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

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Abstract
Regulated endocytosis of α-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 occludens-domain 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.