GLUT1 GLUCOSE-TRANSPORTER EXPRESSION IN THE DIABETIC AND NONDIABETIC HUMAN EYE

Purpose. The GLUT1 glucose transporter is expressed in endothelial and epithelial barriers, including the retinal capillary endothelium and the retinal pigment epithelium (RPE) of the eye. The present studies w ere undertaken to determine whether GLUT1 is expressed in additional c ell types within the human eye and whether retinal endothelial GLUT1 i s aberrantly expressed in diabetic proliferative retinopathy in humans . Methods. Immunohistochemical staining of sections of human eyes obta ined at surgery or autopsy from patients with and without diabetes was performed with polyclonal antisera directed against the human GLUT1 g lucose transporter. Results. In the course of this study, an unexpecte d multicellular localization of GLUT1 in different cellular barriers o f the human eye was observed. In the nondiabetic eye, specific stainin g for GLUT1 was seen in the nerve fiber layer, the ganglion and photor eceptor cell bodies, the capillaries and the RPE of the retina, the ba sal infoldings of the pigmented and nonpigmented layers of the ciliary body, the capillary endothelium and posterior epithelium of the iris, the corneal epithelium and endothelium, and the endothelium lining of the canal of Schlemm. Muller cells, a type of retinal glial cell iden tified by morphology and by parallel staining for glial fibrillary aci dic protein, also stained intensely positive for GLUT1. The pattern of GLUT1 immunoreactivity in the diabetic eyes was virtually identical t o that in the nondiabetic specimens, with the notable exception that t he neovascular endothelium of proliferative retinopathy did not stain for GLUT1. Conclusions. These studies describe the heretofore unrecogn ized expression of immunoreactive GLUT1 in the ganglion cell layer of the retina, the endothelium lining the canal of Schlemm, the corneal e ndothelium, and the basal cells of the corneal epithelium of the human eye. The present study also provides evidence for immunoreactive GLUT 1 in glial cells of the central nervous system. Because the expression of GLUT1 is characteristic of tissues that possess a barrier function , the absence of GLUT1 immunoreactivity in the neovascular tissue of p roliferative diabetic retinopathy suggests that the loss of selective permeability is associated with an absence of facilitated glucose tran sport in this disorder.