背景:小胶质细胞(MC)是中枢神经系统的哨兵。在健康方面,他们被称为测量MC,因为他们检查组织以维持体内平衡。在疾病中,他们激活,在其他功能中,变得吞噬以清洁细胞碎片。在这项工作中,我们已经在两种单侧完全眶内视神经轴突切开术模型中研究了大鼠视网膜MC的行为,这些模型引起了视网膜神经节细胞(RGC)丢失的不同时间过程。
方法:白化Sprague-Dawley大鼠分为以下组:(a)完整(无手术),(b)来自上丘的氟金(FG)示踪,和(c)FG示踪+左侧视神经的挤压或横切。病变后2天至2个月解剖视网膜(n=4-12组/病变和时间点),然后进行Brn3a和Iba1双重免疫检测。在每个完整的视网膜中,对Brn3a+RGC和Iba+MC的总数进行了定量.在每个追踪的视网膜(B和C组)中,FG追踪的RGC和吞噬小胶质细胞(PMC,FG+Iba+)也被定量。通过邻居地图评估地形分布。
结果:在完整的视网膜中,测量MC均匀分布在神经节细胞层和内部丛状层中。独立于轴突切开术模型,RGC死亡分为两个阶段,一个快速,一个持久,PMCs的外观与追踪RGC的丢失之间存在线性和地形相关性。此外,PMC对FG+RGC的清除发生在标志着RGC死亡的Brn3a表达的实际丧失后3天。此外,在RGC丢失的快速阶段,来自内部丛状层的近50%的MC迁移到神经节细胞层,在缓慢变性阶段返回到内部丛状层。最后,与老鼠身上发生的情况相反,在老鼠身上,在对侧未损伤的视网膜中没有小胶质细胞吞噬作用。
结论:轴突切开术诱导的RGC死亡发生早于RGC清除,RGC消失与PMC外观呈负相关,在数字和地形上,这表明吞噬作用是对RGC死亡而不是轴突损伤的直接反应。
BACKGROUND: Microglial cells (MCs) are the sentries of the central nervous system. In health, they are known as surveying MCs because they examine the tissue to maintain the homeostasis. In disease, they activate and, among other functions, become phagocytic to clean the cellular debris. In this work, we have studied the behavior of rat retinal MCs in two models of unilateral complete intraorbital optic nerve axotomy which elicit a different time course of retinal ganglion cell (RGC) loss.
METHODS: Albino Sprague-Dawley rats were divided into these groups: (a) intact (no surgery), (b)
fluorogold (FG) tracing from the superior colliculi, and (c) FG tracing + crush or transection of the left optic nerve. The retinas were dissected from 2 days to 2 months after the lesions (n = 4-12 group/lesion and time point) and then were subjected to Brn3a and Iba1 double immunodetection. In each intact retina, the total number of Brn3a+RGCs and Iba+MCs was quantified. In each traced retina (b and c groups), FG-traced RGCs and phagocytic microglial cells (PMCs, FG+Iba+) were also quantified. Topographical distribution was assessed by neighbor maps.
RESULTS: In intact retinas, surveying MCs are homogenously distributed in the ganglion cell layer and the inner plexiform layer. Independently of the axotomy model, RGC death occurs in two phases, one quick and one protracted, and there is a lineal and topographical correlation between the appearance of PMCs and the loss of traced RGCs. Furthermore, the clearance of FG+RGCs by PMCs occurs 3 days after the actual loss of Brn3a expression that marks RGC death. In addition, almost 50% of MCs from the inner plexiform layer migrate to the ganglion cell layer during the quick phase of RGC loss, returning to the inner plexiform layer during the slow degeneration phase. Finally, in contrast to what happens in mice, in rats, there is no microglial phagocytosis in the contralateral uninjured retina.
CONCLUSIONS: Axotomy-induced RGC death occurs earlier than RGC clearance and there is an inverse correlation between RGC loss and PMC appearance, both numerically and topographically, suggesting that phagocytosis occurs as a direct response to RGC death rather than to axonal damage.