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World J Orthop. Nov 18, 2012; 3(11): 175-181
Published online Nov 18, 2012. doi: 10.5312/wjo.v3.i11.175
New roles of osteoblasts involved in osteoclast differentiation
Teruhito Yamashita, Naoyuki Takahashi, Nobuyuki Udagawa
Teruhito Yamashita, Naoyuki Takahashi, Institute for Oral Science, Matsumoto Dental University, 1780 Gobara, Hirooka, Shiojiri, Nagano 399-0781, Japan
Nobuyuki Udagawa, Department of Biochemistry, Matsumoto Dental University, 1780 Gobara, Hirooka, Shiojiri and Nagano 399-0781, Japan
Author contributions: Yamashita T, Takahashi N and Udagawa N wrote the manuscript; Yamashita T and Takahashi N drew the figures and revised the manuscript.
Correspondence to: Teruhito Yamashita, PhD, Institute for Oral Science, Matsumoto Dental University, 1780 Gobara, Hirooka, Shiojiri, Nagano 399-0781, Japan.
Telephone: +81-263-512235 Fax:+81-51-2632223
Received: June 28, 2012
Revised: October 21, 2012
Accepted: November 1, 2012
Published online: November 18, 2012

Bone-resorbing osteoclasts are formed from a monocyte/macrophage lineage under the strict control of bone-forming osteoblasts. So far, macrophage colony-stimulating factor (M-CSF), receptor activator of nuclear factor-κB ligand (RANKL), and osteoprotegerin (OPG) produced by osteoblasts play major roles in the regulation of osteoclast differentiation. Recent studies have shown that osteoblasts regulate osteoclastogenesis through several mechanisms independent of M-CSF, RANKL, and OPG production. Identification of osteoclast-committed precursors in vivo demonstrated that osteoblasts are involved in the distribution of osteoclast precursors in bone. Interleukin 34 (IL-34), a novel ligand for c-Fms, plays a pivotal role in maintaining the splenic reservoir of osteoclast-committed precursors in M-CSF deficient mice. IL-34 is also able to act as a substitute for osteoblast-producing M-CSF in osteoclastogenesis. Wnt5a, produced by osteoblasts, enhances osteoclast differentiation by upregulating RANK expression through activation of the non-canonical Wnt pathway. Semaphorin 3A produced by osteoblasts inhibits RANKL-induced osteoclast differentiation through the suppression of immunoreceptor tyrosine-based activation motif signals. Thus, recent findings show that osteoclast differentiation is tightly regulated by osteoblasts through several different mechanisms. These newly identified molecules are expected to be promising targets of therapeutic agents in bone-related diseases.

Keywords: Osteoclast, Osteoblast, Receptor activator of nuclear factor-κB ligand, Wnt5a, Semaphorin 3A, Interleukin 34