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Parathyroid Hormone‐Related Protein Is Required for Normal Intramembranous Bone Development
Author(s) -
Suda Naoto,
Baba Otto,
Udagawa Nobuyuki,
Terashima Tatsuo,
Kitahara Yutaka,
Takano Yoshiro,
Kuroda Takayuki,
Senior Paul V.,
Beck Felix,
Hammond Vicki E.
Publication year - 2001
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.2001.16.12.2182
Subject(s) - intramembranous ossification , endochondral ossification , osteocalcin , osteopontin , medicine , endocrinology , parathyroid hormone , in situ hybridization , parathyroid hormone related protein , biology , osteoblast , parathyroid hormone receptor , ossification , mutant , bone remodeling , bone resorption , alkaline phosphatase , cartilage , chemistry , messenger rna , microbiology and biotechnology , in vitro , anatomy , hormone receptor , calcium , biochemistry , cancer , gene , breast cancer , enzyme
It is well established that parathyroid hormone‐related protein (PTHrP) regulates chondrocytic differentiation and endochondral bone formation. Besides its effect on cartilage, PTHrP and its major receptor (type I PTH/PTHrP receptor) have been found in osteoblasts, suggesting an important role of PTHrP during the process of intramembranous bone formation. To clarify this issue, we examined intramembranous ossification in homozygous PTHrP‐knockout mice histologically. We also analyzed phenotypic markers of osteoblasts and osteoclasts in vitro and in vivo. A well‐organized branching and anastomosing pattern was seen in the wild‐type mice. In contrast, marked disorganization of the branching pattern of bone trabeculae and irregularly aligned osteoblasts were recognized in the mandible and in the bone collar of the femur of neonatal homozygous mutant mice. In situ hybridization showed that most of the osteoblasts along the bone surfaces of the wild‐type mice and some of the irregularly aligned osteoblastic cells in the homozygous mice expressed osteocalcin. Alkaline phosphatase (ALP) activity and expression of osteopontin messenger RNA (mRNA) in primary osteoblastic cells did not show significant differences between cultures derived from the mixture of heterozygous mutant and wild‐type mice (+/? mice) and those from homozygous mutant mice. However, both mRNA and protein levels of osteocalcin in the osteoblastic cells of homozygous mutant mice were lower than those of +/? mice, and exogenous PTHrP treatment corrected this suppression. Immunohistochemical localization of characteristic markers of osteoclasts and ruffled border formation did not differ between genotypes. Cocultures of calvarial osteoblastic cells and spleen cells of homozygous mutant mice generated an equivalent number of tartrate‐resistant acid phosphatase‐positive (TRAP + ) mononuclear and multinucleated cells and of pit formation to that of +/? mice, suggesting that osteoclast differentiation is not impaired in the homozygous mutant mice. These results suggest that PTHrP is required not only for the regulation of cartilage formation but also for the normal intramembranous bone development.