Alpha-1 proteinase inhibitor levels in keratoconus

The Pathophysiology of Keratoconus

PURPOSE

Keratoconus is a progressive disease characterized by changes in corneal shape, resulting in loss of visual function. There remains a lack of comprehensive understanding regarding its underlying pathophysiology. This review aims to bridge this gap by exploring structural failures and inflammatory processes involved in the etiology and progression of keratoconus.

METHODS

A literature review was conducted using PubMed and Google Scholar databases, screening for articles published in English using the keyword combinations of "keratoconus" with "pathophysiology," "pathology," "metabolism," "inflammatory," "oxidative stress," "cytokines," "enzymes," "collagen," and "cornea." Articles published between January 1, 1970, and June 1, 2023, were queried and reviewed, with greater emphasis placed on more recent data. Fifty-six relevant studies were examined to develop a thorough review of the pathophysiological mechanisms at play in keratoconus.

RESULTS

Biomechanical structural failures in the cornea seem to be the primary militating factors in keratoconus etiology and progression. These include disruptions in the arrangement in the collagen lamellae, a decrease in collagen levels, a decrease in natural collagen crosslinking, and changes in lysosomal enzyme activity. Immunologic changes have also been identified in keratoconus, challenging the traditional view of the condition as noninflammatory. Elevated levels of proinflammatory cytokines like IL-1b, IL-6, IL-17, and TNF-α have been observed, along with increased apoptosis of keratocytes. Increased oxidative stress leads to the activation of collagenase and gelatinase enzymes.

CONCLUSIONS

Keratoconus is a complex condition influenced by both structural defects and inflammatory processes. Understanding these mechanisms can inform clinical management and potentially lead to more effective treatments.

Keratoconus

Keratoconus is a progressive eye disorder primarily affecting individuals in adolescence and early adulthood. The ectatic changes in the cornea cause thinning and cone-like steepening leading to irregular astigmatism and reduced vision. Keratoconus is a complex disorder with a multifaceted aetiology and pathogenesis, including genetic, environmental, biomechanical and cellular factors. Environmental factors, such as eye rubbing, UV light exposure and contact lens wearing, are associated with disease progression. On the cellular level, a complex interplay of hormonal changes, alterations in enzymatic activity that modify extracellular membrane stiffness, and changes in biochemical and biomechanical signalling pathways disrupt collagen cross-linking within the stroma, contributing to structural integrity loss and distortion of normal corneal anatomy. Clinically, keratoconus is diagnosed through clinical examination and corneal imaging. Advanced imaging platforms have improved the detection of keratoconus, facilitating early diagnosis and monitoring of disease progression. Treatment strategies for keratoconus are tailored to disease severity and progression. In early stages, vision correction with glasses or soft contact lenses may suffice. As the condition advances, rigid gas-permeable contact lenses or scleral lenses are prescribed. Corneal cross-linking has emerged as a pivotal treatment aimed at halting the progression of corneal ectasia. In patients with keratoconus with scarring or contact lens intolerance, surgical interventions are performed.

Role of Serine Protease Inhibitors A1 and A3 in Ocular Pathologies

Serine protease inhibitors A1 (SerpinA1) and A3 (SerpinA3) are important members of the serpin family, playing crucial roles in the regulation of serine proteases and influencing various physiological processes. SerpinA1, also known as α-1-antitrypsin, is a versatile glycoprotein predominantly synthesized in the liver, with additional production in inflammatory and epithelial cell types. It exhibits multifaceted functions, including immune modulation, complement activation regulation, and inhibition of endothelial cell apoptosis. SerpinA3, also known as α-1-antichymotrypsin, is expressed both extracellularly and intracellularly in various tissues, particularly in the retina, kidney, liver, and pancreas. It exerts anti-inflammatory, anti-angiogenic, antioxidant, and antifibrotic activities. Both SerpinA1 and SerpinA3 have been implicated in conditions such as keratitis, diabetic retinopathy, age-related macular degeneration, glaucoma, cataracts, dry eye disease, keratoconus, uveitis, and pterygium. Their role in influencing metalloproteinases and cytokines, as well as endothelial permeability, and their protective effects on Müller cells against oxidative stress further highlight their diverse and critical roles in ocular pathologies. This review provides a comprehensive overview of the etiology and functions of SerpinA1 and SerpinA3 in ocular diseases, emphasizing their multifaceted roles and the complexity of their interactions within the ocular microenvironment.

Assessing Patients with Alpha-1 Antitrypsin Deficiency for Corneal Refractive Surgery: A Review and Clinical Experience

Alpha-1 Antitrypsin Deficiency (AATD) is an autosomal inheritable disorder that impairs the protease inhibitor alpha-1 antitrypsin. This disorder presents with various systemic effects, including liver cirrhosis, centrilobular emphysema, and ocular manifestations. Performing corneal refractive surgery in patients with AATD raises concerns regarding the increased rates of corneal erosions, corneal ulcerations, potential developing descemetoceles, and other ocular manifestations. Patient outcomes for laser-assisted in situ keratomileuses (LASIK), photorefractive keratectomy (PRK), small incision lenticule extraction (SMILE), and other ocular corrective surgeries are lacking in this population. This article provides experiences performing corneal refractive surgery, discusses the current understanding of AATD, including its ocular manifestations, and explores factors to consider when evaluating patients for corneal procedures. The aim of this paper is to address the manifestations of AATD prior to performing corrective vision surgery.

Keratoconus: cross-linking the window of the eye

Keratoconus is a condition in which the cornea progressively thins and weakens, leading to severe, irregular astigmatism and a significant reduction in quality of life. Although the precise cause of keratoconus is still not known, biochemical and structural studies indicate that overactive enzymes within the cornea break down the constituent proteins (collagen and proteoglycans) and cause the tissue to weaken. As the disease develops, collagen fibres slip past each other and are redistributed across the cornea, causing it to change shape. In recent years, it was discovered that the photochemical induction of cross-links within the corneal extracellular matrix, through the use of riboflavin and ultraviolet (UVA) light, could increase the strength and enzymatic resistance of the tissue and thereby halt keratoconus progression. Worldwide acceptance and use of riboflavin/UVA corneal cross-linking therapy for halting keratoconus progression has increased rapidly, in accordance with the growing body of evidence supporting its long-term effectiveness. This review focusses on the inception of riboflavin/UVA corneal cross-linking therapy for keratoconus, its clinical effectiveness and the latest scientific advances aimed at reducing patient treatment time, improving patient comfort and increasing patient eligibility for treatment.

Plain language summary

Review of current treatments using cross-linking to halt the progress of keratoconus Keratoconus is a disease in which the curved cornea, the transparent window at the front of the eye, weakens, bulges forward into a cone-shape and becomes thinner. This change of curvature means that light is not focussed onto the retina correctly and vision is progressively impaired. Traditionally, the effects of early keratoconus were alleviated by using glasses, specialist contact lenses, rings inserted into the cornea and in severe cases, by performing a corneal transplant. However, it was discovered that by inducing chemical bonds called cross-links within the cornea, the tissue could be strengthened and further thinning and shape changes prevented. The standard cross-linking procedure takes over an hour to perform and involves the removal of the cells at the front of the cornea, followed by the application of Vitamin B2 eye drops and low energy ultraviolet light (UVA) to create new cross-links within the tissue. Clinical trials have shown this standard procedure to be safe and effective at halting keratoconus progression. However, there are many treatment modifications currently under investigation that aim to reduce patient treatment time and increase comfort, such as accelerated cross-linking procedures and protocols that do not require removal of the surface cells. This review describes the different techniques being developed to carry out corneal cross-linking efficiently and painlessly, to halt keratoconus progression and avoid the need for expensive surgery.

RNA sequencing of corneas from two keratoconus patient groups identifies potential biomarkers and decreased NRF2-antioxidant responses

Keratoconus is a highly prevalent (1 in 2000), genetically complex and multifactorial, degenerative disease of the cornea whose pathogenesis and underlying transcriptomic changes are poorly understood. To identify disease-specific changes and gene expression networks, we performed next generation RNA sequencing from individual corneas of two distinct patient populations - one from the Middle East, as keratoconus is particularly severe in this group, and the second from an African American population in the United States. We conducted a case: control RNA sequencing study of 7 African American, 12 Middle Eastern subjects, and 7 controls. A Principal Component Analysis of all expressed genes was used to ascertain differences between samples. Differentially expressed genes were identified using Cuffdiff and DESeq2 analyses, and identification of over-represented signaling pathways by Ingenuity Pathway Analysis. Although separated by geography and ancestry, key commonalities in the two patient transcriptomes speak of disease - intrinsic gene expression networks. We identified an overwhelming decrease in the expression of anti-oxidant genes regulated by NRF2 and those of the acute phase and tissue injury response pathways, in both patient groups. Concordantly, NRF2 immunofluorescence staining was decreased in patient corneas, while KEAP1, which helps to degrade NRF2, was increased. Diminished NRF2 signaling raises the possibility of NRF2 activators as future treatment strategies in keratoconus. The African American patient group showed increases in extracellular matrix transcripts that may be due to underlying profibrogenic changes in this group. Transcripts increased across all patient samples include Thrombospondin 2 (THBS2), encoding a matricellular protein, and cellular proteins, GAS1, CASR and OTOP2, and are promising biomarker candidates. Our approach of analyzing transcriptomic data from different populations and patient groups will help to develop signatures and biomarkers for keratoconus subtypes. Further, RNA sequence data on individual patients obtained from multiple studies may lead to a core keratoconus signature of deregulated genes and a better understanding of its pathogenesis.

Severe bilateral descemetoceles in Alpha-1 antitrypsin deficiency

Purpose

To report a case of severe bilateral descemetoceles in a patient with alpha-1 antitrypsin (A1AT) deficiency during intensive care unit hospitalization.

Observations

A 42-year-old male presented with sub-acute bilateral vision loss during an intensive care unit hospitalization following liver and kidney transplantations. On exam, this patient's best-corrected visual acuity was 20/80 in both eyes. There were bilateral descemetoceles inferotemporally in both eyes with overlying epithelial defects and dense surrounding punctate epithelial staining. The patient was initially treated with gatifloxacin drops and frequent lubricating ointment. Given the concern for impending perforation, cyanoacrylate glue with bandage contact lens was applied to both eyes. His best corrected visual acuity remained unchanged in the right eye and improved to 20/30 in the left eye. Upon medical stabilization, anterior lamellar graft was performed in the right eye, with plans for the same treatment in the left eye in the future.

Conclusions

As A1AT is found in the tear film and is believed to play a role in regulating protease activity in the cornea, we hypothesize that this patient's A1AT deficiency exacerbated the progression of corneal ulceration leading to severe descemetocele formation.

Comparative proteome analysis of the tear samples in patients with low-grade keratoconus

PURPOSE

To elucidate the metabolic processes playing roles in the formation of keratoconus (KC).

METHODS

Tears samples were collected using capillary glass tubes without stimulation and without prior anesthesia from 17 patients and 16 controls. Proteomic analysis by fluorescent 2D gel electrophoresis (DIGE) coupled with MALDI-TOF/TOF was performed. The identified proteins that were differentially regulated were subjected to Ingenuity Pathway Analysis (IPA). Corneal topography analyses with Sirius topography system (Costruzioni Strumenti Oftalmici, Florence, Italy) were performed on all participants. The steepest keratometry index was lower than 50 diopters in all keratoconus patients.

RESULTS

DIGE analysis showed changes in abundance of nine proteins. Six of these proteins, namely serum albumin, Keratin Type II Cytoskeletal 1, IgG gamma chain-1, GAPDH, alpha-1 antitrypsin and ApoA-I, were down-regulated in the KC samples in comparison with the controls. In addition, we detected up-regulation of lysozyme C, keratin type I cytoskeletal 10 and lipocalin. The subsequent IPA predicted that NADH repair pathway is activated in the KC patients. This pathway involves generation of NADHX as a by-product via catalysis by GAPDH. NADHX is an inhibitor of several dehydrogenases and must be removed.

CONCLUSION

The involvement of NADHX repair pathway in KC should be investigated, since preliminary clues obtained in this study point to that direction. In particular, showing the presence of ATP-dependent NAD(P)H-hydrate dehydratase that eliminates NADHX would strengthen our findings and would be a major step toward understanding KC.

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 and Histopathological Changes Associated with Keratoconus

Keratoconus (KC) is a corneal thinning disorder that leads to loss of visual acuity through ectasia, opacity, and irregular astigmatism. It is one of the leading indicators for corneal transplantation in the Western countries. KC usually starts at puberty and progresses until the third or fourth decade; however its progression differs among patients. In the keratoconic cornea, all layers except the endothelium have been shown to have histopathological structural changes. Despite numerous studies in the last several decades, the mechanisms of KC development and progression remain unclear. Both genetic and environmental factors may contribute to the pathogenesis of KC. Many previous articles have reviewed the genetic aspects of KC, but in this review we summarize the histopathological features of different layers of cornea and discuss the differentially expressed proteins in the KC-affected cornea. This summary will help emphasize the major molecular defects in KC and identify additional research areas related to KC, potentially opening up possibilities for novel methods of KC prevention and therapeutic intervention.

Protective Effects of Soluble Collagen during Ultraviolet-A Crosslinking on Enzyme-Mediated Corneal Ectatic Models

Collagen crosslinking is a relatively new treatment for structural disorders of corneal ectasia, such as keratoconus. However, there is a lack of animal models of keratoconus, which has been an obstacle for carefully analyzing the mechanisms of crosslinking and evaluating new therapies. In this study, we treated rabbit eyes with collagenase and chondroitinase enzymes to generate ex vivo corneal ectatic models that simulate the structural disorder of keratoconus. The models were then used to evaluate the protective effect of soluble collagen in the UVA crosslinking system. After enzyme treatment, the eyes were exposed to riboflavin/UVA crosslinking with and without soluble type I collagen. Corneal morphology, collagen ultrastructure, and thermal stability were evaluated before and after crosslinking. Enzyme treatments resulted in corneal curvature changes, collagen ultrastructural damage, decreased swelling resistance and thermal stability, which are similar to what is observed in keratoconus eyes. UVA crosslinking restored swelling resistance and thermal stability, but ultrastructural damage were found in the crosslinked ectatic corneas. Adding soluble collagen during crosslinking provided ultrastructural protection and further enhanced the swelling resistance. Therefore, UVA crosslinking on the ectatic model mimicked typical clinical treatment for keratoconus, suggesting that this model replicates aspects of human keratoconus and could be used for investigating experimental therapies and treatments prior to translation.

The genetics of keratoconus

Keratoconus is a bilateral, non-inflammatory corneal ectasia characterized by progressive conical thinning and protrusion of the cornea. Its etiology has long been believed to be multifactorial, with environmental, behavioral, and genetic factors all contributing to the disease process. This review focuses specifically on examining the evidence that supports a genetic basis for keratoconus.

Evaluation of corneal microstructure in keratoconus: a confocal microscopy study

PURPOSE

To compare the corneal microstructure in patients with manifest keratoconus (KCN), subclinical KCN, and topographically normal relatives of patients with KCN and in healthy controls.

DESIGN

Prospective and cross-sectional study.

METHODS

We enrolled 145 subjects in the study. The participants were divided into 4 groups, based on clinical and topographical evaluation: the manifest KCN group (n = 30), the subclinical KCN group (n = 32), the KCN relatives group (n = 53), and the control group (n = 30). Corneal microstructure was assessed by corneal in vivo confocal microscopy in all of the individuals. Mean outcome measures were basal epithelial cell density, endothelial cell density, anterior keratocyte density, posterior keratocyte density, sub-basal nerve density, sub-basal nerve diameter, and stromal nerve diameter.

RESULTS

The mean basal epithelial cell density, endothelial cell density, and sub-basal nerve diameter were not significantly different among the 4 groups (P = 0.057, P = 0.592, and P = 0.393, respectively). The mean anterior and posterior stromal keratocyte densities were significantly lower in the manifest group, in the subclinical group, and in the relatives group when compared with the control group (for both parameters; P < 0.001, P < 0.001, and P< 0.001, respectively). The mean stromal nerve diameter in the manifest group, subclinical group, and relatives group was significantly higher than in the control group (P = 0.001, P = 0.049, and P = 0.004, respectively).

CONCLUSION

The anterior and posterior stromal keratocyte densities were statistically lower and stromal nerve diameter was statistically higher in patients with manifest KCN, subclinical KCN, and topographically normal KCN relatives compared with controls. Confocal microscopy may be useful for the determination of early corneal microstructural changes before manifestation of typical or subtle topographic signs.

Changes in tear protein profile in keratoconus disease

PURPOSE

To analyze tear protein profile variations in patients with keratoconus (KC) and to compare them with those of control subjects.

SUBJECTS AND METHODS

Tears from 12 normal subjects and 12 patients with KC were analyzed by two-dimensional gel electrophoresis (2-DE) and liquid chromatography-mass spectrometry (LC-MS). Analysis of the 2-DE gels was performed using Progenesis SameSpots software (Nonlinear Dynamics). Proteins exhibiting high variation in expression levels (P-value <0.05) were identified using matrix-assisted laser desorption/ionization-TOF spectrometry. For LC-MS analysis, a label-free quantification approach was used. Tears were digested with trypsin, subjected to data-independent acquisition (MS(E)) analysis, and identified proteins were relatively quantified using ProteinLynx Global Server software (Waters).

RESULTS

The 2-DE and LC-MS analyses revealed a significant decrease in the levels of members of the cystatin family and an increase in lipocalin-1 in KC patients. A 1.43-fold decrease was observed for cystatin-S by 2-DE, and 1.69- and 1.56-fold for cystatin-SN and cystatin-SA by LC-MS, respectively. The increase in lipocalin-1 was observed by both methods with fold changes of 1.26 in the 2-DE approach and 1.31 according to LC-MS. Significant protein upregulation was also observed for Ig-κ chain C and Ig J chain proteins by 2-DE. Levels of lipophilin-C, lipophilin-A, and phospholipase A2 were decreased in tears from KC patients according to LC-MS. Serum albumin was found to be increased in KC patients according to LC-MS.

CONCLUSION

The results show differences in the tear protein profile of KC and control subjects. These changes are indicative of alterations in tear film stability and in interactions with the corneal surface in KC patients.

Assessment of keratocyte density in patients with keratoconus not using contact lenses

PURPOSE

To assess the keratocyte density (KD) in the cornea of patients with keratoconus not using contact lenses.

METHOD

In this pilot study, the eyes (n = 68) of 35 patients with the diagnosis of keratoconus, who did not use contact lenses and the eyes(n = 70) of 35 healthy controls were prospectively examined using the Heidelberg Retinal Tomography Rostock cornea module (HRT3/RCM). The cases with keratoconus and controls were compared with regard to KD in the anteroposterior stromal layers.

RESULTS

Of the cases with keratoconus, 15 (42.9%) were men and 20 (57.1%) were women. The mean age was 21.1 ± 11.1 (range =14-41) years. Of the controls, 26 (73.9%) were men and 9 (26.1%)were women. The mean age was 23.9 ± 12.9 (range = 14-35) years.Of the 68 eyes with keratoconus, 22 (28.2%) had mild keratoconus, 23 (35.9%) had moderate keratoconus, and 23 (35.9%) had severe keratoconus. The mean anterior stromal KD was 651.4 ± 89 cells per square millimeter in cases with keratoconus and 879.4 ± 75 cells per square millimeter in controls (P < 0.05). The mean anterior stromal KD decreased by 25.9% in corneas with keratoconus. The mean posterior stromal KD was found to be 363.6 ± 74 cells per square millimeter in cases with keratoconus and 469.7 ± 56 cells per square millimeter in controls (P< 0.01). The mean posterior stromal KD decreased by 22.6% in corneas with keratoconus. The anterior stromal KD was higher than the posterior stromal KD (P < 0.001). No significant relationships were found between the stromal KD data and central corneal thickness or steepest keratometric.

CONCLUSIONS

The KD in the anterior and posterior corneal stroma was decreased in patients with keratoconus, but without the use of contact lens, compared with healthy controls. This density difference was independent from the central corneal thickness and the stage of keratoconus.

Differential epithelial and stromal protein profiles in keratoconus and normal human corneas

The purpose of the study was to identify epithelial and stromal proteins that exhibit up- or down-regulation in keratoconus (KC) vs. normal human corneas. Because previous proteomic studies utilized whole human corneas or epithelium alone, thereby diluted the specificity of the proteome of each tissue, we selectively analyzed the epithelium and stromal proteins. Individual preparations of epithelial and stromal proteins from KC and age-matched normal corneas were analyzed by two independent methods, i.e., a shotgun proteomic using a Nano-Electrospray Ionization Liquid Chromatography Tandem Mass Spectrometry [Nano-ESI-LC-MS (MS)(2)] and two-dimensional-difference gel electrophoresis (2D-DIGE) coupled with mass spectrometric methods. The label-free Nano-ESI-LC-MS (MS)(2) method identified 104 epithelial and 44 stromal proteins from both normal and KC corneas, and also quantified relative changes in levels of selected proteins, in both the tissues using spectral counts in a proteomic dataset. Relative to normal corneal epithelial proteins, six KC epithelial proteins (lamin-A/C, keratin type I cytoskeletal 14, tubulin beta chain, heat shock cognate 71 kDa protein, keratin type I cytoskeletal 16 and protein S100-A4) exhibited up-regulation and five proteins (transketolase, pyruvate kinase, 14-3-3 sigma isoform, phosphoglycerate kinase 1, and NADPH dehydrogenase (quinone) 1) showed down-regulation. A similar relative analysis showed that three KC stromal proteins (decorin, vimentin and keratocan) were up-regulated and five stromal proteins (TGF-betaig h3 (Bigh3), serotransferrin, MAM domain-containing protein 2 and isoforms 2C2A of collagen alpha-2[VI] chain) were down-regulated. The 2D-DIGE-mass spectrometry followed by Decyder software analysis showed that relative to normal corneas, the KC corneal epithelium exhibited up-regulation of four proteins (serum albumin, keratin 5, L-lactate dehydrogenase and annexin A8) and down-regulation of four proteins (FTH1 [Ferritin heavy chain protein 1], calpain small subunit 1, heat shock protein beta 1 and annexin A2). A similar relative analysis of stroma by this method also showed up-regulation of aldehyde dehydrogenase 3A1 (ALDH3A1), keratin 12, apolipoprotein A-IV precursor, haptoglobin precursor, prolipoprotein and lipoprotein Gln in KC corneas. Together, the results suggested that the Nano-ESI-LC-MS(MS)(2) method was superior than the 2D-DIGE method as it identified a greater number of proteins with altered levels in KC corneas. Further, the epithelial and stromal structural proteins of KC corneas exhibited altered levels compared to normal corneas, suggesting that they are affected due to structural remodeling during KC development and progression. Additionally, because several epithelial and stromal enzymes exhibited up- or down-regulation in the KC corneas relative to normal corneas, the two layers of KC corneas were under metabolic stress to adjust their remodeling.

Comparison of keratocyte density between keratoconus, post-laser in situ keratomileusis keratectasia, and uncomplicated post-laser in situ keratomileusis cases. A confocal scan study

PURPOSE

To compare keratocyte density in corneal stromal layers in keratoconus, post-laser in situ keratomileusis (LASIK) keratectasia, uncomplicated post-LASIK cases, and normal unoperated corneas by confocal scan.

METHODS

Thirty-one unscarred corneas from 22 patients with keratoconus, 24 clear corneas from 17 cases with post-LASIK keratectasia, 12 corneas from 7 uncomplicated post-LASIK cases, and 26 corneas from 13 normal unoperated cases were evaluated by using confocal scan. None of the cases were contact lens wearers. Keratocyte densities were determined in 3 stromal layers in each cornea and compared with densities in the corresponding layers of normal unoperated corneas. Cell densities in different corneal layers were also compared in each group.

RESULTS

In overall, 93 eyes from 59 patients with mean age of 30 +/- 7.3 years were enrolled. There was no difference in mean keratocyte density at 3 stromal layers between keratoconic and normal unoperated corneas. In post-LASIK keratectasia, keratocyte density in the anterior and posterior stromal layers was significantly lower than that in normal unoperated group. In uncomplicated post-LASIK cases, the keratocyte density at 3 stromal layers was lower than that in normal unoperated group. No difference in keratocyte density was found between post-LASIK keratectasia and uncomplicated post-LASIK cases. Furthermore, in post-LASIK keratectasia, there was a meaningful difference in keratocyte density between the anterior and posterior and between the middle and posterior stromal layers; such a difference was not observed in the uncomplicated post-LASIK cases.

CONCLUSIONS

Mean keratocyte density in post-LASIK keratectasia and uncomplicated post-LASIK cases was lower than that in normal unoperated group. Given the different distribution of keratocytes between the stromal layers in the 2 LASIK groups, there was a nonhomogenous distribution of keratocytes in stromal layers in post-LASIK keratectasia. A homogenous distribution of keratocytes in uncomplicated post-LASIK cases may be a factor in prevention of corneal ectasia.

Effects of Sp1 overexpression on cultured human corneal stromal cells

Sp1, a transcription factor, is upregulated in keratoconus, a cornea-thinning disease. Keratoconus corneas have also been shown to contain increased levels of degradative enzymes such as cathepsin B and decreased proteinase inhibitors such as alpha1-proteinase inhibitor (alpha1-PI). We transfected cultured human corneal stromal cells to overexpress Sp1. The resulting effects on cathepsin B and alpha1-PI levels as well as the cellular proliferative and apoptotic activities were examined by Western blotting and cytochemical staining. It was found that the Sp1 transfected cells contained a greater amount of cathepsin B than did mock transfected controls. The activity of cathepsin B was also increased. By contrast, the protein level of alpha1-PI was lowered in corneal stromal cells upon Sp1 overexpression. The Sp1-induced alterations thus mimicked closely those observed in keratoconus, supporting the notion that Sp1 upregulation may be a key factor contributing directly to the disease development. Furthermore, the apoptotic activity was unaffected in Sp1 transfectants but the proliferation was inhibited, consistent with the idea that Sp1 may play a role in differentiation of corneal cells.

Keratectasia after laser in situ keratomileusis: a histopathologic and immunohistochemical study

OBJECTIVE

To examine histopathologic and immunohistochemical features of human corneal buttons from patients who developed keratectasia after laser in situ keratomileusis (LASIK).

METHODS

Five corneal buttons were obtained during penetrating keratoplasty from patients who developed keratectasia after LASIK. Histologic features were examined by hematoxylin-eosin staining using paraffin-embedded sections and by transmission electron microscopy. Immunostaining for alpha(1)-proteinase inhibitor, Sp1, and matrix metalloproteinases 1, 2, and 3 was performed with 2 healthy corneas and 2 corneas with keratoconus as controls.

RESULTS

Central stromal thinning was observed after hematoxylin-eosin staining in all corneas with keratectasia. No histologic features specific to keratoconus, including Bowman layer disruption, were identified in the corneas with keratectasia. By transmission electron microscopy, collagen fibril thinning and decreased interfibril distance were observed in the stromal bed. Immunostaining intensity and/or pattern for alpha(1)-proteinase inhibitor and Sp1 in the corneas with keratectasia was comparable to that of healthy corneas and differed from that in the corneas with keratoconus. No significant staining with anti-matrix metalloproteinases 1, 2, and 3 antibodies was observed in either the corneas with keratectasia or the healthy corneas.

CONCLUSIONS

Histologic findings suggest that post-LASIK keratectasia results in collagen fibril thinning and decreased interfibril distance within the residual stromal bed. Discrepant results between keratectasia and keratoconus suggest that the pathogenesis of the 2 conditions differ.

Histopathological study of 49 cases of keratoconus

AIMS

Keratoconus is a bilateral and asymmetrical corneal ectasia. The pathophysiology of this disorder has yet to be fully elucidated. The purpose of our study was to document the prevalence of the most common morphological features of keratoconic corneas.

METHODS

A retrospective analysis of 49 cases diagnosed as keratoconus between 2001 and 2006 was undertaken. Histopathological reports were reviewed to obtain data such as age and gender. Specimens were fixed in 10% buffered paraformaldehyde solution for 24 h, bisected through the centre of the button, and embedded in paraffin. Sections were stained with haematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) for light microscopic examination.

RESULTS

The studied group was composed of 29 men and 20 women. Age at the time of the penetrating keratoplasty was 39 +/- 14 years (mean +/- standard deviation). Forty of the 49 specimens (82%) presented with epithelial thinning. Other common features of keratoconus included breaks in Bowman's layer in 35 (71%), compaction of the stromal collagen fibres in 31 (63%), and folds in Descemet's membrane in 31 (63%) cases. Other less common histopathological findings were: presence of superficial iron deposits in 14 (29%), deep stromal scarring in 12 (24%), epithelial scarring in 11 (22%), endothelial cell loss in 11 (22%), and breaks in Descemet's membrane in nine (18%) cases.

CONCLUSIONS

Some of the histopathological findings associated with keratoconus are subtle. It is important to be aware of them in order to properly confirm the clinical diagnosis.

A study of corneal thickness, shape and collagen organisation in keratoconus using videokeratography and X-ray scattering techniques

In keratoconus, the cornea becomes progressively ectactic resulting in severe visual impairment. Here, we use a combination of videokeratography and synchrotron X-ray diffraction to investigate the relationship between corneal shape and thickness, and the distribution and predominant orientation of stromal fibrillar collagen in five keratoconus corneas. In all but the least advanced case, the thinning and ectasia measured in vivo using corneal videokeratography was accompanied by corresponding changes in the relative distribution and orientation of stromal collagen in the excised corneal buttons. Although the most severe case of keratoconus possessed the most pronounced stromal collagen alterations, and only a minor disruption to stromal collagen arrangement was seen in the least advanced case, a variability in the extent of stromal collagen alteration was seen between these clinical extremes. The observed abnormalities in collagen distribution and orientation are consistent with a mechanism of keratoconus progression that involves inter-fibrillar or inter-lamellar slippage causing a redistribution of tissue within the cornea.

The effect of contact lens wear on the ocular surface changes in keratoconus

PURPOSE

To investigate the effects of contact lens wear or the keratoconic shape itself on the changes in the ocular surface in keratoconus.

METHODS

Forty-two patients (84 eyes) were enrolled in this study and divided into four groups. Group 1 comprised 22 eyes with keratoconus that had been wearing rigid gas-permeable (RGP) contact lenses for an average of 5.54 +/- 2.11 years. Group 2 comprised 24 myopic eyes that had been wearing RGP contact lenses for 6.42 +/- 1.79 years. Group 3 comprised 20 eyes with keratoconus without any contact lens wear. Group 4 comprised 18 healthy eyes that were used as controls. The ocular surface changes were evaluated by determining the tear film breakup time and performing conjunctival impression cytology. The goblet cell densities, nucleus-to-cytoplasm ratio, and epithelial cell morphology in the four groups were compared with optical microscopy in the high-power field.

RESULTS

The tear film breakup times in groups 1 and 2 were significantly lower than those in groups 3 and 4. The goblet cell densities were 5.49 +/- 1.75 and 5.82 +/- 1.63 in groups 1 and 2, respectively, which were significantly lower (P < 0.05) than the 8.79 +/- 1.42 and 10.24 +/- 2.10 in groups 3 and 4, respectively. There were no statistically significant differences in the goblet cell densities, nucleus-to-cytoplasm ratios, and epithelial cell morphologies between groups 1 and 2 and groups 3 and 4.

CONCLUSIONS

The ocular surface changes in keratoconus may be directly related to contact lens wear and not to the keratoconic shape itself.

EMMPRIN and MMP-1 in Keratoconus

PURPOSE

This study was conducted to determine the eventual presence and activity of EMMPRIN (extracellular matrix metalloproteinase inducer CD147) and interstitial collagenase MMP-1 in the cornea of keratoconus patients and their eventual interrelationship. MMP-1 was chosen because it is able to degrade fibrillar corneal collagens type I and III and might therefore play a role in stromal thinning in keratoconus.

METHODS

Immunohistochemical labeling of EMMPRIN and MMP-1 in relation to histopathological changes in 5 keratoconus patients and 5 matched healthy controls was investigated.

RESULTS

Relatively strong EMMPRIN expression was found in normal corneal epithelial cells, but moderate expression was also found in stroma. In keratoconus, EMMPRIN was found in all layers of cornea, especially in histopathologically altered areas. In normal cornea, MMP-1 staining was weak and restricted to epithelial cells. In keratoconus, MMP-1 expression was slightly augmented in epithelial cells and also appeared locally in a scattered manner in the stroma. The distribution of MMP-1 did not totally overlap with that of histologically apparent corneal damage and EMMPRIN expression.

CONCLUSIONS

Both EMMPRIN and MMP-1 are upregulated in keratoconus, but MMP-1 may not be the only tissue destructive MMP upregulated by EMMPRIN as only EMMPRIN expression correlated topologically very well with corneal damage.

Histopathological and immunohistochemical studies of lenticules after epikeratoplasty for keratoconus

AIMS

To examine histopathological and immunohistochemical changes in lenticules and host of corneal buttons from patients who previously underwent epikeratoplasty for keratoconus.

METHODS

12 penetrating keratoplasty specimens from patients with keratoconus who had previously undergone epikeratoplasty, eight keratoconus, and seven normal corneas were examined. Immunostaining for Sp1, alpha1-proteinase inhibitor (alpha1-PI), and alpha2-macroglobulin (alpha2M) were performed.

RESULTS

In nine of the 12 lenticules, the keratoconus-like disruptions were found in Bowman's layer. Peripheral and posterior keratocyte repopulation of the lenticules was observed in all cases. Keratocyte repopulation in the anterior and mid-stromal regions of the lenticules appeared related to the time since epikeratoplasty. Sp1 nuclear staining of the basal and wing epithelial cells was more intense in lenticules and keratoconus corneas than in normal corneas. Lenticular, host, and keratoconus keratocytes showed positive Sp1 staining, whereas staining was absent in normal corneas. Compared to normal corneas, alpha1-PI and alpha2M immunostaining was lower in the lenticules, host, and keratoconus specimens.

CONCLUSIONS

The epithelial cells and keratocytes repopulated in the lenticules retain keratoconus-like biochemical abnormalities such as upregulation of Sp1 and downregulation of alpha1-PI and alpha2M. The authors speculate that both keratocytes and the corneal epithelium may participate in the development of keratoconus.

Asymmetric keratoconus attributed to eye rubbing

PURPOSE

To report a series of cases with asymmetric keratoconus attributed to eye rubbing, discuss its pathogenesis, and review the literature.

METHODS

Case reports and literature review.

RESULTS

A careful history obtained from 5 patients with asymmetric keratoconus revealed habitual eye rubbing of the more severely affected eye.

CONCLUSIONS

Trauma, such as occurs with habitual eye rubbing, plays a role in the pathogenesis of keratoconus.

Recurrence of keratoconus characteristics: a clinical and histologic follow-up analysis of donor grafts

PURPOSE

To report on clinical corneal topography, histopathologic analysis, and fine structure findings in failed grafts after penetrating keratoplasty (PK) for keratoconus (KC).

DESIGN

Retrospective, consecutive, interventional case series with histologic and clinical correlation.

PARTICIPANTS

Twelve corneal buttons were obtained from consecutive patients undergoing repeated PK 10 to 28 years after the initial PK for KC. The indication for regrafting was endothelial deficiency in seven cases, irreversible immune graft rejection in two cases, and corneal ectasia in three cases.

METHODS

Removed corneal buttons were examined by light and transmission electron microscopy. A potential correlation between the clinical and videokeratoscopic findings and the microscopic structural observations was analyzed.

RESULTS

Preoperative simulated keratometry measured by TMS-1 (Tomey, New York, NY) or EyeSys CAS (EyeSys Technology, Houston, TX) ranged from 49.8 to 66.1 diopters. A pattern compatible with KC characteristics was observed in all cases. Fine structure analysis revealed Bowman's layer disruption or folds and stromal deposits in all corneal buttons. However, central corneal thinning was not present in any of the removed buttons.

CONCLUSIONS

Structure changes compatible with the diagnosis of KC were observed in all donor buttons many years after PK on KC recipients. Recurrence of the KC characteristics may result from graft repopulation by recipients' keratocytes, aging of the grafted tissue, or both.

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.

Tear function and ocular surface changes in keratoconus

PURPOSE

To describe the ocular surface disorder in patients with keratoconus.

DESIGN

A prospective, case-controlled study.

PARTICIPANTS

Seventy-five eyes of 38 patients with keratoconus seen at Uludag University School of Medicine, Department of Ophthalmology, from March 2000 through April 2001, and 80 eyes of 40 normal control subjects were studied.

INTERVENTION

The subjects underwent routine ophthalmic examinations, corneal sensitivity measurements, Schirmer test, tear film breakup time (BUT), fluorescein and rose bengal staining of the ocular surface, and conjunctival impression cytology.

MAIN OUTCOME MEASURES

Patients and control subjects were compared for corneal sensitivity, tear function, ocular surface staining parameters, goblet cell density, and squamous metaplasia grade. The relation of these parameters to the severity of keratoconus progression was also investigated.

RESULTS

The mean corneal sensitivity was significantly lower in keratoconus patients compared with control subjects (P < 0.001). The BUT values were also significantly lower in the keratoconus group. Patients with keratoconus had significantly higher fluorescein and rose bengal staining scores (P < 0.001). Corneal sensitivity and tear function changes seemed to get worse with advanced stages of keratoconus. Impression cytology showed goblet cell loss and conjunctival squamous metaplasia, both of which again related to the extent of progression of keratoconus.

CONCLUSIONS

The ocular surface disease in keratoconus is characterized by disorder of tear quality, squamous metaplasia, and goblet cell loss, all of which seem to relate to the extent of keratoconus progression.

Mapping of Sp1 regulation sites in the promoter of the human alpha1-proteinase inhibitor gene

Keratoconus is a potentially blinding disease that thins the central cornea. In afflicted corneas, the level of an inhibitor, alpha1-proteinase inhibitor (alpha1-PI), is found reduced. An increased expression of transcription factor Sp1 is also demonstrated. To examine the role of Sp1 in regulation of the human alpha1-PI gene, a 1.4-kb (-1397/+9) 5'-flanking promoter sequence that contains 10 Sp1 sites was cloned. Previous transient transfection experiments showed that Sp1 expression indeed repressed the alpha1-PI promoter activity. In this study, 12 DNA segments, a series of 5', 3', and internal deletions of the 1.4-kb alpha1-PI promoter sequence, were ligated into the SEAP (secreted alkaline phosphatase) reporter gene vector and transfected into human corneal stromal cells. Co-transfection with a Sp1 expression vector pPacSp1 was also performed in parallel. The SEAP enzyme activity was assayed. A fragment with 489 bp (-480/+9) of the 3' sequence, and three fragments with internal deletions, were found to confer a majority of the full promoter activity. Other deletions significantly abolished the promoter activity. Site-directed mutagenesis experiments further revealed that the most proximal Sp1 site (-100/-87) may be an essential element involved in the negative regulation of alpha1-PI promoter activity by Sp1. Interaction between the proximal and distal Sp1 sites also seemed to be important. These results provide the first in-depth characterization of the transcription mechanisms regulating the expression of alpha1-PI. Mapping of the Sp1 sites may help elucidate the molecular pathway leading to the alterations observed in keratoconus.

Keratocyte density in keratoconus. A confocal microscopy study(a)

PURPOSE

To estimate keratocyte density in human corneas with keratoconus by confocal microscopy.

DESIGN

Prospective, observational cohort study.

METHODS

Twenty-nine unscarred corneas of 19 patients with keratoconus and 29 corneas of 19 controls matched for age (+/-3 years) and contact lens wear were examined by using confocal microscopy. Images were recorded from the full-thickness central cornea. A masked observer manually counted bright objects (keratocyte nuclei) in images without motion blur. Cell densities in anteroposterior stromal layers of keratoconus corneas were compared with densities in corresponding layers of control corneas.

RESULTS

In keratoconus patients, age 40 +/- 15 years (mean +/- standard deviation), keratocyte density was 19% lower in those who wore contact lenses (16,894 +/- 4032 cell/mm(3), n = 12) than in those who did not wear contact lenses (20,827 +/- 4934 cell/mm(3), n = 17, P =.03). In control patients, age 39 +/- 16 years, there was no difference in keratocyte density between those who wore contact lenses (n = 12) and those who did not wear contact lenses (n = 17, P =.80). Among contact lens wearers, keratocyte density was 25% lower in keratoconus corneas (16,894 +/- 4, 032 cell/mm(3), n = 12 [9 = rigid gas-permeable lenses, 3 = soft lenses]) than in control corneas (22,579 +/- 2, 387 cell/mm(3), n = 12 [3 = rigid gas-permeable lenses, 9 = soft lenses], P =.002), the result of cell density being lower in the most anterior keratocyte layer (P =.001) and the layers between 0% to 10% (P <.001), 67% to 90% (P <.001), and 91% to 100% (P <.001) of stromal thickness. Among noncontact lens wearers, there was no difference in cell density between keratoconus and controls (P =.41).

CONCLUSION

Keratocyte density is decreased in the anterior and posterior stroma of keratoconus patients who wear contact lenses.

Lysosomal hydrolase staining of conjunctival impression cytology specimens in keratoconus

PURPOSE

This study sought to assess the feasibility of impression cytology for the determination of conjunctival intracellular lysosomal hydrolase (acid esterase) levels in patients with keratoconus.

METHODS

Twenty-two patients with keratoconus currently enrolled in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study and 22 age-and sex-similar controls underwent impression cytology. Samples were collected from each subject and control pair on the same day. The cells of the respective specimens were fixed immediately and were stained for acid esterase with use of identical batches of fixatives and stains. After staining, the specimens were cleared in xylene for mounting in synthetic resin on glass slides. The acid esterase staining intensity of each specimen was quantified as the percentage of light transmitted with use of an image analysis system (Zeiss). Multiple cells from each specimen were analyzed for each sample collected.

RESULTS

Mixed model analysis was used to account for the subject-control pairings and for the multiple cells from each sample. With this method, the mean light transmission for normal controls (mean = 63.0; standard error [SE] = 3.0) was highly statistically significantly different from that for the keratoconus subjects (mean = 52.4; SE = 3.0) (two-tailed p= 0.0032).

CONCLUSIONS

This study establishes the feasibility of adapting an acid esterase staining technique to conjunctival cells collected via impression cytology. Higher levels of lysosomal enzyme staining in patients with keratoconus have been previously reported by other investigators using full-thickness conjunctival specimens. We also demonstrate the value of using objective microspectrophotometry in measuring lysosomal enzyme staining with impression cytology specimens.

Cellular incursion into Bowman's membrane in the peripheral cone of the keratoconic cornea

Analysis of corneal tissue from normal and keratoconic donors has revealed differences which may represent early signs in the pathogenesis of keratoconus. Peripheral areas of keratoconic tissue obtained from transplant surgery were targeted to ascertain cellular disposition and morphological changes which may be masked within the extensive damage of the central keratoconic cone. Peripheral keratoconic corneae exhibited discrete incursion of fine cellular processes into Bowman's membrane. These processes originated from keratocytes and were often observed in conjunction with a defined indentation from the basal epithelium. Comparison of the lysosomal enzymes cathepsin B and G with constitutively expressed cytoplasmic esterase determined that both cathepsins were elevated within keratocytes of keratoconic tissue compared with normal tissue. Some clusters of keratoconic keratocytes had elevated levels of cathepsin exceeding all others. Cathepsin-rich keratocytes localized with morphologically compromised regions of Bowman's membrane. The presence of cell nests deeper within the stroma indicated that the catabolic changes, which are visible within the acellular Bowman's membrane, are probably also occurring deeper within the stroma, but are masked and not readily detectable.

Evidence of apoptotic cell death in keratoconus

PURPOSE

To determine the potential role of apoptosis in the noninflammatory degeneration characteristic of keratoconus.

METHODS

Four normal corneas and 16 keratoconus corneas were obtained as archival specimens. Tissues were examined histopathologically for TUNEL immunoreactivity to detect the presence of DNA fragmentation. Tissues were also subjected to single-stranded DNA (ssDNA) analysis, a more apoptosis-specific stain.

RESULTS

Normal corneas exhibited fewer than five TUNEL-positive epithelial cells per section, these being very lightly stained. All 16 keratoconus corneas demonstrated extensive, intense TUNEL staining in at least one layer. Fifteen of 16 exhibited staining in the epithelial layer, 11 of 16 in the stromal layer, and 13 of 16 in the endothelial layer, whereas 10 of 16 keratoconus cases demonstrated TUNEL immunoreactivity in all three layers. The ssDNA stain was also positive and evident in all three layers of the cornea, although to a lesser degree than the TUNEL assay.

CONCLUSIONS

The noninflammatory nature of keratoconus, coupled with the TUNEL in situ results, suggests apoptosis as a mode of cell death in this degenerative disease.

Reporter gene construct containing 1.4-kB alpha 1-proteinase inhibitor promoter confers expression in the cornea of transgenic mice

A 1.4-kb human alpha1-proteinase inhibitor (alpha1-PI) 5'-flanking sequence fused to the E. coli LacZ gene was used to generate transgenic mice. The 1.4-kb alpha 1-PI fragment was found to target LacZ expression preferentially in the epithelium and stroma of the mouse cornea, and moderately or weakly in white blood cells and a few other tissues, such as the skin and brain. This finding implies that the alpha 1-PI promoter may offer an option for targeting foreign genes in both the epithelial and stromal layers of the cornea in future transgenic experiments.

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.

Cell density regulated expression of transcription factor Sp1 in corneal stromal cultures

Sp1, a ubiquitously expressed transcription factor, has been implicated to have a role in cell differentiation and cell proliferation. In keratoconus, a corneal disease characterized by thinning and scarring of the central cornea, Sp1 is found up-regulated. In the present study, we examined the expression of Sp1 in stromal cells cultured from normal human and keratoconus-afflicted corneas and evaluated the influence of varying cell densities. Immunohistochemical staining, Western blotting and electrophoretic mobility shift assays indicated that in both normal human and keratoconus cultures, Sp1 protein levels and binding activities increased with the density of cells. The basal level of Sp1 in keratoconus cultures was higher than that in normals. These results demonstrate a marked density mediated up-regulation of Sp1 in corneal stromal cells, suggesting that the Sp1 expression may be regulated by differentiation states of the cells in the cornea. In addition, cells from keratoconus corneas in vitro appear to carry and retain the Sp1 abnormality as in vivo. The Sp1 defect may be an inborn error in keratoconus.

Identification of cell types in human diseased corneas

PURPOSE

Activated myofibroblasts and macrophages are often found in corneal wound models. The current study was performed to determine whether human diseased corneas that had active tissue remodeling and enzyme activities also possessed myofibroblasts, macrophages, major histocompatibility complex class II cells, and/or CD-68-positive cells.

METHODS

Normal, keratoconus, keratoconus with hydrops, bullous keratopathy, map-dot-fingerprint dystrophy, failed grafts, and acid burn/neovascularized corneas were collected, frozen in OCT, sectioned, and stained with antibodies to alpha smooth muscle actin (myofibroblast marker), CD14 (macrophage marker), CD68 (lysosomal membrane marker), and HLA-DR (major histocompatibility complex class II cells). Selective histochemical stains identified lysosomal enzymes.

RESULTS

Normal and map-dot-fingerprint dystrophy corneas lacked antibody and enzyme staining. Keratoconus corneas were positive for CD68, HLA-DR, and lysosomal enzymes but were negative for CD14 and smooth muscle actin. Bullous keratopathy corneas had CD68-, CD14-, and HLA-DR-positive cells, relatively normal enzyme levels, and were smooth muscle actin-negative. Failed graft corneas had significant numbers of CD68-, CD14-, and HLA-DR-positive cells and increased acid phosphatase, but these corneas were smooth muscle actin-negative. Ulcerated and vascularized corneas had positive staining with all antibodies that were examined. Cultured stromal cells from normal corneas were CD68-positive, CD14-negative, and alpha smooth muscle actin-negative, and they produced lysosomal enzymes.

CONCLUSIONS

The current study demonstrates that increased presence of lysosomal enzymes, corneal remodeling, and fibrosis can occur in the absence of myofibroblasts and/or macrophages.

Recurrent keratoconus in a patient with Leber congenital amaurosis

PURPOSE

Clinical history of a 17-year-old patient with Leber congenital amaurosis (LCA) with histologically proven recurrent keratoconus (KC) two years after corneal transplantation in one eye and a recurrence-like appearance with a more global contour on the other eye four years after corneal grafting is reported. The possible mechanisms for this recurrence are discussed in light of the fact that this is, to the best of our knowledge, the first penetrating keratoplasty reported in LCA.

METHODS

Computerized videokeratography (CVKG) and specular microscopy were performed preoperatively. The patient underwent regrafting, and the excised corneal button was examined by light microscopy and transmission electron microscopy.

RESULTS

Analysis of CVKG showed a keratoconus-like pattern on the right eye, with the left eye demonstrating the aspects usually seen in keratoglobus. Histologic examination revealed the features usually observed in progressed keratoconus.

CONCLUSION

Recurrence of keratoconus in a graft has not yet been described after such a short time until now. A "true" recurrence of the disease is postulated; it could be caused by an "aggressive" genetic factor that also leads to the frequent KC in patients with LCA. This mechanism also could explain the high incidence and rapid progress of KC in this disease.

Involvement of Sp1 elements in the promoter activity of the alpha1-proteinase inhibitor gene

The transcripts of the alpha1-proteinase inhibitor in the cornea are different from those in hepatocytes and monocytes, suggesting that alpha1-proteinase inhibitor gene transcription may respond to different cell-specific regulatory mechanisms. Although information on alpha1-proteinase inhibitor gene structure has been obtained, little is known regarding the cis- and trans-acting factors that regulate its expression. In this study, we cloned and sequenced a 2. 7-kilobase 5'-flanking region upstream from the corneal transcription initiation site of the gene, demonstrated functional promoter activity, and identified the regulatory elements. Sequencing revealed that the 5'-flanking element was highly G/C-rich in regions proximal to the corneal transcription start site. DNase I footprinting located 10 potential Sp1-binding sites between nucleotides -1519 and +44. The putative promoter was functional in human corneal stromal cells, but not in human skin, scleral, and conjunctival fibroblasts, suggesting that the promoter may be corneal cell-specific. The promoter activity in the corneal cells was repressed when Sp1 was coexpressed. In the cornea-thinning disease keratoconus, down-regulation of the alpha1-proteinase inhibitor gene and increased Sp1 expression have both been demonstrated. The current results suggest that down-regulation of the inhibitor in keratoconus corneas may be related directly to overexpression of the Sp1 gene. This information may help elucidate the molecular pathways leading to the altered alpha1-proteinase inhibitor expression in keratoconus.

Expression of transcription factors in keratoconus, a cornea-thinning disease

Transcription factors are known to regulate gene transcription through the recognition and binding of specific DNA sequences in the promoter or enhancer regions of many genes. Keratoconus is a cornea-thinning disease in which upregulated expression of degradative enzymes and downregulated expression of protease inhibitors have been demonstrated. In view of the alteration in gene expression for multiple proteins, five common transcription factors, AP1, AP2, CREB, Sp1, and NF-kappa B were examined for their possible roles in keratoconus. Immunostaining experiments and Western blotting showed that Sp1 exhibited enhanced expression in keratoconus corneas. Increased binding of Sp1 consensus sequence oligonucleotides with nuclear extracts from the epithelium of keratoconus corneas was also seen by gel mobility shift assays. This is believed to be a first demonstration connecting Sp1 alteration to a human disease. The elevated Sp1 expression may contribute to the enzyme and inhibitor abnormalities found in keratoconus corneas.

Expression of wound healing and stress-related proteins in keratoconus corneas

PURPOSE

Keratoconus is characterized by thinning and scarring of the central portion of the cornea. This study was performed on keratoconus corneas to examine the expression of proteins related to wound healing including vimentin, an intermediate filament protein, and tenascin, and extracellular matrix protein. The expression of stress-related cytokines, heat shock proteins and ubiquitin was also investigated.

METHODS

Corneal buttons were collected from patients with keratoconus, normal subjects and patients with other corneal diseases such as pseudophakic bullous keratopathy. Immunofluorescence staining was performed on frozen sections for vimentin and tenascin, and immunoperoxidase staining was carried out on paraffin sections for cytokines, heat shock proteins and ubiquitin.

RESULTS

To varying degrees, all proteins examined, except tenascin and heat shock protein 90, were found to be expressed in normal human corneas. The expression of vimentin, tenascin, transforming growth factor-beta, interleukin-1, heat shock protein 27, and ubiquitin was enhanced in keratoconus corneas. A similar enhancement however was also observed in other diseased corneas.

CONCLUSIONS

Altered expression of several wound healing or stress-related proteins was noted in keratoconus corneas. The alterations appear to be nonspecific injury or wound responses in association with corneal diseases.

Differences in distribution and synthesis of the functional opponents alpha 1-proteinase inhibitor and neutrophil elastase in eukaryotic cells

Alpha 1-proteinase inhibitor (alpha 1-Pi) is the main physiological inhibitor of neutrophil elastase, a serine protease that has been implicated in tissue degradation at inflammatory sites. We report here on an immunocytochemical study of various eukaryotic cells in order to show their content of alpha 1-Pi. The proteinase inhibitor is present in undifferentiated and differentiated HL-60 and U937 cells, in myeloblasts and neutrophils, and also in tissues such as liver, kidney, colon and eye where local inflammatory processes can take place. Labelling of HL-60, U937, neutrophils and HepG2 cells with [35S] methionine followed by immunoprecipitation of cell homogenates with an anti-alpha 1-Pi antibody revealed that these cells can synthesize alpha 1-Pi de novo, and secrete large amounts of the newly synthesized molecule into the medium. In contrast, neutrophil elastase is only present in white blood cells of myeloid and monocytic lineage but not in other tissues investigated which contain alpha 1-Pi. The results demonstrate the possibility of ubiquitous local synthesis of alpha 1-Pi ready to inhibit the elastase which is imported into the affected tissues during inflammatory processes by circulating cells of the haematopoietic system.