Evaluation of the results of contact lens assisted corneal cross-linking treatment in keratoconus patients with thin corneas.

PURPOSE: We aimed to compare the efficacy and safety of accelerated contact lens-assisted cross-linking (CA-CXL) with Lotrafilcon B and Comfilcon A lenses in keratoconus (KC) patients with thin corneas. STUDY DESIGN: Retrospective, single-center study. MATERIALS AND METHODS: We retrospectively included 51 eyes of 39 KC patients with corneal thickness <400µm after epithelial scraping (Epi-off), who underwent accelerated CA-CXL treatment with Lotrafilcon B (n=20) and Comfilcon A (n=31). Uncorrected and corrected distance visual acuity (UDVA and CDVA), manifest refraction values, corneal topographic data and endothelial cell density were recorded at preoperative and postoperative 1st, 3rd and 6th month controls. RESULTS: CDVA in the Comfilcon A group was higher than CDVA before surgery at 6 months postoperatively (p<0.001). When the two lenses were compared, CDVA was found to be significantly higher in the Lotrafilcon B group in the preoperative, postoperative 1st month and 3rd month values, but there was no significant difference between the postoperative 6th month values (p=0.028, p=0.018, p=0.044, p=0.181, respectively). The maximum keratometry (Kmax) value at the 6th month after surgery in the Comfilcon A group was significantly lower than in the Lotrafilcon B group (p=0,009). There was no significant difference between the endothelial cell density values between the groups (p=0.623, p=0.609, p=0.794, p=0.458, respectively). There was no significant difference between the progression, regression, and stability rates of the two groups (p=0.714). CONCLUSIONS: Accelerated CA-CXL with Lotrafilcon B and Comfilcon A silicone hydrogel lenses is a safe and effective method to stop progression in patients with thin corneas.

Two-phase mechanism in the treatment of corneal stromal fibrosis with topical losartan.

Recent studies in rabbits and case reports in humans have demonstrated the efficacy of topical losartan in the treatment of corneal scarring fibrosis after a wide range of injuries, including chemical burns, infections, surgical complications, and some diseases. It is hypothesized that the effect of losartan on the fibrotic corneal stroma occurs through a two-phase process in which losartan first triggers the elimination of myofibroblasts by directing their apoptosis via inhibition of extracellular signal-regulated kinase (ERK)-mediated signal transduction, and possibly through signaling effects on the viability and development of corneal fibroblast and fibrocyte myofibroblast precursor cells. This first step likely occurs within a week or two in most corneas with fibrosis treated with topical losartan, but the medication must be continued for much longer until the epithelial basement membrane (EBM) is fully regenerated or new myofibroblasts will develop from precursor cells. Once the myofibroblasts are eliminated from the fibrotic stroma, corneal fibroblasts can migrate into the fibrotic tissue and reabsorb/reorganize the disordered extracellular matrix (ECM) previously produced by the myofibroblasts. This second stage is longer and more variable in different eyes of rabbits and humans, and accounts for most of the variability in the time it takes for the stromal opacity to be markedly reduced by topical losartan treatment. Eventually, keratocytes reemerge in the previously fibrotic stromal tissue to fine-tune the collagens and other ECM components and maintain the normal structure of the corneal stroma. The efficacy of losartan in the prevention and treatment of corneal fibrosis suggests that it acts as a surrogate for the EBM, by suppressing TGF beta-directed scarring of the wounded corneal stroma, until control over TGF beta action is re-established by a healed EBM, while also supporting regeneration of the EBM by allowing corneal fibroblasts to occupy the subepithelial stroma in the place of myofibroblasts.

Comparative evaluation of biomechanical changes and aberration profile following accelerated collagen cross-linking using hypo-osmolar and iso-osmolar riboflavin: A prospective study.

PURPOSE: To compare the changes encountered in corneal biomechanics and aberration profile following accelerated corneal collagen cross-linking (CXL) using hypo-osmolar and iso-osmolar riboflavin in corneal thicknesses of <400 and >400 microns, respectively. METHODS: This is a prospective, interventional, comparative study involving 100 eyes of 75 patients with progressive keratoconus. Eyes were divided into two groups based on corneal thickness: group 1 included eyes with a corneal thickness of <400 microns who underwent hypo-osmolar CXL, and group 2 included eyes with a corneal thickness of >400 microns who underwent iso-osmolar CXL. Corneal biomechanical and aberration profiles were evaluated and compared between groups. RESULTS: In group 1, all higher-order aberrations (HOA) except secondary astigmatism significantly decreased from baseline; however, in group 2, only coma and trefoil decreased. The corneal resistance factor and corneal hysteresis significantly improved in both groups, which was significantly greater in group 2 than in group 1. The change in inverse radius, deformation amplitude, and tomographic biomechanical index was significantly improved in group 2 as compared to group 1. CONCLUSION: Improvement in corrected distance visual acuity and decrease in HOA were significantly better in the hypo-osmolar CXL group; however, the improvement in biomechanical strength of the cornea was significantly better in the iso-osmolar group.

Cornea-Specific Human Adipose Stem Cell-Derived Extracellular Matrix for Corneal Stroma Tissue Engineering.

Utilizing tissue-specific extracellular matrices (ECMs) is vital for replicating the composition of native tissues and developing biologically relevant biomaterials. Human- or animal-derived donor tissues and organs are the current gold standard for the source of these ECMs. To overcome the several limitations related to these ECM sources, including the highly limited availability of donor tissues, cell-derived ECM offers an alternative approach for engineering tissue-specific biomaterials, such as bioinks for three-dimensional (3D) bioprinting. 3D bioprinting is a state-of-the-art biofabrication technology that addresses the global need for donor tissues and organs. In fact, there is a vast global demand for human donor corneas that are used for treating corneal blindness, often resulting from damage in the corneal stromal microstructure. Human adipose tissue is one of the most abundant tissues and easy to access, and adipose tissue-derived stem cells (hASCs) are a highly advantageous cell type for tissue engineering. Furthermore, hASCs have already been studied in clinical trials for treating corneal stromal pathologies. In this study, a corneal stroma-specific ECM was engineered without the need for donor corneas by differentiating hASCs toward corneal stromal keratocytes (hASC-CSKs). Furthermore, this ECM was utilized as a component for corneal stroma-specific bioink where hASC-CSKs were printed to produce corneal stroma structures. This cost-effective approach combined with a clinically relevant cell type provides valuable information on developing more sustainable tissue-specific solutions and advances the field of corneal tissue engineering.

Substance P promotes transforming growth factor-ß-induced collagen synthesis in human corneal fibroblasts.

Corneal fibroblasts maintain homeostasis of the corneal stroma by mediating the synthesis and degradation of extracellular collagen, and these actions are promoted by transforming growth factor-ß (TGF-ß) and interleukin-1ß (IL-1ß), respectively. The cornea is densely innervated with sensory nerve fibers that are not only responsible for sensation but also required for physiological processes such as tear secretion and wound healing. Loss or dysfunction of corneal nerves thus impairs corneal epithelial wound healing and can lead to neurotrophic keratopathy. The sensory neurotransmitter substance P (SP) promotes corneal epithelial wound healing by enhancing the stimulatory effects of growth factors and fibronectin. We have now investigated the role of SP in collagen metabolism mediated by human corneal fibroblasts in culture. Although SP alone had no effect on collagen synthesis or degradation by these cells, it promoted the stimulatory effect of TGF-ß on collagen type I synthesis without affecting that of IL-1ß on the expression of matrix metalloproteinase-1. This effect of SP on TGF-ß-induced collagen synthesis was accompanied by activation of p38 mitogen-activated protein kinase (MAPK) signaling and was attenuated by pharmacological inhibition of p38 or of the neurokinin-1 receptor. Our results thus implicate SP as a modulator of TGF-ß-induced collagen type I synthesis by human corneal fibroblasts, and they suggest that loss of this function may contribute to the development of neurotrophic keratopathy.NEW & NOTEWORTHY This study investigates the role of substance P (SP) in collagen metabolism mediated by human corneal fibroblasts in culture. We found that, although SP alone had no effect on collagen synthesis or degradation by corneal fibroblasts, it promoted the stimulatory effect of transforming growth factor-ß on collagen type I synthesis without affecting that of interleukin-1ß on the expression of matrix metalloproteinase-1.

Unilateral Granular Type 2 Corneal Dystrophy With Exacerbation After LASIK.

PURPOSE: The aim of this study was to report a case of unilateral granular corneal dystrophy type 2 (GCD2) with exacerbation after bilateral laser in situ keratomileusis (LASIK). METHODS: Clinical evaluation, Scheimpflug imaging, anterior segment optical coherence tomography (AS-OCT), cytology, and genetic testing were used to confirm the diagnosis of unilateral GCD2 with exacerbation after bilateral LASIK. Detailed literature review for possible unilateral GCD2 presentations was performed. RESULTS: A 54-year-old White woman presented with blurred vision in her left eye and a history of bilateral LASIK performed 8 years before. Examination revealed dense opacities in the left cornea only, which were confirmed to be confined to the LASIK interface and adjacent corneal stromal tissue, as determined by AS-OCT. The patient underwent flap lift, interface debris removal, and stromal bed phototherapeutic keratectomy. Cytological analysis showed eosinophilic corneal stromal deposits that stained with trichrome stain and were congophilic on Congo red stain. Genetic testing was positive for heterozygous GCD2 transforming growth factor ß-induced gene ( TGFBI ), c.371G>A, p.R124H mutation. There were no opacities identifiable in the right eye on serial slit-lamp examination, Scheimpflug imaging, or OCT imaging at 4 or 8 years after bilateral LASIK. Literature review failed to identify any previous reports of unilateral GCD2. CONCLUSIONS: This is the first known reported case of unilateral granular corneal dystrophy type 2. LASIK is contraindicated in eyes with corneal stromal dystrophies related to mutations in TGFBI as both flap creation and laser ablation can exacerbate visually significant opacity formation. Scheimpflug and AS-OCT imaging are useful to identify opacities in GCD2.

Comparison of refractive surgeries (SMILE, LASIK, and PRK) with and without corneal crosslinking: systematic review and meta-analysis.

Corneal crosslinking (CXL) is used for treating keratoconus and post-laser in situ keratomileusis ectasia. However, refractive surgery is not usually performed with prophylactic CXL. Therefore, we performed a meta-analysis comparing outcomes of refractive surgeries with vs without prophylactic CXL. We systematically searched databases for studies comparing refractive surgeries for myopic correction with vs without prophylactic corneal crosslinking. Review Manager 5.4.1 was used to perform statistical analysis. We included 2820 eyes from 28 studies. Compared with refractive surgery alone, surgery with prophylactic CXL resulted in decreased central corneal thickness, corrected distance visual acuity logMAR, and safety and efficacy indices. There were no significant differences in postoperative uncorrected distance visual acuity of 20/20 or better at ≥12 months and other visual outcomes among both groups. More randomized controlled trials with standard crosslinking protocols are needed to analyze the prophylactic use of crosslinking with refractive surgeries.

Mesenchymal Stem Cell-Laden In Situ-Forming Hydrogel for Preventing Corneal Stromal Opacity.

PURPOSE: The aims of this study were to construct a mesenchymal stem cell (MSC)-laden in situ-forming hydrogel and study its effects on preventing corneal stromal opacity. METHODS: The native gellan gum was modified by high temperature and pressure, and the rabbit bone marrow MSCs were encapsulated before adding Ca 2+ to initiate cross-linking. The effects of the hydrogel on 3D culture and gene expression of the rabbit bone marrow MSCs were observed in vitro. Then, the MSC-hydrogel was used to repair corneal stromal injury in New Zealand white rabbits within 28 days postoperation. RESULTS: The short-chain gellan gum solution has a very low viscosity (<0.1 Pa·s) that is ideal for encapsulating cells. Moreover, mRNA expressions of 3D-cultured MSCs coding for corneal stromal components (decorin, lumican, and keratocan) were upregulated (by 127.8, 165.5, and 25.4 times, respectively) ( P < 0.05) on day 21 in vitro and were verified by Western blotting results. For the in vivo study, the corneal densitometry of the experimental group was (20.73 ± 1.85) grayscale units which was lower than the other groups ( P < 0.05). The MSC-hydrogel downregulated mRNA expression coding for fibrosis markers (α-smooth muscle actin, vimentin, collagen type 5-α1, and collagen type 1-α1) in the rabbit corneal stroma. Furthermore, some of the 5-ethynyl-2'-deoxyuridine (EdU)-labeled MSCs integrated into the upper corneal stroma and expressed keratocyte-specific antigens on day 28 postoperation. CONCLUSIONS: The short-chain gellan gum allows MSCs to slowly release to the corneal stromal defect and prevent corneal stromal opacity. Some of the implanted MSCs can integrate into the corneal stroma and differentiate into keratocytes.

Effects of hypoxia in the diabetic corneal stroma microenvironment.

Corneal dysfunctions associated with Diabetes Mellitus (DM), termed diabetic keratopathy (DK), can cause impaired vision and/or blindness. Hypoxia affects both Type 1 (T1DM) and Type 2 (T2DM) surprisingly, the role of hypoxia in DK is unexplored. The aim of this study was to examine the impact of hypoxia in vitro on primary human corneal stromal cells derived from Healthy (HCFs), and diabetic (T1DMs and T2DMs) subjects, by exposing them to normoxic (21% O2) or hypoxic (2% O2) conditions through 2D and 3D in vitro models. Our data revealed that hypoxia affected T2DMs by slowing their wound healing capacity, leading to significant alterations in oxidative stress-related markers, mitochondrial health, cellular homeostasis, and endoplasmic reticulum health (ER) along with fibrotic development. In T1DMs, hypoxia significantly modulated markers related to membrane permeabilization, oxidative stress via apoptotic marker (BAX), and protein degradation. Hypoxic environment induced oxidative stress (NOQ1 mediated reduction of superoxide in T1DMs and Nrf2 mediated oxidative stress in T2DMs), modulation in mitochondrial health (Heat shock protein 27 (HSP27), and dysregulation of cellular homeostasis (HSP90) in both T1DMs and T2DMs. This data underscores the significant impact of hypoxia on the diabetic cornea. Further studies are warranted to delineate the complex interactions.

Corneal stromal localization of TGF beta isoforms in spontaneous persistent epithelial defects after PRK in rabbits.

The purpose of this study was to evaluate transforming growth factor beta (TGFß) isoform localization in rabbit corneas with spontaneous persistent epithelial defects (PEDs) after photorefractive keratectomy (PRK). Four cryofixed corneas from a previously reported series of PEDs in rabbits that had PRK were evaluated with triplex immunohistochemistry (IHC) for TGFß3, myofibroblast marker alpha-smooth muscle actin (α-SMA) and mesenchymal marker vimentin. One cornea had sufficient remaining tissue for triplex IHC for TGFß1, TGFß2, or TGFß3 (each with α-SMA and vimentin) using isoform-specific antibodies. All three TGFß isoforms were detected in the subepithelial stroma at and surrounding the PED. Some of each TGFß isoform co-localized with α-SMA of myofibroblasts, which could be TGFß isoform autocrine production by myofibroblasts or TGFß-1, -2, and -3 binding to these myofibroblasts.

Exploration of the pathophysiology of high myopia via proteomic profiling of human corneal stromal lenticules.

This study aimed to investigate the underlying pathophysiology of high myopia by analyzing the proteome of human corneal stromal lenticule samples obtained through small incision lenticule extraction (SMILE). A total of thirty-two patients who underwent SMILE were included in the study. Label-free quantitative proteomic analysis was performed on corneal stromal lenticule samples, equally representing high myopia (n = 10) and low myopia (n = 10) groups. The identified and profiled lenticule proteomes were analyzed using in silico tools to explore biological characteristics of differentially expressed proteins (DEPs). Additionally, LASSO regression and random forest model were employed to identify key proteins associated with the pathophysiology of high myopia. The DEPs were found to be closely linked to immune activation, extracellular matrix, and cell adhesion-related pathways according to gene ontology analysis. Specifically, decreased expression of COL1A1 and increased expression of CDH11 were associated with the pathogenesis of high myopia and validated by western blotting (n = 6) and quantitative real time polymerase chain reaction (n = 6). Overall, this study provides evidence that COL1A1 and CDH11 may contribute to the pathophysiology of high myopia based on comparative proteomic profiling of human corneal stromal lenticules obtained through SMILE.

Long-term outcomes of tailored stromal expansion with refractive lenticule for crosslinking thin corneas.

PURPOSE: To assess the long-term safety and stability of visual outcomes following the modified technique of collagen crosslinking (CXL) using refractive lenticule in eyes with thin corneas (<400 µm) and progressive keratoconus. SETTING: A tertiary eye care hospital in India. DESIGN: Prospective, interventional case series. METHODS: Eyes with progressive keratoconus and thin corneas (<400 µm) underwent CXL with intraoperative stromal augmentation using a refractive lenticule obtained from small-incision lenticule extraction (SMILE). Preoperative and postoperative evaluation (3 months, and then yearly thereafter) included corneal tomography (Oculus Pentacam), uncorrected and corrected distance visual acuity (UDVA and CDVA, respectively), manifest refraction, and endothelial cell count (specular microscopy), and adverse events, if any, were noted. The patients were followed up for a period of 5 years. RESULTS: Seven eyes were included in the analysis. Mean corneal flattening of -4.29 D was noted from preoperative maximum keratometry (P = 0.018). An improvement in UDVA and CDVA of 0.38 logarithm of minimum angle of resolution (logMAR) and 0.36 logMAR, respectively, was noted at 5 years postoperative visit. Four eyes demonstrated a gain of two lines in CDVA. Mean spherical equivalent improved from -6.85 D preoperatively to -6.05 D at 5 years postoperatively. Clear demarcation line was noted between 230 to 270 µm on anterior segment optical coherence topography. No significant endothelial cell loss was noted postoperatively. CONCLUSION: Long-term outcomes demonstrated safety and disease stability following lenticule-assisted CXL.

Benzalkonium chloride greatly deteriorates the biological activities of human corneal stroma fibroblasts in a concentration-dependent manner.

BACKGROUND: Corneal tissues indirectly obtain nutritional needs and oxygen to maintain their homeostasis, and therefore, benzalkonium chloride (BAC) containing ocular instillations for medical therapy may, in turn, induce toxic effects more than expected in corneal tissues, especially the inside stroma layer. METHODS: To evaluate the effects of very low concentrations (10-8%, 10-6%, or 10-4%) of BAC on human corneal stroma, we used two-dimensional (2D) cultures of human corneal stromal fibroblast (HCSF) cells and carried out the following analyses: (1) cell viability measurements, (2) Seahorse cellular bio-metabolism analysis, and (3) the expression of ECM molecules and endoplasmic reticulum (ER) stress-related molecules. RESULTS: In the absence and presence of 10-8%, 10-6%, or 10-4% concentrations of BAC, cell viability deteriorated and this deterioration was dose-dependent. The results showed that maximal mitochondrial respiration was decreased, the mRNA expression of most of ECM proteins was decreased, and ER stress-related molecules were substantially and dose-dependently down-regulated in HCSFs by the BAC treatment. CONCLUSIONS: The findings reported herein indicate that the presence of BAC, even at such low concentrations, is capable of causing the deterioration of cellular metabolic functions and negatively affecting the response to ER stress in HCSF cells resulting in a substantially decreased cellular viability.

Comparative Proteomics Reveals Prolonged Corneal Preservation Impaired Ocular Surface Immunity Accompanied by Fibrosis in Human Stroma.

Cornea transplantation is one of the most commonly performed allotransplantations worldwide. Prolonged storage of donor corneas leads to decreased endothelial cell viability, severe stromal edema, and opacification, significantly compromising the success rate of corneal transplantation. Corneal stroma, which constitutes the majority of the cornea, plays a crucial role in maintaining its shape and transparency. In this study, we conducted proteomic analysis of corneal stroma preserved in Optisol-GS medium at 4 °C for 7 or 14 days to investigate molecular changes during storage. Among 1923 identified proteins, 1634 were quantifiable and 387 were significantly regulated with longer preservation. Compared to stroma preserved for 7 days, proteins involved in ocular surface immunomodulation were largely downregulated while proteins associated with extracellular matrix reorganization and fibrosis were upregulated in those preserved for 14 days. The increase in extracellular matrix structural proteins together with upregulation of growth factor signaling implies the occurrence of stromal fibrosis, which may compromise tissue clarity and cause vision impairments. This study is the first to provide insights into how storage duration affects corneal stroma from a proteomic perspective. Our findings may contribute to future research efforts aimed at developing long-term preservation techniques and improving the quality of preserved corneas, thus maximizing their clinical application.

Cell sheet-based approach to study the diabetic corneal stroma.

Prolonged hyperglycemia during diabetes mellitus (DM) is associated with severe complications that may affect both the anterior and posterior ocular segments, leading to impaired vision or blindness. The cornea is a vital part of the eye that has a dual role as a protective transparent barrier and as a major refractive structure and is likewise negatively affected by hyperglycemia in DM. Understanding the cellular and molecular mechanisms underlying the phenotypic changes associated with DM is critical to developing targeted therapies to promote tissue integrity. In this proof-of-concept study, we applied a cell sheet-based approach to generate stacked constructs of physiological corneal thickness using primary human corneal fibroblasts isolated from cadaveric control (healthy), Type 1 DM and Type 2 DM corneal tissues. Self-assembled corneal stromal sheets were generated after 2 weeks in culture, isolated, and subsequently assembled to create stacked constructs, which were evaluated using transmission electron microscopy. Analysis of gene expression patterns revealed significant downregulation of fibrotic markers, α-smooth muscle actin, and collagen type 3, with stacking in Type 2 DM constructs when compared to controls. IGF1 expression was significantly upregulated in Type 2 DM constructs compared to controls with a significant reduction induced by stacking. This study describes the development of a thicker, self-assembled corneal stromal construct as a platform to evaluate phenotypic differences associated with DM-derived corneal fibroblasts and enable the development of targeted therapeutics to promote corneal integrity.

Unveiling Cellular Diversity in the Buffalo Corneal Stroma: Insights into Telocytes and Keratocytes Using Light Microscope, Transmission Electron Microscope, and Immunofluorescence Analysis.

Telocytes and keratocytes are important cells that maintain the structure and function of the cornea. The buffalo cornea, known for its resilience in harsh conditions, has not been extensively studied regarding the presence and role of telocytes and keratocytes. We used light microscopy, transmission electron microscopy (TEM), and immunofluorescence assays with platelet-derived growth factor receptor alpha (PDGFRα), CD34, and Vimentin markers to investigate their expression and localization in the cornea. TEM analysis confirmed the presence of spindle-shaped keratocytes with intercellular connections, while telocytes exhibited small spindle-shaped bodies with long, thin branches connecting to corneal keratocytes. Immunofluorescence findings showed that CD34 was more abundant near the endothelium, Vimentin was prominently expressed near the epithelium, and PDGFRα was uniformly distributed throughout the corneal stroma. Co-expression of CD34 and Vimentin, PDGFRα and Vimentin, as well as CD34 and PDGFRα, was observed in keratocytes and telocytes within the stroma, indicating the potential presence of mesenchymal cells. These results suggest the involvement of telocytes and keratocytes in corneal wound healing, transparency maintenance, and homeostasis. The co-expression of these markers highlights the critical role of telocytes and keratocytes in regulating corneal physiological functions, further enhancing our understanding of corneal biology in the buffalo model.

Role of Fibroblast Growth Factor Receptor 2 (FGFR2) in Corneal Stromal Thinning.

Purpose: To determine the role of fibroblast growth factor receptor 2 (FGFR2)-mediated signaling in keratocytes during corneal development, a keratocyte-specific FGFR2-knockout (named FGFR2cKO) mouse model was generated, and its phenotypic characteristics were determined. Methods: A FGFR2cKO mouse model was generated by the following method: FGFR2 flox mice were crossed with the inducible keratocyte specific-Cre mice (Kera-rtTA/tet-O-Cre). Both male and female FGFR2cKO- and control mice (1 to 3-months-old) were analyzed for changes in corneal topography and pachymetry maps using the optical coherence tomography (OCT) method. The comparative TUNEL assay and immunohistochemical analyses were performed using corneas of FGFR2cKO and control mice to determine apoptotic cells, and expression of collagen-1 and fibronectin. Transmission electron microscopic analysis was conducted to determine collagen structures and their diameters in corneas of FGFR2cKO and control mice. Results: OCT-analyses of corneas of FGFR2cKO mice (n = 24) showed localized central thinning and an increased corneal steepness compared to control mice (n = 23). FGFR2cKO mice further showed a decreased expression in collagen-1, decreased collagen diameters, acute corneal hydrops, an increased fibronectin expression, and an increased number of TUNEL-positive cells suggesting altered collagen structures and keratocytes' apoptosis in the corneas of FGFR2cKO mice compared to control mice. Conclusions: The FGFR2cKO mice showed several corneal phenotypes (as described above in the results) that are also exhibited by the human keratoconus corneas. The results suggested that the FGFR2cKO mouse model serves to elucidate not only the yet unknown role of FGFR2-mediated signaling in corneal physiology but also serves as a model to determine molecular mechanism of human keratoconus development.

Transforming growth factor beta-3 localization in the corneal response to epithelial-stromal injury and effects on corneal fibroblast transition to myofibroblasts.

The purpose of this study was to evaluate the localization of TGF beta-3 in situ in unwounded rabbit corneas and corneas that had epithelial-stromal injuries produced by photorefractive keratectomy (PRK) in rabbits and to evaluate the in vitro effects of TGF beta-3 compared to TGF beta-1 on alpha-smooth muscle actin (α-SMA) protein expression and myofibroblast development in corneal fibroblasts. Forty-eight New Zealand white rabbits underwent either -3 diopter (D) or -9D PRK and were studied from one to eight weeks (four corneas in each group at each time point) after surgery with immunohistochemistry for TGF beta-3, laminin alpha-5, and alpha-smooth muscle actin (α-SMA). Rabbit corneal fibroblasts were treated with activated TGF beta-1 and/or TGF beta-3 at different concentrations and duration of exposure and studied with immunocytochemistry for myofibroblast development and the expression of α-SMA using Jess automated Western blotting. TGF beta-3 was detected at high levels in the stroma of unwounded corneas and corneas at one to eight weeks after -3D or -9D PRK, as well as in the epithelium and epithelial basement membrane (EBM). No difference was noted between corneas that healed with and without myofibroblast-mediated fibrosis, although TGF beta-3 was commonly associated with myofibroblasts. TGF beta-3 effects on corneal fibroblasts in vitro were similar to TGF beta-1 in stimulating transition to α-SMA-positive myofibroblasts and promoting α-SMA protein expression. The corneal stromal localization pattern of TGF beta-3 protein in unwounded corneas and corneas after epithelial-stromal injury was found to be higher and different from TGF beta-1 and TGF beta-2 reported in previous studies. TGF beta-3 had similar effects to TGF beta-1 in driving myofibroblast development and α-SMA expression in corneal fibroblasts cultured in medium with 1% fetal bovine serum.

The relationship between keratan sulfate glycosaminoglycan density and mechanical stiffening of CXL treatment.

The corneal stroma is primarily composed of collagen fibrils, proteoglycans, and glycosaminoglycans (GAGs). It is known that corneal crosslinking (CXL) treatment improves mechanical properties of the cornea. However, the influence of stromal composition on the strengthening effect of CXL procedure has not been thoroughly investigated. The primary objective of the present research was to characterize the effect of keratan sulfate (KS) GAGs on the efficacy of CXL therapy. To this end, the CXL method was used to crosslink porcine corneal samples from which KS GAGs were enzymatically removed by keratanase II enzyme. Alcian blue staining was done to confirm the successful digestion of GAGs and uniaxial tensile experiments were performed for characterizing corneal mechanical properties. The influence of GAG removal and CXL treatment on resistance of corneal samples against enzymatic pepsin degradation was also quantified. It was found that removal of KS GAGs significantly softened corneal tensile properties (P < 0.05). Moreover, the CXL therapy significantly increased the tensile stiffness of GAG-depleted strips (P < 0.05). GAG-depleted corneal buttons were dissolved in the pepsin digestion solution significantly faster than control samples (P < 0.05). The CXL treatment significantly increased the time needed for complete pepsin digestion of GAG-depleted disks (P < 0.05). Based on these observations, we concluded that KS GAGs play a significant role in defining tensile properties and structural integrity of porcine cornea. Furthermore, the stiffening influence of the CXL treatment does not significantly depend on the density of corneal KS GAGs. The findings of the present study provided new information on the relation between corneal composition and CXL procedure mechanical effects.

Basement membrane regeneration and TGF-ß1 expression in rabbits with corneal perforating injury.

Purpose: To evaluate the relationship between basement membrane (BM) regeneration and the spatiotemporal expression of TGF-ß1 during wound healing in rabbits with corneal perforating injury. Methods: Forty-two rabbits were randomly allocated into 7 experimental groups, with 6 rabbits per group at each time point. The central cornea of the left eye was injured with 2.0 mm trephine to establish the perforating injury model. Six rabbits that received no treatment were used as controls. The cornea was evaluated at 3 days, 1-3 weeks, and 1-3 months after injury with a slit lamp for haze levels. Real-time quantitative polymerase chain reaction (qRT-PCR) was performed to quantify the relative expression of TGF-ß1 and α-SMA mRNA. Immunofluorescence (IF) was used to assess TGF-ß1 and alpha-smooth actin (α-SMA) expression and localization. BM regeneration was assessed using transmission electron microscopy (TEM). Results: After injury, dense haze appeared at 1 month and then gradually faded. The relative expression of TGF-ß1 mRNA peaked at 1 week and then decreased until 2 months. The relative α-SMA mRNA expression reached its peak at 1 week, then reached a small peak again at 1 month. IF results showed that TGF-ß1 was initially detected in the fibrin clot at 3 days and then in the entire repairing stroma at 1 week. TGF-ß1 localization gradually diminished from the anterior region to the posterior region at 2 weeks to 1 month, and it was nearly absent at 2 months. The myofibroblast marker α-SMA was observed in the entire healing stroma at 2 weeks. Localization of α-SMA gradually disappeared from the anterior region at 3 weeks to 1 month, remaining only in the posterior region at 2 months and disappearing at 3 months. Defective epithelial basement membrane (EBM) was first detected at 3 weeks after injury, then gradually repaired, and was nearly regenerated at 3 months. A thin and uneven Descemet's membrane (DM) was initially detected at 2 months after injury, then gradually regenerated to some extent, but remained abnormal at 3 months. Conclusions: In the rabbit corneal perforating injury model, EBM regeneration was observed earlier than DM. At 3 months, complete EBM regeneration was observed, while the regenerated DM was still defective. TGF-ß1 was distributed throughout the entire wound area in the early stages and then decreased from the anterior to the posterior region. α-SMA exhibited a similar temporospatial expression to TGF-ß1. EBM regeneration may play a key role in low expression of TGF-ß1 and α-SMA in the anterior stroma. Meanwhile, incomplete DM regeneration may contribute to the sustained expression of TGF-ß1 and α-SMA in the posterior stroma.