Insulin and IGF-I Affect the Protein Composition of the Lens Fibre Cell with Possible Consequences for Cataract

Abstract

Explanted newborn rat lens epithelial cells were cultured with various concentrations of FGF-2 and/or insulin or IGF-I for 8–20 days. The accumulation of αA-, αB-, βA3/1-, βB2- and γA-F-crystallin was measured. During culture with insulin only, i.e. in the absence of fibre cell differentiation, αA- and αB-crystallin accumulated to the same level as found in differentiating cells. Culture of epithelial cells with IGF-I led to an increase in αB-crystallin, but not in αA-crystallin. The addition of insulin under differentiation conditions (in the presence of 25ng ml−1FGF-2) augmented the accumulation of αA-crystallin 1.5-fold, the accumulation of βB2-crystallin two-fold and the accumulation of γA-F-crystallin five-fold over that found with FGF-2 only. The accumulation of αB- and βA3/1-crystallin was not affected by insulin in the presence of FGF-2. Adding IGF-I to fibre cells differentiating in the presence of 25ng ml−1FGF-2 resulted in a 1.5-fold increase (of questionable statistical significance) in both αA- and αB-crystallin and a two to three-fold increase in γA-F-crystallin compared to cells cultured with FGF-2 only, no significant effect of IGF-I on the accumulation of βA3/1- or βB2-crystallin was found. Comparison of the levels of mRNA and protein suggests that insulin acts to increase the level of transcription. Our results show that the response of fibre cells to insulin or IGF-I differs. Hence, even though half the maximum dosage required for the insulin effect was rather high (between 0.1 and >5μ g), the effect of insulin cannot be merely transmitted by the IGF-I receptor. Our data further predict that insulin or IGF-I increases the overall ratio of β- and γ-crystallin to α-crystallin in the fibre cell, which could predispose the lens to cataract.