IgG immune complexes with Staphylococcus aureus protein A enhance osteoclast differentiation and bone resorption by stimulating Fc receptors and TLR2

Non-infectious immune complexes downregulate the production of interferons and tumor necrosis factor-α in primary porcine alveolar macrophages in vitro

Porcine reproductive and respiratory syndrome (PRRS) caused by the PRRS virus (PRRSV) has been harming the pig industry worldwide for nearly 40 years. Although scientific researchers have made substantial efforts to explore PRRSV pathogenesis, the immune factors influencing PRRSV infection still need to be better understood. Infectious virus-antibody immune complexes (ICs) formed by PRRSV and sub-or non-neutralizing antibodies specific for PRRSV may significantly promote the development of PRRS by enhancing PRRSV replication through antibody-dependent enhancement. However, nothing is known about whether PRRSV infection is affected by non-infectious ICs (NICs) formed by non-pathogenic/infectious antigens and corresponding specific antibodies. Here, we found that PRRSV significantly induced the transcripts and proteins of interferon-α (IFN-α), IFN-β, IFN-γ, IFN-λ1, and tumor necrosis factor-α (TNF-α) in vitro primary porcine alveolar macrophages (PAMs) in the early stage of infection. Our results showed that NICs formed by rabbit-negative IgG (RNI) and pig anti-RNI specific IgG significantly reduced the transcripts and proteins of IFN-α, IFN-β, IFN-γ, IFN-λ1, and TNF-α in vitro PAMs and significantly elevated the transcripts and proteins of interleukine-10 (IL-10) and transforming growth factor-β1 (TGF-β1) in vitro PAMs. NICs-mediated PRRSV infection showed that NICs not only significantly decreased the induction of IFN-α, IFN-β, IFN-γ, IFN-λ1, and TNF-α by PRRSV but also significantly increased the induction of IL-10 and TGF-β1 by PRRSV and considerably enhanced PRRSV replication in vitro PAMs. Our data suggested that NICs could downregulate the production of antiviral cytokines (IFN-α/β/γ/λ1 and TNF-α) during PRRSV infection in vitro and facilitated PRRSV proliferation in its host cells by inhibiting innate antiviral immune response. This study elucidated one novel immune response to PRRSV infection, which would enhance our understanding of the pathogenesis of PRRSV.

Essential role of local antibody distribution in mediating bone-resorbing effects

The link between antibodies and bone mass is debated. Activated IgG, which interacts directly with Fc gamma receptors, stimulates osteoclastogenesis in vitro, and local injection in immune-activated mice leads to bone loss. Multiple myeloma patients with high serum IgG levels have induced osteoclast activation and display bone loss. In addition, bone loss has been linked to serum autoantibodies in autoimmune diseases, including anti-citrullinated protein antibodies (ACPA) in individuals with rheumatoid arthritis (RA). Whether serum IgG or autoantibodies regulate bone mass under healthy conditions is poorly studied. In elderly men, neither serum levels of polyclonal IgG nor autoantibody were associated with areal bone mineral density in the MrOS Sweden study. Repetitive systemic injections of high-dose polyclonal IgG complexes in mice did not exert any discernible impact on bone mineral density. However, repetitive local intra-articular injection of the same IgG complexes led to a localized reduction of trabecular bone density. These results indicate antibodies may only impact bone density when close to the bone, such as within the synovial joint.

Toll-like Receptor 2 Mediated Immune Regulation in Simian Immunodeficiency Virus-Infected Rhesus Macaques

Toll-like receptors (TLRs) are crucial to the innate immune response. They regulate inflammatory reactions by initiating the production of pro-inflammatory cytokines and chemokines. TLRs also play a role in shaping the adaptive immune responses. While this protective response is important for eliminating infectious pathogens, persistent activation of TLRs may result in chronic immune activation, leading to detrimental effects. The role of TLR2 in regulating HIV-1 infection in vivo has yet to be well described. In this study, we used an SIV-infected rhesus macaque model to simulate HIV infection in humans. We evaluated the plasma of the macaques longitudinally and found a significant increase in the soluble TLR2 (sTLR2) level after SIV infection. We also observed an increase in membrane-bound TLR2 (mb-TLR2) in cytotoxic T cells, B cells, and NK cells in PBMC and NK cells in the gut after infection. Our results suggest that sTLR2 regulates the production of various cytokines and chemokines, including IL-18, IL-1RA, IL-15, IL-13, IL-9, TPO, FLT3L, and IL-17F, as well as chemokines, including IP-10, MCP-1, MCP-2, ENA-78, GRO-α, I-TAC, Fractalkine, SDF-1α, and MIP-3α. Interestingly, these cytokines and chemokines were also upregulated after the infection. The positive correlation between SIV copy number and sTLR2 in the plasma indicated the involvement of TLR2 in the regulation of viral replication. These cytokines and chemokines could directly or indirectly regulate viral replication through the TLR2 signaling pathways. When we stimulated PBMC with the TLR2 agonist in vitro, we observed a direct induction of various cytokines and chemokines. Some of these cytokines and chemokines, such as IL-1RA, IL-9, IL-15, GRO-α, and ENA-78, were positively correlated with sTLR2 in vivo, highlighting the direct involvement of TLR2 in the regulation of the production of these factors. Our findings suggest that TLR2 expression may be a target for developing new therapeutic strategies to combat HIV infection.

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.

In Silico Genome-Scale Analysis of Molecular Mechanisms Contributing to the Development of a Persistent Infection with Methicillin-Resistant Staphylococcus aureus (MRSA) ST239

The increasing frequency of isolation of methicillin-resistant Staphylococcus aureus (MRSA) limits the chances for the effective antibacterial therapy of staphylococcal diseases and results in the development of persistent infection such as bacteremia and osteomyelitis. The aim of this study was to identify features of the MRSA_ST239 0943-1505-2016 (SA943) genome that contribute to the formation of both acute and chronic musculoskeletal infections. The analysis was performed using comparative genomics data of the dominant epidemic S. aureus lineages, namely ST1, ST8, ST30, ST36, and ST239. The SA943 genome encodes proteins that provide resistance to the host's immune system, suppress immunological memory, and form biofilms. The molecular mechanisms of adaptation responsible for the development of persistent infection were as follows: amino acid substitution in PBP2 and PBP2a, providing resistance to ceftaroline; loss of a large part of prophage DNA and restoration of the nucleotide sequence of beta-hemolysin, that greatly facilitates the escape of phagocytosed bacteria from the phagosome and formation of biofilms; dysfunction of the AgrA system due to the presence of psm-mec and several amino acid substitutions in the AgrC; partial deletion of the nucleotide sequence in genomic island vSAβ resulting in the loss of two proteases of Spl-operon; and deletion of SD repeats in the SdrE amino acid sequence.

Transcriptome profiling of osteoclast subsets associated with arthritis: A pathogenic role of CCR2hi osteoclast progenitors

Introduction

The existence of different osteoclast progenitor (OCP) subsets has been confirmed by numerous studies. However, pathological inflammation-induced osteoclastogenesis remains incompletely understood. Detailed characterization of OCP subsets may elucidate the pathophysiology of increased osteoclast activity causing periarticular and systemic bone resorption in arthritis. In our study, we rely on previously defined OCP subsets categorized by the level of CCR2 expression as circulatory-like committed CCR2^hi OCPs, which are substantially expanded in arthritis, and marrow-resident CCR2^lo OCPs of immature phenotype and behavior.

Methods

In order to perform transcriptome characterization of those subsets in the context of collagen-induced arthritis (CIA), we sorted CCR2^hi and CCR2^lo periarticular bone marrow OCPs of control and arthritic mice, and performed next-generation RNA sequencing (n=4 for each group) to evaluate the differential gene expression profile using gene set enrichment analysis with further validation.

Results

A disparity between CCR2^hi and CCR2^lo subset transcriptomes (863 genes) was detected, with the enrichment of pathways for osteoclast differentiation, chemokine and NOD-like receptor signaling in the CCR2^hi OCP subset, and ribosome biogenesis in eukaryotes and ribosome pathways in the CCR2^lo OCP subset. The effect of intervention (CIA) within each subset was greater in CCR2^hi (92 genes) than in CCR2^lo (43 genes) OCPs. Genes associated with the osteoclastogenic pathway (Fcgr1, Socs3), and several genes involved in cell adhesion and migration (F11r, Cd38, Lrg1) identified the CCR2^hi subset and distinguish CIA from control group, as validated by qPCR (n=6 for control mice, n=9 for CIA mice). The latter gene set showed a significant positive correlation with arthritis clinical score and frequency of CCR2^hi OCPs. Protein-level validation by flow cytometry showed increased proportion of OCPs expressing F11r/CD321, CD38 and Lrg1 in CIA, indicating that they could be used as disease markers. Moreover, osteoclast pathway-identifying genes remained similarly expressed (Fcgr1) or even induced by several fold (Socs3) in preosteoclasts differentiated in vitro from CIA mice compared to pre-cultured levels, suggesting their importance for enhanced osteoclastogenesis of the CCR2^hi OCPs in arthritis.

Conclusion

Our approach detected differentially expressed genes that could identify distinct subset of OCPs associated with arthritis as well as indicate possible therapeutic targets aimed to modulate osteoclast activity.

Dual-functional composite scaffolds for inhibiting infection and promoting bone regeneration

The treatment of infected bone defects is an intractable problem in orthopedics. It comprises two critical parts, namely that of infection control and bone defect repair. According to these two core tasks during treatment, the ideal approach of simultaneously controlling infection and repairing bone defects is promising treatment strategy. Several engineered biomaterials and drug delivery systems with dual functions of anti-bacterial action and ostogenesis-promotion have been developed and demonstrated excellent therapeutic effects. Compared with the conventional treatment method, the dual-functional composite scaffold can provide one-stage treatment avoiding multiple surgeries, thereby remarkably simplifying the treatment process and reducing the treatment time, overcoming the disadvantages of conventional bone transplantation. In this review, the impaired bone repair ability and its specific mechanisms in the microenvironment of pathogen infection and excessive inflammation were analyzed, providing a theoretical basis for the treatment of infectious bone defects. Furthermore, we discussed the composite dual-functional scaffold composed of a combination of antibacterial and osteogenic material. Finally, a series of advanced drug delivery systems with antibacterial and bone-promoting capabilities were summarized and discussed. This review provides a comprehensive understanding for the microenvironment of infectious bone defects and leading-edge design strategies for the antibacterial and bone-promoting dual-function scaffold, thus providing clinically significant treatment methods for infectious bone defects.

•

Antibacterial and bone-promoting dual-function scaffolds are ideal strategies for treatment of infectious bone defects.

•

The effect of infection on bone repair was summarized in detail from four important aspects.

•

A variety of dual-function scaffolds based on antibacterial and osteogenic materials were discussed.

•

Dual-function drug delivery systems promoting repair of infectious bone defects by locally releasing functional agents.

•

Leading-edge design strategies, challenges and prospects for dual-functional biomaterials were provided.

Cholesteatoma has an altered microbiota with a higher abundance of Staphylococcus species

Objective

To compare the microbiota between cholesteatoma and chronic suppurative otitis media (COM) and to identify potential pathogens that explain the relevant phenotypes of cholesteatoma.

Study Design

Prospective cohort study.

Methods

Surgical specimens collected from 20 cholesteatomas and nine COMs were treated to dissolve biofilms and subjected to 16S ribosomal RNA (rRNA) gene sequencing and amplicon sequence variant-level analysis for microbiota profiling and quantitative comparison. Correlations between the relative abundance of potential pathogens and the volume of the primary resected cholesteatomas were examined.

Results

Differences in bacterial composition (beta diversity) were observed between cholesteatomas and COM (p = .002), with a higher abundance of Staphylococcus in cholesteatomas than in COM (p = .005). Common genera in the external auditory canal (EAC) flora, such as Staphylococcus, Corynebacterium, and Cutibacterium, were predominant in both cholesteatoma and COM; Staphylococcus aureus and Pseudomonas aeruginosa were increased in both diseases compared with the EAC flora. Furthermore, coagulase-negative staphylococci (CoNS) were more abundant in cholesteatomas than in COM (p = 0.002). Linear discriminant analysis coupled with effect size measurements (LEfSe) identified four CoNS as potential biomarkers for cholesteatoma. The relative abundance of S. aureus, a potential pathogen, was positively correlated with cholesteatoma volume (r = .60, p = .02).

Conclusion

The microbiota of cholesteatoma and COM originated from EAC flora, but the bacterial composition was largely altered. Our results suggested that S. aureus infection is involved in cholesteatoma progression.

Level of Evidence

3b.

Mechanisms of promoting the differentiation and bone resorption function of osteoclasts by Staphylococcus aureus infection

Bone infection is a common and serious complication in the field of orthopedics, which frequently leads to excessive bone destruction and fracture nonunion. Staphylococcus aureus (S. aureus) infection affects bone cell function which, in turn, causes bone destruction. Bone is mainly regulated by osteoblasts and osteoclasts. Osteoclasts are the only cell type with bone resorptive function. Their over-activation is closely associated with excessive bone loss. Understanding how S. aureus changes the functional state of osteoclasts is the key to effective treatment. By reviewing the literature, this paper summarizes several mechanisms of bone destruction caused by S. aureus influencing osteoclasts, thereby stimulating new ideas for the treatment of bone infection.

Inflammatory stimuli alter bone marrow composition and compromise bone health in the malnourished host

Inflammation has a role in the pathogenesis of childhood malnutrition. We investigated the effect of malnutrition and inflammatory challenge on bone marrow composition and bone health. We studied an established murine model of moderate acute malnutrition at baseline and after acute inflammatory challenge with bacterial lipopolysaccharide (LPS), a surrogate of Gram-negative bacterial sepsis, or Leishmania donovani, the cause of visceral leishmaniasis. Both of these infections cause significant morbidity and mortality in malnourished children. Of the 2 stimuli, LPS caused more pronounced bone marrow changes that were amplified in malnourished mice. LPS challenge led to increased inflammatory cytokine expression (Il1b, Il6, and Tnf), inflammasome activation, and inflammatory monocyte accumulation in the bone marrow of malnourished mice. Depletion of inflammatory monocytes in Csfr1-LysMcre-DT malnourished mice significantly reduced the inflammasome activation and IL1-ß production after LPS challenge. The inflammatory challenge also led to increased expansion of mesenchymal stem cells (MSCs), bone marrow adiposity, and expression of genes (Pparg, Adipoq, and Srbp1) associated with adipogenesis in malnourished mice. This suggests that inflammatory challenge promotes differentiation of BM MSCs toward the adipocyte lineage rather than toward bone-forming osteoblasts in the malnourished host. Concurrent with this reduced osteoblastic potential there was an increase in bone-resorbing osteoclasts, enhanced osteoclast activity, upregulation of inflammatory genes, and IL-1B involved in osteoclast differentiation and activation. The resulting weakened bone formation and increased bone resorption would contribute to the bone fragility associated with malnutrition. Lastly, we evaluated the effect of replacing lipid rich in omega-6 fatty acids (corn oil) with lipid-rich in omega-3 fatty acids (fish oil) in the nutrient-deficient diet. LPS-challenged malnourished mice that received dietary fish oil showed decreased expression of inflammatory cytokines and Rankl and reduced osteoclast differentiation and activation in the bone marrow. This work demonstrates that the negative effect of inflammatory challenge on bone marrow is amplified in the malnourished host. Increasing dietary intake of omega-3 fatty acids may be a means to reduce inflammation and improve bone health in malnourished children.

Clindamycin-loaded titanium prevents implant-related infection through blocking biofilm formation

Implant-related infection is a disastrous complication. Surface modification of titanium is considered as an important strategy to prevent implant-related infection. However, there is no recognized surface modification strategy that can be applied in clinic so far. We explored a new strategy of coating. The clindamycin-loaded titanium was constructed by layer-by-layer self-assembly. The release of clindamycin from titanium was detected through high performance liquid chromatography. Different titanium was co-cultured with Staphylococcus aureus for 24 h in vitro, then the effect of different titanium on bacterial colonization and biofilm formation was determined by spread plate method and scanning electron microscopy. Cytotoxicity and cytocompatibility of clindamycin-loaded titanium on MC3T3-E1 cells were measured by CCK8. The antibacterial ability of clindamycin-loaded titanium in vivo was also evaluated using a rat model of osteomyelitis. The number of osteoclasts in bone defect was observed by tartrate-resistant acid phosphatase staining. Bacterial burden of surrounding tissues around the site of infection was calculated by tissue homogenate and colony count. Clindamycin-loaded titanium could release clindamycin slowly within 160 h. It reduced bacterial colonization by three orders of magnitude compare to control (p < .05) and inhibits biofilm formation in vitro. Cells proliferation and adhesion were similar on three titanium surfaces (p > .05). In vivo, clindamycin-loaded titanium improved bone healing, reduced microbial burden, and decreased the number of osteoclasts compared control titanium in the rat model of osteomyelitis. This study demonstrated that clindamycin-loaded titanium exhibited good biocompatibility, and showed antibacterial activity both in vivo and in vitro. It is promising and might have potential for clinical application.

The Synergistic Effect of Nicotine and Staphylococcus aureus on Peri-Implant Infections

Smoking is considered a key risk factor for implant survival; however, how it interacts with the pathogens in peri-implant infections is not clear. Here, we identified that nicotine, the key component of cigarette smoking, can interact with Staphylococcus aureus and synergistically induce peri-implant infections in a rat osteolysis model. The nicotine–S. aureus combination group increased the gross bone pathology, osteolysis, periosteal reactions, and bone resorption compared to the nicotine or S. aureus single treated group (p < 0.05). Nicotine did not promote the proliferation of S. aureus both in vitro and in vivo, but it can significantly upregulate the expression of staphylococcal protein A (SpA), a key virulence factor of S. aureus. The nicotine–S. aureus combination also synergistically activated the expression of RANKL (receptor activator of nuclear factor-kappa B ligand, p < 0.05) to promote the development of peri-implant infections. The synergistic effects between nicotine and S. aureus infection can be a new target to reduce the peri-implant infections.

Fc Gamma Receptors as Regulators of Bone Destruction in Inflammatory Arthritis

Bone erosion is one of the primary features of inflammatory arthritis and is caused by excessive differentiation and activation of osteoclasts. Fc gamma receptors (FcγRs) have been implicated in osteoclastogenesis. Our recent studies demonstrate that joint-deposited lupus IgG inhibited RANKL-induced osteoclastogenesis. FcγRI is required for RANKL-induced osteoclastogenesis and lupus IgG-induced signaling transduction. We reviewed the results of studies that analyzed the association between FcγRs and bone erosion in inflammatory arthritis. The analysis revealed the dual roles of FcγRs in bone destruction in inflammatory arthritis. Thus, IgG/FcγR signaling molecules may serve as potential therapeutic targets against bone erosion.

Biological Effects of β-Glucans on Osteoclastogenesis

Although the anti-tumor and anti-infective properties of β-glucans have been well-discussed, their role in bone metabolism has not been reviewed so far. This review discusses the biological effects of β-glucans on bone metabolisms, especially on bone-resorbing osteoclasts, which are differentiated from hematopoietic precursors. Multiple immunoreceptors that can recognize β-glucans were reported to be expressed in osteoclast precursors. Coordinated co-stimulatory signals mediated by these immunoreceptors are important for the regulation of osteoclastogenesis and bone remodeling. Curdlan from the bacterium Alcaligenes faecalis negatively regulates osteoclast differentiation in vitro by affecting both the osteoclast precursors and osteoclast-supporting cells. We also showed that laminarin, lichenan, and glucan from baker’s yeast, as well as β-1,3-glucan from Euglema gracilisas, inhibit the osteoclast formation in bone marrow cells. Consistent with these findings, systemic and local administration of β-glucan derived from Aureobasidium pullulans and Saccharomyces cerevisiae suppressed bone resorption in vivo. However, zymosan derived from S. cerevisiae stimulated the bone resorption activity and is widely used to induce arthritis in animal models. Additional research concerning the relationship between the molecular structure of β-glucan and its effect on osteoclastic bone resorption will be beneficial for the development of novel treatment strategies for bone-related diseases.

Multitasking by the OC Lineage during Bone Infection: Bone Resorption, Immune Modulation, and Microbial Niche

Bone infections, also known as infectious osteomyelitis, are accompanied by significant inflammation, osteolysis, and necrosis. Osteoclasts (OCs) are the bone-resorbing cells that work in concert with osteoblasts and osteocytes to properly maintain skeletal health and are well known to respond to inflammation by increasing their resorptive activity. OCs have typically been viewed merely as effectors of pathologic bone resorption, but recent evidence suggests they may play an active role in the progression of infections through direct effects on pathogens and via the immune system. This review discusses the host- and pathogen-derived factors involved in the in generation of OCs during infection, the crosstalk between OCs and immune cells, and the role of OC lineage cells in the growth and survival of pathogens, and highlights unanswered questions in the field.

A comprehensive review of bacterial osteomyelitis with emphasis on Staphylococcus aureus

Osteomyelitis, a significant infection of bone tissue, gives rise to two main groups of infection: acute and chronic. These groups are further categorized in terms of the duration of infection. Usually, children and adults are more susceptible to acute and chronic infections, respectively. The aforementioned groups of osteomyelitis share almost 80% of the corresponding bacterial pathogens. Among all bacteria, Staphylococcus aureus (S. aureus) is a significant pathogen and is associated with a high range of osteomyelitis symptoms. S. aureus has many strategies for interacting with host cells including Small Colony Variant (SCV), biofilm formation, and toxin secretion. In addition, it induces an inflammatory response and causes host cell death by apoptosis and necrosis. However, any possible step to take in this respect is dependent on the conditions and host responses. In the absence of any immune responses and antibiotics, bacteria actively duplicate themselves; however, in the presence of phagocytic cell and harassing conditions, they turn into a SCV, remaining sustainable for a long time. SCV is characterized by notable advantages such as (a) intracellular life that mediates a dam against immune cells and (b) low ATP production that mediates resistance against antibiotics.