Objective       To investigate the changes of bone volume in vertebral body and the underlying possible mechanism in osterix knock-out (Osx-KO) and constitutive-activation (Osx-CA) mice.       Methods       A total of 24 male mice at 12-week old including

wild type (WT)

Osx-KO and Osx-CA groups (

n

=8) were subjected in this study. X-ray radiology and HE staining were used to evaluate the change of bone volume. TRAP staining was used to assess the activity of osteoclasts. Immunohistochemical assay (IHC) was used to examine the expression levels of RANKL

BSP and OPN. IHC and TRAP sta

ining results were semi-quantitive analyzed by manual counting.       Results       X-ray examination and HE staining showed that the bone density and bone volume in the lumbar vertebral body was increased significantly in OSX-KO mice

while TRAP staining showed that the number of osteoclasts was decreased (

P

<

0.01)

and IHC revealed that the expression levels of RANKL

BSP and OPN were down-regulated (

P

<

0.01) in OSX-KO mice. However

no obvious change was found in the bone density

bone volume and the number of osteoclasts in Osterix-KO mice compared with the WT mice.       Conclusion       Osterix knock-out may weaken bone resorption activity and osteoblast differentiation in the lumbar vertebral body

and result in an increased bone volume.