Localization and ontogeny of GLUT3 expression in the rat retina

This study investigates the presence, localization, and developmental expression of a neuron-specific facilitated-diffusion glucose transporter, GLUT3, in the rat retina so as to elucidate molecular mechanisms regulating glucose homeostasis in support of the visual function. Immunoblot analysis using anti-GLUT3 antibody (ALM3-C) revealed the presence of GLUT3 as a heterogeneously glycosylated protein with an average molecular weight of approximately 44 kDa. Although immunofluorescence staining showed it to be localized primarily in the inner and outer plexiform layers, some of the cell bodies in the inner nuclear layer also showed weak immunoreactivity. Immunoblot analysis of developing rat retinal tissues revealed the presence of the GLUT3 protein as early as embryonic day 15 (E15), and immunofluorescence staining revealed its expression in the inner plexiform layer near the time of birth and in the outer plexiform layer at postnatal day 14 (P14), i.e., when the eyes normally open and retinal activity commences. The protein's abundance remained at a relatively low level during the embryonic stages and up until the end of the first postnatal week (P7), though a transient increase was confirmed to occur at E18. From P13, however, the abundance steadily increased, rapidly reaching the adult level at P24. Based on these observations, we hypothesize that GLUT3 is expressed in some subsets of retinal neurons, being preferentially abundant in their neuronal processes, and that its ontogeny is closely associated with morphological and functional development of the retina. As such, this suggests that GLUT3 plays some important role(s) in the retina where glucose metabolism is essential.