Ex vivo Caprine Model to Study Virulence Factors in Keratitis

Tissue Inhibitor of Metalloproteinase (TIMP) Peptidomimetic as an Adjunctive Therapy for Infectious Keratitis

Matrix metalloproteinase 9 (MMP-9) has a key role in many biological processes, and while it is crucial for a normal immune response, excessive release of this enzyme can lead to severe tissue damage, as evidenced by proteolytic digestion and perforation of the cornea during infectious keratitis. Current medical management strategies for keratitis mostly focus on antibacterial effects, but largely neglect the role of excess MMP activity. Here, a cyclic tissue inhibitor of metalloproteinase (TIMP) peptidomimetic, which downregulated MMP-9 expression both at the mRNA and protein levels as well as MMP-9 activity in THP-1-derived macrophages, is reported. A similar downregulating effect could also be observed on α smooth muscle actin (α-SMA) expression in fibroblasts. Furthermore, the TIMP peptidomimetic reduced Pseudomonas aeruginosa-induced MMP-9 activity in an ex vivo porcine infectious keratitis model and histological examinations demonstrated that a decrease of corneal thickness, associated with keratitis progression, was inhibited upon peptidomimetic treatment. The presented approach to reduce MMP-9 activity thus holds great potential to decrease corneal tissue damage and improve the clinical success of current treatment strategies for infectious keratitis.

Identification of Proteases: Carboxypeptidase and Aminopeptidase as Putative Virulence Factors of Fusarium solani Species Complex

Background:

Fusarium keratitis accounts for around 50% of mycotic keratitis cases. Major virulence factors produced by keratopathogenic fungi are proteases.

Objective:

The aim of the current study was to identify proteases contributing to corneal pathogenicity of Fusarium species.

Methods:

Culture filtrates from fourteen Fusarium solani species complex (FSSC) isolates and three F. delphinoides isolates were evaluated for protease activity and gelatine zymography. Mass spectroscopy was carried out using a partially purified enzyme and total extracellular extract. Protease gene expression in an in-vitro condition and an ex-vivo goat corneal infection model was measured using qRT-PCR. Specific activity was observed in a wide range and at a broad pH range; and isolates Cs1 (maximum) and Cc50 (minimum) were selected for the infection model.

Results:

Gene expression in in-vitro condition showed the highest fold change for proteases (C7YY94, C7Z7U2 and C7Z6W1) while in an ex-vivo infection highest fold change was seen for proteases (C7Z6W1, C7YQJ2 and C7Z7U2); in decreasing order, respectively. Expression of aminopeptidase (C7Z6W1) was 50-fold higher in the infected cornea in both isolates (Cs1 and Cc50); while expression of carboxypeptidase (C7YVF3) was 15-fold higher only in isolate Cs1. Corneal histology showed less penetration of Cc50 than Cs1 into the stroma. Mass spectrometry showed the presence of carboxypeptidase (C7YVF3) and tripeptidyl amino peptidase.

Conclusion:

It can be concluded that clinical isolates of FSSC produce varying amounts of proteases and differ in specific activity and gene expression in both conditions (in vitro and ex vivo). Carboxypeptidase and aminopeptidase contribute to the pathogenic potential of Fusarium solani species complex.

Corneal Infection Models: Tools to Investigate the Role of Biofilms in Bacterial Keratitis

Bacterial keratitis is a corneal infection which may cause visual impairment or even loss of the infected eye. It remains a major cause of blindness in the developing world. Staphylococcus aureus and Pseudomonas aeruginosa are common causative agents and these bacterial species are known to colonise the corneal surface as biofilm populations. Biofilms are complex bacterial communities encased in an extracellular polymeric matrix and are notoriously difficult to eradicate once established. Biofilm bacteria exhibit different phenotypic characteristics from their planktonic counterparts, including an increased resistance to antibiotics and the host immune response. Therefore, understanding the role of biofilms will be essential in the development of new ophthalmic antimicrobials. A brief overview of biofilm-specific resistance mechanisms is provided, but this is a highly multifactorial and rapidly expanding field that warrants further research. Progression in this field is dependent on the development of suitable biofilm models that acknowledge the complexity of the ocular environment. Abiotic models of biofilm formation (where biofilms are studied on non-living surfaces) currently dominate the literature, but co-culture infection models are beginning to emerge. In vitro, ex vivo and in vivo corneal infection models have now been reported which use a variety of different experimental techniques and animal models. In this review, we will discuss existing corneal infection models and their application in the study of biofilms and host-pathogen interactions at the corneal surface.

Mini-review: from in vitro to ex vivo studies: an overview of alternative methods for the study of medical biofilms

Microbial biofilms are a natural adaptation of microorganisms, typically composed of multiple microbial species, exhibiting complex community organization and cooperation. Biofilm dynamics and their complex architecture are challenging for basic analyses, including the number of viable cells, biomass accumulation, biofilm morphology, among others. The methods used to study biofilms range from in vitro techniques to complex in vivo models. However, animal welfare has become a major concern, not only in society, but also in the academic and scientific field. Thus, the pursuit for alternatives to in vivo biofilm analyses presenting characteristics that mimic in vivo conditions has become essential. In this context, the present review proposes to provide an overview of strategies to study biofilms of medical interest, with emphasis on alternatives that approximate experimental conditions to host-associated environments, such as the use of medical devices as substrata for biofilm formation, microcosm and ex vivo models.

Experimental Models for Fungal Keratitis: An Overview of Principles and Protocols

Fungal keratitis is a potentially blinding infection of the cornea that afflicts diverse patient populations worldwide. The development of better treatment options requires a more thorough understanding of both microbial and host determinants of pathology, and a spectrum of experimental models have been developed toward this end. In vivo (animal) models most accurately capture complex pathological outcomes, but protocols may be challenging to implement and vary widely across research groups. In vitro models allow for the molecular dissection of specific host cell–fungal interactions, but they do so without the appropriate environmental/structural context; ex vivo (corneal explant) models provide the benefits of intact corneal tissue, but they do not provide certain pathological features, such as inflammation. In this review, we endeavor to outline the key features of these experimental models as well as describe key technical variations that could impact study design and outcomes.

Characterizing the impact of 2D and 3D culture conditions on the therapeutic effects of human mesenchymal stem cell secretome on corneal wound healing in vitro and ex vivo

The therapeutic effects of secreted factors (secretome) produced by bone marrow-derived human mesenchymal stem cells (MSCs) were evaluated as a function of their growth in 2D culture conditions and on 3D electrospun fiber scaffolds. Electrospun fiber scaffolds composed of polycaprolactone and gelatin were fabricated to provide a 3D microenvironment for MSCs, and their mechanical properties were optimized to be similar to corneal tissue. The secretome produced by the MSCs cultured on 3D fiber matrices versus 2D culture dishes were analyzed using a Luminex immunoassay, and the secretome of MSCs cultured on the 3D versus 2D substrates showed substantial compositional differences. Concentrations of factors such as HGF and ICAM-1 were increased over 5 times in 3D cultures compared to 2D cultures. In vitro proliferation and scratch-based wound healing assays were performed to compare the effects of the secretome on corneal fibroblast cells (CFCs) when delivered synchronously from co-cultured MSCs through a trans-well co-culture system versus asynchronously after harvesting the factors separately and adding them to the media. Cell viability of CFCs was sustained for 6 days when co-cultured with MSCs seeded on the fibers but decreased with time under other conditions. Scratch assays showed 95% closure at 48 h when CFCs were co-cultured with MSCs seeded on fibers, while the control group only exhibited 50% closure at 48 h. Electrospun fibers seeded with MSCs were then applied to a rabbit corneal organ culture system, and MSCs seeded on fibers promoted faster epithelialization and less scarring. Corneas were fixed and stained for alpha smooth muscle actin (α-SMA), and then analyzed by confocal microscopy. Immunostaining showed that expression of α-SMA was lower in corneas treated with MSCs seeded on fibers, suggesting suppression of myofibroblastic transformation. MSCs cultured on electrospun fibers facilitate wound healing in CFCs and on explanted corneas through differential secretome profiles compared to MSCs cultured on 2D substrates. Future work is merited to further understand the nature and basis of these differences and their effects in animal models. STATEMENT OF SIGNIFICANCE: Previous studies have shown that the secretome of bone marrow-derived mesenchymal stem cells (MSC) is promotes corneal wound healing by facilitating improved wound closure rates and reduction of scarring and neovascularization. The present research is significant because it provides evidence for the modulation of the secretome as a function of the MSC culture environment. This leads to differential expression of therapeutic factors secreted, which can impact corneal epithelial and stromal healing after severe injury. In addition, this article shows that co-continuous delivery of the MSC secretome improves cell migration and proliferation over aliquoted delivery, and that MSCs grown on three-dimensional electrospun fiber constructs may provide a favorable microenvironment for cultured MSCs and as a carrier to deliver their secreted factors to the ocular surface.

Pseudomonas aeruginosa Keratitis: Protease IV and PASP as Corneal Virulence Mediators

Pseudomonas aeruginosa is a leading cause of bacterial keratitis, especially in users of contact lenses. These infections are characterized by extensive degradation of the corneal tissue mediated by Pseudomonas protease activities, including both Pseudomonas protease IV (PIV) and the P. aeruginosa small protease (PASP). The virulence role of PIV was determined by the reduced virulence of a PIV-deficient mutant relative to its parent strain and the mutant after genetic complementation (rescue). Additionally, the non-ocular pathogen Pseudomonas putida acquired corneal virulence when it produced active PIV from a plasmid-borne piv gene. The virulence of PIV is not limited to the mammalian cornea, as evidenced by its destruction of respiratory surfactant proteins and the cytokine interleukin-22 (IL-22), the key inducer of anti-bacterial peptides. Furthermore, PIV contributes to the P. aeruginosa infection of both insects and plants. A possible limitation of PIV is its inefficient digestion of collagens; however, PASP, in addition to cleaving multiple soluble proteins, is able to efficiently cleave collagens. A PASP-deficient mutant lacks the corneal virulence of its parent or rescue strain evidencing its contribution to corneal damage, especially epithelial erosion. Pseudomonas-secreted proteases contribute importantly to infections of the cornea, mammalian lung, insects, and plants.