* Division of Pediatric Surgery, Shin-Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan.
‡ School of Medicine, Fu-Jen Catholic University, New Taipei City, Taiwan.
Am J Chin Med. 2017;45(6):1273-1291. doi: 10.1142/S0192415X17500707.
Lutein is a carotenoid with anti-oxidant properties. Autophagy, an evolutionarily conserved catabolic cellular pathway for coping with stress conditions, is responsive to reactive oxygen species (ROS) and degrades damaged organelles. We previously demonstrated that lutein can induce anti-oxidant enzymes to relieve methotrexate-induced ROS stress. We therefore hypothesized that lutein, which activates ROS-scavenging enzymes, can also induce autophagy for cell survival. In this study, we demonstrated that lutein treatment attenuated the reduction in cell viability caused by HO. Lutein dose-dependently induced the processing of microtubule-associated protein light chain 3 (LC3)-II, an autophagy marker protein, and accumulation of LC3-positive puncta in rat intestinal IEC-6 cells. Furthermore, (a) direct observation of autophagosome formation through transmission electron microscopy, (b) upregulation of autophagy-related genes including ATG4A, ATG5, ATG7, ATG12, and beclin-1 (BENC1), and (c) increased BECN1/Bcl-2 ratio confirmed the induction of autophagy by lutein. The results revealed that bafilomycin-A1-induced inhibition of autophagy reduced cell viability and increased apoptosis in lutein-treated cells, indicating a protective role of lutein-induced autophagy. Lutein treatment also activated adenosine monophosphate-activated protein kinase (AMPK), c-Jun N-terminal kinase (JNK), and p-38, but had no effects on the induction of extracellular signal-related kinase or inhibition of mTOR; however, the inhibition of activated AMPK, JNK, or p-38 did not attenuate lutein-induced autophagy. Finally, increased BECN1 expression levels were detected in lutein-treated cells, and BECN1 knockdown abolished autophagy induction. These results suggest that lutein-induced autophagy was mediated by the upregulation of BECN1 in IEC-6 cells. We are the first to demonstrate that lutein induces autophagy. Elevated autophagy in lutein-treated IEC-6 cells may have a protective role against various stresses, and this warrants further investigation.
叶黄素是一种具有抗氧化特性的类胡萝卜素。自噬是一种进化上保守的细胞分解代谢途径，可应对应激条件，对活性氧（ROS）有反应，并降解受损的细胞器。我们之前的研究表明，叶黄素可以诱导抗氧化酶来缓解甲氨蝶呤诱导的 ROS 应激。因此，我们假设，激活 ROS 清除酶的叶黄素也可以诱导自噬以促进细胞存活。在这项研究中，我们证明了叶黄素处理可以减轻 HO 引起的细胞活力下降。叶黄素剂量依赖性地诱导微管相关蛋白轻链 3（LC3）-II 的加工，这是一种自噬标记蛋白，并且在大鼠肠 IEC-6 细胞中积累 LC3 阳性斑点。此外，（a）通过透射电子显微镜直接观察自噬体的形成，（b）上调自噬相关基因，包括 ATG4A、ATG5、ATG7、ATG12 和 beclin-1（BENC1），以及（c）增加 BECN1/Bcl-2 比值，证实了叶黄素诱导自噬。结果表明，巴弗洛霉素 A1 诱导的自噬抑制降低了叶黄素处理细胞的细胞活力并增加了细胞凋亡，表明叶黄素诱导的自噬具有保护作用。叶黄素处理还激活了腺苷单磷酸激活蛋白激酶（AMPK）、c-Jun N 末端激酶（JNK）和 p-38，但对细胞外信号相关激酶的诱导或 mTOR 的抑制没有影响；然而，激活的 AMPK、JNK 或 p-38 的抑制并不能减轻叶黄素诱导的自噬。最后，在叶黄素处理的细胞中检测到 BECN1 表达水平增加，并且 BECN1 敲低消除了自噬诱导。这些结果表明，叶黄素诱导的自噬是通过 IEC-6 细胞中 BECN1 的上调介导的。我们是第一个证明叶黄素诱导自噬的人。在叶黄素处理的 IEC-6 细胞中，自噬的增加可能对各种应激具有保护作用，这值得进一步研究。
