Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany; Research Unit Protein Science, Helmholtz Zentrum München, Neuherberg, Germany.
J Neurochem. 2014 Jul;130(2):227-40. doi: 10.1111/jnc.12704. Epub 2014 Mar 27.
Subretinal injections with glial cell line-derived neurotrophic factor (GDNF) rescue morphology as well as function of rod cells in mouse and rat animal models of retinitis pigmentosa. At the same time, it is postulated that this effect is indirect, mediated by activation of retinal Müller glial (RMG) cells. Here, we show that Cyr61/CCN1, one of the secreted proteins up-regulated in primary RMG after glial cell line-derived neurotrophic factor stimulation, provides neuroprotective and pro-survival capacities: Recombinant Cyr61 significantly reduced photoreceptor (PR) cells death in organotypic cultures of Pde6b(rd1) retinas. To identify stimulated pathways in the retina, we treated Pde6b(rd1) retinal explants with Cyr61 and observed an overall increase in activated Erk1/2 and Stat3 signalling molecules characterized by activation-site-specific phosphorylation. To identify Cyr61 retinal target cells, we isolated primary porcine PR, RMG and retinal pigment epithelium (RPE) cells and exposed them separately to Cyr61. Here, RMG as well as RPE cells responded with induced phosphorylation of Erk1/2, Stat3 and Akt. In PR, no increase in phosphorylation in any of the studied proteins was detected, suggesting an indirect neuroprotective effect of Cyr61. Cyr61 may thus act as an endogenous pro-survival factor for PR, contributing to the complex repertoire of neuroprotective activities generated by RMG and RPE cells. We propose the following model of Cyr61 neuroprotection within the retina: Cyr61 stimulates retinal Müller glial (RMG) and retinal pigment epithelium (RPE) cells and activates PI3K/Akt, mitogen-activated protein kinase(MAPK)/Erk and Janus kinase(JAK)/Stat-signalling pathways in these cells. Phosphorylated Stat3 and Erk1/2 presumably translocate to the nucleus, induce transcriptional changes, which increase secretion of neuroprotective agents that protect photoreceptors (PR) from mutation-induced death.
胶质细胞源性神经营养因子（GDNF）的视网膜下注射挽救了色素性视网膜炎小鼠和大鼠动物模型中视杆细胞的形态和功能。同时，据推测这种作用是间接的，通过激活视网膜 Müller 胶质（RMG）细胞来介导。在这里，我们表明 Cyr61/CCN1 是 GDNF 刺激后上调的初级 RMG 中的一种分泌蛋白，它提供了神经保护和生存能力：重组 Cyr61 显著减少了 Pde6b（rd1）视网膜器官型培养物中的光感受器（PR）细胞死亡。为了鉴定受刺激的视网膜途径，我们用 Cyr61 处理 Pde6b（rd1）视网膜外植体，观察到激活的 Erk1/2 和 Stat3 信号分子的整体增加，其特征是激活部位特异性磷酸化。为了鉴定 Cyr61 视网膜靶细胞，我们分离了原代猪 PR、RMG 和视网膜色素上皮（RPE）细胞，并分别将它们暴露于 Cyr61 中。在这里，RMG 和 RPE 细胞都表现出 Erk1/2、Stat3 和 Akt 的诱导性磷酸化。在 PR 中，没有检测到任何研究蛋白的磷酸化增加，这表明 Cyr61 的间接神经保护作用。因此，Cyr61 可能作为 PR 的内源性生存因子发挥作用，为 RMG 和 RPE 细胞产生的复杂神经保护活性做出贡献。我们提出了 Cyr61 神经保护在视网膜内的以下模型：Cyr61 刺激视网膜 Müller 胶质（RMG）和视网膜色素上皮（RPE）细胞，并激活这些细胞中的 PI3K/Akt、丝裂原激活蛋白激酶（MAPK）/Erk 和 Janus 激酶（JAK）/Stat 信号通路。磷酸化的 Stat3 和 Erk1/2 可能易位到细胞核，诱导转录变化，增加神经保护剂的分泌，从而保护光感受器（PR）免受突变诱导的死亡。
