The Role Of SH2-Bβ In Asthma Mediated By NGF

ObjectiveAsthma is one of the most common diseases and is characterized by airway obstruction, airway inflammation and increased airway responsiveness. Nerve growth factor (NGF) is increasingly recognized to play an important role in asthma. NGF regulates the airway inflammation, constractivity and hyperresponsiveness through direct and/or indirect effect on inflammation cells and the neurons in asthma , is a bridge connecting the airway inflammation with airway hyperresponsiveness. Our previous results confirmed that the expression of NGF is increased remarkably in the lower respiratory tract and viscerosensory afferent sites of the asthmatic guinea pigs. NGF upregulates the expression of TrkA , the contents of calcitonin gene related peptide (CGRP), Tumor necrosis factor— a(TNF — a) and interleukin— 1β(IL—1β). The intracellular signal transduction system mediated by TrkA might be one of the main routes for the involvement of NGF in the pathogenesis of asthma. SH2 — B is a downstream protein of TrkA, has multiple protein—protein interaction motifs, including an Src homology 2 (SH2) domain, a pleckstrin homology (PH) domain, multiple proline — rich regions, and numerous potential phosphorylation sites. Four isoforms of SH2 — B ( α,β,γ and δ) have been described to date. They are identical except for the short C— terminal portion after the SH2 domain. NGF stimulates the association of TrkA with SH2—B β and phosphorylate it. SH2—B β plays an important role in the neuron differenciation and survival mediated by NGF throughbinding with TrkA. Overexpression of SH2 — B |3 enhanced the tension and maintained long time of TrkA autophosphorylation, enhanced the TrkA signal. Moreover, SH2 —B (3 was identified as a JAK2 — interacting protein with one or more lower—affinity binding sites for JAK2. The interaction via this site(s) with inactive JAK2 seems likely to increase the local concentration of SH2 —B (3 around JAK2, thereby facilitating binding of the SH2 domain to ligand—activated JAK2. This would result in a more rapid and robust cellular response to hormones and cytokines that activate JAK2. SH2 —B (3 is an important intracellular mediator of NGF/ TrkA signaling in neurons and SH2 —B also associate with the high—affinity receptor immunoglobulin E(IgE)FceRIy subunit. This study evaluated the expression of SH2 — B(3 in the lower respiratory tract and viscer-osensory afferent sites of the murine asthma model. ( The bodies of sensory neurons of lower respiratory tract are located at nodose ganglion and C7 ~ T5 spinal ganglia and the central axons terminate at spinal dorsal horn and solitary nucleus). Whether SH2 —Bj3 is involved in TrkA signal mediated asthma? What is the effect of NGF on the expression of SH2 — BJ3? What is the effect of SH2 — Bj3 on airway resistance, the synthesis and release of the inflammation mediators in the murine asthma model. No reference was reported about these. Answer for these questions will make the machnism of asthma clear and provide evidence for novel treatment.MethodsAsthma was induced in BALB/c mice by exposure to chicken egg ovalbumin(OVA). By means of immunohistochemistry and Western blot to investigate the changes of SH2 — Bj3 immunoreactivity and the regulatory effect of NGF and dexamethasone in the lower respiratory tract and viscerosensory afferent sites of the murine asthma model. After inhibition of SH2—B|3,by means of ELISA to investigate the production of IL — 4 and IgE in the bronchoalveolar lavage fluid (BALF), serum and culturesupernant of spleen cells;by means of AniRes 2003 animal lungs function analysis system to investigate the changes of the airway resistance.Results1. Immunohistochemistry ,Western blot showed:The expression of SH2 —BJ3 was increased significantly in lower respiratory tract and visceral sensory afferent sites (C7 —T5 spinal ganglia and the corresponding posterior horn of the spinal cord) of the murine asthma model compared with the normal control group (p