Aims. Tissue inhibitors of metalloproteinases (TIMPs) are the endogenous inhibitors of the zinc-dependent matrix metalloproteinases (MMP) and A disintegrin and metalloproteinases (ADAM) involved in extracellular matrix modulation. The present study aims to develop the TIMPs as biologics for osteoclast-related disorders. Methods. We examine the inhibitory effect of a high affinity, glycosyl-phosphatidylinositol-anchored TIMP variant named ‘T1. PrαTACE. ’ on receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced osteoclast differentiation. Results. Osteoclast progenitor cells transduced with T1. PrαTACE. failed to form tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts or exhibit bone-resorbing activity following treatment with RANKL. At the messenger RNA level, T1. PrαTACE. strongly attenuated expression of key osteoclast marker genes that included TRAP, cathepsin K, osteoclast stimulatory transmembrane protein (OC-STAMP), dendritic cell-specific transmembrane protein (DC-STAMP), osteoclast-associated receptor (OSCAR), and ATPase H. +. -transporting V0 subunit d2 (ATP6V0D2) by blocking autoamplification of nuclear factor of activated T cells 1 (NFATc1), the osteoclastogenic transcription factor. T1. PrαTACE. selectively extended p44/42 mitogen-activated protein kinase activation, an action that may have interrupted terminal differentiation of osteoclasts. Inhibition studies with broad-spectrum hydroxamate inhibitors confirmed that the anti-resorptive activity of T1. PrαTACE. was not reliant on its metalloproteinase-inhibitory activity. Conclusion. T1. PrαTACE. disrupts the RANKL-NFATc1 signalling pathway, which leads to osteoclast dysfunction. As a novel candidate in the prevention of osteoclastogenesis, the TIMP could potentially be developed for the treatment of osteoclast-related disorders such as osteoporosis. Cite this article: Bone Joint Res 2022;11(11):763–776

Aims. The management of periprosthetic joint infection (PJI) remains a major challenge in orthopaedic surgery. In this study, we aimed to characterize the local bone microstructure and metabolism in a clinical cohort of patients with chronic PJI. Methods. Periprosthetic femoral trabecular bone specimens were obtained from patients suffering from chronic PJI of the hip and knee (n = 20). Microbiological analysis was performed on preoperative joint aspirates and tissue specimens obtained during revision surgery. Microstructural and cellular bone parameters were analyzed in bone specimens by histomorphometry on undecalcified sections complemented by tartrate-resistant acid phosphatase immunohistochemistry. Data were compared with control specimens obtained during primary arthroplasty (n = 20) and aseptic revision (n = 20). Results. PJI specimens exhibited a higher bone volume, thickened trabeculae, and increased osteoid parameters compared to both control groups, suggesting an accelerated bone turnover with sclerotic microstructure. On the cellular level, osteoblast and osteoclast parameters were markedly increased in the PJI cohort. Furthermore, a positive association between serum (CRP) but not synovial (white blood cell (WBC) count) inflammatory markers and osteoclast indices could be detected. Comparison between different pathogens revealed increased osteoclastic bone resorption parameters without a concomitant increase in osteoblasts in bone specimens from patients with Staphylococcus aureus infection, compared to those with detection of Staphylococcus epidermidis and Cutibacterium spp. Conclusion. This study provides insights into the local bone metabolism in chronic PJI, demonstrating osteosclerosis with high bone turnover. The fact that Staphylococcus aureus was associated with distinctly increased osteoclast indices strongly suggests early surgical treatment to prevent periprosthetic bone alterations. Cite this article: Bone Joint Res 2023;12(10):644–653

Aims. The association of auraptene (AUR), a 7-geranyloxycoumarin, on osteoporosis and its potential pathway was predicted by network pharmacology and confirmed in experimental osteoporotic mice. Methods. The network of AUR was constructed and a potential pathway predicted by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and Gene Ontology (GO) terms enrichment. Female ovariectomized (OVX) Institute of Cancer Research mice were intraperitoneally injected with 0.01, 0.1, and 1 mM AUR for four weeks. The bone mineral density (BMD) level was measured by dual-energy X-ray absorptiometry. The bone microstructure was determined by histomorphological changes in the femora. In addition, biochemical analysis of the serum and assessment of the messenger RNA (mRNA) levels of osteoclastic markers were performed. Results. In total, 65.93% of the genes of the AUR network matched with osteoporosis-related genes. Osteoclast differentiation was predicted to be a potential pathway of AUR in osteoporosis. Based on the network pharmacology, the BMD and bone mineral content levels were significantly (p < 0.05) increased in the whole body, femur, tibia, and lumbar spine by AUR. AUR normalized the bone microstructure and the serum alkaline phosphatase (ALP), bone-specific alkaline phosphatase (bALP), osteocalcin, and calcium in comparison with the OVX group. In addition, AUR treatment reduced TRAP-positive osteoclasts and receptor activator of nuclear factor kappa-B ligand (RANKL). +. nuclear factor of activated T cells 1 (NFATc1). +. expression in the femoral body. Moreover, the expressions of initiators for osteoclastic resorption and bone matrix degradation were significantly (p < 0.05) regulated by AUR in the lumbar spine of the osteoporotic mice. Conclusion. AUR ameliorated bone loss by downregulating the RANKL/NFATc1 pathway, resulting in improvement of osteoporosis. In conclusion, AUR might be an ameliorative cure that alleviates bone loss in osteoporosis via inhibition of osteoclastic activity. Cite this article: Bone Joint Res 2022;11(5):304–316

Aims. The role of N,N-dimethylformamide (DMF) in diabetes-induced osteoporosis (DM-OS) progression remains unclear. Here, we aimed to explore the effect of DMF on DM-OS development. Methods. Diabetic models of mice, RAW 264.7 cells, and bone marrow macrophages (BMMs) were established by streptozotocin stimulation, high glucose treatment, and receptor activator of nuclear factor-κB ligand (RANKL) treatment, respectively. The effects of DMF on DM-OS development in these models were examined by micro-CT analysis, haematoxylin and eosin (H&E) staining, osteoclast differentiation of RAW 264.7 cells and BMMs, H&E and tartrate-resistant acid phosphatase (TRAP) staining, enzyme-linked immunosorbent assay (ELISA) of TRAP5b and c-terminal telopeptides of type 1 (CTX1) analyses, reactive oxygen species (ROS) analysis, quantitative reverse transcription polymerase chain reaction (qRT-PCR), Cell Counting Kit-8 (CCK-8) assay, and Western blot. Results. The established diabetic mice were more sensitive to ovariectomy (OVX)-induced osteoporosis, and DMF treatment inhibited the sensitivity. OVX-treated diabetic mice exhibited higher TRAP5b and c-terminal telopeptides of type 1 (CTX1) levels, and DMF treatment inhibited the enhancement. DMF reduced RAW 264.7 cell viability. Glucose treatment enhanced the levels of TRAP5b, cathepsin K, Atp6v0d2, and H. +. -ATPase, ROS, while DMF reversed this phenotype. The glucose-increased protein levels were inhibited by DMF in cells treated with RANKL. The expression levels of antioxidant enzymes Gclc, Gclm, Ho-1, and Nqo1 were upregulated by DMF. DMF attenuated high glucose-caused osteoclast differentiation by targeting mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signalling in BMMs. Conclusion. DMF inhibits high glucose-induced osteoporosis by targeting MAPK and NF-κB signalling. Cite this article: Bone Joint Res 2022;11(4):200–209

Several bisphosphonates are now available for the treatment of osteoporosis. Porous hydroxyapatite/collagen (HA/Col) composite is an osteoconductive bone substitute which is resorbed by osteoclasts. The effects of the bisphosphonate alendronate on the formation of bone in porous HA/Col and its resorption by osteoclasts were evaluated using a rabbit model. Porous HA/Col cylinders measuring 6 mm in diameter and 8 mm in length, with a pore size of 100 μm to 500 μm and 95% porosity, were inserted into a defect produced in the lateral femoral condyles of 72 rabbits. The rabbits were divided into four groups based on the protocol of alendronate administration: the control group did not receive any alendronate, the pre group had alendronate treatment for three weeks prior to the implantation of the HA/Col, the post group had alendronate treatment following implantation until euthanasia, and the pre+post group had continuous alendronate treatment from three weeks prior to surgery until euthanasia. All rabbits were injected intravenously with either saline or alendronate (7.5 μg/kg) once a week. Each group had 18 rabbits, six in each group being killed at three, six and 12 weeks post-operatively. Alendronate administration suppressed the resorption of the implants. Additionally, the mineral densities of newly formed bone in the alendronate-treated groups were lower than those in the control group at 12 weeks post-operatively. Interestingly, the number of osteoclasts attached to the implant correlated with the extent of bone formation at three weeks. In conclusion, the systemic administration of alendronate in our rabbit model at a dose-for-weight equivalent to the clinical dose used in the treatment of osteoporosis in Japan affected the mineral density and remodelling of bone tissue in implanted porous HA/Col composites

Mononuclear osteoclast precursors are present in the wear-particle-associated macrophage infiltrate found in the membrane surrounding loose implants. These cells are capable of differentiating into osteoclastic bone-resorbing cells when co-cultured with the rat osteoblast-like cell line, UMR 106, in the presence of 1,25(OH). 2. vitamin D. 3. In order to develop an in vitro model of osteoclast differentiation which more closely parallels the cellular microenvironment at the bone-implant interface in situ, we determined whether osteoblast-like human bone-derived cells were capable of supporting the differentiation of osteoclasts from arthroplasty-derived cells and analysed the humoral conditions required for this to occur. Long-term co-culture of arthroplasty-derived cells and human trabecular-bone-derived cells (HBDCs) resulted in the formation of numerous tartrate-resistant-acid-phosphatase (TRAP) and vitronectin-receptor (VNR)-positive multinucleated cells capable of extensive resorption of lacunar bone. The addition of 1,25(OH). 2. vitamin D. 3. was not required for the formation of osteoclasts and bone resorption. During the formation there was release of substantial levels of M-CSF and PGE. 2. Exogenous PGE. 2. (10. −8. to 10. −6. M) was found to stimulate strongly the resorption of osteoclastic bone. Our study has shown that HBDCs are capable of supporting the formation of osteoclasts from mononuclear phagocyte precursors present in the periprosthetic tissues surrounding a loose implant. The release of M-CSF and PGE. 2. by activated cells at the bone-implant interface may be important for the formation of osteoclasts at sites of pathological bone resorption associated with aseptic loosening

Osteoarthritis (OA) is mainly caused by ageing, strain, trauma, and congenital joint abnormalities, resulting in articular cartilage degeneration. During the pathogenesis of OA, the changes in subchondral bone (SB) are not only secondary manifestations of OA, but also an active part of the disease, and are closely associated with the severity of OA. In different stages of OA, there were microstructural changes in SB. Osteocytes, osteoblasts, and osteoclasts in SB are important in the pathogenesis of OA. The signal transduction mechanism in SB is necessary to maintain the balance of a stable phenotype, extracellular matrix (ECM) synthesis, and bone remodelling between articular cartilage and SB. An imbalance in signal transduction can lead to reduced cartilage quality and SB thickening, which leads to the progression of OA. By understanding changes in SB in OA, researchers are exploring drugs that can regulate these changes, which will help to provide new ideas for the treatment of OA. Cite this article: Bone Joint Res 2023;12(9):536–545

Aims. Osteoporosis is characterized by decreased trabecular bone volume, and microarchitectural deterioration in the medullary cavity. Interleukin-19 (IL-19), a member of the IL-10 family, is an anti-inflammatory cytokine produced primarily by macrophages. The aim of our study was to investigate the effect of IL-19 on osteoporosis. Methods. Blood and femoral bone marrow suspension IL-19 levels were first measured in the lipopolysaccharide (LPS)-induced bone loss model. Small interfering RNA (siRNA) was applied to knock down IL-19 for further validation. Thereafter, osteoclast production was stimulated with IL-19 in combination with mouse macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL). The effect of IL-19 was subsequently evaluated using tartrate-resistant acid phosphatase (TRAP) staining and quantitative real-time polymerase chain reaction (RT-qPCR). The effect of IL-19 on osteoprotegerin (OPG) was then assessed using in vitro recombinant IL-19 treatment of primary osteoblasts and MLO-Y4 osteoblast cell line. Finally, transient transfection experiments and chromatin immunoprecipitation (ChIP) experiments were used to examine the exact mechanism of action. Results. In the LPS-induced bone loss mouse model, the levels of IL-19 in peripheral blood serum and femoral bone marrow suspension were significantly increased. The in vivo results indicated that global IL-19 deletion had no significant effect on RANKL content in the serum and bone marrow, but could increase the content of OPG in serum and femoral bone marrow, suggesting that IL-19 inhibits OPG expression in bone marrow mesenchymal stem cells (BMSCs) and thus increases bone resorption. Conclusion. IL-19 promotes bone resorption by suppressing OPG expression in BMSCs in a LPS-induced bone loss mouse model, which highlights the potential benefits and side effects of IL-19 for future clinical applications. Cite this article: Bone Joint Res 2023;12(11):691–701

Aims. Currently, the effect of drug treatment for osteoporosis is relatively poor, and the side effects are numerous and serious. Melatonin is a potential drug to improve bone mass in postmenopausal women. Unfortunately, the mechanism by which melatonin improves bone metabolism remains unclear. The aim of this study was to further investigate the potential mechanism of melatonin in the treatment of osteoporosis. Methods. The effects of melatonin on mitochondrial apoptosis protein, bmal1 gene, and related pathway proteins of RAW264.7 (mouse mononuclear macrophage leukaemia cells) were analyzed by western blot. Cell Counting Kit-8 was used to evaluate the effect of melatonin on cell viability. Flow cytometry was used to evaluate the effect of melatonin on the apoptosis of RAW264.7 cells and mitochondrial membrane potential. A reactive oxygen species (ROS) detection kit was used to evaluate the level of ROS in osteoclast precursors. We used bmal1-small interfering RNAs (siRNAs) to downregulate the Bmal1 gene. We established a postmenopausal mouse model and verified the effect of melatonin on the bone mass of postmenopausal osteoporosis in mice via micro-CT. Bmal1 lentiviral activation particles were used to establish an in vitro model of overexpression of the bmal1 gene. Results. Melatonin promoted apoptosis of RAW264.7 cells and increased the expression of BMAL1 to inhibit the activation of ROS and phosphorylation of mitogen-activated protein kinase (MAPK)-p38. Silencing the bmal1 gene weakened the above effects of melatonin. After that, we used dehydrocorydaline (DHC) to enhance the activation of MAPK-p38, and the effects of melatonin on reducing ROS levels and promoting apoptosis of RAW264.7 cells were also blocked. Then, we constructed a mouse model of postmenopausal osteoporosis and administered melatonin. The results showed that melatonin improves bone loss in ovariectomized mice. Finally, we established a model of overexpression of the bmal1 gene, and these results suggest that the bmal1 gene can regulate ROS activity and change the level of the MAPK-p38 signalling pathway. Conclusion. Our study confirmed that melatonin promotes the apoptosis of RAW264.7 cells through BMAL1/ROS/MAPK-p38, and revealed the therapeutic effect and mechanism of melatonin in postmenopausal osteoporosis. This finding enriches BMAL1 as a potential target for the treatment of osteoporosis and the pathogenesis of postmenopausal osteoporosis. Cite this article: Bone Joint Res 2023;12(11):677–690

Aims. LY3023414 is a novel oral phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitor designed for advanced cancers, for which a phase II clinical study was completed in March 2020; however, little is known about its effect on bone modelling/remodelling. In this study, we aimed to explore the function of LY3023414 in bone modelling/remodelling. Methods. The function of LY3023414 was explored in the context of osteogenesis (bone formation by osteoblasts) and osteoclastogenesis (osteoclast formation and bone resorption). Murine preosteoblast MC3T3-E1 cell line and murine bone marrow-derived macrophage cells (BMMs) were subjected to different treatments. An MTS cell proliferation assay was used to examine the cytotoxicity. Thereafter, different induction conditions were applied, such as MCSF and RANKL for osteoclastogenesis and osteogenic media for osteogenesis. Specific staining, a bone resorption assay, and quantitative real-time polymerase chain reaction (qRT-PCR) were subsequently used to evaluate the effect of LY3023414. Moreover, small interfering RNA (siRNA) was applied to knockdown Akt1 or Akt2 for further validation. Lastly, western blot was used to examine the exact mechanism of action. Results. LY3023414 attenuated PI3K/protein kinase B (Akt)/GSK3-dependent activation of β-catenin and nuclear factor-activated T cell 1 (NFATc1) during osteogenesis and osteoclastogenesis, respectively. LY3023414 mainly inhibited osteoclast formation instead of mature osteoclast function. Moreover, it suppressed osteogenesis both in the early stage of differentiation and late stage of calcification. Similarly, gene knockdown of Akt isoforms by siRNA downregulated osteogenic and osteoclastogenic processes, indicating that Akt1 and Akt2 acted synergistically. Conclusion. LY3023414 can suppress osteogenesis and osteoclastogenesis through inhibition of the PI3K/Akt/GSK3 signalling pathway, which highlights the potential benefits and side effects of LY3023414 for future clinical applications. Cite this article: Bone Joint Res 2021;10(4):237–249

Objectives. The role of mechanical stress and transforming growth factor beta 1 (TGF-β1) is important in the initiation and progression of osteoarthritis (OA). However, the underlying molecular mechanisms are not clearly known. Methods. In this study, TGF-β1 from osteoclasts and knee joints were analyzed using a co-cultured cell model and an OA rat model, respectively. Five patients with a femoral neck fracture (four female and one male, mean 73.4 years (68 to 79)) were recruited between January 2015 and December 2015. Results showed that TGF-β1 was significantly upregulated in osteoclasts by cyclic loading in a time- and dose-dependent mode. The osteoclasts were subjected to cyclic loading before being co-cultured with chondrocytes for 24 hours. Results. A significant decrease in the survival rate of co-cultured chondrocytes was found. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) assay demonstrated that mechanical stress-induced apoptosis occurred significantly in co-cultured chondrocytes but administration of the TGF-β1 receptor inhibitor, SB-505124, can significantly reverse these effects. Abdominal administration of SB-505124 can attenuate markedly articular cartilage degradation in OA rats. Conclusion. Mechanical stress-induced overexpression of TGF-β1 from osteoclasts is responsible for chondrocyte apoptosis and cartilage degeneration in OA. Administration of a TGF-β1 inhibitor can inhibit articular cartilage degradation. Cite this article: R-K. Zhang, G-W. Li, C. Zeng, C-X. Lin, L-S. Huang, G-X. Huang, C. Zhao, S-Y. Feng, H. Fang. Mechanical stress contributes to osteoarthritis development through the activation of transforming growth factor beta 1 (TGF-β1). Bone Joint Res 2018;7:587–594. DOI: 10.1302/2046-3758.711.BJR-2018-0057.R1

Objectives. To elucidate the effects of age on the expression levels of the receptor activator of the nuclear factor-κB ligand (RANKL) and osteoclasts in the periodontal ligament during orthodontic mechanical loading and post-orthodontic retention. Materials and Methods. The study included 20 male Sprague-Dawley rats, ten in the young group (aged four to five weeks) and ten in the adult group (aged 18 to 20 weeks). In each rat, the upper-left first molar was subjected to a seven-day orthodontic force loading followed by a seven-day retention period. The upper-right first molar served as a control. The amount of orthodontic tooth movement was measured after seven-day force application and seven-day post-orthodontic retention. The expression levels of RANKL and the tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts were evaluated on day 7 (end of mechanical force loading) and day 14 (after seven days of post-orthodontic retention). Statistical analysis was performed using the t-test, and significance was set at p < 0.05. Results. There was no significant difference between the amount of tooth movement in the young group (0.96, standard deviation (. sd. ) 0.30mm) and that in the adult group (0.80mm, . sd. 0.28) (p > 0.05) after the seven-day force application. On the compression side, the expression of RANKL and TRAP-positive osteoclasts in both the young and the adult groups increased after the application of force for seven days, and then decreased at the end of the seven-day retention period. However, by the end of the period, the expression of RANKL on the compression side dropped to the control level in the young group (p > 0.05), while it was still higher than that on the control side in the adult group (p < 0.05). The expression of RANKL on the compression side did not show significant difference between the young and the adult groups after seven-day force application (p > 0.05), but it was significantly higher in the adult group than that in the young group after seven-day post-orthodontic retention (p < 0.05). Similarly, the decreasing trend of TRAP-positive osteoclasts during the retention period in the adult group was less obvious than that in the young group. Conclusions. The bone-resorptive activity in the young rats was more dynamic than that in the adult rats. The expression of RANKL and the number of osteoclasts in adult rats did not drop to the control level during the post-orthodontic retention period while RANKL expression and the number of osteoclasts in young rats had returned to the baseline. Cite this article: X. Li, M. Li, J. Lu, Y. Hu, L. Cui, D. Zhang, Y. Yang. Age-related effects on osteoclastic activities after orthodontic tooth movement. Bone Joint Res 2016;5:492–499. DOI: 10.1302/2046-3758.510.BJR-2016-0004.R2

Aims. Osteoporosis is common in total hip arthroplasty (THA) patients. It plays a substantial factor in the surgery’s outcome, and previous studies have revealed that pharmacological treatment for osteoporosis influences implant survival rate. The purpose of this study was to examine the prevalence of and treatment rates for osteoporosis prior to THA, and to explore differences in osteoporosis-related biomarkers between patients treated and untreated for osteoporosis. Methods. This single-centre retrospective study included 398 hip joints of patients who underwent THA. Using medical records, we examined preoperative bone mineral density measures of the hip and lumbar spine using dual energy X-ray absorptiometry (DXA) scans and the medications used to treat osteoporosis at the time of admission. We also assessed the following osteoporosis-related biomarkers: tartrate-resistant acid phosphatase 5b (TRACP-5b); total procollagen type 1 amino-terminal propeptide (total P1NP); intact parathyroid hormone; and homocysteine. Results. The prevalence of DXA-proven hip osteoporosis (T-score ≤ -2.5) among THA patients was 8.8% (35 of 398). The spinal osteoporosis prevalence rate was 4.5% (18 of 398), and 244 patients (61.3%; 244 of 398) had osteopenia (-2.5 < T-score ≤ -1) or osteoporosis of either the hip or spine. The rate of pharmacological osteoporosis treatment was 22.1% (88 of 398). TRACP-5b was significantly lower in the osteoporosis-treated group than in the untreated group (p < 0.001). Conclusion. Osteoporosis is common in patients undergoing THA, but the diagnosis and treatment for osteoporosis were insufficient. The lower TRACP-5b levels in the osteoporosis-treated group — that is, osteoclast suppression — may contribute to the reduction of the postoperative revision rate after THA. Cite this article: Bone Joint Res 2022;11(12):873–880

Aims. To characterize the intracellular penetration of osteoblasts and osteoclasts by methicillin-resistant Staphylococcus aureus (MRSA) and the antibiotic and detergent susceptibility of MRSA in bone. Methods. Time-lapse confocal microscopy was used to analyze the interaction of MRSA strain USA300 with primary murine osteoblasts and osteoclasts. The effects of early and delayed antibiotic treatments on intracellular and extracellular bacterial colony formation and cell death were quantified. We tested the effects of cefazolin, gentamicin, vancomycin, tetracycline, rifampicin, and ampicillin, as well as agents used in surgical preparation and irrigation. Results. MRSA infiltrated bone-resident cells within 15 to 30 minutes. Penetration was most effectively prevented with early (i.e. 30 minutes) antibiotic administration. The combined administration of rifampicin with other antibiotics potentiated their protective effects against MRSA-induced cytotoxicity and most significantly reduced extracellular bacterial bioburden. Gentamicin-containing compounds were most effective in reducing intracellular MRSA bioburden. Of the surgical preparation agents evaluated, betadine reduced in vitro MRSA growth to the greatest extent. Conclusion. The standard of care for open fractures involves debridement and antibiotics within the first six hours of injury but does not account for the window in which bacteria penetrate cells. Antibiotics must be administered as early as possible after injury or prior to incision to prevent intracellular infestation. Rifampicin can potentiate the capacity of antibiotic regimens to reduce MRSA-induced cytotoxicity. Cite this article:Bone Joint Res. 2020;9(2):49–59

Aims. Exosomes derived from bone marrow mesenchymal stem cells (BMSCs) have been reported to be a promising cellular therapeutic approach for various human diseases. The current study aimed to investigate the mechanism of BMSC-derived exosomes carrying microRNA (miR)-136-5p in fracture healing. Methods. A mouse fracture model was initially established by surgical means. Exosomes were isolated from BMSCs from mice. The endocytosis of the mouse osteoblast MC3T3-E1 cell line was analyzed. CCK-8 and disodium phenyl phosphate microplate methods were employed to detect cell proliferation and alkaline phosphatase (ALP) activity, respectively. The binding of miR-136-5p to low-density lipoprotein receptor related protein 4 (LRP4) was analyzed by dual luciferase reporter gene assay. HE staining, tartrate-resistant acid phosphatase (TRAP) staining, and immunohistochemistry were performed to evaluate the healing of the bone tissue ends, the positive number of osteoclasts, and the positive expression of β-catenin protein, respectively. Results. miR-136-5p promoted fracture healing and osteoblast proliferation and differentiation. BMSC-derived exosomes exhibited an enriched miR-136-5p level, and were internalized by MC3T3-E1 cells. LRP4 was identified as a downstream target gene of miR-136-5p. Moreover, miR-136-5p or exosomes isolated from BMSCs (BMSC-Exos) containing miR-136-5p activated the Wnt/β-catenin pathway through the inhibition of LRP4 expression. Furthermore, BMSC-derived exosomes carrying miR-136-5p promoted osteoblast proliferation and differentiation, thereby promoting fracture healing. Conclusion. BMSC-derived exosomes carrying miR-136-5p inhibited LRP4 and activated the Wnt/β-catenin pathway, thus facilitating fracture healing. Cite this article: Bone Joint Res 2021;10(12):744–758

Objectives. Osteoporosis is a metabolic disease resulting in progressive loss of bone mass as measured by bone mineral density (BMD). Physical exercise has a positive effect on increasing or maintaining BMD in postmenopausal women. The contribution of exercise to the regulation of osteogenesis in osteoblasts remains unclear. We therefore investigated the effect of exercise on osteoblasts in ovariectomized mice. Methods. We compared the activity of differentially expressed genes of osteoblasts in ovariectomized mice that undertook exercise (OVX+T) with those that did not (OVX), using microarray and bioinformatics. Results. Many inflammatory pathways were significantly downregulated in the osteoblasts after exercise. Meanwhile, IBSP and SLc13A5 gene expressions were upregulated in the OVX+T group. Furthermore, in in vitro assay, IBSP and SLc13A5 mRNAs were also upregulated during the osteogenic differentiation of MC3T3-E1 and 7F2 cells. Conclusion. These findings suggest that exercise may not only reduce the inflammatory environment in ovariectomized mice, indirectly suppressing the overactivated osteoclasts, but may also directly activate osteogenesis-related genes in osteoblasts. Exercise may thus prevent the bone loss caused by oestrogen deficiency through mediating the imbalance between the bone resorptive activity of osteoclasts and the bone formation activity of osteoblasts. Cite this article: W-B. Hsu, W-H. Hsu, J-S. Hung, W-J. Shen, R. W-W. Hsu. Transcriptome analysis of osteoblasts in an ovariectomized mouse model in response to physical exercise. Bone Joint Res 2018;7:601–608. DOI: 10.1302/2046-3758.711.BJR-2018-0075.R2

Peri-prosthetic osteolysis and subsequent aseptic loosening is the most common reason for revising total hip replacements. Wear particles originating from the prosthetic components interact with multiple cell types in the peri-prosthetic region resulting in an inflammatory process that ultimately leads to peri-prosthetic bone loss. These cells include macrophages, osteoclasts, osteoblasts and fibroblasts. The majority of research in peri-prosthetic osteolysis has concentrated on the role played by osteoclasts and macrophages. The purpose of this review is to assess the role of the osteoblast in peri-prosthetic osteolysis. In peri-prosthetic osteolysis, wear particles may affect osteoblasts and contribute to the osteolytic process by two mechanisms. First, particles and metallic ions have been shown to inhibit the osteoblast in terms of its ability to secrete mineralised bone matrix, by reducing calcium deposition, alkaline phosphatase activity and its ability to proliferate. Secondly, particles and metallic ions have been shown to stimulate osteoblasts to produce pro inflammatory mediators in vitro. In vivo, these mediators have the potential to attract pro-inflammatory cells to the peri-prosthetic area and stimulate osteoclasts to absorb bone. Further research is needed to fully define the role of the osteoblast in peri-prosthetic osteolysis and to explore its potential role as a therapeutic target in this condition. Cite this article: Bone Joint J 2013;95-B:1021–5

Carbonate-substituted hydroxyapatite (CHA) is more osteoconductive and more resorbable than hydroxyapatite (HA), but the underlying mode of its action is unclear. We hypothesised that increased resorption of the ceramic by osteoclasts might subsequently upregulate osteoblasts by a coupling mechanism, and sought to test this in a large animal model. Defects were created in both the lateral femoral condyles of 12 adult sheep. Six were implanted with CHA granules bilaterally, and six with HA. Six of the animals in each group received the bisphosphonate zoledronate (0.05 mg/kg), which inhibits the function of osteoclasts, intra-operatively. After six weeks bony ingrowth was greater in the CHA implants than in HA, but not in the animals given zoledronate. Functional osteoclasts are necessary for the enhanced osteoconduction seen in CHA compared with HA

Aims. Osteoarthritis (OA) is a disabling joint disorder and mechanical loading is an important pathogenesis. This study aims to investigate the benefits of less mechanical loading created by intermittent tail suspension for knee OA. Methods. A post-traumatic OA model was established in 20 rats (12 weeks old, male). Ten rats were treated with less mechanical loading through intermittent tail suspension, while another ten rats were treated with normal mechanical loading. Cartilage damage was determined by gross appearance, Safranin O/Fast Green staining, and immunohistochemistry examinations. Subchondral bone changes were analyzed by micro-CT and tartrate-resistant acid phosphatase (TRAP) staining, and serum inflammatory cytokines were evaluated by enzyme-linked immunosorbent assay (ELISA). Results. Our radiographs showed that joint space was significantly enlarged in rats with less mechanical loading. Moreover, cartilage destruction was attenuated in the less mechanical loading group with lower histological damage scores, and lower expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-5, matrix metalloproteinase (MMP)-3, and MMP-13. In addition, subchondral bone abnormal changes were ameliorated in OA rats with less mechanical loading, as reduced bone mineral density (BMD), bone volume/tissue volume (BV/TV), and number of osteophytes and osteoclasts in the subchondral bone were observed. Finally, the level of serum inflammatory cytokines was significantly downregulated in the less mechanical loading group compared with the normal mechanical loading group, as well as the expression of NACHT, LRR, and PYD domains-containing protein 3 (NLRP3), caspase-1, and interleukin 1β (IL-1β) in the cartilage. Conclusion. Less mechanical loading alleviates cartilage destruction, subchondral bone changes, and secondary inflammation in OA joints. This study provides fundamental insights into the benefit of non-weight loading rest for patients with OA. Cite this article: Bone Joint Res 2020;9(10):731–741