Department of Ophthalmology and Eye Hospital, University of Leipzig, Leipzig, Germany.
J Neurosci Res. 2012 Jan;90(1):257-66. doi: 10.1002/jnr.22732. Epub 2011 Sep 15.
Neuronal degeneration and aberrant neovascularization are common problems of ischemic retinopathies. Pigment epithelium-derived factor (PEDF), a neuroprotective protein and an inhibitor of angiogenesis, is produced by retinal glial (Müller) cells and can counterbalance elevated levels of vascular endothelial growth factor (VEGF), the expression of which is regulated primarily by hypoxia-inducible factor (HIF)-1. In an approach to mimic transient ischemia in vitro, primary Müller cells were cultured under transient and strong hypoxia (0.2% O(2) ), followed by reoxygenation at 2.5% O(2) , and molecular mechanisms that might contribute to changes in the intraretinal PEDF level were determined. Hypoxic conditions caused an increasing expression of HIF-1α and led to upregulation of both PEDF and VEGF. Treatment of the cells with synthetic HIF-1α blockers or neutralization of VEGF binding to VEGF receptors (VEGFR-1 and-2) suppressed hypoxia-induced PEDF upregulation. Furthermore, the presence of CoCl(2) (a hypoxia mimetic) induced an accumulation of elevated HIF-1α protein in the nucleus and an upregulation of PEDF expression in Müller cells. Increasing PEDF expression was attenuated when HIF-1α levels were suppressed using HIF-1α small interfering RNA (siRNA). On the other hand, siRNA-mediated depletion of PEDF facilitated HIF-1α upregulation caused by CoCl(2) and resulted in increasing VEGF mRNA and protein levels. These results demonstrate that VEGF and PEDF may be unidirectionally regulated in hypoxia through HIF-1α activation, with upregulation of PEDF, which may occur in a VEGF-dependent manner. However, endogenously produced PEDF seems to be an inherent control element of HIF-1α expression in Müller cells, indicating an important feedback mechanism for limiting upregulation of VEGF.
神经元变性和异常血管生成是缺血性视网膜病变的常见问题。色素上皮衍生因子（PEDF）是一种神经营养蛋白和血管生成抑制剂，由视网膜神经胶质（Müller）细胞产生，可以对抗血管内皮生长因子（VEGF）水平的升高，VEGF 的表达主要受缺氧诱导因子（HIF）-1 的调节。为了模拟体外短暂性缺血，将原代 Müller 细胞在短暂而强烈的低氧（0.2% O2）条件下培养，然后在 2.5% O2 下复氧，并确定可能导致视网膜内 PEDF 水平变化的分子机制。低氧条件导致 HIF-1α表达增加，并导致 PEDF 和 VEGF 的上调。用合成 HIF-1α 阻断剂或中和 VEGF 与 VEGF 受体（VEGFR-1 和 VEGFR-2）的结合来处理细胞，可抑制低氧诱导的 PEDF 上调。此外，CoCl2（一种低氧模拟物）的存在诱导核内 HIF-1α蛋白的积累和 Müller 细胞中 PEDF 表达的上调。使用 HIF-1α 小干扰 RNA（siRNA）抑制 HIF-1α 水平时，PEDF 表达的增加会减弱。另一方面，siRNA 介导的 PEDF 耗竭促进了 CoCl2 引起的 HIF-1α 上调，并导致 VEGF mRNA 和蛋白水平的增加。这些结果表明，在低氧条件下，VEGF 和 PEDF 可能通过 HIF-1α 激活单向调节，PEDF 的上调可能以 VEGF 依赖的方式发生。然而，内源性产生的 PEDF 似乎是 Müller 细胞中 HIF-1α 表达的固有控制元件，表明 VEGF 上调的限制存在重要的反馈机制。
