Silybin A enhances circadian clock by targeting CRY1 and disrupting its interaction with CLOCK

Abstract

Circadian clock governs a large array of physiological and metabolic functions. The amplitude decline of circadian rhythm is associated with various chronic diseases. However, few clock enhancing-molecules are known. CRY1 is one of the main components of the core circadian clock and its binding with CLOCK leads to decreased transcriptional activity. Thus, compounds interfering with CRY1-CLOCK interaction may enhance circadian rhythm. Natural products are rich sources of drug discovery and herb-based virtual screen provides an efficient way to identify active herbs. Here, by performing herb-based virtual screen against the CLOCK interacting pocket in CRY1 and cell-based assays, we found that Silybum marianum, a widely used medical plant, can activate circadian clock transcription. Molecular level studies showed that its extract silymarin can bind to CRY1 and disrupt CRY1-CLOCK interaction. Further computational and experimental analysis revealed that silybin A is the main bioactive compound that enhances the amplitude of circadian rhythm by reducing the negative arm of the transcription/translation feedback loop. Silybum marianum and its main extract, silymarin, were reported to have hepatoprotective, cardiovascular-protective, antidiabetic, anti-inflammatory, antioxidative, and anti-cancer effects with unclear mechanism. Our study revealed that silymarin and the purified compound silybin A may perform their pharmacological functions by modulating circadian clock. We also demonstrate that disrupting CRY1-CLOCK interaction provides a new route for upregulating circadian rhythm and the CLOCK binding site in CRY1 serves as a druggable pocket for discovering clock enhancing molecules for treating related diseases.