Revanth Vadlamudi

Introduction. This study investigates the potential influence of circadian rhythms and clock genes on the infection and pathogenesis of SARS-CoV-2 to preface future targets for prophylaxis, chronotherapeutics during infection, and long-term secondary illness. SARS-CoV-2 is a pneumotropic RNA beta-coronavirus of zoonotic origin; human transmission occurs primarily via respiratory droplets.¹ Interaction between SARS-CoV-2 spike glycoproteins and ACE2 receptors on Type II alveolar cells internalizes the virus. Circadian rhythms regulate and coordinate the innate and adaptive immune response and other physiological processes via changes in core clock genes and nuclear factors.² Circadian rhythms may play a role in SARS-CoV-2 pathogenesis during the phases of infection into host lung epithelium, viral replication, and severity of illness. Circadian rhythms also regulate expression of pro-inflammatory cytokines which cause secondary damages to inflammation. The primary genes in focus are Bmal1, a transcription factor and REV-ERB, a nuclear receptor. Methods. Human calu-3 cells were transduced with lentivirus encoding shBmal1 and ACE2, Bmal1 expression was assessed by western blotting. These cells were infected with lentiviral pseudotypes expressing spike variants, viral entry was measured 24 hours later via luciferase activity. Calu-3 cells transfected with BMAL1/CLOCK plasmids were infected with SARS-CoV-2pp and lysed after 24 hours to quantify luciferase activity. SARS-CoV-2pp or VSV-Gpp infected Calu-3 cells were treated with SR9009 for 24 hours, luciferase activity was quantified to assess viral entry compared to control. Calu-3 cells were treated with REV-ERB agonist SR9009 or the cryptochrome stabilizer KL001 for 24h and infected with SARS-CoV-2, after which intracellular viral RNA was measured. Results indicated the influence of circadian rhythm pathways in all proposed stages of SARS-CoV-2 pathogenesis. A vaccine study found stronger long-term immune response in morning vaccination groups with increased immune cells.³ Both Bmal1 and REV-ERB alter susceptibility to viral invasion. REV-ERB agonists decreased the interaction between the spike-glycoprotein and ACE-2 receptors, while Bmal1 regulates the expression of ACE-2 receptors on host cell surfaces.⁴ Circadian rhythms influence viral replication. Bmal1^-/- mice demonstrated 5 to 10-fold increase in intracellular RSV replication.⁵ Treating Bmal1^-/- mice with a REV-ERB agonist reduced intracellular SARS-CoV-2 RNA levels in a dose-dependent manner.⁴ Circadian rhythms also mediate the immune response itself. Bmal1 mediates the cytokine storm via the melatonergic-pituitary pathway; Bmal1^-/- mice with viral respiratory infections displayed higher severe granulocyte-predominant lung inflammation due to pro-inflammatory cytokines.⁶ Disrupting cytokine regulation contributes to SARS-CoV-2 multiorgan failure.⁷ Discussion. Circadian rhythms and clock genes affect the pathogenesis of SARS-CoV-2. Understanding this relationship may inform chronotherapeutic strategies such “clocking” drugs and altering clocks.

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