Influence of early neutrophil depletion on MMPs/TIMP-1 balance in bleomycin-induced lung fibrosis

Pulmonary fibrosis is characterized by excessive deposition of extracellular matrix in interstitium resulting in respiratory failure associated with inflammation showing mainly neutrophil (PMN) recruitment. The turn over of extracellular matrix is partially regulated by proteases such as metalloproteinases (MMPs) and their inhibitors (TIMPs). We investigated the impact of PMN depletion on the MMP/TIMP-1 imbalance and the development of fibrosis in mice induced by bleomycin (0.3 mg/mouse). Administration of 200 μL of rabbit anti-mouse PMN antibody i.p. blunted the neutrophil influx detected in BAL and in whole blood one day after bleomycin administration. At day14, hydroxyproline content was increased both in anti-PMN treated and control mice, without any difference between groups. At day one, bleomycin elicited a raise in pro-MMP-9 level in BAL that was significantly attenuated in anti-PMN depleted mice, whereas TIMP-1 and MMP-2 release were similar in both groups at day1 and day14. Higher RNA levels were observed in PMN-treated mice at day1 for MMP-9 and MMP-2 and at day14 for MMP-2 only. At day14, bleomycin elicited a raise of TIMP-1 protein and RNA levels regardless of anti-PMN treatment, whereas MMP-9 returned to basal level. Bleomycin enhanced MMP-8 level in BAL at day14 only for the control group. The amount of MMP-8 was more important in BAL from anti-PMN treated mice than in control mice at day1 and day14. PMN-depletion and the associated modifications in pro-MMP-9/TIMP-1 imbalance in lung during the early inflammatory phase do not alter susceptibility to bleomycin-induced pulmonary fibrosis.