A research team has made a noteworthy discovery: in mammals, protein kinase A (PKA) fosters wakefulness, whereas protein phosphatase 1 (PP1) and calcineurin promote sleep. This significant study emphasizes the crucial interplay of various enzymes in regulating the balance between sleep and wakefulness, which holds promise for better understanding and managing sleep durations and feelings of sleepiness on a molecular level.
Recent investigations have highlighted how chemical changes known as phosphorylation of different proteins*1) in brain neurons play a dynamic role in regulating sleep and wakefulness. However, the specific protein kinases that inhibit sleep and the dephosphorylation enzymes that modulate these cycles are not yet fully understood. All animals, including humans, require a certain amount of sleep daily; a deficiency leads to “sleep deprivation.” Despite this, the underlying molecular mechanisms governing sleep regulation are still unclear.
A research team led by Professor Hiroki Ueda, along with Doctoral Students Yimeng Wang and Siyu Cao, and Lecturer Koji Ode at the Graduate School of Medicine, University of Tokyo, has found that protein kinase A (PKA)*2) promotes waking, while the dephosphorylation enzymes protein phosphatase 1 (PP1) and calcineurin*3) facilitate sleep in mammals.
By concentrating on PKA and the dephosphorylation enzymes, the team developed comprehensive gene knockout mice and conducted experiments to induce the expression of modified functional enzymes via viral vectors*4). They observed that activating PKA resulted in reduced sleep duration and diminished delta power, which indicates sleep needs. Conversely, activating PP1 and calcineurin increased both sleep duration and delta power. For these sleep-wake regulating processes to occur, PKA, PP1, and calcineurin must function at post-synapses responsible for neurotransmission between neurons. Additionally, they showed that PKA and PP1/calcineurin may operate competitively to influence daily sleep duration.
This research has clarified that the equilibrium between sleep and wakefulness is maintained through the actions of various enzymes—an important discovery for developing strategies to manage sleep duration and feelings of sleepiness at a molecular level.
These findings were part of the Ueda Biological Timing Project, a research initiative funded by the Exploratory Research for Advanced Technology (ERATO) through the Japan Science and Technology Agency (JST). This project aims to develop “systems biology for understanding humans” utilizing sleep-wake patterns as a model, focusing on the concept of “biological time” spanning from molecular to individual human levels within society.
(*1) Protein phosphorylation
After proteins are synthesized through transcription and translation, their functions can be modified chemically in several ways. Phosphorylation is the most common type of modification found in cells. Enzymes that catalyze the transfer of phosphate groups to proteins using adenosine triphosphate (ATP) are called protein kinases, while those that remove phosphorylation from phosphoproteins are known as protein phosphatases.
(*2) Protein kinase A (PKA)
PKA is a protein kinase that is activated by cyclic adenosine monophosphate (cAMP), an intracellular signaling molecule. It is composed of a catalytic subunit that carries out kinase activity and a regulatory subunit that inhibits that activity.
(*3) Protein phosphatase 1 (PP1) and calcineurin
Among the protein phosphatases, PP1, PP2A, and calcineurin are highly expressed in the brain. This study has shown that both PP1 and calcineurin function in sleep regulation. These enzymes have a catalytic subunit that performs dephosphorylation and a regulatory subunit that affects the localization and activity of the enzyme. Notably, calcineurin is distinguished by its activation through calcium.
(*4) Viral vectors
Viral vectors are tools used for introducing genes into cells, utilizing the viral capacity for cellular infection. The adeno-associated virus (AAV)-PHP.eB, a modified type of AAV, was employed in this research. This viral vector is effective at transferring genes, particularly to the central nervous system.
