Neuroprotective effects of nonfeminizing estrogens in retinal photoreceptor neurons

Abstract

Purpose: Retinal diseases such as macular degeneration and glaucoma are disorders that target specific retinal neurons that can ultimately lead to vision loss. Under these conditions and pathologies, retinal neurons can die via apoptosis that may be due to increased oxidative stress. The neuroprotective effects of 17β-estradiol (E2) and three synthetic nonfeminizing estrogen analogs (ZYC-26, ZYC-23, and ZYC-3) were investigated to examine their abilities to protect retinal neurons against glutamate toxicity.

Methods: Using an in vitro model of glutamate-induced cell death in 661W cells, a mouse cone photoreceptor cell line, shown to express both estrogen receptors (ERs) via immunoblotting, was pretreated with E2 and its analogs and cell viability were assessed.

Results: It was observed that E2 and estrogen analogs, ZYC-26 and ZYC-3, were protective against a 5 mM glutamate insult in 661W cells. The neuroprotective abilities of ZYC-26 and ZYC-3 were autonomous of estrogen receptor-α (ERα) and ERβ demonstrated by their ability to protect in the presence of ICI 182780, a pan-ER antagonist with a high affinity for the estrogen receptor. Treatment with PPT and DPN, ERα- and ERβ-specific agonists, respectively, did not protect the 661W cells from the glutamate insult. Studying the membrane ER (mER) or GPR30 did show that activation of the receptor by G1 protected the retinal neuron from insult, whereas G15, an antagonist of the mER was not able to antagonize the protection previously seen.

Conclusions: These data demonstrate that nonfeminizing estrogens may emerge as useful compounds for neuroprotection of retinal cells.

Figure 1

Structures of compounds used to evaluate neuroprotection against glutamate toxicity in 661W cells.

Figure 2

ERα is expressed in the 661W cells.

Figure 3

Effects of glutamate on cell viability of 661W cells. Depicted are mean ± SD (n = 8 per group). *P < 0.05 vs. vehicle control.

Figure 4

Effects of E2 (A) and nonfeminizing estrogen analogs ZYC-26 (B), ZYC-3 (C), and ZYC-23 (D) on cell viability in glutamate-treated 661W cells. Depicted are mean ± SD (n = 8 per group). *P < 0.05 vs. glutamate alone–treated cells. ICI, ICI 182780.

Figure 5

Effects of ERα preferring agonist, PPT (A) and an ERβ-preferring agonist DPN (B) on cell viability in glutamate-treated 661W cells. Depicted are mean ± SD (n = 8 per group). *P < 0.05 vs. glutamate alone–treated cells.

Figure 6

Effects of G1 on cell viability in glutamate-treated 661W cells. Depicted are mean ± SD (n = 8 per group). *P < 0.05 vs. glutamate alone–treated cells.

Figure 7

Effects of the GPR30 antagonist, G15, on G1 (A), E2 (B), ZYC-26 (C), and ZYC-3 (D)–induced neuroprotection of cell viability in glutamate-treated 661W cells. Depicted are mean ± SD (n = 8 per group). *P < 0.05 vs. glutamate alone–treated cells.