Characterization and antagonism of cytokine-induced eosinophil priming

Abstract

Allergic asthma is an inflammatory disease characterized by bronchial hyper-responsiveness, airway inflammation, and reversible obstruction of the airways. In humans, cytokine activated eosinophils are thought to be important players in this process since they can release inflammatory mediators after cellular activation. Eosinophil differentiation, survival, and regulation of many of its cellular functions are regulated by interleukin (IL)-5, a T helper-2-derived cytokine. The IL-5 receptor (IL-5R) is expressed on the cell surface of eosinophils, and it is composed of an ?-chain that specifically binds IL-5 and a ?-chain, which is shared with the receptors for IL-3 and granulocyte–macrophage colony-stimulating factor (GM-CSF). An understanding of the molecular mechanisms regulating eosinophil production and function is essential for the development of molecules that can potentially be utilized in the treatment of asthma and other eosinophil-associated diseases. In this study, we firstly elucidate the mechanisms by which IL-5 regulates cell survival. We found that binding of IL-5 to its receptor results in phosphorylation of the phosphatidylinositol 3-kinase (PI3K) and its effector protein kinase B (PKB/c-Akt), which have been implicated as critical mediators of cytokine-induced survival signals in other cell types. We identified PI3K-PKB downstream targets that are inhibited by IL-5 stimulation, and proposed novel mechanism describing a role for the glycogen synthase kinase –3 (GSK-3) and ?-catenin in eosinophils. We also studied the effects of a novel IL-5R antagonist peptide finding that it specifically inhibits IL-5-mediated signaling pathways as well as eosinophils functions including chemotaxis and cell adhesion. Furthermore, we analyzed the use of protein transduction domains (PTD) to deliver proteins than can inhibit eosinophil intracellular signaling, and thereby eosinophil function. Our work contributes to the development of safe antagonists that specifically target IL-5 and eosinophil function. Alternative therapies are necessary for the treatment of asthmatic responses since the continued use of oral steroids could cause severe side effects.