Macular corneal dystrophy type I and type II are caused by distinct mutations in a new sulphotransferase gene.

Macular corneal dystrophy (MCD; MIM 217800) is an autosomal recessive hereditary disease in which progressive punctate opacities in the cornea result in bilateral loss of vision, eventually necessitating corneal transplantation. MCD is classified into two subtypes, type I and type II, defined by the respective absence and presence of sulphated keratan sulphate in the patient serum, although both types have clinically indistinguishable phenotypes. The gene responsible for MCD type I has been mapped to chromosome 16q22, and that responsible for MCD type II may involve the same locus. Here we identify a new carbohydrate sulphotransferase gene (CHST6), encoding an enzyme designated corneal N-acetylglucosamine-6-sulphotransferase (C-GlcNAc6ST), within the critical region of MCD type I. In MCD type I, we identified several mutations that may lead to inactivation of C-GlcNAc6ST within the coding region of CHST6. In MCD type II, we found large deletions and/or replacements caused by homologous recombination in the upstream region of CHST6. In situ hybridization analysis did not detect CHST6 transcripts in corneal epithelium in an MCD type II patient, suggesting that the mutations found in type II lead to loss of cornea-specific expression of CHST6.

Elevated expression of transglutaminase 1 and keratinization-related proteins in conjunctiva in severe ocular surface disease.

PURPOSE: In severe ocular surface diseases, pathologic keratinization of the ordinarily nonkeratinized corneal and conjunctival mucosal epithelia results in severe visual loss. The expression in conjunctivalized corneas of various proteins known to play important roles in the physiological keratinization process in human epidermis was examined to better understand the mechanism of keratinization. METHODS: Conjunctiva covering the cornea was examined in 12 eyes with ocular surface disease in the chronic cicatricial phase. These comprised four Stevens-Johnson syndrome, four ocular cicatricial pemphigoid, and four chemical injuries. Normal conjunctivas from four age-matched individuals served as controls. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to investigate transglutaminase 1 gene expression and immunohistochemistry to study the expression of transglutaminase 1 protein along with other keratinization-related proteins (involucrin, loricrin, filaggrin, and cytokeratins 1 and 10) and cytokeratin pairs 4/13 and 3/12. RESULTS: Semiquantitative RT-PCR showed that transglutaminase 1 mRNA expression was upregulated in keratinized conjunctiva compared with normal. Also, in this tissue, immunohistochemistry demonstrated elevated levels of transglutaminase 1, involucrin, filaggrin, and the cytokeratin pair 1/10. Levels of loricrin and cytokeratin pairs 4/13 and 3/12, however, remained the same. CONCLUSIONS: Various keratinization-related proteins, transglutaminase 1 included, are most likely involved in the pathogenesis of cicatrizing ocular surface diseases.

Gelatino-lattice corneal dystrophy: clinical features and mutational analysis.

PURPOSE: To report five unrelated Japanese individuals with "gelatino-lattice corneal dystrophy that clinically resembled, to some extent, gelatinous drop-like corneal dystrophy and lattice corneal dystrophy type 1. METHODS: Genomic DNA isolated from the five individuals with "gelatino-lattice corneal dystrophy was used as a template for polymerase chain reaction to amplify all exons of the candidate gene betaig-h3 and M1S1. The polymerase chain reaction product was then sequenced. RESULTS: In all cases, betaig-h3 was mutated in "gelatino-lattice corneal dystrophy (Arg124Cys), which is the same nucleotide change examined previously in lattice corneal dystrophy type 1. On the other hand, no mutation was detected in the entire coding region of M1S1. CONCLUSION: Based on the results of this study, it is suggested that "gelatino-lattice corneal dystrophy may be a subtype of lattice corneal dystrophy type 1.

Gelatinous drop-like corneal dystrophy is not one of the beta ig-h3-mutated corneal amyloidoses.

PURPOSE: To discover if beta ig-h3 is mutated in gelatinous drop-like corneal dystrophy, as has been suggested. METHODS: Genomic DNA was isolated from unrelated individuals with lattice corneal dystrophy type I (n = 3), Avellino corneal dystrophy (n = 3), and gelatinous drop-like corneal dystrophy (n = 3) and used as a template for polymerase chain reaction to amplify all exons in beta ig-h3. The polymerase chain reaction product was then sequenced. RESULTS: Beta ig-h3 is mutated in lattice corneal dystrophy type I (Arg124Cys) and Avellino corneal dystrophy (Arg124His). In gelatinous drop-like corneal dystrophy, on the other hand, no mutation was detected in the entire coding region of beta ig-h3 (all 17 exons). CONCLUSION: Unlike the amyloidotic corneal dystrophies lattice type I and Avellino, gelatinous drop-like corneal dystrophy is not likely to be caused by a mutation in beta ig-h3.

Amyloid and Pro501 Thr-mutated (beta)ig-h3 gene product colocalize in lattice corneal dystrophy type IIIA.

PURPOSE: To assess the relative distribution in the cornea of amyloid and (beta)ig-h3 gene product in lattice corneal dystrophy type IIIA (LCD-IIIA). METHODS: Serial sections from the cornea of a patient with LCD-IIIA were subjected to either Congo red staining or immunohistochemistry employing an antibody to (beta)ig-h3. Also, genomic DNA was isolated from peripheral blood and used as a template for polymerase chain reaction to amplify all exons of (beta)ig-h3. RESULTS: Exon 11 of (beta)ig-h3 was mutated (Pro501Thr). Subepithelial and intrastromal congophilic deposits exhibited a birefringency characteristic of amyloid. These regions of the tissue were also highly immunoreactive with the antibody to the (beta)ig-h3 gene product. CONCLUSION: Amyloid and Pro501Thr-mutated (beta)ig-h3 protein accumulate and colocalize in LCD-IIIA.

Apolipoproteins J and E co-localise with amyloid in gelatinous drop-like and lattice type I corneal dystrophies.

AIMS: Apolipoprotein J (apoJ) and apolipoprotein E (apoE) are thought to contribute to amyloid formation in patients with Alzheimer's disease. The aim of this investigation was to discover whether or not these apolipoproteins associate with corneal amyloid in gelatinous drop-like corneal dystrophy (GDCD) and lattice corneal dystrophy type I (LCD-I). METHODS: Corneas from three eyes of three patients with GDCD and one eye of one patient with LCD-I were examined immunohistochemically using antibodies against apoJ and apoE. Two normal corneas were similarly examined. Tissue sections of brain from a patient with Alzheimer's disease were used as positive controls for the antibodies. For all negative controls, mouse IgG was used instead of the primary antibody. RESULTS: Intense apoJ and apoE immunoreactivities were found in congophilic amyloid deposits in GDCD and LCD-I. These deposits were located subepithelially in GDCD, and subepithelially and intrastromally in LCD-I. In GDCD, immunostaining of subepithelial amyloid with anti-apoJ was noticeably stronger than with anti-apoE. CONCLUSIONS: As in senile plaques in brain from a patient with Alzheimer's disease, apoJ and apoE co-localise with amyloid in corneas with GDCD and LCD-I.

Detection of herpes simplex virus DNA in atypical epithelial keratitis using polymerase chain reaction.

AIM: To study herpes simplex virus (HSV) DNA in tears from patients with atypical epithelial keratitis of unknown aetiology. METHODS: Tear samples were collected from 17 affected eyes of 17 consecutive patients suffering from epithelial keratitis in whom HSV keratitis was suspected but whose diagnosis was difficult on the basis of clinical manifestations alone. Using reduced sensitivity polymerase chain reaction (PCR), tear samples were tested for HSV DNA. Tears from the unaffected eyes of the 17 patients were also examined, along with 38 tear samples from 19 normal volunteers. Southern blot analysis was performed to confirm that amplified DNA bands were specific for HSV. Clinical correlation with photographs of corneal lesions was also investigated. RESULTS: HSV DNA was detected in tears from the affected eyes of eight of the 17 patients with suspected HSV keratitis. Tears from the affected eyes of the other patients were PCR negative, as were tears from the unaffected eyes of all 17 patients, and from the 38 normal eyes. There was no correlation between PCR results and clinical manifestation of keratitis. CONCLUSIONS: Based on the sensitivity of the PCR system, eight of 17 suspected HSV keratitis patients were confirmed as suffering from HSV keratitis. HSV keratitis should therefore be considered as a possible diagnosis in atypical epithelial keratitis.

Amniotic membrane as a substrate for cultivating limbal corneal epithelial cells for autologous transplantation in rabbits.

PURPOSE: To examine the viability of using human amniotic membrane as substrate for culturing corneal epithelial cells and transplanting them onto severely injured rabbit eyes. METHODS: An ocular-surface injury was created in the right eye of eight rabbits by a lamellar keratectomy extending 5 mm outside the limbus. Next, from the limbal region of the uninjured left eyes of five of these animals, a small biopsy of corneal epithelial cells was taken and cultured on acellular human amniotic membrane. One month later, the invading conjunctiva that covered the corneal surface of all eight injured eyes was surgically removed. Five of the eyes then received grafts of amniotic membrane containing autologous cultured epithelial cells, whereas the other three received grafts of acellular amniotic membrane alone. RESULTS: A confluent primary culture of limbal corneal epithelial cells was established on acellular human amniotic membrane after 14 days. Cells were partially stratified and fairly well attached to the underlying amniotic membrane, although a fully formed basement membrane was not evident. The three rabbits that received amniotic membrane transplantation alone all had total epithelial defects on the graft in the early postoperative period. Eyes that were grafted with amniotic membrane that contained cultivated epithelial cells, however, were all successfully epithelialized up to 5 days after surgery. CONCLUSION: Autologous transplantation of cultivated corneal epithelium is feasible by using acellular amniotic membrane as a carrier.

Epithelial barrier function and ultrastructure of gelatinous drop-like corneal dystrophy.

PURPOSE: Recently, mutations in the M1S1 gene have been identified as responsible for gelatinous drop-like corneal dystrophy (GDLD). How the abnormal M1S1 gene product causes GDLD is not known, although evidence suggests that it may compromise corneal epithelial function. This investigation attempted to determine the effect of the abnormal M1S1 gene product by assessing epithelial barrier function and epithelial ultrastructure in GDLD corneas. METHODS: Epithelial barrier function was assessed on the basis of fluorescein uptake. The method used a modified slit-lamp fluorophotometer. High-resolution scanning electron and atomic force microscopy was used to investigate the amyloid deposits and epithelial cell structure. RESULTS: Epithelial permeability was orders of magnitude higher in GDLD corneas than normal. The structure of the amyloid deposits was characterized, and clear abnormalities in epithelial morphology and cell junctions were observed. CONCLUSIONS: The high epithelial permeability observed in GDLD corneas was directly correlated with abnormalities in epithelial structure, including irregular cell junctions. This suggests that the abnormal M1S1 gene product may affect epithelial cell junctions resulting in increased cell permeability in GDLD corneas.

Induction of differentiation of embryonal carcinoma F9 cells by iron chelators.

The effects of several chelators, including hinokitiol, on embryonal carcinoma F9 cell differentiation were assessed by assaying the production of plasminogen activator (PA) as a differentiation marker protein. Hinokitiol and tropolone which were potent differentiation inducers lost their activity following preincubation with Fe2+ and Fe3+ ions. Other metal ions had no or little effect on the hinokitiol-induced differentiation. Of several chelators examined, dithizone induced differentiation as effectively as did hinokitiol and tropolone. Dithizone-induced differentiation was also inhibited by preincubation with Fe3+ ions. It was concluded that some potent iron chelators could trigger the teratocarcinoma F9 cells to differentiate through the chelation with intracellular iron ions.

An expression profile of active genes in human conjunctival epithelium.

The purpose of this study was to describe the quantitatively and qualitatively genes expressed in in vivo human conjunctival epithelium. A cDNA library was created from human conjunctival epithelial cells obtained from 38 normal eyes by brush cytology. Poly A(+)RNA isolated from these cells was used as a template for cDNA synthesis by the vector-priming method. A 3'-directed cDNA library consisting of the cDNA moiety covering the poly A(+)RNA tail through the nearest Mbo I site was constructed and transformed into Escherichia coli. Inserts in 933 randomly chosen clones were sequenced. The resulting sequences were compared to determine frequency of appearance in the library, and to establish an expression profile of genes in the conjunctival epithelium. The sequences were sent to GenBank for gene identification. The result was an expression profile of active genes reflecting their relative abundance in the conjunctival epithelial mRNA population. The expression profile of human conjunctival epithelium showed that the most abundant gene transcript in human conjunctival epithelium was that for cytokeratin 13. Altogether 102 genes were found to be very active, including beta-2 microglobulin, lipocortin I and insulin-like growth factor binding protein-3. The gene expression profile of the conjunctival epithelium reflects the unique properties and functions of this tissue. Comparison of this expression profile with that obtained from corneal epithelium discloses clear differences and helps us better understand the physiology and pathophysiology of the ocular surface in humans.

Hinokitiol induces differentiation of teratocarcinoma F9 cells.

Hinokitiol, a constituent of the wood of Chamaecyparis taiwanensis, was found to induce differentiation of teratocarcinoma F9 cells. When examined by the agar-overlay method, in which expression of plasminogen activator as a differentiation marker protein was detected, this compound exhibited a dose- and time-dependent induction. Induction of differentiation by hinokitiol occurred irreversibly and required its addition for more than 12h. Among its structure-related compounds tested, tropolone and two colchicine-related compounds exerted potent activities comparable to that of hinokitiol. These findings indicate that free tropolone structure in the molecules plays an essential role in inducing differentiation of F9 cells. Hinokitiol showed a strong inhibitory effect of DNA synthesis in very early stages of culture, suggesting that this effect may be responsible for triggering differentiation of F9 cells.

Epithelial hyperproliferation and transglutaminase 1 gene expression in Stevens-Johnson syndrome conjunctiva.

In Stevens-Johnson syndrome, pathological keratinization of the ordinarily nonkeratinized corneal and conjunctival mucosal epithelia results in severe visual loss. We examined conjunctiva covering cornea in five eyes in the chronic cicatricial phase of Stevens-Johnson syndrome. Normal conjunctiva from five age-matched individuals was studied also. The number of epithelial cells in Stevens-Johnson syndrome conjunctiva that were immunoreactive with a monoclonal antibody, Ki-67, to a nuclear antigen found only in proliferating cells was greater than normal (93.8+/-19.8 cells above 100 basal cells versus 12.8+/-0.5 cells above 100 basal cells; P = 0.009). In addition, although clinical inflammation was mild, massive lymphocytic infiltration was seen in the substantia propria of conjunctiva covering cornea. In situ hybridization documented transglutaminase 1 (keratinocyte transglutaminase) mRNA in suprabasal cells of the abnormally thickened conjunctival epithelium in all Stevens-Johnson syndrome patients. In contrast, no message was detected in normal conjunctival or corneal epithelia. Transglutaminase 1 is expressed during the terminal differentiation of keratinocytes where it helps synthesize cornified cell envelopes. We speculate that in Stevens-Johnson syndrome, epithelial hyperproliferation, and transglutaminase 1 gene expression lead to the pathological keratinization of ocular surface mucosal epithelia.

Isolation and chromosomal localization of a cornea-specific human keratin 12 gene and detection of four mutations in Meesmann corneal epithelial dystrophy.

Keratin 12 (K12) is an intermediate-filament protein expressed specifically in corneal epithelium. Recently, we isolated K12 cDNA from a human corneal epithelial cDNA library and determined its full sequence. Herein, we present the exon-intron boundary structure and chromosomal localization of human K12. In addition, we report four K12 mutations in Meesmann corneal epithelial dystrophy (MCD), an autosomal dominant disorder characterized by intraepithelial microcysts and corneal epithelial fragility in which mutations in keratin 3 (K3) and K12 have recently been implicated. In the human K12 gene, we identified seven introns, defining eight individual exons that cover the coding sequence. Together the exons and introns span approximately 6 kb of genomic DNA. Using FISH, we found that the K12 gene mapped to 17q12, where a type I keratin cluster exists. In this study, four new K12 mutations (Arg135Gly, Arg135Ile, Tyr429Asp, and Leu140Arg) were identified in three unrelated MCD pedigrees and in one individual with MCD. All mutations were either in the highly conserved alpha-helix-initiation motif of rod domain 1A or in the alpha-helix-termination motif of rod domain 2B. These sites are essential for keratin filament assembly, suggesting that the mutations described above may be causative for MCD. Of particular interest, one of these mutations (Tyr429Asp), detected in both affected individuals in one of our pedigrees, is the first mutation to be identified within the alpha-helix-termination motif in type I keratin.