Fig 2: Calcitonin treatment increases the osteoclastic Wnt10b expression in metaphysis of femoral bone in ovariectomy-induced osteoporotic rats. Sham-operated rats and ovariectomized (OVX) rats were treated as indicated in Figure 1. Immunohistochemistry labeling of Wnt10b (green) and TRAP stain (red) were performed near resorption zone of growth plate in femoral bone. Decreased Wnt10b expression was found in OVX rats. CT treatment increased Wnt10b expression. The number of the osteoblast, osteoclast, and osteoclast with Wnt10b were counted. Green arrow showed osteoclasts to secret Wnt10b; White arrow showed osteoclasts that did not secret Wnt10b. Scale bar = 50 µm. *Indicates a significant difference (p < 0.05). N = 6 in each group.

Fig 3: Calcitonin indirectly increases osteoblast mineralization. Osteoblasts were isolated from the calvariae of 1-day-old newborn SD rats and cultured in groups a-f medium as indicated in Materials and Methods. Analysis of osteoblast mineralization was performed by ALP (A) and alizarin red staining (B). (C) Quantitative results of the experiment shown in (A,B), and Wnt10b concentration in mediums of each group before cultured with osteoblasts. *Indicates a significant difference (p < 0.05). Bar = 500 µm.

Fig 4: Calcitonin increases Wnt10b levels in osteoclasts. Osteoclasts were prepared and treated as indicated in Figure 4. Western blot analysis was performed on osteoclasts treated with 3 nM calcitonin alone or with C59 for the various times indicated. Protein levels were quantified by densitometry, corrected for sample loading on the basis of actin levels, and expressed as the fold change relative to the control lane. Each blot is representative of at least three replicate experiments.

Fig 5: Model of calcitonin-induced bone formation through action on osteoclasts. Bones undergo constant remodeling throughout the lifetime of the organism, and this involves the continuous activity of osteoblasts and osteoclasts. Osteoblastic bone formation is communicated to osteoclastic bone resorption by positive and negative modulators (RANKL/OPG or WNT). Osteoclasts also communicate to osteoblasts by clastokines (Wnt10b and S1P). Bone anabolic such as PTH also increase osteoclastic bone resorption through their control of RANKL/OPG and WNT signaling. Anti-resorptive inhibit osteoclast resorption, which usually causes the inhibition of bone formation. Uncoupling anti-resorptive, such as calcitonin, may modulate osteoblast mineralization through the controlled secretion of Wnt10b and S1P.