Abstract
Abstract: :
Purpose: Exposure to 17ß–estradiol (17ß–E2) prior to introduction of H2O2 insult protects cultured lens epithelial cells by minimizing the degree of depolarization of mitochondrial membrane potential (ΔΨm) consequential to oxidative insult. We investigated whether one of the safeguards produced by estrogen is mediated by the hormone acting as a positive regulator of the survival signal transduction pathway, MAPK which, in turn, influences regulation of mitochondrial function by stabilizing ΔΨm, in effect, attenuating the extent of depolarization of mitochondrial membrane potential in the face of acute oxidative stress. Methods: The SV–40 viral transformed human cell line, HLE–B3 was serum–deprived for 24 hours and subsequently treated with 17ß–E2 (1 µM) over a time course of 60 minutes and phosphorylation of ERK1/2 was analyzed by Western blot. Cell cultures were exposed to the MEK1/2 inhibitor, UO126, or vehicle prior to the bolus addition of 100 µM H2O2 ± 17ß–E2 and the ΔΨm examined using JC–1, a potentiometric dye which serves as an indicator for the state of mitochondrial membrane potential. Results: ERK1/2 was rapidly phosphorylated to pERK within 5 to 15 min in the presence of 17ß–E2 and remained evident by 60 minutes. UO126 treatment attenuated pERK irrespective of whether estradiol was administered. Mitochondrial membrane depolarization resulting from H2O2 stress was substantially greater in the presence of UO126 indicating that the relative degree of pERK influences mitochondrial stability with oxidative insult. The greater the extent of depolarization, the less effective 17ß–E2 treatment was in checking mitochondrial membrane depolarization. Conclusions: The multifaceted protective mechanisms activated by 17ß–E2 likely function by genomic and non–genomic pathways integrating at a point of mitochondrial control which regulates the mitochondrial defense state to advance antioxidative protection. This data identifies a rapid and non–genomic means by which 17ß–E2–induced stimulation of ERK1/2 phosphorylation converges with downstream mitochondrial stabilization to prevent collapse of ΔΨm. Targeting mitochondrial function to reduce oxidative stress, thereby preventing activation of the permeability transition pore, characterizes a novel concept which will contribute to innovative regimens to prevent or delay onset of cataractogenesis.
Keywords: signal transduction • mitochondria • antioxidants