Asthmatic responses are induced by environmental oxidants and allergens. A component of the asthmatic response is lung eosinophilia. Eosinophilia with asthma is a risk factor for mortality from chronic obstructive pulmonary disease. Infiltration of eosinophils into the lung in experimental asthma is dependent on the adhesion molecule vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. We have discovered a signal transduction pathway for VCAM-1. VCAM-1 activates endothelial cell NADPH oxidase production of low levels of reactive oxygen species (ROS). These ROS are required for localized endothelial cell retraction during VCAM- 1-dependent leukocyte migration in vitro. Thus, VCAM-1 is not simply a scaffold for leukocyte migration but activates an endothelial cell 'gate-like' function. We propose to examine VCAM-1-dependent signals in vivo and structure/function analysis of the cytoplasmic domain of VCAM-1. To test whether these VCAM-1 signals function in vivo, VCAM-1-dependent eosinophilia in experimental asthma will be examined. We hypothesize that in experimental asthma, endothelial cell gp91 phox is required for lung eosinophilia. To study the pathogenesis of asthma, we will use a NADPH oxidase deficient model consisting of chimeric mice with wild type leukocytes and gp91 phox deficient nonhematopoietic cells.
In specific aims 1 -2, we will determine whether ovalbumin-challenged chimeric mice exhibit alterations in lung 1) leukocyte infiltration, 2) expression of adhesion molecules, cytokines and chemokines that regulate eosinophilia, and 3) airway hyperresponsiveness. It will be determined whether endothelial cell gp91 phox-mediated changes in the lung inflammation are rescued using transgenic and adoptive cell transfer approaches. To examine the structure/function of the cytoplasmic domain of VCAM-1, VCAM-1 signals will be examined in vitro using wild type and chimeric VCAM-1 molecules. The 13 amino acid cytoplasmic domain of VCAM-1 is identical in mice and humans, suggesting that it has an important function. This domain contains potential phosphorylation sites. We hypothesize that ligand binding to VCAM-1 activates phosphorylation of the VCAM-1 cytoplasmic domain for stimulation of endothelial cell ROS generation and endothelial cell actin restructuring. Biochemical, pharmacologic and genetic approaches will be used to address this hypothesis.
In aim 3, it will be determined whether mutations in serines and tyrosine in the cytoplasmic domain of VCAM-1 alters VCAM-1 activation of NADPH oxidase.
In aim 4, it will be determined whether ligand binding to VCAM-1 activates phosphorylation of serines and tyrosine in the cytoplasmic domain of VCAM-1. The identification of mechanisms for VCAM-1 modulation of lung eosinophilia will provide new insights into regulation of lung eosinophilia as well as provide a basis towards proposing interventions in the VCAM-1-dependent eosinophilia component of asthma.
