Purpose: To determine whether the expression levels and cellular distribution of the facilitative glucose transporters GLUT1 and -3 undergo changes in the hyperglycemic lens.
Methods: Hyperglycemia was induced in vivo by injecting rats with streptozotocin or in vitro by culturing lenses in the presence of 50 mM glucose. Northern blot analysis and quantitative RT-PCR were used to detect changes in GLUT1 and -3 transcript levels, and Western blot analysis was used to monitor changes in GLUT3 protein expression levels in diabetic rats. Immunocytochemistry was used to map the cellular distribution of GLUT3 in normal and hyperglycemic lenses.
Results: GLUT1 and -3 were found to be differentially expressed in the epithelial and fiber cells, respectively. In the fiber cells, the distribution of GLUT3 protein changed as a function of fiber cell differentiation. In young differentiating fiber cells, GLUT3 was mainly found in the cytoplasm, but with increasing depth into the lens became inserted into the narrow sides of older fiber cells, before becoming completely dispersed around the entire membrane of the oldest fiber cells. Hyperglycemia had similar effects on tissue damage and transporter expression in both the in vitro and in vivo models. Tissue damage was characterized by an initial local cell swelling that with prolonged insult gradually spread and resulted in the creation of large areas of tissue liquefaction. Northern blot analysis and quantitative RT-PCR showed that transcript for GLUT3 but not GLUT1 was upregulated under hyperglycemic conditions. This increase in GLUT3 expression was confirmed at the protein level by both Western blot analysis and immunocytochemistry. In hyperglycemic lenses, GLUT3 antibody labeling was localized to the region of tissue liquefaction.
Conclusions: GLUT3 in the lens exhibits dynamic changes in expression levels and cellular localization as a function of fiber cell differentiation and hyperglycemia. In the lens cortex, regions of GLUT3 overexpression and hyperglycemic tissue damage overlap, suggesting a functional relationship.