Mechanical Unloading Promotes Osteoclastic Differentiation and Bone Resorption by Modulating the MSC Secretome to Favor Inflammation.

Aging, space flight, and prolonged bed rest have all been linked to bone loss, and no effective treatments are clinically available at present. Here, with the rodent hindlimb unloading (HU) model, we report that the bone marrow (BM) microenvironment was significantly altered, with an increased number of myeloid cells and elevated inflammatory cytokines. In such inflammatory BM, the osteoclast-mediated bone resorption was greatly enhanced, leading to a shifted bone remodeling balance that ultimately ends up with disuse-induced osteoporosis. Using Piezo1 conditional knockout (KO) mice (Piezo1fl/fl;LepRCre), we proved that lack of mechanical stimuli on LepR+ mesenchymal stem cells (MSCs) is the main reason for the pathological BM inflammation. Mechanically, the secretome of MSCs was regulated by mechanical stimuli. Inadequate mechanical load leads to increased production of inflammatory cytokines, such as interleukin (IL)-1α, IL-6, macrophage colony-stimulating factor 1 (M-CSF-1), and so on, which promotes monocyte proliferation and osteoclastic differentiation. Interestingly, transplantation of 10% cyclic mechanical stretch (CMS)-treated MSCs into HU animals significantly alleviated the BM microenvironment and rebalanced bone remodeling. In summary, our research revealed a new mechanism underlying mechanical unloading-induced bone loss and suggested a novel stem cell-based therapy to potentially prevent disuse-induced osteoporosis.

Alveolar Ridge Preservation Using the One-Piece Autologous Tuberosity Graft: A Clinical, Radiological, and Histological Pilot Study.

This prospective study investigated clinically and radiologically the effectiveness of the use of a combined hard and soft tissue graft retrieved from the maxillary tuberosity and designed for alveolar ridge preservation following tooth extraction. Seven patients scheduled for a single mono-rooted tooth extraction were included in the study. After atraumatic extraction, sockets were filled with a "one-piece" dual tissue graft harvested from the tuberosity using an adjusted trephine. CBCTs were performed before the extraction and 4 months after ridge preservation, to analyze the vertical and horizontal alterations of the ridge, using ITK-Snap software. Clinical measurements of both soft and hard tissues were also assessed during the extraction and implant placement. All sites healed uneventfully. After 4 months, the 3D super-imposition of both CBCTs showed a mean bone volume resorption of 65 ± 76.7 mm3 (10.2 ± 10%). The mean horizontal reduction at 2, 4, and 6 mm from the top of the crest was respectively 1.5 ± 1.3 mm, 0.47 ± 1.4 mm and 0.57 ± 0.7 mm, while the mean vertical loss was 0.026 mm ± 2 mm. The mean soft tissue horizontal gain was 1.73 ± 1.12 mm. The "one-piece" autologous tuberosity graft was proven to be a safe and effective alveolar ridge preservation technique and may represent a feasible, user-friendly, time saving, low-cost solution for minimizing dimensional loss following tooth extraction.

Exploring the therapeutic potential of isoorientin in the treatment of osteoporosis: a study using network pharmacology and experimental validation.

BACKGROUND: Isoorientin (ISO) is a glycosylated flavonoid with antitumor, anti-inflammatory, and antioxidant properties. However, its effects on bone metabolism remain largely unknown. METHODS: In this study, we aimed to investigate the effects of ISO on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation in vitro and bone loss in post-ovariectomy (OVX) rats, as well as to elucidate the underlying mechanism. First, network pharmacology analysis indicated that MAPK1 and AKT1 may be potential therapeutic targets of ISO and that ISO has potential regulatory effects on the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathways, as well as oxidative stress. ISO was added to RAW264.7 cells stimulated by RANKL, and its effects on osteoclast differentiation were evaluated using tartrate-resistant acid phosphatase (TRAP) staining, TRAP activity measurement, and F-actin ring analysis. Reactive oxygen species (ROS) production in osteoclasts was detected using a ROS assay kit. The effects of ISO on RANKL-triggered molecular cascade response were further investigated by Western blotting, quantitative real-time polymerase chain reaction, and immunofluorescence staining. In addition, the therapeutic effects of ISO were evaluated in vivo. RESULTS: ISO inhibited osteoclastogenesis in a time- and concentration-dependent manner. Mechanistically, ISO downregulated the expression of the main transcription factor for osteoclast differentiation by inhibiting MAPK and PI3K/AKT1 signaling pathways. Moreover, ISO exhibited protective effects in OVX-induced bone loss rats. This was consistent with the results derived from network pharmacology. CONCLUSION: Our findings suggest a potential therapeutic utility of ISO in the management of osteoclast-associated bone diseases, including osteoporosis.

Inhibitory effects of norcantharidin on titanium particle-induced osteolysis, osteoclast activation and bone resorption via MAPK pathways.

Wear particles generated from the surface of implanted prostheses can lead to peri-implant osteolysis and subsequent aseptic loosening. In the inflammatory environment, extensive formation and activation of osteoclasts are considered the underlying cause of peri-implant osteolysis. Current medications targeting osteoclasts for the treatment of particle-induced bone resorption are not ideal due to significant side effects. Therefore, there is an urgent need to develop more effective drugs with fewer side effects. Norcantharidin (NCTD), a derivative of cantharidin extracted from blister beetles, is currently primarily used for the treatment of solid tumors in clinical settings. However, the potential role of NCTD in treating aseptic loosening of the prosthesis has not been reported. In this study, the in vitro results demonstrated that NCTD could effectively inhibit the formation of osteoclasts and bone resorption induced by the RANKL. Consistently, NCTD strongly inhibited RANKL-induced mRNA and protein levels of c-Fos and NFATc1, concomitant with reduced expression of osteoclast specific genes including TRAP, CTR and CTSK. The in vivo data showed that NCTD exerted significant protective actions against titanium particle-induced inflammation and subsequent osteolysis. The molecular mechanism investigation revealed that NCTD could suppress the activations of RANKL-induced MAPK (p38, ERK). Overall, these findings support the potential use of NCTD for the treatment of aseptic loosening following total joint arthroplasty.

Bone Resorption in Apical Periodontitis Enhanced by Cigarette Smoke Inhalation: Histometric, Immunohistochemical, and Microtomographic Analysis in Rats.

INTRODUCTION: This study evaluated the effects of cigarette smoke inhalation (CSI) on apical periodontitis (AP) induced in rats by histometric, immunohistochemical, and microtomographic analysis. METHODS: A total of 32 male Wistar rats were divided into 4 experimental groups (n = 8): control, CSI, AP, and CSI + AP. Rats in the CSI and CSI + AP groups inhaled cigarette smoke by remaining inside a smoking chamber for 8 minutes 3 times a day for 50 days. After 20 days of smoke inhalation, rats in the AP and CSI + AP groups had the pulp of their first right lower molar exposed to induce AP. Blood was collected on day 50 to evaluate nicotine and serum cotinine levels. The animals' mandibles were removed for histologic processing to evaluate bone resorption by histometric, immunohistochemical (receptor activator of nuclear factor kappa B ligand/osteoprotegerin), and microtomographic analysis. The Student t test was applied. RESULTS: Histometric analysis showed a larger area of bone resorption (P < .05) and microtomographic analysis found greater resorption volume (P < .001) for the CSI + AP group compared with the AP group. The CSI + AP group presented a high RANKL immunostaining pattern compared with the AP group (P < .001). CONCLUSIONS: CSI increased bone resorption caused by AP.

Osteoclast differentiation in rheumatoid arthritis.

Osteoclasts, derived from the monocyte/macrophage line of bone marrow hematopoietic stem cell progenitors, are the sole bone-resorbing cells of the body. Conventional osteoclast differentiation requires macrophage colony-stimulating factor and receptor activator of nuclear factor kappa-B ligand (RANKL) signaling. Rheumatoid arthritis (RA) is the most prevalent systemic autoimmune disease and inflammatory arthritis characterized by bone destruction. Increased levels of proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), in the serum and joints, cause excessive bone destruction. We have recently reported that stimulation of human peripheral blood monocytes with TNF-α and IL-6 induces the differentiation of osteoclasts with bone resorption activity. This review presents the functional differences between representative osteoclasts, conventional RANKL-induced osteoclasts, and recently identified proinflammatory cytokine (TNF-α and IL-6)-induced osteoclasts in RA patients. We believe novel pathological osteoclasts associated with RA will be identified, and new therapeutic strategies will be developed to target these osteoclasts and prevent the progression of bone destruction.

Intervention with extracellular matrix metalloproteinase inducer in osteoclasts attenuates periodontitis-induced bone resorption.

Extracellular matrix metalloproteinase inducer (EMMPRIN) plays critical roles in the regulation of inflammation and bone metabolism. The roles of EMMPRIN signaling in osteoclasts are worthy of deep study. The present study aimed to investigate bone resorption in periodontitis through the intervention of EMMPRIN signaling. The distribution of EMMPRIN in human periodontitis was observed. RANKL-induced osteoclast differentiation of mouse bone marrow-derived macrophages (BMMs) were treated with EMMPRIN inhibitor in vitro. Rats with ligation-induced periodontitis were treated with EMMPRIN inhibitor and harvested for microcomputed tomography scanning, histologic observation, immunohistochemistry, and double immunofluorescence analysis. Positive expressions of EMMPRIN could be found in the CD68+-infiltrating cells. Downregulated EMMPRIN restrained osteoclast differentiation of BMMs in vitro, which also inhibited MMP-9 expression (*P < 0.05). In vivo, EMMPRIN inhibitor restrained ligation-induced bone resorption by decreasing tartrate-resistant acid phosphatase-positive osteoclasts. Both EMMPRIN-positive and MMP-9-positive osteoclasts were less common in the EMMPRIN inhibitor groups than in the control groups. Intervention of EMMPRIN signaling in osteoclasts could probably provide a potential therapeutic target for attenuating ligation-induced bone resorption.

Sesamin inhibits RANKL-induced osteoclastogenesis and attenuates LPS-induced osteolysis via suppression of ERK and NF-κB signalling pathways.

Infection by bacterial products in the implant and endotoxin introduced by wear particles activate immune cells, enhance pro-inflammatory cytokines production, and ultimately promote osteoclast recruitment and activity. These factors are known to play an important role in osteolysis as well as potential targets for the treatment of osteolysis. Sesamin has been shown to have a variety of biological functions, such as inhibiting inflammation, anti-tumour and involvement in the regulation of fatty acid and cholesterol metabolism. However, the therapeutic effect of sesamin on osteolysis and its mechanism remain unclear. Present studies shown that in the condition of in vitro, sesamin could inhibit osteoclastogenesis and bone resorption, as well as suppressing the expression of osteoclast-specific genes. Further studies on the mechanism suggest that the effect of sesamin on human osteoclasts was mediated by blocking the ERK and NF-κB signalling pathways. Besides, sesamin was found to be effective in treating LPS-induced osteolysis by decreasing the production of pro-inflammatory cytokines and inhibiting osteoclastogenesis in vivo. Sesamin was non-toxic to heart, liver, kidney, lung and spleen. Therefore, sesamin is a promising phytochemical agent for the therapy of osteolysis-related diseases caused by inflammation and excessive osteoclast activation.

Vascular Pericyte-Derived Exosomes Inhibit Bone Resorption via Traf3.

Purpose: Blood vessels distribute cells, oxygen, and nutrients throughout the body to support tissue growth and balance. Pericytes and endothelial cells form the inner wall of blood vessels, crucial for organ development and tissue homeostasis by producing paracrine signaling molecules. In the skeletal system, pericyte-derived vascular factors along with angiogenic factors released by bone cells regulate angiogenesis and bone formation. Although the involvement of angiogenic factors and skeletal blood vessels in bone homeostasis is relatively clear, the role of pericytes and the underlying mechanisms remain unknown. Here, our objective was to elucidate the significance of pericytes in regulating osteoclast differentiation. Methods: We used tissue staining to detect the coverage of pericytes and osteoclasts in femoral tissues of osteoporotic mice and mice of different ages, analyzing their correlation. We developed mice with conditionally deleted pericytes, observing changes in bone mass and osteoclast activity using micro-computer tomography and tissue staining to detect the regulatory effect of pericytes on osteoclasts. Pericytes-derived exosomes (PC-EVs) were collected and co-cultured with monocytes that induce osteoclast differentiation to detect the effect of the former on the exosomes. Finally, the specific mechanism of PC-EVs regulating osteoclast differentiation was verified using RNA sequencing and Western blotting. Results: Our study indicates a significant correlation between pericytes and age-related bone resorption. Conditional deletion of pericytes activated bone resorption and led to osteopenia in vivo. We discovered that PC-EVs inhibited the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, which is mediated by tumor necrosis factor receptor-associated factor 3 (Traf3), negatively regulating osteoclast development and bone resorption. Silencing Traf3 in PC-EVs canceled their inhibitory effect on osteoclast differentiation. Conclusion: Our study provides a novel perspective into the regulatory role of pericytes on bone resorption and may provide potential strategies for developing novel anti-bone resorption therapies.

Role and Regulation of Transcription Factors in Osteoclastogenesis.

Bones serve mechanical and defensive functions, as well as regulating the balance of calcium ions and housing bone marrow.. The qualities of bones do not remain constant. Instead, they fluctuate throughout life, with functions increasing in some situations while deteriorating in others. The synchronization of osteoblast-mediated bone formation and osteoclast-mediated bone resorption is critical for maintaining bone mass and microstructure integrity in a steady state. This equilibrium, however, can be disrupted by a variety of bone pathologies. Excessive osteoclast differentiation can result in osteoporosis, Paget's disease, osteolytic bone metastases, and rheumatoid arthritis, all of which can adversely affect people's health. Osteoclast differentiation is regulated by transcription factors NFATc1, MITF, C/EBPα, PU.1, NF-κB, and c-Fos. The transcriptional activity of osteoclasts is largely influenced by developmental and environmental signals with the involvement of co-factors, RNAs, epigenetics, systemic factors, and the microenvironment. In this paper, we review these themes in regard to transcriptional regulation in osteoclastogenesis.

Myrislignan targets extracellular signal-regulated kinase (ERK) and modulates mitochondrial function to dampen osteoclastogenesis and ovariectomy-induced osteoporosis.

BACKGROUND: Activated osteoclasts cause excessive bone resorption, and disrupt bone homeostasis, leading to osteoporosis. The extracellular signal-regulated kinase (ERK) signaling is the classical pathway related to osteoclast differentiation, and mitochondrial reactive oxygen species are closely associated with the differentiation of osteoclasts. Myrislignan (MRL), a natural product derived from nutmeg, has multiple pharmacological activities; however, its therapeutic effect on osteoporosis is unclear. Here, we investigated whether MRL could inhibit osteoclastogenesis and bone mass loss in an ovariectomy mouse model by suppressing mitochondrial function and ERK signaling. METHODS: Tartrate-resistant and phosphatase (TRAP) and bone resorption assays were performed to observe the effect of MRL on osteoclastogenesis of bone marrow macrophages. MitoSOX RED and tetramethyl rhodamine methyl ester (TMRM) staining was performed to evaluate the inhibitory effect of MRL on mitochondria. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay was performed to detect whether MRL suppressed the expression of osteoclast-specific genes. The impact of MRL on the protein involved in the mitogen-activated protein kinase (MAPK) and nuclear factor-κB pathways was evaluated using western blotting. In addition, a specific ERK agonist LM22B-10, was used to revalidate the inhibitory effect of MRL on ERK. Finally, we established an ovariectomy mouse model to assess the therapeutic effect of MRL on osteoporosis in vivo. RESULTS: MRL inhibited osteoclast differentiation and the associated bone resorption, by significantly decreasing osteoclastic gene expression. Mechanistically, MRL inhibited the phosphorylation of ERK by suppressing the mitochondrial function, thereby downregulating the nuclear factor of activated T cells 1 (NFATc1) signaling. LM22B-10 treatment further verified the targeted inhibition effect of MRL on ERK. Microscopic computed tomographic and histologic analyses of the tibial tissue sections indicated that ovariectomized mice had lower bone mass and higher expression of ERK compared with normal controls. However, MRL treatment significantly reversed these effects, indicating the anti-osteoporosis effect of MRL. CONCLUSION: We report for the first time that MRL inhibits ERK signaling by suppressing mitochondrial function, thereby ameliorating ovariectomy-induced osteoporosis. Our findings can provide a basis for the development of a novel therapeutic strategy for osteoporosis.

The effect of osteocyte-derived RANKL on bone graft remodeling: An in vivo experimental study.

OBJECTIVES: Autologous bone is considered the gold standard for grafting, yet it suffers from a tendency to undergo resorption over time. While the exact mechanisms of this resorption remain elusive, osteocytes have been shown to play an important role in stimulating osteoclastic activity through their expression of receptor activator of NF-κB (RANK) ligand (RANKL). The aim of this study was to assess the function of osteocyte-derived RANKL in bone graft remodeling. MATERIALS AND METHODS: In Tnfsf11fl/fl ;Dmp1-Cre mice without osteocyte-specific RANKL as well as in Dmp1-Cre control mice, 2.6 mm calvarial bone disks were harvested and transplanted into mice with matching genetic backgrounds either subcutaneously or subperiosteally, creating 4 groups in total. Histology and micro-computed tomography of the grafts and the donor regions were performed 28 days after grafting. RESULTS: Histology revealed marked resorption of subcutaneous control Dmp1-Cre grafts and new bone formation around subperiosteal Dmp1-Cre grafts. In contrast, Tnfsf11fl/fl ;Dmp1-Cre grafts showed effectively neither signs of bone resorption nor formation. Quantitative micro-computed tomography revealed a significant difference in residual graft area between subcutaneous and subperiosteal Dmp1-Cre grafts (p < .01). This difference was not observed between subcutaneous and subperiosteal Tnfsf11fl/fl ;Dmp1-Cre grafts (p = .17). Residual graft volume (p = .08) and thickness (p = .13) did not differ significantly among the groups. Donor area regeneration was comparable between Tnfsf11fl/fl ;Dmp1-Cre and Dmp1-Cre mice and restricted to the defect margins. CONCLUSIONS: The results suggest an active function of osteocyte-derived RANKL in bone graft remodeling.

CR6-Interacting Factor-1 Promotes Osteoclastogenesis Through the NF-κB Signaling Pathway after Irradiation.

Radiation exposure arising from radiotherapy may induce rapid bone loss and an increase in the extent of bone resorption. Reactive oxygen species (ROS) caused by radiation exposure play a crucial role during the process of osteoclastogenesis. However, the pathological mechanisms underlying radiation-induced osteoclastogenesis have yet to be fully elucidated. CR6-interacting factor-1 (Crif1) as a multifunctional protein is involved in regulating multiple biological functions in cells. Here, we investigated the role of Crif1 in radiation-induced osteoclastogenesis and found that radiation exposure induced an increase in the expression level of Crif1 and enhanced osteoclastogenesis in osteoclast progenitors. Crif1 and NF-κB p65 co-localized in the cytoplasm after radiation exposure. Crif1 knockdown did not affect the phosphorylation and total protein levels of extracellular signal-regulated kinases (ERK), c-Jun amino (N)-terminal kinases (JNK), p38, and IκB-α before and after irradiation. However, Crif1 knockdown did lead to the reduced phosphorylation and nuclear translocation of NF-κB p65 after irradiation and resulted in a reduced level of osteoclastogenesis in RAW264.7 cells after irradiation. In vivo studies involving Lyz2Cre;Crif1fl/fl mice possessing the myeloid-specific deletion of Crif1 demonstrated the alleviation of bone loss after irradiation when compared with Crif1fl/fl mice. Our findings demonstrate that Crif1 mediated the phosphorylation and nuclear translocation of NF-κB p65 and promoted osteoclastogenesis via the NF-κB signaling pathway after radiation exposure. Thus, our analysis revealed a specific role for Crif1 in the mediation of radiation-induced bone loss and may provide new insight into potential therapeutic strategies for radiation-induced bone loss.

[Long-term effectiveness of uncemented allograft-prosthesis composite for reconstruction of bone defects after proximal femur tumor resection].

Objective: To investigate the long-term effectiveness of uncemented allograft-prosthesis composite (APC) for reconstruction of bone defects after proximal femur tumor resection. Methods: Between June 2007 and March 2014, 21 patients who underwent uncemented APC reconstruction of proximal femur after tumor resection were retrospectively evaluated. There were 9 males and 12 females with an average age of 33.2 years (range, 19-54 years). There were 9 cases of giant cell tumor of bone, 5 cases of osteosarcoma, 4 cases of osteoblastic osteosarcoma, 2 cases of chondrosarcoma, and 1 case of undifferentiated pleomorphic sarcoma. Thirteen cases of benign bone tumors were all classified as stage 3 by Enneking staging; and 8 cases of malignant bone tumors were classified as grade ⅡB in 7 cases and grade ⅡA in 1 case according to the American Joint Committee on Cancer (AJCC) staging system. Among them, 7 patients underwent reoperation after recurrence, and the rest were primary operations; 8 patients presented with pathological fractures. The preoperative Harris hip score (HHS) and American Musculoskeletal Tumor Society (MSTS) score was 40 (30, 49) and 9.1±3.5, respectively. The length of osteotomy was 80-154 mm, with an average of 110 mm. At 1 year after operation and last follow-up, HHS and MSTS scores were utilized to evaluate the function of hip joint; the gluteus medius strength score was used to evaluation of the hip abduction function. Image examinations were taken at 1, 3, 6, 9, and 12 months after operation and every year thereafter to assess the union of allograft-host bone interfaces. Intra- and post-operative complications were also recorded. Results: All patients were followed up 84-163 months (mean, 123.5 months). At 1 year after operation and last follow-up, the HHS and MSTS scores significantly improved when compared with the preoperative scores ( P<0.05). However, there was no significant difference in the HHS score, MSTS score, and gluteus medius strength score between the two time points after operation ( P>0.05). Image examination showed that all allograft-host bone interfaces achieved union after 5-10 months (mean, 7.6 months). At last follow-up, all patients had bone resorption, including 11 severe cases, 4 moderate cases, and 6 mild cases; the bone resorption sites included Gruen 1, 2, and 7 regions. Complications included 10 fractures and 1 prosthetic fracture. Local recurrence occurred in 3 patients and pulmonary metastasis in 3 patients. Conclusion: Uncemented APC is a reliable method for the reconstruction of bone defects after proximal femur tumor resection. It has the good long-term effectiveness and possesses obvious advantages in the union at the bone-bone surface.

HIV patients' bone loss before and after antiretroviral treatment and its possible mechanisms.

HIV infection has been reported to cause bone loss and a higher risk of fracture. Under normal conditions, bone metabolism is regulated by mesenchymal cells, osteoclasts differentiated from mononuclear macrophages, osteoblasts, and their expression of regulatory factors, such as receptor activator of nuclear factor-kappa B ligand (RANKL), M-SCF, and transforming growth factor-beta. The balance between bone resorption and osteogenesis depends on the balance between osteoclasts and osteoblasts. In addition, some immune cells, such as B-cells, T-cells, and other non-immune cells expressing RANKL, can contribute to osteoporosis under inflammatory conditions. HIV proteins consist of three types: regulatory proteins, accessory proteins, and structural proteins, which contribute to HIV-mediated bone loss partly by upregulating NF-κB expression, tumor necrosis factor alpha content, and release of inflammatory cytokines. Even worse, although antiretroviral therapy has reduced HIV infection mortality and successfully transformed acquired immunodeficiency syndrome into a chronic disease, its impact on bone loss should not be overlooked, especially when the drug contains tenofovir. This review analyzes some reports focusing on the overall osteolytic situation due to imbalances in osteogenesis and bone resorption due to HIV infection and antiviral therapy. The intrinsic mechanism of bone loss provides a reference for researchers to analyze the risk factors for HIV patients complicated with bone loss and helps clinicians to provide ideas for the intervention and prevention of bone loss during clinical treatment and chronic disease management of HIV patients.

Brevilin A inhibits RANKL-induced osteoclast differentiation and bone resorption.

Brevilin A (BA) is the primary component of Centipeda minima, which is widely used in Chinese traditional medicine. The anti-inflammatory and anti-tumor properties of BA have been established; however, its function in bone metabolism is not well understood. This study revealed that concentrations of BA below 1.0 µM did not inhibit the proliferation of bone marrow macrophages but did impede the differentiation and bone resorption activity of osteoclasts. Furthermore, BA suppressed the expression of osteoclast-specific genes Mmp9, Acp5, Dc-stamp, Ctsk, and Atp6v0d2. In addition, mTOR, ERK, and NFATc1 activation in bone marrow macrophages were suppressed by BA. As a whole, BA blocks the mTOR and ERK signaling pathways, which is responsible for the development and activity of osteoclasts, and the resorption of bone.

The Multifarious Functions of Leukotrienes in Bone Metabolism.

Leukotrienes (LTs) are derived from arachidonic acid metabolism by the 5-lipoxygenase (5-LO) enzyme. The production of LTs is stimulated in the pathogenesis of rheumatoid arthritis (RA), osteoarthritis, and periodontitis, with a relevant contribution to bone resorption. However, its role in bone turnover, particularly the suppression of bone formation by modulating the function of osteoclasts and osteoblasts, remains unclear. We investigated the effects of LTs on bone metabolism and their impact on osteogenic differentiation and osteoclastogenesis using a 5-LO knockout (KO) mouse model. Results from micro-computed tomography (µCT) analysis of femur from 8-week-old 5-LO-deficient mice showed increased cortical bone and medullary region in females and males and decreased trabecular bone in females. In the vertebra, we observed increased marrow area in both females and males 5-LO KO and decreased trabecular bone only in females 5-LO KO. Immunohistochemistry (IHC) analysis showed higher levels of osteogenic markers tissue-nonspecific alkaline phosphatase (TNAP) and osteopontin (OPN) and lower expression of osteoclastogenic marker tartrate-resistant acid phosphatase (TRAP) in the femurs of 5-LO KO mice versus wild-type (WT). Alkaline phosphatase activity and mineralization assay results showed that the 5-LO absence enhances osteoblasts differentiation and mineralization but decreases the proliferation. Alkaline phosphatase (ALP), Bglap, and Sp7 gene expression were higher in 5-LO KO osteoblasts compared to WT cells. Eicosanoids production was higher in 5-LO KO osteoblasts except for thromboxane 2, which was lower in 5-LO-deficient mice. Proteomic analysis identified the downregulation of proteins related to adenosine triphosphate (ATP) metabolism in 5-LO KO osteoblasts, and the upregulation of transcription factors such as the adaptor-related protein complex 1 (AP-1 complex) in long bones from 5-LO KO mice leading to an increased bone formation pattern in 5-LO-deficient mice. We observed enormous differences in the morphology and function of osteoclasts with reduced bone resorption markers and impaired osteoclasts in 5-LO KO compared to WT osteoclasts. Altogether, these results demonstrate that the absence of 5-LO is related to the greater osteogenic profile. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Influence of age and gender on alveolar bone healing post tooth extraction in 129 Sv mice: a microtomographic, histological, and biochemical characterization.

OBJECTIVES: To analyze the effect of biological sex and aging on craniofacial bone features in 129 Sv mice and their influence on dental socket healing post tooth extraction. MATERIALS AND METHODS: A total of 52 129 Sv mice were used, of which 28 were young (3-4 months) and 24 were aged (17-18 months), equally distributed according to biological sex. After an upper right incisor extraction, mice specimens were collected at 7, 14, and 21-days post-surgery for microtomographic (microCT) and comprehensive histological analysis. Mandible, skull bones, and maxillae at 21 days were analyzed by microCT, while blood plasma samples were collected for the detection of key bone turnover markers (P1NP and CTX-1) by enzyme-linked immunosorbent (ELISA) assay. RESULTS: Aged females depicted significantly decreased mineralized bone content in alveolar sockets in comparison to young females and aged males at day 7, and aged males at day 14. Mandible RCA and Ma.AR of aged females were also significantly decreased in comparison with young females. Histological evaluation revealed that all alveolar sockets healed at 21 days with inflammation resolution and deposition of new bone. Immunohistochemistry for TRAP revealed increased area density for osteoclasts in alveolar sockets of aged females when compared to young females at 21 days. While a significant increase in CTX-1 levels was detected in blood plasma of aged females when compared to young females, P1NP levels did not significantly change between young and older females. No significant changes were observed for males. CONCLUSIONS: Age and gender can significantly affect craniofacial bones of 129 Sv mice, especially maxilla and mandible in females. Considering the altered bone resorption parameters and delayed alveolar bone healing in older females, careful deliberation is necessary during development of pre-clinical models for craniofacial research. CLINICAL RELEVANCE: Aging can be a contributing factor to slower bone healing in craniofacial bones. However, there are no sufficient experimental studies that have addressed this phenomenon along with biological sex taken into consideration.

Osteoimmunology research in rheumatoid arthritis: From single-cell omics approach.

ABSTRACT: Cellular immune responses as well as generalized and periarticular bone loss are the key pathogenic features of rheumatoid arthritis (RA). Under the pathological conditions of RA, dysregulated inflammation and immune processes tightly interact with skeletal system, resulting in pathological bone damage via inhibition of bone formation or induction of bone resorption. Single-cell omics technologies are revolutionary tools in the field of modern biological research.They enable the display of the state and function of cells in various environments from a single-cell resolution, thus making it conducive to identify the dysregulated molecular mechanisms of bone destruction in RA as well as the discovery of potential therapeutic targets and biomarkers. Here, we summarize the latest findings of single-cell omics technologies in osteoimmunology research in RA. These results suggest that single-cell omics have made significant contributions to transcriptomics and dynamics of specific cells involved in bone remodeling, providing a new direction for our understanding of cellular heterogeneity in the study of osteoimmunology in RA.

[Research progress of bone graft resorption after Latarjet procedure for treatment of recurrent anterior shoulder dislocation].

Objective: To review the research progress of bone graft resorption after Latarjet procedure for the treatment of recurrent anterior shoulder dislocation, and provide a guide for further research on bone graft resorption. Methods: The relevant literature in recent years was extensively reviewed. The pathogenesis, classification, risk factors, clinical function impact, and management of bone graft resorption after Latarjet procedure for the treatment of recurrent anterior shoulder dislocation were summarized. Results: Bone graft resorption is the common complication after Latarjet procedure for the treatment of recurrent anterior shoulder dislocation. Stress shielding and poor blood supply may contribute to the occurrence of bone graft resorption. The absence of significant preoperative glenoid bone loss, open procedure, earlier graft healing may to be the risk factors for bone graft resorption. Various assessment methods and classification systems are used to evaluate the region and severity of bone graft resorption. Partial resorption may be considered as a natural glenoid remodeling process after the surgery, but severe and complete resorption is proved to be one of the reasons for failed procedures and there is no effective measure to prevent it, except for accepting revision surgery. Conclusion: The pathogenesis, risk factors, clinical function impact of bone graft resorption after Latarjet procedure for the treatment of recurrent anterior shoulder dislocation has not been fully elucidated and there is a lack of effective management strategies, so further clinical and basic researches are needed.