The miR-183/96/182 cluster regulates sensory innervation, resident myeloid cells and functions of the cornea through cell type-specific target genes

The conserved miR-183/96/182 cluster (miR-183C) is expressed in both corneal resident myeloid cells (CRMCs) and sensory nerves (CSN) and modulates corneal immune/inflammatory responses. To uncover cell type-specific roles of miR-183C in CRMC and CSN and their contributions to corneal physiology, myeloid-specific miR-183C conditional knockout (MS-CKO), and sensory nerve-specific CKO (SNS-CKO) mice were produced and characterized in comparison to the conventional miR-183C KO. Immunofluorescence and confocal microscopy of flatmount corneas, corneal sensitivity, and tear volume assays were performed in young adult naïve mice; 3' RNA sequencing (Seq) and proteomics in the trigeminal ganglion (TG), cornea and CRMCs. Our results showed that, similar to conventional KO mice, the numbers of CRMCs were increased in both MS-CKO and SNS-CKO vs age- and sex-matched WT control littermates, suggesting intrinsic and extrinsic regulations of miR-183C on CRMCs. The number of CRMCs was increased in male vs female MS-CKO mice, suggesting sex-dependent regulation of miR-183C on CRMCs. In the miR-183C KO and SNS-CKO, but not the MS-CKO mice, CSN density was decreased in the epithelial layer of the cornea, but not the stromal layer. Functionally, corneal sensitivity and basal tear volume were reduced in the KO and SNS-CKO, but not the MS-CKO mice. Tear volume in males is consistently higher than female WT mice. Bioinformatic analyses of the transcriptomes revealed a series of cell-type specific target genes of miR-183C in TG sensory neurons and CRMCs. Our data elucidate that miR-183C imposes intrinsic and extrinsic regulation on the establishment and function of CSN and CRMCs by cell-specific target genes. miR-183C modulates corneal sensitivity and tear production through its regulation of corneal sensory innervation.

Mechanisms of PM10 Disruption of the Nrf2 Pathway in Cornea

We have previously shown that PM10 exposure causes oxidative stress and reduces Nrf2 protein levels, and SKQ1 pre-treatment protects against this damage in human corneal epithelial cells (HCE-2). The current study focuses on uncovering the mechanisms underlying acute PM10 toxicity and SKQ1-mediated protection. HCE-2 were pre-treated with SKQ1 and then exposed to 100 μg/mL PM10. Cell viability, oxidative stress markers, programmed cell death, DNA damage, senescence markers, and pro-inflammatory cytokines were analyzed. Nrf2 cellular location and its transcriptional activity were determined. Effects of the Nrf2 inhibitor ML385 were similarly evaluated. Data showed that PM10 decreased cell viability, Nrf2 transcriptional activity, and mRNA levels of antioxidant enzymes, but increased p-PI3K, p-NFκB, COX-2, and iNOS proteins levels. Additionally, PM10 exposure significantly increased DNA damage, phosphor-p53, p16 and p21 protein levels, and β-galactosidase (β-gal) staining, which confirmed the senescence. SKQ1 pre-treatment reversed these effects. ML385 lowered the Nrf2 protein levels and mRNA levels of its downstream targets. ML385 also abrogated the protective effects of SKQ1 against PM10 toxicity by preventing the restoration of cell viability and reduced oxidative stress. In conclusion, PM10 induces inflammation, reduces Nrf2 transcriptional activity, and causes DNA damage, leading to a senescence-like phenotype, which is prevented by SKQ1.

PM10 and Pseudomonas aeruginosa: effects on corneal epithelium

Purpose

In vivo data indicate that mouse corneas exposed to PM10 showed early perforation and thinning after infection with Pseudomonas aeruginosa. To understand the mechanisms underlying this finding, we tested the effects of PM10 and the mitochondria targeted anti-oxidant SKQ1 in immortalized human corneal epithelial cells (HCET) that were challenged with Pseudomonas aeruginosa strain 19660.

Methods

Mouse corneas were infected with strain 19660 after a 2 week whole-body exposure to PM10 or control air and assessed by clinical scores, slit lamp photography and western blot. HCET were exposed to 100μg/ml PM10 for 24h before challenge with strain 19660 (MOI 20). A subset of cells were pre-treated with 50nM SKQ1 for 1h before PM10 exposure. Phase contrast microscopy was used to study cell morphology, cell viability was measured by an MTT assay, and ROS by DCFH-DA. Levels of pro-inflammatory markers and anti-oxidant enzymes were evaluated by RT-PCR, western blot and ELISA. Reduced glutathione (GSH) and malondialdehyde (MDA) levels were evaluated by assay kits.

Results

In vivo, whole body exposure to PM10 vs. control air exposed mouse corneas showed early perforation and/or corneal thinning at 3 days post infection, accompanied by increased TNF-α and decreased SOD2 protein levels. In vitro, PM10 induced a dose dependent reduction in cell viability of HCET and significantly increased mRNA levels of pro-inflammatory molecules compared to control. Exposure to PM10 before bacterial challenge further amplified the reduction in cell viability and GSH levels. Furthermore, PM10 exposure also exacerbated the increase in MDA and ROS levels and phase contrast microscopy revealed more rounded cells after strain 19660 challenge. PM10 exposure also further increased the mRNA and protein levels of pro-inflammatory molecules, while anti-inflammatory IL-10 was decreased. SKQ1 reversed the rounded cell morphology observed by phase contrast microscopy, increased levels of MDA, ROS and pro-inflammatory molecules, and restored IL-10.

Conclusions

PM10 induces decreased cell viability, oxidative stress and inflammation in HCET and has an additive effect upon bacterial challenge. SKQ1 protects against oxidative stress and inflammation induced by PM10 after bacterial challenge by reversing these effects. The findings provide insight into mechanisms underlying early perforation and thinning observed in infected corneas of PM10 exposed mice.

The miR-183/96/182 cluster is a checkpoint for resident immune cells and shapes the cellular landscape of the cornea

PURPOSE

The conserved miR-183/96/182 cluster (miR-183C) regulates both corneal sensory innervation and corneal resident immune cells (CRICs). This study is to uncover its role in CRICs and in shaping the corneal cellular landscape at a single-cell (sc) level.

METHODS

Corneas of naïve, young adult [2 and 6 months old (mo)], female miR-183C knockout (KO) mice and wild-type (WT) littermates were harvested and dissociated into single cells. Dead cells were removed using a Dead Cell Removal kit. CD45+ CRICs were enriched by Magnetic Activated Cell Sorting (MACS). scRNA libraries were constructed and sequenced followed by comprehensive bioinformatic analyses.

RESULTS

The composition of major cell types of the cornea stays relatively stable in WT mice from 2 to 6 mo, however the compositions of subtypes of corneal cells shift with age. Inactivation of miR-183C disrupts the stability of the major cell-type composition and age-related transcriptomic shifts of subtypes of corneal cells. The diversity of CRICs is enhanced with age. Naïve mouse cornea contains previously-unrecognized resident fibrocytes and neutrophils. Resident macrophages (ResMφ) adopt cornea-specific function by expressing abundant extracellular matrix (ECM) and ECM organization-related genes. Naïve cornea is endowed with partially-differentiated proliferative ResMφ and contains microglia-like Mφ. Resident lymphocytes, including innate lymphoid cells (ILCs), NKT and γδT cells, are the major source of innate IL-17a. miR-183C limits the diversity and polarity of ResMφ.

CONCLUSION

miR-183C serves as a checkpoint for CRICs and imposes a global regulation of the cellular landscape of the cornea.

Host-microbe interactions in cornea

Corneal infections result through interaction between microbes and host innate immune receptors. Damage to the cornea occurs as a result of microbial virulence factors and is often exacerbated by lack of a controlled host immune response; the latter contributing to bystander damage to corneal structure. Understanding mechanisms involved in host microbial interactions is critical to development of novel therapeutic targets, ultimate control of microbial pathogenesis, and restoration of tissue homeostasis. Studies on these interactions continue to provide exciting findings directly related to this ultimate goal.

Airborne Exposure of the Cornea to PM10 Induces Oxidative Stress and Disrupts Nrf2 Mediated Anti-Oxidant Defenses

The purpose of this study is to test the effects of whole-body animal exposure to airborne particulate matter (PM) with an aerodynamic diameter of <10 μm (PM10) in the mouse cornea and in vitro. C57BL/6 mice were exposed to control or 500 µg/m3 PM10 for 2 weeks. In vivo, reduced glutathione (GSH) and malondialdehyde (MDA) were analyzed. RT-PCR and ELISA evaluated levels of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling and inflammatory markers. SKQ1, a novel mitochondrial antioxidant, was applied topically and GSH, MDA and Nrf2 levels were tested. In vitro, cells were treated with PM10 ± SKQ1 and cell viability, MDA, mitochondrial ROS, ATP and Nrf2 protein were tested. In vivo, PM10 vs. control exposure significantly reduced GSH, corneal thickness and increased MDA levels. PM10-exposed corneas showed significantly higher mRNA levels for downstream targets, pro-inflammatory molecules and reduced Nrf2 protein. In PM10-exposed corneas, SKQ1 restored GSH and Nrf2 levels and lowered MDA. In vitro, PM10 reduced cell viability, Nrf2 protein, and ATP, and increased MDA, and mitochondrial ROS; while SKQ1 reversed these effects. Whole-body PM10 exposure triggers oxidative stress, disrupting the Nrf2 pathway. SKQ1 reverses these deleterious effects in vivo and in vitro, suggesting applicability to humans.

The links of fine airborne particulate matter exposure to occurrence of cardiovascular and metabolic diseases in Michigan, USA

Air pollutants, particularly airborne particulate matter with aerodynamic diameter < 2.5μm (PM2.5), have been linked to the increase in mortality and morbidity associated with cardiovascular and metabolic diseases. In this study, we investigated the dose-risk relationships between PM2.5 concentrations and occurrences of cardiovascular and metabolic diseases as well as the confounding socioeconomic factors in Michigan, USA, where PM2.5 levels are generally considered acceptable. Multivariate linear regression analyses were performed to investigate the relationship between health outcome and annual ground-level PM2.5 concentrations of 82 counties in Michigan. The analyses revelated significant linear dose-response associations between PM2.5 concentrations and cardiovascular disease (CVD) hospitalization. A 10 μg/m3 increase in PM2.5 exposure was found to be associated with a 3.0% increase in total CVD, 0.45% increase in Stroke, and a 0.3% increase in Hypertension hospitalization rates in Medicare beneficiaries. While the hospitalization rates of Total Stroke, Hemorrhagic Stroke, and Hypertension in urbanized counties were significantly higher than those of rural counties, the death rates of coronary heart disease and ischemic stroke in urbanized counties were significantly lower than those of rural counties. These results were correlated with the facts that PM2.5 levels in urbanized counties were significantly higher than that in rural counties and that the percentage of the population with health insurance and the median household income in rural counties were significantly lower. While obesity prevalence showed evidence of a weak positive correlation (ρ = 0.20, p-value = 0.078) with PM2.5 levels, there was no significant dose-response association between county diabetes prevalence rates and PM2.5 exposure in Michigan. In summary, this study revealed strong dose-response associations between PM2.5 concentrations and CVD incidence in Michigan, USA. The socioeconomic factors, such as access to healthcare resources and median household income, represent important confounding factors that could override the impact of PM2.5 exposure on CVD mortality.

Ocular Effects of Glycyrrhizin at Acidic and Neutral pH

Purpose

To test the effects of acidic vs. neutral pH glycyrrhizin (GLY) on the unwounded and wounded normal mouse cornea and after infection with Pseudomonas aeruginosa isolates KEI 1025 and multidrug-resistant MDR9.

Methods

Acidic or neutral GLY vs. phosphate-buffered saline (PBS) was topically applied to normal or wounded corneas of C57BL/6 mice. In unwounded corneas, goblet cells and corneal nerves were stained and quantitated. After wounding, corneas were fluorescein stained and photographed using a slit lamp. Mice also were infected with KEI 1025 or MDR9 and the protective effects of GLY pH evaluated comparatively.

Results

In the unwounded cornea, application of acidic or neutral GLY vs. PBS reduced the number of bulbar conjunctival goblet cells but did not alter corneal nerve density. Similar application of GLY to scarified corneas delayed wound closure. After KEI 1025 infection, none of the GLY vs. PBS-treated corneas perforated; GLY treatment also decreased plate count (neutral pH more effective) and reduced MPO and several cytokines. Similarly, for MDR9, GLY at either pH was protective and also enhanced the effects of moxifloxacin to which MDR9 is resistant.

Conclusion

Acidic or neutral pH GLY decreased goblet cell number but had no effect on nerve density. After corneal wounding, GLY at either pH (1) delayed wound closure and, (2) after infection, decreased keratitis when used alone or in combination with moxifloxacin. Neutral pH did not alter the therapeutic effect of GLY and would be preferred if used clinically.

Prophylactic Knockdown of the miR-183/96/182 Cluster Ameliorates Pseudomonas aeruginosa-Induced Keratitis

Purpose

Previously, we demonstrated that miR-183/96/182 cluster (miR-183C) knockout mice exhibit decreased severity of Pseudomonas aeruginosa (PA)-induced keratitis. This study tests the hypothesis that prophylactic knockdown of miR-183C ameliorates PA keratitis indicative of a therapeutic potential.

Methods

Eight-week-old miR-183C wild-type and C57BL/6J inbred mice were used. Locked nucleic acid-modified anti-miR-183C or negative control oligoribonucleotides with scrambled sequences (NC ORNs) were injected subconjunctivally 1 day before and then topically applied once daily for 5 days post-infection (dpi) (strain 19660). Corneal disease was graded at 1, 3, and 5 dpi. Corneas were harvested for RT-PCR, ELISA, immunofluorescence (IF), myeloperoxidase and plate count assays, and flow cytometry. Corneal nerve density was evaluated in flatmounted corneas by IF staining with anti-β-III tubulin antibody.

Results

Anti-miR-183C downregulated miR-183C in the cornea. It resulted in an increase in IL-1β at 1 dpi, which was decreased at 5 dpi; fewer polymorphonuclear leukocytes (PMNs) at 5 dpi; lower viable bacterial plate count at both 1 and 5 dpi; increased percentages of MHCII+ macrophages (Mϕ) and dendritic cells (DCs), consistent with enhanced activation/maturation; and decreased severity of PA keratitis. Anti-miR-183C treatment in the cornea of naïve mice resulted in a transient reduction of corneal nerve density, which was fully recovered one week after the last anti-miR application. miR-183C targets repulsive axon-guidance receptor molecule Neuropilin 1, which may mediate the effect of anti-miR-183C on corneal nerve regression.

Conclusions

Prophylactic miR-183C knockdown is protective against PA keratitis through its regulation of innate immunity, corneal innervation, and neuroimmune interactions.

Targeting Inflammation Driven by HMGB1 in Bacterial Keratitis-A Review

Pseudomonas (P.) aeruginosa is a Gram-negative bacteria that causes human infectionsinfections. It can cause keratitis, a severe eye infection, that develops quickly and is a major cause of ulceration of the cornea and ocular complications globally. Contact lens wear is the greatest causative reason in developed countries, but in other countries, trauma and predominates. Use of non-human models of the disease are critical and may provide promising alternative argets for therapy to bolster a lack of new antibiotics and increasing antibiotic resistance. In this regard, we have shown promising data after inhibiting high mobility group box 1 (HMGB1), using small interfering RNA (siRNA). Success has also been obtained after other means to inhinit HMGB1 and include: use of HMGB1 Box A (one of three HMGB1 domains), anti-HMGB1 antibody blockage of HMGB1 and/or its receptors, Toll like receptor (TLR) 4, treatment with thrombomodulin (TM) or vasoactive intestinal peptide (VIP) and glycyrrhizin (GLY, a triterpenoid saponin) that directly binds to HMGB1. ReducingHMGB1 levels in P. aeruginosa keratitis appears a viable treatment alternative.

Effects of Glycyrrhizin Treatment on Diabetic Cornea

Purpose: To test how glycyrrhizin (GLY) affects mouse corneal epithelial cells (MCEC) and the diabetic murine cornea. Methods: Viability of MCEC grown under normal or high glucose (HG) with/without GLY was tested by an MTT assay. In addition, C57BL/6 mice were injected with streptozotocin and a subset of control and diabetic mice received GLY in their drinking water. mRNA and protein levels of proinflammatory and oxidative stress molecules were tested by reverse transcription-polymerase chain reaction (RT-PCR) in both models. Ex vivo studies using human diabetic versus control corneas analyzed proinflammatory and oxidative stress markers using RT-PCR and enzyme-linked immunosorbent assay. Results: GLY protected against loss of cell viability induced by HG and significantly reduced HMGB1, IL-1β, TLR2, TLR4, NLRP3, COX2, SOD2, HO-1, GPX2, and GR1. In vivo, corneas of GLY-treated diabetic mice showed significantly decreased mRNA expression for CXCL2, iNOS, and all molecules listed above; GLY also lowered HMGB1 and IL-1β proteins (in vitro and in vivo). Ex vivo studies using diabetic human corneas revealed elevated mRNA levels of inflammatory and oxidative stress molecules (as listed above for in vivo) versus normal age-matched controls. Protein levels for HMGB1 and IL-1β also were elevated in diabetic human versus control corneas. Conclusions: The data provide evidence that GLY treatment attenuates inflammation and oxidative stress in vitro in MCEC and in vivo in the cornea of diabetic mice. Ex vivo data support the similarities of proinflammatory and oxidative stress data in mouse compared to human, suggesting that GLY treatment would have relevancy to patient care.

The miR-183/96/182 Cluster Regulates the Functions of Corneal Resident Macrophages

Tissue-resident macrophages (ResMϕ) play important roles in the normal development and physiological functions as well as tissue repair and immune/inflammatory response to both internal and external insults. In cornea, ResMϕ are critical to the homeostasis and maintenance, wound healing, ocular immune privilege, and immune/inflammatory response to injury and microbial infection. However, the roles of microRNAs in corneal ResMϕ are utterly unknown. Previously, we demonstrated that the conserved miR-183/96/182 cluster (miR-183/96/182) plays important roles in sensory neurons and subgroups of both innate and adaptive immune cells and modulates corneal response to bacterial infection. In this study, we provide direct evidence that the mouse corneal ResMϕ constitutively produce both IL-17f and IL-10. This function is regulated by miR-183/96/182 through targeting Runx1 and Maf, key transcriptional regulators for IL-17f and IL-10 expression, respectively. In addition, we show that miR-183/96/182 has a negative feedback regulation on the TLR4 pathway in mouse corneal ResMϕ. Furthermore, miR-183/96/182 regulates the number of corneal ResMϕ. Inactivation of miR-183/96/182 in mouse results in more steady-state corneal resident immune cells, including ResMϕ, and leads to a simultaneous early upregulation of innate IL-17f and IL-10 production in the cornea after Pseudomonas aeruginosa infection. Its multiplex regulations on the simultaneous production of IL-17f and IL-10, TLR4 signaling pathway and the number of corneal ResMϕ place miR-183/96/182 in the center of corneal innate immunity, which is key to the homeostasis of the cornea, ocular immune privilege, and the corneal response to microbial infections.

Effects of Glycyrrhizin on Multi-Drug Resistant Pseudomonas aeruginosa

The effects of glycyrrhizin (GLY) on multi-drug resistant (MDR) systemic (MDR9) vs. ocular (B1045) Pseudomonas aeruginosa clinical isolates were determined. Proteomes of each isolate with/without GLY treatment were profiled using liquid chromatography mass spectrometry (LC-MS/MS). The effect of GLY on adherence of MDR isolates to immortalized human (HCET) and mouse (MCEC) corneal epithelial cells, and biofilm and dispersal was tested. Both isolates were treated with GLY (0.25 minimum inhibitory concentration (MIC), 10 mg/mL for MDR9 and 3.75 mg/mL for B1045) and subjected to proteomic analysis. MDR9 had a greater response to GLY (51% of identified proteins affected vs. <1% in B1045). In MDR9 vs. controls, GLY decreased the abundance of proteins for: antibiotic resistance, biofilm formation, and type III secretion. Further, antibiotic resistance and type III secretion proteins had higher control abundances in MDR9 vs. B1045. GLY (5 and 10 mg/mL) significantly reduced binding of both isolates to MCEC, and B1045 to HCET. MDR9 binding to HCET was only reduced at 10 mg/mL GLY. GLY (5 and 10 mg/mL) enhanced dispersal for both isolates, at early (6.5 h) but not later times (24–72 h). This study provides evidence that GLY has a greater effect on the proteome of MDR9 vs. B1045, yet it was equally effective at disrupting adherence and early biofilm dispersal.

Airborne Particulates Affect Corneal Homeostasis and Immunity

Purpose

To determine the effects of airborne particulate matter (PM) <2.5 µm in vitro and on the normal and Pseudomonas aeruginosa (PA)-infected cornea.

Methods

An MTT viability assay tested the effects of PM_2.5 on mouse corneal epithelial cells (MCEC) and human corneal epithelial cells (HCET). MCEC were tested for reactive oxygen species using a 2′,7′-dichlorodihydrofluorescein assay; RT-PCR determined mRNA levels of inflammatory and oxidative stress markers in MCEC (HMGB1, toll-like receptor 2, IL-1β, CXCL2, GPX1, GPX2, GR1, superoxide dismutase 2, and heme oxygenase 1) and HCET (high mobility group box 1, CXCL2, and IL-1β). C57BL/6 mice also were infected and after 6 hours, the PM_2.5 was topically applied. Disease was graded by clinical score and evaluated by histology, plate count, myeloperoxidase assay, RT-PCR, ELISA, and Western blot.

Results

After PM_2.5 (25–200 µg/mL), 80% to 90% of MCEC and HCET were viable and PM exposure increased reactive oxygen species in MCEC and mRNA expression levels for inflammatory and oxidative stress markers in mouse and human cells. In vivo, the cornea of PA+PM_2.5 exposed mice exhibited earlier perforation over PA alone (confirmed histologically). In cornea, plate counts were increased after PA+PM_2.5, whereas myeloperoxidase activity was significantly increased after PA+PM_2.5 over other groups. The mRNA levels for several proinflammatory and oxidative stress markers were increased in the cornea in the PA+PM_2.5 over other groups; protein levels were elevated for high mobility group box 1, but not toll-like receptor 4 or glutathione reductase 1. Uninfected corneas treated with PM_2.5 did not differ from normal.

Conclusions

PM_2.5 triggers reactive oxygen species, upregulates mRNA levels of oxidative stress, inflammatory markers, and high mobility group box 1 protein, contributing to perforation in PA-infected corneas.

Glycyrrhizin Use for Multi-Drug Resistant Pseudomonas aeruginosa: In Vitro and In Vivo Studies

Purpose

Our purpose was to test glycyrrhizin (GLY) effects and ciprofloxacin interactions on multidrug resistant (MDR) isolates of Pseudomonas aeruginosa in vitro and in vivo in a mouse model of keratitis.

Methods

A Hardy-disk tested antibiotic sensitivity of isolates MDR9 (nonocular) and B1045 (ocular). GLY MIC (both isolates) and ciprofloxacin was determined spectrophotometrically. A live/dead assay using confocal microscopy and plate count, tested GLY effects on bacterial permeabilization/viability. Proteomics profiled bacterial efflux pumps (MDR9 vs. PAO1); RT-PCR comparatively tested GLY effects on their mRNA expression levels. The activity of efflux pumps was tested using ethidium bromide (EB); and scanning electron microscopy (SEM) visualized the effects of GLY treatment of bacteria. A combination of GLY and ciprofloxacin was tested in C57BL/6 mice (begun 18 hours after infection) and disease scored, photographed and MPO and plate counts done.

Results

MDR9 was resistant to 6/12 and B1045 to 7/12 antibiotics (both to ciprofloxacin). MIC GLY for MDR9 was 40 mg/mL and 15 mg/mL for B1045. Ciprofloxacin MIC (32 μg/mL) was reduced 2-fold to 16 μg/mL when ciprofloxacin and GLY were combined. GLY altered bacterial membrane permeability and reduced viability. Proteomics revealed increased efflux pumps in MDR9 versus PAO1; GLY reduced their mRNA expression levels and EB suggested decreased activity. In C57BL/6 mice, treatment with GLY and ciprofloxacin versus ciprofloxacin, significantly reduced clinical scores, plate count, and MPO.

Conclusions

GLY decreases MDR by: altering bacterial parameters, including viability and efflux pump activity. In vivo, it increases the effectiveness of ciprofloxacin, reducing ocular disease, plate count, and MPO activity.

MicroRNAs in Ocular Infection

MicroRNAs (miRNAs) are small, non-coding, regulatory RNA molecules and constitute a newly recognized, important layer of gene-expression regulation at post-transcriptional levels. miRNAs quantitatively fine tune the expression of their downstream genes in a cell type- and developmental stage-specific fashion. miRNAs have been proven to play important roles in the normal development and function as well as in the pathogenesis of diseases in all tissues and organ systems. miRNAs have emerged as new therapeutic targets and biomarkers for treatment and diagnosis of various diseases. Although miRNA research in ocular infection remains in its early stages, a handful of pioneering studies have provided insight into the roles of miRNAs in the pathogenesis of parasitic, fungal, bacterial, and viral ocular infections. Here, we review the current status of research in miRNAs in several major ocular infectious diseases. We predict that the field of miRNAs in ocular infection will greatly expand with the discovery of novel miRNA-involved molecular mechanisms that will inform development of new therapies and identify novel diagnostic biomarkers.

The miR-183/96/182 Cluster Regulates Macrophage Functions in Response to Pseudomonas aeruginosa

Macrophages (Mϕ) are an important component of the innate immune system; they play critical roles in the first line of defense to pathogen invasion and modulate adaptive immunity. MicroRNAs (miRNAs) are a newly recognized, important level of gene expression regulation. However, their roles in the regulation of Mϕ and the immune system are still not fully understood. In this report, we provide evidence that the conserved miR-183/96/182 cluster (miR-183/96/182) modulates Mϕ function in their production of reactive nitrogen (RNS) and oxygen species (ROS) and their inflammatory response to Pseudomonas aeruginosa (PA) infection and/or lipopolysaccharide (LPS) treatment. We show that knockdown of miR-183/96/182 results in decreased production of multiple proinflammatory cytokines in response to PA or LPS treatment in Mϕ-like Raw264.7 cells. Consistently, peritoneal Mϕ from miR-183/96/182-knockout versus wild-type mice are less responsive to PA or LPS, although their basal levels of proinflammatory cytokines are increased. In addition, overexpression of miR-183/96/182 results in decreased production of nitrite and ROS in Raw264.7 cells. We also provide evidence that DAP12 and Nox2 are downstream target genes of miR-183/96/182. These data suggest that miR-183/96/182 imposes global regulation on various aspects of Mϕ function through different downstream target genes.

HMGB1 Antagonist, Box A, Reduces TLR4, RAGE, and Inflammatory Cytokines in the Cornea of P. aeruginosa-Infected Mice

PURPOSE

High mobility group box 1 (HMGB1) contributes to adverse disease outcome in Pseudomonas aeruginosa keratitis. This study tests Box A, an HMGB1 antagonist, in a model of the disease.

METHODS

C57BL/6 mice (B6) were injected subconjunctivally (1 day before infection) with Box A or phosphate-buffered saline (PBS), infected with P. aeruginosa strain ATCC 19660, and injected intraperitoneally with Box A or PBS at 1 and 3 days postinfection (p.i.). Clinical scores, photographs with a slit lamp camera, real-time polymerase chain reaction (RT-PCR), western blot, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), myeloperoxidase (MPO), and bacterial plate count were used to assess disease outcome. In separate experiments, the therapeutic potential of Box A was tested as described above, but with treatment begun at 6 h p.i.

RESULTS

Box A versus PBS prophylactic treatment significantly reduced clinical scores, MPO activity, bacterial load, and expression of TLR4, RAGE, IL-1β, CXCL2, and TNF-α in the infected cornea. Box A blocked co-localization of HMGB1/TLR4 in infiltrated cells in the stroma at 3 and 5 days p.i., but only at 5 days p.i. for HMGB1/RAGE. Box A versus PBS therapeutic treatment significantly reduced clinical scores, MPO activity, bacterial load, and protein levels of IL-1β, CXCL2, and IL-6 in the infected cornea.

CONCLUSION

Overall, Box A lessens the severity of Pseudomonas keratitis in mice by decreasing expression of TLR4, RAGE (their interaction with HMGB1), IL-1β, CXCL2 (decreasing neutrophil infiltrate), and bacterial plate count when given prophylactically. Therapeutic treatment was not as effective at reducing opacity (disease), but shared similar features with pretreatment of the mice.

Short Tandem Repeat (STR) Profiles of Commonly Used Human Ocular Surface Cell Lines

PURPOSE

The purpose of this study is to establish the short tandem repeat (STR) profiles of several human cell lines commonly used in ocular surface research.

MATERIALS AND METHODS

Independently DNA was extracted from multiple passages of three human corneal epithelial cell lines, two human conjunctival epithelial cell lines and one meibomian gland cell line, from different laboratories actively involved in ocular surface research. The samples were then subjected to STR analysis on a fee-for-service basis in an academic setting and the data compared against that in available databases.

RESULTS

The STR profiles for the human corneal epithelial cells were different among the three cell lines studied and for each line the profiles were identical across the samples provided by three laboratories. Profiles for the human conjunctival epithelial cells were different among the two cell lines studied. Profiles for the meibomian gland cell line were identical across the samples provided by three laboratories. No samples were contaminated by elements of other cell lines such as HeLa.

CONCLUSIONS

This comprehensive study provides verification of STR profiles for commonly used human ocular surface cell lines that can now be used as a reference by others in the field to authenticate the cell lines in use in their own laboratories.

Topical Glycyrrhizin Is Therapeutic for Pseudomonas aeruginosa Keratitis

PURPOSE

Glycyrrhizin (GLY), an inhibitor of high-mobility group box 1 (HMGB1) protects prophylactically against Pseudomonas aeruginosa keratitis. However, the therapeutic potential of GLY to enhance an antibiotic has not been tested and is our purpose.

METHODS

C57BL/6 mice (B6) were infected with a clinical isolate (KEI 1025) of P. aeruginosa and treated topically at 6 h postinfection (p.i.) with GLY or phosphate-buffered saline (PBS). Clinical scores, photography with a slit lamp, enzyme-linked immunosorbent assay, myeloperoxidase assay, bacterial plate counts, histopathology, reactive oxygen/nitrogen species (ROS/RNS) assays, and in vitro macrophage (Mφ) stimulation assays were used to assess effects of GLY treatment. In separate similar experiments, the ability of GLY to bioenhance the antibiotic, tobramycin (TOB), was assessed.

RESULTS

In vivo, GLY versus PBS topical treatment began at 6 h p.i., improved disease outcome by significantly reducing clinical scores, proinflammatory proteins (HMGB1, RAGE, TLR4, TNF-α, and CXCL2), neutrophil infiltrate, bacterial load, ROS/RNS, and nitric oxide. In vitro, GLY downregulated iNOS and COX-2 expression (mRNA) in both mouse and human (THP-1) Mφ. At 6 and 24 h p.i., treatment with GLY enhanced the effects of TOB compared with TOB alone by significantly reducing corneal bacterial load and/or protein levels of cytokines CXCL2 and IL-1β.

CONCLUSIONS

Data provide evidence that GLY is not only therapeutic for Pseudomonas keratitis through its ability to reduce HMGB1, bacterial load, and oxidative damage but also through its bioenhancement of an antibiotic, even when treatment is initiated at 24 h after infection.

NLRC4 regulates caspase-1 and IL-1beta production in a CD11blowLy6Glow population of cells required for resistance to Pseudomonas aeruginosa keratitis

Psbetaeudomonas (P.) aeruginosa infection of the cornea in BALB/c mice does not result in perforation and the mice have been classified as resistant. However, regulation of this response via inflammasome activation remained untested. Therefore, BALB/c mice were infected with P. aeruginosa ATCC strain 19660 and NLRP3 and NLRC4 protein tested by ELISA. Since NLRC4 vs NLRP3 protein levels were significantly higher in the corneas of BALB/c at 1 and 5 days postinfection we used silencing to knockdown NLRC4. Silencing NLRC4 vs scrambled siRNA treatment exacerbated disease in BALB/c mice, reduced myeloperoxidase levels and elevated bacterial plate counts at 5 days postinfection. It also increased pro IL-1beta, but reduced total protein for IL-1beta and IL-18 at 5 days postinfection. Flow cytometry to identify cells affected by silencing, showed reduced caspase-1 levels in a CD11b^lowLy6G^low population of cells, (but not PMN or macrophages) from the infected cornea of siNLRC4 treated mice that produced less mature IL-1beta. These data provide evidence that the NLRC4 inflammasome contributes to resistance through regulation of caspase-1, IL-1beta and IL-18 in a CD11b^lowLy6G^low population of cells.

Glycyrrhizin Reduces HMGB1 and Bacterial Load in Pseudomonas aeruginosa Keratitis

Purpose

High mobility group box 1 (HMGB1) contributes to poor disease outcome in Pseudomonas aeruginosa keratitis. This study tests the prophylactic effect of treatment with HMGB1 inhibitors, glycyrrhizin (GLY) and its derivative, carbenoxolone (CBX), for Pseudomonas keratitis.

Methods

We treated C57BL/6 (B6) mice subconjunctivally with GLY or CBX, infected with a noncytotoxic clinical isolate (KEI 1025) or a cytotoxic strain (ATCC 19660) of P. aeruginosa, and injected intraperitoneally with either agent. Clinical score, photography with a slit lamp, real-time RT-PCR, ELISA, myeloperoxidase (MPO) assay, bacterial plate count, histopathology, and absorbance assays were used to assess treatment efficacy and bacteriostatic activity.

Results

After KEI 1025 infection, GLY treatment reduced HMGB1 (mRNA and protein levels) and improved disease outcome with significant reduction in mRNA levels of IL-1β, TLR4, CXCL2, and IL-12; protein expression (IL-1β, CXCL2); neutrophil infiltrate; and bacterial load. Treatment with GLY enhanced antimicrobial proteins, including CRAMP and mBD2, but not mBD3. Glycyrrhizin also reduced clinical scores and improved disease outcome in corneas infected with strain 19660. However, neither HMGB1 mRNA or protein levels were reduced, but rather, CXCL2 expression (mRNA and protein), neutrophil infiltrate, and bacterial load were reduced statistically. Treatment with GLY initiated 6 hours after infection reduced plate count; GLY also was bacteriostatic for KEI 1025 and ATCC 19660.

Conclusions

Glycyrrhizin reduces HMGB1 and is protective against P. aeruginosa-induced keratitis with a clinical isolate that is noncytotoxic. It was similar, but less effective when used after infection with a cytotoxic strain, which did not reduce HMGB1.

Kruppel-like Factor 6 Promotes Macrophage-mediated Inflammation by Suppressing B Cell Leukemia/Lymphoma 6 Expression

Macrophages are the predominant innate immune cells recruited to tissues following injury or infection. These early-responding, pro-inflammatory macrophages play an essential role in the amplification of inflammation. However, macrophage pro-inflammatory gene expression should be tightly regulated to avert host tissue damage. In this study, we identify the Kruppel-like transcription factor 6 (KLF6)-B cell leukemia/lymphoma 6 (BCL6) signaling axis as a novel regulator of macrophage inflammatory gene expression and function. Utilizing complementary gain- and loss-of-function studies, we observed that KLF6 is essential for macrophage motility under ex vivo and in vivo conditions. Concordant with these observations, myeloid-specific deficiency of KLF6 significantly attenuates macrophage pro-inflammatory gene expression, recruitment, and progression of inflammation. At the molecular level, KLF6 suppresses BCL6 mRNA and protein expression by elevating PR domain-containing 1 with ZNF domain (PRDM1) levels in macrophages. Interestingly, pharmacological or genetic inhibition of BCL6 in KLF6-deficient macrophages completely abrogated the attenuation of pro-inflammatory cytokine/chemokine expression and cellular motility. Collectively, our observations reveal that KLF6 repress BCL6 to enhance macrophage inflammatory gene expression and function.

Decreasing HMGB1 levels improves outcome of Pseudomonas aeruginosa keratitis in mice

Pseudomonas (P.) aeruginosa is a Gram negative bacterium widely dispersed in the environment which can cause acute and chronic infections in humans. According to the Centers for Disease Control and Prevention (CDC), the overall incidence of P. aeruginosa infections in USA hospitals averages about 0.4% (4/1000 discharges), and the bacterium is the fourth most commonly-isolated nosocomial pathogen accounting for 10.1% of all hospital-acquired infections. P. aeruginosa keratitis is a severe infection of the eye, progresses rapidly and remains a leading cause of corneal ulcers worldwide. Use of contact lenses is the major risk factor in the USA, while in less industrialized countries, trauma from agricultural accidents are of importance. Animal models of bacterial keratitis are of value in the study of this disease and suggest potential alternative therapeutic targets that are needed urgently due to increasing antibiotic resistance. Recently we have shown success and improved disease outcome after down-regulation of one promising target, high mobility group box1 (HMGB1) using small interfering RNA (siRNA). Testing more clinically relevant approaches are underway to reduce HMGB1 levels in P. aeruginosa keratitis which may hold promise for its treatment.

Thrombomodulin Protects Against Bacterial Keratitis, Is Anti-Inflammatory, but Not Angiogenic

PURPOSE

Thrombomodulin (TM) is a multidomain, transmembrane protein with anti-inflammatory properties. Thrombomodulin domain (D) 1 is lectin-like, interacting with Lewis Y antigen on lipopolysaccharide, and with HMGB1, while TMD23 is associated with angiogenic and anti-inflammatory functions. Thus, we tested if TM is protective against Pseudomonas aeruginosa keratitis and whether it enhanced corneal vascularity.

METHODS

Eyes of C57BL/6 (B6) mice were injected with recombinant TM (rTM), rTMD1, or PBS subconjunctivally before and intraperitoneally after infection with P. aeruginosa. Clinical scores, photography with a slit lamp, RT-PCR, ELISA, myeloperoxidase (MPO) assay, viable bacterial plate counts, and India ink perfusion were used to assess the disease response and corneal vascularity (rTM only).

RESULTS

Recombinant TM versus PBS treatment reduced clinical scores and corneal opacity. Corneal mRNA levels for HMGB1 were unchanged, but proinflammatory molecules IL-1β, CXCL2, NF-κB, TLR4, and RAGE were decreased; anti-inflammatory molecules SIGIRR and ST2 were increased. ELISA confirmed the mRNA data for HMGB1, IL-1β, and CXCL2 proteins. Both neutrophil influx and viable bacterial plate counts also were decreased after rTM treatment. Protein levels for angiogenic molecules VEGF, VEGFR-1, and VEGFR-2 were measured at 5 days post infection and were not different or reduced significantly after rTM treatment. Further, perfusion with India ink revealed similar vessel ingrowth between the two groups. Similar studies were performed with rTMD1, but disease severity, mRNA, proteins, MPO, and plate counts were not changed from controls.

CONCLUSIONS

These data provide evidence that rTM treatment is protective against bacterial keratitis, does not reduce HMGB1, and is not angiogenic.

Inactivation of the miR-183/96/182 Cluster Decreases the Severity of Pseudomonas aeruginosa-Induced Keratitis

PURPOSE

The microRNA-183/96/182 cluster (miR-183/96/182) plays important roles in sensory organs. Because the cornea is replete with sensory innervation, we hypothesized that miR-183/96/182 modulates the corneal response to bacterial infection through regulation of neuroimmune interactions.

METHODS

Eight-week-old miR-183/96/182 knockout (ko) mice and their wild-type littermates (wt) were used. The central cornea of anesthetized mice was scarred and infected with Pseudomonas aeruginosa (PA), strain 19660. Corneal disease was graded at 1, 3, and 5 days postinfection (dpi). Corneal RNA was harvested for quantitative RT-PCR. Polymorphonuclear neutrophils (PMN) were enumerated by myeloperoxidase assays; the number of viable bacteria was determined by plate counts, and ELISA assays were performed to determine cytokine protein levels. A macrophage (Mϕ) cell line and elicited peritoneal PMN were used for in vitro functional assays.

RESULTS

MicroRNA-183/96/182 is expressed in the cornea, and in Mϕ and PMN of both mice and humans. Inactivation of miR-183/96/182 resulted in decreased corneal nerve density compared with wt mice. Overexpression of miR-183/96/182 in Mϕ decreased, whereas knockdown or inactivation of miR-183/96/182 in Mϕ and PMN increased their capacity for phagocytosis and intracellular killing of PA. In PA-infected corneas, ko mice showed decreased proinflammatory neuropeptides such as substance P and chemoattractant molecules, MIP-2, MCP1, and ICAM1; decreased number of PMN at 1 and 5 dpi; increased viable bacterial load at 1 dpi, but decreased at 5 dpi; and markedly decreased corneal disease.

CONCLUSIONS

MicroRNA-183/96/182 modulates the corneal response to bacterial infection through its regulation of corneal innervation and innate immunity.

High-mobility group box 1: a novel target for treatment of Pseudomonas aeruginosa keratitis

High-mobility group box 1 (HMGB1), a prototypic alarmin, mediates the systemic inflammatory response syndrome. Treatment with vasoactive intestinal peptide, an anti-inflammatory neuropeptide, downregulates proinflammatory cytokines and promotes healing in a susceptible (cornea perforates) model of Pseudomonas aeruginosa keratitis, and also significantly downregulates HMGB1 expression. Therefore, we examined targeting HMGB1 for the treatment of P. aeruginosa keratitis to avoid delivery and other issues associated with vasoactive intestinal peptide. For this, HMGB1 was silenced using small interfering RNA, whereas controls were treated with a nonspecific scrambled sequence small interfering RNA. Less disease was seen postinfection in siHMGB1 compared with control mice and was documented by clinical score and photographs with a slit lamp. Real-time RT-PCR and ELISA confirmed HMGB1 knockdown. RT-PCR analysis also revealed reduced mRNA levels of IL-1β, MIP-2, TNF-α, TLR4, and receptor for advanced glycation end products, whereas mRNA levels of anti-inflammatory TLRs single Ig IL-1-related receptor and ST2 were increased significantly. HMGB1 knockdown also decreased IL-1β and MIP-2 proteins, reducing polymorphonuclear cell number in the infected cornea. mRNA and protein levels of CXCL12 and CXCR4, as well as mononuclear cells, were reduced significantly after HMGB1 knockdown. Ab neutralization of HMGB1, infection with a clinical isolate, and recombinant HMGB1 treatment of resistant mice supported the silencing studies. These data provide evidence that silencing HMGB1 promotes better resolution of P. aeruginosa keratitis by decreasing levels of proinflammatory mediators (decreasing polymorphonuclear cell infiltration), increasing anti-inflammatory TLRs, reducing CXCL12 (preventing HMGB1/CXCL12 heterodimer formation), and signaling through CXCR4, reducing monocyte/macrophage infiltration.

Interleukin 17 regulates Mer tyrosine kinase-positive cells in Pseudomonas aeruginosa keratitis

PURPOSE

To determine if IL-17 regulates Mer tyrosine kinase-positive (MerTK+) cells in Pseudomonas aeruginosa keratitis.

METHODS

Interleukin 17 was tested in normal and infected cornea of susceptible C57BL/6 and resistant BALB/c mice. The latter were treated with recombinant mouse (rm) IL-17; both groups were treated with IL-17 neutralizing antibody. Mice were infected, and clinical score, PCR, ELISA, and myeloperoxidase (MPO) assays tested expression of proinflammatory and anti-inflammatory mediators and polymorphonuclear neutrophilic leukocyte (PMN) infiltrate. Fas and Fas ligand (FasL) protein levels were assessed in both mouse strains, while MerTK+ cells were examined by immunostaining and cell sorting before and after IL-17 neutralization.

RESULTS

The IL-17 mRNA and protein were higher in C57BL/6 versus BALB/c cornea after infection. The rmIL-17 treatment of BALB/c mice modified proinflammatory and anti-inflammatory mediators, but clinical score and MPO assay revealed no differences. However, only BALB/c mice treated with IL-17 neutralizing antibody showed increased disease, macrophage inflammatory protein (MIP) 2, and MPO levels. Fas and FasL protein levels, elevated earlier in BALB/c versus C57BL/6 mice, correlated with significantly more MerTK+ cells in BALB/c cornea at 3 days after infection. Neutralization of IL-17 in C57BL/6 mice elevated MerTK+ cells, while similar treatment of BALB/c mice significantly decreased them.

CONCLUSIONS

These data provide evidence that IL-17 expression is higher in C57BL/6 versus BALB/c cornea after infection and that the latter group has more MerTK+ cells. Exogenous rmIL-17 failed to shift the disease response in resistant mice, but its neutralization resulted in worsened disease and reduced MerTK+ cells. Neutralization of IL-17 in C57BL/6 mice increased MerTK+ cells but did not dramatically shift the disease response.

IL-10 function, regulation, and in bacterial keratitis

The immune system protects the host from pathogenic microbes, but tight regulation of the evoked response is requisite to limit bystander damage. The interleukin (IL)-10 family of cytokines, composed of 9 members: IL-10, IL-19, IL-20, IL-22, IL-24, IL-26, and 3 distantly related members, IL-28A, IL-28B, and IL-29, plays a central role in this regulation. IL-10 family cytokines emerged before the adaptive immune response and elicit diverse host defense mechanisms, especially from epithelial cells during an infection. IL-10 family cytokines are also essential for maintenance and integrity of tissue epithelial layers. These cytokines promote innate immune responses from tissue epithelia that limit the damage caused by both viral and bacterial infections. They also facilitate tissue healing after infection/inflammation. In this regard, IL-10 suppresses pro-inflammatory responses, limiting tissue disruption resulting from an inflammatory response. Thus, a central functional theme of IL-10 family cytokines is their role in tissue protection. This review focuses on IL-10, the founding member of this family of cytokines, and integrates recent data on the function and regulation of IL-10 during bacterial infections. Emphasis is placed on the role of IL-10 in Pseudomonas aeruginosa keratitis and the subsequent infectious/inflammatory processes evoked.

HGF signaling impacts severity of Pseudomonas aeruginosa keratitis

PURPOSE

To determine whether rapamycin altered corneal growth factor levels to impact severity of Pseudomonas aeruginosa keratitis.

METHODS

BALB/c mice were injected intraperitoneally with rapamycin or PBS and infected with P. aeruginosa. Corneas were harvested and mRNA levels of growth factors (EGF, HGF, FGF-7/KGF), receptors (EGFR, c-met, FGFR-2), and signaling molecules (PI3K, Akt, S6K1, and IGF-1R) tested. ELISA determined HGF/c-met, IGF-1, and Substance P (SP) protein levels. Corneal application of recombinant (r)HGF was assessed by clinical score, photography with a slit lamp, real-time RT-PCR (mRNA for mT0R, IL-10, IL-12, IL-18, PI3KCα, Akt), and ELISA (total and phosphorylated [p]c-met); rIGF-1 effects also were tested by ELISA. In vitro, RAW cells and peritoneal macrophages were stimulated with LPS ± rHGF ± c-met inhibitor (CI) and mTOR mRNA levels tested.

RESULTS

Rapamycin disparately regulated infected corneal mRNA levels of EGF/EGFR and FGF-7/FGFR-2, but HGF/c-met mRNA levels both increased. ELISA confirmed elevated HGF protein. Rapamycin did not change PI3KCα or Akt signaling molecule expression, downregulated S6K1, but upregulated IGF-1R mRNA levels; IGF-1 and SP proteins also were upregulated. After infection, topical rHGF versus PBS increased mRNA levels of IL-12p40, IL-18, PI3KCα, and Akt; mTOR and IL-10 mRNA were downregulated; rIGF-1 increased HGF protein. In vitro, rHGF and LPS lowered RAW cell and macrophage mTOR levels; CI addition restored them.

CONCLUSIONS

Collectively, these data provide evidence that enhanced corneal HGF levels increase signaling through the c-met receptor, decrease mTOR levels, and enhance proinflammatory cytokines, while decreasing anti-inflammatory cytokines, and that HGF signaling is central to disease outcome.

HIF-1α is essential for effective PMN bacterial killing, antimicrobial peptide production and apoptosis in Pseudomonas aeruginosa keratitis

Hypoxia-inducible factor (HIF)-1α, is a transcription factor that controls energy metabolism and angiogenesis under hypoxic conditions, and a potent regulator of innate immunity. The studies described herein examined the role of HIF-1α in disease resolution in BALB/c (resistant, cornea heals) mice after ocular infection with Pseudomonas (P.) aeruginosa. Furthermore, the current studies focused on the neutrophil (PMN), the predominant cell infiltrate in keratitis. Using both siRNA and an antagonist (17-DMAG), the role of HIF-1α was assessed in P. aeruginosa-infected BALB/c mice. Clinical score and slit lamp photography indicated HIF-1α inhibition exacerbated disease and corneal destruction. Real time RT-PCR, immunohistochemistry, ELISA, Greiss and MPO assays, bacterial load, intracellular killing, phagocytosis and apoptosis assays further tested the regulatory role of HIF-1α. Despite increased pro-inflammatory cytokine expression and increased MPO levels after knocking down HIF-1α expression, in vivo studies revealed a decrease in NO production and higher bacterial load. In vitro studies using PMN provided evidence that although inhibition of HIF-1α did not affect phagocytosis, both bacterial killing and apoptosis were significantly affected, as was production of antimicrobial peptides. Overall, data provide evidence that inhibition of HIF-1α converts a normally resistant disease response to susceptible (corneal thinning and perforation) after induction of bacterial keratitis. Although this inhibition does not appear to affect PMN transmigration or phagocytosis, both in vivo and in vitro approaches indicate that the transcriptional factor is essential for effective bacterial killing, apoptosis and antimicrobial peptide production.

TREM-2 promotes host resistance against Pseudomonas aeruginosa infection by suppressing corneal inflammation via a PI3K/Akt signaling pathway

PURPOSE

To explore the role of triggering receptor expressed on myeloid cells 2 (TREM-2) in Pseudomonas aeruginosa (PA) keratitis.

METHODS

BALB/c mice were routinely infected with PA and evaluated at various postinfection time points for corneal expression of TREM-2, by real-time PCR, Western blot, and flow cytometry. Next, BALB/c and C57BL/6 mice were respectively treated with TREM-2 siRNA or agonistic anti-TREM-2 antibody, to determine the role of TREM-2 in PA keratitis. Bacterial load and neutrophil infiltration were tested by plate count and myeloperoxidase assay, respectively. Th1-/Th2-type and proinflammatory cytokine expression were tested by real-time PCR and ELISA after in vivo and in vitro silencing of TREM-2. Moreover, phosphorylated Akt levels were tested by Western blot in murine macrophages after treatment with agonistic anti-TREM-2 antibody. mRNA levels of proinflammatory cytokines were examined in murine macrophages after TREM-2 activation and lipopolysaccharide stimulation, following pretreatment with inhibitors for PI3K or Akt, to determine whether PI3K/Akt is required in TREM-2-mediated immune modulation. In addition, BALB/c mice were treated with wortmannin and analyzed for bacterial load and proinflammatory cytokine expression.

RESULTS

TREM-2 expression was elevated in the infected BALB/c corneas at 3 or 5 days postinfection. Silencing of TREM-2 accelerated disease progression by enhancing bacterial load and corneal inflammation, whereas activation of TREM-2 promoted host resistance to PA keratitis. PI3K/Akt signaling is required in the TREM-2-mediated immune modulation, and inhibition of PI3K resulted in worsened disease after PA corneal infection.

CONCLUSIONS

TREM-2 promoted host resistance to PA infection by suppressing corneal inflammation via activation of the PI3K/Akt pathway.

Mammalian target of rapamycin regulates IL-10 and resistance to Pseudomonas aeruginosa corneal infection

IL-10 is important in the resistance response of BALB/c mice to experimental Pseudomonas aeruginosa corneal infection. However, the cellular mechanisms by which this anti-inflammatory cytokine is regulated remain unknown. Because the mammalian target of rapamycin (mTOR) regulates IL-10 in other disease models, the present study tested its role in bacterial keratitis. After infection, corneas of rapamycin versus control-treated BALB/c mice showed worsened disease, and real-time RT-PCR confirmed that mTOR mRNA levels were significantly decreased. Rapamycin treatment also increased clinical score, polymorphonuclear neutrophil (PMN) infiltration (determined by myeloperoxidase assay), and bacterial load, but it diminished PMN bactericidal activity. Inhibition of mTOR also led to elevated mRNA and protein levels of IL-12p40, matrix metalloproteinase 9, and inducible NO synthase, whereas mRNA and protein levels of IL-10, its regulator/effector STAT-3, and suppressor of cytokine signaling 3 (a proinflammatory cytokine regulator) were decreased. Furthermore, mTOR inhibition reduced levels of proapoptotic caspase-3 and increased levels of B cell lymphoma-2 (antiapoptotic), indicative of delayed apoptosis. mTOR inhibition also altered genes related to TLR signaling, including elevation of TLR4, TLR5, and IL-1R1, with decreases in IL-1R-associated kinase 1 and an inhibitor of NF-κB, NF-κB inhibitor-like 1. Rapamycin treatment also increased levels of IFN-γ and CCAAT/enhancer binding protein, β, a gene that regulates expression of preprotachykinin-A (the precursor of substance P). Collectively, these data, as well as a rescue experiment using rIL-10 together with rapamycin, which decreased PMN in cornea, provide concrete evidence that mTOR regulates IL-10 in P. aeruginosa-induced bacterial keratitis and is critical to balancing pro- and anti-inflammatory events, resulting in better disease outcome.

The role of VIP in cornea

PURPOSE

Exogenous vasoactive intestinal peptide (VIP) down-regulates pro-inflammatory but up-regulates anti-inflammatory cytokines, growth factors (GFs) and Toll-like receptors promoting healing in experimental Pseudomonas aeruginosa (P. aeruginosa) keratitis. Whether VIP is required for GF or GF receptor (R) expression in normal and infected corneas is unknown and is the purpose of this study.

METHODS

VIP knockout ((-/-)) and wild-type (WT) C57BL/6 (B6) mice were infected and tested using PCR array, real-time RT-PCR, ELISA, and immunostaining. VIP antagonist treatment studies also were done using B6 and BALB/c mice.

RESULTS

Infected corneas of VIP(-/-) versus WT B6 mice perforated earlier (2 vs. 5 days postinfection [p.i.]), and array data showed that GFs were differentially changed between groups. RT-PCR revealed that the infected cornea of VIP(-/-) versus WT mice expressed higher mRNA levels of epidermal growth factor (EGF) and hepatocyte growth factor (HGF), reduced FGF, EGFR, and HGFR, with no difference in FGFR; differences between groups were not seen in normal cornea. Immunostaining for GF and GFR in the normal cornea of VIP(-/-) versus WT mice was similar. However, at 1 day p.i., VIP(-/-) versus WT mice had more intense EGF and HGF, similar FGFR, and reduced FGF, EGFR, and HGFR staining. VIP antagonist treatment decreased protein levels for GFR at 5 days p.i. in both B6 and BALB/c mice, with no significant changes in normal cornea.

CONCLUSIONS

The data showed that endogenous VIP is not requisite for GF or GFR expression in the normal cornea but, after infection, its absence or reduction is critical for their regulation.

Effects of VIP on corneal reconstitution and homeostasis following Pseudomonas aeruginosa induced keratitis

PURPOSE

Studies from our laboratory have demonstrated that vasoactive intestinal peptide (VIP) directly converts the normally susceptible C57BL/6J (B6) mouse to resistant after ocular infection through modulation of the inflammatory response. This study examines mechanisms by which VIP influences the healing phase following infection--specifically reconstitution of the extracellular matrix (ECM).

METHODS

B6 mice received daily intraperitoneal (IP) injections of VIP, while control mice were similarly injected with sterile phosphate buffered saline (PBS). Real-time RT-PCR, ELISA, and immunofluorescent staining were used to assess the effects of VIP treatment on ECM molecule expression after Pseudomonas aeruginosa-induced keratitis. We also compared the effect of VIP treatment on lipopolysaccharide (LPS)-stimulated B6- and BALB/c-derived fibroblasts.

RESULTS

In vivo analyses revealed that VIP treatment of P. aeruginosa-infected B6 corneas led to a significant increase in ECM molecules associated with healing/homeostasis, while those associated with ECM degradation were significantly down-regulated when compared to wild-type (WT) controls. In vitro studies revealed that VIP treatment of lipopolysaccharide-stimulated fibroblasts derived from susceptible B6 and resistant BALB/c mice expressed distinct differences in ECM molecule expression, whereby the latter expressed higher levels of ECM molecules aimed at reconstitution. Furthermore, differential expression of VIP receptor-1/VIP receptor-2 (VIPR1/VIPR2) was observed between B6 and BALB/c after VIP treatment of LPS-stimulated fibroblasts.

CONCLUSIONS

VIP treatment functions to enhance ECM reconstitution, which appears to be carried out in large part by fibroblasts via VIPR2. Overall, the data from this study suggest that VIP not only regulates disease pathogenesis, but also functions to restore integrity of the corneal stroma.

Substance P affects growth factors in Pseudomonas aeruginosa-infected mouse cornea

PURPOSE

This study analyzed the influence of substance P (SP) on growth factors related to wound healing in mice in the presence of infectious keratitis.

METHODS

Naturally resistant mice were injected intraperitoneally with SP or phosphate-buffered saline and infected with Pseudomonas aeruginosa, and corneal messenger RNA (mRNA) levels of growth factors and apoptosis genes were tested. Enzyme-linked immunosorbent assay determined the protein levels, whereas immunohistochemistry tested the distribution, macrophage phenotype, and cell quantitation. In vitro, macrophages were stimulated with lipopolysaccharide (LPS; with or without SP) and mRNA levels of proinflammatory and antiinflammatory cytokines and apoptosis genes were tested.

RESULTS

After SP, epidermal growth factor mRNA and protein levels were disparately regulated early, with no differences later in the disease. Hepatocyte growth factor and fibroblast growth factor-7 mRNA and protein levels were increased after SP treatment. Enumerating dual-labeled stromal cells revealed no difference between SP-treated versus phosphate-buffered saline-treated groups in the percentage of epidermal growth factor-labeled fibroblasts or macrophages, but there were significant increases in both hepatocyte growth factor- and fibroblast growth factor-7-labeled cells. Type 2 (M2) macrophages and caspase-3 mRNA levels were decreased, whereas B-cell lymphoma-2 mRNA expression was increased after SP treatment. In vitro, mRNA levels of several proinflammatory cytokines and B-cell lymphoma-2 were elevated, whereas transforming growth factor β was decreased after macrophage stimulation with SP (with LPS) over LPS alone. (Mice: n = 105 control; 105 experimental.)

CONCLUSIONS

These data show that treatment with SP in infectious keratitis elevates growth factors but also adversely affects the disease by enhancing the inflammatory response and its sequelae.

Vasoactive intestinal peptide downregulates proinflammatory TLRs while upregulating anti-inflammatory TLRs in the infected cornea

TLRs recognize microbial pathogens and trigger an immune response, but their regulation by neuropeptides, such as vasoactive intestinal peptide (VIP), during Pseudomonas aeruginosa corneal infection remains unexplored. Therefore, C57BL/6 (B6) mice were injected i.p. with VIP, and mRNA, protein, and immunostaining assays were performed. After VIP treatment, PCR array and real-time RT-PCR demonstrated that proinflammatory TLRs (conserved helix-loop-helix ubiquitous kinase, IRAK1, TLR1, TLR4, TLR6, TLR8, TLR9, and TNFR-associated factor 6) were downregulated, whereas anti-inflammatory TLRs (single Ig IL-1-related receptor [SIGIRR] and ST2) were upregulated. ELISA showed that VIP modestly downregulated phosphorylated inhibitor of NF-κB kinase subunit α but upregulated ST2 ~2-fold. SIGIRR was also upregulated, whereas TLR4 immunostaining was reduced in cornea; all confirmed the mRNA data. To determine whether VIP effects were cAMP dependent, mice were injected with small interfering RNA for type 7 adenylate cyclase (AC7), with or without VIP treatment. After silencing AC7, changes in mRNA levels of TLR1, TNFR-associated factor 6, and ST2 were seen and unchanged with addition of VIP, indicating that their regulation was cAMP dependent. In contrast, changes were seen in mRNA levels of conserved helix-loop-helix ubiquitous kinase, IRAK1, 2, TLR4, 9 and SIGIRR following AC7 silencing alone; these were modified by VIP addition, indicating their cAMP independence. In vitro studies assessed the effects of VIP on TLR regulation in macrophages and Langerhans cells. VIP downregulated mRNA expression of proinflammatory TLRs while upregulating anti-inflammatory TLRs in both cell types. Collectively, the data provide evidence that VIP downregulates proinflammatory TLRs and upregulates anti-inflammatory TLRs and that this regulation is both cAMP dependent and independent and involves immune cell types found in the infected cornea.

VIP and growth factors in the infected cornea

PURPOSE

Vasoactive intestinal peptide (VIP) is an anti-inflammatory neuropeptide that downregulates proinflammatory cytokines and promotes healing in a susceptible model of P. aeruginosa keratitis. Growth factors also play a role in corneal healing and restoration of tissue homeostasis after wounding. However, whether VIP treatment modulates growth factors to promote healing in the infected cornea remains untested and is the purpose of this study.

METHODS

C57BL/6 (B6) mice were injected with VIP and mRNA and protein levels, and immunostaining for EGF, FGF, HGF, and VEGF-A were done. Exogenous treatment with a mixture of the growth factors also was tested and levels of cytokines, defensins, and bacterial counts were determined.

RESULTS

Real-time RT-PCR, immunostaining, and ELISA data demonstrated that treatment with VIP enhanced levels of EGF, FGF, and HGF during disease, and that VEGF-A, and associated angiogenic molecules also were increased by VIP. Moreover, immunohistochemical studies confirmed that both epithelial and stromal cells participated in growth factor production. Most notably, treatment with a mixture of EGF, FGF, and HGF after disease onset, prevented corneal perforation when compared with controls. This outcome was associated with downregulation of proinflammatory cytokines such as macrophage inflammatory protein-2 (MIP-2), upregulation of anti-inflammatory cytokines such as TGF-β, and antimicrobials β-defensins 2 and 3, as well as decreased plate counts at 1 day postinfection (p.i.) (P = 0.0001).

CONCLUSIONS

Collectively, the data provide evidence that VIP treatment modulates growth factors, angiogenic molecules, and defensins in the infected cornea and that this in turn promotes healing and restoration of tissue homeostasis.

Testican-1 promotes resistance against Pseudomonas aeruginosa-induced keratitis through regulation of MMP-2 expression and activation

PURPOSE

Testican-1 (or SPOCK) is a highly conserved chimeric proteoglycan encoded by the SPOCK1 gene. Protease regulatory activity has recently been demonstrated by this molecule and its family members testican-2 and -3. The present study tested the hypothesis that testican-1 regulates corneal matrix metalloproteinase (MMP)-2 expression, thus improving disease outcome after Pseudomonas aeruginosa-induced keratitis.

METHODS

C57BL/6 (B6) and BALB/c mice were routinely infected with P. aeruginosa and were evaluated at various postinfection (pi) times for corneal expression of testican-1 and MMP-2, by PCR array, real-time RT-PCR, ELISA, activity assays, zymography, and immunohistochemistry. Next, B6 mice were treated with recombinant human (rh) testican-1, and expression was knocked down in BALB/c ice by siTestican-1 treatment, to determine the relationship between the two molecules.

RESULTS

BALB/c versus B6 mice expressed significantly higher mRNA and protein levels of testican-1 after P. aeruginosa-induced ocular infection. MMP-2 expression and activation was also disparate between the two mouse strains. After rhTestican-1 treatment in B6 mice, overall disease response was significantly improved, whereas siRNA treatment of BALB/c mice converted the normally resistant response to susceptible. Testican-1 was shown to influence MMP-2 expression, activation, and regulation, as well.

CONCLUSIONS

This study demonstrates corneal expression of testican-1 and its temporal regulation of MMP-2 expression and activation after induction of bacterial keratitis. Furthermore, the data collectively indicate that testican-1 is a novel target for disease treatment to promote better disease outcome regarding chronic inflammation and infection and diseases involving pathologic tissue destruction.

Reviews for immune privilege in the year 2010: immune privilege and infection

Advances in understanding host innate/adaptive immunity and abrogation of immune privilege in ocular viral and bacterial infections have been accomplished using animal models. In Pseudomonas aeruginosa keratitis, mouse models have shown that IL-12-driven IFN-gamma production in Th1 responder strains such as C57BL/6 contributes to corneal perforation, while IL-18-driven IFN-gamma production is associated with bacterial killing and less disease in Th2 responders (BALB/c). The role of neuropeptides, macrophages, and regulation of neutrophil apoptosis is discussed. The potentially blinding Th1 CD4 T-cell-mediated immunopathology referred to as herpes stromal keratitis (HSK) is characterized by breakdown of the normal barrier to blood and lymph angiogenesis in the cornea, a dramatic increase in mature professional antigen-presenting cells, and a heavy leukocytic infiltrate composed primarily of neutrophils. HSK is more frequent and severe in BALB/c than C57BL/6 mice, and varies in severity with the strain and dose of HSV-1 used to infect the cornea.

VIP promotes resistance in the Pseudomonas aeruginosa-infected cornea by modulating adhesion molecule expression

PURPOSE

This study tested the hypothesis that the neuropeptide vasoactive intestinal peptide (VIP) regulates adhesion molecule expression, reduces inflammatory cell migration and infiltration into the Pseudomonas aeruginosa-infected cornea of susceptible B6 mice, and promotes corneal healing and resistance.

METHODS

B6 mice received daily intraperitoneal (IP) injections of VIP from -1 through 5 days after infection. Control mice were similarly injected with sterile phosphate-buffered saline (PBS). Transcript levels of adhesion molecules were determined by PCR array, then select molecules were tested individually by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and confirmed at the protein level by enzyme-linked immunosorbent assay (ELISA) or immunofluorescent staining with confocal laser scanning microscopy at various time points after infection to assess the effects of VIP treatment in the regulation of adhesion molecule expression.

RESULTS

Injection of B6 mice with VIP compared with PBS resulted in significant downregulation of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, platelet-endothelial cell adhesion molecule-1, and P-selectin and L-selectin mRNA expression. Protein levels for ICAM-1 and VCAM-1, detected by ELISA, supported the mRNA data at similar time points. Immunofluorescence staining further confirmed the effects of VIP treatment, showing reduced corneal expression of ICAM-1/leukocyte function-associated antigen (LFA-1) and VCAM-1/very late antigen-4 (VLA-4) at select time points compared with PBS-treated animals.

CONCLUSIONS

VIP treatment downregulates the production of adhesion molecules integral to the transmigration process of host inflammatory cells (polymorphonuclear neutrophils, macrophages) into the infected cornea. This results directly in reduced cellular infiltration, less stromal destruction, and better disease outcome.

IL-33 shifts macrophage polarization, promoting resistance against Pseudomonas aeruginosa keratitis

PURPOSE

To determine the role of IL-33 in resistance to Pseudomonas aeruginosa keratitis.

METHODS

Corneal IL-33 mRNA and protein levels were tested in susceptible C57BL/6 (B6) and resistant BALB/c mice. B6 mice were injected with recombinant mouse IL-33 (rmIL-33) and disease severity, bacterial load, polymorphonuclear neutrophils (PMN) infiltrate, gene expression of inflammatory, and T-helper (Th)1/Th2 cytokines were tested by RT-PCR. IL-33 signaling and macrophage (Mvarphi) polarization also were examined.

RESULTS

IL-33 mRNA and protein were expressed constitutively in the normal corneas of both groups and were significantly elevated at 1 to 5 days after infection in BALB/c over B6 mice. rmIL-33-treated B6 mice showed less severe disease than did PBS controls and exhibited decreased bacterial load, PMN infiltrate, and corneal mRNA levels for IL-1beta, MIP-2, and TNF-alpha. Th2-type cytokines (IL-4, -5, -10) also were significantly upregulated, and protein levels for TNF-alpha and IL-10 confirmed the mRNA data. To further investigate IL-33 in corneal inflammation, it was overexpressed in Mvarphi (RAW264.7 cells). This significantly increased IL-5 and IL-10, while it decreased IFN-gamma and other pro-inflammatory cytokines. The role of the Mvarphi was further tested in infected rmIL-33 compared with PBS-injected mice. Immunostaining showed that rmIL-33 injection shifted Mvarphi polarization from NO synthase 2 to arginase production. Furthermore, peritoneally elicited cells (B6 mice) treated with lipopolysaccharide and rmIL-33 exhibited elevated ST2 levels and a shift from IL-12 to IL-10 mRNA production.

CONCLUSIONS

These data provide evidence that IL-33 promotes a Th2-type immune response and reduces inflammation by polarizing the Mvarphi production of anti-inflammatory mediators in the cornea.

Beta-defensins 2 and 3 together promote resistance to Pseudomonas aeruginosa keratitis

Defensins play an important role in both innate and adaptive immunity due to their antimicrobial, regulatory, and chemotactic effects. Nonetheless, the role of murine beta-defensins (mBD) 3 and 4, the murine homologs of human beta-defensins (hBD) 2 and 3, remains unknown in Pseudomonas aeruginosa keratitis. This study explored their role in corneal infection and potential synergy with mBD2, a defensin associated with better outcome in this disease. Immunostaining and real-time RT-PCR data demonstrated that mBD3 and mBD4 expression was inducible and differentially regulated in the infected cornea of resistant BALB/c vs susceptible C57BL/6 (B6) mice. Knockdown studies using small interfering RNA treatment indicated that mBD3, but not mBD4, is required in ocular defense. Moreover, in vivo studies demonstrated individual and combined effects of mBD2 and mBD3 that modulate bacterial load, polymorphonuclear neutrophil (PMN) infiltration, and production of IFN-gamma, MIP-2, IL-1beta, TNF-alpha, inducible NO synthase (iNOS), TLR2, TLR4, MyD88, and NF-kappaB. Most notably, bacterial load was increased at 5 days postinfection by silencing either mBD2 or mBD3, but it was elevated at both 1 and 5 days postinfection when silencing both defensins. PMN infiltration was increased at 1 day postinfection by silencing both defensins or mBD3, but not mBD2 alone. iNOS expression was elevated by silencing mBD2, but it was reduced after silencing mBD3 or both defensins. Additionally, cell sources of mBD2 (macrophages, PMN and fibroblasts) and mBD3 (PMN) in corneal stroma were identified by dual label immunostaining after infection. Collectively, the data provide evidence that mBD2 and mBD3 together promote resistance against corneal infection.

Role of the Fas pathway in Pseudomonas aeruginosa keratitis

PURPOSE

The role of the Fas pathway was tested in Pseudomonas aeruginosa-infected mouse cornea by contrasting the responses of FasL(-/-) and wild-type (WT) mice.

METHODS

TUNEL staining, real-time RT-PCR, immunostaining, and ELISA assay were used.

RESULTS

Compared with WT (resistant) mice, BALB/c FasL(-/-) exhibited significantly elevated bacterial counts and polymorphonuclear leukocyte numbers at 1 and 3 days postinfection (p.i.) and worse outcomes from disease. Similar bacterial challenges in C57BL/6 FasL(-/-) compared with WT mice also led to worsened disease as evidenced by earlier corneal perforation in the susceptible mouse strain. Intense TUNEL staining of apoptotic cells was seen earlier (1 day vs. 3 days) p.i. in BALB/c WT than in knockout mice, This earlier apoptotic pattern correlated with increased expression of caspases 3, 8, and 9 and BAX and with decreased expression of the antiapoptotic molecule Bcl-2. Furthermore, expression levels of the proinflammatory molecule TNF-alpha and its receptor, MIP-2, inducible nitric oxide synthase (iNOS), and nitrite also were significantly elevated in the infected cornea of BALB/c FasL(-/-) compared with WT mice. In vitro, LPS-stimulated Mphi from BALB/c FasL(-/-) mice expressed significantly less caspase 3 and 9, BAX, and IL-10 and more TNF-alpha, MIP-2, and IL-1beta than did cells from WT mice.

CONCLUSIONS

Fas-FasL interaction in the cornea balances the host innate immune response to improve disease outcome by promoting earlier apoptosis and regulating proinflammatory cytokines/chemokines and nitric oxide (nitrite) production. Dysregulation of this interaction contributes to bystander tissue damage, enhancing nutrients for bacterial growth and worsened disease outcome after P. aeruginosa infection.

Role of Innate and Adaptive Immunity in the Pathogenesis of Keratitis

Pseudomonas aeruginosa is a common organism associated with bacterial keratitis primarily resulting from contact lens usage. Advances in our understanding of host innate and adaptive immune responses to experimental infection have been achieved using animal models, including inbred mouse models that are classed as resistant (cornea heals) vs. susceptible (cornea perforates). Evidence has shown that sustained IL-12-driven IFN-gamma production in dominant Th1 responder strains such as C57BL/6 (B6) contributes to corneal destruction and perforation. In contrast, in Th2-responder BALB/c mice, IL-18-driven IFN-gamma production regulates bacterial killing with less corneal destruction. IL-1 and chemotactic cytokines (e.g., MIP-2) recruit PMN to the cornea. The critical role of these cells in the innate immune response and their regulation after bacterial infection has been established. The studies provide a better understanding of the regulatory mechanisms that operate in the cornea after P. aeruginosa challenge, determining susceptibility vs. resistance to disease, and are consistent with long-term goals of providing targets for better treatment of disease.

IFN-γ: Regulation of Nitric Oxide in theP. aeruginosa-Infected Cornea

PURPOSE

BALB/c mice are resistant to Pseudomonas aeruginosa (P. aeruginosa) keratitis and bacterial killing/stasis requires nitric oxide (NO). NO regulation in the cornea is unknown and was tested in this model.

METHODS

Nitrite detection, IFN-gamma-knockout mice, TNF-alpha neutralization, ELISA, aminoguanidine (AG) treatment, MPO, and plate counts were done.

RESULTS

Evidence shows (i) without IFN-gamma, nitrite levels are elevated, (ii) neutralization of TNF-alpha does not change nitrite levels, and (iii) absence of IFN-alpha and reduced NO synergistically increases disease progress and upregulates pro-inflammatory cytokines, PMN number, and bacterial load.

CONCLUSION

IFN-gamma regulates NO levels, and synergistic interaction between the two regulates disease outcome in resistant mice.

Beta-defensin-2 promotes resistance against infection with P. aeruginosa

Corneal infection with Pseudomonas aeruginosa results in corneal perforation in susceptible C57BL/6 (B6) mice, but not in resistant BALB/c mice. To explore the role of two important defensins, murine beta-defensin-1 (mBD1) and mBD2, in the ocular immune defense system, their mRNA and protein expression levels were tested by real-time RT-PCR and Western blot, respectively. mRNA, protein, and immunostaining data demonstrated that both mBD1 and mBD2 were constitutively expressed in normal BALB/c and B6 corneas, and they were disparately up-regulated in BALB/c (more) vs B6 (less) corneas after infection. To determine whether either defensin played a role in host resistance, BALB/c mice were treated with either mBD1 or mBD2 small interfering RNA by subconjunctival injection together with topical application. Increased corneal opacity and worsened disease were displayed after knockdown of mBD2 but not of mBD1. mBD2 silencing also increased bacterial counts and polymorphonuclear neutrophil infiltration in BALB/c corneas. Real-time RT-PCR data further demonstrated that mBD2, not mBD1, differentially modulated mRNA expression of proinflammatory cytokines/molecules such as IFN-gamma, MIP-2, IL-1beta, TNF-alpha, IL-6, and inducible NO synthase; TLR signaling molecules, including TLR2, TLR4, TLR9, and MyD88; and the transcription factor NF-kappaB. Additionally, in vivo studies indicated that mBD2 silencing enhanced corneal nitrite levels and NF-kappaB activation. Collectively, the data provide evidence that mBD2, but not mBD1, is required for host resistance against P. aeruginosa-induced corneal infection.

Rat silicone hydrogel contact lens model: effects of high- versus low-Dk lens wear

OBJECTIVES

This study used a rat contact lens (CL) model to test if high- versus low-Dk lens wear caused changes in (1) conjunctival Langerhans cell (LC) number or location; (2) Bcl-2 expression; and (3) infection risk.

METHODS

Female, Lewis rats wore a high- or low-Dk CL continuously for 2 weeks. Afterward, corneas were harvested and processed for ADPase activity to identify LCs, for immunostaining and for real time-polymerase chain reaction. Contact lens-wearing rats also were challenged with Pseudomonas aeruginosa by placing a bacterial-soaked CL on the eye followed by topical delivery of bacteria. After 48 hrs, slit lamp examination and real time-polymerase chain reaction were used to evaluate the corneal response.

RESULTS

Conjunctival LC were significantly increased after low- versus high-Dk CL wear (P<0.0001). In contrast, conjunctival LC in non-lens wearing rats was not significantly different from the high-Dk lens wearing group. Bcl-2 mRNA levels were significantly decreased in low- versus high-Dk CL wearing rats, while Bax, FasL, caspase 3, and caspase 9 levels were unchanged. Immunostaining for Bcl-2 showed fewer positively stained epithelial cells in the low- versus high-Dk lens wearing group. After bacterial challenge, 30% of low- versus none of the high-Dk CL wearing corneas became infected and showed increased mRNA levels for several proinflammatory cytokines/chemokines, inducible nitric oxide synthase and matrix metalloproteinase-9.

CONCLUSION

Low- versus high-Dk or non-CL wear led to an increased number of conjunctival LC, decreased Bcl-2 levels, and increased the risk of bacterial infection.