Presynaptic Terminals Independently Regulate Synaptic Clustering and Autophagy of GABA_AReceptors inCaenorhabditis elegans

Abstract

Synaptic clustering of GABA A receptors is important for the function of inhibitory synapses, influencing synapse strength and, consequently, the balance of excitation and inhibition in the brain. Presynaptic terminals are known to induce GABA A receptor clustering during synaptogenesis, but the mechanisms of cluster formation and maintenance are not known. To study how presynaptic neurons direct the formation of GABA A receptor clusters, we have investigated GABA A receptor localization in postsynaptic cells that fail to receive presynaptic contacts in Caenorhabditis elegans. Postsynaptic muscles in C. elegans receive acetylcholine and GABA motor innervation, and GABA A receptors cluster opposite GABA terminals. Selective loss of GABA inputs caused GABA A receptors to be diffusely distributed at or near the muscle cell surface, confirming that GABA presynaptic terminals induce GABA A receptor clustering. In contrast, selective loss of acetylcholine innervation had no effect on GABA A receptor localization. However, loss of both GABA and acetylcholine inputs together caused GABA A receptors to traffic to intracellular autophagosomes. Autophagosomes normally transport bulk cytoplasm to the lysosome for degradation. However, we show that GABA A receptors traffic to autophagosomes after endocytic removal from the cell surface and that acetylcholine receptors in the same cells do not traffic to autophagosomes. Thus, autophagy can degrade cell-surface receptors and can do so selectively. Our results show that presynaptic terminals induce GABA A receptor clustering by independently controlling synaptic localization and surface stability of GABA A receptors. They also demonstrate a novel function for autophagy in GABA A receptor degradative trafficking.

The autophagosomal protein LGG-2 acts synergistically with LGG-1 in dauer formation and longevity in C. elegans

“…Interestingly, a role of autophagy in the specific degradation of GABA receptors at the neuromuscular junction has been reported. 16 Another striking observation is the presence in the embryo of numerous puncta positive for GFP::LGG-1 or GFP::LGG-2 which suggests a particular role for autophagy during embryogenesis. The massive reduction of these puncta in GFP::LGG-2(G130A) animals strongly support that they correspond to autophagosomal structures.…”

Autophagy in synaptic development, function, and pathology

“…for the fi rst time reported that the cell-surface GABA A Rs, but not acetylcholine receptors, targeted to autophagosomes for degradation [49] (Fig. 1C).…”

“…1C). Rowland et al showed that acetylcholine receptors do not traffi c to autophagosomes in the non-innervated muscle cells of C. elegans [49] . In contrast, a recent report demonstrated that in mouse tibialis anterior muscles, autophagy contributes to the basal and atrophy-induced turnover of muscletype cholinergic receptors, nicotinic/nicotinic acetylcholine receptors in a tripartite motif containing 63 (TRIM63)-dependent manner [53] .…”

Inactivation of GABAA receptor is related to heat shock stress response in organism model Caenorhabditis elegans

“…EG1653 and TJ375 strains have been regularly used, respectively, to quantify the expression of UNC-49 (Abraham et al 2011;Byrd et al 2001;Garafalo et al 2015;Knobel et al 2001;Rowland et al 2006) and HSP-16.2 (Abbas and Wink 2010;Lamark and Johansen 2012;Leroy et al 2012;Rea et al 2005;Shore et al 2012;Strayer et al 2003;Wang et al 2012;Wu et al 2006) based on the quantitation of their GFP fluorescence intensities.…”

“…This UNC-49B-GFP translational fusion protein fully rescues the uncoordinated phenotype of unc-49 (e407) and localizes to synapses. Also, GABA A receptors in C. elegans muscle cells are simple and uniform, in contrast to the structurally complex mammalian GABA A receptors (Bamber et al 1999;Gally and Bessereau 2003;Rowland et al 2006). UNC-49 receptors normally form clusters opposite inhibitory presynaptic terminals and, if this is not the case, are internalized and traffic to autophagosomes for degradation.…”