TNF-alpha inhibits macrophage clearance of apoptotic cells via cytosolic phospholipase A2 and oxidant-dependent mechanisms.
Removal of apoptotic cells from inflammatory sites is an important step in the resolution of inflammation. Both murine and human macrophages stimulated with TNF-alpha or directly administered arachidonic acid showed an impaired ability to ingest apoptotic cells (efferocytosis). The inhibition was shown to be due to generation of reactive oxygen species, was blocked with a superoxide dismutase mimetic, MnTBAP, and was mimicked by direct addition of H2O2. To determine the mechanism of TNF-alpha-stimulated oxidant production, bone marrow-derived macrophages from gp91(phox)-deficient mice were examined but shown to still produce oxidants and exhibit defective apoptotic cell uptake. In contrast, a specific cytosolic phospholipase A2 inhibitor blocked the oxidant production and reversed the inhibited uptake. The suppressive effect of endogenous or exogenous oxidants on efferocytosis was mediated through activation of the GTPase, Rho. It was reversed in macrophages pretreated with C3 transferase to inactivate Rho or with an inhibitor of Rho kinase. During maturation of human monocyte-derived macrophages, only mature cells exhibited TNF-alpha-induced suppression of apoptotic cell clearance. The resistance of immature macrophages to such inhibition was shown to result not from defective generation of oxidants, but rather, from lack of response of these cells to the oxidants. Overall, the data suggest that macrophages in a TNF-alpha- and oxidant-rich inflammatory environment are less able to remove apoptotic cells and, thereby, may contribute to the local intensity of the inflammatory response.
McPhillips
Kathleen
K
Department of Pathology, University of Colorado Health Sciences Center, Denver, CO 80262, USA.
Janssen
William J
WJ
Ghosh
Moumita
M
Byrne
Aideen
A
Gardai
Shyra
S
Remigio
Linda
L
Bratton
Donna L
DL
Kang
Jihee L
JL
Henson
Peter
P
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000276:immunology*; D016718:Arachidonic Acid / Q000378:metabolism / Q000494:pharmacology; D002478:Cells, Cultured; D054513:Group IV Phospholipases A2; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects* / Q000201:enzymology / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics; D008665:Metalloporphyrins / Q000494:pharmacology; D051379:Mice; D009000:Monocytes / Q000187:drug effects / Q000276:immunology; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics; D016877:Oxidants / Q000378:metabolism* / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D017382:Reactive Oxygen Species / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000187:drug effects / Q000378:metabolism; D047889:Receptors, Tumor Necrosis Factor, Type II / Q000187:drug effects / Q000378:metabolism; D013482:Superoxide Dismutase / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D020741:rho GTP-Binding Proteins / Q000378:metabolism
D000975:Antioxidants; D008562:Membrane Glycoproteins; D008665:Metalloporphyrins; D016877:Oxidants; C516390:Pla2g4a protein, mouse; D017382:Reactive Oxygen Species; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D014409:Tumor Necrosis Factor-alpha; C097284:manganese(III)-tetrakis(4-benzoic acid)porphyrin; D016718:Arachidonic Acid; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D010741:Phospholipases A; D054513:Group IV Phospholipases A2; C516389:PLA2G4A protein, human; D054467:Phospholipases A2; D020741:rho GTP-Binding Proteins