TRANCE is necessary and sufficient for osteoblast-mediated activation of bone resorption in osteoclasts

Abstract

TRANCE (tumor necrosis factor-related activation-induced cytokine) is a recently described member of the tumor necrosis factor superfamily that stimulates dendritic cell survival and has also been found to induce osteoclastic differentiation from hemopoietic precursors. However, its effects on mature osteoclasts have not been defined. It has long been recognized that stimulation of osteoclasts by agents such as parathyroid hormone (PTH) occurs through a hormonal interaction with osteoblastic cells, which are thereby induced to activate osteoclasts. To determine whether TRANCE accounts for this activity, we tested its effects on mature osteoclasts. TRANCE rapidly induced a dramatic change in osteoclast motility and spreading and inhibited apoptosis. In populations of osteoclasts that were unresponsive to PTH, TRANCE caused activation of bone resorption equivalent to that induced by PTH in the presence of osteoblastic cells. Moreover, osteoblast-mediated stimulation of bone resorption was abrogated by soluble TRANCE receptor and by the soluble decoy receptor osteoprotegerin (OPG), and stimulation of isolated osteoclasts by TRANCE was neutralized by OPG. Thus, TRANCE expression by osteoblasts appears to be both necessary and sufficient for hormone-mediated activation of mature osteoclasts, and TRANCE-R is likely to be a receptor for signal transduction for activation of the osteoclast and its survival.

Figure 1

An osteoclast photographed 30 (A) and 1 (B) min before, and 30 (C) and 60 (D) min after addition of hCD8-TRANCE to culture (100 ng/ml). Bar = 2 μm. E, spread area of osteoclasts after incubation for 1 h with or without hM-CSF (5 ng/ml) or hCD8-TRANCE (CD8-T; 100 ng/ml). F, number of TRAP-positive multinuclear cells (MNC) present on coverslips in cultures of osteoclasts disaggregated from rat bone and incubated for 24 h in M-CSF (5 ng/ml) or hCD8-TRANCE (12 cultures per variable). Number of osteoclasts remaining after 24 h in hCD8-TRANCE (1,000 ng/ml) and M-CSF did not differ significantly from number present on coverslips incubated for 1 h. *P < 0.05 versus control (Student's t test).

Figure 2

Bone resorption by osteoclasts freshly isolated from neonatal rat bones and incubated for 24 h on bone slices without (A) or with (B) UMR 106 cells. A, osteoclasts incubated with M-CSF (5 ng/ml) with or without PTH (0.1 U/ml) or hCD8-TRANCE. B, osteoclasts incubated with hCD8-TRANCE (100 ng/ml) and/or PTH (0.1 U/ml) and/or M-CSF (5 ng/ml). n = 12 cultures per variable. *P < 0.05 versus control. Number of TRAP-positive cells present after incubation did not differ significantly between groups (range of means: A, 11.5–14.7; B, 17.8– 20.8). CD8-T, hCD8-TRANCE.

Figure 3

Bone resorption by osteoclasts freshly isolated from neonatal rat bones and incubated for 24 h on bone slices with calvarial cells (A) or UMR 106 cells (B), or alone (C). hCD8-TRANCE, 100 ng/ml; OPG, 100 ng/ml. n = 12 cultures per variable. *P < 0.05 versus all other groups (A and C) or versus PTH 0 and TR-Fc 2,000 ng/ml. CD8-T, hCD8-TRANCE; TR-Fc, TRANCE-R- IgG1 fusion protein.

Figure 3

Bone resorption by osteoclasts freshly isolated from neonatal rat bones and incubated for 24 h on bone slices with calvarial cells (A) or UMR 106 cells (B), or alone (C). hCD8-TRANCE, 100 ng/ml; OPG, 100 ng/ml. n = 12 cultures per variable. *P < 0.05 versus all other groups (A and C) or versus PTH 0 and TR-Fc 2,000 ng/ml. CD8-T, hCD8-TRANCE; TR-Fc, TRANCE-R- IgG1 fusion protein.

Figure 4

(A) Bone resorption by mature osteoclasts incubated for 18 h on bone slices with calvarial cells (CC oc) or UMR 106 cells (UMR oc) in the presence and absence of PTH (0.1 U/ml), 1,25(OH)₂vitamin D₃ (10⁻⁸ M), and/or OPG (100 ng/ml). n = 12 cultures per variable. *P < 0.01 versus all other groups (Student's t test). (B) Bone resorption by mature osteoclasts disaggregated from neonatal rat long bones and incubated for 18 h on bone slices alone (oc) or with added osteoblastic UMR 10⁶ cells (UMR oc). At no concentration did OPG significantly stimulate bone resorption. Significant suppression of bone resorption by OPG (*P < 0.01 versus O+PTH group) occurred at 100 ng/ml. n = 12 cultures per variable.