Astrocytes have diverse functions that are supported by their anatomic localization between neurons and blood vessels. One of these functions is the clearance of extracellular glutamate. Astrocytes clear glutamate using two Na⁺-dependent glutamate transporters, GLT-1 (also called EAAT2) and GLAST (also called EAAT1). GLT-1 expression increases during synaptogenesis and is a marker of astrocyte maturation. Over 20 years ago, several groups demonstrated that astrocytes in culture express little or no GLT-1 and that neurons induce expression. We recently demonstrated that co-culturing endothelia with mouse astrocytes also induced expression of GLT-1 and GLAST. These increases were blocked by an inhibitor of γ-secretase. This and other observations are consistent with the hypothesis that Notch signaling is required, but the ligands involved were not identified. In the present study, we used rat astrocyte cultures to further define the mechanisms by which endothelia induce expression of GLT-1 and GLAST. We found that co-cultures of astrocytes and endothelia express higher levels of GLT-1 and GLAST protein and mRNA. That endothelia activate Hes5, a transcription factor target of Notch, in astrocytes. Using recombinant Notch ligands, anti-Notch ligand neutralizing antibodies, and shRNAs, we provide evidence that both Dll1 and Dll4 contribute to endothelia-dependent regulation of GLT-1. We also provide evidence that astrocytes secrete a factor(s) that induces expression of Dll4 in endothelia and that this effect is required for Notch-dependent induction of GLT-1. Together these studies indicate that reciprocal communication between astrocytes and endothelia is required for appropriate astrocyte maturation and that endothelia likely deploy additional non-Notch signals to induce GLT-1.

星形胶质细胞具有多种功能，这些功能由它们在神经元和血管之间的解剖定位支持。这些功能之一是清除细胞外谷氨酸。星形胶质细胞使用两种 Na ⁺依赖性谷氨酸转运蛋白 GLT-1（也称为 EAAT2）和 GLAST（也称为 EAAT1）清除谷氨酸。GLT-1 表达在突触形成过程中增加，是星形胶质细胞成熟的标志。20 多年前，几个小组证明，培养中的星形胶质细胞很少或不表达 GLT-1，而神经元诱导表达。我们最近证明了与小鼠共培养内皮细胞星形胶质细胞还诱导 GLT-1 和 GLAST 的表达。这些增加被γ-分泌酶抑制剂阻断。这和其他观察结果与需要 Notch 信号传导的假设一致，但未鉴定出所涉及的配体。在本研究中，我们使用大鼠星形胶质细胞培养以进一步确定内皮细胞诱导 GLT-1 和 GLAST 表达的机制。我们发现星形胶质细胞和内皮细胞的共培养表达更高水平的 GLT-1 和 GLAST 蛋白和 mRNA。该内皮细胞在星形胶质细胞中激活 Hes5，这是 Notch 的转录因子靶标。使用重组 Notch 配体、抗 Notch 配体中和抗体和 shRNA，我们提供了 Dll1 和 Dll4 都有助于 GLT-1 的内皮依赖性调节的证据。我们还提供证据表明星形胶质细胞分泌一种诱导内皮细胞中 Dll4 表达的因子，并且这种效应是 Notch 依赖性 GLT-1 诱导所必需的。