[Study on the function of osteopontin in hyperoxia-induced acute lung injury and its mechanism]

To examine the role of osteopontin (OPN) in hyperoxia-induced acute lung injury (ALI) and its relationships with matrix metalloproteinases (MMP).

Seventy-two OPN gene wild type (OPN(+/+)) mice were divided into normal control group (WN group), hyperoxia for 24 hours group (WO(1) group), hyperoxia for 48 hours group (WO(2) group) and hyperoxia for 72 hours group (WO(3) group) randomly, 18 mice in each group; another seventy-two OPN gene knock-out (OPN(-/-)) mice were also divided into normal control group (DN group), hyperoxia for 24 hours group (DO(1) group), hyperoxia for 48 hours group (DO(2) group) and hyperoxia for 72 hours group (DO(3) group) randomly. The hyperoxia group mice were exposed in sealed cages > 95% oxygen, and their matched background control were put outside of sealed cages and breath room air. Severity of lung injury was assessed and the survival curve was calculated. Cell count and differentials in bronchoalveolar lavage fluid (BALF) in every group were performed, while another 40 OPN(-/-) mice and their matched OPN(+/+) mice were used for survival study. Samples obtained from BALF at the end of the experiment (24, 48 and 72 h) and control animals were used for the measurement of MMP-2, MMP-9 by gelatin zymography, and reverse transcript-polymerase chain reaction (RT-PCR) was used for the semiquantitative assay of mRNA coding for OPN, MMP-2, MMP-9, tissue-inhibitors of metalloproteinase-1, 2 (TIMP-1, TIMP-2).

DO(3) group mice developed more severe ALI than WO(3) group mice and the survival times of OPN(-/-) mice were shorter than their matched OPN(+/+) mice (P < 0.01). The total cell count in BALF from DO(3) group mice was higher than WO(3) group mice [(72.2 +/- 22.3) x 10(4)/L, (39.7 +/- 10.4) x 10(4)/L, P < 0.05], the count of polymorphonuclear cells in BALF from DO(3) group mice was almost 8 folds higher than WO(3) group mice [(207.54 +/- 36.45) x 10(3)/L, (25.33 +/- 6.43) x 10(3)/L, P < 0.01]. Gelatin zymography showed that the level of activated MMP-9 in BALF from DO(3) group mice was significantly higher than WO(3) group mice [(4.36 +/- 0.65) x 10(4), (2.84 +/- 0.44) x 10(4), P < 0.01]. The level of OPN mRNA in WO(2) and WO(3) group mice was higher than in WN group mice (0.87 +/- 0.08, 0.92 +/- 0.07, 0.69 +/- 0.04, P < 0.05). TIMP-1 mRNA expression in WO(3) group mice was significantly increased than in DO(3) group mice (1.09 +/- 0.12, 0.62 +/- 0.09, P < 0.05). TIMP-2 mRNA expression in WO(2) and WO(3) group mice was significantly increased than their matched OPN(-/-) mice (48 h 1.05 +/- 0.23, 0.59 +/- 0.11, P < 0.01, 72 h 0.99 +/- 0.13, 0.75 +/- 0.16, P < 0.05).

OPN can protect against hyperoxia-induced ALI by promoting the expression of TIMP and inhibiting the activation of MMP.