-
[show abstract]
[hide abstract]
ABSTRACT: Photoreceptor cell death is an irreversible, pathologic event in many blinding retinal diseases including retinitis pigmentosa, age-related macular disease, and retinal detachment. Light exposure can exacerbate a variety of human retinal diseases by increasing the rate of photoreceptor cell death. In the present study, we characterize the kinetics of photoreceptor cell death in Tubby (homozygous tub/tub, which have inherited, progressive retinal degeneration) mice born and raised in a bright cyclic light environment. Our data show that raising tub/tub mice in a bright cyclic light environment induces rapid loss of photoreceptors. This effect can be slowed, but not prevented, by raising animals in constant darkness, which suggests the involvement of phototransduction in the accelerated death of photoreceptors in this animal. We further demonstrated that the activities of cytosolic cytochrome c and caspases-3 and -9 were significantly increased in the retinas of tub/tub mice. Raising animals in darkness significantly reduced the increased activities of caspases-3 and -9, as well as cytosolic cytochrome c. We also observed that rhodopsin, a phototransduction protein, is not restricted to the rod outer segment, but is distributed throughout the rod cell, including the inner segments, cell bodies, and synapses. In addition, the light-dependent translocation and compartmentalization of arrestin and transducin are affected by the tubby mutation. Our results support the interpretation that problems in protein trafficking in the photoreceptors of the tub/tub mouse may contribute to retinal degeneration.
Neurobiology of Disease 04/2006; 21(3):468-77. · 5.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To determine the temporal kinetics of the simultaneous translocation of arrestin and rod alpha-transducin in mice exposed to different lighting environments and to compare the subcellular compartmentation of cone alpha-transducin with arrestin.
Double labeling immunofluorescence microscopy and image analysis are used to visualize and quantify the concentrations of rod arrestin and alpha-transducin in the subcellular compartments of the rod outer segments, the rod inner segments and the synaptic terminals.
The magnitude of the effects of the translocation are clearly contrasted in images of the retinas of animals that have been maximally light adapted verses retinas that have been maximally dark adapted. The onset of light results in a rapid, simultaneous, translocation of arrestin and alpha-transducin from their respective compartments (alpha-transducin in the rod outer segment and arrestin in the rod inner segment) to the opposite compartment. Almost all of alpha-transducin has translocated in less than two min whereas the translocation of the majority of arrestin requires at least five to six min. Translocation in the opposite direction, from light to dark, occurs more slowly for both proteins with arrestin requiring almost 30 min and alpha-T needing more than 200 min to complete its journey. Under the same lighting conditions, cone arrestin translocation is incomplete. Cone alpha-transducin does not translocate under any the lighting conditions tested. Unlike the frog, continuous exposure of mice to light does not result in arrestin translocating back to the rod inner segment.
These data suggest that there are four mechanisms involved in the translocation of these two proteins. They also support the conclusion that the more important cellular function of the translocation process is to terminate phototransduction in rod and cone photoreceptors, which could provide protection against light damage. The secondary function of translocation is to maximize rod sensitivity to light during dark adaptation. The restricted localization of cone alpha-transducin to the cone outer segment is consistent with the function of cones in bright light, just as the concentration of rod alpha-transducin in dark adapted rod outer segment is consistent with their functioning in dim light.
Molecular vision 10/2004; 10:672-81. · 2.20 Impact Factor
-
Xiaorui Yu,
Raju V S Rajala,
James F McGinnis,
Feng Li,
Robert E Anderson,
Xiaorong Yan,
Sheng Li, Rajesh V Elias,
Ryan R Knapp,
Xiaohong Zhou,
Wei Cao
[show abstract]
[hide abstract]
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.
Journal of Biological Chemistry 04/2004; 279(13):13086-94. · 4.77 Impact Factor
