An international team of researchers have found that angiotensin-converting enzyme 2 (ACE2) levels in lung cells change throughout the day, affecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. ..There is also a rhythmic cycle in the invasion and replication of the virus into lung cells, suggesting that the circadian process may affect the viral life cycle...
Circadian rhythms are internal processes that control the sleep and wake cycle of an organism and regulate how the organism responds to the environment. Recent studies have shown that the circadian clock also regulates the susceptibility of organisms to viral infections. Influenza infection in mice lacking circadian regulators causes higher viral replication and severe bronchitis, suggesting a role for circadian function in respiration.
Almost every cell has a circadian signal controlled by a translation and transcriptional feedback loop. The molecular clock has a 24-hour cycle. The transcription factor BMAL1-CLOCK activates transcription of the target gene promoter. The gene product provides feedback to suppress the transcriptional activity of activators.
In a new study published in bioRxiv* Preprint servers, researchers report that the circadian route affects the SARS-CoV-2) life cycle.
ACE2 level shows rhythmic cycle
The authors infected lung epithelial cells Calu-3 with SARS-CoV-2 at different circadian times. They found that the virus showed a rhythmic pattern in replication, with replication rates changing over a 24-hour period.
To see if this periodic replication occurs at the level of viral entry, researchers infected cells with SARS-CoV-2-expressing lentivirus pseudoparticles. Spike protein.. The invasion of the virus into the cells also followed a periodic pattern. Infection increases and decreases in a 24-hour cycle and depends on the interaction of peplomer proteins and the receptor ACE2. In contrast, pseudoparticles of vesicular stomatitis virus (VSV) always infect cells with similar efficiency and did not show periodicity.
SARS-CoV-2 infection is a circadian rhythm
This suggests that the circadian signaling pathway plays a role in regulating the susceptibility of Calu-3 cells to SARS-CoV-2 infection.
When researchers measure ACE2 expression TMPRSS2, Another enzyme that carries SARS-CoV-2 infection, they found that ACE2 levels changed over a 24-hour period. Consistent with SARS-CoV-2 infection, there was a valley at 6 hours and a peak at 18 hours. TMPRSS2 levels were constant throughout.
Although circadian regulation is thought to be under transcriptional control, quantification of ACE2 and TMPRSS2 transcripts did not show a periodic pattern in Calu-3 cells. However, they saw the expression of some circadian patterns in the lungs, liver, and intestines of mouse models to study circadian rhythms.
When silencing, the major circadian transcriptional activator, Bmal1, Calu-3 cells showed decreased ACE2 expression but no effect on TMPRSS2. These Calu-3 cells also showed reduced infection with SARS-CoV-2 pseudoparticles. There was no difference in VSV infection.
The team then tested the effect of the synthetic agonist S9009 on the SARS-CoV-2 infection, which regulates the circadian pathway by activating the BMAL1 repressor REV-ERB. Treatment of Calu-3 cells with S9009 reduced BMAL1 activity and ACE2, but had no effect on TMPRSS2 expression, and S9009 also reduced SARS-CoV-2 infection. Treatment of primary bronchial epithelial cells with SR9009 also reduced infection with SARS-CoV-2 pseudoparticles.
Circadian process affects SARS-CoV-2 life cycle
Therefore, the results show a circadian regulation of ACE2 expression in lung cells, which has a significant impact on SARS-CoV-2 infection. This suggests that post-transcriptional and post-translational mechanisms may play a role in the regulation of the circadian clock. MicroRNA has been shown to regulate the circadian clock, regulate ACE2 expression, and provide possible mechanisms.
In addition, bioinformatics analysis suggested that approximately 30% of SARS-CoV-2 host factors could be regulated by BMAL1 / REV-ERB. Experimentally, they found a significant reduction in SARS-CoV-2 replication in BMAL1-silented Calu-3 cells compared to the original cells. Therefore, the circadian process can play a role in influencing several steps of the SARS-CoV-2 life cycle, including entry and replication.
Therefore, there may be potential uses for drugs that regulate the circadian clock, such as dexamethasone, which has been shown to reduce the severity of COVID-19 and synchronize the circadian pathway. Several compounds targeting clock proteins have recently been developed and have been shown to inhibit hepatitis C virus and HIV replication.
Circadian clocks can also affect drug response. Night shift workers are at increased risk of developing chronic inflammatory diseases. Therefore, identifying whether shift workers are susceptible to SARS-CoV-2 infection can help with public policy measures.
bioRxiv Publish preliminary scientific reports that should not be considered definitive as they are not peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.