Inhibition of p21-mediated ROS accumulation can rescue p21-induced senescence

Cooperative stabilisation of 14-3-3σ protein-protein interactions via covalent protein modification

14-3-3 proteins are an important family of hub proteins that play important roles in many cellular processes via a large network of interactions with partner proteins. Many of these protein-protein interactions (PPI) are implicated in human diseases such as cancer and neurodegeneration. The stabilisation of selected 14-3-3 PPIs using drug-like 'molecular glues' is a novel therapeutic strategy with high potential. However, the examples reported to date have a number of drawbacks in terms of selectivity and potency. Here, we report that WR-1065, the active species of the approved drug amifostine, covalently modifies 14-3-3σ at an isoform-unique cysteine residue, Cys38. This modification leads to isoform-specific stabilisation of two 14-3-3σ PPIs in a manner that is cooperative with a well characterised molecular glue, fusicoccin A. Our findings reveal a novel stabilisation mechanism for 14-3-3σ, an isoform with particular involvement in cancer pathways. This mechanism can be exploited to harness the enhanced potency conveyed by covalent drug molecules and dual ligand cooperativity. This is demonstrated in two cancer cell lines whereby the cooperative behaviour of fusicoccin A and WR-1065 leads to enhanced efficacy for inducing cell death and attenuating cell growth.

Targeted clearance of senescent cells using an antibody-drug conjugate against a specific membrane marker

A wide range of diseases have been shown to be influenced by the accumulation of senescent cells, from fibrosis to diabetes, cancer, Alzheimer's and other age-related pathologies. Consistent with this, clearance of senescent cells can prolong healthspan and lifespan in in vivo models. This provided a rationale for developing a new class of drugs, called senolytics, designed to selectively eliminate senescent cells in human tissues. The senolytics tested so far lack specificity and have significant off-target effects, suggesting that a targeted approach could be more clinically relevant. Here, we propose to use an extracellular epitope of B2M, a recently identified membrane marker of senescence, as a target for the specific delivery of toxic drugs into senescent cells. We show that an antibody-drug conjugate (ADC) against B2M clears senescent cells by releasing duocarmycin into them, while an isotype control ADC was not toxic for these cells. This effect was dependent on p53 expression and therefore more evident in stress-induced senescence. Non-senescent cells were not affected by either antibody, confirming the specificity of the treatment. Our results provide a proof-of-principle assessment of a novel approach for the specific elimination of senescent cells using a second generation targeted senolytic against proteins of their surfaceome, which could have clinical applications in pathological ageing and associated diseases.

Platelet-Derived Growth Factor Induces SASP-Associated Gene Expression in Human Multipotent Mesenchymal Stromal Cells but Does Not Promote Cell Senescence

Activation of multipotent mesenchymal stromal cells (MSCs) is a central part of tissue response to damage. Platelet-derived growth factor (PDGF-BB), which is abundantly released in the damaged area, potently stimulates the proliferation and migration of MSCs. Recent evidence indicates that tissue injury is associated with the accumulation of senescent cells, including ones of MSC origin. Therefore, we hypothesized that PDGF-BB induces MSC senescence. To evaluate mechanisms of early activation of MSCs by PDGF-BB, we performed transcriptome profiling of human MSCs isolated from adipose tissue after exposure to PDGF-BB for 12 and 24 h. We demonstrated that PDGF-BB induced the expression of several genes encoding the components of senescence-associated secretory phenotype (SASP) in MSCs such as plasminogen activator inhibitor-1 (PAI-1), urokinase-type plasminogen activator and its receptor (uPA and uPAR), and some matrix metalloproteases. However, further experimental validation of transcriptomic data clearly indicated that PDGF-BB exerted mitogenic and pro-migratory effects on MSCs, and augmented their pro-angiogenic activity, but did not significantly stimulate MSC senescence.

MHY1485 enhances X-irradiation-induced apoptosis and senescence in tumor cells

The mammalian target of rapamycin (mTOR) is a sensor of nutrient status and plays an important role in cell growth and metabolism. Although inhibition of mTOR signaling promotes tumor cell death and several mTOR inhibitors have been used clinically, recent reports have shown that co-treatment with MHY1485, an mTOR activator, enhances the anti-cancer effects of anti-PD-1 antibody and 5-fluorouracil. However, it remains unclear whether MHY1485 treatment alters the effects of radiation on tumor cells. In this study, the radiosensitizing effects of MHY1485 were investigated using murine CT26 and LLC cell lines. We examined mTOR signaling, tumor cell growth, colony formation, apoptosis, senescence, oxidative stress, p21 accumulation and endoplasmic reticulum (ER) stress levels in cells treated with MHY1485 and radiation, either alone or together. We found that MHY1485 treatment inhibited growth and colony formation in both cell lines under irradiation and no-irradiation conditions, results that were not fully consistent with MHY1485's known role in activating mTOR signaling. Furthermore, we found that combined treatment with MHY1485 and radiation significantly increased apoptosis and senescence in tumor cells in association with oxidative stress, ER stress and p21 stabilization, compared to radiation treatment alone. Our results suggested that MHY1485 enhances the radiosensitivity of tumor cells by a mechanism that may differ from MHY1485's role in mTOR activation.

Mitochondrial Dysfunction in Chronic Respiratory Diseases: Implications for the Pathogenesis and Potential Therapeutics

Mitochondria are indispensable for energy metabolism and cell signaling. Mitochondrial homeostasis is sustained with stabilization of mitochondrial membrane potential, balance of mitochondrial calcium, integrity of mitochondrial DNA, and timely clearance of damaged mitochondria via mitophagy. Mitochondrial dysfunction is featured by increased generation of mitochondrial reactive oxygen species, reduced mitochondrial membrane potential, mitochondrial calcium imbalance, mitochondrial DNA damage, and abnormal mitophagy. Accumulating evidence indicates that mitochondrial dysregulation causes oxidative stress, inflammasome activation, apoptosis, senescence, and metabolic reprogramming. All these cellular processes participate in the pathogenesis and progression of chronic respiratory diseases, including chronic obstructive pulmonary disease, pulmonary fibrosis, and asthma. In this review, we provide a comprehensive and updated overview of the impact of mitochondrial dysfunction on cellular processes involved in the development of these respiratory diseases. This not only implicates mechanisms of mitochondrial dysfunction for the pathogenesis of chronic lung diseases but also provides potential therapeutic approaches for these diseases by targeting dysfunctional mitochondria.

Multi-Walled Carbon Nanotubes (MWCNTs) Cause Cellular Senescence in TGF-β Stimulated Lung Epithelial Cells

Multi-walled carbon nanotubes are engineered nanomaterials (ENMs) that have a fiber-like structure which may be a concern for the development of cellular senescence. Premature senescence, a state of irreversible cell cycle arrest, is implicated in the pathogenesis of chronic lung diseases such as pulmonary fibrosis (PF). However, the crosstalk between downstream pathways mediating fibrotic and senescent responses of MWCNTs is not well-defined. Here, we exposed human bronchial epithelial cells (BEAS-2B) to MWCNTs for up to 72 h and demonstrate that MWCNTs increase reactive oxygen species (ROS) production accompanied by inhibition of cell proliferation. In addition, MWCNT exposure resulted in the increase of p21 protein abundance and senescence associated β-galactosidase (SA β-gal) activity. We also determined that co-exposure with the cytokine, transforming growth factor-β (TGF-β) exacerbated cellular senescence indicated by increased protein levels of p21, p16, and γH2A.X. Furthermore, the production of fibronectin and plasminogen activator inhibitor (PAI-1) was significantly elevated with the co-exposure compared to MWCNT or TGF-β alone. Together, our study suggests that the cellular senescence potential of MWCNTs may be enhanced by pro-fibrotic mediators, such as TGF-β in the surrounding microenvironment.

The redox-senescence axis and its therapeutic targeting

Significance

Cellular growth arrest, associated with ‘senescence’, helps to safeguard against the accumulation of DNA damage which is often recognized as the underlying mechanism of a wide variety of age-related pathologies including cancer. Cellular senescence has also been described as a ‘double-edged sword’. In cancer, for example, the creation of an immune-suppressive milieu by senescent tumor cells through the senescence-associated secretory phenotype contributes toward carcinogenesis and cancer progression.

Recent advances

The potential for cellular senescence to confer multi-faceted effects on tissue fate has led to a rejuvenated interest in its landscape and targeting. Interestingly, redox pathways have been described as both triggers and propagators of cellular senescence, leading to intricate cross-links between both pathways.

Critical issues

In this review, we describe the mechanisms driving cellular senescence, the interface with cellular redox metabolism as well as the role that chemotherapy-induced senescence plays in secondary carcinogenesis. Notably, the role that anti-apoptotic proteins of the Bcl-2 family play in inducing drug resistance via mechanisms that involve senescence induction.

Future directions

Though the therapeutic targeting of senescent cells as cancer therapy remains in its infancy, we summarize the current development of senotherapeutics, including recognized senotherapies, as well as the repurposing of drugs as senomorphic/senolytic candidates.

Maternal diabetes induces senescence and neural tube defects sensitive to the senomorphic rapamycin

Neural tube defects (NTDs) are the second most common structural birth defect. Senescence, a state of permanent cell cycle arrest, occurs only after neural tube closure. Maternal diabetes-induced NTDs are severe diabetic complications that lead to infant mortality or lifelong morbidity and may be linked to premature senescence. Here, we report that premature senescence occurs in the mouse neuroepithelium and disrupts neurulation, leading to NTDs in diabetic pregnancy. Premature senescence and NTDs were abolished by knockout of the transcription factor Foxo3a, the miR-200c gene, and the cell cycle inhibitors p21 and p27; transgenic expression of the dominant-negative FoxO3a mutant; or the senomorphic rapamycin. Double transgenic expression of p21 and p27 mimicked maternal diabetes in inducing premature neuroepithelium senescence and NTDs. These findings integrate transcription- and epigenome-regulated miRNAs and cell cycle regulators in premature neuroepithelium senescence and provide a mechanistic basis for targeting premature senescence and NTDs using senomorphics.

Bryonia multiflora Extract Induces Autophagy via Regulating Long Non-coding RNAs in Breast Cancer Cells

Bryonia multiflora, one of the species of Bryonia L. (Cucurbitaceae) genus, is a perennial, dioecious, herbaceous plant with rhizome-shaped roots. Bryonia species have anti-inflammatory, antimicrobial, cytotoxic, antioxidant, etc., activities and their components consume antitumoral effects. Purpose of the study to investigate the effect of Bryonia Multiflora extract (BMST) on breast cancer cells. Our results revealed that MCF-7 and MDA-MB-231 cells underwent significant morphological changes leading to cell rounding. No significant changes were observed in the cell viability by MTT. Acridine orange staining of our cells gave rise to think that BMST might lead our cells to autophagy. Therefore, possible molecular mechanisms underlying morphological changes such as autophagy (LC-3B, Beclin, AMBRA1) and apoptosis (Bcl-2) were evaluated on mRNA and protein levels. BMST treated MCF-7 and MDA-MB-231 cells had increased levels of autophagy markers whereas decreased levels of Bcl-2. p21 levels were also found to be increased in both cells. Analysis of lncRNA expressions has shown that BMST treatment led to changes in the expression levels of several lncRNAs playing roles in autophagy. The current study has shown that BMST induces autophagy in MCF-7 and MDA-MB-231 cells via regulating the lncRNAs revealing that BMST could be a promising therapeutic agent.

Autophagy and senescence in cancer therapy

Tumor cells can undergo diverse responses to cancer therapy. While apoptosis represents the most desirable outcome, tumor cells can alternatively undergo autophagy and senescence. Both autophagy and senescence have the potential to make complex contributions to tumor cell survival via both cell autonomous and cell non-autonomous pathways. The induction of autophagy and senescence in tumor cells, preclinically and clinically, either individually or concomitantly, has generated interest in the utilization of autophagy modulating and senolytic therapies to target autophagy and senescence, respectively. This chapter summarizes the current evidence for the promotion of autophagy and senescence as fundamental responses to cancer therapy and discusses the complexity of their functional contributions to cell survival and disease outcomes. We also highlight current modalities designed to exploit autophagy and senescence in efforts to improve the efficacy of cancer therapy.

Autophagy and PTEN in DNA damage-induced senescence

The use of DNA-damaging agents such as radiotherapy and chemotherapy has been a mainstay treatment protocol for many cancers, including lung and prostate. Recently, FDA approval of inhibitors of DNA repair, and targeting innate immunity to enhance the efficacy of DNA-damaging agents have gained much attention. Yet, inherent or acquired resistance against DNA-damaging therapies persists as a fundamental drawback. While cancer eradication by causing cancer cell death through induction of apoptosis is the ultimate goal of anti-cancer treatments, autophagy and senescence are two major cellular responses induced by clinically tolerable doses of DNA-damaging therapies. Unlike apoptosis, autophagy and senescence can act as both pro-tumorigenic as well as tumor suppressive mechanisms. DNA damage-induced senescence is associated with a pro-inflammatory secretory phenotype, which contributes to reshaping the tumor- immune microenvironment. Moreover, PTEN (phosphatase and tensin homolog) is a tumor supressor deleted in many tumors, and has been implicated in both senescence and autophagy. This review presents an overview of the literature on the regulation and consequences of DNA damage- induced senescence in cancer cells, with a specific focus on autophagy and PTEN. Both autophagy and senescence occur concurrently in the same cells in response to DNA damaging agents. However, a deterministic relationship between these fundamental processes has been controversial. We present experimental evidence obtained with tumor cells, with a prime focus on two models of cancer, prostate and lung. A better understanding of mechanisms associated with DNA damage-induced cellular senescence is central to fully exploit the potential of DNA-damaging agents against cancer.

AMPK-mTOR-ULK1-mediated autophagy protects carbon tetrachloride-induced acute hepatic failure by inhibiting p21 in rats

Autophagy is a lysosomal-dependent degradation pathway in eukaryotic cells. Recent studies have reported that autophagy can facilitate the activation of hepatic stellate cells (HSCs) and fibrogenesis of the liver during long-term carbon tetrachloride (CCl₄) exposure. However, little is known about the role of autophagy in CCl₄-induced acute hepatic failure (AHF). This study aimed to identify whether modulation of autophagy can affect CCl₄-induced AHF and evaluate the upstream signaling pathways mediated by CCl₄-induced autophagy in rats. The accumulation of specific punctate distribution of endogenous LC3-II, increased expression of LC3-II, Atg5, and Atg7 genes/proteins, and decreased expression of p62 gene were observed after acute liver injury was induced by CCl₄ in rats, indicating that CCl₄ resulted in a high level of autophagy. Moreover, loss of autophagic function by using chloroquine (CQ, an autophagic inhibitor) aggravated liver function, leading to increased expression of p21 (a cyclin-dependent kinase inhibitor) in CCl₄-treated rats. Furthermore, the AMPK-mTORC1-ULK1 axis was found to serve a function in CCl₄-induced autophagy. These results reveal that AMPK-mTORC1-ULK1 signaling-induced autophagy has a protective role in CCl₄-induced hepatotoxicity by inhibiting the p21 pathway. This study suggests a useful strategy aimed at ameliorating CCl₄-induced acute hepatotoxicity by autophagy.

Protoflavones in melanoma therapy: Prooxidant and pro-senescence effect of protoapigenone and its synthetic alkyl derivative in A375 cells

AIMS

In our study, the anticancer effects of a semisynthetic p-quinol, protoapigenone 1'-O-butyl ether (PABut), were tested in human melanoma A375 cells also in comparison with natural congener, protoapigenone (PA).

MAIN METHODS

The cytotoxic effect of PABut and PA was determined using MTT assay. Flow cytometry analysis was used to evaluate the influence of the compounds tested on ROS generation and cell cycle distribution in A375 cells. Moreover, apoptosis was evaluated by AO/EB dual staining as well as by flow cytometry. Markers of senescence were quantified by spectrofluorimetry and by Western blot analysis.

KEY FINDINGS

Both PABut and PA showed significant cytotoxicity against melanoma A375 cells at sub-micromolar concentrations. Both protoflavones induced comparable cell cycle arrest in G2/M phase. However, a more profound upregulation of intracellular ROS levels was found following PABut treatment. An increased apoptosis in the cells following 48 h treatment with both protoflavones tested was also confirmed. Both compounds tested remarkably upregulated p21 protein levels in A375 cells. Unlike PA, PABut significantly decreased protein levels of NAD⁺-dependent deacetylase SirT1 and β-actin accompanied by mild significant upregulation of mitochondrial SOD2 and senescence markers, p16 protein and SA-β-Gal activity. However, a significant upregulation of p53 only following PA treatment was found.

SIGNIFICANCE

These results suggest that PABut and PA confer high chemotherapeutic potential in melanoma cells and are suitable for further testing. Furthermore, modification of protoapigenone with 1'-O-butyl ether moiety can be associated with improved senescence-inducing effect and, thus, enhanced chemotherapeutic potency of PABut compared to the unmodified natural protoflavone.

The Roles of Autophagy and Senescence in the Tumor Cell Response to Radiation

Radiation is a critical pillar in cancer therapeutics, exerting its anti-tumor DNA-damaging effects through various direct and indirect mechanisms. Radiation has served as an effective mode of treatment for a number of cancer types, providing both curative and palliative treatment; however, resistance to therapy persists as a fundamental limitation. While cancer cell death is the ideal outcome of any anti-tumor treatment, radiation induces several responses, including apoptotic cell death, mitotic catastrophe, autophagy and senescence, where autophagy and senescence may promote cell survival. In most cases, autophagy, a conventionally cytoprotective mechanism, is a "first" responder to damage incurred from chemotherapy and radiation treatment. The paradigm developed on the premise that autophagy is cytoprotective in nature has provided the rationale for current clinical trials designed with the goal of radiosensitizing cancer cells through the use of autophagy inhibitors; however, these have failed to produce consistent results. Delving further into pre-clinical studies, autophagy has actually been shown to take diverse, sometimes opposing, forms, such as acting in a cytotoxic or nonprotective fashion, which may be partially responsible for the inconsistency of clinical outcomes. Furthermore, autophagy can have both pro- and anti-tumorigenic effects, while also having an important immune modulatory function. Senescence often occurs in tandem with autophagy, which is also the case with radiation. Radiation-induced senescence is frequently followed by a phase of proliferative recovery in a subset of cells and has been proposed as a tumor dormancy model, which can contribute to resistance to therapy and possibly also disease recurrence. Senescence induction is often accompanied by a unique secretory phenotype that can either promote or suppress immune functions, depending on the expression profile of cytokines and chemokines. Novel therapeutics selectively cytotoxic to senescent cells (senolytics) may prove to prolong remission by delaying disease recurrence in patients. Accurate assessment of primary responses to radiation may provide potential targets that can be manipulated for therapeutic benefit to sensitize cancer cells to radiotherapy, while sparing normal tissue.

Cannabinoids as anti-ROS in aged pancreatic islet cells

AIMS

Cannabinoids are the chemical compounds with a high affinity for cannabinoid receptors affecting the central nervous system through the release of neurotransmitters. However, the current knowledge related to the role of such compounds in the regulation of cellular aging is limited. This study aimed to investigate the effect of cannabidiol and tetrahydrocannabinol on the function of aged pancreatic islets.

MAIN METHODS

The expression of p53, p38, p21, p16, and Glut2 genes and β-galactosidase activity were measured as hallmarks of cell aging applying real-time PCR, ELISA, and immunocytochemistry techniques. Pdx1 protein expression, insulin release, and oxidative stress markers were compared between young and aged rat pancreatic islet cells.

KEY FINDINGS

Upon the treatment of aged pancreatic islets cells with cannabidiol and tetrahydrocannabinol, the expression of p53, p38, p21 and the activity of β-galactosidase were reduced. Cannabidiol and tetrahydrocannabinol increase insulin release, Pdx1, Glut2, and thiol molecules expression, while the oxidative stress parameters were decreased. The enhanced expression of Pdx1 and insulin release in aged pancreatic islet cells reflects the extension of cell healthy aging due to the significant reduction of ROS.

SIGNIFICANCE

This study provides evidence for the involvement of cannabidiol and tetrahydrocannabinol in the oxidation process of cellular aging.

Phorbol myristate acetate induces cellular senescence in rat microglia in vitro

The present study aimed to establish a cellular model to test the hypothesis that oncogene-induced senescence (OIS) is triggered by aging-related activation of microglia. Primary microglia were incubated with phorbol 12-myristate 13-acetate (PMA), and β-galactosidase (β-Gal) staining was applied to subsequent assessment of cellular senescence. Moreover, flow cytometry was employed for examinations of cell cycle arrest and senescence-associated proteins, p53 and p21 were measured by western blotting. Furthermore, examination of tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β) were carried out with microglia supernatants undergoing age-related degenerative diseases in the nervous system, using ELISA. PC12 cells were co-cultured with microglia activated by aging-related alteration(s) to evaluate whether apoptosis was increased in PC12 cells. Cellular senescence-associated β-Gal staining showed that microglial β-Gal expression gradually increased with prolonged PMA stimulation. Microglia in the group receiving 72 h of PMA stimulation displayed the highest percentage of cells arrested in G0/G1, the highest amount of senescence-associated expression of p53 and p21, and the most prominent secretion of TNF-α and IL-1β. In comparison with controls, an increase of apoptotic PC12 cells was detected, which were co-cultured with aging microglia. Taken together, microglia tend to undergo senescence after PMA treatment, suggesting that microglial senescence is associated with inactivation of certain oncogenes.

Telomeres: beacons of autocrine and paracrine DNA damage during skin aging

Cellular senescence is an irreversible cell cycle arrest, which can be triggered by a number of stressors, including telomere damage. Among many other phenotypic changes, senescence is accompanied by increased secretion of pro-inflammatory molecules, also known as the senescence-associated secretory phenotype (SASP). It is thought that accumulation of senescent cells contributes to age-associated tissue dysfunction partly by inducing senescence in neighboring cells through mechanisms involving SASP factors. Here, we will review evidence suggesting that telomeres can become dysfunctional irrespectively of shortening, and that this may be a mechanism-driving senescence in post-mitotic or slow dividing cells. Furthermore, we review recent evidence that supports that senescent melanocytes induce paracrine telomere damage during skin aging, which may be the mechanism responsible for propagation of senescent cells. We propose that telomeres are sensors of imbalances in the cellular milieu and act as beacons of stress, contributing to autocrine and paracrine senescence.

TNPO2 operates downstream of DYNC1I1 and promotes gastric cancer cell proliferation and inhibits apoptosis

The import of proteins into the nucleus plays an important role in tumor development. In addition to the classical nuclear import proteins importin-β and importin-α, there are many nonclassical nuclear import proteins that include TNPO2. The role of TNPO2 as a nonclassical nuclear import protein in tumors is limited. Our previous studies have shown that DYNC1I1 is a poor prognostic factor for gastric cancer and can promote the proliferation and metastasis of gastric cancer cells. An expression profile chip showed that TNPO2 was its potential downstream. DYNC1I1 upregulated TNPO2 expression by upregulating SP1, following which, SP1 recruited and bound to the P300-acetylated TNPO2 promoter region histones, and thus promoted TNPO2 expression. At the same time, TNPO2 promoted gastric cancer cell proliferation and inhibited apoptosis by a mechanism that might be depending on the functional expression of P21.

The role of cellular senescence in diabetes mellitus and osteoporosis: molecular pathways and potential interventions

The improving effectiveness of health care leads inevitably to a rapid increase in the elderly population worldwide. At advanced ages, however, people experience chronic disabilities, which significantly increase the social and economic burden while curtailing survival, independence, and quality of life of the aging population. As aging is a multifactorial process, apart from genetic predisposition, other environmental factors, such as chronic sterile inflammation and cellular senescence, contribute as crucial participants and have been targeted to reverse their deleterious effects on tissue homeostasis and functional integrity. Cellular senescence refers to the essentially irreversible inhibition of cellular proliferation when cells are subjected to extrinsic or endogenous stress. Although the process of cellular senescence has long been known, recent evidence demonstrated that it characterizes many aging phenotypes and that elimination of senescent cells at the tissue level can improve age-related tissue dysfunction. These observations have renewed scientific interest in possible therapeutic interventions. Two major chronic diseases associated with aging that impose an enormous burden on global health systems are type 2 diabetes and osteoporosis. This review presents current data on (i) the underlying molecular mechanisms of cellular senescence, (ii) its relationship to these two endocrine diseases that are today prevalent worldwide, and (iii) future prospects of targeted intervention with the aim of simultaneously improving the progression and prognosis of these serious problems of aging.

Natural Compounds as a Strategy to Optimize "In Vitro" Expansion of Stem Cells

The efficient use of stem cells for transplantation is often limited by the relatively low number of stem cells collected. The ex vivo expansion of human stem cells for clinical use is a potentially valuable approach to increase stem cell number. Currently, most of the procedures used to expand stem cells are carried out using a 21% oxygen concentration, which is about 4- to 10-fold greater than the concentration characteristic of their natural niches. Hyperoxia might cause oxidative stress with a deleterious effect on the physiology of cultured stem cells. In this review, we investigate and critically examine the available information on the ability of natural compounds to counteract hyperoxia-induced damage in different types of stem cells ex vivo. In particular, we focused on proliferation and stemness maintenance in an attempt to draw up useful indications to define new culture media with a promoting activity on cell expansion in vitro.

p21cip1/waf1 Coordinate Autophagy, Proliferation and Apoptosis in Response to Metabolic Stress

Cancer cells possess metabolic properties that are different from benign cells. These unique characteristics have become attractive targets that are being actively investigated for cancer therapy. p21cip1/waf1, also known as Cyclin-Dependent Kinase inhibitor 1A, is encoded by the CDKN1A gene. It is a major p53 target gene involved in cell cycle progression that has been extensively evaluated. To date, p21 has been reported to regulate various cell functions, both dependent and independent of p53. Besides regulating the cell cycle, p21 also modulates apoptosis, induces senescence, and maintains cellular quiescence in response to various stimuli. p21 transcription is induced in response to stresses, including those from oxidative and chemotherapeutic treatment. A recent study has shown that in response to metabolic stresses such as nutrient and energy depletion, p21 expression is induced to regulate various cell functions. Despite the biological significance, the mechanism of p21 regulation in cancer adaptation to metabolic stress is underexplored and thus represents an exciting field. This review focuses on the recent development of p21 regulation in response to metabolic stress and its impact in inducing cell cycle arrest and death in cancer cells.

Expansion and Cell-Cycle Arrest: Common Denominators of Cellular Senescence

Cellular senescence is a major driver of age-related diseases, and senotherapies are being tested in clinical trials. Despite its popularity, cellular senescence is weakly defined and is frequently referred to as irreversible cell-cycle arrest. In this article we hypothesize that cellular senescence is a phenotype that results from the coordination of two processes: cell expansion and cell-cycle arrest. We provide evidence for the compatibility of the proposed model with recent findings showing senescence in postmitotic tissues, wound healing, obesity, and development. We believe our model also explains why some characteristics of senescence can be found in non-senescent cells. Finally, we propose new avenues for research from our model.

Mitochondrial Homeostasis and Cellular Senescence

Cellular senescence refers to a stress response aiming to preserve cellular and, therefore, organismal homeostasis. Importantly, deregulation of mitochondrial homeostatic mechanisms, manifested as impaired mitochondrial biogenesis, metabolism and dynamics, has emerged as a hallmark of cellular senescence. On the other hand, impaired mitostasis has been suggested to induce cellular senescence. This review aims to provide an overview of homeostatic mechanisms operating within mitochondria and a comprehensive insight into the interplay between cellular senescence and mitochondrial dysfunction.

Mitochondrial dysfunction and cell senescence: deciphering a complex relationship

Cellular senescence and mitochondrial dysfunction have both been defined as classical hallmarks of the ageing process. Here, we review the intricate relationship between the two. In the context of ageing, it is now well regarded that cellular senescence is a key driver in both ageing and the onset of a number of age-related pathologies. Emerging evidence has pinpointed mitochondria as one of the key modulators in the development of the senescence phenotype, particularly the pro-inflammatory senescence associated secretory phenotype (SASP). This review focuses on the contribution of homeostatic mechanisms, as well as of reactive oxygen species and mitochondrial metabolites in the senescence programme. Furthermore, we discuss emerging pathways and mitochondrial-mediated mechanisms that may be influencing the SASP and, subsequently, explore how these may be exploited to open up new therapeutic avenues.

Peroxiredoxin II negatively regulates BMP2-induced osteoblast differentiation and bone formation via PP2A Cα-mediated Smad1/5/9 dephosphorylation

Peroxiredoxin II (Prx II), an antioxidant enzyme in the Prx family, reduces oxidative stress by decreasing the intracellular ROS levels. Osteoblast differentiation is promoted by bone morphogenetic protein 2 (BMP2), which upregulates the expression of osteoblast differentiation marker genes, through Smad1/5/9 phosphorylation. We found that Prx II expression was increased by a high dose of lipopolysaccharide (LPS) but was not increased by a low dose of LPS. Prx II itself caused a decrease in the osteogenic gene expression, alkaline phosphatase (ALP) activity, and Smad1/5/9 phosphorylation induced by BMP2. In addition, BMP2-induced osteogenic gene expression and ALP activity were higher in Prx II knockout (KO) cells than they were in wild-type (WT) cells. These inhibitory effects were mediated by protein phosphatase 2A Cα (PP2A Cα), which was increased and is known to induce the dephosphorylation of Smad1/5/9. The overexpression of Prx II increased the expression of PP2A Cα, and PP2A Cα was not expressed in Prx II KO cells. Moreover, PP2A Cα reduced the level of BMP2-induced osteogenic gene expression and Smad1/5/9 phosphorylation. LPS inhibited BMP2-induced Smad1/5/9 phosphorylation and the suppressed phosphorylation was restored by the PP2A inhibitor okadaic acid (OA). Bone phenotype analyses using microcomputed tomography (μCT) revealed that the Prx II KO mice had higher levels of bone mass than the levels of the WT mice. We hypothesize that Prx II has a negative role in osteoblast differentiation through the PP2A-dependent dephosphorylation of Smad1/5/9.

An antioxidant enzyme actively works to reduce bone synthesis under oxidative stress conditions in order to protect bone cells from damage and cell death. Bone is generated by cells called osteoblasts, which differentiate from stem cells. In osteoporosis and diabetes, excessive reactive oxygen species (ROS) within cells can disrupt osteoblast differentiation. South Korean researchers led by Eun-jung Kim at Kyungpook National University, Daegu, and Won-Gu Jang at Daegu University, Gyeongbuk, have shown that an antioxidant enzyme, peroxiredoxin II (PrxII), helps regulate bone formation under oxidative stress. The team generated PrxII-deficient mice and compared them with healthy normal mice. Under oxidative stress conditions, the mice had higher bone mass and higher expression of genes related to bone formation than the normal mice. PrxII limits osteoblast differentiation during elevated ROS by influencing associated protein activity and signalling pathways.

A cmap-enabled gene expression signature-matching approach identifies small-molecule inducers of accelerated cell senescence

BACKGROUND

Diverse stresses including genotoxic therapy can induce proliferating cancer cells to undergo cellular senescence and take on the characteristic phenotypes of replicative cellular aging. This accelerated or therapy-induced senescence has been alternatively proposed to contribute to therapeutic efficacy or resistance. Toward better understanding this cell state, we sought to define the core transcriptome of accelerated senescence in cancer cells.

RESULTS

We examined senescence induced by ionizing irradiation or ectopic overexpression of the stoichiometric cyclin-dependent kinase (CDK) inhibitor p21CIP/WAF1/SDI1 in the human breast cancer cell line MCF7. While radiation produces a strong DNA damage response, ectopic expression of p21 arrests cell cycle progression independently of DNA damage. Both conditions promoted senescence within 5 days. Microarray analysis revealed 378 up- and 391 down-regulated genes that were shared between the two conditions, representing a candidate signature. Systems analysis of the shared differentially expressed genes (DEGs) revealed strong signals for cell cycle control and DNA damage response pathways and predicted multiple upstream regulators previously linked to senescence. Querying the shared DEGs against the Connectivity Map (cmap) database of transcriptional responses to small molecules yielded 20 compounds that induce a similar gene expression pattern in MCF7 cells. Of 16 agents evaluated, six induced senescence on their own. Of these, the selective estrogen receptor degrader fulvestrant and the histone acetyltransferase inhibitor vorinostat did so without causing chromosomal damage.

CONCLUSIONS

Using a systems biology approach with experimental validation, we have defined a core gene expression signature for therapy-induced senescence.

Activation of the mTORC1/PGC-1 axis promotes mitochondrial biogenesis and induces cellular senescence in the lung epithelium

Cellular senescence is a biological process by which cells lose their capacity to proliferate yet remain metabolically active. Although originally considered a protective mechanism to limit the formation of cancer, it is now appreciated that cellular senescence also contributes to the development of disease, including common respiratory ailments such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. While many factors have been linked to the development of cellular senescence, mitochondrial dysfunction has emerged as an important causative factor. In this study, we uncovered that the mitochondrial biogenesis pathway driven by the mammalian target of rapamycin/peroxisome proliferator-activated receptor-γ complex 1α/β (mTOR/PGC-1α/β) axis is markedly upregulated in senescent lung epithelial cells. Using two different models, we show that activation of this pathway is associated with other features characteristic of enhanced mitochondrial biogenesis, including elevated number of mitochondrion per cell, increased oxidative phosphorylation, and augmented mitochondrial reactive oxygen species (ROS) production. Furthermore, we found that pharmacological inhibition of the mTORC1 complex with rapamycin not only restored mitochondrial homeostasis but also reduced cellular senescence to bleomycin in lung epithelial cells. Likewise, mitochondrial-specific antioxidant therapy also effectively inhibited mTORC1 activation in these cells while concomitantly reducing mitochondrial biogenesis and cellular senescence. In summary, this study provides a mechanistic link between mitochondrial biogenesis and cellular senescence in lung epithelium and suggests that strategies aimed at blocking the mTORC1/PGC-1α/β axis or reducing ROS-induced molecular damage could be effective in the treatment of senescence-associated lung diseases.

Radiotherapy-Induced Senescence and its Effects on Responses to Treatment

Radiotherapy is still a treatment of choice for many malignancies, often in combination with other strategies. However, its efficacy is limited by the dose that can be safely administered without eliciting serious side-effects, as well as the fact that recurrence is common, particularly in large tumours. Combining radiotherapy with drugs that could sensitise cells to radiation and/or reduce the factors that promote the recovery of the surviving cancer cells is a promising approach. Ionising radiation has been shown to induce senescence and the accumulation of senescent cells creates a microenvironment that facilitates neoplastic growth. This provides a rationale to test the addition of anti-senescent drugs, some of which are already available in the clinic, to radiotherapy protocols. Here, we discuss the relevance of radiotherapy-induced senescent cell accumulation and the potential interventions to minimise its negative effects.

Reactive Oxygen Species Detection in Senescent Cells

Cumulative evidence suggests that cellular senescence plays a variety of important physiological roles, including tumor suppression, embryonic development and ageing. Senescent cells are characterized by increased production of reactive oxygen species (ROS), mostly produced by dysfunctional mitochondria. Both intracellular and extracellular ROS have been shown to contribute to the induction of senescence. ROS have also been shown to act as signaling molecules during senescence, stabilizing the cell-cycle arrest. In this chapter, we present a detailed description of protocols that allow us to characterize intracellular and extracellular ROS in live senescent cells.

N-acetylcysteine ameliorates cisplatin-induced renal senescence and renal interstitial fibrosis through sirtuin1 activation and p53 deacetylation

The mechanism underlying the development of chronic kidney disease (CKD) after acute kidney injury (AKI) remains unclear. Maladaptive repair has been considered an important mechanism of CKD post AKI. Renal tubular cells under maladaptive repair have characteristics of premature senescence. These premature senescent cells can generate profibrotic factors that promote organ fibrosis. The purpose of this study was to investigate whether cisplatin induces premature renal senescence and the role of premature renal senescence in the progression of CKD post AKI. As oxidative stress is a major cause of senescence, we further evaluated whether antioxidant therapy could protect renal tubular cells from cisplatin-induced premature senescence and retard the progression of CKD post AKI. The molecular mechanism of this protection was also investigated. We found that cisplatin induced premature renal senescence in vitro and in vivo. In a multiple-cisplatin-treatment murine model, renal interstitial fibrosis was accompanied by premature renal senescence. N-acetylcysteine (NAC), an antioxidant, attenuated premature senescence and decreased renal fibrosis, and its effects were dependent on sirtuin1 (SIRT1) activation and p53 deacetylation. These results indicate that cisplatin can induce premature renal senescence, which is associated with the development of CKD post cisplatin-induced AKI. SIRT1 activation and p53 deacetylation might be identified as potential targets for attenuating premature renal senescence and retarding the progression of CKD post AKI.

Effect of Myricetin on Primary Open-angle Glaucoma

Background

Primary open angle glaucoma (POAG) is the most common form of glaucoma, with a multifactorial etiology that results in retinal ganglion cell death and loss of vision. In this study, we assessed the effects of myricetin on the trabecular meshwork cells in POAG.

Methods

In the in-vivo model, glaucoma was induced in Sprague-Dawley rats by injecting hyaluronic acid into the anterior chamber of the eye (every week for six-weeks). Treatment group rats were administered myricetin (25, 50 or 100 mg/ kg body weight via oral gavage) each day for of six weeks.

Results

POAG TM cells exposed to myricetin (25, 50 or 100 μM) exhibited significantly lowered reactive oxidative species (ROS) levels and lipid peroxidation products. The expressions of transforming growth factors (TGFβ1/β2), vascular endothelial growth factor, and senescence markers (senescence associated-β-galactosidase, cyclin-dependent kinase inhibitors-p16 and p21) were substantially down-regulated in POAG TM cells exposed to myricetin. Myricetin effectively prevented IOP elevation in glaucoma-induced rats and decreased inflammatory cytokines (IL-1α, IL-1β, IL-6, Il-8, TNF-α) in the aqueous humor and POAG TM cells of glaucoma-induced rats.

Conclusion

The observations of the study illustrate the protective effects of myricetin in glaucomatous TM cells.

Defenses against Pro-oxidant Forces - Maintenance of Cellular and Genomic Integrity and Longevity

There has been enormous recent progress in understanding how human cells respond to oxidative stress, such as that caused by exposure to ionizing radiation. We have witnessed a significant deciphering of the events that underlie how antioxidant responses counter pro-oxidant damage to key biological targets in all cellular compartments, including the genome and mitochondria. These cytoprotective responses include: 1. The basal cellular repertoire of antioxidant capabilities and its supporting cast of facilitator enzymes; and 2. The inducible phase of the antioxidant response, notably that mediated by the Nrf2 transcription factor. There has also been frenetic progress in defining how reactive electrophilic species swamp existing protective mechanisms to augment DNA damage, events that are embodied in the cellular "DNA-damage response", including cell cycle checkpoint activation and DNA repair, which occur on a time scale of hours to days, as well as the implementation of cellular responses such as apoptosis, autophagy, senescence and reprograming that extend the time period of damage sensing and response into weeks, months and years. It has become apparent that, in addition to the initial oxidative insult, cells typically undergo further waves of secondary reactive oxygen/nitrogen species generation, DNA damage and signaling and that these may reemerge long after the initial events have subsided, probably being driven, at least in part, by persisting DNA damage. These reactive oxygen/nitrogen species are an integral part of the pathological consequences of radiation exposure and may persist across multiple cell divisions. Because of the pervasive nature of oxidative stress, a cell will manifest different responses in different subcellular compartments and to different levels of stress injury. Aspects of these compartmentalized responses can involve the same proteins (such as ATM, p53 and p21) but in different functional guises, e.g., in cytoplasmic versus nuclear responses or in early- versus late-phase events. Many of these responses involve gene activation and new protein synthesis as well as a plethora of post-translational modifications of both basal and induced response proteins. It is these responses that we focus on in this review.

Targeting senescence to delay progression of multiple sclerosis

Multiple sclerosis (MS) is a chronic and often progressive, demyelinating disease of the central nervous system (CNS) white and gray matter and the single most common cause of disability in young adults. Age is one of the factors most strongly influencing the course of progression in MS. One of the hallmarks of aging is cellular senescence. The elimination of senescent cells with senolytics has very recently been shown to delay age-related dysfunction in animal models for other neurological diseases. In this review, the possible link between cellular senescence and the progression of MS is discussed, and the potential use of senolytics as a treatment for progressive MS is explored. Currently, there is no cure for MS and there are limited treatment options to slow the progression of MS. Current treatment is based on immunomodulatory approaches. Various cell types present in the CNS can become senescent and thus potentially contribute to MS disease progression. We propose that, after cellular senescence has indeed been shown to be directly implicated in disease progression, administration of senolytics should be tested as a potential therapeutic approach for the treatment of progressive MS.

Mechanisms of Dysfunction in the Aging Vasculature and Role in Age-Related Disease

Advancing age promotes cardiovascular disease (CVD), the leading cause of death in the United States and many developed nations. Two major age-related arterial phenotypes, large elastic artery stiffening and endothelial dysfunction, are independent predictors of future CVD diagnosis and likely are responsible for the development of CVD in older adults. Not limited to traditional CVD, these age-related changes in the vasculature also contribute to other age-related diseases that influence mammalian health span and potential life span. This review explores mechanisms that influence age-related large elastic artery stiffening and endothelial dysfunction at the tissue level via inflammation and oxidative stress and at the cellular level via Klotho and energy-sensing pathways (AMPK [AMP-activated protein kinase], SIRT [sirtuins], and mTOR [mammalian target of rapamycin]). We also discuss how long-term calorie restriction-a health span- and life span-extending intervention-can prevent many of these age-related vascular phenotypes through the prevention of deleterious alterations in these mechanisms. Lastly, we discuss emerging novel mechanisms of vascular aging, including senescence and genomic instability within cells of the vasculature. As the population of older adults steadily expands, elucidating the cellular and molecular mechanisms of vascular dysfunction with age is critical to better direct appropriate and measured strategies that use pharmacological and lifestyle interventions to reduce risk of CVD within this population.

Prophylactic vs. Therapeutic Treatment With P2Et Polyphenol-Rich Extract Has Opposite Effects on Tumor Growth

Polyphenols have tumoricidal effects via anti-proliferative, anti-angiogenic and cytotoxic mechanisms and have recently been demonstrated to modulate the immune response through their anti- or pro- oxidant activity. Nevertheless, it remains controversial whether antioxidant-rich supplements have real beneficial effects on health, especially in complex diseases such as cancer. We previously identified a polyphenol-rich extract obtained from Caesalpinia spinosa (P2Et) with anti-tumor activity in both breast carcinoma and melanoma. The present work evaluated the ability of P2Et extract to modulate the immune system in either the steady state or following tumor challenge. We found that the prophylactic treatment of healthy mice increased the number of CD4⁺ and CD8⁺ activated T, NK, regulatory T, dendritic and myeloid-derived suppressor cells in lymphoid organs together with a significant increase in plasma IL-6. Interestingly, this pre-conditioning of the host immune system with P2Et did not involve a protective effect against the control of tumor growth and metastasis in transplantable models of melanoma (B16) and breast cancer (4T1), but in contrast, a detrimental effect was observed in both models. We further demonstrated that this effect was at least partly due to an increase in regulatory T cells, myeloid-derived suppressor cells, and proinflammatory cytokines, with a concomitant decrease in CD4⁺ and CD8⁺ T cells. Taken together, these results suggest that the anti-tumor and immunomodulation properties of the P2Et extract critically depend on the presence of the tumor and might be mediated by the complex interactions between the tumor cells and the other components of the tumor microenvironment.

Upregulation of EID3 sensitizes breast cancer cells to ionizing radiation-induced cellular senescence

Previous studies have shown that BMS-345541 (BMS, a specific IκB kinase β inhibitor) sensitized various tumor cells including MCF-7 breast cancer cells to ionizing radiation (IR). However, the mechanisms of BMS action are unknown. Since the expression of E1A-like inhibitor of differentiation 3 (EID3) was highly upregulated in MCF-7 cells after BMS treatment, we investigated the role of EID3 in the response of MCF-7 cells to IR. We found that BMS induced EID3 expression in MCF-7 cells in a time- and dose-dependent manner. Knockdown of EID3 by specific shRNA attenuated BMS-induced radiosensitization in MCF-7 cells. In contrast, induction of EID3 expression in an inducible EID3 expressing MCF-7 cell line with doxycycline sensitized the cells to IR. EID3-mediated sensitization of MCF-7 cells to IR was not attributed to an increase in apoptosis. Instead, EID3-expressing MCF-7 cells exhibited significantly higher levels of senescence associated β-galactosidase (SA-β-gal) activity and higher levels of p21 and p57 than EID3-MCF-7 cells without induction of EID3 after exposure to IR. Similar findings were observed when EID3-expressing MCF-7 cells were treated with etoposide, a topoisomerase II inhibitor. Taken together, our findings reveal a novel function of EID3 and suggest that the induction of EID3 by BMS may be exploited as a new strategy to sensitize breast cancer cells to IR and chemotherapy by inducing cancer cell senescence.

Nrf2-Mediated Fibroblast Reprogramming Drives Cellular Senescence by Targeting the Matrisome

Nrf2 is a key regulator of the antioxidant defense system, and pharmacological Nrf2 activation is a promising strategy for cancer prevention and promotion of tissue repair. Here we show, however, that activation of Nrf2 in fibroblasts induces cellular senescence. Using a combination of transcriptomics, matrix proteomics, chromatin immunoprecipitation and bioinformatics we demonstrate that fibroblasts with activated Nrf2 deposit a senescence-promoting matrix, with plasminogen activator inhibitor-1 being a key inducer of the senescence program. In vivo, activation of Nrf2 in fibroblasts promoted re-epithelialization of skin wounds, but also skin tumorigenesis. The pro-tumorigenic activity is of general relevance, since Nrf2 activation in skin fibroblasts induced the expression of genes characteristic for cancer-associated fibroblasts from different mouse and human tumors. Therefore, activated Nrf2 qualifies as a marker of the cancer-associated fibroblast phenotype. These data highlight the bright and the dark sides of Nrf2 and the need for time-controlled activation of this transcription factor.

Role of sphingolipids in senescence: implication in aging and age-related diseases

Aging is defined as the progressive deterioration of physiological function with age. Incidence of many pathologies increases with age, including neurological and cardiovascular diseases and cancer. Aging tissues become less adaptable and renewable, and cells undergo senescence, a process by which they "irreversibly" stop dividing. Senescence has been shown to serve as a tumor suppression mechanism with clear desirable effects. However, senescence also has deleterious consequences, especially for cardiovascular, metabolic, and immune systems. Sphingolipids are a major class of lipids that regulate cell biology, owing to their structural and bioactive properties and diversity. Their involvement in the regulation of aging and senescence has been demonstrated and studied in multiple organisms and cell types, especially that of ceramide and sphingosine-1-phosphate; ceramide induces cellular senescence and sphingosine-1-phosphate delays it. These discoveries could be very useful in the future to understand aging mechanisms and improve therapeutic interventions.

Huperzine A attenuates nonalcoholic fatty liver disease by regulating hepatocyte senescence and apoptosis: an in vitro study

Objective

This study was undertaken to detect if free fatty acids (FFA) induce hepatocyte senescence in L-02 cells and if huperzine A has an anti-aging effect in fatty liver cells.

Methods

L-02 cells were treated with a FFA mixture (oleate/palmitate, at 3:0, 2:1, 1:1, 1:2 and 0:3 ratios) at different concentrations. Cell viability and fat accumulation rate were assessed by a Cell Counting Kit 8 and Nile Red staining, respectively. The mixture with the highest cell viability and fat accumulation rate was selected to continue with the following experiment. The L-02 cells were divided into five groups, including the control group, FFA group, FFA + 0.1 μmol/L huperzine A (LH) group, FFA + 1.0 μmol/L huperzine A (MH) group and FFA + 10 μmol/L huperzine A (HH) group, and were cultured for 24 h. The expression of senescence-associated β-galactosidase (SA-β-gal) was detected by an SA-β-gal staining kit. The expression levels of aging genes were measured by qRT-PCR. The expression levels of apoptosis proteins were detected by a Western blot. ELISA kits were used to detect inflammatory factors and oxidative stress products. The expression of nuclear factor (NF-κB) and IκBα were detected by immunofluorescence.

Results

The FFA mixture (oleate/palmitate, at a 2:1 ratio) of 0.5 mmol/L had the highest cell viability and fat accumulation rate, which was preferable for establishing an in vitro fatty liver model. The expression of inflammatory factors (TNF-α and IL-6) and oxidants Malonaldehyde (MDA), 4-hydroxynonenal (HNE) and reactive oxygen species (ROS) also increased in the L-02 fatty liver cells. The expression levels of aging markers and aging genes, such as SA-β-gal, p16, p21, p53 and pRb, increased more in the L-02 fatty liver cells than in the L-02 cells. The total levels of the apoptosis-associated proteins Bcl2, Bax, Bax/Bcl-2, CyCt and cleaved caspase 9 were also upregulated in the L-02 fatty liver cells. All of the above genes and proteins were downregulated in the huperzine A and FFA co-treatment group. In the L-02 fatty liver cells, the expression of IκBα decreased, while the expression of NF-κB increased. After the huperzine A and FFA co-treatment, the expression of IκBα increased, while the expression of NF-κB decreased.

Conclusion

Fatty liver cells showed an obvious senescence and apoptosis phenomenon. Huperzine A suppressed hepatocyte senescence, and it might exert its anti-aging effect via the NF-κB pathway.

Camptothecin induces G2/M phase arrest through the ATM-Chk2-Cdc25C axis as a result of autophagy-induced cytoprotection: Implications of reactive oxygen species

In the present study, we report that camptothecin (CPT) caused irreversible cell cycle arrest at the G₂/M phase, and was associated with decreased levels of cell division cycle 25C (Cdc25C) and increased levels of cyclin B1, p21, and phospho-H3. Interestingly, the reactive oxygen species (ROS) inhibitor, glutathione, decreased CPT-induced G₂/M phase arrest and moderately induced S phase arrest, indicating that the ROS is required for the regulation of CPT-induced G₂/M phase arrest. Furthermore, transient knockdown of nuclear factor-erythroid 2-related factor 2 (Nrf2), in the presence of CPT, increased the ROS’ level and further shifted the cell cycle from early S phase to the G₂/M phase, indicating that Nrf2 delayed the S phase in response to CPT. We also found that CPT-induced G₂/M phase arrest increased, along with the ataxia telangiectasia-mutated (ATM)-checkpoint kinase 2 (Chk2)-Cdc25C axis. Additionally, the proteasome inhibitor, MG132, restored the decrease in Cdc25C levels in response to CPT, and significantly downregulated CPT-induced G₂/M phase arrest, suggesting that CPT enhances G₂/M phase arrest through proteasome-mediated Cdc25C degradation. Our data also indicated that inhibition of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) inhibited CPT-induced p21 and cyclin B1 levels; however, inhibition of ERK blocked CPT-induced G₂/M phase arrest, and inhibition of JNK enhanced apoptosis in response to CPT. Finally, we found that CPT-induced G₂/M phase arrest circumvented apoptosis by activating autophagy through ATM activation. These findings suggest that CPT-induced G₂/M phase arrest through the ROS-ATM-Chk2-Cdc25C axis is accompanied by the activation of autophagy.

Mutational signatures reveal the role of RAD52 in p53-independent p21-driven genomic instability

Background

Genomic instability promotes evolution and heterogeneity of tumors. Unraveling its mechanistic basis is essential for the design of appropriate therapeutic strategies. In a previous study, we reported an unexpected oncogenic property of p21^WAF1/Cip1, showing that its chronic expression in a p53-deficient environment causes genomic instability by deregulation of the replication licensing machinery.

Results

We now demonstrate that p21^WAF1/Cip1 can further fuel genomic instability by suppressing the repair capacity of low- and high-fidelity pathways that deal with nucleotide abnormalities. Consequently, fewer single nucleotide substitutions (SNSs) occur, while formation of highly deleterious DNA double-strand breaks (DSBs) is enhanced, crafting a characteristic mutational signature landscape. Guided by the mutational signatures formed, we find that the DSBs are repaired by Rad52-dependent break-induced replication (BIR) and single-strand annealing (SSA) repair pathways. Conversely, the error-free synthesis-dependent strand annealing (SDSA) repair route is deficient. Surprisingly, Rad52 is activated transcriptionally in an E2F1-dependent manner, rather than post-translationally as is common for DNA repair factor activation.

Conclusions

Our results signify the importance of mutational signatures as guides to disclose the repair history leading to genomic instability. We unveil how chronic p21^WAF1/Cip1 expression rewires the repair process and identifies Rad52 as a source of genomic instability and a candidate therapeutic target.

Electronic supplementary material

The online version of this article (10.1186/s13059-018-1401-9) contains supplementary material, which is available to authorized users.

Innate immunity and cellular senescence: The good and the bad in the developmental and aged brain

Ongoing studies evidence cellular senescence in undifferentiated and specialized cells from tissues of all ages. Although it is believed that senescence plays a wider role in several stress responses in the mature age, its participation in certain physiological and pathological processes throughout life is coming to light. The "senescence machinery" has been observed in all brain cell populations, including components of innate immunity (e.g., microglia and astrocytes). As the beneficial versus detrimental implications of senescence is an open question, we aimed to analyze the contribution of immune responses in regulatory mechanisms governing its distinct functions in healthy (development, organogenesis, danger patrolling events) and diseased brain (glioma, neuroinflammation, neurodeneration), and the putative connection between cellular and molecular events governing the 2 states. Particularly this review offers new insights into the complex roles of senescence both as a chronological event as age advances, and as a molecular mechanism of brain homeostasis through the important contribution of innate immune responses and their crosstalk with neighboring cells in brain parenchyma. We also highlight the impact of the recently described glymphatic system and brain lymphatic vasculature in the interplay between peripheral and central immune surveillance and its potential implication during aging. This will open new ways to understand brain development, its deterioration during aging, and the occurrence of several oncological and neurodegenerative diseases.

Senescence-messaging secretome factors trigger premature senescence in human endometrium-derived stem cells

Accumulating evidence suggests that the senescence-messaging secretome (SMS) factors released by senescent cells play a key role in cellular senescence and physiological aging. Phenomenon of the senescence induction in human endometrium-derived mesenchymal stem cells (MESCs) in response to SMS factors has not yet been described. In present study, we examine a hypothesis whether the conditioned medium from senescent cells (CM-old) may promote premature senescence of young MESCs. In this case, we assume that SMS factors, containing in CM-old are capable to trigger senescence mechanism in a paracrine manner. A long-term cultivation MESCs in the presence of CM-old caused deceleration of cell proliferation along with emerging senescence phenotype, including increase in both the cell size and SA-β-Gal activity. The phosphorylation of p53 and MAPKAPK-2, a direct target of p38MAPK, as well as the expression of p21Cip1 and p16Ink4a were increased in CM-old treated cells with senescence developing whereas the Rb phosphorylation was diminished. The senescence progression was accompanied by both enhanced ROS generation and persistent activation of DNA damage response, comprising protein kinase ATM, histone H2A.X, and adapter protein 53BP1. Thus, we suggest that a senescence inducing signal is transmitted through p16/MAPKAPK-2/Rb and DDR-mediated p53/p21/Rb signaling pathways. This study is the first to demonstrate that the SMS factors secreted in conditioned medium of senescent MESCs trigger a paracrine mechanism of premature senescence in young cells.

NADPH oxidase 4 mediates ROS production in radiation-induced senescent cells and promotes migration of inflammatory cells

Excessive DNA damage induced by ionising radiation (IR) to normal tissue cells is known to trigger cellular senescence, a process termed stress-induced premature senescence (SIPS). SIPS is often accompanied by the production of reactive oxygen species (ROS), and this is reported to be important for the initiation and maintenance of SIPS. However, the source of ROS during SIPS after IR and their significance in radiation-induced normal tissue damage remain elusive. In the present study, we tested the hypothesis that the NADPH oxidase (NOX) family of proteins mediates ROS production in SIPS-induced cells after IR and plays a role in SIPS-associated biological events. X-irradiation of primary mouse embryonic fibroblasts (MEFs) resulted in cellular senescence and the concomitant increase of intracellular ROS. Among all six murine NOX isoforms (NOX1-4 and DUOX1/2), only NOX4 was detectable under basal conditions and was upregulated following IR. In addition, radiation-induced ROS production was diminished by genetic or pharmacological inhibition of NOX4. Meanwhile, NOX4 deficiency did not affect the induction of cellular senescence after IR. Furthermore, the migration of human monocytic U937 cells to the culture medium collected from irradiated MEFs was significantly reduced by NOX4 inhibition, suggesting that NOX4 promotes the recruitment of inflammatory cells. Collectively, our findings imply that NOX4 mediates ROS production in radiation-induced senescent cells and contributes to normal tissue damage after IR via the recruitment of inflammatory cells and the exacerbation of tissue inflammation.

Hyperphosphatemia induces senescence in human endothelial cells by increasing endothelin-1 production

Hyperphosphatemia is related to some pathologies, affecting vascular cell behavior. This work analyzes whether high concentration of extracellular phosphate induces endothelial senescence through up‐regulation of endothelin‐1 (ET‐1), exploring the mechanisms involved. The phosphate donor β‐glycerophosphate (BGP) in human endothelial cells increased ET‐1 production, endothelin‐converting enzyme‐1 (ECE‐1) protein, and mRNA expression, which depend on the AP‐1 activation through ROS production. In parallel, BGP also induced endothelial senescence by increasing p16 expression and the senescence‐associated β‐galactosidase (SA‐ß‐GAL) activity. ET‐1 itself was able to induce endothelial senescence, increasing p16 expression and SA‐ß‐GAL activity. In addition, senescence induced by BGP was blocked when different ET‐1 system antagonists were used. BGP increased ROS production at short times, and the presence of antioxidants prevented the effect of BGP on AP1 activation, ECE‐1 expression, and endothelial senescence. These findings were confirmed in vivo with two animal models in which phosphate serum levels were increased: seven/eight nephrectomized rats as chronic kidney disease models fed on a high phosphate diet and aged mice. Both models showed hyperphosphatemia, higher levels of ET‐1, and up‐regulation in aortic ECE‐1, suggesting a direct relationship between hyperphosphatemia and ET‐1. Present results point to a new and relevant role of hyperphosphatemia on the regulation of ET‐1 system and senescence induction at endothelial level, both in endothelial cells and aorta from two animal models. The mechanism involved showed a higher ROS production, which probably activates AP‐1 transcription factor and, as a result, ECE‐1 expression, increasing ET‐1 synthesis, which in consequence induces endothelial senescence.

Preterm labor in the absence of acute histologic chorioamnionitis is characterized by cellular senescence of the chorioamniotic membranes

BACKGROUND

Decidual senescence has been considered a mechanism of disease for spontaneous preterm labor in the absence of severe acute inflammation. Yet, signs of cellular senescence have also been observed in the chorioamniotic membranes from women who underwent the physiological process of labor at term.

OBJECTIVE

We aimed to investigate whether, in the absence of acute histologic chorioamnionitis, the chorioamniotic membranes from women who underwent spontaneous preterm labor or labor at term exhibit signs of cellular senescence.

STUDY DESIGN

Chorioamniotic membrane samples were collected from women who underwent spontaneous preterm labor or labor at term. Gestational age-matched nonlabor controls were also included. Senescence-associated genes/proteins were determined using reverse transcription quantitative polymerase chain reaction analysis (n = 7-9 each for array; n = 26-28 each for validation), enzyme-linked immunosorbent assays (n = 7-9 each), immunoblotting (n = 6-7 each), and immunohistochemistry (n = 7-8 each). Senescence-associated β-galactosidase activity (n = 7-11 each) and telomere length (n = 15-22 each) were also evaluated.

RESULTS

In the chorioamniotic membranes without acute histologic chorioamnionitis: (1) the expression profile of senescence-associated genes was different between the labor groups (term in labor and preterm in labor) and the nonlabor groups (term no labor and preterm no labor), yet there were differences between the term in labor and preterm in labor groups; (2) most of the differentially expressed genes among the groups were closely related to the tumor suppressor protein (TP53) pathway; (3) the expression of TP53 was down-regulated in the term in labor and preterm in labor groups compared to their nonlabor counterparts; (4) the expression of CDKN1A (gene coding for p21) was up-regulated in the term in labor and preterm in labor groups compared to their nonlabor counterparts; (5) the expression of the cyclin kinase CDK2 and cyclins CCNA2, CCNB1, and CCNE1 was down-regulated in the preterm in labor group compared to the preterm no labor group; (6) the concentration of TP53 was lower in the preterm in labor group than in the preterm no labor and term in labor groups; (7) the senescence-associated β-galactosidase activity was greater in the preterm in labor group than in the preterm no labor and term in labor groups; (8) the concentration of phospho-S6 ribosomal protein was reduced in the term in labor group compared to its nonlabor counterpart, but no differences were observed between the preterm in labor and preterm no labor groups; and (9) no significant differences were observed in relative telomere length among the study groups (term no labor, term in labor, preterm no labor, and preterm in labor).

CONCLUSION

In the absence of acute histologic chorioamnionitis, signs of cellular senescence are present in the chorioamniotic membranes from women who underwent spontaneous preterm labor compared to those who delivered preterm in the absence of labor. However, the chorioamniotic membranes from women who underwent spontaneous labor at term did not show consistent signs of cellular senescence in the absence of histologic chorioamnionitis. These results suggest that different pathways are implicated in the pathological and physiological processes of labor.

Regiospecific Synthesis of Ring A Fused Withaferin A Isoxazoline Analogues: Induction of Premature Senescence by W-2b in Proliferating Cancer Cells

Induction of premature senescence represents a novel functional strategy to curb the uncontrolled proliferation of malignant cancer cells. This study unveils the regiospecific synthesis of novel isoxazoline derivatives condensed to ring A of medicinal plant product Withaferin-A. Intriguingly, the cis fused products with β-oriented hydrogen exhibited excellent cytotoxic activities against proliferating human breast cancer MCF7 and colorectal cancer HCT-116 cells. The most potent derivative W-2b triggered premature senescence along with increase in senescence-associated β-galactosidase activity, G2/M cell cycle arrest, and induction of senescence-specific marker p21^Waf1/Cip1 at its sub-toxic concentration. W-2b conferred a robust increase in phosphorylation of mammalian checkpoint kinase-2 (Chk2) in cancer cells in a dose-dependent manner. Silencing of endogenous Chk2 by siRNA divulged that the amplification of p21 expression and senescence by W-2b was Chk2-dependent. Chk2 activation (either by ectopic overexpression or through treatment with W-2b) suppressed NM23-H1 signaling axis involved in cancer cell proliferation. Finally, W-2b showed excellent in vivo efficacy with 83.8% inhibition of tumor growth at a dose of 25 mg/kg, b.w. in mouse mammary carcinoma model. Our study claims that W-2b could be a potential candidate to limit aberrant cellular proliferation rendering promising improvement in the treatment regime in cancer patients.