Date of Award

4-30-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Dr. Barbara Baumstark - Chair

Second Advisor

Dr. Zehava Eichenbaum

Third Advisor

Dr. Phang-Cheng Tai

Fourth Advisor

Dr. Julia Hilliard

Abstract

The genus Bartonella comprises emerging pathogens that are causative agents of a wide range of clinical manifestations such as cat scratch disease, bacillary angiomatosis, and Carrion’s disease. All species are transmitted by blood-sucking arthropods and infect erythrocytes and endothelial cells of hosts. Carrion’s disease is a bi-phasic infection caused by Bartonella bacilliformis which is characterized by hemolysis of infected erythrocytes followed by invasion of the vascular endothelium. This provokes pronounced cellular proliferation, angiogenesis and skin eruptions called verruga peruana. Endothelial cells are thought to be the primary niche wherein bacteria reside between inoculation and erythrocyte infection. This study aims to elucidate some of the endothelial factors involved during the verruga peruana phase of Carrion’s disease. In order to adhere to and invade human microvascular endothelial cells (HMEC-1), B. bacilliformis engages a family of cell receptors called integrins. We used anti-integrin antibodies to show that the primary integrin involved is the fibronectin receptor á5â1, although the vitronectin receptor áVâ3 also plays a minor role. We show B. bacilliformis invasion is also dependent on integrin ligands, fibronectin and vitronectin as antibodies against these proteins decreased invasion and attachment, whereas pre-treatment of the bacteria with these molecules enhanced infection of endothelial cells. Bacterial uptake requires various host cytoplasmic signaling pathways to work in tandem, and our study identified three mitogen activated protein kinases involved. Apart from MAPKs, phosphotidylinositol 3 kinase plays a role during invasion and cell survival. PI3K inhibitors blocked bacterial internalization and B. bacilliformis infected cells showed accelerated apoptosis. Lastly, microarray analysis was performed to study the gene expression profile of B. bacilliformis infected HMEC-1 cells. Numerous molecules of the integrin signaling pathways are involved, suggesting integrins as the major receptor recruited for the successful infection by B. bacilliformis. In summary this is the first study to demonstrate the role of integrins as B. bacilliformis receptors and integrin ligands as facilitators of infection. Gene expression analysis suggests the possibility that integrin mediated signaling pathways are the key modulators of cellular alterations during B. bacilliformis infection. This hypothesis is supported by the identification of some members of the integrin signaling pathway necessary for B. bacilliformis entry into endothelial cells.

Included in

Biology Commons

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