[Frontiers in Bioscience E4, 2085-2100, January 1, 2012]

Histology of epiphyseal cartilage calcification and endochondral ossification

Norio Amizuka1, Tomoka Hasegawa1, Kimimitsu Oda2, Paulo Henrique Luiz de Freitas1,3, Kazuto Hoshi4, Minqi Li1, Hidehiro Ozawa5

1Departments of Developmental Biology of Hard Tissue, Graduate School of Dental Medicine, Hokkaido University, Sapporo, Japan, 2Division of Biochemistry, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan, 3Oral and Maxillofacial Surgery, Mario Gatti Hospital, Campinas, Brazil, 4Division of Tissue Engineering, The University of Tokyo Hospital, Tokyo, Japan, 5Institute for Dental Science, Matsumoto Dental Collage, Shiojiri, Japan

TABLE OF CONTENTS

1. Abstract
2. Introduction
2.1. Calcification in hypertrophic zone of cartilage
3. Matrix vesicle-mediated calcification
4. Function of ALPase in cartilage calcification
5. Non-collagenous organic constitutes in cartilage calcification
5.1. Osteopontin
5.2. Osteocalcin and matrix Gla protein
5.3. Proteoglycans
6. Invasion of endothelial cells into hypertrophic zone and osteoclastic resorption of calcified cartilage matrix
7. Apoptosis of hypertrophic chondrocytes
8. Function of MMP-9, -13 and MT1-MMP in endochondral ossification
9. Concluding remarks
10. References

1. ABSTRACT

Cartilage calcification is carried out by chondrocytes as they hypertrophy and begin to secrete matrix vesicles. Calcification initiates when calcium phosphates appear inside these matrix vesicles, forming hydroxyapatite crystals that eventually break through the membrane to form calcifying globules, as in bone calcification. However, the extracellular environment in cartilage is different from that in bone: cartilage is abundant in proteoglycans but contains a small amount of osteopontin. Hypertrophic chondrocytes secrete vesicles in the cartilaginous matrix of intercolumnar septae only, forming well-calcified longitudinal septae and poorly-calcified transverse partitions. Such pattern of vesicle deposition permits the invasion of endothelial cells, which infiltrate into cartilage and induce migration of osteogenic and osteoclastic cells. Osteoclasts resorb the excess of calcified globules in the partitions, shaping calcified cartilage cores paralleling the longitudinal axis of long bones. After the formation of these calcified cartilage cores, endochondral ossification involves a series of well-defined events in which osteogenic cells deposit new bone onto the cartilage core and form primary trabecules. This review presents the histology of epiphyseal cartilage calcification and endochondral ossification.