Immunity to pathogenic fungi in the eye

Rutin resists Aspergillus fumigatus keratitis by activating Nrf2/HO-1 pathway, inhibiting Dectin-1/p-Syk pathway and affecting fungal structures

Fungal keratitis (FK) is a severe vision-threatening eye disease. The fungal invasiveness and excessive inflammatory response contribute to corneal tissue damage. Rutin (RT) possesses anti-inflammatory, antimicrobial, antioxidant, and improved wound-healing characteristics. This study aimed to evaluate antifungal, anti-inflammatory, and therapeutic effects of RT in FK. The results showed that RT exerted antifungal effects by inhibiting fungal growth, altering hyphal morphology, destroying biofilm, and disrupting fungal cellular structures. RT exhibited anti-inflammatory benefits by suppressing the Dectin-1/p-Syk pathway, activating the Nrf2/HO-1 pathway, and decreasing the expression of inflammatory factors in vivo and in vitro. RT demonstrated therapeutic effects by reducing clinical scores, fungal load, macrophage recruitment, and neutrophil activity. In conclusion, RT exhibited anti-inflammatory, antifungal, and therapeutic effects in Aspergillus fumigatus keratitis, and has the potential to become a novel therapeutic strategy for FK.

The therapeutic effect and mechanism of carnosic acid in Aspergillus fumigatus keratitis

Fungal keratitis is a vision-threatening corneal infectious disease. However, clinically therapeutic medicines cannot attain ideal efficacy due to limited control of fungal virulence and excessive inflammatory response. Carnosic acid (CA) is a phenolic diterpene, which has been reported to have multiple abilities including antibacterial, anti-inflammatory and antioxidant. The therapeutic efficacy and potential mechanism of CA in fungal keratitis remain unknown. This study aimed to confirm the therapeutic role and potential mechanism of CA in Aspergillus fumigatus (A. fumigatus)-caused keratitis. In this study, we demonstrated that CA markedly suppressed the growth of A. fumigatus hyphae, the generation of biofilms and the integrity of the hyphal membrane. A. fumigatus-related genes (RodA, RodB, FKs, Rho1, CshA-C and Cyp51A-B) levels were suppressed under CA treatment. CA at 5 μg/mL and 10 μg/mL obviously promoted cell proliferation. In A. fumigatus-infected mice cornea, CA relieved the severity of corneal impairment, inhibited neutrophil recruitment and fungal load. Compared with inactivated hyphae, CA down-regulated the mRNA and protein levels of inflammatory cytokines, Dectin-1, NLRP3, cleaved caspase-1, IL-18 and IL-1β. Moreover, Curdlan (a specific agonist of Dectin-1) stimulation could promote the expression of NLRP3, cleaved caspase-1, IL-18 and IL-1β, which could be down-regulated by CA treatment. In conclusion, CA displays antifungal function on A. fumigatus. CA ameliorates the prognosis of keratomycosis by suppressing inflammatory cytokines production, which is regulated by Dectin-1 and pyroptosis.

Zeolitic Imidazolate Framework-90 Treats Fungal Keratitis by Promoting Macrophage Apoptosis and Targeting Increased Mitochondrial Reactive Oxygen Species in Aspergillus Fumigatus

Background

Fungal keratitis is a severe vision-threatening corneal infection with a prognosis influenced by fungal virulence and the host's immune defense mechanisms. However, there is still a lack of effective drugs that attenuate fungal virulence while relieving the inflammatory response caused by fungal keratitis.

Purpose

Finding an effective treatment to solve these problems is particularly important.

Methods

We synthesized Zeolitic imidazolate framework-90 (ZIF-90) by water-based synthesis method and characterized it. In vitro experiments included mycelium electron microscopy, Cell Counting Kit-8 (CCK-8), and Enzyme-linked immunosorbent assay (ELISA). These trials verified the disruptive effects of ZIF-90 on morphology, cell membrane, cell wall, and biofilm formation of Aspergillus fumigatus (A. fumigatus). These experiments also demonstrated the impact of ZIF-90 on the proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Moreover, the effect of ZIF-90 on mitochondrial reactive oxygen species (mtROS) of cells and fungi was verified by MitoSOX Red Mitochondrial Superoxide Indicator (MitoSOX). In vivo, corneal toxicity test, establishment and treatment of mycotic keratitis mouse model, and immunofluorescence staining were used to evaluate the efficacy of ZIF-90 in the procedure of fungal keratitis. In addition, to investigate whether the metal-ligand zinc and the organic ligand imidazole acted as essential factors in ZIF-90, we investigated the in vitro antimicrobial and anti-inflammatory effects of ZIF-8, ZIF-67 and Metal-Organic Frameworks-74 (Zn) (MOF-74 (Zn)) by Minimum Inhibitory Concentration (MIC) and ELISA experiments.

Results

ZIF-90 has therapeutic effects on fungal keratitis, which could break the protective organelles of A. fumigatus, such as the cell wall. In addition, ZIF-90 can also be targeted to increase the amount of mtROS in fungi and promote apoptosis of macrophages. The results demonstrated that both zinc ions and imidazole possessed antimicrobial and anti-inflammatory effects. In addition, ZIF-90 exhibited better antifungal properties than ZIF-8, ZIF-67, and MOF-74 (Zn).

New Biomarkers for Patients With Fungal Keratitis From Blood Routine Examination: Neutrophil-to-Lymphocyte Ratio and Platelet-to-Lymphocyte Ratio

Purpose: To assess the potential of neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) as novel diagnostic and prognostic biomarkers in fungal keratitis (FK). Methods: This study was carried out retrospectively in 77 FK patients and 77 matched cataract controls from Henan Eye Hospital. Peripheral venous blood samples were collected via venipuncture and analyzed using complete blood count for routine clinical evaluation. FK patients were classified into three subgroups: Fusarium, Aspergillus, and Candida groups. Inflammation severity was quantified using standardized clinical scoring. The treatment modalities were used to divide the FK patients into enucleation and nonenucleation groups. Results: NLR and PLR were significantly elevated in FK versus controls (p < 0.001). NLR correlated strongly with inflammation scores (r = 0.535, p < 0.0001), exceeding PLR's moderate correlation (r = 0.311, p=0.0059). FK patients in the enucleation group had significantly higher NLR (p=0.012) and PLR (p=0.021) values than those in the nonenucleation group. There were no significant biomarker differences across fungal species (p > 0.05). Conclusion: Elevated NLR and PLR values during routine laboratory testing might serve as supplementary indicators for early suspicion of FK and monitoring inflammatory progression, particularly in resource-limited settings where specialized ophthalmic diagnostics are unavailable.

Antifungal susceptibility, clinical findings, and biofilm resistance of Fusarium species causing keratitis: a challenge for disease control

Fusarium keratitis (FK) is an important clinical condition that can lead to blindness and eye loss, and is most commonly caused by the Fusarium solani species complex (FSSC). This study evaluated the susceptibility of planktonic cells and biofilms of FSSC (n = 7) and non-FSSC (n = 7) isolates obtained from patients with keratitis from a semi-arid tropical region to amphotericin B (AMB), natamycin (NAT), voriconazole (VRZ), efinaconazole (EFZ), and luliconazole (LCZ). Analysis of clinical data showed that trauma was the most common risk factor for FK patients. Disease onset was longer in non-FSSC group (3-30 days) than in the FSSC group (3-7 days). FSSC strains were less susceptible to AMB and VRZ than non-FSSC strains (p < 0.05). Susceptibility to NAT, LCZ and EFZ was similar between isolates of FSSC and non-FSSC groups. Overall, patients infected with non-FSSC showed a better response to antifungal treatment. Corneal transplantation was more common in patients infected with FSSC (3/7) than in those infected with non-FSSC (1/7). Mature biofilms showed a poor response to antifungal treatment. Patients infected with Fusarium strains capable of forming antifungal tolerant biofilms had more complex therapeutic management, requiring two antifungals and/or corneal transplantation (p < 0.05). This study highlights the importance of mycological diagnosis and the antifungal susceptibility testing in the clinical management of FK. The ability of Fusarium to form antifungal tolerant biofilms poses a challenge to clinicians and urges the development of new antibiofilm therapeutics.

Inhibition of LRRK2 Ameliorates Aspergillus fumigatus Keratitis by Regulating STING Signaling Pathways

Purpose

The purpose of this study was to investigate the role of LRRK2 in the inflammatory response to fungal keratitis (FK) and elucidate the underlying mechanisms.

Methods

The protein levels of leucine-rich repeat kinase 2 (LRRK2), p-LRRK2, and stimulator of interferon genes (STING)-related proteins were assessed by western blot analysis. ELISA and quantitative real-time polymerase chain reaction (qRT-PCR) were employed to evaluate the inflammatory response induced by Aspergillus fumigatus. Mass spectrometry was performed to identify the interaction partners of LRRK2. The glutathione S-transferase (GST) pull-down assay and co-immunoprecipitation (co-IP) were used to verify the interaction between LRRK2 and STING. Additionally, fungal load determinations and clinical score assessments were conducted to determine corneal infection in a mouse model.

Results

A. fumigatus stimulation promoted the phosphorylation of LRRK2 through Toll-like receptor 2 (TLR2) in human corneal epithelial cells (HCECs) and mouse corneas. LRRK2 overexpression enhanced the A. fumigatus-induced inflammatory response, and LRRK2 knockdown alleviated A. fumigatus keratitis both in vitro and in vivo. Mass spectrometry identified STING as a novel interaction partner of LRRK2. Moreover, A. fumigatus treatment enhanced the interaction between LRRK2 and STING, resulting in the phosphorylation and activation of STING. The phosphorylated STING then triggered its downstream signaling pathways, exacerbating the severity of A. fumigatus keratitis. LRRK2 inhibitor (LRRK2-IN-1) significantly mitigated the inflammatory response and corneal damage caused by A. fumigatus stimulation.

Conclusions

LRRK2 inhibition ameliorates A. fumigatus-induced inflammation through modulating STING signaling pathways in both HCECs and mouse models. Our results suggest that targeted inhibition of LRRK2 could be a promising strategy for FK treatment.

Role of MYO1F in neutrophil and macrophage recruitment and pro-inflammatory cytokine production in Aspergillus fumigatus keratitis

PURPOSE

Myosin 1f (Myo1f), an unconventional long-tailed class Ⅰ myosin, plays significant roles in immune cell motility and innate antifungal immunity. This study was aimed to assess the expression and role of Myo1f in Aspergillus fumigatus (AF) keratitis.

METHODS

Myo1f expression in the corneas of mice afflicted with AF keratitis and in AF keratitis-related cells was assessed using protein mass spectrometry, quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and immunofluorescence. Myo1f expression following pre-treatment with inhibitors of dendritic cell-associated C-type lectin-1 (Dectin-1), Toll-like receptor 4 (TLR-4), and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) was also examined. In AF keratitis mouse models, Myo1f small interfering RNA (siRNA) was administered via subconjunctival injection to observe disease progression, inflammatory cell recruitment, and protein production using slit lamp examination, immunofluorescence, hematoxylin-eosin (HE) staining, and western blotting.

RESULTS

Myo1f expression was upregulated in both AF keratitis mouse models and AF keratitis-related cells. Dectin-1, TLR-4, and LOX-1 were found to be essential for the production of Myo1f in response to the infection with AF. In mice with AF keratitis, knockdown of Myo1f reduced disease severity, decreased the recruitment of neutrophils alongside macrophages to inflammatory areas, suppressed the myeloid differentiation factor 88 (MyD88)/ nuclear factor-kappaB (NF-κB) signaling pathway, and decreased the production of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, along with IL-6. Additionally, Myo1f was associated with apoptosis and pyroptosis in mice with AF keratitis.

CONCLUSIONS

These findings demonstrated that Myo1f contributed to the recruitment of neutrophils and macrophages, the production of pro-inflammatory cytokines, and was associated with apoptosis and pyroptosis during AF keratitis.

Macrophage Membrane-Coated Nanoparticles for the Delivery of Natamycin Exhibit Increased Antifungal and Anti-Inflammatory Activities in Fungal Keratitis

This study aims to explore the efficacy and safety of macrophage membrane-coated nanoparticles for the delivery of natamycin (NAT) in the therapy of fungal keratitis (FK). Macrophage membranes were isolated and identified by immunofluorescence staining (IFS). NAT was encapsulated into poly(lactic-co-glycolic acid) (PLGA). Fungal stimulated macrophage membranes (M1) or unstimulated membranes (M) were separately mixed and sonicated with PLGA nanoparticles. The biocompatible nanoparticles (PLGA-NAT, PLGA-NAT@M, and PLGA-NAT@M1) were characterized with zeta-sizer analysis, transmission electron microscopy (TEM), and Western blot. Drug encapsulation and loading efficiency and the release of NAT in the nanoparticles were detected by ultraviolet spectrophotometry. The cytotoxicity, ocular surface toxicity and irritability, and systemic safety of nanoparticles with different concentrations were assessed. In vitro, we examined the antifungal properties of the nanoparticles. The eye surface retention time, drug release, and curative effects on FK were evaluated in vitro and in vivo. IFS results showed the separation of the macrophage membrane and nucleus. The prepared nanoparticles had a typical "core-shell" structure and uniform nanometer size, and the membrane proteins were retained on the membrane allowing to exert functional effects of macrophage. The loading efficiencies of PLGA-NAT@M and PLGA-NAT@M1 were 7.6 and 6.7%, respectively. The encapsulation efficiencies of PLGA-NAT@M and PLGA-NAT@M1 were 51.2 and 41.5%, respectively. PLGA-NAT@M and PLGA-NAT@M1 could gradually release NAT and reduce the clearance of the ocular surface. Macrophage membranes enhanced the antifungal activity of PLGA-NAT. Furthermore, the membrane coated with macrophage increased the biocompatibility and decreased the corneal toxicity of nanoparticles. In vivo, PLGA-NAT@M1 significantly alleviated the severity of FK. In vitro, PLGA@M and PLGA@M1 reduced the protein levels of inflammatory cytokines after fungal stimulation. The prepared PLGA-NAT@M1 has good physical properties and biosafety. It could evade ocular surface clearance, release NAT gradually, and achieve high antifungal and anti-inflammatory efficiencies to FK. Macrophage membrane-coated nanoparticles clinically have high application potential to the treatment of FK.

Licochalcone A Ameliorates Aspergillus fumigatus Keratitis by Reducing Fungal Load and Activating the Nrf2/HO-1 Signaling Pathway

Fungal keratitis (FK) is a blinding corneal infectious disease. The prognosis is frequently unfavorable due to fungal invasion and an excessive host inflammatory response. Licochalcone A (Lico A) exhibits a broad spectrum of pharmacological activities, encompassing antifungal, anti-inflammatory, antioxidation, and antitumor properties. However, the role of Lico A has not yet been studied in FK. In this study, we discovered that Lico A could disrupt Aspergillus fumigatus (A. fumigatus) biofilms, inhibit fungal growth and adhesion to host cells, induce alterations of hyphal morphology, and impair the cell membrane and cell wall integrity and mitochondrial structure of A. fumigatus. Lico A can alleviate the severity of FK in mice, reduce neutrophil infiltration and fungal load, and significantly decrease the pro-inflammatory cytokines in mouse corneas infected with A. fumigatus. In vitro, we also demonstrated that Lico A increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) around the nucleus in human corneal epithelial cells (HCECs) stimulated with A. fumigatus. We verified that the anti-inflammatory effect of Lico A is associated with the activation of the Nrf2/HO-1 axis. These results indicated that Lico A could provide a protective role in A. fumigatus keratitis through its anti-inflammatory and antifungal activities.

Ebselen improves fungal keratitis through exerting anti-inflammation, anti-oxidative stress, and antifungal effects

Fungal keratitis is a severely vision-threatening corneal infection, where the prognosis depends on both fungal virulence and host immune defense. Inappropriate host responses can induce substantial inflammatory damage to the cornea. Therefore, in the treatment of fungal keratitis, it is important to concurrently regulate the immune response while efforts are made to eliminate the pathogen. Ebselen is a widely studied organo-selenium compound and has been demonstrated to have antifungal, antibacterial, anti-inflammatory, and oxidative stress-regulatory properties. The effectiveness of ebselen for the treatment of fungal keratitis remains unknown. In this study, ebselen was demonstrated to produce a marked inhibitory effect on Aspergillus fumigatus (A. fumigatus), including spore germination inhibition, mycelial growth reduction, and fungal biofilm disruption. The antifungal activity of ebselen was related to the cell membrane damage caused by thioredoxin (Trx) system inhibition-mediated oxidative stress. On the contrary, ebselen enhanced the antioxidation of Trx system in mammalian cells. Further, ebselen was proven to suppress the expressions of inflammatory mediators (IL-1β, IL-6, TNF-α, COX-2, iNOS, and CCL2) and reduce the production of oxidative stress-associated indicators (ROS, NO, and MDA) in fungi-stimulated RAW264.7 cells. In addition, ebselen regulated PI3K/Akt/Nrf2 and p38 MAPK signaling pathways, which contributed to the improvement of inflammation and oxidative stress. Finally, we verified the therapeutic effect of ebselen on mouse fungal keratitis. Ebselen improved the prognosis and reduced the fungal burden in mouse corneas. Expressions of inflammatory mediators, as well as the infiltration of macrophages and neutrophils in the cornea were also obviously decreased by ebselen. In summary, ebselen exerted therapeutic effects by reducing fungal load and protecting host tissues in fungal keratitis, making it a promising treatment for fungal infections.

The differential virulence of Fusarium strains causing corneal infections and plant diseases is associated with accessory chromosome composition

Fusarium oxysporum is a cross-kingdom pathogen. While some strains cause disseminated fusariosis and blinding corneal infections in humans, others are responsible for devastating vascular wilt diseases in plants. To better understand the distinct adaptations of F. oxysporum to animal or plant hosts, we conducted a comparative phenotypic and genetic analysis of two strains: MRL8996 (isolated from a keratitis patient) and Fol4287 (isolated from a wilted tomato [Solanum lycopersicum]). In vivo infection of mouse corneas and tomato plants revealed that, while both strains cause symptoms in both hosts, MRL8996 caused more severe corneal ulceration and perforation in mice, whereas Fol4287 induced more pronounced wilting symptoms in tomato. In vitro assays using abiotic stress treatments revealed that the human pathogen MRL8996 was better adapted to elevated temperatures, whereas the plant pathogen Fol4287 was more tolerant of osmotic and cell wall stresses. Both strains displayed broad resistance to antifungal treatment, with MRL8996 exhibiting the paradoxical effect of increased tolerance to higher concentrations of the antifungal caspofungin. We identified a set of accessory chromosomes (ACs) and protein-encoding genes with distinct transposon profiles and functions, respectively, between MRL8996 and Fol4287. Interestingly, ACs from both genomes also encode proteins with shared functions, such as chromatin remodeling and post-translational protein modifications. Our phenotypic assays and comparative genomics analyses lay the foundation for future studies correlating genotype with phenotype and for developing targeted antifungals for agricultural and clinical uses.

CD3ε of a pan T cell marker involved in mouse Aspergillus fumigatus keratitis

AIM

To explore whether CD3ε is involved in the adaptive immunity of Aspergillus fumigatus (A. fumigatus) keratitis in mice and the role of innate and adaptive immunity in it.

METHODS

Mice models of A. fumigatus keratitis were established by intra-stromal injection and corneal epithelial scratching. Subconjunctival injections of natamycin, wedelolactone, LOX-1 inhibitor (poly I) or Dectin-1 inhibitor (laminarin) were used to treat mice with A. fumigatus keratitis. Mice were pretreated by intraperitoneal injection of anti-mouse CD3ε. We observed the corneal infection of mice under the slit lamp microscope and made a clinical score. The protein expression of CD3ε and interleukin-10 (IL-10) was determined by Western blotting.

RESULTS

With the disease progresses, the degree of corneal opacity and edema augmented. In the intra-stromal injection models, CD3ε protein expression began to increase significantly on the 2nd day. However, in the scraping epithelial method models, CD3ε only began to increase on the 3rd day. After natamycin treatment, the degree of corneal inflammation in mice was significantly attenuated on the 3rd day. After wedelolactone treatment, the severity of keratitis worsened. And the amount of CD3ε protein was also reduced, compared with the control group. By inhibiting LOX-1 and Dectin-1, there was no significant difference in CD3ε production compared with the control group. After inhibiting CD3ε, corneal ulcer area and clinical score increased, and IL-10 expression was downregulated.

CONCLUSION

As a pan T cell marker, CD3ε participate in the adaptive immunity of A. fumigatus keratitis in mice. In our mice models, the corneas will enter the adaptive immune stage faster. By regulating IL-10, CD3ε exerts anti-inflammatory and repairs effects in the adaptive immune stage.

A20 ameliorates Aspergillus fumigatus keratitis by promoting autophagy and inhibiting NF-κB signaling

Fungal keratitis (FK) is a serious, potentially sight-threatening corneal infection, which is associated with poor prognosis. A20, also called TNFAIP3, plays significant roles in the negative regulation of inflammation and immunity. However, the function of A20 in Aspergillus fumigatus (A. fumigatus) keratitis remains obscure. Herein, we found that the level of A20 is increased in human corneal epithelial cells (HCECs) and in mouse corneas with A. fumigatus infection, and that nuclear factor-κB (NF-κB) signaling is required for A20 upregulation. A20 overexpression inhibits A. fumigatus-mediated inflammatory responses, while A20 knockdown results in opposite effect. Mechanically, we showed that A20 inhibits NF-κB signaling and activates autophagy in infected HCECs. We also showed that inhibition of NF-κB signaling reverses the increased inflammatory responses in infected HCECs with A20 knockdown. Furthermore, autophagy blockage impedes the anti-inflammatory effect of A20 in A. fumigatus infected HCECs. Moreover, A20 ameliorates the corneal damage and inflammation in A. fumigatus infected mouse corneas. In conclusion, this study reveals that A20 alleviates A. fumigatus keratitis by activating autophagy and inhibiting NF-κB signaling. This suggests that exogenous use of A20 protein may be a potentially promising therapeutic strategy for FK treatment.