Immature Dendritic Cell-Derived Exosomes Rescue Septic Animals Via Milk Fat Globule Epidermal Growth Factor VIII

Abstract

Sepsis, a highly lethal systemic inflammatory syndrome, is associated with increases of proinflammatory cytokines (e.g., TNF-α, HMGB1) and the accumulation of apoptotic cells that have the potential to be detrimental. Depending on the timing and tissue, prevention of apoptosis in sepsis is beneficial; however, thwarting the development of secondary necrosis through the active removal of apoptotic cells by phagocytosis may offer a novel anti-sepsis therapy. Immature dendritic cells (IDCs) release exosomes that contain milk fat globule EGF factor VIII (MFGE8), a protein required to opsonize apoptotic cells for phagocytosis. In an experimental sepsis model using cecal ligation and puncture, we found that MFGE8 levels decreased in the spleen and blood, which was associated with impaired apoptotic cell clearance. Administration of IDC-derived exosomes promoted phagocytosis of apoptotic cells and significantly reduced mortality. Treatment with recombinant MFGE8 was equally protective, whereas MFGE8-deficient mice suffered from increased mortality. IDC exosomes also attenuated the release of proinflammatory cytokines in septic rats. Liberation of HMGB1, a nuclear protein that contributes to inflammation upon release from unengulfed apoptotic cells, was prevented by MFGE8-mediated phagocytosis in vitro. We conclude that IDC-derived exosomes attenuate the acute systemic inflammatory response in sepsis by enhancing apoptotic cell clearance via MFGE8.

Milk Fat Globule-EGF Factor VIII in Sepsis and Ischemia-Reperfusion Injury

“…The blood level also was decreased by 45%, indicating the systemic scale of MFG-E8 depletion under septic condition (36). We also showed that LPS from Gramnegative bacteria, which play a pivotal role for the pathogenesis of CLP sepsis, downregulate this protein production from cultured RAW 264.7 macrophages (murine macrophage cell line) and peritoneal macrophages in vitro (31,35).…”

“…Besides LPS-CD14-TLR4 pathway, sepsis-derived apoptosis of immune cells as a source of MFG-E8 is suggested to be responsible for the depletion of MFG-E8 in sepsis (36). It also is reported that MFG-E8 is expressed constitutively in intestinal lamina propria macrophages of mice and CLP sepsis downregulates MFG-E8 production (10).…”

“…Then we developed a novel phagocytosis assay using pHrodo succinimidyl ester-labeled apoptotic lymphocytes as targets and tissue macrophages as phagocytes, which is quick and reliable to evaluate the internalization of apoptotic cells, and is able to clearly distinguish the engulfment, rather than the attachment, of apoptotic cells by phagocytes (64). Using this method, the decreased phagocytic activity of isolated splenic and peritoneal macrophages was reconfirmed in CLP sepsis models (34,36).…”

“…The MFG-E8 production from macrophages is increased by granulocyte/monocyte colony-stimulating factor (27,29) and fractalkine (CX 3 CL1) (30,31). Furthermore, it is reported that MFG-E8 expression, which is evaluated in human and animal models, is downregulated in some disease conditions such as autoimmune disease (14), Alzheimer disease (32), atherosclerosis (33), acute colitis (20), sepsis (10,31,(34)(35)(36) and I/R injury (37,38). However, in contrast, MFG-E8 is highly expressed in systemic lupus erythematosus (39), lung fibrosis (40), breast cancer (19) and melanoma (41).…”

The modulation of co-stimulatory molecules by circulating exosomes in primary biliary cirrhosis

“…Importantly, exosomes from a variety of cell populations can mediate either immune activation or immune suppression based on the individual immunological microenvironment. [34][35][36][37] In autoimmunity, it has also been suggested that exosomes play a role in the chronic inflammatory response and that the cellular origin of exosomes will differentially influence the immune response in autoimmune disease. 6,38,39 Our data are important because they emphasize that co-stimulatory molecules play a pivotal role in APC-mediated immune responses, particularly T-cell activation and proliferation.…”