All ETDs from UAB

Advisory Committee Chair

Xu Feng

Advisory Committee Members

Joseph E Busby

Susan L Bellis

Joanne Murphy-Ullrich

Majd Zayzafoon

Document Type

Dissertation

Date of Award

2011

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

The mucin-like Lysosome Associated Membrane Protein (LAMP) family member CD68 is a primarily myeloid lineage restricted transmembrane protein that is expressed in macrophages and osteoclasts. While the existence and expression pattern of human CD68 and mouse CD68 (sometimes called macrosialin) are well-known, and these molecules are routinely used as histological markers of tissue macrophages, the functional signific-ance of CD68 expression remains an unanswered question. Our overall goal is to deter-mine the significance and characterize the function of CD68 in osteoclasts and explore the effects of Receptor Activator of Nuclear Factor κB (RANK) signaling on CD68 post-translational modification. To achieve this goal, I used homologous recombination to generate a mouse line that lacks expression of CD68. Mice that lack CD68 expression have increased trabecular bone and dysfunctional, morphologically aberrant osteoclasts demonstrating the importance of CD68 expression for proper osteoclast function. Next, altered glycosylation of CD68 that occurs with RANK ligand (RANKL)-stimulated os-teoclastogenesis was investigated. I found that RANKL induces an increase in terminal sialylation of CD68, and this change is dependent upon the signaling of RANK Tumor Necrosis Factor Associated Factor (TRAF) binding motifs 539PVQEET564 and 604PVQEQG609 and the non-TRAF motif 535IVVY538 perhaps through the action of the sialating enzyme ST3Gal1. Finally, I developed an assay to identify inhibitors of the sig-naling from 539PVQEET564 and 604PVQEQG609. In addition to contributing to the RANKL-induced modification of CD68, these signaling motifs are also necessary for the normal formation of osteoclasts, and inhibitors of these motifs may serve as valuable new anti-resorptive therapeutics. Importantly, the work of this dissertation establishes CD68 as an important molecule for osteoclast function and marks it as a potential therapeutic target for treating disorders of bone loss. In addition, this work should open new avenues of research into functions of CD68 and the significance of its RANKL-induced alterna-tive glycosylation.

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