Hayashi Mariko Kato, Yasui Masato
Department of Pharmacology, Keio University School of Medicine, Shinjuku, Tokyo 160-8582, Japan.
Sci Rep. 2015 Mar 12;5:9032. doi: 10.1038/srep09032.
Glutamate transporters in the central nervous system remove glutamate released from neurons to terminate the signal. These transporters localize to astrocyte process tips approaching neuronal synapses. The mechanisms underlying the localization of glutamate transporters to these processes, however, are not known. In this study, we demonstrate that the trimeric transmembrane transporter domain fragment of glutamate transporters, lacking both N- and C-terminal cytoplasmic regions, localized to filopodia tips. This is a common property of trimeric transporters including a neutral amino acid transporter ASCT1. Astrocyte specific proteins are not required for the filopodia tip localization. An extracellular loop at the centre of the 4(th) transmembrane helices, unique for metazoans, is required for the localization. Moreover, a C186S mutation at the 4(th) transmembrane region of EAAT1, found in episodic ataxia patients, significantly decreased its process tip localization. The transmembrane transporter domain fragments of glutamate transporters also localized to astrocyte process tips in cultured hippocampal slice. These results indicate that the transmembrane transporter domain of glutamate transporters have an additional function as a sorting signal to process tips.
中枢神经系统中的谷氨酸转运体可清除神经元释放的谷氨酸以终止信号。这些转运体定位于靠近神经元突触的星形胶质细胞突起末端。然而，谷氨酸转运体定位于这些突起的潜在机制尚不清楚。在本研究中，我们证明了谷氨酸转运体的三聚体跨膜转运结构域片段，缺乏N端和C端胞质区域，定位于丝状伪足末端。这是包括中性氨基酸转运体ASCT1在内的三聚体转运体的共同特性。丝状伪足末端定位不需要星形胶质细胞特异性蛋白。后生动物特有的第4个跨膜螺旋中心的细胞外环是定位所必需的。此外，在发作性共济失调患者中发现的EAAT1第4个跨膜区域的C186S突变显著降低了其在突起末端的定位。谷氨酸转运体的跨膜转运结构域片段也定位于培养的海马切片中的星形胶质细胞突起末端。这些结果表明，谷氨酸转运体的跨膜转运结构域具有作为突起末端分选信号的额外功能。
