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Exp Hematol ; 36(5): 545-558, 2008 May.
Artículo en Inglés | MEDLINE | ID: mdl-18439488

RESUMEN

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. MATERIALS AND 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.


Asunto(s)
Médula Ósea/inmunología , Células Endoteliales/inmunología , Inflamación/inmunología , Receptores Notch/metabolismo , Transducción de Señal/inmunología , Factor de Necrosis Tumoral alfa/fisiología , Animales , Médula Ósea/irrigación sanguínea , Médula Ósea/efectos de los fármacos , Células Cultivadas , Células Endoteliales/efectos de los fármacos , Células Madre Hematopoyéticas/inmunología , Humanos , Péptidos y Proteínas de Señalización Intercelular/genética , Péptidos y Proteínas de Señalización Intercelular/metabolismo , Proteína Jagged-2 , Ligandos , Lipopolisacáridos/farmacología , Proteínas de la Membrana/efectos de los fármacos , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Ratones , Ratones Endogámicos , Ratones Transgénicos , Receptores Notch/efectos de los fármacos , Receptores Notch/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal/efectos de los fármacos , Factor de Necrosis Tumoral alfa/farmacología , Regulación hacia Arriba/efectos de los fármacos , Regulación hacia Arriba/inmunología
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