Lung-Specific Loss of α3 Laminin Worsens Bleomycin-Induced Pulmonary Fibrosis

Laminins are heterotrimeric proteins that are secreted by the alveolar epithelium into the basement membrane, and their expression is altered in extracellular matrices from patients with pulmonary fibrosis. In a small number of patients with pulmonary fibrosis, we found that the normal basement membrane distribution of the alpha 3 laminin subunit was lost in fibrotic regions of the lung. To determine if these changes play a causal role in the development of fibrosis, we generated mice lacking the alpha 3 laminin subunit specifically in the lung epithelium by crossing mice expressing Cre recombinase driven by the surfactant protein C promoter (SPC-Cre) with mice expressing floxed alleles encoding the alpha 3 laminin gene (Lama3(fl/fl)). These mice exhibited no developmental abnormalities in the lungs up to 6 months of age, but, compared with control mice, had worsened mortality, increased inflammation, and increased fibrosis after the intratracheal administration of bleomycin. Similarly, the severity of fibrosis induced by an adenovirus encoding an active form of transforming growth factor-beta was worse in mice deficient in alpha 3 laminin in the lung. Taken together, our results suggest that the loss of alpha 3 laminin in the lung epithelium does not affect lung development, but plays a causal role in the development of fibrosis in response to bleomycin or adenovirally delivered transforming growth factor-beta. Thus, we speculate that the loss of the normal basement membrane organization of alpha 3 laminin that we observe in fibrotic regions from the lungs of patients with pulmonary fibrosis contributes to their disease progression.