Separation of newly formed bone from older compact bone reveals clear compositional differences in bone matrix

Bone sialoprotein stimulates cancer cell adhesion through the RGD motif and the αvβ3 and αvβ5 integrin receptors

Being implicated in bone metastasis development, bone sialoprotein (BSP) expression is upregulated in patients with cancer. While BSP regulates cancer cell adhesion to the extracellular matrix, to the best of our knowledge, the specific adhesive molecular interactions in metastatic bone disease remain unclear. The present study aimed to improve the understanding of the arginine-glycine-aspartic acid (RGD) sequence of BSP and the integrin receptors αvβ3 and αvβ5 in BSP-mediated cancer cell adhesion. Human breast cancer (MDA-MB-231), prostate cancer (PC-3) and non-small cell lung cancer (NSCLC; NCI-H460) cell lines were cultured on BSP-coated plates. Adhesion assays with varying BSP concentrations were performed to evaluate the effect of exogenous glycine-arginine-glycine-aspartic acid-serine-proline (GRGDSP) peptide and anti-integrin antibodies on the attachment of cancer cells to BSP. Cell attachment was assessed using the alamarBlue® assay. The present results indicated that BSP supported the adhesion of cancer cells. The RGD counterpart GRGDSP peptide reduced the attachment of all tested cancer cell lines to BSP by ≤98.4%. Experiments with anti-integrin antibodies demonstrated differences among integrin receptors and cancer cell types. The αvβ5 antibody decreased NSCLC cell adhesion to BSP by 84.3%, while the αvβ3 antibody decreased adhesion by 14%. The αvβ3 antibody decreased PC-3 cell adhesion to BSP by 46.4%, while the αvβ5 antibody decreased adhesion by 9.5%. Adhesion of MDA-MB-231 cells to BSP was inhibited by 54.7% with αvβ5 antibody. The present results demonstrated that BSP-induced cancer cell adhesion occurs through the binding of the RGD sequence of BSP to the cell integrin receptors αvβ3 and αvβ5. Differences between cancer types were found regarding the mediation via αvβ3 or αvβ5 receptors. The present findings may explain why certain cancer cells preferentially spread to the bone tissue, suggesting that targeting the RGD-integrin binding interaction could be a promising novel cancer treatment option.

Beyond bone volume: Understanding tissue-level quality in healing of maxillary vs. femoral defects

Currently, principles of tissue engineering and implantology are uniformly applied to all bone sites, disregarding inherent differences in collagen, mineral composition, and healing rates between craniofacial and long bones. These differences could potentially influence bone quality during the healing process. Evaluating bone quality during healing is crucial for understanding local mechanical properties in regeneration and implant osseointegration. However, site-specific changes in bone quality during healing remain poorly understood. In this study, we assessed newly formed bone quality in sub-critical defects in the maxilla and femur, while impairing collagen cross-linking using β-aminopropionitrile (BAPN). Our findings revealed that femoral healing bone exhibited a 73 % increase in bone volume but showed significantly greater viscoelastic and collagen changes compared to surrounding bone, leading to increased deformation during long-term loading and poorer bone quality in early healing. In contrast, the healing maxilla maintained equivalent hardness and viscoelastic constants compared to surrounding bone, with minimal new bone formation and consistent bone quality. However, BAPN-impaired collagen cross-linking induced viscoelastic changes in the healing maxilla, with no further changes observed in the femur. These results challenge the conventional belief that increased bone volume correlates with enhanced tissue-level bone quality, providing crucial insights for tissue engineering and site-specific implant strategies. The observed differences in bone quality between sites underscore the need for a nuanced approach in assessing the success of regeneration and implant designs and emphasize the importance of exploring site-specific tissue engineering interventions. STATEMENT OF SIGNIFICANCE: Accurate measurement of bone quality is crucial for tissue engineering and implant therapies. Bone quality varies between craniofacial and long bones, yet it's often overlooked in the healing process. Our study is the first to comprehensively analyze bone quality during healing in both the maxilla and femur. Surprisingly, despite significant volume increase, femur healing bone had poorer quality compared to the surrounding bone. Conversely, maxilla healing bone maintained consistent quality despite minimal bone formation. Impaired collagen diminished maxillary healing bone quality, but had no further effect on femur bone quality. These findings challenge the notion that more bone volume equals better quality, offering insights for improving tissue engineering and implant strategies for different bone sites.

FAM20C plays a critical role in the development of mouse vertebra

BACKGROUND CONTEXT

Family with sequence similarity 20-member C (FAM20C) is a protein kinase that is responsible for the phosphorylation of many secretory proteins; however, its roles in spine or vertebra development have not be studied.

PURPOSE

The aim of this investigation is to analyze the roles of FAM20C in vertebra development.

STUDY DESIGN/SETTING

A mouse study of the Fam20c gene using conditional knockout to assess the effects of its inactivation on vertebra development.

METHODS

By breeding Sox2-Cre mice with Fam20c^flox/flox mice, Sox2-Cre;Fam20c^flox/flox mice (abbreviated as cKO mice) are created. X-ray radiography, resin-casted scanning electron microscopy, Hematoxylin and Eosin staining, safranin O staining, Goldner's Masson trichrome staining, Von Kossa staining, tartrate-resistant alkaline phosphatase staining, immunohistochemistry staining, Western Immunoblotting and real-time PCR were employed to characterize the vertebrae of cKO mice compared to the normal control mice.

RESULTS

Inactivation of Fam20c in mice results in remarkable spine deformity, severe morphology and mineralization defects, altered levels of osteoblast differentiation markers, reduction of activity of the Wnt/β-catenin signaling pathway and reduced level of osteoclastogenesis in the vertebrae.

CONCLUSIONS

FAM20C plays an essential role in vertebral development; it may regulate vertebral formation through the Wnt/β-catenin signaling pathway.

CLINICAL SIGNIFICANCE

Mutations in the human FAM20C gene are associated with Raine syndrome. The findings of this study provide valuable clues for the clinical management of Raine syndrome regarding spine manifestations in patients.

Mast Cell Mediators Inhibit Osteoblastic Differentiation and Extracellular Matrix Mineralization

Mast cells are multifunctional immune cells that participate in many important processes such as defense against pathogens, allergic reactions, and tissue repair. These cells perform their functions through the release of a wide variety of mediators. This release occurs mainly through cross-linking IgE (immunoglobulin E) bound to high affinity IgE receptors by multivalent antigens. The abundance of mast cells in connective tissue, surrounding blood vessels, and their involvement in the early stages of bone repair support the possibility of physiological and pathological interactions between mast cells and osteoblasts. However, the participation of mast cell mediators in osteogenesis is not fully understood. Therefore, the objective of this work was to investigate the role of mast cell mediators in the acquisition of the osteogenic phenotype in vitro. The results show that pooled mast cell mediators can affect proliferation, morphology, and cytoskeleton of osteoblastic cells, and impair the activity and expression of alkaline phosphatase as well as the expression of bone sialoprotein. Also, mast cell mediators inhibit the expression of mRNA for those proteins and inhibit the formation and maturation of calcium nodules and consequently inhibit mineralization. Therefore, mast cell mediators can modulate osteogenesis and are potential therapeutic targets for treatments of bone disorders.

Thrombospondins: A Role in Cardiovascular Disease

Thrombospondins (TSPs) represent extracellular matrix (ECM) proteins belonging to the TSP family that comprises five members. All TSPs have a complex multidomain structure that permits the interaction with various partners including other ECM proteins, cytokines, receptors, growth factors, etc. Among TSPs, TSP1, TSP2, and TSP4 are the most studied and functionally tested. TSP1 possesses anti-angiogenic activity and is able to activate transforming growth factor (TGF)-β, a potent profibrotic and anti-inflammatory factor. Both TSP2 and TSP4 are implicated in the control of ECM composition in hypertrophic hearts. TSP1, TSP2, and TSP4 also influence cardiac remodeling by affecting collagen production, activity of matrix metalloproteinases and TGF-β signaling, myofibroblast differentiation, cardiomyocyte apoptosis, and stretch-mediated enhancement of myocardial contraction. The development and evaluation of TSP-deficient animal models provided an option to assess the contribution of TSPs to cardiovascular pathology such as (myocardial infarction) MI, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis. Targeting of TSPs has a significant therapeutic value for treatment of cardiovascular disease. The activation of cardiac TSP signaling in stress and pressure overload may be therefore beneficial.

An in situ hybridization study of perlecan, DMP1, and MEPE in developing condylar cartilage of the fetal mouse mandible and limb bud cartilage

The main purpose of this in situ hybridization study was to investigate mRNA expression of three bone/cartilage matrix components (perlecan, DMP1, and MEPE) in developing primary (tibial) and secondary (condylar) cartilage. Perlecan mRNA expression was first detected in newly formed chondrocytes in tibial cartilage at E13.0, but this expression decreased in hypertrophic chondrocytes at E14.0. In contrast, at E15.0, perlecan mRNA was first detected in the newly formed chondrocytes of condylar cartilage; these chondrocytes had characteristics of hypertrophic chondrocytes, which confirmed the previous observation that progenitor cells of developing secondary cartilage rapidly differentiate into hypertrophic chondrocytes. DMP1 mRNA was detected in many chondrocytes within the lower hypertrophic cell zone in tibial cartilage at E14.0. In contrast, DMP1 mRNA expression was only transiently detected in a few chondrocytes of condylar cartilage at E15.0. Thus, DMP1 may be less important in the developing condylar cartilage than in the tibial cartilage. Another purpose of this study was to test the hypothesis that MEPE may be a useful marker molecule for cartilage. MEPE mRNA was not detected in any chondrocytes in either tibial or condylar cartilage; however, MEPE immunoreactivity was detected throughout the cartilage matrix. Western immunoblot analysis demonstrated that MEPE antibody recognized two bands, one of 67 kDa and another of 59 kDa, in cartilage-derived samples. Thus MEPE protein may gradually accumulate in the cartilage, even though mRNA expression levels were below the limits of detection of in situ hybridization. Ultimately, we could not designate MEPE as a marker molecule for cartilage, and would modify our original hypothesis.

Human mesenchymal stem cell-derived matrices for enhanced osteoregeneration

The methodology for the repair of critical-sized or non-union bone lesions has unpredictable efficacy due in part to our incomplete knowledge of bone repair and the biocompatibility of bone substitutes. Although human mesenchymal stem cells (hMSCs) differentiate into osteoblasts, which promote bone growth, their ability to repair bone in vivo has been variable. We hypothesized that given the multistage process of osteogenesis, hMSC-mediated repair might be maximal at a specific time point of healing. Using a mouse model of calvarial healing, we demonstrate that the osteo-repair capacity of hMSCs can be substantially augmented by treatment with an inhibitor of peroxisome proliferator-activated receptor γ, but efficacy is confined to the rapid osteogenic phase. Upon entry into the bone-remodeling phase, hMSC retention signals are lost, resulting in truncation of healing. To solve this limitation, we prepared a scaffold consisting of hMSC-derived extracellular matrix (ECM) containing the necessary biomolecules for extended site-specific hMSC retention. When inhibitor-treated hMSCs were coadministered with ECM, they remained at the injury, well into the remodeling phase of healing, which resulted in reproducible and complete repair of critical-sized bone defects in mice in 3 weeks. These data suggest that hMSC-derived ECM and inhibitor-treated hMSCs could be used at optimal times to substantially and reproducibly improve bone repair.