The role of B-cells in regulating osteoclastogenesis is contentious and remains poorly understood. We have recently evaluated the role of B-cells in osteoclast formation in a human model system and demonstrated that contrary to some previous reports, B-cells are inhibitory to osteoclastogenesis in vitro. We find that B-cell depleted cultures generate higher numbers of osteoclasts than B-cell replete cultures. This inhibitory factor is resident in B-cell conditioned medium and induces apoptosis of osteoclast precursors and multinucleated mature osteoclasts. We have determined that these apoptotic effects of B-cells are the result of TGFbeta secretion. Secretion of TGFbeta by B-cells thus represents a new and important mechanism of bone regulation. Our data also shows that IL-7 downregulates the production of TGFbeta in vitro. We thus hypothesize that stromal cell secretion of IL-7 in the bone marrow may constitute a key mechanism of regulating the B-cell production of TGFbeta, thus playing a pivotal role in regulating bone homeostasis. We now propose to investigate the mechanism by which IL-7 regulates TGFbeta production, by making a detailed examination of the human TGFbeta promoter. We plan to utilize an IL-7 promoter-luciferase reporter construct to investigate which transcription factor motifs for IL-7 responsive. We plan to initially explore the relative contributions of different transcription factor binding motifs such as SP-1, TRE, and NF1, that are known to be present in the TGFbeta promoter. Using site-directed mutagenesis we will mutate these sites to render them inoperable and then assess the ability of IL-7 to inhibit transcription. If these sites are not found to explain TGFbeta responsiveness we will generate systematic 5' deletions of the promoter to identify the relevant IL-7 responsive sequences.
| Rifas, Leonard; Arackal, Sophia; Weitzmann, M Neale (2003) Inflammatory T cells rapidly induce differentiation of human bone marrow stromal cells into mature osteoblasts. J Cell Biochem 88:650-9 |
| Toraldo, Gianluca; Roggia, Cristiana; Qian, Wei-Ping et al. (2003) IL-7 induces bone loss in vivo by induction of receptor activator of nuclear factor kappa B ligand and tumor necrosis factor alpha from T cells. Proc Natl Acad Sci U S A 100:125-30 |
| Weitzmann, M Neale; Roggia, Cristiana; Toraldo, Gianluca et al. (2002) Increased production of IL-7 uncouples bone formation from bone resorption during estrogen deficiency. J Clin Invest 110:1643-50 |
| Roggia, C; Gao, Y; Cenci, S et al. (2001) Up-regulation of TNF-producing T cells in the bone marrow: a key mechanism by which estrogen deficiency induces bone loss in vivo. Proc Natl Acad Sci U S A 98:13960-5 |
