Estrogen Signaling Protects Mitochondrial Membrane Potential Integrity from Oxidative Stress in Lens Epithelial Cells




Flynn, James Martin


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Flynn, James Martin, Estrogen Signaling Protects Mitochondrial Membrane Potential Integrity from Oxidative Stress in Lens Epithelial Cells. Doctor of Philosophy, (Cell Biology and Genetics) May, 2008, 265 pages, 36 figures, bibliography, 190 titles. Loss of mitochondrial membrane potential has been determined to be one of the initiating factors in activation of apoptosis after cellular damage. Estrogen and estrogen analogues have been shown to enhance cell survival in numerous tissues through rapid pro-survival cell signaling. This study was focused on elucidating mechanisms through which estrogen protects the cells by preventing the activation of mitochondrial permeability transition pores and the subsequent loss of mitochondrial membrane potential. It is hypothesized that the anti-apoptotic mitochondrial protein BAD, once phosphorylated by estrogen activated upstream kinases, can prevent the formation of the permeability transition pre via direct interaction. To address this, lens epithelial cells were used as a model system for the examination of mitochondrial depolarization during periods of either oxidative or hyperglycemic stress. Estrogen attenuated the loss of impermeability of the mitochondrial membrane, thus maintaining the cells during acute periods of stress. It was discovered that a number of the estrogen receptor isoforms are expressed in lens epithelium, and that the wild-type estrogen receptor-β1 isoform is localized to the mitochondria in lens epithelial cultures derived from both human males and females. siRNA treatment against estrogen receptor-β determined that is a required component to elicit estrogen’s protective abilities against oxidative stress induced mitochondrial depolarization. Furthermore, administration of exogenous estrogen rapidly activated signaling pathways, particularly ERK, which were shown to have influence over the loss of mitochondrial membrane potential. Studies using both pharmacological inhibitors of MAPK signaling, as well as siRNA of ERK2 kinase demonstrate a correlation between the activation of ERK and the severity of response to oxidative stress. Investigation of downstream substrates of ERK revealed that the mitochondrial protein BAD is phosphorylated after the administration of estrogen, yet it is not required for the prevention of mitochondrial depolarization as originally hypothesized. In conclusion, these studies have confirmed a mitochondrial targeted mechanism activated by estrogen which is rapid, gender independent, estrogen receptor-β mediated signal transduction pathway. The targeting of mitochondrial function to reduce oxidative or hyperglycemic stress, thereby preventing activation of the permeability transition pore, defines a novel concept which will contribute to innovative regimens for prevention or treatment of mitochondrial pathology.