Reduced expression of thrombospondins and craniofacial dysmorphism in mice overexpressing Fra1.
Fra1 transgenic (Tg) mice develop osteosclerosis and exhibit altered expression of bone matrix proteins. We found that expression of Thbs1 and Thbs2 was reduced in Fra1 Tg osteoblasts. Fra1 Tg and non-osteosclerotic Thbs1-/-Thbs2-/- mice share an edge-to-edge bite. Therefore, reduced expression of thrombospondins may contribute to craniofacial dysmorphism independently of osteosclerosis.


BACKGROUND
Tg mice overexpressing Fra1, a component of the transcription factor activator protein-1 (AP-1), show progressive osteosclerosis caused by cell autonomous abnormalities in osteoblasts. The expression of several bone matrix proteins, including matrix gla protein, is dysregulated in Fra1 Tg osteoblasts.


METHODS
In osteoblastogenic cultures, altered bone matrix production by Fra1 overexpression was monitored using Alizarin red staining, quantitative RT-PCR, and Western blotting. Responsiveness to ovariectomy was examined by bone histomorphometry. Craniofacial parameters were measured on radiographs and using CT.


RESULTS
Thrombospondin-1 (Thbs1) and thrombospondin-2 (Thbs2) were reduced in Fra1 Tg osteoblasts differentiated in vitro and in bones from Fra1 Tg mice. Despite alterations in bone matrix proteins, ovariectomy induces high turnover bone loss in Fra1 Tg mice as in wildtype mice. Fra1 Tg mice, as well as Thbs1-/- Thbs2-/- mice, which do not show osteosclerosis, exhibit an edge-to-edge bite phenotype associated with craniofacial dysmorphism.


CONCLUSIONS
These data suggest that reduced expression of thrombospondins in Fra1 Tg mice underlies craniofacial dysmorphism, independent of osteosclerosis.
Nishiwaki
Toru
T
Department of Orthopaedics, School of Medicine, Keio University, Tokyo, Japan.
Yamaguchi
Toru
T
Zhao
Chen
C
Amano
Hitoshi
H
Hankenson
Kurt D
KD
Bornstein
Paul
P
Toyama
Yoshiaki
Y
Matsuo
Koichi
K
D000818:Animals; D019465:Craniofacial Abnormalities / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010012:Osteogenesis; D010052:Ovariectomy; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D019699:Thrombospondins / Q000235:genetics / Q000378:metabolism*; D000099169:Fos-Related Antigen 1
D016760:Proto-Oncogene Proteins c-fos; D019699:Thrombospondins; D000099169:Fos-Related Antigen 1