Knocking down dickkopf-1 alleviates estrogen deficiency induction of bone loss. A histomorphological study in ovariectomized rats

Dickkopf-1 (DKK1) has been found to act as a potent Wnt signaling-inhibitory factor for regulating skeletal disorders. We investigated whether modulation of DKK1 expression by end-capped phosphorothioate DKK1 antisense oligonucleotide could alter estrogen loss-induced bone loss. Ovariectomized or sham-operated rats were given 20 μg/kg/day DKK1 sense or antisense oligonucleotide or vehicle for 28 days. Femurs and tibiae were dissected to assess bone mass, biomechanical strength, immunohistochemistry and ex vivo osteoclast formation. We found that DKK1 antisense oligonucleotide significantly abrogated the suppressing effect of ovariectomy on weight, mineral content, mineral density and peak load of femurs. DKK1 antisense oligonucleotide treatment reduced ovariectomy promotion of ex vivo osteoclast differentiation of primary M-CSF-dependent bone marrow macrophages. Histomorphometric observation demonstrated that DKK1 antisense oligonucleotide treatment increased osteoblast number and impaired ovariectomy-promoted trabecular bone loss and osteoclast number in bone tissue. Osteoblastic cells adjacent to endosteum of trabecular bone and chondrocytes at calcified cartilage expressed intensive DKK1 and RANKL and weak OPG immunostaining in ovariectomized rat bone microenvironments. Osteogenic cells and chondral cells displayed weak DKK1, RANKL and OPG expression of bone tissue after DKK1 antisense oligonucleotide treatment. Taken together, attenuation of DKK1 expression in ovariectomized rat bone tissue alleviated loss of bone mass and biomechanical property. The regulatory action of DKK1 antisense oligonucleotide treatment on bone tissue appeared to suppress the promoting effect of estrogen deficiency on osteoclastogenesis-stimulatory factor RANKL expression and osteoclast differentiation. Control of DKK1 signaling can be used in the future as an alternative strategy for protecting estrogen deficiency induction of bone loss.