Department of Pathology and Laboratory Medicine, Jules Stein Eye Institute, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA.
J Neuroophthalmol. 2012 Sep;32(3):227-37. doi: 10.1097/WNO.0b013e3182589589.
During mouse retina maturation, the final number of retinal ganglion cells (RGCs) is determined by highly regulated programmed cell death. Previous studies demonstrated that the immunoregulatory receptor programmed cell death-1 (PD-1) promotes developmental RGC death. To identify the functional signaling partner(s) for PD-1, we identified retinal expression of PD-1 ligands and examined the effect of PD-1 ligand expression on RGC number. We also explored the hypothesis that PD-1 signaling promotes the development of functional visual circuitry.
Characterization of retinal and brain programmed cell death-1 ligand 1 (PD-L1) expression were examined by immunofluorescence on tissue sections. The contribution of PD-ligands, PD-L1, and programmed cell death-1 ligand 2 (PD-L2) to RGC number was examined in PD-ligand knockout mice lacking 1 or both ligands. Retinal architecture was assessed by spectral-domain optical coherence tomography, and retinal function was analyzed by electroretinography in wild-type and PD-L1/L2 double-deficient mice.
PD-L1 expression is found throughout the neonatal retina and persists in adult RGCs, bipolar interneurons, and Müller glia. In the absence of both PD-ligands, there is a significant numerical increase in RGCs (34% at postnatal day 2 [P2] and 18% in adult), as compared to wild type, and PD-ligands have redundant function in this process. Despite the increased RGC number, adult PD-L1/L2 double-knockout mice have normal retinal architecture and outer retina function.
This study demonstrates that PD-L1 and PD-L2 together impact the final number of RGCs in adult mice and supports a novel role for active promotion of neuronal cell death through PD-1 receptor-ligand engagement.
在小鼠视网膜成熟过程中，视网膜神经节细胞（RGCs）的最终数量由高度调控的程序性细胞死亡决定。先前的研究表明，免疫调节受体程序性细胞死亡蛋白-1（PD-1）促进发育中的 RGC 死亡。为了确定 PD-1 的功能信号伙伴，我们鉴定了 PD-1 配体在视网膜中的表达，并研究了 PD-1 配体表达对 RGC 数量的影响。我们还探讨了 PD-1 信号促进功能性视觉回路发育的假说。
通过组织切片免疫荧光法检测视网膜和脑程序性细胞死亡-1 配体 1（PD-L1）的表达特征。在缺乏 1 种或 2 种配体的 PD-配体敲除小鼠中，研究 PD-配体、PD-L1 和 PD-L2 对 RGC 数量的贡献。通过频域光相干断层扫描评估视网膜结构，并在野生型和 PD-L1/L2 双缺失小鼠中通过视网膜电图分析视网膜功能。
PD-L1 在新生鼠视网膜中广泛表达，并在成年 RGCs、双极神经元和 Müller 胶质细胞中持续表达。在缺乏 2 种 PD-配体的情况下，与野生型相比，RGC 数量显著增加（生后第 2 天增加 34%，成年时增加 18%），并且 PD-配体在这一过程中具有冗余功能。尽管 RGC 数量增加，但成年 PD-L1/L2 双敲除小鼠的视网膜结构和外核层功能正常。
本研究表明，PD-L1 和 PD-L2 共同影响成年小鼠中 RGC 的最终数量，并支持 PD-1 受体-配体结合通过主动促进神经元细胞死亡来发挥新的作用。
