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4ß1 Integrin Interactions Regulate Metalloproteinase-9 Expression in Steatotic Liver Ischemia and Reperfusion Injury
From the Dumont-University of California, Los Angeles (UCLA) Transplant Center, Division of Liver and Pancreas Transplantation, Department of Surgery, David Geffen School of Medicine at UCLA, Los Angeles, California
Ischemia/reperfusion injury is a major cause of the highly dysfunctional rate observed in marginal steatotic orthotopic liver transplantation. In this study, we document that the interactions between fibronectin, a key extracellular matrix protein, and its integrin receptor
4ß1, expressed on leukocytes, specifically up-regulated the expression and activation of metalloproteinase-9 (MMP-9, gelatinase B) in a well-established steatotic rat liver model of ex vivo ice-cold ischemia followed by isotransplantation. The presence of the active form of MMP-9 was accompanied by massive intragraft leukocyte infiltration, high levels of proinflammatory cytokines, such as interleukin-1ß and tumor necrosis factor-
, and impaired liver function. Interestingly, MMP-9 activity in steatotic liver grafts was, to a certain extent, independent of the expression of its natural inhibitor, the tissue inhibitor of metalloproteinases-1. Moreover, the blockade of fibronectin-
4ß1-integrin interactions inhibited the expression/activation of MMP-9 in steatotic orthotopic liver transplantations without significantly affecting the expression of metalloproteinase-2 (MMP-2, gelatinase A). Finally, we identified T lymphocytes and monocytes/macrophages as major sources of MMP-9 in steatotic liver grafts. Hence, these findings reveal a novel aspect of the function of fibronectin-
4ß1 integrin interactions that holds significance for the successful use of marginal steatotic livers in transplantation.
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