TABLE 1.
Detection of senescence: senescence hallmarks, markers, biological consequences and limitations
| Senescence hallmarks | Markers | Limitations | Biological consequences |
|---|---|---|---|
| Cell‐cycle withdrawal | Ki67 negativity, phopho‐histone H3 negativity, EdU exclusion | Also in quiescence | Irreversible cell‐cycle arrest |
| p21Cip1 positivity, CDKN1A upregulation | Also in quiescence | CDK2 inhibitor p21Cip1 accumulation | |
| p16INK4a positivity, CDKN2A upregulation | Express by non‐senescent cells (macrophages), not express by all senescent cells | CDK4/6 inhibitor p16INK4A accumulation | |
| p15INK4b positivity, CDK2B upregulation | Other cyclin inhibitors accumulation | ||
| Cyclin‐A2 (CCNA2) and Cyclin‐E2 (CCNE2) downregulation | Decreased expression of cyclins | ||
| Persistent activation of RB family proteins (e.g phosphorylation of RB1, p107, p130) | Also in quiescence | Stability of the senescent state | |
| Heterochromatinization of E2F target genes | |||
| Macromolecular damage | Telomere shortening | DNA Damage | |
| Persistent nuclear DNA damage foci | |||
| Expression of γ‐H2AX and PARP‐1 | |||
| Phosphorylation of DNA‐PKcs and ATM | |||
| Ubiquitin proteasome system active | Protein Damage | ||
| Autophagy | |||
| Fatty acids and free cholesterol increase/phospholipids and cholesteryl decrease | High variability of the senescence‐associated lipid profile | Lipid Damage | |
| Secretory phenotype (SASP) | NF‐κB, C/EBPβ, GATA4, mTOR and p38MAPK signaling pathways (phosphorylation of IkBa, p38,…) | High Variability: duration, cell type, inducer stimuli, and cell‐to‐cell variability | Activation of transcription factors |
| IL6; IL7; IL1; IL1B; IL13; IL15 ; TGFβ; GM‐CSE; G‐CSE; IFN‐γ; BLC; MIF | Pro‐inflammatory cytokines release | ||
| IL8; GRO‐a, ‐b, ‐g; MCP‐2; MCP‐4; MIP‐1a; MIP‐3a; HCC‐4; eotaxin; eotaxin‐3; TECK; ENA‐78; I‐309; I‐TAC | Chemokines production | ||
| Amphiregulin; epiregulin; heregulin; EGF; bFGF; HGF; KGF (FGF7); VEGF; angiogenin; SCF; CXCL12; PIGF; NGF; IGFBP2, IGFBP3, IGFBP4, IGFBP6, IGFBP7 | Growth modulators, angiogenic factors | ||
| MMP‐1, ‐3, ‐10, ‐12, ‐13, ‐14; TIMP‐1; TIMP‐2; PAI‐1, ‐2; tPA; uPA; cathepsin B | Proteases, matrix metalloproteinases | ||
| ICAM‐1, ‐3; OPG; sTNFRI; sTNFRII; TRAIL‐R3; Fas; uPAR; SGP130; EGF‐R ; Fibronectin; collagens; laminin | Secretion of other factors | ||
| Deregulated metabolism | Increase number, decreased membrane potential, increased proton leak | Less functional mitochondria | |
| PML nuclear bodies (isoform IV) | Also during apoptosis | Reactive oxygen species (ROS) production | |
| Senescence‐associated beta‐galactosidasde (SA‐β‐gal) activity | Not required for the senescent phenotype | Lysosomes increase in number and size | |
| Galactosidase, beta 1 (GLB1) upregulation | |||
| LAMP1, LAMP2, Lysozime C upregulation | |||
| Senescence‐associated epigenetic | H4K16ac, H3.3, H4K20me3 and H3K9me3 | Global increase in chromatin accessibility | |
| Senescence‐associated heterochromatin foci (SAHFs) | |||
| Global loss of linker histone H1 | |||
| Lamin B1 (LMNB1) loss and reduced nuclear integrity | |||
| Upregulation of specific miRNAs (e.g. miR‐504, miR‐605) | Change in miRNAs expression | ||
| Resistance to apoptosis | Increased expression of BCL‐2 family members | Anti‐apoptotic protein upregulation | |
| TRAIL‐Decoy Receptor DcR2 over expression | Markers not present in mice | Hiding from Immune system | |
| NKG2D ligands over expression |