Programmed surface platform orchestrates anti-bacterial ability and time-sequential bone healing for implant-associated infection.

Implant-associated infection (IAI) has become an intractable challenge in clinic. The healing of IAI is a complex physiological process involving a series of spatiotemporal connected events. However, existing titanium-based implants in clinic suffer from poor antibacterial effect and single function. Herein, a versatile surface platform based on the presentation of sequential function is developed. Fabrication of titania nanotubes and poly-γ-glutamic acid (γ-PGA) achieves the efficient incorporation of silver ions (Ag+) and the pH-sensitive release in response to acidic bone infection microenvironment. The optimized PGA/Ag platform exhibits satisfactory biocompatibility and converts macrophages from pro-inflammatory M1 to pro-healing M2 phenotype during the subsequent healing stage, which creates a beneficial osteoimmune microenvironment and promotes angio/osteogenesis. Furthermore, the PGA/Ag platform mediates osteoblast/osteoclast coupling through inhibiting CCL3/CCR1 signaling. These biological effects synergistically improve osseointegration under bacterial infection in vivo, matching the healing process of IAI. Overall, the novel integrated PGA/Ag surface platform proposed in this study fulfills function cascades under pathological state and shows great potential in IAI therapy.

Targeting osteoblastic 11ß-HSD1 to combat high-fat diet-induced bone loss and obesity.

Excessive glucocorticoid (GC) action is linked to various metabolic disorders. Recent findings suggest that disrupting skeletal GC signaling prevents bone loss and alleviates metabolic disorders in high-fat diet (HFD)-fed obese mice, underpinning the neglected contribution of skeletal GC action to obesity and related bone loss. Here, we show that the elevated expression of 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1), the enzyme driving local GC activation, and GC signaling in osteoblasts, are associated with bone loss and obesity in HFD-fed male mice. Osteoblast-specific 11ß-HSD1 knockout male mice exhibit resistance to HFD-induced bone loss and metabolic disorders. Mechanistically, elevated 11ß-HSD1 restrains glucose uptake and osteogenic activity in osteoblast. Pharmacologically inhibiting osteoblastic 11ß-HSD1 by using bone-targeted 11ß-HSD1 inhibitor markedly promotes bone formation, ameliorates glucose handling and mitigated obesity in HFD-fed male mice. Taken together, our study demonstrates that osteoblastic 11ß-HSD1 directly contributes to HFD-induced bone loss, glucose handling impairment and obesity.

The short-chain fatty acid receptors Gpr41/43 regulate bone mass by promoting adipogenic differentiation of mesenchymal stem cells.

Bone is a dynamic tissue that is constantly remodeled throughout adult life. Recently, it has been shown that bone turnover decreases shortly after food consumption. This process has been linked to the fermentation of non-digestible food ingredients such as inulin by gut microbes, which results in the production of the short-chain fatty acids (SCFAs) acetate, propionate and butyrate. SCFAs exert various metabolic functions, which in part can be explained by activation of G protein-coupled receptors (Gpr) 41 and 43. However, the potential relevance of a SCFA-Gpr41/43 signaling axis for bone metabolism has not been established. The aim of our study is to investigate the role of Gpr41/43 in bone metabolism and osteogenic differentiation of mesenchymal stem cells. For this purpose, we analyzed the skeletal phenotype of wild type controls (WT) and Gpr41/43 double knockout (Gpr41/43 dKO) mice fed either a chow or an inulin-enriched diet. In addition, we isolated bone marrow derived mesenchymal stem cells from WT and Gpr41/43 dKO mice and differentiated them into osteoblasts in the absence or presence of acetate. MicroCT scanning of femoral bones of Gpr41/43 dKO mice revealed a significant increase of trabecular bone volume and trabecular compared to WT controls. Treatment of WT bone marrow-derived osteoblasts with acetate resulted in decreased mineralization and substantial downregulation of bone formation markers such as Phex, Ptgs2 and Col1a1. Notably, this effect was strongly attenuated in differentiated osteoblasts lacking Gpr41/43. Inversely, acetate supplementation resulted in higher levels of adipocyte marker genes including Pparg, Lpl and Adipoq in bone marrow-derived cells from WT mice, an effect blunted in differentiated cells isolated from Gpr41/43 dKO mice. Overall, these data indicate that acetate regulates bone architecture via SCFA-Gpr41/43 signaling by modulating the osteogenic versus adipogenic differentiation of mesenchymal stem cells.

Legumain is a paracrine regulator of osteoblast differentiation and mediates the inhibitory effect of TGF-ß1 on osteoblast maturation.

Transforming growth factor-beta 1 (TGF-ß1) is a critical regulator of skeletal homeostasis and has diverse effects on osteoblastogenesis. To date, the mechanisms behind the intriguing inhibitory effect of TGF-ß1 on osteoblast maturation are not fully understood. Here, we demonstrate a novel mechanism by which TGF-ß1 modulates osteoblast maturation through the lysosomal protease legumain. We observed that addition of TGF-ß1 to osteogenic cultures of human bone marrow derived mesenchymal stromal (stem) cells enhanced legumain activity and secretion, in-spite of decreased legumain mRNA expression, suggesting post-transcriptional regulation. We further showed that osteogenic cells internalize and activate prolegumain, associated with inhibited osteoblast maturation, revealing legumain as a paracrine regulator of osteoblast maturation. Interestingly, TGF-ß1 treatment exacerbated legumain internalization and activity, and showed an additive effect on legumain-induced inhibition of osteoblast maturation. Importantly, pharmacological inhibition of legumain abolished the inhibitory effect of TGF-ß1 on osteoblast maturation. Our findings reveal that TGF-ß1 inhibits osteoblast maturation by stimulating secretion and activity of endogenous legumain, as well as enhancing internalization and activation of extracellular prolegumain. Therefore, our study provides a deeper understanding of the complex regulation of osteoblastogenesis and unveils a novel TGF-ß1-legumain axis in regulation of osteoblast maturation, offering novel insights for possible therapeutic interventions related to bone diseases associated with aberrant TGF-ß1 signaling.

Tissue-Engineered Bone Regeneration for Medium-to-Large Osteonecrosis of the Femoral Head in the Weight-Bearing Portion: An Observational Study.

Background: Stem cell therapy for the treatment of osteonecrosis of the femoral head (ONFH) showed promising outcomes. However, ONFH with a large lesion in the weight-bearing portion is a poor prognostic factor and still challenging issue to be solved. We aimed to evaluate the effect of tissue-engineered bone regeneration for this challenging condition to preserve the femoral head. Methods: A total of 7 patients (9 hips) with ONFH who received osteoblasts expanded ex vivo from bone marrow-derived mesenchymal stem cells (BMdMSCs) and calcium metaphosphate (CMP) as scaffolds from March 2002 to March 2004 were retrospectively reviewed. The median age was 27.0 years (interquartile range [IQR], 23.0-34.0 years), and the median follow-up period was 20.0 years (IQR, 11.0-20.0 years). After culture and expansion of stem cells, we performed core decompression with BMdMSC implantation at a median number of 10.1 ×107 (IQR, 9.9-10.9 ×107). To evaluate radiographic outcomes, the Association Research Circulation Osseous (ARCO) classifications, the Japanese Investigation Committee (JIC) classification, and modified Kerboul combined necrotic angle (mKCNA) were evaluated preoperatively and during follow-up. Clinical outcomes were evaluated by a visual analog scale (VAS) and Harris Hip Score (HHS). Results: The preoperative stage of ONFH was ARCO 2 in 5 hips and ARCO 3a in 4 hips. The ARCO staging was maintained in 3 hips of ARCO 2 and 4 hips of ARCO 3a. Two hips of ARCO 2 with radiographic progression underwent total hip arthroplasty. According to mKCNA, 2 hips showed medium lesions, and 7 hips showed large lesions. The size of necrotic lesion was decreased in 4 hips (2 were ARCO 2 and 2 were ARCO 3a). There were no significant changes in JIC classification in all hips (type C1: 3 hips and type C2: 6 hips) (p = 0.655). Clinically, there were no significant changes in the VAS and HHS between preoperative and last follow-up (p = 0.072 and p = 0.635, respectively). Conclusions: Tissue engineering technique using osteoblasts expanded ex vivo from BMdMSC and CMP showed promising outcomes for the treatment of pre-collapsed and early-collapsed stage ONFH with medium-to-large size, mainly located in weight-bearing areas.

Osteoporosis and inflammation: Cause to effect or comorbidity?

Osteoporosis (OP) was long viewed as an inevitable process of aging, due to an imbalance between osteoclast bone resorbing and osteoblast bone formation function, leading to a negative balance in bone remodeling. This leads to low bone mass and increased bone fragility putting the patient at risk for fracture. While this view still holds, a better understanding disclosed that OP can occur at any age, as a comorbidity or a complication of many diseases and treatments. Differentiation, maturation, and function of osteoclasts and osteoblasts are affected by many factors from different morbidities: endocrine, metabolic, mechanical and inflammatory. Inflammatory diseases are often complicated by a generalized bone loss that subsequently leads to OP. Factors such as glucocorticoid treatment, immobilization, malnutrition, and insufficient intake of vitamin D play a role. However, the inflammatory process itself is involved and the resulting bone loss is termed immune-mediated bone loss. Experiments on animals and on humans, in addition to clinical studies, shed light on the role of inflammation in OP.

Synthesis and Evaluation of a Novel Series of Diphenylamine and Diphenylether Derivatives with Osteoblastogenic and Osteogenic Effects via CDK8 Inhibition.

Osteoporosis is induced by an imbalance between osteogenesis and bone resorption, and is treated with osteogenic drugs and/or resorption inhibitors. Resorption inhibitors, such as bisphosphonates, are orally used; however, orally active small molecules with osteogenic activity are not clinically available. We synthesized various types of small molecules and identified a series of diphenylamine and diphenylether derivatives that promoted osteoblast differentiation. Among them, diphenylether derivatives 13a, 13g, and 13h potently promoted osteoblast differentiation (EC200 for increasing alkaline phosphatase activity = 11.3, 31.1, and 12.3 nM, respectively) and inhibited cyclin-dependent kinase 8 (CDK8) activity (IC50 = 2.5, 7.8, and 3.9 nM, respectively), suggesting that their osteoblastgenic effects are mediated by the inhibition of CDK8. The ratio of the maximal plasma concentration after oral administration at 10 mg/kg in female rats and EC200 for osteoblastogenesis was 148.1 for compound 13a, 53.4 for 13g, and 101.8 for 13h, indicating possible in vivo osteoblastogenic and osteogenic effects. In ovariectomized female rats, 13g and 13h at 10 mg/kg/d for 8 weeks increased plasma bone-type alkaline phosphatase activity, indicating enhanced in vivo osteoblastogenesis. Furthermore, micro-computed tomography (micro-CT) showed that both compounds increased femoral cortical bone volume and mineral contents, which were unaffected by ovariectomy, while having negligible effects on trabecular bone volume and mineral contents, which were markedly reduced by ovariectomy. In conclusion, diphenylamine and diphenylether structures are novel scaffolds for osteoblastogenesis enhancers via the inhibition of CDK8. Among them, 13g and 13h are candidates for anti-osteoporotic drugs with cortical bone-selective osteogenic effects.

Bone regeneration-enhancing effects of extremely low-frequency electromag- netic fields: Analysis using fish scales as a bone model.

Electromagnetic fields (EMFs) noninvasively promote fracture healing, prevent osteoporosis, promote diaphyseal growth, enhance differentiation, and stimulate cell division. However, no good model systems for analyzing bone regeneration have been reported. In this study, we examined the in vivo regeneration of scales having osteoblasts and osteoclasts using a new magnetic field generator for exposing aquatic animals to EMFs at a sine-wave frequency of 60 Hz. Goldfish scales were put into a fish-breeding space with the developed magnetic field generator and exposed to extremely low-frequency electromagnetic fields (ELF-EMFs) of 60 Hz at an intensity of 1, 3, and 5 mT for 10 days while being regenerated the scales. After exposure, alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) activities in the goldfish scales were measured as markers of osteoblasts and osteoclasts, respectively. As a result, both ALP and TRAP activities in regenerating scales exposed to 3 mT ELF-EMFs were higher than those in regenerating scales exposed to 1 and 5 mT ELF-EMFs. Exposure of scales to 3 mT ELF-EMFs significantly enhanced the scale regeneration rate. Exposure of rat calvaria to 3 mT ELF-EMFs also increased both ALP and TRAP activities like in goldfish scales. Thus, we concluded that 3 mT ELF-EMFs contribute to the medical treatment of bone diseases.

AEBP1 restores osteoblastic differentiation under dexamethasone treatment by activating PI3K/AKT signalling.

Adipocyte enhancer-binding protein 1 (AEBP1) is closely implicated in osteoblastic differentiation and bone fracture; this research aimed to investigate the effect of AEBP1 on restoring osteoblastic differentiation under dexamethasone (Dex) treatment, and its interaction with the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. Pre-osteoblastic MC3T3-E1 cells were cultured in osteogenic medium and treated by Dex to mimic steroid-induced osteonecrosis cellular model. They were then further transfected with control or AEBP1-overexpressed lentiviral vectors. Finally, cells were treated with the PI3K inhibitor LY294002, with or without AEBP1-overexpressed lentiviral vectors. AEBP1 expression showed a downward trend in MC3T3-E1 cells under Dex treatment in a dose-dependent manner. AEBP1-overexpressed lentiviral vectors increased relative cell viability, alkaline phosphatase (ALP) staining, Alizarin red staining and osteoblastic differentiation markers including osteocalcin (OCN), osteopontin (OPN), collagen type I alpha 1 (COL1A1), runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein 2 (BMP2), but decreased cell apoptosis rate in MC3T3-E1 cells under Dex treatment; besides, AEBP1-overexpressed lentiviral vectors positively regulated p-PI3K and p-AKT expressions. Furthermore, LY294002 treatment decreased relative cell viability, Alizarin red staining, osteoblastic differentiation markers including OCN, OPN, RUNX2 and BMP, increased cell apoptosis rate and did not affect ALP staining in MC3T3-E1 cells under Dex treatment; meanwhile, LY294002 treatment weakened the effect of AEBP1 overexpression vectors on the above cell functions. AEBP1 restores osteoblastic differentiation under Dex treatment by activating the PI3K/AKT pathway.

Investigating the Promising P28 Peptide-Loaded Chitosan/Ceramic Bone Scaffolds for Bone Regeneration.

Bone has the ability to heal itself; however, bone defects fail to heal once the damage exceeds a critical size. Bone regeneration remains a significant clinical challenge, with autograft considered the ideal bone graft material due to its sufficient porosity, osteogenic cells, and biological growth factors. However, limitations to bone grafting, such as limited bone stock and high resorption rates, have led to a great deal of research into developing bone graft substitutes. The P28 peptide is a small molecule bioactive biomimetic alternative to mimic the bone morphogenetic protein 2 (BMP-2). In this study, we investigated the potential of P28-loaded hybrid scaffolds to mimic the natural bone structure for enhancing the bone regeneration process. We hypothesized that the peptide-loaded scaffolds and nude scaffolds both have the potential to promote bone healing, and the bone healing process is accelerated by the release of the peptide. To verify our hypothesis, C2C12 cells were evaluated for the presence of calcium deposits by histological stain at 7 and 14 days in cultures with hybrid scaffolds. Total RNA was isolated from C2C12 cells cultured with hybrid scaffolds for 7 and 14 days to assess osteoblast differentiation. The project findings demonstrated that the hybrid scaffold could enhance osteoblast differentiation and significantly improve the therapeutic effects of the scaffold in bone regeneration.

Modulation of osteoblastogenesis by NRF2: NRF2 activation suppresses osteogenic differentiation and enhances mineralization in human bone marrow-derived mesenchymal stromal cells.

Mesenchymal stromal stem cells (MSCs) or skeletal stem cells (SSCs) play a major role in tissue repair due to their robust ability to differentiate into osteoblasts, chondrocytes, and adipocytes. Complex cell signaling cascades tightly regulate this differentiation. In osteogenic differentiation, Runt-related transcription factor 2 (RUNX2) and ALP activity are essential. Furthermore, during the latter stages of osteogenic differentiation, mineral formation mediated by the osteoblast occurs with the secretion of a collagenous extracellular matrix and calcium deposition. Activation of nuclear factor erythroid 2-related factor 2 (NRF2), an important transcription factor against oxidative stress, inhibits osteogenic differentiation and mineralization via modulation of RUNX2 function; however, the exact role of NRF2 in osteoblastogenesis remains unclear. Here, we demonstrate that NRF2 activation in human bone marrow-derived stromal cells (HBMSCs) suppressed osteogenic differentiation. NRF2 activation increased the expression of STRO-1 and KITLG (stem cell markers), indicating NRF2 protects HBMSCs stemness against osteogenic differentiation. In contrast, NRF2 activation enhanced mineralization, which is typically linked to osteogenic differentiation. We determined that these divergent results were due in part to the modulation of cellular calcium flux genes by NRF2 activation. The current findings demonstrate a dual role for NRF2 as a HBMSC maintenance factor as well as a central factor in mineralization, with implications therein for elucidation of bone formation and cellular Ca2+ kinetics, dystrophic calcification and, potentially, application in the modulation of bone formation.

Enhancing bone regeneration: Unleashing the potential of magnetic nanoparticles in a microtissue model.

Bone tissue engineering addresses the limitations of autologous resources and the risk of allograft disease transmission in bone diseases. In this regard, engineered three-dimensional (3D) models emerge as biomimetic alternatives to natural tissues, replicating intracellular communication. Moreover, the unique properties of super-paramagnetic iron oxide nanoparticles (SPIONs) were shown to promote bone regeneration via enhanced osteogenesis and angiogenesis in bone models. This study aimed to investigate the effects of SPION on both osteogenesis and angiogenesis and characterized a co-culture of Human umbilical vein endothelial cells (HUVEC) and MG-63 cells as a model of bone microtissue. HUVECs: MG-63s with a ratio of 4:1 demonstrated the best results among other cell ratios, and 50 µg/mL of SPION was the optimum concentration for maximum survival, cell migration and mineralization. In addition, the data from gene expression illustrated that the expression of osteogenesis-related genes, including osteopontin, osteocalcin, alkaline phosphatase, and collagen-I, as well as the expression of the angiogenesis-related marker, CD-31, and the tube formation, is significantly elevated when the 50 µg/mL concentration of SPION is applied to the microtissue samples. SPION application in a designed 3D bone microtissue model involving a co-culture of osteoblast and endothelial cells resulted in increased expression of specific markers related to angiogenesis and osteogenesis. This includes the design of a novel biomimetic model to boost blood compatibility and biocompatibility of primary materials while promoting osteogenic activity in microtissue bone models. Moreover, this can improve interaction with surrounding tissues and broaden the knowledge to promote superior-performance implants, preventing device failure.

Poly(ε-Caprolactone)-Based Composites Modified With Polymer-Grafted Magnetic Nanoparticles and L-Ascorbic Acid for Bone Tissue Engineering.

The aim of this study was to develop multifunctional magnetic poly(ε-caprolactone) (PCL) mats with antibacterial properties for bone tissue engineering and osteosarcoma prevention. To provide good dispersion of magnetic iron oxide nanoparticles (IONs), they were first grafted with PCL using a novel three-step approach. Then, a series of PCL-based mats containing a fixed amount of ION@PCL particles and an increasing content of ascorbic acid (AA) was prepared by electrospinning. AA is known for increasing osteoblast activity and suppressing osteosarcoma cells. Composites were characterized in terms of morphology, mechanical properties, hydrolytic stability, antibacterial performance, and biocompatibility. AA affected both the fiber diameter and the mechanical properties of the nanocomposites. All produced mats were nontoxic to rat bone marrow-derived mesenchymal cells; however, a composite with 5 wt.% of AA suppressed the initial proliferation of SAOS-2 osteoblast-like cells. Moreover, AA improved antibacterial properties against Staphylococcus aureus and Escherichia coli compared to PCL. Overall, these magnetic composites, reported for the very first time, can be used as scaffolds for both tissue regeneration and osteosarcoma prevention.

Role of oxytocin in bone.

Oxytocin (OT) is a posterior pituitary hormone that, in addition to its role in regulating childbirth and lactation, also exerts direct regulatory effects on the skeleton through peripheral OT and oxytocin receptor (OTR). Bone marrow mesenchymal stem cells (BMSCs), osteoblasts (OB), osteoclasts (OC), chondrocytes, and adipocytes all express OT and OTR. OT upregulates RUNX2, BMP2, ALP, and OCN, thereby enhancing the activity of BMSCs and promoting their differentiation towards OB rather than adipocytes. OT also directly regulates OPG/RANKL to inhibit adipocyte generation, increase the expression of SOX9 and COMP, and enhance chondrocyte differentiation. OB can secrete OT, exerting influence on the surrounding environment through autocrine and paracrine mechanisms. OT directly increases OC formation through the NκB/MAP kinase signaling pathway, inhibits osteoclast proliferation by triggering cytoplasmic Ca2+ release and nitric oxide synthesis, and has a dual regulatory effect on OCs. Under the stimulation of estrogen, OB synthesizes OT, amplifying the biological effects of estrogen and OT. Mediated by estrogen, the OT/OTR forms a feedforward loop with OB. Apart from estrogen, OT also interacts with arginine vasopressin (AVP), prostaglandins (PGE2), leptin, and adiponectin to regulate bone metabolism. This review summarizes recent research on the regulation of bone metabolism by OT and OTR, aiming to provide insights into their clinical applications and further research.

Ultrasound-triggered piezoelectric polyetheretherketone with boosted osteogenesis via regulating Akt/GSK3ß/ß-catenin pathway.

Maxillofacial bone defects can severely impact quality of life by impairing physiological functions such as chewing, breathing, swallowing, and pronunciation. Polyether ether ketone (PEEK) is commonly used for the repair of maxillofacial defects due to its mechanical adaptability, while its osteogenic properties still need refinement. Herein, we have utilized the piezoelectric effect exhibited by barium titanate (BTO) under low-intensity pulsed ultrasound (LIPUS) to develop an ultrasound responsive PEEK (PDA@BTO-SPEEK, PBSP) through the mediating effect of polydopamine (PDA), for repairing maxillofacial bone defects. After modification by PDA@BTO, PBSP possesses better hydrophilicity, which is conducive to cell growth and adhesion. Simultaneously, by virtue of the piezoelectric characteristics of BTO, PBSP obtains a piezoelectric coefficient that matches the bone cortex. Notably, when PBSP is stimulated by LIPUS, it can generate stable electricity and effectively accelerate the osteogenic differentiation of osteoblasts through the regulation of the Piezo1-induced calcium (Ca2+) influx and Akt/GSK3ß/ß-catenin pathway. In addition, PBSP presents satisfactory therapeutic effects in rat skull defect models, and its osteogenic efficiency can be further improved under LIPUS stimulation with high tissue penetration. Collectively, PBSP + LIPUS exhibits great potential as a promising alternative strategy for the repair of maxillofacial bone defects.

KIAA0753 enhances osteoblast differentiation suppressed by diabetes.

Diabetes-related bone loss represents a significant complication that persistently jeopardizes the bone health of individuals with diabetes. Primary cilia proteins have been reported to play a vital role in regulating osteoblast differentiation in diabetes-related bone loss. However, the specific contribution of KIAA0753, a primary cilia protein, in bone loss induced by diabetes remains unclear. In this investigation, we elucidated the pivotal role of KIAA0753 as a promoter of osteoblast differentiation in diabetes. RNA sequencing demonstrated a marked downregulation of KIAA0753 expression in pro-bone MC3T3 cells exposed to a high glucose environment. Diabetes mouse models further validated the downregulation of KIAA0753 protein in the femur. Diabetes was observed to inhibit osteoblast differentiation in vitro, evidenced by downregulating the protein expression of OCN, OPN and ALP, decreasing primary cilia biosynthesis, and suppressing the Hedgehog signalling pathway. Knocking down KIAA0753 using shRNA methods was found to shorten primary cilia. Conversely, overexpression KIAA0753 rescued these changes. Additional insights indicated that KIAA0753 effectively restored osteoblast differentiation by directly interacting with SHH, OCN and Gli2, thereby activating the Hedgehog signalling pathway and mitigating the ubiquitination of Gli2 in diabetes. In summary, we report a negative regulatory relationship between KIAA0753 and diabetes-related bone loss. The clarification of KIAA0753's role offers valuable insights into the intricate mechanisms underlying diabetic bone complications.

The people behind the papers - Yukiko Kuroda and Koichi Matsuo.

Developing bones can adapt their shape in response to mechanical stresses from neighbouring growing organs. In a new study, Koichi Matsuo and colleagues examine how bone-forming osteoblasts and bone-resorbing osteoclasts coordinate growth in the mouse fibula. They describe the process called 'endo-forming trans-pairing', where bone resorption by osteoclasts in the outer periosteum is paired with bone formation by osteoblasts in the inner endosteum to shape the growing bone. To learn more about the story behind the paper, we caught up with first author Yukiko Kuroda and the corresponding author Koichi Matsuo, Professor at the School of Medicine, Keio University, Japan.

Two-Photon Laser-Mediated Ablation of Osteoblasts in Developing Zebrafish Larvae.

Zebrafish (Danio rerio) have an outstanding capacity to regenerate different organs and appendages. Bone regeneration in zebrafish has been studied using different methods such as fin amputation, scale plucking, skull trepanation, and microscopic approaches. Using a confocal laser scanning setup equipped with a two-photon laser, a laser ablation method was developed as a lesion paradigm to ablate bone-forming cells (osteoblasts) in the developing opercle of zebrafish larvae. The method described here allows the ablation of cells in a precise manner, as the area, shape, and depth can be finely adjusted. In addition, this method allows imaging of the area before and just after the ablation, so that short-term effects of the injury can be analyzed. In this experimental setup, the immune response after ablation of osteoblasts in the injured area was studied. An increase in the recruitment of macrophages was observed after ablation, indicating the relevance of their presence during bone regeneration.

Salidroside alleviates simulated microgravity-induced bone loss by activating the Nrf2/HO-1 pathway.

BACKGROUND: Bone loss caused by microgravity exposure presents a serious threat to the health of astronauts, but existing treatment strategies have specific restrictions. This research aimed to investigate whether salidroside (SAL) can mitigate microgravity-induced bone loss and its underlying mechanism. METHODS: In this research, we used hindlimb unloading (HLU) and the Rotary Cell Culture System (RCCS) to imitate microgravity in vivo and in vitro. RESULTS: The results showed that salidroside primarily enhances bone density, microstructure, and biomechanical properties by stimulating bone formation and suppressing bone resorption, thereby preserving bone mass in HLU rats. In MC3T3-E1 cells cultured under simulated microgravity in rotary wall vessel bioreactors, the expression of osteogenic genes significantly increased after salidroside administration, indicating that salidroside can promote osteoblast differentiation under microgravity conditions. Furthermore, the Nrf2 inhibitor ML385 diminished the therapeutic impact of salidroside on microgravity-induced bone loss. Overall, this research provides the first evidence that salidroside can mitigate bone loss induced by microgravity exposure through stimulating the Nrf2/HO-1 pathway. CONCLUSION: These findings indicate that salidroside has great potential for treating space-related bone loss in astronauts and suggest that Nrf2/HO-1 is a viable target for counteracting microgravity-induced bone damage.

Chitosan coatings on titanium-based implants - From development to characterization and behavior: A systematic review.

Chitosan is a promising natural polymer for coatings, it combines intrinsic antibacterial and pro-osteoblastic properties, but the literature still has a gap from the development to behavior of these coatings, so this systematic review aimed to answer, "What is the relationship between the physical and chemical properties of polymeric chitosan coatings on titanium implants on antibacterial activity and osteoblast viability?". PRISMA guidelines was followed, the search was applied into 4 databases and grey literature, without the restriction of time and language. The selection process occurred in 2 blinded steps by the authors. The criteria of eligibility were in vitro studies that evaluated the physical, chemical, microbiological, and biological properties of chitosan coatings on titanium surfaces. The risk of bias was analyzed by the specific tool. Of 734 potential articles 10 were included; all had low risk of bias. The coating was assessed according to the technique of fabrication, FT-IR, thickness, adhesion, roughness, wettability, antibacterial activity, and osteoblast viability. The analyzed coatings showed efficacy on antibacterial activity and cytocompatibility dependent on the class of material incorporated. Thus, this review motivates the development of time-dependent studies to optimize manufacturing and allow for an increase in patents and availability on the market.