Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Biology and Biomedical Sciences: Molecular Cell Biology

Language

English (en)

Date of Award

January 2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Daniel Link

Abstract

The number of neutrophils in the blood is tightly regulated to ensure adequate protection against microbial pathogens while minimizing damage to host tissue. Neutrophil homeostasis in the blood is achieved through a balance of neutrophil production, release from the bone marrow, and clearance from the circulation. Accumulating evidence suggests that chemokine signaling in the bone marrow may play a key role in maintaining neutrophil homeostasis. Based on this evidence, we developed a "tug-of-war" model in which opposing chemokine gradients, specifically release-inducing CXCR2 signals and retention-promoting CXCR4 signals, act antagonistically to regulate neutrophil release from the bone marrow. We generated mice with neutrophils genetically deficient for the receptors CXCR2: CXCR2-/-), CXCR4: CXCR4-/-), or both: double knock-out or DKO) in order to define the mechanisms by which chemokine signals regulate neutrophil homeostasis. We show that CXCR4 negatively regulates neutrophil release from the bone marrow in a cell autonomous fashion. However, CXCR4 is dispensable for neutrophil clearance from the circulation. Neutrophil mobilization responses to granulocyte colony stimulating factor: G-CSF), CXCL2, or Listeria monocytogenes infection are absent or impaired in CXCR4-/- neutrophils, suggesting that disruption of CXCR4 signaling may be a common step mediating neutrophil release. CXCR2-/- neutrophils exhibit abnormal retention in the bone marrow and a peripheral neutropenia, which replicates the phenotype of the human disease myelokathexis and indicates that CXCR2 positively regulates neutrophil release from the bone marrow. CXCR2-/- neutrophils do not mobilize in response to an inhibitor of CXCR4 and have an impaired response to G-CSF, suggesting that neutrophil release requires the coordinated regulation of CXCR2 and CXCR4 signals. However, DKO neutrophils exhibit a shift from the bone marrow to the blood that is similar to CXCR4-/- cells, indicating that CXCR4 is dominant to CXCR2 and that there are likely to be CXCR2-independent mechanisms for directing neutrophil release. Finally, we show that there is differential production of CXCR2 and CXCR4 ligands by bone marrow osteoblasts and endothelial cells that can be regulated by G-CSF. Taken together, our data suggest that coordinated osteoblast and endothelial production of CXCR2 and CXCR4 ligands is a common mechanism controlling neutrophil release from the bone marrow.

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Permanent URL: http://dx.doi.org/10.7936/K7JS9NF7

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