Attachment of Staphylococcus aureus is required for activation of nuclear factor kappa B in human osteoblasts

Long non-coding RNA SNHG5 suppresses the development of acute respiratory distress syndrome by targeting miR-205/COMMD1 axis

Previous studies have reported the important roles of long non-coding RNAs (lncRNAs) in acute respiratory distress syndrome (ARDS). Here, we focus on the role and regulatory mechanism of lncRNA SNHG5 in ARDS. LPS was used to induce mice to establish ARDS model in vivo and to induce A549 cells to establish ARDS model in vitro. qRT-PCR was performed to determine the expressions of SNHG5, miR-205, and inflammatory cytokines. MTT assay was applied to detect cell viability. Dual-luciferase reporter (DLR) assay was performed to test the interactions among SNHG5, miR-205 and COMMD1. Western blot was used to detect the protein expression of COMMD1. Lung injury was evaluated by evaluating the score of lung injury, lung wet/dry weight ratio, and myeloperoxidase (MPO) activity. SNHG5 was downregulated, while miR-205 was upregulated in the serum of ARDS patients and lung tissues of LPS-induced mice. Upregulation of SNHG5 or down-regulation of miR-205 inhibited inflammation and promoted the viability of LPS-induced A549 cells. SNHG5 alleviated the lung injury of ARDS mice. MiR-205 was a target of SNHG5 and inversely correlated with SNHG5. COMMD1 was targeted by miR-205, and was positively regulated by SNHG5. MiR-205 mimics or sh-COMMD1 reversed the promoting effect of SNHG5 on cell viability and the suppressing effect of SNHG5 on inflammation in cellular model of ARDS. Meantime, miR-205 mimics reversed the relieving effect of SNHG5 on lung injury in mouse model of ARDS. SNHG5 acted as a sponge for miR-205 to ameliorate LPS-induced ARDS by regulating COMMD1.

Tet38 of Staphylococcus aureus Binds to Host Cell Receptor Complex CD36-Toll-Like Receptor 2 and Protects from Teichoic Acid Synthesis Inhibitors Tunicamycin and Congo Red

Using an affinity column retention assay, we showed that the purified Tet38 membrane transporter of Staphylococcus aureus bound specifically to host cell CD36 and to the complex CD36-Toll-like receptor 2 (TLR-2), but not to TLR-2 alone or TLR-2 and S. aureus lipoteichoic acid (LTA). We tested the effect of LTA on the internalization of S. aureus tet38 mutant QT7 versus RN6390 by A549 epithelial cells. Addition of anti-LTA antibody to the bacteria prior to adding to A549 cells reduced internalization of QT7 2-fold compared to that with nonspecific antibody treatment. QT7 internalized 4- to 6-fold less than RN6390 with or without anti-LTA antibody. These data suggested that Tet38 and LTA were independently involved in the invasion process. The wall teichoic acid (WTA) inhibitor tunicamycin had an 8-fold decrease in activity with overexpression of tet38 and a 2-fold increase in activity in QT7 (tet38). Reserpine (an inhibitor of efflux pumps) reduced the effect of tet38 overexpression on tunicamycin resistance 4-fold. In addition, tet38 affected growth in the presence of LTA inhibitor Congo red, with overexpression increasing growth and deletion of tet38 reducing growth. In conclusion, Tet38 contributes to S. aureus invasion of A549 via direct binding to CD36 of the complex CD36-TLR-2, and LTA independently bound to TLR-2. The reduction of tunicamycin resistance in the presence of reserpine and the survival ability of the tet38 overexpressor in the presence of Congo red suggest that Tet38 can also protect the synthesis of LTA and WTA in S. aureus against their inhibitors, possibly functioning as an efflux pump.

PI3K/Akt-Beclin1 signaling pathway positively regulates phagocytosis and negatively mediates NF-κB-dependent inflammation in Staphylococcus aureus-infected macrophages

Although autophagy and phagocytosis are involved in the regulation of host inflammatory response to bacterial infection in macrophages, the underlying mechanisms have not been completely elucidated. In the present study, we found that infecting RAW264.7 macrophages with Staphylococcus aureus (S. aureus) activated multiple signaling pathways including phosphatidylinositide 3-kinase (PI3K)/protein kinase B (Akt), nuclear factor-κB (NF-κB), and Rac1, as well as triggered autophagy. LY294002, a specific PI3K activity inhibitor, significantly decreased autophagy and phagocytosis of macrophages upon S. aureus infection. Similarly, knockdown of Beclin1 by specific siRNA significantly inhibited autophagy and phagocytosis of S. aureus-infected macrophages. Additionally, we showed that although administration of Beclin1 siRNA had no effects on phosphorylation of Akt (p-Akt), inhibition of PI3K activity by LY294002 significantly decreased the expression of Beclin1, suggesting that Beclin1 is a downstream molecular of PI3K. Furthermore, inhibition of autophagy significantly increased the production of NF-κB-dependent TNFα/IL-1β in S. aureus-infected macrophages. Collectively, these findings demonstrated, for the first time, that the PI3K/Akt-Beclin1 signaling pathway positively regulates phagocytosis and negatively mediates NF-κB-dependent inflammation in S. aureus-infected macrophages.

A potential microRNA regulation of immune-related genes in invertebrate haemocytes

Bivalve mollusks have been employed as sentinel organisms in environmental health programs due to their sedentary lifestyle, filter-feeding behavior and their ability to accumulate pathogens or toxin molecules inside tissues. Endocrine disrupting chemicals (EDCs) can be up taken and bioaccumulated, and due to sensibility of mollusks to these EDCs, being able to cause immune alterations. Recently, microRNAs (miRNAs) were shown to be involved in modulation and buffering developmental processes against the effects of environmental alterations and pathogenic microorganisms. Moreover, it is suggested that this miRNAs are incorporated into the estrogen-controlled immune network, regulating mechanism of immune gene expression at the posttranscriptional level, modulating immune responses as phagocytosis, redox reaction and apoptosis in bivalve haemocytes. Thus, miRNAs can be used as biomarkers that specifically elucidate immunotoxic effects caused by exogenous biotic or abiotic factors, and can act as useful tools in integrated monitoring environmental health programs. In this review, we aim to describe the investigations that have been carried out on miRNAs in bivalve mollusks, especially those associated with immune responses against infectious agents and xenobiotic exposure.

The Anti-Inflammatory Effects of Interferon Tau by Suppressing NF-κB/MMP9 in Macrophages Stimulated with Staphylococcus aureus

Previous studies have reported that interferon tau (IFNT) significantly mitigates tissue inflammation. However, this effect and its regulating pathways have not been reported for Staphylococcus aureus-induced inflammation. In this study, RAW 264.7 cells stimulated with S. aureus were used to identify the anti-inflammatory effects and mechanism of IFNT. First, IFNT was found to be noncytotoxic to macrophages treated with the high dose of 200 ng/mL IFNT. ELISA and qPCR revealed that IFNT decreased the expression of proinflammatory cytokines such as TNF-α, IL-1β, and IL-6. TLR2, which is involved in the immune response during S. aureus infection, directly affected NF-κB pathway activation and was also downregulated by IFNT. Subsequent Western blotting showed that the phosphorylation of IκBα and NF-κB p65 was inhibited by IFNT. Therefore, although the MMP9 levels were significantly downregulated in a dose-dependent manner by IFNT, little change in MMP2 was observed in S. aureus-stimulated RAW 264.7 cells. Furthermore, PDTC, an inhibitor of NF-κB, also significantly decreased MMP9 levels by inhibiting NF-κB p65 activation. All of these findings strongly suggested that IFNT suppresses the NF-κB/MMP9 signal transduction pathway and subsequently exerts its anti-inflammatory effects in S. aureus-stimulated RAW 264.7 cells.

Staphylococcus aureus vs. Osteoblast: Relationship and Consequences in Osteomyelitis

Bone cells, namely osteoblasts and osteoclasts work in concert and are responsible for bone extracellular matrix formation and resorption. This homeostasis is, in part, altered during infections by Staphylococcus aureus through the induction of various responses from the osteoblasts. This includes the over-production of chemokines, cytokines and growth factors, thus suggesting a role for these cells in both innate and adaptive immunity. S. aureus decreases the activity and viability of osteoblasts, by induction of apoptosis-dependent and independent mechanisms. The tight relationship between osteoclasts and osteoblasts is also modulated by S. aureus infection. The present review provides a survey of the relevant literature discussing the important aspects of S. aureus and osteoblast interaction as well as the ability for antimicrobial peptides to kill intra-osteoblastic S. aureus, hence emphasizing the necessity for new anti-infectious therapeutics.

Staphylococcus aureus protein A binding to osteoblast tumour necrosis factor receptor 1 results in activation of nuclear factor kappa B and release of interleukin-6 in bone infection

Staphylococcus aureus is the major pathogen among the staphylococci and the most common cause of bone infections. These infections are mainly characterized by bone destruction and inflammation, and are often debilitating and very difficult to treat. Previously we demonstrated that S. aureus protein A (SpA) can bind to osteoblasts, which results in inhibition of osteoblast proliferation and mineralization, apoptosis, and activation of osteoclasts. In this study we used small interfering RNA (siRNA) to demonstrate that osteoblast tumour necrosis factor receptor-1 (TNFR-1) is responsible for the recognition of and binding to SpA. TNFR-1 binding to SpA results in the activation of nuclear factor kappa B (NFκB). In turn, NFκB translocates to the nucleus of the osteoblast, which leads to release of interleukin 6 (IL-6). Silencing TNFR-1 in osteoblasts or disruption of the spa gene in S. aureus prevented both NFκB activation and IL-6 release. As well as playing a key role in proinflammatory reactions, IL-6 is also an important osteotropic factor. Release of IL-6 from osteoblasts results in the activation of the bone-resorbing cells, the osteoclasts. Consistent with our results described above, both silencing TNFR-1 in osteoblasts and disruption of spa in S. aureus prevented osteoclast activation. These studies are the first to demonstrate the importance of the TNFR-1-SpA interaction in bone infection, and may help explain the mechanism through which osteoclasts become overactivated, leading to bone destruction. Anti-inflammatory drug therapy could be used either alone or in conjunction with antibiotics to treat osteomyelitis or for prophylaxis in high-risk patients.

Actin cytoskeleton-dependent pathways for ADMA-induced NF-κB activation and TGF-β high expression in human renal glomerular endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is considered to be an independent risk factor in the progression of chronic kidney diseases (CKD). It can induce kidney fibrosis by increasing transforming growth factor (TGF)-β1 expression, but its molecular mechanism is unclear. The aim of the present study was to investigate the role of actin cytoskeleton in ADMA-induced TGF-β1 high expression in human renal glomerular endothelial cells (HRGECs). The structure of stress fibers was visualized by immunofluorescence, nuclear factor-κB (NF-κB) DNA-binding activity was assessed by an electrophoretic mobility shift assay and TGF-β1 expression was assessed by western blot analysis. Results showed that ADMA induced the assembly of stress fibers, DNA binding of NF-κB, and increasing expression of TGF-β1. When the dynamics of actin cytoskeleton was perturbed by the actin-depolymerizing agent cytochalasin D and the actin-stabilizing agent jasplakinolide, or ablation of stress fiber bundles by the nicotineamide adenine dinucleotide phosphate oxidase inhibitor apocynin and p38 mitogen-activated protein kinase inhibitor SB203580, ADMA-induced DNA binding of NF-κB and TGF-β1 expression were inhibited. These results revealed an actin cytoskeleton-dependent mechanism in ADMA-induced NF-κB activation and TGF-β1 high expression in HRGECs. The specific targeting of the actin cytoskeleton may be a useful strategy to prevent ADMA-activated kidney fibrosis in CKD.

Ultrasonically enhanced rifampin activity against internalized Staphylococcus aureus

Staphylococcus aureus (S. aureus) is the principle causative agent of osteomyelitis, accounting for 80% of all human cases. S. aureus internalized in osteoblasts escapes immune response, including engulfment by phagocytes. It also escapes the action of a number of antibiotics. Ultrasound increases cell membrane permeability to a number of drugs. Following an internalization assay, we used low-frequency, low-power ultrasound combined with the antibiotic rifampin to target S. aureus internalized in human osteoblasts. Tryptic soy agar (TSA) was used to quantitate the antibacterial effect of rifampin combined with low-frequency ultrasound. A Cell Counting Kit-8 (CCK-8) assay was used to evaluate cell viability following exposure to ultrasound. Our data revealed that rifampin successfully penetrates into osteoblasts and kills internalized S. aureus in osteoblasts, while low-frequency ultrasound promotes this process. Ultrasound had a negative impact on the cell viability of osteoblasts; however, this damage was slight and reversible. Ultrasound-enhanced antibiotic efficiency to bacteria internalized in the osteoblasts may contribute to the control of chronic infection to reduce recurrence.

Interaction of Staphylococcus aureus with osteoblasts (Review)

Orthopedic infection is refractory to cure. Staphylococcus aureus (S. aureus) is the main causative pathogen responsible for orthopedic infection. S. aureus is capable of not only colonizing bone matrix, but also invading osteoblasts, which may play a significant role in the persistence and recurrence of osteomyelitis. Internalization requires the involvement of cytoskeletal elements, including actin microfilaments, microtubules and clathrin-coated pits. Microfilaments are most significant in the invasion process. S. aureus is capable of remaining alive in osteoblasts for a long period of time. Decreased sensitivity to antibiotics capable of penetrating host cells increases the difficulties of eradicating S. aureus. Osteoblasts, invaded by S. aureus, play a significant role in the initiation and maintenance of inflammatory immune responses. These osteoblasts recruit leukocytes and phagocytes to the site of inflammation via the expression of cytokines. Apoptosis is observed in osteoblasts invaded by S. aureus. Recruitment of osteoclasts and other immunocytes plays a crucial role in the resorption and destruction of bone.