Deletion of GLUT1 from Ocular Epithelium Leads to Cataract Formation and Photoreceptor Degeneration in Mice
Glucose is the primary energy source of most organisms and is transported into cells via glucose transporters. GLUT1 is a facilitated glucose transporter, ubiquitously expressed in epithelial tissues and at the surface of blood-tissue barriers. GLUT1 distribution is tissue and species dependent and has not yet been characterized in the mouse lens. The first aim of this thesis was to determine the localization of GLUT1 in the mouse lens and study the effects of deletion of GLUT1 on the lens. GLUT1 was found to be expressed only in the lens epithelium (LE) in mice and deletion of GLUT1 from the LE lead to disorganization of fiber cells and formation of cataracts. SD-OCT was used to non-invasively image the formation of cataracts. In the mouse retina, GLUT1 is expressed at the apical and basolateral membranes of the retinal pigment epithelium (RPE) and allows for uptake of glucose from the choroidal blood circulation. The retina requires energy for various anabolic and catabolic activities, such as renewal of outer segments and maintaining visual function. In the early 1980’s Warburg discovered that the retina is highly glycolytic however, it is not clear whether Müller cells or photoreceptor cells are producing all of the lactate. The second aim of this thesis was to determine the impact of deletion of GLUT1 from the RPE on the neural retina. Transgenic mice were used to delete GLUT1 specifically from the RPE thus disrupting the transport of glucose into the outer retina from the choroid. Glucose deprivation in the outer retina led to a decrease in outer segment length and photoreceptor cell death. Deletion of GLUT1 from the RPE did not alter the polarity, differentiation or function of the RPE therefore the effects observed in the outer retina were attributed solely to glucose deprivation. Photoreceptor outer segments are shed at light onset daily, and are ingested and cleared by RPE. Impairment of any step in the phagocytosis process by the RPE can lead to age related ocular diseases. The third aim of this thesis was to use a systems biology approach to determine the changes in gene expression pattern of cultured human fetal (hfRPE) cells after outer segment phagocytosis compared to untreated hfRPE cells. Microarray analysis showed that genes involved in lipid metabolism and in the inflammatory pathways were found to be upregulated after outer segment phagocytosis in hfRPE. However, the same genes were not found to be upregulated in publicly available microarray data from primary mouse RPE after phagocytosis, indicating that cultured hfRPE cells may be responding to stress caused by the outer segments rather than the outer segments themselves. Overall, these results highlight the role of GLUT1 in ocular epithelia and in maintaining the structure, viability and function in the lens and retina. They also bring to light that cultured hfRPE cells may not be accurate for studying changes in the regulation of outer segment phagocytosis.
Swarup, Aditi, "Deletion of GLUT1 from Ocular Epithelium Leads to Cataract Formation and Photoreceptor Degeneration in Mice" (2019). ETD Collection for Thomas Jefferson University. AAI13808197.