The sleep-wake cycle regulates brain interstitial fluid tau in mice and CSF tau in humans

Abstract

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.

Fig. 1.

ISF tau exhibits diurnal fluctuation and increases following manual sleep deprivation (SD) but not in the presence of TTX. (A) ISF tau levels normalized to baseline (06:00–09:00) over the 24-hour analysis period. Manual SD and TTX infusion occurred from 09:00–15:00 (shaded), control animals were undisturbed. (B) Average ISF tau is significantly increased during dark (wake) compared to light (sleep) in control animals, demonstrating diurnal fluctuation (n=8, paired t-test). (C) Average ISF tau (normalized to baseline) during SD (09:00–15:00) was significantly increased in sleep-deprived mice compared to controls or mice with SD in the presence of TTX (n=8, One-Way ANOVA p=0.007, Bonferroni post-hoc). (D) ISF lactate over the 24-hour analysis period. (E) As with ISF tau, average ISF lactate was significantly increased during dark compared to light in control animals and (F) increased during SD (n=8, (E) paired t-test (F) Kruskal-Wallis. All data represent mean ± SEM. All mice 3–5 months, all conditions: 3F, 5M. *p<0.05, **p<0.01.

Fig. 2.

CSF tau levels increase and are correlated with Aβ in sleep-deprived human subjects and chronic SD in mice increases tau spreading. (A) Human CSF tau and (B) synuclein (α-syn) levels normalized to baseline (07:00–19:00). SD began at 21:00 and CSF compared from 01:00–11:00 (shaded). (C) Tau levels during SD are significantly increased by 51.5% and α-syn increased by 36.4% compared to undisturbed sleep (n=6 (tau), n=4–6 (α-syn)), GLMM, first-order autoregressive). (D) Total CSF Aβ is significantly correlated with CSF tau in control and SD conditions during the SD time period (n=6, Pearson’s correlation). (E) CSF NfL is unchanged by SD (n=6). (F) Ipsilateral hippocampal AT8 p-tau staining in grid control and chronic SD P301S male mice with unilateral hippocampal tau fibril injection. (G) SD does not alter p-tau staining in the ipsilateral hippocampus (n=14–16). (H) The ipsilateral LC/hippocampus AT8 ratio is increased in SD mice (n=13–16, Mann-Whitney). (I) AT8 staining in the LC of SD and control hippocampal-seeded P301S mice (scale bar (F, H): 125 μm). (J) p-Tau is significantly increased in the ipsilateral LC (n=13–16, unpaired t-test) and (K) trended towards an increase in the contralateral LC (n=14–16, Mann-Whitney) of SD compared to control animals. All data represent mean ± SEM. **p<0.01, ***p<0.001.

Fig. 3.

Chemogenetic (hM3Dq) activation of glutamatergic supramammillary neurons drives sustained wakefulness without inducing sleep rebound. (A) Diagram depicting Cre-dependent recombination of AAV-DIO-hM3Dq-mCherry in Vglut2-ires-Cre:APPSwe/PS1δE9 mice. (B) Labeling of mCherry-tagged hM3Dq using an anti-DsRed antibody (counterstain cresyl violet, scale bar 500 μm). (C) Timeline of hM3Dq-mediated manipulation of the SuM. (D) EEG data showing significantly increased wakefulness over 9 hours following CNO injection compared to the non-treated day (n=8: 4F, 4M, two-way repeated measures ANOVA, interaction: p<0.0001, Bonferroni post-hoc). (E) NaCl injection in AAV-hM3Dq mice showed no effect on % wakefulness (n=6: 1F, 5M). (F-H) Analysis of % wakefulness (F), % NREM sleep (G) and % REM sleep (H) between 06:00–09:00 (before CNO), 09:00–18:00 (after injection of CNO), and 18:00–06:00 (following night) showed significantly increased wakefulness and decreased sleep following CNO injection (red) compared to the non-treated day (black) but no differences prior to CNO injection. Analysis of the dark period (18:00–06:00) showed similar levels of % wakefulness and sleep in both groups demonstrating a lack of NREM or REM sleep rebound following sustained wakefulness over a period of 9 hrs (two-way repeated measures ANOVA, interaction: p<0.0001, Bonferroni post-hoc). All data represent mean ± SEM. **p<0.01, ***p<0.001.

Fig. 4.

Chemogenetic activation of glutamatergic supramammillary neurons increases hippocampal ISF Aβ, tau, and lactate levels. (A) ISF Aβ levels normalized to baseline (06:00–09:00) during a 24-hour untreated period (black) and 24-hour period with CNO (red, n=8: 4F, 4M) or (B) NaCl injection (blue, n=6: 1F, 5M). (C) Average ISF Aβ was significantly increased after injection of CNO (09:00–18:00) compared to the untreated day (n=8, paired t-test). (D) NaCl control injection did not alter average ISF Aβ (n=6). (E) Normalized ISF lactate levels before and after CNO (n=7: 4F, 3M) and (F) NaCl injection (n=6). (G) Average ISF lactate was significantly increased after CNO injection (09:00–18:00) compared to the untreated day (n=7, Wilcoxon signed rank). (H) Average ISF lactate following control NaCl injection (09:00–18:00) was unchanged. (I) ISF tau levels normalized to baseline (06:00–09:00) in CNO-treated mice (n=9: 3F, 6M) and NaCl-injected controls (n=8: 4F, 4M). (J) ISF tau post CNO treatment (09:00–18:00) was significantly increased compared to NaCl controls (n=8–9, unpaired t-test). (K) Normalized ISF lactate levels of CNO (n=8: 3F, 5M) and NaCl-treated mice (n=8: 4F, 4M). (L) Average ISF lactate post CNO treatment (09:00–18:00) was increased compared to NaCl controls (n=8, Mann-Whitney). All data represent mean ± SEM. *p<0.05, ***p<0.001.