Microglia regulate sleep and thermoregulatory stability.

Sleep fragmentation disrupts physiological homeostasis, including thermoregulation, metabolism, and immune signaling; however, cellular mechanisms that stabilize core body temperature and sleep architecture during disrupted sleep remain poorly understood. Microglia are the resident immune cells of the central nervous system and play a central role in integrating neuroimmune signaling with hypothalamic regulation of thermoregulation and sleep-wake control. We tested the hypothesis that microglia are required to maintain both thermoregulatory and sleep stability during physiological sleep and when sleep is disrupted. Male and female C57BL/6J mice (n = 128) were implanted with telemetry devices for continuous core body temperature monitoring and maintained on either a control diet or diet containing the CSF1R-inhibitor PLX5622 (PLX) to pharmacologically deplete microglia. Body temperature and sleep-wake behavior were assessed across a two-week depletion period and during a subsequent 7-day sleep fragmentation paradigm. Hierarchical models were used to quantify the effects of microglial depletion (via diet), sex, and time-of-day (light/dark period). Microglial depletion produced sex- and diet-dependent alterations in both thermoregulation and sleep measures. PLX increased body temperature in females early during the depletion period, after which body temperature normalized and subsequently declined to pre-PLX baseline values. In contrast, PLX minimally influenced outcome metrics in males. During sleep fragmentation, microglial depletion induced time-of-day-specific hypothermia in males and females during the dark and light periods, respectively. Notably, microglial depletion dissociated components of sleep in a sex-dependent manner: Total sleep time increased in females, whereas males exhibited reduced sleep-wake transitions, suggesting increased sleep consolidation and therefore distinct regulation of sleep quantity versus stability. Across experimental conditions, body temperature was a strong nonlinear predictor of sleep, with higher temperatures (>35°C) associated with substantially reduced total sleep time (5-10 min reduction for every 1℃ increase), particularly during the dark (active) period. These findings collectively support that microglia contribute to thermoregulatory processes and sleep stability in a sex-dependent manner, supporting a role for microglia in coordinating physiological homeostasis. Together, our results support a neuroimmune framework in which microglia may help coordinate thermoregulation and sleep, as microglial depletion was associated with dysregulation of both processes.