Regulatory mechanisms of osteoblast and osteoclast differentiation

Cellular, molecular, and tissue-level reactions to orthodontic force

Remodeling changes in paradental tissues are considered essential in effecting orthodontic tooth movement. The force-induced tissue strain produces local alterations in vascularity, as well as cellular and extracellular matrix reorganization, leading to the synthesis and release of various neurotransmitters, cytokines, growth factors, colony-stimulating factors, and metabolites of arachidonic acid. Recent research in the biological basis of tooth movement has provided detailed insight into molecular, cellular, and tissue-level reactions to orthodontic forces. Although many studies have been reported in the orthodontic and related scientific literature, a concise convergence of all data is still lacking. Such an amalgamation of the rapidly accumulating scientific information should help orthodontic clinicians and educators understand the biological processes that underlie the phenomenon of tooth movement with mechanics (removable, fixed, or functional appliances). This review aims to achieve this goal and is organized to include all major findings from the beginning of research in the biology of tooth movement. It highlights recent developments in cellular, molecular, tissue, and genetic reactions in response to orthodontic force application. It reviews briefly the processes of bone, periodontal ligament, and gingival remodeling in response to orthodontic force. This review also provides insight into the biological background of various deleterious effects of orthodontic forces.

Osteoclastic activity begins early and increases over the course of bone healing

Osteoclasts are specialised bone-resorbing cells. This particular ability makes osteoclasts irreplaceable for the continual physiological process of bone remodelling as well as for the repair process during bone healing. Whereas the effects of systemic diseases on osteoclasts have been described by many authors, the spatial and temporal distribution of osteoclasts during bone healing seems to be unclear so far. In the present study, healing of a tibial osteotomy under standardised external fixation was examined after 2, 3, 6 and 9 weeks (n = 8) in sheep. The osteoclastic number was counted, the area of mineralised bone tissue was measured histomorphometrically and density of osteoclasts per square millimetre mineralised tissue was calculated. The osteoclastic density in the endosteal region increased, whereas the density in the periosteal region remained relatively constant. The density of osteoclasts within the cortical bone increased slightly over the first 6 weeks, however, there was a more rapid increase between the sixth and ninth weeks. The findings of this study imply that remodelling and resorption take place already in the very early phase of bone healing. The most frequent remodelling process can be found in the periosteal callus, emphasising its role as the main stabiliser. The endosteal space undergoes resorption in order to recanalise the medullary cavity, a process also started in the very early phase of healing at a low level and increasing significantly during healing. The cortical bone adapts in its outward appearance to the surrounding callus structure. This paradoxic loosening is caused by the continually increasing number and density of osteoclasts in the cortical bone ends. This study clearly emphasises the osteoclastic role especially during early bone healing. These cells do not simply resorb bone but participate in a fine adjusted system with the bone-producing osteoblasts in order to maintain and improve the structural strength of bone tissue.

Cytokine pattern determines the progression of experimental periodontal disease induced by Actinobacillus actinomycetemcomitans through the modulation of MMPs, RANKL, and their physiological inhibitors

OBJECTIVE

Inflammatory and immune reactions raised in response to periodontopathogens are thought to trigger periodontal tissue destruction. We therefore investigated the expression of matrix metalloproteinases (MMPs) and the osteoclastogenic factor RANKL (receptor activator of nuclear factor-kappaB ligand), their respective inhibitors TIMPs (tissue inhibitors of metalloproteinases) and OPG (osteoprotegerin) and their possible correlation with the expression of inflammatory and regulatory cytokines in the course of experimental periodontal disease in mice.

METHODS

We characterized the time course of leukocyte migration and alveolar bone loss in C57BL/6 mice infected with Actinobacillus actinomycetemcomitans. Quantitative polymerase chain reaction (RealTime PCR) and ELISA were performed to determine the expression of MMPs, TIMPs, RANKL, OPG and cathepsin K, interleukin-1beta, tumor necrosis factor-alpha, interferon-gamma, interleukin-12, interleukin-4 and interleukin-10 in periodontal tissue samples harvested throughout the course of experimental disease.

RESULTS

Oral inoculation of A. actinomycetemcomitans results in an intense and widespread migration of leukocytes to the gingival tissues, besides marked alveolar bone resorption. Our data also demonstrate two distinct patterns of MMP/TIMP and RANKL/OPG expression in the course of experimental periodontal disease. The expression of MMPs (MMP-1, 2 and 9) and RANKL was correlated with the expression of interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma, in a time period characterized by the intense increase of inflammatory reaction and alveolar bone loss. On the other hand, interleukin-4 and interleukin-10 were associated with higher expression of TIMPs (TIMP 1, 2 and 3) and OPG, with a lower expression of MMPs and RANKL, and with reduced rates of increase of cellular infiltration in periodontal tissues and alveolar bone loss.

CONCLUSIONS

It is possible that the pattern of cytokines produced in periodontal tissues determines the progression and the severity of experimental periodontal disease, controlling the breakdown of soft and bone tissues through the balance between MMPs/TIMP and RANKL/OPG expression in gingival tissues.

Transforming growth factor-beta stimulates Interleukin-11 production by human periodontal ligament and gingival fibroblasts

BACKGROUND

Transforming growth factor (TGF)-beta is a potent multifunctional polypeptide, abundant in the bone matrix. Interleukin (IL)-11 is a pleiotropic cytokine with effects on multiple cell types. The present study was performed to evaluate the regulatory effects of TGF-beta on IL-11 production by human periodontal ligament cells (PDL) and human gingival fibroblasts (HGF).

MATERIAL AND METHODS

The expression of TGF-beta receptor in PDL and HGF were observed using flow cytometry. PDL and HGF were stimulated with TGF-beta with or without protein kinase C (PKC) inhibitors and activator. IL-11, bone morphogenetic protein-2 (BMP-2) and TGF-beta mRNA expression was quantified by real-time polymerase chain reaction (PCR). IL-11 production was measured using enzyme-linked immunosorbent assay.

RESULTS

PDL and HGF expressed both TGF-beta receptor I and TGF-beta receptor II on the cell surfaces. IL-11 mRNA expression and IL-11 production were augmented by TGF-beta in both PDL and HGF, with higher values in PDL. PKC inhibitors partially suppressed TGF-beta-induced IL-11 production in PDL and HGF, whereas activator enhanced it. TGF-beta mRNA and BMP-2 mRNA expression were up-regulated by TGF-beta in PDL.

CONCLUSION

These results suggest that PDL produce IL-11 in response to TGF-beta.

Osteoprotegerin (OPG) and RANKL expression and distribution in developing human craniomandibular joint

During embryogenesis the bone tissue of craniomandibular joint (CMJ) is formed through two pathways: intramembranous ossification and endochondral ossification. The development process is under the control of regulatory factors. The osteoprotegerin (OPG) and the receptor activator of nuclear factor (NF)-kappaB ligand are key regulators of osteoclastogenesis. The aim of this study is the localization of OPG and RANKL mRNA and protein in the foetal CMJ by immunohistochemistry (IHC) and in situ hybridization (ISH). The main results were: OPG and RANKL mRNA and protein were co-localized in the same cell types; OPG and RANKL were specially immunolocated in osteogenic cells; immunolabeling was often seen in the nucleus and cytoplasm of otherwise negative hypertrophic chondrocytes; IHC and ISH labeling decreased from proliferative to hypertrophic chondrocytes; early osteocytes showed dual protein expression and some of the mature osteocytes were ISH-negative; periosteal osteoclasts and chondroclasts were mostly stained by IHC and variably labeled by ISH; the new bone matrix and trabecular borders showed intense immunolabeling. The co-expression of OPG and RANKL in the same bone cell types confirms their strictly coupled action in the regulation of bone metabolism in the CMJ development and their extracellular presence in the new bone matrix and trabecular borders suggests a local regulatory role.

Comparative appraisal of clodronate, aspirin and dexamethasone as agents reducing alendronate-induced inflammation in a murine model

Among the bisphosphonates, the nitrogen-containing bisphosphonates have much stronger anti-bone-resorptive activities than bisphosphonates containing no nitrogen, but nitrogen-containing bisphosphonates mostly have inflammatory side effects. Our previous murine-model experiments with a single intraperitoneal bisphosphonate injection demonstrated that (i) nitrogen-containing bisphosphonates induce various inflammatory reactions via an IL-1-dependent mechanism, (ii) alendronate (an nitrogen-containing bisphosphonate) produces a clear sclerotic line in the tibia that is easily detectable by radiography a few weeks later (tentatively called the bisphosphonate line, a useful marker for the anti-bone-resorptive activities of bisphosphonates), and (iii) clodronate (a non-nitrogen-containing bisphosphonate) reduces the inflammatory reactions induced by alendronate but does not reduce the bisphosphonate line formation induced by alendronate. We compared the effects of clodronate, aspirin and dexamethasone on the inflammatory reactions induced by alendronate (40 micromol/kg) (induction of the histamine-forming enzyme, accumulation of pleural exudate and splenomegaly) and on the bisphosphonate line formation induced by alendronate (0.1 micromol/kg). The effects of aspirin (833 micromol/kg) were weak. However, like clodronate, dexamethasone (10 micromol/kg, injected 5 min. after alendronate), strongly inhibited the alendronate-induced inflammatory reactions but did not reduce the alendronate-induced bisphosphonate line formation. Alendronate produced normal bisphosphonate lines in IL-1-deficient mice, too. These results suggest that clodronate and/or dexamethasone may be suitable for preventing or reducing the inflammatory side effects of nitrogen-containing bisphosphonates while preserving their powerful anti-bone-resorptive activities (although in practice the known side effects of dexamethasone may limit its use), and that the anti-bone resorptive activities of nitrogen-containing bisphosphonates are not influenced by IL-1.

Biological factors involved in the osseointegration of oral titanium implants with different surfaces: a pilot study in minipigs

BACKGROUND

The stability of titanium implants is determined by the rigid load-bearing connections that are formed by the bone, a process that involves a complex network of cells, pro- and anti-inflammatory mediators, and growth factors. The osseointegration processes at the interfaces of machined and porous implants were studied using molecular and histological techniques.

METHODS

Two machined and two porous titanium implants were inserted into the tibiae of four minipigs. The animals were sacrificed at 15, 30, 60, and 90 days post-implantation. The levels of bone morphogenetic protein (BMP)-4, transforming growth factor (TGF)-beta1, and tumor necrosis factor (TNF)-alpha were quantified in the peri-implant osseous samples. The levels of interleukin (IL)-1beta, IL-6, IL-10, and TNF-alpha in the serum were also assessed.

RESULTS

Histomorphological analysis showed evidence of bone ossification around the porous implant at 60 days. Surrounding the machined implants, highly sclerotic fibrous pads started the healing response at 90 days, and the levels of TGF-beta1 and BMP-4 began to increase at 60 days, at which time bone ossification around the porous implants was already evident. TNF-alpha was not present in the bone next to the implants. The serum levels of cytokines IL-1beta, IL-6, and IL-10 were not increased. The serum level of TNF-alpha increased during the healing process.

CONCLUSIONS

We observed that the levels of BMP-4 and TGF-beta1, which play essential roles in the osteogenesis process, increased earlier around the porous implants than around the machined implants. Similarly, the ossification process was initiated earlier at the surfaces of the porous implants than at the surfaces of the machined implants.

2-methoxyestradiol inhibits differentiation and is cytotoxic to osteoclasts

2-Methoxyestradiol (2-ME), a naturally occurring metabolite of 17beta-estradiol, is highly cytotoxic to a wide range of tumor cells but is harmless to most normal cells. However, 2-ME prevented bone loss in ovariectomized rats, suggesting it inhibits bone resorption. These studies were performed to determine the direct effects of 2-ME on cultured osteoclasts. 2-ME (2 microM) reduced osteoclast number by more than 95% and induced apoptosis in three cultured osteoclast model systems (RAW 264.7 cells cultured with RANKL, marrow cells co-cultured with stromal support cells, and spleen cells cultured without support cells in media supplemented with RANKL and macrophage colony stimulating factor (M-CSF)). The 2-ME-mediated effect was ligand specific; 2-hydroxyestradiol (2-OHE), the immediate precursor to 2-ME, exhibited less cytotoxicity; and 2-methoxyestrone (2-MEOE1) the estrone analog of 2-ME, was not cytotoxic. Co-treatment with ICI 182,780 did not antagonize 2-ME, suggesting that the cytotoxicity was not estrogen receptor-dependent. 2-ME-induced cell death in RAW 264.7 cells coincided with an increase in gene expression of cytokines implicated in inhibition of differentiation and induction of apoptosis. In addition, the 2-ME-mediated decrease in cell survival was partially inhibited by anti-lymphotoxin(LT)beta antibodies, suggesting that 2-ME-dependent effects involve LTbeta. These results suggest that 2-ME could be useful for treating skeletal diseases in which bone resorption is increased, such as postmenopausal osteoporosis and cancer metastasis to bone.

T-cell cytokine induction of BMP-2 regulates human mesenchymal stromal cell differentiation and mineralization

How T-cells, attracted to local sites of inflammation in arthritides, affect heterotopic ossification is presently unknown. Here, we tested the hypothesis that T-cell cytokines play a role in the differentiation of human mesenchymal stromal cells (HMSC) into the osteoblast phenotype by inducing autologous BMP-2, providing a possible mechanism for heterotopic ossification. HMSC from multiple donor bones were treated with either activated T-cell conditioned medium (ACTTCM) or physiological concentrations of the major inflammatory cytokines, TNF-alpha, TGF-beta, IFN-gamma, and IL-17 (TTII), individually or in combinations. ACTTCM induced BMP-2 protein in a time-dependent manner over a 48 h period and alkaline phosphatase (AlkP) within 7 days. In combination, TTII, like ACTTCM, induced AlkP and synergistically induced BMP-2 protein. Either individually, or in combinations of up to three, the T-cell cytokines failed to induce BMP-2 above control levels while a combination of all four cytokines synergistically induced BMP-2 10-fold as assessed by ELISA. TTII induced mineralized matrix as effectively as dexamethasone. Inhibition of p38 MAPK completely inhibited TTII-induced BMP-2 production and matrix mineralization. Real time RT-PCR analysis demonstrated a striking early (within 4 h) increase in BMP-2 gene expression by TTII, which was suppressed by p38 MAP kinase inhibition. In localized chronic inflammatory diseases, T-cell cytokines released at localized sites of inflammation may be the driving force for differentiation of local mesenchymal stromal cells into the osteoblast phenotype thereby playing a significant role in the heterotopic ossification observed in these diseases.

Quercetin, a bioflavonoid, accelerates TNF-α-induced growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells

The bioflavonoid quercetin is believed to play an important role in preventing bone loss by affecting osteoclastogenesis and regulating many systemic and local factors including hormones and cytokines. This study examined how quercetin acts on tumor necrosis factor-alpha (TNF-alpha)-mediated growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells. Tritium uptake assay showed that a quercetin treatment accelerated TNF-alpha-induced inhibition of DNA synthesis in the cells in a dose-dependent manner. Both the 3-(4,5-dimethylthiazol-2yl-)-2,5-diphenyl tetrazolium bromide and trypan blue staining assays also showed the quercetin-mediated facilitation of TNF-alpha-induced cytotoxicity in the cells. Apoptosis assays revealed an accelerating effect of quercetin on TNF-alpha-induced apoptosis in MC3T3-E1 cells. In addition, Fas activation and poly (ADP ribose) polymerase cleavage are thought to be closely associated with the TNF-alpha-induced apoptosis and its acceleration by the quercetin treatment in the cells. Collectively, this study showed that quercetin accelerates the TNF-alpha-induced growth inhibition and apoptosis in MC3T3-E1 osteoblastic cells.

Functional Dissection of Osteoprotegerin and Its Interaction with Receptor Activator of NF-κB Ligand

The receptor activator of NF-kappaB (RANK) belongs to the neuregulin/tumor necrosis factor (TNF) receptor superfamily and is activated by RANK ligand (RANK-L), a homotrimeric, TNF-like cytokine. RANK is present on the surface of osteoclast cell precursors, where its interaction with RANK-L induces their terminal differentiation into osteoclasts, thus increasing bone breakdown. The secreted, soluble receptor osteoprotegerin (OPG) interrupts this activation by binding directly to RANK-L. Therefore, osteoclast maturation (and bone homeostasis) is regulated in vivo by OPG levels of expression. We have studied the assembly state and affinity of OPG for RANK-L by sedimentation analyses and surface plasmon resonance (Biacore). Full-length, homodimeric OPG binds to RANK-L with a KD of 10 nM. OPG is also a member of the TNF receptor superfamily and contains four disulfide-rich ligand-binding domains, yet lacks a transmembrane region separating the ligand-binding region from the two death domains, as observed for other receptor family members. We showed that dimerization of OPG results from noncovalent interactions mediated by the death domains and to a lesser extent by a C-terminal heparin-binding region. In contrast, a C-terminal intermolecular disulfide bond does not contribute to the formation or stability of OPG dimers. A truncate of osteoprotegerin, containing the ligand-binding domains but lacking the dimerization domains, bound RANK-L with a KD of approximately 3 microM, indicating that monomer oligomerization for the OPG provides an increase of 3 orders of magnitude in the affinity for RANK-L. Therefore, OPG dimer formation is required for the mechanism of inhibition of the RANK-L/RANK receptor interaction.

Interaction of Fas Ligand and Fas Expressed on Osteoclast Precursors Increases Osteoclastogenesis

We incidentally found that osteoclast precursors and mature osteoclasts express Fas ligand (FasL) as well as Fas, which was confirmed by flow cytometry, immunofluorescent staining, and RT-PCR. The aim of this study was to determine the role of FasL in differentiation and cell death of osteoclasts. To study the role of FasL in osteoclastogenesis, neutralizing anti-FasL mAb or rFasL was added during receptor activator of NF-kappaB ligand (RANKL)-induced osteoclastogenesis using bone marrow-derived macrophages. Neutralization of endogenous FasL by anti-FasL mAb decreased osteoclastogenesis, whereas rFasL enhanced osteoclast differentiation in a dose-dependent manner. In addition, rFasL up-regulated the secretion of osteoclastogenic cytokines, such as IL-1beta and TNF-alpha, and the activation of NF-kappaB. Functional blocking of IL-1beta and TNF-alpha using IL-1 receptor antagonist and soluble TNFR confirmed that those cytokines mediated the effect of FasL on osteoclastogenesis. The osteoclast precursors were relatively resistant to rFasL-induced apoptosis especially before RANKL treatment, resulting in minimal cell loss by rFasL treatment during osteoclastogenesis. Although rFasL increased the cell death of mature osteoclasts, growth factor withdrawal induced much more cell death. However, anti-FasL mAb did not affect the survival of mature osteoclasts, suggesting that the endogenous FasL does not have a role in the apoptosis of osteoclasts. Finally, in contrast to the effect on apoptosis, rFasL-assisted osteoclastogenesis was not mediated by caspases. In conclusion, FasL has a novel function in bone homeostasis by enhancing the differentiation of osteoclasts, which was not considered previously.

Genetic Control of the Immune Response in Pathogenesis

BACKGROUND

Epidemiological studies have suggested that there is a genetic component to susceptibility to chronic periodontitis. Studies in humans and in animal models have suggested that some of the important components may be polymorphisms in key immunological genes.

METHODS

This paper summarizes previously published data from a mouse model in which alveolar bone loss is induced by oral infection with Porphyromonas gingivalis. Mice of different inbred immune-normal strains were used, as well as the F1 heterozygotes from crosses between strains. In addition, tissue expression of an array of immunological genes was measured in the gingiva and spleen of these mice by quantitative reverse transcription-polymerase chain reaction (QPCR).

RESULTS

Not all strains of mice are susceptible to bone loss. Intercross experiments demonstrate that susceptibility is an inherited trait. A subset of immunological genes tested showed differential basal expression in the gingiva or spleens (or both). Tumor necrosis factor and osteoprotegerin mRNAs are more highly expressed in the gingiva and interleukin-1 mRNA is more highly expressed in both the gingiva and the spleens of susceptible mice than resistant mice. In the resistant mice, interleukin-15 mRNA in the gingiva and Selp mRNA in the spleen are present at higher levels. In the resistant mice no genes changed expression after P. gingivalis infection, while mRNA for interleukin-1, osteoprotegerin, and STAT6 all increased in the susceptible mice.

CONCLUSIONS

Susceptibility and resistance are heritable traits. Strain differences in basal mRNA expression correlate with differences in susceptibility. Genes that change expression in response to infection also correlate with differences in susceptibility.

Manipulation of the anabolic and catabolic responses with OP-1 and zoledronic acid in a rat critical defect model

Bone repair involves both anabolic and catabolic responses. We hypothesized that anabolic treatment with OP-1 (BMP-7) and anti-catabolic treatment with zoledronic acid could be synergistic. In a rat critical defect, this combination therapy produced significant increases in new bone volume and strength.

INTRODUCTION

When used to augment bone healing, osteogenic protein 1 (OP-1/BMP-7) and other BMPs stimulate the anabolic response, inducing osteoblast recruitment, differentiation, and bone production. However, BMPs can also upregulate catabolism by direct stimulation of osteoclasts and indirectly by osteoblasts through RANKL/RANK. We hypothesized that if such osteoclastic upregulation were modulated by zoledronic acid (ZA), the combination of OP-1 and ZA should produce increased new bone over OP-1 alone.

MATERIALS AND METHODS

Rats with a surgically induced 6-mm femoral critical size defect were separated into five dosing groups: Carrier, Carrier + ZA, OP-1, OP-1 + ZA, and OP-1 + ZA administered 2 weeks after surgery (2W). Carrier +/- 50 microg OP-1 was placed in the defect, and 0.1 mg/kg ZA or saline was administered subcutaneously. Bone repair was analyzed by radiographs, QCT, mechanical testing, histology, and histomorphometry.

RESULTS

Carrier alone and Carrier ZA groups did not unite by 8 weeks. Radiological union occurred in all OP-1 groups but was tenuous in some animals treated with OP-1 alone. BMC was increased by 45% in the OP-1 ZA group and 96% in the OP-1 ZA 2W group over OP-1 alone (p < 0.01). Callus volume increased over OP-1 alone by 45% and 86% in the OP-1 ZA and OP-1 ZA 2W groups, respectively (p < 0.01). The increased callus volume in the OP-1 ZA 2W group translated to increases in strength of 107% and stiffness of 148% (p < 0.05). BFR was not significantly different between OP-1 groups regardless of ZA treatment.

CONCLUSIONS

ZA treatment significantly increased the BMC, volume, and strength of OP-1-mediated callus in a critical size defect in rats at 8 weeks. Thus, modulation of both anabolic and catabolic responses may optimize the amount and mineral content of callus produced, which could be of clinical benefit in obtaining bone union.

High-dose fish oil and antioxidants in Crohn's disease and the response of bone turnover: a randomised controlled trial

Crohn's disease is associated with altered bone turnover that may be influenced by nutritional status, the systemic inflammatory response, cytokine production by circulating (peripheral blood) mononuclear cells (PBMC) and antioxidant micronutrient intake. High-dose fish oil is associated with reductions in disease relapse and inflammatory markers, and modulates PBMC function. The effect of fish oil plus antioxidants on bone turnover and PBMC function (the production of interferon-gamma and prostaglandin E2) in Crohn's disease was investigated in a randomised-controlled trial. Patients with currently or recently raised biochemical markers of inflammation (C-reactive protein > or = 6.9 mg/l or erythrocyte sedimentation rate > or =18 mm/h) received fish oil (providing 2.7 g/d EPA and DHA) and antioxidants (vitamins A, C and E, and Se) (n 31) or placebo (n 30) for 24 weeks. Bone turnover was assessed by measuring the concentrations of urinary deoxypyridinoline (bone resorption) and serum osteocalcin (bone formation). Fish oil plus antioxidants were associated with increases in EPA, DHA Se in plasma (all P < 0.01), and with a reduction in interferon-gamma production by mitogen-stimulated PBMC, which demonstrated a negative correlation with deoxypyridinoline/creatinine:osteocalcin ratio (r - 0.33, P = 0.009). There were no differences between the groups at 24 weeks in the response of deoxypyridinoline or osteocalcin or their ratio, or in nutritional status. Dietary supplementation in Crohn's disease with high intakes of EPA and DHA, as fish oil, plus antioxidants was associated with a modulated production of interferon-gamma by PBMC but not altered indices of bone turnover.

Selective Runx2-II deficiency leads to low-turnover osteopenia in adult mice

Runx2 transcribes Runx2-II and Runx2-I isoforms with distinct N-termini. Deletion of both isoforms results in complete arrest of bone development, whereas selective loss of Runx2-II is sufficient to form a grossly intact skeleton with impaired endochondral bone development. To elucidate the role of Runx2-II in osteoblast function in adult mice, we examined heterozygous Runx2-II (Runx2-II(+/-)) and homozygous Runx2-II (Runx2-II(-/-))-deficient mice, which, respectively, lack one or both copies of Runx2-II but intact Runx2-I expression. Compared to wild-type mice, 6-week-old Runx2-II(+/-) had reduced trabecular bone volume (BV/TV%), cortical thickness (Ct.Th), and bone mineral density (BMD), decreased osteoblastic and osteoclastic markers, lower bone formation rates, impaired osteoblast maturation of BMSCs in vitro, and significant reductions in mechanical properties. Homozygous Runx2-II(-/-) mice had a more severe reduction in BMD, BV/TV%, and Ct.Th, and greater suppression of osteoblastic and osteoclastic markers than Runx2-II(+/-) mice. Non-selective Runx2(+/-) mice, which have an equivalent reduction in Runx2 expression due to the lack one copy of Runx2-I and II, however, had an intermediate reduction in BMD. Thus, selective Runx2-II mutation causes diminished osteoblastic function in an adult mouse leading to low-turnover osteopenia and suggest that Runx2-I and II have distinct functions imparted by their different N-termini.

Treatment of senile osteoporosis in SAMP6 mice by intra-bone marrow injection of allogeneic bone marrow cells

A substrain of the senescence-accelerated mouse, SAMP6 (senescence-accelerated mouse prone 6), spontaneously develops osteoporosis early in life. Therefore, this strain is a useful animal model for developing new strategies for the treatment of osteoporosis in humans. We succeeded in treating osteoporosis in SAMP6 mice after the onset of this disease, using a newly developed method of bone marrow transplantation (BMT): Allogeneic bone marrow cells obtained from normal mouse strains were directly injected into the bone marrow cavity of irradiated SAMP6 mice (intra-bone marrow BMT [IBM-BMT]). After the treatment with IBM-BMT, hematolymphoid cells were completely reconstituted by donor-derived cells, and bone marrow stromal cells were also found to be of donor origin. The treated SAMP6 mice showed histologically-normal trabecular bone. In addition, bone mineral density and urinary deoxypiridinoline, a hallmark of bone destruction, were normalized. When the message levels of cytokines (tumor necrosis factor alpha, interleukin-6 [IL-6], IL-11, and receptor activator of nuclear factor-kappa B ligand [RANKL]) were examined, IL-11, RANKL (from bone marrow stromal cells), and IL-6 (from osteoclasts), which regulate bone remodeling, were restored to levels similar to those in normal B6 mice. These findings indicate that not only the hemopoietic system but also the bone marrow microenvironment were normalized after IBM-BMT, resulting in an amelioration of the imbalance between bone absorption and formation.

Adiponectin increases bone mass by suppressing osteoclast and activating osteoblast

Adiponectin, an adipose-derived hormone, exhibits various biological functions, such as increasing insulin sensitivity, protecting hypertension, and suppression of atherosclerosis, liver fibrosis, and tumor growth. Here, we report the role of adiponectin on bone metabolism. C57BL/6J mice were treated with adenovirus expressing lacZ or adiponectin, and their bones were analyzed by three-dimensional microcomputed tomography. Adiponectin-adenovirus treatment increased trabecular bone mass, accompanied by decreased number of osteoclasts and levels of plasma NTx, a bone-resorption marker. In vitro studies showed that adiponectin inhibited M-CSF- and RANKL-induced differentiation of mouse bone marrow macrophages and human CD14-positive mononuclear cells into osteoclasts and also suppressed the bone-resorption activity of osteoclasts. Furthermore, adiponectin enhanced mRNA expression of alkaline phosphatase and mineralization activity of MC3T3-E1 osteoblasts. Our results indicate that adiponectin exerts an activity to increase bone mass by suppressing osteoclastogenesis and by activating osteoblastogenesis, suggesting that adiponectin manipulation could be therapeutically beneficial for patients with osteopenia.

Annexin II stimulates RANKL expression through MAPK

We report that AX-II, in addition to inducing GM-CSF expression, also increases membrane-bound RANKL synthesis by marrow stromal cells and does so through a previously unreported MAPK-dependent pathway. Thus, both GM-CSF and RANKL are required for AX-II stimulation of OCL formation.

INTRODUCTION

Annexin II (AX-II) is an autocrine/paracrine factor secreted by osteoclasts (OCLs) that stimulates human OCL formation and bone resorption in vitro by inducing bone marrow stromal cells and activated CD4+ T cells to produce granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF in turn increases OCL precursor proliferation and further enhances OCL formation. However, the induction of GM-CSF by AX-II cannot fully explain its effects on OCL formation. In this study, we tested the capacity of AX-II to induce the expression of RANKL and the corresponding signaling pathways AX-II employs in human marrow stromal cells to induce RANKL. We also showed that both GM-CSF and RANKL are required for OCL formation induced by AX-II.

MATERIALS AND METHODS

Real-time RT-PCR and Western blot analysis were used to detect RANKL and osteoprotegerin (OPG) mRNA and protein expression in unfractionated human bone marrow mononuclear cells stimulated with AX-II. Soluble RANKL in the conditioned medium was analyzed by ELISA. Activation of the MAPK pathway by AX-II was tested by Western blot. The effects of OPG and anti-GM-CSF on AX-II-induced OCL formation were also examined.

RESULTS AND CONCLUSION

In addition to upregulating GM-CSF mRNA, AX-II increased RANKL mRNA expression dose-dependently in unfractionated human bone marrow mononuclear cells and modestly increased soluble RANKL in unfractionated human bone marrow mononuclear cell conditioned medium. However, AX-II markedly increased membrane-bound RANKL on human bone marrow stromal cells. Treatment of marrow stromal cells with AX-II activated MAP-kinase (ERKs) and PD 98059 abolished the effect but did not block the increase in GM-CSF. Interestingly, OPG, a natural decoy receptor for RANKL, or anti-GM-CSF partially inhibited OCL formation by AX-II in human bone marrow cells, and the combination of OPG and anti-GM-CSF completely blocked AX-II-induced OCL formation. These data show that AX-II stimulates both the proliferation and differentiation of OCL precursors through production of GM-CSF and RANKL respectively.

RANK ligand and TNF-alpha mediate acid-induced bone calcium efflux in vitro

Chronic metabolic acidosis stimulates net calcium efflux from bone due to increased osteoclastic bone resorption and decreased osteoblastic collagen synthesis. Previously, we determined that incubation of neonatal mouse calvariae in medium simulating physiological metabolic acidosis leads to a significant, cyclooxygenase-dependent, increase in RNA for bone cell receptor activator of NF-kappaB ligand (RANKL) compared with incubation in neutral pH medium. In this study, we tested the hypothesis that the acid-mediated increase in RANKL expression is a primary mechanism for the stimulated osteoclastic resorption. Acid medium increased the medium concentration of sRANKL without altering the concentration of the decoy receptor osteoprotegerin (OPG). Inhibition of the RANKL pathway with concentrations of OPG up to 25 ng/ml, far greater than physiological, did not significantly decrease the robust acid-induced Ca efflux from bone nor did incubation of the calvariae with a different inhibitor, RANK/Fc (up to 50 ng/ml). Thus acid-induced net Ca efflux appears to involve mechanisms in addition to the RANK/RANKL pathway. Osteoblasts also produce TNF-alpha, another cytokine that stimulates the maturation and activity of osteoclasts. Incubation of calvariae in acid medium caused a significant increase in TNF-alpha levels. Incubation of calvariae with anti-TNF (up to 250 ng/ml) did not significantly decrease acid-induced net Ca efflux. However, the combination of RANK/Fc plus anti-TNF caused a significant but subtotal reduction in acid-induced Ca efflux, whereas the combination of RANK/Fc plus an isotype-matched control for the anti-TNF had no effect on Ca release. Thus simultaneous inhibition of RANKL and TNF-alpha is necessary to reduce acid-induced, cell-mediated net Ca efflux from bone; however, additional osteoblast-produced factors must also be involved in acid-induced, cell-mediated bone resorption.

Collaborative action of M-CSF and CTGF/CCN2 in articular chondrocytes: possible regenerative roles in articular cartilage metabolism

It is known that expression of the macrophage colony-stimulating factor (M-CSF) gene is induced in articular chondrocytes upon inflammation. However, the functional role of M-CSF in cartilage has been unclear. In this study, we describe possible roles of M-CSF in the protection and maintenance of the articular cartilage based on the results of experiments using human chondrocytic cells and rat primary chondrocytes. Connective tissue growth factor (CTGF/CCN2) is known to be a potent molecule to regenerate damaged cartilage by promoting the growth and differentiation of articular chondrocytes. Here, we uncovered the fact that M-CSF induced the mRNA expression of the ctgf/ccn2 gene in those cells. Enhanced production of CTGF/CCN2 protein by M-CSF was also confirmed. Furthermore, M-CSF could autoactivate the m-csf gene, forming a positive feed-back network to amplify and prolong the observed effects. Finally, promotion of proteoglycan synthesis was observed by the addition of M-CSF. These findings taken together indicate novel roles of M-CSF in articular cartilage metabolism in collaboration with CTGF/CCN2, particularly during an inflammatory response. Such roles of M-CSF were further supported by the distribution of M-CSF producing chondrocytes in experimentally induced rat osteoarthritis cartilage in vivo.

[In vivo and in vitro bone regeneration from cord blood derived mesenchymal stem cells]

BACKGROUND

Mesenchymal stem cells with an osteoblastic differentiating potency are investigated in regard of probable tissue engineering for further clinical application. The following report describes the use of cord blood derived stem cells as an alternative to other stem cell populations for bone regenerating tissue engineering.

METHODS

To demonstrate the multipotency of cord blood derived mesenchymal stem cells, unrestringated somatic stem cells (USSC) were isolated from cord blood and underwent an osteo-, chondro- and adipoblastic in vitro stimulation. To evaluate the osteoinductive potency of a porcine collagen I/III cell carrier USSC were incubated on this matrix. To investigate the in vivo effects of human USSC an athymic rat model was developed. These cells were transplanted into a femoral defect.

RESULTS

Cord blood derived mesenchymal stem cells (USSC) have an in vitro multipotency and show adipo-, chondro- and osteogenic differentiation. The porcine collagen I/III carrier promoted an osteoblastic differentiation. USSC survived after xenotransplantation in an athymic rat and differentiated into osteoblasts filling the bony defect zone.

CONCLUSION

Human USSC are a mesenchymal multipotent stem cell population that shows osteoblastic differentiation onto a collagen I/III carrier in vitro as well as in an athymic rat in vivo.

Inhibitory effect of CGRP on osteoclast formation by mouse bone marrow cells treated with isoproterenol

The present study was designed to elucidate the mode of action of isoproterenol (Isp; adrenergic beta-agonist) and to characterize the effect of the calcitonin gene-related peptide (CGRP; sensory neuropeptide) on osteoclast formation induced by Isp in a mouse bone marrow culture system. Treatment of mouse bone marrow cells with Isp generated tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cells (MNCs) capable of excavating resorptive pits on dentine slices, and caused an increase in receptor activator of NF-kappaB ligand (RANKL) and a decrease in osteoprotegerin (OPG) production by the marrow cells. The osteoclast formation was significantly inhibited by OPG, suggesting the involvement of the RANKL-RANK system. CGRP inhibited the osteoclast formation caused by Isp or soluble RANKL (s-RANKL) but had no influence on RANKL or OPG production by the bone marrow cells treated with Isp, suggesting that CGRP inhibited the osteoclast formation by interfering with the action of RANKL produced by the Isp-treated bone marrow cells without affecting RANKL or OPG production. This in vitro data suggest the physiological interaction of sympathetic and sensory nerves in osteoclastogenesis in vivo.

Osteo-Promoter Database (OPD) -- promoter analysis in skeletal cells

Background

Increasing our knowledge about the complex expression of genes in skeletal tissue will provide a better understanding of the physiology of skeletal cells. The study summarizes transcriptional regulation factors interacting and cooperating at promoter regions that regulate gene expression. Specifically, we analyzed A/T rich elements along the promoter sequences.

Description

The Osteo-Promoter Database (OPD) is a collection of genes and promoters expressed in skeletal cells. We have compiled a new viewer, OPD, as unique database developed and created as an accessible tool for skeletal promoter sequences. OPD can navigate to identify genes specific to skeletal cDNA databases and promoter analysis sites. OPD offers exclusive access to facilitate a dynamic extraction of promoters' gene-specific analyses in skeletal tissue. The data on promoters included in OPD contains cloned promoters or predicted promoters that were analyzed by bioinformatics tools. OPD offers MAR-analysis, which allocates A/T rich elements along these promoter sequences.

Conclusion

The analysis leads to a better insight of proteins that bind to DNA, regulate DNA, and function in chromatin remodeling. The OPD is a distinctive tool for understanding the complex function of chromatin remodeling and transcriptional regulation of specific gene expression in skeletal tissue.

Comparison of Human Mandibular Osteoblasts Grown on Two Commercially Available Titanium Implant Surfaces

BACKGROUND

Surface characteristics play a major role in determining tissue response to implants and therefore their clinical outcome. The aim of the present study was to compare two commercially available titanium surfaces: plasma sprayed (TPS) and sand-blasted, acid-etched surface (SLA).

METHODS

The surfaces were characterized by roughness testing, scanning electronic microscopy (SEM), Raman spectroscopy, and protein adsorption to determine their microtopographic and chemical properties. The effect of the surfaces on human mandibular osteoblasts was then studied in terms of cell morphology, adhesion, proliferation, and differentiation. Human osteoblasts from the mandible were cultured on these two surfaces and evaluated at 3, 6, 24, and 48 hours to determine cell attachment and morphology. Growth and differentiation kinetics were subsequently investigated by evaluating cell growth, alkaline phosphatase activity, osteocalcin and osteoprotegerin production at 7, 14, and 21 days.

RESULTS

Although roughness was quite similar, the two surfaces presented strong differences in their topography, and cell morphology varied as a consequence. Osteoblasts on SLA appeared more elongated and spindle shaped than those on TPS, and their adhesion at 3 and 6 hours was weaker, but reached that of cells on TPS at hour 24. Cell proliferation was greater on SLA surfaces but differentiation parameters; i.e., alkaline phosphatase and osteocalcin, provided better results on TPS surfaces. Osteoprotegerin production was enhanced on TPS surfaces at days 14 and 21.

CONCLUSION

Although cells grown on both surfaces exhibited good adhesion capabilities, a well-differentiated osteoblastic phenotype, and maintained a clear proliferation potential, our study suggests that plasma-sprayed treatment offers a better performance than SLA by creating, at least in the early phases, better conditions for tissue healing.

Characterisation of cytosolic FK506 binding protein 12 and its role in modulating expression of Cbfa1 and osterix in ROS 17/2.8 cells

FK506 is a commonly used immunosuppressant that mediates its action by exclusively interacting with the cytosolic immunophilin, FK506 binding protein 12 (FKBP12). Although FK506-induced acute osteoporosis is now well recognised, its precise mode of action in osteoblasts remains unclear. Therefore, in the present study we characterised FKBP12 in osteoblasts and investigated the role of FK506 in modulating osteoblast-specific transcription factors, core-binding factor alpha1 (Cbfa1) and osterix gene expression in ROS 17/2.8 cells. RT-PCR, immunolocalisation and Western blotting studies were employed to identify and characterise FKBP12 in rat primary osteoblasts and osteoblast-like osteosarcoma ROS 17/2.8 cells. Western blotting extracts of these cells revealed the 12 kDa and hitherto unreported 10 kDa FKBP isoform that were immunolocalised predominantly to the cytosol. The transient exposure of ROS 17/2.8 cells to H2O2 (100 microM) was found to elevate FKBP12 mRNA after 10 min and protein expression after 24 h. Both PTH (10(-9) M) and 1,25 (OH)2D3 (Vitamin D3) (10(-7) M) suppressed FKBP12 protein expression. FK506 in the therapeutic range (25 nmol/L) suppressed expression of Cbfa1 and osterix mRNA. The inhibition of Cbfa1 isoforms II/III expression was evident at 30 min and the extent of inhibition was sustained at 6 h. Osterix inhibition was also seen after 30 min, however, it became maximal after 6 h. The dose-dependant inhibition of osterix in these cells, carried out using 1.25, 12.5 and 125 nmol/L of FK506 was maximal at 1.25 nmol/L. Cbfa1 isoforms II/III were also maximally inhibited at 1.25 nmol/L; interestingly, the inhibition became less marked at higher concentrations of FK506. Similar dose of FK506 was found to inhibit ROS 17/2.8 cell proliferation; the inhibitory effect however was greater in insulin-stimulated cells. The results of this study suggest that immunosuppressant-induced osteoporosis, which is known to involve accelerated bone resorption by increase in osteoclastogenesis, may in fact also be accentuated by the inhibition of osteoblast differentiation and function.

Effects of bone morphogenetic protein-2 and transforming growth factor beta1 on gene expression of transcription factors, AJ18 and Runx2 in cultured osteoblastic cells

Osteoblast differentiation is controlled by multiple transcription factors, Runx2, AJ18, Osterix, Dlx5 and Msx2. The mechanisms of regulation of AJ18 mRNA expression by the transforming growth factor beta (TGF-beta) superfamily remain poorly understood. However, it is known that BMP-2 induces differentiation of C26 cells into more mature osteoblastic cells. The present study, using Northern blot and real-time reverse transcription polymerase chain reaction analyses, investigated the effects of bone morphogenetic protein-2 (BMP-2) and TGF-beta1 on mRNA expression of AJ18 and Runx2 in a clonal osteoblast precursor cell line ROB-C26 (C26) cultured for 3, 6 or 9 days in the presence or absence of BMP-2. Although mRNA expression of Osterix and bone sialoprotein (BSP) was undetectable in the C26 culture, BMP-2 induced Osterix expression on days 3-9, but not BSP expression. BMP-2 also stimulated significantly Dlx5 expression on days 3-9, Msx2 and matrix Gla protein expressions on days 3 and 6, Runx2, alkaline phosphatase and osteocalcin expressions on days 6 and 9 in the culture. Furthermore, BMP-2 increased significantly Smad5 mRNA in the culture on day 3, indicating BMP-2 involvement in the regulation of Smad5 mRNA expression. In contrast, the inhibitory effects of BMP-2 on AJ18 mRNA expression were significant on days 3-9, indicating that a decrease in AJ18 mRNA expression is essential for the increased osteoblastic differentiation. Furthermore, TGF-beta1 (0, 0.1, 1.0 and 5.0 ng/ml) treatment of C26 cells cultured for 6 days in the presence or absence of BMP-2 for 24h stimulated mRNA levels of AJ18 and Runx2, maximal stimulation occurring principally at 1.0 ng/ml. These observations indicate that the expression of AJ18 and Runx2 mRNAs in C26 cells is under the control of BMP-2 and TGF-beta1, which exert different effects on AJ18 mRNA expression, but are potent stimulators of Runx2 mRNA expression during osteoblast differentiation.

Glucocorticoid-induced osteoporosis: from basic mechanisms to clinical aspects

Glucocorticoid (GC)-induced osteoporosis (GCOP) is the most common cause of osteoporosis in adults aged 20-45 years as well as the most common cause of iatrogenic osteoporosis. GC excess, either endogenous or exogenous, induces bone loss in 30-50% of cases. Indeed, bone loss leading to fractures is perhaps the most incapacitating, sometimes partially irreversible, complication of GC therapy. Nevertheless, GCOP is often underdiagnosed and left untreated. The following article provides an update on the cellular and molecular mechanisms implicated in the pathophysiology of GC-induced bone loss, as well as some guidelines on diagnostic, preventive and therapeutic strategies for this medical condition, in an effort to promote a better knowledge and greater awareness of GCOP by both the patient and the physician.

Fish oil and antioxidants alter the composition and function of circulating mononuclear cells in Crohn disease

BACKGROUND

Crohn disease (CD) is associated with osteoporosis and other extraintestinal manifestations that might be mediated by cytokines from circulating (peripheral blood) mononuclear cells (PBMCs). Fish oil rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) reduces disease activity in patients with CD with raised laboratory markers of inflammation and in healthy subjects alters PBMC function.

OBJECTIVE

We investigated the effect of fish oil plus antioxidants on cytokine production by PBMCs from patients with CD with raised C-reactive protein concentrations (>/=6.9 mg/L) or erythrocyte sedimentation rates (>/=18 mm/h).

DESIGN

A randomized placebo-controlled trial of fish oil (2.7 g EPA and DHA/d; n = 31) or placebo (olive oil; n = 31) for 24 wk was conducted in patients with CD. The fish-oil group additionally received an antioxidant preparation (vitamins A, C, and E and selenium). Exclusion criteria included corticosteroid use. Fatty acid composition was measured by gas chromatography. Production of tumor necrosis factor alpha, interferon gamma (IFN-gamma), and prostaglandin E(2) (PGE(2)) was measured by enzyme-linked immunosorbent assays after stimulation with mitogen and endotoxin (lipopolysaccharide).

RESULTS

Fish-oil plus antioxidant dietary supplementation was associated with higher EPA and DHA incorporation into PBMCs (P < 0.001) and lower arachidonic acid (P = 0.006) and lower production of IFN-gamma by mitogen-stimulated PBMCs (P = 0.012) and of PGE(2) by lipopolysaccharide-stimulated PBMCs (P = 0.047).

CONCLUSION

Dietary supplementation with fish oil plus antioxidants is associated with modified PBMC composition and lower production of PGE(2) and IFN-gamma by circulating monocytes or macrophages. The response of extraintestinal manifestations of CD should be investigated in a randomized controlled trial.

Induction of RANKL expression and osteoclast maturation by the binding of fibroblast growth factor 2 to heparan sulfate proteoglycan on rheumatoid synovial fibroblasts

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by progressive joint destruction. The aim of this study was to clarify the relevance of RA synovial fibroblasts (RASFs) and fibroblast growth factor 2 (FGF-2), which is produced abundantly by RASFs, to the osteoclastogenesis and bone resorption in RA.

METHODS

Synovial fibroblasts were prepared from the synovial tissues of 10 patients with active RA and 7 patients with osteoarthritis (OA). The expression of RANKL, intercellular adhesion molecule 1 (ICAM-1), FGF receptor 1 (FGFR-1), and heparan sulfate proteoglycan (HSPG) on synovial fibroblasts was measured by FACScan. Osteoclast formation in cocultures of RASFs and peripheral blood mononuclear cells (PBMCs) was evaluated by tartrate-resistant acid phosphatase staining and a pit-formation assay using dentin slices.

RESULTS

FGF-2 induced the expression of both RANKL and ICAM-1 on RASFs more so than on OA synovial fibroblasts (OASFs). FGF-2-induced up-regulation of RANKL and ICAM-1 was inhibited by anti-FGF-2 antibody. Although FGFR-1 was equally expressed on RASFs and OASFs, HSPG was highly expressed on RASFs. Up-regulation of RANKL by FGF-2 on RASFs was diminished by the removal of heparan sulfate with heparitinase. Osteoclast formation from PBMCs induced by RASFs was inhibited by the addition of either heparitinase, anti-ICAM-1 antibody, anti-FGF-2 antibody, or osteoprotegerin. FGF-2-induced RANKL on RASFs and osteoclast formation were suppressed by an inhibitor of ERK.

CONCLUSION

FGF-2 was transferred to FGFR-1 through binding to HSPG, which is characteristically expressed on RASFs, resulting in RANKL- and ICAM-1-mediated maturation of osteoclasts via ERK activation. Thus, we propose that FGF-2 not only augments the proliferation of RASFs, but also is involved in osteoclast maturation, which leads to bone destruction in RA.

Matrix metalloproteinases, their physiological inhibitors and osteoclast factors are differentially regulated by the cytokine profile in human periodontal disease

OBJECTIVE

Inflammatory reactions raised in response to periodontopathogens are thought to trigger pathways of periodontal tissue destruction. We therefore investigated the expression of matrix metalloproteinases (MMPs) and the osteoclastogenic factor receptor activator of nuclear factor-kappaB ligand (RANKL), their respective tissue inhibitors of metalloproteinases (TIMPs) and osteoprotegerin (OPG) in different forms of human periodontal diseases (PDs), and the possible correlation with the expression of inflammatory and regulatory cytokines.

MATERIAL AND METHODS

Quantitative polymerase chain reaction (real-time PCR) was performed with gingival biopsies mRNA from aggressive (AP) and chronic periodontitis (CP) patients.

RESULTS

Periodontitis patients exhibit higher expression of all analyzed factors when compared with healthy tissues. The expression of MMPs and RANKL were similar in AP and CP, as well as the expression of TNF-alpha. On the other hand, the expression of TIMPs and OPG was higher in CP, and was associated with lower IFN-gamma and higher IL-10 expression, compared with AP.

CONCLUSION

It is possible that the pattern of cytokines expressed determines the stable or progressive nature of the lesions and regulates the severity of PD, driving the balance between MMPs and TIMPs, RANKL and OPG expression in the gingival tissues controlling the breakdown of soft and bone tissues and, consequently, the disease severity.

Strategies for directing the differentiation of stem cells into the osteogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in bone reconstruction and bone tissue engineering. This will require well-defined and efficient protocols for directing the differentiation of stem cells into the osteogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages on transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying osteogenesis and bone development, and facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for bone-related biomaterials and drugs could also use protocols developed for the osteogenic differentiation of stem cells. This review critically examines the various strategies that could be used to direct the differentiation of stem cells into the osteogenic lineage in vitro.

BMP2 initiates chondrogenic lineage development of adult human mesenchymal stem cells in high-density culture

Human bone marrow-derived mesenchymal stem cells (MSCs) have been shown to differentiate into distinct mesenchymal tissues including bone and cartilage. The capacity of MSCs to replicate undifferentiated and to mature into cartilaginous tissues suggests these cells as an attractive cell source for cartilage tissue engineering. Here we show that the stimulation of human bone marrow-derived MSCs with recombinant bone morphogenetic protein-2 (BMP2) results in chondrogenic lineage development under serum-free conditions. Histological staining of proteoglycan with Alcian blue and immunohistochemical staining of cartilage-specific type II collagen revealed the deposition of typical cartilage extracellular matrix components. Semi-quantitative real-time gene expression analysis of characteristic chondrocytic matrix genes, such as cartilage link protein, cartilage oligomeric matrix protein, aggrecan, and types I, II, and IX collagen, confirmed the induction of the chondrocytic phenotype in high-density culture upon stimulation with BMP2 and transforming growth factor-beta3 (TGFbeta3). Histologic staining of mineralized extracellular matrix with von Kossa, immunostaining of type X collagen (typical for hypertrophic chondrocytes), and gene expression analysis of osteocalcin and adipocyte-specific fatty acid binding protein (aP2) further documented that BMP2 induced chondrogenic lineage development and not osteogenesis and/or adipogenesis in human MSCs. These results suggest BMP2 as a promising candidate for tissue engineering approaches regenerating articular cartilage on the basis of mesenchymal progenitors from bone marrow.

Quantitative gene expression profiling implicates genes for susceptibility and resistance to alveolar bone loss

Periodontal disease is one of the most prevalent chronic inflammatory diseases. There is a genetic component to susceptibility and resistance to this disease. Using a mouse model, we investigated the progression of alveolar bone loss by gene expression profiling of susceptible and resistant mouse strains (BALB/cByJ and A/J, respectively). We employed a novel and sensitive quantitative real-time PCR method to compare basal RNA transcription of a 48-gene set in the gingiva and the spleen and the subsequent changes in gene expression due to Porphyromonas gingivalis oral infection. Basal expression of interleukin-1 beta (Il1b) and tumor necrosis factor alpha (Tnf) mRNA was higher in the gingiva of the susceptible BALB/cByJ mice than in the gingiva of resistant A/J mice. Gingival Il1b gene expression increased further and Stat6 gene expression was turned on after P. gingivalis infection in BALB/cByJ mice but not in A/J mice. The basal expression of interleukin-15 (Il15) in the gingiva and the basal expression of p-selectin (Selp) in the spleen were higher in the resistant A/J mice than in the susceptible BALB/cByJ mice. In the resistant A/J mice the expression of no genes detectably changed in the gingiva after infection. These results suggest a molecular phenotype in which discrete sets of differentially expressed genes are associated with genetically determined susceptibility (Il1b, Tnf, and Stat6) or resistance (Il15 and Selp) to alveolar bone loss, providing insight into the genetic etiology of this complex disease.

A bit of give and take: the relationship between the extracellular matrix and the developing chondrocyte

The extracellular matrix (ECM), once thought to be a static structural component of tissues, is now known to play a complex and dynamic role in a variety of cellular functions in a number of diverse tissues. A significant body of literature attests to the ability of the ECM to communicate both spatial and temporal information to adherent cells, thereby directing cell behavior via interactions between the ECM and cell-surface receptors. Moreover, volumes of experimental data show that a great deal of communication travels in the opposite direction, from the cell to the ECM, allowing for regulation of the cues transmitted by the ECM. As such, the ECM, with respect to its components and their organization, is not a fixed reflection of the state the local microenvironment in which a cell finds itself at a particular time, but rather is able to respond to and effect changes in its local microenvironment. As an example of the developmental consequences of ECM interactions, this review gives an overview of the 'give and take' relationship between the ECM and the cells of the developing skeletal elements, in particular, the chondrocyte.

Oxysterols regulate differentiation of mesenchymal stem cells: pro-bone and anti-fat

Pluripotent mesenchymal stem cells can undergo lineage-specific differentiation in adult organisms. However, understanding of the factors and mechanisms that drive this differentiation is limited. We show the novel ability of specific oxysterols to regulate lineage-specific differentiation of mesenchymal stem cells into osteogenic cells while inhibiting their adipogenic differentiation. Such effects may have important implications for intervention with osteoporosis.

INTRODUCTION

Oxysterols are products of cholesterol oxidation and are formed in vivo by a variety of cells including osteoblasts. Novel pro-osteogenic and anti-adipogenic effects of specific oxysterols on pluripotent mesenchymal cells are demonstrated in this report. Aging and osteoporosis are associated with a decrease in the number and activity of osteoblastic cells and a parallel increase in the number of adipocytic cells.

MATERIALS AND METHODS

The M2-10B4 pluripotent marrow stromal cell line, as well as several other mesenchymal cell lines and primary marrow stromal cells, was used to assess the effects of oxysterols. All results were analyzed for statistical significance using ANOVA.

RESULTS AND CONCLUSION

Pro-osteogenic and anti-adipogenic effects of specific oxysterols were assessed by the increase in early and late markers of osteogenic differentiation, including alkaline phosphatase activity, osteocalcin mRNA expression and mineralization, and the decrease in markers of adipogenic differentiation including lipoprotein lipase and adipocyte P2 mRNA expression and adipocyte formation. Complete osteogenic differentiation of M2 cells into cells expressing early and late markers of differentiation was achieved only when using combinations of specific oxysterols, whereas inhibition of adipogenesis could be achieved with individual oxysterols. Oxysterol effects were in part mediated by extracellular signal-regulated kinase and enzymes in the arachidonic acid metabolic pathway, i.e., cyclo-oxygenase and phospholipase A(2). Furthermore, we show that these specific oxysterols act in synergy with bone morphogenetic protein 2 in inducing osteogenic differentiation. These findings suggest that oxysterols may play an important role in the differentiation of mesenchymal stem cells and may have significant, previously unrecognized, importance in stem cell biology and potential therapeutic interventions.

Mouse Reduced in Osteosclerosis Transporter Functions as an Organic Anion Transporter 3 and Is Localized at Abluminal Membrane of Blood-Brain Barrier

The "reduced in osteosclerosis" transporter (Roct), which shows decreased expression in the osteosclerosis (oc) mutant mouse, has high homology with rat and human organic anion transporter 3 (OAT3). However, its transport properties and involvement in bone turnover are poorly understood. Here, we examined Roct-mediated transport using a Xenopus laevis oocyte expression system. Roct-expressing oocytes exhibited uptake of [(3)H]estrone sulfate, [(3)H]p-aminohippuric acid, [(3)H]benzylpenicillin, [(3)H]estradiol 17beta-glucronide, [(3)H]indoxyl sulfate, [(14)C]indomethacin, [(3)H]homovanillic acid, [(3)H]cimetidine, [(14)C]glutarate, [(14)C]salicylic acid, and [(3)H]methotrexate. Furthermore, the uptake of [(3)H]benzylpenicillin by Roct coexpressed with Na(+)-dicarboxylate cotransporter was trans-stimulated by glutarate preloading, and [(3)H]estrone sulfate uptake showed a similar tendency, suggesting that Roct is a dicarboxylate exchanger. [(3)H]Benzylpenicillin uptake by Roct was inhibited by OAT3 substrates and inhibitors, and by sulfate or glucuronide conjugates, and compounds involved in bone turnover. Roct mRNA is expressed abundantly in the kidney and was also detected in the brain, choroid plexus, and eye. Immunohistochemical analysis revealed that Roct is localized in brain capillary endothelial cells. These results indicate that the transport properties and tissue distribution of Roct are similar to those of OAT3, suggesting that Roct functions as mouse OAT3. Because Roct is expressed in the kidney and at the blood-brain barrier, it may play a role in the excretion of substrates such as conjugates and bone turnover factors.

Expression of alternatively spliced isoforms of human Sp7 in osteoblast-like cells

BACKGROUND

Osteogenic and chondrocytic differentiation involves a cascade of coordinated transcription factor gene expression that regulates proliferation and matrix protein formation in a defined temporo-spatial manner. Bone morphogenetic protein-2 induces expression of the murine Osterix/Specificity protein-7 (Sp7) transcription factor that is required for osteoblast differentiation and bone formation. Regulation of its expression may prove useful for mediating skeletal repair.

RESULTS

Sp7, the human homologue of the mouse Osterix gene, maps to 12q13.13, close to Sp1 and homeobox gene cluster-C. The first two exons of the 3-exon gene are alternatively spliced, encoding a 431-residue long protein isoform and an amino-terminus truncated 413-residue short protein isoform. The human Sp7 protein is a member of the Sp family having 78% identity with Sp1 in the three, Cys2-His2 type, DNA-binding zinc-fingers, but there is little homology elsewhere. The Sp7 mRNA was expressed in human foetal osteoblasts and craniofacial osteoblasts, chondrocytes and the osteosarcoma cell lines HOS and MG63, but was not detected in adult femoral osteoblasts. Generally, the expression of the short (or beta) protein isoform of Sp7 was much higher than the long (or alpha) protein isoform. No expression of either isoform was found in a panel of other cell types. However, in tissues, low levels of Sp7 were detected in testis, heart, brain, placenta, lung, pancreas, ovary and spleen.

CONCLUSIONS

Sp7 expression in humans is largely confined to osteoblasts and chondrocytes, both of which differentiate from the mesenchymal lineage. Of the two protein isoforms, the short isoform is most abundant.

Sulfated polysaccharides enhance the biological activities of bone morphogenetic proteins

Bone morphogenetic proteins (BMPs), which have been shown to be heparin-binding proteins, induce osteoblast differentiation in mesenchymal cells. In the present study, we examined the effects of heparin on the BMP activities in C2C12 myoblasts. Heparin dose dependently enhanced the osteoblast differentiation induced by not only homodimers of BMP-2 or BMP-4 but also heterodimers of BMP-2/6 or BMP-2/7. However, the osteoblast differentiation induced by the constitutively active BMPR-IA, a functional BMP type I receptor, was not affected by heparin. Heparan sulfate and dextran sulfate also enhanced the BMP-2 activity, although the chemically desulfated heparin-derivatives have lost this stimulatory capacity. Heparin dose-dependently suppressed the accumulation of BMP-2 from the culture media into the cell layer or BMPR-IA, and retained a large amount of BMP-2 in the culture media. The biological activity of BMP-2, which was evaluated using a BMP-responsive reporter gene expression, was prolonged in the presence of heparin. Taken together, these results suggest that sulfated polysaccharides enhance the biological activity of both homodimers and heterodimers of BMPs by continuously serving the ligands to their signaling receptors expressed on cell membranes.

The role of calmodulin in the regulation of osteoclastogenesis

Calmodulin plays an important role in regulating the function of mature osteoclasts. However, its role in osteoclastogenesis has not been investigated. In the present study, we examined the role of calmodulin in osteoclastogenesis using in vivo and in vitro systems. Calmodulin antagonists, trifluoperazine (TFP), W7, and tamoxifen, dose-dependently inhibited osteoclast formation, which occurred only in the last 24 h of a 4-d osteoclastogenesis culture using mouse bone marrow macrophages. Inhibitory effects were quantitated by measuring tartrate-resistant acid phosphatase activity and counting osteoclast numbers. In contrast, bis indolylmaleimide, a protein kinase C inhibitor, showed no such inhibitory effect even when applied at a concentration that was 10-fold greater than its IC50. Overexpressing calmodulin by recombinant retrovirus reversed the inhibitory effect of TFP on osteoclast-like differentiation in RAW264.7 cells. Furthermore, administration of TFP to mice was as effective as estrogen in abolishing the ovariectomy-induced increment of osteoclastogenesis as determined by quantitative assessment of tartrate-resistant acid phosphatase activity in tibias, which led to the recovery of the ovariectomy-induced decrement in trabecular bone volume. To investigate potential cellular and molecular mechanisms by which calmodulin antagonists inhibit osteoclastogenesis, Z-VAD-FMK, a broad caspase inhibitor, failed to block the inhibitory effect of TFP on mouse osteoclast formation, indicating that apoptosis is not the underlying mechanism. Pretreatment of RAW264.7 cells with different concentrations of TFP dose-dependently inhibited receptor activator of nuclear factor kappaB ligand-stimulated phosphorylation of c-Jun N-terminal kinase and inhibitory kappaBalpha but not that of p38. Taken together, our data indicate that calmodulin mediates osteoclast differentiation, possibly via modulating specific receptor activator of NF-kappaB-signaling pathways.

Molecular mechanisms underlying osteoclast formation and activation

Osteoporosis is one of the leading causes of morbidity in the elderly and is characterized by a progressive loss of total bone mass and bone density. Bone loss in osteoporosis is due to the persistent excess of osteoclastic bone resorption over osteoblastic bone formation. Receptor activator of NFkappaB ligand (RANKL) critically regulates both osteoclast differentiation and activation. TRAFs appear to be central coupling molecules in the signal transduction pathways that regulate osteoclastogenesis, cathepsin K is the major mediator of osteoclastic bone resorption, and sex steroids and aging also affect osteoclastogenesis and osteoclast activity. However, bone homeostasis depends upon the intimate coupling of bone formation and bone resorption, wherein both osteoclasts and osteoblasts exert vital stimulatory and inhibitory effects upon each other via molecules such as RANKL, TGFbeta, PDGF, BMP2, and Mim-1. This review will highlight some of the major features of the complex circuit of cytokines, growth factors, and hormones that underlies the formation and function of osteoclasts and the dynamic equilibrium that marks the interaction between osteoclasts and osteoblasts.

Effect of soluble receptors to interleukin-1 and tumor necrosis factor alpha on experimentally induced root resorption in rats

OBJECTIVE

In this study, the role of the inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) in the course of mechanically induced root resorption was investigated.

METHODS

Mechanical induction of root resorption was performed on the upper left first molars in 18 male Wistar rats according to the method of Nakane and Kameyama. Starting on day minus 1, six animals received daily intraperitoneal injections of 2 ml of 1 micro g/ml soluble receptors to IL-1 (sIL-1RII) and another six animals were administered the same dose of soluble receptors to TNFalpha (sTNFalpha-RI). Six animals served as a control. On d 7 the left maxillae were prepared for histological and morphometric analysis of the extent of the root resorption that had developed.

RESULTS

The qualitative and quantitative results demonstrated that in both receptor groups the amount of root resorption was significantly reduced. Especially following systemic application of sTNFalpha-RI, root resorption was nearly completely prevented.

CONCLUSIONS

Our results indicate that IL-1 and more particularly TNFalpha are important for the induction and the further process of mechanically induced root resorption in the rat.