Osteoclast function is activated by osteoblastic cells through a mechanism involving cell-to-cell contact.

Abstract

We have established a method for obtaining an enriched preparation of functionally active osteoclast-like multinucleated cells (enriched OCLs) from co-cultures of mouse primary osteoblasts and bone marrow cells. Using these enriched OCLs, the effect of osteoblastic cells on osteoclast function was examined in two assays: a pit formation assay and an assay for actin ring formation. The enriched OCLs cultured for 24 h on dentine slices formed only a few resorption pits. When various numbers of primary osteoblasts were added to the enriched OCLs, the areas of the resorption pits increased proportionally to the number of osteoblasts added. Like primary osteoblasts, the established cell lines of osteoblastic cells (MC3T3-E1 and KS-4) and bone marrow-derived stromal cells (MC3T3-G2/PA6 and ST2) potentiated the pit formation caused by enriched OCLs. In contrast, the fibroblastic cell lines NIH3T3 and C3H10T1/2) and the myoblastic cell line (C2C12) failed to activate OCL function. When cell-to-cell contact between MC3T3-E1 cells and enriched OCLs was prevented, only a few resorption pits were formed. Pit formation by enriched rat osteoclasts placed on dentine slices was also stimulated by adding MC3T3-E1 cells. Actin ring formation and pit forming activity were well correlated in either culture of enriched mouse OCLs or authentic rat osteoclasts on dentine slices. These results indicate that osteoclast function is activated by osteoblastic cells through a mechanism involving cell-to-cell and/or cell-to matrix contact.

Rab27a and Rab27b are involved in stimulation-dependent RANKL release from secretory lysosomes in osteoblastic cells

“…Osteoblasts can support osteoclastogenesis by expressing RANKL molecules on their surface, (12)(13)(14) suggesting the importance of both RANKL expression levels at the whole-cell level and RANKL subcellular localization. While numerous studies have focused on RANKL transcriptional regulation, contributing to an understanding of the regulatory mechanisms of RANKL expression at the whole-cell level, (40)(41)(42) the subcellular localization of RANKL in osteoblastic cells has not been widely investigated.…”

“…(9)(10)(11) However, only RANKL molecules expressed at the cell surface actually can bind to RANK, which is located at the cell surface of osteoclast precursor cells. (12)(13)(14) Therefore, the quantity of RANKL on the osteoblastic cell surface could determine the magnitude of the signal input and the degree of osteoclastogenesis.…”

Effects of compressive stress on the expression of M-CSF, IL-1β, RANKL and OPG mRNA in periodontal ligament cells

“…[3][4][5][6] M-CSF is essential for not only the proliferation of osteoclast progenitors, but also for differentiation into mature osteoclasts and survival in vitro. 27 In contrast, OPG was reported to inhibit osteclastogenesis competing with the binding of RANKL to the RANK.…”

“…Membrane-bound proteins, receptor activator of nuclear factor κB ligand (RANKL), and soluble macrophage colony-stimulating factor (M-CSF) are considered essential factors for osteoclastogenesis produced by osteoblasts and bone marrow stromal cells. [3][4][5][6] In contrast, osteoprotegerin (OPG), a soluble tumor necrosis factor (TNF) receptor homolog, was found to inhibit osteclastogenesis by competing with the binding of RANKL to the RANK (receptor of RANKL). 7 …”

Function of OPG as a traffic regulator for RANKL is crucial for controlled osteoclastogenesis

“…(6)(7)(8) Therefore, the amount of RANK ligand (RANKL) on the osteoblastic cell surface, where RANKL binds to RANK through cell-to-cell contact and triggers downstream signaling in osteoclast precursors, is considered to determine the magnitude of the signal input and the degree of osteoclastogenesis. (9,10) Previously, we have shown that most of the newly synthesized RANKL is transferred from the Golgi apparatus to the lysosomal storage compartment via the route involving vacuolar protein sorting 33a (Vps33a) in osteoblastic cells. (11) There also exists the minor pathway transporting RANKL from the Golgi apparatus to the plasma membrane.…”