Lens epithelial cell adhesion to lens capsule: a model system for cell-basement membrane interaction

Inhibitory effects of Arg-Gly-Asp (RGD) peptide on cell attachment and migration in a human lens epithelial cell line

Posterior capsule opacification (PCO) after cataract surgery is caused by growth of residual human lens epithelial (HLE) cells on the posterior capsule. We have shown that extracellular matrix (ECM) is an essential factor for HLE cell attachment and migration. The purpose of this study was to examine the inhibitory effects of Arg-Gly-Asp (RGD) peptide on cell attachment and migration in an HLE cell line. HLE cell line cells (SRA 01/04) that were obtained by transfection of large T antigen of SV40 were cultured in the absence of serum. The culture dishes were coated with type IV collagen, laminin or fibronectin, and Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) RGD peptide (0.1, 0.3, 1.0, 2.0 mg/ml) was added to the medium. The number of attached cells was counted after 90 min of incubation, and the inhibitory effects of GRGDSP RGD peptide on cell attachment were calculated. Cell attachment on the fibronectin-coated dishes was inhibited by GRGDSP RGD peptide at concentrations higher than 0.3 mg/ml; the inhibitory rate was 80% at a concentration of 2.0 mg/ml. The inhibition of cell attachment by GRGDSP RGD peptide on laminin-coated dishes appeared only at a concentration of 2.0 mg/ml, whereas no effects were observed on the type IV collagen-coated dishes. The inhibitory effects of GRGDSP RGD peptide on cell migration were measured in medium containing 2.0 mg/ml of GRGDSP RGD peptide after 1, 3, 5 and 7 days of culture. Cell migration was inhibited by GRGDSP RGD peptide from 1 day of culture on the fibronectin-coated dishes and from 5 days of culture on the laminin-coated dishes, whereas no effects were observed on the type IV collagen-coated dishes. GRGDSP RGD peptide inhibited cell attachment and migration on laminin and fibronectin that have RGD sequences. These data suggested that RGD peptide may have the potential to prevent PCO.

Vitronectin is significant in the adhesion of lens epithelial cells to PMMA polymers

A major complication of intraocular lens surgery is diminished visual acuity caused by the regrowth of lens epithelial cells (secondary cataract). Polymethylmethacrylate (PMMA) is a commonly used intraocular lens material. This study addresses the mechanisms underlying the initial adhesion of lens epithelial cells to PMMA and a functionalized PMMA-based terpolymer known to inhibit cell proliferation. Rabbit lens epithelial cells were cultured on the test polymer surfaces in medium containing serum depleted of either fibronectin or vitronectin (or both) to identify the role of these proteins in the initial process of cell adhesion. Adherent cells were quantitated after 60 min, and the actin cytoskeleton and focal contact formation were compared in each serum treatment on both polymers. Vitronectin was significantly more effective for initial cell attachment to both polymers than fibronectin. Normal cell spreading on PMMA required vitronectin and was independent of fibronectin, whereas cell spreading on the terpolymer was abnormal and required the presence of fibronectin and vitronectin together. Together, these results help to explain the inhibition of cell proliferation previously shown on the functionalized PMMA. This work contributes to the design of a polymer for use in intraocular lenses that inhibits proliferation of the target cells.

The effects of extracellular matrix on cell attachment, proliferation and migration in a human lens epithelial cell line

Lens capsule consists of several kinds of extracellular matrix (ECM) which may play an important role in cell attachment, migration and proliferation of lens epithelial cells as a basement membrane. We have investigated the effects of ECM on cell attachment, proliferation and migration in a human lens epithelial (HLE) cell line. The HLE cell line, SRA 01/04, which was transfected with large T-antigen of SV40 was cultured in the absence of serum. Culture plates were coated with human type IV collagen, laminin or fibronectin. The number of cells were counted at 30-180 min and 3, 5 and 7 days of culture. The rate of BrdU incorporation was measured to study the cell proliferation. The cell migration was measured 1, 3, 5 and 7 days after seeding cells. Integrins, the receptors of ECM, were also detected using antibodies for the cell membrane antigens (CD49b, CD49c, CD49e) by an immunohistochemical method. Although less than 10% of cells attached to the non-coated plate and 50-60% of cells attached to the ECM-coated plates, there was no difference of cell attachment among each ECM used. The cell attachment was almost complete during the first 30 min of culture. Cell proliferation was not enhanced, but cell survival was aided by culture on the ECM components for up to 7 days. The area of cell attachment enlarged on the ECM-coated plates, whereas no migration was observed on the non-coated plate. These data indicate that ECM is the essential factor for cell attachment and increases migration of HLE cells.

Reversal of galactosemic-induced inhibition of PGH synthase activity in cultured lens epithelial cells

Inhibition of prostaglandin synthesis as determined by prostaglandin endoperoxide synthetase (PGH synthase) activity is associated with polyol accumulation in cultured bovine lens epithelial cells (BLECs) incubated six days in minimal essential medium (MEM) containing 40 mM galactose (Gal). In order to better understand the nature of the correlation between hypergalactosemic exposure, polyol accumulation and inhibition of prostaglandin synthesis, a series of culture media reversal and sorbinil (an aldose reductase inhibitor) addition studies were carried out. BLECs were incubated in Gal for six days, then changed to galactose-free MEM +/- sorbinil for a three day recovery period. PGH synthase activity reduced to 66% of control after six days of exposure to Gal. The simultaneous administration of sorbinil during a nine day Gal incubation significantly protected the enzymatic activity, while the activity of PGH synthase further declined to 41% of control under the same conditions in the absence of sorbinil. Within 72 hours of media reversal, PGH synthase activity equaled or exceeded control values in BLECs switched to either MEM or MEM + sorbinil. Indeed, an enhanced prostaglandin biosynthetic capacity as demonstrated by radioimmunoassay was exhibited with microsomes prepared from cells switched from Gal into Gal-free MEM +/- sorbinil, corroborating the beneficial effect of media reversal. Furthermore, following 72 hours of reversal, the cellular dulcitol level was 93 nmol/micrograms PO4 for BLECs switched to MEM alone; no detectable level of polyol was observed in BLECs changed to MEM + sorbinil. In contrast, the polyol content in BLECs after six days of exposure to Gal was 185 nmol/micrograms PO4 and increased to 334 nmol/micrograms PO4 after nine days of continuous incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of daunomycin toxicity on lens epithelium in vitro

Posterior capsule opacification is the major complication of extracapsular cataract extraction (ECCE). Lens epithelial cells derived from the periphery of the lens are thought to migrate posteriorly and contribute significantly to the postoperative proliferations at the posterior pole. We have evaluated the effects of the antiproliferative drug daunomycin on cultured porcine lens epithelial cell viability and proliferation. We observed that the mitotic activity of the cells is suppressed by a single short time treatment with daunomycin at a concentration as low as 2.5 mg/l. Long term effects on the reproductive capacity of the lens epithelial cells may not be as pronounced as the inhibition of other cells examined before e.g. retinal pigment epithelium and fibroblasts. Our results indicate that daunomycin may be useful for the pharmacologic prevention of postoperative proliferations in patients treated by ECCE.

Attachment of blastocysts to lens capsule: a model system for trophoblast-epithelial cell interaction on a natural basement membrane

The bovine lens capsule has previously been shown to provide an optimal surface for the examination of epithelial cell interaction with a basement membrane. This native substrate has been used to investigate some initial aspects of attachment of mouse blastocysts and trophoblastic cellular outgrowth. Mouse blastocysts were presented to the cell-free humoral side of the anterior lens capsule, incubated for 72 h, and examined by scanning and transmission electron microscopy. Blastocysts hatch and attach from their zonae pellucidae by 30 h. Trophoblastic cells proliferate rapidly in a coronal direction, display extensive surface microvilli, and advance by the extension of numerous filipodia, many of which terminate with bulbous projections. These projections were shown by transmission electron microscopy to contain numerous vacuoles and polysomes. To simulate further the initial blastocyst-uterine interaction, a suspension of lens epithelial cells was introduced to the capsule and permitted to form a monolayer prior to the addition of the blastocysts. At 72 h the monolayer of lens cells remained intact. We observed that: a) lens cells appear to recede from the advancing trophoblastic cells, and b) trophoblastic cells extend beneath the monolayer of lens cells and thereby dislodge the cells from the lens capsule substrate. No infiltration of the capsule by the advancing trophoblastic cells was observed. The lens capsule appears to offer a promising system for the study of trophoblast-epithelial cell interaction on a natural basement membrane.

Colocalization of laminin and fibronectin in bovine lens epithelial cells in vitro

The distribution and organization of the extracellular matrix (ECM) proteins laminin, fibronectin, entactin, and type IV collagen were investigated in primary colonies and secondary cultures of bovine lens epithelial cells using species-specific antisera and indirect immunofluorescence microscopy. Primary cell colonies fixed in formaldehyde and permeabilized with Triton X-100 displayed diffuse intracellular patterns for type IV collagen and entactin, observed to a similar degree throughout the colonies. In contrast, thick bundles of laminin and fibronectin were located on the basal cell surfaces and in between cells in the densely packed center of the colonies, and as "adhesive plaques" and fine extracellular matrix cords in the sparsely populated (migratory) outer edge of the colonies. The distribution of ECM proteins observed in secondary lens epithelial cell cultures was similar to that observed at the periphery of the primary colony. Extraction of the secondary cell cultures with sodium deoxycholate confirmed that laminin and fibronectin were deposited on the basal cell surface. Indeed, the patterns of laminin and fibronectin deposition suggested that these proteins codistribute. These results establish that lens epithelial cells in culture can be used as a model system to study the synthesis and extracellular deposition of the basement membrane proteins, laminin and fibronectin.

Comparison of basement membrane matrix degradation by purified proteases and by metastatic tumor cells

We have examined the nature of biochemical degradation of an isolated basement membrane matrix (bovine lens capsule) using different methodologies. The first strategy was quantitation of the release of surface-bound 125I and a second the documentation by SDS-PAGE of the appearance of putative cleavage products and the loss of high-molecular-weight components from the matrix. Basement membrane matrix bands resolved on SDS-PAGE were identified by their protease sensitivities as well as by Western immunoblots using monoclonal antibodies developed for this study. Radioiodinated components were found predominantly at positions on the gel equivalent to 160-200 kd and 400 kd proteins. Since these labeled moieties were sensitive to bacterial collagenase digestion and stained with anticollagen type IV antibodies, they were determined to represent various configurations of collagen type IV. Several other lower-molecular-weight bands also stained with the anticollagen IV antibodies. Monoclonal antibodies reactive with laminin exhibited a complex staining pattern on the gels, which included the expected 200 and 400 kd components. We confirmed that lens capsule basement membrane contained only a single heparan sulfate glycosaminoglycan species, and tumor cell-induced glycosaminoglycan degradation within the basement membrane matrix was detected using cellulose acetate electrophoresis. Distinctive putative cleavage products were resolved on SDS-PAGE gels from matrices subjected to digestion by a variety of purified proteases as well as by metastatic tumor cells or their conditioned media. Tumor cells of different histiotypes produced different characteristic cleavage patterns, suggestive of the existence of several pathways of matrix degradation. Overall, primary tumor cells exhibited a greater degradative activity towards the basement membrane matrix than did long-term tissue culture-passaged cells. The same tumor cell line could exhibit considerably different patterns of both protein and glycosaminoglycan degradation depending on recent culture history. The relevance of these biochemical studies to the pathogenesis of malignant neoplasms is shown by: 1) the evaluation of degradative activities of B16 tumor cell populations exhibiting enhanced lung-colonizing phenotypes, and 2) the ability of a known antimetastatic moiety with antiprotease activity (Haementeria leech species salivary gland extract) to protect matrix components from degradation by tumor cell-conditioned medium.

Molecular basis of the isozymes of bovine glucose-6-phosphate isomerase

Glucose-6-phosphate isomerase occurs in different bovine tissues as multiple, catalytically active isozymes which can be resolved by polyacrylamide gel electrophoresis (PAGE) and isoelectric focusing (IEF). Most differentiated tissues have five distinct forms with apparent pI values of 7.2, 7.0, 6.8, 6.6, and 6.4. Young, mitotically active, cells of the intestinal mucosa and the epithelium of the eye lens show only the two more basic isozymes, while old cells in the cortex and nucleus of the eye lens accumulate the more acidic isozymes. All of the isozymes exhibit equal separation based on charge-to-mass ratio (PAGE) and charge (IEF), thus indicating only charge changes. The isozyme patterns are unchanged in the presence of reducing agents or protease inhibitors. Each isozyme was purified to homogeneity and shown to exhibit identical subunit molecular weights (59,000) on SDS-gel electrophoresis. Each of the isolated isozymes, when subjected to PAGE or IEF, exhibited a single band, indicating that the isozymes are not generated as a result of electrophoresis. When the most basic isozyme was incubated in vitro under mild alkaline conditions, there was a spontaneous generation of the more acidic isozymes with properties identical to those found in vivo. The isozymes, thus, appear to be the result of spontaneous, postsynthetic modifications involving the addition of equal numbers of negative charges and are consistent with the deamidation of specific asparagine and/or glutamine residues.

Macromolecular organization of bovine lens capsule

Rabbit antisera to type IV collagen, laminin, entactin, heparan sulfate proteoglycan and fibronectin were used to localize these proteins in cross-sections of bovine anterior lens capsule. The antisera were exposed to (a) 10-micron frozen-thawed sections of formaldehyde-fixed tissue for examination in the light microscope by the indirect immunofluorescence method and (b) formaldehyde-fixed and L. R. White plastic-embedded thin sections for electron microscopic examination by the protein A-gold technique. The intensity of immunofluorescence was both uniform and strong throughout for type IV collagen, laminin and entactin, but patchy and weak for fibronectin. Electron microscopic immunolabeling with protein A-gold showed that all five components were distributed throughout the full thickness of the membrane, albeit the density of gold particles was not identical for all basement membrane proteins. In general, the number of particles per micron2 was greatest for type IV collagen and entactin, moderate for laminin and heparan sulfate proteoglycan and low for fibronectin. The ultrastructure of the lens capsule as examined by the electron microscope revealed a relatively uniform parallel alignment of filaments, thought to be collagenous. Since the distribution of the filaments corresponds well with the observed immunocytochemical pattern it is concluded that type IV collagen, laminin, entactin, heparan sulfate proteoglycan and fibronectin co-localize throughout the cross-section of the anterior lens capsule.

Identification of noncollagenous components of calf lens capsule: evaluation of their adhesion-promoting activity

Extraction of calf anterior and posterior lens capsules with 5 M guanidine HCI resulted in the solubilization of protein (12% of total) with a noncollagenous amino acid composition leaving behind the collagen matrix. Polyacrylamide gel electrophoresis of the solubilized material revealed a number of components, all of which were susceptible to trypsin but resistant to collagenase digestion. Fractionation of the extracted proteins by Sepharose CL-6B filtration as well as by affinity chromatography was undertaken, and laminin, fibronectin, entactin, and beta-crystallin were identified by electrophoresis and solid-phase radioimmunoassays in both anterior and posterior capsules. An entactin (Mr = 150,000), which constituted the most prominent component on electrophoresis, was purified after Sepharose CL-6B filtration by a two-step lectin affinity chromatography procedure, which was based on the failure of this protein to bind to Bandeiraea simplicifolia I but its positive reactivity with wheat germ lectin. Neither the mixture of proteins extracted from lens capsules by guanidine nor fractions prepared therefrom were able to enhance lens epithelial cell attachment to type I or type IV collagen-coated surfaces or to guanidine-prepared lens capsules; adhesion-stimulating activity could not be demonstrated even when cycloheximide-treated cells were employed. Furthermore, the cells were observed to attach as effectively to guanidine-extracted as to native capsules. These observations indicate that noncollagenous proteins are not essential for the in vitro attachment of epithelial cells to lens capsule; it appears that the collagen component itself provides an optimal surface for cell-basement membrane interaction.

Biosynthesis of sulphated macromolecules by rabbit lens epithelium. II. Relationship to basement membrane formation

Rabbit lens epithelial cells display a similar "cobblestone" morphology and produce the same complement of sulphated macromolecules (also see Heathcote, J.G., and R.W. Orkin, 1984, J. Cell Biol., 99:852-860) whether grown on plastic or glass, dried films of gelatin or type IV collagen with laminin, or on gels of type I collagen. There was no evidence of basement membrane formation by these cells when they were grown on plastic, glass, or dried films. In contrast, cultures that had been grown on gels deposited a discrete basement membrane that followed the contours of the basal surfaces of the cells and in addition, they secreted amorphous basement membrane-like material that diffused into the interstices of the gel and associated with the collagen fibrils of the gel. A significant proportion (approximately 70%) of the heparan sulphate proteoglycan fraction that was secreted into the culture medium (fraction MI) when the cells were grown on plastic became associated with the cell-gel layer in the gel cultures. Further, when basement membrane was isolated by detergent extraction, greater than 90% of the 35S-labeled material present was in this heparan sulphate proteoglycan.

Cell attachment and spreading on extracellular matrix-coated beads

Parietal yolk sac cells M1536 -B3 grown on cytodex 2 beads deposited an extracellular matrix on the surface of the beads. Cell-free matrix-coated beads were isolated by treatment of the cell monolayer with cytochalasin B (CB) at a concentration of 10 micrograms/ml of phosphate-buffered saline (PBS). The matrix when analysed by electrophoresis on polyacrylamide gels (PAGE) revealed that the major components were laminin and entactin . The matrix-coated beads were used to study the attachment, spreading, and growth of African Green monkey BSC-40, human mammary MCF-7, mouse fibroblast L929, rat liver clone 9, and rat hepatoma H-4-II-E cells in defined serum-free growth medium. The different cell lines exhibited varying responses to matrix-coated vs uncoated beads with respect to rate of attachment, spreading, and growth. One of the most consistent responses observed was the enhancement of cell spreading on matrix-coated beads. The results suggested that the matrix-coated beads will provide a readily available and valuable tool for studies on cell surface-extracellular matrix interactions and the physiological consequences of those interactions.

Differentiation of human scalp hair follicle keratinocytes in culture

The morphology of human scalp hair follicle keratinocytes, cultured on the bovine eye lens capsule, is studied by light and electron microscopy. The hair follicle keratinocytes in the stratified cultures are characterized by the presence of numerous tonofilaments, desmosomes and lysosomes and by the presence of glycogen accumulations. The cells in the upper layers develop a cornified envelope. Moreover, an incomplete basal lamina is found between the capsule and the basal cells. However, some features of epidermal keratinocytes in vivo, such as keratohyalin granules and stratum corneum formation, are absent. Analysis of the polypeptides by sodium dodecylsulfate polyacrylamide gel electrophoresis also reveals differences between the cultured hair follicle cells and epidermis, whilst the patterns of cultured cells and hair follicle sheaths are similar. The morphological and protein biosynthetic aspects of terminal differentiation of the keratinocytes in vitro are correlated. These results are discussed in the light of the findings with cultured epidermal keratinocytes, reported in the literature.

Interaction of bovine epithelial lens (BEL) cells with extracellular matrix (ECM) and eye-derived growth factor (EDGF). I. Effects on short-term adhesiveness and on long-term organization of the culture

A growth factor (EDGF) derived from the retina controls the proliferation and shape of adult bovine epithelial lens (BEL) cells in vitro as well as extracellular matrix (ECM) assembly. In order to analyse this mechanism and the specificity of the interactions between BEL cells and the extracellular matrix we have investigated the adhesion and growth of BEL cells on various substrata (fibronectin, laminin, ECM). BEL cells treated with EDGF adhered more slowly to plastic Petri dishes than untreated cells, in part due to EDGF inhibition of fibronectin deposition. The untreated BEL cells spread less well on ECM or laminin than on fibronectin-coated plastic. The preferential adhesiveness of BEL cells on fibronectin vs laminin was confirmed by attachment experiments performed on replicas of SDS-PAGE of these proteins. However, in long-term cultures, 8 days after seeding, BEL cells were very differently arranged on plastic or on ECM. ECM by itself did not increase the proliferation rate but helped to restore an organized cell monolayer. BEL cells stimulated to grow on ECM by treatment with EDGF exhibited at least transiently contact inhibition producing a perfectly organized epithelium similar to the one observed in vivo. These results suggest specific interactions between ECM or ECM components with BEL cell that restrain excessive cell spreading and restore an original polarized phenotype of the cells seen in vivo.