Abstract
Living beings spend their lives and carry out their daily activities interacting with environmental situations that present space-time variations and that involve contact with other life forms, which may behave as commensals or as invaders and/or parasites. The characteristics of the environment, as well as the processes that support the maintenance of life and that characterize the execution of activities of daily life generally present periodic variations, which are mostly synchronized with the light–dark cycle determined by Earth’s rotation on its axis. These rhythms with 24-h periodicity, defined as circadian, influence events linked to the interaction between hosts and hosted microorganisms and can dramatically determine the outcome of this interplay. As for the various pathological conditions resulting from host–microorganism interactions, a particularly interesting scenario concerns infections by viruses. When a viral agent enters the body, it alters the biological processes of the infected cells in order to favour its replication and to spread to various tissues. Though our knowledge concerning the mutual influence between the biological clock and viruses is still limited, recent studies start to unravel interesting aspects of the clock–virus molecular interplay. Three different aspects of this interplay are addressed in this mini-review and include the circadian regulation of both innate and adaptive immune systems, the impact of the biological clock on viral infection itself, and finally the putative perturbations that the virus may confer to the clock leading to its deregulation.
Highlights
Rotation of the planet Earth around its axis generates rhythmic day/night alternations with a period of approximately 24 h
The CLOCK:BMAL1 heterodimer activates another auxiliary loop operated by the PAR-bZip transcription factors D-Box Binding PAR BZIP (DBP), Thyrotrophic Embryonic Factor (TEF), and Hepatic Leukemia Factor (HLF); bind to D-box-containing sites within the promoter region of the transcriptional repressor NFIL3; and prompts numerous downstream transcriptional events [34]
The time of day of herpes simplex virus type 2 (HSV-2) infection impacted the outcome of the pathology in wild-type mice kept under 12-h light and 12-h darkness (LD 12:12), probably due to the circadian rhythmic expression of the HSV-2 receptor in the skin Nectin1
Summary
Rotation of the planet Earth around its axis generates rhythmic day/night alternations with a period of approximately 24 h (circadian). Circadian rhythms, generated by the endogenous circadian clock, allow living beings to anticipate environmental daily changes and provide an evolutionary advantage that favours survival despite strong selective pressure. The circadian clock is evolutionary conserved and thought to be roughly 2.5 billion years. The biological clock is a molecular network which generates oscillations in gene and protein expression that control cellular functioning and allows for the timely separation of biological processes that cannot or should not coexist. These include redox reactions and DNA replication [4], switches in metabolic pathways [5,6,7], as well as behavioural and physiological rhythms [8]. The endogenously driven rhythms are synchronized by external cues, such as environmental light and temperature, and feeding times [4,7,9] and are resilient to temperature fluctuations within the physiological range [10,11]
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