M2b macrophage polarization accompanied with reduction of long noncoding RNA GAS5.

Macrophages (Mϕ) are highly plastic and change their functional phenotypes depending on microenvironmental signals. Recent studies have shown that microRNAs are involved in the polarization of Mϕ. In this study, we demonstrated that the phenotype of M2bMϕ [CCL1(+) IL-10(+) LIGHT(+)] switches to other phenotypes with interchangeability attained through the increased expression of growth arrest-specific 5 RNA (GAS5 RNA), a long noncoding RNA. GAS5 RNA has been described as a silencer of the CCL1 gene. Various phenotypes of Mϕ were prepared from bone marrow-derived Mϕ (BMDMϕ) after stimulation with IFNγ [M(IFNγ)/M1Mϕ], IL-4 [M(IL-4)/M2aMϕ], LPS and immobilized IgG [M(LPS + IC)/M2bMϕ], and IL-10 [M(IL-10)/M2cMϕ]. BMDMϕ cultured with medium [M(no)/quiescent Mϕ] were used as a control. As compared to Μ(no), M(IFNγ), M(IL-4) and M(IL-10), the reduced level of GAS5 RNA was shown in M(LPS + IC). CCL1 and LIGHT mRNAs (typical biomarkers of M2bMϕ) were not expressed by M(LPS + IC) transduced with a GAS5 gene using lentiviral vector. The reduction of GAS5 RNA in M(LPS + IC) was mediated by the activation of nonsense-mediated RNA decay (NMD) pathway. BMDMϕ overexpressed with GAS5 RNA after GAS5 gene transduction did not polarize to M2bMϕ even though they were stimulated with LPS and IC in combination. These results indicate that the reduction of GAS5 RNA influenced by the NMD pathway activation leads to the Mϕ polarization stimulated with LPS and IC in combination.