Characterization of the bone-resorptive effect of interleukin-11 in cultured mouse calvarial bones

Interleukin-11 (IL-11) is a stromal cell-derived cytokine that can enhance osteoclast formation and stimulate bone resorption. In the present study, the characteristics of the resorptive effect of IL-11 in mouse calvarial bones were investigated. Both recombinant mouse IL-11 and human IL-11 caused concentration- and time-dependent stimulations of Ca-45 release from prelabeled mouse calvariae. Half-maximal responses were obtained at 0.7 ng/mL (approximate to40 pmol/L). Mouse and human IL-11 also stimulated release of H-3 from [H-3]proline-labeled bones. The magnitude of the Ca-45 and H-3 release (1.4-1.6-fold) caused by a maximally effective concentration of IL-11 was less than the stimulation (2.5-4.0-fold) elicited by a maximum concentration of parathyroid hormone (PTH). Release of Ca-45 by IL-11 was unaffected by the mitotic inhibitors, hydroxyurea and aphidicolin. In addition to resorption of bone, IL-11 caused a small (1.5-2.0-fold) enhancement of prostaglandin E-2 (PGE(2)) biosynthesis in calvariae, but had no effect on the mRNA expression of cyclooxygenase-1 and -2, or cytosolic phospholipase A(2). Indomethacin and flurbiprofen abolished the formation of PGE(2) and partially reduced Ca-45 release stimulated by IL-11. When either mouse interleukin-4 (IL-4) or interleukin-13 (IL-13) was added to calvariae treated with IL-11, Ca-45 release was inhibited. Resorption caused by IL-11 was also inhibited by both anti-mouse glycoprotein 130 (gp130) and an antibody neutralizing IL-11, but these agents had no effect on Ca-45 release caused by PTH or 1,25(OH)(2)vitamin D-3 (D-3). Real-time, quantitative polymerase chain reaction (PCR) analysis (TaqMan PCR) and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) demonstrated that IL-11 caused concentration-dependent enhancements of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG) mRNA, without affecting the mRNA expression of RANK. Mouse RANKL stimulated Ca-45 release in the calvarial bones. The stimulatory effects of RANKL and IL-11 were inhibited by mouse OPG. These data demonstrate that IL-11 stimulates osteoclastic resorption in mouse calvariae by mechanisms that are independent of cell proliferation; partially dependent on prostaglandin biosynthesis; sensitive to inhibition by IL-4, IL-13, and OPG; and associated with enhanced expression of RANKL and OPG. In addition, IL-11 was not found to play an essential role in resorption stimulated by other calciotropic agents in calvariae.