The effect of selenium on the autophagy of macrophage infected by Staphylococcus aureus.

Selenium can alleviate the inflammatory reaction infected by Staphylococcus aureus (S. aureus). However, the role of selenium on the autophagy in RAW264.7 macrophages infected by S. aureus has not been reported. The goal of this study was to clarify the effect of selenium on the autophagy and related inflammatory pathways (MAPK and NF-κB) in RAW264.7 macrophages infected by S. aureus. RAW264.7 macrophages were co-treated with Na2SeO3 and S. aureus. The expression of related inflammatory pathways (MAPK and NF-κB) and autophagy-related proteins were detected by Western blotting. The microtubule-binding protein light chain 3 (LC3) puncta were measured with immunofluorescence staining. The ultrastructure of RAW264.7 macrophages infected by S. aureus was detected by transmission electron microscope (TEM). And plate counting method was used to detect the proliferation of S. aureus in RAW264.7 macrophages. The results showed that the expression levels of LC3 II increased and the expression levels of p62 decreased after adding selenium, compared with S. aureus infection group. Compared with S. aureus infection group, the intracellular LC3 puncta and autophagic vesicles, autophagosomes, and autolysosomes increased with selenium supplementation. The number of S. aureus proliferation decreased with addition of selenium, compared with S. aureus infection group. Selenium could significantly inhibit the phosphorylation of MAPK and NF-κB signaling pathway key proteins, compared with S. aureus infection group. In summary, selenium could promote the autophagy in macrophages infected by S. aureus, alleviate the blockade of autophagic flow, depress the transcription of MAPK and NF-κB signaling pathways, and inhibit the proliferation of S. aureus in RAW264.7 macrophages.

Staphylococcus aureus induces autophagy in bovine mammary epithelial cells and the formation of autophagosomes facilitates intracellular replication of Staph. aureus.

Staphylococcus aureus is an important pathogen causing chronic and subclinical mastitis of cows. Autophagy is an important regulatory mechanism that participates in the elimination of invading pathogenic organisms. Here, we hypothesize that autophagy is involved in the process of Staph. aureus survival in bovine mammary epithelial cells (BMEC). In this study, we detected the expression of autophagy-related proteins during infection and assessed the effect of autophagosome formation and degradation on the proliferation of intracellular Staph. aureus. Infection with Staph. aureus increased the protein expression of microtubule-associated protein 1 light chain 3-II (MAP1LC3, also called LC3-II) and sequestosome-1 (SQSTM1, also called p62) in BMEC. After infection, the formation of the autophagosomes increased but the autophagosomes and lysosomes could not fuse normally to form autolysosomes. When the formation of the autophagosomes was enhanced or the degradation of the autolysosomes was inhibited, the number of Staph. aureus in the BMEC increased. However, the intracellular proliferation of Staph. aureus was slowed when formation of autophagosomes was inhibited. Therefore, autophagy was induced in BMEC challenged by Staph. aureus but the autophagic flux was obstructed. Inhibiting the formation of autophagosomes in BMEC facilitated the clearance of intracellular Staph. aureus, which may offer a new strategy for the treatment of mastitis in cows.