Signaling mechanism for Aspergillus fumigatus tolerance in corneal fibroblasts induced by LPS pretreatment

Rose Bengal Photodynamic Therapy (RB-PDT) Modulates the Inflammatory Response in LPS-Stimulated Human Corneal Fibroblasts By Influencing NF-κB and p38 MAPK Signaling Pathways

PURPOSE

To investigate the effect of rose bengal photodynamic therapy on lipopolysaccharide-induced inflammation in human corneal fibroblasts. Furthermore, to analyze potential involvement of the mitogen-activated protein kinase and nuclear factor kappa B signaling pathways in this process.

METHODS

Human corneal fibroblast cultures underwent 0-2.0 µg/mL lipopolysaccharide treatment, and 24 h later rose bengal photodynamic therapy (0.001% RB, 565 nm wavelength illumination, 0.17 J/cm2 fluence). Interleukin-6, interleukin-8, intercellular adhesion molecule-1, interferon regulatory factor-3, interferon α2, and interferon β1 gene expressions were determined by quantitative PCR. Interleukin-6, interleukin-8, and C-C motif chemokine ligand-4 concentrations in the cell culture supernatant were measured by enzyme-linked immunosorbent assays and intercellular adhesion molecule-1 protein level in human corneal fibroblasts by western blot. In addition, the nuclear factor kappa B and mitogen-activated protein kinase signaling pathways were investigated by quantitative PCR and phosphorylation of nuclear factor kappa B p65 and p38 mitogen-activated protein kinase by western blot.

RESULTS

Rose bengal photodynamic therapy in 2.0 µg/mL lipopolysaccharide-stimulated human corneal fibroblasts triggered interleukin-6 and interleukin-8 mRNA (p < .0001) and interleukin-6 protein increase (p < .0001), and downregulated intercellular adhesion molecule-1 expression (p < .001). C-C motif chemokine ligand-4, interferon regulatory factor-3, interferon α2, and interferon β1 expressions remained unchanged (p ≥ .2). Rose bengal photodynamic therapy increased IκB kinase subunit beta, nuclear factor kappa B p65, extracellular signal-regulated kinases-2, c-Jun amino terminal kinase, and p38 transcription (p ≤ .01), and triggered nuclear factor kappa B p65 and p38 mitogen-activated protein kinase phosphorylation (p ≤ .04) in lipopolysaccharide treated human corneal fibroblasts.

CONCLUSION

Rose bengal photodynamic therapy of lipopolysaccharide-stimulated human corneal fibroblasts can modify the inflammatory response by inducing interleukin-6 and interleukin-8 expression, and decreasing intercellular adhesion molecule-1 production. C-C motif chemokine ligand-4, interferon regulatory factor-3, and interferon α and β expressions are not affected by rose bengal photodynamic therapy in these cells. The underlying mechanisms may be associated with nuclear factor kappa B and p38 mitogen-activated protein kinase pathway activation.

Thymic stromal lymphopoietin participates in the TLR2-and TLR4-dependent immune response triggered by Aspergillus fumigatus in human corneal cells

Fungal keratitis constitutes a serious vision-threatening disease. Toll-like receptors (TLRs) comprise key mediators of innate immunity triggered by Aspergillus fumigatus (AF) in the cornea, but the messenger between innate and adaptive immunity remained unknown. Thymic stromal lymphopoietin (TSLP) represents a critical factor of adaptive immunity. Here we investigated the expression of TSLP in corneal epithelial and stromal cells challenged by AF and its relationship with TLRs. We stimulated corneal cells with TLR ligands zymosan or lipopolysaccharide (LPS), human recombinant TSLP, or AF hyphae for various periods, with or without prior TLR2, TLR4, or TSLP inhibition. TLR2, TLR4, TSLP, IL-8, and TNF-α release and expression were measured via enzyme-linked immunosorbent analysis, quantitative polymerase chain reaction, or western blot. Corneal cell stimulation with zymosan or LPS induced up-regulated TSLP expression. Enhanced TSLP expression was associated with AF treatment in human corneal cells; TLR2 or TLR4 inhibition impaired the AF-induced TSLP levels. Human recombinant TSLP augmented TLR2 and TLR4 expression; RNA interference of TSLP attenuated TLR, IL-8, and TNF-α expression stimulated by AF hyphae. These findings indicated that TSLP participates in the immune response of corneal cells triggered by AF, which is closely related to TLR function, and the innate immunity mediated by TLRs could be enhanced by TSLP. Innate immunity may therefore transmit inflammatory signals to adaptive immunity through activation of TSLP; in turn, adaptive immunity likely exerts certain regulatory effects on innate immunity via TSLP. That is, TSLP could interact with innate immunity mediated by TLR2 and TLR4 in human corneal cells challenged by AF and thus may serve as a messenger between the innate and adaptive immune responses in AF keratitis.

The Effect of SPARC on the Proliferation and Migration of Limbal Epithelial Stem Cells During the Corneal Epithelial Wound Healing

Secreted protein acidic and rich in cysteine (SPARC) shows a specific colocalization with limbal epithelial stem cells (LESCs) in vivo; however, the inherent relationship between SPARC and LESCs is still unclear. This study investigated the effects of SPARC on the maintenance of LESC stemness and corneal wound healing. To test the influence of different concentration of exogenous SPARC on the proliferation of LESCs, cell counting kit-8 assay and 5-ethynyl-2'-deoxyuridine staining were performed and the results indicated that 1 μg/mL SPARC was the optimum concentration for enhanced LESC proliferation. Compared with a control group, SPARC-treated group showed a higher expression of LESC-positive markers p63α, ABCG-2, and Bmi-1, and a lower level of differentiation marker cytokeratin-3 (CK3), thereby suggesting that SPARC could maintain LESC characteristic phenotype and suppress spontaneous epithelial differentiation in vitro. In vivo, exogenous SPARC accelerated the wound-healing process by both the enhancement of LESC proliferation and promoting the migration of the proliferating cells. However, the intact epithelium impaired this function of SPARC by contact inhibition.

SPARC promotes self-renewal of limbal epithelial stem cells and ocular surface restoration through JNK and p38-MAPK signaling pathways

The purpose of this study was to investigate the effects of secreted protein acidic and rich in cysteine (SPARC) on the maintenance of limbal epithelial stem cell (LESC) stemness and restoration of ocular surface. To determine the suitable concentration of SPARC for LESC culture, the marker expression, mitogenic effect, and holoclone-forming capacity of LESCs treated with different concentrations of SPARC were analyzed. To investigate the mechanism of SPARC's action on the preservation of LESCs stemness, the phosphorylation of related signaling pathways was evaluated by Western blotting. A corneal wound model was established to verify the function of SPARC in ocular surface repair. Consecutive subculturing, colony-forming efficiency, immunofluorescence, and 5-ethynyl-2-deoxyuridine incorporation assays indicated that 1 μg/mL SPARC was a suitable concentration to stimulate LESC proliferation and preserve their proliferative potential. Compared with a control group, 1 μg/mL SPARC effectively increased the expression of ABCG-2, Bmi-1, and Ki67, while decreasing that of CK3/12. The mitogenic effect of SPARC on LESCs was found to be mediated by the phosphorylation of c-Jun N-terminal kinase (JNK) and p38-MAPK signaling pathways, whereas the inhibitors of JNK and p38 MAPK reduced the marker expression and mitogenic capacity of LESCs. In a corneal injury model, SPARC facilitated corneal epithelial wound healing and promoted the proliferation of p63α-positive cells both in the limbus and in the epithelial healing front. SPARC promotes proliferation while suppressing spontaneous differentiation of LESCs through JNK and p38-MAPK signaling pathways, suggesting that SPARC is a promising factor for the improvement of LESCs culture in vitro and in vivo.

Interactions of thymic stromal lymphopoietin with TLR2 and TLR4 regulate anti-fungal innate immunity in Aspergillus fumigatus-induced corneal infection

Thymic stromal lymphopoietin (TSLP) is an interleukin 7 (IL-7)-like four helix bundle cytokine that plays diverse roles in the regulation of immune responses. In fungal infection, pattern recognition receptors (PRRs), including the cell surface Toll-like receptors (TLRs) and cytoplasmic NOD-like receptors, recognize pathogen-associated molecular patterns to initiate downstream signal cascades to active immune responses. Our previous studies reported that, in vitro human cornea epithelium cells represented a novel target of TSLP and that TSLP/TSLPR/STAT5 signaling played an important role in the response to Aspergillus fumigatus challenge. TSLP downstream signaling molecules upregulated TLR2 and MyD88/NF kappa B-p65 signaling. This phenomenon suggested that TSLP had an impact on PRRs in antifungal immunity. In mouse fungal keratitis induced by A. fumigatus, TSLP was mainly expressed in the epithelium as well as in some infiltrated immune cells in a time-dependent manner. Exogenous TSLP with Aspergillus led to severe keratitis and worse corneal recovery with higher levels of TLR2, TLR4, IL-6, and IL-8 as well as increased neutrophil infiltration. By contrast, when TSLP was suppressed by siRNA, fungal keratitis was mild with higher levels of antimicrobial peptides such as human beta-defensin (hBD9). Taken together, our data revealed an unreported function of TSLP in mediating an anti-fungal inflammatory response and serving as a target to control tissue injury and infection in A. fumigatus keratitis.

Evaluation of murine lung epithelial cells (TC-1 JHU-1) line to develop Th2-promoting cytokines IL-25/IL-33/TSLP and genes Tlr2/Tlr4 in response to Aspergillus fumigatus

OBJECTIVE

The aims of this study were to determine the role of live and heat-killed Aspergillus fumigatus conidia in releasing interleukin (IL)-25, IL-33 and thymic stromal lymphopoietin (TSLP) and to express Toll-like receptor (Tlr)2 and Tlr4 genes.

MATERIALS AND METHODS

Murine lung epithelial cells were incubated with live and heat-killed A. fumigatus conidia at 37°C for 6, 24 and 48h. After treatments, ELISA was performed to measure the concentrations of IL-25, IL-33 and TSLP in the supernatants. Quantitative real-time PCR (qPCR) was performed to assess the expression levels of Tlr2 and Tlr4 genes.

RESULTS

The concentrations of IL-25 and IL-33 significantly increased after exposure to live and heat-killed conidia for various times when compared with untreated control (P<0.05). The secretion of TSLP at different concentrations of heat-killed conidia was significantly higher than both live conidia and untreated control (P<0.05). qRT-PCR results indicated a up-regulation from 1.08 to 3.60-fold for Tlr2 gene expression and 1.20 to 1.80-fold for Tlr4 gene expression exposed to heat-killed conidia.

CONCLUSION

A. fumigatus has a potential ability to stimulate murine lung epithelial cells to produce IL-25/IL-33/TSLP, as well as to express Tlr2/Tlr4 genes, indicating an important role of lung epithelial cells in innate immune responses to A. fumigatus interaction.

A potential link between TSLP/TSLPR/STAT5 and TLR2/MyD88/NFκB-p65 in human corneal epithelial cells for Aspergillus fumigatus tolerance

Our previous studies reported that pattern recognition receptors (PRRs), including the cell surface Toll-like receptors (TLRs) and cytoplasmic NOD-like receptors (NLRs), recognize pathogen-associated molecular patterns (PAMPS) to initiate downstream signal cascades to active immunity responses. Thymic stromal lymphopoietin (TSLP) has recently emerged as a key cytokine in the development of type 2 adaptive immune responses. However, the crosstalk between PRRs and TSLP has not been well elucidated in Aspergillus fumigates keratitis. Our studies demonstrated that HCECs not only respond to TSLP, but also initiate immunological regulation through TSLP/TSLPR/STAT5 signaling pathway. In addition, we revealed that zymosan TLR2 agonist enhanced the expression of TSLP and TSLPR and phosphorylation of STAT5. Furthermore, neutralization of TLR2 with monoclonal Ab prevented the production of TSLP and TSLPR and phosphorylation of STAT5 from increasing which induced by A. fumigatus hyphae. Interestingly, we also found that human recombinant TSLP induced the increase of TLR2 downstream signal molecules, and TSLP knockdown could reduce the increase of TLR2 downstream signaling molecules(MyD88 and NF-κB-p65) induced by A. fumigatus hyphae. These studies indicated that HCECs represent a novel target of TSLP, TSLP/TSLPR/STAT5 signaling plays an important role in response to A. fumigatus infection in HCECs, and TLR2 downstream signaling molecules up regulate TSLP/TSLPR/STAT5 signaling as well as TSLP downstream signaling molecules up regulate TLR2/MyD88/NFκB-p65 signaling in this phenomenon.