Osteopontin protects against hyperoxia-induced lung injury by inhibiting nitric oxide synthases.
BACKGROUND
Exposure of adult mice to more than 95% O(2) produces a lethal injury by 72 hours. Nitric oxide synthase (NOS) is thought to contribute to the pathophysiology of murine hyperoxia-induced acute lung injury (ALI). Osteopontin (OPN) is a phosphorylated glycoprotein produced principally by macrophages. OPN inhibits inducible nitric oxide synthase (iNOS), which generates large amounts of nitric oxide production. However, the relationship between nitric oxide and endogenous OPN in lung tissue during hyperoxia-induced ALI has not yet been elucidated, thus we examined the role that OPN plays in the hyperoxia-induced lung injury and its relationships with NOS.


METHODS
One hundred and forty-four osteopontin knock-out (KO) mice and their matched wild type background control (WT) were exposed in sealed cages > 95% oxygen or room air for 24- 72 hours, and the severity of lung injury was assessed; expression of OPN, endothelial nitric oxide synthase (eNOS) and iNOS mRNA in lung tissues at 24, 48 and 72 hours of hyperoxia were studied by reverse transcription-polymerase chain reaction (RT-PCR); immunohistochemistry (IHC) was performed for the detection of iNOS, eNOS, and OPN protein in lung tissues.


RESULTS
OPN KO mice developed more severe acute lung injury at 72 hours of hyperoxia. The wet/dry weight ratio increased to 6.85 +/- 0.66 in the KO mice at 72 hours of hyperoxia as compared to 5.31 +/- 0.92 in the WT group (P < 0.05). iNOS mRNA (48 hours: 1.04 +/- 0.08 vs. 0.63 +/- 0.09, P < 0.01; 72 hours: 0.89 +/- 0.08 vs. 0.72 +/- 0.09, P < 0.05) and eNOS mRNA (48 hours: 0.62 +/- 0.08 vs. 0.43 +/- 0.09, P < 0.05; 72 hours: 0.67 +/- 0.08 vs. 0.45 +/- 0.09, P < 0.05) expression was more significantly increased in OPN KO mice than their matched WT mice when exposed to hyperoxia. IHC study showed higher expression of iNOS (20.54 +/- 3.18 vs. 12.52 +/- 2.46, P < 0.05) and eNOS (19.83 +/- 5.64 vs. 9.45 +/- 3.82, P < 0.05) in lung tissues of OPN KO mice at 72 hours of hyperoxia.


CONCLUSIONS
OPN can protect against hyperoxia-induced lung injury by inhibiting NOS.
Zhang
Xiang-Feng
XF
Division of Pulmonary Medicine, Beijing Anzhen Hospital, Capital Medical University, Beijing 100029, China.
Liu
Shuang
S
Zhou
Yu-Jie
YJ
Zhu
Guang-Fa
GF
Foda
Hussein D
HD
D000818:Animals; D018496:Hyperoxia / Q000235:genetics / Q000503:physiopathology*; D007150:Immunohistochemistry; D008168:Lung / Q000378:metabolism; D055370:Lung Injury / Q000209:etiology / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000235:genetics; D052250:Nitric Oxide Synthase Type III / Q000235:genetics; D053495:Osteopontin / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D053495:Osteopontin; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III