The role of growth factors in the embryogenesis and differentiation of 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.

Distinctive Features of Orbital Adipose Tissue (OAT) in Graves' Orbitopathy

Depot specific expansion of orbital-adipose-tissue (OAT) in Graves' Orbitopathy (GO) is associated with lipid metabolism signaling defects. We hypothesize that the unique adipocyte biology of OAT facilitates its expansion in GO. A comprehensive comparison of OAT and white-adipose-tissue (WAT) was performed by light/electron-microscopy, lipidomic and transcriptional analysis using ex vivo WAT, healthy OAT (OAT-H) and OAT from GO (OAT-GO). OAT-H/OAT-GO have a single lipid-vacuole and low mitochondrial number. Lower lipolytic activity and smaller adipocytes of OAT-H/OAT-GO, accompanied by similar essential linoleic fatty acid (FA) and (low) FA synthesis to WAT, revealed a hyperplastic OAT expansion through external FA-uptake via abundant SLC27A6 (FA-transporter) expression. Mitochondrial dysfunction of OAT in GO was apparent, as evidenced by the increased mRNA expression of uncoupling protein 1 (UCP1) and mitofusin-2 (MFN2) in OAT-GO compared to OAT-H. Transcriptional profiles of OAT-H revealed high expression of Iroquois homeobox-family (IRX-3&5), and low expression in HOX-family/TBX5 (essential for WAT/BAT (brown-adipose-tissue)/BRITE (BRown-in-whITE) development). We demonstrated unique features of OAT not presented in either WAT or BAT/BRITE. This study reveals that the pathologically enhanced FA-uptake driven hyperplastic expansion of OAT in GO is associated with a depot specific mechanism (the SLC27A6 FA-transporter) and mitochondrial dysfunction. We uncovered that OAT functions as a distinctive fat depot, providing novel insights into adipocyte biology and the pathological development of OAT expansion in GO.

Laminin α4 overexpression in the anterior lens capsule may contribute to the senescence of human lens epithelial cells in age-related cataract

Senescence is a leading cause of age-related cataract (ARC). The current study indicated that the senescence-associated protein, p53, total laminin (LM), LMα4, and transforming growth factor-beta1 (TGF-β1) in the cataractous anterior lens capsules (ALCs) increase with the grades of ARC. In cataractous ALCs, patient age, total LM, LMα4, TGF-β1, were all positively correlated with p53. In lens epithelial cell (HLE B-3) senescence models, matrix metalloproteinase-9 (MMP-9) alleviated senescence by decreasing the expression of total LM and LMα4; TGF-β1 induced senescence by increasing the expression of total LM and LMα4. Furthermore, MMP-9 silencing increased p-p38 and LMα4 expression; anti-LMα4 globular domain antibody alleviated senescence by decreasing the expression of p-p38 and LMα4; pharmacological inhibition of p38 MAPK signaling alleviated senescence by decreasing the expression of LMα4. Finally, in cataractous ALCs, positive correlations were found between LMα4 and total LM, as well as between LMα4 and TGF-β1. Taken together, our results implied that the elevated LMα4, which was possibly caused by the decreased MMP-9, increased TGF-β1 and activated p38 MAPK signaling during senescence, leading to the development of ARC. LMα4 and its regulatory factors show potential as targets for drug development for prevention and treatment of ARC.

Roles of TGF β and FGF Signals in the Lens: Tropomyosin Regulation for Posterior Capsule Opacity

Transforming growth factor (TGF) β and fibroblast growth factor (FGF) 2 are related to the development of posterior capsule opacification (PCO) after lens extraction surgery and other processes of epithelial–mesenchymal transition (EMT). Oxidative stress seems to activate TGF β1 largely through reactive oxygen species (ROS) production, which in turn alters the transcription of several survival genes, including lens epithelium-cell derived growth factor (LEDGF). Higher ROS levels attenuate LEDGF function, leading to down-regulation of peroxiredoxin 6 (Prdx6). TGF β is regulated by ROS in Prdx6 knock-out lens epithelial cells (LECs) and induces the up-regulation of tropomyosins (Tpms) 1/2, and EMT of LECs. Mouse and rat PCO are accompanied by elevated expression of Tpm2. Further, the expression of Tpm1/2 is induced by TGF β2 in LECs. Importantly, we previously showed that TGF β2 and FGF2 play regulatory roles in LECs in a contrasting manner. An injury-induced EMT of a mouse lens as a PCO model was attenuated in the absence of Tpm2. In this review, we present findings regarding the roles of TGF β and FGF2 in the differential regulation of EMT in the lens. Tpms may be associated with TGF β2- and FGF2-related EMT and PCO development.

Tropomyosin 2 heterozygous knockout in mice using CRISPR-Cas9 system displays the inhibition of injury-induced epithelial-mesenchymal transition, and lens opacity

The process of epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) after cataract surgery contributes to tissue fibrosis, wound healing and lens regeneration via a mechanism not yet fully understood. Here, we show that tropomyosin 2 (Tpm2) plays a critical role in wound healing and lens aging. Posterior capsular opacification (PCO) after lens extraction surgery was accompanied by elevated expression of Tpm2. Tpm2 heterozygous knockout mice, generated via the clustered regularly interspaced short palindromic repeat/Cas9 (CRISPR/Cas9) system showed promoted progression of cataract with age. Further, injury-induced EMT of the mouse lens epithelium, as evaluated histologically and by the expression patterns of Tpm1 and Tpm2, was attenuated in the absence of Tpm2. In conclusion, Tpm2 may be important in maintaining lens physiology and morphology. However, Tpm2 is involved in the progression of EMT during the wound healing process of mouse LECs, suggesting that inhibition of Tpm2 may suppress PCO.

FGF2 antagonizes aberrant TGFβ regulation of tropomyosin: role for posterior capsule opacity

Transforming growth factor (TGF) β2 and fibroblast growth factor (FGF) 2 are involved in regulation of posterior capsule opacification (PCO) and other processes of epithelial–mesenchymal transition (EMT) such as cancer progression, wound healing and tissue fibrosis as well as normal embryonic development. We previously used an in vivo rodent PCO model to show the expression of tropomyosin (Tpm) 1/2 was aberrantly up‐regulated in remodelling the actin cytoskeleton during EMT. In this in vitro study, we show the Tpms family of cytoskeleton proteins are involved in regulating and stabilizing actin microfilaments (F‐actin) and are induced by TGFβ2 during EMT in lens epithelial cells (LECs). Importantly, we found TGFβ2 and FGF2 played contrasting roles. Stress fibre formation and up‐regulation of α‐smooth muscle actin (αSMA) induced by TGFβ2 could be reversed by Tpm1/2 knock‐down by siRNA. Expression of Tpm1/2 and stress fibre formation induced by TGFβ2 could be reversed by FGF2. Furthermore, FGF2 delivery to TGFβ‐treated LECs perturbed EMT by reactivating the mitogen‐activated protein kinase (MAPK)/ extracellular signal‐regulated kinase (ERK) pathway and subsequently enhanced EMT. Conversely, MEK inhibitor (PD98059) abated the FGF2‐mediated Tpm1/2 and αSMA suppression. However, we found that normal LECs which underwent EMT showed enhanced migration in response to combined TGFβ and FGF2 stimulation. These findings may help clarify the mechanism reprogramming the actin cytoskeleton during morphogenetic EMT cell proliferation and fibre regeneration in PCO. We propose that understanding the physiological link between levels of FGF2, Tpm1/2 expression and TGFβs‐driven EMT orchestration may provide clue(s) to develop therapeutic strategies to treat PCO based on Tpm1/2.

The Drosophila T-box transcription factor Midline functions within the Notch-Delta signaling pathway to specify sensory organ precursor cell fates and regulates cell survival within the eye imaginal disc

We report that the T-box transcription factor Midline (Mid), an evolutionary conserved homolog of the vertebrate Tbx20 protein, functions within the Notch-Delta signaling pathway essential for specifying the fates of sensory organ precursor (SOP) cells. These findings complement an established history of research showing that Mid regulates the cell-fate specification of diverse cell types within the developing heart, epidermis and central nervous system. Tbx20 has been detected in unique neuronal and epithelial cells of embryonic eye tissues in both mice and humans. However, the mechanisms by which either Mid or Tbx20 function to regulate cell-fate specification or other critical aspects of eye development including cell survival have not yet been elucidated. We have also gathered preliminary evidence suggesting that Mid may play an indirect, but vital role in selecting SOP cells within the third-instar larval eye disc by regulating the expression of the proneural gene atonal. During subsequent pupal stages, Mid specifies SOP cell fates as a member of the Notch-Delta signaling hierarchy and is essential for maintaining cell viability by inhibiting apoptotic pathways. We present several new hypotheses that seek to understand the role of Mid in regulating developmental processes downstream of the Notch receptor that are critical for specifying unique cell fates, patterning the adult eye and maintaining cellular homeostasis during eye disc morphogenesis.

Dynamic and differential regulation in the microRNA expression in the developing and mature cataractous rat lens

Recent evidence supports a role for microRNAs (miRNAs) in regulating gene expression, and alterations in gene expression are known to affect cells involved in the development of ageing disorders. Using developing rat lens epithelial cells (LECs), we profiled the expression of miRNAs by a microarray-based approach. Few gene expression changes known to be involved in pathogenesis or cytoprotection were uniquely influenced by miRNA expression. Most miRNAs increased or decreased in abundance (let 7b, let 7c, miR29a, miR29c, miR126 and miR551b) in LECs/lenses during late embryonic and post-natal development and in cataract. Among them, miR29a, miR29c and miR126 were dramatically decreased in cataractous LECs from Shumiya Cataract Rats (SCRs). Specifically, the cytoskeleton remodelling genes tropomyosin (Tm) 1α and 2β, which have been implicated in the initiation of pathophysiology, were targets of miR29c and were over-stimulated as demonstrated by inhibitor experiments. In transfection experiments, increasing the level of miR29c caused a corresponding decrease in the expression of Tm1α and 2β, suggesting that miR29c may regulate the translation of Tm1α and 2β. 3′UTR luciferase activity of Tm1α, not 2β, was significantly decreased in miR29c-transfected mouse LECs. These findings demonstrate changes in miRNAs expression, and target molecules have potential as diagnostic indicators of ageing and as a foundation of miR-based therapeutics for age-related diseases.

Elevated tropomyosin expression is associated with epithelial-mesenchymal transition of lens epithelial cells

Injury to lens epithelial cells (LECs) leads to epithelial–mesenchymal transition (EMT) with resultant fibrosis. The tropomyosin (Tpm) family of cytoskeleton proteins is involved in regulating and stabilizing actin microfilaments. Aberrant expression of Tpms leads to abnormal morphological changes with disintegration of epithelial integrity. The EMT of LECs has been proposed as a major cause of posterior capsule opacification (PCO) after cataract surgery. Using in vivo rodent PCO and human cataractous LECs, we demonstrated that the aberrant expression of rat Tpm and human Tpm1α/2β suggested their association in remodelling of the actin cytoskeleton during EMT of LECs. Expression analysis from abnormally growing LECs after lens extraction revealed elevated expression of α-smooth muscle actin (α-SMA), a marker for EMT. Importantly, these cells displayed increased expression of Tpm1α/2β following EMT/PCO formation. Expression of Tpm1α/2β was up-regulated in LECs isolated from cataractous lenses of Shumiya Cataract Rats (SCRs), compared with non-cataractous lenses. Also, LECs from human patients with nuclear cataract and anterior subcapsular fibrosis (ASF) displayed significantly increased expression of Tpm2β mRNA, suggesting that similar signalling invokes the expression of these molecules in LECs of cataractous SCR and human lenses. EMT was observed in LECs overexpressed with Tpm1α/2β, as evidenced by increased expression of α-SMA. These conditions were correlated with remodelling of actin filaments, possibly leading to EMT/PCO and ASF. The present findings may help clarify the condition of the actin cytoskeleton during morphogenetic EMT, and may contribute to development of Tpm-based inhibitors for postponing PCO and cataractogenesis.

Progenitors for the corneal endothelium and trabecular meshwork: a potential source for personalized stem cell therapy in corneal endothelial diseases and glaucoma

Several adult stem cell types have been found in different parts of the eye, including the corneal epithelium, conjunctiva, and retina. In addition to these, there have been accumulating evidence that some stem-like cells reside in the transition area between the peripheral corneal endothelium (CE) and the anterior nonfiltering portion of the trabecular meshwork (TM), which is known as the Schwalbe's Ring region. These stem/progenitor cells may supply new cells for the CE and TM. In fact, the CE and TM share certain similarities in terms of their embryonic origin and proliferative capacity in vivo. In this paper, we discuss the putative stem cell source which has the potential for replacement of lost and nonfunctional cells in CE diseases and glaucoma. The future development of personalized stem cell therapies for the CE and TM may reduce the requirement of corneal grafts and surgical treatments in glaucoma.

Time-specific blockade of PDGFR with Imatinib (Glivec®) causes cataract and disruption of lens fiber cells in neonatal mice

This study aimed at investigating the response of lens epithelial cells in postnatal mice to Imatinib (Glivec®, a potent inhibitor of platelet-derived growth factor receptor (PDGFR)) treatment. Mouse eyes were sampled 10 days after administration of Imatinib (0.5 mg·g(-1)·day(-1)) for 3 days, at either 7, 14, or 21 days postpartum. Structural changes of lens were revealed by routine H.E. staining. Levels of proliferation and apoptosis were revealed by BrdU incorporation and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, respectively, and immunofluorescent staining with anti-PDGFRα antibody was carried out on the sections of eyeball. PDGFRα and p-PDGFRαprotein levels were evaluated by Western blot. Our results indicated that administration of Imatinib led to blockade of PDGFR signaling. Formation of cataracts was found only in those mice where treatment started from 7 days postpartum (P7), but was not observed in those samples from P14 nor P21. Fiber cells were disorganized in cataract lens core as observed histologically, and migration of epithelial cells was also inhibited. No apoptosis was detected with the TUNEL method. Our results indicated blockade of PDGFR at the neonatal stage (P7) would lead to cataracts and lens fiber cells disorganization, suggesting that PDGFR signaling plays a time-specific and crucial role in the postnatal development of lens in the mouse, and also may provide a new approach to produce a congenital cataract animal model.

Protein expression profiling of lens epithelial cells from Prdx6-depleted mice and their vulnerability to UV radiation exposure

Oxidative stress is one of the causative factors in progression and etiology of age-related cataract. Peroxiredoxin 6 (Prdx6), a savior for cells from internal or external environmental stresses, plays a role in cellular signaling by detoxifying reactive oxygen species (ROS) and thereby controlling gene regulation. Using targeted inactivation of the Prdx6 gene, we show that Prdx6-deficient lens epithelial cells (LECs) are more vulnerable to UV-triggered cell death, a major cause of skin disorders including cataractogenesis, and these cells display abnormal protein profiles. PRDX6-depleted LECs showed phenotypic changes and formed lentoid body, a characteristic of terminal cell differentiation and epithelial-mesenchymal transition. Prdx6(-/-) LECs exposed to UV-B showed higher ROS expression and were prone to apoptosis compared with wild-type LECs, underscoring a protective role for Prdx6. Comparative proteomic analysis using fluorescence-based difference gel electrophoresis along with mass spectrometry and database searching revealed a total of 13 proteins that were differentially expressed in Prdx6(-/-) cells. Six proteins were upregulated, whereas expression of seven proteins was decreased compared with Prdx6(+/+) LECs. Among the cytoskeleton-associated proteins that were highly expressed in Prdx6-deficient LECs was tropomyosin (Tm)2beta. Protein blot and real-time PCR validated dramatic increase of Tm2beta and Tm1alpha expression in these cells. Importantly, Prdx6(+/+) LECs showed a similar pattern of Tm2beta protein expression after transforming growth factor (TGF)-beta or H(2)O(2) treatment. An extrinsic supply of PRDX6 could restore Tm2beta expression, demonstrating that PRDX6 may attenuate adverse signaling in cells and thereby maintain cellular homeostasis. Exploring redox-proteomics (Prdx6(-/-)) and characterization and identification of abnormally expressed proteins and their attenuation by PRDX6 delivery should provide a basis for development of novel therapeutic interventions to postpone ROS-mediated abnormal signaling deleterious to cells or tissues.

Stem cells of the adult cornea: from cytometric markers to therapeutic applications

The cornea is a major protective shield of the interior of the eye and represents two thirds of its refractive power. It is made up of three tissue layers that have different developmental origins: the outer, epithelial layer develops from the ectoderm overlying the lens vesicle, whereas the stroma and the endothelium have mesenchymal origin. In the adult organism, the outermost corneal epithelium is the most exposed to environmental damage, and its constant renewal is assured by the epithelial stem cells that reside in the limbus, the circular border of the cornea. Cell turnover in the stromal layer is very slow and the endothelial cells probably do not reproduce in the adult organism. However, recent experimental evidence indicates that stem cells may be found in these layers. Damage to any of the corneal layers leads to loss of transparency and low vision. Corneal limbal stem cell deficiency results in severe ocular surface disease and its treatment by transplantating ex vivo expanded limbal epithelial cells is becoming widely accepted today. Stromal and endothelial stem cells are potential tools of tissue engineering and regenerative therapies of corneal ulcers and endothelial cell loss. In the past few years, intensive research has focused on corneal stem cells aiming to improve the outcomes of the current corneal stem cell transplantation techniques. This review summarizes the current state of knowledge on corneal epithelial, stromal and endothelial stem cells. Special emphasis is placed on the molecular markers that may help to identify these cells, and the recently revealed mechanisms that could maintain their "stemness" or drive their differentiation. The techniques for isolating and culturing/expanding these cells are also described.

Physiological Significance and Expression of P450s in the Developing Eye

Expression of 10 CYP orthologs (Families 1-3) in developing mouse conceptus is constitutive. These forms have specific temporal and spatial expression. Studies on CYP1B1 indicate its requirement for normal eye development, both in human and mouse. The distribution of the enzyme in the mouse eye is in three regions, which may reflect three different, perhaps equally important, functions in this organ. Its presence in the inner ciliary and lens epithelia appears to be necessary for normal development of the trabecular meshwork and its function in regulating intraocular pressure. Its expression in the retinal ganglion and inner nuclear layers may reflect a role in maintenance of the visual cycle. Its expression in the corneal epithelium may indicate a function in metabolism of environmental xenobiotics.

Peptide hormones as developmental growth and differentiation factors

Peptide hormones, usually considered to be endocrine factors responsible for communication between tissues remotely located from each other, are increasingly being found to be synthesized in developing tissues, where they act locally. Several hormones are now known to be produced in developing tissues that are unrelated to the endocrine gland of origin in the adult. These hormones are synthesized locally, and are active as differentiation and survival factors, before the developing adult endocrine tissue becomes functional. There is increasing evidence for paracrine and/or autocrine actions for these factors during development, thus, placing them among the conventional growth and differentiation factors. We review the evidence for the view that thyroid hormones, growth hormone, prolactin, insulin, and parathyroid hormone-related protein are developmental growth and differentiation factors.

Immunohistochemical markers for corneal stem cells in the early developing human eye

The corneal epithelium is continuously being renewed. Differentiated epithelial cells originate from limbal stem cells (LSCs) located in the periphery of the cornea, the corneoscleral limbus. We have recently identified superoxide dismutase 2 (SOD2) and cytokeratin (CK) 15 as limbal basal cell markers and potential markers for LSCs and early transient amplifying cells in human adults. In this study, we describe the development of the ectodermally derived LSCs and the mesodermally derived niche cells from the time at which the cornea is defined (week 6) until the formation of the early limbal niche (week 14) in human embryos and fetuses. The expression of SOD2 and CK15 was investigated together with other recently identified limbal proteins. Previously suggested LSC and differentiation markers (PAX6, aquaporin-1 and nestin) were also investigated. Both SOD2 and CK15 were present in the corneal epithelium from week 6. However, in week 14 they were predominantly expressed in the limbal epithelium. Both proteins were expressed already from week 7 in a stromal triangular region from which the early mesodermal limbal niche most likely originates. PAX6 was expressed in both ectodermally and mesodermally derived parts of the limbal niche, underscoring the importance of PAX6 in niche formation.

TAT-mediated PRDX6 protein transduction protects against eye lens epithelial cell death and delays lens opacity

A diminished level of endogenous antioxidant in cells/tissues is associated with reduced resistance to oxidative stress. Peroxiredoxin 6 (PRDX6), a protective molecule, regulates gene expression/function by controlling reactive oxygen species (ROS) levels. Using PRDX6 protein linked to TAT, the transduction domain from human immunodeficiency virus type 1 TAT protein, we demonstrated that PRDX6 was transduced into lens epithelial cells derived from rat or mouse lenses. The protein was biologically active, negatively regulating apoptosis and delaying progression of cataractogenesis by attenuating deleterious signaling. Lens epithelial cells from cataractous lenses bore elevated levels of ROS and were susceptible to oxidative stress. These cells harbored increased levels of active transforming growth factor (TGF)-beta 1 and of alpha-smooth muscle actin and beta ig-h3, markers for cataractogenesis. Importantly, cataractous lenses showed a 10-fold reduction in PRDX6 expression, whereas TGF-beta1 mRNA and protein levels were elevated. The changes were reversed, and cataractogenesis was delayed when PRDX6 was supplied. Results suggest that delivery of PRDX6 can postpone cataractogenesis, and this should be an effective approach to delaying cataracts and other degenerative diseases that are associated with increased ROS.

The use of transgenic and knock-out mice in the investigation of ocular surface cell biology

The transgenic and knock-out mice created by transgenesis and gene targeting techniques are very useful for elucidating the pathophysiology of human diseases caused by altered genetic functions. Many of the experimental mouse lines exhibit ocular surface disorders. However, embryonic lethality and congenital defects found in many of the transgenic and knock-out mice preclude their use for studying the consequences of altered genetic functions in adult animals. To circumvent these difficulties, we have established binary inducible mouse models, using the corneal keratocyte-specific keratocan promoter, and the tetracycline-inducible gene expression system (reverse tetracycline transcription activator--rtTA). In these models, the animals function normally until they are fed doxycycline, thus inducing the overexpression of inserted transgenes by keratocytes. We have also developed inserted rtTA and Cre reporter gene constructs to create genetically modified mouse lines that have tissue-specific gene alterations to study acquired conditions, e.g., wound healing and irregular hormone and cytokine signaling that offsets homeostasis in adults. Furthermore, the genes that are ubiquitously expressed in many tissues can be specifically ablated solely in ocular surface tissues to examine their function, since the loss of such a gene in ocular surface tissues will not be life-threatening. It is noteworthy that these altered mouse lines can also be used as models for the development of therapeutic treatment regimens of diseases using gene therapy and stem cell strategies.

Ocular Surface Tissue Morphogenesis in Normal and Disease States Revealed by Genetically Modified Mice

Many transgenic and knockout mice exhibit pathogenic processes resembling human ocular surface diseases. Thus, the clinical manifestations of mouse lines can provide clues for identifying heritable human diseases of unknown etiology. However, mouse lines using conventional techniques of transgenesis and gene targeting often exhibit embryonic lethality and congenital defects, which preclude the use of such mouse models to study acquired ocular surface tissue diseases. These difficulties can be in part overcome by preparing mouse lines of inducible transgene expression, tissue-specific gene ablation, and inducible tissue-specific gene ablation. Conditional transgenic mouse lines live normally until administration of doxycycline and hormones that induce expression of the transgene and ablation of gene of interest. Toward this goal, we prepared 2 groups of genetically modified mouse lines: (1) transgenesis using keratocan promoter was used to create Kera-rtTA mice (doxycycline-inducible mice) and Cre-LoxP system (ie, Kera-Cre mice; conditional gene ablation in neural crest cell lineage and adult stromal keratocyte) and Kera-CrePR mice (RU-486 inducible); and (2) knock-in strategies were used to create Krt12-rtTA mice (doxycycline inducible), Krt12-Cre mice (conditional ablation in corneal epithelium), and Krt12rtTA-tet-O-Cre mice (doxycycline-inducible corneal epithelium-specific gene ablation). Using these mouse lines, we showed that transforming growth factor (TGF)-beta2 is essential for eye morphogenesis, TGF-alpha is a morphogen for eyelid formation, and lumican is a matrikine that has multiple regulatory functions on cell activities (eg, migration proliferation and gene expression) besides serving as a regulatory molecule of collagen fibrillogenesis. These mouse lines can also be used as models for development of therapeutic treatment regimens of ocular surface diseases using gene therapy and stem cell strategies.

Macrophage localization in the developing lens primordium of the mouse embryo – An immunohistochemical study

In mammals, macrophages are known to play an important role in lens development. Macrophages in the embryonic lens are positive for F4/80 monoclonal antibody, and, from 10.5 days to 12 days of gestation, numerous macrophages were observed in the ectoderm, lens vesicle, lens cavity and surrounding mesenchymal tissue, phagocytosing and removing degenerating epithelial cells. During primary lens fiber differentiation, the narrowing lens cavity contained numerous macrophages. Most of the macrophages in the cavity attached to the anterior epithelial wall of the lens vesicle, but a few macrophages were found within the lens epithelial cell layer. Conversely, the thickening posterior wall of the vesicle did not contain any positive cells. After the lens cavity was filled, intralental positive cells disappeared. These characteristic localizations of macrophages in the developing lens to remove apoptotic dead cells may indicate that cell death took place mainly in the anterior wall of the lens vesicle, that is, in the lens epithelium.

Growth hormone as an early embryonic growth and differentiation factor

In this review we consider the evidence that growth hormone (GH) acts in the embryo as a local growth, differentiation, and cell survival factor. Because both GH and its receptors are present in the early embryo before the functional differentiation of pituitary somatotrophs and before the establishment of a functioning circulatory system, the conditions are such that GH may be a member of the large battery of autocrine/paracrine growth factors that control embryonic development. It has been clearly established that GH is able to exert direct effects, independent of insulin-like growth factor-I (IGF-I), on the differentiation, proliferation, and survival of cells in a wide variety of tissues in the embryo, fetus, and adult. The signaling pathways behind these effects of GH are now beginning to be determined, establishing early extrapituitary GH as a bona fide developmental growth factor.

Lens epithelium-derived growth factor relieves transforming growth factor-beta1-induced transcription repression of heat shock proteins in human lens epithelial cells

Lens epithelium-cell derived growth factor (LEDGF) is a transcriptional activator. It protects the cells by binding to cis-stress response ((A/T)GGGG(T/A)), and heat shock (HSE; nGAAn) elements in the stress genes and activating their transcription. Transforming growth factor-beta (TGF-beta) has been implicated in the control of tissue homeostasis, terminal differentiation, and apoptosis. Here we provide evidence that TGF-beta1 down-regulates LEDGF expression and diminishes its affinity for DNA during TGF-beta1-induced phenotypic changes and apoptosis in human lens epithelial cells. Surprisingly, TGF-beta1 treatment for 48 h markedly decreased the LEDGF, Hsp27, and alphaB-crystallin promoter activities with the decrease of abundance of LEDGF mRNA and protein. Deletion mutants of the LEDGF promoter showed that one TGF-beta1 inhibitory element (TIE) like sequence nnnTTGGnnn (-444 to -433) contributed to this negative regulation. Mutation of TIE (TTGG to TATT) abolished the down-regulation of the LEDGF promoter. Gel mobility and supershift assays showed that LEDGF in the nuclear extracts of TGF-beta1-treated human lens epithelial cells did not bind to stress-response elements and HSE. The TGF-beta1-induced down-regulation of LEDGF, Hsp27, and alphaB-crystallin promoters activity was reversed by cotransfection with a plasmid expressing LEDGF. Because overexpression of LEDGF was able to relieve TGF-beta1 and/or stress-induced changes, it would be a candidate molecule to postpone age-related degenerating disorders.

Expression of AP-1 (c-fos/c-jun) in developing mouse corneal epithelium

BACKGROUND

Activator protein-1 (AP-1) is a ubiquitous transcription factor which is believed to modulate cell behaviors such as proliferation and differentiation during wound healing and embryonic tissue morphogenesis. AP-1 consists of Fos family and Jun family proteins.

METHODS

We examined expression pattern of c-fos mRNA and c-Fos protein in developing mouse cornea. Expression of c-jun mRNA and c-Jun protein were also examined for comparison.

RESULTS

While no c-fos mRNAs were detected on embryonic day (E) 12.5, mRNA for c-fos was detected from E14.5 until postnatal day (P)14. The mRNAs for c-jun were also detected, although the temporal expression patterns differed. c-Fos-immunoreactive nuclei were present from E14.5 through P10 and c-Jun-immunoreactive nuclei were detected from E14.5 through P3.

CONCLUSION

These findings indicate that AP-1 ( c-fos/c-jun) transcription factor may play a role in the development and maturation of the corneal epithelium in mice.

Probing teleost eye development by lens transplantation

Experimental manipulation and other lines of evidence indicate that the lens plays a prominent role in the growth and differentiation of the vertebrate eye. Here we describe a lens transplantation method for studying the role of the lens in teleost eye development. The method involves three steps: (1) preparing embryos for the operations by embedding them in agar, (2) microsurgery with tungsten needles to remove the lens from a donor embryo and insert it into the optic cup of a host embryo lacking its own lens, and (3) a recovery period allowing surface ectoderm to close over the wound left by insertion of the lens into the host embryo. A movie illustrating the method can be found at http://www.life.umd.edu/labs/jeffery. A troubleshooting guide and summary of assays for evaluating the development of the transplanted lens and its effects on other eye parts, including the retina, are presented. Finally, some current applications of the lens transplantation method are briefly described: (1) determination of the autonomy of zebrafish lens mutants and (2) investigation of the role of the lens in eye degeneration in the cavefish Astyanax. The transplantation method will help characterize the mechanisms through which vertebrate eye development is regulated by the lens.

TGFbeta2 in corneal morphogenesis during mouse embryonic development

To examine the roles of TGFbeta isoforms on corneal morphogenesis, the eyes of mice that lack TGFbetas were analyzed at different developmental stages for cell proliferation, migration and apoptosis, and for expression patterns of keratin 12, lumican, keratocan and collagen I. Among the three Tgfb(-/-) mice, only Tgfb2(-/-) mice have abnormal ocular morphogenesis characterized by thin corneal stroma, absence of corneal endothelium, fusion of cornea to lens (a Peters'-like anomaly phenotype), and accumulation of hyaline cells in vitreous. In Tgfb2(-/-) mice, fewer keratocytes were found in stroma that has a decreased accumulation of ECM; for example, lumican, keratocan and collagen I were greatly diminished. The absence of TGFbeta2 did not compromise cell proliferation, nor enhance apoptosis. The thinner stroma resulting from decreased ECM synthesis may account for the decreased cell number in the stroma of Tgfb2 null mice. Keratin 12 expression was not altered in Tgfb2(-/-) mice, implicating normal corneal type epithelial differentiation. Delayed appearance of macrophages in ocular tissues was observed in Tgfb2(-/-) mice. Malfunctioning macrophages may account for accumulation of cell mass in vitreous of Tgfb2 null mice.

Visual deprivation stimulates the exchange of the fibrous sclera into the cartilaginous sclera in chicks

Form deprivation myopia in chicks is a widely accepted model to study visually-regulated postnatal ocular growth. The chick sclera has a cartilaginous layer as well as the fibrous layer found in mammals. It appears that a dynamic relationship exists between these two layers during visual deprivation-induced growth. The changes in the fibrous sclera of myopic eyes, however, have not been previously described. This investigation is focused on the comparative morphological analyses of the cartilaginous and fibrous scleral changes in myopic chick eyes. The fibrous scleral changes in the posterior segment of myopic eyes were examined in detail using light and electron microscopy, and the expression of growth factors was analysed by immunohistochemistry. In the posterior segment of myopic eyes the border between the cartilaginous and fibrous layers was indistinct because of collagen bundles of the fibrous sclera that spread into the cartilaginous sclera, whereas in control eyes the distinction was clear. Various types of transitional cells, from fibroblast-like mesenchymal cells to chondrocytes, were found in the border between the cartilaginous and fibrous layers. Collagen fibrillar diameters of the fibrous sclera in the posterior segment of myopic eyes were smaller than in control, whereas those in the equatorial segment were almost the same in myopic and control eyes although the distribution of sizes was obviously different. Thus, changes in the fibrous sclera in myopic eyes of chicks seem to be similar to scleral changes in myopic eyes of mammals. The cells in the posterior sclera of myopic eyes were more intensely immunostained for TGF-beta and IGF-II than control, whereas no immunoreaction of TGF-alpha could be detected in either control or myopic eyes. These results suggest that the structural characteristics of the posterior sclera are different from those of the anterior and equatorial segments. Undifferentiated mesenchymal cells might be concentrically distributed exclusively in the innermost layer of posterior fibrous sclera. TGF-beta and IGF-II might influence cell growth, differentiation, and migration in the exaggerated scleral growth accompanying myopia.

Chondroitin sulphate proteoglycan is involved in lens vesicle morphogenesis in chick embryos

Proteoglycans have been implicated in the invagination and formation of various embryonal cavitied primordia. In this paper the expression of chondroitin sulphate proteoglycan (CSPG) is analysed in the lens primordium during lens vesicle formation, and demonstrate that this proteoglycan has a specific distribution pattern with regard to invagination and fusion processes in the transformation of placode into lens vesicle. More specifically, CSPG was detected in: (1) the apical surface of lens epithelial cells, where early CSPG expression was observed in the whole of the lens placode whilst in the vesicle phase it was restricted to the posterior epithelium; (2) intense CSPG expression in the basal lamina, which remained constant for the entire period under study; (3) CSPG expression in the intercellular spaces of the lens primordium epithelium, which increased during the invagination of the primordium and which at the vesicle stage was more evident in the posterior epithelium; and (4) CSPG expression on the edges of the lens placode both prior to and during fusion. Treatment with beta- D -xyloside causes significant CSPG depletion in the lens primordium together with severe alterations in the invagination and fusion of the lens vesicle; this leads to the formation of lens primordia which in some cases remain practically flat or show partial invagination defects or fusion disruption. Similar results were obtained by enzyme digestion with chondroitinase AC but not with type II heparinase, which indicates that alterations induced by beta- D -xyloside were due to interference in CSPG synthesis. The findings demonstrate that CSPG is a common component of the lens primordium at the earliest developmental stages during which it undergoes specific modifications. It also includes experimental evidence to show that 'in vivo' CSPG plays an important role in the invagination and fusion processes of the lens primordium.

Identification of choroidal ovotransferrin as a potential ocular growth regulator

PURPOSE

In an effort to identify choroidal factors potentially involved in the regulation of ocular growth, proteins released into culture medium of organ-cultured choroids were compared between control eyes and eyes recovering from form deprivation myopia.

METHODS

The choroids were obtained from the posterior poles of control and recovering chick eyes, and placed into organ culture containing ( 35)S-methionine/(35)S-cysteine. Culture medium was collected after 24 hours and proteins were separated and identified by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), fluorography, immunoprecipitation, western blot analysis and by amino acid sequencing. Choroidal proteins were tested for their effect on scleral proteoglycan synthesis by measuring (35)SO( 4) incorporation into scleral glycosaminoglycans (GAG) in vitro. Choroidal thickness and axial elongation were measured in control and recovering eyes using high frequency A-scan ultrasound.

RESULTS

The synthesis of an 80 kD protein was greatly increased in the choroids of recovering eyes compared with those of control eyes. Amino acid sequencing and immunoprecipitation indicated that the newly synthesized 80 kD protein was ovotransferrin (transferrin, conalbumin). Ovotransferrin release into the culture medium by isolated recovering choroids was associated with a decrease in the rate of axial elongation in recovering eyes. When tested in vitro, ovotransferrin (500 ng/micro) inhibited scleral proteoglycan synthesis in the sclera by 62% in a dose-dependent manner.

CONCLUSIONS

Chick choroids of recovering eyes synthesize and release ovotransferrin during the recovery from form deprivation myopia. Ovotransferrin significantly inhibited proteoglycan synthesis by the sclera, indicating that ovotransferrin may play a role in slowing the rate of vitreous chamber elongation and facilitating the recovery from induced myopia.

Axonal regeneration of retinal ganglion cells: effect of trophic factors

A variety of neurotrophic factors can influence the cell functions of the developing, mature and injured retinal ganglion cells. The discovery that retinal ganglion cell loss can be alleviated by neurotrophic factors has generated a great deal of interest in the therapeutic potential of these molecules. Recently, evidence has provided valuable information on the receptors that mediate these events and the intracellular signaling cascades after the binding of these ligands. Signaling by neurotrophic factors does not seem to restrict to retrograde messenger from the target but also includes local interactions with neighbouring cells along the axonal pathways, anterograde signaling from the afferents and autocrine signaling. More insight into the mechanisms of action of neurotrophic factors and the signal transduction pathway leading to the protection and regeneration of retinal ganglion cells may allow the design of new therapeutic strategies.

New insights into the pathophysiology of diabetic retinopathy: potential cell-specific therapeutic targets

Diabetic retinopathy, a leading cause of vision impairment, is classically defined by its vascular lesions. This review examines how diabetes affects vascular cells, as well as neurons, macroglia, and microglia. The cellular and clinical elements of diabetic retinopathy have many features of chronic inflammation. Understanding the individual cell-specific and global inflammatory changes in the retina may lead to novel therapeutic approaches to prevent vision loss.

Apoptosis in early ocular morphogenesis in the mouse

Development of the eye requires complex interactions between tissues, extracellular matrix and growth factors. Most cells of the optic primordia grow and differentiate into discrete ocular structures; however, other cells have death as their developmental fate. The most common mechanisms of cell death are apoptosis and necrosis. We have identified the cell death that occurs during ocular morphogenesis in ZRDCT-N mice as apoptosis. Mouse embryos, ages E8.5-E11.5, were embedded in paraffin, sectioned at 5 microns and stained with hematoxylin or by the terminal deoxytransferase-mediated dUTP-biotin nick end-labeling (TUNEL) method. The spatial and temporal distribution of apoptotic cells was mapped at 0.5 day intervals using a computerized image analysis system, and 3-D reconstructions were made at each embryonic age. Our data indicate that apoptosis plays a role in normal ocular morphogenesis and provides the groundwork for studies of abnormal ocular development.

Structure, development and function of cytoskeletal elements in non-neuronal cells of the human eye

The cytoskeleton, of which the main components in the human eye are actin microfilaments, intermediate filaments and microtubules with their associated proteins, is essential for the normal growth, maturation, differentiation, integrity and function of its cells. These components interact with intra- and extracellular environment and each other, and their profile frequently changes during development, according to physiologic demands, and in various diseases. The ocular cytoskeleton is unique in many ways. A special pair of cytokeratins, CK 3 and 12, has apparently evolved only for the purposes of the corneal epithelium. However, other cytokeratins such as CK 4, 5, 14, and 19 are also important for the normal ocular surface epithelia, and other types may be acquired in keratinizing diseases. The intraocular tissues, which have a relatively simple cytoskeleton consisting mainly of vimentin and simple epithelial CK 8 and 18, differ in many details from extraocular ones. The iris and lens epithelium characteristically lack cytokeratins in adults, and the intraocular muscles all have a cytoskeletal profile of their own. The dilator of the iris contains vimentin, desmin and cytokeratins, being an example of triple intermediate filament expression, but the ciliary muscle lacks cytokeratin and the sphincter of the iris is devoid even of vimentin. Conversion from extraocular-type cytoskeletal profile occurs during fetal life. It seems that posttranslational modification of cytokeratins in the eye may also differ from that of extraocular tissues. So far, it has not been possible to reconcile the cytoskeletal profile of intraocular tissues with their specific functional demands, but many theories have been put forward. Systematic search for cytoskeletal elements has also revealed novel cell populations in the human eye. These include transitional cells of the cornea that may represent stem cells on migration, myofibroblasts of the scleral spur and juxtacanalicular tissue that may modulate aqueous outflow, and subepithelial matrix cells of the ciliary body and myofibroblasts of the choroid that may both participate in accommodation. In contrast to the structure and development of the ocular cytoskeleton, changes that take place in ocular disease have not been analysed systematically. Nevertheless, potentially meaningful changes have already been observed in corneal dystrophies (Meesmann's dystrophy, posterior polymorphous dystrophy and iridocorneal endothelial syndrome), degenerations (pterygium) and inflammatory diseases (Pseudomonas keratitis), in opacification of the lens (anterior subcapsular and secondary cataract), in diseases characterized by proliferation of the retinal pigment epithelium (macular degeneration and proliferative vitreoretinopathy), and in intraocular tumours (uveal melanoma). In particular, upregulation of alpha-smooth muscle actin seems to be a relatively general response typical of spreading and migrating corneal stromal and lens epithelial cells, trabecular cells and retinal pigment epithelial cells.

Cloning and characterization of developmental endothelial locus-1: an embryonic endothelial cell protein that binds the alphavbeta3 integrin receptor

We have taken advantage of an enhancer trap event in a line of transgenic mice to identify a unique developmentally regulated endothelial cell locus (Del1). The protein encoded in this locus contains three EGF-like repeats homologous to those in Notch and related proteins, including an EGF-like repeat that contains an RGD motif, and two discoidin I-like domains. Del1 is shown to be a matrix protein and to promote adhesion of endothelial cells through interaction with the alphavbeta3 integrin receptor. Embryonic endothelial-like yolk sac cells expressing recombinant Del1 protein, or grown on an extracellular matrix containing Del1 protein, are inhibited from forming vascular-like structures. Expression of Del1 protein in the chick chorioallantoic membrane leads to loss of vascular integrity and promotes vessel remodeling. Del1 is thus a new ligand for the alphavbeta3 integrin receptor and may function to regulate vascular morphogenesis or remodeling in embryonic development.

TGFbeta2 knockout mice have multiple developmental defects that are non-overlapping with other TGFbeta knockout phenotypes

The growth and differentiation factor transforming growth factor-beta2 (TGFbeta2) is thought to play important roles in multiple developmental processes. Targeted disruption of the TGFbeta2 gene was undertaken to determine its essential role in vivo. TGFbeta2-null mice exhibit perinatal mortality and a wide range of developmental defects for a single gene disruption. These include cardiac, lung, craniofacial, limb, spinal column, eye, inner ear and urogenital defects. The developmental processes most commonly involved in the affected tissues include epithelial-mesenchymal interactions, cell growth, extracellular matrix production and tissue remodeling. In addition, many affected tissues have neural crest-derived components and simulate neural crest deficiencies. There is no phenotypic overlap with TGFbeta1- and TGFbeta3-null mice indicating numerous non-compensated functions between the TGFbeta isoforms.

Homeostasis of ocular surface epithelium in the rat is regulated by opioid growth factor

Endogenous opioid peptides serve as growth factors in developing, renewing, and neoplastic cells and tissues. This study examined the hypothesis that opioids serve to modulate the homeostatic renewal of ocular surface epithelium in the rat. DNA synthesis in the epithelium of the central (CC) and peripheral (PC) cornea, limbus (LM), and conjunctiva (CN) was investigated using adult male rats. Animals received an injection of opioid growth factor (OGF), [Met5]-enkephalin, OGF and naloxone (NAL), NAL alone, naltrexone (NTX), or an equivalent volume of sterile water (CO) and sacrificed 4 h later (i.e. 16:00 h). [3H]thymidine was administered 1 h before sacrifice. With the exception of NTX (20 mg/kg), all compounds were given at 10 mg/kg. Examination of 5 time points over an 18-h period revealed no variation in DNA synthesis within a region of ocular surface basal epithelium (BE). OGF depressed DNA synthesis of the BE by 25, 48, and 50% in the PC, LM, and CN, respectively; little labeling was recorded in the BE of the CC. Exposure to OGF-NAL or NAL alone did not alter DNA synthesis of the BE. Complete blockade of OGF-zeta receptor interaction by administration of the potent opioid antagonist, NTX, increased the number of epithelial cells in the PC, LM, and CN undergoing DNA synthesis by 30 to 72%. The effects of OGF and NTX on DNA synthesis of BE also were observed in an organ culture setting. Utilizing immunocytochemistry, OGF and its receptor zeta were associated with both the basal and the suprabasal cells of the ocular surface epithelium. These results indicate that an endogenous opioid peptide, OGF, and its receptor are present and govern homeostatic cellular renewal processes in ocular surface epithelium. OGF regulates DNA synthesis in a direct manner, and does so by a tonic, inhibitory, and receptor-mediated mechanism.

Expression of neurotrophic factors in cultured human retinal pigment epithelial cells

PURPOSE

To see if cultured human retinal pigment epithelial (RPE) cells have the capacity to synthesize neurotrophins, including nerve growth factor (NGF), brain-derived growth factor (BDNF), and neurotrophin-3 (NT-3).

METHODS

Expression of mRNAs for the neurotrophins was studied by the reverse transcription polymerase chain reaction (PCR) method. Quantitative analysis of the gene expression was done by using a semiquantitative PCR method. Secretion of NGF-like immunoreactivity (NGF-LI) into the culture medium was analyzed by enzyme immunoassay (EIA).

RESULTS

Cultured human RPE cells were found to express mRNAs for NGF, BDNF and NT-3. In the conditioned culture medium of the human RPE, 9.44 +/- 0.62 pg/ml (mean +/- SEM, n = 6) NGF-LI was found. Pretreatment of human RPE cells with interleukin-l (IL-1) (20 ng/ml), phorbol myristate acetate (PMA) (100 ng/ml) or tumor necrosis factor-alpha (TNF-alpha) (40 ng/ml) was found to increase the mRNA expression of neurotrophins and also to increase secretion of NGF-LI into the culture medium.

CONCLUSIONS

Our data demonstrate that cultured human RPE cells have the capacity to synthesize neurotrophins, and that various stimulations can up-regulate gene and protein expression of NGF by these cells.

Fibroblast growth factor receptors and regeneration of the eye lens

If the eye lens of the adult newt, Notophthalmus viridescens, is removed, a new lens will regenerate and only from the dorsal, not the ventral, iris. The source, pigmented epithelial cells, would normally no longer divide, but upon lentectomy they do re-enter the cell cycle and form lens. The cause for this capability is unknown, but the mitogenic Fibroblast Growth Factors and their receptors may be involved. We have demonstrated that FGF receptors are present and operative in lens regeneration, since receptor-directed mitotoxins inhibit regeneration; heterogeneity and differential density in FGF-binding and receptor localization in iris sectors is also present. We propose that the spatial distribution of FGF receptors, especially the amphibian homolog of FGFR-3, is important in initiation of regeneration of eye lens.

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.

Ontogeny of preproenkephalin mRNA expression in the rat retina

Endogenous opioid systems (i.e. opioid peptides and opioid receptors) modulate developmental events in the neonatal mammalian retina. In the present study, the mRNA encoding preproenkephalin A (PPE), the prohormone for the opioid growth factor (OGF), [Met5]-enkephalin, was studied in the developing and the adult retinas of rats. Northern analysis indicated the presence of a 1.4-kb message in the developing and adult retinas corresponding to rat PPE mRNA. Quantitation showed that PPE message was present on postnatal day 1 at 5% of the adult level, and increased during development until the adult quantity was reached by postnatal day 27. In situ hybridization experiments first detected the presence of PPE mRNA in retinal tissues during late gestation. In late prenatal and neonatal retinas, PPE message was associated with areas of the developing retina containing proliferating neuroblasts and postmitotic cells. Later in development, message appeared to be located primarily within the inner retina, with abundant PPE mRNA associated with putative horizontal cells of the inner nuclear layer (INL). The adult retina showed a similar pattern of PPE gene expression in the cells of the INL. These findings document that the gene expression in the retina for PPE begins in the fetus, continues during retinal development, and coincides with the presence of a PPE mRNA derivative ([Met5]-enkephalin) that regulates DNA synthesis during retinal ontogeny. Our results are also the first to show the presence of PPE message in the adult mammalian retina, suggesting transcription of an opioid gene in the mature visual system.

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.

The retinal pigmented epithelium is required for development and maintenance of the mouse neural retina

BACKGROUND

During development of the vertebrate eye, there is a series of reciprocal cellular interactions that determine the fate of the eye components. Although evidence from organ culture suggests that the retinal pigmented epithelium (RPE) organizes the laminar structure of the differentiated neural retina, no role has been identified for the RPE in early eye development, nor has the later function of RPE been demonstrated in vivo.

RESULTS

To investigate the role of RPE cells in eye development, we generated transgenic mice that carry the attenuated diphtheria toxin-A gene; this transgene was driven by the promoter of the gene encoding the tyrosinase-related protein-1, which is specifically expressed in pigment cells. Depending on the expression level of the transgene, the retinal epithelium was ablated before or after its differentiation into a pigmented cell layer. We show that an early ablation (embryonic day E10-11) resulted in disorganization of the retinal layer, immediate arrest of eye growth and subsequent eye resorption. A later ablation (E11.5-12.5) allowed the eye to be maintained during embryogenesis, but the laminar structure of the retina became disrupted by the end of gestation, the vitreous failed to accumulate the adults were anophthalmic or severely microphthalmic. In some microphthalmic eyes, a number of RPE cells escaped ablation and formed patches of pigmented cells; the laminar structure of the retina was maintained immediately adjacent to such pigmented areas but disrupted elsewhere. In both cases--early or late ablation of the RPE--the retina appears to be the primary affected tissue.

CONCLUSIONS

We conclude that presence of the RPE is required for the normal development of the eye in vivo. Its presence early in development is necessary for the correct morphogenesis of the neural retina. After the neural retina has started to differentiate, the RPE is still necessary, either directly or indirectly, to maintain the organization of the retinal lamina.

Autocrine/paracrine role of insulin-related growth factors in neurogenesis: local expression and effects on cell proliferation and differentiation in retina

Early neurogenesis progresses by an initial massive proliferation of neuroepithelial cells followed by a sequential differentiation of the various mature neural cell types. The regulation of these processes by growth factors is poorly understood. We intend to understand, in a well-defined biological system, the embryonic chicken retina, the role of the insulin-related growth factors in neurogenesis. We demonstrate the local presence of signaling elements together with a biological response to the factors. Neuroretina at days 6-8 of embryonic development (E6-E8) expressed proinsulin/insulin and insulin-like growth factor I (IGF-I) mRNAs as well as insulin receptor and IGF type I receptor mRNAs. In parallel with this in vivo gene expression, E5 cultured neuroretinas synthesized and released to the medium a metabolically radiolabeled immunoprecipitable insulin-related peptide. Furthermore, insulin-related immunoreactive material with a HPLC mobility close to that of proinsulin was found in the E6-E8 vitreous humor. Exogenous chicken IGF-I, human insulin, and human proinsulin added to E6 cultured neuroretinas showed relatively close potencies stimulating proliferation, as determined by [methyl-3H]thymidine incorporation, with a plateau reached at 10(-8) M. These factors also stimulated neuronal differentiation, indicated by the expression of the neuron-specific antigen G4. Thus, insulin-related growth factors, interestingly including proinsulin, are present in the developing chicken retina and appear to play an autocrine/paracrine stimulatory role in the progression of neurogenesis.

Ontogeny of the opioid growth factor, [Met5]-enkephalin, and its binding activity in the rat retina

The endogenous opioid peptide [Met5]-enkephalin is a tonically active opioid growth factor (OGF) with an inhibitory action on DNA synthesis in the developing rat retina. In this study, the ontogeny of the spatial and temporal expression of OGF and its binding activity was examined. OGF-like immunoreactivity was detected in the retina at gestation day (E) 20, but not at E18, and was localized to ganglion cell and neuroblast layers; immunochemical reaction was no longer seen in the retina by postnatal day 6. Native OGF was further identified and characterized by high-performance liquid chromatography (HPLC) studies and immunodot assays, which revealed that [Met5]-enkephalin was present in the neonatal, but not adult, rat retina. OGF binding activity was detected as early as E18 using [125I]-[Met5]-enkephalin and in vitro receptor autoradiography. Little OGF binding activity was noted for prenatal retinas, but appreciable activity was observed from birth to postnatal day 4; no OGF binding could be detected after postnatal day 5 or in the adult. These results reveal the transient appearance of the OGF, [Met5]-enkephalin, and its receptor binding activity in the developing mammalian retina, and show that their ontogeny coincides with the timetable of DNA synthesis of retinal neuroblasts.