Type I and III collagen protein precursors and mRNA in the developing human lung.

Extracellular matrix proteins have a prominent role in both ontogenesis and fibrogenesis in the human lung. The aim of this study was to analyse the expression of newly formed precursor proteins and mRNA of collagen types I and III in developing human lung tissues from 12 to 40 weeks of gestation, and also in neonatal disorders such as respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD). Lung tissues were obtained at autopsy from 60 non-malformed cases. All tissues were analysed by immunohistochemistry and 24 were also investigated by mRNA in situ hybridization. The precursor proteins and mRNA of both collagens were expressed in abundance in pulmonary arteries and veins during all developmental periods. In RDS and BPD, precursor proteins and mRNAs of both collagen types were increased within alveolar walls. The cells in these locations showed alpha-smooth muscle actin, vimentin, and variable desmin immunoreactivity. Collagen I and III precursor proteins and mRNA were also observed in pleura, bronchi, bronchioles, and around chondrocytes during all developmental periods and in diseased lung. In conclusion, collagens I and III were expressed in a similar way in and around various cell types in the developing lung and their expression was increased within alveolar walls in RDS and BPD. Myofibroblast-type cells appeared to produce mRNA for both types of collagen in alveoli.