Dong Enheng, Bachleda Amelia, Xiong Yubin, Osawa Shoji, Weiss Ellen R
Department of Cell Biology and Physiology, The University of North Carolina at Chapel Hill, NC.
The Neuroscience Center, The University of North Carolina at Chapel Hill, NC.
Mol Vis. 2017 Mar 8;23:90-102. eCollection 2017.
The mechanisms that trigger retinal degeneration are not well understood, despite the availability of several animal models with different mutations. In the present report, the mouse, a model for retinitis pigmentosa (RP) that contains a mutation in the gene for PDE6β (), is used to evaluate gliosis, as a marker for retinal stress, and cyclic AMP response element binding protein (CREB) phosphorylation, which may be important early in retinal degeneration.
Wild-type C57Bl6J and mice raised under cyclic light were examined for changes in gliosis and CREB phosphorylation for approximately 3 weeks beginning at P14 to P17 using immunocytochemistry. Mice raised under normal cyclic light and in complete darkness were also compared for changes in CREB phosphorylation.
Gliosis in mice raised under cyclic light was apparent at P17, before extensive degeneration of the photoreceptor layer is visible, and increased over time. Phosphorylation of CREB at Ser133 (pCREB) was detected in Müller glia (MG) in the wild-type and mice. However, at all phases of photoreceptor degeneration, the pCREB levels were lower in the mice. We also observed extensive migration of MG cell bodies to the outer nuclear layer (ONL) during degeneration. In contrast to the mice raised under cyclic light, the mice raised in the dark exhibited slower rates of degeneration. When the dark-reared mice were exposed to cyclic light, the photoreceptor layer degenerated within 4 days to approximately one to two rows of nuclei. Interestingly, the pCREB levels in the MG also decreased during this 4-day cyclic light exposure compared to the levels in the mice raised continuously in the dark.
The results of these studies suggest that photoreceptors communicate directly or indirectly with MG at early stages, inducing gliosis before extensive retinal degeneration is apparent in mice. Surprisingly, phosphorylation of CREB is downregulated in the MG. These results raise the interesting possibility that Müller glia undergo CREB-mediated transcriptional changes that influence photoreceptor degeneration either positively or negatively. Unlike canine models of RP, no increase in pCREB was observed in photoreceptor cells during this period suggesting possible mechanistic differences in the role of CREB in photoreceptors between these species.
尽管有几种携带不同突变的动物模型，但引发视网膜变性的机制仍未完全明确。在本报告中，利用一种患有视锥视杆细胞营养不良（RP）的小鼠模型（该模型的PDE6β基因发生了突变）来评估神经胶质增生（作为视网膜应激的标志物）以及环磷酸腺苷反应元件结合蛋白（CREB）磷酸化情况，这在视网膜变性早期可能具有重要意义。
从出生后第14天至第17天开始，对在周期性光照下饲养的野生型C57Bl6J小鼠和该突变小鼠进行大约3周的观察，通过免疫细胞化学检测神经胶质增生和CREB磷酸化的变化。还比较了在正常周期性光照和完全黑暗环境中饲养的小鼠CREB磷酸化的变化情况。
在周期性光照下饲养的该突变小鼠，在第17天就出现了明显的神经胶质增生，此时光感受器层尚未出现广泛变性，且随着时间推移而增加。在野生型和该突变小鼠的Müller胶质细胞（MG）中均检测到了Ser133位点的CREB磷酸化（pCREB）。然而，在光感受器变性的各个阶段，该突变小鼠的pCREB水平均较低。我们还观察到在变性过程中MG细胞体大量迁移至外核层（ONL）。与在周期性光照下饲养的小鼠不同，在黑暗中饲养的该突变小鼠变性速度较慢。当将在黑暗中饲养的小鼠暴露于周期性光照下时，光感受器层在4天内退化至大约一到两排细胞核。有趣的是，与一直在黑暗中饲养的该突变小鼠相比，在这4天的周期性光照暴露期间，MG中的pCREB水平也有所下降。
这些研究结果表明，在该突变小鼠中，光感受器在早期直接或间接与MG进行沟通，在视网膜广泛变性明显之前就诱导了神经胶质增生。令人惊讶的是，MG中的CREB磷酸化被下调。这些结果提出了一个有趣的可能性，即Müller胶质细胞经历了CREB介导的转录变化，这种变化对光感受器变性可能产生正向或负向影响。与犬类RP模型不同，在此期间光感受器细胞中未观察到pCREB增加，这表明这些物种之间CREB在光感受器中的作用可能存在机制差异。
