Drusen are Cold Spots for Proteolysis: Expression of Matrix Metalloproteinases and Their Tissue Inhibitor Proteins in Age-related Macular Degeneration

Pathogenesis of Common Ocular Diseases: Emerging Trends in Extracellular Matrix Remodeling

The prevalence of visual impairments in human societies is worrying due to retinopathy complications of several chronic diseases such as diabetes, cardiovascular diseases, and many more that are on the rise worldwide. Since the proper function of this organ plays a pivotal role in people's quality of life, identifying factors affecting the development/exacerbation of ocular diseases is of particular interest among ophthalmology researchers. The extracellular matrix (ECM) is a reticular, three-dimensional (3D) structure that determines the shape and dimensions of tissues in the body. The ECM remodeling/hemostasis is a critical process in both physiological and pathological conditions. It consists of ECM deposition, degradation, and decrease/increase in the ECM components. However, disregulation of this process and an imbalance between the synthesis and degradation of ECM components are associated with many pathological situations, including ocular disorders. Despite the impact of ECM alterations on the development of ocular diseases, there is not much research conducted in this regard. Therefore, a better understanding in this regard, can pave the way toward discovering plausible strategies to either prevent or treat eye disorders. In this review, we will discuss the importance of ECM changes as a sentimental factor in various ocular diseases based on the research done up to now.

Disturbed Matrix Metalloproteinases Activity in Age-Related Macular Degeneration

Matrix metalloproteinases (MMPs) are a tightly regulated family of proteolytic enzymes that break down extracellular matrix (ECM) and basement membrane components. Because it is associated with development, morphogenesis, tissue remodeling, and repair, ECM remodeling is an important mechanism. MMPs are thought to act as a double-edged sword, as they contribute to maintaining photoreceptors/retinal pigment epithelium (RPE)/Bruch's membrane (BM)/choroid complex homeostasis and also contribute to the onset and progression of age-related macular degeneration (AMD). Polymorphisms and/or altered expression in MMPs and their tissue inhibitors (TIMPs) are associated with age-related macular degeneration (AMD). Here, we review the evidence for MMPs' role in the onset and progression of AMD via addressing their regulation and TIMPs' significant regulatory functions.

The Role of Metalloproteinases and Their Tissue Inhibitors on Ocular Diseases: Focusing on Potential Mechanisms

Eye diseases are associated with visual impairment, reduced quality of life, and may even lead to vision loss. The efficacy of available treatment of eye diseases is not satisfactory. The unique environment of the eye related to anatomical and physiological barriers and constraints limits the bioavailability of existing agents. In turn, complex ethiopathogenesis of ocular disorders that used drugs generally are non-disease specific and do not act causally. Therefore, there is a need for the development of a new therapeutic and preventive approach. It seems that matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have a significant role in the development and progression of eye diseases and could be used in the therapy of these disorders as pharmacological targets. MMPs and TIMPs play an important role in the angiogenesis, epithelial-mesenchymal transition, cell invasion, and migration, which occur in ocular diseases. In this review, we aim to describe the participation of MMPs and TIMPs in the eye diseases, such as age-related macular degeneration, cataract, diabetic retinopathy, dry eye syndrome, glaucoma, and ocular cancers, posterior capsule opacification focusing on potential mechanisms.

Non-neglectable therapeutic options for age-related macular degeneration: A promising perspective from traditional Chinese medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Age-related macular degeneration (AMD) is a chronic neurodegenerative disease which causes irreversible central vision loss among the elderly population. Traditional Chinese Medicine (TCM), including formulas, acupuncture and herbs, has been used in the treatment of AMD for thousands of years and is currently used by many AMD patients around the world.

AIM OF THE REVIEW

A comprehensive, in-depth literature review examining the use of TCM in the treatment of AMD has yet to be compiled. This review will improve current knowledge relating to the use of TCM and will open new avenues of exploration in developing new drugs for the treatment of AMD.

METHODS

A literature search of the PubMed database, Web of Science, Google Scholar and China National Knowledge Infrastructure (CNKI) was performed using relevant terms and keywords related to TCM in the treatment of AMD. Related books, PhD and master's theses were also researched.

RESULTS

The TCM-based interpretation of AMD has been used to establish a theoretical foundation for understanding the effect of TCM formulas and acupuncture on AMD. The possible mechanism of action of common Chinese herbs has also been discussed in detail.

CONCLUSION

TCM is a promising treatment option of AMD patients. However, lack of rigorous scientific evidence has limited the impact and uptake of TCM therapy. Future research should focus on improving understanding of the mechanism of action and bioactive components of TCM therapies.

Complement C5 is not critical for the formation of sub-RPE deposits in Efemp1 mutant mice

The complement system plays a role in the formation of sub-retinal pigment epithelial (RPE) deposits in early stages of age-related macular degeneration (AMD). But the specific mechanisms that connect complement activation and deposit formation in AMD patients are unknown, which limits the development of efficient therapies to reduce or stop disease progression. We have previously demonstrated that C3 blockage prevents the formation of sub-RPE deposits in a mouse model of EFEMP1-associated macular degeneration. In this study, we have used double mutant Efemp1R345W/R345W:C5-/- mice to investigate the role of C5 in the formation of sub-RPE deposits in vivo and in vitro. The data revealed that the genetic ablation of C5 does not eliminate the formation of sub-RPE deposits. Contrarily, the absence of C5 in RPE cultures promotes complement dysregulation that results in increased activation of C3, which likely contributes to deposit formation even in the absence of EFEMP1-R345W mutant protein. The results also suggest that genetic ablation of C5 alters the extracellular matrix turnover through an effect on matrix metalloproteinases in RPE cell cultures. These results confirm that C3 rather than C5 could be an effective therapeutic target to treat early AMD.

Collagen I Based Enzymatically Degradable Membranes for Organ-on-a-Chip Barrier Models

Organs-on-chips are microphysiological in vitro models of human organs and tissues that rely on culturing cells in a well-controlled microenvironment that has been engineered to include key physical and biochemical parameters. Some systems contain a single perfused microfluidic channel or a patterned hydrogel, whereas more complex devices typically employ two or more microchannels that are separated by a porous membrane, simulating the tissue interface found in many organ subunits. The membranes are typically made of synthetic and biologically inert materials that are then coated with extracellular matrix (ECM) molecules to enhance cell attachment. However, the majority of the material remains foreign and fails to recapitulate the native microenvironment of the barrier tissue. Here, we study microfluidic devices that integrate a vitrified membrane made of collagen-I hydrogel (VC). The biocompatibility of this membrane was confirmed by growing a healthy population of stem cell derived endothelial cells (iPSC-EC) and immortalized retinal pigment epithelium (ARPE-19) on it and assessing morphology by fluorescence microscopy. Moreover, VC membranes were subjected to biochemical degradation using collagenase II. The effects of this biochemical degradation were characterized by the permeability changes to fluorescein. Topographical changes on the VC membrane after enzymatic degradation were also analyzed using scanning electron microscopy. Altogether, we present a dynamically bioresponsive membrane integrated in an organ-on-chip device with which disease-related ECM remodeling can be studied.

Retinal pigment epithelium transcriptome analysis in chronic smoking reveals a suppressed innate immune response and activation of differentiation pathways

Cigarette smoking, a powerful mixture of chemical oxidants, is the strongest environmental risk factor for developing age-related macular degeneration (AMD), the most common cause of blindness among the elderly in western societies. Despite intensive study, the full impact of smoking on the retinal pigment epithelium (RPE), a central cell type involved in AMD pathobiology, remains unknown. The relative contribution of the known dysfunctional pathways to AMD, at what stage they are most pathogenic, or whether other processes are relevant, is poorly understood, and furthermore, whether smoking activates them, is unknown. We performed global RNA-sequencing of the RPE from C57BL/6J mice exposed to chronic cigarette smoke for 6 months to identify potential pathogenic and cytoprotective pathways. The RPE transcriptome induced by chronic cigarette smoking exhibited a mixed response of marked suppression of the innate immune response including type I and II interferons and upregulation of cell differentiation and morphogenic gene clusters, suggesting an attempt by the RPE to maintain its differentiated state despite smoke-induced injury. Given that mice exposed to chronic smoke develop early features of AMD, these novel findings are potentially relevant to the transition from aging to AMD.

Matrix Metalloproteinases in Age-Related Macular Degeneration (AMD)

Age-related macular degeneration (AMD) is a complex, multifactorial and progressive retinal disease affecting millions of people worldwide. In developed countries, it is the leading cause of vision loss and legal blindness among the elderly. Although the pathogenesis of AMD is still barely understood, recent studies have reported that disorders in the regulation of the extracellular matrix (ECM) play an important role in its etiopathogenesis. The dynamic metabolism of the ECM is closely regulated by matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs). The present review focuses on the crucial processes that occur at the level of the Bruch’s membrane, with special emphasis on MMPs, TIMPs, and the polymorphisms associated with increased susceptibility to AMD development. A systematic literature search was performed, covering the years 1990–2020, using the following keywords: AMD, extracellular matrix, Bruch’s membrane, MMPs, TIMPs, and MMPs polymorphisms in AMD. In both early and advanced AMD, the pathological dynamic changes of ECM structural components are caused by the dysfunction of specific regulators and by the influence of other regulatory systems connected with both genetic and environmental factors. Better insight into the pathological role of MMP/TIMP complexes may lead to the development of new strategies for AMD treatment and prevention.

Molecular Mechanisms of Complement System Proteins and Matrix Metalloproteinases in the Pathogenesis of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is an eye disorder affecting predominantly the older people above the age of 50 years in which the macular region of the retina deteriorates, resulting in the loss of central vision. The key factors associated with the pathogenesis of AMD are age, smoking, dietary, and genetic risk factors. There are few associated and plausible genes involved in AMD pathogenesis. Common genetic variants (with a minor allele frequency of >5% in the population) near the complement genes explain 40-60% of the heritability of AMD. The complement system is a group of proteins that work together to destroy foreign invaders, trigger inflammation, and remove debris from cells and tissues. Genetic changes in and around several complement system genes, including the CFH, contribute to the formation of drusen and progression of AMD. Similarly, Matrix metalloproteinases (MMPs) that are normally involved in tissue remodeling also play a critical role in the pathogenesis of AMD. MMPs are involved in the degradation of cell debris and lipid deposits beneath retina but with age their functions get affected and result in the drusen formation, succeeding to macular degeneration. In this review, AMD pathology, existing knowledge about the normal and pathological role of complement system proteins and MMPs in the eye is reviewed. The scattered data of complement system proteins, MMPs, drusenogenesis, and lipofusogenesis have been gathered and discussed in detail. This might add new dimensions to the understanding of molecular mechanisms of AMD pathophysiology and might help in finding new therapeutic options for AMD.

Characterization of a tissue-engineered choroid

The choroid of the eye is a vascularized and pigmented connective tissue lying between the retina and the sclera. Increasing evidence demonstrates that, beyond supplying nutrients to the outer retina, the different choroidal cells contribute to the retina's homeostasis, especially by paracrine signaling. However, the precise role of each cell type is currently unclear. Here, we developed a choroidal substitute using the self-assembly approach of tissue engineering. Retinal pigment epithelial (RPE) cells, as well as choroidal stromal fibroblasts, vascular endothelial cells and melanocytes, were isolated from human eye bank donor eyes. Fibroblasts were cultured in a medium containing serum and ascorbic acid. After six weeks, cells formed sheets of extracellular matrix (ECM), which were stacked to produce a tissue-engineered choroidal stroma (TECS). These stromal substitutes were then characterized and compared to the native choroid. Their ECM composition (collagens and proteoglycans) and biomechanical properties (ultimate tensile strength, strain and elasticity) were similar. Furthermore, RPE cells, human umbilical vein endothelial cells and choroidal melanocytes successfully repopulated the stromas. Physiological structures were established, such as a confluent monolayer of RPE cells, vascular-like structures and a pigmentation of the stroma. Our TECS thus recaptured the biophysical environment of the native choroid, and can serve as study models to understand the normal interactions between the RPE and choroidal cells, as well as their reciprocal exchanges with the ECM. This will consequently pave the way to derive accurate insight in the pathophysiological mechanisms of diseases affecting the choroid. STATEMENT OF SIGNIFICANCE: The choroid is traditionally known for supplying blood to the avascular outer retina. There has been a renewed attention directed towards the choroid partly due to its implication in the development of age-related macular degeneration (AMD), the leading cause of blindness in industrialized countries. Since AMD involves the dysfunction of the choroid/retinal pigment epithelium (RPE) complex, a three-dimensional (3D) model of RPE comprising the choroid layer is warranted. We used human choroidal cells to engineer a choroidal substitute. Our approach takes advantage of the ability of cells to recreate their own environment, without exogenous materials. Our model could help to better understand the role of each choroidal cell type as well as to advance the development of new therapeutics for AMD.

Effects of dihydromyricetin on ARPE-19 cell migration through regulating matrix metalloproteinase-2 expression

Dihydromyricetin (DHM), a flavanonol compound in Ampelopsis grossedentata, possesses several biological activities. However, the molecular mechanism underlying the effects of DHM on human proliferative vitreoretinopathy (PVR) remains unclear. We explored the effects of DHM on cell migration and the metastasis-promoting proteins in human retinal pigment epithelial (RPE) cells (ARPE-19 cells). Our results revealed that DHM attenuated ARPE-19 cell invasion and migration by reducing matrix metalloproteinase-2 (MMP-2) expression. Furthermore, a Western blot analysis revealed that DHM significantly reduced levels of phosphorylated c-Jun N-terminal kinase 1/2, but not those of extracellular signal-regulated kinase 1/2 and p38. In conclusion, our findings shown that DHM inhibits human RPE cell migration through the inhibition of MMP-2 expression; therefore, DHM may have potential therapeutic value in treating PVR as adjuvant therapy.

The Association Between Variants of Receptor for Advanced Glycation End Products (RAGE) Gene Polymorphisms and Age-Related Macular Degeneration

Background

Age-related macular degeneration (AMD) is the leading cause of blindness in people aged 65 years and older in developed countries. The pathogenesis of AMD has been linked to mechanisms involving inflammation, oxidative stress, and basal laminar deposit formation between retinal pigment epithelium (RPE) cells and the basal membrane, caused by advanced glycation end products (AGEs). AGEs are implicated in the pathogenesis of AMD through the AGE-and receptor for AGE (RAGE) interaction, which can be altered by polymorphisms of the RAGE gene. We examined RAGE rs1800624 and rs1800625 gene polymorphisms contributing to AMD development.

Material/Methods

The study enrolled 300 patients with early AMD, 300 patients with exudative AMD, and 800 healthy controls. The genotyping was carried out using the RT-PCR method.

Results

The analysis of two single nucleotide polymorphisms (SNPs) in the RAGE gene showed that rs1800624 was associated with a 1.6-fold decreased risk for exudative AMD under the dominant model after adjustment for age (OR=0.616; 95% CI: 0.394–0.963; p=0.034) and each copy of allele T at rs1800624 was associated with a 1.4-fold decreased risk for exudative AMD development under the additive model after adjustment for age (OR=0.701; 95% CI: 0.510–0.962; p=0.028). Analysis revealed that the rs1800625 allele G at rs1800625 was associated with a 1.5-fold increased risk for exudative AMD after adjustment for age (OR=1.545; 95% CI: 1.003–2.379; p=0.048). These results suggested that the allele G at rs1800625 was a risk-allele for exudative AMD development. In haplotype analysis, A-G haplotype was significantly more frequently observed in exudative AMD patients compared to healthy controls (3.3% versus 1.4%, p=0.035).

Conclusions

We revealed a significant association between RAGE gene rs1800624 and rs1800625 polymorphisms and AMD risk. We considered T allele at rs1800624 to be protective against AMD development, while allele G at rs1800625 was considered to be a marker of poor prognosis in AMD development.

Metalloproteinases as mediators of inflammation and the eyes: molecular genetic underpinnings governing ocular pathophysiology

There are many vision threatening diseases of the eye affecting millions of people worldwide. In this article, we are summarizing potential role of various matrix metalloproteinases (MMPs); the Zn (2+)-dependent endoproteases in eye health along with pathogenesis of prominent ocular diseases such as macular degeneration, diabetic retinopathy, and glaucoma via understanding MMPs regulation in affected patients, interactions of MMPs with their substrate molecules, and key regulatory functions of tissue inhibitor of metalloproteinases (TIMPs) towards maintaining overall homeostasis.

Serum Levels of TIMP-3, LIPC, IER3, and SLC16A8 in CFH-Negative AMD Cases

AMD is a complex eye disease predominantly occurring in aged population. Till now about 53 genetic loci have been found to be associated with the AMD pathology. AMD pathogenesis is being increasingly known to progress through mechanisms independent of the CFH mediated pathway. Therefore, our aim for current study was to examine the genes by analyzing their expression levels in AMD. We recruited about 50 AMD and same number of age matched controls. We analyzed the CFH duplication and deletion by multiplex ligation probe amplification (MLPA) and found no duplication and deletion in CFH gene in AMD patients. We also estimated the IER-3, SLC16A8, LIPC, and TIMP-3 expression levels in both CFH-negative AMD cases (i.e. no duplication and deletion in CFH gene) besides examining these in AMD and controls. We found that the expression level of LIPC, SLC16A8, and TIMP-3 was significantly associated with AMD pathology in both groups (LIPC: P = 0.008, SLC16A8: P < 0.001, TIMP-3: P < 0.001, respectively). However, we did not find any significant difference in IER-3 levels in AMD and controls. Therefore, the evidence from current study, suggests that AMD pathology may be mediated through mechanistic pathways linked to other genetic loci. J. Cell. Biochem. 118: 2087-2095, 2017. © 2016 Wiley Periodicals, Inc.

Minireview: Fibronectin in retinal disease

Retinal fibrosis, characterized by dysregulation of extracellular matrix (ECM) protein deposition by retinal endothelial cells, pigment epithelial cells, and other resident cell-types, is a unifying feature of several common retinal diseases. Fibronectin is an early constituent of newly deposited ECM and serves as a template for assembly of other ECM proteins, including collagens. Under physiologic conditions, fibronectin is found in all layers of Bruch's membrane. Proliferative vitreoretinopathy (PVR), a complication of retinal surgery, is characterized by ECM accumulation. Among the earliest histologic manifestations of diabetic retinopathy (DR) is capillary basement membrane thickening, which occurs due to perturbations in ECM homeostasis. Neovascularization, the hallmark of late stage DR as well as exudative age-related macular degeneration (AMD), involves ECM assembly as a scaffold for the aberrant new vessel architecture. Rodent models of retinal injury demonstrate a key role for fibronectin in complications characteristic of PVR, including retinal detachment. In mouse models of DR, reducing fibronectin gene expression has been shown to arrest the accumulation of ECM in the capillary basement membrane. Alterations in matrix metalloproteinase activity thought to be important in the pathogenesis of AMD impact the turnover of fibronectin matrix as well as collagens. Growth factors involved in PVR, AMD, and DR, such as PDGF and TGFβ, are known to stimulate fibronectin matrix assembly. A deeper understanding of how pathologic ECM deposition contributes to disease progression may help to identify novel targets for therapeutic intervention.

MMP-3 Deficiency Alleviates Endotoxin-Induced Acute Inflammation in the Posterior Eye Segment

Matrix metalloproteinase-3 (MMP-3) is known to mediate neuroinflammatory processes by activating microglia, disrupting blood-central nervous system barriers and supporting neutrophil influx into the brain. In addition, the posterior part of the eye, more specifically the retina, the retinal pigment epithelium (RPE) and the blood-retinal barrier, is affected upon neuroinflammation, but a role for MMP-3 during ocular inflammation remains elusive. We investigated whether MMP-3 contributes to acute inflammation in the eye using the endotoxin-induced uveitis (EIU) model. Systemic administration of lipopolysaccharide induced an increase in MMP-3 mRNA and protein expression level in the posterior part of the eye. MMP-3 deficiency or knockdown suppressed retinal leukocyte adhesion and leukocyte infiltration into the vitreous cavity in mice subjected to EIU. Moreover, retinal and RPE mRNA levels of intercellular adhesion molecule 1 (Icam1), interleukin 6 (Il6), cytokine-inducible nitrogen oxide synthase (Nos2) and tumor necrosis factor α (Tnfα), which are key molecules involved in EIU, were clearly reduced in MMP-3 deficient mice. In addition, loss of MMP-3 repressed the upregulation of the chemokines monocyte chemoattractant protein (MCP)-1 and (C-X-C motif) ligand 1 (CXCL1). These findings suggest a contribution of MMP-3 during EIU, and its potential use as a therapeutic drug target in reducing ocular inflammation.

Extracellular Matrix Alterations and Deposit Formation in AMD

Age related macular degeneration (AMD) is the primary cause of vision loss in the western world (Friedman et al., Arch Ophthalmol 122:564-572, 2004). The first clinical indication of AMD is the presence of drusen. However, with age and prior to the formation of drusen, extracellular basal deposits accumulate between the retinal pigment epithelium (RPE) and Bruch's membrane (BrM). Many studies on the molecular composition of the basal deposits and drusen have demonstrated the presence of extracellular matrix (ECM) proteins, complement components and cellular debris. The evidence reviewed here suggests that alteration in RPE cell function might be the primary cause for the accumulation of ECM and cellular debri found in basal deposits. Further studies are obviously needed in order to unravel the specific pathways that lead to abnormal formation of ECM and complement activation.

Mice that produce ApoB100 lipoproteins in the RPE do not develop drusen yet are still a valuable experimental system

PURPOSE

Mice typically produce apolipoprotein B (apoB)-48 and not apoB100. Apolipoprotein B100 accumulates in Bruch's membrane prior to basal deposit and drusen formation during the onset of AMD, raising the possibility that they are a trigger for these Bruch's membrane alterations. The purpose herein, was to determine whether mice that predominantly produce apoB100 develop features of AMD.

METHODS

The eyes of mice that produce apoB100 were examined for apoB100 synthesis, cholesteryl esterase/filipin labeling for cholesteryl esters, and transmission electron microscopy for lipid particles and phenotype.

RESULTS

Apolipoprotein B100 was abundant in the RPE-choroid of apoB100, but not wild-type mice by Western blot analysis. The apolipoprotein B100,(35)S-radiolabeled and immunoprecipitated from RPE explants, confirmed that apoB100 was synthesized by RPE. Apolipoprotein B100, but not control mice, had cholesteryl esters and lipid particles in Bruch's membrane. Immunoreactivity of ApoB100 was present in the RPE and Bruch's membrane, but not choroidal endothelium of apoB100 mice. Ultrastructural changes were consistent with aging, but not AMD when aged up to 18 months. The induction of advanced glycation end products to alter Bruch's membrane, did not promote basal linear deposit or drusen formation.

CONCLUSIONS

Mice that produce apoB100 in the RPE and liver secrete lipoproteins into Bruch's membrane, but not to the extent that distinct features of AMD develop, which suggests that either additional lipoprotein accumulation or additional factors are necessary to initiate their formation.

Age-related macular degeneration and changes in the extracellular matrix

Age-related macular degeneration (AMD) is the leading cause of permanent, irreversible, central blindness (scotoma in the central visual field that makes reading and writing impossible, stereoscopic vision, recognition of colors and details) in patients over the age of 50 years in European and North America countries, and an important role is attributed to disorders in the regulation of the extracellular matrix (ECM). The main aim of this article is to present the crucial processes that occur on the level of Bruch’s membrane, with special consideration of the metalloproteinase substrates, metalloproteinase, and tissue inhibitor of metalloproteinase (TIMP).

A comprehensive review of the literature was performed through MEDLINE and PubMed searches, covering the years 2005–2012, using the following keywords: AMD, extracellular matrix, metalloproteinases, tissue inhibitors of metalloproteinases, Bruch’s membrane, collagen, elastin.

In the pathogenesis of AMD, a significant role is played by collagen type I and type IV; elastin; fibulin-3, -5, and -6; matrix metalloproteinase (MMP)-2, MMP-9, MMP-14, and MMP-1; and TIMP-3. Other important mechanisms include: ARMS2 and HTR1 proteins, the complement system, the urokinase plasminogen activator system, and pro-renin receptor activation.

Continuous rebuilding of the extracellular matrix occurs in both early and advanced AMD, simultaneously with the dysfunction of retinal pigment epithelium (RPE) cells and endothelial cells. The pathological degradation or accumulation of ECM structural components are caused by impairment or hyperactivity of specific MMPs/TIMPs complexes, and is also endangered by the influence of other mechanisms connected with both genetic and environmental factors.

The choroid as a sclera growth regulator

Emmetropization is a vision dependent mechanism that attempts to minimize refractive error through coordinated growth of the cornea, lens and sclera such that the axial length matches the focal length of the eye. It is generally accepted that this visually guided eye growth is controlled via a cascade of locally generated chemical events that are initiated in the retina and ultimately cause changes in scleral extracellular matrix (ECM) remodeling which lead to changes in eye size and refraction. Of much interest, therefore, are the molecular mechanisms that underpin emmetropization and visually guided ocular growth. The choroid, a highly vascularized layer located between the retina and the sclera is uniquely situated to relay retina-derived signals to the sclera to effect changes in ECM synthesis and ocular size. Studies initiated by Josh Wallman clearly demonstrate that the choroid plays an active role in emmetropization, both by modulation of its thickness to adjust the retina to the focal plane of the eye (choroidal accommodation), and well as through the release of growth factors that have the potential to regulate scleral extracellular matrix remodeling. His discoveries prompted numerous investigations on the molecular composition of the choroid and changes in gene expression associated with visually guided ocular growth. This article will review molecular and functional studies of the choroid to provide support for the hypothesis that the choroid is a source of sclera growth regulators that effect changes in ocular growth in response to visual stimuli.

Stem cells: a new paradigm for disease modeling and developing therapies for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in people over age 55 in the U.S. and the developed world. This condition leads to the progressive impairment of central visual acuity. There are significant limitations in the understanding of disease progression in AMD as well as a lack of effective methods of treatment. Lately, there has been considerable enthusiasm for application of stem cell biology for both disease modeling and therapeutic application. Human embryonic stem cells and induced pluripotent stem cells (iPSCs) have been used in cell culture assays and in vivo animal models. Recently a clinical trial was approved by FDA to investigate the safety and efficacy of the human embryonic stem cell-derived retinal pigment epithelium (RPE) transplantation in sub-retinal space of patients with dry AMD These studies suggest that stem cell research may provide both insight regarding disease development and progression, as well as direction for therapeutic innovation for the millions of patients afflicted with AMD.

Indocyanine green increases light-induced oxidative stress, senescence, and matrix metalloproteinases 1 and 3 in human RPE cells

PURPOSE

Indocyanine green (ICG) is a commonly used vital dye for macular surgery. Recent reports implicate that its use might be associated with less favourable results regarding postoperative visual outcome and damage of retinal cells, and atrophic degeneration of the retinal pigment epithelium (RPE) has been described. This study investigates the effects of ICG on light-induced senescence of RPE cells.

METHODS

Primary human RPE cells were either pre-incubated with ICG in concentrations of 0.005% and 0.05% or not and then exposed to white light. After 10 min of irradiation viability, induction of intracellular reactive oxygen species (ROS) and senescence-associated β-galactosidase activity (SA β-Gal) were determined. Expression and secretion of matrix metalloproteinases (MMPs) 1 and 3 and their mRNA were determined by RT-PCR and ELISA.

RESULTS

Light exposure decreased RPE cell viability by 46%. Treatment with 0.005% and 0.05% ICG alone decreased RPE cell viability by 7% and 21%. In addition, expression of ROS, SA β-Gal, and MMP-1 and 3 was significantly increased. When 0.005% and 0.05% ICG treatments were combined with light exposure, viability decreased by 69% and 82% compared to the untreated control. Effects on the expression of ROS, SA β-Gal, and MMP-1 and 3 were, depending on the ICG dose, significantly increased when cells were pre-incubated with ICG and then illuminated.

CONCLUSION

In this study, pretreatment with ICG significantly increased light-induced oxidative stress and senescence. This might indicate a potential, supplementary mechanism that could explain RPE alterations and reduced functional results after ICG-assisted internal limiting membrane peeling.

Expression of MMP-2 and MMP-9 in retinoblastoma and their significance

AIM

To investigate the expression of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) in retinoblastoma (Rb), and their relationships with tumor development stage.

METHODS

Immunohistochemical technique was used to detect the expression of MMP-2 and MMP-9 in 41 cases of paraffin embedded Rb samples. Quantitative analysis of the expression of MMP-2 and MMP-9 was assessed by HMIAS-2000 Color Pathologic Analysis System. The differences of the expression of MMP-2 and MMP-9 in each clinical and pathological stage were analyzed statistically.

RESULTS

In all the 41 Rb specimens, MMP-2 and MMP-9 expression was found in tumor cells. The expression of MMP-2 and MMP-9 was significantly higher in tumors with optic nerve invasion than in tumors without optic nerve invasion (P<0.05); the expression of MMP-2 and MMP-9 was significantly higher in tumors of extra-ocular stage than in tumors of glaucomatous stage or intra-ocular stage (P<0.05).

CONCLUSION

MMP-2 and MMP-9 exist in retinoblastoma cells. The level of MMP-2 and MMP-9 is related to optic nerve invasion and clinical stage of Rb, which suggests the expression of MMP-2 and MMP-9 could be connected to the invasion and development of tumor cells. Further research is needed for deeper understanding of the biological behavior and better evaluation of the prognosis of Rb.

(Pro)renin receptor is expressed in human retinal pigment epithelium and participates in extracellular matrix remodeling

The (pro)renin receptor (PRR) is believed to potentiate the renin-angiotensin system (RAS), conferring to prorenin, a likely pathological role at tissue level. The PRR has been identified in the microvascular endothelial cells of the retina, in which it seems to be involved in pathological neovascularization processes. In the present study, we sought to explore PRR expression and prorenin action in human retinal pigment epithelium (RPE) cells, as well as its potential implication in extracellular matrix (ECM) turnover. Isolated RPE cells from donor human eyes as well as freshly isolated human retinas demonstrated expression of PRR at mRNA and protein levels. Moreover, we demonstrate that PRR expressed in the RPE cells is functional, as shown by prorenin-induced increases in Erk1/2 phosphorylation. PRR expression was also shown to be regulated by its main physiological agonist prorenin. We found evidence that the PRR may be involved in ECM-remodeling processes through a prorenin-induced upregulation of type I collagen. Immunostaining analysis of human retinas revealed higher PRR and type I collagen expression in the RPE of eye donors with dry age-related macular degeneration (AMD) and hypertension, supporting the in vitro findings using human-isolated RPE cells. Taken together, the present study demonstrates for the first time that the PRR is expressed in human RPE and suggests a molecular mechanism by which hypertension may exacerbate the pathology of dry AMD.

Hypoxia/reoxygenation induces CTGF and PAI-1 in cultured human retinal pigment epithelium cells

Early age-related macular degeneration (AMD) is characterized by thickening of Bruch's membrane due to the accumulation of extracellular matrix (ECM). This finding could be related to hypoxia of the retinal pigment epithelium (RPE). In the present study, we investigated the effects of hypoxia and reoxygenation on the expression of connective tissue growth factor (CTGF), plasminogen activator inhibitor-1 (PAI-1), collagen type IV (Col IV) and fibronectin (Fn) in cultured human RPE cells. Cultured human RPE cells were kept for 12-36h under hypoxic conditions (1% O(2)). Reoxygenation was conducted for 24h. Hypoxia-mediated CTGF and PAI-1 expression were analyzed by using immunohistochemistry, Northern and Western blot analysis. Actinomycin D was added to examine whether hypoxia induces the transcription of CTGF and PAI-1 mRNA. Furthermore, cells were transfected with siRNA against hypoxia-inducible factor-1alpha (HIF-1alpha) and kept under hypoxic conditions. The effects of antioxidants on hypoxia/reoxygenation-mediated CTGF and PAI-1 expression were tested by real-time PCR analysis. Production of Col IV and Fn were investigated by real-time PCR and Western blot analysis. Both hypoxia and hypoxia/reoxygenation increased the expression of CTGF, PAI-1, Col IV and Fn. Actinomycin D prevented the new transcription of CTGF and PAI-1 mRNA by hypoxia. Using siRNA against HIF-1alpha, the hypoxia-mediated increase of CTGF and PAI-1 was inhibited. Antioxidants attenuated the reoxygenation-mediated increase of CTGF and PAI-1. The process of hypoxia/reoxygenation in the RPE may lead to an increase of ECM in the RPE and thus may contribute to the accumulation of ECM in Bruch's membrane.

CTGF is increased in basal deposits and regulates matrix production through the ERK (p42/p44mapk) MAPK and the p38 MAPK signaling pathways

PURPOSE

Matrix expansion is an early change in age-related maculopathy. The aim of this study was to determine whether connective tissue growth factor (CTGF) regulates the production of extracellular matrix components by retinal pigmented epithelial (RPE) cells.

METHODS

ARPE-19 cells were treated with CTGF and analyzed for fibronectin, laminin, and MMP-2 by RT-qPCR, Western blot analysis, or zymography. Cells were also pretreated with an MEK-1/2 inhibitor (PD98059) or a p38 inhibitor (SB203580) and an anti-CTGF antibody to analyze the signaling contributing to fibronectin, laminin, and MMP-2 production. Human maculas were analyzed for mRNA using laser capture microdissected RPE cells and by immunohistochemistry for the topographic distribution of CTGF.

RESULTS

CTGF induced fibronectin mRNA (P=0.006) and protein (P=0.006), and laminin mRNA (P=0.006) and protein (P=0.02) by ARPE-19 cells. CTGF also induced MMP-2 mRNA (P=0.002) and protein secretion (P=0.04). Using zymography, CTGF increased the latent and active forms of MMP-2 compared to controls (P=0.02). An anti-CTGF antibody inhibited fibronectin, laminin, and MMP-2 after CTGF stimulation. CTGF increased the phosphorylation of p38 and ERK1/2. Fibronectin and MMP-2 mRNA and protein were suppressed by a MEK-1/2 inhibitor, but not with a p38 inhibitor. Laminin expression was suppressed by both inhibitors. RT-qPCR analysis showed that macular RPE cells from human donors express CTGF. Immunohistochemistry of human maculas showed strong labeling of CTGF in Bruch membrane, including basal deposits and drusen.

CONCLUSIONS

CTGF is increased in basal deposits and drusen of AMD specimens, and it induces matrix protein production in ARPE-19 cells through the ERK (p42/p44(mapk)) and p38(mapk) signaling pathways.

Chronic cigarette smoke causes oxidative damage and apoptosis to retinal pigmented epithelial cells in mice

The purpose of this study was to determine whether mice exposed to chronic cigarette smoke develop features of early age-related macular degeneration (AMD). Two month old C57Bl6 mice were exposed to either filtered air or cigarette smoke in a smoking chamber for 5 h/day, 5 days/week for 6 months. Eyes were fixed in 2.5% glutaraldehyde/2% paraformaldehyde and examined for ultrastructural changes by transmission electron microscopy. The contralateral eye was fixed in 2% paraformaldehyde and examined for oxidative injury to the retinal pigmented epithelium (RPE) by 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-OHdG) immunolabeling and apoptosis by TUNEL labeling. Mice exposed to cigarette smoke had immunolabeling for 8-OHdG in 85±3.7% of RPE cells counted compared to 9.5±3.9% in controls (p<0.00001). Bruch membrane was thicker in mice exposed to smoke (1086±332 nm) than those raised in air (543±132 nm; p = 0.0069). The two most pronounced ultrastructural changes (severity grading scale from 0–3) seen were a loss of basal infoldings (mean difference in grade = 1.98; p<0.0001), and an increase in intracellular vacuoles (mean difference in grade = 1.7; p<0.0001). Ultrastructural changes to Bruch membrane in cigarette-smoke exposed mice were smaller in magnitude but consistently demonstrated significantly higher grade injury in cigarette-exposed mice, including basal laminar deposits (mean difference in grade = 0.54; p<0.0001), increased outer collagenous layer deposits (mean difference in grade = 0.59; p = 0.002), and increased basal laminar deposit continuity (mean difference in grade = 0.4; p<0.0001). TUNEL assay showed a higher percentage of apoptotic RPE from mice exposed to cigarette smoke (average 8.0±1.1%) than room air (average 0±0%; p = 0.043). Mice exposed to chronic cigarette smoke develop evidence of oxidative damage with ultrastructural degeneration to the RPE and Bruch membrane, and RPE cell apoptosis. This model could be useful for studying the mechanism of smoke induced changes during early AMD.

Correlation of the extent and duration of rhegmatogenous retinal detachment with the expression of matrix metalloproteinases in the vitreous

BACKGROUND

Investigation of the activity of matrix metalloproteinase (MMP)-2 and -9 and protein levels of MMP-1, -3, -8, and the tissue inhibitor of MMPs (TIMP)-1 in the vitreous of patients with rhegmatogenous retinal detachment (RRD) and establishment of potential correlations of MMPs with clinical parameters.

METHODS

Thirty-two vitreous samples from patients with RRD and 9 vitreous samples from human organ donors (controls) were assayed for MMP-1,-3, -8, and TIMP-1 levels using enzyme-linked immunosorbent assay and MMP-2 and -9 activity employing gelatin zymography.

RESULTS

MMP-1, MMP-3, proMMP-2, proMMP-9, MMP-9, and TIMP-1 were higher in vitreous from patients with RRD as compared to organ donors. Overall, MMPs and TIMPs were differentially expressed in vitreous from RRD with respect to the duration and extent of RRD. Regression analysis for all data indicated that a model consisting of MMP-2 and TIMP-1 could estimate the extent of RRD.

CONCLUSION

Levels of MMPs and TIMP-1 studied are elevated in vitreous during RRD. MMP-2 and TIMP-1 may have a more prominent and persistent role than other MMPs in the wound healing process of the retina during RRD. A regression model consisting of MMP-2 and TIMP-1 may prove to be of potential use in providing information for the evaluation of the extent of RRD.

The effect of ultraviolet radiation on choroidal melanocytes and melanoma cell lines: cell survival and matrix metalloproteinase production

BACKGROUND

Ultraviolet radiation (UVR) can induce DNA damage and regulate the expression of factors important for tumour growth and metastasis, including matrix metalloproteinases (MMPs). Epidemiological studies suggest that chronic UVR exposure, especially during early adulthood, may be a risk factor in patients with choroidal melanoma. However, the effects of UV(R)-B on human choroidal melanocyte survival and growth are unknown. In this study, we investigated if UV(R)-B affected the in vitro survival, growth and MMP production of choroidal melanocytes and melanoma cells.

METHODS

Cultures of primary choroidal melanocytes and melanoma cell lines (OCM-1 and OCM-8) were exposed to UV(R)-B (0-30 mJ/cm(2)). The cell morphology and growth were examined, and cell viability was assessed using an MTT assay. Gelatin zymography was used to assess the enzymatic activity for MMP-2 and -9 in conditioned media following UV(R)-B treatment.

RESULTS

UV(R)-B > or =20 mJ/cm(2) was cytotoxic for choroidal melanocytes. Cytotoxic doses of 5 to 10 mJ/cm(2) were found for OCM-8 and OCM-1 melanoma cell lines. Low levels of UV(R)-B (2.5 and 3.5 mJ/cm(2)) significantly reduced melanoma cell viability after 48 h, although melanocyte viability was not affected by doses of UV(R)-B <10 mJ/cm(2). Conditioned media from melanoma cells and melanocytes displayed pro-MMP-2 activity independent of UV(R)-B. Control and UV(R)-B-treated OCM-1 cells secreted active MMP-2 up to 72 h. Pro-MMP-9 activity was seen from 36 h for control and UV(R)-B-treated OCM-1 and OCM-8 cells.

CONCLUSIONS

Melanocytes appeared more resistant to physiological doses of UV(R)-B than melanoma cells; the potential of melanocytes to initially survive DNA damage following UV(R)-B exposure may be relevant to the subsequent transformation of melanocytes to melanomas. Although UV(R)-B did not induce the production and/or activation of MMP-2 and -9 in melanocytes or melanoma cells, we are currently investigating whether DNA damage-response genes such as p53 and p21 can be regulated following UVR exposure, and whether they are important for choroidal melanoma development.

Expression of matrix metalloproteinases in the subretinal fluid correlates with the extent of rhegmatogenous retinal detachment

BACKGROUND

We investigated the activity of matrix metalloproteinase (MMP)-2 and -9 and the protein levels of MMP-1, -3, -8 and the tissue inhibitor of MMPs (TIMP)-1 in the subretinal fluid (SRF) of patients with rhegmatogenous retinal detachment (RRD) and establishment of potential correlations with clinical parameters.

METHODS

Thirty-seven SRF from RRD patients and nine vitreous samples from the human eye of organ donors (controls) were collected and assayed for MMP-1,-3,-8 and TIMP-1 levels using ELISA and for MMP-2 and -9 activity employing gelatin zymography.

RESULTS

MMP-1, MMP-3, MMP-8, proMMP-2, proMMP-9, MMP-9 and TIMP-1 levels were higher in SRF compared with vitreous fluid. Overall, MMPs and TIMPs were differentially expressed in SRF with respect to duration and extent of RRD, as well as to stage of proliferative vitreoretinopathy. Regression analysis for all data indicated that a model consisting of MMP-3, MMP-8 and proMMP-9 could estimate the extent of RRD.

CONCLUSIONS

MMPs and TIMP-1 levels are elevated in SRF during RRD. A regression model consisting of MMP-3, MMP-8 and proMMP-9 may be proved to be of potential use in providing information for evaluation of the extent of RRD.

Retinal pigment epithelium protection from oxidant-mediated loss of MMP-2 activation requires both MMP-14 and TIMP-2

PURPOSE

Eyes with age-related macular degeneration (AMD) demonstrate accumulation of specific deposits and extracellular matrix (ECM) molecules under the retinal pigment epithelium (RPE). Metalloproteinases (MMP) are crucial regulators of basement membrane and ECM turnover. Accordingly, loss of RPE MMP activity most likely leads to excessive accumulation of collagen and other ECM, a potential mechanism for formation of deposits. A prior study showed that MMP-2 activity, but not pro-MMP-2 protein, decreases after RPE oxidative injury, indicating that oxidant injury disrupts the enzymatic cleavage of pro-MMP-2. Activation of MMP-2 requires the formation of a tri-molecular complex of pro-MMP-2, MMP-14, and tissue inhibitor of metalloproteinases (TIMP)-2. Therefore, a study was conducted to investigate the impact of oxidant injury on the interaction between these three molecules.

METHODS

Human GFP-RPE cells were oxidant injured by transient exposure to H2O2 and myeloperoxidase, and the time course of recovery determined. Supernatants and cell lysates were collected for analysis of MMP-2, MMP-14, and TIMP-2 activity, mRNA and protein expression. In some studies, overexpression with either MMP-14 or TIMP-2 was performed to revert the cells to a preinjury phenotype.

RESULTS

Transient injury resulted in a decrease of both MMP-14 and TIMP-2 activity and protein. Overexpression of each single molecule failed to prevent the injury-induced decrease of MMP-2 activity. In contrast, overexpression of MMP-14 together with the addition of exogenous TIMP-2 prevented the reduction of MMP-2 activation.

CONCLUSIONS

Loss of MMP-2 activity after oxidant injury is caused by the downregulation of MMP-14 and TIMP-2. Overexpression of either MMP-14 or TIMP-2 alone before oxidant injury is not enough to prevent loss of MMP-2 activity. All three components of the tri-molecular complex must be present to preserve normal MMP-2 activity after oxidant injury.

The expression of advanced glycation endproduct receptors in rpe cells associated with basal deposits in human maculas

Basal deposits within Bruch's membrane are associated with aging and age-related macular degeneration (AMD) although the factors causing their formation are incompletely understood. Advanced glycation endproducts (AGEs) accumulate in Bruch's membrane including basal deposits and drusen with aging. One mechanism by which AGEs alter a cell's phenotype is via AGE receptors. The purpose of this study was to immunolocalize and quantify the expression of AGE receptors by RPE cells associated with basal deposits or normal Bruch's membrane that were microdissected from human maculas. Postmortem eyes from 14 aged control donors and five donors with non-neovascular AMD were cryopreserved. RPE cells associated with normal Bruch's membrane or basal deposits were laser capture microdissected. The RNA was extracted and used for RT-qPCR to quantify the expression of RAGE, AGE R1, AGE R2, and AGE R3. Streptavidin alkaline phosphatase immunohistochemistry for these receptors was also performed and sections were bleached from 14 normal and nine AMD donors. RT-qPCR showed significant upregulation of RAGE, AGE R1, and AGE R3 in RPE cells overlying basal deposits compared to cells attached to morphologically normal Bruch's membrane. Immunohistochemical analysis for RAGE, AGER1, R2, and R3 showed diffuse, light staining of RPE cells and strong choriocapillaris staining in areas of normal Bruch's membrane. In areas of basal deposits, the RPE had more intense staining for RAGE and AGER1 compared to regions of normal Bruch's membrane. These results suggest that AGE receptors could influence the formation of basal deposits during aging and AMD.

Advanced glycation endproduct-induced aging of the retinal pigment epithelium and choroid: a comprehensive transcriptional response

Advanced glycation endproduct (AGE) formation is a trigger for the onset of age-related disease. To evaluate AGE-induced change in the ocular fundus, 5-mo-old C57BL/6 mice were given low-dose D-galactose (D-gal) for 8 wk and evaluated by AGE fluorescence, electroretinography (ERG), electron microscopy, and microarray analysis for 20 wk. Although AGE fluorescence was increased in D-gal-treated retinal pigment epithelium (RPE)-choroid compared with controls at all time points, ERG showed no AGE-induced functional toxicity. Progressive ultrastructural aging in the RPE-choroid was associated temporally with a transcriptional response of early inflammation, matrix expansion, and aberrant lipid processing and, later, down-regulation of energy metabolism genes, up-regulation of crystallin genes, and altered expression of cell structure genes. The overall transcriptome is similar to the generalized aging response of unrelated cell types. A subset of transcriptional changes is similar to early atherosclerosis, a chronic inflammatory disease characterized by matrix expansion and lipid deposition. These changes suggest an important contribution of a single environmental stimulus to the complex aging response.

Matrix metalloproteases: degradation of the inhibitory environment of the transected optic nerve and the scar by regenerating axons

After injury to the central nervous system, a glial/collagen scar forms at the lesion site, which is thought to act as a physicochemical barrier to regenerating axons. We have shown that scar formation in the transected optic nerve (ON) is attenuated when robust growth of axons is stimulated. Matrix metalloproteases (MMP), modulated by tissue inhibitors of MMP (TIMP), degrade a wide variety of extracellular matrix components (ECM) and may be activated by growing axons to remodel the ECM to allow regeneration through the inhibitory environment of the glial or collagen scar. Here, we investigate whether MMP levels are modulated in a nonregenerating (scarring) versus a regenerating (nonscarring) model of ON injury in vivo. Western blotting and immunohistochemistry revealed that MMP-1, -2, and -9 levels were higher and TIMP-1 and TIMP-2 levels were lower in regenerating compared to nonregenerating ON and retinae. In situ zymography demonstrated significantly greater MMP-related gelatinase activity in the regenerating model, mainly colocalized to astrocytes in the proximal ON stump and around the lesion site. These results suggest that activation of MMP and coincident down-regulation of TIMP may act to attenuate the inhibitory scarring in the regenerating ON, thus transforming the ON into a noninhibitory pathway for axon regrowth.

Uveal Melanocytes Produce Matrix Metalloproteinases-2 and -9 In Vitro

The purpose of the present study was to investigate the expression of matrix metalloproteinase (MMP)-2 and MMP-9 by cultured human uveal melanocytes, and to test the effects of 12-O-tetradecanoyl-phorbol-13-acetate on the expression of these MMPs. Gelatin zymography of conditioned culture medium from four cultures of human uveal melanocytes (two cultures of iridal melanocytes and two cultures of choroidal melanocytes) detected MMP-2 (72 kDa) and a relatively small amount of MMP-9 (92 kDa), both in the latent form. RT-PCR analysis revealed the MMP-2 mRNA and MMP-9 mRNA in cultured uveal melanocytes. Addition of 12-O-tetradecanoyl-phorbol-13-acetate (10 ng/ml) to the culture medium caused an increase of production of MMP-2 and MMP-9 by cultured uveal melanocytes, and also stimulated the transcription of MMP-2 and MMP-9 of these cells.

Collagens and collagen-related matrix components in the human and mouse eye

The three-dimensional structure of the eye plays an important role in providing a correct optical environment for vision. Much of this function is dependent on the unique structural features of ocular connective tissue, especially of the collagen types and their supramolecular structures. For example, the organization of collagen fibrils is largely responsible for transparency and refraction of cornea, lens and vitreous body, and collagens present in the sclera are largely responsible for the structural strength of the eye. Phylogenetically, most of the collagens are highly conserved between different species, which suggests that collagens also share similar functions in mice and men. Despite considerable differences between the mouse and the human eye, particularly in the proportion of the different tissue components, the difficulty of performing systematic histologic and molecular studies on the human eye has made mouse an appealing alternative to studies addressing the role of individual genes and their mutations in ocular diseases. From a genetic standpoint, the mouse has major advantages over other experimental animals as its genome is better known than that of other species and it can be manipulated by the modern techniques of genetic engineering. Furthermore, it is easy, quick and relatively cheap to produce large quantities of mice for systematic studies. Thus, transgenic techniques have made it possible to study consequences of specific mutations in genes coding for structural components of ocular connective tissues in mice. As these changes in mice have been shown to resemble those in human diseases, mouse models are likely to provide efficient tools for pathogenetic studies on human disorders affecting the extracellular matrix. This review is aimed to clarify the role of collagenous components in the mouse and human eye with a closer look at the new findings of the collagens in the cartilage and the eye, the so-called "cartilage collagens".

Products of lipid peroxidation induce missorting of the principal lysosomal protease in retinal pigment epithelium

Phagocytosis of photoreceptor outer segments (OS) by retinal pigment epithelium (RPE) is essential for OS renewal and survival of photoreceptors. Internalized, oxidatively modified macromolecules perturb the lysosomal function of the RPE and can lead to impaired processing of photoreceptor outer segments. In this study, we sought to investigate the impact of intracellular accumulation of oxidatively damaged lipid-protein complexes on maturation and distribution of cathepsin D, the major lysosomal protease in the RPE. Primary cultures of human RPE cells were treated with copper-oxidized low density lipoprotein (LDL) and then challenged with serum-coated latex beads to stimulate phagocytosis. Three observations were noted to occur in this experimental system. First, immature forms of cathepsin D (52 and 46 kDa) were exclusively associated with latex-containing phagosomes. Second, maturation of cathepsin D was severely impaired in RPE cells loaded with oxidized LDL (oxLDL) prior to the phagocytic challenge. Third, pre-treatment with oxLDL caused sustained secretion of pro-cathepsin D and the latent form of gelatinase A into the extracellular space in a dose-dependent manner. These data stimulate the hypothesis that intracellular accumulation of poorly degradable, oxidized lipid-protein cross-links, may alter the turnover of cathepsin D, causing its mistargeting into the extracellular space together with the enhanced secretion of a gelatinase.

Application of an ex ovo chicken chorioallantoic membrane model for two-photon excitation photodynamic therapy of age-related macular degeneration

Two-photon excitation photodynamic therapy (TPE-PDT) is being investigated as a clinical treatment for age-related macular degeneration (AMD). TPE-PDT has the potential to provide a more specific and therefore advantageous therapy regime than traditional one-photon excitation PDT. The highly vascularized 8 to 9-day-old chicken chorioallantoic membrane (CAM) is used to model the rapid growth of blood vessels in the wet form of AMD. Using an ex ovo model system for the CAM, ablation studies were successful in mimicking the leaky vessels found in AMD. In addition, the distribution and localization of liposomal Verteporfin were investigated in order to characterize the photosensitizing drug in vivo. Localization of the photosensitizer appears to be greatest on the upper vessel wall, which indicates a potentially strong treatment locale for TPE-PDT.