17ß-estradiol prevents reduction of retinal phosphorylated 14-3-3 zeta protein levels following a neurotoxic insult.

Previous studies demonstrated the substantial protective role of 17ß-estradiol (E2) in several types of neuron, although its mechanism of action remains to be elucidated. In this study, we found that the levels of 14-3-3 zeta mRNA and phosphorylated and total 14-3-3 zeta proteins were significantly decreased in the rat retina after intravitreal injection of N-methyl-d-aspartate (NMDA). 17ß-E2 implantation significantly inhibited NMDA-induced decreases in phosphorylated but not in total 14-3-3 zeta protein levels in the retina. There was a decrease in both phosphorylated and total 14-3-3 protein levels in RGC-5 cells, a retinal ganglion cell line, after glutamate and buthionine sulfoximine (BSO) exposure, and 17ß-E2 treatment significantly inhibited only the decrease in phosphorylated but not in total 14-3-3 zeta protein levels. The cell viability assay showed substantial cell death after glutamate and BSO exposure and that 17ß-E2 treatment significantly protects against this cell death. 17ß-E2 treatment also significantly increased the level of phosphorylated 14-3-3 protein in RGC-5 cells without other treatments. These results suggest that a decrease in 14-3-3 zeta expression may be associated with retinal neurotoxicity induced by NMDA or the combination of glutamate and BSO. The regulation of 14-3-3 zeta phosphorylation is one possible mechanism of the protective effect of 17ß-E2 in the retina.

Axonal protection by 17ß-estradiol through thioredoxin-1 in tumor necrosis factor-induced optic neuropathy.

Axonal degeneration often leads to the death of neuronal cell bodies. Previous studies demonstrated the substantial protective role of 17ß-estradiol (E2) in several types of neuron. However, most studies examined cell body protection, and the role of 17ß-E2 in axonal degeneration of retinal ganglion cells (RGC) remains unclear. In this study, we showed the presence of thioredoxin-1 (Trx1) in the optic nerve axons and found that the levels of Trx1 protein were significantly decreased in isolated RGC and the optic nerve after intravitreal injection of TNF, which was shown previously to induce optic nerve degeneration and subsequent loss of RGC. These changes were concomitant with disorganization of the microtubules with neurofilament accumulation, which were blocked by 17ß-E2 implantation. 17ß-E2 treatment also totally abolished TNF-induced decreases in Trx1 protein levels in isolated RGC and the optic nerve. The induction of Trx1 by 17ß-E2 in the optic nerve was significantly inhibited by simultaneous injection of Trx1 small interfering RNA (siRNA) with TNF. Up-regulation of Trx1 by 17ß-E2 in RGC-5 cells was prevented by Trx1 siRNA treatment. 17ß-E2 significantly prevented TNF-induced axonal loss, and this axonal-protective effect was inhibited by intravitreal injection of Trx1 siRNA. This finding was also supported by the quantification of microtubules and neurofilaments. These results suggest that a Trx1 decrease in RGC bodies and their axons may be associated with TNF-induced optic nerve axonal degeneration. Axonal protection by 17ß-E2 may be related to its regulatory effect on Trx1 induction.