The transcriptional activator hypoxia inducible factor 2 (HIF-2/EPAS-1) regulates the oxygen-dependent expression of erythropoietin in cortical astrocytes
The transcriptional activator hypoxia inducible factor 2 (HIF-2/EPAS-1) regulates the oxygen-dependent expression of erythropoietin in cortical astrocytes
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DOI：
10.1523/jneurosci.2838-06.2006
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发表时间：
2006-09-13
影响因子：
5.3
通讯作者：
Pichiule, Paola
中科院分区：
文献类型：
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作者：
Chavez, Juan C.;Baranova, Oxana;Pichiule, Paola
在缺血或缺氧的大脑中，星形胶质细胞似乎是促红细胞生成素（EPO）的主要来源之一。在这项研究中，我们研究了缺氧诱导因子 (HIF) 亚型对培养星形胶质细胞缺氧 EPO 表达调节的差异贡献。此外，利用氧糖剥夺 (OGD) 的体外模型，我们研究了 HIF-1 α 和 HIF-2 α 在星形胶质细胞产生旁分泌保护信号中的作用，这些信号调节暴露于 OGD 的神经元的存活。通过用编码 HIF-1 α 或 HIF-2 α 特异性小干扰 RNA（siHIF-1 α 或 siHIF-2 α）的慢病毒颗粒感染星形胶质细胞，消除 HIF-1 α 或 HIF-2 α 的表达。感染siHIF-1α的星形胶质细胞表现出血管内皮生长因子（VEGF）和乳酸脱氢酶（LDH）的缺氧诱导被消除，但EPO诱导正常。相反，siHIF-2α减少HIF-2α表达导致EPO缺氧表达急剧减少，但不影响LDH或VEGF上调。为了进一步测试 HIF-2 是否足以驱动 EPO 上调，我们表达了 HIF-1 α(mtHIF-1 α) (P402A/ P577A) 和 HIF-2 α(mtHIF-2 α) (P405A/P530A) 的氧不敏感突变体形式。在含氧量正常的星形胶质细胞中，mtHIF-2 α 的表达而非 mtHIF-1 α 的表达导致 EPO mRNA 和蛋白质的显着上调。因此，通过染色质免疫沉淀测定，发现 HIF-2 α 而不是 HIF-1 α 与 EPO 缺氧反应元件相关。有趣的是，受到亚致死 OGD 攻击的星形胶质细胞的条件培养基提高了神经元对 OGD 的存活率。然而，在使用 siHIF-2 α 下调星形细胞 HIF-2 α 过程中，这种效应被消除。这些结果表明HIF-2α介导星形胶质细胞中EPO表达的转录激活，并且该途径可能促进缺血期间星形胶质细胞旁分泌依赖性神经元的存活。
In the ischemic or hypoxic brain, astrocytes appear to be one of the main sources of erythropoietin (EPO). In this study, we investigated the differential contribution of hypoxia inducible factor (HIF) isoforms to the regulation of hypoxic EPO expression in cultured astrocytes. In addition, using an in vitro model of oxygen-glucose deprivation (OGD), we studied the role of HIF-1 alpha and HIF-2 alpha in the generation of paracrine protective signals by astrocytes that modulate the survival of neurons exposed to OGD. Expression of HIF-1 alpha or HIF-2 alpha was abrogated by infecting astrocytes with lentiviral particles encoding small interference RNA specific for HIF-1 alpha or HIF-2 alpha (siHIF-1 alpha or siHIF-2 alpha). Astrocytes infected with siHIF-1 alpha showed abrogated hypoxic induction of vascular endothelial growth factor (VEGF) and lactate dehydrogenase (LDH) but normal EPO induction. In contrast, reduction of HIF-2 alpha expression by siHIF-2 alpha led to a drastic decrease of EPO hypoxic expression, but it did not affect LDH or VEGF upregulation. To further test whether HIF- 2 is sufficient to drive EPO upregulation, we expressed oxygen-insensitive mutant forms of HIF-1 alpha(mtHIF-1 alpha) (P402A/ P577A) and HIF-2 alpha( mtHIF-2 alpha) (P405A/P530A). Expression of mtHIF-2 alpha but not mtHIF-1 alpha in normoxic astrocytes resulted in a significant upregulation of EPO mRNA and protein. Accordingly, HIF-2 alpha but not HIF-1 alpha was found to be associated with the EPO hypoxia-response element by a chromatin immunoprecipitation assay. Interestingly, conditioned medium from astrocytes challenged by sublethal OGD improved neuronal survival to OGD; however, this effect was abolished during the downregulation of astrocytic HIF-2 alpha using siHIF-2 alpha. These results indicate that HIF-2 alpha mediates the transcriptional activation of EPO expression in astrocytes, and this pathway may promote astrocytic paracrinedependent neuronal survival during ischemia.