Contribution of interleukin-11 and prostaglandin(s) in lipopolysaccharide-induced bone resorption in vivo

Abstract

We previously demonstrated that interleukin-1 (IL-1) and tumor necrosis factor (TNF) activities only partially account for calvarial bone resorption induced by local application of lipopolysaccharide (LPS) in mice. The present study was undertaken to determine the role and relative contribution of IL-11 and prostaglandin(s) (PG[s]) in LPS-induced bone resorption in vivo. A one-time dose of LPS was injected into the subcutaneous tissue overlying calvaria of mice lacking IL-1 receptor type I (IL-1RI(-/-)), mice lacking TNF receptor p55 and IL-1RI (TNFRp55(-/-)-IL-1RI(-/-)), and wild-type mice. Mice were then treated with injections of anti-IL-11 monoclonal antibody (MAb), indomethacin, or phosphate-buffered saline (PBS) and sacrificed 5 days later. Histological sections stained for tartrate-resistant acid phosphatase (TRAP) were quantified by histomorphometric analysis. At low doses of LPS (100 microg/mouse), the percentages of bone surface covered by osteoclasts were found to be similar in three strains of mice. The increase was reduced by 37% with anti-IL-11 MAb and by 46% with indomethacin. At higher doses of LPS (500 microg/mouse), we found an eightfold increase in these percentages in wild-type mice and a fivefold increase in these percentages in IL-1RI(-/-) and TNFRp55(-/-)-IL-1RI(-/-) mice after normalizing with the value from the saline-PBS control group in the same strain of mice. The increase was reduced by 55 and 69% in wild-type mice and by 50 and 57% in IL-1RI(-/-) and TNFRp55(-/-)-IL-1RI(-/-) mice treated with anti-IL-11 MAb or indomethacin, respectively. Our findings suggest that in vivo, at low doses of LPS (100 microg/mouse), LPS-induced bone resorption is mediated by IL-11 and PGs, while at high doses of LPS (500 microg/mouse), it is mediated by IL-11, PGs, IL-1, and TNF signaling. IL-11 and PGs mediate LPS-induced bone resorption by enhancing osteoclastogenesis independently of the IL-1 or TNF signaling.

FIG. 1.

Percentage of bone surface covered by osteoclasts in mice challenged with a low dose of LPS. All mice received a one-time low dose of LPS (100 μg/mouse) (LPS100) or saline, which was followed by anti-IL-11 MAb (four injections of 465 μg/mouse), indomethacin (Indo) (nine injections of 50 μg/mouse), or PBS injections. Mice were sacrificed on day 5. Bars represent means (error bars, SD), and n was 7 for each group. Symbols: ∗∗ and ∗∗∗, P < 0.01 and P < 0.001, respectively (for comparison with wild-type mice in the LPS100+PBS group); #, P < 0.01 (for comparison with mice of the same strain in the other three groups).

FIG. 2.

Percentage of bone surface covered by osteoclasts in mice challenged with a high dose of LPS (500 μg/mouse [LPS500]). The treatments are identical to those described in the legend to Fig. 1. Bars represent means (error bars, SD), and n was 7 for each group. Indo, indomethacin. Symbols: @, P < 0.001 (for comparison with all other groups in this figure); #, P < 0.01 (for comparison with mice of the same strain in the other three groups; ∗, P ≤ 0.05 (for comparison of mice of the same strain in the LPS500+Anti-IL-11 group and the LPS500+Indo group).

FIG. 3.

Light micrographs of mouse calvaria injected with 500 μg of LPS and treated with either PBS (panels 1), anti-IL-11 MAb (panels 2), or indomethacin (panels 3) in wild-type (A), IL-1RI^−/− (B), and TNFRp55^−/−-IL-1RI^−/− (C) mice. Histological sections of the calvarial bone were stained for TRAP and counterstained with hematoxylin. An arrow indicates TRAP-positive (red-staining) multinucleated cells in Howship's lacunae. Abbreviations: BM, bone marrow; Indo, indomethacin. Magnification, ×200.

FIG. 4.

ON of the calvarial bone surface in mice challenged with a low dose of LPS. All mice received a one-time dose of LPS (100 μg/mouse) (LPS100) or saline, which was followed by anti-IL-11 MAb (four injections of 465 μg/mouse), indomethacin (Indo) (nine injections of 50 μg/mouse), or PBS injections. Mice were sacrificed on day 5. Bars represent means (error bars, SD), and n was 7 for each group. Symbols: ∗∗ and ∗∗∗ P < 0.01 and P < 0.001, respectively (for comparison with wild-type mice in the LPS100+PBS group); #, P < 0.01 (for comparison with mice of the same strain in the other three groups).

FIG. 5.

ON of the calvarial bone surface in mice challenged with a high dose of LPS (500 μg/mouse [LPS500]). The treatments are identical to those described in the legend to Fig. 4. Bars represent means (error bars, SD), and n was 7 for each group. Indo, indomethacin. Symbols: @, P < 0.01 (for comparison with all other groups in this figure); #, P < 0.001 (for comparison with mice of the same strain in the other three groups).