Osteoclast fusion and bone loss are restricted by interferon inducible guanylate binding proteins

Electrospun nanofibrous membranes meet antibacterial nanomaterials: From preparation strategies to biomedical applications

Electrospun nanofibrous membranes (eNFMs) have been extensively developed for bio-applications due to their structural and compositional similarity to the natural extracellular matrix. However, the emergence of antibiotic resistance in bacterial infections significantly impedes the further development and applications of eNFMs. The development of antibacterial nanomaterials substantially nourishes the engineering design of antibacterial eNFMs for combating bacterial infections without relying on antibiotics. Herein, a comprehensive review of diverse fabrication techniques for incorporating antibacterial nanomaterials into eNFMs is presented, encompassing an exhaustive introduction to various nanomaterials and their bactericidal mechanisms. Furthermore, the latest achievements and breakthroughs in the application of these antibacterial eNFMs in tissue regenerative therapy, mainly focusing on skin, bone, periodontal and tendon tissues regeneration and repair, are systematically summarized and discussed. In particular, for the treatment of skin infection wounds, we highlight the antibiotic-free antibacterial therapy strategies of antibacterial eNFMs, including (i) single model therapies such as metal ion therapy, chemodynamic therapy, photothermal therapy, and photodynamic therapy; and (ii) multi-model therapies involving arbitrary combinations of these single models. Additionally, the limitations, challenges and future opportunities of antibacterial eNFMs in biomedical applications are also discussed. We anticipate that this comprehensive review will provide novel insights for the design and utilization of antibacterial eNFMs in future research.

The role of infection in signalling root resorption: A narrative review

BACKGROUND

Root resorption consists of complex, multistep processes that involve cell signalling caused by inflammation and stromal cells, which promotes the secretion of receptor activator of nuclear factor κB ligand/ macrophage-colony stimulating factor (RANKL/M-CSF) resulting in a resorptive process.

OBJECTIVE

The aim of this narrative review was to analyse the literature related to root resorption resulting from microbial infection and to comparing it with non-microbial infection.

METHODS

An electronic literature search was performed using the PubMed database and applying keywords of articles published in English. Eligible papers were reviewed to reveal the descriptions of bone and root resorption processes. The abstracts were searched manually to identify articles about infection-stimulating bone and root resorption.

RESULTS

Three main types of root resorption were identified, two associated with primary bacterial infection and one secondary to bacterial infection. These include external inflammatory resorption, internal inflammatory resorption and external cervical (invasive) resorption.

DISCUSSION

The magnitude of cytokine involvement that promotes resorption and M-CSF/RANKL production depends on multiple factors, including pathogen virulence, site of infection and host genetic factors that activate the inflammation at the infection site. Two mechanisms activate the resorption mechanisms-the canonical and non-canonical pathways that can activate clastic cells independently of the RANKL/RANK canonical pathways.

CONCLUSIONS

Two pathways of root resorption co-exist in the body. When resorption is caused by infection, chronic inflammation due to bacterial infection prolongs the secretions of pro-inflammatory cytokines that intensify root and bone resorption. The second pathway is bacterial independent of the non-infection root resorption that is part of the wound healing process, which is limited in time due to its innate ability.

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.

SrTiO3 Nanotube-Based "Pneumatic Nanocannon" for On-Demand Delivery of Antibacterial and Sustained Osseointegration Enhancement

Infection and aseptic loosening caused by bacteria and poor osseointegration remain serious challenges for orthopedic implants. The advanced surface modification of implants is an effective strategy for addressing these challenges. This study presents a "pneumatic nanocannon" coating for titanium orthopedic implants to achieve on-demand release of antibacterial and sustained release of osteogenic agents. SrTiO3 nanotubes (SrNT) were constructed on the surface of Ti implants as "cannon barrel," the "cannonball" (antibiotic) and "propellant" (NH4HCO3) were codeposited into SrNT with assistance of mussel-inspired copolymerization of dopamine and subsequently sealed by a layer of polydopamine. The encapsulated NH4HCO3 within the nanotubes could be thermally decomposed into gases under near-infrared irradiation, propelling the on-demand delivery of antibiotics. This coating demonstrated significant efficacy in eliminating typical pathogenic bacteria both in planktonic and biofilm forms. Additionally, this coating exhibited a continuous release of strontium ions, which significantly enhanced the osteogenic differentiation of preosteoblasts. In an implant-associated infection rat model, this coating demonstrated substantial antibacterial efficiency (>99%) and significant promotion of osseointegration, along with alleviated postoperative inflammation. This pneumatic nanocannon coating presents a promising approach to achieving on-demand infection inhibition and sustained osseointegration enhancement for titanium orthopedic implants.

New perspectives on the therapeutic potential of quercetin in non-communicable diseases: Targeting Nrf2 to counteract oxidative stress and inflammation

Non-communicable diseases (NCDs), including cardiovascular diseases, cancer, metabolic diseases, and skeletal diseases, pose significant challenges to public health worldwide. The complex pathogenesis of these diseases is closely linked to oxidative stress and inflammatory damage. Nuclear factor erythroid 2-related factor 2 (Nrf2), a critical transcription factor, plays an important role in regulating antioxidant and anti-inflammatory responses to protect the cells from oxidative damage and inflammation-mediated injury. Therefore, Nrf2-targeting therapies hold promise for preventing and treating NCDs. Quercetin (Que) is a widely available flavonoid that has significant antioxidant and anti-inflammatory properties. It modulates the Nrf2 signaling pathway to ameliorate oxidative stress and inflammation. Que modulates mitochondrial function, apoptosis, autophagy, and cell damage biomarkers to regulate oxidative stress and inflammation, highlighting its efficacy as a therapeutic agent against NCDs. Here, we discussed, for the first time, the close association between NCD pathogenesis and the Nrf2 signaling pathway, involved in neurodegenerative diseases (NDDs), cardiovascular disease, cancers, organ damage, and bone damage. Furthermore, we reviewed the availability, pharmacokinetics, pharmaceutics, and therapeutic applications of Que in treating NCDs. In addition, we focused on the challenges and prospects for its clinical use. Que represents a promising candidate for the treatment of NCDs due to its Nrf2-targeting properties.

The impact of age and sex on the inflammatory response during bone fracture healing

Inflammation is thought to be dysregulated with age leading to impaired bone fracture healing. However, broad analyses of inflammatory processes during homeostatic bone aging and during repair are lacking. Here, we assessed changes in inflammatory cell and cytokine profiles in circulation and in bone tissue to identify age- and sex-dependent differences during homeostasis and repair. During homeostatic aging, male mice demonstrated accumulation of CD4+ helper T cells and CD8+ cytotoxic T cells within bone while both pro-inflammatory "M1" and anti-inflammatory "M2" macrophage numbers decreased. Female mice saw no age-associated changes in immune-cell population in homeostatic bone. Concentrations of IL-1β, IL-9, IFNγ, and CCL3/MIP-1α increased with age in both male and female mice, whereas concentrations of IL-2, TNFα, TNFR1, IL-4, and IL-10 increased only in female mice - thus we termed these "age-accumulated" cytokines. There were no notable changes in immune cell populations nor cytokines within circulation during aging. Sex-dependent analysis demonstrated slight changes in immune cell and cytokine levels within bone and circulation, which were lost upon fracture injury. Fracture in young male mice caused a sharp decrease in number of M1 macrophages; however, this was not seen in aged male mice nor in female mice of any age. Injury itself induced a decrease in the number of CD8+ T cells within the local tissue of aged male and of female mice but not of young mice. Cytokine analysis of fractured mice revealed that age-accumulated cytokines quickly dissipated after fracture injury, and did not re-accumulate in newly regenerated tissue. Conversely, CXCL1/KC-GRO, CXCL2/MIP-2, IL-6, and CCL2/MCP-1 acted as "fracture response" cytokines: increasing sharply after fracture, eventually returning to baseline. Collectively, we classify measured cytokines into three groups: (1) age-accumulated cytokines, (2) female-specific age-accumulated cytokines, and (3) fracture response cytokines. These inflammatory molecules represent potential points of intervention to improve fracture healing outcome.

Mitigation of Osteoclast-Mediated Arthritic Bone Remodeling By Short Chain Fatty Acids

OBJECTIVE

The objective for this study was to evaluate the effects of short chain fatty acids (SCFAs) on arthritic bone remodeling.

METHODS

We treated a recently described preclinical murine model of psoriatic arthritis (PsA), R26STAT3Cstopfl/fl CD4Cre mice, with SCFA-supplemented water. We also performed in vitro osteoclast differentiation assays in the presence of serum-level SCFAs to evaluate the direct impact of these microbial metabolites on maturation and function of osteoclasts. We further characterized the molecular mechanism of SCFAs by transcriptional analysis.

RESULTS

The osteoporosis condition in R26STAT3Cstopfl/fl CD4Cre animals is attributed primarily to robust osteoclast differentiation driven by an expansion of osteoclast progenitor cells (OCPs), accompanied by impaired osteoblast development. We show that SCFA supplementation can rescue the osteoporosis phenotype in this model of PsA. Our in vitro experiments revealed an inhibitory effect of the SCFAs on osteoclast differentiation, even at very low serum concentrations. This suppression of osteoclast differentiation enabled SCFAs to impede osteoporosis development in R26STAT3Cstopfl/fl CD4Cre mice. Further interrogation revealed that bone marrow-derived OCPs from diseased mice expressed a higher level of SCFA receptors than those of control mice and that the progenitor cells in the bone marrow of SCFA-treated mice presented a modified transcriptomic landscape, suggesting a direct impact of SCFAs on bone marrow progenitors in the context of osteoporosis.

CONCLUSION

We demonstrated how gut microbiota-derived SCFAs can regulate distal pathology (ie, osteoporosis) and identified a potential therapeutic option for restoring bone density in rheumatic disease, further highlighting the critical role of the gut-bone axis in these disorders.

Carnitine functions as an enhancer of NRF2 to inhibit osteoclastogenesis via regulating macrophage polarization in osteoporosis

Osteoporosis, which manifests as reduced bone mass and deteriorated bone quality, is common in the elderly population. It is characterized by persistent elevation of macrophage-associated inflammation and active osteoclast bone resorption. Currently, the roles of intracellular metabolism in regulating these processes remain unclear. In this study, we initially performed bioinformatics analysis and observed a significant increase in the proportion of M1 macrophages in bone marrow with aging. Further metabolomics analysis demonstrated a notable reduction in the expression of carnitine metabolites in aged macrophages, while carnitine was not detected in osteoclasts. During the differentiation process, osteoclasts took up carnitine synthesized by macrophages to regulate their own activity. Mechanistically, carnitine enhanced the function of Nrf2 by inhibiting the Keap1-Nrf2 interaction, reducing the proteasome-dependent ubiquitination and degradation of Nrf2. In silico molecular ligand docking analysis of the interaction between carnitine and Keap1 showed that carnitine binds to Keap1 to stabilize Nrf2 and enhance its function. In this study, we found that the decrease in carnitine levels in aging macrophages causes overactivation of osteoclasts, ultimately leading to osteoporosis. A decrease in serum carnitine levels in patients with osteoporosis was found to have good diagnostic and predictive value. Moreover, supplementation with carnitine was shown to be effective in the treatment of osteoporosis.

Breast Tumor Metastasis and Its Microenvironment: It Takes Both Seed and Soil to Grow a Tumor and Target It for Treatment

Metastasis remains a major challenge in treating breast cancer. Breast tumors metastasize to organ-specific locations such as the brain, lungs, and bone, but why some organs are favored over others remains unclear. Breast tumors also show heterogeneity, plasticity, and distinct microenvironments. This contributes to treatment failure and relapse. The interaction of breast cancer cells with their metastatic microenvironment has led to the concept that primary breast cancer cells act as seeds, whereas the metastatic tissue microenvironment (TME) is the soil. Improving our understanding of this interaction could lead to better treatment strategies for metastatic breast cancer. Targeted treatments for different subtypes of breast cancers have improved overall patient survival, even with metastasis. However, these targeted treatments are based upon the biology of the primary tumor and often these patients' relapse, after therapy, with metastatic tumors. The advent of immunotherapy allowed the immune system to target metastatic tumors. Unfortunately, immunotherapy has not been as effective in metastatic breast cancer relative to other cancers with metastases, such as melanoma. This review will describe the heterogeneic nature of breast cancer cells and their microenvironments. The distinct properties of metastatic breast cancer cells and their microenvironments that allow interactions, especially in bone and brain metastasis, will also be described. Finally, we will review immunotherapy approaches to treat metastatic breast tumors and discuss future therapeutic approaches to improve treatments for metastatic breast cancer.

Suppression of IRF9 Promotes Osteoclast Differentiation by Decreased Ferroptosis via STAT3 Activation

Osteoporosis is a chronic disease that endangers the health of the elderly. Inhibiting osteoclast hyperactivity is a key aspect of osteoporosis prevention and treatment. Several studies have shown that interferon regulatory factor 9 (IRF9) not only regulates innate and adaptive immune responses but also plays an important role in inflammation, antiviral response, and cell development. However, the exact role of IRF9 in osteoclasts has not been reported. To elucidate the role of IRF9 in osteoclast differentiation, we established the ovariectomized mouse model of postmenopausal osteoporosis and found that IRF9 expression was reduced in ovariectomized mice with overactive osteoclasts. Furthermore, knockdown of IRF9 expression enhanced osteoclast differentiation in vitro. Using RNA sequencing, we identified that the differentially expressed genes enriched by IRF9 knockdown were related to ferroptosis. We observed that IRF9 knockdown promoted osteoclast differentiation via decreased ferroptosis in vitro and further verified that IRF9 knockdown reduced ferroptosis by activating signal transducer and activator of transcription 3 (STAT3) to promote osteoclastogenesis. In conclusion, we identified an essential role of IRF9 in the regulation of osteoclastogenesis in osteoporosis and its underlying mechanism.

Exosome-derived miR-5p-72106_14 in vascular endothelial cells regulates fate determination of BMSCs

Vascular endothelial cells have recently been shown to be associated with osteogenic activity. However, the mechanism of vascular endothelial cells promoting osteogenesis is unclear. Here, we found that exosomes secreted from human microvascular endothelial cells (HMEC-1) promoted osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and inhibited adipogenic differentiation. Aged and ovariectomy mice treated with exosomes showed increased bone formation and decreased lipid accumulation in the bone marrow cavity. Additionally, we screened out novel exosomal miR-5p-72106_14 by miRNA-seq and confirmed that miR-5p-72106_14 promoted osteogenic differentiation and inhibited adipogenic differentiation of BMSCs by inhibiting STAT1. Our results suggest that vascular endothelial cell-derived exosomes are involved in BMSC differentiation and exosomal miR-5p-72106_14 is a major factor in regulating fate determination of BMSCs.

Apoptosis-resistant megakaryocytes produce large and hyperreactive platelets in response to radiation injury

BACKGROUND

The essential roles of platelets in thrombosis have been well recognized. Unexpectedly, thrombosis is prevalent during thrombocytopenia induced by cytotoxicity of biological, physical and chemical origins, which could be suffered by military personnel and civilians during chemical, biological, radioactive, and nuclear events. Especially, thrombosis is considered a major cause of mortality from radiation injury-induced thrombocytopenia, while the underlying pathogenic mechanism remains elusive.

METHODS

A mouse model of radiation injury-induced thrombocytopenia was built by exposing mice to a sublethal dose of ionizing radiation (IR). The phenotypic and functional changes of platelets and megakaryocytes (MKs) were determined by a comprehensive set of in vitro and in vivo assays, including flow cytometry, flow chamber, histopathology, Western blotting, and chromatin immunoprecipitation, in combination with transcriptomic analysis. The molecular mechanism was investigated both in vitro and in vivo, and was consolidated using MK-specific knockout mice. The translational potential was evaluated using a human MK cell line and several pharmacological inhibitors.

RESULTS

In contrast to primitive MKs, mature MKs (mMKs) are intrinsically programmed to be apoptosis-resistant through reprogramming the Bcl-xL-BAX/BAK axis. Interestingly, mMKs undergo minority mitochondrial outer membrane permeabilization (MOMP) post IR, resulting in the activation of the cyclic GMP-AMP synthase-stimulator of IFN genes (cGAS-STING) pathway via the release of mitochondrial DNA. The subsequent interferon-β (IFN-β) response in mMKs upregulates a GTPase guanylate-binding protein 2 (GBP2) to produce large and hyperreactive platelets that favor thrombosis. Further, we unmask that autophagy restrains minority MOMP in mMKs post IR.

CONCLUSIONS

Our study identifies that megakaryocytic mitochondria-cGAS/STING-IFN-β-GBP2 axis serves as a fundamental checkpoint that instructs the size and function of platelets upon radiation injury and can be harnessed to treat platelet pathologies.

Pathogenesis of non-infection related inflammatory root resorption in permanent teeth: A narrative review

BACKGROUND

The mechanism of action of root resorption in a permanent tooth can be classified as infection-related (e.g., microbial infection) or non-infection-related (e.g., sterile damage). Infection induced root resorption occurs due to bacterial invasion. Non-infection-related root resorption stimulates the immune system through a different mechanism.

OBJECTIVES

The aim of this narrative review is to describe the pathophysiologic process of non-infection-related inflammatory processes involved in root resorption of permanent teeth.

METHODS

A literature search on root resorption was conducted using Scopus (PubMed and Medline) and Google Scholar databases to highlight the pathophysiology of bone and root resorption in non-infection-related situations. The search included key words covering the relevant category. It included in vitro and in vivo studies, systematic reviews, case series, reviews, and textbooks in English. Conference proceedings, lectures and letters to the editor were excluded.

RESULTS

Three types of root resorption are related to the non-infection mechanism of action, which includes surface resorption due to either trauma or excessive orthodontic forces, external replacement resorption and external cervical resorption. The triggers are usually damage associated molecular patterns and hypoxia conditions. During this phase macrophages and clastic cells act to eliminate the damaged tissue and bone, eventually enabling root resorption and bone repair as part of wound healing.

DISCUSSION

The resorption of the root occurs during the inflammatory phase of wound healing. In this phase, damaged tissues are recognized by macrophages and neutrophiles that secrete interlaukines such as TNF-α, IL-1, IL-6, IL-8. Together with the hypoxia condition that accelarates the secretion of growth factors, the repair of the damaged perioduntiom, including damaged bone, is initiated. If the precementum and cementoblast are injured, root resorption can occur.

CONCLUSIONS

Wound healing exhibits different patterns of action that involves immune stimulation in a bio-physiological activity, that occurs in the proper sequence, with overlapping phases. Two pathologic conditions, DAMPs and hypoxia, can activate the immune cells including clastic cells, eliminating damaged tissue and bone. Under certain conditions, root resorption occurs as a side effect.

Osteoprotective Role of the Mir338 Cluster Ablation during Periodontitis

Periodontitis is a chronic inflammatory disease that compromises the integrity of the supporting tissues of the teeth and leads to the loss of the alveolar bone. The Mir338 cluster has been proven to be a potential target for the treatment of osteoporosis and is also enriched in gingival tissues with periodontitis; however, its role in periodontitis remains unknown. Here, we aimed to use periodontitis as a model to expand our understanding of the Mir338 cluster in osteoimmunology and propose a new target to protect against bone loss during periodontitis progression. Significant enrichment of the Mir338 cluster was validated in gingival tissues from patients with chronic periodontitis and a ligature-induced periodontitis mouse model. In vivo, attenuation of alveolar bone loss after 7 d of ligature was observed in the Mir338 cluster knockout (KO) mice. Interestingly, immunofluorescence and RNA sequencing showed that ablation of the Mir338 cluster reduced osteoclast formation and elevated the inflammatory response, with enrichment of IFN-γ and JAK-STAT signaling pathways. Ablation of the Mir338 cluster also skewed macrophages toward the M1 phenotype and inhibited osteoclastogenesis via Stat1 in vitro and in vivo. Furthermore, the local administration of miR-338-3p antagomir prevented alveolar bone loss from periodontitis. In conclusion, the Mir338 cluster balanced M1 macrophage polarization and osteoclastogenesis and could serve as a novel therapeutic target against periodontitis-related alveolar bone loss.

Trim21 depletion alleviates bone loss in osteoporosis via activation of YAP1/β-catenin signaling

Despite the diverse roles of tripartite motif (Trim)-containing proteins in the regulation of autophagy, the innate immune response, and cell differentiation, their roles in skeletal diseases are largely unknown. We recently demonstrated that Trim21 plays a crucial role in regulating osteoblast (OB) differentiation in osteosarcoma. However, how Trim21 contributes to skeletal degenerative disorders, including osteoporosis, remains unknown. First, human and mouse bone specimens were evaluated, and the results showed that Trim21 expression was significantly elevated in bone tissues obtained from osteoporosis patients. Next, we found that global knockout of the Trim21 gene (KO, Trim21-/-) resulted in higher bone mass compared to that of the control littermates. We further demonstrated that loss of Trim21 promoted bone formation by enhancing the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and elevating the activity of OBs; moreover, Trim21 depletion suppressed osteoclast (OC) formation of RAW264.7 cells. In addition, the differentiation of OCs from bone marrow-derived macrophages (BMMs) isolated from Trim21-/- and Ctsk-cre; Trim21f/f mice was largely compromised compared to that of the littermate control mice. Mechanistically, YAP1/β-catenin signaling was identified and demonstrated to be required for the Trim21-mediated osteogenic differentiation of BMSCs. More importantly, the loss of Trim21 prevented ovariectomy (OVX)- and lipopolysaccharide (LPS)-induced bone loss in vivo by orchestrating the coupling of OBs and OCs through YAP1 signaling. Our current study demonstrated that Trim21 is crucial for regulating OB-mediated bone formation and OC-mediated bone resorption, thereby providing a basis for exploring Trim21 as a novel dual-targeting approach for treating osteoporosis and pathological bone loss.

Bisphosphonate-incorporated coatings for orthopedic implants functionalization

Bisphosphonates (BPs), the stable analogs of pyrophosphate, are well-known inhibitors of osteoclastogenesis to prevent osteoporotic bone loss and improve implant osseointegration in patients suffering from osteoporosis. Compared to systemic administration, BPs-incorporated coatings enable the direct delivery of BPs to the local area, which will precisely enhance osseointegration and bone repair without the systemic side effects. However, an elaborate and comprehensive review of BP coatings of implants is lacking. Herein, the cellular level (e.g., osteoclasts, osteocytes, osteoblasts, osteoclast precursors, and bone mesenchymal stem cells) and molecular biological regulatory mechanism of BPs in regulating bone homeostasis are overviewed systematically. Moreover, the currently available methods (e.g., chemical reaction, porous carriers, and organic material films) of BP coatings construction are outlined and summarized in detail. As one of the key directions, the latest advances of BP-coated implants to enhance bone repair and osseointegration in basic experiments and clinical trials are presented and critically evaluated. Finally, the challenges and prospects of BP coatings are also purposed, and it will open a new chapter in clinical translation for BP-coated implants.

The Effects of n-3 PUFA Supplementation on Bone Metabolism Markers and Body Bone Mineral Density in Adults: A Systematic Review and Meta-Analysis of RCTs

Supplemental n-3 polyunsaturated fatty acids (PUFA) on bone metabolism have yielded inconsistent results. This study aimed to examine the effects of n-3 PUFA supplementation on bone metabolism markers and bone mineral density through a meta-analysis of randomized controlled trials. A systematic literature search was conducted using the PubMed, Web of Science, and EBSCO databases, updated to 1 March 2023. The intervention effects were measured as standard mean differences (SMD) and mean differences (MD). Additionally, n-3 PUFA with the untreated control, placebo control, or lower-dose n-3 PUFA supplements were compared, respectively. Further, 19 randomized controlled trials (RCTs) (22 comparisons, n = 2546) showed that n-3 PUFA supplementation significantly increased blood n-3 PUFA (SMD: 2.612; 95% CI: 1.649 to 3.575). However, no significant effects were found on BMD, CTx-1, NTx-1, BAP, serum calcium, 25(OH)D, PTH, CRP, and IL-6. Subgroup analyses showed significant increases in femoral neck BMD in females (0.01, 95% CI: 0.01 to 0.02), people aged <60 years (0.01, 95% CI: 0.01 to 0.01), and those people in Eastern countries (0.02, 95% CI: 0.02 to 0.03), and for 25(OH)D in people aged ≥60 years (0.43, 95% CI: 0.11 to 0.74), treated with n-3 PUFA only (0.36, 95% CI: 0.06 to 0.66), and in studies lasting ≤6 months (0.29, 95% CI: 0.11 to 0.47). NTx-1 decreased in both genders (-9.66, 95% CI: -15.60 to -3.71), and serum calcium reduction was found in studies lasting >6 months (-0.19, 95% CI: -0.37 to -0.01). The present study demonstrated that n-3 PUFA supplementation might not have a significant effect on bone mineral density or bone metabolism markers, but have some potential benefits for younger postmenopausal subjects in the short term. Therefore, additional high-quality, long-term randomized controlled trials (RCTs) are warranted to fully elucidate the potential benefits of n-3 PUFA supplementation, as well as the combined supplementation of n-3 PUFA, on bone health.

Novel one-pot strategy for fabrication of a pH-Responsive bone-targeted drug self-frame delivery system for treatment of osteoporosis

Osteoporosis (OP) is a systemic metabolic orthopedic disorder prevalent in elderly people, that is characterized by a decrease in bone mass. Although many therapeutics have been adopted for OP treatment, many of them are still not well satisfied clinical requirements and therefore development of novel therapeutics is of great significance. In this work, a novel bone-targeting drug self-frame delivery system (DSFDS) with high drug loading efficiency and pH responsive drug release was fabricated by condensation of curcumin (Cur), amino group terminated polyethylene glycol (NH₂-PEG), and alendronate (ALN) using hexachlorocyclotriphosphonitrile (HCCP) as the linker. The final product named as HCCP-Cur-PEG-ALN (HCPA NPs) displayed excellent water dispersity with small size (181.9 ​± ​25.9 ​nm). Furthermore, the drug loading capacity of Cur can reach 25.8%, and Cur can be released from HCPA NPs under acidic environment. Owing to the introduction of ALN, HCPA NPs exhibited strong binding to HAp in vitro and excellent bone-targeting effect in vivo. Results from cellular and biochemical analyses revealed that HCPA NPs could effectively inhibit the formation and differentiation function of osteoclasts. More importantly, we also demonstrated that HCPA NPs could effectively reduce bone loss in OVX mice with low toxicity to major organs. The above results clearly demonstrated that HCPA NPs are promising for OP treatment. Given the simplicity and well designability of fabrication strategy, explicit therapy efficacy and low toxicity of HCPA NPs, we believe that this work should be of great interest for fabrication of various DSFDS to deal with many diseases.

Monocytes differentiate along two alternative pathways during sterile inflammation

During inflammation, monocytes differentiate within tissues into macrophages (mo-Mac) or dendritic cells (mo-DC). Whether these two populations derive from alternative differentiation pathways or represent different stages along a continuum remains unclear. Here, we address this question using temporal single-cell RNA sequencing in an in vitro model, allowing the simultaneous differentiation of human mo-Mac and mo-DC. We find divergent differentiation paths, with a fate decision occurring within the first 24 h and confirm this result in vivo using a mouse model of sterile peritonitis. Using a computational approach, we identify candidate transcription factors potentially involved in monocyte fate commitment. We demonstrate that IRF1 is necessary for mo-Mac differentiation, independently of its role in regulating transcription of interferon-stimulated genes. In addition, we describe the transcription factors ZNF366 and MAFF as regulators of mo-DC development. Our results indicate that mo-Macs and mo-DCs represent two alternative cell fates requiring distinct transcription factors for their differentiation.

STING-dependent interferon signatures restrict osteoclast differentiation and bone loss in mice

Stimulator of interferon genes (STING) is a key mediator of type-I interferon (IFN-I) signaling in response to a variety of stimuli, but the contribution of STING to homeostatic processes is not fully characterized. Previous studies showed that ligand activation of STING limits osteoclast differentiation in vitro through the induction of IFNβ and IFN-I interferon-stimulated genes (ISGs). In a disease model (SAVI) driven by the V154M gain-of-function mutation in STING, fewer osteoclasts form from SAVI precursors in response to receptor activator of NF-kappaB ligand (RANKL) in an IFN-I-dependent manner. Due to the described role of STING-mediated regulation of osteoclastogenesis in activation settings, we sought to determine whether basal STING signaling contributes to bone homeostasis, an unexplored area. Using whole-body and myeloid-specific deficiency, we show that STING signaling prevents trabecular bone loss in mice over time and that myeloid-restricted STING activity is sufficient for this effect. STING-deficient osteoclast precursors differentiate with greater efficiency than wild types. RNA sequencing of wild-type and STING-deficient osteoclast precursor cells and differentiating osteoclasts reveals unique clusters of ISGs including a previously undescribed ISG set expressed in RANKL naïve precursors (tonic expression) and down-regulated during differentiation. We identify a 50 gene tonic ISG signature that is STING dependent and shapes osteoclast differentiation. From this list, we identify interferon-stimulated gene 15 (ISG15) as a tonic STING-regulated ISG that limits osteoclast formation. Thus, STING is an important upstream regulator of tonic IFN-I signatures shaping the commitment to osteoclast fates, providing evidence for a nuanced and unique role for this pathway in bone homeostasis.

Functional cross-species conservation of guanylate-binding proteins in innate immunity

Guanylate binding proteins (GBPs) represent an evolutionary ancient protein family widely distributed among eukaryotes. They are interferon (IFN)-inducible guanosine triphosphatases that belong to the dynamin superfamily. GBPs are known to have a major role in the cell-autonomous innate immune response against bacterial, parasitic and viral infections and are also involved in inflammasome activation. Evolutionary studies depicted that GBPs present a pattern of gain and loss of genes in each family with several genes pseudogenized and some genes more divergent, indicative for the birth-and-death evolution process. Most species harbor large GBP gene clusters encoding multiple paralogs. Previous functional studies mainly focused on mouse and human GBPs, but more data are becoming available, broadening the understanding of this multifunctional protein family. In this review, we will provide new insights and give a broad overview about GBP evolution, conservation and their roles in all studied species, including plants, invertebrates and vertebrates, revealing how far the described features of GBPs can be transferred to other species.

Genetic dissection of triplicated chromosome 21 orthologs yields varying skeletal traits in Down syndrome model mice

Down syndrome (DS) phenotypes result from triplicated genes, but the effects of three copy genes are not well known. A mouse mapping panel genetically dissecting human chromosome 21 (Hsa21) syntenic regions was used to investigate the contributions and interactions of triplicated Hsa21 orthologous genes on mouse chromosome 16 (Mmu16) on skeletal phenotypes. Skeletal structure and mechanical properties were assessed in femurs of male and female Dp9Tyb, Dp2Tyb, Dp3Tyb, Dp4Tyb, Dp5Tyb, Dp6Tyb, Ts1Rhr and Dp1Tyb;Dyrk1a+/+/- mice. Dp1Tyb mice, with the entire Hsa21 homologous region of Mmu16 triplicated, display bone deficits similar to those of humans with DS and served as a baseline for other strains in the panel. Bone phenotypes varied based on triplicated gene content, sex and bone compartment. Three copies of Dyrk1a played a sex-specific, essential role in trabecular deficits and may interact with other genes to influence cortical deficits related to DS. Triplicated genes in Dp9Tyb and Dp2Tyb mice improved some skeletal parameters. As triplicated genes can both improve and worsen bone deficits, it is important to understand the interaction between and molecular mechanisms of skeletal alterations affected by these genes.

BRD9-mediated chromatin remodeling suppresses osteoclastogenesis through negative feedback mechanism

Bromodomain-containing protein 9 (BRD9), a component of non-canonical BAF chromatin remodeling complex, has been identified as a critical therapeutic target in hematological diseases. Despite the hematopoietic origin of osteoclasts, the role of BRD9 in osteoclastogenesis and bone diseases remains unresolved. Here, we show Brd9 deficiency in myeloid lineage enhances osteoclast lineage commitment and bone resorption through downregulating interferon-beta (IFN-β) signaling with released constraint on osteoclastogenesis. Notably, we show that BRD9 interacts with transcription factor FOXP1 activating Stat1 transcription and IFN-β signaling thereafter. Besides, function specificity of BRD9 distinguished from BRD4 during osteoclastogenesis has been evaluated. Leveraging advantages of pharmacological modulation of BRD9 and flexible injectable silk fibroin hydrogel, we design a local deliver system for effectively mitigating zoledronate related osteonecrosis of the jaw and alleviating acute bone loss in lipopolysaccharide-induced localized aggressive periodontitis. Overall, these results demonstrate the function of BRD9 in osteoclastogenesis and its therapeutic potential for bone diseases.

Identification of key genes and pathways associated with gender difference in osteonecrosis of the femoral head based on bioinformatics analysis

OBJECTIVE

To identify different key genes and pathways between males and females by studying differentially expressed genes (DEGs).

METHODS

The gene expression data of GSE123568 were downloaded from GEO database, including osteonecrosis of the femoral head (ONFH) samples from 3 females and 7 males, and DEGs between different gender were identified with R software. Protein-protein interaction (PPI) network was constructed to further analyze the interactions between overlapping DEGs, and finally, GO, KEGG and gene set enrichment analysis (GSEA) were conducted for enrichment analysis.

RESULTS

131 DEGs were identified between ONFH females and ONFH males, including 76 up-regulated genes and 55 down-regulated genes. And 10 hub genes were identified in PPI network, including SLC4A1, GYPA, CXCL8, IFIT1, GBP5, IFI44, IFI44L, IFIT3, KEL and AHSP. Functional enrichment analysis revealed that these genes were mainly enriched in cGMP-PKG signaling pathway, Fatty acid degradation, Non-alcoholic fatty liver disease, Systemic lupus erythematosus, Hematopoietic cell lineage and NO-cGMP-PKG signaling.

CONCLUSIONS

NO-cGMP-PKG signaling may play an important role in the occurrence and development of ONFH. SLC4A1, GYPA, CXCL8, GBP5 and AHSP may be key genes associated with gender difference in the progression of ONFH, which may be ideal targets or prognostic markers for the treatment of ONFH.

Substance P Exacerbates the Inflammatory and Pro-osteoclastogenic Responses of Murine Osteoclasts and Osteoblasts to Staphylococcus aureus

Staphylococcus aureus infections of bone tissue are associated with inflammatory bone loss. Resident bone cells, including osteoblasts and osteoclasts, can perceive S. aureus and produce an array of inflammatory and pro-osteoclastogenic mediators, thereby contributing to such damage. The neuropeptide substance P (SP) has been shown to exacerbate microbially induced inflammation at sites such as the gut and the brain and has previously been shown to affect bone cell differentiation and activity. Here we demonstrate that the interaction of SP with its high affinity receptor, neurokinin-1 receptor (NK-1R), expressed on murine osteoblasts and osteoclasts, augments the inflammatory responses of these cells to S. aureus challenge. Additionally, SP alters the production of pro- and anti-osteoclastogenic factors by bacterially challenged bone cells and their proteolytic functions in a manner that would be anticipated to exacerbate inflammatory bone loss at sites of infection. Furthermore, we have demonstrated that the clinically approved NK-1R antagonist, aprepitant, attenuates local inflammatory and pro-osteoclastogenic mediator expression in an in vivo mouse model of post-traumatic staphylococcal osteomyelitis. Taken together, these results indicate that SP/NK-1R interactions could play a significant role in the initiation and/or progression of damaging inflammation in S. aureus bone infections and suggest that the repurposing of currently approved NK-1R antagonists might represent a promising new adjunct therapy for such conditions.

D-Mannose prevents bone loss under weightlessness

BACKGROUND

Astronauts undergo significant microgravity-induced bone loss during space missions, which has become one of the three major medical problems hindering human's long-term space flight. A risk-free and antiresorptive drug is urgently needed to prevent bone loss during space missions. D-mannose is a natural C-2 epimer of D-glucose and is abundant in cranberries. This study aimed to investigate the protective effects and potential mechanisms of D-mannose against bone loss under weightlessness.

METHODS

The hind legs of tail-suspended (TS) rats were used to mimic weightlessness on Earth. Rats were administered D-mannose intragastrically. The osteoclastogenic and osteogenic capacity of D-mannose in vitro and in vivo was analyzed by micro-computed tomography, biomechanical assessment, bone histology, serum markers of bone metabolism, cell proliferation assay, quantitative polymerase chain reaction, and western blotting. RNA-seq transcriptomic analysis was performed to detect the underlying mechanisms of D-mannose in bone protection.

RESULTS

The TS rats showed lower bone mineral density (BMD) and poorer bone morphological indices. D-mannose could improve BMD in TS rats. D-mannose inhibited osteoclast proliferation and fusion in vitro, without apparent effects on osteoblasts. RNA-seq transcriptomic analysis showed that D-mannose administration significantly inhibited the cell fusion molecule dendritic cell-specific transmembrane protein (DC-STAMP) and two indispensable transcription factors for osteoclast fusion (c-Fos and nuclear factor of activated T cells 1 [NFATc1]). Finally, TS rats tended to experience dysuria-related urinary tract infections (UTIs), which were suppressed by treatment with D-mannose.

CONCLUSION

D-mannose protected against bone loss and UTIs in rats under weightlessness. The bone protective effects of D-mannose were mediated by inhibiting osteoclast cell fusion. Our findings provide a potential strategy to protect against bone loss and UTIs during space missions.

FTY720 Attenuates LPS-Induced Inflammatory Bone Loss by Inhibiting Osteoclastogenesis via the NF-κB and HDAC4/ATF Pathways

Osteoclast (OC) abnormalities lead to many osteolytic diseases, such as osteoporosis, inflammatory bone erosion, and tumor-induced osteolysis. Exploring effective strategies to remediate OCs dysregulation is essential. FTY720, also known as fingolimod, has been approved for the treatment of multiple sclerosis and has anti-inflammatory and immunosuppressive effects. Here, we found that FTY720 inhibited osteoclastogenesis and OC function by inhibiting nuclear factor kappa-B (NF-κB) signaling. Interestingly, we also found that FTY720 inhibited osteoclastogenesis by upregulating histone deacetylase 4 (HDAC4) expression levels and downregulating activating transcription factor 4 (ATF4) expression levels. In vivo, FTY720 treatment prevented lipopolysaccharide- (LPS-) induced calvarial osteolysis and significantly reduced the number of tartrate-resistant acid phosphatase- (TRAP-) positive OCs. Taken together, these results demonstrate that FTY720 can inhibit osteoclastogenesis and ameliorate inflammation-induced bone loss. Which may provide evidence of a new therapeutic target for skeletal diseases caused by OC abnormalities.

GBP5 Inhibition Ameliorates the Progression of Lupus Nephritis by Suppressing NLRP3 Inflammasome Activation

BACKGROUND

The inflammatory response and NLRP3 inflammasome activation are typical characteristics of lupus nephritis (LN). Guanylate-binding protein 5 (GBP5) has effects on the release of proinflammatory cytokines and the activation of NLRP3 inflammasome. However, it is largely unknown whether and how GBP5 contributes to the progression of LN.

METHODS

To detect the role of GBP5 in LN, MRL/lpr mice were administrated with the lentiviral vectors that knockdown GBP5 via tail vein. Proximal tubular epithelial HK-2 cells were treated with LPS and ATP to mimic the inflammatory response of LN in vitro.

RESULTS

GBP5 expression was increased in the renal cortical tissues of LN mice. The in vivo results showed that GBP5 inhibition prevented the progression of LN, as evidenced by the decreased levels of 24-hour proteinuria, blood urea nitrogen and creatinine, accompanied by the ameliorated renal pathological damages. The increased mRNA and protein levels of proinflammatory factors (IL-6, TNF-α, iNOS and COX-2) in the renal cortex of LN mice were suppressed by GBP5 knockdown. In vitro, we demonstrated that the treatment of LPS combined with ATP induced an increase in GBP5 mRNA and protein expression in HK-2 cells. Mechanically, knockdown of GBP5 inhibited the activation of NLRP3 inflammasome and the secretion of IL-1β and IL-18 both in vivo and in vitro.

CONCLUSION

Our findings reveal that GBP5 inhibition prevents the progression of LN, most likely by suppressing NLRP3 inflammasome activation. It provides a novel insight into the therapeutic interventions for LN.

Neutrophil extracellular traps induce the bone erosion of gout

OBJECTIVE

To investigate the relationships between monosodium urate (MSU) crystals -induced neutrophil extracellular traps (NETs) and bone erosion in gout.

METHODS

Animal models were used to study the relationship between NETs induced by MSU crystals and bone erosion. Neutrophils were treated with MSU crystals to induce NETs. The osteoblasts-like cells (OB) were then treated with NETs, and the supernatant was co-incubated with osteoclasts-like cells (OC). The NETs were digested with DNase, and the neutrophil elastase (NE) was inhibited with sivelestat sodium. Cell viability, mRNA, and protein expression were also assessed.

RESULTS

After treating OB with NETs, the cell viability decreased. Yet, after digesting the DNA and inhibiting NE, the viability was moderately improved. The expression level of osteoprotegerin (OPG) and alkaline phosphatase (ALP) was up-regulated, while the expression level of receptor activator of nuclear factor kappa-B ligand (RANKL) was down-regulated in the sivelestat sodium + MSU group compared with MSU group. The number of OC was significantly elevated. In contrast, the number of OB was not increased in the tibia after establishing the gout model. The supernatant obtained from OB was treated with NETs promoting OC differentiation. The expression level of receptor activator of nuclear factor kappa-B (RANK), tartrate-resistant acid phosphatase (TRAP), and cathepsin K (Cst K) was up-regulated in the MSU group compared with the normal control (NC) group.

CONCLUSION

NETs induced by MSU crystals could inhibit osteoblasts viability and enhance the activity of osteoclasts.

Single-cell RNA-seq reveals interferon-induced guanylate-binding proteins are linked with sarcopenia

BACKGROUND

Sarcopenia is defined as an age-related progressive loss of muscle mass and/or strength. Although different factors can contribute to this disease, the underlying mechanisms remain unclear. We assessed transcriptional heterogeneity in skeletal muscles from sarcopenic and control mice at single-cell resolution.

METHODS

A mouse model was established to study sarcopenic skeletal muscles. Single-cell RNA-seq was performed on tibialis anterior (TA) muscle cells collected from sarcopenic and control mice. A series of bioinformatic analyses were carried out to identify and compare different cell types under different conditions. Immunofluorescence staining and western blotting were used to validate the findings from single-cell experiments. Tube formation assays were conducted to further evaluate the effects of Gbp2 on endothelial cells during angiogenesis.

RESULTS

A murine sarcopenia model was successfully established using a senescence-accelerated mouse strain (SAMP6, n = 5). Sarcopenia phenotype was induced by administration of dexamethasone (20 mg/kg) and reduced physical activity. Senescence-resistant mice strain (SAMR1) and SAMP6 strain with similar activity but injected with PBS were recruited as two control groups. As signs of sarcopenia, body weight, muscle cell counts and cross-sectional fibre area were all significantly decreased in sarcopenic mice (P value = 0.004, 0.03 and 0.035, respectively). After quality control, 13 612 TA muscle single-cell transcriptomes were retained for analysis. Fourteen cell clusters were identified from the profiled cells. Among them, two distinct endothelial subtypes were found to be dominant in the sarcopenia group (42.2% cells) and in the two control groups (59.1% and 47.9% cells), respectively. 191 differentially expressed genes were detected between the two endothelial subtypes. Sarcopenia-specific endothelial cell subtype exhibited a dramatic increase in the interferon family genes and the interferon-inducible guanylate-binding protein (GBP) family gene expressions. For example, Igtp and Gbp2 in sarcopenic endothelial cells were 5.4 and 13.3 times higher than those in the control groups, respectively. We further validated our findings in muscle specimens of sarcopenia patients and observed that GBP2 levels were increased in endothelial cells of a subset of patients (11 of 40 patients, 27.5%), and we identified significantly higher CD31 and GBP2 co-localization (P value = 0.001128). Finally, we overexpressed Gbp2 in human umbilical vein endothelial cells in vitro. The endothelial cells with elevated Gbp2 expression displayed compromised tube formation.

CONCLUSIONS

Our single-cell-based results suggested that endothelial cells may play critical roles in sarcopenia development through interferon-GBP signalling pathways, highlighting new therapeutic directions to slow down or even reverse age-related sarcopenia.

Immune mechanism of low bone mineral density caused by ankylosing spondylitis based on bioinformatics and machine learning

Background and Objective: This study aims to find the key immune genes and mechanisms of low bone mineral density (LBMD) in ankylosing spondylitis (AS) patients. Methods: AS and LBMD datasets were downloaded from the GEO database, and differential expression gene analysis was performed to obtain DEGs. Immune-related genes (IRGs) were obtained from ImmPort. Overlapping DEGs and IRGs got I-DEGs. Pearson coefficients were used to calculate DEGs and IRGs correlations in the AS and LBMD datasets. Louvain community discovery was used to cluster the co-expression network to get gene modules. The module most related to the immune module was defined as the key module. Metascape was used for enrichment analysis of key modules. Further, I-DEGs with the same trend in AS and LBMD were considered key I-DEGs. Multiple machine learning methods were used to construct diagnostic models based on key I-DEGs. IID database was used to find the context of I-DEGs, especially in the skeletal system. Gene-biological process and gene-pathway networks were constructed based on key I-DEGs. In addition, immune infiltration was analyzed on the AS dataset using the CIBERSORT algorithm. Results: A total of 19 genes were identified I-DEGs, of which IFNAR1, PIK3CG, PTGER2, TNF, and CCL3 were considered the key I-DEGs. These key I-DEGs had a good relationship with the hub genes of key modules. Multiple machine learning showed that key I-DEGs, as a signature, had an excellent diagnostic performance in both AS and LBMD, and the SVM model had the highest AUC value. Key I-DEGs were closely linked through bridge genes, especially in the skeletal system. Pathway analysis showed that PIK3CG, IFNAR1, CCL3, and TNF participated in NETs formation through pathways such as the MAPK signaling pathway. Immune infiltration analysis showed neutrophils had the most significant differences between case and control groups and a good correlation with key I-DEG. Conclusion: The key I-DEGs, TNF, CCL3, PIK3CG, PTGER2, and IFNAR1, can be utilized as biomarkers to determine the risk of LBMD in AS patients. They may affect neutrophil infiltration and NETs formation to influence the bone remodeling process in AS.

IFN-β mediates the anti-osteoclastic effect of bisphosphonates and dexamethasone

Zoledronic acid (Zol) is a potent bisphosphonate that inhibits the differentiation of monocytes into osteoclasts. It is often used in combination with dexamethasone (Dex), a glucocorticoid that promotes the resolution of inflammation, to treat malignant diseases, such as multiple myeloma. This treatment can result in bone pathologies, namely medication related osteonecrosis of the jaw, with a poor understanding of the molecular mechanism on monocyte differentiation. IFN-β is a pro-resolving cytokine well-known as an osteoclast differentiation inhibitor. Here, we explored whether Zol and/or Dex regulate macrophage osteoclastic differentiation via IFN-β. RAW 264.7 and peritoneal macrophages were treated with Zol and/or Dex for 4-24 h, and IFN-β secretion was examined by ELISA, while the IFN stimulated gene (ISG) 15 expression was evaluated by Western blotting. RANKL-induced osteoclastogenesis of RAW 264.7 cells was determined by TRAP staining following treatment with Zol+Dex or IFN-β and anti-IFN-β antibodies. We found only the combination of Zol and Dex increased IFN-β secretion by RAW 264.7 macrophages at 4 h and, correspondingly, ISG15 expression in these cells at 24 h. Moreover, Zol+Dex blocked osteoclast differentiation to a similar extent as recombinant IFN-β. Neutralizing anti-IFN-β antibodies reversed the effect of Zol+Dex on ISG15 expression and partially recovered osteoclastic differentiation induced by each drug alone or in combination. Finally, we found Zol+Dex also induced IFN-β expression in peritoneal resolution phase macrophages, suggesting these drugs might be used to enhance the resolution of acute inflammation. Altogether, our findings suggest Zol+Dex block the differentiation of osteoclasts through the expression of IFN-β. Revealing the molecular pathway behind this regulation may lead to the development of IFN-β-based therapy to inhibit osteoclastogenesis in multiple myeloma patients.

Erythropoietin Receptor (EPOR) Signaling in the Osteoclast Lineage Contributes to EPO-Induced Bone Loss in Mice

Erythropoietin (EPO) is a pleiotropic cytokine that classically drives erythropoiesis but can also induce bone loss by decreasing bone formation and increasing resorption. Deletion of the EPO receptor (EPOR) on osteoblasts or B cells partially mitigates the skeletal effects of EPO, thereby implicating a contribution by EPOR on other cell lineages. This study was designed to define the role of monocyte EPOR in EPO-mediated bone loss, by using two mouse lines with conditional deletion of EPOR in the monocytic lineage. Low-dose EPO attenuated the reduction in bone volume (BV/TV) in Cx3cr1^Cre EPOR^f/f female mice (27.05%) compared to controls (39.26%), but the difference was not statistically significant. To validate these findings, we increased the EPO dose in LysM^Cre model mice, a model more commonly used to target preosteoclasts. There was a significant reduction in both the increase in the proportion of bone marrow preosteoclasts (CD115⁺) observed following high-dose EPO administration and the resulting bone loss in LysM^Cre EPOR^f/f female mice (44.46% reduction in BV/TV) as compared to controls (77.28%), without interference with the erythropoietic activity. Our data suggest that EPOR in the monocytic lineage is at least partially responsible for driving the effect of EPO on bone mass.

Therapeutic potential of dietary flavonoid hyperoside against non-communicable diseases: targeting underlying properties of diseases

Non-communicable diseases (NCDs) are a global epidemic with diverse pathogenesis. Among them, oxidative stress and inflammation are the most fundamental co-morbid features. Therefore, multi-targets and multi-pathways therapies with significant anti-oxidant and anti-inflammatory activities are potential effective measures for preventing and treating NCDs. The flavonol glycoside compound hyperoside (Hyp) is widely found in a variety of fruits, vegetables, beverages, and medicinal plants and has various health benefits, especially excellent anti-oxidant and anti-inflammatory properties targeting nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF-κB) signaling pathways. In this review, we summarize the pathogenesis associated with oxidative stress and inflammation in NCDs and the biological activity and therapeutic potential of Hyp. Our findings reveal that the anti-oxidant and anti-inflammatory activities regulated by Hyp are associated with numerous biological mechanisms, including positive regulation of mitochondrial function, apoptosis, autophagy, and higher-level biological damage activities. Hyp is thought to be beneficial against organ injuries, cancer, depression, diabetes, and osteoporosis, and is a potent anti-NCDs agent. Additionally, the sources, bioavailability, pharmacy, and safety of Hyp have been established, highlighting the potential to develop Hyp into dietary supplements and nutraceuticals.

Alpinetin ameliorates bone loss in LPS-induced inflammation osteolysis via ROS mediated P38/PI3K signaling pathway

BACKGROUND AND OBJECTIVE

Bone loss occurs in several inflammatory diseases because of chronic persistent inflammation that activates osteoclasts (OCs) to increase bone resorption. Currently available antiresorptive drugs have severe side effects or contraindications. Herein, we explored the effects and mechanism of Alpinetin (Alp) on receptor activator of nuclear factor κB ligand (RANKL)-mediated OCs differentiation, function, and in inflammatory osteolysis of mice.

METHOD

Primary mouse bone marrow-derived macrophages (BMMs) induced by RANKL and macrophage colony-stimulating factor (M-CSF) were utilized to test the impact of Alp on OCs differentiation, function, and intracellular reactive oxygen species (ROS) production, respectively. Expression of oxidant stress relevant factors and OCs specific genes were assessed via real-time quantitative PCR. Further, oxidative stress-related factors, NF-κB, MAPK, PI3K/AKT/GSK3-β, and NFATc1 pathways were examined via Western blot. Finally, LPS-induced mouse calvarial osteolysis was used to investigate the effect of Alp on inflammatory osteolysis in vivo.

RESULT

Alp suppressed OCs differentiation and resorption function, and down-regulated the ROS production. Alp inhibited IL-1β, TNF-α and osteoclast-specific gene transcription. It also blocked the gene and protein expression of Nox1 and Keap1, but enhanced Nrf2, CAT, and HO-1 protein levels. Additionally, Alp suppressed the phosphorylation of PI3K and P38, and restrained the expression of osteoclast-specific gene Nfatc1 and its auto-amplification, hence minimizing LPS-induced osteolysis in mice.

CONCLUSION

Alp is a novel candidate or therapeutics for the osteoclast-associated inflammatory osteolytic ailment.

Dynamic changes in O-GlcNAcylation regulate osteoclast differentiation and bone loss via nucleoporin 153

Bone mass is maintained by the balance between osteoclast-induced bone resorption and osteoblast-triggered bone formation. In inflammatory arthritis such as rheumatoid arthritis (RA), however, increased osteoclast differentiation and activity skew this balance resulting in progressive bone loss. O-GlcNAcylation is a posttranslational modification with attachment of a single O-linked β-D-N-acetylglucosamine (O-GlcNAc) residue to serine or threonine residues of target proteins. Although O-GlcNAcylation is one of the most common protein modifications, its role in bone homeostasis has not been systematically investigated. We demonstrate that dynamic changes in O-GlcNAcylation are required for osteoclastogenesis. Increased O-GlcNAcylation promotes osteoclast differentiation during the early stages, whereas its downregulation is required for osteoclast maturation. At the molecular level, O-GlcNAcylation affects several pathways including oxidative phosphorylation and cell-cell fusion. TNFα fosters the dynamic regulation of O-GlcNAcylation to promote osteoclastogenesis in inflammatory arthritis. Targeted pharmaceutical or genetic inhibition of O-GlcNAc transferase (OGT) or O-GlcNAcase (OGA) arrests osteoclast differentiation during early stages of differentiation and during later maturation, respectively, and ameliorates bone loss in experimental arthritis. Knockdown of NUP153, an O-GlcNAcylation target, has similar effects as OGT inhibition and inhibits osteoclastogenesis. These findings highlight an important role of O-GlcNAcylation in osteoclastogenesis and may offer the potential to therapeutically interfere with pathologic bone resorption.

Mechanisms of bone remodeling and therapeutic strategies in chronic apical periodontitis

Chronic periapical periodontitis (CAP) is a typical oral disease in which periodontal inflammation caused by an odontogenic infection eventually leads to bone loss. Uncontrolled infections often lead to extensive bone loss around the root tip, which ultimately leads to tooth loss. The main clinical issue in the treatment of periapical periodontitis is the repair of jawbone defects, and infection control is the first priority. However, the oral cavity is an open environment, and the distribution of microorganisms through the mouth in jawbone defects is inevitable. The subversion of host cell metabolism by oral microorganisms initiates disease. The presence of microorganisms stimulates a series of immune responses, which in turn stimulates bone healing. Given the above background, we intended to examine the paradoxes and connections between microorganisms and jaw defect repair in anticipation of new ideas for jaw defect repair. To this end, we reviewed the microbial factors, human signaling pathways, immune cells, and cytokines involved in the development of CAP, as well as concentrated growth factor (CGF) and stem cells in bone defect repair, with the aim of understanding the impact of microbial factors on host cell metabolism to inform the etiology and clinical management of CAP.

Monocyte-Macrophage Lineage Cell Fusion

Cell fusion (fusogenesis) occurs in natural and pathological conditions in prokaryotes and eukaryotes. Cells of monocyte–macrophage lineage are highly fusogenic. They create syncytial multinucleated giant cells (MGCs) such as osteoclasts (OCs), MGCs associated with the areas of infection/inflammation, and foreign body-induced giant cells (FBGCs). The fusion of monocytes/macrophages with tumor cells may promote cancer metastasis. We describe types and examples of monocyte–macrophage lineage cell fusion and the role of actin-based structures in cell fusion.

Microarray analysis of lipopolysaccharide-induced endotoxemia in the cochlea

Lipopolysaccharide (LPS)-induced endotoxemia alters intracochlear homeostasis and potentiates aminoglycoside-induced ototoxicity. However, the pathological mechanisms in the cochlea following systemic LPS-induced inflammation are unclear. In this study, three groups of mice received intraperitoneal injections [group A, saline control (n = 10); group B, 1 mg/kg LPS (n = 10); group C, 10 mg/kg LPS (n = 10)]. After 24 h, gene expression in cochlea samples was analyzed using DNA microarrays covering 28,853 genes in a duplicate manner. A total of 505 differentially expressed genes (DEGs) (≥2.0-fold change; p < 0.05) were identified. Interferon- and chemotaxis-related genes, including gbp2, gbp5, cxcl10, and Rnf125, were dose-dependently upregulated by LPS-induced endotoxemia. These results were verified by RT-qPCR. Upregulated DEGs were associated with inflammation, positive regulation of immune responses, and regulation of cell adhesion, while downregulated ones were associated with chemical synaptic transmission and the synaptic vesicle cycle. Protein-protein interaction included four functional clusters associated with interleukin-4, -10, and -13 and G protein-coupled receptor (GPCR) ligand binding; activation of matrix metalloproteinases and collagen degradation; recruitment of amyloid A proteins; and neutrophil degranulation. The findings of this study provide an additional basis on changes in the expression of genes in the cochlea in response to LPS-induced endotoxemia.

Naringenin is a Potential Anabolic Treatment for Bone Loss by Modulating Osteogenesis, Osteoclastogenesis, and Macrophage Polarization

Bone undergoes constant remodeling of formation by osteoblasts and resorption by osteoclasts. In particular, macrophages have been reported to play an essential role in the regulation of bone homeostasis and regeneration. Naringenin, the predominant flavanone in citrus fruits, is reported to exert anti-inflammatory, anti-osteoclastic, and osteogenic effects. However, whether naringenin could modulate the crosstalk between macrophages and osteoblasts/osteoclasts remains to be investigated. In this study, we confirmed that naringenin enhanced osteogenesis and inhibited osteoclastogenesis directly. Naringenin promoted M2 transition and the secretion of osteogenic cytokines including IL-4, IL-10, BMP2, and TGF-β, while suppressing LPS-induced M1 polarization and the production of proinflammatory factors such as TNF-α and IL-1β. In addition, the coculture of primary bone mesenchymal stem cells (BMSCs)/bone marrow monocytes (BMMs) with macrophages showed that the naringenin-treated medium significantly enhanced osteogenic differentiation and impeded osteoclastic differentiation in both inflammatory and non-inflammatory environment. Moreover, in vivo experiments demonstrated that naringenin remarkably reversed LPS-induced bone loss and assisted the healing of calvarial defect. Taken together, naringenin serves as a potential anabolic treatment for pathological bone loss.

Toxoplasma gondii infection as a risk factor for osteoporosis: a case-control study

Background

More than one-third of the total world population is infected by Toxoplasma gondii (T. gondii). T. gondii has been linked to various diseases, such as cancer, mental disorders, type 2 diabetes mellitus (T2DM), etc. However, the effects of T. gondii infection on the risk of osteoporosis are unclear. Our study aimed to uncover evidence to determine whether patients exposed to T. gondii have an increased or decreased risk of osteoporosis in people with abnormal bone mineral density (BMD) by using case–control study.

Methods

A total of 729 patients, including 316 osteopenia and 413 osteoporosis patients of Han Chinese ancestry were selected in the study. Their blood samples were collected and the levels of specific IgG antibodies against T. gondii were measured using ELISA assay. We obtained some information about the patients from the medical record that included demographic indexes and clinical data. A logistic regression analysis was used to evaluate the effects of T. gondii infection on femur osteoporosis, lumbar osteoporosis and compound osteoporosis. Potential interaction was analyzed using multifactor dimensionality reduction software 1.0.0 (MDR 1.0.0).

Results

113 positive patients with T. gondii infections have been detected, including 80 cases of osteoporosis and 33 cases of osteopenia, the infection rates of T. gondii were 19.37% (80/413) and 10.44% (33/316), respectively. The patients with T.gondii infections were at a 2.60 times higher risk of suffering from compound osteoporosis than those without T. gondii infections (OR = 2.60, 95% CI 1.54–4.39, P < 0.001), but not associated with femur osteoporosis (OR = 1.01, 95% CI 0.43–2.34, P = 0.989) and lumbar osteoporosis (OR = 0.84, 95% CI 0.34–2.07, P = 0.705) after adjusting for the covariates. Moreover, a significantly higher risk of compound osteoporosis in the individuals with all two factors (T. gondii infection, Female) was observed compared with reference group (without T. gondii infection, male) under the interaction model (OR = 11.44, 95%CI = 5.44–24.05, P < 0.001). And the individuals with all two factors (T. gondii infection, over 70 years) exhibited a 8.14-fold higher possibility of developing compound osteoporosis compared with reference group (without T. gondii infection, under 70 years) (OR = 8.14, 95% CI 3.91–16.93, P < 0.001). We further stratified by age and sex, and found that women with T. gondii infection was more likely to develop compound osteoporosis than those without infection(OR = 3.12, 95% CI  1.67–5.81, P < 0.001), but we not found the association between T. gondii infection and compound osteoporosis in males (OR = 1.36, 95% CI 0.37–4.94, P = 0.645).

Conclusions

T. gondii infection is a risk factor for osteoporosis, especially compound osteoporosis. Meanwhile, it is very necessary for patients with osteoporosis to further diagnose and treat T. gondii infection, especially women.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05257-z.

Construction of a magnesium hydroxide/graphene oxide/hydroxyapatite composite coating on Mg–Ca–Zn–Ag alloy to inhibit bacterial infection and promote bone regeneration

The improved corrosion resistance, osteogenic activity, and antibacterial ability are the key factors for promoting the large-scale clinical application of magnesium (Mg)-based implants. In the present study, a novel nanocomposite coating composed of inner magnesium hydroxide, middle graphene oxide, and outer hydroxyapatite (Mg(OH)₂/GO/HA) is constructed on the surface of Mg-0.8Ca–5Zn-1.5Ag by a combined strategy of hydrothermal treatment, electrophoretic deposition, and electrochemical deposition. The results of material characterization and electrochemical corrosion test showed that all the three coatings have high bonding strength, hydrophilicity and corrosion resistance. In vitro studies show that Mg(OH)₂ indeed improves the antibacterial activity of the substrate. The next GO and GO/HA coating procedures both promote the osteogenic differentiation of MC3T3-E1 cells and show no harm to the antibacterial activity of Mg(OH)₂ coating, but the latter exhibits the best promoting effect. In vivo studies demonstrate that the Mg alloy with the composite coating not only ameliorates osteolysis induced by bacterial invasion but also promotes bone regeneration under both normal and infected conditions. The current study provides a promising surface modification strategy for developing multifunctional Mg-based implants with good corrosion resistance, antibacterial ability and osteogenic activity to enlarge their biomedical applications.

•

A Mg(OH)₂/GO/HA composite coating with high bonding strength was constructed on the surface of Mg–Ca–Zn–Ag alloy.

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The outer HA layer with excellent osteogenic activity recovered the high corrosion resistance of inner Mg(OH)₂ layer.

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The Mg(OH)₂/GO/HA composite coating promoted new bone regeneration significantly under both normal and infected conditions.

The Rising Era of “Immunoporosis”: Role of Immune System in the Pathophysiology of Osteoporosis

Discoveries in the last few years have emphasized the existence of an enormous breadth of communication between bone and the immune system in maintaining skeletal homeostasis. Originally, the discovery of various factors was assigned to the immune system viz. interleukin (IL)-6, IL-10, IL-17, tumor necrosis factor (TNF)-α, receptor activator of nuclear factor kappa B ligand (RANKL), nuclear factor of activated T cells (NFATc1), etc., but now these factors have also been shown to have a significant impact on osteoblasts (OBs) and osteoclasts (OCs) biology. These discoveries led to an alteration in the approach for the treatment of several bone pathologies including osteoporosis. Osteoporosis is an inflammatory bone anomaly affecting more than 500 million people globally. In 2018, to highlight the importance of the immune system in the pathophysiology of osteoporosis, our group coined the term “immunoporosis”. In the present review, we exhaustively revisit the characteristics, mechanism of action, and function of both innate and adaptive immune cells with the goal of understanding the potential of immune cells in osteoporosis. We also highlight the Immunoporotic role of gut microbiota (GM) for the treatment and management of osteoporosis. Importantly, we further discuss whether an immune cell-based strategy to treat and manage osteoporosis is feasible and relevant in clinical settings.

A Nitrobenzoyl Sesquiterpenoid Insulicolide A Prevents Osteoclast Formation via Suppressing c-Fos-NFATc1 Signaling Pathway

It is a viable strategy to inhibit osteoclast differentiation for the treatment of osteolytic diseases such as osteoporosis, rheumatoid arthritis and tumor bone metastases. Here we assessed the effects of insulicolide A, a natural nitrobenzoyl sesquiterpenoid derived from marine fungus, on receptor activator of nuclear factor-κB ligand (RANKL)-stimulated osteoclastogenesis in vitro and its protective effects on LPS-induced osteolysis mice model in vivo. The results demonstrated that insulicolide A inhibited osteoclastogenesis from 1 μM in vitro. Insulicolide A could prevent c-Fos and nuclear factor of activated T-cell cytoplasmic 1 (NFATc1) nuclear translocation and attenuate the expression levels of osteoclast-related genes and DC-STAMP during RANKL-stimulated osteoclastogenesis but have no effects on NF-κB and MAPKs. Insulicolide A can also protect the mice from LPS-induced osteolysis. Our research provides the first evidence that insulicolide A may inhibit osteoclastogenesis both in vitro and in vivo, and indicates that it may have potential for the treatment of osteoclast-related diseases.

Interplay between Inflammation and Pathological Bone Resorption: Insights into Recent Mechanisms and Pathways in Related Diseases for Future Perspectives

Bone is a mineralized and elastic connective tissue that provides fundamental functions in the human body, including mechanical support to the muscles and joints, protection of vital organs and storage of minerals. Bone is a metabolically active organ that undergoes continuous remodeling processes to maintain its architecture, shape, and function throughout life. One of the most important medical discoveries of recent decades has been that the immune system is involved in bone remodeling. Indeed, chronic inflammation has been recognized as the most significant factor influencing bone homeostasis, causing a shift in the bone remodeling process toward pathological bone resorption. Bone osteolytic diseases typified by excessive bone resorption account for one of the greatest causes of disability worldwide, with significant economic and public health burdens. From this perspective, we discuss the recent findings and discoveries highlighting the cellular and molecular mechanisms that regulate this process in the bone microenvironment, in addition to the current therapeutic strategies for the treatment of osteolytic bone diseases.

Cardiotrophin Like Cytokine Factor 1 (CLCF1) alleviates bone loss in osteoporosis mouse models by suppressing osteoclast differentiation through activating interferon signaling and repressing the nuclear factor-κB signaling pathway

A growing body of evidence suggests that immune factors that regulate osteoclast differentiation and bone resorption might be promising therapeutic agents for the treatment of osteoporosis. The expression of CLCF1, an immune cell-derived molecule, has been reported to be reduced in patients with postmenopausal osteoporosis. This suggests that it may be involved in bone remodeling. Thus, we explored the functional role of CLCF1 in osteoclastogenesis and bone loss associated with osteoporosis. Surprisingly, the administration of recombinant CLCF1 repressed excessive bone loss in ovariectomized mice and prevented RANKL-induced bone loss in calvarial mouse model. Likewise, the addition of recombinant CLCF1 to RANKL-stimulated monocytes resulted in a significant suppression in the number of differentiated osteoclasts with small resorption areas being observed on dentine slices in vitro. At the same dosage, CLCF1 did not exhibit any detectable negative effects on the differentiation of osteoblasts. Mechanistically, the inhibition of osteoclast differentiation by the CLCF1 treatment appears to be related to the activation of interferon signaling (IFN) and the suppression of the NF-κB signaling pathway. Interestingly, the expression of the main components of IFN-signaling namely, STAT1 and IRF1, was detected in macrophages as early as 1 h after stimulation with CLCF1. Consistent with these results, the blockade of STAT1 in macrophages abolished the inhibitory effect of CLCF1 on osteoclast differentiation in vitro. These collective findings point to a novel immunoregulatory function of CLCF1 in bone remodeling and highlight it as a potentially useful therapeutic agent for the treatment of osteoporosis.

Oroxylin A reduces osteoclast formation and bone resorption via suppressing RANKL-induced ROS and NFATc1 activation

Excessive bone erosion by osteoclasts is associated with osteoporosis, rheumatoid arthritis, and periprosthetic osteolysis. Targeting osteoclasts may serve as an effective treatment for osteolytic diseases. Although drugs are currently available for the treatment of these diseases, exploring potential anti-osteoclast natural compounds with safe and effective treatment remains needed. Oroxylin A (OA), a natural flavonoid isolated from the root of Scutellaria baicalensis Georgi, has numerous beneficial pharmacological characteristics, including anti-inflammatory and antioxidant activity. However, its effects and mechanisms on osteoclast formation and bone resorption have not yet been clarified. Our research showed that OA attenuated the formation and function of osteoclast induced by RANKL in a time- and concentration-dependent manner without any cytotoxicity. Mechanistically, OA suppressed intracellular reactive oxygen species (ROS) levels through the Nrf2-mediated antioxidant response. Moreover, OA inhibited the activity of NFATc1, the master transcriptional regulator of RANKL-induced osteoclastogenesis. OA exhibited protective effects in mouse models of post-ovariectomy (OVX)- and lipopolysaccharide (LPS)-induced bone loss, in accordance with its in vitro anti-osteoclastogenic effect. Collectively, our findings highlight the potential of OA as a pharmacological agent for the prevention of osteoclast-mediated osteolytic diseases.

Sites of Cre-recombinase activity in mouse lines targeting skeletal cells

The Cre/Lox system is a powerful tool in the biologist's toolbox, allowing loss-of-function and gain-of-function studies, as well as lineage tracing, through gene recombination in a tissue-specific and inducible manner. Evidence indicates, however, that Cre transgenic lines have a far more nuanced and broader pattern of Cre activity than initially thought, exhibiting "off-target" activity in tissues/cells other than the ones they were originally designed to target. With the goal of facilitating the comparison and selection of optimal Cre lines to be used for the study of gene function, we have summarized in a single manuscript the major sites and timing of Cre activity of the main Cre lines available to target bone mesenchymal stem cells, chondrocytes, osteoblasts, osteocytes, tenocytes, and osteoclasts, along with their reported sites of "off-target" Cre activity. We also discuss characteristics, advantages, and limitations of these Cre lines for users to avoid common risks related to overinterpretation or misinterpretation based on the assumption of strict cell-type specificity or unaccounted effect of the Cre transgene or Cre inducers. © 2021 American Society for Bone and Mineral Research (ASBMR).