Metabotropic glutamate receptors: modulators of context-dependent feeding behaviour in C. elegans

Dillon J, Franks CJ, Murray C, Edwards RJ, Calahorro F, Ishihara T, Katsura I, Holden-Dye L, O’Connor V (in press). Metabotropic glutamate receptors: modulators of context-dependent feeding behaviour in C. elegans. J Biol Chem. Apr 13. pii: jbc.M114.606608.

Abstract

Glutamatergic neurotransmission is evolutionarily conserved across animal phyla. A major class of glutamate receptors are the metabotropic glutamate receptors (mGluRs). In C. elegans three mGluR genes mgl-1, mgl-2 and mgl-3 are organised into three sub-groups, similar to their mammalian counterparts. Cellular reporters identified expression of the mgls in the nervous system of C. elegans and overlapping expression in the pharyngeal microcircuit that controls pharyngeal muscle activity and feeding behaviour. The overlapping expression of mgls within this circuit allowed investigation of receptor signalling per se and in the context of receptor interactions within a neural network that regulates feeding. We utilized the pharmacological manipulation of neuronally regulated pumping of the pharyngeal muscle in wild type and mutants to investigate mgl function. This defined a net mgl-1 dependent inhibition of pharyngeal pumping which is modulated by mgl-3 excitation. Optogenetic activation of the pharyngeal glutamatergic inputs combined with electrophysiological recordings from the isolated pharyngeal preparations provided further evidence for a presynaptic mgl-1 dependent regulation of pharyngeal activity. Analysis of mgl-1, mgl-2 and mgl-3 mutant feeding behaviour in the intact organism after acute food removal identified a significant role for mgl-1 in the regulation of an adaptive feeding response. Our data describes the molecular and cellular organisation of mgl-1, mgl-2 and mgl-3. Pharmacological analysis identified that in these paradigms mgl-1 and mgl-3, but not mgl-2, can modulate the pharyngeal microcircuit. Behavioural analysis identified mgl-1 as a significant determinant of the glutamate-dependent modulation of feeding, further highlighting the significance of mGluRs in complex C. elegans behaviour.

PMID: 25869139

HSP-4 endoplasmic reticulum (ER) stress pathway is not activated in a C. elegans model of ethanol intoxication and withdrawal

Ient B, Edwards RJ, Mould R, Hannah M, Holden-Dye LM & O’Connor V (2012): HSP-4 endoplasmic reticulum (ER) stress pathway is not activated in a C. elegans model of ethanol intoxication and withdrawal. Invertebrate Neuroscience 12(2): 93-102.

Abstract

Acute and chronic exposure of Caenorhabditis elegans to concentrations of ethanol in the range 250-350 mM elicits distinct behaviours. Previous genetic analysis highlights specific neurobiological substrates for these effects. However, ethanol may also elicit cellular stress responses which may contribute to the repertoire of ethanol-induced behaviours. Here, we have studied the effect of ethanol on an important arm of the cellular stress pathways, which emanates from the endoplasmic reticulum (ER) in response to several conditions including heat shock and chemical or genetic perturbations that lead to protein misfolding. HSP-4 is a heat shock protein and homologue of mammalian BiP. It is a pivotal upstream component of the ER stress response. Therefore, we used a C. elegans heat shock protein mutant, hsp-4, and a strain carrying a transcriptional reporter, Phsp-4::gfp, to test the role of the ER following chronic ethanol conditioning. We found no evidence for an overt ER response during acute or prolonged exposure to concentrations of ethanol that lead to defined ethanol-induced behaviours. Furthermore, whilst hsp-4 was strongly induced by tunicamycin, pre-exposure of C. elegans to low doses of tunicamycin followed by ethanol was not sufficient to induce an additive ER stress response. Behavioural analysis of an hsp-4 mutant indicated no difference compared to wild type in susceptibility to ethanol intoxication and withdrawal. There is a clear precedent for a significance of ER stress pathways particularly in clinical conditions associated with toxic or pathological effects of high doses of alcohol consumption. The concentrations of ethanol used in this C. elegans study equate to the highest blood alcohol levels measured in patients with chronic alcohol dependency. Taken together, these observations imply that the classic ER stress pathway in C. elegans is relatively refractory to induction by ethanol.

PMID: 22661239

Selective toxicity of the anthelmintic emodepside revealed by heterologous expression of human KCNMA1 in Caenorhabditis elegans

Crisford A, Murray C, O’Connor V, Edwards RJ, Kruger N, Welz C, von Samson-Himmelstjerna G, Harder A, Walker RJ & Holden-Dye L. (2011): Selective Toxicity of the Anthelmintic Emodepside Revealed by Heterologous Expression of Human KCNMA1 in Caenorhabditis elegans. Molecular Pharmacology 79 (6): 1031-43.

Abstract

Emodepside is a resistance-breaking anthelmintic of a new chemical class, the cyclooctadepsipeptides. A major determinant of its anthelmintic effect is the calcium-activated potassium channel SLO-1. SLO-1 belongs to a family of channels that are highly conserved across the animal phyla and regulate neurosecretion, hormone release, muscle contraction, and neuronal network excitability. To investigate the selective toxicity of emodepside, we performed transgenic experiments in which the nematode SLO-1 channel was swapped for a mammalian ortholog, human KCNMA1. Expression of either the human channel or Caenorhabditis elegans slo-1 from the native slo-1 promoter in a C. elegans slo-1 functional null mutant rescued behavioral deficits that otherwise resulted from loss of slo-1 signaling. However, worms expressing the human channel were 10- to 100-fold less sensitive to emodepside than those expressing the nematode channel. Strains expressing the human KCNMA1 channel were preferentially sensitive to the mammalian channel agonists NS1619 and rottlerin. In the C. elegans pharyngeal nervous system, slo-1 is expressed in neurons, not muscle, and cell-specific rescue experiments have previously shown that emodepside inhibits serotonin-stimulated feeding by interfering with SLO-1 signaling in the nervous system. Here we show that ectopic overexpression of slo-1 in pharyngeal muscle confers sensitivity of the muscle to emodepside, consistent with a direct interaction of emodepside with the channel. Taken together, these data predict an emodepside-selective pharmacophore harbored by SLO-1. This has implications for the development of this drug/target interface for the treatment of helminth infections.

PMID: 21415309