Small molecule compounds that induce cellular senescence

Therapy-Induced Stromal Senescence Promoting Aggressiveness of Prostate and Ovarian Cancer

Cancer progression is supported by the cross-talk between tumor cells and the surrounding stroma. In this context, senescent cells in the tumor microenvironment contribute to the development of a pro-inflammatory milieu and the acquisition of aggressive traits by cancer cells. Anticancer treatments induce cellular senescence (therapy-induced senescence, TIS) in both tumor and non-cancerous cells, contributing to many detrimental side effects of therapies. Thus, we focused on the effects of chemotherapy on the stromal compartment of prostate and ovarian cancer. We demonstrated that anticancer chemotherapeutics, regardless of their specific mechanism of action, promote a senescent phenotype in stromal fibroblasts, resulting in metabolic alterations and secretion of paracrine factors, sustaining the invasive and clonogenic potential of both prostate and ovarian cancer cells. The clearance of senescent stromal cells, through senolytic drug treatment, reverts the malignant phenotype of tumor cells. The clinical relevance of TIS was validated in ovarian and prostate cancer patients, highlighting increased accumulation of lipofuscin aggregates, a marker of the senescent phenotype, in the stromal compartment of tissues from chemotherapy-treated patients. These data provide new insights into the potential efficacy of combining traditional anticancer strategies with innovative senotherapy to potentiate anticancer treatments and overcome the adverse effects of chemotherapy.

A novel prognostic model based on cellular senescence-related gene signature for bladder cancer

Background

Cellular senescence plays crucial role in the progression of tumors. However, the expression patterns and clinical significance of cellular senescence-related genes in bladder cancer (BCa) are still not clearly clarified. This study aimed to establish a prognosis model based on senescence-related genes in BCa.

Methods

The transcriptional profile data and clinical information of BCa were downloaded from TCGA and GEO databases. The least absolute shrinkage and selection operator (LASSO), univariate and multivariate Cox regression analyses were performed to develop a prognostic model in the TCGA cohort. The GSE13507 cohort were used for validation. Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and single-sample gene set enrichment analysis (ssGSEA) were performed to investigate underlying mechanisms.

Results

A six-gene signature (CBX7, EPHA3, STK40, TGFB1I1, SREBF1, MYC) was constructed in the TCGA databases. Patients were classified into high risk and low risk group in terms of the median risk score. Survival analysis revealed that patients in the higher risk group presented significantly worse prognosis. Receiver operating characteristic (ROC) curve analysis verified the moderate predictive power of the risk model based on the six senescence-related genes signature. Further analysis indicated that the clinicopathological features analysis were significantly different between the two risk groups. As expected, the signature presented prognostic significance in the GSE13507 cohort. Functional analysis indicated that immune-related pathways activity, immune cell infiltration and immune-related function were different between two risk groups. In addition, risk score were positively correlated with multiple immunotherapy biomarkers.

Conclusion

Our study revealed that a novel model based on senescence-related genes could serve as a reliable predictor of survival for patients with BCa.

Nicandra physalodes Extract Exerts Antiaging Effects in Multiple Models and Extends the Lifespan of Caenorhabditis elegans via DAF-16 and HSF-1

The development of safe and effective therapeutic interventions is an important issue for delaying aging and reducing the risk of aging-related diseases. Chinese herbal medicines for the treatment of aging and other complex diseases are desired due to their multiple components and targets. Through screening for effects on lifespan of 836 Chinese herbal medicine extracts, Nicandra physalodes extract (HL0285) was found to exhibit lifespan extension activity in Caenorhabditis elegans (C. elegans). In further experiments, HL0285 improved healthspan, enhanced stress resistance, and delayed the progression of neurodegenerative diseases in C. elegans. Additionally, it ameliorated senescence in human lung fibroblasts (MRC-5 cells) and reversed liver function damage and reduced senescence marker levels in doxorubicin- (Dox-) induced aging mice. In addition, the longevity effect of HL0285 in C. elegans was dependent on the DAF-16 and HSF-1 signaling pathways, as demonstrated by the results of the mutant lifespan, gene level, and GFP level assays. In summary, we discovered that HL0285 had an antiaging effect in C. elegans, MRC-5 cells, and Dox-induced aging mice and deserves to be explored in the future studies on antiaging agents.

Cellular senescence: the good, the bad and the unknown

Cellular senescence is a ubiquitous process with roles in tissue remodelling, including wound repair and embryogenesis. However, prolonged senescence can be maladaptive, leading to cancer development and age-related diseases. Cellular senescence involves cell-cycle arrest and the release of inflammatory cytokines with autocrine, paracrine and endocrine activities. Senescent cells also exhibit morphological alterations, including flattened cell bodies, vacuolization and granularity in the cytoplasm and abnormal organelles. Several biomarkers of cellular senescence have been identified, including SA-βgal, p16 and p21; however, few markers have high sensitivity and specificity. In addition to driving ageing, senescence of immune and parenchymal cells contributes to the development of a variety of diseases and metabolic disorders. In the kidney, senescence might have beneficial roles during development and recovery from injury, but can also contribute to the progression of acute kidney injury and chronic kidney disease. Therapies that target senescence, including senolytic and senomorphic drugs, stem cell therapies and other interventions, have been shown to extend lifespan and reduce tissue injury in various animal models. Early clinical trials confirm that senotherapeutic approaches could be beneficial in human disease. However, larger clinical trials are needed to translate these approaches to patient care.

The interaction between cellular senescence and chronic kidney disease as a therapeutic opportunity

Chronic kidney disease (CKD) is an increasingly serious public health problem in the world, but the effective therapeutic approach is quite limited at present. Cellular senescence is characterized by the irreversible cell cycle arrest, senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Renal senescence shares many similarities with CKD, including etiology, mechanism, pathological change, phenotype and outcome, however, it is difficult to judge whether renal senescence is a trigger or a consequence of CKD, since there is a complex correlation between them. A variety of cellular signaling mechanisms are involved in their interactive association, which provides new potential targets for the intervention of CKD, and then extends the researches on senotherapy. Our review summarizes the common features of renal senescence and CKD, the interaction between them, the strategies of senotherapy, and the open questions for future research.

Senescence of alveolar epithelial cells impacts initiation and chronic phases of murine fibrosing interstitial lung disease

Fibrosing interstitial lung disease (ILD) develops due to the impaired reparative processes following lung tissue damage. Cellular senescence has been reported to contribute to the progression of fibrosis. However, the mechanisms by which these senescent cells initiate and/or drive the progression of lung tissue fibrosis are not yet fully understood. We demonstrated that p21^WAF1/CIP1- and p16^INK4A-pathway-dependent senescence in type 2 alveolar epithelial cells (AEC2) were both involved in the initiation and progression of lung fibrosis in murine bleomycin (BLM)-induced ILD. p21^WAF1/CIP1-senescent AEC2 emerged rapidly, as early as 1 day after the intratracheal instillation of BLM. Their number subsequently increased and persisted until the later fibrosis phase. Very few p16^INK4A-senescent AEC2 emerged upon the instillation of BLM, and their increase was slower and milder than that of p21^WAF1/CIP1+ AEC2. AEC2 enriched with senescent cells sorted from BLM-ILD lungs expressed senescence-associated secretory phenotype (SASP)-related genes, including Il6, Serpin1, Tnfa, Ccl2, Tgfb, and Pdgfa, at the initiation and chronic phases of fibrosis, exhibiting distinct expression patterns of magnitude that were dependent on the disease phase. Ly6C⁺ inflammatory monocytes increased in the lungs immediately after the instillation of BLM and interstitial macrophages increased from day 3. The expression of Acta2 and Col1a1 was upregulated as early as day 1, indicating the activation of fibroblasts. We speculated that IL-6, plasminogen activator inhibitor-1 (PAI-1), and TGF-β contributed to the accumulation of senescent cells during the progression of fibrosis in an autocrine and paracrine manner. In addition, CCL2, produced in large amounts by senescent AEC2, may have induced the infiltration of Ly6C⁺ inflammatory monocytes in the early phase, and TGF-β and PDGFa from senescent AEC2 may contribute to the activation of fibroblasts in the very early phases. Our study indicated that senescent AEC2 plays a role in the pathogenesis of fibrosing ILD throughout the course of the disease and provides insights into its pathogenesis, which may lead to the development of new therapeutic methods targeting senescent cells or SASP molecules.

Accelerated neuronal aging in vitro ∼melting watch ∼

In developed countries, the aging of the population and the associated increase in age-related diseases are causing major unresolved medical, social, and environmental matters. Therefore, research on aging has become one of the most important and urgent issues in life sciences. If the molecular mechanisms of the onset and progression of neurodegenerative diseases are elucidated, we can expect to develop disease-modifying methods to prevent neurodegeneration itself. Since the discovery of induced pluripotent stem cells (iPSCs), there has been an explosion of disease models using disease-specific iPSCs derived from patient-derived somatic cells. By inducing the differentiation of iPSCs into neurons, disease models that reflect the patient-derived pathology can be reproduced in culture dishes, and are playing an active role in elucidating new pathological mechanisms and as a platform for new drug discovery. At the same time, however, we are faced with a new problem: how to recapitulate aging in culture dishes. It has been pointed out that cells differentiated from pluripotent stem cells are juvenile, retain embryonic traits, and may not be fully mature. Therefore, attempts are being made to induce cell maturation, senescence, and stress signals through culture conditions. It has also been reported that direct conversion of fibroblasts into neurons can reproduce human neurons with an aged phenotype. Here, we outline some state-of-the-art insights into models of neuronal aging in vitro. New frontiers in which stem cells and methods for inducing differentiation of tissue regeneration can be applied to aging research are just now approaching, and we need to keep a close eye on them. These models are forefront and intended to advance our knowledge of the molecular mechanisms of aging and contribute to the development of novel therapies for human neurodegenerative diseases associated with aging.

DNA repair as a shared hallmark in cancer and ageing

Increasing evidence demonstrates that DNA damage and genome instability play a crucial role in ageing. Mammalian cells have developed a wide range of complex and well‐orchestrated DNA repair pathways to respond to and resolve many different types of DNA lesions that occur from exogenous and endogenous sources. Defects in these repair pathways lead to accelerated or premature ageing syndromes and increase the likelihood of cancer development. Understanding the fundamental mechanisms of DNA repair will help develop novel strategies to treat ageing‐related diseases. Here, we revisit the processes involved in DNA damage repair and how these can contribute to diseases, including ageing and cancer. We also review recent mechanistic insights into DNA repair and discuss how these insights are being used to develop novel therapeutic strategies for treating human disease. We discuss the use of PARP inhibitors in the clinic for the treatment of breast and ovarian cancer and the challenges associated with acquired drug resistance. Finally, we discuss how DNA repair pathway‐targeted therapeutics are moving beyond PARP inhibition in the search for ever more innovative and efficacious cancer therapies.

Applying C. elegans to the Industrial Drug Discovery Process to Slow Aging

The increase in our molecular understanding of the biology of aging, coupled with a recent surge in investment, has led to the formation of several companies developing pharmaceuticals to slow aging. Research using the tiny nematode worm Caenorhabditis elegans was the first to show that mutations in single genes can extend lifespan, and subsequent research has shown that this model organism is uniquely suited to testing interventions to slow aging. Yet, with a few notable exceptions, C. elegans is not in the standard toolkit of longevity companies. Here we discuss the paths to overcome the barriers to using C. elegans in industrial drug discovery. We address the predictive power of C. elegans for human aging, how C. elegans research can be applied to specific challenges in the typical drug discovery pipeline, and how standardised and quantitative assays will help C. elegans fulfil its potential in the biotech and pharmaceutical industry. We argue that correct application of this model and its knowledge base will significantly accelerate progress to slow human aging.

Potential Methods of Targeting Cellular Aging Hallmarks to Reverse Osteoarthritic Phenotype of Chondrocytes

Osteoarthritis (OA) is a chronic degenerative joint disease that causes pain, physical disability, and life quality impairment. The pathophysiology of OA remains largely unclear, and currently no FDA-approved disease-modifying OA drugs (DMOADs) are available. As has been acknowledged, aging is the primary independent risk factor for OA, but the mechanisms underlying such a connection are not fully understood. In this review, we first revisit the changes in OA chondrocytes from the perspective of cellular hallmarks of aging. It is concluded that OA chondrocytes share many alterations similar to cellular aging. Next, based on the findings from studies on other cell types and diseases, we propose methods that can potentially reverse osteoarthritic phenotype of chondrocytes back to a healthier state. Lastly, current challenges and future perspectives are summarized.

Exploiting senescence for the treatment of cancer

Senescence is a cellular response to a variety of stress signals that is characterized by a stable withdrawal from the cell cycle and major changes in cell morphology and physiology. While most research on senescence has been performed on non-cancer cells, it is evident that cancer cells can also mount a senescence response. In this Review, we discuss how senescence can be induced in cancer cells. We describe the distinctive features of senescent cancer cells and how these changes in cellular physiology might be exploited for the selective eradication of these cells (senolysis). We discuss activation of the host immune system as a particularly attractive way to clear senescent cancer cells. Finally, we consider the challenges and opportunities provided by a 'one-two punch' sequential treatment of cancer with pro-senescence therapy followed by senolytic therapy.

Translation of Cellular Senescence to Novel Therapeutics: Insights From Alternative Tools and Models

Increasing chronological age is the greatest risk factor for human diseases. Cellular senescence (CS), which is characterized by permanent cell-cycle arrest, has recently emerged as a fundamental mechanism in developing aging-related pathologies. During the aging process, senescent cell accumulation results in senescence-associated secretory phenotype (SASP) which plays an essential role in tissue dysfunction. Although discovered very recently, senotherapeutic drugs have been already involved in clinical studies. This review gives a summary of the molecular mechanisms of CS and its role particularly in the development of cardiovascular diseases (CVD) as the leading cause of death. In addition, it addresses alternative research tools including the nonhuman and human models as well as computational techniques for the discovery of novel therapies. Finally, senotherapeutic approaches that are mainly classified as senolytics and senomorphics are discussed.

Cancer and aging: A call to action

Background

The intersection of cancer and aging is an emerging public health challenge in developed countries because of the aging and expansion of the population.

Aims

We convened a panel of experts to share their insights on this topic at the inaugural University of Florida Health Cancer Center's (UFHCC's) Cancer and Aging Symposium, which was held virtually in February 2022.

Methods

We featured presentations from four leading scientists, whose research spans multiple disciplines including basic science, translational research, geriatric oncology, and population science.

Results

Each speaker offered their unique perspective and insight on the intersection between cancer and aging and discussed their current and ongoing research in this field. In addition to this panel of experts, scientists from the National Institutes of Health and the National Cancer Institute, as well as a UFHCC-affiliated citizen scientist, shared their perspectives on strategies to move the field forward. Some of the key open questions and opportunities for future research offered by these presenters in aging and cancer include but are not limited to infusing health disparities research into the field of cancer and aging, assessing the value of geriatric assessment in identifying early vulnerabilities that may affect response to emerging cancer therapies in older patients, and assessing biological age and other biomarkers (e.g., clonal hematopoiesis) in relation to clinical endpoints and the development of primary, secondary, and tertiary cancer prevention interventions.

Conclusion

Research is needed to accelerate knowledge regarding the dynamic interplay of cancer and aging and optimize care in diverse older adults to achieve equity in cancer outcomes.

Association between mitochondrial and nuclear DNA damages and cellular senescence in the patients with biliary atresia undergoing Kasai portoenterostomy and liver transplantation

Biliary atresia (BA) is a cholestatic disease with extrahepatic bile duct obstruction that requires early surgical intervention and occasionally liver transplantation (LT). Accumulation of toxic bile acids induces oxidative stress that results in cell damage, such as cell senescence, mitochondrial dysfunction and others. However, details of their reciprocal association and clinical significance are unexplored. Therefore, we used immuno-localization of markers for cell senescence (p16 and p21), nuclear double-strand DNA damage (γH2AX), autophagy (p62), and mtDNA damage (mtDNA copy number) in patients with BA who underwent Kasai portoenterostomy (KP) and LT. We studied liver biopsy specimens from 54 patients with BA, 14 who underwent LT and 11 from the livers of neonates and infants obtained at autopsy. In hepatocytes, p21 expression was significantly increased in KP. In cholangiocytes, p16 expression was significantly increased in LT, and p21 expression was significantly increased in KP. p62 expression was significantly increased in the KP hepatocytes and LT cholangiocytes. Furthermore, mtDNA copy number significantly decreased in KP and LT compared with the control. Cell senescence and mitochondrial DNA damage progression were dependent on the BA clinical stages and could possibly serve as the markers of indication of LT.

MicroRNAs, Long Non-Coding RNAs, and Circular RNAs in the Redox Control of Cell Senescence

Cell senescence is critical in diverse aspects of organism life. It is involved in tissue development and homeostasis, as well as in tumor suppression. Consequently, it is tightly integrated with basic physiological processes during life. On the other hand, senescence is gradually being considered as a major contributor of organismal aging and age-related diseases. Increased oxidative stress is one of the main risk factors for cellular damages, and thus a driver of senescence. In fact, there is an intimate link between cell senescence and response to different types of cellular stress. Oxidative stress occurs when the production of reactive oxygen species/reactive nitrogen species (ROS/RNS) is not adequately detoxified by the antioxidant defense systems. Non-coding RNAs are endogenous transcripts that govern gene regulatory networks, thus impacting both physiological and pathological events. Among these molecules, microRNAs, long non-coding RNAs, and more recently circular RNAs are considered crucial mediators of almost all cellular processes, including those implicated in oxidative stress responses. Here, we will describe recent data on the link between ROS/RNS-induced senescence and the current knowledge on the role of non-coding RNAs in the senescence program.

MicroRNA-Mediated Downregulation of HMGB2 Contributes to Cellular Senescence in Microvascular Endothelial Cells

High mobility group box 2 (HMGB2) is a non-histone chromosomal protein involved in various biological processes, including cellular senescence. However, its role in cellular senescence has not been evaluated extensively. To determine the regulatory role and mechanism of HMGB2 in cellular senescence, we performed gene expression analysis, senescence staining, and tube formation assays using young and senescent microvascular endothelial cells (MVECs) after small RNA treatment or HMGB2 overexpression. HMGB2 expression decreased with age and was regulated at the transcriptional level. siRNA-mediated downregulation inhibited cell proliferation and accelerated cellular senescence. In contrast, ectopic overexpression delayed senescence and maintained relatively higher tube-forming activity. To determine the HMGB2 downregulation mechanism, we screened miRNAs that were significantly upregulated in senescent MVECs and selected HMGB2-targeting miRNAs. Six miRNAs, miR-23a-3p, 23b-3p, -181a-5p, -181b-5p, -221-3p, and -222-3p, were overexpressed in senescent MVECs. Ectopic introduction of miR-23a-3p, -23b-3p, -181a-5p, -181b-5p, and -221-3p, with the exception of miR-222-3p, led to the downregulation of HMGB2, upregulation of senescence-associated markers, and decreased tube formation activity. Inhibition of miR-23a-3p, -181a-5p, -181b-5p, and -221-3p delayed cellular senescence. Restoration of HMGB2 expression using miRNA inhibitors represents a potential strategy to overcome the detrimental effects of cellular senescence in endothelial cells.

Systems approaches to investigate the role of NF-κB signaling in aging

The nuclear factor-κB (NF-κB) signaling pathway is one of the most well-studied pathways related to inflammation, and its involvement in aging has attracted considerable attention. As aging is a complex phenomenon and is the result of a multi-step process, the involvement of the NF-κB pathway in aging remains unclear. To elucidate the role of NF-κB in the regulation of aging, different systems biology approaches have been employed. A multi-omics data-driven approach can be used to interpret and clarify unknown mechanisms but cannot generate mechanistic regulatory structures alone. In contrast, combining this approach with a mathematical modeling approach can identify the mechanistics of the phenomena of interest. The development of single-cell technologies has also helped clarify the heterogeneity of the NF-κB response and underlying mechanisms. Here, we review advances in the understanding of the regulation of aging by NF-κB by focusing on omics approaches, single-cell analysis, and mathematical modeling of the NF-κB network.

Approaches and Protocols to Analyze Autophagy and Its Role in Death of Apoptosis-Resistant Senescent Tumor Cells

Anticancer therapy is complicated by the ability of malignant cells to activate cytoprotective autophagy that rescues treated cells. This protocol describes methods for analysis of autophagic process in apoptosis-resistant tumor cells treated with damaging agents. Induction of autophagy in these cells can activate apoptotic death. Protocol provides methods for Western blotting, immunofluorescent analysis, and transfection of cells with fluorescent protein-tagged LC3-encoding plasmids to analyze autophagy. Different approaches to change autophagy in tumor cells are suggested. A special approach is connected with induction of cellular senescence. Senescent cells, which are resistant to apoptosis, are vulnerable to certain damaging agents, in particular, to kinase inhibitors. Methods to induce and analyze senescence are considered. They include detection of proliferation arrest by different ways, mTORC1 activity assay and fluorescent analysis of mTORC1 and lysosome localization as a novel senescence hallmark. Incapability of senescent cells to complete autophagy after damage allows to force them to apoptosis. To demonstrate apoptotic cell death, analysis of caspase activity, Annexin V-FITC binding, DNA fragmentation, and mitochondria and lysosome damage are suggested. The methods described can be applied in studies aimed on developing different strategies of tumor cell elimination through changing autophagy.

Chemically induced senescence in human stem cell-derived neurons promotes phenotypic presentation of neurodegeneration

Modeling age‐related neurodegenerative disorders with human stem cells are difficult due to the embryonic nature of stem cell‐derived neurons. We developed a chemical cocktail to induce senescence of iPSC‐derived neurons to address this challenge. We first screened small molecules that induce embryonic fibroblasts to exhibit features characteristic of aged fibroblasts. We then optimized a cocktail of small molecules that induced senescence in fibroblasts and cortical neurons without causing DNA damage. The utility of the “senescence cocktail” was validated in motor neurons derived from ALS patient iPSCs which exhibited protein aggregation and axonal degeneration substantially earlier than those without cocktail treatment. Our “senescence cocktail” will likely enhance the manifestation of disease‐related phenotypes in neurons derived from iPSCs, enabling the generation of reliable drug discovery platforms.

α-1 Adrenergic receptor antagonist doxazosin reverses hepatic stellate cells activation via induction of senescence

BACKGROUND

Activated hepatic stellate cells (aHSCs) are the main effector cells during liver fibrogenesis. α-1 adrenergic antagonist doxazosin (DX) was shown to be anti-fibrotic in an in vivo model of liver fibrosis (LF), but the mechanism remains to be elucidated. Recent studies suggest that reversion of LF can be achieved by inducing cellular senescence characterized by irreversible cell-cycle arrest and acquisition of the senescence-associated secretory phenotype (SASP).

AIM

To elucidate the mechanism of the anti-fibrotic effect of DX and determine whether it induces senescence.

METHODS

Primary culture-activated rat HSCs were used. mRNA and protein expression were measured by qPCR and Western blot, respectively. Cell proliferation was assessed by BrdU incorporation and xCelligence analysis. TGF-β was used for maximal HSC activation. Norepinephrine (NE), PMA and m-3M3FBS were used to activate alpha-1 adrenergic signaling.

RESULTS

Expression of Col1α1 was significantly decreased by DX (10 µmol/L) at mRNA (-30 %) and protein level (-50 %) in TGF-β treated aHSCs. DX significantly reduced aHSCs proliferation and increased expression of senescence and SASP markers. PMA and m-3M3FBS reversed the effect of DX on senescence markers.

CONCLUSION

Doxazosin reverses the fibrogenic phenotype of aHSCs and induces the senescence phenotype.

Senescence Alterations in Pulmonary Hypertension

Cellular senescence is the arrest of normal cell division and is commonly associated with aging. The interest in the role of cellular senescence in lung diseases derives from the observation of markers of senescence in chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (IPF), and pulmonary hypertension (PH). Accumulation of senescent cells and the senescence-associated secretory phenotype in the lung of aged patients may lead to mild persistent inflammation, which results in tissue damage. Oxidative stress due to environmental exposures such as cigarette smoke also promotes cellular senescence, together with additional forms of cellular stress such as mitochondrial dysfunction and endoplasmic reticulum stress. Growing recent evidence indicate that senescent cell phenotypes are observed in pulmonary artery smooth muscle cells and endothelial cells of patients with PH, contributing to pulmonary artery remodeling and PH development. In this review, we analyze the role of different senescence cell phenotypes contributing to the pulmonary artery remodeling process in different PH clinical entities. Different molecular pathway activation and cellular functions derived from senescence activation will be analyzed and discussed as promising targets to develop future senotherapies as promising treatments to attenuate pulmonary artery remodeling in PH.

JAB1 deletion in oligodendrocytes causes senescence-induced inflammation and neurodegeneration in mice

Oligodendrocytes are the primary target of demyelinating disorders and progressive neurodegenerative changes may evolve in the CNS. DNA damage and oxidative stress are considered key pathogenic events, but the underlying molecular mechanisms remain unclear. Moreover, animal models do not fully recapitulate human diseases, complicating the path to effective treatments. Here we report that mice with cell autonomous deletion of the nuclear COP9 signalosome component CSN5 (JAB1) in oligodendrocytes develop DNA damage and defective DNA repair in myelinating glial cells. Interestingly, oligodendrocytes lacking JAB1 expression underwent a senescence-like phenotype that fostered chronic inflammation and oxidative stress. These mutants developed progressive CNS demyelination, microglia inflammation and neurodegeneration, with severe motor deficits and premature death. Notably, blocking microglia inflammation did not prevent neurodegeneration, whereas the deletion of p21CIP1 but not p16INK4a pathway ameliorated the disease. We suggest that senescence is key to sustaining neurodegeneration in demyelinating disorders and may be considered a potential therapeutic target.

Enhanced Platelet-Rich Plasma (ePRP) Stimulates Wound Healing through Effects on Metabolic Reprogramming in Fibroblasts

As a source of growth factors for expediting wound healing and tissue regeneration, plasma-rich plasma (PRP) has been extensively applied in diverse fields including orthopaedics, ophthalmology, oral and maxillofacial surgery, dentistry, and gynaecology. However, the function of PRP in metabolic regulations remains enigmatic. A standardized method was devised herein to enrich growth factors and to lyophilize it as enhanced PRP (ePRP) powder, which could become ubiquitously available without mechanical centrifugation in clinical practice. To identify metabolic reprogramming in human dermal fibroblasts under ePRP treatment, putative metabolic targets were identified by transcriptome profiling and validated for their metabolic effects and mechanism. ePRP does not only promote wound healing but re-aligns energy metabolism by shifting to glycolysis through stimulation of glycolytic enzyme activity in fibroblasts. On the contrary, oxygen consumption rates and several mitochondrial respiration activities were attenuated in ePRP-treated fibroblasts. Furthermore, ePRP treatment drives the mitochondrial resetting by hindering the mitochondrial biogenesis-related genes and results in a dampened mitochondrial mass. Antioxidant production was further increased by ePRP treatment to prevent reactive oxygen species formation. Besides, ePRP also halts the senescence progression of fibroblasts by activating SIRT1 expression. Importantly, the glycolytic inhibitor 2-DG can completely reverse the ePRP-enhanced wound healing capacity, whereas the mitochondrial inhibitor oligomycin cannot. This is the first study to utilize PRP for comprehensively investigating its effects on the metabolic reprogramming of fibroblasts. These findings indicate that PRP’s primary metabolic regulation is to promote metabolic reprogramming toward glycolytic energy metabolism in fibroblasts, preserving redox equilibrium and allowing anabolic pathways necessary for the healing and anti-ageing process.

Skin Aging, Cellular Senescence and Natural Polyphenols

The skin, being the barrier organ of the body, is constitutively exposed to various stimuli impacting its morphology and function. Senescent cells have been found to accumulate with age and may contribute to age-related skin changes and pathologies. Natural polyphenols exert many health benefits, including ameliorative effects on skin aging. By affecting molecular pathways of senescence, polyphenols are able to prevent or delay the senescence formation and, consequently, avoid or ameliorate aging and age-associated pathologies of the skin. This review aims to provide an overview of the current state of knowledge in skin aging and cellular senescence, and to summarize the recent in vitro studies related to the anti-senescent mechanisms of natural polyphenols carried out on keratinocytes, melanocytes and fibroblasts. Aged skin in the context of the COVID-19 pandemic will be also discussed.

Podocyte Aging: Why and How Getting Old Matters

The effects of healthy aging on the kidney, and how these effects intersect with superimposed diseases, are highly relevant in the context of the population's increasing longevity. Age-associated changes to podocytes, which are terminally differentiated glomerular epithelial cells, adversely affect kidney health. This review discusses the molecular and cellular mechanisms underlying podocyte aging, how these mechanisms might be augmented by disease in the aged kidney, and approaches to mitigate progressive damage to podocytes. Furthermore, we address how biologic pathways such as those associated with cellular growth confound aging in humans and rodents.

Mechanisms of Hydroxyurea-Induced Cellular Senescence: An Oxidative Stress Connection?

Hydroxyurea (HU) is a water-soluble antiproliferative agent used for decades in neoplastic and nonneoplastic conditions. HU is considered an essential medicine because of its cytoreduction functions. HU is an antimetabolite that inhibits ribonucleotide reductase, which causes a depletion of the deoxyribonucleotide pool and dramatically reduces cell proliferation. The proliferation arrest, depending on drug concentration and exposure, may promote a cellular senescence phenotype associated with cancer cell therapy resistance and inflammation, influencing neighboring cell functions, immunosuppression, and potential cancer relapse. HU can induce cellular senescence in both healthy and transformed cells in vitro, in part, because of increased reactive oxygen species (ROS). Here, we analyze the main molecular mechanisms involved in cytotoxic/genotoxic HU function, the potential to increase intracellular ROS levels, and the principal features of cellular senescence induction. Understanding the mechanisms involved in HU's ability to induce cellular senescence may help to improve current chemotherapy strategies and control undesirable treatment effects in cancer patients and other diseases.

Hydroxyurea Induces Bone Marrow Mesenchymal Stromal Cells Senescence and Modifies Cell Functionality In Vitro

Hydroxyurea (HU) is an antineoplastic agent that functions as an antimetabolite compound by inhibiting the ribonucleotide reductase. HU acts mainly as a cytostatic drug that through DNA replication stress may trigger a premature senescence-like cell phenotype, though its influence on bone marrow-derived mesenchymal stem/stromal cell (BMMSC) functions has not elucidated yet. Our results indicate that HU inhibits the growth of human BMMSC alongside senescence-like changes in both morphology and replicative potential, provokes cell cycle arrest at the S phase without affecting cellular viability and induces the expression of senescence-associated β-galactosidase and p16INK4. Moreover, HU-induced senescent BMMSC, although they did not change MSC markers expression, exhibited reduced capacity osteogenic and adipogenic differentiation. Conversely, HU treatment increased immunoregulatory functions of BMMSC compared with untreated cells and determined by T-cell proliferation. Interestingly, HU did not influence the capacity of BMMSC to induce monocytic myeloid-derived suppressor cells. Thus, these results suggest that HU improves the BMMSC functions on the T-cell inhibition and preserves their interaction with myeloid cell compartment. Mechanistically, BMMSC under HU treatment displayed a downregulation of mTOR and p38 MAPK signaling that may explain the reduced cell differentiation and increased immunomodulation activities. Together, the results obtained in this investigation suggest that HU by inducing senescence-like phenotype of BMMSC influences their cellular differentiation and immunoregulatory functions.

Hydroxyurea Induces Bone Marrow Mesenchymal Stromal Cells Senescence and Modifies Cell Functionality In Vitro

Hydroxyurea (HU) is an antineoplastic agent that functions as an antimetabolite compound by inhibiting the ribonucleotide reductase. HU acts mainly as a cytostatic drug that through DNA replication stress may trigger a premature senescence-like cell phenotype, though its influence on bone marrow-derived mesenchymal stem/stromal cell (BMMSC) functions has not elucidated yet. Our results indicate that HU inhibits the growth of human BMMSC alongside senescence-like changes in both morphology and replicative potential, provokes cell cycle arrest at the S phase without affecting cellular viability and induces the expression of senescence-associated β-galactosidase and p16INK4. Moreover, HU-induced senescent BMMSC, although they did not change MSC markers expression, exhibited reduced capacity osteogenic and adipogenic differentiation. Conversely, HU treatment increased immunoregulatory functions of BMMSC compared with untreated cells and determined by T-cell proliferation. Interestingly, HU did not influence the capacity of BMMSC to induce monocytic myeloid-derived suppressor cells. Thus, these results suggest that HU improves the BMMSC functions on the T-cell inhibition and preserves their interaction with myeloid cell compartment. Mechanistically, BMMSC under HU treatment displayed a downregulation of mTOR and p38 MAPK signaling that may explain the reduced cell differentiation and increased immunomodulation activities. Together, the results obtained in this investigation suggest that HU by inducing senescence-like phenotype of BMMSC influences their cellular differentiation and immunoregulatory functions.

One-Two Punch Therapy for the Treatment of T-Cell Malignancies Involving p53-Dependent Cellular Senescence

T-cell malignancies are still difficult to treat due to a paucity of plans that target critical dependencies. Drug-induced cellular senescence provides a permanent cell cycle arrest during tumorigenesis and cancer development, particularly when combined with senolytics to promote apoptosis of senescent cells, which is an innovation for cancer therapy. Here, our research found that wogonin, a well-known natural flavonoid compound, not only had a potential to inhibit cell growth and proliferation but also induced cellular senescence in T-cell malignancies with nonlethal concentration. Transcription activity of senescence-suppression human telomerase reverse transcriptase (hTERT) and oncogenic C-MYC was suppressed in wogonin-induced senescent cells, resulting in the inhibition of telomerase activity. We also substantiated the occurrence of DNA damage during the wogonin-induced aging process. Results showed that wogonin increased the activity of senescence-associated β-galactosidase (SA-β-Gal) and activated the DNA damage response pathway mediated by p53. In addition, we found the upregulated expression of BCL-2 in senescent T-cell malignancies because of the antiapoptotic properties of senescent cells. Following up this result, we identified a BCL-2 inhibitor Navitoclax (ABT-263), which was highly effective in decreasing cell viability and inducing apoptotic cell death in wogonin-induced senescent cells. Thus, the “one-two punch” approach increased the sensibility of T-cell malignancies with low expression of BCL-2 to Navitoclax. In conclusion, our research revealed that wogonin possesses potential antitumor effects based on senescence induction, offering a better insight into the development of novel therapeutic methods for T-cell malignancies.

Therapy-Induced Senescence: Opportunities to Improve Anticancer Therapy

Cellular senescence is an essential tumor suppressive mechanism that prevents the propagation of oncogenically activated, genetically unstable, and/or damaged cells. Induction of tumor cell senescence is also one of the underlying mechanisms by which cancer therapies exert antitumor activity. However, an increasing body of evidence from preclinical studies demonstrates that radiation and chemotherapy cause accumulation of senescent cells (SnCs) both in tumor and normal tissue. SnCs in tumors can, paradoxically, promote tumor relapse, metastasis, and resistance to therapy, in part, through expression of the senescence-associated secretory phenotype. In addition, SnCs in normal tissue can contribute to certain radiation- and chemotherapy-induced side effects. Because of its multiple roles, cellular senescence could serve as an important target in the fight against cancer. This commentary provides a summary of the discussion at the National Cancer Institute Workshop on Radiation, Senescence, and Cancer (August 10-11, 2020, National Cancer Institute, Bethesda, MD) regarding the current status of senescence research, heterogeneity of therapy-induced senescence, current status of senotherapeutics and molecular biomarkers, a concept of "one-two punch" cancer therapy (consisting of therapeutics to induce tumor cell senescence followed by selective clearance of SnCs), and its integration with personalized adaptive tumor therapy. It also identifies key knowledge gaps and outlines future directions in this emerging field to improve treatment outcomes for cancer patients.

Cellular senescence in cancer: from mechanisms to detection

Senescence refers to a cellular state featuring a stable cell-cycle arrest triggered in response to stress. This response also involves other distinct morphological and intracellular changes including alterations in gene expression and epigenetic modifications, elevated macromolecular damage, metabolism deregulation and a complex pro-inflammatory secretory phenotype. The initial demonstration of oncogene-induced senescence in vitro established senescence as an important tumour-suppressive mechanism, in addition to apoptosis. Senescence not only halts the proliferation of premalignant cells but also facilitates the clearance of affected cells through immunosurveillance. Failure to clear senescent cells owing to deficient immunosurveillance may, however, lead to a state of chronic inflammation that nurtures a pro-tumorigenic microenvironment favouring cancer initiation, migration and metastasis. In addition, senescence is a response to post-therapy genotoxic stress. Therefore, tracking the emergence of senescent cells becomes pivotal to detect potential pro-tumorigenic events. Current protocols for the in vivo detection of senescence require the analysis of fixed or deep-frozen tissues, despite a significant clinical need for real-time bioimaging methods. Accuracy and efficiency of senescence detection are further hampered by a lack of universal and more specific senescence biomarkers. Recently, in an attempt to overcome these hurdles, an assortment of detection tools has been developed. These strategies all have significant potential for clinical utilisation and include flow cytometry combined with histo- or cytochemical approaches, nanoparticle-based targeted delivery of imaging contrast agents, OFF-ON fluorescent senoprobes, positron emission tomography senoprobes and analysis of circulating SASP factors, extracellular vesicles and cell-free nucleic acids isolated from plasma. Here, we highlight the occurrence of senescence in neoplasia and advanced tumours, assess the impact of senescence on tumorigenesis and discuss how the ongoing development of senescence detection tools might improve early detection of multiple cancers and response to therapy in the near future.

Role of Aberrantly Activated Lysophosphatidic Acid Receptor 1 Signaling Mediated Inflammation in Renal Aging

The increasing load of senescent cells is a source of aging, and chronic inflammation plays a pivotal role in cellular senescence. In addition, senescent renal tubular epithelial cells are closely associated with renal aging. Lysophosphatidic acid (LPA) is a bioactive lipid mainly produced by the catalytic action of autotaxin (ATX), and its ligation to LPA receptor-1 (LPAR1) is associated with chronic inflammation and renal fibrosis; however, its role in renal aging is unclear. Male 2-, 12-, and 24-month-old C57BL/6 mice and Human renal proximal tubular epithelial cells (HRPTEpiC) were used in the present study. DNA damage and oxidative stress-induced senescence were simulated using doxorubicin (DOXO) and H₂O₂, respectively. The aged kidney showed decreased renal function, increased fractional mesangial area, and tubulointerstitial fibrosis. Both aged kidney and senescent cells showed increased levels of LPAR1, Nuclear factor κB (NF-κB), and inflammatory cytokines. In addition, LPAR1-knockdown reduced NF-κB and subsequent inflammatory cytokine induction, and NF-κB-knockdown resulted in decreased LPAR1 expression. Our study revealed a positive feedback loop between LPAR1 and NF-κB, which reinforces the role of inflammatory response, suggesting that blocking of aberrantly activated LPAR1 may reduce excessive inflammation, thereby providing a new possible therapeutic strategy to attenuate renal aging.

Keeping zombies alive: The ER-mitochondria Ca2+ transfer in cellular senescence

Cellular senescence generates a permanent cell cycle arrest, characterized by apoptosis resistance and a pro-inflammatory senescence-associated secretory phenotype (SASP). Physiologically, senescent cells promote tissue remodeling during development and after injury. However, when accumulated over a certain threshold as happens during aging or after cellular stress, senescent cells contribute to the functional decline of tissues, participating in the generation of several diseases. Cellular senescence is accompanied by increased mitochondrial metabolism. How mitochondrial function is regulated and what role it plays in senescent cell homeostasis is poorly understood. Mitochondria are functionally and physically coupled to the endoplasmic reticulum (ER), the major calcium (Ca²⁺) storage organelle in mammalian cells, through special domains known as mitochondria-ER contacts (MERCs). In this domain, the release of Ca²⁺ from the ER is mainly regulated by inositol 1,4,5-trisphosphate receptors (IP3Rs), a family of three Ca²⁺ release channels activated by a ligand (IP3). IP3R-mediated Ca²⁺ release is transferred to mitochondria through the mitochondrial Ca²⁺ uniporter (MCU), where it modulates the activity of several enzymes and transporters impacting its bioenergetic and biosynthetic function. Here, we review the possible connection between ER to mitochondria Ca²⁺ transfer and senescence. Understanding the pathways that contribute to senescence is essential to reveal new therapeutic targets that allow either delaying senescent cell accumulation or reduce senescent cell burden to alleviate multiple diseases.

HDAC2 and 7 down-regulation induces senescence in dermal fibroblasts

Originally simply reported to be in a stable and irreversible growth arrest in vitro, senescent cells are now clearly associated with normal and pathological ageing in vivo. They are characterized by several biomarkers and changes in gene expression that may depend on epigenetic factors, such as histone acetylation, involving a balance between histone acetyltransferases (HATs) and histone deacetylases (HDACs). In this study, we investigate the expression and the role of HDACs on the senescent phenotype of dermal fibroblasts. We report that during replicative senescence, most canonical HDACs are less expressed. Moreover, treatment with SAHA, a histone deacetylase inhibitor (HDACi) also known as Vorinostat, or the specific downregulation of HDAC2 or HDAC7 by siRNA, induces the appearance of senescence biomarkers of dermal fibroblasts. Conversely, the ectopic re-expression of HDAC7 by lentiviral transduction in pre-senescent dermal fibroblasts extends their proliferative lifespan. These results demonstrate that HDACs expression can modulate the senescent phenotype, highlighting their pharmaceutical interest in the context of healthy ageing.

Molecular Hydrogen Attenuated N-methyl-N-Nitrosourea Induced Corneal Endothelial Injury by Upregulating Anti-Apoptotic Pathway

Purpose

Previous work by our group has demonstrated the value of N-methyl-N-nitrosourea (MNU)-induced corneal endothelial decompensation in animal models. The aim of this study was to investigate the effect of molecular hydrogen (H2) on MNU-induced corneal endothelial cell (CEC) injury and the underlying mechanism.

Methods

MNU-induced animal models of CEC injury were washed with hydrogen-rich saline (HRS) for 14 days. Immunofluorescence staining, immunohistochemical staining, and corneal endothelial assessment were applied to determine architectural and cellular changes on the corneal endothelium following HRS treatment. MNU-induced cell models of CEC injury were co-cultured with H2. The effect of H2 was examined using morphological and functional assays.

Results

It was shown that MNU could inhibit the proliferation and specific physiological functions of CECs by increasing apoptosis and decreasing the expression of ZO-1 and Na+/K+-ATPase, whereas H2 improved the proliferation and physiological function of CECs by anti-apoptosis. Cell experiments further confirmed that H2 could reverse MNU damage to CECs by decreasing oxidative stress injury, interfering with the NF-κB/NLRP3 pathway and the FOXO3a/p53/p21 pathway.

Conclusions

This study suggests that topical application of H2 could protect CECs against corneal damage factors through anti-apoptotic effect, reduce the incidence and severity of corneal endothelial decompensation, and maintain corneal transparency.

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.

Breast cancer type 1 and neurodegeneration: consequences of deficient DNA repair

Numerous cellular processes, including toxic protein aggregation and oxidative stress, have been studied extensively as potential mechanisms underlying neurodegeneration. However, limited therapeutic efficacy targeting these processes has prompted other mechanisms to be explored. Previous research has emphasized a link between cellular senescence and neurodegeneration, where senescence induced by excess DNA damage and deficient DNA repair results in structural and functional changes that ultimately contribute to brain dysfunction and increased vulnerability for neurodegeneration. Specific DNA repair proteins, such as breast cancer type 1, have been associated with both stress-induced senescence and neurodegenerative diseases, however, specific mechanisms remain unclear. Therefore, this review explores DNA damage-induced senescence in the brain as a driver of neurodegeneration, with particular focus on breast cancer type 1, and its potential contribution to sex-specific differences associated with neurodegenerative disease.

Interphase Chromosomes in Replicative Senescence: Chromosome Positioning as a Senescence Biomarker and the Lack of Nuclear Motor-Driven Chromosome Repositioning in Senescent Cells

This study demonstrates, and confirms, that chromosome territory positioning is altered in primary senescent human dermal fibroblasts (HDFs). The chromosome territory positioning pattern is very similar to that found in HDFs made quiescent either by serum starvation or confluence; but not completely. A few chromosomes are found in different locations. One chromosome in particular stands out, chromosome 10, which is located in an intermediate location in young proliferating HDFs, but is found at the nuclear periphery in quiescent cells and in an opposing location of the nuclear interior in senescent HDFs. We have previously demonstrated that individual chromosome territories can be actively and rapidly relocated, with 15 min, after removal of serum from the culture media. These chromosome relocations require nuclear motor activity through the presence of nuclear myosin 1β (NM1β). We now also demonstrate rapid chromosome movement in HDFs after heat-shock at 42°C. Others have shown that heat shock genes are actively relocated using nuclear motor protein activity via actin or NM1β (Khanna et al., 2014; Pradhan et al., 2020). However, this current study reveals, that in senescent HDFs, chromosomes can no longer be relocated to expected nuclear locations upon these two types of stimuli. This coincides with a entirely different organisation and distribution of NM1β within senescent HDFs.

Anti-Leukemic Properties of Aplysinopsin Derivative EE-84 Alone and Combined to BH3 Mimetic A-1210477

Aplysinopsins are a class of marine indole alkaloids that exhibit a wide range of biological activities. Although both the indole and N-benzyl moieties of aplysinopsins are known to possess antiproliferative activity against cancer cells, their mechanism of action remains unclear. Through in vitro and in vivo proliferation and viability screening of newly synthesized aplysinopsin analogs on myelogenous leukemia cell lines and zebrafish toxicity tests, as well as analysis of differential toxicity in noncancerous RPMI 1788 cells and PBMCs, we identified EE-84 as a promising novel drug candidate against chronic myeloid leukemia. This indole derivative demonstrated drug-likeness in agreement with Lipinski’s rule of five. Furthermore, EE-84 induced a senescent-like phenotype in K562 cells in line with its cytostatic effect. EE-84-treated K562 cells underwent morphological changes in line with mitochondrial dysfunction concomitant with autophagy and ER stress induction. Finally, we demonstrated the synergistic cytotoxic effect of EE-84 with a BH3 mimetic, the Mcl-1 inhibitor A-1210477, against imatinib-sensitive and resistant K562 cells, highlighting the inhibition of antiapoptotic Bcl-2 proteins as a promising novel senolytic approach against chronic myeloid leukemia.

Aging associated altered response to intracellular bacterial infections and its implication on the host

The effects of senescence on geriatric disorders are well explored, but how it influences infections in the elderly is poorly addressed. Here, we show that several anti-microbial responses are elevated in senescent epithelial cells and old mice, which results in decreased bacterial survival in the host after infection. We identify higher levels of iNOS as a crucial host response and show that p38 MAPK in senescent epithelial cells acts as a negative regulator of iNOS transcription. However, in older mice, the ability to impede bacterial infection does not result in enhanced survival, possibly because elevated pro-inflammatory responses are not countered by a robust host protective anti-inflammatory response. Overall, while addressing an alternate advantage of senescent cells, our study demonstrates that infection-associated morbidity in the elderly may not be the sole outcome of pathogen loads but may also be influenced by the host's ability to resolve inflammation-induced damage.

Chromatin-Directed Proteomics Identifies ZNF84 as a p53-Independent Regulator of p21 in Genotoxic Stress Response

Simple Summary

Chemotherapy is a commonly applied anticancer treatment, however therapy-induced senescent growth arrest has been associated with aggressive disease recurrence. The p21 protein, encoded by CDKN1A, plays a vital role in the induction of senescence. Its transcriptional control by p53 is well-established. However, in many cancers where TP53 is mutated, p21 expression must be triggered by p53-independent mechanisms. We here used a chromatin-directed proteomic approach and identified ZNF84 as a regulator of CDKN1A gene expression in various p53-deficient cell lines. Knock-down of ZNF84, an as-yet un-characterized protein, inhibited p21 gene and protein expression in response to doxorubicin and facilitated senescence bypass. Intriguingly, ZNF84 depletion diminished genotoxic burden evoked by doxorubicin. Clinical data association studies indicated the relevance of ZNF84 expression for patient survival. Collectively, we identified ZNF84 as a critical regulator of senescence-proliferation outcome of chemotherapy, opening possibilities for its targeting in novel anti-cancer therapies of p53-mutated tumours.

Abstract

The p21^WAF1/Cip1 protein, encoded by CDKN1A, plays a vital role in senescence, and its transcriptional control by the tumour suppressor p53 is well-established. However, p21 can also be regulated in a p53-independent manner, by mechanisms that still remain less understood. We aimed to expand the knowledge about p53-independent senescence by looking for novel players involved in CDKN1A regulation. We used a chromatin-directed proteomic approach and identified ZNF84 as a novel regulator of p21 in various p53-deficient cell lines treated with cytostatic dose of doxorubicin. Knock-down of ZNF84, an as-yet un-characterized protein, inhibited p21 gene and protein expression in response to doxorubicin, it attenuated senescence and was associated with enhanced proliferation, indicating that ZNF84-deficiency can favor senescence bypass. ZNF84 deficiency was also associated with transcriptomic changes in genes governing various cancer-relevant processes e.g., mitosis. In cells with ZNF84 knock-down we discovered significantly lower level of H2AX Ser139 phosphorylation (γH2AX), which is triggered by DNA double strand breaks. Intriguingly, we observed a reverse correlation between the level of ZNF84 expression and survival rate of colon cancer patients. In conclusion, ZNF84, whose function was previously not recognized, was identified here as a critical p53-independent regulator of senescence, opening possibilities for its targeting in novel therapies of p53-null cancers.

Mechanisms of Cellular Senescence: Cell Cycle Arrest and Senescence Associated Secretory Phenotype

Cellular senescence is a stable cell cycle arrest that can be triggered in normal cells in response to various intrinsic and extrinsic stimuli, as well as developmental signals. Senescence is considered to be a highly dynamic, multi-step process, during which the properties of senescent cells continuously evolve and diversify in a context dependent manner. It is associated with multiple cellular and molecular changes and distinct phenotypic alterations, including a stable proliferation arrest unresponsive to mitogenic stimuli. Senescent cells remain viable, have alterations in metabolic activity and undergo dramatic changes in gene expression and develop a complex senescence-associated secretory phenotype. Cellular senescence can compromise tissue repair and regeneration, thereby contributing toward aging. Removal of senescent cells can attenuate age-related tissue dysfunction and extend health span. Senescence can also act as a potent anti-tumor mechanism, by preventing proliferation of potentially cancerous cells. It is a cellular program which acts as a double-edged sword, with both beneficial and detrimental effects on the health of the organism, and considered to be an example of evolutionary antagonistic pleiotropy. Activation of the p53/p21^WAF1/CIP1 and p16^INK4A/pRB tumor suppressor pathways play a central role in regulating senescence. Several other pathways have recently been implicated in mediating senescence and the senescent phenotype. Herein we review the molecular mechanisms that underlie cellular senescence and the senescence associated growth arrest with a particular focus on why cells stop dividing, the stability of the growth arrest, the hypersecretory phenotype and how the different pathways are all integrated.

Cellular senescence and tumor promotion: Role of the Unfolded Protein Response

Senescence is a cellular state which can be viewed as a stress response phenotype implicated in various physiological and pathological processes, including cancer. Therefore, it is of fundamental importance to understand why and how a cell acquires and maintains a senescent phenotype. Direct evidence has pointed to the homeostasis of the endoplasmic reticulum whose control appears strikingly affected during senescence. The endoplasmic reticulum is one of the sensing organelles that transduce signals between different pathways in order to adapt a functional proteome upon intrinsic or extrinsic challenges. One of these signaling pathways is the Unfolded Protein Response (UPR), which has been shown to be activated during senescence. Its exact contribution to senescence onset, maintenance, and escape, however, is still poorly understood. In this article, we review the mechanisms through which the UPR contributes to the appearance and maintenance of characteristic senescent features. We also discuss whether the perturbation of the endoplasmic reticulum proteostasis or accumulation of misfolded proteins could be possible causes of senescence, and-as a consequence-to what extent the UPR components could be considered as therapeutic targets allowing for the elimination of senescent cells or altering their secretome to prevent neoplastic transformation.

Cellular senescence and hematological malignancies: From pathogenesis to therapeutics

Cellular senescence constitutes a permanent state of cell cycle arrest in proliferative cells induced by different stresses. The exploration of tumor pathogenesis and therapies has been a research hotspot in recent years. Cellular senescence is a significant mechanism to prevent the proliferation of potential tumor cells, but it can also promote tumor growth. Increasing evidence suggests that cellular senescence is involved in the pathogenesis and development of hematological malignancies, including leukemia, myelodysplastic syndrome (MDS) and multiple myeloma (MM). Cellular senescence is associated with functional decline of hematopoietic stem cells (HSCs) and increased risk of hematological malignancies. Moreover, the bone marrow (BM) microenvironment has a crucial regulatory effect in the process of these diseases. The senescence-associated secretory phenotype (SASP) in the BM microenvironment establishes a protumor environment that supports the proliferation and survival of tumor cells. Therefore, a series of therapeutic strategies targeting cellular senescence have been gradually developed, including the induction of cellular senescence and elimination of senescent cells. This review systematically summarizes the emerging information describing the roles of cellular senescence in tumorigenesis and potential clinical applications, which may be beneficial for designing rational therapeutic strategies for various hematopoietic malignancies.

Cancer Response to Therapy-Induced Senescence: A Matter of Dose and Timing

Cellular senescence participates to fundamental processes like tissue remodeling in embryo development, wound healing and inhibition of preneoplastic cell growth. Most senescent cells display common hallmarks, among which the most characteristic is a permanent (or long lasting) arrest of cell division. However, upon senescence, different cell types acquire distinct phenotypes, which also depend on the specific inducing stimuli. Senescent cells are metabolically active and secrete a collection of growth factors, cytokines, proteases, and matrix-remodeling proteins collectively defined as senescence-associated secretory phenotype, SASP. Through SASP, senescent cells modify their microenvironment and engage in a dynamic dialog with neighbor cells. Senescence of neoplastic cells, at least temporarily, reduces tumor expansion, but SASP of senescent cancer cells as well as SASP of senescent stromal cells in the tumor microenvironment may promote the growth of more aggressive cancer subclones. Here, we will review recent data on the mechanisms and the consequences of cancer-therapy induced senescence, enlightening the potentiality and the risk of senescence inducing treatments.

The Jekyll and Hyde of Cellular Senescence in Cancer

Cellular senescence is a state of stable cell cycle arrest that can be triggered in response to various insults and is characterized by distinct morphological hallmarks, gene expression profiles, and the senescence-associated secretory phenotype (SASP). Importantly, cellular senescence is a key component of normal physiology with tumor suppressive functions. In the last few decades, novel cancer treatment strategies exploiting pro-senescence therapies have attracted considerable interest. Recent insight, however, suggests that therapy-induced senescence (TIS) elicits cell-autonomous and non-cell-autonomous implications that potentially entail detrimental consequences, reflecting the Jekyll and Hyde nature of cancer cell senescence. In essence, the undesirable manifestations that generally culminate in inflammation, cancer stemness, senescence reversal, therapy resistance, and disease recurrence are dictated by the persistent accumulation of senescent cells and the SASP. Thus, mitigating these pro-tumorigenic effects by eliminating these cells or inhibiting their SASP production holds great promise for developing innovative therapeutic strategies. In this review, we describe the fundamental aspects and dynamics of cancer cell senescence and summarize the comprehensive research on the adverse outcomes of TIS. Furthermore, we underline the rationale and motivation of emerging senotherapeutic modalities surrounding the removal of senescent cells and the SASP to help maximize the overall efficacy of cancer therapies.

Senescence under appraisal: hopes and challenges revisited

In recent years, cellular senescence has become the focus of attention in multiple areas of biomedical research. Typically defined as an irreversible cell cycle arrest accompanied by increased cellular growth, metabolic activity and by a characteristic messaging secretome, cellular senescence can impact on multiple physiological and pathological processes such as wound healing, fibrosis, cancer and ageing. These unjustly called 'zombie cells' are indeed a rich source of opportunities for innovative therapeutic development. In this review, we collate the current understanding of the process of cellular senescence and its two-faced nature, i.e. beneficial/detrimental, and reason this duality is linked to contextual aspects. We propose the senescence programme as an endogenous pro-resolving mechanism that may lead to sustained inflammation and damage when dysregulated or when senescent cells are not cleared efficiently. This pro-resolving model reconciles the paradoxical two faces of senescence by emphasising that it is the unsuccessful completion of the programme, and not senescence itself, what leads to pathology. Thus, pro-senescence therapies under the right context, may favour inflammation resolution. We also review the evidence for the multiple therapeutic approaches under development based on senescence, including its induction, prevention, clearance and the use of senolytic and senomorphic drugs. In particular, we highlight the importance of the immune system in the favourable outcome of senescence and the implications of an inefficient immune surveillance in completion of the senescent cycle. Finally, we identify and discuss a number of challenges and existing gaps to encourage and stimulate further research in this exciting and unravelled field, with the hope of promoting and accelerating the clinical success of senescence-based therapies.

Characterization of TGF-β by Induced Oxidative Stress in Human Trabecular Meshwork Cells

Oxidative stress generated by reactive oxygen species (ROS) plays a critical role in the pathomechanism of glaucoma, which is a multifactorial blinding disease that may cause irreversible damage within human trabecular meshwork cells (HTMCs). It is known that the transforming growth factor-β (TGF-β) signaling pathway is an important component of oxidative stress-induced damage related to extracellular matrix (ECM) fibrosis and activates cell antioxidative mechanisms. To elucidate the dual potential roles and regulatory mechanisms of TGF-β in effects on HTMCs, we established an in vitro oxidative model using hydrogen peroxide (H₂O₂) and further focused on TGF-β-related oxidative stress pathways and the related signal transduction. Via a series of cell functional qualitative analyses to detect related protein level alterations and cell fibrosis status, we illustrated the role of TGF-β1 and TGF-β2 in oxidative stress-induced injury by shTGF-β1 and shTGF-β2 knockdown or added recombinant human TGF-β1 protein (rhTGF-β1). The results of protein level showed that p38 MAPK, TGF-β, and its related SMAD family were activated after H₂O₂ stimulation. Cell functional assays showed that HTMCs with H₂O₂ exposure duration had a more irregular actin architecture compared to normal TM cells. Data with rhTGF-β1 (1 ng/mL) pretreatment reduced the cell apoptosis rate and amount of reactive oxygen species (ROS), while it also enhanced survival. Furthermore, TGF-β1 and TGF-β2 in terms of antioxidant signaling were related to the activation of collagen I and laminin, which are fibrosis-response proteins. Succinctly, our study demonstrated that low concentrations of TGF-β1 (1 ng/mL) preserves HTMCs from free radical-mediated injury by p-p38 MAPK level and p-AKT signaling balance, presenting a signaling transduction mechanism of TGF-β1 in HTMC oxidative stress-related therapies.

The ageing kidney: Molecular mechanisms and clinical implications

As human life expectancy keeps increasing, ageing populations present a growing challenge for clinical practices. Human ageing is associated with molecular, structural, and functional changes in a variety of organ systems, including the kidney. During the ageing process, the kidney experiences progressive functional decline as well as macroscopic and microscopic histological alterations, which are accentuated by systemic comorbidities like hypertension and diabetes mellitus, or by preexisting or underlying kidney diseases. Although ageing per se does not cause kidney injury, physiologic changes associated with normal ageing processes are likely to impair the reparative capacity of the kidney and thus predispose older people to acute kidney disease, chronic kidney disease and other renal diseases. Mechanistically, cell senescence plays a key role in renal ageing, involving a number of cellular signaling mechanisms, many of which may be harnessed as international targets for slowing or even reversing kidney ageing. This review summarizes the clinical characteristics of renal ageing, highlights the latest progresses in deciphering the role of cell senescence in renal ageing, and envisages potential interventional strategies and novel therapeutic targets for preventing or improving renal ageing in the hope of maintaining long-term kidney health and function across the life course.

A water-soluble probe with p-hydroxybenzyl quaternary ammonium linker for selective imaging in senescent cells

A water-soluble probe with p-hydroxybenzyl quaternary ammonium linker, FR-2a, for selective imaging in senescent cells is reported. Probe FR-2a integrated water-soluble fluorophore (HT-4a) and β-galactosidase (β-gal) trigger into one entity by a p-hydroxybenzyl quaternary ammonium linker. HT-4a is a styryl-based push-pull benzothiazole fluorophore with attractive properties, including excellent water-solubility, intense fluorescence emission and a large Stokes shift (161 nm), characterized by an intramolecular charge transfer (ICT) excited state. The formation of quaternary ammonium deactivated the ICT state, resulting in fluorescence quenching of FR-2a. In the presence of β-gal, the glycosidic bond was hydrolyzed and fluorophore HT-4a was released through self-immolative process, resulting in effective fluorescence recovery. FR-2a shows high affinity to β-gal (K_m = 1.33 μM), exhibiting good sensitivity, selectivity and stability for imaging in senescent cells.