Evaluation of the osteogenic activity of the BMP-2 mimetic peptide, PEP7, in vitro and in vivo.

PURPOSE: To evaluate the osteogenic activity of a novel synthetic peptide, PEP7, derived from bone morphogenetic protein 2 (BMP-2) on MG-63, a human osteoblast-like cell line, and on new bone formation in vivo. MATERIALS AND METHODS: The novel synthetic peptide was synthesized by a standard Fmoc method and purified to 98% purity. Cell adhesion, proliferation, and differentiation of MG-63 were observed in the presence of different concentrations of PEP7. Eight micropigs were used to evaluate new bone formation in a supra-alveolar peri-implant defect model. The PEP7-coated implants were randomly allocated to mandible defect sites. The animals were sacrificed after 8 weeks for histologic analysis. RESULTS: PEP7 affected an early stage of adhesion and dose-dependently stimulated differentiation of MG-63 cells. The cell adhesion rate in the group coated with 1 µM PEP7 increased approximately 47% compared to the uncoated group and 32% compared to the group coated with recombinant human bone morphogenetic protein 2 (rhBMP-2) (P < .05). The alkaline phosphatase activities of groups treated with 50 µM of PEP7 were higher than for the other groups. PEP7 induced production of osteoblast-specific proteins in MG-63 cells. The largest effect was caused by 50 µM PEP7, followed by the groups treated with 20 µM synthetic peptide and 10 ng/mL rhBMP-2 (P < .05). CONCLUSIONS: A novel synthetic peptide derived from BMP-2 has osteoinductivity and new bone formation effects, including vertical augmentation of the alveolar ridge.

Expression of MMP-1 and TIMP-1 in irradiated mandibles during distraction osteogenesis.

OBJECTIVES: The study aimed to evaluate the expression of MMP-1 and TIMP-1 in irradiated mandibles during distraction osteogenesis. STUDY DESIGN: Rabbits in the experimental group received preoperative radiation of 9 Gy for 5 fractions. After 1 month, all rabbits underwent osteotomy and distraction osteogenesis with 7 days of latency. Three rabbits in the control and experimental groups were killed at days 7, 12, 18, and 25. Specimens were subjected to immunohistochemical examination and real-time polymerase chain reaction analysis. RESULTS: At day 7, expression of MMP-1 and TIMP-1 was significantly suppressed in the radiotherapy group in contrast to the control group. At day 12, expression of MMP-1 was significantly higher in the control group. At day 18, expression of MMP-1 and TIMP-1 was significantly higher in the control than in the radiotherapy group. CONCLUSIONS: Radiotherapy changes the expression pattern of MMP-1 and TIMP-1.

A clinical study of alveolar bone tissue engineering with cultured autogenous periosteal cells: coordinated activation of bone formation and resorption.

In ongoing clinical research into the use of cultured autogenous periosteal cells (CAPCs) in alveolar bone regeneration, CAPCs were grafted into 33 sites (15 for alveolar ridge augmentation and 18 for maxillary sinus lift) in 25 cases. CAPCs were cultured for 6weeks, mixed with particulate autogenous bone and platelet-rich plasma, and then grafted into the sites. Clinical outcomes were determined from high-resolution three-dimensional computed tomography (3D-CT) images and histological findings. No serious adverse events were attributable to the use of grafted CAPCs. Bone regeneration was satisfactory even in cases of advanced atrophy of the alveolar process. Bone biopsy after bone grafting with CAPCs revealed prominent recruitment of osteoblasts and osteoclasts accompanied by angiogenesis around the regenerated bone. 3D-CT imaging suggested that remodeling of the grafted autogenous cortical bone particles was faster in bone grafting with CAPCs than in conventional bone grafting. The use of CAPCs offers cell-based bone regeneration therapy, affording complex bone regeneration across a wide area, and thus expanding the indications for dental implants. Also, it enables the content of particulate autogenous bone in the graft material to be reduced to as low as 40%, making the procedure less invasive, or enabling larger amounts of graft materials to be prepared. It may also be possible to dispense with the use of autogenous bone altogether in the future. The results suggest that CAPC grafting induces bone remodeling, thereby enhancing osseointegration and consequently reducing postoperative waiting time after dental implant placement.

Comparison of gene expression of tissue inhibitor of matrix metalloproteinase-1 between continuous and intermittent distraction osteogenesis: a quantitative study on rabbits.

BACKGROUND: Distraction osteogenesis is a controlled surgical procedure that initiates a regenerative process and uses mechanical strain to enhance the biological responses of the injured tissues to create new bone. To explore the effect of high-frequency mechanical traction on the expression of tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), we compared the gene expression of TIMP-1 between continuous and intermittent distraction osteogenesis using a rabbit model of mandibular lengthening. MATERIALS AND METHODS: Forty adult New Zealand white rabbits were randomly assigned to the intermittent and continuous distraction groups. A unilateral mandibular osteotomy was performed and a custom-designed manual-driven or auto-driven distractor was bridged over the osteotomy segments. Animals were sacrificed at day-6, day-10, day-14 and day-21 after osteotomy. Samples were examined with real-time polymerase chain reaction (PCR). RESULTS: Real-time PCR examination showed significantly higher mRNA levels of TIMP-1 under continuous distraction than that under intermittent distraction at day-6 and day-10. No significant differences were found at day-14 and day-21. CONCLUSION: High-frequency traction provides a good mechanical environment for accelerating bone formation by up-regulating TIMP-1.

Sulfotransferase Ndst1 is needed for mandibular and TMJ development.

Heparan sulfate proteoglycans (HS-PGs) regulate several developmental processes, but their possible roles in mandibular and TMJ formation are largely unclear. To uncover such roles, we generated mice lacking Golgi-associated N-sulfotransferase 1 (Ndst1) that catalyzes sulfation of HS-PG glycosaminoglycan chains. Ndst1-null mouse embryos exhibited different degrees of phenotypic penetrance. Severely affected mutants lacked the temporomandibular joint and condyle, but had a mandibular remnant that displayed abnormal tooth germs, substandard angiogenesis, and enhanced apoptosis. In mildly affected mutants, the condylar growth plate was dysfunctional and exhibited thicker superficial and polymorphic cell zones, a much wider distribution of Indian hedgehog signaling activity, and ectopic ossification along its lateral border. Interestingly, mildly affected mutants also exhibited facial asymmetry resembling that seen in individuals with hemifacial microsomia. Our findings indicate that Ndst1-dependent HS sulfation is critical for mandibular and TMJ development and allows HS-PGs to exert their roles via regulation of Ihh signaling topography and action.

Dlx homeobox gene family expression in osteoclasts.

Skeletal growth and homeostasis require the finely orchestrated secretion of mineralized tissue matrices by highly specialized cells, balanced with their degradation by osteoclasts. Time- and site-specific expression of Dlx and Msx homeobox genes in the cells secreting these matrices have been identified as important elements in the regulation of skeletal morphology. Such specific expression patterns have also been reported in osteoclasts for Msx genes. The aim of the present study was to establish the expression patterns of Dlx genes in osteoclasts and identify their function in regulating skeletal morphology. The expression patterns of all Dlx genes were examined during the whole osteoclastogenesis using different in vitro models. The results revealed that Dlx1 and Dlx2 are the only Dlx family members with a possible function in osteoclastogenesis as well as in mature osteoclasts. Dlx5 and Dlx6 were detected in the cultures but appear to be markers of monocytes and their derivatives. In vivo, Dlx2 expression in osteoclasts was examined using a Dlx2/LacZ transgenic mouse. Dlx2 is expressed in a subpopulation of osteoclasts in association with tooth, brain, nerve, and bone marrow volumetric growths. Altogether the present data suggest a role for Dlx2 in regulation of skeletal morphogenesis via functions within osteoclasts.

In situ zymography and immunolabeling in fixed and decalcified craniofacial tissues.

In situ zymography is a very important technique that shows the proteolytic activity in sections and allows researchers to observe the specific sites of proteolysis in tissues or cells. It is normally performed in non-fixed frozen sections and is not routinely performed in calcified tissues. In this study, we describe a technique that maintains proteolytic activity in fixed and decalcified sections obtained after routine paraffin sectioning in conventional microtome and cryostat sections. We used adult rat hemimandibles, which presented bone, enamel, and dentine matrices; the substrate used was dye-quenched-gelatin. Gelatinolytic activity was colocalized with MMP-2 using fluorescent antibodies. Specific proteolytic activity was observed in all sections, compatible with metalloproteinase activity, particularly in dentine and bone. Furthermore, matrix metalloproteinase-2 was colocalized to the sites of green fluorescence in dentine. In conclusion, the technique presented here will allow in situ zymography reactions in fixed, decalcified, and paraffin-embedded tissues, and we showed that paraformaldehyde-lysine-periodate-fixed cryostat sections are suitable for colocalization of gelatinolytic activity and protein labeling with antibodies.

Oxidative stress causes alveolar bone loss in metabolic syndrome model mice with type 2 diabetes.

BACKGROUND AND OBJECTIVE: Alveolar bone loss is caused by a host response to periodontal pathogens, and its progression is often enhanced by systemic conditions such as insulin resistance. Alveolar bone dehiscence has been observed in KK-A(y) mice, which are metabolic syndrome model mice with type 2 diabetes. The aim of this study was to investigate inducements responsible for alveolar bone dehiscence in the KK-A(y) mice. MATERIAL AND METHODS: The expression of endothelial nitric oxide synthase in the mandibles of mice was detected using immunohistochemical staining and the reverse transcription-polymerase chain reaction. After administration of N-acetylcysteine, an antioxidant, to KK-A(y) mice, alveolar bone loss and the expression of endothelial nitric oxide synthase protein in gingival keratinocytes and of hydrogen peroxide concentrations in plasma, were analyzed. The effect of hydrogen peroxide on endothelial nitric oxide synthase expression in keratinocytes was examined using cultured keratinocytes. RESULTS: The expression of endothelial nitric oxide synthase was decreased in gingival keratinocytes from KK-A(y) mice compared with gingival keratinocytes from control mice. Administration of N-acetylcysteine to the mice restored endothelial nitric oxide synthase expression in the gingival keratinocytes, suppressed the alveolar bone loss and decreased the hydrogen peroxide concentrations in plasma without the improvement of obesity or diabetes. In vitro, stimulation with hydrogen peroxide decreased the expression level of endothelial nitric oxide synthase in cultured keratinocytes, which was restored by the addition of N-acetylcysteine. CONCLUSION: Reactive oxygen species, such as hydrogen peroxide, are responsible for the alveolar bone loss accompanied by decreased endothelial nitric oxide synthase expression in KK-A(y) mice. Therefore, we propose a working hypothesis that the generation of oxidative stress is an underlying systemic condition that enhances alveolar bone loss in periodontitis occurring as a complication of diabetes.

Decreased cardiac glutathione peroxidase levels and enhanced mandibular apoptosis in malformed embryos of diabetic rats.

OBJECTIVE: To characterize normal and malformed embryos within the same litters from control and diabetic rats for expression of genes related to metabolism of reactive oxygen species (ROS) or glucose as well as developmental genes. RESEARCH DESIGN AND METHODS: Embryos from nondiabetic and streptozotocin-induced diabetic rats were collected on gestational day 11 and evaluated for gene expression (PCR) and distribution of activated caspase-3 and glutathione peroxidase (Gpx)-1 by immunohistochemistry. RESULTS: Maternal diabetes (MD group) caused growth retardation and an increased malformation rate in the embryos of MD group rats compared with those of controls (N group). We found decreased gene expression of Gpx-1 and increased expression of vascular endothelial growth factor-A (Vegf-A) in malformed embryos of diabetic rats (MDm group) compared with nonmalformed littermates (MDn group). Alterations of messenger RNA levels of other genes were similar in MDm and MDn embryos. Thus, expression of copper zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), and sonic hedgehog homolog (Shh) were decreased, and bone morphogenetic protein-4 (Bmp-4) was increased, in the MD embryos compared with the N embryos. In MDm embryos, we detected increased activated caspase-3 immunostaining in the first visceral arch and cardiac area and decreased Gpx-1 immunostaining in the cardiac tissue; both findings differed from the caspase/Gpx-1 immunostaining of the MDn and N embryos. CONCLUSIONS: Maternal diabetes causes growth retardation, congenital malformations, and decreased general antioxidative gene expression in the embryo. In particular, enhanced apoptosis of the first visceral arch and heart, together with decreased cardiac Gpx-1 levels, may compromise the mandible and heart and thus cause an increased risk of developing congenital malformation.

Temporospatial localization of acetylcholinesterase activity in the dental epithelium during mouse tooth development.

Acetylcholinesterase (AChE), a principal modulator of cholinergic neurotransmission, also has been demonstrated to be involved in the morphogenetic processes of neuronal and non-neuronal tissues. This study shows that AChE exhibits temporospatial activity in the dental epithelium of the developing mouse tooth. To identify the AChE activity in the mouse tooth during development, we performed enzyme histochemistry on the mouse embryos from embryonic day 13 (E13) to E18 and on the incisors and molars of the neonatal mouse at 10 days after birth (P10). In the developing molars of mouse embryos, AChE activity was not found in the dental epithelium at E13 (bud stage). AChE activity first appeared in the developing cervical loops of the enamel organ at E14 (cap stage), but was not found in the enamel knot. At E18 (bell stage), AChE activity was localized in the inner enamel epithelium except the cervical-loop area. In the incisors and molars of neonatal mice (P10), AChE activity was localized in the inner enamel epithelium of the cervical-loop and enamel-free area. Overall, AChE activity was localized in the differentiating dental epithelium while the activity of butyrylcholinesterse, another cholinesterase, was located primarily in the cells of the dental follicle. The results suggest that AChE may play a role in the histo- and cytodifferentiation of dental epithelium during tooth development.

Contributions of matrix metalloproteinases toward Meckel's cartilage resorption in mice: immunohistochemical studies, including comparisons with developing endochondral bones.

The middle portion of Meckel's cartilage (one of four portions that disappear with unique fate) degrades via hypertrophy and the cell death of chondrocytes and via the resorption of cartilage by chondroclasts. We have examined the immunolocalization of matrix metalloproteinase-2 (MMP-2), MMP-9, MMP-13, and MMP-14 (members of the MMP activation cascade) and galectin-3 (an endogenous substrate for MMP-9 and an anti-apoptotic factor) during resorption of Meckel's cartilage in embryonic mice and have compared the results with those of developing endochondral bones in hind limbs. MMP immunoreactivity, except for MMP-2, is present in nearly all chondrocytes in the middle portion of Meckel's cartilage. On embryonic day 15 (E15), faint MMP-2-immunoreactive and intense MMP-13-immunoreactive signals occur in the periosteal bone matrix deposited by periosteal osteoblasts on the lateral surface, whereas MMP-9 and MMP-14 are immunolocalized in the peripheral chondrocytes of Meckel's cartilage. The activation cascade of MMPs by face-to-face cross-talk between cells may thus contribute to the initiation of Meckel's cartilage degradation. On E16, immunopositive signaling for MMP-13 is detectable in the ruffled border of chondroclasts at the resorption front, whereas immunostaining for galectin-3 is present at all stages of chondrocyte differentiation, especially in hypertrophic chondrocytes adjacent to chondroclasts. Galectin-3-positive hypertrophic chondrocytes may therefore coordinate the resorption of calcified cartilage through cell-to-cell contact with chondroclasts. In metatarsal specimens from E16, MMPs are detected in osteoblasts, young osteocytes, and the bone matrix of the periosteal envelope, whereas galectin-3 immunoreactivity is intense in young periosteal osteocytes. In addition, intense MMP-9 and MMP-14 immunostaining has been preferentially found in pre-hypertrophic chondrocytes, although galectin-3 immunoreactivity markedly decreases in hypertrophic chondrocytes. These results indicate that the degradation of Meckel's cartilage involves an activation cascade of MMPs that differs from that in endochondral bone formation.

Fibroblast growth factors 2, 4, and 8 exert both negative and positive effects on limb, frontonasal, and mandibular chondrogenesis via MEK-ERK activation.

Fibroblast growth factors (FGFs) and their receptors play fundamental roles regulating growth, morphogenesis, and cartilage formation in embryonic limbs and facial primordia. However, the intracellular pathways that transduce FGF signals during the differentiation of pluripotent mesenchymal cells into chondrocytes are currently unknown. Our present study demonstrates that FGF8, 4, and 2 treatments exert both inhibitory and stimulatory effects on cartilage differentiation in micromass cultures prepared from mesenchymal cells of the chick embryo wing bud, frontonasal mass, and mandibular arch through activation of the MEK-ERK mitogen-activated protein kinase (MAPK) cascade. In cultures of stage 23/24 and stage 28/29 wing bud mesenchyme, as well as stage 24/25 and stage 28/29 frontonasal cells, FGF treatments depressed cartilage matrix production and decreased transcript levels for three cartilage-specific genes: col2a1, aggrecan, and sox9. Conversely, FGF treatment increased cartilage differentiation in cultures of stage 24/25 and stage 28/29 mandibular mesenchyme. In all cell types, FGF treatment elevated endogenous ERK phosphorylation. Moreover, both the stimulatory effects of FGFs on mandibular chondrogenesis, as well as the inhibitory effects of FGFs on wing mesenchyme and stage 24/25 frontonasal cells, were completely blocked when cultures were treated with MEK inhibitor U0126 or transfected with dominant negative ERK2. Thus, MEK-ERK activation is an essential component of the signal transduction pathway that mediates both positive and negative effects of FGFs 8, 4, and 2 on chondrogenesis in embryonic limb, mandibular, and early-stage frontonasal mesenchyme cells. Interestingly, the effects of FGF on late-stage frontonasal cells appear to be relayed by an ERK-independent system.

Histological and histomorphometrical changes in rat alveolar bone following antagonistic tooth extraction and/or ovariectomy.

OBJECTIVE: To examine changes appearing in the alveolar bone following the removal of the mechanical stress of occlusal loading, as well as the added influence of estrogen deficiency on such changes. DESIGN: The right mandibular molars of female rats were extracted. After 8 weeks, 12 animals were ovariectomized (OVX), and the other 12 were subjected to sham surgery (sham). Four weeks after surgery, all rats were sacrificed. The left-half and right-half maxillas of the sham group (the sham-occluded side and the sham-extruded side, respectively) and right-half maxilla of OVX group (the OVX-extruded side) were examined by histological observation and bone histomorphometry. RESULTS: The vertical height of alveolar bone in the sham-extruded and the OVX-extruded sides increased as compared with that of the sham-occluded side. In both extruded sides, active bone formation occurred on the surface of the alveolar bone facing the periodontal ligament, but the bone marrow was expanded and the bone volume had decreased in the internal area of the alveolar bone. In the OVX-extruded side, the bone marrow expanded more remarkably than that of the sham-extruded side, and the highest percentage of osteoclast surface was detected. CONCLUSIONS: Around the extruded teeth, there were regional differences in bone dynamics between the internal area of the alveolar bone and the bone surface facing the periodontal ligament, and estrogen deficiency seems to have caused further loss of bone volume in the interior of the alveolar bone supporting the extruded tooth.

Mast cell activation and degranulation occur early during induction of periosteal bone resorption.

We have previously postulated that mast cells participate in the cellular network involved in osteoclastic resorption, probably through histamine release. In this study, we examined mast cell activation and histamine release during origination of resorption. Groups of 10 rats were killed 0, 0.5, 1, 1.5, 3, 6, 9, 12 and 18 h after induction of resorption in a synchronized model of cortical resorption along the mandible. The total number of mast cells was transiently decreased by about one-third at 1 and 9 h. Mast cell activation was monitored by Alcian blue-safranin staining. Early after induction, mast cells started to release their mediator stores; complete release led to the apparent disappearance of the cells with the staining technique used. Histamine immunostaining confirmed the release of histamine and its diffusion in the extracellular environment. Massive degranulation was observed at 1.5 and 9 h with toluidine blue staining. Cell recovery, assessed in terms of histidine decarboxylase expression, occurred gradually. The number of ED1+ osteoclast precursors strongly increased from 12 h up to 18 h. Most parameters had returned to baseline at 18 h, except the ED1+ cells. H2 receptor inhibition with famotidine strongly decreased ED1+ osteoclast precursors at 12 h and subsequently osteoclasts at the peak of resorption. These data support a role of mast cells in resorption origination. They show an early and transient intervention of mast cells in the events regulating the recruitment of circulating osteoclast precursors and ultimately of resorption. Mast cell activation and degranulation induce the release of mediators, particularly histamine acting through its H2 receptors, which are likely involved in these reactions.

Accelerated bone formation and increased osteoblast number contribute to the abnormal tooth germ development in parathyroid hormone-related protein knockout mice.

Our previous study showed that tooth germs at late embryonic stage [later than embryonic day 17.5 (E17.5)] and neonatal homozygous parathyroid hormone-related protein (PTHrP)-knockout mice are compressed or penetrated by the surrounding alveolar bone tissue. In vivo and in vitro studies have shown that the development of the tooth germ proper is not disturbed, but insufficient alveolar bone resorption, due to the decreased number and hypofunction of osteoclasts, is the main cause of this abnormality. In addition to the insufficient alveolar bone resorption, progressive bone formation toward tooth germs was observed in homozygous mice, suggesting that accelerated bone formation also contributes to this abnormality. To further investigate this, homozygous mice at E14.0 and E15.5, when alveolar bone is forming, were used for histochemical and bone histomorphometric analyses. In contrast to the late embryonic stage, the alveolar bone did not yet compress developing tooth germs in homozygous mice on E14.0, but a larger amount of bone tissue was seen compared to wild-type littermates. Histomorphometric analysis of bone at E14.0 revealed that the osteoblast numbers and surfaces in the mandibles and in the bone collar of femora of homozygous mice were significantly higher than those of wild-type mice. However, unlike our previous study showing the osteoclast surface on E18.5 in homozygous mice to be significantly lower than that of wild-type mice, this study at E14.0 showed no significant difference between the two genotypes. To evaluate the amount of calcification around tooth germs, 3D images of mandibles were reconstructed from the calcein-labeled sections of the wild-type and mutant mice. Labeling was performed at E14.0, and the mice were sacrificed 1 h after the calcein injection to minimize the effect of bone resorption. Comparison of the 3D images revealed that the labeled surface was larger around developing tooth germs in homozygous mouse than in wild-type mouse. On day E15.5, osteoblasts approached the enamel organ of homozygous mice but this was not observed in wild-type mice. In this study, we report a systemic increase in osteoblast number and accelerated bone formation in homozygous PTHrP-knockout mice, both of which contribute to the abnormal tooth development.

Purification and characterization of a mandibular organ protein from the American lobster, Homarus americanus: a putative farnesoic acid O-methyltransferase.

Methyl farnesoate (MF) appears to have important roles in the development, morphogenesis, and reproduction of crustaceans. To better understand the regulation of MF synthesis, we studied farnesoic acid O-methyltransferase (FAOMeT, the final enzyme in the MF biosynthetic pathway) in the American lobster (Homarus americanus). FAOMeT purified from mandibular organ (MO) homogenates had a MW of approximately 38,000. The sequences of trypsin fragments of purified FAOMeT were used to design PCR primers to amplify a cDNA fragment, which was used to isolate a full-length cDNA containing a single open reading frame (ORF) of 828 bp encoding a protein of 276 amino acids. The deduced amino acid sequence of this putative FAOMeT protein contained two copies of a conserved approximately 135 amino acid domain we term the CF (CPAMD8/FAOMeT) domain; single copies of this domain also occur in the human CPAMD8 protein (a member of the alpha-2 macroglobulin family) and an uncharacterized Drosophila protein. The recombinant protein had no FAOMeT activity. However, its addition to MO homogenates from eyestalk ablated (ESA) lobsters increased enzyme activity by up to 75%, suggesting that FAOMeT may require an additional factor or modification (e.g., phosphorylation) for its activation. The mRNA for the putative FAOMeT was primarily found in the proximal region of the MO, the predominant site of MF synthesis. FAOMeT transcripts were found in muscle tissue from ESA animals, but not in green gland, hepatopancreas, or in muscle tissue from intact animals. FAOMeT mRNA was also detected in embryos and larval stages. This is the first comprehensive report of this protein in the lobster, and is an important step in elucidating the functions of MF in these animals.

Effects of selenium-containing compounds and their metabolism in intact rats and in animals with bone fractures.

Blood content of MDA in rats increased 1 and 2 weeks after mandibular bone fracture at stages of cellular fibrous and chondroid callus and decreased 4 weeks after fracture at the stage of primary bone callus. Treatment with Se (intragastrically and electrophoretically) reduced this increase by activating selenium-containing glutathione peroxidase. In order to clear out the relationship between Se and carbohydrate metabolism in different ages, the distribution of Se between the blood and mandibular bone, diaphysis and metaepiphyseal zone of the femoral bone was studied using the bone/blood relative radioactivity coefficient after intraperitoneal injection of [(75)Se]selenate. In control 1-month-old rats the radioactivity had 2 peaks corresponding to 6 and 48 h. The first peak was presumably caused by Se adsorption on hydroxyapatite, the second by chemosorption on hydroxyapatite and protein binding. Only one peak of relative radioactivity (after 12-48 h) was observed in 3-month-old control rats, and it could be increased by sucrose diet. The relative radioactivity was higher in rats receiving sucrose ration for 2 months starting from the age of 1 month in comparison with the control.

The lobster mandibular organ produces soluble and membrane-bound forms of 3-hydroxy-3-methylglutaryl-CoA reductase.

In a previous study [Li, Wagner, Friesen and Borst (2003) Gen. Comp. Endocrinol. 134, 147-155], we showed that the MO (mandibular organ) of the lobster Homarus americanus has high levels of HMGR (3-hydroxy-3-methylglutaryl-CoA reductase) and that most (approx. 75%) of the enzyme activity is soluble. In the present study, we report the biochemical and molecular characteristics of this enzyme. HMGR had two forms in the MO: a more abundant soluble form (66 kDa) and a less abundant membrane-bound form (72 kDa). Two cDNAs for HMGR were isolated from the MO. A 2.6-kb cDNA encoded HMGR1, a 599-amino-acid protein (63 kDa), and a 3.2-kb cDNA encoded HMGR2, a 655-amino-acid protein (69 kDa). These two cDNAs had identical 3'-ends and appeared to be products of a single gene. The deduced amino acid sequences of these two proteins revealed a high degree of similarity to other class I HMGRs. Hydropathy plots indicated that the N-terminus of HMGR1 lacked a transmembrane region and HMGR2 had a single transmembrane segment. Recombinant HMGR1 expressed in Sf9 insect cells was soluble and had kinetic characteristics similar to native HMGR from the MO. Treatment with phosphatase did not affect HMGR activity, consistent with the observation that neither HMGR1 nor HMGR2 has a serine at position 490 or 546, the position of a conserved phosphorylation site found in class I HMGR from higher eukaryotes. Other lobster tissues (i.e. midgut, brain and muscles) had low HMGR activities and mRNA levels. MO with higher HMGR activities had higher HMGR mRNA levels, implying that HMGR is regulated, in part, at the transcription level.

Focal adhesion kinase expression during mandibular distraction osteogenesis: evidence for mechanotransduction.

Distraction osteogenesis is an established treatment strategy in the reconstruction of the craniofacial skeleton. The underlying mechanisms that drive bone formation during this process are largely unknown, but a regulatory role for mechanical force is believed to be critical. The integrin-mediated signal transduction cascade is a primary pathway by which signal transduction of mechanical stimuli (i.e., mechanotransduction) occurs. Focal adhesion kinase (FAK) is a significant regulator in this pathway. The authors hypothesize that mechanical forces created during distraction osteogenesis are responsible for the osteogenic response that takes place, and that these changes arise through integrin-dependent mechanotransduction. Using a rat model of distraction osteogenesis, the authors examined the expression of FAK in critical size defects (n = 15), subcritical size defects (n = 15), and mandibles undergoing distraction osteogenesis (n = 15). Their findings demonstrated FAK immunolocalization in mandibles undergoing distraction osteogenesis, but not in the critical size defects or in subcritical size defects, despite varying degrees of bone formation in the latter two groups. Furthermore, bone sialoprotein mRNA in situ hybridization patterns were found to mirror FAK immunolocalization patterns in mandibles undergoing distraction osteogenesis, demonstrating an association of FAK expression with the osteogenic process specific to distraction osteogenesis. These findings suggest that the bone formation in distraction osteogenesis is regulated by mechanical force by means of integrin-dependent mechanotransduction pathways.

Matrix metalloproteinases and their inhibitors in bone remodelling following distraction osteogenesis of the sheep mandible.

AIM: Matrix metalloproteinases (MMPs), together with their tissue inhibitors (TIMPs), are responsible for the controlled degradation of collagen and other matrix substrates in bone and other tissues. This study evaluated the expression of MMPs and TIMPs in bony remodelling in a bilateral sheep mandible model up to 12 months following lengthening by distraction osteogenesis. METHODOLOGY: Sheep mandibles were harvested 3, 6, 9 or 12 months following lengthening by bilateral mandibular distraction (1 mm/day for 20 days). Undistracted sheep mandibles were used as controls. The tissues underwent routine histology and immunohistochemical staining with monoclonal antibodies specific to MMPs 1-3 and TIMP-1, 2. Matrix and cell staining was assessed using a semi-quantitative analysis. RESULTS: Matrix metalloproteinases and their tissue inhibitors (TIMPs) expression levels were marked at 3 months and decreased thereafter becoming similar to undistracted controls by 12 months. The histologic development of mature lamellar cortical bone was similar to undistracted controls by 9 months following distraction. CONCLUSIONS: A temporal expression of MMPs and TIMPs was found in distraction osteogenesis. MMPs and TIMPS may, in part, reflect the state of bony remodelling following mandibular lengthening by distraction osteogenesis. Matrix metalloproteinases and TIMP expression were comparable to undistracted controls by 12 months, suggesting that equilibrium had been achieved and that bony relapse is unlikely.