cGMP increases antioxidant function and attenuates oxidant cell death in mouse lung microvascular endothelial cells by a protein kinase G-dependent mechanism

Increasing evidence suggests that endothelial cytotoxicity from reactive oxygen species (ROS) contributes to the pathogenesis of acute lung injury. Treatments designed to increase intracellular cGMP attenuate ROS-mediated apoptosis and necrosis in several cell types, but the mechanisms are not understood, and the effect of cGMP on pulmonary endothelial cell death remains controversial. In the current study, increasing intracellular cGMP by either 8pCPT-cGMP (50 μM) or atrial natriuretic peptide (10 nM) significantly attenuated cell death in H₂O₂-challenged mouse lung microvascular (MLMVEC) monolayers. 8pCPT-cGMP also decreased perfusate LDH release in isolated mouse lungs exposed to H₂O₂ or ischemia-reperfusion. The protective effect of increasing cGMP in MLMVECs was accompanied by enhanced endothelial H₂O₂ scavenging (measured by H₂O₂ electrode) and decreased intracellular ROS concentration (measured by 2′,7′-dichlorofluorescin fluorescence) as well as decreased phosphorylation of p38 MAPK and Akt. The cGMP-mediated cytoprotection and increased H₂O₂ scavenging required >2 h of 8pCPT-cGMP incubation in wild-type MLMVEC and were absent in MLMVEC from protein kinase G (PKG_I)-/- mice suggesting a PKG _I-mediated effect on gene regulation. Catalase and glutathione peroxidase 1 (Gpx-1) protein were increased by cGMP in wild-type but not PKG_I-/-MLMVEC monolayers. Both the cGMP-mediated increases in antioxidant proteins and H₂O₂ scavenging were prevented by inhibition of translation with cycloheximide. 8pCPT-cGMP had minimal effects on catalase and Gpx-1 mRNA. We conclude that cGMP, through PKGI, attenuated H ₂O₂-induced cytotoxicity in MLMVEC by increasing catalase and Gpx-1 expression through an unknown posttranscriptional effect.