Transgenic expression of IGF-1 modifies the proliferative potential of human retinal pigment epithelial cells

Abstract

Purpose: To induce the expression of insulin-like growth factor (IGF)-1, by using gene transfer methods, to modify the growth characteristics of human retinal pigment epithelial cells.

Methods: Human retinal pigment epithelial cells were transfected in vitro with plasmid vector pcDNA:IGF-1, which encodes an epitope-tagged human IGF-1 fusion protein and a selectable neomycin resistance gene. Transduced cells were cloned in G418 and expanded for analysis of IGF-1 transgene expression and its effect on the cell phenotype. The expression of the IGF-1 transgene in cloned cells was confirmed by reverse transcription-polymerase chain reaction and quantified by Western blot analysis. The growth characteristics of transduced clones were compared with the control by spectrophotometric and flow cytometric cell proliferation assays.

Results: Cloned retinal pigment epithelial cells expressed the IGF-1 transgene and secreted the IGF-1 fusion protein into the tissue culture medium. Transduced clones demonstrated a dose-dependent, enhanced ability to proliferate in low serum conditions, compared with the control. Clones that expressed moderate and high levels of the IGF-1 fusion protein were isolated and grew at a significantly faster rate and showed a statistically significant increase in the number of cells after 6 days, compared with the control (P < 0.002, paired samples, t-test). Expression of the IGF-1 transgene in synchronized clones enhanced cell cycle kinetics by increasing recruitment of the G(0)-G(1)-phase cells into the proliferative phase of the cell cycle.

Conclusions: The human IGF-1 fusion protein encoded by the pcDNA:IGF-1 vector demonstrates paracrine biological activity in human retinal pigment epithelial cells in vitro. Expression and secretion of the IGF-1 transgene enhances growth characteristics in a dose-dependent manner and can modulate the proliferative potential of the retinal pigment epithelial cell.