title: Involvement of insulin/phosphoinositide 3-kinase/Akt signal pathway in 17 beta-estradiol-mediated neuroprotection.
abstract: In the present study, we tested the hypothesis that 17beta-estradiol (betaE2) is a neuroprotectant in the retina, using two experimental approaches: 1) hydrogen peroxide (H(2)O(2))-induced retinal neuron degeneration in vitro, and 2) light-induced photoreceptor degeneration in vivo. We demonstrated that both betaE2 and 17alpha-estradiol (alphaE2) significantly protected against H(2)O(2)-induced retinal neuron degeneration; however, progesterone had no effect. betaE2 transiently increased the phosphoinositide 3-kinase (PI3K) activity, when phosphoinositide 4,5-bisphosphate and [(32)gammaATP] were used as substrate. Phospho-Akt levels were also transiently increased by betaE2 treatment. Addition of the estrogen receptor antagonist tamoxifen did not reverse the protective effect of betaE2, whereas the PI3K inhibitor LY294002 inhibited the protective effect of betaE2, suggesting that betaE2 mediates its effect through some PI3K-dependent pathway, independent of the estrogen receptor. Pull-down experiments with glutathione S-transferase fused to the N-Src homology 2 domain of p85, the regulatory subunit of PI3K, indicated that betaE2 and alphaE2, but not progesterone, identified phosphorylated insulin receptor beta-subunit (IRbeta) as a binding partner. Pretreatment with insulin receptor inhibitor, HNMPA, inhibited IRbeta activation of PI3K. Systemic administration of betaE2 significantly protected the structure and function of rat retinas against light-induced photoreceptor cell degeneration and inhibited photoreceptor apoptosis. In addition, systemic administration of betaE2 activated retinal IRbeta, but not the insulin-like growth factor receptor-1, and produced a transient increase in PI3K activity and phosphorylation of Akt in rat retinas. The results show that estrogen has retinal neuroprotective properties in vivo and in vitro and suggest that the insulin receptor/PI3K/Akt signaling pathway is involved in estrogen-mediated retinal neuroprotection.
authors.affiliation: Department of Ophthalmology, Dean A. McGee Eye Institute, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Boulevard, Oklahoma City, OK 73104, USA.
authors.forename: Xiaorui
authors.initials: X
authors.lastname: Yu
authors.forename: Raju V S
authors.initials: RV
authors.lastname: Rajala
authors.forename: James F
authors.initials: JF
authors.lastname: McGinnis
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.forename: Robert E
authors.initials: RE
authors.lastname: Anderson
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Yan
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.forename: Rajesh V
authors.initials: RV
authors.lastname: Elias
authors.forename: Ryan R
authors.initials: RR
authors.lastname: Knapp
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhou
authors.forename: Wei
authors.initials: W
authors.lastname: Cao
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004396:Coloring Agents / Q000494:pharmacology; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004596:Electroretinography; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism*; D005136:Eye Proteins; D005982:Glutathione Transferase / Q000378:metabolism; D051597:Hippocalcin; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007328:Insulin / Q000378:metabolism*; D008027:Light; D008074:Lipoproteins; D009025:Morpholines / Q000494:pharmacology; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011374:Progesterone / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000037:antagonists & inhibitors; D051603:Recoverin; D012160:Retina / Q000166:cytology / Q000378:metabolism; D015398:Signal Transduction; D013629:Tamoxifen / Q000494:pharmacology; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D018909:src Homology Domains
chemical_list: D002135:Calcium-Binding Proteins; D002867:Chromones; D004396:Coloring Agents; D004791:Enzyme Inhibitors; D004958:Estradiol; D005136:Eye Proteins; D005982:Glutathione Transferase; D051597:Hippocalcin; D006861:Hydrogen Peroxide; D007328:Insulin; D008074:Lipoproteins; D009025:Morpholines; D009419:Nerve Tissue Proteins; D019869:Phosphatidylinositol 3-Kinases; D011374:Progesterone; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D051603:Recoverin; D013629:Tamoxifen; D013778:Tetrazolium Salts; D013844:Thiazoles; C496733:Rcvrn protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494920:Akt1 protein, rat; C022616:thiazolyl blue