Spred-2 Deficiency Exacerbates Lipopolysaccharide-Induced Acute Lung Inflammation in Mice

<div><p>Background</p><p>Acute respiratory distress syndrome (ARDS) is a severe and life-threatening acute lung injury (ALI) that is caused by noxious stimuli and pathogens. ALI is characterized by marked acute inflammation with elevated alveolar cytokine levels. Mitogen-activated protein kinase (MAPK) pathways are involved in cytokine production, but the mechanisms that regulate these pathways remain poorly characterized. Here, we focused on the role of Sprouty-related EVH1-domain-containing protein (Spred)-2, a negative regulator of the Ras-Raf-extracellular signal-regulated kinase (ERK)-MAPK pathway, in lipopolysaccharide (LPS)-induced acute lung inflammation.</p><p>Methods</p><p>Wild-type (WT) mice and <i>Spred-2^−/−</i> mice were exposed to intratracheal LPS (50 µg in 50 µL PBS) to induce pulmonary inflammation. After LPS-injection, the lungs were harvested to assess leukocyte infiltration, cytokine and chemokine production, ERK-MAPK activation and immunopathology. For <i>ex</i><i>vivo</i> experiments, alveolar macrophages were harvested from untreated WT and <i>Spred-2^−/−</i> mice and stimulated with LPS. In <i>in</i><i>vitro</i> experiments, specific knock down of <i>Spred-2</i> by siRNA or overexpression of <i>Spred-2</i> by transfection with a plasmid encoding the <i>Spred-2</i> sense sequence was introduced into murine RAW264.7 macrophage cells or MLE-12 lung epithelial cells.</p><p>Results</p><p>LPS-induced acute lung inflammation was significantly exacerbated in <i>Spred-2^−/−</i> mice compared with WT mice, as indicated by the numbers of infiltrating leukocytes, levels of alveolar TNF-α, CXCL2 and CCL2 in a later phase, and lung pathology. U0126, a selective MEK/ERK inhibitor, reduced the augmented LPS-induced inflammation in <i>Spred-2^−/−</i> mice. Specific knock down of <i>Spred-2</i> augmented LPS-induced cytokine and chemokine responses in RAW264.7 cells and MLE-12 cells, whereas <i>Spred-2</i> overexpression decreased this response in RAW264.7 cells.</p><p>Conclusions</p><p>The ERK-MAPK pathway is involved in LPS-induced acute lung inflammation. Spred-2 controls the development of LPS-induced lung inflammation by negatively regulating the ERK-MAPK pathway. Thus, Spred-2 may represent a therapeutic target for the treatment of ALI.</p>