Microfibrillar protein and phospholipid in granular corneal dystrophy

Granular Dystrophy Associated with Congenital Cataracts

Seven members of the same family suffering from Groenow I granular dystrophy and associated congenital cataracts have been studied. Three patients had corneal dystrophy at various stages and three others had a fetal nuclear congenital cataract. A penetrating keratoplasty button was studied under light and electron microscopies. This association has not been described previously. However we must emphasize that there is no general validity for a correlation between granular dystrophy and congenital cataract.

Pathogenesis and treatments of TGFBI corneal dystrophies

Transforming growth factor beta-induced (TGFBI) corneal dystrophies are a group of inherited progressive corneal diseases. Accumulation of transforming growth factor beta-induced protein (TGFBIp) is involved in the pathogenesis of TGFBI corneal dystrophies; however, the exact molecular mechanisms are not fully elucidated. In this review article, we summarize the current knowledge of TGFBI corneal dystrophies including clinical manifestations, epidemiology, most common and recently reported associated mutations for each disease, and treatment modalities. We review our current understanding of the molecular mechanisms of granular corneal dystrophy type 2 (GCD2) and studies of other TGFBI corneal dystrophies. In GCD2 corneal fibroblasts, alterations of morphological characteristics of corneal fibroblasts, increased susceptibility to intracellular oxidative stress, dysfunctional and fragmented mitochondria, defective autophagy, and alterations of cell cycle were observed. Other studies of mutated TGFBIp show changes in conformational structure, stability and proteolytic properties in lattice and granular corneal dystrophies. Future research should be directed toward elucidation of the biochemical mechanism of deposit formation, the relationship between the mutated TGFBIp and the other materials in the extracellular matrix, and the development of gene therapy and pharmaceutical agents.

Significance of lipid mediators in corneal injury and repair

Corneal injury induces an inflammatory reaction and damages the sensory nerves that exert trophic influences in the corneal epithelium. Alterations in normal healing disrupt the integrity and function of the tissue with undesirable consequences, ranging from dry eye and loss of transparency to ulceration and perforation. Lipids play important roles in this complex process. Whereas lipid mediators such as platelet activating factor (PAF) and cyclooxygenease-2 metabolites contribute to tissue damage and neovascularization, other mediators, such as the lipoxygenase (LOX) derivatives from arachidonic acid, 12- and 15-hydroxy/hydroperoxyeicosatetraenoic acids, and lipoxin A4, act as second messengers for epidermal growth factor to promote proliferation and repair. Stimulation of the cornea with pigment epithelial derived factor in the presence of docosahexaenoic acid gives rise to the synthesis of neuroprotectin D1, a derivative of LOX activity, and increases regeneration of corneal nerves. More knowledge about the role that lipids play in corneal wound healing can provide insight into the development of new therapeutic approaches for treating corneal injuries. PAF antagonists, lipoxins, and neuroprotectins can be effective therapeutic tools for maintaining the integrity of the cornea.

Cellular and molecular events in corneal wound healing: significance of lipid signalling

Alterations in the normal healing process after corneal injury can produce undesirable outcomes that range from corneal haze to ulceration and perforation. Lipids play important roles in the complex inflammatory processes that occur after corneal wounding. While some lipid mediators, such as the lipoxygenase derivatives of arachidonic acid, 12-hydroxyeicosatetraenoic acid (12[S]-HETE and 15[S]-HETE), act as second messengers to promote cell proliferation and are possibly involved in the synthesis of other molecules that suppress inflammation, others, such as platelet-activating factor (PAF), exert their actions through specific receptors, play key roles during sustained corneal inflammation (as might occur with chemical burns), and contribute to tissue destruction and neovascularization. PAF is also a strong inducer of selective metalloproteinases (MMPs) that degrade the extracellular matrix. The use of a new PAF antagonist has shown great promise for the treatment of diffuse lamellar keratitis (DLK) and alkali-burned corneas.

[BIG-H3 protein: mutation of codon 124 and corneal amyloidosis]

In 1997, a group of hereditary corneal dystrophies was related to mutations in the TGFBI (BIGH3) gene. Within this group, some corneal dystrophies present particular biochemical features in that they are characterized by corneal amyloid deposition. Contrary to clinical and genetic knowledge, the biochemical characteristics of the encoded protein (Big-h3) and the mechanisms of its amyloid conversion remain unclear. We review the current knowledge on the Big-h3 protein and focus on the behavior of the codon 124 region. We discuss this protein's mechanisms of amyloid conversion from our results and previous reports as well as from other types of amyloidosis. These data provide a better understanding of the putative processes leading to the phenotypic variations linked with their respective codon 124 mutation.

Characteristics of the human ocular surface epithelium

An appreciation of the biological characteristics of the human ocular surface epithelium affords us a great insight into the physiology of the human ocular surface in health and disease. Here, we review five important aspects of the human ocular surface epithelium. First, we recognize the discovery of corneal epithelial stem cells, and note how the palisades of Vogt have been suggested as a clinical marker of their presence. Second, we introduce the concept of the gene expression profile of the ocular surface epithelium as arrived at using a new strategy for the systematic analysis of active genes. We also provide a summary of several genes abundantly or uniquely expressed in the human corneal epithelium, namely clusterin, keratin 3, keratin 12, aldehyde dehydrogenase 3 (ALDH3), troponin-I fast-twitch isoform, ssig-h3, cathepsin L2 (cathepsin V), uroplakin Ib, and Ca(2+)-activated chloride channel. Genes related to limbal and conjunctival epithelia are also described. Third, we touch upon the genetic abnormalities thought to be involved with epithelial dysfunction in Meesmann's dystrophy, gelatinous drop-like corneal dystrophy, and the ssig-h3-mutated corneal dystrophies. Fourth, we provide an update regarding the current state of knowledge of the role of cytokines, growth factors and apoptosis in relation to ocular surface homeostasis and tissue reconstruction; the main factors being epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), transforming growth factor-ss (TGF-ss), and some inflammatory cytokines. Fifth, corneal epithelial barrier function and dysfunction as measured by fluorophotometry is remarked upon, with an explanation of the FL-500 fluorophotometer and its ability to detect corneal epithelial dysfunction at a subclinical level. The research described in this review has undoubtedly generated a complete understanding of corneal epithelial pathophysiology-an understanding that, directly or indirectly, has helped advance the development of new therapeutic modalities for ocular surface reconstruction.

Genetics of the corneal dystrophies: what we have learned in the past twenty-five years

PURPOSE

To indicate important changes in our understanding of the corneal dystrophies.

METHODS

A review of the literature of the last quarter of a century.

RESULTS

The earliest clinical classifications of the corneal dystrophies were based on the application of clinical, biological, histochemical, and ultrastructural methods. Since then, the first great impetus to our understanding has come from the application of techniques to map disorders to specific chromosome loci, using polymorphic markers. More recently, using candidate gene and related approaches, it has been possible to identify genes causing several of the corneal dystrophies and the mutations responsible for their phenotypic variation. A notable success has been to show that several important "stromal" dystrophies result from mutations in the gene beta ig-h3, which encodes for the protein keratoepithelin (beta ig-h3).

CONCLUSIONS

For the corneal dystrophies, as with other inherited disorders, there is room for two sorts of classification system, one based mainly on clinical presentation and the other on an up-to-date understanding of the genetic mechanisms. They are not mutually exclusive. Some developmental corneal disorders are also discussed.

Transforming growth factor-beta induced protein, betaIG-H3, is present in degraded form and altered localization in lattice corneal dystrophy type I

Lattice corneal dystrophy type I (LCDI) is an inherited autosomal dominant local amyloidosis, restricted to the corneal stroma. Comparison of electrophoretic profiles of normal and dystrophic corneas revealed a 42 kD protein, which was present only in dystrophic corneas. The N-terminal sequence of this protein showed identity to transforming growth factor-beta induced gene product (betaIG-H3). A polyclonal antiserum was raised in chicken against a synthetic peptide identical to the N-terminal portion of betaIG-H3. On immunoblots, the antiserum stained the 42 kD band, and also a 68 kD band corresponding to the reported molecular weight of the intact betaIG-H3. In normal corneas, only the 68 kD band was present. Immunohistologically, the antiserum stained corneal subepithelial regions, including subepithelial deposits, in dystrophic corneas. In normal corneas, the staining was observed only in the epithelium. These results may reflect the role of betaIG-H3 in extracellular matrix construction and/or amyloid formation.

Vimentin and cytokeratin pattern in granular corneal dystrophy

BACKGROUND

Corneal granular dystrophy is usually classified as a hereditary stromal disease of the cornea. Some investigations, however, have indicated an epithelial rather than a stromal origin of the granular deposits. In early stages and in recurrences of granular dystrophy after keratoplasty, the deposits are most often found in the upper microlayers of the cornea and even intraepithelially.

METHODS

In this study we tried to identify immunohistochemical epithelial markers in the corneal granular deposits.

RESULTS

A positive reaction with anti-cytokeratin 18 and polyclonal anti-vimentin were found both in the corneal epithelium and in the granular deposits.

CONCLUSION

The immunohistochemical findings support the hypothesis of an epithelial origin of the corneal deposits in granular dystrophy.

Combined granular lattice dystrophy (Avellino corneal dystrophy)

Images

Clinical and histopathologic features of corneal dystrophies in Japan

PURPOSE

To examine retrospectively the frequency of various corneal dystrophies among Japanese patients who underwent keratoplasty or keratectomy at the authors' institution over a 34-year period, and to compare the histopathologic features of these disorders in the Japanese population with those reported in the Western literature.

METHODS

Corneal specimens obtained during keratectomy or keratoplasty (lamellar and penetrating) performed at the authors' institution from 1959 through 1992 were reviewed. Immunohistochemical studies were performed using monoclonal antibodies to keratan sulfate and gelsolin, as well as two lectins (concanavalin A and wheat germ agglutinin).

RESULTS

Of 1259 corneal specimens, 159 (12.6%) specimens from a total of 80 patients showed corneal dystrophy. Virtually all were non-Fuchs dystrophies; only one case of primary Fuchs dystrophy was identified histologically. Granular dystrophy and gelatinous drop-like dystrophy were the most common dystrophies identified in the specimens, largely because of multiple specimens from individual patients with recurrent disease. These two disorders accounted for 86 of the 159 specimens. In terms of numbers of patients, lattice dystrophy was the most common (26 patients, 32.5%), followed by macular dystrophy (16 patients, 20%), gelatinous drop-like dystrophy (15 patients, 18.8%), granular dystrophy (14 patients, 17.5%), and Avellino dystrophy (3 patients, 3.75%). Dystrophies represented by only one or two patients included congenital hereditary endothelial dystrophy, primary spheroidal keratopathy, posterior polymorphous dystrophy, Schnyder crystalline dystrophy, and Fuchs dystrophy.

CONCLUSIONS

This histopathologic study showed a very low incidence of Fuchs dystrophy in the authors' Japanese patient population, compared with the incidences seen in studies of populations in Western countries. Of the non-Fuchs dystrophies, lattice dystrophy was the most common among the patients, although there were large numbers of specimens with granular dystrophy and gelatinous drop-like dystrophy due to their recurrent character. The causes of clinical and histopathologic differences and similarities among the Japanese patients and the patients described in the Western literature are likely related to genetic factors, but a complete understanding of their specific mechanisms awaits future molecular biologic and genetic elucidation.

Granular corneal dystrophy. Visual results and pattern of recurrence after lamellar or penetrating keratoplasty

BACKGROUND

Granular corneal dystrophy is a rare indication for corneal transplantation. Both penetrating and lamellar keratoplasty have been recommended, but because granular corneal dystrophy is known to recur within the donor material and multiple grafts may be necessary, the best surgical option has not been clearly established. The cellular cause of the dystrophy is unknown and the authors hypothesized that the rate and pattern of recurrence within lamellar and penetrating grafts might give clues to its etiology.

METHODS

The authors compared the visual outcome, rate, and pattern of recurrence after 20 penetrating keratoplasties and 11 lamellar keratoplasties for granular corneal dystrophy.

RESULTS

Penetrating keratoplasty and lamellar keratoplasty have a good visual outcome in granular corneal dystrophy. Visual acuities after both procedures were not statistically different. Recurrence of the dystrophy within the graft material was almost universal within 4 years. It first appeared centrally and superficially, occasionally adopting a vortex pattern suggesting epithelial involvement. The recurrence-free interval was independent of size and type of graft performed.

CONCLUSION

The authors recommend lamellar keratoplasty as a primary procedure in managing visually disabling granular corneal dystrophy if the deposits are limited to the superficial cornea. This is particularly applicable in younger patients in whom multiple procedures may be necessary over a lifetime due to recurrence of the dystrophy, and the lower morbidity rate associated with lamellar keratoplasty becomes appreciable. Although granular corneal dystrophy generally is classified as a stromal dystrophy, the pattern of recurrence is more consistent with an epithelial or tear-borne abnormality than a disease of the stromal keratocyte.

Immunoglobulins in granular corneal dystrophy Groenouw type I

Three patients with granular corneal dystrophy Groenouw type I underwent corneal grafting, and cryostat sections of the corneal buttons were examined immunohistochemically for immunoglobulins. Positive results were obtained for IgG, Kappa-, and Lambda chains with immunofluorescence technique. The reactions were seen exclusively in the same localizations as the Masson trichrome positive deposits.

Superficial juvenile granular dystrophy

Seventeen cases of a superficial corneal dystrophy are presented. The lesions are subepithelial, limited mainly to Bowman's layer. This dystrophy, although clinically different from classic granular dystrophy, is pathologically similar to it. Treatment, consisting of superficial keratectomy to 15% to 20% of corneal thickness, did not require lamellar grafting and produced good visual results. A new classification of granular dystrophy is proposed.

P-31 NMR analysis of phospholipids from cultured human corneal epithelial, fibroblast and endothelial cells

Corneal epithelial, fibroblast and endothelial cells, cultured from human donors, were analyzed to determine their characteristic phospholipid profiles by 31P NMR. Tissue phospholipid profiles from epithelial, fibroblast and endothelial cell cultures were evaluated to differentiate the individual cell types and to identify resonances that typically appear in high-resolution phospholipid profiles of whole corneas. Phosphatidylcholine, phosphatidylethanolamine plasmalogen, an uncharacterized phospholipid at 0.13 delta, phosphatidylinositol, phosphatidylserine and sphingomyelin were determined to be, in decreasing order of concentration, the major phospholipids detected in these three cultured corneal cell types. Indices of phospholipid metabolism representing total plasmalogen content, total choline-containing lipids and the total choline-containing lipids less those synthesized through the plasmalogen pathway were found to differentiate the three cell types. Minor phospholipids cardiolipin, lysophosphatidylcholine, phosphatidylethanolamine, lysophosphatidylcholine (LPC) and LPC plasmalogen not usually reported in studies of corneal phospholipids using other techniques, were useful in discriminating between cell types. Phospholipid profiles of the whole cornea provide important information concerning the biochemistry and pathology of the tissue, however, phospholipid analysis of individual components of the cornea, such as the epithelial, fibroblast and endothelial cells, makes it possible to understand the contribution of specific cellular constituents to the spectral information obtained from the whole cornea.

Granular corneal dystrophy Groenouw type I (GrI) and Reis-Bücklers' corneal dystrophy (R-B). One entity?

This paper maintains that Reis-Bücklers' corneal dystrophy and granular corneal dystrophy Groenouw type I are one and the same disease. Included are some of the technically best photographs of Reis-Bücklers' dystrophy found in the literature, and these are compared with photographs from patients with granular corneal dystrophy examined by the author. It is argued that most of the histological and ultrastructural findings on Reis Bücklers' dystrophy described in the literature are either congruent with what is found in granular corneal dystrophy or unspecific.

Clinically atypical granular corneal dystrophy with pathologic features of lattice-like amyloid deposits. A study of these families

Four patients from families in Pennsylvania, Massachusetts, and Argentina were diagnosed clinically as having granular dystrophy. Results of pathologic examination of the corneal buttons from each patient after penetrating keratoplasty confirmed granular deposits in the anterior third of the stroma. Amyloid was demonstrated within some of these granular deposits by Congo red staining with birefringence and dichroism and by electron microscopy. In addition to the morphologically granular deposits, numerous fusiform deposits identified as amyloid by histochemistry and electron microscopy and morphologically identical to those seen in lattice corneal dystrophy were detected deep to the granular deposits. It was further shown that the histochemical pattern of staining of the granular material by a series of lectins was similar to that present in corneas with lattice dystrophy. Although a relationship between these patients cannot be definitively proven, each family traces its origins to the Italian province of Avellino.

Collagen staining in corneal tissues

We adapted a previously described procedure to quantitate collagen in corneal tissue sections prepared from paraffin-embedded samples. The method entailed staining the deparaffinized tissue sections with Sirius red, eluting the bound dye with NaOH-methanol, and estimating the color in a spectrophotometer as an indication of the collagen content. This simple, rapid and reproducible method is comparable to biochemical assays and can be applied to study various corneal specimens readily available from eye pathology laboratories. We examined corneal sections from patients with aphakic bullous keratopathy, pseudophakic bullous keratopathy, Fuchs' dystrophy and lattice corneal dystrophy with this method. No significant difference in collagen staining was found between these pathologic specimens and normal control tissues. Biochemical assays also confirmed these findings. Sections from patients with macular and granular corneal dystrophies showed reduced staining suggesting a possible alteration in collagen content. This possibility, however, was not supported by data from biochemical analysis.

Composition of phospholipids and free fatty acids and incorporation of labeled arachidonic acid in rabbit cornea. Comparison of epithelium, stroma and endothelium

Fatty acid composition of phospholipids and free fatty acids were analyzed in the epithelium, stroma and endothelium of rabbit corneas. Phospholipids from endothelium had the highest proportion of arachidonate and epithelium had the lowest degree of unsaturation. Epithelium had the highest levels of free arachidonic acid. Labeled arachidonic acid was incorporated into membrane lipids of the three layers, primarily in phosphatidylcholine, phosphatidylinositol and triacylglycerols. In conclusion, the three layers of the cornea differ in the fatty acid composition of membrane lipids, particularly with regard to the polyunsaturated chains, and in the metabolism of the arachidonate chain.