Hypothesis: EP300 functions as a bistable epigenetic switch that determines whether airway club cells adopt a detoxifying, proliferative phenotype or a senescent, secretory state. EP300 acetylates histone H3K27 at enhancers of cytochrome P450 genes (CYP2F2, CYP1A, CYP2J2) and simultaneously acetylates the transcription factor FOXM1, boosting its activity and promoting cell‑cycle progression. At the same time, EP300‑mediated acetylation of p53 attenuates its ability to induce CDKN2A/p16, thereby restraining senescence[1][2]. In young lungs, high EP300 activity keeps the switch in the “detox” position, maintaining CYP expression, low ROS, and robust proliferative capacity after injury. With age, declining EP300 activity—or increased activity of opposing HDACs—allows deacetylation of these targets, shifting the switch to the “senescent” position: CYP enhancers lose H3K27ac, FOXM1 activity drops, p53 drives p16 expression, and club cells accumulate oxidative damage and SASP factors[3][4][5]. It's predicted that pharmacological activation of EP300 in aged club cells will re‑establish the detox state even without altering upstream signals, whereas EP300 inhibition in young cells will precipitate senescence despite a youthful microenvironment.

Testable predictions: (1) Inducible EP300 overexpression in club cells of aged mice (using Scgb1a1‑CreERT2;Rosa26‑LSL‑EP300) will restore CYP2F2 and CYP1A mRNA to levels comparable to young controls after naphthalene challenge, reduce γH2AX and 8‑oxo‑dG oxidative marks, and lower p16^Ink4a^ and SA‑β‑gal positivity[1][6]. (2) Conversely, inducible EP300 knockdown (Scgb1a1‑CreERT2;EP300^fl/fl) in young mice will cause premature loss of CYP expression, increased ROS, and senescent markers even in the absence of injury[3][7]. (3) Chromatin immunoprecipitation sequencing (ChIP‑seq) for H3K27ac and EP300 will show concurrent loss/gain of acetylation at CYP enhancers and FOXM1 binding sites correlating with phenotypic state[2]. (4) Rescue experiments with a FOXM1 acetylation‑mimic mutant will bypass EP300 loss and maintain proliferative capacity, confirming FOXM1 as a critical non‑histone substrate. These experiments are feasible with existing transgenic lines, pharmacological EP300 activators (e.g., C646 analogues with inverse activity) or proteolysis‑targeting chimeras, and standard lung injury assays. Falsification would occur if EP300 manipulation fails to alter CYP expression or senescence markers, indicating that EP300 is not a coordinating node but a passive bystander.