Realization of phosphorylation hypothesis of sleep by mammalian CaMKIIβ

The reduced sleep duration observed in Camk2a and Camk2b knockout mice revealed the role of Ca2+/calmodulin-dependent protein kinase II (CaMKII)α/CAMKIIβ as sleep-promoting kinases and lead to the phosphorylation hypothesis of sleep. However, the underlying mechanism of sleep regulation by kinases and protein phosphorylation is largely unknown. Here, we demonstrate that the phosphorylation states of CaMKIIβ regulates sleep duration and sleep needs. Importantly, the activation or inhibition of CaMKIIβ can increase or decrease sleep duration by almost two-fold, supporting the role of CaMKIIβ as a core sleep regulator in mammals. This sleep regulation depends on the kinase activity of CaMKIIβ in excitatory neurons. Furthermore, CaMKIIβ mutants mimicking different phosphorylation states can regulate various sleep steps including sleep induction, sleep maintenance, and sleep cancelation. Key CaMKIIβ residues responsible for the mode switch undergo ordered (auto-)phosphorylation. We thus propose that ordered multi-site phosphorylation of CaMKIIβ underlies multi-step sleep regulation in mammals. ### Competing Interest Statement H.R.U conducted a collaborative research project with Thermo Fisher Scientific Inc. Y.N. is an employee of Thermo Fisher Scientific, Inc. The company provided support in the form of salary for Y.N., and technical advice on the setup of mass spectrometers. However, the company did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.