Topical interleukin-1 receptor antagonist inhibits inflammatory cell infiltration into the cornea

In Vitro Effect of Propofol on the Expression of Genes Involved in Inflammation and Apoptosis in Corneal Activated Keratocytes

PURPOSE

We investigated the effect of propofol (0.5, 5, and 50 μM) on the gene expression of inflammatory cytokines [ IL-1β , IL-6 , transforming growth factor β ( TGF-β ), and LIF ] and apoptosis process ( BCL-2 and Bax ) in corneal activated keratocytes (CAKs).

METHODS

CAKs (10 6 cells/10 cm 2 ) were exposed to propofol at a concentration of 0.5, 5, and 50 μM for 24 hours at 37°C. The control group did not receive propofol at the same time or under the same condition. Ribonucleic acid (RNA) extraction, complementary DNA (cDNA) synthesis, and real-time polymerase chain reaction (PCR) were performed to quantify the relative expression of IL-1β , IL-6 , TGF-β , LIF , BCL-2 , and Bax expression in the treated versus control cells.

RESULT

The results of this study showed that propofol treatment (0.5 and 5 μM) led to the downregulation of IL-1β and IL-6 gene expression in CAKs. TGF-β (with a role in fibrogenesis) was not changed in 0.5 and 5 μM propofol-treated CAKs, whereas CAKs treated with 50 μM propofol showed upregulation of the TGF-β gene. LIF (with a role in regeneration) was upregulated in 0.5 and 5 μM propofol-treated CAKs. The BCL-2/Bax ratio (as the antiapoptosis index) was increased in CAKs treated with 0.5 μM propofol and indicated the induction of an antiapoptotic effect.

CONCLUSIONS

We showed that CAKs treatment with propofol, at concentrations of 0.5 and 5 μM, could decrease the expression of genes related to inflammation and enhance the genes associated with cell regeneration. While 50 μM propofol treatment might induce CAK fibrogenesis. This proof-of-concept study could preserve a groundwork for future drug design for the treatment of corneal stromal diseases and ocular regenerative medicine.

Therapeutic effects of a novel venom abstract (ZK002) solution in an alkali-burned corneal wound-healing model

Purpose

Corneal alkali burns can progress to corneal epithelial defects, inflammation, scarring, and angiogenesis, potentially leading to blindness. Therefore, we examined the therapeutic effects of a novel ophthalmic solution (ZK002) on wound healing in alkali-burned rat corneas.

Methods

In this study, we attempted to treat alkali-exposed rat corneas using topical application of either an ophthalmic solution with ZK002 or an anti-vascular endothelial growth factor agent for 14 days. We evaluated corneal edema, corneal neovascularization area, and histological changes. We also assessed the inflammatory (MMP-9, MMP-2, and interleukin-1β) and angiogenic (vascular endothelial growth factor receptor 2, VEGFR2) markers. Levels of inflammatory (matrix metalloproteinase (MMP)-9, MMP-2, and interleukin-1β), profibrotic (α-smooth muscle actin, α-SMA; transforming growth factor-β2,TGF-β2), and angiogenic (vascular endothelial growth factor-receptor 2, VEGFR2) factors, as well as peroxisome proliferator-activated receptor γ (PPARγ) mRNA expression, were measured.

Results

The analyses showed that alkali exposure caused an increase in corneal edema and fibrosis with corneal neovascularization. The accumulation of α-smooth muscle actin-positive myofibroblasts and the deposition of transforming growth factor-β2 on the alkali-exposed corneas were noted on day 14. The mRNA expression levels of interleukin-1β, MMP-9, MMP-2, VEGFR2, and profibrotic factors were decreased in the ZK002 group compared with the control group during the early period of corneal alkali burns on day 14. However, the expression level of PPARγ mRNA was increased in the ZK002 group.

Conclusions

ZK002 decreased the fibrotic reaction and prevented neovascularization in the cornea after an alkali burn. Therefore, the novel ophthalmic solution ZK002 could be a potentially promising therapeutic clinical treatment for corneal wound healing.

ABCB5+ Limbal Epithelial Stem Cells Inhibit Developmental but Promote Inflammatory (Lymph) Angiogenesis While Preventing Corneal Inflammation

The limbus, the vascularized junction between the cornea and conjunctiva, is thought to function as a barrier against corneal neovascularization. However, the exact mechanisms regulating this remain unknown. In this study, the limbal epithelial stem cell (LESC) marker ABCB5 was used to investigate the role of LESCs in corneal neovascularization. In an ABCB5KO model, a mild but significant increase of limbal lymphatic and blood vascular network complexity was observed in developing mice (4 weeks) but not in adult mice. Conversely, when using a cornea suture model, the WT animals exhibited a mild but significant increase in the number of lymphatic vessel sprouts compared to the ABCB5KO, suggesting a contextual anti-lymphangiogenic effect of ABCB5 on the limbal vasculature during development, but a pro-lymphangiogenic effect under inflammatory challenge in adulthood. In addition, conditioned media from ABCB5-positive cultured human limbal epithelial cells (ABCB5+) stimulated human blood and lymphatic endothelial cell proliferation and migration. Finally, a proteomic analysis demonstrated ABCB5+ cells have a pro(lymph)angiogenic as well as an anti-inflammatory profile. These data suggest a novel dual, context-dependent role of ABCB5+ LESCs, inhibiting developmental but promoting inflammatory (lymph)angiogenesis in adulthood and exerting anti-inflammatory effects. These findings are of high clinical relevance in relation to LESC therapy against blindness.

CXCR3 deletion aggravates corneal neovascularization in a corneal alkali-burn model

Corneal neovascularization can cause devastating consequences including vision impairment and even blindness. Corneal inflammation is a crucial factor for the induction of corneal neovascularization. Current anti-inflammatory approaches are of limited value with poor therapeutic effects. Therefore, there is an urgent need to develop new therapies that specifically modulate inflammatory pathways and inhibit neovascularization in the cornea. The interaction of chemokines and their receptors plays a key role in regulating leukocyte migration during inflammatory response. CXCR3 is essential for mediating the recruitment of activated T cells and microglia/macrophages, but the role of CXCR3 in the initiation and promotion of corneal neovascularization remains unclear. Here, we showed that the expression of CXCL10 and CXCR3 was significantly increased in the cornea after alkali burn. Compared with WT mice, CXCR3-/- mice exhibited significantly increased corneal hemangiogenesis and lymphangiogenesis after alkali burn. In addition, exaggerated leukocyte infiltration and leukostasis, and elevated expression of inflammatory cytokines and angiogenic factor were also found in the corneas of CXCR3-/- mice subjected to alkali burn. With bone marrow (BM) transplantation, we further demonstrated that the deletion of CXCR3 in BM-derived leukocytes plays a key role in the acceleration of alkali burn-induced corneal neovascularization. Taken together, our results suggest that upregulation of CXCR3 does not exhibit its conventional action as a proinflammatory cytokine but instead serves as a self-protective mechanism for the modulation of inflammation and maintenance of corneal avascularity after corneal alkali burn.

Biological Compositions of Canine Amniotic Membrane and Its Extracts and the Investigation of Corneal Wound Healing Efficacy In Vitro

The usage of canine amniotic membrane (cAM) is mainly of interest in veterinary ophthalmology. Topical formulations of cAM could deliver the beneficial properties of cAM without the need for surgical intervention. The present study aimed to investigate biological compositions of cAM and its extracts, including their corneal wound healing efficacy. In this study, canine amniotic membrane extract (cAME) and lyophilized canine amniotic membrane extract (cAMX) were developed. Bioactive molecules related to corneal wound healing, including hepatocyte growth factor, tissue inhibitor of metalloproteinase-1 and -2, Thrombospondin-1 and Interleukin-1 receptor antagonist were studied at both gene and protein expression levels. Cell viability and wound healing assays were investigated for the possibility of cAME and cAMX as topical applications. The results demonstrated that all of the relevant genes and proteins were detected in cAM, cAME and cAMX. Both cAME and cAMX showed wound healing properties in vitro and cAME at 1.0 mg/mL concentration appeared to have the best healing efficacy. In conclusion, cAME and cAMX generated for topical use provided promising results in the healing of corneal defects.

Role of Damage-Associated Molecular Patterns (DAMPs/Alarmins) in Severe Ocular Allergic Diseases

Severe ocular allergic diseases, such as atopic keratoconjunctivitis and vernal keratoconjunctivitis, cause severe allergic inflammation in the conjunctiva and corneal epithelial damage, resulting in visual disturbances. The involvement of damage (danger)-associated molecular patterns (DAMPs/alarmins) in the pathogenesis of these diseases has been recognized. Alarmins released from damaged corneal epithelial cells or eosinophils play a critical role in the induction of corneal lesions, vicious loop of corneal injury, and exacerbation of conjunctival allergic inflammation. Alarmins in the conjunctiva also play an essential role in the development of both allergic inflammation, based on the acquired immune system, and type 2 inflammation by innate immune responses in the ocular surface. Therefore, alarmins may be a potentially important therapeutic target in severe refractory ocular allergic diseases.

Gold-based blood serum treatment promotes wound closure of corneal epithelial cell defects in primary in vitro experiments

BACKGROUND

Wound healing disorders characterised by impaired or delayed reepithelialisation are a serious medical problem. In the present study, we show that gold-based blood serum therapy is a suitable therapeutic approach and shows a supportive effect in wound closure of human corneal epithelial cells (HCE) in primary in vitro experiments.

METHODS

For this purpose, blood from healthy individuals was incubated without (S.Ctrl) or with gold-microparticles (S.Therapy) for 24 h. Prior to human epithelial cell stimulation (HCE), the gold particles were removed and the serum was diluted in DMEM (10 % or 30 %). Both groups of serum were compared after injury. HCE were cultured and injured (corneal in vitro wound model) and then stimulated with S.Ctrl or S.

THERAPY

RESULTS

Treatment with serum from a gold-based serum therapy (S.Therapy) shows a supportive effect on wound healing in HCE cells in vitro. In addition, gold therapy supports the secretion of important cytokines normally associated with ocular surface wound healing (IL-1β, IL-6, TNF-α and TGF-β) in HCE cells.

CONCLUSIONS

Therapy with gold-based blood serum significantly promotes the secretion and expression of cytokines and growth factors in HCE cells in vitro. Further preclinical experiments are necessary to demonstrate the influence of this therapy on HCE cells for possible clinical application on the human ocular surface and to prove its function also in poorly healing corneal lesions.

Protective roles of the TIR/BB-loop mimetic AS-1 in alkali-induced corneal neovascularization by inhibiting ERK phosphorylation

Hydrocinnamoyl-L-valylpyrrolidine (AS-1), a synthetic low-molecule mimetic of myeloid differentiation primary response gene 88 (MyD88), inhibits inflammation by disrupting the interaction between the interleukin-1 receptor (IL-1R) and MyD88. Here, we describe the effects of AS-1 on injury-induced increases in inflammation and neovascularization in mouse corneas. Mice were administered a subconjunctival injection of 8 μL AS-1 diluent before or after corneal alkali burn, followed by evaluation of corneal resurfacing and corneal neovascularization (CNV) by slit-lamp biomicroscopy and clinical assessment. Corneal inflammation was assessed by whole-mount CD45⁺ immunofluorescence staining, and corneal hemangiogenesis and lymphangiogenesis following injury were evaluated by immunostaining for the vascular markers isolectin B4 (IB4) and the lymphatic vascularized marker lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), respectively. Additionally, corneal tissues were collected to determine the expression of 35 cytokines, and we detected activation of IL-1RI, MyD88, and mitogen-activated protein kinase (MAPK). The results showed that alkali conditions increased the number of CD45⁺ cells and expression of vascular endothelial growth factor (VEGF)-A, VEGF-C, and LYVE1 in corneas, with these levels decreased in the AS-1-treated group. Moreover, AS-1 effectively prevented alkali-induced cytokine production, blocked interactions between IL-1RI and MyD88, and inhibited MAPK activation post-alkali burn. These results indicated that AS-1 prevented alkali-induced corneal hemangiogenesis and lymphangiogenesis by blocking IL-1RI-MyD88 interaction, as well as extracellular signal-regulated kinase phosphorylation, and could be efficacious for the prevention and treatment of corneal alkali burn.

The Human Tissue-Engineered Cornea (hTEC): Recent Progress

Each day, about 2000 U.S. workers have a job-related eye injury requiring medical treatment. Corneal diseases are the fifth cause of blindness worldwide. Most of these diseases can be cured using one form or another of corneal transplantation, which is the most successful transplantation in humans. In 2012, it was estimated that 12.7 million people were waiting for a corneal transplantation worldwide. Unfortunately, only 1 in 70 patients received a corneal graft that same year. In order to provide alternatives to the shortage of graftable corneas, considerable progress has been achieved in the development of living corneal substitutes produced by tissue engineering and designed to mimic their in vivo counterpart in terms of cell phenotype and tissue architecture. Most of these substitutes use synthetic biomaterials combined with immortalized cells, which makes them dissimilar from the native cornea. However, studies have emerged that describe the production of tridimensional (3D) tissue-engineered corneas using untransformed human corneal epithelial cells grown on a totally natural stroma synthesized by living corneal fibroblasts, that also show appropriate histology and expression of both extracellular matrix (ECM) components and integrins. This review highlights contributions from laboratories working on the production of human tissue-engineered corneas (hTECs) as future substitutes for grafting purposes. It overviews alternative models to the grafting of cadaveric corneas where cell organization is provided by the substrate, and then focuses on their 3D counterparts that are closer to the native human corneal architecture because of their tissue development and cell arrangement properties. These completely biological hTECs are therefore very promising as models that may help understand many aspects of the molecular and cellular mechanistic response of the cornea toward different types of diseases or wounds, as well as assist in the development of novel drugs that might be promising for therapeutic purposes.

Evaluation of Tear Protein Markers in Dry Eye Disease with Different Lymphotoxin-Alpha Expression Levels

PURPOSE

To compare tear protein markers between normal subjects and patients with dry eye (DE) and high and low lymphotoxin-alpha (LT-α) levels.

DESIGN

Prospective cross-sectional study.

METHODS

Patients with DE were divided into low (≤700 pg/mL) and high (>700 pg/mL) LT-α groups. Twelve protein markers were measured by microsphere-based immunoassay and ocular surface parameters were determined in right eyes (33 high LT-α DE, 27 low LT-α DE, and 20 control eyes) and left eyes (21 high LT-α DE, 39 low LT-α DE, and 20 control eyes).

RESULTS

In both eyes, tumor necrosis factor-α (TNF-α), interleukin (IL)-10, IL-1β, IL-1 receptor antagonist (IL-1Ra), IL-17A, and IL-12/23 p40 levels in high LT-α DE were significantly higher (P < .01) than in low LT-α DE. Significant correlations identified in high LT-α DE were: Standard Patient Evaluation Eye Dryness with IL-10 (R = 0.43, P = .013), IL-1β (R = 0.48, P = .005), and IL-12/23 p40 (R = 0.50, P = .003), IL-12/23 p40 with ocular surface disease index (R = 0.35, P = .049), and epidermal growth factor with corneal fluorescein staining score (R = -0.36, P = .038). Significant correlations in low LT-α DE were: Standard Patient Evaluation Eye Dryness with IL-10 (R = -0.39, P = .046), TNF-α (R = -0.39, P = .047), and IL-17A (R = -0.48, P = .013), ocular surface disease index with TNF-α (R = -0.47, P = .017) and IL-17A (R = -0.46, P = .018), and IL-6 with tear breakup time (R = -0.40, P = .044). Lastly, IL-1Ra levels significantly increased in DE patients, positively correlated with temporal conjunctival hyperemia index, and negatively correlated with Schirmer I test (P < .05).

CONCLUSIONS

Our study identified tear IL-1Ra level as a potential biomarker to replace the Schirmer I test. Multiple tear protein marker levels increased in high LT-α DE, indicating that high LT-α DE might have a different pathogenesis.

Sirt6 deficiency impairs corneal epithelial wound healing

Corneal transparency, dependent on the integrity of epithelial cells, is essential for vision. Corneal epithelial damage is one of the most commonly observed ocular conditions and proper wound healing is necessary for corneal transparency. Sirt6, a histone deacetylase, has been shown to regulate many cellular events including aging and inflammation. However, its specific role in corneal epithelial wound healing remains unknown. Here we demonstrated that Sirt6 was expressed in corneal epithelial cells and its expression decreased with age. In an in vivo corneal epithelial wound healing model, Sirt6 deficiency resulted in delayed and incomplete wound healing and was associated excessive inflammation in the corneal stroma and dysfunction of Notch signaling, leading to keratinization of the corneal epithelium and corneal opacity. Aging Sirt6-deficient mice spontaneously developed corneal keratitis with extensive infiltration of inflammatory cells into the cornea. In vitro experiments demonstrated that primary corneal epithelial cells with Sirt6 downregulation expressed increased basal levels of inflammatory genes and exhibited hyper-inflammatory reactivity to IL-1β and TNFα treatment. These results provide compelling evidence that Sirt6 is a critical regulator of inflammation in the cornea, and is responsible for corneal epithelial wound healing, thus contributing to the maintenance of epithelial integrity and corneal transparency.

Co-culture of human bone marrow mesenchymal stem cells and macrophages attenuates lipopolysaccharide-induced inflammation in human corneal epithelial cells

Dry eye syndrome (DES) is considered as an ocular surface inflammatory disease. Previous studies have shown inflammation plays an important role in the progression and onset of DES. Co-culture of human bone marrow mesenchymal stem cells (HBMSCs) and macrophages showed immunomodulatory effects via regulation of cytokine regulation. Thus, the aim of this study was to investigate the effect of the interaction of these cells on in vitro DES model. The conditioned media (CM) from macrophages, HBMSCs, and HBMSCs + macrophages were treated to human corneal epithelial cells, which showed significant reduction in IL-1α and IL-1β expression levels in HBMSCs + macrophages group. Moreover, the IL-1 Receptor Antagonist (IL-1RA) was highly expressed in the CM from the HBMSCs + macrophages group. Wounded eyes of mice were treated with IL-1RA at 0-100 ng/mL for 16 h, the wound size was reduced. The results of this study might lead to the identification of new therapeutic targets for DES.

The expression of matrix metalloproteinases and their inhibitors in corneal fibroblasts by alarmins from necrotic corneal epithelial cells

PURPOSE

Sterile ulceration is frequently observed in the cornea following persistent corneal epithelial damage. We examined the effect of alarmins released by necrotic corneal epithelial cells (HCE) on the production of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) by corneal fibroblasts.

METHODS

IL-1α and high-mobility group box 1 protein (HMGB1) released into the supernatant derived from necrotic HCE cells were measured with enzyme-linked immunosorbent assay (ELISA). MMPs and TIMPs produced by corneal fibroblasts, stimulated with the supernatant from necrotic HCE cells, were analyzed and measured with protein array and ELISA. To investigate dynamic expression of alarmins in the corneal epithelium, we used immunohistochemistry to observe the expression of human IL-1α in the corneal epithelium of human IL-1α Tg mice with or without cryopexy. We also investigated the expression of MMPs in corneal stroma of the mice treated with cryopexy, using RT-PCR.

RESULTS

We detected IL-1α and HMGB-1 in the supernatant of necrotic HCE cells. These supernatants increased the expression of MMP-3 and MMP-1, and decreased that of TIMP-1 and TIMP-2 in human corneal fibroblasts. Almost always these were inhibited by IL-1 receptor antagonist. Recombinant IL-1α increased the production MMP-3 and MMP-1 in corneal fibroblasts. After cryopexy of the epithelium of human IL-1α Tg mice, the expression of human IL-1α was recognized in the cytoplasm but not nucleus of epithelial cells. The level of MMP-3 and MMP-1 mRNAs was elevated in the corneal stroma in mice treated with cryopexy.

CONCLUSION

Alarmins, especially IL-1α, released from necrotic HCE cells may play an important role in the expression of MMPs and TIMPs by corneal fibroblast, resulting in sterile ulceration.

Effect of Different Antibiotic Chemotherapies on Pseudomonas aeruginosa Infection In Vitro of Primary Human Corneal Fibroblast Cells

Pseudomonas aeruginosa is a major cause of bacterial keratitis (BK) worldwide. Inappropriate or non-optimal antibiotic chemotherapy can lead to corneal perforation and rapid sight loss. In this study, we tested the hypothesis that P. aeruginosa strain PAO1 invades primary human corneal fibroblasts (hCFs) in vitro and persists intracellularly, despite chemotherapy with antibiotics used commonly to treat BK. In rank order, ciprofloxacin, levofloxacin and polymyxin B showed the highest activity against planktonic PAO1 growth (100% inhibitory concentration ≤10 μg/mL; 50% inhibitory concentration ≤1 μg/mL), followed by gentamicin and ofloxacin (100% inhibitory concentration ≤50 μg/mL; 50% inhibitory concentration ≤10 μg/mL). These bactericidal antibiotics (50–200 μg/mL concentrations) all killed PAO1 in the extracellular environment of infected hCF monolayers. By contrast, the bactericidal antibiotic cefuroxime and the bacteriostatic antibiotic chloramphenicol failed to sterilize both PAO1 broth cultures, even at a concentration of ≥200 μg/mL) and infected hCF monolayers. Statistically, all antibiotics were able to prevent LDH release from PAO1-infected hCF monolayers at both concentrations tested. Intracellular Pseudomonas were significantly reduced (>99%, P < 0.05) following treatment with ciprofloxacin, levofloxacin and ofloxacin, whereas gentamicin, polymyxin B and cefuroxime failed to clear intracellular bacteria over 24 h. Intracellular Pseudomonas infection was resistant to chloramphenicol, with hCF death observed by 9 h. Eventual growth of remaining intracellular Pseudomonas was observed in hCF after removal of all antibiotics, resulting in re-infection cycles and cell death by 48 h. All of the antibiotics reduced significantly (P < 0.05) IL-1β secretion by hCF infected with a Multiplicity Of Infection (MOI) = 1 of PAO1. With higher MOI, no pro-inflammatory effects were observed with antibiotic treatment, expect with polymyxin B and ofloxacin, which induced significant increased IL-1β secretion (P < 0.001). The findings from our study demonstrated that bactericidal and bacteriostatic antibiotics, routinely used to treat BK, failed to eradicate Pseudomonas infection of hCFs in vitro and that their bactericidal efficacies were influenced by the cellular location of the organism.

Cytokine expression and barrier disruption in human corneal epithelial cells induced by alarmin released from necrotic cells

PURPOSE

Dying cells release endogenous molecules known as alarmins that signal danger to surrounding tissue. We investigated the effects of necrotic cell-derived alarmins on cytokine expression and barrier function in human corneal epithelial cells.

METHODS

The release of interleukin (IL)-6 and IL-8 from immortalized human corneal epithelial (HCE) cells in culture was measured with enzyme-linked immunosorbent assays. The abundance of IL-6 and 8 mRNAs was quantitated by reverse transcription and real-time polymerase chain reaction analysis. Barrier function of HCE cells was evaluated by measurement of transepithelial electrical resistance (TER). The subcellular localization of the p65 subunit of the transcription factor NF-κB was determined by immunofluorescence analysis, and phosphorylation of the endogenous NF-κB inhibitor IκBα was examined by immunoblot analysis.

RESULTS

A necrotic cell supernatant prepared from HCE cells induced the up-regulation of IL-6 and 8 expression at both mRNA and protein levels as well as reduced TER in intact HCE cells. Among alarmins tested, only IL-1α (not IL-33 or HMGB1) mimicked these effects of the necrotic cell supernatant. Furthermore, IL-1 receptor antagonist (IL-1RA) and neutralizing antibodies to IL-1α (but not those to IL-1β) each attenuated the effects of the necrotic cell supernatant. Exposure of HCE cells to the necrotic cell supernatant also induced the phosphorylation and degradation of IκBα as well as translocation of the p65 subunit of NF-κB to the nucleus.

CONCLUSION

IL-1α released from necrotic corneal epithelial cells may trigger inflammatory responses at the ocular surface, including cytokine production and barrier disruption.

Wound-Healing Studies in Cornea and Skin: Parallels, Differences and Opportunities

The cornea and the skin are both organs that provide the outer barrier of the body. Both tissues have developed intrinsic mechanisms that protect the organism from a wide range of external threats, but at the same time also enable rapid restoration of tissue integrity and organ-specific function. The easy accessibility makes the skin an attractive model system to study tissue damage and repair. Findings from skin research have contributed to unravelling novel fundamental principles in regenerative biology and the repair of other epithelial-mesenchymal tissues, such as the cornea. Following barrier disruption, the influx of inflammatory cells, myofibroblast differentiation, extracellular matrix synthesis and scar formation present parallel repair mechanisms in cornea and skin wound healing. Yet, capillary sprouting, while pivotal in proper skin wound healing, is a process that is rather associated with pathological repair of the cornea. Understanding the parallels and differences of the cellular and molecular networks that coordinate the wound healing response in skin and cornea are likely of mutual importance for both organs with regard to the development of regenerative therapies and understanding of the disease pathologies that affect epithelial-mesenchymal interactions. Here, we review the principal events in corneal wound healing and the mechanisms to restore corneal transparency and barrier function. We also refer to skin repair mechanisms and their potential implications for regenerative processes in the cornea.

Targeting Imbalance between IL-1β and IL-1 Receptor Antagonist Ameliorates Delayed Epithelium Wound Healing in Diabetic Mouse Corneas

Patients with diabetes mellitus often develop corneal complications and delayed wound healing. How diabetes might alter acute inflammatory responses to tissue injury, leading to delayed wound healing, remains mostly elusive. Using a streptozotocin-induced type I diabetes mellitus mice and corneal epithelium-debridement wound model, we discovered that although wounding induced marked expression of IL-1β and the secreted form of IL-1 receptor antagonist (sIL-1Ra), diabetes suppressed the expressions of sIL-1Ra but not IL-1β in healing epithelia and both in whole cornea. In normoglycemic mice, IL-1β or sIL-1Ra blockade delayed wound healing and influenced each other's expression. In diabetic mice, in addition to delayed reepithelization, diabetes weakened phosphatidylinositol 3-kinase-Akt signaling, caused cell apoptosis, diminished cell proliferation, suppressed neutrophil and natural killer cell infiltrations, and impaired sensory nerve reinnervation in healing mouse corneas. Local administration of recombinant IL-1Ra partially, but significantly, reversed these pathological changes in the diabetic corneas. CXCL10 was a downstream chemokine of IL-1β-IL-1Ra, and exogenous CXCL10 alleviated delayed wound healing in the diabetic, but attenuated it in the normal corneas. In conclusion, the suppressed early innate/inflammatory responses instigated by the imbalance between IL-1β and IL-1Ra is an underlying cause for delayed wound healing in the diabetic corneas. Local application of IL-1Ra accelerates reepithelialization and may be used to treat chronic corneal and potential skin wounds of diabetic patients.

Characterization of Inhibitor of differentiation (Id) proteins in human cornea

Inhibitor of differentiation (Id) proteins are DNA-binding transcription factors involved in cellular proliferation, migration, inflammation, angiogenesis and fibrosis. However, their expression and role in the cornea is unknown. The present study was undertaken to characterize the expression of Id proteins and their interactions with the pro-fibrotic cytokine Transforming Growth Factor β1 (TGFβ1) and anti-fibrotic cytokine, bone morphogenic protein 7 (BMP7) in human cornea. Human donor corneas procured from Eye Bank were used. Id proteins were localized in human corneal sections using immunofluorescence. Primary cultures of human corneal fibroblasts (HCF) were established and treated with either TGFβ1 (5 ng/ml) or BMP7 (10 ng/ml) for 24 h in serum free medium. Expression of Id's in response to TGFβ1, BMP7 and TGFβ1 + BMP7 was analyzed by quantitative real time PCR (qRT-PCR) and western blot analysis. Id1 and Id2 proteins were ubiquitously expressed in the epithelial cells and stromal keratocytes in human cornea. The Id1 was localized to the basal epithelial cells as seen by immunohistochemistry. HCF expressed all known mammalian Id genes (Id1-Id4). In addition, Id1 and Id2 are selectively expressed in HCF. Treatment of human recombinant TGFβ1 (5 ng/ml) to serum-starved HCF showed a significant increase in Id genes (Id1, Id2 and Id4) at 2 h time point compared to BMP7 treatment, which showed time dependent increase in the expression of Id1-Id3 at 24-48 h. Combined treatment with TGFβ1 + BMP7 to HCF showed a significant increase in Id1 transcript and an increasing trend in Id3 and Id4 expression. The results of this study suggest that Id family of genes (Id1-Id4) are localized in the human cornea and expressed in the corneal fibroblasts. Also, Id's were differentially regulated with TGFβ1 and/or BMP7 in a time dependent manner and might serve as a therapeutic target in corneal fibrosis.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Neuroprotective effects of intravitreally transplanted adipose tissue and bone marrow-derived mesenchymal stem cells in an experimental ocular hypertension model

BACKGROUND AIMS

The purpose of this study was to investigate the neuroprotective effects of bone marrow bone marrow-derived and adipose tissue-derived mesenchymal stromal cells (MSCs) that were intravitreally transplanted in an experimental ocular hypertension (OHT) model.

METHODS

An OHT rat model was generated by means of intracameral injection of hyaluronic acid into the anterior chamber. MSCs labeled with green fluorescence protein were transplanted intravitreally 1 week after OHT induction. At the end of the second and fourth weeks, retinal ganglion cells were visualized with the use of a flat-mount retina method and were evaluated by means of immunofluorescence staining against green fluorescence protein, vimentin, CD105, and cytokines (interleukin [IL]-1Ra, prostaglandin E2 receptor, IL-6, transforming growth factor-β1, interferon-γ and tumor necrosis factor-α).

RESULTS

The retinal ganglion cell numbers per area were significantly improved in stem cell-treated OHT groups compared with that in the non-treated OHT group (P < 0.05). The results of immunohistochemical analyses indicated that a limited number of stem cells had integrated into the ganglion cell layer and the inner nuclear layer. The number of cells expressing proinflammatory cytokines (interferon-γ and tumor necrosis factor-α) decreased in the MSC-transferred group compared with that in the OHT group after 4 weeks (P < 0.01). On the other hand, IL-1Ra and prostaglandin E2 receptor expressions were increased in the rat bone marrow-derived MSC group but were more significant in the rat adipose tissue-derived MSC group (P < 0.01).

CONCLUSIONS

After intravitreal transplantation, MSCs showed a neuroprotective effect in the rat OHT model. Therefore, MSCs promise an alternative therapy approach for functional recovery in the treatment of glaucoma.

Corneal inflammation after miniature keratoprosthesis implantation

PURPOSE

To compare corneal inflammation after syngeneic and allogeneic penetrating keratoplasty (PK) with miniature Keratoprosthesis (m-KPro) implantation in mice.

METHODS

BALB/C (syngeneic) or C57BL/6 (allogeneic) corneas were transplanted onto BALB/C host beds as part of PK or m-KPro implantation. Corneal inflammation was assessed by determining the frequencies of CD45(+) leukocytes, CD4(+) T cells, CD11b(+) cells, and Gr-1(+) granulocytes/monocytes by flow cytometry at 2, 4, and 8 weeks post transplantation. In addition, expression levels of the proinflammatory cytokines TNF-α and IL-1β were analyzed using real-time qPCR at 8 weeks post transplantation.

RESULTS

Cell frequencies in the syngeneic (syn) and allogeneic (allo) m-KPro groups were higher compared with the syngeneic and allogeneic PK groups, respectively, at all time points. However, after week 4, frequencies of all analyzed immune cells were higher in the alloPK group as compared with synKPro group. At 8 weeks, the expression of TNF-α was higher in synKPro, alloPK, and alloKPro groups compared with the naïve and synPK groups. The expression of IL-1β was significantly higher in both KPro groups as compared with PK groups.

CONCLUSIONS

Although the m-KPro device augments the inflammatory response in the cornea after its implantation, allogenicity (of the carrier tissue) is also a significant contributor to corneal inflammation. These data suggest that using syngeneic or decellularized corneal tissue as a Boston-KPro carrier could reduce the postoperative inflammation response.

Hevin plays a pivotal role in corneal wound healing

Background

Hevin is a matricellular protein involved in tissue repair and remodeling via interaction with the surrounding extracellular matrix (ECM) proteins. In this study, we examined the functional role of hevin using a corneal stromal wound healing model achieved by an excimer laser-induced irregular phototherapeutic keratectomy (IrrPTK) in hevin-null (hevin^-/-) mice. We also investigated the effects of exogenous supplementation of recombinant human hevin (rhHevin) to rescue the stromal cellular components damaged by the excimer laser.

Methodology/Principal Findings

Wild type (WT) and hevin^-/- mice were divided into three groups at 4 time points- 1, 2, 3 and 4 weeks. Group I served as naïve without any treatment. Group II received epithelial debridement and underwent IrrPTK using excimer laser. Group III received topical application of rhHevin after IrrPTK surgery for 3 days. Eyes were analyzed for corneal haze and matrix remodeling components using slit lamp biomicroscopy, in vivo confocal microscopy, light microscopy (LM), transmission electron microscopy (TEM), immunohistochemistry (IHC) and western blotting (WB). IHC showed upregulation of hevin in IrrPTK-injured WT mice. Hevin^-/- mice developed corneal haze as early as 1-2 weeks post IrrPTK-treatment compared to the WT group, which peaked at 3-4 weeks. They also exhibited accumulation of inflammatory cells, fibrotic components of ECM proteins and vascularized corneas as seen by IHC and WB. LM and TEM showed activated keratocytes (myofibroblasts), inflammatory debris and vascular tissues in the stroma. Exogenous application of rhHevin for 3 days reinstated inflammatory index of the corneal stroma similar to WT mice.

Conclusions/Significance

Hevin is transiently expressed in the IrrPTK-injured corneas and loss of hevin predisposes them to aberrant wound healing. Hevin^-/- mice develop early corneal haze characterized by severe chronic inflammation and stromal fibrosis that can be rescued with exogenous administration of rhHevin. Thus, hevin plays a pivotal role in the corneal wound healing.

Topical administration of interleukin-1 receptor antagonist as a therapy for aqueous-deficient dry eye in autoimmune disease

PURPOSE

Dry eye is commonly associated with autoimmune diseases such as Sjögren's syndrome (SS), in which exocrinopathy of the lacrimal gland leads to aqueous tear deficiency and keratoconjunctivitis sicca (KCS). KCS is among the most common and debilitating clinical manifestations of SS that is often recalcitrant to therapy. We established mice deficient in the autoimmune regulator (Aire) gene as a model for autoimmune-mediated aqueous-deficient dry eye. In Aire-deficient mice, CD4+ T cells represent the main effector cells and local signaling via the interleukin-1 (IL-1/IL-1R1) pathway provides an essential link between autoreactive CD4+ T cells and ocular surface disease. In the current study, we evaluated the efficacy of topical administration of IL-1R1 antagonist (IL-1RA) anakinra in alleviating ocular surface damage resulting from aqueous-deficient dry eye in the setting of autoimmune disease.

METHODS

We compared the effect of commercially available IL-1R1 antagonist, anakinra (50 μg/mL concentration) to that of carboxymethylcellulose (CMC) vehicle control as a treatment for dry eye. Age-matched, Aire-deficient mice were treated three times daily with anakinra or CMC vehicle for 14 days using side-by-side (n = 4 mice/group) and paired-eye (n = 5) comparisons. We assessed (1) ocular surface damage with lissamine green staining; (2) tear secretion with wetting of phenol-red threads; (3) goblet cell (GC) mucin glycosylation with lectin histochemistry; (4) immune cell infiltration using anti-F4/80, CD11c, and CD4 T cell antibodies; and (5) gene expression of cornified envelope protein, Small Proline-Rich Protein-1B (SPRR1B) with real-time quantitative polymerase chain reaction.

RESULTS

Aire-deficient mice treated with anakinra experienced significant improvements in ocular surface integrity and tear secretion. After 7 days of treatment, lissamine green staining decreased in eyes treated with anakinra compared to an equivalent increase in staining following treatment with CMC vehicle alone. By day 14, lissamine green staining in anakinra-treated eyes remained stable while eyes treated with CMC vehicle continued to worsen. Accordingly, there was a progressive decline in tear secretion in eyes treated with the CMC vehicle compared to a progressive increase in the anakinra-treated eyes over the 2-week treatment period. Aberrant acidification of GC mucins and pathological keratinization of the ocular surface were significantly reduced in anakinra-treated eyes. Significantly fewer Maackia amurensis leukoagglutinin positive goblet cells were noted in the conjunctiva of anakinra-treated eyes with a corresponding decrease in the expression of the pathological keratinization marker, SPRR1B. Finally, there was a downward trend in the infiltration of each immune cell type following anakinra treatment, but the cell counts compared to eyes treated with the vehicle alone were not significantly different.

CONCLUSIONS

IL-1R antagonist, anakinra, demonstrates therapeutic benefits as a topical treatment for aqueous-deficient dry eye in a spontaneous mouse model of autoimmune KCS that mimics the clinical characteristics of SS. Targeting the IL-1/IL-1R1 signaling pathway through topical administration of IL-1RA may provide a novel option to improve ocular surface integrity, increase tear secretion, and restore the normal glycosylation pattern of GC mucins in patients with SS.

Concise review: immunological properties of ocular surface and importance of limbal stem cells for transplantation

Cornea transplantation has been considered to be different from other solid organ transplantation because of the assumed immune-privileged state of the anterior chamber of the eye. Three major lines of thought regarding the molecular mechanisms of immune privilege in the eye are as follows: (a) anatomical, cellular, and molecular barriers in the eye; (b) anterior chamber-associated immune deviation; and (c) immunosuppressive microenvironment in the eye. However, cornea transplants suffer allograft rejection when breached by vascularization. In recent developments, cellular corneal transplantation from cultivated limbal epithelial cells has shown impressive advances as a future therapy. The limbal stem cell niche contains stem cells that promote proliferation and migration and have immunosuppressive mechanisms to protect them from immunological reactions. Limbal stem cells are also noted to display an enhanced expression of genes for the antiapoptotic proteins, a property that is imperative for the survival of transplanted tissues. Further investigation of the molecular mechanisms regulating the immune regulation of limbal stem cells is relevant in the clinical setting to promote the survival of whole corneal and limbal stem cell transplantation.

Minocycline inhibits alkali burn-induced corneal neovascularization in mice

The purpose of this study was to investigate the effects of minocycline on alkali burn-induced corneal neovascularization (CNV). A total of 105 mice treated with alkali burns were randomly divided into three groups to receive intraperitoneal injections of either phosphate buffered saline (PBS) or minocycline twice a day (60 mg/kg or 30 mg/kg) for 14 consecutive days. The area of CNV and corneal epithelial defects was measured on day 4, 7, 10, and14 after alkali burns. On day 14, a histopathological examination was performed to assess morphological change and the infiltration of polymorphonuclear neutrophils (PMNs). The mRNA expression levels of vascular endothelial growth factor (VEGF) and its receptors (VEGFRs), basic fibroblast growth factor (bFGF), matrix metalloproteinases (MMPs), interleukin-1α, 1β, 6 (IL-1α, IL-1β, IL-6) were analyzed using real-time quantitative polymerase chain reaction. The expression of MMP-2 and MMP-9 proteins was determined by gelatin zymography. In addition, enzyme-linked immunosorbent assay was used to analyze the protein levels of VEGFR1, VEGFR2, IL-1β and IL-6. Minocycline at a dose of 60 mg/kg or 30 mg/kg significantly enhanced the recovery of the corneal epithelial defects more than PBS did. There were significant decreases of corneal neovascularization in the group of high-dosage minocycline compared with the control group at all checkpoints. On day 14, the infiltrated PMNs was reduced, and the mRNA expression of VEGFR1, VEGFR2, bFGF, IL-1β, IL-6, MMP-2, MMP-9, -13 as well as the protein expression of VEGFR2, MMP-2, -9, IL-1β, IL-6 in the corneas were down-regulated with the use of 60 mg/kg minocycline twice a day. Our results showed that the intraperitoneal injection of minocycline (60 mg/kg b.i.d.) can significantly inhibit alkali burn-induced corneal neovascularization in mice, possibly by accelerating corneal wound healing and by reducing the production of angiogenic factors, inflammatory cytokines and MMPs.

Efficacy of topical blockade of interleukin-1 in experimental dry eye disease

PURPOSE

To evaluate the therapeutic efficacy of topical interleukin-1 receptor antagonist (IL-1Ra) in the treatment of dry eye disease.

DESIGN

Laboratory investigation.

METHODS

Dry eye disease was induced in C57BL/6 female mice through exposure to a desiccating environment within a controlled environment chamber. Topical formulations containing 5% IL-1Ra, 1% methylprednisolone, 0.05% cyclosporin A, and a vehicle control containing carboxymethylcellulose sodium were applied after the induction of dry eye. Corneal fluorescein staining was performed by a masked observer in the different treatment groups. Immunohistochemical studies were undertaken to enumerate corneal CD11b+ cells, as well as to evaluate corneal lymphangiogenesis. Real-time polymerase reaction was used to quantify the expression of interleukin-1β in the cornea.

RESULTS

A significant decrease in corneal fluorescein staining was observed after topical treatment with 5% IL-1Ra (P < .01), 1% methylprednisolone (P < .01), and 0.05% cyclosporin A (P < .03). Additionally, a significant decrease in the numbers of central corneal CD11b+ cells (P < .05), corneal lymphatic growth (P < .05), and corneal interleukin-1β expression (P < .003), compared with vehicle treated, were demonstrated only after treatment with 5% IL-1Ra and 1% methylprednisolone, and were absent after cyclosporin A treatment.

CONCLUSIONS

Topical treatment with IL-1Ra is effective in ameliorating the clinical signs of the dry eye disease, as well as in reducing underlying inflammation. These effects are comparable with those resulting from treatment with topical methylprednisolone. Topical IL-1Ra may hold promise as a novel therapeutic strategy in the treatment of dry eye.

Interleukin-1 receptor role in the viability of corneal myofibroblasts

The purpose of this study was to investigate the role of interleukin-1 (IL-1) in modulating myofibroblast viability in mouse corneas with stromal opacity. Twenty-four female B6; 129S1-Il1r1tm1Roml/J homozygous IL-1RI knockout mice and 24 control B6129SF2/J mice were included in this study. Each mouse had opacity-generating irregular phototherapeutic keratectomy (PTK) performed with an excimer laser in one eye. Groups of 8 mice from each group were euthanized at one month, three months and six months after surgery and the eyes cryo-preserved. The contralateral eye served as unwounded control. Immunohistochemistry was performed for α-smooth muscle actin (SMA) in central sections of all corneas. The TUNEL assay for apoptosis was performed on 8 sections of four eyes from each group. No SMA+ cells were detected in the stroma of unwounded control or knockout corneas. SMA+ myofibroblast density was significantly higher (p < 0.001) in the IL-1RI knockout group than in the control group at one month, three and six months after irregular PTK. Mean TUNEL+ stromal cells in the anterior 50 μm of stroma was significantly lower in the IL-1RI knockout group compared to the control group at six months after irregular PTK (p = 0.04). These results corroborate the findings of recent in vitro work that demonstrated an antagonistic effect of TGFβ and IL-1 on myofibroblast viability, and found that IL-1-triggered myofibroblast apoptosis was suppressed by TGFβ. Thus, IL-1 is an important modulator of myofibroblast viability during corneal wound healing.

A mouse model of lamellar intrastromal femtosecond laser keratotomy: ultra-structural, inflammatory, and wound healing responses

PURPOSE

The availability of knockout mouse species provide a highly versatile platform for critically examining the corneal wound healing response. We aimed to develop and characterize the wound healing response in a mouse model of intrastromal femtosecond laser (FSL) keratotomy.

METHODS

An intrastromal lamellar dissection using a Visumax FSL was performed on 16 wild type mice (C57BL6) . The energy level was optimized at 150nJ. The FSL was programmed to perform a lamellar dissection at 50 µM depth without sidecut. The flap was not lifted. Fellow eyes were used as controls. Slit lamp photography and confocal microscopy were performed immediately before the mice were sacrificed 4 h, 1, 3, and 7 days post surgery. Corneas were harvested for immunocytochemistry, transmission electron microscopy (TEM) and light microscopy (LM).

RESULTS

Confocal microscopy showed an absence of keratocytes in the area immediately surrounding the dissection plane. The dissection plane and individual FSL plasma cavitation bubbles were clearly evident on TEM. There was evidence of Keratocyte cell death along the laser resection plane on TEM. LM revealed the dissection plane at a 20 µM depth, although not all epithelial cell layers were intact. Staining for monocytes using antibodies for CD11b (cluster of differentiation 11b) showed early migration at the peripheries at 4 h that increased at 24 h and became more central in treated corneas (p<0.001). Apoptotic cells were evident on TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay in the immediate ablation zone and were significantly raised at 4 and 24 h (p<0.001). Ki67 (Kiel 67 protein) positive proliferating keratocytes are evident at 3 days and increased significantly by 7 days (p<0.001). Minimal fibroblast (cluster of differentiation 90, CD90) transformation was seen at 1 week. No myofibroblasts were detected.

DISCUSSION

We have demonstrated that FSL lamellar cuts can be effectively performed on mice and that this model exhibits typical signs of the corneal wound healing response. This model could provide a ubiquitous platform in which to study corneal wound healing responses in both wild type and knockout mice species. The ability to create such a lamellar pocket may be utilizzd for intrastromal drug delivery.

Effects of interleukin-1 receptor antagonist on tumor stroma in experimental uveal melanoma

PURPOSE

In contrast to many malignancies showing evidence that interleukin-1 (IL-1) promotes progression through effects on tumor vascularity and myeloid suppressor cell populations, in uveal melanoma there is evidence that IL-1 can inhibit progression.

METHODS

The effects of the IL-1 receptor antagonist IL-1ra against the aggressive/invasive MUM2B and the nonaggressive/noninvasive OCM1 uveal melanoma models were examined in vitro and in vivo in mouse xenografts. Vascularity and myeloid suppressor cell populations and their regulators were assessed.

RESULTS

In vitro, IL-1, and IL-1ra did not affect the proliferation of the uveal melanoma cells or their production of IL-1, IL-6, transforming growth factor (TGF) β, or VEGF. In vivo, IL-1ra treatment resulted in substantial growth inhibition of MUM2B tumors; less inhibition was observed against OCM1 tumors. Periodic acid-Schiff loops and CD11b⁺ macrophages within the tumor stroma decreased in vivo; CD31⁺ blood vessels were not altered. IL-1ra treatment in vivo did not affect tumor-derived IL-1, IL-6, TGF-β, or VEGF. In contrast, host IL-1β, IL-6, and tumor necrosis factor decreased. Host VEGF was not altered. Intratumoral IL-12(p40) and CXCL10, markers of host M1 polarization, increased, and intratumoral arginase and CD206, markers of myeloid-derived suppressor cells (MDSC) and M2 macrophage polarization, decreased. IL-1ra treatment in vivo also reduced splenic CD11b⁺Gr1⁺ MDSC.

CONCLUSIONS

IL-1 may play a role in promoting uveal melanoma progression. Inhibiting IL-1 with IL-1ra inhibits tumor growth in vivo but not in vitro. Tumor stroma is modified, myeloid suppressor cells are reduced, and M1 macrophage polarization is increased in vivo.

Stromal interleukin-1 expression in the cornea after haze-associated injury

The purpose of this study was to determine whether myofibroblasts or other cells in the stroma in the cornea produce interleukin (IL)-1alpha or IL-1beta that could modulate myofibroblast viability in corneas with haze after photorefractive keratectomy (PRK). Twenty-four female rabbits had haze-generating PRK for 9 diopters of myopia and were sacrificed at 1 week, 2 weeks, 3 weeks or 4 weeks after surgery. Corneal rims were removed, frozen in OCT at -80 degrees C, and analyzed by immunocytochemistry using primary antibodies to IL-1alpha, IL-1beta and alpha smooth muscle actin (SMA). Double immunostaining was performed for the co-localization of SMA with IL-1alpha or IL-1beta. Central dense haze and peripheral slight haze regions of each cornea were analyzed. SMA+ cells that expressed IL-1alpha protein were detected in both regions of the corneas at most time points following PRK. However, in the haze region at the 1, 3 and 4 week time points, significantly more (p<0.01) SMA+ cells did not express IL-1alpha. Also, in the haze region at all three time points, significantly more (p<0.01) SMA- cells than SMA+ cells expressed interleukin-1alpha protein. IL-1beta expression patterns in SMA+ and SMA- stromal cells was similar to that of IL-1alpha after PRK. Previous studies have demonstrated that IL-1alpha or IL-1beta triggers myofibroblast apoptosis in vitro, depending on the available concentration of apoptosis-suppressive TGFbeta. This study demonstrates that SMA- cells such as corneal fibroblasts, keratocytes, or inflammatory cells may produce IL-1alpha and/or IL-1beta that could act in paracrine fashion to regulate myofibroblast apoptosis--especially in the region where there is haze in the cornea after PRK was performed and SMA+ myofibroblasts are present at higher density. However, some SMA+ myofibroblasts themselves produce IL-1alpha and/or IL-1beta, suggesting that myofibroblast viability could also be regulated via autocrine mechanisms.

The molecular basis of corneal transparency

The cornea consists primarily of three layers: an outer layer containing an epithelium, a middle stromal layer consisting of a collagen-rich extracellular matrix (ECM) interspersed with keratocytes and an inner layer of endothelial cells. The stroma consists of dense, regularly packed collagen fibrils arranged as orthogonal layers or lamellae. The corneal stroma is unique in having a homogeneous distribution of small diameter 25-30 nm fibrils that are regularly packed within lamellae and this arrangement minimizes light scattering permitting transparency. The ECM of the corneal stroma consists primarily of collagen type I with lesser amounts of collagen type V and four proteoglycans: three with keratan sulfate chains; lumican, keratocan, osteoglycin and one with a chondroitin sulfate chain; decorin. It is the core proteins of these proteoglycans and collagen type V that regulate the growth of collagen fibrils. The overall size of the proteoglycans are small enough to fit in the spaces between the collagen fibrils and regulate their spacing. The stroma is formed during development by neural crest cells that migrate into the space between the corneal epithelium and corneal endothelium and become keratoblasts. The keratoblasts proliferate and synthesize high levels of hyaluronan to form an embryonic corneal stroma ECM. The keratoblasts differentiate into keratocytes which synthesize high levels of collagens and keratan sulfate proteoglycans that replace the hyaluronan/water-rich ECM with the densely packed collagen fibril-type ECM seen in transparent adult corneas. When an incisional wound through the epithelium into stroma occurs the keratocytes become hypercellular myofibroblasts. These can later become wound fibroblasts, which provides continued transparency or become myofibroblasts that produce a disorganized ECM resulting in corneal opacity. The growth factors IGF-I/II are likely responsible for the formation of the well organized ECM associated with transparency produced by keratocytes during development and by the wound fibroblast during repair. In contrast, TGF-beta would cause the formation of the myofibroblast that produces corneal scaring. Thus, the growth factor mediated synthesis of several different collagen types and the core proteins of several different leucine-rich type proteoglycans as well as posttranslational modifications of the collagens and the proteoglycans are required to produce collagen fibrils with the size and spacing needed for corneal stromal transparency.

Corneal myofibroblast generation from bone marrow-derived cells

The purpose of this study was to determine whether bone marrow-derived cells can differentiate into myofibroblasts, as defined by alpha-smooth muscle actin (SMA) expression, that arise in the corneal stroma after irregular phototherapeutic keratectomy and whose presence within the cornea is associated with corneal stromal haze. C57BL/6J-GFP chimeric mice were generated through bone marrow transplantation from donor mice that expressed enhanced green fluorescent protein (GFP) in a high proportion of their bone marrow-derived cells. Twenty-four GFP chimeric mice underwent haze-generating corneal epithelial scrape followed by irregular phototherapeutic keratectomy (PTK) with an excimer laser in one eye. Mice were euthanized at 2 weeks or 4 weeks after PTK and the treated and control contralateral eyes were removed and cryo-preserved for sectioning for immunocytochemistry. Double immunocytochemistry for GFP and myofibroblast marker alpha-smooth muscle actin (SMA) were performed and the number of SMA+GFP+, SMA+GFP-, SMA-GFP+ and SMA-GFP- cells, as well as the number of DAPI+ cell nuclei, per 400x field of stroma was determined in the central, mid-peripheral and peri-limbal cornea. In this mouse model, there were no SMA+ cells and only a few GFP+ cells detected in unwounded control corneas. No SMA+ cells were detected in the stroma at two weeks after irregular PTK, even though there were numerous GFP+ cells present. At 4 weeks after irregular PTK, all corneas developed mild to moderately severe corneal haze. In each of the three regions of the corneas examined, there were on average more than 9x more SMA+GFP+ than SMA+GFP- myofibroblasts. This difference was significant (p < 0.01). There were significantly more (p < 0.01) SMA-GFP+ cells, which likely include inflammatory cells, than SMA+GFP+ or SMA+GFP- cells, although SMA-GFP- cells represent the largest population of cells in the corneas. In this mouse model, the majority of myofibroblasts developed from bone marrow-derived cells. It is possible that all myofibroblasts in these animals developed from bone marrow-derived cells since mouse chimeras produced using this method had only 60-95% of bone marrow-derived cells that were GFP+ and it is not possible to achieve 100% chimerization. This model, therefore, cannot exclude the possibility of myofibroblasts also developed from keratocytes and/or corneal fibroblasts.

Expression of interleukin-1 receptor antagonist in human cornea

The purpose of this study was to confirm the expression of interleukin-1 receptor antagonist (IL-1 Ra) in the human cornea. Four samples of human ex vivo corneal epithelium were obtained from patients undergoing photorefractive keratectomy. RT-PCR was performed using mRNA isolated from the corneal epithelium and oligo-dT primers. PCR was performed on the cDNA products using primers specific for human IL-1 Ra. The PCR products were subcloned and sequenced. Human cornea sections were prepared from eyes enucleated for choroidal melanoma. Immunocytochemistry was performed using goat anti-mouse polyclonal IL-1 Ra IgG and NL-577 conjugated donkey anti-goat IgG. IL-1 Ra mRNA was expressed in all ex vivo corneal epithelium samples as confirmed by sequencing of the PCR products. Immunofluorescence studies revealed strongest expression of IL-1 Ra in the superficial apical layer of corneal epithelium. Expression of IL-1 Ra may represent an endogenous mechanism of down-regulating the effects of epithelial- and tear-derived IL-1alpha and IL-1beta on the intact epithelium in the unwounded cornea and stromal cells after injury.