ATG4D and chronic obstructive pulmonary disease: In detail, a statistically significant increased expression of ATG4A (p = 0.0047) (Figure 1A), ATG4D (p = 0.018) (Figure 1B), and ATG5 (p = 0.019) (Figure 1C) was documented in the bronchiolar epithelium in patients with stable COPD compared to CS and CNS groups (Figure 1D).