Expression of interleukin-34 and colony stimulating factor-1 in the stimulated periodontal ligament cells with tumor necrosis factor-α.

Tumor necrosis factor-α (TNF-α) directly and indirectly plays a crucial role in osteoclastogenesis. However, the indirect effects of TNF-α on colony-stimulating factor-1 receptor (CSF-1R)-mediated osteoclastogenesis achieved via periodontal ligament (PDL) cells are not fully understood. We herein examined the potency of osteoclast differentiation and maturation induced by fivefold supernatants in the stimulated human PDL cells with a physiologically high concentration (10 ng/mL) of recombinant TNF-α to human peripheral blood monocytes/macrophages in the simultaneous presence of the receptor activator of nuclear factor kappa-B ligand. The number of tartrate-resistant acid phosphatase-positive cells with multiple nuclei, but not those with a single nucleus, was decreased by approximately 50% by neutralization with rabbit IgG against either interleukin-34 (IL-34) or CSF-1. Small and large amounts of IL34 and CSF1 transcripts were measured in the stimulated PDL cells using real-time polymerase chain reaction. The corresponding amounts of proteins to IL34 and CSF1 transcripts were observed in the stimulated PDL cells on immunohistochemical staining or Western blotting. Moreover, 0.13 ng/mL of IL-34 and 5.0 ng/mL of CSF-1 were measured in the supernatants of the stimulated PDL cells using an enzyme-linked immunosorbent assay. IL-34 derived from the stimulated PDL cells with TNF-α appeared to synergistically function with CSF-1 in the CSF-1R-mediated maturation of osteoclastogenesis.