Altered expression of the Smad signalling pathway: implications for COPD pathogenesis

Pulmonary emphysema, as a feature of chronic obstructive pulmonary disease (COPD), is characterised by destruction of alveolar tissue. The present authors previously demonstrated reduced decorin expression in the peribronchial area of COPD patients, reflecting an altered extracellular matrix (ECM) modulation. Decorin transcription is regulated by the transforming growth factor (TGF)-beta-Smad pathway, the key intracellular signal route for initiation of ECM component gene transcription. Whether this pathway is aberrantly expressed in COPD is not known. An immunohistochemical study was performed to compare protein expression of TGF-beta1 and TGF-beta receptors, Smad 2, 3, 4 and 7, and decorin in lung tissue of Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages II and IV COPD patients and controls. Epithelial expression of the inhibitory Smad 7 was significantly lower in patients with GOLD stages II and IV than in controls, with other Smad protein expressions being similar in the groups. The expression of TGF-beta1 and TGF-beta receptor type I was significantly lower in stage II patients. Decorin staining of the adventitia and alveolar walls was significantly reduced in COPD stage IV. In conclusion, the transforming growth factor-beta-Smad pathway is aberrantly expressed in chronic obstructive pulmonary disease patients, implying an abnormal tissue repair ultimately resulting in reduced decorin production. The results of the present study contribute to better understanding of the pathogenesis of emphysema and the airway fibrosis observed in chronic obstructive pulmonary disease patients.