The transmembrane transporter domain of glutamate transporters is a process tip localizer

Abstract

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 4th transmembrane helices, unique for metazoans, is required for the localization. Moreover, a C186S mutation at the 4th 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.

Hyaluronan synthesis supports glutamate transporter activity

“…The TM transporter domains of the two glutamate transporters (mEGFP‐GLT1‐TM and mEGFP‐GLAST‐TM), with all TM helices and their connecting loops, but without cytoplasmic tails, localized to cellular process tips. This result shows that cellular process tip localization is a common feature of trimeric TM transporters, while the cytoplasmic tails of GLT1 facilitate plasma membrane delivery (Hayashi and Yasui ).…”

“…The difference in action of hyaluronidase from bovine testis and Streptomyces hyalurolyticus we observed could be attributed to whether these hyaluronidases are able to trim short hyaluronan chains anchored to HAS so that newly synthesized hyaluronan do not reach glutamate transporters. We previously reported that an extracellular loop connecting the transport subdomain and trimerization subdomain of GLT1 is required for cellular process localization (Hayashi and Yasui ). We speculate that the interaction between the extracellular loop of GLT1 and a short chain of hyaluronan anchored to neighboring hyaluronan synthase affects conformational change between subdomains for substrate transport.…”

Purinergic P2Y1 Receptors Control Rapid Expression of Plasma Membrane Processes in Hippocampal Astrocytes

“…Neuronal glutamate release determines retraction of APs, reducing then astrocyte capability to effectively remove glutamate from synapses, even if a recent study shows that glutamate transporters influence APs tip position [66]. In these conditions, ATP derived from astrocytes might lose its capability to act on neighboring neurons [67] impairing synaptic transmission.…”

Involvement of Astrocytes in Mediating the Central Effects of Ghrelin

“…The glutamate transporters glutamate transporter 1 (GLT1) and glutamate aspartate transporter (GLAST) are highly expressed on astrocytes [121,122]. We have shown that ghrelin treatment icv rapidly stimulates GLT1 and GLAST levels, while only GLAST levels were found to increase in vitro [19].…”