CDKN1A and chronic obstructive pulmonary disease: We found that despite only a subset of DEGs overlapping in COPD and IPF (Figure 1A), the gene expression of the senescence marker CDKN1A/P21 is negatively correlated with predicted DLCO in age-matched COPD and IPF patients, suggesting that the degree of senescence correlates with disease severity in both diseases (Figure 1B).