Effects of long-term diabetes and galactosaemia upon lens and retinal mRNA levels in the rat

Abstract

The levels of mRNAs encoding the α1 chain of collagen IV and the B1 chain of laminin were assayed in the lenses and retinas of long-term (28-week) diabetic and galactosaemic rats in order to gain some insight into the effects on basement membrane (BM) synthesis in these tissues. mRNAs coding for β-actin, glucose transporter protein and the α2 catalytic subunit of Na +,K +-ATPase were also assayed to determine whether any effects on BM-coding mRNA levels were specific. Long-term diabetes had no significant effect on the levels of α1(IV) collagen mRNA but caused a significant reduction in the laminin B1 message in the lens. In the same samples, the level of the glucose transporter protein mRNA was found to be elevated significantly in the diabetic tissue, whereas the mRNAsen coding β-actin and α2 Na +,K +-ATPase were unaffected in comparison with age-matched controls. Long-term galactosaemia resulted in significant increases in the levels of all mRNAs assayed when expressed per μg total RNA used for each analysis. However, this effect appeared to be due to a specific loss of ribosomal RNA from these severely cataractous lenses. When related to the β-actin mRNA internal control, the levels of mRNA in the galactosaemic lenses were very similar to that found in the diabetics. Laminin B1 mRNA levels were decreased significantly. Diabetes had little influence on any of the mRNAs assayed in the retina. mRNAs coding for the glucose transporter protein and α2 Na +,K +-ATPase increased slightly but these levels were not of statistical significance. In the galactosaemic rat retinas, no significant differences were detected in the levels of mRNAs coding for α1(IV) collagen, laminin B1, β-actin or glucose transporter protein in comparison with age-matched controls. However, the α2 Na +,K +-ATPase mRNA was increased 2·3-fold in comparison with controls. The data demonstrate that whereas long-term diabetes and galactosaemia induce specific increases in certain mRNA levels, neither condition affects the levels of mRNAs coding for the BM components examined. These results, therefore, provide no support for the hypothesis that the thickening of BMs apparent in diabetes and galactosaemia is the result of increased synthesis of the extracellular matrix components studied.