MicroRNA-21* regulates the prosurvival effect of GM-CSF on human eosinophils

Eosinophils are the principal effector cells of allergic inflammation, and hematopoietic cytokine granulocyte macrophage colony-stimulating factor (GM-CSF) is the primary cytokine that activates and prolongs the survival of eosinophils in local inflammatory sites by mediating anti-apoptotic activity in allergic inflammation. To investigate the immunopathological role of microRNA (miRNA) in allergic inflammation, we elucidated the regulatory mechanisms of miRNA on the GM-CSF-mediated in vitro survival in eosinophils. Eosinophils were purified from fresh human peripheral blood buffy coat fraction obtained from adult volunteer using microbead magnetic cell sorting. The apoptosis, viability and phosphorylation of extracellular signal-regulated kinase (ERK) were assessed by flow cytometry, and the expression of miRNA was analyzed using Agilent Human miRNA Microarray with Human miRNA Microarray Version 3 and real time RT-PCR. We have confirmed the increased in vitro viability of GM-CSF-treated eosinophils and upregulated expression of miRNA-21* (miR-21*), a complementary miRNA of miR-21, in GM-CSF-treated eosinophils. The transfection of pre-miR miR-21* precursor molecule could up-regulate the miR-21* expression, subsequently enhance the GM-CSF-activated ERK pathway and reverse the apoptosis of eosinophils, while anti-miR-21* inhibitor could down-regulate the miR-21* expression, suppress the GM-CSF-activated ERK pathway and enhance the apoptosis. Our results should shed light on the potential immunopathological role of miRNA-21* regulating the in vitro apoptosis of eosinophils and development of novel molecular treatment of allergic inflammation.