Targeting EZH2 attenuates the ferroptosis-mediated osteoblast-osteoclast imbalance in rheumatoid arthritis.

OBJECTIVE: The enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) can regulate osteogenesis and osteoclastogenesis. This study aimed to further explore the effects of EZH2 modification on ferroptosis and the osteoblast-osteoclast balance in rheumatoid arthritis (RA) in vitro and in vivo. METHODS: Bone marrow mesenchymal stromal cells were transfected with EZH2 overexpression (oeEZH2) and EZH2 shRNA (shEZH2) plasmids with or without ferrostatin-1 (Fer-1) treatment and subjected to an osteoblast differentiation assay. The cells were then cocultured with bone marrow-derived macrophages and subjected to an osteoclast differentiation assay. Collagen-induced arthritis (CIA) mice were generated and injected with shEZH2 adeno-associated virus (AAV). RESULTS: OeEZH2 repressed osteoblast differentiation, as reflected by decreased ALP and Alizarin Red S staining and increased OPN, RUNX2, OPG and RANKL; however, shEZH2 had the opposite effects. Besides, oeEZH2 promoted osteoblast ferroptosis, as suggested by increased MDA, Fe2+, ROS, and PTGS2 but decreased GPX4 and SLC7A11; these effects could be attenuated by Fer-1 treatment. In contrast, shEZH2 ameliorated osteoblast ferroptosis. OeEZH2 subsequently increased osteoclast differentiation, as indicated by increased TRAP+ multinucleated cells, NFATC1, CTSK, and c-FOS; however, shEZH2 had the opposite effect, except that it did not regulate CTSK. In CIA mice, shEZH2 AAV decreased the clinical symptom score, histological score of cartilage, and systemic inflammation (TNF-α and IL-6) and repressed bone ferroptosis and restored the osteoblast-osteoclast balance to some extent, as reflected by immunohistochemical staining of related markers. CONCLUSION: Targeting EZH2 attenuates the ferroptosis-mediated osteoblast-osteoclast imbalance in RA, revealing its potential as a treatment target.

Effect of recombinant irisin on recombinant human bone morphogenetic protein-2 induced osteogenesis and osteoblast differentiation.

Osteoporotic fragility fractures substantially impact aging societies, necessitating long-term care and increasing healthcare costs. Myokine irisin, secreted by skeletal muscle, influences bone metabolism; however, a comprehensive understanding of the mechanisms by which irisin affects bone metabolism is still lacking. Therefore, this study aimed to explore the effects of irisin on osteogenesis and osteoblast differentiation triggered by bone morphogenetic protein-2 (BMP-2). We used 4-week-old male ICR mice and implanted polyethylene glycol pellets containing recombinant human BMP-2 (rh-BMP-2) into the left dorsal muscle pouch. Mice received weekly intraperitoneal injections of either phosphate-buffered saline or recombinant irisin (re-irisin). Ectopic bone formation was evaluated 3 weeks post-surgery using micro-computed tomography (µ-CT) and histological analysis. In vitro experiments, C2C12 cells were treated with or without rh-BMP-2 and re-irisin, and we assessed osteoblast differentiation markers, e.g., runt-related transcription factor 2, alkaline phosphatase, osteocalcin, and osteopontin, using real-time reverse transcription-polymerase chain reaction. The µ-CT analyses showed that re-irisin significantly increased bone mineral content and bone volume of ectopic bones newly formed by rh-BMP-2. The gene expressions of the osteoblast markers were significantly increased by rh-BMP-2 and further upregulated by re-irisin. The treatment of cyclic AMP response element-binding protein (CREB) small interfering RNA attenuated these effects, suggesting that CREB signaling pathway was involved in rh-BMP-2/re-irisin-induced osteoblastic differentiation. This study demonstrates the potential of irisin to enhance osteogenesis through BMP signaling, offering insights for osteoporosis treatment and highlighting irisin as a promising therapeutic target for improving bone health and extending a healthy lifespan.

BMSCs-derived exosomes carrying miR-668-3p promote progression of osteoblasts in osteonecrosis of the femoral head: Expression of proteins CD63 and CD9.

Recently, exosomes that are derived from bone marrow mesenchymal stem cells (BMSCs) have garnered considerable interest due to their significant roles in the processes of bone regeneration and repair. Among the various molecular components present within these exosomes, miR-668-3p has emerged as a pivotal microRNA that may be instrumental in modulating the function and proliferation of osteoblasts, the cells responsible for bone formation. The primary objective of this research was to examine the enhancing effects of BMSC-derived exosomes that are enriched with miR-668-3p on the advancement of osteoblasts in the context of osteonecrosis of the femoral head. Furthermore, the study aimed to analyze how the expression of specific exosomal proteins, namely CD63 and CD9, influences this biological process. To conduct the investigation, BMSCs were isolated from healthy rat models, followed by the extraction of their secreted exosomes. The subsequent phase of the study involved assessing the proliferation and differentiation of osteoblasts by introducing the exosomes enriched with miR-668-3p into an experimental setup representing osteonecrosis of the femoral head. The findings revealed that exosomes derived from BMSCs, which contained miR-668-3p, significantly enhanced the proliferation of osteoblasts as well as the expression of key osteogenic marker genes. Notably, the levels of CD63 and CD9 proteins were markedly increased in the treated groups, indicating that the mechanisms underlying this promotion might involve cell adhesion and the endocytic uptake of exosomes.

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.

[Calcifications and phosphocalcic metabolism]. / Calcifications et métabolisme phosphocalcique.

Extraosseous calcifications correspond to ubiquitous deposits of intra-tissue calcium salts leading to dysfunction of the affected tissue or organ. There are two types: metastatic calcifications and dystrophic calcifications. Their formation mechanism is by mimicking the physiological mineralization process with an "osteoblast-like" cell. The cause of extra-osseous calcification is variable and depends on risk factors. If the subject is young, you will have to think about a genetic syndrome!

Europium-Containing Nanospheres for Treating Ovariectomy-Induced Osteoporosis: Targeted Bone Remodeling and Macrophage Polarization Modulation.

Purpose: Osteoporosis, characterized by reduced bone mass and structural deterioration, poses a significant healthcare challenge. Traditional treatments, while effective in reducing fracture risks, are often limited by side effects. This study introduces a novel nanocomplex, europium (Eu) ions-doped superparamagnetic iron oxide (SPIO) nanocrystals encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanospheres, abbreviated as SPIO:Eu@PLGA nanospheres, as a potential therapeutic agent for osteoporosis by modulating macrophage polarization, enhancing osteoblast differentiation and inhibiting osteoclastogenesis. Methods: SPIO and SPIO:Eu nanocrystals were synthesized through pyrolysis and encapsulated in PLGA using an emulsification method. To evaluate the impact of SPIO:Eu@PLGA nanospheres on macrophage reprogramming and reactive oxygen species (ROS) production, flow cytometry analysis was conducted. Furthermore, an ovariectomized (OVX) rat model was employed to assess the therapeutic efficacy of SPIO:Eu@PLGA nanospheres in preventing the deterioration of osteoporosis. Results: In vitro, SPIO:Eu@PLGA nanospheres significantly attenuated M1 macrophage activation induced by lipopolysaccharides, promoting a shift towards the M2 phenotype. This action is linked to the modulation of ROS and the NF-κB pathway. Unlike free Eu ions, which do not achieve similar results when not incorporated into the SPIO nanocrystals. SPIO:Eu@PLGA nanospheres enhanced osteoblast differentiation and matrix mineralization while inhibiting RANKL-induced osteoclastogenesis. In vivo studies demonstrated that SPIO:Eu@PLGA nanospheres effectively targeted trabecular bone surfaces in OVX rats under magnetic guidance, preserving their structure and repairing trabecular bone loss by modulating macrophage polarization, thus restoring bone remodeling homeostasis. The study underscores the critical role of Eu doping in boosting the anti-osteoporotic effects of SPIO:Eu@PLGA nanospheres, evident at both cellular and tissue levels in vitro and in vivo. Conclusion: The inclusion of Eu into SPIO matrix suggests a novel approach for developing more effective osteoporosis treatments, particularly for conditions induced by OVX. This research provides essential insights into SPIO:Eu@PLGA nanospheres as an innovative osteoporosis treatment, addressing the limitations of conventional therapies through targeted delivery and macrophage polarization modulation.

microRNA-324 mediates bone homeostasis and the regulation of osteoblast and osteoclast differentiation and activity.

MicroRNAs (miRNAs) modulate the expression of other RNA molecules. One miRNA can target many transcripts, allowing each miRNA to play key roles in many biological pathways. Defects in bone homeostasis result in common age-related diseases including osteoporosis. Serum levels of miR-324-3p positively correlate with several features of bone maintenance. In contrast here, using in vivo micro-computed tomography and histology, global miR-324-null mice demonstrated increased bone mineral density and both trabecular and cortical thickness, with effect magnitudes increasing with age. The bone marrow of miR-324-null mice had reduced lipid content while TRAP staining revealed a decrease in osteoclasts, with histomorphometry demonstrating an increased rate of bone formation. Ex vivo assays showed that the high bone mass phenotype of miR-324-null mice resulted from both increased osteoblast activity and decreased osteoclastogenesis. RNA-seq analysis of osteoblasts, osteoclasts and bone marrow macrophages and target validation assays identified that the osteoclast fusion regulator Pin1 and the master osteogenic regulator Runx2 were targets of miR-324-5p in osteoclast lineage cells and osteoblasts, respectively. Indeed, in vitro Runx2 overexpression recapitulated the increased osteogenesis and decreased adipogenesis phenotype observed in vivo by the loss of miR-324. Overall, these data demonstrate the importance of miR-324 in bone homeostasis by regulating aspects of both bone formation and remodelling. Elucidation of pathways regulated by miR-324 offer promise for the treatment of bone diseases such as osteoporosis.

Effect of Hydroxyapatite Nanowires on Formation and Bioactivity of Osteoblastic Cell Spheroid.

Compared with traditional high-density cell spheroids, which are more prone to core necrosis, nanowires effectively improve the biological activity of core cells in spheroids, emanating more innovations for optimizing the internal cell survival environment and providing differentiation signals. In this study, hydroxyapatite nanowires (HAW), which provide numerous material exchange channels for internal cells by interpenetrating into cell spheroids, were added to osteoblast precursor (MC3T3-E1) cell spheroids. HAW, synthesized using the hydrothermal method, was used as a regulatory material to prepare uniformly sized 3D composite spheroids with good biological activity. Subsequently, material characterization and biocompatibility tests were performed on HAW, and the biological activity and osteogenic differentiation ability of the cell spheroids were tested. Notably, in 2D coculture, HAW displayed a certain attraction to MC3T3-E1 cells and promoted cell aggregation toward it. The content of HAW determined whether composite cell spheroids can form aggregated spherical structures, and incorporation of HAW alleviated core necrosis and enhanced the osteogenic phenotype. In summary, these findings indicate that the prepared HAW-bone cell composite spheroids can potentially be used as building blocks for the construction of large high-density biomimetic tissues and organoids using 3D bioprinting technology.

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.

Differentiation of osteoblastic metastases and bone islands on dual-energy computed tomography in patients with untreated lung cancer.

OBJECTIVE: To evaluate the diagnostic efficacy of quantitative dual-energy computed tomography (CT) parameters for distinguishing osteoblastic metastases (OBMs) from bone islands (BIs) in untreated lung cancer. MATERIAL AND METHODS: Dual-energy CT images of 24 patients with OBMs and 56 patients with BIs obtained between January 2019 and December 2021 were retrospectively analyzed. The CT70keV value, calcium(water) density [Dcalcium(water)], and water(calcium) density [Dwater(calcium)] were analyzed. Diagnostic performance was assessed by measuring the area under the curve (AUC), and specificity, sensitivity, and accuracy were determined. RESULTS: A total of 70 OBMs and 67 BIs were included. The AUC values of CT70keV, Dcalcium(water), and Dwater(calcium) showed no significant differences (0.950 vs. 0.947 vs. 0.929, respectively; P > 0.05). The optimal CT70keV cutoff value was 885.1 HU, with specificity, sensitivity, and accuracy of 81.4 %, 92.5 %, and 86.9 %, respectively. When using Dcalcium(water) < 254.9 mg/cm3 and Dwater(calcium) < 1250.6 mg/cm3, respectively, 119 of 137 lesions showed consistent diagnostic results (true or false). Sub-analysis of these 119 lesions showed specificity of 92.1 %, which was higher than that of CT70keV (P = 0.021). The AUC, sensitivity, and accuracy were 0.974, 92.9 %, and 92.4 %, respectively, which were not significantly different from those of CT70keV (P = 0.230, 0.906, and 0.220, respectively). Among the 18 lesions showing inconsistent diagnoses, Dcalcium(water) diagnosed 11 lesions correctly, and Dwater(calcium) diagnosed the remaining seven lesions correctly. CONCLUSION: The combination of Dcalcium(water) and Dwater(calcium) demonstrated a promising role in the differentiation of OBMs from BIs in lung cancer patients.

Adiposity and Mineral Balance in Chronic Kidney Disease.

PURPOSE OF REVIEW: Bone homeostasis is balanced between formation and resorption activities and remain in relative equilibrium. Under disease states this process is disrupted, favoring more resorption over formation, leading to significant bone loss and fracture incidence. This aspect is a hallmark for patients with chronic kidney disease mineral and bone disorder (CKD-MBD) affecting a significant portion of the population, both in the United States and worldwide. Further study into the underlying effects of the uremic microenvironment within bone during CKD-MBD are critical as fracture incidence in this patient population not only leads to increased morbidity, but also increased mortality. Lack of bone homeostasis also leads to mineral imbalance contributing to cardiovascular calcifications. One area understudied is the possible involvement of bone marrow adipose tissue (BMAT) during the progression of CKD-MBD. RECENT FINDINGS: BMAT accumulation is found during aging and in several disease states, some of which overlap as CKD etiologies. Importantly, research has found presence of BMAT inversely correlates with bone density and volume. Understanding the underlying molecular mechanisms for BMAT formation and accumulation during CKD-MBD may offer a potential therapeutic avenue to improve bone homeostasis and ultimately mineral metabolism.

Wnt3a-induced LRP6 phosphorylation enhances osteoblast differentiation to alleviate osteoporosis through activation of mTORC1/ß-catenin signaling.

OBJECTIVE: Osteoporosis (OP) is a common cause of morbidity and mortality in older individuals. The importance of Wnt3a in osteogenic activity and bone tissue homeostasis is well known. Here, we explored the possible molecular mechanism by which Wnt3a mediates the LRP6/mTORC1/ß-catenin axis to regulate osteoblast differentiation in OP. METHODS: OP-related key genes were identified through a bioinformatics analysis. A ROS17/2.8 cell differentiation system for rat osteogenic progenitors and a rat model of senile OP were constructed for in vitro and in vivo mechanism verification. RESULTS: Bioinformatics analysis revealed that LRP6 was poorly expressed in OP and may play a key role in the occurrence of OP by affecting osteoblast differentiation. LRP6 knockdown inhibited osteoblast differentiation in an in vitro model. In addition, Wnt3a promoted osteoblast differentiation by inducing LRP6 phosphorylation. Moreover, LRP6 promoted mTORC1 expression, which indirectly promoted ß-catenin expression, thus promoting osteoblast differentiation. Finally, an in vivo assay revealed that LRP6 inhibition improved OP. CONCLUSION: Our study provides evidence that Wnt3a induces phosphorylation of LRP6 to activate the mTORC1/ß-catenin axis, thus promoting osteoblast differentiation and ultimately improving OP in aged rats.

Examining the level of inflammatory cytokines TNF-α and IL-8 produced by osteoblasts differentiated from dental pulp stem cells.

BACKGROUND: The use of dental pulp stem cells (DPSCs) in clinical applications instead of bone marrow stem cells is a very promising method capable of significantly changing the future of medical treatment. If further studies prove that DPSCs and the cells differentiated from them do not stimulate the immune system, these cells can be used more reliably in treatment of autoimmune diseases. METHODS: In this research, we examined the isolated DPSCs and differentiated osteoblasts from them in medium without inflammatory stimulants in terms of TLR3 and TLR4 gene expression and inflammatory cytokines, including TNF-α and IL-8 using qRT-PCR, and measured the concentration of inflammatory cytokines IL-8 and TNF-α produced by these two types of cells through ELISA. RESULTS: The obtained results showed that the expression level of inflammatory cytokines IL-8 and TNF-α in differentiated osteoblasts is significantly different as compared with DPSCs. However, no significant difference was observed in TLR-4 expression between two groups. An increase in TNF-α expression level was found to directly correlate with an increase in the expression of IL-8. The concentration of cytokine TNF-α in osteoblasts was significantly higher than that of IL-8 in DPSCs. CONCLUSION: In comparison to DPSCs, osteoblast cells first lead to inflammatory responses. These responses reduce overtime. However, DPSCs retain their immunomodulatory properties and do not show inflammatory responses.

Cyclophilin D, regulator of the mitochondrial permeability transition, impacts bone development and fracture repair.

Mitochondrial Permeability Transition Pore (MPTP) and its key positive regulator, Cyclophilin D (CypD), control activity of cell oxidative metabolism important for differentiation of stem cells of various lineages including osteogenic lineage. Our previous work (Sautchuk et al., 2022) showed that CypD gene, Ppif, is transcriptionally repressed during osteogenic differentiation by regulatory Smad transcription factors in BMP canonical pathway, a major driver of osteoblast (OB) differentiation. Such a repression favors closure of the MPTP, priming OBs to higher usage of mitochondrial oxidative metabolism. The physiological role of CypD/MPTP regulation was demonstrated by its inverse correlation with BMP signaling in aging and bone fracture healing in addition to the negative effect of CypD gain-of-function (GOF) on bone maintenance. Here we show evidence that CypD GOF also negatively affects bone development and growth as well as fracture healing in adult mice. Developing craniofacial and long bones presented with delayed ossification and decreased growth rate, respectively, whereas in fracture, bony callus volume was diminished. Given that Genome Wide Association Studies showed that PPIF locus is associated with both body height and bone mineral density, our new data provide functional evidence for the role of PPIF gene product, CypD, and thus MPTP in bone growth and repair.

Regulation of Skeletal Development and Maintenance by Runx2 and Sp7.

Runx2 (runt related transcription factor 2) and Sp7 (Sp7 transcription factor 7) are crucial transcription factors for bone development. The cotranscription factor Cbfb (core binding factor beta), which enhances the DNA-binding capacity of Runx2 and stabilizes the Runx2 protein, is necessary for bone development. Runx2 is essential for chondrocyte maturation, and Sp7 is partly involved. Runx2 induces the commitment of multipotent mesenchymal cells to osteoblast lineage cells and enhances the proliferation of osteoprogenitors. Reciprocal regulation between Runx2 and the Hedgehog, fibroblast growth factor (Fgf), Wnt, and parathyroid hormone-like hormone (Pthlh) signaling pathways and Dlx5 (distal-less homeobox 5) plays an important role in these processes. The induction of Fgfr2 (Fgf receptor 2) and Fgfr3 expression by Runx2 is important for the proliferation of osteoblast lineage cells. Runx2 induces Sp7 expression, and Runx2+ osteoprogenitors become Runx2+Sp7+ preosteoblasts. Sp7 induces the differentiation of preosteoblasts into osteoblasts without enhancing their proliferation. In osteoblasts, Runx2 is required for bone formation by inducing the expression of major bone matrix protein genes, including Col1a1 (collagen type I alpha 1), Col1a2, Spp1 (secreted phosphoprotein 1), Ibsp (integrin binding sialoprotein), and Bglap (bone gamma carboxyglutamate protein)/Bglap2. Bglap/Bglap2 (osteocalcin) regulates the alignment of apatite crystals parallel to collagen fibrils but does not function as a hormone that regulates glucose metabolism, testosterone synthesis, and muscle mass. Sp7 is also involved in Co1a1 expression and regulates osteoblast/osteocyte process formation, which is necessary for the survival of osteocytes and the prevention of cortical porosity. SP7 mutations cause osteogenesis imperfecta in rare cases. Runx2 is an important pathogenic factor, while Runx1, Runx3, and Cbfb are protective factors in osteoarthritis development.

Wnt family members regulating osteogenesis and their origins.

Wnt signaling plays an important role in the regulation of bone metabolism. Wnt activates the ß-catenin-mediated canonical pathway and ß-catenin-independent non-canonical pathway. When Wnt ligands bind to the co-receptors low density lipoprotein receptor-related protein (Lrp)5 or Lrp6, and a seven-transmembrane receptor frizzled, the canonical pathway is activated. On the other hand, when Wnt ligands bind to the receptor complex consisting of the co-receptor receptor tyrosine kinase-like orphan receptor (Ror)1 and Ror2 or Ryk and frizzled, the non-canonical pathway is activated. An analysis of loss-of-function and gain-of-function mutations in molecules involved in Wnt signaling (ligands, receptors, and inhibitors) has revealed the mechanisms by which Wnt signaling regulates bone metabolism. In this review, based on transcriptome analyses of Wnt expression in bone tissues including single cell RNA sequence analysis and previous literatures, we herein introduce and discussed the latest findings on the mechanisms by which Wnt ligand mutations impair bone metabolism, especially bone formation.

sEV-mediated Lipid Droplets Transferred from Bone Marrow Adipocytes promote ferroptosis and impair Osteoblast Function.

Osteoporosis is linked to increased bone marrow adipocyte (BMAd) proliferation, which displaces bone-forming cells and alters the local environment. The impact of BMAd lipid droplets on bone health and osteoblast function remains unclear. This study investigates the interplay between BMAd-derived lipid droplets and osteoblast functionality, focusing on ferroptosis pathways. Osteoblast cultures were treated with conditioned media from adipocytes to simulate in vivo conditions. High-throughput mRNA sequencing and Western blot analysis were used to profile changes in gene expression and protein levels related to ferroptosis, oxidative phosphorylation, and osteogenic markers. Cellular assays assessed the direct impact of lipid droplets on osteoblast activity. Results showed that osteoblasts exposed to adipocyte-conditioned media had increased intracellular lipid droplet accumulation, upregulation of ferroptosis-related genes and proteins, and downregulation of oxidative phosphorylation and osteoblast differentiation markers. Treatment with ferroptosis inhibitors reversed the detrimental effects on osteoblasts, indicating the functional relevance of this pathway in osteoporosis. BMAd-derived lipid droplets contribute to osteoblast dysfunction through ferroptosis induction. Inhibiting ferroptosis could preserve osteoblast function and combat osteoporosis-related bone issues, suggesting that modulating lipid metabolism and redox balance in bone cells may be promising for future treatments.

Hdac3 deficiency limits periosteal reaction associated with Western diet feeding in female mice.

Diet-induced obesity is associated with enhanced systemic inflammation that limits bone regeneration. HDAC inhibitors are currently being explored as anti-inflammatory agents. Prior reports show that myeloid progenitor-directed Hdac3 ablation enhances intramembranous bone healing in female mice. In this study, we determined if Hdac3 ablation increased intramembranous bone regeneration in mice fed a high-fat/high-sugar (HFD) diet. Micro-CT analyses demonstrated that HFD-feeding enhanced the formation of periosteal reaction tissue of control littermates, reflective of suboptimal bone healing. We confirmed enhanced bone volume within the defect of Hdac3-ablated females and showed that Hdac3 ablation reduced the amount of periosteal reaction tissue following HFD feeding. Osteoblasts cultured in a conditioned medium derived from Hdac3-ablated cells exhibited a four-fold increase in mineralization and enhanced osteogenic gene expression. We found that Hdac3 ablation elevated the secretion of several chemokines, including CCL2. We then confirmed that Hdac3 deficiency increased the expression of Ccl2. Lastly, we show that the proportion of CCL2-positve cells within bone defects was significantly higher in Hdac3-deficient mice and was further enhanced by HFD. Overall, our studies demonstrate that Hdac3 deletion enhances intramembranous bone healing in a setting of diet-induced obesity, possibly through increased production of CCL2 by macrophages within the defect.

Effect of Huoxue Jiegu compound capsule on osteoblast differentiation and fracture healing by regulating the PI3K/Akt/mTOR signaling pathway in rabbits.

Objective: To examine and talk about the mechanism of the Huoxue Jiegu compound capsule's effects on osteoblasts and the PI3K/Akt/mTOR signal pathway in rabbits suffering from tibial fractures. Method: In vitro, CCK8 was used to assess the survival rates. Alizarinred staining was used to evaluate mineralized nodules. ALP staining was used to observe the osteoblasts. qRT-PCR was used to determine the mRNA expression of the bone formation-related factors BMP-2, bFGF, and TGF-ß. In vivo, three groups of nine male rabbits each were randomly assigned to three groups: the Model group, the Huoxue Jiegu compound capsule group (HXJGC group), and the inhibitor group (HXJGC+3-MA), four weeks following the intervention. HE staining was employed to examine the rabbits' bone histology. immunohistochemistry was employed to examine the relative expression of the proteins VEGF and LC3-II. Western Blot was utilized to examine the relative expression of the proteins Beclin-1, LC3-II/Ⅰ, p62, p-PI3K, p-AKT, and p-mTOR. Results: Compared to the control group, the medium- and high-dose groups exhibited considerably higher survival rates (P < 0.05), as well as enhanced cell proliferation and differentiation (P < 0.05) and more pronounced mineralized nodules. (P < 0.05), but the low-dose groups showed no appreciable variation. In the low, medium, and high-dose groups, there was a substantial reduction in the expression of bFGF mRNA, whereas the levels of BMP-2 and TGF-ß mRNA were considerably higher than in the control group (P < 0.05). In vivo, after four weeks of treatment, the model control group and inhibito group had a large amount of fibrous hyperplasia accompanied by bleeding and a small amount of inflammatory cell infiltration. But in the HXJGC group, new cartilage appeared, and the surface of the cartilage was smooth and flat. Beclin-1 and LC3-II/I expression in the HXJGC+3 MA group was significantly lower than in the HXJGC and Model groups (P < 0.05). The HXJGC group showed lower p62 expression than the HXJGC+3 MA and model groups (P < 0.05). The HXJGC group exhibited significantly reduced levels of p-PI3K, p-AKT, and p-mTOR expression in comparison to HXJGC+3 MA groups (P < 0.05). Conclusion: Rabbits with tibial fractures can be treated with HXJGC, which can control the expression of the PI3K/Akt/mTOR signal pathway. It can promote the differentiation and maturation of osteoblasts at the fracture end of rabbits, accelerate the recovery of fractures, and achieve the purpose of treating the disease.

Natural Compounds for Bone Remodeling: Targeting osteoblasts and relevant signaling pathways.

In the process of bone metabolism and bone remodeling, bone marrow mesenchymal stem cells (BM-MSCs) differentiate into osteoblasts (OBs) under certain conditions to enable the formation of new bone, and normal bone reconstruction and pathological bone alteration are closely related to the differentiation and proliferation functions of OBs. Osteogenic differentiation of BM-MSCs involves multiple signaling pathways, which function individually but interconnect intricately to form a complex signaling regulatory network. Natural compounds have fewer adverse effects than chemically synthesized drugs, optimize bone health, and are more suitable for long-term use. In this paper, we focus on OBs, summarize the current research progress of signaling pathways related to OBs differentiation, and review the molecular mechanisms by which chemically synthesized drugs with potential anti-osteoporosis properties regulate OBs-mediated bone formation.