Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany.
Neuroscience. 2013 Aug 29;246:59-72. doi: 10.1016/j.neuroscience.2013.04.045. Epub 2013 Apr 30.
Osmotic swelling of retinal neurons and glial cells is an important pathogenic factor of retinal edema formation. Here, we show that the neuroprotective factor osteopontin (OPN), which is released from retinal glial (Müller) cells after stimulation of the cells with glial cell line-derived neurotrophic factor (Del Río et al., 2011, Glia 59:821-832), inhibits the swelling of rat Müller cells induced by hypoosmotic exposure of retinal slices in the presence of barium ions and H₂O₂, respectively, and in slices of postischemic retinas. OPN did not inhibit the hypoosmotic swelling of bipolar cells in slices of control and postischemic retinas. The inhibitory effect of OPN on Müller cell swelling was dose-dependent, with a half-maximal effect at ∼0.6 ng/ml. The effect of OPN was abrogated in the presence of pharmacological blockers of vascular endothelial growth factor (VEGF) receptor-2, metabotropic glutamate receptors, and purinergic receptors (P2Y₁, adenosine A1 receptors), as well as of a neutralizing anti-VEGF antibody. The data suggest that OPN induces the release of VEGF, glutamate, ATP, and adenosine from Müller cells. The effect of OPN was also prevented by blockers of voltage-gated sodium channels (tetrodotoxin), T-type voltage-gated calcium channels (kurtoxin), potassium channels (clofilium), and chloride channels 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). The swelling-inhibitory effect of OPN was dependent on intracellular calcium signaling, activation of phospholipase C and protein kinase C, and vesicular exocytosis of glutamate. In retinal slices, Müller glial cells display immunoreactivity of OPN. The data suggest that Müller cell-derived OPN has (in addition to the effects on photoreceptors and retinal neurons) autocrine effects. The neuroprotective effects of OPN may be in part mediated by the prevention of cytotoxic Müller cell swelling and the release of VEGF and adenosine from Müller cells.
视网膜神经元和神经胶质细胞的渗透性肿胀是视网膜水肿形成的一个重要致病因素。在这里，我们表明，神经营养因子骨桥蛋白（OPN）在细胞受到胶质细胞衍生的神经营养因子（Del Río 等人，2011 年，Glia 59：821-832）刺激后从视网膜神经胶质（Müller）细胞中释放出来，可以抑制视网膜切片在钡离子和 H₂O₂存在下的低渗暴露诱导的大鼠 Müller 细胞肿胀，以及在缺血后视网膜切片中。OPN 不会抑制对照和缺血后视网膜切片中双极细胞的低渗肿胀。OPN 对 Müller 细胞肿胀的抑制作用呈剂量依赖性，半最大效应约为 0.6ng/ml。在血管内皮生长因子（VEGF）受体-2、代谢型谷氨酸受体和嘌呤能受体（P2Y₁、腺苷 A1 受体）的药理学阻滞剂以及中和抗 VEGF 抗体存在的情况下，OPN 的作用被消除。数据表明，OPN 诱导 Müller 细胞释放 VEGF、谷氨酸、ATP 和腺苷。OPN 的作用也被电压门控钠通道（河豚毒素）、T 型电压门控钙通道（kurtoxin）、钾通道（氯菲立姆）和氯离子通道 5-硝基-2-（3-苯丙基氨基）苯甲酸（NPPB）的阻滞剂阻止。OPN 的肿胀抑制作用依赖于细胞内钙信号转导、磷脂酶 C 和蛋白激酶 C 的激活以及谷氨酸的囊泡胞吐作用。在视网膜切片中，Müller 神经胶质细胞显示 OPN 的免疫反应性。数据表明，Müller 细胞衍生的 OPN 具有（除了对光感受器和视网膜神经元的影响之外）自分泌作用。OPN 的神经保护作用部分可能是通过防止细胞毒性 Müller 细胞肿胀和从 Müller 细胞中释放 VEGF 和腺苷来介导的。
