Buckingham Brian P, Inman Denise M, Lambert Wendi, Oglesby Ericka, Calkins David J, Steele Michael R, Vetter Monica L, Marsh-Armstrong Nicholas, Horner Philip J
Department of Neurological Surgery, University of Washington, Seattle, Washington 98104, USA.
J Neurosci. 2008 Mar 12;28(11):2735-44. doi: 10.1523/JNEUROSCI.4443-07.2008.
Glaucoma is characterized by retinal ganglion cell (RGC) pathology and a progressive loss of vision. Previous studies suggest RGC death is responsible for vision loss in glaucoma, yet evidence from other neurodegenerative diseases suggests axonal degeneration, in the absence of neuronal loss, can significantly affect neuronal function. To characterize RGC degeneration in the DBA/2 mouse model of glaucoma, we quantified RGCs in mice of various ages using neuronal-specific nuclear protein (NeuN) immunolabeling, retrograde labeling, and optic nerve axon counts. Surprisingly, the number of NeuN-labeled RGCs did not decline significantly until 18 months of age, at which time a significant decrease in RGC somal size was also observed. Axon dysfunction and degeneration occurred before loss of NeuN-positive RGCs, because significant declines in RGC number assayed by retrograde tracers and axon counts were observed at 13 months. To examine whether axonal dysfunction/degeneration affected gene expression in RGC axons or somas, NeuN and neurofilament-heavy (NF-H) immunolabeling was performed along with quantitative reverse transcription-PCR for RGC-specific genes in retinas of aged DBA/2 mice. Although these mice had similar numbers of NeuN-positive RGCs, the expression of neurofilament light, Brn-3b, and Sncg mRNA varied; this variation in RGC-specific gene expression was correlated with the appearance of NF-H immunoreactive RGC axons. Together, these data support a progression of RGC degeneration in this model of glaucoma, beginning with loss of retrograde label, where axon dysfunction and degeneration precede neuronal loss. This progression of degeneration suggests a need to examine the RGC axon as a locus of pathology in glaucoma.
青光眼的特征是视网膜神经节细胞（RGC）病变和视力逐渐丧失。先前的研究表明，RGC死亡是青光眼视力丧失的原因，但来自其他神经退行性疾病的证据表明，在没有神经元损失的情况下，轴突退化会显著影响神经元功能。为了在DBA/2青光眼小鼠模型中表征RGC退化，我们使用神经元特异性核蛋白（NeuN）免疫标记、逆行标记和视神经轴突计数对不同年龄小鼠的RGC进行了定量。令人惊讶的是，NeuN标记的RGC数量直到18个月大时才显著下降，此时还观察到RGC胞体大小显著减小。轴突功能障碍和退化发生在NeuN阳性RGC丧失之前，因为在13个月时通过逆行示踪剂和轴突计数检测到RGC数量显著下降。为了检查轴突功能障碍/退化是否影响RGC轴突或胞体中的基因表达，对老年DBA/2小鼠视网膜中的RGC特异性基因进行了NeuN和重链神经丝（NF-H）免疫标记以及定量逆转录PCR。尽管这些小鼠的NeuN阳性RGC数量相似，但神经丝轻链、Brn-3b和Sncg mRNA的表达有所不同；RGC特异性基因表达的这种变化与NF-H免疫反应性RGC轴突的出现相关。总之，这些数据支持了该青光眼模型中RGC退化的进展，始于逆行标记的丧失，其中轴突功能障碍和退化先于神经元损失。这种退化进展表明有必要将RGC轴突作为青光眼病理的一个位点进行研究。
