The hypothesis: Club cells lose CYP1A and CYP2J2 expression as they age, while CYP1B1 holds steady or even increases. This creates a two-pronged problem: they can no longer detoxify inhaled xenobiotics and lipid peroxidation products effectively, and they can't produce the EETs needed to keep NRF2-driven antioxidant genes turned on. The result is that aged club cells can't repair the airway after injury the way younger cells can.

Why this might be true: CYP1A enzymes handle F₂-isoprostanes and isofurans, while CYP2J2 pumps out EETs that activate antioxidant defenses. Both enzyme families shift with age and stress. I've found that aged club cells show diminished NRF2 activity alongside lower HMOX1 and NQO1 levels. The idea here is that club cells rely on a CYP-EET-NRF2 feedback loop—the EETs keep NRF2 active, which keeps the antioxidants coming, which keeps the cells protected. When CYP2J2 drops off in aging cells, that loop breaks. What's interesting is this seems to be a club cell-specific vulnerability; other airway cell types don't depend on this same pathway the same way.

What we'd expect to see: First, aged mouse club cells should have at least half the CYP1A2 and CYP2J2 transcripts of young cells, while CYP1B1 stays the same or goes up. Second, knocking out CYP2J2 specifically in club cells should impair NRF2's ability to move into the nucleus and slow recovery of SCGB1A1+ cells after ozone exposure. Third, adding EETs back to aged club cells in organoid culture should restore NRF2 target gene expression and improve spheroid formation.

How we'd know we're wrong: If aged club cells actually maintain similar CYP1A and CYP2J2 levels to young cells, or if activating NRF2 on its own fixes the regeneration problem without involving these CYP enzymes, then this whole model falls apart.