Impact of GLUT1 Transporter Knockout in Optic Nerve Head Astrocytes and Retinal Ganglion Cells

Abstract

Purpose: Astrocytes and axons are the primary constituents of the optic nerve head, the initial site of neurodegeneration in glaucoma. This study was intended to understand the metabolic relationship between astrocytes and RGC axons. We hypothesized that reducing glucose transporter-1 (GLUT1) expression in astrocytes will increase the RGC-associated pathology after ocular hypertension (OHT). Methods: Mice expressing a GLUT1 gene flanked by loxP sites behind the GFAP promoter ("GFAP-GLUT1”) mice were used (n=40) and were divided into 4 groups: GLUT1-knockout+OHT, Control OHT, GLUT1-knockout+No OHT, and Control+No OHT. Baseline and final intra-ocular pressure (IOP), pattern electroretinogram (PERG), and visual evoked potential (VEP) measurements were taken. OHT was induced via magnetic microbead injection into the anterior chamber. Retinas, optic nerves, and brains were collected for retinal ganglion cell (RGC) quantification, anterograde transport analysis, biochemical assays, and protein analysis. Results: Statistically significant increases were noted in the IOP data between mice subjected to OHT and the No OHT groups. OHT led to statistically significant decreases in RGC number, regardless of GLUT1 status. A statistically significant decrease in PERG amplitude was noted in all groups subjected to OHT. Interestingly, GLUT1 knockout PERG amplitude was significantly lower than Control at the outset, suggesting a negative impact on retinal physiology from loss of the GLUT1 in astrocytes. Conclusion: Initial observations indicate glial metabolic homeostasis can impact retinal physiology, but GLUT1 knockout did not appear to negatively impact RGC survival. Ongoing analysis will determine if other structures or functions have been compromised by loss of GLUT1 in astrocytes, as well as provide greater insight into the mechanism of physiological change.