Tumor necrosis factor-alpha and endothelial cells modulate Notch signaling in the bone marrow microenvironment during inflammation.
OBJECTIVE
Homeostasis of the hematopoietic compartment is challenged and maintained during conditions of stress by mechanisms that are poorly defined. To understand how the bone marrow (BM) microenvironment influences hematopoiesis, we explored the role of Notch signaling and BM endothelial cells in providing microenvironmental cues to hematopoietic cells in the presence of inflammatory stimuli.


METHODS
The human BM endothelial cell line (BMEC) and primary human BM endothelial cells were analyzed for expression of Notch ligands and the ability to expand hematopoietic progenitors in an in vitro coculture system. In vivo experiments were carried out to identify modulation of Notch signaling in BM endothelial and hematopoietic cells in mice challenged with tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS), or in Tie2-tmTNF-alpha transgenic mice characterized by constitutive TNF-alpha activation.


RESULTS
BM endothelial cells were found to express Jagged ligands and to greatly support progenitor's colony-forming ability. This effect was markedly decreased by Notch antagonists and augmented by increasing levels of Jagged2. Physiologic upregulation of Jagged2 expression on BMEC was observed upon TNF-alpha activation. Injection of TNF-alpha or LPS upregulated three- to fourfold Jagged2 expression on murine BM endothelial cells in vivo and resulted in increased Notch activation on murine hematopoietic stem/progenitor cells. Similarly, constitutive activation of endothelial cells in Tie2-tmTNF-alpha mice was characterized by increased expression of Jagged2 and by augmented Notch activation on hematopoietic stem/progenitor cells.


CONCLUSIONS
Our results provide the first evidence that BM endothelial cells promote expansion of hematopoietic progenitor cells by a Notch-dependent mechanism and that TNF-alpha and LPS can modulate the levels of Notch ligand expression and Notch activation in the BM microenvironment in vivo.
Fernandez
Luis
L
Center of Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass., USA.
Rodriguez
Sonia
S
Huang
Hui
H
Chora
Angelo
A
Fernandes
Jacquenilson
J
Mumaw
Christin
C
Cruz
Eugenia
E
Pollok
Karen
K
Cristina
Filipa
F
Price
Joanne E
JE
Ferkowicz
Michael J
MJ
Scadden
David T
DT
Clauss
Matthias
M
Cardoso
Angelo A
AA
Carlesso
Nadia
N
D000818:Animals; D001853:Bone Marrow / Q000098:blood supply / Q000187:drug effects / Q000276:immunology*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000276:immunology*; D006412:Hematopoietic Stem Cells / Q000276:immunology; D006801:Humans; D007249:Inflammation / Q000276:immunology*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D000072101:Jagged-2 Protein; D008024:Ligands; D008070:Lipopolysaccharides / Q000494:pharmacology; D008565:Membrane Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D008822:Mice, Transgenic; D051880:Receptors, Notch / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects / Q000276:immunology
D036341:Intercellular Signaling Peptides and Proteins; C490504:JAG2 protein, human; D000072101:Jagged-2 Protein; D008024:Ligands; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D051880:Receptors, Notch; D014409:Tumor Necrosis Factor-alpha