FKBP51 overexpression in the corticolimbic system stabilizes circadian rhythms

Abstract

Circadian rhythm disruptions have been associated with a wide range of health issues and complications, including an increased risk of circadian rhythm sleep disorders (CRSDs). CRSDs are common among individuals who have been through a traumatic event, particularly in those who have post-traumatic stress disorder (PTSD). Allelic variations in the gene encoding for FK506-binding protein 51 (FKBP51) can increase the susceptibility for PTSD and other stress-related disorders following trauma. At least one of these variants increases the levels of FKBP51 following stress through a glucocorticoid receptor-mediated process. Here, we used a mouse model that overexpresses human FKBP51 throughout the forebrain, rTgFKBP5, to investigate if elevated FKBP51 contributes to circadian rhythm disruption. Surprisingly, our findings indicate a greater rhythm amplitude and decreased rhythm fragmentation in rTgFKBP5 mice, particularly females, compared to controls. Female rTgFKBP5 mice also showed higher corticosterone levels basally and following stress exposure. Overall, this study associates FKBP51 overexpression with beneficial circadian rhythm outcomes.

Keywords: Circadian clock; Circadian rhythm sleep disorders; FKBP5; FKBP51; Transgenic mouse.

Fig. 1

Circadian period is not affected by FKBP51 overexpression. (a) Male and female rTgFKBP5, aged 4–5 months, and control littermates (wild-type and tTA) were placed in circadian phenotyping cages. Wheel-running activity was measured as a proxy of circadian rhythmicity during different lighting conditions: LD baseline, DD, LD stress, and phase advance. Half of the mice were exposed to acute tube restraint stress at specific intervals to assess stress effects. Blood was collected from the submandibular vein at four-time points (ZT 0, ZT 6, ZT 12, and ZT 18) for corticosterone (CORT) assessment. Circadian period length during (b) representative actogram of daily wheel-running data displaying activity onset over a 24-h time period in wild-type, tTA, and rTgFKBP5 mice. (c) Semiquantitative heatmaps of the relative FKBP51 levels in major areas of the brain from wild-type, tTA, and rTgFKBP5 mice. Areas not quantified are shown in gray. Corresponding images and graphs are shown in Supplementary Figure 1. Circadian period length during (d) LD baseline and (e) DD in wild-type, tTA, and rTgFKBP5 male and female mice. Results represented as mean ± SEM (n = 8–12/sex/genotype). Data analyzed using SPSS MANOVA and ANOVA. Abbreviations used: DD, 24-h dark; FKBP51, FK506-binding protein 51; LD, 12-h light:12-hour dark; rTgFKBP5, transgenic mouse model overexpressing FKBP51; tTA, tetracycline transactivator; SEM, standard error of the mean; SPSS, Statistical Package for the Social Sciences; MANOVA, Multivariate analysis of variance; and ANOVA, Analysis of variance.

Fig. 2

rTgFKBP5 mice have increased activity. Hourly activity profiles of wild-type, tTA, and rTgFKBP5 (a) male and (b) female mice generated in 60-min bins. Gray shading indicates when the lights are off. Wild-type, tTA, and rTgFKBP5 male and female mice were assessed for (c) total wheel-running activity counts during LD baseline as well as (d) activity during the active phase (lights off) and (e) activity during the rest phase (lights on). Results represented as mean ± SEM (n = 8–12/sex/genotype). Data analyzed using ANOVA with Tukey post hoc test. Statistical significance is indicated by *P < 0.05, ***P < 0.001. Abbreviations used: LD, 12-h light:12-hour dark; rTgFKBP5, transgenic mouse model overexpressing FKBP51; tTA, tetracycline transactivator; SEM, standard error of the mean; and ANOVA, Analysis of variance.

Fig. 3

rTgFKBP5 mice show increased CORT, higher amplitude, and lower variability in females. Wheel-running activity was used to determine (a and b) rhythm amplitude, (c and d) intradaily variability, and (e and f) interdaily stability in male and female wild-type, tTA, and rTgFKBP5 mice during entrainment (LD baseline) and the free-running period (DD), as indicated. Data analyzed using SPSS MANOVA and ANOVA with Tukey post hoc test. Results represented as mean ± SEM (n = 10–12/sex/genotype). Serum CORT levels from blood collections at four-time points (ZT 0, ZT 6, ZT 12, and ZT 18) in (g) male and (h) female wild-type, tTA, or rTgFKBP5 mice. Open and filled bars represent 12 h light and dark cycles. Results represented as mean ± SEM (n =6–7/sex/genotype/ZT). Time is denoted as Zeitgeber Time (ZT), where ZT 0 = lights on and ZT 12 = lights off. Statistical significance is indicated by *P < 0.05, **P < 0.01, ***P < 0.001. Abbreviations used: DD, 24-h dark; LD, 12-h light:12-hour dark; rTgFKBP5, transgenic mouse model overexpressing FKBP51; tTA, tetracycline transactivator; SEM, standard error of the mean; SPSS, Statistical Package for the Social Sciences; MANOVA, Multivariate analysis of variance; and ANOVA, Analysis of variance.

Fig. 4

Acute stress enhances CORT sensitivity in rTgFKBP5 female mice but does not alter the circadian rhythm profile. Wheel-running activity was used to determine (a) Period and (b) amplitude in control and stress-exposed male and female wild-type, tTA, and rTgFKBP5 mice during LD stress. Data analyzed using SPSS MANOVA and ANOVA with Tukey post hoc test. Results represented as mean ± SEM (n = 5–7/sex/genotype/stress). Serum corticosterone (CORT) levels from blood collections at four-time points (ZT 0, ZT 6, ZT 12, and ZT 18) in (c) wild-type, (d) tTA, and (e) rTgFKBP5 males and females. Open and filled bars represent 12 h light and dark cycles. Results represented as mean ± SEM (n = 5–7/sex/genotype/stress/ZT). Time is denoted as zeitgeber time (ZT), where ZT 0 = lights on and ZT 12 = lights off. Statistical significance is indicated by *P < 0.05, **P < 0.01, ***P < 0.001. Abbreviations used: LD, 12-h light:12-hour dark; rTgFKBP5, transgenic mouse model overexpressing FKBP51; tTA, tetracycline transactivator; SEM, standard error of the mean; SPSS, Statistical Package for the Social Sciences; MANOVA, Multivariate analysis of variance; and ANOVA, Analysis of variance.

Fig. 5

FKBP51 overexpression does not alter resynchronization to phase shifts. rTgFKBP5, tTA, and wild-type mice were subjected to a 7-h phase advance and the time needed (days) to resynchronize to the new light-dark cycle was measured. Results represented as mean days ± SEM (n = 10–13/sex/genotype). Data analyzed using ANOVA with Tukey post hoc test. Statistical significance is indicated by *P < 0.05, **P < 0.01. Abbreviations used: FKBP51, FK506-binding protein 51; rTgFKBP5, transgenic mouse model overexpressing FKBP51; tTA, tetracycline transactivator; SEM, standard error of the mean; and ANOVA, Analysis of variance.