北海道歯学雑誌 = Hokkaido Journal of Dental Science;第39巻 第1号

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The diversity of preosteoblastic morphology : Preosteoblastic response to parathyroid hormone

Qiu, Zixuan;Miyamoto, Yukina;Yamamoto, Tomomaya;Hongo, Hiromi;Abe, Miki;Yoshida, Taiji;Yoshino, Hirona;Sasaki, Muneteru;Nagai, Tomoya;Khadiza, Naznin;Yokoyama, Ayako;Zhao, Shen;Mae, Takahito;Kirikoshi, Shoko;Moritani, Yasuhito;Haraguchi, Mai;de Freitas, Paulo Henrique Luiz;Li, Minqi;Amizuka, Norio;Hasegawa, Tomoka

Permalink : http://hdl.handle.net/2115/71543
KEYWORDS : preosteoblast;PTH;ALPase;Runx2;transmission electron microscopy

Abstract

The current concept of a preosteoblast is a precursor of an osteoblast, which is regarded as a transient cell type during osteoblastic differentiation. We have previously demonstrated different phenotypes of preosteoblasts expressing Runx2, ALPase, and BrdU incorporation. Transmission electron microscopy revealed following four distinct preosteoblastic cell types : 1) cells rich in rough endoplasmic reticulum (rER) but with a few vesicles and vacuoles (ERrich/vesicle-poor preosteoblasts), 2) cells extending their cytoplasmic processes connecting distant cells, with a small amount of scattered cisterns of rER and many vesicles and vacuoles (ER-poor/vesicle-rich preosteoblasts), 3) translucent cells showing few dispersed cell organelles and irregular cell shape with a translucent cytoplasm (translucent cells), and 4) small cells without developed cell organelles (small undifferentiated cells). ER-rich/vesicle-poor preosteoblasts were often closely adjacent to mature osteoblasts and therefore appeared to be ready for differentiation into osteoblasts. In contrast, after the administration of parathyroid hormone (PTH), ER-poor/vesicle-rich preosteoblasts rather than ER-rich/vesicle-poor cells significantly increased in number, forming a huge meshwork overlying mature osteoblasts. Thus, ERpoor/vesicle-rich preosteoblasts appeared to respond well to PTH. We also attempted to unveil the cellular behavior of these preosteoblasts against PTH and to dissect the role of osteoclasts on the mediation of PTH anabolic actions. PTH stimulated the proliferation of ER-poor/vesicle-rich preosteoblasts and bone formation in mature osteoblasts. However, an increased population of ER-poor/vesicle-rich preosteoblasts appears to require cell coupling from osteoclasts to differentiate into ER-rich/vesicle-poor preosteoblasts and mature osteoblasts. Without osteoclasts, PTH could induce neither preosteoblastic differentiation into mature osteoblasts nor subsequent bone formation. In this mini-review, we will introduce preosteoblasts in vivo consisting of several cell types with different ultrastructural properties and PTH action on preosteoblasts.

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