Selective induction of tissue inhibitor of metalloproteinase-1 in bleomycin-induced pulmonary fibrosis

Tissue inhibitors of metalloproteinases (TIMPs) are multifunctional protein s that have the capacity to modify cellular activities and to modulate matr ix turnover. We demonstrate that TIMP-1 messenger RNA (mRNA) and protein ex pression are selectively and markedly increased in a murine model of bleomy cin-induced pulmonary fibrosis. Northern analysis showed that lung steady-s tate TIMP-1 mRNA levels increased 14-fold after bleomycin administration co mpared with control mice. Expression of the genes for TIMP-2, TIMP-3, and i nterstitial collagenase (matrix metalloproteinase-13) was unaltered in the injured lung. In situ hybridization demonstrated that TIMP-1 gene induction was spatially restricted to areas of lung injury. Metalloproteinase inhibi tory activity of relative molecular mass of similar to 21 to 28 kD, corresp onding to the molecular weights for TIMP-1 and TIMP-2, was identified in lu ng extracts of bleomycin-injured mice by reverse zymography. Western analys is demonstrated that TIMP-1 protein levels in bronchoalveolar lavage fluid (BALF) of bleomycin-treated mice increased 220- and 151-fold at Days 4 and 28, respectively, compared with control mice. TIMP-2 immunoreactive protein in the BALF increased 20- and 103-fold relative to controls at Days 4 and 28, respectively. These results demonstrate that TIMP-1 gene expression is selectively increased, and that the expression of TIMP-1 and TIMP-2 is diff erentially regulated in bleomycin-induced pulmonary fibrosis. The profound and durable increase in TIMP-1 and TIMP-2 proteins suggests an important re gulatory role for these antiproteases in the inflammatory and fibrotic resp onses to bleomycin-induced lung injury.