Aldose reductase mRNA is an epithelial cell-specific gene transcript in both normal and cataractous rat lens

Aldose reductase (AR) is implicated in the development of sugar cataracts by its reduction of galactose or glucose to polyols. The authors' recent work suggested that AR mRNA is found to be expressed in high concentrations in rat-lens epithelial cells after exposure of the animal to a diet containing 50% galactose. They localized the AR mRNA in the lens cells by in situ hybridization with a previously described AR clone. The data establish that AR mRNA is apparently an epithelial and not a fiber-cell gene transcript. It accumulates in the epithelial cell, then it is carried into the newly differentiated fiber cell, and finally it concentrates in the posterior region of the matured fiber cell. The AR mRNA is found in all of the anterior epithelial cells including the equatorial and central epithelia. It is present at highest concentrations in the elongating epithelial cells, and it is distributed equally throughout the secondary fiber cells at the bow, with no indication of a preferential buildup of AR mRNA in any of the nucleated fiber cells in the cortex. This differs from what the authors reported to occur with MP26 mRNA, a fiber cell-specific gene transcript. They found that MP26 mRNA was absent from the epithelial cells but was preferentially found in the secondary fiber cells. Present data suggest that the increase in AR mRNA concentration observed to occur in cataractous lenses is a result of epithelial cell proliferation, where every cell appears to be competent in expressing AR mRNA. The results of this research imply that AR mRNA is a lens epithelial cell-specific gene transcript in both normal and cataractous lenses.