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The development of genetic tools allowed for the validation of the pro-aging and pro-disease functions of senescent cells in vivo. These discoveries prompted the development of senotherapies-pharmaceutical interventions aimed at interfering with the detrimental effect of senescent cells-that are now entering the clinical stage. However, unequivocal identification and examination of cellular senescence remains highly difficult because of the lack of universal and specific markers. Here, to overcome the limitation of measuring individual markers, we describe a detailed two-phase algorithmic assessment to quantify various senescence-associated parameters in the same specimen. In the first phase, we combine the measurement of lysosomal and proliferative features with the expression of general senescence-associated genes to validate the presence of senescent cells. In the second phase we measure the levels of pro-inflammatory markers for specification of the type of senescence. The protocol can help graduate-level basic scientists to improve the characterization of senescence-associated phenotypes and the identification of specific senescent subtypes. Moreover, it can serve as an important tool for the clinical validation of the role of senescent cells and the effectiveness of anti-senescence therapies.

Histones are the major proteinaceous component of chromatin in eukaryotic cells and an important part of the epigenome, affecting most DNA‐related events, including transcription, DNA replication, and chromosome segregation. The properties of histones are greatly influenced by their post‐translational modifications (PTMs), over 200 of which are known today. Given this large number, researchers need sophisticated methods to study histone PTMs comprehensively. In particular, mass spectrometry (MS)−based approaches have gained popularity, allowing for the quantification of dozens of histone PTMs at once. Using these approaches, even the study of co‐occurring PTMs and the discovery of novel PTMs become feasible. The success of MS‐based approaches relies substantially on obtaining pure and well‐preserved histones for analysis, which can be difficult depending on the source material. Caenorhabditis elegans has been a popular model organism to study the epigenome, but isolation of pure histones from these animals has been challenging. Here, we address this issue, presenting a method for efficient isolation of pure histone proteins from C. elegans at good yield. Further, we describe an MS pipeline optimized for accurate relative quantification of histone PTMs from C. elegans. We alkylate and tryptically digest the histones, analyze them by bottom‐up MS, and then evaluate the resulting data by a C. elegans−adapted version of the software EpiProfile 2.0. Finally, we show the utility of this pipeline by determining differences in histone PTMs between C. elegans strains that age at different rates and thereby achieve very different lifespans. © 2020 The Authors. Basic Protocol 1: Large‐scale growth and harvesting of synchronized C. elegans Basic Protocol 2: Nuclear preparation, histone extraction, and histone purification Basic Protocol 3: Bottom‐up mass spectrometry analysis of histone PTMs and histone variants

Cellular senescence is a state of stable growth arrest that acts as a tumor suppressive mechanism. Several anti-cancer interventions function partly by inducing malignant cells into senescence. However, because of systemic administration and lack of specificity, anti-cancer treatments are associated with premature senescence of various non-malignant cells. Therapy-induced non-malignant senescent cells can have profound detrimental pro-tumorigenic and pro-disease functions via activation of a pro-inflammatory and NF-κB-mediated secretory phenotype (SASP). Inhibitors of the cyclin-dependent kinases 4/6 (CDK4/6i) has recently shown to have potent cytostatic effects with reduced toxicities. Here, we show that CDK4/6i lead non-malignant cells to a senescent state that lacks the pro-inflammatory and NF-κB-associated SASP. Interestingly, CDK4/6i-induced senescence overexpressed a number of genes encoding for secreted proteins, which we show being dependent on p53 transcriptional activity. CDK4/6i-induced p16+ senescent cells with a p53-associated (PASP), but not NF-κB-associated (NASP), secretory phenotype do not exert detrimental and pro-tumorigenic functions, but still retain the capacity to induce paracrine senescence and undergo clearance in vivo. Our data suggest that that senescent cells with a PASP but without a NASP may be well-tolerated and may represent a less toxic outcome for cancer interventions.

COPD is characterized by chronic lung inflammation and irreversible lung tissue damage. Inhaled noxious gases, including cigarette smoke, are the major risk factor for COPD. Inhaled smoke first encounters the epithelial lining of the lungs, causing oxidative stress and mitochondrial dysfunction. We investigated whether a mitochondrial defect may contribute to increased lung epithelial pro-inflammatory responses, impaired epithelial repair and reduced corticosteroid sensitivity as observed in COPD. We used wild-type alveolar epithelial cells A549 and mitochondrial DNA-depleted A549 cells (A549 Rho-0) and studied pro-inflammatory responses using (multiplex) ELISA as well as epithelial barrier function and repair (real-time impedance measurements), in the presence and absence of the inhaled corticosteroid budesonide. We observed that A549 Rho-0 cells secrete higher levels of pro-inflammatory cytokines than wild-type A549 cells and display impaired repair upon wounding. Budesonide strongly suppressed the production of neutrophil attractant CXCL8, and promoted epithelial integrity in A549 wild-type cells, while A549 Rho-0 cells displayed reduced corticosteroid sensitivity compared to wild-type cells. The reduced corticosteroid responsiveness may be mediated by glycolytic reprogramming, specifically glycolysis-associated PI3K signaling, as PI3K inhibitor LY294002 restored the sensitivity of CXCL8 secretion to corticosteroids in A549 Rho-0 cells. In conclusion, mitochondrial defects may lead to increased lung epithelial pro-inflammatory responses, reduced epithelial repair and reduced corticosteroid responsiveness in lung epithelium, thus potentially contributing to the pathogenesis of COPD.

Cellular senescence is a state of stable proliferative arrest triggered by damaging signals. Senescent cells persist during aging and promote age-related pathologies via the pro-inflammatory senescence-associated secretory phenotype (SASP), whose regulation depends on environmental factors. In vivo, a major environmental variable is oxygenation, which varies among and within tissues. Here, we demonstrate that senescent cells express lower levels of detrimental pro-inflammatory SASP factors in physiologically hypoxic environments, as measured in culture and in tissues. Mechanistically, exposure of senescent cells to low-oxygen conditions leads to AMPK activation and AMPK-mediated suppression of the mTOR-NF-kappa B signaling loop. Finally, we demonstrate that treatment with hypoxia-mimetic compounds reduces SASP in cells and tissues and improves strength in chemotherapy-treated and aged mice. Our findings highlight the importance of oxygen as a determinant for pro-inflammatory SASP expression and offer a potential new strategy to reduce detrimental paracrine effects of senescent cells.

Cellular senescence is a state of permanent cell cycle arrest activated in response to different damaging stimuli. Activation of cellular senescence is a hallmark of various pathophysiological conditions including tumor suppression, tissue remodeling and aging. The inducers of cellular senescence in vivo are still poorly characterized. However, a number of stimuli can be used to promote cellular senescence ex vivo. Among them, most common senescence-inducers are replicative exhaustion, ionizing and non-ionizing radiation, genotoxic drugs, oxidative stress, and demethylating and acetylating agents. Here, we will provide detailed instructions on how to use these stimuli to induce fibroblasts into senescence. This protocol can easily be adapted for different types of primary cells and cell lines, including cancer cells. We also describe different methods for the validation of senescence induction. In particular, we focus on measuring the activity of the lysosomal enzyme Senescence-Associated β-galactosidase (SA-β-gal), the rate of DNA synthesis using 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay, the levels of expression of the cell cycle inhibitors p16 and p21, and the expression and secretion of members of the Senescence-Associated Secretory Phenotype (SASP). Finally, we provide example results and discuss further applications of these protocols.

Background WNT signalling is activated during lung tissue damage and inflammation. We investigated whether lung epithelial expression of WNT ligands, receptors (frizzled; FZD) or target genes is dysregulated on cigarette smoking and/or in chronic obstructive pulmonary disease (COPD).Methods We studied this in human lung epithelial cell lines and primary bronchial epithelial cells (PBEC) from COPD patients and control (non-)smokers, at baseline and on cigarette smoke extract (CSE) exposure.Results CSE significantly decreased WNT-4, WNT-10B and FZD2 and increased WNT-5B mRNA expression in 16HBE, but did not affect WNT-4 protein. The mRNA expression of WNT-4, but not other WNT ligands, was lower in PBEC from smokers than non-smokers and downregulated by CSE in PBEC from all groups, yet higher in PBEC from COPD patients than control smokers. Moreover, PBEC from COPD patients displayed higher WNT-4 protein expression than both smokers and non-smokers. Exogenously added WNT-4 significantly increased CXCL8/IL-8, IL-6, CCL5/RANTES, CCL2/MCP-1 and vascular endothelial growth factor (VEGF) secretion in 16HBE, but did not affect the canonical WNT target genes MMP-2, MMP-9, fibronectin, beta-catenin, Dickkopf and axin-2, and induced activation of the non-canonical signalling molecule p38. Moreover, WNT-4 potentiated the CSE-induced upregulation of IL-8 and VEGF.Conclusions WNT-4 mRNA and protein levels are higher in PBEC from COPD patients than control (non-) smokers, while cigarette smoke downregulates airway epithelial WNT-4 mRNA, but not protein expression. As WNT-4 further increases CSE-induced pro-inflammatory cytokine release in bronchial epithelium, we propose that higher epithelial WNT-4 levels in combination with cigarette smoking may have important implications for the development of airway inflammation in COPD.

Research on epithelial cell lines and primary epithelium is required to dissect the mechanisms underlying the structural abnormalities in airway epithelium observed for respiratory diseases, including asthma and chronic obstructive pulmonary disease.The novel electric cell-substrate impedance sensing technique was used to monitor cell adhesion/spreading, barrier function and wound healing. Primary bronchial epithelium was compared with airway epithelial cell lines 16HBE14o-, BEAS-2B, NCI-H292 and A549.BEAS-2B, A549 and primary cells form a confluent monolayer more rapidly than do 16HBE14o-cells. In contrast, 16HBE14o- cells form stronger intercellular contacts, with a 10-fold higher resistance than BEAS-2B, A549 and NCI-H292 cells and a five-fold increase over primary cells. Accordingly, expression of the adhesion molecules zona occludens-1 and E-cadherin was highest in 16HBE14o- cells. These molecules were localised in intercellular junctions in both 16HBE14o-and primary cells. Finally, restoration of barrier function upon injury was impaired in BEAS-2B compared to 16HBE14o- cells.In conclusion, epithelial cell types display remarkable phenotypic differences and should, accordingly, be used to address specific research questions. 16HBE14o- cells appear most suitable for studies on barrier formation, whereas resemblance in attachment of primary and BEAS-2B and A549 cells makes the latter more important for translational research on cell-matrix contact.

Cigarette smoking, the major cause of chronic obstructive pulmonary disease (COPD), induces aberrant airway epithelial structure and function. The underlying mechanisms are unresolved so far.We studied effects of cigarette smoke extract (CSE) on epithelial barrier function and wound regeneration in human bronchial epithelial 16HBE cells and primary bronchial epithelial cells (PBECs) from COPD patients, nonsmokers and healthy smokers.We demonstrate that CSE rapidly and transiently impairs 16HBE barrier function, largely due to disruption of cell-cell contacts. CSE induced a similar, but stronger and more sustained, defect in PBECs. Application of the specific epidermal growth factor receptor (EGFR) inhibitor AG1478 showed that EGFR activation contributes to the CSE-induced defects in both 16HBE cells and PBECs. Furthermore, our data indicate that the endogenous protease calpain mediates these defects through tight junction protein degradation. CSE also delayed the reconstitution of 16HBE intercellular contacts during wound healing and attenuated PBEC barrier function upon wound regeneration. These findings were comparable between PBECs from smokers, healthy smokers and COPD patients.In conclusion, we demonstrate for the first time that CSE reduces epithelial integrity, probably by EGFR and calpain-dependent disruption of intercellular contacts. This may increase susceptibility to environmental insults, e. g. inhaled pathogens. Thus, EGFR may be a promising target for therapeutic strategies to improve mucosal barrier function in cigarette smoking-related disease.

Background Cigarette smoke, the major risk factor for COPD, is known to activate matrix metalloproteinases in airway epithelium. We investigated whether metalloproteinases, particularly A Disintegrin and Metalloproteinase (ADAM)17, contribute to increased pro-inflammatory epithelial responses with respect to the release of IL-8 and TGF-α, cytokines implicated in COPD pathogenesis. Methods We studied the effects of cigarette smoke extract (CSE) and metalloproteinase inhibitors on TGF-α and IL-8 release in primary bronchial epithelial cells (PBECs) from COPD patients, healthy smokers and non-smokers. Results We observed that TGF-α was mainly shed by ADAM17 in PBECs from all groups. Interestingly, IL-8 production occurred independently from ADAM17 and TGF-α shedding, but was significantly inhibited by broad-spectrum metalloproteinase inhibitor TAPI-2. CSE did not induce ADAM17-dependent TGF-α shedding, while it slightly augmented the production of IL-8. This was accompanied by reduced endogenous inhibitor of metalloproteinase (TIMP)-3 levels, suggesting that CSE does not directly but rather indirectly alter activity of ADAM17 through the regulation of its endogenous inhibitor. Furthermore, whereas baseline TGF-α shedding was lower in COPD PBECs, the early release of IL-8 (likely due to its shedding) was higher in PBECs from COPD than healthy smokers. Importantly, this was accompanied by lower TIMP-2 levels in COPD PBECs, while baseline TIMP-3 levels were similar between groups. Conclusions Our data indicate that IL-8 secretion is regulated independently from ADAM17 activity and TGF-α shedding and that particularly its early release is differentially regulated in PBECs from COPD and healthy smokers. Since TIMP-2-sensitive metalloproteinases could potentially contribute to IL-8 release, these may be interesting targets to further investigate novel therapeutic strategies in COPD.

Background Cigarette smoking is the major risk factor for COPD, leading to chronic airway inflammation. We hypothesized that cigarette smoke induces structural and functional changes of airway epithelial mitochondria, with important implications for lung inflammation and COPD pathogenesis. Methods We studied changes in mitochondrial morphology and in expression of markers for mitochondrial capacity, damage/biogenesis and fission/fusion in the human bronchial epithelial cell line BEAS-2B upon 6-months from ex-smoking COPD GOLD stage IV patients to age-matched smoking and never-smoking controls. Results We observed that long-term CSE exposure induces robust changes in mitochondrial structure, including fragmentation, branching and quantity of cristae. The majority of these changes were persistent upon CSE depletion. Furthermore, long-term CSE exposure significantly increased the expression of specific fission/fusion markers (Fis1, Mfn1, Mfn2, Drp1 and Opa1), oxidative phosphorylation (OXPHOS) proteins (Complex II, III and V), and oxidative stress (Mn-SOD) markers. These changes were accompanied by increased levels of the pro-inflammatory mediators IL-6, IL-8, and IL-1β. Importantly, COPD primary bronchial epithelial cells (PBECs) displayed similar changes in mitochondrial morphology as observed in long-term CSE-exposure BEAS-2B cells. Moreover, expression of specific OXPHOS proteins was higher in PBECs from COPD patients than control smokers, as was the expression of mitochondrial stress marker PINK1. Conclusion The observed mitochondrial changes in COPD epithelium are potentially the consequence of long-term exposure to cigarette smoke, leading to impaired mitochondrial function and may play a role in the pathogenesis of COPD. © 2013 Hoffmann et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.