In the current study, we examined the role of CD14 in regulating LPS activation of corneal epithelial cells and Pseudomonas aeruginosa corneal infection. Our findings demonstrate that LPS induces TLR4 internalization in corneal epithelial cells and that blocking with anti-CD14 selectively inhibits TLR4 endocytosis, Syk and IRF3 phosphorylation, and production of CCL5/RANTES and IFN-?, but not IL-8. Using a murine model of P. aeruginosa corneal infection, we show that although infected CD14-/- corneas produce less CCL5, they exhibit significantly increased CXC chemokine production, neutrophil recruitment to the corneal stroma and bacterial clearance than C57BL/6 mice. We conclude that CD14 has a critical role in mediating TLR4 signaling through IRF3 in resident corneal epithelial cells and macrophages, and thereby modulates TLR4 cell surface activation of the MyD88/NF?B/AP-1 pathway and production of CXC chemokines and neutrophil infiltration to infected tissues.
Here we identified a population of bone marrow neutrophils that constitutively expressed the transcription factor ROR?t and produced and responded to interleukin 17A (IL-17A (IL-17)). IL-6, IL-23 and ROR?t, but not T cells or natural killer (NK) cells, were required for IL-17 production in neutrophils. IL-6 and IL-23 induced expression of the receptors IL-17RC and dectin-2 on neutrophils, and IL-17RC expression was augmented by activation of dectin-2. Autocrine activity of IL-17A and its receptor induced the production of reactive oxygen species (ROS), and increased fungal killing in vitro and in a model of Aspergillus-induced keratitis. Human neutrophils also expressed ROR?t and induced the expression of IL-17A, IL-17RC and dectin-2 following stimulation with IL-6 and IL-23. Our findings identify a population of human and mouse neutrophils with autocrine IL-17 activity that probably contribute to the etiology of microbial and inflammatory diseases.
Filamentous fungi are an important cause of pulmonary and systemic morbidity and mortality, and also cause corneal blindness and visual impairment worldwide. Utilizing in vitro neutrophil killing assays and a model of fungal infection of the cornea, we demonstrated that Dectin-1 dependent IL-6 production regulates expression of iron chelators, heme and siderophore binding proteins and hepcidin in infected mice. In addition, we show that human neutrophils synthesize lipocalin-1, which sequesters fungal siderophores, and that topical lipocalin-1 or lactoferrin restricts fungal growth in vivo. Conversely, we show that exogenous iron or the xenosiderophore deferroxamine enhances fungal growth in infected mice. By examining mutant Aspergillus and Fusarium strains, we found that fungal transcriptional responses to low iron levels and extracellular siderophores are essential for fungal growth during infection. Further, we showed that targeting fungal iron acquisition or siderophore biosynthesis by topical application of iron chelators or statins reduces fungal growth in the cornea by 60% and that dual therapy with the iron chelator deferiprone and statins further restricts fungal growth by 75%. Together, these studies identify specific host iron-chelating and fungal iron-acquisition mediators that regulate fungal growth, and demonstrate that therapeutic inhibition of fungal iron acquisition can be utilized to treat topical fungal infections.
Microbial infections of the cornea frequently cause painful, blinding and debilitating disease that is often difficult to treat and may require corneal transplantation. In addition, sterile corneal infiltrates that are associated with contact lens wear cause pain, visual impairment and photophobia. In this article, we review the role of Toll-Like Receptors (TLR) in bacterial keratitis and sterile corneal infiltrates, and describe the role of MD-2 regulation in LPS responsiveness by corneal epithelial cells. We conclude that both live bacteria and bacterial products activate Toll-Like Receptors in the cornea, which leads to chemokine production and neutrophil recruitment to the corneal stroma. While neutrophils are essential for bacterial killing, they also cause tissue damage that results in loss of corneal clarity. These disparate outcomes, therefore, represent a spectrum of disease severity based on this pathway, and further indicate that targeting the TLR pathway is a feasible approach to treating inflammation caused by live bacteria and microbial products. Further, as the P. aeruginosa type III secretion system (T3SS) also plays a critical role in disease pathogenesis by inducing neutrophil apoptosis and facilitating bacterial growth in the cornea, T3SS exotoxins are additional targets for therapy for P. aeruginosa keratitis.
Although P. aeruginosa is especially dangerous in cystic fibrosis (CF), there is no consensus as to how it kills representative cell types that are of key importance in the lung. This study concerns the acute toxicity of the sequenced strain, PAO1, toward a murine macrophage cell line (RAW 264.7). Toxicity requires brief contact with the target cell, but is then delayed for more than 12 h. None of the classical toxic effectors of this organism is required and cell death occurs without phagocytosis or acute perturbation of the actin cytoskeleton. Apoptosis is not required for toxicity toward either RAW 264.7 cells or for alveolar macrophages. Transcriptional profiling shows that encounter between PAO1 and RAW 264.7 cells elicits an early inflammatory response, followed by growth arrest. As an independent strategy to understand the mechanism of toxicity, we selected variant RAW 264.7 cells that resist PAO1. Upon exposure to P. aeruginosa, they are hyper-responsive with regard to classical inflammatory cytokine production and show transient downregulation of transcripts that are required for cell growth. They do not show obvious morphologic changes. Although they do not increase interferon transcripts, when exposed to PAO1 they dramatically upregulate a subset of the responses that are characteristic of exposure to g-interferon, including several guanylate-binding proteins. The present observations provide a novel foundation for learning how to equip cells with resistance to a complex challenge.
The inability of epithelial cells from the cornea and other tissues to respond to LPS is reportedly due to low expression of the TLR4 co-receptor MD-2. We generated MD-2(-/-) bone marrow chimeras, and showed that MD-2 expression on non-myeloid cells was sufficient to mediate LPS-induced corneal inflammation. As IFN-? is produced during Pseudomonas aeruginosa corneal infection, we examined the role of this cytokine on MD-2 expression by primary human corneal epithelial (HCE) cells and HCE cell lines. Exogenous IFN-? was found to induce MD-2 mRNA, MD-2 cell surface expression, and LPS responsiveness as determined by p65 translocation to the nucleus and production of IL-6, CXCL1, and CXCL8/IL-8. Incubation with either the AG490 JAK2 inhibitor or with STAT1 siRNA blocked STAT1 phosphorylation and MD-2 transcription. Furthermore, EMSA analysis demonstrated that STAT1 binds to the MD-2 promoter, indicating that STAT1 is an MD-2 transcription factor. Together, these findings demonstrate that IFN-? induces MD-2 expression and LPS responsiveness in HCE cells by JAK-2-dependent STAT1 activation and direct binding to the MD-2 promoter. Furthermore, given our findings on LPS-induced corneal inflammation, it is likely that IFN-?-induced MD-2 expression by corneal epithelial cells contributes to the host response in vivo, determining the extent of tissue damage and bacterial clearance.
Chronic inflammation is an important component that contributes to many age-related neurodegenerative diseases, including macular degeneration. Here, we report a role for toll-like receptor 3 (TLR3) in cone-rod dystrophy (CORD) of mice lacking ATP-binding cassette transporter 4 (ABCA4) and retinol dehydrogenase 8 (RDH8), proteins critical for all-trans-retinal clearance in the retina. Increased expression of toll-like receptor-signaling elements and inflammatory changes were observed in Rdh8(-/-)Abca4(-/-) eyes by RNA expression analysis. Unlike 3-month-old Rdh8(-/-)Abca4(-/-) mice that developed CORD, 6-month-old Tlr3(-/-)Rdh8(-/-)Abca4(-/-) mice did not evidence an abnormal retinal phenotype. Light-induced retinal degeneration in Tlr3(-/-)Rdh8(-/-)Abca4(-/-) mice was milder than that in Rdh8(-/-)Abca4(-/-) mice, and a 2-fold increased TLR3 expression was detected in light-illuminated retinas of Rdh8(-/-)Abca4(-/-) mice compared with nonilluminated retinas. Poly(I-C), a TLR3 ligand, caused caspase-8-independent cellular apoptosis. Whereas poly(I-C) induced retinal cell death in Rdh8(-/-)Abca4(-/-) and WT mice both in vivo and ex vivo, this was not seen in mice lacking Tlr3. Far fewer invasive macrophage/microglial cells in the subretinal space and weaker activation of Muller glial cells were exhibited by Tlr3(-/-)Rdh8(-/-) Abca4(-/-) mice compared with Rdh8(-/-)Abca4(-/-) mice at 3 and 6 months of age, indicating that loss of TLR3 inhibits local inflammation in the retina. Both poly(I-C) and endogenous products emanating from dying/dead retinal cells induced NF-?B and IRF3 activation. These findings demonstrate that endogenous products from degenerating retina stimulate TLR3 that causes cellular apoptosis and retinal inflammation and that loss of TLR3 protects mice from CORD.
Winged bean chymotrypsin trypsin inhibitor (WbCTI) is a Kunitz type serine protease inhibitor that inhibits both trypsin and chymotrypsin at 1:1 molar ratio. Site-directed mutagenesis study was employed to generate two mutants of WbCTI, with an aim to explore its dual inhibitory properties against the proteases. The mutants were expressed in Escherichia coli and, were purified to homogeneity using a single step immunoaffinity column. The two mutants, each containing a single mutation at the amino acid sequence positions of 63 and 64, were named as L63A and R64A, respectively. Purified L63A-WbCTI exhibited anti-trypsin activity with no anti-chymotrypsin activity whereas R64A-WbCTI could inhibit chymotrypsin but not trypsin. To investigate the binding interactions between the mutated forms of WbCTI with the putative proteases, binding studies were carried out using gel filtration chromatography which further confirmed the formation of enzyme-inhibitor complexes. Finally, 3D model structure of WbCTI was designed using computer simulations which further emphasize the roles of L63 and R64 residues for dual inhibitory characteristics of WbCTI.
Pseudomonas aeruginosa is a major cause of blindness and visual impairment in the United States and worldwide. Using a murine model of keratitis in which abraded corneas are infected with P. aeruginosa parent and ?fliC (aflagellar) strains 19660 and PAO1, we found that F4/80(+) macrophages were the predominant cell type in the cornea expressing TLR2, TLR4, and TLR5. Depletion of macrophages and dendritic cells using transgenic Mafia mice, in which Fas ligand is selectively activated in these cells, resulted in diminished cytokine production and cellular infiltration to the corneal stroma and unimpaired bacterial growth. TLR4(-/-) mice showed a similar phenotype postinfection with ?fliC strains, whereas TLR4/5(-/-) mice were susceptible to corneal infection with parent strains. Bone marrow-derived macrophages stimulated with ?fliC bacteria induced Toll/IL-1R intracellular domain (TIR)-containing adaptor inducing IFN-? (TRIF)-dependent phosphorylation of IFN regulatory factor 3 in addition to TIR-containing adaptor protein/MyD88-dependent phosphorylation of I?B and nuclear translocation of the p65 subunit of NF?B. Furthermore, TRIF(-/-) mice showed a similar phenotype as TLR4(-/-) mice in regulating only ?fliC bacteria, whereas MyD88(-/-) mice were unable to clear parent or ?fliC bacteria. Finally, IL-1R1(-/-) and IL-1?/?(-/-) mice were highly susceptible to infection. Taken together, these findings indicate that P. aeruginosa activates TLR4/5 on resident corneal macrophages, which signal through TRIF and TIR-containing adaptor protein/MyD88 pathways, leading to NF-?B translocation to the nucleus, transcription of CXCL1 and other CXC chemokines, recruitment of neutrophils to the corneal stroma, and subsequent bacterial killing and tissue damage. IL-1? and IL-1? are also produced, which activate an IL-1R1/MyD88-positive feedback loop in macrophages and IL-1R on other resident cells in the cornea.
A 516-bp winged bean chymotrypsin-trypsin inhibitor (WbCTI) gene was amplified from genomic DNA and cDNA isolated from winged bean using a pair of degenerate primers designed on the basis of the amino acid sequences of WbCTI. The amplified PCR products were cloned and sequenced to confirm their authenticity. DNA sequence analysis of the genomic and cDNA clones of WbCTI revealed the same nucleotide sequence in the coding region and showed WbCTI to be an intron less gene. WbCTI was subcloned into pTrc99A and expressed in Escherichia coli to yield a recombinant protein (rWbCTI). rWbCTI was purified by a rapid and single step immunoaffinity chromatography method, with an overall yield of 1.1 mg/g of wet cells. The homogeneity of the purified protein was checked by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which showed the presence of a single protein band. Functionally rWbCTI is indistinguishable from WbCTI, since both inhibit bovine trypsin and chymotrypsin in a 1:1 molar ratio. FPLC binding studies also confirmed that rWbCTI binds the proteases in a 1:1 molar ratio.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.