MicroRNA-Mediated Down-Regulation of M-CSF Receptor Contributes to Maturation of Mouse Monocyte-Derived Dendritic Cells

Joey Riepsaame,Berlinda J H Den Broeder,Joris Pothof,Pieter J M Leenen,Adri Van Oudenaren,Wilfred F J Van Ijcken

doi:10.3389/fimmu.2013.00353

Abstract

Dendritic cell (DC) maturation is a tightly regulated process that requires coordinated and timed developmental cues. Here we investigate whether microRNAs are involved in this process. We identify microRNAs in mouse GM-CSF-generated, monocyte-related DC (GM-DC) that are differentially expressed during both spontaneous and LPS-induced maturation and characterize M-CSF receptor (M-CSFR), encoded by the Csf1r gene, as a key target for microRNA-mediated regulation in the final step toward mature DC. MicroRNA-22, -34a, and -155 are up-regulated in mature MHCIIhi CD86hi DC and mediate Csf1r mRNA and protein down-regulation. Experimental inhibition of Csf1r-targeting microRNAs in vitro results not only in sustained high level M-CSFR protein expression but also in impaired DC maturation upon stimulation by LPS. Accordingly, over-expression of Csf1r in GM-DC inhibits terminal differentiation. Taken together, these results show that developmentally regulated microRNAs control Csf1r expression, supplementing previously identified mechanisms that regulate its transcription and protein surface expression. Furthermore, our data indicate a novel function for Csf1r in mouse monocyte-derived DC, showing that down-regulation of M-CSFR expression is essential for final DC maturation.

Highlights

Dendritic cells (DC) constitute a heterogeneous population of leukocytes that interconnect the innate and the adaptive immune response, in particular through their capacity to activate naïve T lymphocytes [1]
Flt3L drives the development of various DC populations, in particular plasmacytoid and conventional DC, in peripheral tissues and lymphoid organs in the steady-state [3], whereas GM-CSF is important in generating inflammatory, monocyte-derived TNF/iNOS-producing DC (TipDC) [1, 4]
MiR-200b and -215 levels were down-regulated approximately threefold in both mature DC (mDC) and LPS-mDC compared to Immature DC (iDC). These results demonstrate that microRNA levels change during DC development in vitro and that iDC and mDC are characterized by distinct microRNA expression profiles

Summary

Introduction

Dendritic cells (DC) constitute a heterogeneous population of leukocytes that interconnect the innate and the adaptive immune response, in particular through their capacity to activate naïve T lymphocytes [1]. Flt3L drives the development of various DC populations, in particular plasmacytoid and conventional DC (cDC), in peripheral tissues and lymphoid organs in the steady-state [3], whereas GM-CSF is important in generating inflammatory, monocyte-derived TNF/iNOS-producing DC (TipDC) [1, 4]. M-CSF has been shown to induce plasmacytoid and cDC development, in addition to development of macrophages, from BM cells of normal and Flt3L-knock out mice [10, 11]. These observations underline a critical role of M-CSF signaling in the development of several DC populations

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Conclusion