Fig 2: Calcitonin increases Wnt10b and bone formation but decreases bone resorption in ovariectomized osteoporotic rats. Sham-operated rats and ovariectomized (OVX) rats were treated as indicated in Figure 1. Serum samples obtained from rats were analyzed by ELISA. (A) Quantitative analysis of Wnt10b (B) Quantitative analysis of TRAP5b (C) Quantitative analysis of CTX-1 (D) Quantitative analysis of osteocalcin (E) Quantitative analysis of P1NP. *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: 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.

Fig 5: 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.