Melatonin modulates nitric oxide-regulated WNK-SPAK/OSR1-NKCC1 signaling in dorsal raphe nucleus of rats
Hye Jin Yang1,#, Mi Jung Kim2,3,#, Sung Soo Kim3,4, and Young-Wuk Cho1,2,3,*
1Department of Biomedical Science, Graduate School, Kyung Hee University, 2Department of Physiology, College of Medicine, Kyung Hee University,3Biomedical Science Institute and Medical Research Center for Reactive Oxygen Species, College of Medicine, Kyung Hee University, 4Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Seoul 02447, Korea
The sleep-wake cycle is regulated by the alternating activity of sleep- and wake-promoting neurons. The dorsal raphe nucleus (DRN) secretes 5-hydroxytryptamine (5-HT, serotonin), promoting wakefulness. Melatonin secreted from the pineal gland also promotes wakefulness in rats. Our laboratory recently demonstrated that daily changes in nitric oxide (NO) production regulates a signaling pathway involving with-no-lysine kinase (WNK), Ste20-related proline alanine rich kinase (SPAK)/oxidative stress response kinase 1 (OSR1), and cation-chloride co-transporters (CCC) in rat DRN serotonergic neurons. This study was designed to investigate the effect of melatonin on NO-regulated WNK-SPAK/OSR1-CCC signaling in wake-inducing DRN neurons to elucidate the mechanism underlying melatonin’s wake-promoting actions in rats. Ex vivo treatment of DRN slices with melatonin suppressed neuronal nitric oxide synthase (nNOS) expression and increased WNK4 expression without altering WNK1, 2, or 3. Melatonin increased phosphorylation of OSR1 and the expression of sodium-potassium-chloride co-transporter 1 (NKCC1), while potassium-chloride cotransporter 2 (KCC2) remained unchanged. Melatonin increased the expression of tryptophan hydroxylase 2 (TPH2, serotonin-synthesizing enzyme). The present study suggests that melatonin may promote its wakefulness by modulating NO-regulated WNK-SPAK/OSR1-KNCC1 signaling in rat DRN serotonergic neurons.