RPamide neuropeptides NLP-22 and NLP-2 act through GnRH-like receptors to promote sleep and wakefulness in C. elegans

Petrus Van Der Auwera,Wouter De Haes,David M Raizen,Ryan T Vance,Alexander Gottschalk,Liliane Schoofs,Olivier Mirabeau,Isabel Beets,Luca Fancsalszky,Liesbet Temmerman,Lotte Frooninckx,Matthew D Nelson,Jan Watteyne,Kristen Buscemi

doi:10.1038/s41598-020-66536-2

Abstract

Sleep and wakefulness are fundamental behavioral states of which the underlying molecular principles are becoming slowly elucidated. Transitions between these states require the coordination of multiple neurochemical and modulatory systems. In Caenorhabditis elegans sleep occurs during a larval transition stage called lethargus and is induced by somnogenic neuropeptides. Here, we identify two opposing neuropeptide/receptor signaling pathways: NLP-22 promotes behavioral quiescence, whereas NLP-2 promotes movement during lethargus, by signaling through gonadotropin-releasing hormone (GnRH) related receptors. Both NLP-2 and NLP-22 belong to the RPamide neuropeptide family and share sequence similarities with neuropeptides of the bilaterian GnRH, adipokinetic hormone (AKH) and corazonin family. RPamide neuropeptides dose-dependently activate the GnRH/AKH-like receptors GNRR-3 and GNRR-6 in a cellular receptor activation assay. In addition, nlp-22-induced locomotion quiescence requires the receptor gnrr-6. By contrast, wakefulness induced by nlp-2 overexpression is diminished by deletion of either gnrr-3 or gnrr-6. nlp-2 is expressed in a pair of olfactory AWA neurons and cycles with larval periodicity, as reported for nlp-22, which is expressed in RIA. Our data suggest that the somnogenic NLP-22 neuropeptide signals through GNRR-6, and that both GNRR-3 and GNRR-6 are required for the wake-promoting action of NLP-2 neuropeptides.

Highlights

Sleep and wakefulness are fundamental behavioral states of which the underlying molecular principles are becoming slowly elucidated
We show that two of these GNRRs are activated by the RPamide neuropeptides neuropeptide-like protein (NLP)-22 and NLP-2, displaying sequence similarities to gonadotropin-releasing hormone (GnRH)/adipokinetic hormone (AKH)-like peptides, and demonstrate that they act opposingly to control sleep and wakefulness in C. elegans
The nematode cluster can be subdivided in two groups consisting of GNRR-1, which is located more basal to the clade node, and a paralogous group formed by 7 other GnRH/AKH-like receptors

Summary

Introduction

Sleep and wakefulness are fundamental behavioral states of which the underlying molecular principles are becoming slowly elucidated. We identify two opposing neuropeptide/receptor signaling pathways: NLP-22 promotes behavioral quiescence, whereas NLP-2 promotes movement during lethargus, by signaling through gonadotropin-releasing hormone (GnRH) related receptors. Because animals display a remarkable diversity of sleep traits, a consensus definition for sleep-like states has been set based on behavioral changes shared with human sleep These include behavioral quiescence, reduced sensory responsiveness, reversibility, the assumption of a specific posture, and homeostatic regulation[1,4,6,7]. Neuropeptidergic signaling systems conserved in C. elegans comprise the PDF orthologous system PDF-1/PDFR-1 and the RFamide neuropeptide system FLP-2/FRPR-18, which promote arousal by increasing sensory activity[30,40] Inhibition of these wake-promoting neuropeptides by FLP-18/NPR-1 and FLP-21/NPR-1 signaling reduces sensory responsiveness during lethargus[21]. Human patients with primary insomnia display altered GnRH levels[51]

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Results

Conclusion