Characterization of NPR-14 in the Regulation of Sleep-Like Behaviour in Caenorhabditis elegans

Sleep-like quiescence is an evolutionarily conserved state essential for physiological homeostasis; however, its dysregulation can lead to sleep disorders such as narcolepsy, which can be caused by abnormal neuropeptide signaling. In Caenorhabditis elegans, the G-protein-coupled receptor NPR-14 belongs to the orexin/allatotropin receptor family and has been proposed as a homolog of mammalian orexin receptors. Using npr-14 loss-of-function (lf) mutants, we demonstrate that NPR-14 promotes arousal and inhibits sleep-like quiescence. npr-14(lf) mutants exhibit prolonged quiescence, reduced locomotion, impaired sensory responses, and metabolic defects including elevated fat accumulation and decreased feeding and egg-laying. NPR-14 is expressed in ASH and ASI sensory neurons and in GABAergic DD, VD, and VC motor neurons, positioning it to modulate both sensory-motor integration and motor output directly. Genetic epistasis analysis revealed that NPR-14 functions upstream of EGL-4/protein kinase G (PKG): egl-4 loss-of-function suppressed the enhanced quiescence of npr-14 mutants, while egl-4 gain-of-function phenotypes were not enhanced by loss of npr-14. Caffeine treatment partially suppressed npr-14 mutant quiescence, suggesting convergence with adenosine-sensitive arousal pathways. These findings establish NPR-14 as a wake-promoting GPCR that inhibits EGL-4/PKG signalling to regulate quiescence and arousal. The NPR-14-EGL-4 axis suggests functional parallels to arousal regulation in other systems.