Sphingomyelin Synthase 2 Deficiency Attenuates NFκB Activation

Abstract

Background— NFκB has long been regarded as a proatherogenic factor, mainly because of its regulation of many of the proinflammatory genes linked to atherosclerosis. Metabolism of sphingomyelin (SM) has been suggested to affect NFκB activation, but the mechanism is largely unknown. SMS2 regulates SM levels in cell plasma membrane and lipid rafts and has a potential to regulate NFκB activation. Methods and Results— To investigate the role of SMS2 in NFκB activation we used macrophages from SMS2 knockout (KO) mice and SMS2 siRNA-treated HEK 293 cells. We found that NFκB activation and its target gene expression are attenuated in macrophages from SMS2 KO mice in response to lipopolysaccharide (LPS) stimulation and in SMS2 siRNA- treated HEK 293 cells after tumor necrosis factor (TNF)–α simulation. In line with attenuated NFκB activation, we found that SMS2 deficiency substantially diminished the abundance of toll like receptor 4 (TLR4)-MD2 complex levels on the surface of macrophages after LPS stimulation, and SMS2 siRNA treatment reduced TNF-α-stimulated lipid raft recruitment of TNF receptor-1 (TNFR1) in HEK293 cells. SMS2 deficiency decreased the relative amounts of SM and diacylglycerol (DAG) and increased ceramide, suggesting multiple mechanisms for the decrease in NFκB activation. Conclusions— SMS2 is a modulator of NFκB activation, and thus it could play an important role in NFκB-mediated proatherogenic process.