Bone sialoprotein deficiency impairs osteoclastogenesis and mineral resorption in vitro

OPN, BSP, and Bone Quality-Structural, Biochemical, and Biomechanical Assessment in OPN-/-, BSP-/-, and DKO Mice

Osteopontin (OPN) and Bone Sialoprotein (BSP), abundantly expressed by osteoblasts and osteoclasts, appear to have important, partly overlapping functions in bone. In gene-knockout (KO, -/-) models of either protein and their double (D)KO in the same CD1/129sv genetic background, we analyzed the morphology, matrix characteristics, and biomechanical properties of femur bone in 2 and 4 month old, male and female mice. OPN-/- mice display inconsistent, perhaps localized hypermineralization, while the BSP-/- are hypomineralized throughout ages and sexes, and the low mineralization of young DKO mice recovers with age. The higher contribution of primary bone remnants in OPN-/- shafts suggests a slow turnover, while their lower percentage in BSP-/- indicates rapid remodeling, despite FTIR-based evidence in this genotype of a high maturity of the mineralized matrix. In 3-point bending assays, OPN-/- bones consistently display higher Maximal Load, Work to Max. Load and in young mice Ultimate Stress, an intrinsic characteristic of the matrix. Young male and old female BSP-/- also display high Work to Max. Load along with low Ultimate Stress. Principal Component Analysis confirms the major role of morphological traits in mechanical competence, and evidences a grouping of the WT phenotype with the OPN-/- and of BSP-/- with DKO, driven by both structural and matrix parameters, suggesting that the presence or absence of BSP has the most profound effects on skeletal properties. Single or double gene KO of OPN and BSP thus have multiple distinct effects on skeletal phenotypes, confirming their importance in bone biology and their interplay in its regulation.

Guided Bone Regeneration in a Periodontally Compromised Individual with Autogenous Tooth Bone Graft: A Radiomics Analysis

BACKGROUND

Autogenous tooth bone graft material (AutoBT) has been advocated as a bone substitute when conducting alveolar ridge preservation. This study is aimed at using a radiomics approach in order to evaluate and testify whether AutoBT can stimulate bone growth during socket preservation in severe periodontal cases.

MATERIALS AND METHODS

For this study, 25 cases with severe periodontal diseases were selected. The patients' AutoBTs were inserted into the extraction sockets and covered with Bio-Gide^® collagen membranes. 3D CBCT scans and 2D X-rays were taken of the patients before surgery and after 6 months post-surgery. For the retrospective radiomics analysis, the maxillary and mandibular images were compared in different groups. Maxillary bone height was analyzed at the buccal, middle, and palatal crest sites, while the mandibular bone height was compared at the buccal, center, and lingual crest sites.

RESULTS

In the maxilla, the alveolar height was increased by -2.15 ± 2.90 mm at the buccal crest; -2.45 ± 2.36 mm at the center of the socket, and -1.62 ± 3.19 mm at the palatal crest, while the height of the buccal crest was increased by 0.19 ± 3.52 mm, and the height at the center of the socket was increased by -0.70 ± 2.71 mm in the mandible. The three-dimensional radiomics analysis demonstrated significant bone growth in the local alveolar height and high density.

CONCLUSION

Based on clinical radiomics analysis, AutoBT could be used as an alternative bone material in socket preservation after tooth extraction in patients with severe periodontitis.

Bone Sialoprotein Is Critical for Alveolar Bone Healing in Mice

Bone sialoprotein (BSP) is an extracellular matrix (ECM) protein associated with mineralized tissues, particularly bone and cementum. BSP includes functional domains implicated in collagen binding, hydroxyapatite nucleation, and cell signaling, although its function(s) in osteoblast and osteoclast differentiation and function remain incompletely understood. Genetic ablation of BSP in Ibsp knockout (Ibsp-/-) mice results in developmental bone mineralization and remodeling defects, with alveolar bone more severely affected than the femurs and tibias of the postcranial skeleton. The role of BSP in alveolar bone healing has not been studied. We hypothesized that BSP ablation would cause defective alveolar bone healing. We employed a maxillary first molar extraction socket healing model in 42-d postnatalIbsp-/- and wild-type (WT) control mice. Tissues were collected at 0, 7, 14, 21, and 56 d postprocedure (dpp) for analysis by micro-computed tomography (microCT), histology, in situ hybridization (ISH), immunohistochemistry (IHC), and quantitative polymerase chain reaction (qPCR) array. As expected, alveolar bone healing progressed in WT mice with increasing bone volume fraction (BV/TV), bone mineral density (BMD), and tissue mineral density (TMD), transitioning from woven to mature bone from 7 to 56 dpp. Ibsp messenger RNA (mRNA) and BSP protein were strongly expressed during alveolar bone healing in parallel with other osteogenic markers. Compared to WT, Ibsp-/- mice exhibited 50% to 70% reduced BV/TV and BMD at all time points, 7% reduced TMD at 21 dpp, abnormally increased Col1a1 and Alpl mRNA expression, and persistent presence of woven bone and increased bone marrow in healing sockets. qPCR revealed substantially dysregulated gene expression in alveolar bone of Ibsp-/- versus WT mice, with significantly disrupted expression of 45% of tested genes in functional groups, including markers for osteoblasts, osteoclasts, mineralization, ECM, cell signaling, and inflammation. We conclude that BSP is a critical and nonredundant factor for alveolar bone healing, and its absence disrupts multiple major pathways involved in appropriate healing.

The Bone Sialoprotein RGD Domain Modulates and Maintains Periodontal Development

Bone sialoprotein (gene: Ibsp; protein: BSP) is a multifunctional extracellular matrix protein present in bone, cementum, and dentin. Accumulating evidence supports BSP as a key regulator of mineralized tissue formation via evolutionarily conserved functional domains, including a C-terminal integrin-binding Arg-Gly-Asp (RGD) domain implicated in extracellular matrix-cell signaling. Ablation of Ibsp in mice (Ibsp-/-) results in impaired bone growth and mineralization and defective osteoclastogenesis, with effects in the craniofacial region including reduced acellular cementum formation, detachment of the periodontal ligament (PDL), alveolar bone hypomineralization, and severe periodontal breakdown. We hypothesized that BSP-RGD plays an important role in cementum and alveolar bone formation and mineralization, as well as periodontal function. This hypothesis was tested by replacing the RGD motif with a nonfunctional Lys-Ala-Glu (KAE) sequence in (IbspKAE/KAE) mice and OCCM.30 murine (IbspKAE) cementoblasts. The RGD domain was not critical for acellular or cellular cementum formation in IbspKAE/KAE mice. However, PDL volume and thickness were increased, and significantly more tartrate-resistant acid phosphatase-positive osteoclasts were found on alveolar bone surfaces of IbspKAE/KAE mice versus wild type mice. PDL organization was disrupted as indicated by picrosirius red stain, second harmonic generation imaging, dynamic mechanical analysis, and decreased asporin proteoglycan localization. In vitro studies implicated RGD functions in cell migration, adhesion, and mineralization, and this was confirmed by an ossicle implant model where cells lacking BSP-RGD showed substantial defects as compared with controls. In total, the BSP-RGD domain is implicated in periodontal development, though the scale and scope of changes indicated by in vitro studies indicate that other factors may partially compensate for and reduce the phenotypic severity of mice lacking BSP-RGD in vivo.

miRNA-92a-3p regulates osteoblast differentiation in patients with concomitant limb fractures and TBI via IBSP/PI3K-AKT inhibition

Patients who sustain concomitant fractures and traumatic brain injury (TBI) are known to have significantly quicker fracture-healing rates than patients with isolated fractures. The mechanisms underlying this phenomenon have yet to be identified. In the present study, we found that the upregulation of microRNA-92a-3p (miRNA-92a-3p) induced by TBI correlated with a decrease in integrin binding sialoprotein (IBSP) expression in callus formation. In vitro, overexpressing miRNA-92a-3p inhibited IBSP expression and accelerated osteoblast differentiation, whereas silencing of miRNA-92a-3p inhibited osteoblast activity. A decrease in IBSP facilitated osteoblast differentiation via the Phosphatidylinositol 3-kinase/threonine kinase 1 (PI3K/AKT) signaling pathway. Through luciferase assays, we found evidence that IBSP is a miRNA-92a-3p target gene that negatively regulates osteoblast differentiation. Moreover, the present study confirmed that pre-injection of agomiR-92a-3p leads to increased bone formation. Collectively, these results indicate that miRNA-92a-3p overexpression may be a key factor underlying the improved fracture healing observed in TBI patients. Upregulation of miRNA-92a-3p may therefore be a promising therapeutic strategy for promoting fracture healing and preventing nonunion.

The Bone Extracellular Matrix in Bone Formation and Regeneration

Bone regeneration repairs bone tissue lost due to trauma, fractures, and tumors, or absent due to congenital disorders. The extracellular matrix (ECM) is an intricate dynamic bio-environment with precisely regulated mechanical and biochemical properties. In bone, ECMs are involved in regulating cell adhesion, proliferation, and responses to growth factors, differentiation, and ultimately, the functional characteristics of the mature bone. Bone ECM can induce the production of new bone by osteoblast-lineage cells, such as MSCs, osteoblasts, and osteocytes and the absorption of bone by osteoclasts. With the rapid development of bone regenerative medicine, the osteoinductive, osteoconductive, and osteogenic potential of ECM-based scaffolds has attracted increasing attention. ECM-based scaffolds for bone tissue engineering can be divided into two types, that is, ECM-modified biomaterial scaffold and decellularized ECM scaffold. Tissue engineering strategies that utilize the functional ECM are superior at guiding the formation of specific tissues at the implantation site. In this review, we provide an overview of the function of various types of bone ECMs in bone tissue and their regulation roles in the behaviors of osteoblast-lineage cells and osteoclasts. We also summarize the application of bone ECM in bone repair and regeneration. A better understanding of the role of bone ECM in guiding cellular behavior and tissue function is essential for its future applications in bone repair and regenerative medicine.

Bone sialoprotein-αvβ3 integrin axis promotes breast cancer metastasis to the bone

The underlying mechanisms of breast cancer cells metastasizing to distant sites are complex and multifactorial. Bone sialoprotein (BSP) and αvβ3 integrin were reported to promote the metastatic progress of breast cancer cells, particularly metastasis to bone. Most theories presume that BSP promotes breast cancer metastasis by binding to αvβ3 integrin. Interestingly, we found the αvβ3 integrin decreased in BSP silenced cells (BSPi), which have weak ability to form bone metastases. However, the relevance of their expression in primary tumor and the way they participate in metastasis are not clear. In this study, we evaluated the relationship between BSP, αvβ3 integrin levels, and the bone metastatic ability of breast cancer cells in patient tissues, and the data indicated that the αvβ3 integrin level is closely correlated to BSP level and metastatic potential. Overexpression of αvβ3 integrin in cancer cells could reverse the effect of BSPi in vitro and promote bone metastasis in a mouse model, whereas knockdown of αvβ3 integrin have effects just like BSPi. Moreover, The Cancer Genome Atlas data and RT‐PCR analysis have also shown that SPP1, KCNK2, and PTK2B might be involved in this process. Thus, we propose that αvβ3 integrin is one of the downstream factors regulated by BSP in the breast cancer‐bone metastatic cascade.

Deletion of OPN in BSP knockout mice does not correct bone hypomineralization but results in high bone turnover

The two SIBLING (Small Integrin Binding Ligand N-linked Glycoproteins), bone sialoprotein (BSP) and osteopontin (OPN) are expressed in osteoblasts and osteoclasts. In mature BSP knockout (KO, ^-/-) mice, both bone formation and resorption as well as mineralization are impaired. OPN^-/- mice display impaired resorption, and OPN is described as an inhibitor of mineralization. However, OPN is overexpressed in BSP^-/- mice, complicating the understanding of their phenotype. We have generated and characterized mice with a double KO (DKO) of OPN and BSP, to try and unravel their respective contributions. Despite the absence of OPN, DKO bones are still hypomineralized. The SIBLING, matrix extracellular phosphoglycoprotein with ASARM motif (MEPE) is highly overexpressed in both BSP^-/- and DKO and may impair mineralization through liberation of its ASARM (Acidic Serine-Aspartate Rich MEPE associated) peptides. DKO mice also display evidence of active formation of trabecular, secondary bone as well as primary bone in the marrow-ablation repair model. A higher number of osteoclasts form in DKO marrow cultures, with higher resorption activity, and DKO long bones display a localized and conspicuous cortical macroporosity. High bone formation and resorption parameters, and high cortical porosity in DKO mice suggest an active bone modeling/remodeling, in the absence of two key regulators of bone cell performance. This first double KO of SIBLING proteins thus results in a singular, non-trivial phenotype leading to reconsider the interpretation of each single KO, concerning in particular matrix mineralization and the regulation of bone cell activity.

Cancer Secretome May Influence BSP and DSP Expression in Human Salivary Gland Cells

One of the biggest challenges in managing head and neck cancers, especially salivary gland cancers, is the identification of secreted biomarkers of the disease that can be evaluated noninvasively. A relevant source of enriched tumor markers could potentially be found in the tumor secretome. Although numerous studies have evaluated secretomes from various cancers, the influence of the cancer secretome derived from salivary gland cancers on the behavior of normal cells has not yet been elucidated. Our data indicate that secretome derived from salivary gland cancer cells can influence the expression of two potential biomarkers of oral cancer-namely, bone sialoprotein (BSP) and dentin sialoprotein (DSP)-in normal salivary gland cells. Using routine immunohistochemistry, immunofluorescence, and immunoblotting techniques, we demonstrate an enrichment of BSP and DSP in human salivary gland (HSG) cancer tissue, unique localizations of BSP and DSP in HSG cancer cells, and enriched expression of BSP and DSP in normal salivary gland cells exposed to a cancer secretome. The secretome domain of the cancer microenvironment could alter signaling cascades responsible for normal cell proliferation, migration, and invasion, thus enhancing cancer cell survival and the potential for cancer progression. The cancer secretome may be critical in maintaining and stimulating "cancer-ness," thus potentially promoting specific hallmarks of metastasis.

The role of the SIBLING, Bone Sialoprotein in skeletal biology - Contribution of mouse experimental genetics

Bone Sialoprotein (BSP) is a member of the "Small Integrin-Binding Ligand N-linked Glycoproteins" (SIBLING) extracellular matrix protein family of mineralized tissues. BSP has been less studied than other SIBLING proteins such as Osteopontin (OPN), which is coexpressed with it in several skeletal cell types. Here we review the contribution of genetically engineered mice (BSP gene knockout and overexpression) to the understanding of the role of BSP in the bone organ. The studies made so far highlight the role of BSP in skeletal mineralization, as well as its importance for proper osteoblast and osteoclast differentiation and activity, most prominently in primary/repair bone. The absence of BSP also affects the local environment of the bone tissue, in particular hematopoiesis and vascularization. Interestingly, lack of BSP induces an overexpression of OPN, and the cognate protein could be responsible for some aspects of the BSP gene knockout skeletal phenotype, while replacing BSP for some of its functions. Such interplay between the partly overlapping functions of SIBLING proteins, as well as the network of cross-regulations in which they are involved should now be the focus of further work.

Mineralization defects in cementum and craniofacial bone from loss of bone sialoprotein

Bone sialoprotein (BSP) is a multifunctional extracellular matrix protein found in mineralized tissues, including bone, cartilage, tooth root cementum (both acellular and cellular types), and dentin. In order to define the role BSP plays in the process of biomineralization of these tissues, we analyzed cementogenesis, dentinogenesis, and osteogenesis (intramembranous and endochondral) in craniofacial bone in Bsp null mice and wild-type (WT) controls over a developmental period (1-60 days post natal; dpn) by histology, immunohistochemistry, undecalcified histochemistry, microcomputed tomography (microCT), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and quantitative PCR (qPCR). Regions of intramembranous ossification in the alveolus, mandible, and calvaria presented delayed mineralization and osteoid accumulation, assessed by von Kossa and Goldner's trichrome stains at 1 and 14 dpn. Moreover, Bsp(-/-) mice featured increased cranial suture size at the early time point, 1 dpn. Immunostaining and PCR demonstrated that osteoblast markers, osterix, alkaline phosphatase, and osteopontin were unchanged in Bsp null mandibles compared to WT. Bsp(-/-) mouse molars featured a lack of functional acellular cementum formation by histology, SEM, and TEM, and subsequent loss of Sharpey's collagen fiber insertion into the tooth root structure. Bsp(-/-) mouse alveolar and mandibular bone featured equivalent or fewer osteoclasts at early ages (1 and 14 dpn), however, increased RANKL immunostaining and mRNA, and significantly increased number of osteoclast-like cells (2-5 fold) were found at later ages (26 and 60 dpn), corresponding to periodontal breakdown and severe alveolar bone resorption observed following molar teeth entering occlusion. Dentin formation was unperturbed in Bsp(-/-) mouse molars, with no delay in mineralization, no alteration in dentin dimensions, and no differences in odontoblast markers analyzed. No defects were identified in endochondral ossification in the cranial base, and craniofacial morphology was unaffected in Bsp(-/-) mice. These analyses confirm a critical role for BSP in processes of cementogenesis and intramembranous ossification of craniofacial bone, whereas endochondral ossification in the cranial base was minimally affected and dentinogenesis was normal in Bsp(-/-) molar teeth. Dissimilar effects of loss of BSP on mineralization of dental and craniofacial tissues suggest local differences in the role of BSP and/or yet to be defined interactions with site-specific factors.

Mechanical Forces Exacerbate Periodontal Defects in Bsp-null Mice

Bone sialoprotein (BSP) is an acidic phosphoprotein with collagen-binding, cell attachment, and hydroxyapatite-nucleating properties. BSP expression in mineralized tissues is upregulated at onset of mineralization. Bsp-null (Bsp(-/-)) mice exhibit reductions in bone mineral density, bone turnover, osteoclast activation, and impaired bone healing. Furthermore, Bsp(-/-) mice have marked periodontal tissue breakdown, with a lack of acellular cementum leading to periodontal ligament detachment, extensive alveolar bone and tooth root resorption, and incisor malocclusion. We hypothesized that altered mechanical stress from mastication contributes to periodontal destruction observed in Bsp(-/-) mice. This hypothesis was tested by comparing Bsp(-/-) and wild-type mice fed with standard hard pellet diet or soft powder diet. Dentoalveolar tissues were analyzed using histology and micro-computed tomography. By 8 wk of age, Bsp(-/-) mice exhibited molar and incisor malocclusion regardless of diet. Bsp(-/-) mice with hard pellet diet exhibited high incidence (30%) of severe incisor malocclusion, 10% lower body weight, 3% reduced femur length, and 30% elevated serum alkaline phosphatase activity compared to wild type. Soft powder diet reduced severe incisor malocclusion incidence to 3% in Bsp(-/-) mice, supporting the hypothesis that occlusal loading contributed to the malocclusion phenotype. Furthermore, Bsp(-/-) mice in the soft powder diet group featured normal body weight, long bone length, and serum alkaline phosphatase activity, suggesting that tooth dysfunction and malnutrition contribute to growth and skeletal defects reported in Bsp(-/-) mice. Bsp(-/-) incisors also erupt at a slower rate, which likely leads to the observed thickened dentin and enhanced mineralization of dentin and enamel toward the apical end. We propose that the decrease in eruption rate is due to a lack of acellular cementum and associated defective periodontal attachment. These data demonstrate the importance of BSP in maintaining proper periodontal function and alveolar bone remodeling and point to dental dysfunction as causative factor of skeletal defects observed in Bsp(-/-) mice.

The impairment of osteogenesis in bone sialoprotein (BSP) knockout calvaria cell cultures is cell density dependent

Bone sialoprotein (BSP) belongs to the "small integrin-binding ligand N-linked glycoprotein" (SIBLING) family, whose members interact with bone cells and bone mineral. BSP is strongly expressed in bone and we previously showed that BSP knockout (BSP-/-) mice have a higher bone mass than wild type (BSP+/+) littermates, with lower bone remodelling. Because baseline bone formation activity is constitutively lower in BSP-/- mice, we studied the impact of the absence of BSP on in vitro osteogenesis in mouse calvaria cell (MCC) cultures. MCC BSP-/- cultures exhibit fewer fibroblast (CFU-F), preosteoblast (CFU-ALP) and osteoblast colonies (bone nodules) than wild type, indicative of a lower number of osteoprogenitors. No mineralized colonies were observed in BSP-/- cultures, along with little/no expression of either osteogenic markers or SIBLING proteins MEPE or DMP1. Osteopontin (OPN) is the only SIBLING expressed in standard density BSP-/- culture, at higher levels than in wild type in early culture times. At higher plating density, the effects of the absence of BSP were partly rescued, with resumed expression of osteoblast markers and cognate SIBLING proteins, and mineralization of the mutant cultures. OPN expression and amount are further increased in high density BSP-/- cultures, while PHEX and CatB expression are differentiatlly regulated in a manner that may favor mineralization. Altogether, we found that BSP regulates mouse calvaria osteoblast cell clonogenicity, differentiation and activity in vitro in a cell density dependent manner, consistent with the effective skeletogenesis but the low levels of bone formation observed in vivo. The BSP knockout bone microenvironment may alter the proliferation/cell fate of early osteoprogenitors.

Blocking the expression of both bone sialoprotein (BSP) and osteopontin (OPN) impairs the anabolic action of PTH in mouse calvaria bone

Osteopontin (OPN) and bone sialoprotein (BSP) are coexpressed in osteoblasts and osteoclasts, and display overlapping properties. We used daily injection of parathyroid hormone 1-84 (iPTH) over the calvaria of BSP knockout (-/-) mice to investigate further their functional specificity and redundancy. iPTH stimulated bone formation in both +/+ and -/- mice, increasing to the same degree periosteum, osteoid and total bone thickness. Expression of OPN, osterix, osteocalcin (OCN) and DMP1 was also increased by iPTH in both genotypes. In contrast to +/+, calvaria cell cultures from -/- mice revealed few osteoblast colonies, no mineralization and little expression of OCN, MEPE or DMP1. In contrast, OPN levels were 5× higher in -/- versus +/+ cultures. iPTH increased alkaline phosphatase (ALP) activity in cell cultures of both genotypes, with higher OCN and the induction of mineralization in -/- cultures. siRNA blocking of OPN expression did not alter the anabolic action of the hormone in BSP +/+ calvaria, while it blunted iPTH effects in -/- mice, reduced to a modest increase in periosteum thickness. In -/- (not +/+) cell cultures, siOPN blocked the stimulation by iPTH of ALP activity and OCN expression, as well as the induction of mineralization. Thus, full expression of either OPN or BSP is necessary for the anabolic effect of PTH at least in the ectopic calvaria injection model. This suggests that OPN may compensate for the lack of BSP in the response to this hormonal challenge, and provides evidence of functional overlap between these cognate proteins.

Refinement of collagen-mineral interaction: a possible role for osteocalcin in apatite crystal nucleation, growth and development

Mineralization of vertebrate tissues such as bone, dentin, cementum, and calcifying tendon involves type I collagen, which has been proposed as a template for calcium and phosphate ion binding and subsequent nucleation of apatite crystals. Type I collagen thereby has been suggested to be responsible for the deposition of apatite mineral without the need for non-collagenous proteins or other extracellular matrix molecules. Based on studies in vitro, non-collagenous proteins, including osteocalcin and bone sialoprotein, are thought to mediate vertebrate mineralization associated with type I collagen. These proteins, as possibly related to mineral deposition, have not been definitively localized in vivo. The present study has reexamined their localization in the leg tendons of avian turkeys, a representative model of vertebrate mineralization. Immunocytochemistry of osteocalcin demonstrates its presence at the surface of, outside and within type I collagen while that of bone sialoprotein appears to be localized at the surface of or outside type I collagen. The association between osteocalcin and type I collagen structure is revealed optimally when calcium ions are added to the antibody solution in the methodology. In this manner, osteocalcin is found specifically located along the a4-1, b1, c2 and d bands defining in part the hole and overlap zones within type I collagen. From these data, while type I collagen itself may be considered a stereochemical guide for intrafibrillar mineral nucleation and subsequent deposition, osteocalcin bound to type I collagen may also possibly mediate nucleation, growth and development of platelet-shaped apatite crystals. Bone sialoprotein and osteocalcin as well, each immunolocalized at the surface of or outside type I collagen, may affect mineral deposition in these portions of the avian tendon.

Deficiency of G-protein coupled receptor 40, a lipid-activated receptor, heightens in vitro- and in vivo-induced murine osteoarthritis

Osteoarthritis (OA) is an age-related degenerative joint disease. To date, its management is focused on symptoms (pain and inflammation). Studies suggest that fatty acids can reduce the expression of inflammatory and catalytic mediators, and improve in vivo joint function. Free fatty acid receptors (FFARs) such as G-protein coupled receptor 40 (GPR40) are proposed as attractive therapeutic targets to counteract inflammation and cartilage degradation observed in OA. This study aims to elucidate the involvement of GPR40 in OA. In this study, we used an in vitro model of OA, and surgically induced OA by ligament transection and partial meniscectomy in wild-type and GPR40 deficient mice. OA phenotype was investigated in vivo by histology and genes expression. We demonstrate that IL-1β-treated GPR40(-/-) chondrocytes secret more inflammatory mediators (nitric oxide, interleukin-6, prostaglandin E2) and active catabolic enzymes (metalloproteinase-2, -9 [MMP-2, MMP-9]), and show decreased anabolism (glycoaminoglycan) compared to GPR40(+/+) cells. In accordance with these results, we show that GPR40(-/-) mice exhibit an aggravated OA-induced phenotype characterized by higher tidemark exposure, frequency of osteophyte formation and subchondral bone sclerosis. Altogether our results demonstrate that GPR40 deficiency leads to an extended OA phenotype, providing evidence that increasing GPR40 activity, by natural or synthetic ligands, could be a new strategy in the management of OA.

Analysis of genetic regulation and cytokine expressions of distraction osteogenesis reconstruction for cleft palate

Because cleft palate (CP) is one of the most common congenital deformities, surgeons have tried for longtime to achieve an ideal reconstruction of the palatal bone defects and restoration of muscle attachments. In this study, a new CP model on rhesus was established and corrected by an approach of distraction osteogenesis (DO), and then quantitative studies of regulation of osteogenesis genes and expression of alkaline phosphatase (ALP), insulin-like growth factor-I (IGF-I), osteopontin (OPN), and osteocalcin (OC) in different phases of new bone formation were preformed. The CP models (23 animals) were established surgically. In the experimental group (21 animals), the tissue defects were repaired by means of DO at the rhythm of 0.4 mm twice per day. The specimens were retrieved in 1, 2, 4, 6, 8, 12, and 24 weeks (3 animals each) after completion of distraction. The IGF-I, ALP, OPN, and OC messenger RNA (mRNA) were detected by real-time reverse transcription polymerase chain reaction, and their proteins were then analyzed by enzyme-linked immunosorbent assay tests. The results are compared with those of the experimental control and empty control groups (2 animals each). In the distraction gap, the mRNA and protein expressions levels of IGF-I and ALP were both highly upregulated and reaching apex in the early phase of new bone formation. Otherwise, the mRNA and protein expressions of OPN and OC demonstrated high level during intermediate and later remodeling stages. These results suggest that the reconstruction of CP bone defect by means of DO could get definitely intramembraneous new bone formation and eventually quite normal bone structure via consecutive remodeling in situ.

Abdominal Fat and Sarcopenia in Women Significantly Alter Osteoblasts Homeostasis In Vitro by a WNT/ β -Catenin Dependent Mechanism

Obesity and sarcopenia have been associated with mineral metabolism derangement and low bone mineral density (BMD). We investigated whether imbalance of serum factors in obese or obese sarcopenic patients could affect bone cell activity in vitro. To evaluate and characterize potential cellular and molecular changes of human osteoblasts, cells were exposed to sera of four groups of patients: (1) affected by obesity with normal BMD (O), (2) affected by obesity with low BMD (OO), (3) affected by obesity and sarcopenia (OS), and (4) affected by obesity, sarcopenia, and low BMD (OOS) as compared to subjects with normal body weight and normal BMD (CTL). Patients were previously investigated and characterized for body composition, biochemical and bone turnover markers. Then, sera of different groups of patients were used to incubate human osteoblasts and evaluate potential alterations in cell homeostasis. Exposure to OO, OS, and OOS sera significantly reduced alkaline phosphatase, osteopontin, and BMP4 expression compared to cells exposed to O and CTL, indicating a detrimental effect on osteoblast differentiation. Interestingly, sera of all groups of patients induced intracellular alteration in Wnt/ β -catenin molecular pathway, as demonstrated by the significant alteration of specific target genes expression and by altered β -catenin cellular compartmentalization and GSK3 β phosphorylation. In conclusion our results show for the first time that sera of obese subjects with low bone mineral density and sarcopenia significantly alter osteoblasts homeostasis in vitro, indicating potential detrimental effects of trunk fat on bone formation and skeletal homeostasis.

Skeletal development of mice lacking bone sialoprotein (BSP)--impairment of long bone growth and progressive establishment of high trabecular bone mass

Adult Ibsp-knockout mice (BSP−/−) display shorter stature, lower bone turnover and higher trabecular bone mass than wild type, the latter resulting from impaired bone resorption. Unexpectedly, BSP knockout also affects reproductive behavior, as female mice do not construct a proper "nest" for their offsprings. Multiple crossing experiments nonetheless indicated that the shorter stature and lower weight of BSP−/− mice, since birth and throughout life, as well as their shorter femur and tibia bones are independent of the genotype of the mothers, and thus reflect genetic inheritance. In BSP−/− newborns, µCT analysis revealed a delay in membranous primary ossification, with wider cranial sutures, as well as thinner femoral cortical bone and lower tissue mineral density, reflected in lower expression of bone formation markers. However, trabecular bone volume and osteoclast parameters of long bones do not differ between genotypes. Three weeks after birth, osteoclast number and surface drop in the mutants, concomitant with trabecular bone accumulation. The growth plates present a thinner hypertrophic zone in newborns with lower whole bone expression of IGF-1 and higher IHH in 6 days old BSP−/− mice. At 3 weeks the proliferating zone is thinner and the hypertrophic zone thicker in BSP−/− than in BSP+/+ mice of either sex, maybe reflecting a combination of lower chondrocyte proliferation and impaired cartilage resorption. Six days old BSP−/− mice display lower osteoblast marker expression but higher MEPE and higher osteopontin(Opn)/Runx2 ratio. Serum Opn is higher in mutants at day 6 and in adults. Thus, lack of BSP alters long bone growth and membranous/cortical primary bone formation and mineralization. Endochondral development is however normal in mutant mice and the accumulation of trabecular bone observed in adults develops progressively in the weeks following birth. Compensatory high Opn may allow normal endochondral development in BSP−/− mice, while impairing primary mineralization.

The effect of five proteins on stem cells used for osteoblast differentiation and proliferation: a current review of the literature

Bone-tissue engineering is a therapeutic target in the field of dental implant and orthopedic surgery. It is therefore essential to find a microenvironment that enhances the growth and differentiation of osteoblasts both from mesenchymal stem cells (MSCs) and those derived from dental pulp. The aim of this review is to determine the relationship among the proteins fibronectin (FN), osteopontin (OPN), tenascin (TN), bone sialoprotein (BSP), and bone morphogenetic protein (BMP2) and their ability to coat different types of biomaterials and surfaces to enhance osteoblast differentiation. Pre-treatment of biomaterials with FN during the initial phase of osteogenic differentiation on all types of surfaces, including slotted titanium and polymers, provides an ideal microenvironment that enhances adhesion, morphology, and proliferation of pluripotent and multipotent cells. Likewise, in the second stage of differentiation, surface coating with BMP2 decreases the diameter and the pore size of the scaffold, causing better adhesion and reduced proliferation of BMP-MSCs. Coating oligomerization surfaces with OPN and BSP promotes cell adhesion, but it is clear that the polymeric coating material BSP alone is insufficient to induce priming of MSCs and functional osteoblastic differentiation in vivo. Finally, TN is involved in mineralization and can accelerate new bone formation in a multicellular environment but has no effect on the initial stage of osteogenesis.

BSP gene silencing inhibits migration, invasion, and bone metastasis of MDA-MB-231BO human breast cancer cells

Bone sialoprotein (BSP) has been implicated in a variety of physiological and pathophysiological events, including tumor cell invasion, bone homing, adhesion, and matrix degradation. To explore the potential involvement of BSP in human breast cancer cell invasion and metastasis, we used retrovirus-mediated RNAi to deplete BSP levels in the human bone-seeking breast cancer cell line MDA-MB-231BO (231BO) and established the 231BO-BSP27 and 231BO-BSP81 cell clones. Cell proliferation, colony formation, wound healing, and the ability to invade into matrigel of these BSP-depleted clones were all decreased. Both 231BO-BSP27 cells and 231BO-BSP81 cells showed a significant (15.4% and 28.6% respectively) reduction of bone metastatic potential following intracardiac injection as determined by X-ray detection and by hematoxylin and eosin staining. Moreover, the expression of integrins αvβ3 and β3 was decreased in the BSP-silenced cells whereas ectopic BSP expression increased the integrins αvβ3 and β3 levels. These results together suggest that BSP silencing decreased the integrin αvβ3 and β3 levels, in turn inhibiting cell migration and invasion and decreasing the ability of the cells to metastasize to bone.

Maxillary sinus augmentation procedures through equine-derived biomaterial or calvaria autologous bone: immunohistochemical evaluation of OPG/RANKL in humans

Autologous bone is considered the gold standard for bone regeneration, even if different heterologous bone substitutes have been proposed to overcome the limits related to its use. The aim of this study was to analyze and to compare the molecular events switched on by autologous or heterologous bone graft insertion, focusing on TGFβ1 expression and OPG/RANKL ratio, to analyze resorption process, and estimating graft vascularization, new bone tissue deposition and its mineralization, through VEGF, BSP and SPARC expression evaluation, respectively. Patients needing pre-prosthetic rehabilitation of the posterior maxilla were treated using an equine-derived biomaterial (Group 1) or calvaria autologous bone (Group 2), according to the morphology of the bone defect. Bone graft integration was evaluated on bone samples obtained from the treated areas at the moment of dental implant insertion, by morphological and immunohistochemical analyses for TGFβ1, OPG, RANKL, VEGF, BSP, and SPARC expression. Morpho - logical analysis shows the presence of biomaterial residual granules in Group 1, in parallel to a good integration between graft and host tissue. Moderate TGFβ1 expression is seen in both Group 1 and Group 2. OPG/RANKL ratio appears higher in Group 1; VEGF expression appears very strong in Group 1 and strong in Group 2, while BSP and SPARC expression results weak in Group 1 and moderate in Group 2. Our results reveal the good integration between both types of graft and the host tissue, even though autologous graft seems to produce a faster regenerative process, as evidenced by the different expression of the investigated molecules. According to these observations, the clinical use of heterologous particulate equine-derived biomaterial may ensure long-term predictability of implantprosthetic rehabilitation, comparable to that obtained with autologous bone graft.

Deficiency in acellular cementum and periodontal attachment in bsp null mice

Bone sialoprotein (BSP) is an extracellular matrix protein found in mineralized tissues of the skeleton and dentition. BSP is multifunctional, affecting cell attachment and signaling through an RGD integrin-binding region, and acting as a positive regulator for mineral precipitation by nucleating hydroxyapatite crystals. BSP is present in cementum, the hard tissue covering the tooth root that anchors periodontal ligament (PDL) attachment. To test our hypothesis that BSP plays an important role in cementogenesis, we analyzed tooth development in a Bsp null ((-/-)) mouse model. Developmental analysis by histology, histochemistry, and SEM revealed a significant reduction in acellular cementum formation on Bsp (-/-) mouse molar and incisor roots, and the cementum deposited appeared hypomineralized. Structural defects in cementum-PDL interfaces in Bsp (-/-) mice caused PDL detachment, likely contributing to the high incidence of incisor malocclusion. Loss of BSP caused progressively disorganized PDL and significantly increased epithelial down-growth with aging. Bsp (-/-) mice displayed extensive root and alveolar bone resorption, mediated by increased RANKL and the presence of osteoclasts. Results collected here suggest that BSP plays a non-redundant role in acellular cementum formation, likely involved in initiating mineralization on the root surface. Through its importance to cementum integrity, BSP is essential for periodontal function.

Sequential expression of osteoblast phenotypic genes during medullary bone formation and resorption in estrogen-treated male Japanese quails

Medullary bone is formed reticularly in the bone marrow cavity of the long bones of female birds. Although this bone matrix contains fewer collagen fibers and more acid mucopolysaccharides than cortical bone, it is not clear that the expression pattern of osteoblast phenotypic genes during bone remodeling. Therefore, 17β-estradiol (E2)-treated male Japanese quails were used to examine the temporal expression patterns of osteoblast phenotypic genes, and to simultaneously confirm the morphological changes occurring in the bone marrow cavity during medullary bone formation and resorption. After E2 treatment, bone lining cells proliferated and developed into mature osteoblasts that had intense alkaline phosphatase (ALP) activity. These cells began to form medullary bone that contained acid mucopolysaccharides and tartrate-resistantacid phosphatase. Runt-related gene 2 (Runx2) mRNA was stably expressed throughout the process. The expression of both ALP and type I collagen mRNAs increased initially, and then rapidly decreased after day 7, while osteoclasts began to resorb medullary bone at day 5. The expression of bone matrix-related genes peaked at day 5, and suddenly decreased at day 7, except for osteopontin. Taken together with these results, the expression patterns of bone matrix-related genes during the later stages might be related to osteoclast activity. Additionally, the constant expression of Runx2 during bone formation and resorption suggested that osteoprogenitor cells always exist in the bone marrow cavity. Therefore, the expression patterns of these genes and the characteristics of bone matrix might extremely be related to the quick remodeling of medullary bone.

Osteopontin deficiency delays inflammatory infiltration and the onset of muscle regeneration in a mouse model of muscle injury

Osteopontin is secreted by skeletal muscle myoblasts and stimulates their proliferation. Expression of osteopontin in skeletal muscle is upregulated in pathological conditions including Duchenne muscular dystrophy, and recent evidence suggests that osteopontin might influence the course of this disease. The current study was undertaken to determine whether osteopontin regulates skeletal muscle regeneration. A whole muscle autografting model of regeneration in osteopontin-null and wild-type mice was used. Osteopontin expression was found to be strongly upregulated in wild-type grafts during the initial degeneration and subsequent early regeneration phases that are observed in this model. Grafted muscle from osteopontin-null mice degenerated more slowly than that of wild-type mice, as determined by histological assessment, fibre diameter and fibre number. The delayed degeneration in osteopontin-null grafts was associated with a delay in neutrophil and macrophage infiltration. Centrally nucleated (regenerating) muscle fibres also appeared more slowly in osteopontin-null grafts than in wild-type grafts. These results demonstrate that osteopontin plays a non-redundant role in muscle remodelling following injury.

Absence of bone sialoprotein (BSP) impairs primary bone formation and resorption: the marrow ablation model under PTH challenge

Bone sialoprotein (BSP) is highly expressed in early bone deposition and may play a part in primary bone mineralization. We previously showed that while BSP−/− mice have a mild secondary bone phenotype and are responsive to mechanical (unloading) and hormonal (ovariectomy, parathyroid hormone (PTH)) challenges, repair of a cortical bone defect, which involves primary bone deposition is significantly delayed in these mice. In the present study, we investigated the role of BSP in a pure model of primary bone modeling. Bone marrow was ablated by trans-epiphysis aspiration in the femora of BSP+/+ and BSP−/− mice, and 7 days post surgery μCT analysis showed vigorous new bone formation in the shaft of BSP+/+ animals but much less in BSP−/− mice. After 14 days, the volume of medullary bone was significantly decreased as expected in BSP+/+ mice, while it remained stable in the BSP−/−. Osteoid thickness and surface were higher in BSP−/− at day 7, suggesting delayed mineralization, while osteoclast surface and number were significantly lower at day 14, a stage of high medullary bone resorption. At day 7, mRNA expression of early osteoblast marker genes (RUNX2, osterix, alkaline phosphatase, osteopontin) did not differ between the two genotypes, while markers of terminal differentiation (MEPE, DMP1, osteocalcin) as well as receptor activator of NF-kappaB ligand (RANKL) and tartrate-resistant acid phosphatase (TRAP) were significantly lower in BSP−/− than in BSP+/+ mice. PTH treatment maintained the volume of medullary bone up to 12 days after ablation in BSP+/+ mice, but failed to do so in BSP−/− mice. PTH significantly increased bone formation rate in both genotype, while it reduced osteoclast number and surface in BSP+/+, but not in BSP−/− medullary bone. In summary, medullary bone formation after marrow ablation is blunted in BSP−/− mice, with delayed resorption and impaired response to PTH. These findings confirm the hypothesis of a crucial role for BSP in primary ossification, which has long been suspected for mineralization, but here extends to bone deposition and turnover.

Biomineralization of bone: a fresh view of the roles of non-collagenous proteins

The impact of genetics has dramatically affected our understanding of the functions of non-collagenous proteins. Specifically, mutations and knockouts have defined their cellular spectrum of actions. However, the biochemical mechanisms mediated by non-collagenous proteins in biomineralization remain elusive. It is likely that this understanding will require more focused functional testing at the protein, cell, and tissue level. Although initially viewed as rather redundant and static acidic calcium binding proteins, it is now clear that non-collagenous proteins in mineralizing tissues represent diverse entities capable of forming multiple protein-protein interactions which act in positive and negative ways to regulate the process of bone mineralization. Several new examples from the author's laboratory are provided which illustrate this theme including an apparent activating effect of hydroxyapatite crystals on metalloproteinases. This review emphasizes the view that secreted non-collagenous proteins in mineralizing bone actively participate in the mineralization process and ultimately control where and how much mineral crystal is deposited, as well as determining the quality and biomechanical properties of the mineralized matrix produced.