Macrophage tumor necrosis factor-alpha induces epithelial expression of granulocyte-macrophage colony-stimulating factor: impact on alveolar epithelial repair.
BACKGROUND
Resident alveolar macrophages have been attributed a crucial role in host defense toward pulmonary infection. Their contribution to alveolar repair processes, however, remains elusive.


OBJECTIVE
We investigated whether activated resident alveolar macrophages contribute to alveolar epithelial repair on lipopolysaccharide (LPS) challenge in vitro and in vivo and analyzed the molecular interaction pathways involved.


METHODS
We evaluated macrophage-epithelial cross-talk mediators for epithelial cell proliferation in an in vitro coculture system and an in vivo model of LPS-induced acute lung injury comparing wild-type, granulocyte-macrophage colony-stimulating factor (GM-CSF)-deficient (GM(-/-)), and human SPC-GM mice (GM(-/-) mice expressing an SPC-promotor-regulated GM-CSF transgene).


RESULTS
Using reverse transcription-polymerase chain reaction and ELISA we showed that LPS-activated alveolar macrophages stimulated alveolar epithelial cells (AEC) to express growth factors, particularly GM-CSF, in coculture. Antibody neutralization experiments revealed epithelial GM-CSF expression to be macrophage tumor necrosis factor (TNF)-alpha dependent. GM-CSF elicited proliferative signaling in AEC via autocrine stimulation. Notably, macrophage TNF-alpha induced epithelial proliferation in wild-type but not in GM-CSF-deficient AEC as shown by [(3)H]-thymidine incorporation and cell counting. Moreover, intraalveolar TNF-alpha neutralization impaired AEC proliferation in LPS-injured mice, as investigated by flow cytometric Ki-67 staining. Additionally, GM-CSF-deficient mice displayed reduced AEC proliferation and sustained alveolar barrier dysfunction on LPS treatment compared with wild-type mice.


CONCLUSIONS
Collectively, these findings indicate that TNF-alpha released from activated resident alveolar macrophages induces epithelial GM-CSF expression, which in turn initiates AEC proliferation and contributes to restoring alveolar barrier function.
Cakarova
Lidija
L
University of Giessen Lung Center, Department of Internal Medicine II, Klinikstr. 36, D-35392 Giessen, Germany.
Marsh
Leigh M
LM
Wilhelm
Jochen
J
Mayer
Konstantin
K
Grimminger
Friedrich
F
Seeger
Werner
W
Lohmeyer
Juergen
J
Herold
Susanne
S
D000818:Animals; D015153:Blotting, Western; D004797:Enzyme-Linked Immunosorbent Assay; D004847:Epithelial Cells / Q000276:immunology / Q000473:pathology; D005434:Flow Cytometry; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000096:biosynthesis* / Q000276:immunology; D066298:In Vitro Techniques; D018836:Inflammation Mediators / Q000276:immunology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008168:Lung / Q000276:immunology / Q000473:pathology; D055370:Lung Injury / Q000276:immunology* / Q000473:pathology; D008262:Macrophage Activation / Q000276:immunology*; D016676:Macrophages, Alveolar / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology*
D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D016178:Granulocyte-Macrophage Colony-Stimulating Factor