Abstract
Macrophages are polarized by various stimuli and produce inflammatory cytokines and reactive oxygen species (ROS). ROS are messengers that propagate inflammation. Conversely, selenium supplied by selenoprotein P (SeP) induces the expression of glutathione peroxidase (GPx), an antioxidant enzyme, and is involved in the termination of inflammation by ROS regulation. We aimed to elucidate the variations of selenium metabolism and its regulation in inflammatory macrophages.
We utilized SeP purified from human plasma and sodium selenite as selenium sources. Mouse macrophage RAW264.7 cells were polarized into an inflammatory state by lipopolysaccharide (LPS) stimuli.
Polarization to inflammatory macrophages suppressed SeP-induced GPx1/4 expression, and the levels of ApoER2 were also low. SeP accumulation was observed due to the inhibition of its degradation. The induction of GPx1/4 expression via sodium selenite treatment was also suppressed, suggesting that the intracellular selenium utilization is inhibited.
We focused on the role of nitric oxide (NO), which is induced in inflammatory macrophages. NO donor (DETA NONOate) stimuli of unpolarized RAW264.7 cells reproduced the reduction of GPx1/4. Through the aBPML assay, developed by our research group to detect selenocysteine (Sec)-specific modifications, we revealed that Sec within SeP is modified by NO. Furthermore, NO inhibited Sec lyase activity, as determined by using the lead complexation method.
These results suggest that selenium utilization is suppressed in inflammatory macrophages, with NO playing a crucial role as the mediator of selenium metabolic remodeling.
