Interleukin 37 expression in mice alters sleep responses to inflammatory agents and influenza virus infection

Abstract

Multiple interactions between the immune system and sleep are known, including the effects of microbial challenge on sleep or the effects of sleep loss on facets of the immune response. Cytokines regulate, in part, sleep and immune responses. Here we examine the role of an anti-inflammatory cytokine, interleukin-37 (IL-37) on sleep in a mouse strain that expresses human IL-37b (IL37tg mice). Constitutive expression of the IL-37 gene in the brains of these mice under resting conditions is low; however, upon an inflammatory stimulus, expression increases dramatically. We measured sleep in three conditions; a) under baseline conditions and after 6 h of sleep loss, b) after bolus intraperitoneal administration of lipopolysaccharide (LPS) or IL-1β and c) after intranasal influenza virus challenge. Under baseline conditions, the IL37tg mice had 7% more spontaneous non-rapid eye movement sleep (NREMS) during the light period than wild-type (WT) mice. After sleep deprivation both WT mice and IL37tg mice slept an extra 21% and 12%, respectively, during the first 6 h of recovery. NREMS responses after sleep deprivation did not significantly differ between WT mice and IL37tg mice. However, in response to either IL-1β or LPS, the increases in time spent in NREMS were about four-fold greater in the WT mice than in the IL37tg mice. In contrast, in response to a low dose of mouse-adapted H1N1 influenza virus, sleep responses developed slowly over the 6 day recording period. By day 6, NREMS increased by 10% and REMS increased by 18% in the IL37tg mice compared to the WT mice. Further, by day 4 IL37tg mice lost less weight, remained more active, and retained their body temperatures closer to baseline values than WT mice. We conclude that conditions that promote IL-37 expression attenuate morbidity to severe inflammatory challenge.

Keywords: IL-1F7; IL-37; body weight; influenza virus H1N1; interleukin-1β; lipopolysaccharide; sleep deprivation.

Fig. 1

IL37tg mice have more spontaneous NREMS and similar sleep rebounds compared to WT mice. NREMS amounts [A], REMS amounts [B] and NREMS EEG SWA [C] in 12 h periods corresponding to the light or dark phase (gray fill) for WT mice (white bars; n=24) and IL37tg mice (black bars; n=23; ## p<0.01, WT vs. IL37tg) are shown. NREMS EEG power [D] during the 12 h light period (ZT0-12) is depicted. After 6 h sleep deprivation, NREMS amounts [E], REMS amounts [F] and NREMS EEG SWA [G] in the subsequent 6 h light period and 12 h dark period (shaded areas) for WT (n=7) and IL37tg mice (n=9) are expressed as change from baseline values. NREMS EEG power [H] during the 6 h light period following sleep deprivation (ZT6-12) is reported (all data expressed as mean±SEM; asterisks indicate within strain, treatment differences,* = p<0.05; ** = p<0.01; *** = p<0.001).

Fig. 2

IL37tg mice show attenuated sleep responses to IL-1β and LPS. WT mice (white symbols) and IL37tg mice (black symbols) were IP injected with saline (0.2 ml) just prior to dark onset and EEG/EMG was recorded for 24 h. Mice (n=7/strain) then received 180 ng of IL-1β [A, B, C] or 500 ng lipopolysaccharide (LPS; n=8/strain; D, E, F) and recording continued. Duration in state data are presented as differences from saline in NREMS [A,D] and REMS [B, E] averaged over 12 h periods corresponding to dark and light periods. EEG power spectra (1–20 Hz) from artifact-free NREMS-scored epochs over the first 2 h post-injection (ZT12-14) are depicted [C, F; WT top upper panels, IL37tg bottom panels]. Asterisks indicate within strain, treatment differences (* = p<0.05; ** = p<0.01) and pound signs indicate differences between strains (# = p<0.05; ## = p<0.01; gray fill indicates dark period).

Fig. 3

IL37tg mice have enhanced sleep responses to influenza virus challenge on post infection (PI) day 6.IL37tg mice (n=10) had more NREMS [A] during light and/or dark hours (shaded areas representing the 12 h dark period) than WT mice (n=12) and their own baseline values. Both strains manifest an increased number of NREMS episodes [D] during the dark period following viral challenge. REMS amounts [B] during the dark and REMS bout frequency [E] during the light and dark were inhibited in WT mice, but not IL37tg mice after infection. There were no changes in NREMS EEG SWA in on PI day 6 in either strain regardless of the photoperiod [C]. Power spectra [F] decreased with infection in WT mice but not IL37tg mice (PI day 6 ZT0-12 shown; *p<0.05, **p<0.01, ***p<0.001, WT baseline vs. PI day 6; +p<0.05, IL37tg baseline vs. PI day 6 and #p<0.05, WT vs. IL37tg; statistical symbols derived from 12 h data analyses; all data expressed as mean ± SEM).

Fig. 4

IL37tg mice are more active, less hypothermic, and have less weight loss than WT mice following viral challenge. Strain differences in [A] locomotor activity (6 h means±SEM), [B] temperature (6 min means and positive SEM for IL37tg and negative SEM for WT) and [C] body weights (daily means and negative SEM) are most apparent on post-infection days 3–5 (#p<0.05, WT vs. IL37tg; n=9/strain).