MicroRNA Regulation of Neutrophil Function

Neutrophils are significant players in both acute and chronic inflammatory conditions, and function in infectious and autoimmune ailments. MicroRNAs regulate homeostasis in health and disease by fine tuning the expression of a network of genes through post transcriptional regulation. Many microRNAs are expressed in restricted tissues, regulated by physiological conditions such as stress and disease, and are emerging as mediators for intercellular communication that shape the tissue environments. MicroRNA profiles have been recently utilized as biomarkers for diagnosis and prognostic purposes for their stability in plasma and significant correlation with the disease progress. In addition, several microRNAs are in clinical trials for infectious diseases, cardiovascular disorders and cancer. As for neutrophil biology, microRNAs that regulate hematopoiesis and neutrophil development are well known. However, only a few microRNAs are characterized in the context of neutrophil migration and activation by loss of function studies either in mice or in cell culture. In this work we characterize the role of total microRNA regulation on neutrophil function through whole body and neutrophil specific Dicer1 knockout, and identify a microRNA regulator of neutrophil motility. MiR-722 downregulates the transcript level of rac2 through binding to a seed match in the rac2 3'UTR. Furthermore, miR-722 over-expressing larvae display improved outcomes in both sterile and bacterial systemic models. Finally, the miR-722 mimics protect zebrafish from lethal LPS challenge, providing evidence and mechanism of an anti-inflammatory microRNA that restrains detrimental systemic inflammation. We further investigated the role of the inflammatory response in an ischemia-reperfusion model. Extensive future work is required, especially in animal models, to illustrate the pivotal and complex microRNA mediated regulatory network in neutrophils, which is expected to provide the foundation for highly selective microRNA based therapy to control neutrophil behavior in infection and inflammatory disorders