Knockdown of TNFR1 Suppresses Expression of TLR2 in the Cellular Response to Staphylococcus aureus Infection

Intracellular Staphylococcus aureus in osteoblasts and osteocytes and its impact on bone homeostasis during osteomyelitis

Osteomyelitis is a severe infection of bone tissue that can lead to bone loss and even osteonecrosis. This condition is mostly caused by Gram-positive bacteria, with Staphylococcus aureus being the most common etiological agent. Among the pathophysiological mechanisms involved in osteomyelitis, the ability of S. aureus to be internalized by osteoblasts or osteocytes and to survive within these cells, is particularly noteworthy. Infected osteoblasts and osteocytes not only serve as reservoirs in chronic cases of osteomyelitis but also play an active role in the osteoimmunology process, notably by producing mediators that promote the bone resorption activity of osteoclasts, thereby disrupting bone homeostasis. The present review explores both historical and recent literature on the internalization of S. aureus by osteoblasts and osteocytes, its intracellular behavior following internalization, and its mechanisms for inducing cell death. Additionally, it examines how S. aureus affects bone formation activity and promotes the production of inflammatory and pro-osteoclastic mediators. This review aims to highlight the limitations of current findings and outline key questions for future investigations.

Artificial Bone Materials for Infected Bone Defects: Advances in Antimicrobial Functions

Infected bone defects, caused by bacterial contamination following disease or injury, result in the partial loss or destruction of bone tissue. Traditional bone transplantation and other clinical approaches often fail to address the therapeutic complexities of these conditions effectively. In recent years, advanced biomaterials have attracted significant attention for their potential to enhance treatment outcomes. This review explores the pathogenic mechanisms underlying infected bone defects, including biofilm formation and bacterial internalization into bone cells, which allow bacteria to evade the host immune system. To control bacterial infection and facilitate bone repair, we focus on antibacterial materials for bone regeneration. A detailed introduction is given on intrinsically antibacterial materials (e.g., metal alloys, oxide materials, carbon-based materials, hydroxyapatite, chitosan, and Sericin). The antibacterial functionality of bone repair materials can be enhanced through strategies such as the incorporation of antimicrobial ions, surface modification, and the combined use of multiple materials to treat infected bone defects. Key innovations discussed include biomaterials that release therapeutic agents, functional contact biomaterials, and bioresponsive materials, which collectively enhance antibacterial efficacy. Research on the clinical translation of antimicrobial bone materials has also facilitated their practical application in infection prevention and bone healing. In conclusion, advancements in biomaterials provide promising pathways for developing more biocompatible, effective, and personalized therapies to reconstruct infected bone defects.

A review of bacterial and osteoclast differentiation in bone infection

Bone infections are characterized by bacterial invasion of the bone microenvironment and subsequent bone structure deterioration. This holds significance because osteoclasts, which are the only cells responsible for bone resorption, are abnormally stimulated during bone infections. Multiple communication factors secreted by bone stromal cells regulate the membrane of osteoclast progenitor cells, thereby maintaining bone homeostasis through the expression of many types of receptors. During infection, the immunoinflammatory response triggered by bacterial invasion and multiple virulence factors of bacterial origin can disrupt osteoclast homeostasis. Therefore, clarifying the pathways through which bacteria affect osteoclasts can offer a theoretical basis for preventing and treating bone infections. This review summarizes studies investigating bone destruction caused by different bacterial infections. In conclusion, bacteria can affect osteoclast metabolic activity through multiple pathways, including direct contact, release of virulence factors, induction of immunoinflammatory responses, influence on bone stromal cell metabolism, and intracellular infections.

Cell-wall-anchored proteins affect invasive host colonization and biofilm formation in Staphylococcus aureus

As a major human and animal pathogen, Staphylococcus aureus can attach to medical implants (abiotic surface) or host tissues (biotic surface), and further establish robust biofilms which enhances resistance and persistence to host immune system and antibiotics. Cell-wall-anchored proteins (CWAPs) covalently link to peptidoglycan, and largely facilitate the colonization of S. aureus on various surfaces (including adhesion and biofilm formation) and invasion into host cells (including adhesion, immune evasion, iron acquisition and biofilm formation). During biofilm formation, CWAPs function in adhesion, aggregation, collagen-like fiber network formation, and consortia formation. In this review, we firstly focus on the structural features of CWAPs, including their intracellular function and interactions with host cells, as well as the functions and ligand binding of CWAPs in different stages of S. aureus biofilm formation. Then, the roles of CWAPs in different biofilm processes with regards in development of therapeutic approaches are clarified, followed by the association between CWAPs genes and clonal lineages. By touching upon these aspects, we hope to provide comprehensive knowledge and clearer understanding on the CWAPs of S. aureus and their roles in biofilm formation, which may further aid in prevention and treatment infection and vaccine development.

Myricetin exerts anti-biofilm activity and attenuates osteomyelitis by inhibiting the TLR2/MAPK pathway in experimental mice

AIMS

To evaluate the potential of Myricetin against S.aureus induced osteomyelitis.

BACKGROUND

Osteomyelitis is infected condition of bone by micro-organisms. The mitogen-activated protein kinase (MAPK), inflammatory cytokines and Toll-like receptor-2 (TLR-2) pathway are mainly involved in osteomyelitis. Myricetin is a plant-food derived flavonoid which shows anti-inflammatory activity.

OBJECTIVE

In the present study, we evaluated the potential of Myricetin against S.aureus induced osteomyelitis. MC3T3-E1 cells were used for in vitro studies.

METHOD

Murine model of osteomyelitis was developed in BALB/c mice by injecting S.aureus in the medullary cavity of the femur. The mice were studied for bone destruction, anti-biofilm activity, osteoblast growth markers alkaline phosphatase (ALP), osteopontin (OCN) and collagen type-I (COLL-1) were studied by RT-PCR, ELISA analysis for levels of proinflammatory factors CRP, IL-6 and IL-1β. Expression of proteins by Western blot analysis and anti-biofilm effect by Sytox green dye fluorescence assay. Target confirmation was done by performing in silico docking analysis.

RESULTS

Myricetin reduced bone destruction in osteomyelitis induced mice. The treatment decreased bone levels of ALP, OCN, COLL-1 and TLR2. Myricetin decreased serum levels of CRP, IL-6 and IL-1β. The treatment suppressed activation of MAPK pathway and showed anti-biofilm effect. Docking studies suggested high binding affinity of Myricetin with MAPK protein in silico, by showing lower binding energies.

CONCLUSION

Myricetin suppresses osteomyelitis by inhibiting ALP, OCN, COLL-1 via the TLR2 and MAPK pathway involving inhibition of biofilm formation. In silico studies suggested MAPK as potential binding protein for myricetin.

Macrophage migration inhibitory factor (MIF) inhibitor iSO-1 promotes staphylococcal protein A-induced osteogenic differentiation by inhibiting NF-κB signaling pathway

BACKGROUND

Osteomyelitis is among the most difficult to treat diseases in the field of orthopedics, and there is a lack of effective treatment modalities. Exploring the mechanisms of its development is beneficial for finding molecular targets for treatment. Increasing evidence suggests that macrophage migration inhibitory factor (MIF), as a proinflammatory mediator, is not only involved in various pathophysiological processes of inflammation but also plays an important role in osteogenic differentiation, while its specific regulatory mechanism in osteomyelitis remains unclear.

METHODS

In the present study, staphylococcal protein A (SPA)-treated rat bone marrow mesenchymal stem cells (rBMSCs) were used to construct cell models of osteomyelitis. Rat and cell models of osteomyelitis were used to validate the expression levels of MIF, and to further explore the regulatory mechanisms of the MIF inhibitor methyl ester of (S, R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid (iSO-1) and MIF knockdown on cell model of osteomyelitis toward osteogenic differentiation.

RESULTS

We found that the expression level of MIF was upregulated in rat and cell models of osteomyelitis and subsequently demonstrated by the GSE30119 dataset that the expression level of MIF was also significantly upregulated in patients with osteomyelitis. Furthermore, SPA promotes MIF expression in rBMSCs while inhibiting the expression of osteogenic-related genes such as Runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), osteopontin (OPN) and collagen type-1 (COL-1) through activation of the nuclear factor kappa-B (NF-κB) pathway. In vivo, we further demonstrated that local injection of iSO-1 significantly increased the osteogenic activity in rat model of osteomyelitis. Importantly, we also demonstrated that MIF knockdown and the MIF inhibitor iSO-1 reversed the SPA-mediated inhibition of osteogenic differentiation of rBMSCs by inhibiting the activation of the NF-κB pathway, as evidenced by the upregulation of osteogenic-related gene expression and enhanced bone mineralization.

CONCLUSION

ISO-1 and MIF knockdown can reverse the SPA-mediated inhibition of osteogenic differentiation in the rBMSCs model of osteomyelitis by inhibiting the NF-κB signaling pathway, providing a potential target for the treatment of osteomyelitis.

Electroactive Biomaterials for Facilitating Bone Defect Repair under Pathological Conditions

Bone degeneration associated with various diseases is increasing due to rapid aging, sedentary lifestyles, and unhealthy diets. Living bone tissue has bioelectric properties critical to bone remodeling, and bone degeneration under various pathological conditions results in significant changes to these bioelectric properties. There is growing interest in utilizing biomimetic electroactive biomaterials that recapitulate the natural electrophysiological microenvironment of healthy bone tissue to promote bone repair. This review first summarizes the etiology of degenerative bone conditions associated with various diseases such as type II diabetes, osteoporosis, periodontitis, osteoarthritis, rheumatoid arthritis, osteomyelitis, and metastatic osteolysis. Next, the diverse array of natural and synthetic electroactive biomaterials with therapeutic potential are discussed. Putative mechanistic pathways by which electroactive biomaterials can mitigate bone degeneration are critically examined, including the enhancement of osteogenesis and angiogenesis, suppression of inflammation and osteoclastogenesis, as well as their anti-bacterial effects. Finally, the limited research on utilization of electroactive biomaterials in the treatment of bone degeneration associated with the aforementioned diseases are examined. Previous studies have mostly focused on using electroactive biomaterials to treat bone traumatic injuries. It is hoped that this review will encourage more research efforts on the use of electroactive biomaterials for treating degenerative bone conditions.

The osteoblast secretome in Staphylococcus aureus osteomyelitis

Osteomyelitis (OM) is an infectious disease of the bone predominantly caused by the opportunistic bacterium Staphylococcus aureus (S. aureus). Typically established upon hematogenous spread of the pathogen to the musculoskeletal system or contamination of the bone after fracture or surgery, osteomyelitis has a complex pathogenesis with a critical involvement of both osteal and immune components. Colonization of the bone by S. aureus is traditionally proposed to induce functional inhibition and/or apoptosis of osteoblasts, alteration of the RANKL/OPG ratio in the bone microenvironment and activation of osteoclasts; all together, these events locally subvert tissue homeostasis causing pathological bone loss. However, this paradigm has been challenged in recent years, in fact osteoblasts are emerging as active players in the induction and orientation of the immune reaction that mounts in the bone during an infection. The interaction with immune cells has been mostly ascribed to osteoblast-derived soluble mediators that add on and synergize with those contributed by professional immune cells. In this respect, several preclinical and clinical observations indicate that osteomyelitis is accompanied by alterations in the local and (sometimes) systemic levels of both pro-inflammatory (e.g., IL-6, IL-1α, TNF-α, IL-1β) and anti-inflammatory (e.g., TGF-β1) cytokines. Here we revisit the role of osteoblasts in bacterial OM, with a focus on their secretome and its crosstalk with cellular and molecular components of the bone microenvironment and immune system.

Role of the Interaction of Tumor Necrosis Factor-α and Tumor Necrosis Factor Receptors 1 and 2 in Bone-Related Cells

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine expressed by macrophages, monocytes, and T cells, and its expression is triggered by the immune system in response to pathogens and their products, such as endotoxins. TNF-α plays an important role in host defense by inducing inflammatory reactions such as phagocytes and cytocidal systems activation. TNF-α also plays an important role in bone metabolism and is associated with inflammatory bone diseases. TNF-α binds to two cell surface receptors, the 55kDa TNF receptor-1 (TNFR1) and the 75kDa TNF receptor-2 (TNFR2). Bone is in a constant state of turnover; it is continuously degraded and built via the process of bone remodeling, which results from the regulated balance between bone-resorbing osteoclasts, bone-forming osteoblasts, and the mechanosensory cell type osteocytes. Precise interactions between these cells maintain skeletal homeostasis. Studies have shown that TNF-α affects bone-related cells via TNFRs. Signaling through either receptor results in different outcomes in different cell types as well as in the same cell type. This review summarizes and discusses current research on the TNF-α and TNFR interaction and its role in bone-related cells.

Mangiferin Inhibits Apoptosis and Autophagy Induced by Staphylococcus aureus in RAW264.7 Cells

Purpose

Staphylococcus aureus (S. aureus) is an important bacterial pathogen, which creates infective inflammation to human being and animals. Mangiferin (MG) is one of the natural flavonoids with anti-inflammatory, anti-bacterial, and anti-oxidative properties. However, the anti-apoptosis and anti-autophagy of MG are unknown. Hence, this study was aimed to research the inhibition of MG on S. aureus-induced apoptosis and autophagy in RAW264.7 cells.

Methods

The RAW264.7 cells were pretreated with MG, or pretreated with SP600125 or anisomycin synchronously, and then infected with S. aureus (MOI=100:1). The viability and proliferation status of RAW264.7 cells were detected by MTT and EdU assay. The relative expression of TNF-α, IL-6 and IL-10 protein was tested with ELISA. The levels of Bax, Bcl-2, caspase-3, c-Jun N-terminal kinase (JNK), extracellular-regulated protein kinase (ERK), p38, LC3, Beclin-1, p62, phosphorylated JNK, phosphorylated p38 and phosphorylated ERK in cells were detected by Western blotting. The apoptosis rate of RAW264.7 cells was analyzed by flow cytometric assay.

Results

The study showed that MG significantly attenuated RAW264.7 cells apoptosis and autophagy caused by S. aureus. MG alleviated S. aureus-induced apoptosis by down-regulating the protein level of active caspase-3 and Bax and up-regulating the level of Bcl-2. MG also inhibited S. aureus-induced autophagy via decreasing the protein level of LC3-II/LC3-I and Beclin-1 or increasing the protein expression of p62. This protective role was dependent on the up-regulation of JNK signal pathway, which was confirmed by using JNK agonist and inhibitor.

Conclusion

Our results demonstrated that MG might protect RAW264.7 cells from S. aureus-induced apoptosis and autophagy via inhibiting JNK/Bax-dependent signal pathway. Therefore, MG may be a potential agent against pathological cell damage induced by S. aureus infection.

Clitoria ternatea flower petals: Effect on TNFR1 neutralization via downregulation of synovial matrix metalloproteases

ETHNOPHARMACOLOGICAL RELEVANCE

Clitoria ternatea Linn. (C. ternatea) is a traditionally used herb in arthritis, and its anti-arthritic activity has been attributed to polyphenols (e.g. quercetins) from its flower petal.

AIM OF THE STUDY

The present study was designed to investigate whether C. ternatea or quercetin-3ß-D-glucoside (QG) support the antibody mediated TNFα-receptor 1 (TNFR1) neutralization to ameliorate arthritis in mice.

MATERIALS AND METHODS

Development of collagen-induced arthritis (CIA) in male Swiss mice (20-22g, 3-4 weeks of age) was followed by estimation of synovial polymorphonuclear cell (PMN) accumulation (in terms of myeloperoxidase activity), synovial and systemic release of cytokines, chemokines and C-reactive protein (CRP) by enzyme-linked immunosorbent assay (ELISA), biochemical estimation of synovial free radical generation and antioxidant status, as well as immunoblot assessment of synovial TNFR1, toll-like receptor 2(TLR2), cyclooxygenase-2(COX-2) and inducible nitric oxide synthase (iNOS) expression; and zymographic analysis of synovial matrix-metalloprotease-2 (MMP-2) activity.

RESULTS

CIA was induced from day 2 post-secondary immunizations as evidenced from arthritic scores and joint swelling in parallel to increased inflammatory and oxidative stress parameters in synovial joints. Long term supplementation with extract from Clitoria ternatea flower petals CTE (50mg/kg) and QG (2.5mg/kg) upto 24 days post booster immunization augmented anti-arthritic potential of TNFR1 neutralization with anti-TNFR1 antibody (10μg per mice) in terms of reduced MPO activity, decrease in release of pro-inflammatory cytokines, chemokines, reactive oxygen species (ROS)/ reactive nitrogen species (RNS) production in parallel to significant (p<0.05) reduction in TNFR1, TLR2, iNOS, COX-2 and MMP-2 expression.

CONCLUSION

CTE and QG possess potential anti-arthritic activity which targets synovial MMP-2 in arthritic joints and TNFR1 targeting followed by CTE or QG treatment might become a combinatorial approach in future therapeutic research in treatment of arthritis.

Adipogenic miR-27a in adipose tissue upregulates macrophage activation via inhibiting PPARγ of insulin resistance induced by high-fat diet-associated obesity

Chronic low degree inflammation caused by macrophage activation is a crucial factor underlying insulin resistance induced by obesity. To illustrate the mechanism of regulating of macrophage activation in adipose tissue, the role of adipogenic miR-27a activating M1 macrophage polarization via blocking PPARγ was evaluated. Obese mice model and miR-27a overexpression or knockdown mice model were established and related biochemical index were examined. Raw264.7 and 3T3-L1 were cultured and co-cultured for mimicking the microenvironment of local inflammation. Macrophage infiltration was observed. MiR-27a and cytokines levels in serum and adipose tissue were measured. Macrophage polarization markers and protein expression in insulin or inflammatory signaling pathways were observed. Impaired glucose tolerance and insulin tolerance was observed in 4w, 8w and 12w of high fat diet and miR-27a overexpression mice. Concurrently, miR-27a was increased in serum in a time-dependent manner, along with M1 cytokines and M1 macrophages increasing in adipose tissue clearly. Insulin signaling pathway was blocked, and PPARγ was suppressed. However, NF-κB was activated. On the other hand, activated macrophages and hypertrophic adipocytes induced by miR-27a could increase the ratio of Raw264.7 migration, including improving cytokines generation, and blocking PPARγ expression markedly. The present studies are conducted to clarify that miR-27a has increased along with up-regulation in the process of proinflammatory cytokines generation, macrophage influx and M1 macrophage polarization in obesity. These indicate that miR-27a gives the novel target of intervention for inflammation and insulin resistance in obesity.

Identification and Characterization of Staphylococcus aureus Strains with an Incomplete Hemolytic Phenotype

Staphylococcus aureus is a common pathogen causing both hospital and community-acquired infections. Hemolysin is one of the important virulence factors for S. aureus and causes the typical β-hemolytic phenotype which is called complete hemolytic phenotype as well. Recently, S. aureus with an incomplete hemolytic phenotype (SIHP) was isolated from clinical samples. To study the microbiologic characteristics of SIHP, the special hemolytic phenotype of SIHP was verified on the sheep blood agar plates supplied by different manufacturers. Expression of hemolysin genes hla, hlb, hlgC, and hld of SIHP was detected by qRT-PCR and it was showed that expression of hlb in SIHP was obviously increased compared to the control S. aureus strains with complete hemolytic phenotype (SCHP), while the expression of hla, hlgC, and hld in SIHP was significantly decreased. In addition, the α-hemolysin encoded by gene hla was decreased obviously in SIHP compared to SCHP by western blot. All 60 SIHP strains were identified to be the methicillin resistant S. aureus (MRSA), and moreover these SIHP strains all contains mecA gene. The virulence gene tst were all present in SIHP, and the intracellular survival ability of SIHP was much greater than that of the gene tst negative S. aureus. We also found that IL-2, IL-6, and IL-17A secreted in the supernatant of SIHP infected macrophages increased significantly compared to tst negative control strains infected ones. MLST analysis showed that all of SIHP strains were classified into ST5 clone. To our knowledge, this study firstly showed that SIHP strains are a kind of methicillin resistant strains which express β-hemolysin highly and possess a potential high virulence, and it was suggested that SIHP should be paid more attention in hospital.