Matrix Vesicle-Mediated Mineralization and Osteocytic Regulation of Bone Mineralization

Bioceramic-mediated chondrocyte hypertrophy promotes calcified cartilage formation for rabbit osteochondral defect repair

Osteochondral tissue is a highly specialized and complex tissue composed of articular cartilage and subchondral bone that are separated by a calcified cartilage interface. Multilayered or gradient scaffolds, often in conjunction with stem cells and growth factors, have been developed to mimic the respective layers for osteochondral defect repair. In this study, we designed a hyaline cartilage-hypertrophic cartilage bilayer graft (RGD/RGDW) with chondrocytes. Previously, we demonstrated that RGD peptide-modified chondroitin sulfate cryogel (RGD group) is chondro-conductive and capable of hyaline cartilage formation. Here, we incorporated whitlockite (WH), a Mg2+-containing calcium phosphate, into RGD cryogel (RGDW group) to induce chondrocyte hypertrophy and form collagen X-rich hypertrophic cartilage. This is the first study to use WH to produce hypertrophic cartilage. Chondrocytes-laden RGDW cryogel exhibited significantly upregulated expression of hypertrophy markers in vitro and formed ectopic hypertrophic cartilage in vivo, which mineralized into calcified cartilage in bone microenvironment. Subsequently, RGD cryogel and RGDW cryogel were combined into bilayer (RGD/RGDW group) and implanted into rabbit osteochondral defect, where RGD layer supports hyaline cartilage regeneration and bioceramic-containing RGDW layer promotes calcified cartilage formation. While the RGD group (monolayer) formed hyaline-like neotissue that extends into the subchondral bone, the RGD/RGDW group (bilayer) regenerated hyaline cartilage tissue confined to its respective layer and promoted osseointegration for integrative defect repair.

Effects of handheld nonthermal plasma on the biological responses, mineralization, and inflammatory reactions of polyaryletherketone implant materials

Background/purpose

The handheld nonthermal plasma (HNP) treatment may alter the surface properties, bone metabolism, and inflammatory reactions of polyaryletherketone (PAEK) dental implant materials. This study tested whether the HNP treatment might increase the biocompatibility, surface hydrophilicity, surface free energies (SFEs), and the cell adhesion and mineralization capability of PAEK materials.

Materials and methods

Disk-shaped samples of titanium (Ti), zirconia (Zr), polyetheretherketone (PEEK [PE]), and polyetherketoneketone (PEKK [PK]) were subjected to HNP treatment and termed as TiPL, ZrPL, PEPL, and PKPL, respectively. Water-surface reactions were examined using a goniometer. MG-63 cells were cultured on all samples to assess the cell viability, cytotoxicity, cell attachment, and mineralization characteristics. The expression of pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) and key mineralization markers (alkaline phosphatase [ALKP], osteopontin [OPN], and dentin matrix protein 1 [DMP1]) was measured using enzyme-linked immunosorbent assay kits.

Results

The HNP-treated samples exhibited significantly enhanced surface hydrophilicities and SFEs compared to the untreated samples. The cell viability remained high across all samples, indicating no cytotoxic effects. The HNP treatment significantly enhanced MG-63 cell adherence and proliferation. Elevated levels of ALKP and OPN were observed for the plasma-treated PEPL and PKPL specimens, while DMP1 levels increased significantly only in the PKPL specimen. Pro-inflammatory cytokine levels were low across all samples, suggesting no inflammatory response.

Conclusion

The HNP-treated PAEKs have enhanced the surface hydrophilicity and SFEs as well as superior cell adhesion and mineralization capability, and thus may be good clinical dental implant materials.

Regional difference in the distribution of alkaline phosphatase, PHOSPHO1, and calcein labeling in the femoral metaphyseal trabeculae in parathyroid hormone-administered mice

OBJECTIVES

This study aimed to elucidate whether the administration of parathyroid hormone (PTH) results in remodeling- or modeling-based bone formation in different regions of the murine femora, and whether the PTH-driven bone formation would facilitate osteoblastic differentiation into osteocytes.

METHODS

Six-week-old male C57BL/6J mice were employed to examine the distribution of alkaline phosphatase (ALP), PHOSPHO1, podoplanin, and calcein labeling in two distinct long bone regions: the metaphyseal trabeculae close to the chondro-osseous junction (COJ) and those distant from the COJ in three mouse groups, a control group receiving a vehicle (sham group) and groups receiving hPTH (1-34) twice a day (PTH BID group) or four times a day (PTH QID group) for two weeks.

RESULTS

The sham group showed PHOSPHO1-reactive mature osteoblasts localized primarily at the COJ, whereas the PTH BID/QID groups exhibited extended lines of PHOSPHO1-reactive osteoblasts even in regions distant from the COJ. The PTH QID group displayed fragmented calcein labeling in trabeculae close to the COJ, whereas continuous labeling was observed in trabeculae distant from the COJ. Osteoblasts tended to express podoplanin and PHOSPHO1 independently in the close and distant regions of the sham group, while osteoblasts in the PTH-administered groups showed immunoreactivity of podoplanin and PHOSPHO1 together in the close and distant regions.

CONCLUSIONS

Administration of PTH may accelerate remodeling-based bone formation in regions close to the COJ while predominantly inducing modeling-based bone formation in distant regions. PTH appeared to simultaneously facilitate osteoblastic bone mineralization and differentiation into osteocytes in both remodeling- and modeling-based bone formation.

Octacalcium phosphate with incorporated terephthalate ion derivatives: novel guest molecules and unique fluorescence properties

Octacalcium phosphate (OCP), an inorganic compound with a layered structure that can incorporate various carboxylic acids, exhibits fluorescence when aromatic carboxylate ions are present in the interlayers. However, the incorporation of carboxylate ions into OCP involves molecular selectivity, and the synthesis of novel OCP materials with incorporated terephthalate ion derivatives is particularly challenging. In this study, we incorporated 4-(carboxymethyl)benzoate and 1,4-phenylenediacetate ions into OCP for the first time and investigated the resulting fluorescence properties. The relationship between the (100) interplanar spacing and size of the incorporated dicarboxylate ions revealed that 4-(carboxymethyl)benzoate ions have a relaxed structure in the OCP interlayers, whereas the structure of the 1,4-phenylenediacetate ions is elongated by approximately 10% relative to that of the stable conformation. OCP with incorporated 1,4-phenylenediacetate ions showed blue fluorescence at 286 nm under 254 nm excitation. In contrast, distinct from previously reported fluorescent OCPs, OCP with incorporated 4-(carboxymethyl)benzoate ions exhibited two-colour fluorescence, with pink emission under 254 nm excitation and blue emission under 312 and 365 nm excitation. This OCP material exhibiting fluorescence at two wavelengths in the visible-light range offers new possibilities for practical applications. In particular, these unique fluorescence characteristics combined with the excellent biological properties of OCP can be exploited to develop novel biofriendly fluorescent probes. These findings contribute to an improved understanding of fundamental calcium phosphate chemistry and should encourage further research on functional OCP materials.

Transcriptome analysis to explore the mechanism of downregulated TNIK influencing the effect of risperidone

Background

Risperidone is one of the most reliable and effective antipsychotics for schizophrenia treatment. However, the mechanism of action of risperidone is not yet fully understood. Traf2 and Nck-interacting protein kinase (TNIK), a schizophrenia susceptibility gene, is associated with risperidone treatment response. Our previous in vitro experiments confirmed that downregulated TNIK affected the effect of risperidone on downstream targets. However, the effect of downregulated TNIK on risperidone-induced molecular expression remains to be further explored.

Methods

Transcriptome analysis was performed on U251 cells subjected to risperidone, TNIK siRNA, and no treatment, respectively. Compared to the no-treatment group, two groups of DEGs were screened out and then intersected with the schizophrenia-related genes to screen the cross-talk genes. Those DEGs were analyzed using GO and KEGG. STRING and Cytoscape were used to construct a protein-protein interaction (PPI) network for the cross-talk gene.

Results

The results showed that the parathyroid hormone synthesis, secretion, and action were significantly enriched after risperidone treatment. Downregulated TNIK could have an impact on the collagen-containing extracellular matrix, signaling receptor activator activity, and PI3K-Akt signaling pathway. Interestingly, bone mineralization function and calcium signaling pathway were enriched in the cross-talk genes. Additionally, FGFR2, FGF1, and FGFR might be the potential targets for TNIK affecting the effects of risperidone.

Conclusion

The study indicated that risperidone primarily influences functions and/or pathways associated with bone metabolism, potentially contributing to the adverse effect of osteoporosis. Our study may offer a novel perspective on investigating the mechanisms underlying the adverse effects of risperidone.

Optic disc drusen: Dystrophic calcification, a potential target for treatment

Optic disc drusen (ODD) are calcified, acellular bodies, seen in the optic nerve head of up to 2% of the population. Although seldomly affecting visual acuity, visual field defects are common, and severe, ischemic complications causing irreversible vision loss are known to occur. Different treatment strategies for ODD have been explored, but so far without success. This review focuses on the unique, calcified property of ODD, describing what we know about ODD pathogenesis and previously tried treatment strategies. In this context, we discuss current knowledge about calcium and pathological calcifications, including intracranial and ocular calcifications. We also explore some of the obstacles that must be addressed to develop a therapy centred on the concept of calcification, should calcification be identified as a pathogenic factor contributing to vision loss.

Regulation of bone homeostasis by traditional Chinese medicine active scaffolds and enhancement for the osteoporosis bone regeneration

ETHNOPHARMACOLOGICAL RELEVANCE

The active ingredients of traditional Chinese medicine (TCM), such as naringin (NG), Eucommiol, isopsoralen, icariin, Astragalus polysaccharides, and chondroitin sulfate, contained in Drynariae Rhizoma, Eucommiae Cortex, Psoralea corylifolia, Herba Epimedii, Astragalus radix and deer antler, are considered promising candidates for enhancing the healing of osteoporotic defects due to their outstanding bone homeostasis regulating properties. They are commonly used to activate bone repair scaffolds.

AIM OF THE REVIEW

Bone repair scaffolds are inadequate to meet the demands of osteoporotic defect healing due to the lack of regulation of bone homeostasis. Therefore, selecting bone scaffolds activated with TCM to improve the therapeutic effect of repairing osteoporotic bone defects.

MATERIALS AND METHODS

To gather information on bone scaffold activated by traditional Chinese medicine, we conducted a thorough search of several scientific databases, including Google Scholar, Web of Science, Scifinder, Baidu Scholar, PubMed, and China National Knowledge Infrastructure (CNKI).

RESULTS

This review discusses the mechanism of TCM active ingredients in regulating bone homeostasis, including stimulating bone formation and inhibiting bone resorption process and the healing mechanism of traditional bone repair scaffolds activated by them for osteoporotic defect healing.

CONCLUSION

In general, the introduction of TCM active ingredients provides a novel therapeutic approach for modulating bone homeostasis and facilitating osteoporotic defect healing, and also offers a new strategy for design of other unconventional bone defect healing materials.

Decorin in the spatial control of collagen mineralization

Understanding the molecular mechanism by which the periodontal ligament (PDL) is maintained uncalcified between two mineralized tissues (cementum and bone) may facilitate the functional repair and regeneration of the periodontium complex, disrupted in the context of periodontal diseases. However, research that explores the control of type I collagen (COL I) mineralization fails to clarify the detailed mechanism of regulating spatial collagen mineralization, especially in the periodontium complex. In the present study, decorin (DCN), which is characterized as abundant in the PDL region and rare in mineralized tissues, was hypothesized to be a key regulator in the spatial control of collagen mineralization. The circular dichroism results confirmed that DCN regulated the secondary structure of COL I, and the surface plasmon resonance results indicated that COL I possessed a higher affinity for DCN than for other mineralization promoters, such as DMP-1, OPN, BSP and DSPP. These features of DCN may contribute to blocking intrafibrillar mineralization in COL I fibrils during the polymer-induced liquid-precursor mineralization process when the fibrils are cross-linked with DCN. This effect was more remarkable when the fibrils were phosphorylated by sodium trimetaphosphate, as shown by the observation of a tube-like morphology via TEM and mineral sheath via SEM. This study enhances the understanding of the role of DCN in mineralization regulation among periodontal tissues. This provides insights for the development of biomaterials for the regeneration of interfaces between soft and hard tissues.

Advancing bone regeneration: Unveiling the potential of 3D cell models in the evaluation of bone regenerative materials

Bone, a rigid yet regenerative tissue, has garnered extensive attention for its impressive healing abilities. Despite advancements in understanding bone repair and creating treatments for bone injuries, handling nonunions and large defects remains a major challenge in orthopedics. The rise of bone regenerative materials is transforming the approach to bone repair, offering innovative solutions for nonunions and significant defects, and thus reshaping orthopedic care. Evaluating these materials effectively is key to advancing bone tissue regeneration, especially in difficult healing scenarios, making it a critical research area. Traditional evaluation methods, including two-dimensional cell models and animal models, have limitations in predicting accurately. This has led to exploring alternative methods, like 3D cell models, which provide fresh perspectives for assessing bone materials' regenerative potential. This paper discusses various techniques for constructing 3D cell models, their pros and cons, and crucial factors to consider when using these models to evaluate bone regenerative materials. We also highlight the significance of 3D cell models in the in vitro assessments of these materials, discuss their current drawbacks and limitations, and suggest future research directions. STATEMENT OF SIGNIFICANCE: This work addresses the challenge of evaluating bone regenerative materials (BRMs) crucial for bone tissue engineering. It explores the emerging role of 3D cell models as superior alternatives to traditional methods for assessing these materials. By dissecting the construction, key factors of evaluating, advantages, limitations, and practical considerations of 3D cell models, the paper elucidates their significance in overcoming current evaluation method shortcomings. It highlights how these models offer a more physiologically relevant and ethically preferable platform for the precise assessment of BRMs. This contribution is particularly significant for "Acta Biomaterialia" readership, as it not only synthesizes current knowledge but also propels the discourse forward in the search for advanced solutions in bone tissue engineering and regeneration.

Fluorescent monitoring osteogenic differentiation of osteosarcoma cells with an aggregation-induced emission probe

Osteosarcoma is widely believed to be an osteogenic differentiation disorder. In recent years, to further understand this disease, a lot resources were poured into the potential link between differentiation defects and tumorigenesis. Long-term monitoring of the differentiation progress of osteosarcoma cells is of great importance. In order to better promote the research, we have developed a novel fluorescent probe called PTB-EDTA, which exhibits remarkable bio-compatibility and demonstrates high selectivity towards osteosarcoma cells. Not only is the PTB-EDTA is capable of live cell imaging while conventional histology requires to kill the cells, its fluorescence is also enhanced as the osteogenic differentiation proceeding. These properties make PTB-EDTA a promising tool for monitoring osteosarcoma cells.

Tumor-induced osteomalacia

Tumor-induced osteomalacia is one of paraneoplastic syndromes characterized by hypophosphatemia caused by excessive actions of fibroblast growth factor 23 (FGF23). Since the cloning of FGF23 about 20 years ago, more widespread awareness of this disease has been achieved. However, there still remain several difficulties in the management of patients with this disease. In this review, these clinical problems are discussed together with the physiological and pathophysiological functions of FGF23. Personal proposals in the management of patients with suspected patients with tumor-induced osteomalacia are also presented.

The Na+/Ca2+ exchanger NCX3 mediates Ca2+ entry into matrix vesicles to facilitate initial steps of mineralization in osteoblasts

Matrix vesicles (MVs) provide the initial site for amorphous hydroxyapatite (HA) formation within mineralizing osteoblasts. Although Na+/Ca2+ exchanger isoform-3 (NCX3, SLC8A3) was presumed to function as major Ca2+ transporter responsible for Ca2+ extrusion out of osteoblast into the calcifying bone matrix, its presence and functional role in MVs have not been investigated. In this study, we investigated the involvement of NCX3 in MV-mediated mineralization process and its impact on bone formation. Using differentiated MC3T3-E1 cells, we demonstrated that NCX3 knockout in these cells resulted in a significant reduction of Ca2+ deposition due to reduced Ca2+ entry within the MVs, leading to impaired mineralization. Consequently, the capacity of MVs to promote extracellular HA formation was diminished. Moreover, primary osteoblast isolated from NCX3 deficient mice (NCX3-/-) exhibits reduced mineralization efficacy without any effect on osteoclast activity. To validate this in vitro finding, μCT analysis revealed a substantial decrease in trabecular bone mineral density in both genders of NCX3-/- mice, thus supporting the critical role of NCX3 in facilitating Ca2+ uptake into the MVs to initiate osteoblast-mediated mineralization. NCX3 expression was also found to be the target of downregulation by inflammatory mediators in vitro and in vivo. This newfound understanding of NCX3's functional role in MVs opens new avenues for therapeutic interventions aimed at enhancing bone mineralization and treating mineralization-related disorders.

Eldecalcitol Induces Minimodeling-Based Bone Formation and Inhibits Sclerostin Synthesis Preferentially in the Epiphyses Rather than the Metaphyses of the Long Bones in Rats

This study aimed to examine minimodeling-based bone formation between the epiphyses and metaphyses of the long bones of eldecalcitol (ELD)-administered ovariectomized rats. Sixteen-week-old female rats were divided into four groups: sham-operated rats receiving vehicle (Sham group), ovariectomized (OVX) rats receiving vehicle (Vehicle group), or ELDs (30 or 90 ng/kg BW, respectively; ELD30 and ELD90 groups). ELD administration increased bone volume and trabecular thickness, reducing the number of osteoclasts in both the epiphyses and metaphyses of OVX rats. The Sham and Vehicle groups exhibited mainly remodeling-based bone formation in both regions. The epiphyses of the ELD groups showed a significantly higher frequency of minimodeling-based bone formation than remodeling-based bone formation. In contrast, the metaphyses exhibited significantly more minimodeling-based bone formation in the ELD90 group compared with the ELD30 group. However, there was no significant difference between minimodeling-based bone formation and remodeling-based bone formation in the ELD90 group. While the minimodeling-induced new bone contained few sclerostin-immunoreactive osteocytes, the underlying pre-existing bone harbored many. The percentage of sclerostin-positive osteocytes was significantly reduced in the minimodeling-induced bone in the epiphyses but not in the metaphyses of the ELD groups. Thus, it seems likely that ELD could induce minimodeling-based bone formation in the epiphyses rather than in the metaphyses, and that ELD-driven minimodeling may be associated with the inhibition of sclerostin synthesis.

Impaired breakdown of Herwig's epithelial root sheath disturbs tooth root development

BACKGROUND

Wnt/β-catenin signaling plays a variety of roles in both the dental epithelium and mesenchyme at most stages of tooth development. In this study, we verified the roles of Hertwig's epithelial root sheath (HERS) breakdown in tooth root development. This breakdown results in formation of epithelial cell rests of Malassez (ERM).

RESULTS

Following induction of β-catenin stabilization in the epithelium of developing tooth at the moment of HERS breakdown, HERS failed to break down for ERM formation. HERS with stabilized β-catenin was altered into a multicellular layer enveloping elongated root dentin with higher expression of junctional proteins such as Zo-1 and E-cadherin. Importantly, this impairment of HERS breakdown led to arrest of further root elongation. In addition, the portion of root dentin enveloped by the undissociated HERS remained in a hypomineralized state. The odontoblasts showed ectopically higher expression of pyrophosphate regulators including Ank and Npp1, whereas Tnap expression was unchanged.

CONCLUSIONS

Our data suggest that Wnt/β-catenin signaling is decreased in HERS for ERM formation during root development. Furthermore, ERM formation is important for further elongation and dentin mineralization of the tooth roots. These findings may provide new insight to understand the contribution of ERM to root formation.

Transcriptomic Analysis of Mineralized Adipose-Derived Stem Cell Tissues for Calcific Valve Disease Modelling

Calcific aortic valve disease (CAVD) is characterized by the fibrosis and mineralization of the aortic valve, which leads to aortic stenosis and heart failure. At the cellular level, this is due to the osteoblastic-like differentiation of valve interstitial cells (VICs), resulting in the calcification of the tissue. Unfortunately, human VICs are not readily available to study CAVD pathogenesis and the implicated mechanisms in vitro; however, adipose-derived stromal/stem cells (ASCs), carrying the patient's specific genomic features, have emerged as a promising cell source to model cardiovascular diseases due to their multipotent nature, availability, and patient-specific characteristics. In this study, we describe a comprehensive transcriptomic analysis of tissue-engineered, scaffold-free, ASC-embedded mineralized tissue sheets using bulk RNA sequencing. Bioinformatic and gene set enrichment analyses revealed the up-regulation of genes associated with the organization of the extracellular matrix (ECM), suggesting that the ECM could play a vital role in the enhanced mineralization observed in these tissue-engineered ASC-embedded sheets. Upon comparison with publicly available gene expression datasets from CAVD patients, striking similarities emerged regarding cardiovascular diseases and ECM functions, suggesting a potential link between ECM gene expression and CAVDs pathogenesis. A matrisome-related sub-analysis revealed the ECM microenvironment promotes the transcriptional activation of the master gene runt-related transcription factor 2 (RUNX2), which is essential in CAVD development. Tissue-engineered ASC-embedded sheets with enhanced mineralization could be a valuable tool for research and a promising avenue for the identification of more effective aortic valve replacement therapies.

Osteoinductive activity of photobiomodulation in an organotypic bone model

Photobiomodulation (PBM) is a technique that harnesses non-ionizing light at specific wavelengths, triggering the modulation of metabolic pathways, engendering favourable biological outcomes that reduce inflammation and foster enhanced tissue healing and regeneration. PBM holds significant promise for bone tissue applications due to its non-invasive nature and ability to stimulate cellular activity and vascularization within the healing framework. Notwithstanding, the impact of PBM on bone functionality remains largely undisclosed, particularly in the absence of influencing factors such as pathologies or regenerative therapies. This study aims to investigate the potential effects of PBM using red (660 nm) (RED) and near-infrared (808 nm) (NIR) wavelengths within an ex vivo bone culture system - the organotypic embryonic chicken femur model. A continuous irradiation mode was used, administering a total energy dose of 1.0 J, at an intensity of 100 mW for 10 s, which was repeated four times over the course of the 11-day culture period. The primary focus is on characterizing the expression of pivotal osteoblastic genes, the maturation and deposition of collagen, and the formation of bone mineral. Exposing femora to both RED and NIR wavelengths led to a notable increase in the expression of osteochondrogenic transcription factors (i.e., SOX9 and RUNX2), correlating with enhanced mineralization. Notably, NIR irradiation further elevated the expression of bone matrix-related genes and fostered enhanced deposition and maturation of fibrillar collagen. This study demonstrates that PBM has the potential to enhance osteogenic functionality within a translational organotypic bone culture system, with the NIR wavelength showing remarkable capabilities in augmenting the formation and maturation of the collagenous matrix.

Enhancing the effectiveness of Alkaline Phosphatase and bone matrix proteins by tunable metal-organic composite for accelerated mineralization

The irregular expression of bone matrix proteins occurring during the mineralization of bone regeneration results in various deformities which poses a major concern of orthopedic reconstruction. The limitations of the existing reconstruction practice paved a way for the development of a metal-organic composite [TQ-Sr-Fe] with Metal ions strontium [Sr] and iron [Fe] and a biomolecule Thymoquinone [TQ] in an attempt to enhance the bone mineralization due to their positive significance in osteoblast differentiation, proliferation and maturation. TQ-Sr-Fe was synthesized by in-situ coprecipitation and subjected to various characterization to determine their nature, compatibility and osteogenic efficiency. The crystallographic and electron microscopy analysis reveals sheet like structure of the composite. The negative cytotoxicity of TQ-Sr-Fe in the MG 63 cell line signified their biocompatibility. Cell adhesion and proliferation rate affirmed osteoconductive and osteoinductive nature of the composites and it was further supported by the gene expression of osteoblastic differentiation. The sequential expression of bone matrix proteins such as OCN, SPARC, COL 1, and Alkaline Phosphatase elevate the calcium deposition of MG-63 osteoblast like cells and initiates mineralization compared to control. Thus, the metal-organic composite TQ-Sr-Fe would make a suitable composite for accelerating mineralization process which would leads to faster bone regeneration.

Differential osteoblastic activity in primary metaphyseal trabecular and secondary trabeculae of c-fos deficient mice

OBJECTIVES

It has been highlighted that osteoblastic activities in remodeling-based bone formation are coupled with osteoclastic bone resorption while those in modeling-based bone formation are independent of osteoclasts. This study aimed to verify whether modeling-based bone formation can occur in the absence of osteoclasts.

METHODS

We performed histochemical analyses on the bone of eight-week-old male wild-type and c-fos-/- mice. Histochemical analyses were conducted on primary trabeculae near the chondro-osseous junction (COJ), sites of modeling-based bone formation, and secondary trabeculae, sites of remodeling-based bone formation, in the femora and tibiae of mice.

RESULTS

Alkaline phosphatase (ALP) immunoreactivity, a marker of osteoblastic lineages, was observed in the metaphyseal trabeculae of wild-type mice, while ALP was scattered throughout the femora of c-fos-/- mice. PHOSPHO1, an enzyme involved in matrix vesicle-mediated mineralization, was predominantly detected in primary trabeculae and also within short lines of osteoblasts in secondary trabeculae of wild-type mice. In contrast, femora of c-fos-/- mice showed several patches of PHOSPHO1 positivity in the primary trabeculae, but there were hardly any patches of PHOSPHO1 in secondary trabeculae. Calcein labeling was consistently observed in primary trabeculae close to the COJ in both wild-type and c-fos-/- mice; however, calcein labeling in the secondary trabeculae was only detected in wild-type mice. Transmission electron microscopic examination demonstrated abundant rough endoplasmic reticulum in the osteoblasts in secondary trabeculae of wild-type mice, but not in those of c-fos-/- mice.

CONCLUSIONS

Osteoblastic activities at the sites of modeling-based bone formation may be maintained in the absence of osteoclasts.

The mechanism of biomineralization: Progress in mineralization from intracellular generation to extracellular deposition

Biomineralization is a highly regulated process that results in the deposition of minerals in a precise manner, ultimately producing skeletal and dental hard tissues. Recent studies have highlighted the crucial role played by intracellular processes in initiating biomineralization. These processes involve various organelles, such as the endoplasmic reticulum(ER), mitochondria, and lysosomes, in the formation, accumulation, maturation, and secretion of calcium phosphate (CaP) particles. Particularly, the recent in-depth study of the dynamic process of the formation of amorphous calcium phosphate(ACP) precursors among organelles has made great progress in the development of the integrity of the biomineralization chain. However, the precise mechanisms underlying these intracellular processes remain unclear, and they cannot be fully integrated with the extracellular mineralization mechanism and the physicochemical structure development of the mineralization particles. In this review, we aim to focus on the recent progress made in understanding intracellular mineralization organelles' processes and their relationship with the physicochemical structure development of CaP and extracellular deposition of CaP particles.

Vascular calcification: from the perspective of crosstalk

Vascular calcification (VC) is highly correlated with cardiovascular disease morbidity and mortality, but anti-VC treatment remains an area to be tackled due to the ill-defined molecular mechanisms. Regardless of the type of VC, it does not depend on a single cell but involves multi-cells/organs to form a complex cellular communication network through the vascular microenvironment to participate in the occurrence and development of VC. Therefore, focusing only on the direct effect of pathological factors on vascular smooth muscle cells (VSMCs) tends to overlook the combined effect of other cells and VSMCs, including VSMCs-VSMCs, ECs-VMSCs, Macrophages-VSMCs, etc. Extracellular vesicles (EVs) are a collective term for tiny vesicles with a membrane structure that are actively secreted by cells, and almost all cells secrete EVs. EVs docked on the surface of receptor cells can directly mediate signal transduction or transfer their contents into the cell to elicit a functional response from the receptor cells. They have been proven to participate in the VC process and have also shown attractive therapeutic prospects. Based on the advantages of EVs and the ability to be detected in body fluids, they may become a novel therapeutic agent, drug delivery vehicle, diagnostic and prognostic biomarker, and potential therapeutic target in the future. This review focuses on the new insight into VC molecular mechanisms from the perspective of crosstalk, summarizes how multi-cells/organs interactions communicate via EVs to regulate VC and the emerging potential of EVs as therapeutic methods in VC. We also summarize preclinical experiments on crosstalk-based and the current state of clinical studies on VC-related measures.

Phosphorylated pullulan promotes calcification during bone regeneration in the bone defects of rat tibiae

The current study aimed to evaluate bone tissue regeneration using a combination of β-tricalcium phosphate (βTCP) and phosphorylated pullulan (PPL, a phosphate-rich polysaccharide polymer consisting of maltotriose units). Round defects of 2 mm diameter were created in the arterial center of rat tibiae, which were further treated with vehicle (control group), βTCP (βTCP group), or βTCP + PPL (βTCP + PPL group) grafts. The control specimens without bone grafts exhibited rapid bone formation after 1 week; however, the regenerated bone was not resorbed until 4 weeks. In contrast, βTCP-grafted specimens exhibited fewer but thicker trabeculae, whereas the βTCP + PPL group displayed many fine trabeculae at 4 weeks. In the βTCP + PPL group, new bone was associated with the βTCP granules and PPL. Similarly, PHOSPHO1-positive osteoblasts were localized on the βTCP granules as well as the PPL. On the other hand, TRAP-reactive osteoclasts predominantly localized on newly-formed bone and βTCP granules rather than on the PPL. No significant differences were observed in the expression of Alp, Integrin αv, Osteopontin, Osteocalcin, and Dmp-1 in PPL-treated MC3T3-E1 osteoblastic cells, suggesting that PPL did not facilitate osteoblastic differentiation. However, von Kossa staining identified abundant needle-like calcified structures extending inside the PPL. Furthermore, transmission electron microscopy (TEM) revealed many globular structures identical to calcified nodules. In addition, calcified collagen fibrils were observed in the superficial layer of the PPL. Thus, PPL may serve as a scaffold for osteoblastic bone formation and promotes calcification on its surface. In conclusion, we speculated that βTCP and PPL might promote bone regeneration and could be integrated into promising osteoconductive materials.

Magnetic Field Boosts the Transmembrane Transport Efficiency of Magnesium Ions from PLLA Bone Scaffold

In the system of magnesium-loaded scaffolds, the effect of magnesium ions (Mg2+ ) on the osteogenesis induction is restricted due to the low transmembrane transport efficiency of Mg2+ into the cell, which limits the application for bone defect repair. Inspired by the fact that magnetic field can regulate ion channel proteins on the cell membrane, magnetite nanoparticle is introduced into the poly (l-lactic acid) /magnesium oxide composite in this study, and a magnetic magnesium-loaded bone scaffold is prepared via selective laser sintering . Notably, the activities of the Mg2+ channel protein (MAGT1) on the membrane of bone marrow mesenchymal stem cells (rBMSCs) are enhanced via magnetic torque effect (via integrin αV β3/actin), under the action of static magnetic field (SMF), which promoted rBMSCs to capture Mg2+ in the microenvironment and induced osteogenesis. In vitro experiments showed that the magnetic magnesium-loaded scaffold, under the action of SMF, can accelerate the inflow of Mg2+ from surrounding microenvironment, which improved cellular activities, osteogenesis-related gene expression (ALP, Runx2, OCN, and OPN), and mineralization. Besides, in vivo skull defect repair experiments showed that the scaffolds possessed good ability to promote bone differentiation and new bone regeneration.

AnnexinA6: a potential therapeutic target gene for extracellular matrix mineralization

The mineralization of the extracellular matrix (ECM) is an essential and crucial process for physiological bone formation and pathological calcification. The abnormal function of ECM mineralization contributes to the worldwide risk of developing mineralization-related diseases; for instance, vascular calcification is attributed to the hyperfunction of ECM mineralization, while osteoporosis is due to hypofunction. AnnexinA6 (AnxA6), a Ca2+-dependent phospholipid-binding protein, has been extensively reported as an essential target in mineralization-related diseases such as osteoporosis, osteoarthritis, atherosclerosis, osteosarcoma, and calcific aortic valve disease. To date, AnxA6, as the largest member of the Annexin family, has attracted much attention due to its significant contribution to matrix vesicles (MVs) production and release, MVs-ECM interaction, cytoplasmic Ca2+ influx, and maturation of hydroxyapatite, making it an essential target in ECM mineralization. In this review, we outlined the recent advancements in the role of AnxA6 in mineralization-related diseases and the potential mechanisms of AnxA6 under normal and mineralization-related pathological conditions. AnxA6 could promote ECM mineralization for bone regeneration in the manner described previously. Therefore, AnxA6 may be a potential osteogenic target for ECM mineralization.

Wnt3a-Loaded Hydroxyapatite Nanowire@Mesoporous Silica Core-Shell Nanocomposite Promotes the Regeneration of Dentin-Pulp Complex via Angiogenesis, Oxidative Stress Resistance, and Odontogenic Induction of Stem Cells

Pulp exposure often leads to pulp necrosis, root fractures, and ultimate tooth loss. The repair of the exposure site with pulp capping treatment is of great significance to preserving pulp vitality, but its efficacy is impaired by the low bioactivity of capping materials and cell injuries from the local accumulation of oxidative stress. This study develops a Wnt3a-loaded hydroxyapatite nanowire@mesoporous silica (Wnt3a-HANW@MpSi) core-shell nanocomposite for pulp capping treatments. The ultralong and highly flexible hydroxyapatite nanowires provide the framework for the composites, and the mesoporous silica shell endows the composite with the capacity of efficiently loading/releasing Wnt3a and Si ions. Under in vitro investigation, Wnt3a-HANW@MpSi not only promotes the oxidative stress resistance of dental pulp stem cells (DPSCs), enhances their migration and odontogenic differentiation, but also exhibits superior properties of angiogenesis in vitro. Revealed by the transcriptome analysis, the underlying mechanisms of odontogenic enhancement by Wnt3a-HANW@MpSi are closely related to multiple biological processes and signaling pathways toward pulp/dentin regeneration. Furthermore, an animal model of subcutaneous transplantation demonstrates the significant reinforcement of the formation of dentin-pulp complex-like tissues and blood vessels by Wnt3a-HANW@MpSi in vivo. These results indicate the promising potential of Wnt3a-HANW@MpSi in treatments of dental pulp exposure.

Prenatal and Neonatal Bone Health: Updated Review on Early Identification of Newborns at High Risk for Osteopenia

Bone health starts with maternal health and nutrition, which influences bone mass and density already in utero. The mechanisms underlying the effect of the intrauterine environment on bone health are partly unknown but certainly include the 'foetal programming' of oxidative stress and endocrine systems, which influence later skeletal growth and development. With this narrative review, we describe the current evidence for identifying patients with risk factors for developing osteopenia, today's management of these populations, and screening and prevention programs based on gestational age, weight, and morbidity. Challenges for bone health prevention include the need for new technologies that are specific and applicable to pregnant women, the foetus, and, later, the newborn. Radiofrequency ultrasound spectrometry (REMS) has proven to be a useful tool in the assessment of bone mineral density (BMD) in pregnant women. Few studies have reported that transmission ultrasound can also be used to assess BMD in newborns. The advantages of this technology in the foetus and newborn are the absence of ionising radiation, ease of use, and, above all, the possibility of performing longitudinal studies from intrauterine to extrauterine life. The use of these technologies already in the intrauterine period could help prevent associated diseases, such as osteoporosis and osteopenia, which are characterised by a reduction in bone mass and degeneration of bone structure and lead to an increased risk of fractures in adulthood with considerable social repercussions for the related direct and indirect costs.

Immunolocalization of Enzymes/Membrane Transporters Related to Bone Mineralization in the Metaphyses of the Long Bones of Parathyroid-Hormone-Administered Mice

The present study aimed to demonstrate the immunolocalization and/or gene expressions of the enzymes and membrane transporters involved in bone mineralization after the intermittent administration of parathyroid hormone (PTH). The study especially focused on TNALP, ENPP1, and PHOSPHO1, which are involved in matrix vesicle-mediated mineralization, as well as PHEX and the SIBLING family, which regulate mineralization deep inside bone. Six-week-old male mice were subcutaneously injected with 20 μg/kg/day of human PTH (1-34) two times per day (n = 6) or four times per day (n = 6) for two weeks. Additionally, control mice (n = 6) received a vehicle. Consistently with an increase in the volume of the femoral trabeculae, the mineral appositional rate increased after PTH administration. The areas positive for PHOSPHO1, TNALP, and ENPP1 in the femoral metaphyses expanded, and the gene expressions assessed by real-time PCR were elevated in PTH-administered specimens when compared with the findings in control specimens. The immunoreactivity and/or gene expressions of PHEX and the SIBLING family (MEPE, osteopontin, and DMP1) significantly increased after PTH administration. For example, MEPE immunoreactivity was evident in some osteocytes in PTH-administered specimens but was hardly observed in control specimens. In contrast, mRNA encoding cathepsin B was significantly reduced. Therefore, the bone matrix deep inside might be further mineralized by PHEX/SIBLING family after PTH administration. In summary, it is likely that PTH accelerates mineralization to maintain a balance with elevated matrix synthesis, presumably by mediating TNALP/ENPP1 cooperation and stimulating PHEX/SIBLING family expression.

Histochemical assessment on osteoclasts in long bones of toll-like receptor 2 (TLR2) deficient mice

OBJECTIVE

Toll-like receptor 2 (TLR2), recognizes a wide variety of pathogen-associated molecular patterns such as lipopolysaccharides, peptidoglycans, and lipopeptides, and is generally believed to be present in monocytes, macrophages, dendritic cells, and vascular endothelial cells. However, no histological examination of osteoclasts, which differentiate from precursors common to macrophages/monocytes, has been performed in a non-infected state of TLR2 deficiency. The objective of this study was to examine the histological properties and function of osteoclasts in the long bones of 8-week-old male TLR2 deficient (TLR2^-/-) mice to gain insight into TLR2 function in biological circumstances without microbial infection.

METHODS

Eight-week-old male wild-type and TLR2^-/- mice were fixed with paraformaldehyde solution, and their tibiae and femora were used for micro-CT analysis, immunohistochemistry, transmission electron microscopy, and real-time PCR analysis.

RESULTS

TLR2^-/- tibiae and femora exhibited increased bone volume of metaphyseal trabeculae and elevated numbers of TRAP-positive osteoclasts. However, the number of multinucleated TRAP-positive osteoclasts was reduced, whereas mononuclear TRAP-positive cells increased, despite the high expression levels of Dc-Stamp and Oc-Stamp. Although TRAP-positive multinucleated and mononuclear osteoclasts showed the immunoreactivity and elevated expression of RANK and siglec-15, they revealed weak cathepsin K-positivity and less incorporation of the mineralized bone matrix, and often missing ruffled borders. It seemed likely that, despite the increased numbers, TLR2^-/- osteoclasts reduced cell fusion and bone resorption activity.

CONCLUSION

It seems likely that even without bacterial infection, TLR2 might participate in cell fusion and subsequent bone resorption of osteoclasts.

Bone and Cartilage Biology

Recent technical and conceptual advances in molecular and cellular biology have dramatically advanced bone and cartilage biology [...]

Histological Assessment of Endochondral Ossification and Bone Mineralization

Finely tuned cartilage mineralization, endochondral ossification, and normal bone formation are necessary for normal bone growth. Hypertrophic chondrocytes in the epiphyseal cartilage secrete matrix vesicles, which are small extracellular vesicles initiating mineralization, into the intercolumnar septa but not the transverse partitions of the cartilage columns. Bone-specific blood vessels invade the unmineralized transverse septum, exposing the mineralized cartilage cores. Many osteoblast precursors migrate to the cartilage cores, where they synthesize abundant bone matrices, and mineralize them in a process of matrix vesicle-mediated bone mineralization. Matrix vesicle-mediated mineralization concentrates calcium (Ca) and inorganic phosphates (Pi), which are converted into hydroxyapatite crystals. These crystals grow radially and are eventually get out of the vesicles to form spherical mineralized nodules, leading to collagen mineralization. The influx of Ca and Pi into the matrix vesicle is regulated by several enzymes and transporters such as TNAP, ENPP1, PiT1, PHOSPHO1, annexins, and others. Such matrix vesicle-mediated mineralization is regulated by osteoblastic activities, synchronizing the synthesis of organic bone material. However, osteocytes reportedly regulate peripheral mineralization, e.g., osteocytic osteolysis. The interplay between cartilage mineralization and vascular invasion during endochondral ossification, as well as that of osteoblasts and osteocytes for normal mineralization, appears to be crucial for normal bone growth.

Scaffold Guided Bone Regeneration for the Treatment of Large Segmental Defects in Long Bones

Bone generally displays a high intrinsic capacity to regenerate. Nonetheless, large osseous defects sometimes fail to heal. The treatment of such large segmental defects still represents a considerable clinical challenge. The regeneration of large bone defects often proves difficult, since it relies on the formation of large amounts of bone within an environment impedimental to osteogenesis, characterized by soft tissue damage and hampered vascularization. Consequently, research efforts have concentrated on tissue engineering and regenerative medical strategies to resolve this multifaceted challenge. In this review, we summarize, critically evaluate, and discuss present approaches in light of their clinical relevance; we also present future advanced techniques for bone tissue engineering, outlining the steps to realize for their translation from bench to bedside. The discussion includes the physiology of bone healing, requirements and properties of natural and synthetic biomaterials for bone reconstruction, their use in conjunction with cellular components and suitable growth factors, and strategies to improve vascularization and the translation of these regenerative concepts to in vivo applications. We conclude that the ideal all-purpose material for scaffold-guided bone regeneration is currently not available. It seems that a variety of different solutions will be employed, according to the clinical treatment necessary.

Biocompatibility Evaluation of Carbon Nanohorns in Bone Tissues

With the advent of nanotechnology, the use of nanoparticles as drug delivery system (DDS) has attracted great interest. We aimed to apply carbon nanohorns (CNHs) as DDS in the development of new treatments for bone diseases. We evaluated the in vitro and in vivo cellular responses of CNHs in bone-related cells compared with carbon blacks (CBs), which are similar in particle size but differ in surface and structural morphologies. Although in vitro experiments revealed that both CNHs and CBs were incorporated into the lysosomes of RAW264-induced osteoclast-like cells (OCs) and MC3T3-E1 osteoblast-like cells (OBs), no severe cytotoxicity was observed. CNHs reduced the tartrate-resistant acid phosphatase activity and expression of the differentiation marker genes in OCs at noncytotoxic concentrations, whereas the alkaline phosphatase activity and differentiation of OBs increased. Under calcification of OBs, CNHs increased the number of calcified nodules and were intra- and extracellularly incorporated into calcified vesicles to form crystal nuclei. The in vivo experiments showed significant promotion of bone regeneration in the CNH group alone, with localized CNHs being found in the bone matrix and lacunae. The suppression of OCs and promotion of OBs suggested that CNHs may be effective against bone diseases and could be applied as DDS.

Concentration-Dependent Efficacy of Recombinant Human Bone Morphogenetic Protein-2 Using a HA/β-TCP Hydrogel Carrier in a Mini-Pig Vertebral Oblique Lateral Interbody Fusion Model

Bone morphogenetic protein-2 (BMP-2) is used in the treatment of degenerative spinal disease and vertebral fractures, spine fusion, dental surgery, and facial surgery. However, high doses are associated with side effects such as inflammation and osteophytes. In this study, we performed spinal fusion surgery on mini-pigs using BMP-2 and a HA/β-TCP hydrogel carrier, and evaluated the degree of fusion and osteophyte growth according to time and dosage. Increasing the dose of BMP-2 led to a significantly higher fusion rate than was observed in the control group, and there was no significant difference between the 8-week and 16-week samples. We also found that the HA + β-TCP hydrogel combination helped maintain the rate of BMP-2 release. In conclusion, the BMP-2-loaded HA/β-TCP hydrogel carrier used in this study overcame the drawback of potentially causing side effects when used at high concentrations by enabling the sustained release of BMP-2. This method is also highly efficient, since it provides mineral matter to accelerate the fusion rate of the spine and improve bone quality.

Advances in Multifunctional Bioactive Coatings for Metallic Bone Implants

To fix the bone in orthopedics, it is almost always necessary to use implants. Metals provide the needed physical and mechanical properties for load-bearing applications. Although widely used as biomedical materials for the replacement of hard tissue, metallic implants still confront challenges, among which the foremost is their low biocompatibility. Some of them also suffer from excessive wear, low corrosion resistance, infections and shielding stress. To address these issues, various coatings have been applied to enhance their in vitro and in vivo performance. When merged with the beneficial properties of various bio-ceramic or polymer coatings remarkable bioactive, osteogenic, antibacterial, or biodegradable composite implants can be created. In this review, bioactive and high-performance coatings for metallic bone implants are systematically reviewed and their biocompatibility is discussed. Updates in coating materials and formulations for metallic implants, as well as their production routes, have been provided. The ways of improving the bioactive coating performance by incorporating bioactive moieties such as growth factors, osteogenic factors, immunomodulatory factors, antibiotics, or other drugs that are locally released in a controlled manner have also been addressed.