Senescent cells generate circadian dead zones that propagate aging via SASP‑driven transcriptional reprogramming of neighboring cells

Hypothesis: Senescent cells act as sources of circadian desynchrony that radiate into surrounding tissue, establishing expanding “circadian dead zones” where core clock gene oscillations are dampened, thereby accelerating local aging phenotypes. Mechanistically, SASP factors (e.g., IL‑6, TGF‑β) activate MAPK/ERK and JAK/STAT pathways in neighboring cells, leading to post‑translational modification and transcriptional repression of BMAL1/CLOCK targets while paradoxically increasing total BMAL1 protein that is sequestered in cytoplasmic aggregates, mirroring the cell‑autonomous senescence‑associated clock rewiring. This creates a feed‑forward loop: neighboring cells develop a senescent‑like transcriptional profile (↑p16, ↑SASP) and further amplify the signal, allowing the dead zone to expand radially over days to weeks.

Testable predictions:

1. In spatial transcriptomics of young vs. aged mouse lung (GSE278620), PER1/2 and CRY1 expression will show a gradient of decreasing amplitude with distance from p16⁺ foci, whereas total Bmal1 mRNA will be elevated but its nuclear protein signal will be reduced.
2. Pharmacological blockade of IL‑6 signaling (anti‑IL‑6R antibody) will flatten the PER2::luciferase rhythm attenuation in co‑cultures of senescent fibroblasts and naïve epithelial cells, restoring amplitude to >80 % of control.
3. Inducing focal senescence via UV‑laser microirradiation in a PER2::luciferase reporter mouse will generate a detectable wave of circadian dampening that spreads at ~10 µm/h, which can be halted by a MAPK inhibitor (U0126).
4. Genetic rescue of nuclear BMAL1 (BMAL1‑NLS transgene) in the microenvironment will suppress the emergence of new p16⁺ cells beyond the initial senescent cluster, limiting dead‑zone expansion.

Falsifiability: If spatial maps reveal no statistically significant decline in core‑clock oscillation metrics around senescent cells, or if blocking SASP fails to rescue circadian amplitudes in neighbors, the hypothesis is refuted.

Potential experiments: Use live‑imaging of PER2::luciferase in organoid slices combined with multiplexed immunofluorescence for p16, phospho‑ERK, and nuclear BMAL1; apply DeepScence to segment senescent cells and compute radial expression profiles; apply spatial transcriptomics (10x Visium) on aged tissues to validate gradient predictions.