Analysis of the ARMD1 locus: evidence that a mutation in HEMICENTIN-1 is associated with age-related macular degeneration in a large family

Age-related macular degeneration (AMD) is a common cause of severe vision loss. Identification of the genes involved in AMD will lead to a better understanding of this disease at the molecular level, which will eventually lead to early detection, prevention and treatment. Previously, we mapped the ARMD1 gene to 1q25-31 in a large family with AMD. Here, we narrow the ARMD1 locus to 14.9 Mb between LAMB2 and D1S3469, a region containing 50 known genes. Twenty candidate genes within this region were screened for mutations. Only one DNA variation, an A16,263G transition in exon 104 of HEMICENTIN-1, was found to segregate exclusively with the disease haplotype in members of this large family with AMD. This variation produces a non-conservative substitution of arginine for glutamine at amino acid position 5345 (Gln5345Arg). It was also identified in 11 other individuals, all of whom share a haplotype, which envelops HEMICENTIN-1, with the large AMD family. The affected status of all but one of those individuals conforms to the age-dependent penetrance observed in AMD. The amino acid at position 5345 of HEMICENTIN-1 was conserved as glutamine in eight species analyzed. RT-PCR analysis demonstrated that exon 104 of HEMICENTIN-1 is alternatively spliced in various cell types. Exclusive segregation of Gln5345Arg with the disease haplotype in this large family, amino acid conservation of glutamine at this position among mammals, the non-conservative nature of the substitution and similarities to EFEMP1 support the conclusion that HEMICENTIN-1 is the ARMD1 gene.

Age-related macular degeneration--a genome scan in extended families

We performed a genomewide scan and genetic linkage analysis, to identify loci associated with age-related macular degeneration (AMD). We collected 70 families, ranging from small nuclear families to extended multigenerational pedigrees and consisting of a total of 344 affected and 217 unaffected members available for genotyping. We performed linkage analyses using parametric and allele-sharing models. We performed the analyses on the complete pedigrees but also subdivided the families into nuclear pedigrees. Finally, to dissect potential genetic factors responsible for differences in disease manifestation, we stratified the sample by two major AMD phenotypes (neovascular AMD and geographic atrophy) and by age of affected family members at the time of our evaluation. We have previously demonstrated linkage between AMD and 1q25-31 in a single large family. In the combined sample, we have detected the following loci with scores exceeding a LOD=2 cutoff under at least one of the models considered: 1q31 (HLOD=2.07 at D1S518), 3p13 (HLOD=2.19 at D3S1304/D3S4545), 4q32 (HLOD=2.66 at D4S2368, for the subset of families with predominantly dry AMD), 9q33 (LODZlr=2.01 at D9S930/D9S934), and 10q26 (HLOD=3.06 at D10S1230). Using correlation analysis, we have found a statistically significant correlation between LOD scores at 3p13 and 10q26, providing evidence for epistatic interactions between the loci and, hence, a complex basis of AMD. Our study has identified new loci that should be considered in future mapping and mutational analyses of AMD and has strengthened the evidence in support of loci suggested by other studies.

Lack of an association of apolipoprotein E gene polymorphisms with familial age-related macular degeneration

BACKGROUND

Previously, the epsilon 4 allele of apolipoprotein E (APOE) was reported to have a significant association with a decreased risk of age-related macular degeneration (AMD). In addition, the epsilon 2 allele of APOE was reported to be possibly associated with an increased risk of AMD.

OBJECTIVE

To determine if APOE polymorphisms, previously reported to be associated with AMD, affect its expression in medium to large families, as well as in unrelated patients with AMD.

METHODS

The APOE genotype was determined by HhaI restriction digests of polymerase chain reaction-amplified products in a collection of 259 affected and 207 unaffected individuals from 56 AMD families. Genotypes were determined similarly in a set of 104 unrelated AMD patients and in 113 unaffected control subjects. Diagnosis of AMD was based on clinical examination and evaluation of fundus photographs. Evidence of an association between alleles of APOE and AMD in families was tested by the following 4 statistical methods: chi2 analysis of simple allele counting, logistic regression analysis adjusting for age, construction of likelihood ratios of haplotype frequencies, and the pedigree disequilibrium test.

RESULTS

None of the statistical methods used showed a significant association between the common alleles of APOE and AMD in our collection of families or in the set of unrelated AMD patients.

CONCLUSIONS

No evidence was found to support an association between AMD in medium to large families and the epsilon 4 or epsilon 2 alleles of APOE. Neither was any evidence found for an association of APOE polymorphisms with the set of unrelated patients with AMD. However, a trend for a decreased risk of AMD associated with APOE epsilon 4 was observed in the set of unrelated patients with a family history of AMD.

Involvement of the Erk-MAP kinase pathway in TNFalpha regulation of trabecular matrix metalloproteinases and TIMPs

PURPOSE

TNFalpha is a strong modulator expression of trabecular meshwork (TM) matrix metalloproteinase (MMP) and tissue inhibitor (TIMP). Laser trabeculoplasty appears to rely on this process to restore normal aqueous humor outflow facility. Thus, studies were conducted to determine whether the extracellular signal-regulated kinase (Erk)-mitogen-activated protein (MAP) kinase signal-transduction pathway is involved.

METHODS

Porcine TM cells were treated with TNFalpha, and changes in MMPs and TIMPs were evaluated by zymography and Western immunoblot assay. Phosphospecific antibodies to proteins from the Erk pathway were used to evaluate responses to treatment with TNFalpha. Inhibitors of Mek, the kinase that activates Erk, and of protein kinase C (PKC) isoforms were used to define pathway involvement.

RESULTS

Treatment with TNFalpha increased MMP-1, -3, and -9 and TIMP-1, whereas expression of MMP-2 was not affected and expression of TIMP-2 was decreased. Erk and Mek were rapidly phosphorylated after treatment with TNFalpha, and c-Raf-1 showed a significant bandshift. A specific inhibitor of Mek blocked the TNFalpha induction of the MMPs and TIMPs and the phosphorylation of Erk. An inhibitor of the PKC- micro isoform, which also blocks the effects of MMP-TIMP of TNFalpha, did not affect phosphorylation of Erk.

CONCLUSIONS

The components of this MAP kinase pathway in the TM are dramatically affected by TNFalpha and inhibition of Erk's phosphorylation blocks the changes in MMP and TIMP expression. PKC micro, which is also required in this transduction process, does not appear to be upstream from Erk in the signaling cascade. Manipulation of this and related TM signal-transduction pathways may provide targets for developing improved glaucoma treatments.

Expression profile and genome location of cDNA clones from an infant human trabecular meshwork cell library

PURPOSE

To delineate the profile of genes expressed in infant human trabecular meshwork and identify candidate genes for glaucoma.

METHODS

Human trabecular meshwork cell cultures were established from six young donors. A cDNA library was made from the combined trabecular meshwork mRNA. The end-sequence of random clones was determined by direct sequencing. These sequences were then analyzed by a National Center for Biotechnology Information (NCBI, Bethesda, MD) database search. Nucleotide searches were performed using the BLASTN (ver. 2.1.3; against the nonredundant nucleic acid sequence) and dbEST databases (both provided by NCBI in the public domain at www.ncbi.nlm.nih.gov).

RESULTS

Sequences from 1118 clones from this nonamplified trabecular meshwork cDNA library were categorized. Of these, 877 expressed sequence tags (ESTs) (78.7%) were known genes. One hundred thirty-nine ESTs (12.5%) showed close identity to EST sequences reported in the public domain database (dbEST). Thirteen ESTs (1.2%) showed no significant similarity to known genes or ESTs in the public databases and were thus defined as novel ESTs. The most abundant genes expressed by the human trabecular meshwork included ferritin H, eukaryotic translation elongation factor 1-alpha, ferritin L, fibronectin, and TIMP-1. Ferritin H was the most abundant transcript, making up more than 4% of the genes expressed by the human trabecular meshwork. Extracellular matrix proteins were also highly expressed. The chromosome location of the trabecular meshwork ESTs is reported.

CONCLUSIONS

A profile of genes expressed by human trabecular meshwork is presented. Thirteen novel ESTs were identified. The combined information obtained from expression analysis and chromosomal localization of trabecular meshwork cDNAs should be valuable in identifying candidate genes for glaucoma.

Involvement of protein kinase C in TNFalpha regulation of trabecular matrix metalloproteinases and TIMPs

PURPOSE

The cytokine TNFalpha is a strong modulator of trabecular meshwork (TM) matrix metalloproteinase (MMP) and tissue inhibitor (TIMP) expression. Studies were conducted to identify signal-transduction pathways involved.

METHODS

Porcine TM cells were treated with TNFalpha, and MMP and TIMP levels were evaluated by zymography and Western immunoblot. Inhibitors and activators of several signal-transduction pathways were used to select pathways that could be involved. Trabecular protein kinase C (PKC) isoforms were identified and localized by using Western immunoblots and confocal immunohistochemistry. Changes in subcellular distribution of PKC isoforms were evaluated. PKC isoform downregulation and additional inhibition profiles were used to refine the involvement pattern of different isoforms.

RESULTS

TNFalpha treatment increased MMP-1, -3, and -9 and TIMP-1 expression, whereas MMP-2 expression was not affected and TIMP-2 expression decreased. Agents that modulate protein kinase A (PKA) or inhibit phosphatidylinositol 3-kinase (PI3K) had minimal effects on trabecular MMP or TIMP induction by TNFalpha, whereas several agents that modulate PKC activity were effective. Trabecular cells expressed several PKC isoforms, which exhibited distinctive subcellular localization. TNFalpha treatment triggered some PKC isoform translocations. Exposure of trabecular cells to TNFalpha for 72 hours differentially downregulated several PKC isoforms. Treatment with a phorbol mitogen that stimulates most PKC isoforms produced strong increases in these MMPs. TNFalpha's effects on MMP and TIMP expression were completely blocked by only one PKC inhibitor.

CONCLUSIONS

The PKA and PI3K pathways appear not to be involved directly in transducing this TNFalpha signal, but at least one isoform of PKC seems to be required. Based on the inhibitor profiles and the downregulation and translocation studies, PKC(mu) appears to be critical in transducing this signal. Unraveling the remaining steps in this and in additional related TM signal-transduction pathways may provide targets for developing improved glaucoma treatments.

Effects of mechanical stretching on trabecular matrix metalloproteinases

PURPOSE

The homeostatic mechanisms responsible for intraocular pressure (IOP) regulation are not understood. Studies were conducted to evaluate the hypothesis that trabecular meshwork (TM) cells sense increases in IOP as stretching or distortion of their extracellular matrix (ECM) and respond by increasing ECM turnover enzymes.

METHODS

Flow rates were increased in perfused human anterior segment organ cultures and the matrix metalloproteinase (MMP) levels and IOP were evaluated. Human TMs in stationary anterior segment organ culture were mechanically stretched, and MMP levels were analyzed. TM cells were grown on membranes, which were then stretched, and MMP levels were evaluated. Western immunoblots, zymography, and confocal immunohistochemistry were used to evaluate changes in MMPs and their tissue inhibitors, the TIMPS:

RESULTS

Doubling the flow rate in perfused human organ cultures increased gelatinase A levels in the perfusate by 30% to 50% without affecting gelatinase B or stromelysin levels. Immediately after doubling the flow rate, the measured IOP doubled. However, over the next few days the IOP gradually returned to the initial level, although the flow rate was maintained at double the initial value. Stretching stationary organ cultures or stretching TM cells grown on membranes resulted in similar increases in gelatinase A without changes in gelatinase B or stromelysin levels. The gelatinase A increases occurred between 24 and 72 hours and were approximately proportional to the degree of stretching. Although coating the membranes with different ECM molecule affected the gelatinase A response, the optimum response occurred when the cells had been grown long enough to produce their own ECM. By Western immunoblot and confocal immunohistochemistry, the stretch-induced increases in gelatinase A were accompanied by strong decreases in TIMP-2 levels and moderate increases in one membrane type MMP, MT1-MMP. After mechanical stretching of the membrane, gelatinase A, MT1-MMP and TIMP-2 all exhibited a similar punctate immunostaining pattern over the TM cell surface.

CONCLUSIONS

These results are compatible with the hypothesis that elevations in IOP are sensed by TM cells as ECM stretch/distortion. TM cells respond by increasing gelatinase A and MT1-MMP, while decreasing TIMP-2 levels. This will increase ECM turnover rates, reduce the trabecular resistance to aqueous humor outflow, and restore normal IOP levels. This hypothesis provides a regulatory feedback mechanism for IOP homeostasis.

Identification and expression of a novel type I procollagen C-proteinase enhancer protein gene from the glaucoma candidate region on 3q21-q24

A novel human Type I procollagen C-proteinase enhancer protein-like gene, PCOLCE2, was identified by sequencing an EST in the primary open-angle glaucoma (POAG) region on 3q21. The total cDNA encoded a 415-amino-acid protein that has 43% identity to the Type I procollagen C-proteinase enhancer protein (PCOLCE1). PCOLCE2 contains two CUB domains, which are thought to be involved in protein-protein interactions, and an NTR module. PCOLCE2 message is expressed in the trabecular meshwork, lungs, heart, brain, liver, skeletal muscle, kidney, pancreas, and placenta as a 2-kb message. PCOLCE2, a 52-kDa protein, is expressed in the trabecular meshwork. A novel gene, PCOLCE2, has been identified and characterized. Based upon its homology with collagen-binding proteins, its expression in the trabecular meshwork, and its chromosome location, PCOLCE2 is a candidate gene for GLC1C. However, no coding sequence mutations were detected in PCOLCE2 in a POAG patient from the GLC1C family.

Mediation of laser trabeculoplasty-induced matrix metalloproteinase expression by IL-1beta and TNFalpha

PURPOSE

Laser trabeculoplasty of the anterior uveal region of the trabecular meshwork induces sustained matrix metafloproteinase expression within the juxtacanalicular region of the meshwork. Studies were conducted to test the hypothesis that a factor mediates this response and to identify the factor.

METHODS

Human anterior segment organ cultures were subjected to laser treatment using standard clinical parameters and were returned to culture for 8 hours. The resultant 8-hour-conditioned culture medium was then tested for factor activity by evaluating its ability to produce two typical trabecular responses to laser treatment, that is, to induce stromelysin expression or to trigger cell division, when applied to fresh organ cultures or to cell cultures. Confocal immunohistochemistry of the laser-treated organ cultures and western immunoblot analysis of the conditioned medium were used to evaluate changes in potential candidates for the factor activity. The ability of the interleukin (IL)-1 receptor antagonist (IL-1ra)- and of tumor necrosis factor alpha (TNFalpha)- blocking antibodies to eliminate the stromelysin induction was evaluated.

RESULTS

Medium conditioned for 8 hours induced typical trabecular cell division in anterior segment organ cultures. Medium conditioned for 8 hours, but not for 30 minutes, induced typical increases in stromelysin expression in these organ cultures and in cell cultures. After 8 hours, both trabecular cells in laser-treated organ cultures and in the conditioned medium contained elevated levels of IL-1beta and TNFalpha. The laser-treated organ cultures contained elevated levels of IL-1alpha, but it was not secreted into the medium. The ability of conditioned media to induce stromelysin expression was partially blocked by either the IL-1ra- or the TNFalpha-blocking antibody.

CONCLUSIONS

Laser trabeculoplasty induces the expression and secretion of both IL-1beta and TNFalpha within the first 8 hours after treatment. These cytokines then mediate increased trabecular stromelysin expression. Putatively, this initiates remodeling of the juxtacanalicular extracellular matrix, a likely site for the aqueous outflow resistance, and thus restores normal outflow facility.

Autosomal dominant Stargardt-like macular dystrophy: I. Clinical characterization, longitudinal follow-up, and evidence for a common ancestry in families linked to chromosome 6q14

PURPOSE

Characterize the phenotype of autosomal dominant Stargardt-like macular dystrophy in two families linked to chromosome 6q14 and determine whether they share a common ancestry.

METHODS

Two families spanning 10 generations were identified and studied independently. Participating members were examined and genetic linkage and genotyping performed.

RESULTS

Presenting symptoms included decreased vision, hemeralopia, and mild photophobia. The subjective onset of visual loss ranged from age 3 to 50 with a mean of 14 years. A Snellen acuity of 20/200 occurred at a mean age of 22 years. Over decades, the macular lesion enlarged and visual acuity decreased to 20/300 to 20/800. The typical phenotype was well-circumscribed, homogenous atrophy of the retinal pigment epithelium and choriocapillaris in the macula, with surrounding yellow flecks and temporal optic nerve pallor. The phenotypic spectrum included a pattern dystrophy-like appearance, diffuse geographic atrophy, and extensive fundus flecks. Genotyping revealed that the two families were linked to chromosome 6q14 and shared a common haplotype spanning 21 cM between D6S430 and D6S300. The two families were subsequently shown by genealogic investigation to represent different branches of a common kindred.

CONCLUSIONS

Families with autosomal dominant Stargardt-like macular dystrophy linked to chromosome 6q14 share a common phenotype and in some cases can be distinguished from similar dystrophies by inheritance pattern and clinical features. The finding that these two families shared a common ancestor suggests the existence of a founder effect. Characterization of the gene for autosomal dominant Stargardt-like macular dystrophy may enable better understanding of this condition and elucidation of its potential role in other forms of macular degeneration.

GLC1F, a new primary open-angle glaucoma locus, maps to 7q35-q36

BACKGROUND

A large family with adult-onset primary open-angle glaucoma (POAG) was identified.

OBJECTIVE

To initiate a genome-wide scan to map the POAG locus in this family.

METHODS

Blood samples or buccal swabs were obtained from 25 members of a large family with POAG after informed consent was obtained. Members and their spouses were evaluated clinically for POAG on the basis of intraocular pressures, cupping of discs, and visual fields. DNA samples were used for a genome-wide screen using microsatellite markers.

RESULTS

Ten affected family members in 4 generations showed evidence of POAG including intraocular pressures of 22 mm Hg or more, and/or optic cup-disc ratios of 0.6 or more, and/or visual field defects consistent with glaucomatous damage. Primary open-angle glaucoma segregated as an autosomal dominant trait, with the disease locus mapping to 7q35-q36 between markers D7S2442 and D7S483 with a multipoint lod score of 4.06.

CONCLUSION

A sixth gene for POAG (GLC1F) has been mapped to 7q35-q36 in a family with at least 4 generations affected.

CLINICAL RELEVANCE

The mapping of this locus further confirms that primary open-angle glaucoma is a heterogeneous group of diseases with at least 6 different loci resulting in a similar phenotype. The eventual ability to classify which major POAG gene an affected person carries could have ramifications for selecting the most effective treatment regimen for that person.

Effect of matrix metalloproteinases activity on outflow in perfused human organ culture

PURPOSE

To test the hypothesis that extracellular matrix turnover, mediated by the matrix metalloproteinases, modulates aqueous humor outflow facility in a human outflow model.

METHODS

Matrix metalloproteinase activity was manipulated and outflow facility evaluated using perfused human anterior segment organ culture. Purified matrix metalloproteinases, tissue inhibitors of metalloproteinases (TIMPs), and several families of synthetic inhibitors of matrix metalloproteinases were added to the perfusion medium. Matrix metalloproteinase expression was increased by adding recombinant interleukin (IL)-1alpha. Kinetic inhibition analysis was conducted for stromelysin, gelatinase A, and gelatinase B with the various inhibitors. Live-dead staining was used to evaluate culture viability.

RESULTS

Increasing metalloproteinase activity, by adding purified metalloproteinases or by inducing their expression by IL-1alpha treatment, increased outflow facility. Inhibition of endogenous trabecular metalloproteinase activity using TIMP or several families of synthetic metalloproteinase inhibitors reduced outflow rates. The elevation and the reduction of outflow rates were reversible, with changes requiring 1 to 3 days. Kinetic enzyme inhibition analysis produced 50% inhibitory concentration values for these inhibitors that were compatible with the concentration ranges for outflow inhibition. CONCLUSIONS. The ability of several specific matrix metalloproteinase inhibitors to reduce outflow facility implies that endogenous extracellular matrix turnover by these enzymes was required for the maintenance of trabecular outflow resistance, at least in this human culture model. These observations provide support for the hypothesis that controlled extracellular matrix turnover is important in the regulation of aqueous humor outflow facility.

Prospects for genetic intervention in primary open-angle glaucoma

Recent advances in glaucoma genetics hold potential for dramatically changing the clinical care of glaucoma patients. To date, 5 primary open-angle glaucoma genes and 2 congenital glaucoma genes have been mapped. As more glaucoma genes are identified, earlier diagnosis for glaucoma should become more readily available. Progress in molecular genetics holds considerable promise for both current and future therapy of glaucoma. Glaucoma classification will be tailored to each individual based upon that person's family history, i.e. family glaucoma genotype. In the future, the optimum treatment for a specific glaucoma patient might rely on the knowledge of the phenotype of that person's causal gene, without having to resort to 'trial and error'. At this time, glaucoma treatment is restricted to lowering intraocular pressure. In the near future, with the knowledge of the pathophysiology caused by the defective glaucoma gene, more traditional drug treatments may be used to bypass the gene defect. Ultimately, gene therapy would replace the mutant gene with a normal one before visual loss has occurred as has been done with a model for retinitis pigmentosa, the retinal degeneration mouse.

Malattia leventinese: refinement of the genetic locus and phenotypic variability in autosomal dominant macular drusen

PURPOSE

To study the phenotypic variability in patients inheriting the disease gene for malattia leventinese (dominant macular drusen) and refine the localization of the gene.

METHODS

A family with dominant radial drusen was ascertained and studied with clinical examination and DNA linkage analysis. Inheritance of the disease gene was determined by DNA analysis and used to document the variability in phenotypic expression.

RESULTS

Fifty family members were studied with fundus photography and genotyping. Linkage analysis showed that the disease in this family was linked to chromosome 2p16-21 with a maximum lod score of 3.72 at D2S2153. An affected patient with obligate recombinations allowed refinement of the disease interval to a 6.2-cM region between D2S2227 and D2S378. The phenotype of older affected patients varied from severe geographic atrophy or subretinal fibrosis to a single druse adjacent to the optic disk. Small and medium-sized, nonradial, and soft macular drusen seen in four older individuals in the family were not specifically associated with the disease haplotype.

CONCLUSIONS

Refinement of the localization of the gene for malattia leventinese will facilitate its positional cloning. Genotypic documentation of the variable expression of the disease shows that a single, large, subretinal druse adjacent to the optic disk is consistent with inheritance of the disease gene. Soft macular drusen in low abundance were not specifically associated with inheritance of the disease gene. These results will facilitate the genetic counseling of patients with malattia leventinese. It is unknown what proportion of age-related macular degeneration arises from mutations in disease genes for dominant drusen.

Age-related macular degeneration. Clinical features in a large family and linkage to chromosome 1q

OBJECTIVES

To identify the chromosomal location of a disease-causing gene and to describe the clinical characteristics of a large family with age-related macular degeneration (ARMD).

METHODS

An ARMD pedigree was identified, and the disease state of family members was documented by stereoscopic fundus photography and was classified using a modified version of the Wisconsin Age-Related Maculopathy Grading System. A genome-wide screen at approximately 6-centimorgan spacing using a DNA-pooling strategy combined with shared-segment analysis was used to identify likely chromosomal regions. The entire family was then screened at each likely locus, and 1 positive locus was refined by screening with markers at an average density of 0.5 centimorgan and subjected to parametric linkage analysis.

RESULTS

In the 10 affected family members, ARMD was manifest by the presence of large, soft, confluent drusen accompanied by varying degrees of retinal pigment epithelial degeneration and/or geographic atrophy. Age-related macular degeneration segregated as an autosomal-dominant trait, with the disease locus mapping to chromosome 1q25-q31 between markers D1S466 and D1S413, with a multipoint lod score of 3.00.

CONCLUSION

Age-related macular degeneration localized to chromosome 1q25-q31 (gene symbol, ARMD1) as a dominant trait in a large family with a predominantly dry phenotype.

CLINICAL RELEVANCE

Identification of ARMD genes will facilitate early diagnosis and aid in understanding the molecular pathophysiological mechanisms of ARMD. This knowledge will contribute to the development of preventive and improved treatment strategies.

Growth factor and cytokine modulation of trabecular meshwork matrix metalloproteinase and TIMP expression

PURPOSE

We hypothesize that regulated trabecular extracellular matrix (ECM) turnover, initiated by the matrix metalloproteinases, is critical for the maintenance of normal aqueous humor outflow rates. However, very little is known about the regulation of trabecular ECM turnover. To identify candidate trabecular regulators, we evaluated the effects of several growth factors and cytokines on trabecular matrix metalloproteinase and TIMP expression.

METHODS

Porcine trabecular meshwork cells were treated with several doses of a variety of growth factors and cytokines and culture media was analyzed after 24, 48, and 72 h. Zymograms were used to evaluate stromelysin, gelatinase A and B activity levels, while immunoblots of Western transfers were used to evaluate stromelysin, collagenase, TIMP-1 and TIMP-2 protein levels.

RESULTS

A phorbol mitogen (TPA), and TNF alpha and beta, interleukin-1 alpha and PDGF BB stimulate gelatinase B, stromelysin, interstitial collagenase and TIMP-1 expression, while having negligible effects on gelatinase A expression; TIMP-2 levels are reduced by TNF but not affected by the other treatments. Acidic and basic FGF, IL-1 beta, TGF beta and PDGF AB produce similar but smaller effects, while HGF, VEGF, EGF, KGF, and LIF produce small to moderate elevations in stromelysin with minimal other responses. PDGF AA, gamma INF, oncostatin-M and endothelin-1 produce negligible changes in these proteinases and inhibitors.

CONCLUSIONS

In addition to providing potential ways to modulate trabecular metalloproteinase and TIMP levels, the responsiveness of these cells to some of these growth factors and cytokines suggests possible roles in normal or pathogenic trabecular cell regulation and some may affect aqueous humor outflow.

Insulin-like growth factor binding protein-5 expression by human trabecular meshwork

PURPOSE

The authors found transcript expression for insulin-like growth factor binding protein-5 (IGFBP-5) while screening for uniquely expressed trabecular meshwork (TM) mRNAs. Because the insulin-like growth factor (IGF) autocrine-paracrine system may provide an important signaling mechanism between TM cells and the outflow pathway, the expression of IGFBP-5 and IGF-I receptor in the TM was characterized.

METHODS

Poly(A+) RNA was isolated from cell cultures of human TM, ciliary body, retinal pigment epithelium, and skin fibroblasts and subjected to reverse transcription-polymerase chain reaction (RT-PCR) differential display analysis. A unique 980-bp band present in the TM was cloned and sequenced. Additional PCR and Northern analyses were used to define trabecular IGFBP-5 expression. Western immunoblots and confocal immunohistochemistry were used to evaluate the protein expression patterns of IGFBP-5 and the IGF-I receptor. IGF-I and IGF-II were added to trabecular cells in culture, and matrix metalloproteinase production was evaluated.

RESULTS

A unique differential display band was identified in the TM. Sequencing of this band identified it as the 3'-untranslated region of IGFBP-5. RT-PCR, using a variety of specific primers for IGFBP-5, Northern analysis, Western immunoblots, and immunohistochemical analysis, confirmed that IGFBP-5 was expressed in the TM. However, IGFBP-5 was also present at low levels in the ciliary body and skin fibroblasts by Northern and Western analysis, in contrast with the differential display findings. In addition, the IGF-I receptor was expressed by the TM and showed cell-surface staining by immunohistochemistry. Trabecular IGFBP-5 was distributed throughout the meshwork in the extracellular matrix and the cells with more staining in the juxtacanalicular region than in the uveal meshwork. IGF-I, but not IGF-II, modestly increased trabecular stromelysin and gelatinase B but not collagenase, gelatinase A, or tissue inhibitor of metalloproteinases 1 or 2.

CONCLUSIONS

IGFBP-5 and IGF-I receptor were expressed at significant levels by TM cells and may serve an important role in trabecular function.

Proteoglycan expression by human trabecular meshworks

PURPOSE

Proteoglycans may serve important roles in trabecular meshwork structure or function. Detailed molecular characterization and identification of specific trabecular proteoglycan core proteins has been limited.

METHODS

Radiolabeled proteoglycans were extracted from cultured human trabecular meshworks and subjected to ion exchange and molecular sieve chromatography. Peaks were subjected to glycosaminoglycan content analysis. Reverse transcription with polymerase chain reaction was used to identify trabecular mRNAs of several common proteoglycan core proteins. Western immunoblots of trabecular extracts were also utilized to identify these proteoglycan core proteins.

RESULTS

The proteoglycans elute from ion exchange columns at high salt and molecular sieve column profiles, and they exhibit broad peaks typical of the proteoglycan microheterogeneity seen in other tissues. The four common glycosaminoglycan side-chains were identified on these proteoglycans. Trabecular cells in organ or cell culture contain mRNAs coding for decorin, biglycan, versican, perlecan and a basement membrane glycoprotein, SPARC. Syndecan-1 transcripts were present at very low levels, while aggrecan transcripts were not detectable. Decorin, biglycan, versican and perlecan core proteins were also identified by immunoblots of trabecular cell extracts.

CONCLUSIONS

Several common proteoglycans are expressed by trabecular cells in organ explant or cell culture. Their general characteristics are not unlike those found in other tissues. These proteoglycans may serve important functions in the trabecular outflow pathway.

Mapping a gene for adult-onset primary open-angle glaucoma to chromosome 3q

Glaucoma is the third-leading cause of blindness in the world, affecting >13.5 million people. Adult-onset primary open-angle glaucoma (POAG) is the most common form of glaucoma in the United States. We present a family in which adult-onset POAG is inherited as an autosomal dominant trait. Twelve affected family members were identified from 44 at-risk individuals. The disease-causing gene was mapped to chromosome 3q21-24, with analysis of recombinant haplotypes suggesting a total inclusion region of 11.1 cM between markers D3S3637 and D3S1744. This is the first report of mapping of an adult-onset POAG gene to chromosome 3q, gene symbol GLC1C.

Discrete expression and distribution pattern of TIMP-3 in the human retina and choroid

PURPOSE

Extracellular matrix homeostasis is dependent in part upon a family of matrix metalloproteinases and their specific inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). Recently, gene defects in TIMP-3 have been identified in the affected individuals of several families with Sorsby's fundus dystrophy (SFD). Very little information is available regarding TIMP-3 function or even its existence in the retina or choroid.

METHODS

We used reverse transcription-polymerase chain reaction and Northern analysis to evaluate the expression of TIMP mRNA and Western immunoblots to evaluate TIMP protein produced by select cells of the human retina and choroid. We also used these methods and immunohistochemistry to localize the TIMPs in the retina and choroid.

RESULTS

TIMP-3 transcripts are found in cultured human retinal pigment epithelium (RPE), choroidal microcapillary endothelium and pericytes. RPE cells also express and secrete TIMP-3 protein, which is localized to the extracellular matrix and is not found in culture medium; TIMP-1 and -2 are found almost exclusively in the medium. Immunohistochemistry of human retina/choroid sections shows pronounced TIMP-3 immunostaining in Bruch's membrane, particularly near the surface of the RPE and endothelial cells, presumably in their basement membranes, with minimal staining in other portions of the retina. Immunostaining for TIMP-1 is absent and for TIMP-2 is much less prevalent, but detectable in Bruch's membrane.

CONCLUSIONS

TIMP-1, -2 and -3 exhibit distinctive expression patterns in the retina and choroid. This distribution and expression pattern partially explains why TIMP-3 mutations result in SFD, rather than other retinal pathologies, such as those associated with proliferative diabetic retinopathy.

Weill-Marchesani syndrome--possible linkage of the autosomal dominant form to 15q21.1

Weill-Marchesani syndrome comprises short stature, brachydactyly, microspherophakia, glaucoma, and ectopia lentis is regarded as an autosomal recessive trait (McKusick 277600). We present two families each with affected individuals in 3 generations demonstrating autosomal dominant inheritance of Weill-Marchesani syndrome. Linkage analysis in these 2 families suggests a gene for Weill-Marchesani syndrome maps to 15q21.1. The dislocated lenses and connective tissue disorder in these families suggests that fibrillin-1 and microfibril-associated protein 1, which both map to 15q21.1, are candidate genes for Weill-Marchesani syndrome. Immunohistochemistry staining of skin sections from family 1 showed an apparent decrease in fibrillin staining compared to control individuals.

Laser trabeculoplasty induces stromelysin expression by trabecular juxtacanalicular cells

PURPOSE

The mechanism by which laser trabeculoplasty reduces elevated intraocular pressure in primary open-angle glaucoma has been established. To test the hypothesis that trabecular extracellular matrix turnover is involved, stromelysin expression after laser treatment of anterior segment organ cultures was evaluated.

METHODS

Argon laser trabeculoplasty, using typical clinical treatment parameters, was applied to anterior segment organ cultures. Stromelysin levels and activity were then evaluated at various times by immunoblots of Western transfers and by zymography. Stromelysin mRNA levels were evaluated by dot blot and by reverse transcription, followed by polymerase chain reaction amplification. Stromelysin protein was localized by immunohistochemistry, and image analysis was used for quantitation. Stromelysin mRNA was localized by in situ hybridization.

RESULTS

Trabecular stromelysin protein, activity, and mRNA levels were detectably elevated by 8 hours and were several-fold higher by 24 hours after treatment. Stromelysin immunostaining was elevated dramatically in the juxtacanalicular and insert regions of the meshwork, but only modestly in other regions. Stromelysin mRNA increases also were localized primarily to these regions. The juxtacanalicular stromelysin immunostaining increase was sustained for at least 1 week, whereas the insert levels declined somewhat after day 2.

CONCLUSIONS

A stromelysin increase, localized primarily to the juxtacanalicular region of the meshwork, the putative site of the aqueous humor outflow resistance, should degrade trabecular proteoglycans, the putative outflow resistance source, and allow their uptake and further degradation by the juxtacanalicular cells. If diminished juxtacanalicular extracellular matrix turnover is responsible for the glaucomatous reduction in aqueous humor outflow, an increase in stromelysin in this specific area of the meshwork should ameliorate the problem. Thus, the observations support the working hypothesis and may explain the efficacy of this treatment for glaucoma.

Early changes in matrix metalloproteinases and inhibitors after in vitro laser treatment to the trabecular meshwork

Extracellular matrix turnover in the trabecular meshwork may play a role in regulating aqueous humor outflow. Laser trabeculoplasty is a common treatment for open-angle glaucoma. The mechanism of this treatment is not understood. We investigated changes in the levels and expression of the matrix metalloproteinases and their tissue inhibitors (TIMPs) in this tissue using cultured human anterior segment explants and standard clinical-parameter laser treatment. Medium gelatinase A activity levels are relatively high for sham-treated controls and are not changed dramatically following laser treatment. Medium gelatinase B and stromelysin activity levels are low in sham-treated explants and increase significantly by 24 h after treatment. TIMP1 levels, as assessed by immunoblots of Western transfers, are initially low. However, by 24 h TIMP1 levels have increased significantly. Using semi-quantitative reverse transcription and the polymerase chain reaction, mRNA levels of stromelysin, gelatinase B and TIMP1 are shown to increase after laser treatment, while gelatinase A and TIMP2 remain relatively constant. The increases in trabecular stromelysin and gelatinase B in response to laser trabeculoplasty may have important implications for the mechanism of action of this treatment for open-angle glaucoma.