Circadian Misalignment Induced by Chronic Night Shift Work Promotes Endoplasmic Reticulum Stress Activation Impacting Directly on Human Metabolism

Abstract

Night work has become necessary in our modern society. However, sleep deprivation induces a circadian misalignment that effectively contributes to the development of diseases associated with metabolic syndrome, such as obesity and diabetes. Here, we evaluated the pattern of circadian clock genes and endoplasmic reticulum stress (ERS) genes in addition to metabolic and anthropometric measures in subjects that work during a nocturnal period compared with day workers. We study 20 night workers (NW) and 20 day workers (DW) submitted to a work schedule of 12 h of work for 36 h of rest for at least 5 years in a hospital. The present report shows that NW have increased fasting blood glucose, glycated hemoglobin (HbA1c), triglycerides, and low-density lipoprotein (LDL)-cholesterol levels, and lower high-density lipoprotein (HDL)-cholesterol levels compared to DW. In addition, we observed that waist circumference (WC), waist-hip ratio (WHR), and systemic blood pressure are also increased in NW. Interestingly, gene expression analysis showed changes in CLOCK gene expression in peripheral blood mononuclear cells (PBMC) samples of NW compared to the DW, evidencing a peripheral circadian misalignment. This metabolic adaptation was accompanied by the up-regulation of many genes of ERS in NW. These findings support the hypothesis that night shift work results in disturbed glycemic and lipid control and affects the circadian cycle through the deregulation of peripheral CLOCK genes, which is possibly due to the activation of ERS. Thus, night work induces important metabolic changes that increase the risk of developing metabolic syndrome.

Keywords: CLOCK genes; circadian rhythm; endoplasmic reticulum stress; metabolic syndrome; night shift.

Figure 1

Metabolic changes between day and night workers. Twenty day hospital workers and twenty night hospital workers were evaluated for their metabolic parameters. (a) Fasting glucose levels (p = 0.0024), (b) Hb1Ac (p < 0.0001), (c) Cholesterol (p = 0.2153), (d) Triglycerides (p = 0.0359), (e) HDL-cholesterol (p = 0.0456), (f) LDL-cholesterol (p < 0.0001), (g) C Reactive Protein (p = 0.9099). Cortisol level was determined in two different blood collections at the beginning of work and another at the end of work. (h) Cortisol level, night worker 0700 h vs. 1900 h (p = 0.0395), day worker 0700 h vs. 1900 h (p = 0.0001). Data are presented as dot plot with mean. Unpaired, one-tailed t-test was performed in figures a–g. One-way ANOVA followed by Tukey’s post hoc test, was performed in figure h. * p < 0.05; ** p < 0.01; *** p = 0.001; **** p < 0.0001.

Figure 2

Blood pressure analysis and anthropometric parameters at day and night workers. (a) The blood pressure of day and night workers was verified after 20 min of total rest. Systolic pressure (p = 0.0496), Diastolic pressure (p = 0.0172), (b) BMI assessment (p = 0.7801), (c) Measurement of waist circumference (p = 0.0010), (d) Waist–hip ratio (p = 0.0153), (e) Quantification of fat mass (p = 0.0887). Data are presented as box plot or dot plot with mean. Unpaired, one-tailed t-test. * p < 0.05, ** p < 0.01. (n = 20 per group).

Figure 3

Determination of the gene expression of clock genes in peripheral blood mononuclear cells (PBMC) samples of day and night workers at different times. Gene expression was evaluated by RT-qPCR (n = 20 per group). (a) Gene expression of the clock genes of day workers at 0700 h and 1900 h. (b) Gene expression of the clock genes of night workers at 0700 h and 1900 h. Data are presented as dot plot with mean. Unpaired, one-tailed t-test. Data were normalized for values at 0700 h. * p < 0.05, ** p < 0.01, *** p = 0.001, **** p < 0.0001.

Figure 4

Determination of the gene expression of clock genes in PBMC samples of day and night workers. Gene expression was evaluated by RT-qPCR (n = 20 per group). (a) Gene expression of the clock genes at 0700 h compared DW and NW. (b) Gene expression of the clock genes at 1900 h compared DW and NW. Data are presented as dot plot with mean. Unpaired, one-tailed t-test. Data were normalized for DW. ** p < 0.01, **** p < 0.0001. (n = 20 per group).

Figure 5

Determination of the expression of genes related to endoplasmic reticulum stress in PBMC samples of day and night workers at 0700 h and 1900 h. (a) Graph representing diurnal variations in gene expression of genes related to endoplasmic reticulum stress (ERS). The data were normalized by day workers (DW) 0700 h. (b) Graph representing the nocturnal variations of gene expression of genes related to ERS. The data were normalized by DW 1900 h. Gene expression was evaluated by RT-qPCR (n = 20 per group). Data are presented as dot plot with mean. Unpaired, one-tailed t-test. ** p < 0.01, *** p = 0.001, **** p < 0.0001.