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Method Article
Here, we discuss a series of protocols for induction and validation of cellular senescence in cultured cells. We focus on different senescence-inducing stimuli and describe the quantification of common senescence-associated markers. We provide technical details using fibroblasts as a model, but the protocols can be adapted to various cellular models.
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.
In 1961, Hayflick and Moorhead reported that primary fibroblasts in culture lose their proliferative potential after successive passages1. This process is caused by the sequential shortening of telomeres after each cell division. When telomeres reach a critically short length, they are recognized by the DNA-damage response (DDR) that activates an irreversible arrest of proliferation — also defined as replicative senescence. Replicative senescence is currently one of the many stimuli that are known to induce a state of permanent cell cycle arrest that renders cells insensitive both to mitogens and to apoptotic signals2,3. The senescence program is normally characterized by additional features including high lysosomal activity, mitochondrial dysfunction, nuclear changes, chromatin rearrangements, endoplasmic reticulum stress, DNA damage and a senescence-associated secretory phenotype (SASP)3,4. Senescent cells have multiple functions in the body: development, wound healing and tumor suppression2. Equally, they are known to play an important role in aging and, paradoxically, in tumor progression5. The negative, and partially contradictory, effects of senescence are often attributed to the SASP6.
Recently, it was shown that elimination of senescent cells from mice leads to lifespan extension and to elimination of many of the aging features7,8,9,10,11,12. In the same way, multiple drugs have been developed to either eliminate senescent cells (senolytics) or to target the SASP13,14. The anti-aging therapeutic potential has recently attracted more attention to the field.
The study of mechanisms associated to cellular senescence and the screenings for pharmacological interventions heavily rely on ex vivo models, particularly on human primary fibroblasts. While there are some common features activated by diverse senescence inducers, a large variability in the senescence phenotype is observed and dependent on various factors including cell type, stimulus and time point3,15,16,17. It is imperative to consider the heterogeneity for studying and targeting senescent cells. Therefore, this protocol aims to provide a series of methods used to induce senescence in primary fibroblasts by using different treatments. As it will be explained, the methods can easily be adapted to other cell types.
Apart from replicative senescence, we describe five other senescence-inducing treatments: ionizing radiation, ultraviolet (UV) radiation, doxorubicin, oxidative stress and epigenetic changes (namely promotion of histone acetylation or DNA demethylation). Both, ionizing radiation and UV-radiation cause direct DNA damage and, at the appropriate dose, trigger senescence18,19. Doxorubicin also causes senescence mainly through DNA damage by intercalating into the DNA and disrupting topoisomerase II function and thus halting DNA repair mechanisms20. The expression of genes essential for senescence is normally controlled by histone acetylation and DNA methylation. As a consequence, histone deacetylase inhibitors (e.g., sodium butyrate and SAHA) and DNA demethylating (e.g., 5-aza) agents trigger senescence in otherwise normal cells21,22.
Finally, four of the most common markers associated to senescent cells will be explained: activity of the senescence associated-β-galactosidase (SA-β-gal), rate of DNA synthesis by EdU incorporation assay, overexpression of the cell cycle regulators and cyclin-dependent kinase inhibitors p16 and p21, and overexpression and secretion of members of the SASP.
1. General Preparation
2. Induction of Senescence
3. Markers of Senescence
Enrichment of SA-β-gal staining in senescent fibroblasts
Β-galactosidase (β-gal) is a lysosomal enzyme that is expressed in all cells and that has an optimum pH of 4.025,26. However, during senescence, lysosomes increase in size and, consequently, senescent cells accumulate β-gal. The increased amounts of this enzyme make it possible to detect its activi...
The protocols explained here were optimized for human primary fibroblasts, particularly BJ and WI-38 cells. The protocols for replicative senescence, ionizing radiation and doxorubicin, have been successfully applied to other types of fibroblasts (HCA2 and IMR90) and in other cell types (namely neonatal melanocytes and keratinocytes or iPSC-derived cardiomyocytes) in our laboratory. However, adaptations for additional cell types can be optimized by adjusting some details such as the number of seeded cells, the methods an...
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We thank members of the Demaria lab for fruitful discussions, and Thijmen van Vliet for sharing data and protocol on the UV-induced senescence.
Name | Company | Catalog Number | Comments |
DMEM Media - GlutaMAX | Gibco | 31966-047 | |
Fetal Bovine Serum | Hyclone | SV30160.03 | |
Penicillin-Streptomycin (P/S; 10,000 U/ml) | Lonza | DE17-602E | |
Dimethyl Sulfoxide (DMSO) | Sigma-Aldrich | SC-202581 | |
Nuclease-Free Water (not DEPC-Treated) | Ambion | AM9937 | |
T75 flask | Sarstedt | 833911002 | |
Trypsin/EDTA Solution | Lonza | CC-5012 | |
PBS tablets | Gibco | 18912-014 | |
1.5 ml microcentrifuge tubes | Sigma-Aldrich | T9661-1000EA | |
Corning 15 mL centrifuge tubes | Sigma-Aldrich | CLS430791 | |
6-well plate | Sarstedt | 83.3920 | |
24-well plate | Sarstedt | 83.3922 | |
13mm round coverslips | Sarstedt | 83.1840.002 | |
Steriflip | Merck Chemicals | SCGP00525 | |
Cesium137-source | IBL 637 Cesium-137γ-ray machine | ||
UV radiation chamber | Opsytec, Dr. Göbel BS-02 | ||
Doxorubicin dihydrochloride | BioAustralis Fine Chemicals | BIA-D1202-1 | |
Hydrogen peroxide solution | Sigma-Aldrich | 7722-84-1 | |
5-aza-2’-deoxycytidine | Sigma-Aldrich | A3656 | |
SAHA | Sigma-Aldrich | SML0061 | |
Sodium Butyrate | Sigma-Aldrich | B5887 | |
X-gal (5-Bromo-4-chloro-3-indolyl-β-D-galactopyranoside) | Fisher Scientific | 7240-90-6 | |
Citric acid monohydrate | Sigma-Aldrich | 5949-29-1 | |
Sodium dibasic phosphate | Acros organics | 7782-85-6 | |
Potassium ferrocyanide | Fisher Scientific | 14459-95-1 | |
Potassium ferricyanide | Fisher Scientific | 13746-66-2 | |
Sodium Chloride | Merck Millipore | 7647-14-5 | |
Magnesium Chloride | Fisher Chemicals | 7791-18-6 | |
25% glutaraldehyde | Fisher Scientific | 111-30-8,7732-18-5 | |
16% formaldehyde (w/v) | Thermo-Fisher Scientific | 28908 | |
EdU (5-ethynyl-2’-deoxyuridine) | Lumiprobe | 10540 | |
Sulfo-Cyanine3 azide (Sulfo-Cy3-Azide) | Lumiprobe | D1330 | |
Sodium ascorbate | Sigma-Aldrich | A4034 | |
Copper(II) sulfate pentahydrate (Cu(II)SO4.5H2O) | Sigma-Aldrich | 209198 | |
Triton X-100 | Acros organics | 215682500 | |
TRIS base | Roche | 11814273001 | |
LightCycler 480 Multiwell Plate 384, white | Roche | 4729749001 | |
Lightcycler 480 sealing foil | Roche | 4729757001 | |
Sensifast Probe Lo-ROX kit | Bioline | BIO-84020 | |
UPL Probe Library | Sigma-Aldrich | Various | |
Human IL-6 DuoSet ELISA | R&D | D6050 | |
Bio-Rad TC20 | Bio-Rad | ||
Counting slides | Bio-Rad | 145-0017 | |
Dry incubator | Thermo-Fisher Scientific | Heratherm | |
Dimethylformamide | Merck Millipore | 1.10983 | |
Parafilm 'M' laboratory film | Bemis | #PM992 | |
Tweezers | |||
Needles |
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