All-Trans Retinoic Acid Promotes M2 Macrophage Polarization in Vitro by Activating the p38MAPK/STAT6 Signaling Pathway

Background: M2-type macrophages are inflammation-suppressing cells that are differentiated after induction by cytokines such as IL-4 or IL-13, which play an important regulatory role in inflammation and influence the regression of inflammation-related diseases. All-trans retinoic acid (ATRA) has an important role in suppressing immune-mediated inflammatory responses but the effect and underlying mechanism of ATRA on the polarization of M2 macrophages remains unclear. Methods: Macrophages were isolated from peritoneal wash fluid, and IL-4 (20ng/mL) was used to construct a m2-type macrophage polarization model. The model was incubated with different concentrations of ATRA (15 mu g/ml, 30 mu g/ml, 45 mu g/ml) for 24h, and pretreated macrophages with p38MAPK alpha inhibitor SB202190 (20 mu M). MTT, Trypan blue staining, Annexin V-PE/7-AAD staining, flow cytometry, real-time PCR and western blotting were used to investigate the effect and mechanism of ATRA on the polarization of M2 macrophages. Results: Compared with the IL-4 group, the proportion of F4/80(+)CD206(+) M2-type macrophages was significantly higher in the ATRA group (P<0.01). mRNA and protein expression levels of Arg-1, IL-10 and TGF-beta 1 were as significantly higher (P<0.01) in the ATRA group as phosphorylation levels of STAT6 and p38MAPK (P<0.01). After pretreatment with the addition of the inhibitor SB202190, M2-type macrophages proportion and their associated factors expression were significantly (P<0.01) reduced, as compared with those in the ATRA group, but they were comparable (P>0.05) with the IL-4 group. Conclusion: The combination of ATRA and IL-4 activated the p38MAPK/STAT6-signaling pathway to promote polarization of M2 macrophages.

Automated summary

ATRA promotes polarization of M2 macrophages by activating the p38MAPK/STAT6 signaling pathway.