Growth factors in the eye

Roles of growth factors in eye development and ophthalmic diseases

Growth factors are active substances secreted by a variety of cells, which act as messengers to regulate cell migration, proliferation and differentiation. Many growth factors are involved in the eye development or the pathophysiological processes of eye diseases. Growth factors such as vascular endothelial growth factor and basic fibroblast growth factor mediate the occurrence and development of diabetic retinopathy, choroidal neovascularization, cataract, diabetic macular edema, and other retinal diseases. On the other hand, growth factors like nerve growth factor, ciliary neurotrophic factor, glial cell line-derived neurotrophic factor, pigment epithelial-derived factor and granulocyte colony-stimulating factor are known to promote optic nerve injury repair. Growth factors are also related to the pathogenesis of myopia. Fibroblast growth factor, transforming growth factor-β, and insulin-like growth factor regulate scleral thickness and influence the occurrence and development of myopia. This article reviews growth factors involved in ocular development and ocular pathophysiology, discusses the relationship between growth factors and ocular diseases, to provide reference for the application of growth factors in ophthalmology.

Frs2α enhances fibroblast growth factor-mediated survival and differentiation in lens development

Most growth factor receptor tyrosine kinases (RTKs) signal through similar intracellular pathways, but they often have divergent biological effects. Therefore, elucidating the mechanism of channeling the intracellular effect of RTK stimulation to facilitate specific biological responses represents a fundamental biological challenge. Lens epithelial cells express numerous RTKs with the ability to initiate the phosphorylation (activation) of Erk1/2 and PI3-K/Akt signaling. However, only Fgfr stimulation leads to lens fiber cell differentiation in the developing mammalian embryo. Additionally, within the lens, only Fgfrs activate the signal transduction molecule Frs2α. Loss of Frs2α in the lens significantly increases apoptosis and decreases phosphorylation of both Erk1/2 and Akt. Also, Frs2α deficiency decreases the expression of several proteins characteristic of lens fiber cell differentiation, including Prox1, p57(KIP2), aquaporin 0 and β-crystallins. Although not normally expressed in the lens, the RTK TrkC phosphorylates Frs2α in response to binding the ligand NT3. Transgenic lens epithelial cells expressing both TrkC and NT3 exhibit several features characteristic of lens fiber cells. These include elongation, increased Erk1/2 and Akt phosphorylation, and the expression of β-crystallins. All these characteristics of NT3-TrkC transgenic lens epithelial cells depend on Frs2α. Therefore, tyrosine phosphorylation of Frs2α mediates Fgfr-dependent lens cell survival and provides a mechanistic basis for the unique fiber-differentiating capacity of Fgfs on mammalian lens epithelial cells.

Understanding the role of growth factors in embryonic development: insights from the lens

Growth factors play key roles in influencing cell fate and behaviour during development. The epithelial cells and fibre cells that arise from the lens vesicle during lens morphogenesis are bathed by aqueous and vitreous, respectively. Vitreous has been shown to generate a high level of fibroblast growth factor (FGF) signalling that is required for secondary lens fibre differentiation. However, studies also show that FGF signalling is not sufficient and roles have been identified for transforming growth factor-β and Wnt/Frizzled families in regulating aspects of fibre differentiation. In the case of the epithelium, key roles for Wnt/β-catenin and Notch signalling have been demonstrated in embryonic development, but it is not known if other factors are required for its formation and maintenance. This review provides an overview of current knowledge about growth factor regulation of differentiation and maintenance of lens cells. It also highlights areas that warrant future study.

New therapeutic approaches in the treatment of diabetic keratopathy: a review

The cornea is densely innervated, and the integrity of these nerve fibres is critical in maintaining the refractive and protective functions of the cornea. Many ocular and systemic diseases can adversely affect corneal sensory nerves and consequently impair their function, with vision loss being the inevitable consequence of severe corneal neurotrophic ulceration. However, current standard treatments regimens are often ineffective. Over the past three decades, the role of growth factors in maintaining the normal structure and function of the cornea, and in corneal epithelial healing, has become increasingly evident. Many preclinical and clinical trials have shown that growth factors and cytokines can significantly enhance epithelialization (epithelial proliferation and migration) and consequently accelerate wound healing. More recently, local/topical administration of insulin, naltrexone (opioid antagonist) and nicergoline (ergoline derivatives) were found to improve, and significantly increase, the corneal wound healing rate. This report reviews the major attributes of these growth factors and therapeutic agents that may be used in ameliorating impaired corneal wound healing, and presents a perspective on the potential clinical use of these agents as a new generation of ophthalmic pharmaceuticals for the treatment of diabetic keratopathy.

Curcumin prevents experimental diabetic retinopathy in rats through its hypoglycemic, antioxidant, and anti-inflammatory mechanisms

PURPOSE

The purpose of this study was to evaluate the therapeutic potential of oral curcumin (1 g/kg body weight of rat) in the prevention and treatment of streptozotocin-induced diabetic retinopathy in Wistar albino rats.

METHODS

The treatment was carried out for a period of 16 weeks in diabetic rats and evaluated for hyperglycemic, antioxidant (superoxide dismutase, catalase, and glutathione), and inflammatory parameters (tumor necrosis factor-α, vascular endothelial growth factor). Rat fundus was observed weekly to see any visible changes in the retina, such as tortuosity and dilation of retinal vessels. Histological changes were evaluated by transmission electron microscopy.

RESULTS

Treatment with curcumin showed significant hypoglycemic activity compared with the diabetic group. Retinal glutathione levels were decreased by 1.5-fold, and antioxidant enzymes, superoxide dismutase and catalase, showed >2-fold decrease in activity in the diabetic group; on the other hand, curcumin positively modulated the antioxidant system. Proinflammatory cytokines, tumor necrosis factor-α and vascular endothelial growth factor, were elevated >2-fold in the diabetic retinae, but prevented by curcumin. Transmission electron microscopy showed degeneration of endothelial cell organelles and increase in capillary basement membrane thickness in diabetic retina, but curcumin prevented the structural degeneration and increase in capillary basement membrane thickness in the diabetic rat retinae.

CONCLUSION

Based on the above results, it may be concluded that curcumin may have potential benefits in the prevention of retinopathy in diabetic patients.

Protein phosphatase-1 regulates Akt1 signal transduction pathway to control gene expression, cell survival and differentiation

AKT pathway has a critical role in mediating signaling transductions for cell proliferation, differentiation and survival. Previous studies have shown that AKT activation is achieved through a series of phosphorylation steps: first, AKT is phosphorylated at Thr-450 by JNK kinases to prime its activation; then, phosphoinositide-dependent kinase 1 phosphorylates AKT at Thr-308 to expose the Ser-473 residue; and finally, AKT is phosphorylated at Ser-473 by several kinases (PKD2 and others) to achieve its full activation. For its inactivation, the PH-domain containing phosphatases dephosphorylate AKT at Ser-473, and protein serine/threonine phosphatase-2A (PP-2A) dephosphorylates it at Thr-308. However, it remains unknown regarding which phosphatase dephosphorylates AKT at Thr-450 during its inactivation. In this study, we present both in vitro and in vivo evidence to show that protein serine/threonine phosphatase-1 (PP-1) is a major phosphatase that directly dephosphorylates AKT to modulate its activation. First, purified PP-1 directly dephosphorylates AKT in vitro. Second, immunoprecipitation and immunocolocalization showed that PP-1 interacts with AKT. Third, stable knock down of PP-1alpha or PP-1beta but not PP-1gamma, PP-2Aalpha or PP-2Abeta by shRNA leads to enhanced phosphorylation of AKT at Thr-450. Finally, overexpression of PP-1alpha or PP-1beta but not PP-1gamma, PP-2Aalpha or PP-2Abeta results in attenuated phosphorylation of AKT at Thr-450. Moreover, our results also show that dephosphorylation of AKT by PP-1 significantly modulates its functions in regulating the expression of downstream genes, promoting cell survival and modulating differentiation. These results show that PP-1 acts as a major phosphatase to dephosphorylate AKT at Thr-450 and thus modulate its functions.

Growth factor signaling in vitreous humor-induced lens fiber differentiation

PURPOSE. Although some of the factors and signaling pathways that are involved in induction of fiber differentiation have been defined, such as FGF-mediated MAPK/ERK and PI3-K/Akt signaling, the factors in the vitreous that regulate this differentiation process in vivo have yet to be identified. The purpose of this study was to better understand the role of growth factors in vitreous that regulate this process by further characterizing the signaling pathways involved in lens fiber differentiation. METHODS. Rat lens epithelial explants were used to compare the ability of vitreous, IGF-1, PDGF-A, EGF, and FGF-2 to stimulate the phosphorylation of ERK1/2 and Akt leading to fiber differentiation, in the presence or absence of selective receptor tyrosine kinase (RTK) inhibitors. RESULTS. Similar to vitreous, FGF induced a sustained ERK1/2 signaling profile, unlike IGF, PDGF, and EGF, which induced a more transient (shorter) activation of ERK1/2. For Akt activation, IGF was the only factor that induced a profile similar to vitreous. IGF, PDGF, and EGF potentiated the effects of a low dose of FGF on lens fiber differentiation by extending the duration of ERK1/2 phosphorylation. In the presence of selective RTK inhibitors, although the sustained vitreous-induced ERK1/2 signaling profile and subsequent fiber differentiation was perturbed, the results also showed that, although prolonged ERK1/2 phosphorylation was necessary, it was not sufficient for fiber differentiation to proceed. CONCLUSIONS. These results are consistent with FGF's being the key growth factor involved in vitreous-induced signaling leading to lens fiber differentiation; however, they also indicate that other vitreal growth factors such as IGF may be involved in fine-tuning ERK1/2- and Akt-phosphorylation to the level that is necessary for initiation and/or maintenance of lens fiber differentiation in vivo.

Notch signaling is required for lateral induction of Jagged1 during FGF-induced lens fiber differentiation

Previous studies of the developing lens have shown that Notch signaling regulates differentiation of lens fiber cells by maintaining a proliferating precursor pool in the anterior epithelium. However, whether Notch signaling is further required after the onset of fiber cell differentiation is not clear. This work investigates the role of Notch2 and Jagged1 (Jag1) in secondary fiber cell differentiation using rat lens epithelial explants undergoing FGF-2 dependent differentiation in vitro. FGF induced Jag1 expression and Notch2 signaling (as judged by the appearance of activated Notch2 Intracellular Domain (N2ICD)) within 12-24 h. These changes were correlated with induction of the Notch effector, Hes5, upregulation of N-cadherin (N-cad), and downregulation of E-cadherin (E-cad), a cadherin switch characteristic of fiber cell differentiation. Induction of Jag1 was efficiently blocked by U0126, a specific inhibitor of MAPK/ERK signaling, indicating a requirement for signaling through this pathway downstream of the FGF receptor. Other growth factors that activate MAPK/ERK signaling (EGF, PDGF, IGF) did not induce Jag1. Inhibition of Notch signaling using gamma secretase inhibitors DAPT and L-685,458 or anti-Jag1 antibody markedly decreased FGF-dependent expression of Jag1 demonstrating Notch-dependent lateral induction. In addition, inhibition of Notch signaling reduced expression of N-cad, and the cyclin dependent kinase inhibitor, p57Kip2, indicating a direct role for Notch signaling in secondary fiber cell differentiation. These results demonstrate that Notch-mediated lateral induction of Jag1 is an essential component of FGF-dependent lens fiber cell differentiation.

Growth factors involved in aqueous humour-induced lens cell proliferation

Lens epithelial cell proliferation is regulated by growth factors in the aqueous humour of the eye. Although the lens fibre cell-differentiating factors are well defined, the factors in aqueous that promote lens cell proliferation are not. Mitogens present in aqueous primarily signal through the MAPK/ERK and PI3-K/Akt pathways. By characterising the signalling pathways involved in lens cell proliferation, we aim to identify the factors in aqueous that regulate this process in vivo. Using rat lens epithelial explants, 5'-2'-bromo-deoxyuridine and H(3)-thymidine incorporation were used to compare the effects of aqueous, insulin-like growth factor (IGF-1), platelet-derived growth factor (PDGF-A), epidermal growth factor (EGF) and fibroblast growth factor (FGF-2) on lens cell proliferation. Western blotting was employed to characterise ERK1/2 and Akt signalling induced by these mitogens. The above assays were also repeated in the presence of selective receptor inhibitors. Similar to aqueous, FGF induced a sustained ERK1/2 signalling profile (up to 6 h), unlike IGF, PDGF and EGF that induced a transient activation of ERK1/2. In the presence of a FGF receptor (FGFR) inhibitor, the sustained aqueous-induced ERK1/2 signalling profile was perturbed, resembling the transient IGF-, PDGF- or EGF-induced profile. In the presence of other growth factor receptor inhibitors, aqueous maintained its sustained, 6 h, ERK1/2 signalling profile, although ERK1/2 phosphorylation at earlier time periods was reduced. No one-specific receptor inhibitor could block aqueous-induced lens cell proliferation; however, combinations of inhibitors could, providing FGFR signalling was blocked. Multiple growth factors are likely to regulate lens cell proliferation in vivo, with a key role for FGF in aqueous-induced signalling and lens cell proliferation.

Structural function of MIP/aquaporin 0 in the eye lens; genetic defects lead to congenital inherited cataracts

Aquaporin 0 (AQP0) was originally characterized as a membrane intrinsic protein, specifically expressed in the lens fibers of the ocular lens and designated MIP, for major intrinsic protein of the lens. Once the gene was cloned, an internal repeat was identified, encoding for the amino acids Asp-Pro-Ala, the NPA repeat. Shortly, the MIP gene family was emerging, with members being characterized in mammals, insects, and plants. Once Peter Agre's laboratory developed a functional assay for water channels, the MIP family became the aquaporin family and MIP became known as aquaporin 0. Besides functioning as a water channel, aquaporin 0 also plays a structural role, being required for maintaining the transparency and optical accommodation of the ocular lens. Mutations in the AQP0 gene in human and mice result in genetic cataracts; deletion of the MIP/AQP0 gene in mice results in lack of suture formation required for maintenance of the lens fiber architecture, resulting in perturbed accommodation and focus properties of the ocular lens. Crystallography studies support the notion of the double function of aquaporin 0 as a water channel (open configuration) or adhesion molecule (closed configuration) in the ocular lens fibers. The functions of MIP/AQP0, both as a water channel and an adhesive molecule in the lens fibers, contribute to the narrow intercellular space of the lens fibers that is required for lens transparency and accommodation.

RCE1 Corneal Epithelial Cell Line: Its Variability on Phenotype Expression and Differential Response to Growth Factors

BACKGROUND

By serial transfer of rabbit corneal epithelial cells, the spontaneous RCE1 cell line was previously established. These cells mimic the stage-dependent differentiation of the corresponding cell type.

METHODS

RCE1 cells were cultured either on plastic culture dishes or on collagen rafts to compare the epithelial ultrastructure after growth on these substrata. Phenotypic variability was studied after subcloning of cells. The differentiation ability of each subclone was determined by Western blot with antibodies against the differentiation-linked keratin pair K3/K12 and by measuring LDH activity and LDH isozymes in cytosolic extracts. The proliferative response of RCE1 cells to EGF, TGFalpha, amphiregulin, bFGF or IL-6 was determined under serum-free culture conditions.

RESULTS

Cells grown on collagen rafts formed 5- to 7-layered epithelia with characteristics closer to those found in normal corneal epithelium than cells cultivated on plastic substrata, which formed 3- to 5-layered epithelia. Subcloning experiments demonstrated that every proliferative cell is able to grow and constitute stratified epithelia expressing K3/K12 keratins. LDH levels in RCE1 epithelia were similar to those of cultured or freshly harvested corneal epithelia; however, they showed a slightly altered LDH isozyme set, with prevalence of LDH-3 isoform. Whereas EGF and TGF-alpha were equipotent, amphiregulin elicited a 4-fold lower proliferative response. Also, bFGF was 10-fold less mitogenic than EGF, and IL-6 had the lowest effect with an ED(50) 20-fold lower than EGF.

CONCLUSIONS

The results demonstrate that every RCE1 proliferative cell has the ability to generate epithelial sheets. We conclude that EGF and TGF-alpha are the major effectors of RCE1 cell proliferation.

Control of cellular pattern formation in the vertebrate inner retina by homotypic regulation of cell-fate decisions

The vertebrate retina is composed of cellular arrays that are nonrandom across two-dimensional space. The determinants of these nonrandom two-dimensional cellular patterns in the inner nuclear layer of the retina were investigated using empirical and computational modeling techniques. In normal and experimental models of goldfish retinal growth, the patterns of tyrosine hydroxylase- and serotonin-positive cells indicated that neither cell death nor lateral migration of differentiated cells were dominant mechanisms of cellular pattern formation. A computational model of cellular pattern formation that used a signaling mechanism arising from differentiated cells that inhibited homotypic cell-fate decisions generated accurate simulations of the empirically observed patterns in normal retina. This model also predicted the principal atypical cellular pattern characteristic, a transient cell-type-specific hyperplasia, which was empirically observed in the growing retina subsequent to selective ablation of differentiated retinal cells, either tyrosine hydroxylase positive or serotonin positive. The results support the hypothesis that inhibitory spatiotemporal regulation of homotypic cell-fate decisions is a dominant mechanistic determinant of nonrandom cellular patterns in the vertebrate retina.

Expression patterns of Wnt genes during development of an anterior part of the chicken eye

To address the roles of Wnts in the development of the anterior eye, we used a chicken model to perform comprehensive expression analysis of all Wnt genes during anterior eye development. In analyzing the available genomic sequences, we found that the chicken genome encodes 18 Wnt proteins that are homologous to corresponding human and mouse proteins. The mRNA sequences for 12 chicken Wnt genes are available in GenBank, and mRNAs for six other Wnt genes (Wnt2, Wnt5b, Wnt7b, Wnt8b, Wnt9b, and Wnt16) were identified and cloned based on the homology to the genes from other species. In addition, we found that chicken Wnt3a and Wnt7b genes encode two alternative mRNA isoforms containing different first exons. Following in situ hybridization, we found that out of 18 Wnt genes, 11 genes were expressed in the anterior eye, exhibiting distinct temporal-spatial patterns. Several Wnts were expressed in the lens, including Wnt2 and Wnt2b in the anterior epithelium and Wnt5a, Wnt5b, Wnt7a, and Wnt7b in the differentiating lens fiber cells. In the cornea, we detected Wnt3a, Wnt6, and Wnt9b in the ocular surface ectoderm, including the corneal epithelium, and Wnt9a in the corneal endothelium from the onset of its differentiation. In the optic cup, Wnt2, Wnt2b, and Wnt9a were localized in the rim of the optic cup (presumptive iris), while Wnt5a and Wnt16 were detected in the ciliary epithelium/iris zone of the differentiated optic cup, and Wnt6 was expressed in the iridial mesenchyme. These data suggest that Wnt signaling might play important roles in anterior eye development.

Transforming growth factor-beta-induced epithelial-mesenchymal transition in the lens: a model for cataract formation

The vertebrate lens has a distinct polarity and structure that are regulated by growth factors resident in the ocular media. Fibroblast growth factors, in concert with other growth factors, are key regulators of lens fiber cell differentiation. While members of the transforming growth factor (TGFbeta) superfamily have also been implicated to play a role in lens fiber differentiation, inappropriate TGFbeta signaling in the anterior lens epithelial cells results in an epithelial-mesenchymal transition (EMT) that bears morphological and molecular resemblance to forms of human cataract, including anterior subcapsular (ASC) and posterior capsule opacification (PCO; also known as secondary cataract or after-cataract), which occurs after cataract surgery. Numerous in vitro and in vivo studies indicate that this TGFbeta-induced EMT is part of a wound healing response in lens epithelial cells and is characterized by induced expression of numerous extracellular matrix proteins (laminin, collagens I, III, tenascin, fibronectin, proteoglycans), intermediate filaments (desmin, alpha-smooth muscle actin) and various integrins (alpha2, alpha5, alpha7B), as well as the loss of epithelial genes [Pax6, Cx43, CP49, alpha-crystallin, E-cadherin, zonula occludens-1 protein (ZO-1)]. The signaling pathways involved in initiating the EMT seem to primarily involve the Smad-dependent pathway, whereby TGFbeta binding to specific high affinity cell surface receptors activates the receptor-Smad/Smad4 complex. Recent studies implicate other factors [such as fibroblast growth factor (FGFs), hepatocyte growth factor, integrins], present in the lens and ocular environment, in the pathogenesis of ASC and PCO. For example, FGF signaling can augment many of the effects of TGFbeta, and integrin signaling, possibly via ILK, appears to mediate some of the morphological features of EMT initiated by TGFbeta. Increasing attention is now being directed at the network of signaling pathways that effect the EMT in lens epithelial cells, with the aim of identifying potential therapeutic targets to inhibit cataract, particularly PCO, which remains a significant clinical problem in ophthalmology.

Upregulation of alphavbeta6 integrin, a potent TGF-beta1 activator, and posterior capsule opacification

PURPOSE

To identify the predominant activation pathway of transforming growth factor (TGF)-beta1 in the lens capsule, studying the spatial and temporal expression pattern of alphavbeta6 and thrombospondin-1. Other PCO-related proteins were also studied.

SETTING

Departments of Ophthalmology and Optometrics and Clinical Pathology, Medical School, University of Vienna, Vienna, Austria.

METHODS

The lens capsules of 12 human donor eyes were cultivated in a protein-free medium for up to 28 days (cultivated lens capsules [CLCs]) after lens extraction. Ten intact lenses (ILs) served as the control group and were also cultured. During the culture period, cell dynamics were observed by phase-contrast microscopy. Proteins were detected by double immunofluorescence on frozen sections.

RESULTS

In ILs, alphavbeta6 was absent but 91.6% of the CLCs showed extensive staining. Remnant lens epithelial cells (LECs) expressed alphavbeta6 immediately after lens extraction. The alphavbeta6 was detected throughout the culture period in all regions of the capsule. Thrombospondin-1 was absent in ILs and CLCs, suggesting that this protein is not significant in TGF-beta1 activation in the lens. Transforming growth factor-beta1 was abundantly expressed in all ILs and CLCs, slightly decreasing during intensive LEC proliferation and migration. The TGF-beta receptor II (RII) was expressed equally in all specimens, decreasing with culture time. Nonresident extracellular matrix proteins and alpha-smooth muscle actin were partially detected in CLCs but not in ILs. Latent TGF-beta binding protein 1 and collagen III were absent in all specimens. All cells found in the cultures expressed vimentin and alphaB-crystallin (LEC markers).

CONCLUSION

Alphavbeta6 is the main activator of TGF-beta1 in the lens capsule and represents a new target for PCO prevention.

A role for Wnt/beta-catenin signaling in lens epithelial differentiation

The differentiation of epithelial cells and fiber cells from the anterior and posterior compartments of the lens vesicle, respectively, give the mammalian lens its distinctive polarity. While much progress has been made in understanding the molecular basis of fiber differentiation, little is known about factors that govern the differentiation of the epithelium. Members of the Wnt growth factor family appear to be key regulators of epithelial differentiation in various organ systems. Wnts are ligands for Frizzled receptors and can activate several signaling pathways, of which the best understood is the Wnt/beta-catenin pathway. The presence of LDL-related protein coreceptors (LRPs) 5 or 6 has been shown to be a requirement for Wnt signaling through the beta-catenin pathway. To access the role of this signaling pathway in the lens, we analyzed mice with a null mutation of lrp6. These mice had small eyes and aberrant lenses, characterized by an incompletely formed anterior epithelium resulting in extrusion of the lens fibers into the overlying corneal stroma. We also showed that multiple Wnts, including 5a, 5b, 7a, 7b, 8a, 8b, and Frizzled receptors 1, 2, 3, 4, and 6, were detected in the lens. Expression of these molecules was generally present throughout the lens epithelium and extended into the transitional zone, where early fiber elongation occurs. In addition to both LRP5 and LRP6, we also showed the expression of other molecules involved in Wnt signaling and its regulation, including Dishevelleds, Dickkopfs, and secreted Frizzled-related proteins. Taken together, these results indicate a role for Wnt signaling in regulating the differentiation and behavior of lens cells.

Inflammatory mediators in uveitis: differential induction of cytokines and chemokines in Th1- versus Th2-mediated ocular inflammation

Ocular inflammation leads to vision loss through the destruction and scarring of delicate tissues along the visual axis. To identify inflammatory mediators involved in this process, we used real time RT-PCR to quantify the expression of mRNA transcripts of 34 cytokines, 26 chemokines, and 14 chemokine receptors at certain time points during T cell-mediated ocular inflammation. We induced disease by adoptive transfer of Ag-specific Th1 or Th2 cells into recipients expressing the target Ag in their eyes. We also compared the mediator expression patterns seen in adoptive transfer-induced inflammation with that seen in mouse eyes developing experimental autoimmune uveoretinitis. In addition, we used laser capture microdissection to examine chemokine mRNA production by both retinal pigment epithelium cells and infiltrating leukocytes in inflamed eyes. Major findings included the following: 1) Three patterns of expression of the inflammation-related molecules were seen in recipients of adoptively transferred Th cells: preferential expression in Th1 recipients, or in Th2 recipients, or similar expression in both recipient groups. 2) In experimental autoimmune uveoretinitis, the inflammatory mediator expression pattern largely paralleled that seen in Th1-induced disease. 3) Both retinal pigment epithelium and infiltrating leukocytes expressed chemokine transcripts in distinct, but overlapping patterns in inflamed eyes. 4) Interestingly, transcripts of multiple cytokines, chemokines, and chemokine receptors were constitutively expressed in high levels in mouse eyes. Seven of these molecules have not been previously associated with the eye. These data underscore the multiplicity of mediators that participate in the pathogenesis of eye inflammation and point to upstream cytokines as potential therapeutic targets.

Circadian variations of transforming growth factor-beta2 and basic fibroblast growth factor in the rabbit aqueous humor

PURPOSE

To compare levels of transforming growth factor-beta2 (TGF-beta2) and basic fibroblast growth factor (bFGF) in the ocular fluids of rabbits at various times of the day.

METHODS

Seventy-two young adult New Zealand albino rabbits were entrained to a daily 12-hour light (6 AM to 6 PM) and 12-hour dark cycle. Eight rabbits were sacrificed at each of 6 time points: 4 AM, 8 AM, noon, 4 PM, 8 PM, and midnight. Under an acute 24-hour constant dark condition, 8 additional rabbits were sacrificed at each of 3 time points in the accustomed light period (8 AM, noon, and 4 PM). Samples of aqueous humor and vitreous humor were collected from both eyes. Using enzyme immunoassay, samples from one eye were assayed for total TGF-beta2 and active form of TGF-beta2 and samples from the other eye were assayed for bFGF. Concentrations at various time points were analyzed using one-way ANOVA and post-hoc Bonferroni t-test for multiple comparisons.

RESULTS

Aqueous humor levels of total TGF-beta2, active TGF-beta2, and bFGF changed during the 24-hour period. Total TGF-beta2 and bFGF levels increased between 4 AM and 8 AM. Active TGF-beta2 level increased between 8 PM and midnight. Similar patterns of changes were found when considering aqueous humor samples collected under the acute constant dark condition. In the vitreous humor, total TGF-beta2, active TGF-beta2, and bFGF remained unchanged throughout the 24 hours.

CONCLUSIONS

Endogenous circadian rhythms of total TGF-beta2, active TGF-beta2, and bFGF occur in the rabbit aqueous humor. These two extracellular signaling molecules may be associated with specific physiological functions in the anterior segment according to the time of the day.

Altered expression of growth factors and cytokines in keratoconus, bullous keratopathy and diabetic human corneas

The purpose of this study was to identify the growth factors and cytokines present in normal and diseased corneas. Total RNA was isolated from normal and diseased corneas. cDNA was synthesized from individual corneas and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was performed with primers to IL-1alpha, 1IL-8, PDGF-B, BMP-2, BMP-4, IGF-I, TGF-beta2, FGF-2, and VEGF. After normalization to beta2-microglobulin, several factors were identified that were significantly different from normal. Antibodies to IGF-I, BMP-2, VEGF and TGF-beta2 were used for immunohistochemistry. A total of 93 corneas were used for this study including 31 normal, 20 keratoconus, 19 bullous keratopathy (pseudophakic and aphakic, PBK/ABK), and 23 diabetic corneas. The VEGF RNA levels were significantly decreased in the keratoconus and PBK/ABK corneas but increased in the diabetic corneas. BMP-2 gene expression was lower than normal in the PBK/ABK and diabetic corneas. IGF-I and BMP-4 RNA levels were increased in PBK/ABK. In the immunohistochemical studies, the protein patterns paralleled those found at the mRNA level. The only exception was IGF-I in diabetic corneas that showed increased staining in the epithelium and its basement membrane without a significant increase in mRNA levels. TGF-beta2 mRNA and protein levels were similar to normal in all diseased corneas. Thus, no alterations in the tested growth factors/cytokines were unique to keratoconus corneas. In contrast, PBK/ABK corneas had specific significant elevations of BMP-4 and IGF-I. Diabetic corneas were unique in their increased VEGF mRNA levels. These data suggest that while some growth factor/cytokine alterations are non-specific and can be found in multiple corneal diseases, there are others that are unique to that disease.

18 kDa protein tyrosine phosphatase in the ocular lens

Protein tyrosyl phosphorylation and dephosphorylation play essential roles in regulating cellular events such as proliferation and differentiation, and their involvement in the lens development and transparency is also suggested. The level of tyrosine phosphorylation in a given protein is regulated by the opposing actions of protein-tyrosine kinases (Tyr kinases) and protein-tyrosine phosphatases (TyrPases). Recent studies have revealed that some Tyr kinases, such as platelet-derived growth factor receptor and fibroblast growth factor receptor, are present in the lens, however, little is known about TyrPases in the lens. In this study, we found a 18 kDa protein tyrosine phosphatase (18 kDa TyrPase) predominantly present in the ocular lens of various animals. We purified the phosphatase from the lens of chick embryo and characterized its activity.Phosphatase activity was determined in chick embryo, mouse, rabbit and bovine lenses using p -nitrophenyl phosphate (p NPP) as substrate. All lenses examined dephosphorylated p NPP under acidic conditions, and a large portion of the activity resided in a low molecular weight protein, ca. 18 kDa, following high-resolution gel permeation column chromatography. The brain and liver showed high dephosphorylation activities, but most of their activity was present in high molecular weight fractions, unlike that in the lens. The 18 kDa phosphatase was purified from the lens of 17 day old chick embryos to near-homogeneity with two-step rapid chromatography. This phosphatase showed strict substrate specificity for phosphotyrosine and phosphotyrosyl peptides, suggesting that it was a kind of protein tyrosine phosphatases (TyrPases). Several known inhibitors of TyrPases, such as SH blockers, vanadate and phenylarsine oxide, strongly inhibited the enzyme activity. The molecular weight, substrate specificity, and responses to various inhibitors and activators coincide well with those reported for the low molecular weight protein tyrosine phosphatase (LMW-TyrPase), belonging to the TyrPase superfamily. These results suggest that the 18 kDa phosphatase found in the lens is a LMW-TyrPase. The 18 kDa TyrPase is the predominant phosphatase in the ocular lens. It may be involved in regulation of lens cell proliferation, differentiation and/or lens transparency.

Immunohistochemical analysis of lens epithelial-derived membranes following cataract extraction in the dog

The objective of the study was to characterize the morphologic and immunohistochemical features of lens epithelial-derived proliferative membranes from the anterior segment of canine globes. These features were correlated with those previously identified for diseases resulting from lens epithelial cell (LEC) proliferation including posterior capsular opacification, traumatic subcapsular cataract, and subcapsular plaques associated with hypermature cataracts. Sixteen canine globes were removed as a result of glaucoma or other complications following cataract extraction. Light microscopic and immunohistochemical analysis was performed on sections from formalin-fixed, paraffin-embedded globes. The tissues were stained with a variety of antibodies for cellular markers for LECs, growth factors or other cellular constituents relevant to cellular metaplasia and proliferation. The membranes were composed of monolayers or multilayers of spindle-shaped cells on the external surfaces of the anterior and posterior lens capsule, ciliary processes, iris leaflets, and iridocorneal angle, and they could be seen extending from an obvious monolayer of LEC within the capsular sac. Variably, scattered pigment cells, presumably of uveal origin, were concurrently present. Cellular components of the membranes stained positive for vimentin, transforming growth factor-beta, basic fibroblast growth factor, and smooth muscle actin. An amorphous eosinophilic extracellular matrix consisting predominately of collagen was associated with the membranes. Proliferative anterior segment membranes following cataract surgery were morphologically and immunohistochemically similar to cellular and matrix components of posterior capsular opacification and capsular plaques seen with hypermature cataracts, both of which result from metaplasia and proliferation of LEC. The presence of these LEC-derived membranes in association with secondary glaucoma suggests that exuberant proliferation of LEC outside the confines of the lens capsular sac may cause pathologic alterations in the eye following cataract surgery in the dog.

Pax6 activity in the lens primordium is required for lens formation and for correct placement of a single retina in the eye

The Pax6 transcription factor plays a key role in ocular development of vertebrates and invertebrates. Homozygosity of the Pax6 null mutation in human and mice results in arrest of optic vesicle development and failure to initiate lens formation. This phenotype obscures the understanding of autonomous function of Pax6 in these tissue components and during later developmental stages. We employed the Cre/loxP approach to inactivate Pax6 specifically in the eye surface ectoderm concomitantly with lens induction. Although lens induction occurred in the mutant, as indicated by Sox2 up-regulation in the surface ectoderm, further development of the lens was arrested. Hence, Pax6 activity was found to be essential in the specified ectoderm for lens placode formation. Furthermore, this mutant model allowed us for the first time to address in vivo the development of a completely normal retina in the absence of early lens structures. Remarkably, several independent, fully differentiated neuroretinas developed in a single optic vesicle in the absence of a lens, demonstrating that the developing lens is not necessary to instruct the differentiation of the neuroretina but is, rather, required for the correct placement of a single retina in the eye.

Diabetic retinopathy is associated with decreased serum levels of free IGF-I and changes of IGF-binding proteins

In patients with diabetic retinopathy, elevated serum levels of total circulating insulin-like growth factor-I (IGF-I) have been implicated as an important mediator of the disease. There is no study, however, measuring free IGF-I levels in patients with diabetic retinopathy which mediate the biological effects of IGF-I and are modulated by a complex system of six specific IGF binding proteins (IGFBPs) and several IGFBP proteases.

Calcium cell signalling and cataract: role of the endoplasmic reticulum

The lens possesses an impressive array of G-protein receptors that are coupled to the release of intracellular calcium. They include members of the muscarinic, adrenergic and purinergic families and activation of the former has been implicated in cataract for some time. There are several possible mechanisms whereby activation of such receptors could give rise to cataract. A prolonged increase in intracellular calcium would be expected to activate proteases such as calpain and so could induce unscheduled and irreversible breakdown of important structural proteins. It has recently been shown that activation of G-protein receptors also modulates lens cell growth, and any interference with the highly controlled pattern of cell growth and development within the lens is also likely to have catastrophic consequences. If the calcium store is totally inactivated in lens cells, for example by exposure to thapsigargin, then growth ceases. This finding provides a means of inhibiting the lens cell growth which leads to posterior capsular opacification (PCO). For example, it has been shown that thapsigargin-coated intraocular lenses totally inhibit lens cell growth within cultured capsular bags, and if this technology could be transferred to the clinic then it could provide a simple and relatively inexpensive means of preventing PCO.

Increased vitreous concentrations of human hepatocyte growth factor in proliferative diabetic retinopathy

Human hepatocyte GF (hHGF) has strong neoangiogenesis activity. The present study was designed to investigate the possible involvement of hHGF in neovascularization in proliferative diabetic retinopathy (PDR) by measuring vitreous hHGF concentrations. The mean vitreous hHGF concentration was higher in subjects with PDR (5.70 +/- 0.68 ng/mL, n = 33) than in nondiabetic control subjects (1.50 +/- 0.20 ng/mL, n = 18, P < 0.01), nondiabetic subjects with proliferative vitreoretinopathy (3.31 +/- 0.57 ng//mL, n = 10, P < 0.05), or diabetic subjects without PDR (1.29 +/- 0.28 ng/mL, n = 8, P < 0.01). PDR subjects with neovascularization of iris, which suggests advanced retinal ischemia, showed a higher mean vitreous hHGF concentration than those without iridal neovascularization [7.33 +/- 1.16 ng/mL (n = 14) vs. 4.49 +/- 0.72 ng/mL (n = 19), P < 0.05]. The mean vitreous hHGF concentration was higher in PDR subjects with retinal neovascularization at the optic disc than in those with neovascularization elsewhere [7.3 +/- 1.1 ng/mL (n = 15) vs. 4.4 +/- 0.7 ng/mL (n = 18), P < 0.05]. Our results indicate that vitreous hHGF may play a role in retinal neovascularization in PDR.

Increased vascular endothelial growth factor (VEGF) and transforming growth factor beta (TGFbeta) in experimental autoimmune uveoretinitis: upregulation of VEGF without neovascularization

Experimental autoimmune uveoretinitis (EAU) was induced in Lewis rats and B10.A mice by immunization with S-antigen (S-Ag) to study the potential roles of vascular endothelial growth factor (VEGF) and the beta1 and beta2 isoforms of transforming growth factor (TGFbeta1 and TGFbeta2) during the progression of the disease. VEGF has been implicated as an angiogenic factor in ischemic retinopathies; however, Lewis rats developing EAU have high levels of VEGF in the retina, but no neovascularization. In the present study, immunohistochemical staining for VEGF, TGFbeta1 and TGFbeta2 was performed on the retinas of Lewis rats developing EAU or with oxygen-induced ischemic retinopathy. In rats immunized with S-antigen, a marked upregulation of VEGF was immunohistochemically visualized from the inner nuclear layer to the inner limiting membrane prior to blood-retinal barrier (BRB) failure and lymphocytic infiltration. VEGF is normally induced by hypoxia and its induction leads to neovascularization. Coincident with the increase in VEGF, there was increased immunoreactivity for TGFbeta1 and TGFbeta2 within the same layers of the retina. In contrast, rats with ischemic retinopathy and retinal neovascularization showed only a modest increase in VEGF immunoreactivity, which is largely confined to retinal ganglion cells and inner retinal vessels, and little or no increase in TGFbeta1 or TGFbeta2. In addition, in mice developing EAU, which does not have an abrupt onset as it does in rats and may involve neovascularization, a comparable upregulation of VEGF in the inner retina to that seen in rats developing EAU occurs with no increase in TGFbeta1 or TGFbeta2. Since TGFbeta can inhibit endothelial cell proliferation, it is likely that an increase in TGFbeta may prevent VEGF from exerting its endothelial growth activity in the rat EAU model, but VEGF may be operative in inducing BRB failure. These data suggest that there is a complex interaction among growth factors in the retina and that retinal neovascularization may require an imbalance between stimulatory and inhibitory factors.

FGF1 patterns the optic vesicle by directing the placement of the neural retina domain

Patterning of the bipotential retinal primordia (the optic vesicles) into neural retina and retinal pigmented epithelium depends on its interaction with overlaying surface ectoderm. The surface ectoderm expresses FGFs and the optic vesicles express FGF receptors. Previous FGF-expression data and in vitro analyses support the hypothesis that FGF signaling plays a significant role in patterning the optic vesicle. To test this hypothesis in vivo we removed surface ectoderm, a rich source of FGFs. This ablation generated retinas in which neural and pigmented cell phenotypes were co-mingled. Two in vivo protocols were used to replace FGF secretion by surface ectoderm: (1) implantation of FGF-secreting fibroblasts, and (2) injection of replication-incompetent FGF retroviral expression vectors. The retinas in such embryos exhibited segregated neural and pigmented epithelial domains. The neural retina domains were always close to a source of FGF secretion. These results indicate that, in the absense of surface ectoderm, cells of the optic vesicles display both neural and pigmented retinal phenotypes, and that positional cues provided by FGF organize the bipotential optic vesicle into specific neural retina and pigmented epithelium domains. We conclude that FGF can mimic one of the earliest functions of surface ectoderm during eye development, namely the demarcation of neural retina from pigmented epithelium.

Elschnig pearl formation along the posterior capsulotomy margin after neodymium:YAG capsulotomy

PURPOSE

To determine the incidence of Elschnig pearl formation along the capsulotomy margin (string of pearls) after neodymium:YAG (Nd:YAG) laser posterior capsulotomy and to elucidate its clinical features, predisposing factors, effect on visual function, and association with additional capsulotomy.

SETTING

Keio University Hospital, Tokyo, Japan.

METHODS

The records of 418 eyes that had had Nd:YAG posterior capsulotomy after cataract surgery were retrospectively reviewed. Of those, 315 were excluded for short follow-up (fewer than 12 months) or insufficient clinical examination data. In the remaining 103 eyes, the incidence of string of pearls was calculated, and its clinical features, predisposing factors, effect on visual function, and correlation with additional capsulotomy were evaluated.

RESULTS

String of pearls was identified in 49 eyes (47.6%); 37 (75.5%) developed pearls within 1 year after Nd:YAG capsulotomy. The incidence was significantly higher in patients having intraocular lens implantation and continuous curvilinear capsulorhexis (CCC) than in those without (95.9 versus 61.1% and 97.9 versus 55.6%, respectively). No significant differences were found in patient age and sex, total Nd:YAG energy, and the presence of diabetes mellitus or high myopia. String of pearls caused visual disturbances in 17 eyes (34.7%). The rate of repeat capsulotomy was higher in patients with string of pearls than in those without (36.7 and 9.3%, respectively).

CONCLUSIONS

String of pearls formation was a common and significant complication after Nd:YAG posterior capsulotomy. Intraocular lens implantation and CCC may promote its formation.

Proliferative response of cultured human tenon's capsule fibroblasts to platelet-derived growth factor isoforms

BACKGROUND

Although platelet-derived growth factor (PDGF) has been thought to be critical in the wound-healing response of Tenon's capsule fibroblasts after glaucoma filtration surgery, no information is currently available concerning the proliferative effect of PDGF isoforms on this cell type. The aim of the present study was to evaluate the proliferative effect of PDGF-AB heterodimer and PDGF-AA and -BB homodimers on cultured human Tenon's capsule fibroblasts.

METHODS

Human Tenon's capsule fibroblasts, cultured under serum-free conditions, were stimulated with PDGF-AA, -AB and -BB isoforms in concentrations ranging from 1 to 100 ng/ml. Cell numbers were determined on days 1, 3, 5 and 7, using a cell counter.

RESULTS

Addition of PDGF-AB and -BB led to a dose-dependent increase in cell proliferation. A maximal response (79.9% over control) was obtained after 7 days with 30 ng/ml of PDGF-BB, with an EC50 of 8.9 ng/ml. The maximal increase in cell proliferation caused by PDGF-AB (30 ng/ml) was 54.9%, with an EC50 of 12.5 ng/ml. Stimulation with PDGF-AA revealed a significant effect only with concentrations higher than 30 ng/ml.

CONCLUSION

Our results indicate that PDGF-AB and -BB isoforms are potent stimulators of proliferation of human Tenon's capsule fibroblasts, suggesting that PDGF-AB and -BB isoforms play an important role in the wound-healing response after glaucoma filtration surgery.

Basic fibroblast growth factor (FGF-2) induced transdifferentiation of retinal pigment epithelium: generation of retinal neurons and glia

In the present study we report that basic fibroblast growth factor (bFGF, FGF-2) promotes the transdifferentiation of Xenopus laevis larval retinal pigment epithelium (RPE) into neural retina. Using specific antibodies we have examined the cellular composition of the regenerated retinal tissue. Our results show that, in addition to retinal neurons and photoreceptors, glial cells were also regenerated from the transdifferentiated RPE. These results were specific to FGF-2, since other factors that were tested, including acidic FGF (aFGF, FGF-1), epidermal growth factor (EGF), laminin, ECL, and Matrigel, exhibited no activity in inducing retinal regeneration. These results are the first in amphibians demonstrating the functional role of FGF-2 in inducing RPE transdifferentiation. Transplantation studies were carried out to investigate retinal regeneration from the RPE in an in vivo environment. Sheets of RPE implanted into the lens-less eyes of larval hosts transformed into neurons and glial cells only when under the influence of host retinal factors. In contrast, no retinal transdifferentiation occurred if the RPE was implanted into the enucleated orbit. Taken together, these results show that the amphibian RPE is capable of transdifferentiation into neuronal and glial cell-phenotypes and implicate FGF-2 as an important factor in inducing retinal regeneration in vitro.

Regional glycoprotein expression in the chicken lens

PURPOSE

Several previous studies have shown that glycoconjugates of extracellular matrix, cell membrane and nucleus play an important role in the mediation of cell proliferation, migration and differentiation. Lens epithelial cells and lens fiber cells show regional differences with regard to these parameters. If glycoconjugates participate in the regulation of these patterns in the lens, there should be regional differences in the expression of glycoconjugates. The investigation was focused on the anterior pole, equator and nuclear bow regions, which differ extensively in lens cell proliferation and differentiation.

METHODS

To check this hypothesis, the regional binding pattern of twelve different FITC-conjugated lectins was studied glycohistochemically, using paraffin embedded material. The investigation was focused on the anterior pole, equator and nuclear bow regions.

RESULTS

Regional differences in lectin binding patterns were identified in the lens capsule, epithelium and the nuclear bow regions. The lens capsule was fluorescently labeled with GS-I, UEA-I, LPA, MAA, SNA only at the anterior pole and with CON-A, WGA, DBA, SBA only at the equator. Staining of the entire anterior surface of the lens capsule was observed with LFA. Cell membranes of the lens epithelium showed binding of MAA and LFA only at the equator. LFA, LPA, MAA and SNA only stained the nuclei of fiber cells at the nuclear bow region but not of lens epithelial cells. WGA strongly labeled the nuclei of equatorial epithelial cells and fiber cells at the bow region.

CONCLUSIONS

It is assumed that the observed regional variations in glycoprotein expression in the extracellular matrix and lens cells contribute to the regulation of cell behavior in different areas of the lens.

Differential effects of transforming growth factors on localization of adhesion complex proteins following corneal epithelial cell wounding

PURPOSE

The differential effects of transforming growth factor (TGF) alpha, beta 1 and beta 2 on the de novo localization of heparan sulfate proteoglycan, collagen type VII and laminin-1 to the adhesion complex were analyzed using an in vitro model of corneal epithelial cell wound healing.

METHODS

Bovine corneal explants were maintained in culture media containing either no growth factor or 1, 5, or 10 ng/ml TGF alpha, TGF beta 1 or TGF beta 2. After 24 or 48 hours in culture, cryostat sections of explants were processed for immunofluorescence microscopy using antibodies directed against heparan sulfate proteoglycan, collagen type VII or laminin-1.

RESULTS

A comparison of antibody labeling patterns and relative fluorescence intensity of antibody labeling to controls suggested that TGF alpha inhibits the spatial polarization of proteins into the reforming adhesion complex during early stages of wound healing. Both TGF beta 1 and beta 2 enhanced the linear localization of the three proteins to the site of the reforming adhesion complex. However, in our model TGF beta isoforms did not have identical functions. TGF beta 2 accelerated the temporal localization of collagen type VII to the adhesion complex, an effect which was not observed with TGF beta 1.

CONCLUSIONS

TGF beta, but not TGF alpha, may play an important role in corneal epithelial cell wound healing by accelerating the reformation of the adhesion complex and subsequent epithelial cell-extracellular matrix adhesion.

Cellular and molecular features of lens differentiation: a review of recent advances

In this paper, the more recent literature pertaining to differentiation in the developing vertebrate lens is reviewed in relation to previous work. The literature reviewed reveals that the developing lens has been, and will continue to be, a useful model system for the examination of many fundamental processes occurring during embryonic development. Areas of lens development reviewed here include: the induction and early embryology of the lens; lens cell culture techniques; the role of growth factors and cytokines; the involvement of gap junctions in lens cell-cell communication; the role of cell adhesion molecules, integrins, and the extracellular matrix; the role of the cytoskeleton; the processes of programmed cell death (apoptosis) and lens fibre cell denucleation; the involvement of Pax and Homeobox genes; and crystallin gene regulation. Finally, some speculation is provided as to possible directions for further research in lens development.

Corneal endothelium and growth factors

Human corneal endothelium is characterized by a low regenerative capacity, mainly because of a low mitotic activity, and therefore complete regeneration of the endothelial layer after injury is precluded. A decrease in endothelial cell density and an abnormal cell mosaic, which may occur after many conditions, can compromise the integrity of the endothelial monolayer, resulting in corneal decompensation with reduced vision and eventual need for penetrating keratoplasty. It would be beneficial to have growth factors that can help to maintain or restore the integrity of this delicate endothelial monolayer by maintaining or increasing the endothelial cell density or to stimulate the regeneration during wound healing. Growth factors represent a group of signalling peptides which influence diverse cellular processes, including cell proliferation, differentiation, migration and survival. One of the areas that has received great interest is its enhancement of wound healing. In this review the effects of three most effective growth factors (EGF, PDGF, FGF) on corneal endothelium, especially on wound healing in human corneal buttons, will be discussed.

Immunohistochemical localization of basic fibroblast growth factor, platelet derived growth factor, transforming growth factor-beta and tumor necrosis factor-alpha in the pterygium

Some fibroangiogenic factors have recently been shown to play potential roles in fibrovascular diseases. The aim of this study was to examine whether there is any relationship between growth factors and pterygium genesis. Twenty-three primary pterygia and 4 normal conjunctiva specimens were analyzed by indirect immunohistochemistry using specific antibodies against basic fibroblast growth factor (b-FGF), platelet derived growth factor (PDGF), transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha). Positive immunostaining of these growth factors was located in the epithelial cells, endothelial cells of vessels, basement membranes of vessels and epithelium, fibroblasts and infiltrating inflammatory cells in the pterygium. In the normal conjunctiva, positive immunolabeling for TGF-beta and PDGF was much weaker than in the pterygium. We conclude that growth factors may interact directly or indirectly in the pathogenesis of pterygium although proof of this awaits further studies.

The effects of growth factors on Tenon's capsule fibroblasts in serum-free culture

This study was performed to develop and improve a completely defined in vitro ocular wound-healing model of fibroblast proliferation for glaucoma filtration surgery. This model is essential for the investigation of protein-sensitive drugs and cytokines. Tenon's capsule fibroblasts in their third passage were incubated overnight, washed free of serum, and fed defined media, Aim V or Clonetics FBM serum-free medium containing platelet-derived growth factor, basic fibroblast growth factor, epidermal growth factor, or fibronectin at various dilutions and in combinations at optimum concentrations. Proliferation was measured by 3H-thymidine incorporation at 1, 3, and 7 days. Morphology was compared to controls fed Minimum Essential Medium + 10% serum. Single factors stimulated the greatest amount of thymidine uptake on day 3. Optimum concentrations were epidermal growth factor at 5 ng/ml, basic fibroblast growth factor at 10 ng/ml and platelet-derived growth factor at 20 ng/ml. Identical combinations of factors stimulated nearly twice the thymidine uptake in Clonetics medium as in Aim V. Epidermal growth factor activity was inhibited by either basic fibroblast growth factor or platelet-derived growth factor. Basic fibroblast growth factor and platelet-derived growth factor together produced a less than additive effect. The performance of either serum-free medium may be improved by the addition of basic fibroblast growth factor or platelet-derived growth factor. The optimum serum-free medium (Clonetics FBM) with growth factors was unable to stimulate proliferation as much as Minimum Essential Medium + 10% NBS, but was successful in maintaining viability during the 7 day test period.

Effects of the cytokines on the proliferation of and collagen synthesis by human cataract lens epithelial cells

AIMS

To assess the effects of the cytokines, interleukin-1 (IL-1), IL-1 receptor antagonist (IL-1ra), transforming growth factor-beta 2 (TGF-beta 2) and basic fibroblast growth factor (b-FGF), on the mitosis of and collagen synthesis by lens epithelial cells (LECs) of human cataracts.

METHODS

The anterior lens capsule with attached LECs was obtained by capsulotomy during cataract surgery and cultured. The cultures at 2 to 3 weeks before confluency were used for the experiments. To quantify the mitosis and collagen synthesis, the incorporation of 3H-thymidine and 3H-proline, respectively, into the LECs was measured by a scintillation counter at 48 hours and 24 hours, respectively, after addition of the cytokine at various concentrations into the incubation medium.

RESULTS

IL-1 and b-FGF increased the mitosis and collagen synthesis significantly, but IL-1ra significantly decreased the mitosis while leaving the collagen synthesis intact. TGF-beta 2 decreased the mitosis significantly, but increased the collagen synthesis significantly.

CONCLUSION

These cytokines may play an important role in an autocrine or paracrine pathway in the proliferation of residual LECs after cataract surgery. Elucidation of the role of these cytokines may lead to the development of new therapies for the prevention of secondary cataract.

Activation of phosphotyrosine phosphatase activity is associated with decreased differentiation in adult bovine lens

The postnatal vertebrate eye lens provides an opportunity to study possible involvement of reversible protein phosphorylation in the differentiation process of epithelial cells. Epithelial cells at the lens equator, indeed, differentiate continuously into fiber cells throughout life but this capacity progressively decreases with age. Here we describe the characterization of a phosphotyrosine-protein phosphatase(s) (PTPase(s)) in the equatorial epithelium of bovine lens which exhibits a high level of specific activity. PTPase(s) is detected in cellular detergent extracts using phospholabeled synthetic peptides, p-nitrophenyl phosphate, and lens epithelial membranes as substrates. We show that activity of this PTPase(s) is increased in the equatorial epithelium as the age is increased. We also show that this enzyme(s) exerts its dephosphorylating activity predominantly on a calpactin-like protein associated with lens epithelial membranes. Dephosphorylation of this protein is only obtained when membranes are subjected to extracts in the presence of fibroblast growth factor (FGF). It is suggested that an FGF-activated PTPase(s) might conceivably counteract effects of differentiation stimulatory factors for limiting differentiation of lens throughout life.

Role of glucose regulatory mechanisms in diabetic retinopathy

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Glial reactivity in the retina of adult rats

The present study aimed to characterize the reaction of mammalian (rat) retinal macroglia (Müller cells and astrocytes) to disturbances of their environment in the form of intraorbital section of the optic nerve, intraocular insertion of a thin glass capillary (without damage to the retina) or a combination of both. Glial reactivity was assessed through the use of a battery of antibodies which recognise four different proteins--glial fibrillary protein (GFAP) and three other proteins designated respectively MA1, 4D6 and 4H11. Retinal astrocytes did not exhibit any changes in normally expressed GFAP or MA1. By contrast, the expression of GFAP and MA1 in Müller cells increased 14 days following section of the optic nerve and/or intravitreal insertions of a glass capillary. Three days postoperatively, the expression of GFAP, but not MA1, had already increased significantly in Müller cells. 4D6 and 4H11 proteins were not expressed in astrocytes. In Müller cells, the levels of these proteins increased significantly following combined optic nerve section and intraocular insertion of a glass capillary. Thus, a mechanical disturbance of the intraocular environment constitutes a more effective stimulus in increasing the expression of some Müllerian proteins than damage to the axons of retinal ganglion cells. Such changes have important implications for various ocular treatments that involve intraocular administration of drugs, as well as for the survival/regeneration potential of retinal ganglion cells undergoing Wallerian degeneration.

TGF alpha can act as a chemoattractant to perioptic mesenchymal cells in developing mouse eyes

Growth factors are believed to play an important role in regulating cell fate and cell behavior during embryonic development. Transforming growth factor alpha (TGF alpha), a member of the epidermal growth factor (EGF) superfamily, is a small polypeptide growth factor. Upon binding to its receptor, the EGF receptor (EGFR), TGF alpha can exert diverse biological activities, such as induction of cell proliferation or differentiation. To explore the possibility that TGF alpha might regulate cell fate during murine eye development, we generated transgenic mice that express human TGF alpha in the lens under the control of the mouse alpha A-crystallin promoter. The transgenic mice displayed multiple eye defects, including corneal opacities, cataracts and microphthalmia. At early embryonic stages TGF alpha induced the perioptic mesenchymal cells to migrate abnormally into the eye and accumulate around the lens. In situ hybridization revealed that the EGFR mRNA is highly expressed in the perioptic mesenchyme, suggesting that the migratory response is mediated by receptor activation. In order to test this model, the TGF alpha transgenic mice were bred to EGFR mutant waved-2 (wa-2) mice. We found that the eye defects of the TGF alpha transgenic mice are significantly abated in the wa-2 homozygote background. Because the EGFR mutation in the wa-2 mice is located in the receptor kinase domain, this result indicates that the receptor tyrosine kinase activity is critical for signaling the migratory response. Taken together, our studies demonstrate that TGF alpha is capable of altering the migratory decisions and behavior of perioptic mesenchyme during eye development.

Massive proliferation of lens epithelial remnants after Nd-YAG laser capsulotomy

Eight eyes exhibited massive proliferation of lens epithelial remnants following Nd-YAG posterior capsulotomy. All eyes had pre-existing retinal pathology. Six had undergone vitrectomy (four for proliferative diabetic retinopathy) before extracapsular cataract extraction with posterior chamber intraocular lens implantation. The other two eyes had familial exudative vitreoretinopathy or retinopathy of prematurity, respectively. Five eyes required removal of the lens proliferations via a pars plana approach. High levels of growth factors in the posterior segment associated with proliferative disorders of the retina may play a role in lens cell proliferation.

Effect of collicular proteoglycan on the survival of adult rat retinal ganglion cells following axotomy

Consistent with numerous previous studies, we have found that in adult rats 29% of cells retrogradely prelabelled by injections into retino-recipient nuclei are lost 1 week after intraorbital section of the optic nerve. This figure increases to 76% 2 weeks after axotomy. Intraocular injections of 150 ng of 480 kDa chondroitin sulphate proteoglycan purified from the superior colliculi of neonatal rats were performed every third day after axotomy. This procedure resulted in the loss of only 3 and 28% of the axotomized retinal ganglion cells 7 and 14 days respectively after optic nerve section. Intraocular injections of chondroitin sulphate type C, one of the sugar types present on the collicular proteoglycan, also resulted in a significant saving of axotomized ganglion cells (with the loss of only 48% 14 days after optic nerve lesion). These findings suggest that the collicular proteoglycan, and to a lesser extent its sugar moieties, substantially slows down the degeneration of adult retinal ganglion cells following axotomy.

Retinal and preretinal localisation of epidermal growth factor, transforming growth factor alpha, and their receptor in proliferative diabetic retinopathy

A number of growth factors have been implicated in the development and perpetuation of preretinal fibrovascular membranes in patients with proliferative diabetic retinopathy (PDR). The aim of this study was to determine the potential role of epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), and their receptor (EGF-R) in PDR development. Immunostaining for EGF, TGF-alpha, and EGF-R was compared between normal retina, PDR retina, and PDR preretinal membranes. Weak staining for EGF and EGF-R was observed throughout the neural retina from non-diabetic eyes while weak to moderate staining for TGF-alpha was observed in the ganglion cell layer and the inner and outer nuclear layers. In contrast, intense staining for EGF and TGF-alpha and moderate staining for EGF-R were observed throughout the PDR retina. Immunoreactivity for EGF, TGF-alpha, and EGF-R was seen in the majority of the 11 excised membranes studied and, though variable, was generally greater than that observed in normal retinas. These results suggest an autocrine/paracrine role for EGF, TGF-alpha, and EGF-R in PDR.

Phosphotyrosine inhibition and control of vascular endothelial cell proliferation by genistein

Genistein (4',5,7-trihydroxyisoflavone) is a potent anti-angiogenic compound. We investigated the inhibition of phosphotyrosine as a putative signaling mechanism utilized by the drug in modulating basic fibroblast growth factor (bFGF)-mediated vascular endothelial cell proliferation. The studies included the effect of genistein on DNA synthesis, cell viability, phosphotyrosine induction and characterization of the FGF receptor (FGFR). DNA synthesis was attenuated significantly by genistein in a concentration- and time course-dependent manner with relatively low cytotoxicity during a 16-24 hr exposure (IC50 = 12.5 microM; LC50 = 300 microM). Ligand-stimulated cells exhibited significant increases in phosphotyrosine, affecting FGFR and several tyrosine kinase substrates, ranging in size from M(r) 28 to 200 kDa. Inhibition of phosphotyrosine induction as shown by western blots occurred only at high concentrations of the drug (> 500 microM). These results were supported by results obtained using fluorescence immunocytochemistry. FGFR was shown to be FGF-R1 beta 2, a dimer of approximately 85 and 62 kDa, which was prevented from being autophosphorylated when relatively high concentrations of the drug were applied. Low dose (< 20 microM) inhibition of DNA synthesis by genistein did not correlate with the high concentration required for phosphotyrosine inhibition. The data suggest that although cell stimulation results in phosphotyrosine induction, inhibition of phosphotyrosine is not required for inhibition of DNA synthesis. Furthermore, in endothelial cells, inhibition of DNA synthesis by genistein is not mediated primarily by the inhibition of protein tyrosine kinase activity.