Protective Effect of Bax Ablation Against Cell Loss in the Retinal Ganglion Layer Induced by Optic Nerve Crush in Transgenic Mice

Abstract

Bax expression is a prerequisite for retinal ganglion cell (RGC) apoptosis. Experimental studies have reported Bax protein upregulation following optic nerve transection. The stimuli that trigger apoptosis share a common executioner proteolysis cascade, including caspase-3 and poly-(adenosine diphosphate ribose) polymerase cleavage. This study sought to elucidate the role of the mitochondrial apoptotic pathway in RGCs using a Bax transgenic knockout mouse model. The right optic nerves of 26 C57BL mice, 7 Bax, 7 Bax, and 12 Bax, were subjected to crush injury and analyzed for apoptosis and neuronal cell loss on days 1, 3, and 21. Levels of Bax, Bcl-2, and caspase-3 messenger RNA expression were determined with real-time polymerase chain reaction. Multiple apoptotic cells were detected in the retinas of the Bax and Bax mice at days 1 and 3, but not in the Bax mice. The Bax/Bcl-2 ratio was higher in the Bax than in the Bax mice on day 1 (1.33 and 0.83, respectively), with a trend toward an increase on day 3 (1.47 and 1.66, respectively); Bax/Bcl-X showed the same elevation on day 1 in the wild-type mice (1.34) but decreased on day 3 (0.8). Bax gene expression was undetectable in the Bax mice. Caspase-3 gene expression was higher in the Bax than in the Bax mice on day 1 and dropped toward baseline on day 3. The opposite trend was noted in the Bax mice. The lack of apoptosis combined with the reduction in proapoptotic genes in the Bax mice after injury compared to the Bax and Bax mice suggests that Bax plays a crucial role in the induction of apoptosis. Suppression of Bax expression may reduce retinal cell loss.