MiR-222 stimulates M2b macrophage polarization in severely burned mice through the degradation of long noncoding RNA GAS5

Abstract

Abstract M2bMφ have been characterized as cells responsible for the increased susceptibility of severely burned mice to various opportunistic infections. We have previously demonstrated that a long noncoding RNA GAS5 is not expressed by M2bMφ, significantly. This RNA is involved in CCL1 gene silencing, and CCL1 is essential for the prolongation of M2bMφ. In this study, the mechanism involved in the reduction of a GAS5 level in M2bMφ was investigated. Mφ were isolated from the mesenteric lymph nodes of mice 1–15 days after severe burn injury (3rd degree, 25% TBSA burn). The level of phosphorylated UPF1 (pUPF1), a marker of the nonsense-mediated RNA decay (NMD) pathway, was determined in various Mφ preparations by Western blotting. In some experiments, these Mφ were transfected with miR-222 mimic, and tested for the GAS5 RNA and CCL1 mRNA levels. miR-222 has been shown to directly binds to GAS5. In the results, the levels of pUPF1 and miR-222 were increased in Mφ from mice 10–15 days after burn injury. These Mφ did not express GAS5 RNA and expressed CCL1 mRNA. The GAS5 reduction was also demonstrated in normal mouse Mφ transfected with miR-222, but not in the same Mφ treated with an inhibitor of the NMD pathway. M2bMφ were not demonstrated in severely burned mice injected with an miR-222 inhibitor. These results suggest that, through the reduction of long noncoding RNA GAS5, miR-222 appeared in Mφ of severely burned mice stimulates the M2bMφ polarization.