Mechanism by which MLO-A5 late osteoblasts/early osteocytes mineralize in culture: Similarities with mineralization of lamellar bone

C. Barragan-Adjemian, D. Nicolella, V. Dusevich, M. R. Dallas, J. D. Eick, L. F. Bonewald

Research output: Contribution to journalArticle

92 Scopus citations

Abstract

The mechanisms whereby bone mineralizes are unclear. To study this process, we used a cell line, MLO-A5, which has highly elevated expression of markers of the late osteoblast such as alkaline phosphatase, bone sialoprotein, parathyroid hormone type 1 receptor, and osteocalcin and will mineralize in sheets, not nodules. In culture, markers of osteocytes and dendricity increase with time, features of differentiation from a late osteoblast to an early osteocyte. Mineral formation was examined using transmission electron microscopy, scanning electron microscopy with energy-dispersive X-ray analysis, and atomic force microscopy. At 3-4 days of culture, spheres of approximately 20-50 nm containing calcium and phosphorus were observed budding from and associated with developing cellular projections. By 5-6 days, these calcified spheres were associated with collagen fibrils, where over time they continued to enlarge and to engulf the collagen network. Coalescence of these mineralized spheres and collagen-mediated mineralization were responsible for the mineralization of the matrix. Similar calcified spheres were observed in cultured fetal rat calvarial cells and in murine lamellar bone. We propose that osteoid-osteocytes generate spherical structures that calcify during the budding process and are fully mineralized on their developing cellular processes. As the cellular process narrows in diameter, these mineralized structures become associated with and initiate collagen-mediated mineralization.

Original languageEnglish (US)
Pages (from-to)340-353
Number of pages14
JournalCalcified Tissue International
Volume79
Issue number5
DOIs
StatePublished - Nov 1 2006
Externally publishedYes

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Keywords

  • MLO-A5 cells
  • Mineralization
  • Osteoblast
  • Osteocyte
  • Osteoid

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Orthopedics and Sports Medicine
  • Endocrinology

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