Staphylococcus aureus protein A causes osteoblasts to hyper-mineralise in a 3D extra-cellular matrix environment

Technologies for the fabrication of crosslinked polysaccharide-based hydrogels and its role in microbial three-dimensional bioprinting - A review

Three-Dimensional bioprinting has recently gained more attraction among researchers for its wide variety of applicability. This technology involving in developing structures that mimic the natural anatomy, and also aims in developing novel biomaterials, bioinks which have a better printable ability. Different hydrogels (cross-linked polysaccharides) can be used and optimized for good adhesion and cell proliferation. Manufacturing hydrogels with adjustable characteristics allows for fine-tuning of the cellular microenvironment. Different printing technologies can be used to create hydrogels on a micro-scale which will allow regular, patterned integration of cells into hydrogels. Controlling tissue constructions' structural architecture is the important key to ensuring its function as it is designed. The designed tiny hydrogels will be useful in investigating the cellular behaviour within the environments. Three-Dimensional designs can be constructed by modifying their shape and behaviour analogous concerning pressure, heat, electricity, ultraviolet radiation or other environmental elements. Yet, its application in in vitro infection models needs more research and practical study. Microbial bioprinting has become an advancing field with promising potential to develop various biomedical as well as environmental applications. This review elucidates the properties and usage of different hydrogels for Three-Dimensional bioprinting.

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.

miR-146a Protects against Staphylococcus aureus-Induced Osteomyelitis by Regulating Inflammation and Osteogenesis

Osteomyelitis is a Staphylococcus aureus-caused bone infection. In this study, the effects of miR-146a on osteomyelitis were evaluated. Using the osteoblast cell model and S. aureus-induced osteomyelitis mice model, we monitored the miR-146 expression and explored the effects of miR-146a on cell proliferation of osteoblasts, bone remodeling, osteoclastogenesis, inflammatory cytokine production, and bacterial burden. Upregulated miR-146a was found in mice with S. aureus-induced osteomyelitis. miR-146a attenuated S. aureus-induced cell loss of osteoblasts, rescued the expression of osteogenic markers, altered the bone remodeling, and inhibited inflammatory cytokine production and osteoclastogenesis. miR-146a knockout mice had higher S. aureus burden. In conclusion, miR-146a protects against S. aureus-induced osteomyelitis by regulating inflammation and osteogenesis.

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.

Patient-specific effects of soluble factors from Staphylococcus aureus and Staphylococcus epidermidis biofilms on osteogenic differentiation of primary human osteoblasts

Due to the frequency of biofilm-forming Staphylococcus aureus and Staphylococcus epidermidis in orthopedics, it is crucial to understand the interaction between the soluble factors produced by prokaryotes and their effects on eukaryotes. Our knowledge concerning the effect of soluble biofilm factors (SBF) and their virulence potential on osteogenic differentiation is limited to few studies, particularly when there is no direct contact between prokaryotic and eukaryotic cells. SBF were produced by incubating biofilm from S. aureus and S. epidermidis in osteogenic media. Osteoblasts of seven donors were included in this study. Our results demonstrate that the detrimental effects of these pathogens do not require direct contact between prokaryotic and eukaryotic cells. SBF produced by S. aureus and S. epidermidis affect the metabolic activity of osteoblasts. However, the effect of SBF derived from S. aureus seems to be more pronounced compared to that of S. epidermidis. The influence of SBF of S. aureus and S. epidermidis on gene expression of COL1A1, ALPL, BGLAP, SPP1, RUNX2 is bacteria-, patient-, concentration-, and incubation time dependent. Mineralization was monitored by staining the calcium and phosphate deposition and revealed that the SBF of S. epidermidis markedly inhibits calcium deposition; however, S. aureus shows a less inhibitory effect. Therefore, these new findings support the hypotheses that soluble biofilm factors affect the osteogenic processes substantially, particularly when there is no direct interaction between bacteria and osteoblast.

Staphylococcus aureus Internalization in Osteoblast Cells: Mechanisms, Interactions and Biochemical Processes. What Did We Learn from Experimental Models?

Bacterial internalization is a strategy that non-intracellular microorganisms use to escape the host immune system and survive inside the human body. Among bacterial species, Staphylococcus aureus showed the ability to interact with and infect osteoblasts, causing osteomyelitis as well as bone and joint infection, while also becoming increasingly resistant to antibiotic therapy and a reservoir of bacteria that can make the infection difficult to cure. Despite being a serious issue in orthopedic surgery, little is known about the mechanisms that allow bacteria to enter and survive inside the osteoblasts, due to the lack of consistent experimental models. In this review, we describe the current knowledge about S. aureus internalization mechanisms and various aspects of the interaction between bacteria and osteoblasts (e.g., best experimental conditions, bacteria-induced damages and immune system response), focusing on studies performed using the MG-63 osteoblastic cell line, the best traditional (2D) model for the study of this phenomenon to date. At the same time, as it has been widely demonstrated that 2D culture systems are not completely indicative of the dynamic environment in vivo, and more recent 3D models—representative of bone infection—have also been investigated.

Antimicrobial activity of mesenchymal stem cells against Staphylococcus aureus

Introduction

There have been limited advances in the treatment of bone and joint infections, which currently involves a combination of surgery and antibiotic administration. There is a timely need in orthopedics to develop more effective and less invasive forms of antimicrobial prophylaxis and treatment. The antibacterial effect of adult tissue-derived mesenchymal stem cells (MSCs) has recently been investigated against Escherichia coli and Staphylococcus aureus. The main mechanism of action is postulated to be via MSC production of the cationic antimicrobial peptide, LL-37.

Methods

This study examines the antimicrobial activity of adipose-derived human MSCs (ASCs) on S. aureus, specifically examining the role of LL-37 and regulation of its expression. Bacteria colony-forming unit (CFU) assay was used to assess antimicrobial activity.

Results

Our results showed that the ASC-conditioned medium significantly inhibited the growth of S. aureus under standard culture conditions with or without the continued presence of ASCs. Also, the treatment of ASCs with 1,25-dihydroxy vitamin D₃ elevated LL-37 expression and enhanced their antimicrobial activity. In support, treatment with the vitamin D receptor inhibitor, GW0742, blocked the antimicrobial activity of ASCs.

Conclusion

Our findings clearly demonstrate the antimicrobial activity of adult ASCs against S. aureus and implicate a key regulatory role for vitamin D. Further testing in in vivo models is being pursued to assess the potential application of ASCs as a biocompatible, adjunct treatment for musculoskeletal infections.

Biomaterials against Bone Infection

Chronic bone infection is considered as one of the most problematic biofilm-related infections. Its recurrent and resistant nature, high morbidity, prolonged hospitalization, and costly medical care expenses have driven the efforts of the scientific community to develop new therapies to improve the standards used today. There is great debate on the management of this kind of infection in order to establish consistent and agreed guidelines in national health systems. The scientific research is oriented toward the design of anti-infective biomaterials both for prevention and cure. The properties of these materials must be adapted to achieve better anti-infective performance and good compatibility, which allow a good integration of the implant with the surrounding tissue. The objective of this review is to study in-depth the antibacterial biomaterials and the strategies underlying them. In this sense, this manuscript focuses on antimicrobial coatings, including the new technological advances on surface modification; scaffolding design including multifunctional scaffolds with both antimicrobial and bone regeneration properties; and nanocarriers based on mesoporous silica nanoparticles with advanced properties (targeting and stimuli-response capabilities).

Boron doped silver-copper alloy nanoparticle targeting intracellular S. aureus in bone cells

OBJECTIVES

Alloyed metallic nanoparticles of silver and copper are effective against intracellular infection. However, systemic toxicity may arise due to the non-specific delivery of the nanoparticles. In addressing the issue, this study deals with the targeting of silver-copper-boron (ACB) nanoparticles to infected osteoblasts, which could decrease systemic toxicity and form the basis of targeting specific markers expressed in bone infections.

METHODS

ACB nanoparticles were synthesized and conjugated to the Cadherin-11 antibody (OBAb). The effect of targeting nanoparticles against extracellular and intracellular S. aureus was determined by enumeration of bacterial growth. The binding of the targeting nanoparticles to infected osteoblasts as well as the visualization of live/dead bacteria due to treatment was carried out using fluorescence microscopy. MTT assay was used to determine the viability of osteoblasts with different concentrations of the nanoparticles.

RESULTS

The ACB nanoparticles conjugated to OBAb (ACB-OBAb) were effective against extracellular S. aureus. The ACB-OBAb nanoparticles showed a 1.32 log reduction of intracellular S. aureus at a concentration of 1mg/L. The ACB-OBAb nanoparticles were able to bind to the infected osteoblast and showed toxicity to osteoblasts at levels ≥20mg/L. Also, the percentage of silver, copper, and boron in the nanoparticles determined the effectiveness of their antibacterial activity.

CONCLUSION

The ACB-OBAb nanoparticles were able to target the osteoblasts and demonstrated significant antibacterial activity against intracellular S. aureus. Targeting shows promise as a strategy to target specific markers expressed on infected osteoblasts for efficient nanoparticle delivery, and further animal studies are recommended to test its efficacy in vivo.

Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly

The inflammation of bone tissue is called osteomyelitis, and most cases are caused by an infection with the bacterium Staphylococcus aureus. To date, the bone-building cells, osteoblasts, have been implicated in the progression of these infections, but not much is known about how the bone-resorbing cells, osteoclasts, participate. In this study, we show that S. aureus can infect osteoclasts and proliferate inside these cells, whereas bone-residing macrophages, immune cells related to osteoclasts, destroy the bacteria. These findings elucidate a unique role for osteoclasts to harbor bacteria during infection, providing a possible mechanism by which bacteria could evade destruction by the immune system.

Osteomyelitis (OM), or inflammation of bone tissue, occurs most frequently as a result of bacterial infection and severely perturbs bone structure. OM is predominantly caused by Staphylococcus aureus, and even with proper treatment, OM has a high rate of recurrence and chronicity. While S. aureus has been shown to infect osteoblasts, it remains unclear whether osteoclasts (OCs) are also a target of intracellular infection. Here, we demonstrate the ability of S. aureus to intracellularly infect and divide within OCs. OCs were differentiated from bone marrow macrophages (BMMs) by exposure to receptor activator of nuclear factor kappa-B ligand (RANKL). By utilizing an intracellular survival assay and flow cytometry, we found that at 18 h postinfection the intracellular burden of S. aureus increased dramatically in cells with at least 2 days of RANKL exposure, while the bacterial burden decreased in BMMs. To further explore the signals downstream of RANKL, we manipulated factors controlling OC differentiation, NFATc1 and alternative NF-κB, and found that intracellular bacterial growth correlates with NFATc1 levels in RANKL-treated cells. Confocal and time-lapse microscopy in mature OCs showed a range of intracellular infection that correlated inversely with S. aureus-phagolysosome colocalization. The propensity of OCs to become infected, paired with their diminished bactericidal capacity compared to BMMs, could promote OM progression by allowing S. aureus to evade initial immune regulation and proliferate at the periphery of lesions where OCs are most abundant.

G-CSF partially mediates bone loss induced by Staphylococcus aureus infection in mice

Bone loss in Staphylococcus aureus (S. aureus) osteomyelitis poses a serious challenge to orthopedic treatment. The present study aimed to elucidate how S. aureus infection in bone might induce bone loss. The C57BL/6 mice were injected with S. aureus (10⁶ CFU/ml, 100 μl) or with the same amount of vehicle (control) via the tail vein. Microcomputed tomography (microCT) analysis showed bone loss progressing from week 1 to week 5 after infection, accompanied by a decreased number of osteocalcin-positive stained osteoblasts and the suppressed mRNA expression of Runx2 and osteocalcin. Transcriptome profiles of GSE30119 were downloaded and analyzed to determine the differences in expression of inflammatory factors between patients with S. aureus infected osteomyelitis and healthy controls, the data showed significantly higher mRNA expression of granulocyte colony-stimulating factor (G-CSF) in the whole blood from patients with S. aureus infection. Enzyme-linked immunosorbent assay (ELISA) analysis confirmed an increased level of G-CSF in the bone marrow and serum from S. aureus infected mice, which might have been due to the increased amount of F4/80⁺ macrophages. Interestingly, G-CSF neutralizing antibody treatment significantly rescued the bone loss after S. aureus infection, as evidenced by its roles in improving BV/TV and preserving osteocalcin- and osterix-positive stained cells. Importantly, we found that G-CSF level was significantly up-regulated in the serum from osteomyelitis patients infected by S. aureus Together, S. aureus infection might suppress the function of osteoblastic cells and induce progressive bone loss by up-regulating the level G-CSF, suggesting a therapeutic potential for G-CSF neutralization in combating bone loss in S. aureus osteomyelitis.