Bone remodeling: Multiple cellular interactions required for coupling of bone formation and resorption

In vivo dynamics of hard tissue-forming cell origins: Insights from Cre/loxP-based cell lineage tracing studies

Bone tissue provides structural support for our bodies, with the inner bone marrow (BM) acting as a hematopoietic organ. Within the BM tissue, two types of stem cells play crucial roles: mesenchymal stem cells (MSCs) (or skeletal stem cells) and hematopoietic stem cells (HSCs). These stem cells are intricately connected, where BM-MSCs give rise to bone-forming osteoblasts and serve as essential components in the BM microenvironment for sustaining HSCs. Despite the mid-20th century proposal of BM-MSCs, their in vivo identification remained elusive owing to a lack of tools for analyzing stemness, specifically self-renewal and multipotency. To address this challenge, Cre/loxP-based cell lineage tracing analyses are being employed. This technology facilitated the in vivo labeling of specific cells, enabling the tracking of their lineage, determining their stemness, and providing a deeper understanding of the in vivo dynamics governing stem cell populations responsible for maintaining hard tissues. This review delves into cell lineage tracing studies conducted using commonly employed genetically modified mice expressing Cre under the influence of LepR, Gli1, and Axin2 genes. These studies focus on research fields spanning long bones and oral/maxillofacial hard tissues, offering insights into the in vivo dynamics of stem cell populations crucial for hard tissue homeostasis.

The Role of Pericyte Migration and Osteogenesis in Periodontitis

A ligature-induced periodontitis model was established in wild-type and CD146CreERT2; RosatdTomato mice to explore the function of pericytes in alveolar bone formation. We found that during periodontitis progression and periodontal wound healing, CD146+/NG2+ pericytes were enriched in the periodontal tissue areas, which could migrate to the alveolar bone surface and colocalize with ALP+/OCN+ osteoblasts. Chemokine C-X-C motif receptor 4 (CXCR4) inhibition using AMD3100 blocked CD146-Cre+ pericyte migration and osteogenesis, as well as further exacerbated periodontitis-associated bone loss. Next, primary pericytes were sorted out by magnetic-activated cell sorting and demonstrated that C-X-C motif chemokine ligand 12 (CXCL12) promotes pericyte migration and osteogenesis via CXCL12-CXCR4-Rac1 signaling. Finally, the local administration of an adeno-associated virus for Rac1 overexpression in NG2+ pericytes promotes osteoblast differentiation of pericytes and increases alveolar bone volume in periodontitis. Thus, our results provided the evidence that pericytes may migrate and osteogenesis via the CXCL12-CXCR4-Rac1 axis during the pathological process of periodontitis.

Mass spectrometry-based proteomic applications in dental implants research

Dental implants have been established as successful treatment options for missing teeth with steadily increasing demands. Today, the primary areas of research in dental implantology revolve around osseointegration, soft and hard tissue grafting as well as peri-implantitis diagnostics, prevention, and treatment. This review provides a comprehensive overview of the current literature on the application of MS-based proteomics in dental implant research, highlights how explorative proteomics provided insights into the biology of peri-implant soft and hard tissues and how proteomics facilitated the stratification between healthy and diseased implants, enabling the identification of potential new diagnostic markers. Additionally, this review illuminates technical aspects, and provides recommendations for future study designs based on the current evidence.

Current perspectives on the multiple roles of osteoclasts: Mechanisms of osteoclast-osteoblast communication and potential clinical implications

Bone remodeling is a complex process involving the coordinated actions of osteoblasts and osteoclasts to maintain bone homeostasis. While the influence of osteoblasts on osteoclast differentiation is well established, the reciprocal regulation of osteoblasts by osteoclasts has long remained enigmatic. In the past few years, a fascinating new role for osteoclasts has been unveiled in promoting bone formation and facilitating osteoblast migration to the remodeling sites through a number of different mechanisms, including the release of factors from the bone matrix following bone resorption and direct cell-cell interactions. Additionally, considerable evidence has shown that osteoclasts can secrete coupling factors known as clastokines, emphasizing the crucial role of these cells in maintaining bone homeostasis. Due to their osteoprotective function, clastokines hold great promise as potential therapeutic targets for bone diseases. However, despite long-standing work to uncover new clastokines and their effect in vivo, more substantial efforts are still required to decipher the mechanisms and pathways behind their activity in order to translate them into therapies. This comprehensive review provides insights into our evolving understanding of the osteoclast function, highlights the significance of clastokines in bone remodeling, and explores their potential as treatments for bone diseases suggesting future directions for the field.

In Situ Photo-Crosslinkable Protein Bioadhesive for Bone Graft Fixation

Bone grafting is a fundamental dental surgery procedure widely used for implant placement and periodontal disease management treatments. Despite its broad applications, vertical bone augmentation presents unique challenges, including the risk of graft displacement due to gravitational and masticatory forces. Traditional physical stabilization methods introduce additional complexities and risks, underscoring the need for innovative fixation technologies. This study aimed to develop an in situ photo-crosslinkable bioadhesive hydrogel (iPBAH) as a multifunctional bone graft binder to enhance the process of bone reconstruction. The bioadhesive is composed of mussel-derived adhesive protein (MAP) fused with the cell-adhesive peptide RGD. The numerous tyrosine residues in MAP facilitate rapid photo-crosslinking, enabling efficient hydrogel formation using visible blue light. Subsequently, iPBAH underwent comprehensive characterization to evaluate its suitability as a multifunctional bone graft binder. iPBAH efficiently underwent in situ crosslinking through harmless exposure to visible light within minutes and displayed several exceptional properties, including a microporous structure, underwater adhesion, extended durability, high compressive strength, and biocompatibility. In vivo assessments, using male Sprague-Dawley rats, demonstrated that iPBAH binder significantly enhanced bone regeneration in a rat calvarial bone defect model. The in situ crosslinking of the iPBAH binder during bone graft transplantation can effectively fill irregular and complex defect shapes while simultaneously preventing graft material leakage. The improved physical attributes of the bound graft material can enhance its resistance to external forces, thereby ensuring sustained retention over time. Moreover, the interaction between iPBAH and surrounding tissues promotes adhesion and integration of the graft material with host tissues in the defect area. In addition, the included RGD peptide in iPBAH can augment inherent cell recruitment, adhesion, and growth, consequently expediting osteogenesis.

Catalpol attenuates osteoporosis in ovariectomized rats through promoting osteoclast apoptosis via the Sirt6-ERα-FasL axis

BACKGROUND

Catalpol, a major active component of the Chinese herb Rehmannia glutinosa, possesses various pharmacological benefits, including anti-inflammatory, antidiabetic, and antitumor properties. Recent studies have reported that catalpol can attenuate bone loss and enhance bone formation. Nevertheless, the molecular mechanisms underlying its effects on osteoporosis pathogenesis remain unclear.

PURPOSE

We investigated whether catalpol had a protective effect against postmenopausal osteoporosis (PMOP) and explored its exact mechanism of action.

METHODS

Seventy-two rats were randomly divided into six groups: sham, model, low-dose catalpol (5 mg/kg/day), medium-dose catalpol (10 mg/kg/day), high-dose catalpol (20 mg/kg/day), and positive control (alendronate, 2.5 mg/kg). In this experiment, a ovariectomy was performed to establish a female rat model of PMOP. After 12 weeks of gavage, micro-computed tomography (micro-CT) and histochemical staining were performed to evaluate bone mass, bone microstructure and histological parameters. Furthermore, RAW 264.7 cells were induced by RANKL to form mature osteoclasts to investigate the effect of catalpol on osteoclast differentiation and apoptosis in vitro. Additionally, the osteoclast apoptosis-related proteins of Sirt6, ERα, FasL, NFATc1, cleaved-caspase 8, cleaved-caspase 3, and Bax were assessed using western blotting. The expressions of NFATc1, Ctsk, Oscar, and Trap were quantified using RT-qPCR. The apoptotic rate of the osteoclasts was determined using flow cytometry. Sirt6 knockdown was performed using siRNA gene silencing in experiments to investigate its role in catalpol-mediated osteoclast apoptosis. The deacetylation of ERα in osteoclasts was tested via co-immunoprecipitation.

RESULTS

Catalpol (10 and 20 mg/kg) and alendronate (2.5 mg/kg) could significantly improve bone mineral density (BMD) and microstructure and decrease osteoclast density in ovariectomized (OVX) rats. In addition, catalpol (10 and 20 mg/kg) upregulated the expression of Sirt6, ERα, FasL, cleaved-caspase 8, cleaved-caspase 3, Bax, and downregulated the expression of NFATc1, Ctsk, Oscar, Trap both in vivo and in vitro. Catalpol also promoted ERα deacetylation and stabilized ERα protein to enhance the expression of FasL. In addition, Sirt6 knockdown by siRNA prevented ERα deacetylation and eliminated catalpol-mediated osteoclast apoptosis.

CONCLUSIONS

The present study demonstrated that catalpol prevents estrogen deficiency-induced osteoporosis by promoting osteoclast apoptosis via the Sirt6-ERα-FasL axis. These findings revealed a novel molecular mechanism underpinning the impact of catalpol in the progression of osteoporosis and provided novel insights into the treatment of osteoporosis.

The association of lipid metabolism with bone metabolism and the role of human traits: a Mendelian randomization study

Background

The impact of lipid metabolism on bone metabolism remains controversial, and the extent to which human traits mediate the effects of lipid metabolism on bone metabolism remains unclear.

Objective

This study utilized mendelian randomization to investigate the effects of blood lipids on bone mineral density (BMD) at various skeletal sites and examined the mediating role of human traits in this process.

Methods

We leveraged genetic data from large-scale genome-wide association studies on blood lipids (n=1,320,016), forearm bone mineral density (FA-BMD) (n=10,805), lumbar spine bone mineral density (LS-BMD) (n=44,731), and femoral neck bone mineral density (FN-BMD) (n=49,988) to infer causal relationships between lipid and bone metabolism. The coefficient product method was employed to calculate the indirect effects of human traits and the proportion of mediating effects.

Results

The results showed that a 1 standard deviation(SD) increase in HDL-C, LDL-C and TC was associated with a decrease in LS-BMD of 0.039 g/cm2, 0.045 g/cm2 and 0.054 g/cm2, respectively. The proportion of mediating effects of systolic blood pressure (SBP) on HDL-C to LS-BMD was 3.17%, but suppression effects occurred in the causal relationship of LDL-C and TC to LS-BMD. Additionally, the proportion of mediating effects of hand grip strength (HGS) on the TC to LS-BMD pathway were 6.90% and 4.60% for the left and right hands, respectively.

Conclusion

In conclusion, a negative causal relationship was established between lipid metabolism and bone metabolism. Our results indicated that SBP and HGS served as mediators for the effects of lipid metabolism on bone metabolism.

RANKL-dependent osteoclast differentiation and gene expression in bone marrow-derived cells from adult mice is sexually dimorphic

Sex-specific differences in bone integrity and properties are associated with age as well as the number and activity of cells involved in bone remodeling. The aim of this study was to investigate sex-specific differences in adhesion, proliferation, and differentiation of mouse bone marrow derived cells into osteoclasts. The adherent fraction of bone marrow- derived cells from 12-week-old male and female C57BL/6J mice were assessed for their adhesion, proliferation, and receptor activator of nuclear factor κB (RANKL)-induced differentiation into osteoclasts. Female bone marrow derived macrophages (BMDMs) displayed higher adhesion and proliferation ratio upon macrophage colony stimulating factor (M-CSF) (day 0) and M-CSF + RANKL (day 4) treatment, respectively. On the contrary, male BMDMs differentiated more efficiently into osteoclasts upon RANKL-treatment compared to females (day 5). To further understand these sex-specific differences at the gene expression level, BMDMs treated with M-CSF (day 0) and M-CSF + RANKL (day 4), were assessed for their differential expression of genes through RNA sequencing. M-CSF treatment resulted in 1106 differentially expressed genes, while RANKL-treatment gave 473 differentially expressed genes. Integrin, adhesion, and proliferation-associated genes were elevated in the M-CSF-treated female BMDMs. RANKL-treatment further enhanced the expression of the proliferation- associated genes, and of genes associated with inhibition of osteoclast differentiation in the females, while RANK-signaling-associated genes were upregulated in males. In conclusion, BMDM adhesion, proliferation and differentiation into osteoclasts are sex-specific and may be directed by the PI3K-Akt signaling pathway for proliferation, and the colony stimulating factor 1-receptor and the RANKLsignaling pathway for the differentiation.

Focal adhesion kinase (FAK): its structure, characteristics, and signaling in skeletal system

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase and distributes important regulatory functions in skeletal system. Mesenchymal stem cell (MSC) possesses significant migration and differentiation capacity, is an important source of distinctive bone cells production and a prominent bone development pathway. MSC has a wide range of applications in tissue bioengineering and regenerative medicine, and is frequently employed for hematopoietic support, immunological regulation, and defect repair, although current research is insufficient. FAK has been identified to cross-link with many other keys signaling pathways in bone biology and is considered as a fundamental "crossroad" on the signal transduction pathway and a "node" in the signal network to mediate MSC lineage development in skeletal system. In this review, we summarized the structure, characteristics, cellular signaling, and the interactions of FAK with other signaling pathways in the skeletal system. The discovery of FAK and its mediated molecules will lead to a new knowledge of bone development and bone construction as well as considerable potential for therapeutic use in the treatment of bone-related disorders such as osteoporosis, osteoarthritis, and osteosarcoma.

Euonymus alatus (Thunb.) Siebold Prevents Osteoclast Differentiation and Osteoporosis

Euonymus alatus (Thunb.) Siebold, a traditional medicinal plant, has been used in China and several other Asian countries to address a variety of health concerns. The extensive research conducted on E. alatus is driven by its diverse pharmacological applications. However, its biological effects on osteoclastogenesis and osteoporosis have not been previously studied. In this research, we investigated the impact of an ethanolic extract of E. alatus (EEEA) on osteoclast differentiation and function as well as estrogen deficiency-induced bone loss. We found that EEEA inhibits osteoclast differentiation by downregulating the expression of the receptor activator of nuclear factor-κB ligand (RANKL) in osteoclast-supporting cells and by directly impeding RANKL-mediated signaling pathways for osteoclastogenesis in precursor cells. In addition, EEEA inhibited the bone-resorptive function of mature osteoclasts in vitro. Furthermore, oral administration of EEEA significantly alleviated bone loss in an ovariectomy-induced osteoporosis mouse model. Additionally, we identified phytochemicals in EEEA that have suppressive effects on osteoclast differentiation and bone loss. Collectively, these results suggest that EEEA holds potential as a biotherapeutic candidate for anti-postmenopausal osteoporosis.

Dlk2 interacts with Syap1 to activate Akt signaling pathway during osteoclast formation

Excessive osteoclast formation and bone resorption are related to osteolytic diseases. Delta drosophila homolog-like 2 (Dlk2), a member of the epidermal growth factor (EGF)-like superfamily, reportedly regulates adipocyte differentiation, but its roles in bone homeostasis are unclear. In this study, we demonstrated that Dlk2 deletion in osteoclasts significantly inhibited osteoclast formation in vitro and contributed to a high-bone-mass phenotype in vivo. Importantly, Dlk2 was shown to interact with synapse-associated protein 1 (Syap1), which regulates Akt phosphorylation at Ser473. Dlk2 deletion inhibited Syap1-mediated activation of the AktSer473, ERK1/2 and p38 signaling cascades. Additionally, Dlk2 deficiency exhibits increased bone mass in ovariectomized mice. Our results reveal the important roles of the Dlk2-Syap1 signaling pathway in osteoclast differentiation and osteoclast-related bone disorders.

Adjuvant pharmacological strategies for the musculoskeletal system during long-term space missions

Despite 2 h of daily exercise training, muscle wasting and bone loss are still present after 6-month missions to the international space station. Some crew members lose bone much faster than others. In preparation for missions to the Moon and Mars, space agencies are therefore reviewing their countermeasure portfolios. Here, we discuss the potential of current pharmacological strategies. Bone loss in space is fuelled by bone resorption. Alendronate, an oral bisphosphonate, reduced bone losses in experimental bed rest and space. However, gastrointestinal side effects precluded its further utilization in space. Zoledronate (a potent bisphosphonate), denosumab (RANKL antagonist) and romosozumab (sclerostin antagonist) are all administered via injection. They effectively suppress bone resorption and are routinely prescribed against osteoporosis. Their serious adverse effects, namely, osteonecrosis of the jaw and atypical femur fractures occur very rarely when the usage is limited to 1 or 2 years. Hence, utilization of one of these compounds may outweigh the bone risks of space travelling, in particular in those with high bone resorption rates. Muscle wasting in space is likely due to hampered muscle protein synthesis. Even though this might theoretically be countered by the synthesis-boosting effects of anabolic steroids, the practical grounds for such recommendation are currently weak. Moreover, they reveal their full potential only when combined with an anabolic exercise stimulus, for example, via strength training. It therefore seems that a combination of exercise and pharmacological countermeasures should be considered for musculoskeletal health on the way to the Moon and Mars and back.

Pharmacological options in the treatment of osteogenesis imperfecta: A comprehensive review of clinical and potential alternatives

Osteogenesis imperfecta (OI) is a genetically heterogeneous connective tissue disorder characterized by bone fragility and different extra-skeletal manifestations. The severity of these manifestations makes it possible to classify OI into different subtypes based on the main clinical features. This review aims to outline and describe the current pharmacological alternatives for treating OI, grounded on clinical and preclinical reports, such as antiresorptive agents, anabolic agents, growth hormone, and anti-TGFβ antibody, among other less used agents. The different options and their pharmacokinetic and pharmacodynamic properties will be reviewed and discussed, focusing on the variability of their response and the molecular mechanisms involved to attain the main clinical goals, which include decreasing fracture incidence, improving pain, and promoting growth, mobility, and functional independence.

YAP/TEAD1 and β-catenin/LEF1 synergistically induce estrogen receptor α to promote osteogenic differentiation of bone marrow stromal cells

Bone remodeling is vital to the maintenance of bone homeostasis and may lead to destructive skeletal diseases once the balance is disrupted. Crosstalk between Wnt and estrogen receptor (ER) signaling has been proposed in bone remodeling, but the underlying mechanism remains unclear. This study was designed to explore the effect of Wnt-ER signaling during the osteogenic differentiation of bone marrow stromal cells (BMSCs). Rat BMSCs were isolated and identified using flow cytometry and stimulated with Wnt3a. Wnt3a treatment promoted osteogenic differentiation and mineralization of the BMSCs. Meanwhile, Wnt3a enhanced the expression of ERα as well as the canonical Wnt signaling mediator β-catenin and the alternative Wnt signaling effector Yes-associated protein 1 (YAP1). Interestingly, DNA pulldown assay revealed direct binding of transcriptional enhanced associate domain 1 (TEAD1) and lymphoid enhancer binding factor 1 (LEF1), transcriptional partners of YAP1 and β-catenin, respectively, to the promoter region of ERα. In addition, inhibition of TEAD1 and LEF1 suppressed Wnt3-promoted BMSC osteogenic differentiation and blocked Wnt3a-induced ERα expression. Furthermore, an in vivo model of femoral bone defect also supported that Wnt3a facilitated bone healing in an ERα-dependent way. Together, we suggest that Wnt3a promotes the osteogenic activity of BMSCs through YAP1 and β-catenin-dependent activation of ERα, via direct binding of TEAD1 and LEF1 to the ERα promoter.

Osteoimmunology: A Link between Gastrointestinal Diseases and Skeletal Health in Chickens

Bone serves as a multifunctional organ in avian species, giving structural integrity to the body, aiding locomotion and flight, regulating mineral homeostasis, and supplementing calcium for eggshell formation. Furthermore, immune cells originate and reside in the bone marrow, sharing a milieu with bone cells, indicating a potential interaction in functions. In avian species, the prevalence of gastrointestinal diseases can alter the growth and the immune response, which costs a great fortune to the poultry industry. Previous studies have shown that coccidiosis and necrotic enteritis can dramatically reduce bone quality as well. However, possible mechanisms on how bone quality is influenced by these disease conditions have not yet been completely understood, other than the reduced feed intake. On the other hand, several mediators of the immune response, such as chemokines and cytokines, play a vital role in the differentiation and activation of osteoclasts responsible for bone resorption and osteoblasts for bone formation. In the case of Eimeria spp./Clostridium perfringens coinfection, these mediators are upregulated. One possible mechanism for accelerated bone loss after gastrointestinal illnesses might be immune-mediated osteoclastogenesis via cytokines-RANKL-mediated pathways. This review article thus focuses on osteoimmunological pathways and the interaction between host immune responses and bone biology in gastrointestinal diseases like coccidiosis and necrotic enteritis affecting skeletal health.

The evolution of the adolescent growth spurt: Urinary biomarkers of bone turnover in wild chimpanzees (Pan troglodytes)

Life history theory addresses how organisms balance development and reproduction. Mammals usually invest considerable energy into growth in infancy, and they do so incrementally less until reaching adult body size, when they shift energy to reproduction. Humans are unusual in having a long adolescence when energy is invested in both reproduction and growth, including rapid skeletal growth around puberty. Although many primates, especially in captivity, experience accelerated growth in mass around puberty, it remains unclear whether this represents skeletal growth. Without data on skeletal growth in nonhuman primates, anthropologists have often assumed the adolescent growth spurt is uniquely human, and hypotheses for its evolution have focused on other uniquely human traits. The lack of data is largely due to methodological difficulties of assessing skeletal growth in wild primates. Here, we use two urinary markers of bone turnover-osteocalcin and collagen-to study skeletal growth in a large, cross-sectional sample of wild chimpanzees (Pan troglodytes) at Ngogo, Kibale National Park, Uganda. For both bone turnover markers, we found a nonlinear effect of age, which was largely driven by males. For male chimpanzees, values for osteocalcin and collagen peaked at age 9.4 years and 10.8 years, respectively, which corresponds to early and middle adolescence. Notably, collagen values increased from 4.5 to 9 years, suggesting faster growth during early adolescence compared to late infancy. Biomarker levels plateaued at 20 years in both sexes, suggesting skeletal growth continues until then. Additional data, notably on females and infants of both sexes, are needed, as are longitudinal samples. However, our cross-sectional analysis suggests an adolescent growth spurt in the skeleton of chimpanzees, especially for males. Biologists should avoid claiming that the adolescent growth spurt is uniquely human, and hypotheses for the patterns of human growth should consider variation in our primate relatives.

Investigating bone resorption in Atlantic herring fish intermuscular bones with solid-state NMR

Bones are connective tissues mainly made of collagen proteins with calcium phosphate deposits. They undergo constant remodeling, including destroying existing bones tissues (known as bone resorption) and rebuilding new ones. Bone remodeling has been well-described in mammals, but it is not the case in fish. Here, we focused on the mobile phase of the bone vascular system by carefully preserving moisture in adult Atlantic herring intermuscular bones. We detected pore water with high ionic strength and soluble degraded peptides whose ¹H-transverse relaxation times, T₂s, exceed 15 milliseconds. With favorable T₂s, we incorporated a solution state spinlock scheme into the INEPT techniques to unequivocally demonstrate collagen degradation. In addition, we detected a substantial amount of inorganic phosphate in solution with ³¹P-NMR in the considerable background of solid hydroxyapatite calcium phosphate by saturation recovery experiment. It is consistent with the idea that bone resorption degrades bone collagen and releases calcium ions and phosphate ions in the pore water with increased ionic strength. Our report is the first to probe the resorption process in the heterogenous bone microstructure with a rigorous characterization of ¹H and ¹³C relaxation behavior and direct assignments. In addition, we contribute to the fish bones literature by investigating fish bone remodeling using NMR for the first time.

Total knee arthroplasty coronal alignment and tibial base stress-a new numerical evaluation

Background

Total knee arthroplasty (TKA) is one of the most frequently performed orthopedic procedures. The correct positioning and alignment of the components significantly affects prosthesis survival. Considering the current controversy regarding the target of postoperative alignment of TKA, this study evaluated the tension at tibial component interface using two numerical methods.

Methods

The stress of the prosthesis/bone interface of the proximal tibial component was evaluated using two numerical methods: the finite element method (FEM) and the new meshless method: natural neighbor radial point interpolation method (NNRPIM). The construction of the model was based on Zimmers NexGen LPS-Flex Mobile® prosthesis and simulated the forces by using a free-body diagram.

Results

Tibiofemoral mechanical axis (TFMA) for which a higher number of nodes are under optimal mechanical tension is between 1° valgus 2° varus. For values outside the interval, there are regions under the tibial plate at risk of bone absorption. At the extremities of the tibial plate of the prosthesis, both medial and lateral, independent of the alignment, are under a low stress. In all nodes evaluated for all TFMA, the values of the effective stresses were higher in the NNRPIM when compared with the FEM.

Conclusion

Through this study, we can corroborate that the optimal postoperative alignment is within the values that are currently considered of 0 ± 3° varus. It was verified that the meshless methods obtain smoother and more conservative results, which may make them safer when transposed to the clinical practice.

A comparative study of bone bioactivity and osteogenic potential of different bioceramics in methacrylated collagen hydrogels

Biomimetic scaffolds composed of bioactive ceramic-based materials incorporated within a polymeric framework have shown immense promise for use in bone tissue engineering (BTE) applications. However, studies on direct comparison of the efficacy of different bioceramics on bone bioactivity and osteogenic differentiation are lacking. Herein, we performed an in vitro direct comparison of three different bioceramics-Bioglass 45S5 (BG), Laponite XLG (LAP), and β-Tricalcium Phosphate (TCP)-on the physical properties and bone bioactivity of methacrylated collagen (CMA) hydrogels (10% w/w bioceramic:CMA). In addition, human MSCs (hMSCs) were encapsulated in bioceramic-laden CMA hydrogels and the effect of different bioceramics on osteogenic differentiation of hMSCs was investigated in two different culture medium-osteoconductive (without dexamethasone [DEX]) and osteoinductive (with DEX). Results showed that the stability of CMA hydrogels was maintained upon bioceramic addition. Compression testing revealed that BG incorporation significantly decreased (p < 0.05) the modulus of photochemically crosslinked CMA hydrogels. Incubation of TCP-CMA and LAP-CMA hydrogels in simulated body fluid showed deposition of hydroxycarbonate apatite layer on the surface indicating that these hydrogels may be more bone bioactive than BG-CMA and CMA only hydrogels. Cell cytoskeleton staining results showed greater cell spreading in TCP-CMA hydrogels. Furthermore, TCP incorporation significantly increased alkaline phosphatase activity (ALP; p < 0.05) in hMSCs. Together, these results indicate that TCP has superior osteogenic potential compared with BG and LAP and hence should be considered as a bioceramic of preferred choice for use in the biomimetic design of cell-laden hydrogels for BTE applications.

Bone regeneration in osteoporosis: opportunities and challenges

Osteoporosis is a bone disorder characterised by low bone mineral density, reduced bone strength, increased bone fragility, and impaired mineralisation of bones causing an increased risk of bone fracture. Several therapies are available for treating osteoporosis which include bisphosphonates, anti-resorptive agents, oestrogen modulators, etc. These therapies primarily focus on decreasing bone resorption and do not assist in bone regeneration or offering permanent curative solutions. Additionally, these therapies are associated with severe adverse events like thromboembolism, increased risk of stroke, and hypocalcaemia. To overcome these limitations, bone regenerative pathways and approaches are now considered to manage osteoporosis. The bone regenerative pathways involved in bone regeneration include wingless-related integration site/β-catenin signalling pathway, notch signalling pathway, calcium signalling, etc. The various regenerative approaches which possess potential to heal and replace the bone defect site include scaffolds, cements, cell therapy, and other alternative medicines. The review focuses on describing the challenges and opportunities in bone regeneration for osteoporosis.

Targeting Agents in Biomaterial-Mediated Bone Regeneration

Bone diseases are a global public concern that affect millions of people. Even though current treatments present high efficacy, they also show several side effects. In this sense, the development of biocompatible nanoparticles and macroscopic scaffolds has been shown to improve bone regeneration while diminishing side effects. In this review, we present a new trend in these materials, reporting several examples of materials that specifically recognize several agents of the bone microenvironment. Briefly, we provide a subtle introduction to the bone microenvironment. Then, the different targeting agents are exposed. Afterward, several examples of nanoparticles and scaffolds modified with these agents are shown. Finally, we provide some future perspectives and conclusions. Overall, this topic presents high potential to create promising translational strategies for the treatment of bone-related diseases. We expect this review to provide a comprehensive description of the incipient state-of-the-art of bone-targeting agents in bone regeneration.

Transcriptomic analysis reveals the molecular mechanisms underlying osteoclast differentiation in the estrogen-deficient pullets

Several previous reports have suggested that estrogen (E2) is a vital signal responsible for the regulation of skeletal homeostasis and bone remodeling in mammals. E2 could efficiently accelerate the growth of medullary bone in pullets during sexual maturity. Furthermore, the low E2 level can strengthen the mechanical bone functions in female hens. However, mechanistic studies to describe the effects of E2 on bone in pullets during the initiation of the puberty period are remaining elusive. Therefore, the aim of this study was to explore the effect of inhibiting E2 biosynthesis on the biomechanical properties and its molecular mechanism during sexual maturity of pullets. In this study, a total of 90 Hy-line Sonia pullets with comparable body weight at 13 wk of age were selected and categorized into 2 separate groups. Daily, 0.5 mg/4 mL of letrozole (LZ) was orally administered to the treatment (TRT) group and 4 mL of saline to the control (CON) group of pullets for 6 wk. Compared with the CON group, a lower plasma E2 level was observed in the TRT group. Furthermore, plasma P, Gla protein (BGP), and 1,25-dihydroxy vitamin D3 (1,25-(OH)₂D₃) levels were markedly suppressed, whereas the plasma alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) levels were significantly elevated. Moreover, the cortical bone thickness and breaking strength of the tibia and femur, the bone mineral density of the humerus, and the bone mineral content of the humerus as well as the femur were increased significantly. The expression levels of 340 differentially expressed genes (DEGs) differed significantly between the CON and TRT group in the tibia at 19 wk of age. Among them, 32 genes were up-regulated, whereas 308 were down-regulated in the TRT group. The variations in candidate genes associated with osteoclast differentiation and cell adhesion may indicate that LZ inhibits E2 biosynthesis, consequently, reduces osteoclast differentiation by suppressing inter-cellular communication and cells attaching to extracellular matrix components. Taken together, the present study demonstrated that inhibiting E2 synthesis during sexual maturity of pullets decreased osteoclast differentiation and considerably enhanced bone quality.

Tuning the resorption-formation balance in an in vitro 3D osteoblast-osteoclast co-culture model of bone

The aim of the present study was to further improve an in vitro 3D osteoblast (OB) - osteoclast (OC) co-culture model of bone by tuning it towards states of formation, resorption, and equilibrium for their future applications in fundamental research, drug development and personalized medicine. This was achieved by varying culture medium composition and monocyte seeding density, the two external parameters that affect cell behavior the most. Monocytes were seeded at two seeding densities onto 3D silk-fibroin constructs pre-mineralized by MSC-derived OBs and were co-cultured in one of three different media (OC stimulating, Neutral and OB stimulating medium) for three weeks. Histology showed mineralized matrix after co-culture and OC markers in the OC medium group. Scanning Electron Microscopy showed large OC-like cells in the OC medium group. Micro-computed tomography showed increased formation in the OB medium group, equilibrium in the Neutral medium group and resorption in the OC medium group. Culture supernatant samples showed high early tartrate resistant acid phosphatase (TRAP) release in the OC medium group, a later and lower release in the Neutral medium group, and almost no release in the OB medium group. Increased monocyte seeding density showed a less-than-proportional increase in TRAP release and resorption in OC medium, while it proportionally increased TRAP release in Neutral medium without affecting net resorption. The 3D OB-OC co-culture model was effectively used to show an excess of mineral deposition using OB medium, resorption using OC medium, or an equilibrium using Neutral medium. All three media applied to the model may have their own distinct applications in fundamental research, drug development, and personalized medicine.

Autophagy: An important target for natural products in the treatment of bone metabolic diseases

Bone homeostasis depends on a precise dynamic balance between bone resorption and bone formation, involving a series of complex and highly regulated steps. Any imbalance in this process can cause disturbances in bone metabolism and lead to the development of many associated bone diseases. Autophagy, one of the fundamental pathways for the degradation and recycling of proteins and organelles, is a fundamental process that regulates cellular and organismal homeostasis. Importantly, basic levels of autophagy are present in all types of bone-associated cells. Due to the cyclic nature of autophagy and the ongoing bone metabolism processes, autophagy is considered a new participant in bone maintenance. Novel therapeutic targets have emerged as a result of new mechanisms, and bone metabolism can be controlled by interfering with autophagy by focusing on certain regulatory molecules in autophagy. In parallel, several studies have reported that various natural products exhibit a good potential to mediate autophagy for the treatment of metabolic bone diseases. Therefore, we briefly described the process of autophagy, emphasizing its function in different cell types involved in bone development and metabolism (including bone marrow mesenchymal stem cells, osteoblasts, osteocytes, chondrocytes, and osteoclasts), and also summarized research advances in natural product-mediated autophagy for the treatment of metabolic bone disease caused by dysfunction of these cells (including osteoporosis, rheumatoid joints, osteoarthritis, fracture nonunion/delayed union). The objective of the study was to identify the function that autophagy serves in metabolic bone disease and the effects, potential, and challenges of natural products for the treatment of these diseases by targeting autophagy.

Dental Implants: Enhancing Biological Response Through Surface Modifications

Surface characteristics are an important factor for long-term clinical success of dental implants. Alterations of implant surface characteristics accelerate or improve osseointegration by interacting with the physiology of bone healing. Dental implant surfaces have been traditionally modified at the microlevel. Recently, researchers have actively investigated nano-modifications in dental implants. This review explores implant surface modifications that enhance biological response at the interface between a bone and the implant.

AAV-mediated delivery of osteoblast/osteoclast-regulating miRNAs for osteoporosis therapy

Osteoporosis occurs due to a dysregulation in bone remodeling, a process requiring both bone-forming osteoblasts and bone-resorbing osteoclasts. Current leading osteoporosis therapies suppress osteoclast-mediated bone resorption but show limited therapeutic effects because osteoblast-mediated bone formation decreases concurrently. We developed a gene therapy strategy for osteoporosis that simultaneously promotes bone formation and suppresses bone resorption by targeting two microRNAs (miRNAs)-miR-214-3p and miR-34a-5p. We modulated the expression of these miRNAs using systemically delivered recombinant adeno-associated viral (rAAV) vectors targeting the bone. rAAV-mediated overexpression of miR-214-3p or inhibition of miR-34a-5p in the skeleton resulted in bone loss in adult mice, resembling osteoporotic bones. Conversely, rAAV-mediated inhibition of miR-214-3p or overexpression of miR-34a-5p reversed bone loss in mouse models for postmenopausal and senile osteoporosis by increasing osteoblast-mediated bone formation and decreasing osteoclast-mediated bone resorption. Notably, these mice did not show any apparent pathological phenotypes in non-skeletal tissues. Mechanistically, inhibiting miR-214-3p upregulated activating transcription factor 4 in osteoblasts and phatase and tensin homolog in osteoclasts, while overexpressing miR-34a-5p downregulated Notch1 in osteoblasts and TGF-β-induced factor homeobox 2 in osteoclasts. In summary, bone-targeting rAAV-mediated regulation of miR-214-3p or miR-34a-5p is a promising new approach to treat osteoporosis, while limiting adverse effects in non-skeletal tissues.

Loureirin B downregulates osteoclast differentiation of bone marrow macrophages by targeting the MAPK signaling pathway

Excessive absorption of osteoclasts will break the balance between osteoclasts and osteoblasts, leading to bone loss, decreased bone density, and increased bone fragility. We have shown that Loureirin B (LrB) can inhibit osteoclasts. In this study, we demonstrated the targeting-inhibitory mechanism of LrB acting on osteoclast precursor. Using SPR, HPLC and MALDI-TOF-MS to capture and analyze the target protein of Loureirin B in bone marrow macrophages (BMMs), we used this method to detect all target proteins that LrB acts on BMMs, and analyzed the distribution and enrichment rate of the target protein by DAVID enrichment analysis. Ledock molecular docking was used to detect the binding of LrB. We used Western Blot for verification. The target proteins of LrB acting on BMMs were Serpine1, Atp6ap1, Dvl1, Rhd, Fzd2, MAPK1, MAP2K2, MAPK3 and so on. MAPK1, MAP2K2 and MAPK3 were the most relevant. LrB treatment attenuated the expression of phosphorylated JNK and p38 kinases of the MAPK signaling pathway. Our research further confirmed that LrB affects the MAPK signaling pathway in BMMs, thereby inhibiting the differentiation of BMMs into osteoclasts. This discovery can confirm the mechanism by which LrB acts on BMMs.

Attenuation by HSP90 inhibitors of EGF-elicited migration of osteoblasts: involvement of p44/p42 MAP kinase

BACKGROUND

We have demonstrated that epidermal growth factor (EGF)-induced migration of osteoblast-like MC3T3-E1 cells is mediated through p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase, stress-activated protein kinase/ c-Jun N-terminal kinase (SAPK/JNK), and Akt.The molecular chaperone heat shock protein 90 (HSP90) is abundantly expressed in osteoblasts. However, the role of HSP90 in osteoblast migration remains obscure.

OBJECTIVE

In this study, we investigated the effect of HSP90 inhibitors on the EGF-induced migration of MC3T3-E1 cells and the mechanism.

METHODS

Clonal osteoblast-like MC3T3-E1 cells were treated with the HSP90 inhibitors geldanamycin or onalespib and then stimulated with EGF. Cell migration was evaluated using the transwell cell migration assay and wound-healing assay. The viability of MC3T3-E1 cells was analyzed using the Cell Counting Kit-8. The phosphorylation of p44/p42 MAP kinase, p38 MAP kinase, SAPK/JNK, Akt, and protein kinase-like endoplasmic reticulum kinase (PERK) was evaluated by western blot analysis.

RESULTS

EGF-induced migration was significantly suppressed by geldanamycin and onalespib, evaluated by both transwell cell migration assay and wound-healing assay. Geldanamycin and onalespib did not significantly alter cell viability. Geldanamycin and onalespib markedly reduced the EGF-induced phosphorylation of p44/p42 MAP kinase, but not p38 MAP kinase or Akt. By contrast, geldanamycin and onalespib increased the EGF-induced phosphorylation of SAPK/JNK. PERK phosphorylation was not significantly affected by geldanamycin or onalespib.

CONCLUSION

Our results strongly suggest that HSP90 inhibitors reduce the EGF-induced osteoblast migration through the p44/p42 MAP kinase.

Mechanism of Huangqi Sanxian Decoction Inhibiting Osteoclast Differentiation Based on Network Pharmacology

Osteoclasts (OCs) have been the unique cell type exhibiting the bone-resorption activity in body. It is important to identify drugs to resist osteoclastogenesis to manage the bone-loss disorders. Huangqi Sanxian decoction (HQSXD) is utilized for the treatment of postmenopausal osteoporosis (PMOP) for a long history in East Asia. This work aimed to examine HQSXD’s activity in OC differentiation. Based on staining with tartrate-resistant acid phosphatase (TRAP), it was found that HQSXD suppressed OC generation under the induction of RANKL produced in the bone marrow-derived monocytes/macrophages (BMMs), with no cytotoxic effect. Later analysis like molecular exploration and network pharmacology (NP) suggested the role of HQSXD in suppressing genes associated with osteoclastogenesis via PI3K/Akt-mediated mechanism dose-dependently. This work might illustrate the molecular pharmacological mechanism involved in HQSXD’s effect on treating OC-associated disorders. Moreover, NP was found to modernize traditional Chinese medicine (TCM) research.

Evaluation on antiosteoporosis of collagen peptides prepared by immobilized protease with eggshell membrane

Collagen peptides are a potential treatment for osteoporosis due to their antiosteoporosis activity. In this study, we prepared immobilized protease with eggshell membrane as carrier, and then hydrolyzed collagen to obtain collagen peptide. The antiosteoporosis of collagen peptides was confirmed by hBMSC osteogenic differentiation and bone mineralization improvement results. Surprisingly, antiosteoporosis of collagen peptides was related to the molecular weight of collagen peptides. This was derived from the osteoblast marker gene expressions, and mineral elements in P1 treatment were higher than those in P3 treatment. Consequently, these results confirmed that antiosteoporosis of low molecular weight collagen peptides is higher than that of higher molecular weight collagen peptides. Furthermore, the antiosteoporosis activity of P1 was due to its peptide sequences with known antiosteoporosis activity in P1. PRACTICAL APPLICATION: Using eggshell membrane as carrier to prepare immobilized protease was meaningful for solving the problem of resource waste. In addition, the results showed that collagen peptides possessed antiosteoporosis, and the effect of low molecular weight collagen peptides was better. This study provides a theoretical basis for developing high antiosteoporosis collagen peptides able to treat osteoporosis.

Three interfaces of the dental implant system and their clinical effects on hard and soft tissues

Anatomically, the human tooth has structures both embedded within and forming part of the exterior surface of the human body. When a tooth is lost, it is often replaced by a dental implant, to facilitate the chewing of food and for esthetic purposes. For successful substitution of the lost tooth, hard tissue should be integrated into the implant surface. The microtopography and chemistry of the implant surface have been explored with the aim of enhancing osseointegration. Additionally, clinical implant success is dependent on ensuring that a barrier, comprising strong gingival attachment to an abutment, does not allow the infiltration of oral bacteria into the bone-integrated surface. Epithelial and connective tissue cells respond to the abutment surface, depending on its surface characteristics and the materials from which it is made. In particular, the biomechanics of the implant-abutment connection structure (i.e., the biomechanics of the interface between implant and abutment surfaces, and the screw mechanics of the implant-abutment assembly) are critical for both the soft tissue seal and hard tissue integration. Herein, we discuss the clinical importance of these three interfaces: bone-implant, gingiva-abutment, and implant-abutment.

Molecular differences in collagen organization and in organic-inorganic interfacial structure of bones with and without osteocytes

Bone is a fascinating biomaterial composed mostly of type-I collagen fibers as an organic phase, apatite as an inorganic phase, and water molecules residing at the interfaces between these phases. They are hierarchically organized with minor constituents such as non-collagenous proteins, citrate ions and glycosaminoglycans into a composite structure that is mechanically durable yet contains enough porosity to accommodate cells and blood vessels. The nanometer scale organization of the collagen fibrous structure and the mineral constituents in bone were recently extensively scrutinized. However, molecular details at the lowest hierarchical level still need to be unraveled to better understand the exact atomic-level arrangement of all these important components in the context of the integral structure of the bone. In this report, we unfold some of the molecular characteristics differentiating between two load-bearing (cleithrum) bones, one from sturgeon fish, where the matrix contains osteocytes and one from pike fish where the bone tissue is devoid of these bone cells. Using enhanced solid-state NMR measurements, we underpin disparities in the collagen fibril structure and dynamics, the mineral phases, the citrate content at the organic-inorganic interface and water penetrability in the two bones. These findings suggest that different strategies are undertaken in the erection of the mineral-organic interfaces in various bones characterized by dissimilar osteogenesis or remodeling pathways and may have implications for the mechanical properties of the particular bone. STATEMENT OF SIGNIFICANCE: Bone boasts unique interactions between collagen fibers and mineral phases through interfaces holding together this bio-composite structure. Over evolution, fish have gone from mineralizing their bones aided by certain bone cells called osteocytes, like tetrapod, to mineralization without these cells. Here, we report atomic level differences in collagen fiber cross linking and organization, porosity of the mineral phases and content of citrate molecules at the bio-mineral interface in bones from modern versus ancient fish. The dissimilar structural features may suggest disparate mechanical properties for the two bones. Fundamental level understanding of the organic and inorganic components in bone and the interfacial interactions holding them together is essential for successful bone repair and for treating better tissue pathologies.

Positive and Negative Regulators of Sclerostin Expression

Sclerostin is secreted from osteocytes, binds to the Wnt co-receptor Lrp5/6, and affects the interaction between Wnt ligands and Lrp5/6, which inhibits Wnt/β-catenin signals and suppresses bone formation. Sclerostin plays an important role in the preservation of bone mass by functioning as a negative regulator of bone formation. A sclerostin deficiency causes sclerosteosis, which is characterized by an excess bone mass with enhanced bone formation in humans and mice. The expression of sclerostin is positively and negatively regulated by many factors, which also govern bone metabolism. Positive and negative regulators of sclerostin expression and their effects are introduced and discussed herein based on recent and previous findings, including our research.

Evaluating the Role of Probiotics in the Prevention and Management of Age-Related Diseases

The human lifespan has been significantly increased due to scientific advancements in the management of disease; however, the health span of the aging population does not follow the same trend. Aging is the major risk factor for multimorbidity that is derived from the progressive loss of homeostasis, immunological and stem cell exhaustion, as well as exacerbated inflammation responses. Age-related diseases presenting with high frequencies include neurodegenerative, musculoskeletal, cardiovascular, metabolic diseases and cancer. These diseases can be co-morbid and are usually managed using a disease-specific approach that can eventually lead to polypharmacy, low medication adherence rates and undesired drug-drug interactions. Novel studies suggest targeting the shared biological basis of age-related diseases to retard the onset and manage their manifestations. Harvesting the anti-inflammatory and immunomodulatory capacity of probiotics to tackle the root cause of these diseases, could pose a viable alternative. In this article, a comprehensive review of the effects of probiotic supplementation on the molecular pathogenesis of age-related diseases, and the potential of probiotic treatments as preventative or alleviatory means is attempted. Furthermore, issues on the safety and efficiency of probiotic supplementation, as well as the pitfalls of current clinical studies are discussed, while new perspectives for systematic characterization of probiotic benefits on aged hosts are outlined.

Dissociation of Bone Resorption and Formation in Spaceflight and Simulated Microgravity: Potential Role of Myokines and Osteokines?

The dissociation of bone formation and resorption is an important physiological process during spaceflight. It also occurs during local skeletal unloading or immobilization, such as in people with neuromuscular disorders or those who are on bed rest. Under these conditions, the physiological systems of the human body are perturbed down to the cellular level. Through the absence of mechanical stimuli, the musculoskeletal system and, predominantly, the postural skeletal muscles are largely affected. Despite in-flight exercise countermeasures, muscle wasting and bone loss occur, which are associated with spaceflight duration. Nevertheless, countermeasures can be effective, especially by preventing muscle wasting to rescue both postural and dynamic as well as muscle performance. Thus far, it is largely unknown how changes in bone microarchitecture evolve over the long term in the absence of a gravity vector and whether bone loss incurred in space or following the return to the Earth fully recovers or partly persists. In this review, we highlight the different mechanisms and factors that regulate the humoral crosstalk between the muscle and the bone. Further we focus on the interplay between currently known myokines and osteokines and their mutual regulation.

Differentiation of Cells Isolated from Human Femoral Heads into Functional Osteoclasts

Proper formation of the skeleton during development is crucial for the mobility of humans and the maintenance of essential organs. The production of bone is regulated by osteoblasts and osteoclasts. An imbalance of these cells can lead to a decrease in bone mineral density, which leads to fractures. While many studies are emerging to understand the role of osteoblasts, less studies are present about the role of osteoclasts. This present study utilized bone marrow cells isolated directly from the bone marrow of femoral heads obtained from osteoarthritic (OA) patients after undergoing hip replacement surgery. Here, we used tartrate resistant acid phosphatase (TRAP) staining, Cathepsin K, and nuclei to identity osteoclasts and their functionality after stimulation with macrophage-colony stimulation factor (M-CSF) and receptor activator of nuclear factor kappa-β ligand (RANKL). Our data demonstrated that isolated cells can be differentiated into functional osteoclasts, as indicated by the 92% and 83% of cells that stained positive for TRAP and Cathepsin K, respectively. Furthermore, isolated cells remain viable and terminally differentiate into osteoclasts when stimulated with RANKL. These data demonstrate that cells isolated from human femoral heads can be differentiated into osteoclasts to study bone disorders during development and adulthood.

The Effects of Selenium on Bone Health: From Element to Therapeutics

Osteoporosis, characterized by low bone mass and a disruption of bone microarchitecture, is traditionally treated using drugs or lifestyle modifications. Recently, several preclinical and clinical studies have investigated the effects of selenium on bone health, although the results are controversial. Selenium, an important trace element, is required for selenoprotein synthesis and acts crucially for proper growth and skeletal development. However, the intake of an optimum amount of selenium is critical, as both selenium deficiency and toxicity are hazardous for health. In this review, we have systematically analyzed the existing literature in this field to determine whether dietary or serum selenium concentrations are associated with bone health. In addition, the mode of administration of selenium as a supplement for treating bone disease is important. We have also highlighted the importance of using green-synthesized selenium nanoparticles as therapeutics for bone disease. Novel nanobiotechnology will be a bridgehead for clinical applications of trace elements and natural products.

Focusing on OB-OC-MΦ Axis and miR-23a to Explore the Pathogenesis and Treatment Strategy of Osteoporosis

Osteoporosis is a bone metabolic disorder characterized by decreased bone density and deteriorated microstructure, which increases the risk of fractures. The imbalance between bone formation and bone resorption results in the occurrence and progression of osteoporosis. Osteoblast-mediated bone formation, osteoclast-mediated bone resorption and macrophage-regulated inflammatory response play a central role in the process of bone remodeling, which together maintain the balance of the osteoblast-osteoclast-macrophage (OB-OC-MΦ) axis under physiological conditions. Bone formation and bone resorption disorders caused by the imbalance of OB-OC-MΦ axis contribute to osteoporosis. Many microRNAs are involved in the regulation of OB-OC-MΦ axis homeostasis, with microRNA-23a (miR-23a) being particularly crucial. MiR-23a is highly expressed in the pathological process of osteoporosis, which eventually leads to the occurrence and further progression of osteoporosis by inhibiting osteogenesis, promoting bone resorption and inflammatory polarization of macrophages. This review focuses on the role and mechanism of miR-23a in regulating the OB-OC-MΦ axis to provide new clinical strategies for the prevention and treatment of osteoporosis.

Experimental Rat Model of Bony Defects in the Facet Joint Maintained with Bone Wax for the Study of Spinal Pain

Purpose

Studies using experimental rat models for low back pain due to facet-joint defects are scarce. This study used a novel experimental rat model to determine whether bony defects induced by facetectomy could be maintained by bone wax, thus mimicking spondylolysis, and to analyze the effect of the facetectomy on rat behavior.

Patients and Methods

Twelve 10-week-old male Wistar rats weighing 300–350 g were divided into group A (n = 6) that underwent unilateral facetectomy of the right L5-6 facet joint and group B (n = 6) that additionally applied water-soluble bone wax at the facetectomy site. The difference in the left and right stride length, detected by the footprint test, and change in the left and right facet joint area were compared before and 4 weeks after the experiment.

Results

Even though the difference between the left and right stride lengths of groups A and B was not statistically significant, in contrast to group A, group B showed a shorter stride length on the right side (p = 0.22 and 0.46, in group A and group B, respectively). The right facet joint area, where the facetectomy was performed, was significantly smaller in group B 4 weeks after surgery, but not in group A (p = 0.50 and < 0.01, in group A and group B, respectively).

Conclusion

Based on the results, we concluded that the bony defects, induced by facetectomy at the L5-6 facet joint, were maintained with bone wax. This study will provide an experimental model for bony defects in the facet joint.

Eggshell Microparticle Reinforced Scaffolds for Regeneration of Critical Sized Cranial Defects

Scaffold-based approaches for bone regeneration have been studied using a wide range of biomaterials as reinforcing agents to improve the mechanical strength and bioactivity of the 3D constructs. Eggshells are sustainable and inexpensive materials with unique biological and chemical properties to support bone differentiation. The incorporation of eggshell particles within hydrogels yields highly osteoinductive and osteoconductive scaffolds. This study reveals the effects of microparticles of whole eggshells, eggshells without a membrane, and a pristine eggshell membrane on osteogenic differentiation in protein-derived hydrogels. The in vitro studies showed that gels reinforced with eggshells with and without a membrane demonstrated comparable cellular proliferation, osteogenic gene expression, and osteogenic differentiation. Subsequently, in vivo studies were performed to implant eggshell microparticle-reinforced composite hydrogel scaffolds into critical-sized cranial defects in Sprague Dawley (SD) rats for up to 12 weeks to study bone regeneration. The in vivo results showed that the eggshell microparticle-based scaffolds supported an average bone volume of 60 mm³ and a bone density of 2000 HU 12 weeks post implantation. Furthermore, histological analyses of the explanted scaffolds showed that the eggshell microparticle-reinforced scaffolds permitted tissue infiltration and induced bone tissue formation over 12 weeks. The histology staining also indicated that these scaffolds induced significantly higher bone regeneration at 6 and 12 weeks as compared to the blank (no scaffold) and pristine gel scaffolds. The eggshell microparticle-reinforced scaffolds also supported significantly higher bone formation, remodeling, and vascularization over 6 and 12 weeks as confirmed by immunohistochemistry analysis. Collectively, our results indicated that eggshell microparticle-reinforced scaffolds facilitated significant bone regeneration in critical-sized cranial defects.

Differential Effects of Neurectomy and Botox-induced Muscle Paralysis on Bone Phenotype and Titanium Implant Osseointegration

Metabolic bone is highly innervated by both sensory and sympathetic nerves. In addition to skeletal development, neural regulation participates in local bone remodeling, which is important for successful osseointegration of titanium implants. Neurectomy is a model used to investigate the lack of neural function on bone homeostasis, but the relative impacts of direct denervation to bone or denervation-induced muscle paralysis are less well defined. To investigate this difference, we used two nerve intervention models, sciatic and femoral neurectomy (SFN) v. botox-induced muscle paralysis (BTX) and assessed the resulting femoral bone phenotype and Ti implant osseointegration. Male Sprague Dawley rats (19) were randomly divided into three groups: implant control (n = 5), SFN (n = 7), and BTX (n = 7). Ti implants (microrough/hydrophilic [modSLA], Institut Straumann AG) were placed in the distal metaphysis of each femur on day 24 post-SFN or BTX. Bone and muscle were examined on day 28 after implant insertion. Both nerve intervention models impaired osseointegration. MicroCT and histology indicated that both models had reduced trabecular bone formation. Only BTX reduced cortical bone formation and increased cortical bone porosity. BTX resulted in more bone loss characterized by the least trabecular and cortical bone, as well as osseointegration. Osteoblasts isolated from the tibia exhibited a model-specific phenotype when they were grown on Ti substrates in vitro. Neurectomy caused more severe muscle atrophy than botox injection. These results indicate that neural regulation directly modulates bone formation and osseointegration. Muscle paralysis modulated the effects of loss of neural inputs into bone, supporting the hypothesis that mechanical loading of bone is a factor in achieving successful osseointegration. The different effects of botox and neurectomy on bone phenotype indicated that the sensory and sympathetic nerves had a role in the osseointegration process.

Bone formation recovery with gold nanoparticle-induced M2 macrophage polarization in mice

The prevention of fractures induced by inflammatory bone disease remains a clinical challenge. This is because of a lack of bone formation to fill in the bone defects, which are believed to be due in part to persistent inflammation caused by the imbalance of M1 over M2 macrophages. In this study, gold nanoparticles (AuNPs) were synthesized to shift the balance of macrophages at the site of bone damage to improve osteanagenesis in a mouse model of LPS-induced inflammatory bone erosion. Specifically, the AuNPs treatment improved bone structure and increased bone mineral density (BMD) by ~14% compared with model group. Macrophages recruited by LPS treatment were reduced by ~11% after AuNPs injection. Compared to LPS treatment only, the percentage of M2 macrophages increased threefold by AuNPs, while the proportion of M1 macrophages decreased by 59%. This promoted the regeneration of bone matrix proteins in the bone defect site, which finally leads to increased bone mass and improved bone structure in model mice. These data suggest that AuNPs could be a novel candidate therapeutic for inflammatory bone disease rather than a drug carrier.

The Role of Galectin-3 in 1α,25(OH)2D3-Regulated Osteoclast Formation from White Leghorn Chickens In Vitro

Bones play an important role in maintaining the level of calcium in blood. They provide support for soft tissues and hematopoiesis and undergo continuous renewal throughout life. In addition, vitamin D is involved in regulating bone and calcium homeostasis. Galectin-3 (Gal-3) is a β-galactoside-binding protein that can regulate bone cell differentiation and function. Here, we aimed to study the regulatory effects of Gal-3 on vitamin-D-regulated osteoclastogenesis and bone resorption in chicken. Gal-3 expression in bone marrow stromal cells (BMSCs) from 18-day-old chicken embryos was inhibited or overexpressed. BMSCs were then co-cultured with bone marrow monocytes/macrophages (BMMs) with or without addition of 1α,25(OH)₂D₃. The results showed that 1α,25(OH)₂D₃ upregulated the expression of Gal-3 mRNA and receptor activator of nuclear-factor κB ligand (RANKL) expression in BMSCs and promoted osteoclastogenesis, as shown by the upregulated expression of osteoclast (OC) markers (CtsK, CAII, MMP-9, and TRAP) and increased bone resorption, a method for measuring the bone resorption area in vitro. Knockdown of Gal-3 by small-interfering RNA (siRNA) in BMSCs downregulated the expression of RANKL mRNA and attenuated the effects of 1α,25(OH)₂D₃ on osteoclastogenesis and bone resorption. Conversely, overexpression of Gal-3 in BMSCs enhanced the effects of osteoclastogenesis and bone resorption by increasing the expression of RANKL mRNA. These results demonstrated that Gal-3 mediates the differentiation and bone resorption of osteoclasts regulated by 1α,25(OH)₂D₃.