The induction of HMGB1 release from RAW 264.7 cells by transfected DNA

Inflammasome activation in acute lung injury

Inflammasomes are multiprotein complexes tasked with sensing endogenous or exogenous inflammatory signals and integrating this signal into a downstream response. Inflammasome activation has been implicated in a variety of pulmonary diseases, including pulmonary hypertension, bacterial pneumonia, COPD, and asthma. Of increasing interest is the contribution of inflammasome activation in the context of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Inflammasome activation in both the lung parenchyma and resident immune cells generates intereukin-1β (IL-1β) and IL-18, both of which drive the cascade of lung inflammation forward. Blockade of these responses has been shown to be beneficial in animal models and is a focus of translational research in the field. In this review, we will discuss the assembly and regulation of inflammasomes during lung inflammation, highlighting therapeutically viable effector steps. We will examine the importance of IL-1β and IL-18, two key products of inflammasome activation, in ALI, as well as the contribution of the pulmonary endothelial cell to this process. Finally, we will explore translational research moving toward anti-inflammasome therapies for ALI/ARDS and speculate toward future directions for the field.

TLR3 deficiency exacerbates the loss of epithelial barrier function during genital tract Chlamydia muridarum infection

Problem

Chlamydia trachomatis infections are often associated with acute syndromes including cervicitis, urethritis, and endometritis, which can lead to chronic sequelae such as pelvic inflammatory disease (PID), chronic pelvic pain, ectopic pregnancy, and tubal infertility. As epithelial cells are the primary cell type productively infected during genital tract Chlamydia infections, we investigated whether Chlamydia has any impact on the integrity of the host epithelial barrier as a possible mechanism to facilitate the dissemination of infection, and examined whether TLR3 function modulates its impact.

Method of study

We used wild-type and TLR3-deficient murine oviduct epithelial (OE) cells to ascertain whether C. muridarum infection had any effect on the epithelial barrier integrity of these cells as measured by transepithelial resistance (TER) and cell permeability assays. We next assessed whether infection impacted the transcription and protein function of the cellular tight-junction (TJ) genes for claudins1-4, ZO-1, JAM1 and occludin via quantitative real-time PCR (qPCR) and western blot.

Results

qPCR, immunoblotting, transwell permeability assays, and TER studies show that Chlamydia compromises cellular TJ function throughout infection in murine OE cells and that TLR3 deficiency significantly exacerbates this effect.

Conclusion

Our data show that TLR3 plays a role in modulating epithelial barrier function during Chlamydia infection of epithelial cells lining the genital tract. These findings propose a role for TLR3 signaling in maintaining the integrity of epithelial barrier function during genital tract Chlamydia infection, a function that we hypothesize is important in helping limit the chlamydial spread and subsequent genital tract pathology.

HMGB1 blockade differentially impacts pulmonary inflammation and defense responses in poly(I:C)/LPS-exposed heart transplant mice

A large number of recipients are in a compromised immune defense condition because of the routine application of immunosuppressive regimens after heart transplantation. Our previous work demonstrated that blockade of high-mobility group box 1 (HMGB1) prolongs the graft survival. Whether and how HMGB1 blockade impacts respiratory responses against pathogen-like challenge in organ transplant recipients when it improves cardiac graft are not elucidated. At the present study, after abdominal heterotopic heart transplantation, the recipient mice were treated with HMGB1 mAb, and then challenged with poly(I:C) or LPS intratracheally on day 7 post transplantation. We found that the level of bronchoalveolar lavage (BAL) HMGB1 was elevated after heart transplantation, and aggravated responses to respiratory tract poly(I:C)/LPS challenge were observed. HMGB1 neutralizing mAb treatment in poly(I:C)-challenged recipient mice alleviated pulmonary histopathological changes, neutrophil infiltration and inflammatory cytokine release, but unaffected the level of IFN-β, the distribution of CD11b(+)CD27(+)/CD11b(+)CD27(-) NK cell subsets, and CD8(+) T cell responses. In LPS-exposed recipient mice, HMGB1 mAb treatment ameliorated pulmonary inflammatory damage and enhanced the phagocytosis of phagocytic cells. Thus, this study may establish a basis for the application of HMGB1 blockade to improve the outcomes of heart transplant recipients because HMGB1 inhibition ameliorates pulmonary inflammation, but maintains defense-associated responses.

Cationic polyaspartamide-based nanocomplexes mediate siRNA entry and down-regulation of the pro-inflammatory mediator high mobility group box 1 in airway epithelial cells

High-mobility group box 1 (HMGB1) is a nonhistone protein secreted by airway epithelial cells in hyperinflammatory diseases such as asthma. In order to down-regulate HMGB1 expression in airway epithelial cells, siRNA directed against HMGB1 was delivered through nanocomplexes based on a cationic copolymer of poly(N-2-hydroxyethyl)-d,l-aspartamide (PHEA) by using H441 cells. Two copolymers were used in these experiments bearing respectively spermine side chains (PHEA-Spm) and both spermine and PEG2000 chains (PHEA-PEG-Spm). PHEA-Spm and PHEA-PEG-Spm derivatives complexed dsDNA oligonucleotides with a w/w ratio of 1 and higher as shown by a gel retardation assay. PHEA-Spm and PHEA-PEG-Spm siRNA polyplexes were sized 350-650 nm and 100-400 nm respectively and ranged from negativity/neutrality (at 0.5 ratio) to positivity (at 5 ratio) as ζ potential. Polyplexes formed either at a ratio of 0.5 (partially complexing) or at the ratio of 5 (fully complexing) were tested in subsequent experiments. Epifluorescence revealed that nanocomplexes favored siRNA entry into H441 cells in comparison with naked siRNA. As determined by flow cytometry and a trypan blue assay, PHEA-Spm and PHEA-PEG-Spm allowed siRNA uptake in 42-47% and 30% of cells respectively, however only with PHEA-Spm at w/w ratio of 5 these percentages were significantly higher than those obtained with naked siRNA (20%). Naked siRNA or complexed scrambled siRNA did not exert any effect on HMGB1mRNA levels, whereas PHEA-Spm/siRNA at the w/w ratio of 5 down-regulated HMGB1 mRNA up to 58% of control levels (untransfected cells). PEGylated PHEA-Spm/siRNA nanocomplexes were able to down-regulate HMGB1 mRNA levels up to 61% of control cells. MTT assay revealed excellent biocompatibility of copolymer/siRNA polyplexes with cells. In conclusion, we have found optimal conditions for down-regulation of HMGB1 by siRNA delivery mediated by polyaminoacidic polymers in airway epithelial cells in the absence of cytotoxicity. Functional and in-vivo studies are warranted.

Transfecting RAW264.7 Cells with a Luciferase Reporter Gene

Transfection of desired genetic materials into cells is an inevitable procedure in biomedical research studies. While numerous methods have been described, certain types of cells are resistant to many of these methods and yield low transfection efficiency(1), potentially hindering research in those cell types. In this protocol, we present an optimized transfection procedure to introduce luciferase reporter genes as a plasmid DNA into the RAW264.7 macrophage cell line. Two different types of transfection reagents (lipid-based and polyamine-based) are described, and important notes are given throughout the protocol to ensure that the RAW264.7 cells are minimally altered by the transfection procedure and any experimental data obtained are the direct results of the experimental treatment. While transfection efficiency may not be higher compared to other transfection methods, the described procedure is robust enough for detecting luciferase signal in RAW264.7 without changing the physiological response of the cells to stimuli.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

The complex role of DNA, histones and HMGB1 in the pathogenesis of SLE

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of antinuclear antibodies (ANA) in association with protean clinic manifestations. ANA can bind to nuclear molecules, most prominently DNA and histones in nucleosomes, to form complexes to promote pathogenesis. Because of the intrinsic immunological activity of the nuclear components, these complexes can amplify responses by interacting with diverse pattern recognition receptors and internal sensing systems. Among molecules associated with nucleosomal components, HMGB1, a non-histone protein, can emanate from activated and dying cells; HMGB1's immune activity is determined by post-translational modifications, redox state, and binding to other immune mediators. Although ANAs form complexes that deposit in the kidney or induce type 1 interferon, ANAs may also block immune activity. Together, these studies highlight the importance of complexes in the pathogenesis of lupus and their role as antigens, immunogens, and adjuvants.

The origin and properties of extracellular DNA: from PAMP to DAMP

DNA is a polymeric macromolecule whose biological activities depend on location as well as binding to associated molecules. Inside the cell, DNA is the source of genetic information and binds histones to form nucleosomes. DNA can exit the cell, however, to enter the extracellular space primarily during cell death, either apoptosis or necrosis, as well as NETosis. While bacterial DNA is a potent immune stimulant by virtue of its CpG motifs, mammalian DNA, which is ordinarily inactive, can acquire activity by associating with nuclear, cytoplasmic and serum proteins which promote its uptake into cells to stimulate internal DNA sensors, including Toll-like receptor 9. Among these proteins, anti-DNA autoantibodies can form immune complexes with DNA to stimulate plasmacytoid dendritic cells to produce type 1 interferon. Together, these findings suggest that the immune properties of DNA are mutable and diverse, reflecting its context and the array of attached molecules.

Identifying a role for Toll-like receptor 3 in the innate immune response to Chlamydia muridarum infection in murine oviduct epithelial cells

Because epithelial cells are the major cell type productively infected with Chlamydia during genital tract infections, the overall goal of our research was to understand the contribution of infected epithelial cells to the host defense. We previously showed that Toll-like receptor 3 (TLR3) is the critical pattern recognition receptor in oviduct epithelial (OE) cells that is stimulated during Chlamydia infection, resulting in the synthesis of beta interferon (IFN-β). Here, we present data that implicates TLR3 in the expression of a multitude of other innate-inflammatory immune modulators including interleukin-6 (IL-6), CXCL10, CXCL16, and CCL5. We demonstrate that Chlamydia-induced expression of these cytokines is severely disrupted in TLR3-deficient OE cells, whereas Chlamydia replication in the TLR3-deficient cells is more efficient than in wild-type OE cells. Pretreatment of the TLR3-deficient OE cells with 50 U of IFN-β/ml prior to infection diminished Chlamydia replication and restored the ability of Chlamydia infection to induce IL-6, CXCL10, and CCL5 expression in TLR3-deficient OE cells; however, CXCL16 induction was not restored by IFN-β preincubation. Our findings were corroborated in pathway-focused PCR arrays, which demonstrated a multitude of different inflammatory genes that were defectively regulated during Chlamydia infection of the TLR3-deficient OE cells, and we found that some of these genes were induced only when IFN-β was added prior to infection. Our OE cell data implicate TLR3 as an essential inducer of IFN-β and other inflammatory mediators by epithelial cells during Chlamydia infection and highlight the contribution of TLR3 to the inflammatory cytokine response.

High-mobility group box 1 represents a potential marker of disease activity and novel therapeutic target in systemic lupus erythematosus

High-mobility group box 1 (HMGB1) protein is a nuclear DNA-binding protein, which functions as an alarmin when released from cells. Recent studies implicate extracellular HMGB1 in the pathogenesis of systemic lupus erythematosus (SLE), a prototypical autoimmune disease characterized by the formation of multiple autoantibodies, especially those directed against nucleosomes and double-stranded (ds)DNA. Elevated concentrations of HMGB1 are observed in sera as well as in skin lesions of patients with lupus. Of importance, serum HMGB1 and anti-HMGB1 autoantibody levels correlate with disease activity. In the blood of patients with SLE, HMGB1 is complexed with nucleosomes, at least partially. Moreover, HMGB1-nucleosome complexes from apoptotic cells activate antigen-presenting cells. Injection of HMGB1-nucleosome complexes into nonautoimmune mice results in the formation of autoantibodies against dsDNA and histones in a Toll-like receptor (TLR) 2-dependent manner. Additionally, HMGB1, as a part of DNA-anti-DNA immune complexes, can interact with receptor for advanced glycation end products (RAGE) on the surface of plasmacytoid dendritic cells and B cells leading to TLR9-dependent interferon (IFN)α release and activation of autoreactive B cells, respectively. HMGB1 attached to neutrophil extracellular traps may contribute to IFNα production by facilitating the recognition of self-nucleic acids. Furthermore, HMGB1, complexed with DNA and pathogenic anti-DNA autoantibodies, activates its receptors, TLR2, TLR4 and RAGE, and may thereby be involved in anti-DNA autoantibody-induced kidney damage in lupus nephritis. Collectively, these findings suggest that HMGB1 is a potential marker of disease activity and, because of its probable involvement in the pathogenesis, a novel therapeutic target in SLE.

Fas (CD95) induces rapid, TLR4/IRAK4-dependent release of pro-inflammatory HMGB1 from macrophages

Although Fas (CD95) is recognized as a death receptor that induces apoptosis, recent studies indicate that the Fas/FasL system can induce pro-inflammatory cytokine production by macrophages independent of conventional caspase-mediated apoptotic signaling. The precise mechanism(s) by which Fas activates macrophage inflammation is unknown. We hypothesized that Fas stimulates rapid release of high mobility group box 1 (HMGB1) that acts in an autocrine and/or paracrine manner to stimulate pro-inflammatory cytokine production via a Toll-like receptor-4 (TLR4)/Interleukin-1 receptor associated kinase-4 (IRAK4)-dependent mechanism. Following Fas activation, HMGB1 was released within 1 hr from viable RAW267.4 cells and primary murine peritoneal macrophages. HMGB1 release was more rapid following Fas activation compared to LPS stimulation. Neutralization of HMGB1 with an inhibitory anti-HMGB1 monoclonal antibody strongly inhibited Fas-induced production of tumor necrosis factor (TNF) and macrophage inflammatory protein-2 (MIP-2). Both Fas-induced HMGB1 release and associated pro-inflammatory cytokine production were significantly decreased from Tlr4^-/- and Irak4^-/- macrophages, but not Tlr2^-/- macrophages. These findings reveal a novel mechanism underlying Fas-mediated pro-inflammatory physiological responses in macrophages. We conclude that Fas activation induces rapid, TLR4/IRAK4-dependent release of HMGB1 that contributes to Fas-mediated pro-inflammatory cytokine production by viable macrophages.

Microparticles as autoadjuvants in the pathogenesis of SLE

Nucleic acids represent the main source of autoantigens in systemic lupus erythematosus (SLE). DNA and RNA can exit the cell during cell death and, in the extracellular space, can be immunostimulatory. Also extracellularly, DNA and RNA can be incorporated into microparticles (MPs)-small, membrane-bound vesicles released from dying cells by blebbing. We suggest that MPs display autoantigens, such as RNA and DNA, in a highly immunostimulatory manner, enabling them to function as autoadjuvants. In the bone marrow, nucleic-acid-containing MP autoadjuvants might induce B-cell tolerance, whereas in the periphery, they might stimulate mature B cells that have escaped central tolerance. Indeed, because MP autoadjuvants can trigger several receptors, they could effectively provide apoptotic or activating signals to B cells. We would therefore advance the idea that a model for SLE based on MP autoadjuvants can provide a new paradigm to elucidate the mechanisms by which DNA and RNA affect the immune system and critically influence B-cell fate.