Daytime variation in hepatitis C virus replication kinetics following liver transplant

Alterations in Circadian Rhythms, Sleep, and Physical Activity in COVID-19: Mechanisms, Interventions, and Lessons for the Future

Although the world is acquitting from the throes of COVID-19 and returning to the regularity of life, its effects on physical and mental health are prominently evident in the post-pandemic era. The pandemic subjected us to inadequate sleep and physical activities, stress, irregular eating patterns, and work hours beyond the regular rest-activity cycle. Thus, perturbing the synchrony of the regular circadian clock functions led to chronic psychiatric and neurological disorders and poor immunological response in several COVID-19 survivors. Understanding the links between the host immune system and viral replication machinery from a clock-infection biology perspective promises novel avenues of intervention. Behavioral improvements in our daily lifestyle can reduce the severity and expedite the convalescent stage of COVID-19 by maintaining consistent eating, sleep, and physical activity schedules. Including dietary supplements and nutraceuticals with prophylactic value aids in combating COVID-19, as their deficiency can lead to a higher risk of infection, vulnerability, and severity of COVID-19. Thus, besides developing therapeutic measures, perpetual healthy practices could also contribute to combating the upcoming pandemics. This review highlights the impact of the COVID-19 pandemic on biological rhythms, sleep-wake cycles, physical activities, and eating patterns and how those disruptions possibly contribute to the response, severity, and outcome of SARS-CoV-2 infection.

The role of circadian clock pathways in viral replication

The daily oscillations of bi ological and behavioural processes are controlled by the circadian clock circuitry that drives the physiology of the organism and, in particular, the functioning of the immune system in response to infectious agents. Circadian rhythmicity is known to affect both the pharmacokinetics and pharmacodynamics of pharmacological agents and vaccine-elicited immune responses. A better understanding of the role circadian pathways play in the regulation of virus replication will impact our clinical management of these diseases. This review summarises the experimental and clinical evidence on the interplay between different viral pathogens and our biological clocks, emphasising the importance of continuing research on the role played by the biological clock in virus-host organism interaction.

The Circadian Clock and Viral Infections

The circadian clock controls several aspects of mammalian physiology and orchestrates the daily oscillations of biological processes and behavior. Our circadian rhythms are driven by an endogenous central clock in the brain that synchronizes with clocks in peripheral tissues, thereby regulating our immune system and the severity of infections. These rhythms affect the pharmacokinetics and efficacy of therapeutic agents and vaccines. The core circadian regulatory circuits and clock-regulated host pathways provide fertile ground to identify novel antiviral therapies. An increased understanding of the role circadian systems play in regulating virus infection and the host response to the virus will inform our clinical management of these diseases. This review provides an overview of the experimental and clinical evidence reporting on the interplay between the circadian clock and viral infections, highlighting the importance of virus-clock research.

Pharmacological activation of the circadian component REV-ERB inhibits HIV-1 replication

Human immunodeficiency virus 1 (HIV-1) is a life-threatening pathogen that still lacks a curative therapy or vaccine. Despite the reduction in AIDS-related deaths achieved by current antiretroviral therapies, drawbacks including drug resistance and the failure to eradicate infection highlight the need to identify new pathways to target the infection. Circadian rhythms are endogenous 24-h oscillations which regulate physiological processes including immune responses to infection, and there is an emerging role for the circadian components in regulating viral replication. The molecular clock consists of transcriptional/translational feedback loops that generate rhythms. In mammals, BMAL1 and CLOCK activate rhythmic transcription of genes including the nuclear receptor REV-ERBα, which represses BMAL1 and plays an essential role in sustaining a functional clock. We investigated whether REV-ERB activity regulates HIV-1 replication and found REV-ERB agonists inhibited HIV-1 promoter activity in cell lines, primary human CD4 T cells and macrophages, whilst antagonism or genetic disruption of REV-ERB increased promoter activity. The REV-ERB agonist SR9009 inhibited promoter activity of diverse HIV-subtypes and HIV-1 replication in primary T cells. This study shows a role for REV-ERB synthetic agonists to inhibit HIV-1 LTR promoter activity and viral replication, supporting a role for circadian clock components in regulating HIV-1 replication.

For Whom the Clock Ticks: Clinical Chronobiology for Infectious Diseases

The host defense against pathogens varies among individuals. Among the factors influencing host response, those associated with circadian disruptions are emerging. These latter depend on molecular clocks, which control the two partners of host defense: microbes and immune system. There is some evidence that infections are closely related to circadian rhythms in terms of susceptibility, clinical presentation and severity. In this review, we overview what is known about circadian rhythms in infectious diseases and update the knowledge about circadian rhythms in immune system, pathogens and vectors. This heuristic approach opens a new fascinating field of time-based personalized treatment of infected patients.

The circadian clock components BMAL1 and REV-ERBα regulate flavivirus replication

The circadian clock regulates immune responses to microbes and affects pathogen replication, but the underlying molecular mechanisms are not well understood. Here we demonstrate that the circadian components BMAL1 and REV-ERBα influence several steps in the hepatitis C virus (HCV) life cycle, including particle entry into hepatocytes and RNA genome replication. Genetic knock out of Bmal1 and over-expression or activation of REV-ERB with synthetic agonists inhibits the replication of HCV and the related flaviruses dengue and Zika via perturbation of lipid signaling pathways. This study highlights a role for the circadian clock component REV-ERBα in regulating flavivirus replication.