At baseline, a significant association between PKA and CREB was observed in the COPD group (p=0.000, β=0.929); however, at the second time point, a significant association was noted for both the asthma group (p=0.016, β=0.506) and the COPD group (p=0.028, β=0.458). Here, CREB1 is linked to chronic obstructive pulmonary disease.