Content area
Full Text
Calcif Tissue Int (2004) 75:253261DOI: 10.1007/s00223-004-0172-3Osteoblast-like Cells Complete Osteoclastic Bone Resorption and Form
New Mineralized Bone Matrix In VitroM. T. K. Mulari,1 Q. Qu,2 P. L. Harkonen,1 H. K. Vaananen11Department of Anatomy and MediCity Research Laboratory, Institute of Biomedicine, University of Turku, Turku, Finland2Department of Liver Surgery, General Post and Telecommunication Hospital/8th Teaching Hospital of Peking University, Beijing, ChinaReceived: 12 December 2003 / Accepted: 4 February 2004 / Online publication: 19 May 2004Abstract. Bone remodeling involves old bone resorption
by osteoclasts and new bone formation by osteoblasts.
However, the precise cellular mechanisms underlying
these consecutive events remain obscure. To address this
question in vitro, we have established a cell culture
model in which the resorption lacunae are rst created
by osteoclasts and osteoblast-like cells accomplish the
subsequent bone formation. We isolated osteoclasts
from rat bone marrow and cultured them on bovine
bone slices for 48 hours to create resorption lacunae.
After removing osteoclasts, conuent dierentiated
primary osteoblast cultures were trypsinized and the
cells were replaced on the resorbed bone slices for up to
14 days. The cultures were then examined by confocal
microscopy, eld emission scanning electron microscopy
(FESEM), and transmission electron microscopy
(TEM). Our data suggest that after osteoclastic bone
resorption, osteoblast-like cells, not macrophages, remove the remaining organic matrix in the lacuna. After
cleaning the lacuna, osteoblast-like cells deposit new
collagen brils at the bottom of the lacuna and calcify
the newly formed matrix only, as visualized by labeled
tetracycline accumulation merely in the lacuna during
the osteoblast culture. Furthermore, an electron-dense
layer rich in osteopontin separates the old and new
matrices suggesting formation of the cement line. Since
the morphology of the newly formed matrix is similar to
the natural bone with respect to the cement line and
osteoid formation as well as matrix mineralization, the
present method provides for the rst time a powerful in
vitro method to study the cellular mechanisms leading to
bone remodeling also in vivo.Key words: Bone remodeling Bone resorption
Osteoblast Osteoclast OsteopontinHighly regulated bone remodeling is necessary for adequate bone metabolism. Old bone is resorbed by osteoclasts, and new bone is subsequently formed by
osteoblasts. In the normal adult skeleton, bone formation occurs in sites where bone resorption has previously
occurred. Thus, these processes are coupled...