RAB-10 Regulates Glutamate Receptor Recycling in a Cholesterol-dependent Endocytosis Pathway

Abstract

Regulated endocytosis of ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors (AMPARs) is critical for synaptic plasticity. However, the specific combination of clathrin-dependent and -independent mechanisms that mediate AMPAR trafficking in vivo have not been fully characterized. Here, we examine the trafficking of the AMPAR subunit GLR-1 in Caenorhabditis elegans. GLR-1 is localized on synaptic membranes, where it regulates reversals of locomotion in a simple behavioral circuit. Animals lacking RAB-10, a small GTPase required for endocytic recycling of intestinal cargo, are similar in phenotype to animals lacking LIN-10, a postsynaptic density 95/disc-large/zona occludensdomain containing protein: GLR-1 accumulates in large accretions and animals display a decreased frequency of reversals. Mutations in unc-11 (AP180) or itsn-1 (Intersectin 1), which reduce clathrin-dependent endocytosis, suppress the lin-10 but not rab-10 mutant phenotype, suggesting that LIN-10 functions after clathrin-mediated endocytosis. By contrast, cholesterol depletion, which impairs lipid raft formation and clathrin-independent endocytosis, suppresses the rab-10 but not the lin-10 phenotype, suggesting that RAB-10 functions after clathrin-independent endocytosis. Animals lacking both genes display additive GLR-1 trafficking defects. We propose that RAB-10 and LIN-10 recycle AMPARs from intracellular endosomal compartments to synapses along distinct pathways, each with distinct sensitivities to cholesterol and the clathrin-mediated endocytosis machinery. INTRODUCTIONContinuous movement of ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) into and out of synaptic membranes is a key mechanism for the regulation of excitatory synaptic strength. Previous work has shown that insertion of AMPARs into the plasma membrane strengthens synapses and that it is required to convert silent synapses into active synapses (Bredt and Nicoll, 2003;Malenka, 2003;Malinow, 2003;Sheng and Hyoung Lee, 2003;Gerges et al., 2005). Furthermore, it has recently been shown that recycling of AMPARs from internal endosomal compartments back to the plasma membrane is important for long-term potentiation (Park et al., 2004). By contrast, endocytosis of AMPARs at sites adjacent to the postsynaptic density is important for long-term depression (Carroll et al., 2001;Racz et al., 2004). Thus, molecular machinery required for endocytosis, as well as intracellular membrane trafficking processes, ultimately regulates the character of signal transmitted at each synapse.Multiple endocytosis trafficking pathways have been observed in cells. Clathrin-dependent endocytosis occurs at clathrin-coated pits, where transmembrane protein cargo and adaptor molecules recruit soluble clathrin (Le Roy and Wrana, 2005). Vesicles coated with a clathrin lattice are then pinched off from the membrane. Members of the Rab family of small guanosine triphosphate (GTP)ases mediate the intracellular membrane trafficking of endocytose...

A Presynaptic Regulatory System Acts Transsynaptically via Mon1 to Regulate Glutamate Receptor Levels in Drosophila

“…Neurotransmitter release at the synapse is modulated by factors that control synaptic growth, synaptic vesicle recycling, and receptor turnover at postsynaptic sites (Sweeney and Davis 2002;Glodowski et al 2007;Kim and Kandler 2010;Fernandes et al 2014). Endolysosomal trafficking modulates the function of these factors and therefore plays an important role in regulating synaptic development and function.…”

Caenorhabditis elegansIntersectin: A Synaptic Protein Regulating Neurotransmission

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