Median Preoptic Astrocytes: Role in Sleep Regulation and Potential Mediators of Sex Differences

One in three Americans suffer from chronic sleep disorders, and women are 40% more likely than men to experience sleep disorders. This disparity emerges at puberty and is strongly associated with fluctuations in the ovarian hormone, estrogen (E2), suggesting that E2 and biological sex are a risk factor for sleep disorders. Previous work in the lab has demonstrated that E2 suppresses sleep in female rats, including in sleep deprived rats whose homeostatic need for sleep is increased. However, the specific mechanism for E2 induced decrease in sleep remains unknown. Work in the lab suggests a role for adenosine in mediating E2s sleep suppressive effects; E2 significantly increases Median Preoptic Nucleus (MnPO) extracellular adenosine and attenuates the action of specific agonists on the sleep promoting A2A-Receptor. Astrocytes represent a major source of adenosine in the CNS and have been shown to influence neuronal activity and downstream behaviors. In this project, we tested the hypothesis that astrocytes mediate E2s sleep suppressive effects. We used Gq-linked designer receptors exclusively activated by designer drugs (DREADDs) to evaluate the Gq pathway, which represents a core signaling mechanism in astrocyte activity. We found that, in female rats, activation of Gq signaling in astrocytes decreased sleep and inhibited homeostatic need for sleep. We further expressed the Pleckstrin Homology domain of PLC-like protein (p130PH), which has been shown to attenuate astrocyte activity and functions, in median preoptic nucleus (MnPO) astrocytes. We found that p130PH expression in MnPO astrocytes raised homeostatic sleep pressure to the same extent as 6 hours of sleep deprivation. We further report that inhibiting astrocytic function did not prevent E2s sleep suppressing effects suggesting that astrocytes may not play a role in estrogenic modulation of sleep. However, we did discover that MnPO astrocyte effects on sleep are sex-dependent. p130PH expression in MnPO astrocytes increased sleep and homeostatic sleep drive in female rats but showed a trend towards decreasing sleep and homeostatic sleep need in males. Further, while astrocyte effects on homeostatic sleep need are relegated to the dark phase in female rats, astrocytes appear to influence homeostatic sleep need in both the dark and light phase. To our knowledge, this is the first demonstration of a sex-based difference in astrocyte effects on sleep and homeostatic sleep pressure.