Large scale analysis of osteocyte lacunae in klotho hypomorphic mice using high-resolution micro-computed tomography

BACKGROUND

Osteocytes are the most abundant cell type in adult bone, and the morphological characteristics of osteocytes and their lacunae appear to influence bone mass and fragility. Although conventional computed tomography (CT) has contributed greatly to advances in bone morphometry, capturing details of the entire hierarchical assembly, e.g., osteocyte lacuna parameters, has been limited by the analytical performance of CT (> 1 µm resolution).

METHODS

We used high-resolution (700 nm) micro-CT to evaluate and compare the osteocyte lacuna parameters over a large scale, i.e., in a maximum of about 45,700 lacunae (average), in tibial metaphyseal cortical bones of wild-type (WT) and αKlotho-hypomorphic (kl/kl) mice, the latter a model that exhibits osteopenia and aberrant osteocytes.

RESULTS

Of osteocyte lacuna parameters, lacunar surface per lacunar volume were significantly lower and lacuna diameter were significantly larger in kl/kl mice compared to WT mice. By analysis of individual osteocyte lacunae, we found that lacunar sphericity in kl/kl mice was higher than that in WT mice, and the diameters in the major and the minor axes were respectively lower and higher in kl/kl mice, especially at the proximal site of the region of interest.

CONCLUSION

We successfully assessed osteocyte lacuna parameters on the largest scale in mice reported to date and found that the shape of osteocyte lacunae of kl/kl mice are significantly different from those of WT mice. Although the mechanisms underlying the lacunar shape differences observed are not yet clear, changes in lacunar geometry are known to affect the transitions of strains to the osteocyte microenvironment and likely local osteocyte response(s). Thus, the fact that the differences are limited to the mesial region near the primary spongiosa suggests the likelihood of site-specific anomalies in mechanosensitive effects in kl/kl osteocytes with consequent site-specific effects bone metabolism and function.

Developmental impairments of craniofacial bone and cartilage in transgenic mice expressing FGF10

Mutations in a common extracellular domain of fibroblast growth factor receptor (FGFR)-2 isoforms (type IIIb and IIIc) cause craniosynostosis syndrome and chondrodysplasia syndrome. FGF10, a major ligand for FGFR2-IIIb and FGFR1-IIIb, is a key participant in the epithelial-mesenchymal interactions required for morphogenetic events. FGF10 also regulates preadipocyte differentiation and early chondrogenesis in vitro, suggesting that FGF10-FGFR signaling may be involved in craniofacial skeletogenesis in vivo. To test this hypothesis, we used a tet-on doxycycline-inducible transgenic mouse model (FGF10 Tg) to overexpress Fgf10 from embryonic day 12.5. Fgf10 expression was 73.3-fold higher in FGF10 Tg than in wild-type mice. FGF10 Tg mice exhibited craniofacial anomalies, such as a short rostrum and mandible, an underdeveloped (cleft) palate, and no tympanic ring. Opposite effects on chondrogenesis in different anatomical regions were seen, e.g., hyperplasia in the nasal septum and hypoplasia in the mandibular condyle. We found an alternative splicing variant of Fgfr2-IIIb with a predicted translation product lacking the transmembrane domain, and suggesting a soluble form of FGFR2-IIIb (sFGFR2-IIIb), differentially expressed in some of the craniofacial bones and cartilages. Thus, excessive FGF10 may perturb signal transduction of the FGF-FGFR, leading to craniofacial skeletal abnormalities in FGF10 Tg mice.

Lignin-facilitated growth of Ag/CuNPs on surface-activated polyacryloamidoxime nanofibers for superior antibacterial activity with improved biocompatibility

INTRODUCTION

Nanofibers are one of the role-playing innovations of nanotechnology. Their high surface-to-volume ratio allows them to be actively functionalized with a wide range of materials for a variety of applications. The functionalization of nanofibers with different metal nanoparticles (NPs) has been studied widely to fabricate antibacterial substrates to battle antibiotic-resistant bacteria. However, metal NPs show cytotoxicity to living cells, thereby restricting their application in biomedicine.

OBJECTIVES

To minimize the cytotoxicity of NPs, biomacromolecule lignin was employed as both a reducing and capping agent to green synthesize silver (Ag) and copper (Cu) NPs on the surface of highly activated polyacryloamidoxime nanofibers. The activation of polyacrylonitrile (PAN) nanofibers via amidoximation was employed for enhanced loading of NPs to achieve superior antibacterial activity.

METHODOLOGY

At first, electrospun PAN nanofibers (PANNM) were activated to produce polyacryloamidoxime nanofibers (AO-PANNM) by immersing PANNM in a solution of Hydroxylamine hydrochloride (HH) and Na₂CO₃ under controlled conditions. Later, Ag and Cu ions were loaded by immersing AO-PANNM in different molar concentrations of AgNO₃ and CuSO₄ solutions in a stepwise manner. The reduction of Ag and Cu ions into NPs to fabricate bimetal-coated PANNM (BM-PANNM) was carried out via alkali lignin at 37 °C for 3 h in a shaking incubator with ultrasonication every 1 h.

RESULTS

AO-APNNM and BM-PANNM hold their nano-morphology except for some changes in fiber orientation. XRD analysis demonstrated the formation of Ag and CuNPs as evident from their respective spectral band. Maximum 8.46 ± 0.14 wt% and 0.98 ± 0.04 wt% Ag and Cu species were loaded on AO-PANNM, respectively as revealed by ICP spectrometric analysis. The hydrophobic PANNM turned into super hydrophilic, having WCA of 14 ± 3.32° after amidoximation which further reduced to 0° for BM-PANNM. However, the swelling ratio of PANNM reduced from 13.19 ± 0.18 g/g to 3.72 ± 0.20 g/g for AO-PANNM. Even at the third cycle test against S. aureus strains, 0.1Ag/Cu-PANNM, 0.3Ag/Cu-PANNM, and 0.5Ag/Cu-PANNM displayed bacterial reduction of 71.3 ± 1.64 %, 75.2 ± 1.91 %, and 77.24 ± 1.25 %, respectively. On 3rd cycle test against E. coli, above 82 % bacterial reduction was noticed for all BM-PANNM. Amidoximation increased COS-7 cell viability up to 82 %. The cell viability of 0.1Ag/Cu-PANNM, 0.3Ag/Cu-PANNM, and 0.5Ag/Cu-PANNM was found to be ~68 %, ~62, and 54 %, respectively. In LDH assay, almost no release of LDH was detected, suggesting the compatibility of the cell membrane in contact with BM-PANNM. The improved biocompatibility of BM-PANNM even at higher loading (%) of NPs must be ascribed to the controlled release of metal species in the early stage, antioxidant, and biocompatible lignin capping of NPs.

CONCLUSIONS

BM-PANNM displayed superior antibacterial activity against E. coli and S. aureus bacterial strains and acceptable biocompatibility of COS-7 cells even at higher loading (%) of Ag/CuNPs. Our findings suggest that BM-PANNM can be used as a potential antibacterial wound dressing and other antibacterial applications where sustained antibacterial activity is needed.

Synthesized bioactive lignin nanoparticles/polycaprolactone nanofibers: A novel nanobiocomposite for bone tissue engineering

The use of artificial biomaterial with enhanced bioactivity for osteostimulation is a major research concern at present days. In this research, antibacterial and osteostimulative core-shell lignin nanoparticles (LgNP) were synthesized from alkali lignin using tetrahydrofuran (THF) as solvent via a simultaneous pH and solvent shifting technology. Later, LgNP-loaded polycaprolactone (PCL) composite nanofibers were fabricated via the electrospinning technique. The addition of LgNP significantly increased the diameter of the nanofibers, ranging from 400 to 2200 nm. The addition of LgNP reduced the mechanical performance, crystallinity, and porosity of the nanofibers while improving surface wetting and swelling properties of the inherently hydrophobic PCL polymer. The prepared nanofibers showed excellent bactericidal efficacy against major bone infectious Gram-positive Staphylococcus aureus bacterial strains. The incorporation of LgNP imparted superior antioxidant activity and boosted the biodegradation process of the nanofibers. The deposition of biomineral apatite with platelet-like clustered protrusions having a Ca/P ratio of 1.67 was observed while incubating the scaffold in simulated body fluid. Based on the results of the LDH and WST-1 assay, it was demonstrated that the composite nanofibers are non-toxic to pre-osteoblastic cell line (MC3T3-E1) when they are placed in direct contact with the LgNP/PCL scaffold nanofibers. The MC3T3-E1 cells exhibited excellent proliferation and attachment on the prepared composite scaffold via filopodial and lamellipodial expansion with cell-secreted Ca deposition. According to the alkaline phosphatase activity test, LgNP/PCL nanofiber scaffolds significantly improved osteogenic differentiation of MC3T3-E1 cells compared to neat PCL nanofibers. Overall, our findings suggest that LgNP/PCL nanofiber scaffold could be a promising functional biomaterial for bone tissue engineering.

Occlusal Trauma and Bisphosphonate-Related Osteonecrosis of the Jaw in Mice

Osteonecrosis of the jaw (ONJ) is a serious adverse event that is associated with antiresorptive agents, and it manifests as bone exposure in the maxillofacial region. Previous clinical reports suggest that mechanical trauma would trigger ONJ in a manner that is similar to tooth extractions. To the best of our knowledge, there have been few detailed pathophysiological investigations of the mechanisms by which occlusal/mechanical trauma influences ONJ. Here, we developed a novel mouse model that exhibits ONJ following experimental hyperocclusion and nitrogen-containing bisphosphonate (N-BP) treatment. This in vivo model exhibited ONJ in alveolar bone, particularly in the mandible. Moreover, the experimental hyperocclusion induced remarkable alveolar bone resorption in both mouse mandible and maxilla, whereas N-BP treatment completely prevented alveolar bone resorption. In this study, we also modeled trauma by exposing clumps of mesenchymal stem cells (MSCs)/extracellular matrix complex to hydrostatic pressure in combination with N-BP. Hydrostatic pressure loading induced lactate dehydrogenase (LDH) release by calcified cell clumps that were differentiated from MSCs; this LDH release was enhanced by N-BP priming. These in vivo and in vitro models may contribute further insights into the effect of excessive mechanical loading on ONJ onset in patients with occlusal trauma.

MiRNA-Nanofiber, the Next Generation of Bioactive Scaffolds for Bone Regeneration: A Review

Scaffold-based bone tissue engineering has been introduced as an alternative treatment option for bone grafting due to limitations in the allograft. Not only physical conditions but also biological conditions such as gene expression significantly impact bone regeneration. Scaffolds in composition with bioactive molecules such as miRNA mimics provide a platform to enhance migration, proliferation, and differentiation of osteoprogenitor cells for bone regeneration. Among scaffolds, fibrous structures showed significant advantages in promoting osteogenic differentiation and bone regeneration via delivering bioactive molecules over the past decade. Here, we reviewed the bone and bone fracture healing considerations for the impact of miRNAs on bone regeneration. We also examined the methods used to improve miRNA mimics uptake by cells, the fabrication of fibrous scaffolds, and the effective delivery of miRNA mimics using fibrous scaffold and their processes for bone development. Finally, we offer our view on the principal challenges of miRNA mimics delivery by nanofibers for bone tissue engineering.

Single-Cell RNA-Sequencing Reveals the Breadth of Osteoblast Heterogeneity

The current paradigm of osteoblast fate is that the majority undergo apoptosis, while some further differentiate into osteocytes and others flatten and cover bone surfaces as bone lining cells. Osteoblasts have been described to exhibit heterogeneous expression of a variety of osteoblast markers at both transcriptional and protein levels. To explore further this heterogeneity and its biological significance, Venus‐positive (Venus⁺) cells expressing the fluorescent protein Venus under the control of the 2.3‐kb Col1a1 promoter were isolated from newborn mouse calvariae and subjected to single‐cell RNA sequencing. Functional annotation of the genes expressed in 272 Venus⁺ single cells indicated that Venus⁺ cells are osteoblasts that can be categorized into four clusters. Of these, three clusters (clusters 1 to 3) exhibited similarities in their expression of osteoblast markers, while one (cluster 4) was distinctly different. We identified a total of 1920 cluster‐specific genes and pseudotime ordering analyses based on established concepts and known markers showed that clusters 1 to 3 captured osteoblasts at different maturational stages. Analysis of gene co‐expression networks showed that genes involved in protein synthesis and protein trafficking between endoplasmic reticulum (ER) and Golgi are active in these clusters. However, the cells in these clusters were also defined by extensive heterogeneity of gene expression, independently of maturational stage. Cells of cluster 4 expressed Cd34 and Cxcl12 with relatively lower levels of osteoblast markers, suggesting that this cell type differs from actively bone‐forming osteoblasts and retain or reacquire progenitor properties. Based on expression and machine learning analyses of the transcriptomes of individual osteoblasts, we also identified genes that may be useful as new markers of osteoblast maturational stages. Taken together, our data show much more extensive heterogeneity of osteoblasts than previously documented, with gene profiles supporting diversity of osteoblast functional activities and developmental fates. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Active sites of human MEPE-ASARM regulating bone matrix mineralization

The proteolytic fragment ASARM (acidic serine- and aspartate-rich motif) of MEPE (matrix extracellular phosphoglycoprotein) (MEPE-ASARM) may act as an endogenous anti-mineralization factor involved in X-linked hypophosphatemic rickets/osteomalacia (XLH). We synthesized MEPE-ASARM peptides and relevant peptide fragments with or without phosphorylated Ser residues (pSer) to determine the active site(s) of MEPE-ASARM in a rat calvaria cell culture model. None of the synthetic peptides elicited changes in cell death, proliferation or differentiation, but the peptide (pASARM) with three pSer residues inhibited mineralization without causing changes in gene expression of osteoblast markers tested. The anti-mineralization effect was maintained in peptides in which any one of three pSer residues was deleted. Polyclonal antibodies recognizing pASARM but not ASARM abolished the pASARM effect. Deletion of six N-terminal residues but leaving the recognition sites for PHEX (phosphate regulating endopeptidase homolog, X-linked), a membrane endopeptidase responsible for XLH, intact and two C-terminal amino acid residues did not alter the anti-mineralization activity of pASARM. Our results strengthen understanding of the active sites of MEPE-pASARM and allowed us to identify a shorter more stable sequence with fewer pSer residues still exhibiting hypomineralization activity, reducing peptide synthesis cost and increasing reliability for exploring biological and potential therapeutic effects.

ERRα Expression in Bone Metastases Leads to an Exacerbated Antitumor Immune Response

Bone is the most common metastatic site for breast cancer. Although the estrogen-related receptor alpha (ERRα) has been implicated in breast cancer cell dissemination to the bone from the primary tumor, its role after tumor cell anchorage in the bone microenvironment remains elusive. Here, we reveal that ERRα inhibits the progression of bone metastases of breast cancer cells by increasing the immune activity of the bone microenvironment. Overexpression of ERRα in breast cancer bone metastases induced expression of chemokines CCL17 and CCL20 and repressed production of TGFβ3. Subsequently, CD8+ T lymphocytes recruited to bone metastases escaped TGFβ signaling control and were endowed with exacerbated cytotoxic features, resulting in significant reduction in metastases. The clinical relevance of our findings in mice was confirmed in over 240 patients with breast cancer. Thus, this study reveals that ERRα regulates immune properties in the bone microenvironment that contributes to decreasing metastatic growth. SIGNIFICANCE: This study places ERRα at the interplay between the immune response and bone metastases of breast cancer, highlighting a potential target for intervention in advanced disease.

Emerging roles of microRNAs as extracellular vesicle cargo secreted from osteoblasts

BACKGROUND

Extracellular vesicles (EVs) have come into the spotlight as messengers, delivering cargo for cell-cell communication. Concomitantly, increasing attention has been focused on microRNAs (miRNAs) as EV cargo. Besides their well-known role in extracellular matrix mineralization, whether matrix vesicles (MVs) - which are in a broad sense a class of EV - also deliver miRNAs to regulate the function of recipient cells remains unclear.

HIGHLIGHT

We recently found that MVs budding from osteoblasts contain many miRNAs that can be transferred to the bone matrix. Of these, miR-125b was released into the bone marrow microenvironment during bone resorption, where it targeted the transcriptional repressor Prdm1 in osteoclast precursors, resulting in increased expression of anti-osteoclastogenic factors and suppression of osteoclastogenesis, thereby increasing bone mass in mice.

CONCLUSION

Beyond their well-established action in bone mineralization, MVs play a role in the transport of miRNAs from osteoblasts into the bone matrix. Similar to the miR-125b axis in osteoclastogenesis, it seems likely that other miRNAs that accumulate in bone via MV transport may also act as mediators of cell-cell communication in the skeletal system.

Soluble Klotho causes hypomineralization in Klotho-deficient mice

The type I transmembrane protein αKlotho (Klotho) serves as a coreceptor for the phosphaturic hormone fibroblast growth factor 23 (FGF23) in kidney, while a truncated form of Klotho (soluble Klotho, sKL) is thought to exhibit multiple activities, including acting as a hormone, but whose mode(s) of action in different organ systems remains to be fully elucidated. FGF23 is expressed primarily in osteoblasts/osteocytes and aberrantly high levels in the circulation acting via signaling through an FGF receptor (FGFR)-Klotho coreceptor complex cause renal phosphate wasting and osteomalacia. We assessed the effects of exogenously added sKL on osteoblasts and bone using Klotho-deficient (kl/kl) mice and cell and organ cultures. sKL induced FGF23 signaling in bone and exacerbated the hypomineralization without exacerbating the hyperphosphatemia, hypercalcemia and hypervitaminosis D in kl/kl mice. The same effects were seen in rodent bone models in vitro, in which we also detected formation of a sKL complex with FGF23-FGFR and decreased Phex (gene responsible for X-linked hypophosphatemic rickets (XLH)/osteomalacia) expression. Further, sKL-FGF23-dependent hypomineralization in vitro was rescued by soluble PHEX. These data suggest that exogenously added sKL directly participates in FGF23 signaling in bone and that PHEX is a downstream effector of the sKL-FGF23-FGFR axis in bone.

The Roles of Long Non-Protein-Coding RNAs in Osteo-Adipogenic Lineage Commitment

Osteoblasts and adipocytes share a common mesenchymal progenitor in the bone marrow. This implies that a reciprocal relationship exists between osteogenic and adipogenic differentiation. Further, cells of osteoblast lineage transdifferentiate into adipocytes under some circumstances. Dysregulation of osteo-adipogenic fate-determination leads to bone diseases such as osteoporosis, accompanied by an increase in bone marrow adipose tissue. Thus, the fine-tuning of osteo-adipogenesis is necessary for bone homeostasis. Osteo-adipogenic progression is governed by a complex crosstalk of extrinsic signals, transcription factors, and epigenetic factors. Long non-protein-coding RNAs (lncRNAs) act in part as epigenetic regulators in a broad range of biological activities, such as chromatin organization, transcriptional regulation, post-translational modifications, and histone modification. In this review, we highlight the roles of epigenetic regulators, particularly lncRNAs, in the osteo-adipogenic lineage commitment of bone marrow mesenchymal stem cells and the adipogenic transdifferentiation of osteoblasts.

Imaging and mapping of mouse bone using MALDI-imaging mass spectrometry

Matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS) is an advanced method used globally to analyze the distribution of biomolecules on tissue cryosections without any probes. In bones, however, hydroxyapatite crystals make it difficult to determine the distribution of biomolecules using MALDI-IMS. Additionally, there is limited information regarding the use of this method to analyze bone tissues. To determine whether MALDI-IMS analysis of bone tissues can facilitate comprehensive mapping of biomolecules in mouse bone, we first dissected femurs and tibiae from 8-week-old male mice and characterized the quality of multiple fixation and decalcification methods for preparation of the samples. Cryosections were mounted on indium tin oxide-coated glass slides, dried, and then a matrix solution was sprayed on the tissue surface. Images were acquired using an iMScope at a mass-to-charge range of 100-1000. Hematoxylin-eosin, Alcian blue, Azan, and periodic acid-Schiff staining of adjacent sections was used to evaluate histological and histochemical features. Among the various fixation and decalcification conditions, sections from trichloroacetic acid-treated samples were most suitable to examine both histology and comprehensive MS images. However, histotypic MS signals were detected in all sections. In addition to the MS images, phosphocholine was identified as a candidate metabolite. These results indicate successful detection of biomolecules in bone using MALDI-IMS. Although analytical procedures and compositional adjustment regarding the performance of the device still require further development, IMS appears to be a powerful tool to determine the distribution of biomolecules in bone tissues.

The bioactive acidic serine- and aspartate-rich motif peptide

The organic component of the bone matrix comprises 40% dry weight of bone. The organic component is mostly composed of type I collagen and small amounts of non-collagenous proteins (NCPs) (10-15% of the total bone protein content). The small integrin-binding ligand N-linked glycoprotein (SIBLING) family, a NCP, is considered to play a key role in bone mineralization. SIBLING family of proteins share common structural features and includes the arginine-glycine-aspartic acid (RGD) motif and acidic serine- and aspartic acid-rich motif (ASARM). Clinical manifestations of gene mutations and/or genetically modified mice indicate that SIBLINGs play diverse roles in bone and extraskeletal tissues. ASARM peptides might not be primary responsible for the functional diversity of SIBLINGs, but this motif is suggested to be a key domain of SIBLINGs. However, the exact function of ASARM peptides is poorly understood. In this article, we discuss the considerable progress made in understanding the role of ASARM as a bioactive peptide.

Functional diversity of fibroblast growth factors in bone formation

The functional significance of fibroblast growth factor (FGF) signaling in bone formation has been demonstrated through genetic loss-of-function and gain-of-function approaches. FGFs, comprising 22 family members, are classified into three subfamilies: canonical, hormone-like, and intracellular. The former two subfamilies activate their signaling pathways through FGF receptors (FGFRs). Currently, intracellular FGFs appear to be primarily involved in the nervous system. Canonical FGFs such as FGF2 play significant roles in bone formation, and precise spatiotemporal control of FGFs and FGFRs at the transcriptional and posttranscriptional levels may allow for the functional diversity of FGFs during bone formation. Recently, several research groups, including ours, have shown that FGF23, a member of the hormone-like FGF subfamily, is primarily expressed in osteocytes/osteoblasts. This polypeptide decreases serum phosphate levels by inhibiting renal phosphate reabsorption and vitamin D3 activation, resulting in mineralization defects in the bone. Thus, FGFs are involved in the positive and negative regulation of bone formation. In this review, we focus on the reciprocal roles of FGFs in bone formation in relation to their local versus systemic effects.

Delphinidin, one of the major anthocyanidins, prevents bone loss through the inhibition of excessive osteoclastogenesis in osteoporosis model mice

Anthocyanins, one of the flavonoid subtypes, are a large family of water-soluble phytopigments and have a wide range of health-promoting benefits. Recently, an anthocyanin-rich compound from blueberries was reported to possess protective property against bone loss in ovariectomized (OVX) animal models. However, the active ingredients in the anthocyanin compound have not been identified. Here we show that delphinidin, one of the major anthocyanidins in berries, is a potent active ingredient in anti-osteoporotic bone resorption through the suppression of osteoclast formation. In vitro examinations revealed that delphinidin treatment markedly inhibited the differentiation of RAW264.7 cells into osteoclasts compared with other anthocyanidins, cyanidin and peonidin. Oral administration of delphinidin significantly prevented bone loss in both RANKL-induced osteoporosis model mice and OVX model mice. We further provide evidence that delphinidin suppressed the activity of NF-κB, c-fos, and Nfatc1, master transcriptional factors for osteoclastogenesis. These results strongly suggest that delphinidin is the most potent inhibitor of osteoclast differentiation and will be an effective agent for preventing bone loss in postmenopausal osteoporosis.

The EP4-ERK-dependent pathway stimulates osteo-adipogenic progenitor proliferation resulting in increased adipogenesis in fetal rat calvaria cell cultures

We previously reported that fetal rat calvaria (RC) cells are osteo-adipogenic bipotential and that PGE(2) receptors EP2 and EP4 are involved in bone nodule formation via both common and distinct MAPK pathways in RC cell cultures. Because PGE(2) participates in multiple biological processes including adipogenesis, it is of interest to determine the additional role(s) of PGE(2) in RC cells. PGE(2) increased the number of adipocyte colonies when RC cells were treated during proliferation but not other development stages. Of four EP agonists tested, the EP4 agonist ONO-AE1-437 (EP4A) was the most effective in promoting adipogenesis. Concomitantly, EP4A increased the number of cells with BrdU labeling and gene expression of CCAAT/enhancer binding protein (C/EBP)δ and c-fos but not peroxisome proliferator-activated receptor γ2 and C/EBPα. Amongst MAPK inhibitors, U0126, an inhibitor of MEK1/2, abrogated the EP4A-dependent effects. Our results suggest that the PGE(2)-EP4-ERK pathway increases the number of osteo-adipogenic bipotential progenitor cells, with a resultant increase in adipogenesis in RC cell cultures.

Incisor enamel formation is impaired in transgenic rats overexpressing the type III NaPi transporter Slc20a1

Inorganic phosphate (Pi) is required in many biological processes, including signaling cascades, skeletal development, tooth mineralization, and nucleic acid synthesis. Recently, we showed that Pi transport in osteoblasts, mediated by Slc20a1, a member of the type III sodium-dependent phosphate transporter family, is indispensable for osteoid mineralization in rapidly growing rat bone. In addition, we found that bone mineral density decreased slightly with dysfunction of Pi homeostasis in aged transgenic rats overexpressing mouse Slc20a1 (Slc20a1-Tg). Bone and tooth share certain common molecular features, and thus, we focused on tooth development in Slc20a1-Tg mandibular incisors in order to determine the role of Slc20a1 in tooth mineralization. Around the time of weaning, there were no significant differences in serologic parameters between wild-type and Slc20a1-Tg rats. However, histological analysis showed that Slc20a1-Tg ameloblasts formed clusters in the papillary layer during the maturation stage as early as 4 weeks of age. These pathologies became more severe with age and included the formation of cyst-like or multilayer ameloblast structures, accompanied by a chalky white appearance with abnormal attrition and fracture. Hyperphosphatemia was also observed in aging Slc20a1-Tg rats. Micro-computed tomography and electron probe microanalysis revealed impairments in enamel, such as delayed mineralization and hypomineralization. Our results suggest that enamel formation is sensitive to imbalances in Pit1-mediated cellular function as seen in bone, although these processes are under the control of systemic Pi homeostasis.

1alpha,25-dihydroxyvitamin D3 acts predominately in mature osteoblasts under conditions of high extracellular phosphate to increase fibroblast growth factor 23 production in vitro

Osteoblasts/osteocytes are the principle sources of fibroblast growth factor 23 (FGF23), a phosphaturic hormone, but the regulation of FGF23 expression during osteoblast development remains uncertain. Because 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) and inorganic phosphate (Pi) may act as potent activators of FGF23 expression, we estimated how these molecules regulate FGF23 expression during rat osteoblast development in vitro. 1,25(OH)(2)D(3)-dependent FGF23 production was restricted largely to mature cells in correlation with increased vitamin D receptor (VDR) mRNA levels, in particular, when Pi was present. Pi alone and more so in combination with 1,25(OH)(2)D(3) increased FGF23 production and VDR mRNA expression. Parathyroid hormone, stanniocalcin 1, prostaglandin E(2), FGF2, and foscarnet did not increase FGF23 mRNA expression. Thus, these results suggest that 1,25(OH)(2)D(3) may exert its largest effect on FGF23 expression/production when exposed to high levels of extracellular Pi in osteoblasts/osteocytes.

A subset of osteoblasts expressing high endogenous levels of PPARgamma switches fate to adipocytes in the rat calvaria cell culture model

BACKGROUND

Understanding fate choice and fate switching between the osteoblast lineage (ObL) and adipocyte lineage (AdL) is important to understand both the developmental inter-relationships between osteoblasts and adipocytes and the impact of changes in fate allocation between the two lineages in normal aging and certain diseases. The goal of this study was to determine when during lineage progression ObL cells are susceptible to an AdL fate switch by activation of endogenous peroxisome proliferator-activated receptor (PPAR)gamma.

METHODOLOGY/PRINCIPAL FINDINGS

Multiple rat calvaria cells within the ObL developmental hierarchy were isolated by either fractionation on the basis of expression of alkaline phosphatase or retrospective identification of single cell-derived colonies, and treated with BRL-49653 (BRL), a synthetic ligand for PPARgamma. About 30% of the total single cell-derived colonies expressed adipogenic potential (defined cytochemically) when BRL was present. Profiling of ObL and AdL markers by qRT-PCR on amplified cRNA from over 160 colonies revealed that BRL-dependent adipogenic potential correlated with endogenous PPARgamma mRNA levels. Unexpectedly, a significant subset of relatively mature ObL cells exhibited osteo-adipogenic bipotentiality. Western blotting and immunocytochemistry confirmed that ObL cells co-expressed multiple mesenchymal lineage determinants (runt-related transcription factor 2 (Runx2), PPARgamma, Sox9 and MyoD which localized in the cytoplasm initially, and only Runx2 translocated to the nucleus during ObL progression. Notably, however, some cells exhibited both PPARgamma and Runx2 nuclear labeling with concomitant upregulation of expression of their target genes with BRL treatment.

CONCLUSIONS/SIGNIFICANCE

We conclude that not only immature but a subset of relatively mature ObL cells characterized by relatively high levels of endogenous PPARgamma expression can be switched to the AdL. The fact that some ObL cells maintain capacity for adipogenic fate selection even at relatively mature developmental stages implies an unexpected plasticity with important implications in normal and pathological bone development.

EP2 and EP4 receptors differentially mediate MAPK pathways underlying anabolic actions of prostaglandin E2 on bone formation in rat calvaria cell cultures

Of the four prostaglandin (PG) E receptor subtypes (EP1-EP4), EP2 and EP4 have been proposed to mediate the anabolic action of PGE(2) on bone formation but comparative evaluation studies of EPs on bone formation do not necessarily share a common mechanism, implying that their additional features including downstream MAPK pathways may be beneficial to resolve this issue. We systematically assessed the roles of EPs in the rat calvaria (RC) cell culture model by using four selective EP agonists (EPAs). Consistent with relative expression levels of the respective receptors, multiple phenotypic traits of bone formation in vitro, including proliferation of nodule-associated cells, osteoblast marker expression and mineralized nodule formation were upregulated not only by PGE(2) but equally by EP2A and EP4A, but not by EP1A and EP3A. EP2A and EP4A were effective when cells were treated chronically or pulse-treated during nascent nodule formation. EP2A and EP4A equally stimulated the endogenous PGE(2) production, while EP2A caused a greater increase in cAMP production and c-Fos gene expression compared to EP4A. EP2A and EP4A activated predominantly p38 MAPK and ERK respectively, while c-Jun N-terminal kinase (JNK) was equally activated by both agonists. SB203580 (p38 MAPK inhibitor) blocked the PGE(2) effect on mineralized nodule formation, while U0126 (ERK inhibitor) and dicumarol (JNK inhibitor) were less effective. PGE(2)-dependent phosphorylation of the MAPKs was affected not only by protein kinase (PK)A and PKC inhibitors but also by adenylate cyclase and PKC activators. Co-treatment of RC cells with EP2A or EP4A and bone morphogenetic protein (BMP)2, whose effects on bone nodule formation is known to be, in part, mediated through the PKA and p38 MAPK pathways, resulted in an additive effect on mineralized nodule formation. Further, PGE(2), EP2A and EP4A did not increase BMP2/4 mRNA levels in RC cells, and EP2-induced phosphorylation of p38 MAPK was not eliminated by Noggin. These results suggest that, in the RC cell model, the anabolic actions of PGE(2) on mineralized nodule formation are mediated at least in part by activation of the EP2 and EP4 receptor subtype-specific MAPK pathways, independently of BMP signaling, in cells associated with nascent bone nodules.

The PPARgamma-selective ligand BRL-49653 differentially regulates the fate choices of rat calvaria versus rat bone marrow stromal cell populations

Background

Osteoblasts and adipocytes are derived from a common mesenchymal progenitor and an inverse relationship between expression of the two lineages is seen with certain experimental manipulations and in certain diseases, i.e., osteoporosis, but the cellular pathway(s) and developmental stages underlying the inverse relationship is still under active investigation. To determine which precursor mesenchymal cell types can differentiate into adipocytes, we compared the effects of BRL-49653 (BRL), a selective ligand for peroxisome proliferators-activated receptor (PPAR)γ, a master transcription factor of adipogenesis, on osteo/adipogeneis in two different osteoblast culture models: the rat bone marrow (RBM) versus the fetal rat calvaria (RC) cell system.

Results

BRL increased the number of adipocytes and corresponding marker expression, such as lipoprotein lipase, fatty acid-binding protein (aP2), and adipsin, in both culture models, but affected osteoblastogenesis only in RBM cultures, where a reciprocal decrease in bone nodule formation and osteoblast markers, e.g., osteopontin, alkaline phosphatase (ALP), bone sialoprotein, and osteocalcin was seen, and not in RC cell cultures. Even though adipocytes were histologically undetectable in RC cultures not treated with BRL, RC cells expressed PPAR and CCAAT/enhancer binding protein (C/EBP) mRNAs throughout osteoblast development and their expression was increased by BRL. Some single cell-derived BRL-treated osteogenic RC colonies were stained not only with ALP/von Kossa but also with oil red O and co-expressed the mature adipocyte marker adipsin and the mature osteoblast marker OCN, as well as PPAR and C/EBP mRNAs.

Conclusion

The data show that there are clear differences in the capacity of BRL to alter the fate choices of precursor cells in stromal (RBM) versus calvarial (RC) cell populations and that recruitment of adipocytes can occur from multiple precursor cell pools (committed preadipocyte pool, multi-/bipotential osteo-adipoprogenitor pool and conversion of osteoprogenitor cells or osteoblasts into adipocytes (transdifferentiation or plasticity)). They also show that mechanisms beyond activation of PPARγ by its ligand are required for changing the fate of committed osteoprogenitor cells and/or osteoblasts into adipocytes.

Mineralized tissue cells are a principal source of FGF23

While fibroblast growth factor (FGF) 23 is known as a phosphaturic factor in inherited and/or acquired hypophosphatemic disorders, it also serves an endocrine role in normal phosphate homeostasis. FGF23 acts negatively on the NaPi2a cotransporter and 25-hydroxy D(3)-1 alpha-hydroxylase with a resultant decrease in renal phosphate (Pi) reabsorption, while osteoblasts appear to be a primary source of FGF23 whose expression is counter-upregulated by 1 alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). Here we have shown the distribution of FGF23 in normal rat bone and tooth, and its expression profile in fetal rat calvaria (RC) cell cultures. FGF23 mRNA was detectable in multiple fetal and adult tissues but levels were much higher in adult calvaria, femur and incisor, compared to the other tissues tested. Immunoreactive FGF23 was predominantly localized to osteoblasts, cementoblasts, and odontoblasts, with sporadic labeling in some chondrocytes, osteocytes and cementocytes. Notably, osteoclasts were also found to be a possible source of FGF23. Fetal bone and tooth germ cells labeled much less intensely than young adult osteoblasts and odontoblasts. In the RC cell model, FGF23 was expressed during osteoblast development. During matrix mineralization induced by beta-glycerophosphate (beta GP), FGF23 expression was transiently upregulated and then decreased to levels lower than in their non-beta GP-treated counterparts. 1,25(OH)(2)D(3) markedly increased FGF23 expression concomitant with the inhibition of beta GP-induced mineralization. Our data suggest that FGF23 expression in bone is closely correlated with bone formation in vitro and vivo, and points towards an important role(s) for FGF23 in young adult but not fetal mineralized tissues as a systemic factor for Pi homeostasis.

Osteoblast autonomous Pi regulation via Pit1 plays a role in bone mineralization

The complex pathogenesis of mineralization defects seen in inherited and/or acquired hypophosphatemic disorders suggests that local inorganic phosphate (P(i)) regulation by osteoblasts may be a rate-limiting step in physiological bone mineralization. To test whether an osteoblast autonomous phosphate regulatory system regulates mineralization, we manipulated well-established in vivo and in vitro models to study mineralization stages separately from cellular proliferation/differentiation stages of osteogenesis. Foscarnet, an inhibitor of NaP(i) transport, blocked mineralization of osteoid formation in osteoblast cultures and local mineralization after injection over the calvariae of newborn rats. Mineralization was also down- and upregulated, respectively, with under- and overexpression of the type III NaP(i) transporter Pit1 in osteoblast cultures. Among molecules expressed in osteoblasts and known to be related to P(i) handling, stanniocalcin 1 was identified as an early response gene after foscarnet treatment; it was also regulated by extracellular P(i), and itself increased Pit1 accumulation in both osteoblast cultures and in vivo. These results provide new insights into the functional role of osteoblast autonomous P(i) handling in normal bone mineralization and the abnormalities seen in skeletal tissue in hypophosphatemic disorders.

Stanniocalcin 1 acts as a paracrine regulator of growth plate chondrogenesis

During embryogenesis, the expression of mammalian stanniocalcin (STC1) in the appendicular skeleton suggests its involvement in the regulation of longitudinal bone growth. Such a role is further supported by the presence of dwarfism in mice overexpressing STC1. Yet, the STC 1 inhibitory effect on growth may be related to both postnatal metabolic abnormalities and prenatal defective bone formation. In our study, we used an organ culture system to evaluate the effects of STC on growth plate chondrogenesis, which is the primary determinant of longitudinal bone growth. Fetal rat metatarsal bones were cultured in the presence of recombinant human STC (rhSTC). After 3 days, rhSTC suppressed metatarsal growth, growth plate chondrocyte proliferation and hypertrophy/differentiation, and extracellular matrix synthesis. In addition, rhSTC increased the number of apoptotic chondrocytes in the growth plate. In cultured chondrocytes, rhSTC increased phosphate uptake, reduced chondrocyte proliferation and matrix synthesis, and induced apoptosis. All these effects were reversed by culturing chondrocytes with rhSTC and phosphonoformic acid, an inhibitor of phosphate transport. The rhSTC-mediated inhibition of metatarsal growth and growth plate chondrocyte proliferation and hypertrophy/differentiation was abolished by culturing metatarsals with rhSTC and phosphonoformic acid. Taken together, our findings indicate that STC1 inhibits longitudinal bone growth directly at the growth plate. Such growth inhibition, likely mediated by an increased chondrocyte phosphate uptake, results from suppressed chondrocyte proliferation, hypertrophy/differentiation, and matrix synthesis and by increased apoptosis. Last, the expression of both STC1 and its binding site in the growth plate would support an autocrine/paracrine role for this growth factor in the regulation of growth plate chondrogenesis.

Stanniocalcin 1 as a pleiotropic factor in mammals

Stanniocalcin (STC)1 is the mammalian homologue of STC which was originally identified as a calcium/phosphate-regulating hormone in bony fishes. STC1 is a homodimeric phosphoglycoprotein with few if any identified unique motifs in its structure with the exception of CAG repeats in the 5'-untranslated region. In contrast to fish STC which is expressed mainly in the corpuscles of Stannius, STC1 is expressed in a wide variety of tissues, but unexpectedly is not detected in the circulation under normal circumstances. Thus, STC1 may play an autocrine/paracrine rather than a classic endocrine role in mammals. Consistent with this, pleiotropic effects of STC1 have been postulated in physiological and measured in pathological situations. There is much current interest in identifying a specific STC1 receptor and putative signaling pathways to which it may be coupled. In this regard, STC1 may regulate intracellular calcium and/or phosphate (Pi) levels. In the skeletal system, for example, Pi uptake in bone-forming osteoblasts via a direct effect of STC1 on expression of the NaPi transporter Pit1 may contribute to bone formation. Here we review current understanding of the role of STC1 and its possible molecular mechanisms in the skeleton and elsewhere.

Estrogen regulates the production of VEGF for osteoclast formation and activity in op/op mice

Op/op mice have a severe deficiency of osteoclasts because of lacking functional M-CSF that is an essential factor of osteoclast differentiation and function. We now report that OVX induces osteoclast formation and cures osteopetrosis by increasing the VEGF that regulates osteoclast formation in these mice.

INTRODUCTION

We have found that estrogen deficiency induced by ovariectomy (OVX) upregulated osteoclast formation in op/op mice. We have recently demonstrated that vascular endothelial growth factor (VEGF) could substitute for macrophage colony-stimulating factor (M-CSF) in the support of osteoclastic bone resorption in these mice. Therefore, in this study, we wished to assess the effects of VEGF on bone loss induced by OVX in these mice.

MATERIALS AND METHODS

Eight-week-old op/op mice were bilateral OVX or sham-operated. Mice were killed at 8, 10, and 12 weeks of age, and femurs were removed for preparations. Some OVX mice were treated with three consecutive injections of 120 microl/body of VEGF-neutralizing antibody at 12-h intervals starting from 36 h before death at 4 weeks after OVX. VEGFR-1/Fc chimeric protein (600 microg/kg/day) or 17beta-estradiol (0.16 microg/day) was administered in a dorsal subcutaneous pocket of the mice at the time of OVX. These mice were killed 2 weeks after surgery. Changes of serum levels of VEGF were measured by ELISA. Changes of mRNA levels of VEGF, Flt-1, interleukin-6, and osteoclast differentiation factor (ODF/TRANCE/RANKL) in bone tissue were measured by reverse transcriptase-polymerase chain reaction.

RESULTS

In OVX op/op mice, trabecular bone volume of the femur was decreased, and the number of osteoclasts was significantly increased. Serum levels of VEGF were demonstrated to be higher in OVX mice than in sham-operated mice. VEGF mRNA, Flt-1 mRNA, interleukin-6 mRNA, and RANKL mRNA levels in bone tissue were elevated in OVX mice over that in sham-operated mice. The increase in osteoclast number was inhibited by VEGF antagonist treatment in OVX mice.

CONCLUSIONS

In this study, we have demonstrated that the production of VEGF and RANKL stimulated by OVX results in increased osteoclast formation in op/op mice.

Stanniocalcin 1 stimulates osteoblast differentiation in rat calvaria cell cultures

Stanniocalcin 1 (STC1) is a mammalian homolog of STC, the fish calcium/phosphate-regulating polypeptide whose functions are only beginning to be elucidated. Recently, we demonstrated that STC1 stimulates, in an autocrine/paracrine fashion, bone mineralization by increasing phosphate uptake in osteoblasts apparently via the functional activity of the sodium-dependent phosphate transporter, Pit1. We have now assessed the role of STC1 on osteoblast development in fetal rat calvaria (RC) cell cultures. STC1 mRNA and protein were differentially expressed over the time course of cultures, and dexamethasone, a potent stimulator of differentiation in this model, shifted peak STC1 expression levels to earlier times. Overexpression [recombinant human (rh) STC1] and underexpression (antisense oligonucleotides) of STC1 accelerated and retarded, respectively, osteogenic development as well as osteopontin and osteocalcin mRNA expression in mature osteoblast cultures, but not osteoprogenitor cell cultures. Dexamethasone shifted the effective doses required for these effects to higher and lower concentrations of antisense oligonucleotides and rhSTC1, respectively. Concomitantly, rhSTC1 increased both sodium-dependent phosphate uptake and Pit1 gene expression in nodule formation stages, but not in primitive progenitor stages of RC cell cultures. Thus, STC1 accelerates osteoblast development in an autocrine/paracrine manner in the RC cell culture model.

Differentiation in C(2)C(12) myoblasts depends on the expression of endogenous IGFs and not serum depletion

Myogenic differentiation in vitro has been usually viewed as being negatively controlled by serum mitogens. A depletion of critical serum components from medium has been considered to be essential for permanent withdrawal from the cell cycle and terminal differentiation of myoblasts. Removal of serum mitogens induces the expression of insulin-like growth factors (IGFs), whereas it inhibits that of basic fibroblast growth factor (bFGF) and transforming growth factor (TGF)-beta in myoblasts. These responses of growth factors to medium conditioning seem to be well matched to their functions in proliferation/differentiation. In the present study, we showed that C(2)C(12) myoblasts differentiated actively, even in mitogen-rich medium, and that this medium offered an advantage over mitogen-poor medium in terms of increasing differentiation. Our attention focused on endogenous growth factors, as described above, especially IGFs in mitogen-rich medium. During differentiation, IGF-I and IGF-II mRNA levels increased, but bFGF and TGF-beta(1) mRNAs decreased. Differentiation was commensurable with IGF mRNA levels and suppressed by antisense oligodeoxynucleotides and neutralizing monoclonal antibodies against IGFs. These results suggest that an autocrine/paracrine loop of IGFs, bFGF, and TGF-beta(1) is active in proliferating and differentiating C(2)C(12) cells without a depletion of serum and that endogenous IGFs actively override the negative control of differentiation by serum mitogens.

Stanniocalcin 1 (STC1) protein and mRNA are developmentally regulated during embryonic mouse osteogenesis: the potential of stc1 as an autocrine/paracrine factor for osteoblast development and bone formation

STC1, a mammalian homologue of stanniocalcin (STC) which plays a major role in calcium/phosphate homeostasis in fish, has been recently isolated. We have characterized the spatiotemporal distribution of STC1 mRNA and protein during mouse embryonic development generally and osteogenesis specifically. Northern blotting analysis of whole embryos showed that STC1 mRNA is highly and differentially expressed during embryogenesis. By in situ hybridization, STC1 mRNA was detected early in mesenchymal condensations and was then found to be highly expressed in perichondrial cells, periosteal cells, and then osteoblasts during endochondral bone formation. In bones forming by intramembranous ossification, STC1 mRNA was not detected until osteogenic cells appeared. The cellular distribution of STC1 protein closely corresponded to that of its mRNA, but the protein was also detected in hypertrophic chondrocytes. In the MC3T3-E1 osteogenic cell model, STC1 protein and mRNA were detectable throughout proliferation and differentiation stages but levels were relatively higher late during nodule formation/mineralization phases. For comparison, STC1 mRNA was also found in epithelial cells of both embryonic and adult intestine that had not previously been described among tissues responsive to calcium/phosphate transport. These results suggest that STC1 is expressed in a time- and cell-specific manner and may play an autocrine/paracrine role during osteoblast development and bone formation.

Evidence for stanniocalcin gene expression in mammalian bone

Stanniocalcin (STC) acts as a regulator of calcium and phosphate homeostasis in an endocrine manner in bony fish. Recently, complementary DNAs encoding human and mouse STC have been characterized, and the messenger RNA (mRNA) expression was identified in various tissues, such as kidney, small intestine, prostate, thyroid, and ovary. Because previous studies concerning the effects of fish STC on mammalian bone have been discussed, there is a good possibility that mammalian STC is a local factor in bone. Here, we demonstrated STC mRNA expression in neonatal mouse calvaria, the primary cultured mouse osteoblast-rich fractions, and human and mouse osteoblastic cell lines. We also mapped the cellular distribution of the STC mRNA in femur and calvaria in developing mice. Several transcripts with a major 4-kb band were detected in all samples. The cellular distribution of the mRNA expression corresponded closely to osteoblasts in both femur and calvaria. Significant labeling of the STC mRNA was also identified in chondrocytes but not in osteoclasts and other bone marrow elements. These results are the first evidence that hormone may be actually expressed in osteoblasts and chondrocytes, and they strongly implicate the involvement of local STC in both endochondral and membrane bone as an autocrine/paracrine factor.

Dexamethasone regulates the actions of endogenous insulin-like growth factor-II during myogenic differentiation

The effect of dexamethasone (DEX) on the action of endogenous insulin-like growth factor (IGF)-II during myogenic differentiation was investigated by culturing C2C12 mouse myogenic cells in serum-free medium. DEX treatment maintained a high level of creatine kinase (CK) activity, and caused an increase in the number of nuclei per cell, hypertrophy and IGF-II mRNA accumulation in the cells. These effects were abrogated by the glucocorticoid receptor antagonist RU-38486. An anti-IGF-II monoclonal antibody neutralized DEX-dependent CK activity. Thus, we conclude that DEX increases the level of IGF-II mRNA in C2C12 cells, and that DEX may assist myogenic differentiation via, at least in part, its promotive action on IGF-II gene expression.

In situ hybridization analysis of stanniocalcin mRNA expressing cells in the mouse kidney

Stanniocalcin (STC) is a glycoprotein hormone first identified in bony fish in which it regulates calcium and phosphate homeostasis. A mammalian homologue has recently been isolated and STC mRNA is expressed in many tissues including kidney. Mammalian STC appears to inhibit renal phosphate reabsorption in rats, and its immunoreactive cells were detected in specific segments of the renal tubules in humans and rats. We used in situ hybridization with a digoxigenin-labelled cRNA for STC to characterize the intrarenal distribution of STC mRNA in mice. The labelling was detected in most of the cells in nephron tubules and glomerular mesangial cells, suggesting that STC is synthesized in the nephron system and acts in an autocrine/paracrine fashion.

Restoration of disturbed tooth eruption in osteopetrotic (op/op) mice by injection of macrophage colony-stimulating factor

Osteopetrotic (op/op) mice show severe osteosclerosis caused by an inherited deficiency of osteoclast and resultant failure of tooth eruption, which can be cured by the injection of macrophage colony-stimulating factor (M-CSF). The present study revealed that consecutive injections of M-CSF in these mutant mice brought about a recovery of bone resorption resulting in the resumption of growth of tooth root and periodontal ligament. Bone resorption at the inner surface of bony crypts was noted on the 5th day after the start of M-CSF injections. This activity was reduced with the progress of root and periodontal ligament formation, being confined to the basal and crestal portion of bony crypts by the 15th day of the experiment. Second molars emerged into the oral cavity on the 15th day, but no eruption of first molars was observed until the 20th day. Throughout the experiment, first molars exhibited appreciable root deformity, which was less severe in second molars. Delayed eruption of first molars was thought to be related to the severity of the disturbance of root formation.

Autonomous control of expression of genes for insulin-like growth factors during the proliferation and differentiation of C2C12 mouse myoblasts in serum-free culture

The proliferation and differentiation of skeletal muscle cells in culture are usually controlled by serum components, and the differentiation can be induced by a reduction in the serum concentration. Insulin-like growth factors (IGFs) play a critical role in stimulating myoblast differentiation, and the expression of their genes is controlled by serum factors. We have found that C2C12 myoblasts are capable of proliferation and differentiation even in serum-free medium that does not contain peptide mitogens. During these processes in serum-free medium, the accumulation of mRNAs for IGFs in the cells was observed; and their levels increased with concomitant increases in creatine kinase activity and myotube formation and a decrease in DNA synthesis. Thus, the present results suggest that proliferation and differentiation of C2C12 cells are autonomously controlled and that the increase in the expression of the IGFs may be independent of exogenous components.

Effects of a synthetic N-terminal fragment of stanniocalcin on the metabolism of mammalian bone in vitro

A synthetic peptide corresponding to the N-terminal amino acid residues of stanniocalcin (STC1-20) and including a region that is known to be an active site in teleosts was prepared and tested for its effects on the metabolism of mammalian bone in vitro. STC1-20 (10(-10)-10(-12) M) inhibited increases in the number of tartrate-resistant acid phosphatase-positive, multinucleated cells promoted by an N-terminal fragment of human parathyroid hormone (hPTH1-34) in cultures of murine hemopoietic cells. STC1-20 also slightly decreased the rate of loss of radioactivity from calvariae of fetal rats that had been prelabeled with 45Ca, both with and without stimulation by hPTH1-34. The accumulation of cAMP induced by hPTH1-34 in ROS 17/2.8-5 cells was suppressed by STC1-20 (10(-10)-10(-12) M). Treatment with STC1-20 (10(-11)-10(-13) M) caused increases of the rate of incorporation of [3H]proline into the collagenase-digestible protein of calvariae in newborn mice. From these results, it appears that STC1-20 has diverse effects on the metabolism of mammalian bone, causing a biphasic response. Such effects have not been observed with intact stanniocalcin or with materials from the corpuscles of Stannius and they are also different from the effects of hPTH1-34.

Effects of 17 beta-oestradiol and 5 alpha-dihydrotestosterone on the expression of the muscle and heart types of lactate dehydrogenase isozymes in the masseter muscle of developing mice

17 beta-oestradiol (E2) and/or 5 alpha-dihydrotestosterone (5 alpha-DHT) had no effect on the expression of isozymes of lactate dehydrogenase (LDH) in the masseter muscle of intact male mice. However, treatment with E2 restored the level of the muscle (M) type of LDH isozyme, which had been reduced by testectomy, to that found in intact male mice treated with vehicle only. Moreover, 5 alpha-DHT alone was more effective than E2 in increasing the relative level of this isozyme in testectomized mice. 5 alpha-DHT had a more significant effect on the increase in the relative level of the M-type LDH isozyme when combined with E2. These results suggest that androgens promote, in the presence of oestrogens, the postnatal changes in the characteristics of the masseter muscle of developing male animals.