Systemic characterization of macrophage phenotypes in allergic airway inflammation

Introduction: Macrophages are central players in lung pathology with both regulatory and effector properties. Besides activation toward the M1 subtype (classic activation), alternatively activated M2 macrophages have been implicated in pneumonia and allergy. We investigate the role of microRNAs in macrophage polarization-associated diseases. Here, we analyzed the systemic RNA phenotype of murine lung macrophages in allergic airway inflammation. We are establishing an in vitro model with bone-marrow-derived macrophages (BMMs) to mimick the transcriptome changes which we observed here.

Methods: Macrophages from the bronchoalveolar lavage fluid (BALF) and lung homogenate of mice with acute OVA-induced eosinophilic airway inflammation were sorted on the basis of the CD11 and SiglecF surface markers, and total RNA was analyzed subsequently. The transcriptome was investigated with Ingenuity Pathway Analysis to identify core regulatory units of the OVA-induced inflammation.

Results: Differential miRNA expression could be observed that seems to be tissue- and asthma dependent, as illustrated by principal component analysis (PCA). In the interstitial macrophage fraction, up-regulation of the M1-associated miR-155 – 5 p and down-regulation of the equally M1-associated miR-146a-5 p was observed, among others. On mRNA level, prominent markers of alternative macrophage activation were found to be up-regulated, such as Arginase (Arg1) and the IL4-induced Retnla (FIZZ1), CCL17 and Mgl2. In total, IL-4 and IL-13 were identified as the crucial cytokines that cause the OVA-induced transcriptome profile. We are reproducing these findings in vitro in IL-4 and Il-13 treated BMMs.

Discussion: In accordance with the TH2-skewed environment in eosinophilic airway inflammation, we could identify IL-4 and IL-13 as decisive for the activation of macrophages upon OVA-stimulation. We could partly reproduce this pattern by administration of IL-4 and IL-13 to BMMS. We aim to interfere with this polarization trajectory by manipulating key miRNAs that target genes which are central for OVA-induced macrophage activation, such as mafB and IRF4.