Loss of miR-146a skews the dendritic cell milieu in favor of CD8a+CD103+ cross-presenting migratory dendritic cells and reduces production of IL-27

Abstract

Abstract miR-146a is a micro-RNA that acts on transcripts upregulated in response to LPS induced TLR4 signaling. Activation of TLR4 results in maturation and survival of dendritic cells (DCs) to activate T cells in the spleen. Interestingly, little is known how miR-146a regulates DC phenotype/function and whether it has direct effects on the regulation of effector T cell function. To probe this question, we utilized a miR-146a knockout mouse model to study both DCs and lymphocytes. Splenocytes were analyzed by multi-parameter flow cytometry and we found that miR-146a mice had a greater population of cross-presenting CD8a+CD103+ DCs compared to wild-type mice. T cells from miR-146a mice had increased CD44 and CD69 expression, and decreased CD62L expression. Bone marrow derived DCs (BMDCs) were sorted (via multi-parameter flow cytometry) and subjected to RNA isolation and transcript analysis. BMDCs lacking miR-146a had 2.5-fold higher IL1R2 and 1.3-fold higher STAT1 transcript levels in addition to 13 increased genes. Supernatants from control and miR-146a knockout BMDCs were analyzed in vitro for a cytokine profile. In the presence of LPS, miR-146a knockout BMDCs had decreased IL-27 protein concentration compared to control mice. Our data indicate that the lack of miR-146a results in a skewing of DC subsets to favor CD8a+CD103+ DCs who are known to excel at cross-presentation and migrate through tissues. RNA transcript analysis suggests spontaneous maturation of the DCs from miR-146a knockout mice. IL-27 signaling in DCs has been shown to limit TH1 responses in mice. Our data suggest that miR-146a is important for regulation of IL-27 signaling in DCs. We are now using a collagen induced arthritis model to further understand the role of miR-146a in DCs.