Methionine sulfoxide reductase A protects against lipopolysaccharide-induced septic shock via negative regulation of the proinflammatory responses.

Methionine sulfoxide reductase A (MsrA) is a major antioxidant enzyme that specifically catalyzes the reduction of methionine S-sulfoxide. In this study, we used MsrA gene-knockout (MsrA-/- ) mice and bone marrow-derived macrophages (BMDMs) to investigate the role of MsrA in the regulation of inflammatory responses induced by lipopolysaccharide (LPS). MsrA-/- mice were more susceptible to LPS-induced lethal shock than wild-type (MsrA+/+ ) mice. Serum levels of the proinflammatory cytokines IL-6 and TNF-α induced by LPS were higher in MsrA-/- than in MsrA+/+ mice. MsrA deficiency in the BMDMs also increased the LPS-induced cytotoxicity as well as TNF-α level. Basal and LPS-induced reactive oxygen species (ROS) levels were higher in MsrA-/- than in MsrA+/+ BMDMs. Phosphorylation levels of p38, JNK, and ERK were higher in MsrA-/- than in MsrA+/+ BMDMs in response to LPS, suggesting that MsrA deficiency increases MAPK activation. Furthermore, MsrA deficiency increased the expression and nuclear translocation of NF-κB and the expression of inducible nitric oxide synthase, a target gene of NF-κB, in response to LPS. Taken together, our results suggest that MsrA protects against LPS-induced septic shock, and negatively regulates proinflammatory responses via inhibition of the ROS-MAPK-NF-κB signaling pathways.