The control of matrix metalloproteinase-2 expression in normal and keratoconic corneal keratocyte cultures

Comparison of Two Different Accelerated Corneal Cross-linking Procedure Outcomes in Patients with Keratoconus

Background

Corneal cross-linking treatment is the unique treatment method that can cease the progression of keratoconus disease. Because of the long duration of conventional treatment, accelerated cross-linking treatment methods are being developed.

Aims

To compare two different accelerated corneal cross-linking protocols in terms of postoperative visual acuity and topographic findings (higher-order aberrations and keratometry values).

Study Design

Retrospective comparative study.

Methods

Sixty-five eyes of 43 patients (30 men and 13 women) who underwent two different accelerated corneal cross-linking protocols (10 min, 9 mW/cm² and 5 min, 18 mW/cm²) for progressive keratoconus were retrospectively analyzed. Patients were divided into two groups according to the accelerated corneal cross-linking treatment protocol: group 1 (10 min, 9 mW/cm², 32 eyes of 21 patients) and group 2 (5 min, 18 mW/cm², 33 eyes of 22 patients). Uncorrected visual acuity and best-corrected visual acuity values and topographic findings (central corneal thickness and flat and steep keratometry values) were recorded preoperatively and 6 months after corneal cross-linking treatment. High-order aberration values measured with Pentacam preoperatively and 6 months after corneal cross-linking were also recorded.

Results

In both groups, a significant improvement was detected in the uncorrected visual acuity and best-corrected visual acuity levels preoperatively and 6 months postoperatively (group 1: p=0.001, p=0.001 and group 2: p=0.001, p=0.001, respectively). In addition, central corneal thickness values decreased significantly in both groups (p=0.006 and 0.001). Trefoil values showed no significant difference preoperatively and 6 months postoperatively in group 1 (p=0.160 and 0.620, respectively). In groups 1 and 2, coma values were found to decrease significantly in the 6^th postoperative month compared with preoperative values (p=0.001 and 0.020, respectively). There was no significant difference between preoperative and 6^th month postoperative horizontal and vertical trefoil values in both groups (p=0.850 and 0.140, respectively). There was no significant difference between the two groups in terms of preoperative and 6^th month postoperative higher-order aberrations, refractive errors, keratometry values, and uncorrected visual acuity and best-corrected visual acuity levels.

Conclusion

Both accelerated corneal cross-linking procedures provide similar improvement in topographic findings, coma values and visual acuity.

Choroidal thickness in keratoconus

PURPOSE

Keratoconus is an ectatic eye disease characterized by progressive thinning and steepening of the cornea which leads to irregular astigmatism and visual function loss. Determination of choroidal thickness in keratoconus patients may help us to better understand and manage the keratoconus disease. Choroidal thickness may be a potential marker for disease activity in keratoconus patients. In this study, we aimed to determine choroidal thickness in keratoconus patients and compare the results with the age-matched control group.

METHODS

This is a prospective study with a control group. Keratometry and thinnest corneal thickness was measured and recorded in keratoconus patients. Choroidal thickness of all subjects was measured using an optical coherence tomography device (Spectralis OCT, version 6.0, Heidelberg Engineering, Germany) with an enhanced depth imaging mode without pupil dilation. Mean choroidal thickness of keratoconus patients was compared with healthy subjects.

RESULTS

One hundred and sixty eyes of 80 healthy subjects and 160 eyes of 80 keratoconus patients were included in the study. Mean thinnest corneal thickness of the keratoconus patients was 449.7 ± 3.2 microns. Mean corneal keratometry value and cylindrical refraction error in the keratoconus patients were 53.2 ± 0.2 and 3.3 ± 0.1 diopters, respectively. Mean choroidal thickness was 363.9 ± 59.8 and 328.4 ± 67.2 microns in keratoconus patients and healthy subjects, respectively. There was a very significant difference between keratoconus patients and healthy subjects in terms of choroidal thickness (P = 0.000). There was not a statistically significant correlation between choroidal thickness and thinnest corneal thickness in keratoconus patients (P = 0.814).

CONCLUSION

Choroidal thickness was found to be increased in keratoconus patients. Choroidal thickness could potentially become a new clinical marker for disease activity in keratoconus patients.

Female Hormone 17β-Estradiol Downregulated MMP-2 Expression and Upregulated A1PI Expression in Human Corneal Stromal Cells

Collagens are essential for cornea functions. In non-ocular tissues, it has been demonstrated that sex hormones modulate the collagen remodeling. In this study, we investigated whether the primary female hormone 17β-estradiol plays a role in the expressions of matrix metalloproteinases and proteinase inhibitors in cultured human corneal stromal cells. We found that 17β-estradiol treatment significantly reduced the matrix metalloproteinase-2 mRNA in human corneal stromal cells as well as the matrix metalloproteinase-2 proteins, while the matrix metalloproteinase-9 mRNA level was not significantly altered. 17β-estradiol also upregulated the expression of proteinase inhibitor, alpha1-proteinase inhibitor. The expression of transcription factor specificity protein 1 was reduced by 17β-estradiol. Furthermore, 17β-estradiol did not change the viability and apoptosis of the corneal stromal cells. The downregulation of matrix metalloproteinase-2 and upregulation of alpha1-proteinase inhibitor by 17β-estradiol possibly serve as protective factor for the normal tomography in antagonizing the extracellular matrix degeneration in many cornea diseases.

Molecular mechanisms of suberoylanilide hydroxamic acid in the inhibition of TGF-β1-mediated canine corneal fibrosis

OBJECTIVE

To investigate molecular mechanisms mediating anti-fibrotic effect of SAHA in the canine cornea using an in vitro model. We hypothesized that SAHA attenuates corneal fibrosis by modulating Smad-dependent and, to a lesser extent, Smad-independent signaling pathways activated by TGF-β1, as well as matrix metalloproteinase (MMP) activity.

METHODS

Cultured canine corneal fibroblasts (CCF) were incubated in the presence/absence of TGF-β1 (5 ng/mL) and SAHA (2.5 μm) for 24 h. Western blot analysis was used to quantify non-phosphorylated and phosphorylated isoforms of Smad2/3, p38 MAP kinase (MAPK), ERK1/2, and JNK1. Real-time PCR and zymography were utilized to quantify MMP1, MMP2, MMP8, and MMP9 mRNA expressions and MMP2 and MMP9 protein activities, respectively.

RESULTS

TGF-β1 treatment caused a significant increase in phospho-Smad2/3 and phospho-p38 MAPK. SAHA treatment reduced TGF-β1-induced phosphorylation of Smad2/3 but not of p38 MAPK. TGF-β1 did not modulate the phosphorylation of ERK1/2 or JNK1. SAHA caused a significant reduction in phospho-ERK1/2 expression regardless of concurrent TGF-β1 treatment. Neither SAHA alone nor in combination with TGF-β1 altered phospho-JNK1 expression. TGF-β1 significantly increased MMP1 and MMP9 mRNA expressions but did not alter MMP2 mRNA. SAHA treatment attenuated TGF-β1-induced MMP9 mRNA expression while significantly enhancing TGF-β1-induced MMP1 mRNA expression. Zymography detected reduced expression of MMP2 and MMP9 proteins in untreated control CCF. TGF-β1 treatment did not alter their expression, but SAHA treatment +/-TGF-β1 significantly increased MMP2 and MMP9 protein expressions.

CONCLUSIONS

The corneal anti-fibrotic effects of SAHA involve multiple mechanisms including modulation of canonical and non-canonical components of TGF-β1 intracellular signaling and MMP activity.

MMP regulation of corneal keratocyte motility and mechanics in 3-D collagen matrices

Previous studies have shown that platelet derived growth factor (PDGF) can stimulate corneal keratocyte spreading and migration within 3-D collagen matrices, without inducing transformation to a contractile, fibroblastic phenotype. The goal of this study was to investigate the role of matrix metalloproteinases (MMPs) in regulating PDGF-induced changes in keratocyte motility and mechanical differentiation. Rabbit corneal keratocytes were isolated and cultured in serum-free media (S-) to maintain their quiescent phenotype. A nested collagen matrix construct was used to assess 3-D cell migration, and a standard collagen matrix model was used to assess cell morphology and cell-mediated matrix contraction. In both cases constructs were cultured in S- supplemented with PDGF, with or without the broad spectrum MMP inhibitors GM6001 or BB-94. After 4 days, f-actin, nuclei and collagen fibrils were imaged using confocal microscopy. To assess sub-cellular mechanical activity (extension and retraction of cell processes), time-lapse DIC imaging was also performed. MT1-MMP expression and MMP-mediated collagen degradation were also examined. Results demonstrated that neither GM6001 nor BB-94 affected corneal keratocyte viability or proliferation in 3-D culture. PDGF stimulated elongation and migration of corneal keratocytes within type I collagen matrices, without causing a loss of their dendritic morphology or inducing formation of intracellular stress fibers. Treatment with GM6001 and BB-94 inhibited PDGF-induced keratocyte spreading and migration. Relatively low levels of keratocyte-induced matrix contraction were also maintained in PDGF, and the amount of PDGF-induced collagen degradation was similar to that observed in S- controls. The collagen degradation pattern was consistent with membrane-associated MMP activity, and keratocytes showed positive staining for MT1-MMP, albeit weak. Both matrix contraction and collagen degradation were reduced by MMP inhibition. For most outcome measures, the inhibitory effect of BB-94 was significantly greater than that of GM6001. Overall, the data demonstrate for the first time that even under conditions in which low levels of contractility and extracellular matrix proteolysis are maintained, MMPs still play an important role in mediating cell spreading and migration within 3-D collagen matrices. This appears to be mediated at least in part by membrane-tethered MMPs, such as MT1-MMP.

Role of nuclear factor-κB in interleukin-1-induced collagen degradation by corneal fibroblasts

The proinflammatory cytokine interleukin (IL)-1 is implicated in corneal ulceration. The role of nuclear factor (NF)-kappaB in the IL-1-induced degradation of collagen by corneal fibroblasts that underlies corneal ulceration was investigated. Rabbit corneal fibroblasts were cultured in three-dimensional gels of type I collagen with or without IL-1 and sulfasalazine, an inhibitor of NF-kappaB activation. Collagen degradation was assessed from the amount of hydroxyproline generated by acid-heat hydrolysis of culture supernatants. The release of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) into culture supernatants was examined by immunoblot analysis and gelatin zymography, and the cellular abundance of MMP and TIMP mRNAs was determined by reverse transcription and real-time polymerase chain reaction analysis. The phosphorylation and degradation of the NF-kappaB-inhibitory protein IkappaB-alpha were examined by immunoblot analysis. The subcellular localization and DNA binding activity of the p65 subunit of NF-kappaB were evaluated by immunofluorescence analysis and with a colorimetric assay, respectively. The transactivation activity of NF-kappaB was assessed with a reporter gene assay. Sulfasalazine inhibited IL-1-induced collagen degradation by corneal fibroblasts in a concentration-dependent manner. It also inhibited the stimulatory effects of IL-1 on the synthesis or activation of various MMPs in a concentration-dependent manner. IL-1 induced the phosphorylation and degradation of IkappaB-alpha, the nuclear translocation and up-regulation of the DNA binding activity of the p65 subunit of NF-kappaB, and the activation of NF-kappaB in a manner sensitive to sulfasalazine. These results suggest that NF-kappaB contributes to the IL-1-induced degradation of collagen by corneal fibroblasts and is therefore a potential therapeutic target for treatment of corneal ulcers.

In Vivo Confocal Microscopy Findings in Keratoconus

PURPOSE

: To evaluate corneal structure in eyes with keratoconus by using in vivo confocal microscopy.

METHODS

: In a prospective institutional study, 48 eyes of 24 consecutive patients with keratoconus were examined by in vivo confocal microscopy. Forty-four eyes of 22 healthy subjects served as the control. The main outcome measures were qualitative and quantitative changes encountered at confocal microscopy examination.

RESULTS

: In the keratoconus group, in vivo confocal microscopy findings included elongated, exfoliating superficial epithelial cells; brightly reflective material deposition within the basal epithelial cells; prominent, thickened subbasal nerves; structural changes in subbasal nerve fibers; pronounced reflectivity and irregular arrangement of stromal keratocytes; structurally abnormal anterior stromal keratocyte nuclei; folds in the anterior, mid, and posterior stroma; folds in Descemet's membrane; pleomorphism and enlargement of endothelial cells; and endothelial guttata. No such abnormal findings were present in the control group. There were significant differences between the two groups in terms of the mean basal epithelial, anterior and posterior stromal keratocyte densities, the mean basal epithelial cell area, and the mean endothelial cell hexagonality percentages.

CONCLUSIONS

: Quantitative and qualitative structural changes were observed in all corneal layers in eyes with keratoconus by using slit-scanning confocal microscopy. The changes at all levels were more prominent in eyes with severe keratoconus. This noninvasive in vivo technique may prove to be useful in the diagnosis and follow-up of keratoconus and in the understanding of its pathophysiology.

Quantitative analysis of corneal microstructure in keratoconus utilising in vivo confocal microscopy

PURPOSE

To establish and quantify the in vivo confocal microscopic features of moderate to advanced keratoconus.

METHODS

Nineteen keratoconus subjects were catergorised using Orbscan-derived corneal apex power and pachymetry as exhibiting moderate (n=7) and advanced (n=12) keratoconus. Control subjects included 23 noncontact lens wearers (Group A) and 15 contact lens wearers (Group B). All subjects underwent Confoscan slit scanning in vivo confocal microscopy.

RESULTS

Compared with Group A (4912+/-434 cells/mm(2)), basal epithelial density was significantly lower in both moderate (4592+/-414 cells/mm(2), P<0.05) and advanced keratoconus (4530+/-596 cells/mm(2), P=0.01). In comparison to Group A (761+/-118 cells/mm(2)), anterior stroma keratocyte density was significantly greater in both moderate keratoconus (883+/-111 cells/mm(2), P=0.001) and advanced keratoconus (952+/-122 cells/mm(2), P<0.001). Compared to Group A (504+/-80 cells/mm(2)) posterior stroma keratocyte density was also significantly greater in advanced keratoconus (599+/-97 cells/mm(2), P<0.001) and posterior stromal keratocyte density appeared to increase with increasing severity of keratoconus (P<0.05). However, comparing control Groups A and B, contact lens wear per se, was associated with significantly reduced (P=0.000) keratocyte density in the anterior stroma (609+/-66 cells/mm(2)) and demonstrated a trend (P=0.056) in the posterior stroma (470+/-63 cells/mm(2)). Keratoconic corneas (429+/-72 microm) were significantly thinner than control Groups A (508+/-77 mm) and B (495+/-80 microm). The presence of keratoconus did not affect the endothelial cell density (P=0.54).

CONCLUSION

In vivo confocal microscopy can provide insight into the microstructural changes that occur in keratoconus.

The possible relationship between keratoconus and magnesium deficiency

The cause of keratoconus is unknown. However, an earlier report demonstrated magnesium deficiency in keratoconus patients, and suggested that magnesium deficiency could pathologically affect the mechanisms of the cornea. Experimental and clinical papers concerning a possible relationship between keratoconus and magnesium deficiency were reviewed. These studies have demonstrated molecular and cellular alterations specific to the keratoconic cornea, including: thinning and fragmentation of membranes, degenerated cells and collagen fibres, swelling of the mitochondria, and biochemical abnormalities in protein synthesis. Similar alterations have reportedly been induced by magnesium deficiency. This review suggests a possible relationship between the specific keratoconic disorders and the alteration induced by magnesium deficiency at the intracellular and extracellular levels. Although the etiology of keratoconus is still unknown, this paper may give some new ideas for further experimental and clinical studies on the etiology of keratoconus.

The Cascade Hypothesis of Keratoconus

Keratoconus, a non-inflammatory thinning of the cornea, is a leading indication for corneal transplantation. For its causation, we propose a "Cascade Hypothesis" stating that keratoconus corneas have abnormal or defective enzymes in the lipid peroxidation and/or nitric oxide pathways leading to oxidative damage. The accumulation of oxidative, cytotoxic by-products causes an alteration of various corneal proteins, triggering a cascade of events, (i.e. apoptosis, altered signaling pathways, increased enzyme activities, fibrosis). This hypothesis is supported by biochemical, immunohistochemical and molecular data presented in this review. Based upon this evidence, one can speculate that keratoconus patients should minimize their exposure to oxidative stress. Protective steps should include wearing ultraviolet (UV) protection (in the contact lenses and/or sunglasses), minimizing the mechanical trauma (eye rubbing, poorly fit contact lenses) and keeping eyes comfortable with artificial tears, non-steroidal anti-inflammatory drugs and/or allergy medications.

Is the corneal degradation in keratoconus caused by matrix-metalloproteinases?

The thinning of the cornea that occurs in keratoconus has been well described; however, the mechanism of tissue degradation remains unknown. Elevated proteinase activity is one possibility and approximately 20 publications over the last 20 years have addressed this hypothesis. Early studies reported increased collagenase and gelatinase activities in the medium of keratoconus corneal cultures. After the characterization of the matrix metalloproteinase (MMP) enzymes, studies focused on the expression of specific MMPs, in particular the gelatinases, MMP-2 and MMP-9. Matrix metalloproteinase-2 was found to be the major MMP of the cornea and was constitutively produced in normal tissue, whereas MMP-9 expression was induced by various stimuli, including phorbol esters and even tissue culturing. These studies suggested that there were no differences in the amounts or states of activation of MMP between normal and keratoconus corneas, although the amounts of some proteinase inhibitors, including tissue inhibitors of metalloproteinases, alpha-1-proteinase inhibitor and alpha-2-macroglobulin, were decreased in keratoconus. Most recently, the lysosomal proteinases, cathepsin B and cathepsin G were reported to be elevated in keratoconus corneas, and it is possible that it was cathepsin activity, not MMP activity, that was measured in some early studies. Nevertheless, there are now about 20 human MMPs identified and it is possible that some of these, other than the well known collagenase (MMP-1) and gelatinases (MMP-2 and MMP-9), could be implicated in the pathology of keratoconus. Studies have begun to address more recently described MMPs and it has been reported that the membrane-bound MT1-MMP (MMP-14), which activates latent MMP-2, was found to have increased expression in keratoconus corneas, whereas the stromelysins, MMP-3 and MMP-10, were not.