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Departments of Pediatric Dentistry (M.N., H.N., H.M.), Biochemistry (N.U.), and Oral Histology (S.M., H.O.), Institute for Oral Science (B.Y.H., Y.K., H.O., H.M., N.T.), Matsumoto Dental University, Nagano 399-0781, Japan; Department of Pharmacology, Aichi Gakuin University School of Dentistry (M.M.), Nagoya 464-8650, Japan; Department of Orthopedic Surgery, Shinshu University School of Medicine (H.H., N.S.), Nagano 399-0781, Japan; and Department of Orthopedic Surgery, Osaka City University School of Medicine (K.T.), Osaka 545-8585, Japan
Address all correspondence and requests for reprints to: Naoyuki Takahashi, Ph.D., Institute for Oral Science, Matsumoto Dental University, 1780 Gobara, Hiro-oka, Shiojiri, Nagano 399-0781, Japan. E-mail: takahashinao{at}po.mdu.ac.jp.
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Abstract |
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B ligand (RANKL), in mice induces osteoporosis caused by enhanced bone resorption, but also accelerates bone formation. We examined whether bone formation is coupled with bone resorption in OPG-deficient (OPG-/-) mice using risedronate, an inhibitor of bone resorption. Histomorphometric analysis showed that bone formation-related parameters (e.g. mineral apposition rate and osteoblast surface/bone surface) in OPG-/- mice sharply decreased with suppression of bone resorption by daily injection of risedronate for 30 d. OPG-/- mice exhibited high serum alkaline phosphatase activity and osteocalcin concentration, both of which were decreased to the levels in wild-type mice by the risedronate injection. Serum levels of RANKL were markedly elevated in OPG-/- mice, but were unaffected by risedronate. The ectopic bone formation induced by bone morphogenetic protein-2 implantation into OPG-/- mice was not accelerated even with a high turnover rate of bone, but attenuation of mineral density from the ectopic bone was more pronounced than that in wild-type mice. These results suggest that bone formation is coupled with bone resorption at local sites in OPG-/- mice, and that serum RANKL levels do not reflect this coupling. |
Introduction |
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The discovery of a receptor activator of nuclear factor-B ligand (RANKL) helps elucidate the mechanisms of osteoclast differentiation and function that are regulated by osteoblasts (3, 4, 5). Osteoprotegerin (OPG), a soluble decoy receptor of RANKL, inhibits both differentiation and function of osteoclasts by inhibiting the interaction between RANKL and RANK (the receptor of RANKL) (3, 4, 5). OPG-deficient (OPG-/-) mice exhibited severe osteoporosis due to enhanced osteoclastogenesis as adults (6, 7). Compared with wild-type (WT) mice, adult OPG-/- mice had lower bone mineral density (BMD), characterized by severe trabecular and cortical bone porosity, marked thinning of parietal bones of the skull, and a high incidence of fractures (6, 7). Despite this lower density, osteoblastic bone formation was higher, and serum alkaline phosphatase (ALP) activity was elevated in OPG-/- mice (6). These results suggest that bone formation is coupled with bone resorption in OPG-/- mice.
Juvenile Paget’s disease, an autosomal recessive osteopathy, is characterized by rapidly remodeling woven bone, osteopenia, fractures, and progressive skeletal deformity. A homozygous deletion of the gene encoding OPG was found in two Navajo patients with juvenile Paget’s disease (8). Serum ALP activities and RANKL of these patients were significantly much higher than age-matched control values (8). Thus, OPG is a critical regulator of postnatal skeletal development and homeostasis in humans as well as mice. Mutations of RANK that cause an increase in RANK-mediated nuclear factor-B signaling in vitro have been found in patients suffering from familial expansile osteolysis and familial Paget’s disease of bone (9). The homozygous deletion of an aspartate residue from OPG, which induces loss of function, causes an idiopathic hyperphosphatasia with high bone turnover (10). These results suggest that excessive RANKL-RANK signaling leads to a high turnover state of bone with stimulated osteoblastic bone formation. Lam et al. (11) also reported that RANKL increased anabolic bone formation in vivo when administered as an amino-terminal glutathione-S-transferase fusion protein into mice, suggesting that soluble RANKL in serum might be involved in the high bone turnover.
Bisphosphonates, compounds with a carbon-substituted pyrophosphate structure (P-C-P), inhibit osteoclastic bone resorption in vivo and in vitro (12). Accumulated studies revealed the action mechanism of bisphosphonates as follows: 1) bisphosphonates bind rapidly and tightly to bone mineral when administered in vivo (13); 2) osteoclasts incorporate bisphosphonates during bone resorption (12, 13, 14); and 3) the incorporated bisphosphonate disrupts the cytoskeleton and induces apoptosis of osteoclasts (14, 15). Thus, bisphosphonates inhibit osteoclast function directly and specifically.
Bone morphogenetic proteins (BMPs) induce ectopic bone formation when implanted into muscular tissues (16). We have shown that phosphodiesterase inhibitors, such as pentoxifyline and rolipram, stimulated the recombinant human BMP-2 (rhBMP-2)-induced ectopic bone formation (17, 18). When phosphodiesterase inhibitors were injected into mice bearing rhBMP-2-containing implants, both the size and the mineral content in the ectopic bones induced by rhBMP-2 were higher in the inhibitor-treated mice than in control mice (17, 18). These results suggest that stimulatory or inhibitory circulating factors for bone formation in mice can be detected using a system of rhBMP-2-induced ectopic bone formation.
In the present study we examined whether bone formation is coupled with bone resorption in OPG-/- mice by injecting the mice daily with risedronate, a bisphosphonate, for 30 d. Histomorphometric and histochemical analyses were then performed on the femurs and vertebrae. Concentrations of serum calcium, phosphorous, osteocalcin, OPG, RANKL, and the complex of OPG and RANKL were measured. To determine whether a coupling factor is a systemic factor, circulating factors for bone formation were also examined in OPG-/- mice using a system of rhBMP-2-induced ectopic bone formation. When risedronate was daily injected into OPG-/- and WT mice for 30 d, bone formation-related parameters (e.g. mineral apposition rate and osteoblast surface/bone surface) were sharply decreased with the suppression of osteoclastic bone resorption in OPG-/- mice. However, ectopic bone formation was similarly induced by the implantation of rhBMP-2 in OPG-/- and WT mice. The serum concentration of RANKL was markedly elevated in OPG-/- mice, but was unaffected by the administration of risedronate. These results suggest that bone formation is tightly coupled with bone resorption at local sites in OPG-/- mice, and that serum levels of RANKL do not reflect the coupling.
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Materials and Methods |
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Bone histomorphometry
Zero (saline solution alone) or 0.01 mg risedronate/kg body weight·d was sc injected into OPG-/- (14-wk-old), OPG+/- (6-wk-old), and WT (14-wk-old) mice daily for 30 d (11 animals/group). Tetracycline hydrochloride (Sigma-Aldrich Corp., St. Louis, MO; 30 mg/kg body weight) and calcein (Sigma-Aldrich Corp.; 6 mg/kg body weight) were injected on d 26 and 28, respectively, for in vivo fluorescent labeling of mineralization sites. Nine mice of each group were killed on d 30 for bone histomorphometric analysis. Their femurs and vertebrae were then removed, fixed in 70% ethanol, and embedded in glycol-methacrylate without decalcification. Sections were prepared and stained with Villanueva Goldner to discriminate between mineralized and unmineralized bone and to identify cellular components. Quantitative histomorphometric analysis was performed in a blind fashion. Images were also visualized by fluorescent microscopy. Nomenclature and units were used according to the recommendation of the nomenclature committee of the American Society for Bone and Mineral Research (19).
Tissue preparation for the histological analysis of bone
Two mice from each group were anesthetized with Ketalar (Sankyo, Tokyo, Japan) and were perfused for 15 min with 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.3) through the left ventricle on d 30. Femurs were removed and immersed immediately in the same fixative for an additional 20 h at 4 C. After specimens were washed with phosphate buffer, they were decalcified in 10% EDTA-2Na in 0.1 M Tris buffer (pH 7.3) for 3–4 wk at 4 C. Decalcified specimens were then washed in phosphate buffer, dehydrated in a graded series of ethanol, and embedded in semi-water-soluble resin (Immuno-Bed kit, Polysciences, Inc., Warrington, PA). Tartrate-resistant acid phosphatase, a marker enzyme of osteoclasts, was detected using enzyme histochemistry with naphthol AS-MX phosphate (Sigma-Aldrich Corp.) as a substrate and Fast Violet LB salt (Sigma-Aldrich Corp.) as a dye as previously described (7, 20).
Measurements of serum calcium, phosphorous, and osteocalcin
Blood from 18-wk-old male OPG-/- mice and WT mice with or without risedronate treatment was collected by heart puncture under anesthesia with diethylether. Serum concentrations of calcium and phosphorus were measured using a calcium E kit (Wako, Osaka, Japan) and an inorganic phosphorus C kit (Wako), respectively. Serum ALP activity was determined by the method of Woltgens et al. (21) with a slight modification as described previously (22). The amount of osteocalcin in serum was measured using a sensitive ELISA kit (Biomedical Technologies, Inc., Stoughton, MA).
Measurements of serum OPG, RANKL, and the complex of OPG and RANKL
Serum concentrations of OPG and RANKL in OPG-/-, OPG+/-, and WT mice treated with or without risedronate were measured using the respective ELISA kits (R&D Systems, Inc., Minneapolis, MN) as described previously (23). Serum concentrations of the complex of RANKL and OPG were also determined by the quantitative sandwich ELISA system using microplates precoated with anti-RANKL polyclonal antibodies and peroxidase-linked anti-OPG polyclonal antibodies (R&D Systems, Inc.). Quantitative analysis of the complex form of RANKL and OPG showed that RANKL bound to OPG in an equivalent molarity, and that preincubation of RANKL and OPG for 30 min at 25 C was enough to form the complex. Serum and the various concentrations of the RANKL and OPG complex were pipetted into the wells of microplates precoated with anti-RANKL polyclonal antibodies, and incubated for 12 h at 4 C to allow the binding of RANKL present in the samples to the immobilized anti-RANKL antibodies. After washing away unbound substances using PBS, peroxidase-linked polyclonal antibodies against mouse OPG were added to the wells for 2 h at room temperature. The wells were washed with PBS and then incubated with a substrate solution (tetramethylbenzidine and hydrogen peroxide) as described. The enzyme reaction yielded a blue product that turned yellow when a stop solution (1 M HCl) was added. Measurement of the complex was conducted at 450 nm using a plate reader (Biolumin 960, Amersham Pharmacia Biotech, Arlington Heights, IL). The intra- and interassay coefficients of variation were less than 11.2%.
Ectopic bone formation
rhBMP-2 was produced by Genetic Institute (Cambridge, MA) and was donated to us through Yamanouchi Pharmaceutical (Tokyo, Japan). rhBMP-2 was provided in a buffer solution (5 mM glutamic acid, 2.5% glycine, 0.5% sucrose, and 0.01% Tween 80) at a concentration of 1 µg/µl after filter sterilization. Individual implant pellets were prepared as follows: 5 µl of the rhBMP-2 solution (1 mg/ml) were added to 20 µl 0.01 M HCl, then blotted onto a collagen sponge disk (6-mm diameter, 1-mm thickness) fabricated from commercially available bovine collagen sheets (Helistat, Integra Life Sciences Co., Plainsboro, NJ), freeze-dried as a pellet, and kept at -20 C until implantation into mice. Before the surgery for implantation, mice were anesthetized with diethylether. The pellets were implanted into the left dorsal muscle pouches (one pellet per animal) in OPG-/- and WT mice and then harvested after 3, 6, 9, and 12 wk. At the end of the implantation periods, the implants were harvested to evaluate size, BMD, and bone mineral content of the rhBMP-2-induced ossicle. All harvested tissues were radiophotographed with a soft x-ray apparatus (Sofron Co., Tokyo, Japan). BMD (milligrams per square centimeter) of each ossicle was measured by single energy x-ray absorptiometry using a bone mineral analyzer (DCS-600R, Aloka Co., Tokyo, Japan) (17, 18).
Statistics
Data are expressed as the mean ± SEM. Statistical analysis was performed by t test.
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Results |
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). Treatment of OPG-/- mice as well as WT mice with risedronate increased the trabecular bones in the femoral neck portions (Fig. 1A). High magnification of the femoral cortical bone showed that osteoblasts of untreated OPG-/- mice existed as cuboidal osteoblasts along the bone surface (Fig. 1B). Risedronate treatment changed the shape of osteoblasts from cuboidal to flat. Cross-sections of femurs of untreated OPG-/- mice revealed excessive osteoclastic bone resorption in the endosteal sites (Fig. 1C). Risedronate treatment of OPG-/- mice inhibited bone resorption and increased the bone volume of femoral cortical portions. Te porous area of cortical bone was strikingly larger in untreated OPG-/- mice than in WT mice (Fig. 1E). Risedronate treatment of OPG-/- mice significantly reduced the porous area/cortical area. The double labeling study with tetracycline and calceine revealed that the width of double labels was increased in both endosteal and periosteal surfaces of cortical bones in untreated OPG-/- mice (Fig. 1D). Risedronate treatment narrowed this width. Bone formation rates of cortical bones in untreated OPG-/- mice were 2.5-fold in the endosteal surface and 1.4-fold higher in the periosteal surface than those in WT mice (Fig. 1E). Risedronate treatment of OPG-/- mice returned the elevated bone formation rates to those of WT mice.
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). Risedronate treatment markedly increased vertebral trabecular bones in OPG-/- mice as well as in WT mice. Bone resorption-related parameters (osteoclast surface/bone surface, osteoclast number/bone surface, and eroded surface/bone surface) were all elevated in untreated OPG-/- mice (Fig. 2B). Risedronate treatment significantly decreased these elevated parameters. Risedronate treatment only slightly decreased these bone resorption-related parameters in WT mice (Fig. 2B).
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), osteoblasts along the vertebral trabecular bones of untreated OPG-/- mice were more cuboidal than those in WT mice (Fig. 3A). Risedronate treatment of OPG-/- mice changed the shape of the osteoblasts from cuboidal to flat. A double-labeling study revealed that mineralization of trabecular bones in untreated OPG-/- mice was markedly elevated, and treatment with risedronate apparently suppressed the mineralization of these bones, as evidenced by the disappearance of the thickly labeled surfaces (arrows in Fig. 3B). The static histomorphometric measurements showed that bone formation-related parameters (osteoid volume/bone volume, mineral apposition rate, osteoblast surface/bone surface, and bone formation rate/bone surface) were all significantly higher in untreated OPG-/- mice than in WT mice (Fig. 3C). Risedronate treatment decreased these elevated bone formation-related parameters to levels lower than those in WT mice. Risedronate treatment also decreased the bone formation-related parameters in WT mice (Fig. 3C). Bone volume/tissue volume and trabecular number of vertebrae were significantly lower in OPG-/- mice than in WT mice (Fig. 3D). Risedronate treatment increased bone volume and trabecular number in both OPG-/- and WT mice. These results suggest that the increase in bone resorption due to OPG deficiency is more accelerated than the compensatory increase in bone formation in OPG-/- mice.
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). Serum phosphorus levels in risedronate-treated mice were significantly lower than those in WT mice (Fig. 4). Serum parameters of bone formation (ALP activity and osteocalcin concentration) were about four and three times higher, respectively, in OPG-/- mice than in WT mice (Fig. 4). Risedronate treatment of OPG-/- mice resulted in decreases in serum ALP activity and osteocalcin concentration to the levels found in WT mice.
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). Although serum OPG was detectable in OPG+/- and WT mice, the level in OPG+/- mice was significantly lower than that in WT mice. The serum level of RANKL was extremely low in WT mice, but was markedly elevated in OPG-/- mice. The serum level of RANKL in OPG+/- mice was significantly higher than that in WT mice, but lower than that in OPG-/- mice. There was a possibility that OPG interfered with the interaction between anti-RANKL antibodies and RANKL in the ELISA when OPG formed a complex with RANKL in serum. Therefore, we established an ELISA for the complex of OPG-RANKL and then compared the serum levels of the complex among OPG-/-, OPG+/-, and WT mice (Fig. 5). The complex of OPG-RANKL in serum was detected in OPG+/- mice but not in WT mice (Fig. 5). Treatment of OPG-/-, OPG+/-, and WT mice with risedronate showed no effect on the circulating levels of RANKL, OPG, and the complex of OPG and RANKL (Fig. 5). These results suggest that circulating RANKL does not reflect the status of bone resorption and formation in OPG-/- mice, and that the serum concentration of RANKL is tightly regulated by circulating OPG.
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). rhBMP-2-containing collagen disks were implanted into the left dorsal muscular pouches of OPG-/- and WT mice and then recovered after 3, 6, 9, and 12 wk. Soft x-ray images reveal that in collagen disks recovered after 3 wk the areas of calcified mass in the OPG-/- mice were similar in size to those in WT mice, whereas in disks recovered at 6 wk the areas were apparently less in the OPG-/- mice than in the WT mice (Fig. 6A). BMD of the implants recovered after 3 wk from OPG-/- mice was similar to that from WT mice, but BMD after 6 wk was significantly lower in OPG-/- mice than in WT mice (Fig. 6B). There was no significant difference in bone mineral content between OPG-/- and WT mice at 3 wk (data not shown). In addition, histological examination revealed that rhBMP-2 similarly stimulated trabecular bone formation in OPG-/- and WT mice at 3 wk (data not shown). These results suggest that ectopic bone formation induced by rhBMP-2 was not accelerated even with a high turnover rate of bone in OPG-/- mice.
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Discussion |
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Our histomorphometric analysis clearly showed that the elevated osteoblast function in OPG-/- mice was sharply decreased after the suppression of bone resorption by daily injection of risedronate. OPG-/- mice also showed high serum levels of ALP activity and osteocalcin, both of which were decreased to levels lower than those in WT mice by bisphosphonate administration. Thus, the osteocalcin concentration as well as ALP activity in serum sharply reflected the status of osteoblast function. Treatment of primary osteoblasts with risedronate at 10-7 M showed no inhibitory effect on ALP activity (data not shown), whereas the same concentration of risedronate significantly inhibited pit-forming activity of osteoclasts placed on dentine slices (24). Neither RANKL (1–300 ng/ml) nor OPG (1–1000 ng/ml) showed inhibitory or stimulatory effects on the proliferation and ALP activity in the culture of primary osteoblasts derived from OPG-/- mice and WT mice (data not shown). These results suggest that bone formation is tightly coupled with bone resorption in OPG-/- mice.
To date, many studies have shown that induction of bone resorption by bone-resorbing factors (e.g. PTH, 1,25-dihydroxyvitamin D3, and prostaglandin E2) resulted in the stimulation of bone formation (25, 26, 27). However, these factors act on osteoblasts to induce RANKL expression (5). Therefore, it is difficult to determine whether the bone formation induced by bone-resorbing factors is the result of bone resorption or is a phenomenon independent of bone resorption. Our results showed that inhibition of osteoclast activity in OPG-/- mice by a bisphosphonate results in suppression of osteoblast function without any change in the RANKL-RANK interaction. High serum concentrations of RANKL in OPG-/- mice remained unchanged even after suppression of bone resorption by bisphosphonate. These results further support the hypothesis that osteoclastic bone resorption directly activates osteoblast function.
Clarifying the mechanism of coupling between bone resorption and formation is important for understanding the regulation of bone metabolism. Activated osteoblasts with cuboidal shape were often observed near sites where osteoclasts were actively resorbing bones. Such osteoblasts were observed not only in trabecular bones, but also in cortical bones in OPG-/- mice. Wide double lines of calceine and tetracycline, which indicate accelerated bone formation, were localized at sites where osteoclastic bone resorption appeared to have taken place. These results suggest that a coupling factor is released during osteoclastic bone resorption as a local factor. In our preliminary experiments osteoclasts produced a factor that induced differentiation of immature mesenchymal cells into ALP-expressing cells (28). However, the width of the double labeling in the periosteal surface of cortical bones was also increased in OPG-/- mice. Bone resorption in the periosteal surface was not as clearly evident as resorption in the endosteal surface. Osteocyte-mediated signals that relate to bone strain induced by bone resorption may stimulate osteoblast function (29). This would explain the increase in periosteal bone formation when bone resorption was not increased.
Although increases in the width of the double labeling were observed in the periosteal surface of cortical bones in OPG-/- mice, cortical bone parameters (cortical area and cortical thickness) were not significantly increased in the mutant mice (data not shown). These results suggest that turnover in cortical bone and that in trabecular bone in growing mice are regulated differently. The coupling itself or the coupling factor might not be directly involved in the determination of the size of cortical bone. However, it should be noted that enlarged porous areas of the cortical bone were observed only in OPG-/- mice, and risedronate treatment significantly reduced the porous areas. These results suggest that OPG plays an important role in turnover in cortical bone.
Whyte et al. (8) reported that serum levels of RANKL were markedly elevated in a patient with juvenile Paget’s disease. We confirmed that serum RANKL was similarly elevated in OPG-/- mice. Risedronate treatment of OPG-/-, OPG+/-, and WT mice showed no effect on the circulating levels of RANKL and OPG in both types of mice. We examined RANKL mRNA expression in tibiae obtained from OPG-/- and WT mice using RT-PCR techniques. The level of tibial RANKL mRNA expression in OPG-/- mice was similar to that in WT mice (data not shown). This result was consistent with our previous finding that calvarial osteoblasts prepared from OPG-/-, OPG+/-, and WT mice constitutively expressed similar levels of RANKL mRNA, which were similarly elevated by the treatment with 1,25-dihydroxyvitamin D3 (30). We have also shown that RANKL expressed by OPG-deficient osteoblasts functions as a membrane- or matrix-associated form (30). These results suggest that OPG deficiency does not affect local expression of RANKL mRNA, and the serum concentration of RANKL is tightly regulated by circulating OPG at the posttranslational level. RANKL expressed by osteoblasts as a membrane- or matrix-associated form appears to play essential roles in increased osteoclast differentiation and function in OPG-/- mice. However, the possibility that circulating RANKL as well as locally expressed RANKL have important roles in OPG deficiency-induced bone resorption cannot be excluded.
Lam et al. (11) reported that RANKL increased anabolic bone formation in vivo when administered as an amino-terminal glutathione-S-transferase fusion protein into mice. However, our results suggest that circulating RANKL does not reflect the status of bone formation in OPG-/- mice. It is therefore unlikely that circulating soluble RANKL is a coupling factor transmitting bone resorption and bone formation in OPG-/- mice. Serum levels of RANKL and OPG in OPG+/- mice were intermediate between those of OPG-/- and WT mice. Interestingly, the complex of OPG and RANKL was detected only in the serum of OPG+/- mice. Serum concentrations of RANKL in OPG+/- mice were similar to those of the RANKL-OPG complex, suggesting that most of RANKL detected in the serum of OPG+/- mice forms the complex with OPG. Although several reports showed that T cells release RANKL as the soluble form (31, 32, 33), the origin of serum RANKL remains unknown. The mechanism of action of OPG in the release of RANKL and the origin of soluble RANKL in OPG-/- mice are currently under investigation in our laboratories.
To determine whether the coupling factor is a systemic factor, we examined ectopic bone formation induced by implantation of BMP-2 into OPG-/- and WT mice. BMD of ectopic bone evaluated 3 wk after the implantation showed no significant difference between OPG-/- and WT mice. Thus, BMP-induced ectopic bone formation in OPG-/- mice was not accelerated even in the high turnover state of bone, suggesting that the coupling factor is a local factor. Attenuation of minerals from ectopic bones 6 wk after implantation was clearly more pronounced in OPG-/- mice than in WT mice. The number of osteoclasts appearing in the ectopic bones was higher in OPG-/- mice than in WT mice (data not shown). Thus, the increase in osteoclastic bone resorption in BMP-induced ectopic bone may have masked systemic and anabolic signals for bone formation in OPG-/- mice. Further experiments are needed to determine the role of osteoclastic bone resorption in ectopic bone formation.
Both bone resorption and formation were extremely enhanced in OPG-/- mice, but bone volume in these mice was gradually decreased after birth. This suggests that bone resorption induced by OPG deficiency exceeds bone formation induced by the coupling mechanism. The decrease in bone volume even in the high turnover state of bone is also observed in postmenopausal osteoporosis. Recently, Kawano et al. (34) reported that androgen receptor-deficient male mice exhibited high bone turnover with increased bone resorption and formation, but their trabecular and cortical bone masses were significantly reduced. They also found that deficiency in androgen receptors enhanced RANKL expression in osteoblasts that resulted in the stimulation of osteoclastogenesis (34). These results suggest that bone loss is induced even in the high turnover state of bone if bone resorption exceeds bone formation in some bone deceases.
In conclusion, bone formation was tightly coupled with bone resorption in OPG-/- mice. BMP-induced ectopic bone formation was not accelerated even at the high turnover state of bone in OPG-/- mice. Bisphosphonates appear to be first choice medicines for the treatment of diseases that have a high turnover rate of bone, such as Paget’s disease (12). Moreover, our results support the usefulness of bisphosphonate treatment in children with OPG deficiency-related idiopathic hyperphosphatasia and suggest that a coupling factor transmitted from bone resorption to bone formation exists at the local sites of bone. Further studies are necessary to elucidate the characteristics of this coupling factor. Such an approach will provide valuable information for the treatment of metabolic bone diseases such as osteoporosis and rheumatoid arthritis.
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Acknowledgments |
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Footnotes |
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Abbreviations: ALP, Alkaline phosphatase; BMD, bone mineral density; OPG, osteoprotegerin; RANKL, receptor activator of nuclear factor-B ligand; rh, recombinant human; WT, wild-type.
Received June 9, 2003.
Accepted for publication September 9, 2003.
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References |
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|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
,25-dihydroxyvitamin D3 in osteoclast differentiation and function. Methods Enzymol 282:223–235[Medline]
B ligand and tumor necrosis factor- in bone destruction in rheumatoid arthritis. Bone 30:340–346[Medline]
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|
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S. Yang, N. Takahashi, T. Yamashita, N. Sato, M. Takahashi, M. Mogi, T. Uematsu, Y. Kobayashi, Y. Nakamichi, K. Takeda, et al. Muramyl Dipeptide Enhances Osteoclast Formation Induced by Lipopolysaccharide, IL-1{alpha}, and TNF-{alpha} through Nucleotide-Binding Oligomerization Domain 2-Mediated Signaling in Osteoblasts J. Immunol., August 1, 2005; 175(3): 1956 - 1964. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Hamerman Osteoporosis and atherosclerosis: biological linkages and the emergence of dual-purpose therapies QJM, July 1, 2005; 98(7): 467 - 484. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Karsdal, K. Henriksen, M. G. Sorensen, J. Gram, S. Schaller, M. H. Dziegiel, A.-M. Heegaard, P. Christophersen, T. J. Martin, C. Christiansen, et al. Acidification of the Osteoclastic Resorption Compartment Provides Insight into the Coupling of Bone Formation to Bone Resorption Am. J. Pathol., February 1, 2005; 166(2): 467 - 476. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Sato, N. Takahashi, K. Suda, M. Nakamura, M. Yamaki, T. Ninomiya, Y. Kobayashi, H. Takada, K. Shibata, M. Yamamoto, et al. MyD88 But Not TRIF Is Essential for Osteoclastogenesis Induced by Lipopolysaccharide, Diacyl Lipopeptide, and IL-1{alpha} J. Exp. Med., September 7, 2004; 200(5): 601 - 611. [Abstract] [Full Text] [PDF]
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