Role Of LOX-1in Hyperoxia-induced Acute Lung Injury And The Underlying Mechanism

Background The clinical management of severe respiratory failure patients and premature infants may require the supplementation of mechanical ventilation with high concentrations of oxygen. However, prolonged exposure to elevated oxygen tension can cause multiple organic injuries, particularly lung injury. Hyperoxia-induced acute lung injury is characterized by excessive activation of inflammation response and apoptosis of pulmonary cells, ultimately leading to acute respiratory distress syndrome.Lectin-like oxidized low density lipoprotein receptor-1(LOX-1) responsible for the uptake and metabolism of oxidized low density lipoprotein, is the natural receptor of oxidized low density lipoprotein and mainly expressed in endothelial cells. It has well documented that LOX-1plays an important role in vascular inflammation. LOX-1mediates oxidized low density lipoprotein-induced inflammation and endothelial cell dysfunction leading to the genesis and development of atherosclerosis. LOX-1is also involved in lipopolysaccharide-induced acute lung injury. The present study aims to explore whether LOX-1 mediates hyperoxia-induced acute lung injury and the underlying mechanisms.Methods Animal study:Mice were maintained under hyperoxia (95%O2) for72h to establish acute lung injury model. Twenty male C57BL6mice (6-8weeks) were randomly divided into2groups (n=10): control group and hyperoxia group. At the end of experiments, the cell count, protein concentration, level of TNF-a and IL-6in bronchoalveolar lavage fluid (B ALF), the activity of caspase3and the protein expression of LOX-1and apoptosis related proteins (Bax and Bcl-2) in lung tissues were determined. The histopathological change in lung tissues was detected by HE staining.Cell study:Before hyperoxia exposure, LOX-1small interfering RNA (siRNA) was transfected into cultured human A549pulmonary carcinoma cells. The experiment was divided into four groups:control group, hyperoxia group, hyperoxia puls LOX-1siRNA group and hyperoxia puls siRNA negative control group. Cell viability was evaluated by MTS assay. Lactic dehydrogenase (LDH) leakage and the level of TNF-a and IL-6were measured in the supernatant of cultured A549cells. The protein expression of LOX-1and apoptosis related proteins (Bax and Bcl-2) were determined in A549cells.Results1. Compared with normal control group, the body weight of mice in hyperoxia group was significantly decreased; the total cell numbers, total protein and the level of TNF-α and IL-6in BALF was significantly increased in hyperoxia group.2. Compared with control group, the caspase3activity and the protein expression of LOX-1and Bax were significantly increased, while Bcl-2protein expression was decreased in lung tissues in hyperoxia group.3. Treatment with hyperoxia for72h significantly decreased cell viability, and increased the leakage of LDH and the level of TNF-α and IL-6in the supernatant of cultured A549cells.4. Compared with control group, treatment of A549cells with hyperoxia for72h significantly up-regulated the protein expression of LOX-1and Bax, while down-regulated Bcl-2protein expression.5. Silencing the expression of LOX-1attenuated hyperoxia-induced cell injury, pro-apoptotic protein expression and the increase in inflammation cytokines level.Conclusions LOX-1mediates hyperoxia-induced acute lung injury which is related to the activation of inflammation response and apoptosis.