Inflammatory osteolysis: a conspiracy against bone

Oral cell lysates reduce osteoclastogenesis in murine bone marrow cultures

Mechanical and thermal cell damage can occur due to invasive procedures related to drilling, the insertion of dental implants, and periodontal treatments. Necrotic cells release the content of their cytoplasm and membrane fragments, thereby signaling the need for repair, which includes bone resorption by osteoclasts and inflammation. Here we screened lysates from human gingival fibroblasts, HSC2 and TR146 oral squamous carcinoma cell lines, as well as murine IDG-SW3 osteocytic and RAW264.7 macrophage cell lines for their potential to modulate in vitro osteoclastogenesis in murine bone marrow cultures. We also tested the impact of necrotic lysates on modulating the expression of inflammatory cues in murine ST2 bone marrow stromal cells. We report here that independent of human or murine origin, all cell lysates significantly reduced in vitro osteoclastogenesis in bone marrow cultures, as indicated by the expression of the osteoclast marker genes cathepsin K and tartrate-resistant acid phosphatase and the respective histochemical staining in multinucleated cells. We also found that lysates from HSC2 and TR146 cells significantly pushed the expression of CCL2, CCL5, CXCL1, IL1, and IL6 in ST2 cells. These findings suggest that oral cell lysates reduce in vitro osteoclastogenesis, but only damaged oral squamous carcinoma cells can force murine stromal cells to produce an inflammatory environment.

Progress in Designing Therapeutic Antimicrobial Hydrogels Targeting Implant-associated Infections: Paving the Way for a Sustainable Platform Applied to Biomedical Devices

Implantable biomedical devices have found widespread use in restoring lost functions or structures within the human body, but they face a significant challenge from microbial-related infections, which often lead to implant failure. In this context, antimicrobial hydrogels emerge as a promising strategy for treating implant-associated infections owing to their tunable physicochemical properties. However, the literature lacks a comprehensive analysis of antimicrobial hydrogels, encompassing their development, mechanisms, and effect on implant-associated infections, mainly in light of existing in vitro, in vivo, and clinical evidence. Thus, this review addresses the strategies employed by existing studies to tailor hydrogel properties to meet the specific needs of each application. Furthermore, this comprehensive review critically appraises the development of antimicrobial hydrogels, with a particular focus on solving infections related to metallic orthopedic or dental implants. Then, preclinical and clinical studies centering on providing quantitative microbiological results associated with the application of antimicrobial hydrogels are systematically summarized. Overall, antimicrobial hydrogels benefit from the tunable properties of polymers and hold promise as an effective strategy for the local treatment of implant-associated infections. However, future clinical investigations, grounded on robust evidence from in vitro and preclinical studies, are required to explore and validate new antimicrobial hydrogels for clinical use.

Targeting APJ drives BNIP3-PINK1-PARKIN induced mitophagy and improves systemic inflammatory bone loss

INTRODUCTION

Inflammatory diseases, such as diabetes mellitus, rheumatoid arthritis, and inflammatory bowel disease, lead to systemic immune microenvironment disturbances, contributing to bone loss, yet the mechanisms by which specific receptors regulate this process in inflammatory bone loss remain poorly understood. As a G-protein-coupled receptor, the Apelin receptor plays a crucial role in the regulation of inflammation and immune microenvironment. However, the precise mechanisms governing its role in inflammatory bone loss remain incompletely understood.

OBJECTIVE

This study aims to investigate how APJ regulates macrophage polarization to mitigate inflammatory bone loss.

METHODS

Lipopolysaccharide induced systemic inflammatory bone loss model in mice was used to explore the relationship between bone loss and osteoclast activation, macrophage polarization and APJ. In vitro studies, Bone marrow derived macrophages and siRNA were used to elucidate the regulatory influence of APJ on the immune microenvironment and osteoclast differentiation, while high-throughput sequencing is leveraged to uncover the underlying mechanisms through which APJ modulates macrophage polarization.

RESULTS

Our study established a link between APJ and macrophage M1 polarization in systemic inflammatory bone loss mice. The activation of APJ effectively mitigated M1 polarization in macrophages, suppressed excessive osteoclast activation, and alleviated systemic inflammatory bone loss. In vitro high-throughput sequencing analysis revealed that APJ modulates macrophage polarization, linking to mitochondrial autophagy and the NOD-like receptor signaling pathway and the involvement of the AMPK and MAPK signaling pathways in signal transduction after APJ activation was also suggested. Subsequent experiments substantiated that APJ predominantly enhances mitophagy and diminishes the accumulation of reactive oxygen species by regulating the AMPK/BNIP3/PINK1/PARKIN axis, thereby suppressing the activation of macrophage M1 polarization and osteoclastogenesis.

CONCLUSION

This study elucidated the underlying mechanism by which APJ modulates macrophage polarization, thereby proposing a new therapeutic target for addressing inflammatory bone loss.

Transcriptomic Characterization Reveals Mitochondrial Involvement in Nrf2/Keap1-Mediated Osteoclastogenesis

Although osteoclasts play crucial roles in the skeletal system, the mechanisms that underlie oxidative stress during osteoclastogenesis remain unclear. The transcription factor Nrf2 and its suppressor, Keap1, function as central mediators of oxidative stress. To further elucidate the function of Nrf2/Keap1-mediated oxidative stress regulation in osteoclastogenesis, DNA microarray analysis was conducted in this study using wild-type (WT), Keap1 knockout (Keap1 KO), and Nrf2 knockout (Nrf2 KO) osteoclasts. Principal component analysis showed that 403 genes, including Nqo1, Il1f9, and Mmp12, were upregulated in Keap1 KO compared with WT osteoclasts, whereas 24 genes, including Snhg6, Ccdc109b, and Wfdc17, were upregulated in Nrf2 KO compared with WT osteoclasts. Moreover, 683 genes, including Car2, Calcr, and Pate4, were upregulated in Nrf2 KO cells compared to Keap1 KO cells. Functional analysis by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis showed upregulated genes in Nrf2 KO osteoclasts were mostly enriched in oxidative phosphorylation. Furthermore, GeneMANIA predicted the protein-protein interaction network of novel molecules such as Rufy4 from genes upregulated in Nrf2 KO osteoclasts. Understanding the complex interactions between these molecules may pave the way for developing promising therapeutic strategies against bone metabolic diseases caused by increased osteoclast differentiation under oxidative stress.

Inflammatory Response of THP1 and U937 Cells: The RNAseq Approach

THP1 and U937 are monocytic cell lines that are common bioassays to reflect monocyte and macrophage activities in inflammation research. However, THP-1 is a human monocytic leukemia cell line, and U937 originates from pleural effusion of histiocytic lymphoma; thus, even though they serve as bioassay in inflammation research, their response to agonists is not identical. Consequently, there has yet to be a consensus about the panel of strongly regulated genes in THP1 and U937 cells representing the inflammatory response to LPS and IFNG. Therefore, we have performed an RNAseq of THP1 and U937 exposed to LPS and IFNG to identify the most sensitive genes and the unique properties of each individual cell line. When applying a highly stringent threshold, we could identify 43, 8 up and 94, 103 down-regulated genes in THP1 and U937 cells, respectively. In THP1 cells, among the most strongly up-regulated genes are CCL1, CXCL2, CXCL3, IL1A, IL1B, IL6, and PTGES. In U937 cells, the strongest up-regulated genes include CSF2, CSF3, CXCL2, CXCL5, CXCL6, IL1A, IL19, IL36G, IL6, ITGA1, ITGA2, and PTGS2. Even though THP1 is considerably less responsive than U937, there are genes commonly upregulated by LPS and IFNG, including the CCL1, CCL3, CCL20, CXCL2, CXCL3, CXCL8, as well as IL1A, IL1B, IL23A, IL6, and genes of prostaglandin synthesis PTGES and PTGS2. Downregulated genes are limited to NRGN and CD36. This head-to-head comparison revealed that THP1 is less responsive than U937 cells to LPS and IFNG and identified a panel of highly regulated genes that can be applied in bioassays in inflammation research. Our data further propose bulk RNAseq as a standard method in bioassay research.

One arrow two eagles: Multifunctional nano-system for macrophage reprogramming and osteoclastogenesis inhibition against inflammatory osteolysis

Inflammatory osteolysis poses a significant worldwide threat to public health. However, current monotherapies, which target either the prevention of the inflammatory response or the attenuation of osteoclast (OC) formation, have limited efficacy due to the complexity of the bone immune system being overlooked. Herein, by means of modifying salmon calcitonin (sCT), a multifunctional nano-system (AuNDs-sCT) was designed to synergistically inhibit OC differentiation and reverse the inflammatory microenvironment against inflammatory osteolysis. On the one hand, AuNDs-sCT effectively restrained OC differentiation by binding to the calcitonin receptors on the surface of OC precursors, resulting in the down-regulation of OC-specific genes and proteins. The targeted capacity of AuNDs-sCT provided a more durable and precise therapeutic effect. On the other hand, AuNDs-sCT exhibited antioxidant and anti-inflammatory effects, which regulated the polarization "switch" from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype in macrophages by the inhibition of NF-κB p65 phosphorylation, thereby effectively reversed the local inflammatory microenvironment. Additionally, AuNDs-sCT served as a promising fluorescent probe, enabling real-time visualization of the therapeutic process. This capability is expected to optimize drug administration and evaluate therapeutic effects. In summary, by inhibiting OC differentiation and reprogramming macrophages, AuNDs-sCT successfully realized drug repurposing and achieved the "one arrow two eagles" therapeutic strategy, which offers a synergistic and effective treatment option for the clinical management of inflammatory osteolysis.

Acod1-mediated inhibition of aerobic glycolysis suppresses osteoclast differentiation and attenuates bone erosion in arthritis

OBJECTIVES

Metabolic changes are crucially involved in osteoclast development and may contribute to bone degradation in rheumatoid arthritis (RA). The enzyme aconitate decarboxylase 1 (Acod1) is known to link the cellular function of monocyte-derived macrophages to their metabolic status. As osteoclasts derive from the monocyte lineage, we hypothesised a role for Acod1 and its metabolite itaconate in osteoclast differentiation and arthritis-associated bone loss.

METHODS

Itaconate levels were measured in human peripheral blood mononuclear cells (PBMCs) of patients with RA and healthy controls by mass spectrometry. Human and murine osteoclasts were treated with the itaconate derivative 4-octyl-itaconate (4-OI) in vitro. We examined the impact of Acod1-deficiency and 4-OI treatment on bone erosion in mice using K/BxN serum-induced arthritis and human TNF transgenic (hTNFtg) mice. SCENITH and extracellular flux analyses were used to evaluate the metabolic activity of osteoclasts and osteoclast progenitors. Acod1-dependent and itaconate-dependent changes in the osteoclast transcriptome were identified by RNA sequencing. CRISPR/Cas9 gene editing was used to investigate the role of hypoxia-inducible factor (Hif)-1α in Acod1-mediated regulation of osteoclast development.

RESULTS

Itaconate levels in PBMCs from patients with RA were inversely correlated with disease activity. Acod1-deficient mice exhibited increased osteoclast numbers and bone erosion in experimental arthritis while 4-OI treatment alleviated inflammatory bone loss in vivo and inhibited human and murine osteoclast differentiation in vitro. Mechanistically, Acod1 suppressed osteoclast differentiation by inhibiting succinate dehydrogenase-dependent production of reactive oxygen species and Hif1α-mediated induction of aerobic glycolysis.

CONCLUSION

Acod1 and itaconate are crucial regulators of osteoclast differentiation and bone loss in inflammatory arthritis.

Beyond the Surface: Uncovering Secondary Causes of Osteoporosis for Optimal Management

Osteoporosis (OP), a condition marked by reduced bone mineral density and increased fracture risk, can arise either as a primary disorder or secondary to other diseases and medications. While primary OP typically relates to age-related or postmenopausal changes, secondary OP results from underlying conditions or drug exposures, complicating diagnosis and management. This review explores the pathophysiology, prevalence, and treatment approaches for secondary OP arising from endocrine, renal, gastrointestinal, hematological, and autoimmune disorders, as well as medication side effects. The findings highlight that secondary OP is frequently undiagnosed, particularly in premenopausal women and men, with conditions such as chronic kidney disease, glucocorticoid use, and diabetes among the primary contributors. Management strategies must be tailored to address the underlying conditions to effectively reduce fracture risk and improve outcomes. Ultimately, this review underscores the necessity for increased clinical awareness and more targeted interventions for optimal management of secondary OP.

The CD163/TWEAK/Fn14 axis: A potential therapeutic target for alleviating inflammatory bone loss

Objective

Osteoclast (OC) over-activation is an important cause of bone loss that is strongly correlated with inflammation. Although the CD163/TWEAK/Fn14 axis has been implicated in several inflammatory pathologies, its contributions to inflammatory bone loss remain poorly understood. This study aimed to evaluate the interaction of the CD163/TWEAK/Fn14 axis with OC in inflammatory bone loss.

Methods

To assess the role of CD163 in bone homeostasis, we characterized the bone phenotypes of CD163-deficient mice and their wild-type littermates. CD163 and TWEAK levels were evaluated in the bone marrow of mice with LPS-induced bone loss and individuals with rheumatoid arthritis (RA). Bone mass changes were assessed using uCT and histology following supplementation with recombinant mouse CD163 protein (rCD163) or blockade of TWEAK/Fn14 signaling in CD163-deficient mice and mice with LPS-induced bone loss. The impact of CD163/TWEAK on OC differentiation and bone resorption capacity was analyzed in vitro.

Results

CD163 deficiency caused decreased bone mass and increased OC abundance. Lower CD163 expression and higher TWEAK expression were observed in the bone marrow of mice with LPS-induced bone loss and individuals with RA. TWEAK, mainly derived from CD68+ macrophages, was responsible for bone loss, and supplementing rCD163 or blocking TWEAK/Fn14 signaling contributed to rescue bone loss. TWEAK/Fn14 synergistically promoted RANKL-dependent OC differentiation and bone resorption capability through downstream mitogen-activated protein kinases (MAPK) signaling, while the pro-osteoclastic effect of TWEAK was suppressed by CD163.

Conclusion

Our findings suggest that the CD163/TWEAK/Fn14 axis is a potential therapeutic target for inflammatory bone loss by regulating osteoclastogenesis.

Urolithin B inhibits the differentiation of M1 macrophages and relieves the inflammation around the implants under osteoporosis via down-regulating the phosphorylation of VEGFR2

The inflammation causes the destroyed osseointegration at the implant-bone interface, significantly increasing the probability of implant loosening in osteoporotic patients. Currently, inhibiting the differentiation of M1 macrophages and the inflammatory response could be a solution to stabilize the microenvironment of implants. Interestingly, some natural products have anti-inflammatory and anti-polarization effects, which could be a promising candidate for stabilizing the implants' microenvironment in osteoporotic patients. This research aims to explore the inhibitory effect of Urolithin B(UB) on macrophage M1 polarization, which ameliorates inflammation, thus alleviating implant instability. We established an osteoporosis mouse model of implant loosening. The mouse tissues were taken out for morphological analysis, staining analysis, and bone metabolic index analysis. In in vitro experiments, RAW264.7 cells were polarized to M1 macrophages using lipopolysaccharide (LPS) and analyzed by immunofluorescence (IF) staining, Western blot (WB), and flow cytometry. The CSP100 plus chip experiments were used to explore the potential mechanisms behind the inhibiting effects of UB. Through observation of these experiments, UB can improve the osseointegration between the implants and femurs in osteoporotic mice and enhance the stability of implants. The UB can inhibit the differentiation of M1 macrophages and local inflammation via inhibiting the phosphorylation of VEGFR2, which can be further proved by the weakened inhibited effects of UB in macrophages with lentivirus-induced overexpression of VEGFR2. Overall, UB can specifically inhibit the activation of VEGFR2, alleviate local inflammation, and improve the stability of implants in osteoporotic mice.

Metabolic reprogramming in skeletal cell differentiation

The human skeleton is a multifunctional organ made up of multiple cell types working in concert to maintain bone and mineral homeostasis and to perform critical mechanical and endocrine functions. From the beginning steps of chondrogenesis that prefigures most of the skeleton, to the rapid bone accrual during skeletal growth, followed by bone remodeling of the mature skeleton, cell differentiation is integral to skeletal health. While growth factors and nuclear proteins that influence skeletal cell differentiation have been extensively studied, the role of cellular metabolism is just beginning to be uncovered. Besides energy production, metabolic pathways have been shown to exert epigenetic regulation via key metabolites to influence cell fate in both cancerous and normal tissues. In this review, we will assess the role of growth factors and transcription factors in reprogramming cellular metabolism to meet the energetic and biosynthetic needs of chondrocytes, osteoblasts, or osteoclasts. We will also summarize the emerging evidence linking metabolic changes to epigenetic modifications during skeletal cell differentiation.

A comparative study on the effects of biodegradable high-purity magnesium screw and polymer screw for fixation in epiphyseal trabecular bone

With mechanical strength close to cortical bone, biodegradable and osteopromotive properties, magnesium (Mg)-based implants are promising biomaterials for orthopedic applications. However, during the degradation of such implants, there are still concerns on the potential adverse effects such as formation of cavities, osteolytic phenomena and chronic inflammation. Therefore, to transform Mg-based implants into clinical practice, the present study evaluated the local effects of high-purity Mg screws (HP-Mg, 99.99 wt%) by comparing with clinically approved polylactic acid (PLA) screws in epiphyseal trabecular bone of rabbits. After implantation of screws at the rabbit distal femur, bone microstructural, histomorphometric and biomechanical properties were measured at various time points (weeks 4, 8 and 16) using micro-CT, histology and histomorphometry, micro-indentation and scanning electron microscope. HP-Mg screws promoted peri-implant bone ingrowth with higher bone mass (BV/TV at week 4: 0.189 ± 0.022 in PLA group versus 0.313 ± 0.053 in Mg group), higher biomechanical properties (hardness at week 4: 35.045 ± 1.000 HV in PLA group versus 51.975 ± 2.565 HV in Mg group), more mature osteocyte LCN architecture, accelerated bone remodeling process and alleviated immunoreactive score (IRS of Ram11 at week 4: 5.8 ± 0.712 in PLA group versus 3.75 ± 0.866 in Mg group) as compared to PLA screws. Furthermore, we conducted finite element analysis to validate the superiority of HP-Mg screws as orthopedic implants by demonstrating reduced stress concentration and uniform stress distribution around the bone tunnel, which led to lower risks of trabecular microfractures. In conclusion, HP-Mg screws demonstrated greater osteogenic bioactivity and limited inflammatory response compared to PLA screws in the epiphyseal trabecular bone of rabbits. Our findings have paved a promising way for the clinical application of Mg-based implants.

Bone lesions and intestinal barrier disruption caused by the isolated novel goose parvovirus infection in ducks

Short beak and dwarfism syndrome (SBDS) is attributed to Novel Goose Parvovirus (NGPV), which has inflicted significant economic losses on farming in China. Despite its significant impact, limited research has been conducted on the pathogenesis of this disease. The SD strain, a parvovirus variant isolated from ducks in Shandong province, was identified and characterized in our study. Phylogenetic analysis and sequence comparisons confirmed the classification of the SD strain as a member of NGPV. Based on this information, we established an animal model of SBDS by inoculating Cherry Valley ducks with the SD strain. Our findings indicate that infection with the SD strain leads to a reduction in body weight, beak length, width, and tibia length. Notably, significant histopathological alterations were observed in the thymus, spleen, and intestine of the infected ducks. Furthermore, the SD strain induces bone disorders and inflammatory responses. To evaluate the impact of NGPV on intestinal homeostasis, we performed 16S rDNA sequencing and gas chromatography to analyze the composition of intestinal flora and levels of short-chain fatty acids (SCFAs) in the cecal contents. Our findings revealed that SD strain infection induces dysbiosis in cecal microbial and a decrease in SCFAs production. Subsequent analysis revealed a significant correlation between bacterial genera and the clinical symptoms in NGPV SD infected ducks. Our research providing novel insights into clinical pathology of NGPV in ducks and providing a foundation for the research of NGPV treatment targeting gut microbiota.

SREBP2 restricts osteoclast differentiation and activity by regulating IRF7 and limits inflammatory bone erosion

Osteoclasts are multinucleated bone-resorbing cells, and their formation is tightly regulated to prevent excessive bone loss. However, the mechanisms by which osteoclast formation is restricted remain incompletely determined. Here, we found that sterol regulatory element binding protein 2 (SREBP2) functions as a negative regulator of osteoclast formation and inflammatory bone loss. Cholesterols and SREBP2, a key transcription factor for cholesterol biosynthesis, increased in the late phase of osteoclastogenesis. The ablation of SREBP2 in myeloid cells resulted in increased in vivo and in vitro osteoclastogenesis, leading to low bone mass. Moreover, deletion of SREBP2 accelerated inflammatory bone destruction in murine inflammatory osteolysis and arthritis models. SREBP2-mediated regulation of osteoclastogenesis is independent of its canonical function in cholesterol biosynthesis but is mediated, in part, by its downstream target, interferon regulatory factor 7 (IRF7). Taken together, our study highlights a previously undescribed role of the SREBP2-IRF7 regulatory circuit as a negative feedback loop in osteoclast differentiation and represents a novel mechanism to restrain pathological bone destruction.

Preventing periprosthetic osteolysis in aging populations through lymphatic activation and stem cell-associated secretory phenotype inhibition

With increases in life expectancy, the number of patients requiring joint replacement therapy and experiencing periprosthetic osteolysis, the most common complication leading to implant failure, is growing or underestimated. In this study, we found that osteolysis progression and osteoclast differentiation in the surface of the skull bone of adult mice were accompanied by significant expansion of lymphatic vessels within bones. Using recombinant VEGF-C protein to activate VEGFR3 and promote proliferation of lymphatic vessels in bone, we counteracted excessive differentiation of osteoclasts and osteolysis caused by titanium alloy particles or inflammatory cytokines LPS/TNF-α. However, this effect was not observed in aged mice because adipogenically differentiated mesenchymal stem cells (MSCs) inhibited the response of lymphatic endothelial cells to agonist proteins. The addition of the JAK inhibitor ruxolitinib restored the response of lymphatic vessels to external stimuli in aged mice to protect against osteolysis progression. These findings suggest that inhibiting SASP secretion by adipogenically differentiated MSCs while activating lymphatic vessels in bone offers a new method to prevent periprosthetic osteolysis during joint replacement follow-up.

Graphene oxide-decorated microporous sulfonated polyetheretherketone for guiding osteoporotic bone regeneration

Recent studies have indicated that the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is an ideal therapeutic target for osteoporosis because it affects the differentiation of osteoblasts and osteoclasts. RNA sequencing utilizing multifunctional graphene oxide (GO) nanosheets revealed a correlation between GO nanomaterials and the NLRP3 inflammasome, as well as osteogenic genes in macrophages. This study aimed to construct a bone microenvironment-responsive multifunctional two-dimensional GO coating on the surface of microporous sulfonated polyetheretherketone (SPEEK) via polydopamine modification (SPEEK@PDA-GO). In vitro analysis showed that the SPEEK@PDA-GO implants weakened the STAT3-mediated NLRP3/caspase-1/IL-1β signaling pathway in macrophages and subsequently prevented the formation of an extracellular inflammatory microenvironment, which is crucial for osteoclastogenesis. SPEEK@PDA-GO displayed significantly higher expression of M2 macrophage markers and osteogenic genes, indicating that the multifunctional GO nanosheets could facilitate bone regeneration via their immunomodulatory properties. The ability of SPEEK@PDA-GO to stimulate new bone formation and block bone loss caused by estrogen loss due to ovariectomy was also analyzed. The findings of this study offer valuable information on the possible involvement of the NLRP3 inflammasome in the interaction between the immune system and bone health in patients with osteoporosis.

A Rare Cause of Pain in the Oral Cavity: Osteomyelitis of Tori

A 63-year-old man presented with a 1-month history of worsening mouth pain, particularly under the tongue bilaterally, with left more than right. A physical examination revealed multiple dental caries and bilateral mandibular tori, with the left mandibular torus being exquisitely tender to palpation. Lab tests showed increased inflammatory markers in the absence of leukocytosis. A maxillofacial computed tomography scan revealed findings concerning for chronic osteomyelitis with osteolysis of the left mandibular torus. The patient was started on intravenous antibiotics and transferred to another institution for further management through their oral and maxillofacial surgery service. The surgical pathology after torectomy confirmed the diagnosis of acute osteomyelitis with osteonecrosis. Although rare, this case underscores the importance of familiarity with osteomyelitis in tori of the oral cavity, also highlighting the imaging and clinical correlation. Further research is necessary to understand the risk factors and optimal management strategies for similar cases.

The miR-29-3p family suppresses inflammatory osteolysis

Osteoclasts are the cells primarily responsible for inflammation-induced bone loss, as is particularly seen in rheumatoid arthritis. Increasing evidence suggests that osteoclasts formed under homeostatic versus inflammatory conditions may differ in phenotype. While microRNA-29-3p family members (miR-29a-3p, miR-29b-3p, miR-29c-3p) promote the function of RANKL-induced osteoclasts, the role of miR-29-3p during inflammatory TNF-α-induced osteoclastogenesis is unknown. We used bulk RNA-seq, histology, qRT-PCR, reporter assays, and western blot analysis to examine bone marrow monocytic cell cultures and tissue from male mice in which the function of miR-29-3p family members was decreased by expression of a miR-29-3p tough decoy (TuD) competitive inhibitor in the myeloid lineage (LysM-cre). We found that RANKL-treated monocytic cells expressing the miR-29-3p TuD developed a hypercytokinemia/proinflammatory gene expression profile in vitro, which is associated with macrophages. These data support the concept that miR-29-3p suppresses macrophage lineage commitment and may have anti-inflammatory effects. In correlation, when miR-29-3p activity was decreased, TNF-α-induced osteoclast formation was accentuated in an in vivo model of localized osteolysis and in a cell-autonomous manner in vitro. Further, miR-29-3p targets mouse TNF receptor 1 (TNFR1/Tnfrsf1a), an evolutionarily conserved regulatory mechanism, which likely contributes to the increased TNF-α signaling sensitivity observed in the miR-29-3p decoy cells. Whereas our previous studies demonstrated that the miR-29-3p family promotes RANKL-induced bone resorption, the present work shows that miR-29-3p dampens TNF-α-induced osteoclastogenesis, indicating that miR-29-3p has pleiotropic effects in bone homeostasis and inflammatory osteolysis. Our data supports the concept that the knockdown of miR-29-3p activity could prime myeloid cells to respond to an inflammatory challenge and potentially shift lineage commitment toward macrophage, making the miR-29-3p family a potential therapeutic target for modulating inflammatory response.

NAT10 promotes osteoclastogenesis in inflammatory bone loss by catalyzing Fos mRNA ac4C modification and upregulating MAPK signaling pathway

INTRODUCTION

Excessive osteoclastogenesis is a key driver of inflammatory bone loss. Suppressing osteoclastogenesis has always been considered essential for the treatment of inflammatory bone loss. N-acetyltransferase 10 (NAT10) is the sole enzyme responsible for N4-acetylcytidine (ac4C) modification of mRNA, and is involved in cell development. However, its role in osteoclastogenesis and inflammatory bone loss remained elusive.

OBJECTIVES

We aimed to clarify the regulatory mechanism of NAT10 and ac4C modification in osteoclastogenesis and inflammatory bone loss.

METHODS

NAT10 expression and ac4C modification during osteoclastogenesis were determined by quantitative real-time PCR (qPCR), western blotting, dot blot and immunofluorescent staining, and the effect of NAT10 inhibition on osteoclast differentiation in vitro was measured by the tartrate-resistant acid phosphatase staining, podosome belts staining assay and bone resorption pit assay. Then, acRIP-qPCR and NAT10RIP-qPCR, ac4C site prediction, mRNA decay assay and luciferase reporter assay were performed to further study the underlying mechanisms. At last, mice models of inflammatory bone loss were applied to verify the therapeutic effect of NAT10 inhibition in vivo.

RESULTS

NAT10 expression was upregulated during osteoclast differentiation and highly expressed in alveolar bone osteoclasts from periodontitis mice. Inhibition of NAT10 notably reduced osteoclast differentiation in vitro, as indicated by great reduction of tartrated resistant acid phosphatse positive multinuclear cells, osteoclast-specific gene expression, F-actin ring formation and bone resorption capacity. Mechanistically, NAT10 catalyzed ac4C modification of Fos (encoding AP-1 component c-Fos) mRNA and maintained its stabilization. Besides, NAT10 promoted MAPK signaling pathway and thereby activated AP-1 (c-Fos/c-Jun) transcription for osteoclastogenesis. Therapeutically, administration of Remodelin, the specific inhibitor of NAT10, remarkably impeded the ligature-induced alveolar bone loss and lipopolysaccharide-induced inflammatory calvarial osteolysis.

CONCLUSIONS

Our study demonstrated that NAT10-mediated ac4C modification is an important epigenetic regulation of osteoclast differentiation and proposed a promising therapeutic target for inflammatory bone loss.

Anti-inflammatory effect of the combined treatment of LMT-28 and kaempferol in a collagen-induced arthritis mouse model

Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation and swelling. Several studies have demonstrated that RA fibroblast-like synovial cells (RA-FLS) play an important role in RA pathogenesis. Activated RA-FLS contribute to synovial inflammation by secreting inflammatory cytokines including interleukin (IL)-1β, IL-6 and tumor necrosis factor-α. LMT-28 is derivative of oxazolidone and exerts anti-inflammatory effects on RA via IL-6 signaling pathway regulation. LMT-28 also regulates T cell differentiation in RA condition. However, the effect of LMT-28 on the migration and invasion of RA-FLS remains unknown. Kaempferol has been reported to have pharmacological effects on various diseases, such as inflammatory diseases, autoimmune diseases, and cancer. Additionally, kaempferol has been reported to inhibit RA-FLS migration and invasion, but it is not known about the therapeutic mechanism including molecular mechanism such as receptor. The present study aimed to investigate the synergistic effects of the combined treatment of LMT-28 and kaempferol on RA-FLS activation and RA pathogenesis in mouse model. LMT-28 and kaempferol co-administration inhibited RA disease severity and histological collapse in the joint tissues of CIA mice, as well as downregulated the levels of pro-inflammatory cytokines in mouse serum. Additionally, the combined treatment inhibited excessive differentiation of T helper 17 cells and osteoclasts. Furthermore, compared with single treatments, combined treatment showed enhanced inhibitory effects on the hyperactivation of IL-6-induced signaling pathway in RA-FLS. Combined treatment also inhibited RA-FLS cell proliferation, migration, and invasion and suppressed the expression of matrix metalloproteinase in RA-FLS. Furthermore, we confirmed that the combined treatment inhibited chondrocyte proliferation, migration, and invasion. In conclusion, our results suggest that the combined treatment of LMT-28 and kaempferol exerts a synergistic effect on the RA development via the regulation of IL-6-induced hyperactivation of RA-FLS. Furthermore, this study suggests that combination therapies can be an effective therapeutic option for arthritis.

PRF Lysates Modulate Chemokine Expression in Oral Squamous Carcinoma and Healthy Epithelial Cells

Platelet-rich fibrin (PRF), originally used to support soft tissue healing, is also considered a therapeutic option for treating oral lichen planus and leukoplakia. The progression from the two premalignant lesions to the aggressive malignant oral squamous cell carcinoma involves an inflammatory process linked to chemokine expression. Thus, there is a rationale for studying how PRF modulates the expression of chemokines in oral squamous carcinoma cells. To this aim, we expose the oral squamous carcinoma cell line HSC2 to IL1β and TNFα either alone or in the presence of lysates obtained from solid PRF membranes. We report here that in HSC2 cells, PRF lysates significantly reduce the forced transcription of chemokines, e.g., CXCL1, CXCL2, CXCL8, CXCL10, and CCL5. Moreover, PRF lysates attenuate the nuclear translocation of p65 in HSC2 oral epithelial cells when exposed to IL1β and TNFα. PRF lysates further reduce chemokine expression provoked by poly:IC HMW. Even though less pronounced, PRF lysates reduce IL1β- and TNFα-induced chemokine expression in TR146 cells. In primary oral epithelial cells, however, PRF lysates increase the basal expression of CXCL1, CXCL2 and CXCL8. Thus, PRF can exert a biphasic effect on chemokine expression in oral squamous cell carcinoma cell lines and primary oral epithelial cells. These findings suggest that PRF may reduce inflammation in a malignant environment while provoking an immunological response in healthy oral epithelium.

Pulmonary osteoclast-like cells in silica induced pulmonary fibrosis

The pathophysiology of silicosis is poorly understood, limiting development of therapies for those who have been exposed to the respirable particle. We explored mechanisms of silica-induced pulmonary fibrosis in human lung samples collected from patients with occupational exposure to silica and in a longitudinal mouse model of silicosis using multiple modalities including whole-lung single-cell RNA sequencing and histological, biochemical, and physiologic assessments. In addition to pulmonary inflammation and fibrosis, intratracheal silica challenge induced osteoclast-like differentiation of alveolar macrophages and recruited monocytes, driven by induction of the osteoclastogenic cytokine, receptor activator of nuclear factor κΒ ligand (RANKL) in pulmonary lymphocytes, and alveolar type II cells. Anti-RANKL monoclonal antibody treatment suppressed silica-induced osteoclast-like differentiation in the lung and attenuated pulmonary fibrosis. We conclude that silica induces differentiation of pulmonary osteoclast-like cells leading to progressive lung injury, likely due to sustained elaboration of bone-resorbing proteases and hydrochloric acid. Interrupting osteoclast-like differentiation may therefore constitute a promising avenue for moderating lung damage in silicosis.

Toll-like receptor-2 induced inflammation causes local bone formation and activates canonical Wnt signaling

It is well established that inflammatory processes in the vicinity of bone often induce osteoclast formation and bone resorption. Effects of inflammatory processes on bone formation are less studied. Therefore, we investigated the effect of locally induced inflammation on bone formation. Toll-like receptor (TLR) 2 agonists LPS from Porphyromonas gingivalis and PAM2 were injected once subcutaneously above mouse calvarial bones. After five days, both agonists induced bone formation mainly at endocranial surfaces. The injection resulted in progressively increased calvarial thickness during 21 days. Excessive new bone formation was mainly observed separated from bone resorption cavities. Anti-RANKL did not affect the increase of bone formation. Inflammation caused increased bone formation rate due to increased mineralizing surfaces as assessed by dynamic histomorphometry. In areas close to new bone formation, an abundance of proliferating cells was observed as well as cells robustly stained for Runx2 and alkaline phosphatase. PAM2 increased the mRNA expression of Lrp5, Lrp6 and Wnt7b, and decreased the expression of Sost and Dkk1. In situ hybridization demonstrated decreased Sost mRNA expression in osteocytes present in old bone. An abundance of cells expressed Wnt7b in Runx2-positive osteoblasts and ß-catenin in areas with new bone formation. These data demonstrate that inflammation, not only induces osteoclastogenesis, but also locally activates canonical WNT signaling and stimulates new bone formation independent on bone resorption.

The Function and Mechanism of Anti-Inflammatory Factor Metrnl Prevents the Progression of Inflammatory-Mediated Pathological Bone Osteolytic Diseases

Metrnl, recently identified as an adipokine, is a secreted protein notably expressed in white adipose tissue, barrier tissues, and activated macrophages. This adipokine plays a pivotal role in counteracting obesity-induced insulin resistance. It enhances adipose tissue functionality by promoting adipocyte differentiation, activating metabolic pathways, and exerting anti-inflammatory effects. Extensive research has identified Metrnl as a key player in modulating inflammatory responses and as an integral regulator of muscle regeneration. These findings position Metrnl as a promising biomarker and potential therapeutic target in treating inflammation-associated pathologies. Despite this, the specific anti-inflammatory mechanisms of Metrnl in immune-mediated osteolysis and arthritis remain elusive, warranting further investigation. In this review, we will briefly elaborate on the role of Metrnl in anti-inflammation function in inflammation-related osteolysis, arthritis, and pathological bone resorption, which could facilitate Metrnl's clinical application as a novel therapeutic strategy to prevent bone loss. While the pathogenesis of elbow stiffness remains elusive, current literature suggests that Metrnl likely exerts a pivotal role in its development.

Implants coating strategies for antibacterial treatment in fracture and defect models: A systematic review of animal studies

Objective

Fracture-related infection (FRI) remains a major concern in orthopaedic trauma. Functionalizing implants with antibacterial coatings are a promising strategy in mitigating FRI. Numerous implant coatings have been reported but the preventive and therapeutic effects vary. This systematic review aimed to provide a comprehensive overview of current implant coating strategies to prevent and treat FRI in animal fracture and bone defect models.

Methods

A literature search was performed in three databases: PubMed, Web of Science and Embase, with predetermined keywords and criteria up to 28 February 2023. Preclinical studies on implant coatings in animal fracture or defect models that assessed antibacterial and bone healing effects were included.

Results

A total of 14 studies were included in this systematic review, seven of which used fracture models and seven used defect models. Passive coatings with bacteria adhesion resistance were investigated in two studies. Active coatings with bactericidal effects were investigated in 12 studies, four of which used metal ions including Ag+ and Cu2+; five studies used antibiotics including chlorhexidine, tigecycline, vancomycin, and gentamicin sulfate; and the other three studies used natural antibacterial materials including chitosan, antimicrobial peptides, and lysostaphin. Overall, these implant coatings exhibited promising efficacy in antibacterial effects and bone formation.

Conclusion

Antibacterial coating strategies reduced bacterial infections in animal models and favored bone healing in vivo. Future studies of implant coatings should focus on optimal biocompatibility, antibacterial effects against multi-drug resistant bacteria and polymicrobial infections, and osseointegration and osteogenesis promotion especially in osteoporotic bone by constructing multi-functional coatings for FRI therapy.

The translational potential of this paper

The clinical treatment of FRI is complex and challenging. This review summarizes novel orthopaedic implant coating strategies applied to FRI in preclinical studies, and offers a perspective on the future development of orthopaedic implant coatings, which can potentially contribute to alternative strategies in clinical practice.

IKK/NF-κB and ROS signal axes are involved in Tenacissoside H mediated inhibitory effects on LPS-induced inflammatory osteolysis

Periodontal disease and arthroplasty prosthesis loosening and destabilization are both associated with osteolysis, which is predominantly caused by abnormal bone resorption triggered by pro-inflammatory cytokines. Osteoclasts (OCs) are critical players in the process. Concerns regarding the long-term efficacy and side effects of current frontline therapies, however, remain. Alternative therapies are still required. The aim of this work was to investigate the involvement of Tenacissoside H (TDH) in RANKL-mediated OC differentiation, as well as inflammatory osteolysis and associated processes. In vitro, bone marrow-derived macrophages (BMMs) cultured with RANKL and M-CSF were used to detect TDH in the differentiation and function of OCs. Real-time quantitative PCR was used to measure the expression of specific genes and inflammatory factors in OCs. Western blot was used to identify NFATc1, IKK, NF-κB, MAPK pathway, and oxidative stress-related components. Finally, an LPS-mediated calvarial osteolysis mouse model was employed to explore TDH's role in inflammatory osteolysis. The results showed that in vivo TDH inhibited the differentiation and resorption functions of OCs and down-regulated the transcription of osteoclast-specific genes, as well as Il-1β, Il-6 and Tnf-α. In addition, TDH inhibited the IKK and NF-κB signalling pathways and down-regulated the level of ROS. In vivo studies revealed that TDH improves the bone loss caused by LPS. TDH may be a new candidate or treatment for osteoclast-associated inflammatory osteolytic disease.

A dual-functional strontium-decorated titanium implants that guides the immune response for osseointegration of osteoporotic rats

Due to the dynamic imbalance between osteogenesis and osteoclasis and the abnormal inflammatory microenvironment in situ, osteoporosis hampers the early osseointegration between implants and bones. To improve osseointegration with the osteoporosis, we first coated the titanium implants (Ti) with polydopamine (PDA) coating (Ti-PDA), followed by modification with strontium (Sr) to prepare the Ti-PDA-Sr implants. An osteoporotic rat model with femoral bone defect was verified to estimate the osseointegration of the implants. The Ti-PDA-Sr implants exhibited good biocompatibility with continuous release of Sr ions for up to 21 days. Ti-PDA-Sr implants promoted the osteogenesis of BMSCs and the polarization of BMMs to M2 phenotype compared to that of Ti and Ti-PDA implants, revealing the double-regulated effects in bone induction and immune regulation. According to the Micro-CT and histopathology results, Ti-PDA-Sr implants exhibited the most stable osseointegration between bone tissues and implants. According to the immunohistochemistry results, the Ti-PDA-Sr implants differentiated the BMMs to M2 phenotype, alleviating the abnormal inflammation in osteoporosis and preventing the consistent bone destruction between the implants and bone tissues. This study provides a practical and effective strategy in preparing bi-functional implants that can promote osseointegration with osteoporosis.

Regulatory mechanisms of autophagy-related ncRNAs in bone metabolic diseases

Bone metabolic diseases have been tormented and are plaguing people worldwide due to the lack of effective and thorough medical interventions and the poor understanding of their pathogenesis. Non-coding RNAs (ncRNAs) are heterogeneous transcripts that cannot encode the proteins but can affect the expressions of other genes. Autophagy is a fundamental mechanism for keeping cell viability, recycling cellular contents through the lysosomal pathway, and maintaining the homeostasis of the intracellular environment. There is growing evidence that ncRNAs, autophagy, and crosstalk between ncRNAs and autophagy play complex roles in progression of metabolic bone disease. This review investigated the complex mechanisms by which ncRNAs, mainly micro RNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), regulate autophagic pathway to assist in treating bone metabolism disorders. It aimed at identifying the autophagy role in bone metabolism disorders and understanding the role, potential, and challenges of crosstalk between ncRNAs and autophagy for bone metabolism disorders treatment.

Immunomodulation by mesenchymal stem cells during osteogenic differentiation: Clinical implications during bone regeneration

Critical bone defects resulting in delayed and non-union are a major concern in the field of orthopedics. Over the past decade, mesenchymal stem cells (MSCs) have become a promising frontier for bone repair and regeneration owing to their high expansion rate and osteogenic differentiation potential ex vivo. MSCs have also long been associated with their ability to modulate immune response in the recipients. These can even skew the immune response towards pro-inflammatory or anti-inflammatory type by sensing their local microenvironment. MSCs adopt anti-inflammatory phenotype at bone injury site and secrete various immunomodulatory factors such as IDO, NO, TGFβ1 and PGE-2 which have redundant role in osteoblast differentiation and bone formation. As such, several studies have also sought to decipher the immunomodulatory effects of osteogenically differentiated MSCs. The present review discusses the immunomodulatory status of MSCs during their osteogenic differentiation and summarizes few mechanisms that cause immunosuppression by osteogenically differentiated MSCs and its implication during bone healing.

Quercetin suppresses ovariectomy-induced osteoporosis in rat mandibles by regulating autophagy and the NLRP3 pathway

With the aging population and the popularity of implant prostheses, an increasing number of postmenopausal osteoporosis (PMOP) patients require implant restorations; however, poor bone condition affects the long-term stability of implant prostheses. This study aimed to investigate the therapeutic effect of quercetin (QR) compared with alendronate (ALN), the primary treatment for PMOP, on mandibular osteoporosis (OP) induced by ovariectomy (OVX) in female rats. Adult female rats were treated with QR (50 mg/kg/day), ALN (6.25 mg/kg/week) by gavage for 8 weeks, chloroquine (CQ, 10 mg/kg/twice a week), and cytokine release inhibitory drug 3 (MCC950, 10 mg/kg/three times a week) by intraperitoneal injection for 8 weeks after bilateral OVX. Blood samples were collected prior to euthanasia; the mandibles were harvested and subjected to micro-computed tomography (micro-CT) and pathological analysis. QR administration controlled weight gain and significantly improved the bone microstructure in OVX rats, increasing bone mass, and bone mineral density (BMD), reducing bone trabecular spacing, and decreasing osteoclast numbers. Western blotting, real-time quantitative PCR (RT-qPCR), and serum markers confirmed that QR inhibited interleukin- 1β (IL-1β) and interleukin-18 (IL-18) on the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) protein 3 (NLRP3) pathway thereby inhibiting osteoclast differentiation, immunofluorescence and western blotting also confirmed that QR inhibited autophagy in OVX rats and suppressed the number of tartrate-resistant acid phosphatase (TRAP)-stained positive osteoclasts. The findings suggest that QR may protect the bone structure and prevent bone loss in osteoporotic rats by inhibiting the NLRP3 pathway and autophagy in osteoclasts with comparable effects to ALN, thus QR may have the potential to be a promising alternative supplement for the preventive and therapeutic treatment of PMOP.

Inflammatory Processes Affecting Bone Health and Repair

PURPOSE OF REVIEW

The purpose of this article is to review the current understanding of inflammatory processes on bone, including direct impacts of inflammatory factors on bone cells, the effect of senescence on inflamed bone, and the critical role of inflammation in bone pain and healing.

RECENT FINDINGS

Advances in osteoimmunology have provided new perspectives on inflammatory bone loss in recent years. Characterization of so-called inflammatory osteoclasts has revealed insights into physiological and pathological bone loss. The identification of inflammation-associated senescent markers in bone cells indicates that therapies that reduce senescent cell burden may reverse bone loss caused by inflammatory processes. Finally, novel studies have refined the role of inflammation in bone healing, including cross talk between nerves and bone cells. Except for the initial stages of fracture healing, inflammation has predominately negative effects on bone and increases fracture risk. Eliminating senescent cells, priming the osteo-immune axis in bone cells, and alleviating pro-inflammatory cytokine burden may ameliorate the negative effects of inflammation on bone.

Screening diagnostic markers of osteoporosis based on ferroptosis of osteoblast and osteoclast

BACKGROUND

Osteoporosis is a negative balance of bone metabolism caused by the lower bone formation of osteoblasts than the bone absorption of osteoclasts. Ferroptosis plays an important role in osteoporosis, but its effects on osteoblasts and osteoclasts are still unclear.

METHODS

First, we compared the osteogenic differentiation potential of MSCs and osteoclast differentiation potential of monocytes between osteoporosis mice and control. Then, we obtained gene expression profiles of MSCs and monocytes, and screened differentially expressed genes for enrichment analysis. Next, we cluster the patients with osteoporosis according to genes related to osteogenesis inhibition and osteoclast promotion. Finally, according to the expression of different subtypes of ferroptosis genes, diagnostic markers were screened and verified.

RESULTS

The osteogenic differentiation ability of MSCs in osteoporosis mice was decreased, while the osteoclast differentiation ability of monocytes was enhanced. The DEGs of MSCs are enriched in iron ion, oxygen binding and cytokine activity, while the DEGs of monocytes are enriched in iron ion transmembrane transport and ferroptosis. Compared with the osteogenic inhibition subtype, the osteoclast promoting subtype has a higher correlation with ferroptosis, and its functions are enriched in fatty acids, reactive oxygen species metabolism and oxidoreductase activity of metal ions. SLC40A1 may be the hub gene of ferroptosis in osteoporosis by promoting osteoclast differentiation.

CONCLUSION

Ferroptosis may inhibit bone formation and promote bone absorption through oxidative stress, thus leading to osteoporosis. The study of ferroptosis on osteoblasts and osteoclasts provides a new idea for the diagnosis and treatment of osteoporosis.

Identification of a Biallelic Missense Variant in Gasdermin D (c.823G > C, p.Asp275His) in a Patient of Atypical Gorham-Stout Disease in a Consanguineous Family

Gorham-Stout disease (GSD), also called vanishing bone disease, is a rare osteolytic disease, frequently associated with lymphangiomatous tissue proliferation. The causative genetic background has not been noted except for a case with a somatic mutation in KRAS. However, in the present study, we encountered a case of GSD from a consanguineous family member. Whole-exome sequencing (WES) analysis focusing on rare recessive variants with zero homozygotes in population databases identified a homozygous missense variant (c.823G > C, p.Asp275His) in gasdermin D (GSDMD) in the patient and heterozygous in his unaffected brother. Because this variant affects the Asp275 residue that is involved in proteolytic cleavage by caspase-11 (as well as -4 and -5) to generate an activating p30 fragment required for pyroptotic cell death and proinflammation, we confirmed the absence of this cleavage product in peripheral monocytic fractions from the patient. A recent study indicated that a shorter p20 fragment, generated by further cleavage at Asp88, has a cell-autonomous function to suppress the maturation of osteoclasts to resorb bone matrix. Thus, the present study suggests for the first time the existence of hereditary GSD cases or novel GSD-like diseases caused by GSDMD deficiency. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

A Dual-Targeted Metal-Organic Framework Based Nanoplatform for the Treatment of Rheumatoid Arthritis by Restoring the Macrophage Niche

Inflammatory infiltration and bone destruction are important pathological features of rheumatoid arthritis (RA), which originate from the disturbed niche of macrophages. Here, we identified a niche-disrupting process in RA: due to overactivation of complement, the barrier function of VSIg4⁺ lining macrophages is disrupted and mediates inflammatory infiltration within the joint, thereby activating excessive osteoclastogenesis and bone resorption. However, complement antagonists have poor biological applications due to superphysiologic dose requirements and inadequate effects on bone resorption. Therefore, we developed a dual-targeted therapeutic nanoplatform based on the MOF framework to achieve bone-targeted delivery of the complement inhibitor CRIg-CD59 and pH-responsive sustained release. The surface-mineralized zoledronic acid (ZA) of ZIF8@CRIg-CD59@HA@ZA targets the skeletal acidic microenvironment in RA, and the sustained release of CRIg-CD59 can recognize and prevent the complement membrane attack complex (MAC) from forming on the surface of healthy cells. Importantly, ZA can inhibit osteoclast-mediated bone resorption, and CRIg-CD59 can promote the repair of the VSIg4⁺ lining macrophage barrier to achieve sequential niche remodeling. This combination therapy is expected to treat RA by reversing the core pathological process, circumventing the pitfalls of traditional therapy.

Mechanistic insight of interleukin-9 induced osteoclastogenesis

Interleukin (IL)-9 is an emerging player in the pathogenesis of various chronic inflammatory diseases including bone disorders like rheumatoid arthritis (RA) and psoriatic arthritis. Recently, IL-9 was shown to enhance the osteoclast formation and their function in RA. However, the mechanisms by which IL-9 influences osteoclastogenesis are not known. Therefore, in this study we aimed to unravel the direct and indirect ways by which IL-9 can influence osteoclast formation. We used mouse bone marrow precursor cells for checking the effect of IL-9 on osteoclast differentiation and its function. Next, IL-9 induced signalling pathway were checked in the process of osteoclastogenesis. T cells play an important role in enhancing osteoclastogenesis in inflammatory conditions. We used splenic T cells to understand the impact of IL-9 on the functions of T effector (Teff) and regulatory T (Treg) cells. Furthermore, the effect of IL-9 mediated modulation of the T cell response on osteoclasts was checked using a coculture model of T cells with osteoclast precursors. We showed that IL-9 enhanced osteoclast formation and its function. We found that IL-9 activates STAT3, P38 MAPK, ERK1/2, NFκB and we hypothesize that it mediates the effect on osteoclastogenesis by accelerating mitochondrial biogenesis. Additionally, IL-9 was observed to facilitate the functions of pro-osteoclastogenic IL-17 producing T cells, but inhibits the function of anti-osteoclastogenic Treg cells. Our observations suggest that IL-9 can influence osteoclastogenesis directly by modulating the signalling cascade in the precursor cells; indirectly by enhancing IL-17 producing T cells and by reducing the functions of Treg cells.

Rapamycin Inhibits Osteoclastogenesis and Prevents LPS-Induced Alveolar Bone Loss by Oxidative Stress Suppression

Periodontitis is a progressive inflammatory skeletal disease characterized by periodontal tissue destruction, alveolar bone resorption, and tooth loss. Chronic inflammatory response and excessive osteoclastogenesis play essential roles in periodontitis progression. Unfortunately, the pathogenesis that contributes to periodontitis remains unclear. As a specific inhibitor of the mTOR (mammalian/mechanistic target of rapamycin) signaling pathway and the most common autophagy activator, rapamycin plays a vital role in regulating various cellular processes. The present study investigated the effects of rapamycin on osteoclast (OC) formation in vitro and its effects on the rat periodontitis model. The results showed that rapamycin inhibited OC formation in a dose-dependent manner by up-regulating the Nrf2/GCLC signaling pathway, thus suppressing the intracellular redox status, as measured by 2',7'-dichlorofluorescein diacetate and MitoSOX. In addition, rather than simply increasing the autophagosome formation, rapamycin increased the autophagy flux during OC formation. Importantly, the anti-oxidative effect of rapamycin was regulated by an increase in autophagy flux, which could be attenuated by blocking autophagy with bafilomycin A1. In line with the in vitro results, rapamycin treatment attenuated alveolar bone resorption in rats with lipopolysaccharide-induced periodontitis in a dose-dependent manner, as assessed by micro-computed tomography, hematoxylin-eosin staining, and tartrate-resistant acid phosphatase staining. Besides, high-dose rapamycin treatment could reduce the serum levels of proinflammatory factors and oxidative stress in periodontitis rats. In conclusion, this study expanded our understanding of rapamycin's role in OC formation and protection from inflammatory bone diseases.

Immunoglobulin G-dependent inhibition of inflammatory bone remodeling requires pattern recognition receptor Dectin-1

Immunoglobulin G (IgG) antibodies are major drivers of inflammation during infectious and autoimmune diseases. In pooled serum IgG (IVIg), however, antibodies have a potent immunomodulatory and anti-inflammatory activity, but how this is mediated is unclear. We studied IgG-dependent initiation of resolution of inflammation in cytokine- and autoantibody-driven models of rheumatoid arthritis and found IVIg sialylation inhibited joint inflammation, whereas inhibition of osteoclastogenesis was sialic acid independent. Instead, IVIg-dependent inhibition of osteoclastogenesis was abrogated in mice lacking receptors Dectin-1 or FcγRIIb. Atomistic molecular dynamics simulations and super-resolution microscopy revealed that Dectin-1 promoted FcγRIIb membrane conformations that allowed productive IgG binding and enhanced interactions with mouse and human IgG subclasses. IVIg reprogrammed monocytes via FcγRIIb-dependent signaling that required Dectin-1. Our data identify a pathogen-independent function of Dectin-1 as a co-inhibitory checkpoint for IgG-dependent inhibition of mouse and human osteoclastogenesis. These findings may have implications for therapeutic targeting of autoantibody and cytokine-driven inflammation.

HSC70 mediated autophagic degradation of oxidized PRL2 is responsible for osteoclastogenesis and inflammatory bone destruction

Inflammation leads to systemic osteoporosis or local bone destruction, however, the underlying molecular mechanisms are still poorly understood. In this study, we report that PRL2 is a negative regulator of osteoclastogenesis and bone absorption. Mice with PRL2 deficiency exhibit a decrease in bone volume and an increase in osteoclast numbers. PRL2 negatively regulates RANKL-induced reactive oxygen species production through the activation of RAC1, thus PRL2 deficient osteoclast precursors have both increased osteoclast differentiation ability and bone resorptive capacity. During inflammation, oxidized PRL2 is a selected substrate of HSC70 and conditions of oxidative stress trigger rapid degradation of PRL2 by HSC70 mediated endosomal microautophagy and chaperone-mediated autophagy. Ablation of PRL2 in mouse models of inflammatory bone disease leads to an increase in the number of osteoclasts and exacerbation of bone damage. Moreover, reduced PRL2 protein levels in peripheral myeloid cells are highly correlated with bone destruction in a mouse arthritis model and in human rheumatoid arthritis, while the autophagy inhibitor hydroxychloroquine blocked inflammation-induced PRL2 degradation and bone destruction in vivo. Therefore, our findings identify PRL2 as a new regulator in osteoimmunity, providing a link between inflammation and osteoporosis. As such, PRL2 is a potential therapeutic target for inflammatory bone disease and inhibition of HSC70 mediated autophagic degradation of PRL2 may offer new therapeutic tools for the treatment of inflammatory bone disease.

FasL is a catabolic factor in alveolar bone homeostasis

AIM

Fas ligand (FasL) belongs to the tumour necrosis factor superfamily regulating bone turnover, inflammation, and apoptosis. The appendicular and axial skeleton phenotype of mature Faslgld mice has been reported. The impact of FasL on the alveolar bone providing support for the teeth at mature stages under healthy and induced inflammatory conditions remains unknown.

MATERIALS AND METHODS

We performed a phenotypical analysis of mice carrying the homozygous Faslgld mutation and wild-type (WT) mice (C57BL/6) under healthy conditions and upon ligature-induced periodontitis. After 12 days, micro-computed tomography analysis revealed the distance between the cement enamel junction and the alveolar bone crest. Additional structural parameters, such as the bone volume fraction (BV/TV) and the periodontal ligament space volume, were measured. Histological analyses were performed to visualize the catabolic changes at the defect site.

RESULTS

Healthy Faslgld mice were found to have more periodontal bone than their WT littermates. Faslgld had no significant effect on inflammatory osteolysis compared to WT controls with ligatures. Histology revealed eroded surfaces at the root and in the inter-proximal bone in both strains.

CONCLUSIONS

Our findings suggest that FasL is a catabolic factor in alveolar bone homeostasis but it does not affect the inflammatory osteolysis.

Pulmonary osteoclast-like cells in silica induced pulmonary fibrosis

The pathophysiology of silicosis is poorly understood, limiting development of therapies for those who have been exposed to the respirable particle. We explored the mechanisms of silica-induced pulmonary fibrosis in a mouse model using multiple modalities including whole-lung single-nucleus RNA sequencing. These analyses revealed that in addition to pulmonary inflammation and fibrosis, intratracheal silica challenge induced osteoclast-like differentiation of alveolar macrophages and recruited monocytes, driven by induction of the osteoclastogenic cytokine, receptor activator of nuclear factor-κB ligand (RANKL) in pulmonary lymphocytes and alveolar type II cells. Furthermore, anti-RANKL monoclonal antibody treatment suppressed silica-induced osteoclast-like differentiation in the lung and attenuated silica-induced pulmonary fibrosis. We conclude that silica induces osteoclast-like differentiation of distinct recruited and tissue resident monocyte populations, leading to progressive lung injury, likely due to sustained elaboration of bone resorbing proteases and hydrochloric acid. Interrupting osteoclast-like differentiation may therefore constitute a promising avenue for moderating lung damage in silicosis.

STAT3/Mitophagy Axis Coordinates Macrophage NLRP3 Inflammasome Activation and Inflammatory Bone Loss

Signal transducer and activator of transcription 3 (STAT3), a cytokine-responsive transcription factor, is known to play a role in immunity and bone remodeling. However, whether and how STAT3 impacts macrophage NLR family pyrin domain containing 3 (NLRP3) inflammasome activation associated with inflammatory bone loss remains unknown. Here, STAT3 signaling is hyperactivated in macrophages in the context of both non-sterile and sterile inflammatory osteolysis, and this was highly correlated with the cleaved interleukin-1β (IL-1β) expression pattern. Strikingly, pharmacological inhibition of STAT3 markedly blocks macrophage NLRP3 inflammasome activation in vitro, thereby relieving inflammatory macrophage-amplified osteoclast formation and bone-resorptive activity. Mechanistically, STAT3 inhibition in macrophages triggers PTEN-induced kinase 1 (PINK1)-dependent mitophagy that eliminates dysfunctional mitochondria, reverses mitochondrial membrane potential collapse, and inhibits mitochondrial reactive oxygen species release, thus inactivating the NLRP3 inflammasome. In vivo, STAT3 inhibition effectively protects mice from both infection-induced periapical lesions and aseptic titanium particle-mediated calvarial bone erosion with potent induction of PINK1 and downregulation of inflammasome activation, macrophage infiltration, and osteoclast formation. This study reveals the regulatory role of the STAT3/mitophagy axis at the osteo-immune interface and highlights a potential therapeutic intervention to prevent inflammatory bone loss. © 2022 American Society for Bone and Mineral Research (ASBMR).

Avicularin alleviates osteoporosis-induced implant loosening by attenuating macrophage M1 polarization via its inhibitory effect on the activation of NF-κB

Currently, the failure rate for internal fixation in patients with osteoporosis can be reduced by antiosteoporosis therapy alone. However, the administration of anti-osteoporotic drugs is not a complete solution. Therefore, it is necessary to investigate other causes of surgical failure, such as inflammation. In recent years, the inflammation caused by macrophage M1 polarization has garnered wide attention. The purpose of this research is to explore the inhibitory effect of avicularin (AL) on macrophage M1 polarization, by which it ameliorates inflammation, thus alleviating implant instability. We established an osteoporosis mouse model of implant loosening. The mouse tissues were taken out for morphological analysis, staining analysis and bone metabolic index analysis. In in vitro experiments, bone marrow derived macrophages (BMDM) and RAW264.7 cells were polarized to M1 macrophages using lipopolysaccharide (LPS), and analyzed by immunofluorescence (IF) staining, Western blot (WB) and flow cytometry. WB was also used to analyze the nuclear factor kappa-B (NF-κB) pathway. In addition, the expression levels of inflammatory cytokines were detected in cell supernatant using ELISA kits. Through observation of this experiments, we found that AL can inhibit M1 polarization of macrophages. Moreover, it can significantly inhibit the release of inflammatory factors to improve multiple mouse femur parameters. Furthermore, AL inhibited the phosphorylation of IKBα and P65 in the NF-κB pathway. The above data indicate that AL ameliorates inflammatory responses by inhibiting macrophage M1 polarization via its inhibitory effect on the NF-κB pathway, thus alleviating the instability of implants in mice with osteoporosis.

Osteoclasts, Master Sculptors of Bone

Osteoclasts are multinucleated cells with the unique ability to resorb bone matrix. Excessive production or activation of osteoclasts leads to skeletal pathologies that affect a significant portion of the population. Although therapies that effectively target osteoclasts have been developed, they are associated with sometimes severe side effects, and a fuller understanding of osteoclast biology may lead to more specific treatments. Along those lines, a rich body of work has defined essential signaling pathways required for osteoclast formation, function, and survival. Nonetheless, recent studies have cast new light on long-held views regarding the origin of these cells during development and homeostasis, their life span, and the cellular sources of factors that drive their production and activity during homeostasis and disease. In this review, we discuss these new findings in the context of existing work and highlight areas of ongoing and future investigation.

γδT cells in oral tissue immune surveillance and pathology

The oral mucosa's immune system is composed of tissue-resident and specifically recruited leukocytes that could effectively tolerate a wide range of microbial and mechanical assaults. Shortly after CD4⁺ helper T cells (TH17 cells) that produce interleukin 17 (IL-17) were identified, it was discovered that γδT cells could also induce substantial levels of this pro-inflammatory cytokine. In the past decades, it has become clear that due to a complicated thymic program of development, γδT cells frequently serve as the primary sources of IL-17 in numerous models of inflammatory diseases while also assisting in the maintenance of tissue homeostasis in the skin and intestine. But it wasn't until recently that we took thorough insight into the complex features of γδT cells in the oral mucosa. Most gingival intraepithelial γδT cells reside in the junctional epithelium adjacent to the dental biofilm, suggesting their potential role in regulating oral microbiota. However, inconsistent results have been published in this regard. Similarly, recent findings showed contradictory data about the role of γδT lymphocytes in experimental periodontitis based on different models. In addition, conflicting findings were presented in terms of alveolar bone physiology and pathology underlying the oral mucosa. This review provided an overview of current knowledge and viewpoints regarding the complex roles played by oral-resident γδT cells in host-microbiota interactions, gingivitis and periodontitis, bone physiology and pathology.

Phosphatidyl Inositol 3-Kinase (PI3K)-Inhibitor CDZ173 protects against LPS-induced osteolysis

A major complication of a joint replacement is prosthesis loosening caused by inflammatory osteolysis, leading to the revision of the operation. This is due to the abnormal activation of osteoclast differentiation and function caused by periprosthetic infection. Therefore, targeting abnormally activated osteoclasts is still effective for treating osteolytic inflammatory diseases. CDZ173 is a selective PI3K inhibitor widely used in autoimmune-related diseases and inflammatory diseases and is currently under clinical development. However, the role and mechanism of CDZ173 in osteoclast-related bone metabolism remain unclear. The possibility for treating aseptic prosthesis loosening brought on by inflammatory osteolysis illness can be assessed using an LPS-induced mouse cranial calcium osteolysis model. In this study, we report for the first time that CDZ173 has a protective effect on LPS-induced osteolysis. The data show that this protective effect is due to CDZ173 inhibiting the activation of osteoclasts in vivo. Meanwhile, our result demonstrated that CDZ173 had a significant inhibitory effect on RANKL-induced osteoclasts. Furthermore, using the hydroxyapatite resorption pit assay and podosol actin belt staining, respectively, the inhibitory impact of CDZ173 on bone resorption and osteoclast fusion of pre-OC was determined. In addition, staining with alkaline phosphatase (ALP) and alizarin red (AR) revealed that CDZ173 had no effect on osteoblast development in vitro. Lastly, CDZ173 inhibited the differentiation and function of osteoclasts by weakening the signal axis of PI3K-AKT/MAPK-NFATc1 in osteoclasts. In conclusion, our results highlight the potential pharmacological role of CDZ173 in preventing osteoclast-mediated inflammatory osteolysis and its potential clinical application.

Ultrasmall PtAu2 nanoclusters activate endogenous anti-inflammatory and anti-oxidative systems to prevent inflammatory osteolysis

Rationale: Inflammatory osteolysis, characterized by abundant immune cell infiltration and osteoclast (OC) formation, is a common complication induced by bacterial products and/or wear particles at the bone-prosthesis interface that severely reduces long-term stability after implantation. Molecular nanoclusters are ultrasmall particles with unique physicochemical and biological properties that have great potential as theranostic agents for treating inflammatory diseases. Methods: In this study, heterometallic PtAu₂ nanoclusters with sensitive nitric oxide-responsive phosphorescence turn-on characteristics and strong binding interactions with cysteine were designed, making them desirable candidates for the treatment of inflammatory osteolysis. Results: PtAu₂ clusters exhibited satisfactory biocompatibility and cellular uptake behavior, with potent anti-inflammatory and anti-OC activities in vitro. In addition, PtAu₂ clusters alleviated lipopolysaccharide-induced calvarial osteolysis in vivo and activated nuclear factor erythroid 2-related factor 2 (Nrf2) expression by disrupting its association with Kelch-like ECH-associated protein 1 (Keap1), thereby upregulating the expression of endogenous anti-inflammatory and anti-oxidative products. Conclusion: Through the rational design of novel heterometallic nanoclusters that activate the endogenous anti-inflammatory system, this study provides new insights into the development of multifunctional molecular therapeutic agents for inflammatory osteolysis and other inflammatory diseases.

The role of myeloid derived suppressor cells in musculoskeletal disorders

The immune system is closely linked to bone homeostasis and plays a pivotal role in several pathological and inflammatory conditions. Through various pathways it modulates various bone cells and subsequently sustains the physiological bone metabolism. Myeloid-derived suppressor cells (MDSCs) are a group of heterogeneous immature myeloid-derived cells that can exert an immunosuppressive function through a direct cell-to-cell contact, secretion of anti-inflammatory cytokines or specific exosomes. These cells mediate the innate immune response to chronic stress on the skeletal system. In chronic inflammation, MDSCs act as an inner offset to rebalance overactivation of the immune system. Moreover, they have been found to be involved in processes responsible for bone remodeling in different musculoskeletal disorders, autoimmune diseases, infection, and cancer. These cells can not only cause bone erosion by differentiating into osteoclasts, but also alleviate the immune reaction, subsequently leading to long-lastingly impacted bone remodeling. In this review, we discuss the impact of MDSCs on the bone metabolism under several pathological conditions, the involved modulatory pathways as well as potential therapeutic targets in MDSCs to improve bone health.

CSF1R as a Therapeutic Target in Bone Diseases: Obvious but Not so Simple

PURPOSE OF REVIEW

The purpose of the review is to summarize the expression and function of CSF1R and its ligands in bone homeostasis and constraints on therapeutic targeting of this axis.

RECENT FINDINGS

Bone development and homeostasis depends upon interactions between mesenchymal cells and cells of the mononuclear phagocyte lineage (MPS), macrophages, and osteoclasts (OCL). The homeostatic interaction is mediated in part by the systemic and local production of growth factors, macrophage colony-stimulating factor (CSF1), and interleukin 34 (IL34) that interact with a receptor (CSF1R) expressed exclusively by MPS cells and their progenitors. Loss-of-function mutations in CSF1 or CSF1R lead to loss of OCL and macrophages and dysregulation of postnatal bone development. MPS cells continuously degrade CSF1R ligands via receptor-mediated endocytosis. As a consequence, any local or systemic increase or decrease in macrophage or OCL abundance is rapidly reversible. In principle, both CSF1R agonists and antagonists have potential in bone regenerative medicine but their evaluation in disease models and therapeutic application needs to carefully consider the intrinsic feedback control of MPS biology.

Context-Dependent Roles for Toll-Like Receptors 2 and 9 in the Pathogenesis of Staphylococcus aureus Osteomyelitis

Staphylococcus aureus is the major causative agent of bacterial osteomyelitis, an invasive infection of bone. Inflammation generated by the immune response to S. aureus contributes to bone damage by altering bone homeostasis. Increases in the differentiation of monocyte lineage cells into bone-resorbing osteoclasts (osteoclastogenesis) promote bone loss in the setting of osteomyelitis. In this study, we sought to define the role of Toll-like receptor (TLR) signaling in the pathogenesis of S. aureus osteomyelitis. We hypothesized that S. aureus-sensing TLRs 2 and 9, both of which are known to alter osteoclastogenesis in vitro, promote pathological changes to bone, including increased osteoclast abundance, bone loss, and altered callus formation during osteomyelitis. Stimulation of osteoclast precursors with S. aureus supernatant increased osteoclastogenesis in a TLR2-dependent, but not a TLR9-dependent, manner. However, in vivo studies using a posttraumatic murine model of osteomyelitis revealed that TLR2-null mice experienced similar bone damage and increased osteoclastogenesis compared to wild type (WT) mice. Therefore, we tested the hypothesis that compensation between TLR2 and TLR9 contributes to osteomyelitis pathogenesis. We found that mice deficient in both TLR2 and TLR9 (Tlr2/9^-/-) have decreased trabecular bone loss in response to infection compared to WT mice. However, osteoclastogenesis is comparable between WT and Tlr2/9^-/- mice, suggesting that alternative mechanisms enhance osteoclastogenesis in vivo during osteomyelitis. Indeed, we discovered that osteoclast precursors intracellularly infected with S. aureus undergo significantly increased osteoclast formation, even in the absence of TLR2 and TLR9. These results suggest that TLR2 and TLR9 have context-dependent roles in the alteration of bone homeostasis during osteomyelitis.

Intradiscal injection of human recombinant BMP-4 does not reverse intervertebral disc degeneration induced by nuclectomy in sheep

Background

Methods

Results

Conclusion

The Translational Potential of This Article