Enhanced expression of TNF-R1 protein in NMDA-mediated cell death in the retina

Multiple apoptosis-related genes are expressed in the retina after exposure to N-methyl-D-aspartic acid (NMDA). For example, the mRNAs for TNF-R1, FasL, and Nur77 are up-regulated between 2.8 and 7-fold [Mol. Brain Res. 91 (2001) 34-42]. The purpose of the present study is to examine prospective changes in protein expression for these genes and to determine their cellular localizations subsequent to NMDA stimulation. Following anesthesia, a single intravitreal injection of 4 mM NMDA was administered into the right eye of anesthetized rats. The left eye was injected with phosphate-buffered saline. Retinae were harvested at 2 and 24 h postinjection. Western-blot and immunocytochemical techniques were used to detect changes in protein expression levels, and to localize their distributions within the retina. Analyses of Western blots demonstrated a significant increase in TNF-R1 (100 and 80%) compared to the sham-controls at 2 and 24 h postinjection with NMDA. Immunolabeling of TNF-R1 was observed in the inner nuclear layer (INL) at 2 h postinjection with NMDA. TNF-R1 was also clearly evident in cells within the INL and ganglion cell layers (GCL) at 24 h post-injection with NMDA. In contrast to these changes in TNF-R1 there were no significant changes in the levels or distributions of FasL or Nur77 in NMDA-stimulated animals at either 2 or 24 h when compared to the sham-controls. These results implicate the TNF-R1 signal transduction pathway in NMDA-induced cell death in the INL and GCL of the retina.