Protective effect of Bax ablation against cell loss in the retinal ganglion layer induced by optic nerve crush in transgenic mice.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Possible neuroprotective effect of brimonidine in a mouse model of ischaemic optic neuropathy.

PURPOSE: To investigate the neuroprotective effect of brimonidine following induction of ischaemic optic neuropathy in rodents (rAION). METHODS: Mice were treated with an intraperitoneal injection of brimonidine 48, 24 or 0 h before rAION induction or eye drops for 5 days after rAION induction. Retinal ganglion cell (RGC) loss and expression of genes involved in the angiogenesis (vascular endothelial growth factor [VEGF], pigment epithelium-derived factor [PEDF], The epidermal growth factor homology domains-2 [Tie-2]), ischaemia (haem oxygense-1 [HO-1], hypoxia-inducible factor 1alpha[HIF-1alpha], endothelial nitric oxide synthase [eNOS]) and oxidative stress (superoxide dismutase-1 [SOD-1], glutathione peroxidase-1 [GPX-1]) response to ischaemic damage were compared with sham or rAION-untreated mice. RESULTS: No RGC loss was detected in the brimonidine-treated mice. Effect of post-rAION eye drops: day 1--no decrease in retinal mRNA levels of angiogenesis-related genes, increase in ischaemia- and oxidative stress-related genes except HIF-1alpha; day 3--baseline or higher levels of oxidative and ischaemia-related genes except HIF-1alpha, increase in VEGF, decrease in PEDF; day 21--no change in angiogenesis-related genes. Effect of pre-rAION injection: baseline levels of angiogenesis-related genes with all injection schedules; increase in ischaemia-related genes with 48-h and 0-h pretreatment; decrease in HO-1 and eNOS with 24-h pretreatment; increase in oxidative-related genes except GPX-1. In optic nerve tissue, HO-1, HIF-1alpha and SOD-1 decreased on day 1 after topical administration and were still below baseline on day 3. CONCLUSIONS: The increase in HO-1 associated with rAION is mitigated with brimonidine treatment, especially when administered intraperitoneally. Topical brimonidine apparently reduces VEGF, Tie-2, HIF-1alpha and GPX-1 expression on day 21. These results agree with published data and may have therapeutic implications for patients diagnosed with AION in the acute phase.