Osteocytes produce interferon-{beta} as a negative regulator of osteoclastogenesis [Immunology]

March 7th, 2014 by Hayashida, C., Ito, J., Nakayachi, M., Okayasu, M., Ohyama, Y., Hakeda, Y., Sato, T.

Osteoclastogenesis is controlled by osteocytes; osteocytic osteoclastogenesis regulatory molecules are largely unknown. We searched for such factors using newly developed culture methods. Our culture system mimics the three-dimensional cellular structure of bone, consisting of collagen gel-embedded osteocytic MLO-Y4 cells, stromal ST2 cells on the gel as bone lining cells, and bone marrow (BM) cells. The gel-embedded MLO-Y4 cells inhibited the osteoclastogenesis induced by 1,25(OH)2D3 without modulating receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) production by the ST2 cells, despite MLO-Y4 cells supported osteoclastogenesis in the absence of ST2 cells. In the BM cell culture, the conditioned medium from MLO-Y4 cells (MLO-Y4-CM) decreased the capability of osteoclastic differentiation from the cells induced by macrophage colony-stimulating factor (M-CSF). This decreased capability was concomitant with an increase in protein kinase R mRNA expression and an inhibition of c-Fos translation. These changes were partially normalized by the simultaneous addition of an anti-interferon (IFN)-β neutralizing antibody (α-IFN-β-Ab) to MLO-Y4-CM. To study primary osteocytes, we prepared non-osteocytic cell-free osteocyte-enriched bone fragments (OEBFs). When osteoclast precursors were induced by M-CSF in the presence of OEBFs, the generated cells exhibited a diminished capacity for osteoclastogenesis. OEBFs prepared from OPG-knockout mice exhibited a similar effect, indicating OPG-independent inhibition. The addition of α-IFN-β-Ab during the co-culture with OEBFs partially recovered the osteoclastogenic potential of the generated cells. The MLO-Y4 cells and OEBFs expressed IFN-β mRNA. Although osteocytic RANKL is known to be important for osteoclastogenesis, our data suggest that osteocytes also produce IFN-β as an inhibitor of osteoclastogenesis.