Inducible Nuclear Factor (NF)–B Activity in Müller Glia Contributes to NMDA–Mediated Neuronal Death in the Adult Retina

Abstract

Abstract: : Purpose: The Nuclear Factor (NF)–ΚB is an essential transcriptional regulator of genes involved in the control of cell survival and death. Here we investigated the role of endogenous NF–ΚB activation in NMDA–induced neurotoxicity in the adult mice retina. Methods: Transgenic mice containing the NF–ΚB promoter/enhancer sequence upstream of the ß–gal reporter gene were used as read out for endogenous NF–ΚB transcriptional activity in intact and NMDA–injured retinas. Double labeling with a ß–gal antibody and cell–specific markers for astrocytes, Müller, bipolar and retinal ganglion cells (RGCs) was performed to identify the cellular localization of endogenous and NMDA–induced NF–ΚB activity. The cell–permeable SN50 peptide was used to selectively block NF–ΚB nuclear translocation. Cell death after NMDA injection with or without SN50 was quantified by TUNEL staining. In addition, RGC survival was quantified following retrograde labeling with the fluorescent tracer FluoroGold. Results: Intact retinas displayed only a few NF–ΚB/ß–gal positive cells in the entire retina. In contrast, NMDA injection induced a rapid and dramatic increase in the number of NF–ΚB/ß–gal positive cells in the inner nuclear layer (INL). Co–localization studies demonstrated that only Müller glial cells upregulated NF–ΚB activity upon NMDA treatment. The highest density of NF–ΚB/ß–gal–positive Müller cells coincided with the peak of apoptotic death observed in the ganglion cell layer (GCL) and INL at 24 hrs after injection of NMDA. Co–injection of NMDA and the SN50 peptide resulted in a 9–fold and a 4–fold reduction in apoptotic cell death in the GCL and the INL, respectively. Conclusions: Our data show that: i) NF–ΚB activity is strongly induced in Müller cells following an excitotoxic insult, and ii) inhibition of NF–ΚB activation in Müller glia protects retinal neurons from NMDA–induced apoptosis. To our knowledge, this study is the first to show that NF–ΚB activity in glial cells indirectly affects excitotoxic neuronal death in the mature retina.

Keywords: Muller cells • cell death/apoptosis • transcription factors