Semaphorin 3E Regulates the Response of Macrophages to Lipopolysaccharide-Induced Systemic Inflammation

Abstract

Semaphorin 3E (Sema3E) is a secreted protein that was initially discovered as a neuronal guidance cue. Recent evidence showed that Sema3E plays an essential role in regulating the activities of various immune cells. However, the exact role of Sema3E in macrophage function, particularly during inflammation, is not fully understood. We studied the impact of <i>Sema3E</i> gene deletion on macrophage function during the LPS-induced acute inflammatory response. We found that Sema3E-deficient (<i>Sema3e^-/-</i> ) mice were better protected from LPS-induced acute inflammation as exemplified by their superior clinical score and effective temperature control compared with their wild-type littermates. This superior control of inflammatory response in <i>Sema3e^-/-</i> mice was associated with significantly lower phosphorylation of ERK1/2, AKT, STAT3, and NF-κB, and a concomitant reduction in inducible NO synthase expression and production of TNF and IL-6 compared with their <i>Sema3e^+/+</i> littermates. <i>Sema3e^-/-</i> mice also contained significantly higher numbers of activated macrophages compared with their <i>Sema3e^+/+</i> littermates at both baselines and after LPS challenge. In vivo-specific deletion of the Sema3E high-affinity receptor, plexinD1, on macrophages led to the improvement in clinical disease following exposure to a lethal dose of LPS. Collectively, our data show that Sema3E plays an essential role in dampening the early inflammatory response to LPS by regulating macrophage function, suggesting an essential role of this pathway in macrophage inflammatory response.