Regulation of osteoclast function.
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Animals↗
Biomedical subjects
E Jimi
Publications and source records attributed to E Jimi.
Specific inhibitors of vacuolar H(+)-ATPase trigger apoptotic cell death of osteoclasts.
Osteoclasts are multinucleated bone-resorbing cells that play a critical role in bone remodeling. Specific inhibitors of vacuolar H(+)-ATPase (V-ATPase), concanamycin A and bafilomycin A1, abolish bone resorption by osteoclasts. In this study, we examined whether these V-ATPase inhibitors trigger apoptotic cell death in osteoclasts, using murine osteoclast-like multinucleated cells (OCLs) formed in vitro. Acridine orange staining revealed that the treatment of OCLs with concanamycin A resulted in chromatin condensation and alterations in nuclear morphology within a few hours. The TdT-mediated dUTP-nick-end labeling (TUNEL) reaction confirmed the apoptotic features of OCLs treated with concanamycin A. The accelerated apoptotic cell death induced by concanamycin A occurred in OCLs treated with interleukin-1 alpha or macrophage colony-stimulating factor as well, which are known to elongate the survival time of osteoclasts. In contrast, these inhibitors did not induce cell death of osteoblastic cells isolated from mouse calvaria. These results suggest that functional impairment of V-ATPase triggers apoptotic cell death in osteoclasts.
Animals↗
Interleukin-1 alpha activates an NF-kappaB-like factor in osteoclast-like cells.
We investigated the NF-kappaB transcription factor in osteoclast-like cells. Osteoclast-like cells were differentiated from mouse bone marrow cells in co-culture with mouse calvaria-derived primary osteoblasts in the presence of 1alpha,25-dihydroxyvitamin D3 and prostaglandin E2 in collagen gel-coated dishes. We enriched osteoclast-like cells from the co-cultures by Pronase treatment. When the enriched osteoclast-like cells were treated with phorbol 12-myristate 13-acetate, interleukin-1 (IL-1), calcitonin, or macrophage colony-stimulating factor, only IL-1 activated an NF-kappaB-like factor, which specifically bound to a kappaB motif DNA sequence, as detected by an electrophoretic mobility shift assay. IL-1 also activated NF-kappaB induction in osteoblasts. However, the NF-kappaB-like factor induced by IL-1-stimulated osteoclast-like cells is of smaller molecular size than the factor in osteoblasts, as shown by an electrophoretic mobility shift assay. The NF-kappaB activity of osteoclast-like cells was recognized completely by antibodies against the p50 subunit, and only partially by antibodies against the p65 subunit of NF-++kappaB. Antibodies against c-Rel, Rel B, and p52 did not recognize the NF-kappaB-like factor. These results suggest that IL-1 activates an NF-kappaB-like factor in osteoclast-like cells, which contains p50 and p65-related proteins.
Animals↗
Basic fibroblast growth factor inhibits osteoclast-like cell formation.
Basic fibroblast growth factor (bFGF) inhibited osteoclast-like cell formation in co-cultures of mouse bone marrow cells either with the mouse stromal cell line, ST2, or with primary osteoblastic cells. Basic FGF significantly inhibited the osteoclast-like cell formation, induced by 1 alpha,25-dihydroxyvitamin D3[1 alpha, 25(OH)2D3] when the cytokine was added to the culture, at an intermediate stage, suggesting that bFGF inhibits the differentiation of the osteoclast progenitors. With regard to target cells, bFGF directly affected ST2; it increased [3H] thymidine uptake and decreased the number of alkaline phosphatase-positive cells. In contrast, bFGF had no inhibitory effect on the colony formation of bone marrow cells induced by macrophage colony stimulating factor in methylcellulose culture. In addition, ST2 cells treated with bFGF produced similar amounts of colony forming activity to those without the cytokine. These findings indicated that the bFGF is not involved in the proliferation of progenitor cells even in the presence of ST2 cells. Furthermore, bFGF inhibited osteoclast-like cell formation induced not only by 1 alpha,25(OH)2D3, but also by prostaglandin E2 and by interleukin-11. These results suggest that bFGF inhibits the common site of osteoclast-like cell formation, as induced by different mechanisms. Our data also indicated that the target cells for bFGF in inhibiting osteoclast formation are not osteoclast progenitors but stromal cells such as ST2 and osteoblastic cells, which support osteoclast development.
Acid Phosphatase↗
Chemical and physical properties of the extracellular matrix are required for the actin ring formation in osteoclasts.
To examine the effect of extracellular matrix on osteoclast polarization, we focused on the actin organization in osteoclasts, using murine osteoclast-like multinucleated cells (OCLs) formed in cocultures of osteoblastic cells and bone marrow cells. When OCLs were cultured on either a plastic plate, calcified dentine, or calcium phosphate thin films in the presence of fetal bovine serum (FBS), they similarly formed ringed structures of F-actin dots (actin rings). However, OCLs placed on demineralized dentine or type I collagen gel matrix (collagen gel) failed to form actin rings. In the absence of FBS, actin ring formation in OCLs was induced on plastic plates coated with vitronectin, fibronectin, or type I collagen, but not on those coated with laminin, poly-L-lysine, or bovine serum albumin. Actin ring formation appeared to depend on integrins, since the GRGDS, but not the GRGES, peptide inhibited it in a dose-dependent manner. Moreover, immunoelectron microscopic examination revealed that vacuolar proton ATPase (V-ATPase) was localized along the apical membrane in much higher densities than the basolateral membrane in OCLs placed on plastic coverslips. In OCLs placed on collagen gel, however, V-ATPase was found to be distributed throughout the cytoplasm without polarity. These results suggest that actin ring formation in osteoclasts was dependent on matrix substrates, matrix proteins and integrins, and was closely related to osteoclast function.
Actins↗
Osteoclast function is activated by osteoblastic cells through a mechanism involving cell-to-cell contact.
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.
3T3 Cells↗
Osteoclast function is activated by osteoblastic cells through a mechanism involving cell-to-cell contact.
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 cell (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.
Animals↗
Macrophage colony-stimulating factor and interleukin-1 alpha maintain the survival of osteoclast-like cells.
When mouse bone marrow cells were co-cultured with a stromal cell line. ST2, numerous osteoclast-like multinucleated cells (MNCs) were formed. To enrich the MNCs which were tartrate-resistant acid phosphatase (TRAP)-positive, we treated the cultures with dispase. Enriched TRAP-positive MNCs adhering to the bottom of the dish were cultured for a further 24h with medium containing 15% fetal calf serum. More than 80% of TRAP-positive MNCs were detached from the dish during the culture. However, when ST2 cells were included during the culture period, survival of TRAP-positive MNCs were significantly increased. Moreover, among various factors examined for the survival of TRAP-positive MNCs, only M-CSF and IL-1 alpha were effective in prolonging viability of TRAP-positive MNCs.
Acid Phosphatase↗
Granulocyte-macrophage colony stimulating factor suppresses lipopolysaccharide-induced osteoclast-like cell formation in mouse bone marrow cultures.
Lipopolysaccharide (LPS) is a potent bone resorbing factor. We investigated the effect of LPS on osteoclast formation in three types of cultures. LPS inhibited osteoclast formation induced by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], in a dose-dependent manner, in cultures of whole bone marrow cells without dexamethasone. LPS increased the amount of granulocyte-macrophage colony stimulating factor (GM-CSF) in the culture supernatant, and anti-GM-CSF antiserum almost abolished the inhibition of osteoclast formation by LPS, thereby indicating that GM-CSF generated by treatment with LPS may be responsible for the inhibition of osteoclast formation. In cultures with dexamethasone, the amount of GM-CSF was decreased to one-third of that with 1,25(OH)2D3 alone and was not changed by treatment with LPS. In this culture system, LPS enhanced osteoclast formation. In the coculture system of nonadherent bone marrow cells and a stromal cell line in the presence of 1,25(OH)2D3 and dexamethasone, where no detectable GM-CSF was present in the supernatant, LPS markedly enhanced osteoclast formation, whereas exogenously added GM-CSF (100 pg/ml) almost completely inhibited osteoclast formation. LPS stimulated pit formation on dentin slices by the osteoclast-like cells formed by in vitro culture system.
Animals↗
Dexamethasone stimulates osteoclast-like cell formation by inhibiting granulocyte-macrophage colony-stimulating factor production in mouse bone marrow cultures.
We investigated the effect of glucocorticoid on the generation of osteoclasts. In mouse bone marrow culture systems, dexamethasone, a synthetic glucocorticoid analog, enhanced osteoclast-like cell formation induced by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in a dose-dependent manner. Conversely, dexamethasone inhibited the endogenous production of granulocyte-macrophage colony-stimulating factor (GM-CSF) in bone marrow cultures. GM-CSF, when added exogenously, suppressed not only the osteoclast-like cell formation induced by 1,25-(OH)2D3, but also the stimulatory effect of dexamethasone, and addition of anti-GM-CSF neutralizing antibody to the cultures significantly increased the osteoclast-like cell formation induced by 1,25-(OH)2D3. These observations suggest that dexamethasone directly affects bone marrow cells and enhances osteoclast generation by inhibiting the endogenous production of GM-CSF, which may function as a negative regulator of osteoclast formation.
Acid Phosphatase↗