Recording and analysing DNA from osteocytes in resin-embedded bone samples.

We report on a process to record the presence and the location of osteocyte nuclei using two nucleic staining dyes, Diamond™ Nucleic Acids Dye (DD) and DAPI (4',6-diamidino-2-phenylindole). Knowledge of the presence and number of osteocytes is key to any success in subsequent DNA profiling. Osteocytes are most numerous cells and thus the main source of DNA in bone samples, which can be preserved for histological analyses. Archived samples are either fixed in formalin or preserved in ethanol prior to embedding in resin. These resin-embedded samples are potentially used as ante mortem reference samples. Cases of a missing person investigation are one example where this type of preserved reference material may be of value. When resin is required for sample preservation it represents a problem for subsequent DNA profiling, if needed as a reference sample in human identification. It is essential therefore to remove the resin prior to DNA analyses as resin is a known inhibitor of DNA profiling. Current methods of resin removal are lengthy and require toxic chemicals. This report describes a simplified process to remove resin and visualise the location of nucleated osteocytes. Eight sections of bone samples at 5-µm thickness were stained with DD and DAPI. A further three samples were processed using a formalin-fixed method and three additional samples treated following an ethanol-preserved method (11 samples for both the formalin-fixed and 11 for the ethanol-preserved with eight in common). The location and number of nuclei could be recorded clearly due to the fluorescence created by the dye binding to DNA. The number of stained nuclei correlated with the mass of DNA isolated from the sections (r = 0.873, p = 1.21 × 10-10). A significant difference between the degradation indices of two groups (p = 8.505 × 10-5) showed that ethanol preservation is a preferred method to yield DNA of the quality needed for subsequent short tandem repeats (STR) profiling. Ten of the 11 samples isolated using the ethanol-preserved process recorded a complete STR profile (30/30 alleles), whereas eight of the formalin-fixed samples generated full profiles, and only one of the 11 samples amplified less than 23 alleles. Both the ethanol-preserved and formalin-fixed methods are an improvement on current methods by removing the need for strong solutes in resin removal, and the method leads to STR profiles from resin-embedded bone samples within 24 h.

Functionalization of Electrospun Polycaprolactone Scaffolds with Matrix-Binding Osteocyte-Derived Extracellular Vesicles Promotes Osteoblastic Differentiation and Mineralization.

Synthetic polymeric materials have demonstrated great promise for bone tissue engineering based on their compatibility with a wide array of scaffold-manufacturing techniques, but are limited in terms of the bioactivity when compared to naturally occurring materials. To enhance the regenerative properties of these materials, they are commonly functionalised with bioactive factors to guide growth within the developing tissue. Extracellular matrix vesicles (EVs) play an important role in facilitating endochondral ossification during long bone development and have recently emerged as important mediators of cell-cell communication coordinating bone regeneration, and thus represent an ideal target to enhance the regenerative properties of synthetic scaffolds. Therefore, in this paper we developed tools and protocols to enable the attachment of MLO-Y4 osteocyte-derived EVs onto electrospun polycaprolactone (PCL) scaffolds for bone repair. Initially, we optimize a method for the functionalization of PCL materials with collagen type-1 and fibronectin, inspired by the behaviour of matrix vesicles during endochondral ossification, and demonstrate that this is an effective method for the adhesion of EVs to the material surface. We then used this functionalization process to attach osteogenic EVs, collected from mechanically stimulated MLO-Y4 osteocytes, to collagen-coated electrospun PCL scaffolds. The EV-functionalized scaffold promoted osteogenic differentiation (measured by increased ALP activity) and mineralization of the matrix. In particular, EV-functionalised scaffolds exhibited significant increases in matrix mineralization particularly at earlier time points compared to uncoated and collagen-coated controls. This approach to matrix-based adhesion of EVs provides a mechanism for incorporating vesicle signalling into polyester scaffolds and demonstrates the potential of osteocyte derived EVs to enhance the rate of bone tissue regeneration.

The Analysis of Gap Junctional Intercellular Communication Among Osteocytes in Chick Calvariae by Fluorescence Recovery After Photobleaching.

This chapter describes the use of fluorescence recovery after photobleaching (FRAP) for analyzing gap junctional intercellular communication (GJIC) among osteocytes in chick calvariae by confocal laser scanning microscope.

Immunocytochemical assessment of cell differentiation of podoplanin-positive osteoblasts into osteocytes in murine bone.

In this study, we examined the immunolocalization of podoplanin/E11, CD44, actin filaments, and phosphorylated ezrin in the osteoblasts on the verge of differentiating into osteocytes in murine femora and tibiae. When observing under stimulated emission depletion microscopy, unlike podoplanin-negative osteoblasts, podoplanin-positive osteoblasts showed a rearranged assembly of actin filaments along the cell membranes which resembled that of embedded osteocytes. In the metaphysis, i.e., the bone remodeling site, CD44-bearing osteoclasts were either proximal to or in contact with podoplanin-positive osteoblasts, but the podoplanin-positive osteoblasts also localized CD44 on their own cell surface. These podoplanin-positive osteoblasts, which either possessed CD44 on their cell surface or were close to CD44-bearing osteoclasts, showed phosphorylated ezrin-positivity on the cell membranes. Therefore, the CD44/podoplanin interaction on the cell surface may be involved in the osteoblastic differentiation into osteocytes in the metaphyses, via the mediation of podoplanin-driven ezrin phosphorylation and the subsequent reorganized assembly of actin filaments. Consistently, the protein expression of phosphorylated ezrin was increased after CD44 administration in calvarial culture. Conversely, in modeling sites such as the cortical bones, podoplanin-positive osteoblasts were uniformly localized at certain intervals even without contact with CD44-positive bone marrow cells; furthermore, they also exhibited phosphorylated ezrin immunoreactivity along their cell membranes. Taken together, it seems likely that the CD44/podoplanin interaction is involved in osteoblastic differentiation into osteocytes in the bone remodeling area but not in modeling sites.

Optimization and validation of a chiral CE-LIF method for quantitation of aspartate, glutamate and serine in murine osteocytic and osteoblastic cells.

Asp, Glu, and D-Ser are chiral amino acids and neurotransmitters binding to the N-methyl-D-aspartate receptor (NMDA) and they participate in glutamate signalization. D-amino acids are increasingly being recognized as important signaling molecules and variations in their levels are considered a marker of different pathologies, however, there is still a lack of knowledge about the role of most of D-amino acids in living organisms such as bone cells. A method for determination of concentrations of L/D-Asp, L/D-Glu and L/D-Ser in two types of bone cell lines: murine osteocytes (MLOY4) and osteoblasts (MC3T3-E1) is presented. It is based on capillary electrophoresis coupled to laser-induced fluorescence detection in normal polarity with 4-fluoro-7-nitro-2,1,3-benzoxadiazole as derivatizing agent suitable for an Argon ion laser source. The electrolyte consists of 137.5 mM borate buffer and 12.5 mM ß-cyclodextrins as chiral selectors and the separation lasts 25 min. The method was optimized and validated for specificity, sensitivity, linearity, accuracy, and precision in murine osteocytes and osteoblasts. LLOQ was 0.25 µmol L-1 for the three D-amino acids and linearity was confirmed with r > 0.995 for all D-and L-amino acids. Accuracy ranged between 81.9% and 111.7% and intra-day precision ranged between 1.8% and 10.9%. Concentrations of D- and L- Asp, Glu, and Ser are given and statistical differences between osteocytes and osteoblasts were found. The highest differences corresponded to L- and D-Glu. This method could play a fundamental role in the study of therapeutic targets in the treatment of bone diseases.

A method for isolating RNA from canine bone.

Extracting sufficient quantity and quality RNA from bone is essential for downstream application, such as transcriptomic sequencing, to evaluate gene expression. Isolation of RNA from bone presents a unique challenge owing to the hypocellular, brittle and mineralized matrix, which makes homogenizing the tissue difficult and provides little RNA to work with. Removal of contaminating tissue, such as bone marrow and connective tissue, is essential for isolating RNA that is unique to osteoblasts, osteoclasts and osteocytes. This study established a method to effectively isolate RNA from normal canine bone cells using the phalanges, without contamination from other tissue types, for downstream transcriptomic analysis.

MiR-20b promotes osteocyte apoptosis in rats with steroid-induced necrosis of the femoral head through BMP signaling pathway.

OBJECTIVE: To study the effect of micro-ribonucleic acid (miR)-20b on osteocyte apoptosis in rats with steroid-induced necrosis of the femoral head (SNFH) and to analyze whether the bone morphogenetic protein (BMP) signaling pathway is involved in the regulation. MATERIALS AND METHODS: A total of 36 Sprague-Dawley rats were randomly divided into control group (n=12), model group (n=12) and intervention group (n=12). The rat model of SNFH was established in the model and intervention groups, while the rats in the intervention group were intraperitoneally injected with the bone morphogenetic protein (BMP) signaling pathway inhibitor. After modeling, the femoral head in each group was taken, and the morphology of osteocytes was observed via hematoxylin-eosin (HE) staining. The apoptosis level of femoral head cells was detected via terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. The miR-20b expression level in femoral head cells in each group was detected via quantitative Polymerase Chain Reaction (qPCR). The expression levels of inflammatory factors in femoral head cells in each group were detected via enzyme-linked immunosorbent assay (ELISA). The expression levels of apoptotic proteins and BMP signaling pathway-related proteins in femoral head cells in each group were detected via Western blotting. RESULTS: Compared with those in the control group, the bone trabecula was sparse, the number of osteocytes significantly declined and the number of apoptotic osteocytes markedly increased (p<0.01); the expression level of miR-20b in bone tissues remarkably increased (p<0.01), the content of interleukin-1ß (IL-1ß), IL-6 and tumor necrosis factor-α (TNF-α) in bone tissues increased (p<0.01), the content of IL-10 significantly declined (p<0.01), the expression level of cleaved caspase-3 protein in bone tissues markedly increased (p<0.01), the Bcl-2/Bax expression level evidently declined (p<0.01) and the expression levels of anaplastic lymphoma kinase3 (ALK3), GATA4 and NKX2.5 in bone tissues remarkably increased (p<0.01) in the model group. Compared with those in the model group, the necrosis of bone tissues significantly decreased, the apoptosis level of osteocytes remarkably declined (p<0.01), the content of IL-1ß, IL-6 and TNF-α in bone tissues markedly decreased (p<0.01), the content of IL-10 increased (p<0.01), the expression level of cleaved caspase-3 protein in bone tissues significantly declined (p<0.01), the B-cell lymphoma 2/BCL2-Associated X (Bcl-2/Bax) expression level markedly increased (p<0.01) and the expression levels of ALK3, GATA4 and NKX2.5 in bone tissues significantly decreased (p<0.01) in the intervention group. CONCLUSIONS: SNFH will significantly increase the expression level of miR-20b in bone tissues, thereby activating the BMP signaling pathway, promoting the release of inflammatory factors and leading to osteocyte apoptosis. Inhibiting the BMP signaling pathway can effectively reduce the osteocyte apoptosis level.

Reversal of Osteoporotic Activity by Endothelial Cell-Secreted Bone Targeting and Biocompatible Exosomes.

Exosomes, also known as extracellular vesicles, are naturally occurring, biocompatible, and bioacive nanoparticles ranging from 40 to 150 nm in diameter. Bone-secreted exosomes play important roles in bone homeostasis, the interruption of which can lead to diseases such as osteoporosis, rheumatoid arthritis, and osteopetrosis. Though the relationship between vascular and bone homeostasis has been recognized recently, the role of vascular endothelial cell (EC)-secreted exosomes (EC-Exos) in bone homeostasis is not well understood. Herein, we found that EC-Exos show more efficient bone targeting than osteoblast-derived exosomes or bone marrow mesenchymal stem cell-derived exosomes. We also found that EC-Exos can be internalized by bone marrow-derived macrophages (BMMs) to alter their morphology. EC-Exos can inhibit osteoclast activity in vitro and inhibit osteoporosis in an ovariectomized mouse model. Sequencing of exosome miRNA revealed that miR-155 was highly expressed in EC-Exos-treated BMMs. The miR-155 level in EC-Exos was much higher than that in BMMs and ECs, indicating that miR-155 was endogenous cargo of EC-derived vesicles. Blockage of BMMs miR-155 levels reversed the suppression by EC-Exos of osteoclast induction, confirming that exosomal miR-155 may have therapeutic potential against osteoporosis. Taken together, our findings suggest that EC-Exos may be utilized as a bone targeting and nontoxic nanomedicine for the treatment of bone resorption disorders.

[Intravital bone imaging ~Osteocyte.]

Osteocytes are the most abundant cellular component of bone and have been considered dormant until recent evidence has demonstrated their critical roles in bone homeostasis and endocrine regulation. Until now the location of osteocytes within mineralized bone has restricted experimental access, especially in vivo. Here, intravital bone imaging by two-photon excitation microscopy allowed us to directly visualize the osteocytic lacuno-canalicular system. We demonstrated that sciatic neurectomy causes significant acidification around osteocytic lacunae and enlargement of lacuno-canalicular areas. These results show that two-photon intravital microscopy is useful for analysis of osteocytes in vivo.

Micrometer-Sized Magnesium Whitlockite Crystals in Micropetrosis of Bisphosphonate-Exposed Human Alveolar Bone.

Osteocytes are contained within spaces called lacunae and play a central role in bone remodelling. Administered frequently to prevent osteoporotic fractures, antiresorptive agents such as bisphosphonates suppress osteocyte apoptosis and may be localized within osteocyte lacunae. Bisphosphonates also reduce osteoclast viability and thereby hinder the repair of damaged tissue. Osteocyte lacunae contribute to toughening mechanisms. Following osteocyte apoptosis, the lacunar space undergoes mineralization, termed "micropetrosis". Hypermineralized lacunae are believed to increase bone fragility. Using nanoanalytical electron microscopy with complementary spectroscopic and crystallographic experiments, postapoptotic mineralization of osteocyte lacunae in bisphosphonate-exposed human bone was investigated. We report an unprecedented presence of ∼80 nm to ∼3 µm wide, distinctly faceted, magnesium whitlockite [Ca18Mg2(HPO4)2(PO4)12] crystals and consequently altered local nanomechanical properties. These findings have broad implications on the role of therapeutic agents in driving biomineralization and shed new insights into a possible relationship between bisphosphonate exposure, availability of intracellular magnesium, and pathological calcification inside lacunae.

Inhibiting the osteocyte-specific protein sclerostin increases bone mass and fracture resistance in multiple myeloma.

Multiple myeloma (MM) is a plasma cell cancer that develops in the skeleton causing profound bone destruction and fractures. The bone disease is mediated by increased osteoclastic bone resorption and suppressed bone formation. Bisphosphonates used for treatment inhibit bone resorption and prevent bone loss but fail to influence bone formation and do not replace lost bone, so patients continue to fracture. Stimulating bone formation to increase bone mass and fracture resistance is a priority; however, targeting tumor-derived modulators of bone formation has had limited success. Sclerostin is an osteocyte-specific Wnt antagonist that inhibits bone formation. We hypothesized that inhibiting sclerostin would prevent development of bone disease and increase resistance to fracture in MM. Sclerostin was expressed in osteocytes from bones from naive and myeloma-bearing mice. In contrast, sclerostin was not expressed by plasma cells from 630 patients with myeloma or 54 myeloma cell lines. Mice injected with 5TGM1-eGFP, 5T2MM, or MM1.S myeloma cells demonstrated significant bone loss, which was associated with a decrease in fracture resistance in the vertebrae. Treatment with anti-sclerostin antibody increased osteoblast numbers and bone formation rate but did not inhibit bone resorption or reduce tumor burden. Treatment with anti-sclerostin antibody prevented myeloma-induced bone loss, reduced osteolytic bone lesions, and increased fracture resistance. Treatment with anti-sclerostin antibody and zoledronic acid combined increased bone mass and fracture resistance when compared with treatment with zoledronic acid alone. This study defines a therapeutic strategy superior to the current standard of care that will reduce fractures for patients with MM.

Evaluating differential nuclear DNA yield rates and osteocyte numbers among human bone tissue types: A synchrotron radiation micro-CT approach.

Molecular human identification has conventionally focused on DNA sampling from dense, weight-bearing cortical bone tissue, typically from femora or tibiae. A comparison of skeletal elements from three contemporary individuals demonstrated that elements with high quantities of cancellous bone yielded nuclear DNA at the highest rates, suggesting that preferentially sampling cortical bone may be suboptimal (Mundorff & Davoren, 2014). Despite these findings, the reason for the differential DNA yields between cortical and cancellous bone tissues remains unknown. The primary goal of this work is to ascertain whether differences in bone microstructure can be used to explain differential nuclear DNA yield among bone tissue types observed by Mundorff and Davoren (2014), with a focus on osteocytes and the three-dimensional (3D) quantification of their associated lacunae. Osteocytes and other bone cells are recognized to house DNA in bone tissue, thus examining the density of their lacunae may explain why nuclear DNA yield rates differ among bone tissue types. Lacunae were visualized and quantified using synchrotron radiation-based micro-Computed Tomographic imaging (SR micro-CT). Volumes of interest (VOIs) from cortical and cancellous bone tissues (n=129) were comparatively analyzed from the three skeletons sampled for Mundorff and Davoren's (2014) study. Analyses tested the primary hypothesis that the abundance and density of osteocytes (inferred from their lacunar spaces) vary between cortical and cancellous bone tissue types. Results demonstrated that osteocyte lacunar abundance and density vary between cortical and cancellous bone tissue types, with cortical bone VOIs containing a higher lacunar abundance and density. We found that the osteocyte lacunar density values are independent of nuclear DNA yield, suggesting an alternative explanation for the higher nuclear DNA yields from bones with greater quantities of cancellous bone tissue. The use of SR micro-CT allowed for a scale of analysis that revealed a high range of variation in lacunar abundance in both tissue types. Moreover, high-resolution SR micro-CT imaging revealed potential soft tissue remnants within marrow spaces not visible macroscopically. It is hypothesized that soft tissue remnants observed among the trabeculae of skeletal elements with high quantities of cancellous bone tissue are responsible for the high nuclear DNA yields. These findings have significant implications for bone-sample selection for nuclear DNA analysis in a forensic context when skeletal remains are recovered from the ground surface.

Differences in expression of Wnt antagonist Dkk1 in healthy versus pathological bone samples.

Wnt/ß-catenin signalling components was shown to affect bone cells function including chondrocytes.Secreted Dkk1, a potent osteogenesis inhibiting factor mediates bone loss in diseased bones by suppressing the biological actions of Wnt proteins. In addition, increased Dkk1 signalling inhibits chondrogenesis in new bone formation. Recent findings also show there exists a cross-talk between the chondrocytes and the cells of the osteoblast lineage, which are the most affected cell types in muskuloskeletal disorders. This study investigated whether spatial expression of Dkk1 is confined to only osteoblasts, osteocytes or chondrocytes. The second objective was to detect a difference in the Dkk1 expression pattern in healthy subjects when compared to pathological state. To elucidate the cell specificity of Dickkopf-1 (Dkk1) in healthy bones, samples from female Sprague-Dawley rats were tested against two different antibodies with the two most widely accepted visualization system (ABC and Envision). The findings show Dkk1 specificity predominantly for osteoblasts, chondrocytes and osteocytes depending upon the antibody used. In addition, Dkk1 expression was evaluated in different cells of human osteoarthritis (OA) and rheumatoid arthritis (OA) patients. Its overexpression in pathologic state also suggests the role of Dkk1 in bone formation. This is scientifically and clinically important in studying the effect of Dkk1 in bone healing and in designing treatments for patients with compromised bone status. Taking into consideration the paradigm that cartilage and subchondral bone behave as an interconnected functional unit, normalization of cell behaviour in one compartment may have benefits in both tissues.

Histological evidence that metformin reverses the adverse effects of diabetes on orthodontic tooth movement in rats.

This study evaluated the effects of metformin on orthodontic tooth movement in a rat model of type 2 diabetes mellitus. Rats were fed a high-fat diet for 4 weeks to induce fat accumulation and insulin resistance, and then injected with a low dose of streptozotocin (35 mg/kg) intraperitoneally to induce type 2 diabetes. An orthodontic appliance was placed in normoglycemic, type 2 diabetes, and type 2 diabetes with metformin-administrated rats. After 14 days, type 2 diabetes rats exhibited greater orthodontic tooth movement and had a higher number of tartrate-resistant acid phosphatase-positive osteoclasts, stronger cathepsin K expression, and weaker alkaline phosphatase immunostaining than normoglycemic rats. Metformin administration resulted in normalization of osteoclast numbers, cathepsin K immunostaining, and of tooth movement as well as partly recovery of alkaline phosphatase expression in diabetic rats. Metformin also reduced sclerostin expression and improved the immunolocalization of dentin matrix protein 1 in osteocytes of type 2 diabetes rats. These results suggest that metformin administration reversed the adverse effects of diabetes on orthodontic tooth movement.

Visual reporters for study of the osteoblast lineage.

Advancing our understanding of osteoblast biology and differentiation is critical to elucidate the pathological mechanisms responsible for skeletal diseases such as osteoporosis. Histology and histomorphometry, the classical methods to study osteoblast biology, identify osteoblasts based on their location and morphology and ability to mineralize matrix, but do not clearly define their stage of differentiation. Introduction of visual transgenes into the cells of osteoblast lineage has revolutionized the field and resulted in a paradigm shift that allowed for specific identification and isolation of subpopulations within the osteoblast lineage. Knowledge acquired from the studies based on GFP transgenes has allowed for more precise interpretation of studies analyzing targeted overexpression or deletion of genes in the osteoblast lineage. Here, we provide a condensed overview of the currently available promoter-fluorescent reporter transgenic mice that have been generated and evaluated to varying extents. We cover different stages of the lineage as transgenes have been utilized to identify osteoprogenitors, pre-osteoblasts, osteoblasts, or osteocytes. We show that each of these promoters present with advantages and disadvantages. The studies based on the use of these reporter mice have improved our understanding of bone biology. They constitute attractive models to target osteoblasts and help to understand their cell biology.

A Novel Osteoblast/Osteocyte Selection Method in Primary Isolated Chick Bone Cells by Atomic Force Microscopy.

Selection of bone cells, particularly osteoblasts and osteocytes, for analysis of cellular processes and differentiation is a very important issue because bone remodeling is a highly complex and harmonized process, which includes molecular and cellular interactions and communications. In this study, we introduce a novel osteoblast and osteocyte selection method that uses atomic force microscopy and OB7.3, an antibody of Phex, which is a specific protein marker expressed on the surface of osteocytes. The elasticity and Phex expression levels were simultaneously detected by force spectroscopy using the OB7.3-modified atomic force microscopy probe on the bone cell surface. The elastic modulus was different between osteoblasts and osteocytes. Phex expression level was analyzed by the distribution of Phex-OB7.3 rupturing.

The Wnt Inhibitor Sclerostin Is Up-regulated by Mechanical Unloading in Osteocytes in Vitro.

Although bone responds to its mechanical environment, the cellular and molecular mechanisms underlying the response of the skeleton to mechanical unloading are not completely understood. Osteocytes are the most abundant but least understood cells in bones and are thought to be responsible for sensing stresses and strains in bone. Sclerostin, a product of the SOST gene, is produced postnatally primarily by osteocytes and is a negative regulator of bone formation. Recent studies show that SOST is mechanically regulated at both the mRNA and protein levels. During prolonged bed rest and immobilization, circulating sclerostin increases both in humans and in animal models, and its increase is associated with a decrease in parathyroid hormone. To investigate whether SOST/sclerostin up-regulation in mechanical unloading is a cell-autonomous response or a hormonal response to decreased parathyroid hormone levels, we subjected osteocytes to an in vitro unloading environment achieved by the NASA rotating wall vessel system. To perform these studies, we generated a novel osteocytic cell line (Ocy454) that produces high levels of SOST/sclerostin at early time points and in the absence of differentiation factors. Importantly, these osteocytes recapitulated the in vivo response to mechanical unloading with increased expression of SOST (3.4 ± 1.9-fold, p < 0.001), sclerostin (4.7 ± 0.1-fold, p < 0.001), and the receptor activator of nuclear factor κΒ ligand (RANKL)/osteoprotegerin (OPG) (2.5 ± 0.7-fold, p < 0.001) ratio. These data demonstrate for the first time a cell-autonomous increase in SOST/sclerostin and RANKL/OPG ratio in the setting of unloading. Thus, targeted osteocyte therapies could hold promise as novel osteoporosis and disuse-induced bone loss treatments by directly modulating the mechanosensing cells in bone.

Osteocytic Sclerostin Expression in Alveolar Bone in Rats With Diabetes Mellitus and Ligature-Induced Periodontitis.

BACKGROUND: Osteocytic sclerostin inhibits bone formation, and its expression is stimulated by tumor necrosis factor (TNF)-α. This study investigates sclerostin and TNF-α expression in rats with diabetes mellitus (DM) and periodontitis. METHODS: Rats were divided into control (C), periodontitis (P), and DM + periodontitis (DP) groups. After induction of DM by streptozotocin, periodontitis was induced by ligature. At day 0 (control) and at days 3 and 20 after induction of periodontitis, alveolar bone, osteoclasts, osteoid area, and TNF-α and sclerostin expression were evaluated. RESULTS: The distance between the cemento-enamel junction and the alveolar bone crest of the DP group was longer than that of the P group at day 20 after induction of periodontitis, but the number of osteoclasts was not different. Osteoid area decreased in both the P and DP groups by day 3, but whereas sustained osteoid suppression was observed in the DP group at day 20, osteoid formation was increased in the P group. The number of sclerostin-positive osteocytes increased in both groups at day 3, but the increased number of sclerostin-positive osteocytes was maintained only in the DP group through day 20. The number of TNF-α-positive cells increased more in the DP group than in the P group. CONCLUSIONS: Enhanced alveolar bone loss, suppressed bone formation, and prevalent TNF-α expression were characteristic of the DP group compared with the P group. Suppressed bone formation in the DP group was observed simultaneously with increased sclerostin and TNF-α expression. These results suggest that upregulated osteocytic sclerostin expression in periodontitis accompanied by DM may play a role in suppressed bone formation.

Receptor activator of nuclear factor-κB ligand and sclerostin expression in osteocytes of alveolar bone in rats with ligature-induced periodontitis.

BACKGROUND: Osteocytes are increasingly recognized as significant sources of osteoclast differentiation factor, receptor activator of nuclear factor-κB ligand (RANKL), and osteoblast differentiation inhibitory factor, sclerostin. In this study, RANKL and sclerostin expression of osteocytes is investigated in rats with ligature-induced periodontitis. METHODS: Rats were divided into control and periodontitis groups, and periodontitis was induced by ligature on the mandibular first molars. At 1, 3, 10, and 20 days after ligature, histologic analyses of alveolar bone (AB) and osteoid areas in the molar furcation were performed. The numbers of osteoclasts and RANKL- and sclerostin-positive osteocytes were estimated by tartrate-resistant acid phosphatase staining and immunohistochemistry, respectively. RESULTS: The AB area gradually decreased at day 10 after ligature and increased at day 20. The number of osteoclasts markedly increased at day 3 and then decreased. Conversely, osteoid formation was suppressed up to day 3 and then showed a remarkable increase above control level at day 20. The number of RANKL-positive osteocytes increased at days 1 and 3 and then decreased. Sclerostin-positive osteocytes markedly increased at days 3 and 10 but decreased below control level at day 20. CONCLUSIONS: These results show that AB loss is accompanied by enhanced osteoclast formation and suppressed osteoid formation. Osteocytes express RANKL when osteoclast formation increases, and they express sclerostin when osteoid formation is suppressed. Conversely, osteocytic sclerostin expression decreases when osteoid formation increases. These findings suggest that osteocytes may be important in AB loss via RANKL and sclerostin expression in periodontitis.

Evaluation of BSP expression and apoptosis in the periodontal ligament during orthodontic relapse: a preliminary study.

OBJECTIVE: To examine the expression of bone sialoprotein (BSP) and apoptosis in an in vivo orthodontic relapse model. MATERIALS AND METHODS: Male mice (10-12 weeks old), either transgenic [green fluorescent protein (GFP) driven by the BSP promoter] or wild type, were used in this study. To achieve orthodontic tooth movement (OTM), maxillary right first molars were moved mesially using closed-coil springs. Animals were divided into an OTM group (14 days continuous orthodontic force - 11 animals) or Relapse group (10 days of force application followed by 4 days of relapse - 8 animals). The control group was comprised of the contralateral maxillary molars. The periodontal ligament (PDL) was analyzed in areas of compression and tension for transgenic expression, osteoclast localization, and the presence of apoptotic cells. RESULTS: There was a significant decrease in GFP-labeled cells on the compression and tension sides of the PDL in the OTM group compared with control. In the relapse group, GFP-labeled cells were significantly decreased only on the old compression side. Osteoclasts were localized on the compression side of the OTM group, whereas in the Relapse group, they were present on both sides. PDL apoptosis significantly increased on the compression side in OTM and Relapse groups. CONCLUSION: Both OTM and Relapse groups exhibited a decreased number of GFP-labeled cells in areas of compression and tension. There was significant PDL apoptosis in regions under compressive forces following OTM and to a lesser extent following relapse.