PDE5A and chronic obstructive pulmonary disease: Among these genes was PDE5A, which was involved in smooth muscle contraction and relaxation, as well as cell proliferation, cell signalling and included pro-inflammatory w Inhibition of PDE5A is involved in preventing tobacco smoke-induced emphysema39, suggesting a protective role of this miRNA in current smokers with COPD as an attempt to limit the harmful effects of smoking40.