Regulation of alkaline phosphatase and alpha 2(I) procollagen synthesis during early intramembranous bone formation in the rat mandible

Expression of mRNAs for neuropeptide receptors and beta-adrenergic receptors in human osteoblasts and human osteogenic sarcoma cells

In human periosteum-derived osteoblastic cells (SaM-1) and human osteosarcoma-derived cells (SaOS-2, HOS, MG-63), the mRNA expressions of calcitonin gene-related peptide receptor (CGRP-R), substance P receptor (SP-R), neuropeptide Y receptor (NPY-R), beta-adrenergic receptors (beta1-R, beta2-R, beta3-R), vasoactive intestinal polypeptide type 1 and type 2 receptors (VIP-1R, VIP-2R) and pituitary adenylate cyclase activating polypeptide receptor (PACAP-R) were examined by reverse transcription-polymerase chain reaction (RT-PCR). According to the magnitude of the mRNA expression of alkaline phosphatase (ALP), the relative state of commitment of these osteoblastic cell lines to the osteoblast lineage was SaM-1 > SaOS-2 > HOS > MG-63. CGRP-R, NPY-R, VIP-1R and beta2-R, but not SP-R, VIP-2R, PACAP-R, beta1-R and beta3-R, were expressed in osteoblasts as well as osteosarcoma cells. Expression of these receptors seems to be a common feature in osteoblastic cells, but the magnitude of expression was not dependent upon the relative state of commitment of the osteoblastic cells to the osteoblast lineage. In addition, VIP mRNA was not expressed in osteoblastic cells, suggesting the absence of an autocrine system of VIP in osteoblasts. These observations suggest that these neuropeptides and norepinephrine are involved in local regulation of human bone metabolism.

Stage-specific expression patterns of alkaline phosphatase during development of the first arch skeleton in inbred C57BL/6 mouse embryos

Timing and pattern of expression of alkaline phosphatase was examined during early differentiation of the 1st arch skeleton in inbred C57BL/6 mice. Embryos were recovered between 10 and 18 d of gestation and staged using a detailed staging table of craniofacial development prior to histochemical examination. Expression of alkaline phosphatase is initiated at stage 20.2 in the plasma membrane of mesenchymal cells in the distal region of the first arch. Expression is strongest in osteoid (unmineralised bone matrix) and presumptive periosteum at stage 21.32. Mineralisation begins at stage E23. Expression is present in the mineralised bone matrix. Secondary cartilages form in the condylar and angular processes by stage M24. The cartilaginous cells and surrounding cells in the processes are all alkaline phosphatase-positive and surrounded by the common periosteum, suggesting that progenitor cells of the processes, dentary ramus and secondary cartilages all originate from a common pool. Nonhypertrophied chondrocytes of Meckel's cartilage express alkaline phosphatase at stage M23. Expression in these chondrocytes is preceded by the expression in their adjacent perichondrium. This is true of chondrocytes in all other cranial cartilages examined. 3-D reconstruction of expression in Meckel's cartilage also revealed that the chondrocytes of Meckel's cartilage which express alkaline phosphatase and the matrix of which undergoes mineralisation are those surrounded by the alkaline phosphatase-positive dentary ramus. By stage 25, coincident with mineralisation in the distal section of Meckel's cartilage, most chondrocytes are strongly positive. The perichondria of malleus and incus cartilages express alkaline phosphatase at stage M24. Nonhypertrophied chondrocytes along these perichondria also express alkaline phosphatase. Superficial and deep cells in the dental laminae of incisor and 1st molar teeth become alkaline phosphatase-positive at the bud stage, stages 21.16 and 21.32, respectively. Dental papillae are negative until stage M24 when alkaline phosphatase expression begins in the dental papillae and follicles of the incisor teeth and the dental follicles of the 1st molar teeth. The dental papillae of the 1st molar teeth express alkaline phosphatase at stage 25. Expression in the dental papillae and follicles appears to coincide with cellular differentiation of follicle from papilla. The presumptive squamosal, ectotympanic and gonial membrane bones, lingual oral epithelial cells connected to the dental laminae of the incisor teeth, hair follicle papillae and sheath and surrounding dermis all express alkaline phosphatase in a stage-specific manner.

Monoclonal antibodies as tools for studying the osteoblast lineage

Knowledge of the number and kinds of differentiation steps characterizing cells of the osteoblast lineage is inadequate. To analyze further osteoblast differentiation, a number of labs have generated monoclonal antibodies to osteogenic cells, derived from both normal bone and osteosarcomas. A variety of immunolabelling patterns on primary cell cultures, cell lines, and tissue sections has been reported, including cell surface, cytoplasmic, and extracellular matrix-associated patterns. Most of the antibodies selected recognize predominantly the mature osteoblast and osteocyte; in addition, however, antibodies have been generated that recognize pre-osteoblasts. Some recognize cells of both the osteoblast and chondroblast lineages and may contribute to a better understanding of the lineage and phenotypic relationships between these two cell types. In addition to recognition in vivo of cell subpopulations of discrete maturational stages, changes in the immunolabelling patterns in vitro have also documented a differentiation sequence in cells undergoing osteogenesis in cell and tissue cultures. In at least two cases, the antibodies have been used to isolate subpopulations of cells from bone, including relatively pure populations of osteocytes. With the exception of several antibodies that are against alkaline phosphatase or known matrix proteins including osteocalcin, the nature of the macromolecular species recognized by most of the antibodies generated to date are unknown. Recently, however, one antibody was used to clone the cDNA for the beta-galactoside-binding lectin, galectin 3 or epsilon binding protein (epsilon BP; IgE-binding protein; Mac-2), from a lambda gt11 osteoblast expression library; another was used to clone from an ROS 17/2.8-COS cell expression library the cDNA for OTS-8, a putative target gene of early response genes stimulated in response to phorbol esters in MC3T3-E1 cells. Neither of these macromolecules had previously been identified in bone cells, but the recent molecular and cellular analyses have shown them to be developmentally and/or hormonally regulated in osteoblastic cells. These antibodies extend the available markers and support earlier observations that a variety of molecules are differentially expressed by cells at different stages of the osteoblast lineage. This chapter will not be an exhaustive survey of all immunocytochemical and immunohistochemical analyses of osteogenic cells and tissues but will focus on the approach of eliciting novel monoclonal antibodies by the injection of osteogenic cells or crude bone extracts and its potential for establishing new markers of the osteoblast lineage. We have not included a large number of studies documenting the use of antibodies raised against several known bone matrix proteins; while these have been crucial in developing our current understanding of osteogenic differentiation, we sought rather to highlight the potential of the "random" injection approach.

Tenascin-C is associated with early stages of chondrogenesis by chick mandibular ectomesenchymal cells in vivo and in vitro

Tenascin-C is an extracellular matrix protein thought to be involved in skeletogenesis. We have examined the distribution of tenascin-C in the developing chick mandibular arch between stages 18-36, and during in vitro chondrogenesis of mandibular ectomesenchymal cells in micromass cultures using a probe and antibody that correspond to the portion of the tenascin-C transcript conserved in all of the three known chick splice variants. In situ hybridization and immunohistochemical analyses demonstrate that tenascin-C is predominantly expressed in the condensing mesenchyme of developing cartilage, and in the perichondrium of differentiated cartilage. Tenascin-C expression, although detected in differentiating chondroblasts, was not detected in differentiated cartilage. Tenascin-C was also expressed in the developing membranous bones. In addition, the expression of tenascin-C transcripts during in vitro chondrogenesis of mandibular ectomesenchymal cells in micromass cultures was compared to the patterns of expression of aggrecan core protein and alpha 1(I) collagen transcripts. Our in situ hybridization analyses of micromass cultures demonstrate the expression of tenascin-C and aggrecan core protein mRNAs by pre-chondrogenic aggregates in the 1-day cultures and by chondroblasts in differentiating cartilage nodules in 2-day cultures. In 4- and 9-day cultures, the pattern of expression of tenascin-C mRNA was different from the patterns of expression of aggrecan core protein mRNA, and appeared to be more closely related to the expression of alpha 1(I) collagen mRNA. Aggrecan core protein mRNA was expressed by chondrocytes in cartilage nodules in 4- and 9-day cultures. On the other hand, tenascin-C and alpha 1(I) collagen mRNAs, in addition to being expressed in the loose connective tissues in the inter-nodular spaces, were predominantly expressed by the elongated, flattened, and fibroblast-like cells around the cartilage nodules. These results indicate that during the in vitro chondrogenesis of mandibular ectomesenchymal cells, expression of tenascin-C mRNA identifies chondrocytes in their early stages of differentiation. The patterns of expression of tenascin-C mRNA in 4- and 9-day cultures further suggest that tenascin-C is expressed in the perichondrium-like structures that form around the cartilage nodules in micromass cultures. Therefore, our in vitro studies, in agreement with our in vivo studies, suggest an association of tenascin-C with the initial or early stages of chondrogenesis in the chicken mandibular arch.

Temperature sensitive simian virus 40 large T antigen immortalization of murine odontoblast cell cultures: establishment of clonal odontoblast cell line

During tooth formation instructive epithelial-mesenchymal interactions result in the cytodifferentiation of ectomesenchymal cells into odontoblasts which produce the dentin extracellular matrix (DECM). The purpose of our study was to establish a stable murine odontoblast cell line by immortalization of odontoblasts using retrovirus transfection. In order to accomplish this goal, we utilized a previously characterized odontoblast monolayer cell culture system supportive of odontoblast cytodifferentiation from dental papilla mesenchyme (DPM), expression and secretion of a DECM and dentin biomineralization. First mandibular molars from E-18 Swiss Webster mice were dissected, the DPM isolated, and pulp cells dissociated. Pulp cells (5 x 10(5)/well) were plated as monolayers and grown in alpha-MEM supplemented with 10% FCS, 100 units/ml penicillin and streptomycin, 50 micrograms/ml ascorbic acid. Cultures were maintained for 6 days at 37 degrees C in a humidified atmosphere of 95% air and 5% CO2, with media changes every two days. Immortalization was performed using a recombinant defective retrovirus containing the temperature sensitive SV-40 large T antigen cDNA and the neomycin (G418) resistance gene recovered from CRE packaging cells. Cultures were infected for 24 h with CRE conditioned medium containing 8 micrograms/ml of polybrene, the media was replaced with selective media containing 300 micrograms/ml of G418, and the cultures incubated at 33 degrees C for one month with media changes every 3-5 days. Neomycin resistant cells were cloned by serial dilution to single cells in 96-well culture plates and grown in selection medium at 33 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-traumatic dynamic change of carboxyterminal propeptide of type I procollagen, alkaline phosphatase and its isoenzymes as predictors for enhanced osteogenesis in patients with severe head injury

Patients suffering from severe head injury and fractures of long bones or large joints often show enhanced osteogenesis, with hypertrophic callus formation and/or heterotopic ossifications. The advantage of this phenomenon is early consolidation of the fractures. An extreme disadvantage is extensive periarticular calcification, resulting in complete ankylosis of the affected joint. In spite of numerous efforts aimed at clarifying the way in which severe head injury can influence osteogenesis at a distant site, this phenomenon is still not understood. The process, once started, seems irreversible, but if diagnosed in time, could be prevented with non-steroid anti-inflammatory drugs that inhibit development of heterotopic ossifications. The major prerequisite for testing this possibility is to define parameters of an early diagnosis of enhanced osteogenesis. Thus, the aim of this study was to test whether serum values of some parameters related to bone regeneration could allow an early prediction of enhanced ossification following bone fracture in patients with severe head injury. Samples of sera were obtained from three groups of injured patients: fractures of long bones or large joints only (n = 6), severe head injury only (n = 8), severe head injury and fractures of long bones and large joints (n = 7) and from a group of apparently healthy volunteers (n = 10). The values for alkaline phosphatase (ALP), the bone isoenzyme, and the carboxy terminal propeptide of type I procollagen (PICP) were significantly higher (5-20 times as high) in patients with severe head injury and bone or joint fractures than in any other group. Significantly increased concentrations of PICP were already found in the 1st week after injury, and those of ALP and of the bone isoenzyme increased during the 2nd week after injury. Results show that these parameters are helpful for an early diagnosis of enhanced osteogenesis and heterotopic ossifications in patients with severe head injury and bone fractures. Further studies are necessary to verify these findings, while analysis of reasons for the specific patterns of dynamic change of these parameters could lead to better understanding of the mechanisms underlying the uncontrolled bone formation.

Kinetics of in vitro mineralization by an osteogenic clonal cell line (C1) derived from mouse teratocarcinoma

We have previously reported the isolation of an osteogenic clonal cell line (C1) derived from mouse teratocarcinoma and immortalized by the SV 40 oncogenes. In this report we describe the kinetics of osteogenic differentiation of aggregated C1 cells by following the matrix deposition and mineralization and the expression of alkaline phosphatase. We show that after addition of beta-glycerophosphate and ascorbic acid, more than 95% of C1 aggregates synthesize a bone matrix which is deposited as early as 2 days and increases progressively with time in culture. Matrix calcification is evidenced by von Kossa staining and tetracycline incorporation into the mineral whereas no calcification appears in control cultures. Calcium is detectable in mineralizing aggregates at 2 days and calcium content increases linearly with time in culture, being 125-fold higher in mineralizing nodules than in control aggregates at 30 days. Aggregated C1 cells are characterized by a high activity of the bone type isoenzyme of alkaline phosphatase, a marker of osteoblast phenotype. Upon addition of inducers, alkaline phosphatase activity decreases by five-fold after the onset of mineralization and remains stable thereafter. The down-regulation of alkaline phosphatase activity is confirmed at the cellular level by histochemical staining. The mRNA levels for alkaline phosphatase decline during osteogenesis, following a pattern similar to the decrease in protein activity. Analysis of DNA synthesis by (3H)-thymidine incorporation and quantification of labelled nuclei on autoradiographs shows that C1 cells proliferation is not down-regulated during the time course of differentiation and that proliferating C1 cells still express alkaline phosphatase activity during osteogenic differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone matrix mRNA expression in differentiating fetal bovine osteoblasts

In the accompanying study, we report an in vitro culture system from bovine bone cells that can be applied to investigate bone cell growth and differentiation. In this system, bovine bone cells placed in mineralization medium formed multilayers (days 2-3), began deposition of mineral (days 5-6), and eventually acquired a mineralized matrix sheet (days 14-20) through the stages of mineralizing nodules and trabecular-like structure. In the current study we used this system to investigate the relative expression of bone matrix genes that may play an important role in bone development and metabolism. alpha 1(I)-collagen, alkaline phosphatase, osteonectin, biglycan (PgI), decorin (PgII), osteopontin, and bone sialoprotein mRNA gene expression were measured on days 0, 2, 6, 10, and 20 (date when the cells were placed in mineralization medium as day 0). Total RNA was purified and analyzed by northern blot using radiolabeled cDNA encoding these genes. To comprehend the relationship between gene expression and mineralization, total calcium content in the cultures was also measured. During the culture period we observed several very different gene expression profiles. The expression of both alpha 1(I)-collagen and biglycan increased 3- to 4-fold by day 6 and then returned to basal levels by day 20. The osteonectin gene was highly expressed throughout the culture, with no significant increase in induction found during any time of culture. A significant induction of alkaline phosphatase (13.8-fold) gene expression was observed by day 6. Osteopontin showed a similar profile to that of alkaline phosphatase but had a much greater level of relative expression (26-fold) compared to day 0. Interestingly, downregulation during mineral accumulation seemed a common occurrence among many of the genes measured. In contrast, the bone sialoprotein gene showed a significant and distinct expression pattern, increasing rapidly after the onset of mineralization on day 6 and ultimately reaching 140-fold that of day 0. Decorin (Pg II) showed an increasing pattern, with the final relative level of induction 5-fold on day 20. These data suggest that the development of the mature osteoblastic phenotype, complete with the ability to produce a thick mineralized matrix, requires the differential regulation of a series of genes and their gene products over the culture period.

The membranous skeleton: the role of cell condensations in vertebrate skeletogenesis

Elements of the vertebrate skeleton are initiated as cell condensations, collectively termed the 'membranous skeleton' whether cartilages or bones by Grüneberg (1963). Condensations, which were identified as the basic cellular units in a recent model of morphological change in development and evolution (Atchley and Hall 1991) are reviewed in this paper. Condensations are initiated either by increased mitotic activity or by aggregation of cells towards a centre. Prechondrogenic (limb bud) and preosteogenic (scleral ossicle) condensations are discussed and contrasted. Both types of skeletogenic condensations arise following epithelial-mesenchymal interactions; condensations are identified as the first cellular product of such tissue interactions. Molecular characteristics of condensations are discussed, including peanut agglutinin lectin, which is used to visualize prechondrogenic condensations, and hyaluronan, hyaladherins, heparan sulphate proteoglycan, chondroitin sulphate proteoglycan, versican, tenascin, syndecan, N-CAM, alkaline phosphatase, retinoic acid and homeo-box-containing genes. The importance for the initiation of chondrogenesis or osteogenesis of upper and lower limits to condensation size and the numbers of cells in a condensation are discussed, as illustrated by in vitro studies and by mutant embryos, including Talpid3 in the chick and Brachypod, Congenital hydrocephalus and Phocomelia in the mouse. Evidence that genes specific to the skeletal type are selectively activated at condensation is discussed, as is a recent model involving TGF-beta and fibronectin in condensation formation. Condensations emerge as a pivotal stage in initiation of the vertebrate skeleton in embryonic development and in the modification of skeletal morphology during evolution.

Tissue-specific and dexamethasone-inducible expression of alkaline phosphatase from alternative promoters of the rat bone/liver/kidney/placenta gene

The rat Bone/Liver/kidney/Placenta Alkaline Phosphatase (ALP) is transcribed from two alternative promoters spaced over 25 kb apart, resulting in two variant transcripts that are identical in their coding sequence. We investigated the steady-state levels of the two variant transcripts in various rat tissues and cell lines using the polymerase chain reaction (PCR) amplification for RNA phenotyping, RNase protection, and northern blot analysis. Our results demonstrate that ALP transcripts from the upstream promoter are preferentially expressed in calvariae, and are almost exclusively expressed in ROS17/2.8 osteogenic sarcoma cells. In contrast, the downstream promoter is preferentially expressed in kidney. Moreover, the increase in ALP activity and mRNA levels following dexamethasone treatment of ROS17/2.8 cells is correlated with an increase in the level of transcripts from the upstream promoter. Thus, the two alternative promoters of the rat BLKP ALP gene are involved in cell-specific and dexamethasone-inducible regulation of its expression.