Expression of the pro–apoptotic BH3–only protein Bim after optic nerve axotomy and transient retinal ischemia

Abstract

Abstract: : Purpose: To study the effect of two common retinal injuries, optic nerve transection and transient ischemia, on the relative mRNA levels of the pro–apoptotic BH3–only protein Bim in the retina. Methods: In adult Sprague–Dawley rats, the left eye underwent optic nerve transection (ONT) or 90 minutes of selective ligature of the ophthalmic vessels (SLOV). Rats were sacrificed 3, 4 or 14 days after injury and both retinas were collected for analysis. RNA was extracted from the whole retina and used for cDNA preparation and real time PCR analysis. Localization of the protein in the retina was studied using immunohistochemical staining. Results: As a response to axotomy, the relative mRNA level of Bim was increased 4 days after the operation and decreased to control levels thereafter. In contrast, Bim mRNA level remained unchanged 3 days after SLOV but was increased (up to 7–fold) 14 days after ischemia. Bim immunoreactivity (IR) was found in the retinal ganglion cell layer and co–localized with retrograde TrueBlue labelling of retinal ganglion cells. 4 days after ONT an increase in Bim IR was detected on ganglion cells, whereas no major changes in Bim IR could be seen in retinas 3 days after SLOV. Conclusions: Bim expression is altered after both kinds of lesions. The results suggest that Bim is likely to be involved in the ganglion cell death after axotomy. However this is not as clear after transient ischemia since Bim expression increases first after 3–4 days (most clearly after 14 days). This delayed increase suggests that retinal cells, other than ganglion cells, might start to express Bim since a large proportion of the retinal ganglion cell population has been lost at this time.

Keywords: cell death/apoptosis • retina: proximal (bipolar, amacrine, and ganglion cells) • ischemia