Monday, March 11, 2019

How sleep aids recovery from infection, may protect brain from Alzheimer's disease

Dimitrov et al. show how a good night's sleep accelerates recovering from an infection. Glue like proteins (integrins) used by immune system T cells to attach to virus particles and mark them for destruction are produced at greater levels during sleep. In the awake state, signaling molecules like adrenaline are produced at greater levels and inhibit integrin production, reducing the ability of T cells to attach to invading microbes. Here is their technical abstract:

Efficient T cell responses require the firm adhesion of T cells to their targets, e.g., virus-infected cells, which depends on T cell receptor (TCR)–mediated activation of β2-integrins. Gαs-coupled receptor agonists are known to have immunosuppressive effects, but their impact on TCR-mediated integrin activation is unknown. Using multimers of peptide major histocompatibility complex molecules (pMHC) and of ICAM-1—the ligand of β2-integrins—we show that the Gαs-coupled receptor agonists isoproterenol, epinephrine, norepinephrine, prostaglandin (PG) E2, PGD2, and adenosine strongly inhibit integrin activation on human CMV- and EBV-specific CD8+ T cells in a dose-dependent manner. In contrast, sleep, a natural condition of low levels of Gαs-coupled receptor agonists, up-regulates integrin activation compared with nocturnal wakefulness, a mechanism possibly underlying some of the immune-supportive effects of sleep. The findings are also relevant for several pathologies associated with increased levels of Gαs-coupled receptor agonists (e.g., tumor growth, malaria, hypoxia, stress, and sleep disturbances).

Also, Holth et al. show that sleep appears to have a direct protective effect on a key protein that drives AD pathology. They provide direct evidence that disrupting sleep, or stimulating excitatory neurons in brain nuclei that control wakefulness and arousal, promotes the release and spread of damaging tau aggregates across the brains of mice, and that sleep deprivation leads to increased extracellular Aβ and tau in people.
The sleep-wake cycle regulates interstitial fluid (ISF) and cerebrospinal fluid (CSF) levels of β-amyloid (Aβ) that accumulates in Alzheimer’s disease (AD). Furthermore, chronic sleep deprivation (SD) increases Aβ plaques. However, tau, not Aβ, accumulation appears to drive AD neurodegeneration. We tested whether ISF/CSF tau and tau seeding and spreading were influenced by the sleep-wake cycle and SD. Mouse ISF tau was increased ~90% during normal wakefulness versus sleep and ~100% during SD. Human CSF tau also increased more than 50% during SD. In a tau seeding-and-spreading model, chronic SD increased tau pathology spreading. Chemogenetically driven wakefulness in mice also significantly increased both ISF Aβ and tau. Thus, the sleep-wake cycle regulates ISF tau, and SD increases ISF and CSF tau as well as tau pathology spreading.

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