Institute of Physiology and Pathophysiology, University of Heidelberg, Im Neuenheimer Feld 326, 69120 Heidelberg, Germany.
Stroke. 2012 Oct;43(10):2748-56. doi: 10.1161/STROKEAHA.112.669598. Epub 2012 Aug 28.
Numerous factors involved in the adaptive response to hypoxia, including erythropoietin and vascular endothelial growth factor are transcriptionally regulated by hypoxia-inducible factors (HIFs). During normoxia, prolyl-4-hydroxylase domain (PHD) proteins hydroxylate HIF-α subunits, resulting in their degradation. We investigated the effect of neuronal deletion of PHD2, the most abundant isoform in brain, for stroke outcome.
We generated neuron-specific Phd2 knockout mice and subjected animals to systemic hypoxia or transient middle cerebral artery occlusion. Infarct volume and cell death were determined by histology. HIF-1α, HIF-2α, and HIF target genes were analyzed by immunoblotting and real-time polymerase chain reaction, respectively.
Neuron-specific ablation of Phd2 significantly increased protein stability of HIF-1α and HIF-2α in the forebrain and enhanced expression of the neuroprotective HIF target genes erythropoietin and vascular endothelial growth factor as well as glucose transporter and glycolysis-related enzymes under hypoxic and ischemic conditions. Mice with Phd2-deficient neurons subjected to transient cerebral ischemia exhibited a strong reduction in infarct size, and cell death of hippocampal CA1 neurons located in the peri-infarct region was dramatically reduced in these mice. Vessel density in forebrain subregions, except for caudate-putamen, was not altered in Phd2-deficient animals.
Our findings denote that the endogenous adaptive response on hypoxic-ischemic insults in the brain is at least partly dependent on the activity of HIFs and identify PHD2 as the key regulator for the protective hypoxia response. The results suggest that specific inhibition of PHD2 may provide a useful therapeutic strategy to protect brain tissue from ischemic injury.
参与低氧适应反应的众多因素，包括促红细胞生成素和血管内皮生长因子，均受低氧诱导因子（HIFs）的转录调控。在常氧条件下，脯氨酰-4-羟化酶结构域（PHD）蛋白羟化 HIF-α 亚基，导致其降解。我们研究了脑内丰度最高的同工型 PHD2 神经元缺失对卒中结局的影响。
我们生成了神经元特异性 Phd2 敲除小鼠，并使动物处于系统性低氧或短暂性大脑中动脉闭塞状态。通过组织学确定梗死体积和细胞死亡。通过免疫印迹和实时聚合酶链反应分别分析 HIF-1α、HIF-2α 和 HIF 靶基因。
神经元特异性 Phd2 缺失显著增加了前脑 HIF-1α 和 HIF-2α 的蛋白稳定性，并增强了神经保护 HIF 靶基因促红细胞生成素和血管内皮生长因子以及葡萄糖转运体和糖酵解相关酶在低氧和缺血条件下的表达。短暂性脑缺血小鼠 Phd2 缺失神经元减少，梗死体积明显减小，海马 CA1 神经元的细胞死亡明显减少。PHD2 缺失动物的前脑亚区（除尾壳核外）血管密度没有改变。
我们的研究结果表明，脑内低氧缺血损伤的内源性适应反应至少部分依赖于 HIFs 的活性，并确定 PHD2 是保护性低氧反应的关键调节因子。结果表明，特异性抑制 PHD2 可能为保护脑组织免受缺血性损伤提供一种有用的治疗策略。
