17β-Estradiol Impedes Bax-Involved Mitochondrial Apoptosis of Retinal Nerve Cells Induced by Oxidative Damage via the Phosphatidylinositol 3-Kinase/Akt Signal Pathway

Abstract

Oxidative stress leading to retinal nerve cells (RNCs) apoptosis is a major cause of neurodegenerative disorders of the retina. 17β-Estradiol (E2) has been suggested to be a neuroprotective agent in the central nervous system; however, at present, the underlying mechanisms are not well understood, and the related research on the RNCs is less reported. Here, in order to investigate the protective role and mechanism of E2 against oxidative stress-induced damage on RNCs, the transmission electron microscopy and annexin V-FITC/propidium iodide assay were applied to detect the RNCs apoptosis. Western blot and real-time PCR were used to determine the expression of the critical molecules in Bcl-2 and caspase family associated with apoptosis. The transmission electron microscopy results showed that H(2)O(2) could induce typical features of apoptosis in RNCs, including formation of the apoptosome. E2 could, however, suppress the H(2)O(2)-induced morphological changes of apoptosis. Intriguingly, we observed E2-mediated phagocytic scavenging of apoptosome. In response to H(2)O(2)-induced apoptosis, Bax, acting as one of the pivotal pro-apoptotic members of Bcl-2 family, increased significantly, which directly resulted in an increased ratio of Bax to anti-apoptotic protein Bcl-2 (Bax/Bcl-2). Additionally, caspases 9 and 3, which are the critical molecules of the mitochondrial apoptosis pathway, were activated by H(2)O(2). In contrast, E2 exerted anti-apoptotic effects by reducing the expression of Bax to decrease the ratio of Bax/Bcl-2 and impeded the caspases 9/3 activation. Moreover, LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, could sharply block the effect of E2 in reducing the percentage of apoptotic cells resistance to H(2)O(2). And the attenuation of Bax, the reduced activities of caspases 9/3 and the impeded release of mitochondrial cytochrome c mediated by E2 resistance to H(2)O(2) damage were significantly retrieved by LY294002 administration. Taken together, E2 protects the RNCs against H(2)O(2)-induced apoptosis by significantly inhibiting the Bax-involved mitochondrial apoptosis via the activation of PI3K/Akt signal pathway.

Hepatitis B virus X protein sensitizes HL-7702 cells to oxidative stress-induced apoptosis through modulation of the mitochondrial permeability transition pore

“…Bax is the key effector of the intrinsic apoptotic pathway initiated in response to diverse stimuli (23,31). Evidence indicates that Bax maintains a balance between the cytosol and mitochondria in the non-apoptotic state, while under the stimulation of apoptosis, cytosolic Bax changes its formation and then insert into the mitochondrial outer membrane, forming large channels at the mitochondrial outer membrane leading to the release of cytochrome c (32).…”

17β-Estradiol up-regulates Nrf2 via PI3K/AKT and estrogen receptor signaling pathways to suppress light-induced degeneration in rat retina

“…(Feng et al, 2013;Li et al, 2013a;Mo et al, 2013). Moreover, pretreatment with 10 µM LY was sufficient to inhibit pAKT protein expression in rats.…”

“…The PI3K/AKT signaling pathway is activated when retinal cells are exposed to oxidative stress, which can subsequently alter downstream signaling cascades (Wang et al, 2008). We additionally demonstrated that PI3K/AKT regulates downstream signaling, such as the nuclear factor kappa B (NF-κB) (Mo et al, 2013), mitochondrial apoptosis signaling (Li et al, 2013a), and Ca 2+ -regulated signaling pathways (Feng et al, 2013). We additionally demonstrated that PI3K/AKT regulates downstream signaling, such as the nuclear factor kappa B (NF-κB) (Mo et al, 2013), mitochondrial apoptosis signaling (Li et al, 2013a), and Ca 2+ -regulated signaling pathways (Feng et al, 2013).…”

Severe, Early Axonal Degeneration Following Experimental Anterior Ischemic Optic Neuropathy

“…Annexin-V staining has been co-localized with other apoptosis markers such as terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), a marker for apoptosis 35 ; Trypan blue, which labels cells with disrupted membrane 56,57 ; and propidium iodide (PI), 50,58 a late marker for cell death. [59][60][61][62] As a marker for apoptosis, annexin-V is used in various in vivo applications, such as the Detection of Apoptosing Retinal Cells (DARC) with cSLO, 30,31 which has been used to demonstrate the neuroprotective effect of topical CoQ10 following experimental glaucoma. 40 Because of its low toxicity and capacity to be recombined with radionuclides, recent clinical trial studies have utilized 99m-Technetiumannexin-V ( 99m Tc-Annexin-V) scintigraphy to label dying cell in vivo in patients with type 1 diabetes mellitus, 63 arrhythmogenic right ventricular cardiomyopathy/dysplasia, 64 and different types of cancer.…”