NOTCH1 mediates a switch between two distinct secretomes during senescence

Regulation of cell function and identity by cellular senescence

During aging and in some contexts, like embryonic development, wound healing, and diseases such as cancer, senescent cells accumulate and play a key role in different pathophysiological functions. A long-held belief was that cellular senescence decreased normal cell functions, given the loss of proliferation of senescent cells. This view radically changed following the discovery of the senescence-associated secretory phenotype (SASP), factors released by senescent cells into their microenvironment. There is now accumulating evidence that cellular senescence also promotes gain-of-function effects by establishing, reinforcing, or changing cell identity, which can have a beneficial or deleterious impact on pathophysiology. These effects may involve both proliferation arrest and autocrine SASP production, although they largely remain to be defined. Here, we provide a historical overview of the first studies on senescence and an insight into emerging trends regarding the effects of senescence on cell identity.

Progressive senescence programs induce intrinsic vulnerability to aging-related female breast cancer

Cancer incidence escalates exponentially with advancing age; however, the underlying mechanism remains unclear. In this study, we build a chronological molecular clock at single-cell transcription level with a mammary stem cell-enriched population to depict physiological aging dynamics in female mice. We find that the mammary aging process is asynchronous and progressive, initiated by an early senescence program, succeeded by an entropic late senescence program with elevated cancer associated pathways, vulnerable to cancer predisposition. The transition towards senescence program is governed by a stem cell factor Bcl11b, loss of which accelerates mammary ageing with enhanced DMBA-induced tumor formation. We have identified a drug TPCA-1 that can rejuvenate mammary cells and significantly reduce aging-related cancer incidence. Our findings establish a molecular portrait of progressive mammary cell aging and elucidate the transcriptional regulatory network bridging mammary aging and cancer predisposition, which has potential implications for the management of cancer prevalence in the aged.

The transcription factor PAX5 activates human LINE1 retrotransposons to induce cellular senescence

As a hallmark of senescent cells, the derepression of Long Interspersed Elements 1 (LINE1) transcription results in accumulated LINE1 cDNA, which triggers the secretion of the senescence-associated secretory phenotype (SASP) and paracrine senescence in a cGAS-STING pathway-dependent manner. However, transcription factors that govern senescence-associated LINE1 reactivation remain ill-defined. Here, we predict several transcription factors that bind to human LINE1 elements to regulate their transcription by analyzing the conserved binding motifs in the 5'-untranslated regions (UTR) of the commonly upregulated LINE1 elements in different types of senescent cells. Further analysis reveals that PAX5 directly binds to LINE1 5'-UTR and the binding is enhanced in senescent cells. The enrichment of PAX5 at the 5'-UTR promotes cellular senescence and SASP by activating LINE1. We also demonstrate that the longevity gene SIRT6 suppresses PAX5 transcription by directly binding to the PAX5 promoter, and overexpressing PAX5 abrogates the suppressive effect of SIRT6 on stress-dependent cellular senescence. Our work suggests that PAX5 could serve as a potential target for drug development aiming to suppress LINE1 activation and treat senescence-associated diseases.

Endothelial-specific telomerase inactivation causes telomere-independent cell senescence and multi-organ dysfunction characteristic of aging

It has remained unclear how aging of endothelial cells (EC) contributes to pathophysiology of individual organs. Cell senescence results in part from inactivation of telomerase (TERT). Here, we analyzed mice with Tert knockout specifically in EC. Tert loss in EC induced transcriptional changes indicative of senescence and tissue hypoxia in EC and in other cells. We demonstrate that EC-Tert-KO mice have leaky blood vessels. The blood-brain barrier of EC-Tert-KO mice is compromised, and their cognitive function is impaired. EC-Tert-KO mice display reduced muscle endurance and decreased expression of enzymes responsible for oxidative metabolism. Our data indicate that Tert-KO EC have reduced mitochondrial content and function, which results in increased dependence on glycolysis. Consistent with this, EC-Tert-KO mice have metabolism changes indicative of increased glucose utilization. In EC-Tert-KO mice, expedited telomere attrition is observed for EC of adipose tissue (AT), while brain and skeletal muscle EC have normal telomere length but still display features of senescence. Our data indicate that the loss of Tert causes EC senescence in part through a telomere length-independent mechanism undermining mitochondrial function. We conclude that EC-Tert-KO mice is a model of expedited vascular senescence recapitulating the hallmarks aging, which can be useful for developing revitalization therapies.

Precise immunofluorescence canceling for highly multiplexed imaging to capture specific cell states

Cell states are regulated by the response of signaling pathways to receptor ligand-binding and intercellular interactions. High-resolution imaging has been attempted to explore the dynamics of these processes and, recently, multiplexed imaging has profiled cell states by achieving a comprehensive acquisition of spatial protein information from cells. However, the specificity of antibodies is still compromised when visualizing activated signals. Here, we develop Precise Emission Canceling Antibodies (PECAbs) that have cleavable fluorescent labeling. PECAbs enable high-specificity sequential imaging using hundreds of antibodies, allowing for reconstruction of the spatiotemporal dynamics of signaling pathways. Additionally, combining this approach with seq-smFISH can effectively classify cells and identify their signal activation states in human tissue. Overall, the PECAb system can serve as a comprehensive platform for analyzing complex cell processes.

Single-cell senescence identification reveals senescence heterogeneity, trajectory, and modulators

Cellular senescence underlies many aging-related pathologies, but its heterogeneity poses challenges for studying and targeting senescent cells. We present here a machine learning program senescent cell identification (SenCID), which accurately identifies senescent cells in both bulk and single-cell transcriptome. Trained on 602 samples from 52 senescence transcriptome datasets spanning 30 cell types, SenCID identifies six major senescence identities (SIDs). Different SIDs exhibit different senescence baselines, stemness, gene functions, and responses to senolytics. SenCID enables the reconstruction of senescent trajectories under normal aging, chronic diseases, and COVID-19. Additionally, when applied to single-cell Perturb-seq data, SenCID helps reveal a hierarchy of senescence modulators. Overall, SenCID is an essential tool for precise single-cell analysis of cellular senescence, enabling targeted interventions against senescent cells.

Therapeutic strategies targeting cellular senescence for cancer and other diseases

Cellular senescence occurs in response to endogenous or exogenous stresses and is characterized by stable cell cycle arrest, alterations in nuclear morphology and secretion of proinflammatory factors, referred to as the senescence-associated secretory phenotype (SASP). An increase of senescent cells is associated with the development of several types of cancer and aging-related diseases. Therefore, senolytic agents that selectively remove senescent cells may offer opportunities for developing new therapeutic strategies against such cancers and aging-related diseases. This review outlines senescence inducers and the general characteristics of senescent cells. We also discuss the involvement of senescent cells in certain cancers and diseases. Finally, we describe a series of senolytic agents and their utilization in therapeutic strategies.

Cellular senescence in lung cancer: Molecular mechanisms and therapeutic interventions

Lung cancer stands as the primary contributor to cancer-related fatalities worldwide, affecting both genders. Two primary types exist where non-small cell lung cancer (NSCLC), accounts for 80-85% and SCLC accounts for 10-15% of cases. NSCLC subtypes include adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. Smoking, second-hand smoke, radon gas, asbestos, and other pollutants, genetic predisposition, and COPD are lung cancer risk factors. On the other hand, stresses such as DNA damage, telomere shortening, and oncogene activation cause a prolonged cell cycle halt, known as senescence. Despite its initial role as a tumor-suppressing mechanism that slows cell growth, excessive or improper control of this process can cause age-related diseases, including cancer. Cellular senescence has two purposes in lung cancer. Researchers report that senescence slows tumor growth by constraining multiplication of impaired cells. However, senescent cells also demonstrate the pro-inflammatory senescence-associated secretory phenotype (SASP), which is widely reported to promote cancer. This review will look at the role of cellular senescence in lung cancer, describe its diagnostic markers, ask about current treatments to control it, look at case studies and clinical trials that show how senescence-targeting therapies can be used in lung cancer, and talk about problems currently being faced, and possible solutions for the same in the future.

The senescence-associated secretory phenotype and its physiological and pathological implications

Cellular senescence is a state of terminal growth arrest associated with the upregulation of different cell cycle inhibitors, mainly p16 and p21, structural and metabolic alterations, chronic DNA damage responses, and a hypersecretory state known as the senescence-associated secretory phenotype (SASP). The SASP is the major mediator of the paracrine effects of senescent cells in their tissue microenvironment and of various local and systemic biological functions. In this Review, we discuss the composition, dynamics and heterogeneity of the SASP as well as the mechanisms underlying its induction and regulation. We describe the various biological properties of the SASP, its beneficial and detrimental effects in different physiological and pathological settings, and its impact on overall health span. Finally, we discuss the use of the SASP as a biomarker and of SASP inhibitors as senomorphic interventions to treat cancer and other age-related conditions.

A senescence restriction point acting on chromatin integrates oncogenic signals

We identify a senescence restriction point (SeRP) as a critical event for cells to commit to senescence. The SeRP integrates the intensity and duration of oncogenic stress, keeps a memory of previous stresses, and combines oncogenic signals acting on different pathways by modulating chromatin accessibility. Chromatin regions opened upon commitment to senescence are enriched in nucleolar-associated domains, which are gene-poor regions enriched in repeated sequences. Once committed to senescence, cells no longer depend on the initial stress signal and exhibit a characteristic transcriptome regulated by a transcription factor network that includes ETV4, RUNX1, OCT1, and MAFB. Consistent with a tumor suppressor role for this network, the levels of ETV4 and RUNX1 are very high in benign lesions of the pancreas but decrease dramatically in pancreatic ductal adenocarcinomas. The discovery of senescence commitment and its chromatin-linked regulation suggests potential strategies for reinstating tumor suppression in human cancers.

Senescence and senolysis in cancer: The latest findings

Aging is a life phenomenon that occurs in most living organisms and is a major risk factor for many diseases, including cancer. Cellular senescence is a cellular trait induced by various genomic and epigenetic stresses. Senescent cells are characterized by irreversible cell growth arrest and excessive secretion of inflammatory cytokines (senescence-associated secretory phenotypes, SASP). Chronic tissue microinflammation induced by SASP contributes to the pathogenesis of a variety of age-related diseases, including cancer. Senolysis is a promising new strategy to selectively eliminate senescent cells in order to suppress chronic inflammation, suggesting its potential use as an anticancer therapy. This review summarizes recent findings on the molecular basis of senescence in cancer cells and senolysis.

Cell Senescence-Independent Changes of Human Skin Fibroblasts with Age

Skin ageing is defined, in part, by collagen depletion and fragmentation that leads to a loss of mechanical tension. This is currently believed to reflect, in part, the accumulation of senescent cells. We compared the expression of genes and proteins for components of the extracellular matrix (ECM) as well as their regulators and found that in vitro senescent cells produced more matrix metalloproteinases (MMPs) than proliferating cells from adult and neonatal donors. This was consistent with previous reports of senescent cells contributing to increased matrix degradation with age; however, cells from adult donors proved significantly less capable of producing new collagen than neonatal or senescent cells, and they showed significantly lower myofibroblast activation as determined by the marker α-SMA. Functionally, adult cells also showed slower migration than neonatal cells. We concluded that the increased collagen degradation of aged fibroblasts might reflect senescence, the reduced collagen production likely reflects senescence-independent processes.

Cellular senescence: Neither irreversible nor reversible

Cellular senescence is a critical stress response program implicated in embryonic development, wound healing, aging, and immunity, and it backs up apoptosis as an ultimate cell-cycle exit mechanism. In analogy to replicative exhaustion of telomere-eroded cells, premature types of senescence-referring to oncogene-, therapy-, or virus-induced senescence-are widely considered irreversible growth arrest states as well. We discuss here that entry into full-featured senescence is not necessarily a permanent endpoint, but dependent on essential maintenance components, potentially transient. Unlike a binary state switch, we view senescence with its extensive epigenomic reorganization, profound cytomorphological remodeling, and distinctive metabolic rewiring rather as a journey toward a full-featured arrest condition of variable strength and depth. Senescence-underlying maintenance-essential molecular mechanisms may allow cell-cycle reentry if not continuously provided. Importantly, senescent cells that resumed proliferation fundamentally differ from those that never entered senescence, and hence would not reflect a reversion but a dynamic progression to a post-senescent state that comes with distinct functional and clinically relevant ramifications.

The senescence journey in cancer immunoediting

Cancer progression is continuously controlled by the immune system which can identify and destroy nascent tumor cells or inhibit metastatic spreading. However, the immune system and its deregulated activity in the tumor microenvironment can also promote tumor progression favoring the outgrowth of cancers capable of escaping immune control, in a process termed cancer immunoediting. This process, which has been classified into three phases, i.e. "elimination", "equilibrium" and "escape", is influenced by several cancer- and microenvironment-dependent factors. Senescence is a cellular program primed by cells in response to different pathophysiological stimuli, which is based on long-lasting cell cycle arrest and the secretion of numerous bioactive and inflammatory molecules. Because of this, cellular senescence is a potent immunomodulatory factor promptly recruiting immune cells and actively promoting tissue remodeling. In the context of cancer, these functions can lead to both cancer immunosurveillance and immunosuppression. In this review, the authors will discuss the role of senescence in cancer immunoediting, highlighting its context- and timing-dependent effects on the different three phases, describing how senescent cells promote immune cell recruitment for cancer cell elimination or sustain tumor microenvironment inflammation for immune escape. A potential contribution of senescent cells in cancer dormancy, as a mechanism of therapy resistance and cancer relapse, will be discussed with the final objective to unravel the immunotherapeutic implications of senescence modulation in cancer.

Subcellular structure, heterogeneity, and plasticity of senescent cells

Cellular senescence is a state of permanent growth arrest. It can be triggered by telomere shortening (replicative senescence) or prematurely induced by stresses such as DNA damage, oncogene overactivation, loss of tumor suppressor genes, oxidative stress, tissue factors, and others. Advances in techniques and experimental designs have provided new evidence about the biology of senescent cells (SnCs) and their importance in human health and disease. This review aims to describe the main aspects of SnCs phenotype focusing on alterations in subcellular compartments like plasma membrane, cytoskeleton, organelles, and nuclei. We also discuss the heterogeneity, dynamics, and plasticity of SnCs' phenotype, including the SASP, and pro-survival mechanisms. We advance on the multiple layers of phenotypic heterogeneity of SnCs, such as the heterogeneity between inducers, tissues and within a population of SnCs, discussing the relevance of these aspects to human health and disease. We also raise the main challenges as well alternatives to overcome them. Ultimately, we present open questions and perspectives in understanding the phenotype of SnCs from the perspective of basic and applied questions.

Emerging role of cellular senescence in normal lung development and perinatal lung injury

Cellular senescence is a status of irreversible growth arrest, which can be triggered by the p53/p21cip1 and p16INK4/Rb pathways via intrinsic and external factors. Senescent cells are typically enlarged and flattened, and characterized by numerous molecular features. The latter consists of increased surfaceome, increased residual lysosomal activity at pH 6.0 (manifested by increased activity of senescence-associated beta-galactosidase [SA-β-gal]), senescence-associated mitochondrial dysfunction, cytoplasmic chromatin fragment, nuclear lamin b1 exclusion, telomere-associated foci, and the senescence-associated secretory phenotype. These features vary depending on the stressor leading to senescence and the type of senescence. Cellular senescence plays pivotal roles in organismal aging and in the pathogenesis of aging-related diseases. Interestingly, senescence can also both promote and inhibit wound healing processes. We recently report that senescence as a programmed process contributes to normal lung development. Lung senescence is also observed in Down Syndrome, as well as in premature infants with bronchopulmonary dysplasia and in a hyperoxia-induced rodent model of this disease. Furthermore, this senescence results in neonatal lung injury. In this review, we briefly discuss the molecular features of senescence. We then focus on the emerging role of senescence in normal lung development and in the pathogenesis of bronchopulmonary dysplasia as well as putative signaling pathways driving senescence. Finally, we discuss potential therapeutic approaches targeting senescent cells to prevent perinatal lung diseases.

Establishing evidence for immune surveillance of β-cell senescence

Cellular senescence is a programmed state of cell cycle arrest that involves a complex immunogenic secretome, eliciting immune surveillance and senescent cell clearance. Recent work has shown that a subpopulation of pancreatic β-cells becomes senescent in the context of diabetes; however, it is not known whether these cells are normally subject to immune surveillance. In this opinion article, we advance the hypothesis that immune surveillance of β-cells undergoing a senescence stress response normally limits their accumulation during aging and that the breakdown of these mechanisms is a driver of senescent β-cell accumulation in diabetes. Elucidation and therapeutic activation of immune surveillance mechanisms in the pancreas holds promise for the improvement of approaches to target stressed senescent β-cells in the treatment of diabetes.

Therapeutic targeting of cellular senescence in diabetic macular edema: preclinical and phase 1 trial results

Compromised vascular endothelial barrier function is a salient feature of diabetic complications such as sight-threatening diabetic macular edema (DME). Current standards of care for DME manage aspects of the disease, but require frequent intravitreal administration and are poorly effective in large subsets of patients. Here we provide evidence that an elevated burden of senescent cells in the retina triggers cardinal features of DME pathology and conduct an initial test of senolytic therapy in patients with DME. In cell culture models, sustained hyperglycemia provoked cellular senescence in subsets of vascular endothelial cells displaying perturbed transendothelial junctions associated with poor barrier function and leading to micro-inflammation. Pharmacological elimination of senescent cells in a mouse model of DME reduces diabetes-induced retinal vascular leakage and preserves retinal function. We then conducted a phase 1 single ascending dose safety study of UBX1325 (foselutoclax), a senolytic small-molecule inhibitor of BCL-xL, in patients with advanced DME for whom anti-vascular endothelial growth factor therapy was no longer considered beneficial. The primary objective of assessment of safety and tolerability of UBX1325 was achieved. Collectively, our data suggest that therapeutic targeting of senescent cells in the diabetic retina with a BCL-xL inhibitor may provide a long-lasting, disease-modifying intervention for DME. This hypothesis will need to be verified in larger clinical trials. ClinicalTrials.gov identifier: NCT04537884 .

Mechanisms of carboplatin- and paclitaxel-dependent induction of premature senescence and pro-cancerogenic conversion of normal peritoneal mesothelium and fibroblasts

Carboplatin (CPT) and paclitaxel (PCT) are the optimal non-surgical treatment of epithelial ovarian cancer (EOC). Although their growth-restricting influence on EOC cells is well known, their impact on normal peritoneal cells, including mesothelium (PMCs) and fibroblasts (PFBs), is poorly understood. Here, we investigated whether, and if so, by what mechanism, CPT and PCT induce senescence of omental PMCs and PFBs. In addition, we tested whether PMC and PFB exposure to the drugs promotes the development of a pro-cancerogenic phenotype. The results showed that CPT and PCT induce G2/M growth arrest-associated senescence of normal peritoneal cells and that the strongest induction occurs when the drugs act together. PMCs senesce telomere-independently with an elevated p16 level and via activation of AKT and STAT3. In PFBs, telomeres shorten along with an induction of p21 and p53, and their senescence proceeds via the activation of ERK1/2. Oxidative stress in CPT + PCT-treated PMCs and PFBs is extensive and contributes causatively to their premature senescence. Both PMCs and PFBs exposed to CPT + PCT fuel the proliferation, migration, and invasion of established (A2780, OVCAR-3, SKOV-3) and primary EOCs, and this activity is linked with an overproduction of multiple cytokines altering the cancer cell transcriptome and controlled by p38 MAPK, NF-κB, STAT3, Notch1, and JAK1. Collectively, our findings indicate that CPT and PCT lead to iatrogenic senescence of normal peritoneal cells, which paradoxically and opposing therapeutic needs alters their phenotype towards pro-cancerogenic. It cannot be excluded that these adverse outcomes of chemotherapy may contribute to EOC relapse in the case of incomplete tumor eradication and residual disease initiation. © 2023 The Pathological Society of Great Britain and Ireland.

Metastasis and cancer associated fibroblasts: taking it up a NOTCH

Metastasis is the least understood aspect of cancer biology. 90% of cancer related deaths occur due extensive metastatic burden in patients. Apart from metastasizing cancer cells, the pro-tumorigenic and pro-metastatic role of the tumor stroma plays a crucial part in this complex process often leading to disease relapse and therapy resistance. Cellular signaling processes play a crucial role in the process of tumorigenesis and metastasis when aberrantly turned on, not just in the cancer cells, but also in the cells of the tumor microenvironment (TME). One of the most conserved pathways includes the Notch signaling pathway that plays a crucial role in the development and progression of many cancers. In addition to its well documented role in cancer cells, recent evidence suggests crucial involvement of Notch signaling in the stroma as well. This review aims to highlight the current findings focusing on the oncogenic role of notch signaling in cancer cells and the TME, with a specific focus on cancer associated fibroblasts (CAFs), which constitute a major part of the tumor stroma and are important for tumor progression. Recent efforts have focused on the development of anti-cancer and anti-metastatic therapies targeting TME. Understanding the importance of Notch signaling in the TME would help identify important drivers for stromal reprogramming, metastasis and importantly, drive future research in the effort to develop TME-targeted therapies utilizing Notch.

Modulation of fracture healing by senescence-associated secretory phenotype (SASP): a narrative review of the current literature

The senescence-associated secretory phenotype (SASP) is a generic term for the secretion of cytokines, such as pro-inflammatory factors and proteases. It is a crucial feature of senescent cells. SASP factors induce tissue remodeling and immune cell recruitment. Previous studies have focused on the beneficial role of SASP during embryonic development, wound healing, tissue healing in general, immunoregulation properties, and cancer. However, some recent studies have identified several negative effects of SASP on fracture healing. Senolytics is a drug that selectively eliminates senescent cells. Senolytics can inhibit the function of senescent cells and SASP, which has been found to have positive effects on a variety of aging-related diseases. At the same time, recent data suggest that removing senescent cells may promote fracture healing. Here, we reviewed the latest research progress about SASP and illustrated the inflammatory response and the influence of SASP on fracture healing. This review aims to understand the role of SASP in fracture healing, aiming to provide an important clinical prevention and treatment strategy for fracture. Clinical trials of some senolytics agents are underway and are expected to clarify the effectiveness of their targeted therapy in the clinic in the future. Meanwhile, the adverse effects of this treatment method still need further study.

scResolve: Recovering single cell expression profiles from multi-cellular spatial transcriptomics

Many popular spatial transcriptomics techniques lack single-cell resolution. Instead, these methods measure the collective gene expression for each location from a mixture of cells, potentially containing multiple cell types. Here, we developed scResolve, a method for recovering single-cell expression profiles from spatial transcriptomics measurements at multi-cellular resolution. scResolve accurately restores expression profiles of individual cells at their locations, which is unattainable from cell type deconvolution. Applications of scResolve on human breast cancer data and human lung disease data demonstrate that scResolve enables cell type-specific differential gene expression analysis between different tissue contexts and accurate identification of rare cell populations. The spatially resolved cellular-level expression profiles obtained through scResolve facilitate more flexible and precise spatial analysis that complements raw multi-cellular level analysis.

Targeting the redox system for cardiovascular regeneration in aging

Cardiovascular aging presents a formidable challenge, as the aging process can lead to reduced cardiac function and heightened susceptibility to cardiovascular diseases. Consequently, there is an escalating, unmet medical need for innovative and effective cardiovascular regeneration strategies aimed at restoring and rejuvenating aging cardiovascular tissues. Altered redox homeostasis and the accumulation of oxidative damage play a pivotal role in detrimental changes to stem cell function and cellular senescence, hampering regenerative capacity in aged cardiovascular system. A mounting body of evidence underscores the significance of targeting redox machinery to restore stem cell self-renewal and enhance their differentiation potential into youthful cardiovascular lineages. Hence, the redox machinery holds promise as a target for optimizing cardiovascular regenerative therapies. In this context, we delve into the current understanding of redox homeostasis in regulating stem cell function and reprogramming processes that impact the regenerative potential of the cardiovascular system. Furthermore, we offer insights into the recent translational and clinical implications of redox-targeting compounds aimed at enhancing current regenerative therapies for aging cardiovascular tissues.

RSK3 switches cell fate: from stress-induced senescence to malignant progression

BACKGROUND

TGFβ induces several cell phenotypes including senescence, a stable cell cycle arrest accompanied by a secretory program, and epithelial-mesenchymal transition (EMT) in normal epithelial cells. During carcinogenesis cells lose the ability to undergo senescence in response to TGFβ but they maintain an EMT, which can contribute to tumor progression. Our aim was to identify mechanisms promoting TGFβ-induced senescence escape.

METHODS

In vitro experiments were performed with primary human mammary epithelial cells (HMEC) immortalized by hTert. For kinase library screen and modulation of gene expression retroviral transduction was used. To characterize gene expression, RNA microarray with GSEA analysis and RT-qPCR were used. For protein level and localization, Western blot and immunofluorescence were performed. For senescence characterization crystal violet assay, Senescence Associated-β-Galactosidase activity, EdU staining were conducted. To determine RSK3 partners FLAG-baited immunoprecipitation and mass spectrometry-based proteomic analyses were performed. Proteosome activity and proteasome enrichment assays were performed. To validate the role of RSK3 in human breast cancer, analysis of METABRIC database was performed. Murine intraductal xenografts using MCF10DCIS.com cells were carried out, with histological and immunofluorescence analysis of mouse tissue sections.

RESULTS

A screen with active kinases in HMECs upon TGFβ treatment identified that the serine threonine kinase RSK3, or RPS6KA2, a kinase mainly known to regulate cancer cell death including in breast cancer, reverted TGFβ-induced senescence. Interestingly, RSK3 expression decreased in response to TGFβ in a SMAD3-dependent manner, and its constitutive expression rescued SMAD3-induced senescence, indicating that a decrease in RSK3 itself contributes to TGFβ-induced senescence. Using transcriptomic analyses and affinity purification coupled to mass spectrometry-based proteomics, we unveiled that RSK3 regulates senescence by inhibiting the NF-κΒ pathway through the decrease in proteasome-mediated IκBα degradation. Strikingly, senescent TGFβ-treated HMECs display features of epithelial to mesenchymal transition (EMT) and during RSK3-induced senescence escaped HMECs conserve EMT features. Importantly, RSK3 expression is correlated with EMT and invasion, and inversely correlated with senescence and NF-κΒ in human claudin-low breast tumors and its expression enhances the formation of breast invasive tumors in the mouse mammary gland.

CONCLUSIONS

We conclude that RSK3 switches cell fate from senescence to malignancy in response to TGFβ signaling.

SLC35D3 promotes white adipose tissue browning to ameliorate obesity by NOTCH signaling

White adipose tissue browning can promote lipid burning to increase energy expenditure and improve adiposity. Here, we show that Slc35d3 expression is significantly lower in adipose tissues of obese mice. While adipocyte-specific Slc35d3 knockin is protected against diet-induced obesity, adipocyte-specific Slc35d3 knockout inhibits white adipose tissue browning and causes decreased energy expenditure and impaired insulin sensitivity in mice. Mechanistically, we confirm that SLC35D3 interacts with the NOTCH1 extracellular domain, which leads to the accumulation of NOTCH1 in the endoplasmic reticulum and thus inhibits the NOTCH1 signaling pathway. In addition, knockdown of Notch1 in mouse inguinal white adipose tissue mediated by orthotopic injection of AAV8-adiponectin-shNotch1 shows considerable improvement in obesity and glucolipid metabolism, which is more pronounced in adipocyte-specific Slc35d3 knockout mice than in knockin mice. Overall, in this study, we reveal that SLC35D3 is involved in obesity via NOTCH1 signaling, and low adipose SLC35D3 expression in obesity might be a therapeutic target for obesity and associated metabolic disorders.

Cellular senescence promotes progenitor cell expansion during axolotl limb regeneration

Axolotl limb regeneration is accompanied by the transient induction of cellular senescence within the blastema, the structure that nucleates regeneration. The precise role of this blastemal senescent cell (bSC) population, however, remains unknown. Here, through a combination of gain- and loss-of-function assays, we elucidate the functions and molecular features of cellular senescence in vivo. We demonstrate that cellular senescence plays a positive role during axolotl regeneration by creating a pro-proliferative niche that supports progenitor cell expansion and blastema outgrowth. Senescent cells impact their microenvironment via Wnt pathway modulation. Further, we identify a link between Wnt signaling and senescence induction and propose that bSC-derived Wnt signals facilitate the proliferation of neighboring cells in part by preventing their induction into senescence. This work defines the roles of cellular senescence in the regeneration of complex structures.

Composition of Conditioned Media from Radioresistant and Chemoresistant Cancer Cells Reveals miRNA and Other Secretory Factors Implicated in the Development of Resistance

Resistance to chemo- or radiotherapy is the main obstacle to consistent treatment outcomes in oncology patients. A deeper understanding of the mechanisms driving the development of resistance is required. This review focuses on secretory factors derived from chemo- and radioresistant cancer cells, cancer-associated fibroblasts (CAFs), mesenchymal stem cells (MSCs), and cancer stem cells (CSCs) that mediate the development of resistance in unexposed cells. The first line of evidence considers the experiments with conditioned media (CM) from chemo- and radioresistant cells, CAFs, MSCs, and CSCs that elevate resistance upon the ionizing radiation or anti-cancer drug exposure of previously untreated cells. The composition of CM revealed factors such as circular RNAs; interleukins; plasminogen activator inhibitor; and oncosome-shuttled lncRNAs, mRNAs, and miRNAs that aid in cellular communication and transmit signals inducing the chemo- and radioresistance of sensitive cancer cells. Data, demonstrating that radioresistant cancer cells become resistant to anti-neoplastic drug exposure and vice versa, are also discussed. The mechanisms driving the development of cross-resistance between chemotherapy and radiotherapy are highlighted. The secretion of resistance-mediating factors to intercellular fluid and blood brings attention to its diagnostic potential. Highly stable serum miRNA candidates were proposed by several studies as prognostic markers of radioresistance; however, clinical studies are needed to validate their utility. The ability to predict a treatment response with the help of the miRNA resistance status database will help with the selection of an effective therapeutic strategy. The possibility of miRNA-based therapy is currently being investigated with ongoing clinical studies, and such approaches can be used to alleviate resistance in oncology patients.

Cellular senescence and ophthalmic diseases: narrative review

PURPOSE

Cellular senescence is a state of permanent growth arrest whereby a cell reaches its replicative limit. However, senescence can also be triggered prematurely in certain stressors including radiation, oxidative stress, and chemotherapy. This stress-induced senescence has been studied in the context of promoting inflammation, tumor development, and several chronic degenerative diseases of aging. Emerging research has elucidated the role of senescence in various ocular diseases.

METHODS

The literature search was performed using PubMed with using the query (senescence OR aging) AND (eye disease OR ocular disease OR ophthalmic disease OR cornea OR glaucoma OR cataract OR retina) on October 20th, 2022. No time restriction was proposed. Articles were excluded if they were not referenced in English.

RESULTS

Overall, 51 articles regarding senescence and ocular diseases were found and summarized in this study. Several signaling pathways have been implicated in the development of senescence. Currently, senescence has been linked to various corneal and retinal pathologies, as well as cataract and glaucoma. Given the number of pathologies, senolytics, which are small molecules with the ability to selective targeting of senescent cells, can be used as therapeutic or prophylactic agents.

CONCLUSIONS

Senescence has been shown to underlie the pathogenesis of numerous ocular diseases. The overall literature on senescence and ocular disease is growing rapidly. There is an ongoing debate whether or not cellular senescence detected in experiments contributes in a significant way to diseases. Research on understanding the mechanism of senescence from ocular cells and tissues is just beginning. Multiple animal models are required to test potential senolytics. Currently, no studies exist to date which have demonstrated the benefits of senolytic therapies in human studies.

Typhoid toxin hijacks Wnt5a to establish host senescence and Salmonella infection

Damage to our genome causes acute senescence in mammalian cells, which undergo growth arrest and release a senescence-associated secretory phenotype (SASP) that propagates the stress response to bystander cells. Thus, acute senescence is a powerful tumor suppressor. Salmonella enterica hijacks senescence through its typhoid toxin, which usurps unidentified factors in the stress secretome of senescent cells to mediate intracellular infections. Here, transcriptomics of toxin-induced senescent cells (TxSCs) and proteomics of their secretome identify the factors as Wnt5a, INHBA, and GDF15. Wnt5a establishes a positive feedback loop, driving INHBA and GDF15 expression. In fibroblasts, Wnt5a and INHBA mediate autocrine senescence in TxSCs and paracrine senescence in naive cells. Wnt5a synergizes with GDF15 to increase Salmonella invasion. Intestinal TxSCs undergo apoptosis without Wnt5a, which is required for establishing intestinal TxSCs. The study reveals how an innate defense against cancer is co-opted by a bacterial pathogen to cause widespread damage and mediate infections.

Reliable Hallmarks and Biomarkers of Senescent Lymphocytes

The phenomenon of accumulation of senescent adaptive immunity cells in the elderly is attracting attention due to the increasing risk of global epidemics and aging of the global population. Elderly people are predisposed to various infectious and age-related diseases and are at higher risk of vaccination failure. The accumulation of senescent cells increases age-related background inflammation, "Inflammaging", causing lymphocyte exhaustion and cardiovascular, neurodegenerative, autoimmune and cancer diseases. Here, we present a comprehensive contemporary review of the mechanisms and phenotype of senescence in the adaptive immune system. Although modern research has not yet identified specific markers of aging lymphocytes, several sets of markers facilitate the separation of the aging population based on normal memory and exhausted cells for further genetic and functional analysis. The reasons for the higher predisposition of CD8+ T-lymphocytes to senescence compared to the CD4+ population are also discussed. We point out approaches for senescent-lymphocyte-targeting markers using small molecules (senolytics), antibodies and immunization against senescent cells. The suppression of immune senescence is the most relevant area of research aimed at developing anti-aging and anti-cancer therapy for prolonging the lifespan of the global population.

The senescent secretome drives PLVAP expression in cultured human hepatic endothelial cells to promote monocyte transmigration

Liver sinusoidal endothelial cells (LSEC) undergo significant phenotypic change in chronic liver disease (CLD), and yet the factors that drive this process and the impact on their function as a vascular barrier and gatekeeper for immune cell recruitment are poorly understood. Plasmalemma-vesicle-associated protein (PLVAP) has been characterized as a marker of LSEC in CLD; notably we found that PLVAP upregulation strongly correlated with markers of tissue senescence. Furthermore, exposure of human LSEC to the senescence-associated secretory phenotype (SASP) led to a significant upregulation of PLVAP. Flow-based assays demonstrated that SASP-driven leukocyte recruitment was characterized by paracellular transmigration of monocytes while the majority of lymphocytes migrated transcellularly. Knockdown studies confirmed that PLVAP selectively supported monocyte transmigration mediated through PLVAP's impact on LSEC permeability by regulating phospho-VE-cadherin expression and endothelial gap formation. PLVAP may therefore represent an endothelial target that selectively shapes the senescence-mediated immune microenvironment in liver disease.

An immunosuppressive subtype of senescent tumor cells predicted worse immunotherapy response in lung adenocarcinoma

Senescent tumor cells (STCs) can induce immunosuppression, promoting tumor progression and therapy resistance. However, the specific characteristics of immunosuppressive STC have not been thoroughly investigated. This study aimed to characterize and elucidate the immunosuppressive phenotype of STC in lung adenocarcinoma by employing single-cell and bulk transcriptomics, as well as serum proteomics profiling. We identified senescence-related genes specific to tumors and identified Cluster10 of STC as the immunomodulatory subtype. Cluster10 exhibited a distinct secretome dominated by cytokines such as CXCL1, CXCL2, and CXCL8 and showed activation of transcription factors associated with cytokine secretion, including NFKB1, RELA, and STAT3. Notably, Cluster10 demonstrated the highest degree of intercellular communication among all cell types, with interactions as LGALS9-TIM3 and MIF-CD74. Furthermore, Cluster10 showed significant associations with poor prognosis and diminished response to immunotherapy. Analysis of serum proteomics data from our in-house cohort identified CXCL8 as a potential marker for predicting immunotherapeutic outcomes.

Impact of senolytic treatment on immunity, aging, and disease

Cellular senescence has been implicated in the pathophysiology of many age-related diseases. However, it also plays an important protective role in the context of tumor suppression and wound healing. Reducing senescence burden through treatment with senolytic drugs or the use of genetically targeted models of senescent cell elimination in animals has shown positive results in the context of mitigating disease and age-associated inflammation. Despite positive, albeit heterogenous, outcomes in clinical trials, very little is known about the short-term and long-term immunological consequences of using senolytics as a treatment for age-related conditions. Further, many studies examining cellular senescence and senolytic treatment have been demonstrated in non-infectious disease models. Several recent reports suggest that senescent cell elimination may have benefits in COVID-19 and influenza resolution and disease prognosis. In this review, we discuss the current clinical trials and pre-clinical studies that are exploring the impact of senolytics on cellular immunity. We propose that while eliminating senescent cells may have an acute beneficial impact on primary immune responses, immunological memory may be negatively impacted. Closer investigation of senolytics on immune function and memory generation would provide insight as to whether senolytics could be used to enhance the aging immune system and have potential to be used as therapeutics or prophylactics in populations that are severely and disproportionately affected by infections such as the elderly and immunocompromised.

Translating Senotherapeutic Interventions into the Clinic with Emerging Proteomic Technologies

Cellular senescence is a state of irreversible growth arrest with profound phenotypic changes, including the senescence-associated secretory phenotype (SASP). Senescent cell accumulation contributes to aging and many pathologies including chronic inflammation, type 2 diabetes, cancer, and neurodegeneration. Targeted removal of senescent cells in preclinical models promotes health and longevity, suggesting that the selective elimination of senescent cells is a promising therapeutic approach for mitigating a myriad of age-related pathologies in humans. However, moving senescence-targeting drugs (senotherapeutics) into the clinic will require therapeutic targets and biomarkers, fueled by an improved understanding of the complex and dynamic biology of senescent cell populations and their molecular profiles, as well as the mechanisms underlying the emergence and maintenance of senescence cells and the SASP. Advances in mass spectrometry-based proteomic technologies and workflows have the potential to address these needs. Here, we review the state of translational senescence research and how proteomic approaches have added to our knowledge of senescence biology to date. Further, we lay out a roadmap from fundamental biological discovery to the clinical translation of senotherapeutic approaches through the development and application of emerging proteomic technologies, including targeted and untargeted proteomic approaches, bottom-up and top-down methods, stability proteomics, and surfaceomics. These technologies are integral for probing the cellular composition and dynamics of senescent cells and, ultimately, the development of senotype-specific biomarkers and senotherapeutics (senolytics and senomorphics). This review aims to highlight emerging areas and applications of proteomics that will aid in exploring new senescent cell biology and the future translation of senotherapeutics.

Yearning for machine learning: applications for the classification and characterisation of senescence

Senescence is a widely appreciated tumour suppressive mechanism, which acts as a barrier to cancer development by arresting cell cycle progression in response to harmful stimuli. However, senescent cell accumulation becomes deleterious in aging and contributes to a wide range of age-related pathologies. Furthermore, senescence has beneficial roles and is associated with a growing list of normal physiological processes including wound healing and embryonic development. Therefore, the biological role of senescent cells has become increasingly nuanced and complex. The emergence of sophisticated, next-generation profiling technologies, such as single-cell RNA sequencing, has accelerated our understanding of the heterogeneity of senescence, with distinct final cell states emerging within models as well as between cell types and tissues. In order to explore data sets of increasing size and complexity, the senescence field has begun to employ machine learning (ML) methodologies to probe these intricacies. Most notably, ML has been used to aid the classification of cells as senescent, as well as to characterise the final senescence phenotypes. Here, we provide a background to the principles of ML tasks, as well as some of the most commonly used methodologies from both traditional and deep ML. We focus on the application of these within the context of senescence research, by addressing the utility of ML for the analysis of data from different laboratory technologies (microscopy, transcriptomics, proteomics, methylomics), as well as the potential within senolytic drug discovery. Together, we aim to highlight both the progress and potential for the application of ML within senescence research.

Senescent Cells: Dual Implications on the Retinal Vascular System

Cellular senescence, a state of permanent cell cycle arrest in response to endogenous and exogenous stimuli, triggers a series of gradual alterations in structure, metabolism, and function, as well as inflammatory gene expression that nurtures a low-grade proinflammatory milieu in human tissue. A growing body of evidence indicates an accumulation of senescent neurons and blood vessels in response to stress and aging in the retina. Prolonged accumulation of senescent cells and long-term activation of stress signaling responses may lead to multiple chronic diseases, tissue dysfunction, and age-related pathologies by exposing neighboring cells to the heightened pathological senescence-associated secretory phenotype (SASP). However, the ultimate impacts of cellular senescence on the retinal vasculopathies and retinal vascular development remain ill-defined. In this review, we first summarize the molecular players and fundamental mechanisms driving cellular senescence, as well as the beneficial implications of senescent cells in driving vital physiological processes such as embryogenesis, wound healing, and tissue regeneration. Then, the dual implications of senescent cells on the growth, hemostasis, and remodeling of retinal blood vessels are described to document how senescent cells contribute to both retinal vascular development and the severity of proliferative retinopathies. Finally, we discuss the two main senotherapeutic strategies-senolytics and senomorphics-that are being considered to safely interfere with the detrimental effects of cellular senescence.

Pancreatic β-cell senescence in diabetes: mechanisms, markers and therapies

Cellular senescence is a response to a wide variety of stressors, including DNA damage, oncogene activation and physiologic aging, and pathologically accelerated senescence contributes to human disease, including diabetes mellitus. Indeed, recent work in this field has demonstrated a role for pancreatic β-cell senescence in the pathogenesis of Type 1 Diabetes, Type 2 Diabetes and monogenic diabetes. Small molecule or genetic targeting of senescent β-cells has shown promise as a novel therapeutic approach for preventing and treating diabetes. Despite these advances, major questions remain around the molecular mechanisms driving senescence in the β-cell, identification of molecular markers that distinguish senescent from non-senescent β-cell subpopulations, and translation of proof-of-concept therapies into novel treatments for diabetes in humans. Here, we summarize the current state of the field of β-cell senescence, highlighting insights from mouse models as well as studies on human islets and β-cells. We identify markers that have been used to detect β-cell senescence to unify future research efforts in this field. We discuss emerging concepts of the natural history of senescence in β-cells, heterogeneity of senescent β-cells subpopulations, role of sex differences in senescent responses, and the consequences of senescence on integrated islet function and microenvironment. As a young and developing field, there remain many open research questions which need to be addressed to move senescence-targeted approaches towards clinical investigation.

Identification of novel key markers that are induced during traumatic brain injury in mice

Background

Traumatic brain injury (TBI) has emerged as an increasing public health problem but has not been well studied, particularly the mechanisms of brain cellular behaviors during TBI.

Methods

In this study, we established an ischemia/reperfusion (I/R) brain injury mice model using transient middle cerebral artery occlusion (tMCAO) strategy. After then, RNA-sequencing of frontal lobes was performed to screen key inducers during TBI. To further verify the selected genes, we collected peripheral blood mononuclear cells (PBMCs) from TBI patients within 24 h who attended intensive care unit (ICU) in the Affiliated Hospital of Yangzhou University and analyzed the genes expression using RT-qPCR. Finally, the receiver operator characteristic (ROC) curves and co-expression with cellular senescence markers were applied to evaluate the predictive value of the genes.

Results

A total of six genes were screened out from the RNA-sequencing based on their novelty in TBI and implications in apoptosis and cellular senescence signaling. RT-qPCR analysis of PBMCs from patients showed the six genes were all up-regulated during TBI after comparing with healthy volunteers who attended the hospital for physical examination. The area under ROC (AUC) curves were all >0.7, and the co-expression scores of the six genes with senescence markers were all significantly positive. We thus identified TGM1, TGM2, ATF3, RCN3, ORAI1 and ITPR3 as novel key markers that are induced during TBI, and these markers may also serve as potential predictors for the progression of TBI.

Modelling the dynamics of senescence spread

Cellular senescence is a cell surveillance mechanism that arrests the cell cycle in damaged cells. The senescent phenotype can spread from cell to cell through paracrine and juxtacrine signalling, but the dynamics of this process are not well understood. Although senescent cells are important in ageing, wound healing and cancer, it is unclear how the spread of senescence is contained in senescent lesions. In the absence of the immune system, senescence could theoretically spread infinitely from one cell to another, but this contradicts experimental evidence. To investigate this issue, we developed both a minimal mathematical model and a stochastic simulation of senescence spread. Our results suggest that differences in the number of signalling molecules secreted between subtypes of senescent cells can limit the spread of senescence. We found that dynamic, time-dependent paracrine signalling prevents the uncontrolled spread of senescence, and we demonstrate how model parameters can be determined using Bayesian inference in a proposed experiment.

Beyond SAHF: An integrative view of chromatin compartmentalization during senescence

Cellular senescence, a persistent form of cell cycle arrest, has been linked to the formation of heterochromatic foci, accompanied by additional concentric epigenetic layers. However, senescence is a highly heterogeneous phenotype, and the formation of these structures is context dependent. Recent developments in the understanding of the high-order chromatin organization have opened new avenues for contextualizing the nuclear and chromatin phenotypes of senescence. Oncogene-induced senescence displays prominent foci and typically exhibits increased chromatin compartmentalization, based on the chromosome conformation assays, as marked by increased transcompaction and segregation of the heterochromatin and euchromatin. However, other types of senescence (e.g., replicative senescence) exhibit comparatively lower levels of compartmentalization. Thus, a more integrative view of the global rearrangement of the chromatin architecture that occurs during senescence is emerging, with potential functional implications for the heterogeneity of the senescence phenotype.

Exploring a deep learning neural architecture for closed Literature-based discovery

Scientific literature presents a wealth of information yet to be explored. As the number of researchers increase with each passing year and publications are released, this contributes to an era where specialized fields of research are becoming more prevalent. As this trend continues, this further propagates the separation of interdisciplinary publications and makes keeping up to date with literature a laborious task. Literature-based discovery (LBD) aims to mitigate these concerns by promoting information sharing among non-interacting literature while extracting potentially meaningful information. Furthermore, recent advances in neural network architectures and data representation techniques have fueled their respective research communities in achieving state-of-the-art performance in many downstream tasks. However, studies of neural network-based methods for LBD remain to be explored. We introduce and explore a deep learning neural network-based approach for LBD. Additionally, we investigate various approaches to represent terms as concepts and analyze the affect of feature scaling representations into our model. We compare the evaluation performance of our method on five hallmarks of cancer datasets utilized for closed discovery. Our results show the chosen representation as input into our model affects evaluation performance. We found feature scaling our input representations increases evaluation performance and decreases the necessary number of epochs needed to achieve model generalization. We also explore two approaches to represent model output. We found reducing the model's output to capturing a subset of concepts improved evaluation performance at the cost of model generalizability. We also compare the efficacy of our method on the five hallmarks of cancer datasets to a set of randomly chosen relations between concepts. We found these experiments confirm our method's suitability for LBD.

Exploring the Communication of the SASP: Dynamic, Interactive, and Adaptive Effects on the Microenvironment

Cellular senescence is a complex cell state that can occur during physiological ageing or after exposure to stress signals, regardless of age. It is a dynamic process that continuously evolves in a context-dependent manner. Senescent cells interact with their microenvironment by producing a heterogenous and plastic secretome referred to as the senescence-associated secretory phenotype (SASP). Hence, understanding the cross-talk between SASP and the microenvironment can be challenging due to the complexity of signal exchanges. In this review, we first aim to update the definition of senescence and its associated biomarkers from its discovery to the present day. We detail the regulatory mechanisms involved in the expression of SASP at multiple levels and develop how SASP can orchestrate microenvironment modifications, by focusing on extracellular matrix modifications, neighboring cells' fate, and intercellular communications. We present hypotheses on how these microenvironmental events may affect dynamic changes in SASP composition in return. Finally, we discuss the various existing approaches to targeting SASP and clarify what is currently known about the biological effects of these modified SASPs on the cellular environment.

Beyond the Complement Cascade: Insights into Systemic Immunosenescence and Inflammaging in Age-Related Macular Degeneration and Current Barriers to Treatment

Landmark genetic studies have revealed the effect of complement biology and its regulation on the pathogenesis of age-related macular degeneration (AMD). Limited phase 3 clinical trial data showing a benefit of complement inhibition in AMD raises the prospect of more complex mediators at play. Substantial evidence supports the role of para-inflammation in maintaining homeostasis in the retina and choroid. With increasing age, a decline in immune system regulation, known as immunosenescence, has been shown to alter the equilibrium maintained by para-inflammation. The altered equilibrium results in chronic, sterile inflammation with aging, termed 'inflammaging', including in the retina and choroid. The chronic inflammatory state in AMD is complex, with contributions from cells of the innate and adaptive branches of the immune system, sometimes with overlapping features, and the interaction of their secretory products with retinal cells such as microglia and retinal pigment epithelium (RPE), extracellular matrix and choroidal vascular endothelial cells. In this review, the chronic inflammatory state in AMD will be explored by immune cell type, with a discussion of factors that will need to be overcome in the development of curative therapies.

Reshaping of the tumor microenvironment by cellular senescence: An opportunity for senotherapies

Cellular senescence is a stress response associated with aging and disease, including cancer. Senescent cells undergo a stable cell cycle arrest, undergo a change in morphology and metabolic reprogramming, and produce a bioactive secretome termed the senescence-associated secretory phenotype (SASP). In cancer, senescence is an important barrier to tumor progression. Induction of senescence in preneoplastic cells limits cancer initiation, and many cancer therapies act in part by inducing senescence in cancer cells. Paradoxically, senescent cells lingering in the tumor microenvironment (TME) can contribute to tumor progression, metastasis, and therapy resistance. In this review, we discuss the different types of senescent cells present in the TME and how these senescent cells and their SASP reshape the TME, affect immune responses, and influence cancer progression. Furthermore, we will highlight the importance of senotherapies, including senolytic drugs that eliminate senescent cells and impede tumor progression and metastasis by restoring anti-tumor immune responses and influencing the TME.

EZH2 inhibition remodels the inflammatory senescence-associated secretory phenotype to potentiate pancreatic cancer immune surveillance

Immunotherapies that produce durable responses in some malignancies have failed in pancreatic ductal adenocarcinoma (PDAC) due to rampant immune suppression and poor tumor immunogenicity. We and others have demonstrated that induction of the senescence-associated secretory phenotype (SASP) can be an effective approach to activate anti-tumor natural killer (NK) cell and T cell immunity. In the present study, we found that the pancreas tumor microenvironment suppresses NK cell and T cell surveillance after therapy-induced senescence through enhancer of zeste homolog 2 (EZH2)-mediated epigenetic repression of proinflammatory SASP genes. EZH2 blockade stimulated production of SASP chemokines CCL2 and CXCL9/10, leading to enhanced NK cell and T cell infiltration and PDAC eradication in mouse models. EZH2 activity was also associated with suppression of chemokine signaling and cytotoxic lymphocytes and reduced survival in patients with PDAC. These results demonstrate that EZH2 represses the proinflammatory SASP and that EZH2 inhibition combined with senescence-inducing therapy could be a powerful means to achieve immune-mediated tumor control in PDAC.

Endothelial cell senescence exacerbates pulmonary hypertension by inducing juxtacrine Notch signaling in smooth muscle cells

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by a progressive increase in pulmonary artery pressure caused by pathological pulmonary artery remodeling. Here, we demonstrate that endothelial cell (EC) senescence plays a negative role in pulmonary hypertension via juxtacrine interaction with smooth muscle cells (SMCs). By using EC-specific progeroid mice, we discovered that EC progeria deteriorated vascular remodeling in the lungs, and exacerbated pulmonary hypertension in mice. Mechanistically, senescent ECs overexpressed Notch ligands, which resulted in increased Notch signaling and activated proliferation and migration capacities in neighboring SMCs. Pharmacological inhibition of Notch signaling reduced the effects of senescent ECs on SMCs functions in vitro, and improved the worsened pulmonary hypertension in EC-specific progeroid mice in vivo. Our findings show that EC senescence is a critical disease-modifying factor in PAH and that EC-mediated Notch signaling is a pharmacotherapeutic target for the treatment of PAH, particularly in the elderly.

Senescence: a double-edged sword in beta-cell health and failure?

Cellular senescence is a complex process marked by permanent cell-cycle arrest in response to a variety of stressors, and acts as a safeguard against the proliferation of damaged cells. Senescence is not only a key process underlying aging and development of many diseases, but has also been shown to play a vital role in embryogenesis as well as tissue regeneration and repair. In context of the pancreatic beta-cells, that are essential for maintaining glucose homeostasis, replicative senescence is responsible for the age-related decline in regenerative capacity. Stress induced premature senescence is also a key early event underlying beta-cell failure in both type 1 and type 2 diabetes. Targeting senescence has therefore emerged as a promising therapeutic avenue for diabetes. However, the molecular mechanisms that mediate the induction of beta-cell senescence in response to various stressors remain unclear. Nor do we know if senescence plays any role during beta-cell growth and development. In this perspective, we discuss the significance of senescence in beta-cell homeostasis and pathology and highlight emerging directions in this area that warrant our attention.

Aging, cell senescence, the pathogenesis and targeted therapies of intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) refers to the aging and degenerative diseases of intervertebral disc components such as nucleus pulposus, annulus fibrosus, and cartilage endplate, and is the main cause of chronic low back pain. Over the past few years, many researchers around the world concerned that the degeneration of nucleus pulposus (NP) cells plays the main role in IVDD. The degeneration of NP cells is caused by a series of pathological processes, including oxidative stress, inflammatory response, apoptosis, abnormal proliferation, and autophagy. Interestingly, many studies have found a close relationship between the senescence of NP cells and the progression of NP degeneration. The classical aging pathways also have been confirmed to be involved in the pathological process of IVDD. Moreover, several anti-aging drugs have been used to treat IVDD by inhibiting NP cells senescence, such as proanthocyanidins, resveratrol and bone morphogenetic protein 2. Therefore, this article will systematically list and discuss aging, cell senescence, the pathogenesis and targeted therapies of IVDD, in order to provide new ideas for the treatment of IVDD in the future.

Fibroblasts in cancer: Unity in heterogeneity

Tumor cells do not exist in isolation in vivo, and carcinogenesis depends on the surrounding tumor microenvironment (TME), composed of a myriad of cell types and biophysical and biochemical components. Fibroblasts are integral in maintaining tissue homeostasis. However, even before a tumor develops, pro-tumorigenic fibroblasts in close proximity can provide the fertile 'soil' to the cancer 'seed' and are known as cancer-associated fibroblasts (CAFs). In response to intrinsic and extrinsic stressors, CAFs reorganize the TME enabling metastasis, therapeutic resistance, dormancy and reactivation by secreting cellular and acellular factors. In this review, we summarize the recent discoveries on CAF-mediated cancer progression with a particular focus on fibroblast heterogeneity and plasticity.

Rapid emergence of transcriptional heterogeneity upon molecular stress predisposes cells to two distinct states of senescence

Slowing aging can reduce the risk of chronic diseases. In particular, eliminating senescent cells is a promising approach to slow aging. Previous studies found that both cells from older animals and senescent cells have noisy gene expression. Here, we performed a large-scale single-cell RNA-sequencing time course to understand how transcriptional heterogeneity develops among senescent cells. We found that cells experiencing senescence-inducing oxidative stress rapidly adopt one of two major transcriptional states. One senescent cell state is associated with stress response, and the other is associated with tissue remodeling. We did not observe increased stochastic gene expression. This data is consistent with the idea that reproducible, limited, distinct, and coherent transcriptional states exist in senescent cell populations. These physiologically distinct senescent cell subtypes may each affect the aging process in unique ways and constitute a source of heterogeneity in aging.