α‐Asarone augments autophagophore elongation in oxysterol‐challenged macrophages

Abstract

Macrophage apoptosis plays a major role in the advanced atherosclerotic lesions, which is induced by several stimuli including endoplasmic reticulum (ER) stress and oxidative stress. In the recent studies, autophagic responses make cells escape from cellular apoptosis through promoting phagocytosis of misfolded proteins. α‐Asarone is isolated from Perilla frutescens, a traditional herb in the East‐Asia, and this compound possesses several effects on allergic inflammation. This study investigated whether α‐asarone alleviated macrophage apoptosis by promoting autophagic responses. To induce lipotoxicity in macrophages, this study treated 7β‐hydroxycholesterol in richly present in oxidized LDL. 7β‐Hydroxycholesterol induced cellular apoptosis by decreasing cell viability by ≈70% within 18 h, which were recovered by treating 10 μM α‐asarone. To induce ER stress by this oxysterol, the activation and induction of pancreatic ER kinase (PERK), translation initiation factor (eIF) 2α, activating transcription factor (ATF) 4 were determined. α‐Asarone down‐regulated the activation and induction of these ER stress‐related proteins. In addition, the oxysterol induced C/EBP homologous‐protein (CHOP) and DNA damage‐inducible protein (GADD34), which was dose‐dependently ameliorated by supplementing α‐asarone. Furthermore, to reveal a relationship between cellular apoptosis and autophagy, autophagy protein (ATG) 5 siRNA was employed in oxysterol‐challenged macrophages. The CHOP induction was up‐regulated in ATG5‐deleted macrophages free of autophagy, indicating that cellular apoptosis and autophagy was reciprocal in oxysterol‐challenged macrophages. The oxysterol enhanced the formation of ATG5/12/16L complex by instigating autophagy and increased LC3 induction for the autophagosome formation. α‐Asarone attenuated the formation autophagosomes through disturbing the formation of ATG5/12/16L complex and the LC3 conversion to LC3II for mature. Therefore, α‐asarone is a protective agent inhibiting atherosclerosis by ameliorating oxysterol‐mediated macrophage apoptosis and by augmenting autophagosome formation.Support or Funding InformationThis study was supported by Food, Agriculture, Forestry and Fisheries (112085‐03‐1‐SB010) and Brain Korea 21 plus program by Ministry of Education of Korea (22A20130012421).