A transformed neonatal rat retinal pigment epithelial cell line: secreted protein analysis and fibroblast growth factor and receptor expression

Abstract

PURPOSE. A newly-derived transformed neonatal rat retinal pigment epithelial (tnrRPE) cell line was investigated: for secreted proteins by electrophoresis, and for basic and acidic fibroblast growth factor (FGF) by immunocytochemistry, Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR). The FGFR-1(flg) receptor, which is recognized by aFGF and bFGF, was studied by RT-PCR. METHODS. Retinal pigment epithelial (RPE) cells were isolated from 6-day-old pigmented normal Long Evans rats, and became spontaneously transformed after the second passage. RESULTS. RPE cells at the 5th through 28th passages expressed the epithelial cell marker cytokeratin and cellular retinaldehyde binding protein (CRALBP), an RPE cell marker, but were negative for glial fibrillary acidic protein (GFAP), as shown by immunofluorescence. Secreted proteins of late passage tnrRPE cells were in a narrow molecular weight range of 60–80kDa, while early passage cells exhibited multiple proteins from 20–200kDa. These tnrRPE cells increased by 17–30 fold over a 4-day culture period. At 5th and 28th passage, immunostaining for bFGF and aFGF was dense within nuclei, but light and diffuse within the cytoplasm of transformed RPE cells. As shown by Northern blot, similar levels of message for bFGF were detected in 5th and 30th passage RPE cells. Furthermore, as shown by RT-PCR, bFGF mRNA was found in freshly isolated and transformed neonatal rat RPE cells. However, the message for FGFR-1(flg) receptor was detected only in the transformed RPE cells. CONCLUSIONS. This study demonstrated a neonatal rat RPE cell line that proliferated rapidly in vitro, expressed high levels of message for bFGF and FGFR-1(flg) receptor, and continued to express RPE-cell characteristics. Importantly, mRNA levels of confluent cultures of these cells were sufficient for bFGF mRNA blot analysis, which eliminates the necessity for PCR and for using excessive numbers of animals for such studies.