key: cord-1023823-wbq6qltm
authors: Bellet, Marina Maria; Eckel-Mahan, Kristin; Romani, Luigina
title: Editorial: Circadian Rhythm: From Microbes to Hosts
date: 2020-11-02
journal: Front Cell Infect Microbiol
DOI: 10.3389/fcimb.2020.613181
sha: 57414a1cb95da67af3360a962c86b8f315ac8595
doc_id: 1023823
cord_uid: wbq6qltm

nan

clock of T. brucei is discussed, including how it controls many aspect of parasite metabolism, including its own susceptibility to antiparasitic drugs. How parasite and other microbes' rhythm dictate changes in their hosts, and what the evolutionary advantage may hold for microbial species in this process still remain elusive.

In their mini review, Murakami and Tognini summarize the results of a series of works that have described the reciprocal circadian regulation between hosts and the commensal microbial population constituting the gut microbiota. The authors cover the role of the host circadian clock in dictating the structure and composition of the gut microbiota and the production of microbial metabolites, which in turn, are recognized by the innate immune system through which they signal to intestinal epitelial cells, by changing their circadian transcriptional program. Intriguingly, this is likely to occur through (among other mechanisms) epigenetic mechanisms, as suggested by Orozco-Solis and Aguilar-Arnal. The circadian regulation mostly relies on epigenetic modifications of chromatin accessibility (Sassone-Corsi, 2016), and the authors describe common epigenetic mechamisms shared by the circadian and immune system that might provide reciprocal interaction between the two systems.

Almost every aspect of the immune response in mammals is tightly regulated by the circadian clock, including immune cells abundance, trafficking, differentiation and cytokines production (Scheiermann et al., 2018) , but also the activity of soluble mediators such as the complement system, for which there are evidence which suggest its dysregulation during circadian disruption, as summarized in the review by Shivshankar et al. The rhythmicity of immune functions, both at the steady-state and during infections, clearly affects host immune response to pathogens, as revealed in the last two decades through the use of many different murine models of infection. Even one of the most fearful evolutions of bacterial infections, which is sepsis, is under circadian regulation. Mul Fedele et al. in their article further characterize the diurnal response to septic shock, and clearly highlight the central role of TNFa signaling in this circadian response.

Overall, this Research Topic brings together a collection of articles which are meant to provide readers with an overview of our current understanding regarding the circadian regulation of microbial physiology and host immune responses to infections by these microbes. Collectively, they highlight the importance of circadian rhythms in the host-pathogen reciprocal interactions. The application of a circadian medicine in the field of infections, including viral infections, might represet the direct conceptual advance in this field, in which promising developments are expected in the near future (Greco and Sassone-Corsi, 2020) , as evidenced by the urgent needs imposed by the pandemic spread of SARS-CoV-2 infection (Ray and Reddy, 2020) .

The editors of this topic greatly appreciate the contributions to this collection given by all of the authors and reviewers.

MB, KE-M, and LR edited the research topic, contributed to the article and approved the submitted version. 

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