Maspin is involved in bone matrix maturation by enhancing the accumulation of latent TGF-beta.
Maspin, a serine protease inhibitor, is expressed by formative osteoblasts. The repression of maspin expression in osteoblastic cells decreased the level of latent TGF-beta in the extracellular matrix, whereas the overexpression of maspin increased latent TGF-beta. These findings suggest that maspin plays an important role in bone matrix formation, particularly in the accumulation of latent TGF-beta.


BACKGROUND
Maspin is a serine protease inhibitor that exhibits tumor suppressive and anti-angiogenic activities. This study was performed to elucidate a possible role for maspin in bone formation.


METHODS
We performed immunohistochemical analysis of the expression of maspin during endochondral ossification. We evaluated the expression of maspin mRNA and protein in ROS 17/2.8 cells and primary rat osteoblastic cells by RT-PCR, immunocytochemistry, and Western blot analysis. We also examined the accumulation of TGF-beta in the extracellular matrix of cultured ROS 17/2.8 cells after transfection with vectors expressing either maspin or maspin antisense.


RESULTS
We observed expression of maspin by active osteoblasts in vivo. Rat osteoblastic cells also expressed maspin mRNA and protein in vitro. Moreover, the accumulation of latent TGF-beta in the extracellular matrix significantly decreased in cultures exposed to an anti-maspin antibody and when cells were transfected with a maspin antisense-expressing vector. In contrast, accumulation of latent TGF-beta in the extracellular matrix increased after transfection of cells with a vector expressing maspin.


CONCLUSIONS
These findings suggest that maspin expressed in active osteoblasts plays an important physiological role during maturation of the bone matrix, and in particular, during the process of accumulation of latent TGF-beta in the extracellular matrix.
Tokuyama
Reiko
R
Department of Oral and Maxillofacial Surgery, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan.
Satomura
Kazuhito
K
Maeda
Eriko
E
Kudoh
Keiko
K
Yamasaki
Yasuhumi
Y
Nagayama
Masaru
M
D000818:Animals; D000906:Antibodies / Q000276:immunology; D001857:Bone Matrix / Q000166:cytology / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D016372:RNA, Antisense / Q000235:genetics; D051381:Rats; D011916:Rats, Inbred F344; D015843:Serpins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000494:pharmacology
D000906:Antibodies; D016372:RNA, Antisense; C085344:SERPIN-B5; D015843:Serpins; D016212:Transforming Growth Factor beta; D010447:Peptide Hydrolases