Opposing actions of Per1 and Cry2 in the regulation of Per1 target gene expression in the liver and kidney

Mounting evidence suggests that the circadian clock plays an integral role in the regulation of many physiological processes including blood pressure, renal function, and metabolism. The canonical molecular clock functions via activation of circadian target genes by Clock/Bmal1 and repression of Clock/Bmal1 activity by Per1-3 and Cry1/2. However, we have previously shown that Per1 activates genes important for renal sodium reabsorption, which contradicts the canonical role of Per1 as a repressor. Moreover, Per1 knockout (KO) mice exhibit a lowered blood pressure and heavier body weight phenotype similar to Clock KO mice, and opposite that of Cry1/2 KO mice. Recent work has highlighted the potential role of Per1 in repression of Cry2. Therefore, we postulated that Per1 potentially activates target genes through a Cry2-Clock/Bmal1-dependent mechanism, in which Per1 antagonizes Cry2, preventing its repression of Clock/Bmal1. This hypothesis was tested in vitro and in vivo. The Per1 target genes αENaC and Fxyd5 were identified as Clock targets in mpkCCD_c14 cells, a model of the renal cortical collecting duct. We identified PPARα and DEC1 as novel Per1 targets in the mouse hepatocyte cell line, AML12, and in the liver in vivo. Per1 knockdown resulted in upregulation of Cry2 in vitro, and this result was confirmed in vivo in mice with reduced expression of Per1. Importantly, siRNA-mediated knockdown of Cry2 and Per1 demonstrated opposing actions for Cry2 and Per1 on Per1 target genes, supporting the potential Cry2-Clock/Bmal1-dependent mechanism underlying Per1 action in the liver and kidney.