Figure 1. LRAP inhibits osteoclastogenesis. (A) Number of osteoclasts (tartrate-resistant alkaline phosphatase [TRAP])-positive multinucleated cells, as indicated by arrows in the subsequent panels in the co-cultures of wild-type (WT) osteoclast progenitor (bone marrow cells) and amelogenin-KO (KO) or WT-cementoblast/periodontal ligament cells treated with 10^–8 M of 1,25(OH)₂D₃ for 7 days. Increased numbers of osteoclasts were observed in the co-cultures of osteoclast progenitor and KO cementoblast/periodontal ligament cells (compare panels B and G). (B–K) Osteoclast formation in the co-cultures of WT osteoclast progenitor and KO or WT-cementoblast/periodontal ligament cells treated with LRAP or P172 for 7 days in 96-well plates in the presence of 10^–8 M of 1,25(OH)₂D₃. Different amounts of LRAP and P172 (1, 10, and 100 ng/mL) were added in the culture medium. TRAP staining of co-cultures of cementoblast/periodontal ligament cells from KO mice (B–E) and WT mice (G–J) treated with either LRAP or P172 as indicated. Data are expressed as the mean ± SD (n = 18). **P < 0.01. Scale bar: 100 µm.