Eldecalcitol Induces Minimodeling-Based Bone Formation and Inhibits Sclerostin Synthesis Preferentially in the Epiphyses Rather than the Metaphyses of the Long Bones in Rats

This study aimed to examine minimodeling-based bone formation between the epiphyses and metaphyses of the long bones of eldecalcitol (ELD)-administered ovariectomized rats. Sixteen-week-old female rats were divided into four groups: sham-operated rats receiving vehicle (Sham group), ovariectomized (OVX) rats receiving vehicle (Vehicle group), or ELDs (30 or 90 ng/kg BW, respectively; ELD30 and ELD90 groups). ELD administration increased bone volume and trabecular thickness, reducing the number of osteoclasts in both the epiphyses and metaphyses of OVX rats. The Sham and Vehicle groups exhibited mainly remodeling-based bone formation in both regions. The epiphyses of the ELD groups showed a significantly higher frequency of minimodeling-based bone formation than remodeling-based bone formation. In contrast, the metaphyses exhibited significantly more minimodeling-based bone formation in the ELD90 group compared with the ELD30 group. However, there was no significant difference between minimodeling-based bone formation and remodeling-based bone formation in the ELD90 group. While the minimodeling-induced new bone contained few sclerostin-immunoreactive osteocytes, the underlying pre-existing bone harbored many. The percentage of sclerostin-positive osteocytes was significantly reduced in the minimodeling-induced bone in the epiphyses but not in the metaphyses of the ELD groups. Thus, it seems likely that ELD could induce minimodeling-based bone formation in the epiphyses rather than in the metaphyses, and that ELD-driven minimodeling may be associated with the inhibition of sclerostin synthesis.

The microbiome mediates epiphyseal bone loss and metabolomic changes after acute joint trauma in mice

OBJECTIVE

To compare the early responses to joint injury in conventional and germ-free mice.

DESIGN

Post-traumatic osteoarthritis (PTOA) was induced using a non-invasive anterior cruciate ligament rupture model in 20-week old germ-free (GF) and conventional C57BL/6 mice. Injury was induced in the left knees of n = 8 GF and n = 10 conventional mice. To examine the effects of injury, n = 5 GF and n = 9 conventional naïve control mice were used. Mice were euthanized 7 days post-injury, followed by synovial fluid recovery for global metabolomic profiling and analysis of epiphyseal trabecular bone by micro-computed tomography (μCT). Global metabolomic profiling assessed metabolic differences in the joint response to injury between GF and conventional mice. Magnitude of trabecular bone volume loss measured using μCT assessed early OA progression in GF and conventional mice.

RESULTS

μCT found that GF mice had significantly less trabecular bone loss compared to conventional mice, indicating that the GF status was protective against early OA changes in bone structure. Global metabolomic profiling showed that conventional mice had greater variability in their metabolic response to injury, and a more distinct joint metabolome compared to their corresponding controls. Furthermore, differences in the response to injury in GF compared to conventional mice were linked to mouse metabolic pathways that regulate inflammation associated with the innate immune system.

CONCLUSIONS

These results suggest that the gut microbiota promote the development of PTOA during the acute phase following joint trauma possibly through the regulation of the innate immune system.

Experimental Induction of Physeal Injuries by Fracture, Drill, and Ablation Techniques: Analyses of Immunohistochemical Findings

BACKGROUND

Although physeal fractures and physeal bars can result in significant clinical consequences to growth and development of the injured physis, little orthopaedic research has focused upon this topic. Our objective was to extend a previously developed rat model to examine the immunohistochemical features following surgical application of techniques disrupting the physis.

METHODS

Physes were surgically disrupted using fracture (control), epiphyseal scrape (ES), or epiphyseal drill (ED). After 1, 3, 6, 10, or 21 days, animals were euthanized, sites processed for histology and immunohistochemical localization of vascular endothelial growth factor (VEGF), Factor VIII, Sox-9, PTHrP (parathyroid hormone-related protein) and PTHrP-R (parathyroid hormone-related protein receptor) in resting, proliferative, and hypertrophic physeal zones. Incidence of physeal bars, vertical septa and islands within the metaphysis was quantified. Semiquantitative analysis of immunohistochemistry was performed.

RESULTS

Physeal bars, vertical septa, and displaced cartilage islands were present each of the surgical treatments. Fisher's exact test showed a statistically significant increase in the presence of physeal bars (P=0.002) and vertical septa (P=0.012) in the ED group at 10 and 21 days. Analysis of VEGF showed significant differences among the surgical treatments involving the resting zone, and the proliferative zone for days 1, 6, and 21 (P≤0.02) with greater mean scores present in the fracture (control) group, followed by the ED group; the lowest scores were present in the ES group. PTHrP-R immunolocalization showed significant differences among treatments in the hypertrophic zone at days 6 and 21 (P=0.022 and 0.044, respectively).

CONCLUSIONS

On the basis of the type of surgical treatment, results show significant differences in the presence of VEGF (reflecting the vascular bed) in the resting and proliferating zones at days 1, 6, and 21. VEGF localization was less abundant in the ED group (which had more physeal bars), suggesting that lack of vascular ingrowth plays a role in physeal bar formation.

CLINICAL RELEVANCE

Basic science data presented here provide insight into the importance of the various regions of the physis and its repair and continued growth after physeal fracture. We suggest that a better understanding of the cellular basis of physeal arrest following physeal fracture may have future relevance for the development of treatments to prevent or correct arrest.

Analysis of short-term treatment with the phosphodiesterase type 5 inhibitor tadalafil on long bone development in young rats

Cyclic GMP (cGMP) is an important intracellular regulator of endochondral bone growth and skeletal remodeling. Tadalafil, an inhibitor of the phosphodiesterase (PDE) type 5 (PDE5) that specifically hydrolyzes cGMP, is increasingly used to treat children with pulmonary arterial hypertension (PAH), but the effect of tadalafil on bone growth and strength has not been previously investigated. In this study, we first analyzed the expression of transcripts encoding PDEs in primary cultures of chondrocytes from newborn rat epiphyses. We detected robust expression of PDE5 as the major phosphodiesterase hydrolyzing cGMP. Time-course experiments showed that C-type natriuretic peptide increased intracellular levels of cGMP in primary chondrocytes with a peak at 2 min, and in the presence of tadalafil the peak level of intracellular cGMP was 37% greater ( P < 0.01) and the decline was significantly attenuated. Next, we treated 1-mo-old Sprague Dawley rats with vehicle or tadalafil for 3 wk. Although 10 mg·kg^-1·day^-1 tadalafil led to a significant 52% ( P < 0.01) increase in tissue levels of cGMP and a 9% reduction ( P < 0.01) in bodyweight gain, it did not alter long bone length, cortical or trabecular bone properties, and histological features. In conclusion, our results indicate that PDE5 is highly expressed in growth plate chondrocytes, and short-term tadalafil treatment of growing rats at doses comparable to those used in children with PAH has neither obvious beneficial effect on long bone growth nor any observable adverse effect on growth plate structure and trabecular and cortical bone structure.

Cell-nonautonomous local and systemic responses to cell arrest enable long-bone catch-up growth in developing mice

Catch-up growth after insults to growing organs is paramount to achieving robust body proportions. In fly larvae, injury to individual tissues is followed by local and systemic compensatory mechanisms that allow the damaged tissue to regain normal proportions with other tissues. In vertebrates, local catch-up growth has been described after transient reduction of bone growth, but the underlying cellular responses are controversial. We developed an approach to study catch-up growth in foetal mice in which mosaic expression of the cell cycle suppressor p21 is induced in the cartilage cells (chondrocytes) that drive long-bone elongation. By specifically targeting p21 expression to left hindlimb chondrocytes, the right limb serves as an internal control. Unexpectedly, left-right limb symmetry remained normal, revealing deployment of compensatory mechanisms. Above a certain threshold of insult, an orchestrated response was triggered involving local enhancement of bone growth and systemic growth reduction that ensured that body proportions were maintained. The local response entailed hyperproliferation of spared left limb chondrocytes that was associated with reduced chondrocyte density. The systemic effect involved impaired placental function and IGF signalling, revealing bone-placenta communication. Therefore, vertebrates, like invertebrates, can mount coordinated local and systemic responses to developmental insults that ensure that normal body proportions are maintained.

Thyroid hormone receptor-β1 signaling is critically involved in regulating secondary ossification via promoting transcription of the Ihh gene in the epiphysis

Thyroid hormone (TH) action is mediated through two nuclear TH receptors, THRα and THRβ. Although the role of THRα is well established in bone, less is known about the relevance of THRβ-mediated signaling in bone development. On ther basis of our recent finding that TH signaling is essential for initiation and formation of secondary ossification center, we evaluated the role of THRs in mediating TH effects on epiphysial bone formation. Two-day treatment of TH-deficient Tshr(-/-) mice with TH increased THRβ1 mRNA level 3.4-fold at day 7 but had no effect on THRα1 mRNA level at the proximal tibia epiphysis. Treatment of serum-free cultures of tibias from 3-day-old mice with T3 increased THRβ1 expression 2.1- and 13-fold, respectively, at 24 and 72 h. Ten-day treatment of Tshr(-/-) newborns (days 5-14) with THRβ1 agonist GC1 at 0.2 or 2.0 μg/day increased BV/TV at day 21 by 225 and 263%, respectively, compared with vehicle treatment. Two-day treatment with GC1 (0.2 μg/day) increased expression levels of Indian hedgehog (Ihh) 100-fold, osterix 15-fold, and osteocalcin 59-fold compared with vehicle at day 7 in the proximal tibia epiphysis. Gel mobility shift assay demonstrated that a putative TH response element in the distal promoter of mouse Ihh gene interacted with THRβ1. GC1 treatment (1 nM) increased Ihh distal promoter activity 20-fold after 48 h in chondroctyes. Our data suggest a novel role for THRβ1 in secondary ossification at the epiphysis that involves transcriptional upregulation of Ihh gene.

Deficiency of circadian clock protein BMAL1 in mice results in a low bone mass phenotype

The circadian clock is an endogenous time keeping system that controls the physiology and behavior of many organisms. The transcription factor Brain and Muscle ARNT-like Protein 1 (BMAL1) is a component of the circadian clock and necessary for clock function. Bmal1(-/-) mice display accelerated aging and many accompanying age associated pathologies. Here, we report that mice deficient for BMAL1 have a low bone mass phenotype that is absent at birth and progressively worsens over their lifespan. Accelerated aging of these mice is associated with the formation of bony bridges occurring across the metaphysis to the epiphysis, resulting in shorter long bones. Using micro-computed tomography we show that Bmal1(-/-) mice have reductions in cortical and trabecular bone volume and other micro-structural parameters and a lower bone mineral density. Histology shows a deficiency of BMAL1 results in a reduced number of active osteoblasts and osteocytes in vivo. Isolation of bone marrow derived mesenchymal stem cells from Bmal1(-/-) mice demonstrate a reduced ability to differentiate into osteoblasts in vitro, which likely explains the observed reductions in osteoblasts and osteocytes, and may contribute to the observed osteopenia. Our data support the role of the circadian clock in the regulation of bone homeostasis and shows that BMAL1 deficiency results in a low bone mass phenotype.

[MINERAL BONE DENSITY AND BODY COMPOSITION IN PARTICIPANTS IN EXPERIMENT MARS-500]

Investigations of the bone system and body composition in Mars-500 test-subjects (prior to and on completion of the experiment) involved dual-energy X-ray absorptiometry (DXA) using the HOLOGIC Delphy densitometer and the protocol performed to examine cosmonauts. Bone density of lumber vertebrae and femoral proximal epiphysis, and body composition were measured. Reliable changes in vertebral density found in 3 test-subjects displayed different trends from +2.6 to -2.4%. At the same time, the experiment decreased significantly mineral density of the femoral proximal epiphysis, including the neck, in all test-subjects. Four test-subjects had cranial mineralization increased by 5-9%, same as in some cosmonauts after space flight. All tests-subjects incurred adipose loss from 2 to 7 kg; one test-subject lost 20 kg, i.e. his adipose mass became three times less. Changes in lean mass (1-3 kg) typically were negative; as for changes in lean mass of extremities, they could be linked with adherence to one or another type of physical activity. Therefore, extended exposure to confinement may affect mineralization of some parts of the skeleton. Unlike real space missions and long-term bedrest studies conducted at the Institute of Biomedical Problems in the past, Mars-500 did not cause clinically significant mineral losses (osteoporosis, osteopenia), probably because of the absence of effects of microgravity.

Expression of matrix Gla protein and osteocalcin in the developing tibial epiphysis of mice

This study aimed to investigate the expression of matrix Gla protein (MGP) and osteocalcin (OCN) in the tibial epiphysis of developing mice. At 1, 2, 3, and 4 weeks after birth, tibiae were removed and processed for histochemical observations and western blot analyses under anesthesia. To evaluate bone volume, the specimens were scanned with Micro CT Scanner from the articular cartilage through the growth plate, along the long axis of tibia. At 1 week after birth, OCN reactivity was faint in the region of vascular invasion, while hardly any MGP reactivity was discernible. Subsequently, MGP reactivity was seen on the cartilaginous lacunar walls of hypertrophic chondrocytes, while OCN reactivity was evenly found not only in the bone matrix, but also in the cartilaginous lacunar walls and on the bone surfaces. Furthermore, double-immunostaining clearly showed that MGP reactivity appeared closer to the cartilage matrix than OCN reactivity until postnatal week 3. Interestingly, the immunoreactivities for MGP and OCN both showed tidemarks in the articular cartilage at postnatal week 4, and MGP reactivity was more intense than OCN reactivity. Statistical analyses showed an overall upward trend in MGP and OCN expression levels during tibial epiphysis development, even though OCN was more abundant than MGP at every time-point. Taken together, our findings suggest that the expression of MGP and OCN increased gradually in the murine developing tibial epiphysis, and the two mineral-associated proteins may occur at the same location during a particular period, but at different levels.

Does dynamic immobilization reduce chondrocyte apoptosis and disturbance to the femoral head perfusion?

The purpose of this study is to investigate whether the dynamic hip immobilization is more favourable for lessening ischemic injury to the immature femoral head than a static immobilization. 152 Japanese white rabbits were divided into four groups randomly, and the hips were immobilized into "human" position (group A), "frog leg" position (group B) and "dynamic frog leg" position (group C). Group D was used as control. Ten rabbits in each group were killed, and the hip specimens were harvested at 1, 2, and 3 weeks after immobilization. Bcl-2/Bax expression balance and chondrocytes apoptosis were analyzed. The remaining eight rabbits in each group were used to measure the blood supply of capital femoral epiphysis by selective vascular perfusion with Indian ink. The Bcl-2/Bax expression ratio in group C was significantly increased than that in group A and B (p<0.001), while that was not significantly different from control group (p=0.0592). At three weeks after immobilization, the average apoptotic ratio was 36.7%, 45.8%, and 26.7% in group A, B and C, respectively (p<0.01). There was no significant difference between group C and normal control (p=0.0597). The perfusion ratio was 0.03±0.03, 0.03±0.02, and 0.08±0.03 in group A, B and C respectively, and 0.12±0.04 in control group (p<0.05). Thus, the dynamic immobilization model exhibited a relatively less chondrocytes apoptosis and disturbance to the femoral head perfusion than other immobilizations in vivo, which therefore may be useful for reducing avascular necrosis following the treatment of developmental dysplasia of the hip.

Effect of hyperlipidemia on femoral biomechanics and morphology in low-density lipoprotein receptor gene knockout mice

The objective of this study was to evaluate the effect of hyperlipidemia on the biomechanical and morphological properties of the femur of low-density lipoprotein receptor gene knockout mice (LDLr-/-) mice. Ten wild-type mice (C57BL6) and 10 LDLr-/- mice generated on a C57BL6 background were used. Male 3-month-old animals were divided into four groups (n = 5): group W (wild type) and group L (LDLr-/-) receiving low-fat commercial ration, and group WH (wild type) and group LH (LDLr-/-) receiving a high-fat diet. After 60 days, blood samples were collected for laboratory analysis of calcium, triglycerides, and cholesterol. The femur was excised for mechanical testing and morphometric analysis. LDLr-/- mice receiving the high-fat diet presented more marked alterations in the mechanical and morphological properties of femoral cortical and trabecular bone. Changes in the plasma levels of calcium, triglycerides, cholesterol, and fractions were also more pronounced in this group. The present results demonstrate that hyperlipidemia causes alterations in the structure and mechanical properties of the femur of LDLr-/- mice. These effects were more pronounced when associated with a high-fat diet.

Endocrine actions of myostatin: systemic regulation of the IGF and IGF binding protein axis

Myostatin's inhibitory actions on striated muscle growth are believed to be directly mediated by locally produced myostatin and possibly by IGF binding proteins (IGFBPs). We therefore measured skeletal muscle, heart, and liver expression, in neonates and adults, and circulating levels of various IGF axis components (IGF-I, IGFBP-1 to IGFBP-3, and acid labile subunit) in wild-type and mstn-/- mice. Compared with wild type, differences in muscle expression were tissue specific, although IGF-I receptor expression was higher in all mstn-/- neonatal tissues and in adult gastrocnemius. Liver expression of several components also differed between genotype as IGF-I receptor, IGFBP-3 and IGFBP-5 expression was higher in mstn-/- neonates and IGF-I and IGFBP-3 in adults. Circulating IGF-I levels were also higher in mstn-/- adults, whereas IGFBP-1 and IGFBP-2 levels were lower. Comparing IGF-I:IGFBP molar ratios suggested that the relative IGF-binding capacity was potentially lower in mstn-/- mice, and thus, total and "free" IGF-I levels may be elevated. This in turn may increase negative feedback control on GH, because mstn-/- liver weights were lower. Bone growth was similar in both genotypes, suggesting that changes in circulating IGF-I may be more important to muscle, whose mass is enhanced in mstn-/- mice, than to bone. Myostatin receptors, but not myostatin itself, are expressed in the liver. Changes in hepatic production of circulating IGF axis components could therefore result from the loss of endocrine myostatin. Thus, myostatin may inhibit striated muscle growth directly at the cellular level and indirectly through systemic effects on the IGF axis.

The epiphyseal plate: nutritional and hormonal influences; hereditary and other disorders

This article reviews nutritional and hormonal influences, diseases with uncertain etiology, and hereditary disorders affecting the growth and development of the long bones in dogs and cats.

Formation of tethers linking the epiphysis and metaphysis is regulated by vitamin d receptor-mediated signaling

Rat tibial growth plates have X-ray opaque tethers that link the epiphysis and metaphysis and increase with age as the growth plate (GP) becomes thinner. To determine if tether formation is a regulated process of GP maturation, we tested the hypotheses that tether properties and distribution can be quantified by micro-computed tomography (microCT), that rachitic GPs typical of vitamin D receptor knockout (VDR(-/-)) mice have fewer tethers and altered tether distribution, and that tether formation is regulated by signaling via the VDR. Distal femoral GPs from VDR(+/+) and VDR(-/-) 8-week-old mice were analyzed with microCT and then processed for decalcified and undecalcified histomorphometry. A wide range of parameters that assessed GP and tether geometry and morphology, along with tether distribution, were measured using both microCT and histology. Growth plates of 10-week-old VDR(+/+) and VDR(-/-) mice on a high-calcium, phosphorus, lactose, and vitamin D(3) rescue diet were also analyzed. Both microCT and histology showed tethers present throughout normal mice GPs, while reduction in tether number and volume percentage occurred in VDR(-/-) GPs with localization to the central region. Decreased shrinkage in the axial direction during decalcified histological processing correlated with tether formation, suggesting mechanical stability due to tethers. Tether formation increased greatly between 8 and 10 weeks. Rescue diets restored VDR(-/-) GP size but not tether volume percentage. Overall, these results demonstrate microCT imaging's utility for analyzing tether formation and suggest that signaling via the VDR plays a pivotal role in tether formation.

Calmodulin-dependent kinase 1beta is expressed in the epiphyseal growth plate and regulates proliferation of mouse calvarial osteoblasts in vitro

The Ca(2+)/Calmodulin-dependent protein kinase (CaMK) family is activated in response to elevation of intracellular Ca(2+), and includes CaMK1 (as well as CaMK2 and CaMK4), which exists as different isoforms (alpha, beta, gamma and delta). CaMK1 is present in several cell types and may be involved in various cellular processes, but its role in bone is unknown. In situ hybridization was used to determine the spatial and temporal expression of CaMK1beta during endochondral bone development in mouse embryos and newborn pups. The cellular and subcellular distribution of CaMK1 was assessed by quantitative immunogold electron microscopy (EM). The role of CaMK1beta in mouse calvarial osteoblasts was investigated by using small interfering RNA (siRNA) to silence its expression, while in parallel monitoring cell proliferation and levels of skeletogenic transcripts. cRNA in situ hybridization and EM studies show that CaMK1beta is mainly located in developing long bones and vertebrae (from ED14.5 until day 10 after birth), with highest expression in epiphyseal growth plate hypertrophic chondrocytes. By RT-PCR, we show that CaMK1beta2 (but not beta1) is expressed in mouse hind limbs (in vivo) and mouse calvarial osteoblasts (in vitro), and also in primary human articular chondrocyte cultures. Silencing of CaMK1beta in mouse calvarial osteoblasts by siRNA significantly decreases osteoblast proliferation and c-Fos gene expression (approx. 50%), without affecting skeletogenic markers for more differentiated osteoblasts (i.e. Cbfa1/Runx2, Osterix (Osx), Osteocalcin (Oc), Alkaline phosphatase (Alp) and Osteopontin (Opn)). These results identify CaMK1beta as a novel regulator of osteoblast proliferation, via mechanisms that may at least in part involve c-Fos, thus implicating CaMK1beta in the regulation of bone and cartilage development.

HLA-B27 rats develop osteopaenia through increased bone resorption without any change in bone formation

Osteopaenia is a common complication of inflammatory bowel diseases (IBD). However, the mechanisms of bone loss are still the subject of debate. The aims of this study were to investigate bone loss in HLA-B27 transgenic rats, a spontaneous model of colitis and to compare the results provided by the usual markers of bone remodelling and by direct measurement of bone protein synthesis. Systemic inflammation was evaluated in HLA-B27 rats and control rats from 18 to 27 months of age. Then bone mineral density, femoral failure load, biochemical markers of bone remodelling and protein synthesis in tibial epiphysis were measured. Bone mineral density was lower in HLA-B27 rats than in controls. Plasma osteocalcin, a marker of bone formation, and fractional protein synthesis rate in tibial epiphysis did not differ between the two groups of rats. In contrast, urinary excretion of deoxypyridinoline, a marker of bone resorption, was significantly increased in HLA-B27 rats. The present results indicate that bone fragility occurs in HLA-B27 rats and mainly results from an increase in bone resorption. Systemic inflammation may be the major cause of the disruption in bone remodelling homeostasis observed in this experimental model of human IBD.

Gene expression and distribution of connective tissue growth factor (CCN2/CTGF) during secondary ossification center formation

CCN2/connective tissue growth factor (CCN2/CTGF) is a critical signaling modulator of mesenchymal tissue development. This study investigated the localization and expression of CCN2/CTGF as a factor supporting angiogenesis and chondrogenesis during development of secondary ossification centers in the mouse tibial epiphysis. Formation of the secondary ossification center was initiated by cartilage canal formation and blood vessel invasion at 7 days of age, and onset of ossification was observed at 14 days. In situ hybridization showed that CCN2/CTGF mRNA was distinctively expressed in the region of the cartilage canal and capsule-attached marginal tissues at 7 days of age, and distinct expression was also observed in proliferating chondrocytes around the marrow space at 14 days of age. Immunostaining showed that CCN2/CTGF was distributed broadly around the expressed cells located in the central region of the epiphysis, where the chondrocytes become hypertrophic and the cartilage canal enters into the hypertrophic mass. Furthermore, an overlapping distribution of metalloproteinase (MMP)9 and CCN2/CTGF was found in the secondary ossification center. These findings suggest that the CCN2/CTGF is involved in establishing epiphyseal vascularization and remodeling, which eventually determines the secondary ossification center in the developing epiphysial cartilage.

[Thymic factors influence on melatonin-producing pineal function in mice of different age: the possible mechanisms]

The aging peculiarities of thymic factors influence on pineal gland function in CBA mice were investigated. Significant increase of melatonin serum level in 3 h and decrease in 24 h after one injection of thymic preparation "thymalin" in adult mice was shown. The activating influence of thymalin was depended on season and linked with increase of thymic serum factor (FTS, thymulin) level and decrease of corticosterone blood level. Thymic stroma supernatant of adult mice, which had high level of FTS, intensified in vitro melatonin-producing pineal function. The activating influence of thymic factors in vivo and in vitro on pineal function in old mice was not revealed. FTS content increased and cortocosterone level did not change in old mice after injection of thymalin. The mechanisms of thymic factors influence on melatonin level in adult organism and their peculiarities in aging were discussed.

Bone cell transfection in tissue culture using hydroxyapatite microparticles

Coprecipitates of calcium phosphate and DNA have been used in vitro for several decades for cell transfection. We evaluated the efficiency of calcium phosphate ceramics associated to plasmid DNA in the transfection of bone cells in vitro when they are grown in tissue culture. Newborn rat calvariae and tibia epiphyses were grown on an agar surface for a period of 48 h to 30 days. The hydroxyapatite (HA)-particles were loaded with a plasmid bearing a galactosidase reporter gene by incubation of the plasmid solution in PBS with the particles. One milligram of HA-particles was then placed in contact with the bone explants for 8 and 30 days. Histological sections were then performed and the galactosidase activity was revealed using an X-gal solution. At eight days, very few cells expressing the galactosidase activity were detected. By 30 days, however, the explants appeared uniformly stained blue. The staining of sections showed that the osteoblasts, chondroblasts, perichondroblasts, and perisoteal cells all expressed the lacZ gene while the number of cells stained in the control was negligible. The time dependence of the transfection suggests that transfection using ceramics is linked to the degradation of the ceramic by the cells. Furthermore, the cells are stained remote from the particles suggesting that the particles induce a coprecipitate of DNA in the explant.

Expression pattern and functional characterization of connexin29 in transgenic mice

Using newly generated transgenic mice in which the coding region of the connexin29 (Cx29) gene was replaced by the lacZ reporter gene, we confirmed previous immunochemical results that Cx29 is expressed in Schwann cells, oligodendrocytes and Bergmann glia cells. In addition, we detected lacZ/Cx29 in Schwann cells of the sciatic nerve and in particular of the spiral ganglion in the inner ear, as well as at low abundance in the stria vascularis. Furthermore, we found lacZ/Cx29 expression in nonmyelinating Schwann cells of the adrenal gland, in chondrocytes of intervertebral discs and the epiphysis of developing bones. Electron microscopic analyses of myelin sheaths in the central and peripheral nervous system of Cx29-deficient mice detected no abnormalities. The nerve conduction in the sciatic nerve of adult Cx29-deficient mice and the auditory brain stem response as well as visually evoked potentials in 4- to 10-week-old Cx29-deficient mice were not different from wild-type littermate controls. Thus, in contrast to connexin32 and connexin47, which are also expressed in myelinating cells, Cx29 does not contribute to the function of myelin in adult mice.

Increase in bone mineral density through oral administration of shark gelatin to ovariectomized rats

OBJECTIVE

The incidence of bovine spongiform encephalopathy has resulted in marine collagen hydrolysate (low-molecular-weight gelatin) being sold as supplements and cosmetics in Japan. Shark skin collagen is one of the important sources of marine collagen. We examined the effect of shark skin gelatin in an osteoporosis model animal.

METHODS

Shark skin gelatin was orally administered to ovariectomized rats with a low-protein diet. Bone mineral density of the right femur was measured. Collagen and glycosaminoglycan in the tibial end were extracted and analyzed by western blotting and cellulose acetate membrane electrophoresis, respectively.

RESULTS

Administering collagen to the ovariectomized rats resulted in the bone mineral density of the femur epiphysis being higher than that in the sham-operated rats. The contents of type I collagen and glycosaminoglycan in the epiphysis were increased by administering shark skin gelatin.

CONCLUSIONS

These results indicated that shark skin gelatin would be useful as a dietary supplement for treating osteoporosis.

Bsx, an evolutionary conserved Brain Specific homeoboX gene expressed in the septum, epiphysis, mammillary bodies and arcuate nucleus

Shaping and orchestrating the genetic program involved in embryonic modelling of brain structures is a major function played by homeobox containing genes. Recently, analysis of conditional mouse mutants has pointed out additional roles in supporting adult brain functional activities. During a search for novel homeobox genes in the public released genomic sequences derived by the Human and Mouse genome projects, we were able to identify the mouse homologue of the Drosophila brain specific homeobox gene. We named it Bsx and characterized its expression in embryonic and post-natal mouse brain. Interestingly, Bsx shows an expression pattern restricted to a few specific developing brain structures. Pineal gland, telencephalic septum, hypothalamic pre-mammillary body and arcuate nucleus are the only brain structures where we detected Bsx transcriptional activity, which is maintained also after birth. In particular, Bsx might be considered an important molecular marker for early embryonic stages of epiphysis development, being specifically expressed in this neural structure from E9.5 onwards.

Prevention of bone loss in paraplegics over 2 years with alendronate

To assess the effects of long-term treatment of bone loss with alendronate in a group of paraplegic men, 55 patients were evaluated in a prospective randomized controlled open label study that was 2 years in duration comparing alendronate and calcium with calcium alone. Bone loss was stopped at all cortical and trabecular infralesional sites (distal tibial epiphysis, tibial diaphysis, total hip) with alendronate 10 mg daily.

INTRODUCTION

Bone loss after spinal cord injury (SCI) leads to increased fracture risk in the lower limbs of paraplegics. The aim of this study was to document long-term treatment of bone loss with alendronate in a group of paraplegic men with complete motor lesion after SCI.

MATERIALS AND METHODS

Sixty-five men with complete motor post-traumatic medullary lesion between T1 and L2 with total motor and sensory loss (Frankel classification, stage A) or with total motor and partial sensory loss (Frankel classification, stage B) after SCI were included in this prospective randomized controlled open label study that was 2 years in duration. The patients were randomized to either the treatment group with alendronate 10 mg daily and elemental calcium 500 mg daily or to the control group with elemental calcium 500 mg daily alone. The primary endpoint was defined as the effect over 24 months of alendronate and calcium compared with calcium alone on the BMD values at the distal tibial epiphysis (as a surrogate for trabecular bone in the paralyzed zone). The secondary endpoints were changes in BMD at supra- and infralesional sites of measurement. Biochemical markers of bone turnover were assessed.

RESULTS

Fifty-five subjects, 0.1-29.5 years post-SCI, completed the study over 24 months. BMD at the distal tibial epiphysis significantly decreased from baseline in the calcium group (-10.8 +/- 2.7% at 24 months, p < 0.001), whereas it remained stable in the alendronate plus calcium group (-2.0 +/- 2.9% at 24 months, p = not significant versus baseline), leading to a significant intergroup difference over time (p = 0.017). At the tibial diaphysis, similar significant results were observed. At the ultradistal radius and the radial shaft, BMD did not change significantly from baseline in either treatment group. At the total hip, BMD decreased significantly in the calcium group (-4.1 +/- 1.6%, p = 0.038) but remained stable in the alendronate plus calcium group (+0.43 +/- 1.2%), with a significant intergroup difference (p = 0.037). At the lumbar spine, BMD increased significantly (p < 0.0001) from baseline in both groups. Biochemical markers of bone resorption were significantly decreased with alendronate versus baseline and control. Alendronate and calcium were generally safe and well tolerated.

CONCLUSIONS

In paraplegic men, SCI bone loss was stopped at all measured cortical and trabecular infralesional sites over 24 months with alendronate 10 mg daily.

Expression of VEGF isoforms by epiphyseal chondrocytes during low-oxygen tension is HIF-1 alpha dependent

OBJECTIVE

To establish the role of hypoxia and HIF-1 alpha for VEGF expression of murine epiphyseal chondrocytes. To analyze the effect of hypoxia on VEGF isoform expression.

MATERIALS AND METHODS

VEGF mRNA and VEGF isoform expression was investigated in epiphyses of murine newborns by in situ hybridization and real-time PCR. Further, epiphyseal chondrocytes were isolated from newborn mice with homozygous flanking of the HIF-1 alpha gene with lox-P sites. HIF-1 alpha was deleted by infection with adenovirus containing cre-recombinase. After chondrocytes reached confluency they were exposed to 0.5% or 20% oxygen, respectively. Total VEGF and VEGF isoform mRNA expression levels were measured by real-time PCR. Secreted VEGF protein was determined by ELISA.

RESULTS

VEGF mRNA signals were detected in the hypertrophic zone and in the center of the proliferative zone of the murine epiphysis, which is considered to be hypoxic. Real-time PCR revealed that VEGF(120)is the dominant isoform in vivo. In cultured epiphyseal chondrocytes strongly increased VEGF gene expression levels were detected after exposure to hypoxia. Furthermore, secretion of VEGF protein was significantly enhanced under 0.5% oxygen. Remarkably, functional inactivation of HIF-1 alpha abolished the hypoxic increase of VEGF expression in chondrocytes completely. Furthermore, the soluble isoforms VEGF(120)and VEGF(164)are the most abundantly expressed splice variants in chondrocytes exposed to low oxygen levels.

CONCLUSIONS

The data presented here clearly indicate that hypoxia is able to induce the synthesis of soluble VEGF isoforms by epiphyseal chondrocytes, most likely through stabilization of HIF-1 alpha. Thus it can be speculated that HIF-1 alpha is an essential prerequisite for hypoxic VEGF synthesis in the epiphysis, thereby contributing to the formation and invasion of blood vessels in long bone development.

Effects of estrogen replacement therapy on bone turnover in subchondral bone and epiphyseal metaphyseal cancellous bone of ovariectomized cynomolgus monkeys

ERT decreases the severity of OA in OVX cynomolgus monkeys. We show that bone formation is greater in subchondral bone compared with epiphyseal/metaphyseal cancellous bone of the proximal tibia in these animals and that ERT decreases bone formation in both sites. ERT may decrease the risk of OA by decreasing bone formation in the SC bone.

INTRODUCTION

Estrogen replacement therapy (ERT) decreases the risk of osteoporosis and osteoarthritis (OA) in postmenopausal women and has been shown to have direct effects on cells of the bone and cartilage. The effects of ERT have been studied extensively in cancellous bone, but subchondral (SC) bone directly beneath the articular cartilage has not been specifically evaluated.

MATERIALS AND METHODS

Adult feral female cynomolgus monkeys were bilaterally ovariectomized (OVX) to simulate menopause; treated with ERT, soy phytoestrogens (SPE), or no hormones (OVX control group) for 3 years; and labeled with calcein before necropsy. At necropsy, the proximal tibias of 20 randomly selected animals from each treatment group were embedded in bioplastic and sectioned. Areas and labels were measured in a carefully defined region of the SC bone and epiphyseal/metaphyseal cancellous (EMC) bone, and derived dynamic and static indices were compared between the SC and EMC bone and among the three treatment groups. Student's t-tests and ANOVA were used to compare the data.

RESULTS AND CONCLUSIONS

In both the SC and EMC bone, most of the values for the dynamic indices were highest in the OVX control group, intermediate in the SPE group, and lowest in the ERT group. The mineralizing surface, double-labeled surface, and bone formation rate (surface referent) were significantly higher in the SC bone compared with the EMC bone in the OVX control group. The trabecular bone volume was higher in the SPE-treated group compared with the OVX control group. In conclusion, the bone turnover indices were higher in the SC bone compared with the EMC bone, and ERT decreased these indices in both sites. In addition, SPE was protective against loss of bone volume.

Soluble VEGF isoforms are essential for establishing epiphyseal vascularization and regulating chondrocyte development and survival

VEGF is crucial for metaphyseal bone vascularization. In contrast, the angiogenic factors required for vascularization of epiphyseal cartilage are unknown, although this represents a developmentally and clinically important aspect of bone growth. The VEGF gene is alternatively transcribed into VEGF(120), VEGF(164), and VEGF(188) isoforms that differ in matrix association and receptor binding. Their role in bone development was studied in mice expressing single isoforms. Here we report that expression of only VEGF(164) or only VEGF(188) (in VEGF(188/188) mice) was sufficient for metaphyseal development. VEGF(188/188) mice, however, showed dwarfism, disrupted development of growth plates and secondary ossification centers, and knee joint dysplasia. This phenotype was at least partly due to impaired vascularization surrounding the epiphysis, resulting in ectopically increased hypoxia and massive chondrocyte apoptosis in the interior of the epiphyseal cartilage. In addition to the vascular defect, we provide in vitro evidence that the VEGF(188) isoform alone is also insufficient to regulate chondrocyte proliferation and survival responses to hypoxia. Consistent herewith, chondrocytes in or close to the hypoxic zone in VEGF(188/188) mice showed increased proliferation and decreased differentiation. These findings indicate that the insoluble VEGF(188) isoform is insufficient for establishing epiphyseal vascularization and regulating cartilage development during endochondral bone formation.

Sex-specific impact of congenital hypothyroidism due to thyroid dysgenesis on skeletal maturation in term newborns

Newborns with severe congenital hypothyroidism (often defined by the absence of knee epiphyses at diagnosis) are still at risk of loss of intellectual potential despite early treatment. Although there is no significant sexual dimorphism in the age at appearance and size of the knee epiphyses in normal newborns, it was our clinical impression that these epiphyses were more often absent in hypothyroid newborn males than in affected females. Using the large French database of congenital hypothyroidism, we studied the presence or absence of knee epiphyses at diagnosis, as well as the length of gestation and the birth weight of 1827 term newborns with athyreosis or ectopic thyroid. Boys were twice as likely as girls to have absent epiphyses [odds ratio, 2.1 (95% confidence interval, 1.6-2.7), P < 0.001, after adjustment for etiology, plasma free T(4) concentration, and presence or absence of clinical signs at diagnosis, gestational age and birth weight]. Compared with the general population of French newborns, those with congenital hypothyroidism were more often born after a prolonged gestation (> or =42 wk) and with a high birth weight (9% were above the 95th centile, as opposed to the expected 5%), regardless of sex. We conclude that the impact of congenital hypothyroidism on fetal skeletal maturation is sexually dimorphic. This may result from less efficient conversion of T(4) to T(3) by growth plate chondrocytes in males.

Altered expression of integrins in RSV-transformed chick epiphyseal chondrocytes

Chondrocytes have been shown to express both in vivo and in vitro a number of integrins of the beta1-, beta3- and beta5-subfamilies (Biorheology 37 (2000) 109). Normal and v-Src-transformed chick epiphyseal chondrocytes (CEC) display different adhesion properties. While normal CEC with time in culture tends to increase their adhesion to the substrate by organizing focal adhesions and actin stress fibers, v-Src-transformed chondrocytes display a refractile morphology and disorganization of actin cytoskeleton. We wondered whether the reduced adhesion and spreading of v-Src-transformed chondrocytes could be ascribed to changes in integrin expression and/or function. Integrin expression by normal CEC is studied and compared to v-Src-transformed chick chondrocytes, using monoclonal and polyclonal antibodies to integrins alpha- and beta-chains. We show the presence of alpha1-, alpha3-, alphav-, alpha6-, beta1- and beta3-chains on CEC, with very low levels of alpha2- and alpha5-chains. Alphav chain associates with multiple beta subunits in normal and transformed chondrocytes. With the exception of alpha1- and alpha2-chains, the levels of the integrin chains analyzed are higher in transformed chondrocytes as compared with normal chondrocytes. In spite of the increased levels of integrin expression, transformed chondrocytes exhibit loss of focal adhesion and actin stress fibers and low adhesion activity on several extracellular matrix constituents. These observations raise the possibility that, in addition to its effects on global pattern of integrin expression, v-Src can influence integrin function in chondrocytes.

Division and death of cells in developing synovial joints and long bones

Articular chondrocytes are a unique set of cells from the time the cellular condensations that become the anlagen of the long bones develop in the embryo. In the presumptive joint the cells of the opposing bones are packed very closely together, but at cavitation, the central, flattened cells move apart to form the articular surfaces. As the articular cartilage develops the cells are pushed further apart by the cartilaginous matrix. To determine the contributions of cell proliferation and death to cavitation and the subsequent development and growth of articular cartilage, direct observations were made to identify mitotic cells and those with apoptotic bodies in haematoxylin-stained sections of developing joints, and growing and ageing articular cartilage of the rabbit knee. These observations were extended using antibodies to the proliferating cell nuclear antigen (PCNA) and TdT-mediated dUTP nick end labelling (TUNEL) on corresponding sections. Low levels of cell division do occur in the articular cartilage up to 6 weeks postnatally, but matrix formation makes the major contribution to the increase in size of the cartilage. Cell death is not observed during cavitation, nor during the development of the articular cartilage proper. Apoptosis is essential, however, for the removal of the epiphyseal cartilage during ossification of the epiphyses and in the growth plate.

The expression of the nuclear oncogenes c-myc and c-jun in the groove of Ranvier of the rabbit growth plate

An immunohistochemical technique has been used to localise nuclear oncoproteins in the groove of Ranvier. The densely packed cells deep in the groove were immunoreactive positive for the myc protein. Cells and matrix in the same location were immunoreactive positive for the jun protein. These findings confirm the presence of proliferating cells in the groove. Injury to these cells is probably responsible for growth disturbances associated with trauma.

Annexin VIII is differentially expressed by chondrocytes in the mammalian growth plate during endochondral ossification and in osteoarthritic cartilage

Endochondral ossification is the developmental process that leads to the formation and coordinated longitudinal growth of the majority of the vertebrate skeleton. Central to this process is chondrocyte differentiation occurring in the growth plate that lies at the junction between the epiphyseal cartilage and the bone. To identify novel factors involved in this differentiation process, suppression subtractive hybridization was performed to amplify preferentially cDNAs uniquely expressed in fetal bovine growth plate chondrocytes as opposed to epiphyseal chondrocytes. The subtracted product was used to screen a fetal bovine chondrocyte cDNA library. One of the cDNA clones identified encoded the bovine orthologue of annexin VIII, a protein not previously described in the growth plate. Northern and Western blotting confirmed that annexin VIII was expressed by growth plate chondrocytes and not by epiphyseal chondrocytes. Immunohistochemistry of the fetal bovine growth plate identified a gradient of increasing annexin VIII protein from the proliferative to the hypertrophic zone. Immunofluorescence localized annexin VIII largely to the chondrocyte cell membrane. In a preliminary study, we examined the distribution of annexin VIII in normal and osteoarthritic (OA) articular cartilage. In OA cartilage, the protein was located in a subset of mid- to deep zone chondrocytes and in the matrix surrounding these cells; no annexin VIII was detected in normal articular cartilage. Thus annexin VIII is a marker for chondrocyte differentiation during normal endochondral ossification and may act as a marker for cells undergoing inappropriate differentiation in OA.

Gender differences in expression of androgen receptor in tibial growth plate and metaphyseal bone of the rat

In this study, we investigate the expression of the androgen receptor (AR) in the tibial growth plate and metaphyseal bone of male and female rats at the mRNA and protein level. Using in situ hybridization and immunohistochemistry, AR mRNA and protein were demonstrated in proliferating and early hypertrophic chondrocytes in the growth plate of 1-, 4-, and 7-week-old male and female rats. Immunostaining for AR was observed both in the nucleus and the cytoplasm. After sexual maturation at 12 and 16 weeks of age, AR expression decreased in both genders and was confined to a small rim of prehypertrophic chondrocytes. In female rats of 40 weeks of age, this expression pattern was still visible. In most age groups there was a tendency toward an increased AR mRNA expression in male vs. female rats except in the 7-week-old animals. At the protein level, sexually maturing 7-week-old male rats demonstrated a higher staining intensity compared to their female counterparts. At this stage, AR staining in the males was mainly confined to the nucleus, whereas in females staining was predominantly found in the cytoplasm. In the tibial metaphysis, AR mRNA was detected in lining cells, osteoblasts, osteocytes, and osteoclasts at all stages of development. At the protein level, a similar expression pattern was observed, except for an absence of immunostaining in the lining cells. The staining was both nuclear and cytoplasmic. In most age groups, mRNA and protein signals were higher in males compared with females. We have demonstrated the presence of AR mRNA and protein in the tibial growth plate and the underlying metaphyseal bone during development of the rat. In male rats, the presence of higher messenger and protein staining intensities, as well as preferential nuclear staining during sexual maturation, suggests that direct actions of androgens in chondrocytes and in bone forming cells may be involved in establishing the gender differences in the skeleton.

alpha 2-HS glycoprotein/fetuin, a transforming growth factor-beta/bone morphogenetic protein antagonist, regulates postnatal bone growth and remodeling

Soluble transforming growth factor-beta (TGF-beta)/bone morphogenetic protein (BMP)-binding proteins are widely distributed in mammalian tissues and control cytokine access to membrane signaling receptors. The serum and bone-resident glycoprotein alpha2-HS-glycoprotein/fetuin (ASHG) binds to TGF-beta/BMP cytokines and blocks TGF-beta1 binding to cell surface receptors. Therefore, we examined bone growth and remodeling phenotypes in ASHG-deficient mice. The skeletal structure of Ahsg(-/-) mice appeared normal at birth, but abnormalities were observed in adult Ahsg(-/-) mice. Maturation of growth plate chondrocytes was impaired, and femurs lengthened more slowly between 3 and 18 months of age in Ahsg(-/-) mice. However, bone formation was increased in Ahsg(-/-) mice as indicated by greater cortical thickness, accelerated trabecular bone remodeling, and increased osteoblast numbers on bone surfaces. The normal age-related increase in cortical thickness and bone mineral density was accelerated in Ahsg(-/-) mice and was associated with increased energy required to fracture. Bone formation in response to implanted BMP cytokine extended further from the implant in Ahsg(-/-) compared with Ahsg(+/+) mice, confirming the interaction between ASHG and TGF-beta/BMP cytokines in vivo. Our results demonstrate that ASHG blocks TGF-beta-dependent signaling in osteoblastic cells, and mice lacking ASHG display growth plate defects, increased bone formation with age, and enhanced cytokine-dependent osteogenesis.

The mechanism of aggrecan release from cartilage differs with tissue origin and the agent used to stimulate catabolism

The mechanisms of aggrecan degradation in adult human articular, adult bovine nasal and fetal bovine epiphyseal cartilage in response to either interleukin-1beta (IL-1beta) or retinoic acid were compared using an explant culture system. Bovine nasal cartilage cultured with either IL-1beta or retinoic acid exhibited significant release of glycosaminoglycan (GAG). For both factors, aggrecan proteolysis occurred predominantly at the 'aggrecanase' site, with no evidence for the action of matrix metalloproteinases, and resulted in the appearance of the corresponding G1 fragment in tissue extracts and in culture media. In human cartilage, little effect of IL-1beta was seen, but abundant release of GAG occurred in the presence of retinoic acid, with evidence of aggrecanase action. Treatment of fetal epiphyseal cartilage with retinoic acid resulted in significant GAG release, whereas treatment with IL-1beta did not. In the retinoic acid-treated tissue, however, no evidence for the cleavage of aggrecan in the interglobular region was apparent. Thus, in the fetal system, agents in addition to aggrecanase and matrix metalloproteinases appear to be active. Taken together, these data demonstrate that the pathways utilized for aggrecan catabolism may vary between different cartilages for a given stimulatory agent, and that, for a given tissue, different factors may elicit aggrecan release via different pathways.

Effects of zinc on cell proliferation and proteoglycan characteristics of epiphyseal chondrocytes

Zinc has been postulated as an important nutritional factor involved in growth promotion; however, the cellular mechanisms involved in the effects of zinc on linear growth remain to be elucidated. This study was conducted to evaluate the effects of zinc on the proliferation rate of epiphyseal growth plate chondrocytes and on the structural characteristics of the proteoglycans synthesized by these cells. For these purposes, hypertrophic and proliferating chondrocytes were isolated from the tibiae of 1- and 5-week-old chickens, respectively. Chondrocytes were cultured under serum-free conditions and primary cultures were used. The results showed that zinc stimulated proliferation by 40-50% above the baseline in the case of proliferating chondrocytes, but it had no effect on hypertrophic chondrocytes. Zinc had neither any effects on mean charge density of proteoglycans synthesized by hypertrophic chondrocytes nor in their hydrodynamic size. In contrast, zinc induced an increase in mean charge density and a decrease of hydrodynamic size of proteoglycans synthesized by proliferating chondrocytes. In both cell types zinc had no effect on the composition and hydrodynamic size of the glycosaminoglycan chains. The increased ability of proliferating chondrocytes cultured in the presence of zinc to synthesize 3'-phosphoadenosine 5'-phosphosulfate (PAPS) could be explained by the induction of enzymes participating in the sulfation pathway of proteoglycans. Therefore, the increase in mean charge density of proteoglycans observed in this study may be explained by an increase of the degree of sulfation of proteoglycan molecules. We speculate that the effect of zinc on linear growth may be explained at a cellular level by: a) an increase in proliferation rates of proliferating chondrocytes, and b) increased synthesis of highly charged proteoglycan molecules which decreases mineralization.

Testosterone stimulates growth of tibial epiphyseal growth plate and insulin-like growth factor-1 receptor abundance in hypophysectomized and castrated rats

Puberty is associated with an increase in the plasma concentration of sex steroids, growth hormone (GH), and insulin-like growth factor-1 (IGF-1). Gonadal steroid hormones are important for the normal pubertal growth spurt and skeletal growth. The mechanism by which gonadal steroids induces skeletal growth is still not fully understood. To study the GH-independent effect of testosterone on growth, we investigated the effect of testosterone injections on the tibial epiphyseal growth plate (EGP) in an in vivo model of hypophysectomized and castrated male rats. Four groups (six animals each) of 28-d-old male rats were studied. Groups A, B, and C were hypophysectomized and castrated and received 500 microg/(kg x d) of hydrocortisone and 15 microg/(kg x d) of levothyroxine sodium. Groups A and B were also treated with daily sc injections of 10 microg of testosterone/100 g of body wt and 100 microg of testosterone/100 g of body wt, respectively, for 7 d. Group C was injected with vehicle alone. Group D were intact animals injected with saline (controls). Animals were sacrificed on 8 d. As expected, serum GH levels were found to be very low (1.13+/-0.1 ng/mL) in the hypophysectomized animals (group C, hypopit), and testosterone treatment did not change them significantly. Serum IGF-1 decreased from 502.9+/-13 ng/mL in group D to 167+/-41.4 ng/mL in group C (p < 0.001). Testosterone therapy had no stimulatory effect on serum IGF-1 levels in the hypopit + low-dose group (A) (220+/-94.8 ng/mL) and had an inhibitory effect in the hypopit + high-dose group (B) (39.3+/-17.5). Histomorphometric determinations demonstrated an EGP width of 472.3+/-39 microm in the intact animals but only 336.9+/-1.6 microm in the hypopit group (C) (p < 0.01). High-dose testosterone treatment (group B) significantly increased the EGP width (to 438.8+/-27.8), (p < 0.001), whereas low-dose testosterone (group A) did not. Immunohistochemistry studies revealed that the levels of IGF-1 in the EGP of the control animals were almost negligible and that testosterone did not change them. However, testosterone increased in a dose-dependent manner the abundance of IGF-1 receptor EGP. We conclude that testosterone has a direct, local, GH-independent effect on the EGP growth and IGF-1 receptor abundance.

Enzymes active in the areas undergoing cartilage resorption during the development of the secondary ossification center in the tibiae of rats aged 0-21 days: II. Two proteinases, gelatinase B and collagenase-3, are implicated in the lysis of collagen fibrils

In the transformation of the cartilaginous epiphysis into bone, the first indication of change in the surfaces destined for resorption is the cleavage of aggrecan core protein by unidentified matrix metalloproteinases (MMPs) (Lee et al., this issue). In cartilage areas undergoing resorption, the cleavage leaves as superficial, 6-microm-thick band of matrix, referred to as "pre-resorptive layer." This layer harbors G1-fragments of the aggrecan core protein within a framework of collagen-rich fibrils exhibiting various stages of degeneration. Investigation of this layer in every resorption area by gelatin histozymography and TIMP-2 histochemistry demonstrates the presence of an MMP whose histozymographic activity is inhibited by such a low dose of the inhibitor CT1746 as to identify it as gelatinase A or B. Attempts at blocking the histozymographic reactions with neutralizing antibodies capable of inhibiting either gelatinase A or B reveals that only those against gelatinase B do so. Immunostaining of sections with anti-gelatinase B IgG confirms the presence of gelatinase B in every pre-resorptive layer, that is, at the blind end of excavated canals (stage I; 6-day-old rats), at sites along the walls of the forming marrow space (stage II; 7days), at sites within the walls of this space as it becomes the ossification center (stage III; 9 days) and along the wall of the maturing center (stage IV; 10-21 days). We also report the presence of collagenase-3 in precisely the same sites, possibly as active enzyme, but this remains to be proven. Because the results reveal that collagenase-3 is present beside gelatinase B in every pre-resorptive layer and, because these sites exhibit various signs of degradation including fibrillar debris, reduction in fibril number, or overt loss, we propose that gelatinase B and collagenase-3 mediate the lysis of this pre-resorptive layer-most likely through a cooperative attack leading to the disintegration of the collagen fibril framework.

Comparison in localization between cystatin C and cathepsin K in osteoclasts and other cells in mouse tibia epiphysis by immunolight and immunoelectron microscopy

We compared the distribution of a cysteine proteinase inhibitor, cystatin C, with that of cathepsin K in osteoclasts of the mouse tibia by immunolight and immunoelectron microscopy. Light microscopically, strong immunoreactivity for cystatin C was found extracellularly along the resorption lacuna and intracellularly in the organelles of osteoclasts. In serial sections, various patterns of cystatin C and cathepsin K localization were seen, specifically: (1) some resorption lacuna were positive for both cystatin C and cathepsin K; (2) others were positive for either cystatin C or cathepsin K, but not both; and (3) some lacuna were negative for both. In osteoclasts, the localization of cystatin C was similar to that of cathepsin K. Furthermore, cystatin C immunoreactivity was detected in preosteoclasts and osteoblasts, whereas cathepsin K was seen only in preosteoclasts. Electron microscopically, cystatin C immunoreactive products were found in the rough endoplasmic reticulum (ER), Golgi apparatus, vesicles, granules, and vacuoles of osteoclasts. These cystatin C-positive vesicles had fused or were in the process of fusion with the ampullar vacuoles (extracellular spaces) containing cystatin C-positive, fragmented, fibril-like structures. The extracellular cystatin C was deposited on and between the cytoplasmic processes of ruffled borders, and on and between type I collagen fibrils. In the basolateral region of osteoclasts, cystatin C-positive vesicles and granules also fused with vacuoles that contained cystatin C-positive or negative fibril-like structures. These results indicate that osteoclasts not only synthesize and secrete cathepsin K from the ruffled border into the bone resorption lacunae, but also a cysteine proteinase inhibitor, cystatin C. Therefore, it is suggested that cystatin C regulates the degradation of bone matrix by cathepsin K, both extracellularly and intracellularly.

[Physiological and pharmacological characteristics of epiphyseal neuropeptides]

Various epiphyseal neuropeptides, participating in regulation of the secretory processes, are capable of inducing systemic changes. This circumstance determines both pharmacological and therapeutic properties. The drug elitalamine, representing a polypeptide extract, ensures effective treatment of the immune system and brain disorders and tumors and allows a prophylaxis of tissue aging.

Murine fibromodulin: cDNA and genomic structure, and age-related expression and distribution in the knee joint

The genomic structure of murine fibromodulin was determined, and its age-related expression and distribution were characterized in knee epiphyses, with decorin studied for reference. Fibromodulin, as well as decorin, have roles in collagen fibrillogenesis both in vitro and in vivo. The murine fibromodulin gene, Fmod, was similar with that in other species, with three exons and 86% of the translated sequence in exon 2. The 2.7 kb long cDNA contains an open reading frame of 1131 nt. Fibromodulin mRNA levels were highest in tissues rich in fibrillar collagens type I or type II. During growth, the distribution of fibromodulin mRNA was similar with that of type II collagen, with the highest levels between 5 days and 1 month of age. Thereafter, the expression of type II collagen declined to a level near the detection limit, whereas the fibromodulin expression decreased less markedly to a level of approx. 35% of maximum, and remained constant throughout the rest of the observation period. In contrast, decorin mRNA levels were the highest in old animals. Pericellular deposition of fibromodulin was strong around the late-hypertrophic chondrocytes of the secondary ossification centre and in the growth plate. In young epiphyses, both fibromodulin and decorin were found interterritorially, mainly in the uncalcified and deep-calcified cartilage. In the old mice, calcified cartilage became enriched with regard to fibromodulin, while, in contrast, decorin deposition diminished, particularly near the tidemark. In the subchondral bone trabeculae, decorin was found in the endosteum of growing, but not in the mature, epiphyses. Differences in the expression and distribution profiles suggest different roles for fibromodulin and decorin in the regulation of collagen fibrillogenesis, maintenance of the fibril organization and matrix mineralization. As fibromodulin is deposited closer to cells than decorin, it may have a primary role in collagen fibrillogenesis, whereas decorin might be involved in the maintenance of fibril structures in the interterritorial matrix.

Expression of type I, type II, and type X collagen genes during altered endochondral ossification in the femoral epiphysis of osteosclerotic (oc/oc) mice

The osteosclerotic (oc/oc) mouse, a genetically distinct murine mutation that has a functional defect in its osteoclasts, also has rickets and shows an altered endochondral ossification in the epiphyseal growth plate. The disorder is morphologically characterized by an abnormal extension of hypertrophic cartilage at 10 days after birth, which is later (21 days after birth) incorporated into the metaphyseal woven bone without breakdown of the cartilage matrix following vascular invasion of chondrocyte lacunae. In situ hybridization revealed that the extending hypertrophic chondrocytes expressed type I and type II collagen mRNA, as well as that of type X collagen and that the osteoblasts in the metaphysis expressed type II and type X collagen mRNA, in addition to type I collagen mRNA. The topographic distribution of the signals suggests a possible co-expression of each collagen gene in the individual cells. Immunohistochemically, an overlapping deposition of type I, type II, and type X collagen was observed in both the extending cartilage and metaphyseal bony trabeculae. Such aberrant gene expression and synthesis of collagen indicate that pathologic ossification takes place in the epiphyseal/metaphyseal junction of oc/oc mouse femur in different way than in normal endochondral ossification. This abnormality is probably not due to a developmental disorder in the epiphyseal plate but to the failure in conversion of cartilage into bone, since the epiphyseal plate otherwise appeared normal, showing orderly stratified zones with a proper expression of cartilage-specific genes.

Chondromodulin I and pleiotrophin gene expression in bovine cartilage and epiphysis

Pleiotrophin and chondromodulin-I are low molecular weight proteins that are abundant (20 microg/g tissue) in fetal cartilage and difficult to detect in adult cartilage. We characterized their gene and protein expression patterns to gain a better understanding of their roles in the regulation of limb development and growth. In order to compare and contrast the relative amounts of the respective mRNA species within the developing epiphysis, a competitive PCR assay was developed. The results showed that the mRNAs for both proteins were abundant in fetal cartilage and while present in adult cartilage, were at 20-60-fold lower levels. Northern blotting revealed gradients of mRNA for both of these proteins in growth plate cartilage, with the highest levels in the resting zone, and the lowest in the hypertrophic zone. In contrast to pleiotrophin, chondromodulin-1 is down-regulated by retinoic acid with a pattern of expression similar to collagen type II and link protein, and may play a more specific role than pleiotrophin in modulating the chondrocyte phenotype.

Bone morphogenetic protein (BMP) localization in developing human and rat growth plate, metaphysis, epiphysis, and articular cartilage

We assessed the distribution and relative staining intensity of bone morphogenetic protein (BMP)-1-7 by immunohistochemistry in tibial growth plates, epiphyses, metaphyses, and articular cartilage in one 21-week and one 22-week human fetus and in five 10-week-old Sprague-Dawley rats. In the rats, articular cartilage was also examined. BMP proteins were mostly cytoplasmic, with negligible matrix staining. Highest BMP levels were seen in (a) hypertrophic and calcifying zone chondrocytes of growth plate (BMP-1-7), (b) osteoblasts and/or osteoprogenitor fibroblasts and vascular cells of the metaphyseal cortex and medulla (BMP-1-6), (c) osteoclasts of the metaphysis and epiphysis (BMP-1,-4,-5, and -6), and (d) mid to deep zone articular chondrocytes of weanling rats (BMP-1-7). BMP staining in osteoclasts, an unexpected finding, was consistently strong with BMP-4, -5, and -6 but was variable and dependent on osteoclast location with BMP-2,-3, and -7. BMP-1-7 were moderately to intensely stained in vascular canals of human fetal epiphyseal cartilage by endothelial cells and pericytes. BMP-1,-3,-5,-6, and -7 were localized in hypertrophic chondrocytes adjacent to cartilage canals. We conclude that BMP expression is associated with maturing chondrocytes of growth plate and articular cartilage, and may play a role in chondrocyte differentiation and/or apoptosis. BMP appears to be expressed by osteoclasts and might be involved in the intercellular "cross-talk" between osteoclasts and neighboring osteoprogenitor cells at sites of bone remodeling.

Bone tissue composition, dimensions and strength in female rats given an increased dietary level of vitamin A or exposed to 3,3',4, 4',5-pentachlorobiphenyl (PCB126) alone or in combination with vitamin C

In previous studies we have described structural and functional changes in rat bone tissue caused by 3,3',4,4',5-pentachlorobiphenyl (PCB126). Some of the effects caused by PCB126 resemble those found in vitamin C-deficient rats, as well as those found in rats with a high dietary intake of vitamin A. The present investigation was designed to determine if these PCB126-induced changes could be inhibited by addition of vitamin C to the drinking water and if they could be evoked by vitamin A administration. Five groups of female rats were used in this study, which lasted for 12 weeks. Three of the groups were exposed to PCB126 (total dose 320 microgram/kg, bw), either alone or in combination with vitamin C added to the drinking water (1 and 10 g/l, respectively). One group was given feed with increased level of vitamin A (600000 U/kg pellet) and the fifth group served as controls. Using peripheral quantitative computed tomography (pQCT), it was found that PCB126 increased trabecular density and cortical thickness, but reduced the trabecular area. Furthermore, maximum torque and stiffness of the humerus during torsional testing and serum osteocalcin levels were reduced by PCB126. Of the PCB126 induced effects observed, addition of vitamin C only inhibited the reduction of serum osteocalcin. Like PCB126 vitamin A supplementation increased the inorganic content and the bone density and also reduced the trabecular area and polar moment of inertia but did not increase the cortical thickness or reduce maximum torque, stiffness or serum osteocalcin level. Apparently, the effects induced by PCB126 are not mediated either via decreased vitamin C level or increased vitamin A level.

[Effects of zinc deficiency on the c-fos gene expression and transcription in the epiphyses of fetal mouse long bone in culture]

The effects of zinc on c-fos gene expression and transcription in the epiphyses of fetal long bone were studied in mice. The long bones of 16-day fetal mouse were cultured for 48 hours(in medium GBJb) and then used for measuring c-fos gene expression and transcription by immunohistochemistry and in situ hybridization. The result was analyzed by an imaged-analyses system. The experiment was divided into zinc control group(ZC), zinc deficiency group(ZD), zinc deficiency replenish group(ZDR) and zinc stimulatory group(ZS) respectively. The result showed that 1) zinc deficiency caused c-fos protein and mRNA expression and the number of reactive cell decreased. 2) when zinc concentration of medium was 100 mumol/L, the expression and transcription of c-fos gene were increased in hypertrophic, proliferative and resting zone of epiphyses. The research suggested that zinc could affect the expression of c-fos gene in mouse fetal long bone.

Spatiotemporal change of rat collagenase (MMP-13) mRNA expression in the development of the rat femoral neck

The interepiphyseal region between the greater trochanter and the capital femoral epiphysis and the medioproximal portion of the femoral neck exhibit extensive morphological changes during the first 4 weeks after birth in rats. Previous reports show that matrix metalloproteinase-13 (MMP-13, rat collagenase) mRNA is expressed in bone and cartilage during embryonal development and fracture healing. We examined MMP-13 mRNA expression and compared it with the distribution of osteopontin and osteocalcine mRNA in the femoral neck. Moreover, we examined histomorphometric analysis in the femoral neck where the morphology changes rapidly. Histomorphometric analysis of the 4-week-old rat femoral neck showed a high rate of bone formation and resorption in the region where shape changed rapidly. Osteopontin mRNA was expressed diffusely along the endosteum. In contrast, MMP-13 mRNA expression was restricted to the medial endosteal portion near the cartilage-bone interface of the femoral neck in 15- and 28-day-old rats and in the deepest endosteal interepiphyseal region of 15-day-old rats. MMP-13 mRNA-expressing osteoblastic cells were also expressing osteopontin but not osteocalcin mRNA. MMP-13 mRNA-expressing cells differ from tartrate-resistant acid phosphatase (TRAP)-positive cells, and MMP-13 mRNA-positive cells are located adjacent to TRAP-positive cells. The results of the site- and cell-specific expression of MMP-13, taken together with its enzymatic property, suggest that MMP-13 plays an important role in morphological changes in the rat femur, at least during the third and fourth week after birth, and that MMP-13 itself is involved in the interaction between osteoblastic and TRAP-positive cells.

Deletion of Ku86 causes early onset of senescence in mice

DNA double-strand breaks formed during the assembly of antigen receptors or after exposure to ionizing radiation are repaired by proteins important for nonhomologous end joining that include Ku86, Ku70, DNA-PK(CS), Xrcc4, and DNA ligase IV. Here we show that ku86-mutant mice, compared with control littermates, prematurely exhibited age-specific changes characteristic of senescence that include osteopenia, atrophic skin, hepatocellular degeneration, hepatocellular inclusions, hepatic hyperplastic foci, and age-specific mortality. Cancer and likely sepsis (indicated by reactive immune responses) partly contributed to age-specific mortality for both cohorts, and both conditions occurred earlier in ku86(-/-) mice. These data indicate that Ku86-dependent chromosomal metabolism is important for determining the onset of age-specific changes characteristic of senescence in mice.

Effects of TGF-beta1 on proliferation and IGFBP-3 production in a primary culture of human fetal epiphyseal chondrocytes (HFEC)

Proliferation and differentiation of chondrocytes from growth cartilage are modulated by hormones and growth factors, among which TGF-betas have been recognized as some of the more potent regulators although their specific cell effects on cartilage physiology are not fully understood. Primary human fetal epiphyseal chondrocytes (HEFC) constitutively produce TGF-beta1 at different times of culture progression. Treatment of 48-h. serum-deprived semiconfluent HFEC with 0.1-50 ng/ml of TGF-beta1 for 48-h. decreased (3H)Thymidine incorporation by 25-50 % and cell number by 25 %. In addition, IGFBP-3, the main insulin-like bonding protein produced by HFEC, showed a slight increase by TGF-beta1 in culture media. The changes in IGFBP-3 protein levels correlated well with its mRNA, indicating that TGF-beta1 is able to up-regulate IGFBP-3 synthesis in chondrocytes. Nevertheless, the IGFBP-3 accumulation in culture media does not produce a clear growth inhibitory effect on chondrocytes. Thus, we conclude that even though TGF-beta1 is able to up-regulate IGFBP-3, the growth inhibitory action produced by TGF-beta1 is not mediated by IGFBP-3 increase and appears to be mainly a direct TGF-beta1 effect on HFEC.

Immunohistochemical profile of basic fibroblast growth factor and heparan sulphate in adult rat mandibular condylar cartilage

Basic fibroblast growth factor (bFGF) and heparan sulphate (HS) were detected immunohistochemically in mandibular condylar cartilage, and the findings compared with those on epiphyseal articular cartilage. In the condylar cartilage, both bFGF and HS were localized in chondrocytes throughout the various zones including the fibrous, proliferative, mature-cell and hypertrophic zones: bFGF immunostaining was most significant in the proliferative and mature-cell zones, while intense staining for HS was found mainly in the hypertrophic zone. Immunoreaction for bFGF was detected in the nuclei of chondrocytes, whereas HS staining was observed in the cytoplasm. In articular cartilage, only chondrocytes beneath the superficial zone (intermediate zone) demonstrated both bFGF and HS immunoreactivities. Chondrocytes in the deeper calcifying region of the articular cartilage did not immunoreact for either bFGF or HS. These findings suggest that, in contrast to the epiphyseal articular cartilage, a continuous bFGF-mediated remodelling of cells and matrix takes place in mandibular condylar cartilage during the process of endochondral ossification.