Circadian oscillator NPAS2 regulates diurnal expression and activity of CYP1A2 in mouse liver

We aimed to investigate the potential role of NPAS2 in controlling diurnal expression and activity of hepatic CYP1A2 and to determine the underlying mechanisms. Regulatory effects of NPAS2 on CYP1A2 were determined using Npas2 knockout (Npas2-/-) mice as well as AML-12, Hepa1-6 and HepG2 cells. mRNA and protein levels were detected by reverse transcription-quantitative real-time PCR and western blotting, respectively. In vitro and in vivo CYP1A2 activities were respectively evaluated using the probe substrates phenacetin and theophylline. Transcriptional regulation was investigated using luciferase reporter assays and ChIP-Seq analysis. Loss of Npas2 in mice decreased CYP1A2 expression (at both mRNA and protein levels) and blunted its rhythmicity in the liver. Likewise, Npas2 ablation down-regulated the enzymatic activity of CYP1A2 (probed by metabolism of phenacetin and theophylline) and abrogated its time-dependency. Cell-based assays confirmed that NPAS2 positively regulated CYP1A2 expression. Mechanistic study indicated that NPAS2 trans-activated Cyp1a2 through its spe-cific binding to the-416 bp E-box-like element within the gene promoter. In conclusion, NPAS2 was identified as a key transcriptional regulator of diurnal expression of hepatic CYP1A2 in mice. Our findings have implica-tions for improved understanding of circadian metabolism and chronopharmacokinetics.

Automated summary

This study aimed to investigate the potential role of NPAS2 in controlling the diurnal expression and activity of hepatic CYP1A2 and to determine the underlying mechanisms. The results showed that NPAS2 plays a key transcriptional regulatory role in mice, and its loss leads to decreased expression and activity of CYP1A2, which affects its rhythmicity. This study contributes to a better understanding of circadian metabolism and chronopharmacokinetics.