Effect of subcellular matrix on glycosaminoglycan synthesis by human lung fibroblasts.

The influences modulating glycosaminoglycan production by lung cells are not well understood. We examined the effect of three different subcellular matrices, plastic, type I collagen, and reconstituted basement membrane-like material (RBM), on the synthesis of sulfated glycosaminoglycans by cultured IMR-90 human lung fibroblasts. Accumulation of 35SO4-labeled glycosaminoglycans into the cell-matrix layer or medium was measured. Cells on collagen synthesized significantly less total glycosaminoglycans than cells on plastic but had a higher fraction of labeled glycosaminoglycans present in the cell-matrix layer (35 vs. 18%) with the increases being highest for dermatan and chondroitin sulfates. Cells grown on the RBM synthesized significantly more glycosaminoglycans than cells on plastic or collagen and also had 260% more labeled glycosaminoglycans present in the cell-matrix layer than cells on plastic. We conclude that the matrix to which lung fibroblasts are exposed can influence the amount and type of glycosaminoglycans synthesized and the degree of incorporation into the matrix. This may be relevant to fibrotic lungs with increased type I collagen or to severely injured lungs in which intra-alveolar fibroblasts are in contact with denuded basement membranes.

Repair of chronic hyperoxic lung injury: changes in lung ultrastructure and matrix.

We studied changes in lung ultrastructure, fibronectin, and collagen during repair of chronic hyperoxic lung injury induced by exposure of rats to 85% oxygen for 14 days. Morphologically, the most persistent changes were in the alveolar interstitium. After 28 days of repair, the extracellular matrix volume was still twofold normal. Total interstitial cell numbers also remained high and interstitial myofibroblast number actually doubled between Days 7 and 14. These changes contrast markedly with repair of acute lung injury induced by 100% oxygen (Thet et al. (1986) Exp. Lung Res. 11, 209-228) in which matrix volume and interstitial myofibroblast number increased initially but then returned to normal. Biochemically, tissue-associated fibronectin was high initially and peaked at 3 days before slowly declining. Tissue collagen content began to increase after the peak in fibronectin content and was over 150% of controls at 28 days; this correlated with an increase in visible collagen fibers. We conclude that changes in lung morphology and matrix after chronic hyperoxic lung injury are more persistent than after acute hyperoxic lung injury and result in a greater degree of chronic interstitial fibrosis.

Unilateral paraquat-induced lung fibrosis: evolution of changes in lung fibronectin and collagen after graded degrees of lung injury.

We describe a model of pulmonary fibrosis in which doses of paraquat ranging from 0.001 mg/kg to 1.0 mg/kg were instilled into the right lung of rats. Lung injury, as measured by right lung lavage albumin content and differential neutrophil count, ranged from undetectable to extremely severe, depending on the dose. Lung fibrosis, as assessed by collagen content and electron microscopy, showed similar dose-response effects. Mortality was minimal. Lavage fibronectin increased after high doses of paraquat, peaked at 2 d postinjury, decreased sharply after 3 d and was normal by 7 d. The temporal pattern was similar to that for albumin. Cultured alveolar macrophages obtained at 4 d postinjury did not have significant increases in fibronectin release. Tissue fibronectin content increased more slowly than lavage fibronectin, peaking at 4 d postinjury, and was still elevated at 7 and 14 d postinjury. Incorporation of [35S]methionine into tissue fibronectin by lung explants obtained at different times postinjury showed a similar time course. Lung collagen content increased steadily between 4 and 14 d postinjury. We conclude that, in our model, graded degrees of lung injury and fibrosis can be produced by varying the dose of unilaterally instilled paraquat and that the increases in lavage fibronectin were related mainly to capillary permeability whereas increases in tissue fibronectin represented parenchymal synthesis. The time course of changes in lung tissue fibronectin and collagen was consistent with the proposed roles of fibronectin in tissue repair and fibrosis. The ability of our model to produce graduated degrees of lung injury and fibrosis should be useful in further studies on the pathogenesis of postinjury lung fibrosis.