Fig 1.
Time schedules of photoperiod protocols over four weeks.
In each week, shift work animals were exposed to an 8-h phase advance photoperiod for three days, and then the phase of photoperiod returned to the normal light-dark cycle for four days. Control animals were subjected to a fixed light-dark cycle for four weeks. Light phase is indicated by a white bar while dark phase by a black bar. The timings of blood and tissue sampling are shown as triangles. Notes: ZT: Zeitgeber time, ZT0 represents the time of lights on and ZT12 represents the time of lights off.
Fig 2.
The effect of shift work on blood biochemistry, liver glycogen and HOMA-IR.
(A) Plasma glucose, and (B) liver glycogen and plasma (C) insulin, (D) glucagon, (E) corticosterone, (F) homeostasis model assessment of insulin resistance index (HOMA-IR) were detected across a 24-h cycle in control and shift work mice. N = 4–5/time point/group, except glucose and HOMA-IR in the control group at ZT20 (n = 3). The data are mean ± SD. *P<0.05, Two-way ANOVA and Bonferroni post hoc test; +P<0.05, Student’s t test.
Fig 3.
The effect of shift work on clock genes and glycometabolism-related genes in the liver.
Transcript profiles of (A) clock genes and (B) glycometabolism-related genes of the liver were analyzed by qPCR. N = 5/time point/group, except Pparα in the shift work group at ZT4 (n = 4). The data are mean ± SD. Two-way ANOVA with Bonferroni post hoc test were performed. *P<0.05 showed significant difference between two groups at the corresponding time point.
Fig 4.
The effects of shift work on insulin sensitivity and glucose tolerance during the day.
(A–D) Insulin tolerance tests (ITT) and (E–H) glucose tolerance tests (GTT) in control mice and shift work mice at different ZT were performed. (I) Area above the glucose curve for ITT and (J) area under the glucose curve for GTT was calculated for each mouse. (K) Glucose-stimulated insulin secretion test was performed for control and shift work mice at ZT6. N = 7–10/time point/group. The data are shown as mean and SD. Statistically significant differences were detected by two-way repeated measures ANOVA with Bonferroni's post hoc test (A–H) and by two-way ANOVA coupled with Bonferroni's post hoc test (I–K). *P<0.05.
Fig 5.
The effect of shift work on feeding rhythm and activity rhythm.
(A) Food intake rhythms in control and shiftwork mice were monitored over a seven-day period. One scale on the X-axis represents one day. Corresponding light-dark patterns were exhibited as bars below the X-axis (up: shift work condition; down: normal light-dark (LD) condition), in which the light phase is indicated by a white bar while the dark phase is indicated with a black bar. The data are mean values from 8–10 mice in each group. For each day, food intake during ZT0–6, 6–12, 12–18 and 18–24 were represented by 4 consecutive data points, respectively. (B) Total food intake of control and shift work mice over a seven-day cycle. N = 8–10/day/group. (C) Average locomotor activity (meter per hour) in control and shift work mice on the fifth day of the fifth week (n = 4 per group). ZT0–12 represents the light phase and ZT12–24 represents the dark phase. *P<0.05.
Fig 6.
Time restricted feeding withdrew shift work effects on insulin sensitivity of the light phase.
(A) Insulin tolerance tests (ITT) of Control-TRF (n = 7) and Shiftwork-TRF (n = 11) mice at ZT6 were performed. Two-way repeated measures ANOVA (post-injection time*treatment) were performed. No significant difference between groups was observed. (B) Area above curve (AAC) of ITT was calculated for each mouse. The data are mean±SD. Student’s t test was used to detect statistical significance. The AAC of shift work mice are not different from that of control mice under time-restricted feeding condition. TRF: time-restricted feeding.