Abstract
Dim light at night (dLAN) has become a pervasive part of the modern world, and growing evidence shows its association with increased health risks. Though this link is attributed to a disturbed circadian clock, the underlying mechanisms that can explain how circadian disruption from dLAN causes negative health effects remain unclear. Here, we exposed rats to a light–dark cycle (12:12 h) with low-intensity light at night (~2 lx) for 2 and 5 weeks and explored the steady-state pattern of circulating immune cells and renal immune-related markers, which are well controlled by the circadian clock. After 5 weeks, dLAN impaired the daily variation in several types of white blood cells, especially monocytes and T cells. Two-week dLAN caused a reduction in blood monocytes and altered gene expression of macrophage marker Cd68 and monocyte-attracting chemokine Ccl2 in the kidney. Interestingly, dLAN decreased renal 3-nitrotyrosine levels and resulted in up-regulation of the main endogenous antioxidant pathways, indicating a disturbance in the renal redox balance and an activation of compensatory mechanisms. These effects paralleled the altered renal expression of the molecular clock components and increased plasma corticosterone levels. Together, our results show that chronic exposure to dLAN weakened the circadian control of daily variation of circulating immune cells and disturbed renal immune and redox homeostasis. Consequences of this dLAN-disturbed immune balance on the ability of the immune system to cope with other challenges should by clarified in further studies.
Highlights
Photic information affects the proper functioning of almost all biological systems
To test whether dim light at night (dLAN) can influence the number of immune cells in blood and their daily oscillations, we evaluated the immunophenotype of circulating white blood cell (WBC) at ZT9 and ZT21 in rats exposed to dLAN (~2 lx) for 2 and 5 weeks
We found that rats exposed to dLAN for 2 weeks displayed lower Ccl2 mRNA levels in the kidney compared to controls (Figure 2G). dLAN did not affect the gene expression of C-C motif chemokine ligand 5 (Ccl5), intercellular cell adhesion molecule-1 (Icam1), and vascular cell adhesion molecule-1 (Vcam1) (Figures 2G, H)
Summary
Photic information affects the proper functioning of almost all biological systems This is mainly because light mediates visual perception and provides a non-image-forming stimulus responsible for circadian entrainment [1]. Through this process organisms align their endogenous circadian rhythms with the natural 24 h light and dark cycles in order to coordinate the timescale of their physiology and behavior with the cyclic environmental changes [2]. After chronic exposure to dLAN (≤ 5 lx), compromised circadian function has been shown experimentally through suppressed night-time melatonin levels [14, 15], attenuated rhythms in locomotor activity [16] and cardiovascular parameters [14], and altered clock gene oscillations [17]. The underlying physiological and molecular mechanisms, how circadian disruption due to dLAN causes detrimental health effects, are still poorly understood
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