Long Interspersed Element-1 (LINE-1) retroelement showed that BPA induces global transcription deregulation in both cell lines, although with more pronounced effects in HUVEC cells. Whereas there was an increase in global transcription in HT29 exclusively after 24 h of exposure, this chemical had prolonged effects on HUVEC. Immunoblotting revealed that this was not accompanied by alterations in the overall content of H3K9me2 and H3K4me3 epigenetic marks. Importantly, cell viability assays and transcriptional analysis indicated that prolonged BPA exposure affects aging processes in senescent HUVEC. To our knowledge this is the first report that BPA interferes with senescence in primary vascular endothelial cells, therefore, suggesting its association to the etiology of age-related human pathologies, such as atherosclerosis.