Effects of Diabetes and Voluntary Exercise on IgA Concentration and Polymeric Immunoglobulin Receptor Expression in the Submandibular Gland of Rats

Background and Objectives: Patients with diabetes are more susceptible to upper respiratory tract infections (URTIs) because they are easily infected. Salivary IgA (sali-IgA) levels play a major role in transmitting URTIs. Sali-IgA levels are determined by salivary gland IgA production and polymeric immunoglobulin receptor (poly-IgR) expression. However, it is unknown whether salivary gland IgA production and poly-IgR expression are decreased in patients with diabetes. While exercise is reported to increase or decrease the sali-IgA levels, it is unclear how exercise affects the salivary glands of patients with diabetes. This study aimed to determine the effects of diabetes and voluntary exercise on IgA production and poly-IgR expression in the salivary glands of diabetic rats. Materials and Methods: Ten spontaneously diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats (eight-week-old) were divided into two groups of five rats each: a non-exercise group (OLETF-C) and a voluntary wheel-running group (OLETF-E). Five Long-Evans Tokushima Otsuka (LETO) rats without diabetes were bred under the same conditions as the OLETF-C. Sixteen weeks after the study began, the submandibular glands (SGs) were collected and analyzed for IgA and poly-IgR expression levels. Results: IgA concentrations and poly-IgR expression levels in SGs were lower in OLETF-C and OLETF-E than in LETO (p < 0.05). These values did not differ between the OLETF-C and OLETF-E. Conclusions: Diabetes decreases IgA production and poly-IgR expression in the salivary glands of rats. Moreover, voluntary exercise increases sali-IgA levels but does not increase IgA production and poly-IgR expression in the salivary glands of diabetic rats. Increasing IgA production and poly-IgR expression in the salivary glands, which is reduced in diabetes, might require slightly higher-intensity exercise than voluntary exercise under the supervision of a doctor.

Correction of Mass Spectrometric Interferences for Rapid and Precise Isotope Ratio Measurements of Calcium from Biological Samples Using ICP-Mass Spectrometry

Stable isotope compositions of calcium (Ca) provide useful information concerning metabolic alterations of Ca in human and animal bodies. For the measurements of Ca isotope ratio, great care must be taken for the mass spectrometric interferences on Ca isotopes (⁴²Ca⁺, ⁴³Ca⁺, and ⁴⁴Ca⁺) from doubly charged strontium (Sr) ions (⁸⁴Sr²⁺, ⁸⁶Sr²⁺, and ⁸⁸Sr²⁺). To obtain reliable stable isotope data of Ca, we developed a new correction technique for the mass spectrometric interferences by ^mSr²⁺ ions based on standard addition method. Addition of a small fraction of Sr onto a Ca solution shifts the measured Ca isotope ratios on a three-isotope diagram (i.e., δ⁴⁴Ca and δ⁴³Ca) along a mixing line defined by both the true Ca isotope ratio and the Sr isotope ratio. Therefore, the true Ca isotope ratio of a sample can be obtained as the crossover point of mass dependent fractionation line and the mixing line. With the present correction technique, precise and accurate isotope ratio measurements can be made on analyte solutions having a C_Sr/C_Ca ratio (concentration ratio) of 0.03, which is 6 times higher than the C_Sr/C_Ca ratio applicable to the conventional correction technique.

Low-Intensity Pulsed Ultrasound Prevents Development of Bisphosphonate-Related Osteonecrosis of the Jaw-Like Pathophysiology in a Rat Model

We developed a rat model of bisphosphonate-related osteonecrosis of the jaw (BRONJ) by removing a maxillary molar tooth (M1) from ovariectomized rats after treatment with alendronate. To mimic periodontitis, some of the rats were administered Porphyromonas gingivalis (p. gingivalis) at the M1 site every 2 to 3 d for 2 wk. Rats pretreated with alendronate plus p. gingivalis showed delayed healing of socket epithelia, periosteal reaction of alveolar bone formation and lower bone mineral density in the alveolus above adjacent M2 teeth. These abnormalities were prevented by tooth socket exposure to 20 min/d low-intensity pulsed ultrasound (LIPUS), which restored diminished expression of RANKL, Bcl-2, IL-6, Hsp70, NF-κB and TNF-α messenger ribonucleic acids in remote bone marrow, suggesting LIPUS prevented development of BRONJ-like pathophysiology in rat by inducing systemic responses for regeneration, in addition to accelerating local healing. Non-invasive treatment by LIPUS, as well as low-level laser therapy, may be useful for medication-related osteonecrosis of the jaw patients.

In-office bleaching for the remineralization of enamel lesions filled with organic components of red wine

PURPOSE

To investigate the effects of in-office bleaching on the remineralization of enamel lesions filled with organic components of red wine.

METHODS

Enamel specimens were exposed to 0.1% NaF solution for 1 minute immersed in red wine for 5 days at 37°C, and subjected to in-office bleaching followed by remineralization in 1.5 mM CaCl₂, 0.9 mM KH₂PO₄, 130 mM KCl, 20 mM HEPES, pH 7.0, at 37°C for 28 days. The presence of organic substances on the enamel surface was detected by Raman spectroscopy. The specimens were also subjected to transverse microradiography (TMR).

RESULTS

Raman spectroscopy of baseline lesions showed characteristic peaks at 1,300-1,600 cm-1 which disappeared in bleached specimens. TMR showed that red wine formed subsurface lesions with surface content at approximately 22 mineral volume %. The integrated mineral loss (IML) was significantly lower in unbleached remineralized specimens than at baseline (P< 0.05). The IML of bleached remineralized specimens was lower than that of unbleached specimens, although not significantly (P> 0.05). Lesion depth was significantly lower in the bleached than in the unbleached group (P< 0.05).

CLINICAL SIGNIFICANCE

In-office bleaching can enhance the remineralization of enamel lesions filled with organic components of red wine.

Alendronate does not prevent long bone fragility in an inactive rat model

The lack of estrogen and inactivity are both important in the pathogenesis of osteoporosis in elderly women, and there have been no appropriate rodent studies to examine the effects of common bisphosphonates on these two components separately. We compared the efficacy of alendronate (ALN) on the long bones of aged female rats, which were sedentary, estrogen deficient, or both. The rats were either forced to remain in a sitting position or allowed to walk in standard cages with or without ALN administration. The 8-week experimental period began 5 weeks after ovariectomy or sham surgery. Parameters of the hindlimb bones were determined by a three-point bending test, peripheral quantitative computed tomography, microfocus computed tomography, confocal laser Raman microspectroscopy, and dynamic histomorphometry. Regardless of ovariectomy, ALN was ineffective against the deterioration of breaking stress caused by sitting even though the trabecular bone mineral density was significantly higher in the sitting-ALN groups. Toughness was significantly deficient in the ovariectomy sitting-ALN group. This was in agreement with the bone geometry with a greater marrow space. Sitting also increased the mineral-to-matrix ratio and the carbonate-to-phosphate ratio, both indicative of aged bone. A greater loss of proteinaceous amide intensity compared with mineral intensity resulted in an increased mineral-to-matrix ratio in the presence of ALN. Sitting resulted in deficits in the quality and the geometry of cortical bone, resulting in fragility. The use of bisphosphonates, such as ALN, may provide a therapy best suited for osteoporotic individuals whose daily activity is not limited.

Mode & mechanism of low intensity pulsed ultrasound (LIPUS) in fracture repair

It has been 30years since the first level one clinical trial demonstrated low intensity pulsed ultrasound (LIPUS) could accelerate fracture repair. Since 1994 numerous investigations have been performed on the effect of LIPUS. The majority of these studies have used the same signal parameters comprised of an intensity of 30mW/cm(2) SATA, an ultrasound carrier frequency of 1.5MHz, pulsed at 1kHz with an exposure time of 20minutes per day. These studies show that a biological response is stimulated in the cell which produces bioactive molecules. The production of these molecules, linked with observations demonstrating the enhanced effects on mineralization by LIPUS, might be considered the general manner, or mode, of how LIPUS stimulates fractures to heal. We propose a mechanism for how the LIPUS signal can enhance fracture repair by combining the findings of numerous studies. The LIPUS signal is transmitted through tissue to the bone, where cells translate this mechanical signal to a biochemical response via integrin mechano-receptors. The cells enhance the production of cyclo-oxygenese 2 (COX-2) which in turn stimulates molecules to enhance fracture repair. The aim of this review is to present the state of the art data related to LIPUS effects and mechanism.

Disruption of NF-κB1 prevents bone loss caused by mechanical unloading

Mechanical unloading, such as in a microgravity environment in space or during bed rest (for patients who require prolonged bed rest), leads to a decrease in bone mass because of the suppression of bone formation and the stimulation of bone resorption. To address the challenges presented by a prolonged stay in space and the forthcoming era of a super-aged society, it will be important to prevent the bone loss caused by prolonged mechanical unloading. Nuclear factor κB (NF-κB) transcription factors are activated by mechanical loading and inflammatory cytokines. Our objective was to elucidate the role of NF-κB pathways in bone loss that are caused by mechanical unloading. Eight-week-old wild-type (WT) and NF-κB1-deficient mice were randomly assigned to a control or mechanically unloaded with tail suspension group. After 2 weeks, a radiographic analysis indicated a decrease in bone mass in the tibias and femurs of the unloaded WT mice but not in the NF-κB1-deficient mice. An NF-κB1 deficiency suppressed the unloading-induced reduction in bone formation by maintaining the proportion and/or potential of osteoprogenitors or immature osteoblasts, and by suppression of bone resorption through the inhibition of intracellular signaling through the receptor activator of NF-κB ligand (RANKL) in osteoclast precursors. Thus, NF-κB1 is involved in two aspects of rapid reduction in bone mass that are induced by disuse osteoporosis in space or bed rest.

Differential age-related bone architecture changes between female and male STR/Ort mice

The incidence of spontaneous osteoarthritis (OA) in female STR/Ort mice is much lower than that observed in male STR/Ort mice; however, the reason for the differential incidence of OA between sexes has not been elucidated. Here, we investigated and compared age- and sex-related bone mineral density and architectural changes in male and female STR/Ort mice. Bone architecture and bone mineral density (BMD) of femurs were examined in 5-, 10-, 15-, 20-, and 35-week-old male and female STR/Ort mice by microscopic computed tomography (µCT). Angular degrees of internal tibial torsion (ADITT) were also measured in mice at 5, 15, and 35 weeks of age. Earlier decreases of cancellous volume and BMD were found in male STR/Ort mice. Using µCT, an age-related decline of bone marrow space in femoral diaphysis was observed in both males and females but was more dramatic in females. In addition, an earlier increase of ADITT was observed in male STR/Ort mice, suggesting that internal rotation of the tibia may contribute to OA. Age- and sex-related bone architectural changes clearly differ between male and female STR/Ort mice. These differences in bone structure, particularly ADITT, may explain the differential incidence of OA in STR/Ort mice.

Mechanotransduction activates α₅β₁ integrin and PI3K/Akt signaling pathways in mandibular osteoblasts

It is unclear how bone cells at different sites detect mechanical loading and how site-specific mechanotransduction affects bone homeostasis. To differentiate the anabolic mechanical responses of mandibular cells from those of calvarial and long bone cells, we isolated osteoblasts from C57B6J mouse bones, cultured them for 1week, and subjected them to therapeutic low intensity pulsed ultrasound (LIPUS). While the expression of the marker proteins of osteoblasts and osteocytes such as alkaline phosphatase and FGF23, as well as Wnt1 and β-catenin, was equally upregulated, the expression of mandibular osteoblast messages related to bone remodeling and apoptosis differed from that of messages of other osteoblasts, in that the messages encoding the pro-remodeling protein RANKL and the anti-apoptotic protein Bcl-2 were markedly upregulated from the very low baseline levels. Blockage of the PI3K and α(5)β(1) integrin pathways showed that the mandibular osteoblast required mechanotransduction downstream of α(5)β(1) integrin to upregulate expression of the proteins β-catenin, p-Akt, Bcl-2, and RANKL. Mandibular osteoblasts thus must be mechanically loaded to preserve their capability to promote remodeling and to insure osteoblast survival, both of which maintain intact mandibular bone tissue. In contrast, calvarial Bcl-2 is fully expressed, together with ILK and phosphorylated mTOR, in the absence of LIPUS. The antibody blocking α(5)β(1) integrin suppressed both the baseline expression of all calvarial proteins examined and the LIPUS-induced expression of all mandibular proteins examined. These findings indicate that the cellular environment, in addition to the tridermic origin, determines site-specific bone homeostasis through the remodeling and survival of osteoblastic cells. Differentiated cells of the osteoblastic lineage at different sites transmit signals through transmembrane integrins such as α(5)β(1) integrin in mandibular osteoblasts, whose signaling may play a major role in controlling bone homeostasis.

A novel underuse model shows that inactivity but not ovariectomy determines the deteriorated material properties and geometry of cortical bone in the tibia of adult rats

Our goal in this study was to determine to what extent the physiologic consequences of ovariectomy (OVX) in bones are exacerbated by a lack of daily activity such as walking. We forced 14-week-old female rats to be inactive for 15 weeks with a unique experimental system that prevents standing and walking while allowing other movements. Tibiae, femora, and 4th lumbar vertebrae were analyzed by peripheral quantitative computed tomography (pQCT), microfocused X-ray computed tomography (micro-CT), histology, histomorphometry, Raman spectroscopy, and the three-point bending test. Contrary to our expectation, the exacerbation was very much limited to the cancellous bone parameters. Parameters of femur and tibia cortical bone were affected by the forced inactivity but not by OVX: (1) cross-sectional moment of inertia was significantly smaller in Sham-Inactive rat bones than that of their walking counterparts; (2) the number of sclerostin-positive osteocytes per unit cross-sectional area was larger in Sham-Inactive rat bones than in Sham-Walking rat bones; and (3) material properties such as ultimate stress of inactive rat tibia was lower than that of their walking counterparts. Of note, the additive effect of inactivity and OVX was seen only in a few parameters, such as the cancellous bone mineral density of the lumbar vertebrae and the structural parameters of cancellous bone in the lumbar vertebrae/tibiae. It is concluded that the lack of daily activity is detrimental to the strength and quality of cortical bone in the femur and tibia of rats, while lack of estrogen is not. Our inactive rat model, with the older rats, will aid the study of postmenopausal osteoporosis, the etiology of which may be both hormonal and mechanical.

Repeated freeze-thaw cycles reduce the survival rate of osteocytes in bone-tendon constructs without affecting the mechanical properties of tendons

Frozen bone-patellar tendon bone allografts are useful in anterior cruciate ligament reconstruction as the freezing procedure kills tissue cells, thereby reducing immunogenicity of the grafts. However, a small portion of cells in human femoral heads treated by standard bone-bank freezing procedures survive, thus limiting the effectiveness of allografts. Here, we characterized the survival rates and mechanisms of cells isolated from rat bones and tendons that were subjected to freeze–thaw treatments, and evaluated the influence of these treatments on the mechanical properties of tendons. After a single freeze–thaw cycle, most cells isolated from frozen bone appeared morphologically as osteocytes and expressed both osteoblast- and osteocyte-related genes. Transmission electron microscopic observation of frozen cells using freeze-substitution revealed that a small number of osteocytes maintained large nuclei with intact double membranes, indicating that these osteocytes in bone matrix were resistant to ice crystal formation. We found that tendon cells were completely killed by a single freeze–thaw cycle, whereas bone cells exhibited a relatively high survival rate, although survival was significantly reduced after three freeze–thaw cycles. In patella tendons, the ultimate stress, Young’s modulus, and strain at failure showed no significant differences between untreated tendons and those subjected to five freeze–thaw cycles. In conclusion, we identified that cells surviving after freeze–thaw treatment of rat bones were predominantly osteocytes. We propose that repeated freeze–thaw cycles could be applied for processing bone-tendon constructs prior to grafting as the treatment did not affect the mechanical property of tendons and drastically reduced surviving osteocytes, thereby potentially decreasing allograft immunogenecity.

Prolonged endochondral bone healing in senescence is shortened by low-intensity pulsed ultrasound in a manner dependent on COX-2

To test whether mechanical loading produces faster healing in aged mice, fractured femurs of aged 1-year-old mice were subjected to low-intensity pulsed ultrasound (LIPUS), a treatment that is routinely used to help heal fractures in humans. Cyclooxygenase-2 knockout mice (COX-2(-/-)), which lack an immediate early mediator of mechanical stimulation, were also studied by histochemistry, microcomputed tomography and quantitative polymerase chain reaction to determine the role of COX-2. The healing in the aged COX-2(-/-) mice is slow during the endochondral bone remodeling (>30 d), a period generally prolonged in senescence. For aged wild-type mice, LIPUS halved the endochondral phase to about 10 d, whereas that was not the case for aged COX-2(-/-) mice, which showed no apparent shortening of the prolonged endochondral-phase healing time. Injecting prostaglandin E(2) receptor agonists, however, rescued the COX-2(-/-) callus from insensitivity to LIPUS. In conclusion, COX-2 is a limiting factor in the delayed endochondral bone healing and is induced by LIPUS, which normalizes healing rate to the wild-type level.

Prior treatment with vitamin K(2) significantly improves the efficacy of risedronate

Prior 8-week treatment with menatetrenone, MK-4, followed by 8-week risedronate prevented the shortcomings of individual drugs and significantly increased the strength of ovariectomized ICR mouse femur compared to the ovariectomized (OVX) controls. Neither MK-4 following risedronate nor the concomitant administration may be recommended because they brought the least beneficial effect.

INTRODUCTION

The objective of this study was to determine the best combinatory administration of risedronate at 0.25 mg/kg/day (R) with vitamin K(2) at approximately 100 microg MK-4/kg/day (K) to improve strength of osteoporotic mouse bone.

METHODS

Thirteen-week-old ICR mice, ovariectomized at 9-week, were treated for 8 weeks with R, K, or R plus K (R/K), and then, either the treatment was withdrawn (WO) or switched to K or R in the case of R and K. After another 8 weeks, the mice were killed, and mechanical tests and analyses of femur properties by peripheral quantitative computed tomography, microfocus X-ray tube computed tomography, and confocal laser Raman microspectroscopy were carried out.

RESULTS

The K to R femur turned out superior in parameters tested such as material properties, bone mineral density, BMC, trabecular structure, and geometry of the cortex. The increased cross-sectional moment of inertia, which occurred after K withdrawal, was prevented by risedronate in K to R. In addition to K to R, some properties of R to WO diaphysis and K to WO epiphysis were significantly better than OVX controls.

CONCLUSION

Prior treatment with MK-4 followed by risedronate significantly increased femur strength in comparison to the OVX controls.

Therapeutic ultrasound induces periosteal ossification without apparent changes in cartilage

Low intensity pulsed ultrasound (LIPUS) is an extremely useful noninvasive treatment which halves the duration of fracture healing when the bone is exposed once a day for 20 min. To elucidate the direct reactions of bone and cartilage, dissected rat femora were immobilized in culture dish wells, exposed to LIPUS from a certain angle every day, and the local pattern of ossification was analyzed in relation to the ultrasound. Daily 20-min exposures were started 24 hr after isolation of the femora, and at days 5, 10, and 15, samples were harvested for measurements, morphological, and histochemical analyses. While the gross features of the samples were identical to the untreated controls, extended mineralization of the periosteum was observed with alizarin red staining, antiosteocalcin immunohistochemical staining, and micro-three dimensional computed tomography. Interestingly, the newly deposited mineral was found perpendicular to the ultrasound path, strongly suggesting that LIPUS accelerates periosteal bone formation. Zones of epiphyseal cartilage and hypertrophic and calcified cartilage did not exhibit any differences with and without this exposure. LIPUS also did not influence the secreted proteoglycan components or amounts in the culture medium. The absence of any additional longitudinal growth of the femur demonstrated that LIPUS did not accelerate endochondral bone formation. We conclude that cartilage alone does not directly respond to therapeutic ultrasound, whereas the periosteum does.

Osteoarthritic changes of the patellofemoral joint in STR/OrtCrlj mice are the earliest detectable changes and may be caused by internal tibial torsion

STR/ort mice develop a naturally occurring osteoarthritis (OA) of the knee joints. However, the evaluation of early OA changes has been difficult due to variability caused by gender, individual differences, and differences between the right and left lower limbs. The objective of this study was to analyze the variability of the early OA changes with age in STR/ort mice and to identify the cause of onset. A total of 115 STR/OrtCrlj mice aged 10-45 weeks were examined. In addition to conventional radiological and histological evaluation of the knee joints, histological sections were used to examine the patellofemoral, femorotibial, and growth plate cartilage under similar conditions. A morphological evaluation of tibiae, including micro-3-dimensional computed tomography, was performed. Radiological evaluation showed OA changes in the joints of mice over 35 weeks old and histological evaluation showed early OA changes in the femorotibial joints of mice over 26 weeks old. However, these changes were not common in all individuals. In contrast, most common and reproducible OA changes were observed in the bilateral patellofemoral joints of all individuals, and even in subjects ranging from 10 to 20 weeks of age. Morphological evaluations also demonstrated an abnormal tibial internal torsion that increased with age and was associated with medial patellar dislocation. In conclusion, the earliest histological OA change was observed in the patellofemoral joint prior to similar observations in the femorotibial joint. Internal tibial torsion may be a cause of OA in the patellofemoral joints, which leads to the development of medial femorotibial OA.

Low-intensity pulsed ultrasound activates the phosphatidylinositol 3 kinase/Akt pathway and stimulates the growth of chondrocytes in three-dimensional cultures: a basic science study

Introduction

The effect of low-intensity pulsed ultrasound (LIPUS) on cell growth was examined in three-dimensional-cultured chondrocytes with a collagen sponge. To elucidate the mechanisms underlying the mechanical activation of chondrocytes, intracellular signaling pathways through the Ras/mitogen-activated protein kinase (MAPK) and the integrin/phosphatidylinositol 3 kinase (PI3K)/Akt pathways as well as proteins involved in proliferation of chondrocytes were examined in LIPUS-treated chondrocytes.

Methods

Articular cartilage tissue was obtained from the metatarso-phalangeal joints of freshly sacrificed pigs. Isolated chondrocytes mixed with collagen gel and culture medium composites were added to type-I collagen honeycomb sponges. Experimental cells were cultured with daily 20-minute exposures to LIPUS. The chondrocytes proliferated and a collagenous matrix was formed on the surface of the sponge. Cell counting, histological examinations, immunohistochemical analyses and western blotting analysis were performed.

Results

The rate of chondrocyte proliferation was slightly but significantly higher in the LIPUS group in comparison with the control group during the 2-week culture period. Western blot analysis showed intense staining of type-IX collagen, cyclin B₁ and cyclin D₁, phosphorylated focal adhesion kinase, and phosphorylated Akt in the LIPUS group in comparison with the control group. No differences were detected, however, in the MAPK, phosphorylated MAPK and type-II collagen levels.

Conclusion

LIPUS promoted the proliferation of cultured chondrocytes and the production of type-IX collagen in a three-dimensional culture using a collagen sponge. In addition, the anabolic LIPUS signal transduction to the nucleus via the integrin/phosphatidylinositol 3-OH kinase/Akt pathway rather than the integrin/MAPK pathway was generally associated with cell proliferation.

Low-intensity pulsed ultrasound accelerates periodontal wound healing after flap surgery

BACKGROUND AND OBJECTIVE

A study was conducted to evaluate the effects of low-intensity pulsed ultrasound on wound healing in periodontal tissues after mucoperiosteal flap surgery.

MATERIAL AND METHODS

Bony defects were surgically produced bilaterally at the mesial roots of the mandibular fourth premolars in four beagle dogs. The flaps were repositioned to cover the defects and sutured after scaling and planing of the root surface to remove cementum. The affected area in the experimental group was exposed to low-intensity pulsed ultrasound, daily for 20 min, for a period of 4 wk from postoperative day 1 using a probe, 13 mm in diameter. On the control side, no ultrasound was emitted from the probe placed contralaterally. After the experiment, tissue samples were dissected out and fixed in 10% formalin for histological and immunohistochemical analyses.

RESULTS

The experimental group showed that the processes in regeneration of both cementum and mandibular bone were accelerated by low-intensity pulsed ultrasound compared with the control group. In addition, the expression level of heat shock protein 70 was higher in the gingival epithelial cells of the low-intensity pulsed ultrasound-treated tooth.

CONCLUSION

Our results suggest that osteoblasts, as well as cells in periodontal ligament and gingival epithelium, respond to mechanical stress loaded by low-intensity pulsed ultrasound, and that ultrasound accelerates periodontal wound healing and bone repair.

A crucial role for matrix metalloproteinase 2 in osteocytic canalicular formation and bone metabolism

Extracellular matrix production and degradation by bone cells are critical steps in bone metabolism. Mutations of the gene encoding MMP-2, an extracellular matrix-degrading enzyme, are associated with a human genetic disorder characterized by subcutaneous nodules, arthropathy, and focal osteolysis. It is not known how the loss of MMP-2 function results in the pathology. Here, we show that Mmp2(-/-) mice exhibited opposing bone phenotypes caused by an impaired osteocytic canalicular network. Mmp2(-/-) mice showed decreased bone mineral density in the limb and trunk bones but increased bone volume in the calvariae. In the long bones, there was moderate disruption of the osteocytic networks and reduced bone density throughout life, whereas osteoblast and osteoclast function was normal. In contrast, aged but not young Mmp2(-/-) mice had calvarial sclerosis with osteocyte death. Severe disruption of the osteocytic networks preceded osteocyte loss in Mmp2(-/-) calvariae. Successful transplantation of wild-type periosteum restored the osteocytic canalicular networks in the Mmp2(-/-) calvariae, suggesting local roles of MMP-2 in determining bone phenotypes. Our results indicate that MMP-2 plays a crucial role in forming and maintaining the osteocytic canalicular network, and we propose that osteocytic network formation is a determinant of bone remodeling and mineralization.

AlphaVbeta3 integrin ligands enhance volume-sensitive calcium influx in mechanically stretched osteocytes

We propose that specific osteocyte-matrix interactions regulate the volume-sensitive calcium influx pathway, which we have shown is mediated by stretch-activated cation channels (SA-Cat) and is essential for the stretch-activated anabolic response in bone. The current study measured the hypotonic swelling-induced increase in cytosolic calcium concentration, [Ca(2+)](i), in rat osteocytes, and found that cells adherent to different matrices behave differently. Osteopontin and vitronectin, matrix molecules that bind the alpha(V)beta(3) integrin, induced larger responses to the hypotonic swelling than other matrix molecules that bind other integrins. Addition of echistatin, which is a soluble alpha(V)beta(3) ligand, significantly enhanced the hypotonic [Ca(2+)](i) increase in addition to inducing an immediate increase in [Ca(2+)](i) by itself. These results strongly support the contention that alpha(V)beta(3) integrin signaling in osteocytes interacts with that in mechanotransduction, which is downstream of SA-Cat.

Spontaneous differentiation of mesenchymal stem cells obtained from fetal rat circulation

Mesenchymal stem cells (MSCs) are thought to be multipotential, capable of differentiating into multiple lineages. We attempted to characterize rat cells derived from fetal circulating blood (FCBCs) that displayed a fibroblastic morphology and differentiated into osteoblastic and chondrocytic lineages. Notably, they differentiated into a chondrocyte-specific phenotype on plastic culture dishes in medium supplemented only with 10% fetal bovine serum (FBS) without the use of a three-dimensional culture substrate. Bone marrow-derived cells did not convey such phenotypic expression under the same conditions. The characteristic features of these cells were analyzed by reverse transcription polymerase chain reaction, immunohistological and von Kossa staining, and by immuno-dot blotting. In one population, expression of collagen types II and X was detected in differentiated cells at the same levels as observed in chondrocytes derived from rat rib cartilage. In another population, parathyroid hormone receptor, alkaline phosphatase, and osteocalcin were also expressed at levels almost equal to those observed in long bone-derived osteoblasts. After 3 weeks in culture, extensively condensed cell masses, stained with anti-type II collagen antibody, could be distinguished histologically from small, multilayered, von Kossa-positive nodules, which stained with anti-osteocalcin, but not with anti-type II collagen antibody. In addition, the FCBCs differentiated into adipogenic cells in the presence of methyl-isobutyl xanthine, dexamethasone, insulin, and indomethacin. These cells expressed PPARgamma2 mRNA and accumulated lipid vesicles detectable by Oil red-O staining. Our findings suggest that FCBCs have the potential to readily differentiate into multiple lineages and that they are distinct from mesenchymal stem cells derived from bone marrow or circulating blood from more mature and adults in their spontaneous differentiation in the absence of specific factors such as transforming growth factor-beta (TGF-beta) or dexamethasone, or a three-dimensional culture environment.

Distinct anabolic response of osteoblast to low-intensity pulsed ultrasound

Low-intensity pulsed ultrasound, a form of mechanical energy transmitted as high-frequency acoustical pressure waves, provides noninvasive therapeutic treatment for accelerating fracture repair and distraction osteogenesis. Relatively young osteoblasts respond to ultrasound by transiently upregulating message levels of immediate-early genes as well as that of osteocalcin and insulin-like growth factor I (IGF-I). Osteocytes derived from newborn rat tibia and calvaria responded to a lesser extent only in c-fos and cyclooxygenase-2 (COX-2) messages. Compared with the stretched osteocytes, which use stretch-activated and parathyroid hormone (PTH)-potentiated Ca2+ influx as an entry route to the protein kinase A (PKA) signal transduction pathways, there was no evidence of Ca2+ internalization by any of the cells tested on exposure to the ultrasound. On the other hand, inhibitors of p38 mitogen-activated protein kinase (MAPK) and upstream phosphoinositide 3-kinase (PI3K) blocked COX-2 and osteocalcin upregulation by the ultrasound-exposed ST2, murine bone marrow-derived cells. This is distinct from the aforementioned osteocytic response to low-frequency stretching and implies the involvement of integrins. Our findings suggested that accelerated fracture repair and distraction osteogenesis by the low-intensity pulsed ultrasound depend, at least in part, on the stimulation of osteoblastic cells at relatively early stages of osteogenic lineage. Bone is under control of multiple regulatory mechanisms so that diverse physical forces can be reflected to the microenvironment of each cell, in turn, to the entire bone.

The role of calcium channels in osteocyte function

Osteocytic response to stretching, which is potentiated by PTH, is distinct from that of osteoblast to high frequency strain. A MAPK dependent signaling pathway is suggested in the osteoblast response. At least two different types of mechanotransduction pathways are present in bone cells of osteoblastic lineage.

Matrix metalloproteinase-2 in dentin matrix mineralization

In the serum-free culture medium of bovine odontoblasts we detected active gelatinolytic metalloproteinases, matrix metalloproteinase (MMP)-2 and MMP-9 (gelatinases A and B). The activity of MMP-2, in particular, appeared suddenly around day 21 in the culture, coinciding with the development of odontoblastic cell processes and the loss of alkaline phosphatase. Reverse transcriptase-polymerase chain reaction analysis of these odontoblasts demonstrated that messages of MMP-2 but not MMP-9 increased significantly between day 15 and day 21. The in vitro observation indicates that medium conditioned by these odontoblasts and containing significant amounts of MMP-2 degrades not only the collagenous substrates but also purified dentin phosphophoryn as well. We have also observed that dephosphorylated dentin phosphoprotein becomes a better substrate for casein kinase II after limited proteolysis with MMP-2. These results support our working hypothesis that MMP-2-mediated proteolytic processing is an important step in accelerating the process of dentin matrix maturation, which includes phosphorylation and subsequent mineralization. As has been suggested previously, extracellular phosphorylation of matrix proteins is an important step in biomineralization both in bone and in dentin (Mikuni-Takagaki et al., J Bone Miner Res 1995;10:231-42; Zhu et al., Biochem J 1997; 323:637-43). Our present histochemical analysis in MMP-2 knockout mice confirms the concept with the delayed formation of mineralized tissues, dentin, and bone.

Anabolic response of mouse bone-marrow-derived stromal cell clone ST2 cells to low-intensity pulsed ultrasound

The effects of 20-min exposure to low-intensity, pulsed ultrasound were investigated in ST2 cells of bone marrow stromal origin. They responded to ultrasound with elevated levels of IGF mRNAs, osteocalcin, and bone sialoprotein mRNAs. The upregulated expression of these messages appeared in a biphasic manner, with the first peak resistant to the protein synthesis inhibitor cycloheximide, and a second peak that was eliminated by NS398, an inhibitor of the inducive prostaglandin G/H synthase (cyclooxygenase-2). A cumulative effect of mechanical loading called the memory effect, which has been observed in vivo, can be explained from such a biphasic anabolic reaction mediated by prostaglandins. The upregulation of IGF or osteocalcin mRNAs can be observed even at 24 h after the initiation of the 20-min exposure to ultrasound. Our results suggest that this low-intensity, pulsed ultrasound, which has been clinically used to accelerate the healing processes of fractured bone, induces a direct anabolic reaction of osteogenic cells, leading to bone matrix formation.

Parathyroid hormone-activated volume-sensitive calcium influx pathways in mechanically loaded osteocytes

This paper documents for the first time a volume-sensitive Ca(2+) influx pathway in osteocytes, which transmits loading-induced signals into bone formation. Stretch loading by swelling rat and chicken osteocytes in hypo-osmotic solution induced a rapid and progressive increase of cytosolic calcium concentration, [Ca(2+)](i). The influx of extracellular Ca(2+) explains the increased [Ca(2+)](i) that paralleled the increase in the mean cell volume. Gadolinium chloride (Gd(3+)), an inhibitor of stretch- activated cation channels, blocked the [Ca(2+)](i) increase caused by hypotonic solutions. Also, the expression of alpha1C subunit of voltage-operated L-type Ca(2+) channels (alpha1C) is required for the hypotonicity-induced [Ca(2+)](i) increase judging from the effect of alpha1C antisense oligodeoxynucleotides. Parathyroid hormone (PTH) specifically potentiated the hypotonicity-induced [Ca(2+)](i) increase in a dose-dependent manner through the activation of adenyl cyclase. The increases induced by both PTH and hypotonicity were observed primarily in the processes of the osteocytes. In cyclically stretched osteocytes on flexible-bottomed plates, PTH also synergistically elevated the insulin-like growth factor-1 mRNA level. Furthermore, Gd(3+) and alpha1C antisense significantly inhibited the stretch-induced insulin-like growth factor-1 mRNA elevation. The volume-sensitive calcium influx pathways of osteocytes represent a mechanism by which PTH potentiates mechanical responsiveness, an important aspect of bone formation.

Synergistic effect of PTH on the mechanical responses of human alveolar osteocytes

The aim of this study is to characterize the response of alveolar osteocytes to stretching and parathyroid hormone, (1-34) PTH. Osteocytes from primary human alveolar bone were used in the study. Compared to osteoblasts, osteocytes were observed to express lower levels of alkaline phosphatase mRNA and higher levels of osteocalcin mRNA. We found that the effect of PTH and stretching on osteocalcin expression is synergistic. The upregulated steady-state level of osteocalcin mRNA is further upregulated in the presence of PTH (at 1 h after the initiation of stretching). On the other hand, the downregulated level of the message is further downregulated in the presence of PTH (at 3 h after the 3-h stretching). The synergy can be either way, positive or negative, in the course of the response. From this, we presume that related mechanisms are at work between the PTH signaling pathways and the mechanotransduction pathways activated by stretching.

Effects of mechanical stress on the mRNA expression of S100A4 and cytoskeletal components by periodontal ligament cells

The periodontal ligament (PDL) functions under constant mechanical stress, and PDL cells obviously control PDL functions under such conditions. We have previously found that the mRNA expression of the Ca2+-binding protein S100A4 and beta-actin is higher in the PDL from erupted teeth than in the PDL from teeth under eruption. This suggested a role for S100A4 in the response of PDL cells to mechanical stress, possibly by coupling Ca2+ and the cytoskeletal system. In the present study, we investigated the direct effects of cyclical stretching on the mRNA expression of S100A4 and two cytoskeletal components (beta-actin and alpha-tubulin) by PDL cells. In Northern blotting analysis, the expression of S100A4, beta-actin, and alpha-tubulin mRNAs was higher in the PDL from fully erupted and functional bovine teeth than in partially erupted ones. Similarly, when bovine PDL cells were mechanically stimulated by means of the Flexercell Strain Unit, the expression of S100A4, beta-actin, and alpha-tubulin mRNAs increased over the control levels. The results of our present study indicate that S100A4 is involved in the responses of PDL cells to mechanical stress possibly by coupling Ca2+ to the cytoskeletal system in these cells.

Mechanical responses and signal transduction pathways in stretched osteocytes

Mechanotransduction in bone is complex in nature, being influenced by many modulators such as PTH, prostanoids, and extracellular Ca2+. It has been postulated that osteocytes, dendritic resident cells in bone, transduce signals of mechanical loading that result in anabolic responses such as the expression of c-fos, insulin-like growth factor-I (IGF-I), and osteocalcin. To date, however, neither the actual stimuli to which osteocytes respond nor the pathways of signal transduction are well understood. Cultured primary rat bone cells exhibit distinct responses to stretching depending on their developmental stages: young osteocytes that become progressively dendritic show striking responses to strain at physiological levels; these include an early response of cAMP secretion and the late responses such as the production of IGF-I and osteocalcin proteins. The upregulation of steady-state levels of their mRNA is biphasic, being preceded by two peaks of PGHS-2 (inducive prostaglandin G/H synthase; cox-2) gene expression. Compared to a typical transient immediate early expression of c-fos, PGHS-2 shows another distinct peak about 8 h after the initiation of stretching. Second peaks in IGF-I and osteocalcin expression are entirely dependent on the first wave of PGHS-2 expression judging from the inhibition by NS398. PGHS-2 is perhaps critically involved in the prolonged anabolic responses of bone "memory effect" to the osteogenic mechanical stimulation. In these cells, the extracellular Ca2+ is essential to their response to stretching. Furthermore, the blockers of stretch-activated channels, gadolinium (Gd3+), and of epithelial-like Na channels, benzamil, in combination abolish the effects of stretching such as elevated osteocalcin expression. Although voltage-operated or calcium-activated calcium channels or Na+-driven mechanisms, such as a Na-Ca exchanger, for example, are functioning, particulars of secondary Ca entry pathways are not certain at this point. It is conceivable, however, that the calcium influxes, both primary and secondary, trigger the anabolic reaction of bone to stretching via Ser/Thr kinase signaling pathways in osteocytic cells.

Identification of matrix metalloproteinases (MMPs) in synovial fluid from patients with temporomandibular disorder

Proteolytic enzymes with gelatinolytic activity in the synovial fluid (SF) of temporomandibular joint (TMJ) arthropathies were assayed by gelatin-impregnated gel enzymography. SF samples were collected from 10 TMJs in patients with closed lock (CL) condition and 5 TMJs from asymptomatic healthy volunteers. Two proteinases with gelatinolytic activities at 92 kDa and 72 kDa were detected in both the normal and the diseased TMJs. Also detected were weak bands at molecular weights of 83 kDa and 66 kDa. All of these proteinase activities were inhibited by EDTA and tissue inhibitor of metalloproteinases (TIMP), required Ca2+ for activation, and were detected with gelatin but not casein as substrate, suggesting that these enzymes were matrix metalloproteinases (MMPs). The 72 kDa and 66 kDa bands further reacted with anti-MMP-2 antibody by Western blot analysis, and the proteinases in the TMJ-SF could cleave type IV collagen in vitro without any activation. These four activities identified by enzymography were, therefore, identified as 92 kDa-gelatinase (proMMP-9), 83 kDa-gelatinase (active MMP-9), 72 kDa-gelatinase (proMMP-2) and 66 kDa-gelatinase (active MMP-2). Densitometric analyses of these bands revealed higher levels of the active form of MMP-9 in the CL patients compared to controls. These findings suggest that MMP-2 and -9 could be dominant proteinases in the TMJ-SF and possibly reflect TMJ pathology.

In situ phosphorylation of bone and dentin proteins by the casein kinase II-like enzyme

Our previous studies suggested the possibility of extracellular phosphorylation of matrix phosphoproteins into more phosphorylated forms by mature odontoblasts and osteocytes (Mikuni-Takagi et al., 1995; Satoyoshi et al., 1995). To elucidate such phosphorylation of bone and dentin proteins, we developed a histochemical method using frozen sections to determine the sites of enzymatic processing by the casein kinase II-like enzyme. It was observed that proteins in bone, dentin, and predentin are phosphorylated by the endogenous enzyme when the tissue slices were incubated with [gamma-32P] GTP, suggesting that there are both substrates and the enzyme in these matrices. In vivo, phosphate donors, ATP and GTP, may be supplied through dentinal canals and osteocyte canaliculi. Immunohistochemical analysis of frozen sections showed that the extremely intense staining of phosphoserine residues by anti-phosphoserine antibodies appeared in dentin only after demineralization of the tissue samples. It implies that these phosphoserine residues become bound to mineral as soon as the phosphorylation is completed, thereby being inaccessible to the antibodies without demineralization. The data support our notion that the extracellular phosphorylation of dentin/bone proteins, regulated by the developmental stages of bone and dentin cells, occurs prior to matrix mineralization.

Mechanotransduction in stretched osteocytes--temporal expression of immediate early and other genes

Osteocytes, dendritic bone cells, transduce signals of mechanical loading that results in bone formation. We have reported in stretched primary osteocytes that the cAMP level, IGF-I and osteocalcin protein levels were elevated (Endocrinology 137:2028, 1996). Here we report that stretching induces the expression of immediate early genes, c-fos, and COX-2; inducive cyclooxygenase gene. Compared to c-fos, COX-2 as well as IGF-I and osteocalcin mRNA appeared in a biphasic manner; second peaks at 8 (COX-2) or 24 hrs (IGF-I and osteocalcin) later. Furthermore, these second peaks are abolished by including NS398, a specific inhibitor of the inducive cyclooxygenase, during the 3-hr stretching. A sequence that the calcium influx activates PkA which, in turn, activates c-fos and COX-2 transcription resulting in the production of proteins such as IGF-I and osteocalcin. A long-lasting effect of mechanical loading in vivo can be explained from the secondary anabolic reaction we observed through the upregulated COX-2 mRNA.

Distinct responses of different populations of bone cells to mechanical stress

To explore lineage-dependent responses to mechanical stress in bone cells, newborn rat calvarial cells, exhibiting differential characteristics of osteoblastic and osteocytic cells, were compared in their immediate and late responses to stretching. Seven fractions of sequentially prepared cells were cultured on Matrigel to promote their differentiation. By cyclically stretching the flexible bottom of culture plates, cells were exposed to a physiological stress of approximately 4000 microstrain on Matrigel. Cells in fractions IV, V and VI exhibited striking responses; the levels of cAMP and insulin-like growth factor I, bone Gla protein, and mineral accumulation were significantly elevated in the stretched cells. Also, proliferation was significantly inhibited regardless of the presence of 10(-6)M indomethacin. In contrast, osteoblasts in fraction III and osteocyte-like cells in fraction VII exhibited no significant response. Thus, these intermediate cells, very mature osteoblasts to young osteocytes, are likely to serve as a mechanosensor in bone, controlling the metabolic aspects of physical stress. We conclude that the responses of these young osteocytes to low level, physiological strain are transmitted in a manner different from the responses of osteoblasts to higher magnitude of strain in which PGE2 induces cell proliferation, as reported by others.

Extracellular processing of bone and dentin proteins in matrix mineralization

There are two steps in the process of matrix-mediated bone and dentin mineralization. First, as in other soft tissues, osteoblasts/odontoblasts synthesize collagenous matrices and second, mineral deposits in these matrices at a location distant from the cells that synthesized the matrices. We suggest a sequence of events that lead the matrix to mineralization: the phosphoproteins of bone and dentin are posttranslationally processed by limited proteolysis, then they are extracellularly processed into a more phosphorylated species that, we believe, facilitates mineralization. Our in situ phosphorylation experiments done with [gamma-32P] GTP suggest the existence of extracellular phosphorylation by a casein kinase II (CKII)-like enzyme, the enzyme known to phosphorylate most of the phosphate residues in dentin phosphophoryn and bone sialoproteins (osteopontin and BSP II).

Extracellular processing of dentin matrix protein in the mineralizing odontoblast culture

Odontoblasts that we prepared from bovine incisors produced a dentin-specific protein, phosphophoryn, and accumulated it in mineralized nodules. The time course of mineralization was detected by measuring osteocalcin and mineral in the nodules. The sequence of developmental expression of proteins in this mineralizing dentin cell culture is very similar to that in bone cells, suggesting a common mechanism for matrix mineralization in bone and dentin. Casein kinase II, which phosphorylates bone phosphoproteins and dentin phosphorylates bone phosphoproteins and dentin phosphophoryn, also emerges coinciding with the initiation of mineralization. Furthermore, we have detected extracellular phosphorylation by casein kinase II of a dentin protein of M(r) 60,000, which we recovered from the phosphophoryn fraction in CaCl2 precipitate.

Matrix mineralization and the differentiation of osteocyte-like cells in culture

Osteocyte-like cells were prepared by sequentially treating calvaria from newborn rats with collagenase and chelating agents. On a reconstituted gel of basement membrane components, cells from the third collagenase digest displayed a round shape and expressed the highest level of alkaline phosphatase with minimal osteocalcin deposition into the matrix. On the other hand, cells derived from the interior after EDTA treatment exhibited well-developed dendritic cell processes and expressed essentially no alkaline phosphatase. The latter population also showed quite distinct characteristics such as higher extracellular activities of casein kinase II and ecto-5'-nucleotidase and the extracellular accumulation of a large amount of osteocalcin associated with mineral. These diverse phenotypic and protein expressions as well as the sites from which each population of cells were recovered strongly suggest that we have isolated osteoblastic and osteocytic cells. Bone sialoprotein II was extracellularly phosphorylated by casein kinase II in osteocytic cells but not in osteoblastic cells. We discuss the possibility that differentiation of young osteocytes from osteoblasts may facilitate the biochemical sequence of mineral deposition in the bone matrix.

Effect of ipriflavone and estrogen on the differentiation and proliferation of osteogenic cells

The effect of ipriflavone (IP) on the proliferation and differentiation of rat osteoblast-like (ROB) cells and human periodontal ligament fibroblasts (HPLF) was studied in the presence and absence of estrogen. ROB cells were isolated from newborn rat calvaria by sequential collagenase digestion and HPLF from the outgrowth of human periodontal ligament in culture. The alkaline phosphatase (ALP) activity, employed as a marker of bone cell differentiation, was significantly enhanced by IP in both cell types; however, the concentration at which IP had a maximal effect was lower in ROB cells than in HPLF (10(-10) versus 10(-7) M, respectively). Cell proliferation judged by DNA content was either constant (ROB cells) or slightly increased (HPLF) by IP up to 10(-10) M, and decreased significantly above that concentration. In addition, the dose-dependent effect of estrogen on the growth and differentiation of each cell type in the presence and absence of IP was also tested. At the concentrations of IP which showed maximum effects in the induction of ALP, 10(-10) M for ROB cells and 10(-7) M for HPLF, IP inhibited DNA increase in an estrogen-independent manner. Estradiol (10(-11)-10(-9) M) itself increased the growth rate of both cell types significantly in a dose-dependent manner. Regardless of the concentrations of estradiol tested, ALP activities of both ROB cells and HPLF were elevated by the addition of IP. The ratio of ALP in the presence and absence of IP was similar over the range of estradiol concentrations tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-translational processing of chicken bone phosphoproteins. Identification of bone (phospho)protein kinase

We have detected a protein kinase which phosphorylates bone phosphoproteins (BPPs) in the detergent extract of the membranous fractions in the periosteal bone strips of 12-day-embryonic-chick tibia. This enzyme, tentatively named BPP kinase, has a catalytic subunit of Mr approximately 39,000, utilizes GTP as well as ATP as a phospho-group donor, is inhibited by 2,3-bisphosphoglycerate and heparin, and is therefore similar to casein kinase II. The enzyme can phosphorylate dephosphorylated proteins such as casein, phosvitin and chicken BPPs, but the last-named are preferred substrates. The in vitro-phosphorylation-assay products of this enzyme in the extract were indistinguishable on an SDS/polyacrylamide gel from the major [32P]phosphoproteins metabolically labelled in the embryonic-chick bone tissue. The regulatory mechanisms of the phosphorylation process of BPPs by BPP kinase as well as the potential role of this enzyme in mineralization are discussed.

Post-translational processing of chicken bone phosphoproteins. Identification of the bone phosphoproteins of embryonic tibia

In order to understand the mechanism of the post-translational processing of bone phosphoproteins in embryonic bone, periosteal bone strips isolated from 12-day-embryonic-chick tibiae were cultured and the bone proteins labelled with Na2H32PO4. Of the total radiolabelled proteins recovered from the medium and bone extracts in the absence of SDS ('medium', 'EDTA extract' and 'EDTA/guanidinium chloride extract'), nearly 80% of the radioactivity was found in the EDTA extract. The three major radiolabelled phosphoproteins in the EDTA extract of apparent Mr 68,000, 63,000 and 58,000 reacted with polyclonal as well as monoclonal antibodies raised against '32-kDa' and '150-kDa' bone phosphoproteins which were derived from 14-week-old chicken. Therefore these phosphorylated embryonic proteins are identified as chicken bone phosphoproteins. Judging from their common N-terminal sequences, differences in the patterns obtained by labelling them with several radioisotopes, and slightly different amino acid compositions, these components seem to have been derived from the same original protein by sequential proteolytic cleavage and other processing such as glycosylation and phosphorylation.

Preparation of monoclonal antibodies to chicken bone phosphoproteins

Monoclonal and polyclonal antibodies were raised against 150k, 60k, 32k, and 15k phosphoprotein components of 14-week chicken bone. Hybridomas were prepared by immunizing Balb/c mice with 150k, 60k, or 32k phosphoproteins followed by fusion of their spleen cells with X63-Ag8.653 myeloma cells. Polyclonal antibodies to the 60k, 32k, and 15k phosphoprotein components were produced in immunized rabbits. Immunological cross-reactivity between antigen and antibody was examined by enzyme-linked immunosorbent assay (ELISA) and dot-blotting. There was cross-reactivity between the 150k, 32k, and 15k phosphoprotein components and between the 150k, 90k, and 60k components. The antibodies raised against 60k component do not bind 32k and 15k antigens.

Metalloproteinases in endochondral bone formation: appearance of tissue inhibitor-resistant metalloproteinases

Dissected embryonic chick limbs release neutral metalloproteinases during endochondral bone development. These enzymes degrade cartilage proteoglycan and gelatin in culture medium. We found the enzymes active in the medium conditioned by explants of the region adjacent to the bone marrow cavity (cavity-surround). These enzymes degrade proteoglycan (PG) and/or gelatin. These spontaneously active enzymes are resistant to serum and tissue proteinase inhibitors, alpha 2-macroglobulin, and cartilage metalloproteinase inhibitor (TIMP). The other enzymes secreted from tarsus and bone marrow explants are mostly latent in the culture medium. Activated tarsus enzymes (PG degrading and gelatinolytic) are blocked by the above inhibitors. Activated marrow enzyme does not degrade PG but is resistant to those inhibitors. Cavity-surround enzymes may play an important role in embryonic osteogenesis of long bones because of their resistance to tissue and serum inhibitors. The in vivo mechanisms by which cavity-surround enzymes are activated are yet to be determined.

Cartilage-degrading neutral proteinase secreted by Yoshida sarcoma cells. Purification and properties

The Yoshida sarcoma, a malignant rat tumor, has been reported by Machinami ( Machinami , R. (1972) Acta Pathol. JPN 22, 19-39) to destroy cartilage matrix in vivo. We have characterized an enzyme secreted by Yoshida sarcoma cells in culture which degrades cartilage proteoglycan in solution and also in situ in organ culture ( Mikuni - Takagaki , Y., and Gross, J. (1981) in Proceedings of the 6th International Symposium on Glycoconjugates ( Yamakawa , T., Osawa , T., Handa , S., eds) pp. 491-492, Japan Scientific Societies Press, Tokyo) ( Mikuni - Takagaki , Y., and Gross, J. (1982) in The Extracellular Matrix ( Hawkes , S., and Wang, J.L., eds) pp. 379-385, Academic Press, New York). In this report we characterized the isolated enzyme with the help of a new assay system for measurement of proteoglycan core protein degradation, which utilizes aminopropyl glass beads derivatized with hyaluronic acid. This enzyme, with a neutral pH optimum and apparent molecular weight of about 30,000, is secreted into culture medium in an active form. It is resistant to cartilage-derived inhibitors and to alpha 2-macroglobulin as well as to synthetic and natural inhibitors of serine-, thiol- and carboxylproteinases . It is inhibited by a chelating agent, 1,10-phenanthroline and thiol compounds at relatively high concentrations, and therefore is probably a metalloproteinase. The enzyme degrades type V collagen, types I and II denatured collagen (gelatin), and casein in addition to cartilage proteoglycan, but not bovine serum albumin, myoglobin, fibrinogen, elastin or native collagen types I, II, III, and IV. These findings suggest that the Yoshida sarcoma may degrade cartilage matrix in vivo by means of a secreted, active, inhibitor-resistant enzyme.

Hyaluronate-protein complex of rous sarcoma virus-transformed chick embryo fibroblasts

Involvement of covalently linked protein or peptide in the structure or synthesis of hyaluronate has not previously been convincingly demonstrated. We have developed conditions for double-labeling with [3H]leucine and [14C]acetate, then isolating and characterizing the cell-associated and secreted hyaluronate-protein complexes of Rous sarcoma virus-transformed chick embryo fibroblasts. The preparations were purified by Bio-Gel A-15m gel filtration and CsCl density gradient ultracentrifugation under dissociative conditions, followed by acid agarose gel electrophoresis in the presence of 0.1% Nonidet P-40. The purified hyaluronate preparations did not change their 3H:14C ratios after further sodium dodecyl sulfate or alkali treatment. The cell-derived hyaluronate-protein was resistant to pronase but susceptible to proteinase K in the presence of sodium dodecyl sulfate. After chondroitinase ABC digestion, the cell-derived 3H-labeled protein was separated from the 14C-labeled hyaluronate disaccharides, then shown to give a broad band corresponding to Mr approximately 12,000 on sodium dodecyl sulfate-urea polyacrylamide gel electrophoresis and to be susceptible to both pronase and proteinase K. The corresponding 3H-labeled peptide was prepared in the same manner from the medium hyaluronate and the [3H]leucine shown to be present in material smaller in amount and size than that from the cell. We propose from these and other published data that the cell-associated hyaluronate-protein may be bound to the cell surface and that the hyaluronate in the medium may be derived from it as a result of proteolytic scission.

Cell-substratum attachment and cell surface hyaluronate of Rous sarcoma virus-transformed chondrocytes

Hyaluronate is associated with the cell surface of cultured Rous sarcoma virus-transformed chondrocytes. Detachment of these cells from their substratum by a variety of reagents is accompanied by release of 75-100% of this hyaluronate into solution. Treatment of the cells with 200 U/ml protease-free Streptomyces hyaluronidase at 37 degrees C cause release of greater than 90% of the cell surface hyaluronate and complete cell detachment. Treatment with a lower concentration of Streptomyces hyaluronidase (30 U/ml) at 25 degrees C or a corresponding activity of testicular hyaluronidase gives similar results, but only in the presence of mM EGTA. Treatment with the lower activities of either hyaluronidase or with 1 mM EGTA alone release only approximately 45% of the cell surface hyaluronate and does not cause significant cell detachment. It is concluded that there are two populations of cell surface hyaluronate differing in their accessibility or their resistance to dissociation from other components of the cell surface. It is proposed that the less readily released fraction is located between the transformed chondrocyte surface and substratum and is necessary for their interaction.