KDM5B as a Rheostat that Balances H2A.J-Dependent SASP Tuning in Senescent Cells

Hypothesis

KDM5B demethylates H3K4me3 at SASP promoters, limiting H2A.J incorporation and thereby restraining the amplitude of the proinflammatory secretome. In senescent cells, the opposing action of KDM6A removes H3K27me3, permitting H2A.J loading and SASP amplification. The KDM5B/KDM6A ratio thus sets a tunable “negotiator” state: high KDM5B yields a shallow, low‑SASP senescence that signals for clearance without collateral inflammation; low KDM5B lets KDM6A dominate, producing a saboteur phenotype with robust H2A.J‑driven SASP and tissue damage.

Rationale

• Global loss of H3K4me3 is a senescence hallmark [3], consistent with sustained KDM5 activity shaping chromatin.
• KDM6A promotes therapy‑induced endothelial senescence and neuroinflammation [1]; its deletion is protective.
• KDM5B/C suppress STING signaling via H3K4me3 removal [2], indicating a brake on innate immune activation.
• H2A.J accumulation drives inflammatory SASP expression [4], showing senescent cells actively deploy epigenetic tools.
• No direct ChIP‑seq/CUT&RUN data exist on KDM5/KDM6 regulation of bivalent domains in senescent cells, leaving the mechanistic link untested.

Predictions

1. In senescent fibroblasts, KDM5B knockdown will increase H2A.J occupancy at IL6, IL8, and CXCL10 promoters, accompanied by elevated H3K4me3 and H3K27me3 loss at those loci.
2. Conversely, KDM5B overexpression will reduce H2A.J binding, lower SASP mRNA and protein secretion, and preserve a low‑inflammatory senescence phenotype.
3. The KDM5B/KDM6A ratio will correlate inversely with SASP intensity across different senescence inducers (irradiation, oncogene activation, chemotherapeutic agents).
4. In vivo, transplanting senescent cells with high KDM5B into wounded mouse skin will accelerate resolution via efficient macrophage‑mediated clearance, whereas low KDM5B transplants will prolong inflammation and impair healing.

Experimental Approach

• Induce senescence in human IMR‑90 cells using doxorubicin; validate by SA‑β‑gal and p16^INK4a^ expression.
• Perform siRNA‑mediated KD or lentiviral overexpression of KDM5B; include non‑targeting controls.
• Conduct CUT&RUN for H3K4me3, H3K27me3, and H2A.J; follow with qPCR at SASP promoters.
• Measure SASP factors by ELISA and RNA‑seq.
• Assess immune cell attraction using conditioned media in macrophage migration assays.
• Validate findings in a murine wound‑healing model with adoptive transfer of engineered senescent cells; track healing rate, cytokine milieu, and clearance by flow cytometry.

Potential Implications

If KDM5B functions as a rheostat that fine‑tunes H2A.J‑dependent SASP output, modulating its activity could shift senescence from a harmful saboteur to a beneficial negotiator. This predicts that senolytic strategies combined with transient KDM5B activation might clear senescent cells while minimizing inflammatory spillover, offering a refined approach to age‑related pathology and cancer therapy side‑effects.