Studies involving genome-wide association and microarray approaches have led to the identification of orosomucoid 1-like 3 (ORMDL3) as a candidate gene for susceptibility to asthma. Apart from very recent studies demonstrating that ORMDL3 functions as a mediator of sphingolipid homeostasis in yeast and a regulator of endoplasmic reticulum-mediated Ca2+ signaling and cellular stress, very little is known regarding the role played by this protein in the pathogenesis of asthma. Allergic airway inflammation including asthma is characterized by infiltration of the airways by a large number of inflammatory cells, airway hyperresponsiveness and remodeling. Eosinophils (Eos) are one of the most proinflammatory granulocytes that contribute to the pathogenesis and exacerbation of the disease. We have, for the first time, demonstrated that Eos (murine and human) express ORMDL3 at the mRNA and protein level. Further, ORMDL3 expression in murine Eos was induced in response to changes in intracellular Ca2+ levels as well as exposure to mediators of allergic inflammation such as IL-3 (~10 fold) and eotaxin. Based on this observation, we hypothesize that ORMDL3 regulates Eos activation and potentially its adhesive function leading to increased trafficking of Eos in blood vessels and recruitment to inflamed lungs. Accordingly, in the current application, in Aim 1, we propose to evaluate the role of ORMDL3 in cellular trafficking events, such as cell rolling, adhesion and migration that involve Ca2+ mobilization, under conditions of blood flow in lung microvessels as a prelude to recruitment to the asthmatic airways. Using the technique of 2-color intravital video microscopy, we will examine the adhesive interaction of normal Eos versus Eos that have been rendered ORMDL3 deficient by gene silencing or Eos that over-express ORMDL3 within blood vessels of the mouse lung. In addition, recruitment of these Eos populations to the lungs in a model of allergic (cockroach antigen-induced) asthma will be evaluated. Since mediators of airway inflammation (e.g. IL-3 and eotaxin) were found to induce ORMDL3 expression in Eos, in Aim 2 we will evaluate regulation of ORMDL3 expression by cytokines and chemokines present at sites of inflammation such as IL-5, GMCSF, IL-13, IL-17, IL-23 and C5a in addition to IL-3 and eotaxin in further detail. The potential regulation of IL-3-induced ORMDL3 expression via a CD48- mediated pathway will also be investigated. Additionally, we will evaluate whether ORMDL3 expression is associated with Eos survival and Ca2+ mobilization and if ORMDL3 interacts with other intracellular Eos proteins. Lastly, we will ascertain whether Eos recruited to the airways express ORMDL3 using a mouse model of allergic inflammation. Importantly, we are attempting to explore the potential role of this relatively new protein in Eos, regarding which little is known. We anticipate that these studies will shed light on the functional role of Eos-expressed ORMDL3 with important implications on pathogenesis of asthma as well as meet the objectives of NIAID/NHLBI to understand, treat or prevent allergy and lung diseases.
Allergic airway inflammation including asthma affects an estimated 20 million people in the US alone. The current application will elucidate whether ORMDL3, a protein which is encoded by a gene recently identified as a potential risk factor for asthma and expressed by eosinophhils (a novel observation of this study), promotes adhesive interactions of eosinophils in blood vessels to enable their recruitment to the lungs during allergic inflammation. An understanding of how expression of ORMDL3 is regulated in eosinophils in response to specific signals such as mediators of allergic inflammation (cytokines and chemokines) or intracellular calcium levels might provide new approaches to block the function of this protein and thus reduce recruitment of eosinophils to the lungs leading to the likely alleviation of suffering associated with allergic inflammation including asthma.
|Ha, Sung Gil; Ge, Xiao Na; Bahaie, Nooshin S et al. (2013) ORMDL3 promotes eosinophil trafficking and activation via regulation of integrins and CD48. Nat Commun 4:2479|
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