STIMULATION OF OSTEOCLAST DIFFERENTIATION IN VITRO BY MOUSE ONCOSTATIN M, LEUKAEMIA INHIBITORY FACTOR, CARDIOTROPHIN-1 AND INTERLEUKIN 6: SYNERGY WITH DEXAMETHASONE

The role of oncostatin M in bone metabolism is not clearly defined, and the actions of mouse oncostatin M (mOSM) on osteoclast development has not been previously determined. We therefore examined the ability of recombinant mOSM to stimulate osteoclast formation and activity using cocultures of murine calvaria and bone marrow cells, and compared the responses to other members of the interleukin 6 family of cytokines including mouse leukaemia inhibitory factor (LIF), cardiotrophin-1 (CT-1) and IL-6. Mouse OSM, LIF and CT-1 strongly induced the formation of tartrate resistant acid phosphatase positive (TRAP(+)) multinucleated cells (MNC) in a dose-dependent fashion. OSM, LIF or CT-1 also elevated the number and size of resorptive pits when cocultures were added to smooth cortical bone slices, indicating enhancement of osteoclast activity. The activity of OSM was reduced by indomethacin (10(-8)-10(-6) M), whereas addition of dexamethasone (DEX) at 10(-7)-10(-5) M synergistically enhanced OSM-induced numbers of TRAP(+)MNC. DEX (10(-7) M) costimulation also synergistically enhanced TRAP(+)cell numbers of LIF, and CT-1 treated cocultures. IL-6 had no activity alone, but further enhanced TRAP(+)cell formation in mOSM or DEX (10(-7) M) treated cocultures. When added to mouse calvarial osteoblast cultures, mOSM induced secretion of IL-6 protein and elevation of mRNA whereas LIF or CT-1 did not. IL-6 mRNA levels and protein secretion were reduced in osteoblasts by costimulation with DEX. These results show that mouse OSM, LIF and CT-1 induce osteoclast differentiation and activation, that DEX synergizes with each in this activity, and that mouse OSM induces responses in osteoblasts that are not shown by LIF or CT-1. Collectively these data suggest an important role of these cytokines in osteoporosis caused by high levels of corticosteroid.