199: Beta-glucan inducible microRNAs negatively regulate inflammatory response

Abstract

Beta-glucan is key structural component of yeast cell wall. Although the inflammatory response and signaling events following beta-glucan receptor dectin-1 engagement have been relatively well described, the effect of beta-glucans on leukocyte microRNA expression has not been previously characterized in detail. We performed microRNA expression array using primary human macrophages stimulated with beta-glucan Curdlan. After qPCR validation we identified that beta-glucan increased the expression of miR-29b1-5p, miR-132, miR146a, miR-155 and miR-212. In follow-up experiments using various microbial ligands, we observed that miR29b1-5p, miR-132 and miR-212 were specifically induced by beta-glucans while the well characterized inflammatory miR-146a and miR-155 were induced by all stimuli. The sequences of beta-glucan inducible microRNAs are conserved in both human and mouse. To gain in vivo insight into beta-glucan inducible microRNAs we used mouse beta-glucan inhalation model and noticed that the beta-glucan microRNAs were also up-regulated in vivo in mouse lung leukocytes. Moreover, experiments using dectin-1 knockout mice revealed that microRNA expression was dectin-1 dependent. Bioinformatic analysis of microRNA target proteins suggested that beta-glucan inducible microRNAs might regulate inflammatory signaling events. Our functional in vitro experiments revealed that beta-glucan inducible miRNAs act as negative regulators of immune response. More specifically, overexpression of miR-29b1-5p, miR-132 or miR-155 reduced beta-glucan-induced production of IL-1beta and TNF-alpha, while inhibition of these microRNAs during beta-glucan stimulation augmented cytokine response. Although the exact molecular mechanisms are still under investigation, our preliminary findings suggest that modulation of inflammatory response could act via SIRT1, which has been shown to regulate multiple aspects of inflammatory response. In conclusion we show here that beta-glucan induces expression of both unique and common inflammatory microRNAs and that these microRNAs form a negative feedback loop that limits extensive inflammatory response.