Cyclooxygenase-2 deficiency attenuates lipopolysaccharide-induced inflammation, apoptosis, and acute lung injury in adult mice

Many lung diseases are caused by an excessive inflammatory response, and inflammatory lung diseases are often modeled using lipopolysaccharide (LPS) in mice. Cyclooxygenase-2 (COX-2) encoded by the Ptgs2 gene is induced in response to inflam-matory stimuli including LPS. The objective of this study was to test the hypothesis that mice deficient in COX-2 (Ptgs2(-/-)) will be protected from LPS-induced lung injury. Wild-type (WT; CD1 mice) and Ptgs2(-/-)mice (on a CD1 background) were treated with LPS or vehicle for 24 h. LPS treatment resulted in histological evidence of lung injury, which was attenuated in the Ptgs2(-/-)mice. LPS treatment increased the mRNA levels for tumor necrosis factor -a, interleukin-10, and monocyte chemoattractant protein-1 in the lungs of WT mice, and the LPS-induced increases in these levels were attenuated in the Ptgs2(-/-)mice. The protein levels of active caspase-3 and caspase-9 were lower in the LPS-treated lungs of Ptgs2(-/-)mice than in LPS-treated WT mice, as were the number of terminal deoxynucleotide transferase dUTP nick end labeling-positive cells in lung sections. LPS exposure resulted in a greater lung wet-to-dry weight ratio (W/D) in WT mice, suggestive of pulmonary edema, while in LPS-treated Ptgs2(-/-)mice, the W/D was not different from controls and less than in LPS-treated WT mice. These results demonstrate that COX-2 is involved in the inflammatory response to LPS and suggest that COX-2 not only acts as a downstream participant in the inflammatory response, but also acts as a regulator of the inflammatory response likely through a feed-forward mechanism following LPS stimulation.