d-Serine/N-methyl-d-aspartate receptor signaling decreases DNA-binding activity of the transcriptional repressor DREAM in Müller glia from the retina

In the adult retina, N-methyl-d-aspartate (NMDA) neurotoxicity induces Müller cell reactive gliosis which is characterized by changes in gene expression that lead to proliferation and affect retinal physiology. The aminoacid d-serine is synthesized in Müller cells and modulates these processes acting as a coagonist of NMDA receptors. We have found that the transcription factor DREAM (downstream regulatory element antagonist modulator), which acts as a transcriptional repressor by binding as a tetramer to regulatory elements located in the promoter region of target genes, is expressed in these cells and that its DNA-binding activity is modulated by NMDA receptor activation. Consistently, immunocytochemical analysis demonstrates that NMDA receptor activation induces changes in the nuclear localization of this transcription factor. DREAM is a pleiotropic transcription factor capable to repress and activate genes involved in several physiological events in different tissues. These results link, for the first time, this transcription factor with NMDA-receptor activation. Given the relevance of glutamatergic transmission in the retina and the remarkable functional plasticity of Müller cells, these findings support the notion that the NMDA receptor-dependent modulation of DREAM activity could play a role in relevant physiological processes ranging from retinal response to injury to differentiation capacity of retinal progenitor cells.