Effect of Aging and a Dual Orexin Receptor Antagonist on Sleep Architecture and Non-REM Oscillations Including an REM Behavior Disorder Phenotype in the PS19 Mouse Model of Tauopathy

Abstract

The impact of tau pathology on sleep microarchitecture features, including slow oscillations, spindles, and their coupling, has been understudied, despite the proposed importance of these electrophysiological features toward learning and memory. Dual orexin receptor antagonists (DORAs) are known to promote sleep, but whether and how they affect sleep microarchitecture in the setting of tauopathy is unknown. In the PS19 mouse model of tauopathy MAPT (microtubule-associated protein tau) P301S (both male and female), young PS19 mice 2-3 months old show a sleep electrophysiology signature with markedly reduced spindle duration and power and elevated slow oscillation (SO) density compared with littermate controls, although there is no significant tau hyperphosphorylation, tangle formation, or neurodegeneration at this age. With aging, there is evidence for sleep disruption in PS19 mice, characterized by reduced REM duration, increased non-REM and REM fragmentation, and more frequent brief arousals at the macrolevel and reduced spindle density, SO density, and spindle-SO coupling at the microlevel. In ∼33% of aged PS19 mice, we unexpectedly observed abnormal goal-directed behaviors in REM, including mastication, paw grasp, and forelimb/hindlimb extension, seemingly consistent with REM behavior disorder (RBD). Oral administration of DORA-12 in aged PS19 mice increased non-REM and REM duration, albeit with shorter bout lengths, and increased spindle density, spindle duration, and SO density without change to spindle-SO coupling, power in either the SO or spindle bands, or the arousal index. We observed a significant effect of DORA-12 on objective measures of RBD, thereby encouraging future exploration of DORA effects on sleep-mediated cognition and RBD treatment.SIGNIFICANCE STATEMENT The specific effect of tauopathy on sleep macroarchitecture and microarchitecture throughout aging remains unknown. Our key findings include the following: (1) the identification of a sleep EEG signature constituting an early biomarker of impending tauopathy; (2) sleep physiology deteriorates with aging that are also markers of off-line cognitive processing; (3) the novel observation that dream enactment behaviors reminiscent of RBD occur, likely the first such observation in a tauopathy model; and (4) a dual orexin receptor antagonist is capable of restoring several of the sleep macroarchitecture and microarchitecture abnormalities.

Keywords: DORA; REM behavior disorder; sleep; slow oscillations; spindles; tauopathy.

Figure 1.

A, NREM duration across a 24 h recording period was variable (p_genotype = 0.29, p_age = 0.82, p_{genotype×age} = 0.004; post hoc, *p < 0.05 for young WT vs young PS19). B, REM duration across a 24 h period decreased in old PS19 mice (p_genotype = 0.64, p_age = 0.01, p_{genotype×age} = 0.005; post hoc, **p < 0.001 PS19 young vs old). C, NREM bout length was shortest in old PS19 mice (p_genotype = 0.12, p_age = 0.001, p_{genotype×age} = 0.03; post hoc, *p < 0.05 for PS19 old vs young PS19). D, REM bout length was shortest in old PS19 mice (p_genotype = 0.05, p_age = 0.004, p_{genotype×age} = 0.15; post hoc: **p < 0.001 for PS19 old vs young PS19). E, Arousal index was highest in the aged PS19 mice compared with the other groups (p_genotype < 0.001, p_age < 0.001, p_{genotype×age} = 0.009; post hoc, **p < 0.001 for PS19 old vs young PS19 and old WT). For this figure and subsequent figures, two-way ANOVA with Dunn–Sidak post hoc test was used; *p < 0.05, **p < 0.001, ***p < 0.0001. For this figure, n_WTyoung = 12, n_PS19young = 14, n_WTold = 10, n_PS19old = 14. F, Continuity curves (cumulative probability distributions) of NREM sleep runs in young PS19 and WT mice demonstrate more fragmented NREM sleep in the PS19 genotype (**p < 0.001, KS test). G, In old mice, PS19 genotype was also more fragmented compared with WT (***p < 0.0001, KS test). H, No differences were observed in REM sleep continuity for PS19 young and WT young mice (p = 0.118, KS test). I, In old mice, PS19 genotype showed more fragmentation in the bouts of REM sleep longer than 1 min in duration (***p < 0.0001, KS test).

Figure 2.

A, Spindle density was lowest in old PS19 mice with detector 1 (p_genotype = 0.03, p_age = 0.002, p_{genotype×age} = 0.33; post hoc, *p < 0.05 for old PS19 vs young PS19). B, Spindle density was also lowest in old PS19 mice with detector 2 (p_genotype < 0.001, p_age = 0.005, p_{genotype×age} = 0.97; post hoc, **p < 0.001 for old PS19 vs old WT). C, Spindle duration was lowest in old PS19 mice (p_genotype < 0.001, p_age = 0.02, p_{genotype×age} = 0.98; post hoc, *p < 0.05 for old PS19 vs old WT). D, Spindle power was lowest in old PS19 mice (p_genotype < 0.001, p_age = 0.02, p_{genotype×age} = 0.20; post hoc: *p < 0.05 for old PS19 vs old WT). E, SO density was higher in young PS19 mice than in young WT mice (p_genotype = 0.16, p_age = 0.85, p_{genotype×age} = 0.005; post hoc, *p < 0.05 for young PS19 greater than young WT). F, SO power was not different across groups (p_genotype = 0.24, p_age = 0.43, p_{genotype×age} = 0.06). No post hoc comparisons. G, Phase-locking value of the spindle to the SO was lowest in the old PS19 mice (p_genotype = 0.45, p_age < 0.0001, p_{genotype×age} = 0.08; post hoc, **p < 0.001 for young PS19 vs old PS19). H, WT young phase-amplitude coupling grandaveraged heat map. I, PS19 phase-amplitude coupling grandaveraged heat map. J, WT old phase-amplitude coupling grandaveraged heat map. K, PS19 Old phase-amplitude coupling grandaveraged heat map. For this figure, n_WTyoung = 12, n_PS19young = 14, n_WTold = 10, n_PS19old = 14.

Figure 3.

A, Representative section of dorsal hippocampus tissue from a young (2–3 months old) PS19 mouse. B, An old (10–14 months old) PS19 mouse. C, A young (2–3 months old) WT mouse. D, An old (10–14 months old) WT mouse. E, Quantification of the percentage area of the CA3 hippocampal region stained with synaptophysin [p_genotype = 0.006, p_age = 0.002, p_{genotype×age} = 0.01; post hoc, not significant (ns) for young PS19 vs young WT, **p < 0.001 for young PS19 vs old PS19, *p < 0.01 for old PS19 vs old WT]. F, Novel object recognition memory in 2- to 3-month-old PS19 and age-matched WT controls (p = 0.64, n = 10 WT, n = 5 PS19). Immunohistochemistry data for this figure, n_WTyoung = 10, n_PS19young = 10, n_WTold = 5, n_PS19old = 5.

Figure 4.

A, Example REM epoch in a mouse without RBD. EEG from the right and left parietal cortex and the nuchal EMG is shown. Extended Data Figure 4-1 contains additional spectral information for scoring REM with atonia. B, Example REM epoch in a mouse with RBD. Movements within REM sleep are detected as nuchal muscle deflections in the EMG. Extended Data Figure 4-1 contains additional spectral information for scoring REM without atonia. C, Suprathreshold EMG duration during REM was increased in aged mice with RBD (Wilcoxon rank sum test, ***p = 0.005). D, Cumulative EMG area in REM was increased in aged mice with RBD (Wilcoxon rank sum test, ***p = 0.005). E, Normalized cumulative EMG area in REM was increased in aged mice with RBD (Wilcoxon rank sum test, ***p = 0.005). F, Percentage of REM without atonia was increased in aged mice with RBD (Wilcoxon rank sum test, ***p = 0.005). G, Ratio of EMG area in REM divided by the preceding NREM bout was increased in aged mice with RBD (Wilcoxon rank sum test, ***p = 0.005). For this figure, n_PS19RBD− = 8, n_PS19RBD+ = 3.

Figure 5.

A, Non-REM latency to the first bout of a 3 min or greater sleep episode was decreased with acute DORA-12 (*p = 0.002). B, Non-REM duration was increased with acute DORA-12 (*p = 0.01). C, REM duration was also increased with acute DORA-12 (*p = 0.01). D, Non-REM bout length was decreased with acute DORA-12 (*p = 0.02). E, REM bout length was decreased with acute DORA-12 (*p = 0.03). F, Arousal index was not different (not significant (n.s.)) between vehicle and DORA-12 (p = 0.12). G, DORA-12 reduced continuity of non-REM sleep (***p < 0.0001, KS test). H, DORA-12 reduced continuity of REM sleep (***p < 0.0001, KS test) versus vehicle (Veh) in aged PS19 mice as assessed via cumulative probability distribution curves. For this figure, n = 11.

Figure 6.

A, Spindle density by detector 1 was increased with acute DORA-12 treatment compared with vehicle (**p = 0.007). B, Spindle density by detector 2 trended higher compared with vehicle (p = 0.07). C, Spindle duration was increased with acute DORA-12 (*p = 0.01). D, Spindle power was not changed with DORA-12 (p = 0.29). E, Slow oscillation density increased with acute DORA-12 (*p = 0.03). F, There was no change to SO power (p = 0.41). G, There was no change to phase-amplitude coupling of spindles with the slow oscillation (p = 0.98). For this figure, n = 11. n.s. = not significant.

Figure 7.

DORA-12 reduces quantitative measures of REM sleep without atonia in aged PS19 mice. A, Normalized cumulative EMG area in REM (paired t test, *p = 0.02). B, Percentage of REM without atonia (paired t test, **p = 0.004). C, Ratio of EMG area in REM divided by the preceding NREM bout (paired t test, **p = 0.002). For this figure, n = 9.