Donor age influences the growth of rabbit lens epithelial cells in vitro

Inhibitory effects of salmosin, a disintegrin, on posterior capsular opacification in vitro and in vivo

The proliferation, migration and transdifferentiation of the remaining lens epithelial cells (LECs) after cataract surgery are a major cause of posterior capsular opacification (PCO). It has previously been reported that salmosin, a novel disintegrin, significantly inhibits solid tumor growth in mice by perturbation of tumor-specific angiogenesis via blocking alpha v beta 3 integrin expressed on vascular endothelial cells. In this study, the inhibitory function of salmosin in PCO was investigated and was found that salmosin inhibits the attachment of bovine LECs and rabbit lens cells (N/N1003A) to extracellular matrix-coated plates. The anti-adhesive activity of salmosin was approximately 1000 times higher than that of synthetic Arg-Gly-Asp peptide. In addition, the cell proliferation and migration of bovine LECs and N/N1003A were strongly inhibited by salmosin, whereas the proliferation of corneal endothelial cells was less affected. LEC migration and proliferation were also decreased by salmosin treatment in rabbit eyes without any toxic effect in the cornea, iris and retina. In this study, salmosin was shown to specifically inhibit LEC migration and proliferation in an animal model. Therefore, the authors suggest that further investigation may show salmosin to be a good candidate for inhibiting PCO development.

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.

Human lens epithelial cell line

Although primary cultures of human lens epithelial (HLE) cells provide important information concerning the role of epithelium in normal lens and cataract formation, the lack of a cell line precludes a broad range of studies on the metabolism and molecular biology of these cells. We have, therefore developed an HLE cell line. Primary cultures of HLE cells were transfected with plasmid vector DNA containing a large T antigen of SV40. The immortalized cells were characterized with regard to morphology, growth rate, karyotype, and expression of crystallins, aldose reductase and other enzymes. A single clone of the immortalized cells, SRA 01/04, formed a monolayer and grew constantly over 130 passages. Isozyme phenotype showed that SRA 01/04 was of human origin, and the chromosome counts were in the hypotetraploid range. Western blot analysis showed that the cells expressed a very low level of crystallins (alphaA and betaB2) and aldose reductase. Messenger RNA (mRNA) for both alpha and beta crystallins was detected by reverse transcription polymerase chain reaction (RT-PCR) in both early and late passages. Sequence analysis of the PCR products, corresponding to alphaA and betaB2 crystallins in the cell line and in primary cultures of HLE, revealed a 100% match with published human alphaA and betaB2 sequences. These characteristics were unchanged in the cell line in early and late passages. This is the first report of the presence of alphaA and transcripts of mRNA for both alphaA and betaB2 in an established human cell line. This new HLE cell line makes it possible to undertake many future studies on the role of epithelium in lens and cataract formation.

Growth characteristics of human lens epithelial cells in culture. Effect of media and donor age

The effect of different concentrations of fetal calf serum (FCS) on the proliferative capacity of human and bovine lens epithelial cells in culture was evaluated. The effect of donor age on the maximum number of passages achieved using thirty eight individual cultures was also studied. The donor ages ranged from 1-88 years. Fifteen percent FCS was found to be the optimum concentration for both human and bovine cells. The two cell types demonstrated very similar responses across the spectrum of concentrations used. Correlation analysis revealed a significant (p < 0.05) negative correlation between donor age and maximum number of cell passages achieved.

DNA damage and repair in rabbit lens epithelial cells following UVA radiation

Since ultraviolet light may be a contributing factor to cataractogenesis, we investigated the response of the lens epithelium, a potential target for UV insult, to UVA radiation. Cell survival and the induction and repair of DNA single-strand breaks (SSBs) were measured in cultured rabbit lens epithelial cells following UVA exposure. The light was passed through a filter which eliminated wavelengths below 335 nm in order to ensure that the cells were exposed only to UVA. In order to study the effect of various fluences of UVA on cell survival, 2 x 10(6) cells suspended in Tyrode's buffer were exposed to UVA. During all irradiations the cells were maintained at 0.5 degrees C in order to minimize DNA repair. Following UVA treatment, 200 cells were cultured in minimal essential medium containing 10% rabbit serum, and a colony forming assay was used to quantify cell survival. UVA induced cell death in a dose-dependent manner. In additional experiments, confluent epithelial cells on glass slides immersed in Tyrode's buffer were irradiated and SSBs were quantified using the alkaline elution technique. A 30 min exposure to UVA (180 KJ/m2) induced measurable SSBs. An increase in UVA fluence brought about an increase in the number of DNA SSBs. Rejoining of SSBs was measured after the cells were irradiated in Tyrode's for 2 hrs and allowed to repair in the dark for 4 hrs at 36 degrees C in MEM containing 10% serum. Eighty percent of the DNA SSBs were repaired within 4 hrs as determined by analysis of the alkaline elution profile. The repair kinetics were biphasic with an initial fast and subsequently slower component. The results indicate that UVA can induce SSBs in lens epithelial cells, that the cells can repair most UVA-induced SSBs, and that UVA treatment can be toxic to the epithelium.

Effects of aging in vitro on intracellular proteolysis in cultured rabbit lens epithelial cells in the presence and absence of serum

Alterations in proteolytic capabilities have been associated with abnormalities in the aged eye lens, but in vivo tests of this hypothesis have been difficult to pursue. To simulate aging, we cultured cells from an 8-yr-old rabbit to early (population-doubling level 20 to 30) and late (population-doubling level greater than 125) passage. Long-lived (t1/2 greater than 10 h) and short-lived (t1/2 less than 10 h) intracellular proteins were labeled with [3H]leucine, and the ability of the cells to mount a proteolytic response to the stress of serum withdrawal was determined. For early passage cells, the average t1/2 of long-lived proteins in the presence and absence of serum was 62 and 39 h, respectively. For late-passage cells, the average t1/2 of long-lived proteins in the presence and absence of serum was 58 and 43 h, respectively. The net increase in intracellular proteolysis in the absence of serum was 59 and 35% for early and late-passage cells, respectively. Thus, in vitro-aged rabbit lens epithelial cells amount only 60% the proteolytic response to serum removal shown in "younger" cells. The enhanced ability of early passage cells to respond to serum removal seems to involve lower homeostatic levels of proteolysis in the presence of serum and greater enhancement of proteolysis in the absence of serum. Less than 2% of the protein is in the pool of short-lived proteins. Rates of proteolysis of short-lived proteins in the presence and absence of serum were indistinguishable. With respect to basal proteolytic rates in the presence of serum and ability to mount a proteolytic response upon serum withdrawal, these rabbit lens epithelial cells are similar to bovine lens epithelial cells and fibroblasts.

Ageing in the chick lens: in vitro studies

In principle, ageing may be due to the interaction of several factors, including the accumulation of random changes both genomic and non-genomic, secondary changes in a tissue contingent upon the changing function of other tissues, and programmed non-random changes in the tissue-specific expression of various genes. The use of a single tissue comprising one cell type only, in which the major gene products are well defined, in which there is a well attested series of developmental and age-related changes in cell properties and gene expression and which can be studied and compared in vivo and in vitro, offers advantages for investigation of these questions. The vertebrate eye lens possesses these advantages. The crystallins (proteins expressed at super-abundant levels in the lens) are well characterised. The lens epithelial cells (LEC) grow readily and can differentiate into the lens fibre cells in vitro, and, finally, such terminally differentiated cells may also be derived, by a process of transdifferentiation, from neural retina cells (NRC) in vitro. Thus the effect on ageing changes of the tissue of origin may also be studied. This article reviews our previous studies on long-term changes in growth potential, differentiation capacity and crystallin expression of chick lens cells in ageing cultures, their overall similarity to events in vivo and the effect on ageing changes of genotypes affecting the growth rate. It presents new information on these genetic aspects, and on crystallin expression in long-term ageing cultures of transdifferentiated neural retina, and compares the behaviour of ageing chick lens cells with that reported for mammals.

Induction of de novo synthesis of crystalline lenses in aphakic rabbits

The mammalian lens, like other ectodermal tissues, can regenerate itself given the proper environment. Endocapsular phacoemulsification of adult rabbit lenses was performed. A lens capsular bag with posterior and anterior lens capsule relatively intact was left in the eye. Regrowth of material in the capsular bag was followed by slit lamp biomicroscopy and photography over a 12-month period. Histopathology of the new material showed regions of relatively normal epithelial cells and lens fibers as well as regions where growth was irregular. All major lens crystallin classes were present in the regenerated lens. Several specific crystallin subunits, known to arise by post-translational modification of primary gene products, were absent or present in abnormally low concentrations.

Human fetal lens epithelial cells in culture: an in vitro model for the study of crystallin expression and lens differentiation

We have cultured and passaged human fetal lens epithelial cells. Cultured cells exhibited hexagonal, cuboidal shape typical of epithelial cells. Unlike previous observations made with cultured mammalian lens epithelial cells, indirect immunofluorescence and temporal analysis of 35S-labeled proteins demonstrated undiminished levels of alpha B-crystallin in primary, secondary, and tertiary cultures. Among the alpha-crystallins only alpha B synthesis was detected. Two dimensional gel electrophoresis indicated the presence of alpha B2 and no alpha B1. beta B2-crystallin, a fiber cell specific protein hardly detectable in primary cultures, increased significantly upon passaging. Human fetal lens epithelial cell cultures, described in this report, thus present a useful in vitro model for the study of lens epithelial cell differentiation and its pathological manifestations.

Effect of inhibition of the glutathione redox cycle on the ultrastructure of peroxide-treated rabbit epithelial cells

Our previous studies have shown that exposure of cultured rabbit lenses to physiological levels of hydrogen peroxide, following inhibition of the glutathione redox cycle, leads to the formation of distinct vacuoles in the anterior region of the lens at the germinative zone between the epithelium and lens fibers. In the present study the ultrastructure of H2O2-induced membrane damage in the intact lens and in cultured lens epithelial cells was examined by scanning and transmission electron microscopy (SEM and TEM), following the inhibition of glutathione reductase with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Lenses treated with BCNU/H2O2 exhibited swollen epithelial cells which were observed only above the peroxide-induced vacuoles. The apical surface of the swollen cells had membrane blebs which protruded into the underlying vacuolar space. The appearance of the blebs coincided with a change in the organization of the layer of microfilaments which is normally associated with the apical surface of the cell. Cultured lens epithelial cells treated with BCNU/H2O2 showed membrane blebs which increased in size and number with the duration of exposure. Initially, the blebs were seen only on certain regions of the cell surface with other regions appearing normal. TEM revealed a disorganization of microfilaments in the BCNU/H2O2 treated cells. Neither BCNU nor H2O2 alone affected the morphology of intact lenses or of cultured lens epithelial cells. In culture, isolated lens epithelial cells exposed to BCNU/H2O2 were more susceptible to damage than contiguous cells. While the exact mechanism by which H2O2-induced damage leads to bleb formation on the cell surface is not known, the inability of the cells to detoxify H2O2 due to the inhibition of glutathione reductase results in the disturbance of membrane cytoskeleton and a focal weakening of the cell surface. These results indicate a correlation between the active glutathione redox cycle in lens epithelium and maintenance of normal cytoskeletal protein organization.

Intracellular protein degradation in cultured bovine lens epithelial cells

Although several proteases have been identified in homogenates of cultured epithelial cells of the eye lens and in lens tissues, there is little information regarding intracellular protein degradation in intact lens cells in vitro. Cultured lens cells may be useful in the study of intracellular protein degradation in the lens, a tissue with a wide range of protein half-lives. This is of interest because alterations in protein turnover in the lens have been implicated in cataract formation. This study examines intracellular protein degradation in cultured bovine lens epithelial cells (BLEC). Cell cultures were incubated with radiolabeled leucine to label intracellular proteins. Protein degradation was measured by monitoring the release of trichloroacetic-acid-soluble radioactivity into the culture medium. The average half-life of long-lived proteins (half-life greater than 50 h) was typically about 57 h in serum-supplemented medium. Average rates of degradation of long-lived proteins increased by up to 73% when fetal bovine serum was withdrawn from the culture medium. Serum had no effect on the degradation of short-lived proteins (half-life less than 10 h). Degradation of long-lived proteins in the presence and absence of serum was further studied in cultured BLEC from population doubling level (PDL) 2 to 43. Average half-life of proteins in serum-supplemented medium was 52 to 58 h and did not vary significantly as a function of PDL. Degradation rates in serum-free medium increased approximately twofold up to PDL 7, but returned by PDL 25 to original levels, which were maintained through PDL 43.

The influence of the genotype on the process of ageing of chick lens cells in vitro

We reported previously that changes in crystallin expression in differentiating long-term primary cultures of lens cells from five different chick genotypes are similar to those which occur in vivo between hatching and the 8-week-old adult. These changes followed a similar program in all genotypes but occurred more rapidly in cells from the fast-growing than from the slow-growing genotypes. The present study examines ageing changes in lens cell populations from the same five genotypes, over a 4-6 month period, using long-term serial subcultures. The capacity for lentoid differentiation was progressively lost, but the rate of loss was inversely related to the intrinsic growth rate of the cells of these genotypes, occurring at the first passage in the slowest-growing strain, while fifth passage cells of the fastest-growing strain still retained some lentoid-forming capacity. The rate of loss of crystallin expression was also inversely related to the genetic growth rate, but the sequence of changes appears to be nonrandom, since it was broadly similar in all genotypes, starting with a preferential loss of delta-crystallin, as occurs in vivo; although alpha- and beta-crystallins were undetectable in late dedifferentiated cultures, the capacity of the cells for their synthesis was still present. Cultures from both fast-growing genotypes eventually showed senescence, but those from all three slow-growing genotypes underwent transformation. The major cell component in late cultures of all genotypes was actin.

Human lens epithelial cells in culture: a quantitative evaluation of growth rate and proliferative capacity

Human lens epithelial (HLE) cells were explanted into medium containing different concentrations of foetal calf serum (FCS) and serum substitute. The proliferation of cells was measured as a function of time in culture and the growth parameters (growth rate and proliferative capacity) were determined by the application of the Gompertz growth function. Human lens epithelial cells have a limited growth capacity in culture of five to seven population doublings and this decreases with age. The population doubling level (PDL) was determined empirically and from fits of the Gompertz equation. The values of the PDL determined experimentally and theoretically are compared for a series of different culture conditions. Exposure of the cells to raised levels of FCS caused a reduction in proliferative capacity; the PDL decreased from 6.3 to 5.5 when the serum was raised to 50% although the growth rate increased. Serum substitute caused a decrease in the growth rate without changing the proliferative capacity and also altered the cellular morphology. It is hoped that the method described will have applications to the study of posterior capsule opacification following extracapsular cataract extraction and phacoemulsification and will aid in the development of preventive therapies.

Retention of lens specificity in long-term cultures of diploid rabbit lens epithelial cells

Rabbit lens epithelial cells from newborn animals exhibited limited growth when cultured under standard conditions. Cell lines were generated when explants from individual lenses were cultured in medium supplemented with conditioned medium or untreated rabbit serum. All lines exhibited a stable epithelial morphology. One line, N/N1003A, was examined extensively with respect to its growth, ploidy, and maintenance of lens-specific functions. Cells at population-doubling level (pdl) 120 exhibited a normal chromosomal banding pattern, were diploid, were non-tumorigenic in vivo, did not grow in suspension culture, and did not exhibit sustained growth in medium supplemented with low concentrations of serum. The shape of the growth curves and the final density for cells at pdl 24 and 181 exposed to various concentrations of serum were identical. The cells showed no diminution in growth as a function of in vitro age. The cells retained lens-specific functions. Proteins were isolated from cells at pdl 40 and 170, and were separated on polyacrylamide gels. Western immunoblot analysis using antiserum to alpha-crystallin, a tissue-specific protein found in lens epithelial cells in vivo, indicated the presence of alpha-A- and alpha-B-crystallin polypeptides. The cells also contained the transcription factors required for activating the murine alpha-A-crystallin gene promoter, which is known to function with precise tissue specificity. When an expression vector including the bacterial chloramphenicol acetyltransferase (CAT) gene controlled by the alpha-A-crystallin gene promoter was introduced into the lens epithelial cells, the CAT gene was expressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Detoxification of H2O2 by cultured rabbit lens epithelial cells: participation of the glutathione redox cycle

Although it has been shown that cultured rabbit lenses can adequately defend against the 0.03-0.05 mM level of H2O2 normally found in aqueous humor, the contribution of the epithelium in this process has not been well defined. In the present study, the peroxide-detoxifying ability of the epithelium is evaluated in cultured rabbit lens cells established from 4-6-day-old rabbits and compared to that of skin fibroblasts from rabbits of the same age. When cells were cultured in medium containing H2O2, the concentration of peroxide rapidly decreased; however, various concentrations could be maintained for 3-hr periods by using glucose oxidase to enzymically generate H2O2. At an extracellular level of 0.03 mM H2O2, the rate of detoxification of peroxide by epithelial cells was 2 mumol H2O2 (8 x 10(5) cells)-1 3 hr-1, twice as fast as that for fibroblasts. Epithelial cells contained a high level of reduced glutathione (GSH) equal to 36 nmol (8 x 10(5) cells)-1, twice that present in the fibroblasts. The concentration of GSH in 8 x 10(5) epithelial cells, a number of cells normally present in one intact rabbit lens epithelium, remained constant during 3 hr of exposure to H2O2 levels as high as 0.03 mM, even though the amount of H2O2 taken up under these conditions was sufficient to oxidize completely the cellular GSH every 2 min. In contrast, the GSH content of fibroblasts declined at levels of peroxide above 0.01 mM. Participation of the glutathione redox cycle in the H2O2-detoxification process was demonstrated from studies of hexose monophosphate shunt (HMPS) activity as measured by oxidation of [1-14C]-labeled glucose. The oxidation of [1-14C]-glucose in epithelial cells was stimulated 13 times that of controls during exposure to 0.04-0.05 mM H2O2, while the corresponding increase in oxidation of [6-14C]-labeled glucose was only 1.6 times. In contrast, maximum shunt activity in fibroblasts occurred at 0.03-0.04 mM H2O2 and was six times the control value. The growth potential of the cells following a 3-hr exposure to H2O2 was also used as a measure of oxidant toxicity in both cell types. Concentrations of H2O2 up to 0.03 mM had no effect on the growth of 8 x 10(5) epithelial cells but did diminish the growth of the same number of fibroblasts. Cell density was found to be an important parameter in the ability of the cells to tolerate H2O2.(ABSTRACT TRUNCATED AT 400 WORDS)

Proliferation of lens epithelial explants in culture increases with age of donor rat

Lens epithelial cells explanted together with their capsule into serum-free medium underwent cell division. The extent of cell division depended on the age of the donor rat. After explantation, lens epithelia from newborn and 5 day rats showed decreased mitotic activity from day 0 to day 3 whereas epithelia from 15 day rats showed a marked increase in mitotic activity which peaked at day 3. To determine the age when mitosis is first stimulated by explantation, explants were prepared from 10 day and 13 day rats. Explants from 10 day rats showed a slight increase in cell division and explants from 13 day rats showed a substantial increase in cell division. Therefore about 10 days of post-natal development, mitosis is stimulated by explantation and the magnitude of stimulation increased up to 15 days of age. We also found that in 7 week old rats the central epithelium, where most cells are blocked in Go-1 in vivo, showed a similar high level of cell division after 3 days. Moreover, the peripheral epithelium, which includes the zone of highest mitotic activity in vivo, had a significantly lower mitotic response to explantation than the central epithelium. Thus, explantation into serum-free medium must in some way stimulate cells blocked in Go-1 to re-enter the cell cycle. Furthermore, it is suggested that the increased mitotic response of rat lens epithelial cells with post-natal age indicates that the proportion of cells blocked in Go-1 increases substantially from 10-15 days of age.

Rabbit lens cell cultures in the characterization of Spiroplasma mirum pathogenicity

Spiroplasma mirum grew to high titres, 10(8) colour-changing units per ml of supernatant medium, and produced cytopathology which consisted of vacuolization, granulation and polynucleation . S. mirum did not grow in cell culture medium (Dulbecco's MEM+10% foetal bovine serum), thereby indicating the need for cultured cells or a cell culture product. Growth was also obtained from cell-free supernatants from AG-4676 cultures. S. mirum propagated in AG-4676 produced cataracts and death in suckling Wistar rats.

Characterization of Spiroplasma mirum (suckling mouse cataract agent) in a rabbit lens cell culture

Spiroplasma mirum (suckling mouse cataract agent) was studied in an epithelial cell line AG-4676, derived from rabbit eye lens. Rabbit eye lens is a natural target tissue of S. mirum infection. The organism grew rapidly in this cell line, reaching titers of 10(7) to 10(9) color change units per ml at 7 days after infection. This is the same level as that achieved in SP-4 medium designed specifically for S. mirum. No lag period was apparent in growth in AG-4676. S. mirum did not grow in Dulbecco minimal essential medium-10% fetal bovine serum, the medium for AG-4676, indicating the need for cells or a cellular product. S. mirum-infected AG-4676 cells exhibited vacuolization and granulation and an increase in polynucleation compared with uninfected controls (36/100 versus 14/100, P less than 0.001). Infection significantly decreased the growth rate of AG-4676, especially late in the growth cycle. In a representative experiment, growth of AG-4676 at 11 days was reduced from 9 X 10(5) to 2 X 10(4) cells by S. mirum infection. S. mirum grew to high titers in conditioned medium of AG-4676, obtained from cell-free supernatants of 1- to 5-day-old AG-4676 cultures. This growth promotion was not due to osmotic conditioning of the medium. Preliminary characterization of this growth promotion substance showed it to be active after 0.22-micron filtration, heating at 56 degrees C for 30 min, freezing and thawing, and dilution at 10(-1) but not 10(-2). AG-4676-propagated S. mirum produced death or cataracts in suckling Wistar rats at the same frequency (55/60, 91.7%) as SP-4-propagated organisms (60/65, 92.3%).

Establishment and characterization of a lens epithelial cell line from an eight year old rabbit

Although information is available on the in vitro properties of lens epithelia of young adult animals from several species, few, if any reports document the conditions required for the initiation and long-term culture of lens epithelium from animals beyond their medium life-span. We report here on the conditions required for the culture of lens cells from an 8 year old rabbit. New Zealand White rabbits have a median life-span of approximately 7 years. Primary culture was initiated in MEM supplemented with 10% rabbit serum. Cells reached confluency within 25 days, responded to serum in a dose dependent manner and had an average doubling time of 23 h during the logarithmic growth phase. Cells increased in number in a dose dependent manner when insulin, insulin growth factor, epidermal growth factor (EGF), or fibroblast growth factor (FGF) was added to the culture medium. Thus, lens epithelia from this very old rabbit retained the ability to respond to highly purified growth factors. Cells exposed to a medium supplemented with insulin, EGF and FGF showed a five-fold increase in number at day 7 of culture, a value exceeding that brought about by the individual growth factors. An examination of chromosomal preparations indicated that the cells were aneuploid. Whether the aneuploidy was acquired in vitro or is a normal adjunct of aging in the lens in vivo is unknown. Proteins extracted from this line contained polypeptides that migrated to the position of and had apparent molecular weights of lens proteins.

Both human and newborn rabbit lens epithelial cells exhibit similar limited growth properties in tissue culture

Human lens cells from 5-91-year old individuals were cultured in 8 different basal media containing fetal bovine, adult bovine, rabbit or human serum or human plasma or in a serum-containing medium supplemented with insulin, epidermal growth factor, fibroblast growth factor plus other hormones or trace elements. Cultures were initiated from explants of the capsule and epithelium or following enzymatic dissociation of cells from the capsule. Under all conditions the epithelial cells had a limited doubling potential. As a function of time in culture, cells enlarged, displayed numerous filaments and exhibited apparent in vitro senescence. Lens epithelia from 4-6 day old rabbits cultured under identical conditions mimicked the behavior of human lens cells. Lens epithelia from newborn rabbits may be a suitable model for investigating the basis of apparent in vitro senescence in this cell type and could help in defining the conditions required for the long-term growth of human lens cells. The limited growth of human lens epithelia suggests that these cells require tissue-specific nutrients or hormonal supplements not present in standard tissue culture media.