Effects of Dexamethasone on DNA Synthesis in Lens Epithelial Cells Are Dependent on Cell Type and Growth Factor

To determine the factors that influence the ability of dexamethasone (dex) to inhibit or stimulate the growth of lens epithelial cells.

Different growth factors with or without dex (10^-6 M) were added to quiescent cultures of two clones of Nakano mouse lens epithelial cells (NK11) in serum-free medium. DNA synthesis was then measured after 8-12 hours by the incorporation of tritiated thymidine.

Dex was found to both stimulate and inhibit mitogen-induced ³H-thymidine incorporation into the DNA of cultured mouse lens epithelial cells. Enhancement or repression by dex was found to depend on the growth factor used to stimulate the quiescent cell. EGF and insulin were consistently inhibited with dex. Basic fibroblast growth factor (bFGF) and retinoblastoma-derived growth factor (RbDGF) were both enhanced and inhibited by dex, depending on the growth factor concentration and the cell clone used for the experiment. Additionally, RbDGF protects against the dex inhibition of insulin stimulation, but not the inhibition of EGF stimulation. Progesterone, an inhibitor of the activation of the glucocorticoid receptor, blocks the dex inhibitory effect on the EGF and insulin stimulation of DNA synthesis. The ability of progesterone to affect the dex inhibition is consistent with the dex receptor modulating DNA synthesis. The dex effect on DNA synthesis, either stimulatory or inhibitory, was still seen if dex was added as late as 10 hours after the growth factor.

The study demonstrated that dex reduces the overall growth and activity of lens epithelial cells in vitro. This result provides insight into the risk of developing posterior subcapsular cataracts (PSC) in patients on oral glucocorticoid therapy. Understanding the basic mechanisms by which steroids mediate lens cell growth may provide the ability to more accurately predict who will develop PSC. The present studies show the difference in the effect of dex from lens cell to lens cell, but, more importantly, suggest a pattern of dependent variables that might prove useful in such predictions.