Roles of N-glycans on neutrophil beta2 integrins in progression of acute lung injury - PROJECT SUMMARY
Acute lung injury (ALI) and its severe form, acute respiratory distress syndrome (ARDS), are the
common cause of respiratory failure. Despite all medical innovations, treatment of ARDS remains an unsolved
problem. Neutrophils are the first immune cells infiltrated into lungs during ALI, where neutrophils release
proteinases, cytokines, and oxidants to kill invading microbes, as well as to injure lungs. Clinical data and
animal models have proved that neutrophil recruitment and function influences the progression of ALI. Thus,
insights into the fine-tuned neutrophil recruitment and function may provide a novel approach for the treatment
of ALI.
Integrin b2 plays an important role in the regulation of neutrophil recruitment and neutrophil functions.
At inflamed sites, the intracellular signaling upregulates the integrin ligand-binding affinity, which allows ligands
to bind. Ligand binding to integrin b2 in the high-affinity state arrests neutrophils, a prerequisite step for
neutrophil recruitment, as well as causes integrin cluster formation (i.e. integrin valency) to enhance neutrophil
arrest. Currently, the intracellular signaling is the only approach to regulate the integrin ligand-binding
capability. The extracellular domain of integrin b2 is decorated with N-linked glycans. Yet, whether and how N-
glycans regulate the integrin b2-ligand binding has not been studied. In addition, the receptor for advanced
glycation end-products (RAGE) on alveolar epithelial cell type I (AT1) is a major mediator for inflammatory
responses in lungs. Integrin aMb2 on neutrophils is a ligand for RAGE, however, the role of the interaction of
integrin aMb2 with RAGE in the progression of inflammation in ALI is unknown.
Our preliminary studies found that removing N-glycans increased integrin aLb2-mediated neutrophil
adhesion and ligand binding-induced neutrophil cellular responses. Furthermore, removing sialic acids
increased aMb2 binding to RAGE. Thus, we hypothesize that 1) N-glycans on the extracellular domain prevent
integrin aLb2 to adopt the high-affinity state and/or limit the integrin cluster formation; and 2) reduced
glycosylation of integrin aMb2 facilitates its binding to RAGE that may increase inflammatory responses in
lungs. Thus, we propose two Aims to test the hypotheses: Aim 1: Determine if N-glycans on integrin aLb2
negatively regulate its ligand-binding affinity and valency; and Aim 2: Determine if glycans on aMb2 negatively
regulate RAGE-mediated inflammatory responses in AT1 cells. Integrin b2 containing mutations on N-glycan
bearing sites, a novel tool to measuring integrin affinity states, AT1 cells, and mouse models of ALI will be
used to test our hypotheses. Our proposed study will decipher the role of N-glycans on neutrophil b2 integrins
in the pathogenesis of ALI, which may lead to the development of a new therapy for ALI.
