Role of Bcl2 in osteoclastogenesis and PTH anabolic actions in bone.
BACKGROUND
B-cell leukemia/lymphoma 2 (Bcl2) is a proto-oncogene best known for its ability to suppress cell death. However, the role of Bcl2 in the skeletal system is unknown. Bcl2 has been hypothesized to play an important anti-apoptotic role in osteoblasts during anabolic actions of PTH. Although rational, this has not been validated in vivo; hence, the impact of Bcl2 in bone remains unknown.


METHODS
The bone phenotype of Bcl2 homozygous mutant (Bcl2(-/-)) mice was analyzed with histomorphometry and muCT. Calvarial osteoblasts were isolated and evaluated for their cellular activity. Osteoclastogenesis was induced from bone marrow cells using RANKL and macrophage-colony stimulating factor (M-CSF), and their differentiation was analyzed. PTH(1-34) (50 microg/kg) or vehicle was administered daily to Bcl2(+/+) and Bcl2(-/-) mice (4 days old) for 9 days to clarify the influence of Bcl2 ablation on PTH anabolic actions. Western blotting and real-time PCR were performed to detect Bcl2 expression in calvarial osteoblasts in response to PTH ex vivo.


RESULTS
There were reduced numbers of osteoclasts in Bcl2(-/-) mice, with a resultant increase in bone mass. Bcl2(-/-) bone marrow-derived osteoclasts ex vivo were significantly larger in size and short-lived compared with wildtype, suggesting a pro-apoptotic nature of Bcl2(-/-) osteoclasts. In contrast, osteoblasts were entirely normal in their proliferation, differentiation, and mineralization. Intermittent administration of PTH increased bone mass similarly in Bcl2(+/+) and Bcl2(-/-) mice. Finally, Western blotting and real-time PCR showed that Bcl2 levels were not induced in response to PTH in calvarial osteoblasts.


CONCLUSIONS
Bcl2 is critical in osteoclasts but not osteoblasts. Osteoclast suppression is at least in part responsible for increased bone mass of Bcl2(-/-) mice, and Bcl2 is dispensable in PTH anabolic actions during bone growth.
Yamashita
Junro
J
Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, USA.
Datta
Nabanita S
NS
Chun
Yong-Hee P
YH
Yang
Dong-Ye
DY
Carey
Allison A
AA
Kreider
Jaclynn M
JM
Goldstein
Steven A
SA
McCauley
Laurie K
LK
D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D019254:Genes, bcl-2; D051379:Mice; D018345:Mice, Knockout; D010010:Osteoclasts / Q000166:cytology*; D010281:Parathyroid Hormone / Q000502:physiology*; D016133:Polymerase Chain Reaction
D017931:DNA Primers; D010281:Parathyroid Hormone