Lung collagen: definition, diversity and development
Morphologic studies demonstrate collagen as a major component of the tracheobronchial tree, vascular tree, and alveolar interstitium. Functional studies suggest it is an important determinant of lung mechanics and structural stability. Although it comprises 10-15% of the dry weight of the adult lung, it is very difficult to extract intact, presumably because of cross links among collagen chains and the association of collagen with other lung components. Short term explant cultures of different lung structures synthesize collagen α chains which can be extracted and purified. Although there is some overlap, the tracheobronchial tree, vascular tree, and peripheral lung synthesize structurally different α chains, all with mol wt of 100,000 daltons. The mechanisms of collagen synthesis and modification in lung are similar to those elsewhere in the body. However, there are variations in the control of lung collagen synthesis that have major importance for this organ. After birth, there is a rapid increase in both the total amount and concentration of collagen in lung. This is accompanied by a shift in the emphasis of the protein synthesizing machinery of lung toward collagen synthesis. In the adult lung, however, collagen synthesis is at a constant low level. In the rabbit, this can be modified by performing unilateral pneumonectomy. The subsequent rapid growth of the remaining lung includes an accumulation of collagen preceded by a shift in protein synthesis toward collagen synthesis. Continued application of the technologies of protein chemistry, molecular biology and tissue culture to these problems should allow substantial progress in understanding the biochemical basis of pulmonary function.