Dietary compound α-asarone alleviates ER stress-mediated apoptosis in 7β-hydroxycholesterol-challenged macrophages

Scope: Prolonged endoplasmic reticulum (ER) stress has lost the function of protein folding capacity and the ER accumulation of unfolded proteins that eventually triggers apoptosis. Oxysterols are emerging as contributing factors in atherogenesis known to involve macrophage apoptosis. This study determined the inhibitory effect of alpha-asarone present in purple perilla, on 7 beta-hydroxycholesterol-induced macrophage apoptosis, targeting against ER stress signaling pathway. Methods and results: J774A1 murine macrophages were exposed to 28 mu M 7 beta-hydroxycholesterol and treated with 1-10 mu M alpha-asarone. Macrophage apoptosis and ER stress were examined by and alpha-Asarone blocked 7 beta-hydroxycholesterol-induced DNA fragmentation and apoptosome formation. Immunoblotting showed that the oxysterol activated the ER transmembrane resident kinases of IRE1 alpha, PERK and ATF4 and triggered caspase-12 signaling cascades, which was reversed by alpha-asarone. Additionally, 7 beta-hydroxycholesterol activated TRAF2-ASK1-JNK1/2 complex following the IRE1 alpha activation, and alpha-asarone blunted such IRE1 alpha-mediated pathway. Real-time PCR and dual-luciferase reporter analyses revealed that alpha-asarone reduced transcriptional activation of ER stress-responsive genes including XBP1 and CHOP by 7 beta-hydroxycholesterol. Finally, alpha-asarone disturbed oxysterol-elicited signaling of PERK and ATF4 responsible for CHOP induction. Conclusion: alpha-Asarone blocked 7 beta-hydroxycholesterol-induced macrophage apoptosis through allaying ER stress-specific signaling involving caspase activation and CHOP induction. alpha-Asarone was an anti-atherosclerotic agent antagonizing ER stress-mediated macrophage apoptosis by 7 beta-hydroxycholesterol.