Ulbrich Felix, Goebel Ulrich, Böhringer Daniel, Charalambous Petar, Lagrèze Wolf Alexander, Biermann Julia
Department of Anesthesiology and Intensive Care, Medical Center, University of Freiburg, Hugstetter Strasse 55, Freiburg im Breisgau, 79106, Germany.
Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany.
Graefes Arch Clin Exp Ophthalmol. 2016 Oct;254(10):1967-1976. doi: 10.1007/s00417-016-3435-6. Epub 2016 Jul 21.
Ischemia and reperfusion (I/R) injury damages retinal neurons. Retinal injury is accompanied by activation of microglia, which scavenge the dead or dying neurons, but increasing evidence now indicates that amoeboid-shaped microglia cells activated in the brain after ischemia have neurotoxic and damaging properties in their own right. A previous study showed that postconditioning with carbon monoxide (CO) protects retinal ganglion cells (RGCs) after I/R through anti-apoptotic and anti-inflammatory mechanisms. The present study was designed to investigate and quantify the activation of retinal microglia after I/R with and without CO postconditioning.
Adult Sprague-Dawley rats underwent retinal ischemia by increasing the ocular pressure to 120 mmHg for 1 h through a needle inserted into the anterior chamber. Reperfusion was induced by removing the needle. After I/R, one group of animals was kept in a CO (250 ppm) atmosphere for 1 h; the other group was kept in room air (Air). At 1, 2, 3, and 7 days after I/R, the eyes were enucleated and fixed. Intracardiac blood was analyzed for systemic effects of CO or I/R. Retinal cross sections were taken from the middle third of the eye and were stained with anti-Iba-1. Microglia cells were graded as amoeboid or ramified phenotypes according to morphologic criteria. Retinal thicknesses were determined.
Evaluation of retinal tissue revealed a significant reduction of amoeboid microglia cells after I/R + CO when compared to the I/R + Air group. The peak number of amoeboid microglia was observed at day 2 post-I/R + Air. This rise was attenuated by CO postconditioning (815 versus 572 cells/mm for I/R + Air versus I/R + CO, respectively; p = 0.005). CO reduced and further postponed the peak in the numbers of amoeboid and ramified microglia cells in ischemic eyes and prevented microglial activation in the contralateral eyes. I/R-induced leucocytosis was inhibited by CO inhalation. The reduction of retinal thickness after I/R was more serious after Air inhalation when compared to the CO group.
Numerous activated microglia cells appear in the inner retina after I/R, and CO-treatment significantly attenuates this glial response. Antagonism of microglial activation may be a further neuroprotective effect of CO, apart from its direct anti-apoptotic capacity.
缺血再灌注（I/R）损伤会损害视网膜神经元。视网膜损伤伴随着小胶质细胞的激活，小胶质细胞会清除死亡或濒死的神经元，但越来越多的证据表明，脑缺血后激活的阿米巴样小胶质细胞本身具有神经毒性和损伤特性。先前的一项研究表明，一氧化碳（CO）后处理通过抗凋亡和抗炎机制保护I/R后的视网膜神经节细胞（RGCs）。本研究旨在调查和量化I/R后有无CO后处理时视网膜小胶质细胞的激活情况。
成年Sprague-Dawley大鼠通过将一根插入前房的针使眼压升高至120 mmHg持续1小时来进行视网膜缺血。通过拔出针诱导再灌注。I/R后，一组动物置于含CO（250 ppm）的气氛中1小时；另一组置于室内空气（空气）中。在I/R后1、2、3和7天，摘除眼球并固定。分析心内血以评估CO或I/R的全身影响。从眼球中部三分之一处获取视网膜横截面，并用抗Iba-1染色。根据形态学标准将小胶质细胞分为阿米巴样或分支状表型。测定视网膜厚度。
视网膜组织评估显示，与I/R + 空气组相比，I/R + CO后阿米巴样小胶质细胞显著减少。I/R + 空气组在I/R后第2天观察到阿米巴样小胶质细胞数量达到峰值。这种增加通过CO后处理得到缓解（I/R +空气组与I/R + CO组分别为815个细胞/mm与572个细胞/mm；p = 0.005）。CO减少并进一步推迟了缺血眼内阿米巴样和分支状小胶质细胞数量的峰值，并防止对侧眼的小胶质细胞激活。吸入CO可抑制I/R诱导的白细胞增多。与CO组相比，吸入空气后I/R后视网膜厚度的降低更严重。
I/R后内视网膜中出现大量激活的小胶质细胞，CO处理可显著减弱这种胶质细胞反应。除了其直接的抗凋亡能力外，拮抗小胶质细胞激活可能是CO的另一种神经保护作用。
