Immunolocalisation of opticin in the human eye

Intravitreal administration of recombinant human opticin protects against hyperoxia-induced pre-retinal neovascularization

Opticin is an extracellular glycoprotein present in the vitreous. Its antiangiogenic properties offer the potential for therapeutic intervention in conditions such as proliferative diabetic retinopathy and retinopathy of prematurity. Here, we investigated the hypothesis that intravitreal administration of recombinant human opticin can safely protect against the development of pathological angiogenesis and promote its regression. We generated and purified recombinant human opticin and investigated its impact on the development and regression of pathological retinal neovascularization following intravitreal administration in murine oxygen-induced retinopathy. We also investigated its effect on normal retinal vascular development and function, following intravitreal injection in neonatal mice, by histological examination and electroretinography. In oxygen-induced retinopathy, intravitreal administration of human recombinant opticin protected against the development of retinal neovascularization to similar extent as aflibercept, which targets VEGF. Opticin also accelerated regression of established retinal neovascularization, though the effect at 18 h was less than that of aflibercept. Intravitreal administration of human recombinant opticin in neonatal mice caused no detectable perturbation of subsequent retinal vascular development or function. In summary we found that intraocular administration of recombinant human opticin protects against the development of pathological angiogenesis in mice and promotes its regression.

Decreased endostatin in db/db retinas is associated with optic disc intravitreal vascularization

Endostatin, a naturally cleaved fragment of type XVIII collagen with antiangiogenic activity, has been involved in the regulation of neovascularization during diabetic retinopathy. Here, the intracellular distribution of endostatin in healthy mouse and human neuroretinas has been analyzed. In addition, to study the effect of experimental hyperglycemia on retinal endostatin, the db/db mouse model has been used. Endostatin protein expression in mouse and human retinas was studied by immunofluorescence and Western blot, and compared with db/db mice. Eye fundus angiography, histology, and immunofluorescence were used to visualize mouse retinal and intravitreal vessels. For the first time, our results revealed the presence of endostatin in neurons of mouse and human retinas. Endostatin was mainly expressed in bipolar cells and photoreceptors, in contrast to the optic disc, where endostatin expression was undetectable. Diabetic mice showed a reduction of endostatin in their retinas associated with the appearance of intravitreal vessels at the optic disc in 50% of db/db mice. Intravitreal vessels showed GFAP positive neuroglia sheath, basement membrane thickening by collagen IV deposition, and presence of MMP-2 and MMP-9 in the vascular wall. All together, these results point that decreased retinal endostatin during experimental diabetes is associated with optic disc intravitreal vascularization. Based on their phenotype, these intravitreal vessels could be neovessels. However, it cannot be ruled out the possibility that they may also represent persistent hyaloid vessels.

Small Leucine-Rich Proteoglycans (SLRPs) in the Retina

Retinal diseases such as age-related macular degeneration (AMD), retinopathy of prematurity (ROP), and diabetic retinopathy (DR) are the leading causes of visual impairment worldwide. There is a critical need to understand the structural and cellular components that play a vital role in the pathophysiology of retinal diseases. One potential component is the family of structural proteins called small leucine-rich proteoglycans (SLRPs). SLRPs are crucial in many fundamental biological processes involved in the maintenance of retinal homeostasis. They are present within the extracellular matrix (ECM) of connective and vascular tissues and contribute to tissue organization and modulation of cell growth. They play a vital role in cell–matrix interactions in many upstream signaling pathways involved in fibrillogenesis and angiogenesis. In this comprehensive review, we describe the expression patterns and function of SLRPs in the retina, including Biglycan and Decorin from class I; Fibromodulin, Lumican, and a Proline/arginine-rich end leucine-rich repeat protein (PRELP) from class II; Opticin and Osteoglycin/Mimecan from class III; and Chondroadherin (CHAD), Tsukushi and Nyctalopin from class IV.

Cell-Matrix Interactions in the Eye: From Cornea to Choroid

The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.

Novel Outcome Biomarkers Identified With Targeted Proteomic Analyses of Plasma From Critically Ill Coronavirus Disease 2019 Patients

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Coronavirus disease 2019 patients admitted to the ICU have high mortality. The host response to coronavirus disease 2019 has only been partially elucidated, and prognostic biomarkers have not been identified. We performed targeted proteomics on critically ill coronavirus disease 2019 patients to better understand their pathophysiologic mediators and to identify potential outcome markers.

Intravitreal Pharmacokinetic Study of the Antiangiogenic Glycoprotein Opticin

Opticin is an endogenous vitreous glycoprotein that may have therapeutic potential as it has been shown that supranormal concentrations suppress preretinal neovascularization. Herein we investigated the pharmacokinetics of opticin following intravitreal injection in rabbits. To measure simultaneously concentrations of human and rabbit opticin, a selected reaction monitoring mass spectrometry assay was developed. The mean concentration of endogenous rabbit opticin in 7 uninjected eyes was measured and found to be 19.2 nM or 0.62 μg/mL. When the vitreous was separated by centrifugation into a supernatant and collagen-containing pellet, 94% of the rabbit opticin was in the supernatant. Intravitreal injection of human opticin (40 μg) into both eyes of rabbits was followed by enucleation at 5, 24, and 72 h and 7, 14, and 28 days postinjection (n = 6 at each time point) and measurement of vitreous human and rabbit opticin concentrations in the supernatant and collagen-containing pellet following centrifugation. The volume of distribution of human opticin was calculated to be 3.31 mL, and the vitreous half-life was 4.2 days. Assuming that rabbit and human opticin are cleared from rabbit vitreous at the same rate, opticin is secreted into the vitreous at a rate of 0.14 μg/day. We conclude that intravitreally injected opticin has a vitreous half-life that is similar to currently available antiangiogenic therapeutics. While opticin was first identified bound to vitreous collagen fibrils, here we demonstrate that >90% of endogenous opticin is not bound to collagen. Endogenous opticin is secreted by the nonpigmented ciliary epithelium into the rabbit vitreous at a remarkably high rate, and the turnover in vitreous is approximately 15% per day.

Vitreous and Vision Degrading Myodesopsia

Macromolecules comprise only 2% of vitreous, yet are responsible for its gel state, transparency, and physiologic function(s) within the eye. Myopia and aging alter collagen and hyaluronan association causing concurrent gel liquefaction and fibrous degeneration. The resulting vitreous opacities and collapse of the vitreous body during posterior vitreous detachment are the most common causes for the visual phenomenon of vitreous floaters. Previously considered innocuous, the vitreous opacities that cause floaters sometimes impact vision by profoundly degrading contrast sensitivity function and impairing quality-of-life. While many people adapt to vitreous floaters, clinically significant cases can be diagnosed with Vision Degrading Myodesopsia based upon echographic assessment of vitreous structure and by measuring contrast sensitivity function. Perhaps due to the ubiquity of floaters, the medical profession has to date largely ignored the plight of those with Vision Degrading Myodesopsia. Improved diagnostics will enable better disease staging and more accurate identification of severe cases that merit therapy. YAG laser treatments may occasionally be slightly effective, but vitrectomy is currently the definitive cure. Future developments will usher in more informative diagnostic approaches as well as safer and more effective therapeutic strategies. Improved laser treatments, new pharmacotherapies, and possibly non-invasive optical corrections are exciting new approaches to pursue. Ultimately, enhanced understanding of the underlying pathogenesis of Vision Degrading Myodesopsia should result in prevention, the ultimate goal of modern Medicine.

Amblyopia treatment and quality of life: the child's perspective on atropine versus patching

Background: The impact on children of patching versus atropine treatment for amblyopia was assessed using children's perspective Health-Related Quality of Life (HRQoL) scores in 5 to 7-year olds. Methods: Forty-six children on the threshold of commencing either patching or atropine treatment for amblyopia were recruited. Treatment was prescribed for uniocular amblyopia of visual acuity (VA) 0.2 logMAR or worse. After four weeks of their chosen treatment, each child completed the Child Amblyopia Treatment Quality-of-Life Questionnaire (CAT-QoL). The Pediatric Quality of Life Inventory (PedsQL™), Young Child (5-7) Self-Report version, was completed before and after four weeks of treatment. Quality of life scores were compared between the two treatment groups. Results: Sixty-one percent (n = 28) of participants were male and 56.5% (n = 26) were white British. The CAT-QoL has a range of 0-16, with 16 being the worst quality of life. No significant difference was found between the patching group (n = 30, mean age 69.7 months) and the atropine group (n = 16, mean age 69.3 months) for CAT-QoL quality of life scores (Patch median = 6.3, Atropine median = 5.6, U = 199, p = .341, 95% CI of the median difference of -2.3 to 0.9). The Young Child (5-7) Self-Report version of the PedsQL™ has a 'total score' range of 0-100, with 0 being the worst quality of life. There was also no significant difference in PedsQL™ quality of life total scores (Patch median = 80, Atropine median = 83.33, U = 239.5, p = .991, 95% CI of the median difference -13.33 to 10) after four weeks of treatment. Conclusion: Amblyopic children reported that patching and atropine treatments did not have a significant impact on their quality of life. Patching and atropine should continue to be offered as first-line treatments for amblyopia, as children appear to tolerate both well and do not favor one over the other.

Proteomic Analysis of the Bovine and Human Ciliary Zonule

Purpose

The zonule of Zinn (ciliary zonule) is a system of fibers that centers the crystalline lens on the optical axis of the eye. Mutations in zonule components underlie syndromic conditions associated with a broad range of ocular pathologies, including microspherophakia and ectopia lentis. Here, we used HPLC-mass spectrometry to determine the molecular composition of the zonule.

Methods

Tryptic digests of human and bovine zonular samples were analyzed by HPLC-mass spectrometry. The distribution of selected components was confirmed by immunofluorescence confocal microscopy. In bovine samples, the composition of the equatorial zonule was compared to that of the hyaloid zonule and vitreous humor.

Results

The 52 proteins common to the zonules of both species accounted for >95% of the zonular protein. Glycoproteins constituted the main structural components, with two proteins, FBN1 and LTBP2, constituting 70%-80% of the protein. Other abundant components were MFAP2, EMILIN-1, and ADAMTSL-6. Lysyl oxidase-like 1, a crosslinking enzyme implicated in collagen and elastin biogenesis, was detected at significant levels. The equatorial and hyaloid zonular samples were compositionally similar to each other, although the hyaloid sample was relatively enriched in the proteoglycan opticin and the fibrillar collagens COL2A1, COL11A1, COL5A2, and COL5A3.

Conclusions

The zonular proteome was surprisingly complex. In addition to structural components, it contained signaling proteins, protease inhibitors, and crosslinking enzymes. The equatorial and hyaloid zonules were similar in composition, but the latter may form part of a composite structure, the hyaloid membrane, that stabilizes the vitreous face.

Characterization of Vitreous and Aqueous Proteome in Humans With Proliferative Diabetic Retinopathy and Its Clinical Correlation

Aims:

Proliferative diabetic retinopathy (PDR) is associated with microvascular complications that cause biochemical changes in the human retina and alter the proteome of vitreous humor and aqueous humor (AH).

Methods:

Human vitreous humor and AH of PDR subjects were collected. Subjects who had surgery for epiretinal membrane or macular hole served as controls. Protein profiles were obtained and analyzed after running the samples on a liquid chromatography-mass spectrometry/mass spectrometry.

Results:

In vitreous humor, 16 unique proteins were noted in PDR patients, but not in controls. Those were associated mainly with coagulation, complement, and kallikrein-kinin systems. Under coagulation, fibrinogen and prothrombin proteins were more evident and may emphasize the importance of angiogenesis in the development of PDR. Vitreous proteins showed replicative presence in AH too. As for AH samples, we detected 10 proteins found in PDR patients, which were related to transport, coagulation, and inflammatory responses.

Conclusions:

We found 57 proteins in human vitreous and 39 proteins in AH. Identification of these proteins that are involved in various pathways will be helpful to understand diabetic retinopathy pathogenesis and to develop proteome as a biomarker for PDR.

Vitreous Substitutes: Old and New Materials in Vitreoretinal Surgery

Recent developments in vitreoretinal surgery have increased the need for suitable vitreous substitutes. A successful substitute should maintain all the physical and biochemical properties of the original vitreous, be easy to manipulate, and be long lasting. Substitutes can be gaseous or liquid, both of which have associated advantages and disadvantages related to their physical properties and use. Furthermore, new surgical techniques with smaller vitreoretinal instruments have driven the use of more viscous substitutes. In this review, we analyze and discuss the most frequently used vitreous substitutes and look ahead to future alternatives. We classify these compounds based on their composition and structure, discuss their clinical use with respect to their associated advantages and disadvantages, and analyze how new vitreoretinal surgical techniques have modified their use.

Proteomic Analysis of Vitreous Humor in Retinal Vein Occlusion

Purpose

To analyze the protein profile of human vitreous of untreated patients with retinal vein occlusion (RVO).

Methods

Sixty-eight vitreous humor (VH) samples (44 from patients with treatment naïve RVO, 24 controls with idiopathic floaters) were analyzed in this clinical-experimental study using capillary electrophoresis coupled to mass spectrometer and tandem mass spectrometry. To define potential candidate protein markers of RVO, proteomic analysis was performed on RVO patients (n = 30) and compared with controls (n = 16). To determine validity of potential biomarker candidates in RVO, receiver operating characteristic (ROC) was performed by using proteome data of independent RVO (n = 14) and control samples (n = 8).

Results

Ninety-four different proteins (736 tryptic peptides) could be identified. Sixteen proteins were found to be significant when comparing RVO and control samples (P = 1.43E-05 to 4.48E-02). Five proteins (Clusterin, Complement C3, Ig lambda-like polypeptide 5 (IGLL5), Opticin and Vitronectin), remained significant after using correction for multiple testing. These five proteins were also detected significant when comparing subgroups of RVO (central RVO, hemi-central RVO, branch RVO) to controls. Using independent samples ROC-Area under the curve was determined proving the validity of the results: Clusterin 0.884, Complement C3 0.955, IGLL5 1.000, Opticin 0.741, Vitronectin 0.786. In addition, validation through ELISA measurements was performed.

Conclusion

The results of the study reveal that the proteomic composition of VH differed significantly between the patients with RVO and the controls. The proteins identified may serve as potential biomarkers for pathogenesis induced by RVO.

Proteomics of vitreous in neovascular age-related macular degeneration

Neovascular age-related macular degeneration (nAMD) has been described as a predominantly inflammatory and proangiogenic retino-choroidal disease. Vitreous humor (VH) is the adjacent and accessible compartment which, due to the vicinity to the retina, might best represent changes of protein-based mediators of nAMD. The aim of this clinical-experimental study was to analyze the nAMD associated VH proteome of previously untreated patients whilst taking different groups of nAMD into account, based on their clinical presentation (clinical diagnosis groups). Electrophoresis coupled online to mass spectrometry (CE-MS) as well as liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) were used to analyze VH of 108 nAMD patients and 24 controls with idiopathic floaters. A total of 101 different proteins with at least two unique peptides could be identified. Using a stringent statistical analysis with implementation of the closed test principle, we were able to identify four proteins that may be involved in the pathophysiology of nAMD: Clusterin, opticin, pigment epithelium-derived factor and prostaglandin-H2 d-isomerase. Using independent samples, ROC-Area under the curve was determined proving the validity of the results: Clusterin 0.747, opticin 0.656, pigment epithelium-derived factor 0.514, prostaglandin-H2 d-isomerase 0.712. In addition, validation through ELISA measurements was performed. The identified proteins may serve as potential biomarkers or even targets of therapy for nAMD.

Retinal Changes Induced by Epiretinal Tangential Forces

Two kinds of forces are active in vitreoretinal traction diseases: tangential and anterior-posterior forces. However, tangential forces are less characterized and classified in literature compared to the anterior-posterior ones. Tangential epiretinal forces are mainly due to anomalous posterior vitreous detachment (PVD), vitreoschisis, vitreopapillary adhesion (VPA), and epiretinal membranes (ERMs). Anomalous PVD plays a key role in the formation of the tangential vectorial forces on the retinal surface as consequence of gel liquefaction (synchysis) without sufficient and fast vitreous dehiscence at the vitreoretinal interface. The anomalous and persistent adherence of the posterior hyaloid to the retina can lead to vitreomacular/vitreopapillary adhesion or to a formation of avascular fibrocellular tissue (ERM) resulting from the proliferation and transdifferentiation of hyalocytes resident in the cortical vitreous remnants after vitreoschisis. The right interpretation of the forces involved in the epiretinal tangential tractions helps in a better definition of diagnosis, progression, prognosis, and surgical outcomes of vitreomacular interfaces.

The Ultrastructural Localization of Type II, IV, and VI Collagens at the Vitreoretinal Interface

Background

The vitreoretinal interface is the border of the cortical vitreous and the inner surface of the retina. The adhesion of the cortical vitreous to the ILM, namely vitreoretinal adhesion, involves a series of complex molecular adhesion mechanisms and has been considered as an important pathogenic factor in many vitreoretinal diseases. The presence of type VI collagen at the vitreoretinal interface and its possible interaction with collagens and glycoproteins indicates that type VI collagen may contribute to the vitreoretinal adhesion.

Purpose

To clarify the ultrastructural location of type VI collagen and its relationship to type II and IV collagens at the vitreoretinal interface.

Methods

The ultrastructural localization of type II, IV and VI collagens in the adult human vitreoretinal interface of five donor eyes was evaluated by transmission electron microscopy using immunogold labeling.

Results

In the pre-equatorial region, we observed densely packed vitreous lamellae with a partly intraretinal course containing type II and VI collagens, reticular structures containing type IV and VI collagens and a thin inner limiting membrane (ILM) containing type IV and VI collagens in a linear distribution pattern. From the anterior to the posterior retina, the linear pattern of type IV and VI collagen labeling gradually became more diffusely present throughout the entire thickness of the ILM.

Conclusions

The presence of type VI collagen in vitreous lamellae penetrating the ILM into the superficial retina suggests that type VI collagen may be involved in the organization of vitreous fibers into lamellae and in the adhesion of the vitreous fibers to the retina. The close relation of type VI to type IV collagen in the ILM suggests that type VI collagen is an important collagen type in the ILM. The topographic variations of type IV and VI collagens in the different regions of the ILM suggest a regional heterogeneity of the ILM. The reticular labeling pattern of type IV and VI collagens observed in the anterior vitreous are highly similar to labeling patterns of blood vessel walls. In the anterior vitreous, they may represent remnants of the regressed embryonic hyaloid blood vessel system. Their presence is in support of the theory on interactive remodeling of the developing vitreous as opposed to the main stream theory of displacement and compression of the primary by the secondary vitreous.

The role of extracellular matrix in retinal vascular development and preretinal neovascularization

Extracellular matrix (ECM) plays a central role in angiogenesis. ECM degrading enzymes breakdown the pre-existing vascular basement membrane at an early stage of angiogenesis and subsequently degrade stromal ECM as the new vessels invade into tissues. Conversely certain ECM components including collagen, fibronectin or fibrin are required for endothelial cell migration and tube morphogenesis. As the new vessels form they lay down a basement membrane that surrounds the endothelial tubes and is essential for their stability. In the rodent eye the transient expression of fibronectin and matricellular proteins plays a key role in retinal vascular development. In pathological retinal angiogenesis, such as in proliferative diabetic retinopathy, preretinal neovascularization occurs where new blood vessels invade the cortical vitreous gel and these blood vessels require vitreous collagen for their growth. The vitreous is normally anti-angiogenic and contains endogenous ECM inhibitors of angiogenesis including opticin and thombospondins, and ECM fragments such as endostatin. In preretinal neovascularization, the combined anti-angiogenic effects of these molecules are overcome by an excess of growth factors such as vascular endothelial growth factor-A, and new vessels grow into the vitreous with potentially blinding sequelae.

Complement factor H, vitronectin, and opticin are tyrosine-sulfated proteins of the retinal pigment epithelium

Lack of tyrosine sulfation of ocular proteins results in disorganized photoreceptor structure and drastically reduced visual function, demonstrating the importance of this post-translational modification to vision. To understand the role that tyrosine sulfation plays in the function of ocular proteins, we identified some tyrosine-sulfated proteins in the retinal pigment epithelium using two independent methods, immuno-affinity column purification with an anti-sulfotyrosine specific antibody and computer-based sequence analysis of retinal pigment epithelium secretome by means of the prediction program Sulfinator. Radioactive labeling followed by thin layer electrophoresis revealed that three proteins, vitronectin, opticin, and complement factor H (CFH), were post-translationally modified by tyrosine sulfation. The identification of vitronectin and CFH as tyrosine-sulfated proteins is significant, since both are deposited in drusen in the eyes of patients with age-related macular degeneration (AMD). Furthermore, mutations in CFH have been determined to be a major risk factor in the development of AMD. Future studies that seek to understand the role of CFH in the development of AMD should take into account the role that tyrosine sulfation plays in the interaction of this protein with its partners, and examine whether modulating sulfation provides a potential therapeutic target.

Proteomic analysis of human vitreous humor

Background

The vitreous humor is a transparent, gelatinous mass whose main constituent is water. It plays an important role in providing metabolic nutrient requirements of the lens, coordinating eye growth and providing support to the retina. It is in close proximity to the retina and reflects many of the changes occurring in this tissue. The biochemical changes occurring in the vitreous could provide a better understanding about the pathophysiological processes that occur in vitreoretinopathy. In this study, we investigated the proteome of normal human vitreous humor using high resolution Fourier transform mass spectrometry.

Results

The vitreous humor was subjected to multiple fractionation techniques followed by LC-MS/MS analysis. We identified 1,205 proteins, 682 of which have not been described previously in the vitreous humor. Most proteins were localized to the extracellular space (24%), cytoplasm (20%) or plasma membrane (14%). Classification based on molecular function showed that 27% had catalytic activity, 10% structural activity, 10% binding activity, 4% cell and 4% transporter activity. Categorization for biological processes showed 28% participate in metabolism, 20% in cell communication and 13% in cell growth. The data have been deposited to the ProteomeXchange with identifier PXD000957.

Conclusion

This large catalog of vitreous proteins should facilitate biomedical research into pathological conditions of the eye including diabetic retinopathy, retinal detachment and cataract.

Review of application of mass spectrometry for analyses of anterior eye proteome

Proteins have important functional roles in the body, which can be altered in disease states. The eye is a complex organ rich in proteins; in particular, the anterior eye is very sophisticated in function and is most commonly involved in ophthalmic diseases. Proteomics, the large scale study of proteins, has greatly impacted our knowledge and understanding of gene function in the post-genomic period. The most significant breakthrough in proteomics has been mass spectrometric identification of proteins, which extends analysis far beyond the mere display of proteins that classical techniques provide. Mass spectrometry functions as a “mass analyzer” which simplifies the identification and quantification of proteins extracted from biological tissue. Mass spectrometric analysis of the anterior eye proteome provides a differential display for protein comparison of normal and diseased tissue. In this article we present the key proteomic findings in the recent literature related to the cornea, aqueous humor, trabecular meshwork, iris, ciliary body and lens. Through this we identified unique proteins specific to diseases related to the anterior eye.

Idiopathic vitreomacular traction and macular hole: a comprehensive review of pathophysiology, diagnosis, and treatment

Posterior vitreous detachment (PVD) is a common phenomenon in the aging eye. However, this may be complicated by persistent symptomatic vitreomacular adhesions that exert tractional forces on the macula (vitreomacular traction; VMT). VMT itself may be associated with epiretinal membrane formation and the development of idiopathic macular holes (IMH). Such pathologies may cause visual disturbances, including metamorphopsia, photopsia, blurred vision, and decreased visual acuity, which impact an individual's quality of life. Technologies such as optical coherence tomography allow an increasingly more accurate visualisation of the macular anatomy, including quantification of macular hole characteristics, and this facilitates treatment decision-making. Pars plana vitrectomy remains the primary treatment option for many patients with VMT or IMH; for the latter, peeling of the inner limiting membrane (ILM) of the retina has shown improved outcomes when compared with no ILM peeling. The development of narrow-gauge transconjunctival vitrectomy systems has improved the rate of visual recovery following surgery. Ocriplasmin, by degrading laminin and fibronectin at the vitreoretinal interface, may allow induction of PVD in a non-invasive manner. Indeed, clinical studies have supported its use as an alternative to surgery in certain patient populations. However, further research is still needed with respect to greater understanding of the pathophysiology underlying the development of VMT and IMH.

Characterizing the normal proteome of human ciliary body

BACKGROUND

The ciliary body is the circumferential muscular tissue located just behind the iris in the anterior chamber of the eye. It plays a pivotal role in the production of aqueous humor, maintenance of the lens zonules and accommodation by changing the shape of the crystalline lens. The ciliary body is the major target of drugs against glaucoma as its inhibition leads to a drop in intraocular pressure. A molecular study of the ciliary body could provide a better understanding about the pathophysiological processes that occur in glaucoma. Thus far, no large-scale proteomic investigation has been reported for the human ciliary body.

RESULTS

In this study, we have carried out an in-depth LC-MS/MS-based proteomic analysis of normal human ciliary body and have identified 2,815 proteins. We identified a number of proteins that were previously not described in the ciliary body including importin 5 (IPO5), atlastin-2 (ATL2), B-cell receptor associated protein 29 (BCAP29), basigin (BSG), calpain-1 (CAPN1), copine 6 (CPNE6), fibulin 1 (FBLN1) and galectin 1 (LGALS1). We compared the plasma proteome with the ciliary body proteome and found that the large majority of proteins in the ciliary body were also detectable in the plasma while 896 proteins were unique to the ciliary body. We also classified proteins using pathway enrichment analysis and found most of proteins associated with ubiquitin pathway, EIF2 signaling, glycolysis and gluconeogenesis.

CONCLUSIONS

More than 95% of the identified proteins have not been previously described in the ciliary body proteome. This is the largest catalogue of proteins reported thus far in the ciliary body that should provide new insights into our understanding of the factors involved in maintaining the secretion of aqueous humor. The identification of these proteins will aid in understanding various eye diseases of the anterior segment such as glaucoma and presbyopia.

Characterization of opticin digestion by proteases involved in osteoarthritis development

OBJECTIVE

Opticin is a class III member of the small leucine-rich repeat proteoglycan (SLRP) family, produced in articular joint tissues. In normal and osteoarthritic (OA) cartilage, opticin is degraded. This study aimed to assess whether human cartilage opticin is degraded by the main proteases involved in OA pathophysiology, and to determine the protease cleavage sites of this SLRP.

METHODS

We analyzed the proteolytic activity of matrix metalloproteinases (MMPs)-1, -2, -3, -7, -8 and -9, and ADAMTS-4 and -5 on proteoglycan extracts from normal and moderately fibrillated OA human cartilage, and on recombinant human opticin. Opticin degradation was analyzed by Western blotting and cleavage sites were determined by sequence analysis.

RESULTS

All eight proteases digested opticin from proteoglycan extracts from both normal and OA samples, as well as recombinant human opticin, MMP-2 and MMP-7 are the proteases that degrade recombinant human opticin most efficiently. The opticin cleavage site determined for these MMPs was between the glycosylation and leucine-rich repeat domains. MMP-7 had two additional digestion sites near the N-terminal end of opticin.

CONCLUSION

Opticin is a substrate for several MMPs and aggrecanases involved during OA cartilage degradation, and seems to be a preferential substrate for MMP-7. The role of opticin in cartilage degeneration could be related to decreased levels of intact opticin, followed by its proteolytic degradation, which in turn may stimulate some of the modifications observed in the OA cartilage, such as neovascularisation and changes in the extracellular matrix.

Mapping the differential distribution of proteoglycan core proteins in the adult human retina, choroid, and sclera

PURPOSE

To examine the presence and distribution of proteoglycan (PG) core proteins in the adult human retina, choroid, and sclera.

METHODS

Postmortem human eye tissue was dissected into Bruch's membrane/choroid complex, isolated Bruch's membrane, or neurosensory retina. PGs were extracted and partially purified by anion exchange chromatography. Trypsinized peptides were analyzed by tandem mass spectrometry and PG core proteins identified by database search. The distribution of PGs was examined by immunofluorescence microscopy on human macular tissue sections.

RESULTS

The basement membrane PGs perlecan, agrin, and collagen-XVIII were identified in the human retina, and were present in the internal limiting membrane, blood vessel walls, and Bruch's membrane. The hyalectans versican and aggrecan were also detected. Versican was identified in Bruch's membrane, while aggrecan was distributed throughout the retina, choroid, and sclera. The cartilage link protein HAPLN1 was abundant in the interphotoreceptor matrix and sclera, while HAPLN4 (brain link protein 2) was found throughout the retina and choroid. The small leucine-rich repeat PG (SLRP) family members biglycan, decorin, fibromodulin, lumican, mimecan, opticin, and prolargin were present, with different patterns of distribution in the retina, choroid, and sclera.

CONCLUSIONS

A combination of proteomics and immunohistochemistry approaches has provided for the first time a comprehensive analysis of the presence and distribution of PG core proteins throughout the human retina, choroid, and sclera. This complements our knowledge of glycosaminoglycan chain distribution in the human eye, and has important implications for understanding the structure and functional regulation of the eye in health and disease.

Opticin exerts its anti-angiogenic activity by regulating extracellular matrix adhesiveness

Opticin is an extracellular matrix glycoprotein that we identified associated with the collagen network of the vitreous humor of the eye. Recently, we discovered that opticin possesses anti-angiogenic activity using a murine oxygen-induced retinopathy model: here, we investigate the underlying mechanism. Using an ex vivo chick chorioallantoic membrane assay, we show that opticin inhibits angiogenesis when stimulated by a range of growth factors. We show that it suppresses capillary morphogenesis, inhibits endothelial invasion, and promotes capillary network regression in three-dimensional matrices of collagen and Matrigel(TM). We then show that opticin binds to collagen and thereby competitively inhibits endothelial cell interactions with collagen via α(1)β(1) and α(2)β(1) integrins, thereby preventing the strong adhesion that is required for proangiogenic signaling via these integrins.

Opticin production is reduced by hypoxia and VEGF in human retinal pigment epithelium via MMP-2 activation

Opticin, a small leucine rich repeat protein (SLRP) contributes to vitreoretinal adhesion. This study was conducted to investigate the effects of hypoxia and vascular endothelial growth factor (VEGF) on matrix metalloproteinase (MMP) mediated opticin production in retinal pigment epithelium (RPE) cells. Primary cultured human RPE cells were treated with hypoxia (low oxygen and cobalt chloride) or VEGF (0-100 ng/mL). The mRNA levels of opticin and the protein levels of intra and extracellular opticin in RPE cells were examined by RT-PCR and Western blot assay, respectively. Furthermore, the MMP activity was analyzed by zymography, and EDTA was used as an MMP inhibitor. Analysis of the effect of MMP-2 on opticin was performed by recombinant human (rh) MMP-2 stimulation in RPE cultures and by human vitreous sample digestion with activated rhMMP-2. Our results showed that opticin was expressed by primary cultured human RPE cells. Hypoxia and VEGF stimulation did not alter opticin mRNA and protein expression in RPE cells, but markedly decreased the protein levels of extracellular opticin following increased latent MMP-2 activity. The VEGF- and hypoxia induced opticin degradation in the culture medium was blocked by EDTA. Together, opticin levels in the culture medium were also reduced after rhMMP-2 treatment. In addition, opticin in human vitreous samples could be cleaved by rhMMP-2. These results reveal that VEGF and hypoxia could decrease opticin protein levels in the human RPE secretome, and that opticin may be an enzymatic substrate for MMP-2.

The vitreous glycoprotein opticin inhibits preretinal neovascularization

PURPOSE

Opticin is an extracellular matrix glycoprotein that the authors discovered in the vitreous humor of the eye. It is synthesized by the nonpigmented ciliary epithelium and secreted into the vitreous cavity and, unusually for an extracellular matrix molecule, high-level synthesis is maintained into adult life. Here the authors investigated the hypothesis that opticin influences vascular development in the posterior segment of the eye and pathologic angiogenesis into the normally avascular, mature (secondary) vitreous.

METHODS

Opticin was localized in murine eyes by immunohistochemistry. An opticin knockout mouse was established and vascular development was compared between knockout and wild-type mice. Wild-type and opticin null mice were compared in the oxygen-induced retinopathy model, a model of pathologic angiogenesis, and this model was also used to assess the effects of intravitreal injection of recombinant opticin into eyes of wild-type mice.

RESULTS

Opticin colocalizes with the collagen type II-rich fibrillar network of the vitreous, the inner limiting lamina, the lens capsule, the trabecular meshwork, and the iris. Analyses of the hyaloid and retinal vasculature showed that opticin has no effect on hyaloid vascular regression or developmental retinal vascularization. However, using the oxygen-induced retinopathy model, the authors demonstrated that opticin knockout mice produce significantly more preretinal neovascularization than wild-type mice, and the intravitreal delivery of excess opticin inhibited the formation of neovessels in wild-type mice.

CONCLUSIONS

A lack of opticin does not influence vascular development, but opticin is antiangiogenic and inhibits preretinal neovascularization.

Pathogenesis of rhegmatogenous retinal detachment: predisposing anatomy and cell biology

BACKGROUND

The pathogenesis of rhegmatogenous retinal detachment is complex, and our knowledge of the exact mechanism of vitreoretinal attachment and detachment remains incomplete.

METHODS

We performed a Medline, Ovid, and EMBASE search using search words rhegmatogenous, retinal detachment, vitreous, and retinal adhesion. All appropriate articles were reviewed, and the evidence was compiled.

RESULTS

Cortical vitreous contains fibrillar collagens type II, V/XI, and IX. The inner limiting membrane of the retina contains collagens type I, IV, VI, and XVIII as well as numerous other glycoproteins and potential adhesion molecules. The distribution and age-related changes in the structure of these molecules play an important role in the formation of a retinal break, which may compromise and disrupt the normal mechanisms of neurosensory retinal adhesion.

CONCLUSION

Rhegmatogenous retinal detachment development is intimately related to changes in the fibrillar structure of the aging vitreous culminating in posterior vitreous detachment with regions of persistent and tangential vitreoretinal traction predisposing to retinal tear formation. A complex interplay of factors such as weakening of vitreoretinal adhesion, posterior migration of the vitreous base, and molecular changes at the vitreoretinal interface are important in predisposing to focal areas of vitreoretinal traction precipitating rhegmatogenous retinal detachment. Once formed, the passage of liquefied vitreous through a retinal break may overwhelm normal neurosensory-retinal pigment epithelium adhesion perpetuating and extending detachment and causing visual loss. To understand the molecular events underlying rhegmatogenous retinal detachment so that new therapies can be developed, it is important to appreciate the structural organization of the vitreous, the biology underlying vitreous liquefaction and posterior vitreous detachment, and the mechanisms of vitreoretinal attachment and detachment.

Identification of differentially expressed proteins in the aqueous humor of primary congenital glaucoma

Primary Congenital Glaucoma (PCG) is an autosomal recessive disease caused by an abnormal development of the anterior chamber angle. Although, PCG has been linked to several genetic loci, the role that the genes at these loci or their encoded proteins play in the pathophysiology of PCG and development of the anterior chamber is not known. To identify proteins that may be altered in PCG and that may help in understanding the underlying pathophysiology of the disease, we took a global proteomics approach. Tryptic digests of the complex mixtures of proteins in aqueous humor were analyzed using Liquid Chromatography/Mass Spectrometry (LC-MS/MS). Proteins were identified by searching the data against the human subset of the UniProt database. The proteomes of aqueous humor in PCG (n = 7) and patients undergoing cataract surgery as control (n = 4) were compared based on the scan counts of comparable proteins. Using stringent filtering criteria, Apolipoprotein A-IV (APOA-IV), Albumin and Antithrombin 3 (ANT3) were detected at significantly higher levels in PCG AH compared to control, whereas Transthyretin (TTR), Prostaglandin-H2 D-isomerase (PTGDS), Opticin (OPT) and Interphotoreceptor Retinoid Binding Protein (IRBP) were detected at significantly lower levels. Many of these proteins play a role in retinoic acid (RA) binding/transport and have been implicated in the pathogenesis of neurodegenerative diseases such as Alzheimer's (AD). It is possible that similar to AD, the pathologic changes in PCG during development could be influenced by the availability of RA in the anterior chamber.

Localisation of opticin in human proliferative retinal disease

This study sought to determine the distribution of opticin, an extracellular matrix small leucine-rich repeat protein secreted by the non-pigmented ciliary body epithelium (CBE), in pathological eye tissues including posterior hyaloid membranes (PHM) and epiretinal membranes (ERM) from subjects with proliferative diabetic retinopathy (PDR), central retinal vein occlusion (CRVO) and proliferative vitreoretinopathy (PVR). Eight enucleated eyes and eleven surgically excised PHMs/ERMs from patients with PDR, CRVO or PVR were analysed by immunohistochemistry for the presence and distribution of opticin, vitreous (delineated by a type II collagen antibody) and blood vessels (using CD31 and CD34 antibodies as endothelial markers). Opticin was present at the basal surface of the non-pigmented CBE and, in a patchy distribution, within CBE cells in all 8 enucleated globes. It also co-localised with the type II collagen of vitreous, where present, in these eyes. Opticin was present in 16 of the 19 PHMs/ERMs, where it was arranged in layers (10 membranes), diffusely (4 membranes) or in foci (2 membranes). Where in a layered pattern, opticin co-localised with vitreous type II collagen incorporated into the membrane, whereas the other two patterns did not co-localise with type II collagen labelling. We concluded that even in advanced proliferative retinal disease, the CBE continues to express and secrete opticin. Opticin was co-distributed with vitreous type II collagen and was also present in the pre-retinal membranes of proliferative retinopathies, where it could play a role in their development.

An evaluation of OPTC and EPYC as candidate genes for high myopia

PURPOSE

The small leucine-rich repeat proteins (SLRPs) are involved in organizing the collagen fibrils of the sclera and vitreous. The shape of the eyeball is determined by the sclera and vitreous, so defects in SLRP family members may contribute to myopia. The purpose of this study was to test whether mutations in the two members of the class III SLRPs, opticin (OPTC) and dermatan sulfate proteoglycan 3 (EPYC), are responsible for high myopia.

METHODS

DNA was prepared from venous leukocytes of 93 patients with high myopia (refraction of spherical equivalent <or=-6.00D) and 96 controls (refraction of spherical equivalent between -0.50D and +1.00D). The coding regions and adjacent intronic sequences of OPTC and EPYC were amplified by the polymerase chain reaction (PCR), and the products were then analyzed by cycle sequencing. The detected variations were further evaluated in normal controls and available family members by a heteroduplex-single strand conformation polymorphism (heteroduplex-SSCP) analysis or sequencing.

RESULTS

Two substitutions in OPTC, including c.491G>T and c.803T>C, were identified. The c.491G>T mutation (p.Arg164Leu), a novel heterozygous variation, was detected in one of the 93 patients but in none of the 96 controls. The c.803T>C mutation (p.Pro267Leu), a known polymorphism, was detected in 22 of the 93 patients and in 15 of 48 controls. No variation was observed in EPYC.

CONCLUSIONS

Only one novel variation in OPTC was detected in a Chinese patient with high myopia. Our results imply that OPTC and EPYC are unlikely to play a major role in high myopia.

Proteomic analysis of the hyaloid vascular system regression during ocular development

We describe a proteomic approach to investigate the differential protein expression patterns and identify the physiologically relevant angiogenic and antiangiogenic factors involved in the hyaloid vascular system regression. Differentially expressed proteins were identified using two-dimensional gel electrophoresis followed by nanoflow chromatography coupled with tandem mass spectrometry. These proteins are expected to provide insight as to their function in the early maintenance and eventual regression of the hyaloid vascular system.

Identification of opticin, a member of the small leucine-rich repeat proteoglycan family, in human articular tissues: a novel target for MMP-13 in osteoarthritis

OBJECTIVE

One of the proteoglycan families is the small leucine-rich proteoglycans (SLRPs) that are characterized by their association with collagen fibrils and/or some glycosaminoglycans. Opticin is a glycoprotein and class III member of the SLRP family, which was initially identified in the vitreous humour of the eye. In this study, we first investigated whether opticin is expressed and produced in normal and OA human articular tissues/cells. Further, we investigated the ability of the key metalloprotease involved in cartilage pathology, MMP-13, to cleave human cartilage opticin.

METHODS

Opticin gene expression was investigated in normal and OA human chondrocytes, synovial fibroblasts, and subchondral bone osteoblasts by reverse transcriptase-polymerase chain reaction (RT-PCR). Opticin protein production was determined in normal and OA synovial membrane and cartilage by immunohistochemistry. Opticin was isolated from human cartilage using guanidinium chloride extraction, and human MMP-13-induced opticin degradation analyzed by Western blotting. Finally, the opticin MMP-13 cleavage site was determined.

RESULTS

Opticin was expressed in human chondrocytes, synovial fibroblasts and subchondral osteoblasts, and the protein identified in synovial membrane and cartilage. At the protein level, OA cartilage showed a slightly higher level of opticin positive stained chondrocytes than normal cartilage; this did not reach statistical significance. However, in contrast with OA, normal cartilage demonstrated a high level of matrix staining in the superficial zone of the tissue, suggesting that in the OA cartilage matrix, opticin is degraded. Data also showed that cartilage opticin could be cleaved by MMP-13 after only 2h of incubation, indicating a preferential substrate compared to other SLRPs for this enzyme. Microsequencing revealed a major cleavage site at the G(104)/L(105)LAAP and a minor at P(109)/A(110)NHPG upon MMP-13 exposure.

CONCLUSION

We demonstrated, for the first time, that opticin is expressed and produced in human articular tissues. Our data also showed that opticin in OA cartilage is degraded in a process that could be mediated by MMP-13. As opticin may contribute towards the structural stability of cartilage, its cleavage by MMP-13 may predispose cartilage to degeneration, particularly at the surface.

Adult vitreous structure and postnatal changes

This review will focus on the molecular organisation of the adult vitreous and how it undergoes ageing changes throughout life that result in vitreous liquefaction and a predisposition towards posterior vitreous detachment and retinal break formation. At birth, the vitreous humour is in a gel state due to the presence of a network of fine collagen fibrils. With ageing, these collagen fibrils progressively aggregate due to a loss of type IX collagen from their surfaces. The aggregation of collagen fibrils may cause vitreous liquefaction which, when combined with an age-related weakening of postbasal vitreoretinal adhesion, predisposes to posterior vitreous detachment. Throughout postnatal life, the posterior border of the vitreous base migrates posteriorly from the ora serrata into the peripheral retina. This is due to new collagen synthesis by the peripheral retina. This new collagen intertwines with pre-existing cortical vitreous collagen to create new adhesions and thereby extends the vitreous base posteriorly. If irregularities in the posterior border of the vitreous base arise from this process, there is a predisposition towards retinal break formation during posterior vitreous detachment and subsequent rhegmatogenous retinal detachment.

Time course of posterior vitreous detachment in the second eye

PURPOSE OF REVIEW

Posterior vitreous detachment is the principal predisposing event for the development of retinal breaks and rhegmatogenous retinal detachments. Patients with unilateral posterior vitreous detachment are potentially at risk of developing the complications associated with posterior vitreous detachment in the fellow eye. Thus, to identify when posterior vitreous detachment develops in the fellow eye after it develops in the first eye is important for managing patients with unilateral posterior vitreous detachment.

RECENT FINDINGS

The main theme in the literature is research regarding the mechanism of the development of posterior vitreous detachment. Various pharmacologic vitreolysis agents can induce posterior vitreous detachment. Changes in the enzymatic activities in the vitreous and vitreoretinal interface tend to promote vitreous separation from the inner retinal surface with aging. Clinical studies have shown a significant increase in the occurrence of posterior vitreous detachment with aging, and the interval between the development of posterior vitreous detachment in the first eye and in the second eye is short.

SUMMARY

Posterior vitreous detachment is one of the most important age-related changes in human eyes, and age-related changes develop equally in both normal eyes; thus, posterior vitreous detachment may develop in the second eye within a few years of developing in the first eye.

A chronic grey matter penumbra, lateral microvascular intussusception and venous peduncular avulsion underlie diabetic vitreous haemorrhage

The landmark publications that gave such impetus to our understanding of proliferative diabetic retinopathy are reviewed in the light of more recent reports. Briefly, confluence of small areas of capillary closure in the midperipheral and peripheral retina results in arteriovenous shunting and abnormal oxygen partial pressure gradients. These gradients embrace a chronic ischaemic penumbra that stimulates neuroglial secretion of angiogenic growth factors and upregulation of their receptors in the retinal venous endothelium and adventitia. The blood shunting produces biomechanical stresses within the veins and induces microvascular intussusception near arteriovenous crossings, giving way to neovascular outgrowths and/or segmental venous lesions (such as omega loops and coils) that penetrate the inner limiting lamina. The lamellar collagenous matrix of the vitreous cortex is then exploited for integrin-dependent rete expansion along chemotactic gradients. During posterior vitreous detachment, haemorrhaging takes place from the arterialised veins as venous neovascular peduncles are avulsed.

Novel mutations in the small leucine-rich repeat protein/proteoglycan (SLRP) genes in high myopia

The importance of the genetic component in high myopia has been well established in population and family studies, but only a few candidate genes have been explored to date. The extracellular matrix small leucine-rich repeat proteins/proteoglycans (SLRPs) regulate collagen fibril diameter and spacing. Given their role in extracellular matrix assembly and expression in the eye, they are likely to regulate its shape and size. Analysis of 85 English and 40 Finnish subjects with high myopia (refractive error of -6 diopters [D] or greater) resulted in 23 sequence variations in four SLRP genes, LUM, FMOD, PRELP, and OPTC. We observed higher number of variations in OPTC in English patients than in controls (p=0.042), and a possibly protective variation in LUM (c.893-105G>A) with p-value of 0.0043. Two intronic variations, six nonsynonymous and one synonymous amino acid changes, were not found in any of the nonmyopic controls. Five changes were detected in opticin, Thr177Arg, Arg229His, Arg325Trp, Gly329Ser, and Arg330His, and all but one (Arg229His) were shown to cosegregate with high myopia in families with incomplete penetrance. A homology model for opticin revealed that Arg229His and Arg325Trp are likely to disrupt the protein structure, and PolyPhen analysis suggested that Thr177Arg, Arg325Trp, and Gly329Ser changes may be damaging. A Leu199Pro change in lumican and Gly147Asp and Arg324Thr variations in fibromodulin are located in the highly conserved leucine-rich repeat (LRR) domains. This study provides new insight into the genetics of high myopia, suggesting that sequence variations in the SLRP genes expressed in the eye may be among the genetic risk factors underlying the pathogenesis of high myopia.

Neoplastic transformation of ciliary body epithelium is associated with loss of opticin expression

BACKGROUND

Opticin is a recently discovered glycoprotein present predominantly in the vitreous humour. It is synthesised and secreted by the ciliary body epithelium (CBE) from the initiation of CBE development in the embryo, and production continues throughout life.

AIM

To determine whether a variety of ciliary body tumours synthesise opticin to characterise further its role in ciliary body health and disease.

METHODS

Immunohistochemistry was used to determine the distribution of opticin in normal human CBE, and in hyperplastic and neoplastic CBE lesions.

RESULTS

Opticin was immunolocalised to the basal cell surface and basement membrane material of the non-pigmented CBE in nine donor eyes as well as four hyperplastic lesions of the CBE (Fuchs's adenoma). By contrast, none of eight neoplastic lesions (two adenoma and six adenocarcinoma) of CBE stained for opticin.

CONCLUSION

The present series supports the theory that opticin is produced by the non-pigmented CBE throughout adult life. Loss of opticin expression by this tissue is associated with and could contribute towards neoplastic transformation.

Molecular cloning and expression of two small leucine-rich proteoglycan (SLRP) genes, dspg3l and optcl, in zebrafish

Epiphycan (DSPG3) and opticin are two class III small leucine-rich proteoglycans (SLRP). We isolated two zebrafish cDNAs, dspg3l and optcl, that encode proteins homologous to epiphycan and opticin in other vertebrates. Like epiphycans in other species, dspg3l is exclusively expressed in the developing notochord and cartilage. optcl is expressed transiently in the developing nervous system, eyes and somites much like opticin. The zebrafish dspg3l and optcl genes are located in linkage group 4 and 11, respectively. The genomic locations for both genes in zebrafish are syntenic with the genomic locations of dspg3 and opticin (optc) in human and mouse. Synteny and the expression patterns of these genes suggest that the dspg3l and optcl are the orthologs to the mammalian dspg3 and optc genes, respectively.

Proteomic identification of activin receptor-like kinase-1 as a differentially expressed protein during hyaloid vascular system regression

The hyaloid vascular system (HVS) is a transient network of capillaries that nourishes the embryonic lens and the primary vitreous of the developing eye. We used proteomic analysis and immunohistochemical staining to identify activin receptor-like kinase-1 (ALK1), a type I receptor for transforming growth factor-beta1, during the HVS regression phase. In addition, we overexpressed ALK1 in corneas implanted with bFGF (basic fibroblast growth factor) pellets and observed that ALK1 overexpression resulted in inhibition of bFGF-induced corneal neovascularization in vivo. Our data suggest that ALK1 may play a role in HVS regression during ocular development.

The NEIBank project for ocular genomics: data-mining gene expression in human and rodent eye tissues

NEIBank is a project to gather and organize genomic resources for eye research. The first phase of this project covers the construction and sequence analysis of cDNA libraries from human and animal model eye tissues to develop an overview of the repertoire of genes expressed in the eye and a resource of cDNA clones for further studies. The sequence data are grouped and identified using the tools of bioinformatics and the results are displayed through a web site where they can be interrogated by keyword search, chromosome location, by Blast (sequence comparison) or by alignment on completed genomes. Many novel proteins and novel splice forms of known genes have already emerged from analysis of the accumulating data. This review provides an overview of the current state of the database for human eye tissues, with specific comparisons to some parallel data from mouse and rat, and with illustrative examples of the kinds of insights and discoveries these data can produce. One of the major themes that emerges is that at the molecular level human eye tissues have significant differences from those of rodents, encompassing species specific genes, alternative splice forms and great variation in levels of gene expression. These point to specific adaptations and mechanisms in the human eye and emphasize that care needs to be taken in the application of appropriate animal model systems.