The Sophie and Arthur Laboratory for Optic Nerve Biology, Hamilton Glaucoma Center, University of California San Diego, La Jolla, United States of America.
PLoS One. 2012;7(10):e47098. doi: 10.1371/journal.pone.0047098. Epub 2012 Oct 9.
Glutamate excitotoxicity-induced oxidative stress have been linked to mitochondrial dysfunction in retinal ischemia and optic neuropathies including glaucoma. Brimonindine (BMD), an alpha 2-adrenergic receptor agonist, contributes to the neuroprotection of retinal ganglion cells (RGCs) against glutamate excitotoxicity or oxidative stress. However, the molecular mechanisms of BMD-associated mitochondrial preservation in RGC protection against glutamate excitotoxicity-induced oxidative stress following retinal ischemic injury remain largely unknown. Here, we tested whether activation of alpha 2 adrenergic receptor by systemic BMD treatment blocks glutamate excitotoxicity-induced oxidative stress, and preserves the expression of mitochondrial transcription factor A (Tfam) and oxidative phosphorylation (OXPHOS) complex in ischemic retina. Sprague-Dawley rats received BMD (1 mg/kg/day) or vehicle (0.9% saline) systemically and then transient ischemia was induced by acute intraocular pressure elevation. Systemic BMD treatment significantly increased RGC survival at 4 weeks after ischemia. At 24 hours, BMD significantly decreased Bax expression but increased Bcl-xL and phosphorylated Bad protein expression in ischemic retina. Importantly. BMD significantly blocked the upregulations of N-methyl-D-aspartate receptors 1 and 2A protein expression, as well as of SOD2 protein expression in ischemic retina at 24 hours. During the early neurodegeneration following ischemic injury (12-72 hours), Tfam and OXPHOS complex protein expression were significantly increased in vehicle-treated retina. At 24 hours after ischemia, Tfam immunoreactivity was increased in the outer plexiform layer, inner nuclear layer, inner plexiform layer and ganglion cell layer. Further, Tfam protein was expressed predominantly in RGCs. Finally, BMD preserved Tfam immunoreactivity in RGCs as well as Tfam/OXPHOS complex protein expression in the retinal extracts against ischemic injury. Our findings suggest that systemic BMD treatment protects RGCs by blockade of glutamate excitotoxicity-induced oxidative stress and subsequent preservation of Tfam/OXPHOS complex expression in ischemic retina.
谷氨酸兴奋性毒性诱导的氧化应激与视网膜缺血和视神经病变中的线粒体功能障碍有关，包括青光眼。育亨宾（BMD）是一种α2-肾上腺素能受体激动剂，可促进视网膜神经节细胞（RGC）对抗谷氨酸兴奋性毒性或氧化应激的神经保护作用。然而，BMD 与线粒体保存相关的分子机制在 RGC 保护中的作用，以及其对谷氨酸兴奋性毒性诱导的氧化应激的保护作用，在视网膜缺血损伤后仍然很大程度上未知。在这里，我们测试了全身性 BMD 治疗通过激活α2 肾上腺素能受体是否可以阻断谷氨酸兴奋性毒性诱导的氧化应激，并维持缺血视网膜中线粒体转录因子 A（Tfam）和氧化磷酸化（OXPHOS）复合物的表达。Sprague-Dawley 大鼠接受 BMD（1mg/kg/天）或载体（0.9%生理盐水）全身治疗，然后通过急性眼内压升高诱导短暂性缺血。全身 BMD 治疗可显著增加缺血后 4 周的 RGC 存活率。在 24 小时时，BMD 显著降低了缺血视网膜中的 Bax 表达，但增加了 Bcl-xL 和磷酸化 Bad 蛋白的表达。重要的是，BMD 可显著阻断缺血视网膜中 N-甲基-D-天冬氨酸受体 1 和 2A 蛋白表达以及 SOD2 蛋白表达的上调。在缺血损伤后的早期神经退行性变期间（12-72 小时），载体处理的视网膜中 Tfam 和 OXPHOS 复合物蛋白表达显著增加。在缺血后 24 小时，Tfam 免疫反应性增加在外丛状层、内核层、内丛状层和节细胞层。此外，Tfam 蛋白主要在 RGC 中表达。最后，BMD 保存了缺血视网膜中 RGC 中的 Tfam 免疫反应性以及 Tfam/OXPHOS 复合物蛋白表达。我们的研究结果表明，全身性 BMD 治疗通过阻断谷氨酸兴奋性毒性诱导的氧化应激以及随后保存缺血视网膜中的 Tfam/OXPHOS 复合物表达来保护 RGC。
