Tyrosine kinase activation during lung injury, fibrosis, and compensatory lung growth

Changes in tumor necrosis factor in postpneumonectomy lung growth

So that changes in production and binding of tumor necrosis factor-alpha during postpneumonectomy lung growth could be determined, rats underwent left lung resection and were killed 3, 7, or 14 days later, 1 hour after the injection of 3H-thymidine. Serum was collected, and the lungs were lavaged and perfused in vitro. Lung volumes were measured. Lungs were homogenized, and changes in lung weight, protein content, deoxyribonucleic acid content, deoxyribonucleic acid synthesis, and tyrosine kinase activity of different lobes were recorded. Tumor necrosis factor-alpha content of serum, lavage fluid, and perfusate was measured by an enzyme-linked immunoassay. The binding of tumor necrosis factor-alpha to membrane extracts of lung homogenates was measured by immunoblots. Whereas the cardiac lobe of the remaining right lung demonstrated larger increases in size than other lobes after pneumonectomy, there was no difference in any growth parameter between it and the other lung lobes. Serum tumor necrosis factor-alpha was detectable in sham-operated animals and increased significantly after pneumonectomy. However, by day 14, it was not different from the level in sham-operated animals. In contrast, tumor necrosis factor-alpha in lavage fluid remained significantly elevated, and its binding increased gradually throughout the study period. Tumor necrosis factor-alpha in perfusate did not demonstrate any rise. We conclude that lung growth after pneumonectomy is uniform among various lobes, which suggests that it is regulated by humoral factors. Because tumor necrosis factor-alpha, a cytokine known to stimulate cellular proliferation and matrix synthesis, is produced and bound to the lung during this process, it may be one of the humoral factors implicated in postpneumonectomy lung growth.

Dynamic changes in the functional characteristics of the interstitial fibroblast during lung repair

To evaluate the mechanisms involved in the regulation of fibroblast function during the repair of fibrotic lung injury, we isolated lung fibroblasts from adult male Fischer-344 rats before the induction of severe unilateral paraquat lung injury, as well as 1 and 14 days later. Fibroblasts were utilized at an early generation time to avoid senescence. In general, fibroblasts of injured lungs displayed significant increases in proliferative and matrix synthesis properties, with more pronounced increases detected early after the induction of injury. This was true of DNA synthesis, which increased by 3- and 1.4-fold on days 1 and 14, respectively; tyrosine kinase activity, which increased by 4- and 3.5-fold; fibronectin synthesis, 14- and 8-fold, respectively; and glycosaminoglycans synthesis, 4.4- and 3-fold, respectively. The increase in function of fibroblasts isolated from the immediate influence of extrinsic growth factors suggests that fibroblast function during repair may be under intrinsic as well as extrinsic control. In the early phases of repair, intrinsic changes may be more dominant and may result in autoregulation of fibroblast function. In the later phases of repair, despite some reduction in intrinsic fibroblast activation, exposure to extrinsic growth factors may result in maintaining the state of activation and in sustaining the repair process.

Compensatory growth in fibrotic lung injury

We induced severe left-sided lung fibrosis by the unilateral endobronchial instillation of paraquat (1.0 mg/kg) into the left lungs of adult Fischer 344 male rats. Growth of the contralateral lung as well as its proliferative activity were measured 6 or 14 days later. Whereas the left lung underwent severe fibrosis and shrinkage with more than 85% reduction in lung volume, the right lung more than doubled in size. In addition, there was a significant increase in total protein content, DNA content, and DNA synthesis. We conclude that unilateral lung injury resulting in ipsilateral fibrosis and loss of parenchyma is associated with compensatory growth of the contralateral lung.