Regulation of Bone Cell Differentiation and Activation by Microbe-Associated Molecular Patterns

Lactobacillus rhamnosus inhibits osteoclast differentiation by suppressing the TLR2/NF-κB pathway

OBJECTIVE

This study aimed to investigate the role of ultrasonicated Lactobacillus rhamnosus extract in osteoclast differentiation and its underlying mechanism, providing new strategies for the treatment of periodontitis.

MATERIALS AND METHODS

Osteoclasts were induced using macrophage colony-stimulating factor and receptor activator for nuclear factor-κB ligand. Lactobacillus rhamnosus extracts were obtained via ultrasonic crushing and ultracentrifugation. The effects of the LGG extract on osteoclast differentiation were evaluated, and the related signaling pathways were examined using western blotting. A mouse periodontitis model was established, and Lactobacillus rhamnosus extract was injected into the gingival sulcus to evaluate the inhibitory effect of Lactobacillus rhamnosus extract on alveolar bone resorption.

RESULTS

At 50 μg/mL, Lactobacillus rhamnosus extract inhibited osteoclast differentiation with no effect on apoptosis and proliferation. This phenomenon was achieved by deactivating the NF-κB/c-Fos/NFATc1 signaling pathway through toll-like receptor 2. The in vivo results showed that the local injection of Lactobacillus rhamnosus extract suppressed osteoclast differentiation and alveolar bone resorption.

CONCLUSION

The ultrasonicated extract of Lactobacillus rhamnosus inhibited osteoclast differentiation by suppressing the activation of the NF-κB/c-Fos/NFATc1 pathway. Furthermore, it inhibited the destruction of the alveolar bone, providing a new strategy for the use of probiotics in the treatment of periodontitis.

Inducing cyclooxygenase-2 expression, prostaglandin E2 and prostaglandin F2α production of human dental pulp cells by activation of toll-like receptor-3, mitogen-activated protein kinase kinase/extracellular signal-regulated kinase and p38 signaling

Background/purpose

Bacterial infection was the major etiology for pulpal/root canal infection. This study aimed to investigate the activation of toll-like receptor-3 (TLR) on cyclooxygenase-2 (COX-2) expression and prostaglandin E2 (PGE2) and PGF2α production of human dental pulp cells (HDPCs) and associated signaling.

Materials and methods

HDPCs were exposed to different concentrations of Poly (I:C) (a TLR3 activator). Cell viability was determined by 3- (4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay and alkaline phosphatase (ALP) activity was evaluated by ALP staining. Activation of extracellular signal-regulated kinase (ERK) and p38 by Poly (I:C) was determined by immunofluorescent staining. The COX-2 protein expression was analyzed by Western blot. PGE2 and PGF2α production was measured by enzyme-linked immunosorbent assay. The mRNA expression was studied by real-time polymerase-chain reaction. Moreover, HDPCs were exposed to Poly(I:C) with/without U0126 or SB203580 treatment and analysis of COX-2 expression and prostanoid production were conducted.

Results

Poly (I:C) showed little effect on ALP activity, but decreased viability of HDPCs. It stimulated COX-2 mRNA and protein expression. Poly (I:C) induced PGE2 and PGF2α production of HDPCs. Poly (I:C) activated p-ERK, and p-p38 protein expression. Treatment by U0126 (a mitogen-activated protein kinase kinase (MEK)/ERK inhibitor) and SB203580 (a p38 inhibitor) attenuated Poly (I:C)-induced COX-2 mRNA and protein expression as well as PGE2 and PGF2α production.

Conclusion

TLR3 activation is involved in the infection and inflammatory responses of pulp tissues, via MEK/ERK, and p38 signaling to mediate COX-2 expression as well as PGE2 and PGF2α production, contributing to the pathogenesis and progression of pulpal/periapical diseases.

IL-23/IL-17 axis levels in gingival crevicular fluid of subjects with periodontal disease: a systematic review

BACKGROUND

The IL-23/IL-17 axis plays an important role in the immunopathogenesis of periodontal disease. A systematic review was conducted to synthesize all research reporting on the levels of the IL-23/IL-17 axis in gingival crevicular fluid (GCF) from subjects with gingivits, and periodontitis, compared to healthy controls.

METHODS

The protocol followed the PRISMA, and Cochrane guidelines, and was registered with the Open Science Framework (OSF): https://doi.org/10.17605/OSF.IO/7495V . A search was conducted in the electronic databases PubMed/MEDLINE, Scopus, Google Schoolar, and Cochrane from November 15th, 2005, to May 10th, 2023. The quality of the studies was assessed using the JBI tool for cross-sectional studies.

RESULTS

The search strategy provided a total of 2,098 articles, of which 12 investigations met the inclusion criteria. The total number of patients studied was 537, of which 337 represented the case group (subjects with gingivitis, and chronic periodontitis), and 200 represented the control group (periodontally healthy subjects). The ages of the patients ranged from 20 to 50 years, with a mean (SD) of 36,6 ± 4,2, of which 47% were men, and 53% were women. 75% of the investigations collected GCF samples with absorbent paper strips, and analyzed cytokine IL-17 levels individually. In addition, qualitative analysis revealed that there are differences between IL-23/IL-17 axis levels in subjects with chronic periodontitis, gingivitis and healthy controls.

CONCLUSIONS

Thus, IL-23/IL-17 axis levels could be used in the future as a diagnostic tool to distinguish between periodontal diseases.

The impact of arthritogenic viruses in oral tissues

Arthritis and periodontitis are inflammatory diseases that share several immunopathogenic features. The expansion in the study of virus-induced arthritis has shed light on how this condition could impact other parts of the human body, including the mouth. Viral arthritis is an inflammatory joint disease caused by several viruses, most notably the alphaviruses Chikungunya virus (CHIKV), Sindbis virus (SINV), Ross River virus (RRV), Mayaro virus (MAYV), and O'nyong'nyong virus (ONNV). These viruses can induce an upsurge of matrix metalloproteinases and immune-inflammatory mediators such as Interleukin-6 (IL6), IL-1β, tumor necrosis factor, chemokine ligand 2, and receptor activator of nuclear factor kappa-B ligand in the joint and serum of infected individuals. This can lead to the influx of inflammatory cells to the joints and associated muscles as well as osteoclast activation and differentiation, culminating in clinical signs of swelling, pain, and bone resorption. Moreover, several data indicate that these viral infections can affect other sites of the body, including the mouth. The human oral cavity is a rich and diverse microbial ecosystem, and viral infection can disrupt the balance of microbial species, causing local dysbiosis. Such events can result in oral mucosal damage and gingival bleeding, which are indicative of periodontitis. Additionally, infection by RRV, CHIKV, SINV, MAYV, or ONNV can trigger the formation of osteoclasts and upregulate pro-osteoclastogenic inflammatory mediators, interfering with osteoclast activation. As a result, these viruses may be linked to systemic conditions, including oral manifestations. Therefore, this review focuses on the involvement of alphavirus infections in joint and oral health, acting as potential agents associated with oral mucosal inflammation and alveolar bone loss. The findings of this review demonstrate how alphavirus infections could be linked to the comorbidity between arthritis and periodontitis and may provide a better understanding of potential therapeutic management for both conditions.

Repair of Infected Bone Defects with Hydrogel Materials

Infected bone defects represent a common clinical condition involving bone tissue, often necessitating surgical intervention and antibiotic therapy. However, conventional treatment methods face obstacles such as antibiotic resistance and susceptibility to postoperative infections. Hydrogels show great potential for application in the field of tissue engineering due to their advantageous biocompatibility, unique mechanical properties, exceptional processability, and degradability. Recent interest has surged in employing hydrogels as a novel therapeutic intervention for infected bone repair. This article aims to comprehensively review the existing literature on the anti-microbial and osteogenic approaches utilized by hydrogels in repairing infected bones, encompassing their fabrication techniques, biocompatibility, antimicrobial efficacy, and biological activities. Additionally, the potential opportunities and obstacles in their practical implementation will be explored. Lastly, the limitations presently encountered and the prospective avenues for further investigation in the realm of hydrogel materials for the management of infected bone defects will be deliberated. This review provides a theoretical foundation and advanced design strategies for the application of hydrogel materials in the treatment of infected bone defects.

Increased local bone turnover in patients with chronic periprosthetic joint infection

Aims

The management of periprosthetic joint infection (PJI) remains a major challenge in orthopaedic surgery. In this study, we aimed to characterize the local bone microstructure and metabolism in a clinical cohort of patients with chronic PJI.

Methods

Periprosthetic femoral trabecular bone specimens were obtained from patients suffering from chronic PJI of the hip and knee (n = 20). Microbiological analysis was performed on preoperative joint aspirates and tissue specimens obtained during revision surgery. Microstructural and cellular bone parameters were analyzed in bone specimens by histomorphometry on undecalcified sections complemented by tartrate-resistant acid phosphatase immunohistochemistry. Data were compared with control specimens obtained during primary arthroplasty (n = 20) and aseptic revision (n = 20).

Results

PJI specimens exhibited a higher bone volume, thickened trabeculae, and increased osteoid parameters compared to both control groups, suggesting an accelerated bone turnover with sclerotic microstructure. On the cellular level, osteoblast and osteoclast parameters were markedly increased in the PJI cohort. Furthermore, a positive association between serum (CRP) but not synovial (white blood cell (WBC) count) inflammatory markers and osteoclast indices could be detected. Comparison between different pathogens revealed increased osteoclastic bone resorption parameters without a concomitant increase in osteoblasts in bone specimens from patients with Staphylococcus aureus infection, compared to those with detection of Staphylococcus epidermidis and Cutibacterium spp.

Conclusion

This study provides insights into the local bone metabolism in chronic PJI, demonstrating osteosclerosis with high bone turnover. The fact that Staphylococcus aureus was associated with distinctly increased osteoclast indices strongly suggests early surgical treatment to prevent periprosthetic bone alterations.

Tripterygium hypoglaucum extract ameliorates adjuvant-induced arthritis in mice through the gut microbiota

Traditionally, Tripterygium hypoglaucum (Levl.) Hutch (THH) are widely used in Chinese folk to treat rheumatoid arthritis (RA). This study aimed to investigate whether the anti-RA effect of THH is related with the gut microbiota. The main components of prepared THH extract were identified by HPLC-MS. C57BL/6 mice with adjuvant-induced arthritis (AIA) were treated with THH extract by gavage for one month. THH extract significantly alleviated swollen ankle, joint cavity exudation, and articular cartilage destruction in AIA mice. The mRNA and protein levels of inflammatory mediators in muscles and plasma indicated that THH extract attenuated inflammatory responses in the joint by blocking TLR4/MyD88/MAPK signaling pathways. THH extract remarkably restored the dysbiosis of the gut microbiota in AIA mice, featuring the increases of Bifidobacterium, Akkermansia, and Lactobacillus and the decreases of Butyricimonas, Parabacteroides, and Anaeroplasma. Furthermore, the altered bacteria were closely correlated with physiological indices and drove metabolic changes of the intestinal microbiota. In addition, antibiotic-induced pseudo germ-free mice were employed to verify the role of the intestinal flora. Strikingly, THH treatment failed to ameliorate the arthritis symptoms and signaling pathways in pseudo germ-free mice, which validates the indispensable role of the intestinal flora. For the first time, we demonstrated that THH extract protects joint inflammation by manipulating the intestinal flora and regulating the TLR4/MyD88/MAPK signaling pathway. Therefore, THH extract may serve as a microbial modulator to recover RA in clincial practice.ver RA in clincial practice.

Lipoteichoic acid inhibits osteoclast differentiation and bone resorption via interruption of gelsolin-actin dissociation

Bone resorption can be caused by excessive differentiation and/or activation of bone-resorbing osteoclasts. While microbe-associated molecular patterns can influence the differentiation and activation of bone cells, little is known about the role of lipoteichoic acid (LTA), a major cell wall component of Gram-positive bacteria, in the regulation of bone metabolism. In this study, we investigated the effect of LTA on bone metabolism using wild-type Staphylococcus aureus and the LTA-deficient mutant strain. LTA-deficient S. aureus induced higher bone loss and osteoclast differentiation than wild-type S. aureus. LTA isolated from S. aureus (SaLTA) inhibited osteoclast differentiation from committed osteoclast precursors in the presence of various osteoclastogenic factors by downregulating the expression of NFATc1. Remarkably, SaLTA attenuated the osteoclast differentiation from committed osteoclast precursors of TLR2-/- or MyD88-/- mice and from the committed osteoclast precursors transfected with paired immunoglobulin-like receptor B-targeting siRNA. SaLTA directly interacted with gelsolin, interrupting the gelsolin-actin dissociation which is a critical process for osteoclastogenesis. Moreover, SaLTA suppressed the mRNA expression of dendritic cell-specific transmembrane protein, ATPase H+ transporting V0 subunit D2, and Integrin, which encode proteins involved in cell-cell fusion of osteoclasts. Notably, LTAs purified from probiotics, including Bacillus subtilis, Enterococcus faecalis, and Lactobacillus species, also suppressed Pam2CSK4- or RANKL-induced osteoclast differentiation. Taken together, these results suggest that LTAs have anti-resorptive activity through the inhibition of osteoclastogenesis by interfering with the gelsolin-actin dissociation and may be used as effective therapeutic agents for the prevention or treatment of inflammatory bone diseases.

Unveiling the Osteogenic Potential of Tetracyclines: A Comparative Study in Human Mesenchymal Stem Cells

Tetracyclines (TCs) are a class of broad-spectrum antibiotics with diverse pharmacotherapeutic properties due to their various functional groups being attached to a common core structure. Beyond their antibacterial activity, TCs trigger pleiotropic effects on eukaryotic cells, including anti-inflammatory and potentially osteogenic capabilities. Consequently, TCs hold promise for repurposing in various clinical applications, including bone-related conditions. This study presents the first comprehensive comparison of the in vitro osteogenic potential of four TCs-tetracycline, doxycycline, minocycline, and sarecycline, within human mesenchymal stem cells. Cultures were characterized for metabolic activity, cell morphology and cytoskeleton organization, osteogenic gene expression, alkaline phosphatase (ALP) activity, and the activation of relevant signaling pathways. TCs stimulated actin remodeling processes, inducing morphological shifts consistent with osteogenic differentiation. Osteogenic gene expression and ALP activity supported the osteoinduction by TCs, demonstrating significant increases in ALP levels and the upregulation of RUNX2, SP7, and SPARC genes. Minocycline and sarecycline exhibited the most potent osteogenic induction, comparable to conventional osteogenic inducers. Signaling pathway analysis revealed that tetracycline and doxycycline activate the Wnt pathway, while minocycline and sarecycline upregulated Hedgehog signaling. Overall, the present findings suggest that TCs promote osteogenic differentiation through distinct pathways, making them promising candidates for targeted therapy in specific bone-related disorders.

Anti-osteoporotic drugs affect the pathogenesis of gut microbiota and its metabolites: a clinical study

Background

Disordered gut microbiota (GM) structure and function may contribute to osteoporosis (OP). This study explores how traditional Chinese medicine (TCM) intervention affects the structure and function of the GM in patients with OP.

Method

In a 3-month clinical study, 43 patients were randomly divided into two groups receiving conventional treatment and combined TCM (Yigu decoction, YGD) treatment. The correlation between the intestinal flora and its metabolites was analyzed using 16S rDNA and untargeted metabolomics and the combination of the two.

Results

After three months of treatment, patients in the treatment group had better bone mineral density (BMD) than those in the control group (P < 0.05). Patients in the treatment group had obvious abundance changes in GM microbes, such as Bacteroides, Escherichia-Shigella, Faecalibacterium, Megamonas, Blautia, Klebsiella, Romboutsia, Akkermansia, and Prevotella_9. The functional changes observed in the GM mainly involved changes in metabolic function, genetic information processing and cellular processes. The metabolites for which major changes were observed were capsazepine, Phe-Tyr, dichlorprop, D-pyroglutamic acid and tamsulosin. These metabolites may act through metabolic pathways, the citrate cycle (TCA cycle) and beta alanine metabolism. Combined analysis showed that the main acting metabolites were dichlorprop, capsazepine, D-pyroglutamic acid and tamsulosin.

Conclusion

This study showed that TCM influenced the structure and function of the GM in patients with OP, which may be one mechanism by which TCM promotes the rehabilitation of patients with OP through the GM.

Identification of molecular subgroups in osteomyelitis induced by staphylococcus aureus infection through gene expression profiles

BACKGROUND

Staphylococcus aureus (S. aureus) infection-induced osteomyelitis (OM) is an inflammatory bone disease accompanied by persistent bone destruction, and the treatment is challenging because of its tendency to recur. Present study was aimed to explore the molecular subgroups of S. aureus infection-induced OM and to deepen the mechanistic understanding for molecularly targeted treatment of OM.

METHODS

Integration of 164 OM samples and 60 healthy samples from three datasets of the Gene Expression Omnibus (GEO) database. OM patients were classified into different molecular subgroups based on unsupervised algorithms and correlations of clinical characteristics between subgroups were analyzed. Next, The CIBERSORT algorithm was used to evaluate the proportion of immune cell infiltration in different OM subgroups. Weighted gene co-expression analysis (WGCNA) was used to identify different gene modules and explore the relationship with clinical characteristics, and further annotated OM subgroups and gene modules by the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis.

RESULTS

Two subgroups with excellent consistency were identified in this study, subgroup and hospital length of stay were independent predictors of OM. Compared with subgroup I, OM patients in subgroup II had longer hospital length of stay and more severe disease. Meanwhile, the infiltration proportions of monocytes and macrophages M0 were higher in patients of OM subgroup II. Finally, combined with the characteristics of the KEGG enrichment modules, the expression of osteoclast differentiation-related genes such as CTSK was upregulated in OM subgroup II, which may be closely associated with more severe OM patients.

CONCLUSION

The current study showed that OM subgroup II had longer hospital length of stay and more severe disease, the osteoclast differentiation pathway and the main target CTSK contribute to our deeper understanding for the molecular mechanisms associated with S. aureus infection-induced OM, and the construction of molecular subgroups suggested the necessity for different subgroups of patients to receive individualized treatment.

B. abortus Infection Promotes an Imbalance in the Adipocyte–Osteoblast Crosstalk Favoring Bone Resorption

Osteoarticular injury is the most common presentation of active brucellosis in humans. Osteoblasts and adipocytes originate from mesenchymal stem cells (MSC). Since those osteoblasts are bone-forming cells, the predilection of MSC to differentiate into adipocytes or osteoblasts is a potential factor involved in bone loss. In addition, osteoblasts and adipocytes can be converted into each other according to the surrounding microenvironment. Here, we study the incumbency of B. abortus infection in the crosstalk between adipocytes and osteoblasts during differentiation from its precursors. Our results indicate that soluble mediators present in culture supernatants from B. abotus-infected adipocytes inhibit osteoblast mineral matrix deposition in a mechanism dependent on the presence of IL-6 with the concomitant reduction of Runt-related transcription factor 2 (RUNX-2) transcription, but without altering organic matrix deposition and inducing nuclear receptor activator ligand kβ (RANKL) expression. Secondly, B. abortus-infected osteoblasts stimulate adipocyte differentiation with the induction of peroxisome proliferator-activated receptor γ (PPAR-γ) and CCAAT enhancer binding protein β (C/EBP-β). We conclude that adipocyte–osteoblast crosstalk during B. abortus infection could modulate mutual differentiation from its precursor cells, contributing to bone resorption.

Metabolic switching and cell wall remodelling of Mycobacterium tuberculosis during bone tuberculosis

OBJECTIVES

Bone tuberculosis (TB) is the third most common types of extrapulmonary tuberculosis. It is critical to understand mycobacterial adaptive strategies within bone lesions to identify mycobacterial factors that may have role in disease pathogenesis.

METHODS

Whole genome microarray was used to characterize the in-vivo transcriptome of Mycobacterium tuberculosis (M.tb) within bone TB specimens. Mycobacterial virulent proteins were identified by bioinformatic software. An in vitro osteoblast cell line model was used to study the role of these proteins in bone TB pathogenesis.

RESULTS

914 mycobacterial genes were significantly overexpressed and 1688 were repressed in bone TB specimens. Pathway analysis of differentially expressed genes demonstrated a non-replicative and hypometabolic state of M.tb, reinforcement of the mycobacterial cell wall and induction of DNA damage repair responses, suggesting possible survival strategies of M.tb within bone. Bioinformatics mining of microarray data led to identification of five virulence proteins. The genes encoding these proteins were also upregulated in the in vitro MC3T3 osteoblast cell line model of bone TB. Further, exposure of osteoblast cells to two of these virulence proteins (Rv1046c and Rv3663c) significantly inhibited osteoblast differentiation.

CONCLUSION

M.tb alters its transcriptome to establish infection in bone by upregulating certain virulence genes which play a key role in disturbing bone homeostasis.

Effect of Bifidobacterium on osteoclasts: TNF-α/NF-κB inflammatory signal pathway-mediated mechanism

Osteoporosis is a systemic multifactorial bone disease characterized by low bone quality and density and bone microstructure damage, increasing bone fragility and fracture vulnerability. Increased osteoclast differentiation and activity are important factors contributing to bone loss, which is a common pathological manifestation of bone diseases such as osteoporosis. TNF-a/NF-κB is an inflammatory signaling pathway with a key regulatory role in regulating osteoclast formation, and the classical pathway RANKL/RANK/OPG assists osteoclast formation. Activation of this inflammatory pathway promotes the formation of osteoclasts and accelerates the process of osteoporosis. Recent studies and emerging evidence have consistently demonstrated the potential of probiotics to modulate bone health. Secretions of Bifidobacterium, a genus of probiotic bacteria in the phylum Actinobacteria, such as short-chain fatty acids, equol, and exopolysaccharides, have indicated beneficial effects on bone health. This review discusses the molecular mechanisms of the TNF-a/NF-κB inflammatory pathway in regulating osteoclast formation and describes the secretions produced by Bifidobacterium and their potential effects on bone health through this pathway, opening up new directions for future research.

Characterization of Fecal Microbiomes of Osteoporotic Patients in Korea

An imbalanced gut microbiome has been linked to a higher risk of many bone-related diseases. The objective of this study was to discover biomarkers of osteoporosis (OP). So, we collected 76 stool samples (60 human controls and 16 OP patients), extracted DNA, and performed 16S ribosomal ribonucleic acid (rRNA) gene-based amplicon sequencing. Among the taxa with an average taxonomic composition greater than 1%, only the Lachnospira genus showed a significant difference between the two groups. The Linear Discriminant Effect Size analysis and qPCR experiments indicated the Lachnospira genus as a potential biomarker of OP. Moreover, a total of 11 metabolic pathways varied between the two groups. Our study concludes that the genus Lachnospira is potentially crucial for diagnosing and treating osteoporosis. The findings of this study might help researchers better understand OP from a microbiome perspective. This research might develop more effective diagnostic and treatment methods for OP in the future.

The Human Gut Microbiota: A Key Mediator of Osteoporosis and Osteogenesis

An expanding body of research asserts that the gut microbiota has a role in bone metabolism and the pathogenesis of osteoporosis. This review considers the human gut microbiota composition and its role in osteoclastogenesis and the bone healing process, specifically in the case of osteoporosis. Although the natural physiologic processes of bone healing and the pathogenesis of osteoporosis and bone disease are now relatively well known, recent literature suggests that a healthy microbiome is tied to bone homeostasis. Nevertheless, the mechanism underlying this connection is still somewhat enigmatic. Based on the literature, a relationship between the microbiome, osteoblasts, osteoclasts, and receptor activator of nuclear factor-kappa-Β ligand (RANKL) is contemplated and explored in this review. Studies have proposed various mechanisms of gut microbiome interaction with osteoclastogenesis and bone health, including micro-RNA, insulin-like growth factor 1, and immune system mediation. However, alterations to the gut microbiome secondary to pharmaceutical and surgical interventions cannot be discounted and are discussed in the context of clinical therapeutic consideration. The literature on probiotics and their mechanisms of action is examined in the context of bone healing. The known and hypothesized interactions of common osteoporosis drugs and the human gut microbiome are examined. Since dysbiosis in the gut microbiota can function as a biomarker of bone metabolic activity, it may also be a pharmacological and nutraceutical (i.e., pre- and probiotics) therapeutic target to promote bone homeostasis.