Sleep-wake variation in body temperature regulates tau secretion and correlates with CSF and plasma tau.

Sleep disturbance is bidirectionally associated with increased risks of Alzheimer's disease and other tauopathies. While the sleep-wake cycle regulates interstitial and cerebrospinal fluid (CSF) tau levels, the underlying mechanisms remain unknown. Understanding these mechanisms is crucial given evidence indicates that tau pathology spreads through neuron-to-neuron transfer, involving the secretion and internalization of pathological tau forms. Here, we combine in vitro, in vivo and clinical methods to reveal a pathway by which changes in body temperature (BT) over the sleep-wake cycle modulate extracellular tau levels. In mice, higher BT during wakefulness and sleep-deprivation increased CSF and plasma tau levels, while also upregulating unconventional protein secretion pathway-I (UPS-I) components, including (i) intracellular tau dephosphorylation, (ii) caspase-3-mediated cleavage of tau (TauC3) and (iii) its membrane translocation through binding to PIP2 and syndecan-3. In humans, the increase in CSF and plasma tau levels observed post-wakefulness correlated with BT increase during wakefulness. By demonstrating that sleep-wake variation in BT regulates extracellular tau levels, our findings highlight the importance of thermoregulation in linking sleep disturbances to tau-mediated neurodegeneration, and the preventative potential of thermal interventions.