MUC1 and estrogen receptor alpha gene polymorphisms in dry eye patients.

Dry eye syndrome is a collection of common disorders of multifactorial etiology. Although the epidemiology of dry eye has been well studied, reports of genetic patterns that might influence susceptibility to dry eye are few. We reported that the frequency of non-Sjögren's aqueous-deficient dry eye patients expressing only the MUC1/A splice variant of the mucin MUC1 may be lower than that of a normal control group [Imbert, Y., Darling, D.S., Jumblatt, M.M., Foulks, G.N., Couzin, E.G., Steele, P.S., Young, W.W., Jr., 2006. MUC1 splice variants in human ocular surface tissues: possible differences between dry eye patients and normal controls. Exp. Eye Res. 83, 493-501]. Also, He et al. [He, Y., Li, X., Bao, Y., Sun, J., Liu, J., 2006. The correlation of polymorphism of estrogen receptor gene to dry eye syndrome in postmenopausal women. Yan. Ke. Xue. Bao. 22, 233-236] reported a difference between Chinese dry eye and control groups in the frequency of a polymorphism in estrogen receptor alpha (ERalpha). In the present study we determined the statistical significance and generality of these observations and tested if the MUC1 splice variant difference between subject groups reflected a difference in the MUC1 variable number of tandem repeat (VNTR) size class. There was a perfect correlation between the MUC1/A or MUC1/B splice variant pattern and the SNP genotype frequency of the SNP (rs4072037) controlling that splicing event. In contrast, western and Southern blotting indicated that MUC1 VNTR size class corresponded to the MUC1 SNP genotype in only 80% of cases. We determined the status of the MUC1 SNP in normal and dry eye populations all of whom were female Caucasians. The MUC1 SNP genotype frequency of the normal control group was statistically different from both the non-Sjögren's aqueous-deficient dry eye group with ocular surface staining (P=0.017) and the evaporative dry eye group (P=0.015). We also tested SNP rs2234693 to analyze the polymorphism in the ERalpha gene and found no significant difference in the SNP genotype frequency between the control group and either of the dry eye subtypes. Thus, among Caucasians there is no evidence for an association of the ERalpha gene polymorphism with dry eye syndrome as previously described in a Chinese population. In conclusion, the etiologies of evaporative dry eye and non-Sjögren's aqueous-deficient dry eye are known to be different. However, our results suggest that both of these subtypes of dry eye disease may share a common mechanism or factor related to MUC1 genotypic differences that affects susceptibility to ocular surface damage. This altered susceptibility may not be related to the MUC1 VNTR size class. Therefore, mechanisms influencing protection of the ocular surface against inflammation and damage in different types of dry eye disease warrant further investigation particularly in relation to MUC1 genotype.

A new model of experimental autoimmune keratoconjunctivitis sicca (KCS) induced in Lewis rat by the autoantigen Klk1b22.

PURPOSE: This study was designed to generate an inducible autoimmune model of keratoconjunctivitis sicca (KCS) for study of pathogenesis of the disease. METHODS: Lewis rats were immunized with a mixture of lacrimal and salivary gland extract or recombinant mouse protein kallikrein 1b22 (Klk1b22) emulsified in complete Freund's adjuvant (CFA). For disease induction by adoptive transfer of primed cells, donor rats were received with T-cell blasts. KCS were observed by either clinical signs or histology. RESULTS: The autoantigen Klk1b22, isolated from the lacrimal and salivary glands, readily induced Sjögren's syndrome (SS)-like KCS in the recipients. The diseased animals presented the clinical and pathologic symptoms that resemble related human disease. Most immunized rats showed an increase, then a decrease in tear volume, together with corneal opacity and ocular lesions. Histologic examination revealed that the rats displayed the cardinal signs of primary SS-like KCS, including marked lymphocytic infiltration of the lacrimal and salivary glands and destruction of the acinar cells. Immunofluorescence studies showed that both CD8(+) and CD4(+) T cells were heavily infiltrated, with the former cells predominant in the damaged ducts. Finally, adoptive transfer of Klk1b22-reactive T cells induced more severe disease with earlier onset. CONCLUSIONS: Klk1b22 is an autoantigen for inducing an experimental SS-like KCS in Lewis rats. The availability of this new and reproducible rat model should provide a new and needed tool for studying the pathogenesis of SS.

Hyperoxia and thyroxine treatment and the relationships between reactive oxygen species generation, mitochondrial membrane potential, and cardiolipin in human lens epithelial cell cultures.

Thyroxine-treated human lens epithelial cells, HLE B-3, were grown in either a normoxic or hyperoxic atmosphere as a first step in identifying factors related to their increased viability. Reactive oxygen species, ROS, and the apparent mitochondrial membrane potential, Delta Psi(m), were measured using fluorescent probes. ROS were significantly higher in HLE B-3 cells grown in a hyperoxic atmosphere for both thyroxine-treated and untreated samples. However, treatment with thyroxine produced 40% lower ROS levels than untreated cells. A mitochondrial uncoupler concomitantly reduced ROS generation. In cells that were grown in a hyperoxic atmosphere, the Delta Psi(m) was significantly higher for samples treated with thyroxine compared to those that were untreated. ROS generation correlated inversely with the apparent Delta Psi(m) and the amount of cardiolipin, and correlated with the amount of lipid oxidation products. These correlations were valid whether cardiolipin and the Delta Psi(m) were decreased as a result of oxygen or increased as a result of thyroxine treatment. Therapies that protect mitochondria from damage and reduce damaging ROS generation may potentially ameliorate the effects of oxidation that occur in aging tissues and in diseases such as cataract.

Expression in human ocular surface tissues of the GalNAc-transferases that initiate mucin-type O-glycosylation.

PURPOSE: Mucins are highly glycosylated proteins that act as lubricants, protectants, and mediators of signal transduction. The UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (ppGaNTase) family members initiate mucin-type O-glycosylation. Because O-glycosylation provides mucins with the viscoelastic properties required for proper mucin function, ppGaNTase expression is vital to the maintenance of healthy epithelial surfaces including the ocular surface. Differences of expression of ppGaNTase isoforms might be factors influencing susceptibility to dry eye disease. Therefore, we determined the expression of the ppGaNTase isoforms in normal human ocular surface tissues and the conjunctival epithelium from patients with aqueous-deficient dry eye. METHODS: Expression of ppGaNTase isoforms was quantitated by real-time reverse transcriptase polymerase chain rection (RT-PCR). RESULTS: Conjunctiva and cornea expressed multiple ppGaNTase isoforms, with isoforms T12 and T4 being the most strongly expressed in conjunctiva and T12 and T3 in the cornea. In contrast, lacrimal gland expressed fewer isoforms and had lower total ppGaNTase expression. Brush cytology was found to be superior to impression cytology for harvesting conjunctival epithelium in terms of ease of use, safety, and reproducibility of results. Similar to whole conjunctiva, the strongest isoforms in conjunctival epithelial cells were T12 and T4, followed by T3, T1, T5, and T2. No significant differences of ppGaNTase expression were found between the conjunctival epithelium of dry eye and normal control groups. CONCLUSION: Human ocular surface tissues express multiple ppGaNTase isoforms, suggesting a requirement for glycosylating diverse mucin-type substrates. However, there is no evidence to date to suggest that differences of ppGaNTase expression levels might contribute to susceptibility to dry eye disease.

Glycoprotein 340 in normal human ocular surface tissues and tear film.

The tear film is a complex mixture of secreted fluid, ions, proteins, glycoproteins, and lipids that lubricates and protects the ocular surface. Recently, several antimicrobial peptides have been described in the tear fluid. In this study, we describe the presence of the large secreted glycoprotein gp340 in the tear film. Western blot analysis showed that gp340 is abundant in secreted tears and in the lacrimal glands. Lesser amounts of gp340 were detected in the cornea and conjunctiva. Consistent with Western blot data, reverse transcription-PCR and real-time quantitative PCR showed that gp340 transcripts were abundant in lacrimal gland tissue and were also present in the cornea and conjunctiva. Immunohistochemistry localized gp340 to the acinar cells of the lacrimal gland and the deeper layers of the conjunctival epithelium. gp340 was not detected in conjunctival goblet cells. In the cornea, gp340 was present only in a peripheral band of basal epithelial cells, suggesting that gp340 may play a role in the cycle of corneal epithelial renewal. To determine if tear film gp340 may function as a bacterial agglutinin as it does in saliva, tears were incubated with streptococcal cells and the formation of bacterial aggregates was monitored. Addition of tears to late-exponential-phase Streptococcus mutans cells resulted in time- and dose-dependent aggregation of the bacteria. Furthermore, Western blot analysis confirmed the presence of cell-associated gp340 in isolated bacterial aggregates. The ocular pathogen Staphylococcus aureus, but not Pseudomonas aeruginosa, also aggregated when incubated with tears. These results suggest that gp340 is a normal component of the tear film and that the glycoprotein may function as a bacterial agglutinin.

MUC1 splice variants in human ocular surface tissues: possible differences between dry eye patients and normal controls.

Mucins are highly glycosylated proteins that are vital to the maintenance of healthy epithelial surfaces including the ocular surface. Mucins act as lubricants, protectants, and mediators of signal transduction. The majority of the O-glycosylation sites on the transmembrane mucin MUC1 are found in a highly polymorphic core region containing a variable number of tandem repeats (VNTR). MUC1 alleles can be divided into size classes that contain small (30-45) or large (60-90) numbers of repeats. Although at least 12 splice variants of MUC1 have been found in other tissues, no splice variants have been reported in human ocular surface tissues. We have used RT-PCR to identify MUC1 splice variants that were then confirmed by sequencing. We here report the presence in some samples of human cornea, conjunctiva, and lacrimal gland of MUC1/B which features canonical splicing between exons 1 and 2 and MUC1/A, a transcript that retains 27bp from the 3' end of intron 1 and is predicted to add 9 amino acids to the MUC1 sequence upstream of the tandem repeat region. Cornea and conjunctiva both contain the MUC1/SEC splice variant that lacks the transmembrane domain and, therefore, results in a soluble, secreted form of MUC1. Cornea and conjunctiva also contain MUC1/Y and MUC1/Z(X) variants that lack the tandem repeat region. Cornea, conjunctiva, and lacrimal gland also contain a previously undescribed MUC1 variant transcript, termed MUC1/YI, that retains 99bp from the 5' end and 27bp from the 3' end of the first intron, resulting in a frame shift and premature stop codon. This transcript is predicted to produce a novel 27 amino acid peptide after signal peptidase cleavage. Analysis of brush cytology samples revealed that the percentage of dry eye patients expressing the MUC1/A variant in the conjunctival epithelium is lower than in normal control donors. Western blotting confirmed that MUC1/A is associated with alleles containing the large size class of tandem repeats. Therefore, we propose that one factor in susceptibility to dry eye disease may be the lengths of the MUC1 VNTR in conjunctival epithelium based on the rationale that longer VNTR provide better lubrication and greater protection of the ocular surface against inflammation.

MUC7 expression in the human lacrimal gland and conjunctiva.

PURPOSE: Several mucins including MUC1, MUC2, MUC4, and MUC5AC have been identified at the ocular surface and in tears. The lacrimal gland, however, is not generally considered a source of ocular mucin. Because the lacrimal glands are similar to the salivary glands, we hypothesized that the lacrimal gland would express MUC7, a distinctive salivary mucin. We report the presence of MUC7 RNA and protein in normal human lacrimal glands as determined by reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and Western blot analysis. METHODS: RNA from lacrimal glands and conjunctivae was isolated and subjected to RT-PCR with primers specific for MUC7. The identity of the PCR products was confirmed by sequencing. In situ hybridization with PCR product-based riboprobes was used to locate MUC7 transcripts in the lacrimal gland. MUC7 protein was detected by Western blot analysis. RESULTS: Of six normal human lacrimal glands from which relatively intact mRNA could be extracted, four expressed MUC7. Hybridization with an antisense riboprobe for MUC7 indicates the presence of MUC7 transcripts in the cytoplasm of acinar cells. Western blot analysis confirms expression of the protein in the lacrimal gland. The presence of MUC1, MUC4, and MUC5B was also demonstrated by RT-PCR in lacrimal gland tissue. MUC7 transcripts and protein were also detected in normal human conjunctivae. CONCLUSIONS: The mucin profile of the lacrimal gland resembles that of the salivary gland. Both RNA and protein corresponding to MUC7 are present in the normal human lacrimal gland. Reverse transcription-polymerase chain reaction indicates that other transcripts of MUC1, MUC4, and MUC5B are present as well. Ocular MUC7 is also produced by the conjunctival mucosa. The lacrimal gland, therefore, contributes not only to the aqueous component of tears but also, in concert with the conjunctiva, may contribute to the total pool of ocular surface mucins.

Characterization of human ocular mucin secretion mediated by 15(S)-HETE.

PURPOSE: The eicosanoid 15-(S)-hydroxy-5,8,11,13-eicosatetraenoic acid [15(S)-HETE] is reported to stimulate mucin production in both airway and ocular surface epithelia. The current study was undertaken to evaluate the effects of 15(S)-HETE on secretion of specific ocular mucins by human conjunctiva. METHODS: Segments of human bulbar conjunctival tissue were incubated with 15(S)-HETE (1-1000 nM) for 30 minutes at 37 degrees C. Secretion of human ocular mucins MUC1, MUC2, MUC4, and MUC5AC into the incubation media was measured by dot-blot immunoassay using antibodies directed to unique mucin polypeptide epitopes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting were used to verify the specificity of anti-mucin antibody binding and to investigate the presence of MUC1 mucin in human tears. RESULTS: 15(S)-HETE (10(-8)-10(-6) M) stimulated secretion of conjunctival mucins in a concentration-dependent manner. Significant increases in total mucin secretion were observed at 10(-7) M 15(S)-HETE with a maximum response (>50% increase above controls) at 10(-6) M. Results of immunoassays showed that 15(S)-HETE differentially stimulates secretion of MUC1 mucin with no detectable effects on MUC2, MUC4, or MUC5AC release. Western analysis of tear samples from human volunteers indicated that MUC1 is a component of the preocular tear film. CONCLUSIONS: The results demonstrate that 15(S)-HETE is a selective secretogogue for MUC1 in isolated human conjunctival tissue. Although the biochemical mechanism(s) and cellular origins of MUC1 secretion remain to be established, the ubiquitous expression of MUC1 in corneal and conjunctival epithelia and its presence in human tears suggest that secreted MUC1 may contribute to the mucin layer that coats and protects the ocular surface.