Molecular background and physiological consequences of altered peripheral serotonin homeostasis in adult rats perinatally treated with tranylcypromine

Serotonin (5-hydroxytryptamine, 5-HT) is a biologically active molecule present in mammals in the brain and peripheral tissues where it exerts many physiological functions. Developmental exposure to 5-HT-enhancing agents has been reported to induce long-lasting changes in the brain, but the long-term effects of perinatal 5-HT enhancement on 5-HT balance and function in the peripheral compartment have not been explored. Perinatal treatment of rats with monoamine oxidase (MAO) inhibitor tranylcypromine (TCP), leads to persistent imbalance in central (increased 5-HT degradation and decreased 5-HT concentrations in the brain) and peripheral (increased platelet and decreased plasma 5-HT concentrations) 5-HT homeostasis. In this study, we explored the molecular background of peripheral 5-HT imbalance, and its possible consequences on bone remodeling and hematopoiesis. Jejunum, liver and blood samples were collected from TCP- and saline-treated rats on post-natal day 70. Relative mRNA levels for tryptophan hydroxylase 1 (TPH1) and MAO A were analyzed using quantitative RT-PCR, femoral trabecular bone parameters were measured using microcomputed tomography, while peripheral blood cell number was determined by cell counter. TCP-treated rats displayed significant decrease in expression of Tph1, and significant increase in percentage of bone volume, trabecular number, connectivity density, and leukocyte number. In addition, significant negative correlation was observed between relative concentrations of TPH1 mRNA and trabecular bone parameters. Our results: a) show that perinatal exposure to tranylcypromine leads to long-lasting compensatory decrease in Tph1 expression in the peripheral compartment, accompanied with alterations in bone remodeling and hematopoiesis, b) suggest that peripheral and central 5HT compartment use different strategies to compensate for 5-HT imbalances of the same cause, and c) indicate dominant role of peripheral over central 5-HT in the regulation of bone maintenance, as well as possible negative in vivo influence of peripheral 5-HT on leukocyte development and/or sustainment.

TSH prevents bone resorption and with calcitriol synergistically stimulates bone formation in rats with low levels of calciotropic hormones

Thyroid-stimulating hormone exerts both antiresorptive and anabolic effects on bone remodeling in aged ovariectomized rats and thyroid stimulating hormone-receptor null mice, supported by clinical results demonstrating that low thyroid-stimulating hormone level is associated with increased bone loss. To further explore the effect of thyroid-stimulating hormone on bone metabolism we introduced here a rat model with removed thyroid and parathyroid glands to obtain low serum concentrations of thyroid and parathyroid hormone, calcitonin and 1,25(OH)2D3. Surgery resulted in hypocalcemia, low parathyroid and thyroid hormone, 1,25(OH)2D3, C-telopeptide, and osteocalcin serum level. Intermittent administration of thyroid-stimulating hormone resulted in a further decrease of serum calcium and decreased level of serum C-telopeptide due to the suppression of bone resorption, while in the same animals osteocalcin in serum was higher indicating an increased bone formation rate. A combination of thyroid-stimulating hormone and 1,25(OH)2D3 significantly increased the serum Ca2+, C-telopeptide and serum osteocalcin values. MicroCT analyses of the distal femur and proximal tibia showed that rats treated with 1,25(OH)2D3 alone or in a combination with thyroid-stimulating hormone had an increased trabecular bone volume, and enhanced trabecular bone quality. Biomechanical testing of the trabecular bone showed an increased maximal load for 105% and 235%, respectively, in rats treated with 1,25(OH)2D3 alone, or in a combination with thyroid-stimulating hormone. We suggest that thyroid-stimulating hormone independently of calciotropic hormones suppressed bone resorption and stimulated bone formation, while in combination with 1,25(OH)2D3 acted synergistically on bone formation resulting in an increased bone volume.

Effects of 5 years of treatment with lasofoxifene on incidence of breast cancer in older women

Abstract #11

The Postmenopausal Evaluation and Risk-reduction with Lasofoxifene (PEARL) Trial evaluated the effects of 5 years of a new potent SERM on the incidence of estrogen receptor positive (ER+) breast cancer (BC) (co-primary endpoints, invasive alone and invasive plus ductal carcinoma in situ [DCIS] together). 8556 women ages 5980 with femoral neck or spine T-score ≤ –2.5 and > –4.5 were enrolled in 32 countries. Women were randomly assigned to receive 0.25 mg/d or 0.5 mg/d of lasofoxifene (LASO), or placebo (PBO). BC events were ascertained through annual clinical breast exam and mammographic screening and adjudicated by physician oncologists and a BC pathologist blinded to treatment assignment. 77% of women completed 5 years of follow-up and 62–64% remained on study medication until planned trial closure. ITT analyses were conducted using Cox Proportional Hazards models. The protocol-defined primary analysis for all ER+ BCs compared each of the LASO groups to PBO. In the PBO group, 21 women developed invasive or non-invasive ER+ BC (17.3/10,000 person-years (P-Y)) compared to 10 in the LASO 0.25 mg/d group (9.0/10,000 P-Y; HR=0.52, 95%CI 0.25–1.08) and 5 in the 0.5 mg/d LASO group (3.3/10,000 P-Y; HR=0.19, 95% CI 0.07–0.56). For all invasive BCs (ER+ve and ve), 20 women in the PBO group were affected (16.4/10,000) compared to 16 in the LASO 0.25 mg/d group (13.2/10,000 P-Y; HR=0.79, 95%CI 0.41–1.52) and 3 in the 0.5 mg/d LASO group (2.5/10,000 P-Y; HR=0.15, 95% CI 0.04–0.50). For total BC, 24 women in the PBO group were affected (19.8/10,000 P-Y) compared to 20 in the LASO 0.25 mg/d group (16.4/10,000 P-Y; HR=0.82, 95%CI 0.45–1.49) and 5 in the 0.5 mg/d LASO group (4.1/10,000 P-Y; HR=0.21, 95% CI 0.08–0.55). Too few cases of DCIS occurred to determine effects of LASO on noninvasive breast tumors. No significant differences among treatment groups were observed for breast density. LASO also reduced the incidence of vertebral (primary at 3 years) and nonvertebral clinical fractures (co-primary at 5-years). LASO increased risk of venous thromboembolic events, but not stroke, endometrial cancer or endometrial hyperplasia and decreased risk of major coronary events at 0.5 mg/d. Endometrial hypertrophy, uterine polyps, and fibroids were more common with LASO while hypertension and hyperlipidemia was less frequent compared to PBO. We conclude that LASO reduces the incidence of ER+ BC and appears to have a favorable benefit-risk profile for prevention of clinical fractures in postmenopausal women with osteoporosis.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 11.

BMP-6 exerts its osteoinductive effect through activation of IGF-I and EGF pathways

We have recently shown that human recombinant BMP-6 (rhBMP-6), given systematically, can restore bone in animal models of osteoporosis. To further elucidate the underlying mechanisms of new bone formation following systemic application of BMPs, we conducted gene expression profiling experiments using bone samples of oophrectomised mice treated with BMP-6. Gene set enrichment analysis revealed enrichment of insulin-like growth factor-I and epidermal growth factor related pathways in animals treated with BMP-6. Significant upregulation of IGF-I and EGF expression in bones of BMP-6 treated mice was confirmed by quantitative PCR. To develop an in vitro model for evaluation of the effects of BMP-6 on cells of human origin, we cultured primary human osteoblasts. Treatment with rhBMP-6 accelerated cell differentiation as indicated by the formation of mineralised nodules by day 18 of culture versus 28-30 days in vehicle treated cultures. In addition, alkaline phosphatase gene expression and activity were dramatically increased upon BMP-6 treatment. Expression of IGF-I and EGF was upregulated in human osteoblast cells treated with BMP-6. These results collectively indicate that BMP-6 exerts its osteoinductive effect, at least in part, through IGF-I and EGF pathways, which can be observed both in a murine model of osteopenia and in human osteoblasts.

Biological mechanisms of bone and cartilage remodelling--genomic perspective

Rapid advancements in the field of genomics, enabled by the achievements of the Human Genome Project and the complete decoding of the human genome, have opened an unimaginable set of opportunities for scientists to further unveil delicate mechanisms underlying the functional homeostasis of biological systems. The trend of applying whole-genome analysis techniques has also contributed to a better understanding of physiological and pathological processes involved in homeostasis of bone and cartilage tissues. Gene expression profiling studies have yielded novel insights into the complex interplay of osteoblast and osteoclast regulation, as well as paracrine and endocrine control of bone and cartilage remodelling. Mechanisms of new bone formation responsible for fracture healing and distraction osteogenesis, as well as healing of joint cartilage defects, have also been extensively studied. Microarray experiments have been especially useful in studying pathological processes involved in diseases such as osteoporosis or bone tumours. Existing results show that microarrays hold great promise in areas such as identification of targets for novel therapies or development of new biomarkers and classifiers in skeletal diseases.

Human mesenchymal stem cells derived from bone marrow display a better chondrogenic differentiation compared with other sources

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiation into several mesodermal lineages. These cells have been isolated from various tissues, such as adult bone marrow, placenta, and fetal tissues. The comparative potential of these cells originating from different tissues to differentiate into the chondrogenic lineage is still not fully defined. The aim of our study was to investigate the chondrogenic potential of MSCs isolated from different sources. MSCs from fetal and adult tissues were phenotypically characterized and examined for their differentiation capacity, based on morphological criteria and expression of extracellular matrix components. Our results show that both fetal and adult MSCs have chondrogenic potential under appropriate conditions. The capacity of bone marrow-derived MSCs to differentiate into chondrocytes was reduced on passaging of cells. MSCs of bone marrow origin, either fetal or adult, exhibit a better chondrogenesis than fetal lung- and placenta-derived MSCs, as demonstrated by the appearance of typical morphological features of cartilage, the intensity of toluidine blue staining, and the expression of collagen type II, IX, and X after culture under chondrogenic conditions. As MSCs represent an attractive tool for cartilage tissue repair strategies, our data suggest that bone marrow should be considered the preferred MSC source for these therapeutic approaches.

Role of EP2 and EP4 receptor-selective agonists of prostaglandin E2 in acute and chronic kidney failure

We tested the efficacy of three selective agonists of prostaglandin E(2) (PGE(2)) receptor, EP2 (CP-536,745-01), EP2/4 (CP-043,305-02), and EP4 (CP-044,519-02), in two models of acute and chronic kidney failure. In the nephrotoxic mercury chloride (HgCl(2)) rat model of acute kidney failure systemically administered EP4 agonist reduced the serum creatinine values and increased the survival rate. Although the EP2 or the EP2/4 agonist did not change the serum creatinine values, the EP2 receptor agonist increased the survival rate. Histological evaluation of kidneys from EP4-treated rats indicated less proximal tubular necrosis and less apoptotic cells. In a rat model of chronic renal failure, the three receptor agonists decreased the serum creatinine and increased the glomerular filtration rate at 9 weeks following therapy. Kidneys treated with the EP4 agonist had less glomerular sclerosis, better preservation of proximal and distal tubules and blood vessels, increased convoluted epithelium proliferation and less apoptotic cells. Nephrectomy had no influence on the expression of the EP4 receptor, whereas EP2 receptor expression was reduced by 50% and then corrected following treatment with EP2 and EP2/4 receptor agonists. These findings suggest that PGE(2) has an important role in acute kidney failure via the EP4 receptor, whereas in chronic kidney failure both EP2 and EP4 receptors are equally important in preserving the progression of chronic kidney failure. Thus, agonism of EP2 and EP4 receptors may provide a basis for treating acute and chronic kidney failure.

Osteogenic protein-1 (BMP-7) accelerates healing of scaphoid non-union with proximal pole sclerosis

We randomly assigned 17 patients with scaphoid non-union at the proximal pole to three treatment groups: (1) autologous iliac graft (n=6), (2) autologous iliac graft + osteogenic protein-1 (OP-1; n=6), and (3) allogenic iliac graft + OP-1 (n=5). Radiographic, scintigraphic, and clinical assessments were performed throughout the follow-up period of 24 months. OP-1 improved the performance of both autologous and allogenic bone implants and reduced radiographic healing time to 4 weeks compared with 9 weeks in group 1. Helical CT scans and scintigraphy showed that in OP-1-treated patients sclerotic bone was replaced by well-vascularised bone. The addition of OP-1 to allogenic bone implant equalised the clinical outcome with the autologous graft procedure. Consequently the harvesting of autologous graft can be avoided.

Compressed homologous cancellous bone and bone morphogenetic protein (BMP)-7 or bone marrow accelerate healing of long-bone critical defects

We studied 18 adult male New Zealand rabbits with a critical right-sided ulnar defect of 15 mm. In six animals the defect was grafted with homologous compressed cancellous bone, in six animals with homologous compressed cancellous bone including 300 micro g bone morphogenetic protein (BMP)-7 and in six animals with homologous compressed cancellous bone including 0.5 ml autologous bone marrow. The defect was studied using radiographs every second week for 10 weeks. At the conclusion of the experiment the animals were killed and the defect studied by histology and histomorphometry. In all animals treated with the addition of autologous bone marrow and in five of six animals treated with the addition of BMP-7, the defect healed. There was no union in animals treated with homologous compressed cancellous bone without additive. The histological picture of the regenerated area was similar in the two experimental groups. Woven bone contained small marrow spaces with fibrous tissue and capillaries. The osteoid seams were on average greater in animals that received autologous bone marrow as compared to animals that received BMP-7.

An EP2 receptor-selective prostaglandin E2 agonist induces bone healing

The morbidity and mortality associated with impaired/delayed fracture healing remain high. Our objective was to identify a small nonpeptidyl molecule with the ability to promote fracture healing and prevent malunions. Prostaglandin E2 (PGE2) causes significant increases in bone mass and bone strength when administered systemically or locally to the skeleton. However, due to side effects, PGE2 is an unacceptable therapeutic option for fracture healing. PGE2 mediates its tissue-specific pharmacological activity via four different G protein-coupled receptor subtypes, EP1, -2, -3, and -4. The anabolic action of PGE2 in bone has been linked to an elevated level of cAMP, thereby implicating the EP2 and/or EP4 receptor subtypes in bone formation. We identified an EP2 selective agonist, CP-533,536, which has the ability to heal canine long bone segmental and fracture model defects without the objectionable side effects of PGE2, suggesting that the EP2 receptor subtype is a major contributor to PGE2's local bone anabolic activity. The potent bone anabolic activity of CP-533,536 offers a therapeutic alternative for the treatment of fractures and bone defects in patients.

Distraction osteogenesis by Ilizarov and unilateral external fixators in a canine model

We studied distraction osteogenesis in canine experimental model using two types of external fixators, Ilizarov (n=6) or AO unilateral (n=9) external fixator. Distraction started 1 week after surgery (2 x 0.5 mm/day) and lasted for 3 weeks. Specimens were harvested from weeks 7 through 12. The outcome was assessed by X-ray, histology, histomorphometry and microradiography. Bone regeneration as observed by X-rays was satisfactory and similar in both groups. Both endochondral ossification and intramembranous ossification were found simultaneously in both groups. In both groups, bone formation parameters were significantly higher in the area of consolidating bone. No differences in histomorphometric parameters existed between the groups. In the study period, the bone formation was enhanced and prevailed in the distraction area. This study demonstrated the utility of the canine experimental model for the study of distraction osteogenesis.

Regulation of BMP-7 expression by retinoic acid and prostaglandin E(2)

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGF-beta) gene superfamily of growth and differentiation factors. Members of the BMP family were originally cloned and characterized by their ability to induce ectopic bone formation. Of the various BMPs cloned, the bone inductive ability of BMP-7 (OP-1) and BMP-2 has been well characterized. Both BMP-7 and -2 have been shown to have clinical utility in the healing of non-union fractures. However, in spite of the various advances in BMP research, the physiological regulation of BMPs is not well understood. Here we studied the expression of BMP-7 by cloning a 4.6-kB fragment of the human BMP-7 promoter (hBMP-7p) and placing it upstream of a luciferase reporter. The promoter reporter construct was stably transfected into different cell backgrounds and its regulation by various factors was investigated. We show that retinoic acid (RA) treatment results in an upregulation of the hBMP-7p reporter activity. This regulation of the hBMP-7p was further confirmed by Northern blot, PCR, and Western blot analyses, which showed an increase in both BMP-7 mRNA and protein expression upon treatment with RA. We further show that RA specifically upregulates expression of osteocalcin via activation of BMP-7 mRNA and protein in vitro. Similarly, prostaglandin E(2) (PGE(2)) treatment increases BMP-7 mRNA and protein levels, but does not transcriptionally activate the hBMP-7p. Additionally, in vivo expression of BMP-7 in bone was increased upon PGE(2) treatment. In conclusion, RA and PGE(2) upregulate BMP-7 protein expression both in vitro and in vivo.

Regeneration of articular cartilage chondral defects by osteogenic protein-1 (bone morphogenetic protein-7) in sheep

The efficacy of osteogenic protein-1 (OP-1; BMP-7) in regeneration of articular cartilage was examined by creating knee chondral defects in sheep. With a specially designed instrument in both knees, two 10 mm (diameter) chondral defects were created: one in the trochlea and the other on the femoral condyle. The recombinant BMP was delivered via an extra-articulary positioned mini-osmotic pump, which was fixed to the femoral diaphysis above the knee joint, and connected by a polyethylene tubing to the articular space. Prior to use, the compatibility of OP-1 with mini-osmotic pumps was tested in vitro by measuring aggregation/precipitation and modification of the released protein by size exclusion and reversed phase HPLC. The average amount of aggregation was 15% and about 5% of OP-1 was modified. However, the biological activity of OP-1 released from pumps over a period of 2 weeks at 37 degrees C was equal to ROS cell assay OP-1 standard. Following surgery, a total of 55 microg (low dose) or 170 microg (high dose) OP-1 in acetate buffer (pH 4.5) was slowly released from the pump over a period of 2 weeks. The pumps connected to control knees were filled with acetate buffer as a vehicle. Twelve animals were operated, six of which were treated with the low OP-1 dose, and six with the high OP-1 dose. Three sheep of each group were killed either at 3 or 6 months following surgery, based on arthroscopical evaluation. The chondral defects in the control knees remained empty during the observation period. At 3 months following surgery, defects treated with both OP-1 doses were filled with connective tissue and cartilage. At 6 months following surgery, both doses of OP-1 stimulated regeneration in treated knees. The boundaries between new and old cartilage were well fused and mechanically resisted animals' weight bearing. The regenerated cartilage was rich in proteoglycans and type II collagen, as demonstrated by toluidine blue staining and immunohistochemistry. No signs of endochondral bone formation above the bony tidemark were observed. We suggest that a recombinant bone morphogenctic protein stimulates ingrowth of mesenchymal cells into the chondral defects which then transform into newly formed articular cartilage-like tissue.

Reduced expression of BMP-3 due to mechanical loading: a link between mechanical stimuli and tissue differentiation

Mechanical signaling and BMP expression appear to be involved in controlling the differentiation of cartilage in fracture repair, but the connection between mechanics and BMP signaling is not known. In this study of rats, we used a bone chamber to see how BMP gene expression was changed by a mechanical loading regime that induces cartilage formation in this model. We compared the still undifferentiated tissue in loaded and unloaded chambers in the same rat regarding the expression of TGFbeta-1, BMP-2, 3, 4, 5, 6, 7, CDMP-1, 2 and ALK-2 and 3 by using RT-PCR normalized against GAPDH. We found expression of TGFbeta-1, BMP-2 and 4 in all specimens, and BMP 5-7 and CDMPs in none. 1 week after loading started, BMP-3 was strongly expressed in the unloaded control specimens in 7 of 8 animals, but detectable in only I of the contralateral loaded ones. After 2 weeks of loading, the BMP-3 expression pattern was less clear, but with both time groups taken together, there was still less BMP-3 expression on the loaded side in 9 rats, more in 1 and no difference in 5 (p = 0.01). ALK-2 at 1 week was expressed in all specimens expressing BMP-3 and in none of the others. At 2 weeks, ALK-2 was expressed in all specimens. Thus, a loading regime, known to induce cartilage in this model, caused down-regulation of BMP-3 and ALK-2. The results are consistent with the view that BMP-3 inhibits differentiation, as recently described. This role appears to be linked to the ALK-2 receptor. Most importantly, the results indicate a link between mechanical signaling and BMP expression such that mechanically-induced down-regulation of the inhibiting BMP-3 enabled the induction of cartilage.

Characterization of receptors for osteogenic protein-1/bone morphogenetic protein-7 (OP-1/BMP-7) in rat kidneys

BACKGROUND

Osteogenic protein-1/bone morphogenetic protein-7 (OP-1/BMP-7), a member of the transforming growth factor-beta superfamily, has been shown to prevent kidney damage from ischemia/reperfusion injury in rats. The molecular events involved in OP-1 action on kidney are not yet understood.

METHODS

In this study, we evaluated the biodistribution of (125)I-labeled OP-1 in rat kidneys. Adult rats received a single intravenous injection of 250 microg (125)I-labeled OP-1 per kg body wt, a dose that was effective in protecting kidneys from ischemic injury. Tissue localization, in situ hybridization, and immunostaining with a specific receptor antibody were performed to identify OP-1 cellular targets. Also, isolated plasma membranes from kidney cortex and medulla regions were analyzed to identify and characterize receptor structural components that recognize OP-1.

RESULTS

At 10 and 180 minutes following injection, the relative uptake of (125)I-labeled OP-1 was consistently higher in kidney cortex than in medulla region. Upon autoradiography, kidney tissue sections revealed that OP-1 bound to the convoluted tubule epithelium, glomeruli, and collecting ducts. Moreover, in situ hybridization and immunostaining methods have shown localization of mRNA transcripts and the protein for BMP receptor type II in the cortex and medulla in similar areas as (125)I-labeled OP-1. Bulk membranes (enriched with plasma membranes) isolated from the cortex and medulla regions of kidney each bound specifically to (125)I-OP-1, and the binding of (125)I-labeled OP-1 was inhibited by unlabeled OP-1 in a dose-dependent manner. However, platelet-derived growth factor, transforming growth factor-beta, insulin-like growth factor, fibroblast growth factors, and other members of BMP family such as BMP-2 and cartilage-derived morphogenetic protein-1/growth and differentiation factor-5 (CDMP-1/GDF-5) failed to inhibit the binding of (125)I-labeled OP-1 to receptors, suggesting a high degree of specificity with which OP-1 bound to kidney receptors. Scatchard analysis of quantitative binding data indicated that the OP-1 receptors of kidney contained a single class of high-affinity binding sites for OP-1 with an association constant (Ka) of 2.26 x 109 mol/L-1 and a binding capacity of 1.01 pmol of OP-1 per mg membrane protein. When analyzed by a ligand blot technique, plasma membranes isolated from kidney cortex and medulla each showed the presence of a prominent specific band with a relative molecular mass (Mr) of 100 kD. Further analysis by Western blotting indicated that an antibody raised against BMP type II receptor effectively recognized the 100 kD OP-1 binding component of kidney plasma membranes.

CONCLUSIONS

We demonstrated, to our knowledge for the first time, the presence of membrane-bound, specific, high-affinity OP-1 receptors in rat kidney tissues, which are likely to mediate OP-1 actions in the kidney. The major OP-1-binding component of the kidney appears to be a long form of BMP type II receptor with a Mr of 100 kD. In vivo and in vitro evidence suggests that the cellular targets for OP-1 are convoluted tubule epithelium, glomeruli, and collecting ducts. OP-1 does not share receptor binding properties with other growth factors, including BMP-2 and CDMP-1, suggesting that its mode of action in kidney appears to be specific.

Bone morphogenetic protein-7 (osteogenic protein-1) inhibits smooth muscle cell proliferation and stimulates the expression of markers that are characteristic of SMC phenotype in vitro

Vascular proliferative disorders are characterized by migration and proliferation of vascular smooth muscle cells (SMCs), loss of expression of SMC phenotype, and enhanced extracellular matrix synthesis (e.g., type I collagen). We report here that bone morphogenetic protein-7 (BMP-7), a member of the transforming growth factor-beta (TGF-beta) superfamily, is capable of inhibiting both serum-stimulated and growth factor-induced (platelet-derived growth factor [PDGF-BB] and TGF-beta1) cell growth as measured by (3)H-thymidine uptake into DNA synthesis and cell number in primary human aortic smooth muscle (HASM) cell cultures. Concomitantly, addition of BMP-7 stimulates the expression of SMC-specific markers, namely alpha-actin and heavy chain myosin as examined by RT-PCR and Northern blot analyses. The collagen type III/I ratio that becomes lower with the transdifferentiation of SMCs into myofibroblasts is also maintained in BMP-7-treated cultures as compared to untreated controls. Studies on the mechanism of action indicate that BMP-7 treatment inhibits cyclin-dependent kinase 2 (cdk-2) that was stimulated during PDGF-BB-induced proliferation of SMCs and upregulates the expression of the inhibitory Smad, Smad6, which was shown to inhibit TGF-beta superfamily signaling. These results collectively suggest that BMP-7 maintains the expression of vascular SMC phenotype and may prevent vascular proliferative disorders, thus potentially acting as a palliative after damage to the vascular integrity.

Biological repair of thyroid cartilage defects by osteogenic protein-1 (bone morphogenetic protein-7) in dog

The efficacy of human recombinant osteogenic protein-1 (OP-1; bone morphogenetic protein-7) in regeneration of dog larynx was examined by treating thyroid cartilage defects (1.5 cm2) in dogs with thyroid allografts covered with host perichondrium or fascia. Prior to implantation allografts were frozen, thawed and demineralized. The treatment groups were as follows: I--Allograft control implant (n = 3); II--Implants coated with 500 micrograms OP-1 (n = 4); III--Implants coated with 100 micrograms OP-1 (n = 3); IV--Implants coated with 500 micrograms OP-1 and covered with neck fascia (n = 3); and V--Implants extracted with 1 M NaCl and guanidine hydrochloride, and coated with 500 micrograms OP-1 (n = 4). Dogs were sacrificed four months following surgery. Each larynx was removed, carefully dissected and a three-dimensional reconstruction of the defect area was performed on serial sections. The results revealed that the implants of control dogs remained intact with no apparent reduction in size and new tissue formation. OP-1 enriched thyroid allografts, dose dependently induced bone, cartilage and ligament-like structures comprising up to 80% of the total regenerated defect area. Boundaries of the defects healed by formation of new bone when bone resided within the old thyroid cartilage layers. Old cartilage not containing bone within its layers healed by complete integration with newly formed cartilage. Both new bone and cartilage were embedded into layers of new ligament-like tissue which expressed specific morphologic and molecular markers. The three newly formed tissues were tightly connected into a "bone-cartilage-ligament continuum" of tissues, suggesting that OP-1 served as a multiple tissue morphogen in this specific microenvironment.

Osteogenic protein-1 (bone morphogenetic protein-7) reduces severity of injury after ischemic acute renal failure in rat

We have shown that osteogenic protein-1 (OP-1) (bone morphogenetic protein-7) is responsible for the induction of nephrogenic mesenchyme during embryonic kidney development. Gene knock-out studies showed that OP-1 null mutant mice die of renal failure within the first day of postnatal life. In the present study, we evaluated the effect of recombinant human OP-1 for the treatment of acute renal failure after 60 min bilateral renal artery occlusion in rats. Bioavailability studies in normal rats indicate that approximately 1.4 microg OP-1/ml is available in the circulation 1 min after intravenous administration of 250 microg/kg, which then declines steadily with a half life of 30 min. About 0.5% of the administered OP-1 dose/g tissue is targeted for OP-1 receptors in the kidney. We show that OP-1 preserves kidney function, as determined by reduced blood urea nitrogen and serum creatinine, and increased survival rate when administered 10 min before or 1 or 16 h after ischemia, and then at 24-h intervals up to 72 h after reperfusion. Histochemical and molecular analyses demonstrate that OP-1: (a) minimizes infarction and cell necrosis, and decreases the number of plugged tubules; (b) suppresses inflammation by downregulating the expression of intercellular adhesive molecule, and prevents the accumulation and activity of neutrophils; (c) maintains the expression of the vascular smooth muscle cell phenotype in pericellular capillaries; and (d) reduces programmed cell death during the recovery. Collectively, these data suggest that OP-1 prevents the loss of kidney function associated with ischemic injury and may provide a basis for the treatment of acute renal failure.

Cloning and characterization of a novel member of the transforming growth factor-beta/bone morphogenetic protein family

Members of the transforming growth factor-beta (TGF-beta) superfamily of growth and differentiation factors have been identified in a wide variety of organisms, ranging from invertebrates to mammals. Bone morphogenetic proteins (BMPs) constitute a subgroup of proteins belonging to the TGF-beta superfamily. BMPs were initially identified by their ability to induce endochondral bone formation at ectopic sites, suggesting a critical role for this family in development and regeneration of the skeleton. They are also expressed at a variety of nonskeletal sites during development, suggesting possible extraskeletal roles for these proteins. We cloned a novel member of the BMP family that is expressed at high levels in the placenta and the prostate and that we have designated as prostate-derived factor (PDF). Based on cDNA sequence analysis, the predicted PDF protein contains two cysteines in addition to the seven conserved cysteines that are the hallmark of the members of the TGF-beta superfamily. In addition, Northern blot hybridization to poly(A)+ RNA showed low levels of expression in the kidney and pancreas. We further characterized the expression of this member of the BMP family by in situ hybridization and immunohistochemistry. These results show high expression in the terminal villae of the placenta. The expression of the protein as visualized by immunohistochemistry shows an expression pattern identical to that of the message in the terminal villae of the placenta. In day 18 rat embryos, protein expression was also seen in the skin and in the cartilaginous tissue of developing skeleton. Orchidectomy and dihydrotestosterone treatment of rats revealed that PDF expression is regulated by androgens in the prostate. In addition, subcutaneous implantation of recombinant PDF induced cartilage formation and the early stages of endochondral bone formation. These data indicate that PDF has a functional relationship to the BMPs.

Bone morphogenetic protein-7 (osteogenic protein-1, OP-1) and tooth development

Bone morphogenetic proteins (BMPs) form a family of growth factors originally isolated from extracellular bone matrix that are capable of inducing bone formation ectopically. We studied the expression, tissue localization, and function of BMP-7 (OP-1) during tooth development in rodents. Patterns of BMP-7 gene expression and peptide distribution indicated that BMP-7 was present in dental epithelium during the dental lamina, bud, and cap stages. During the bell stage, BMP-7 mRNA expression and protein distribution shifted from dental epithelium toward the dental mesenchyme. With advancing differentiation of odontoblasts, BMP-7 protein staining in the dental papilla became restricted to the layer of fully functional odontoblasts in the process of depositing (pre)dentin. Secretory-stage ameloblasts exhibited weak immunostaining for BMP-7. A restricted pattern of staining in ameloblasts became apparent in post-secretory stages of amelogenesis. Also, cells of the forming periodontal ligament were immunopositive. Histological analysis of tooth development in neonatal BMP-7-deficient mice did not reveal obvious changes compared with wild-type mice. We conclude that, in developing dental tissues, BMP-7 has distribution and expression patterns similar to those of other BMP members but is not an essential growth factor for tooth development, possibly because of functional redundancy with other BMP members or related growth factors.

Osteogenic protein-1 mRNA in the uterine endometrium

OP-1, a bone morphogenetic protein (BMP) in the TGF-beta superfamily, is expressed at high levels in the kidney and in the endometrium of the uterus of non-pregnant mice. During pregnancy the OP-1 mRNA in the endometrium rapidly declined at 4 dpc. Thereafter, OP-1 transcripts were detected in the trophoblastic giant cells of the placenta and the fetal tissues. The uterine OP-1 mRNA downregulation could be mimicked by administration of 17 beta-estradiol but not by progesterone to non-pregnant animals. In contrast, OP-1 mRNA expression in kidneys and ovaries was not affected by pregnancy or estrogen treatment. The selective effect of estrogen on OP-1 mRNA in the uterus suggests that OP-1 expression is regulated by tissue specific mechanisms.

Primary structure and tissue distribution of FRZB, a novel protein related to Drosophila frizzled, suggest a role in skeletal morphogenesis

Articular cartilage extracts were prepared to characterize protein fractions with in vivo chondrogenic activity (Chang, S., Hoang, B., Thomas, J. T., Vukicevic, S., Luyten, F. P., Ryba, N. J. P., Kozak, C. A., Reddi, A. H., and Moos, M. (1994) J. Biol. Chem. 269, 28227-28234). Trypsin digestion of highly purified chondrogenic protein fractions allowed the identification of several unique peptides by amino acid sequencing. We discovered a novel cDNA encoding a deduced 36-kDa protein by using degenerate oligonucleotide primers derived from a 30-residue peptide in reverse transcription polymerase chain reactions. Its N-terminal domain showed approximately 50% amino acid identity to the corresponding region of the Drosophila gene frizzled, which has been implicated in the specification of hair polarity during development. Hydropathy and structural analyses of the open reading frame revealed the presence of a signal peptide and a hydrophobic domain followed by multiple potential serine/threonine phosphorylation sites and a serine-rich C terminus. Cell fractionation studies of primary bovine articular chondrocytes and transfected COS cells suggested that the protein is membrane-associated. In situ hybridization and immunostaining of human embryonic sections demonstrated predominant expression surrounding the chondrifying bone primordia and subsequently in the chondrocytes of the epiphyses in a graded distribution that decreased toward the primary ossification center. Transcripts were present in the craniofacial structures but not in the vertebral bodies. Because it is expressed primarily in the cartilaginous cores of developing long bones during embryonic and fetal development (6-13 weeks) and is homologous to the polarity-determining gene frizzled, we believe that this gene, which we named frzb, is involved in morphogenesis of the mammalian skeleton.

Induction of nephrogenic mesenchyme by osteogenic protein 1 (bone morphogenetic protein 7)

The definitive mammalian kidney forms as the result of reciprocal interactions between the ureteric bud epithelium and metanephric mesenchyme. As osteogenic protein 1 (OP-1/bone morphogenetic protein 7), a member of the TGF-beta superfamily of proteins, is expressed predominantly in the kidney, we examined its involvement during metanephric induction and kidney differentiation. We found that OP-1 mRNA is expressed in the ureteric bud epithelium before mesenchymal condensation and is subsequently seen in the condensing mesenchyme and during glomerulogenesis. Mouse kidney metanephric rudiments cultured without ureteric bud epithelium failed to undergo mesenchymal condensation and further epithelialization, while exogenously added recombinant OP-1 was able to substitute for ureteric bud epithelium in restoring the induction of metanephric mesenchyme. This OP-1-induced nephrogenic mesenchyme differentiation follows a developmental pattern similar to that observed in the presence of the spinal cord, a metanephric inducer. Blocking OP-1 activity using either neutralizing antibodies or antisense oligonucleotides in mouse embryonic day 11.5 mesenchyme, cultured in the presence of metanephric inducers or in intact embryonic day 11.5 kidney rudiment, greatly reduced metanephric differentiation. These results demonstrate that OP-1 is required for metanephric mesenchyme differentiation and plays a functional role during kidney development.

TGF-beta and basement membrane matrigel stimulate the chondrogenic phenotype in osteoblastic cells derived from fetal rat calvaria

Primary cultures of fetal rat calvarial cells contain a spectrum of osteogenic phenotypes including undifferentiated mesenchymal cells, osteoprogenitor cells, and osteoblasts. We recently demonstrated that rat calvarial osteoblast-like cells grown on basement membrane undergo profound morphological changes resembling a canalicular network in bone. In the present study, we examined the effect of reconstituted basement membrane Matrigel on chondroblastic versus osteoblastic differentiation of different cell subpopulations obtained by five consecutive enzymatic digestions of rat calvarial cell populations. We found that the appearance of canalicular cell processes decreased with the later digests. When cells from the fourth and fifth digest were grown on top of Matrigel for 7 days, the majority of the cell aggregates displayed chondrocytic characteristics but none of the cells became hypertrophic. When individual chondroblastic cell aggregates were subsequently transferred from Matrigel to plastic, they started expressing types I and X collagens, alkaline phosphatase, and osteocalcin. Within the next 7 days (days 8-14 of the experiment), the majority of cells increased in size, and at day 17 on plastic (day 24 of the experiment) mineralized bone nodules formed. The chondroblastic differentiation of calvarial cells grown on Matrigel could be inhibited by a specific transforming growth factor-beta 1 (TGF-beta 1) but not by a TGF-beta 2 antibody. Addition of recombinant TGF-beta 1 to similar cultures promoted the appearance of chondroblastic cell aggregates. The cartilage phenotype could not, on the contrary, be promoted by growing the cells on other extracellular matrices such as a collagen I gel. We suggest that TGF-beta 1 in concert with the basement membrane extracellular matrix induces chondroblastic differentiation of rat calvarial osteoprogenitor cells.

Osteogenic protein-1 is produced by human fetal trophoblasts in vivo and regulates the synthesis of chorionic gonadotropin and progesterone by trophoblasts in vitro

Osteogenic protein-1 (OP-1/BMP-7), a member of the transforming growth factor (TGF-beta) superfamily of proteins, is shown to be expressed at sites of epithelial-mesenchymal tissue interaction during human fetal development. In the present study, we examined the expression of OP-1 in human placentas (5-11 weeks of gestation and full term) using in situ hybridization and immunohistochemistry methods. The results show that OP-1 was expressed in cytotrophoblasts (Langhans layer) of the chorionic villi in early and full term placentas. Employing highly purified cytotrophoblast cultures which fused to form functional syncytiotrophoblasts, we showed that exogenously added recombinant OP-1, in the presence of low serum concentration, reduced the secretion of chorionic gonadotropin and progesterone by 60% and 36%, respectively, compared with control cultures. The results suggest that osteogenic protein-1 is synthesized locally by cytotrophoblasts and may be involved in the regulation of human pregnancy by controlling reproductive hormonal secretion.

Expression pattern of osteogenic protein-1 (bone morphogenetic protein-7) in human and mouse development

Osteogenic protein-1 (OP-1; BMP-7) is a member of the bone morphogenetic protein subfamily. Because members of the TGF-beta superfamily have a role in tissue development, the distribution of OP-1 expression in developing human embryos (5-8 gestational weeks) and fetuses (8-14 gestational weeks) and mouse (9.5-17.5 gestational days) fetuses was examined. Northern hybridization with specific OP-1 probes revealed two mRNA species of 4 and 2.2 KB. Highest levels of OP-1 mRNA were found in human fetal kidney and heart between 12-14 weeks of gestation. By in situ hybridization, the OP-1 transcripts were found in various tissues, i.e., the ectodermal epithelium of the mouse fore- and hindlimbs, heart, teeth, intestinal epithelium, perichondrium, hypertrophic chondrocytes, and periosteum/osteoblast layer of developing human bones. In kidneys, transcripts were first detected in the epithelium of the branching uretheric buds, whereas at later stages glomeruli were the major site of OP-1 mRNA accumulation. These data suggest that, although OP-1 has been isolated from bone matrix, it may have additional regulatory roles in the morphogenesis and/or function of the kidney, limb bud, tooth, heart, and intestine.

Osteogenic protein-1 promotes growth and maturation of chick sternal chondrocytes in serum-free cultures

We examined the effect of recombinant human osteogenic protein-1 (OP-1, or bone morphogenetic protein-7), a member of the bone morphogenetic protein family, on growth and maturation of day 11, 15 and 17 chick sternal chondrocytes in high density monolayers, suspension and agarose cultures for up to 5 weeks. OP-1 dose-dependently (10-50 ng/ml) promoted chondrocyte maturation associated with enhanced alkaline phosphatase activity, and increased mRNA levels and protein synthesis of type X collagen in both the presence and absence of serum. In serum-free conditions, OP-1 promoted cell proliferation and chondrocyte maturation, without requiring either thyroid hormone or insulin, agents known to support chick chondrocyte differentiation in vitro. When grown in agarose under the same conditions, TGF-beta 1 and retinoic acid neither initiated nor promoted chondrocyte differentiation. The results demonstrate that OP-1, as the sole medium supplement, supports the maturation of embryonic chick sternal chondrocytes in vitro.

Cartilage-derived morphogenetic proteins. New members of the transforming growth factor-beta superfamily predominantly expressed in long bones during human embryonic development

Partially purified extracts from newborn calf articular cartilage were found to induce cartilage and bone when subcutaneously implanted in rats. This activity showed characteristics of bone morphogenetic proteins (BMPs). Degenerate oligonucleotide primer sets derived from the highly conserved carboxyl-terminal region of the BMP family were designed and used in reverse transcription-polymerase chain reactions with poly(A)+ RNA from articular cartilage as template to determine which BMPs are produced by chondrocytes. Two novel members of the transforming growth factor-beta (TGF-beta) superfamily were identified and designated cartilage-derived morphogenetic protein-1 (CDMP-1) and -2 (CDMP-2). Their carboxyl-terminal TGF-beta domains are 82% identical, thus defining a novel subfamily most closely related to BMP-5, BMP-6, and osteogenic protein-1. Northern analyses showed that both genes are predominantly expressed in cartilaginous tissues. In situ hybridization and immunostaining of sections from human embryos showed that CDMP-1 was predominantly found at the stage of precartilaginous mesenchymal condensation and throughout the cartilaginous cores of the developing long bones, whereas CDMP-2 expression was restricted to the hypertrophic chondrocytes of ossifying long bone centers. Neither gene was detectable in the axial skeleton during human embryonic development. The cartilage-specific localization pattern of these novel TGF-beta superfamily members, which contrasts with the more ubiquitous presence of other BMP family members, suggests a potential role for these proteins in chondrocyte differentiation and growth of long bones.

Developing human lung and kidney are major sites for synthesis of bone morphogenetic protein-3 (osteogenin)

Bone morphogenetic protein-3 (BMP-3; osteogenin) is a member of the transforming growth factor-beta superfamily. We used human BMP-3 cDNA probes and a specific BMP-3 polyclonal peptide antibody to analyze BMP-3 expression and synthesis in human fetal and adult tissues. Northern blot hybridization revealed two mRNA species of 7 and 3 KB. High levels of BMP-3 mRNA were found in fetal lungs. By in situ hybridization, the BMP-3 transcripts were found in lung bronchial epithelium, straight collecting kidney tubules, intestinal mucosa, perichondrium, periosteum, and osteoblasts of human embryos of 6-14 weeks' gestation. Cellular BMP-3 immunostaining co-localized with the distribution of RNA. In addition, bone matrix showed intensive BMP-3 staining. These data suggest that although BMP-3 has been isolated from bone matrix, it may have additional regulatory roles in the morphogenesis and/or function of human lung, kidney, and intestine.

Opposite effects of osteogenic protein and transforming growth factor beta on chondrogenesis in cultured long bone rudiments

Osteogenic protein-1 (OP-1, also called BMP-7) is a bone morphogenetic member of the TGF-beta superfamily. In the present study, we examined the effect of recombinant human OP-1 on cartilage and bone formation in organ cultures of metatarsal long bones of mouse embryos and compared the OP-1 effects with those of human TGF-beta 1 and porcine TGF-beta 1 and beta 2. Cartilage formation was determined by measurement of longitudinal growth of whole bone rudiments during culture and by the incorporation of 35SO4 into glycosaminoglycans. Mineralization was monitored by 45Ca incorporation in the acid-soluble fraction and by measuring the length of the calcifying center of the rudiment. Toluidine blue-stained histologic sections were used for quantitative histomorphometric analysis. We found that OP-1 stimulated cartilage growth as determined by sulfate incorporation and that it increased remarkably the width of the long bones ends compared with controls. This effect was partly caused by differentiation of perichondrial cells into chondrocytes, resulting in increased appositional growth. In contrast to OP-1, TGF-beta 1 and beta 2 inhibited cartilage growth and reduced the length of whole bone rudiments compared with controls. In the ossifying center of the bone rudiments, both OP-1 and TGF-beta inhibited cartilage hypertrophy, growth of the bone collar, and matrix mineralization. These data demonstrate that OP-1 and TGF-beta exhibit opposite effects on cartilage growth but similar effects on osteogenesis in embryonic mouse long bone cultures. Since both OP-1 and TGF-beta have been demonstrated in embryonic cartilage and bone, these results suggest that they act as autocrine or paracrine regulators of embryonic bone development.

Calcium signaling in endothelin- and platelet-derived growth factor-stimulated chondrocytes

In bovine articular chondrocytes, endothelin (ET) and platelet-derived growth factor (PDGF) receptors mediate agonist-induced increases in inositol phosphate hydrolysis, cytoplasmic calcium concentration ([Ca2+]i), and mitogenesis. In most cells, ET stimulated nonoscillatory [Ca2+]i elevations with dose-dependent increases in both spike and plateau amplitudes. However, about 15% of cells showed oscillatory Ca2+ responses with a constant frequency and variable shape and duration of spiking. ET-1 and ET-2 were more potent than ET-3 in stimulating [Ca2+]i responses in inhibiting the specific binding of 125I-ET-1 and 125I-ET-3 and in promoting internalization of the receptor-ligand complex, consistent with actions through endothelin ETA receptors. Similar nonoscillatory and oscillatory patterns of Ca2+ responses were observed in PDGF-stimulated cells. In cells showing nonoscillatory Ca2+ responses to ET-1, subsequent stimulation with PDGF was frequently followed by the development of an oscillatory Ca2+ response. Nonoscillatory responses to both agonists were only slightly reduced in Ca(2+)-deficient medium, but the oscillatory responses were critically dependent on Ca2+ entry. Ca2+ spiking was not altered in the presence of the voltage-sensitive Ca2+ channel blocker, nifedipine; also, depolarization of chondrocytes by high K+ did not induce [Ca2+]i responses, confirming that voltage-sensitive calcium channels are not expressed in these cells. At high agonist concentrations, ET- but not PDGF-stimulated cells underwent rapid desensitization. Activation of ETA and PDGF receptors was associated with differential stimulation of thymidine incorporation; ET-1 induced a low-amplitude bell-shaped dose-response curve; PDGF induced a sustained sigmoidal and dose-dependent rise. These data indicate that two distinct types of Ca(2+)-mobilizing receptors initiate similar patterns of [Ca2+]i responses but have different capacities to maintain and reinitiate the Ca2+ signaling, as well as to promote mitogenesis.

Localization of osteogenic protein-1 (bone morphogenetic protein-7) during human embryonic development: high affinity binding to basement membranes

Osteogenic protein-1 (OP-1) is a member of the bone morphogenetic protein subfamily of the transforming growth factor-beta (TGF-beta) superfamily. Since members of the TGF-beta superfamily have a role in tissue development the distribution of OP-1 in developing human embryos (gestational age 5-14 weeks) was examined by immunohistochemical methods. Positive staining for OP-1 was observed in: sclerotome, hypertrophied chondrocytes, osteoblasts, periosteum, epithelial cells of the adrenal "provisional cortex" and the convoluted tubules of developing kidneys. In the developing lungs, pancreas and skin, OP-1 was localized in basement membranes underlying the epithelium. In vitro binding studies of 125I-OP-1 to various extracellular matrix components revealed high affinity of OP-1 for type IV collagen and less for heparin, collagen types I and VI. Present findings suggest that, in addition to bone formation, OP-1 could have other important regulatory roles in human embryogenesis with high binding affinity to a basement membrane component.

Bovine articular chondrocytes do not undergo hypertrophy when cultured in the presence of serum and osteogenic protein-1

Osteogenic protein-1 (hOP-1, BMP-7) is a member of the transforming growth factor-beta superfamily. We have recently shown that hOP-1 induces and promotes maturation and hypertrophy of chick sternal chondrocytes, cultured in monolayer or suspension in the presence or absence of serum. In the present study we demonstrate that bovine articular chondrocytes, grown for up to 5 weeks in the presence of 0.5% or 10% serum in combination with 30 ng/ml hOP-1, do not undergo hypertrophy, as determined by cell size, the absence of type X collagen expression and synthesis, and of alkaline phosphatase activity. Treatment with hOP-1 (30 ng/ml) resulted in increased matrix synthesis as measured by [35S]sulfate incorporation and by collagen type II synthesis and expression, without influencing cell proliferation. These data suggest that primary mammalian articular chondrocytes are not able to undergo hypertrophy in conditions previously shown to be permissive for hypertrophy of both chick sternal and chick articular chondrocytes.

Identification of multiple active growth factors in basement membrane Matrigel suggests caution in interpretation of cellular activity related to extracellular matrix components

We have recently demonstrated the formation of interconnecting canalicular cell processes in bone cells upon contact with basement membrane components. Here we have determined whether growth factors in the reconstituted basement membrane (Matrigel) were active in influencing the cellular network formation. Various growth factors including transforming growth factor beta (TGF-beta), epidermal growth factor (EGF), insulin-like growth factor 1, bovine fibroblast growth factor (bFGF), and platelet-derived growth factor (PDGF) were identified in Matrigel. Exogenous TGF-beta blocked the cellular network formation. Conversely, addition of TGF-beta 1 neutralizing antibodies to Matrigel stimulated the cellular network formation. bFGF, EGF, and PDGF all promoted cellular migration and organization on Matrigel. Addition of bFGF to MC3T3-E1 cells grown on Matrigel overcame the inhibitory effect of TGF-beta. Some TGF-beta remained bound to type IV collagen purified from the Engelbreth-Holm-Swarm tumor matrix. These data demonstrate that reconstituted basement membrane contains growth factors which influence cellular behavior, suggesting caution in the interpretation of experiments on cellular activity related to Matrigel, collagen type IV, and possibly other extracellular matrix components.

24R,25-dihydroxyvitamin D3 prevents aluminum-induced alteration of brain gangliosides in uremic rats by keeping the metal within perivascular astrocytes of the blood-brain barrier

The administration of aluminum (Al) to uremic rats leads to Al accumulation in different brain regions with subsequent alteration of brain gangliosides. Addition of 24R,25-dihydroxyvitamin D3[24R,25-(OH)2D3] did not influence the brain Al content determined by plasma argon emission spectrometry, but prevented the decrease in brain gangliosides. By using electron microscopy and laser microprobe mass analysis, it was demonstrated that in rats given 24R,25-(OH)2D3 together with Al, the metal was mainly kept within perivascular astrocytes of the blood-brain barrier. On the contrary, in rats given Al only, the metal was evenly distributed throughout the brain areas causing extensive demyelination, chromatolysis of nerve cells in some brain regions (hippocampus) and brain edema. Our results could find application in the prevention of Al-induced encephalopathy in patients on hemodialysis.

Natural bovine osteogenin and recombinant human bone morphogenetic protein-2B are equipotent in the maintenance of proteoglycans in bovine articular cartilage explant cultures

Osteogenin and related bone morphogenetic proteins are members of the transforming growth factor-beta superfamily, and were isolated by their ability to induce cartilage and bone formation in vivo. The influence of osteogenin, purified from bovine bone, and of recombinant human bone morphogenetic protein-2B (BMP-2B) has been examined in bovine articular cartilage explants. Both differentiation factors stimulated in a dose-dependent manner the synthesis of proteoglycans and decreased their rate of degradation. At a dose of 30 ng/ml, proteoglycan synthesis was increased to levels observed with either 20 ng/ml insulin-like growth factor I, 10 ng/ml transforming growth factor-beta, or 20% fetal bovine serum. This increase of biosynthetic rates above basal medium levels was observed in young, adolescent, and adult tissues. Analysis of the size of the newly synthesized proteoglycans, the glycosaminoglycan chain size, and the glycosaminoglycan type of explants treated with osteogenin or BMP-2B were very comparable to each other, and to proteoglycans isolated from cartilage treated with either insulin-like growth factor I or fetal bovine serum. These results demonstrate that osteogenin and BMP-2B alone are capable of stimulating and maintaining the chondrocyte phenotype in vitro.

Differentiation of canalicular cell processes in bone cells by basement membrane matrix components: regulation by discrete domains of laminin

We have investigated the interaction of rat primary calvarial bone cells and a mouse osteoblast-like cell line MC3T3-E1 with basement membrane components. On a reconstituted gel of basement membrane, both cell types attached and formed isolated clusters that developed long interconnecting cell processes similar to the canalicular network observed in bone. The differentiation of the osteoblastic phenotype was stimulated as determined by increased alkaline phosphatase production and the deposition of mineral. Antibodies to laminin and to a 32/67 kd laminin receptor blocked this differentiation. Cell morphology was altered by the addition of active laminin-derived synthetic peptides, YIGSR-NH2 and CSRARKQAASIKVAVSADR-NH2, but not by an active RGD-containing peptide. When coated directly on plastic, all three peptides promoted cell adhesion, demonstrating that bone cells interact with specific molecular domains of laminin. These data demonstrate that basement membrane plays a key role in formation of a network of cytoplasmic processes resembling the osteocyte canalicular network in bone.

Autoradiographic localization of osteogenin binding sites in cartilage and bone during rat embryonic development

Osteogenin, a novel bone differentiation factor isolated from bone, has been recently purified and the amino acid sequence determined. Osteogenin in conjunction with a collagenous bone matrix substratum induces cartilage and bone formation in vivo. In order to understand the developmental role of osteogenin during cartilage and bone morphogenesis we examined the binding and distribution of iodinated osteogenin in developing rat embryos. Whole embryo tissue sections were made from 11, 12, 13, 15, 18, and 20 day fetuses. The specific binding of osteogenin at different stages of rat embryonic development was determined by autoradiography. Maximal binding was observed in mesodermal tissues such as cartilage, bone, perichondrium, and periosteum. During Days 11-15, peak binding was localized to perichondrium during limb and vertebral morphogenesis. By Day 18 periosteum exhibited the highest concentration of autoradiographic grains. Osteogenin was also localized in developing membranous bones of the calvarium and other craniofacial bones. Considerably less binding was observed, in decreasing order, in muscle, liver, spleen, skin, brain, heart, kidney, and intestine. The observed maximal binding during skeletal morphogenesis implies a developmental role for osteogenin.

Osteogenin inhibits proliferation and stimulates differentiation in mouse osteoblast-like cells (MC3T3-E1)

Osteogenin, a novel bone differentiation factor, was recently purified and characterized. We examined its effect on the proliferation and differentiation of MC3T3-E1 osteoblast-like cells. Cell proliferation was inhibited the first 48 h after addition of osteogenin, and this effect was independent of serum. Osteogenin did not influence the cell morphology. Alkaline phosphatase promptly increased in a dose and time-dependent manner and appeared to be specific. Treatment with TGF-beta 1 resulted in inhibition of alkaline phosphatase activity, and was reversed by osteogenin within 48 h. Cell cultures treated with osteogenin for 72 h after confluence became responsive to parathyroid hormone. Synthesis of collagenous proteins was stimulated by osteogenin. The present results demonstrate a significant influence of osteogenin on the differentiation of osteogenic phenotype in MC3T3-E1 cells in vitro.

Stimulation of the expression of osteogenic and chondrogenic phenotypes in vitro by osteogenin

Osteogenin was recently purified and the amino acid sequences of tryptic peptides were determined. Osteogenin in conjunction with insoluble collagenous bone matrix induces cartilage and bone formation in vivo. To understand the mechanism of action of osteogenin, we examined its influence on periosteal cells, osteoblasts, fibroblasts, chondrocytes, and bone marrow stromal cells in vitro. Osteogenin stimulated alkaline phosphatase activity and collagen synthesis in periosteal cells. The cAMP response to parathyroid hormone in periosteal cells was increased by osteogenin. In primary cultures of calvarial osteoblasts, osteogenin stimulated alkaline phosphatase activity, the cAMP response to parathyroid hormone, and the synthesis of collagenous and noncollagenous proteins; however, cell proliferation was not affected. Osteogenin increased the production of sulfated proteoglycans in fetal rat chondroblasts and in rabbit articular chondrocytes. The present experiments demonstrate the significant influence of osteogenin in the stimulation of osteogenic and chondrogenic phenotypes in vitro.