RESUMEN
BACKGROUND: Bartonella species are the only known bacterial pathogens causing vasculoproliferative disorders in humans (bacillary angiomatosis [BA]). Cellular and bacterial pathogenetic mechanisms underlying the induction of BA are largely unknown. METHODS AND RESULTS: Activation of hypoxia-inducible factor-1 (HIF-1), the key transcription factor involved in angiogenesis, was detected in Bartonella henselae-infected host cells in vitro by immunofluorescence, Western blotting, electrophoretic mobility shift, and reporter gene assays and by immunohistochemistry in BA tissue lesions in vivo. Gene microarray analysis revealed that a B henselae infection resulted in the activation of genes typical for the cellular response to hypoxia. HIF-1 was essential for B henselae-induced expression of vascular endothelial growth factor as shown by inhibition with the use of HIF-1-specific short-interfering RNA. Moreover, infection with B henselae resulted in increased oxygen consumption, cellular hypoxia, and decreased ATP levels in host cells. Infection with a pilus-negative variant of B henselae did not lead to cellular hypoxia or activation of HIF-1 or vascular endothelial growth factor secretion, suggesting a crucial role of this bacterial surface protein in the angiogenic reprogramming of the host cells. CONCLUSIONS: B henselae induces a proangiogenic host cell response via HIF-1. Our data provide for the first time evidence that HIF-1 may play a role in bacterial infections.
Asunto(s)
Angiomatosis Bacilar/patología , Proteínas de Unión al ADN/fisiología , Proteínas Nucleares/fisiología , Factores de Transcripción/fisiología , Adenosina Trifosfato/metabolismo , Bartonella henselae/aislamiento & purificación , Bartonella henselae/patogenicidad , Hipoxia de la Célula/fisiología , Proteínas de Unión al ADN/inmunología , Proteínas de Unión al ADN/metabolismo , Células Endoteliales/microbiología , Endotelio Vascular/citología , Fimbrias Bacterianas/metabolismo , Fimbrias Bacterianas/fisiología , Células HeLa/química , Células HeLa/metabolismo , Células HeLa/microbiología , Histiocitos/química , Histiocitos/patología , Humanos , Factor 1 Inducible por Hipoxia , Subunidad alfa del Factor 1 Inducible por Hipoxia , Inmunohistoquímica/métodos , Macrófagos/química , Macrófagos/patología , Neovascularización Patológica/microbiología , Proteínas Nucleares/inmunología , Proteínas Nucleares/metabolismo , Factores de Transcripción/inmunología , Factores de Transcripción/metabolismo , Venas Umbilicales/citología , Regulación hacia Arriba/fisiologíaRESUMEN
Bartonella henselae causes the vasculoproliferative disorders bacillary angiomatosis and peliosis probably resulting from the release of vasculoendothelial growth factor (VEGF) from infected epithelial or monocytic host cells. Here we demonstrate that B. henselae in addition to VEGF induction was also capable of inhibiting the endogenous sucide programme of monocytic host cells. Our results show that B. henselae inhibits pyrrolidine dithiocarbamate (PDTC)-induced apoptosis in Mono Mac 6 cells. B. henselae was observed to be present in a vacuolic compartment of Mono Mac 6 cells. Direct contact of B. henselae with Mono Mac 6 cells was crucial for inhibition of apoptosis as shown by the use of a two-chamber model. Inhibition of apoptosis was paralleled by diminished caspase-3 activity which was significantly reduced in PDTC-stimulated and B. henselae-infected cells. The anti-apoptotic effect of B. henselae was accompanied by (i) the activation of the transcription factor NF-kappaB and (ii) the induction of cellular inhibitor of apoptosis proteins-1 and -2 (cIAP-1, -2). Our results suggest a new synergistic mechanism in B. henselae pathogenicity by (i) inhibition of host cell apoptosis via activation of NF-kappaB and (ii) induction of host cell VEGF secretion.