CRY1/2 regulate rhythmic CYP2A5 in mouse liver through repression of E4BP4

Area of Science:

• Chronobiology
• Molecular Pharmacology
• Hepatology

Background:

• Cytochrome P450 2A5 (CYP2A5) exhibits circadian rhythms in expression and activity, crucial for drug metabolism.
• The precise molecular mechanisms governing CYP2A5's circadian regulation remain incompletely understood.

Purpose of the Study:

• To investigate the role of circadian clock proteins CRY1 and CRY2 in the circadian regulation of hepatic CYP2A5.
• To elucidate the molecular mechanisms by which CRY1/2 influence CYP2A5 expression and activity.

Main Methods:

• Utilized Cry1-null and Cry2-null mice models for in vivo studies.
• Employed AML-12, Hepa1-6, and HepG2 cell lines for in vitro validation.
• Assessed CYP2A5 activity via coumarin 7-hydroxylation, and quantified mRNA/protein levels using qPCR and Western blotting.
• Investigated regulatory mechanisms using luciferase reporter assays, ChIP, and Co-IP.

Main Results:

• Ablation of Cry1 or Cry2 in mice led to reduced hepatic CYP2A5 mRNA and protein levels, and abolished diurnal rhythms.
• CYP2A5 activity was decreased and lost its time-dependency in knockout mice, correlating with increased hepatotoxicity.
• Cell-based assays confirmed CRY1/2 positively regulate CYP2A5 expression and its circadian rhythm.
• CRY1/2 were found to interact with E4BP4, thereby repressing E4BP4's inhibitory effect on Cyp2a5 transcription.

Conclusions:

• CRY1 and CRY2 are key regulators of rhythmic CYP2A5 expression and activity in mouse liver.
• The mechanism involves CRY1/2 repressing the inhibitory action of E4BP4 on Cyp2a5 transcription.
• These findings enhance the understanding of circadian control over drug metabolism and pharmacokinetics.