Interleukin-7 stimulates osteoclast formation by up-regulating the T-cell production of soluble osteoclastogenic cytokines.
In unstimulated conditions osteoclast renewal occurs as a result of the stromal cell production of the key osteoclastogenic factors, receptor activator of NFkB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Inflammation is known to cause increased osteoclastogenesis; however, the mechanisms responsible for this phenomenon are poorly understood. We now show that interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha), cytokines typically produced in inflammatory conditions, increase the stromal cell production of IL-7. This factor, in turn, up-regulates production of osteoclastogenic cytokines by T cells leading to stimulation of osteoclast (OC) formation. Although T cells were found to produce soluble forms of both RANKL and M-CSF, saturating concentrations of osteoprotegerin failed to inhibit approximately 40% of the OC formation, suggesting that IL-7 acts via both RANKL-dependent and RANKL-independent pathways. Despite the identification of T-cell-secreted M-CSF, this cytokine was not essential for either RANKL-dependent or -independent OC formation, suggesting that T cells secrete other cytokines capable of substituting for M-CSF action. On the basis of our data, we propose a novel mechanism for inflammatory bone loss in which induction of IL-7 from stromal cells by IL-1 and TNFalpha leads to the production of soluble osteoclastogenic cytokines by T cells. Thus, the mechanism by which IL-7 causes bone resorption involves the activation of T cells and the T-cell-dependent augmentation of osteoclastogenesis. (Blood. 2000;96:1873-1878)
Weitzmann
M N
MN
Division of Bone and Mineral Diseases, Washington University School of Medicine and Barnes-Jewish Hospital, St Louis, MO 63110, USA.
Cenci
S
S
Rifas
L
L
Brown
C
C
Pacifici
R
R
D000135:Acid Phosphatase / Q000187:drug effects / Q000378:metabolism; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D016207:Cytokines / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D015851:Interleukin-7 / Q000378:metabolism / Q000494:pharmacology*; D007527:Isoenzymes / Q000187:drug effects / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D053245:RANK Ligand; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D017154:Stromal Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000071681:Tartrate-Resistant Acid Phosphatase; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation
D002352:Carrier Proteins; D016207:Cytokines; D007375:Interleukin-1; D015851:Interleukin-7; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D011994:Recombinant Proteins; C505686:TNFRSF11A protein, human; C505688:TNFSF11 protein, human; D014409:Tumor Necrosis Factor-alpha; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase