The striking divergence of ABCB1 mRNA expression and P-glycoprotein protein levels in M1 and M2 macrophages associates with the microRNA miR-21-3p, a regulator of "RNA binding protein, mRNA processing factor".

Macrophages are important hosts for intracellular pathogens. Drug transporters modulate the uptake and thus efficacy of antibiotics in macrophages. However, there is only few data comparing drug transporter expression levels in polarized pro-inflammatory M1 to anti-inflammatory M2 macrophages. THP-1 monocytes were differentiated with 200 nM phorbol 12-myristate 13-acetate for 72 h and subsequently polarized to the M1 (50 ng/mL lipopolysaccharide, 20 ng/mL interferon-gamma; 48 h) or the M2 (20 ng/mL interleukin-4, interleukin-13; 48 h) phenotype. Using a quantitative polymerase-chain reaction array, mRNA levels of 84 drug transporters were evaluated. Western blotting was used to assess P-glycoprotein (P-gp, encoded by ABCB1) protein expression. Finally, expression of 46 P-gp-regulating microRNA species was evaluated as well. Compared to M2 macrophages, seven transporter genes were lower expressed in M1 cells (e.g., ABCG2 threefold; SLCO2B1 7.5-fold) and 21 genes were higher expressed. ABCB1 mRNA was in fact up-regulated threefold, but 2.4-fold lower at the protein level. This discrepancy associated with a 5.5-fold higher expression of miR-21-3p and a 128-fold lower expression of miR-145-3p. In conclusion, M1 and M2 macrophages differ by drug transporter transcriptomics. The discrepancy of ABCB1 mRNA and P-gp protein levels in M1 macrophages associates with the high abundance of miR-21-3p, a regulator of "RNA binding protein, mRNA processing factor."