Fig. 5

mBMMSCs under compression load promote osteoclast differentiation of mBMMs. a Schematic diagram of co-culture of mBMMs and stem cells under compression load. The orange dotted frame shows a schematic diagram of simply applying compressive force on the cell. b–f After simply applying compressive force on the mBMMSCs for 2 days, RT-PCR assay of Alp, Runx2, Ocn, Osterix and Rankl was performed. Results showed that expression levels of Alp, Runx2, Ocn and Osterix in the non-compression group were significantly higher than in the compression group, but Rankl expression in the compression group was significantly higher than in the non-compression group. *P < 0.05 versus compression group, **P < 0.01 versus compression group. g–i Gene expression of osteoclast differentiation markers in all four groups. When co-cultured with mBMMSCs under compression load, osteoclast differentiation markers (TRAP, Ctsk and Mmp-9) produced by mBMMs were approximately twice as high as those produced by mBMMs cultured independently. mBMMSCs under compression promoted expression of TRAP, Ctsk and Mmp-9 in mBMMs compared to mBMMSCs without compression. Gene expression of TRAP, Ctsk and Mmp-9 in mBMMs induced by Rankl and M-CSF was slightly higher than that induced by M-CSF in the co-culture of stem cells and mBMMs under compression. *P < 0.05, **P < 0.01. j TRAP staining images of mBMMs co-cultured with stem cells 7 days after compression in all four groups in vitro. The red arrows represent TRAP-positive multinucleated osteoclasts. The scale bars in e were 50 μm. k Semiquantitative analysis of the number of osteoclasts produced in the TRAP staining assay in all four groups in vitro. * P < 0.05, **P < 0.01