SARS-CoV-2 and Host Response Affected by Circadian Rhythm

In a study, researchers found that the time day can affect infection with the SARS-CoV-2 and guide the host immune response. This could mean that the circadian rhythm could be a novel target to manage viral progression. In addition to the pivotal role of circadian rhythm in regulating biological functions, it had been proposed as a regulator of viral infections. In cases of infections like respiratory syncytial virus, influenza etc. the time of day when the infection occurred was previously found to be quite important for the disease progression.

The rhythm relies on the central and peripheral oscillators, whose activity depends on the feedback loops governed by clock gene cascade under the regulation of the primary clock gene Bmal1. The knockout of Bmal1 decreases the replication of several different viruses. The researchers concluded that the SARS-CoV-2 exploits the clock pathway for its gain. The expression of investigating genes exhibited circadian rhythm in monocytes with a bathyphase (the trough of the rhythm) and an acrophase (peak of the rhythm) at Zeitgeber Time (the German name for synchronizer) 6 and 17  (ZT6 and ZT17).

The two-time points denote the beginning of the active and the resting periods in human individuals. After 48-hours, the amount of SARS-CoV-2 increased in the monocyte after ZT6 as compared to ZT17. This was linked to increased release of IL-6 and Il-10 at ZT6. The interaction of SARS-CoV-2 with human monocytes led to the rise of distinct cytokine patterns according to the daytime.

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