Maturation-induced down-regulation of MFG-E8 impairs apoptotic cell clearance and enhances endotoxin response.
In sepsis, phagocytosis and the killing of bacteria by phagocytes are important. Similarly, the clearance of accumulating apoptotic cells is critical in maintaining normal immunity. Upon maturation, peritoneal macrophages (PM) become a major source of proinflammatory cytokines, while losing their efficacy of phagocytosis. However, the underlying mechanism remains unknown. Here we investigated the differential effects of apoptotic thymocytes (AoTC) on TNF-alpha release in immature thioglycolate-elicited PM (TGPM) and mature resident PM (RPM) in vitro by culturing them with or without AoTC and/or LPS. MFG-E8 expression was assessed using Western blotting and the ability to engulf AoTC was determined histologically. Cytokine secretion was measured by ELISA. MAP kinase phosphorylation was assessed using Western blotting. Mature RPM express <50% of TGPM MFG-E8 levels and have a 30% lower capacity to clear AoTC. The proinflammatory response (TNF-alpha release) to LPS is 5 times higher, and the capability to phagocytose is decreased along with further down-regulation of MFG-E8 after LPS-stimulation. RPMs also lack phagocytosis-induced inhibition of TNF-alpha release after LPS stimulation. LPS-induced phosphorylation of ERK1/2, p38 and JNK is more enhanced in RPM compared to TGPM. MFG-E8-mediated apoptotic cell phagocytosis results in an inhibition of MAPK and NFkappaB signaling pathways. Differential MAPK activation may play a role in the enhanced LPS responsiveness of RPM and the lack of MFG-E8 impedes post-phagocytic suppression of LPS-response through the inhibition of those signaling pathways. These results provide a potential mechanistic insight into the benefit of promoting apoptotic cell clearance via MFG-E8 under inflammatory conditions.
Miksa
Michael
M
Center for Immunology and Inflammation, The Feinstein Institute for Medical Research and Department of Surgery, North Shore University Hospital and Long Island Jewish Medical Center, Manhasset, NY 11030, USA.
Amin
Dhruv
D
Wu
Rongqian
R
Jacob
Asha
A
Zhou
Mian
M
Dong
Weifeng
W
Yang
Weng-Lang
WL
Ravikumar
Thanjavur S
TS
Wang
Ping
P
D000704:Analysis of Variance; D000818:Animals; D000954:Antigens, Surface; D017209:Apoptosis; D015153:Blotting, Western; D015536:Down-Regulation; D007249:Inflammation / Q000139:chemically induced; D007274:Injections, Intraperitoneal; D008070:Lipopolysaccharides / Q000633:toxicity*; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000378:metabolism*; D008894:Milk Proteins / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010587:Phagocytosis; D051381:Rats; D015398:Signal Transduction; D013864:Thioglycolates / Q000008:administration & dosage; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D000954:Antigens, Surface; D008070:Lipopolysaccharides; C499941:MFGE8 protein, rat; D008894:Milk Proteins; D013864:Thioglycolates; D014409:Tumor Necrosis Factor-alpha; C482199:lipopolysaccharide, E coli O55-B5; D020928:Mitogen-Activated Protein Kinases