Monolayered explants in the study of retinal pigment epithelial behavior in culture

A new wound healing model of retinal pigment epithelial cells in sheet culture

PURPOSE

To evaluate some RPE cell functions, such as wound healing, in a preparation more similar to in situ conditions, we developed a method to obtain and culture retinal pigment epithelial (RPE) cells as a sheet. And we assessed the effects of fetal bovine serum (FBS) on the rate of RPE wound healing.

METHODS

We prepared RPE sheet cultures by incubating rat eyes in 0.1% proteinase K for 13 min, peeling away the neural retina-RPE complex, and then incubating the tissue for 1 h to promote spontaneous separation of the RPE sheet from the retina. After several days of incubation, the cultured sheets of RPE cells were examined by phase-contrast microscopy, scanning and transmission electron microscopy and immunocytochemistry. We made round defects 1 mm in diameter in cultured RPE sheets and estimated the rate of wound closure in media with different concentrations of FBS (0 to 10%).

RESULTS

The RPE cells cultured in sheets retained their in situ features, including microvilli, tight junctions and gap junctions, and the distribution of actin and cytokeratin filaments. A wound was noted to close with restoration of a polygonal configuration. The rate of wound closure depended on serum concentration in the culture medium; when supplemented with 10% fetal bovine serum, wound closure was complete in approximately 40 h.

CONCLUSIONS

The RPE sheet-culture technique we developed thus provides a suitable model for studying such RPE cell functions as wound healing or phagocytosis.

Propagation of fetal human RPE cells: preservation of original culture morphology after serial passage

The permissive effects of extracellular matrix (ECM) on in vitro growth and differentiation of fetal human retinal pigment epithelial (RPE) cells have been studied. Factors which enhanced the effect of ECM to support cell division were also examined, including growth factors, culture media, and serum requirement. Under the specific culture conditions we have defined, it is possible to propagate these RPE cells at low density (less than 20 cells/mm2) with excellent growth properties for greater than 72 doublings (fourteen passages) in serial culture. Later-passaged cells maintained the morphological appearance of early-passaged cultures. ECM produced by bovine corneal endothelial cells was by far the most predominant factor in promoting rapid cell proliferation and viability over repeated passaging. Basic fibroblast growth factor (bFGF) exerted a substantial effect on the rate of cell division at different serum concentrations on plastic dishes. In addition, this factor showed profound synergistic effect when RPE cells were maintained on ECM, both in the preservation of cell morphology and also in long term viability. Other growth factors, such as epidermal growth factor (EGF) and transforming growth factor-beta (TGF-B), were also tested, but EGF effects were less prominent than those observed with bFGF, and TGF-B had an inhibitory effect at high concentrations. The ability to obtain a relatively large number of human RPE cells in vitro which preserve the appearance of early passage cells may provide useful opportunities to study the physiological properties and pathological alterations involving this important cell type.

Argon laser lesions in the human RPE in vitro

Argon laser lesions were produced in human retinas in eyes to be enucleated because of choroidal melanomas. Lesions were subsequently isolated and maintained in vitro for one month and evaluated by light, transmission and scanning electron microscopy. In the cultured lesions ingrowing cells with a well recognizable epithelial morphology were observed to cover Bruch's membrane in the photocoagulated area, and to grow as sheets on sensory retinal tissue and on detached necrotic pigment epithelium. This growth was predominantly monolayered. In areas, however, overlapping, detachment of cells from the epithelium into the photocoagulated debris, and formation of tubulovescicular structures were observed. The present study demonstrates that lesions with a known potential for reactive changes in the retinal pigment epithelium in vivo can be isolated and cultured with a maintained potential for some of the typical reactive patterns. This opens for investigations on their genesis and on agents modifying these patterns under controlled in vitro conditions.

Human retinal pigment epithelium in long term explant culture

Explants of human retinal pigment epithelium were maintained in culture in various types of media, and examined by light and transmission electron microscopy. After one month in vitro, the central areas showed a monolayered configuration with distinct polarity and presence of ruthenium red stainable material on the apical surface. On the peripheral areas of Bruch's membrane, multilayered lesions were observed to develop and to extend from the monolayered epithelium and past the cut edge in Bruch's membrane. Cells in these lesions contained little melanin and generally lacked an apico-basal polarity. Ruthenium red staining revealed the presence of electron dense material on the apical surface of the lesions as well as in the extracellular space between cells in the various layers. Development of multilayered lesions with deposition of extracellular material are seen in various chorio-retinal disorders, including senile macular degenerations and also subsequent to laser and cryo-therapy. The findings in the present study point to the explant culture system as a valuable tool in the study of important aspects of chorio-retinal pathology.

Culture of retinal pigment epithelium from chorio-retinal biopsies

The recently devised methods for surgical sampling of chorio-retinal tissue permits morphological evaluation of retina in various diseases. In the present report it is demonstrated, that the retinal pigment epithelium in such samples can be isolated as a viable cell population, and that the cell mass can be increased sufficiently in culture to permit biochemical as well as morphological studies. This procedure thereby expands the diagnostic potential of the sample tissue.