Beneficial Effects of Chemokines in Liver

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Chemokines are low molecular-weight cytokines with a wide range of biological activities. Although initially characterized as leukocyte chemoattractants, chemokines are now recognized to influence many physiologic processes including organogenesis, tumor growth and metastasis, lymphocyte trafficking and wound healing. The two major processes governed by chemokines are cell migration and cell proliferation; recent data in liver, however, suggest that chemokines protect against acute forms of toxic injury. The cytoprotective role of chemokines has been putatively assigned to one subfamily of peptides designated CXC. The beneficial properties of CXC chemokines have not been fully characterized. Documenting the salutary effects of CXC chemokines toward liver cells and elucidating their mechanism of action are the primary objectives of this proposal. Our fundamental hypothesis is that CXC chemokines inhibit hepatocyte apoptosis. Experiments are designed to characterize this anti-apoptotic effect in vivo and in cell culture, using galactosamine and endotoxin as a model hepatotoxin. Particularly important are studies involving bone marrow chimeras between CXCR2 +/+ and CXCR2 -/- mice, which are necessary to distinguish the cytoprotective effects of chemokines toward hepatocytes in vivo from their activity as leukocyte chemoattractants. Studies in isolated hepatocytes are intended to document CXC chemokine receptor expression in hepatocytes, using real-time PCR, FACS, and monitoring of chemokine-induced signaling. Additional studies will focus on the mechanism by which chemokines prevent apoptosis. Findings to date point to activation of PI-3 kinase as a critical step in this process. Experiments will examine relevant anti- apoptotic consequences of PI-3 kinase activation, specifically phosphorylation of Akt, activation of NF-kB, and up-regulation of Bcl-xL. In sum, the proposed studies will provide a comprehensive view of the activity of CXC chemokines in liver. Uncovering a potential benefit of CXC chemokines is of critical importance, because neutralization of these compounds is being considered as a clinical approach to inflammatory diseases. If chemokines have significant cytoprotective effects, then anti-chemokine therapy may be complicated by unwanted side effects.