Milk fat globule-EGF factor VIII in sepsis and ischemia-reperfusion injury

Abstract

Sepsis and ischemia-reperfusion (I/R) injury are among the leading causes of death in critically ill patients at the surgical intensive care unit setting. Both conditions are marked by the excessive inflammatory response which leads to a lethal disease complex such as acute lung injury, systemic inflammatory response syndrome and multiple organ dysfunction syndrome. Despite the advances in the understanding of the pathophysiology of those conditions, very little progress has been made toward therapeutic interventions. One of the key aspects of these conditions is the accumulation of apoptotic cells that have the potential to release toxic and proinflammatory contents due to secondary necrosis without appropriate clearance by phagocytes. Along with the prevention of apoptosis, that is reported to be beneficial in sepsis and I/R injury, thwarting the development of secondary necrosis through the active removal of apoptotic cells via phagocytosis may offer a novel therapy. Milk fat globule-EGF factor VIII (MFG-E8), which is mainly produced by macrophages and dendritic cells, is an opsonin for apoptotic cells and acts as a bridging protein between apoptotic cells and phagocytes. Recently, we have shown that MFG-E8 expression is decreased in experimental sepsis and I/R injury models. Exogenous administration of MFG-E8 attenuated the inflammatory response as well as tissue injury and mortality through the promotion of phagocytosis of apoptotic cells. In this review, we describe novel information available about the involvement of MFG-E8 in the pathophysiology of sepsis and I/R injury, and the therapeutic potential of exogenous MFG-E8 treatment for those conditions.

Figure 1

Schematic representation of pathophysiology of sepsis and I/R injury. Sepsis and I/R injury induce the increased apoptotic cell death in various cells and tissues and decrease apoptotic cell clearance by phagocytes, such as macrophages and dendritic cells, through the downregulation of milk fat globule-EGF factor VIII (MFG-E8). Apoptotic cells, without appropriate phagocytotic removal, have the potential to release toxic and proinflammatory contents due to secondary necrosis, and potentiate tissue injury and mortality. Administration of MFG-E8 enhances phagocytotic activity and therefore attenuates detrimental inflammation, thereby decreasing tissue injury and mortality.