Abstract
Purpose :
The dysregulation of glutamate homeostasis in retina is associated with many retinal diseases, such as glaucoma, diabetic retinopathy and age-related macular degeneration. The study aims to uncover the molecular mechanisms that control retinal glutamate homeostasis via dissecting the regulation of the Glul gene, which is one of the key genes that regulate glutamate homeostasis.
Methods :
Retinal Müller glial cells (MG) play key roles in regulating glutamate homeostasis in the retina by converting glutamate into glutamine via glutamine synthetase (GS), which is encoded by the Glul gene. We first examined whether the expression levels of Glul /GS changes in response to different levels of extracellular glutamate in the retina. We then determined how the Glul expression is regulated by identifying novel cis-regulatory modules (enhancer) and revealing the upstream transcription factors.
Results :
We found that Glul mRNA levels and GS protein levels were significantly upregulated when we increased the extracellular levels of glutamate in the retina via intravitreally injection of Glutamate or NMDA. Based on ENCODE database, we identified a novel enhancer of Glul gene located in the second intron (referred as M11). We found that Glul expression is regulated via the M11 enhancer, and discovered that Sox9 binds to M11 and positively regulates the expression Glul gene. Notably, over-expression of Sox9 can protect the retina from the damage induced by excessive extracellular glutamate.
Conclusions :
Sox9 regulates Glul expression and is essential for glutamate homeostasis in the retina. Elevation of Sox9 levels in MG can protect the retina in acute injury models with excessive extracellular glutamate.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.