Vandana Agrawal

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.

Effect of Femtosecond Laser Energy Level on Corneal Stromal Cell Death and Inflammation

PURPOSE To analyze the effects of variations in femtosecond laser energy level on corneal stromal cell death and inflammatory cell influx following flap creation in a rabbit model. METHODS Eighteen rabbits were stratified in three different groups according to level of energy applied for flap creation (six animals per group). Three different energy levels were chosen for both the lamellar and side cut: 2.7 microJ (high energy), 1.6 microJ (intermediate energy), and 0.5 microJ (low energy) with a 60 kHz, model II, femtosecond laser (IntraLase). The opposite eye of each rabbit served as a control. At the 24-hour time point after surgery, all rabbits were euthanized and the corneoscleral rims were analyzed for the levels of cell death and inflammatory cell influx with the terminal uridine deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and immunocytochemistry for monocyte marker CD11b, respectively. RESULTS The high energy group (31.9+/-7.1 [standard error of mean (SEM) 2.9]) had significantly more TUNEL-positive cells in the central flap compared to the intermediate (22.2+/-1.9 [SEM 0.8], P=.004), low (17.9+/-4.0 [SEM 1.6], P< or =.001), and control eye (0.06+/-0.02 [SEM 0.009], P< or =.001) groups. The intermediate and low energy groups also had significantly more TUNEL-positive cells than the control groups (P< or =.001). The difference between the intermediate and low energy levels was not significant (P=.56). The mean for CD11b-positive cells/400x field at the flap edge was 26.1+/-29.3 (SEM 11.9), 5.8+/-4.1 (SEM 1.6), 1.6+/-4.1 (SEM 1.6), and 0.005+/-0.01 (SEM 0.005) for high energy, intermediate energy, low energy, and control groups, respectively. Only the intermediate energy group showed statistically more inflammatory cells than control eyes (P=.015), most likely due to variability between eyes. CONCLUSIONS Higher energy levels trigger greater cell death when the femtosecond laser is used to create corneal flaps. Greater corneal inflammatory cell infiltration is observed with higher femtosecond laser energy levels.

Corneal myofibroblast viability: Opposing effects of IL-1 and TGF β1

The purpose of this study was to test the effect of corneal epithelial scrape on myofibroblasts associated with haze and elucidate the effect of interleukin-1 and transforming growth factor beta1 on corneal stromal myofibroblasts viability and death in vitro. Corneal epithelial scrape was performed in rabbit eyes with severe haze at one month after -9 diopter photorefractive keratectomy. Corneas were processed for immunocytochemistry for myofibroblast marker alpha-smooth muscle actin (alpha-SMA) and the TUNEL assay to detect apoptosis. Rabbit corneal fibroblasts were cultured with 2 ng/ml of transforming growth factor beta1 (TGF beta1) to induce myofibroblast differentiation confirmed by monitoring alpha-SMA expression. Fluorescence-based TUNEL assay was performed to analyze the apoptotic response of myofibroblasts to IL-1alpha or IL-1beta, in the presence or absence of TGF beta1. Dose response experiments were performed after withdrawal of TGF beta1 and exposure to 1, 5, or 10 ng/ml of IL-1alpha or IL-1beta for 1 h. Subsequent experiments were performed with myofibroblasts exposed to 5 ng/ml of IL-1alpha or IL-1beta in conjunction with 0, 1, 5, or 10 ng/ml of TGF beta1. Corneal epithelial scrape with a scalpel blade produced myofibroblast apoptosis. Exposure to TGF beta1 in vitro resulted in greater than 99% transformation of corneal fibroblasts to alpha-SMA+ myofibroblasts. There was a statistically significant dose-dependent increase in the percentage of TUNEL+ cells with either IL-1alpha or IL-1beta initiated at concentrations as low as 1 ng/ml. For example, after withdrawal of TGF beta1, the % TUNEL+ cells at 1 h after exposure to IL-1alpha increased significantly with increasing concentration (0 ng/ml, 2.4 +/- 0.8% [S.E.M.]; 1 ng/ml, 15.4 +/- 1.8%; 5 ng/ml, 47.4 +/- 3.9%; or 10 ng/ml, 70.3 +/- 3.2%). Similar results were obtained with IL-1beta. The differences between the means of apoptotic myofibroblasts for the different concentrations of cytokine for either IL-1alpha or IL-1beta were significantly different (ANOVA, p < 0.001). When myofibroblasts were exposed to 5 ng/ml of IL-1alpha or IL-1beta, the % TUNEL+ cells at 1 h were reduced in a significant dose-dependent manner when TGF beta1 at a concentration of 5 ng/ml or 10 ng/ml was present in the medium (ANOVA p < 0.01). IL-1alpha or IL-1beta triggers the death of myofibroblasts in vitro and TGF beta1 reduces the IL-1 effect on cell death. TGF beta1 and IL-1 have opposing effects on myofibroblast viability and likely interact to modulate haze generation after corneal injury.

Corneal stroma PDGF blockade and myofibroblast development.

Myofibroblast development and haze generation in the corneal stroma is mediated by cytokines, including transforming growth factor-beta (TGF-beta), and possibly other cytokines. This study examined the effects of stromal PDGF-beta blockade on the development of myofibroblasts in response to -9.0 diopter photorefractive keratectomy in the rabbit. Rabbits that had haze generating photorefractive keratectomy (PRK, for 9 diopters of myopia) in one eye were divided into three different groups: stromal application of plasmid pCMV.PDGFRB.23KDEL expressing a subunit of PDGF receptor b (domains 2-3, which bind PDGF-B), stromal application of empty plasmid pCMV, or stromal application of balanced salt solution (BSS). The plasmids (at a concentration 1000ng/microl) or BSS was applied to the exposed stroma immediately after surgery and every 24h for 4-5 days until the epithelium healed. The group treated with pCMV.PDGFRB.23KDEL showed lower alphaSMA+ myofibroblast density in the anterior stroma compared to either control group (P<or=0.001). Although there was also lower corneal haze at the slit lamp at one month after surgery, the difference in haze after PDGF-B blockade was not statistically significant compared to either control group. Stromal PDGF-B blockade during the early postoperative period following PRK decreases stromal alphaSMA+ myofibroblast generation. PDGF is an important modulator of myofibroblast development in the cornea.

Biological and biomechanical responses to traditional epithelium-off and transepithelial riboflavin-UVA CXL techniques in rabbits.

PURPOSE To compare the biological effects of riboflavin-ultraviolet A (UVA) corneal cross-linking (CXL) performed with a traditional epithelium-off method to several transepithelial methods in a rabbit model. Preliminary experiments on biomechanical rigidity were also performed. METHODS Four treatment groups were included: (1) standard epithelium-off, (2) tetracaine transepithelial, (3) benzal-konium chloride-ethylenediaminetetraacetic acid (BKC-EDTA) transepithelial, and (4) femtosecond laser-assisted transepithelial riboflavin-UVA CXL. Six eyes from each treatment group and the untreated control group were analyzed at 24 hours and 2 months after treatment in wound healing studies. The TUNEL assay was performed to detect the extent of stromal cell death. Optical density was measured with a Scheimpflug analyzer. The corneal stiffening effect was quantitated in three eyes from each group using optical coherence elastography performed 2 months after treatments. RESULTS Twenty-four hours after CXL, stromal cell death extended full corneal thickness with both standard epithelium-off CXL and femtosecond laser-assisted CXL, but only approximately one-third stromal depth after BKC-EDTA transepithelial CXL. Negligible stromal cell death was detected with tetracaine transepithelial CXL. Cell death results were statistically different between the BKC-EDTA transepithelial CXL and standard epithelium-off CXL groups (P < .0001). Significant corneal opacity differences were noted. Standard epithelium-off CXL had the greatest density and tetracaine transepithelial CXL had the least density compared to the control group after treatment. As measured with optical coherence elastography, a trend toward greater mean stiffening was observed with BKC-EDTA transepithelial CXL than with epithelium-off CXL, femtosecond laser-assisted CXL, or tetracaine transepithelial CXL, but the result did not reach statistical significance. All of the CXL treatment groups exhibited significantly smaller variance of stiffness compared to the control group. CONCLUSION In the rabbit model, BKC-EDTA transepithelial CXL produced less stromal cell death and less risk of endothelial cell damage than standard epithelium-off CXL or femtosecond laser-assisted CXL. Additional study is needed to determine whether biomechanical stiffness is significantly different between the epithelium-off CXL and transepithelial CXL groups.

Transmission electron microscopy analysis of epithelial basement membrane repair in rabbit corneas with haze.

PURPOSE To assess the ultrastructure of the epithelial basement membrane using transmission electron microscopy (TEM) in rabbit corneas with and without subepithelial stroma opacity (haze). METHODS Two groups of eight rabbits each were included in this study. Photorefractive keratectomy (PRK) was performed using an excimer laser. The first group had -4.5-diopter (-4.5D) PRK and the second group had -9.0D PRK. Contralateral eyes were unwounded controls. Rabbits were sacrificed at 4 weeks after surgery. Immunohistochemical analysis was performed to detect the myofibroblast marker α-smooth muscle actin (SMA). TEM was performed to analyze the ultrastructure of the epithelial basement membrane and stroma. RESULTS At 4 weeks after PRK, α-SMA+ myofibroblasts were present at high density in the subepithelial stroma of rabbit eyes that had -9.0D PRK, along with prominent disorganized extracellular matrix, whereas few myofibroblasts and little disorganized extracellular matrix were noted in eyes that had -4.5D PRK. The epithelial basement membrane was irregular and discontinuous and lacking typical morphology in all corneas at 1 month after -9D PRK compared to corneas at 1 month in the -4.5D PRK group. CONCLUSIONS The epithelial basement membrane acts as a critical modulator of corneal wound healing. Structural and functional defects in the epithelial basement membrane correlate to both stromal myofibroblast development from precursor cells and continued myofibroblast viability, likely through the modulation of epithelial-stromal interactions mediated by cytokines. Prolonged stromal haze in the cornea is associated with abnormal regeneration of the epithelial basement membrane.

Corneal wound healing after ultraviolet-A/riboflavin collagen cross-linking: a rabbit study.

PURPOSE To investigate corneal wound healing following ultraviolet-A (UVA)/riboflavin corneal collagen cross-linking (CXL) in rabbit corneas. METHODS Thirty-six rabbits were enrolled in the study. Animals were divided into three treatment groups and corneas were analyzed at 24 hours and 4 weeks postoperatively. Thus, each group had 6 rabbits at each time point. Treatment groups were: 1) standard UVA+riboflavin CXL, 2) UVA alone, and 3) riboflavin alone. One eye of each rabbit served as an untreated control eye. TUNEL assay was performed to detect stromal cell apoptosis. Immunocytochemistry was performed to detect the inflammatory marker CD11b expressed in monocytes and the alpha-smooth muscle actin (SMA) marker expressed in myofibroblasts. RESULTS At 24 hours, corneas from the UVA+riboflavin CXL group had significantly more apoptosis than the UVA alone and riboflavin alone groups. Eyes from all three groups had significantly more inflammatory cell influx into the cornea than unwounded controls. Four weeks after the procedure, many corneas in the UVA+riboflavin CXL group had mild haze, but very few SMA-positive myofibroblasts could be detected in the central cornea. CONCLUSIONS Riboflavin+UVA CXL triggers more anterior keratocyte apoptosis than corneal scrape with UVA alone or riboflavin alone. Inflammation monitored by the monocyte marker CD11b was present, but not statistically different among the three groups. Very little myofibroblast generation could be detected after UVA+riboflavin CXL, indicating that the mild stromal haze associated with this procedure is normally related to transient corneal fibroblast generation rather than more persistent haze due to generation of myofibroblasts.

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.

Short-term Cell Death and Inflammation After Intracorneal Inlay Implantation in Rabbits

PURPOSE To investigate the cell death and inflammatory response to insertion of the KAMRA inlay (AcuFocus Inc) for presbyopia. METHODS Twenty-four rabbits were included in the study. Each rabbit had pockets generated in both corneas with a femtosecond laser. One eye of each rabbit had an inlay inserted into the pocket and the opposite control eye had the pocket dissected. Eight rabbits were studied at 24 hours, 48 hours, or 6 weeks after surgery. Tissue sections were analyzed with TUNEL assay to detect cell death and immunohistochemistry for CD11b to detect monocytes as a marker of inflammation. RESULTS The inlay group had significantly more stromal cell death than the control group at 48 hours after surgery (P=.038). At 24 hours and 6 weeks after surgery, no significant difference was noted in stromal cell death between the inlay and control groups. Significantly more CD11b+ cells were noted in the stroma in the inlay group compared to the control group at 24 and 48 hours after surgery (P=.025 and P=.001, respectively). However, at 6 weeks after surgery, no significant difference in CD11b+ cells was observed between the control and inlay groups (P=.05). CONCLUSIONS Although an early increase in stromal cell death and inflammation occurred in eyes that underwent femtosecond laser pocket creation and KAMRA inlay insertion compared to a control group with the pocket only, no significant difference was noted between the inlay and control groups in stromal cell death or inflammation at 6 weeks after surgery.

Expression of PDGF Receptor-α in Corneal Myofibroblasts In Situ

The purpose of this study was to investigate the expression of platelet-derived growth factor receptor-alpha (PDGFR-alpha) in the myofibroblasts of corneas with stromal haze. Central corneal sections from rabbit eyes that had -9 diopter PRK were analyzed by immunocytochemistry (IHC) for the expression of PDGFR-alpha at 4 week after surgery. PDGFR-alpha was expressed immediately beneath the epithelial basement membrane in the anterior stroma. Double IHC studies revealed the expression of PDGFR-alpha in the anterior stroma co-localized with alpha-smooth muscle actin (SMA) marker for myofibroblasts. In vitro studies have suggested that PDGF is important in the development and viability of myofibroblasts after corneal injury. Expression of PDGFR-alpha in myofibroblasts supports these findings.