Bim Expression Indicates the Pathway to Retinal Cell Death in Development and Degeneration

Abstract

Programmed cell death (PCD) during development of the mouse retina involves activation of the mitochondrial pathway. Previous work has shown that the multidomain Bcl-2 family proteins Bax and Bak are fundamentally involved in this process. To induce mitochondrial membrane permeabilization, Bax and Bak require that prosurvival members of the family be inactivated by binding of "BH3-only" members. We showed previously that the BH3-only protein BimEL is highly expressed during postnatal retinal development but decreases dramatically thereafter. The purpose of this study was to investigate a possible role for Bim, in retinal development and degeneration, upstream of Bax and Bak. Bim Ϫ/Ϫ mice analyzed for defective retinal development exhibit an increase in retinal thickness and a delay in PCD, thereby confirming a role for Bim. We also demonstrate that in response to certain death stimuli, bim ϩ/ϩ retinal explants upregulate BimEL leading to caspase activation and cell death, whereas bim Ϫ/Ϫ explants are resistant to apoptosis. Finally, we analyzed Bim expression in the retinal degeneration (rd) mouse, an in vivo model of retinal degeneration. Bim isoforms, which decrease during development, are not reexpressed during retinal degeneration and ultimately photoreceptor cells die by a caspase-independent mechanism. Thus, we conclude that in cases in which BimEL is reexpressed during pathological cell death, developmental cell death pathways are reactivated. However, the absence of BimEL expression correlates with caspase-independent death in the rd model.

Redox survival signalling in retina-derived 661W cells

“…Taken together, these results strengthen our hypothesis that the oxidant burst mediates cell survival signalling under stress conditions. 30 Therefore, we decided to examine a range of concentrations of H 2 O 2 on retinal explants to determine a concentration that was not toxic and that could be used in further experiments. Figure 7a shows terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labelling (TUNEL) staining of P10 mouse retinal explant sections subjected to increasing concentrations of H 2 O 2 for 24 h. We found 50 mM H 2 O 2 did not increase the number of TUNEL-positive nuclei in the outer nuclear layer (ONL) where photoreceptors are located or the ganglion cell layer (GCL) where RGCs are found, above untreated control levels over 24 h. However, 150, 300 and 600 mM H 2 O 2 steadily increased the number of TUNEL-positive nuclei in both the ONL and the GCL in a concentration-dependent manner over 24 h. Interestingly, this study shows an increased sensitivity of retinal explant cultures to H 2 O 2 compared to the 661W photoreceptor cell line and the RGC-5 line (Figure 7b and c).…”

The Bcl-2 proteins Noxa and Bcl-xL co-ordinately regulate oxidative stress-induced apoptosis

“…Murine retinal explants deficient in Bim expression are more resistant to H 2 O 2 treatment compared with retinal explants expressing Bim [30]. In fibroblasts, Bik expression is crucial for H 2 O 2 -triggered cell death [20].…”

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

“…Additionally, external activation of caspase 8 leads to the generation of further internal signals that translocate to the mitochondrial membrane ( Fig. 9) to trigger the cell death process (Doonan et al, 2007).…”