Control of the redox environment at the cell surface regulates critical cellular functions, including cell-cell recognition, cell adhesion and cell migration. We have found that galectin-9 regulates migration of specific types of leukocytes, Th2 cells and eosinophils, through extracellular matrix. Galectin-9 binds to the thioreductase Protein Disulfide Isomerase (PDI) on surface of T cells and retains the enzyme on the cell surface, where the enzyme modifies cell surface proteins to increase the number of reduced thiols on these proteins. Cell surface PDI has been proposed to regulate migration of other types of leukocytes, such as platelets, through modification of integrins, implicating galectin-9 binding as a novel mechanism for regulating integrin-mediated T cell migration through extracellular matrix. The goals of this proposal are 1) to elucidate the mechanism by which galectin-9 regulates Th2 cell and eosinophil migration through extracellular matrix, and 2) to determine the role of galectin-9 in infiltration of Th2 cells and eosinophils into inflamed tissue in vivo, using a murine model of asthma. As galectin-9 is expressed by inflammatory cells, such as mast cells, dendritic cells, and eosinophils, as well as by endothelial cells and bronchial epithelial cells, and as Th2 cells and eosinophils are primary effector cells in asthma, we will determine the role of galectin-9 in an asthma model in vivo. Thus, in Aim1, we will identify all T cell and eosinophil glycoprotein receptors that bind galectin-9 by affinity chromatography and mass spectrometry. We will identify glycan ligands responsible for galectin-9 binding. We will investigate mechanisms by which galectin-9 binding to receptors enhances migration, examining receptor mobility on the cell surface, receptor conformation, and downstream gene expression.
In Aim 2, we will compare galectin-9 and galectin-1 null mice for responsiveness to inducers of airway inflammation and the array of effector cells and cytokines produced. We will determine the effect of exogenously administered galectin-9 on the extent of airway inflammation and recruitment of various effector cells. We will determine the function of leukocyte derived vs. tissue derived galectin-9 by examining airway inflammation in galectin-9 chimeric mice. Investigation of this new mechanism of leukocyte migration in asthma will identify new potential therapeutic approaches to ameliorating the lung inflammation and tissue damage in asthma. The hypothesis that galectin-9 regulates leukocyte function by regulating the cell surface redox environment is very novel, and asthma models are an entirely new area of research for our group. This project is high- risk but potentially very high yield, and thus appropriate for an R21 application.
Relevance to human health: Novel therapies are needed for asthma, a disease that affects approximately 10% of American children and adults. Asthma patients develop permanent tissue damage in their lungs, due to the chronic inflammation that occurs in this devastating disease. Preventing the inflammation in asthma, by blocking the ability of inflammatory cells to enter into and migrate through tissue, is a critical goal in the design of new therapeutic approaches. Our proposal investigates a previously unknown effect of a molecule produced in asthmatic lung that we have found promotes the migration of inflammatory cells. Understanding how this molecule triggers cell migration will allow development of new approaches to prevent the inflammation and subsequent tissue damage seen in the lungs of asthma patients.
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