IADR Abstract Archives
Analysis of skeletal phenotypes in Smad4 conditional knockout mice
Objectives: The transforming growth factor-β (TGF-β) family regulates cell proliferation and differentiation of skeletal cells, such as osteoblasts, osteoclasts and chondrocytes. The TGF-β family includes more than 30 members. Smad4 is an essential co-activator for the intracellular signaling of the TGF-β family. The role of Smad4 in postnatal bone growth is still unclear because Smad4 knockout mice are embryonic lethal.
Methods: We established a mouse line of tamoxifen-inducible Smad4 conditional knockout (Smad4 cKO) by crossing Smad4-floxed mice with CAG-CreERt mice. The mice were injected with tamoxifen at 10-w-old and kept for additional 3 weeks.
Results: The Smad4 cKO mice showed increased primary spongiosa in tibia and femur in micro-CT and bone histomorphometric analysis. The numbers of osteocalcin-positive osteoblasts were increased in the primary spongiosa. The epiphyseal growth plates were expanded in the Smad4 cKO mice. In 12-m-old mice, the tamoxifen injection did not change bone mass but increased thickness of growth plates. Treatment of chondrocytes with TGF-β1 in vitro suppressed chondrogenic differentiation. In contrast, treatment with an TGF-β receptor inhibitor increased the gene expression related to chondrogenic differentiation.
Conclusions: The Smad4-dependent signaling suppresses differentiation of chondrocytes in epiphyseal growth plate and reduces bone formation in postnatal mice.
Methods: We established a mouse line of tamoxifen-inducible Smad4 conditional knockout (Smad4 cKO) by crossing Smad4-floxed mice with CAG-CreERt mice. The mice were injected with tamoxifen at 10-w-old and kept for additional 3 weeks.
Results: The Smad4 cKO mice showed increased primary spongiosa in tibia and femur in micro-CT and bone histomorphometric analysis. The numbers of osteocalcin-positive osteoblasts were increased in the primary spongiosa. The epiphyseal growth plates were expanded in the Smad4 cKO mice. In 12-m-old mice, the tamoxifen injection did not change bone mass but increased thickness of growth plates. Treatment of chondrocytes with TGF-β1 in vitro suppressed chondrogenic differentiation. In contrast, treatment with an TGF-β receptor inhibitor increased the gene expression related to chondrogenic differentiation.
Conclusions: The Smad4-dependent signaling suppresses differentiation of chondrocytes in epiphyseal growth plate and reduces bone formation in postnatal mice.