Lipocalin-type prostaglandin D synthase produces prostaglandin D2 involved in regulation of physiological sleep

Abstract

Prostaglandin (PG) D2 has been proposed to be essential for the initiation and maintenance of the physiological sleep of rats because intracerebroventricular administration of selenium tetrachloride (SeCl4), a selective inhibitor of PGD synthase (PGDS), was shown to reduce promptly and effectively the amounts of sleep during the period of infusion. However, gene knockout (KO) mice of PGDS and prostaglandin D receptor (DP1R) showed essentially the same circadian profiles and daily amounts of sleep as wild-type (WT) mice, raising questions about the involvement of PGD2 in regulating physiological sleep. Here we examined the effect of SeCl4 on the sleep of WT and KO mice for PGDS and DP1R and that of a DP1R antagonist, ONO-4127Na, on the sleep of rats. The i.p. injection of SeCl4 into WT mice decreased the PGD2 content in the brain without affecting the amounts of PGE2 and PGF(2alpha). It inhibited sleep dose-dependently and immediately after the administration during the light period when mice normally sleep, increasing the wake time; and the treatment with this compound resulted in a distinct sleep rebound during the following dark period. The SeCl4-induced insomnia was observed in hematopoietic PGDS KO mice but not at all in lipocalin-type PGDS KO, hematopoietic and lipocalin-type PGDS double KO or DP1R KO mice. Furthermore, the DP1R antagonist ONO-4127Na reduced sleep of rats by 30% during infusion into the subarachnoid space under the rostral basal forebrain at 200 pmol/min. These results clearly show that the lipocalin-type PGDS/PGD2/DP1R system plays pivotal roles in the regulation of physiological sleep.

Fig. 1.

Sleep-stage distribution produced by ONO-4127Na infusion in rats. (A) Time course changes in ONO-4127Na (200 pmol/min) treatment group. Each circle represents the hourly mean ± SEM of NREM and REM sleep and wakefulness. Open and filled circles indicate the baseline and experimental day profiles, respectively. ONO-4127Na was given between 0900 and 1500 for 6 h, as indicated by the horizontal bar, on the experimental day. The horizontal open and filled bars on the x-axes indicate the 12-h light and 12-h dark periods, respectively. (B) Total time spent in NREM and REM sleep and wakefulness for 7 h; that is, during ONO-4127Na perfusion for 6 h and 1 h postinfusion. Open and filled bars show the profiles for the respective baseline day (vehicle infusion) and experimental day (ONO-4127Na infusion). Values are means ± SEM (n = 6). ∗, P < 0.05; ∗∗, P < 0.01 by the paired t test.

Fig. 2.

SeCl₄ inhibition of the enzymatic activity of both recombinant mouse L-PGDS and H-PGDS in vitro (A) and PGD₂, PGE₂, and PGF_2α contents in the brain 2 h after SeCl₄ administration in WT mice (B). Values are means ± SEM (n = 6). ∗∗, P < 0.01 by one-way ANOVA, followed by the Fisher PLSD test.

Fig. 3.

Time courses of the sleep–wake profiles after i.p. administration of SeCl₄ (2.5 and 5 mg/kg) to WT mice (A and B) and SeCl₄ (5 mg/kg) to H-PGDS (C), L-PGDS (D), HL-PGDS double (E), and DP₁R (F) KO mice. Each circle represents the hourly mean ± SEM of NREM and REM sleep and wakefulness. Open and filled circles stand for the baseline- and experimental-day profiles, respectively. SeCl₄ was given at 1100, as indicated by the arrow, on the experimental day; and the vehicle was used for the baseline day. The horizontal open and filled bars on the x-axes indicate the 12-h light and 12-h dark periods, respectively. Values are means ± SEM (n = 6 or 7). ∗, P < 0.05; ∗∗, P < 0.01 by the paired t test.

Fig. 4.

SeCl₄ inhibition of sleep in WT and H-PGDS KO mice, but not in L-PGDS, HL-PGDS double, and DP₁R KO mice. Total time spent in NREM and REM sleep and in wakefulness for 5 h after SeCl₄ administration into WT and KO mice is shown. Open and filled bars show the profiles for the baseline and experimental days, when the mice were treated with vehicle and SeCl₄, respectively. Values are means ± SEM (n = 6 or 7). ∗, P < 0.05; ∗∗, P < 0.01 compared with its own control; †, P < 0.05; ††, P < 0.01 compared with WT mice administered SeCl₄ at 5 mg/kg; ‡, P < 0.05; ‡‡, P < 0.01 compared with H-PGDS KO mice i.p. injected with SeCl₄ at 5 mg/kg, by two-way ANOVA, followed by the Fisher PLSD test.