SILAC Analysis Reveals Increased Secretion of Hemostasis-Related Factors by Senescent Cells

Lianhua qingke alleviates cigarette smoke induced cellular senescence in COPD mice by regulating the Sp1/SIRT1/HIF-1α pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Lianhua Qingke (LHQK) has been utilized as a complementary therapy for respiratory diseases like tracheobronchitis and acute exacerbations of COPD in China. However, its therapeutic efficacy and underlying mechanisms for COPD remain elusive.

AIM OF THE STUDY

This study aimed to elucidate the mechanisms underlying the effects of LHQK on COPD, focusing on its anti-senescence properties.

MATERIALS AND METHODS

The therapeutic effects of LHQK were assessed by chronic cigarette smoke exposure induced COPD mice model. Lung function, histopathology investigation, cytokines detection and bio-molecular analysis were conducted to assess the impact of LHQK on pulmonary inflammation, mucin secretion, and cellular senescence of cigarette smoke (CS)-induced COPD mice.

RESULTS

A comprehensive analysis identified a total of 41 compounds as the key compounds of LHQK. Oral administration of LHQK markedly reversed the decline in pulmonary function, suppressed inflammation and mucus secretion, mitigated emphysema, and histopathology damage in lungs of COPD mice. In addition, LHQK attenuated secretory phenotype associated with cellular senescence in pulmonary and circulatory, and reduced the senescence-associated markers levels, such as SA-β-gal, miR-125a-5p, p21, p27 and p53. Network pharmacology and molecular assays indicated that LHQK enhanced Sp1 and SIRT1 expression, resulting to repression of HIF-1α, finally alleviating cellular senescence in COPD mice.

CONCLUSIONS

LHQK demonstrates potential as a complementary therapy for COPD, attenuating CS-triggered emphysema and pulmonary inflammation by targeting cellular senescence processes and modulation of Sp1/SIRT1/HIF-1α pathway.

Anti-senescence therapies: a new concept to address cardiovascular disease

Accumulation of senescent cells is an increasingly recognized factor in the development and progression of cardiovascular (CV) disease (CVD). Senescent cells of different types display a pro-inflammatory and matrix remodelling molecular programme, known as the 'senescence-associated secretory phenotype' (SASP), which has roots in (epi)genetic changes. Multiple therapeutic options (senolytics, anti-SASP senomorphics, and epigenetic reprogramming) that delete or ameliorate cellular senescence have recently emerged. Some drugs routinely used in the clinics also have anti-senescence effects. However, multiple challenges hinder the application of novel anti-senescence therapeutics in the clinical setting. Understanding the biology of cellular senescence, advantages and pitfalls of anti-senescence treatments, and patients who can profit from these interventions is necessary to introduce this novel therapeutic modality into the clinics. We provide a guide through the molecular machinery of senescent cells, systematize anti-senescence treatments, and propose a pathway towards senescence-adapted clinical trial design to aid future efforts.

Therapy-induced senescence is a transient drug resistance mechanism in breast cancer

BACKGROUND

Therapy-induced senescence (TIS) is considered a permanent cell cycle arrest following DNA-damaging treatments; however, its irreversibility has recently been challenged. Here, we demonstrate that escape from TIS is universal across breast cancer cells. Moreover, TIS provides a reversible drug resistance mechanism that ensures the survival of the population, and could contribute to relapse.

METHODS

TIS was induced in four different breast cancer cell line with high-dose chemotherapy and cultured until cells escaped TIS. Parental, TIS and repopulating cells were analyzed by bulk and single-cell RNA sequencing and surface proteomics. A genetically engineered mouse model of triple-negative breast cancer was used to prove why current senolytics cannot overcome TIS in tumors.

RESULTS

Screening the toxicity of a diverse panel of FDA-approved anticancer drugs revealed that TIS meditates resistance to half of these compounds, despite their distinct mechanism of action. Bulk and single-cell RNA sequencing, along with surface proteome analysis, showed that while parental and repopulating cells are almost identical, TIS cells are significantly different from both, highlighting their transient nature. Furthermore, investigating dozens of known drug resistance mechanisms offered no explanation for this unique drug resistance pattern. Additionally, TIS cells expressed a gene set associated with immune evasion and a potential KRAS-driven escape mechanism from TIS.

CONCLUSION

Our results reveal that TIS, as a transient drug resistance mechanism, could contribute to overcome the immune response and to relapse by reverting to a proliferative stage.

Suppression of thrombospondin-1-mediated inflammaging prolongs hematopoietic health span

Chronic low-grade inflammation observed in older adults, termed inflammaging, is a common feature underlying a multitude of aging-associated maladies including a decline in hematopoietic activity. However, whether suppression of inflammaging can preserve hematopoietic health span remains unclear, in part because of a lack of tools to measure inflammaging within hematopoietic stem cells (HSCs). Here, we identify thrombospondin-1 (Thbs1) as an essential regulator of inflammaging within HSCs. We describe a transcriptomics-based approach for measuring inflammaging within stem cells and demonstrate that deletion of Thbs1 is sufficient to prevent HSC inflammaging. Our results demonstrate that suppression of HSC inflammaging prevents aging-associated defects in hematopoietic activity including loss of HSC self-renewal, myeloid-biased HSC differentiation, and anemia. Our findings indicate that suppression of HSC inflammaging may also prolong overall systemic health span.

Alterations in the placental proteome in association with the presence of black carbon particles: A discovery study

BACKGROUND

Exposure to ambient air pollution is known to cause direct and indirect molecular expression changes in the placenta, on the DNA, mRNA, and protein levels. Ambient black carbon (BC) particles can be found in the human placenta already very early in gestation. However, the effect of in utero BC exposure on the entire placental proteome has never been studied to date.

OBJECTIVES

We explored whether placental proteome differs between mothers exposed to either high or low BC levels throughout the entire pregnancy.

METHODS

We used placental tissue samples from the ENVIRONAGE birth cohort, of 20 non-smoking, maternal- and neonate characteristic-matched women exposed to high (n = 10) or low (n = 10) levels of ambient BC throughout pregnancy. We modeled prenatal BC exposure levels based on the mother's home address and measured BC levels in the fetal side of the placenta. The placental proteome was analyzed by nano-liquid chromatography Q-TOF mass spectrometry. PEAKS software was used for protein identification and label-free quantification. Protein-protein interaction and functional pathway enrichment analyses were performed with the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) software.

RESULTS

The accumulation of BC particles in placenta was 2.19 times higher in the high versus low exposure group (20943.4 vs 9542.7 particles/mm³; p = 0.007). Thirteen proteins showed a ≥2-fold expression difference between the two exposure groups, all overexpressed in the placentas of women prenatally exposed to high BC levels. Three protein-protein interactions were enriched within this group, namely between TIMP3 and COL4A2, SERPINE2 and COL4A2, and SERPINE2 and GP1BB. Functional pathway enrichment analysis put forward pathways involved in extracellular matrix-receptor interaction, fibrin clot formation, and sodium ion transport regulation.

DISCUSSION

Prenatal BC exposure affects the placental proteome. Future research should focus on the potential consequences of these alterations on placental functioning, and health and disease during early childhood development.

SenNet recommendations for detecting senescent cells in different tissues

Once considered a tissue culture-specific phenomenon, cellular senescence has now been linked to various biological processes with both beneficial and detrimental roles in humans, rodents and other species. Much of our understanding of senescent cell biology still originates from tissue culture studies, where each cell in the culture is driven to an irreversible cell cycle arrest. By contrast, in tissues, these cells are relatively rare and difficult to characterize, and it is now established that fully differentiated, postmitotic cells can also acquire a senescence phenotype. The SenNet Biomarkers Working Group was formed to provide recommendations for the use of cellular senescence markers to identify and characterize senescent cells in tissues. Here, we provide recommendations for detecting senescent cells in different tissues based on a comprehensive analysis of existing literature reporting senescence markers in 14 tissues in mice and humans. We discuss some of the recent advances in detecting and characterizing cellular senescence, including molecular senescence signatures and morphological features, and the use of circulating markers. We aim for this work to be a valuable resource for both seasoned investigators in senescence-related studies and newcomers to the field.

To target cellular senescence in diabetic kidney disease: the known and the unknown

Cellular senescence represents a condition of irreversible cell cycle arrest, characterized by heightened senescence-associated beta-galactosidase (SA-β-Gal) activity, senescence-associated secretory phenotype (SASP), and activation of the DNA damage response (DDR). Diabetic kidney disease (DKD) is a significant contributor to end-stage renal disease (ESRD) globally, with ongoing unmet needs in terms of current treatments. The role of senescence in the pathogenesis of DKD has attracted substantial attention with evidence of premature senescence in this condition. The process of cellular senescence in DKD appears to be associated with mitochondrial redox pathways, autophagy, and endoplasmic reticulum (ER) stress. Increasing accumulation of senescent cells in the diabetic kidney not only leads to an impaired capacity for repair of renal injury, but also the secretion of pro-inflammatory and profibrotic cytokines and growth factors causing inflammation and fibrosis. Current treatments for diabetes exhibit varying degrees of renoprotection, potentially via mitigation of senescence in the diabetic kidney. Targeting senescent cell clearance through pharmaceutical interventions could emerge as a promising strategy for preventing and treating DKD. In this paper, we review the current understanding of senescence in DKD and summarize the possible therapeutic interventions relevant to senescence in this field.

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.

A plasma proteomic signature links secretome of senescent monocytes to aging- and obesity-related clinical outcomes in humans

Cellular senescence increases with age and contributes to age-related declines and pathologies. We identified circulating biomarkers of senescence associated with diverse clinical traits in humans to facilitate future non-invasive assessment of individual senescence burden and efficacy testing of novel senotherapeutics. Using a novel nanoparticle-based proteomic workflow, we profiled the senescence-associated secretory phenotype (SASP) in monocytes and examined these proteins in plasma samples (N = 1060) from the Baltimore Longitudinal Study of Aging (BLSA). Machine learning models trained on monocyte SASP associated with several age-related phenotypes in a test cohort, including body fat composition, blood lipids, inflammation, and mobility-related traits, among others. Notably, a subset of SASP-based predictions, including a 'high impact' SASP panel that predicts age- and obesity-related clinical traits, were validated in InCHIANTI, an independent aging cohort. These results demonstrate the clinical relevance of the circulating SASP and identify relevant biomarkers of senescence that could inform future clinical studies.

Comprehensive analysis of gene signatures associated with aging in human aortic dissection

Background

Aortic dissection (AD) is a lethal aortic disease with limited effective therapeutic strategies. Aging increases the risk of AD, yet the underlying mechanisms remain unclear. This study aims to analyze the association of aging-related genes (Args) and AD using bioinformatic analysis. This helps provide novel insights into AD pathogenesis and contributes to developing novel therapeutic strategies.

Methods

mRNA (GSE52093, GSE153434), miRNA (GSE98770) and single-cell RNA-sequencing (scRNA-seq, GSE213740) datasets of AD were downloaded from GEO database. Args were downloaded from Aging Atlas database. Differentially-expressed Args were determined by intersecting Args and differentially-expressed mRNAs of two mRNA datasets. Cytoscape was used to identify hub genes and construct hub gene regulatory networks related to miRNAs. Seurat and clusterProfiler R package were used for investigating expression patterns of hub genes at single-cell level, and functional analysis, respectively. To validate the cellular expression pattern of hub genes, the same analysis was applied to our own scRNA-seq data. Drugs targeting hub Args were determined using the DGIdb database.

Results

HGF, CXCL8, SERPINE1, HIF1A, TIMP1, ESR1 and PLAUR were identified as aging-related hub genes in AD. miR-221-3p was predicted to interact with ESR1. A decreased ESR1 expression in smooth muscle cell subpopulation 4 (SMC4) was observed in AD versus normal aortic tissues, which was validated by sequencing 197,605 aortic cells from 13 AD patients. Additionally, upregulated genes of SMC4 in AD tissues were enriched in the "cellular senescence" pathway. These data indicated that decreased ESR1 might promote SMC4 aging during AD formation. Eleven existing drugs targeting hub genes were identified, including ruxolitinib and filgrastim, which are associated with AD.

Conclusions

By sequencing transcriptomic data, this study revealed aging-related hub genes and regulatory network involved in AD formation. Additionally, this study proposed a noteworthy hypothesis that downregulated ESR1 may exacerbate AD by promoting SMC aging, which requires further investigation.

Discovery of drug targets based on traditional Chinese medicine microspheres (TCM-MPs) fishing strategy combined with bio-layer interferometry (BLI) technology

Target discovery of natural products is a key step in the development of new drugs, and it is also a difficult speed-limiting step. In this study, a traditional Chinese medicine microspheres (TCM-MPs) target fishing strategy was developed to discover the key drug targets from complex system. The microspheres are composed of Fe3O4 magnetic nanolayer, oleic acid modified layer, the photoaffinity group (4- [3-(Trifluoromethyl)-3H-diazirin-3-yl] benzoic acid, TAD) layer and active small molecule layer from inside to outside. TAD produces highly reactive carbene under ultraviolet light, which can realize the self-assembly and fixation of drug active small molecules with non-selective properties. Here, taking Shenqi Jiangtang Granules (SJG) as an example, the constructed TCM-MPs was used to fish the related proteins of human glomerular mesangial cells (HMCs) lysate. 28 differential proteins were screened. According to the target analysis based on bioinformatics, GNAS was selected as the key target, which participated in insulin secretion and cAMP signaling pathway. To further verify the interaction effect of GNAS and small molecules, a reverse fishing technique was established based on bio-layer interferometry (BLI) coupled with UHPLC-Q/TOF-MS/MS. The results displayed that 26 small molecules may potentially interact with GNAS, and 7 of them were found to have strong binding activity. In vitro experiments for HMCs have shown that 7 active compounds can significantly activate the cAMP pathway by binding to GNAS. The developed TCM-MPs target fishing strategy combined with BLI reverse fishing technology to screen out key proteins that directly interact with active ingredients from complex target protein systems is significant for the discovery of drug targets for complex systems of TCM.

Substantial downregulation of mitochondrial and peroxisomal proteins during acute kidney injury revealed by data-independent acquisition proteomics

Acute kidney injury (AKI) manifests as a major health concern, particularly for the elderly. Understanding AKI-related proteome changes is critical for prevention and development of novel therapeutics to recover kidney function and to mitigate the susceptibility for recurrent AKI or development of chronic kidney disease. In this study, mouse kidneys were subjected to ischemia-reperfusion injury, and the contralateral kidneys remained uninjured to enable comparison and assess injury-induced changes in the kidney proteome. A ZenoTOF 7600 mass spectrometer was optimized for data-independent acquisition (DIA) to achieve comprehensive protein identification and quantification. Short microflow gradients and the generation of a deep kidney-specific spectral library allowed for high-throughput, comprehensive protein quantification. Upon AKI, the kidney proteome was completely remodeled, and over half of the 3945 quantified protein groups changed significantly. Downregulated proteins in the injured kidney were involved in energy production, including numerous peroxisomal matrix proteins that function in fatty acid oxidation, such as ACOX1, CAT, EHHADH, ACOT4, ACOT8, and Scp2. Injured kidneys exhibited severely damaged tissues and injury markers. The comprehensive and sensitive kidney-specific DIA-MS assays feature high-throughput analytical capabilities to achieve deep coverage of the kidney proteome, and will serve as useful tools for developing novel therapeutics to remediate kidney function.

Senescent cells at the crossroads of aging, disease, and tissue homeostasis

Originally identified as an outcome of continuous culture of primary cells, cellular senescence has moved beyond the culture dish and is now a bona fide driver of aging and disease in animal models, and growing links to human disease. This cellular stress response consists of a stable proliferative arrest coupled to multiple phenotypic changes. Perhaps the most important of these is the senescence-associated secretory phenotype, or senescence-associated secretory phenotype -a complex and variable collection of secreted molecules release by senescent cells with a number of potent biological activities. Senescent cells appear in multiple age-associated conditions in humans and mice, and interventions that eliminate these cells can prevent or even reverse multiple diseases in mouse models. Here, we review salient aspects of senescent cells in the context of human disease and homeostasis. Senescent cells increase in abundance during several diseases that associated with premature aging. Conversely, senescent cells have a key role in beneficial processes such as development and wound healing, and thus can help maintain tissue homeostasis. Finally, we speculate on mechanisms by which deleterious aspects of senescent cells might be targeted while retaining homeostatic aspects in order to improve age-related outcomes.

Overview of Innate Immune Cell Landscape in Liver Aging

Aging is a biological process with a gradual decline in functional capacity, and this process often enhances the risk of chronic disease morbidity and mortality. With advanced age, the immune system undergoes a process of remodeling that can lead to a chronic inflammatory state, termed immunosenescence and inflammaging, respectively. Immunosenescence is accompanied by changes in the number, proportion, and functional capacity of the innate immune cells. The accumulation of dysfunctional immune cells and the presence of low-grade inflammation can lead to organ damage and expedite the aging process. The liver, crucial in regulating the body's metabolism and immune function, is not exempt from these effects. Age-related modifications affect its immune function and regenerative abilities, potentially increasing the prevalence of age-related liver diseases. While aging's impact on the liver is relatively less severe compared to other organ systems, it still experiences an infiltration of innate immune cells and heightened inflammation levels. This review will elaborate on how aging affects the liver's innate immune cells, such as neutrophils, macrophages, dendritic cells, mast cells, and innate lymphoid cells. It will also explore potential strategies for delaying immunosenescence to alleviate these age-related changes.

The role of cellular senescence in skin aging and age-related skin pathologies

Aging is the result of a gradual functional decline at the cellular, and ultimately, organismal level, resulting in an increased risk of developing a variety of chronic illnesses, such as cardiovascular disease, stroke, cancer and diabetes. The skin is the largest organ of the human body, and the site where signs of aging are most visible. These signs include thin and dry skin, sagging, loss of elasticity, wrinkles, as well as aberrant pigmentation. The appearance of these features is accelerated by exposure to extrinsic factors such as ultraviolet (UV) radiation or pollution, as well as intrinsic factors including time, genetics, and hormonal changes. At the cellular level, aging is associated with impaired proteostasis and an accumulation of macromolecular damage, genomic instability, chromatin reorganization, telomere shortening, remodelling of the nuclear lamina, proliferation defects and premature senescence. Cellular senescence is a state of permanent growth arrest and a key hallmark of aging in many tissues. Due to their inability to proliferate, senescent cells no longer contribute to tissue repair or regeneration. Moreover, senescent cells impair tissue homeostasis, promote inflammation and extracellular matrix (ECM) degradation by secreting molecules collectively known as the "senescence-associated secretory phenotype" (SASP). Senescence can be triggered by a number of different stimuli such as telomere shortening, oncogene expression, or persistent activation of DNA damage checkpoints. As a result, these cells accumulate in aging tissues, including human skin. In this review, we focus on the role of cellular senescence during skin aging and the development of age-related skin pathologies, and discuss potential strategies to rejuvenate aged skin.

Identification and functional analysis of senescent cells in the cardiovascular system using omics approaches

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality worldwide, and senescent cells have emerged as key contributors to its pathogenesis. Senescent cells exhibit cell cycle arrest and secrete a range of proinflammatory factors, termed the senescence-associated secretory phenotype (SASP), which promotes tissue dysfunction and exacerbates CVD progression. Omics technologies, specifically transcriptomics and proteomics, offer powerful tools to uncover and define the molecular signatures of senescent cells in cardiovascular tissue. By analyzing the comprehensive molecular profiles of senescent cells, omics approaches can identify specific genetic alterations, gene expression patterns, protein abundances, and metabolite levels associated with senescence in CVD. These omics-based discoveries provide insights into the mechanisms underlying senescence-induced cardiovascular damage, facilitating the development of novel diagnostic biomarkers and therapeutic targets. Furthermore, integration of multiple omics data sets enables a systems-level understanding of senescence in CVD, paving the way for precision medicine approaches to prevent or treat cardiovascular aging and its associated complications.

Coagulation Dysfunctions in Non-Alcoholic Fatty Liver Disease-Oxidative Stress and Inflammation Relevance

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases. Its incidence is progressively rising and it is possibly becoming a worldwide epidemic. NAFLD encompasses a spectrum of diseases accounting for the chronic accumulation of fat within the hepatocytes due to various causes, excluding excessive alcohol consumption. In this study, we aimed to focus on finding evidence regarding the implications of oxidative stress and inflammatory processes that form the multifaceted pathophysiological tableau in relation to thrombotic events that co-occur in NAFLD and associated chronic liver diseases. Recent evidence on the pathophysiology of NAFLD suggests that a complex pattern of multidirectional components, such as prooxidative, proinflammatory, and prothrombotic components, better explains the multiple factors that promote the mechanisms underlying the fatty acid excess and subsequent processes. As there is extensive evidence on the multi-component nature of NAFLD pathophysiology, further studies could address the complex interactions that underlie the development and progression of the disease. Therefore, this study aimed to describe possible pathophysiological mechanisms connecting the molecular impairments with the various clinical manifestations, focusing especially on the interactions among oxidative stress, inflammation, and coagulation dysfunctions. Thus, we described the possible bidirectional modulation among coagulation homeostasis, oxidative stress, and inflammation that occurs in the various stages of NAFLD.

Secreted phospholipase A2 XIIA triggers a mitochondrial damage-induced senescence in chronic obstructive pulmonary disease fibroblasts

RATIONALE

Lung fibroblast senescence is involved in the pathophysiology of chronic obstructive pulmonary disease (COPD). However, the mechanisms underlining this phenomenon are still poorly understood. Secreted phospholipases (sPLA2, a subclass of phospholipases) are secreted by senescent cells and can in turn induce senescence. However, their role in fibroblasts senescence in COPD is unknown.

OBJECTIVES

The aim of this study was to analyze the role of sPLA2 in pulmonary fibroblast senescence.

METHODS

Fibroblasts were isolated from patients with COPD and control subjects, and senescence markers and inflammatory profile was analyzed. sPLA2 levels were quantified in serum of COPD and controls.

MAIN RESULTS

In comparison with non-smokers and smoker controls, senescent lung COPD fibroblasts exhibited a higher mRNA and protein expression of the sPLA2 isoform XIIA and of syndecan 4 (one of its receptors). sPLA2 XIIA induced in turn senescence of non-senescent pulmonary fibroblasts via a pathway involving consecutively syndecan 4, activation of MAPK and p-serine 727 STAT-3, increased mitochondrial ROS production, and activation of AMPK/p53. This pathway was associated with a specific inflammatory secretome (IL-10, IL-12 and TNFα), globally suggesting occurrence of a mitochondrial damage-induced senescence. COPD fibroblasts were more susceptible to this sPLA2 XIIA effect than cells from controls subjects. sPLA2 XIIA levels were significantly higher in serum from COPD patients as compared to controls.

CONCLUSION

sPLA2 XIIA is involved in senescence in COPD and could be a potential target to dampen this process.

Senescence program and its reprogramming in pancreatic premalignancy

Tumor is a representative of cell immortalization, while senescence irreversibly arrests cell proliferation. Although tumorigenesis and senescence seem contrary to each other, they have similar mechanisms in many aspects. Pancreatic ductal adenocarcinoma (PDA) is highly lethal disease, which occurs and progresses through a multi-step process. Senescence is prevalent in pancreatic premalignancy, as manifested by decreased cell proliferation and increased clearance of pre-malignant cells by immune system. However, the senescent microenvironment cooperates with multiple factors and significantly contributes to tumorigenesis. Evidently, PDA progression requires to evade the effects of cellular senescence. This review will focus on dual roles that senescence plays in PDA development and progression, the signaling effectors that critically regulate senescence in PDA, the identification and reactivation of molecular targets that control senescence program for the treatment of PDA.

Tissue factor is a critical regulator of radiation therapy-induced glioblastoma remodeling

Radiation therapy (RT) provides therapeutic benefits for patients with glioblastoma (GBM), but inevitably induces poorly understood global changes in GBM and its microenvironment (TME) that promote radio-resistance and recurrence. Through a cell surface marker screen, we identified that CD142 (tissue factor or F3) is robustly induced in the senescence-associated β-galactosidase (SA-βGal)-positive GBM cells after irradiation. F3 promotes clonal expansion of irradiated SA-βGal+ GBM cells and orchestrates oncogenic TME remodeling by activating both tumor-autonomous signaling and extrinsic coagulation pathways. Intratumoral F3 signaling induces a mesenchymal-like cell state transition and elevated chemokine secretion. Simultaneously, F3-mediated focal hypercoagulation states lead to activation of tumor-associated macrophages (TAMs) and extracellular matrix (ECM) remodeling. A newly developed F3-targeting agent potently inhibits the aforementioned oncogenic events and impedes tumor relapse in vivo. These findings support F3 as a critical regulator for therapeutic resistance and oncogenic senescence in GBM, opening potential therapeutic avenues.

Heterogeneity in leukemia cells that escape drug-induced senescence-like state

Erythropoietin (EPO) suppresses drug-induced apoptosis in EPO-receptor-positive leukemia cells and allows cells to persist after drug treatment by promoting cellular senescence. Importantly a small proportion of senescent cells can re-enter the cell cycle and resume proliferation after drug treatment, resulting in disease recurrence/persistence. Using a single-cell assay to track individual cells that exit a drug-induced senescence-like state, we show that cells exhibit asynchronous exit from a senescent-like state, and display different rates of proliferation. Escaped cells retain sensitivity to drug treatment, but display inter-clonal variability. We also find heterogeneity in gene expression with some of the escaped clones retaining senescence-associated gene expression. Senescent leukemia cells exhibit changes in gene expression that affect metabolism and senescence-associated secretory phenotype (SASP)-related genes. Herein, we generate a senescence gene signature and show that this signature is a prognostic marker of worse overall survival in AML and multiple other cancers. A portion of senescent leukemia cells depend on lysosome activity; chloroquine, an inhibitor of lysosome activity, promotes senolysis of some senescent leukemia cells. Our study indicates that the serious risks associated with the use of erythropoietin-stimulating agents (ESAs) in anemic cancer patients may be attributed to their ability to promote drug-tolerant cancer cells through the senescence program.

Transfer learning in a biomaterial fibrosis model identifies in vivo senescence heterogeneity and contributions to vascularization and matrix production across species and diverse pathologies

Cellular senescence is a state of permanent growth arrest that plays an important role in wound healing, tissue fibrosis, and tumor suppression. Despite senescent cells' (SnCs) pathological role and therapeutic interest, their phenotype in vivo remains poorly defined. Here, we developed an in vivo-derived senescence signature (SenSig) using a foreign body response-driven fibrosis model in a p16-CreERT2;Ai14 reporter mouse. We identified pericytes and "cartilage-like" fibroblasts as senescent and defined cell type-specific senescence-associated secretory phenotypes (SASPs). Transfer learning and senescence scoring identified these two SnC populations along with endothelial and epithelial SnCs in new and publicly available murine and human data single-cell RNA sequencing (scRNAseq) datasets from diverse pathologies. Signaling analysis uncovered crosstalk between SnCs and myeloid cells via an IL34-CSF1R-TGFβR signaling axis, contributing to tissue balance of vascularization and matrix production. Overall, our study provides a senescence signature and a computational approach that may be broadly applied to identify SnC transcriptional profiles and SASP factors in wound healing, aging, and other pathologies.

"Bone-SASP" in Skeletal Aging

Senescence is a complex cell state characterized by stable cell cycle arrest and a unique secretory pattern known as the senescence-associated secretory phenotype (SASP). The SASP factors, which are heterogeneous and tissue specific, normally include chemokines, cytokines, growth factors, adhesion molecules, and lipid components that can lead to multiple age-associated disorders by eliciting local and systemic consequences. The skeleton is a highly dynamic organ that changes constantly in shape and composition. Senescent cells in bone and bone marrow produce diverse SASP factors that induce alterations of the skeleton through paracrine effects. Herein, we refer to bone cell-associated SASP as "bone-SASP." In this review, we describe current knowledge of cellular senescence and SASP, focusing on the role of senescent cells in mediating bone pathologies during natural aging and premature aging syndromes. We also summarize the role of cellular senescence and the bone-SASP in glucocorticoids-induced bone damage. In addition, we discuss the role of bone-SASP in the development of osteoarthritis, highlighting the mechanisms by which bone-SASP drives subchondral bone changes in metabolic syndrome-associated osteoarthritis.

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.

Inflammation and aging: signaling pathways and intervention therapies

Aging is characterized by systemic chronic inflammation, which is accompanied by cellular senescence, immunosenescence, organ dysfunction, and age-related diseases. Given the multidimensional complexity of aging, there is an urgent need for a systematic organization of inflammaging through dimensionality reduction. Factors secreted by senescent cells, known as the senescence-associated secretory phenotype (SASP), promote chronic inflammation and can induce senescence in normal cells. At the same time, chronic inflammation accelerates the senescence of immune cells, resulting in weakened immune function and an inability to clear senescent cells and inflammatory factors, which creates a vicious cycle of inflammation and senescence. Persistently elevated inflammation levels in organs such as the bone marrow, liver, and lungs cannot be eliminated in time, leading to organ damage and aging-related diseases. Therefore, inflammation has been recognized as an endogenous factor in aging, and the elimination of inflammation could be a potential strategy for anti-aging. Here we discuss inflammaging at the molecular, cellular, organ, and disease levels, and review current aging models, the implications of cutting-edge single cell technologies, as well as anti-aging strategies. Since preventing and alleviating aging-related diseases and improving the overall quality of life are the ultimate goals of aging research, our review highlights the critical features and potential mechanisms of inflammation and aging, along with the latest developments and future directions in aging research, providing a theoretical foundation for novel and practical anti-aging strategies.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

The chemotherapeutic drug doxorubicin does not exacerbate p16Ink4a-positive senescent cell accumulation and cardiometabolic disease development in young adult female LDLR-deficient mice

Cancer survivors who received chemotherapy, such as the anthracycline doxorubicin (DOX), have an increased risk of developing complications later in life, including the development of chronic metabolic diseases. Although the etiology of this increased risk for late metabolic complications in cancer survivors is poorly understood, a causal role of therapy-induced senescent cells has been suggested. To study the role of cellular senescence in chemotherapy-induced metabolic complications, young adult female low-density lipoprotein receptor-deficient (Ldlr^-/-)-p16-3MR mice, in which p16^Ink4a-positive (p16^Ink4a+) senescent cells can be genetically eliminated, were treated with four weekly injections of DOX (2.5 mg/kg) followed by a high-fat high-cholesterol diet for 12 weeks. While DOX treatment induced known short-term effects, such as reduction in body weight, gonadal fat mass, and adipose tissue inflammation, it was not associated with significant long-term effects on glucose homeostasis, hepatic steatosis, or atherosclerosis. We further found no evidence of DOX-induced accumulation of p16^Ink4a+-senescent cells at 1 or 12 weeks after DOX treatment. Neither did we observe an effect of elimination of p16^Ink4a+-senescent cells on the development of diet-induced cardiometabolic complications in DOX-treated mice. Other markers for senescence were generally also not affected except for an increase in p21 and Cxcl10 in gonadal white adipose tissue long-term after DOX treatment. Together, our study does not support a significant role for p16^Ink4a+-senescent cells in the development of diet-induced cardiometabolic disease in young adult DOX-treated female Ldlr^-/- mice. These findings illustrate the need of further studies to understand the link between cancer therapy and cardiometabolic disease development in cancer survivors.

The coagulome of oral squamous cell carcinoma: examining the role and regulation of coagulation in oral cancers using a systems approach

PURPOSE OF REVIEW

Solid tumors often establish a locally hypercoagulant state that promotes vascular complications, such as venous thromboembolism (VTE). Oral squamous cell carcinoma (OSCC) is associated with a broad range of hemostatic complications. Although VTE rarely occurs in ambulatory patients with OSCC, the coagulation cascade is typically activated by surgical resection and local hemorrhage. We present the recent progress in the understanding of the role and regulation of coagulation in OSCC.

RECENT FINDINGS

Application of systems biology, using bulk tumor and single cell genomic analyses, unveiled the landscape of the tumor coagulome. Of all tumor types, OSCC express the highest mRNA levels of F3 and PLAU, the genes that encode the tissue factor (TF) and urokinase-type plasminogen activator (uPA), the key regulators of coagulation and fibrinolysis, respectively. It also brought to light the intimate and reciprocal regulation between coagulation/fibrinolysis and the tumor microenvironment (TME).

SUMMARY

OSCC have a specific coagulome, with consequences that likely extend beyond the vascular risk. We discuss the attractive possibility that biomarkers of the coagulation cascade might reflect some important characteristics of the TME, offering new opportunities to better understand the impact of surgical procedures, better predict their oncological outcome and improve current therapeutic approaches.

Senotherapeutics: An emerging approach to the treatment of viral infectious diseases in the elderly

In the context of the global COVID-19 pandemic, the phenomenon that the elderly have higher morbidity and mortality is of great concern. Existing evidence suggests that senescence and viral infection interact with each other. Viral infection can lead to the aggravation of senescence through multiple pathways, while virus-induced senescence combined with existing senescence in the elderly aggravates the severity of viral infections and promotes excessive age-related inflammation and multiple organ damage or dysfunction, ultimately resulting in higher mortality. The underlying mechanisms may involve mitochondrial dysfunction, abnormal activation of the cGAS-STING pathway and NLRP3 inflammasome, the role of pre-activated macrophages and over-recruited immune cells, and accumulation of immune cells with trained immunity. Thus, senescence-targeted drugs were shown to have positive effects on the treatment of viral infectious diseases in the elderly, which has received great attention and extensive research. Therefore, this review focused on the relationship between senescence and viral infection, as well as the significance of senotherapeutics for the treatment of viral infectious diseases.

Trimethylamine N-oxide: role in cell senescence and age-related diseases

INTRODUCTION

Hayflick and Moorhead first demonstrated cell senescence as the irreversible growth arrest of cells after prolonged cultivation. Telomere shortening and oxidative stress are the fundamental mechanisms that drive cell senescence. Increasing studies have shown that TMAO is closely associated with cellular aging and age-related diseases. An emerging body of evidence from animal models, especially mice, has identified that TMAO contributes to senescence from multiple pathways and appears to accelerate many neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. However, the specific mechanism of how TMAO speeds aging is still not completely clear.

MATERIAL AND METHODS

In this review, we summarize some key findings in TMAO, cell senescence, and age-related diseases. We focused particular attention on the potential mechanisms for clinical transformation to find ways to interfere with the aging process.

CONCLUSION

TMAO can accelerate cell senescence by causing mitochondrial damage, superoxide formation, and promoting the generation of pro-inflammatory factors.

Selective ablation of primary and paracrine senescent cells by targeting iron dyshomeostasis

Senescent cells can spread the senescent phenotype to other cells by secreting senescence-associated secretory phenotype factors. The resulting paracrine senescent cells make a significant contribution to the burden of senescent cell accumulation with age. Previous efforts made to characterize paracrine senescence are unreliable due to analyses being based on mixed populations of senescent and non-senescent cells. Here, we use dipeptidyl peptidase-4 (DPP4) as a surface maker to isolate senescent cells from mixed populations. Using this technique, we enrich the percentage of paracrine senescence from 40% to 85%. We then use this enriched culture to characterize DPP4+ primary and paracrine senescent cells. We observe ferroptosis dysregulation and ferrous iron accumulation as a common phenomenon in both primary and paracrine senescent cells. Finally, we identify ferroptosis induction and ferrous iron-activatable prodrug as a broad-spectrum senolytic approach to ablate multiple types of primary and paracrine senescent cells.

Substantial Downregulation of Mitochondrial and Peroxisomal Proteins during Acute Kidney Injury revealed by Data-Independent Acquisition Proteomics

Acute kidney injury (AKI) manifests as a major health concern, particularly for the elderly. Understanding AKI-related proteome changes is critical for prevention and development of novel therapeutics to recover kidney function and to mitigate the susceptibility for recurrent AKI or development of chronic kidney disease. In this study, mouse kidneys were subjected to ischemia-reperfusion injury, and the contralateral kidneys remained uninjured to enable comparison and assess injury-induced changes in the kidney proteome. A fast-acquisition rate ZenoTOF 7600 mass spectrometer was introduced for data-independent acquisition (DIA) for comprehensive protein identification and quantification. Short microflow gradients and the generation of a deep kidney-specific spectral library allowed for high-throughput, comprehensive protein quantification. Upon AKI, the kidney proteome was completely remodeled, and over half of the 3,945 quantified protein groups changed significantly. Downregulated proteins in the injured kidney were involved in energy production, including numerous peroxisomal matrix proteins that function in fatty acid oxidation, such as ACOX1, CAT, EHHADH, ACOT4, ACOT8, and Scp2. Injured mice exhibited severely declined health. The comprehensive and sensitive kidney-specific DIA assays highlighted here feature high-throughput analytical capabilities to achieve deep coverage of the kidney proteome and will serve as useful tools for developing novel therapeutics to remediate kidney function.

Immunosenescence and inflamm-ageing in COVID-19

The destructive effects of coronavirus disease 2019 (COVID-19) on the elderly and people with cardiovascular disease have been proven. New findings shed light on the role of aging pathways on life span and health age. New therapies that focus on aging-related pathways may positively impact the treatment of this acute respiratory infection. Using new therapies that boost the level of the immune system can support the elderly with co-morbidities against the acute form of COVID-19. This article discusses the effect of the aging immune system against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the pathways affecting this severity of infection.

Senescent cells perturb intestinal stem cell differentiation through Ptk7 induced noncanonical Wnt and YAP signaling

Cellular senescence and the senescence-associated secretory phenotype (SASP) are implicated in aging and age-related disease, and SASP-related inflammation is thought to contribute to tissue dysfunction in aging and diseased animals. However, whether and how SASP factors influence the regenerative capacity of tissues remains unclear. Here, using intestinal organoids as a model of tissue regeneration, we show that SASP factors released by senescent fibroblasts deregulate stem cell activity and differentiation and ultimately impair crypt formation. We identify the secreted N-terminal domain of Ptk7 as a key component of the SASP that activates non-canonical Wnt / Ca2+ signaling through FZD7 in intestinal stem cells (ISCs). Changes in cytosolic [Ca2+] elicited by Ptk7 promote nuclear translocation of YAP and induce expression of YAP/TEAD target genes, impairing symmetry breaking and stem cell differentiation. Our study discovers secreted Ptk7 as a factor released by senescent cells and provides insight into the mechanism by which cellular senescence contributes to tissue dysfunction in aging and disease.

Extracellular Vesicles and Cardiac Aging

Global population aging is a major challenge to health and socioeconomic policies. The prevalence of diseases progressively increases with aging, with cardiovascular disease being the major cause of mortality among elderly people. The allostatic overload imposed by the accumulation of cardiac senescent cells has been suggested to play a pivotal role in the aging-related deterioration of cardiovascular function. Senescent cells exhibit intrinsic disorders and release a senescence-associated secretory phenotype (SASP). Most of these SASP compounds and damaged molecules are released from senescent cells by extracellular vesicles (EVs). Once secreted, these EVs can be readily incorporated by recipient neighboring cells and elicit cellular damage or otherwise can promote extracellular matrix remodeling. This has been associated with the development of cardiac dysfunction, fibrosis, and vascular calcification, among others. The molecular signature of these EVs is highly variable and might provide important information for the development of aging-related biomarkers. Conversely, EVs released by the stem and progenitor cells can exert a rejuvenating effect, raising the possibility of future anti-aging therapies.

NIH SenNet Consortium to map senescent cells throughout the human lifespan to understand physiological health

Cells respond to many stressors by senescing, acquiring stable growth arrest, morphologic and metabolic changes, and a proinflammatory senescence-associated secretory phenotype. The heterogeneity of senescent cells (SnCs) and senescence-associated secretory phenotype are vast, yet ill characterized. SnCs have diverse roles in health and disease and are therapeutically targetable, making characterization of SnCs and their detection a priority. The Cellular Senescence Network (SenNet), a National Institutes of Health Common Fund initiative, was established to address this need. The goal of SenNet is to map SnCs across the human lifespan to advance diagnostic and therapeutic approaches to improve human health. State-of-the-art methods will be applied to identify, define and map SnCs in 18 human tissues. A common coordinate framework will integrate data to create four-dimensional SnC atlases. Other key SenNet deliverables include innovative tools and technologies to detect SnCs, new SnC biomarkers and extensive public multi-omics datasets. This Perspective lays out the impetus, goals, approaches and products of SenNet.

Unbiased proteomic analysis of extracellular vesicles secreted by senescent human vascular smooth muscle cells reveals their ability to modulate immune cell functions

Atherosclerosis, a common age-related disease, is characterized by intense immunological activity. Atherosclerotic plaque is composed of endothelial cells, vascular smooth muscle cells (VSMCs), lipids and immune cells infiltrating from the blood. During progression of the disease, VSMCs undergo senescence within the plaque and secrete SASP (senescence-associated secretory phenotype) factors that can actively modulate plaque microenvironment. We demonstrated that senescent VSMCs secrete increased number of extracellular vesicles (senEVs). Based on unbiased proteomic analysis of VMSC-derived EVs and of the soluble fraction of SASP (sSASP), more than 900 proteins were identified in each of SASP compartments. Comparison of the composition of VMSC-derived EVs with the SASP atlas revealed several proteins, including Serpin Family F Member 1 (SERPINF1) and Thrombospondin 1 (THBS1), as commonly upregulated components of EVs secreted by senescent VSMCs and fibroblasts. Among soluble SASP factors, only Growth Differentiation Factor 15 (GDF15) was universally increased in the secretome of senescent VSMCs, fibroblasts, and epithelial cells. Bioinformatics analysis of EV proteins distinguished functionally organized protein networks involved in immune cell function regulation. Accordingly, EVs released by senescent VSMCs induced secretion of IL-17, INFγ, and IL-10 by T cells and of TNFα produced by monocytes. Moreover senEVs influenced differentiation of monocytes favoring mix M1/M2 polarization with proinflammatory characteristics. Altogether, our studies provide a complex, unbiased analysis of VSMC SASP and prove that EVs derived from senescent VSMCs influence the cytokine milieu by modulating immune cell activity. Our results strengthen the role of senescent cells as an important inducer of inflammation in atherosclerosis.

Anthracycline-induced cardiotoxicity and cell senescence: new therapeutic option?

Anthracyclines are chemotherapeutic drugs widely used in the frontline of cancer treatment. The therapeutic mechanisms involve the stabilization of topoisomerase IIα, DNA, and the anthracycline molecule in a ternary complex that is recognized as DNA damage. Redox imbalance is another vital source of oxidative DNA damage. Together, these mechanisms lead to cytotoxic effects in neoplastic cells. However, anthracycline treatment can elicit cardiotoxicity and heart failure despite the therapeutic benefits. Topoisomerase IIβ and oxidative damage in cardiac cells have been the most reported pathophysiological mechanisms. Alternatively, cardiac cells can undergo stress-induced senescence when exposed to anthracyclines, a state primarily characterized by cell cycle arrest, organelle dysfunction, and a shift to senescence-associated secretory phenotype (SASP). The SASP can propagate senescence to neighboring cells in an ongoing process that leads to the accumulation of senescent cells, promoting cellular dysfunction and extracellular matrix remodeling. Therefore, the accumulation of senescent cardiac cells is an emerging pathophysiological mechanism associated with anthracycline-induced cardiotoxicity. This paradigm also raises the potential for therapeutic approaches to clear senescent cells in treating anthracycline-induced cardiotoxicity (i,e, senolytic therapies).

DNA damage response and GATA4 signaling in cellular senescence and aging-related pathology

Aging is the continuous degradation of biological function and structure with time, and cellular senescence lies at its core. DNA damage response (DDR) can activate Ataxia telangiectasia-mutated serine/threonine kinase (ATM) and Rad3-related serine/threonine kinase (ATR), after which p53 activates p21, stopping the cell cycle and inducing cell senescence. GATA4 is a transcription factor that plays an important role in the development of many organs, such as the heart, testis, ovary, foregut, liver, and ventral pancreas. Studies have shown that GATA4 can also contribute to the DDR, leading to aging. Consistently, there is also evidence that the GATA4 signaling pathway is associated with aging-related diseases, including atherosclerosis and heart failure. This paper reviews the relationship between GATA4, DDR, and cellular senescence, as well as its effect on aging-related diseases.

Role of low-dose radiation in senescence and aging: A beneficial perspective

Cellular senescence refers to the permanent arrest of cell cycle caused by intrinsic and/or extrinsic stressors including oncogene activation, irradiation, DNA damage, oxidative stress, and certain cytokines (including senescence associated secretory phenotype). Cellular senescence is an important factor in aging. Accumulation of senescent cells has been implicated in the causation of various age-related organ disorders, tissue dysfunction, and chronic diseases. It is widely accepted that the biological effects triggered by low-dose radiation (LDR) are different from those caused by high-dose radiation. Experimental evidence suggests that LDR may promote growth and development, enhance longevity, induce embryo production, and delay the progression of chronic diseases. The underlying mechanisms of these effects include modulation of immune response, stimulation of hematopoietic system, antioxidative effect, reduced DNA damage and improved ability for DNA damage repair. In this review, we discuss the possible mechanisms by which LDR prevents senescence and aging from the perspectives of inhibiting cellular senescence and promoting the removal of senescent cells. We review a wide broad of evidence about the beneficial impact of LDR in senescence and aging models (including cardiovascular diseases, neurological diseases, arthritis and osteoporosis, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis) to highlight the potential value of LDR in preventing aging and age-related diseases. However, there is no consensus on the effect of LDR on human health, and several important aspects require further investigation.

Connecting aging biology and inflammation in the omics era

Aging is characterized by the accumulation of damage to macromolecules and cell architecture that triggers a proinflammatory state in blood and solid tissues, termed inflammaging. Inflammaging has been implicated in the pathogenesis of many age-associated chronic diseases as well as loss of physical and cognitive function. The search for mechanisms that underlie inflammaging focused initially on the hallmarks of aging, but it is rapidly expanding in multiple directions. Here, we discuss the threads connecting cellular senescence and mitochondrial dysfunction to impaired mitophagy and DNA damage, which may act as a hub for inflammaging. We explore the emerging multi-omics efforts that aspire to define the complexity of inflammaging - and identify molecular signatures and novel targets for interventions aimed at counteracting excessive inflammation and its deleterious consequences while preserving the physiological immune response. Finally, we review the emerging evidence that inflammation is involved in brain aging and neurodegenerative diseases. Our goal is to broaden the research agenda for inflammaging with an eye on new therapeutic opportunities.

The Senescence Markers p16INK4A, p14ARF/p19ARF, and p21 in Organ Development and Homeostasis

It is widely accepted that senescent cells accumulate with aging. They are characterized by replicative arrest and the release of a myriad of factors commonly called the senescence-associated secretory phenotype. Despite the replicative cell cycle arrest, these cells are metabolically active and functional. The release of SASP factors is mostly thought to cause tissue dysfunction and to induce senescence in surrounding cells. As major markers for aging and senescence, p16INK4, p14ARF/p19ARF, and p21 are established. Importantly, senescence is also implicated in development, cancer, and tissue homeostasis. While many markers of senescence have been identified, none are able to unambiguously identify all senescent cells. However, increased levels of the cyclin-dependent kinase inhibitors p16INK4A and p21 are often used to identify cells with senescence-associated phenotypes. We review here the knowledge of senescence, p16INK4A, p14ARF/p19ARF, and p21 in embryonic and postnatal development and potential functions in pathophysiology and homeostasis. The establishment of senolytic therapies with the ultimate goal to improve healthy aging requires care and detailed knowledge about the involvement of senescence and senescence-associated proteins in developmental processes and homeostatic mechanism. The review contributes to these topics, summarizes open questions, and provides some directions for future research.

The multifaceted role of the SASP in atherosclerosis: from mechanisms to therapeutic opportunities

BACKGROUND

The global population of older individuals is growing, and ageing is a key risk factor for atherosclerotic cardiovascular diseases. Abnormal accumulation of senescent cells can cause potentially deleterious effects on the organism with age. As a vital marker of cellular senescence, the senescence-associated secretory phenotype (SASP) is a novel mechanism to link cellular senescence with atherosclerosis.

MAIN BODY

In this review, we concretely describe the characteristics of the SASP and its regulation mechanisms. Importantly, we provide novel perspectives on how the SASP can promote atherosclerosis. The SASP from different types of senescent cells have vital roles in atherosclerosis progression. As a significant mediator of the harmful effects of senescent cells, it can play a pro-atherogenic role by producing inflammation and immune dysfunction. Furthermore, the SASP can deliver senescence signals to the surrounding vascular cells, gradually contributing to the development of atherosclerosis. Finally, we focus on a variety of novel therapeutic strategies aimed to reduce the burden of atherosclerosis in elderly individuals by targeting senescent cells and inhibiting the regulatory mechanisms of the SASP.

CONCLUSION

This review systematically summarizes the multiple roles of the SASP in atherosclerosis and can contribute to the exploration of new therapeutic opportunities.

Measurement of Protein Turnover Rates in Senescent and Non-Dividing Cultured Cells with Metabolic Labeling and Mass Spectrometry

Mounting evidence has shown that the accumulation of senescent cells in the central nervous system contributes to neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Cellular senescence is a state of permanent cell cycle arrest that typically occurs in response to exposure to sub-lethal stresses. However, like other non-dividing cells, senescent cells remain metabolically active and carry out many functions that require unique transcriptional and translational demands and widespread changes in the intracellular and secreted proteomes. Understanding how protein synthesis and decay rates change during senescence can illuminate the underlying mechanisms of cellular senescence and find potential therapeutic avenues for diseases exacerbated by senescent cells. This paper describes a method for proteome-scale evaluation of protein half-lives in non-dividing cells using pulsed stable isotope labeling by amino acids in cell culture (pSILAC) in combination with mass spectrometry. pSILAC involves metabolic labeling of cells with stable heavy isotope-containing versions of amino acids. Coupled with modern mass spectrometry approaches, pSILAC enables the measurement of protein turnover of hundreds or thousands of proteins in complex mixtures. After metabolic labeling, the turnover dynamics of proteins can be determined based on the relative enrichment of heavy isotopes in peptides detected by mass spectrometry. In this protocol, a workflow is described for the generation of senescent fibroblast cultures and similarly arrested quiescent fibroblasts, as well as a simplified, single-time point pSILAC labeling time-course that maximizes coverage of anticipated protein turnover rates. Further, a pipeline is presented for the analysis of pSILAC mass spectrometry data and user-friendly calculation of protein degradation rates using spreadsheets. The application of this protocol can be extended beyond senescent cells to any non-dividing cultured cells such as neurons.

Genome wide CRISPR/Cas9 screen identifies the coagulation factor IX (F9) as a regulator of senescence

During this last decade, the development of prosenescence therapies has become an attractive strategy as cellular senescence acts as a barrier against tumour progression. In this context, CDK4/6 inhibitors induce senescence and reduce tumour growth in breast cancer patients. However, even though cancer cells are arrested after CDK4/6 inhibitor treatment, genes regulating senescence in this context are still unknown limiting their antitumour activity. Here, using a functional genome-wide CRISPR/Cas9 genetic screen we found several genes that participate in the proliferation arrest induced by CDK4/6 inhibitors. We find that downregulation of the coagulation factor IX (F9) using sgRNA and shRNA prevents the cell cycle arrest and senescent-like phenotype induced in MCF7 breast tumour cells upon Palbociclib treatment. These results were confirmed using another breast cancer cell line, T47D, and with an alternative CDK4/6 inhibitor, Abemaciclib, and further tested in a panel of 22 cancer cells. While F9 knockout prevents the induction of senescence, treatment with a recombinant F9 protein was sufficient to induce a cell cycle arrest and senescence-like state in MCF7 tumour cells. Besides, endogenous F9 is upregulated in different human primary cells cultures undergoing senescence. Importantly, bioinformatics analysis of cancer datasets suggest a role for F9 in human tumours. Altogether, these data collectively propose key genes involved in CDK4/6 inhibitor response that will be useful to design new therapeutic strategies in personalised medicine in order to increase their efficiency, stratify patients and avoid drug resistance.

Therapeutic Potential of Senolytics in Cardiovascular Disease

Ageing is the biggest risk factor for impaired cardiovascular health, with cardiovascular disease being the leading cause of death in 40% of individuals over 65 years old. Ageing is associated with both an increased prevalence of cardiovascular disease including heart failure, coronary artery disease, and myocardial infarction. Furthermore, ageing is associated with a poorer prognosis to these diseases. Genetic models allowing the elimination of senescent cells revealed that an accumulation of senescence contributes to the pathophysiology of cardiovascular ageing and promotes the progression of cardiovascular disease through the expression of a proinflammatory and profibrotic senescence-associated secretory phenotype. These studies have resulted in an effort to identify pharmacological therapeutics that enable the specific elimination of senescent cells through apoptosis induction. These senescent cell apoptosis-inducing compounds are termed senolytics and their potential to ameliorate age-associated cardiovascular disease is the focus of this review.

Regulation of lung epithelial cell senescence in smoking-induced COPD/emphysema by microR-125a-5p via Sp1 mediation of SIRT1/HIF-1a

Chronic obstructive pulmonary disease (COPD) affects the health of more than 300 million people worldwide; at present, there is no effective drug to treat COPD. Smoking is the most important risk factor, but the molecular mechanism by which smoking causes the disease is unclear. The senescence of lung epithelial cells is related to development of COPD. Regulation of miRNAs is the main epigenetic mechanism related to aging. β-Galactose staining showed that the lung tissues of smokers have a higher degree of cellular senescence, and the expression of miR-125a-5p is high. This effect is obvious for smokers with COPD/emphysema, and there is a negative correlation between miR-125a-5p levels and values for forced expiratory volume in one second (FEV1)/forced vital capacity (FVC). After Balb/c mice were chronically exposed to various concentrations of cigarette smoke (CS), plethysmography showed that lung function was impaired, lung tissue senescence was increased, and the senescence-associated secretory phenotype (SASP) in bronchoalveolar lavage fluid was increased. For mouse lung epithelial (MLE)-12 cells treated with cigarette smoke extract (CSE), Sp1 and SIRT1 levels were low, HIF-1α acetylation levels were high, and cell senescence and secretion of SASP factors were elevated. Down-regulation of miR-125a-5p or up-regulation of Sp1 reversed these effects. In addition, compared with mice exposed to CS, knockdown of miR-125a-5p reduced lung epithelial cell senescence and COPD/emphysema. Therefore, in smoking-induced COPD, elevated miR-125a-5p participates in the senescence of lung epithelial cells through Sp1/SIRT1/HIF-1α. These findings provide evidence related to the pathogenesis of COPD/emphysema caused by chronic smoking.

Peroxiredoxin 6 protects irradiated cells from oxidative stress and shapes their senescence-associated cytokine landscape

Cellular senescence is a complex stress response defined as an essentially irreversible cell cycle arrest mediated by the inhibition of cell cycle-specific cyclin dependent kinases. The imbalance in redox homeostasis and oxidative stress have been repeatedly observed as one of the hallmarks of the senescent phenotype. However, a large-scale study investigating protein oxidation and redox signaling in senescent cells in vitro has been lacking. Here we applied a proteome-wide analysis using SILAC-iodoTMT workflow to quantitatively estimate the level of protein sulfhydryl oxidation and proteome level changes in ionizing radiation-induced senescence (IRIS) in hTERT-RPE-1 cells. We observed that senescent cells mobilized the antioxidant system to buffer the increased oxidation stress. Among the antioxidant proteins with increased relative abundance in IRIS, a unique 1-Cys peroxiredoxin family member, peroxiredoxin 6 (PRDX6), was identified as an important contributor to protection against oxidative stress. PRDX6 silencing increased ROS production in senescent cells, decreased their resistance to oxidative stress-induced cell death, and impaired their viability. Subsequent SILAC-iodoTMT and secretome analysis after PRDX6 silencing showed the downregulation of PRDX6 in IRIS affected protein secretory pathways, decreased expression of extracellular matrix proteins, and led to unexpected attenuation of senescence-associated secretory phenotype (SASP). The latter was exemplified by decreased secretion of pro-inflammatory cytokine IL-6 which was also confirmed after treatment with an inhibitor of PRDX6 iPLA2 activity, MJ33. In conclusion, by combining different methodological approaches we discovered a novel role of PRDX6 in senescent cell viability and SASP development. Our results suggest PRDX6 could have a potential as a drug target for senolytic or senomodulatory therapy.

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SILAC-iodoTMT is a powerful tool to quantify redox imbalance in IRIS.

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Senescence in hTERT-RPE-1 cells is not accompanied by bulk cysteine oxidation.

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Antioxidant proteins are upregulated in senescent hTERT-RPE-1 cells.

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PRDX6 silencing affects redox homeostasis and viability of senescent cells.

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PRDX6 silencing alters secretome of senescent RPE-1 cells and suppresses IL-6.

Low Dose Chronic Angiotensin II Induces Selective Senescence of Kidney Endothelial Cells

Angiotensin II can cause oxidative stress and increased blood pressure that result in long term cardiovascular pathologies. Here we evaluated the contribution of cellular senescence to the effect of chronic exposure to low dose angiotensin II in a model that mimics long term tissue damage. We utilized the INK-ATTAC (p16^Ink4a–Apoptosis Through Targeted Activation of Caspase 8) transgenic mouse model that allows for conditional elimination of p16^Ink4a -dependent senescent cells by administration of AP20187. Angiotensin II treatment for 3 weeks induced ATTAC transgene expression in kidneys but not in lung, spleen and brain tissues. In the kidneys increased expression of ATM, p15 and p21 matched with angiotensin II induction of senescence-associated secretory phenotype genes MMP3, FGF2, IGFBP2, and tPA. Senescent cells in the kidneys were identified as endothelial cells by detection of GFP expressed from the ATTAC transgene and increased expression of angiopoietin 2 and von Willebrand Factor, indicative of endothelial cell damage. Furthermore, angiotensin II induced expression of the inflammation-related glycoprotein versican and immune cell recruitment to the kidneys. AP20187-mediated elimination of p16-dependent senescent cells prevented physiologic, cellular and molecular responses to angiotensin II and provides mechanistic evidence of cellular senescence as a driver of angiotensin II effects.