We know calcium is good for our bones, but it might also be the key to a good night sleep. Researchers at the RIKEN Quantitative Biology Center (QBiC) and the University of Tokyo in Japan have unveiled a new theory for how sleep works. Published in the journal Neuron, the work shows how slow-wave sleep depends on the activity of calcium inside neurons.
“Although sleep is a fundamental physiologic function, its mechanism is still a mystery,” according to group director and corresponding author Hiroki Ueda.
A multi-disciplinary research team led by Ueda used a variety of scientific techniques, including computational modeling and studying knockout mice, to search for the fundamental mechanism underlying sleep. Professor Ueda is a medical doctor by training, but as a researcher investigating sleep disorders, he favors a broad and deep approach that relies equally on in silico, in vitro, and in vivo modeling. He explains, “Because our study presents a new theory of sleep, we needed to support it with different methodologies.”
In silico, the team created a computational neural model to predict which currents within a neuron are critical for maintaining the type of neural activity associated with slow-wave sleep.
Fumiya Tatsuki, co-first author and undergraduate student at the University of Tokyo explains, “Our model made four predictions, which provided us with four starting points to search for critical genes involved in sleep. Each prediction was tested and proven correct in experiments with knockout mice or by pharmacological inhibition, and we were ultimately able to identify seven genes that work in the same calcium-related pathway to control sleep duration”.
Twenty-one knockout mice were created using recently developed CRISPR technology, which Ueda’s team has been refining into a highly accurate, highly efficient, in vitro system called triple CRISPR. Results published earlier this year indicated near 100% success rate. Additionally, co-first author Genshiro Sunagawa developed an automated sleep monitoring system for this study that proved invaluable for continuously collecting the necessary behavioral data.
Based on the computer models, triple CRISPR technology, and the new sleep-monitoring system, KO mice lacking target genes were observed in vivo for changes in sleep duration. By identifying mice with abnormal sleep patterns, the team was able to pinpoint seven genes that were critical for increasing or decreasing sleep duration.
All seven genes allow calcium-dependent changes in neurons that make them resist becoming active — a process called hyperpolarization. As predicted by the model, down-regulating six of these genes reduced sleep duration in KO mice and down-regulating the final gene led to longer bouts of sleep.
As Shoi Shi, co-first author and graduate student at the University of Tokyo, explains, “Our paper revealed that sleep is regulated by calcium-related pathways. One surprise was that contrary to current theories, inhibiting NMDA receptors directly evoked neuronal excitation, which contributed to reduced sleep.”
Notes Ueda, “these findings should contribute to the understanding and treatment of sleep disorders and neurologic diseases that have been associated with them. In addition to becoming new molecular targets for sleep drugs, the genes we have identified could also become targets for drugs that treat certain psychiatric disorders that occur with sleep dysfunction.”
Sunagawa cautions that much work is still needed. “Although our study reveals a mechanism for sleep regulation, the molecular details of the mechanism are still unknown, as is the real relationship between sleep dysfunction and psychiatric disorders.”
Source: Adam Phillips – RIKEN
Image Source: The image is credited to RIKEN.
Original Research: Abstract for “Involvement of Ca2+-Dependent Hyperpolarization in Sleep Duration in Mammals” by Fumiya Tatsuki, Genshiro A. Sunagawa, Shoi Shi, Etsuo A. Susaki, Hiroko Yukinaga, Dimitri Perrin, Kenta Sumiyama, Maki Ukai-Tadenuma, Hiroshi Fujishima, Rei-ichiro Ohno, Daisuke Tone, Koji L. Ode, Katsuhiko Matsumoto, and Hiroki R. Ueda in Neuron. Published online January 191 2016 doi:10.1016/j.neuron.2016.02.032
Involvement of Ca2+-Dependent Hyperpolarization in Sleep Duration in Mammals
•A simple model predicts Ca2+-dependent hyperpolarization regulates sleep duration
•Impaired/enhanced Ca2+-dependent hyperpolarization decreases/increases sleep duration
•Impaired Ca2+-dependent hyperpolarization increases neural excitability
•Impaired Ca2+/calmodulin-dependent kinases (Camk2a/Camk2b) decreases sleep duration
The detailed molecular mechanisms underlying the regulation of sleep duration in mammals are still elusive. To address this challenge, we constructed a simple computational model, which recapitulates the electrophysiological characteristics of the slow-wave sleep and awake states. Comprehensive bifurcation analysis predicted that a Ca2+-dependent hyperpolarization pathway may play a role in slow-wave sleep and hence in the regulation of sleep duration. To experimentally validate the prediction, we generate and analyze 21 KO mice. Here we found that impaired Ca2+-dependent K+ channels (Kcnn2 and Kcnn3), voltage-gated Ca2+ channels (Cacna1g and Cacna1h), or Ca2+/calmodulin-dependent kinases (Camk2a and Camk2b) decrease sleep duration, while impaired plasma membrane Ca2+ ATPase (Atp2b3) increases sleep duration. Pharmacological intervention and whole-brain imaging validated that impaired NMDA receptors reduce sleep duration and directly increase the excitability of cells. Based on these results, we propose a hypothesis that a Ca2+-dependent hyperpolarization pathway underlies the regulation of sleep duration in mammals.
“Involvement of Ca2+-Dependent Hyperpolarization in Sleep Duration in Mammals” by Fumiya Tatsuki, Genshiro A. Sunagawa, Shoi Shi, Etsuo A. Susaki, Hiroko Yukinaga, Dimitri Perrin, Kenta Sumiyama, Maki Ukai-Tadenuma, Hiroshi Fujishima, Rei-ichiro Ohno, Daisuke Tone, Koji L. Ode, Katsuhiko Matsumoto, and Hiroki R. Ueda in Neuron. Published online January 191 2016 doi:10.1016/j.neuron.2016.02.032