title: Overexpression of Bcl2 in osteoblasts inhibits osteoblast differentiation and induces osteocyte apoptosis.
abstract: Bcl2 subfamily proteins, including Bcl2 and Bcl-X(L), inhibit apoptosis. As osteoblast apoptosis is in part responsible for osteoporosis in sex steroid deficiency, glucocorticoid excess, and aging, bone loss might be inhibited by the upregulation of Bcl2; however, the effects of Bcl2 overexpression on osteoblast differentiation and bone development and maintenance have not been fully investigated. To investigate these issues, we established two lines of osteoblast-specific BCL2 transgenic mice. In BCL2 transgenic mice, bone volume was increased at 6 weeks of age but not at 10 weeks of age compared with wild-type mice. The numbers of osteoblasts and osteocytes increased, but osteoid thickness and the bone formation rate were reduced in BCL2 transgenic mice with high expression at 10 weeks of age. The number of BrdU-positive cells was increased but that of TUNEL-positive cells was unaltered at 2 and 6 weeks of age. Osteoblast differentiation was inhibited, as shown by reduced Col1a1 and osteocalcin expression. Osteoblast differentiation of calvarial cells from BCL2 transgenic mice also fell in vitro. Overexpression of BCL2 in primary osteoblasts had no effect on osteoclastogenesis in co-culture with bone marrow cells. Unexpectedly, overexpression of BCL2 in osteoblasts eventually caused osteocyte apoptosis. Osteocytes, which had a reduced number of processes, gradually died with apoptotic structural alterations and the expression of apoptosis-related molecules, and dead osteocytes accumulated in cortical bone. These findings indicate that overexpression of BCL2 in osteoblasts inhibits osteoblast differentiation, reduces osteocyte processes, and causes osteocyte apoptosis.
authors: Department of Cell Biology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors: Takeshi
authors: T
authors: Moriishi
authors: Zenjiro
authors: Z
authors: Maruyama
authors: Ryo
authors: R
authors: Fukuyama
authors: Masako
authors: M
authors: Ito
authors: Toshihiro
authors: T
authors: Miyazaki
authors: Hideki
authors: H
authors: Kitaura
authors: Hidetake
authors: H
authors: Ohnishi
authors: Tatsuya
authors: T
authors: Furuichi
authors: Yosuke
authors: Y
authors: Kawai
authors: Ritsuko
authors: R
authors: Masuyama
authors: Hisato
authors: H
authors: Komori
authors: Kenji
authors: K
authors: Takada
authors: Hiroshi
authors: H
authors: Kawaguchi
authors: Toshihisa
authors: T
authors: Komori
mesh_terms: D000818:Animals; D017209:Apoptosis; D015152:Blotting, Northern; D015153:Blotting, Western; D001846:Bone Development; D001842:Bone and Bones; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism*; D010011:Osteocytes / Q000378:metabolism / Q000473:pathology*; D010012:Osteogenesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger